Whenever there is a prosthetic complication in implant restorations, it can be frustrating for both the dentist and the patient. I started my initial post with describing how I deal with broken implant screws. Then I followed up with a post describing possible causes for broken screws as they relate more specifically to single tooth implant restorations. And my last post was about how multiple unit implant restorations can have more clinical and laboratory errors, and if not managed properly, they can lead to misfit in the prosthesis and prosthetic complication of screws breakage.
For this post, I wish to talk about occlusal considerations for implant restorations. To many people, occlusion can be a controversial topic and I wish to approach it at a more personal angle. To me, I’d like to think of occlusion like a bell curve; there is no single occlusal scheme that will fit the entire population. And occlusion is not just how the teeth come together but it is influenced by the jaw muscles and the jaw joints movement. How much each of these variables influences one another is so different from patients to patients.
But one thing I do believe is that the failures I see on anterior restorations from my referred patients, they have some part to do with improper occlusal designs. For most patients who have a skeletal class I jaw relationship and have anterior protected articulation, the posterior teeth separate and mandibular teeth glide off the maxillary front teeth as the lower jaw moves into excursive movements. Most of the time, there are several front teeth to share this load on excursive movements. I believe the masticatory system has a way of balancing out to determine which teeth and how much to share the load on excursive movement.
When an upper front tooth is missing and the dentist decides to replace the tooth with some type of prosthesis, be it an implant crown or a fixed partial denture, it must conform to the pre-existing range of movement as determined by the existing teeth. Therefore it is important to check excursive movement carefully before and after treatment. I tried to describe how I check anterior occlusion in this post.
What if the new upper fixed partial denture or an implant crown does not conform to the pre-existing range of movement but rather it is in occlusal trauma or that is the only tooth touching when the patient goes into excursive movement. If the prosthesis is tooth supported, the prosthesis may try to adjust and compensate by either shifting, chipping, develop discomfort or fremitus in an attempt to return to the normal range of movement. But for an implant restoration, sometimes the weak link is in the screw itself and so the implant screw may loosen frequently. If not recognized that it is an occlusal problem, then the screw may eventually fracture. I take the time to develop this discussion because I also think a large part of the broken screw cases I see on anterior teeth are due to improper occlusal design. The remaining teeth were gliding off that one implant crown on excursion and the screw keeps loosening. In some cases, there was inadequate posterior support and the anterior teeth were overloaded. Rather than removing the screw or redoing the prosthesis, I think some of the cases have to be re-treatment planned to look at the occlusal factors. Sometimes it is as easy as redesigning the occlusal contacts so that it allows the lower jaw to go back to the original range of movement. Sometimes it involves restoring the posterior missing teeth as well and correcting some of the occlusal issues to minimize the risk of broken screws again.
I hope my understanding of occlusion helps you to determine your causes of broken screw so it does not happen again. Thank you for your time in reading my post. For the next post, I wish to explore manufacturing issues as they relate to broken implant screws.
