101 Muscle vectors in the frontal plane
Diagram of the force vectors in the frontal plane (redrawn from Hylander 1992). Through the specific arrangement and activation of the temporal (1), masseter (2), and medial pterygoid (3) muscles, the condyles are directed transversely against the articular protuberance. The direction of the force vectors in the frontal plane is not correlated with the transverse dimensions of the facial skeleton (van Spronsen 1993).
102 Example of a loading vector of the lateral pterygoid muscle
Clinical evidence of a muscle-specific pain in the lateral pterygoid muscle (1) would point to a chronic overloading in the direction of contraction (arrow). The cause could be a centrally stimulated muscle hypertonus or inflammation of the bilaminar zone. In the latter case, the muscle reflexly seeks to relieve pressure on the painful bilaminar zone. Painful decompensation of the lateral pterygoid muscle without lesions in the bilaminar zone has not been observed clinically for a long time.
Tongue Musculature
The extrinsic tongue musculature includes the styloglossus, genioglossus, and hyoglossus muscles. They connect the body of the tongue to the nearby bone structures to give it its ample mobility within the oral cavity (Thiele et al. 1992).
The intrinsic tongue musculature is made up of the longitudinal, transverse, and vertical muscles of the tongue. They help to change the shape of the tongue.
While the balanced antagonistic activity of the muscles of mastication contributes to positioning the condyles on the articular protuberance, the activity of the tongue musculature on the lingual tooth surfaces and the muscles of the cheeks and lips on the facial surfaces influence the position of the teeth in the dental arch. Even though the tongue has little effect on the joints, afferent information from the joint capsules does indirectly alter the position of the tongue (Lowe 1978).
The occurence of dysphagia and limited motor functions of the tongue have not been proven to be age-dependent. (Caruso and Max 1997, Koshino et al. 1997).
103 Extrinsic tongue musculature
The styloglossus muscles pull the tongue back and up. If one muscle acts unilaterally, the tongue becomes concave. With hypofunction the third phase of the swallowing reflex will be absent (Thiele et al. 1992). The genioglossus can move the dorsum of the tongue downward, pull the border of the tongue forward, and help extend the tongue. Hyperfunction of the genioglossus results in tongue thrusting. The hyoglossus lowers the body of the tongue and pulls the tongue back. Its hyperfunction results in a sunken tongue (Thiele et al. 1992).
104 Intrinsic tongue musculature
Diagram of the internal tongue muscles and their positions in relation to the muscles of the floor of the mouth. The longitudinal muscles of the tongue shorten the tongue. The transverse muscles bring the borders of the tongue closer together. Hypotonus of these fibers leads to a widened tongue. The vertical muscles make the tongue flatter and wider, and their hyperfunction frequently accompanies lateral tongue thrusting, which can cause widening of the dental arch.
105 Function of the tongue muscles
A list of the specific functions of the extrinsic and intrinsic muscles of the tongue and their effects on the body of the tongue (from Thiele et al. 1992). Without the stable buttress formed by the musculature of the floor of the mouth, many dysfunctions of the tongue would not be possible. The floor of the mouth is stabilized differently in different individuals. The act of swallowing does not necessarily involve all the muscles of the floor of the mouth in lifting the hyoid bone (Spiro et al. 1994).
Muscles of Expression
The orofacial musculature is made up of the following muscles: nasalis, depressor septi, levator labii superioris alaeque nasi, orbicularis oris, zygomaticus major, zygomaticus minor, risorius, levator labii superioris, levator anguli oris, depressor anguli oris, depressor labii inferioris, mentalis and platysma myoides. Disturbances in the tonus of these muscles can affect the patient’s facial appearance and the position of the teeth within the dental arch (Hoyer and Limbrock 1990. Padovan 1995). In combination with the activation of one or more of the muscles of mastication, they can also influence the condylar position and thereby the loading of the different structures of the joint (Pahkala et al. 1995). The previous statement about the muscles of mastication also holds true for the muscles of expression: no muscle contracts in isolation (Brown 1996). Systematic observation of individual muscles of expression is not appropriate for grasping the complex interactions that occur during function (Smith 1992, Thiele et al. 1992).
A noninvasive, objective study of muscle function is possible, however, with the aid of electromagnetic articulography (Ackermann et al. 1993, Engelke et al. 1990).
106 Anatomical preparation of the left buccinator muscle
This muscle (1) determines the transverse position of the posterior teeth in the dental arch by countering the pressure of the tongue. During chewing, the buccinators and the tongue work together to keep the food between the occlusal surfaces. In playing a wind instrument, each buccinator (Latin for trumpeter) supports the stream of air laterally. Their hyperfunction causes a narrowing of the upper and lower jaws with the formation of an exaggerated linea alba inside the cheeks. From the collection of 8. Tillmann
107 Orbicularis oris muscle
The orbicularis oris is the muscular foundation of the lips (Thiele et al. 1992). It is made up of a pars marginalis, pars labialis, and a system of straight radiating muscles. Strictly speaking, it consists of two arches that are connected by fascia at the corners of the mouth. Hypertonus results in a small, sharp mouth. The orbicularis oris in coming muscles can position the lower lip between the incisors and cause an anterior horizontal overlap (“overjet”).
108 Mentalis muscle
Right: Frontal view of a patient with a hyperactive mentalis muscle. The lip closure. With hyperactivity the closure and the upper lip can be forced upward. This can result in a reduction of lip pressure against the upper incisors.
Left: Same patient in profile view. Because of the hypertonic mentalis, the apex of the chin (pogonion) lies well in front of the alveolar process.
Temporomandibular Joint and the Musculoskeletal System
The relationships between functional disturbances of the temporomandibular joint and the rest of the musculoskeletal system are well known from clinical investigations (Smith 1993, de Wijer et al. 1996b, c, Dvorak and Walchli 1997). The structural and neurophysiological connections, however, are subjects of debate (Graf-Baumann and Lohse-Busch 1997). Head and neck pain, referred pain, pain in the area innervated by the trigeminal nerve, and disturbances in the functions of speech and swallowing are often associated with the upper cervical spine (Wolff 1996). Disturbances in the cervical vertebrae C2 and C3 can bring on dysphonia and the sensation of a lump in the throat. Up to 25% of patients with temporomandibular-joint