Current status on lithium disilicate and zirconia: a narrative review

Direct colour printing on zirconia using 222 nm UV-C photons

OBJECTIVES

To proof the feasibility of direct colour printing on 3Y-TZP using 222 nm UV-C through investigating the degree and durability of the colour changes, and testifying whether surface, mechanical and biological properties are influenced by the treatment.

METHODS

222 nm UV-C light (Irradiance: 1.870 mW/cm2) was used to treat 3Y-TZP for durations from 15 min to 24 h. ΔE*, TP, crystalline structure, surface morphology, Sa, BFS and biological activities were investigated before and after irradiation. SPSS 28.0 was used for statistical analysis (α = 0.05).

RESULTS

222 nm UV-C irradiation was capable to shade white 3Y-TZP into tooth colours. With the increase of ΔE*, TP decreased, such that the longer the irradiation time, the higher the ΔE* (logarithmic relationship) and lower the TP. Despite the induced optical changes being prone to fade, the process can be predicted by inversely proportional relationships between ΔE*, TP and the testing points. The treated surface exhibited enhanced hydrophilicity, while the recovery phenomenon was observed. Other properties were not altered by the treatment.

SIGNIFICANCE

This is the seminal study demonstrating the feasibility of direct colour printing on 3Y-TZP using 222 nm UV-C. The new relationship between the colour centre and Eg of 3Y-TZP was established, whereas the induced optical changes were stabilised after a certain period and were highly predictable by controlling the irradiation periods. The irradiation was only correlated to the electron excitation and oxygen vacancies, and would not lead to any changes of other properties. A simple, safe and promising approach to achieve satisfactory colours on 3Y-TZP in clinical practice can be developed.

Self-Etching Ceramic Primer Affects Surface Topography and Roughness of Two Zirconia-Reinforced Lithium Silicate Ceramics

OBJECTIVE

 This article evaluates the etching efficacy of a self-etching ceramic primer (SECP) on zirconia-reinforced lithium silicate (ZLS) ceramics.

MATERIALS AND METHODS

 Celtra Duo (DeguDent GmbH, Hanau-Wolfgang, Germany) and Vita Suprinity (Vita Zahnfabrik, Bad Säckingen, Germany) were used in this study. A total of 36 ceramic slices were prepared from each ceramic material and randomly distributed into three groups according to the surface treatment applied (n = 12 per group). Group 1 (polished) was polished with silicon carbide paper discs and did not undergo any surface treatment; group 2 (SECP) was surface treated with SECP (Monobond Etch and Prime, Ivoclar Vivadent, Schaan, Liechtenstein); group 3 (hydrofluoric acid [HF]) was surface treated with 4.7% HF etching. Half of the specimens (n = 6) from each group were gold-sputtered, and the surface topographic alterations were evaluated by scanning electron microscopy at magnifications of 5,000× and 10,000 × . The surface roughness of the other half (n = 6) from each group was tested using a three-dimensional optical profiler. Data were statistically analyzed using two-way analysis of variance and Tukey's multiple comparisons test.

RESULTS

 Both SECP and HF etching surface treatments resulted in a statistically significant increase (p < 0.05) in the surface roughness of both ceramic materials, compared to that of their respective control group specimens (polished). HF etching resulted in a significant dissolution of the glassy phase of each ceramic.

CONCLUSION

 SECP can effectively etch ZLS ceramics. The etching patterns created after the application of SECP were mild compared to those produced by HF etching. The topographic surface features of ceramics are affected by both, surface treatment and material composition.

Minimally Invasive Fixed Prosthodontics: A Narrative Review

OBJECTIVE

Minimally invasive dentistry is being widely practiced. The center stone is to be as conservative as possible to minimize unnecessary removal of healthy tooth structure. In prosthodontics the patients have generalized and combined nature of diseases. This narrative literature review analyzed available evidence on minimally invasive treatment protocols in fixed prosthodontics and raised awareness on the importance of longevity of treatments and secondary prevention.

OVERVIEW

The long-term clinical survival of ceramic and resin composite materials was reviewed. Loss of tooth vitality after prosthodontic treatment was also explored. And finally, treatment options for patients with severe wear were examined. The search of the literature resulted in evidence of superior survival of ceramic restorations over resin composites. The literature is also clear that ceramic partial coverage inlay and onlay restorations have excellent long-term clinical performance in posterior dentition. Glass ceramic lithium disilicate showed to be an adequate material not only for anterior but also for posterior dentition, including the patients with severe wear.

CONCLUSIONS

Minimally invasive dentistry as applied in fixed prosthodontics needs updates in its concepts to account for secondary prevention and longevity of chosen treatment techniques.

CLINICAL SIGNIFICANCE

This narrative review article critically reviews available evidence on long-term clinical performance of minimally invasive and traditional treatment concepts and materials in fixed prosthodontics. Awareness is raised for secondary prevention and longevity of chosen treatments.

Effect of crystallization temperature on the flexural strength of lithium disilicate glass ceramics

PURPOSE

This pilot study aimed to compare the flexural strength of Amber Mill CAD to IPS e.max CAD and to determine the impact of different crystallization protocols on the flexural strength of Amber Mill CAD ceramics.

MATERIALS AND METHODS

Amber Mill CAD ceramic blocks of a known Vita Classic shade were selected for testing against control IPS e.max CAD blocks of the same shade. Four different translucencies were selected for Amber Mill CAD blocks: high translucency (HT), medium translucency (MT), low translucency (LT), and medium opacity (MO). Two different translucencies were selected for IPS e.max CAD blocks: HT and LT. The partially crystallized blocks were sectioned and placed into six groups for each temperature protocol for a total of 36 samples for Amber Mill CAD and 18 samples for IPS e.max CAD. The samples were sectioned at a thickness of 1.5 mm to simulate the material thickness recommended by the manufacturer for posterior lithium disilicate (LD) crowns. Four crystallization protocols, as recommended by the manufacturer, were used with Amber Mill CAD blocks, and one crystallization protocol was used with IPS e.max CAD blocks. The samples from each group were subjected to 3-point bending test. A two-way analysis of variance (ANOVA) and Tukey pairwise comparison tests were used for statistical analysis and interpretation of collected data.

RESULTS

The mean averages of maximum flexural strength for Amber Mill CAD samples were 269.54 MPa, 280.10 MPa, 277.55 MPa, and 254.16 MPa for HT, MT, LT, and MO, respectively. The mean averages of maximum flexural strength for the IPS e.max CAD samples were 302.99 MPa and 283.49 MPa for HT and LT, respectively. No significant differences in the mean average flexural strength were found between the Amber Mill CAD and IPS e.max CAD blocks (p > 0.05). Further, there were no statistical differences in flexural strength between the four crystallization protocols of Amber Mill CAD (p > 0.05).

CONCLUSION

Amber Mill CAD shows similar flexural strength to IPS e.max CAD. Further, altering crystallization protocols of the same shade to obtain different translucencies did not affect the flexural strength of Amber Mill CAD.

Effects of home bleaching agents on hybrid ceramics: mechanical properties and color change

BACKGROUND

Home bleaching is a promising option for addressing discolored teeth conservatively. However, its impact on the physical and mechanical properties of indirect restorations remains unknown. This study provides comparative insights into the material responses to aesthetic treatments by assessing the effects of home bleaching agents on two hybrid ceramics: VITA ENAMIC® and Grandio Blocs. The focus is on evaluating color stability and biaxial flexural strength.

METHODS

60 discs (12 × 1 mm) were prepared from hybrid ceramics. Specimens were divided into two groups according to type of hybrid ceramic (30 specimens in each group); group A: VITA ENAMIC®, group B: Grandio Blocs. Each group was further subdivided into 3 subgroups according to the concentration of home bleaching agents used (10 specimens in each subgroup); subgroup C: unbleached control group, subgroup C10%: carbamide peroxide 10% bleaching agent, and subgroup C35%: carbamide peroxide 35% bleaching agent. Samples of subgroup C10% were bleached with Home Bleaching Opalescence PF (10%) for 8 h per day for 14 days, as directed by the manufacturer. Samples of subgroup C35% were bleached using WHITEsmile Carbamide Peroxide (35%), following the manufacturer's directions for 30 min every day for 14 days. Color change (ΔE) was assessed using of the CIE L*a*b* system. Then, the biaxial flexural strength test was done. The data were analyzed using two-way ANOVA tests and Weibull analysis.

RESULTS

VITA ENAMIC samples exhibited significantly higher color change than Grandio Blocs (p < 0.001), while Grandio Blocs showed significantly higher biaxial flexural strength (p < 0.001). The concentration of the bleaching agent had no significant effect on color change (p = 0.086). However, regardless of its concentration, bleaching significantly reduced biaxial flexural strength in both materials (p < 0.001). Weibull analysis showed that Grandio Blocs had higher characteristic strength, while VITA ENAMIC demonstrated more reliable failure behavior.

CONCLUSIONS

Compared to Grandio Blocs, VITA ENAMIC® exhibited a greater color change with both 10% and 35% carbamide peroxide home bleaching agents. Additionally, both concentrations of carbamide peroxide reduced the biaxial flexural strength of hybrid ceramics. These findings can guide clinicians in selecting hybrid ceramics based on clinical demands for aesthetics and durability. VITA ENAMIC® offers greater structural reliability and predictability for aesthetic restorations, while Grandio Blocs provide superior durability and stress resistance for high-stress clinical applications.

Influence of wall thickness on the fracture resistance of hollow zirconia artificial teeth fabricated by 3D zirconia printing

PURPOSE

To determine the effect of wall thickness on the fracture load of hollow-structured zirconia teeth fabricated using 3D printing.

METHODS

The geometry of an artificial ceramic tooth (mandibular right first molar) was copied and modified. The final test group design yielded wall thicknesses of 0.30, 0.50, 0.75, and 1.00 mm. Twenty zirconia specimens from each group were fabricated using a 3D printer. Artificial teeth were divided into subgroups of teeth that remained hollow (hollow teeth) or were filled with resin (filled teeth). Fracture load tests were performed, and each artificial tooth was examined using a digital microscope. Analysis of variance was used to compare the fracture resistance of the artificial zirconia teeth among the conditions, followed by pairwise Tukey's tests. T-tests were used to compare the fracture resistance between the hollow and filled teeth within the test groups.

RESULTS

The fracture resistance of artificial zirconia teeth decreased significantly (P < 0.001) with decreasing wall thickness. The mean fracture load reached ≥500 N for wall thicknesses of 0.75 mm and 1.00 mm. Resin filling of crowns significantly improved the fracture load of very thin walls. Microscopy revealed that most occlusal surfaces of the hollow teeth were completely fractured, whereas all the fracture surfaces of the filled teeth were incompletely fractured.

