Discussing occlusion with a focus on best practices
The vertical dimension of occlusion (VDO) is a concept that dentists learn about in dental school, but remains one of the most misunderstood and controversial subjects in all of dentistry. Some say it cannot be altered for any reason, others say they do it routinely, and most dentists are probably slightly bothered by the debate, so they simply stay away from thinking about it.
This article should help readers understand the critical occlusal goals that will be required should they open the vertical; illustrate the cases when altering the VDO can be helpful; and identify the cases when altering the VDO could increase the probability of instability and ultimately dysfunction.
Before that discussion, let’s review the critical occlusal goals that must be established on any case that alters the VDO.
Occlusal control is about managing force. Anything that can be done to spread out the load that the patient can generate on closure, or decrease the lateral force on the teeth, is a positive.
The first logical step in creating a good occlusion is to make sure all the teeth hit simultaneously on closure. If we can get the functional cusp tips (lower buccal cusps and upper lingual cusps) to land on an opposing flat surface (marginal ridge or central fossa), each tooth will load through its long axis. Even anterior teeth should have a stable contact. The lower incisors and canines should land on the lingual surface of the upper anterior teeth, with simultaneous contact with the posterior teeth. Visualize the mandible closing on its hinge axis (centric relation, or CR) and all the teeth hitting evenly. This is the first step.
The second requirement is to manage force by decreasing muscle activity. Numerous studies have shown that the rubbing of back teeth is the enemy of a good occlusion. Force is delivered to the system if patients have the capacity to rub on posterior inclines.
Getting the lateral force distributed to the anterior teeth during excursive movements will move the force away from the fulcrum point, which is the temporomandibular joint. There is nine times more force on second molars than canines, so getting this force forward is important from a mechanical standpoint.
Additionally, electromyography work by many has shown increased muscle activity when back teeth are involved with lateral, protrusive or retrusive movements. So the best way we can manage force is by obtaining precise, equal-intensity contact on closure (in a stable seated condylar position) and ensuring posterior disclusion by creating a proper anterior guidance.
Anterior guidance in harmony with the envelope of function
We would like the front teeth to disclude the back teeth in any excursive movement. Some have suggested that this “inside-out” movement is not needed because this does not reflect how patients move. Their concept is to make sure there is no contact on front teeth, as the functional movements of the patient are more of an outside-in movement in normal chewing.
These two concepts are not diametrically opposed, as some would suggest. While anterior guidance is definitely an “inside-out” movement, envelope of function is an “outside-in” movement to be worked out.
Envelope of function is the path the lower incisor edges travel, in an outside-in motion, during chewing, speaking and closure.
Dawson’s second requirement of occlusal stability is very clear: anterior guidance in harmony with the envelope of function. The lingual contour of the anterior teeth have to be contoured in a way to provide stable centric contacts, or teeth will erupt into contact; be steep enough to disclude the posterior teeth; and be concave enough to be in harmony with the envelope of function.
There is no need to compromise on either anterior guidance or envelope of function, and both are critical when we need complete control of the occlusion. Altering the vertical dimension of occlusion is one of the times when we need complete control.
Measuring vertical dimension of occlusion
Fig. 1: The vertical dimension of occlusion
is determined in maximum intercuspation.
The vertical dimension of occlusion is always measured in the patient’s maximum intercuspation. The vertical dimension can be determined by picking a fixed point on the nose and a fixed point on the chin when the patient is in their habitual occlusion (Fig. 1).
It’s important to understand the patient’s VDO is set as the person develops. The repetitive contracted length of the masticatory muscles as we swallow creates a physical space between the upper and lower jaws. When the teeth erupt, they erupt through this space until they meet an equal and opposite force: the opposing teeth.
This sets up the patient’s own vertical dimension of occlusion. Further, if the teeth wear and erode, there is compensatory eruption of the teeth and remodeling of the alveolar process that keeps up with the wear. Thus, even in extreme wear (as long as the person hasn’t lost all their back teeth) vertical has not been “lost.” Therefore, we don’t actually restore VDO on patients with worn teeth; we open the VDO for prosthetic convenience. It is also important to know that when we open a vertical, the dentition may adapt, and slowly go back to the original vertical over a six-month period.
The good news: If we have a stable occlusion, as we’ve previously described, the patient will not even be aware this adaptation process is occurring.
When can opening the VDO be helpful?
• Worn dentition
We make the decision on how much to open the vertical on an articulator with properly mounted models in centric relation. It is rarely more then 2–3 millimeters at the pin.
