Managing Ridge Resorption After Tooth Extraction Using Partial Extraction Therapy

Maintenance of the height and width of the facial or buccal alveolar bone wall and, subsequently, all of the peri-implant tissues is critical for successful long-term esthetic outcomes in implant dentistry. A “critical thickness” of 2 mm of the remaining facial bone is recommended to reduce the incidence and amount of facial bone loss¹; however, multiple citations in the literature have demonstrated that the facial bone wall of anterior teeth and premolar teeth is often <1 mm in thickness.^2-4 Loss of a tooth will result in severance of the periodontal ligament (PDL), resulting in loss of blood supply to the alveolar bundle bone. Further, “buccal plate casualties” are prevalent even when experienced clinicians extract teeth where this facial bone is thin.⁵ Loss of the buccal or facial plate and the resulting loss of blood supply will likely lead to resorption of the thin buccal or facial bone that was previously juxtaposed with the tooth, potentially leaving a less-than-desirable site for implant therapy and increasing the risk of further bone resorption long term.^6-8

Partial retention of the tooth root, specifically the aspect of the root that is adjacent to the facial bone, will allow for the maintenance of the PDL that is attached to the facial/buccal plate and minimize the risk of resorption of the facial/buccal bone and peri-implant tissues.⁹ The utilization of partial extraction therapies (PETs) can reduce the risk of facio-lingual collapse after tooth loss regardless of the timing of implant placement, whether immediate, delayed, or delayed-immediate, and help enable pontic site development or ridge preservation.¹⁰

A 34-year-old male patient presented for comprehensive evaluation and treatment. His medical history was non-contributory, consisting simply of a history of childhood asthma and no contraindications for dental treatment. His dental history revealed only routine dental care. The patient's chief concern was a “cracked tooth” and “swollen” tissue (Figure 1). His maxillary left central incisor had fractured subsequent to root canal therapy and an attempt at internal whitening.

The patient stated that he noticed some mobility of his tooth shortly after the internal whitening procedure was performed. He was happy with the condition and esthetics of his teeth otherwise and desired only to have the fractured tooth restored. He stated that he hadn't noticed any changes in his teeth in the past 5 years, noted no joint sounds or soreness, was unaware of any squeezing or clenching to fit his teeth together, and had no difficulty eating hard, sticky, or chewy foods except in the anterior segment where the tooth was fractured.

Periodontal: Clinical and radiographic examination revealed AAP type II classification, slight bleeding on probing and flossing, probing depths ≤3 mm, bone heights within 2 mm of the cementoenamel junction (CEJ), and no appreciable mobility. Several areas of mild recession were noted facially with no relative interproximal bone loss, indicating an anatomical liability as opposed to periodontal disease (Figure 1).

Risk: Low. Although the periodontal risk was low, this type of anatomic liability indicates a thin facial plate that increases the risk of alveolar resorption of the peri-implant tissues following extraction.

Prognosis: Good

Biomechanical: The patient had only a few small occlusal restorations in his past, one root canal treatment on tooth No. 9, and no active carious lesions. The recently received root canal therapy on tooth No. 9 was due to spontaneous pain. The lingual access had then been used for internal whitening. Upon examination, a horizontal fracture was noted with mobility of the coronal segment of tooth No. 9 (Figure 2). The overall biomechanical risk was low with the lone exception of the nonrestorable tooth No. 9, which effectively drove the overall pretreatment risk to moderate.

Risk: Moderate

Prognosis: Fair

Functional: The patient had no awareness that his teeth had changed in the past 5 years and reported no awareness of squeezing or clenching and no difficulty chewing any foods. Joint and muscle examination revealed no joint noises or deviations, a maximum opening of 53 mm, load test negative, and immobilization test negative.

