Survival of posterior fixed partial dentures with minimal tooth reduction and improved esthetics: An in vitro study.

STATEMENT OF PROBLEM: Different designs of posterior minimally invasive fixed partial dentures (MIFPDs) still require additional tooth preparation for guide planes, occlusal rest seats, and grooves and/or slots to increase retention and resistance forms. Whether a design with less tooth reduction can be successful is unclear. PURPOSE: This in vitro study compared the long-term survival and retention after cyclic loading of a conventional MIFPD and a posterior MIFPD that was designed for less tooth reduction and improved esthetics. MATERIAL AND METHODS: Previously frozen extracted human premolars and molars were embedded in polymethylmethacrylate resin blocks to simulate the loss of a first molar. The block specimens were divided into 3 groups (n=10) according to prosthesis design: control, a conventional posterior MIFPD with partial-coverage retainers; A2S, a 2-part posterior MIFPD with a semiprecision attachment; and A3, a 3-part posterior MIFPD. The prostheses were cemented onto the abutments with 4-methacryloxyethyl trimellitate anhydride/methylmethacrylate-tri-n-butylborane (4-META/MMA-TBB) resin. The specimens were subjected to 2 500 000 cyclic loading cycles with a compressive force of 50 to 800 N in a universal testing machine. After cyclic loading, the intact prosthesis was removed by using tensile force at a crosshead speed of 1 mm/min until failure. The mode of failure and bonding interface were evaluated by using stereomicroscopy and scanning electron microscopy. The retention data were analyzed by using 1-way ANOVA and the Tukey honestly significant difference (HSD) test (alpha=.05). RESULTS: No prosthesis detached during cyclic loading. The mean +/-standard deviation retentive forces among the control (396.7 +/-73.2 N), A2S (228.3 +/-52.5 N), and A3 (529.9 +/-86.2 N) groups were significantly different (P<.05). The hybridized enamel layer of the abutments had a consistent thickness after immersion in 6 mol/L hydrochloric acid. CONCLUSIONS: The results suggest that the 2- and 3-part posterior MIFPDs should have a high long-term survival rate in the oral cavity.