CC
A 69-year-old White male presents for evaluation for dental implants. He states, “I am interested in getting implants.”
HPI
The patient was referred by his general dentist for extraction of periodontally involved teeth and evaluation for implant placement. He reports that he has difficulty chewing his food because of discomfort and mobility of several of his posterior teeth.
PMHX/PSHX/medications/allergies/SH/FH
The patient reports hypercholesterolemia, prostatic hypertrophy, gastroesophageal reflux disease (GERD), chronic neck pain, and chronic rhinitis and sinusitis. His current medications include aspirin 81 mg, fenofibrate, alfuzosin, and omeprazole. The past surgical history includes a hernia repair. The patient reports allergies to tramadol and hydrocodone. He also reports a history of cigarette smoking but quit 10 years ago. He denies alcohol and illicit drug use. The family history is negative for heart disease, diabetes, and head and neck malignancy.
Examination
General. The patient is a well-nourished, well-developed 69-year-old White male in no apparent distress.
Vital signs. Blood pressure is 156/87 mm Hg, heart rate is 69 bpm, respiratory rate is 16 breaths per minute, and temperature is 37°C.
Maxillofacial. Normocephalic. The skin is dry and intact, pupils equal, round, and reactive to light and accommodation. There is no scleral icterus. Visual acuity is grossly intact. External auditory canals clear bilaterally. Tympanic membranes are intact, and the nares are patent. Cranial nerves II through XII are grossly intact bilaterally. The neck is supple and without lymphadenopathy.
Intraoral. The mucosa is moist and pink. No ulcers, masses, or discolorations of the oral cavity are noted. Teeth #3, #11 through #15, #19, #20, and #30 are absent. Generalized periodontal disease is noted with root exposure on teeth #2, #4, #18, #21, #28, and #30. A buccal horizontal defect is present at teeth #19, #20, and #30.
Imaging
Panoramic radiograph reveals no pathologic findings of the sinuses, maxilla, temporomandibular joints, or mandible. There is pneumatization of bilateral maxillary sinuses and generalized periodontal disease with periapical radiolucency at teeth #18, #28, and #31.
Labs
No labs are indicated at this time.
Assessment
White male, 69 years old, with a history of hypercholesterolemia, prostatic hypertrophy, GERD, chronic neck pain, and chronic rhinitis and sinusitis presents for an evaluation for dental implant placement after extraction of periodontally involved teeth. The physical examination reveals vertical insufficiency of the right mandibular and bilateral maxillary posterior alveolar ridges in addition to a horizontal alveolar deficiency of the right mandibular posterior alveolar ridge ( Fig. 76.1 ).
Treatment
Alveolar deficiencies of the posterior mandible present unique surgical challenges. Defects must be accurately assessed for the horizontal and vertical deficiencies of bone and the amount of keratinized tissue available to support the final prosthesis. A host of reconstructive techniques and materials must be considered and the most appropriate method selected to maximize the individual patient’s outcome ( Fig. 76.2 ). The success of endosteal implant restorations and prostheses has made augmentation of the posterior mandible a necessary skill for oral and maxillofacial surgeons. The use of titanium mesh, autogenous bone, allogeneic or xenogeneic bone, and inlay bone grafting is discussed later.
Horizontal defects
A horizontal defect is defined as an inadequate buccolingual dimension of bone with an adequate superoinferior dimension. Horizontal defects most commonly occur on the facial aspect of the mandible. Generally, implants 5 mm in diameter are placed in the molar region; this requires 7 to 8 mm of horizontal bone to ensure 1 to 1.5 mm of bone buccal and lingual to the implant.
Block grafts
The autogenous block graft has been widely used for horizontal defects. The harvest site of the cortical bone depends largely on the length of bone required. For smaller defects, harvest from the mandibular symphysis or mandibular ramus allows for easy access with low long-term morbidity. However, temporary V3 paresthesia has been reported in 10% to 50% of symphysis grafts and 0 to 5% of ramus grafts. For larger defects, distant harvest sites of bone are necessary. The calvarial graft, taken from the parietal bone, provides dense cortical bone that is resistant to resorption. Harvesting a split-thickness graft from this region provides an approximately 3-mm-thick segment of bone, and the harvest site has few complications. The ilium may also be used; however, the cortical bone is thinner and less resistant to resorption because of the endochondral origin of the ilium compared with the intramembranous origin of the parietal bone. However, a large amount of bone may be harvested from the iliac crest. The main complications of iliac crest bone grafts include gait disturbances, paresthesia, hematoma or seroma, and fracture of the hip.
