Minimal Implant Article |
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One of the most frequently asked questions relative to dental implant supported restorations is "How many implants should be used to support a given restoration?". The question becomes even more complex when we realize that dentistry has traditionally been a "piece goods" type of profession very often choosing to charge patients by the number of surfaces of a given restoration, the number of units of crowns and bridges or the number of canals in a tooth. Dental implants are similarly treated and with the high cost of each implant, the final number of implants used to support a restoration is particularly pertinent and extremely relevant not only to the success of the treatment, but also to the overall cost. Indeed, determining the number of implants used in a particular situation might be linked to whether or not the patient will be able to afford the procedure, and treatment decisions made on this basis can sometimes be detrimental to the overall outcome. While the answer to this basic question of how many implants should be used varies tremendously from patient to patient and for each particular situation based on bone volumes, type of restoration and many other factors, it is imperative for the profession to provide some guidelines, other than monetary, in this area of dental reconstruction. When Dr. Brånemark presented his research in the mid eighties, it was relevant to a specific situation: Restoring a fully edentulous mandible or maxilla utilizing a high-water design, cantilevered restoration. His indications, based on over ten years of research, were that with four to six implants placed in either the anterior mandible or the anterior maxilla, it would be possible to predictably restore that arch with a long term restoration. Indeed, that is the case, but the profession was never given any guidelines for restoring partially edentulous situations especially in the mandibular or maxillary posterior areas where bone volume and density might be compromised. The number of implants necessary to support a given restoration is dependent on several factors which can be organized into five broad categories.
The five categories above can be used to help us evaluate a given treatment situation in terms of the minimum number of implants necessary to insure the success of a restoration. In making this evaluation, there are two other factors which we should consider. MINIMUM IMPLANT RULE For all partially edentulous situations in excess of the replacement of a single tooth, the minimum number of implants used should be two. This rule is designated to help eliminate rotational and pivoting forces that exist when multiple teeth are restored on a single implant. MAXIMUM IMPLANT RULE In all situations involving crown and bridge restorations in partially edentulous patients, you start with the assumption that one implant will be used for each tooth restored. Crown and bridge restorations in partially dentate patients have very different implications from the restorations in fully edentulous patients. We are dealing with totally different force mechanisms and proprioception, and we must make this assumption to establish a minimum standard and then work from there to see if we can safely use less implants in a given patient treatment. The exception to this rule is large molars where two implants might be indicated for each tooth restored. To determine the number of implants necessary in a dentate situation, a Minimum Implant determination Checklist has been developed based upon the above criteria. In utilizing this checklist, you first assume the maximum implant rule and then you score the appropriate areas by circling a number in each category to indicate whether this is a favorable, average or unfavorable factor of the checklist. The numbers are added to give a total score and we use this score to determine if we can safely eliminate implants from the overall restorative design. [Table #1] A score of 5, which is the minimum score, indicates poor conditions for implant support and that there should definitely be one implant per tooth invoking the maximum rule. A score of 10 indicates average conditions for implant support and that it would be acceptable to use one quarter to one third less implants for the given restoration. That is, if you were replacing four teeth, you could eliminate one implant from the maximum rule and restore the patient with three implants supporting the restoration. A score of 15, the maximum possible score, will indicate the most favorable circumstances for placing implants and that it might be possible to eliminate one third to one half of the implant support. In this situation, if you had six teeth to support, you could use three or four implants. Scores in between will require additional judgment on the part of the dentist to make and assessment of the total number of implants that should be used. This is not an absolute system, but merely a guide that helps us to evaluate the conditions relative to implant success.
Score Each diagnostic category after determining whether it is a poor, average or good condition for implant support. Add all the scores together to get the Total Score. The maximum number of implants represents the total number of teeth supported by the implants and that rule should be enforced if the Total Score is less than 10. If the score is between 10 and 15, the minimum number of implants is derived by reducing the maximum number of implants by 25-33%. If the score is 15, the reduction may be as high as 50%. When in doubt, apply the Maximum Rule. 
Look at the drawing
at the right. Try to figure out how many implants you would use if the
conditions were such that there was only 10mm of available bone, average
bone density, an opposing natural dentition and a situation where there
is no distal natural tooth. Would you then want to use three implants
to support these three restored teeth?
If conditions were more favorable than indicated on the table in this example: More bone height, opposing a full denture and keeping that last molar for proprioception, the score might be high enough to opt for only two implants supporting the three-unit restoration... Now you have a definitive means of discussing the treatment with the patient to make the outcome of treatment as favorable as possible while definitively justifying the number of implants used . . . |
To my way
of thinking, you would end up with a total score of less than ten (7)
and you would need three implants to support the prosthesis.