A New Perspective On Vertical Dimension

The vertical dimension of occlusion has been a topic discussed in great detail over the years. The original discussions regarding vertical dimension were related to the fabrication of full dentures.

When a patient would lose their teeth, the challenge from a restorative viewpoint was to determine where the teeth should be placed in the denture and how much the bite should be opened to restore the occlusion on the denture. The belief was that the vertical dimension should not be opened to restore the teeth in a full denture ¹. Pound ² discussed using tooth-to-tooth and tooth-to-tissue relations in normal speech to control the vertical dimension in denture fabrication.

As patients started keeping their teeth, the discussion about vertical dimension changed from denture fabrication to prosthetic rehabilitation of natural teeth. Vertical dimension became a key discussion in treating planning patients who presented with worn teeth.

Mack ³ suggested that proposed changes to the vertical dimension should be preceded by a stable diagnostic restoration to evaluate the ability of the masticatory muscles to adapt to the change in vertical dimension. Dawson ⁴ discussed opening the vertical dimension if it is necessary to create an acceptable anterior tooth relationship in wear cases. The common belief when opening vertical dimension was to open the bite as little as possible (typically the amount of space necessary for restorative materials) to minimize the amount the muscles had to adapt.

The discussion about vertical dimension has been limited to the front end of the masticatory system. If we redefine occlusion from "how the teeth fit" to "how the lower jaw fits the upper jaw," it is possible to have a new perspective on vertical dimension. By redefining occlusion to include the TM joints, it is possible now to assess the vertical dimension not only at the tooth level, but also at the TM joint level.

In normal or structurally intact TM joints, the soft tissue and hard tissue maintain a vertical dimension at the TM joint level. When joints undergo structural alteration, the initial tissue deformation typically occurs at the soft tissue level, resulting in a loss of ligament attachment between the disk and the condyle. This can occur at the posterior ligament attachment, the lateral ligament attachment, the medial ligament attachment or a combination of the ligament attachments. ⁵

The loss of ligament attachment typically results in an anteriorly displaced disk. If the disk is displaced at the medial aspect of the condyle, there is a resultant change in the occlusion since the medial aspect of the joint maintains the vertical dimension of the joint.

While most of the discussion regarding displaced disks relates to clicking and popping, the more clinically relevant discussion explores the change in vertical dimension in structurally-altered joints. The vertical dimension can increase in a situation where the condyle functions against the thickened posterior band of the disk. More commonly, the vertical dimension of the joint decreases if the disk is completely anteriorly displaced and the condyle moves superiorly through retrodiskal tissue. In either of these scenarios, there will be a change in the occlusion at the tooth level that has been caused by structural changes in the TM joint. ⁶

While the discussion of vertical dimension at the tooth level usually involves an increase of 1 to 3 mm for dental materials to restore worn teeth, the loss of vertical dimension at the joint level can be significantly larger. Vertical dimension loss at the TM joint level can be over 10mm in cases where there is both a loss of soft tissue vertical dimension (disk) and hard tissue vertical dimension (condyle).

The common clinical presentation in cases with greater amounts of vertical dimension at the TM joint level is an uncoupling of the anterior teeth and the development of the Class II occlusion. The other common clinical presentation in these cases is the development of facial asymmetries given the amount of vertical dimension loss at the TM joint level. Schellas ⁷ discussed the effect of pediatric internal derangements of facial development. By redefining occlusion to include not only how the teeth fit, but also how the TM joints fit, we are able to have a better understanding of much of the tooth-based malocclusion we see commonly in clinical practice.

Dr. Jim McKee, Spear Resident Faculty

References

1. Silverman, M. Vertical dimension must not be increased. J Pros Dent; 1952;2,2:188-97

2. Pound W. Controlling anomalies of vertical dimension and speech J Pros Dent; 1976;36,2:124-36

3. Mack, M. Vertical dimension: A dynamic concept based on facial form and oropharyngeal function. J Pros Dent; 1991;66,4:478-85

4. Dawson, PE. Functional Occlusion: From TMJ to Smile Design St. Louis, Mosby 2007,435.

5. Choukas N, Sicher H. The structure of the temporomandibular joint. Oral Surgery, Oral Med Oral Pathol. 1960;13(10):1205-1213.

6. Ahn SJ, Kim TW, Nahm DS. Cephalometric keys to internal derangement of temporomandibular joint in women with Class II malocclusions. Am J Orthod Dentofac Orthop. 2004;126(4):486-494.

7. Schellhas KP, Pollei SR, Wilkes CH. Pediatric internal derangements of the temporomandibular joint: effect on facial development. Am J Orthod Dentofac Orthop 1993;104(1):51–9.