Written by Martha L. Cortes, DDS Sunday, 30 November 2008 19:00
Dental occlusion is the sum of all parts working together harmoniously as one system. It is a dynamic flowing system that involves teeth, bones, muscles, and joints. It has great capacity for adaptation. However, the adaptive capacity has limits that unfortunately can be exceeded. Sometimes the maladaptation is momentary and requires only a temporary stay, such as a splint to switch off the maladaptive behavior or problematic muscle/nerve complex.
There are many cases of malocclusion that can be treated exclusively on a palliative basis, as they do form the majority. However, not all cases can be treated palliatively as the supporting structures of occlusion have deteriorated. Adaptation only occurs when a system is stressed and it is compelled to change, as it is a mechanism of survival and entropy. Severely deteriorated dentitions that lead to malocclusion most often require stabilization and reconstruction. Palliation, although an important part of treatment, is not sufficient to return the patient to a fully functional stage.
A standard cosmetic makeover, that uses the habitual bite as its template, may slightly improve the occlusion since it restores some of the deteriorated structure. However, in most cases, this will tend to just aesthetically mask any deterioration and its causes. If the teeth and/or restorations fractured in the habitual bite before restoring, what would prevent them from fracturing after restoring them to the habitual occlusion? Occlusal structure can be purposively and thoughtfully reintroduced during a cosmetic makeover. After all, form and function go hand in hand—immutably bound together. As dentists we want what is best for our patients; as business people we want our restorations to last, and not to be subject to frequent debonding or breakage; and by following a sound occlusal strategy, we can ensure longer lasting restorations and a functional-cosmetic smile.
This article will be a continuation, and further discussion from a different perspective, of the case report described in Part 1 of this 2-part series.
(A review of the patient as presented in Part 1).
Kathy, a woman in her late 50s, came in for a cosmetic dentistry consultation. The patient was assessed to see if she was a candidate for a full-smile makeover. The patient presented with a deep anterior overbite, severe overjet, extensive occlusal wear, missing molars, ill-fitting restorations, and crowding and wear of the lower anteriors. In this initial consultation, it was determined that her malocclusion was too severe to use a habitual centric occlusion approach for her dental work.
What are we looking for in the initial exam? During the facial analysis we are looking for signs and symptoms that tell us the possible health of the bite. For example, is there a deep submental and/or supramental crease? Are the lips collapsed? Are the facial muscles tense? Is the face very wrinkled (especially if it does not correspond with their physiological age)? Does the patient complain of TMJ pain, muscle soreness, or clicking and/or crepitus? Are there mandibular deviations or deflections during jaw opening and/or closing? Is there obvious popping of the joint(s) when the patient opens/closes the jaw? Are there sensitive areas (trigger points) when the patient is palpated on the neck, shoulders and face? Is the anterior and/or posterior shimbashi measurement less than ideal for the patient? Is the jaw’s range of motion (ROM) when opening between 40 to 50 mm? Are the lateral excursions (ROM bilaterally) at least 10 mm? Is there a posterior collapse evident? Does the patient’s jaw, head, and neck jut outward (forward) into space? (Remember that the patient may be accommodating the mandible to the maxilla position by jutting forward so that the teeth fit). These are quick ways to determine if the habitual occlusion is healthy or not.
Kathy, for instance, had an anterior shimbashi of 12.7 mm, a posterior measurement of 11 mm, as well as a prominent overbite and overjet. Ideally for her, the anterior shimbashi should be around 18 mm, and 14 mm in the posterior. The lateral excursion of the mandible was only at 2.5 mm. The patient was missing all second molars and had posterior collapse. Since the patient was pretty much asymptomatic, palliative treatment was not necessary. Being asymptomatic did not suggest that the patient was healthy—it merely implied that her condition did not cause her physical pain or distress. However, the aesthetics affected her psyche enough for her to be motivated to seek treatment.
Figure 1. Transcranial x-ray: closed, at rest, and wide-open. The transcranial x-ray illustrates a noticeable reduced posterior articular space between the head of the condyle and the posterior wall of the glenoid fossa. The superior space is also reduced—indicative of deficient vertical support, and posterior displacement of the mandible from neuromuscular trajectory.
Figure 2a. Scan 15: Joint sonography and jaw tracking indicating molar avoidance and disc impingement.
Figure 2b. Scan 15: Improved function is noted with less interference and less molar avoidance.
It is far better for the practitioner to know what they are working against instead of assuming that the habitual occlusion is good enough because that is the standard of cosmetics today. Hence, the importance of the following: the transcranial x-ray showed that there was disc impingement bilaterally, and this was confirmed by the sonograph and jaw tracker (Figure 1); the x-ray also showed bilateral bilaminar condyle remodeling; the initial sonogram and jaw tracking showed that the patient deviated to the right to promote molar avoidance (Figures 2a and 2b), which is a neurologically driven physiological protective mechanism inhibiting direct intercuspation and can eventually lead to wear facets, fractures in teeth, and a future need for ongoing/repeated restorative care if the patient’s bite is not corrected. The patient also demonstrated an unstable rest position; this means that, although she was stable in centric occlusion, her muscles did not respond well when her mouth was naturally ajar without guarding (Figures 3a to 3c). The lower jaw “danced” when it was ajar. Her freeway space was at 2 mm, which is within the accepted range. However, this measurement is at the very bottom of the normal range—especially if there has been loss of vertical height, possibly indicating a subclinical pathology. (The freeway space is determined by the muscles and is neurologically induced; it is not necessarily a physical boundary set by the size of the oral cavity). The K7 showed that some of her muscles of mastication (Figure 4) were hypertrophic, while some were exhausted, and others had no readings at all because they were so fatigued (Figures 5a and 5b).
