THE ROLE OF EARLY VERSUS LATE REMOVAL OF GTAM(R) MEMBRANES ON BONE-FORMATION AT ORAL IMPLANTS PLACED INTO IMMEDIATE EXTRACTION SOCKETS - ANEXPERIMENTAL-STUDY IN DOGS

The purpose of this study was to compare the effect of early versus la te removal of expanded polytetrafluoroethylene (e-PTFE) membranes on b one formation at oral implants. Thirty Branemark(TM) fixtures were pla ced into immediate extraction sockets with buccal bone dehiscences aug mented by e-PTFE membranes. At 4 weeks, the membranes and underlying s oft tissues were removed from 5 implants, but at 16 sites only the mem branes were extirpated. In 9 sites, the membranes remained in place du ring the healing period. Sixteen weeks after fixture insertion, the si tes in which the membrane was retained (MRET) showed an average of 5.2 mm of clinical bone height increase (100% of bone fill). For sites wh ere the membrane together with underlying soft tissues were removed (M RB), the corresponding value was 2.0 mm (42% of bone fill). Implants a t which only the membrane was removed (MR) showed the least clinical b one height increase (1.0 mm), resulting in 21% coverage of original th reads. Histometric measurements verified that the MRET sites had the l east distance from the top of the fixture to the newly formed bone lev el (0.4 mm). However, in contrast with the clinical findings, the hist ometric analyses showed that the MRB group had the greatest remaining bone defect (3.3 mm). The clinical and histometric results of the MRET group were statistically better, though, compared with those of the o ther two groups. Biopsies, removed from beneath the membranes, reveale d slightly inflamed connective tissue, containing spicules of newly fo rmed bone, indicating that more bone might have been created if the me mbranes had been retained longer. The current study thus showed that m aximum bone formation around oral implants was created if the membrane augmentation material remained in place during the 16-week healing pe riod. Early removal of membranes, with or without elimination of the u nderlying tissues resulted, however, in less newly formed bone and an incomplete defect bone fill.