Removal Of Different Thicknesses Influences The Repair Of Dental Resin Composites&Cases Report

Resin composites are exposed to complex local factors and conditions such as saliva,bacteria,enzymes,compounds from food and beverages,and physical fatigue,during long-term service in the oral environment;therefore,the degradation and ageing of the resin composite must be a focus of research.Some studies have indicated that the mechanical and physicochemical properties on the surface of resin composites,such as microhardness and contact angle,are influenced by different ageing protocols.Furthermore,unreacted monomers that positively influence repair ability leach from the cured composite during ageing.Because there is no uniform method of describing or classifying defects,little is known about whether different removal thicknesses of aged resin composites would influence the repair bond strength.It is worth noting that in a typical clinical situation,the clinician is unable to distinguish the composition of the aged resin composite and therefore may select a different material.Another important factor is the type of new and aged resin composites.Different resin composites have different physicochemical properties and therefore age differently.Some authors have indicated that nanofilled composites have a higher repair bond strength than hybrid composites.However,Cerda-Rizo et al found that there was no statistically significant difference between the repair bond strength of nanofilled and microhybrid resin composites,and Daiki Nagano et al indicated that nanofilled composites were inferior to microhybrid composites for repair.There is still no consensus on which composite types are more suitable for repairing.Consequently,the primary aim of this study was to investigate the repair bond strength of aged nanofilled and microhybrid resin composites after removing different thicknesses and repairing them using either the same or different composites.The secondary aim was to describe the surfaces of aged nanofilled and microhybrid resin composites after removing different thicknesses.Part 1.Characterization of the treated surfaces after removing different thicknesses of aged resin compositesObjective:To describe the surfaces of aged nanofilled and microhybrid resin composites after removing different thicknesses.Methods:Simulated class I cavities with 4*4*4 mm were prepared in extracted human third molars were randomly divided into 2 groups and restored with a nanofilled(Filtek Z350)or a microhybrid(Clearfil APX)composite.After thermocycling,each group was randomly divided into two subgroups:Group RT1,1 mm removed and Group RT3,3 mm removed,followed by roughening.The surface roughness(Sa),and water contact angle of the remaining five specimens in each subgroup were measured.Finally,the specimens were using FESEM for taking 1,000× magnifification micrographs.Results:Removal thickness had no significant effect on the Sa.The water contact angle decreased with increasing removal thickness.The FESEM figures showed that irregularities were composed of exposed fillers,fillers surrounded by resin matrix,porosities and micro-relief produced by mechanical roughening.Conclusion:Group RT3 implies better wettability than Group RT1,while no significant difference was observed for Sa.Part 2.Microtensile bond strength after removing different thicknesses of aged resin compositesObjective:To investigate the repair bond strength of aged nanofilled and microhybrid resin composites after removing different thicknesses and repairing them using either the same or different composites.Methods:Simulated class I cavities with 4*4*4 mm were prepared in extracted human third molars were randomly divided into 2 groups and restored with a nanofilled(Filtek Z350)or a microhybrid(Clearfil APX)composite.Five specimens without ageing in each group acted as a positive control for microtensile bond strength(MTBS)test.After thermocycling,each group was randomly divided into two subgroups:Group RT1,1 mm removed and Group RT3,3 mm removed,followed by roughening.Ten specimens in each subgroup were repaired with the same or different composites,and MTBS tests were conducted.Results:In the same combination group,a significant difference in MTBS was observed among different removal thicknesses.The control group exhibited significantly higher MTBS values than all other experimental groups.Group RT3 showed significantly higher MTBS values than Group RT1.Three-way ANOVA revealed that the aged resin composite factor and removal thickness factor had significant impacts on the MTBS value.Significant interactions were identified between the aged resin composite and the new resin composite.Individual analysis of aged resin composite and new resin composite has been conducted and when the new resin composite was Z350,the aged resin composite played a significant role in MTBS.In Group RT1,Z350-Z350 showed significantly higher MTBS values than APX-Z350.However,in Group RT3,the results of multiple comparisons indicated that the bond strength in different resin composite combinations was not significantly different.Conclusion:Removal of different thicknesses influences the repair bond strength of dental resin composites whether nanofiller or microhybrid resin composites are used,that is characterized by adhesion to the inner surface in a horizontal layer producing a statistically higher repair bond strength than adhesion at the corresponding external surface in upper horizontal layer.Thermal cycling affects the resin composites with an impact on the repair bond strengths,with higher repair bond strength being attained for non-aged than for aged resin composite.