Ridge Augmentation in a Site of a Previous Implant Failure Using Tenting Screws With Allograft and Collagen Membrane

Implant failure and peri-implantitis can lead to crater-like defects that may cause severe vertical and horizontal alveolar ridge defects. Implant failure rates range from 3% to 8.4%. Implant failures have been associated with a variety of factors, such as the medical status of the patient, smoking habits, quantity and quality of remaining bone, occlusal overload, and improper angulation and positioning of the implant.^1,2

Several techniques have been described for the management of these severely resorbed ridges, including distraction osteogenesis,³ autogenous onlay block grafting,^4,5 the use of bone particulates with resorbable or nonresorbable membranes (with or without titanium reinforcement),^6,7 tenting-pole technique,⁸ and the addition of tenting screws to traditional guided bone regeneration (GBR) techniques. The objective in such cases is to augment the ridge enough to allow for ideal implant placement. Technique selection depends on factors such as the patient's overall medical status; area, size, and shape of the defect; proximity to critical anatomical structures; and the patient's chief complaint and expectations.

The use of tenting screws has shown promising results in bone regeneration procedures; however, there is limited evidence of its efficacy in severe vertical deficiencies.^9,10 Tarnow and Fletcher showed histological proof of new bone formation after GBR with tenting screws and a mixture of bovine xenograft and cancellous allograft with an acellular dermal allograft as a membrane in the anterior sextant.¹¹ The present case report aims to evaluate, clinically and histologically, the effectiveness of tenting screws with freeze-dried bone allograft (FDBA) and a resorbable collagen membrane to augment a site of a previously failed implant with severe vertical and horizontal bone loss in the posterior mandible.

In August 2016, a 60-year-old Caucasian male with no significant medical history presented for a comprehensive periodontal and implant consultation at the Postgraduate Periodontics Clinic, Columbia University College of Dental Medicine, New York, with the chief complaint of wanting to replace his failed implant in the right mandibular molar area to restore primarily esthetics as well as function.

The patient denied any history of tobacco, marijuana, or drug use. Although he could not recall exactly when, the patient had had all of his first premolars and third molars extracted due to orthodontic treatment before receiving implant treatment. In 2006, he had implants Nos. 3, 29, and 30 placed. In 2012, he was diagnosed with peri-implantitis in implants Nos. 29 and 30, however he did not seek the recommended treatment at the time. Radiographic examination of a periapical radiograph from 2012 showed 50% or more bone loss around implant No. 30 and approximately 15% bone loss around implant No. 29 (Figure 1). In December 2014, implant No. 30 dislodged during regular masticatory function, for which the patient did not pursue further treatment. Figure 2 shows the bone defect approximately 2 years after the dislodgement of implant No. 30.

During consultation in 2016, intraoral examination revealed a severe vertical and horizontal hard- and soft-tissue deficiency (Seibert class III)¹² at site No. 30 (Figure 3 through Figure 5), with exposure of four threads on the distal aspect and two threads on the buccal aspect of implant No. 29.Radiographic examination of the defect with periapical radiographs and a cone-beam computed tomography (CBCT) confirmed buccal plate loss of 6 mm to 7 mm, lingual plate loss of 5 mm to 6 mm, and 9 mm to 10 mm of vertical bone deficiency at the center of site No. 30; therefore, it was determined that the defect was a one-wall (distal) to two-wall (distal and lingual) defect. The roof of the inferior alveolar canal was approximately 7 mm below the most apical portion of the defect (Figure 6). The esthetic analysis confirmed that all of the patient's teeth were visible during regular smile. After careful assessment of the patient's chief complaint, his dental history, and clinical and radiographic examinations, GBR with tenting screws was deemed the appropriate treatment, and informed consent was obtained.

Presurgical Management

The patient underwent phase I periodontal therapy, including oral hygiene instructions and prophylaxis. Six-week periodontal re-evaluation showed a significant improvement in the patient's oral hygiene, and it was determined that he was ready to proceed with surgical treatment. At this point, an Essix retainer was fabricated as a temporary replacement for missing tooth No. 30 to address the patient's high concern for esthetics.

Surgical Procedure and Postoperative Instructions

The patient was premedicated with 2 g of amoxicillin, and a preoperative chlorhexidine rinse was given for 30 seconds preoperatively. Due to lack of buccal keratinized tissue, a paracrestal incision 2 mm toward the lingual, along with an intrasulcular incision around tooth No. 31 and a vertical releasing incision at the distobuccal line angle of implant No. 29, were performed with a 15C blade. A full-thickness buccal flap was raised 3 mm to 4 mm beyond the defect's most apical margin, followed by a partial-thickness flap that was apically extended approximately 10 mm to achieve flap advancement and allow for primary closure. A full-thickness flap was raised on the lingual aspect.

