SurveyingSurveying

Ang Kok TeongAng Kok Teong

Outline:Outline:

IntroductionIntroductionObjectives of surveyingObjectives of surveyingInstrument and tools of surveyingInstrument and tools of surveyingGuide surface; path of insertion and path Guide surface; path of insertion and path of displacementof displacementProcedures in surveyingProcedures in surveyingSummarySummary

IntroductionIntroduction

IntroductionIntroductionWhat is surveying?What is surveying? -Marking the line indicating the maximum -Marking the line indicating the maximum

bulbosity of the teeth in the plane of the bulbosity of the teeth in the plane of the path of withdrawal.path of withdrawal.

How?How? -By moving vertical marking edge, such as -By moving vertical marking edge, such as

graphite rod, in contact with the maximum graphite rod, in contact with the maximum bulbosity of the crown of the tooth so that bulbosity of the crown of the tooth so that the side of graphite draw a line around the side of graphite draw a line around circumference of crown. circumference of crown.

Objectives of Objectives of surveyingsurveying

Objectives of surveyingObjectives of surveying

Establish path of insertionDefine those undercuts which may be used to retain the dentureDefine those undercut which require blocking out prior to finish

Instrument and tools Instrument and tools used in surveyingused in surveying

Instrument: SurveyorInstrument: SurveyorMany difference instrument available, but Many difference instrument available, but work on principle of vertical rod or markerwork on principle of vertical rod or markerMost widely used: Ney surveyorMost widely used: Ney surveyorComponents: Components:

1)1) Platform Platform2)2) Vertical armVertical arm3)3) Horizontal armHorizontal arm4)4) TableTable5)5) BaseBase6)6) Paralleling tool or guideline markerParalleling tool or guideline marker7)7) Mandrel Mandrel

Horizontal arm

Vertical column

Tool: Analyzing rod

Surveying arm

Mandrel

Surveying table

Surveying platform

Tools used in surveyorTools used in surveyor

A.A. Analyzing rodAnalyzing rodB.B. Carbon/graphite markerCarbon/graphite markerC.C. Undercut gaugeUndercut gaugeD.D. Chisels or trimmersChisels or trimmers

Functions of the surveying toolFunctions of the surveying toolA)A) Analyzing rod-Analyzing rod- to identify undercut areas and to identify undercut areas and

to determine the parallelism of surfaces to determine the parallelism of surfaces without marking the cast. without marking the cast.

B) Graphite marker-B) Graphite marker- identify and mark the identify and mark the position of maximum convexity (survey line) position of maximum convexity (survey line) separating non-undercut from undercut areas. Tip separating non-undercut from undercut areas. Tip of the marker should be level with the gingival of the marker should be level with the gingival margin.margin.

C) Undercut Gauge-C) Undercut Gauge- to measure the extent of to measure the extent of horizontal undercut and are available in the horizontal undercut and are available in the following sizes: 0.25 mm, 0.50 mm and 0.75 following sizes: 0.25 mm, 0.50 mm and 0.75 mm. mm.

D) Trimming knife-D) Trimming knife- to trim excessto trim excess wax added to wax added to those unwanted undercut areas. those unwanted undercut areas.

Guide surface, Guide surface, path of insertion & path of insertion & path of withdrawalpath of withdrawal

Guide surfacesGuide surfaces

Two or more parallel axial surfaces on Two or more parallel axial surfaces on abutment teeth which can be used to limit abutment teeth which can be used to limit the path of insertion and improve the the path of insertion and improve the stability of a removable prosthesis. Guide stability of a removable prosthesis. Guide surfaces may occur naturally on teeth but surfaces may occur naturally on teeth but more commonly need to be preparedmore commonly need to be prepared

Path of insertionPath of insertion

The path followed by the denture from its The path followed by the denture from its first contact with the teeth until it is fully first contact with the teeth until it is fully seated. This path coincides with the path seated. This path coincides with the path of withdrawal and may or may not coincide of withdrawal and may or may not coincide with the path of displacement. There may with the path of displacement. There may be a single path or multiple paths of be a single path or multiple paths of insertion.insertion.

Single path of insertion through guide surfaces

Two distinct paths of insertion in sectional/ two-part denture

Rotational path of insertion

Multiple paths of insertion when:

point contacts between the saddle of the point contacts between the saddle of the denture and the abutment teeth are denture and the abutment teeth are employed in the 'open' design of saddleemployed in the 'open' design of saddle

guide surfaces are not utilized, for guide surfaces are not utilized, for example where the abutment teethexample where the abutment teethare divergent.are divergent.

