The effects of monomer type, filler size, and filler content of three resin cements on the color stability of laminate veneers exposed to accelerated aging.

STATEMENT OF PROBLEM: Commercially available resin cements consist of various filler sizes, filler content and monomers, and it is unclear which of these factors have the greatest effect on the color stability of laminate veneers. OBJECTIVES: To evaluate the color stability of lithium disilicate-reinforced laminate veneers inserted with three commercial resin cements with various filler sizes/contents and monomers upon accelerated aging. METHODS: Veneers were fabricated and cemented on resin abutments using three commercially available resin cements comprised of two different monomers and varying filler sizes/contents: 1) triethylene glycol dimethacrylate, TEGDMA (RelyX™ Veneer = 0.6 µm/66 %, Calibra® Esthetic Light Cure =1.2 µm/65 %); and 2) urethane dimethacrylate, UDMA (Variolink Esthetic LC = 0.1 µm/38 %). A total of 60 specimens were fabricated (n = 20 for each cement). The relative number of particles (N) and relative surface area (A) were calculated for each filler size/content. Color coordinates (L*, a*, b*) were measured, and color change (ΔE00) was calculated after cementation and following aging at 150, 300, 450, and 600 h using xenon light. Differences in color coordinates and color change were determined using repeated measures ANOVA followed by Tukey's post hoc test (α = .05). A post-hoc power analysis was performed to confirm reliability of the results. RESULTS: Based on a post-hoc power analysis of a repeated measures ANOVA with two between-factors and 1 within-factor, we had 89 % power to detect a difference of effect by cement type, 10 % power to detect a difference by shade, and 100 % power to detect a difference of effect by aging. The UDMA-based cement (0.1 µm/38 %) was least affected by aging, despite having the largest number of particles (N = 1010) and largest particle surface area (A = 7.02). The TEGDMA-based cements exhibited a significant color change, with 0.6 µm/66 % (A = 2.03, N = 8.12) producing a larger ΔE00 than 1.2 µm/65 % (A = 1.00, N = 1.00). CONCLUSIONS: Among the commercial cements tested, UDMA-based resin (0.1 µm/38 %) provided better color stability than TEGDMA-based resin cements. The color change after aging was affected by the relative surface area and relative number of particles for the TEGDMA-based resin cement (0.6 µm/66 % and 1.2 µm/65 %), with a larger surface area and a higher relative number of particles, accelerated color change with aging. The present study demonstrates a novel approach to determine color stability for any resin cement with particulate filler. CLINICAL IMPLICATIONS: The dental practitioner should be selective in choosing a commercial light cure cementation product for laminate veneers, as UDMA containing resin cement is more resistant to color changes over time than TEGDMA, regardless of the filler size/content.

Clinical Survival Rate and Laboratory Failure of Dental Veneers: A Narrative Literature Review.

There is a vast amount of published literature concerning dental veneers; however, the effects of tooth preparation, aging, veneer type, and resin cement type on the failure of dental veneers in laboratory versus clinical scenarios are not clear. The purpose of the present narrative review was to determine the principal factors associated with failures of dental veneers in laboratory tests and to understand how these factors translate into clinical successes/failures. Articles were identified and screened by the lead author in January 2024 using the keywords ''dental veneer", "complication", "survival rate", "failure", and "success rate" using PubMed/Medline, Scopus, Google Scholar, and Science Direct. The inclusion criteria included articles published between January 1999 and January 2024 on the topics of preparation of a tooth, aging processes of the resin cement and veneer, translucency, thickness, fabrication technique of the veneer; shade, and thickness of the resin cement. The exclusion criteria included articles that discussed marginal and internal fit, microhardness, water sorption, solubility, polishability, occlusal veneers, retention, surface treatments, and wear. The results of the present review indicated that dental veneers generally have a high survival rate (>90% for more than 10 years). The amount of preserved enamel layer plays a paramount role in the survival and success rates of veneers, and glass-ceramic veneers with minimal/no preparation showed the highest survival rates. Fracture was the primary failure mechanism associated with decreased survival rate, followed by debonding and color change. Fractures increased in the presence of parafunctional activities. Fewer endodontic complications were associated with veneer restorations. No difference was observed between the maxillary and mandibular teeth. Clinical significance: Fractures can be reduced by evaluation of occlusion immediately after cementation and through the use of high-strength veneer materials, resin cements with low moduli, and thin layers of highly polished veneers. Debonding failures can be reduced with minimal/no preparation, and immediate dentin sealing should be considered when dentin is exposed. Debonding can also be reduced by preventing contamination from blood, saliva, handpiece oil, or fluoride-containing polishing paste; through proper surface treatment (20 s of hydrofluoric acid etching for glass ceramic followed by silane for 60 s); and through use of light-cured polymerization for thin veneers. Long-term color stability may be maintained using resin cements with UDMA-based resin, glass ceramic materials, and light-cure polymerization with thin veneers.

