Cavosurface Angle Amalgam

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Advantages

Disadvantages

Recommended Use

Precautions

Amalgam

Good strength intermediate restoration

Preparation delay Condensation Corrosion No bonding*

Most foundations

Well-supported matrix

Adhesion

Fluoride

Low strength Moisture sensitive!

Smaller lesions

Moisture control

Composite resin

Rapid setting Ease of use

Thermal expansion Setting contraction

Smaller lesions Anterior teeth

Moisture control

Cast gold

Bonding Highest strength Indirect procedure

Delayed expansion Two-visit procedure Provisional needed

Extensive lesions

Alignment of pinholes

*Bonding can be achieved with 4-META products. Resin-modified formulations are less sensitive.

*Bonding can be achieved with 4-META products. Resin-modified formulations are less sensitive.

infection control, and optimum visibility.

Placement follows techniques developed for conventional amalgam restorations, although with extensively damaged teeth, placing the dam can be a problem. Sometimes cotton roll isolation must suffice.

2. Design the tooth preparation with the intended cast restoration in mind. Be sure that the cast restoration does not eliminate reten tion of the foundation. The preparation will differ somewhat from a conventional amalgam restoration. The ensuing discussion highlights these differences .21

3. Limit the extent of the outline form. In contrast to conventional amalgam preparations, which are extended to include unsupported enamel and the deep occlusal fissures, a less extensive outline is recommended for foundation restorations, because the fissures and contacts are removed during crown preparation. Although minimizing foundation outline can help conserve supporting tooth structure, the foundation should be adequate for the detection of any carious lesions (Fig. 6-7, A).

4. Retain unsupported enamel if convenient. For a conventional amalgam tooth preparation, unsupported enamel must always be re moved; otherwise, the enamel may fracture during function and leave a deficient margin. However, for a foundation restoration, the unsupported enamel may be preserved most effectively if it is substantial enough to withstand condensation forces and if it can be determined whether the enamel-dentin junc tion is caries free. Preserving unsupported enamel may facilitate matrix placement and improve amalgam condensation (Fig. 6-7, B).

5. Finish the cavosurface margins. For conventional amalgam restorations, cavosurface margins of 90 degrees are needed to minimize the potential for fracturing the enamel and amalgam during function. However, for foundation restorations, the amalgam-tooth interface will not be subjected to high stresses (they are protected by the crown), and marginal fracture is not likely to be a problem. Therefore, a 46- to 136-degree margin is acceptable. Furthermore, such a margin will conserve useful tooth substance and improve condensation (Fig. 6-7, C).

6. Remove any carious dentin carefully and thoroughly with a hand excavator or large round bur in a low-speed handpiece. Discolored but hard dentin can be left on the pulpal wall, but caries-affected areas at the enamel-dentin junction should be removed completely. If a pulp exposure occurs during the preparation, whether carious or mechanical, endodontics or tooth removal will be necessary. A direct pulp cap is not a good choice for a tooth requiring an FPD; however, if endodontics is elected and the pulp cannot be extirpated immediately, a suitable sedative dressing should be placed.

7. Create optimum resistance form. Good resistance to masticatory forces is as critical for a foundation as for a conventional restoration. Whenever possible, the tooth preparation should be perpendicular to the occlusal

Cavosurface Angle Amalgam

Fig. 6-7. The principles of preparation design for an amalgam foundation restoration differ slightly from those for a conventional extensive amalgam restoration. A, The outline form of a foundation need not include fissures or proximal or occlusal contacts, provided complete caries removal can be accomplished. B, Unsupported enamel (arrow) can sometimes be left when preparing a foundation restoration. It may facilitate matrix placement and is removed when the crown is prepared. C, Acute cavosurface margins are acceptable for a foundation restoration but not for a definitive amalgam. D, Resistance form is improved by preparing the tooth in a series of steps perpendicular to the direction of occlusal force. E, When pin retention is used, pinholes should be drilled slightly pulpal and at an angle to the root surface (solid line) as compared to the way they are placed for a conventional extensive amalgam restoration (dashed line). This will ensure retention for the foundation remains after crown preparation.

Fig. 6-7. The principles of preparation design for an amalgam foundation restoration differ slightly from those for a conventional extensive amalgam restoration. A, The outline form of a foundation need not include fissures or proximal or occlusal contacts, provided complete caries removal can be accomplished. B, Unsupported enamel (arrow) can sometimes be left when preparing a foundation restoration. It may facilitate matrix placement and is removed when the crown is prepared. C, Acute cavosurface margins are acceptable for a foundation restoration but not for a definitive amalgam. D, Resistance form is improved by preparing the tooth in a series of steps perpendicular to the direction of occlusal force. E, When pin retention is used, pinholes should be drilled slightly pulpal and at an angle to the root surface (solid line) as compared to the way they are placed for a conventional extensive amalgam restoration (dashed line). This will ensure retention for the foundation remains after crown preparation.

forces. If a sloping axial wall exists, it should be modified into a series of steps to enhance resistance form.