Risk: Low

Prognosis: Good

Dentofacial: Pleased with his smile at presentation, the patient had medium lip dynamics, normal scallop form, and slight horizontal asymmetry. He was not concerned with crowding of the mandibular anterior teeth or the asymmetry of the maxillary incisal edge positions. He desired no correction other than the left central incisor, stating that he believed this tooth appeared slightly longer than it did before it fractured. In full smile the patient displayed the full length of the maxillary anterior teeth and also some gingival tissue apical to the teeth (Figure 3). His only concern was with the discrepancy of tooth No. 9 and wanted to have this tooth restored to match the adjacent central incisor.

Risk: High

Prognosis: Poor

There is a high incidence of ridge deformity after tooth loss, particularly in the anterior region of the mouth.¹¹ This poses a challenge for the clinician when treating a high-risk dentofacial patient as the presence of any defect may be displayed in full smile and may risk compromise to the esthetic outcome. Radiographic evidence from cone-beam computed tomography (CBCT) has shown nearly 80% of anterior teeth and 40% of premolars exhibit a thin facial wall (<1 mm) bucco-palatally, and many sites have a bone wall thinner than 0.5 mm.³ Figure 4 is a CBCT scan of the nonrestorable tooth No. 9 in this case, showing the presenting thin facial plate and facially prominent root. Figure 5 shows an example of a thin facial plate from a different case after an anterior tooth extraction.

Further reports demonstrate that bone loss, vertically and horizontally, is increased post-extraction when the facial marginal bone during implant placement is thinner than 2 mm.¹ Resorption of the post-extraction socket is inevitable and may result in a significant facial defect that could pose considerable difficulties in achieving a successful esthetic outcome.

When the facial alveolar bone is <2 mm in thickness, partial extraction of the tooth root can help preserve thin facial bone by leaving a portion of the root connected to the facial bone via the PDL. This approach keeps the PDL vasculature in place and better preserves the ridge form by maintaining the bundle bone–PDL apparatus.¹²

The primary risk factors for this patient involved the nonrestorable left central incisor and the full display of teeth and surrounding structures in his full smile. Any treatment would be in full display, carrying risk of an unesthetic outcome. The treatment options presented and the associated risks were as follows:

Maintenance and restoration of the central incisor. Crown-lengthening surgery would be used to achieve an appropriate amount of ferrule, post-and-core build-up, and crown to maintain and restore tooth No. 9. This treatment would increase the biomechanical risk of this tooth leaving it structurally compromised and at risk for root fracture. Reduced height of facial and proximal bone would compromise the dentofacial esthetics of this tooth and the adjacent teeth.

Extraction of central incisor and placement of either a three-unit fixed partial denture (FPD) or two-unit cantilever FPD. This treatment would increase the biomechanical risk of the adjacent abutment teeth and pose a risk for anterior ridge deformity.

Extraction of central incisor, followed by ridge preservation grafting, implant placement, and an implant-supported single crown. The thin facial bone of the presenting anatomy would risk a facial plate casualty and potential bucco-palatal collapse, for short term or long term, whether the implant was placed as immediate, delayed-immediate, or delayed.

Extraction of central incisor and placement of a removable partial denture. This treatment would pose a dentofacial risk and a risk for anterior ridge deformity.

Partial extraction therapies, ridge preservation grafting, implant placement, and an implant-supported single crown. This treatment would reduce the risk of anterior ridge deformity without increasing the dentofacial or biomechanical risks, because the adjacent teeth would remain unaltered.

The patient chose to restore the affected tooth No. 9 with a fixed restorative option, with the intention of achieving an esthetic result without increasing the risk to any adjacent teeth.

