Success and survival rates of mandibular overdentures supported by two or four implants: a systematic review

This systematic review evaluated the influence played by the number of implants on the results of rehabilitation treatment with mandibular overdentures on 2 or 4 implants. The literature search was conducted using PubMed, Embase and Cochrane databases. Specific terms were used in performing a search from January 1980 to January 2013. The search strategy was applied by two reviewers who extracted the data and compared the results. Discrepancies were resolved by discussion. Great heterogeneity was seen among the selected studies, in regard to survival rates, prosthesis failure and function rates. A medium degree of quality and methodological consistency was found in one study, and no studies showed a high degree. When considering the prosthesis success rate for 2 implants, there was a variation of 23% to 100%. However, when considering the survival rate, the result was 92% to 100%. For 4 implants, prosthesis survival rates showed less variation, i.e., 97.7% to 100%. Ball attachments were the most common type of abutment for 2 implants; however, there was a higher prevalence of bar abutments for 4 implants. Rehabilitations with 2 implants showed more complications and required more maintenance according to the connection type. Given the limitations of this review, mandibular overdentures with 4 implants showed better results with respect to survival and success rates, especially those with a bar connection. Further studies comparing these two treatment types are necessary to improve the scientific evidence in this area.本系统评价（systematic review）评估了种植体数量对2颗或4颗种植体支持的下颌覆盖义齿（mandibular overdentures）修复治疗效果的影响。本研究检索了PubMed、Embase及Cochrane数据库，检索时段设定为1980年1月至2013年1月，并采用特定检索词开展检索。由两名评价者执行检索流程、提取研究数据并比对研究结果，研究间分歧通过讨论协商解决。纳入的各项研究在种植体留存率、义齿失败率及功能恢复率方面存在显著异质性。仅1项研究的方法学质量与一致性处于中等水平，未发现高质量研究。针对2颗种植体的义齿成功率，其波动范围为23%至100%；而就种植体留存率而言，结果区间为92%至100%。对于4颗种植体，义齿留存率的变异度更低，区间为97.7%至100%。球附着体（ball attachments）是2颗种植体最常用的基台（abutment）类型，而4颗种植体修复则更普遍采用杆式基台（bar abutments）。根据连接方式的不同，2颗种植体支持的修复治疗并发症更多，且所需维护频次更高。鉴于本评价存在的局限性，4颗种植体支持的下颌覆盖义齿在留存率与成功率方面表现更优，尤其是采用杆式连接的修复方案。未来仍需开展针对这两种治疗方案的对比研究，以提升该领域的科学证据等级。