The masticatory system: generalities and anatomy
- Introduction :
Due to its location at the cephalic extremity of the individual, the oral cavity physiologically participates in sensory and affective activities.
Masticatory and occlusal phenomena constitute important elements in fundamental behaviors; These phenomena depend on a set of elements united in a functional unit called: masticatory apparatus
- Definition of the masticatory system:
The masticatory system is a complex functional unit consisting of passive elements (TMJ, teeth and occlusion) and active elements (neuromuscular system) whose dynamics are coordinated by the neurosensory system.
- Anatomy of the masticatory system:
3 1- dental organs: include the teeth and their supporting tissues:
- Teeth or odontes: which play an important role in chewing.
- Support tissues: consisting of cementum, periodontal ligament, alveolar bone and gingiva. Among all these elements, the periodontal ligament actively participates in functional dynamics.
The desmodont plays several roles:
- Mechanical and protective through its collagen fibers.
- Nutritious through its arteriovenous system.
- Sensory by the elements of the nervous system that it contains.
3-2- the temporomandibular joints (TMJ):
- Definition:
Paired, symmetrical joints that connect the mandible to the skull.
They are considered the only mobile joints of the face,
Together with the dental arches, from which they are inseparable, they form the cranio-bicondylo-occlusal articulation.
- Bone surfaces:
- Temporal surface:
They are present on the exocranial surface of the temporal bone, in its lower part called the basilar field:A- The glenoid cavity:
Also called the mandibular fossa, it is a concave surface inscribed in the angle formed by the two roots of the zygomatic process; it is located in front of the external auditory canal (EAC), behind the temporal condyle, and outside the spine of the sphenoid.
- mandibular articular surface:The mandibular condyle
It is a prominent articular process at the posterior apex of the ascending ramus.
The surface of the mandibular condyle, covered with cartilage, is divided into
two sides: an anterior side and a posterior side.
- Disc apparatus:
- Definition:
According to the current conception, the meniscus is not an isolated element, it is part of a whole which constitutes the disc apparatus of the ATM, inseparable from the mandibular condyle with which it forms the condylo-discal complex.
For some, it represents the intra-articular portion of the tendon of the lateral pterygoid muscle, differentiated with respect to the articular surfaces.
- Suspensory system:
The articular surfaces are maintained in close contact essentially by the tone of the masticatory muscles and secondarily by the capsule.
- The Capsule:
The capsule is a loose, truncated-cone-shaped fibrous sleeve of variable thickness located around the joint.
It is implemented:
• At the top, on the perimeter of the articular surface of the temporal bone
• Below on the neck of the condyle, close to the articular surface towards the front and at a distance behind
- The Synovials: There are two of them:
• The upper or suprameniscal synovium and the lower or submeniscal synovium.
• These two pockets contain the synovial fluid or synovium which plays the role of lubricant of the ATM and which ensures the nutrition of the avascular tissues which line the articular surfaces.
- Ligaments:
We thus distinguish between intrinsic ligaments or proper ligaments, which are adherent to the capsule, and extrinsic ligaments, whose role is secondary, and which are located at a distance from the capsule.
The intrinsic ligaments:
- The external lateral ligament.
- The internal lateral ligament.
3-3- the muscular system:
A-Definition:
The masticatory muscular system consists of elevator, depressor and cervical muscles which are essential for head support and mandibular dynamics.
B- the different types of masticatory muscles
1. The elevator muscles:
These muscles are few in number but very powerful and have a cranial insertion.
- The masseter:
Short, thick muscle, oblique downwards and backwards, stretched between the zygomatic arch and the angular zone of the mandible with 3 heads: superficial, medium and deep
- The superficial head regulates mandibular closing movements and protrusion.
- The deep head which also regulates the movements of mandibular closure but also retrusion.
- The temporal:
Large, fan-shaped, extends from the temporal fossa on the lateral surface of the skull to the coronoid process of the mandible. It is composed of three bundles: anterior, middle and posterior, the anterior and posterior bundles being antagonistic.
- The internal pterygoid:
Quadrangular muscle located in the pterygomaxillary region and extending from the pterygoid fossa to the internal face of the mandibular angle.
Symmetrical to the masseter in relation to the mandible, hence its name internal masseter.
- The external pterygoid:
Short, thick, flattened muscle, located in the pterygomaxillary region, stretched from the pterygoid process to the neck of the condyle with two heads: sphenoid head: horizontal surface of the greater wing of the sphenoid to the neck of the condyle. Lower head: from the pterygoid process to the neck of the condyle.
2. The depressor muscles:
Numerous, weak, they all have a hyoid insertion and their innervation is heterogeneous.
They are classified according to their arrangement relative to the hyoid bone which also provides insertion to the muscles of the tongue.
- Which are essentially the suprahyoids (digastric, mylohyoid and geniohyoid), and secondarily the muscles responsible for head posture: trapezius, sternocleidomastoid.
- The subhyoids: the sternothyroid, the thyrohyoid, the sternocleidohyoid, the omohyoid.
- The cervical muscles.
3-4- the nervous system:
A-Definition:
It is the set of structures that ensure the reception, integration and transmission of information coming from the organism and the environment.
B- composition: This system includes:
- Peripheral sensory receptors:
They play an important role in the regulation of muscular activities and in perceptions. They are located in the muscles, tendons, the ATM and the desmodont, we observe:
Proprioceptors: they transmit information on the movements of this device (stretching, pressure)
- Free endings: (mainly nociceptors) are the starting point of reflexes which can lead to contractures.
A mixed cranial nerve (the trigeminal): whose sensory component carries all the modes of sensitivity of the face and the masticatory system, and whose motor component controls the greater part of the masticatory muscles.
Nerve centers: which integrate sensory-sensory messages and produce motor commands.
- conclusion :
The masticatory system is a very intimate set of several elements, namely passive and active, which are of equal importance.
The efficiency of this device depends on the harmony and balance of its different components which cannot be physiologically dissociated from each other.
The masticatory system must always be considered as a whole, itself closely linked to the cranio-spinal posture.
The masticatory system: generalities and anatomy
Wisdom teeth can cause infections if not removed.
Dental crowns restore the function and appearance of damaged teeth.
Swollen gums are often a sign of periodontal disease.
Orthodontic treatments can be performed at any age.
Composite fillings are discreet and durable.
Composite fillings are discreet and durable.
Interdental brushes effectively clean tight spaces.
Visiting the dentist every six months prevents dental problems.