Factors affecting enamel and ceramic wear: a literature review

Performance of low shrinkage Bis-EFMA based bulk-fill dental resin composites

OBJECTIVES

The purpose of this study was evaluating the performance of new Bis-EFMA based bulk-fill composites with common methacrylate based composites and commercial dental composites.

METHODS

The Bis-EFMA monomer was synthesized and the novel Bis-EFMA based bulk-fill composites were prepared. The resin composite samples were co-cultured with human gingival epithelial cells and human dental pulp stem cells to test the biocompatibility. The edge adaptation was observed under a combination of stereoscope and scanning electron microscope. The internal hardness was measured using a Vickers microhardness tester after one-time filling of cavities prepared in extracted teeth. After friction and wear test on the surface of the resin composites, the surface morphology and volume wear of each group were measured by the optical profilometer. The color stability was measured by a colorimeter.

RESULTS

Direct contact with human gingival epithelial cells and human dental pulp stem cells did not cause significant changes in their growth density and morphology, indicating good biocompatibility of Bis-EFMA group (p > 0.05). The continuous margin proportion of the Bis-EFMA group was as good as commercial bulk-fill composites (p > 0.05). The sectional microhardness results showed that the Bis-EFMA group had the highest microhardness. After the friction and wear test, the volume wear of the Bis-EFMA group was minimal, indicating its good wear resistance and mechanical strength. Color changes in all resin groups after 28 days of immersion were within the clinically acceptable range.

SIGNIFICANCE

The addition of Bis-EFMA demonstrated excellent biocompatibility, edge adaptation and color stability comparable to commonly used clinical bulk-fill composites, along with preferable mechanical strength, friction and wear resistance. Bis-EFMA based bulk-fill composites have the potential to be employed as a bulk filling material in commercial dental composite applications.

Antagonist enamel tooth wear produced by different dental ceramic systems: A systematic review and network meta-analysis of controlled clinical trials

OBJECTIVES

The aim of this study was to evaluate the amount of enamel tooth wear induced by different antagonistic ceramic crown materials in the posterior area within a follow-up period up to 24 months in function. A network meta-analysis was performed to assess the effect of the materials on the mean vertical loss (MVL) of the antagonist enamel tooth surface.

DATA

Main search terms used in combination: ceramic, dental materials, metal ceramic, tooth wear and dental enamel.

SOURCES

An electronic search was conducted in PubMed/Medline, Embase, and Cochrane CENTRAL plus hand-searching.

STUDY SELECTION

Eligibility criteria included clinical studies reporting on MVL on antagonist's tooth up to 24 months following the permanent crown placement. From a total of 5697 articles, 7 studies reporting on 261 crowns for 177 subjects with 3 ceramic materials (Lithium disilicate, metal-ceramic, monolithic zirconia) were included. Among all, metal-ceramic and zirconia caused significantly higher enamel tooth wear on antagonist teeth, representing 82.5 µm [54.4; 110.6]) and 40.1 µm [22.2; 58.0]) more MVL than natural teeth group. In contrast, lithium disilicate showed only 5.0 µm [-48.2; 58.1]) more MVL than occurs on opposing natural teeth.

CONCLUSIONS

This systematic review demonstrated that prosthodontic ceramic materials produced significantly more antagonist enamel tooth wear than opposing natural enamel tooth wear, and ceramic material type was correlated to the degree of enamel tooth wear. Additional well-conducted, randomized controlled trials with homogeneous specimens are required due to inadequate sample size and number of the clinical studies included in the analyses.

CLINICAL SIGNIFICANCE

The amount of wear caused by different restorative materials has a high influence on the antagonistic natural teeth and should therefore be evaluated intensively by the dentist.

Digital technique to analyze the wear of screw-retained implant supported metal-ceramic dental prostheses and natural tooth as antagonist: a pilot study

The aim of this study was to describe a novel digital technique to analyze the wear of screw-retained implant-supported metal-ceramic dental prostheses and natural tooth as antagonist.Materials and methods Ten patients were consecutively included to rehabilitate partial edentulism by dental implants. Both the screw-retained implant-supported metal-ceramic dental prostheses and the natural tooth as antagonist were submitted to a digital impression through an intraoral scan to generate a Standard Tessellation Language digital file preoperatively (STL1), at 3 months (STL2), and 6 months (STL3) follow-up. Afterwards, an alignment procedure of the digital files (STL1-STL3) was performed on a reverse engineering morphometric software (3D Geomagic Capture Wrap) and volume changes at the screw-retained implant-supported metal-ceramic dental prostheses and the natural tooth as antagonist were analyzed using Student's t-test. Moreover, Gage R&R statistical analysis was conducted to analyze the repeatability and reproducibility of the digital technique.Results Gage R&R showed a variability attributable to the digital technique of 3.8% (among the measures of each operator) and 4.5% (among operators) of the total variability; resulting repeatable and reproducible, since the variabilities were under 10%. In addition, statistically significant differences were shown at the wear volume (μm3) of both the natural tooth as antagonist (p < 0.0001) and the screw-retained implant-supported metal-ceramic dental prostheses between 3- and 6-months follow-up (p = 0.0002).Conclusion The novel digital measurement technique results repeatable and reproducible to analyze the wear of screw-retained implant-supported metal-ceramic dental prostheses and natural tooth as antagonist.

Finishing technique effect on strength of zirconia-reinforced lithium silicate ceramic

The aim of this study was to evaluate the effect of two finishing techniques, glazing or polishing, in comparison with the as-cut condition, on the biaxial-flexural-strength (BFS) of a zirconia-reinforced lithium silicate ceramic (ZLS). Cylinders were milled from CAD/CAM blocks and sliced to obtain disc-shaped specimens (ISO6872:2015). Polished and glazed specimens were processed following the manufacturer's instructions. Thirty-three specimens were obtained for each condition and microstructural and BFS/fractographic characterizations were performed. BFS and roughness data were analyzed using Weibull statistics and ANOVA one-way with Tukey post-hoc test, respectively. While a rougher surface was observed for as-cut specimens, smoother surfaces were observed for polished and glazed ZLS at microscopical evaluation and confirmed through surface-roughness evaluation. X-ray spectra depicted a glass phase for all groups and characteristic metasilicate, lithium disilicate, and lithium phosphate peaks for the as-cut and polished specimens. Glazed specimens showed higher characteristic strength than polished and as-cut specimens, which did not differ significantly. While higher Weibull-modulus was observed for the polished than for the as-cut specimens, no statistically significant differences were noted between glazed and polished, and between glazed and as-cut specimens. ZLS presents higher strength when glazed, and polishing increases the structural reliability of the material relative to the as-cut condition. Both finishing techniques reduced surface roughness similarly.

Effect of different ceramic systems on antagonist dental structure by microtomographic analysis

OBJECTIVES

This study aims to identify the two-dimensional and three-dimensional analyses and evaluate the loss of tooth structure in the tooth's different constituent elements and the ceramic antagonist's surface.

METHODS

In this study, three groups (n = 10) represented by different ceramic systems (lithium disilicate [GDis], lithium silicate reinforced with zirconia [GSil], and monolithic zirconia [GZir]) were evaluated. Each group obtained ten ceramic blocks and submitted them to the sintering/crystallization process. To carry out the wear test, healthy mandibular premolars were used as the specimens and the ceramic blocks as antagonists. The premolars were submitted to two-dimensional and three-dimensional analyses using a computerized microtomography (µTC) before and after the wear test. The wear test was performed with 30 N and 300,000 cycles load, with occlusion, laterality, and disocclusion movements.

RESULTS

The statistical analysis comparing the loss of two-dimensional tooth structure showed a statistically significant difference among all groups (p < 0.05). Statistical analysis comparing the percentage of loss of three-dimensional tooth structure showed a statistically significant difference between groups GDis and GSil and between groups GDis and GZir. However, when comparing GSil with GZir, no statistically significant difference was found. The qualitative analysis of the teeth showed that GDis showed considerable enamel loss and dentin exposure, GSil showed enamel wear with flattening the cusp without dentin exposure, and GZir showed minimal enamel wear without dentin exposure. In the qualitative analysis of ceramic antagonists, more significant wear of the ceramic material for GDis was observed, followed by the GSil and GZir groups, respectively.

SIGNIFICANCE

The use of the lithium disilicate should be cautious, restricting it to areas with lower masticatory forces. Areas of higher masticatory forces showed a large amount of antagonist wear, with dentin involvement. This can lead to dentinal hypersensitivity, risk of compromising patients' occlusion, by harming group disocclusion guides, causing pain and temporomandibular disorders.