Relation of Crown Failure Load to Flexural Strength for Three Contemporary Dental Polymers.

Polymeric materials show great promise for use in a variety of dental applications. Manufacturers generally provide flexural strength information based on standardized (ISO and ASTM) specimen dimensions and loading conditions. It is not clear, however, if flexural strength data are predictive of the clinical performance of dental crowns. The objectives of this study were, therefore, to determine whether flexural strengths, as measured via three-point bending (3PB), would be predictive of failure loads assessed via crunch-the-crown (CTC) tests. Three brands of polymers (Trilor, Juvora, and Pekkton) were fabricated into rectangular bars and fully contoured crowns (10 specimens of each polymer brand, 30 specimens of each shape). Differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and burn off tests were used to characterize/confirm the materials. Bars were tested blindly in 3PB to determine flexural strength, and crowns were CTC-tested to determine failure load after luting to resin abutments. The statistical significance of the test results was evaluated via one-way ANOVA (α = 0.05) and Pearson's correlation coefficient, while regression analysis was used to test for a correlation between 3PB and CTC results. The fracture mechanisms and failure surface characteristics were characterized using scanning electron microscopy (SEM). There were significant differences (p < 0.05) in the mean crown failure loads (Trilor (7033 N) > Juvora (5217 N) > Pekkton (3023 N)) and mean flexural strengths of the bars (Trilor (468 MPa) > Juvora (197 MPa) = Pekkton (192 MPa)). The mode of crown fracture was different between the materials and included deformation (Juvora), ductile-to-brittle fracture (Pekkton), and a combination of cracks and deformation (Trilor). Flexural strengths did not correlate with the corresponding crown failure loads for any of the materials tested. These results suggest that dental practitioners should not rely on the flexural strengths reported from three-point bending tests, as advertised by the manufacturer, to predict the performance of polymeric crowns.

Qualitative SEM analysis of fracture surfaces for dental ceramics and polymers broken by flexural strength testing and crown compression.

PURPOSE: To perform qualitative analysis using scanning electron microscopy (SEM) of fracture surfaces for ceramic and polymeric dental materials broken via standardized flexural and crunch-the-crown (CTC) tests. MATERIALS AND METHODS: Zirconia, glass-ceramic, and polymeric (Trilor; TRI, Juvora; JUV, Pekkton; PEK) materials were loaded using crowns for CTC tests, discs (zirconia and glass-ceramics) for piston-on-3 ball tests, bars (polymer) for 3-point bend tests, and bars (zirconia, glass-ceramics) for 4-point bend tests. SEM was used to characterize the fracture surfaces and identify fracture surface features (e.g., origin, mist, hackle, and the direction of crack propagation [DCP]). Electron dispersive spectroscopy was used to identify the local chemistry. RESULTS: Fracture surface features were found to be less visually apparent for glass-ceramics than zirconia. For zirconia bars, fractures originated roughly midway between the corner and center for processing defects related to sintering. Fractures originated at the bottom corners of glass-ceramic bars (void or surface flaw) and PEK bars (surface flaw). TRI bar failures exposed glassy fibers. Fracture features were generally less discernable for discs compared to bars for zirconia and glass-ceramics. Ceramic crowns fractured into 2 to 3 pieces, with fractures originating at the occlusal surface and clear evidence for the DCP. Failures of TRI and JUV specimens (bars and crowns) were less catastrophic than for the ceramics, with exposed fibers (TRI) and surface cracks (JUV). PEK crown and bar fractures presented dimple (ductile) features formed due to microvoid coalescence followed by brittle crack propagation. CONCLUSIONS: The critical flaws responsible for failure initiation were a function of material composition and test configuration. Fractographic analysis can reveal problems associated with the manufacturing of materials, their handling, grinding and finishing/polishing procedures, the structural design and choice of material, and the quality of the final laboratory-delivered restoration.

