Surveying

1 Dr. Mahmoud Ramadan Mahmoud [email protected]

SURVEYING The flexible retentive clasp arm is the only part of the restoration that is allowed to engage an undercut, (fig. 3.1).

Flexible clasp arm engaging tooth undercut, A : undercut area.

Undercuts An undercut is formed when the base of an object is smaller than its top. Undercuts on abutment teeth lie below the height of contour, which is the most bulbous and convex part of the tooth also called maximum bulge.

Buccal view of tooth. A: Height of tooth contour B: Undercut area.

C: Non undercut area.

A partially edentulous mouth has many undercut areas that result due to : a- Bulbous shape of the crowns of natural teeth resulting in buccal and lingual undercuts, fig. b- The inclination of the long axes of teeth in relation to a vertical line drawn from the occlusal surface, resulting in undercut on the proximal surfaces of these teeth, fig. c- The inclination of soft tissues or bone to a vertical line drawn from the occlusal surface resulting in soft tissue or bony undercuts, fig. d- Proliferation of soft tissues covering the edentulous ridge due to the rapid pattern of bone resorption.

Surveying Denture

Removable Partial

2 Dr. Mahmoud Ramadan Mahmoud [email protected]

Types of undercuts : 1) Desirable undercuts : Desirable undercuts are used for retaining the partial denture against dislodging forces usually by incorporating retentive flexible clasp arms, less frequently by the denture base engaging a tissue or bony undercut. 2) Undesirable undercuts : Undercuts other than those used for retention are considered undesirable and should be eliminated. This is done by blocking-out the undercut with wax on the master cast, by the preparation and reduction of the tooth surface in the mouth or by placing a properly contoured crown restoration on the tooth. In planning for removable partial dentures the prosthodontist should: 1- identify tooth contours, soft tissue or bony undercuts that may interfere with the placement of the denture and that should be corrected in the mouth before construction of the prosthesis. 2- analyze the shape of abutment teeth to determine the max. bulge of teeth. 3- The amount of undercut required to provide the best retentive& esthetically satisfactory partial denture. → All of this can be achieved by the aid of the dental surveyor.

The Dental Surveyor The dental surveyor is a "Paralleling instrument used to determine the survey line of teeth, identify and measure tooth undercuts and to determine the relative parallelism of the surfaces of teeth and other areas on the cast". The survey line is a "Line outlined on the cast by a surveyor marking the greatest prominence of tooth contour in relation to the planned path of insertion of a restoration". Parts of the dental surveyor : The most widely used surveyors are the Ney and Jelenko surveyors. The Ney surveyor which is commonly used in our school consists of, fig.: 1- The base: The base is a horizontal platform parallel to the bench top on which a cast holder moves. 2- Vertical upright column : The vertical upright column is attached to the base at one end. The other end supports a fixed cross arm parallel to the base. This end contains a storage compartment for storing the surveyor tools. 3- Cross arm : The cross arm of the surveyor is fixed and extends at right angles to the vertical upright column. It contains a housing and a tightening screw for holding a vertical spindle. 4- The vertical spindle : The vertical spindle moves vertically upwards and downwards at right angles to the base. It can be fixed at the desired height by a tightening screw. The lower end of the spindle contains a tool holder and a tightening screw to fix the tool in position. Surveying Denture

Removable Partial

3 Dr. Mahmoud Ramadan Mahmoud [email protected]

5- Tool rack : The tool rack is a shelf at the end of the upright column for holding th e surveyor tools during surveying. A: Base B: Vertical upright column. C: Cross arm. D: Vertical spindle. E: Tool holder. F: Surveyor tool in place. G: Lock-nut to hold tools in place. H: Screw to lock spindle I: Tool rack. J: Survey table. K: Storage compartment

6- The survey table : The survey table consists of a top and base joined by a ball and socket joint. This joint permits movement of the table top in all directions. The top holds the cast and is equipped with a clamp to lock the cast in place. The clamp is designed with two fixed lugs and a movable joint to allow for variations in the dimensions of models, fig. → The top can be tilted in any horizontal plane to help in analyzing the model in relation to the vertical plane. When a suitable tilt is reached, the table top is fixed by the table tightening screw. → The model can thus be surveyed at any tilt, fig. These tilts are : a) Zero tilt b) Anterior tilt. c) Posterior tilt. d) Right lateral tilt. e) Left lateral tilt. → Deciding the tilt of the cast mainly depends on two factors. • Path of insertion and removal of the appliance. • Path of denture displacement caused by masticatory function. N.B.: • A combination between two tilts could be used. • An anterior ti lt is sometimes preferred in distal extension bases. This increase resistance to vertical displacement by the denture base by undercuts distal to abutment teeth.

