lec-4 prin of tooth prep

8/8/2019 Lec-4 Prin of Tooth Prep

1/44

PRINCIPLES OF TOOTH

PREPARATION

pp:119-133


2/44

PRINCIPLES OF TOOTH

PREPARATION

1. PRESERVATION OF TOOTHSTRUCTURE.

2. RETENTION AND RESISTANCE.

3. STRUCTURAL DURABILITY.4. MARGINAL INTEGRITY.

5. PRESERVATION OF PERIODONTIUM


3/44

PRESERVATION OF TOOTH

STRUCTURE

Partial veneerversus Full veneer

crown

Supra-gingivalmargin versus sub-

gingival.


4/44

RETENTION AND RESISTANCE

Retention prevents removal ofthe restoration along the path ofinsertion or long axis of thetooth preparation.

Resistance preventsdislodgement of the restorationby forces directed in an apicalor oblique direction andprevents any movement of the

restoration under occlusalforces.

Retention and resistance areinterrelated and often

inseparable qualities.


5/44

RETENTION

The essential elementof retention is twoopposing vertical

surfaces of the samepreparation.

These may beexternal surfaces

such as the buccaland lingual walls of afull veneer crown(sleeve retention).


6/44

RETENTION

The opposing surfacescan also be internal,such as the buccal andlingual walls of the

proximal box of a inlay.

An intracoronalrestoration resistsdisplacement by wedgeretention.

Many restorations are acombination of the twotypes.


7/44

RETENTION AND RESISTANCE

1. Taper

2. Freedom ofdisplacement

3. Length

4. Substitution of

internal features

5. Path of insertion


8/44

TAPER

Theoretically, the

more nearly parallel

the opposing walls

of a preparation, the

greater is the

retention.


9/44

TAPER

Tooth preparation

taper should be keptminimum because of

its adverse effect on

retention.


10/44

TAPER

Optimum taper or total

convergence of 16

degrees achievable

clinically while still

affording adequate

retention.

Low as 10 degrees on

anterior teeth and as

high as 22 degrees on

molar teeth.


11/44

STRUCTURAL DURABILITY

Restoration must contain bulk of material that isadequate to withstand the forces of occlusion.

This bulk must be confined to the space createdby the tooth preparation.

Only this way the occlusion will be harmoniousand axial contours normal.


12/44


1. Occlusal reduction.2. Functional cusp

bevel.

3. Axial reduction.


13/44


Occlusal reduction : One ofthe most important featuresfor providing adequate bulkof metal and strength to the

restoration is occlusalclearance.

For gold alloys- 1.5 mmclearance on the functionalcusp (lingual of maxillary

molars and premolars andbuccal of mandibular molarsand premolars ).

1mm clearance on thenonfunctional cusp.


14/44

Occlusal Reduction

The basic inclinedplane pattern of theocclusal surface

duplicated to produceadequate clearancewithout overshortening thepreparation.

A flat occlusal surfacemay over shorten thepreparation.


15/44

Inadequate Occlusal Reduction

Makes the restoration weaker.

will not provide adequate space to allow

good functional morphology under the

anatomical grooves. The restoration easily perforated by

finishing procedures or by wear in the

mouth.


16/44

FUNCTIONAL CUSP BEVEL

An integral part of

occlusal reduction is the

functional cusp bevel.

A wide bevel placed on

the functional cusp

provides space for an

adequate bulk of metal inan area of heavy occlusal

contact.


17/44

Functional Cusp BevelLack of functional cusp bevel may

produce several problems :

1. Can cause a thin area or

perforation.2. May result in over contouring

and poor occlusion

3. Over inclination of the buccal

surface will destroy excessivetooth structure reducing

retention.


18/44

AXIAL REDUCTION

Plays an important role in securing space

for an adequate thickness of the

restorative material.

Inadequate axial reduction will have thinwalls subject to distortion or result in over

contouring the axial surface which could

lead to periodontal problems.


19/44

STRUCTURAL DURABILTY

There are other

features that serve to

provide space for metal

that will improve the

rigidity and durability of

the restoration:

1. Offset

2. Occlusal shoulder

3. Isthmus

4. Proximal groove

5. Box


20/44

MARGINAL INTEGRITY

The restoration

margin should closely

adapt to thecavosurface finish line

of the preparation to

survive in the oral

cavity.


21/44

MARGINAL INTEGRITY

TO BEVEL,

OR .

