CLASS II AMALGAM RESTORATIONSCLASS II AMALGAM RESTORATIONS

Initial Clinical Procedures:

Tooth Preparation

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.

Entering the pit nearest to the involved proximal surface

allow the mesial pit (in this case) not to be included if it is

sound. Proper depth of the initial entry cut is 1.5 to 2mm

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

of a No. 245 bur), 1.5mm as measured at the central

fissure, and approximately 2mm on the prepared external

walls

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

While maintaining the same depth and bur orientation,

move the bur to extend the outline to include the central

fissure and the opposite pit.

For the very conservative preparation, the isthmus width

should be as narrow as possible and no wider than one

quarter the intercuspal distance.

The pulpal floor should be prepared to a uniform

(previously described) depth (and is usually flat). However,

the pulpal floor of the preparation should follow the slight

rise and fall of the DEJ along the central fissure in teeth

with prominent triangular ridges.

During development of the distal pit area of the preparation,

extension to include any distofacial and distolingual

developmental fissures radiating from the pit may be

indicated. The distal pit area provides dovetail retention

form, which may prevent mesial displacement of the

completed restoration.

Before extending in to the involved proximal marginal ridge

visualize the final location of the facial and lingual walls of the

proximal box relative to the contact area.

Viewed from the occlusal a reverse curve in the occlusal outline

of a class II preparation, which often results when developing the

mesiofacial wall perpendicular to the enamel rod direction and

conserving the facial cusp structure.

Lingually, the reverse curve usually is minimal (if necessary at

all) because the embrasure form is larger.

While maintaining the established pulpal depth and with the

bur parallel to the long axis of the tooth crown, extend the

preparation mesially, stopping approximately 0.8mm (the

diameter of the end of the bur) short of cutting through the

marginal ridge in to the contact area.

The location of the DEJ is an important guide in the

development of the proximal preparation.

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 joint

margins).

- Establish (ideally) not more than 0.5mm clearance

with the adjacent proximal surface facially, lingually

and gingivally.

The Initial procedure in preparing the outline form of the

proximal box is the isolation of the proximal (i.e., mesial)

enamel by the proximal ditch cut. This is a very important

procedure in conservative tooth preparation.

With the same orientation of the bur, position it over the DEJ

in the pulpal floor next to the remaining mesial marginal ridge.

Allow the end of the bur to cut a ditch gingivally along the

exposed DEJ, two thirds at the expense of dentin and one third

at the expense of enamel.

The 0.8mm diameter bur end will cut approximately 0.5 to

0.6mm into dentin and 0.2 to 0.3mm into enamel.

Extend the ditch gingivally just beyond the caries or the

proximal contact, whichever is greater. Because dentin is

softer and cuts more easily than enamel, the bur should be

cutting away the dentin immediately supporting the enamel.

A guide for the gingival extension is the visualization that

the finished gingival margin will be only slightly gingival

to the gingival limit of the ditch. This margin should clear

the adjacent tooth by only 0.5mm in a small tooth

preparation.

The location of final proximal margins. (i.e facial, lingual,

gingival) should be established with hand instruments (i.e.,

chisels, hatchets, trimmers) in conservative proximal box

preparations. Otherwise, these margins may be

overextended to achieve 90-degree cavosurface margins

with the No. 245 bur.

The proximal ditch cut should be sufficiently deep in to

dentin (i.e., 0.5 to 0.6mm) that retention locks, if deemed

necessary, can be prepared into the axiolingual and

axiofacial line angles without undermining the proximal

enamel.

G IH

A CB

BA

The proximal ditch cut may be diverged gingivally to ensure

that the faciolingual dimension at the gingival is greater than

at the occlusal.

The gingival divergence contributes to retention form and

provides for desirable extension of the facial and lingual

proximal margins to include defective tooth structure or old

restorative material at the gingival level, while conserving the

marginal ridge and providing for 90 – degree amalgam at the

margins on this ridge.

In completing the proximal extensions, next make two

cuts, one starting at the facial limit of the proximal ditch

and the other starting at the lingual limit, extending toward

and perpendicular to the proximal surface.

This weakens the remaining enamel by which the isolated

portion is held. If this level is judged to be insufficiently

gingival, additional gingival extension should be

accomplished using the isolated proximal enamel that is

still in place to guide the bur. This prevents the bur from

marring the proximal surface of the adjacent tooth.

If additional use of the bur is indicated, a matrix band

may be used around the adjacent tooth to prevent marring

its proximal surface.