Wear characteristics of esthetic resin matrix and zirconia reinforced lithium disilicate CAD/CAM materials: two-body wear and surface topography analysis

BACKGROUND

This in vitro study assessed the wear behavior of different CAD-CAM blocks and the abrasion of the enamel antagonist against these materials.

METHODS

64 disk-shaped specimens were prepared from 8 different CAD/CAM blocks as follow: one lithium disilicate glass ceramics block "IPS Emax CAD" as control group, two zirconia reinforced lithium silicate "Vita Suprinity & Celtra DUO," one interpenetrating network ceramic block "Vita Enamic," Three resin-based block composites "Lava Ultimate, Cerasmart & Brilliant-crios" as well as one hybrid nanoceramic "Shofu block HC". All specimens were mounted against canine and tested for two body wear analysis using a chewing simulating loading machine (100,000 cycles, 50 N, 5/55 °C). The amount of wear loss was measured for each specimen using a digital precise scale. Wear area before and after the chewing simulation were evaluated using an optical profilometer. Data analysed using one-way ANOVA test followed by Tukey's post hoc.

RESULTS

The results showed a significantly higher wear loss in resin matrix ceramics in comparison to glass ceramics. However, for tooth wear glass ceramics had significantly higher value than hybrid ceramics.

CONCLUSIONS

Resin based CAD/CAM Blocks gives a superior result when evaluating the wear behavior and its effect on the opposing tooth surface.

Influence of abrasive dentifrices on polymeric reconstructive material properties after simulated toothbrushing

To assess the influence of dentifrices with different abrasiveness levels on the properties of dental reconstructive materials. Forty-eight cylinders were obtained from four polymeric materials, being two CAD/CAM acrylic resins (Ivotion-Dent and Ivotion-Base), one injected acrylic resin (IvoBase-Hydrid) and one light-cured resin composite (Empress Direct). Specimens were allocated to four subgroups for toothbrushing simulation according to the dentifrice relative dentin abrasivity (RDA) and silica content: (i) RDA 0 = 0%; (ii) RDA 50 = 3%; (iii) RDA 100 = 10%; and (iv) RDA 120 = 25%. Specimens were then subjected to toothbrushing. Surface analyses [surface roughness Ra (SR) and scanning electron microscopy (SEM)] along with hardness and optical properties [translucency parameter (TP) and contrast ratio (CR)] were evaluated before and after toothbrushing. Statistical analyses were performed using ANOVA and Tukey test. A significant increase in SR was observed after toothbrushing with higher RDA toothpastes for Ivotion-Dent (100 and 120) and IvoBase-Hybrid (120). Ivotion-Base and Empress Direct presented no significant differences in SR when analyzed as a function of timepoint and RDA levels. Hardness was not influenced by toothbrushing with different RDA dentifrices, except for Empress Direct with RDA 0 toothpaste, where a decrease in the hardness was observed. TP of Ivotion-Dent and Empress Direct significantly decreased after toothbrushing with higher RDA dentifrices and CR of Ivotion-Dent, Empress Direct and IvoBase-Hybrid significantly increased with higher RDA dentifrices. The levels of dentifrice abrasiveness affected differently the SR, hardness and optical properties of polymeric reconstructive materials after toothbrushing.

Load-bearing capacity and wear characteristics of short fiber-reinforced composite and glass ceramic fixed partial dentures

The aim of this study was to evaluate load-bearing capacity and wear performance of experimental short fiber-reinforced composite (SFRC) and conventional lithium-disilicate CAD/CAM fabricated fixed partial dentures (FPDs). Two groups (n = 12/group) of three-unit CAD/CAM fabricated posterior FPDs were made. The first group used experimental SFRC blocks, and the second group fabricated from lithium-disilicate (IPS e.max CAD). All FPDs were luted on a zirconia testing jig with dual-curing resin cement. Half of FPDs per group were quasi-statically loaded until fracture. The other half experienced cyclic fatigue aging (100.000 cycles, Fmax = 500 N) before loading quasi-statically until fracture. Fracture mode was examined using SEM. Wear test was performed using 15,000 loading cycles. Both material type and aging had a significant effect on the load-bearing capacity of FPDs. Experimental SFRC CAD without fatigue aging had significantly the highest load-bearing capacity (2096 ± 149N). Cyclic fatigue aging decreased the load-bearing capacity of the SFRC group (1709 ± 188N) but increased it for the lithium-disilicate group (1546 ± 155N). Wear depth values of SFRC CAD (29.3μm) were significantly lower compared to lithium-disilicate (54.2μm). Experimental SFRC CAD demonstrated the highest load-bearing capacity before and after cyclic fatigue aging, and superior wear behavior compared to the control material.

A Comparative Evaluation of Enamel Wear Against Different Surface Finished Ceramics: An In Vitro Study

BACKGROUND

An essential factor in the clinical acceptability of all ceramic restorations is the degree of tooth enamel wear. Wear of human enamel has been shown to produce traumatic occlusion, loss of vertical dimension, supra eruption of opposing teeth, periodontal disintegration, and temporomandibular dysfunction. To assess and compare enamel wear against two different ceramics (IPS Empress and Zirconia) and against three different ceramic surface treatments (autoglazed, overglazed, and polished).

METHODS

Zirconia and IPS Empress (Ivoclar Vivadent, Liechtenstein) ceramic samples totaled 30, of which 10 each underwent glaze, overglaze, or polishing with Diaglaze polishing paste. Using a horizontal pin on the disc machine, 60 mounted premolar tooth samples were produced and put through wear tests against ceramic discs. Prior to and following wear, the weight of the tooth samples was measured, and the results were then statistically analyzed using the student t-test, unpaired t-test, and analysis of variance (ANOVA). The qualitative data employed proportions, and the quantitative data used mean and standard deviation to express statistical information. The threshold of significance was set at 5% (α = 0.05).

RESULTS

The results for weight loss after 25,000 cycles for ceramic surfaces that had been overglazed were just a little bit greater than those for ceramic surfaces that had been autoglazed and polished. In each of the various subgroups, it was shown that the weight loss values obtained with polished ceramic after 25,000 cycles were significantly lower than those obtained with autoglazed and overglazed ceramic surfaces (P=0.001). When comparing the results produced by the two separate primary groups, IPS Empress and Zirconia, there was no statistically significant difference between the autoglazed, overglazed, and polished groups. While statistically significant difference was seen for each subgroup of IPS and Zirconia (p ≤ 0.01), particularly Zirconia glazed (1.227) with a highly significant p-value of 0.00.

CONCLUSION

The findings contribute to the understanding of the potential clinical implications of different ceramic materials and surface finishes in restorative dentistry, offering valuable insights for practitioners in their treatment decisions. Further research and clinical observations may be needed to corroborate these findings and guide evidence-based practices in dental restorations.

Effect of the Abutment Rigidity on the Wear Resistance of a Lithium Disilicate Glass Ceramic: An In Vitro Study

Lithium disilicate (LDS) glass ceramics are among the most common biomaterials in conservative dentistry and prosthodontics, and their wear behavior is of paramount clinical interest. An innovative in vitro model is presented, which employs CAD/CAM technology to simulate the periodontal ligament and alveolar bone. The model aims to evaluate the effect of the abutment rigidity on the wear resistance of the LDS glass ceramic. Two experimental groups (LDS restorations supported by dental implants, named LDS-on-Implant, or by hybrid ceramic tooth replicas with artificial periodontal ligament, named LDS-on-Tooth-Replica) and a control group (LDS-Cylinders) were compared. Fifteen samples (n = 15) were fabricated for each group and subjected to testing, with LDS antagonistic cusps opposing them over 120,000 cycles using a dual axis chewing simulator. Wear resistance was analyzed by measuring the vertical wear depth (mm) and the volume loss (mm3) on each LDS sample, as well as the linear antagonist wear (mm) on LDS cusps. Mean values were calculated for LDS-Cylinders (0.186 mm, 0.322 mm3, 0.220 mm, respectively), LDS-on-Implant (0.128 mm, 0.166 mm3, 0.199 mm, respectively), and LDS-on-Tooth-Replica (0.098 mm, 0.107 mm3, 0.172 mm, respectively) and compared using one-way-ANOVA and Tukey's tests. The level of significance was set at 0.05 in all tests. Wear facets were inspected under a scanning electron microscope. Data analysis revealed that abutment rigidity was able to significantly affect the wear pattern of LDS, which seems to be more intense on rigid implant-abutment supports compared to resilient teeth replicas with artificial periodontal ligament.

