Basic Positions of the Jaw and Recording Methods

Vocabulary flashcards generated from lecture notes on basic jaw positions, centric relation induction techniques, axis-tooth interrelationships, and vertical dimension determination.

Mandibular Centric Relation (CR) [Classic Definition]

That position of the jaw in which it places its condyles in the most posterior, upper, and middle position of the glenoid cavity of the temporal bone, and from which all mandibular movements can be initiated.

Mandibular Centric Relation (CR) [Functional Definition]

The intermaxillary relationship in which the condyles are in a terminal hinge position, allowing pure rotational movement around the terminal hinge axis without translation up to approximately $20\,mm$ of incisal opening (about $12^\circ$ angular rotation).

Maximum Intercuspidation (MI)

The maximum interdental relationship of a patient with the shortest intermaxillary distance, representing the largest number of intermaxillary contacts between upper and lower arches.

Centric Occlusion

The occlusal relationship where maximum intercuspidation coincides with centric relation, also designated as THIOP (Terminal Hinge Intercuspal Occlusal Position).

Dawson's Bimanual Technique

A manual CR induction procedure performed from behind the patient where the operator places thumbs on the chin and the remaining fingers under the horizontal mandibular branches to guide movement backwards and upwards.

Electro-induced CR Techniques

Methods using high or low frequency electrical stimulation to relax masticatory muscles and return the mandible to a neuromuscular rest position, requiring a subsequent manual or mechanical procedure to record CR.

Central Support Screw

A self-induced CR recording device comprising an upper metal plate and a lower screw/pin positioned at the level of the first molars line, tracing a gothic arch during mandibular movements where the arrowhead tip represents centric relation.

Lucia's Jig

An anterior self-curing acrylic inclined plane placed around upper incisors that alters vertical dimension, eliminates posterior tooth interferences, and guides the mandible into centric relation.

Long's Lamellas

A variation of Lucia's jig consisting of removable plastic blades that can be progressively removed until the first occlusal interference is located.

THIOP

Terminal Hinge Intercuspal Occlusal Position; an axis-tooth position where maximum intercuspidation occurs while the condyles are positioned on the terminal hinge axis.

MIOP

Mesialized Intercuspal Occlusal Position; a closing relation where both the right and left ends of the hinge axis translate forward (mesially) from CR to achieve maximum intercuspidation.

LIOP

Lateralized Intercuspal Occlusal Position; a closing relation where only one end (right or left) of the hinge axis translates forward from CR to achieve maximum intercuspidation.

THOP

Terminal Hinge Occlusal Position; a centric relation recording position representing a premature tooth contact occurring in THR before maximum intercuspidation is reached.

MOP

A protrusive interocclusal record used to adjust the angle of the condylar slope on an articulator.

LOP

A pure laterality interocclusal record used to adjust Bennett's angle on an articulator.

Vertical Dimension in Intercuspidation

The height of the lower third of the face measured when the occlusal surfaces of posterior teeth are in maximum contact.

Vertical Dimension at Rest

The height of the lower third of the face maintained by postural muscle tone when the lifting and depressing masticatory muscles are in equilibrium against gravity.

Interocclusal Free Space (IFS)

The space generated between the upper and lower dental arches when the mandible is at rest, calculated as: $\text{IFS} = \text{Dimension at rest} - \text{Dimension in IOP}$.

Class I Interocclusal Clearance

The normal interocclusal free space range in a Class I skeletal relationship, measured between $3\,mm$ and $5\,mm$.

Class II Division 2 Interocclusal Clearance

The normal interocclusal free space range in a Class II division 2 skeletal relationship, measured between $7\,mm$ and $9\,mm$.

Class III Interocclusal Clearance

The normal interocclusal free space range in a Class III skeletal relationship, measured up to $3\,mm$.

Niswonger Deglutition Technique

A method for determining the mandibular rest position based on the physiological principle that the mandible assumes its rest position immediately after swallowing.

Boos' Technique of Maximum Muscular Power

A technique using a gnathodynamometer to determine the vertical dimension corresponding to the point of maximum muscular closure force.

Phonetic Technique for Interocclusal Space

A clinical method utilizing pronunciation of specific phonemes (S, F, V, M) or words like 'misisipi' to assess interocclusal clearance, where 'S' leaves a $1\,mm$ incisal gap and 'F'/'V' positions the upper incisor on the lower lip.

Extraoral Vertical Dimension Determination Technique

A clinical method where two skin reference points (nasal area and chin area) are measured using a dry-tip compass in maximum intercuspidation (IOP) and at rest (PR) to calculate interocclusal clearance.

Facial Proportions Technique

A method of evaluating correct vertical dimension by confirming equality among three vertical facial segments: hairline to eyebrows, eyebrows to base of nose, and base of nose to chin.

Law of Priority of the Senses

A physiological concept stating that visual or hearing impairments alter head positioning, thereby modifying the resting position of the mandible and affecting interocclusal clearance.