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AN OVERVIEW OF IMPLANTS A. INTRODUCTION What I hope to do with this handout, is to introduce you to the tangle of implant dentistry. For a number of reasons, this is a difficult task. Difficult, because of the very nature of implantology and its evolution over the years. First of all, even a definition is difficult. Just about anything you put into a patient can be considered an implant; so first we must narrow our scope. Implants in this context refers to artificial devices used to replace the supporting structures of the dentition. The rational for placing implants is straight forward enough. Through their lifetimes some people will lose teeth and along with them, the supporting dental alveolus. From the simple single tooth to the fully edentulous situation, the process is the same. The tooth is lost and the bone slowly follows. Conventional prosthetic rehabilitation; therefore, needs to deal with a progressively deteriorating situation. In some cases, this proves unsatisfactory, and the dentist will search for solutions. There is a general rule in clinical dentistry that goes like this: The fewer ways to do something, the more likely is success. The corollary, of course, is also true: The more ways there are to accomplish a given objective, the less likely that any given technique will work. Let us cast our eye then on a short list of jaw reconstructive and dental implant techniques: (please do NOT try to memorize this list) A. Ridge augmentation: 1) Autogenous bone - split rib - iliac crest - cortical blocks - particulate cancellous - superior border - inferior border - interpositional - visor +/- graft cartilage 2) Allogeneic bone - demineralized - deantigenized - deproteinated - freeze dried B. Subperiosteal C. Endosteal 3) Xenogeneic bone -demineralized - deproteinated - freeze dried 4) Alloplastic silastic proplast hydroxylapatite - Calcitite - Durapatite blocks particles collagen impregnated mixed with bone mixed with blood 1) cast frameworks 2) ramus frames 3) plus bone grafts 1) vitreous carbon 2) crystal saffire 3) stainless steel - blades - screws - pins 4) titanium - screws - cylinders - blades and on and on................ The problem is obvious...... over the decades implantology has encompassed an enormous range of materials and techniques, some of which worked better than others. Until very recently , there was little science. The recent revolution in implant dentistry has occurred as a direct result of the reversal of that trend. B. BASIC SCIENCE Over the last forty years, a Swedish group, headed by Professor P.I. Branemark has pioneered and developed a reliable, scientifically proven system of replacing teeth for the virtual lifespan of the patient. Interestingly enough this was a rather serendipitous discovery. Dr. Branemark's training was as an orthopaedic surgeon and the lab he was working in was the Institute for vital microscopy. Their interest was in placing metal boxes with glass windows into rabbit legs and then peering into the windows with microscopes in order to watch the bone heal. These boxes were placed as carefully as possible, the observations were made over a period of time and when the experiment finished, the animal sacrificed and the boxes removed for use in another animal. One of the problems was that the boxes corroded and influenced healing, so various materials were tested in order to minimize this effect. As it turned out, the titanium boxes were impossible to remove and in actual fact, the bone broke around them before they would loosen their grip on the bone. They had to be literally cut out of the bone. Realizing the potential value of this discovery, Dr. Branemark looked for applications of this technology. In this way, the modern era of dental implants was begun. Over the last forty years, the Swedish group and then other groups throughout the world performed extensive laboratory and clinical testing of the system. The end result was presented to the North American market in the early 1980's and this changed clinical dentistry. What these studies did was debunk the pseudo-science and poor track record of the previous systems and replace them with scientifically and clinically proven alternatives. Along the way, these studies redefined implants in a number of ways. What then, made these new implants different from the old ones? Distinctions lay in a number of key areas: Material: titanium Technique: minimally traumatic surgery Healing: unloaded (or minimally loaded) bone healing (3 to 6 months) The combination of these three critical factors led to the enormous success of this system. The newer systems on the market represent modifications and adaptations of the basic principles. C. PROVIDING THE SERVICE What then is modern implant dentistry all about? Essentially it boils down to a series of nine basic steps: 1. Diagnosis 2. Treatment Plan 3. Preliminary procedures: a. Non-surgical procedures include b. Surgical intervention 4. Primary Surgery 5. Primary Healing 6. Secondary Surgery 7. Secondary Healing 8. Prosthesis Fabrication 9. Follow Up 1. Diagnosis: As in all clinical dentistry, the diagnosis is the most critical step. From a systemic health point of view you want to rule out things like uncontrolled diabetes, renal disease or metabolic bone disease. These significantly reduce the success of implants. All of the usual questions regarding systemic health and the patient's ability to withstand one or more surgical procedures also have to be answered. From an oral point of view, the patient needs to have enough bone to support the fixtures. In the maxilla this is particularly important in the posterior where the maxillary sinus sweeps into the alveolus. In the mandible the main consideration is the height of the canal in the bone and the antero-posterior position of the mental foramen. In addition to absolute height; width and configuration of the bone is critical. The bone must support the implant in height as well as circumferentially. The status of the occlusion is also very important, specifically intra- and inter-arch relationships. This issue is all the more important in partially edentulous cases. The following is a check list of issues