Current ceramic materials and systems with clinical recommendations: A systematic review

Marginal and internal fit of feldspathic ceramic CAD/CAM crowns fabricated via different extraoral digitization methods: a micro-computed tomography analysis

The aim of this study was to compare the fit of feldspathic ceramic crowns fabricated via 3 different extraoral digitizing methods. Twelve maxillary first premolars were prepared and 36 single crowns were fabricated via 3 extraoral digitizing methods using a laboratory scanner (n = 12): (1) scanning the typodont (ST [control] group); (2) scanning the impression (SI group); (3) scanning the stone cast (SC group). Micro-computed tomography was used to calculate two-dimensional marginal-internal gap and the three-dimensional volumetric gap between the crowns and their corresponding dies. The measured gaps were divided into 6 location categories as follows: marginal gap (MG), finish line gap (FLG), axial wall gap (AWG), cuspal gap (CG), proximal transition gap (PTG), and central fossa gap (CFG). The correlation between each of the 3 extraoral digitizing methods and the adaptation status of the crown margins were also evaluated. The Wilcoxon signed-rank test, Spearman's rank test, and Chi-square test were used for data analysis (α = 0.05). The marginal gaps in the ST, SI, and SC groups differed significantly (24, 198 and 117.6 µm, respectively) (p < 0.05). Significant differences were found between the groups with regard to internal gap measurements, with SI representing higher gap measurements at FLG, PTG and CFG locations (p < 0.05). 3D volumetric gap measurements did not differ significantly (p > 0.05). Under-extended margins observed in the SI and SC groups were correlated with the digitizing method (Cramer's V-square: 0.14). When performing extraoral digitalization, clinicians should choose to scan the stone cast as scanning the stone cast resulted in better internal and marginal fit compared to scanning the impression.

Evaluation of Changes in Temperature of Zirconia Frameworks During Grinding Under Different Chair-Side Conditions: An In Vitro Study

Aim:

To evaluate the changes in the temperature of zirconia during grinding under different clinical conditions.

Materials and Methods:

A total of 60 zirconia framework specimens were fabricated and divided into groups of 10 specimens each. Two different handpieces, namely, a high-speed handpiece (HSH) and a low-speed handpiece (LSH), were used for grinding with and without water cooling. Fine- and coarse-grit diamond burrs were used with the HSH, separately. The following six groups were created: (a) HSH fine-grit with water cooling, (b) HSH coarse grit with water cooling, (c) HSH fine grit without water cooling, (d) HSH coarse grit without water cooling, (e) LSH with water cooling, and (f) LSH without water cooling. Each zirconia framework was ground until 1 mm3 of the material was removed. Temperature values corresponding to the grinding techniques were compared and statistically analyzed. One-way analysis of variance was used to compare the group parameters, while the Tukey honest significant difference test was used to detect significant differences between the groups. The significance level was set at P <.05.

Results:

The highest mean temperature was measured in the case of grinding with the LSH without water cooling (54.7 °C ± 11.6 °C), while the lowest mean temperature was observed in the case of grinding with the HSH using the coarse-grit diamond rotary instrument under water cooling (22.6 °C ± 0.6 °C).

Conclusions:

The grinding of zirconia must be performed with an HSH under water cooling. Further, when water cooling is used, neither the type of handpiece nor the grain type of the rotary instrument used as it has a significant effect on the temperature.

Current status and research trends of lithium disilicate in dentistry: A bibliometric analysis

STATEMENT OF PROBLEM

Lithium disilicate (LD) is a popular dental ceramic and has been a focus of dental research. Nevertheless, a quantified literature analysis focusing on the research of lithium disilicate is lacking.

PURPOSE

The purpose of this bibliometric analysis was to review the progress of research into lithium disilicate in dentistry, including the identification of contributing researchers, organizations, countries or regions, journals, and the analysis of high-impact keywords and research trending.

MATERIAL AND METHODS

The search was carried out within the topic field of the Web of Science (WoS) database, collecting publications related to LD from between 1996 and 2019. Metadata including the titles, abstracts, keywords, authors, affiliations, countries or regions, and references were extracted. Bibliometric indicators in terms of documents, authors, journals, and keywords were analyzed.

RESULTS

Between 1996 and 2019, the dental research on LD trended upward. Scholars in the United States, Germany, Switzerland, and Brazil actively participated in the research on LD, and publications from the United States had the most citations. The Journal of Prosthetic Dentistry and Dental Materials were the major contributing journals. High-impact terms could be categorized into types of restorative material, types of prostheses, and properties or techniques of materials. Co-occurrence and relative normalized citation analysis of keywords highlighted several research interests, such as comparison studies between LD and zirconia, computer-aided design and computer-aided manufacturing (CAD-CAM) techniques, and the performance of complete coverage LD restorations.

CONCLUSIONS

With the global upsurge in research on lithium disilicate, extensive collaborations and citations have been noted among authors, institutions, and countries or regions. Research hotspots include types of restorative material, types of prostheses, and properties or techniques of materials.

Effect of luting agent type on fracture loads of implant-supported ceramic premolar prostheses

To investigate the effect of luting agent type on fracture loads of implant-supported ceramic prostheses in premolar region. Ninety-nine implant-abutment complexes were divided into three different implant-supported prostheses: monolithic yttria-partially stabilized zirconia (Y-PSZ) restorations (MPZ specimens), porcelain layered on yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) restorations (PLZ specimens), and monolithic lithium disilicate ceramic restorations (MLD specimens). Implant-supported prostheses were luted with adhesive resin luting agent (RLA), glass ionomer cement (GIC), or zinc phosphate cement (ZPC). For MPZ and MLD specimens, fracture loads were significantly higher for RLA group than for GIC and ZPC groups. For PLZ specimens, fracture loads did not significantly differ in relation to luting agent. Fracture loads were significantly higher for MPZ specimens than for other test specimens, regardless of luting agent. Use of an adhesive resin luting agent is recommended for placement of premolar implant-supported monolithic Y-PSZ and lithium disilicate ceramic prostheses.

Influence of different surface treatments on two-body wear and fracture load of monolithic CAD/CAM ceramics

OBJECTIVES

To investigate two-body wear (2BW) and fracture load (FL) of monolithic ceramics after different surface pretreatments.

MATERIALS AND METHODS

Zirconia (MOZ), lithium-disilicate (LIT), and leucite-reinforced (LEU) specimens (n = 60/group) were manufactured with CAD/CAM-technology and underwent (n = 15/subgroup): 1) grinding + polishing (GrPo), 2) grinding + glazing (GrGz), 3) grinding (Gr), or 4) glazing (Gz). Scanning electron microscope (n = 3/subgroup) and 3D measurements of the ceramic crowns and antagonists (N = 180) were performed to determine 2BW before and after 120,000/1,200,000 masticatory cycles. FL was examined for all specimens (N = 180). Data were analyzed using Kolmogorov-Smirnov, one-way ANOVA, Scheffé post hoc, Kruskal-Wallis, Mann-Whitney-U, and Wilcoxon (p < 0.05).

