dental surveyor

Clinical Application of Dental Surveyor and Surveying Procedure

Introduction

  • The practice of removable partial denture (RPD) design and fabrication requires an understanding of the structural details of the prosthesis.

What is Dental Surveying

  • Surveying involves the procedure of locating and delineating the contours and position of the abutment teeth and associated structures prior to RPD design.

  • It serves as a diagnostic procedure analyzing the dimensional relationships of oral hard and soft tissues.

  • Conducted alongside decisions about choosing abutments and determining the location of rests.

Aims & Objectives

  • Locate proximal tooth surfaces that can be parallel to function as guiding surfaces.

  • Measure recesses or undercuts that provide mechanical retention.

  • Identify potential hard or soft tissue interferences.

  • Determine a path of insertion/dislodgement aligned with aesthetic requirements.

  • Delineate the height of contour on abutment teeth, avoiding undercut areas that need to be reduced or preserved.

  • Assist in restoring procedures planning.

  • Document the optimal cast position for future reference (tripoding the cast).

  • Create a formal plan for RPD design and necessary mouth preparation.

Types of Surveyor

  • Electronic Surveyors:

    • Complicated and expensive.

    • Primarily used in research and large commercial dental labs.

  • Mechanical Surveyors:

    • Relatively inexpensive and user-friendly.

Historical Context

  • Dr. Fortunati is credited with the introduction of the first mechanical device to determine the relative parallelism of tooth surfaces.

  • The Ney surveyor, launched in 1923, was the first commercial surveyor, widely adopted afterward.

  • The Will’s surveyor, developed by Jelenko.

Types of Dental Surveyor

  • Original Ney Surveyor:

    • Introduced in 1923 with a palm rest on the vertical arm.

  • Currently Used Surveyor:

    • Redesigned and developed by Weinstein and Roth in 1937.

Parts of a Dental Surveyor

  1. Base

  2. Vertical Upright Column

  3. Cross Arm with Spindle Housing

  4. Vertical Spindle with Tool Holder

  5. Screw to Lock Spindle

  6. Tool Adaptor Holder

  7. Surveying Tool Holder

  8. Surveyor Table

  9. Surveying Tool

  10. Model Clamp

  11. Model Table Lock Nut

  12. Model Rotating Ball & Socket

  13. Ball Rotating Ring

  14. Tool Rack

  15. Storage Compartment

  16. Model Lock Nut

Uses of Surveyor

  • Verify parallelism of tooth preparations.

  • Survey diagnostic casts.

  • Contour wax patterns for crowns.

  • Align precision and semi-precision attachments.

  • Mark survey lines and undercuts on casts before outlining RPD frameworks.

  • Block out master casts for RPD.

Surveying Tools

  1. Analyzing Rods

    • Used to detect undercut areas without marking the cast.

  2. Carbon Marker

    • Used to mark positions of maximum convexity (Survey Line) along teeth and alveolar ridge.

  3. Undercut Gauge

    • Measures horizontal undercuts available in sizes 0.25 (0.01), 0.50 (0.02), and 0.75 (0.03).

  4. Wax Trimmer

    • Used for removing excess wax blocking unwanted undercuts.

Classification of Survey Lines (Blatterfein)

  1. High Survey Line:

    • Near the occlusal surface, often parallel to the gingival margin, typically found on lingual surfaces of lower teeth.

  2. Medium Survey Line:

    • Crosses the center of the tooth with a slight incline.

  3. Low Survey Line:

    • Close to and parallel with gingival margin, found on conically shaped teeth.

  4. Diagonal Survey Line:

    • Runs diagonally from occlusal surface to gingiva.

Ney's Classification of Survey Lines

  1. Class I:

    • Survey line diagonally across tooth surface suggesting occlusally approaching cast clasp.

  2. Class II:

    • Opposite of Class I, suggesting a gingivally approaching clasp arm.

  3. Class III:

    • Parallel to the occlusal surface just below it.

Undercut Definition and Types

  • An undercut occurs when a part of an object is narrower at the base than at its top.

  • Undercut: A dig or burrow below the height of contour, which is the most bulbous area of the tooth.

  • Types of Undercuts:

    1. Tooth Undercuts (Proximal)

    2. Soft Tissue or Bony Undercuts (Lingual side of ridge)

    3. Desirable Undercuts - for retention.

    4. Undesirable Undercuts - do not provide useful retention.

Guide planes

  • Parallel axial surfaces on abutment teeth that limit the path of insertion and enhance stability.

  • Can be naturally occurring or require preparation.

Path of Insertion

  • The trajectory a restoration or prosthesis travels from initial contact to resting position.

  • Coincides with path of withdrawal; may differ from path of displacement.

  • Types of paths:

    • Single Path

    • Multiple Paths

    • Rotational Paths

  • Influenced by retentive undercuts, interferences, esthetics, and guide planes.

Factors Affecting Path of Insertion

  • Sufficient guide surfaces may lead to a single path of insertion.

  • Multiple paths arise when guide surfaces are not utilized or with divergent abutment teeth.

  • Rotational paths can also occur in some prostheses.

Path of Removal

  • Inverse of the Path of Insertion; the method of dislodgment.

  • Typically derived at right angles to the occlusal plane.

Selection of Path of Insertion

  • Ideal to place clasp tips optimally for aesthetics.

  • Creates suitable undercuts and avoids excessive anterior tilting of the cast.

Surveying Process Steps

  1. Initial Visual Analysis (Eyeballing):

    • Basic stage of surveying, casting inspection for general forms and teeth arrangement.

  2. Initial Survey:

    • Cast placed horizontally; teeth and ridge surveyed for undercut areas using a graphite marker.

    • Judging undercut amount via the triangle of light concept.

  3. Analysis:

    • Designing RPD paths aligned with paths of insertion and removal with possible table tilting.

    • Using analyzing rods to review various tooth positions without marking.

  4. Final Survey:

    • Conducting a second survey with a different colored marker and potentially a tilted cast position.

    • Marks ensuring optimal retention based on newly observed survey lines.

Principles of Surveying

  • Changing tilting levels alters the location of undercut areas, influencing design efficacy.

  • Proper guiding planes enhance clasp efficiency and retention in expected oral forces.

Retention Considerations

  • Retention is ensured when undercuts are present relative to a horizontal survey.

  • Misconceptions regarding tilting for retention when none exists in a horizontal plane.

  • Optimum retention involves creating engagement with undercuts that enhances aesthetics and functionality.

  • Final alignment of clasps needs evaluation in the context of the converging survey lines for best results.

Tripoding the Cast

  • Essential to record tilt degree when the cast is tilted during the final survey.

  • Two recording methods:

    1. Tripod Method: Marking points on the cast, one on each side and one anteriorly while maintaining tilt.

    2. Scoring/Line Method: Drawing lines parallel to the analyzing rod to document cast orientation.

Clinical Objectives of Surveying

  1. Path of insertion and removal:

    • Achieving pleasing aesthetics via guide planes.

    • Utilizing guide planes for retention.

    • Avoiding interferences.

  2. Choice of clasp design.

  3. Materials for clasp construction.

Conclusion

  • Surveying is a critical component in planning for removable prostheses.

  • It necessitates understanding materials plus anatomical relationships of hard and soft tissue supporting the denture.

  • Restoration success heavily relies on the tooth response to functional forces directed by the partial denture, necessitating accurate surveying for a correct path of insertion and adequate retention.