Class I Amalgam Preparations Elizangela Bertoli, DDS, MS

Overview Indications and contraindications for amalgams Advantages and disadvantages for amalgams Conservative Class I Preparations Bur Depth Cuts Initial Tooth Preparation Outline Resistance Retention Convenience Forms Final Tooth Preparation Extensive Class II Preparations

Indications and Contraindications Where esthetics is not highly important Moderate to large preparations Area that will have heavy occlusal contacts Field cannot be well isolated Root surface Foundation for a full coverage restoration Tooth that serves as an abutment for a removable partial denture

Indications and Contraindications Esthetically prominent areas of posterior teeth Small to moderate Class I and II defects that can be well isolated Small Class VI defects

Advantages and Disadvantages Ease of use and the simplicity of the procedure Disadvantages Complex and larger tooth preparations than composite resins Non-esthetic

Conservative Class I Preparations Outcomes Protect the pulp: minimal pulp irritation Preserve the strength of the tooth: remaining tooth structure is strong Reduce deterioration of the amalgam restoration: enhances marginal integrity and restoration

Initial Tooth Preparations Establish the outline form by extension of the external walls to sound tooth structure while maintaining a specified, limited depth (usually just inside the DEJ) and providing resistance and retention forms

Outline Form Should include only the defective occlusal pits and fissures (in a way that sharp angles in the marginal outline are avoided)

Outline Form Friable and/or weakened enamel should be removed Faulty and defective occlusal pits & fissures should be included in the preparation Margins preparation should be placed so the restoration margins can be easily finished and polished

Resistance Form Definition Shape and placement of the preparation walls that best enable the remaining tooth structure and the restoration to withstand, without fracture, masticatory forces delivered principally in the long axis of the tooth.

Resistance Form Summary of Features Relatively flat floors Box shape Inclusion of weakened tooth structure Preservation of cusps and marginal ridges Rounded internal line angles Adequate thickness of restorative material Reduction of cusps for capping

Resistance Form Establish optimal, conservative depth of the pulpal walls 1.5 mm at the central fossa and 2.0 mm along the cuspal inclines Resistance may be in the form of locks, grooves, or coves which are placed in line angles or point angles of your preparation we usually think of locks, grooves, and coves as secondary resistance features

Retention Form Definition of retention - The shape or form of the conventional preparation that prevents displacement or removal of the restoration by tipping or lifting forces for non-bonded restorations

Retention Form Amalgam is retained in the tooth by developing external facial and lingual walls that converge occlusally (or are nearly parallel)

Retention Form Preparation is centered on major grooves Facial-lingual width at isthmus does not exceed 1.5mm Inclusion of mesial and distal pits No extension to marginal ridges (1.5mm) Tooth # 19 1.5 mm

Retention Form Occlusal internal form Facial and lingual wall converse occlusally Mesial and distal wall diverse occlusally Pulpal depth is uniform (1.5-2.0 mm) Internal angles are defined but not sharp Cavity is aligned with long axis of the anatomical crown

How do I begin my Class I Preparation? Enter the deepest or most carious pit using a punch cut with a high speed handpiece If M and D pits are carious, enter the distal pit first Why? Visibility

How do I begin my Class I Preparation? Minimize extending into the marginal ridge. Why? For strength of marginal ridge

Class I Preparation Depth Cuts Keep the bur rotating until removed from the tooth Dentinal caries initially spreads at the DEJ the goal of the initial cut is to reach the DEJ On posterior teeth, the approximate depth of the DEJ is located at 1.5 to 2 mm from the occlusal surface Depth is 1.5 mm along the central fossa (or 1/2 length of a No. 245 bur) Cuspal incline may extend up to 2 mm Desired pulpal depth is .1-.2 mm into dentin Most textbooks will state .5 mm

Bur Depth Cuts

Bur Depth Cuts The No. 330 bur head length is 1 mm (1.5 mm) and it’s shorter than the No. 245 bur Shape of No. 330 is also pear shaped (.8 mm diameter head) No. 330 indicated for most conservative amalgam preparations

