Three years in vivo wear: core-ceramic, veneers, and enamel antagonists.

OBJECTIVES: Test the hypotheses that there are equivalent wear rates for enamel-versus-enamel and ceramic-versus-enamel, analyzing the in vivo wear of crown ceramics, their natural enamel antagonists, and the corresponding two contralateral teeth; and, that bite force does not correlate with the wear. METHODS: A controlled, clinical trial was conducted involving patients needing full coverage crowns opposing enamel antagonists. Bite forces were measured using a bilateral gnathodynamometer. Single-unit restorations of metal/ceramic (Argedent 62, Argen Corp/IPS d.SIGN veneer); or, core-ceramic/veneer from either, Empress2/Eris, or e.max Press core/e.max Ceram glaze (ceramics: Ivoclar Vivadent, USA) were randomly assigned, fabricated and cemented. Impressions were made of the ceramic crowns, as well as each maxillary and mandibular quadrant at one week (baseline) and one, two and three years. Resulting models were scanned (3D laser scanner). Maximum wear was calculated by superimposing baseline with annual images. RESULTS: There were a total of thirty-six crowns required for thirty-one patients. Each restoration had three associated enamel teeth: crown, (1) antagonist, (2) contralateral and (3) contralateral-antagonist. SAS PROC MIXED (α=0.05) indicated no statistical significance for mean maximum wear among crown ceramics, enamel antagonists and contralaterals. However, enamel wear was statistically significant in relation to intraoral location (p=0.04) and among years (p<0.02). Analyzed alone, the enamel contralateral-antagonist exhibited significantly greater wear (p<0.001). Considering all wear sites, there was no correlation with bite force (p=0.15). SIGNIFICANCE: The ceramics and their antagonists exhibited in vivo wear rates within the range of normal enamel. Future studies should examine the wear implications of the contralateral-antagonist enamel.

Visual and instrumental agreement in dental shade selection: three distinct observer populations and shade matching protocols.

OBJECTIVES: This study tested the hypothesis that the agreement between observer visual dental shade matches and instrumental shade identification is higher using the Vita 3D-Master (3D) shade guide than the Vita classical (VC) shade guide. METHODS: Three populations selected shade matches: non-dental observers (GP) matched shade tabs-to-tabs and dental students (DS) and dentists (DD) matched an in vivo natural right upper central incisor (RUCI). All observers (n=600) used both shade guides (3D and VC) in two lighting conditions, cool white fluorescent lighting (CWF) and natural sunlight (NSL). The shade tabs and natural teeth were identified using an intra-oral spectrophotometer (Vita Easyshade) to determine the instrumental agreement with the visual shade selection. The percent visual-instrumental shade agreement (PVIA) was analyzed statistically considering: observer population, shade guide set, and lighting condition. RESULTS: A "substantial" intra-examiner agreement (k=0.76) was observed. The PVIA ranged from 12% (DS) for the 3D-NSL condition to 42% (DD) with the VC-CWF condition, which also resulted in the highest PVIA for GP (38.5%) and DS (35%). Results indicated that the GP with neither dental knowledge nor shade guide experience had a significantly higher PVIA using the VC rather than the 3D shade guide. Dentists demonstrated the highest PVIA (42%) for both lighting conditions and shade guides, thereby rejecting the study hypothesis. SIGNIFICANCE: A significantly higher visual-instrumental shade agreement was demonstrated by the clinically experienced dentists (DD), regardless of shade guides and lighting conditions.

Characterization of glass-infiltrated alumina-based ceramics.

