Inadequate Bone

 The maxillary posterior teeth are most often the first to be lost in chronic periodontal disease.  Not only does periodontal disease reduce the maxillary bone height, but, upon the loss of the maxillary posteriors, the maxillary sinus undergoes a pneumatization.  This reduces the alveolar ridge height beyond the alveolar resorption that may occur during extraction site repair.  In addition, we see cases of patients who have lost ridge width and height wearing removable appliances they now wish to replace.  This makes the maxillary posterior a difficult area to sustain and increase alveolar bone support for implant care.  This newsletter discusses when and how bone mass can be increased in the maxillary posterior segments. 

 

    The three problems faced by the clincian preparing for maxillary implants are the pneumatized sinus, the loss of alveolar ridge height in the maxilla and loss of buccolingual width in the maxilla.  Several procedures are available to increase bone in this maxillary posterior segment.  They include vertical ridge augmentation for height increases of the maxillary alveolus, lateral ridge augmentation and ridge splitting for maxillary width problems, and lateral window sinus grafting and up-fracture of the sinus floor for increasing bone volume at the sinus-alveolus interface.  A primary question is how to determine what alveolar increases may be necessary to complete a fixed treatment regimen replacing lost posteriors in the maxilla.

 

    The most difficult of the procedures mentioned above has to be vertical ridge augmentation.  Vertical augmentation is desirable when the space between the upper ridge and the lower teeth has enlarged at the expense of the alveolar height in the maxilla.  This spacing mandates very large pontics to contact the alveolar ridge soft tissues and is not resolved by sinus grafting, although sinus grafting may raise the sinus floor adequately to place implants.  Vertical augmentation usually requires space making with reinforced membranes and osteoinductive grafting materials.  Vertical augmentation supplemented with other techniques can produce successful cases.

 

    When there is adequate height of the residual maxilla, 8-10 millimeters of bone between the sinus and the crest of the ridge but inadequate  buccolingual width, ridge splitting and/or lateral augmentation are options.  Lateral ridge augmentation is most commonly used with isolated ridge concavities, or with ridge deficiencies that would mandate the implant be placed too far lingually to occlude in a cusp-fossa relationship with the lower teeth.  When the ridge width is 2-3mm too narrow but well formed the ridge splitting technique is an excellent method which allows the implants to be placed immediately in the channel formed during the splitting process.  Osseous grafts can be used to fill the residual portions of the channel following implant placement.  The accompanying clinical series shows the combination of ridge splitting with upfracture of the sinus floor to produce both height and width adequate for the implant placement and retention.  Often, split thickness flaps initiated on the lingual side of the ridge crest are used to ensure that soft tissues cover the bone altering procedures post-surgically.  Up-fracturing can be best employed when there is 5-8mm of bone between the sinus floor and the crest of the residual maxillary ridge.  An increase of 3mm of bone height is routine for this process, but larger increase are less predictable.  Many clinicians up-fracture the sinus by preparing an osteotomy to within 1-2mm of the sinus floor and use an osteotome to complete the fracturing process.  They then place graft material in the prepared up-fractured osteotomy and compress the material into the space around the uplifted sinus membrane.  Implants can be placed immediately if enough cortical plate is present on the residual maxillary ridge to stabilize the implant.  Clinical observation and animal research indicates small tears in the Schneiderian membrane lining the sinus repair without consequence in this technique.  This method has less postoperative swelling and discomfort than the more traditional lateral window sinus augmentation.  While only the area immediately adjacent to the implants will generate bone, this does not seem to adversely affect implant stability or function.  In fact, pneumatization of the sinus can be seen to recur over several years following the implant process, but does not appear to affect the implant function or stability.

 

    When the floor of the sinus is within 5mm of the alveolar ridge crest, lateral window sinus elevation techniques are indicated.  The accompanying illustration shows a lateral wall sinus lifting procedure.  The sinus is located via radiographs and an entry window is prepared, generally somewhere between the maxillary first bicuspid and the first molar region.  A window is prepared by cutting a channel into the buccal bone until it is paper-thin. The eggshell of bone is fractured inward and upward to produce a slight separation of the membrane from the bone at one end of the sinus cavity.  A broad, blunt instrument is used to separate the sinus lining from the adjoining bone being especially careful to extend the lifting of the membrane unto the septum, which may separate the sinus into compartments. The sinus membrane must be lifted at its lateral extent in order to prevent immediate relapse of the sinus cavity into the grafted area.  The lifted sinus cavity is filled with a bone substitute.  When adequate cortical bone exists on the maxillary ridge, some clinicians place immediate implants into the grafts.

 

    Like other clinical processes, the success rate of ridge and sinus augmentation continues to improve while technical advances have reduced the discomfort associated with this process.  We hope this explanation of the augmentation process for maxillary posterior implants helps you in evaluating, making decisions and explaining implant procedures to your patients.