Medical Apparatus: Imaging Guide to Orthopedic Devices

Dental Devices

Dental Devices - Introduction

Dental Devices Page 1

Dental Devices Page 2

Dental Devices Page 3 - Temporomandibular Joint (TMJ) Dysfunction

Mandibular Fractures


Dental References




Dental Devices

by Tim B Hunter, MD, MSc and Rick Light, DDS


Temporomandibular Joint (TMJ) Dysfunction and Treatment

Temporomandibular joint (TMJ) dysfunction and associated muscle disorders are a variety of conditions which cause pain in the jaw and the muscles that control jaw movement. There are probably over ten million persons in the United States affected by TMJ dysfunction, and it appears to be more common in women (NIH). Up to 30% of adults will experience jaw pain and dysfunction at some time in their lives (NHS).

In most people pain in the TMJ or jaw musculature is temporary and occasional requiring no specific treatment. However, in a small subset of patients significant long-term symptoms develop. TMJ disorders fall into three main categories - a) myofascial pain involving the jaw musculature; b) internal derangement of the temporomandibular joint with a displaced disk, dislocated jaw, or deformity of the mandibular condyle from prior trauma; c) degenerative osteoarthritis of the TMJ or inflammatory TMJ arthritis, usually rheumatoid arthritis (NIH).

In those patients with significant symptom, the cause of TMJ dysfunction is often best divided into physical and psychological stress factors. Co-morbid physical stress relates to internal and external TMJ postural collapse, arthrogenic joint stress, and muscular myogenic stress. Psychological stress factors include the patient's perception of pain and the patient's pain coping mechanisms. It is important to diagnose a "cause" for any pathological condition present and not just provide "palliative" treatment of symptoms.

For those patients with chronic long-term TMJ symptoms, treatment is usually warranted. Conservative, non-surgical intervention is the treatment of choice for all but a very small number of patients. Conservative therapy involves some combination of anti-inflammatory medication, self-help physiotherapy-type treatments, TMJ injections, and possible dental orthotics (NHS).

TMJ complexity derives from its unique properties. It is classified as a ginglymoarthrodial joint (ginglimus-hinging joint and arthrodial-sliding joint). Its anatomy and physiology sets humans apart from other animals, because the TMJ is extensively involved in human communication (vocalization and facial expression). 

The TMJ’s anatomy consists of two bones-the mandibular fossa of the temporal bone and the head of the mandible (figure: mandibular anatomy). The mandibular fossa comprises the non-moving or female component of the joint, while the mandibular condyle (mandibular head and neck) is the male component.  Most importantly, in a normal healthy state these two bones should never come in direct contact with each other. 

The space between the mandibular fossa and the mandibular head is occupied by a cartilaginous meniscus or articular disk. In its normal fluid filled environment, the meniscus is attached to both bones via ligaments and focally to the superior portion of the lateral pterygoid muscle from its anterior body (figure: mandibular musculature). 

The superior head of the lateral pterygoid exerts force on the TMJ articular disc during the last phase of jaw closing, preventing posterior displacement of the articular disk that would otherwise result from the brief bursts of joint space compression preceding complete interdigitation of the teeth in centric occlusion (the closing of opposing teeth when the mandible is centered relative to the maxilla). With normal TMJ function, at no other time should any compressive force be exerted upon the TMJ meniscus. The meniscus must be maintained in its normal state for there to be a healthy temporomandibular joint.

Most articulating joints have muscles and ligaments, so-called "soft" end points, which govern their normal range-of-motion. The exception to this rule is the temporomandibular joint in the normal closed jaw position or when the teeth come together in habitual centric occlusion. In this case there is no soft end point but an end point determined by hard, bony structures (the teeth). Since the meniscus sits between the mandibular fossa of the temporal bone and the mandibular head, these two bony structures normally do not contact each other directly.

TMJ posture and health may be adversely affected by abnormal jaw closure. This takes place not through brief bursts of joint space compression (jaw closing), but jaw closing that is abnormally continuous or from habitual occlusion with the presence of malpositioned teeth, destroyed teeth, or missing teeth. Habitual occlusion is the usual relationship between the maxillary and mandibular teeth at maximum contact. It varies from person to person and may not be ideal or true centric. Since the TMJ meniscus is merely a cartilaginous disk, it does not have the structural capability to hold joint spacing and joint posture for prolonged periods. It will eventually lose its form and degenerate. Thus, temporomandibular joint posture is controlled by occlusion posture.

The proper positioning of closed “hard end point” dentition or centric occlusion benefits the temporomandibular joint. It benefits the accommodating jaw soft tissues including the supporting jaw musculature. It is the jaw musculature that controls teeth position. The jaw musculature maintains tooth posture which determines TMJ posture. If there is improper teeth occlusion, the jaw musculature will be continually strained.

