August 1, 2006
by Blake Nicolucci, BSc., DDS
In the following presentation, I would like to illustrate two different approaches used to restore the anterior mandible which has one or two missing teeth. Although they are totally different approaches, the goal of maintaining bone around the implants and adjacent teeth is attained in both cases. In each of the following cases, there isn’t enough space to make conventional implant placement a routine event.
In the first case, there is not enough space into which a normal ‘A’ ridge implant can be placed. In the second case, there is also a lack of space–enough space for a single implant, but not enough space to place two standard implants.
It is generally accepted protocol that there should be at least 1 1/2mm of crestal bone remaining adjacent a natural tooth beside which an implant is inserted, so that any crestal bone loss on the implant will not affect the bone around the natural tooth. It is also generally accepted that there should be a minimum of 2mm of crestal bone distance between successive implant crest modules. This generally accepted rule is predicated on the fact that there is a horizontal component to bone loss next to the implant when the bone “stops at the first thread”. This protocol will leave an adequate amount of crestal bone on an adjacent tooth and/or on an adjacent implant. This crestal bone is required to maintain the inter-dental papilla, and protect the esthetic component of the case.
Case one involves a single missing mandibular central. The space to replace this tooth is at very best minimal, and the chance of touching an adjacent root during implant placement is more probable compared to any other position in the mouth. The mesial distal distance between the adjacent teeth prohibits the use of the standard implant, and even using a ‘B’ ridge implant, the risks are greater than we would like, but using the ‘B’ ridge implant, the chance of placing an implant at least becomes an option. Since there are crowns on each of the adjacent natural teeth, and the natural tooth of these crowns have been reduced to the point that a bridge would not be a viable long termed option, an implant was considered the best option.
The second case illustrates the use of a single ‘A’ ridge implant with a ‘Gemini’ Crown placed on the single root form implant. This single implant is supporting two crowns, to replace two missing teeth. This isn’t ideal, since we are building a cantilever into the system, but in the anterior mandible, the force vectors are in our favor. This would not be a smart move in the posterior mandible, just as placing a crown on an implant in the posterior that looks like a normal tooth has built in cantilevers that will adversely affect the system. The more a posterior crown looks like a natural tooth, the more the implant is at risk. These posterior crowns should be thinner buccal-lingually then a natural tooth. This is not a concern in the anterior mandible.
Dr. Nicolucci is president of the Canadian Society of Oral Implantology and is Oral Health’s editorial board member for Implantology.
Oral Health welcomes this original article.