is very similar to that described for fixed
prostheses.
forces to supporting tissues nor interfere in
intercuspal position or in functional
movements. The occlusal form is usually
confirmative with the natural teeth.
Occasionally a reconstructive approach using
onlays is used.
significant differences:
may present significant difficulties in determining an
acceptable occlusal vertical dimension (OVD).
2) Complete denture occlusion is always a
‘reorganised’occlusion.
stability (resistance to displacement by lateral forces),
particularly of the mandibular complete denture. The
stability of complete dentures is optimised by a
balanced occlusion.
PARTIAL DENTURES:
(in respect of the occlusion) is to position the
artificial teeth so that there is even contact
and maximum intercuspation (MI) in the
intercuspal position (ICP). For more
extensive partial dentures, such as bilateral
distal extension saddle dentures, the aim
might also be to achieve a balanced occlusion.
Treatment planning for partial dentures
When replacing missing teeth, it is of evident
importance that treatment is based on a
comprehensive treatment plan. The treatment
plan must be derived from a careful history,
examination and the use of appropriate special
investigations. For the partially dentate patient,
special investigations include radiographs, tooth
vitality tests and usually articulated, surveyed
study casts. And include a detailed design of
any prosthesis.
Clinical stages
occlusal record if centric occlusion (CO) is coincident
with CR and if there are sufficient teeth to provide
stable ICP of the casts, if there are insufficient teeth,
wax occlusal rims are used. The wax may be placed
on shellac or acrylic base plates, or more commonly
on the metal framework. If the wax rims are to be
placed on the framework it is important to ensure
beforehand that the framework fits accurately and
does not interfere with the occlusion in retruded
contact position (RCP, ICP) or in lateral excursions.
.
2
Insertion – occlusal correction Minor interferences are often present, as in complete dentures, due to previous clinical or laboratory errors. The dentures must be adjusted so that the natural teeth meet in precisely the same way both with and without the Dentures in place. Often chair side adjustment by selective grinding is Sufficient. Marks produced by articulating paper must be interpreted with caution, by visual confirmation and by asking the patient for his or her perception of how the teeth contact. The patient should be asked whether the teeth contact evenly or meet on one side first. If aware of a premature contact, can the patient feel which tooth or teeth meet first. Again, this information must be used with caution.
When maxillary and mandibular dentures are being inserted, each denture must be checked and corrected separately. A final correction is done with both dentures in place. Very occasionally the occlusal errors are so large that chair side correction is not possible. In these cases, the artificial teeth causing the interferences should be ground off. Wax can be placed on the base in those regions and CR can be rerecorded. If the denture has been returned to the clinic with the casts, a new occlusal record can be taken, the casts remounted and the occlusion corrected in the laboratory. Otherwise an overall impression should be taken with the denture(s) in place. The impressions should be cast and the dentures rearticulated, reset and retried.
COMPLETE DENTURES:
occlusal considerations in complete
plays only a minor part. Further, there is
little evidence to support of tooth form,
tooth arrangement or occlusal schemes.
Patient satisfaction with dentures does not correlate closely with technical quality. For example, patients with greatly decreased vertical dimension and severely worn occlusal surfaces may have no complaint about their dentures. Indeed they may be unable to adapt to new ‘better’ dentures. Nevertheless, it is important to understand the principles of occlusion related to removable prostheses in order to try to provide optimum treatment best suited to each individual. The clinician should have a clear picture of the occlusion that he or she is trying to achieve for each patient.
Recommended occlusion for complete dentures
Recommended practice is to develop maximum
intercuspation of complete dentures to coincide with
CR at an acceptable OVD. Failure to achieve that can
lead to intolerance, usually because of instability of
the dentures or because of pain of the alveolar
mucosa as a result of uneven load distribution and
high stress concentrations.
harmonious contacts between maxillary and
mandibular teeth in all excursive movements) is
provided in order to help give occlusal stability.
Occlusal vertical dimension(OVD)
There is much evidence to show that it is possible to
increase OVD without adverse consequences, in both
the natural dentition and in complete dentures (Palla
1997).