The initial phase of treatment was to perform PET for tooth No. 9. After appropriate local anesthesia was administered the tooth was decoronated (Figure 6), which consisted only of removing the fractured clinical crown. If the tooth had not already been fractured, the clinical crown of the nonrestorable tooth would be decoronated with a bur to the gingival level, taking care not to damage the gingiva. The remaining root was then carefully sectioned mesio-distally from the coronal aspect, and the sectioning was continued longitudinally to the apex using a long shank carbide bur with copious irrigation, taking care to not remove any proximal bone, contact the adjacent teeth, or damage the surrounding gingiva (Figure 7). Care was also taken to remain within the bony housing on the facial aspect beyond the apex of the tooth utilizing 6.5X magnification. The root was segmented into halves, and the palatal portion was elevated with a periotome and proximator and extracted with micro forceps.

All of the contents of the canal were removed, and the remaining facial portion of the root, hereafter referred to as the shield or pontic shield, was thinned to about 1 mm thickness facio-lingually or about half the thickness from the root canal space to the labial aspect.⁹ The height of the shield was reduced to the level of the osseous crest and the socket was thoroughly curetted and irrigated with sterile saline. In the literature on PET technique presented by Gluckman et al,^9,10 the recommendation is to leave the shield 1 mm above the bony crest. It is this author's opinion that routinely leaving the shield 1 mm coronal to the bony crest will increase the risk of exposure of the shield postoperatively, an example of which is shown from a different case in Figure 8. The author's preference is to trim the height of the shield to the equicrestal position, as shown for example purposes from another case in Figure 9.

After the shield was prepared, given the presence of the active infection in the coronal aspect of the tooth, the decision was made to utilize the pontic-shield protocol and perform a ridge preservation graft rather than risk a complication with immediate implant placement. The site was provisionalized with an interim removable partial denture during the initial healing period. After 3 months, the site was checked for adequate healing and prepared for implant placement (Figure 10).

Given a clinical scenario where either no infection is present or any infection and debris can be thoroughly removed with curettage and irrigation, an osteotomy may be prepared and an immediate implant placed palatally to the shield, an example of which is shown from another case in Figure 11. The recommendation of this author is to leave a space between the implant and the shield to allow for grafting of the facial gap and the formation of new bone. Literature reports have shown new bone formation in this gap.¹³

Adequate anesthesia was delivered and a tissue punch was employed to remove a minimal amount of tissue and expose the bony crest and allow for the osteotomy. The osteotomy was performed with sterile saline and osteotomy drills palatal to the shield. The implant was placed 3 mm apical to the proposed CEJ, palatal to and 1 mm apical to the pontic shield (Figure 12). A screw-retained temporary crown was fabricated on a temporary abutment and placed to shape the peri-implant tissues. At this time, it was evident that the pontic shield had maintained the bony and gingival tissues and a ridge deformity had been prevented.

After 3 months, an open-tray impression was made with a customized impression pick-up and delivered to the laboratory for fabrication of the final abutment and crown (Figure 13). Following laboratory fabrication of the custom abutment and crown, the final restoration was delivered. Figure 14 shows the final restoration at the immediate delivery appointment. Figure 15 depicts the successful restoration at the 5-year follow-up.

An excellent esthetic outcome was achieved in this case by managing a challenging anatomic presentation using PET. The patient's biomechanical and esthetic risk was lowered without increasing functional or periodontal risk. Common findings in implant dentistry, particularly in the anterior region of the mouth, are the presence of a facially prominent root and thin alveolar facial/buccal bone.^2-5 Loss of a tooth in this area poses a significant challenge for the restoring clinician, particularly with a high-risk dentofacial patient.

In the author's opinion and clinical experience, PETs provide a viable treatment modality option and a highly conservative strategy to manage resorption of bone resulting from tooth loss, minimize the need for further hard- and soft-tissue augmentation, and reduce the risk of long-term peri-implant tissue recession, thus maximizing functional and esthetic success. A well-maintained shield also effectively functions as a barrier membrane and scaffold to support new bone formation either around the implant or for ridge preservation. Further long-term studies, clinical outcomes, and post-procedure histology are needed to support the long-term success of this treatment modality.

Jeff H. Bynum, DDS
Private Practice, Valrico, Florida