The defect was thoroughly degranulated and irrigated with saline solution. Decortication was then performed using a #6 diamond round bur and a high-speed surgical handpiece. Two tenting screws (3 mm diameter screw head x 1.5 mm diameter shank x 7 mm total length) were placed within the defect to tent up the allograft and collagen membrane and achieve the desired vertical and horizontal augmentations (Figure 7). A 20 mm x 30 mm collagen membrane was trimmed and shaped to extend 3 mm to 4 mm beyond the defect's most apical margin buccally and lingually, and close adaptation to bone was achieved. The lingual portion of the membrane was tucked under the lingual flap, and the defect was overfilled with 1 cc of previously hydrated cortico-cancellous (70:30) FDBA (250 μm to 1000 μm particle size) around and over the tenting screws (Figure 8). The collagen membrane was then placed over the graft and tucked under the buccal flap beyond the defect margin. The collagen membrane covered the bone defect and allograft and closely adapted to native bone (Figure 9). Primary closure without tension was achieved with nonresorbable 5.0 polypropylene monofilament sutures. The site was irrigated using saline solution and 0.12% chlorhexidine rinse.

The patient was given an extraoral cold-pack and instructed to continue applying cold intermittently during the first 24 hours to prevent swelling. The patient was prescribed amoxicillin 875 mg twice per day for 7 days, ibuprofen 400 mg every 4 to 6 hours, and 0.12% chlorhexidine rinse for 30 seconds twice per day for 14 days. Postoperative instructions were thoroughly discussed, and the patient was told not to brush or apply any pressure on the surgical site for 4 weeks and avoid mastication for 6 to 8 weeks.

Follow-up Appointments

The patient was followed up at 1, 2, 4, 6 (suture removal), 8, 12, 16, and 24 weeks (Figure 10). The patient was highly compliant, and plaque control was excellent. Six-month prophylaxis was performed at 14 weeks. Clinical examination at 24 weeks revealed horizontal and vertical augmentation (Figure 11) compared to baseline (Figure 3 through Figure 5). Standard radiographs were taken immediately postoperatively and at 8 and 24 weeks (Figure 10). A second CBCT was taken at 24 weeks (Figure 12), and after interpretation, it was determined that the GBR had provided enough vertical and horizontal augmentation to proceed with implant placement (Figure 6 vs Figure 12).

At week 30, a bone core was obtained at the time of No. 30 implant placement. Local anesthesia was achieved, a paracrestal incision was again made in the site toward the lingual to increase keratinized tissue width, and full-thickness buccal and lingual flaps were raised. First, a 2 mm x 10 mm bone core was obtained with a 2 mm trephine (Figure 13). Upon clinical examination, granulation tissue was seen at the distal portion of the augmented site and removed with hand instruments. The trephined site was used as the initial preparation for the implant osteotomy, which was further enlarged to receive a 5 mm x 10 mm implant following the manufacturer's instructions. The implant was placed 0.5 mm to 1 mm subcrestally, primary stability was achieved (60 Ncm), and a cover screw was placed. Primary closure was attained.

Surgical Outcomes: Clinical, Radiographic, and
Histological Findings

Healing was uneventful after GBR, implant placement, and follow-up visits. Radiographic measurements at 24 weeks (Figure 12) revealed new bone formation in the vertical and horizontal axes. Specifically, the overlaying of pre- and postoperative CBCTs established a vertical and horizontal bone augmentation of 7 mm to 9 mm throughout the defect (Figure 6 vs Figure 12). One year after implant loading, clinical and radiographic examinations showed maintenance of the achieved bone regeneration (Figure 14).

Microscopic examination of the obtained bone core revealed both dense and lamellar cortical bone and pools of amorphous, basophilic graft material containing foci of newly forming osteoid bone. Additionally, a cap of fibrous connective tissue was found in the most coronal aspect of the specimen.The length of the core was divided into thirds: the coronal third showed the highest ratio of residual graft material, and, while areas of dystrophic calcifications were identified within the residual graft material, no osteoid production was observed; within the middle third, the ratio of graft material to bone was approximately 50:50, and pockets of new osteoid bone formation were identified; lastly, the apical third showed the highest concentration of lamellar bone and the least residual graft material (Figure 15).

