Clinical, Histological and Cellular Evaluation of Vertico-Lateral Maxillary Reconstruction Associating Alveolar Osteogenic Distraction and Fresh-Frozen Bone Allograft

The rehabilitation of edentulous anterior maxillary defects with implant-supported prosthesis remains a challenge, since loss of teeth can lead to extensive vertical and horizontal bone resorption, compromising the aesthetical and functional results.^1–3 

Vertical alveolar defects higher than 5 mm are the most difficult to restore with high incidence of failure mainly due to either resorption or dehiscence. Several modalities of treatment have been proposed, such as autografts from distinct donor sites, allografts, xenografts, osteogenic distraction, and titanium meshes among others.⁴  Although autografts are considered the gold standard based on their osseoinduction, osseoconduction, and osteogenesis properties, some disadvantages like morbidity, time consuming and cost should be taken onto consideration before selecting this technique.³  In this context, alveolar osteogenic distraction (AOD) is a good alternative to gain both bone and soft tissue augmentation⁴  and fresh-frozen bone allograft (FFBA) has been successfully grafted to reconstruct bone defects in oral implantology.⁵  Beyond the unlimited availability, FFBA avoids the morbidity commonly associated with autograft harvesting.⁶ 

The selection of treatment should be based on adequate quality and amount of hard and soft tissues to get a suitable rehabilitation.⁷  U-shaped defects, usually present in the anterior maxilla area, are characterized by lack of structures that prevents initial soft tissue closure over a large bone graft.²  Considering that a tension-free closure must be performed to prevent incision breakdown on a large onlay bone graft,^8–10  strategies to increase the soft tissue drape over a bone defect include free grafts, tissue expanders, and the use of gradual distraction of the residual bone.^2,10 

The purpose of this letter is to report a case presenting clinical, histological, and cellular evidences to support the combination of AOD and cortico-cancellous FFBA as a good alternative for reconstructing a vertico-lateral maxillary defect, allowing implant-supported rehabilitation.

A 42-year-old patient had been referred to the Department of Oral and Maxillofacial Surgery of the School of Dentistry of Ribeirão Preto, University of São Paulo, for implant-supported rehabilitation. Clinical and radiographic evaluation revealed a 9-mm U-shaped bone defect in the left anterior maxilla (Figure 1a and b). The proposed treatment was AOD to increase bone height and soft tissue availability followed by FFBA to improve lateral dimension. All surgical procedures were performed under local anesthesia with the patient agreement based on signed informed consent. Surgical AOD technique consisted of a horizontal incision and a full-thickness mucoperiosteal flap (Figure 1c). Horizontal and vertical osteotomies were created with a sagittal saw and the crest segment was gently mobilized. The osteogenic distractor (OD - Conexão, São Paulo, SP, Brazil) device was fixed in the original position with monocortical screws (1.5 mm in diameter and 5 mm in length), activated to check the osteotomies (Figure 1d) and deactivated to the initial position. After 1-week latency period, the OD device was activated at a ratio of 0.5 mm/d to obtain both vertical bone and soft tissue augmentation until obtaining a suitable crest level (Figure 1e through h). After the consolidation period of 4 months, a crest incision and 2 vertical incisions allowed to raise a full-thickness mucoperiosteal flap. The OD device was removed and the recipient bed was prepared by decortication holes using a 1-mm drill (Figure 2a). A cortico-cancellous FFBA (Musculoskeletal Tissue Bank of Marilia Hospital, Unioss, Marília, SP, Brazil) was shaped to get passive adaptation and fixed with noncompressive 2 bicortical titanium screws (Synthes, West Chester, Pa, 1.5 mm in diameter and 12 mm in length) with the cancellous portion facing the recipient bed (Figure 2b). FFBA allowed a width gain of 5 mm resulting in a reconstructed alveolar ridge with 8 mm in width. Through a periosteal releasing incision the wound was passively closed with 5.0 nylon sutures (Figure 2c). Six months later (Figure 2d), fixation screws were removed and 2 dental implants (Nobel Biocare, Yorba Linda, Calif) were installed (Figure 3a and b) and kept unloaded during 6 months previous to prosthetic rehabilitation. At 5-year follow-up, clinical and radiographic evaluation evidenced that the prosthetic rehabilitation was very satisfactory in terms of functional, periodontal and aesthetic parameters (Figure 3c through f). At this time-point, bone biopsies from grafted area and maxillary tuberosity (autogenous bone [AB]) were taken and processed for histological and cellular analysis. Light microscopy of block biopsies revealed trabeculae of cancellous bone intermingled with a vascularized, fibrous connective tissue. The bone trabeculae were composed of areas of lamellar bone with empty osteocytic lacunae surrounded by either a viable lamellar bone or bundle bone, with Sharpey's fibers (Figure 4a and b). Osteoblastic cells from grafted and AB sites were harvested by enzymatic digestion and cultured as described elsewhere.¹¹  Cell proliferation, alkaline phosphatase (ALP) activity and extracellular matrix mineralization were evaluated to compare cultures derived from both sites. The data were compared by analysis of variance followed by Tukey test or t-test when appropriated and the level of significance was set at P ≤ 0.05. Cell proliferation was not affected by cell source (P = 0.710), but was affected by time (P = 0.001) and by the interaction cell source vs time (P = 0.001; Figure 5a). The culture growth peaked at day 10 for cells from both sites. ALP activity was not affected by either cell source (P = 0.964) or time (P = 0.505; Figure 5b). Extracellular matrix mineralization evaluated at day 17 was similar (P = 0.223) in cultures derived from both sites (Figure 5c).

