modification in cavity preparation in primary teeth

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					MODIFICATION OF CAVITY
     PREPARATION
          IN
    PRIMARY TEETH
Classification
         Modified by G.V. Black classification for primary teeth.

      CLASS I
                  Those pits & fissures of the occlusal surfaces of the molars
                  teeth and the buccal & lingual pits of all teeth.

      CLASS II
                  All proximal surfaces of molar teeth with access established
                  from the occlusal surface.

      CLASS III
                  All proximal surfaces of anterior teeth which may or may
                  not involve a labial or a lingual extension & not involving incisal
                  edge.
CLASS IV
           All proximal surfaces of anterior teeth which involves the
 incisal edge.

CLASS V
          On the cervical third of all teeth, including the proximal
          surface where the marginal ridge is not included in the
          cavity preparation.
Steps In The Cavity Preparation


       Obtaining outline form
       Obtaining resistance & retention form
       Obtaining convenience form
       Removing remaining caries
       Finishing enamel wall
       Performing toilet of the cavity
Class I cavity preparation


    External out line form :

          Start preparation by penetrating the occlusal surface with no.330
          tungsten carbide bur. go from distal to mesial.9
          Include all deep & defective groves.
          Contour the outline parallel to the mesial & distal marginal ridge.
          Maintain a bulk of tooth structure as the marginal ridge.
          Maintain a width approximately as third the width of the occlusal
          table.
The Occlusal Form :
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
         in the primary maxillary & mandibular first molar.
         For the primary mandibular second molar extend the step completely
         across the occlusal surface.
         The primary maxillary second molar preparation includes only the
         nearest occlusal pit. The transverse ridge is not included unless
         undermined with carious lesion.
Internal outline form :

Penetrate approximately 1.5mm into the dentin.
Round the line angles ,provided the bur is kept somewhat vertical.
The pulpal floor is slightly concave. All internal line angles should be rounded.
Establish a sharp cavosurface angle. The wall are parallel or slightly undercut to
the external surface of the tooth.
     Class I preparation design for direct posterior
composite resin restoration :

            Incipient pit & fissure lesions can be prepared by using a no. 2 small,
            round or a no.330 bur to carefully remove the carious enamel.
Class I carious lesions that extend further & penetrate into the
dentin, removing all the carious dentin with round bur & spoon
excavators.
Class II cavity preparation for amalgum restoration



        Complete a class 1 cavity outline.
        Use a no.330 bur to extend the occlusal outline through the marginal
        ridge.
        Extend the no.330 bur into the proximal surfaces. Keep the bur
        parallel to the long axis of the tooth. Move the bur in a pendulating
        motion from lingual to buccal.
        Extend the proximal box gingivaly beneath the contact area to the
        interproximal area. This area is determined by the clearance of an
        explorer tip.
The axial wall, as determined by carious lesion depth, should
follow the contour of the tooth.
Use the enamel hatchet to remove any overhanging enamel in
the proximal box.
      The principal features of the occlusal form :

   Outline the outline follows the fissure pattern so as to prevent
   secondary caries occurring adjacent to the restoration.
A smooth flowing outline reduces stress & permits better packing of the amalgam.

   of the amalgam.



 Isthmus this should be between ¼ & ½ of the intercuspal distance



    (approximately 1.5 mm)
 Depth this should be 0.5 mm below the amelodentinal junction or

 1.5-2.0 mm from the cavosurface the amelodentinal junction or
Depth this should be 0.5 mm below angle (a).

1.5-2.0 mm from the cavosurface angle (a).




Transverse & marginal ridges these should be at least 1 mm in width.
This can be slightly divergent or a right angle otherwise they will

fracture.




 Internal angles all internal angles should be rounded so as to limit
 stress & to ensure that amalgam can be easily packed into these
  regions.
Pulpal floor this should be slightly concave.




