Jaw and Temporomandibular Joint: Anatomy

Development

The pharyngeal arches Pharyngeal arches The branchial arches, also known as pharyngeal or visceral arches, are embryonic structures seen in the development of vertebrates that serve as precursors for many structures of the face, neck, and head. These arches are composed of a central core of mesoderm, which is covered externally by ectoderm and internally by endoderm. Branchial Apparatus and Aortic Arches are embryonic structures that serve as precursors for many structures of the face, neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess, and head. The arches are composed of mesoderm Mesoderm The middle germ layer of an embryo derived from three paired mesenchymal aggregates along the neural tube. Gastrulation and Neurulation and neural crest cells Neural crest cells Gastrulation and Neurulation and are accompanied externally by ectoderm Ectoderm The outer of the three germ layers of an embryo. Gastrulation and Neurulation and internally by endoderm Endoderm The inner of the three germ layers of an embryo. Gastrulation and Neurulation.

• The jaw arises from the 1st pharyngeal arch.
• Neural crest cells Neural crest cells Gastrulation and Neurulation create the 1st pharyngeal arch.
• The 1st pharyngeal arch gives rise to the mandible, maxilla Maxilla One of a pair of irregularly shaped bones that form the upper jaw. A maxillary bone provides tooth sockets for the superior teeth, forms part of the orbit, and contains the maxillary sinus. Skull: Anatomy, and muscles of mastication.

Bones of the Jaw

The jaw consists of 3 bones: the maxilla Maxilla One of a pair of irregularly shaped bones that form the upper jaw. A maxillary bone provides tooth sockets for the superior teeth, forms part of the orbit, and contains the maxillary sinus. Skull: Anatomy, the mandible, and the temporal bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types.

Maxilla Maxilla One of a pair of irregularly shaped bones that form the upper jaw. A maxillary bone provides tooth sockets for the superior teeth, forms part of the orbit, and contains the maxillary sinus. Skull: Anatomy

• Paired bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types, fused at the midline (intermaxillary suture)
• The upper jaw Upper jaw One of a pair of irregularly shaped bones that form the upper jaw. A maxillary bone provides tooth sockets for the superior teeth, forms part of the orbit, and contains the maxillary sinus. Skull: Anatomy is composed mainly of the alveolar process, which forms the maxillary dental arch, housing the upper teeth Teeth Normally, an adult has 32 teeth: 16 maxillary and 16 mandibular. These teeth are divided into 4 quadrants with 8 teeth each. Each quadrant consists of 2 incisors (dentes incisivi), 1 canine (dens caninus), 2 premolars (dentes premolares), and 3 molars (dentes molares). Teeth are composed of enamel, dentin, and dental cement. Teeth: Anatomy
• Does not articulate with the mandible or contribute to movements of mastication

Mandible

• Single, horseshoe-shaped bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types
• Site of attachment for all 4 mastication muscles—temporalis, masseter, lateral pterygoid, and medial pterygoid (see below)
• Ramus: vertical projection, site of protrusion of 2 processes separated by the mandibular notch
  • Coronoid process: anterior, attachment for the temporalis
  • Condylar process: posterior, component of the temporomandibular joint (TMJ)
• Body: forms the chin Chin The anatomical frontal portion of the mandible, also known as the mentum, that contains the line of fusion of the two separate halves of the mandible (symphysis menti). This line of fusion divides inferiorly to enclose a triangular area called the mental protuberance. On each side, inferior to the second premolar tooth, is the mental foramen for the passage of blood vessels and a nerve. Melasma (mental protuberance), site of attachment for muscles of facial expression Muscles of facial expression The facial muscles (also called mimetic muscles) control facial expression and are supplied by the facial nerve. Most of them originate from the skull and attach to the skin around the facial openings, which serve as a method to group or classify them. Facial Muscles: Anatomy
  • Base: the inferior portion of the body, features the mental protuberance ( chin Chin The anatomical frontal portion of the mandible, also known as the mentum, that contains the line of fusion of the two separate halves of the mandible (symphysis menti). This line of fusion divides inferiorly to enclose a triangular area called the mental protuberance. On each side, inferior to the second premolar tooth, is the mental foramen for the passage of blood vessels and a nerve. Melasma), mental tubercle (2, on either side of the protuberance), and mental foramen (2, opening in the mandible located below the 2nd premolar for the passage of the mental nerve)
  • Alveolar process: superior border of the body of the mandible, forms the mandibular dental arch
•  Angle: the angle between the body and the ramus of the mandible

Temporal bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types

The mandibular fossa is the articular surface in which the condylar process of the ramus of the mandible articulates with the skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull: Anatomy, forming the TMJ.

