Optimizing Digital Workflows: A Comprehensive Approach for Pathway Wear

What are the top five procedures in restorative dentistry that excel with a digital workflow application? In my opinion, the top two are single-tooth dental implant-supported restorations and full arch dental implant-supported restorations, followed by single crowns, dentures, and any application in maxillofacial prosthodontics.

We have all heard the truism that the result is only as good as the captured data. What if the data is captured in the form of a static position?

The movement of the mandible relative to the maxilla plays a significant role when assessing probabilities of success for patients with pathway wear. How would you manage this patient in the analog world?

During the first appointment in the office, the dentist takes impressions of the patient's teeth to make diagnostic casts and to create measurements relating the lower teeth to the upper teeth. The dentist may also create records for the centric relation, protrusive position, and possibly a facebow. In the lab, the models created can be mounted on an adjustable articulator, and the condylar elements adjusted to mimic the mandibular movement. Then, a custom incisal guide table is made to create a boundary in terms of the palatal contours. With all this information, the dentist can proceed with the goal of increasing the likelihood of a successful restorative treatment for the patient.

Using Analog Techniques to Develop Digital Processes

You may have heard a version of the statement: “If we can do it in the analog world, we can apply the technique in the digital world.” 

What information would you like to capture for a patient with significant wear visible in the lower anterior segment? Is there a way to capture information in a static image in the digital world that would help create the desired outcome?

One technique (taken from analog techniques) is to work with a provisional restoration designed as a prototype, adjusted to fit the patient’s mandibular movements, and verified through function. Traditionally, an impression would then be made with the verified provisional in place to record the contours accepted by the patient. A silicone index could be made to relate the contours of the provisionals to the tooth preparations to provide a visual boundary, and the definitive restoration would be refined using the mounted models on the articulator with the custom incisal guide table.

A digital image could be made of the carefully adjusted and verified provisional restorations for the patient in this example with pathway wear. This image could be connected to another image of the tooth preparations in the digital design software, creating a virtual boundary while creating the contours of the definitive restoration. The relative opacity of the layer with the provisional restorations can be adjusted to help with visibility while designing the definitive restoration.

This can raise the question: how would you make the acrylic or bis-acrylic provisional?

There are two main options:

1. Use the “egg-shell technique” based on either the pre-op model or the diagnostic wax-up, using an orientation matrix to maintain the palatal contours designed by the custom incisal guide table.
2. Mill an acrylic provisional (PMMA) from a modified version of the pre-treatment model work or the tooth preparations on a digitized version of the working model.

A milled wax pattern is another option designed to capture the palatal contours created by mandibular movement, digitally transferring information meaningful to the definitive restoration.

A milled wax pattern is noticeably more detailed than what can be achieved through milling PMMA, with the added benefit of milling from the exact machine that will create the definitive restoration. The wax pattern could be milled as individual units, eliminating the potential confounding variable created by splinting several teeth together. The wax pattern is easily adjusted to remove material as required, creating a scenario where wax can be added as necessary to enhance the contour.

The wax pattern can then be evaluated in the most customized articulator available — the patient's condylar elements with the maxilla perfectly related to a hinge axis and the patient’s mandible, making the movements corresponding to the wear facets visible on the patient’s teeth. The wax pattern can then be captured digitally relative to the adjacent teeth, creating a guideline for creating palatal contours tested intraorally. The goal of the extra work is to optimize the restorative contours, essential to increase the probability of success for a patient with pathway wear.

Comparing the Three Processes

Now, let’s take a moment to evaluate the steps in the treatment process in the construction of a restoration for a patient with pathway wear. Estimate the amount of chair time (Direct) required and lab time along with the lab expense (Indirect) for each of the three processes. 

Some dentists enjoy incorporating laboratory work in the process in the office, while others prefer to send everything to the lab to complete the steps behind the scenes. To compare the costs of each approach, assign a value to the indirect steps involved in the process.

The Analog Process 

1) Direct: Diagnostic casts and records

Indirect: Create models, mount, set articulator, custom incisal guide table, wax-up

2) Direct: Prep, final impression, and provisional

Indirect: Create working models

3) Direct: Evaluate/refine provisional contour, impression of provisional

Indirect: Cross-mount models pre-treatment to working models to provisional; construct definitive restoration

4) Direct: Evaluate/refine/insert definitive restoration

5) Direct: Post-insertion evaluation

The Digital Workflow Process:

1) Direct: Pre-op impression/scan, prep, final impression/scan and provisional

Indirect: Create virtual model work, first design of definitive restoration, mill wax pattern

2) Direct: Evaluate/refine wax pattern with patient’s mandibular movement, impression/scan of refined wax pattern, evaluate/refine provisional

Indirect: Add to virtual model work, second design of definitive restoration based on contours of the wax pattern, mill as intended

3) Direct: Evaluate/refine/insert definitive restoration

4) Direct: Post-insertion evaluation

The Hybrid Analog & Digital Workflow Process:

1) Direct: Diagnostic casts & records

Indirect: Create models, Mount, set articulator, custom incisal guide table, wax-up

2) Direct: Prep, final impression & provisional

Indirect: Create stone working models, digitize stone models, first design of definitive restoration, mill wax pattern

3) Direct: Evaluate/Refine wax pattern with patient’s mandibular movement; evaluate/refine provisional

Indirect: Add to model work & digitize, second design of definitive restoration based on contours of the wax pattern, mill as intended, evaluate with mounted models.

4) Direct: Evaluate/refine/insert definitive restoration

5) Direct: Post-insertion evaluation

Digital Workflows in the Restoration Process

The goal of this exercise is to assign a value based on the time required to create a restoration for a patient with pathway wear. One crucial decision in this process is whether to work with mounted models on an articulator, as this can significantly save time and indirect costs. By using only digital design software, we have the potential to save on the indirect cost of creating the final restoration.

Still, moving away from stone models requires trust in technology and a history of successful outcomes. With the wealth of information available through digital records such as digital scans, CBCT, MRI, and mandibular movement mapping, it is possible and reasonable to create a digital workflow that can improve efficiency and increase the success rate for patients with pathway wear.

Douglas G. Benting, D.D.S., M.S., F.A.C.P. is a member of Spear Resident Faculty.