Diagnostic Applications of Intraoral Scanners: A Systematic Review

In addition to their recognized value for obtaining 3D digital dental models, intraoral scanners (IOSs) have recently been proven to be promising tools for oral health diagnostics. In this work, the most recent literature on IOSs was reviewed with a focus on their applications as detection systems of oral cavity pathologies. Those applications of IOSs falling in the general area of detection systems for oral health diagnostics (e.g., caries, dental wear, periodontal diseases, oral cancer) were included, while excluding those works mainly focused on 3D dental model reconstruction for implantology, orthodontics, or prosthodontics. Three major scientific databases, namely Scopus, PubMed, and Web of Science, were searched and explored by three independent reviewers. The synthesis and analysis of the studies was carried out by considering the type and technical features of the IOS, the study objectives, and the specific diagnostic applications. From the synthesis of the twenty-five included studies, the main diagnostic fields where IOS technology applies were highlighted, ranging from the detection of tooth wear and caries to the diagnosis of plaques, periodontal defects, and other complications. This shows how additional diagnostic information can be obtained by combining the IOS technology with other radiographic techniques. Despite some promising results, the clinical evidence regarding the use of IOSs as oral health probes is still limited, and further efforts are needed to validate the diagnostic potential of IOSs over conventional tools.

Surface Properties and Wear Resistance of Injectable and Computer-Aided Design/Computer Aided Manufacturing-Milled Resin Composite Thin Occlusal Veneers

OBJECTIVES

 This study was conducted to investigate the microhardness, surface roughness (Ra), and wear behavior of thin occlusal veneers (TOV) fabricated from different injectable composite materials and compare them to a Computer-Aided Design (CAD)/Computer-Aided Manufacturing (CAM) resin-based material.

MATERIALS AND METHODS

 A 1-mm occusal veneer preparation was done in a mandibular right second molar typodont tooth. The prepared model was duplicated to fabricate 32 replicas and divided into four groups (n = 8). Standard TOV were fabricated either indirectly from Cerasmart blocks, Cerasmart, GC (CS), or directly from Beautifil Injectable X, Shofu (BF), G-ænial Universal injectable, GC (GU), or SonicFill 2, Kerr (SF) using the injection molding technique. All the specimens were subjected to both thermomechanical cyclic loading (TMC) in a chewing simulator. Wear measurement was conducted by three-dimensional (3D) scanning of the veneered models before and after TMC, and the difference in the volume of the sample was recorded as the volumetric material loss due to wear. Ra before and after TMC and Vickers microhardness (VHN) of the tested materials were measured using standardized samples (n = 8). Representative samples from each group were investigated under a stereomicroscope and a scanning electron microscope.

STATISTICAL ANALYSIS

 One-way analysis of variance (ANOVA) was applied to detect the effect of material on VHN and wear. Two-way ANOVA was utilized to examine the impact of material and TMC on Ra. Multiple comparisons between the groups were conducted using Tukey's post hoc test (α = 0.05). The Pearson's correlation coefficient was used to determine the relationship between hardness and wear and between roughness and wear (α = 0.05).

RESULTS

 CS exhibited the highest mean VHN (p ≤ 0.001), followed by GU and SF which were statistically similar (p = 0.883) but significantly higher than BF (p < 0.001). After TMC, GU revealed the lowest Ra and volumetric wear (VW), followed by CS, BF, and SF (p < 0.5). A highly significant correlation existed between Ra and VW (p = 0.001, R 2 = 0.9803).

CONCLUSION

 The effect of TMC on the surface properties and wear resistance of the investigated TOV is material-dependent. GU injectable TOV are less influenced by TMC than CS milled TOV. In contrast, BF and SF demonstrated significant VW and Ra which might limit their clinical use as TOV.

The mechanical properties, tribological behaviors and color stability of a feldspar nanoceramics strengthening extrinsic stain for high-translucent zirconia

The present work is aimed to explore the mechanical properties, tribological behaviors and color stability of nanoceramics and microceramics strengthened extrinsic stain coatings (NS and MS) upon high-translucent zirconia (TZ). The Na-rich feldspar ceramics component, microstructure and particle size of NS and MS were verified. The mechanical properties including elastic modulus and hardness of NS were enhanced compared to MS. Reciprocating wear tests under a ball-on-plate configuration manifested that the reduced coefficient of friction, wear depth and wear volume loss of NS was evaluated after 1 × 10 ⁴ cycles and the wear scar morphology of NS characterized by microcracks while MS featured more delamination and wear debris. Post toothbrushing simulation revealed that the color stability of extrinsic stain coatings was elevated with the addition of feldspar nanoceramics. The feldspar nanoceramics strengthening extrinsic stain exhibited enhanced elastic modulus, hardness, wear resistance and color stability, especially for TZ.

AFM Analysis of a Three-Point Flexure Tested, 3D Printing Definitive Restoration Material for Dentistry

Background: Three-dimensional printing is a rapidly developing technology across all industries. In medicine recent developments include 3D bioprinting, personalized medication and custom prosthetics and implants. To ensure safety and long-term usability in a clinical setting, it is essential to understand material specific properties. This study aims to analyze possible surface changes of a commercially available and approved DLP 3D printed definitive restoration material for dentistry after three-point flexure testing. Furthermore, this study explores whether Atomic Force Microscopy (AFM) is a feasible method for examination of 3D printed dental materials in general. This is a pilot study, as there are currently no studies that analyze 3D printed dental materials using an AFM. Methods: The present study consisted of a pretest followed by the main test. The resulting break force of the preliminary test was used to determine the force used in the main test. The main test consisted of atomic force microscopy (AFM) surface analysis of the test specimen followed by a three-point flexure procedure. After bending, the same specimen was analyzed with the AFM again, to observe possible surface changes. Results: The mean root mean square (RMS) roughness of the segments with the most stress was 20.27 nm (±5.16) before bending, while it was 26.48 nm (±6.67) afterward. The corresponding mean roughness (Ra) values were 16.05 nm (±4.25) and 21.19 nm (±5.71) Conclusions: Under three-point flexure testing, the surface roughness increased significantly. The p-value for RMS roughness was p = 0.003, while it was p = 0.006 for Ra. Furthermore, this study showed that AFM surface analysis is a suitable procedure to investigate surface changes in 3D printed dental materials.

Effect of surface treatments on wear and surface properties of different CAD-CAM materials and their enamel antagonists

STATEMENT OF PROBLEM

Which surface treatment provides optimal surface roughness, microhardness, and wear behavior for computer-aided design and computer-aided manufacturing (CAD-CAM) materials and their enamel antagonists is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of surface treatment on the surface roughness, microhardness, and 2-body wear of different CAD-CAM materials and their enamel antagonists.

MATERIAL AND METHODS

Monolithic zirconia, polymer-infiltrated ceramic network, lithium disilicate, leucite-reinforced ceramic, zirconia-reinforced lithium silicate, and feldspathic ceramic specimens were sliced into 2-mm-thick rectangular plates and divided into polished or glazed subgroups (n=6). After surface roughness and microhardness measurements, the specimens were loaded at 49 N for 250 000 cycles and simultaneously thermocycled (5 °C and 55 °C). All specimens were scanned before and after the wear test by using a scanner. The volumetric loss and wear depth of the materials and the volumetric and height loss of the enamel were calculated, and scanning electron microscope images of the specimens were made. Multiple 2-way ANOVAs and Tukey honestly significant difference tests were used to assess the effect of material and surface treatment on surface roughness, microhardness, and wear behavior of materials and enamel (α=.05).

RESULTS

Material and surface treatment interactions affected the surface roughness (P<.001), microhardness (P<.001), volumetric loss of materials (P=.044), and height loss of enamel (P<.001).

CONCLUSIONS

Polishing resulted in higher surface roughness and microhardness than glazing. Volumetric loss depended on the material, which affected the height loss of the antagonists. Glazing and polishing had similar effects on the volumetric loss of materials and antagonists. No correlation was found between the wear of materials and the antagonists, nor between the surface roughness of materials and the volumetric loss of materials or antagonists.

Aging resistance of highly translucent zirconia ceramics with rapid sintering

PURPOSE

Rapid sintering technology has become one of the most direct methods for shortening the manufacturing time of zirconia restorations. This study aimed to explore the aging resistance of rapid-sintered 5 mol% yttria-partially-stabilized zirconia (5Y-PSZ).

