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Vertical dimension of occlusion (VDO) is defined as the distance between any two points measured in the maxilla and the mandible when the teeth are in maximum intercuspation.1,2 Interestingly, the concept of altering a patient’s VDO instills fear in many dentists. Reports detailing side effects such as headaches, bruxism, pressure pain of the masticatory muscles, and pain during jaw movements around the temporomandibular joint3 that may occur when these alterations are made outside of what a patient can tolerate are suspected to cause this apprehension. Animal studies have shown excessively raised VDO to induce some acute and chronic pathological changes in the oral–facial structures, including mandibular deformation and changes in muscular attachments.4-6 Studies such as these cultivate a needed respect for the patient’s own VDO, and make the profession leery of altering it.
Yet clinicians still confront situations in which it is impossible to resolve an occlusal problem, or create and ideal esthetic result, without altering the patient’s VDO. It is important, therefore, to develop a protocol on when it should be altered, when it should not be altered, and to be clear on the options available to predictably accomplish this. Lastly, clinicians should remember that the first responsibility as dentists is to solve the patient’s problems with the least amount of dentistry possible while creating the desired elective esthetic result. Changing the VDO will always involve a great a lot of dentistry; it should be considered only when absolutely necessary.
Understanding Vertical Dimension
This discussion of VDO begins with a few premises:
Premise 1: VDO is determined by the repetitive, contracted length of the closing muscles, hence increases in VDO cannot be maintained, as the jaw-to-jaw relationship will always return to the original dimension. Even extreme wear does not result in loss of VDO, as the alveolar process lengthens to match the pace of the wear.7-9
This premise, described by Dawson, draws its supporting evidence from unpublished work by a Florida orthodontist named McAndrews, and thus is viewed as theory by some dentists. McAndrews opened and closed the VDO of his patients as much as 8 mm and 7 mm, respectively. Close clinical observation and serial cephalometric x-rays after the initial procedure found that within 1 year, both patients returned to their original VDO.10 Reverting to the original VDO did not adversely affect the intercuspal position of the teeth, a finding of great significance. In other words, it is possible to safely alter the vertical dimension without causing pain or occlusal instability. This would indicate that the change back to pretreatment VDO occurs from, as Varrela et al suggested,11 the progressive and regressive remodeling of the alveolar bone.
Recent animal studies support this premise. Yagil et al studied the temporal change of the VDO in young bite-raised guinea pigs. The VDO was raised by fixation of a bite-raising appliance to the lower incisors, and by increasing the VDO either 3 mm or 1.5 mm at the first molars. The space produced between the upper and lower molars was filled within 10 days due to eruption of the molars and the appliance was removed. In the bite-raised animals, the raised VDO was reduced until it attained conditions observed in the control animals, after which the VDO increased according to cranial growth. These results show that the VDO is developmentally altered and strictly controlled.12 This study provides additional evidence to support the vertical dimension premise described by Dawson.
Premise 2: When altering VDO, the clinician must treat at least one full arch, and follow the requirements of a stable occlusion.13
To achieve occlusal stability, all teeth must have simultaneous contact in centric relation. Opening the VDO in one segment of the mouth is never indicated; at least one full arch must be treated. Before discussing treatment options, which will be done later in this article, it is important to note that the requirements of a stable occlusion must be strictly adhered to in order to achieve success. The occlusal requirements Dawson describes have stood the test of time.14 These requirements are as follows:
- Healthy, stable temporomandibular joints (TMJs) with the condyles seated in centric relation
- Equal intensity contacts on all teeth
- Anterior guidance in harmony with the envelope of function
- Immediate disclusion of the posterior teeth on the balancing side
- Immediate disclusion of the posterior teeth on the working side
Premise 3: When looking at changes in VDO, it is paramount to mount the study casts in centric relation (when the condyles are in their most superior position within their fossae, with the discs properly aligned and full neuromuscular release).15
Accurate models, mounted on an articulator with a facebow and centric-relation bite record, are the only way to predictably see how alterations in VDO will affect the occlusion. Then, and only then, can the relationship of the interocclusal space, as well coupling of the anterior teeth, be studied in detail. When working cases in this fashion, it is often discovered that minor changes in VDO can dramatically change the occlusion. Proper occlusal analysis is the key to solving simple as well as complex occlusal problems.
