Cl-2cavity for Amalgam & Cast Metal Inlay.

Dept.Conservative dentistry & Endodontics

SEMINAR TOPIC - “ Class – II cavity preparation for [amalgam restoration and cast metal inlay] ”

by, A . Arif Bhasha,

3rd year junior batch,, Department Of Conservative Dentistry &

Endodontics..


Tooth preparation is defined as the mechanical alteration of a defective, injured, or diseased tooth to best receive a restorative material that will reestablish a healthy state for the tooth, including esthetic corrections where indicated, along with normal form and function.

What is TOOTH PREPARATION?????????


is to-------(1) remove all defects and provide necessary protectionto the pulp, (2) extend the restoration as conservativelyas possible, (3) form the tooth preparation so thatunder the force of mastication the tooth or the

restorationor both will not fracture and the restoration will not

displaced.

What are the

OBJECTIVES ?????????


Greene Vardiman Black, M.D., D.D.S., LL.D., Sc.D. (1836-1915)


CLASS II AMALGAM RESTORATIONS……...........................


Amalgam restorations that restore one or both of the proximal surfaces of the tooth may provide years of service to the patient when the:

(1) matrix is suitable,(2) tooth preparation is correct,(3) operating field is isolated, and (4) restorative material is manipulate properly.


I NITIAL CLINICAL PROCEDURES…………………………..


Occlusal contacts should be marked with

articulating paper before tooth preparation.

The operator should make a mental

image of these contacts to serve as guide in tooth preparation and restoration.


Any opposing "plunging cusp" or other

pointed cusp may need to be recontoured to reduce the risk of fracture of the new restoration or the cusp from occlusal forces.


Initial Tooth

Preparation………………………………


Occlusal outline form (occlusal step).

The occlusal outline form of a

Class II tooth preparation for amalgam is similar to that for the Class I tooth preparation.

Using high speed with air-water spray, enter the pit nearest the involved proximal surface with a punch cut using a No. 245 bur.


The long axis of the bur and the long axis of

the crown should remain parallel during

cutting procedures.

Proper depth of the initial entry cut is

1.5 to 2 mm

(i.e., one half to two thirds the length of the

cutting portion of a No. 245 bur).

This pulpal depth is usually 0.1 to 0.2mm into the dentin.


Ideally width of isthmus should be the width of the No. 245 bur.

Narrow restorations provide a greater length of clinical service.

Generally the amount of remaining tooth structure is more important to restoration longevity than the restorative material used.

The pulpal floor should be prepared to a uniform depth

and is usually flat.


Reverse curve is usually created in mesio-facial aspect , parallel to enamel rod direction . Lingually, reverse curve is very slight, often unnecessary.


Proximal outline form (proximal box)..........


The objectives for extension of proximal margins are to:

Include all caries, faults, or existing restorative material.

Create 90-degree cavosurface margins (i.e., butt jointmargins).

Establish (ideally) not more than 0.5 mm clearancewith the adjacent proximal surface facially, lingually,and gingivally.


Isolation of proximal enamel.

A, Bur position to begin proximal ditch cut.

B, Proximal ditch is extended gingivally to desired level of gingival wall (i.e., floor).

C, Variance in pulpal depth of axiogingival line angle as extension of gingival wall varies: a, at minimal gingival extension; b, at moderate extension; c, at extension in cementum,.


Proximal ditch cut results in axial wall that follows outside contour of proximal surface. When small lesion is prepared, gingival margin should clear adjacent tooth by only 0.5 mm.


Faciolingual dimension of proximal ditch is greater at gingival than at occlusal level.

To further isolate and weaken proximal enamel, bur is moved toward and perpendicular to proximal surface .


When a rotary instrument is used in a proximal box

after the proximal enamel is removed, there is a danger

of the instrument either marring the adjacent proximal surface ………………


Removing isolated

enamel………………………


Using spoon excavator to fracture out weakened proximal enamel………

Occlusal view with proximal enamel removed……….

Proximal view with proximalenamel removed..


