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Dental Implantology Update: June 1998
1/23/2004 |
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The Use of Ramus Grafts for Ridge Augmentation Bone augmentation techniques should be determined by the ideal implant position for prosthetic support. For onlay ridge augmentation, research and clinical experience have shown that alloplastic materials, such as resorbable hydroxyapatite, and allografts, such as demineralized freeze-dried bone, yield poor results. For the repair of larger defects, guided bone regeneration techniques require expensive membranes and long healing times. The use of these membranes often results in poorer-quality hard tissue. According to Craig Misch, DDS, MDS, mandibular cortical bone grafts provide very predictable increases in bone volume with a short healing time, and yield a highly dense osseous architecture for implant placement. "Using autogenous bone obviously decreases the overhead costs of grafting supplies. These procedures can be performed as outpatient surgery in the office," Misch says. He is resident in oral and maxillofacial surgery at St. Francis Medical Center in Pittsburgh, and clinical assistant professor, division of periodontics at University of Pittsburgh School of Dental Medicine. Using the ramus as a donor site, a rectangular piece of bone that is approximately 4 mm thick can be obtained. "This is ideal for use as a veneer graft for onlay width augmentation," Misch says. The size of the graft may extend beyond 3 cm in length, but it is usually no larger than approximately 1 cm in height. Indications for Using Ramus Grafts The dimensions of a ramus graft are well-suited for increasing the bone width from one to three tooth sites. The thin posterior mandible is a perfect site for using ramus grafts because the donor and the recipient sites are within the same field. The ramus graft is useful for simultaneous bone harvesting with third molar removal in younger patients with congenitally missing teeth. In addition, this graft can be used as a source for sinus grafting and lateral grafting of the posterior maxilla. When combined with other intraoral donor sites, such as the tuberosity and symphysis, the need for iliac crest grafting can sometimes be eliminated. According to Misch, it is not uncommon for symphysis graft patients to complain of some numbness of the chin or gingival and altered sensation of the lower anterior teeth. Although these symptoms are usually temporary, they can be bothersome to the patient. "Use of the ramus graft procedure has not resulted in postoperative sensory changes of the buccal soft tissues or the molar teeth," Misch says. In addition, patient complaints of pain and soreness after surgery are usually less severe after ramus surgery. Many patients express concern regarding the removal of bone from the chin because of fear of a change in their appearance. "For this reason, I usually harvest bone from the ramus if the defect dimensions can be managed with the size of this graft," Misch says. Harvest of a bilateral ramus graft is ideal for augmenting the thinner edentulous maxilla in preparation for an implant over-denture. However, if the defect is larger and a thick graft is required for proper restoration of the alveolus, the symphysis is the site of choice. Diagnostic wax-up of the ideal tooth position is helpful for determining graft dimension requirements. "I also like the chin for harvesting several bone cores for sinus grafting," Misch says. "Softer trabecular bone from the tuberosity is usually limited to sockets, sinus grafting, or smaller dehiscent-type defects." Dental Implantology Update has previously covered Misch's discussion of techniques for harvesting bone from the ramus (see DIU, April 1998, p. 31). To expand on this, Misch provides some suggestions for facilitating bone removal from this area. "Access to the ramus region can be more challenging than the symphysis," he says. It is important to extend the initial incision high enough up the ascending ramus. A good guideline is the height of the occlusal plane. Blunt reflection superiorly will prevent exposure of the buccal fat pad and limit muscle bleeding or damage to the buccal artery. It is also necessary to extend the flap reflection well beyond the local area of bone harvest. "I reflect to the inferior border of the mandible in the posterior region," he says. Use Straight Handpiece for Bone Cuts Flap reflection is facilitated by a modified notched ramus retractor (Misch Ramus Retractor, ACE Surgical Supply, Brockton, MA), which rests on the external