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Class 1 amalgam cavity preparation | PPT

| December 18, 2011 | 0 Comments

Class 1 amalgam cavity preparation | PPT

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Class 1 Cavities

Definition:
These are pit and fissure type cavities that involve the occlusal surfaces of molars and premolars, the occlusal 2/3 of buccal and lingual surfaces of molars, and the palatal pits in maxillary anterior teeth.
These are self-cleansable areas. However, they may get involved by caries due to their inherent defective structure as areas of imperfect coalescence of lobes of calcification of these teeth. These areas are retentive for food and thus invite caries.
These lesions are clinically characterized by:
1.A small surface opening which may remain unnoticed until the lesion becomes of a considerable size.
2.A conical spread in both enamel and dentin, with the bases of cones at the Amelo-Dentinal Junction, “A. J.D.”
3.Its rapid burrowing at the dento-enamel junction. These lesions may involve one or more surfaces and hence a simple or compound cavity should be prepared.
Application of principles
A     Simple occlusal cavities
Designing the Outline Form.
The outline form of a routine class I cavity should describe a symmetrical design running in sweeping curves along all pits, fissures, and angular grooves between the cusps and with a minimum width.
The mesial and distal margins are placed midway between the bottom of the proximal fossae and the crest of the proximal ridges and in a direction parallel to these ridges.

 

In a bucco-Iingual direction, the cavity is extended just sufficient to eliminate the defective and susceptible tissues. The lingual and the buccal wail should be parallel to the respective tooth surface.
It must be reemphasized that the outline form for class 1 cavities should be very conservative since they involve cleansable areas.
It is governed only by the extent of caries in both enamel and dentin and the amount of extension or need to eliminate pits and fissures to secure smooth margins.
Obtaining the Resistance and Retention Forms
The resistance form here consists chiefly of a pulpal wall parallel to the occlusal plane with dentin walls at right angles to it., i.e. Boxing the preparation.
The form of this cavity provides automatically for effective retention and, therefore, no special retentive features are required.
Removal of Carious Dentin
In small size cavities, the carious dentin should have been removed during making the cavity extensions.
In moderately deep and deep cavities, the carious dentin is peeled off carefully at the sides using large spoon excavators, and then scooped out in few and large pieces.
Only light pressure in a direction parallel to that of the pulp is utilized. This is continued until a sound dentin floor is reached.
Planning of Enamel Walls
The enamel walls of the cavity should be finished free from any loose, short, or undermined enamel, and trimmed to meet the tooth surface at a right cavo-surface angle.
This may be done by sharp and regular-edged chisels and hatchets, plane fissure burs, stones, or sand-paper discs.
All sharp corners in enamel must be rounded, as they may contain short enamel rods.
Performing of the toilet of the cavity
A sharp explorer is then used to check the details of the prepared cavity and to loosen the tooth debris which are then blasted out with warm air.
Operative Procedures
Armamentarium
High speed handpiece
Burs #330, 56
Hoe
Hatchet R&L
Wedel staedt chisel
Procedure
 The outline form is performed by first gaining access through the enamel to the carious dentin floor of the cavity followed by making the necessary cavity extensions.
In case of initial carious lesions, access is obtained by employing a small pear but #330.
In big carious lesions, access is obtained easily by breaking down the undermined enamel overlying the carious dentin, using a suitable size chisel.
In either case, access is started at the most defective area of enamel, i.e., a carious pit or fissure.
The bur is held at a right angle to the involved surface of, the tooth and light pressure in an in-and-out direction is exerted. Cutting is continued until the amelo-dentinal junction (A.D.J.) is reached.
The necessary cavity extensions through pits, fissures, and deep developmental grooves are made using a #330 pear bur held at right angle to the surface of the tooth.
The bur is rotated, and carefully introduced through the opening just obtained, so that its weak corners do not touch the enamel and get dulled.
With the bur seated in the cavity just below the amelo-dential junction 1/z-1 mm. gentle pressure is applied in the direction of required extension.
During cutting, the bur should be kept moving in-and-out of the cavity and at right angle to the tooth surface. In this way, the bur will undermine and lift the cut enamel, and at the same time unclog itself.
Provision of ample resistance and adequate retention through boxing of the preparation could be obtained.
This is obtained by using a #56 fissure bur held perpendicular to the surface of the tooth. All the line angle in dentin must be squared up hoe excavators.
B.  Buccal Pit Cavities
The outline of these cavities usually describes a triangle with its base faming the gingival wall and its sides forming the mesial and distal walls.
The gingival wall is placed at or slightly occlusal to the height of contour of the tooth.
All walls are extended just enough to eliminate defective enamel and dentin.
The enamel walls are planed in the direction of enamel rods and perpendicular to the axial wall.
Hoe excavators are used to smooth the axial wall and make it parallel with the external surface of the tooth.
It should be re-emphasize that the shape of the cavity will be governed by the extension of caries, accordingly the outline of these cavities may be a rounded or oval in shape.
C.  Buccal and Lingual Extensions
In case of occluso-buccal and occluso-lingual cavities extensions are made through the fissures and towards the respective surfaces.
The cutting is done in dentin at the amelo-dntinal junction using a #56 bur until the ocdusal ridge is undermined and removed.
If  the caries is still gingival to the level of the pulpal seat, a step is indicated: a #330 or 56 but is used to cut the dentin at the amelo-dentinal junction, applying pressure in a gingival direction and at the same time moving the bur mesio-distally.
The enamel thus undermined, is broken down with chisels.
Retention grooves are then cut in dentin along the axio-mesial and axio-distal line angles. The cavity walls and margins are finished as previously described.
In case of deeply-seated caries, where removal of the carious dentin will leave a round cavity floor, flattening of which to obtain the required resistance form, will expose the pulp.
The following technique is used:
a)The cavity floor is covered with a sub base of calcium hydroxide, followed by a base of glass ionomer cement which fills it to the routine cavity depth.
b)A ledge is cut on the expense of the buccal and lingual side walls of the cavity for obtaining the required resistance in sound dentin.
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