Allograft Customized Bone Block in the Edentulous Maxilla: A 6-Month CBCT Analysis and 15-Month Follow-up

In the rapidly evolving field of dental implantology, techniques change quickly. Today, clinicians can use computer-aided design/computer-aided manufacturing (CAD/CAM) technology to fully digitally plan a guided bone regeneration (GBR) procedure based on a cone-beam computed tomography (CBCT) or CT scan to create individualized patient-specific bone blocks to reconstruct hard-tissue volumes. Virtual 3-dimensional (3D) planning of a patient-specific bone block requires thorough knowledge of anatomical structures and implant considerations. The use of this approach and technology has yielded promising results in multiple case reports over the past decade or so.^1-7

Allograft customized bone blocks (ACBBs) such as Puros® Allograft Customized Block (ZimVie, zimvie.com) became available on the market around 2014. These particular blocks are manufactured based on the multistep Tutoplast® tissue sterilization process, which was developed in 1969 and is used for the preparation of donated human tissues.⁴ Commonly utilized in dentistry for bone grafts and soft-tissue grafting, the process first involves purification of the donor material, followed by block milling done in a clean environment; afterward, the block is packaged and sterilized with low-dose gamma irradiation.⁸

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Using ACBBs, the placement of implants can be executed after about 6 months of healing time, as this is the length of time the allograft blocks need to integrate with the adjacent host bone and remodel by so-called “creeping substitution,” which occurs 5 to 6 months after placing the ACBB.^9,10 In an article on autogenous corticocancellous blocks, Romanos reported the bone dynamics and remodeling that can be extrapolated for the use of ACBBs.¹¹ The first healing period may show some initial resorption of the ACBB, a process that may be the result of the initial remodeling of the graft. Because collagen-rich allogenous bone remodels relatively fast, it can be accompanied by superficial bone loss. Soft-tissue management during the surgery is crucial and impacts the healing process.²

Attaining Sufficient Bone Volume

Bone volume is critical when installing implants. In cases where bone volume is insufficient to place an implant, bone grafting becomes necessary to ensure there is enough bone for subsequent implant placement.

GBR has been a highly predictable procedure in implantology. The success of the ACBB technique is dependent on several biological principles, described as “PASS”: Primary wound closure to make sure that undisturbed and uninterrupted wound healing can occur; Angiogenesis to accommodate necessary blood supply and proliferation of undifferentiated mesenchymal cells; Space maintenance to facilitate the needed space for bone ingrowth; and Stability of the wound and implant to induce blood clot formation and uneventful healing.¹²

Various successful cases have been described to reach the goal of achieving new bone formation, including those that utilized direct implant placement combined with a titanium-reinforced membrane^13,14 or titanium meshes.^15,16 An innovative method of achieving GBR is to utilize CAD/CAM-designed ACBBs. The following case report describes the use of ACBB in a severely atrophic maxilla to attain extensive bone augmentation. The case adhered to the CARE guidelines.¹⁷

Case Presentation

The patient was a 77-year-old woman who was a smoker with arrhythmia and recently had a cardioversion with a significant amount of aftercare. She used several medications, including metaprolol, flecainide, Xeralto®, and omeprazole for her heart condition. She had lost her teeth in the maxilla 22 years prior at the age of 55, and since then had a full prosthesis (denture) resulting in extensive resorption and pneumatization of the alveolar ridges. Over the years this led to a poorly functional prosthesis.

The patient’s main subjective complaint was a lack of retention of her maxillary prosthesis, which was otherwise esthetically sufficient and technically proper. Objectively, the clinician ascertained a severe atrophy of the tuberosities and a shallow palatal depth. On the buccal aspect a high attachment of several frenula was present, making it impossible to provide the patient with a good functioning conventional non-implant-retained prosthesis. To place implants, an extensive bone augmentation in the maxilla would be required (Figure 1 and Figure 2).

