Centric relation record is made at the correct occlusal vertical dimension. At the correct occlusal vertical dimension the patient is asked to relax as much as possible and the dentist guides mandible into unstrained retruded position.
Methods for assisting the patient to retrude the mandible.
Instruct the patient by saying “ let your jaw relax, pull it back, close slowly and easily on your back teeth. ”
Instruct the patient by saying “ get the feeling of pushing your upper jaw out and closing your back teeth together. ”
Instruct the patient to turn the tongue backward towards the posterior border of the upper denture.
Tilt the patient’s head back while the various exercises just listed are carried out.
Extraoral tracing devices:
A needlepoint tracing made on a tracing table coated with carbon or wax can be used to indicate the relative position of upper and lower jaws in the horizontal plane. These tracings are shaped like a gothic arch and therefore are referred to as “gothic arch tracings. ” Also known as “ arrow point tracings. ”
Intraoral tracing devices:
A hole may be drilled in the plate at the apex of the intraoral tracing or a plastic disc with a hole in it may be placed over the apex of the tracing. The hole or the depression is used to ensure that the patient’s jaw is in the retruded position while the registration is being done with plaster or some such material.
Heat the surface of one of the rims and have the patient close into this softened surface to make a new maxillo mandibular relation impression.
Soften the wax rims by deep heating posterior portion of the mandibular wax rim and leaving the anterior portion cool to maintain the predetermined vertical dimension of occlusion. Deep heating is referred to as Pooling. The heated portion will readily collapse under closing pressure. Swallowing method: when swallowing the jaws go back to centric and cones of wax are compressed against maxillary occlusal rims.
Intraocclusal centric relation recording in detail:
After establishing the vertical dimension record, 3 mm of wax from the mandibular rim is removed from the first premolar and molar areas both on right and left sides.
Cut 2 or 3 notches on the corresponding maxillary rim.
After lubricating this surface with petrolatum place both the upper and lower rim in the patient’s mouth.
Check for any interferences and train the patient to close in centric relation by assisting the patient in retruding the mandible by placing the index fingers on the buccal flanges of the mandibular occlusal rim in both premolar regions with the thumbs under the patients chin.
Instruct the patient to close slowly and gently on the back teeth, if centric relation position satisfactory, soft baseplate wax or bite registration paste is placed from were 3 mm of wax was removed.
The registration material should be placed 1 ½ mm above the original height of the rim.
After the registration material is placed, the patient is guided in retruding the jaw and closing it slowly with minimum force until the anterior occlusal rims are uniformly touches each other.
Trim the excess material from the buccal and lingual sides and recheck to see if the bases contact simultaneously and in the proper position.
Graphic methods in detail
Graphic methods are either intra oral or extra oral dpending on placement of recording device.
Made at predetermined vertical dimension.
Intraoral tracing cannot be observed during tracing
Extra-oral tracing can be examined as it is made. The apex can be identified easily.
Factors affecting accuracy of graphic tracing:
Stability of the denture base.
Resistance by the occlusal rims against occlusal forces.
Presence of flabby tissue.
Interference from the tongue.
Lack of coordinated movement can cause double tracing.(advvanced age)
INTRA-ORAL ARROW-POINT TRACERS:
The central bearing device is located intra-orally and hence the name.
The central bearing point and the central-bearing plate (coated with chalk) attached to record bases are inserted into the patient's mouth.
The central bearing point is adjusted to a pre determined vertical dimension such that it contacts the central-bearing plate when the patient closes his mouth.
When the patient is asked to make antero posterior and lateral movements, the central-bearing point will draw the tracing pattern on the central-bearing plate.
After completing the movements, the tracing should resemble an arrow point with a sharp apex. If the apex is blunt, the record is repeated.
The tracer is not visible during the procedure.
The size of the tracing is very small, hence to determine the apex of the tracing is difficult.
It cannot be used in patients who cannot retract the tongue.