Cavity Preparation Principles

Cavity Preparation Principles (General)

• The shape and extent of the preparation should be visualized multiple times.

Buccal Pit - Lower Molars

• When preparing the buccal pit, visualize the shape and extent of the preparation.
• Align the bur perpendicular to the buccal surface.
• Enter the center of the pit.
• Variations exist in buccal pit preparations.

Lingual Pit

• Visualize the shape and extent of the preparation.
• Align the bur perpendicular to the lingual surface.
• Enter the center of the pit.

Common for Both Pits

• Check depth should be 1.5 mm (typodont).
• The floor should be flat and parallel to the buccal/lingual surface.

Occlusolingual Extension

• Occlusolingual extensions involve preparing the distolingual groove.

Occlusolingual Extension Technique

• Enter the distal pit with a straight bur, aligning with the long axis of the tooth.
• Angulate the bur slightly towards the buccal, following the DEJ as it curves towards the lingual cusp.
• Establish a depth of 1.5mm.
• The floor should follow the contour of the DEJ.
• Shift to a 90-degree angulation at the lingual surface.
• Maintain an axial wall depth of 0.5mm.
• Continue gingivally with the bur perpendicular to the long axis of the tooth.
• Angulate the bur at 45 degrees at the pulpogingival line angle to alleviate stress in the area.

Occlusal & Lingual Considerations for Extension

• Occlusal walls should be parallel to the long axis of the crown.
• Lingual walls and the gingival floor should be perpendicular to the lingual surface.
• Create an undercut using a 1/4 round bur along the mesial and distoaxial line angle, fading towards the pulpal floor.

Upper Molars (Shapes)

• Mesial and distal pits may exist without a crossing transverse ridge.
• A mesial pit may have an occlusolingual extension of the distal groove.
• Class I can involve crossing the transverse ridge with an occlusiolingual extension.

Class II Amalgam Preparation - Outline Form

• The preparation should be centered on the central groove.
• There should be no contact with the adjacent tooth, maintaining a clearance of 0.5mm.
• The preparation should feature graceful and reverse (S-curve) curves.
• Axial, mesial, and distal walls should be parallel to the long axis of the tooth.
• An S-curve involves a smooth, gradual curvature transitioning from the occlusal prep to the proximal box, ensuring a seamless connection, preserving tooth structure, and preventing sharp angles.

Class II Amalgam Preparation - Resistance Form

• Pulpal floor depth should be 1.5-2.0mm.
• The pulpal floor should be flat and smooth with uniform depth.
• The isthmus width should be 1/4 of the intercuspal distance.
• The axiopulpal line angle should be beveled.
• The axial wall should be angled 2-3° medially.
• The horizontal gingival floor width should be PM = 1.0mm and M = 1.2mm.

Class II Amalgam Preparation - Retention Form

• There should be a presence of an occlusal dovetail.
• Occlusal buccal and lingual walls should be converging.
• Proximal buccal and lingual walls should be converging.
• Retention grooves should be present on axiobuccal and axiolingual line angles.

Class II Amalgam Preparation - Convenience Form

• Ensure sufficient cavity width and extensions.
• Axial wall orientation is important.

Class II Amalgam Prep 14/24 MO

• Begins with mentally visualizing the final shape and extent of the preparation with a small Class I outline.
• A Class I preparation should be created, measuring 1.0mm in depth.
• Use a straight bur, move towards the crest of the MESIAL marginal ridge
• Cut a buccolingual ditch on the mesial side, leaving a thin enamel shell (.25mm).
• Fracture or remove the enamel shell using a chisel or hatchet.
• Establish a flat gingival and pulpal floor.
• Ensure a clearance of 0.5mm from the adjacent tooth, assess with an explorer tip.
• Blend the occlusal preparation with the proximal preparation using an S-curve, converging walls, and an axial wall.
• Confirm the buccal and lingual walls of the proximal box are just past the contact area.
• Add retention grooves on the axiobuccal and axiolingual line angles.
• Bevel the axiopulpal line angle using a handcutting instrument.
• Bevel the gingival cavosurface margin.
• Clean and dry the cavity.

Class III, IV, & V Amalgam Preparation Considerations

• Class III amalgam preps are rarely used.
• Access is typically lingual only with the distal surface involved.
• The gingival margin is often on cementum.
• Moisture control can be difficult.
• An undercut at the axiogingival line angle provides retention.
• Class IV amalgam preps treat caries that extend to the incisal edge of anteriors or to the cusp tips of posterior teeth.
• Attrition is a common cause of Class IV issues.

Amalgam Advantages

• Amalgam is known for its resistance to wear and longevity.

Class V Amalgam Prep

• Used on posterior teeth and in cases with gingival recession.
• May be combined with a mucopereosteal flap.
• Can be used for RPD abutments.
• Undercut the axiogingival and axioocclusal line angles for retention.
• Indicated for lesions near the CEJ requiring a retraction cord.
• Treats subgingival lesions when a mucopereosteal flap is needed.