The use of chairside intraoral scanners has increased significantly in recent years. Often clinicians will invest in this technology with a restorative or orthodontic treatment in mind. Often overlooked, however, is the role chairside scanning can play in occlusal analysis, for instance in evaluating worn dentition from a digital file, which is what I will address here.

In a restorative practice, occlusal analysis allows the clinician to evaluate the mechanical aspects of a patient's existing occlusion. Working with articulated casts, the clinician is able to visualize occlusal relationships that may otherwise be difficult to detect clinically due to soft tissues and saliva; evaluating a patient's slide from centric relation to maximum intercuspation and the presence of non-working interferences are just two examples.

Classically, functional analysis requires:

  • accurate casts of the existing dentition.
  • a facebow to transfer esthetic and functional information about position of the maxilla to an articulator.
  • a jaw relationship record, typically made in centric relation.
  • an articulator, as a means to simulate the patient's mandibular movements.

Taken together, this information allows the clinician to appreciate the patient's existing occlusal relationships more fully and, since the case is already articulated, sets the stage for treatment planning functional aspects related to the case.

As dentistry continues its transition toward digital acquisition, design, and manufacturing, a looming question is how clinicians can effectively analyze an occlusion in the (gypsum-free) digital space. Accuracy of the digital model (as a digital file or a digitally manufactured, tangible model), accuracy and repeatability of the arch positions inside a virtual articulator, managing bite records in the digital era, and options for digital trial equilibration--these are all topics that need to be addressed.

Even taking into account any of these lingering questions, it is evident that digital impressions do have a place with occlusal analysis in the present. In order to understand this, I will focus in this article on what could really be considered the first step in occlusal analysis: tooth wear identification—with a specific focus on evaluating the patient's “models” for patterns of tooth wear.

Analyzing a Digital File for Worn Dentition: The First Step in Occlusal Analysis

The patient in Figure 1 presented for a loose provisional restoration on the maxillary left central incisor. Both centrals have a history of restorative and endodontic treatment. Due to the presence of a number of functional “red flags” (including history of poor sleep, fractured restoration and worn teeth), as well as more general esthetic concerns, the patient agreed to a comprehensive evaluation. As a part of the exam, digital impressions were made.

This patient presented with esthetic concerns and loose provisional restoration on the upper left central incisor. In addition to the worn lower anterior teeth visible in the photograph, the irregular incisal/occlusal planes, irregular gingival levels, and short maxillary central incisors contribute to the functional risk assessment.

 

Figure 1: This patient presented with esthetic concerns and loose provisional restoration on the upper left central incisor. In addition to the worn lower anterior teeth visible in the photograph, the irregular incisal/occlusal planes, irregular gingival levels, and short maxillary central incisors contribute to the functional risk assessment..

Most modern chairside scanners record intraoral color as well as surface morphology (Figure 2). While colorized files do present some advantages, the realistic effect can prevent the clinician from fully appreciating areas of tooth wear present in the digital file (Figure 3, right). Simulated reflections and “over-stimulation” from the colors can both negatively impact the clinician’s perception of these areas.

One possible solution might be to digitally manufacture a model from the file and treat the model as if it were a stone cast. Current printers for this are readily available; however, most are not able to faithfully replicate the crisp transition angles present clinically due to attrition and may result in the clinician, again, under-appreciating areas of tooth wear.

Instead of printing the model and accepting the risks, there is another option. In the case of tooth wear analysis, clinicians may choose to leave the file on the computer and then, simply, remove all color from the file (Figure 3, left). The resulting desaturated file maintains all the same levels of accuracy as the full color version, but without the distracting additional elements.

Digital impressions ((CEREC™ Primescan, Dentsply Sirona) were made as part of the comprehensive evaluation. Most modern chairside scanners record realistic clinical colors. Left is a clinical photograph and right is the full-color digital representation from the chairside scan. Arguably, compared to the photograph, the chairside scan does a better job in demonstrating the dark gingiva surrounding the maxillary right central incisor, as well as the color mismatch between both maxillary centrals.

 

Figure 2:  Digital impressions (CEREC™ Primescan, Dentsply Sirona) were made as part of the comprehensive evaluation. Most modern chairside scanners record realistic clinical colors. Left is a clinical photograph and right is the full-color digital representation from the chairside scan. Arguably, compared to the photograph, the chairside scan does a better job in demonstrating the dark gingiva surrounding the maxillary right central incisor, as well as the color mismatch between both maxillary centrals.