CONCLUSIONS

Artificial zirconia teeth offer sufficient fracture resistance for clinical use when the wall thickness is ≥0.75 mm, regardless of the presence of resin filling.

Properties of New Partially Crystallized Lithium Disilicate CAD-CAM Materials

OBJECTIVE

The purpose of this study was to compare the optical, mechanical, and biological properties of two new, inexpensive lithium disilicate (LS2) materials (Lodden (LOD), LD Medical Technology; and BeautyZir (BZ), BeautyZir Technology) to a clinically established LS2 material (IPS e.max CAD (EMAX), Ivoclar Vivadent).

METHODS AND MATERIALS

The optical properties of the translucency parameter (TP) and opalescence parameter (OP) were obtained with a dental spectrophotometer. The mechanical properties of flexural strength (FS) and flexural modulus (FM) were determined through a three-point bend test conducted using a universal testing machine. Biocompatibility tests were conducted by analyzing cell proliferation using spectrophotometric absorbance (optical density) to determine relative growth rate and cytotoxicity. Representative specimens of the three LS2 materials were analyzed with X-ray diffraction to determine the relative crystalline phases. Data were analyzed with oneway ANOVA and Tukey's post hoc test (α=0.05).

RESULTS

Significant differences in optical and mechanical properties were found amongst the groups (p<0.05). Both LOD and BZ had significantly greater TP and OP compared to EMAX. EMAX and LOD had greater FS and FM than BZ. No significant differences in optical density or relative growth rate were found among any of the LS2 groups (p>0.05). EMAX and LOD had greater weight percent of lithium disilicate than BZ.

CONCLUSIONS

The new lithium disilicate LS2 material, LOD, exhibited better optical properties while maintaining mechanical and biological properties similar to the established LS2 material, EMAX.

Fracture Resistance of Chairside CAD/CAM Lithium Disilicate Partial and Full Coverage Crowns and Veneers for Maxillary Canines

OBJECTIVE

This study aimed to assess the fracture resistance of chairside computer assisted design and computer assisted manufacturing (CAD-CAM) lithium disilicate partial and full-coverage crowns and veneers for maxillary canines.

METHODS AND MATERIALS

Forty-eight restorations for maxillary right canines (12 per group) were designed as follows: (1) partial crown with finish line in the upper middle third; (2) partial crown with finish line in the lower middle third; (3) traditional labial veneer; and (4) traditional full-coverage crown. Restorations were fabricated out of lithium disilicate (Amber Mill, Hassbio) using a chairside CAD-CAM system (Cerec Dentsply Sirona). Partial and full crowns and veneers were treated with a primer system (Monobond Plus, Ivoclar Vivadent) and cemented using dual-cure resin cement (Variolink Esthetic, Ivoclar Vivadent) and cemented to printed resin dies. Subsequently, the restorations were subjected to 10,000 thermocycles between 5°C and 55°C with a dwell time of 30 seconds. The restorations were then loaded axially on the incisal edge in compression to fracture with a flat indenter.

RESULTS

Full-coverage crowns displayed the highest fracture resistance (809±28.57 N) followed by partial crowns with finish line in lower third (649±21.74 N) and crowns with finish line in upper third (421±17.46 N). Veneers displayed the lowest fracture resistance values (259±15.69 N).

CONCLUSIONS

The fracture resistance of partial and full-coverage crowns and veneers was significantly influenced by the design. Full coverage crowns displayed the highest fracture resistance and partial crowns showed higher fracture resistance than traditional veneers.

Two-Year Clinical Evaluation of Enamel Wear Antagonistic to Polished and Glazed Monolithic Zirconia Endocrowns

OBJECTIVE

To assess the effect of chairside adjustment and polishing on the clinical performance of zirconia endocrowns and digitally calculate the opposing enamel wear.

MATERIALS AND METHODS

A total of 20 participants received zirconia endocrowns on their endodontically treated lower first molars. All endocrowns were fabricated using CAD/CAM technology. According to the occlusal adjustments needed for the restorations, patients were divided into two groups: Group ZG with 10 glazed monolithic zirconia endocrowns and Group ZP with 10 adjusted and polished zirconia endocrowns. Bonded endocrowns were evaluated clinically and radiographically for 24 months following modified FDI criteria. Wear of the antagonistic enamel was calculated at 6, 12, 18, and 24 months using an intraoral scanner and Geomagic software.

RESULTS

The overall survival rate of the 20 endocrowns was 100%, according to the Kaplan-Meier survival method. None of the endocrowns were replaced during the follow-up. After 2 years, polished zirconia caused enamel wear (0.422 ± 0.130 mm3), while glazed zirconia caused enamel wear (0.491 ± 0.105 mm3), with no statistically significant difference (p = 0.108).

CONCLUSION

Both glazed and polished monolithic zirconia endocrowns showed comparable enamel wear after a 2-year clinical follow-up, with no significant difference.

CLINICAL SIGNIFICANCE

Glazing or intra-oral polishing could be applied to monolithic zirconia endocrowns with minimal antagonist enamel wear.

Crystallization by microwave energy: Effects on the survival probability of lithia-based glass ceramics

This study evaluated the survival probabilities of two lithia-based glass-ceramics after final crystallization in a microwave furnace using conventional crystallization as a reference. Disc-shaped samples of a lithium silicate (LS, Celtra Duo) and a lithium disilicate (LD, e.max CAD) were prepared and divided into two groups according to the crystallization method (n = 30): microwave (M) or conventional furnaces (C). The biaxial flexural strength test was used to determine the fatigue test profile and its parameters. Then, specimens were submitted to an accelerated life test (step stress) using three profile levels - mild, moderate, and aggressive - varying the load increments and the number of cycles until fracture (4 Hz). Survival data were used to calculate Weibull's beta (β) value and reliability of the assigned missions. Scanning electron microscopy was employed to analyze surface morphology, fracture characteristics, and failure patterns. Beta (β) values for the LS-C, LS-M, LD-C, and LD-M groups were 2.65, 0.25, 0.62, and 0.3, respectively. Similar reliability was observed in all groups after 50,000 cycles at 100 and 150 Mpa. At 200 Mpa, the crystallization method did not affect the reliability within LS or LD. However, LD showed greater reliability than LS when crystallized by microwave energy. Thus, microwave energy can be suggested as an alternative to the process of conventional lithia-based glass-ceramics crystallization without damaging their survival probabilities.

The influence of core-build up materials on biaxial flexural strength of strength-gradient zirconia and lithium disilicate ceramics: an in-vitro study

The aim of this study was to investigate the effect of using different core build-up materials on biaxial flexural strength (BFS) of multilayered strength-gradient zirconia ceramic in comparison to lithium disilicate ceramic. Thirty zirconia discs were fabricated from IPS e.max ZirCAD Prime (Zir), 30 discs from IPS e.max CAD (LS2), 30 composite discs were prepared from Tetric N-Ceram (TNC) and 30 from MultiCore Flow (MCF). The ceramic discs were adhesively cemented to composite discs forming 4 groups (n = 15) (Zir-MCF, Zir-TNC, LS2-MCF and LS2-TNC). BFS was determined using a piston-on-3-ball test. The data were statistically analyzed with independent t-tests for significant differences (p = 0.05). In zirconia groups, significantly higher stress values were recorded in the composite and the ceramic for Zir-TNC, compared to Zir-MCF (p < 0.001), while for LS2 groups, no significant differences were found between the 2 composites (p = 0.157) but stresses in LS2 were significantly higher for LS2-TNC than LS2-MCF (p < 0.001). Comparing the values between the ceramic groups, stresses were significantly higher for zirconia than LS2 (p < 0.001). It was concluded that the tested composite materials significantly differ in their strength, which also influenced the strength of the overlying ceramics, and that strength-gradient zirconia had higher strength than LS2. Monolithic strength-gradient zirconia restorations supported by composite core build-up materials with superior mechanical properties can be durable restorative options for high stress-bearing areas.

Comparing the effect of two polishing systems on surface roughness of feldspathic, lithium disilicate, and translucent zirconia ceramics after orthodontic bracket debonding: An in vitro study

INTRODUCTION

Debonding of orthodontic brackets on ceramic restorations leave a rough surface which should be efficiently polished. In this study the effect of two diamond polishing systems (DPS), namely Optra Fine® (OF) and Diapol Twist® (DT) on surface roughness (SR) of feldspathic (F), lithium disilicate (LD), and translucent zirconia (TZ) ceramics assessed after bracket debonding.

MATERIALS AND METHODS

Ninety disc-shaped specimens fabricated from F, LD, and TZ ceramics and glazed (Gl). Ten glazed specimens of 3 ceramic types served as control (C) groups (n=30). Other 60 specimens were deglazed, and after specific surface preparation according to ceramic type, upper central incisor brackets were bonded. After debonding, the remaining adhesive composite removed with tungsten carbide bur and specimens randomly assigned into 6 groups. The nine experimental groups defined as: Glazed F specimens (C), Deglazed F specimens polished with DT, Deglazed F specimens polished with OF, Glazed LD specimens (C), Deglazed LD specimens polished with DT, Deglazed LD specimens polished with OF, Glazed TZ specimens (C), Deglazed TZ specimens polished with DT, Deglazed TZ specimens polished with OF. The SR assessed quantitatively by profilometry (Ra and Rz parameter) and qualitatively by scanning electron microscopy (SEM). Quantitative data were statistically analysed using Kolmogorov-Smirnov test, two-way ANOVA and Tukey post-hoc test (α=0.05).

RESULTS

No significant difference found in SR of three glazed ceramic types (P=0.293 for Ra and P=0.473 for Rz). There was no significant difference of Ra between polished and glazed groups (P>0.05). However, difference in Rz was significant (P<0.05), and only TZ specimens could reach to the level of smoothness caused by glazing.

CONCLUSIONS

Both diamond polishing systems can efficiently reduce the surface roughness, despite of ceramic type. Optra Fine® system showed a superior performance than Diapol Twist® without significant difference.

LIMITATIONS

In this study only one brand of each ceramic type was investigated. This study was approved by Ethical Review Committee (IR.IAU.KHUISF.REC.1401.156).

Assessing the Current Landscape and Future Directions of Digital Denture Technology

Digital dentures are removable dental prostheses fabricated using computer-aided design/computer-aided manufacturing (CAD/CAM) technology. This study aimed to explore the trends in digital dentures. A comprehensive four-phase search and selection strategy was framed.

Dimensions and Lens.org databases were used. Boolean operators were used to combine keywords.

