[Surface and circumference determination in resin-bonded retainer elements: a possibility for long-term prognosis?]

An evaluation of about 300 abutment teeth of resin-bonded bridges (Rochette, electrochemically etched) and resin-bonded extracoronal attachments was performed to determine the surface area and the length of the circumference of the retainers. By using a combined indirect (preparation of the specimen) and direct (automatic image analysis) method for the determination of both parameters a mean value of 50 mm2 for the surface area and 30 mm for the circumference, respectively, was evaluated. In addition, two indices (loading-index (BI): sigma surface area/width of pontic tooth; moisture penetration-index (FPI): sigma surface area/sigma circumferences) as predictors for the longevity of resin-bonded reconstructions were calculated. The loading-index was a good predictor for successful reconstructions: the clinical success was the better, the bigger the retention area, and the smaller the circumference of the retainer and the smaller the pontic tooth.