8. Be sure that the foundation restoration has adequate retention (augmented if necessary by pins, slots, or wells). Proper placement of retention features is essential to the preparation of a successful foundation. The features must be incorporated into the design so they are not eliminated during preparation of the crown (Fig. 6-7, D, E).

This can be a particular problem with the extensive reduction necessary for a metal-ceramic restoration. Pin placement is dictated by root furcations and the size of the pulp chamber. Generally, pins should be placed further pulpally than when conventional extensive pin amalgams are being provided; to prevent pulp perforation, they should be positioned at a slight angle to the long axis of the tooth. If a pin is slightly exposed during crown preparation, this may not be a problem-in contrast to the conventional pin-amalgam restoration. With a foundation restoration, the pin-amalgam interface receives little stress during function.

Retention can also be provided by slots or wells. These will create less residual stress in the dentin and will thus reduce the risk of pulp exposure or damage . They should be placed pulpal to the intended crown margin, at a depth of about 1 mm, with a small carbide bur. Careful condensation of amalgam into the slots will ensure good restoration retention.

Bonding agents can assist amalgam retention, but adhesion is not adequate to resist occlusal loading. Currently retention is best provided by conventional means. An example of the use of bonding agents appears in Figure 6-8. If bonding agents are used, the clinician should follow the manufacturer's directions about storage and manipulation.

Bases and Varnishes. A base is necessary to prevent thermal irritation if the preparation extends close to the pulp. A material with good physical properties, such as glass ionomer or zinc phosphate, should be chosen, because weaker materials are likely to fracture during amalgam condensation. Excessively thick bases should be avoided if they would leave inadequate thickness of amalgam foundation after tooth preparation. Postoperative sensitivity can be prevented with two or more coats of cavity varnish or a dentin bonding agent. The coats should be placed after any pinholes are drilled but before the pins are placed to avoid material at the pin-amalgam interface.

Calcium hydroxide liners should be reserved for use in deep cavities when a microscopic pulp exposure is suspected. They generally have low strength and do not resist condensation forces well. Macroscopic exposures should receive endodontic treatment or, if direct pulp-capping is the only option, a conventional pin-amalgam should be placed as the definitive restoration, at least until the success of the pulp-capping can be guaranteed.

Matrix Placement. A rigid, well-contoured matrix allows the amalgam to be properly condensed and facilitates carving. However, it can present a problem when much tooth structure is missing. Conventional matrix retainers, such as the Tofflemire, are unstable if both the lingual and the buccal walls are missing. A circumferential matrix (e.g., the Automatrix*) is useful for extensive restorations. Alternatives include copper bands or orthodontic bands. These are removed by cutting with a bur after the amalgam has set. Stability of the matrix is improved by proximal wedging, by crimping to shape, and by using modeling plastic or autopolymerizing acrylic resin for external stabilization2 7<Fig. 6-9).

Condensation. Condensation follows conventional practice, with particular attention paid to condensing into wells and around pins. If the foundation is prepared during the same visit, a high-copper spherical alloy is chosen. A mechanical condenser is useful for large amalgam restorations.

Contouring and Finishing. Care is needed to prevent amalgam fracture during matrix removal. After allowing time for setting, the dentist trims the amalgam away from the occlusal edge of the matrix and removes the wedges and matrix retainer. At this stage it is helpful to cut the buccal ends of the matrix band with scissors close to the tooth. Then the band can be pulled through the proximal contacts toward the lingual. Pulling the band occlusally is more likely to fracture the freshly placed amalgam.

Contouring follows conventional practice if the foundation is to serve for a significant period. Such a foundation should also be finished to facilitate plaque control. If the foundation is to be prepared shortly after placement, a more rudimentary oc-clusal contour is acceptable. However, the occlusal contour should be adequate to provide proper tooth stability. Moreover, all margins should be carved properly, because flash will lead to plaque retention and will make crown margin placement difficult.

*Caulk, Dentsply.

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Responses

  • amalgam separator
    Dentists often prefer dental amalgam because it is easier to work with than other alternatives. Many dentists consider amalgam stronger than the resin-based composite, and therefore use amalgam for back teeth fillings. Thanks for sharing your informative post.<br />
    7 years ago
  • melba
    What Is A Cavosurfaceangle Dentistry?
    8 years ago
  • abel
    What is cavosurface finish?
    8 years ago
  • futsum
    Why amalgam should be properly condensed?
    8 years ago
  • darcy
    What is 90 degree cavosurface margin?
    8 years ago
  • Christian
    What is a lingual cavosurface?
    8 years ago
  • Danielle
    What is cavosurface angle as in full crown tooth preparation?
    8 years ago
  • Jenny Guzman
    Are cavosurface margins for resistance or retention?
    7 years ago
  • kelly
    Why cavosurface angle is 90 degree?
    2 years ago
  • PAULA
    Why cavosurface angle is 90 degree for amalgam?
    2 years ago
  • Patrick
    Why amalgam preparation margin 90 degree?
    1 year ago
  • aristide
    What is a cavosurface margin angle?
    5 months ago

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