Removing remaining undermined proximal enamel with enamel hatchet…………………


On lingual proximal wall

On facial proximal wall

On gingival wall


Primary resistance form is provided by:

The pulpal and gingival walls being relatively flat and perpendicular to forces directed with the long axis of the tooth;

Restricting the occlusal outline form (where possible) to areas receiving minimal occlusal contact.


The reverse curve optimizing the strength of both the amalgam and tooth structure at the junction of the occlusal step and proximal box;

Slightly rounding the internal line angles to reduce stress concentration in tooth structure (automatically created by bur design, except for the axiopulpal line angle); and

Providing enough thickness of restorative material to prevent its fracture under mastication


Dovetail design.Occlusal convergence.

Retention form


Retention locks, groove, rounden axiopulppal angles.

Secondary retention and resistance form


Simple box preparation-only proximal boxSlot preparation-similar to cl V but done at

proximal sideConservative design-preserves tranverse or

oblique ridgeModification to preserve esthetics-45 d rotation of

the box.Adjoining restoration-joining MO with existing DOModifications for abutment teeth for removal

partial denturesCusp capping.

modifications


Removal of remaining defective enamel and infected carious dentin

Pulp protectionSecondary retention and resistance formsFinishing the external wallsCleaning the cavity preparation.

Final cavity preparation


A, Failure caused by weak enamelmargin.

B, Failure caused by weak-amalgammargin.

C, Proper direction to proximal walls resultsin full-length enamel rods and 90-degreeamalgam at preparation margin. Note also thatretention locks have been cut 0.2 mm inside DEJ,and their direction of depth is parallel to DEJ.

TOOTH PREPARATION FOR CAST METAL INLAY

Inlay is defined as a fixed intracoronal restoration, a dental restoration made outside of a tooth to correspond to the form of prepared cavity, which is then luted into the tooth (Rosensteil)

Class II inlay involves occlusal surfaces and proximal surfaces of a posterior tooth and may cap one or more but not all of the cusps (John R.Sturdevant, Clifford M. Sturdevant)

DEFINITION OF INLAY

Indications

It is an alternative to amalgam and composite when higher strength and superior control of contours & contacts is desired.

Used instead of amalgam in patients with low caries rate who require class II with ample supporting dentin

High caries rate Young patients Esthetic concernsSmall restorations Unless sufficient bulk of tooth is there to

provide retention and resistance, it is contraindicated

Contraindications

Strength Biocompatibility Low wearControl of contours & contacts

Advantages

Higher chair side time & increased appointments

Temporary required between preparation & delivery appointments

Cost factor Technique sensitive

Disadvantages

Preparation path Inlay taperPreparation features of circumferential tie

Occlusal & gingival Bevels Types Functions

Facial & lingual FlaresPrimarySecondary

Basic concepts of cavity design for cast restoration

Preparation path

Single insertion pathAll reductions

oriented towards one path

The “line of draw” – path of removal & re-insertion should be perpendicular to plane across cusp tips or parallel to long axis of tooth crown

Inlay taper

Apico-occlusal taper

Cavity walls must diverge from floor outwards

To permit unobstructed removal & placement of wax pattern & casting

According to Sturdevant : 2 ° – 5 ° from line of

draw Short vertical walls : 2

° Long vertical walls : >

2 °

According to Charbeneau :10 ° – 16 ° of

convergent angle 5 ° – 8 ° on each wall

According to Marzouk :2 ° – 5 ° from path of

preparation

Taper may be increased or decreased according to following factors :

Wall length Taper required (< 10°)

Surface involvement in preparation

Taper required (< 10°)

Need for retention Taper

Circumferential tie – peripheral marginal anatomy

Features : Margins terminating on enamel should fulfill

requirements advocated by Noy In an intracoronal cavity, the circumferential tie is in the

form of a bevel, which is a plane of a cavity wall or floor directed away from cavity preparation

Occlusal & gingival Bevels Types Functions

Facial & lingual FlaresPrimarySecondary

PREPARATION FEATURES OF CIRCUMFERENTIAL TIE

BEVELS

“Flexible extentions” of a cavity preparation, allowing the inclusion of surface defects, supplementary grooves, or other areas on tooth surface.