Temporomandibular Joint

Joint type and surfaces

• The TMJ is a hinge-and-plane synovial joint
  • Hinge motion allows the jaw to open with a set axis (rotational movement).
  • Plane motion allows the jaw to move side to side (translational movement).
  • Note: The articular surfaces of synovial joints are usually covered in hyaline cartilage Hyaline cartilage A type of cartilage characterized by a homogeneous amorphous matrix containing predominantly type II collagen and ground substance. Hyaline cartilage is found in articular cartilage; costal cartilage; laryngeal cartilages; and the nasal septum. Cartilage: Histology. The TMJ has fibrocartilage Fibrocartilage A type of cartilage whose matrix contains large bundles of collagen type I. Fibrocartilage is typically found in the intervertebral disk; pubic symphysis; tibial menisci; and articular discs in synovial joints. Cartilage: Histology instead, to prevent degeneration.
• Articular surfaces:
  • Condylar process (or mandibular condyle) of the mandible
  • Mandibular fossa in the squamous portion of the temporal bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types
  • Articular disc: biconcave, divides the joint cavity into superior and inferior compartments

Compartments

• Separated by the articular disk
• Each lined by separate synovial membranes and filled with synovial fluid
• Superior compartment
  • Also called discotemporal space
  • Allows for translational movements
• Inferior compartment
  • Also called discomandibular space
  • Allows for rotational movements

Supporting structures

• Joint capsule Capsule An envelope of loose gel surrounding a bacterial cell which is associated with the virulence of pathogenic bacteria. Some capsules have a well-defined border, whereas others form a slime layer that trails off into the medium. Most capsules consist of relatively simple polysaccharides but there are some bacteria whose capsules are made of polypeptides. Bacteroides: from the border of the mandibular fossa to the neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess of the mandible 
• Temporomandibular ligament
  • A horizontal band that covers the lateral portion of the capsule Capsule An envelope of loose gel surrounding a bacterial cell which is associated with the virulence of pathogenic bacteria. Some capsules have a well-defined border, whereas others form a slime layer that trails off into the medium. Most capsules consist of relatively simple polysaccharides but there are some bacteria whose capsules are made of polypeptides. Bacteroides
  • Prevents lateral/posterior displacement Displacement The process by which an emotional or behavioral response that is appropriate for one situation appears in another situation for which it is inappropriate. Defense Mechanisms of the condyle
• Stylomandibular ligament
  • A thickened band of deep cervical fascia Fascia Layers of connective tissue of variable thickness. The superficial fascia is found immediately below the skin; the deep fascia invests muscles, nerves, and other organs. Cellulitis that extends from the styloid process to the mandibular angle 
  • Does not limit Limit A value (e.g., pressure or time) that should not be exceeded and which is specified by the operator to protect the lung Invasive Mechanical Ventilation movement of the jaw 
• Sphenomandibular ligament
  • From the spine Spine The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy of the sphenoid to the mandibular lingula
  • Limits extensive protrusion/opening
  • Note: the only ligament of the TMJ not fused to the joint capsule Capsule An envelope of loose gel surrounding a bacterial cell which is associated with the virulence of pathogenic bacteria. Some capsules have a well-defined border, whereas others form a slime layer that trails off into the medium. Most capsules consist of relatively simple polysaccharides but there are some bacteria whose capsules are made of polypeptides. Bacteroides
• Collateral ligaments
  • Medial and lateral
  • Connect the articular disk to the ipsilateral condyle

Muscles of Mastication

Neurovasculature

Blood supply

• TMJ:
  • Deep auricular artery
  • Superficial temporal artery Superficial Temporal Artery Giant Cell Arteritis
  • Anterior tympanic artery
• Muscles of mastication: branches from the maxillary artery
• Venous drainage:
  • Superficial temporal vein
  • Maxillary vein

Nerve supply

• Mandibular nerve:
  • 3rd branch of the trigeminal nerve Trigeminal nerve The 5th and largest cranial nerve. The trigeminal nerve is a mixed motor and sensory nerve. The larger sensory part forms the ophthalmic, mandibular, and maxillary nerves which carry afferents sensitive to external or internal stimuli from the skin, muscles, and joints of the face and mouth and from the teeth. Most of these fibers originate from cells of the trigeminal ganglion and project to the trigeminal nucleus of the brain stem. The smaller motor part arises from the brain stem trigeminal motor nucleus and innervates the muscles of mastication. The 12 Cranial Nerves: Overview and Functions
  • Motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology supply to muscles of mastication
• Otic ganglion:
  • Parasympathetic fibers 
  • Stimulate synovial fluid production
• Superior cervical ganglion:
  • Sympathetic fibers 
  • Pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways reception within TMJ

