Maxillomandibular Relations Notes

Maxillomandibular Relations Definitions

1.  Jaw relation: Any relation of the mandible to the maxilla
2. Orientation jaw relation: 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 through or near the condyles
3. Vertical jaw relation: The length of the face as determined by the amount ofseparation of the jaws
4. Horizontal jaw relation: It is the relationship of the mandible to the maxilla in horizontal plane
5. Centric jaw relation: The maxillomandibular relation in which the condyles articulate with the thinnest avascular portion of their re- spective disc with the complex in the anterior-superior position against the slopes of the articular eminence 6.
6. Face bow: A calliper like device which is used to record the relationship of the jaws to the temporomandibular joints & to orient the casts on the articulator to the relationship of the opening axis of the temporomandibular joint
7. Occlusal rim: Occluding surfaces built on temporary or permanent denture bases for the purpose of making maxillomandibular relation records & arranging teeth
8. Physiological rest position: The mandibular position assumed when the head is in an upright position & the involved muscles, particularly the elevator & depressor groups, are in equilibrium in tonic contraction, & the condyles are in a neutral, un- strained position”
9. Balanced occlusion: The simultaneous contacting of the maxillary & mandibular teeth on the right & left & in the anterior & posterior occlusal areas in centric & eccentric positions, developed to lessen or limit tipping or rotating of the denture bases in relation to the supporting structures

Maxillomandibular Relations Important Notes

1. Types of jaw relations:

• Orientation jaw relation
• Vertical jaw relation
• Horizontal jaw relation

2. Dimensions of maxillary occlusal rim

• 22 mm – at canine eminence
• Anterior edge of occlusal rim at midline – 8 mm away from incisive papilla
• Width
  • In anterior region – 4-6 mm
  • In posterior region – 8-12 mm
• Occlusal table
  • Above crest of alveolar ridge in anterior region – 10-12 mm
  • From crest of alveolar ridge in posterior region – 5-7 mm
  • From depth of sulcus in posterior region – 18 mm
  • The anterior part of the maxillary occlusal plane should be 2mm below the upper lip line or smile line.
  • The posterior part of the maxillary plane should be parallel to Campers line of Ala-tragus line.

3. Tracing:

• Jaw movements can be recorded by the simple tracer assembly method. Tracing may be extraoral or intraoral.
• Intraoral tracing is less complicated. Extraoral tracers are less widely used
  • Extra-oral tracers:
    • High extraoral tracer assembly
    • Sears extraoral tracer assembly
  • Intraoral tracers:
    • Microtracer

Read And Learn More: Prosthodontics Question And Answers

4. Freeway space:

• The distance between to arbitrary points on maxilla and mandible when the patient is relaxing is called vertical dimension at rest.
• The same distance when the patient is occluding on rims is called vertical dimension in occlusion.
• The difference between VDR and VDO is called interocclusal distance or “Free-way space”.
• It is usually 2-4 mm when observed at the position of 1 premolars.
• Free way space less than normal means increased vertical dimension of occlusion which results in :-
  • Reversible soft tissue changes and irreversible ridge resorption.
  • Difficulty in swallowing.
  • Diffuse pain of ridge area.
  • Clicking of dentures during speaking.
  • Trauma to TMJ.

5. Gothic arch tracing:

• Gothic arch tracing (also known as arrow point or needle point tracing) is an extra oral method recording centric relation in horizontal jaw relations.
• It indicates the relative position of upper and lower jaws in horizontal plane.

6. Immediate side shift or Bennett movement:

• Here the mandible shifts before the forward movement of the non-working condyle occurs.
• This movement occurs in 86% of the condyles.
• This shift ranges 1 to 4 mm in dimension.

7. Progressive side shift or Bennett side shift:

• Lateral translation that continues linearly after 2-3mm of forward movement of the non working condyle.

8. Beyron point:

• It is a line extending from the counter canthus of the eye to the top of the tragus of the ear and approximately 13mm in front of the external auditory meatus’
• This placement generally locates the rods within 5mm of the true center of the opening axis of the jaws.
• The imaginary line joining the two Beyron points is an approximate hinge axis.