oblique ridge at the base of the coronoid process. According to Misch, it is imperative that a straight handpiece be used to make the bone cuts. A Lindemann or fissure bur is used to make the cuts through the cortex. A round diamond or carbide bur is rested against the bone to make the inferior shallow cut that parallels the external oblique ridge. The cortical graft will usually split off quite easily. If difficulty is encountered during harvesting of the graft, the cuts should be refined, with attention to the corners of the graft. The use of careful techniques can eliminate injury to the inferior alveolar nerve. "Because the greatest amount of cancellous bone between the canal and the cortex is found in the first and second molar region, the anterior vertical cut should always be made in this area," Misch says. The bone chisel should never be directed medially during splitting or prying of the graft. Retraction of the masseter muscle may cause some trismus. According to Misch, after harvesting of large cortical blocks, patients should be advised to avoid contact sports because the integrity of the mandible could be compromised. Before placement of a ramus graft, the cortex of the recipient site should be perforated with a round bur to enhance revascularization. The graft should have intimate contact with the host bone. The main complication associated with onlay bone grafts is wound dehiscence with graft exposure. "Tension-free wound closure is imperative," Misch says, "and this point cannot be compromised." The recipient site flap should be broad-based and well-reflected beyond the borders of the defect. An incision just through the periosteum at the base of the flap will usually allow for tissue coverage, he says. Nonresorbable suture, such as polytetrafluoroethylene (W.L. Gore & Associates, Flagstaff, AZ) can be used to prevent incision line opening with loss of the tensile strength of the suture material. Graft Placement For fixation of a block graft, Misch prefers to use titanium alloy screws that are at least 1.5 mm in diameter (OsteoMed Corp.,Dallas, TX). The bone block should be fixated using a lag screw technique. With this technique, the hole that is drilled through the graft is larger than the screw threads. The bur that is used to drill the underlying host bone should be smaller than the diameter of the screw. When the head of the screw is tightened against the block, the graft is compressed onto the host bone surface. The graft must remain immobile during healing. According to Misch, several manufacturers have claimed that resorption can be reduced by covering the bone graft with a barrier membrane. However, he says barrier membranes are not necessary with mandibular block bone grafts, which already show minimal resorption (0% to 25%). Several studies have been performed in which membranes have not been used with intraoral cortical block grafts, and none have reported the inability to place implants in the grafted sites. "The use of membranes may also contribute to complications, such as wound dehiscence and graft infection," Misch says. Although barrier membranes may have some indications when particulate or cancellous bone is used, their use with block grafts is questionable and their additional cost is unjustified, he says. Healing Time Because membranous grafts have been shown to revascularize earlier, a shortened healing time has been applied to grafts harvested from the mandible. Misch says the healing time required for ramus bone grafts depends more on the recipient bone. The cortex is porous in the maxilla, and excellent graft incorporation has been found at four months. In the mandible, the cortex is denser; therefore, a slightly longer healing time is given to provide for a solid union. "Because implant placement is often at the junction between the host and bone-graft interface, care should be taken during drilling and threading of the osteotomy," he says. Contact: Craig Misch, DDS, MDS, 1082 Bower Hill Road, Pittsburgh, PA 15243. Telephone: (412) 941-4145. Related Readings Misch CM, Misch CE. The repair of localized severe ridge defects for implant
placement using mandibular bone grafts. Impant Dentistry 1995; 4:261-267.
EDITOR Arun K. Garg, DMD EDITORIAL ADVISORS Editor Emeritus: Morton L. Perel, DDS, MScD Charles A. Babbush, DDS, MScD Thomas J. Balshi, DDS, FACP Charles E. English, DDS Paul A. Fugazzotto, DDS Jack A. Hahn, DDS Kenneth W.M. Judy, DDS Jack T. Krauser, DMD Robert E. Marx, DDS Carl E. Misch, DDS, MDS Leonard B. Schulman, DMD, MS Daniel Y. Sullivan, DDS Special
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