**4. Development and growth of the TMJ**

The mandible is formed and developed as a membranous bone originating from mesenchymal tissue [4].

## **4.1 Theories governing the growth of the facial skeleton**

In his 1771 book *The Natural History of the Human Teeth*, John Hunter stated that growth of the mandible occurred as result of activation of the growth center in the condyle [1].

The functional matrix hypothesis introduced by Melvin Moss in 1962 proposed that growth of the mandible and facial skeleton occur due to functional demand of the periosteal matrix of the muscles of mastication [2].

The author believes that the true nature of the growth of the facial skeleton lies within a combination of both theories. To support his hypothesis, the author performed experiments on newly born rabbits in which he excised their condyles. After three months the rabbits showed severe deformities of their lower jaws and their mandibles were twisted to the affected side.

### **4.2 Functional activity of the TMJ**

There are two types of movements in the TMJ: passive and active. Passive movements are used for speaking, laughing, yawning, singing, swallowing, and smoking. Active movements are used for the masticatory process, which is coordinated by four receptors.

Ruffini receptors function as static mechanoreceptors that position the mandible. Pacinian corpuscles are dynamic mechanoreceptors that accelerate movements during reflexes. The Golgi-Mazzoni corpuscles function as static mechanoreceptors for protection of themselves.

#### **4.3 Histology of newly growing condyle**

A newly growing condyle consists of four layers. The first layer is the articular fibrocartilage layer, the second layer consists of several zones of small, round mesenchymal stem cells, the third layer consists of an immature chondrocyte and newly formed osteoblasts, and the fourth layer consists of the mature trabecular bone with bone marrow in between and osteoblasts.

#### **4.4 Reconstruction techniques for TMJ diseases**

#### *4.4.1 TMJ ankylosis in children*

TMJ ankylosis is a painful disease that limits the opening of the mouth due to fusion of the condyle with the glenoid fossa in the skull base. Difficulties in mastication and swallowing are obvious signs.

There are three types of TMJ ankylosis: fibrous, bony, or a combination of both.

Facial deformity is obvious; the mandible is twisted to the affected side with short ramus and bowing of the lower border on the affected side, making a depression or concavity called the antegonial notch. This notch is a diagnostic sign of ankylosis with hyperplasia of the coronoid process. The floor of the mouth is underdeveloped and the tongue is in the retro position with changes and deformity of the upper respiratory tract, hyperplasia of epiglottis, and deformity of the larynx. The trachea is deviated and shifted to the affected side and the larynx is positioned more anterior.

These changes cause great difficulties in intubation during anesthesia by blind intubation and thus anesthesia should be done via guided endoscopic tube. With difficulties in intubation, a tracheotomy might be indicated.

The cause of this disease is mainly trauma to the chin in childhood, transmitted through the long access of the ramus to the condyle.

The condyle is a spongy type and vascular in children with short nek, the traumatic injuries to the condyle was crushing the condyle with fragmentation of the meniscus and damages to cartilaginous part of the TMJ.

Bleeding inside the joint causing hemarthrosis and the trauma may extend to the base of skull causing injuries to petrous bone and sagittal sutures of the base of skull the quelea for that was callus formation in the base of skull changing the length of transverse axis and longitudinal axis of the skull base.

Bleeding that occurs due to injuries to petrous bone of skull base, come out with CSF from the ear due to rupture of tympanic membrane. This type of case should be considered a head injury case and should be managed as such.

Surgical management of ankylosis in children is quite different from that in adults where the deformity of the facial skeleton already exists and growth is diminished.

In children, our choice is to use the Kummoona chondro-osseous graft for reconstruction of the TMJ after excision of all ankylosed bone with excision of hyper elongated coronoid process and reattachment of all muscles surrounding the ramus [5].

The chondro-osseous graft is harvested from the iliac crest. The length of the graft is between 4 and 5 cm and is covered by cup of 1-cm cartilage and small amount of muscle to work as the meniscus.

We approach the TMJ via modified incision starting from the periauricular region and going up the temporal region as a full-thickness fascio-cutaneous flap.

The dissection begins behind the temporalis muscle, from the posterior fibers of the temporalis muscle as a full-thickness Kummoona fascio-cutaneous flap and dissected down to the capsule of the joint. An L-shaped incision is made in the capsule to expose the ankylosed joint.

After decortication of both bone graft and ascending ramus, the graft is inserted via submandibular incision and fixed after positioning the head of the graft inside the glenoid fossa covered by muscle fibers from the iliac crest.

The graft is fixed firmly to the posterior side of the ramus using soft stainless-steel 0.5-mm wire in three points as rigid fixation to prevent any movement of the graft during function.

