Occlusion: Foundations in Clinical Skills

• Occlusion is a key topic in Foundations in Clinical Skills and Practice (FCSP) module.
• Monica Patel BDS, MFDS RCS(Glasgow), PgCert (DentEd) is the tutor.

GDC Learning Outcomes

• Identify relevant aspects of dental, oral, craniofacial, and general anatomy, considering diversity and relevance to patient management.
• Recognize signs of normal and abnormal facial growth, physical, mental, and dental development milestones.
• Assess and manage occlusion.

Intended Learning Outcomes

• Ability to describe the anatomy of the TMJ and mastication muscles.
• Ability to describe jaw movements.
• Understand the definition of ideal occlusion.
• Describe different malocclusions.
• Describe Angle's classification.
• Know how to examine and record occlusion.
• Understand the importance of occlusion in restorative procedures.

Occlusion Definition

• The way maxillary and mandibular teeth come together.
• Alignment of teeth in each jaw.
• Mandible movement in relation to maxilla via the TMJ and neuromuscular systems.

Importance of Occlusion

• Success of restorative work relies on restorations within the patient’s physiological occlusion.
• Simple fillings can cause problems if they alter the patient's bite, affecting the restoration, tooth, or rarely TMJ.

Dentition Stages

• Dentition describes the natural teeth in the maxilla and mandible.
• Primary/Deciduous dentition involves deciduous teeth in children.
• Mixed dentition includes both deciduous and permanent teeth.
• Permanent dentition describes adult dentition.

Mixed Dentition

• Usually occurs between ages 6-12.
• Both deciduous and permanent teeth are present.
• The period starts with the eruption of the first permanent tooth, usually the mandibular first molar (LL6/LR6).
• The transition ends when the last deciduous tooth sheds, transitioning to permanent dentition.

Permanent Dentition

• This is adult dentition
• Jawbone growth slows and stops after puberty.

Dental Arches

• The Maxillary Arch is fixed and not capable of movement
• The Mandibular Arch can move through the action of the TMJ.

Curve of Spee

• Natural antero-posterior curvature along the occlusal surfaces of molars and premolars is needed for efficient mastication.

Curve of Wilson

• Imaginary line drawn across the occlusal surface of mandubular first molars, across arch.

Temporomandibular Joint (TMJ)

• The TMJ connects the mandible and temporal bone.
• 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 and the articular disc.
• The lower component is bordered by the articular disc and the condyle of the mandible.

Muscles of Mastication

• Temporalis
• Masseter
• Medial pterygoid
• Lateral pterygoid

Jaw Opening

• Slight opening involves condyle rotation in the glenoid fossa.
• Wider opening involves the condyle head moving forward, called translation, sliding over the articular eminence.
• Jaw closing returns the condylar head to rest in the glenoid fossa after displacement.

Jaw Muscle function

• Masseter: Originates from the zygomatic arch, inserts on the angle of the mandible, functions in closing the jaw.
• Temporalis: Originates from the temporal fossa, inserts on the coronoid process, functions in closing the jaw.
• Lateral Pterygoid: Originates from the sphenoid bone (superior belly) and pterygoid plate (inferior belly), inserts on the articular capsule and condylar neck. Functions include opening, protrusion, and lateral deviation.
• Medial Pterygoid: Originates from the pterygoid bone and pyramidal process of the palatine bone, attaches to the medial angle of mandible. Functions include closing and protrusion.

Ideal Functional Occlusion

• Immediate and permanent posterior separation.
• Multiple, simultaneous, bilateral contacts of posterior teeth in ICP.
• ICP coincident with RCP.

Malocclusion

• Defined as the imperfect positioning of teeth when the jaws are closed.

Influences on Occlusion

• Proper eruption of permanent teeth depends on the occlusion of primary teeth as they are shed.
• Habits like thumb sucking affect occlusion.
• Overbite is the vertical overlap of upper incisors over lower incisors. The average value for both is 2mm.
• Overjet is the horizontal advancement of upper incisors over lower incisors and the average value for both is 2mm.