There are limits to an individual’s ability to adapt to
opening or closing an OVD. The OVD has a great
influence on facial appearance. Complete dentures
with insufficient freeway space cause difficulties with
speech and may result in pain beneath the denture. It
can be very difficult to determine an acceptable
correct OVD once it is lost and many methods have
been developed to help establish OVD.
.
‘resting vertical dimension’). OVD is then
established 2–4 mm less than PJP. PJP is not
constant, however, and methods used to
measure it generally have poor reproducibility.
It varies with, among other things, head
posture, the instructions given to the patient to
achieve ‘rest’ and with time. It is also known
that altering an OVD will lead to the
establishment of a new PJP.
The clinician must register an OVD and pass that
information to the technician. Experienced clinicians
usually rely on a combination of methods at the
registration stage; for example, measuring PJP,
observing patient appearance at selected OVD and
measuring the OVD of previously satisfactory
dentures. Clinicians must then try to verify the
dimension at try-in stage, again by the use of a similar
combination of methods. It is usually possible to
provide a patient with new dentures with a greater
OVD than that of the previous old dentures. It is wise
to test any increase by the progressive addition of
autopolymerising acrylic to the occlusal surfaces of
the artificial teeth of the old dentures.
Artificial teeth: Artificial teeth are made from
either acrylic resin or porcelain. The quality of
acrylic teeth has improved greatly in recent
years and porcelain teeth are no longer
commonly used. Two types of posterior cusp
form are produced by manufacturers of
artificial teeth
angulations, e.g. 20°, 30° or 40° cuspal angle;
20° cuspal angle teeth are commonly used for
complete dentures.
Zero-degree teeth (flat-cusped, cuspless) – are said to be indicated for cases with flat alveolar ridges or where there is great difficulty recording CR.
Research has not provided evidence to support commonly held views on advantages and disadvantages of artificial tooth form. For example, while it is possible that selection of artificial posterior teeth, such as cusped rather than cuspless, may have a marginal effect on chewing efficiency, other factors, in particular retention and stability of the dentures, have far more effect.
Balanced occlusion
Balanced occlusion refers to occlusion with
simultaneous contacts of the occlusal surface
of all or some of the teeth on both sides of the
arch in all mandibular positions. A balanced
occlusion is developed on the articulator.
The five determinants or variables affecting occlusal contacts are known as Hanau’s quint:
1. Orientation of occlusal plane. Average-value articulators have preset distances between the condylar components and the incisal tips. The orientation of the occlusal plane is determined by the clinician when trimming the upper occlusal rim.
2. Condylar guidance. Condylar angles of average value articulators are also preset, usually at 30°.
3. Incisal guidance. Incisal guidance is commonly set arbitrarily at 10 or 15°.
4. Cuspal angle. The cuspal angles of the artificial teeth are produced by the manufacturer.
.
4
The extent to which the balanced occlusion/articulation developed on an articulator will be present in the mouth will depend on the accuracy of the centric jaw registration used to articulate the casts. It will also depend on the degree to which the settings of the articulator replicate the corresponding parameters of the patient’s jaws. Use of a semi adjustable articulator and a facebow record, and lateral and protrusive records to set condylar angles, will more accurately replicate the mouth than an average value articulator. In most cases when inserting dentures it will be necessary to adjust the occlusion, for example using articulating foil in the mouth and specific occlusal adjustment at the chairside, in order to produce a balanced occlusion.
Lingualised occlusion:
In conventional artificial tooth arrangement the lower artificial buccal cusps occlude with the fossae opposing upper teeth. The upper palatal cusps occlude with the fossae of the lower teeth. In a so-called lingualised occlusion, the lower buccal cusps are cut back so that there is only contact on the upper palatal cusps. This scheme allows the ease of obtaining a balanced occlusion comparable with the use of zero cusped teeth, together with the advantage of retaining posterior tooth cusp form and therefore a pleasing appearance.
Clinical considerations relating to occlusion:
Determining occlusal vertical dimension:
usually rely on a combination of methods at
the registration.
Recording centric jaw relation :
Centric jaw relationship is a reproducible position that is used to articulate edentulous casts. The artificial teeth are set so that maximum intercuspation occurs at this position for complete dentures. Many different methods have been described for recording CR. They may be classified as static or functional. Most methods are capable of giving accurate results but functional techniques such as ‘chew-in’ techniques are not commonly used. The most common is the use of interocclusal wax occlusal rims.
