I am frequently asked why occlusal and interproximal contacts of single tooth restorations commonly need more adjusting than multiple tooth restorations. Routine dental treatment commonly involves restoring single posterior teeth with indirect restorations. The procedures leading up to and including fabrication of the restorations can result in clinical and technical practices that result in interproximal contacts that are tight or loose.
One of the clinical practices is related to taking impressions. What do you say to the patient when you have them bite into the impression? “Bite and hold still,” “Bite and squeeze,” “Bite as hard as you can and don't move?” The correct answer is: “Bite firmly without squeezing,” but there's more.
Impression materials go through a timeline of setting. It is possible that during this time the patient begins to relax their muscles, moving slightly and causing distortion of the setting impression material. This will affect the fit of the restoration intraorally, even if it appears good on the stone die and solid cast. It is impossible to detect minor distortions in the setting of impression material.
To avoid this problem, try the following technique:
- The tray must be ridged in design. Any flexibility in the tray may introduce distortion, which will be impossible to detect in a set impression.
- Before the impression, have the patient bite in ICP. Identify contact points on the contralateral side of the preparation. Practice having the patient close into the tray without impression material and confirm there is consistency in the contacts.
- At the time of the impression, be certain to dry the prepared tooth, adjacent teeth and the opposing teeth, thoroughly.
- Insert the loaded tray, being certain to have a sufficient amount of material to impress not only the teeth, but also the soft tissue in both arches. Instruct the patient to “close firmly without squeezing.”
- Check the contralateral side to confirm proper intercuspation.
- Ask the patient to “Hold still with their teeth in firm contact.” In addition, have them hold a fisted hand under their chin and apply pressure to help them remember to hold firmly. Using this technique makes it less likely that the masseter muscles will fatigue. For single teeth, a fast setting material is recommended.
- Let the material set for one minute longer than the manufacturers recommended set time.
- Remove and inspect the impression for consistent detail of the margins and identify any significant bubbles or pulls in critical areas. If distortion of the impression occurs, not only will it affect the occlusion and proximal contacts, it will affect the marginal integrity and proper seating of the restoration (i.e. rocking).
- The proximal and occlusal contacts of the provisional restoration should be similar to what is expected in the final restoration. If the provisional is in “light” occlusion or the interproximal contacts are too loose or tight, the prepared adjacent or opposing tooth will move. This movement will occur within days, negatively impacting the fit of the final restoration on the day of insertion.
From the laboratory perspective, areas that could negatively impact the fit are:
- The expansion of the stone is wrong, creating casts that are too big or small.
- Abrading of the stone, for example trying the restoration on the cast multiple times, can affect the mesial or lateral interproximal aspects of the adjacent teeth.
- Creating contacts that are too tight or loose on the final restoration. Does the articulating paper “hold,” “hold firmly,” “drag through,” or see a “slight” amount of light through the contact. Even the thickness of the articulating paper can make a significant difference. Is paper or ribbon used? Doctors have strong preferences concerning the firmness of interproximal contacts, so it is important to clearly articulate these expectations to the laboratory.
In contrast to single tooth restorations, multiple tooth restorations usually have the teeth splinted together during provisionalization. There is significantly less likelihood of tooth movement unless one of the teeth becomes uncemented and the tooth “drifts” under the provisional.
Using strong provisional cements such as calcium hydroxide, Fynal, or Duralon, can create great stability and retention. From a clinical perspective, when you try-in the restorations or during final cementation, there is subtle shifting of the restorations which allows the contacts to become more ideal, resulting in less adjustment being needed.
Why could there be a difference between the solid stone model and the intraoral outcome? Why do single tooth restorations seem to require more adjustment than multiple tooth cases? Hopefully this has helped answer some of those questions. Identifying the source or sources of the error can be very difficult. Paying attention to every detail both clinically and technically is critical to reaching the desired outcome.