Premise 4: VDO is unrelated to temporomandibular disease (TMD) and there is no evidence to suggest that by changing VDO one can treat TMD. However, VDO can be increased or decreased, within the patient’s tolerance, for the best functional and esthetic results.16
Okeson states that orthopedic stability exists when the stable intercuspal position of the teeth is in harmony with the musculoskeletally stable position of the condyles in the fossa. As the discrepancy between an orthopedically stable TMJ and maximum intercuspation (MI) of the teeth increases, there is an increased risk for intra-capsular TMJ disorders to occur. The concept of orthopedic stability takes the TMJ, the masticatory muscles and ligaments, and the skeletal–dental relationships into consideration. There is no epidemiologic evidence to suggest that vertical change is necessarily associated with signs or symptoms of TMD. Rather it is the relationship between the optimum joint position and the occlusal surfaces of the teeth that seem to be most important.17
Additionally, others have suggested that clinical evidence to support the theory that VDO can be altered safely to solve many functional, as well as esthetic problems, exists.18 This gives restorative dentists, orthodontists, and maxillofacial surgeons an additional option (alteration of VDO when necessary) to create optimum treatment plans.19-21
Reasons to Change VDO
As previously stated, due to the amount of dentistry that is required when altering vertical dimension, careful analysis of the patient’s mounted casts, photographs, and the information gathered at the clinical examination must be completed to determine if changing VDO is required. If it is, it will usually fall into one of two categories.
Category 1: To gain space for restorative material (prosthetic convenience).
Patients with extreme cases of wear or erosion have a compensatory eruption of the teeth that keeps up with the pace of the destruction. In extreme cases, the crown length after tooth preparation may not have adequate length (a minimum of 4 mm for molars, 3 mm for other teeth) to allow for adequate retention and resistance form.22 Before opening the VDO, the patient should be considered for crown lengthening. Crown lengthening should be considered a primary option as it often lessens the amount of restorative dentistry that will be required. If the positions of the furcations on the posterior teeth prohibit this from happening, then the VDO may need to be opened to limit the amount of occlusal reduction, which will optimize the occlusal–cervical dimension of the restorative preparations. As previously stated, close study of the mounted diagnostic models allows the clinician to determine the least amount of VDO required to solve the functional/restorative problem.
Category 2: To improve esthetics without increasing functional risk.
Many patients presenting with a desire to achieve an ideal esthetic result will have an underlying functional problem. Patients presenting with worn anterior teeth may require additional incisal length to produce an ideal smile. Lengthening the anterior teeth will deepen the overbite. If the patient happens to function horizontally, this new incisal edge position could interfere with the patient’s envelope of function. By relating the improved incisal edge position to the patient’s VDO, the restorative team will gain additional freedom in creating a beautiful tooth length, while at the same time, providing a guidance angle that will be in harmony with the functional path of the lower incisors.23
It is important to recognize that there are four options to alter an occlusion and the VDO. They are:
1. Occlusal equilibration
3. Restorative dentistry
4. Orthognathic procedures
When solving complex functional–esthetic problems, it is important to work with a competent interdisciplinary team to find the best and most conservative method to tackle these challenges.
Testing Changes to the VDO After Restorative Alterations
When the decision to restoratively alter the VDO has been made, there are two foundational principles by which clinicians must abide. First, the starting point for the reconstruction of the new VDO must be made with healthy mandibular condyles in centric relation. Second, the reconstruction must be performed within the neuromuscular adaption of the individual patient. While the second principle is more nebulous, it is prudent to open the VDO as little as possible to fulfill the occlusal requirements previously described. In the author’s experience, creating a maximum opening of 1 mm to 3 mm at the articulator pin is all that is required to solve the most complex vertical challenge.
Additionally, it is wise to verify the occlusal/vertical changes in provisional restorations before continuing to the definitive restorations. If the patient is unable to tolerate the changes in the provisional phase esthetically, phonetically, or functionally, then changes to the provisionals must be made. Once the optimum tooth size, shape, and interocclusal relationship has been verified, models of temporaries can be cross-mounted with the die models, and the laboratory can follow these proven contours to create optimum restorations.24
The decision to alter a patient’s VDO should not be taken lightly. This type of procedure requires a significant amount of dentistry. If, after careful study with diagnostic photographs, mounted diagnostic casts, and appropriate imaging, the conclusion is that it is necessary to obtain an ideal esthetic and/or occlusal result, then it should be part of the patient’s treatment plan. While there seems to be anxiety concerning this subject, clinical data supports this simple fact: if clinicians pay close attention to the details of creating occlusal stability, open the patient only the length necessary to get the job done, then functional as well as esthetic predictability can be a reality.
[CLICK HERE TO READ A CASE REPORT DEMONSTRATING THE PRINCIPLES DISCUSSED IN THIS ARTICLE]
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