The use of block allografts has been presented in case series. Nissen and colleagues placed 29 cancellous block allografts in 21 patients with posterior mandibular atrophy; the graft failure rate was 20.7%, and the implant survival rate in the remaining grafts was 95.2% at 37-month follow-up. However, long-term outcomes for allogeneic block grafts from prospective, randomized clinical trials are lacking. A systematic review by Waasdorp and Reynolds found only nine articles that met inclusion criteria, and eight of the articles were case reports or case series. The authors concluded that although the case reports demonstrated potential for allogeneic block grafts for alveolar ridge augmentation, there is insufficient evidence to establish treatment efficacy with regard to graft stability and long-term implant survival.
Procedure
The defect site is exposed using a crestal incision. The defect is then measured for the size of the graft needed. The appropriate-sized block graft is harvested from the donor site and is contoured to approximate the defect. The facial surface of the defect site is also contoured to allow for maximum surface area contact with the graft. Multiple sites of decortication are created on the defect site with a small round bur to promote neovascularization of the graft. The graft is secured with one or two resorbable or titanium screws. Particulate bone is packed into any gaps, and the site is covered with a resorbable or nonresorbable membrane. Tension-free closure is obtained using a periosteal releasing incision if necessary.
Particulate bone
Particulate bone graft material is available from a wide array of sources, including autografts (from the patient), allografts (from a human donor), xenografts (from an animal donor), and alloplastic material (synthetic material). Autogenous particulate bone may be harvested from intraoral sites, including cortical shaving from the symphysis, ramus, or zygoma, and cancellous bone can be harvested from the ilium or tibia. Autogenous bone is often combined with banked particulate bone; this increases the volume of graft material while maintaining the osteogenic and osteoinductive properties of the autogenous bone. The choice of graft material depends on the amount of particulate bone needed, osteoinductive versus osteoconductive properties, and the desires of the patient. Whether the graft is mineralized or demineralized determines the type of membrane required for graft stabilization. In general, mineralized particulate bone is able to better withstand the forces exerted on the surgical site during healing, requiring only a nonrigid membrane at the time of graft placement. Demineralized bone, however, requires a rigid membrane during the healing phase. Titanium mesh is well suited to protecting demineralized bone and can tolerate exposure to the oral cavity without a significant rate of graft failure. The titanium mesh is contoured and adapted to the alveolar ridge and secured with titanium screws.
Procedure
A crestal or vestibular incision is used to expose the defect. Decortication of the defect is performed using a small round bur. The particulate graft is placed. If a nonrigid membrane is used, the edges are trimmed and tucked underneath the flaps. If a rigid membrane is used, the membrane is contoured, packed with particulate bone, and then secured with screws to prevent movement. Tension-free closure is obtained using a periosteal releasing incision if necessary. The vestibular incision usually allows for tension-free closure without release of the periosteum.
Inlay bone graft
First described by Simion and colleagues in 1992, the alveolar split osteotomy technique for horizontal bone defects and subsequent implant placement has shown predictable results. The surgery is usually performed in a two-stage fashion in the mandible because of the dense cortical buccal plate. At least 3 mm of horizontal width is preferred for a controlled fracture; however, widths as narrow as 2 mm have been reported. The goal of the technique is to produce a vascularized bone flap through controlled fracture of the buccal plate. The gap produced by the fracture at the second stage can then be grafted with block or particulate bone, or implants can be placed along with a particulate graft. A membrane is generally used to protect the graft and implants during healing.
Procedure
The initial surgery requires a full-thickness flap to expose the buccal cortical plate. A crestal incision with releasing incisions away from the planned corticotomy sites is used. Crestal, apical, and two vertical corticotomies are performed and connected to create an outline of the intended bone flap. A piezoelectric drill is often used to preserve bone. The mucosal flap is then sutured. Stage 2 is performed after approximately 4 weeks; with this interval, the periosteal blood supply to the bone is restored, but callus is still present at the corticotomy sites. The crestal incision is made along the crestal corticotomy, with care taken to reflect as little periosteum as possible. Osteotomes are used to gently outfracture the bone flap. The bone graft or implants (or both) can then be placed. Primary closure can be attempted using a periosteal releasing incision, but primary closure is often difficult, requiring the use of a membrane. If implants are not placed, 4 to 6 months of healing is allowed before implant placement.
Vertical defects
Vertical defects of the posterior mandible refer to inadequate height of alveolar bone in relation to the inferior alveolar nerve. Vertical defects can be challenging to treat because of a small surface area of crestal mandibular bone for onlay grafting, difficulty with exposure of the graft because of tension of the soft tissue after augmentation, and resorption of graft material. Techniques described include onlay grafting, particulate bone grafts, inlay grafts, and distraction osteogenesis.