The most significant growth occurred by 2021, with 71 publications and 984 citations. Egypt had the highest publication rankings, with 46 total publications (TP) and 45 total citations (TC). The University of Geneva played a significant role in contributing to 16 TP and 491 TC. Egyptian Dental Journal ranked at the top. The group with four authors had an even higher number of authorships, with a total of 60. The top four keywords were CAD/CAM, 3D printing, CAD-CAM, complete denture, and digital dentistry. The Glossary of Prosthodontic Terms, Ninth Edition, was referenced 614 times and had the highest average number of citations (75.2). The top three writers had strong relationships with the three sources and preferred to publish using four keywords. The 11-author group, cluster 6, had the highest level of network cooperation.

In conclusion, research on digital dentures has grown in terms of number of articles and citations.

Comparative Assessment of Post-Fatigue Resistance of Mandibular First Molars Restored With Polyether Ether Ketone and Lithium Disilicate Endocrowns

Background and Objectives: Contemporary dentistry focuses on more conservative treatment options such as endocrown restorations and application of dental materials with higher resemblance to tooth structure. Polyether ether ketone (PEEK) polymer is a material used for the fabrication of endocrowns. This study aimed to compare the post-fatigue resistance (PFR) of mandibular first molars restored with PEEK and lithium disilicate (LS2) endocrown restorations. Materials and Methods: This in vitro, experimental study was conducted on 20 human mandibular first molars with similar dimensions. The teeth were prepared for endocrown restoration and were assigned to two groups (n = 10) of PEEK and LS2 endocrowns. After fabrication by the computer-aided design and computer-aided manufacturing (CAD-CAM) technique, the restorations were cemented with resin cement. Next, the teeth underwent 15,000 thermal cycles followed by cyclic loading with 600,000 cycles of compressive force (100 N, 4 Hz) and were then subjected to compressive load application in a universal testing machine. The load causing endocrown failure was recorded as the PFR of the respective restoration. The failure mode was also inspected under a light microscope. Data were analyzed by the independent t-test and also chi-square, Mann-Whitney, and Fisher's exact tests (α < 0.05). Results: The teeth with PEEK endocrowns showed significantly higher PFR than those with LS2 endocrowns. Irreparable fractures were dominant in both groups. Conclusion: PEEK may serve as a suitable alternative to LS2 for the fabrication of endocrown restorations.

Mechanical Behavior of Thin Ceramic Laminates on Central Incisors

Restorative dentistry often uses ceramic laminate veneers for aesthetic anterior teeth restorations due to their natural appearance and minimal invasiveness. However, the understanding of their clinical performance and how ceramic microstructure and processing affect longevity is limited. Objective: This study aimed to address this gap by determining the mechanical behavior, fracture load, and failure modes of CAD-CAM processed laminate veneers made of either lithium-disilicate-based glass ceramic (IPS e.max CAD) or feldspathic porcelain (Vita Mark II). It also aimed to develop a mechanical cycling methodology capable of determining the lifetime and failure modes of thin ceramic laminate veneers. Materials and Methods: Eighteen human maxillary central incisors were used to create the specimens. Minimal enamel preparation was required to ensure the proper adaptation of the thin ceramic laminates. Ceramic laminates made from lithium disilicate and feldspathic porcelain (Vita Mark II) were produced via CAD-CAM, with the final thicknesses less than 0.5 mm, then cemented with resin cement. Results: The mean fracture load for the glass ceramic was 431.8 ± 217.9 N, while for the porcelain, it was 454.4 ± 72.1 N. Failure modes differed considerably: porcelain showed more chipping, while lithium disilicate was associated with tooth structure failure. Conclusion: The material used did not significantly affect the fracture load of thin ceramic laminates in static tests. However, failure modes differed considerably. It was not possible to determine a set of mechanical cycling parameters that could establish the fatigue properties of thin ceramic laminates, as the maximum number of cycles reached was 536,818.

Mechanical and biocompatibility testing of zirconia and lithium disilicate ceramics: An in vitro study

STATEMENT OF PROBLEM

High-translucency zirconia and lithium disilicate are among the most used materials in contemporary fixed prosthodontics because of their excellent esthetic and mechanical properties. However, their different cementation techniques, physical properties, and biocompatibility profiles can influence the clinician's choice.

PURPOSE

The purpose of this in vitro study was to evaluate the mechanical strength and adhesive cementation techniques for zirconia and lithium disilicate materials through mechanical testing, including compressive and pull-out tests. The biocompatibility of these materials was also assessed.

MATERIAL AND METHODS

A total of 72 human maxillary molars that were free from damage were embedded in acrylic resin and prepared 1 mm occlusal to the enamel-cementum junction. The specimens were divided into 3 groups: lithium disilicate (CAD), zirconia High-Translucency HT (CAD), and lithium disilicate (PRESS). Following the recommended cementation protocols, compression and pull-out tests were performed. Twelve disks of each group were fabricated to test the integration of gingival fibroblasts. Human gingival fibroblasts were isolated from gingival biopsies and cultured in Dulbecco modified Eagle medium (DMEM). Cell viability was determined using the 3-(4,5-di-methylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, serving as an indicator of cellular respiration.

RESULTS

Zirconia was the most mechanically efficient material, with a high resistance value (2081.4 ±405.4 N). The pull-out test determined that CAD-CAM lithium disilicate had similar adhesive cementation strength (244.3 ±29.3 N) to the other groups. In terms of biocompatibility, all materials demonstrated good results, with lithium disilicate CAD emerging as the most biocompatible material. Statistically significant differences were observed between the zirconia HT material and lithium disilicate PRESS (P=.006) and between lithium disilicate CAD and lithium disilicate PRESS (P=.002).

CONCLUSIONS

All the monolithic restorations analyzed have shown excellent results in terms of mechanical properties, adhesion, and biocompatibility. Zirconia exhibited outstanding mechanical properties, making it an ideal choice for applications requiring high strength. To achieve adhesion results comparable with those of lithium disilicate, a protocol using airborne-particle abrasion and silane with 10-MDP is recommended. This approach ensures optimal adhesion, enhancing the longevity and effectiveness of the restoration.

Influence of microstructure on optical properties of CAD-CAM lithium disilicate glass-ceramics

OBJECTIVES

To evaluate the influence of microstructure and chemical composition on the optical properties of CAD-CAM lithium disilicate glass-ceramics.

METHODS

Samples (n = 5; 1.0 mm thickness) of shades A1, A2, and A3 were fabricated from CAD-CAM ceramic blocks (Ivoclar Vivadent): IPS e.max® CAD LT (emLT) and HT (emHT). Samples were polished to 1.0 ± 0.01 mm in thickness. The optical properties (R- reflectance; T- transmittance; μs'- reduced scattering and μa- absorption coefficients) from the post-crystallized samples were determined using the inverse adding-doubling (IAD) method based on integrating-sphere measurements. Additionally, scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were used to evaluate the microstructural properties. Energy-dispersive X-ray (EDX) was employed to analyze the chemical composition. The chemical and structural characterization were performed before and after crystallization of the ceramic samples.

RESULTS

emLT showed higher values of μs'and lower values of μa and T than emHT for each shade in all wavelengths (p < 0.003). Considering T for emHT, there were no statistical differences for shades A1 and A2 at 488 nm and 514.5 nm (p > 0.003) and shades A1 and A3 at 457.9 nm (p > 0.003). emLT showed particle length ranging from 0.74 to 2.78 µm (mean = 1.57 µm and RF-relative frequency = 28 %) and particle width ranging from 0.21 to 0.74 µm (mean = 0.30 µm and RF = 31 %). emHT showed particle length ranging from 0.83 to 3.08 µm (mean = 1.86 µm and RF = 21 %) and particle width ranging from 0.24 to 1.12 µm (mean = 0.56 µm and RF = 28 %). In comparison with emHT, emLT showed greater vol% for C, K, and Zr and lower vol% for O and Al.

SIGNIFICANCE

The optical properties of CAD-CAM lithium disilicate glass-ceramics are influenced by the chemical composition and, consequently, by the material microstructure.

Monolithic Hybrid Abutment Crowns (Screw-Retained) Versus Monolithic Hybrid Abutments With Monolithic Crowns (Adhesively Cemented): Three-Year Data of a Prospective Clinical Split-Mouth Study

OBJECTIVES

This study compares the restoration of single-tooth implants with screw-retained lithium-disilicate hybrid-abutment crowns and single-tooth lithium-disilicate crowns adhesively bonded to hybrid abutments with regard to objective clinical and subjective patient-specific evaluation criteria over a time of observation of 3 years.

MATERIALS AND METHODS

Two bone-level implants were placed in contralateral sides of the same jaw in 10 patients, each with two single-tooth gaps. After osseointegration, implants were uncovered and an impression was taken. In accordance with the split-mouth design, one implant in each patient was restored with a screw-retained hybrid abutment crown and the other implant with a hybrid abutment and an adhesively bonded single-tooth crown. The restorations were randomly allocated to the implants. Prefabricated titanium bases were used. The ceramic abutments and restorations were fabricated monolithically with pressed lithium-disilicate ceramic. An objective evaluation (survival, technical, or biological complications, FIPS) by the practitioner and a subjective evaluation (satisfaction, OHIP) by the patient were carried out after 3, 6, 12, 24, and 36 months after restoration placement.

RESULTS

Both restoration types showed a survival rate of 100% after 3 years of observation. No technical or biological complications occurred. No significant difference was observed between the two types of restoration neither for objective (survival, technical or biological complications, FIPS) nor subjective (satisfaction, OHIP) evaluation criteria (p > 0.05).

CONCLUSION

No statistically significant differences were observed between screw-retained and cemented pressed lithium-disilicate restorations on bone-level implants for both objective and subjective evaluation criteria, respectively.

CLINICAL SIGNIFICANCE

Monolithic hybrid-abutment crowns (screw-retained) and monolithic hybrid abutments with single-tooth crowns (cemented) made of pressed lithium disilicate can be used to successfully restore single implants.

Nonthermal Atmospheric Plasma Promotes Bonding Between Adhesive Monomers and Zirconia

OBJECTIVE

To investigate whether nonthermal atmospheric plasma (NTAP) can promote bonding between commonly used adhesive monomers and zirconia.

MATERIALS AND METHODS

The zirconia surface and monomers (HEMA, BisGMA, TEGDMA, and MDP) were treated with different NTAP approaches (10 w, 30 s), and the surface characteristics and chemical structures between the zirconia surface and monomers were verified by the contact angle, scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared (ATR/FT-IR) spectroscopy, and x-ray photoelectron spectroscopy (XPS). Scotchbond Universal adhesive with two different resin cements, RelyX Ultimate and RelyX Unicem 2, was applied, followed by NTAP-aided clinical procedures, and then microtensile bond strength test (μTBS) and failure mode evaluation were tested for preliminary mechanical properties assessment. One-way ANOVA was employed for the statistical analysis.

