Tooth preparation class II amalgam

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INITIAL TOOTH PREPARATIONMesio-occlusal class II preparation • Occlusal outline form:

Enter the pit nearest the involved proximal surface with a punch cut using a No. 245 bur.

• Viewed from the proximal and lingual aspects, the long axis of bur should be parallel to the long axis of tooth crown during cutting.

Bur position for entry;proximal view

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• Proper depth of the initial entry cut is 1.5-2mm.The pulpal depth is usually 0.1-0.2 mm in to the dentin.

While maintaining the same depth and orientation ,bur is moved to extend the outline to include the central fissure and opposite pit ,if necessary.

Completed occlusal stepOcclusal view

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• Include all the carious occlusal pits and fissures in such a manner that sharp angles in the marginal outline are avoided.

• The isthmus width should be as narrow as possible, ideally should be 1/4th of the intercuspal distance

• Enameloplasty should be used where indicated to conserve tooth structure.

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Before extending into the involved proximal marginal ridge, the final location of the facial and lingual walls of the proximal box relative to the contact area should be visualized ,to prevent overextension of the occlusal outline form (i.e., occlusal step) where it joins the proximal outline form (i.e., proximal box).

Visualization of final location of proximo-occlusal margin

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While maintaining the established pulpal depth and with the bur parallel to the long axis of the tooth crown, the preparation is extended mesially, stopping approximately 0.8 mm short of cutting through the marginal ridge into the contact area.

Removing remaining undermined enamel

Breaking proximal contact

Isolating proximal enamel

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PROXIMAL OUTLINE FORM

• Again we visualizes the desired final location of the facial and lingual walls of the proximal box relative to the contact area.

• 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 0.5 mm clearance with the

adjacent proximal surface facially, lingually, and gingivally.

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• The initial procedure in preparation of outline form is the isolation of the proximal enamel by giving the proximal ditch cut.

• 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 0.8-mm diameter bur end will cut approximately 0.5 to 0.6 mm into dentin and 0.2 to 0.3 mm into enamel.

• The ditch is extended gingivally just beyond the caries or the proximal contact, whichever is greater.

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• When extension places the gingival margin in cementum, the initial pulpal depth of the axiogingival line angle should be 0.7 to 0.8 mm (the diameter of the tip end of the No. 245 bur is 0.8 mm). The bur may shave the side of the wedge that is protecting the rubber dam and underlying gingiva.

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Ideally the extension of facial and lingual margins of proximal box should be such that ,it provides clearance of 0.2-0.3 mm from the adjacent tooth.

but this clearance greater than 0.5 mm is excessive unless indicated to include caries, undermined enamel, or existing restorative material.Ideally the gingival margin should clear the adjacent tooth by only 0.5mm ,which may be measured with the side of explorer.

Preparation of Axial wall-• It is an internal prepared wall that is parallel to the long axis of

the tooth & It is always placed in dentin to obtain:

It is always placed in the dentin to obtain:-• Resistance & elasticity of dentin• Bulk of the restoration.• Placement of retentive locks.

• Length of the axial wall :- 0.4-0.6 mm from the axio-pulpal line angle to the axio-gingival line angle.

• the axial wall should be straight or convex but it should never be concave.• It should follow the contour of proximal surface .

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PREPRATION OF GINGIVAL SEAT:-

It is an external cavity wall that is perpendicular to the long axis of the tooth.

It is extended beyond the contact area or up to the proximal lesion whichever is more. This also help in providing a contact clearance gingivally.

It is made flat so that the masticatory forces are distributed equally.

The width of gingival seat:- 0.6-0.8mm(premolars) 0.8-1.0mm(molars) It consists of 2/3rd of dentin and 1/3rd of enamel.

GINGIVAL DIVERGENCE OF FACIAL AND LINGUAL WAALS OF PROXIMAL BOX The proximal ditch cut may be diverged gingivally to ensure that the faciolingual dimension at the gingival is greater than at the occlusal. This gingival divergence :- Increases the retention form .- Provides desirable extension of the facial and lingual proximal

margins to include defective tooth structure or old restorative material at the gingival level. - Conserve the marginal ridge strength.- Provides 90-degree amalgam at the margins on this ridge .

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• 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 (until the bur is nearly through the enamel at contact level).

• The side of the bur may emerge slightly through the surface at the level of the gingival floor.

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• a matrix band may be used around the adjacent tooth to prevent marring its proximal surface.

• The isolated enamel, if still in place, may be fractured out with a spoon excavator or by additional movement of the bur.

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• To protect the gingiva and the rubber dam when extending the gingival wall gingivally, a wooden wedge should already be in place in the gingival embrasure to depress the soft tissue and rubber dam.

Rounded toothpick wedge Triangular wedge

Indicated in deepGingival extension

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• 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. .

• Proximal margins having cavosurface angles of 90 degrees are indicated.