METHODS

Specimens were made from two types of 5Y-PSZ material and subjected to rapid sintering (RS) and conventional sintering (CS). After in vitro aging for 5 h, morphology observation, grain size measurement, and phase composition analysis were performed. The mechanical properties were evaluated by biaxial, three-point flexural tests, and the Vickers microhardness test. Results were analyzed by 3-way ANOVA.

RESULTS

Both the RS group and the CS group had a dense microstructure. The tested zirconia ceramics had different grain sizes, which were affected by the interaction between the sintering method and aging. Both groups revealed the same characteristic peaks of the cubic phase after aging. Regardless of the sintering method used, there was no significant difference in the mechanical properties of the tested zirconia before and after aging.

CONCLUSION

The rapid-sintered 5Y-PSZ materials had a microstructure, phase composition and mechanical properties similar to those of conventional sintered materials. The characteristics of the materials prepared using the two sintering methods did not change significantly after aging.

Effect of acidic media on flexural strength and fatigue of CAD-CAM dental materials

OBJECTIVE

To investigate the effect of acidic media, including beverages and gastric fluids on flexural strength and fatigue of CAD-CAM materials.

METHODS

Four CAD-CAM materials (high-translucency zirconia (Ceramill Zolid HT+), lithium disilicate (IPS e-max CAD), hybrid ceramic (Vita Enamic), and nanohybrid resin composite (Grandio Blocs) were prepared and immersed in one of five media (gastric HCl, white wine, Coca-Cola, orange juice, and artificial saliva) in an incubator (37 ℃, 24 h). Surface topography and roughness were obtained using a scanning electron microscope (SEM) and a stylus contact profilometer, respectively. Initial 3-point flexural strength was measured for half of the bars (n = 20/gp) using a universal testing machine (0.5 mm/min). The other bars underwent 10⁶ cyclic fatigue loadings before measurement of residual 3-point flexural strength. Data were statistically analyzed (two-way and three-way ANOVA, Tukey's post-hoc, p < 0.05). Weibull distributions were plotted for reliability analysis.

RESULTS

Zirconia bars has the highest initial flexural strengths followed by lithium disilicate, while resin composite and hybrid ceramic groups had the lowest strength regardless of the erosive medium. Cyclic fatigue significantly reduced initial flexural strengths for all materials except for hybrid ceramic and resin composite. Weibull moduli were the highest for zirconia, lithium disilicate and resin composite and lowest for hybrid ceramic.

SIGNIFICANCE

Erosive media significantly changed surface roughness of CAD-CAM materials except for zirconia and resin composite without jeopardizing the flexural strength of the CAD-CAM materials. Despite the higher flexural strengths for zirconia and lithium disilicate, resin composite and hybrid ceramic were more resistant to cyclic fatigue.

Indirect restorative systems-A narrative review

OBJECTIVE

The background and clinical understanding of the properties of currently available indirect restorative systems and fabrication methods is, along with manufacturer and evidence-based literature, an important starting point to guide the clinical selection of materials for tooth and/or implant supported reconstructions. Therefore, this review explores most indirect restorative systems available in the market, especially all-ceramic, along with aspects of manufacturing process, clinical survival rates, and esthetic outcomes.

OVERVIEW

Progressive incorporation of new technologies in the dental field and advancements in materials science have enabled the development/improvement of indirect restorative systems and treatment concepts in oral rehabilitation, resulting in reliable and predictable workflows and successful esthetic and functional outcomes. Indirect restorative systems have evolved from metal ceramics and polymers to glass ceramics, polycrystalline ceramics, and resin-matrix ceramics, aiming to improve not only biological and mechanical properties, but especially the optical properties and esthetic quality of the reconstructions, in attempt to mimic natural teeth.

CONCLUSIONS

Based on several clinical research, materials, and patient-related parameters, a decision tree for the selection of indirect restorative materials was suggested to guide clinicians in the rehabilitation process.

CLINICAL SIGNIFICANCE

The pace of materials development is faster than that of clinical research aimed to support their use. Since no single material provides an ideal solution to every case, professionals must continuously seek information from well designed, long-term clinical trials in order to incorporate or not new materials and technological advancements.

Silica infiltration on translucent zirconia restorations: Effects on the antagonist wear and survivability

OBJECTIVE

To assess potential antagonist wear and survival probability of silica-infiltrated zirconia compared to glass-graded, glazed, and polished zirconia.

METHODS

Table top restorations made of 3Y-TZP (3Y), 5Y-PSZ (5Y), and lithium disilicate (LD) were bonded onto epoxy resin preparations. Each zirconia was divided into five groups according to the surface treatment: polishing; glaze; polishing-glaze; glass infiltration; and silica infiltration. The LD restorations received a glaze layer. Specimens were subjected to sliding fatigue wear using a steatite antagonist (1.25 ×106 cycles, 200 N). The presence of cracks, fractures, and/or debonding was checked every one/third of the total number of cycles was completed. Roughness, microstructural, Scanning electron microscopy, wear and residual stress analyses were conducted. Kaplan-Meier, Mantel-Cox (log-rank) and ANOVA tests were performed for statistical analyses.

RESULTS

The survival probability was different among the groups. Silica infiltration and polishing-glaze led to lower volume loss than glaze and glass-infiltration. Difference was observed for roughness among the zirconia and surface treatment, while lithium disilicate presented similar roughness compared to both glazed zirconia. Scanning electron microscopy revealed the removal of the surface treatment after sliding fatigue wear in all groups. Compressive stress was detected on 3Y surfaces, while tensile stress was observed on 5Y.

SIGNIFICANCE

3Y and 5Y zirconia behaved similarly regarding antagonist wear, presenting higher antagonist wear than the glass ceramic. Silica-infiltrated and polished-glazed zirconia produced lower antagonist volume loss than glazed and glass-infiltrated zirconia. Silica-infiltrated 3Y and lithium disilicate restorations were the only groups to show survival probabilities lower than 85%.

Comparative evaluation of enamel wear against monolithic zirconia and layered zirconia after polishing and glazing: An in vitro study

Aim

The aim of this study was to compare the wear behavior of human tooth enamel opposing monolithic zirconia and layered zirconia after glazing and polishing by a two-body wear mechanism using a wear simulator.

Settings and Design

This In-vitro study was done in Department of Prosthodontics, Sri Sai College of Dental Research, Vikarabad.

Materials and Methods

Zirconia specimens were divided into four groups (n = 15), Group monolithic glazed zirconia (MG), Group monolithic polished zirconia (MP), Group zirconia layered with E. max ceram and glazed (LG), Group zirconia layered with E. max ceram and polished without glaze (LP). Sixty human premolar teeth were subjected to wear test against the zirconia specimens using a Pin on Disc wear tester under a constant load of 5 kg (49 N) at 30 rpm for 10,000 cycles. The loss of enamel was recorded before and after the wear test and mean loss of height of tooth enamel after 10,000 cycles of wear was measured with a profile projector. The surface characteristics of all the four group zirconia specimens were evaluated qualitatively with scanning electron microscope.

Statistical Analysis Used

One way ANOVA, Tukey Post hoc.

Results

One-way analysis of variance test revealed that the mean loss of enamel of four groups was statistically different with P < 0.001. A further Tukey post hoc test revealed that the MP group had lesser mean scores than group LP, MG, and LG.

Conclusion

It was concluded that MP caused less wear to opposing natural teeth, and polished surfaces of both monolithic and layered zirconia showed less tooth wear compared to glazed surfaces of monolithic and layered zirconia.

Wear of various restorative materials against 5Y-ZP zirconia

STATEMENT OF PROBLEM

The ceramic 5-mol% yttria-stabilized zirconia (5Y-ZP) has been developed for dental use in the esthetic zone with greater translucency than 3-mol% yttria-stabilized zirconia (3Y-ZP). However, studies on the wear behavior of 5Y-ZP zirconia against clinically relevant antagonist materials are lacking.

PURPOSE

The purpose of this in vitro study was to investigate the wear behavior of 5Y-ZP zirconia against the antagonists 5Y-ZP zirconia, lithium disilicate, palladium alloy, and human enamel.

MATERIALS AND METHODS

Flat specimens (n=8) were fabricated from 5Y-ZP zirconia, lithium disilicate, palladium alloy, and human central incisor enamel. A custom wear-simulating device with a sliding pin-on-plate configuration was used for a total of 120 000 wear cycles at 1.6-Hz frequency under a 49-N vertical load while submerged in distilled water at room temperature. The wear volume and maximum wear depth of flat specimens were evaluated with a 3D profilometer. Scanning electron microscopy was used to analyze the characteristics of the worn surfaces.