RESULTS

MOZ presented the highest FL independent on pretreatment (6960-9250 N), while LEU (1405-2320 N) showed the lowest (p < 0.001). Ceramic and antagonist wear increased between 120,000 and 1,200,000 masticatory cycles (p < 0.001). For pretreatments GrPo, GrGz, and Gz, MOZ showed the lowest wear of the ceramic, while causing the highest antagonist wear (p < 0.001). GrPo resulted in the lowest wear for MOZ (p < 0.001), with Gr leading to the highest antagonist wear (p = 0.008). LIT specimens presented the highest wear of the ceramic and antagonist after Gz (p < 0.001), while GrPo resulted in the lowest antagonist wear (p < 0.001). GrGz led to the highest antagonist wear for LEU (p < 0.001).

CONCLUSIONS

With FL exceeding maximum masticatory forces, the three tested ceramics can be recommended for restorations, even in posterior regions. While glazing resulted in higher wear and impaired FL, polishing improved mechanical properties while largely preserving the antagonist.

CLINICAL RELEVANCE

While surface pretreatment after grinding is vital to ensure a ceramic's optimal mechanical properties, glazing and polishing varies with regard to material properties, costs, and time.

Flexural Strength of Different Monolithic Computer-Assisted Design and Computer-Assisted Manufacturing Ceramic Materials upon Different Thermal Tempering Processes

Objective  Strength of ceramics related with sintering procedure. This study investigated the influence of different tempering processes on flexural strength of three monolithic ceramic materials.

Materials and Methods  Specimens were prepared in bar-shape (width × length × thickness = 4 × 14 × 1.2 mm) from yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP, inCoris TZI [I]), zirconia-reinforced lithium silicate (ZLS, Vita Suprinity [V]), and lithium disilicate (LS ₂ , IPS e.max CAD [E]), and sintered with different tempering processes: slow (S), normal (N), and fast (F) cooling procedure ( n = 15/group). Flexural strength (σ ) was determined using three-point bending test apparatus at 1 mm/min crosshead speed.

Statistical Analysis  The analysis of variance and Bonferroni’s multiple comparisons were determined for significant difference (α = 0.05). Weibull analysis was applied for survival probability, Weibull modulus (m), and characteristics strength (σ _o ). Microstructures were evaluated with scanning electron microscope and X-ray diffraction.

Results  The mean ± standard deviation (MPa) of σ, m, and σ _o were: 1,183.98 ± 204.26, 6.23, 1,271.80 for IS; 1,084.43 ± 204.79, 5.76, 1,170.08 for IN; 777.19 ± 99.77, 8.78, 819.96 for IF; 267.15 ± 32.71, 9.11, 281.48 for VS; 218.43 ± 38.46, 6.40, 234.23 for VN; 252.67 ± 37.58, 7.20, 269.23 for VF; 392.09 ± 37.91, 11.37, 409.23 for ES; 378.88 ± 55.38, 7.45, 403.11 for EN, and 390.94 ± 25.34, 16.00, 403.51 for EF. Thermal tempering significantly affected flexural strength of Y-TZP ( p < 0.05), but not either ZLS or LS ₂ ( p > 0.05). Y-TZP indicated significantly higher flexural strength upon slow tempering than others.

Conclusion  Enhancing flexural strength of Y-TZP can be achieved through slow tempering process and was suggested as a process for monolithic zirconia. Strengthening of ZLS and LS ₂ cannot be accomplished through tempering; thus, either S-, N-, or F- tempering procedure can be performed. Nevertheless, to minimize sintering time, rapid thermal tempering is more preferable for both ZLS and LS ₂ .

Effect of different fabrication techniques on the marginal precision of polyetheretherketone single-crown copings

STATEMENT OF PROBLEM

Demand is increasing for polyetheretherketone (PEEK) as a fixed dental prosthesis core material. However, information is lacking about how the precision of these restorations is affected by the fabrication procedures.

PURPOSE

The purpose of this in vitro study was to evaluate the influence of different fabrication techniques on the marginal precision of PEEK single-crown copings.

MATERIAL AND METHODS

A stainless-steel master die was designed to simulate a prepared mandibular second molar to receive ceramic crowns. Thirty PEEK copings were fabricated and divided into 3 groups (n=10) according to the fabrication technique: milled from a prefabricated PEEK blank by using a computer-aided design and computer-aided manufacturing (CAD-CAM) system (PC); pressed from prefabricated PEEK pellets (PP); and pressed from PEEK granules (PG); in addition, 3-mol yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) copings (n=10) were produced by using the same CAD-CAM system and served as a control. Marginal precision measurements (in μm) were recorded at 4 reference points on each coping by using a digital microscope. The data obtained were statistically analyzed by using 1-way ANOVA and the pair-wise Tukey (HSD) test to study the difference between group mean values (α=.05).

RESULTS

The overall mean ±standard deviation marginal gap at the marginal opening for the copings was 78 ±10 μm for PEEK granules copings, 72 ±9 μm for PEEK pellet copings, 45 ±6 μm for PEEK CAD-CAM copings, and 43 ±1 μm for the 3Y-TZP CAD-CAM control. A statistically significant difference was found between the milled and pressed copings as indicated by the ANOVA test (P<.001). The pair-wise Tukey honestly significant difference (HSD) test showed a nonsignificant difference (P>.05) between milled 3Y-TZP and milled PEEK copings; moreover, no significant difference was observed between the PEEK copings pressed from pellets or granules (P>.05).

CONCLUSIONS

The marginal precision of PEEK CAD-CAM-fabricated copings showed significantly lower mean marginal gap values than PEEK pressed copings. The marginal gap mean values recorded were all within a clinically acceptable range (120 μm).

Evaluation of marginal discrepancy in metal frameworks fabricated by sintering-based computer-aided manufacturing methods

PURPOSE

The aim of this in vitro study was to evaluate the effect of sintering procedures on marginal discrepancies of fixed partial metal frameworks fabricated using different sintering-based computer-aided design and computer/aided manufacturing (CAD/CAM) techniques.

MATERIALS AND METHODS

Forty resin die models of prepared premolar and molar abutment teeth were fabricated using a three-dimensional (3D) printer and divided into four groups (n = 10) according to the fabrication method of metal frameworks used: HM (via hard milling), SM (via soft metal milling), L25 (via direct metal laser melting [DMLM] with a 25 µm layer thickness), and L50 (via direct DMLM with a 50 µm layer thickness). After the metal frameworks were fabricated and cemented, five vertical marginal discrepancy measurements were recorded in each site (i.e., buccal, facing the pontic, lingual, and facing away from the pontic) of both abutment teeth under a stereomicroscope (×40). Data were statistically analyzed at a significance level of 0.05.

RESULTS

No statistically significant differences (P>.05) were found among the four axial sites of metal frameworks fabricated by sintering-based CAD/CAM techniques. The HM and L25 groups showed significantly (P<.001) lower marginal discrepancy values than the SM and L50 groups.

CONCLUSION

Marginal discrepancy in the sites facing the pontic was not influenced by the type of sintering procedure. All fabrication methods exhibited clinically acceptable results in terms of marginal discrepancies.

Fracture toughness of zirconia with a nanometer size notch fabricated using focused ion beam milling

OBJECTIVES

Zirconia with 3 mol% yttria (3Y-TZP) has been used for dental crowns and bridges due to its excellent mechanical behavior. Performing fracture toughness testing on this nanograin material, however, can be a challenge. For reliable results, fracture toughness testing requires an extremely sharp notch in the test specimen that closely approximates a very sharp crack. This study was to investigate an alternative method to produce nanometer-sized notches, which are less than the average grain size of 3Y-TZP, during the preparation of single-edge V-notched beam specimens and report the resulting fracture toughness value.

