ARP with a crosslinked xenograft in an open healing mode: clinical and microscopic characteristics of a case series.

OBJECTIVE: This case series aims to report clinical, radiographic, and microscopic outcomes of replacing extracted teeth with a crosslinked collagen/hydroxyapatite-enhanced porcine sponge for alveolar ridge preservation. Reporting includes the 12-month survival rate of implants placed after the alveolar ridge preservation period was completed. METHOD AND MATERIALS: Following gentle tooth extraction and degranulation of the socket, tactile examination revealed the morphologic configuration of remaining bone. Sockets presenting with ≥ 50% of residual buccal bone were included, and received - regardless of the present soft tissue contour - treatment with sugar-crosslinked collagen/hydroxyapatite-enhanced (SCLC/HA) sponge. The sponge was inserted into the socket, positioning it at the same height as the soft-tissue margins of the orifice. No soft tissue closure was intended, and a cross-suture stabilized the graft for the initial 7 days of healing. After alveolar ridge preservation was considered complete, a reentry surgery followed for implant placement in sites initially planned for implant treatment. Eleven patients agreed to donate 12 tissue samples obtained at implant placement to assess tissue assembly and to understand the remodeling process of the graft. Implants were placed if the site appeared suitable, and different loading protocols were initiated. Samples were processed in decalcified mode. Microscopic analysis used hematoxylin-eosin and Azan stain, von Willebrand factor (vWF) expression, alveolar ridge preservation, RUNX2, ED-1, periostin, osteopontin and osteocalcin; activity was evaluated by means of immunohistochemistry, while TRAP (tartrate-resistant acid phosphatase)-positive cells were histochemically labeled. One year after implant loading the survival of the implants placed after alveolar ridge preservation was calculated. RESULTS: A total of 49 patients with 62 treated sites were included. From 62 sites, 54 were planned to receive an implant following a period of alveolar ridge preservation healing. This period varied among patients from 3.5 months to over 12 months, and the outcome was separated into early- and late-reentry groups. Clinically, all sites healed without complications, consistently showing a new layer of soft tissue cover at the former orifice 3 to 4 weeks after tooth extraction. Microscopic analysis supported this time-based separation, as the specimens showed varying amounts of residual graft material per group. The soft tissue showed well-keratinized epithelium microscopically, with a layer of newly arranged lamina propria beneath the rete pegs. The duration of the alveolar ridge preservation healing period was identified as a factor in whether the xenograft underwent incomplete or complete remodeling. Of the 54 implant-receiving sites, 39 showed sufficient orofacial width and vertical dimension for implant placement without additional intervention. Additionally, 12 sites required either vertical extension of subantral bone or concomitant lateral guided bone regeneration at implant placement. In three sites, another staged augmentation was required. The 1-year survival rate after implant loading was 98.2%, as one of the 54 inserted implants experienced early loss due to disintegration under immediate temporalization conditions. CONCLUSIONS: Despite the limitations of a case series, it can be concluded that the alveolar ridge preservation procedure using the SCLC/HA sponge results in predictable secondary healing and well-maintained ridge dimensions suitable for implant placement and function. Soft tissue healing was consistent across all cases and sites, with only a few requiring additional staged augmentation. Microscopic analysis revealed complete remodeling of the xenograft in sites with healing period lasting > 6 months.