MOD ONLAYS

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MOD ONLAYS
dr shabeel p n

• INDICATIONS
• Broken down teeth with intact buccal and lingual
  cusps
• MOD restorations with wide isthmus
• As a post endodontic restoration
• To correct the occlusal plane of a tilted tooth

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CONTRA INDICATIONS

• Patients with high caries rate
• Young patients
• Teeth with short clinical crown height

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INITIAL PREPARATION

• 1. OCCLUSAL REDUCTION
• FIRST STEP IS THE REDUCTION OF THE CUSPS WHICH
  IMPROVES THE
• ACCESS AND VISIBILITY FOR SUBSEQUENT STEPS IN
  TOOTH PREPARATION.
• EFFECIENCY OF THE CUTTING INSTRUMENT AND THE
  AIR-WATER COOLING SPRAY.
• IT IS EASIER TO ASSESS THE HEIGHT OF THE
  REMAINING CLINICAL CROWN OF THE TOOTH.

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• USING THE NO.271 CARBIDE BUR HELD PARALLEL TO THE
  LONG AXIS OF THE CROWN, PREPARE 2 mm DEEP PULPAL
  FLOOR ALONG THE CENTRAL GROOVE.
• THE OCCLUSAL PREPARATION IS EXTENDED FACIALLY AND
  LINGUALLY JUST BEYOND THE CARIES TO SOUND TOOTH
  STRUCTURE, TO VERIFY NEED FOR CUSP CAPPING.

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• WITH THE SIDE OF THE NO.271 CARBIDE BUR, PREPARE
  UNIFORM 1.5 mm DEEP DEPTH CUTS ON THE REMAINING
  OCCLUSAL SURFACE. THEY ARE USUALLY PLACED ON THE
  CREST OF THE TRIANGULAR RIDGES AND IN THE FACIAL
  AND LINGUAL GROOVE REGIONS.
• THE DEPTH CUTS SERVES AS GUIDES FOR THE AMOUNT OF
  REDUCTION.

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• CUSP REDUCTION IS COMPLETED WITH THE SIDE OF THE
  NO.271 BUR, AND THE REDUCTION SHOULD REFLECT THE
  GENERAL TOPOGRAPHY OF THE ORIGINAL OCCLUSAL
  SURFACE.
• SHOULD NOT ATTEMPT TO REDUCE THE MESIAL AND
  DISTAL MARGINAL RIDGES AT THIS TIME( TO AVOID
  HITTING ADJACENT TOOTH).
• THE GINGIVAL-TO-OCCLUSAL DIVERGENCE OF THESE
  PREPARATION WALLS SHOULD RANGE FROM 2-5 degrees
  DEPENDING ON THEIR HEIGHTS.

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• 2. OCCLUSAL STEP
• AFTER CUSP REDUCTION, THERE SHOULD BE A 0.5 mm
  DEEP OCCLUSAL STEP IN THE CENTRAL GROOVE REGION
  BETWEEN THE REDUCED CUSPAL INLCINES AND THE
  PULPAL FLOOR.
• OCCLUSAL STEP IS EXTENDED FACIALLY AND LINGUALLY
  BEYOND THE CARIOUS AREAS AND THE WALLS SHOULD
  GO AROUND THE CUSPS IN GRACEFUL CURVES THEN
  EXTENDED MESIALLY AND DISTALLY TO EXPOSE THE
  PROXIMAL DEJ IN ANTICIPATION OF PROXIMAL BOXING.

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• 3. PROXIMAL BOX
• CONTINUING WITH NO.271 CARBIDE BUR A PROXIMAL
  DITCH IS PREPARED.
• THE MESIODISTAL WIDTH OF THE DITCH SHOULD BE 0.8
  mm AND PREPARED APPROX. TWO-THIRDS AT THE EXPENSE
  OF DENTIN AND ONE-THIRD OF ENAMEL.
• IDEAL EXTENSION GINGIVALLY OF A MINIMAL CAVITATED
  LESION ELIMINATES CARIES ON THE GINGIVAL FLOOR
  AND PROVIDES 0.5 mm CLEARANCE OF THE UNBEVELED
  GINGIVAL MARGIN WITH THE ADJACENT TOOTH.

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FINAL PREPARATION

• REMOVAL OF THE INFECTED CARIOUS DENTIN AND
  DEFECTIVE RESTORATIVE MATERIALS ON THE PULPAL AND
  AXIAL WALLS.
• A CEMENT BASE CAN BE GIVEN IF IT IS INDICATED.

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• PREPARATION OF BEVELS AND FLARES.
• A DIAMOND INSTRUMENT IS USED TO PLACE COUNTER
  BEVELS ON THE REDUCED CUSPS, TO APPLY GINGIVAL
  BEVELS AND TO CREATE SECONDARY FLARES ON THE
  FACIAL AND LINGUAL WALLS OF THE PROXIMAL BOXES.

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• FISSURE THAT EXTENDS SLIGHTLY LINGUAL TO NORMAL
  POSITION OF COUNTER BEVEL MAY BE INCLUDED BY
  SLIGHTLY DEEPENING COUNTER BEVEL IN FISSURED AREA.

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• AFTER BEVELILNG AND FLARING SHARP JUNCTIONS
  BETWEEN THE COUNTER BEVELS AND THE SECONDARY
  FLARES ARE ROUNDED SLIGHTLY.
• LIGHTLY BEVEL AXIOPULPAL LINE ANGLE ALSO.

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• IF NECESSARY, SHALLOW( 3 mm DEEP) RETENTION
  GROOVES MAY BE CUT IN THE FACIOAXIAL AND THE
  LINGOAXIAL LINE ANGLES WITH NO.169 L CARBIDE BUR.
  

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COMPLETED MESIO OCCLUSO DISTAL ONLAY PREPARATION