Heeje Lee D.D.S.
Maxillary implant overdentures supported by four or more implants with a bar attachment had a higher survival rate than overdentures supported by fewer implants and ball attachment.
The authors used accepted methodology, but 29 out of 31 included studies were of low-to-moderate quality.
In maxillary edentulous patients fitted with implant overdentures, what is the survival of the implant, survival of the maxillary overdenture, and condition of the surrounding gingiva and alveolar bone after one year?
The authors searched three electronic databases for articles and studies published up to August 2009. They completed their search by checking references of the identified articles and studies for additional relevant publications. Inclusion criteria were clearly defined. Two reviewers independently extracted data for the outcome measures (survival of both implants and overdentures, condition of hard and soft tissues). Agreement was reached by a consensus discussion and, if necessary, a third reviewer was consulted. The authors performed a meta-analysis for outcome measures that could be meaningfully combined.
The search identified 147 articles for full-text analysis, of which 31 articles met inclusion criteria. A meta-analysis showed the implant survival rate was 98.2 percent for six or more implants and a bar anchorage, 96.3 percent for four or fewer implants and a bar anchorage, and 95.2 percent for four or fewer implants and a ball anchorage. Because of the diversity of the studies, the reviewers were unable to the combine other clinical outcomes for meta-analysis. Maxillary overdentures supported by six implants and a bar attachment had a higher survival rate than those supported by four implants or fewer and a bar attachment. Overdentures supported by four or fewer implants and a ball attachment had the lowest survival rate. Data heterogeneity precluded the authors from reaching conclusions about the effect of implants and overdentures on hard and soft tissues.
The number of implants and type of anchorage system affected the survival rate of both implants and overdentures.
Source of Funding:
No conflicts of interest were noted and no external funding was obtained.
Importance and Context:
Implant-supported overdenture has been used and studied more frequently for the mandible. Few studies have been conducted on maxillary implant-supported overdentures as a treatment option for edentulous patients. The existing studies suggest maxillary overdentures as a favorable treatment option for patients who have insufficient bone volume or who have complaints about retention and stability of the full denture. However, differences between the two bone structures could affect the clinical outcomes of the maxillary overdentures and supporting implant systems.
Strengths and Weaknesses of the Systematic Review:
The current systematic review used accepted methods. The authors clearly stated their search strategy; more than one reviewer searched multiple databases; the authors clearly defined the inclusion criteria; they listed the exclusion criteria for excluded articles; and they performed a meta-analysis. However, the authors limited their search to only English-only results; they did not evaluate for publication bias; and although they followed appropriate reporting guidelines they did not give a confidence interval for the implant survival rates.
Strengths and Weaknesses of the Evidence:
Most of the original studies were either retrospective or prospective with few randomized clinical trials. The majority of the implants were machined-surface implants, which is no longer considered an industry standard. Also, the meta-analysis for the group of four or fewer implants with a ball attachment was heavily weighed by a study that used a rare implant system with significantly lower implant survival rate.
Implications for Dental Practice:
From a mechanical standpoint, the results of the systematic review appear reasonable. The larger number of implants and types of attachment that could distribute the occlusal forces more evenly were associated with higher implant survival rates. The differences between the evaluated available options were not considered clinically significant. However, the implant and anchorage systems have significantly improved since the ones evaluated in the selected studies. Therefore, conclusions should be made cautiously. Regarding adverse conditions of surrounding hard and soft tissues, no conclusions were made.