3.11 what is masticatalory muscle forces. mastication pressure

what is gnathology

science that focuses on morphology, physiology, pathology and functional integrity of anatomic triad:

• TMJ

• dental arches

• muscles

Priority in gnathology is ensuring proper position of condyles in TMJ fossa

what is occlusodontia?

studies the morphological features and functional changes of the occlusal surface of the teeth and the contact among antagonists.

Aim is to create perfect relationship among the natural and artificial occlusal surfaces

Physiological rest

• condyles slightly rotated close to basis of tuberculum

• passive position of lower jaw, occurring after swallowing or after pronouncing the words Mississippi or minimum

articulation

• Dynamic process involving various actions of the jaw due to muscle contraction

• Involves initial contact and articulatory blockages which may lead to occluso-articulating traumatism

occlusion

• static contact among all teeth from both dental arches

• It is an element of articulating process. In some countries, term dynamic occlusion is used instead of articulation

who introduced central occlusion?

• Gysi 1922

describe the muscles, dental arch and condyles at central occlusion

muscle - maximum contraction

Dental arch - maximum teeth contacts, considered priority

Condyles - at basis of tuberculum

who introduced central relation?

McCollum 1926

what is state of muscles, dental arches and condyles at central relation?

muscles - minimum contraction

dental arches - single or multiple weak contacts

condyles - distal position in fossa, allows trasnversal sliding movements. priority given to this position

what is the percentage of centric occlusions that align with centric relation?

40%

60% of the time centric relation is located how distally from centric occlusion? what is this called?

• 0.46 mm

• this movement of TMJ is known as centric sliding

what is the goal of restorative treatment?

• to create occlusal contacts in the posterior teeth that stabilise the mandibular position, rather than creating deflective contacts that may destabilise it.

• The occlusion should be in harmony with optimum condylar position, which is centric relation. This position is considered the most orthopedically stable position.

whcih position is considered the most orthopedically stable position?

centric relation

who introduced myocentric occlusion?

Janckelson in 1990

state of muscles, dental arches and condyles in myocentric occlusion?

muscles - bilateral, uniform contraction, but not maximum. Priority is given

Dental arches - multiple weak contacts in distal area

Condyles - upper middle position. CR-MO-CO alignment

what is state of muscles, dental arches and condyles in utmost distal occlusion?

muscles - forced maximum retraction

dental arches - few weak contacts

condyles - utmost distal position in fossa, transversal sliding movements cannot be done

which occlusion is considered clinically insignificant due to TMJ discomfort and patient?

Utmost distal occlusion

when is the term central position used?

• general statement when the exact position of the mandible is uncertain. not precise but practically significant

what does central psoition refer to?

could refer to CO,CR or MO

state of muscles, dental arches and condyles in central position

position of condyles, dental arches and muscle tone are not precisely determined

whoc introduced morphological occlusion?

Angle in 1899

what is morphological occlusion based on and what are the types?

• bases on position of the first molars

• Neutrocclusion, distocclusion and mesiocclusion

who introduced perfect occlusion?

A. Filtchev in 1990

what are the types of perfect occlusion?

1. Neutrocclusion

2. multiple dense contacts in CO

3. ultimate occlusion variants - canine guidance, group function, balanced occlusion

4. edge-to-edge occlusion

5. CO=CR

6. No trauma

describe multiple dense contacts in Co of perfect occlusion

• In Co, multiple solid contacts between teeth

• Number and density of contacts increase distally

• Last couple of anatgonists have maximum number of contacts

describe occlusion variations of perfect occlusion

• In perfect occlusion there can be different occlusion on left and right side:

  • Canine guidance in young patients

  • Group function or unilateral balance occlusion in mature age

  • Bilaterally balanced occlusion with attrition in grown-up patients

describe edge-to-edge occlusion of perfect occlusion

• contact among incisors (canines), which premolars and molars are in distocclusion (not in contact)

describe no traum in perfect occlusion

• no preliminary contacts, occluso-articulating blockages or pathological changes in the periodontium, muscles or TMJ

• No trauma or negative impact on oral structure

what are the 3 recognised concepts that describe the manner in which teeth should and should not contact with the various functional and excursive positions of the mandible (organisation of occlusion)?

• Bilateral balanced occlusion

• Unilateral balanced occlusion - group function

• Mutually protected occlusion

what is bilateral balanced occlusion based on?

work of Von Spee and Monson

what does bilateral balanced occlusion dictate?

• that the maximum number of teeth should contact in all excursive positions of the mandible

when is bilateral balanced occlusion particularly useful?

• in complete denture construction and complete occlusal rehabilitation

what is a con of bilateral balanced occlusion?

• results in excessive frictional wear of teeth as a result of multiple tooth contacts that occurred as the mandible moved through its various excursions

what does the unilateral balanced occlusion (group function) consist of?

• all working side teeth are in contact in lateral excursion

• Teeth of non working side are contoured so free of contact

• Group function of teeth one working side, distributed occlusal load

• Absence of contact on non working side prevents those teeth

which is obvious advantages of unilateral balanced occlusion?

• maintenance of occlusion

what is mutually protected occlusion also known as ?

• canine-protected occlusion or organic occlusion

what is theory behind mutually protected occlusion?

• in patients with healthy gums and minimal tooth wear, the arrangement of the teeth allows the anterior teeth to overlap, preventing the posterior teeth from making contact during jaw movements.

• This separation from occlusion is called disocclusion.

what is important for a mouth to have to have mutually protected occlusion?

healthy anterior teeth

what should be done if there is anterior bone loss or missing canines (unable to do mutually protected occlusion)?

mouth should be restored to group function or unilateral balance

what is the goal of treatment for molar disocclusion?