RESULTS

After wear simulation, the 5Y-ZP zirconia and palladium-silver alloy specimens exhibited the least amount of material loss, both in terms of maximum wear depth and wear volume (0.079 ±0.042 μm, 0.001 ±0.001 mm³ and 0.637 ±0.307 μm, 0.001 ±0.000 mm³, respectively). This was followed by human enamel (6.034 ±1.086 μm, 0.009 ±0.001 mm³) and by lithium disilicate, which showed excessive material loss (38.342 ±2.569 μm, 0.213 ±0.024 mm³). Scanning electron microscopy revealed variations in wear mechanisms among the materials.

CONCLUSIONS

The 5Y-ZP zirconia and palladium-silver alloy exhibited the lowest wear, followed by human enamel and lithium disilicate. Slight grain dislodgement was displayed on worn 5Y-ZP surfaces, while more apparent grain dislodgement and wear grooves were found on lithium disilicate. Plastic deformation of worn palladium-silver alloy accumulated at the end of wear track. Cracks were detected in the human enamel specimens.

Wear Behavior between Aesthetic Restorative Materials and Bovine Tooth Enamel

Tooth enamel wear occurs because of daily mastication and occlusion. This study investigated the wear behavior of bovine teeth against aesthetic restorative materials in vitro. Abrader specimens were fabricated using four tooth-colored restorative materials (zirconia, lithium disilicate glass ceramic, dental porcelain, and resin composite), with bovine tooth enamel as a control. Flattened bovine tooth enamel was used as the substrate specimen. These materials were characterized by Vickers hardness tests and surface roughness measurements. Two-body wear tests between the abrader and substrate specimens were performed, and the worn topographies were evaluated using a contour-measuring instrument and 3D laser microscope. The restorative materials and bovine tooth enamel had similar surface roughness but different hardness and wear behaviors. Bovine teeth showed the largest wear in tooth–tooth contact as the abrader and substrate specimens. Compared to bovine teeth, zirconia, lithium disilicate glass ceramic, and dental porcelain showed greater hardness and less wear on their surfaces, and less substrate wear of the opposite tooth enamel. The lowest hardness resin composite showed intermediate wear on its surface, resulting in the lowest substrate wear. Accordingly, dentists should pay attention to the selection of restorative materials to reconstruct their morphologies owing to different wear behaviors.

Wear Behaviour of Polymer-Infiltrated Network Ceramics, Lithium Disilicate and Cubic Zirconia against Enamel in a Bruxism-Simulated Scenario

The present study aimed to evaluate the wear rate of polymer-infiltrated network composites and ceramics against enamel in a bruxism-simulated scenario. Ninety-six (n = 96) molars were divided into six groups (n = 16) according to their occlusal material: group 1—a polymer-infiltrated network ceramic (PINC); group 2—a second polymer-infiltrated network ceramic (PINC2); group 3—nanohybrid resin-based composite (CO); group 4—cubic zirconia (ZR); group 5—lithium disilicate (LS); and group 6—sound enamel (EN). A laser scanner was used to digitalize all of the occlusal surfaces before and after a fatigue test, which was conducted with a chewing simulator set at 80 N and semicircular movement in order to simulate bruxist movement and loads. Statistical analysis of volume loss was performed with a one-way ANOVA and post hoc Bonferroni test. ZR had significantly inferior wear to PINC (p ≤ 0.01) and CO (p = 0.04). LS wore the antagonist enamel significantly more than PINC, CO, PINC2 and EN (p ≤ 0.01). On the other hand, ZR wore the antagonist enamel significantly more than CO (p ≤ 0.01) and PINC2 (p = 0.05). In conclusion, PINCs better preserved antagonist enamel at the expense of a higher wear of their own. LS causes significantly higher enamel wear compared with PINCs. ZR caused significantly higher enamel wear compared with CO and PINC2, but it was wear-resistant.

Wear behavior and abrasiveness of monolithic CAD/CAM ceramics after simulated mastication

Objectives

To evaluate the wear resistance and abrasiveness of monolithic CAD/CAM ceramics.

Materials and methods

Rectangular-shaped specimens (12 mm × 6.5 mm × 1.5 mm) were sectioned from the following CAD/CAM blocks (n = 10); partially crystallized lithium disilicate (PLD), experimental fully crystallized lithium disilicate (FLD), zirconia-reinforced lithium silicate (ZLS), super-translucent monolithic zirconia (SMZ), and ultra-translucent monolithic zirconia (UMZ). Silicon carbide papers were used to mechanically flatten and polish the surfaces. PLD specimens were subjected to a combined crystallization/glazing firing cycle. Ceramic specimens were mounted to the wear device and tested for 200,000 cycles against human premolars at 20 N force and 2 mm sliding distance. Artificial saliva was used as a lubricant. The teeth were scanned using micro-CT before and after the wear test and the generated models were overlapped to determine the volumetric tooth loss. Before and after the test, specimens’ weights and surface roughness (R_a) values were measured, and the differences were calculated. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were utilized for microstructural and chemical analysis. Statistical analysis was performed using one-way ANOVA or an equivalent test for non-parametric results. Significance level was set at P ≤ 0.05.

Results

The type of ceramic material affected the ceramic and antagonist wear rates (P < 0.001). PLD and ZLS had the highest ceramic and antagonist wear, whereas UMZ and SMZ demonstrated the lowest wear values. The FLD group showed comparable antagonist wear and significantly less ceramic wear than PLD and ZLS.

Conclusions

Monolithic zirconia demonstrated the best wear resistance and least abrasiveness to the antagonist. The experimental lithium disilicate was more wear-resistant than other glass–ceramic groups.

Clinical relevance

Monolithic zirconia is wear-resistant and gentle on the antagonist. In contrast, glass–ceramics are more abrasive to enamel.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00784-022-04611-w.

Effect of erosive media on microhardness and fracture toughness of CAD-CAM dental materials

Background

Erosive acids might create surface flaws and deteriorate the mechanical properties of CAD-CAM materials. This invitro study aimed to investigate the effect of simulated gastric HCl and extrinsic erosive acids on surface microhardness and fracture toughness of CAD-CAM materials.

Methods

400 bar-shaped specimens (17×4×2 mm³) were prepared from 4 different CAD-CAM dental materials (n = 100/group); monolithic zirconia (Ceramill Zolid HT+, Amanngirbach, Austria), lithium disilicate ceramic (IPS e.max CAD, Ivoclar Vivadent, Liechtenstein), nanohybrid resin composite (Grandio Blocs, VOCO) and polymer-infiltrated glass network (Vita Enamic, VITA Zahnfabrik). Specimens from each material type were further subdivided into 5 groups (n = 20) according to the erosive media applied (simulated gastric HCl, white wine, Coca-Cola®, orange juice, and artificial saliva that served as a control). Specimens were immersed for 24 h in an incubator at 37 ℃, then ultrasonically cleaned in distilled water and air-dried. Half of the specimens were tested for Vickers microhardness (VHN) at parameters of 500 gf for 10 s, while the rest of the specimens underwent 3-point flexure till fracture. Fractured surfaces were examined under a scanning electron microscope (SEM) for fracture toughness (K_IC) calculation using the quantitative fractographic analysis method. Data collected were statistically analyzed using two-way analysis of variance (α = 0.05) after verification of data normality and homogeneity of variances.

Results

Erosive media created surface flaws that lowered the surface microhardness of the material and initiated the fracture pattern under different loads according to material type. The material type was a more predominant factor than erosive media that affected either the microhardness or the fracture toughness of CAD-CAM dental materials. The highest VHN and K_IC values were found among Ceramill Zolid HT+ groups followed by IPS e.max CAD and Grandio Blocs regardless of the erosive media employed. Erosive media significantly reduced the VHN and K_IC in Vita Enamic specimens compared to the rest of the material types.

Conclusion

All CAD-CAM materials used, except Vita Enamic, showed high resistance against the erosive acids indicating higher longevity of the material in patients frequently exposed to either extrinsic or intrinsic acid.

Effect of aqueous environment on wear resistance of dental glass-ceramics

Background

Wear resistance affects dental ceramics longevity and the functions of the opposing teeth. However, data for the effect of aqueous environment on wear resistance of dental ceramics are lacking. This study evaluated the effect of aqueous environment on wear resistance of typical dental glass–ceramics.