RESULTS

The contact angle analysis, SEM, and ATR-FTIR confirmed that NTAP can promote the polymerization of BisGMA, TEGDMA, and MDP on the zirconia surface, while XPS confirmed that NTAP can induce a chemical reaction between MDP and zirconia.

CONCLUSIONS

Nonthermal atmospheric plasma can increase the affinity between selected monomers and zirconia and promote the chemical bonding strength between phosphate monomers and zirconia; besides, it can enhance the bonding strength of two different adhesive systems.

CLINICAL SIGNIFICANCE

The mechanism of how NTAP improved common adhesive monomers interacting with zirconia surfaces was revealed in this study. NTAP, as a relatively high energy-boosting method, could not only improve the surface affinity of zirconia and chemical bonding in-between monomers and zirconia but also enhance the polymerization of different monomers onto zirconia, resulting in improved bonding properties. Thus, further exploration of versatile bonding materials and/or onto different dental substrates could take this into account.

Monolithic hybrid abutment crowns: Influence of crown height, crown morphology and material on the implant-abutment complex

PURPOSE

This in vitro study investigated the influence of material selection, crown morphology, and vertical crown height on the biomechanical behavior of screw-retained monolithic hybrid abutment crowns (HACs).

METHODS

Ninety implants were embedded in accordance with ISO standard 14801; ninety HACs were mounted (N=90). Monolithic crowns with varying group-specific designs were luted using titanium bases. HACs were fabricated from monolithic lithium disilicate ceramic (LD) or zirconia-reinforced lithium silicate ceramic (ZLS). The crown morphology was either maxillary premolar (LD_PM, ZLS_PM) or molar (LD_MO). The three groups were further divided into three subgroups of ten specimens, each designed with a small (7.5 mm), middle (10.5 mm), and high (13.5 mm) configuration of crown heights (N=10). A load-to-failure test at 30° off-axis was conducted using a universal testing machine until failure. For statistical analysis, Kolmogorov-Smirnov and Mann-Whitney U tests were conducted (P < 0.05).

RESULTS

All LD_MO groups presented the highest failure values (808.7 to 947.9 N), followed by the LD_PM (525.8 to 722.8 N) and ZLS_PM groups (312.6 to 478.8N). A comparison between LD and ZLS materials (P < 0.001) as well as the crown morphology (P < 0.001) showed significant differences in failure values. The values in the subgroups of ZLS_PM (low, middle, high) decreased as the crown height increased. The fracture modes showed no consistent patterns across the test groups.

CONCLUSIONS

Material selection, crown morphology, and vertical crown height appear to be important factors that may influence the clinical failure values and patterns of screw-retained single implant crowns.

Polishing systems for modern aesthetic dental materials: a narrative review

Objectives To review the current literature surrounding chairside polishing systems for resin composites, zirconia and lithium disilicate restorations.Methods A literature search was undertaken and databases were hand-searched for the most relevant articles.Discussion The current marketplace contains a wide variety of polishing systems, each with different abrasive compounds and number of steps. Current efforts are aimed at reducing the number of steps required for polishing to improve clinical effectiveness. Reduced step systems showed some comparable results to the more traditional multi-step protocols, but the most effective results were achieved with the use of polishing paste as an additional step.Conclusions Based on the current available literature, the use of material-specific polishing systems is effective for chairside polishing of direct and indirect restorative materials. However, it is important to emphasise that, for optimum outcomes, it is essential to follow manufacturers' recommendations for each step, with particular considerations of the handpiece speed, time spent per step and use of adjunct water coolant.

Effect of brushing simulation on the wear behavior of repaired CAD-CAM restorations

OBJECTIVE

The aim of the present study was to evaluate the influence of multidirectional brushing on the surface roughness, morphology, and bonding interface of resin-repaired CAD-CAM ceramic and composite restorations.

MATERIALS AND METHODS

Twelve (N = 12) blocks (4 mm × 4 mm × 2 mm for parallel axis; 5 mm × 4 mm × 2 mm for perpendicular axis) of lithium disilicate glass-ceramic (IPS e.max CAD, Ivoclar AG) and CAD-CAM resin composite (Tetric CAD, Ivoclar AG) were obtained and repaired with direct resin composite (Clearfil AP-X, Kuraray). An abrasive slurry was prepared and the brushing was performed according to each restorative material and axis of brushing (n = 6; perpendicular to repair interface and parallel to repair interface) during 3,650 cycles (240 strokes per minute) to simulate 3 years of brushing. The surface roughness (Ra) and the profile variation for each material (restoration and direct repair resin composite) were measured at the baseline condition and after brushing, and the mean roughness and presence of steps at the repair interface were evaluated through factorial analysis of Variance (ANOVA). Scanning Electron Microscopy (SEM) images were taken to evaluate the surface topography of the repaired materials after brushing.

RESULTS

The mean roughness of the repaired CAD-CAM restorations was affected by the brushing (P < .05), mainly when evaluating the repair material and the interface (P < .05), while the restorative CAD-CAM materials presented more stable values. The profile evaluation showed higher steps at the interface when repairing lithium disilicate than for CAD-CAM resin composite.

CONCLUSION

Repaired CAD-CAM restorations were susceptible to wear after brushing simulation. The surface roughness of the direct resin composite was the most affected leading to step development at the interface, particularly in the repaired lithium disilicate samples. Cinical maintenance recalls and polishing protocols must be considered to enhance the longevity of such restorations.

Aesthetical and Functional Rehabilitation for an Ankylosed Maxillary Canine-A Case Report

Background: As the functional and aesthetical importance of the canine cannot be overstated, the management of a missing canine is challenging. This case report describes the treatment of an infra-occluded ankylosed maxillary canine in a patient with previously failed orthodontic treatment. Case description: A 20-year-old patient sought a second opinion for orthodontic treatment failure. The patient presented with an impacted, ankylosed, and severely infra-occluded right maxillary canine, as well as an iatrogenic clockwise cant of the maxillary occlusal plane and several root resorptions. The treatment corrected the cant of the occlusal plane while avoiding further root resorption, partially extracted the upper right canine, improved the quality and quantity of the soft tissue in the newly edentulous area, and provided a prosthetic rehabilitation using a lithium disilicate ceramic resin-bonded cantilever bridge. Conclusions: The use of a cantilevered bridge resulted in an aesthetically pleasing and minimally invasive rehabilitation. This technique is reversible, does not affect pulp vitality, and is a viable solution for rehabilitating the smiles of young patients. Clinical significance: The smile rehabilitation for an ankylosed maxillary canine, especially in the case of a previously failed orthodontic treatment, is an important clinical challenge. A minimally invasive long-term restoration with a cantilever bridge is a viable solution. Functional and aesthetically pleasant results can be achieved with a multidisciplinary approach.

Cutting efficiency of different dental diamond rotary instruments for sectioning monolithic zirconia and lithium disilicate crowns

BACKGROUND

The aim of this study was to determine the cutting efficiency of different diamond rotary instrument types for sectioning monolithic zirconia and lithium disilicate anatomical crowns.

MATERIALS AND METHODS

The study used 30 diamond rotary instruments divided into three groups: Zirconia cutting diamond bur (White Z), super coarse grit diamond bur (KBlack), and medium coarse grit diamond bur (KBlue); Two subgroups were assigned based on the crown materials including monolithic zirconia (5YSZ) and lithium disilicate (e.max) ceramics. The cutting efficiency was assessed by measuring the time required to fully section the crowns, followed by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) of the dental burs before use and after every sectioned crown. A three-way ANOVA examined the effects of bur type, material type, and sectioning stage. If interaction exists, one-way ANOVA was used to compare the different subgroups, followed by the Tukey post hoc test. The significance level was assigned at α ≤ 0.05.

RESULTS

The results exhibited various cutting efficiencies among diamond rotary instruments and ceramic crown materials. White Z demonstrated superior cutting efficiency of zirconia crown compared with KBlack and KBlue for the first cutting cycles (p ≤ 0.05); the results tend to be more comparable at the third cutting cycle. However, the super coarse diamond bur exhibited higher efficiency in cutting lithium disilicate crowns than white Z and KBlue burs through all three cutting cycles(p ≤ 0.05). The diamond bur-cutting efficiency diminished after each use, irrespective of the bur type or the crown material (p ≤ 0.05); this was represented by the reduction of carbon and increased nickel matrix ratio after each bur usage.

CONCLUSION

White Z diamond bur showed higher cutting efficiency of zirconia in the first two cutting cycles; super coarse diamond bur is more efficient for cutting lithium disilicate crown in all of the cutting cycles. The amount of diamond on the burs reduced after each use, with no great impact on the material type when sectioning lithium disilicate and 5YSZ crowns.

CLINICAL SIGNIFICANCE

This study provides valuable insights for dental practitioners in selecting the appropriate diamond rotary instrument for crown sectioning. Practitioners can minimize the risk of damage and reduce the time required for crown removal, improving patient outcomes.

Internal fit and marginal adaptation of all-ceramic implant-supported hybrid abutment crowns with custom-milled screw-channels on Titanium-base: in-vitro study

BACKGROUND

Advancements in digital dentistry helped in custom-milling screw-channels in implant-supported restorations; however, the fit of these restorations is still unclear especially for contemporary computer aided designing/computer aided manufacturing (CAD/CAM) materials. This study aimed to compare the internal and marginal fit of Ultra translucent multilayered zirconia versus lithium disilicate implant-supported hybrid abutment crowns (HACs) constructed with custom-milled screw-channels on Titanium-base.

MATERIALS AND METHODS

A total of 24 HACs with custom-milled screw-channels were constructed from lithium disilicate (Group LDS) and Ultra translucent multilayered zirconia (Group UT) using digital workflow (n = 12). The internal and marginal gaps of HACs on their corresponding Titanium-bases were assessed using replica technique and stereomicroscope, respectively. After testing for normality, quantitative data were expressed as mean and standard deviation and compared using independent t-test at a level of significance (P ≤ 0.05).

RESULTS

There was no statistically significant difference between Group LDS and Group UT in terms of marginal and internal fit. The internal and marginal gaps in both groups were within the accepted values reported in literature.

CONCLUSIONS

UT and LDS HACs with custom-milled screw-channels demonstrated comparable and acceptable internal fit and marginal adaptations to Ti-base, which lied within the range reported in literature.

