title: Fracture resistance and gap formation of MOD restorations: influence of restorative technique, bevel preparation and water storage.
abstract: This in vitro study evaluated the effect of technique, use of a bevel and thermal cycling on the fracture resistance and gap formation of resin composite MOD restorations. Fracture resistance was measured on standard MOD cavities prepared in 100 upper premolars that were stored for 24 hours and 6 months with 1000 thermal cycles. Subgroups (n=10) were: beveled or non-beveled preparations and direct restorations (Adper Single Bond/Filtek Z250) and indirect restorations (prepolymerized Filtek Z250 cemented with Rely XARC). Ten sound teeth and 10 specimens with MOD preparations without restorations served as the positive and negative controls, respectively. The specimens were subjected to axial compression in a universal testing machine at a crosshead speed of 0.5 mm/minute. Failure patterns were analyzed by stereomicroscopy (40x). To evaluate gap presence or absence, proximal box cavities were prepared in 24 human third molars that were restored as described above. The specimens were evaluated under SEM examination after 24 hours and six months. Data were statistically analyzed by ANOVA and multiple comparison tests at the 0.05 level of significance. After 24 hours, the beveled restorations exhibited higher fracture strength values than the non-beveled restorations, and all groups showed resistance similar or superior to sound teeth. After six months, the highest fracture resistance was obtained for beveled inlays and the lowest values were observed for direct restorations with butt joints. Thermal cycling decreased fracture resistance in the majority of the groups. The main fracture pattern observed was cohesive failure in the material, but adhesive failures increased over time, especially in the non-beveled restorations. Under SEM examination, no difference was observed among the groups after 24 hours. However, after six months, the beveled restorations exhibited no gap formation. It was concluded that storage with thermal cycling decreased fracture resistance, bevels improved fracture resistance and, in general, indirect restorations were not superior to direct restorations.
authors.affiliation: Department of Dentistry, Lutheran University of Brazil, Cachoeira do Sul, RS, Brazil.
authors.forename: Fábio Herrmann
authors.initials: FH
authors.lastname: Coelho-De-Souza
authors.forename: Guilherme Brião
authors.initials: GB
authors.lastname: Camacho
authors.forename: Flávio Fernando
authors.initials: FF
authors.lastname: Demarco
authors.forename: John M
authors.initials: JM
authors.lastname: Powers
mesh_terms: D000704:Analysis of Variance; D001641:Bicuspid; D017438:Bisphenol A-Glycidyl Methacrylate; D003188:Composite Resins; D019245:Compressive Strength; D001840:Dental Bonding; D003737:Dental Cavity Preparation / Q000379:methods*; D018772:Dental Marginal Adaptation; D019232:Dental Restoration Failure; D003793:Dental Restoration, Permanent / Q000379:methods*; D003799:Dental Stress Analysis; D017220:Dentin-Bonding Agents; D004356:Drug Storage; D006801:Humans; D007284:Inlays; D008855:Microscopy, Electron, Scanning; D011092:Polyethylene Glycols; D011109:Polymethacrylic Acids; D019279:Resin Cements; D014867:Water
chemical_list: D003188:Composite Resins; D017220:Dentin-Bonding Agents; C444701:Filtek Z250; D011109:Polymethacrylic Acids; C462240:RelyX ARC; D019279:Resin Cements; C115612:single bond; D014867:Water; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate