engleski

Influence of overlay restorative materials and load cusps on the fatigue resistance of endodontically treated molars

Aims: Evaluate the influence of material selection (composite resin vs. CAD/CAM porcelain), simulated load cusp (composite resin vs. stainless steel) and their effect on the in-vitro fatigue resistance and failure mode for overlay-type restoration of endodontically treated molars. Methods: Thirty extracted molars received root canal treatment followed by a standardized tooth preparation (3 mm coverage of all cusps, a mesial box located 1.5 mm below the CEJ, a distal box located in enamel, with a glass-ionomer base, and immediate sealed dentin with Optibond FL). Overlays of standardized thickness and occlusal anatomy were fabricated using Cerec 3. Twenty restorations were milled in the ceramic Vita MKII block (groups MKIIGL and MKIIGL-Z) and 10 restorations were duplicated with a composite resin, Miris 2 (group M2). All MKII restorations were oven-glazed. The intaglio surfaces of the ceramic restorations were sandblasted, etched with hydrofluoric acid and silanated. The intaglio surfaces of the composite resin overlays were sandblasted and silanated. Preparations were sandblasted and etched before insertion of the restoration. All restorations were luted with Optibond FL adhesive resin and preheated Filtek Z100. A closed-loop servo-hydraulic unit was used for simulating cyclic isometric chewing at 5 Hz, starting with a load of 200N (5, 000 cycles), followed by stages of 400, 600, 800, 1000, 1200 and 1, 400N at a maximum of 30, 000 cycles each. A stainless steal load sphere was used for groups MKIIGL and M2, while a composite resin load sphere was used in group MKIIGL-Z. All samples were loaded until fracture or to a maximum of 185, 000 cycles. Groups were compared using the Kaplan-Meier survival curves. Results: None of the restored molars of group MKIIGL and MKIIGL-Z withstood all 185, 000 loading cycles (survival=0%). The average fractured load for MKIIGL was 1, 060N and for MKIIGL-Z 1, 280N. In group M2, the survival rate was 50%. The rate of fracture below the CEJ was 40%, 30% and 20% for MKIIGL, MKIIGL-Z and M2, respectively. Survival of MKIIGL-Z and M2 was not significantly different (p=.002). Conclusions: Miris 2 composite resin onlays showed higher fatigue resistance than MKII porcelain when loaded with a stainless steel antagonist. The simulated cusp in composite resin increased the fatigue resistance of MKII restorations compared to the stainless steel cusp. Clinical relevance: The results of this simulated fatigue study favor the use of composite resin, rather than porcelain, for the fabrication of CAD-CAM overlays on endodontically-treated molars, especially in high load situations. However, both materials, withstood the normal range of bite forces which were simulated in the first part of the fatigue test. Therefore both materials may remain equally resistant to fracture under normal clinical conditions.

fatigue resistance; composite resin; porcelain; CEREC; overlay restorations; endodontically-treated molars

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