Buccal & lingual walls these should be converging, so making the
cavity retentive. Also, the cavosurface angle needs to be a right angle
to ensure maximum strength at the enamel-amalgam junction.
Proximal walls these should converge so as to meet at the marginal
ridge, while allowing only the tip of an explorer to pass between the
margins of the box & the adjacent tooth.
Resistance form this should be built in so as to prevent lateral
displacement of the restoration.
The principal features of the proximal box :

   Gingival floor this should be located just below the contact area with
   the adjacent tooth.
   Axial wall the width (a) of the floor of the box should be
   approximately 1mm….and be parallel to the external proximal
   surface….this prevents the pulp from being exposed to excessive
   trauma during preparation.
Buccal & lingual walls these should be convergent, parallel

appropriate external surface & make a cavosurface angle of 90*.




Cavosurface angle this angle on the buccal & lingual sides of the
proximal box should be 90*.
Internal angles the angle between the axial wall & the gingival floor

should be rounded…….




…….as should the axiopulpal line angle. This gives the maximum
thickness of amalgam with the minimum of stress in this area.
Class II preparation design for direct posterior
          composite resin restoration :
    Lutz et al. have suggested adhesive restoration designs cavity size is as
    small as technically possible. The cavity form has been designed to
    minimize micro leakage at the cavosurface margins.
When class II carious lesions exist on posterior teeth in
the absence of class I lesion
       Modified slot preparation this involves access to the carious lesion
       from either the occlusal, buccal or lingual direction. After removal of
       all carious tooth structure, remove the grossly undermined tooth
       structure. Then place a bevel on all cavosurface margins.
A proximal slice-type preparation :
Tunnel-style preparation :


   If a class I lesion is being prepared & there is an adjacent class II
   carious lesion, tunnel-style preparation can be applied.
   Objective to maintain the sound enamel in the marginal ridge area.
   First ideal class I cavity preparation done, when it is completed
   prepare a small tunnel toward the proximal carious area using a
   small, round bur.
   The marginal ridge can therefore be maintained intact.
Class III cavity preparation lingual lock


           Extension the lock should be positioned to one side of the midline in
           the middle one third of the lingual surface.




           outline Outline the lock should have a smooth flowing & rounded.
           Bevel a 45 bevel increases surface area for retention.
Isthmus as in a class II cavity the isthmus should have rounded
margins & be large enough to accommodate amalgam & composite.
                 area.




 as to afford maximum strength at the restoration enamel junction.
Depth extended 0.5mm into dentine & follow the contour of
external surface.




Resistance form the lock is intended to prevent the restoration from
being dislodged. Therefore it should be resist lateral displacement
Proximal box :
     Extension in order to be self cleansing the box should extend just
     beyond the contact area of the adjacent tooth to as to allow the tip of
     a probe to be passed between the cavity wall & the adjacent tooth.




   Outline this may be curved or triangular (with the apex incisally
     positioned) with gently curving rounded margins.
Axial wall this should follow the contour of the external surface.




Depth the interproximal box ideally should extend just into the
dentine.
Additional retention may be gained from a pit placed at the gingivo-
labial junction or grooves in the dentine running parallel to the pulpal
wall of the box.
Maxillary primary canine dovetail is on the lingual surface.
Mandibular primary canine dovetail is on labial surface.
Class IV cavity preparation


           For class IV fractured incisal edges, use a tapered diamond bur to
           obtain a bevel on the entire incisal & gingival cavosurface margin.
           The bevel extending about 2mm or at least 1mm beyond the
           fractured margin & tapered.
           Additional retention, if needed, may be obtained by the use of the
           lingual dovetail.
Class V cavity preparation

           The outline form should be limited to the carious lesion & any
           adjacent decalcified areas.
           Cavity may be kidney shaped.
           The no.330 bur can be used to cut the cavity.
           Dentinal undercuts for mechanical retention will be placed if the pear
           shaped bur is used.
Class III cavity preparation

           Primary incisors teeth the earliest access is from the labial side. Use
           an inverted cone bur.
           The gingival cavity wall should incline slightly occlusally.
           Cavity depth should be 0.5mm pulpal to the amelodentinal junction.
           The interproximal area of the cavity should be shaped like the letter c
           when observed directly.

				
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posted:8/7/2012
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