A Comparison of Failure Loads for Polycrystalline Zirconia Ceramics with Varying Amounts of Yttria, Glass-Ceramics and Polymers in Two Different Test Conditions.

It is unclear how zirconia dental crowns with different yttria compositions will perform clinically, and how they will compare with crowns made of glass-ceramics and polymers. The present objective was to determine failure loads of crowns and discs made of glass ceramics or polymers as compared to yttria-partially stabilized zirconia (Y-PSZ) crowns and discs with varying yttria concentrations. Crowns of zirconia (Cercon XT, Katana UTML, BruxZir Anterior), glass ceramic (Celtra press, IPS e.max press, Lisi press), and polymeric materials (Trilor, Juvora, Pekkton) were fabricated and cemented to epoxy abutments. The total number of specimens was 135 for crowns and 135 for discs (n = 15 specimens per material type and design). A universal testing machine was used to perform compressive loading of crowns/discs to failure with a steel piston along the longitudinal axis of the abutments. Energy dispersive spectroscopy (EDS) was used to identify the yttria concentration for each zirconia brand. The data were analyzed using generalized linear models and regression analyses. The results revealed significant differences (p < 0.05) in mean failure loads for different crown materials: Trilor (6811 ± 960 N) > Juvora (5215 ± 151 N) > Cercon (4260 ± 520 N) = BruxZir (4186 ± 269 N) = e.max (3981 ± 384 N) > Katana (3195 ± 350 N) = Lisi (3173 ± 234 N) = Pekkton (3105 ± 398 N) > Celtra (2696 ± 393 N). The general linear model revealed significant differences (p < 0.05) in mean failure loads when comparing the different materials for the discs, i.e., Trilor (5456 ± 1748 N) > Juvora (4274 ± 869 N) > Pekkton (3771 ± 294 N) > Katana (2859 ± 527 N) > Cercon (2319 ± 342 N) = BuxZir (2250 ± 515 N) = e.max (2303 ± 721 N) = Lisi (2333 ± 535 N) > Celtra (1965 ± 659 N). EDS showed that the zirconia materials contained yttria at different concentrations (BruxZir = 5Y-PSZ, Cercon = 4Y-PSZ, Katana = 3Y-PSZ). The yttria concentration had a significant effect on the failure load of the Katana (3Y-PSZ) crowns, which revealed lower failure loads than the Cercon (4Y-PSZ) and BruxZir (5Y-PSZ) crowns, whose failure loads were comparable or higher than e.max glass ceramic. The failure load of the trilayer disc specimens did not correlate with the failure load of the respective crown specimens for the zirconia, glass-ceramic and polymeric materials.

Flexural strengths, failure load, and hardness of glass-ceramics for dental applications.

STATEMENT OF PROBLEM: Glass-ceramics are often selected for use in dental restorations based upon advertised flexural strengths obtained from standardized tests on prefabricated specimens (bars and disks); these may not accurately reflect their performance in dental applications. PURPOSE: The purpose of this in vitro study was to determine and compare 4-point flexural strength, biaxial flexural strength, hardness, and crown failure loads for 3 commercially available glass-ceramics. MATERIAL AND METHODS: Specimens were pressed and prepared from 3 brands of glass-ceramics: Celtra (CEL), IPS e.max (EMA), and Lisi (LIS). Rectangular bars, circular disks, and fully contoured crowns were created (n=15 specimens per glass-ceramic, 45 specimens per geometry, totaling 135 specimens). Disks were tested for biaxial flexural strength by using a piston-on-3-ball (POB) test, while bars were tested for 4-point flexural strength by using 4-point bending (4PB) and Vickers hardness (VH) tests. Crown failure loads were assessed in "crunch-the-crown" (CTC) tests. The results were analyzed by using general linear modeling, the Pearson correlation coefficient, and Weibull analysis. RESULTS: The general linear modeling revealed significant differences (P<.05) in the failure load for crown specimens (EMA>LIS>CEL), the 4-point flexural strength (EMA>LIS>CEL), and the biaxial flexural strength (EMA>LIS=CEL). The disk specimens had higher flexural strengths than the bar specimens for CEL and EMA materials. LIS had a higher Weibull modulus than EMA and CEL for bar and crown specimens. CEL had a higher Weibull modulus than LIS and EMA for disk specimens. There was no correlation among the VH (R2=0.86 and P=.24), biaxial flexural strength (R2=0.84 and P=.26), and crown failure load. However, there was a high correlation between the failure load (crown specimens) and 4-point flexural strength (bar specimens) (R2=0.99 and P=.03). CONCLUSIONS: The 4-point flexural strength correlated significantly with crown failure load.