Path of displacementPath of displacement

This is the direction in which the denture This is the direction in which the denture tends to be displaced in function. The path tends to be displaced in function. The path is variable but is assumed for the purpose is variable but is assumed for the purpose of design to be at right angles to the of design to be at right angles to the occlusal plane.occlusal plane.

Surveying Surveying proceduresprocedures

Surveying proceduresSurveying procedures

1)1) Preliminary visual assessment Preliminary visual assessment 2)2) Initial surveyInitial survey3)3) Analysis- appearance, interference & Analysis- appearance, interference & retention retention 4)4) Final survey Final survey

1) Preliminary visual assessment1) Preliminary visual assessment'eyeballing' the cast'eyeballing' the castuseful preliminary to the surveying procedureuseful preliminary to the surveying procedurecast is held in the hand and inspected from cast is held in the hand and inspected from aboveabovegeneral form and arrangement of the teeth and general form and arrangement of the teeth and ridge can be observed, any obvious problems ridge can be observed, any obvious problems are notedare notedto assess whether or not a tilted survey should to assess whether or not a tilted survey should be employed.be employed.

2) Initial survey2) Initial surveycast is positioned horizontal parallel to the occlusal planeteeth and ridges then surveyed to identify undercut areas that might be utilized to provide retention in relation to the most likely path of displacementposition of the survey lines and the variations in the horizontal extent of undercut associated with them should be noted.assessment can then be made as to whether the horizontal extent of undercut is sufficient for retention purposes.

3) Analysis3) Analysis

RPD can be designed on a cast which has been surveyed with the occlusal plane horizontal (so that the path of insertion same as the path of displacement).However, there are occasions when tilting of the cast is indicated so that the paths of insertion and displacement differ.

Before deciding if the cast should be tilted for the final survey, graphite marker in the surveyor is changed for an analyzing rod so that various positions of the cast can be examined without marking the teeth.

The aspects which might necessitate a final The aspects which might necessitate a final survey with the cast tilted: survey with the cast tilted:

I.I. Appearance. Appearance. II.II. Interference. Interference. III.III. Retention.Retention.

i) Appearancei) AppearanceIf a maxillary cast containing an anterior edentulous If a maxillary cast containing an anterior edentulous area is surveyed with the horizontal occlusal plane, area is surveyed with the horizontal occlusal plane, undercuts will always present on the mesial surface undercuts will always present on the mesial surface of abutment teeth.of abutment teeth.Therefore, is the RPD is constructed with this Therefore, is the RPD is constructed with this vertical path of insertion, there will be an unsightly vertical path of insertion, there will be an unsightly gap between the denture saddle and the abutment gap between the denture saddle and the abutment teeth gingival to the contact point.teeth gingival to the contact point.

This unsightly gap can be avoided by tilting the cast a posteriorly (heels down) so that the analyzing rod is parallel with the mesiolabial surface of the abutment tooth.

With this posterior path of insertion the saddle can be made to contact the abutment tooth over the whole of the mesiolabial surface and a much esthetic appearance results.

ii) Inteferenceii) InteferenceSometimes an undercut tooth or ridge would Sometimes an undercut tooth or ridge would obstruct the insertion and correct placement of a obstruct the insertion and correct placement of a rigid part of the denture. rigid part of the denture. For example, if a bony undercut is present For example, if a bony undercut is present labially, insertion of a flanged denture along a labially, insertion of a flanged denture along a path at right angles to the occlusal plane will path at right angles to the occlusal plane will only be possible if the flange stands away from only be possible if the flange stands away from the mucosa or is finished short of the undercut the mucosa or is finished short of the undercut area. This can result in poor retention as well as area. This can result in poor retention as well as a poor appearancea poor appearanceBy tilting the cast, a path of insertion may be By tilting the cast, a path of insertion may be found which avoids this interference. found which avoids this interference.

-By giving the cast an anterior (heels up) tilt, a path of insertion that avoids this interference is revealed.

-However, if interference from a tooth cannot be avoided by selecting an appropriate path of insertion, consideration should be given to eliminate the interference by tooth preparation.

iii) Retentioniii) Retention-To obtain retention, undercuts must be present on -To obtain retention, undercuts must be present on teeth relative to the horizontal survey. teeth relative to the horizontal survey. If none is exists, changing the tilt of the cast will If none is exists, changing the tilt of the cast will never produce any retentive undercuts.never produce any retentive undercuts.