Methods

Disk specimens were prepared from lithium disilicate glass–ceramics (LD) and leucite reinforced glass–ceramics (LEU). The disk specimens paired with steatite antagonists were tested in a pin-on-disk tribometer under both wet and dry conditions with 10 N up to 500,000 wear cycles. The wear analysis of glass–ceramics was performed using a 3D profilometer after 100,000, 300,000 and 500,000 wear cycles. Wear morphologies were analyzed by employing scanning electron microscopy (SEM). The crystalline compositions of specimens stored in a dry environment and subsequently immersed in distilled water for 40 h were separately determined using X-ray diffraction (XRD). The chemical states of the wear surfaces for LD were analyzed by X-ray photoelectron spectroscopy (XPS). The data analysis and multiple pair-wise comparisons of means were performed by using one-way analysis of variance (ANOVA) and Tukey’s post-hoc test.

Results

LEU in a wet environment exhibited less wear volume loss than that in a dry environment (p < 0.05). The volume loss of LD in a wet environment was higher than that in a dry environment (p < 0.05). The wear volumes of steatite antagonists paired with two glass–ceramics under dry conditions were higher than under wet conditions.

Conclusions

XPS spectra of LD under wet conditions indicated that high wear loss might result from the effect of stress corrosion by water and reaction of water with the ionic-covalent bonds at the crack tip. XPS spectra and SEM images of LD under dry conditions showed a possible formation of tribofilm. Within the limitations of this in vitro study, water was wear-friendly to LEU and all opposing steatites but aggravated wear for LD.

Enamel wear against monolithic zirconia restorations: A meta-analysis and systematic review of in vitro studies

OBJECTIVE

An assessment was performed to identify and evaluate dental enamel wear caused by monolithic zirconia restoration. Literature searches were conducted in PubMed, Science Direct, Cochrane Evidence, and the Cochrane Library up to May 2020.

MATERIAL AND METHODS

Studies were selected for systematic review according to the inclusion (articles conducted on the wear of enamel samples opposing monolithic zirconia) and exclusion (case reports, non-English articles, and monolithic zirconia samples facing other materials rather than human enamel) criteria. Of those, articles on polished and glazed monolithic zirconia subjected to a 50 N vertical load with a range of 240,000-250,000 cycles, equivalent to 1 year of in vivo mastication, were included in the meta-analysis.

RESULTS

In total, 3968 articles were pooled. Twenty-five articles met the inclusion criteria for the systematic review. Three studies were included in the meta-analysis. The results showed that the enamel wear against monolithic zirconia was within the statistically accepted level. Moreover, the polished monolithic zirconia surface caused less enamel wear than the glazed surface.

CONCLUSION

This review indicates that monolithic zirconia restorations cause acceptable antagonist enamel wear. Moreover, the meta-analysis results agreed that the final restoration's surface texture plays an essential role in the wear process.

CLINICAL SIGNIFICANCE

Monolithic zirconia restorations have been widely used in dental practice because they eliminate the chipping problems resulting from using veneered restorations. With recent technology development, monolithic zirconia has obtained more esthetic features and a more natural look. However, due to the high strength and surface roughness of monolithic zirconia, wear on the antagonist's teeth was detected. The results showed that this wear amount was statistically acceptable and lower than other ceramics such as feldspathic porcelain and enamel. Furthermore, surface treatment methods must be applied to minimize tooth wear, as polished or glazed surfaces interfere with enamel loss.

Evaluation of intaglio surface trueness, wear, and fracture resistance of zirconia crown under simulated mastication: a comparative analysis between subtractive and additive manufacturing

PURPOSE

This in-vitro analysis aimed to compare the intaglio trueness, the antagonist's wear volume loss, and fracture load of various single-unit zirconia prostheses fabricated by different manufacturing techniques.

MATERIALS AND METHODS

Zirconia crowns were prepared into four different groups (n = 14 per group) according to the manufacturing techniques and generations of the materials. The intaglio surface trueness (root-mean-square estimates, RMS) of the crown was measured at the marginal, axial, occlusal, and inner surface areas. Half of the specimens were artificially aged in the chewing simulator with 120,000 cycles, and the antagonist's volume loss after aging was calculated. The fracture load for each crown group was measured before and after hydrothermal aging. The intaglio trueness was evaluated with Welch's ANOVA and the antagonist's volume loss was assessed by the Kruskal-Wallis tests. The effects of manufacturing and aging on the fracture resistance of the tested zirconia crowns were determined by two-way ANOVA.

RESULTS

The trueness analysis of the crown intaglio surfaces showed surface deviation (RMS) within 50 µm, regardless of the manufacturing methods (P = .053). After simulated mastication, no significant differences in the volume loss of the antagonists were observed among the zirconia groups (P = .946). The manufacturing methods and simulated chewing had statistically significant effects on the fracture resistance (P < .001).

CONCLUSION

The intaglio surface trueness, fracture resistance, and antagonist's wear volume of the additively manufactured 3Y-TZP crown were clinically acceptable, as compared with those of the 4Y- or 5Y-PSZ crowns produced by subtractive milling.

Wear Behavior of Different Generations of Zirconia: Present Literature

Objective. The wear behavior of the novel zirconia generation is less well understood and may be affected by compositional modifications compared to the conventional zirconia. Materials and Methods. Combinations of keywords such as “zirconia,” “high translucent,” and “wear” were searched in PubMed and Google Scholar databases up to May 2021. The total of 23 relevant articles was selected according to inclusion criteria. Results. Reports show comparable wear resistance of translucent zirconia to the conventional zirconia despite an increased cubic phase content and lower mean flexural strength. A meticulously polished surface creates the lowest surface roughness, producing favorable zirconia wear resistance and antagonist wear compared to a glazed surface. In comparison to other ceramic materials, zirconia produces the least wear on an enamel antagonist and almost undetectable wear when opposed by zirconia. Wear when paired against resin materials yields a favorable outcome, whereas wear behavior against a metal antagonist varies with the surface hardness of the metal. Conclusions. All zirconia generations are considered wear-friendly to all types of antagonists. Nonetheless, comparative studies on antagonist wear opposing zirconia of different compositions are still limited and further investigation is required.

Revolution of Current Dental Zirconia: A Comprehensive Review

The aim of this article is to comprehensively review the revolution of dental zirconia (Zir), including its types, properties, applications, and cementation procedures. A comprehensive search of PubMed and Embase was conducted. The search was limited to manuscripts published in English. The final search was conducted in October 2021. Newly developed monolithic Zir ceramics have substantially enhanced esthetics and translucency. However, this material must be further studied in vitro and in vivo to determine its long-term ability to maintain its exceptional properties. According to the literature, monolithic translucent Zir has had promising results and a high survival rate. Thus, the utilization of this material is indicated when strength and esthetics are needed. Both the materials and methods used for cementation of monolithic Zir have significantly improved, encouraging dentists to use this material, especially when a conservative approach is required. Zir restorations showed promising outcomes, particularly for monolithic Zir crowns supported with implant and fixed dental prostheses.

Wear evaluation of CAD-CAM dental ceramic materials by chewing simulation

PURPOSE

To evaluate the wear of computer-aided design/computer-aided manufacturing (CAD-CAM) dental ceramic materials opposed by enamel as a function of increased chewing forces.

MATERIALS AND METHODS

The enamel cusps of healthy human third molar teeth (n = 40) opposed by materials from CAD-CAM dental ceramic groups (n = 10), including Vita Enamic® (ENA), a polymer-infiltrated ceramic network (PICN); GC Cerasmart® (CERA), a resin nanoceramic; Celtra® Duo (DUO), a zirconia-reinforced lithium silicate (ZLS) ceramic; and IPS e.max ZirCAD (ZIR), a polycrystalline zirconia, were exposed to chewing simulation (1,200,000 cycles; 120 N load; 1 Hz frequency; 0.7 mm lateral and 2 mm vertical motion). The wear of both enamel cusps and materials was quantified using a 3D laser scanner, and the wear mechanisms were evaluated by scanning electron microscopy (SEM). The results were analysed using Welch ANOVA and Kruskal Wallis test (α = .05).

RESULTS

ZIR showed lower volume loss (0.02 ± 0.01 mm³) than ENA, CERA and DUO (P = .001, P = .018 and P = .005, respectively). The wear of cusp/DUO [0.59 mm³ (0.50-1.63 mm³)] was higher than cusp/CERA[0.17 mm³ (0.04-0.41 mm³)] (P = .007). ZIR showed completely different wear mechanism in SEM.

