The future after wax
The Hornbrook Group has been teaching the Ultimate Occlusion course for the past eight years. During the development of ‘Ultimate Occlusion’ we created a five-step occlusal process for the general practioner to create a comprehensive occlusion review of every patient regardless of the proposed treatment plan. The five-step programme includes:
Step 1: Speed occlusal examination record taking
Step 2: TMD/TMJ exam and treatment considerations
Step 3: Recording apex of force location (similar to CR)
Step 4: Vertical dimension records
Step 5: MAP Techniques for locating and treatment planning to eliminate fulcruming interferences.
It was in step three, once we had fully deprogrammed the proprioceptive engrams of the patient habitual bite muscles activities, that we realised we required an absolute rigid material to record an open bite (teeth apart) record.
As many clinicians know, we do not want to have any further tooth contact once fully deprogrammed. Historically, it was determined that a tooth apart occlusal record was the best to allow for proper hinge motion to be replicated on an articulator. The problems we ran into were two-fold.
First, there was difficulty in replacing polyvinyl siloxane bite materials (most having a shore A hardness of less than 90) back into the mouth to verify our record. Secondly we felt that the record never really fit as accurately as we demanded.
Many of the pioneers in CR dentistry used hard wax materials to record this position and then verify the position intraorally. Educators such as Dr Pete Dawson recognised the importance of occlusal verification and was one of the first to show its importance in general practice.
Laboratory technicians also recognised the importance of rigid occlusal records in the final accuracy of the articulation and ultimately minimising post insertion adjustments. We tried the improved registration wax materials but had many complaints about distortion during transportation to the labs.
For a period of time we started using conventional Bis-acrylic provisional materials (Luxatemp) for our open bite apex-of-force records. We found the material would give us a bite like stone but without the fracturing when removed from the teeth. We learned the use of these materials the hard way. In the early days of its use for a bite registration material, we did not have good control of the flow and we did look into undercuts. We also found the shrinkage of these materials was too great to do a cross arch registration. The bite would simply not fit the model.
Over a two-year period, we asked several companies to modify their provisional bis-acrylics to have the following three improvements so as to use these materials for arch-to-arch tooth registrations. The first was to change the colour to a green or blue shade so we could better see the material in the mouth. The second was to decrease the flow and create a more mousse-like consistency. The third request made was to decrease the shrinkage.
Many people ask how we use the Bisacrylic materials. One of the most outstanding lectures using this material I have ever heard was presented by Dr Mark Montgomery. This lecture is interestingly enough called ‘Do a Little Dance, Make a Little Love, and Get Down Tonight’. It is exclusively presented at the Hornbrook Group ultimate occlusion course.
When I first saw this course title it stopped me and I had to hear how someone was going to teach a room full of dentists about taking open bite, precise VDO records, and verifying those records with a title like that. The concept is to feel the arch of rotation and not to manipulate the patient into an unwanted uncomfortable position; this is the dance.
The second aspect of the concept is to make a custom repeatable stop in the anterior region using a customised composite ball and a precise VDO. This would be similar to a Lucia jig, Pankey Jig or NTI but customised to the final VDO planned for the case. This is the part in the title, make a little love (actually a ball)…I think the local dental boards would frown on the love part. (Figures 1 and 2)
The last part of the title is accomplished using the super rigid Bisacrylic material. Dr Montgomery, instead of ‘getting down tonight’, he just makes the bite. He does this is by having the anterior fulcrum in place, the condyle seated into the idea apex-of-force location. The registration material is injected into the posterior segments of the patient’s teeth.
At 45 seconds, the patient is asked to open slightly then close back into the recording material. By this time the materials are into the initial set and the small fragments that would be responsible for locking into undercuts are fractured away.
After the bite is completed in its set (approximately 3:30) the anterior composite ball is removed. The anterior tripod is also created with Bisacrylic, which results in an incredibly rigid and stable record for the lab to mount the case.
It should be noted: Bisacrylics have an accuracy far exceeding many of the standard registration materials so high quality polyvinyl impression (Virtual, Ivoclar-Vivadent) should be used for the fabrication of all working models requiring accurate articulation.