-Tilting the cast may enhance the retention by so -Tilting the cast may enhance the retention by so altering the path of insertionaltering the path of insertion-A rigid part of the denture can enter an area of the -A rigid part of the denture can enter an area of the tooth surface or an area of the ridge which is tooth surface or an area of the ridge which is undercut relative to the path of displacement, undercut relative to the path of displacement, hence improve the retention of the RPD.hence improve the retention of the RPD.

4) Final survey4) Final survey

If it is decided that the cast is to be tilted, the analysing rod is exchanged for a marker different in color from that used in the first survey, and the final survey is carried out. It will then usually be found that the teeth to be clasped have two separate survey lines which cross each other. In order to obtain optimum retention it is necessary to understand how to position the clasps correctly in relation to the two survey lines.

The aims for optimum retention should be to provide:1)Resistance along the path of

displacement. (guide surfaces/clasps)

2)Resistance along the path of withdrawal. (clasps only)

When guide surfaces are used to provide When guide surfaces are used to provide resistance to displacement of the denture resistance to displacement of the denture in an occlusal direction, the retentive in an occlusal direction, the retentive portion of the clasp needs only to resist portion of the clasp needs only to resist movement along the path of withdrawal movement along the path of withdrawal and therefore can be positioned solely with and therefore can be positioned solely with reference to the reference to the redred survey line. survey line.

Green line is the survey line marked on the horizontal plane Red line is the survey line marked on the tilted plane

When the denture does not contact guide When the denture does not contact guide surfaces on the clasped tooth the clasp surfaces on the clasped tooth the clasp will have to resist movement of the will have to resist movement of the denture along both the path of withdrawal denture along both the path of withdrawal and the path of displacement.and the path of displacement.

The clasp will thus need to be positioned The clasp will thus need to be positioned in the correct depth of undercut relative to in the correct depth of undercut relative to both survey lines. both survey lines.

The degree of tilt must be recorded so it The degree of tilt must be recorded so it can be reproduced in the laboratory.can be reproduced in the laboratory.There are 2 methods:There are 2 methods:a) Tripod method- the vertical arm of the surveyor is a) Tripod method- the vertical arm of the surveyor is

locked at a height that allows the tip of the marker to locked at a height that allows the tip of the marker to contact the palatal surface of the ridge in the molar contact the palatal surface of the ridge in the molar and incisal regions. Three points are marked with and incisal regions. Three points are marked with the graphite marker, one on each side posteriorly the graphite marker, one on each side posteriorly and one anteriorly. The points will then be ringed and one anteriorly. The points will then be ringed with a pencil so that they are clearly visible.with a pencil so that they are clearly visible.

b) The analysing rod is placed against one side of the b) The analysing rod is placed against one side of the base of the cast and a line drawn on the cast base of the cast and a line drawn on the cast parallel to the rod. This is repeated on the other side parallel to the rod. This is repeated on the other side and at the back of the cast so that there are three and at the back of the cast so that there are three widely spaced lines parallel to the path of insertion.widely spaced lines parallel to the path of insertion.

SummarySummary

SummarySummarySurveying is undertaken to obtain information so asSurveying is undertaken to obtain information so asto decide:to decide:1) The choice of the path of insertion, which is 1) The choice of the path of insertion, which is

influenced by: influenced by: -the need to use guiding surfaces to achieve a -the need to use guiding surfaces to achieve a

pleasing appearance and retention.pleasing appearance and retention. -the need to avoid interference by the teeth or ridges -the need to avoid interference by the teeth or ridges

with correct positioning of denture components. with correct positioning of denture components. (2) The design, material and position of clasps.(2) The design, material and position of clasps. -according to the horizontal extent of undercut on -according to the horizontal extent of undercut on

abutment teeth and the identification of sites on the abutment teeth and the identification of sites on the teeth to provide reciprocation either from guiding teeth to provide reciprocation either from guiding surfaces or from cross-arch reciprocationsurfaces or from cross-arch reciprocation

ReferencesReferences

• British dental journal, 2000British dental journal, 2000• Oxford Handbook of dentistry, 3Oxford Handbook of dentistry, 3rdrd edition edition

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