The aim of the chondro-osseous graft is to restore the growth potential of the mandible and midface with full functional activities required from the TMJ.

We ask the child to chew food after 3–4 days to obtain more growth by functional demand of the periosteal matrix, according to the functional matrix theory [2].

This technique has also been applied to treat first arch syndrome and hypoplasia of the condyle in children.

#### **4.5 TMJ ankylosis in adults**

TMJ ankylosis in adults can be managed using a two-part chrome–cobalt prosthesis developed by the author [6, 7]. This prosthesis is used in adults because growth of the face has already completed and thus there is no place for a chondro-osseous graft.

Before its application in humans, the prosthesis was used to replace the TMJ of *Macaca* monkeys in experiments carried out at the Royal College of Surgeons of England in 1975–1978.

The prosthesis was tested after animal scarified; the histology of the ramus carrying the shaft of implant was done by (H&E), a nice granulation tissue was formed and healthy fibroblasts were nicely formed and surrounding the prosthesis and the orientation of fibrous tissue fibers by the effect of masticatory process. Ground sections and microradiographs were also done to prove the biological viability of the prosthesis and proper orientation of the prosthesis shaft of the lower prosthesis. This TMJ prosthesis allows for full functional movements, including lateral excursion movements [7].

In our research, we found that a wide band of fibrous tissue was formed between the upper and lower parts of the prosthesis. This band prevented rubbing of metal ions between the parts, which can cause microthrombi to develop in the joint and induce necrosis and failure of the prosthesis [6, 7].

#### *4.5.1 Reconstruction of hypoplasia of the condyle and first arch syndrome*

Hypoplasia of the condyle in children can occur as result of intrauterine trauma to the condyle or trauma during birth or early childhood. The ideal technique for treating hypoplasia of the condyle is the chondro-osseous graft [8].

#### *4.5.2 Management of first arch syndrome*

First arch dysplasia syndrome or hemifacial microsomia is a congenital disease caused by early embryonic occlusion of the stapedial artery, the nutrient vessel of the first and second arches. There are three types of first arch deformities: mild, moderate, and severe.

The mild form is characterized by slight deformity of the ear and presence of small Tages in front of the ear with underdeveloped mandible, condyle, and masseter muscle. The condyle might be absent, but abnormal formation of bone simulating the condyle usually double with receding chin was observed.

Moderate disease is characterized by microsomia in the affected side with slight deformity of the mandible, absence of the TMJ and upper part of the ramus, deformity of the ear, and small Tages in front of the ear as remnants of Meckel's cartilage.

The severe form is characterized by wide microsomia, severe cleft in the angle of the mouth, severe deformity of the mandible, and absence of the TMJ, the upper part of the ramus, glenoid fossa, zygomatic root of the temporal bone, and the ear.

The management of these complicated cases requires expert surgical skills. The first step is to reconstruct the zygomatic root of temporal bone via bone graft harvested either from the ilium or rib. The glenoid fossa is reconstructed via cartilage graft taken from the patient's unaffected ear, followed by reconstruction of the cleft of the angle (commissuroplasty) by measuring the upper lip from midline to the angle of the mouth on the normal side. This measurement is applied on the cleft side with excision of skin access. Reconstruction begins with closure of the oral mucosa

and bringing the orbicularis muscle and surrounding muscle to modules. Finally, the overlying skin is closed.

In the second step, the platysma muscle flap is mobilized a superiorly based muscle platysma flap from side of the neck to reconstruct the atrophied masseter muscle (Kummoona Platysma Muscle Flap). After a few months, the TMJ is reconstructed via chondro-osseous graft harvested from the iliac crest because the bony graft requires bulky muscle to overlap the graft for nourishment.

The chondro-osseous graft was designed for reconstruction of the TMJ during the growth period at age 4–6 years for restoration of the growth of the mandible and midface.

The graft contains mesenchymal stem cells responsible for growth, repair, and remodeling of the TMJ before reconstruction of the ear, chin reconstruction by Sialastic implant as genioplasty, bone grafting in this area might showed resorption.

The final stage of reconstruction of the first arch is to reconstruct the ear and correct occlusion via orthodontic treatment. Osteotomy or distraction techniques may be required for correction of jaw deformities [5, 9].

#### **4.6 TMJ dislocation and recurrent subluxation**

Acute dislocation of the TMJ is always associated with pain and spasm of masseter, temporalis, and internal pterygoid muscles, leading to trismus and preventing return of the condyle to the glenoid fossa [10]. It occurs when the condyles suddenly jump out of the glenoid fossa ventral to the articular eminence and become locked anterior and superior to the articular eminence. It can result from extreme opening of the mouth, for example, during extensive dental work or yawning.

