INFLUENCE OF WATER STORAGE AND THERMAL CYCLING ON THE FRACTURE STRENGTH OF ALL-PORCELAIN, RESIN-BONDED FIXED PARTIAL DENTURES

The purpose of this in vitro study was to evaluate the influence of water storage and thermal cycling on the fracture strength of two designs of all-porcelain, resin-bonded fixed partial dentures made with the glass-infiltrated alumina ceramic In-Ceram. Forty frameworks of In-Ceram ceramic veneered with Vitadur-N porcelain were made to replace an upper central incisor bonded to extracted natural teeth. In 20 of the restorations the pontic was veneered only labially with Vitadur-N porcelain and no proximal box preparations were made (design A). The other 20 restorations had additional box preparations proximal to the pontic and the In-Ceram ceramic pontic framework was shifted to the labial aspect and veneered circumferentially with Vitadur-N porcelain (design B). Subgroups of 10 restorations were stored for 7 days in thymol solution or alternatively for 150 days in artificial saliva with thermal cycling for 18,750 cycles between 5-degrees and 55-degrees-C. Restorations with design B had a statistically significantly higher fracture strength than restorations with design A. Storage in artificial saliva with thermal cycling significantly reduced the fracture strength of the resin-bonded In-Ceram fixed partial dentures. Therefore, the long-term clinical behavior of resin-bonded In-Ceram fixed partial dentures must be evaluated before general clinical use can be recommended.