The stability of the masticatory system is imperative to ensure the long-term success of the dentition. However, instability can lead to breakdown and unpredictable results in restorative, orthodontic, and orthognathic treatment plans. Often, we address instability after the breakdown has occurred. What if the signs could be recognized early, avoiding the negative consequences? Here is how to recognize the early signs of occlusal instability and minimize risks.

Starting with the Muscle in Addressing Occlusal Instability

In the past, it was assumed that stability would follow if balance were achieved in the head and neck muscles. However, identifying the source of the muscle dysfunction is imperative before managing or treating the instability. The DC/TMD criteria states,

“For the criterion of familiar pain to lead logically to the specific diagnosis, the signs must explain the symptom history, or additional assessment must effectively rule out other competing diagnoses.”  

Signs almost always precede symptoms. Therefore, the risks can be minimized if the signs of instability are recognized early. 

The SPEAR education center systematically evaluates the dentition using the EFSB (Esthetics, Function, Structure, Biology) protocol, but recently airway was added. A healthy airway contributes to growth and development, but stability is affected when growth disturbances occur. Therein lies the problem: poor function will inevitably result in instability, occlusal breakdown, and pain.

The inability to breathe through the nose because of enlarged tonsils and adenoids, deviated septum, and enlarged turbinates will lead to mouth breathing and, in the adolescent population, affect the growth of the maxillomandibular complex. Christian Guilleminault proposed that continuous interaction between the nasomaxillary complex and the mandible during nasal breathing is vital to guiding the entire facial-skeletal complex in a forward and horizontal orientation. 

Resting the tongue against the hard palate applies light and consistent pressure, counterbalancing the facial muscles and serving as a guide to advance and widen the maxilla. The inability to breathe through the nose can contribute to oral breathing, a narrow and retrognathic maxillary arch. Another reason the tongue can’t rest against the palate is ankyloglossia or tongue tie. 

How Maxillary Growth is Stunted

Mouth breathing and ankyloglossia are two reasons the tongue isn’t positioned to the palate, thus stunting maxillary growth. A study in the 1980s with Rhesus monkeys blocked their nasal passages during the first six months of life. After six months, the monkeys were found to have narrowed the dental arches, decreased maxillary arch length, anterior crossbite, maxillary overjet, and an increased anterior face height. Interestingly, after the monkeys established nasal breathing, their facial profile and malocclusion were corrected. Although, in humans, restoration of nasal breathing does not seem to reverse the anatomical changes that occur with mouth breathing. 

Sagittal and coronal views of a dolichocephalic patient
Figure 1: Sagittal and Coronal Views of Dolichocephalic Patient.

Mandibular growth can also impact the airway and development of the maxilla. A primary growth center in the mandible lives in the condyles, and normal growth leads to a counterclockwise rotation of the mandible and an anterior projection of the chin. Improper mandibular growth results in a dolichocephalic or long face, as seen in Fig 1. 

As physicians of the masticatory system, it’s imperative to understand the why before we treat the conditions presented by patients. There has been much discussion on diagnosing the inhibition of maxillary growth early to avoid long-term maxillary deficiencies through the restoration of nasal breathing and proper tongue positioning. Patients with a dolichocephalic profile or high mandibular plane angle typically have a class II occlusion, making it difficult for the tongue to reach the anterior portion of the palate, resulting in retrognathia in both the maxillary and mandibular arches. 

Dual jaw retrognathia will ultimately result in a poor occlusal relationship and instability in the masticatory system, affecting the airway. Airway was added to EFSB because of the importance of nasal breathing for growth and development and occlusal stability. Airway-disordered breathing leads to poor oxygenation, which can increase inflammatory factors throughout the body. These inflammatory factors may lead to ligament hyperlaxity, making patients more susceptible to ligament tears, resulting in a herniation of the articular disk. 

When Articular Disk Displacement Causes Condylar Growth Disruption

A common reason for a disruption in condylar growth is a displacement of the articular disk due to torn ligaments on the medial and lateral poles of the condyle, leading to premature closure of the condylar growth center. The purpose of the articular disk is to act as a cushion, and under compression, it secretes synovial fluid, which lubricates and provides nutrition to the temporomandibular joint, and in the growing patient, the disk protects the growth center in the condylar head. (Fig. 2) 

Coronal and Sagittal Views of Temporomandibular Joint.
Figure 2: Coronal and sagittal views illustrating the purpose of the articular disk in the temporomandibular joint. The articular disk acts as a cushion and secretes synovial fluid to lubricate and provide nutrition to the joint. Additionally, in growing patients, the disk protects the growth center in the condylar head.

Ligament tears can be due to one significant injury or multiple minor insults to the TM joint because of ligament hyperlaxity. The result is the same, resulting in a disk herniation. A displaced articular disk in the adolescent patient will ultimately lead to a mandibular growth deficiency, and like the maxilla, early repair or management is imperative to achieve regular growth. The dentist must find the root of the skeletal deficiency and intervene early for normal development.

Comparison of MR images acquired in the class 1 molar or treatment position for an OFA in 10-year-old patients.
Figure 3: Comparison of MR Images in Treatment Position for OFA in 10-Year-Old Patients. The image on the left shows the condyle protected by the disk, while the image on the right depicts an anteriorly displaced disk in the treatment position. (Red - Condyle; Yellow - Fossa; Blue - Disk).

Maxillary growth is most significant during the first five years postnatal, and early restoration of growth is essential since it’s difficult to retrain the tongue to position itself to the palate after prolonged mouth breathing. Similarly, disk displacement must be addressed early to prevent the condylar growth center from premature closure. A class II occlusion greater than 2 mm evaluated in the fully seated condylar position (FSCP) in the adolescent population is at higher risk of disk displacement. When an orthodontic functional appliance (OFA) is prescribed to stimulate mandibular growth, an MRI is needed to verify the condyle is positioned under the disk in the treatment position — fig 3. 

With an understanding of the position of the disk, growth is predictable. Vertical condylar growth is likely when the articular disk protects the condyle, and the growth center is viable. A “fuzzy” cortical plate in a CBCT indicates active cell division in the adolescent patient and coupled with a disk reduction, results in a greater potential for mandibular growth. Fig 4. Although an anterior disk displacement without reduction, using an OFA may lead to increased stress on the growth center, resulting in a failure to grow or condylar resorption. In these cases, a disk repair is the most predictable manner to restore growth and increase the patient's ability to achieve a healthy maxillomandibular skeletal relationship. 

CBCT image showing the temporomandibular joints of a 10-year-old.
Figure 4: BCT image showing the temporomandibular joints of a 10-year-old. The condyle on the left displays a "Fuzzy" cortical plate (arrow), indicating active cell division, while the condyle on the right exhibits a closed growth center indicated by the cortication of the head of the condyle (Open Arrow).

In conclusion, recognizing the signs of growth deficiencies in the adolescent population increases the chances of reestablishing growth and intervening in early occlusal instability. However, before starting treatment, a diagnosis is needed. The dentist needs to understand the origin of the growth inhibition, and once a diagnosis is made, the patient can be predictably treated. 

Curt Ringhofer, DDS, is a member of Spear Resident Faculty. 


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Commenter's Profile Image Rex B.
April 30th, 2024
Nice capsulation of a complex topic