Bill Baum MDT, CDT
Slight contouring may avoid food entrapment
Food entrapment interproximally after placing restorations can be a frustrating issue to resolve after completing treatment. For both natural abutment, implant supported crowns and fixed partial dentures often slight modification to adjacent teeth prior to final impression or scan can, in many cases, prevent this. The issue is usually occurs because the contact surface areas of teeth adjacent to the restoration are contoured in such a way as to only allow for a point contact. When analyzed on a dental cast surveyor a height of contour can be observed. Remembering that all tooth surface apical to the survey line is in an infra-bulge and cannot be in contact with the restoration. The deeper this infra-bulge is contoured into undercut the more likely it will cause a food entrapment. Most of time this can be corrected by analyzing the adjacent contact surface areas intra-orally and determining an approximate survey line thus disclosing the depth of the infra-bulge undercut. Adjusting the adjacent teeth with a parallel walled burr so that it is in harmony with the long axis of the abutment being restored will enable the restorations to have proper contact surface areas.
Although this same concept will apply to implant prosthodontics it is compounded by implant placement. The more distant and shallow an implant is placed the more challenging it can be to address this issue. Many prosthetic concerns can be avoided by incorporating appropriate pre-surgical planning which is prosthetically driven. With this in mind we can minimize potential issues for both screw retained and cement retained restorations. For screw retention be sure parallel the adjacent contact surfaces to the long axis of the implant body itself. With cemented crowns, be sure the contact surfaces interfacing with the restoration are in harmony with each other and in a path the will allow the laboratory to design a patient-specific abutment with a long axis on the same path as the adjacent teeth.
As with all of dentistry proper planning can make our work more predictable and run smoother. Sometimes, however, details can be overlooked prior to sending the case to the laboratory. If this issue is missed there are options. First, communication, be sure to have a discussion with your laboratory technician as to how you prefer your contact surfaces to be contoured and what your clinical goals are. Let them know that if they receive an impression that has mal-contoured teeth to call you. Decisions can be made as to how to proceed at this point easier than if you notice it at your seating appointment and the patient is expecting the restoration to be delivered. At this initial stage in the laboratory, you may decide to keep it as is, not perfect but still acceptable. You can also have the laboratory make just a framework at this stage and at the next visit you can try in the substructure, adjust the adjacent teeth as necessary and then pick the frame up in a new impression for completion. Lastly, you can have the laboratory make you an adjustment jig and alter the contacts on the cast and make an ideally contoured crown. This is risky but it can be helpful.
Working with a laboratory technician that is aware of your goals and desires and that will be willing to communicate is valuable for every aspect of restorative dentistry and should be a goal for the entire dental team. My laboratory provides all types of restorations to some wonderful dentists. If you are looking to work with an experienced technician please contact me.