OBJECTIVE: Characterize the microstructure, composition, and important properties of glass-infiltrated alumina-based ceramics similar to the In-Ceram system. METHODS: Materials used were: IA, In-Ceram Alumina (Vita); IAE, IA electrophoretically deposited (Vita); AEM, IA using a vacuum driven method (Vita); VC, Vitro-Ceram (Angelus); TC, Turkom-Cera (Turkom-Ceramic); CC, Ceramcap (Foto-Ceram); and AG, Alglass (EDG). Ceramic specimens were fabricated following manufacturers' instructions and ISO6872 standard and polished successively through 1 microm alumina abrasive. Semi-quantitative and qualitative analyses were performed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and stereology (Vv). The elastic modulus (E) and Poisson's ratio (nu) were determined using time-of-flight data measured in an ultrasonic pulser/receiver and the density (rho) was determined using a helium pycnometer. Vicker's indentation was used to calculate hardness (H). Bar specimens (25 mm x 4 mm x 1.2 mm) were loaded in three-point bending to fracture using a universal testing machine with cross-head speed of 1mm/min. Flexural strength (sigma(3P)) was calculated and statistically analyzed using ANOVA, Tukey (alpha = 0.05) and Weibull (m = modulus, sigma(0) = characteristic strength). RESULTS: SEM and EDS analyses revealed similar microstructure for all-ceramics, except for a lead-based matrix in CC and a zirconia phase in VC. TC, AG and CC showed significantly lower mean sigma(3P) values than the other ceramics (p< or =0.05). AEM showed the greatest m (16). CONCLUSION: Despite few differences in microstructure and composition, the IA, IAE, AEM and VC ceramics have similar properties. SIGNIFICANCE: The glass-infiltrated alumina-based ceramics from different manufacturers presented distinct characteristics. It is necessary to characterize new commercially available materials to understand their properties.

Thermal compatibility of dental ceramic systems using cylindrical and spherical geometries.

OBJECTIVE: To test the hypothesis that bilayer ceramic cylinders and spheres can provide valid confirmation of thermal incompatibility stresses predicted by finite element analyses. METHODS: A commercial core ceramic and an experimental core ceramic were used to fabricate open-ended cylinders and core ceramic spheres. The core cylinders and spheres were veneered with one of four commercial dental ceramics representing four thermally compatible groups and four thermally incompatible groups. Axisymmetric thermal and viscoelastic elements in the ANSYS finite element program were used to calculate temperatures and stresses for each geometry and ceramic combination. This process required a transient heat transfer analysis for each combination to determine input temperatures for the structural model. RESULTS: After fabrication, each specimen was examined visually using fiberoptic transillumination for evidence of cracking. There were 100% failures of the thermally incompatible cylinders while none of the thermally compatible combinations failed. Among the spheres, 100% of the thermally incompatible systems failed, 16% of one of the thermally compatible systems failed, and none of the remaining compatible combinations failed. The calculated stress values were in general agreement with the experimental observations, i.e., low residual stresses for the specimens that did not fail and high residual stresses for the specimens that did fail. SIGNIFICANCE: Simple screening geometries can be used to identify highly incompatible ceramic combinations, but they do not identify marginally incompatible systems.

Characterization and surface treatment effects on topography of a glass-infiltrated alumina/zirconia-reinforced ceramic.

OBJECTIVE: Characterize the microstructure, composition and some physical properties of a glass-infiltrated alumina/zirconia-reinforced ceramic (IZ) and the effect of surface treatment on topography. METHODS: IZ ceramic specimens were fabricated according to ISO6872 instructions and polished through 1 microm alumina abrasive. Quantitative and qualitative analyses were performed using scanning electron microscopy (SEM), backscattered imaging (BSI), electron dispersive spectroscopy (EDS) and stereology. The elastic modulus (E) and Poisson's ratio (nu) were determined using ultrasonic waves, and the density (rho) using a helium pycnometer. The following ceramic surface treatments were used: AP-as-polished; HF-etching with 9.5% hydrofluoric acid for 90 s; SB-sandblasting with 25 microm aluminum oxide particles for 15s and SC-blasting with 30 microm aluminum oxide particles modified by silica (silica coating) for 15s. An optical profilometer was used to examine the surface roughness (Ra) and SEM-EDS were used to measure the amount of silica after all treatments. RESULTS: The IZ mean property values were as follows: rho=4.45+/-0.01 g/cm(3); nu=0.26 and E=245 GPa. Mean Ra values were similar for AP- and HF-treated IZ but significantly increased after either SC or SB treatment (p

The effect of surface finishing and storage solutions on the color stability of resin-based composites.

