1. Amalgam
cavity
preparation
DR.SHATHA AL-RUSHOUD

2. Dental amalgam has been used in operative dentistry for not less than 150
years. Almost 80% of single tooth restorations are fabricated from amalgam,
in view of its numerous advantages, which include:

3. Advantages
1- Good adaptability to cavity walls and margins  i.e. provides good seal that prevents:
1) Recurrence of caries.
2) Irritation to dentin and pulp.
2- High compressive strength → minimum 80 MN / m2.
3- Low coefficient of thermal expansion when compared to other restorative materials: →
 Amalgam → 25 x 10-6.
 Tooth → 11.5 x

4. Advantages
4- Indestructible in oral fluids → i.e. maintains marginal seal, proximal contact and contour.
5- Biologically compatible with oral tissues.
6- Convenience of manipulation.
7- Could take and maintain high surface polish that increases the strength.
8- Low coast.

5. Disadvantages 4- Thermal conductivity.
5- Dimensional changes during setting →  20  / cm.
6- Poor esthetic.

6. Fracture

7. INDICATIONS
Amalgam should be considered together with posterior composite and cast gold as a restorative for classes I, II, the distal surface of cuspids and class V in posterior teeth. Material selection in such cases will depend on:

8. A) THE EXTENT OF THE LESION:
The most suitable indication for amalgam is the small and medium sized class I and II cavities especially those with four walls and a floor, where the amalgam will be confined and not subjected to tensile loads.

9. Extensive lesions especially those including undermined cusps will require cusp capping and tooth supported against high loads including tensile, where cast gold will serve better.

10. B) ESTHETICS:
For esthetic-conscious patients, amalgam will be objectionable particularly in conspicuous areas of teeth and posterior composites may be favored.

11. C) CARIES INCIDENCE:
Amalgam may be favored if repair or remake is likely to include extensions for original cavities and for patients with moderately high caries incidence; being less costly and having good sealing ability.

12. D) ECONOMICS:
Although amalgam restorations cost far less than cast gold restorations yet costing per se may not be in favor of amalgam in the long run if the restoration has to be repeatedly be made. Amalgam can also be used for core build-up under full crowns.

13. Cavity preparation
Cavity preparation for amalgam restoration is characterized by: →
CSA 90C.
Cavity walls parallel or perpendicular to the direction of occlusal force.
Enough depth to provide bulk to the material.

14. Cavity preparation
If a cusp is undermined and is to be capped with amalgam, it must be reduced minimum of 2 mm, to provide enough bulk of the amalgam enables it to withstand the tensile stresses.
The isthmus area shows: → Minimal bucco-lingual width.
→ Axio-pulpal line angle beveled, rounded or saucerized to provide:
a) Elimination of stress concentration area.
b) Bulk of amalgam.

15. B) DESIGNS OF CLASS I CAVITY PREPARATION
Cavity preparation for Class I lesions for amalgam restoration. It may be either:
A- Class I simple cavity.
B- Class I buccal pit cavity.
C- Class I extension cavity.

16. Definition: CLASS 1 CAVITIES
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.
DR.SHATHA AL-RUSHOUD

17. These are self-cleansable areas
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.
DR.SHATHA AL-RUSHOUD

18. These lesions are clinically characterized by:
A small surface opening which may remain unnoticed until the lesion becomes of a considerable size.
A conical spread in both enamel and dentin, with the bases of cones at the Amelo-Dentinal Junction, "A. D."J.
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.
DR.SHATHA AL-RUSHOUD

19. Application of Principles:
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.
DR.SHATHA AL-RUSHOUD

20. 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.
DR.SHATHA AL-RUSHOUD

21. The mesial and distal wall should have a slant or slight divergence from the pulpal floor outward to avoid undermining the marginal ridges.
DR.SHATHA AL-RUSHOUD

22. 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.
DR.SHATHA AL-RUSHOUD

23. 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.
DR.SHATHA AL-RUSHOUD

24. Again:
The outline form for simple design of Class I cavity preparation should include all carious and undermined enamel, all pits and fissures and extended to area self-cleansable in the shape of multi curves without any
sharp line angles.

25. Bucco-lingually, it should not extend beyond the intercuspal line except if there is caries with minimal width of the cavity about 1/4 - 1/3 the inter-cuspal distance. Mesio-distally, it should be extended mid way between the triangular fossa and the crest of the marginal ridge.