METHODS

We present a method using focused ion beam (FIB) milling to fabricate nanometer-sized notches in 3Y-TZP. The notch tip is <100 nm wide, which is smaller than the grain size, and is consistent throughout the thickness of the specimen.

RESULTS

The FIB-notched specimens show a much reduced average fracture toughness of 5.64 ± 1.14 MPa√m compared to 8.90 ± 0.23 MPa√m for the specimens without FIB-notches. The FIB-milling did not appear to create any monoclinic phase prior to fracture toughness testing. Fractures originated at the FIB-notches, and the notch size can be readily identified post-mortem using a microscope. A considerable amount of tetragonal-to-monoclinic phase transformation was observed throughout the fracture surfaces.

SIGNIFICANCE

FIB milling provides an alternative method to fabricate nanometer-sized notches that are smaller than the grain size of tetragonal zirconia polycrystal. The fracture toughness determined using FIB-notches was ~5.64 MPa√m, smaller than the specimens with V-notches fabricated using saw blades.

Influence of electronic nicotine delivery systems (ENDS) in comparison to conventional cigarette on color stability of dental restorative materials

Objective:

The use of Electronic Nicotine Delivery Systems (ENDS) is increasing rapidly. However, its discoloring effect on dental restorations is not known. This study aimed to evaluate the effect of ENDS aerosol when compared to conventional cigarette smoke (CS) on the color stability of dental ceramic (DC) and resin composite (RC).

Methods:

This research project was conducted from November 2018 to May 2019. In this study 30 discs each for DC and RC materials were fabricated to be equally divided into groups of exposure to CS, ENDS aerosol and storage in distilled water (No smoke; NS) respectively (n=10). Specimens were exposed for a total of 7 days, with a rate of 10 cycles per day, each cycle represented 10 puffs. The color change was assessed using the CIELAB color space, by calculating ΔE. Data was analysed using ANOVA and multiple comparisons test.

Results:

Ceramic specimens in CS (2.422 ± 0.771) and ENDS (2.396 ± 0.396) groups showed comparable ΔE (color change) (p=0.992). Similarly, composite specimens in CS (42.871 ± 2.442) and ENDS (46.866 ± 3.64) groups showed comparable ΔE (p>0.05). NS specimens in both composite and ceramic samples showed lower ΔE than CS and ENDS specimens respectively.

Conclusions:

Aerosol from Electronic nicotine delivery systems (ENDS) showed similar discoloration levels as cigarette smoking (CS). The level of discoloration for ceramic samples for both ENDS and CS was below clinically perceptible levels (Mean ΔE < 2.5). Discoloration of composite resin due to CS and ENDS was visually perceptible (Mean ΔE > 4.0).

Evaluation of bond strength of dual resin cements to CAD/CAM-created lithium disilicate ceramic

BACKGROUND

The objective was to examine the microshear bond strength values of different dual resin cements to computer-aided design (CAD)/computer-aided manufacturing (CAM)-created ceramics containing lithium disilicate, which underwent different surface treatments.

METHODS

Two dual resin cements (RelyX ARC and RelyX Ultimate) and three surface treatments of lithium disilicate ceramic blocks (Ceramic Primer (CP; containing silane) plus Adper Scotchbond Multipurpose (ASM) adhesive; CP plus Single Bond Universal (SBU) adhesive; and SBU adhesive alone) were tested. The SBU adhesive includes silane in its formulation. Each sample underwent a microshear test and bond strength values were subjected to analysis of variance (ANOVA) followed by Tukey's test (α=0.05). Fracture patterns were also observed with light microscopy.

RESULTS

RelyX ARC treated with CP+ASM or CP+SBU presented resistance values that were significantly higher than the same treatments for RelyX Ultimate. Conversely, for the blocks treated with SBU alone, the mean resistance value for RelyX Ultimate was higher than that of RelyX ARC. Regarding the different types of treatment for each resin, the mean resistance value of RelyX ARC treated with CP+ASM was significantly highest, followed by treatment with CP+SBU and SBU treatment alone. Meanwhile, RelyX Ultimate treated with CP+ASM or CP+SBU presented resistance values that were significantly higher than SBU treatment alone. In all of the groups, an adhesive fracture pattern was predominantly observed.

CONCLUSIONS

The present results indicate that silanization is important for ASM and SBU adhesives to be effective.

Impact of high-speed sintering, layer thickness and artificial aging on the fracture load and two-body wear of zirconia crowns

OBJECTIVE

To investigate the impact of high-speed sintering, layer thickness and artificial aging in a chewing simulator on the fracture load (FL) and two-body wear (2BW) of 4Y-TZP crowns.

METHODS

4Y-TZP crowns (Ceramill Zolid HT+, Amann Girrbach AG) in three different layer thicknesses (0.5, 1.0, 1.5; N=192, n=64/group) were manufactured using CAD/CAM technology and sintered at 1580°C (high-speed sintering) or 1450°C (control group). Specimens were polished in two-steps and bonded to standardized CoCr abutments with Multilink Automix (Ivoclar Vivadent). 2BW after 6000 thermo- and 1,200,000 chewing-cycles employing enamel antagonists was determined using best fit machining. FL was tested before and after artificial aging. Univariate ANOVAs, post hoc Scheffé, unpaired t-, Kruskal-Wallis- and Mann-Whitney-U-test were computed (p<0.05).

RESULTS

High-speed sintering resulted in less 2BW of the zirconia than the control group (p=0.013). High-speed sintering (p=0.001-0.006) and an increase in layer thickness (p<0.001-0.012) resulted in higher FL values, while artificial aging led to a reduction of FL (p<0.001).

SIGNIFICANCE

As high-speed sintering resulted in less two-body wear of the zirconia and comparable or even higher fracture load results than the control group, this cost- and time efficient alternative presents promising mechanical results.

Dentistry 4.0 Concept in the Design and Manufacturing of Prosthetic Dental Restorations

The paper is a comprehensive but compact review of the literature on the state of illnesses of the human stomatognathic system, related consequences in the form of dental deficiencies, and the resulting need for prosthetic treatment. Types of prosthetic restorations, including implants, as well as new classes of implantable devices called implant-scaffolds with a porous part integrated with a solid core, as well as biological engineering materials with the use of living cells, have been characterized. A review of works on current trends in the technical development of dental prosthetics aiding, called Dentistry 4.0, analogous to the concept of the highest stage of Industry 4.0 of the industrial revolution, has been presented. Authors’ own augmented holistic model of Industry 4.0 has been developed and presented. The studies on the significance of cone-beam computed tomography (CBCT) in planning prosthetic treatment, as well as in the design and manufacture of prosthetic restorations, have been described. The presented and fully digital approach is a radical turnaround in both clinical procedures and the technologies of implant preparation using computer-aided design and manufacturing methods (CAD/CAM) and additive manufacturing (AM) technologies, including selective laser sintering (SLS). The authors’ research illustrates the practical application of the Dentistry 4.0 approach for several types of prosthetic restorations. The development process of the modern approach is being observed all over the world. The use of the principles of the augmented holistic model of Industry 4.0 in advanced dental engineering indicates a change in the traditional relationship between a dentist and a dental engineer. The overall conclusion demonstrates that it is inevitable and extremely beneficial to implement the idea of Dentistry 4.0 following the assumptions of the authors’ own, holistic Industry 4.0 model.