Incisor Classification

• Determined by the British Standards Institute
• Class I: Lower incisor edges align with or directly below the cingulum plateau of the upper incisors, featuring average overbite and overjet.
• Class II division 1: Lower incisors lie behind the cingulum plateau of the upper incisors along with proclined/upright with increased overjet.
• Class II division 2: Lower incisor edges lie behind the cingulum plateau with retroclined upper incisors, increased overbite, and proclined lateral incisors.
• Class III: Lower incisor edges lie in front of the cingulum plateau of the upper incisors, often seen in advanced lower jaws with edge-to-edge incisor relationship, or a reverse overbite and/or overjet.

Malocclusion Classification

• How the normal is set, can impact malocclusion statistics.
• Approximately ½-⅓ of children need orthodontic treatment for malocclusions.
• Can be classified in the coronal plane (crossbite unilateral/bilateral).
• Can be classified in the vertical plane (increased/decreased overbite/open bite).

Maximal Intercuspal Position (ICP)

• Also known as centric occlusion.
• Jaws are closed in a way that creates maximum stable contact between maxillary and mandibular teeth.
• Most restorations get adjusted to the patient's maximum intercuspation, seldom employed when the teeth are at rest.
• If ICP is satisfactory then a new restoration is to make local alterations to occlusion when doing a single unit restoration or short span bridge.

Centric Stops

• Parts of the teeth that make contact during maximal intercuspal interdigitation.

Retruded Contact Position (RCP)

• Mandible position where initial tooth contact when the mandible rotates on the hinge axis.
• Independent of tooth contact, only 20% ICP and RCP coincident but 80% slide from RCP to ICP

Mandibular Excursions

• Movements of the mandible with teeth in contact.
• Protrusion: Anterior movement from ICP, lower incisors touch the palatal surfaces ,posterior teeth disclude as incisors meet edge-to-edge.
• Lateral excursions: Sideways movements.

Lateral Excursions

• Working side: The side the mandible moves to during lateral excursion.
• Non-working side: The side the mandible moves away from.
• Types of contact during lateral excursion: 1. Canine guidance 2. Group function

Canine Guidance

• Contact restricted to canines on the working side
• All other teeth on the working side disclude with no contacts on non-working side.

Group Function

• Multiple tooth contacts, on working side during lateral excursion.

Tooth Interferences

• During working movement, tooth contact on the non-working side is a non-working interference.
• There can be working or protrusive interferences, but not non-working interference.

Occlusal Vertical Dimension

• The vertical dimension of the face when the teeth are in occlusion in maximal intercuspal position (ICP).
• The difference between the rest position and OVD is the Freeway Space.

Examining Occlusion

• Check for missing teeth, misaligned teeth, crowding, spacing and tooth wear/tooth surface loss.
• Look at restorations-occlusal form & function and ICP-overbite/overjet, crossbite.
• Check stable contacting cusp/fossa relationships and lateral/ protrusive excursions.
• Evaluate any non-working interferences.

Recording Occlusion

• Impressions: study models.
• Facebow: Record relationship between upper teeth and condyles
• Records of ICP, RCP, Protrusion & Lateral excursions needed.
• Record the relationship between upper & lower teeth

Articulators

• Mechanical systems replicate mandibular movement.
• Types range from simple hinge to complex fully adjustable types that replicate mandibular movements.
• Semi adjustable are commonly that simulate condylar pathways via measurements and cast orientation.

Occlusal Stability & Restorative Implications

• Individuals adapt to occlusal irregularities from lost/restored teeth, but with limits.
• New restorations must blend and maintain stable ICP for occlusal harmony.
• Natural cusp/fossa is hard to reproduce freehand.
• The best restorations small, so contacts remain on enamel tissue.

Problems with Occlusion

• Overuse of muscles leads to bruxism, attrition, tooth movement, and temporomandibular dysfunction (TMD).
• Temporomandibular joint dysfunction has multifactorial etiology.
• May be related to the occlusion: i.e. minor premature during stress.
• The joint clicks occur when the disc becomes displaced and bone surfaces rub together.

Occlusion and Periodontal Disease

• The periodontium distribute forces of occlusion.
• Occlusal trauma is defined as pathological and adaptive changes in result of excess forces or reduced bone height