Dr. Gary Wessels, Vernon, BC
Whether you’re working with PVS bite registration materials or taking an intraoral scan, the capture of an occlusal registration that is representative of reality is paramount. An accurate bite registration means quicker cementation with fewer adjustments, improved patient experience and post-op comfort, and more enjoyment for you and your team.
I’ve developed a workflow around crown preps that takes into account quality of outcome, quality of patient experience, and efficient use of resources, energy, and time.
Anaesthesia, patient fatigue, and patient position often contribute to difficulty finding or replicating MIP (Maximum Intercuspal Position), and these difficulties manifest as inaccurate bite registrations. Once the patient is reclined past 45 degrees, the mandible will, in many cases, displace posteriorly and display an altered path of closure.
My assistant seats the patient and leaves the chair in an upright position, encouraging the patient to sit up straight with a relaxed, non-slumped posture with their lower back well into contact with the chair back. They then have the patient occlude into MIP and observe full closure. Use of very thin occlusion paper or shim stock between back teeth is very helpful here in determining if good contact is being made at any stage of this process; give it a light tug to feel resistance.
In cases with an uncertain MIP, I recommend that the dentist establish the desired occlusion at this point.
Once it’s clear that the patient can replicate this fully occluded position, have the patient open no more than halfway. Inject blue bite registration material in a ball (roughly the size of a small grape) onto the incisal edges of 31/41, and have the patient occlude gently until the material sets, confirming closure into the same position. The goal is to create a small bulb of material on the lowers that will be bisected by the upper teeth in occlusion.
Remove the bite registration once set and lay it aside for later, anaesthetize, and proceed.
Once your crown prep is complete, with the patient reclined, replace the anterior jig and instruct the patient to gently bite into it into full closure.
Now, check your occlusal reduction and make any necessary adjustments. Scan your post-op occlusion and your prepared tooth or teeth, or make a PVS occlusion registration and impression.
Fabrication of the Temporary Crown
During the fabrication of the temp crown, your assistant may elect to use the jig again to ensure habitual MIP for try-ins, removing the temp crown for incremental occlusal adjustments. This technique, coupled with a slight enlargement of the interior axial surfaces of your temporary crown with a bur, will result in fewer adjustments for the dentist to make after temp cementation. I have my assistants establish 1 or 2 sharply defined point contacts in grooves or on cusp tips, wiping the adjacent teeth clean for each check. When contacts are observed on the temp (as described) and on adjacent, unprepped teeth, it’s time to cement the temp.
Extra Tip: Beware the single tooth contact!
Prior to anaesthesia, when establishing habitual MIP with shim stock, place shim on the tooth (or each of the teeth) to be prepped. If any tooth to be prepped is the only tooth that holds shim in that quadrant, beware! Elimination and subsequent restoration of that occlusal contact, if not exactly the same, can lead to multiple occlusal adjustments, discomfort, and joint issues. If you encounter this situation, take a bilateral bite registration prior to anaesthesia, in a sitting position, as well full arch scans /impressions upper and lower. Importantly, alert your lab team regarding the situation with instructions to ensure positive contact on the tooth in question.