Survival Probability, Weibull Characteristics, Stress Distribution, and Fractographic Analysis of Polymer-Infiltrated Ceramic Network Restorations Cemented on a Chairside Titanium Base: An In Vitro and In Silico Study

Different techniques are available to manufacture polymer-infiltrated ceramic restorations cemented on a chairside titanium base. To compare the influence of these techniques in the mechanical response, 75 implant-supported crowns were divided in three groups: CME (crown cemented on a mesostructure), a two-piece prosthetic solution consisting of a crown and hybrid abutment; MC (monolithic crown), a one-piece prosthetic solution consisting of a crown; and MP (monolithic crown with perforation), a one-piece prosthetic solution consisting of a crown with a screw access hole. All specimens were stepwise fatigued (50 N in each 20,000 cycles until 1200 N and 350,000 cycles). The failed crowns were inspected under scanning electron microscopy. The finite element method was applied to analyze mechanical behavior under 300 N axial load. Log-Rank (p = 0.17) and Wilcoxon (p = 0.11) tests revealed similar survival probability at 300 and 900 N. Higher stress concentration was observed in the crowns’ emergence profiles. The MP and CME techniques showed similar survival and can be applied to manufacture an implant-supported crown. In all groups, the stress concentration associated with fractographic analysis suggests that the region of the emergence profile should always be evaluated due to the high prevalence of failures in this area.

Digital evaluation of laser scanning speed effects on the intaglio surface adaptation of laser-sintered metal frameworks

STATEMENT OF PROBLEM

Laser sintering has several processing parameters, typically under the control of dental laboratory technicians. Laser scan speed is an important parameter, which has a significant effect on manufacturing time but may also affect the adaptation of restorations. However, limited information is available regarding its impact.

PURPOSE

The purpose of this in vitro study was to evaluate the intaglio surface adaptation of laser-sintered cobalt-chromium single-crown frameworks sintered at laser scanning speeds of 1, 3, and 6 m/s.

MATERIAL AND METHODS

A master bronze metal die was prepared and scanned by using a laboratory scanner to fabricate the metal frameworks for 4 groups (n=10). In group C, the frameworks were fabricated by using the lost-wax method (control). In group L1, L3, and L6, the frameworks were fabricated by using direct metal laser melting (DMLM) at laser scanning speeds of 1, 3, and 6 m/s. After fabrication, 3 scanning data sets were used to evaluate the intaglio surface adaptation: the master die, the intaglio surface of each metal framework, and each metal framework seated on the master die. The intaglio surface adaptation of the metal frameworks was evaluated by using a metrology software program. The data were statistically analyzed by using a 1-way ANOVA, the Tukey honestly significant difference test, and the Tamhane T2 test (α=.05).

RESULTS

The highest mean intaglio surface discrepancy value was obtained from group L6, and this was significantly different from the other 3 groups (P<.001). No significant intaglio surface discrepancy differences were found among the other groups.

CONCLUSION

The amount of intaglio surface discrepancy increased when the laser scanning speed reached 6 m/s.

Suitability of 3D printed pieces of nanocrystalline zirconia for dental applications

OBJECTIVES

The main goal of this work is to evaluate the suitability of nanostructured zirconia pieces obtained by robocasting additive manufacturing (AM), for dental applications.

METHODS

The density, crystalline structure, morphology/porosity, surface roughness, hardness, toughness, wettability and biocompatibility of the produced samples were compared with those of samples obtained by conventional subtractive manufacturing (SM) of a similar commercial zirconia material. Chewing simulation studies were carried out against dental human cusps in artificial saliva. The wear of the material was quantified and the wear mechanisms investigated, as well as the influence of glaze coating.

RESULTS

AM samples, that revealed to be biocompatible, are slightly less dense and more porous than SM samples, showing lower hardness, toughness and wettability than SM samples. After chewing tests, no wear was found both on AM and SM samples. However, the dental wear was significantly lower when AM samples were used as counterbody. Concerning the glazed samples, both coated surfaces and dental cusps suffered wear, being the cusps' wear higher than that found for unglazed samples. More, cusps tested against AM coated samples suffered less wear comparatively to those opposed to SM coated samples.

SIGNIFICANCE

Overall, the results presented in this paper show that AM processed nanostructured zirconia can be used in dental restorations, with important advantages from the point of view of processing and tribological performance. Moreover, the option for glaze finishing should be carefully considered both in SM and AM processed specimens.

Effect of surface treatments and universal adhesive application on the microshear bond strength of CAD/CAM materials

PURPOSE

The aim of this study was to evaluate the microshear bond strength (µSBS) of four computer-aided design/computer-aided manufacturing (CAD/CAM) blocks repaired with composite resin using three different surface treatment protocols.

MATERIALS AND METHODS

Four different CAD/CAM blocks were used in this study: (1) flexible hybrid ceramic (FHC), (2) resin nanoceramic (RNC), (c) polymer infiltrated ceramic network (PICN) and (4) feldspar ceramic (FC). All groups were further divided into four subgroups according to surface treatment: control, hydrofluoric acid etching (HF), air-borne particle abrasion with aluminum oxide (AlO), and tribochemical silica coating (TSC). After surface treatments, silane was applied to half of the specimens. Then, a silane-containing universal adhesive was applied, and specimens were repaired with a composite, Next, μSBS test was performed. Additional specimens were examined with a contact profilometer and scanning electron microscopy. The data were analyzed with ANOVA and Tukey tests.

RESULTS

The findings revealed that silane application yielded higher µSBS values (P<.05). All surface treatments were showed a significant increase in µSBS values compared to the control (P<.05). For FHC and RNC, the most influential treatments were AlO and TSC (P<.05).

CONCLUSION

Surface treatment is mandatory when the silane is not preferred, but the best bond strength values were obtained with the combination of surface treatment and silane application. HF provides improved bond strength when the ceramic content of material increases, whereas AlO and TSC gives improved bond strength when the composite content of material increases.

Effect of Various Surface Treatments on Ti-Base Coping Retention

Clinical Relevance

Mechanical surface roughening of the titanium-abutment base is necessary to increase the pull-off bond strength of the lithium disilicate abutment material. Additional chemical surface treatment may further increase the bond strength, but the effects are product specific.

SUMMARY

Objective:

The titanium-cement interface of a Ti-Base implant crown must be able to resist intraoral pull-off forces. The purpose of this study was to evaluate the effect of mechanical and chemical surface treatments of a titanium-abutment base (Ti-Base, Dentsply/Sirona) on the pull-off bond strength of a lithium disilicate abutment coping.

Methods and Materials:

Ti-Bases were divided into nine groups of 10 copings each that varied in both mechanical surface treatment (none; Al2O3 air abrasion; CoJet silicoating, 3M ESPE) and chemical treatments (none; Monobond Plus, Ivoclar Vivadent; Alloy Primer, Kuraray). Lithium disilicate abutment copings (IPS e.max CAD, Ivoclar Vivadent) were designed and milled. After crystallization, the copings were cemented onto the Ti-Bases with a resin cement (MultiLink Hybrid-Abutment Cement, Ivoclar Vivadent) according to the manufacturer's recommendations. The copings were torqued to a mounted implant, and the access channel was sealed with composite. After 24-hour storage and 2000 thermal-cycles in distilled water, the copings were subjected to a removal force parallel to the long axis of the interface until fracture. Data were analyzed with multiple one-way analyses of variance and Tukey post hoc tests (α=0.05).

