Surveying for Removable Partial Dentures

Surveying

• Surveying is the process of locating and delineating the contour and position of teeth and associated structures before designing a removable partial denture.
• The objectives of the lecture include understanding surveyor tools and how to use the surveyor.

Objectives of the Lecture

• Understand surveyor tools
• How to use the surveyor

Removable Partial Prosthodontics

• This is a dental procedure covered in Chapter 11 of McCracken's Removable Partial Prosthodontics.

Component Parts of Removable Partial Dentures

• Denture Base
• Artificial Teeth
• Supporting Rests
• Connectors (Major and Minor)
• Retainers (Direct and Indirect)

Undercuts on Teeth

• Undercuts are areas below the height of the tooth contour, a dig or burrow
• The height of the contour represents the most bulbous and convex part of the tooth, also known as the maximum bulge or survey line
• The survey line is a line outlined on a cast by a surveyor, marking the greatest prominence of tooth contour

Types of Undercuts

• Desirable
• Undesirable (except for denture retention)

Components of Metallic Removable Partial Dentures

• Clasp arms are located in undercut areas to retain the restoration against dislodging forces
• The clasp arms are flexible, unlike other parts of the denture

Path of Insertion/Removal

• Path of Insertion (PI): The direction a restoration moves from initial contact with supporting teeth to resting position, where occlusal rests are seated, and the denture base is in contact with the tissue
• Path of Removal: The opposite direction of the path of insertion

Selection of the Path of Insertion

• Most favorable PI is perpendicular to the occlusal plane
• Patients often insert dentures under biting force
• If displacement is anticipated, use the least displacing forces
• If undercuts are present but not efficient (zero tilt), another path should be decided

Factors Affecting Path of Insertion

• Interferences (changing the path of insertion, contouring the tooth surface, or surgery to remove interfering structures)
• Retentive undercuts (equal depth and permitting the location of clasp tips in the gingival third of the tooth)
• Esthetics (made possible with less clasp metal and less base material displayed)
• Guiding planes

Guiding Planes

• Flat axial surfaces in an occluso-gingival direction on the proximal or lingual surfaces of teeth, parallel to the path of insertion
• Guiding the prosthesis in or out of place without excessive forces against the teeth
• Providing bracing and stability when located on the axial lingual surface of the tooth
• Minimizing wedging stresses on abutment teeth and spaces that the denture makes with the teeth. making the prosthesis easier to clean

The Denial/Dental Surveyor

• "Paralleling Instrument" used to determine the survey line of teeth, identify and measure undercuts and determine the relative parallelism of surfaces
• Enables a person to draw a contour map on the teeth and tissue areas of the cast.

Surveyor Tools

• Analyzing rods
• Carbon marker
• Undercut Gauge
• Wax trimmer

Procedures of Surveying

• Placement of the casting
• Altering the cast position anteroposteriorly
• Tilting the cast laterally until equal retentive areas exist
• Eliminating areas of interference by reshaping tooth surfaces; permits more aesthetic placement
• Drawing the survey line
• Locating clasp terminals
• Blocking undesirable undercuts
• Tripoding/scoring the cast

Errors/reference points

• Errors of 0.2 mm are anticipated when a cast has three reference points

Locations of Undercuts

• Undercuts location can changed by tiliting the cast anteriorly and laterally

The Master Cast

• Selecting most suitable placement path following mouth preparations
• Measuring retentive areas; finding appropriate location for clasp terminals
• Trimming blockout parallel to placement path
• Determining factors of placement and removal including guiding planes, retentive areas, interference, and esthetics

Machining Cast Restorations

• Procedure for manipulating the cast restoration using machine tools.

Surveying Ceramic Veneer Crowns

• Procedure of surveying ceramic veneer crowns.

• Thank you