Surveyed crowns/semi-precision attachment

lecture given 10/20/2026

survey crown

a full coverage crown designed to support, retain, and stabilize a removable partial denture (RPD)

design incorporates specific features that accommodate the RPDs path of insertion (GP), support (rest seat), and retention (undercut) requirements

support

resistance of prothesis to move towards the ridge

provided by rest seats

retention

resistance of prosthesis to move away from the ridge

provided by retentive arm

stability

resistance of prosthesis to move in lateral direction

provided by GP, minor connectors, retentive arm, ect

what are indications for survey crowns?

heavily restored or broken down tooth which will serve as a primary or secondary abutment for an RPD

replacing an existing crown on a tooth which will serve as an abutment for an RPD

unable to satisfy the requirements for the RPD design by minor modifications of the abutment tooth

correction of occlusal plane

develop acceptable RPD path of insertion

esthetics- attachment-retained RPD’s

splinting- double abutting for stress distribution or attachment retained RPD’s / FPD to replace a single missing tooth or splint a lone standing tooth

primary abutment

rest seat + clasp

secondary abutment

rest seat only

why would you splint teeth for an RPD?

better stress distribution

can be a better option than complete mandibular denture

what are contra-indications for survey crowns?

teeth with questionable prognosis or poor long term prognosis

satisfaction of the RPD design requirement can be ahcieved with minor tooth modification (more conservative approach)

full cast (gold) survey crown

pros: conservative prep, no risk of fracture

cons: esthetics, high cost

PFM survey crown

pros: esthetics

cons: aggressive prep, risk of porcelain fracture, high cost

all-ceramic zirconia survey crown

pros: conservative prep, esthetics, low cost, efficient workflow, good fracture reistance, facilitates retro fitting crown to existing RPD

cons: lack of long-term research and clinical documentation

material selection

preferred crown material- PFM, full cast

zirconia may be considered for retrofitting crown to an existing RPD

what are the steps for fabrication of survey crown- diagnostic phase?

diagnosis and treatment planning

mounted diagnostic casts- occlusal plane analysis, ensure sufficient inter arch space present

survey of study cast and finalize RPD design

wax up, incorporate GP and rest seat in wax up, putty matrix of wax up

optional but highly recommended- duplicate wax up cast and fabricate a clear vaccuform stent to be used as a prep guide to ensure sufficient reduction

how much reduction is needed for a rest seat?

1-2mm, average of 1.5mm

what are the steps for fabrication of survey crown- clinical phase?

prep and temp- putty matrix to fabricate provisional, clear vaccuform stent to verify reduction

RPD abutment preps: rest seats, GP, and undercuts must be done prior to crown final impression

final impression for crown fabrication (full arch, must capture the RPD abutments and edentulous ridge), consider using a custom tray

what are the steps for fabrication of survey crown- lab phase?

pouring of final impression and mounting- pour the impression twice (first pour master cast that gets sectioned and pindexed, second pour is solid cast)

if case can be hand articulated proceed to mounting

if case cannot be hand articulated (insufficient/unstable posterior stops), a record base and wax rim must be fabricated on the second pour (solid cast)

survey and tripod of master cast

mounting of master cast

case sent to lab for crown fabrication

after crown returns from lab, it must be re-surveyed prior to insertion appt, if any modifications needed must be done prior to cementation

what are the steps for fabrication of survey crown- crown insertion phase?

crown insertion

preliminary impression for RPD design verification

final impression for RPD frame fabrication

guide planes- designing a survey crown

fabricated in metal

tooth borne RPD- maximum length in occlusogingival direction (min 2/3), flat in occlusalgingival direction, curved in buccolingual direction

distal extension RPD- reduced occlusogingival length (<1/2), flat in occlusogingival direction, curved in buccolingual direction

rest seats- designing a survey crown for posterior teeth

fabricated in metal

round, the floor slopes towards the center of the tooth, broad buccolingually (1/3-1/2 occlusal BL width), if the tooth receiving a survey crown has an adjacent tooth the rest seat must be designed with a flare, sufficient clearance (min 1mm of metal thickness, preferably 2mm), rounded angle between the guide plane and rest seat

