Dental Occlusion: TMJ and Mastication

• Monica Patel is the tutor for Foundations in Clinical Skills and Practice (FCSP) module
• The module focuses on occlusion

GDC Learning Outcomes

• Understanding dental, oral, craniofacial, and general anatomy and its relevance to patient management are key skills
• Being able to identify normal and abnormal facial growth, physical, mental and dental development milestones is important
• Occlusion should be assessed and managed within the scope of practice

Intended Learning Outcomes

• Students should be able to describe the anatomy of the TMJ and muscles of mastication
• The movements of the jaws should be understood
• The term ‘ideal’ occlusion should be clear
• Different malocclusions should be described
• Angle’s classification needs to be understood
• Occlusion examination and recording is an important skill
• The importance of occlusion in restorative procedures should be clear

What is Occlusion

• How the maxillary and mandibular teeth come together defines occlusion
• Occlusion also refers to the way teeth are aligned in each jaw
• Occlusion encompasses the mandible's movement in relation to the maxilla, via the temporomandibular joint (TMJ) and neuromuscular systems

Why is Occlusion Important?

• Success in restorative work relies on restorations that operate within the patient's physiological occlusion
• Even a simple filling can cause problems with the restoration, tooth, or TMJ if it changes way the patient bites

Dentition Stages

• Dentition describes the natural teeth in the maxilla and mandible
• Primary/deciduous dentition refers to a child's deciduous teeth
• Mixed dentition includes both deciduous and permanent teeth
• Permanent dentition describes adult teeth

Mixed Dentition

• Mixed dentition occurs between ages 6-12
• Both deciduous and permanent teeth are present in the mouth during this stage
• The period starts when the first permanent tooth erupts, specifically the mandibular first molar (LL6/LR6)
• The period ends when the last deciduous tooth sheds, progressing to permanent dentition

Permanent Dentition

• Permanent dentition consists of adult teeth
• Jawbone growth slows and stops after puberty

Dental Arches

• The maxillary arch is fixed and not capable of movement
• The mandibular arch has movement capabilities through TMJ action

Curve of Spee

• The natural antero-posterior curvature along the occlusal surfaces of molars and premolars
• Normal occlusal curvature is required for efficient mastication

Curve of Wilson

• A line drawn across the occlusal surface of the left mandibular first molar, across the arch, and through the occlusal surface of the right mandibular first molar

Temporomandibular Joint (TMJ)

• The TMJ is where the mandible and temporal bone meet
• It is a synovial joint with upper and lower compartments, separated by an intra-capsular disc
• The upper component is bordered by the mandibular fossa superiorly and the articular disc inferiorly
• The lower component is bordered by the articular disc superiorly and the condyle of the mandible inferiorly

Muscles of Mastication

• Key muscles include temporalis, masseter, medial pterygoid, and lateral pterygoid

Jaw Opening

• Slight opening occurs as the condyle rotates within the glenoid fossa
• Wider mouth opening includes condyle head moving forward
• Wider opening is called translation
• During translation, the condyle moves forward and downwards, sliding over the articular eminence

Jaw Closing

• The condylar head returns to rest in the glenoid fossa after displacement

Ideal Functional Occlusion

• It involves immediate and permanent posterior disocclusion in lateral and protrusive contact
• The absence of non-working side interferences is key
• Multiple, simultaneous, bilateral contacts of the posterior teeth should be present in ICP
• ICP should be coincident with RCP

Malocclusion

• "Imperfect positioning of the teeth when the jaws are closed"
• Malocclusion depends on the range of normal set
• Malocclusions are present in 25-50% of children, warranting orthodontic treatment
• Malocclusion can be classified in the coronal (cross bite) and vertical (overbite) planes

Factors Influencing Occlusion

• Proper occlusion of permanent teeth depends on the primary teeth shed
• Habits such as thumb sucking or tongue thrusts can affect occlusion

Overbite and Overjet

• The average value for both is 2mm
• Overbite refers to the vertical overlap of the upper incisors over the lower incisors
• Overjet refers to the horizontal distance between the upper and lower incisors

Incisor Classification

• The British Standards Institute definitions are used for classification
• Class I: lower incisor edges lie on or directly below the cingulum plateau of the upper incisors, with average overbite/overjet
• Class II division 1: lower incisor edges lie behind the cingulum plateau, upper incisors are proclined/upright, overjet is increased, advanced upper jaw
• Class II division 2: lower incisor edges lie behind the cingulum plateau, upper incisors are retroclined, advanced upper jaw, increased overbite, proclined lateral incisors
• Class III: lower incisor edges lie in front of the cingulum plateau, advanced lower jaw, edge-to-edge incisor relationship, reverse overbite and/or overjet

Malocclusion (cont.)