BACKGROUND: The authors tested the hypothesis that surface-finishing treatments and the type of storage solutions significantly affected the staining of resin-based composites, or RBCs, and unfilled resins, or URs. METHODS: Fifty-four RBC and 54 UR disks were polymerized through a polyester film strip (Mylar, DuPont, Wilmington, Del.) and polished in one of three groups: 1-micrometer aluminum oxide, 15-microm diamond plate and no treatment (polyester film). All specimens were immersed in water for two days and then in coffee, cola or red wine for seven more days at 37 C. The authors recorded tristimulus color measurements before the immersions; after one and two days in water; and after one, two, three and seven days in the storage solutions. RESULTS: Most of the color changes occurred between day 2 in water and day 7 in the staining solution. Analysis of variance showed that the finishing treatment and storage solution significantly influenced the overall color change (deltaE), and interactions occurred between the finishing treatment and the storage solution (P < .0001) for both materials. RBC specimens generally exhibited greater color changes than did UR specimens. The polyester film finishing exhibited the greatest amount of color change, while the diamond finishing exhibited the least amount of color change. Immersion in wine caused the greatest color change for both materials; cola and coffee resulted in the smallest color change for RBC and UR specimens, respectively. CONCLUSIONS: Finishing treatments and storage solutions significantly affect the surface staining of RBC materials. Polyester film finishing and red wine produced the greatest color change after seven days for RBC specimens. CLINICAL IMPLICATIONS: Clinicians should remove the polyester film-finished surface and advise patients that drinking wine could intensify surface staining on RBC restorations.

Effect of fluoride varnishes on color stability of esthetic restorative materials.

Fluoride varnish applications were applied to two hybrid resin composite materials, Z-100 (3M Dental Products, St Paul, MN, USA) and Esthet-X (Dentsply Caulk, Milford, DE, USA), shades A1 and A2 and a glass ionomer, GC Fuji IX GP Fast (GC Corporation, Tokyo, Japan), shade A2, to evaluate color stability. Specimens (12.6-mm dia x 2.3 mm) were prepared using a polyethylene frame, light-cured and polished through a 1-microm alumina finish. After the initial baseline color measurements, the discs were suspended in Fusayama artificial saliva (FAS) solution at 37 degrees C for 48 hours. Post immersion, the specimens were divided into five groups (n=15 each). The following fluoride varnishes were applied to four groups of test specimens: Duraphat (Colgate Oral Pharmaceutical, Inc, Canton MA, USA), Cavity Shield (OMNII Oral Pharmaceuticals, West Palm Beach, FL, USA), Duraflor (Pharmascience Inc, Montreal, Canada) and Fluor Protector (Vivadent, Ivoclar North America, Amherst, NY, USA). The varnish was allowed to dry for five minutes before immersion. The control group was not coated with varnish, although the specimens were immersed in FAS. All specimens were incubated in newly prepared FAS at 37 degrees C for 24 hours, cleaned with an electric toothbrush and the process repeated using newly prepared FAS. CIE L*a*b* color measurements were recorded five times: at baseline, after 48 hours FAS immersion, after cleaning the first and second fluoride varnish applications and after the final brushing using a commercial toothpaste (Crest). A Minolta CR-300 tristimulus colorimeter with an 8-mm aperture (Ramsey, NJ, USA) was used to record color measurements with the daylight (D65) setting. Calculations were performed for using CIE parameters deltaE*, deltaL*, delta a*, delta b*. Analysis of variance (ANOVA) and post-hoc test (Fisher's PLSD) were used for statistical analysis. After immersion in saliva, the tested glass ionomer (Fuji IX) produced the most significant color changes (deltaE*=1.19 and deltaL*=-1.03), indicating the effect of the color change was due to absorption. After fluoride varnish applications, Duraphat varnish produced significant changes in all tested materials and shades, resulting in color changes with deltaE greater than (>) 1 but less than (<) 3. These color changes are considered visually perceptible, yet have been reported in dental literature as clinically acceptable. Fluoride varnishes can be used without adversely affecting the color of restorative materials.