Selecting an articulator for complete denture
prosthodontics:
articulator can be used with good results.
However, in order to produce dentures with a
balanced occlusion/articulation that should
of a facebow, and lateral and protrusive
transfer records, should be considered.
Split-cast technique
processing of complete dentures, the artificial
teeth can move slightly in the moulds. A split-
cast technique is recommended to relocate
complete dentures on the articulator following
processing. This allows any minor occlusal
errors that have occurred during processing to
be corrected.
insertion stage as a result of inaccuracy of
recording CR and limitations imposed by the
articulator. Three methods are used to correct
the occlusion: selective grinding, precentric
(check)record and rerecording CR.
use of articulating foil and corrected at the
chair side. Because of the inherent instability
of the denture bases, caution must be used
when interpreting the marks made by the
paper. Some clinicians consider that any
adjustments should only be made with the use
of a precentric (check) record, as described
below.
The first objective is to ensure maximum
intercuspation occurs in CR. Two possible errors
may be present. One error occurs when the cusp–
fossa relationships are correct but one or more teeth
meet prematurely. To correct this type of error, the
opposing fossae should be deepened until there is
even bilateral contact. The other error is when there is
misalignment of cusp–fossa relationships. This is
corrected by first grinding mesial and distal slopes of
opposing teeth, until cusp–fossa realignment is
regained. The opposing fossae can then be deepened
until even contact is established.
The second objective of occlusal adjustment is
to obtain a balanced occlusion. To readily
achieve this the BULL (buccal upper, lingual
lower) rule is recommended. It is the
contacting surfaces of these cusps (the palatal
surface of the upper buccal cusps and the
buccal surfaces of the lower lingual cusps) that
are ground, rather than the cusp tips
If there is misalignment of cusp–fossa
relationships, the cusps and their opposing
embrasures should be adjusted by grinding
mesial and distal cusp slopes of opposing
teeth. The adjustment process should be
continued until balanced occlusion is achieved
Precentric (check) record more extensive
errors can be eliminated using a precentric
record. To do this, two layers of warm
softened baseplate wax are placed on the lower
premolars and molars. The patient is
instructed/guided to close into the wax (but not
to close into tooth contact) in the retruded
position. The dentures are then articulated
using this record and any errors are removed .
When the dentures are inserted, minor errors
can be readily corrected as described.
.
errors may be so large that chairside
adjustment or even a check record could not
correct the problem. In these cases, if the
appearance of the anterior teeth is satisfactory,
the posterior teeth should be ground off, wax
can be placed on the base in those regions and
CR can be rerecorded. The dentures can then
be rearticulated, teeth reset and a denture try-in
is repeated.
INTRODUCTION
• Until 1950s most RPD were designed and constructed by time honored method of “eye balling”.A prosthesis made on the basis of educated guesses.
• The turning point in the partial denture construction from guess work based on clinical experience to scientifically based procedure was the appearance of dental surveyors in 1918.
• A dental surveyor has been designed as an instrument used to determine the relative parallelism of two or more surfaces of the teeth or other parts of the arch.
• Dr.A.J.Fortunati is thought to be first person to employ a mechanical device to determine the relative parallelism of tooth surfaces.
• Boston in 1918 he demonstrated a method for charting correct clasp placement by using a parallelometer.
.
• Surveying by using parallelometer.
TERMINOLOGY:-
SURVEY:-the procedure of locating and delineating the contour and position of the abutment teeth and associated structures before designing a removable
partial denture.
SURVEYING:-An analysis and comparison of the prominence of intraoral contours associated with
the fabrication of prosthesis.
• Survey line:-a line produced on a cast by surveyor by marking at the greatest
prominence of contour in relation to the planned path of insertion.
• SURVEYOR:-A paralleling instrument used in construction prosthesis to locate and delineate the contours and relative positions of abutment teeth and associated structures.
• CLASP:-The component of clasp assembly that engages a portion of the tooth surface and either enters an undercut for retention or remains entirely above the height of contour to act as a reciprocating element.Generally,it is used to stabilize and retain a removable prosthesis.
• Cingulum rest:- A portion of a cast partial denture that contacts on natural
cingulum of tooth.
