types of tooth preparations
TRANSCRIPT
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.