JAW RELATIOSMAXILLO-MANDIBULAR RELATIONS

(MMR) CLINICAL STEPS

& PROCEDURES

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Recording MMRs / JRs /IMRs:Very important Clinical Step When Making CDs.Error in these result in CDs that:

- will be esthically poor / unacceptable.- Uncomfortable, or un-wearable.- May cause lasting damage to DBAs and:- Components of the stomato-gnathic system.

MMRs three-dimensional & has three elements:- Establishment of jaw separation in Vertical Plane.- Recording of A-P & Lateral Relations.- Registering Orientation Relation.

Maxillo-mandibular Relations (MMRs): Clinical Steps & Procedures:- Determining Form & Support for Lips & Cheeks.- Establishment of Incisal & Occlusal Planes.- Establishment of Occluso-Vertical Dimension (OVD).- Registering Retruded Position of Mandible to Maxillae:

- Horizontal / Antero-posterior Relation.- Centric Relation

- Registering Orientation Relations: Relation of maxilla to:- Hinge Axis (Inter-condylar axis).- Base of cranium (Antero-posterior plane).- Frankfort plane (Vertical plane).

- Selecting Teeth for Patients’ Dentures.

Determining Form & Support for Lips & Cheeks:Stabilize the upper record rim in mouth.When biometrically positioned, record rim will require:

- only minor adjustment on its labial / buccal aspects.The infra-nasal tissues be harmonious with the soft tissues of

the middle third of the face. Failure to do this may affect the form and length of the upper lip by raising the lip inappropriately.

Lip support is considered adequate if the:- Vermilion border of lip is seen.- Philtrum is neither too deep nor flattened.- Vertical naso-labial angle is 90° .- maxillary lip commisure angle is 120-degrees.- naso-labial fold appears normal- lips / cheeks not appearing strained.

Appropriate Lip & Cheeks Support with the Upper Record Rim in Mouth

Buccal Corridors Created by Properly Contoured Rim

Overly Supported & Distorted Maxillary Lip

Determine the position of incisal point relative to the resting lip. (upper rim is 2 mm inferior to the resting upper lip):- for younger patients it is 4–5 mm (Class 2 div 1 JRs).- very older patients have incisal point level with the resting lip, or possibly 1 mm above this.

Verify the antero-posterior position of the incisal point by: - asking the patient to say word containing a fricative consonant (labio-dental sound) e.g 'fish';.- incisal point corresponds to vermilion border of lower lip.

Determine incisal plane for upper 6 ant. teeth by making rim parallel to the inter-pupillary line .

Determine occlusal plane for posterior teeth by making rim parallel to Ala-Tragus Line (Fox's Occlusal Plane Guide / any device giving a horizontal plane e.g a wooden spatula).

Adequate incisal show with the upper lip in resting position

Aligning Incisal Plane of Front Teeth Parallel to Inter-Pupillary Line with Fox Occlusal Plane Guide

Mal-alignined Occlusal Plane of Posterior Teeth not Parallel to Ala-Tragus Line as can be seen here with Fox Occlusal Plane Guide

The rim having parallel relation to smiling position of the upper lip.

Determining the position of the mid points of the upper canine teeth by using;- photograph of the patient when patient was dentate. A clear, face-on photograph is required:- regrettably not always available.

- using pupils as stable reference points the position of upper canine teeth is determined using a ratio / equation.

Measure Inter-alar width & adding + 2mm to it (Alameter). Also done by extending dental floss from the inner canthus of

the eye, via the lateral border of ala (patient smiling) onto the incisal edge of the upper rim.

Draw on the faciolabial aspect of the upper rim:- Centre line, High smile line & Canine points.

The Establishment of Vertical Jaw Relationship:When at rest & with head upright, dentate subjects

demonstrate:- IOS / IOD (FWS) b/w occlusal surfaces of opposing teeth.

FWS) determined by a balance b/w elevator & depressor muscles: - attached to mandible, & 'elastic' nature of the surrounding soft tissue in a natural dentition.

FWS = RVD (RVFH) – OVD (OVFH) as measured by Willis gauge.

RVD not a stable position throughout life for a given individual.

FWS presence ensures:- comfortable CD wearing w/o oral tissue damage.- satisfactory appearance with CD wearing.

RVD is the starting point from which the OVD is estimated.

Factors Influencing RVD:Weight of the soft tissues attached to the mandible.Head position:

- tilting head back pulls mandible away from maxilla.- Head inclined forward pushes mandible closer to maxilla.

Infections / spasms, Tension states, apprehension.Drugs (skeletal muscle relaxants).Presence / absence of one or both prostheses in mouth.Methods for RVD measurement include:

- Measurements (facial measurements, biting force measurement).- swallowing, phonetic & tactile methods.- electro-myographic measurements.

Better to use a combination of the above.

Clinical Determination of RVD:Place two measuring points in the midline of face:

– one related to nose, and one to chin. Points on area of minimal influence from muscles of

facial expression (Points not on moveable skin).When placing points carefully observe patient seated in:

- dental chair (head erect) unsupported back & head.Measurement made with patient in a relaxed &

comfortable position while:- wearing previously developed upper base & rim.

Willis gauge used for measurement, as it incorporates a suitable scale.

A pair of dividers & a scale can also be used.

Patient moistens lips with tongue.Patient brings lips into light contact or;

- instructing patient to swallow & relax jaws. Verify measured value while patient says 'meem' & holding:

- facial expression whilst measurement is made. Appearance of face & its proportions also considered.

Control of skin movement during RVD recording necessary. After RVD, upper & lower corrected record bases placed in:

- the mouth after the upper rim has been moulded. Lower rim adjusted in height (add or trim) until it:

- contacts evenly upper rim at a VDO < 2–4 mm of RVD. This Incorporates a freeway space of 2–4 mm.And thus RVD is used to relatively establish the OVD.

Establish the height of lower rim, consider:- the relative height of both the upper and lower rims:

Reasonable balance between the two rims is desirable.Excessive height of lower rim cause the effect of 'walling in'

the tongue. - causing a resultant unstable lower denture.

On the other hand, deficient depth of the lower rim results in: - poor aesthetics and may result in tongue biting.

Conventional wisdom indicate that the occlusal plane:- should be below the dorsum of the tongue at rest.- lateral borders of resting tongue on occl. surface of rim..

Errors in OVDExcessive OVD:A risk of trauma to DBAs leading to excessive RRR. Absent FWS a cause continuous teeth clenching. Absent FWS cause painful mucosa over DBAs.Teeth contact cause clicking sounds during speech.Other speech problems caused by difficulty in

bringing the lips together (eg 'p', 'b' and 'm' sounds) may occur.

Poor aesthetics may be apparent. Masticatory muscle soreness ( masseter). Possibility of developing TMD / joint dysfunction.

Excessive OVD (orbicularis oris muscle group strained to create lip seal

Insufficient OVD:Lack of support of the angles of the mouth causing:

- dribbling and possibly angular cheilitis.Reduced masticatory efficiency.Poor aesthetics: Lack of adequate support of lips & cheeks: - Nose-chin approximation.

- Chin protrusion on jaw closure (Senile appearance). Smaller value FWS for young patients (Esthetics).Larger value FWS for older patients & those with atrophic

mucosa (to prevent /reduce trauma to mandibular tissues).Tests used to verify the established OVD.As occlusal rims are very different from teeth set-up on bases,

it is very difficult to apply tests for suitability of the chosen OVD value at this preliminary JR stage.

Established OVD better verified at the next “Trial” stage.

Insufficient OVD resulting in an ageing effect of this patient