General rules of class III., IV. andV. cavity preparations for composite filling

1. General rules of class III., IV. andV. cavity preparations for composite filling For III. years students Juhász Alexander

2. Cavity preparation • Define: as the mechanical alteration of a defective, injured or diseased tooth in order to best receive a restorative material which will reestablish a healthy state for the tooth including esthetic corrections where indicated along with normal form and function.

3. Need for restoration • After destruction from a carious lesion • Replacement or repair of a restoration with a serious defect: improper proximal contact, gingival excess, caries risk margins, poor esthetics • Fracture • Simple restore form or function absent as a result of congenital malformation

4. Objectives of cavity preparation • Remove all defects and give the necessary protection to the pulp • Locate the margins of the restoration as conservatively as possible • Form the cavity so that under the force of mastication the tooth or the restoration or both will not fracture and the restoration will not be displaced • Allow for the esthetic and functional placement of a restorative material

5. The rules • G.W.Black laid down the foundation of cavity preparation • Few modifications formed the basis for most operative cavity preparation procedures because of the new restorative materials, instruments, techniques and the increased knowledge and application of preventive measures for caries and periodontal disease.

6. Composites • In an effort to improve the physical characteristics of unfilled acrylic resins, Bowen developed a polymeric dental restorative material reinforced with silica particles. The introduction of this filled resin material in 1962 became the basis for restaurations that are generally termed composites.

7. Composites • Basicly, composite restorative materials consist of the continuous polymeric or resin matrix in which an inorganic filler is dispersed. This inorganic phase significantly enhances the physical properties of the composite compared to previous tooth-colored materials.

8. Composites • . For a composite to have good mechanical properties a strong bond must exist between the organic resin matrix and inorganic filler. This bond is achieved by coasting the filler particles with a silane coupling agent.

9. Composites • Composites are divided into four types based primarily on the size, amount, and composition of the inorganic filler: • (1) conventional composites, • (2) microfill composites, • (3) hybrid composites, • (4) nanofill composites

10. Conventional composites • Conventional composites generally contain appr. 75 % to 80 % inorganic filler by weight. The average particle size of conventional composites in the 1970s was approximately 8 µm. Because of the relatively large size and extreme hardness of the filler particles, conventional composites typically exhibit a rough surface texture. The resin matrix wears at a faster rate than the filler particles, resulting further in a roughened surface. Conventional composites have a higher amount of initial wear at occlusal contact areas than do the microfill or hybrid types.

11. Microfill composites • In the late 1980s the microfill composites or „polishable composites” were introduced. Instead of containing large filler particles typical of the conventional composites, the microfill composites have colloidal silica particles whose average diameter ranges from 0,02 to 0,04 µm. however, because of the greater surface area per unit volume of these microfine particles, the microfill composites cannot be as heavily filled, an inorganic filler content of approximately 35% to 60% by weight. Because these materials contain considerably less filler than do conventional composite resins, their physical and mechanical characteristics are somewhat inferior.

12. Hybrid composites • In an effort to combine the good physical and mechanical properties characteristic of conventional composites with the smooth surface typical of the microfill composites, the hybrid types of composite were developed. These materials generally have an inorganic filler content of approximately 70% to 80% by weight. The filler is a mixtureof conventional and microfill particles that has a smaller average particle size than that of conventional composites. Because of the relatively high content of inorganic fillers, the physical and mechanical characteristics are similar to those of conventional composites.

13. General consideration for direct composite restoration Cavity preparations for composite materials should be as conservative as possible

14. Acid etch phenomenon • An innovative method of removing the enamel smear layer and obtaining micro-mechanical retention for resin restorations by acid etching the enamel was developed by Buonoconore and reported in 1955. The technique consist of applying a solution of gel of 30% to 50% phosphoric acid to enamel for 30 to 60 seconds, followed by thorough rinsing and drying of the area.

15. Acid etch phenomenon

16. The advantage of the enamel bevel is that the ends of the enamel rods are more eeffectively etched than otherwise occurs when only the sides of the enamel rods are exposed to the acid etchant.

