lecture 5 - surveying, rest and rest seats

Question 1

• The act of using a surveyor and is referred to as ____________.
• The process of determining the most suitable ____________ for RPD without exerting undue stress to the abutment teeth and without causing trauma to the soft tissues.
• The process of __________ for the purpose of establishing the structural design details of the RPD.
• Considered as the _________ of the RPD design.

Answer 1

surveying
path of insertion
analyzing the study cast
blueprint

Question 2

• Is a diagnostic instrument used to select the most favorable path of insertion and aid in the preparation of guiding planes.
• First introduced to the dental profession in 1918.

Answer 2

DENTAL SURVEYOR

Question 3

other term for dental surveyor

Answer 3

parallelometer

Question 4

Are complicated and expensive and their use is restricted to research and large commercial dental laboratories.

Answer 4

ELECTRONIC SURVEYORS

Question 5

 Are relatively inexpensive and easy to use.
 Every dentist learns to use a surveyor as a student in dental school and should continue to use one in practice if he or she is constructing RPD / FPD.

Answer 5

MECHANICAL SURVEYORS

Question 6

USES OF DENTAL SURVEYOR (6)

Answer 6

Ø Locating soft tissue undercuts, which can influence the extent of the denture base, the type of direct retainers and the path of insertion selected.

Ø Contouring wax patterns for fixed restorations that will be partial denture abutments.

Ø Machining parallel surfaces on cast restorations.

Ø Blocking out undesirable undercuts on master casts.

Ø Placing intracoronal retainers (precision attachments).

Ø Recording the cast position in relation to the selected path of insertion (tripoding).

Question 7

BASIC PARTS OF DENTAL SURVEYOR

Answer 7

Platform and Vertical Tool
Survey Table / Adjustable Surveying Table (Cast Holder)
Surveying Arm
Surveying Tools

Question 8

Platform and Vertical Tool (5)

Answer 8

(1) Vertical Column
(2) Horizontal Arm
(3) Vertical Spindle
(4) Tool Holder & Screw
(5) Horizontal Base

Question 9

The part of the surveyor to which a cast can be attached.

Answer 9

Survey Table / Adjustable Surveying Table (Cast Holder)

Question 10

Allows anterior, posterior and lateral tilts.

Answer 10

• Tilt Top

Question 11

 Allow the cast to stay in place.

Answer 11

• Cast Clamp & Screw

Question 12

 Allows tilting of the tilt top.

Answer 12

• Ball Pivot & Ball Retaining Ring

Question 13

• A vertical arm used to analyze the parallelism of various axial cast surfaces.
• It contains a holder so that several surveying tools may be attached & used.

Answer 13

Surveying Arm

Question 14

• These are various small recording tools attached interchangeable in a dental surveyor.
• Each tool has a specific function and usage.

Answer 14

Surveying Tools

Question 15

o A thin straight metal rod used to analyze contours & undercuts. This is the principal tool used in surveying.
o The side of analyzing rod is brought into contact with surfaces of the proposed abutment teeth to analyze their axial inclinations.

Answer 15

 Analyzing Rod

Question 16

o Rods similar to pencil leads which can be used to mark the location of height of contour on a dental cast.
o Some surveyors use a protective sheath to prevent or reduce breakage of the carbon markers.

Answer 16

 Carbon Marker

Question 17

o Metal rods with terminal ledges or lips of various widths (the most commonly used are 0.01” and 0.02”).

Answer 17

 Metal Gauges

Question 18

o A tool with a straight sharp edge, which parallels the surveying arm.
o It is used to contour waxed crowns for partial denture abutments, or to place block- out for a partial denture framework.
o It is used with a dragging or shaving motion to remove thin layers.

Answer 18

 Wax Trimmer

Question 19

Is the path along which a prosthesis is placed or removed intraorally. An RPD is usually fabricated to have a single path of insertion or path of removal from the mouth.

Answer 19

PATH OF INSERTION (REMOVAL)

Question 20

The area on a tooth occlusal to the height of contour is called the ____________. All portions of a direct retainer that are rigid or semi-rigid must be located in this area.

Answer 20

supra-bulge area

Question 21

The area gingival to the height of contour is an undercut and is called the ____________. The retentive portions of direct retainers are located in this area, since they can flex to pass over the height of contour.

Answer 21

infra-bulge area

Question 22

• equalized on all abutments.
• Clasp has different path of escapement (dashed arrow) than guiding plane (solid arrows) and therefore must flex when the denture is removed.
• This provides retention for the denture.

Answer 22

Retentive undercuts

Question 23

A path of insertion must be selected so that the prosthesis may be inserted and removed without encountering tooth or soft tissue interferences.
* Tooth interferences are usually encountered where rigid elements of the partial denture would require placement in areas of undercut. Since rigid elements do not flex, such a partial denture will not seat.

Answer 23

Interferences

Question 24

A path of insertion should be selected to provide the most esthetic placement of artificial teeth and the least amount of visible metal on the abutment teeth.
* Ensure that the retentive undercut and the height of contour are not placed too far occlusally, so that the retentive clasp and that anterior proximal plates are close to the gingival contours making these components as inconspicuous as possible.