Implant planning was performed utilizing 3D planning software (RealGUIDE®, ZimVie). Based on this plan, the required amount of augmented bone was determined (indicated by the yellow lines on the CBCT imaging, Figure 3 and Figure 4), and two ACBBs were designed for the right and left sides of the maxilla (Figure 5 and Figure 6). The grafts were milled from square bone blocks. Table 1 provides the measurements of the allograft customized bone blocks.

First Surgical Phase: ACBB Placement

The patient was prescribed amoxicillin 500 mg with 125 mg clavulanic acid 3 times a day for 7 days (starting the day of the surgery).^18,19 A full-thickness flap was elevated from a full-arch mid-crestal incision with two distal vertical incisions in the tuberosities and one mesial vertical incision in the midline of the maxilla. Once the flap was elevated, a thin, knife-edge ridge presented itself (Figure 7).

The ACBBs were hydrated sufficiently in sterile saline (0.9% sodium chloride) to enhance their ductility and lower the risk of fracture (as per Puros® Allograft instructions for use) before being adapted onto the maxilla. The precision of the design of the blocks was such that it enabled the ACBBs to fit perfectly into place, just as planned digitally. Before definitive placement of the ACBBs, the clinician made an extensive periosteal incision on the buccal flap, ensuring sufficient tension-free release to obtain complete closure. The maxilla was not perforated with a 1.1-mm diameter round bur for decortication because of risk of perforating the thin bone plate.²⁰ Both ACBBs were fixated with three fixation screws each (Stoma®/Storz am Mark GmbH, stoma.de/en/) (Figure 8 and Figure 9).

A barrier membrane (CopiOs® Pericardium Membrane, ZimVie) was placed for exclusion of cells with high proliferation. The membrane covered the ACBB site completely and extended 2 mm to 3 mm from the ACBB margins. To stabilize the membranes, multiple horizontal sutures were placed with resorbable 4-0 monofilament (Monosyn®, B. Braun, bbraun.com) (Figure 10). The membranes were then covered with platelet-rich fibrin (PRF) membranes, created from blood drawn from the patient (Figure 11).²¹ Modified vertical mattress sutures were applied to coronally advance the flap and secure passive primary closure of the wound, utilizing a nonresorbable 5-0 monofilament (Prolene®, Ethicon, jnj.com). The surgery site was further secured using simple interrupted sutures with nonresorbable 5-0 polyamide monofilament (Dafilon®, Henry Schein, henryschein.com) (Figure 12).

After the surgery the prosthesis was fully adjusted by removing the buccal flange of the denture and easing the crestal pressure to avoid any pressure on the wound. Prosthesis stability would be provided only by support from the palate. After 2 weeks of healing the exterior sutures were removed. A soft relining of the prosthesis was performed after 8 weeks to improve the fit of the removable prosthesis. A total healing period of 6 months was needed before implant placement.²²

Healing was uneventful. Postoperative photographs were taken 2 weeks and 6 months after surgery (Figure 13 and Figure 14). A CBCT was recorded, and, using the 3D planning software (RealGUIDE), the design of the ACBBs was compared with the outcome revealing a resultant ridge width of between 6.9 mm and 8.9 mm and confirming that the outcome 6 months post-surgical was exactly the same as the design (Figure 15 through Figure 17).

Second Surgical Phase: Implant Placement

For implant placement, a mid-crestal incision with two vertical incisions bilaterally at the tuberosities and one vertical incision at the facial midline were done to raise a full-thickness flap. After elevation of the flap a wide ridge of bone was visible (Figure 18) and was confirmed on the CBCT. The six fixation screws that had been placed were removed. Osteotomies were then made using osseodensification burs (Densah®, Versah, versah.com).²³

An additional crestal bone augmentation procedure was performed at sites Nos. 3 and 14 with allograft cortical bone particles (Puros®, ZimVie) and leukocyte-PRF (L-PRF) to create “sticky bone.” Six implants (Tapered Screw-Vent®, ZimVie) (Table 2) were placed with a medium range of insertion torque values but good primary stability, and cover screws were placed (Figure 19).