An experimental study of flexural strength and hardness of zirconia and their relation to crown failure loads.

STATEMENT OF PROBLEM: Dental zirconia is often marketed and selected for restorative use based upon the biaxial flexural strength of prefabricated specimens (disks) without considering other mechanical and physical properties. PURPOSE: The purpose of this in vitro study was to test whether 4-point flexural strength, biaxial flexural strength, and/or hardness may correlate with failure loads for crowns made of different zirconia materials. MATERIAL AND METHODS: Three brands of zirconia (BruxZir, Cercon, and Katana) were used to fabricate anatomically contoured crowns, rectangular bars, and circular disks. The sample size was n=15 specimens per zirconia brand and specimen shape. The bars were tested for 4-point flexural strength by using the 4-point bending (4PB) test and Vickers hardness (VH), while the disks were tested for biaxial flexural strength by using a piston-on-3 ball (POB) test. Crowns were attached to resin abutments and compressed with a steel spherical indenter through a polyethylene sheet to assess the failure loads by using the "crunch the crown" (CTC) test. One-way ANOVA (α=.05) was used to test for statistically significant differences between groups, and Weibull analysis was used to assess the variability of the measured flexural strengths, failure load, and hardness. RESULTS: Statistical differences (P<.001) were found in comparing Cercon, BruxZir, and Katana ([4260 N=4186 N]>3195 N, respectively) with the CTC test and (396 MPa>[281 MPa=275 MPa], respectively) the 4PB test. No statistical differences (P=.084) were found among the zirconia brands (Cercon [384 MPa]=Bruxzir [359 MPa]=Katana [416 MPa]) for the POB test. No significant correlations (P>.05) were found between the 4PB, POB, or VH tests and the corresponding CTC test. The Weibull modulus varied for the different specimen geometries. CONCLUSIONS: The piston-on-3 ball, 4-point bending, and Vickers hardness test results were not correlated with the corresponding crunch-the-crown test.

The effect of extended aging on the optical properties of different zirconia materials.

PURPOSE: The purpose of this study was to determine if the optical properties of zirconia and glass-ceramic (e.max) were affected by low-temperature degradation (aging). METHODS: Experiment samples were fabricated with seven zirconia brands (n=10): Zenostar, Zirlux, Katana, Bruxzir, DD-BioZX2, DD-cubeX2, NexxZr; and e.max were used as a control. This resulted in a total of 80 samples in the experiment. The L*, a* and b* were measured for each sample, and then the optical properties including translucency parameter (TP), contrast ratio (CR), and opalescence parameter (OP) were calculated. The samples were aged (20, 40, 60, 80, 100h), and the optical properties were calculated after each interval. RESULTS: Most zirconia brands had lower L*, higher a*, higher b* with increased aging, which visually corresponds to darker, redder, and more yellow. Aging also increased CR, lowered TP, and lowered OP. e.max was also affected by aging but still had the highest TP (23.9±2.8), L* (81.7±3.4), and lowest CR (0.41±0.05) compared to any zirconia. The Zenostar had the closest TP (24.1±0.4), and L* (90.2±0.5) values to e.max before aging. However, after 100h of aging, the DD-cubeX2 was least effected and had the highest TP (22.2±0.6) and lowest CR (0.43±0.01) compared with other zirconia samples and highest OP (11.3±0.2) of all ceramic samples. CONCLUSIONS: The optical properties of zirconia and e.max materials were affected by aging with the effects increasing with time. The magnitude of change was affected by seven brands of dental zirconia.