Adequate bone volume in the anterior maxilla is essential for a proper aesthetic and functional implant-supported oral rehabilitation. Vertico-lateral ridge augmentation remains a challenging situation in reconstruction of maxillary defects, particularly due to the combination of bony defect with the lack of soft tissue.⁴  Here, we presented a case report in which a vertico-lateral defect had been successfully managed by combining AOD and FFBA.

AOD is a biologic process originally applied in orthopedic procedures by which new bone is generated through incremental lengthening of osseous segments.¹²  One of the advantages of this technique is the promotion of concomitant increase of bone and soft tissues avoiding donor site morbidity.¹³  Preclinical studies reported mandibular vertical augmentation as large as 9 mm, with histological evidences of new bone formation at both sides of the distraction gap and maintenance of crest levels after load application.^14,15  Furthermore, there is clinical evidence that implants placed into autogenous grafted or AOD reconstructed areas present the same success rate.¹³ 

FFBA has been successfully used for horizontal and vertical improvement in ridge augmentation that allowed implant placement.¹⁶  The good osseoconductive capacity of allografts allowing new bone formation adjacent to residual graft after 6 months is in agreement with our histological findings at 5-years post-grafting.¹⁷  This case report supports previous conclusions that allografts are biocompatible and osseoconductive, allowing new bone formation after anterior maxilla augmentation and implant placement.¹⁸ 

In addition to clinical and histological evidences, here we present data of cultured osteoblastic cells harvested from graft compared with those from AB. In general, graft and autogenous-derived cells were capable of proliferation with increasing cell growth along the culture progression. Both cultures presented the same level of ALP activity and production of extracellular matrix mineralization suggesting they displayed similar osteoblastic phenotype expression. At least in part it could be attributed to the homolog origin of this graft as different bovine bones have been showed to impair osteoblastic phenotype expression.^19,20  These cellular analyses strengthen clinical and histological outcomes, showing the suitable biocompatibility and osseoconductive properties of FFBA.

This case report showed that the association of osteogenic distraction and allograft represent a feasible strategy to repair anterior maxillary defects for successful rehabilitation.

Abbreviations

ALP

alkaline phosphatase

AOD

alveolar osteogenic distraction

FFBA

fresh-frozen human bone allograft

OD

osteogenic distractor