• Lingual rest seat:- The depressed prepared on the lingual surface of an
abutment to accept the metal rest of partial denture.
.
3
• Incisal rest:-A rigid extension of a partial denture that contacts the incisal rest.
• Occlusal rest:-A rigid extension of a removable partial denture that contacts the occlusal surface of a tooth or a restoration,the occlusal surface which may been prepared to relieve it.
• PARTIAL DENTURE REST:-A rigid extension of a fixed or removable partial denture that prevents movement toward the mucosa and transmits functional forces to the teeth.
• RETAINER:-Any type of device used for stabilization or retention of a prosthesis.
• DIRECT RETAINER:-That component of removable partial denture used to retain and prevent dislodgement,consisting of clasp assembly or precision attachment.
• INDIRECT RETAINER:-The component of RPD that assists the direct retainers in preventing displacement of distal extension denture base by functioning through lever action on the opposite side of the fulcrum line when the denture base moves away from the tissues in pure rotation around the fulcrum line.
• GUIDING-PLANES:-Vertically parallel surfaces on abutment teeth oriented so as to contribute to the direction of path of placement and removal of partial denture.
• INTERNAL REST:-A pre-fabricated,rigid metallic extension in a fixed or removable partial denture that fits intimately into the box type rest seat or keyway portion of a precision attachment in a cast
restoration.
• INTERNAL ATTACHMENT:-An inter locking device,one component of which is fixed to an abutment or abutments, and the other is
integrated into a removable prosthesis to stabilize and/or retain it.
• BLOCK-OUT:-1.Elimination of undesirable under cuts on the cast.
• 2.The process of applying wax or another similar temporary substance to undercut portions of cast
.
4
• All rigid components of the partial denture must be kept occlusal it.
• Normally only the terminal third of the retentive clasp is placed gingival to the survey line.
• The survey line also helps locate areas of undesirable tooth undercuts that must be avoided or eliminated by contouring or placing restoration on the teeth.
• HEIGHT OF CONTOUR
• The term first used by KENNEDY.
• It represents the greatest bulge of diameter of a crown when viewed from a specific angle or changes as the vertical position of the tooth changed.
• Tipping or tilting the cast will cause the height of contour to move accordingly.
• DE VAN 1935 used some clarifying terms to describe retention.
• He referred to the surface of a tooth that is occlusal to the height of contour as
SUPRA BULGE and surface inclining cervically as INFRA BULGE.
• A survey line is a line drawn round the greatest contour of a tooth in relation to the common path of placement or removal (DAVID M WATT)
• A survey line is indicated those parts of teeth that can be used to used for retention ,those parts of the teeth on the occlusal side of the line can not be used.
BLATTERFEIN’S CLASSIFICATION OF BUCCAL &LINGUAL SURVEY LINES.
• NEAR ZONE & FAR ZONE:-
• If the buccal and lingual tooth surfaces are divided into two halves by vertical line through long axis, the near zone is that half which lies nearer to the saddle and far zone is more remote from the saddle.
• DIAGONAL SURVEY LINE:-
• Lies nearer the occlusal surface than the gingival margin in the near zone of the tooth, but opposite condition exists in the far zone.
• Commonly found in buccal surfaces of canines and premolars,
.
• MEDIUM SURVEY LINE:-
• This appears on the buccal or lingual surface of the tooth, approximately equidistance from the occlusal surface and gingival margin in the near zone and slightly nearer the gingival margin in the far zone.
• This indicates the use of occlusally approaching clasp.
HIGH SURVRY LINE & LOW SURVEY LINE
• High survey line:-appears much nearer to the occlusal than gingival of the tooth in both near and far zone.
• It may arise as a result of abnormal tooth form where occlusal surface has a considerable longer perimeter than
cemento-enamel junction.
It frequently found on the buccal surfaces of the uppers.
• LOW SURVEY LINE:-frequently occurs as a result of marked inclination of the tooth, when it is associated with the high survey line of the opposite side.
• A tooth surface with the low survey line cannot bear retentive clasp arm.
SURVEYING BY PARALLALOMETERS.
PARTS OF SURVEYORS
• 2.Vertical arm:-supports the super structure.
• Horizontal arm:-from which the surveying tools suspends.
• Table to which the cast is attached.