CONCLUSION

Composite structured materials such as PICN and ZLS ceramic exhibit more abrasive effect on opposing enamel due to their loss against wear, compared to uniform structured zirconia. The resin nanoceramic causes the lowest enamel wear thanks to its flexible nano-ceramic microstructure. While zirconia appears to be an enamel-friendly material in wear volume loss, it can cause microstructural defects of enamel.

Longevity of Polymer-Infiltrated Ceramic Network and Zirconia-Reinforced Lithium Silicate Restorations: A Systematic Review and Meta-Analysis

The purpose of this study was to systematically review the existing literature to assess the clinical survival and success of PICN and ZLS indirect restorations as the clinical evidence for them remains lacking. PubMed, SCOPUS, Embase, Cochrane Library, Web of Science, LILACs, and SciElo databases were searched from 1 January 2000 to 1 February 2021. Clinical trials and cohort studies published in English were included while case studies, case series, and in vitro studies were excluded. Results were analyzed qualitatively and a meta-analysis using a random effects model was performed. A strength of recommendation taxonomy (SORT) analysis was conducted and risk of bias (RoB) was assessed using the Newcastle-Ottawa scale and Cochrane RoB tools. An electronic search through the databases yielded 2454 articles, of which 825 remained after duplicate removal. Five studies investigating PICN and four investigating ZLS indirect restorations remained after assessing for eligibility. The overall survival rate of PICN over 1 year was 99.6% and 99.2% over 2 years. The overall survival rate of ZLS over 1 year was 99%. The main mode of failure for both materials was catastrophic fracture. One study had a high RoB, four had a moderate RoB, and four had a low RoB. Both materials demonstrated moderate strength of recommendation at a level 2 evidence for all studies based on SORT analysis. PICN and ZLS show promising short-term clinical performance as full and partial coverage indirect restorations, but longer follow-up studies are required to confirm their long-term performance.

Clinical wear and quality assessment of monolithic and lithium disilicate layered zirconia restorations

BACKGROUND

Wear and quality assessments of translucent monolithic zirconia and CAD-on^® restorations were performed.

METHODS

Forty 3-unit posterior fixed partial denture (FPD) in 18 patients (age:18-50 years) were made from translucent monolithic zirconia (tm) (Zenostar T) and zirconia-frameworked, lithium disilicate layered (c) (CAD-on), materials in a split-mouth design. Restorations were digitally fabricated and their internal and marginal adaptations were measured before cementation followed by luting (Multilink Speed). Clinical evaluations were made by modified United States Public Health Service criteria at baseline, 6, 12, and 24-months. Wear of the restorations and the antagonists were digitally evaluated after optical scanning of stone casts at 1st week and 24 m through a software (Cerec 4.4). Statistical analysis was made (analysis of variance, Shapiro-Wilk, Friedman and Wilcoxon tests (SPSS 20)) at α = 0.05 significance level.

RESULTS

At 24 m, all restorations were clinically acceptable. Insignificant differences were found between tm and c restorations (P > 0.05). Mean internal and marginal adaptation of c restorations were significantly better (145 µm (premolar)-174 µm (molar)) than tm (190 µm (premolar)-207 µm (molar)) (P < 0.05). C restorations significantly caused more wear (0.3 ± 0.1 mm) than tm (0.1 ± 0.07 mm) on the antagonistic dentition (P < 0.05).

CONCLUSIONS

Translucent monolithic zirconia restorations caused less wear and antagonist wear than CAD-on restorations. CAD-on restorations exhibited higher internal and marginal adaptation.

Wear of 3D printed and CAD/CAM milled interim resin materials after chewing simulation

PURPOSE

The purpose of this in vitro study was to investigate the wear resistance and surface roughness of three interim resin materials, which were subjected to chewing simulation.

MATERIALS AND METHODS

Three interim resin materials were evaluated: (1) three-dimensional (3D) printed (digital light processing type), (2) computer-aided design and computer-aided manufacturing (CAD/CAM) milled, and (3) conventional polymethyl methacrylate interim resin materials. A total of 48 substrate specimens were prepared. The specimens were divided into two subgroups and subjected to 30,000 or 60,000 cycles of chewing simulation (n = 8). The wear volume loss and surface roughness of the materials were compared. Statistical analysis was performed using one-way analysis of variance and Tukey's post-hoc test (α=.05).

RESULTS

The mean ± standard deviation values of wear volume loss (in mm³) against the metal abrader after 60,000 cycles were 0.10 ± 0.01 for the 3D printed resin, 0.21 ± 0.02 for the milled resin, and 0.44 ± 0.01 for the conventional resin. Statistically significant differences among volume losses were found in the order of 3D printed, milled, and conventional interim materials (P<.001). After 60,000 cycles of simulated chewing, the mean surface roughness (Ra; μm) values for 3D printed, milled, and conventional materials were 0.59 ± 0.06, 1.27 ± 0.49, and 1.64 ± 0.44, respectively. A significant difference was found in the Ra value between 3D printed and conventional materials (P=.01).

CONCLUSION

The interim restorative materials for additive and subtractive manufacturing digital technologies exhibited less wear volume loss than the conventional interim resin. The 3D printed interim restorative material showed a smoother surface than the conventional interim material after simulated chewing.

Effects of surface roughness on the time-dependent wear performance of lithium disilicate glass ceramic for dental applications

OBJECTIVES

Purpose of the present study was to evaluate the effect of surface roughness on the time-dependent wear performance of lithium disilicate (LD) glass-ceramic.

METHODS

Friction pairs (pin and disk specimens) were prepared by IPS e.max® Press lithium disilicate glass-ceramic. The lateral faces of friction pairs (N = 12) were grinded with silicon carbide papers, and 6 friction pairs were polished with a 0.25 μm diamond suspension after grinding. The friction pairs were tested for wear performance using a pin-on-disk tribometer with 10 N for 1.02 × 10⁶ wear cycles in artificial saliva. Wear analysis of the pin and disk was performed with a 3D profilometer. The microstructure and worn surface morphology were examined with scanning electron microscopy. One-way analysis of variance and Tukey's post-hoc pairwise comparison were used to analyze the wear data.

RESULTS

The two group LD friction pairs presented strong time-dependent wear performance. The polished group (GP) exhibited a high wear rate and extensive surface wear during 0-1 × 10⁵ cycles (running-in wear stage). The wear rate, height loss and surface roughness were obviously lower than those of grinded group (GG) in running-in wear stage. However, these wear parameters were similar during the steady wear stage. The worn surface topographies of the pin and disk in GP were smoother at the same cycle before the GG entering the steady wear stage.

CONCLUSION

Running-in, which means the initial stage of wear process, is a critical period to determine the final wear loss and surface degradation, when compare the wear behavior of lithium disilicate ceramic with different initial surface states. Ceramic layer with smooth contact area leads to low wear rate and short running-in wear stage.

Risk Indicators Affecting the Survival of the Mandibular First Molar Adjacent to an Implant at the Mandibular Second Molar Site: A Retrospective Study

This study aimed to compare the survival of mandibular first molars (MnM1s) adjacent to implants placed in mandibular second molar sites (ImM2s) with MnM1s adjacent to mandibular second molars (MnM2s) and to investigate risk indicators affecting the survival of MnM1s adjacent to ImM2s. A total of 144 patients who had MnM1s adjacent to ImM2s and MnM1s adjacent to MnM2s on the contralateral side were included in this study. Clinical variables and radiographic bone levels were evaluated. The survival of MnM1s adjacent to ImM2s or MnM2s was evaluated using a Kaplan–Meier analysis and Cox proportional hazards model. The 5-year cumulative survival rates of MnM1s adjacent to ImM2s and MnM2s were 85% and 95%, respectively. MnM1s adjacent to ImM2s of the internal implant-abutment connection type had higher multivariate hazard ratios (HR) for loss. MnM1s that had antagonists with implant-supported prostheses also had higher HR for loss. The multivariate HR for the loss of MnM1s adjacent to ImM2s with peri-implant mucositis was 3.74 times higher than MnM1s adjacent to healthy ImM2s. This study demonstrated several risk indicators affecting the survival of MnM1s adjacent to ImM2s. It is suggested that supportive periodontal and peri-implant therapy combined with meticulous occlusal adjustment can prolong the survival of MnM1s and ImM2s.

Fabrication of enamel-like structure on polymer-infiltrated zirconia ceramics

OBJECTIVES

The aim of this study is to improve the biological and mechanical properties of zirconia-based PICN (polymer-infiltrated-ceramic-network) materials by fabrication an enamel-like structure on its surface.

