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.