Figure 3a. All demonstrated in Scan 9: Freeway space; habitual freeway space (original unstable rest position with the mandible dancing); and tracing-confirmed vertical over-closure suggestive of a patient who is a clencher/bruxer.
Figure 3b. Orthotic (with a maxillary-planed provisional) just prior to prepping case. Patient is in a stable vertical and anterior/posterior position.
Figure 3c. Three years post-insertion: Patient presents with a stable vertical and anterior/posterior position.
|Figure 4. EMG-PreTENS (electrodes and leads placed on 9 muscle groups). EMG Rest Test before TENS pulsing. The marked and elevated anterior temporalis resting levels indicate inadequate posterior support with posterior displacement of the mandible from neuromuscular trajectory. Patient is recruiting her temporalis muscles instead of appropriately recruiting her masseters during mandibular closure.|
|Figure 5a. Scan 11: EMG Clench, ORIGINAL Natural, Natural—Cotton, Cotton roll. Muscles are not fully engaged during clenching.|
|Figure 5b. Scan 11: EMG Clench Natural, Natural—Cotton, Cotton roll. Three-year post full-mouth insertion; note the increase in muscle recruitment evidence of a healthier stomatognathic system.|
The muscular and occlusal instability required proper “structural scaffolding” in order to return the patient to a functional bite. The K7 evaluation system, or any other occlusal computerized system, is essential in finding where that scaffolding should be. To begin with, the patient is evaluated as is and without any attempt at changing the occlusal patterns or the measured data stored. During the same visit, an ultralow-frequency (ULF) TENS (Transcutaneous Electrical Nerve Stimulator [Myotronics]) unit is used to stimulate the occlusal muscles into the rest position. (The TENS supplies a low frequency and low amplitude stimulus to the muscles innervated by the trigeminal nerve complex). The patient is then remeasured afterwards to see what new patterns emerge. This stored data is then used to help evaluate where the patient’s occlusion “wants to be” if muscular interference is removed. In the vast majority of cases, the TENS unit helps promote a balanced muscular system that directly benefits the entire occlusal system.
Figure 6. Original mandibular cast. (Note the lower anterior crowding and extrusion on tooth No. 26).
Figure 7a. Original diagnostic cast.
Figure 7b. Completed lower arch.
Figure 8a. Lower fixed orthotic (with a ULF TENS generated trajectory in combination with a planed maxillary posterior fixed orthotic overlay) with anterior provisionals that were lingualized. The maxilla was planed to the established mandibular neuromuscular trajectory and vertical dimension.
Figure 8b. Original maxillary diagnostic cast.
Figure 8c. Incisally mounted maxillary diagnostic cast on an AccuLiner articulator with a face-bow/diagnostic wax-up study model for horizontal plane.
Figure 9a. Mounted diagnostic wax study models.
Figure 9b. The completed restorations were returned from the dental laboratory.
Figure 9c. Complete full-mouth restorations.
|Figure 10. The patient, 3 years postoperatively.|
During orthotic therapy, the patient was remeasured with the K7 (6 weeks later) to determine how treatment was progressing (Figures 7a and 7b). The patient was asymptomatic and was now recruiting muscles. The musculature was active and balanced without hypertonicity, exhaustion, or fatigue. The patient no longer demonstrated a destructive traumatic bite that may have once contributed to her periodontitis and loss of teeth. Instead, the patient demonstrated a smooth trajectory when opening and closing the mandible. The orthotic provided sufficient height to maintain the myocentric bite. It also contributed proprioceptively to patient’s correct use of her occlusal structure. (Again, please refer to Part 1). The patient was able to maintain a stable rest position with the fixed orthotic, indicating that her occlusion was stabilizing. Kathy also demonstrated normal swallow patterns. This was unlike that exhibited in her initial K7 analysis, which had shown anterior and lateral tongue thrusting, which contributed to a pathologic occlusal system affecting teeth alignment.
All together, the patient had approximately 6 weeks of orthotic therapy before restorative work was begun. The important thing in a case like this one is to make sure that the occlusal load is distributed throughout the whole system; otherwise the imbalance can cause problems in the future. Therefore, we want to achieve a dynamic bite with a dynamic trajectory that is neuromuscularly balanced. In this way, by removing or neutralizing pathologic occlusal forces before restoring the dentition, the patient’s dental work will last for many years. This is especially important for a patient who is in her late 50s and somewhat of a dental phobic.
The K7 is used to evaluate the status of the bite before initiating the smile makeover in order to confirm stability, balance, and placement. Once this is achieved, we are ready to aesthetically restore the smile to the new OVD (Figures 8a to 8c) appropriate for the patient. A final model is taken with the fixed-orthotic (or any transitional bonding in place) before prepping to make the provisional restorations with a silicone matrix (Sil-Tech [Ivoclar Vivadent]). (This also temporarily maintains the new OVD).
The goals of treatment involve identifying and maintaining the most ideal mandibular relationship, and transferring this relationship to the permanent restorations while neutralizing the adaptive/habitual bite of the patient. In this case, the adaptive/habitual bite had been particularly destructive to the occlusal morphology and if she had been restored at that interocclusal position would have led to a less than desired outcome. As stated in Part 1 of this article, the quality of the occlusion is only as good as the foundation that it was built on. Building on a good foundation makes all the difference.
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The author would like to give special thanks to Glen Adams, MDT, CDT, of Yes Dental Laboratory, formerly with Americus Dental Laboratory.
Disclosure: Dr. Cortes has lectured for both BIOLASE and Millenium Dental.
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