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.

中文翻译：

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后牙固定局部义齿在减少牙齿减少和改善美学的情况下的生存：一项体外研究

问题陈述

后路微创固定局部义齿 (MIFPD) 的不同设计仍然需要额外的牙齿准备，用于引导平面、咬合座以及凹槽和/或槽，以增加固位和阻力形式。减少牙齿减少的设计是否能成功尚不清楚。

目的

这项体外研究比较了传统 MIFPD 和旨在减少牙齿减少和改善美观的后部 MIFPD 循环加载后的长期存活和保留。

材料与方法

先前冷冻提取的人类前磨牙和磨牙被嵌入聚甲基丙烯酸甲酯树脂块中，以模拟第一磨牙的损失。根据假体设计将块标本分为 3 组（n=10）：对照组，带有部分覆盖保持器的常规后路 MIFPD；A2S，带有半精密附件的两部分后部 MIFPD；和 A3，一个 3 部分的后部 MIFPD。使用 4-甲基丙烯酰氧基乙基偏苯三酸酐/甲基丙烯酸甲酯-三正丁基硼烷 (4-META/MMA-TBB) 树脂将修复体粘接到基台上。试样在万能试验机中以 50 至 800 N 的压缩力经受 2 500 000 次循环加载循环。循环加载后，使用拉力以 1 mm/min 的十字头速度移除完整的假体，直至失效。通过使用立体显微镜和扫描电子显微镜评估失效模式和键合界面。通过使用 1-way ANOVA 和 Tukey 诚实显着性差异 (HSD) 检验 (α=.05) 分析保留数据。

结果

循环加载期间没有假体脱落。对照组（396.7 ±73.2 N）、A2S（228.3 ±52.5 N）和A3（529.9 ±86.2 N）组之间的平均±标准差保持力有显着差异（P <.05）。基台的杂交牙釉质层在浸入 6 mol/L 盐酸后具有一致的厚度。

结论

结果表明，2 部分和 3 部分后部 MIFPD 在口腔中应具有较高的长期存活率。