Developmental Abnormalities

Treatment of TMJ developmental abnormalities is a unique subspecialty of TMJ surgery. A thorough understanding of the causes, treatment options, variations, and surgical procedures is necessary to provide comprehensive treatment. Surgical execution of the required procedures should be performed by a facial reconstructive surgeon experienced in complex TMJ and jaw reconstructive procedures in order to achieve the best possible outcome. All of the surgeons at our center have an extensive knowledge of condylar hyperplasia and are an integral part of the New Jersey Institute for Craniofacial Surgery. The members of our team function as Craniofacial Surgeons, Plastic & Reconstructive Surgeons, and Oral & Maxillofacial Surgeons for the Institute and have led the center for more than 35 years.

 

Anatomy and Function Of  The TMJ Condyle

 

 

The condyles are very important portions of the mandible and serve three main functions:

 

  1. The condyles contain the growth regulation centers of the entire mandible.

  2. The condyles are the portions of the mandible that function in the temporomandibular joint (TMJ), allowing the mandible to open and close properly.

  3. The condyles provide a “stop” for the mandible. They are the only portion of the mandible touching another bone. Without this “stop,” the mandible is able to move into areas in which it is not meant to be. Imagine a stool with one short leg: the stool will tilt until the short leg hits the ground, providing a new “stop” but tilting the stool.

Condylar Hypoplasia (not enough growth)

Although there can be a lack of growth in all areas of the mandible (chin, body, angle, etc.), growth abnormalities that produce a small condyle present significant issues because they can alter these three functions.

 

If the condyle is deficient to the point that the vertical height of the jaw on the affected side is decreased, the position of the entire lower jaw will be altered. If the decrease in size is unilateral (on one side), it will result in canting (tilting) of the mandible toward the affected side. As the lower jaw becomes canted, the upper jaw will not be able to grow into its normal position, resulting in a canted upper jaw as well. This canting of the upper and lower jaw is referred to as “canting of the maxillo-mandibular complex.”

 

If the deficiency is bilateral (on both sides), the mandible will rotate backward, resulting in a gap between the upper and lower front teeth (anterior open bite). This gap may allow the upper jaw to grow down more than usual, resulting in a gummy smile (vertical maxillary excess).

When evaluating a small, malformed, or absent condyle, there are five main questions to answer:

 

What is the cause (etiology)?

Determining the cause is important to determine if the deficiency is growth related or a resorptive process. If it is a resorptive process, the cause must be determined and proper consultations must made (e.g., rheumatologists). Treatment is typically delayed until the resorption has “burned out” or stopped. Once it is confirmed that the resorptive process has stopped, a treatment plan may be formulated.

 

How significant is the deficiency?

The degree of hypoplasia will determine the treatment. In mild cases in which the condyle is present but just small, traditional jaw surgery techniques may be used. In more severe cases, the need for reconstruction of a condyle will need to be determined. This is usually accomplished using rib grafts or a custom-fabricated titanium prosthesis.

 

Is the deficiency unilateral (one side) or bilateral (both sides)?

Any of the hypoplastic or degenerative processes can occur in either one or both condyles. Some are more likely to occur on one side (hemifacial microsomia), and some occur more commonly on both sides (Treacher Collins syndrome). The amount and degree of deficiency can vary from one side to the other, and degeneration can progress at a different rate on one side than on the other. These factors need to be identified in order to formulate a comprehensive treatment plan.

 

Is the rest of the mandible on that side small or just the condyle?

Commonly it is not just the condyle that is underdeveloped, but it is the entire side of the mandible that is small (hemimandibular hypoplasia). It is important to determine this when developing a surgical treatment plan so that plans to correct this cosmetic aspect can be addressed as well. If present, this may be corrected with repositioning of the mandible or may require the use of custom facial implants in addition to repositioning.

 

Is the maxilla (upper jaw) canted also?

Typically the maxilla (upper jaw) accommodates to the canted mandible (lower jaw), resulting in a canting of both jaws. This needs to be identified and treatment planned, so that it can be corrected at the time of surgery.

 

References

Obwegeser H. Mandibular Growth Anomalies: Terminology ‒ Aetology Diagnosis ‒ Treatment. Berlin, Heidelberg: Springer, 2001.

Posnick JC, Amato J. Treacher Collins syndrome: evaluation and staging of reconstruction. In: Fonseca R, ed. Oral and Maxillofacial Surgery. 2nd ed. Vol III. St. Louis, MO: Elsevier Saunders, 2009:45:936-960.

 

 

Condylar Hyperplasia (too much growth)

Overgrowth of the condyles presents significant issues because it can alter these three functions.

 

Growth Regulation

There appears to be two separate growth regulators in the condyle: a regulator for the mass or volume of the mandible (M) and a separate regulator for the length of the mandible (L). Because the growth regulation centers are in the condyle, condylar hyperactivity typically will produce increased growth of the entire affected side of the mandible. Because there are two separate regulators of growth, there are three possible scenarios of growth dysregulation.

 

Type I

A dysregulation of the (M) regulator affecting the mass of the mandible only. This leads to a pattern of mandibular overgrowth referred to as “hemimandibular hyperplasia.”

 

Type II

A dysregulation of the (L) regulator affecting the length of the mandible only. This leads to a pattern of mandibular overgrowth referred to as “hemimandibular elongation.”