With the enamel hatchet, the bin angle chisel or both,

cleave away any remaining undermined proximal

enamel, establishing the proper direction to the

mesiolingual and mesiofacial walls.

Primary resistance form is provided

The pulpal and gingival walls being relatively flat and

perpendicular to forces directed with the long axis of

the tooth;

Restricting extension of the walls to allow strong

cusps and ridges areas to remain with sufficient dentin

support

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

Providing enough thickness of restorative material to

prevent its fracture under mastication.

Primary retention form is provided by the

occlusal convergence of facial and lingual walls and by

the dovetail design of the occlusal step, if present.

A B C

FINAL TOOTH PREPARATION:

The presence of infected carious dentin on a portion of either

the pulpal wall (floor) or axial wall does not indicate

deepening the entire wall. Infected carious dentin is removed

with a slowly revolving round bur of appropriate size or a

discoid-type spoon excavator or both.

Stop excavating when a hard or firm feel with an explorer or

small spoon excavator is achieved.

Secondary resistance and retention

forms:

Secondary resistance form in final tooth preparation

involves both resistance of the remaining tooth structure

against fracture from oblique forces and resistance of

restorative material against fracture.

Restricting extensions of external walls provides the

former; the latter is enhanced by using the gingival margin

trimmer to bevel or rounden the axiopulpal line angle,

thereby increasing the bulk of and decreasing the stress

concentration within the restorative material.

The occlusal convergence of the facial and lingual walls and

the dovetail design (if needed) provide sufficient retention

form to the occlusal portion of the tooth preparation.

The occlusal convergence of the mesiofacial and mesiolingual

walls offers retention in the proximal portion of the

preparation against displacement occlusally.

To enhance retention form of the proximal portion,

proximal locks may be indicated to counter proximal

displacement.

It is important to note that the retention locks should be

placed 0.2 mm inside the DEJ, regardless of the depth of

the axial walls and axial line angles.

Ideally there should be a 90-degree cavosurface angle

(maximum of 100 degrees) at the proximal margin.

The occlusal line angle may be 90 to 100 degrees or

greater. This angle aids in obtaining a marginal amalgam

angle of 90 degrees (no less than 80 degrees).

Clinical experience has established that this “butt joint”

relationship of enamel and amalgam creates the strongest

margin.

Reverse Curve

Matrix systemMatrix system

AA matrix systemmatrix system provides and takes the provides and takes the place of the proximal tooth surface that place of the proximal tooth surface that was removed to restore the proximal was removed to restore the proximal contours and contact to their normal contours and contact to their normal shape and function.shape and function.

Posterior Matrix SystemPosterior Matrix System► Matrix bandsMatrix bands

Matrix bands are made of flexible stainless Matrix bands are made of flexible stainless steel and are available in premolar, molar, steel and are available in premolar, molar, and universal sizes and thicknesses.and universal sizes and thicknesses.

►The The largerlarger circumference of the band is circumference of the band is the the occlusal edgeocclusal edge and is always placed and is always placed toward the occlusal surface.toward the occlusal surface.

►The The smallersmaller circumference of the band is circumference of the band is the the gingival edgegingival edge and it is always placed and it is always placed toward the gingiva.toward the gingiva.

Posterior Matrix SystemPosterior Matrix System

► Universal retainerUniversal retainer Also referred to as the Also referred to as the Tofflemire retainerTofflemire retainer. .

This device holds the matrix band in This device holds the matrix band in position. The retainer is positioned most position. The retainer is positioned most commonly from the buccal surface of the commonly from the buccal surface of the tooth being restored. tooth being restored.

Matrix retainerMatrix retainer

Components of a Universal RetainerComponents of a Universal Retainer

Sectional MatricesSectional Matrices

► A thin polished A thin polished palodentpalodent-type band -type band and a tension ring produce a tight and a tension ring produce a tight anatomic contact for composite resin anatomic contact for composite resin materials for class II restorations.materials for class II restorations.

Sectional matrices.Sectional matrices.

Ivory matrix retainer 1 & 8Ivory matrix retainer 1 & 8

AutomatrixAutomatrix

Compound Supported matrixCompound Supported matrix

Copper BandCopper Band

WedgesWedges

► A A wedgewedge is either triangular or round is either triangular or round and made of wood or plastic. and made of wood or plastic.

► The wedge is inserted into the lingual The wedge is inserted into the lingual embrasure to position the matrix band embrasure to position the matrix band firmly against the gingival margin of the firmly against the gingival margin of the preparation.preparation.

A wedge correctly positioned.A wedge correctly positioned.