Answer 24

Esthetics

Question 25

are used to control and limit the directions of movement of a removable partial denture as it is being inserted, removed or while it is in function.
o To do this, bracing elements or proximal plates should, whenever possible, be the initial portions of the partial denture to contact the abutments.
o In this way, the teeth are stabilized from the potential moving forces as retentive elements of direct retainers flex over the heights of contour into the retentive undercuts.

Answer 25

GUIDING PLANES

Question 26

• When marked with carbon marker, well prepared guiding planes appear as __________
• Specifically prepared for: (3)

Answer 26

wide survey lines
o Proximal plates
o Bracing arms
o Rigid portions of retentive clasps

Question 27

A rigid component of a removable partial denture which rests in a recessed preparation on the occlusal, lingual or incisal surface of a tooth to provide vertical support for the denture. Although it is a component of a direct retainer (retentive unit, clasp assembly), it is classified as a supporting element due to the nature of its function.

Answer 27

REST

Question 28

A portion of a tooth selected and prepared to receive an occlusal, incisal or lingual rest.

Answer 28

REST SEAT

Question 29

FUNCTIONS OF RESTS (6)

Answer 29

1) To direct forces along the long axis of the abutment tooth.

2) To prevent the denture base from moving cervically and impinging gingival tissue.

3) To maintain a planned clasp-tooth relationship.

4) To prevent extrusion of abutment teeth.

5) To provide positive reference seats in rebasing and/or impression procedures.

6) To serve as an indirect retainer by preventing rotation of the partial denture (Class I or II RPD’s only).

Question 30

REST SEAT FORM

Answer 30

1) OCCLUSAL REST SEAT
2) LINGUAL REST SEATS
3) INCISAL RESTS

Question 31

b) The base of the triangular shape is at the marginal ridge and should be approximately ___________ the bucco-lingual width of the tooth.

Answer 31

one third

Question 32

c) The marginal ridge must be lowered and rounded to permit a sufficient bulk of metal to prevent fracture of the rest from the minor connector (_________).

Answer 32

(1 to 1.5 mm)

Question 33

d) The floor of the rest seat should be inclined towards the _____ of the tooth, so that the angle formed by the rest and the minor connector should be ___________. This helps to direct the occlusal forces along the long axis of the tooth.

Answer 33

centre
less than 90°

Question 34

e) The floor of the rest seat should be _________________ to create a ball-and-socket type of joint. This will prevent horizontal stresses and torque on the abutment tooth.

Answer 34

concave or spoon shaped

Question 35

When occlusal rest seats are prepared next to an edentulous space the morphology follows _________ form.

When embrasure occlusal rest seats are prepared on adjacent teeth, the form is also modified. Additional tooth structure is removed in the marginal areas to provide _______________ of room for the embrasure clasps. The rest seats are flared more dramatically to the facial and the lingual line angles to provide additional space for the retentive arms and minor connector. Inadequate clearance in these areas will result in occlusal interferences with the opposing teeth and/or inadequate thickness and strength of framework. Care must be taken to ensure all line angles are smoothed.

Answer 35

conventional
at least 1.5 mm

Question 36

o The cingulum rest seat should be prepared in the bulk of the cingulum to minimize tooth reduction. The cavosurface should be ___________ to prevent orthodontic movements of the tooth.

Answer 36

less than 90°

Question 37

o If the preparation is started too low, much of the cingulum will need to be reduced, in order to obtain sufficient width for support. Enamel is thinner in this area, and preparation could result in _____________, resulting in sensitivity. If correction of the outline form or depth is required, there will be little tooth structure remaining to make such changes.

Answer 37

dentinal exposure

Question 38

• Care must be taken not to create an enamel undercut that would interfere with the placement of the denture. A medium or large diameter cylindrical fissure bur should be utilized approaching ____________ of the tooth. Approach from a horizontal direction will often result in creation of an undercut incisal to the rest seat.

Answer 38

along the long axis

Question 39

The following factors should be considered prior to the preparation of a cingulum rest seat on a natural tooth: (2)

Answer 39

a. The prominence and shape of the natural cingulum. Cingulum rest seats must be placed in sound tooth structure or restorations.

b. The inter-occlusal relationship of a maxillary tooth with the incisal edge of the opposing mandibular tooth when the former will be prepared for a cingulum rest.

Question 40

• When a cingulum is poorly developed, with insufficient bulk for preparation for a cingulum rest seat, a rest seat can be made using ____________.
• Research has demonstrated that these “bonded rest seats” can provide acceptable strength and longevity.

Answer 40

composite resin

Question 41

• Incisal rests are _________ to lingual rests both mechanically and esthetically. Normally they should not be used unless it is impossible to place a lingual rest seat or a composite bonded rest seat.

Answer 41

inferior

Question 42

• An incisal rest seat is usually placed on the ___________________ of the incisor teeth with the deepest portion towards the centre of the tooth. It is predominantly used as an auxiliary rest or an indirect retainer.
• It is usually used on the mandibular incisor where the lower lip can cover, as much as possible, the metal of the rest that shows at the incisal edge. Mechanically, a lingual rest is preferable to an incisal rest, because the lingual rest is placed nearer to the center of rotation of the tooth and therefore, will have less tendency to tip the tooth.

Answer 42

mesio- or disto- incisal angle