Restoring dental implants is not easy.
There are a whole host of headaches awaiting us if we don’t follow certain rules. Prosthetic implant complications can be neatly filed into esthetic, hygienic, and functional categories. In this post we’ll review the various functional complications and the three rules that will keep us out of trouble.
Fortunately some of the most common functional prosthetic complications are relatively minor annoyances. Cementable crowns that keep coming uncemented, abutment and prosthetic screws that loosen, discomfort on opposing teeth… these are minor headaches that can usually be solved with an occlusal adjustment. However there are nastier functional complications that will pretty much ruin your day, such as catastrophic fractures of materials. What all of these headaches have in common is that they are usually caused by excess stress.
Normal occlusal forces should not cause any of the above functional complications. So what causes the harmful stress forces? There are three possible sources that may be hard to detect. Let’s sort them out.
(1) Overload
Normal occlusal forces should be sustained by our implant solution. However the patient may clench, brux, or have a silly parafunctional habit that introduces abnormal, stressful forces into the system. I try to detect these clues during the treatment planning phase. But perhaps the best way to find out how our patients will function on our restorations is to have them wear an implant-supported provisional before the final is made. I’ve been doing this more and more in my practice since it will also help me evaluate potential esthetic and hygienic complications. If I’m concerned a patient will overload the restoration, I will reduce the occlusion on the final crown to help protect it. For a full discussion on implant protective occlusion, check out this post.
Note the open margins on the mesial aspects of the abutments. This framework also failed the quarter-turn test for passive fit.
(2) Misfit
This is a big problem. Abutments must be fully and passively seated into the implant. If not, even normal occlusal loads may not be transferred down the long axis of the implant, but rather to a weak link in the system. That weak link could be the abutment screw, prosthetic screw, cement, etc. That’s in the best case scenario. The worst case scenario is that the normal occlusal forces are transferred to the implant and cause excessive peri-implant bone loss, implant fracture, or other nightmares. Check for passive fit and make sure you have complete seating.
(3) Poor Design
Normal occlusal forces can overwhelm our implant solution if our solution is under-engineered. Small diameter implants, short implants, and large cantilevers are some examples of engineering decisions that may end up failing us if used in the wrong situation. Proper treatment planning and communication with the team (surgical dentist, restorative dentist, laboratory and patient) should avoid this problem entirely. If under-engineering cannot be avoided, then reduce the occlusion as described above.