The Use of Composite Xenograft and Allograft in Post-Explantation Ridge Defect Augmentation: A Case Report

Although the use of a dental implant to replace a missing tooth has become a standard treatment modality, failures of dental implants in various stages of treatment have been reported.^1,2 Implant failures can be categorized as early or late failure depending on the timepoint of the event. Early failures are those that occur before the implant is functionally loaded and represent failed or inadequate healing and osseointegration at the initial stage of healing.³ The reported prevalence of early failure (implant level) ranges from 0.5% to 5.2%. When the failed implant is removed (ie, explanted) and treatment planned to be replaced with a dental implant, site development via augmentation of the ridge defect is often required.² Depending on the degree of residual infection and the defect morphology, ridge defect augmentation may be attempted at the time of explanation.²

Alveolar ridge preservation (ARP) is a procedure aimed at minimizing the dimensional change associated with tooth extraction to achieve a functional and esthetic outcome.^4-6 The defect morphology is critical when deciding on the need for ARP and the type of materials to use for the ridge preservation.⁷ In post-extraction sites, the loss of one or more socket walls is a frequent occurrence. In a study by Zitzmann et al, two-wall defects presented 52% of the time, one wall was found 16% of the time, and the proportion of three-wall and two-wall sites diminished as time after tooth extraction increased.⁸ In cases where minimal walls with poor containability are present, defects are not considered containable and the use of a combination of xenogeneic and allogeneic composite has been validated as a bone substitute in ARP procedures.⁹ The wide array of allograft configurations, including granules and fibers, in both demineralized and mineralized forms, and available in cortical and cancellous types, combined with xenograft granules, enables tailored customization to harness the range of unique attributes. This includes leveraging the osteoinductive properties of the allografts and the volume stability provided by the xenografts. Histomorphometric evaluation showed a mean of 22.3% vital bone presented after 18 to 20 weeks and residual bone graft materials of a mean of 33.2%.^10,11 With the residual graft materials, the composite augmentation can serve as a scaffold for vascularization and new bone formation as well as long-term volume stability.¹¹

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When early implant failure occurs, it usually demonstrates rapid, progressive bone resorption. As a result, bone loss around the implant exhibits a saucer-like defect and requires a staging approach with site development.^2,12 This case report describes and illustrates the clinical and radiographic outcomes attained by employing a combination of a demineralized cortical fiber, which has been validated for its osteoinductive potential, and a xenograft bone substitute for ridge defect augmentation following an early-stage failure of post-implantation healing.

Case Report

A 54-year-old male patient presented with generalized periodontitis, stage III grade C (Figure 1). The patient had no significant medical history or current medication regimen. After initial periodontal therapy, teeth Nos. 23 through 26 were extracted due to a hopeless prognosis. These teeth were extracted atraumatically.

At 1-year post-extraction, implant planning was conducted for a fixed partial denture at site Nos. 23 through 26, where adequate bone height and width were evident (Figure 2 and Figure 3), with Nos. 23 and 26 planned as implant abutments. Six weeks post-placement, the No. 23 implant was found to be unsuccessful radiographically and was scheduled for removal along with guided bone regeneration. At the time of guided bone regeneration, upon examination of the area, it was decided to also remove the No. 26 implant due to lack of osteointegration.

After explantation and the removal of all remaining granulation tissues, decortication was created on the buccal aspect and ridge crest. Ridge defect augmentation was performed using a composite allograft/xenograft (vallos^®/Bio-Oss^®, Geistlich Pharma North America, geistlich-na.com) covered by a porcine collagen membrane (Bio-Gide^®, Geistlich Pharma North America). Figure 4 through Figure 11 show various stages from initial implant placements to post-explantation ridge augmentation.

Four months later, another attempt at implant placement was made at the same sites. The bone substitute was found to be well incorporated, and a satisfactory bone volume for stable implant placement was achieved with greater than 35 Ncm. Figure 12 through Figure 16 depict surgical site re-entry and implant placement at sites Nos. 23 and 26.

The second-stage treatment was performed 3 months after the implant placements, and a fixed partial denture Nos. 23 through 26 prosthesis was delivered in 5 weeks (Figure 17 and Figure 18). Insignificant bone change was noted compared to the time of implant placement from 5 months post-ARP. Because of the existing recession of adjacent teeth, soft-tissue grafting was not indicated; therefore, pink-colored zirconia material was utilized to compensate for the mucosal height discrepancy. A radiograph was taken and provided evidence of proper seating of the abutment and bone level at the time of prosthesis delivery (Figure 19).

Two-year post-loading of the prosthesis, stability of the grafted site using the allograft/xenograft composite as a regenerative material was evident. No bleeding on probing or increased pocket depths were recognizable at six measuring points per implant. There was no evidence of peri-mucositis or peri-implantitis. Figure 20 through Figure 23 show radiographic and photographic imaging at 1-year through 3-year follow-ups.

Discussion

This case report demonstrates ridge defect augmentation following the removal of failed implants using a composite allograft/xenograft, and the successful re-attempt of implant placements in 4 months with a 3-year follow-up after delivery of the final prosthesis. When the early failure of implants occurs and requires explantation, it often leads to loss of the surrounding bony ridge and/or the socket wall, thus requiring a staged restorative approach.² In this case, adequate ridge volume for obtaining implant primary stability without the need for additional bone grafting was achieved in 4 months with a composite allograft/xenograft, and the prosthesis was restored as early as 5 months post-placement.