27. The resistance form
Achieved by maximum conservation of sound tooth structure. Also, considering the amalgam as a brittle material, cavo-surface
margin configuration of 90oC provides both the enamel margins and the amalgam restoration with enough bulk at margins to resist the fracturing forces

28. Minimal cavity width and providing bulk of the restoration through a cavity depth at level of mm beyond the DEJ will provide minimal surface area of the restoration exposed to the occlusal loading force with bulk strength through the depth.

29. Flat and smooth pulpal floor parallel to the occlusal plane will help in proper distribution of occlusal forces and provides stability that deletes the wedging action of the restoration upon the tooth structure. Roundation of axial line angles also eliminates stress concentration.

30. Retention form:
Only retention against axial displacement is needed in the form of mechanical undercuts in dentin by converging the cavity walls occlusally about ° from the tooth long axis.

31. Convenience form
In simple Class I cavity design, no need for convenience in as it is easily seen and instrumented.
Only, accentuation of cavity walls, line and
point angles and selection of suitable sized instruments is considered as a satisfactory convenience.

32. 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.
DR.SHATHA AL-RUSHOUD

33. 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.
DR.SHATHA AL-RUSHOUD

34. 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.
DR.SHATHA AL-RUSHOUD

35. II
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.
DR.SHATHA AL-RUSHOUD

36. In case of initial carious lesions, access is obtained by employing a small sized round bur.
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.
DR.SHATHA AL-RUSHOUD

37. 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.
DR.SHATHA AL-RUSHOUD

38. The necessary cavity extensions through pits, fissures, and deep developmental grooves are made using an inverted cone 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.
DR.SHATHA AL-RUSHOUD

39. With the bur seated in the cavity just below the amelo-dential junction ½ -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.
DR.SHATHA AL-RUSHOUD

40. Provision of ample resistance and adequate retention through boxing of the preparation could be obtained.
This is obtained by using a fissure bur held perpendicular to the surface of the tooth. All the line angle in dentin must be squared up hoe excavators.
DR.SHATHA AL-RUSHOUD

41. 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.
DR.SHATHA AL-RUSHOUD

42. 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.
DR.SHATHA AL-RUSHOUD

43. 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.
DR.SHATHA AL-RUSHOUD

44. Class I extension cavity:
Compound or complex Class I cavity design is an extension of the occlusal cavity to buccal or/and lingual surfaces

45. It is indicated in: 1. Deep caries in buccal or / and lingual pits.
2. Deep fissure or groove extended from the occlusal to the lingual or / and buccal surfaces.
3. Fissure crossing the oblique ridge in upper molars.

46. 4. When the remaining oblique ridge in upper molars or transverse ridge in lower premolars is weak (Fig. 4-4, A and B), it is a must to be included in the cavity outline to avoid its fracture.

48. The outline form:
The outline form of compound or complex Class I design is the she same as simple Class I cavity preparation in addition to extension to include the carious or retentive area either buccal or/and lingually.

49. It may be extended with step, forming axial wall and gingival floor, or without step, in
cases showing extended caries or fissure at the level of the pulpal floor.
The formed step will provide inclusion of the carious or retentive area without
endangering the pulp.

50. Resistance form:
The same features of resistance form as simple Class I is performed in addition to: roundation of axio-pulpal line angle to prevent stress concentration and to provide bulk to the restoration at this critical area.

51. The axial wall direction should be parallel to the corresponding external tooth
surface,
i.e. convex, in order to prevent pulp exposure and provide uniform thickness of the restoration.

52. Axial retention in the form of mechanical undercuts in dentin, the same as simple Class I, in addition to occlusal lock against lateral displacement. Extension for retention to the other opposing surface to
provide lateral retention in extensive cavities.

53. Convenience form:
When the cavity design becomes compound or complex Class I preparation no need for extra convenience than that of simple Class I cavity as the extension portion is also easily seen and reached.

54. Finishing of enamel walls
The enamel wall should take the same direction of enamel rods without undermining or weakening with cavo-surface margin of 90°.

55. The mesial and distal walls of the extension will be completely parallel to each other and to the long axis of the tooth,
while the gingival floor of the extension portion will be slightly slanting gingivally to be in the same direction of enamel rods.

56. Designs of Class II cavity preparation
Class II cavity preparation for amalgam restoration mat be:
1. Class II compound or complex cavity with proximal step.
2. Class II compound or complex cavity without proximal step.
3. Class II simple cavity.

57. 1. Class II compound or complex cavity with proximal step:
Compound or complex Class II cavity preparation with step consists of three portions, occlusal, isthmus and proximal portion.
The isthmus portion is defined as the narrowest connection between the occlusal and proximal portions of class II compound or complex cavity.

