Cavity preparation for Amalgam, class I
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Transcript of Cavity preparation for Amalgam, class I
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Cavity preparation for Amalgam, class I
Dr Heba Mohd El khodary
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Definition
Cavity preparation is defined as the mechanical alteration of a defective, injured or disease tooth in order to best receive a restorative material which will reestablish a healthy state of the tooth including esthetic corrections where indicated, along with normal form and function.
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What are class I lesions?
• Caries in occlusal pits and fissures of posterior teeth
• Caries in the occlusal two-thirds of the facial and lingual of posterior teeth
• Caries in the lingual pits of maxillary incisors
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-Softening at the base of a pit or fissure (WHO).-Opacity surrounding the pit or fissure, enamel appears chalky when dried.-Softened enamel that may be flaked away by explorer. -Brown-gray enamel ( caused by lateral spread of caries into dentin ). -Radiographic evidence.
Diagnosing Class I Caries
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INCIPIENT CLASS I CAVITY
• Small carious lesion in the central fossa of primary molars with all other teeth being sound.
• May be made without local anesthetic.• A No. 329 or No. 330 bur is used.• Restored with amalgam or a resin modified glass ionomer.• A preventive resin restoration may be done if needed.
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PIT OR FISSURE CLASS I CAVITY Outline form • should include all fissures, areas of caries, pits and developmental grooves and should be dovetailed.
• Facial & lingual margins should not extend more than halfway between central groove and cusp tips (one- quarter to one- third of the intercuspal width)
• Leave marginal ridges supported by dentin.
• Keep bur perpendicular to the occlusal plane of the tooth while preparing the outline
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The extension of the occlusal portion of the cavity preparation depends on the primary molar involved:
-The occlusal portion usually is extended about one half the way across on the primary maxillary and mandibular first molar.
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-For the primary mandibular second molar, extend the step completely across the occlucal surface.
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-The primary maxillary second molar preparation includes only the nearest occlucal pit. The oblique ridge is not included unless undermined with carious lesions.
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Resistance form• Proper form prevents fracture of tooth and restoration during function.
• Slightly rounded line angles 2.
• Enamel supported by sound dentin.• Weak tooth structure is removed.• Amalgam requires a thickness of at least 1.5 mm to prevent
fracture of the material (0.5 mm beneath dentino enamel junction 1).
• The walls converge slightly with the greater width at the
pulpal floor 3.
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Retention Form• Correct retention form ensures that the restorationwill not dislodge due to lifting or tipping forces.
• Facial and lingual walls are parallel or slightly convergent.
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Finish of the enamel walls
The cavosurface angle 4 for amalgam restoration should be 90-110 degrees.
This is called a butt joint.
What is the cavosurface angle 4?
(The angle formed by the junction of a cavity wall and the surface of a tooth).
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Convenience Form
• The cavity allows operator to visualize all remaining caries and to use the proper instruments in the preparation when condensing the amalgam.
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DEEP-SEATED CLASS I CAVITY
• Plane back the enamel that overhangs the extensive lesion.
• The cavity should extend through out the remaining grooves and anatomical occlusal defects.
• The carious dentine should next be removed with large round burs or spoon excavators.
• Then , the cavity walls should be finished as previously described.
• With deep carious lesions and near pulp exposures, the depth should be covered with a biocompatible base material for adequate thermal protection of the pulp.
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Lab Guidelines for Class I
• Mark pits and fissures with a sharp pencil Using a 329 or 330 bur drop to length of bur in a pit.
• Follow fissures at depth of bur. • Place dove tails mesial and distal.• Diverge mesial and distal walls.• Take prep to 1.5 mm depth. • Smooth walls and floor.
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Thank you
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