Mesiodistal longitudinal section Faciolingual longitudinal section

Class I Preparation Depth Cuts Distal extension into the distal marginal ridge to include a fissure or caries occasionally requires a slight tilting of the bur distally (≤10 degrees) This creates a slight occlusal divergence to the distal wall to prevent undermining the marginal ridge of its dentin support

Class I Preparation If the marginal ridge is 1.6 mm or greater, you can allow the M and D walls to converge. If the marginal ridge is less than 1.6 mm, then the M and D walls must diverge

Class I Preparation The strongest and most ideal enamel margin will have full- length enamel rods resting on sound dentin, and supported by shorter rods on the restoration side Enamel cavosurface angles, once again, should be close to 900 Remember: amalgam has a low edge strength (very brittle)

Summary Class I preparations Outline form Preparation is centered on major grooves Facial-lingual width at isthmus does not exceed 1.5mm Inclusion of mesial and distal pits No extension to marginal ridges (1.5mm) Tooth # 19

Summary Class I preparations Occlusal internal form Facial and lingual wall converse occlusally Mesial and distal wall diverse occlusally Pulpal depth is uniform (1.5-2.0 mm) Internal angles are defined but not sharp Cavity is aligned with long axis of the anatomical crown

Summary Class I preparations Cavosurface angles and margins Cavosurface angles are 90-110˚ Cavosurface margins are definite & free of irregularities

Summary Class I preparations Finish No gauges or large scratches in the lateral or pulpal walls

Initial Tooth Preparation Occasionally for maxillary premolars, the outline may be butterfly-shaped (if you need to include all carious fissures facially or lingually)

Final Tooth Preparation Caries may be removed spoon excavator round bur with a low speed handpiece starting with the largest spoon excavator or the largest bur Why the largest? you’re less likely to get a pulp exposure and it allows visibility!

Final Tooth Preparation Ensure all caries is removed from the DEJ. Why? 59% of the caries is missed at the DEJ

Deep Fissure on the Floor Tooth Preparation Remove any defective enamel pit and fissure, but if the central fissure remains on the entire pulpal floor, go ahead and extend your preparation to maximum depth of 2 mm

Principles of Final Tooth Preparation If there are isolated pit and fissure remnants and they are very small, simply use a small round bur (such as # ½, #1, or #2) to remove the caries

Final Tooth Preparation Remember: don’t bevel amalgam occlusal preparations. Why? Butt joint margins of enamel and amalgam approximating 90-100 on the occlusal surface

Final Tooth Preparation Remove any remaining defective(unsupported) enamel and infected dentin on the pulpal floor Secondary resistance & retention forms Finish the external walls (refine, remove scratches, etc) Clean and inspect your tooth preparation Consider pulpal protection (sealers, bases, or liners)

Conservative Class I Preparation Maxillary 2nd Molar

Conservative Class I Preparation Mandibular Second Premolar

Extensive Class I Amalgam Preparations Extensive caries The distance between infected dentin and the pulp is judged to be less than 1 mm Wider faciolingual distances Deeper and larger preparations A more traditional indication for amalgam

Extensive Class I Amalgam Preparations Procedure Rubber dam isolation Risk of pulp exposure The preparation is extended laterally at the DEJ to remove all enamel undermined by caries For caries extending up the cuspal inclines: it may be necessary to alter the bur's long axis to prepare a 90- to 100-degree cavosurface angle while maintaining the initial depth

Tooth #30

What’s wrong with this preparation?

converging walls? Rough pulpal floor marginal ridge width?

What’s this black stuff? rough margin Rough pulpal floor

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Copyright Most of pictures in this presentation comes from the text book adopted in the restoratives classes with permission from the publisher. No pictures may be reproduced without written permission from the publisher. Sturdevant’s Art and Science of Operative Dentistry 6th Edition Sturdevant’s Art and Science of Operative Dentistry 6th Edition Fundamentals of Operative Dentistry 4th Edition