Critical Evaluation Of Various Methods Of Recording Centric Jaw Relation

Critical Evaluation Of Various Methods Of Recording Centric Jaw Relation

Question 1. Define centric relation and explain graphic methods in detail.
Answer:

Centric Relation Definition

The maxillomandibular relationship in which the condyles articulate with the thinnest avascular portion of their respective discs with the complex in the anterosuperior position against the shapes of the articular eminences.

Centric Relation Graphic Methods

These methods use graphs or tracings to record the centric jaw relation. Graphic methods are of two types:

1. Arrow point tracing
2. Pantograph.

Read And Learn More: Complete Dentures Question and Answers

The arrow point tracing is a graphic record measured in a single plane whereas the pantograph is measured three-dimensionally.

Centric relation Factors affecting the accuracy of graphic tracing

1. Stability of the denture base.
2. Resistance by the occlusal rims against occlusal forces.
3. Difficulty in placing the central-bearing device in certain clinical situations.
4. Presence of flabby tissue.
5. Height of the residual alveolar ridge.
6. Interference from the tongue.
7. The efficiency of the recording devices.
8. Obtaining a pointed apex in the tracing pattern.
9. Lack of coordinated movement can cause double tracing.
10. These graphic tracings should harmonize with the centric relation and centric occlusion.

Centric relation Arrow Point Tracing

• It is a single-plane graphic tracing using an arrow-point tracer. The characteristic pattern created is called central arrow-point tracing.
• It is defined as, “The pattern obtained on the horizontal plate used with a central-bearing tracking device.”–GPT
• The apex of the arrow point tracing gives the centric relation.

Centric relation Parts of the tracer

• A pen-like pointer is attached to one occlusal rim and a 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. The pointer and the plate together are called the central-bearing device.
• The central-bearing device is defined as, “A device that provides a central point of bearing or support between the maxillary and mandibular dental arches. First attributed to Alfred Gysi, Swiss Prosthodontist, in 1910.”
• It is a triangular plate of metal with a central metal pointer and with extensions to attach itself to the occlusal rim. The pointer in the center can be adjusted in height. It is usually attached to the mandibular occlusal rim and also can be attached to the maxillary rim.
• The central bearing plate is a triangular piece of metal with extensions at the three corners provided to attach the plate to the maxillary occlusal rim.
• A mixture of denatured spirit and precipitated chalk is coated on this plate and when the spirit dries, a fine layer of precipitated chalk is left behind. The tracing is marked on this layer of precipitated chalk.

Centric relation Types of arrow point tracers (Based on the location of the tracer)

• Intraoral tracers
• Extraoral tracers.

Centric relation Intraoral Arrow Point Tracers

The central bearing device is located intraorally and hence the name.

Centric relation procedure

1. The central bearing point and the central-bearing plate (coated with chalk) attached to record bases are inserted into the patient’s mouth.
2. The central bearing point is adjusted to a predetermined vertical dimension such that it contacts the central-bearing plate when the patient closes his mouth.
3. When the patient is asked to make anteroposterior and lateral movements, the central bearing point will draw the tracing pattern on the central-bearing plate.
4. After completing the movements, the tracing should resemble an arrow point with a sharp apex. If the apex is blunt, the record is repeated.

Centric relation Disadvantages

1. The tracer is not visible during the procedure.
2. The size of the tracing is very small, hence to determine the apex of the tracing is difficult.
3. It cannot be used in patients who cannot retract the tongue and in cases of macroglossia.

Centric relation Extraoral Arrow Point Tracers

The concept is the same as for intraoral tracer.

Centric relation Parts of Extraoral Tracers

A central-bearing device is attached to the occlusal rims (central bearing point and central bearing plate).

• Extraoral tracing pointer attached to the maxillary rim.
• Recording plates are attached to the mandibular rim.

Centric relation Procedure

1. A tentative vertical dimension is established.
2. The maxillary cast is mounted in the articulator using face-bow transfer and the mandibular cast is positioned against the maxillary in a tentative centric relation and articulated.
3. The mandibular occlusal rim is reduced to obtain interocclusal distance.
4. The recording plate is attached to the mandibular occlusal rim coinciding with the midline of the rim.
5. The stylus or the central bearing point is attached to the maxillary occlusal rim.
6. The record bases attached to the recording devices are inserted in the patient’s mouth.
7. The Ney excursion guide can be used to train the patient for proper jaw movements.
8. The recording plate projecting extraorally (attached to the mandibular rim), is coated with precipitated chalk and denatured alcohol.
9. Intraorally, the central-bearing point should touch the central-bearing plate at the predetermined vertical dimension.
10. The patient is asked to perform protrusive, lateral, and anteroposterior movements.
11. It is an extraoral tracing on the recording plate by the tracing pointer. The tracing should have a sharp apex.
12. After finalizing the records, quick-setting plaster is injected between the occlusal rims.
13. The assembly is removed and articulated and should be checked using an interocclusal check record.

Centric relation Advantages

1. Extraoral tracing can be examined as it is made.
2. The size of the tracing pattern is easily seen.
3. The apex can be identified easily.

Centric relation Pantographic Tracing

• It is defined as, “A graphic record of mandibular movement in three planes as registered by the style on the recording tables of a pantograph; tracings of mandibular movement recorded on plates in the horizontal and sagittal planes.”–GPT
• The instrument used to do pantographic tracing is called a pantographic tracer. A pantographic tracer is defined as, “An instrument used to graphically record one or more planes paths of the mandibular movement and to provide information for the programming of the articulator.”–GPT

Centric relation Parts of a pantograph

• A pantographic tracer has six flags (The surface over which the tracing is done is called a flag).
• A stylus (tracing pointer) is present for each flag (It draws tracing patterns on the flags).

Location of the flags

• Two flags are located perpendicular to one another near the condyles. Two for the right and two for the left condylar guidance. They locate the actual (true) hinge axis.
• Two flags are placed in the anterior region. They record the anteroposterior movements.

Location of the flags Advantages

1. The most accurate method is available to record centric jaw relation.
2. Eccentric jaw relation can be recorded using these instruments.
3. Used for full-mouth rehabilitation of edentulous patients.

Location of the flags Disadvantages

1. Are very sophisticated
2. Cannot be used in the fabrication of complete dentures as the complete dentures have a relief factor that aids to compensate for minor fabrication errors.