If we consider the patient in Figs. 2–4, we see a mouth with significant wear and erosion. If we were to consider crowning these teeth at the patient’s present occlusion, it would result in too much reduction, pulpal impingement, and decreased retention and resistance form.
Additionally, as these patients wear their teeth, they often end up with very little overjet and very steep guidance angles that often interfere with the envelop of function. In Fig. 5, notice when the vertical is opened (on the arc), the lower incisors drop down and back, creating decreased overbite and increased overjet, lending itself to shallower guidance angles that puts far less horizontal load on the front teeth.
We gain much-needed space on the posterior teeth to add back what is missing. This gives us many options to restore the posterior teeth. In our example, because of the age of the patient and the desire to phase treatment, we used bonded resin “tops” and simply added back the tooth structure that was missing, allowing us to set up an ideal occlusal relationship and focus our attention on the final aesthetic restorations on the front teeth. Figs. 6–9 show the virtual wax up with ideal anterior relationships with posterior “topper design.”
Figs. 10–13 show the final restorations on the anterior, the bonded toppers on the posterior and the ideal occlusal result.
Figs. 10a–d: We do cases four times. 10a: In our minds
10b: in wax
10c: in provisional prototypes
10d: in porcelain
Fig. 12: AccuFilm II articulating film, left, and TrollFoil articulating foil.
Fig. 13a: In patient’s maximum intercuspation at the patient’s VDO.
Fig. 13b: As the jaw arcs open and leaves MI, the lower incisor drops down and back, decreasing overbite and increasing overjet.
• Pseudo-Class III patients
The pseudo-Class III patient appears as a skeletal Class III occlusion, but if you seat the condyles in CR, the result is more of an end-to-end occlusion. As the lower incisors contact the upper incisal edges on closure, it causes the mandible to skid into a more forward maximum intercuspation.
Fig. 14 shows side-by-side images of the preoperative and provisionals in such a case. The key to a successful, stable result is working in CR and opening the VDO. As you open the vertical, the lower incisor drops down and back into a more Class I occlusion, as seen in Fig. 15.
The point is to be sure to take a close look at the actual skeletal relationship in CR before you choose a treatment option. Pseudo-Class IIIs can often be helped with restorative dentistry alone.
Figs. 15a and 15b: With the pseudo-Class III occlusion, note how working in CR and opening the VDO on the arch allows for a more ideal occlusal result. Fig. 15a: Habitual bite
Fig. 15b: Provisionals in CR at 2.5mm VDO increase.
Figs. 16a and 16b: The problem with altering vertical and Class II malocclusions.
16a: In maximum intercuspation.
16b: As bite opens, the patient becomes more Class II.
When can opening the VDO be harmful?
• Class II malocclusions
It is almost impossible to open the vertical on a Class II patient (in CR) without making their occlusion worse. This is because many times, the lower incisors already lack contact with the upper maxillary teeth. As the patient opens on the arc, the lower incisors rapidly drop down and back, making the Class II worse.
If you believe in the requirements of occlusion as previously described, these patients are better treated with orthodontics and or orthognathic surgery. Fig.?16 illustrates the problem.
• Full-arch cases involving teeth and implants
It can be problematic to alter the VDO on cases involving implants. Remember that when we open the VDO on teeth, the teeth, soft tissues and alveolar processes have the capacity to adapt. Implants do not.
If you have a case involving implants and teeth, place the implants at the time of tooth preparation, and place provisionals on the teeth (over the buried implants) at the new VDO.
Let the temporaries stay in place six months, allowing adaptation to occur, then finish the restorative requirements of the case. If you load the implants and teeth too early, the teeth may intrude, leaving the implants in hyperocclusion—a clinical observation I have seen more than once.
Solving complex occlusal problems, especially ones with an aesthetic component, can be one of the most rewarding things we do as a dentist. It can also be incredibly frustrating if we lose our way during the process. It is important for dentists who tackle these kinds of cases to anchor their efforts in sound treatment-planning principles involving biologic health, tooth-by-tooth structural integrity, smile design and occlusal control. The purpose of this article was to focus on sound occlusal principles and to explain how and when altering the vertical dimension of occlusion could be helpful as well as harmful.
Restoratively altering the VDO involves at least one full arch of dentistry. Because of the commitment to full arch, these types of cases will be the exception rather than the rule. However, many cases cannot be fixed properly unless we can execute this kind of treatment effectively.
It is my recommendation that every dentist gets the necessary training to add these protocols into their armamentaria.