Closure of the wound was accomplished with vertical modified mattress sutures using a nonresorbable 5-0 monofilament (Prolene®) suture material. Single sutures were added for complete closure of the wound (Figure 20). A panoramic radiograph after implant placement is shown in Figure 21. After 2 weeks of healing, the sutures were removed. A total healing period of 4 months was introduced.

Third Surgical Phase: Placement of Healing Abutments

After the 4-month healing period following implant placement, an extensive apically repositioned flap was performed to replace the vestibular and mucogingival junction more buccally and apically, creating a sufficient amount of keratinized mucosa around the implants. A split-thickness crestal incision was made (slightly more palatal), with two vertical releasing incisions distally and two vertical incisions mesially (Figure 22). Healing abutments were placed.

Periosteal sutures were able to fixate the flap more apically (Figure 22). The sutures were removed after 1 week (Figure 23).

Prosthetic Phase

After a healing period of a month following the implant uncovering, the prosthetic phase could start. Healing abutments were replaced with screw-retained multi-unit abutments on the implants.

After placement of the multi-unit abutments, a tissue response occurred at implant site No. 7. There was swelling of soft tissue combined with sensitivity and bleeding on probing. The treatment protocol began with disruption of the biofilm with prophylaxis powder (Air-Flow® Perio powder applied with a Perioflow® handpiece, EMS Electro Medical Systems, ems-dental.com) for several minutes. A 35% phosphoric acid gel (Temrex Corp., temrex.com) was applied for 1 minute. Afterward, the site was flushed with an antiseptic mouthrinse (Perio-Aid®, Dentaid, dentaid.com), followed by repeating the Perioflow sequence above. Finally, an oral gel (blue®m, bluemcare.com) was applied. An evaluation after 2 weeks showed positive and complication-free results: the probing depths at implant site No. 7 went from 5/6/6 buccal (mesial to distal) and 6/5/5 palatal (mesial to distal) to 3/3/4 buccal (mesial to distal) and 4/3/4 palatal (mesial to distal).

Using a custom open tray, an analog impression was made, and a screw-retained fixed prosthesis with a titanium mesostructure and pink resin for improved esthetics was placed. Screw channels were filled with Teflon tape and composite for complete closure (Figure 24 through Figure 26).

Evaluation Phase

Six months after implant loading, a radiographic evaluation was performed. The crest of bone was observed at the implant platform or coronally, demonstrating excellent wound healing and good implant osseointegration (Figure 27). Pocket depth measurements showed healthy periodontium around the implants.

The implants were re-evaluated 1 year after placement. No clinical mobility was observed. Periapical radiographs (Figure 28 through Figure 30) showed good bone levels with minimal bone resorption at implant No. 7. Peri-implant charting showed shallow pockets around the implants: all pocket depths were 2 mm or 3 mm, except for just two 4 mm pockets (No. 7 direct buccal and No. 12 distal buccal).

Discussion

Although a patient’s own (ie, autogenous) bone is still considered the “gold standard” material for bone augmentation procedures, showing excellent results,^22,24 long-term outcomes with autogenous bone blocks continue to be associated with controversial effects. Resorption rates between 20% and 100% of the grafted volume have been reported, which clinicians must consider when grafting with autogenous bone blocks.^25,26

Also, clinical trials that compared autogenous grafts with bone block substitutes have showed no differences in clinical outcomes.²⁷ Used worldwide, the Tutoplast-processed allografts have been researched extensively.^28-32 Up to 127% more vital bone formation has been found after sinus grafting with allograft bone substitutes compared with nonresorbable xenografts.^30,33 Little residual grafting material was found to be present after 6 to 7 months of healing time, confirming the active remodeling of the allograft.³⁴ This remodeling process appears to complete after 11 months.³⁴ The Tutoplast-processed allografts have been compared to other freeze-dried allografts and have demonstrated greater bone formation after several months of healing time and a lower percentage of remaining allograft particulates.^35,36