Effect of Surface Treatment with Zirconium Dioxide Slurry on the Bond Strength of Resin Cement to Ultratranslucent Zirconia

This laboratory study aimed to evaluate the effects of zirconium dioxide (ZrO2) slurry surface treatment on the bond strength of ultratranslucent zirconia to resin cement using different ceramic primers. The surface morphology was evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and the interface was evaluated by SEM. Additionally, the phase composition was analyzed by X-ray diffraction (XRD). Specimens of zirconia (n=120) were obtained and divided into two groups according to the surface treatment: (1) airborne particle abrasion with 50-μm aluminum oxide (n=60) and (2) ZrO2 slurry (n=60). The 60 specimens were then further divided into three groups (n=20) according to the ceramic primer application: no primer (NP), Monobond N (MB), and Clearfil ceramic primer (CP). Four resin cement cylinders were built on each ceramic specimen. Half of the specimens (n=10) were subjected to a microshear bond strength (μSBS) test after 24 hours of storage in distilled water, and the other half (n=10) were subjected to a μSBS test after thermocycling. Additional specimens were prepared for SEM, AFM, and XRD analyses. According to the Kruskal-Wallis and Student-Newman-Keuls post hoc tests, the μSBS values were significantly higher for MB and CP than for NP (p<0.05), and there were no significant differences in μSBS for both surface treatments associated with MB and CP after 24 hours of storage (p>0.05). Thermocycling significantly decreased the μSBS values for all specimens, especially for the NP groups and ZrO2 slurry treatment groups, and gaps at the interface were observed by SEM. SEM and AFM analyses showed agglomerate-type irregularities on the ceramic surface for ZrO2 slurry treatment. XRD spectra showed that ZrO2 slurry did not cause phase transformation. It was concluded that ZrO2 slurry promoted irregularities on the ultratranslucent zirconia surface, not causing phase transformation; moreover, the values of μSBS were comparable to those of airborne particle abrasion with aluminum oxide. However, neither surface treatment nor ceramic primer prevented the degradation of the interface.

Effect of Acidulated Phosphate Fluoride Gel on Zirconia Intaglio Surface: An In-Vitro Study

Aim

To evaluate the micro-shear bond strength (µ-SBS) of resin-modified glass ionomer cement and to assess the chemical and topographical changes in the zirconia fitting surface induced by acidulated phosphate fluoride (APF) gel using scanning electron microscope (SEM) analysis and Fourier transform infrared (FTIR) spectroscopy.

Materials and Methods

Thirty-two samples were prepared from two zirconia materials, UPCERA HT White and BruxZir® Solid Zirconia, milled by a computer-aided design/computer-aided manufacturing system. From each zirconia sample, six plates were prepared for FTIR and SEM testing. Following sintering, the samples were divided into control and test groups for each material. The APF gel (1.23%) was applied to the intaglio surface of each test group. To measure the µ-SBS between the zirconia materials and luting cement, 20 rectangular samples of zirconia material were prepared. Ten samples were obtained from Upcera and ten from Bruxzir, with five assigned to the control and five to APF groups.

Statistical Analysis

For the µ-SBS test, independent samples t test was conducted to determine the level of significance between the tested groups.

Results

FTIR spectroscopy revealed new bands for Upcera and Bruxzir zirconia owing to ion exchange between the formed sodium phosphate and the zirconia surface and the formation of zirconium phosphate by an ester reaction. SEM assessment identified lines, scratches, or surface dissociation that appeared on the intaglio-zirconia surface after conditioning. The µ-SBS test, as indicated by the independent samples t test, showed a significant increase in bond strength of 1.266 and 1.566 MPa for Upcera and Bruxzir zirconia, respectively.

Conclusion

This study offers new practical, cost-effective, and accurate tests to enhance the µ-SBS of luting cement to yttria-stabilized tetragonal zirconia polycrystal ceramics.

The Fracture Resistance Comparison between Titanium and Zirconia Implant Abutments with and without Ageing: Systematic Review and Meta-Analysis

Implant abutments are essential components of implant prosthetic restorations. The golden standard for abutment material is titanium; however, due to its properties, the esthetic result can be compromised. The most popular esthetic material alternatives are one- and two-piece zirconia. The study aimed to answer the questions of whether zirconia abutments can be used interchangeably with titanium in both anterior and posterior regions and how aging of the abutment affects durability. For this study, an electronic search of MEDLINE (PubMed) and Scopus (Embase) was conducted. The PRISMA guidelines were followed, and a systematic review was registered with PROSPERO. The search revealed 4031 results, of which 17 studies were selected. The strongest material for abutments is titanium, closely followed by two-piece zirconia. One-piece zirconia abutments were the weakest. The cyclic loading above 1,000,000 cycles decreased the fracture resistance of the abutments. Differences in implant diameter, angulation, and restoration affected the fracture strength of all compared materials. The main mode of failure for titanium abutments was screw bending or screw fracture. One-piece zirconia most often presented catastrophic failure with internal hexagon fracture below the implant neck. Two-piece zirconia exhibits a combination of failure modes. Two-piece zirconia abutments may be suitable for use in the posterior region, given their comparable fracture resistance to titanium abutments. Despite the fact that one-piece zirconia is capable of withstanding forces that exceed those exerted during mastication, it is recommended that it be employed primarily in the anterior dentition due to its propensity for unfavorable failure modes.

Advanced Material Strategy for Restoring Damaged Endodontically Treated Teeth: A Comprehensive Review

The restoration of endodontically treated teeth (ETT) remains a significant challenge in modern dentistry. These teeth often suffer from substantial structural damage due to both the original pathology and the invasive nature of endodontic procedures. Consequently, ETT are more susceptible to fractures compared to vital teeth, necessitating restorative strategies that can effectively restore both function and aesthetics while minimizing the risk of failure. In recent years, advances in adhesive dentistry and the development of high-strength ceramics have further expanded the restorative options for ETT. Bonded restorations have gained popularity as they preserve more tooth structure and enhance the overall strenght of the tooth-restoration complex. The choice of restorative material and technique is influenced by numerous factors, including the amount of remaining tooth structure, the functional requirements of the tooth, and the aesthetic demands of the patient. Despite the plethora of available materials and techniques, the optimal approach to restoring ETT remains a topic of ongoing research and debate. In this comprehensive review, the current state of and recent advances in restoring damaged endodontically treated teeth are explored. Numerous therapeutic options exist, involving a wide range of materials. This article aims to present the biomaterial advancements of the past decade and their applications, offering alternative approaches to treating damaged ETT with the goal of prolonging their retention on the dental arch and serving as a valuable resource for dental practitioners who face this issue daily.

Enhancement of Biocompatibility of High-Transparency Zirconia Abutments with Human Gingival Fibroblasts via Cold Atmospheric Plasma Treatment: An In Vitro Study

The objective of this study was to explore the effects of cold atmospheric plasma (CAP) treatment on the biological behavior of human gingival fibroblasts (HGFs) cultured on the surface of high-transparency zirconia. Two types of zirconia, 3Y-ZTP and 4Y-PSZ, were subjected to a CAP treatment for various treatment durations. Analyses of the physical and chemical properties of 3Y-ZTP and 4Y-PSZ were conducted using scanning electron microscopy, contact angle measurements, and X-ray photoelectron spectroscopy, both before and after CAP treatment. The biological responses of HGFs on both surfaces were assessed using CCK-8 assay, confocal laser scanning microscopy, and real-time PCR. Initially, the oxygen and hydroxyl contents on the surface of 4Y-PSZ exceeded those on 3Y-ZTP. CAP treatment enhanced the surface hydrophilicity and the reactive oxygen species (ROS) content of 4Y-PSZ, while not altering the surface morphology. After CAP treatment, HGFs' adhesion on 4Y-PSZ was superior, with more pronounced effects compared to 3Y-ZTP. Notably, HGFs counts and the expression of adhesion-related genes on 4Y-PSZ peaked following the CAP exposures for 30 s and 60 s. Consequently, this study demonstrates that, following identical CAP treatments, 4Y-PSZ is more effective in promoting HGFs adhesion compared to traditional 3Y-ZTP zirconia.

An In Vitro Study of Retention and Marginal Adaptation of Endocrowns With Different Intracoronal Depths

BACKGROUND

Marginal adaptation and retention of endocrowns are crucial for the success and survival of endocrowns. This study aimed to investigate the effect of different materials and intracoronal depth on the retention and marginal adaptation of CAD/CAM fabricated all-ceramic endocrowns.

METHODS

Thirty-six mandibular premolar teeth with an average surface area of 64.49 mm2 were prepared to receive CAM/CAM fabricated endocrowns. Samples were divided randomly and equally into groups of lithium disilicate with 2 mm intracoronal depth (LD2), lithium disilicate with 4 mm intracoronal depth (LD4), polymer infiltrated ceramic network with 2 mm intracoronal depth (PICN2) and polymer infiltrated ceramic network with 4 mm intracoronal depth (PICN4). All endocrowns were cemented using ParaCore resin cement with 14N pressure and cured for 20 seconds. Fifty measurements of absolute marginal discrepancy (AMD) were done using a stereomicroscope after cementation. After 24 hours, all samples were subjected to thermocycling before the retention test. This involved using a universal testing machine with a crosshead speed of 0.5 mm/min and applying a load of 500N. The maximum force to detach the crown was recorded in newtons and the mode of failure was identified.

RESULTS

Two-way ANOVA revealed that the AMD for PICN was statistically significantly better than lithium disilicate (p=0.01). No statistically significant difference was detected in the AMD between the two intracoronal depths (p=0.72). PICN and endocrowns with 4 mm intracoronal depth had statistically significant better retention (p<0.05). 72.22% of the sample suffered from cohesive failures and 10 LD endocrowns suffered adhesive failures.

CONCLUSIONS

Within the limitations of this study, we found that different materials and intracoronal depths can indeed influence the retention of CAD/CAM fabricated endocrowns. Based on the controlled setting findings, PICN was found to have better retention and better marginal adaptation than similar lithium disilicate premolar endocrowns.

Aesthetic outcomes of different materials for delayed, single-tooth restorations for immediately placed implants. A randomized controlled clinical trial

OBJECTIVES

The aim of this study is to compare the aesthetic outcomes of metal porcelain (C), lithium disilicate (T1) and porcelain-layered zirconium (T2) immediate implant-supported single crowns in the anterior maxilla.

MATERIALS AND METHODS

Forty-five immediate dental implants were provided for 45 patients that required the extraction of a single tooth in the anterior maxilla. A temporary prosthesis was provided at 8 weeks after placement followed by the final prosthesis at 24 weeks post-implantation. The patients were randomly allocated into 3 groups: 15 patients in the control group (C) received a metal-porcelain restoration, 15 patients (T1) received a lithium disilicate (LD) restoration and 15 patients (T2) received a porcelain-layered, zirconium (Z) restoration. Pink (PES) and White (WES) esthetic scores, radiographic bone levels, periodontal parameters and patient's esthetic satisfaction using a visual analogue scale (VAS) were evaluated at the time of final restoration placement (t0) and at 12-months post-loading (t12).

