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The aim of this retrospective clinical study was to compare the longevity of cervical restorations between resin composite (RC) and glass ionomer (GI) and to investigate variables predictive of their outcome. The clinical performance of the two restorative materials in function was compared using the ratings of the modified United States Public Health Service (USPHS) criteria. A total of 479 cervical restorations were included in the study. Ninety-one already-replaced restorations were reviewed from dental records. The other 388 restorations still in function were evaluated according to the modified USPHS criteria by two investigators. Longevity and prognostic variables were analyzed with the Kaplan-Meier survival analysis and multivariate Cox proportional hazard model. The clinical performances of the two materials were evaluated according to the ratings of the USPHS criteria and compared using the Pearson chi-square test and Fisher exact test. The longevity was not significantly different between RC and GI (median survival time, 10.4 ± 0.7 and 11.5 ± 1.1 years, respectively). The main reasons for failure were loss of retention (82.2%) and secondary caries (17.8%). The longevity of cervical restoration was significantly influenced by tooth group and operator group (Wald test, p<0.05), while material, gender, presence or absence of systemic diseases, arch, and reason for treatment did not affect the longevity. Contrary to the longevity, the clinical performance of RC was superior to GI in the criteria of retention, marginal discoloration, and marginal adaptation, but similar in secondary caries, wear, and postoperative sensitivity. [ABSTRACT FROM AUTHOR]

Shrinkage in light curing resin composites is assumed to be directed toward the light source. However, the strong bond at the dentin-resin interface achieved by newer generation dentin bonding systems may affect the direction of polymerization shrinkage. In this study, various curing modes of adhesive resin simulating different bond qualities were applied to determine the extent of interfacial gap formation with a scanning electron microscope. We also measured the free surface depression with a profilometer. The direction of polymerization shrinkage was inferred from the ratio of the interfacial gap measurement at the floor to the free surface depression. Various curing modes used in this study include Group 1: light curing of resin composite without the bonding agent as the negative control; Group 2: simultaneous light curing of the bonding agent and resin composite; Group 3: start of the chemical cure of the dual-cured bonding agent before light curing the resin composite; Group 4: curing the light-initiated bonding agent before insertion and light curing of the resin composite. When the bonding agent was light cured prior to inserting the resin composite (Group 4), the free surface depression was the greatest and the interfacial gap smallest among those in all groups. Therefore, if a good bond between dentin and resin composite can be established, the shrinkage flow will be directed toward a center located near the bonded interface rather than toward the incident light , thus reducing detrimental shrinkage stress. [ABSTRACT FROM AUTHOR]

After polishing or glazing, slight color changes of machined porcelain restorations may be perceived, compared to the originally selected shade. This study compared the precision of the tristimulus colorimeter with the spectrophotometer to quantitatively measure the color changes of milled porcelain restorations after polishing or glazing and to evaluate the relationship between the color changes and the surface roughness. Ten two-millimeter thickness specimens of each shade were prepared from five shades of Vita Cerec Mark II porcelain blocks. Each specimen was ground with #220 grit SiC paper on an automatic polishing machine to simulate the surface roughness of milled restoration ground with 54 or 64 µm diamond grinding tools. To compare the precision of the spectrophotometer with the tristimulus colorimeter, CIE Lab* values of each specimen were measured and the coefficients of variation (CV) for each instrument computed. Ra values were also obtained using a Surface Analyzer. After verifying the precision of the tristimulus colorimeter, a second set of measurements were taken after the polishing or glazing procedure to quantitatively evaluate the effect of these procedures on the shade of the milled restorations. To evaluate the relationship between the color change and the surface roughness, a second set of Ra measurements were taken and the correlation between them analyzed. The tristimulus colorimeter measured the L* value more precisely than the spectrophotometer (p<0.05), but on the a* and b* color coordinates, it was not significantly superior to the spectrophotometer (p>0.05). The color difference values produced by polishing or glazing were greater than 2 ΔE units. After polishing and glazing, among the three coordinates examined, ΔL* was the most prominent determinant on ΔE*(ΔR²/polishing=0.9744 and ΔR²/glazing=0.9413), but Δa* and Δb* had little effect. There was no statistically significant correlation between the changes in surface roughness and color in either polishing (r=0.3555, p=0.0812) or glazing (r=-0.1570, p=0.4520). [ABSTRACT FROM AUTHOR]