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

The purpose of this study was to compare the effect of early versus late removal of expanded polytetrafluoroethylene (e-PTFE) membranes on bone formation at oral implants. Thirty Branemark(TM) fixtures were placed into immediate extraction sockets with buccal bone dehiscences augmented by e-PTFE membranes. At 4 weeks, the membranes and underlying soft tissues were removed from 5 implants, but at 16 sites only the membranes were extirpated. In 9 sites, the membranes remained in place during the healing period. Sixteen weeks after fixture insertion, the sites 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 where the membrane together with underlying soft tissues were removed (MRB), the corresponding value was 2.0 mm (42% of bone fill). Implants at which only the membrane was removed (MR) showed the least clinical bone height increase (1.0 mm), resulting in 21% coverage of original threads. Histometric measurements verified that the MRET sites had the least distance from the top of the fixture to the newly formed bone level (0.4 mm). However, in contrast with the clinical findings, the histometric 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 other two groups. Biopsies, removed from beneath the membranes, revealed slightly inflamed connective tissue, containing spicules of newly formed bone, indicating that more bone might have been created if the membranes had been retained longer. The current study thus showed that maximum bone formation around oral implants was created if the membrane augmentation material remained in place during the 16-week healing period. Early removal of membranes, with or without elimination of the underlying tissues resulted, however, in less newly formed bone and an incomplete defect bone fill.