VERTICAL JAW RELATION, Prosthodontics UG

Vertical Jaw relation

1. VERTICAL JAW RELATION Dr SHRADHA ANIL KUZHIVILAYIL

2. DEFINITION The vertical jaw relation or vertical dimension is defined as the length of the face as determined by the amount of separation of the jaws under specified conditions.

3. CLASSIFICATION Vertical dimension at rest. ○ Vertical dimension of occlusion or occlusal vertical dimension. ○ Vertical dimension in other positions of mandible.

4. Vertical dimension at rest: The length of the face when the mandible is in rest position (GPT). Physiologic rest position: The postural position of the mandible when an individual is resting comfortably in an upright position and the associated muscles are in a state of minimal contractual activity (GPT8). Vertical dimension of occlusion or occlusal vertical dimension: The length of the face when the teeth are in contact in MIP (maximal intercuspation). It is imperative that teeth should not contact at rest position and a space exists. This is important because the rest position is a comfortable position and the individual returns to this position most of the time that allows the supporting hard and soft tissues to rest. The vertical distance between the teeth at rest position is termed as ‘freeway space’ or ‘interocclusal rest space’. In the dentulous individuals this space varies from 1 to 10 mm with an average of 2–4 mm. The older the complete denture patient, more interocclusal rest space is provided. VD AT OCCLUSION = VD AT REST – 2–4 MM

5. METHODS OF DETERMINING VERTICAL DIMENSION AT REST The following factors influence the rest position: The posture of the patient A relaxed patient : Neuromuscular disturbance : Duration Use of several methods :

6. 1. The posture of the patient : The rest position is affected by postural changes. The patient should be sitting upright or standing with the head erect and looking straight ahead, when the rest position is determined. 2. A relaxed patient : When a patient is nervous, tense, irritable or tired, the rest position may be inaccurate. It should be determined when the patient is relaxed. 3. Neuromuscular disturbance : It will be difficult to determine the rest position in patients with such problems. The dentist should be more considerate, patient and spend more time to establish the rest position in such individuals. 4. Duration : As it is a position in space, the patient cannot maintain the rest position for long periods. The dentist should make the measurement without delay when the patient assumes this position. 5. Use of several methods : Although the rest position is measurable and repeatable, there is no single scientific method of establishing the same. A combination of various methods is used to verify the position.

7. FACIAL MEASUREMENTS The following methods are used to make the patient assume the postural rest position: ( i ) Swallowing: The patient is instructed to drop the shoulders, wipe his/her lips with tongue, swallow and close the mouth. This makes the mandible assume the rest position, which is immediately measured. (ii) Tactile sense: The patient is instructed to open the mouth wide until strain is felt in the muscles (may be for 1–2 min). They are then asked to close the mouth slowly until they feel comfortable and relaxed. Measurement is made in this position. (iii) Phonetics: The patient is instructed to repeatedly say words that contain the letter ‘m’. The lips meet when this is pronounced and the patient is instructed to stop all jaw movements when this happens. Measurement is made between the two points of reference. Alternately, the patient can be engaged in a conversation and measurement made when the patient pauses during the dialogue. The mandible assumes rest position at this point. (iv) Facial expression: The following indicates rest position: ○ Lips are even anteroposteriorly with slight contact. ○ Skin around the eyes and chin is relaxed. ○ Relaxation around the nostrils with unobstructed breathing. With experience the dentist learns to recognize, these features depicting rest position and will make measurements accordingly.

8. MEASUREMENT OF ANATOMICAL LANDMARKS The Willis guide states that the distance from the pupil of the eye to the rima oris (corner of mouth) should be equal to the distance from the anterior nasal spine to the lower border of the mandible, when the mandible is in its physiologic rest position.

9. METHODS OF RECORDING VERTICAL DIMENSION OF OCCLUSION The methods employed to determine vertical dimension of occlusion can be classified as physiologic and mechanical methods. 1. PHYSIOLOGIC METHODS ( i ) Niswonger’s method (physiologic rest position) This is the most commonly used method to establish occlusal vertical dimension. It uses the physiologic rest position (vertical dimension at rest) to determine the occlusal vertical dimension. As discussed previously in this chapter, Niswonger stated that: VD at Occlusion = VD at rest – freeway space (2–4 mm) (ii) Swallowing threshold The concept that maxillary and mandibular teeth come into light contact at the beginning of the swallowing cycle is used as a guide to determine occlusal vertical dimension.

10. The procedure involves building a cone of soft wax on the lower denture base in such a way that it contacts the upper occlusion rim when the jaws are open. Flow of saliva is stimulated by a piece of chocolate. The lower wax cone is softened and the patient is asked to repeat the action of swallowing. This will gradually reduce the height of the wax cone until it just touches the upper rim while swallowing. However, this method has not proven to be consistent (iii) Phonetics This uses phonetics to determine the vertical dimension. Closest speaking space: The space between the anterior teeth that, according to Dr Earl Pound, should not be more or less than 1–2 mm of clearance between the incisal edges of the teeth when the patient is unconsciously repeating the letter ‘s’. The production of ‘ ch ’ and ‘j’ sounds also brings the anterior teeth close together. When correctly placed, the lower incisors should move forward to a position nearly directly under and almost touching the upper central incisors.

