Bone Regeneration Around Immediate Implants Utilizing a Dense Polytetrafluoroethylene Membrane Without Primary Closure: A Report of 3 Cases

The immediate placement of dental implants into extraction sites is a predictable, successful procedure.^1,2  After insertion of the implant, the horizontal distance between the walls of the socket and surface of the implant may require augmentation and/or soft tissue exclusion to predictably achieve bone-implant contact^3,4  and prevent soft tissue ingrowth associated with natural socket healing.⁵  Socket healing begins with clot formation, which then supports development of granulation and connective tissue, followed by osteoid formation and bone maturation.^5,6  Bone formation begins at the apical and lateral socket walls, and epithelial downgrowth occurs at the coronal aspect of the socket fundus.

Various barrier techniques have been used to inhibit epithelial migration and soft tissue formation on the coronal aspect of the implant through augmentation of the horizontal defect and/or soft tissue exclusion;^7,8  evidence suggests that expanded polytetrafluoroethylene (ePTFE),^8,9  collagen,¹⁰  and autogenous connective tissue barriers¹¹  can be successfully used. Typically, primary closure is much desired with guided bone regeneration using collagen and ePTFE membranes,¹²  a technique that increases surgical complexity, increases patient morbidity, and disrupts the soft tissue architecture of the area. Furthermore, the occurrence of wound dehiscence has been shown to be detrimental to bone formation,¹²  and resorption patterns of exposed resorbable barriers can be unpredictable.¹³  To overcome this limitation, membranes made of high-density polytetrafluoroethylene (dPTFE), which are nonresorbable and designed to withstand exposure to the oral cavity because of their microporosity, can be a useful alternative because their pore size makes them impenetrable to bacteria and epithelial cells.

Limited evidence suggests that these membranes are efficacious in bone augmentation and socket grafting applications.^14–17  Hoffman et al,¹⁸  in a retrospective human study, found that intentionally exposed dPTFE membranes, left in place for 4 weeks, predictably preserved the hard and soft tissue in extraction sites and supported socket bone formation. The following case reports describe this procedure, first described by Bartee¹⁹  for extraction sites, for augmenting horizontal defects with immediate dental implants and provide observational data to support further controlled trials.

All patients treated were medically stable nonsmokers with no contraindications for dental implant surgery. Patients premedicated with amoxicillin 500 mg every 8 hours beginning the day before surgery and continuing for 7 days postoperatively, a protocol used by the authors for immediate implant placement. Although evidence suggests the benefit of antibiotic prophylaxis before dental implant therapy,²⁰  questions exist regarding the optimal regimen in regards to immediate implants and whether postoperative coverage is beneficial.^21–23  The authors use their own protocol and prefer to continue coverage after immediate implants to conceivably prevent postoperative infection.

Implant placement was completed if there was 3 mm of bone apical to the socket or if the base of the socket was thin enough in diameter so that 3 mm of the implant was surrounded in native bone to engage the implant and provide initial stability of 35 Ncm while submerging the platform of the implant 2 to 4 mm²⁴  from the buccal marginal soft tissue for proper emergence. Augmentation of the implant socket gap was performed with freeze-dried cortical particulate bone if the horizontal gap was greater than 2 mm and/or the buccal plate was thin (1 mm or less), as immediate implants placed into extraction sockets with thin buccal cortices have been shown to demonstrate greater resorption,²⁵  which may be minimized with placement of graft materials.²⁶ 

A 54-year-old white man with a history of hypercholesterolemia and hypertension required extraction of tooth 20 because of extensive caries and crown fracture (Figure 1). The patient was taking 81 mg of aspirin/day and hydrochlorothiazide. A sulcular incision was made buccal and lingually, and full-thickness flaps were elevated to access the root, reflecting the mesial and distal papilla and exposing the buccal and lingual cortices. After extraction and socket debridement to remove any possible apical granulation tissue, the site was prepared following a tapered implant osteotomy protocol and a 4.3 × 11.5 mm (Nobel Replace, Nobel Biocare, Yorba Linda, Calif) implant was placed with an insertion torque of 35 Ncm (Figure 2a and b). The horizontal defect was grafted with freeze-dried cortical bone (Oragraft, Lifenet Biomedical, Virginia Beach, Va), and a PTFE membrane (Cytoplast GBR 200, Osteogenics Biomedical, Lubbock, Tex) (Figure 3a) was placed under the buccal and lingual flaps using PTFE sutures to approximate the tissues and hold down the membrane (Figure 3b).

Postoperative care consisted of rinsing with chlorhexidine 12% for 2 weeks, followed by topical application until membrane removal. At 6 weeks the membrane was removed (Figure 4a and b) without anesthesia. A stage 2 reentry was performed 4 months after implant placement via a full-thickness flap with mesial and distal papilla sparing vertical incisions for access. The coronal aspect of the flap was trimmed and sutured to adapt to a healing abutment. The implant demonstrated absence of soft tissue invagination and clinical bone fill at the macrosopic level as it felt hard upon probing (Figure 5). The final screw-retained crown was placed 6 weeks later (Figure 6a and b).

