Types of tooth preparations

Dr Ishani SharmaMDS 1st Year

Paedodontics

Conten t s Preparations for full veneer crowns- Full metal crown preparation- Anterior metal ceramic crowns and posterior

metal ceramic crowns- All ceramic crowns

Definition Preparation: The selected form given to

a natural tooth when it is reduced by instrumentation to receive a prosthesis, guided by clinical circumstances and physical properties of the material.

Types Complete Crown / Full Veneer Crown:

A restoration that covers the entire coronal tooth surfaces (mesial, distal, facial, lingual and occlusal)

Partial veneer crown: A restoration that restores all but one coronal surface of a tooth or dental implant abutment, usually not covering the facial surface(GPT-8)

Full metal crowns

Full metal crownsUsed where the break down of tooth structure is

severe to the extent that has been described in operative dentistry as “the final attempt to preserve the tooth”

Most retentive of veneer preparations

Indications Extensive destruction from cariesEndodontically treated toothExisting restoration that needs the use of a more

conservative restorationNecessity for maximum retentionMinor correction of malinclinationsRecontouring of axial surfaces.Provide contour to receive removable appliancesCorrection of occlusal plane

Contraindications Less than maximum retention necessaryAesthetics

Advantages StrongHigh retentive qualitiesEasy to obtain adequate resistance formOption to modify form and occlusion

Disadvantages Removal of large amount of tooth structureAdverse effects on tissueVitality testing not easily feasibleDisplay of metal

Preparation

ArmamentariumTapered carbide bur- for occlusal guiding grooves.

Narrow round-tipped tapered diamond (regular grit) (0.8mm)- for occlusal reduction , axial alignment grooves, axial reduction, chamfer prep

Wide round tipped tapered diamond (fine grit) (1.2 mm)- for finishing

Step by step procedureGuiding grooves for occlusal reduction:- Tapered carbide is recommended.Place depth groove holes app 1mm deep in central,

mesial, and distal fossa and connect them.Guiding grooves in buccal and lingual developmental

groovesPlace a functional cusp bevelDepth – 0.8 mm for central groove & nonfunctional

cusp, 1.3 mm for functional cusp

Occlusal reduction :- by 2 stepsHalf occlusal surface is reduced first and other half

can be maintained as referenceMinimum clearence of 1.5 mm on functional cusp and

1mm on nonfunctional cusp.

Axial reduction :- place 3 alignment groove on each buccal and lingual

wall with narrow round end tapered diamond.The bur should be parallel to proposed path of

withdrawal of restoration. diamond bur with 6 degree taper is used and

identical axial taper will result in preparation.

The remaining islands of tooth structure between alignment grooves are removed while the chamfer margin is placed.

Place cervical chamfer of app 0.5 mm width.Finishing – with fine grit carbide bur.Round off all line angles.

Chamfer and seating grooves

Features of full metal crown preparation

Metal ceramic crowns

Metal-ceramic crowns (PFM)Use grew with the development of first

commercially successful porcelain/gold alloy by Weinstein etal in 1950s.

Ceramic layer bonded to a thin cast metal coping that fits over the tooth preparation

Greater strength than all ceramic crowns

Indications AestheticsIf porcelain-jacket crown is contraindicated Contraindication Large pulp chamberIntact buccal wallWhen more conservative retainer is technically

feasible

Advantages Superior aestheticsretentive

Disadvantage Removal of substantial tooth structureSubject to fracture because porcelain is brittleShade selection can be difficultInferior aesthetic compared to all ceramic Expensive

Preparation

ArmamentariumRound tipped rotary diamonds (regular grit for buccal

reduction, fine grit for finishing)Foot ball or wheel shaped diamonds ( for lingual

reduction)Flat end tapered ( for shoulder prepration)Finishing stonesHatchet and chisel

Steps of prepration Guiding grooves:- place 3 depth grooves- centre, mesiofacial and

distofacial line angles.Place in 2 planes- the cervical portion is parallel to

long axis of tooth, for incisal (occlusal) follows normal facial contour.

1.3 mm deep

Incisal (occlusal)reduction:-Bur – tapered round tipped diamond bur.Criteria – 1.2 to 1.5mm reduction for the metal and

porcelain.

Labial reduction guide grooves ( two plane):-Bur – tapered- round tipped diamond burCriteria- 1.2- 1.5mm reduction for metal and

porcelain.

Labial reduction ( two plane):-Bur – tapered flat- tipped diamond

Axial reduction:-Bur – tapered round tipped diamond

Lingual reduction:-Bur – football shaped diamondCriteria- 1mm clearance .

Finishing of shoulder (or beveled shoulder):-Bur – tapered flat tipped bur , hand instrumentCriteria – extend 1mm lingual to proximal contact

area.

Finishing :-Bur – tapered round tipped diamond or carbide burCriteria – round off all line angles

Metal-ceramic crowns

Radial shoulder

Features of metal ceramic preparation

Metal ceramic preparation for posteriors

Posterior metal-ceramic crowns

All ceramic crowns

Indications:1. High aesthetic requirement2. Incisal egde reasonably intact3. Endodontically treated teeth4. Considerable proximal caries5. Favourable distribution of occlusal load.

Contraindications: 1. When superior strength is needed2. Insufficient coronal tooth structure3. Thin teeth faciolingually4. Unfavourable distribution of occlusal load.

Advantages: 1. Excellent aesthetic2. Good tissue response3. More conservative of facial wall

Disadvantages:1. Less strength.2. Proper preparation extremely critical.3. Brittle nature of material.4. Expensive

Preparation

Depth grooves for the incisal reduction:-Bur – tapered diamondCriteria – 1.3 mm deep to allow the for additional

reduction during finishing, perpendicular to the long axis of opposing tooth.

Incisal reduction :-Bur – tapered diamond Criteria – clearance 1.5 mm

Depth grooves for the facial reduction:-Bur – tapered diamondCriteria – 0.8mm needed for the additional reduction

during finishing.

Facial reduction:-Bur- tapered diamondCriteria – reduction of 1mm is needed

Depth grooves and lingual reduction:-Bur –tapered and football-shaped diamondsCriteria – initial depth 0.8mm , recreate the concave

configuration (avoid stress)

Depth grooves for cingulum reduction:-Burs – tapered diamondCriteria – parallel to cervical aspect of facial

preparation. - 1mm reduction - shoulder follows free gingival margin

Lingual shoulder preparation:-Bur – square-tipped diamond Criteria – shoulder 1mm wide , 90 degree cavosurface

angle.

Finishing :-Bur – fine grit diamond or carbide Criteria- all surfaces smooth and continous - no unsupported enamel - 90 degree cavosurface angle

Preparation:

Features of all-ceramic crowns

Thank you.