One of the most challenging situations for a restorative dentist is the restorative movement of teeth. Having a vision of the outcome before a bur touches a tooth is imperative.
The most challenging aspect is how to prepare teeth most effectively to achieve the desired outcome as determined by both dentist and patient. This article will outline a step-by-step approach taken by both the dentist and ceramist to make these tough clinical situations more predictable.
Planning the Restoration – The Dentist
After collecting comprehensive diagnostic information – including a medical and dental history, photos, radiographic images, appropriately mounted diagnostic models, and a comprehensive exam of all oral structures including muscles and joints – a thorough interview of the patient's esthetic expectations is vital. Once the data is collected and analyzed, the patient is presented a review of findings via Keynote. This provides the patient an additional opportunity to review esthetic expectations.
The patient pictured in Figure 1 was previously treated with ceramic veneers on teeth #7, #9 and #10, and a full coverage crown on tooth #8. The existing restorations had several cracks, and the patient wasn't pleased with the lingual position of #7 and #10. The agreed upon goal is to normalize the arch form. The challenge is how to bring #7 and #10 out facially without making them appear too narrow.
Rather than putting this in the hands of the ceramist to figure out, a rough wax-up (Figure 2) is created. If the arch form was fully normalized, the lateral incisors did appear too narrow. Figure 2 is the agreed upon compromise as determined by the patient and dentist. The lateral incisors will remain slightly lingual to the centrals, which allows us to maintain acceptable length-to-width ratios of all incisors. Working within the confines of the canines not included in the restoration is normally a challenge.
This “rough wax-up” is included in the diagnostic package that is then sent to the ceramist, Michael Roberts of CMR Dental Lab. Other items in the diagnostic package included unaltered mounted models, radiographs and photographs. This is presented to the ceramist in a presentation (Keynote) format. The presentation includes annotations to help guide the ceramist. (Figure 3)
Planning the Restoration – The Ceramist
The ceramist analyzes the diagnostic data to ensure accuracy. This includes an analysis of the stone models (or scans) to ensure CEJs, papillae and the palate are all represented accurately as well as the bite registration to ensure models articulate properly. Photos are analyzed – most importantly the full-face smiling photo, paying careful attention to having the face level with the horizon. Expectations of the case are then reviewed. If any goals of the case aren't clear, the dentist and ceramist must communicate before they proceed. Once approved, the analog models are converted into a digital format.
Using 3Shape, the 3-D model is virtually prepared with the dentist's guidance and overlaid and aligned with the pre-op model using the provided photographs. We now have a virtual representation of the analog diagnostic information. This provides the basis for the creation of a diagnostic wax-up based on facially generated esthetics. The model can then be analyzed to show how much tooth reduction is required to achieve the desired esthetic result.
As seen in the cross section of the wax-up (Figure 4), the design is additive and reductive. If the dentist were to press a mockup based on the final design, it would not fit the patient's current dentition. To ensure predictability, we need a way to know where to reduce before the pre-prep mockup is pressed. 3Shape has the ability to create a combined output model. This model includes only the additive portions of the design overlaid on the patient's current dentition as seen in Figure 5. A copyplast matrix will then be produced based off the combined output model to show the dentist where to reduce. A copyplast based on the final design (Figure 6) is also produced.
On preparation day, the first step is to use the combined output (additive only) copyplast to create a pre-prep mockup (Figures 7a and 7b). A mismatched shade of bisacryl is used to easily delineate between tooth structure and mockup. Before preparation begins, certain aspects of the mockup are confirmed, such as incisal edge position and the absence or presence of cants, etc. Once the patient has approved the design, preparation begins. The first step is to eliminate the original incisal edges to the lingual to create a more harmonious lingual contour. This is done with a coarse high-speed football.
Tooth structure is then examined to help determine type of preparation need. Only tooth #7 was prepared into dentin. (Figure 8) The goal of preparation from here is to ensure that we will have ceramic coverage of exposed dentin. The extent of initial depth cuts is determined by the amount of shade changes requested by the patient. The patient had requested two shade changes from the initial shade, so the facial reduction chosen is a .5/.7/.9 reduction from gingival to incisal. This is competed with a Winter conventional veneer bur (Brasseler WDLCONV). The depth of the cuts is marked with a red pencil. (Figure 9) These lines are to be maintained throughout the preparation to prevent over preparation. Next, a 2mm incisal depth cut is completed to allow for adequate incisal layering.
Preparations are gradually brought to finish with progressively slower speeds and fine diamonds. To ensure proper facial reductions to meet treatment goals, a putty “window guide” is inserted and evaluated. (Figure 10b) Please note the even facial reductions that can be visualized within the guide. This process has resulted in veneers on #7, #9 and #10. Tooth #8 was an existing crown. (Figure 10a) The preparations are then polished, paying special attention to polishing the area where the previous incisal edges were removed.
It is often thought that restorative movement of teeth has limited capabilities. Planning lets us know what our limitations may be and how conservative or aggressive we need to be in order to accomplish our treatment goals. Involving the entire team early on in the process is crucial to having an accurate vision of the outcome.
It is equally important for the patient to understand that if tooth preparations need to be aggressive to accomplish their goals that there are alternatives. It's often surprising during the planning process to learn that treatment does not need to be nearly as aggressive as initially projected. Through this collaborative approach we can deliver minimally invasive treatment that is highly predictable.
Josh Rogoff, D.M.D., is a member of Spear Visiting Faculty