SEM ANALYSIS OF MARGINAL EXPANSION AND GAP FORMATION IN CLASS-II COMPOSITE RESTORATIONS

Objectives. Morphological changes in terms of marginal expansion have been observed at the dentin-composite interface of resin composite res torations with the scanning electron microscope (SEM), which could not be described with the criteria conventionally used for quantitative m arginal analysis. The purpose of the present study was to elucidate th e influence of marginal expansion upon marginal integrity and clarify the cause of these morphological changes. Methods. A total of 22 extra cted human molars were restored with Class II resin composite restorat ions, with and without the use of a dentin bonding agent. The cervical restoration margin was located below the cemento-enamel-junction (CEJ ). The marginal adaptation at the dentin-and enamel-composite interfac es was evaluated and measured on replicas using quantitative SEM analy sis after different storage periods. The chemical composition of the m arginal expansion was determined qualitatively by EDX (Energy Dispersi ve X-Ray) analysis using original tooth samples. The results obtained from quantitative SEM analysis were statistically analyzed by applying the Mann-Whitney U-test and the error rates method. Results. Signific antly less marginal expansion occurred at the enamel interface than at the dentin-composite interface (p less than or equal to 0.01). Within the dentin, less marginal expansion was observed with the use of a de ntin bonding agent than without a dentin bonding agent (p less than or equal to 0.05). At 1 y, a significant (p less than or equal to 0.05) decrease in marginal expansion was observed in both groups. EDX analys is revealed that the chemical composition of the marginal expansion is comparable to the resin composite, since peaks for silicon, barium an d ytterbium could be found at these sites. Significance. In Class II r esin composite restorations below the CEJ, partial disruption of the a dhesive bond may occur initially when curing the restoration. Water so rption causes gap reduction by hygroscopic expansion, seen in the SEM as a volume increase. Thus, the observed morphological changes can be regarded as an early sign of insufficient adhesion between composite a nd dentin at sites where disruption of the bond occurred initially, wh ether or not a dentin bonding agent was used.