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PRIMARY RESISTANCE FORM

1. Pulpal & gingival walls being flat and perpendicular to the forces directed to the long axis of the tooth.

2. Restrict the extension of the walls to allow strong cusps & ridges to remain with sufficient dentin support.

3. Restricting the occlusal outline form to areas receiving minimal occlusal contact.

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4.Reverse curve optimizing the strength of both the amalgam and tooth structure at the junction of the occlusal step and proximal box.

5. Rounding off the internal line angles.

6.Providing enough thickness of the restorative material.

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REVERSE CURVE

• When the direction of the mesiofacial wall is parallel to the direction of the enamel rods, thus creating a ‘s’ shaped curve in the proximal outline.

It is created to:

• Provide butt joint in the preparation margin.• To relieve the contact• To place the proximal margins in a self cleansing area.

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PRIMARY RETENTION FORM• Occlusal convergence of facial & lingual walls

• Dovetail design of occlusal step(when present).

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FINAL TOOTH PREPARATION• Removal of any remaining defective enamel and infected

carious dentin• Accomplished in the same manner as in the Class I

preparation.• Infected carious dentin is removed with a slowly revolving

round bur of appropriate size or a discoid-type spoon excavator or both.

. A, Infected carious dentin extending beyond ideal pulpal wall position. B, Incorrect lowering of pulpal wall to include infected carious dentin. C, Correct extension facially and lingually beyond infectedcarious dentin.

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• 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 on axial wall does not call for preparing axial wall toward pulp as shown by dotted lines. It should be removed with round bur

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• A partial extension of a facial or lingual wall is permissible if:

• The entire wall is not weakened

• The extension remains accessible and visible

• Sufficient gingival seats remain to support the restoration

• A butt joint fit at the amalgam and enamel margin (90-degree amalgam angle and 90-degree cavosurface angle) is possible.

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PULP PROTECTION

It is desirable to have approx 2mm bulk beneath the pulp and metallic restoration which may be Dentin, Liner or a Base.

• Liner/Base- Mechanical, Chemical, Thermal Pulp protection and act as a barrier that protects the dentin.

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• Remaining Dentin Thickness 0.5-1 mm -Zinc Phosphate Cement, Glass Ionomer Cement base is used followed by calcium hydroxide liner.

The base insulates the pulp from thermal changes, bonds to the dentin, releases fluoride, and is strong enough to resist the forces of condensation.

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SECONDARY RESISTANCE AND RETENTION FORMS

• Using the gingival margin trimmer to bevel or round the axiopulpal line angle.

• Proximal retention locks:• Placed on axiofacial and axiolingual line angles.• Terminate at axiopulpal point angle.• Prepared with No. 169L bur or No. ¼ bur• There are four characteristics or determinants of proximal locks:

(1) position, (2) translation, (3) depth, and (4) occlusogingival orientation

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Proximal retention locksA, Position of No. 169L bur and pulpally. B, Lingual lock..C, Completed locks. D, Locks preparedwith No. '/, bur. E, Completed locks

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• Retention grooves:• Placed on axiofacial and axiolingual line

angles.• Extend from the gingival floor to the occlusal

surface• Prepared with No. ¼ round bur with head

diameter of 0.5mm or No. 1/8 bur with head diameter of 0.4mm

• In preparation with deep proximal box grooves should be in the proximal walls just inside the DEJ and not in the corners of the box

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• Circumferential slots:• Prepared with No. 33 ½ inverted cone bur• 0.5 to 1 mm deep inside DEJ• 0.6 mm deep

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• Amalgapins:• Depth of 1.5 to 2mm is adequate• Diameter 0.8 to 1mm• Prepared with No.1156, No.1157, No.330 or No.56 burs

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• Amalgam bonding agents:• Should have auto-polymerizing property as amalgam

does not allow light transmission• Ex: All bond-2, Amalgam bond plus, etc.

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PROCEDURE FOR FINISHING EXTERNAL WALLS:

1. There should be no unsupported enamel and marginal irregularities present.

2. There should be a butt joint relation between the tooth & amalgam

3. Cavosurface bevel [20°] at the gingival margin can be given by G.M.T , to remove the unsupported enamel rods.

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• When the gingival margin is positioned gingival to the cementoenamel junction (CEJ) on the tooth root, the bevel is not indicated.

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Final procedures: cleaning, inspecting, desensitizing,and bonding

• First step includes removing all chips and loose debris and then drying the preparation(not dessicating) and check for any infected dentin and any unsound enamel margins.• Cleaning is to free the preparation of visible debris with warm

water from syringe and then to remove moisture with a few light surges of air syringe.• Varnishes should be applied on all the preparation walls to

prevent the microleakege.• GLUMA desensitizer can also be used to reduce the

postoperative sensitivity.• Disinfection of the preparation walls can be done by silver

nitrate, phenol,ethyl alchol (short duration).

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