Replacement of Molars in Dental Implant Surgery

Dr. Jeffery Lemler is a Clinical Assistant Professor of Surgical Sciences in the Departments of Periodontology and Implant Dentistry at the New York University College of Dentistry. Dr. Lemler is a Diplomate of the American Board of Periodontology and a Diplomate of the International Congress of Oral Implantologists. Dr. Lemler maintains a practice limited to Periodontics and Implant Dentistry at 236 East 46th Street in New York City.

OsseoNews, Inc.(ON): One of the more controversial areas in implant dentistry is the replacement of molars with single, wide platform implants. What is your experience in this area?
Dr. Lemler:
I agree that this is one of the more controversial areas and what comes to mind is whether to place an implant or place a fixed prosthesis in the area of a missing molar. While some dentists are hardened to one approach or the other, I believe that cases need to be evaluated on an individual basis. The criteria I look at are the status of the adjacent teeth and the recipient site. As for the adjacent teeth, I evaluate the periodontal and endodontic status, their restorative requirements as well as their position in relation to the space and the opposing dentition. I evaluate the recipient site for bone volume and quality and keratinized gingival tissue present for correct implant placement. In some cases bone or soft tissue augmentation is a factor. Other factors to consider from a risk management perspective are the proximity of the mandibular nerve, location of lingual concavities or the boundaries of the maxillary sinus. I also consider age, health, timeline and priorities of the patient. If there are virgin teeth and the extent of the grafting required can be accomplished at the time of implant placement, I lean toward implant placement. When the opposite scenario presents, I will recommend the fixed prosthesis. If the restorative dentist and I feel that the long-term prognosis of the abutment teeth are guarded (i.e., compromised endodontic results, poor crown to root ratio etc.), then we will likely opt for the implant. Many cases fall somewhere in between and therefore the option chosen depends on the biases and comfort zone of the practitioners tempered, as always, by the patient issues.

(ON): What about cases where the first molar is still present but requires root canal treatment and crown lengthening or periodontal regenerative procedures?
Dr. Lemler:
This is a whole other discussion about whether to retain or extract compromised teeth. The situation you present requires the same evaluation criteria as we just discussed with the addition of economic considerations. Sometimes one option will cost the patient significantly more without giving a better or more predictable long-term result. This is certainly a factor that needs to be presented and discussed with the patient.

(ON): Getting back to conventional prosthetics, what about the use of a cantilevered bridge to replace a single molar?
Dr. Lemler:
Occlusion and periodontal status of the abutment teeth become quite an important factor if you are considering a cantilevered fixed partial denture. Cantilevered fixed partial dentures can provide health, function and esthetics for long periods of time but can also be responsible for fracture, periodontal breakdown and loss of the abutment teeth. The size of the pontic can be another area of concern. The pontic would not be fabricated with the same occlusal surface area as a molar implant restoration. This is just another set of risks versus benefits that has to be considered when deciding on a reconstructive approach.

(ON): Let us assume that the dentist has decided to replace a single molar with an implant. How important are the diameter of the implant and the width of the platform?
Dr. Lemler:
The width of the platform is of great consequence. In fact, it is more important then the length once a certain minimum dimension is reached. As a rule, there is no need to place an implant longer then 13mm and, if you do, there is increased risk of generating heat at the apex while creating the osteotomy. With today’s surfaces, even an osseointegrated 5mm by 8mm implant will adequately support a first molar in most circumstances. I’m focusing here on the 5mm platform because that is the ideal width of an implant to support a molar with the present technology available. The 6mm platform was developed as a bail out for a weak osteotomy but too often it led to loss of alveolar support adjacent to the crestal threads and thereby resulting in compromised or failed implants. Today I would close and wait until a later time rather then place a 6mm platform implant. As for placing a standard width implant, that creates a poor emergence profile with an overcontoured restoration or interproximal embrasures that are too wide causing lateral food impaction. In addition, the average molar has a mesial distal diameter of 9-11mm. The standard diameter implant is 4.1 mm and the occlusal forces create a lot of non-axial loading and torque on the restoration and the implant fixture. This has been associated with screw loosening, loss of cement seal and even deintegration.

(ON): What about replacing a molar with two regular platform implants?
Dr. Lemler
If multiple molars are missing or if there is a large enough space that may be a reasonable option. When placing standard diameter or regular platform implants to avoid the need to augment the width of the ridge, the position of the implants must allow for proper occlusion with the opposing dentition without cantilevering the restoration buccolingually. This is not a good option with a normal molar space or modestly large space. The standard implant is 4.1mm. We know from the literature that a minimum of 3mm is required between two implants to maintain alveolar support. Furthermore, a minimum of 2mm is required between an implant and a tooth. (Personally I prefer 3mm). If we total these measurements, no less then 15mm is required to place two implants for one molar. Therefore when 15mm or less is available, only place one 5mm implant and augment the ridge as necessary.