Custom incisal guidance

Once the decision is made to make a custom incisal guide table, the following sequence of steps should be followed. Determine if you are going to restore the patient in a seated condylar position (CR) or in maximum intercuspal position (MIP). If the two positions do not coincide, decide if you want to perform an equilibration.
1. Make accurate impressions and casts of the maxillary and mandibular teeth.
2. Take a facebow transfer.
3. Take a protrusive bite registration record.
4. Mount the maxillary cast with the facebow jig, and then hand-articulate the mandibular cast to mount it to the upper. The protrusive record is used to set the condylar inclinations.
5. The materials that can be used for the custom incisal guide table are as listed below.  Place a small amount of the material approximately 1.0 cm thick onto a stock incisal table. If Triad is used, it is light cured after the movements are all completed. All of the other materials are auto-curing, so you must move efficiently to avoid distortions.
6. Lubricate the incisal guide pin with Vaseline so it glides smoothly through the material you have selected.
7. Close the articulator with condyles locked so the incisal guide pin penetrates through the material and strikes the top of the table. This establishes the home position which represents maximum intercuspation.
8. Open the articulator and release the condylar locks. Position the casts so the incisal edges are now touching as in straight protrusive position. Confirm the teeth are touching as you move the maxillary cast to the home position. This establishes the straight protrusive incline on the custom incisal guide table.
9. Open the articulator and position the casts in a pure right lateral edge-to-edge position. Move the maxillary cast to the home position making certain the teeth are touching. This records the right lateral incline on the guide table. Repeat for the left side. The pathways have been recorded after completing the protrusive, right and left, movements.
10. Now record all the lateral protrusive movements by moving the maxillary cast. Repeated movements will be necessary to establish a smooth custom guide table.

After completion of these steps, all of the functional movement patterns have been recorded for this patient. If the patient goes into cross-over during parafunction, this will need to be addressed in the new

 

Posted: 15 Jul 2013 01:50 PM PDT
This is a continuation of the discussion about the patient from Part I that was referred to the office in need of new restorations. As a
reminder, at the time her veneers had only been in place for three months, during that time she had fractured five out of the six restorations.  I used her original models to fabricate a custom incisal guide table to create an analog of her movement pattern. As I moved the initial model into protrusion, the pin of the articulator rode up the guide table until it reached end-to-end
position. When I replaced the model with the ceramic veneers on the articulator and went through the same movements, the pin remained in contact with the guide table in protrusion when the lower anteriors were contacting the natural tooth structure on the palatal of the upper anteriors, but as soon as the lower incisal edges started to run up on the ceramic, the pin lifted itself off the guide table. This difference is what was fracturing the restorations. To determine if the VDO should be increased of the lower incisal edges moved apically, we need to evaluate the lower occlusal plane. Since her lower occlusal plane has a step from the anteriors to the posterior, it was decided that her lower incisal edge position needed to be altered either by ortho intrusion or by shortening the edges with a bur. Both options were discussed with the patient, who chose to forgo orthodontic treatment.
The first step in treating her was to esthetically wax the maxillary incisors (incisal edges and facial surfaces) leaving the pathway un-waxed. To determine how much to shorten the lower incisors, bring the models into the end-to-end position and shorten the lower anteriors until the pin regains contact with the guide table. In this patient, the lower incisors were shortened ~1.5mm. Once completed, the centric contact was waxed back and the guide table was used to determine the pathway.  After finishing the wax-up, I took the information back to the mouth and created full coverage restorations on her six anterior teeth and placed the provisionals. I then shortened the lower anteriors to match what was done on the diagnostic models.  After four months of trial
therapy, the only thing that changed in the temporaries was the color had darkened slightly – there were no fractures, the provisional never became loose or uncemented. I proceeded in taking my final impressions and made a new guide table off of the provisional model for the definitive restorations which were porcelain jacket crowns made out of feldspathic ceramic. The restorations have now been in the mouth 12 years with no problems to report

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