SURYEYING

(PROSTODONTIC LECTURE NOTE)

DENTAL SURVEYOR• Define: an instrument used to

determine the relative parallelism of 2 or more surfaces of the teeth or other parts of the cast of the dental arch.

• Therefore: primary purpose of surveying is – to identify the modifications of oral structures that are necessary to fabricate a removable partial denture (RPD) that wll have a successful prognosis.

Description of Dental Surveyor

• The principle parts:- Platform on which the base is moved- Vertical arm that supports superstructure- Horizontal arm form which surveying tool suspends- Table to which the cast is attached- Base on which the table swivels- Paralleling tool or guideline marker- Mandrel for holding special tools

Surveying the Master Cast• The objectives of surveying the master cast as follows:

1. To select the most suitable path of placement by following mouth preparations that satisfy the requirements of guiding planes, retention, noninterference, and esthetics.

2. To permit measurement of retentive areas and to identify the location of clasp terminals in proportion to the flexibility of the clasp arm being used; flexibility will depend on many of the following factors:

- The alloy used for the clasp- Design n type of the clasp- The form (round or half round)- The length of the clasp from its point of origin to its terminal end- And retention; (depend on the flexibility of the clasp arm, a magnitude of the

tooth undercut and the depth of clasp terminal is placed into this undercut).3. To locate undesirable undercut areas that will be crossed by rigid part of the

restoration during placement and removable and must be eliminated by blockout (with wax or plaster).

4. To trim blockout material parallel to the path of placement before duplication.

The RPD must be designed so that:a) It will not stress abutment teethb)It can easily placed and removed by the patientc) Retained against reasonable dislodging forcesd)Not create unfavorable appearance

Step by Step Procedures in Surveying a Diagnostic Cast

• Surveying of diagnostic cast• Final path of placement• Outlining the design on diagnostic cast• Surveying master cast• Measuring retentive undercuts• Outlining design on master cast with graphite

pencil

Step by Step Procedures in Surveying a Diagnostic Cast

Placement of cast : Attach the cast to the adjustable surveyor table by means of the clamp provided. Position of adjustable table do that occlusal surfaces of the teeth are approximately parallel to the platform.

1) Guiding Planes-determine the relative parallelism of proximal surfaces of all the potential abutment teeth by contacting the proximal surfaces with the surveyor blade or diagnostic stylus.

1) Guiding Planes• Alter the cast

anteroposteriorly until these proximal surfaces are in as close to parallel relations to one another as possible, or near enough that they can made parallel by recountouring.

• In making choice between having contact with a proximal surface at the cervical area/contact the marginal ridge ONLY.

2) Retentive Areas• By contacting buccal and

lingual surfaces of abutment teeth with the surveyor blade, the amount of retention existing below their height of convexity may be determined.

• The angle of convergence is best observed as a triangle of light between the surveyor blade and the apical portion of the tooth surface.

2) Retentive Areas

• Alter the cast position by tilting it laterally until similar retentive areas exist on the principle abutment teeth.

• In tilting the cast laterally to establish reasonable uniformity of retention, it is necessary that the table be rotated about an imaginary longitudinal axis without disturbing the anteroposterior tilt previously established.

3) Interference• For mandibular arch:- Check the lingual surfaces that will be crossed by a lingual

bar major connector (if is the choice) during placement and removal.

- Bony prominence and lingually inclined premolar teeth are most common causes of interference to a lingual bar connector.

- If bilateral interference is present, surgery or recountouring of lingual tooth surfaces is required.

- If is only unilateral, change in a lateral tilt can avoid the interference. In changing the path of placement, to prevent interference, previously establish guiding planes and an ideal location for retentive elements may lost.

3) Interference• For maxillary arch: - Interference to major connectors rarely exists in the

maxillary arch.- Areas of interference are usually found on buccally

inclined posterior teeth and those bony areas on the buccal aspect of edentulous spaces.

- This interference can either be blocked out, alter by tilt, recountoured or cast restoration can be on the tooth with interference.

- Nonretentive and stabilizing clasp arms are best located between the middle third and gingival third of the crown rather than the occlusal third.

4) Esthetic

• The path of placement determines the location of clasps and position of artificial teeth.

• Depending on esthetics, the clasp designed can be modified as:

- gingivally approaching bar clasp- Slightly placing the circumferential clasp arms

cervically.