Results:

Significant differences were found between groups based on type of surface treatment (p&lt;0.05).

Conclusions:

Chemical surface treatment with Monobond Plus and mechanical surface treatment with CoJet silicoating or Al2O3 air abrasion resulted in the greatest pull-off bond strength. Alloy Primer did not provide a statistically significant increased pull-off bond strength when the surfaces were mechanically treated with Al2O3 air abrasion or CoJet silicoating. The lack of any mechanical surface treatment resulted in the lowest pull-off bond strength regardless of the type of chemical surface treatment.

Flexural strength, fracture toughness, three-body wear, and Martens parameters of pressable lithium-X-silicate ceramics

OBJECTIVES

To test and compare five pressable lithium-X-silicate-ceramics on their mechanical and wear properties.

METHODS

Specimens were pressed and prepared from: i. Amber Press (AP), ii. Celtra Press (CP), iii. Initial LiSi Press (IL), iv. Livento Press (LP), and v. IPS e.max Press (IE). Four-point flexural strength (FS), SEVNB fracture toughness (K_IC), three-body wear (3BW), Martens hardness (HM) and indentation modulus (E_IT) were measured. For CP, FS and HM were measured with and without additional Power Firing. Each subgroup contained 15 specimens. Data were analyzed using Kolmogorov-Smirnov, one-way ANOVA followed by Scheffé test, Kruskal-Wallis-H-, Mann-Whitney-U-, and Spearman-Rho-test (p < 0.05). The Weibull modulus was calculated using the maximum likelihood estimation method.

RESULTS

AP and CP presented higher FS than IL. LP presented the highest Weibull modulus. CP showed lower K_IC values than AP, and AP was not significant compared to LP and IE. The most 3BW material loss was observed for CP. CP revealed higher HM values than the remaining ceramics. IL presented lower E_IT compared to AP and CP. The following correlations were observed between the test parameters: 3BW with FS (r = 0.279, p = 0.015), with HM (r = -0.378, p = 0.001), and with E_IT (r = -0.344, p = 0.004); E_IT with FS (r = 0.203, p = 0.028); and HM with FT (r = -0.223, p = 0.027) and E_IT (r = 0.884, p < 0.001). No correlations were observed between FS and K_IC (r = 0.046; p = 0.346).

SIGNIFICANCE

AP followed by LP showed the highest and IL followed by CP the lowest properties tested. Power Firing of CP improved the flexural strength. Ceramics with high flexural strength and Martens parameters showed lower wear. Materials with high Martens hardness presented lower fracture toughness values and ones with high indentation modulus showed high flexural strength.

Effect of nanomaterial incorporation on the mechanical and microbiological properties of dental porcelain

STATEMENT OF PROBLEM

Dental porcelain restorations are subject to biological failures related to secondary caries and periodontal disease leading to prosthesis replacement.

PURPOSE

The purpose of this in vitro study was to explore the microbiological and mechanical properties of dental porcelain incorporated with different percentages of silver vanadate (β-AgVO₃) through microbiological analysis, roughness tests, and the Vickers microhardness test.

MATERIAL AND METHODS

IPS InLine porcelain specimens were made by using a cylindrical Teflon matrix in the dimensions of 8×2 mm. For the control group, the porcelain was manipulated according to the manufacturer's instructions. The groups incorporating the nanomaterial were prepared with 2.5%, 5%, and 10% of β-AgVO_3, which was added proportionally by mass to the porcelain powder. In vitro microbiologic analysis, roughness tests, and the Vickers microhardness test were performed.

RESULTS

Against Streptococcus mutans, the control group showed no inhibition halo (0 mm). All groups with AgVO₃ showed a zone of inhibition, the highest for the group with 10% (30 mm) and then the groups with 2.5% (9 mm) and 5% (17 mm). For Vickers microhardness, no statistically significant difference (P<.05) was observed between the evaluated groups. The group with 10% of AgVO₃ had the highest mean roughness and was statistically different (P<.001) from the other groups.

CONCLUSIONS

Adding β-AgVO₃ to dental porcelain demonstrated antimicrobial effectiveness at all concentrations (2.5%, 5%, and 10%), with no effect on Vickers microhardness. The 10% group had higher roughness than the other groups.

A Conservative Approach to Ceramic Veneers: A Case Report

Bonding to enamel has been shown to provide reliable results, and thus conservative tooth preparations are key to the success of ceramic bonded restorations. The wax-up is the first diagnostic tool available to evaluate discrepancies between current and ideal tooth proportions. The clinician's diagnostic mock-up provides the patient with a visual perception of the size and shape of the proposed restorations. The use of reduction guides assists the restorative dentist in evaluating the specific amount of tooth structure to be removed during preparation. Furthermore, total isolation with a rubber dam prior to bonding the final restorations is crucial for the success of adhesive protocols. The aim of this report is to demonstrate a conservative approach to tooth preparation with a complete isolation technique prior to bonding eight ceramic restorations.

Nature-Inspired Nacre-Like Composites Combining Human Tooth-Matching Elasticity and Hardness with Exceptional Damage Tolerance

Making replacements for the human body similar to natural tissue offers significant advantages but remains a key challenge. This is pertinent for synthetic dental materials, which rarely reproduce the actual properties of human teeth and generally demonstrate relatively poor damage tolerance. Here new bioinspired ceramic-polymer composites with nacre-mimetic lamellar and brick-and-mortar architectures are reported, which resemble, respectively, human dentin and enamel in hardness, stiffness, and strength and exhibit exceptional fracture toughness. These composites are additionally distinguished by outstanding machinability, energy-dissipating capability under cyclic loading, and diminished abrasion to antagonist teeth. The underlying design principles and toughening mechanisms of these materials are elucidated in terms of their distinct architectures. It is demonstrated that these composites are promising candidates for dental applications, such as new-generation tooth replacements. Finally, it is believed that this notion of bioinspired design of new materials with unprecedented biologically comparable properties can be extended to a wide range of material systems for improved mechanical performance.

Variables affecting the fit of zirconia fixed partial dentures: A systematic review

STATEMENT OF PROBLEM

Different parameters affect the marginal and internal fit of zirconia fixed partial dentures (FPDs) on natural teeth. Determining a way to optimize these restorations is essential.

PURPOSE

The purpose of this systematic review was to determine the variables affecting the marginal fit and internal accuracy of zirconia FPDs on natural teeth.

MATERIAL AND METHODS

An electronic search was conducted by 2 independent reviewers by using the MEDLINE, Cochrane, Web of Science, and Scopus databases, as well as Google Scholar, for studies published up to July 2018, and a manual search was conducted from the reference lists of related articles. Eligibility criteria included articles in English published in peer-reviewed journals that assessed the marginal and/or internal adaptation of zirconia FPDs on teeth with 3 or more units, with at least 1 of the experimental groups being frameworks or FPDs fabricated from zirconia. Risk of bias was assessed with the aid of the Cochrane Handbook for Systematic Reviews of Interventions.

RESULTS

The search provided 418 records, with 41 fulfilling the inclusion criteria. The selected studies showed considerable heterogeneity regarding materials, state of sintering, manufacturer and computer-aided design and computer-aided manufacturing (CAD-CAM) system, experimental methodology, sample size, and span length. Of the included articles, 36 were in vitro studies and 5 were clinical studies, most of which exhibited high-performance and detection biases. CAD-CAM systems provided more precise marginal and internal fit than CAM systems. An increase of framework span length to 6 or more units decreased both marginal and internal fit. The reported marginal gap tended to increase after the veneering process. The introduction of a conventional impression into an otherwise digital workflow seems to have a negative effect on the marginal fit.