In 2009, Esposito and colleagues performed a Cochrane systematic review of randomized controlled trials (RCTs) for horizontal and vertical ridge augmentation. Of the 13 trials that met the inclusion criteria, 10, enrolling 218 patients, addressed vertical ridge augmentation. Analysis of the trials found that vertical augmentation resulted in a high complication rate (20%–60%) and graft failure rates of 10% to 15%. Interestingly, two split-mouth trials compared alloplastic grafting (anorganic bovine bone and Regenaform, respectively) with autogenous bone grafting (iliac crest and particulate bone) and showed no statistical difference in outcomes. Although both studies had small sample sizes (10 and 5 patients), the reduction in operative time, cost, and patient discomfort certainly justify further investigation. The review also included a meta-analysis of two RCTs examining mandibular ridge augmentation (iliac crest inlay graft and anorganic bovine inlay) versus short implant placement without augmentation. The meta-analysis showed an increased implant failure rate (borderline significance; P = .06) and a statistically significant increase in the complication rate in the augmented group. The additional time, cost (e.g., general anesthesia, hospitalization), and patient discomfort are also important factors. However, the long-term outcomes of short implants in the posterior mandible have not been adequately evaluated to date.
Block grafts
The use of onlay autogenous grafting for vertical augmentation has been widely described in the literature. One of the shortcomings of the onlay graft is resorption of the graft during healing. Studies using intraoral (symphysis, ramus, or both) and posterior iliac crest have reported 17% to 41% resorption of the onlay graft at 4 to 6 months.
Procedure
Autogenous block grafts for vertical augmentation can be harvested in a fashion identical to that previously described. A crestal incision is made, and the block is adapted to the alveolar defect and secured with titanium screws. Gaps are packed with particulate bone, and a membrane is placed. The incision is sutured over the graft after periosteal release for tension-free closure.
Particulate bone
Particulate bone grafting for vertical deficiency has been shown to be effective when used with a rigid membrane or titanium mesh. The use of titanium mesh has been shown to be effective in the reconstruction of alveolar ridge defects regardless of the particulate bone source. The titanium mesh acts as a permanent, rigid barrier that is biocompatible and easily molded to the desired shape. Several studies have demonstrated successful vertical augmentation (maxilla and mandible) using titanium mesh, with average vertical gains of 3.71 to 14 mm and implant success rates in the grafted area of 93% to 100%. Exposure of the titanium mesh during the healing phase is commonly reported, with a rate ranging from 5% to 52%. However, the rates of infection and graft failure remain low compared with other nonresorbable barriers. Watzinger and colleagues demonstrated that the timing of the mesh exposure is critical to the final outcome. If exposure occurred within 4 to 6 weeks of the grafting procedure, graft take was poor. However, if exposure occurred after 4 to 6 weeks, these sites had outcomes similar to those for grafts that did not have exposure. Most areas of late exposure of titanium mesh (after 4–6 weeks) can be managed with local wound care; removal is required only if signs of infection are present.
Procedure
The technique for particulate bone grafting was described previously in the section on particulate bone grafting for horizontal deficiency.
Inlay graft
Inlay grafting, or “sandwich” osteotomy, provides the advantage of having a pedicled segment of alveolar bone overlying the graft material. Felice and colleagues demonstrated significantly less bone resorption of the inlay graft compared with onlay grafting of anterior iliac crest bone, in 20 patients. In another study by Felice, no statistical difference in outcomes was found for inlay grafts with anorganic bovine bone (Geistlich Bio-Oss, Geistlich Pharma North America), compared with iliac crest bone, for vertical augmentation in the posterior mandible. The disadvantages of inlay grafting are the inability to address horizontal defects with the procedure and limitation of the amount of vertical augmentation by the lingual soft tissue pedicle to the mobilized alveolar segment. Additionally, there must be at least 4 mm of bone above the mandibular canal to preserve viability of the mobilized segment while avoiding damage to the nerve.
Procedure
A vestibular incision is made, and a subperiosteal flap is raised to expose the buccal surface of the alveolar ridge. The crestal and lingual tissue is not reflected. A reciprocating saw or piezoelectric handpiece is used to create the horizontal and two vertical oblique osteotomies, with care taken not to damage the lingual tissue. The horizontal osteotomy should be at least 2 mm superior to the mandibular canal, and the alveolar segment should ideally be at least 3 mm tall to tolerate the placement of titanium screws without fracturing. The bone graft is placed, and the transported and basal mandibular segments are plated with titanium miniplates and screws, thus stabilizing the graft. Gaps are filled with particulate bone, and the vestibular incision is closed. A healing period of 3 to 4 months is allowed before the hardware is removed and implants are placed.
Discussion
With the growing popularity of implant restorations, mandibular ridge augmentation has become a necessary skill for oral and maxillofacial surgeons. The posterior mandible can be a particularly difficult area to successfully augment because of the unique anatomy of the area. A thorough understanding of surgical techniques and bone grafting options is vital to maximizing the final functional and esthetic outcomes for the patient ( Fig. 76.3 ).