RESULTS

No implants were lost during the duration of this study. Statistically significant higher WES and VAS scores (p < 0.05) were recorded in T1 vs C and T1 vs T2 groups respectively. Similar radiographic bone levels and periodontal parameters were recorded in all groups.

CONCLUSION

Within the limitations of this study, it was concluded that T1 restorations provided better WES outcomes when compared to C restorations and better VAS scores when compared to T2 restorations at 12 months post-loading. Besides, different material interphases did not have an impact in PES, bone levels or periodontal parameters.

CLINICAL RELEVANCE

There is limited data comparing aesthetic outcomes of implant supported single crowns made of different ceramic materials based on accepted and comparable indexes and the evaluation of the patient's perspective regarding these aesthetic outcomes.

Shear Bond Strength of Simulated Single-Retainer Resin-Bonded Bridges Made of Four CAD/CAM Materials for Maxillary Lateral Incisor Agenesis Rehabilitation

OBJECTIVES

 Maxillary lateral incisor agenesis (MLIA), treated orthodontically by space opening, requires complimentary aesthetic rehabilitation. Resin-bonded bridges (RBBs) can be equated as interim rehabilitation until skeletal maturity is achieved to place an implant-supported crown or as definitive rehabilitation in case of financial restrictions or implant contraindications. Scientific evidence of the best material must be confirmed in specific clinical situations. Computer-aided design and computer-aided manufacturing (CAD/CAM) materials are promising versatile restorative options. This study aimed to identify a straightforward material to deliver interim or definitive RBBs for nonprepared tooth replacement in MLIA.

MATERIALS AND METHODS

 Single-retainer RBB made from CAD/CAM ceramic blocks (Vita Enamic [ENA], Suprinity [SUP], and zirconia [Y-ZPT]) and a three-dimensional (3D) printed material (acrylonitrile butadiene styrene [ABS]) were evaluated by shear bond strength (SBS) and mode of failure, after adherence to an artificial tooth with RelyX Ultimate used in a three-step adhesive strategy.

STATISTICAL ANALYSIS

 The load to fracture (N) was recorded, and the mean shear stress (MPa) was calculated with standard deviations (SD) for each group and compared between materials using boxplot graphics. One-way analysis of variance (ANOVA) followed by the Tukey-Kramer post hoc test was used to compare the differences (α = 0.05). A meta-analysis focusing on CAD/CAM materials evaluated the magnitude of the difference between groups based on differences in means and effect sizes (α = 0.05; 95% confidence interval [CI]; Z-value = 1.96). Failure mode was determined by microscopic observation and correlated with the maximum load to fracture of the specimen.

RESULTS

 The mean ± SD SBS values were ENA (24.24 ± 9.05 MPa) < ABS (24.01 ± 1.94 MPa) < SUP (29.17 ± 4.78 MPa) < Y-ZPT (37.43 ± 12.20 MPa). The failure modes were mainly adhesive for Y-ZPT, cohesive for SUP and ENA, and cohesive with plastic deformation for ABS.

CONCLUSION

 Vita Enamic, Suprinity, Y-ZPT zirconia, and 3D-printed ABS RBBs are optional materials for rehabilitating MLIA. The option for each material is conditioned to estimate the time of use and necessity of removal for orthodontic or surgical techniques.

Quantitative examination of factors influencing the colour reproduction ability of lithium disilicate glass-ceramics

BACKGROUND

Effects of ceramic translucency, layer thickness, and substrate colour on the shade of lithium disilicate glass-ceramic restorations proved to be significant in several studies, however, quantitative, numerical results on the relationship between the colour difference and these parameters are still lacking. The purpose of this in vitro study was to quantitatively determine how the colour reproduction ability of a lithium disilicate glass-ceramic is affected by its translucency, layer thickness, and substrate colour.

METHODS

Ceramic samples were prepared from A2 shade IPS e.max CAD blocks with high and low translucencies (HT and LT) in a thickness range of 0.5-2.5 mm (+/- 0.05 mm). Layered samples were acquired utilizing composite substrates in 9 shades; transparent try-in paste was used. The spectral reflectance of the specimens was assessed under D65 standard illumination with a Konica Minolta CM-3720d spectrophotometer. The CIEDE2000 colour difference (ΔE00) between two samples was analysed using perceptibility and acceptability thresholds set at 50:50%. Statistical analysis involved linear regression analysis and the Kruskal-Wallis test.

RESULTS

An increase in the thickness of 0.5 mm reduced the ΔE00 of the HT samples to 72.8%, and that of the T samples to 71.1% (p < 0.0001). 7 substrates with HT and LT specimens had significantly different results from the mean (p < 0.05). A thickness of 0.5 mm is not sufficient to achieve an acceptable result at any level of translucency, while the low translucency ceramic at a thickness of 1.5 mm gave acceptable results, except for severely discoloured substrates (ND8 and ND9).

CONCLUSIONS

The colour reproduction ability of lithium disilicate glass-ceramics is significantly affected by their translucency, layer thickness, and 7 substrates out of 9 substrates examined.

Clinical Survival of Reduced-Thickness Monolithic Lithium-Disilicate Crowns: A 3-Year Randomized Controlled Trial

Objectives

The aim of this randomized controlled trial was to see if the minimally invasive approach (reduced restoration thickness) would result in good clinical success of monolithic ceramic crowns compared to conventional layered all-ceramic crowns, and thus be an alternative to conventional tooth preparation.

Materials and methods

The ceramic that was investigated was IPS e.max lithium-disilicate ceramic produced using two different processing methods. A comparison was made between monolithic crowns with reduced thickness and standard layered crowns. Fifty-two patients, who had undergone endodontic treatment on either a premolar or molar, were randomly assigned into two groups. The teeth intended for layered crowns underwent to a 2 mm occlusal reduction with a 1 mm rounded shoulder, whereas the teeth intended for monolithic crowns underwent to a 1 mm reduction in the occlusal area with a 0.6 mm rounded shoulder. The clinical success was evaluated in eight categories using modified United States Public Health Service (USPHS) criteria. The observation period was 36 months, with control appointments every 6 months.

Results

There was no significant difference in clinical success between monolithic and conventional layered crowns after 3 years. One monolithic crown fractured while all other crowns were intact and the survival rate was 96%. All layered crowns were intact and the survival rate was 100%.

Conclusion

The results of this study indicate that the minimally invasive approach can be a good alternative to conventional tooth preparation. IPS e.max lithium-disilicate ceramic demonstrated an exceptional three-year survival rate independently of the thickness of the material.

Effect of the difference water amounts and hydrolysis times of silane coupling agent on the shear bond strength between lithium disilicate glass ceramic and composite resin

This study was to evaluate the effect of different water amounts and hydrolysis times of silane coupling agent on shear bond strength between lithium disilicate glass ceramic (LDS) and composite resin. Fourteen groups (n=7) of different water amounts (90, 50 and 10%v/v) and hydrolysis times (5, 19, 75 and 300 s) of experimental silane coupling agent that were prepared for silanization, non-silanization and commercial silane coupling agent (CSC) groups. Two-way analysis of variance (ANOVA) revealed no interaction between water amounts and hydrolysis times of ESC on shear bond strength between LDS and composite resin. One-way ANOVA exhibited the highest shear bond strength and the highest mean percentage in mixed failure mode in the 50%v/v group. Molecular analysis of 13C and 29Si indicated that nuclear magnetic resonance spectra of M2 and M3 hydrolysis species were found in 50%v/v group. The presenting of M2 and M3 which was predominant factor contributing to the highest shear bond strength.

Influence of occlusal thickness on the fracture resistance of chairside milled lithium disilicate posterior full-coverage single-unit prostheses containing virgilite: A comparative in vitro study

PURPOSE

To evaluate the fracture resistance of chairside computer-aided design and computer-aided manufacturing (CAD-CAM) lithium disilicate mandibular posterior crowns with virgilite of different occlusal thicknesses and compare them to traditional lithium disilicate crowns.

MATERIALS AND METHODS

Seventy-five chairside CAD-CAM crowns were fabricated for mandibular right first molars, 60 from novel lithium disilicate with virgilite (CEREC Tessera, Dentsply Sirona), and 15 from traditional lithium disilicate (e.max CAD, Ivoclar Vivadent). These crowns were distributed across five groups based on occlusal thickness and material: Group 1 featured CEREC Tessera crowns with 0.8 mm thickness, Group 2 had 1.0 mm thickness, Group 3 had 1.2 mm thickness, Group 4 with 1.5 mm thickness, and Group 5 included e.max CAD crowns with 1.0 mm thickness. These crowns were luted onto 3D-printed resin dies using Multilink Automix resin cement (Ivoclar Vivadent). Subsequently, they underwent cyclic loading (2,000,000 cycles at 1 Hz with a 275 N force) and loading until fracture. Scanning electron microscopy (SEM) assessed the fractured specimens. Statistical analysis involved one-way ANOVA and the Kruskal-Wallis Test (α = 0.05).

RESULTS

Fracture resistance varied significantly (<0.001) across mandibular molar crowns fabricated from chairside CAD-CAM lithium disilicate containing virgilite, particularly between crowns with 0.8 mm and those with 1.2 and 1.5 mm occlusal thickness. However, no significant differences were found when comparing crowns with 1, 1.2, and 1.5 mm thicknesses. CEREC Tessera crowns with 1.5 mm thickness exhibited the highest resistance (2119 N/mm2), followed by those with 1.2 mm (1982 N/mm2), 1.0 mm (1763 N/mm2), and 0.8 mm (1144 N/mm2) thickness, whereas e.max CAD crowns with 1.0 mm occlusal thickness displayed the lowest resistance (814 N/mm2).

CONCLUSIONS

The relationship between thickness and fracture resistance in the virgilite lithium disilicate full-coverage crowns was directly proportional, indicating that increased thickness corresponded to higher fracture resistance. No significant differences were noted among crowns with thicknesses ranging from 1 to 1.5 mm. This novel ceramic exhibited superior fracture resistance compared to traditional lithium disilicate.

Static and dynamic stress analysis of different crown materials on a titanium base abutment in an implant-supported single crown: a 3D finite element analysis

BACKGROUND

This Finite Element Analysis was conducted to analyze the biomechanical behaviors of titanium base abutments and several crown materials with respect to fatigue lifetime and stress distribution in implants and prosthetic components.

