1 Department of Prosthodontics PDM_Preclinical_I_L5 -_Engl Functional – mechanical equilibrium of the periodontium. Muscle forces. Masticatory pressure. Periodontal pressure. Biomechanics of Mandibular movements. Basic movements. Theory of Mandibular movements Slide 1 The masticatory system is a complex musculoskeletal system, which consists of the jaws.And anatomically complex of muscles, involved in mastication. These muscles bring about mandibular motion and generate forces, which can influence morphology and Material properties of the osseous components. The activation and coordination of the jaw muscles determine the direction of jaw movement, control occlusal force, and load the bones of the skull in various ways. The jaw muscles are involved in a much broader range of motor tasks. Slide 2
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Department of Prosthodontics PDM Preclinical I L5 - Engl · 3/21/2020 · Mandibular movements. Basic movements. Theory of Mandibular movements Slide 1 The masticatory system is
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Department of Prosthodontics
PDM_Preclinical_I_L5 -_Engl
Functional – mechanical equilibrium of the periodontium. Muscle
forces. Masticatory pressure. Periodontal pressure. Biomechanics of
Mandibular movements. Basic movements. Theory of Mandibular movements
Slide 1
The masticatory system is a complex musculoskeletal system, which consists of the
jaws.And anatomically complex of muscles, involved in mastication. These muscles bring about
mandibular motion and generate forces, which can influence morphology and Material properties
of the osseous components. The activation and coordination of the jaw muscles determine the
direction of jaw movement, control occlusal force, and load the bones of the skull in various
ways. The jaw muscles are involved in a much broader range of motor tasks.
Slide 2
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Under physiological conditions, the muscle is activated until nervous stimulation ceases.
The level of muscle activation, and with it the amount of force generated, is controlled by two
major mechanisms: rate modulation, altering the frequency of neuronal action potentials at the
neuromuscular junction and recruitment modulation, altering the number of active motor units in
the muscle.
Slide 3
From a classical anatomical perspective, the jaw muscles are divided into elevator and
depressor groups. As you already know, The elevator group consists of the masseter, temporalis, and medial pterygoid muscles, while the depressor group consists of the geniohyoid, mylohyoid, and digastric muscles. The lateral pterygoid muscle completes the system. Because its two heads have different actions, this muscle cannot be regarded exclusively as elevator or Depressor. Jaw-muscle activity has mostly been characterized by the relative duration of muscle activation during a specified period the so-called “duty time”, which is regarded as a measure for the overall neuromuscular activity. Differences in the duty time between muscles or muscle groups provide information on differential neuromuscular activation by the central nervous system.
Slide 4
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Slide 5
Dental absence interferes in the physiological functioning of the masticatory system, promoting occlusal and functional alterations. These data evidence the strong influence of
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dental loss over the maximal bite force and small correlation between bite force and electromyographic activity. Changes in vertical jaw opening may affect the relative contributions of various masticatory muscles to bite force production. EMG activity usualy has recorded simultaneously from the masseter, and anterior, middle, and posterior temporalis muscles, during controlled isometric biting at different force levels and vertical jaw openings.
Slide 6
Every individual muscle group develop muscle activity with a certain force. The size of
the masticatory pressure is proportional to the size of this aggregate and absolute muscle strength
and it is inverse to the size of the occlusal surface. The Absolute muscle force is in direct
proportion to the mass of muscle groups. This slide shows data for the masticatory muscles as
follows: The thickness determines the absolute muscle strength, which includes the synergetic
action of these symmetrical muscles.
Slide 7
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Three main types of muscle action determine the size of the masticatory pressure on the future fixed partial prosthesis. Absolute and specific are the most important.
Slide 8
It is a great honour for our Department the formulation of the main design principle for
prostheses construction by prof. Balabanov : the chewing surfaces of bridge prosthesis must
comply with state and reserve forces of the abutments periodontium. The corresponding perio
reactions are appeard directed against of the occlusal surfaces. In this reason the abutment’s
periodontium is loaded functional better when reducing the size of the retainer’s chewing
surfaces. The Balabanov Law of the functional - mechanical equilibrium of the abutments
periodontium can be expressed by the above equation, shown on the bottom of the slide down. It
states that the abutments periodontium is in their functional mechanical equilibrium when the
ratio between the total occlusal surface with total periodontal surface is constant and does not
exceed the result 2/1. Total occlusal surface is also mixed including different elements –
retainer’s occlusal surfaces and pontics ones.
Biomechanics of the Temporomandibular Joint Temporomandibular joint (TMJ) connects the mandible or the lower jaw to the skull and
regulates the movement of the jaw. The TMJ is one of the most complex, delicate and highly
used joints in a human body. The most important functions of the TMJ are mastication and
speech.
Slide 9
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TMJ is a bi-condylar joint in which the condyles, the movable round upper ends of the
Mandible, function at the same time. Between the condyle and the articular fossa is a disc made
of fibrocartilage that acts as a cushion to absorb stress and allows the condyle to move easily
when the mouth opens and closes. Mandibular movement around the horizontal axis is an
opening and closing motion. It is referred to as a hinge movement, and the horizontal axis
around which it occurs is therefore referred to as the hinge axis (Figure 4-2). The hinge
movement is probably the only example of mandibular activity in which a “pure” rotational
movement occurs.
Slide 10
Slide 11
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Slide 12
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Slide 13
Mandibular movement refers to the muscle- and ligament-activated border and/or
intraborder movements of the lower jaw. There are five types of mandibular movements
including rotational, horizontal axis, frontal axis, sagittal axis, and translational. Mandibular
movement is affected by several factors such as the muscles used in suspending the jaw,
mandibular articulation, and the synovial joint system. Study of this movement is important for
the fields of dentistry and orthodontics as it describes the concepts related to dental occlusion