CASE SERIES Evaluation of Premature Membrane Exposure and Early Healing in Guided Bone Regeneration of Peri-Implant Dehiscence and Fenestration Defects With a Slowly Resorbing Porcine Collagen Ribose Cross-Linked Membrane: A Consecutive Case Series E. Todd Scheyer* and Michael K. McGuire* Introduction: Guided bone regeneration (GBR) is a well-known and accepted procedure for effective treatment of oral bony defects that is dependent on sustained barrier membrane function for adequate new bone formation. Cross-linking between collagen fibrils with various agents has proven to be effective in prolonging membrane integrity and function, both critical to positive bone regenerative outcomes. Overlying mucosal dehiscence with membrane exposure may lead to less than adequate new bone formation. The current case series examines guided bone regenerative outcomes for peri-implant defects using a ribose cross-linked porcine collagen membrane that appears to reduce the risk of cross-linking– associated membrane exposure. Case Series: Seven patients with nine sites having peri-implant dehiscence and fenestration defects were enrolled in this consecutive case series pilot study. At surgery, the linear range of implant thread exposure was 5 to 10 mm (mean of z6.3 mm). After implant insertion, grafting with mineralized allograft, and placement of a ribose cross-linked collagen mem- brane, patients were followed for a minimum of 6 months. At 6-month reentry surgery, all dehiscence and fenestration de- fects were eliminated with newly regenerated bone covering previously exposed implant threads. No membrane exposure occurred during this study. Conclusions: Successful GBR outcomes may be enhanced by avoiding premature membrane exposure. Although collagen cross-linking may be associated with increased mucosal dehiscence, the ribose cross-linked membrane examined in the current study may help promote positive regenerative outcomes by sustained functional and structural integrity and a reduction in membrane exposure incidence. Clin Adv Periodontics 2015;5:165-170. Key Words: Bone regeneration; collagen; dental implantation; dental implants; membranes; osseointegration. Background Time-tested guided bone regeneration (GBR) continues to play an important role in clinical bone regenerative procedures. Critical to that role are well-functioning barrier membranes with properties essential to positive regenerative outcomes. Such properties include: 1) the ability to exclude unwanted, non-osteogenic cell lines from areas to be regenerated; 2) space creation and maintenance; 3) protection of the underlying blood clot; and 4) wound stabilization. 1-3 Although both non-resorbable and resorbable membranes are used, today’s GBR procedures depend primarily on well- designed resorbable porcine- or bovine-derived collagen membranes that may or may not be cross-linked. Impor- tantly, membranes must maintain their integrity for durations long enough to allow clinically sufficient amounts of new bone to form. 1,3-6 Cross-linking among collagen fibrils has be- come an important method of slowing collagen membrane * Private practice, Houston, TX. Submitted September 17, 2013; accepted for publication January 6, 2014 doi: 10.1902/cap.2014.130080 Clinical Advances in Periodontics, Vol. 5, No. 3, August 2015 165