Introduction: The number of implants required to stabilize an overdenture has always been a question worth addressing, particularly when economic issues are of concern. Four implants have been used successfully to support a mandibular overdenture, however the type of attachment used may affect the outcome of implant survival and bone anatomy around the implants.
Materials and methods: Eight patients were chosen. All patients were completely edentulous, with their maxillary arches restored with conventional dentures. The mandibular arch was restored with a metal reinforced acrylic resin overdenture supported by four implants.
The implants were placed at the lateral and first premolar areas (Implant direct, Legacy II). Four patients received low profile attachments (Locator Abutment, Implant Direct, Legacy II) ( fig 1) and four patients received ball attachments (Ball Abutment, Implant Direct, Legacy II). Over the next 7 years annual bone measurements were taken by measuring from the implants apex to the level of the bone. implant stability was also checked and recorded by placing the smart peg and using ISQ measurements (Ostell).
Results: using independent t test, bone loss around distal implants in both groups were significant especially in the locator group. The stability measurements showed no statistical significance over the course of 7 years.
Conclusion:
Long term follow up on mandibular overdentures supported by four solitary implants, regardless of the attachment, have shown good implant stability, however, significant bone loss around the most distal implants is to be expected.