A Prospective Cohort Study on Cast-metal Slot-retained Resin-bonded Fixed Dental Prostheses in Single Missing First Molar Cases: Results After up to 7.5 Years

Purpose: To evaluate under controlled clinical conditions the outcomes of cast-metal slot-retained resin-bonded fixed dental prostheses (RBFDPs) in which resin composite interlocked the restoration retainers in place after cementation in cases with single missing first molars, and to collect survival data on this esthetic RBFDP design combined with an economical metal fit-surface treatment method and resin luting system. Materials and Methods: Forty-one tub-shaped inlay-retained RBFDPs were clinically observed for up to 7.7 years in 35 recipients of both genders between 18 and 52 years of age. Clinical examinations were performed at baseline and 6 and 12 months after restoration placement, and thereafter at regular 1-year intervals. Modified US Public Health Service (USPHS) parameters, sulcus bleeding index, Silness-Löe plaque index, pocket depths, tooth mobility, pulp vitality, and periapical radiographs regarding the abutment teeth were assessed at these follow-up appointments. The Kaplan-Meier survival estimation method was performed to detect the overall and functional survival rates and mean survival times of the RBFDPs at the end of the study. The Breslow (Generalized Wilcoxon) test was used to evaluate the influence of restoration location and age and gender of the patient regarding the overall survival probability at the end of the follow-up (α = 0.05). Results: At the end of the study, 34 RBFDPs (83%) were still functioning with a mean follow-up of 6.3 years. According to the Kaplan-Meier survival curve, the overall and functional survival probabilities were calculated as 76% and 83%, with mean survival times of 6.8 years and 7.2 years, respectively. All clinical parameters monitored throughout the follow-up period predominantly revealed clinically acceptable results. Breslow test statistics presented nonsignificant differences with better results for the RBFDPs placed in the mandible of female recipients younger than 30 years of age. The most common failure noted with the RBFDPs was fracture of the occlusal veneering composite restoration over the retainer of a single abutment, leading to a predisposition of the restoration to partial debonding. Conclusion: Within the limitations of this prospective cohort study, it can be concluded that cast-metal slot-retained RBFDPs utilizing the interlocking mechanism of a resin composite to obtain additional retention from the abutment cavities show acceptable clinical success rates, and can be considered a minimally invasive, economical, and time-saving treatment alternative for the prosthetic rehabilitation of single missing first molars. Keywords: Resin-bonded FDPs, cast-metal RBFDPs, slot-retained RBFDPs, inlay-retained RBFDPs, posterior RBFDPs