The FAS Aligner System and the treatment of temporomandibular disorders

The literature on the aetiology of TMD describes it as multifactorial, involving biological, environmental, social, emotional and cognitive factors.^2–6 The relationship between malocclusion and the development of TMD is still a matter of debate. There is currently a great deal of controversy regarding the link between TMD and occlusal factors. Authors such as Serrat,⁷ Bottino,⁸ Barker,⁹ Taboada et al.,¹⁰ Cooper and Kleinberg,¹¹ and Selaimen et al.¹² relate malocclusion to mandibular instability and therefore joint instability. In contrast, authors such as Martínez et al.,¹³ Kahn et al.,¹⁴ Gesch et al.,¹⁵ Seligman and Pullinger,¹⁶ and Lipp¹⁷ suggest that occlusal factors do not play an important role in the aetiology of TMD.

As the philosopher Karl Popper rightly said, scientific knowledge is the best and most important type of knowledge we have, although it is far from being the only source of knowledge.¹⁸ In our daily practice, in addition to considering the scientific literature, we must consider our clinical experience and clinical results. Okeson says, “Although orthodontics cannot be linked to prevention or causing TMD, it is difficult to imagine a specialty that changes interocclusal relationships so much and does not impact masticatory structures and function.¹⁹

All the articles written that do not find a relationship between occlusion and TMD define occlusion from a static point of view.^{20, 21} Okeson keenly observes this and writes, “The literature finds a minor relationship between occlusal factors and TMD. It should be noted, however, that these studies report on the static relationship of the teeth as well as the contact pattern of the teeth during various eccentric movements. This represents the traditional approach to evaluating occlusion. Perhaps these static relationships can provide only limited insight into the role of occlusion and TMD.”

Undoubtedly, if we look at occlusion from a dynamic functional aspect as it relates to joint position, it is likely to provide more information regarding the relative risk of developing TMD. As McKee mentions in a guest editorial in Cranio,²² “Much of the confusion about occlusion could be resolved if we redefined the definition of ‘occlusion’.” The problem when defining occlusion solely by the position of the teeth is that the mandible is made up not only of teeth at the anterior end but also of condyles and discs at the posterior end. If we redefine occlusion as the position in which the mandible fits into the maxilla, an occlusal analysis would then consist of evaluating not only how the teeth in the mandible fit with the maxillary teeth but also how the unit of the condyle head and articular disc fits into the glenoid fossa. By evaluating occlusion at both the posterior end and the anterior end of the system, it becomes clear that changes at the TMJ level can explain many of the tooth-based malocclusions that have confounded our profession.

Condyles become displaced for three main reasons (regardless of trauma): Class II Division 2 molar relationship, fulcrums and progressive condylar resorption.

1. Class II Division 2 molar relationship. In a recent doctoral thesis [Spanish] carried out at the University of Seville in Spain, a study of CBCT images observed a more posterior position of the condyle within the glenoid fossa in patients who presented with the aforementioned malocclusion compared with patients with normal occlusion.²³ The displacements were mainly downward and backward condylar displacements, producing compression of the synovial membranes, the posterior ligament and the bilaminar zone. These patients were thus symptomatic.
2. Fulcrum (posterior interference). Authors such as Čimić et al.,²⁴ Palla²⁵ and Isberg²⁶ have observed that occlusal interferences, also known as fulcrums, can lead to an immediate change in condylar position within the TMJ. Most of these fulcrums are caused by the palatal cusps of the maxillary second molars. These fulcrums will take the condyles out of the fossae, since the occlusion determines the condylefossa relationship, regulated by periodontal receptors that in turn activate the muscles. These fulcrums will interfere with the patient’s arc of closure and will not allow the condyles to sit correctly within the fossae with the discs correctly positioned. Therefore, as Padala et al. conclude, the condylar position will play a significant role in the aetio-pathogenesis of TMD.²⁷