58. The outline of the isthmus portion should be extended to involve all the carious enamel and dentin and place the cavity margins in area self-cleansable with freeing of the proximal contact area.

59. According to the occlusal anatomy of the tooth, the position and size of the proximal contact area and width of the embrasure, the isthmus outline form may follow one of the following Ingrham’s lines

60. These lines may be straight; in case of small contact area,
uniform; in case of normal sized contact area .
or reverse curve; in case of broad or wide contact area.

61. The reverse curve outline will be followed in the buccal wall more than the lingual as the contact area is much more shifted buccally.
The width of the cavity at isthmus should be narrow bucco-lingually as much as possible, about 1/4 the inter-cuspal distance. The occlusal outline is similar to that of Class I cavity preparation

62. The proximal outline should be extended enough to ensure involvement of all carious enamel and dentin, freeing the proximal surface out of contact lingually, buccally and gingivally and placing the cavity margins in the embrasures to be in area selfcleansable.

63. The axial wall is about 0. 5 – 0
The axial wall is about 0.5 – 0.8-mm away from the DEJ to provide enough bulk of the restoration.
The axial wall should be in a direction parallel to the external proximal tooth surface,
i.e. it will be either straight or convex to provide enough uniform bulk of the restoration and protection of the pulp against traumatic exposure.

64. It is preferable to complete the proximal outline before breaking the marginal ridge and proximal enamel plate (Proximal ditch cut) (Fig. 4-6,
7 and 11, A and B).

66. This will provide: 1. A guide to proximal design.
2. Protection of the proximal surface of the adjacent tooth from rotary instrument.
3. Save time and effort.
4. Reduce heat generation as cutting in enamel produces much more heat generation.

67. 5. Enamel wall in the direction of enamel rods.
6. CSA 90°.
7. Freeing of the contact area with maximum conservation of the tooth structure.

68. Resistance form:
Resistance of isthmus portion is achieved by minimal width of the cavity bucco-lingually about ¼ the inter-cuspal distance.
This will provide decrease in the surface area of restoration subjected to the occlusal stresses.

69. Roundation, beveling or saucerization of the axio-pulpal line angle, to provide removal of sharp axio-pulpal line angle that acts as stress concentration area and increased bulk of restoration at isthmus area

70. Reverse curve in case of wide proximal contact area will provide maximum conservation of the sound tooth structure during freeing of the contact, removal of all undermined enamel and correct cavo-surface configuration of 90°

71. Resistance of proximal portion is achieved by performing cavosurface configuration of 90°.
The gingival floor should be smooth, flat and parallel to the pulpal floor and the occlusal plane.

72. The axial wall should be parallel to the external proximal tooth surface and be at mm away from the DEJ, To provide uniform bulk of the restoration.

73. The buccal and lingual walls should be parallel to the direction of the corresponding surfaces to avoid weakening of cusps.
In general, the proximal portion should be a box form.

74. Retention form: Axial retention features includes,
1) mechanical undercuts by preparing the cavity walls slightly converging occlusally, 2) the inverted truncated cone shape of the proximal portion,
3) proximal axial grooves
4) pin retention in extensive cavities placed in the gingival floor.

75. Retention form: lateral retention features includes
1) dove tail, which is considered as extension for retention in premolars, considered extension for prevention that provides retention also in molars
2) occlusal lock.
3) proximal axial grooves.
4) pin retention in extensive cavities.

76. Proximal axial grooves are cut in the axio-buccal and axio-lingual line angles, in the expense of buccal and lingual walls rather than the axial wall to avoid pulp exposure. They should extend from the gingival floor in occlusal direction up to the level of the pulpal floor.

77. These grooves are wider internally than externally and wider gingivally than occlusally.
They are prepared using small round bur or small tapered fissure bur

78. Convenience form:
Cutting an occlusal cavity is considered as a convenience form as it provides accessibility to the proximal portion.
The axial wall should be parallel to the tooth long axis in occluso-gingival direction to allow instrumentation up to the depth of the proximal portion..

79. Also, accentuation of cavity walls and margins, roundation of line angles and selection of suitable sized instruments are important convenience features

80. 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.
DR.SHATHA AL-RUSHOUD

81. 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.
DR.SHATHA AL-RUSHOUD

82. 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.
DR.SHATHA AL-RUSHOUD

83. 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.
DR.SHATHA AL-RUSHOUD

84. The following technique is used:
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.
DR.SHATHA AL-RUSHOUD

85. Thank You!!!
DR.SHATHA AL-RUSHOUD