The screw-tenting technique has been described previously in the literature to increase the soft and hard tissues of largely resorbed edentulous sites. One or more tenting screws (small and made of titanium) are placed, usually buccally and for horizontal augmentation, with the head of the screw(s) away from cortical bone as many millimeters as the clinician wishes to augment. The defect is then grafted, covering the screw(s) shank(s) with bone graft, and a barrier membrane is used to cover the area. The use of these tenting screws increases the stability of the graft and maintains its dimensions by decreasing the effects of possible external pressure; this is due to the rigid "tenting effect." This technique results in a successful augmentation that allows for implant placement.^8-11

Allografts, xenografts, and autografts, or a combination of allograft and autograft have been used for this technique. In the present case report, cortico-cancellous FDBA was chosen to avoid increasing morbidity, as with an autogenous graft, and to promote its turnover to cortico-cancellous bone (versus xenograft). Because the defect was present at one edentulous site (No. 30), two tenting screws sufficed to secure a vertical and horizontal augmentation of the area (Figure 7). A collagen resorbable membrane was used to avoid soft-tissue migration to the graft, as commonly seen in the literature, as the clinicians determined that a nonresorbable barrier (more rigid) was not necessary to maintain the desired dimensions. In this case report, the addition of tenting screws to the GBR procedure was successful for the augmentation of a severely resorbed ridge deficiency in the posterior mandible without the need for an autogenous graft or reinforced membrane.

Another aspect of the case worth noting was the lack of keratinized tissue. With the plan calling for placement of an implant at the augmented site, increasing the amount of keratinized tissue was important, and, as previously discussed, a paracrestal incision was performed during both surgical interventions, GBR and implant placement, to augment the tissue. In this case, the incision design prevented the need for a soft-tissue graft.

Complications, such as infection, exposure, and wound dehiscence, and possible consequent failure of the graft have been described previously in the literature. A systematic review by Pourdanesh et al in 2017 discussed the use of tenting screws for horizontal augmentation, and only one of four articles included reports of dehiscence and screw exposure. Another one of the four articles reported infection and failure of the graft (two cases in the FDBA group, and one case in the autogenous group, total of 12.5% infection rate).⁹ In order to avoid these problems, and following Wang and Boyapati's "PASS" principle, in the present case flap advancement was carefully achieved to secure primary closure without tension, and space maintenance was reinforced by the addition of tenting screws.¹³

Postoperative instructions and a compliant patient are also key factors to this procedure. The patient in this case had shown to be compliant, and he was instructed to not apply any pressure to the area for the subsequent 6 to 8 weeks to ensure stability of the graft. Additionally, the polypropylene monofilament sutures used avoided plaque retention, reducing overall inflammation in the area, which could jeopardize the surgical result.

The clinically successful results of this surgical procedure were confirmed radiographically with a CBCT 24 weeks after GBR and histologically with a bone core obtained upon re-entry 30weeks after GBR. A comparison of Figure 6 and Figure 12 demonstrates the bone augmentation radiographically. Histology showed new osteoid bone formation at the site, with the highest rate being at the apical third and lowest at the coronal third, with the greatest proportion of allograft. It was concluded that the FDBA resulted in a high turnover rate, and this is probably the reason for the successful results. At the 3-month follow-up after implant placement, no changes in bone architecture or soft-tissue dimensions were detected, and the implant was deemed integrated. The implant was restored with a porcelain-fused-to-metal screw-retained crown 4 months after placement.

This case report provided clinical, radiographic, and histological evidence that the use of tenting screws with cortico-cancellous FDBA and a collagen barrier membrane is a successful GBR technique for the treatment of severe vertical and horizontal bone deficiencies for future implant placement. Histological evaluation showed allograft particles throughout the bone core, from the most coronal third to the most apical third, from least to most amount of allograft particles, respectively, despite which successful implant placement was achieved.

Jaffer A. Shariff, DDS, MPH, DPH, MS
Director of Research, Assistant Professor, Touro College of Dental Medicine, Hawthorne, New York

Daniela Gurpegui Abud, DDS, MS
Assistant Professor, Touro College of Dental Medicine, Hawthorne, New York

Anjali K. Dave, DDS
Resident, Division of Endodontics, College of Dental Medicine, Columbia University, New York, New York

Dennis P. Tarnow, DDS, MS
Director of Implant Education, Clinical Professor, Division of Periodontics, Section of Oral, Diagnostic and Rehabilitation Sciences, College of Dental Medicine, Columbia University, New York, New York