Allogeneic bone blocks for facial reconstruction were first used by Converse in 1950.³⁷ Since then, allograft bone blocks have been compared with autogenous bone blocks in multiple studies. Laino et al demonstrated that bone formations when using Tutoplast-processed allograft blocks are as good as autogenous blocks in vertical augmentation in the posterior mandible.³⁸ Other research has found that the survival and success of dental implants are similar for autogenous and allograft blocks.^39,40

A resorption and high-volume stability of 94.3% ± 5.45% occurs after grafting with an allograft block graft.⁴¹ Esthetic results can be scored with the pink esthetic score (PES). After treatment, no differences were seen between autogenous and allograft blocks.⁴² Moreover, patients experienced less pain with treatment with an allograft block because no second surgery to harvest a block from elsewhere is needed.⁴²

When performing bone augmentation treatments with an allograft or autograft block, chairside adjustments are typically needed to ensure the block fits well on the defect. Usually the fit will be imperfect, which can influence the ingrowth of blood vessels and integration of the graft. Additionally, such adjustments lead to a longer surgery period and higher patient morbidity.⁴³ Conversely, ACBBs are able to be shaped precisely for an ideal fit, thereby reducing surgery time and the risk of complications.^2,3,40

Because the ACBB is planned beforehand, its form/design can provide a predesigned vertical and horizontal bone gain that is less arbitrary than when using meshes, titanium-reinforced membranes, or other grafting techniques with grafting materials. Also, since there is a large contact area between the ACBB and the patient’s bone, revascularization is enhanced.⁴³

ACBBs have been shown in several clinical indications and case reports to give a stable result through bone remodeling and integration to the donor site after 6 months of healing.^3,7,44,45 Aside from the precise fit of the ACBB, site preparation through cortical perforation may also favorably influence its integration and vascularization. Tresguerres et al found that cortical perforation of the donor site does not have an effect on the angiogenesis and formation of new bone when compared to non-perforated sites.⁴⁶ In the treatment of the maxilla in the present case report, the authors did not perforate the donor site to attempt to stimulate angiogenesis because the bone in the maxilla was very thin and perforation could have easily resulted.

In the present case report of the use of ACBB in the maxilla, the healing period was without complications. After extrapolation of the CBCT the ACBB showed minimal to no volume loss 5 months after placement in comparison to the design of the ACBB. The implants were placed 6 months after bone grafting. After implant placement, an additional 4 months was required for healing, thereby following the traditional healing protocol to allow further maturation of the bone graft before healing abutments were placed.⁶ As suggested by Maiorana et al to improve soft-tissue healing,²¹ resorbable membranes in combination with an advanced-PRF (A-PRF™, Process for PRF Inc., a-prf.com) clot were utilized in this case.

While CAD/CAM technology used in combination with ACBB and/or surgical guides is a reliable approach, mean accuracy must be taken into account. When factoring in the maximum deviation, mean accuracy becomes less precise, especially near vital structures, which require a distance of at least 2 mm.⁴⁷ Thus, CAD/CAM-based techniques are not risk-free, do not necessarily solve all problems, and should be used only by experienced providers to enhance results. A typical learning curve has not been established for static computer-assisted implant surgery.⁴⁸

Movement of soft tissue can be problematic. To aid in this endeavor, a keratinized tissue graft or Kazanjian vestibuloplasty technique can be performed to stabilize the tissue and improve the success of the ACBB and implants.⁴⁹

The presented clinical case is only one example of the use of an allograft customized bone block in the maxilla. Evaluation of the implants at 6 months was done using the panoramic radiographic assessment and clinical measurements of probing pocket depths. Periapical radiographs may provide more detail to accurately evaluate marginal bone level. Longer follow-up evaluations and more similar cases with a standardized protocol and preferably the same implants as used in this case should be done to verify this protocol as a viable treatment option for the rehabilitation of a severely resorbed maxilla.