If an abnormal closed interdental position (abnormal habitual occlusion) compresses TMJ posture (pathologic), then decompression of the TM joint posture (therapeutic) will result in an open interdental position (spacing between the upper and lower teeth signifying a habitual centric occlusion collapsed vertical dimension). Restoration of the temporomandibular joint to a healthy decompressed joint posture is arthrogenically defined as the mandibular head being radiographically in the Gelb 4-7 position and myogenically as a reduction in muscular electromyographic potentials (figure: Gelb positions). It may be obtained with the fairly conservative measures listed above, or it may need to be maintained and guarded by slightly more aggressive measures. The non-surgical approach to this treatment is the use of a mandibular orthopedic repositioning appliance or orthotic (MORA) (figure: examples of various MORAs). By virtue of restoring the TM joint to the Gelb 4-7 position, one is restoring it from a pathological condition. Patient instructions that treat symptoms while ignoring the underlying pathological conditions may result in a short-term relief, but not a long-term benefit.

Surgery is reserved for those with extensive TMJ joint destruction from advanced arthritis or advanced neoplasm. Surgery may also be indicated for fibrous or bony anklylosis of the TMJ or failure of a previous TMJ prosthesis. The current TMJ prostheses available are ball and socket systems similar to a hip prosthesis (figure: TMJ prosthesis radiograph; figure: TMJ prosthesis photograph; figure: TMJ prosthesis drawing; figure: TMJ prosthesis radiograph). The prosthetic temporal mandibular fossa is made of ultra high molecular weight polyethylene (UHMWPE) which replaces the fossa and articular eminence of the temporal bone. The mandibular component replaces the mandibular condyle and is composed of cobalt chromium alloy with an undersuface coated with titanium plasma. Self-retaining and self-tapping fixation screws are made of titanium (Arturo, 2013).

It should be emphasized a surgical implant device for temporomandibular joint dysfunction (TMD) is the last treatment of choice. This is due to the complex nature of the temporomandibular joint (TMJ) and the irreversibility of surgical intervention. Surgical implants themselves may cause pain and permanent jaw damage and are subject to high failure rates (NIH; Arturo, 2013).


Mandibular Trauma

Nasal fractures are the most common facial fracture, and mandibular fractures are the second most common facial fracture. The mandible is the only mobile bone in the face. Mandibular fractures often require open reduction and internal fixation (ORIF). Multidetector CT is the best modality for staging a mandibular fracture and for determining the best treatment options. Multidetector CT is also often the best modality for determining the adequacy of a mandibular reduction and for investigating possible postoperative compiications (Dreizin, 2016).

Implanted mandibular fixation hardware is usually based on titanium. Occlusal reduction is necessary to reduce mandibular fractures. This is performed by mandibulomaxillary fixation (MMF), basically wiring the jaw shut. The actual fracture reduction is performed with plates and screws using the restored occlusion as a template (Dreizin, 2016). Erich arch bars and imtermaxillary fixation screws (IMF) are used sometines in combination for mandibulomaxillary fixation. Erich arch bars are thin stainless steel bars used as scaffolding for interdental wires that in turn secure the bar to mandibular or maxillary teeth (Dreizin, 2016; Iowa Protocals, 2020). The arch bars also have lugs for wiring together the mandibular and maxillary teeth rows.

External fixation minimizes soft tissue injury and interruption of the periosteum and better preserves the blood supply compared to internal fixation. External fixators are made of connecting rods with pins, screws, or wires that are placed percutaneously into the bone proximal and distal to the fracture site (see external fixation). These pins, screws, or wires are connected by various clamps to the external fixation rods which are composed of stainless steel or carbon fiber.

For mandibular fractures rigid internal fixation is preferred to external fixation, because open reduction and internal fixation (ORIF) eliminates interfragmentary motion giving a better patient outcome. External fixation is used for staged repair of mandibular trauma where there is considerable traumatic soft tissue or bone loss with inadequate overlying healthy tissue for bone grafting. This is a common situation with facial gunshot wounds producing severly comminuted fractures and cavitary soff-tissue injury (Dreizin, 2016). External fixation with pins and fixators can be placed with limited surgical time in patients whose definitive facial trauma treatment has to be put on hold while treatment for more life-threatening conditions has priority. Grossly infected nonhealing fractures with poor soft tissue coverage are also treated by staged repair with external fixation.

If avulsed teeth, fractured crowns, or empty tooth sockets are evident after mandibular trauma, missing portions of the teeth or crowns should be accounted for. They may become ingested or aspirated foreign bodies. A tooth fragment or crown entering the digestive tract is usually swallowed going into the stomach without a problem and passing through the digestive tract without incident. Any foreign body in the airway has to be identified and removed. Extensive mandibular trauma with complex unstable fractures and a "flail mandible" is a challenge for not only the surgeons treating the patient but also for the anesthesiologists or anesthetists who have to secure a dependable airway (Raval, 2011).


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Mandibular anatomy Mandibular musculature
Mandible anatomy Mandible anatomy Mandible anatomy Mandibular muscles
Mandibular musculature Gelb positions Temporomandibular joint prosthesis Temporomandibular joint prosthesis
Mandible muscles Gelb positions TMJ prosthesis TMJ prosthesis
    From Inland Empire Oral & Maxillofacial Surgeons Image reprinted with permission from TMJ Concepts
Mandibular orthopedic repositioning appliances (MORA's)
Temporomandibular joint prosthesis - radiograph      
TMJ prosthesis      
Image reprinted with permission From Southern California Center for Surgical Arts, Husam Elias MD, DMD, FACS      

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Dental References


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Tim Hunter

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