To provide “lap joint”

According to their shapes & types of tissue involvement there are 6 types of bevels :Partial bevel Short bevel Long bevel Full bevel Counter bevelHollow ground (concave) bevel

Types & design features of occlusal & gingival bevels

Partial bevel

Involves : part of enamel wall ; not exceeding 2/3 of its dimension

Use : to trim weak enamel rods from margin peripheries

Short bevel

Involves : entire enamel wall ; but not dentin

Use : mostly with Class I alloys specially type 1 & 2

Long bevel

Involves : all enamel wall & up to ½ of dentinal wall

Use : most frequently used for Class I,II & III alloys

Advantage : preserves internal “boxed-up” resistance & retention features of the preparation

Full bevel Involves : all the

dentinal & enamel walls of cavity wall or floor

Use : only if impossible to use other bevels

Disadvantage : deprives the preparation of its internal resistance & retention features

Counter bevel

Use : when capping cusps ; to protect & support them

Used opposite to an axial cavity wall on facial or lingual surface of tooth

It will have gingival inclination facially & lingually

Hollow ground (concave) bevelAny bevel

prepared in concave form

Allows space for cast material bulk ; improves retention & resistance

Ideal for Class IV & V cast materials

Function of Bevels

Satisfies Noy’s requirements

Creates obtuse angled marginal tooth structure strongest configuration of marginal anatomy

Creates acute angled marginal cast alloy most amenable to burnishing

Function of Bevels Reduces error

factors (space between cast & tooth substance)

Bevel – major retention form ; here direct retentive frictional component exists between casting & tooth

Types & design features of facial & lingual flares

Flares – flat or concave peripheral portions of facial & lingual walls

2 types : Primary flare Secondary flare

Conventional & basic part of circumferential tie facially & lingually

Similar to long bevelAlways have specific angulation : 45° to the inner

dentinal wall proper Functions :

(Same as bevels) + they bring proximal margins to cleansable - finishable areas

Indication :Facial & lingual proximal wall

Note : If they do not fulfill the objectives of preparation

circumferential tie, secondary flare must be placed peripheral to them

Primary flare

SECONDARY FLARE• Flat plane superimposed peripherally to a primary flare

• Solely in enamel ; sometimes may contain dentin• May have different angulations, involvement & extent

In very widely extended lesions bucco-lingually

In very broad or malposed contact areas

In ovoid teeth with undercuts at facial & lingual peripheries

Functions :

Tooth preparation for class II cast metal inlays

Tooth preparation for class II cast metal inlays Class II inlay

involves occlusal surfaces and proximaal surfaces of a posterior tooth and may cap one or more but not all of the cusps

Steps : Initial preparation

Occlusal step Proximal box

Final preparationRemoval of infected

carious dentin & pulp protection

Preparation of bevels & flares

Initial preparation

Plane cut tapered fissure carbide burs are used to prepare vertical internal walls of the preparation

Throughout the preparation, the cutting instrument used are oriented to a single “draw” path

Gingival to occlusal divergence of walls : 2 ° – 5 ° from line of draw

Occlusal step

With No. 271 bur enter the fossa / pit to an initial depth of 1.5mm

General rule : long axis of bur parallel to long axis of tooth crown

In mandibular molar & premolar -5 ° to 10 ° lingually tilted

Extend to uninvolved fossa/pit keeping faciolingual width minimum & marginal ridge strong

If a fissure extends on the mesial marginal ridge, it is treated by :

Enameloplasty Bevel

Extension to include faulty facial & lingual fissures radiating from

mesial pit

Slender No. 169L bur is used so that

tooth structure can be

conserved

This provides the desired “Dovetail retention form”

which resists distal displacement of

inlay

The occlusal step is extended distally into distal marginal ridge sufficiently to expose junction of proximal enamel & dentin

As the preparation is extended distally, the faciolingual width is progressively widened – till proximal surfaces clear adjacent teeth by 0.2 – 0.5 mm

Proximal box

Continuing with 271 bur the distal enamel is isolated by cutting a proximal ditch

