Class I Amalgam Cavity PreprationMentorship : Dr. Elham Zajkani Designed by : Fateme Omidi & Mohammad Hosein Nosrati

A. The bur is positioned over the most carious pit (distal) for entry. The distal aspect of the bur is positioned over the distal pit.

B. Mesiodistal longitudinal section. Relationship of head of No. 245 bur to excised central fissure and cavosurface margin at idea pulpal floor depth, which is just inside the dentinoenamel junction (DEJ).

C. Faciolingual longitudinal section. Dotted line indicates the long axis of tooth crown and the direction of the bur.

D. Enter the pit with a punch cut to just inside the dentinoenamel junction (DEJ) (depth of 1.5 to 2 mm or one-half to two-thirds the head length of bur). The -1.5mm depth is measured at central fissure; the measurement of same entry cut (but of prepared external wall) is 2 mm.

E. Incline the bur distally to establish proper occlusal divergence to distal wall to prevent removal of the dentin supporting the marginal ridge enamel when the pulpal floor is in dentin, and distal extension is necessary to include a fissure or caries. For such an extension on premolars, the distance from the margin to the proximal surface (i.e., imaginary projection) must not be less than 1.6 mm (i.e., two diameters of end of bur).

F. Mesiodistal longitudinal section. The pulpal floors are generally flat but may follow the rise and fall of the occlusal surface.

G. Mesial and distal walls should converge occlusally when the distance from a to b is greater than 1.6 mm.

H. When the operator judges that the extension will leave only -1.6mm thickness (two diameters of No. 245 bur) of marginal ridge (i.e., premolars) the mesial and distal walls must diverge occlusally to conserve ridge-supporting dentin.

I. Extending the mesial or distal walls to a two-diameter limit without diverging the wall occlusally undermines the marginal ridge enamel.

J. The ideal and strongest enamel margin is formed by full-length enamel rods (a) resting on sound dentin supported on the preparation side by shorter rods, also resting on sound dentin (b).

K. The cavosurface angle should not exceed 100 degrees, and the margin–amalgam angle should not be less than 80 degrees. Enamel external surface (e) before enameloplasty.

L. Removal of dentinal caries is accomplished with round burs or spoon excavators

M. The resistance form may be improved with a flat floor peripheral to the excavated area or areas.

N. Base application. Inserting resin-modified glass ionomer (RMGI) with periodontal probe.

O. Base application.In moderately deep excavations, a base thickness of 0.5 to 0.75 mm is indicated.

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