Considering that occlusion is proprioceptive and always avoids interferences, the occlusal contacts of the teeth significantly influence the stability of the masticatory system. That is why Okeson asserts so widely that a functionally healthy masticatory system depends entirely on an orthopedically stable condylar position, and the condyles’ most stable musculoskeletal position coincides with maximum intercuspation.^{19, 28, 29} Therefore, orthopaedic stability should be the goal of treatment for any orthodontist. He et al. show that, in most patients with signs and symptoms of TMD, there is a discrepancy between maximum intercuspation of the teeth and stable condylar position.³⁰

A functional physiological occlusion is one in which the following characteristics are present:

• Maximum intercuspation with no interferences occurs in a musculoskeletally stable position of the system.
• Teeth have normal anatomy; cusps, pits and grooves allow vertical mastication without interferences.
• The condyles guide repetitive mandibular movements without parafunctional compensation.
• The agonistic and antagonistic muscles work in coordination and act synergistically.

In a parafunctional occlusion, the following alterations can be observed:

• Occlusal interferences in the arc of closure cause the mandibular movement to adapt to avoid these interferences.
• The interferences often produce wear facets that alter dental anatomy, and patients lose their vertical masticatory pattern. Patients become horizontal chewers, further increasing tooth wear. Some authors have related wear facets to TMD.^31–39 Large discrepancies between maximum intercuspation and stable condylar position frequently contribute to tooth wear and changes in masticatory patterns.^{34, 37, 39–42}
• The patient may have pain, muscular spasm and other signs of TMD.^{32, 37}

3. Progressive condylar resorption (PCR), also called idiopathic condylar resorption. It is an aggressive form of degenerative disease of the TMJ. It is more frequent in adolescent females, although it has also been observed in males. Pathognomonic features of this condition include a loss of condylar mass, loss of condylar morphology, and reduction in size and height of the condyle. There is also a decrease in ramus height and mandibular length, producing postero-rotation of the mandible and a corresponding Class II molar relationship and open bite.

Changes occur in the soft tissue first; advanced cases involve hard tissue. Involvement of hard tissue is often preceded by disc displacement without reduction, which in turn contributes to the destruction of joint tissue and occurs when functional demands have surpassed the adaptive capacity of the tissue. In 67% of cases, PCR is unilateral.⁴³ PCR is often related to unstable occlusion, leading to dysfunctional remodelling and morphological changes to the TMJ.⁴⁴ Although some cases will be asymptomatic, according to Kristensen et al., most patients will develop signs and symptoms of TMD.⁴⁵

Colonna et al. observed that individuals with TMJ pain have a smaller condylar volume and a tendency to hyperdivergent growth.⁴⁶ Manfredini et al. in a systematic review of the literature suggest that individuals with a Class II skeletal pattern and hyper-divergent growth pattern have a higher frequency of disc displacement and degenerative changes.⁴⁷

Oh et al. also observed that facial asymmetry and deviated chins are associated with PCR.⁴⁸ In these cases, we can also observe smaller condyles on the side of the deviation, reduced length of the condylar neck, or reduced volume of the neck and condylar head directly related to the resorption process. However, when these changes occur in one or both TMJs, it is unlikely that the teeth at the other end of the jaw will not be affected.

Thus, there are many manifestations of PCR:

• open bite with only posterior contacts;
• loss of overbite;
• deviation from the midline;
• inclination of the occlusal plane to the affected side;
• flat and worn teeth;
• cervical enamel erosion;
• widening of the periodontal ligament space;
• dentine hypersensitivity;
• acceleration of the progression of periodontal disease; and
• worsening of endodontic lesions.

When the articular tissue changes in volume, shape and morphology to achieve the necessary characteristics to maintain function (to restore congruency of the surfaces), the muscles pull the condyles upwards and forwards, the condyle seats upwards and forwards, and the mandibular plane rotates clockwise so that only the posterior teeth are in contact. When patients want to reach maximum intercuspation, they do so at the expense of the condylar position. The posterior teeth become the fulcrum, where the occlusal plane pivots, pushing the condyles downwards and backwards.