rest seats- designing a survey crown for anterior teeth

fabricated in metal

cingulum rest seats or ML rest seat

same guidelines for cingulum rest in natural teeth

the rest seat should not be over contoured

finish line

on the tooth

champfer, shoulder, bevel

margin

on crown

butt joint, metal collar, ceramo-metal margin

undercut- designing a survey crown for posterior teeth

typically in porcelain (for PFM crowns)

clasp tip 2-3mm coronal to gingival margin

depth and location of undercut is dependent on the clasp design and material used for the retentive arm of the clasp

special considerations for tooth preparation for survey crown

more reduction in the rest seat area may be needed to allow for sufficient thickness of the rest

cases with planned ledges, more reduction required to allow for fabrication of crown within normal contours

how much undercut does a c-clasp or I-bar need?

0.01mm

how much undercut does a ww-clasp?

0.02mm

what are the 3 techniques to retrofit a crown to an existing RPD?

pick up impression with the RPD seated firmly- a second impression without the RPD is required to be used for a master cast

chair-side clasp index using blue mousse (or any rigid bite registration material) and a final impression of the prepared tooth

digital workflow (CAD/CAM)- replicating the shape of the abutment tooth using a preop scan of tooth before the crown prep, a second scan of the prepped tooth is required

retrofitting a crown to existing RPD- pick up impression technique

pick up impression with the RPD seated firmly, a second impression without the RPD is required to be used for a master cast

most accurate technique

disadvantage- the pt will be without the RPD until the case is returned from the lab

retrofitting a crown to existing RPD- clasp index technique

chair-side clasp index using blue moose (or any rigid bite reg material), a final impression of the prepared tooth is needed too

advantage- pt will keep the RPD
disadvantage- more technique sensitive, typically requires more adjustments

retrofitting a crown to existing RPD- digital workflow (CAD/CAM)

replicating the shape of the abutment tooth using a preop scan of tooth before the crown prep, a second scan of the prepped tooth is required

advantages- accurate, less expensive

disadvantage- limitation of crown material (Zr or lithium disilicate)

*implant assisted RPD

first reported around 1991-1993

many descriptions- implant assisted RPD (IARPD), implant retained RPD (IRRPD), implant supported RPD (ISRPD)

beneficial in mandibular RPD’s with DE (K I and K II)

advantages and disadvantages of IARPD

improved support/retention, improved pt comfort, improved esthetics

requires surgery, cost, maintenance

attachment retained RPD

a mechanical device for the fixation, retention, and stabilization of a prosthesis

used for segmented bridges works and RPDs

2 components- matrix component (attached to crown), patrix component (attached to the pontic or the RPD)

advantages and disadvantages of ARRPD

esthetics

cost, maintenance due to wear, close monitoring required esp with DE RPDS

increased technical expertise by the clinician and technician

requires the pt to have adequate manual dexterity

how are attachments classified?

based on the contour of the attachment components- intra or extra coronal

based on the fit of matrix/patrix and the amount of movement- rigid, resilient

based on method of fabrication- precision, semi-precision

intra coronal attachment for attachment retained RPD

pre-fabricated or custom-made attachment for support and retention of a fixed or removable dental prosthesis; the matrix and patrix components are positioned within the normal contours of the abutment tooth

typically used for segmented fixed bridgework

extra coronal attachment for attachment retained RPD

pre-fabricated or custom-made attachment for support and retention of a fixed or removable dental prosthesis; the retentive components (matrix and patrix) are positioned outside the normal contours of the abutment tooth

allows for some rotation

rigid attachment for attachment retained RPD

non-resilient

provides stable, fixed connection between the matrix and patrix with no movement

prefab then soldered or cast to/with the prosthesis or castable resin pattern

indicated for segmented bridgework and tooth borne RPD’s

contraindicated for distal extension RPD

resilient attachment for attachment retained RPD

allows controlled movement between the matrix and patrix, vertical and/or rotational, to reduce stress on the abutment teeth (stress breaker)

can be used for distal extension RPD

ERA is an example

precision attachments for attachment retained RPD

prefabricated then cast-to or soldered

parallel walls

fit- approx 10 microns

semi- precision attachments for attachment retained RPD

wax pattern or resin pattern then cast in metal

tapered walls