17. Enamel/dentin bonding systems • Low viscosity resins used for the adhesion to enamel and/or dentin are generally referred to as bonding agents.

18. The elements of microretention • Enamel bevelling • Acid etching • Using bond systems

19. Cavity preparation designs • Three designs of cavity preparations for composite restorations may be used, sometimes in combination. • conventional • beveled conventional • modified preparation designs

20. Conventional cavity preparation • In all conventional cavity preparations the „box-like” form, the butt joint marginal configuration and retention grooves and coves in dentin are distinguishing features. These preparation designs were used extensively in the past and may be encountered when restoration replacement is indicated. The primary indication for the conventional cavity preparation in composite restorations is when margins are located on root surface (non-enamel areas).

21. Beveled conventional cavity preparations • are similar to conventional preparations in that the outline form has external, „box-like” walls, but with beveled enamel margins. This preparation design typically is indicated when a composit restoration is being used to replace an existing restoration exhibiting a conventional cavity preparation design with enamel margins. To facilitate better marginal sealing and bonding, all enamel margins are beveled and acid etched. The advantage of the enamel bevel is that the ends of the enamel rods are more eeffectively etched than otherwise occurs when only the sides of the enamel rods are exposed to the acid etchant.

22. Modified cavity preparation • have neither specified cavity wall configuration nor specified pulpal depth, and have enamel margins. The objective is to remove the fault as conservatively as possible and rely on the etched enamel to retain the restoration in the tooth. Modified cavity preparation conserve more tooth structure since retention is obtained by acid etching the surrounding enamel rather than by preparation of groove or cove retention form in dentin.

23. Modified cavity preparation • Modified preparations are not prepared to a uniform dentinal depth, and the marginal design similar to a beveled preparation yet less tooth structure is removed in the internal portions of the preparation. • Modified preparations primarily are indicated for the initial restoration of small, new, cavitated, carious lesions surrounded by enamel and for correcting enamel defects.

24. Inicial clinical procedures • Local anestesia • Preparation of the operating site (scaling and polishing) • Shade selection • Isolation of the operating site (cotton role, rubber dam, gingival retraction cord) • Cavity preparation

26. Class III cavity preparations for composite • Class III cavity preparations, by definition, are located on the proximal surfaces of anterior teeth. • When a proximal surface of an anterior tooth is to be restored and there is a choice between facial or lingual entry into the tooth, the lingual approach is preferable.

27. Lingual entry is preferable

28. Conventional Class III cavity preparation • The primary indication for this type of preparation is for the restoration of root surfaces. • The preparation would be identical to the slot preparation for amalgam. • On root surface the cavosurface margins exhibit a 90-degree cavosurface angle and provide butt joints between the tooth and the composite material. The external walls are prepared perpendicular to the root surface. The axial wall depth will be 0,75 mm into dentin assuming no additional caries excavation is required. • The crown areas of the preparation (where enamel margins are present) are prepared having a beveled marginal configuration.

29. Initial preparation: -extended to sound tooth structure in all direction, while adhering to limited pulpal depth -design to retain the restorative material in the tooth and resist potentional fracture of the tooth or restoration from masticatory forces delivered principally in the long axis of the tooth Final preparation: -excavation any remaining infected carious dentin or old restorative material -protecting the pulp -minimize the chance the fracture -maximize the retention Stages of preparation

30. Initial cavity preparation stage • Outline form: Using a carbide or diamond round bur, prepare the outline form, extending the external walls to sound tooth structure while preparing to a limited depth (pulpally) of 0,75mm. Prepare the external walls perpendicular to the root surface, thus forming a 90-degree cavosurface angle. • Primary retention form: The „box-like design is considered a part of retention form, however, at this stage in cavity preparation the external walls may be retentive due to opposing wall parallelism or slight undercuts. • Convenience form: facial or lingual approach.

31. Final cavity preparation stage • Removal of remaining infected dentine or old restorative material: Remove all infected dentine using round burs at low speed or small spoon excavators, or both. • Pulp protection: Apply calcium hydroxide liner or base, if indicated. • Secondary retention form: Groove retention must be used in root surface. Prepare a continuous retention groove in the internal portion of the external walls using a little round, stainless steel bur at low speed. The groove is prepared to a depth of 0,25 mm. • Final procedures: cleaning, inspecting.