Effect of liner and porcelain application on zirconia surface structure and composition.

The purpose of this study was to determine if there is an effect of liner and porcelain application (layering and pressing techniques) on the surface of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP), which were exposed to permutations of liner, layered porcelain, and pressed porcelain. Scanning electron microscope (SEM)/energy dispersive spectroscope (EDS) was used to identify changes in composition and microstructure after removing liner and porcelain with hydrofluoric acid. Simulated aging was also conducted to determine the effect of liner and porcelain on low-temperature degradation. The control group had a typical equiaxed grain structure, referred to as unaffected. When covered with liner or porcelain, some areas changed in structure and composition and were termed affected. The frequency of affected structure decreased when liner was covered with either layered porcelain or pressed porcelain. There were statistical differences (P<0.05) in the composition between affected and unaffected for zirconium (layered porcelain with liner: affected=60% (0.8%) (m/m), unaffected=69% (4%), layered porcelain without liner: affected=59% (3%), unaffected=65% (3%)) and oxygen (layered porcelain with liner: affected=35% (2%), unaffected=26% (4%), layered porcelain without liner: affected=35% (3%), unaffected=30% (2%)). However, there were statistical differences (P<0.05) in the composition for zirconium and oxygen of the aged layered porcelain without liner only. The liner should not be used before porcelain application, especially when using the layering technique for zirconia restorations. Furthermore, pressing should be considered the technique of choice over layering.

Advancements in CAD/CAM technology: Options for practical implementation.

PURPOSE: The purpose of this review is to present a comprehensive review of the current published literature investigating the various methods and techniques for scanning, designing, and fabrication of CAD/CAM generated restorations along with detailing the new classifications of CAD/CAM technology. STUDY SELECTION: I performed a review of a PubMed using the following search terms "CAD/CAM, 3D printing, scanner, digital impression, and zirconia". The articles were screened for further relevant investigations. The search was limited to articles written in English, published from 2001 to 2015. In addition, a manual search was also conducted through articles and reference lists retrieved from the electronic search and peer-reviewed journals. RESULTS: CAD/CAM technology has advantages including digital impressions and models, and use of virtual articulators. However, the implementation of this technology is still considered expensive and requires highly trained personnel. Currently, the design software has more applications including complete dentures and removable partial denture frameworks. The accuracy of restoration fabrication can be best attained with 5 axes milling units. The 3D printing technology has been incorporated into dentistry, but does not include ceramics and is limited to polymers. In the future, optical impressions will be replaced with ultrasound impressions using ultrasonic waves, which have the capability to penetrate the gingiva non-invasively without retraction cords and not be affected by fluids. CONCLUSION: The coming trend for most practitioners will be the use of an acquisition camera attached to a computer with the appropriate software and the capability of forwarding the image to the laboratory.

Correlation of flexural strength of coupons versus strength of crowns fabricated with different zirconia materials with and without aging.