Traditionally, autografts are combined with xenografts to achieve osteogenic, osteoinductive, and/or osteoconductive characteristics. Various mixing protocols or composite grafts have been suggested to leverage each material's desirable properties. A study by Serrano et al compared the clinical and histomorphological outcomes of xenograft/allograft at 50%-50% and 70%-30% ratios, and revealed new bone ranging from 1.8% to 35.2% and the residual graft materials ranging between 5.5% and 45.8%.⁹ The combination of xenograft and allograft can be utilized to optimize the osteoinductive potential of an allograft and the slow resorption rate of a xenograft. This, in turn, may enhance the differentiation and proliferation of osteogenic cells and contribute to long-term volume stability in socket walls presenting with bony defects.¹⁴ The composite allograft/xenograft used in this case contains a 50% mixture of xenograft and demineralized allograft matrix in the form of long fibers. The osteoinductive and osteoconductive properties of the composite graft materials demonstrated that long-term stability was not an issue and that implants can be placed as early as 3 months post-ARP.¹³

Demineralized bone allograft is generally acellular, leaving a collagenous extracellular matrix that contributes to its osteoinductive properties. The unique fiber-form of the allograft used in this case provides osteoconductivity and allows the graft material to be cohesive on its own. A study in a rat posteriolateral fusion model suggested that the fiber-form of the matrix provides greater osteoconductivity than particulate-based materials to aid in new bone formation.¹⁴ The fibers exhibit controlled expansion property after placement in the defect to maximize bone fill and space maintenance. The present report supports this finding, as the composite graft expanded during healing, leading to tissue opening despite primary closure being obtained at the time of surgery. Secondary intention healing was achieved, however, with keratinized tissue width gained.¹⁵

It should be noted that adequate post-extraction curettage of the site is a prerequisite regardless of the future treatment such as implant placement. After the removal of failed implants, the socket condition needs to be free of granulation tissue and evaluated for missing socket walls, dehiscences, or fenestrations.² In the present case, implants placed in the first attempt were possibly placed in an area with residual infection from inadequate curettage at the time of the extraction. The chance of failure might have been reduced with adequate curettage of the site.

Conclusion

Employing allograft/xenograft composite is advocated to harness the advantageous properties of diverse biomaterials to achieve predictable outcomes in post-explantation ridge defect augmentation procedures. The use of fiber-form in the matrix offers volume stability and provides reliable and efficient structural support for the oral soft tissues in the augmented region.

Acknowledgment

The authors thank Katie Lin, DDS, MS, for her contribution as one of the surgical providers.

About the Authors

Hanae Saito, DDS, MS, CCRC
Clinical Associate Professor, Department of Oral Advanced Sciences and Therapeutics, Division of Periodontics, University of Maryland School of Dentistry, Baltimore, Maryland

Kaylie Nguyen, DDS
Periodontic Resident, Advanced Specialty Education in Periodontology, University of Maryland School of Dentistry, Baltimore, Maryland

Figures and Images

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Figure 1

Fig 1. Pre-extraction periapical radiograph (PA) of teeth Nos. 23 through 26, which exhibited bone loss due to periodontal disease. =

Figure 2

Fig 2 and Fig 3. Preoperative CBCT scans of sites Nos. 23 (Fig 2) and 26 (Fig 3) revealed adequate bone height and width for implant placements.

Figure 3

Fig 2 and Fig 3. Preoperative CBCT scans of sites Nos. 23 (Fig 2) and 26 (Fig 3) revealed adequate bone height and width for implant placements.

Figure 4

Fig 4. PA taken after the first attempt at implant placements in sites Nos. 23 and 26.

Figure 5

Fig 5. PA taken after the patient reported that implant No. 23 had come out. The No. 26 implant exhibited radiolucency.

Figure 6

Fig 6. Elevation of flap and explantation of implant No. 26, which was performed with reverse torque.

Figure 7

Fig 7. The allograft/xenograft composite was placed in the intra- and extra-bony ridge defect.

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Fig 8. The graft was secured with porcine collagen membrane.

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Fig 9. Immediate post–ridge defect augmentation, buccal view.

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Fig 10. PA of site Nos. 23 through 26 immediate post–ridge defect augmentation.

Figure 11

Fig 11. Surgical site Nos. 23 through 26, day 14 post–ridge defect augmentation.

Figure 12

Fig 12. Surgical site Nos. 23 through 26, 4 months post–ridge defect augmentation.

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Fig 13. PA of surgical site Nos. 23 through 26, 4 months post–ridge defect augmentation.

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Fig 14. Flap elevation at surgical site Nos. 23 through 26, 4 months post–ridge defect augmentation. Adequate ridge volume was noted.

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Fig 15. Occlusal view of the osteotomies.

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Fig 16. PA showing the implant placements at sites Nos. 23 and 26.

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Fig 17. Second-stage treatment was performed 3 months after the implant placements.

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Fig 18. The final prosthesis was delivered 5 weeks after the second-stage surgery.

Figure 19

Fig 19. PA taken at delivery of the final prosthesis.

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Fig 20. PA taken at 1-year follow-up. Stable bone height was noted.

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Fig 21. Buccal view at 1-year follow-up. Adequate hygiene was noted.

Figure 22

Fig 22. PA taken at 3-year follow-up. Stable bone height was noted.

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Fig 23. Buccal view at 3-year follow-up. Adequate hygiene was noted.