A 62-year-old white man with a noncontributory medical history required extraction of tooth 30 due to fracture of the mesial root and failing endodontic therapy (Figure 7a and b). After root sectioning, minimally traumatic extraction, and socket debridement to remove apical granulation tissue, a 5.0 × 11.5 mm implant (Nobel Biocare Replace) was inserted at 35 Ncm following a tapered osteotomy protocol (Figure 8). Because of the presence of a thin buccal plate, freeze-dried cortical bone was placed (Lifenet Oragraft) and covered with a PTFE membrane (Cytoplast GBR 200) that was placed under the buccal and lingual envelope flaps via blunt dissection; PTFE sutures were used to approximate the tissues without primary closure (Figure 9).

Postoperative care was the same as for patient 1. After 6 weeks the membrane was removed (Figure 10), revealing what appeared to be nonepithelialized soft tissue underneath the barrier, consistent with other reports using this membrane.¹⁸  The reentry surgery demonstrated complete clinical bone fill (Figure 11), with normal healing identified radiographically at the time of the final impression (Figure 12). A custom abutment and porcelain fused to metal crown were fabricated and inserted. Because the implant was placed with bias into the mesial socket, the authors preferred the final restoration to have the majority of centric contact over the implant fixture and to have very light contact on the distal portion of the restoration to minimize cantilever forces.

A 55-year-old white man who was taking atenolol for hypertension required extraction of retained tooth 30 due to caries, crown fracture, and failing endodontic therapy (Figure 13a and 1b). The tooth was extracted atraumatically through sectioning into the mesial and distal roots, and the socket was debrided to remove apical granulation tissue. Following the manufacturer's tapered implant osteotomy protocol, a 5.0 × 11.5 mm implant (Nobel Biocare Replace) was inserted at 35 Ncm (Figure 14). Although the buccal bony plate was thin (<2 mm), no bone replacement material was used because the buccal surface of the implant was enveloped in interseptal bone and no direct buccal gap existed; only a PTFE membrane (Cytoplast GBR 200) was secured, as in the other cases. The membrane was removed at 6 weeks (Figure 15). Stage 2 was completed via an excisional punch technique 3 months later (Figure 16a and b), and the final screw-retained crown was fabricated and inserted (Figures 17a and b).

When placing implants into fresh extraction sites, a horizontal defect often exists between the socket walls and body of the implant. Various studies have documented that if this gap exceeds a certain dimension (2 mm), soft tissue ingrowth can occur on the coronal aspect of the implant as epithelial cells migrate and attach to the implant surface before osteoprogenitor cells. To predictably regenerate bone in the horizontal defect and exclude epithelium, augmentation techniques involving collagen and ePTFE barriers are often used. Most often, these materials are covered via primary closure to predictably ensure success.¹²  Using free gingival and connective tissue graft barriers involves a donor site and increases complexity and morbidity. Obtaining primary closure through coronally advanced and pedicled flaps partially disrupts the blood supply, as vessels are severed through partial-thickness dissection,²⁷  and the soft tissue architecture of the area is altered. The surgical complexity is also increased, as the flap often needs to be apically positioned during uncovering of the implant to bring keratinized tissue to the facial aspect. Dense PTFE membranes, which are designed to withstand exposure of the central portion because of their impermeability to bacteria, may be an alternative that minimizes these concerns.

Studies using this barrier in extraction sockets have demonstrated efficacy^17,18,28,29  comparable to other techniques. As shown in these case reports, this technique can be successfully used with immediate implants. The membranes clinically supported clinical bone formation at the macroscopic level as the peri-implant tissue was hard upon probing and appeared to exclude soft tissue ingrowth. Histologic analysis would be necessary to confirm these findings and should be the subject of future studies.

Although these membranes were left in place for 6 weeks, optimal exposure time is not well understood. Socket healing begins immediately with clot formation, which is then replaced with granulation tissue during the first week. Osteoid begins to appear at the base of the socket around day 7. By day 20, the clot is replaced by connective tissue, and by day 38, at least 2/3 of the socket is filled with trabeculae.⁵  Previous studies have removed the membrane at the 4-week point, at which time the clot is replaced by connective tissue and osteoid formation is taking place. Additionally, the membranes are easy to insert, adapt, and remove without anesthesia.

Although this report is limited in the number of cases and lack of controls, the results and ease of use warrant further research. Animal studies with histologic data would provide valuable insight into socket healing underneath the membranes, and bacterial studies of the inner aspect would validate the true occlusiveness in an intraoral environment. The resorption associated with flap elevation should be also be studied to see if the membranes limited the effects of osteoclastic activity secondary to flap elevation. This, along with controlled clinical human studies comparing this technique to more researched modalities and materials, should be the direction of future research.

The immediate placement of dental implants into extraction sites is a predictable, successful procedure.^1,2  After insertion of the implant, the horizontal distance between the walls of the socket and surface of the implant may require barrier membrane and/or augmentation to achieve bone-implant contact^3,4  and prevent soft tissue ingrowth associated with natural socket healing.⁵  These case reports demonstrate successful clinical use of membranes made of dPTFE without primary closure for this purpose and indicate that well-controlled studies are necessary.

dPTFE

high-density polytetrafluoroethylene

ePTFE

expanded polytetrafluoroethylene

PTFE

polytetrafluoroethylene