BACKGROUND: The purpose of this study was to determine the presence of a correlation between flexural strength and simulated crown strength; a correlation between crown strength and mode of fracture; an effect of aging on the flexural strength; and an effect of aging on the crown strength. METHODS: Two hundred forty zirconia specimens were fabricated with 2 different designs, fully contoured crown shape specimens (n = 120) and rectangular coupons (n = 120), to provide 10 specimens each of 6 brands of zirconia (Lava Plus High Translucency [3M ESPE], Argen HT [Argen Corp], Zirlux [Ardent], BruxZir [Glidewell Laboratories], ZenoStar [Wieland Dental], and DDBioZX(2) [Dental Direkt]). One-half of each sample type was given a severe, simulated low-temperature aging treatment. The coupons were tested by 3-point flexural strength, and crowns were tested after luting to metallic abutments using resin cement. Statistical significance was evaluated by 2-factor analysis of variance (P = .05). RESULTS: Aging increased the mean (standard deviation [SD]) flexural strength for the following groups: Argen HT (995 [140] megapascals versus 677 [121] MPa before aging), Zirlux (939 [101] MPa versus 826 [169] MPa before aging), and ZenoStar (954 [81] MPa versus 764 [77] MPa before aging). There were statistical differences for the mean (SD) crown strengths for the following aged crowns: DDBioZX(2) had higher magnitudes (9,755 [1,095] MPa) than ZenoStar (8,864 [976] MPa), whereas Lava Plus High Translucency crowns had higher magnitudes (9,871 [942] MPa) than ZenoStar (8,864 [976] MPa). There was no effect of aging on the crown strength. There were statistical differences in the mode of fracture for the zirconia crowns between the following groups: nonaged and aged BruxZir (P = .014), nonaged and aged ZenoStar (P = .0226), and nonaged and aged Lava Plus High Translucency (P < .0001). There was no correlation between flexural strength and crown strength. CONCLUSIONS: There was no direct correlation between ranking of flexural strength and crown strength in the range of properties exhibited by these dental zirconias. PRACTICAL IMPLICATIONS: Flexural strength does not predict simulated clinical strengths for crowns.

Evaluation of zirconia-porcelain interface using X-ray diffraction.

The aim of this study was to determine if accelerated aging of porcelain veneering had an effect on the surface properties specific to a tetragonal-to-monoclinic transformation (TMT) of zirconia restorations. Thirty-six zirconia samples were milled and sintered to simulate core fabrication followed by exposure to various combinations of surface treatments including as-received (control), hydrofluoric acid (HF), application of liner plus firings, application of porcelain by manual layering and pressing with firing, plus accelerated aging. The quantity of transformed tetragonal to monoclinic phases was analyzed utilized an X-ray diffractometer and one-way analysis of variance was used to analyze data. The control samples as provided from the dental laboratory after milling and sintering process had no TMT (Xm = 0). There was an effect on zirconia samples of HF application with TMT (Xm = 0.8%) and liner plus HF application with TMT (Xm = 8.7%). There was an effect of aging on zirconia samples (no veneering) with significant TMT (Xm = 70.25%). Both manual and pressing techniques of porcelain applications reduced the TMT (manual, Xm = 4.41%, pressing, Xm = 11.57%), although there was no statistical difference between them. It can be concluded that simulated applications of porcelain demonstrated the ability to protect zirconia from TMT after aging with no effect of a liner between different porcelain applications. The HF treatment also caused TMT.

Effect of imaging powder and CAD/CAM stone types on the marginal gap of zirconia crowns.

OBJECTIVE: To compare the marginal gap using different types of die stones and titanium dies with and without powders for imaging. METHODS: A melamine tooth was prepared and scanned using a laboratory 3-shape scanner to mill a polyurethane die, which was duplicated into different stones (Jade, Lean, CEREC) and titanium. Each die was sprayed with imaging powders (NP, IPS, Optispray, Vita) to form 15 groups. Ten of each combination of stone/titanium and imaging powders were used to mill crowns. A light-bodied impression material was injected into the intaglio surface of each crown and placed on the corresponding die. Each crown was removed, and the monophase material was injected to form a monophase die, which was cut into 8 sections. Digital images were captured using a stereomicroscope to measure marginal gap. Scanning electron microscopy was used to determine the particle size and shape of imaging powders and stones. RESULTS: Marginal gaps ranged from mean (standard deviation) 49.32 to 1.20 micrometers (3.97-42.41 µm). There was no statistical difference (P > .05) in the marginal gap by any combination of stone/titanium and imaging powders. All of the imaging powders had a similar size and rounded shape, whereas the surface of the stones showed different structures. CONCLUSIONS: When a laboratory 3-shape scanner is used, all imaging powders performed the same for scanning titanium abutments. However, there was no added value related to the use of imaging powder on die stone. It is recommended that the selection of stone for a master cast be based on the hysical properties. PRACTICAL IMPLICATIONS: When a laboratory 3-shape scanner is used, the imaging powder is not required for scanning die stone. Whenever scanning titanium implant abutments, select the least expensive imaging powder.

The failure load of CAD/CAM generated zirconia and glass-ceramic laminate veneers with different preparation designs.