32. Conventional Class III prep

33. Beveled conventional Class III cavity preparation • This is indicated primarily for replacing an existing defective restoration in the crown portion of the tooth. It may also be used when restoring a large carious lesion where the need for increased retention form is anticipated. The beveled conventional preparation is characterized by external walls that are perpendicular to the enamel surface, and the margin is beveled. The axial line angles may or may not be of uniform pulpal depth. • If part of the tooth to be restored is located on the root surface, a conventional cavosurface configuration should be used in this area.

34. Beveled conventional Class III cavity preparations • are prepared as conventional preparations with the incorporation of a cavosurface bevel of the enamel rather than a butt joint margin. The cavosurface bevel is best prepared with a coarse, flame-shaped diamond instrument, oriented approximately 45 degrees to the external tooth surface. A bevel width of 0,25 to 0,5 mm is considered sufficient unless the operator elects to increase the retention form by preparing a wider bevel which will increase the surface area to be etched and therefore the retention form. All accessible enamel margins usually are beveled, with the exeption of the gingival margin.

35. Bevelled conventional cavity preparation Class III.

36. Modified Class III cavity preparation • A modified Class III cavity preparation is indicated for a small- to-moderate size lesion or fault and is designed to be as conservative as possible. No effort is made to produce cavity walls that have specific shapes or forms. Usually no groove or cove retention form is indicated. Retention is obtained solely by acid etching all of the prepared enamel. Usually the axial wall not be uniform in depth.

37. Modified cavity preparation Class III.

39. Class IV preparations for composite • To restore fractured, defective, or cariously involved anterior teeth when the incisal edgeis involved.

40. Indications • The conventional cavity preparation design has no clinical application except in those areas of a Class IV restoration that have margins located on root surfaces. The beveled conventional cavity preparation is usually indicated for large ClassIV areas, while the modified cavity preparation is indicated for smaller Class IV needs. If a large amount of tooth structure is missing, groove retention form may be indicated even when the preparation periphery is entirely in enamel. Also, to provide additional retention in these high stess areas, the enamel bevels may be increased in width to provide greater surface area for etching, resulting in a stronger bond between the composite and the tooth.

41. Beveled conventional Class IV cavity preparation • Is indicated for restoring large proximal areas which also involve the incisal surface of an anterior tooth. In addition to the etched enamel margin retention may be obtained by groove or other shaped undercuts, dovetail extensions, threaded pins, or a combination of these.

42. Conventional beveled cavity preparational designs

43. Large Class IV beveled conv.prep.d.

44. Combination preparational design

45. Modified preparational designs

46. Factors affecting cavity preparation • Diagnosis- the reason to place the restoration caries, fracture…. • Esthetic considerations- extension, design, choice the restorative material • Risk potential- high risk patient need cheaper care • Patient’s age- elder need shorter, less stressful appointment • The less tooth structure removed the less potential damage that may occur to the pulp: minimal extensions, supragingival margins, rounded internal line angles

47. Class V cavities • On the gingival third of the facial or lingual surfaces of all teeth • Usually develops because the affected surface is unclean and the patient has a caries inducing diet • Incipient smooth surface enamel caries appears as a milky white line just occlusal or incisal crest of the marginal gingiva usually on the facial surface

48. Indications, contraindications • Class V restorations are difficult because of the limited access and visibility • Caries • Erosion, abrasion • Sensitive areas • Service • Economics • Esthetics • Abutment teeth for removable partial dentures

49. Steps of cavity preparation • Local anaesthesia-pain control, reduce salivation • Isolation –prevents moisture contamination ( saliva, gingival sulcular fluid, gingival hemorrhage), improves asepsis, provides access and visibility. Isolation by cotton rolls and retraction cord or rubber dam and suitable cervical retainer.

50. Cavity preparation • Extending the external walls to sound structure • Limited depth pulpally 0.5mm from dentinoenamel junction, 0.75mm from the cementum • The outline form is primary determined by the location and size of the carious area