Mesiodistal width of ditch : 0.8mm

2/3 at expense of dentin & 1/3 at expense of enamel

While penetrating gingivally, the proximal ditch is extended facially & lingually

Facio & linguoaxial line angles should clear adjacent tooth by 0.2-0.5mm

Make 2 cuts at facial & lingual limit of proximal ditch

Until the bur is nearly through the marginal ridge enamel

If the wall of enamel is still present, it is broken away using a spoon excavator

Modified palm & thumb grasp used in chisel like motion in occluso – gingival direction

Proximal & gingival walls are planed using hand instruments to remove all

remaining enamel

Gingival wall is planed using a hoe in lingual to facial scraping direction ;

Axial wall may be planed with secondary edge of blade

No. 15 Straight chisel / Binangle chisel/ Enamel hatchet may be used

Shallow (0.3mm) retention grooves may be cut on the facioaxial & linguoaxial line angles with No.169L bur

Removal of infected carious dentin & pulp protection

Preparation of bevels & flares

Final preparation

Removal of infected carious dentin & pulp protection

If infected shallow / moderate carious dentin (>= 1mm RDT)

-Satisfactory isolation

-Small round bur(No. 2 or 4) / spoon excavator used

-Light cure GIC placed as base & excess trimmed with No. 271 bur

Preparation of Bevels & Flares

Preparation of Bevels

Slender flame shaped fine grit diamond is used to bevel

Gingival retraction cord – widens sulcus to 0.5mm – results in open sulcus – improves visibility & prevents injury to gingival tissue

The bevel should result in 30° – 40°marginal metal on inlay

The cavosurface design helps seal & protect margins & results in strong enamel margin with an angle on 140° - 150°

To place gingival bevel - The instrument is held parallel to gingival third of proximal surface of adjacent tooth

If the bur is tilted lingually / buccally, undercut will be created at corners of the box (commonly seen fault)

Preparation of Flares

Distolingual wall extends into lingual embrasure in 2 planes :

1st termed – lingual primary flare

2nd termed – lingual secondary flare

Secondary flare are directed to result in 40° marginal metal & 140° marginal enamel

No. 169L or paper disc

Slender flame shaped fine grit

diamond

can be used to prepare

secondary flare

The lingual secondary flare is prepared approaching from lingual embrasure moving the instrument mesiofacially

Preparation of facial secondary flare

Long axis of instrument is along the line of draw with only small tilting mesially & facially

To prevent abrasion to adjacent tooth the instrument may be raised occlusally

40° marginal metal should result

Completed facial secondary flare

Gingival bevel

Should result in 30° marginal metal

Instrument is tilted slightly mesially

0.5-1mm wide

Should blend with lingual secondary flare

Difference between preparation for amalgam and inlay

INLAY PREPARATION AMALGAM PREPARATION

May Support tooth Preparation supported by tooth

Retention achieved by nearly parallel opposing walls ; close adaptation of casting ; cementing medium

From parallel walls & undercuts

Good Resistance to occlusal forces Poor resistance to occlusal forces

Narrower Isthmus width

All Margins beveled Requires right angle margins

No Reverse Curve Present

More extensive Proximal outline (0.5-1mm) [access for disking, finishing, home care ]

0.5mm clearance[access for finishing, home care ]

Rounded Gingival cavosurface point angles [for ease of finishing gold]

Definite angle [for ease of condensing amalgam]

Proximal outline diverges occlusally Converges

INLAY PREPARATION AMALGAM PREPARATION

Preparation must draw ; no undercuts

Preparation must not draw ; retentive undercuts placed

Gingival wall in 2 planes Flat gingival wall

Axiopulpal line angle is rounded to prevent voids in the working die

Axiopulpal line angle is rounded to prevent stress on amalgam

All margins are beveled No cavosurface bevels

Thank you

Date post:	03-Dec-2014
Category:	Documents
Upload:	sankar-ram-mithran
View:	150 times
Download:	9 times

Cl-2cavity for Amalgam & Cast Metal Inlay.

Documents