11. Dental implants


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11. Dental implants

  1. 1. AN OVERVIEW OF IMPLANTSA. INTRODUCTIONWhat I hope to do with this handout, is to introduce you to the tangle of implantdentistry. For a number of reasons, this is a difficult task. Difficult, because of the verynature 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 beconsidered an implant; so first we must narrow our scope. Implants in this contextrefers to artificial devices used to replace the supporting structures of the dentition.The rational for placing implants is straight forward enough. Through their lifetimessome people will lose teeth and along with them, the supporting dental alveolus. Fromthe simple single tooth to the fully edentulous situation, the process is the same. Thetooth is lost and the bone slowly follows. Conventional prosthetic rehabilitation;therefore, needs to deal with a progressively deteriorating situation. In some cases, thisproves unsatisfactory, and the dentist will search for solutions.There is a general rule in clinical dentistry that goes like this: The fewer ways to dosomething, the more likely is success. The corollary, of course, is also true: The moreways there are to accomplish a given objective, the less likely that any given techniquewill work. Let us cast our eye then on a short list of jaw reconstructive and dentalimplant 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
  2. 2. 3) Xenogeneic bone -demineralized - deproteinated - freeze dried 4) Alloplastic silastic proplast hydroxylapatite - Calcitite - Durapatite blocks particles collagen impregnated mixed with bone mixed with bloodB. Subperiosteal 1) cast frameworks 2) ramus frames 3) plus bone graftsC. Endosteal 1) vitreous carbon 2) crystal saffire 3) stainless steel - blades - screws - pins 4) titanium - screws - cylinders - bladesand on and on................The problem is obvious...... over the decades implantology has encompassed anenormous range of materials and techniques, some of which worked better than others.Until very recently , there was little science. The recent revolution in implant dentistryhas occurred as a direct result of the reversal of that trend.B. BASIC SCIENCEOver the last forty years, a Swedish group, headed by Professor P.I. Branemark haspioneered and developed a reliable, scientifically proven system of replacing teeth forthe virtual lifespan of the patient. Interestingly enough this was a rather serendipitousdiscovery. Dr. Branemarks training was as an orthopaedic surgeon and the lab he wasworking in was the Institute for vital microscopy. Their interest was in placing metalboxes with glass windows into rabbit legs and then peering into the windows withmicroscopes in order to watch the bone heal. These boxes were placed as carefully aspossible, the observations were made over a period of time and when the experiment
  3. 3. finished, the animal sacrificed and the boxes removed for use in another animal. Oneof the problems was that the boxes corroded and influenced healing, so variousmaterials were tested in order to minimize this effect. As it turned out, the titaniumboxes were impossible to remove and in actual fact, the bone broke around them beforethey 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 ofthis 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 worldperformed extensive laboratory and clinical testing of the system. The end result waspresented to the North American market in the early 1980s and this changed clinicaldentistry. What these studies did was debunk the pseudo-science and poor trackrecord of the previous systems and replace them with scientifically and clinically provenalternatives. 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 anumber of key areas:Material: titaniumTechnique: minimally traumatic surgeryHealing: unloaded (or minimally loaded) bone healing (3 to 6 months)The combination of these three critical factors led to the enormous success of thissystem. The newer systems on the market represent modifications and adaptations ofthe basic principles.C. PROVIDING THE SERVICEWhat then is modern implant dentistry all about? Essentially it boils down to a series ofnine basic steps:1. Diagnosis2. Treatment Plan3. Preliminary procedures: a. Non-surgical procedures include b. Surgical intervention4. Primary Surgery5. Primary Healing6. Secondary Surgery7. Secondary Healing8. Prosthesis Fabrication9. Follow Up
  4. 4. 1. Diagnosis: As in all clinical dentistry, the diagnosis is the most critical step. From asystemic health point of view you want to rule out things like uncontrolled diabetes,renal disease or metabolic bone disease. These significantly reduce the success ofimplants. All of the usual questions regarding systemic health and the patients ability towithstand 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 thefixtures. In the maxilla this is particularly important in the posterior where the maxillarysinus sweeps into the alveolus. In the mandible the main consideration is the height ofthe canal in the bone and the antero-posterior position of the mental foramen. Inaddition to absolute height; width and configuration of the bone is critical. The bonemust support the implant in height as well as circumferentially. The status of theocclusion is also very important, specifically intra- and inter-arch relationships. Thisissue is all the more important in partially edentulous cases. The following is a checklist of issues that require attention as part of the diagnostic process:Patients 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 toothrelationships, 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 distalwidth 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, restorativeand periodontal status of the adjacent and opposing teeth, root resorption, mesial todistal width of the edentuous space, open bite vs overeruption of opposing teeth, rootproximity to the proposed implant site, proximity of adjacent structures (sinus, floor ofnose, incisive canal, inferior alveolar canal, mental nerve), etc.
  5. 5. The patients degree of compliance with your instructions can also be assessed at thistime. If a patient is unwilling to follow the necessary steps in the diagnostic stage, hewill be unlikely to help you maintain the finished product. Considering the time and costinvolved, this is a key consideration.2. Treatment Plan: The treatment plan is based on diagnosis (systemic health, bonevolume, etc.) and the patients needs (fixed vs. removable and costs)The two basic approaches in the fully edentulous situation are fixed bridgework or clipretained 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, especiallyin the maxilla, and much more dexterity to maintain it.In the partially edentulous situation, the situation is much more complex. This is afunction of having to take into account the current restorative, periodontal and occlusalstatus of the existing dentition. All of these factors must be optimized prior toproceeding 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 orthe removal of pre-existing pathoses (such as infected teeth, impacted teeth, cysts,tumours, soft tissue masses, etc.). Preliminary surgery may also include bone or softtissue graft augmentation of implant sites. The most common sites for boneaugmentation include the posterior maxilla with sinus lift procedures and onlayprocedures for the anterior maxilla and mandible (both vertical and horizontalaugmentation). Soft tissue grafting is required in order to increase attached gingiva orto improve ridge contour short of bone grafting. The most complex cases may requiretransposition of the inferior alveolar nerve or mental foramen or orthognathic surgery toalter 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 theimplants (titanium or titanium alloy) are screwed or tapped into place. The drillingMUST be carried out in a minimally traumatic fashion, most importantly avoidingoverheating and killing of bone cells (critical temperature is 47C) When the implantsare in place, the flap is closed and the patient sent home. The key to successfulsurgery is the precise placement of the implant in the position and orientation requiredto support the eventual prosthesis. This requires accurate diagnostic wax mock-upsand the fabrication of appropriate surgical splints.
  6. 6. 5. Primary Healing: The most critical factor in the immediate post-op period is theNON-loading of the implants. At the time of surgery, The mucosa is closed with theimplants either buried or minimally exposed and the implants are virtually ignored fortwo 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 accuratelyrelined to fit the healing ridge. It is during this period of quiescence in the bone that theprocess of osseointegration occurs. Viable bone will grow up to and fuse with theimplant structure. If immediately over-loaded, the interface with tissue will be fibrous andthe 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 healingabutments are placed. The gingival tissue is then carefully adapted by sutures to theimplants and again minimally loaded.7. Secondary Healing: This two to three week period of time allows formationepithelial hemi-desmosomal attachment to the titanium surface.8. Prosthesis Fabrication: A careful impression technique transfers the positions andorientations 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 overthe years for potential loosening of implants (rare) and for routine maintenance of theteeth. 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, acommitment to lifelong maintenance must be made by both the patient and therestorative dentist.