METHODS

Fluorapatite (FA) arrays were fabricated on zirconia discs by hydrothermal treatment. After polymer infiltration, an enamel-like structure was obtained on zirconia-based PICN materials. Effects of hydrothermal treatment conditions on the FA arrays were investigated by XRD, FTIR and SEM. Human gingival fibroblast cells (HGFs) and Escherichia coli (E. coli) were used to evaluate the cytocompatibility and antibacterial properties. Nanoindentation method was employed to determine elastic modulus and hardness.

RESULTS

A facile and pervasive method was developed in this study to fabricate an enamel-like structure constituted of controlled FA arrays and interstitial resin on zirconia-based PICN materials. The obtained FA arrays can significantly promote the adhesion and proliferation of human gingival fibroblasts (HGFs), and further effectively inhibit the growth of Escherichia coli. Owing to the hierarchical structure, the enamel-like structure has achieved a hardness of 1.79 GPa and a lower Young's modulus of 37.4 GPa.

SIGNIFICANCES

The enamel-like structure, with excellent biological and mechanical properties, is promising for various applications in dentistry.

The need for polishing and occlusal adjustment of zirconia prostheses for wear on antagonist teeth

The attrition of enamel when opposed by ceramics is of great concern. The purpose of this study was to evaluate enamel wear against high translucent zirconia (Zr), lithium disilicate (LD), gold (Au), and enamel (E) with different surface and contact conditions. The materials were divided into two groups: polished and ground (n=8 each). Two-body wear tests were performed against human enamel with vertical and horizontal, horizontal, and vertical repetitive movements as experiments 1 to 3 respectively. The surface roughness of all materials except Zr changed throughout the experiments. In experiment 1, Zr and Au showed less antagonist wear when polished than when ground. In experiment 2, polished groups showed less antagonist wear than ground groups in all materials. In experiment 3, Zr and LD exerted greater antagonist wear than E, regardless of Ra. These findings confirm the importance of polishing and occlusal adjustment of zirconia.

Wear of feldspathic-ceramic-veneered zirconia posterior FPDs after 10 years

Background

The abrasion behavior of various ceramics is rarely investigated, though it is relevant for the clinical success of such restorations. The aim of this in vivo study was to evaluate the wear of feldspathic-ceramic-veneered zirconium oxide frameworks over a period of at least 10 years.

Methods

The abrasion behavior of 15 bridge constructions from 15 different participants was examined after a period of 3, 5, and 10 years using plaster models, which were then subjected to a scanning process on the Atos II industrial scanner and digitized for three-dimensional evaluation of the abrasion by the corresponding software (ATOS Professional 7.6). The individual post-examination models were compared to the baseline model and deviations calculated in the sense of the largest, punctual loss of material in millimeters (“minimal distance”), the average abrasion in millimeters (“mean distance”), and the volume decrease in cubic millimeters (“integrated distance”). Statistical analyses were performed using the Wilcoxon sign rank test or mixed regression models. Multiple testing was considered by Benjamini-Hochberg correction. The significance level was set at 0.05.

Results

We found steadily increasing wear of the ceramic. The average volume decrease was significant (P < 0.001) at 3 years and 10 years (− 3.25 mm³ and − 8.11 mm³, respectively).

Conclusions

The results of this study indicate that the rate of volume loss in feldspathic-ceramic-veneered zirconia frameworks in the posterior region increases significantly over time. An increasing frequency of parameters was observed, particularly in the second half of the study period. However, the use of this class of materials can be considered clinically acceptable.

Trial registration This study is registered in DRKS - German Clinical Trials Register with the register number DRKS00021743. https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00021743

Novel methodology for measuring intraoral wear in enamel and dental restorative materials

Objectives

To test the hypotheses that (a) the chairside/handheld dental scanner combined with a metrology software will measure clinical wear in vivo in agreement with measurements from X‐ray computed microtomography and; (b) polished monolithic zirconia does not cause accelerated wear of opposing enamel.

Materials and methods

Thirty single crowns were randomized to receive a monolithic zirconia or metal‐ceramic crown. Two non‐restored opposing teeth in the same quadrants were identified to serve as enamel controls. After cementation, quadrants were scanned using an intraoral dental scanner. Patients were recalled at 6‐months and 1‐year for re‐scanning. Scanned images were compared using a metrology software to determine maximum vertical wear of teeth. The accuracy of the scanning measurements from this new method was compared with X‐ray computed microtomography (micro‐CT) measurements. Statistical analysis was performed using Mann–Whitney U test to determine significant differences between wear of enamel against zirconia, metal‐ceramic or enamel. Linear regression analysis determined agreement between measurements obtained using intraoral scanning and micro‐CT.

Results

Regression analysis demonstrated that there is a quantitative agreement between depth and volume measurements produced using intraoral scanning and the micro‐CT methodologies. There was no significant difference between the wear of enamel against polished monolithic zirconia crowns and enamel against enamel.

Conclusions

Intraoral scanning combined with a matching software can accurately quantify clinical wear to verify that monolithic zirconia exhibited comparable wear of enamel compared with metal‐ceramic crowns and control enamel. Agreement between the intraoral scanner and the micro‐CT was 99.8%. Clinical Trials.gov NCT02289781.

A State-of-the-Art Review on the Wear of the Occlusal Surfaces of Natural Teeth and Prosthetic Crowns

This review focuses on the wear mechanisms of natural and restorative dental materials, presenting a comprehensive description and analysis of the works published in the last two decades on the wear at the interface of occlusal surfaces. Different groups of tribological pairs were considered: tooth-tooth, tooth-restorative material (tooth-ceramic, tooth-resin-based-materials, and tooth-metal), and restorative-restorative materials. The lack of standardization of the wear tests impairs the direct comparison of the obtained results. However, it was possible to infer about the main wear mechanisms observed on the different classes of dental materials. Concerning ceramics, their toughness and surface finishing determines the wear of antagonist tooth. Abrasion revealed to be the main wear mechanisms at occlusal interface. In the case of resin-based composites, the cohesion of the organic matrix and the nature, shape, and amount of filler particles greatly influences the dental wear. The protruding and detachment of the filler particles are the main causes of abrasion of antagonist enamel. Metallic materials induce lower wear on antagonist enamel than the other classes of materials, because of their low hardness and high ductility. Most of the studies revealed plastic deformation and adhesive wear as the main wear mechanisms. Overall, more research in this area is needed for a better understanding of the mechanisms involved at the occlusal surfaces wear. This would be essential for the development of more suitable restoration materials.

Two-body wear test of enamel against laboratory polished and clinically adjusted zirconia

AIM

A two-body wear test experiment was performed on human enamel, in simulated chewing motion, against non-veneered zirconia ceramic. Aim-1 was to ascertain the effect of zirconia roughness on enamel wear. Aim-2 was to ascertain the relative enamel wear between enamel-zirconia wear pair and enamel-enamel control pair.

MATERIALS

Six molar and premolar human enamel cusps per group were used for a dental wear test against laboratory polished (LP) zirconia and laboratory polished and clinically adjusted (LP + CA) zirconia. Enamel antagonists were tested against incisor teeth as a control group to demonstrate laboratory enamel wear.

METHODOLOGY

Two-body wear tests were conducted in a dual-axis biomimetic dental wear simulator. 49N loading force was used for 120,000 cycles with 1 mm lateral movement of the test specimen at 1.6Hz frequency, under constant ambient temperature water flow. Surface roughness before testing was determined using 3D profilometry. Loss of enamel height and volume i.e. vertical wear and volumetric wear respectively, were measured by superimposition of before and after testing scans by 3D laser scanning. Scanning electron microscopy was used for surface morphology assessment. One-way ANOVA and Post Hoc Multiple Comparisons with Bonferroni corrections were used at the 5% significance level to determine whether surface finish affected volumetric and vertical enamel loss. The relationship between volumetric and vertical loss of enamel was assessed using Pearson's correlation test.

RESULTS

No significant difference was found between LP and LP + CA zirconia in vertical and volumetric enamel wear results. Control enamel had significantly higher vertical and volumetric enamel wear than LP and LP + CA zirconia. Pearson correlation revealed a strong relationship between vertical wear and volumetric wear of enamel.

CONCLUSION

Within the constraints of the test method in this experiment, zirconia irrespective of surface preparation, was found to cause less vertical and volumetric enamel wear compared to control enamel. No statistically significant difference was seen between LP zirconia and LP + CA zirconia.