When there is orthopaedic instability and the teeth are not in occlusion, the condyles are held in their stable musculoskeletal position by the elevator muscles, resulting in a very unstable occlusion. However, when the teeth are brought into occlusion, maximum intercuspation cannot be achieved with the condyles in a stable position. Therefore, the individual has to choose either to maintain a stable condylar position and occlude on a few teeth or to make the teeth contact in a more stable occlusal position, which would compromise joint stability.

Therefore, in diagnosing and planning any orthodontic treatment, a complete vision of the patient’s problems is necessary to determine the ideal solution for each case. Diagnosis is a fundamental part of our specialty if we want to achieve all our goals, especially stability and longevity. Our main goals are orthopaedic stability, TMJ health, dental and facial aesthetics, increased airway, optimal jaw dynamics with a vertical masticatory pattern, periodontal health, dental stability and longevity and of course patient satisfaction.

In the case of orthopaedically unstable patients, a stable arc of closure must be achieved before starting any orthodontic treatment. Stabilisation is achieved with an occlusal splint, and once stabilised, this position must be maintained until the end of treatment to attain orthopaedic stability. Splints must be worn 24 hours a day, seven days a week. We use a two-piece splint, and both parts are constructed at the same vertical dimension of occlusion. The anterior splint covers the six anterior teeth (incisors and canines), and the posterior splint is united by a palatal bridge and covers the premolars and molars.

The anterior splint opens the bite and avoids posterior contacts, diminishing the muscular activity and restoring symmetrical function. By increasing the vertical dimension, we obtain relaxation of the elevator and depressor muscles. Patients wear it during sleep, ideally for at least eight hours. This splint allows repositioning of the condyles upwards and forwards and harmonising of the neuromuscular system by eliminating clenching and parafunction. During the day, patients wear the posterior splint, allowing seating of the condyles, stabilisation of dental contacts and recovery of the true arc of closure. The two-piece splint is much better accepted by patients since it produces no aesthetic problems and thus encourages greater compliance.⁴⁹

Case 1

A 30-year-old female patient presented with the chief complaints of severe muscle and joint pain, open bite and tooth wear. She was treated orthodontically as a teenager with fixed appliances. Extra-orally, we observed slight mandibular asymmetry with deviation of the chin to the right, as well as lip incompetence, insufficient chin projection and a long face typical of a dolichofacial skeletal pattern (Fig. 2). Intra-orally, she had an anterior open bite, retroclined maxillary incisors, moderate crowding in both arches, an asymmetrical arch form uneven gingival margins, a mandibular midline shifted to the right, abfractions, gingival recession and wear facets (Fig. 3). The joint and muscle examination revealed pain on palpation of the masseter, temporalis, and superior right and left lateral pterygoid muscles. She also exhibited pain in the bilaminar zone and both lateral poles of the condyles. Clinically, she had early clicking during mandibular opening and closing owing to anterior displacement of the articular disc in both joints. In the dental panoramic tomogram, she was missing all four third molars, but had no other noteworthy pathology (Fig. 4). Cephalometrically, she had a dolichofacial skeletal pattern and proclination of the mandibular incisors (Fig. 5).

We performed a visual treatment objective, and our goals were to lingualise the mandibular incisors, decrease the vertical dimension through intrusion of the posterior teeth and produce anticlockwise rotation of the mandibular plane. This would improve the patient’s facial profile, lip competence and articular function. The CBCT images of the joints showed that both condyles were improperly located within the fossae (Fig. 6). The joint spaces were increased and the condyles descended. The airway area on the CBCT scan showed compression (Fig. 7). The patient was referred for a polysomnographic study to rule out compromised respiratory function.

