Fixed dental prostheses: rigid and non-rigid connections to implants

Short-span fixed partial dentures and full-arch fixed prostheses have been constructed by connecting teeth and implants. However, biomechanical differences between tooth and implants mean that tooth micro-mobility is around 10 times that of dental implants. Both rigid and non-rigid connections to implants have been used and there is a debate over which is the best approach.

The aim of this review was to assess the survival, technical and biological complication rates of partial fixed dental prostheses (FDPs) supported by implants and teeth.

Methods

Searches were conducted in the Medline, Embase, and Cochrane databases together with a search of Google Scholar. These were supplemented by hand searches in the journals; Journal of Prosthetic Dentistry, International Journal of Prosthodontics, Journal of Prosthodontics, Journal of Periodontology, Journal of Clinical Periodontology, Periodontology 2000, International Journal of Periodontics and Restorative Dentistry, International Journal of Oral and Maxillofacial Implants, Clinical Oral Implants Research, Clinical Implant Dentistry and Related Research, Implant Dentistry, and Journal of Oral Implantology.

Randomised controlled trials (RCTs), prospective and retrospective cohort studies in partially edentulous patients rehabilitated by non-immediately loaded fixed dental prostheses connecting implants to teeth that included details of the connection/attachment mode (rigid or non-rigid) with a follow up of at least 12 months were considered. Two reviewers independently selected studies and abstracted data. The Cochrane risk of bias tool was used to assess study quality included studies excluding the judgments relevant to randomisation.

Results

10 studies (6 retrospective, 4 prospective) were included.
4 studies included a control group.
3 studies included only rigid fixed reconstructions, with 6 studies reporting on both rigid and non-rigid implant to tooth connection fixed dental prostheses.
In all studies, the rigid connection mainly involved a vertical or horizontal locking screw, while the non-rigid involved telescopic crowns or sliding type attachments.
481 patients received 526 FDPs supported by 981 abutment teeth connected with 1072 implants.
Dropouts ranged from 0% -11.7%.
Follow up ranged from 18-120 months.
Apart from 2 studies all used different methods of determining ‘survival’
Overall survival rate for implants ranged between 90% and 100
Survival of the abutment teeth was 94.1-100%,
Prostheses survival was 85-100% for the same time period.
Periapical lesions were the most frequent complications at 11.53%.
The most frequent technical complication were
- porcelain occlusal fracture; 16.6%.
- screw loosening; 15%.
Meta-analysis ( 3 studies), found no intrusion on the rigid connection group, while five teeth (8.19%) were intruded in the non-rigid connection group .

Conclusions

The authors concluded:-

The tooth-implant FDP seems to be a possible alternative to an implant-supported FDP. There is limited evidence that rigid connection between teeth and implants presents better results when compared with the non-rigid one. The major drawback of non-rigidly connected FDPs is tooth intrusion.

Comments

While a good search strategy was undertaken only English language papers were included which means that potentially relevant studies could have been excluded. A range of study designs were included with a majority of the studies being retrospective. Only 4 of the included studies used a control group and none of the studies were randomised. The studies were relatively small and with relatively short follow up periods as noted by the authors. So while this review helpfully summarise the evidence on this topic the evidence itself is of low quality so the findings should be interpreted with caution. Well-conducted randomised controlled trials of appropriate size and duration are needed to address the questions posed by this review.