<em>Figure 3: The full-color scan on the right appears very realistic and yet is distracting from clear visualization of the tooth morphology present. When the color is removed, as shown on the left, tooth wear becomes more apparent. In this case, the mandibular anterior tooth wear is quite easy to see in either image but the posterior tooth wear, particularly the mandibular molars, is difficult to appreciate without first desaturating the colors.</em>

 

Figure 3:  The full-color scan on the right appears very realistic and yet is distracting from clear visualization of the tooth morphology present. When the color is removed, as shown on the left, tooth wear becomes more apparent. In this case, the mandibular anterior tooth wear is quite easy to see in either image but the posterior tooth wear, particularly the mandibular molars, is difficult to appreciate without first desaturating the colors.

Some clinicians may argue that this is a minor point—that the tooth wear could, or perhaps even, should, be identified clinically. Figure 4 demonstrates some of the problems with this argument. In the photograph on the right, wear facets limited to the facial of the mandibular anterior teeth can be identified in the photo, just as they were clinically. But absent a three-dimensional representation (i.e., cast or digital file) it is difficult to assess exactly where the facets are and how many teeth are involved. (Looking back at Figure 3, can you find the non-working interference facets present on the lower second molars? That level of detail is difficult to pick up when covered by saliva and reflecting the operatory lighting!)

<em>Tooth wear can be difficult to fully appreciate photographically, or even during the clinical exam. For this reason, it is common for clinicians to rely on diagnostic casts to evaluate critically the patterns of tooth wear and the nature of the facets present. At present, printed models are deficient in this regard, so it becomes critical to make this evaluation using digital software.</em>

 

Figure 4: Tooth wear can be difficult to fully appreciate photographically, or even during the clinical exam. For this reason, it is common for clinicians to rely on diagnostic casts to evaluate critically the patterns of tooth wear and the nature of the facets present. At present, printed models are deficient in this regard, so it becomes critical to make this evaluation using digital software.

When analyzing an existing occlusion, details matter. Tooth wear that appears to be caused by attrition, or tooth-on-tooth contact, indicates a patient who is at a significantly elevated risk for destroying future restorations when compared with another patient who doesn’t have such features. Additionally, which teeth and which parts of those teeth demonstrate attrition facets can help a clinician understand how the mandible was moving when the tooth damaged occurred (Figures 5,6). Understanding the mandibular movement responsible for the destruction is key for determining the new occlusal design for a patient moving forward with restorative treatment.

<em>The nature and location of existing facets provide insight for the clinician with respect to the mandibular movement present when the facets were developing. This evaluation is typically done on the lower anterior teeth due to the clarity of wear patterns present there. Understanding how the mandible was moving when the facets were generated is key to managing the occlusal design when restoring attrition patients.</em>

 

Figure 5:The nature and location of existing facets provide insight for the clinician with respect to the mandibular movement present when the facets were developing. This evaluation is typically done on the lower anterior teeth due to the clarity of wear patterns present there. Understanding how the mandible was moving when the facets were generated is key to managing the occlusal design when restoring attrition patients.

<em>While it is often easier to evaluate tooth facets on the lower anterior teeth via the diagnostic casts, in this desaturated view of the maxillary arch, the results of attrition are plainly visible.</em>

 

Figure 6: While it is often easier to evaluate tooth facets on the lower anterior teeth via the diagnostic casts, in this desaturated view of the maxillary arch the results of attrition are plainly visible.

Remembering Our “Why” and Our “What”

Digital approaches in dentistry have already changed “how” clinicians and technicians complete many of their day-to-day tasks. Ideally, these tasks would be completed more efficiently with better patient outcomes. The current reality is that workflows for some procedures, such as occlusal analysis, are still emerging.

What hasn’t changed are the concepts—the “why” and the “what” of what we are doing.

As clinicians continue to opt for digital integration, remembering the “why” behind the things we do, such as occlusal analysis, will certainly push manufacturers to provide even better tools for us to do those things. Until then, I hope you find that simply removing the color from your digital scan files will help you be able to better evaluate worn dentition in your patients.

For more on this topic, Dr. Frank Spear provides an incisive look at occlusal considerations in this online course. And Spear offers a comprehensive campus workshop on worn dentition that I highly recommend.

 

Darin Dichter, D.M.D., is a member of the Spear Resident Faculty.

 

References

Abrahamsen, T. C. (2005). The worn dentition—pathognomonic patterns of abrasion and erosion. International dental journal, 55(S4), 268-276.

Johansson, A., Omar, R., & Carlsson, G. E. (2011). Bruxism and prosthetic treatment: a critical review. Journal of prosthodontic research, 55(3), 127-136.

Johansson, A., Johansson, A. K., Omar, R., & Carlsson, G. E. (2008). Rehabilitation of the worn dentition. Journal of oral rehabilitation, 35(7), 548-566.

Verrett, R. G. (2016). Analyzing the etiology of an extremely worn dentition. Journal of Prosthodontics on Complex Restorations, 53-62.

 


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