Jaw relation

Jaw Relation ,Orientation Jaw relation,Vertical Jaw Relation,Facebow

1. JAW RELATION Prepared by:Parvathy Krishnan, 3 rd BDS,Roll No -39

2. Contents Jaw Relation Orientation jaw relation Face bow Vertical jaw relation Reference

3. J aw Relation Jaw relation is defined as, “any relation of the mandible to the maxilla” -GPT There are three different types of jaw relations they are listed in order of the procedure: Orientation jaw relation Vertical jaw relation Horizontal jaw relation

4. Orientation jaw relation It is defined as “the jaw relation when the mandible is kept in its most posterior position, it can rotate in the sagittal plane around an imaginary transverse axis passing though or near the condyles” - GPT This record gives the angulation of the maxilla in relation to the base of the skull.It is necessary to carry out orientation jaw relation before other jaw relations.

5. - To record the inclination of maxilla, a plane should be formed with two posterior ( centre of both condyles A and B) and one anterior point – here infraorbital notch C is used as anterior reference point.

6. -Facebow is used to determine the inclination of maxilla by forming a plane (a–c) using the centre of the two condyles (a and c) as posterior references and infraorbital notch (b) as anterior reference. -The centre of condylar rotation is also determined and the same is transferred to the articulator. - Once the maxilla is oriented, the mandible is oriented with the maxilla using centric and eccentric records

7. Face-bow It is defined as “ A caliper like device which is used to record the relationship of the jaws to the temporomandibular joints and to orient the casts on the articulator to the relationship of the opening axis of the temporomandibular joint” -GPT The parts of a face-bow are U-shaped frame Condylar rods Bite fork Locking device Orbital pointer with clamp

8. Types of face-bows Face-bow can be classified as Arbitrary face-bow Facia type Earpiece type Hanau face-bow (Spring bow) Slidematic ( Denar ) Twirl bow Whipmix Kinematic or hinge bow

9. ARBITARY FACE BOW -Also called ‘Average axis facebow’ -Hinge axis approximately located,It positions the rods within 5 mm of true centre of rotation of condyle. -Commonly used and preferred for fabrication of complete denture.

10. FASICA TYPE In this type of face bow the posterior reference point is 13 mm anterior to the external auditory meatus and the anterior reference point is the orbitale.Face bow has a pointer that can be positioned to the posterior reference point. EARPIECE TYPE In this type the external auditory meatus is considered as referral point to determine the centre of condylar rotation. Anterior reference point is orbitale and earpiece engage in posterior reference point.

11. KINEMATIC FACEBOW - With the adjustable caliper end that locates the true centre of condylar rotation -Used for full mouth reconstruction and requires fully adjustable articulator. -Like facia type condylar rods are 13mm anterior to external auditory meatus on canthotragal line.

12. PARTS OF FACE-BOW 1. U-shaped frame • It is a U-shaped metallic frame, to which all the other components of the facebow are attached . • It extends from the TMJ of one side to the TMJ of the other side, at least 2–3 inches anterior to the face to avoid contact. 2. Condylar rods • These are two calibrated metal extensions fitted on either side of the free end of the U-shaped frame that are placed on the determined centre of condyle. • The calibrations on either side are equalized (to centre the facebow) and then locked.

13. 3. Bite fork • It is a U-shaped rod which is attached to the maxillary occlusal rim while recording the orientation jaw relation. • It is attached to the frame with the help of a metal rod called the ‘stem’. • The bite fork should be inserted about 3 mm above the occlusal surface into the occlusal rim. • Sometimes the bite fork is attached to the occlusal surface of the occlusal rim with the help of impression compound. This is done in order to preserve the occlusal rim.

14. Locking Device This part of the face-bow that helps attach the bite fork to the U-shaped frame. There is locking clamp for bite fork,locking clamp for orbital pointer pin and locking screw for condylar rods.

15. Orbital Pointer: It is designed to mark the anterior reference point ( infraorbital notch) and can be locked in position with a clamp. It is present only in the arbitrary face-bow

16. F ace-bow Transfer • Facebow record • Facebow mounting Clinical procedure for recording orientation jaw relation (using facia type) • The maxillary occlusal rim is inserted into the patient’s mouth and contoured • A point 13 mm from tragus of the ear on the canthotragal line is marked on both sides . • The bite fork is flamed and attached anteriorly to the maxillary occlusal rim, 3 mm above the incisal plane and parallel to the occlusal plane .The maxillary rim with the attached bite fork is inserted into the patient’s mouth. The parallelism and centring of the attached bite fork are verified. • The U-frame is supported by two fingers and gently rotated and inserted into the stem of the bite fork in the patient’s mouth . • The condylar rods are unlocked and the condylar heads are then placed in the patient’s right and left condylar centres on the previously marked points. .