NOT TO BEVEL


22/44

FINISH LINE CONFIGURATION

1. Chamfer

2. Heavy chamfer

3. Shoulder4. Radial shoulder

5. Shoulder with bevel

6. Knife edge


23/44

CHAMFER

The preferred gingival

finish line for full veneer

metal restoration.

This finish line exhibit

least stress to the

underlying cement.

It can be cut with round-end tapered diamond.

Conservative type when

compared with shoulder

finish line.


24/44

PRESERVATION OF THE

PERIODONTIUM

The placement of finish lines has a direct

bearing on the ease of fabrication and the

ultimate success of the restoration.

The best results can be expected from

margins that are as smooth as possibleand are fully exposed to cleansing action.


25/44

MARGIN PLACEMENT

Whenever possible thefinish line should beplaced in an area wherethe margins can be

finished by the dentisteasily and kept clean bythe patient.

In addition,finish linesmust be placed so that

they can be duplicated bythe impression withouttearing or deformation.


26/44

MARGIN PLACEMENT

Finish line should beplaced in enamelwhenever possible.

Supra-gingival versussub-gingival margin.

Many situations inwhich sub-gingivalmargins areunavoidable.

1. Caries

2. To increase retention

3. Esthetics4. Extension of previous

restoration

5. Trauma.


27/44

PREPARATION FOR FULL

VENEER CROWN

PP- 139-141


28/44

PREPARATION FOR FULL

VENEER CROWNS

SELECTION

Full veneer crown exhibits superior retention

and resistance when compared with partialveneer crown.

Selection becomes mandatory when the

abutment tooth is small and the

edentulous span is long.


29/44

FULL VENEER CROWN

Variations of the full veneer crown are

1. Metal-ceramic crown.

2. All-ceramic crown.


30/44

FULL VENEER CROWN

INDICATIONS :

1. Extensive coronal destruction due to

caries or trauma.2. Endodontically treated tooth.

3. Necessity for maximum retention and

strength.4. To correct minor malinclination.

5. To correct occlusal plane.


31/44

FULL VENEER CROWN

Contra-indication :

Full coverage should not be used in mouths

with uncontrolled caries.It does not protect the tooth against the

biological causes of caries.

Caries must be controlled by other meansbefore any restoration can be successful.


32/44

FULL METAL CROWN

PREPARATIONARMAMENTARIUM :

1. Hand piece

2. No : 171L bur

3. Round-end tapereddiamond

4. Short needle diamond

5. Torpedo diamond

6. Torpedo bur7. Red utility wax


33/44

FULL METAL CROWN

PREPARATION

STEP NO :1

OCCLUSAL REDUCTION

1.5 mm of clearance of

functional cusp and 1mmon the nonfunctional

cusp.

Depth orientation grooves

are placed on the

occlusal surface with

round end tapered

diamond.


34/44

Full metal crown preparation

Occlusal reduction :

A round-end tapereddiamond is used to placethe grooves on the ridges

and the primary groovesof the occlusal surface.

If there is already someclearance with theopposing tooth because

of malposition- groovesshould not be made asdeep.


35/44

Full Metal Crown Preparation

OCCLUSAL REDUCTION :

The occlusal reduction

should follow theconfiguration of the

geometric inclines that

make the occlusal surface

of any posterior teeth.


36/44


STEP NO : 2

Functional cusp bevel withround-end tapereddiamond.

A wide bevel is placed onthe functional cusp-depthorientation grooves arealso helpful in thisreduction.

Functional cusp bevel is

integral part of occlusalreduction.

Failure to place this bevelcan produce thin castingor poor morphology.


37/44


OCCLUSAL CLEARANCE :

Is checked by having the

patient to close on redutility wax held over the

preparation.


38/44

Full Metal Crown

PrepSTEP NO : 3

Buccal and lingual walls are

reduced with the round-

end tapered diamond.The

sides of the diamond will

produce the desired axialreduction while the tip

forms the chamfer.


39/44

Full Metal Crown

Preparation

STEP NO : 4

Initial proximal axial

reduction with short

needle diamond

followed by the round-end tapered diamond.


40/44


STEP NO : 6Seating groove with

171L bur.


41/44

Full Veneer Crown Preparation

STEP NO : 5

Axial finishing- round-

end tapered diamond.

All axial surfaces are

smoothed including

all point angles. The

finish line should be

smooth and

continuous.


42/44

Full Veneer Crown Preparation


43/44


44/44

lec-4 prin of tooth prep

Documents