Clinical Relevance

The following conditions can affect the TMJ:

• TMJ dysfunction: syndrome of pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways and dysfunction of the TMJ and the muscles of mastication. The most significant feature of TMJ dysfunction is pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways, followed by restricted mandibular movement and possibly “cracking” or “popping” noises. The etiology of TMJ dysfunction is multifactorial, being attributed to musculoskeletal, psychological, and/or neuromuscular factors. Symptomatology Symptomatology Scarlet Fever may be chronic and difficult to manage. Management includes analgesics, physical therapy Physical Therapy Becker Muscular Dystrophy, and cognitive-behavioral therapy Cognitive-behavioral therapy Cognitive-behavioral therapy corrects faulty assumptions and tries to replace maladaptive behavior with healthier alternatives. Psychotherapy.
• Trismus Trismus Spasmodic contraction of the masseter muscle resulting in forceful jaw closure. This may be seen with a variety of diseases, including tetanus, as a complication of radiation therapy, trauma, or in association with neoplastic conditions. Tetanus: also called lockjaw Lockjaw Spasmodic contraction of the masseter muscle resulting in forceful jaw closure. This may be seen with a variety of diseases, including tetanus, as a complication of radiation therapy, trauma, or in association with neoplastic conditions. Tetanus. Trismus Trismus Spasmodic contraction of the masseter muscle resulting in forceful jaw closure. This may be seen with a variety of diseases, including tetanus, as a complication of radiation therapy, trauma, or in association with neoplastic conditions. Tetanus is a limited range of motion Range of motion The distance and direction to which a bone joint can be extended. Range of motion is a function of the condition of the joints, muscles, and connective tissues involved. Joint flexibility can be improved through appropriate muscle strength exercises. Examination of the Upper Limbs of the jaw that may be caused by a spasm of the muscles of mastication or by an inferior alveolar nerve block injection leading to hemorrhage within the medial pterygoid muscle. Trismus Trismus Spasmodic contraction of the masseter muscle resulting in forceful jaw closure. This may be seen with a variety of diseases, including tetanus, as a complication of radiation therapy, trauma, or in association with neoplastic conditions. Tetanus significantly affect the patient’s quality Quality Activities and programs intended to assure or improve the quality of care in either a defined medical setting or a program. The concept includes the assessment or evaluation of the quality of care; identification of problems or shortcomings in the delivery of care; designing activities to overcome these deficiencies; and follow-up monitoring to ensure effectiveness of corrective steps. Quality Measurement and Improvement of life by interfering with eating, speaking, and maintaining proper oral hygiene. The condition can present with an altered facial appearance and may be distressing and painful for the patient, but in most cases it is temporary.
• Dislocation of the TMJ: painful condition that occurs as a result of trauma or excessive opening of the mandible (e.g., yawning, dental procedures), in which the mandibular condyle becomes fixed in the anterosuperior aspect of the articular eminence. Dislocation of the TMJ most commonly occurs bilaterally. Subsequent spasms Spasms An involuntary contraction of a muscle or group of muscles. Spasms may involve skeletal muscle or smooth muscle. Ion Channel Myopathy of the masseter, temporalis, and internal pterygoid muscles may result in trismus Trismus Spasmodic contraction of the masseter muscle resulting in forceful jaw closure. This may be seen with a variety of diseases, including tetanus, as a complication of radiation therapy, trauma, or in association with neoplastic conditions. Tetanus, preventing the return of the condyle to the temporal fossa Temporal fossa Skull: Anatomy.
• Arthritis Arthritis Acute or chronic inflammation of joints. Osteoarthritis of TMJ: unilateral, degenerative disease of the TMJ. Arthritis Arthritis Acute or chronic inflammation of joints. Osteoarthritis of the TMJ is characterized by the breakdown of the articular cartilage Cartilage Cartilage is a type of connective tissue derived from embryonic mesenchyme that is responsible for structural support, resilience, and the smoothness of physical actions. Perichondrium (connective tissue membrane surrounding cartilage) compensates for the absence of vasculature in cartilage by providing nutrition and support. Cartilage: Histology, architectural changes in bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types, and degeneration of the synovial tissues causing pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways and/or dysfunction during functional movements of the jaw, leading to joint clicking or crepitus Crepitus Osteoarthritis.