11. (iv) Neuromuscular perception • Central bearing device (tactile sense): This utilizes the tactile sense of the individual to establish the vertical dimension. An adjustable central bearing screw is attached to one of the rims and a central bearing plate is attached to the other rim. The central bearing screw is first placed such that it is obviously too long or vertical dimension is increased. Progressively the screw height is reduced till the patient indicates that the jaws are overclosing (reduced vertical dimension). Finally the screw is adjusted until the patient indicates that the length is comfortable. The problem with this method is the presence of foreign objects in the palate and restriction of tongue space. Power point (maximum biting force): Boos (1940) demonstrated that the maximum biting force in an individual is registered at vertical dimension at rest. (v) Aesthetics The vertical dimension also affects aesthetics. When the vertical dimension is increased, the skin of the lips appears stretched compared to the skin over other parts of the face ). The skin appears more flaccid with a decreased vertical dimension. The contour of the lips is also distorted with a change in vertical dimension. The same problems can also occur if the labial contour of the occlusal rims is incorrect. Hence, the labial contour of the occlusal rims should be first developed and verified individually before evaluating the vertical relations.

12. 2. MECHANICAL METHODS ( i ) Ridge relations • Incisive papilla to mandibular incisors: The incisive papilla is a stable landmark whose position changes very little with resorption of the alveolar ridge. The distance of the papilla from the incisal edges of the mandibular anterior teeth should be on an average, approximately 4 mm in CO Ridge parallelism: Parallelism of the maxillary and mandibular ridges with a 5° opening in the posterior region provides a guide of appropriate vertical dimension. Since the clinical crowns of the anterior and posterior natural teeth have similar lengths, their removal makes the residual alveolar ridges nearly parallel to each other. (ii) Pre-extraction records These records can be prepared prior to the extraction of teeth and can be used as a guide to verify the vertical dimension of occlusion during the fabrication of complete dentures. • Profile photographs: Photographs are made of the facial profile when the teeth were present, in occlusion These are enlarged to a life size and similar photographs are made during recording of jaw relations with the rims in occlusion. Distance between similar anatomic landmarks on the photographs taken when the teeth were present and during jaw relation is compared. This allows verification of occlusal vertical dimension.

13. Profile silhouettes: The facial profile of a patient with natural teeth in occlusion before extraction can be carved out in a cardboard or contoured in a wire. The same can be placed on the face when the occlusal vertical dimension is being recorded with occlusal rims in position. This also allows verification of the vertical dimension. • Radiographs: Cephalometric radiographs and radiographs of condyles in fossa have been used similar to previous methods before extraction and during recording jaw relations to verify the vertical dimension. Because of radiation hazards and inaccuracies, they are now avoided Articulated cast : Casts are mounted before extraction and following the recording of the edentulous jaw relation in CR. The interarch distance is compared between the two casts to verify accuracy of vertical dimension. • Facial measurements : Tattoo marks are placed, one in the upper half and other on the lower half of the face The vertical distance between the marks is measured with the teeth in occlusion before extraction. The measurement is compared with the occlusal rims in position during jaw relation procedure to determine occlusal vertical dimension.

14. (iii) Measurement of former dentures The old dentures are placed in the mouth and using facial measurements the vertical distance is measured. This can be done during the jaw relation appointment for the new dentures. This again can only be used as a guide to establish the vertical dimension for the new dentures as there could be loss of vertical dimension with the old dentures due to ridge resorption and wear of the artificial teeth.

15. EFFECTS OF INCREASE IN VERTICAL DIMENSION 1 . Discomfor t : Chewing is a muscular mandibular movement, acquired over a period of many years, which the patient performs automatically and unconsciously. Increasing the vertical dimension alters the environment in which these unconscious movements take place and until the original condition is restored, discomfort will result. The jarring effect of teeth coming into contact sooner than expected also causes discomfort. 2 . Trauma : The sudden and frequent contacting of teeth causes trauma to the denture-bearing area, especially under the lower denture, where the area to resist pressure is less. Correcting the fitting surface of the denture will typically not solve the problem. 3 . TMJ problem : The constant tooth contact will also affect the TMJ causing soreness and pain. 4 . Bone resorption : The increased vertical height does not allow the muscles that close the mouth to complete their contraction. They will continue to exert force to overcome this obstruction and this will lead to resorption of supporting tissues. 5 . Muscular fatigue : Due to the constant effort of the muscles to close the mouth, muscular fatigue will also occur. 6 . Clicking of teeth : The premature contact of teeth sooner than what the individual is used to, will cause clicking of teeth. 7 . Facial distortion : There will be an inability to close the lips, which will produce a strained expression and elongation of face. 8 . Difficulty in swallowing and speech : The inability to close the lips will also cause difficulty in swallowing and speech.

16. EFFECTS OF DECREASE IN VERTICAL DIMENSION 1 . Inefficiency : The biting force exerted by the teeth in occlusion decreases which causes inefficient mastication. 2. Cheek biting : The loss of muscle tone and reduced vertical height causes the flabby cheeks to become trapped during mastication. 3. TMJ problem : The patient has to often protrude the mandible to occlude the teeth and this causes pain and clicking in the TMJ. 4. Facial distortion : The following effects are seen: ○ Nose appears closer to the chin ○ Loss of lip fullness ○ Loss of tonicity of muscles of facial expression ○ Face appears flabby ○ Patient appears older 5. Angular cheilitis : The corners of the mouth form deep folds, which are bathed in saliva. This becomes infected and sore.

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