silver Amalgam cavity preparation for class 1 /certified fixed orthodontic courses by Indian dental academy
Definition:These are pit and fissure typecavities that involve the occlusalsurfaces of molars and premolars,the occlusal 2/3 of buccal andlingual surfaces of molars, and thepalatal pits in maxillary anteriorteeth.
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 areclinicallycharacterized 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.
Simple occlusalcavitiesDesigning the Outline Form.The outline form of a routine class Icavity should describe a symmetricaldesign running in sweeping curves alongall pits, fissures, and angular groovesbetween the cusps and with a minimumwidth.
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.
The mesial and distal wall should have a slant or slight divergence from the pulpal floor outward to avoid undermining the marginal 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 The resistance form hereForms Retention 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 cavityA sharp explorer is then used tocheck the details of the preparedcavity and to loosen the toothdebris which are then blasted outwith warm air.
ProcedureThe outline form is performedby first gaining access throughthe enamel to the cariousdentin floor of the cavityfollowed by making thenecessary 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 extensionsthrough pits, fissures, and deepdevelopmental grooves are madeusing a #330 pear bur held at rightangle to the surface of the tooth.The bur is rotated, and carefullyintroduced through the opening justobtained, so that its weak cornersdo not touch the enamel and getdulled.
With the bur seated in the cavity justbelow the amelo-dential junction 1/z-1mm. gentle pressure is applied in thedirection of required extension.During cutting, the bur should bekept moving in-and-out of the cavityand at right angle to the tooth surface.In this way, the bur will undermine andlift the cut enamel, and at the same timeunclog 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.
Buccal Pit CavitiesThe outline of these cavities usuallydescribes a triangle with its base famingthe gingival wall and its sides forming themesial and distal walls.The gingival wall is placed at or slightlyocclusal to the height of contour of thetooth.
All walls are extended justenough to eliminate defectiveenamel and dentin.The enamel walls are planedin the direction of enamel rodsand perpendicular to the axialwall.
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.
Buccal and Lingual ExtensionsIn 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.
Principles RationaleI. OUTLINE FORM – Angular irregularities in Smooth flowing, the outline are regular curves. susceptible to fracture during condensation – a smooth flowing outline is easier to visualize and carve following condensation.
II. EXTENSIONS – Conservation of toothstructure is the basis for all cavity preparationsin order to preserve the strength of the tooth.However, sufficient extension of cavitypreparations is necessary to ensure access(convenience form) for instrumentation, removalof defective tooth structure, insertion andfinish of the restorative material, andmaintenance of the restoration (prevention).
Principles RationaleA. Extensions circumscribe:1. Caries and eliminates defective decalcifications tooth structure and2. Enamel unsupported by eliminates areas (pits, sound dentin fissures, etc.) which are susceptible to recurrent3. Pits and fossae caries and facilities oral hygiene procedures4. Major fissures and (extension for grooves prevention).5. Existing restorations
Principles RationaleB. Bucco – lingual extension1. Extend fully in areas of to allow a smooth buccal and lingual grooves tooth-restoration to terminate on smooth margin to be created surfaces. (easier to finish and keep clean).
Principles Rationale2. Extend minimally in areas to preserve the of triangular ridges strength and function (optimal isthmus width is of the cups while ¼ intercuspal distance or eliminating susceptible less) terminating on grooves or defective smooth surfaces. tooth structure (must be wide enough to allow condensation).
Principles RationaleC. Mesio-distal extension1. Stop short of the to preserve strength of marginal ridge crest. marginal ridges. to preserve a uniform bulk2. Parallel the contour of (strength) to the mariginal the marginal ridge. ridges.
Principles Rationale3. Groove extensions are to preserve strength of kept narrow (mesio- cusps while eliminating distally) where susceptible grooves possible (consistent and/or defective tooth with access for structure (must be at condensation and least as wide as the outline form), narrowest condenser). terminating on smooth tooth structure.
Principles Rationale4. If marginal ridge is If not included the unsupported or very marginal ridge may fail thin it should be (amalgam will be included, resulting in stronger than the a Class II unsupported enamel) preparation.
Principles RationaleIII. RESISTANCE/ RETENTION FORMA. Depth = ½ mm into Minimum depth is dentin (approx. 2 mm required to provide measured at triangular sufficient bulk to ridges). prevent fracture and retain the amalgam.
Principles RationaleB. Pulpal floor Uniform thickness of1. Smooth and flat restorative material.2. Parallel to the occlusal resists occlusal stress plane (resistance form) and forces of condensation.
Principles RationaleC. Buccal and lingual walls1. Smooth and curved Facilitates adaptation mesio-distally. of amalgam and elimination of weak tooth structure.2. Smooth and straight pulpo-occlusally.
Principles Rationale3. Converge slightly To provide mechanical pulpo-occlusally in lock or retention to the areas of triangular occlusal portion and crate ridges (60). bulk at the margins.
Principles Rationale4.Diverge slightly protects buccal and lingual pulpo-occlusally in surfaces from being buccal and lingual undermined (RESISTANCE groove extensions FORM). (60).
Principles RationaleD. Mesial and distal wall1. Smooth and straight facilitates adaptation of amalgam and elimination of weal tooth structure.
Principles Rationale2. Diverges slightly protects marginal ridge pulpo-occlusally form being undermined or (forms an obtuse weakened (enamel must angle with pulpal be supported be dentin) floor).
Principles RationaleIV. CAVITY FINISHA. Pulpo-occlusal line increases retention of the angle is well defined amalgam restoration and (no point angles are preparation is more easily present) and follows visualized. general configuration of cavosurface outline.
Principles RationaleC. Cleanliness – cavity facilitates adaptation of is free of debris amalgam to the cavity and and moisture. improves the physical properties of the restoration by elimination of void or foreign material.
Principles RationaleV. TISSUE RESERVATION preserves isolation,A. Rubber dam is intact eliminates moisture.B. Adjacent tooth structure conservation of tooth and restorations are structure. intact prevention of post-C. Adjacent soft tissue operative pain and (perio-dontium) is intact inflammation.