Conclusion

Although this is just one retrospective case report, the presented case showed that allograft customized bone blocks could be a reliable treatment option for bone grafting, especially for severe atrophy and extensive horizontal and vertical bone defects. Undoubtedly, proper soft-tissue management is essential in extensive bone augmentation procedures.

ACKNOWLEDGMENT

The CBCT analysis and block design were performed by Stefan Berger, PhD.

DISCLOSURE

The authors declare no conflicts of interest. This case report did not receive any external funding.

About the Authors

Maarten J. Boogaard, DMD
Assistant Professor, Department of Reconstructive Oral Care, Academic Center for Dentistry Amsterdam (ACTA); Private Practice, Amsterdam, The Netherlands

Martijn Kerver, DMD
Private Practice, Garderen, The Netherlands

Georgios E. Romanos, DDS, PhD, Prof. Dr. med. dent.
Professor, Department of Periodontics and Endodontics, School of Dental Medicine, Stony Brook University, Stony Brook, New York; Professor, Department of Oral Surgery, Implant Dentistry, and Oral Medicine, Dental School (Carolinum), Johann Wolfgang Goethe University, Frankfurt, Germany

Figures and Images

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Table 2

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Figure 1

Pretreatment panoramic radiograph showing atrophic maxilla.

Figure 2

Pretreatment intraoral situation, occlusal view of the maxilla.

Figure 3

CBCT showing the design of the bone block at tooth No. 6.

Figure 4

CBCT showing the design of the bone block at tooth No. 3.

Figure 5

Design of the ACBBs on the maxilla, frontal view.

Figure 6

Design of the ACBBs, occlusal view.

Table 1

Figure 7

Knife-edge ridge after raising the full thickness flap.

Figure 8

Fitting of the ACBBs.

Figure 9

ACBBs secured to the maxilla with fixation screws.

Figure 10

The maxilla covered with pericardium membranes, stabilized with horizontal sutures.

Figure 11

PRF membranes placed over the pericardium membranes.

Figure 12

Wound closure showing tension free flap advancement.

Figure 13

At 2 weeks postoperative, complete wound closure was demonstrated.

Fig 14

At 6 months postoperative, uneventful healing was evident.

Figure 15

CBCT after ACBB placement surgery illustrating bone volume similar to the preoperative planning.

Figure 16

Sagittal CBCT view at 6 months postoperative; the green lines indicate new bone formation, which mimicked the original design.

Figure 17

Axial CBCT view at 6 months postoperative; the green lines indicate new bone formation, which mimicked the original design.

Figure 18

Flap elevation at the second surgical phase demonstrating a wide alveolar ridge.

Table 2

Figure 19

Implant placement of six implants.

Figure 20

Wound closure after two-phase implant placement.

Figure 21

Panoramic radiograph after implant placement.

Figure 22

Placement of healing abutments 4 months post–implant placement; suturing of the split-thickness flap.

Figure 23

Healing of the peri-implant mucosa 1 week after placement of healing abutments.

Figure 24

Occlusal view of the screw-retained fixed prosthesis.

Figure 25

Frontal view of the prosthesis.

Figure 26

Panoramic radiograph after placement of the screw-retained fixed prosthesis strengthened with titanium.

Figure 27

Panoramic radiograph 6 months after delivery of the implant-supported bar and prosthesis.

Figure 28

Periapical radiographs of the right side of the implant-supported bar demonstrating crestal bone stability.

Figure 29

Periapical radiographs of the middle of the implant-supported bar demonstrating crestal bone stability.

Figure 30

Periapical radiographs of the left side of the implant-supported bar demonstrating crestal bone stability.