When measuring the size of her teeth and conducting a Bolton analysis, we identified an anterior Bolton discrepancy due to mandibular excess (Fig. 8). In maximum intercuspation, there were bilateral contacts only on the posterior teeth (Fig. 9). In her arc of closure (Fig. 10), a unilateral posterior fulcrum was observed. It was due to premature contact on the maxillary left second molars.

Based on the complete clinical situation, the patient was diagnosed with orthopaedic instability with muscular and joint symptoms, tooth wear, recession, a dental fulcrum, altered joint spaces and anterior articular disc displacement. Therefore, it was paramount to establish condylar stability and achieve a stable arc of closure before starting any orthodontic treatment.

Treatment with the FAS Aligner System, as shown in the FAS OcclusalDesign tool (Fig. 16), was used, aiming at decreasing the vertical dimension through intrusion of the maxillary molars, correcting the arch form, centring the mandibular midline and levelling the maxillary and mandibular occlusal planes. The Bolton discrepancy would be resolved with inferior interproximal reduction. The planned movement was compatible with periodontal health, being within the biological limits of the patient’s alveolar bone (Fig. 17).

After treatment, the patient had bilateral Class I molar and canine relationships, correct overjet and overbite, centred midlines and improved arch forms (Fig. 52). Extra-orally, she had improved arch forms, a wider smile, an improved smile line and less gingival exposure (Fig. 53). The lower facial third had been shortened thanks to mandibular antero-rotation, and there was improvement of the upper lip support thanks to the positive torque of the maxillary incisors. In the post-treatment panoramic radiograph, we observed excellent periodontal status, no resorption of the roots and extraction of the maxillary third molars (Fig. 54). In the post-treatment cephalometric tracing, we saw a decrease of the ANB angle, a reduction in the anterior face height, an increase of the facial axis angle, and a decrease in the distance between the soft pogonion and the true vertical line thanks to the anticlockwise rotation of the mandible (Fig. 54). We also found an increase in the inclination of the maxillary incisors and an improvement in the final inter-incisal angle. Concerning her TMJs, the patient remained totally asymptomatic and had a vertical masticatory pattern and a stable arc of closure. The CBCT scan showed well-corticated condyles in the same position as that obtained after the splint therapy (Fig. 56).

Conclusion

The stabilisation phase with a splint in patients with unstable condylar positions is necessary in many cases before starting orthodontic treatment. Thanks to the splint, we can resolve symptoms, but more importantly, we can achieve the patient’s true arc of closure, which is of the utmost importance for correct diagnosis and treatment planning.

Working on the arc of closure is without any doubt the main reason for our success, not only with aligners but with our TMD patients. When you diagnose and plan treatment on the true arc of closure of the patient, this allows you to know exactly where the problem lies and helps in finding the correct solution. When you capture the true arc of closure and when you see where the first contact is, you can see exactly why the patient has a centric occlusion–maximum intercuspation slide, why and where the mandible is shifting, why the patient’s teeth are wearing, why there is recession, why the patient has muscular symptoms, why there is abfraction and why the patient has TMD. Knowing all of this informs what needs to be done to resolve the discrepancy. We know what needs to be done to obtain the correct vertical dimension, and in the case of a transverse discrepancy, we know whether it can be resolved with orthodontics alone or whether we need miniscrew-assisted rapid maxillary expansion, surgically assisted rapid maxillary expansion or corticotomy. We also know what needs to be done with the sagittal discrepancies. Once we capture the arc of closure, we know exactly whether the sagittal problem is vertical or truly sagittal, and this of course will also lead us to the exact solution.

Working on the true arc of closure helps us to achieve predictable and stable results and, when using aligners, to utilise fewer aligners, reduce the treatment time and finally achieve orthopaedic stability in 100% of our patients. Luckily, the FAS Aligner System allows us to work on the patient’s arc of closure before, during and after orthodontic treatment, and this is what supports predictability in all our decisions.