When an edentulous patient presents for restorative treatment, clinicians are faced with several challenges, whether the treatment will be conventional or implant-retained. One of the most common clinical challenges is determining the optimal occlusal vertical dimension (OVD). This is especially true if the patient presents without existing prostheses.

Fig. 1: How would you determine the occlusal vertical dimension if this was all the information available?

If the patient presents with a set of existing conventional complete dentures a common approach is to transfer that vertical dimension to the newly fabricated prostheses. While utilizing information like OVD from the existing dentures can certainly be useful, this approach is potentially risky for clinicians because it often assumes the existing OVD is correct for the patient, which may not be true.

Fig. 2: Can you trust the existing dentures?

In either scenario, the clinician must be confident in their ability to determine the patient's individualized occlusal vertical dimension. Both the literature and individual clinical experiences are replete with options for doing this. These options could be described as “pre-extraction” or “post-extraction” methods for determining the occlusal vertical dimension.

Pre-extraction vs. post-extraction methods to determine vertical dimension

According to the Glossary of Prosthodontic Terms, occlusal vertical dimension is defined as “the distance between two selected anatomic or marked points when in maximal intercuspal position.” Clinically, the two points used most commonly are the tip of the nose and the tip of the chin, however these points are only useful as a way of referencing the vertical dimension. Since these two points are arbitrary, the absolute distance between them is not a valuable indicator of the OVD.

Records of the patient's clinical situation prior to having their teeth extracted can be incredibly useful for a variety of reasons, but especially for determining the OVD. Pre-extraction methods include:

  • Measurements of intraoral dimensions or distances
  • Tracing the pre-extraction soft tissue profile
  • Pre-extraction cephalometrics
  • Pre-extraction photographs

The real benefit to pre-extraction records comes from a clear appreciation of the patient's initial condition. As it relates to OVD, relying solely on pre-extraction records has two major problems:

  1. Availability of the records. Often pre-extraction records are not available and, as a result, a post-extraction method of determining the OVD must be used.
  2. Acceptability of the pre-extraction OVD. Techniques for using pre-extraction records assume that the pre-extraction vertical dimension was correct and the goal would be to maintain the previous OVD. However, this may not be true. As a result, again, a post-extraction method would be required.
Fig. 3: Intraoral scan for a different patient. Can you trust this vertical dimension?

With these potential problems in mind, clinicians may choose to utilize pre-extraction records if they are available but must know how to determine the OVD for edentulous patients following a post-extraction approach.

Post-extraction methods for OVD determination in edentulous patients include:

  • Freeway space
  • Following existing dentures
  • Facial esthetics
  • Phonetics
  • Swallowing
  • Craniofacial landmarks
  • Cephalometric evaluation
  • Additional methods

The most widely used post-extraction method is the freeway space approach. Since most dentists are familiar with this approach, we’ll look at that method here and then address the additional methods in future articles.

Freeway space approach

In order to understand the freeway space approach, we need to define our terms.

The physiologic rest position, or the rest vertical dimension, “is the postural position of the mandible when an individual is resting comfortably in an upright position and the associated muscles are in a state of minimal contractual activity.”

Freeway space, or the interocclusal rest distance, is “the difference between the rest vertical dimension and the occlusal vertical dimension.”

With the freeway space method for determining OVD, the physiologic rest position is identified clinically and subsequently average values (2-4 mm) for freeway space are subtracted from the physiologic rest position. The resulting mandibular position is the proposed occlusal vertical dimension.

Fig. 4: Physiologic rest position is identified and recorded using two arbitrary points on the face, typically the nose and the chin. Subtracting 2-4 mm from this position would provide the proposed OVD.

While this approach is common in clinical practice, it is not without challenges. The first challenge is clinically determining the physiologic rest position. Common options to identify the physiologic rest position include:

  1. Ask the patient to relax with their lips together without any further instructions. The distance between the two facial reference points may then be evaluated.
  2. Instruct the patient to lick their lips, swallow and relax. As the patient begins to relax, the reference points are evaluated.
  3. Ask the patient to make the “m” sound, keeping the lips together as they finish making the sound.

In practice, more than one of these options will be required often to determine physiologic rest.

The second challenge with the freeway space method for determining the OVD in edentulous patients has to do with the repeatability of the physiologic rest position. The literature is conflicted as to whether the physiologic rest position is stable over time, with some authors suggesting the position is as stable as the fully seated condylar position and others finding wide variability and instability. As a result, it may be better to think of the physiologic rest position as a range rather than a reliably repeatable mandibular position.

The clinical success this technique has demonstrated over time proves that it is, at the very least, a good beginning position from which to evaluate the patient's OVD. However, the lack of repeatability for at least some patients means clinicians should not rely solely on this technique for OVD determination.

As a result, clinicians need to know at least one other post-extraction approach for determining OVD that could be compared against the OVD determined using the freeway space approach. In my next article, we will begin discussing additional and/or alternative methods.

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

References:

Alhajj MN, Khalifa N, Abduo J, Amran AG, Ismail IA. Determination of occlusal vertical dimension for complete dentures patients: an updated review. Journal of Oral Rehabilitation 2017 Vol: 44 (11):896-907.

The Glossary of Prosthodontic Terms, Edition 9. J Prosthet Dent. 2017;117:e1-e105.

Turrell AJ. Clinical assessment of vertical dimension. J Prosthet Dent. 1972;28:238–246.