STATEMENT OF PROBLEM: Fracture of feldspathic porcelain laminate veneers represents a significant mode of clinical failure. Therefore, ceramic materials that withstand a higher load to fracture, especially for patients with parafunctional habits, are needed. PURPOSE: The purpose of this study was to examine the correlation of material (zirconia, TZP, glass-ceramic, IEC, and feldspathic porcelain, FP) design (incisal overlapped preparation, IOP, and three-quarter preparation, TQP), and fracture mode to failure load for veneers supported by composite resin abutments. MATERIAL AND METHODS: A typodont tooth prepared with 2 designs (IOP, TQP) and the corresponding 2 definitive dies were used to fabricate the composite resin abutments (30 for IOP and 30 for TQP). Ten veneer specimens for each system (Y-TZP, IEC, and FP), were fabricated for each design. The veneers were cemented, invested, and tested in compression until failure by using a universal testing machine. Significant differences were evaluated by 2-factor ANOVA (α=.05). RESULTS: No statistical mean load difference was noted between the preparation designs for Y-TZP (IOP: 244 ±81 and TQP: 224 ±58 N), IEC (IOP: 306 ±101 and TQP: 263 ±77 N), and FP veneers (IOP: 161 ±93 and TQP: 246 ±45 N). No statistical difference in the mean load was found among the 3 veneer materials for each preparation design except between IEC (306 ±101 N) and FP (161 ±93 N) veneers for TQP. CONCLUSIONS: Preparation design did not influence the failure load of the veneer materials. Zirconia veneers were the least likely to fracture but the most likely to completely debond; feldspathic porcelain veneers exhibited the opposite characteristics.

Evaluation of the optical properties of CAD-CAM generated yttria-stabilized zirconia and glass-ceramic laminate veneers.

STATEMENT OF PROBLEM: When feldspathic porcelain (FP) laminate veneers are used to mask tooth discoloration that extends into the dentin, significant tooth reduction is needed to provide space for the opaque layer and optimize the bonding of the restoration. PURPOSE: The purpose of this study was to investigate the color effect of trial insertion paste (TP), composite resin abutment (CRA), and veneer regions on the optical properties of feldspathic porcelain (FP), yttria-stabilized zirconia (Y-TZP), and IPS e.max CAD HT (IEC) veneers. MATERIAL AND METHODS: A melamine tooth was prepared for a laminate veneer on a model, and a definitive cast was made. The definitive die was scanned by using the TurboDent System (TDS), then 30 CRA were machined and 10 veneers were fabricated for each ceramic material (FP, Y-TZP, IEC). The optical properties of different veneer materials, CRA (A(1), A(2), A(3)) and TP (bleach XL, opaque white, transparent, and yellow) were evaluated in the cervical, body, and incisal regions with a spectrophotometer. Results were analyzed by using 1-way ANOVA (.05). RESULTS: The color difference for all the veneers was affected by TP and CRA colors in different regions. The mean values for the Y-TZP veneer color coordinates (L*: 74 ±0.34, a*: 0.09 ±0.20, and b*: 17.43 ±0.44) were significantly different (P<.001) from those of IEC veneers (L*: 70.15 ±0.23, a*: -0.69 ±0.073, and b*:11.48 ±0.30) and FP veneers (L*: 70.00 ±0.86, a*: - 0.28 ±0.203, and b*: 13.86 ±1.08). There was no difference between IEC for L* and FP. Significant difference was detected (P<.001) in color coordinates among the 3 veneer materials for a* and b*. CONCLUSIONS: The TP color affected the color difference for all veneer materials except the Y-TZP, while there was no effect on the CRA color. The magnitude of color coordinates changed as a function of TP color and veneer material.

Influence of low-temperature environmental exposure on the mechanical properties and structural stability of dental zirconia.