• Base on which the table swivels.
• Paralleling tool or guideline marker.
• Mandrel for holding special tools.
.
• TOOLS OF SURVEYOR:-
• Analyzing rod→metal rod with parallel sides.Used to analyze the cast to establish the path of insertion.
• Undercut gauges→available in three colors.Used to measure the undercut on the cast.
silver color:-0.01 inch or 0.25mm undercut.
gold color-0.02 inch or 0.50 mm undercut.
black color-0.03inch or 0.75 mm undercut.
• CARBON MARKER-used to scribe the line on the cast.
• Wax knife→used in the late stages of RPD
.
PURPOSES\USES OF SURVEYORS
SURVEYING THE DIAGNOSTIC CAST
1.To determine the most desirable path of placement that will eliminate or minimize interference to placement and removal.
• 2.To identify proximal tooth surfaces that are or need to be made parallel so that they act as guiding planes during placement and removal.
• 3.To determine whether tooth and bony areas of interference will need to be eliminated surgically or by selecting a different path of placement.
• 4.To locate and measure areas of the teeth that may be used for the retention.
• 5.To determine the most suitable path of placement that will permit locating retainers and artificial tooth to the best esthetic advantage.
• 6.To permit an accurate charting of the mouth preparations to be made.
• 7.To delineate the height of contour on abutment teeth.
• 8.To record cast position in relation to the selected path of placement for future reference.
• 9.Contouring the wax patterns.
• 11.Placing intra coronal retainers.
• 14.Surveying and blocking out the master cast.
STEP BY STEP PROCEDURE.
COLOR CODING.
• A color coding system for the various parts of the removable partial denture as well as for other items of information that should be included on the diagnostic casts helps prevent confusion on the part of a dental laboratory technician or any one trying to understand the design being proposed.
• There is not at present a universally accepted color coding system. As result, any system agreed to understood by laboratory and submitting dentist is considered acceptable.
• Brown crayon pencil→ out line the metallic portion.
• Blue crayon pencil→ out line the acrylic portion of the denture base.
• Red crayon pencil→ to indicate areas on the teeth that will be prepared.
• Solid red→ rests and rest seats.
.
STEP BY STEP PROCEDURE. • Examine the occluded diagnostic casts.
• Indicate the proposed rest areas by short vertical lines on the cast below the tooth
with black pencil.
• Indicate by outlining in red any cuspal relief that will be needed to provide
adequate occlusal clearance for rest spaces.
• Examine the lingual aspect of the occluded casts for adequate space for
cingulum rests, indirect retainers. Use black pencil for marking.
.
• Rein forced acrylic pontic→ RAP.
• Place these symbols on the soft tissue portion of the cast, adjacent to the edentulous area.
• 3.Place the cast on the cast holder at horizontal tilt. Examine the teeth to be clapsed for favorable retentive undercuts as well as the shape and contour of the proposed abutment teeth.
If the shape and contour of these teeth necessitate recontouring indicate the location and extent of proposed alteration with red crayon pencil.
Determine the most favorable tilt of the cast that will permit convent and proper placement of clasps,minor connectors anterior teeth, and denture base areas.
CAST TILTING.
• Tilting is changing the position of the cast, which thus changes the long axis of each
tooth on the cast relative to the horizontal plane.
• Change in the tilt then changes the position of survey line and location
and extent of the undercut.
.
11
• Tilting is used to obtain the most favorable path of insertion.
• Tilting is used to increase the desirable undercuts and to decrease undesirable undercuts.
• Through tilting, it is possible to increase the undercuts on side of the tooth while
decrease them on other side of the tooth.
• It is important to remember that when tilting one must examine effect of tilt to establish a more desirable undercuts on other teeth involved in the design.
• Tilting can also used to distribute available undercuts to
produce more uniform retention through out the available abutment.
BASIC CAST TILTS.
• The basic position or tilt of the cast on surveyor should be the horizontal tilt.
• In the horizontal tilt,occlusal surfaces of the teeth at or near parallel to the
horizontal plane.
• In the anterior tilt, the anterior teeth are tilted downwards.
• The anterior tilt increase the mesial undercut on teeth.
• In the posterior tilt,the portion of the cast tilted downwards.
