Introduction and principles
Often the implant surgeon is faced with inadequate volume of bone to place a suitably sized implant in the correct place to allow a functional and aesthetic restoration.
There are various reasons why bone volume may not be sufficient:-
- Post-extraction resorption.
Along with bone growth into the socket there is also resorption of the alveolar ridge bucco-lingually and apico-coronally. Studies have shown that this can be 3-4 mm in both planes within 6 months of anterior tooth extraction.
- Periodontal bone loss
Patients suffering from this disease may lose as much as 15mm of vertical bone height around their teeth before they are lost.
- Trauma, neoplasms, and congenital deficiencies may contribute to lack of alveolar bone volume.
It may therefore be necessary to reconstruct a deficient ridge for bio-mechanical or aesthetic reasons. Ridge augmentation can be achieved through guided tissue regeneration, osteogenic distraction, or onlay bone grafts. This assignment deals with onlay bone grafts harvested from intraoral sites. The principles of bone-graft surgery follow those of fracture healing. If a bone block is immobilized in close contact with the bone of the recipient site, and provided with a blood supply; the graft, like a fracture, will heal in three phases, as detailed by Carl Misch in his review of graft materials1:- ‘During the first phase, the surviving cells are responsible for the formation of osteoid by osteogenesis. They are most active within the first four weeks after grafting. Phase two is an osteoinduction phase and starts 2 weeks after grafting and peaks at 6 weeks to 6 months, then progressively decreases. The blood vessels from the host bone and connective tissue invade the graft. Bone cells from the host tissue follow the blood vessels and remodel the graft by a coupled resorption and formation phenomena. The bone morphogenic protein is derived from the mineral matrix of the grafted bone resorbed by osteoclasts and acts as a mediator for the second phase. The BMP and other proteins must be released prior to the osteoinduction cycle. Phase three occurs as the inorganic component of the bone acts as a matrix and source of minerals during replacement of the matrix by the surrounding bone and resembles an osteoconductive mode of action.’
Intraoral Donor Sites and their selection criteria
The usual intraoral donor sites for bone grafts are the mandibular symphysis or the ramus. Other sites that have been used are the maxillary tuberosity, mandibular tori, and the nasal spine for small amounts of bone scrapings. At least three factors influence which site is used:-
- Ease of surgical access
- The shape of the graft required.
Sethi and Kaus2 show that a graft from the ramus is morphologically suited for repairing combined horizontal and vertical defects.
- The likelihood of post-operative complications.
Many studies including Silva et al. reviewing 104 consecutive patients3, and Joshi4 in a prospective study of 27 consecutive patients with consistent and comprehensive data collection, report that complications, (usually sensory deficits), are more common in the symphysis area.
Before treatment is initiated, comprehensive treatment planning is essential. An estimation of the amount of bone graft required, suitable donor site, and evaluation of the flap required to achieve tension-free closure over the graft, can then be made. Over-contouring should be planned to compensate for re-modelling during revascularization. With labial and/or vertical deficiencies in the maxilla, a remote palatal incision is recommmended by, amongst others, Sethi and Kaus2 in a prospective study of 60 graft-patients, to create a buccal flap. In the mandible a mid-crestal incision is safest, with great care taken to avoid vital structures when making relieving incisions.
Surgery is started at the recipient site to ascertain the exact size and shape of graft required. Once the recipient site has been prepared bone is harvested from the donor site, and transferred in the shortest time possible. Fine fissure burs (and a round bur on the lateral portion of the ramus), or a piezo saw with copious irrigation are used to cut and free the graft. Care must be taken to avoid the root apices of incisors in the symphysis area, and the inferior dental nerve in the ramus. Any further shaping of the graft to give maximum contact with the recipient site is made using a diamond disc or a piezo saw. The graft then secured to the donor site using titanium bone screws. Any small spaces at the edge of the graft can be filled with autogenous bone chips.
If tension free closure of the flap cannot be made over the graft, periosteal relieving incisions will be necessary. Great care must be taken with these in the mandible as vital structures lie just above the periosteum. The flap is adequately sutured using interrupted sutures in the maxilla, and horizontal mattress sutures in the mandible.
The donor site is closed using vertical mattress sutures in the symphysis, or continuous sutures in the ramus. Healing takes 3-6 months and is monitored radiographically.
In short the surgical principles that apply to bone grafts from intraoral donor sites are:-
- Maximum contact between the graft and the host bone to enhance bone healing.
- Tension free closure of flaps over grafts to maintain blood supply.
Ridge-splitting cannot be used where the cortical plates are fused2, or where vertical deficiencies exist. Osteogenic distraction has reported high success rates, but is complicated, especially in the aesthetic zone.
Currently the use of an autogenous bone graft is considered to be the best way to reconstruct a deficient ridge. Deficiencies of up to 6mm in width and 4mm in height can be repaired using grafts from intraoral donor sites2.
Von Arx et al, in a small study following 27 implants for up to three years after functional loading5 concluded that ‘loaded dental implants which have been inserted into an augmented alveolar ridge using autogenous bone grafts and a micro titanium mesh for graft stabilisation, demonstrate clinical and radiographic findings similar to those of implants placed into a pristine ridge.
- Misch CE, Dietsh F. Bone-Grafting Materials in Dentistry. Implant Dent 1993;2:158-167
- Sethi A, Kaus T. Ridge Augmentation using Mandibular Block Bone Grafts: Preliminary results of an Ongoing Prospective Study. Int J Oral Maxillofac Implants. 2001;16:378-88
- Silva FM, Cortez AL, Moreira RW, Mazzonetto R. Complications of intraoral donor sites for bone-grafting prior to implant placement. Implant Dent. 2006 Dec; 15(4):420-6.
- Joshi A. An investigation of post-operative morbidity following chin graft surgery. Br Dent J 2004;196:215-218.
- von Arx T, Wallkamm B, Hardt N. Localised ridge augmentation using a micro titanium mesh: a report on 27 implants followed from 1-3 years after functional loading. Clin Oral Implants Res. 1998;9:123-30.