• Lack of occlusion renders most teeth useless
• Every cusp or ridge on teeth has an occlusal function
• Orthodontic referral is recommended for malocclusion following the IOTN criteria

Maximal Intercuspal Position (ICP)

• Also referred to as centric occlusion
• The jaws are closed in a position where the occluding surfaces of maxillary and mandibular teeth have maximal stable contact
• It can also be called maximum interdigitation
• Most restorations need adjustment to fit the patient's maximum intercuspation
• ICP is seldom employed naturally, as teeth are apart at rest
• ICP is typically achieved during swallowing and deliberate clenching
• If ICP is satisfactory, restorations should match the existing occlusion

Centric Stops

• Parts of the teeth make contact during maximal intercuspal interdigitation
• These can be marked with occlusal indicator tape in black

Retruded Contact Position (RCP)

• The mandible position where initial tooth contact happens on the retruded arc of closure
• This is when the mandible rotates on the hinge axis
• It is independent of tooth contact
• A hinge movement happens that involves no condyle translation
• In RCP the position is reproducible
• RCP is used when ICP is unavailable, namely with edentulous patients or advanced wear cases
• RCP can be difficult to locate
• ICP and RCP coincide with 20% of people
• In 80% of people there is a slide from RCP to ICP

Mandibular Excursions

• These are the movements of the mandible with the teeth in contact

Protrusion

• Anterior movement from ICP, where lower incisors contact upper incisors, discluding posterior teeth

Lateral Excursions

• Sideways mandibular movements
• Working side: The side the mandible moves to during lateral excursion
• Non-working side: The side the mandible moves away from

Lateral Excursions - Working Side Contact

• Canine guidance: Contact on canines only
• All other teeth on the working side disclude
• No contacts exist on the non-working side
• Group function: Where multiple tooth contacts occur on the working side

Tooth Interferences

• Any tooth contact on the non-working side during a working movement
• May have a working side or protrusive interference, but cannot have a non-working interference

Occlusal Vertical Dimension (OVD_

• The vertical dimension of the face with the teeth in occlusion at ICP

Rest Position

• The habitual position of the relaxed mandible

Freeway space

• The difference between the relaxed rest position and the OVD

Examining Occlusion

• Missing or misaligned teeth should have an occlusal examination
• Look for crowding, spacing and tooth wear
• Resorations-occlusal form & function
• ICP-overbite/overjet, crossbite
• Evaluate stable contacting cusp/fossa relationships, and lateral/protrusive excursions
• Non-working interferences should also be examined

Recording Occlusion

• Impressions: Study models
• Facebows: Records relationship between upper teeth and condyles
• Occlusal records include ICP, RCP, protrusion and lateral excursions
• Records relationship between upper & lower teeth

Articulators

• Mechanical systems used to replicate mandibular movement
• Types range from simple hinge articulators to complex fully adjustable articulators
• The most commonly used articulators are semi adjustable instruments
• They simulate condylar pathways by using average measurements
• This is for orientation of the casts relative to the joints

Occlusal Stability and Restorative Implications

• Individuals adapt to occlusal irregularities when teeth are lost/restored, but with limited capacity
• Restorations should blend with the functional pattern
• Maintain a stable ICP position is important
• Natural cusp/fossa relationships is hard to reproduce by freehand carving
• Restorations should be small, ensuring contacts remain on enamel tissue

Consequences of Things Going Wrong

• Overuse of muscles leads to bruxism ending in attrition, tooth movement, and temporomandibular dysfunction (TMD)

Temporomandibular Joint Dysfunction

• A multifactorial aetiology which causes dysfunction
• May relate to occlusion (premature contacts during stress)
• Grinding teeth (bruxism)
• Joint clicking
• Disc displacement occurs during opening movement, and bone surfaces rub together leading to pain and discomfort

Occlusion and Periodontal Disease

• The periodontium absorbs the forces of occlusion and distributes thsese to surrounding tissues
• Occlusal trauma describes the pathological and adaptive changes
• This develops in the periodontium when you experince excess forces produced by masticatory muscles whether "standard" or during a reduced height situation
• Occlusal trauma does not cause periodontal disease, but excess forces can be an issue

Effects of Occlusal Trauma

• Increased tooth mobility, change in tooth position, fremitus
• Wear facets on the tooth/restorations, fractures
• Widening of the periodontal ligament space
• Temporomandibular joint dysfunction
• Hypertrophy of the masticatory muscles
• Pain (tooth sensitivities, tenderness to percussion)
• Death of the pulp

Explore dental occlusion, focusing on the temporomandibular joint (TMJ) and muscles of mastication. Understand jaw movements, ideal occlusion, malocclusions like Angle's classification, and occlusal examination techniques. Learn the importance of occlusion in restorative dentistry.