Studies on posterior composite resins with special reference to class II restorations.

Longevity, clinical performance and some related factors of posterior composite resin restorations were investigated through clinical follow-up and laboratory studies in vivo and in vitro. Class I and Class II restorations using two experimental posterior composite resin materials were followed clinically for a four-year period. USPHS evaluation criteria were used. Assessments of wear were also made indirectly using the Leinfelder method. Marginal leakage of bacteria (in vivo) and of dye (in vitro) were studied on modified loaded Class II composite resin restorations lined with GlumaR and LifeR. The grade of conversion (cure) of the posterior composite resin material and the colonization of bacteria at proximal tooth surfaces restored with posterior composite resins were evaluated. Seven per cent of the restorations were evaluated as failures and had to be replaced during a 4-year period. The failures were mainly due to fractures and postoperative sensitivity. The calculated occlusal wear rate was 34-40 microns/year. Occlusal loading of Class II restorations in vitro resulted in a higher frequency of restorations with marginal leakage. The marginal leakage for occlusally-loaded Class II restorations in vivo and in vitro could be reduced if dentine bonding was utilized. The grade of conversion (cure) was increased in the in vivo situation compared to the in vitro. Bacterial colonization of strepococcus mutans on the proximal surfaces of posterior composite restorations showed higher frequencies compared to that on sound tooth surfaces. From the results of these studies, it may be concluded that the tested posterior composite resin materials can be used in Class I and II restorations with a good prognosis for at least 4 years. When posterior composite resins are used as restorative for posterior teeth, the following conditions should be considered: The occlusal loading should be minimal, dentin bonding should be used, the increased risk of colonization of streptococcus mutans should be acted on and regular clinical and radiographical follow-up should be performed.