17. • The third point of reference (infraorbital notch) is palpated and the orbital pointer is set to the third point of reference . • The condylar rod readings are equalized on both sides and the locking screws are tightened. Following this, the orbital pointer is also tightened in position. • Once the entire apparatus is in position, the condylar rods, orbital pin and the bite fork are verified for any movement, alignment and parallelism. • The contoured mandibular occlusal rim may be used during the transfer to stabilize the maxillary rim. The facebow record is removed from the patient by loosening only the condylar screws . The record is now ready to be mounted on the articulator. This completes the facebow transfer and then it is transferred to the articulator.

18. Mounting on the articulator • The articulator is programmed first (zeroing of articulator): The incisal guide pin is set to correct jaw separation and the anterior stop screws are tightened first. Next the horizontal condylar inclination is set at 40° and the Bennett angle at 20° . •The condylar rods are attached to the auditory pins. The bite fork is stabilized on the tilting support bar provided and the orbital pin is made to coincide with the orbital axis plane indicator. • The incisal pin is locked with its lock screw at zero on calibration and the incisal table is set horizontally. • The upper member of the articulator is swung open, plaster is mixed and placed on the cast and the upper member is closed slowly, until the incisal pin fully touches the incisal table and upper mounting plate is covered with plaster. • Excess plaster is trimmed once the plaster is set. Facebow is now removed by loosening all the locking devices.

19. Vertical Jaw Relation It is defined as, “The length of the face as determined by the amount of separation of the jaws under specified conditions”. - GPT If the vertical dimension is altered there will be severe discomfort in both the TMJ and the muscles of mastication.

20. Vertical Jaw Relation can be Recorded in Two Positions Vertical dimension at rest position Vertical dimension at occlusion In a normal dentulous patient, the teeth do not maintain contact at rest. The space between the teeth at rest is called the ‘free-way space’ which is around 2-4 mm.

21. Vertical Dimension at Rest It is defined as, “The length of the face when the mandible is in rest position” -GPT. This is the position of the mandible in relation to the maxilla when the maxillofacial musculature are in a state of tonic equilibrium. This position is influenced by the muscles of mastication, muscles involved in speech, deglutition and breathing. It can be calculated by VD at rest = VD at occlusion + free-way space. (VD—Vertical dimension)

22. Facial measurements The vertical dimension at rest is calculated by making facial measurements. Two marks are commonly placed, one on the tip of the nose and other on the chin directly below the nose marking. The markings can be made with an indelible marker or pieces of adhesive tape

23. 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.

24. (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.

25. (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.

26. Measurement of anatomical landmarks Distance from pupil of eye to rims oris (B) should be equal to distance from anterior nasal spine to lower Border of mandible (A) when mandible is at rest position,This is known as Wills Guide.

27. Vertical Dimension at Occlusion It is defined as, “The length of the face when the teeth (occlusal rims, central-bearing points, or any other stop) are in contact and the mandible is in centric relation or the teeth are in centric relation” – GPT. Vertical dimension at occlusion can be recorded using the following methods: -Physiologic -Mechanical

28. Physiologic Methods ( i ) Niswonger’s Method - Niswonger stated that: VD at Occlusion = VD at rest – freeway space (2–4 mm) -Hence, the physiologic rest position is first determined. The contoured maxillary occlusal rim is placed in the patient’s mouth and the vertical dimension at rest is determined using facial measurements -The mandibular occlusal rim is then inserted and it is trimmed and contoured until it meets the maxillary rim evenly. The lower rim is adjusted till the facial measurement in occlusion is 2–4 mm less than that in rest position.

29. -This will provide for the necessary interocclusal space or freeway space. -The same can be verified by asking the patient to part the lips without moving the jaws at rest position, with the occlusal rims inserted.

30. (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. 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.

31. (iii) Phonetics Closest speaking space. Position of the anterior teeth govern the vertical separation between them during pronunciation of ‘ ch ’, ‘s’ and ‘j’. Incorrect positioning will result in obliteration or opening of this space (closest speaking space) which will result in altered pronunciation of these words. This is known as Silverman’s Closest Speaking Space.

32. (iv) Neuromuscular perception • Central bearing device (tactile sense): This utilizes the tactile sense of the individual to establish the vertical dimension. • Power point (maximum biting force): Boos (1940) demonstrated that the maximum biting force in an individual is registered at vertical dimension at rest

33. (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.

34. 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.

35. (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 • Profile silhouettes • Radiographs • Articulated cast • Facial measurements (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.

36. Effects of increase or decrease of vertical jaw relation

37. Reference Textbook of Prosthodontics- Deepak Nallaswamy Textbook of Prosthodontics -V Rangarajan

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