CONCLUSIONS

The accuracy of zirconia FPDs or frameworks is considerably influenced by the processing procedure used and the choice of CAD-CAM system.

The potential of additive manufacturing technologies and their processing parameters for the fabrication of all-ceramic crowns: A review

OBJECTIVE

This article aims to provide a review of the additive manufacturing technologies and the processing parameters that have been investigated for the fabrication of all ceramic crowns.

OVERVIEW

Additive manufacturing has crept its way into the field of dentistry for the fabrication of resin and metal prosthesis. To evaluate the current status of additive manufacturing for the fabrication of all ceramic crowns, literature review was targeted to include publications pertaining to the fabrication of dental ceramics and all ceramic crowns. With respect to the additive manufacturing of dental ceramics, five technologies have been investigated to date: stereolithography, material extrusion, powder based fusion, direct inkjet printing, and binder jetting. The processing parameters and experimental outcomes were collated and described for each of the aforementioned technologies.

CONCLUSION

Additive manufacturing has demonstrated promising experimental outcomes and corroborated to the fabrication all ceramic crowns. However, the technology is yet to witness a commercial breakthrough within this domain.

CLINICAL SIGNIFICANCE

Additive manufacturing mitigates raw material wastage and tooling stresses that are associated with milling of ceramics. Continued research and development can lead to its approbation as an alternate technology for manufacturing all ceramic restorations.

Comparison of Bond Strength of Monolithic CAD-CAM Materials to Resin Cement Using Different Surface Treatment Methods

Objective:

To compare the bond strength of monolithic CAD-CAM materials to resin cement using different surface treatment methods.

Materials and Methods:

Lithium disilicate glass ceramic (IPS e-max CAD), zirconia-reinforced lithium silicate ceramic (Vita Suprinity), resin nanoceramic (Lava Ultimate), and hybrid ceramic (Vita Enamic) were used. Five groups of CAD-CAM blocks were treated as follows: control (C), HF etching (HF), HF etching + silanization (HF + S), sandblasting (SB), and sandblasting + silanization (SB + S). After surface treatments, SEM analyses were conducted. Specimens were cemented with self-adhesive resin cement (Theracem) and stored in distilled water at 37°C for 24 h. Shear bond strength (SBS) was measured, and failure types were categorized. Results were analyzed using two-way ANOVA and the post-hoc Tukey test.

Results:

Statistical analysis revealed significant differences between SBS values obtained for different surface treatments and CAD-CAM block types ( P < .001). Among the CAD-CAM materials, the highest SBS was reported in the HF + S group for Vita Enamic. Although IPS e.max CAD, Vita Suprinity, and Vita Enamic showed higher bond strength when treated with HF + S, Lava Ultimate has the highest bond strength value when treated with SB + S.

Conclusions:

The bond strength of CAD-CAM materials was influenced by surface treatment. Additionally, silanization significantly improved the bond strength of all materials except Lava Ultimate.

Evolution of Indirect Restorations for Fixed Prosthodontics: Planning, Preparation and Cementation

The provision of indirect restorations utilising contemporary materials for single or multiple abutment units in primary health care is an essential requirement for all general dental practitioners to ensure predictable patient outcomes. This paper highlights the important considerations for comprehensive planning and adept treatment execution and delivery that can enhance the patient's dental experience and outcome. A selection of clinical cases highlighting established and novel restorative materials utilising conventional and adhesive clinical techniques is presented and discussed.

Digital microscopic evaluation of vertical marginal discrepancies of CAD/CAM fabricated zirconia cores

OBJECTIVE

The aim of this in vitro research study was to evaluate the vertical marginal discrepancies of zirconia (Zr) cores fabricated by five different computer-aided design and manufacturing (CAD/CAM) systems using a digital microscope.

MATERIALS AND METHODS

A total of 60 specimens were prepared and randomly divided into five groups (n=12 each) using the following systems: Ceramill Motion 2 (CM, Amanngirrbach, Germany); Weiland (WI, Ivoclar Vivadent, USA); Cerec (CS, Sirona Dental, USA); Zirkonzahn (ZZ, Gmbh Bruneck, Italy) and Cad4dent (CD, Canada). The specimens were numbered and the vertical marginal discrepancies were evaluated with a digital microscope at 50× magnification.

RESULTS

A one-way analysis of variance showed a statistically significant difference (p=0.002) between the groups. The CM group exhibited the lowest values for the marginal gaps (31.30±15.12 μm), while the ZZ group exhibited the highest values for the marginal gaps (44.83±28.76 μm) compared to other groups. A post hoc Tukey's test for multiple comparisons between the experimental groups showed a statistically significant difference (p<0.05) between the group CM and group CD with group ZZ. The rest of the groups showed no significant differences between them. Variations in the values were observed for the four sites measured with the highest and the least mean marginal gap value of 43.19±23.84 μm and 32.49±12.21 μm for buccal and lingual sites, respectively.

CONCLUSION

Variations existed in the marginal discrepancy values for the CAD/CAM systems investigated in the study. Vertical marginal discrepancy values observed for various systems investigated in the study were well within the clinically acceptable range.

Machinability: Zirconia-reinforced lithium silicate glass ceramic versus lithium disilicate glass ceramic

Diamond grinding used in dental adjustment of high-strength zirconia-reinforced lithium silicate glass ceramic (ZLS) and lithium disilicate glass ceramic (LDGC) is challenging in restorative dentistry. This study aimed to compare the machinability of ZLS and LDGC in diamond grinding in terms of machining forces and energy, debris, surface and edge chipping damage. Grinding experiments in simulation of dental adjustment were conducted using a computer-assisted high-speed dental handpiece and coarse diamond burs. A piezoelectric force dynamometer and a high-speed data acquisition system were used for on-processing monitoring for assessment of grinding forces and energy. Grinding debris and grinding-induced surface and edge chipping damage were examined using scanning electron microscopy. The results show that grinding of ZLS required higher tangential and normal forces and energy than LDGC (p < 0.05). ZLS was ranked the most difficult to machine among dental glass ceramics based on a machinability index associated with the material mechanical properties. The higher machinability indices of ZLS and LDGC pose a challenge for clinicians to conduct high-efficient material removal for dental adjustment and repair. Both ZLS and LDGC debris were micro fractured particles but the former were smaller than the latter due to the finer microstructure of ZLS. Ground ZLS surfaces contained more irregular microchipping and microfracture in comparison with LDGC surfaces with intergranular fracture or grain dislodgement. Grinding-induced edge chipping damage remained a serious issue for both ZLS and LDGC, which depths ranged approximately 20-100 μm and significantly increased with the material removal rate (p < 0.01). As the zirconia-reinforcement in ZLS only slightly reduced edge chipping damage (p > 0.05), continued efforts are required to explore new reinforcement technologies for optimized LDGC.

Fracture resistance of veneers in premolars

Objective

The purpose of the study was to compare the fracture resistance of ceramic veneers and composite resin veneers with and without dental preparation.

