Influence of external and internal surface roughness modifications on ceramic flexural strength.

STATEMENT OF PROBLEM: After the occlusal adjustment of a ceramic restoration, polishing is necessary to promote surface smoothness and increase the ceramic flexural strength. However, the internal adjustment procedure may affect ceramic flexural strength. PURPOSE: The purpose of this study was to evaluate the effect of external adjustment with or without the polishing procedure and of internal adjustments on the surface roughness and flexural strength of a ceramic. MATERIAL AND METHODS: Sixty bar-shaped specimens were fabricated from a reinforced glass ceramic lithium disilicate and divided into 6 groups (n = 10): G, glaze (control); EA, external adjustment; EAP, EA + polishing; IA, internal adjustment; EIA, EA + IA; and EPIA, EA + polishing + IA. The entire external and internal surfaces were ground with an extrafine diamond rotary instrument positioned perpendicularly to the long axis of the specimen. External surface roughness was determined by measuring the Ra of the specimens. All the specimens were submitted to a 3-point bend test. One additional specimen from each group was prepared so that the surface morphology could be observed by scanning electron microscopy (SEM). The data were analyzed with 1-way ANOVA and the Bonferroni and Dunnett tests. RESULTS: Group EAP presented statistically lower surface roughness than G, EA, IA, and EIA but was similar to EPIA (P<.001). No statistically significant differences were found in the flexural strength of the 6 groups (P=.081). CONCLUSIONS: External adjustments without the polishing procedure did not affect the surface roughness of the ceramic. However, when followed by polishing, a significant reduction was found in surface roughness. This reduction in surface roughness did not influence the ceramic flexural strength, as well as the association of the others' surface roughness modifications and internal adjustment.

Effect of finishing time and techniques on marginal sealing ability of two composite restorative materials.

STATEMENT OF PROBLEMS: Finishing of composites may adversely influence the sealing ability of direct adhesive restorations. PURPOSE: This study was conducted to determine whether finishing time and techniques under wet or dry conditions affect the microleakage of 2 types of class V composite restorations. MATERIAL AND METHODS: Eighty class V preparations were made in the buccal surfaces of noncarious molars with the occlusal margins ending in enamel and the gingival margins in dentin. Dental adhesive (Single Bond) was applied according to the manufacturer's instructions. Half of the preparations were restored with a microfilled composite (Silux Plus) and the other half with a hybrid composite (Filtek Z250). Within each major composite group (n = 40), 4 subgroups (n = 10) were established based on finishing technique (diamond finishing burs or aluminum oxide discs) and finishing time (immediate or delayed by 24 hours). The specimens were stored for 24 hours in 37 degrees C water, thermocycled for 250 cycles between 5 degrees C and 55 degrees C, immersed in 2% methylene blue solution for another 24 hours, and sectioned longitudinally. For both enamel and dentin margins, dye solution penetration at the tooth/composite interface was scored from 0 to 4 under stereoscopy at original magnification x 20. Data were analyzed with the Kruskal-Wallis test (P<.05). RESULTS: Significantly lower leakage scores were recorded for teeth restored with microfilled composite and finished under wet conditions after 24 hours (P<.01). No significant differences were found among the hybrid composite groups. CONCLUSION: For microfilled composite restorations on dentin margins, delayed wet finishing with diamond burs resulted in significantly lower microleakage scores than all other finishing protocols. Hybrid composite restorations had equivalent levels of microleakage regardless of the finishing method.