Bone behavior around sleeping and non-sleeping implants retaining a mandibular hinging overdenture.

Since 1984 2 implants in the symphyseal area have been used in our center to retain a hinging overdenture. Because this technique was unknown at that time 1 extra implant was installed in between the 2 others and was left submerged (sleeping). The extra implant served as a rescue implant in case 1 of the 2 others would fail. It was the aim of the present report to compare the marginal bone behavior around those sleeping and non-sleeping implants. Between 1984 and 1987 20 completely edentulous patients were provided with 3 implants (Brånemark system), where from 2 were used to retain a hinging overdenture. Ten years later half of the patients could still be traced. Retroalveolar radiographs were made at the abutment installation and after 10 years. None of the non-sleeping or sleeping implants lost, at an individual basis, more than 1.6 and 0.7 mm of marginal bone respectively. On average, non-sleeping implants lost at the right- and left-hand side of the mandible 0.33 and 0.57 mm of bone respectively. However, sleeping implants lost on average 0.16 mm only. Thus non-sleeping implants lose on average more bone when compared to sleeping implants. Surgical trauma at the abutment connection is believed to be the most plausible cause of marginal bone loss around non-sleeping implants.