9. Face bow:

• Face bow is a calliper like instrument used to orient maxillary cast on the articulator so that it has the same relation- ship to the opening axis of the jaws.
• There are two types, the kinematic and the arbitrary.
• The kinematic is used to locate the true terminal hinge axis and transfer this record to the articulator when mounting the maxillary cast.
• The arbitrary face bow is the one generally used in the construction of complete dentures is based on average computation of an axis opening of the jaw.
• It is simple to use and relatively accurate

10. Effects of change in vertical dimension:

11. Methods used to record centric relation:

1. Physiological methods
   • Tactile method
   • Pressureless method
   • Pressure method
2. Functional method
   • Needle house
   • Petterson method
3. Graphic method
   • Intraoral
   • Extra oral
   • Radiographic method

12. Materials used for interocclusal check records:

• Waxes
• Zinc oxide eugenol
• Decreased vertical dimension
• Increased freeway space

Maxillomandibular Relations Short Answers

Question 1. Effects of increased vertical dimension.
Answer:

• Increased trauma to the denture-bearing area Increased lower facial height
• Cheek biting
• Difficulty in swallowing & speech
• Pain & clicking in TMJ
• Stretching of facial muscles
• Increased space of oral cavity

Question 2. Interocclusal recording media
Answer:

Commonly used materials for inter-occlusal recording are:

Question 3. Christenson phenomenon.
Answer:

• Mandible is guided by the anterior teeth during protrusive movement
• This is followed by complete disocclusion of the posterior teeth
• This characteristic posterior separation seen during anterior protrusion is called Christenson’s phenomenon

Question 4. Lingualized occlusion
Answer:

• Proposed by Alfred Gysi in 1927 It involves the use of a large upper palatal cusp against wide lower central fossa
• The buccal cusps of upper and lower teeth do not contact each other It is preferred due to its superior chewing efficiency
• Payne proposed the use of 30-degree anatomical teeth which are then reshaped to obtain lingual occlusion

Question 5. Interpupillary line.
Answer:

• It is used for evaluation of occlusal plane extra orally
• It is the distance between the two pupils
• The anterior part of the maxillary occlusal plane should be parallel to the interpapillary line It should be 2 mm below the upper lip line or smile line

Question 6. Arbitrary face bow.
Answer:

It is commonly used for complete denture construction The condylar rods are positioned approximately 13 mm anterior to the auditory meatus on a line running from the outer canthus of the eye to the top of the tragus called cantho-tragal line This locates the rods within 5 mm of the true hinge axis of the jaws

Types:

• Facia type
• Earpiece type
• Hanau face bow
• Slidematictype Twirl bow
• Whipmix facebow

Question 7. Atmospheric pressure.
Answer:

• The peripheral seal prevents air entry between the denture & soft tissue
• Hence a low pressure is maintained within the space between the denture and the soft tissues
• To obtain it denture borders should rest on soft & resilient tissues
• On application of forces, a vacuum is created that aid in retention This is a natural suction of denture
• Hence atmospheric pressure is referred as emergency-retentive force or temporary restraining force
• Retention produced by atmospheric pressure is directly proportional to the denture base area

Question 8. Gothic arch tracing.
Answer:

• It is used for recording centric relation
• It is usually recorded in the horizontal plane
• It is done using an arrow point tracer
• A pen-like pointer is attached to one occlusal rim Recording plate is placed on the other rim
• When the mandible moves the pointer draws characteristic patterns on the recording plate
• The pointer is known as the central bearing point and the recording plate is known as the central bearing plate
• They act at the center of the arch and evenly distribute forces across the supporting structures
• The shape of the tracing pattern resembles arrowhead The apex of the arrow gives the centric relation It should be sharp enough

Maxillomandibular Relations Viva Voce

1. A kinematic face bow is usually used for fixed partial dentures
2. The arbitrary face bow is the one most commonly used in complete denture patients.
3. Wax, plaster, ZOE paste, and self-cure resins are commonly used for interocclusal records
4. Lateral movement produces an anterior translation of condyle on the working side and rotation about the center on
   the nonworking side (balancing side)
   Bennett angle is formed by the sagittal plane and the path of the advancing condyle during lateral mandibular movements as viewed in the horizontal plane.
5. Petterson and Needlehouse are functional methods of recording centric relation
6. Intraoral tracing contains a central bearing plate and a central bearing point tracer
7. The graphic method is accurate method of recording centric relation
8. Orientation jaw relation is related to the cranium
9. Vertical jaw relation is related to jaw separation Face bow is used to record hinge axis