 

Type III

A dysregulation of both the (M) and the (L) regulators. This leads to a pattern of mandibular overgrowth referred to as “mixed hemimandibular hyperplasia and elongation.”

 

Most cases of condylar hyperactivity develop without a known cause, and almost all present as one of the three types listed above, but the degree of overgrowth varies considerably. The overgrowth can range from mild and clinically insignificant to an extreme deformation of the mandible. The change in growth can develop slowly over years or very rapidly over weeks or months. The overgrowth may become evident by the age of 6 or 7, or at any time after that. Condylar hyperactivity can occur on one side of the mandible (unilateral) or on both sides of the mandible (bilateral). Typically, when only one side of the mandible is affected, there will be more significant asymmetry of the mandible; however, asymmetry also can be seen when both sides of the mandible are affected, as each side can be affected to a different degree.

 

Treatment

Treatment will vary depending on the type and extent of the hyperactivity. Most of the time, condylar hyperplasia disturbs the position and size of the upper and lower jaws. Definitive correction typically requires surgical repositioning and recontouring of the upper jaw, lower jaw, and chin once growth has ceased.

 

Timing

Definitive corrective jaw surgery is performed once facial growth is completed and once it has been established that the condylar hyperactivity has stopped. Most clinicians use the term “burned out” to describe the cessation of condylar activity.

Various techniques are used to determine if the condylar hyperactivity has “burned out.” The most common techniques are:

  • Review of previous records

    • Radiographs

    • Photographs

    • Dental models

  • A bone scan (See the section on bone scans.)

 

High Condylectomy & Condylar Shaving

In severe cases, sometimes a “high condylectomy” procedure or a “condylar shaving” procedure may be recommended while condylar growth is still active. Both of these procedures involve surgically removing the top portion of the condyle in an attempt to stop the hyperactivity. A “high condylectomy” procedure involves removing 4‒5mm of the condyle, while a “condylar shave” procedure removes 2‒3mm. The long-term results of these procedures are not definitive. Although we do consider these procedures in more severe cases, we follow a conservative approach of waiting until condylar growth has “burned out” if possible.

 

References

Obwegeser H. Mandibular Growth Anomalies: Terminology ‒ Aetology Diagnosis ‒ Treatment. Berlin, Heidelberg: Springer, 2001.

Posnick J. Principles and Practice of Orthognathic Surgery. St. Louis, MO: Elsevier Saunders, 2014.

 

 

Bone Scans To Evaluate Condylar Activity

Skeletal scintigraphy, commonly referred to as a “bone scan,” is a diagnostic test that evaluates the cellular activity of bones. The scan involves the IV injection of compounds called phosphonates that attach to bone cells through physical and chemical methods. These phosphonates have Technetium-99 attached to them which produces low doses of radiation that can be detected with special cameras. Approximately 3 hours after the injection, the phosphonates have attached to bone cells throughout the body. The special cameras can then be used to visualize the Technetium attached to the phosphonates producing the bone scan images.

 

The purpose of a bone scan is to identify areas of bone cell activity. The more active the area, the more phosphonates will attach and the more it will light up on the scan, producing a “hot spot.” However, it is important to understand there are three processes that will cause increased phosphonate uptake:

  1. Infection

  2. Inflammation

  3. Increased metabolic activity

 

This presents a problem when using a bone scan to evaluate for condylar activity. A “hot spot” does not necessarily indicate increased metabolic activity. Infection and inflammation of the area could produce a “hot spot” as well. Therefore, this study is sensitive (it is very good at detecting “hot spots”) however it is not specific (it does not provide information to determine if the hot spot is from increased metabolic activity, inflammation, or infection).

 

In cases of condylar hyperactivity, it is common to have localized inflammation of the TMJ, therefore it becomes unclear if a “hot spot” is from increased bone activity or from inflammation in the area. Experienced radiologists can merge the results of a bone scan and a CT scan together to create a more accurate study, however the results can still be non-definitive. Clinical correlation always needs to be made. On the other hand if there is no evidence of increased uptake in the condyle then it is likely that bone activity has stopped. For this reason we prefer, if possible, using serial radiographs, dental models, and/or CT scans taken every 6-12 months to identify changes that signify growth.

 

References

Kaban LB. Congenital and acquired growth abnormalities of the temporomandibular joint. In: Keith DA, ed. Surgery of the Temporomandibular Joint. London: Blackwell Scientific, 1992:84-115.

Kaban LB, Cisneros GJ, Heymann S, Treves ST. Assessment of mandibular growth by skeletal scintigraphy. J Oral Maxillofacial Surg. 1982; 40:18-22.

Kaban LB, Treves ST, Pogrel MA, Hattner RS. Skeletal scintigraphy for assessment of mandibular growth and asymmetry. In: Treves ST, ed. Pediatric Nuclear Medicine. 2nd ed. New York, Berlin, Heidelberg: Springer, 1995:316-327.

McDougall IR: Skeletal scintigraphy (medical progress). West J Med. 1979 June; 130:503-514.

Obwegeser H. Mandibular Growth Anomalies: Terminology ‒ Aetology Diagnosis ‒ Treatment. Berlin, Heidelberg: Springer, 2001.

Posnick J. Principles and Practice of Orthognathic Surgery. St. Louis, MO: Elsevier Saunders, 2014.

 

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