Survey And Design

Parts A.A level platform B.A vertical column C.A horizontal arm – A surveying arm: capable moving in a vertical direction and contains a mandrel at its lower end. A.mandrel – Surveying tools: placed in the mandrel

Surveying tools – A analyzing rod: determine relative parallelism of surfaces – A carbon marker: mark the height of contour on surfaces – Undercut gauges: .01 .02 .03 identify the positions of desired undercuts on dental casts – A wax knife: used in blockout procedure and in the construction of surveyed restorations

4 critical factors when determine the most favorable tilt – – – –

presents of suitable undercuts elimination of hard and soft tissue interference creation of desirable esthetics the establishment of appropriate guiding planes

1. Retentive undercuts • The first, unchangeable rule: retentive undercuts must be present on the abutment teeth when horizontal tilt • surveying procedure always started with the occlusal surface s parallel to the platform of the surveyor

1. Retentive undercuts • if retentive undercuts are not present, they must be created in the mouth • 1. recontouring enamel surfaces • 2. fixed restorations(completed before RPD fabrication)

1. Retentive undercuts • each of the proposed abutments should display a .010-inch undercut at the most desirable location ( .015 undercut wrought wire) • MB line angle, DB line angle, midfacial surface; apical third of the clinical crown after existence is verified • tilt is changed so that a retentive clasp will be positioned no farther occlusally than the junction of the gingival and middle third of the tooth (esthetic,torque force)

2. Interferences - maxillary arch goal to minimize surgical procedures palatal torus - design of the major connector | surgical removal exostosis on the buccal surfaces surgical correction is relatively simple

2. Interferences - maxillary arch posterior tooth facial tipping =>height of contour move up=>lever arm longer=>more damaging facial tipping=>gingiva tissue in an undercut=>infra bulge clasp food trap just one side=> changing the tipping if not severe=> enameloplasty severe=>surveyed crown anterior ridge undercut - cast tipping | modify or eliminate denture flange

2. Interferences - mandibular arch tori surgery must be considered if prominent lingual tori posterior teeth lingual tipping most common solution: lingual surface recountouring placing restoration orthodontic movement undercuts near pear-shape pads cast tilting | adjust denture base

3.esthetics – The ideal position for a retentive clasp is in the gingival third of the clinical crown – appropriate selection, contouring, and placement of the prosthetic teeth; appropriate tooth selection requires consideration of shade, size, and contour • stock teeth should be modified to reflect the esthetic and functional characteristics of the individual

3.esthetics • one or more missing anterior teeth =>single path of insertion surveyor must be used to determine whether recontouring of the remaining natural teeth is indicated, if not possible, crown or other suitable restoration should be planned. • large undercut may be caused by the shape of the clinical crown or by tipping of the tooth toward an edentulous space. • The undercuts produce triangular spaces - esthetics problem, food trap

4. guiding plane • guiding plane are always parallel to the path of insertion and are rarely greater than 2~4mm in height • guiding planes can be prepared on most enamel surfaces • if abutments are to receive cast restorations: teeth should be prepared, and wax pattern should be shaped so their guiding surfaces are parallel to the established tilt

Path of insertion

• most RPD have 2 or more paths of insertion • the most influencing factor: whether or not edentulous spaces are tooth bounded • unmodified Kennedy Class I,II: bounded at one end =>variety of angles • Class II with modification space: if guiding plane prepared =>single path of insertion • Kennedy Class III: entirely tooth bounded;if guiding plane prepared =>single path of insertion • Kennedy Class IV:single path of insertion

Path of insertion • minor connectors are the only components that contact the guiding planes of the teeth • minor connectors remain in contact with the guiding planes throughout the insertion and removal processes

Tripoding – after ensuing the proper tilt, survey table is locked – lingual surface of the cast, mark with undercut gauge(.03); widely spaces; on areas that not likely to change from cast to cast – resulting shallow grooves; 4mm long and narrow; completed as a crosshair configuration  

Survey lines,Undercut placing survey lines with carbon marker on tooth and soft tissue •   • depth and position of the desired undercut will vary the material and clasping system to be used (.01) •

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selected abutment tooth contacts the undercut gauge

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"scrap" contact be marked with red pencil; 2mm in length

Design  

Philosophy of design – entirely tooth supported=> very straightforward a single impression may be used edentulous ridge does not offer support, can be recorded in anatomic form no noticeable rotation forces=> no indirect retainer, flexible direct retention – main concern is for tooth-tissue supported RPD(I,II,and long-span IV) 1. stress equalization 2. physiological basing 3. broad stress distribution

1. stress equalization • forces applied to a RPD are transmitted to abutments • Think: rigid connection between base and direct retainer are damaging • stress directors are essential to protect abutments • simple hinges interposed between base and clasping assemblies • minimal direct retention

1. stress equalization • used in conjunction with intracoronal attachments • can be used in Class I,II • minimizing the tipping force on abutments=> limiting bone resorption

