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 (α=.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.