Surveying Denture

Removable Partial

4 Dr. Mahmoud Ramadan Mahmoud [email protected]

7- Surveyor tools : Five different surveyor tools are supplied with the surveyor, fig. (3.7), These are :a- Analyzing rod: This is a paralleling tool which consists of a straight shaft of rigid metal. It is used for preliminary survey of the casts. b- carbon marker: The carbon marker is used for drawing the survey line of the teeth and in marking points on the cast. c- Re-inforcing sheath : a metal apron used to protect carbon marker against breakage. d- undercut gauge: Undercut gauges are three in number, and are available in three sizes, 0.010, 0.020, 0.030 of an inch. They are used to locate and measure undercut areas on abutment teeth for the correct placement of the clasp retentive tip. The undercut gauge consists of shaft and head. The shaft touches the tooth at its maximum bulge (survey line), while the head touches the tooth at an undercut depth equal to the size of the gauge used, fig.

e- Wax trimmer : A wax trimmer is a knife used for trimming the excess wax which blocks out undesirable undercut in such away to be parallel to each other and to the pre-determined path of insertion.

Survey Line If a vertical plane like the surveyor analyzing rod comes in contact with the convex tooth surface, it will contact at the maximum convexity of the tooth. Rotating the tooth around the carbon marker placed instead of the analyzing rod, results in drawing a line denoting the height of contour of the tooth called the "Survey line". If this tooth is tilted, another line will be drawn representing the survey line in relation to the new tilt. Therefore changing the tilt of the cast results in changing the survey line on teeth, fig. Surveying Denture

Removable Partial

5 Dr. Mahmoud Ramadan Mahmoud [email protected]

Changing the tilt results in changing the survey line.

The area of the tooth above the survey line is a non undercut area, while that below, is an undercut area. The location and extent of these areas can be varied according to the anterior and posterior, also the side to side tilt of the cast. The significance of the survey line is that all rigid components of the prosthesis must be placed occlusal to this line, only the terminal retentive clasp tip is placed gingival to it.

Path of Insertion The path of insertion of the partial denture is, "The direction in w h i ch a restoration moves from the point of initial contact with the supporting teeth to the terminal resting position where the occlusal rests are seated and the denture base is in contact with the tissues". The path of removal of the partial denture is "The direction of movement of the restoration from its resting position to the last contact with the supporting teeth". It is the reverse of the path of insertion. → The path of insertion and removal of the partial denture is determined by analyzing the cast placed on the cast holder in relation to the vertical rod of the surveyor. The vertical movement of the analyzing rod represents the path of insertion. The path of insertion changes by changing the tilt of the cast in relation to the vertical spindle.

Factors Affecting Path of Insertion : The choice of the best possible path of insertion should consider the following factors : 1- Interferences : The prosthesis must be designed so that it may be inserted and removed without encountering tooth or tissue interferences. Such interferences resulting from inclined teeth, tissue or ridge undercuts tori or bony exostosis, could be avoided by either : • Changing the path of insertion. • Contouring the tooth surface. • Surgery to remove interfering structures as bony exostosis, tori or undercuts. 2- Retentive undercuts : The tilt given to the cast in relation to the analyzing rod should result in undercuts on the abutment teeth. These undercuts should be equal in depth and should also permit the location of clasp tips in the gingival third of the tooth. 3- Guiding planes ': Guiding planes are flat axial surfaces in an occluso-gingival direction on the proximal or Surveying Denture

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6 Dr. Mahmoud Ramadan Mahmoud [email protected]

lingual surfaces of teeth. They are made parallel to the path of insertion help in guiding to the prosthesis during insertion& removal. Fig.

• The function of guiding planes : a- Guide the prosthesis in or out of place without exerting excessive forces against the teeth, fig. b- The frictional contact of the prosthesis against these parallel surfaces can contribute to the retention of the prosthesis. c- Guiding planes can provide bracing and stability when they are located on the axial lingual surface of the tooth. d- Decrease the amount of wax block-out.

4- Esthetics : Esthetic appearance can be considerably improved especially with anterior abutments by trying different paths of insertion. Small changes in cast inclination can be made to seat the components of the denture in less visible areas but without jeopardizing the other factors. Thus, allowing less clasp metal and less base material to be displayed. 5- Health of teeth used as abutment : For example, in tooth-bearing dentures, if the molar is weaker than the bicuspid, an anterior tilt may be advisable, in order to place the clasp on the stronger tooth. * Uses of the dental surveyor : The surveyor is used in surveying both the study and the master cast. This helps in the proper diagnosis, designing and treatment planning. The casts are surveyed to fulfill the following objectives : 1- Determining and drawing the survey line of teeth at the required tilt of the cast. 2- Locating and measuring areas of tooth undercut that may be used for retention. 3- Locating undesirable undercuts that should be avoided, eliminated or blocked out. 4- Trimming of block-out material on the master cast to conform to the path of insertion. 5- To identify proximal tooth surfaces that are or can be made parallel to act as guiding plane. Surveying Denture