Materials and Methods

Forty freshly extracted mandibular premolars were selected and randomly assigned into four groups (n = 10): Group NPR = no dental preparation and direct veneer with 0.2 mm thick composite resin (Amelogen Plus, Ultradent); Group NPC = no dental preparation and 0.2 mm thick lithium disilicate ceramic veneer (IPS e.max Press, Ivoclar Vivadent); Group P2C = Tooth preparation of 0.2 mm and 0.2 mm thick ceramic veneer (IPS e.max Press); and Group P5C = Tooth preparation of 0.5 mm and 0.5 mm-thick ceramic veneer (IPS e.max Press). In all groups, the restorations covered 1 mm of the occlusal surface of the buccal cusp, and the thickness of this area was the same of the buccal area (0.2 mm or 0.5 mm). After the luting procedure, all groups were thermocycled (10,000 cycles, 5°C-55°C) and subjected to fracture resistance test under compression (Instron 4444 with a crosshead speed of 0.5 mm/min). The mode of failure analysis was performed under a ×10 magnification. Data were subjected to one-way ANOVA and Duncan's post hoc test (P < 0.05).

Results

The mean fracture resistance (men ± standard deviation) was NPR = 690.33 ± 233, NPC = 790.52 ± 408, P2C = 1131.34 ± 341, and P5C = 983.56 ± 202. There were significant differences of the fracture resistance values between all groups (P = 0.013). NPR and NPC groups showed mean values of fracture resistance significantly lower than P2C. However, P5C presented intermediate values without a significant difference from the other groups. The mode of failure for all groups was mixed (60%), cohesive failures (20%), root failures (15%), and adhesive failures (5%).

Conclusion

Minimally invasive tooth preparation (0.2-mm) allowed to achieve higher fracture resistance in premolars restored with lithium disilicate ceramic veneers. Attention should be given to the 0.5 mm preparation since catastrophic fractures only happened when this preparation depth was performed.

Influence of thermal tempering processes on color characteristics of different monolithic computer-assisted design and computer-assisted manufacturing ceramic materials

Background

The optical properties of dental restoration were influenced by the sintering parameters. This study investigated the effects of different tempering processes on optical properties of three monolithic Cad-Cam ceramics.

Material and Methods

135 monolithic material bars (4 mm width, 14 mm length, 1.2 mm thickness) were prepared from yttria-stabilized tetragonal zirconia polycrystalline (inCoris TZI, I), zirconia-reinforced lithium silicate (Vita Suprinity, V), and lithium disilicate glass (e.max CAD, E) ceramics, with different tempering processes through slow (S), normal (N), and fast (F) cooling (n=15). The color appearance (∆EW), translucency parameter (TP), contrast ratio (CR), and opalescence parameter (OP) were determined. ANOVA and Bonferroni's multiple comparisons were determined for significant difference (α=0.05). The grain sizes were microscopically examined by scanning electron microscope. The phase transformation of zirconia was determined using X ray diffraction.

Results

The mean±sd of ΔEW, TP, CR, OP were 74.15±0.46, 1.26±0.15, 0.977±0.006, 1.02±0.12 for IS; 74.00±0.83, 1.27±0.19, 0.977±0.007, 1.02±0.12 for IN; 74.44±0.64, 1.70±0.08, 0.965±0.003, 1.30±0.07 for IF; 73.35±1.32, 2.44±0.24, 0.958±0.006, 2.10±0.20 for VS; 66.37±0.88, 4.05±0.3, 0.911±0.010, 3.18±0.20 for VN; 67.02±0.65, 3.79±0.17, 0.919±0.006, 3.01±0.13 for VF; 60.01±0.30, 5.53±0.17, 0.821±0.006, 2.71±0.06 for ES; 60.18±0.23, 5.49±0.17, 0.822±0.006, 2.66±0.05 for EN; and 59.82±0.26, 5.36±0.06, 0.826±0.002, 2.64±0.07 for EF. The color parameters were significantly affected by type of materials, tempering processes, and their interactions (p<0.05). Phase transformation from t→m related with tempering procedure for zirconia.

Conclusions

Rapid thermal tempering process of Y-TZP resulted in larger grain size and t→m phase transformation leading to higher translucency. To achieve optimum translucency, a fast thermal tempering process was suggested for inCoris TZI and IPS e.max CAD, whilst a normal tempering process was recommended for Vita Suprinity. Key words:Color, cooling process, contrast, opalescence, thermal tempering, translucency.

Fracture Resistance of Additively Manufactured Zirconia Crowns when Cemented to Implant Supported Zirconia Abutments: An in vitro Study

PURPOSE

To compare the fracture resistance of implant-supported milled zirconia, milled lithium disilicate, and additively manufactured zirconia crowns.

MATERIALS AND METHODS

Maxillary cast with a dental implant replacing right second bicuspid was obtained. Custom abutments and full-contour crowns for milled zirconia, milled lithium disilicate, and additively manufactured zirconia crowns (n = 10/group) were digitally designed and fabricated. The crowns were cemented to implant-supported zirconia abutments and mounted onto polyurethane blocks. Fracture resistance was determined by vertical force application using a universal testing machine at a crosshead speed of 2 mm/minute. Kruskal-Wallis test was used to analyze data and failure mode was determined for all the groups.

RESULTS

Milled zirconia crowns demonstrated the highest median fracture resistance (1292 ± 189 N), followed by milled lithium disilicate (1289 ± 142 N) and additively manufactured zirconia (1243.5 ± 265.5 N) crowns. Statistical analysis showed no significant differences in fracture resistance between the groups (p = 0.4). All specimens fractured at the implant-abutment interface.

CONCLUSION

Additively manufactured zirconia crowns demonstrated similar fracture resistance to milled ceramic crowns, when cemented to implant supported zirconia abutments. The results of this in vitro study signify the promising potential of additive manufacturing for the fabrication of all ceramic zirconia crowns.

Synthesis of chemically modified BisGMA analog with low viscosity and potential physical and biological properties for dental resin composite

OBJECTIVES

The currently available commercial dental resin composites have limitations in use owing to the high viscosity and water sorption of Bisphenol A glycidyl methacrylate (BisGMA). The objective of this study was to obtain a BisGMA analog with reduced viscosity and hydrophilicity for potential use as an alternative to BisGMA in dental resin composites.

METHODS

The targeted chlorinated BisGMA (Cl-BisGMA) monomer was synthesized via the Appel reaction. The structural modification was confirmed via ¹H- and ¹³C nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and mass spectrometry. Five resin mixtures (70:30wt.%: F1=BisGMA/TEGDMA; F2=Cl-BisGMA/TEGDMA; F3=Cl-BisGMA only; F4=Cl-BisGMA/BisGMA; F5 contained 15% TEGDMA with equal amounts of BisGMA and Cl-BisGMA) were prepared. The viscosity, degree of double-bond conversion (DC), water sorption (W_SP), and solubility (W_SL) were tested. Cell viability and live/dead assays, as well as cell attachment and morphology assessments, were applied for cytotoxicity evaluation.

RESULTS

Cl-BisGMA was successfully synthesized with the viscosity reduced to 7.22 (Pas) compared to BisGMA (909.93,Pas). Interestingly, the DC of the F2 resin was the highest (70.6%). By the addition of equivalence concentration of Cl-BisGMA instead of BisGMA, the W_SP was decreased from 2.95% (F1) to 0.41% (F2) with no significant change in W_SL. However, the W_SL increased with high Cl-BisGMA content. Biological tests revealed that all the resins were biocompatible during CL1 incubation.