Chronic dislocation typically results from untreated TMJ dislocations, and the condyle remains displaced for an extended period. It occurs less often after trauma. Both sides of the condyle slide on articular eminence ventrally to the infratemporal fossa. In chronically dislocated unreduced condyle, the capsule becomes fused and adheres to the infratemporal fascia.

Risk factors for dislocation includes weakness of the joint capsule, anatomic aberration of the joint, or injuries to associated ligaments.

Subluxation of the TMJ is an excessive abnormal excursion of the condyle secondary to flaccidity and laxity of a capsule or a condition where the condylar head moves anterior to the eminence on wide opening of the mouth. In this case, the mouth can be closed again easily but slowly.

Acute subluxation or dislocation is always associated with pain due to presence of intra-articular effusion and muscle spasm.

Chronic recurrent dislocation or subluxation is characterized by the condyle sliding over the articular eminence and catching briefly beyond the eminence before returning to the glenoid fossa.

The pathogenesis of dislocation and recurrent subluxation secondary to weakness or laxity of the capsule has been attributed to trauma or abnormal chewing habits movements. It is found more frequently in people with general joint laxity (Ehlers-Danlos syndrome, Marfan syndrome, and juvenile rheumatoid arthritis), in older persons with laxity of ligaments, weak muscles, and bone resorption, and individuals with internal derangements of the TMJ or with occlusal disturbance. Other predisposing factors include prolonged opening of the mouth during dental treatment/ examination or during general anesthesia or bronchoscopy.

*Surgical Reconstruction of the Temporomandibular Joint DOI: http://dx.doi.org/10.5772/intechopen.108713*

In countries like Yemen, Sudan, Somalia, and South Arabia, some TMJ disorders can be attributed to khat chewing. Khat is a plant found in Southern Arabia and East Africa known for its stimulant effects. Khat chewing is a social tradition. Daily chewing of khat produces an excessive load on the TMJ, changing its normal excursive hinge masticatory movements to habitual rotatory movement, leading to osteoarthritic changes including atrophy of the articular eminence, shallow glenoid fossa, and lax capsule and ligaments of the TMJ. The instability of the lower jaw during speech is due to the effect of khat on the brain stem. The plant exhibits amphetamine-like action and users become very talkative under its influence.

#### *4.6.1 Management of TMJ dislocation*

There are many methods for reducing dislocation of the TMJ, the most common of which is the Hippocratic method. This method involves the practitioner standing in front of the patient and placing a gloved thumb on the posterior lower molars bilaterally with fingers wrapped laterally around the mandible. Then, the practitioner pushes the jaw downward and backward to ease it back into the glenoid fossa.

Other techniques involve injecting sclerosing agents into the capsule or using autologous blood. These methods are mostly no longer used because they can cause damage to some vital structures of the joint and pain during the procedure and postoperatively.

We propose a new technique, in which the practitioner grips the patient's lower jaw from behind and using the angle of lower jaw as pivot with slight rotation on one side immediately the condyle return to its normal position in the glenoid fossa, and immediate return of the condyle in other sides to glenoid fossa. The angle of the jaw mobilizes as a pivot by rotating the mandible in one side, immediately the side reduced and followed by other side [10, 11].

#### *4.6.2 Management of TMJ subluxation*

The ideal surgical technique advocated by the author for treating chronic recurrent subluxation and dislocation involves reinforcing and supporting the weak lax capsule with an inferiorly based, finger-shaped temporal fascia flap for reconstruction of the lateral and anterior walls of the capsule.

With reconstruction of the zygomatic root of temporal bone just in front of the articular eminence by creating an ostectomy in 45 degrees towards the joint and impacted a piece of bone from iliac crest of about 1.5 cm length and 1 cm width, it works as an obstacle for forward movement of the condyle [9, 10].

#### **4.7 TMJ osteoarthritis**

Osteoarthritis is a degenerative disease of aging that causes more severe symptoms in weight-bearing joints like the ankles and hips. It usually affects the TMJ in the early stages before it spreads to other joints of the body. TMJ osteoarthritis is characterized by a breakdown of the articular fibrocartilage layer with architectural changes in the associated bone and damage and degeneration of synovial tissue causing pain in the joint.

X-ray examination of the TMJ shows osteophytes, lipping, and cyst-like lesions (Ely's cysts) with flatting of the articular layer. In the later stages, X-ray may reveal erosion of the condyle articular surface.

In advanced disease, the articular cartilage becomes less elastic with erosion of the surface of the condyle associated with vertical cleft or crack in the subchondral bone.

Reparative attempts of the joint at the periphery of the cartilage result in formation of osteophytes, lipping, and changes in the surface contour of the articular surface [3].
