Effect of different photo-activation methods on push out force, hardness and cross-link density of resin composite restorations.
OBJECTIVE
To evaluate push out force, hardness and cross-link density (CLD) of composite restorations photo-activated by different methods.


METHODS
Z250 (3M ESPE) and XL2500 halogen unit (3M ESPE) were used. For push out force and hardness tests, conical restorations were made in bovine incisors. For CLD evaluation, cylindrical specimens were prepared. Different activation methods were tested: high-intensity continuous (HIC), low-intensity continuous (LIC), soft-start (SS) or pulse-delay (PD), with constant radiant exposure. Knoop readings were performed on bottom and top surfaces. Data were submitted to two-way ANOVA and Tukey's test (alpha=0.05). Push out force data were submitted to ANOVA and Tukey's test (alpha=0.05). Failure modes were classified under magnification (40x). CLD was estimated by hardness readings before and after storage in ethanol. Data were submitted to RM-ANOVA and Tukey's test (alpha=0.05).


RESULTS
No significant differences in top hardness (KHN, N/mm2) were observed for HIC (598), LIC (564), SS (585) and PD (573). LIC presented significantly lower bottom hardness (520) than HIC (574), SS (562) and PD (572). Push out force (N) for SS (246) and PD (238) were similar, but significantly higher compared to LIC (198) and HIC (193). For HIC and LIC, only adhesive and mixed failures were observed. For SS and PD, cohesive failures also occurred. After storage, HIC and LIC presented significantly lower softening than PD. HIC also presented lower softening than SS, and similar results were observed for SS and PD.


CONCLUSIONS
Different activation methods can interfere with push out force, hardness and CLD of composite restorations.
Department of Restorative Dentistry, Dental Materials Division, Piracicaba Dental School, State University of Campinas, UNICAMP, Av. Limeira 901, 13414-903, Piracicaba-SP, Brazil. williamcbrandt@yahoo.com.br
William Cunha
WC
Brandt
Rafael Ratto
RR
de Moraes
Lourenço
L
Correr-Sobrinho
Mário Alexandre Coelho
MA
Sinhoreti
Simonides
S
Consani
D000818:Animals; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D002417:Cattle; D003188:Composite Resins / Q000737:chemistry / Q000528:radiation effects*; D003737:Dental Cavity Preparation / Q000379:methods; D003764:Dental Materials / Q000737:chemistry / Q000528:radiation effects*; D017220:Dentin-Bonding Agents / Q000737:chemistry; D000431:Ethanol / Q000737:chemistry; D006244:Hardness; D008027:Light; D008029:Lighting / Q000295:instrumentation; D008422:Materials Testing; D012997:Solvents / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors
D003188:Composite Resins; D003764:Dental Materials; D017220:Dentin-Bonding Agents; C444701:Filtek Z250; D012997:Solvents; C115612:single bond; D000431:Ethanol; D017438:Bisphenol A-Glycidyl Methacrylate