METHODS

Five distinct designs of implant-supported single crowns were modeled, including a polyetheretherketone (PEEK), polymer-infiltrated ceramic network, monolithic lithium disilicate, and precrystallized and crystallized zirconia-reinforced lithium silicates supported by a titanium base abutment. For the static load, a 100 N oblique load was applied to the buccal incline of the palatal cusp of the maxillary right first premolar. The dynamic load was applied in the same way as in static loading with a frequency of 1 Hz. The principal stresses in the peripheral bone as well as the von Mises stresses and fatigue strength of the implants, abutments, prosthetic screws, and crowns were assessed.

RESULTS

All of the models had comparable von Mises stress values from the implants and abutments, as well as comparable maximum and minimum principal stress values from the cortical and trabecular bones. The PEEK crown showed the lowest stress (46.89 MPa) in the cervical region. The prosthetic screws and implants exhibited the highest von Mises stress among the models. The lithium disilicate crown model had approximately 9.5 times more cycles to fatique values for implants and 1.7 times more cycles to fatique values for abutments than for the lowest ones.

CONCLUSIONS

With the promise of at least ten years of clinical success and favorable stress distributions in implants and prosthetic components, clinicians can suggest using an implant-supported lithium disilicate crown with a titanium base abutment.

Bond Strength of Milled and Printed Zirconia to 10-Methacryloyloxydecyl Dihydrogen Phosphate (10-MDP) Resin Cement as a Function of Ceramic Conditioning, Disinfection and Ageing

This study aimed to assess the suitability of printed zirconia (ZrO2) for adhesive cementation compared to milled ZrO2. Surface conditioning protocols and disinfection effects on bond strength were also investigated. ZrO2 discs (n = 14/group) underwent either alumina (Al2O3) airborne particle abrasion (APA; 50 µm, 0.10 MPa) or tribochemical silicatisation (TSC; 110 µm Al2O3, 0.28 MPa and 110 µm silica-modified Al2O3, 0.28 MPa), followed by disinfection (1 min immersion in 70% isopropanol, 15 s water spray, 10 s drying with oil-free air) for half of the discs. A resin cement containing 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) was used for bonding (for TSC specimens after application of a primer containing silane and 10-MDP). Tensile bond strength was measured after storage for 24 h at 100% relative humidity or after 30 days in water, including 7500 thermocycles. Surface conditioning significantly affected bond strength, with higher values for TSC specimens. Ageing and the interaction of conditioning, disinfection and ageing also impacted bond strength. Disinfection combined with APA mitigated ageing-related bond strength decrease but exacerbated it for TSC specimens. Despite these effects, high bond strengths were maintained even after disinfection and ageing. Adhesive cementation of printed ZrO2 restorations exhibited comparable bond strengths to milled ZrO2, highlighting its feasibility in clinical applications.

Effect of surface treatment and resin cement type on the bond strength of polyetheretherketone to lithium disilicate ceramic

BACKGROUND

This study aims to evaluate the effect of surface treatment and resin cement on the shear bond strength (SBS) and mode of failure of polyetheretherketone (PEEK) to lithium disilicate ceramic (LDC). This is suggested to study alternative veneering of PEEK frameworks with a ceramic material.

METHODS

eighty discs were prepared from PEEK blank and from lithium disilicate ceramic. Samples were divided into four groups according to surface treatment: Group (A) air abraded with 110 μm Al2O3, Group (AP) air abrasion and primer application, Group (S) 98% sulfuric acid etching for 60 s, Group (SP) Sulfuric acid and primer. Each group was subdivided into two subgroups based on resin cement type used for bonding LDC:1) subgroup (L) self- adhesive resin cement and 2) subgroup (B) conventional resin cement (n = 10). Thermocycling was done for all samples. The bond strength was assessed using the shear bond strength test (SBS). Failure mode analysis was done at 50X magnification with a stereomicroscope. Samples were chosen from each group for scanning electron microscope (SEM). The three-way nested ANOVA followed by Tukey's post hoc test were used for statistical analysis of results. Comparisons of effects were done utilizing one way ANOVA and (p < 0.05).

RESULTS

The highest mean of shear bond strength values was demonstrated in Group of air abrasion with primer application using conventional resin cement (APB) (12.21 ± 2.14 MPa). Sulfuric acid groups showed lower shear bond strength values and the majority failed in thermocycling especially when no primer was applied. The failure mode analysis showed that the predominant failure type was adhesive failure between cement and PEEK, while the remaining was mixed failure between cement and PEEK.

CONCLUSION

The air abrasion followed by primer application and conventional resin cement used for bonding Lithium Disilicate to PEEK achieved the best bond strength. Primer application did not have an effect when self-adhesive resin cement was used in air-abraded groups. Priming step is mandatory whenever sulfuric acid etching surface treatment is utilized for PEEK.

Recent advances in dental zirconia: 15 years of material and processing evolution

OBJECTIVES

The objective was to discuss the research on zirconia published in the past 15 years to help the dental materials community understand the key properties of the types of zirconia and their clinical applications.

METHODS

A literature search was performed in May/2023 using Web of Science Core Collection with the term "dental zirconia". The search returned 5102 articles, which were categorized into 31 groups according to the research topic.

RESULTS

The current approach to improving the translucency of zirconia is to decrease the alumina content while increasing the yttria content. The resulting materials (4Y-, 5Y-, and above 5 mol% PSZs) may contain more than 50% of cubic phase, with a decrease in mechanical properties. The market trend for zirconia is the production of CAD/CAM disks containing more fracture resistant 3Y-TZP at the bottom layers and more translucent 5Y-PSZ at the top. Although flaws located between layers in multilayered blocks might represent a problem, newer generations of zirconia layered blocks appear to have solved this problem with novel powder compaction technology. Significant advancements in zirconia processing technologies have been made, but there is still plenty of room for improvement, especially in the fields of high-speed sintering and additive manufacturing.

SIGNIFICANCE

The wide range of zirconia materials currently available in the market may cause confusion in materials selection. It is therefore imperative for dental clinicians and laboratory technicians to get the needed knowledge on zirconia material science, to follow manufacturers' instructions, and to optimize the design of the prosthetic restoration with a good understanding where to reinforce the structure with a tough and strong zirconia.

Two-body wear of novel monolithic lithium-silicate ceramic materials and their corresponding different antagonists

OBJECTIVES

Evaluation of the two-body wear of lithium-silicate ceramics against different antagonists compared to a direct resin composite and human teeth.

METHODS

Initial LiSi Block [LISI], IPS e.max CAD [EMA], and CEREC Tessera [TESE] were investigated and compared with direct resin composite [FILL] and human teeth [tooth]. As antagonists were used: steatite, ceramic, and human enamel. The control group tooth was only tested with enamel antagonist. The combinations underwent thermomechanical aging using a chewing simulator. Material losses were calculated using GOM-analysis software. Kolmogorov-Smirnov test, Kruskal-Wallis H, Mann-Whitney-U-test with Bonferroni correction and Spearman-rho correlation were calculated. A fractographic analysis was performed.

RESULTS

Within TESE, enamel antagonists led to lower restoration losses than steatite and ceramic antagonists. Within FILL, enamel and steatite antagonists caused lower material losses compared to ceramic antagonists. Against steatite antagonists, LISI showed lowest material losses. Against ceramic antagonists, the use of LISI led to lower material losses compared to FILL. Against tooth antagonists, TESE showed lower material losses than tooth and FILL and LISI lower than FILL. Within LISI, steatite antagonists showed lower material losses on the antagonist than ceramic. Within EMA, steatite antagonists showed higher material losses than ceramic ones. Within ceramic antagonists, LISI restoration material showed lower material losses than FILL and EMA.

CONCLUSIONS

Regardless of the antagonist material, the material losses of LISI and EMA were comparable. However, the abrasion resistance of LISI tended to be higher than EMA.

CLINICAL SIGNIFICANCE

LISI is a fully crystallized lithium-silicate ceramic and no longer needs to be processed after milling. In addition, the abrasion resistance is very good, regardless of the antagonist material chosen.

Clinical outcomes of self-glazed zirconia veneers produced by 3D gel deposition: a retrospective study

BACKGROUND

Self-glazed zirconia (SZ) restorations are made by a novel additive three-dimensional gel deposition approach, which are suitable for a straightforward completely digital workflow. SZ has recently been used as minimally invasive veneer, but its clinical outcomes have not been clarified yet. This study aimed to evaluate the preliminary clinical outcomes of SZ veneers compared with the widely used lithium disilicate glass-ceramic veneers made by either pressing (PG) or milling (MG) process.

METHODS

Fifty-six patients treated with SZ, PG, and MG veneers by 2 specialists between June 2018 and October 2022 were identified. Patients were recalled for follow-up at least 1 year after restoration. Clinical outcomes were assessed by 2 independent evaluators according to the modified United States Public Health Service (USPHS) criteria. Overall patient satisfaction was assessed using visual analogue scale (VAS), and analyzed by one-way ANOVA. Chi-square test was applied to compare the difference in the success and survival rates among the 3 groups.

RESULTS

A total of 51 patients restored with 45 SZ, 40 PG, and 41 MG veneers completed the study, with a patient dropout rate of 8.9%. Mean and standard deviation of follow-up period was 35.0 ± 14.7 months. All restorations performed well at baseline, except for 2 SZ veneers with mismatched color (rated Bravo). During follow-up, marginal discrepancy (rated Bravo) was found in 4 MG veneers and 1 PG veneer, and partially fractured (rated Charlie) was found in another 2 PG veneers. The survival rate of SZ, PG, and MG veneers was 100%, 95%, and 100%, with a success rate of 95.56%, 92.50%, and 90.24%, respectively, none of which were significantly different (p = 0.099 and 0.628, respectively). The mean VAS score of SZ, PG, and MG was 95.00 ± 1.57, 93.93 ± 2.40, and 94.89 ± 2.00 respectively, without significant difference (p > 0.05).

CONCLUSION

SZ veneers exhibited comparable preliminary clinical outcomes to PG and MG veneers, which could be considered as a feasible option for minimally invasive restorative treatment.

Optimized 3D printed zirconia-reinforced leucite with antibacterial coating for dental applications

OBJECTIVES

This study aims to produce by robocasting leucite/zirconia pieces with suitable mechanical and tribological performance, convenient aesthetics, and antibacterial properties to be used in dental crown replacement.

METHODS

Leucite pastes reinforced with 12.5%, 25%, and 37.5% wt. ZrO2 nanoparticles were prepared and used to print samples that after sintering were characterized in terms of density, shrinkage, morphology, porosity, mechanical and tribological properties and translucency. A coating of silver diamine fluoride (SDF) and potassium iodide (KI) was applied over the most promising material. The material's antibacterial activity and cytotoxicity were assessed.