• The posterior tilt will increase the distal undercuts, and decrease the mesial
undercuts.
• In the right lateral tilt right portion of the cast tilted downwards.
• The right lateral tilt increase undercuts on buccal surfaces of right side.
• Buccal under cuts are reduced on left side.
.
13
• In the left lateral tilt the left portion of the cast tilted downwards.
• Left lateral tilt will increase undercuts on buccal surface of left and will decrease
undercuts on buccal surfaces of right.
DETEERMINATION OF PATH OF INSERTION
• The tilt of the cast on the surveyor is contemplated to determine at what angle the partial denture will seat over the remaining teeth and any other obstructions that may present.
• This angle that the prosthesis takes as it goes to place is referred to as the PATH OF INSERTION.
• Any exaggerated tilt may be avoided because a patient would be unable to open the mouth sufficiently to accommodate this tilt.
• Numerous factors inhibiting or influencing the seating of restoration are considered.
• The path of insertion will always be parallel to the vertical arm of the surveyor and determined by the tilt of the cast on the surveying table.
• The path of insertion is referred to most often as if it were a single entity.
• Most influential factor as to whether a partial denture will have one or most paths of insertion is whether edentulous space is tooth bounded or distal extension type
.
14
• The minor connector is normally the only portion of the prosthesis that contacts the guiding planes on the teeth;it should be in continual contact with the guiding planes through out process of seating and removing the partial denture.
• The body and the shoulders of the clasp may exert some influence on the path of insertion
• Path of insertion is straight downwards.
• Path of insertion is upward and backwards.
• Path of insertion is upward and forward.
FACTORS INFLUENCING THE PATH
OF INSERTION.
• The following four factors must be considered before path of insertion is selected:
• 1.Retentive undercuts.
• RETENTIVE UNDERCUTS:
• The first unchangeable rule to remember when surveying diagnostic cast for removable partial denture is that retentive undercuts must be present on abutment teeth at horizontal tilt.
• The surveying procedure is always started with the cast to be analyzed positioned in the cast holder so that the occlusal surfaces of the remaining teeth are parallel to the surveying table or base of the surveyor.
• With the analyzing rod attached to the vertical arm,each abutment tooth is examined for the presence of retentive undercuts.
• The occlusal surfaces of the teeth must be viewed
first in the horizontal plane because dislodging forces applied to the partial denture are always perpendicular to the occlusal plane.
• Resistance to this dislodging force must be present when the cast is at a horizontal position.
• If retentive undercuts are not present they must be created.The obvious method is by the use of full crown usually a full crown or porcelain bonded to metal.
• If either of these these types of crowns are planned, it must be placed on the surveyor as it is being formed and contoured to satisfy the requirement of partial denture.
• Enamel surfaces contoured in limited circumstances to provide or improve retentive undercuts.
• Ideally proposed abutment teeth should have 0.010 inch undercut at the most desirable location,either the distobuccal or mesiobuccal line angle and in the gingival third of clinical crown of the tooth.
• Once retentive undercuts have been found at the horizontal tilt,the tilt may be changed to alter the amount of undercut on any given tooth.
• It must be remembered changing the tilt to alter the amount of undercut on one tooth will affect the undercuts on the remaining teeth.
• The tilt is given because the retentive and reciprocal arms are placed gingival or occlusal third of the abutment, which in turn helps in the esthetic result and also helps in reducing the torquing or rotational forces.
INTERFERENCES
• INTERFERENCES IN MANDIBLE:
• Tissues lingual to the remaining teeth that will be crossed by the major connector during insertion.
• One of the greatest errors in planning is attempting to position the major connector to avoid a lingual torus especially if a lingual bar is planned as the major connector.
• Relief or nonrigid connector is the alternative planning for the framework.But the thickness of the bar is compromised and damage to the remaining teeth if nonrigid connector is used.
• Another frequent problem commonly seen is lingually inclined teeth.
• If the lingually inclined teeth are bilateral,the space available for the major connector is reduced.This influences the tongue space.
• One answer to this problem would be to plan a labial bar major connector in place of lingual bar.
• The bulk of the labial bar causes an comfortable and unattractive plumping of the lower lip.
• Another answer to this problem is contouring the lingual surfaces or placing the restorations.