that require attention as part of the diagnostic process: Patient's chief complaint: which teeth does he or she want replaced and how (fixed vs removable) History of chief complaint: how long have the teeth been missing, the present status of prostheses or the history of previous attempts, reason for the loss of teeth, etc. Medical history: medications, allergies (particularly to metals), conditions, radiotherapy, smoking, etc. Examination findings: General: number of teeth, Class I, II or III, oral hygiene, caries, periodontal disease, overbite / overjet, canine rise vs group function occlusion, gingivitis, mucosal changes, mouth opening, status of current appliances, vertical dimension, lip to tooth relationships, height of the smile line, TMJ and muscle of mastication status, etc Local: ridge shape, height and width, gingival width, thickness and condition, restorative and periodontal status of the adjacent and opposing teeth, mesial to distal width of the edentulous space, open bite vs overeruption of opposing teeth, crossbite, etc. Radiographic general: Presence or absence of pathoses (infection, cysts, tumours, impacted teeth, etc), TMJ status, periodontal and restorative status, etc. Radiographic local: ridge shape, height and width, gingival, thickness, restorative and periodontal status of the adjacent and opposing teeth, root resorption, mesial to distal width of the edentuous space, open bite vs overeruption of opposing teeth, root proximity to the proposed implant site, proximity of adjacent structures (sinus, floor of nose, incisive canal, inferior alveolar canal, mental nerve), etc. The patient's degree of compliance with your instructions can also be assessed at this time. If a patient is unwilling to follow the necessary steps in the diagnostic stage, he will be unlikely to help you maintain the finished product. Considering the time and cost involved, this is a key consideration. 2. Treatment Plan: The treatment plan is based on diagnosis (systemic health, bone volume, etc.) and the patient's needs (fixed vs. removable and costs) The two basic approaches in the fully edentulous situation are fixed bridgework or clip retained overdenture. The cost differences is important (approx. $8 to 10,000 vs. approx. $4 to 5,000), fixed bridgework requires much more bone to support it, especially in the maxilla, and much more dexterity to maintain it. In the partially edentulous situation, the situation is much more complex. This is a function of having to take into account the current restorative, periodontal and occlusal status of the existing dentition. All of these factors must be optimized prior to proceeding and the costs can significantly add up. 3. Preliminary procedures: a. Non-surgical procedures include: periodontal therapy for adjacent teeth, restorative dentistry, occlusal adjustment, orthodontics to move, upright or torque teeth, TMJ therapy and so on. b. Surgical intervention: this may include periodontal surgery for adjacent teeth or the removal of pre-existing pathoses (such as infected teeth, impacted teeth, cysts, tumours, soft tissue masses, etc.). Preliminary surgery may also include bone or soft tissue graft augmentation of implant sites. The most common sites for bone augmentation include the posterior maxilla with sinus lift procedures and onlay procedures for the anterior maxilla and mandible (both vertical and horizontal augmentation). Soft tissue grafting is required in order to increase attached gingiva or to improve ridge contour short of bone grafting. The most complex cases may require transposition of the inferior alveolar nerve or mental foramen or orthognathic surgery to alter the relationship of the jaws. 4. Primary Surgery: The primary surgery is the placement of the implants in the bone. A generous flap is raised, holes (appropriate to the system) are drilled in the bone the implants (titanium or titanium alloy) are screwed or tapped into place. The drilling MUST be carried out in a minimally traumatic fashion, most importantly avoiding overheating and killing of bone cells (critical temperature is 47'C) When the implants are in place, the flap is closed and the patient sent home. The key to successful surgery is the precise placement of the implant in the position and orientation required to support the eventual prosthesis. This requires accurate diagnostic wax mock-ups and the fabrication of appropriate surgical splints. 5. Primary Healing: The most critical factor in the immediate post-op period is the NON-loading of the implants. At the time of surgery, The mucosa is closed with the implants either buried or minimally exposed and the implants are virtually ignored for two to six months (depending on location, implant system, quality and quantity of bone, etc.). During that time the patient may wear his or her old denture if it is accurately relined to fit the healing ridge. It is during this period of quiescence in the bone that the process of osseointegration occurs. Viable bone will grow up to and fuse with the implant structure. If immediately over-loaded, the interface with tissue will be fibrous and the implant will ultimately fail. 6. Secondary Surgery: At the completion of the prescribed primary healing time, buried implants are uncovered through gingival incisions and transmucosal healing abutments are placed. The gingival tissue is then carefully adapted by sutures to the implants and again minimally loaded. 7. Secondary Healing: This two to three week period of time allows formation epithelial hemi-desmosomal attachment to the titanium surface. 8. Prosthesis Fabrication: A careful impression technique transfers the positions and orientations of the implants to the working model and the ultimate restoration is waxed, cast and processed in multiple steps. 9. Follow Up: Following insertion of the restoration, the patient must be followed over the years for potential loosening of implants (rare) and for routine maintenance of the teeth. This may include occlusal adjustment, replacement of teeth, cleaning, tightening, etc. Because the implants systems will stay with the patient for the rest of their lives, a commitment to lifelong maintenance must be made by both the patient and the restorative dentist.