MYOLOGY , FUNCTIONS OF MUSCLES OF MASTICATION AND FACIAL EXPRESSIONS

DR. MOHAMED OSMAN BABIKIR BDS, GBOI, MSC CONTENTS

• Introduction • Muscles of Mastication • Muscles of Mandibular Depression • Muscles of Facial Expressions • Effects of Muscle Functions • Conclusion INTRODUCTION

• MYOLOGY : Is the scientific study of muscles. • The MUSCLES are connected with the bones, cartilages, ligaments and skin, either directly, or through the intervention of fibrous structures called tendons or aponeuroses. • The muscles vary extremely in their form and there is considerable variation in the arrangement of the fibers of certain muscles with reference to the tendons to which they are attached. MUSCLES PRODUCING MANDIBULAR MOVEMENT

• They are designated as muscles of mastication: 1. The masseter 2. The temporalis 3. The medial pterygoid 4. The lateral pterygoid

MUSCLES OF MASTICATION

• All the muscles of mastication are innervated by the mandibular branch of the trigeminal nerve. • They are powerful muscles(masseter and temporalis); when contracting they are capable of applying force over 100kg between opposing natural teeth. Muscles of Mastication MUSCLES AND JAW MOVEMENTS

The jaw can move forward and backward, side to side and can open and close. Each of these movements are performed by a number of muscles working together to perform the movement while controlling the position of the condyle within the mandibular fossa. Chewing and talking require a combination of jaw movements in a number of directions. • Opening – inferior head of lateral pterygoid, anterior digastric, mylohyoid. Opening is also controlled by eccentric contraction of the closing muscles against gravity. • Closing – masseter, anterior and middle fibers of temporalis, medial pterygoid, superior head of lateral pterygoid. • Protrusion – bilateral contraction of the lateral pterygoid. • Retrusion – middle and posterior fibers of temporalis, possibly helped by deep posterior portion of masseter • Laterotrusion (side to side) – ipsilateral middle and posterior fibers of temporalis, contralateral inferior head of lateral pterygoid.

MUSCLES OF MANDIBULAR DEPRESSION

• Three groups of muscles (plus gravity) are responsible for mandibular depression. • They are the: 1.Supra hyoids (mylohyoid, geniohyoid, digastric) 2.Infra hyoids (sternohyoid, omohyoid, sternothyroid, thyrohyoid) 3.lateral pterygoid (inferior head) • Only the geniohyoid and mylohyoids have the potential for affecting denture borders. MUSCLES OF FACIAL EXPRESSION

• The action of these muscles is responsible for the facial postures associated with smiling, laughing, frowning or scowling. • When these muscles are relaxed, the face lacks expression. • The actions of these muscles often reflect the mental state, the personality and the well being of an individual. FACIAL EXPRESSION MUSCLES OF FACIAL EXPRESSION MODIOLOUS

• It is a bundle of tissue just lateral to the corner of the mouth. • It represents the origin , insertion or decussation of many fibers of various muscles of facial expression. • It is commonly known as Purse-string muscle, which composed of risorius, zygomaticus, caninus, guadratus labii inferior, triangularis and orbicularis oris.

EFFECTS OF MUSCLE FUNCTIONS

• Muscle functions affect: 1. Impression 2. Occlusal plane 3. Arch arrangement 4. Jaw registrations 5.Occlusal patterns 6. Esthetics 7. Polished surface contour 8. Food trough formation and mastication 9. Neuromuscular skills. EFFECTS OF MUSCLES

1. Impressions: • Muscles and their functional activity affect impression procedures by power, anatomic attachment height, and creation of valve seal borders.

EFFECTS OF MUSCLES

2. 0cclusal Plane: • In approximately 80% of patients studied (Wright et al 1961) found that the lateral borders of the tongue covered the lingual cusps or the occlusal surfaces of the lower posterior teeth. • The tongue therefore can be a powerful adjunct in the achievement of mandibular denture stability. EFFECTS OF MUSCLES

4. Jaw Movement and Registration: • Without muscular contraction and relaxation, movement of the mandible is impossible. CONCLUSION

• As a diagnostic procedure , the patient should be asked to make controlled movements of the mandible and tongue . • Evidence of limited muscular coordination has many clinical implications. REFERENCES

• Hassaballah M., Principles Of Complete Denture Prosthodontics, ( 2nd ed ). • Henry Gray. Anatomy of the Human Body. • Lippincott, modern pharmacology with clinical applications (5th ed ) Thanks for listening