PURPOSE: The effect of dental fabrication procedures of zirconia monolithic restorations and changes in properties during low-temperature exposure in the oral environment is not completely understood. The purpose of this study was to investigate the effect of procedures for fabrication of dental restorations by low-temperature simulation and relative changes of flexural strength, nanoindentation hardness, Young's modulus, surface roughness, and structural stability of yttria-stabilized zirconia. MATERIALS AND METHODS: A total of 64 zirconia specimens were prepared to simulate dental practice. The specimens were divided into the control group and the accelerated aging group. The simulated group followed the same procedure as the control group except for the aging treatment. Atomic force microscopy was used to measure surface roughness. The degree of tetragonal-to-monoclinic transformation was determined using X-ray diffraction. Nanoindentation hardness and modulus measurements were carried out on the surface of the zirconia specimens using a nanoindenter XP/G200 system. The yttria levels for nonaged and aged specimens were measured using energy dispersive spectroscopy. Flexural strength was determined using the piston-on-three-ball test. The t-test was used to determine statistical significance. RESULTS: Means and standard deviations were calculated using all observations for each condition and evaluated using a group t-test (p < 0.05). The LTD treatment resulted in increased surface roughness (from 12.23 nm to 21.56 nm for Ra and 15.06 nm to 27.45 nm for RMS) and monoclinic phase fractions (from 2% to 21%), with a concomitant decrease in hardness (from 16.56 GPa to 15.14 GPa) and modulus (from 275.68 GPa to 256.56 GPa). Yttria content (from 4.43% to 4.46%) and flexural strength (from 586 MPa to 578 MPa) were not significantly altered, supporting longer term in vivo function without biomechanical fracture. CONCLUSION: The LTD treatment induced the tetragonal-to-monoclinic transformation with surface roughening in zirconia prepared using dental procedures.

The effect of different fabrication steps on the marginal adaptation of two types of glass-infiltrated ceramic crown copings fabricated by CAD/CAM technology.

PURPOSE: Marginal adaptation is an important factor affecting the longevity of all-ceramic restorations, although the effects of different fabrication steps on marginal adaptation at various stages of fabrication are not fully understood. The purpose of this study was to assess with an in vitro model whether In-Ceram alumina (IA) or In-Ceram zirconia (IZ) copings produced by the CAD/CAM method would be clinically acceptable, and to evaluate the effect of each fabrication step (post-milling, post-trimming, and post-glass infiltration) on the marginal discrepancy of the coping. MATERIALS AND METHODS: A melamine tooth was prepared, duplicated, poured with inlay wax, and then cast with metal to fabricate a master die. An InLab 3D system was used to scan the master die and to design and mill the copings. Thirty IA and IZ copings each were developed with thicknesses of 0.6 mm and a 30-µm thick computer luting space. Epoxy resin replicas of the master die were fabricated, and the vertical and horizontal marginal discrepancies were measured using a Micro-Vu optical microscope at three stages of the fabrication (post-milling, post-trimming, post-infiltration). One-way ANOVA was used to analyze the data between the three stages of fabrication for each marginal discrepancy, and a t-test was used to compare vertical and horizontal marginal discrepancies (after glass infiltration) between IZ and IA copings RESULTS: There were no significant differences (p > 0.05) in the vertical marginal discrepancies (µm) between IA (36 ± 14) and IZ (40 ± 14) copings after glass infiltration. ANOVA (comparing three stages within horizontal marginal discrepancy for IZ copings) showed that post-milling (40 ± 26) > post-trimming (23 ± 11) = post-infiltration (19 ± 13). ANOVA (comparing three stages within vertical marginal discrepancy for IZ copings) showed that post-milling (53 ± 12) = post-trimming (47 ± 13) > post-infiltration (36 ± 14). ANOVA (comparing three stages within horizontal marginal discrepancy for IA copings) showed that post-milling (52 ± 28) > post-trimming (30 ± 16) > post-infiltration (30 ± 16). ANOVA (comparing three stages within vertical marginal discrepancy for IA copings) showed that post-milling (54 ± 13) = post-trimming (56 ± 26) > post-infiltration (40 ± 14). CONCLUSION: There was no significant difference in the marginal adaptation of both material copings. After the trimming process, the glass infiltration firing cycle improved the vertical marginal discrepancy for both IZ and IA copings. Clinical implications. IA and IZ copings fabricated by CAD/CAM technology have an acceptable marginal fit as documented in the literature, and the glass infiltration process improves the marginal fit after machining.