RESULTS

It was found that the increase of ZrO2 reinforcement up to 25% enhanced both microhardness and fracture toughness of the sintered composite. However, for a superior content of ZrO2, the increase of the porosity negatively affected the mechanical behaviour of the composite. Moreover, the composite with 25% ZrO2 exhibited neglectable wear in chewing simulator tests and induced the lowest wear on the antagonist dental cusps. Although this composite exhibited lower translucency than human teeth, it was three times higher than the ZrO2 glazed material. Coating this composite material with SDF+KI conferred antibacterial properties without inducing cytotoxicity.

SIGNIFICANCE

Robocasting of leucite reinforced with 25% ZrO2 led to best results. The obtained material revealed superior optical properties and tribomechanical behaviour compared to glazed ZrO2 (that is a common option in dental practice). Moreover, the application of SDF+KI coating impaired S. aureus proliferation, which anticipates its potential benefit for preventing pathogenic bacterial complications associated with prosthetic crown placement.

Optical properties of zirconia-reinforced lithium silicate veneers obtained with CAD/CAM milling and hot-pressing techniques: a comparative in vitro study

Background and aims

Dental veneers have become increasingly required among patients, but little is known about the optical properties of veneers obtained from the same ceramic material through different processing techniques.

Methods

In this study we compared the translucency and the opalescence parameters of zirconia-reinforced lithium silicate (ZLS) veneers restorations fabricated through CAD/CAM milling and hot-pressing techniques on the upper central incisor. Eighty specimens divided into 8 groups (n=10) were sectioned (Celtra Duo) and heat pressed (Celtra Press) to obtain 0.8 mm thickness. The optical parameters were calculated from the color difference against different backgrounds. Analysis of variance, one way ANOVA and post-hoc multiple comparison tests were used to evaluate and compare the optical properties of the same material, with a significance level of p < 0.05.

Results

The processing method had significant effect on optical parameters. Celtra Duo HT proved to be the material with the highest transparency degree. The hot-pressing technique led to higher opacity than CAD/CAM milling technique.

Conclusions

For a bio-mimetic aesthetic prosthetic restoration, the ceramic materials must have the same translucency and opacity as the real tooth. The results of this study revealed that high translucency ZLS obtained through hot pressing technique was the material of choice, as it fulfilled these requirements.

3D Printed Porous Zirconia Biomaterials based on Triply Periodic Minimal Surfaces Promote Osseointegration In Vitro by Regulating Osteoimmunomodulation and Osteo/Angiogenesis

The triply periodic minimal surface (TPMS) is a highly useful structure for bone tissue engineering owing to its nearly nonexistent average surface curvature, high surface area-to-volume ratio, and exceptional mechanical energy absorption properties. However, limited literature is available regarding bionic zirconia implants using the TPMS structure for bone regeneration. Herein, we employed the digital light processing (DLP) technology to fabricate four types of zirconia-based TPMS structures: P-cell, S14, IWP, and Gyroid. For cell proliferation, the four porous TPMS structures outperformed the solid zirconia group (P-cell > S14 > Gyroid > IWP > ZrO2). In vitro assessments on the biological responses and osteogenic properties of the distinct porous surfaces identified the IWP and Gyroid structures as promising candidates for future clinical applications of porous zirconia implants because of their superior osteogenic capabilities (IWP > Gyroid > S14 > P-cell > ZrO2) and mechanical properties (ZrO2 > IWP > Gyroid > S14 > P-cell). Furthermore, the physical properties of the IWP/Gyroid surface had more substantial effects on bone immune regulation by reducing macrophage M1 phenotype polarization while increasing M2 phenotype polarization compared with the solid zirconia surface. Additionally, the IWP and Gyroid groups exhibited enhanced immune osteogenesis and angiogenesis abilities. Collectively, these findings highlight the substantial impact of topology on bone/angiogenesis and immune regulation in promoting bone integration.

Interdisciplinary full mouth rehabilitation of a patient with amelogenesis imperfecta from childhood to young adult-hood: A 12-year case report

Treatment of patients with amelogenesis imperfecta extends over many years, from childhood to early adulthood. Their management at any age is complex and has to be adapted in relation to therapies validated in the general population.

Er:YAG laser settings for debonding zirconia restorations: An in vitro study

This in vitro study aimed to determine the optimal frequency and energy settings for debonding zirconia restorations using an erbium-doped yttrium aluminum garnet (Er:YAG) laser. A total of 200 zirconia specimens (5 mm × 5 mm × 1.5 mm) were fabricated from two types of materials: (1) 3 mol% yttria oxide stabilized tetragonal zirconia polycrystalline (3Y-TZP) and (2) 5 mol% yttria oxide stabilized tetragonal zirconia polycrystalline (5Y-TZP). The zirconia specimens were bonded to dentin using resin cement (RelyX Ultimate, 3 M) and divided into 20 groups based on their laser treatments (n = 5). Er:YAG laser treatment was applied at various frequencies (10 Hz and 20 Hz) and energies (80 mJ, 100 mJ, 120 mJ, 140 mJ, 160 mJ, 180 mJ, 200 mJ, 220 mJ, 240 mJ, and 260 mJ). The time required to debond the specimens and the temperature changes that dentin underwent during the laser treatment were recorded. The surface morphologies of the debonded dentin and zirconia specimens were observed using scanning electron microscopy (SEM). Additional zirconia specimens were fabricated for 4-point flexural strength testing and surface roughness measurements. Statistical analyses were conducted using three-way analysis of variance (ANOVA) and Student-Newman-Keuls (SNK)-q tests (α = 0.05). The debonding time of each specimen varied between 4.8 and 160.4 s, with an average value of 59.2 s. The dentin temperature change for each specimen ranged from 2.3 to 3.6 °C, with an average value of 2.7 °C. The debonding time was significantly influenced by the zirconia material type and laser energy, but it was not affected by the laser frequency. Among the specimens, those made of 3Y-TZP needed significantly more time for debonding than 5Y-TZP. The optimal energies were 220 mJ for 3Y-TZP and 200 mJ for 5Y-TZP. The laser frequency, laser energy, and type of zirconia material had no effect on the dentin temperature change. Additionally, no surface alternations were observed on the dentin or zirconia materials after laser treatment. The surface roughness and flexural strength of the zirconia materials remained unchanged after laser treatment. In summary, Er:YAG laser treatment effectively and safely removes zirconia restorations without impacting their mechanical properties, with a safe temperature change of less than 5.6 °C. The optimum frequency and energy settings for debonding 3Y-TZP and 5Y-TZP restorations were found to be 10/20 Hz and 220 mJ and 10/20 Hz and 200 mJ, respectively.

Translucency of chairside monolithic zirconias using different sintering ovens: An in vitro investigation

OBJECTIVE

To evaluate the translucency of several monolithic zirconias (MZ) processed in various sintering ovens designed for single-visit, chairside use.

METHODS

Discs (n = 40) from zirconia blocks were fabricated for each MZ at manufacturer-recommended minimal thicknesses, as provided in each material's instructions for use: IPS e.max ZirCAD LT (ZLT); CEREC Zirconia+ (CZ+); 3M Chairside (3M); KATANA Zirconia (KT). Groups (n = 10) were sintered following manufacturer instructions for each oven: CEREC SpeedFire, Ivoclar CS4, Ivoclar CS6, and Ivoclar S2 (laboratory furnace control). Specimens were highly polished on one side and glazed on the other. Each side was measured with a spectrophotometer against white and black backgrounds to determine translucency parameter (TP) and contrast ratio (CR) values. Results for TP and CR for each material and oven combination were compared with a linear mixed model. Oven precision was evaluated using the Kruskall-Wallis test.

RESULTS

Glazed specimens were more translucent than polished ones (p < 0.001). ZLT and CZ+ were more translucent than 3M and KT regardless of the sintering oven (p < 0.01). Several oven/material combinations reached or exceeded the S2 oven TP: CS4 with CZ+ and 3M; CS6 with ZLT and KT (p < 0.01). SpeedFire was significantly less precise (p < 0.05) and produced lower TP values for ZLT, CZ+, and KT (p < 0.01). Results for TP and CR were highly correlated.

CONCLUSIONS

MZ surface finish, material thickness, and oven used all had a significant effect on translucency. Some chairside-oriented solutions produced results with translucency equal to conventionally processed zirconia.

CLINICAL SIGNIFICANCE

The translucency of a ceramic restoration is an important factor in determining its esthetics. Clinicians desiring the most esthetic outcomes with monolithic zirconia should be aware of the significant effects that surface finishing, material thickness, and the sintering oven used can have on restoration translucency.

Optical properties of dental zirconia, bovine dentin, and enamel-dentin structures

OBJECTIVE

To evaluate the optical properties and the relative translucency parameter of Ceramill ZI White (3Y-TZP) and Ceramill Zolid FX White (5Y-PSZ) zirconia ceramic systems and compare them with those of the bovine dentin and enamel/dentin structures.

MATERIALS AND METHODS

3Y-TZP and 5Y-PSZ zirconia ceramic systems were evaluated. A 0.5-mm-thick 3Y-TZP (3Y-NC.5), 0.5-mm-thick (5Y-NC.5), and 1.4-mm-thick (5Y-C.14) were used. A 0.5-mm-thick dentin specimens and 1.4-mm-thick enamel/dentin specimens (n = 5) were obtained from anterior bovine maxillary teeth. Scattering, absorption, transmittance, and albedo coefficient were calculated using Kubelka-Munk's model. Data were statistically analyzed using Kruskal-Wallis and Mann-Whitney tests (p < 0.001), and goodness-of-fit coefficient (GFC). Relative translucency parameter differences were evaluated using translucency thresholds.

RESULTS

Reflectance, scattering, absorption, and transmittance properties were wavelength dependent. Good matches (GFC ≥ 0.999) in spectral reflectance were observed between 0.5-mm-thick dentin and 1.4-mm-thick enamel/dentin, and 3Y-NC.5 and 5Y-NC.5. Scattering was the main optical extinction process during light interaction with zirconia and dental structures, as indicated by albedo coefficient. Translucency differences were acceptable only for 3Y-NC.5 and the dentin structure, and 5Y-C.14 and the enamel/dentin structure.

CONCLUSIONS

Optical properties of 3Y-TZP and 5Y-PSZ dental zirconia differed from each other and from bovine dental structures. Nevertheless, 3Y-TZP showed similar relative translucency parameter to bovine dentin.

CLINICAL SIGNIFICANCE

To achieve the best esthetic results in restorative dentistry, it is crucial for clinicians to know about the optical properties of 3Y-TZP and 5Y-PSZ and to be able to compare these properties with those of dental structures.