• INTERFERENCES IN THE MAXILLA:
• One of the major sources of interferences in maxilla is torus palatinus.
• Torus interferences with the placement of major connector.
• Usually the design of major must be changed to avoid the torus;if not possible surgical intervention must be accomplished.
• Bony exostoses or undercuts buccal to the posterior edentulous ridge are encountered frequently.
• Surgical procedures are followed for those undercuts.
• Buccally or facially tipped teeth are also source of interferences.
• If these buccally tilted teeth are present on one side of the arch tilting the surveying table away from the teeth may lower the height of contour sufficiently to permit the clasp to be located in a nearly ideal position.
• If these inclined teeth are present both sides of arch,changing the tilt of the cast will have no helpful effect.
• If the tipping is not severe,contour the enamel surface or full crown restoration is given in case of severe tipping.
ESTHETICS
• To obtain optimum esthetics,
• The metal,usually in the form of clasp arms, must be concealed as as possible without compromising necessary support and stability of the prosthesis.
• The artificial teeth must be placed in the most natural position possible.
• Avoiding unnecessary display of the metal,the tilt of the survey table should be such that the survey line on teeth that are visible be as close to the gingival margin.
• The ideal position of the clasp for the retentive purpose is gingival third of the tooth.
• When lost anterior teeth are not replaced immediately, the space remaining is frequently less than the space occupied by the missing because of mesial drifting of remaining teeth.
• To counter this esthetic shortcoming,the use of dental surveyor is necessary.
• When determining the final tilt of the cast, the space of missing anterior teeth must be given high priority
• Tooth bounded partial denture always determines the path of insertion.This means that the surveyor must be used to determine the whether tooth has to contoured, or disking in the proximal surfaces
has to be done to restore the mesiodistal width of the missing teeth.
• The choice is the placement of the full crown restorations.
• The surveyor is necessary for the determining the amount of recontouring that will be needed reduce these undesirable undercuts and to reestablish the space required for optimum results.
GUIDING PLANES
• Guiding planes are formed from the proximal tooth surfaces of the teeth and are contacted by the minor connectors or other rigid components of the partial denture.
• These planes guide the prosthesis for removal and placement.
.
18
• They also help to protect the weakened teeth from destructive forces.
• The surveyor is used to locate the potential surfaces of the teeth that can be converted to guiding guiding planes by selective grinding.
• If the teeth for which guiding planes are planned are receive cast restoration, the wax patterns should be shaped by the surveyor with their surfaces parallel to the path of insertion.
• Once tilt has been selected for given removable partial denture design, this tilt should be preserved, so that it can be reestablished accurately to the surveying table.this procedure is termed TRIPOIDING.
• RECORDING THE RELATION OF CAST TO SURVEYOR.
• This helps in returning the cast to the surveyor for future reference.
• The need for returning is any wax patterns, trimming, block out on master cast or locating clasp arms in under cut areas.
• FOLLOWING METHODS ARE USED:-
• 1.One method to place 3 widely divergent dots on the tissue surface of the cast with the tip of the carbon marker, having the vertical of the surveyor in a locked position.
• Preferably these dots should not be placed on the areas of the cast involved in frame work designing.
• Then the dots should be encircled with a colored pencil for easy identification.
• On returning the cast the cast to the surveyor, it may be tilted until the tip of the surveyor blade on diagnostic stylus again contacts the 3 dots in the same place.
• This method is tripoiding.
19
• Second method is to score two sides and dorsal aspect of the base of the cast with a sharp instrument held against the surveyor blade.
• By tilting the cast until all three lines are again parallel to the surveyor blade, the original position can be reestablished.
• Fortunately the scratch lines will be reproduced in duplication, there by permitting any duplicate cast to be related to the surveyor in a similar manner,
• The third method of locating cast is using thin retentive pins.
• The pins are placed in the desirable place to re-orient the cast in the surveyor.
• 5.Place the carbon marker in the vertical arm of the surveyor and scribe the survey
line on teeth that will be contacted the partial denture.
• 6.With red pencil draw in the extent of rest areas to be prepared in the
mouth
• 7.Out line the exact positioning of the denture base area. Blue pencil indicates
acrylic base; Brown pencil indicates metal denture base
.