Effect of surface finishing and storage media on bi-axial flexure strength and microhardness of resin-based composite.

This in vitro study tested the following null hypotheses: (1) surface finishing treatments do not significantly affect the biaxial flexure strength and microhardness of resin-based composites (RBC) and (2) storage media do not significantly affect these physical properties. Discs (81 RBC and 81 UR; 3M/ESPE) were prepared using a circular polyethylene mold (2.4-mm thick x 16.7 mm in diameter) that was polymerized through a Mylar strip and divided into three surface finishing treatment groups: 1 microm aluminum oxide slurry; 15 microm diamond and a Mylar strip. Randomly selected controls for each finishing group were stored at room temperature in individual vials. Test specimens were immersed in water, stored at 37 degrees C for two days and transferred for an additional seven days to one of three aqueous storage media at 37 degrees C: coffee (pH 5.1), cola (pH 2.4) or red wine (pH 3.7). Post immersion (nine days total), the specimens were tested for biaxial flexure strength (BFS) and Vicker's microhardness (VHN). ANOVA and Tukey's HSD test were used for statistical analysis. ANOVA results indicated that surface finishing treatments had a significant effect on the biaxial flexure strength and microhardness of the RBC and the UR specimens. BFS results for RBC specimens were AL>DD>ML (p<0.0001) and VHN results were AL, DD>ML (p<0.0001). Storage in wine medium reduced the VHN of UR specimens significantly. Both alternative hypotheses were accepted. In addition, the Mylar finishing group, because of the resin-rich surface layer, yielded the lowest mean values of BFS and VHN.

Influence of tab and disk design on shade matching of dental porcelain.

STATEMENT OF PROBLEM: Given the complexity of tooth color, the variations of shade within each tooth, and translucency, it is difficult to view only one small area and select a shade match for restorations. PURPOSE: This study tested the effect of specimen design on porcelain shade matching, hypothesizing that flat disks would be matched to one another with more accuracy than tooth-shaped tabs to tabs. MATERIALS AND METHODS: All testing was conducted in a Macbeth SpectraLight booth with D65 illumination. Seventy-three senior dental students (25 women and 48 men; mean age, 27 years) were asked to match selected Vita porcelain disks and Vita shade tabs to like specimens. The design order, namely matching tabs or disks first, was alternated for each observer. The specimens were handed to the observer individually. No time limit for matching was imposed, although each observer was given explicit instructions related to the observation and handling of the specimens. Upon completion of the matching exercises, each student received his or her standardized test results and reviewed the matching results. The time for testing and review was approximately 20 minutes per observer. An analysis of variance, with gender and order as 2 factors that could affect matching scores, was performed (P <.05). RESULTS: The mean matching scores were 78.4% for disks and 73.6% for tabs (P=.119). Female observers matched 76.5% of the disks and 77.5% of the tabs, whereas male observers matched 79.4% of the disks and 71.6% of the tabs (P=.054). Matching disks before tabs yielded equivalent levels of shade matching (disks, 77.6%; tabs, 77.1%). When tabs were matched first, the scores were as follows: disks, 79.8%, and tabs, 67.3% (P=.010). CONCLUSIONS: Within the limitations of this study, there was no significant difference in shade-matching accuracy between the 2 shapes, although the order of design matching resulted in a difference in shade-matching ability. When tabs were matched first and disks second, improved matching was evident on the second test. The reverse was not true; no learning was demonstrated when the tabs were matched after the disks.