• in placing occlusal restorations, too produce a posterior occlusion with buffer space that equals or surpasses the deviation resulting from natural variations found in TMJ

what is the average angle of inclination of condylar path?

30.4 (33-40) degrees with the horizontal refence line

what is the effect on cusp heigh is protrusive inclination is steep?

if protrusive inclination is steep - cusp heigh may be longer

If protrusive inclination is shallow - cusp heigh must be shorter

Condylar path also affect—— and ——- directions

Ridge and groove directions are affected by the condylar path

how do the lower front teeth move during protrusive movements?

they move forward and downward along the concave surface of supper front teeth

what is protrusive incisal path?

the path folled by incisal edge of lower teeth from maximum intercuspation to edge-to-edge occlusion

what is the range for inclination of protrusive path?

40-50 degrees

what is anterior guidance?

• In protrusive movement of the jaw, the lower front teeth move forward and downward along the concave surface of the upper front teeth.

• Evidence suggesting that condylar inclination and anterior guidance are linked or dependent factors

what is condylar guidance?

• Inclination of condylar path during protrusive movements can vary from steep to shallow in different positions.

• Evidence suggesting that condylar inclination and anterior guidance are linked or dependent factors

what is muscle force?

energy generated from muscle contraction

what is the directions of muscle force?

• vertical

• horizontal

• oblique (including physiological force of Tylman)

whata re muscles involved in mastication?

• masseter

• buccinator

• temporalis

• lalteral and medial pterygoid

what did Veber (1836) find out about muscle force?

1cm section of muscle can generate a force of 98N (equivalent to 10kg)

what is abolute muscle force (PA) during normal physiological activity and during chewing?

• during normal physiological activity is approximately 390kg.

• During chewing, the muscle force (Pm) ranges from 110-120kg.

how can specific chewing force (Ps) be calculated?

Ps = Pm/L

where L represents the lever arm.

Ante’s Law

The total periodontal membrane area of the abutment teeth must be equal or larger than that of the teeth to be replaced

Wusrow 1919

Each tooth can compensate DOUBLE of normal physiological pressure!

Balabanov 1970

postulated the so called "'functional-mechanical equilibrium of periodontium" CONCEPT.

what is the ratio needed between total occlusal surface and total periodontal surface for equilibrium to be reached?

2/1 ratio

Boyanov equation

what is occlusal pressure and periodontal pressure?

• occlusal pressure - specific force Ps/ occlusal area FO

• periodontal pressure - resisting force Rs/ periodontal area Fp

what does masticatory unit consist of?

1. Supporting Part:

   • Tooth

   • Periodontal ligament

   • Bone

2. Motor Part:

   • Muscles involved in mastication

3. Nerve-Sensory Part:

   • Nerves responsible for sensory input from the masticatory unit

4. Trophic Part:

   • Blood vessels that provide nourishment to the masticatory unit

what is masticatory reflex?

pathway from the masticatory unit to the Central Nervous System (CNS) and back to the masticatory muscles.

what does the chewing cycle consist of and what do they come together to form?

• chewing cycle consists of two phases: opening and closing

• together form the power stroke

what does the chewing sequence involve?

• multiple chewing cycles that occur during the process of chewing.

• Each time you chew, you go through a chewing cycle, and there are numerous chewing cycles in a complete chewing sequence.

what is movement of frontal teeth when opening mouth to bite?

• downward and forward

what is movement of frontal teeth when closing mouth to bite?

going up (edge to edge contact), going up sliding on lingual surface

what is movement of distal teeth when opening mouth to chew?

• downward movement

• lateral border movement

what is movement of distal teeth when closing mouth to chew?

• going up (front border position with cusp against cusp)

• Going up sliding on occlusal surface

what are movements of mandible according to planes of border movements?

1. Vertical movement

2. horizontal movement

   • sagittal movement

   • transversal movement

what are the rotation movements of mandible (around axis)?

1. vertical movement

2. horizontal movement

3. sagittal axis of rotation

why does vertical (frontal) movement occur?

Mandibular movement occurs around the frontal axis when one condyle moves anteriorly out of terminal hinge position with the vertical axis of opposite condyle remaining.

what does horizontal movement of mandible entail?

• Mandibular movement around the horizontal axis is an opening and closing motion, known as the hinge movement.

• The horizontal axis around which this movement occurs is referred to as the "hinge axis."

what is an example of mandibular activity where a pure rotational movement occurs?

hinge movement

what is the terminal hinge axis?

When the condyles are in their most superior position in the articular fossae and the mouth is purely rotated open, the axis around which this movement occurs is called the "Terminal Hinge Axis."

why does sagittal axis of rotation occur?

Mandibular movement around the sagittal axis occurs when one condyle moves inferiorly while other remains in the terminal hinge position.

Anatomical and mechanical axis of rotation - anatomical axis

• connects the midpoints of the two condyle heads.

• During rotation, the most prominent point of the condyle head and the top of the chin move on a part of a sphere.

Anatomical and mechanical axis of rotation - mechanical axis

• is located at the intersection of the perpendicular lines drawn from the chords of two spheres

• The mechanical axis is situated about 2.5 cm behind and under the anatomical axis.

what is movement of horizontal condylar path?

forward and backward

what is condyle path and incisal path angles (both measured in horizontal plane)?

• Condylar path - 33-40 degrees (steepness)

• Incisal path - 40-50 degrees

in lateral condylar path what is Bennett angle ?

The angle formed between the sagittal plane and the average path of the advancing condyle as viewed in the horizontal plane during lateral mandibular movements

In lateral condylar path, what is gothic angle?

• During the transversal movements of the mandible the incisal point outlines two segments left and right.

• The angle formed between these segments is called Gothic and is about 120°.