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fragile costly constant maintenance impossible to repair

2. physiologic basing • recording the edentulous ridge in its functional form • this can be accomplished by depressing the mucosa during impression-making procedure or by relining the denture base after it has been constructed • prosthetic teeth and occlusal rest will be positioned above the existing occlusal plane when the prosthesis is not in function • direct retainers provide minimal retention

2. physiologic basing • physiological stimulation effect on the tissue of residual ridge • lightweight prosthesis requiring minimal maintenance and repair • reduction in the forces transmitted t the abutment teeth

• premature contact • difficult to produce effective retention • not well stabilized against lateral forces

3. Broad stress distribution • distributing forces over as many teeth and as much soft tissue area as possible • additional rests and clasp assemblies and by broad base

3. Broad stress distribution • multiple clasp not for more retention,but resistance for horizontal movement (splinting of perio compromised tooth) • no moving parts • rigid, minimize rotational movements and provide horizontal stabilization • ridge do not bear too much occlusal load

increased coverage may not accepted by some pt complicated oral hygiene

Essentials of design

Essentials of design 1.Direct Retention 2.Clasps 3.Rests 4.Indirect retention 5.Major connectors 6.Minor connectors 7.Occlusion 8.Denture bases

Direct retention 

not primary objective

1.clasp assemblies

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main objective:

2.adaption of the framework to guiding planes

− restoration of function and appearance − maintenance of comfort − preservation of remaining oral structures

 extension and adaptation of denture bases

Clasps simplest clasps

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remain passive until activated by functional Stresses 

Clasps: Class I 

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2 clasp assemblies Most posterior tooth on the R/L side of arch DB undercut: infrabulge clasp(T,1/2T) MB undercut: wrought wire clasp cast circumferential clasp Reciprocal : rigid bracing arm / lingual plating

Clasps: Class II 

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3 retentive clasp assemblies 

Distal extension side: Most posterior tooth

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Opposite side: 2 retentive clasp arm −

One as far posterior

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One as far anterior

If modification space is present: clasp the teeth adjacent to the edentulous space

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circumferential clasps Reciprocal : rigid bracing arm / lingual plating

Rests 

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Abutment for max support for prosthesis Rest seats prepared: forces directed within long axis of the abutments adjacent tooth to the edentulous spaces

Indirect retention 

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Neutralize unseating forces As far from the fulcrum line; not anterior than the canines 2 indirect retainers in a Class I design 1 indirect retainer in a Class II design; on the opposite side of distal extension base forces directed within long axis of the abutments Lingiual plating: must be supported by rest-rest seat combinations

Major connectors 

Rigid

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目的 : 

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Occlusion 

MIP should coincide with C.R.

comfort

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Harmony

Cleanliness

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Prosthetic teeth

placement of artificial teeth

1.Fewer teeth / narrower buccolingually 2.Over the residual ridge 3.Sharp cutting edges / escapeways

Denture bases 

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Broad coverage Not interfere with functional movements of the surrounding tissues Selective pressure impressions are recommended for extension base areas of Class I and Class II External surface of a denture base should enable the pt to exercise max neuromuscular control

Kennedy Class III 

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Direct retention: retentive undercuts on individual abutment teeth are not critical Clasps: 

quadrilateral position of direct retainer

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simple circlet clasp

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reciprocal arm must be rigid

Rests: 

adjacent to the edentulous spaces

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support major connectors and lingual plating

Kennedy Class III 

Indirect retention: 

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not required if posterior abutment only vertical support, no retention, entire design must satisfy Class I or II

Bases functional impressions are not required

Kennedy Class IV 

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For esthetics, pronunciation: prosthesis tooth placed anterior to residual ridge Reduce forces 

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Preservation of soft/hard structure of residual ridge Central incisor/other tooth preservation, reduce rotation quadrilateral position of direct retainer most anterior/posterior

Kennedy Class IV 

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Indirect retainer 

Not needed if quadrilateral

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Far away from fulcrum line

Selective pressure impression if extensive residual area

Design procedure  

Design procedures Armamentarium: .01 inch: clasp of chrome alloy and titanium alloys .015 inch: wrought wire (.02 inch: wrought wire) .03 inch: tripod   Color: •red: tripod, prepared (rest:solid ,recontoured( 斜線 ),relieved( 寫 relief) •black:survey line, information (type of tooth replacement, clasp,depth of undercut) •blue: resin base •brown:metallic portion

1. examine occluded Dx cast • Vertical black line for rest area • Red reshape(for rest) • Lingual view, black line

2. tooth placements • Black pencil • • • • •

Tooth on base Reinforced acrylic pontic(RAP) Braided post(BP) Tube(T) Metal pontic(M)

1.place cast on survey table 2.Tripod • Survey line with carbon marker • Undercut on abutment(2mm)

• Solid red rest seats • Diagonal red recontouring surface • Blue, resin base

• Brown major connector (cast stop) minor connector indirect retainer retentive/reciprocal elements