As dentists one of the most disheartening situations we see is the patient who loses their posterior teeth early in adult life and, as a result of posterior forces on a removable appliance, experiences extensive ridge resorption. Equally concerning is the loss of ridge width which comes when thin labial plates lost during extraction or narrowed by lack of function. Patients for whom removable appliances were considered the only alternative often failed to wear the appliances. During the 1970's the dental profession searched to resolve this process with blade implants, sub-periosteal implants, ramus frames, rib grafts and hip marrow transplants. All of these processes involved extensive surgical interventions with variable results. During the mid-70's and early 80's endosseous implants became very predictable but needed adequate host bone for support of the root form of these implants. Minimum width and height requirements were 5mm of buccolingual width and 8-10mm of height coronal to the mandibular canal or maxillary sinus.
Two events brought the process of ridge reconstruction into a viable alternative for mainstream dentistry. First, researchers began to apply compartmentalization and isolation principles to the treatment of periodontal and intraoral defects. Karring, Nyman and Lindhe, as well as others, used isolation of the bone and periodontal ligament from the overlying connective tissues to encourage new bone and ligament formation in periodontal defects. Actually, Murray, Holden and Roachlau had established the ability of bone to repair a bone cavity if the soft tissues were excluded by a non-porous membrane. This study was published in the medical literature over twenty years earlier, in 1957.
The second event was the development of space making abilities beneath membranes allowing bone growth inside a surgically closed compartment. The problems in periodontal defect repair have to do with the so far limited ability of the periodontal ligament tissues to move coronally along the root surface. Complete closure of the soft tissues around the graft area increases dramatically the restoration of alveolar height. Of additional benefit is having materials which encourage the formation of new bone, providing a scaffold and mineral for synthesis of bone.
During the past twelve years the prime regenerative material for periodontal defects has been Gore-Tex, as synthetic fluoroethylene material, which has the ability to exclude cell lines originating in connective tissue from the bone defect. It was not capable of making a space in a ridge resorbed by periodontal disease or pressure loading. In addition, materials placed beneath membranes on a flat ridge would slump and condense so bone height increases were minimal. While membranes and grafting could fill voids and ridge defects, they lacked the ability to sustain space for adequate time to allow osseous invasion.
On two separate tracks for repairing ridge defects, investigators developed titanium reinforced membranes and began using intraoral donors of cancellous and cortical bone, fixed to the remaining alveolus with titanium screws. Donor sites were the mandibular symphysis and the lateral mandibular ramus. With titanium reinforced membranes the membrane is tacked to the alveolus and shaped to create a lateral and coronal space above the existing bone. The existing bone cortex is decorticated to allow blood cells and medullary cells to fill the void. The space is grafted with either autogenous bone or a substitute material and the membrane stabilized by pin fixation on either side of the existing mandible or maxilla. (Most often vertical augmentation is attempted in the mandible and sinus grafting in the maxilla.) Bone formation with the titanium reinforced membrane model is encouraged by the totally passive primary closure of the soft tissues and non-loading during repair. Repair takes six to nine months and, according to Nevins et al, the quality of bone in the graft site most depends on the quality of the host bone. But the success of implants doesn't seem to vary whether the graft contains autogenous or allograft derived graft material. In implant to bone contact studies it has been shown that allogenic grafted sites have 56.4% bone to implant contact while autogenous grafted sites have 63.2% bone to implant contact. In either of these methods a 97.5% success rate was found for the subsequently placed implants.
In 1998, Tinti placed 48 implants with 2-7mm of the implant protruding above the bone. Titanium membranes covered the implants and autogenous bone chips were used to fill the created space. When the membranes were not exposed coverage of the implants with vital bone was always noted. Three of twenty-two membranes were exposed prematurely and removed, but all others were retained for twelve months. Tinti considered the "break point" for easy cases to be three millimeters of coronal bone growth.
Fugazzotto completed 302 ridge augmentation procedures using Gore-Tex with either DFDBA, FDBA, Bio-Oss (bovine bone skeleton) or tricalcium phosphate plus freeze-dried bone. All the synthetics had some drawbacks but 11 of the 12 vertical augmentations were successful. The twelfth failed due to membrane exposure during initial healing. Fugazzotto discontinued the use of tricalcium phosphate as a graft expander because its resorption and replacement by host bone has been so variable. He also felt that freeze-dried bone allograft (FDBA) was un predictable in its resorption as well. DFDBA had the disadvantage of "slumping" which reduced the filled space beneath the membrane. As a result, Fugazzotto selects Bio-Oss (bovine bone skeleton without organic material) as a primary graft material. It is not bone inductive but rather bone conductive.
When Carmagnola et al studied Bio-Oss for ridge augmentation they found the use of a fibrin sealer (Tisseel) to stabilize the graft resulted in separation of the graft from host bone by a fibrous capsule which prevented the integrations of the graft with the host bone. They emphasized that graft stability and growth of new blood vessels into the graft are essential to the formation of bone in the grafted area.
More recently, investigator-clinicians have worked in the development of ridge augmentation protocols, materials that reduce the need to remove membranes at 6-9 months post-augmentation, and utilizing graft materials which are readily available.
Smukler has reported DFDBA with overlying membranes does become replaced and encourages new bone formation. At nine weeks after ridge augmentation he took cores while creating osteotomy sites for implants and found the volume of bone to be 55%, a near normal volume for bone at this date of maturation.
DFDBA has become a favorite of commercial preparations due to its availability. Manufacturers have come up with unique materials processes to stabilize the graft while sustaining its ability to encourage replacement by host bone. Two products are now available in moldable and/or sheet forms. Grafton (Osteotech) is a demineralized bone matrix which is produced by milling oblong fibers from the bone prior to demineralization. After demineralization the bone is treated with glycerol to make it moldable or formed into sheets. The sheets can be onlayed to existing bone with putty being used to fill any voids. The glycerol is water soluble which causes the material to swell and allows host blood vessel invasion.
The second material, manufactured by Regeneration Technologies, Inc. (RTI) is named according to its function. Regenafil is an injectable paste of DFDBA in a gelatin base. Regenaform is Regenafil to which cortical and cancellous chips have been added to increase space maintaining qualities. Both of these materials are heated in a water bath to a few degrees above body temperature where they become moldable. After placement they stiffen as the material returns to body temperature.
In both of these materials, testing is performed to determine bone induction capabilities. Grafton is tested in lot batches while RTI tests each donor for osteoconductive capability. Both materials have been used successfully without membranes in case based studies. In addition, Simion and co-workers compared bone regeneration with resorbable and non-resorbable membranes and autogenous grafts around implant fenestrations and dehiscences. They report 10% less bone fill with resorbable membranes, a level which was not statistically significant.
The use of these newer materials is making posterior ridge augmentation a viable option in your armamentarium for improving posterior tooth replacement, restoring edentulous patients who find removable appliances and crowning unrestored teeth less desirable. We look forward to discussing these options with your patients and welcome the opportunity of working with you to improve your patients' dental status.