SIGNIFICANCE

The experimental resins based on Cl-BisGMA exhibited improved properties compared with the control samples, e.g., biocompatibility and lower viscosity, indicating that Cl-BisGMA can be considered as a potential monomer for application in dental resin composites.

Y-TZP/porcelain graded dental restorations design for improved damping behavior - A study on damping capacity and dynamic Young's modulus

The development of dental restorative materials that mimic tooth-like properties provided by graded structures, aesthetics and properties such as strength, damping capacity and the ability for a continuous remodeling according to the biomechanical solicitation is a great challenge. In this work, damping capacity and dynamic Young's modulus of Y-TZP/porcelain composites for all-ceramic dental restorations were studied. These mechanical properties were assessed by dynamic mechanical analyses (DMA) at frequencies of 1, 5 and 10 Hz, over a temperature ranging from 0 to 60 °C, simulating extreme conditions when a cold or hot drink is experienced. The results showed that porcelain and porcelain-matrix composites exhibited higher damping capacity while Y-TZP and Y-TZP-matrix composites presented higher dynamic Young's modulus. Furthermore, while damping capacity is strongly influenced by the temperature, no significant difference in dynamic Young's modulus was found. For both damping and modulus properties, no significant influence of frequency was found for the tested materials. Based on the obtained results and also on the known advantages of the graded Y-TZP/porcelain structures over traditional bi-layer solutions (e.g., improved bending strength, enhanced mechanical and thermal stress distribution), a novel design of all-ceramic restoration with damping capacity has been proposed at the end of this study. A positive impact on the long-term performance of these all-ceramic restorations may be expected.

Comparison of marginal and internal fit of 3-unit zirconia frameworks fabricated with CAD-CAM technology using direct and indirect digital scans

STATEMENT OF PROBLEM

Accurate marginal and internal fit of dental restorations are essential for their long-term success. The fit of zirconia restorations prepared using digital scan systems has not been fully evaluated.

PURPOSE

The purpose of this in vitro study was to compare the marginal and internal fit of 3-unit zirconia frameworks fabricated using direct and indirect digital scans.

MATERIAL AND METHODS

In a maxillary model, the left first premolar and first molar were prepared to receive 3-unit zirconia fixed dental prostheses. Conventional impressions were made using stock trays and 2-step putty/wash polyvinyl siloxane material and were scanned using laboratory scanner (Conventional Impression-Laboratory scanner [CIL] group). The impressions were then poured, and the stone casts were scanned (Dental Cast-Laboratory scanner [DCL] group). Digital scans were made using TRIOS (TRIOS Intraoral scanner [TRI] group) and CS3600 (CS3600 Intraoral scanner [CSI] group) scanners (n=10). Zirconia copings were designed and milled from presintered blocks and subsequently sintered. Marginal, mid-axial, axio-occlusal, and mid-occlusal discrepancies were measured using the silicone replica technique with stereomicroscopy at ×50 magnification. The data were analyzed using 1-way ANOVA (α=.01).

RESULTS

The ANOVA revealed significant differences among the studied groups in terms of all studied characteristics (P≤.01). Marginal gap was significantly higher in the DCL group (106 ±45 μm) compared with all other groups (P≤.01). However, no significant differences were observed in marginal gap between the TRI (60 ±15 μm) and CSI (55 ±13 μm) groups (P>.01). Internal gap in the mid-occlusal and axio-occlusal regions were significantly higher in the CIL (238 ±92 μm and 227 ±95 μm) and DCL (248 ±71 μm and 216 ±68 μm) groups than those recorded in the TRI (104 ±27 μm and 126 ±31 μm) and CSI (128 ±16 μm and 147 ±28 μm) groups (P≤.01). Internal discrepancies in the mid-axial position were similar between the TRI (70 ±15 μm) and CSI (72 ±23 μm) groups (P>.01), but these values were significantly lower than those recorded in the CIL (88 ±31 μm) and DCL (85 ±30 μm) groups (P≤.01).

CONCLUSIONS

Within the limitations of this study, zirconia frameworks in the TRI and CSI groups had lower marginal and internal gaps compared with those in the DCL and CIL groups. Marginal gap in all groups was within a clinically acceptable range.

Ceramic Fracture in Bilayered All-ceramic Indirect Restoration: A Review of the Literature

Background:

High incidence of fracture of all-ceramic crowns may compromise the clinical outcome and is a source of hassle for both patients and dentist.

Objective:

The objective of the present review was to identify reasons for high ceramic fracture or chipping and to minimize these incidents in dental settings.

Methods:

The final search strategy was executed on Medline via OvidSP, PubMed, and Web of Knowledge. Studies meeting the following inclusion criteria were included in the current review. (1) Literature in English language only, (2) in vitro studies, (3) studies providing evidence on ceramic fracture, and (4) studies only related to indirect restoration and ceramics. Moreover, the exclusion criteria were based on (1) articles other than English, (2) studies reporting direct restoration, (3) any non–peer-reviewed gray literature, and (4) studies discussing fracture other than ceramic material.

Results:

From the initial search strategy, 101 studies were retrieved from different databases. A total of 3 studies were scrutinized through other resources. Following duplicate removal (n = 24), 80 studies were screened for the title and abstract. Moreover (n = 49) studies were shortlisted for full text and review. Following review and discussion in the final result, only 26 studies were included.

Conclusions:

Many improvements in the material, its fabrication process, and surface treatments can reduce the incidence of fracture within the material.

Clinical performance of tooth- or implant-supported veneered zirconia single crowns: 42-month results

OBJECTIVES

The objective of this clinical study was to compare and assess the clinical performance of tooth-supported and implant-supported zirconia single crowns with sintered veneering caps.

METHODS

In this prospective study, 118 patients with a total of 220 single crowns placed on 106 teeth (69 vital teeth, 37 endodontically treated teeth) and 114 implants in molar and premolar regions were examined during a mean observation period of 42 months. The restorations were evaluated for technical failures such as veneering porcelain fractures (chipping), surface quality, marginal fit, and the interface quality of the coping and sintered veneering. The soft tissue status was assessed using the modified Silness and Löe's plaque and gingival index (mPI) and the modified Muhlemann sulcus bleeding index (mSBI). Tooth-supported crowns were checked for secondary caries and hypersensitivity during the follow-up period. Recalls were performed every 6 months.

RESULTS

The 3-year Kaplan-Meier success probability was 98.2% and 100% for implant- and tooth-supported crowns, respectively. A significant difference could be detected between the implant-supported and tooth-supported zirconia single crowns, in terms of their chipping rate (p = 0.039). Veneering material fractures were recorded on two implant-supported restorations (1.8%). No veneering fractures occurred on tooth-supported single crowns. The plaque and gingival index and sulcus bleeding index showed stable and healthy soft peri-implant and periodontal tissues. Neither loss of vitality nor secondary caries occurred on tooth-supported crowns.

CONCLUSIONS

Zirconia-based single crowns with a sintered veneering cap showed promising clinical results on both tooth and implant abutments; however, the dental implants were more prone to complications. In terms of clinical significance, high-strength ceramic with a sintered veneering cap can be recommended for prosthetic treatment of both tooth- and implant-supported single crowns in molar regions.

CLINICAL RELEVANCE

This study provides valuable information for further application of all-ceramic restorations.