Removable Partial

7 Dr. Mahmoud Ramadan Mahmoud [email protected]

6- To determine whether tooth or bony areas of interference will need to be eliminated. 7- To determine the most favorable path of appliance insertion which is free from any interference during insertion or removal without impingement of the oral mucosa. 8- Paralleling crown restorations to have them conform to the determined path of insertion. 9- Permit an accurate charting of the required mouth preparations. This may include : a) The preparation of proximal tooth surfaces to provide guiding planes. b) Reduction or disking of tooth structure to eliminate interferences. c) Modifying tooth contours to permit an acceptable location of reciprocal& retentive clasp arms. 10- Recording the position of the cast in relation to the selected path of insertion for future repositioning of the cast on the surveyor at the predetermined tilt, fig. This can be done by one of the following methods. a- Tripoding: → Tripoding is done by drawing three widely separated cross marks on the tissue side of the cast lingual or palatal to the remaining natural teeth while the tool holder is locked at a certain vertical height. → The cast can be repositioned to the same tilt by allowing the analyzing rod to touch one of the cross marks, the spindle is then locked at this vertical height and the tilt of the cast is modified until the rod touches the three cross marks. b- Scoring : → Two sides& the dorsal aspect of the base of the cast are scored with a sharp instrument held against the surveyor blade, fig. → By tilting the cast until all three lines are parallel to the surveyor blade, the original tilt can be re-established.

Selection of The Path of Insertion : → The most favorable path of insertion (PI) is that perpendicular to the occlusal plane, fig. → Survey analysis should start first with the occlusal plane parallel to the base of the surveyor (zero tilt). This path is preferred because most patients tend to seat their dentures under biting force. However, this inclination (zero tilt) may not be convenient with respect to the factors affecting selection of the path of insertion. → Thus, if undercuts are present but not efficient at the zero tilt and if displacement of the prosthesis is anticipated with the least displacing forces, another path of insertion should be decided. This is achieved either by : 1) A rotating or curved path : → In this path one section of the prosthesis is seated first and the remainder is then rotated into position. 2) Tilting the cast to, fig.: Surveying Denture

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8 Dr. Mahmoud Ramadan Mahmoud [email protected]

a- Create suitable undercuts. b- Equalize undercuts on both sides of the arch. c- Place the clasp tips in a better esthetic position. → The path of insertion may also be slightly off of the zero tilt to allow for reduction in the amount of undercut when rigid minor connectors contacting guiding planes are planned to help in providing retention. → Undercut areas should be present at both zero tilt and the new tilt. → Gross inclination of the cast to create apparent undercuts should be avoided.

The path of insertion can be determined as follows : a) The cast is placed on the surveyor table in a horizontal position (zero tilt), fig. (3.15). b) Analyze the proximal abutment tooth surfaces with the surveyor analyzing rod. Tilt the cast position anteroposteriorly if required until the proximal surfaces are in parallel relation to one another or near enough that they can be made parallel by disking. The end result should provide parallel proximal surfaces that may act as guiding planes. c) The cast position could be tilted laterally until equal retentive areas exist on the principle abutment teeth, fig. (3.16). In tilting the cast laterally, it is necessary that the table be rotated without disturbing the anteroposterior tilt previously established. d) If there is bilateral interference that may prevent the insertion and removal of rigid connector, surgery and/or disking may be unavoidable. If interference is only unilateral, change the path of insertion at the expanse of guiding planes and retention. c) If a choice between two paths of equal merit, one permits a more esthetic placement of clasp arms than the other, that path should be preferred. After selection of the proper path of insertion, the cast is secured in place until the following steps are made : 1. Drawing of the survey line : The analyzing rod is replaced with a carbon marker and the survey line is drawn on abutment teeth.

2. Location of the clasp terminals : The carbon marker is removed from the tool holder and the suitable undercut gauge is fixed in the holder. The undercut gauge is placed in contact with the tooth to be clasped with its shaft touching the tooth surface at the survey line. The head will indicate the undercut area where the clasp will terminate. A sharp pencil is used to mark this point. It is preferable that undercuts be present on both zero tilt and lateral tilt to avoid creation of apparent undercuts. Retentive terminals located in apparent undercuts will Surveying Denture

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9 Dr. Mahmoud Ramadan Mahmoud [email protected]

be displaced by occlusally displacing forces, fig- (3.17).

3. Blocking the undesirable undercuts : The undesirable undercuts especially on the proximal surfaces are filled with wax. The wax trimmer is fitted in the tool holder to trim the excess wax. 4. Tripoding or scoring the cast to preserve the established cast tilt : All these steps are performed while the master cast is still mounted on the survey table without changing the tilt.

Surveying Denture

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