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Jaw Relationships (How is the vertical dimension assessed clinically?…

- - - - Hinge
      - Free plane (average value)
      - Semi-adjustable (Dentatus)
      - Fully adjustable (Dentar)
- - - - Antero-posterior
      - Lateral
- - - - REST VERTICAL DIMENSION (RVD)
        
        The vertical dimension of the face with the jaws in the physiologic rest position (RP)
        
        RP is the habitual postural position of the mandible when the patient is resting comfortably in the upright position with the condules in a neutral unstrained position in the glenoid fossa
        
        Factors which influence RVD
        
        Short term factors
        
        Head posture (decreases when head is tilted forward)
        
        Stress (decreases with stress)
        
        Presence of absence of teeth (decreases following extraction)
        
        Body posture (decreases in supine position)
        
        Long term factors
        
        Age (increases with age due to alveolar growth-- lengthening of lower third of the face)
        
        Chronic neuromuscular disorders e.g. paralysis
        
        Parafunction e.g. bruxism decreases RVD
        
        Drugs (e.g, increases with diazepam, decreases with caffeine)
      - OCCLUSAL VERTICAL DIMENSION (OVD)
        
        The vertical dimension of the face when the teeth are fully intercuspated (MI)
        
        This position is established by the TEETH
        
        What is the OVD you have chosen is excessive?
        
        Trauma to the denture bearing tissues; both soft tissue and alveolus
        
        Clicking during speech
        
        Difficulty in pronouncing words starting with 'p', 'b' and 'm'
        
        Strained appearance
        
        TMJ dysfunction
        
        What if the vertical dimension you have chosen is inadequate?
        
        Lack of facial support; wrinkled
        
        Reduced masticatory effiieicny
        
        Dribbling of saliva
        
        Angular chelitis
        
        Cheek biting
        
        TMJ disorder
      - FREEWAY SPACE (FWS)
        
        (def.) the space between upper and lower teeth when mandible is in resting position
      - Establishing vertical component
        
        When natural teeth are present in the jaws and in a state of normal occlusion -- contact between the opposing teeth determines the OVD
        
        When no contacts are present due to the absnece of teeth, the OVD must be estimated
        
        Basis for estimation of OVD is the RVD
        
        RVD - FWS = OVD (FWS usually about 2-4mm)
    - - Once the correct OVD is established (with allowance for necessary FWS), the jaw relation in the horizontal plane must be established
      - Centric Relation-- the most retruded unstrained position of the mandible from which lateral movements can be made at an established vertical dimension -- CLINICALLY REPRODUCIBLE
      - 2 situations to be considered
        
        Dentate patients with sufficient and stable natural tooth contacts-- MI is the horizontal relationship to be recorded
        
        Patients lacking acceptable tooth contact-- the retruded jaw relationship (CR) must be recorded at the established OVD
      - Reasons for using CR
        
        1) it is reproducuble
        
        2) apparatus used for reproducing some jaw movements and setting the teeth operate from the retruded positon (CR)
        
        3) denture instability results when teeth of denture are set up in other than CR
        
        4) OVD may be altered during function if the teeth are set in other than CR
        
        5) May result in TMJ dysfunction when patient attempts to modify chewing action to accomodate incorrect jaw relationships
      - Retruded Contact Position-- position of the mandible when its condyles are in their retruded position in the glenoid fossa and there is occlusal contact of the teeth or occlusion rims