CLASS V . AMALGAM CAVITY. PREPARATION. Smooth surface lesions located on the gingival third of labial, buccal and more rarely the lingual surfaces of all teeth.. DEFINITION. I.. Always simple lesions as it involves one surface of a tooth.. Limitations:. II.. 1. Caries is not only the reason of cavitation, abrasion and erosion may also responsible for their causation..
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3. Smooth surface lesions located on the gingival third of labial, buccal and more rarely the lingual surfaces of all teeth.
4. Always simple lesions as it involves one surface of a tooth.
6. 2. The carious lesion usually starts as a white or chalky line or area near the center of the gingival 1/3 of the labial or buccal surfaces of teeth. If it occurs on the lingual surface, it is usually associated with denture clasps.
7. 3. Marked sensitivity.
4. Tendency to spread mesially and distally near the axial angles of teeth, it may pass the axial angle of the tooth and unite with a Class II, III or IV cavity.
8. 5. Bell-crowned teeth, and teeth with markedly convex surfaces, are more susceptible to this type of caries.
10. 7. It is usually affects multiple teeth. This indicates that the patient has a high caries susceptibility and requires careful extensions of cavity outline.
11. 8-It is more frequent among old-aged patients and is called senile caries, yet it is not uncommon in childhood and adolescence and is often associated with improper oral hygiene and presence of bacterial plaque. In case of old aged individuals, caries may be found to extend gingivally and affect the cementum of the root. Sensitivity will increase and the caries may tend to recur around the margins in cementum.
12. Application of Principles: The Outline Form:
13. A. General shape: Ferrier design, conventional or typical
This is the most recent and accepted now. Generally the classical Class V cavity usually describe a trapezoidal outline with straight margins and round corners, with the short arm being the gingival.
14. I. OUTLINE FORM - rounded trapezoid in gingival 1/3.
16. A. Occlusal /incisal outline is straight and parallel to the occlusal plane.
17. Proximally: Far enough mesially and distally to include only the defective and/or the decalcified tooth tissues, yet not encroaching on the axial angles of the tooth, and placed just opposite the axial angles of the tooth.
18. Gingivally: At or ideally in the occlusal portion of the gingival sulcus space. In cases of gingival recession, the gingival margin should be located supragingivally.
19. Resistance and Retention Forms: No resistance form necessary for these preparation because they are not subjected to a direct functional loading.
A minimum dept of 0.5 mm in dentin is required for a uniform bulk of amalgam for strength of the material.
20. b. Retention Form For retention, however, as the mandible moves in lateral excursion, the lingual slopes of the buccal and lingual cusps of maxillary teeth load the buccal slopes of the buccal and lingual cusps of mandibular teeth.
24. Internal anatomy: In a mesio - distal cross section:
i. The axial wall will be smooth and slightly curved mesiodistally, following the curvature of the facial or lingual surface. This is to provide resistance to the forces of condensation and to provide a maximal pulp protection.
26. 2. In an occluso - gingival longitudinal section: i. The axial wall:
Will be seen as flat to slightly convex occluso-gingivally depending on the extent of the preparation occluso-gingivally. This will provide maximal pulp protection, while maintaining a uniform minimum dept of 0.5m in dentine.
28. b. If the occlusal margins is located at,the middle third of the facial or lingual surfaces, it will be formed of two planes; a grooved internal plane, and is made of dentin, and an outer amelo-dentinal plane going with the direction of enamel rods. This will provide a mechanical retention lock in occlusal wall without undermining the enamel rods.
29. iii. Gingival wall: Also it can vary in appearance, depending on its location, if it is located on enamel, it requires a small cavo-surface bevel. This will protect the very short gingival enamel rods from fracture during condensation and, at the same time, it terminates the gingival wall with its enamel wall going with the direction of the enamel rods, thus, eliminates the unsupported rods.
30. In such a manner it appears with two planes; an internal grooved plane made of dentinand an outer flat plane made of enamel.
31. If the gingival wall is located on cementum of the root, it also appears with two planes, an internal grooved plane made of dentin and an outer flat plane made of dentin and cementum.
33. Convenience form: The trapesiodal shape with rounded corners and the isolation of the field of operation using the rubber dam will provide a better conveniency for cavity preparation and restoration.
34. Removal of carious dentine: As described before.
35. Finishing of enamel walls and margins: Enamel margins should be smoothened and should be provided with 90° cavo-surface angle . The gingival bevel is to be placed on the gingival walls that are terminated by enamel and not where the preparation terminates in cementum.
36. Cavity Debridement As described before.
37. This Form of the Cavity : 1. Meets the general principles of cavity preparation.
2. Exhibits a pleasant appearance, and
3. Is easier to restore.
38. Armamentarium 1. Rubber dam , punch , clamp forceps and clamp no. 212.
2. Burs nos. 330 , 256 , 1/2, 1 , 35 .
3. Hand instruments : curved chisel, mon - angle hoe , hand excavator.
41. B. Gingival outline is straight and parallel to the occlusal outline.
42. C. Mesial and distal outline is straight and parallel to the mesial and distal tooth outline in the gingival 1/3.
43. II. Extensions Conservation of tooth structure is the basis for all cavity preparation; therefore, extend only far enough to remove defective tooth structure and create sufficient access (convenience form) for instrumentation and insertion of restorative material. In addition, access for finishing and maintenance of the restoration must be provided.
46. C. Mesio-distal extention is to the line angles of the tooth (or to the extent of the lesion mesially and distally).
47. III. RESISTANCE/RETENTION FORM A. Depth
1. 0.5 mm in dentin
2. 1-1.25 mm (may vary slightly depending on size of tooth, thickness of enamel and extensions); occlusally 1.5 1.75 mm depth may be required to achieve 0.5 mm in dentin.
48. B. Axial Wall
2. Slightly curved mesiodistally.
3. Straight or slightly curved occlusogingivally depending on the extent of the preparation occlusogingivally.
49. C. Mesial and distal walls
1. Smooth and straight occlusogingivally.
50. 2. Flare mesially and distally respectively to form 900 metal margins).
51. D. Occlusal or incisal wall
1. Smoothly and straight mesiodistally.
52. 2. Forms a 900 cavosurface angle (occlusal wall is parallel to the enamel rods 900 to a tangent to the external surface).
53. 3. Occlusal retention two undercuts .5 mm deep in the dentin of the occlusal wall at the occluso-axial line angle (one mesially and one distally)
55. 2. Gingival retention an acute axio-gingival angle (700).
56. 3. If terminated on enamel requires a small cavosurface bevel.
58. 2. Mesio occlusal, mesio-gingival, disto-occlusal, and disto-gingival walls form rounded line angles.
59. B. Point angles are rounded
60. C. Cavosurface margins
1. Well defined
2. Strong (sound)
63. B. Surrounding enamel, dentin, and cementum are preserved undamaged.
64. C. Soft tissue undamaged.