20
• 8.With brown pencil outline the frame work design to harmonize and join the major connector, rest seats, indirect retainers and minor connectors.
• 9.Replace the carbon marker with appropriate under cut gauge
• 10.With the brown pencil draw the clasp arm to the actual shape, size, and
location desired.
SURVEYING THE MASTER CAST
• The master cast for a removable partial denture is made following the completion of mouth preparation that was indicated from design drawn on the diagnostic cast.
• Mouth preparation may have included the placement of crowns or other restorations on abutment teeth,the development of the guiding planes,contouring the wax enamel surfaces, and the placement of the rest seat preparations.
• Before the master cast is sent to the laboratory for construction of removable partial denture frame work, it must be surveyed to determine whether he mouth preparation accomplished all it as supposed to.
• With the master cast mounted on the surveying table at the same tilt at which the diagnostic cast was designed.
.
CONTOURING THE WAX PATTRENS
• The surveyor blade is used as a wax carver during this phase.
• The proposed path of placement may be maintained throughout the preparation of cast restorations for abutment teeth.
• Guiding planes on all proximal surfaces of wax patterns adjacent to the edentulous areas should be made parallel.
• The surfaces of restoration on which reciprocal and stabilizing components will be placed should be contoured to permit their location well below occlusal surfaces and on non retentive areas.
• Those surfaces of restorations that are to provide retention for the clasp arms should be contoured so that retentive clasps may be placed in the cervical third of the crown and to the best esthetic advantage.
.
CONTOURING CROWNS AND CAST RESTORATIONS
• The working cast with restorations place in the dies placed on the surveying table.
• A hand piece holder is attached to the vertical arm of the surveyor.
• The hand piece will be parallel to the selected path of insertion and guiding planes can be refined by moving surveying table so that the mounted stone contacts the guiding plane of the crown restoration.
• A final check also made with analyzing rod to determine the height of contour and retentive undercuts remain as planned
PLACING INTERNAL ATTACHMENTS AND RESTS
• The surveyor is used to position the intra coronal retainers or internal attachments, in the wax crown pattern on abutment teeth as the patterns are being formed.absolute parallelism among all the
attachment is essential.
• Internal rests,exaggerated occlusal rest with vertical walls and flat flours,can be created by using surveyor as a form of drill press.
.
24
• With appropriate burs in the hand piece,the internal rests can be machined in the wax patterns for crowns on the abutment teeth.
• After the crowns are cast same hand piece and burs are used to refine the rests.
IMPORTANT COSIDERATIONS IN USE OF DENTAL SURVEYOR
• The ultimate goal in the partial denture service is that it has to go to the place smoothly over the teeth and soft tissue.
• It has to function as it was planned.
• And it has to remain in the place by resisting the dislodging forces.
OPTICAL SURVEYING
• SURVEYING WITH LIGHT BEAMS:-
• Parallel light beams are produced by light bulbs with small,dense filaments and condenser lenses contained in a box.
• The light beams are made parallel with vertical rod of conventional surveyor by fixing the box firmly to an iron bar.
• The cast is placed on the movable table and surveyed in a dark room using parallel light beams.
• The survey line is the border of light bright and dark zones-the line where the light beams are tangent to the cast and create a shadow.
• The geometric location of a conventional lead marked survey line and the one created by the light beams are in same location.
• By tilting the table to establish various paths of insertion,undercuts and survey lines may be inspected without drawing on the cast.
.
• ADVANTAGES OF SURVEYING WITH LIGHT BEAMS:-
• One reason preferring optical surveying is that changes of survey lines and undercuts can be easily inspected for different positions of the cast.
• In addition slight undercuts are may not be determined by the lead marker can be observed with optical surveying.
• Many light beams provide an advantage over one lead marker.
• Optical surveying requires a dark room, and light beams reflecting from cast can create problem in illumination.
• Using colored artificial stone for the casts or covering reflecting areas with black paper may remedy undesirable refection.
RECENT ADVACES IN THE SURVEYORS.
.
27
SUMMARY.
• Proper placement and contour of the components of design can be achieved only through an adequate survey and well planned mouth preparation.
• The components of RPD must be selected to control stress to the abutment teeth and tissues caused forces of occlusion and movements of distal extension bases.