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DIRECT CLASS IV COMPOSITE RESTORATION

TYPES OF COMPOSITE RESINS

BEVELED CONVENTIONAL CLASS IV PREPARATION

Class IV restoration is usually required when an accident or extensive caries destroys or severely weakens the incisal angle

Initial Clinical Procedures

Disadvantages of Composites 1. Gap formation on margins may occur, usually on root surfaces. This occurs because the force of polymerization shrinkage is greater than the initial bond strength of composite to dentin.

2. More difficult, time consuming and costlier than amalgam.

3. More technique sensitive. 4. Greater occlusal wear in areas of high occlusal stress.

  • Same sequence of initial clinical procedures is followed, as done for class III restorations
  • Preoperative assessment of occlusion is more important for class IV restorations.

MODIFIED (CONSERVATIVE) CLASS IV PREPARATION

BONDING GENERATIONS

First Generation Dentin Bonding Agents-Bonding was pitifully low, hence was useful only for class III and class IV cavities.

Second Generation Dentin Bonding Agents -These products attempted to use the smear layer as a bonding substrate. The smear layer because of its comparatively loose attachment to dentin surface was the weakest link in this system.

Third Generation Dentin Bonding Agents

Fourth Generation Dentin Bonding Agents-The high bond strength to dentin (17 to 25 MPa) and decreased postoperative sensitivity in posterior occlusal restorations, encouraged the switchover from amalgam to direct posterior composite fillings.

Fifth Generation Dentin Bonding Agents-These combine the priming and bonding steps but etching is performed separately

Sixth Generation Dentin Bonding Agents-Since 2000 these single bottle adhesives are available which combine etching, priming and bonding in a single solution and as a single step. Etching as a separate step is eliminated.

Seventh Generation Dentin Bonding Agents-Both the sixth and seventh generation adhesives are self-etching, self-priming adhesives which are minimum technique sensitive

Eighth Generation In this there is stable nanofiller that will not settle out of dispersion. It is suitable for direct and indirect restorations

Tooth Preparation Conventional Class IV Preparation

Composite resin can be divided into three types based on the size, amount and composition of the inorganic filler:

  • Conventional composite resins - Average particle size of conventional composite resins is 8 microns (from 5-25 micron) approximately. The surface becomes more rough as the resin matrix being less hard wears at faster rate.
  • Microfilled resins- Average particle size of microfilled resins ranges from 0.01 to 0.04 microns. This small particle size in place of large size as present in conventional composites results in smooth polished surface which is plaque, debris and stain resistant
  • Hybrid composite resins- In order to combine the advantages of conventional and microfilled composites hybrid composites have been developed. The average inorganic particle size is 0.4 to 1 micron
  • Flowable composites-As the name indicates, their consistency is such that they can be flowed into the deep pit and fissure
  • Packable condensable composites-To improve the compressive, tensile and edge strength and handling, condensable composites have been developed.

Contraindications of Composites Composite restorations are contraindicated in the following conditions:

1. When operating field cannot be maintained dry.

2. Where very high occlusal forces are present (especially in case of class I, class II and class VI)

3. Some class V restorations that are not esthetically critical.

4. When proper technic cannot be applied.

5. The restorations that extend up to the root surface.

6. Invisible, very small lesions on distal surface of canines where metallic restoration is treatment of choice.

7. Patients with high caries susceptibility and poorly controlled caries activity.

Advantages of Composites

1. Maximum conservation of tooth structure is possible.

2. Esthetically acceptable.

3. Less complex cavity preparation is required.

4. Insulative, have low thermal conductivity hence no insulation base is required.

5. Restorations are bonded with enamel and dentin hence have good retention.

6. Can be finished immediately after curing.

7. It is reparable.

8. Has low microleakage.

9. Can be used almost universally.

  • A beveled conventional class IV preparation used to restore large areas may require grooves, undercuts, dovetail, threaded pins or any combination for additional retention.
  • One or two TMS threaded pins can be placed in the gingival wall. The walls should be parallel and perpendicular to the long axis of tooth.
  • The initial axial wall depth is established at 0.5 mm pulpally to DEJ.
  • Bevels are prepared at 45 degree angle to tooth surface with a width of 0.25 to 2 mm, depending on the amount of retention required.
  • Retentive grooves are made in the same way as in class III beveled conventional preparation.
  • The instruments used for cavity preparation are almost same.

Advantages of condensable composites over the conventional composites are as follows:

A. Increased wear resistance: Wear resistance is directly proportional to the amount of ceramic fibers present.

B. Deeper depth of cure : Due to light conducting property of the individual ceramic fibers depth of cure is more.

C. Increased flexural modulus due to presence of more ceramic fibers per unit area : Flexural modulus is directly proportional to number of the ceramic fibers present.

D. Decreased polymerization shrinkage: Polymerization shrinkage is indirectly proportional to the number of ceramic fibers present. E. Reduced stickiness: Stickiness is indirectly proportional to the number of ceramic fibers present

Acid Etch Technique

  • It is prepared, keeping in mind the same objectives as those applied for modified class III preparation.
  • Usually, little or no initial tooth preparation is indicated for fractured incisal corners, other than roughing the fractured tooth structure.

  • A beveled conventional preparation is indicated for a large class IV lesion, while the modified preparation is done in small class IV cavity or traumatic defect.
  • However, the preparation in high stress area is more of a conventional type

RESTORATIVE TECHNIQUE

  • Phosphoric acid or citric acid (32 to 37% w/w concentration) is used for acid etching.
  • Acid etching of the dentin results in removal of the smear layer and opening the dentinal tubules. It increases surface area of dentin and of enamel by exposing crystalline structure.
  • Application of the acid is repeated to keep the area moist for 15 to 30 seconds. The area is then rinsed with water for 5 to 10 seconds
  • Etching, priming and adhesive placement
  • Matrix placement
  • I n s e r t i n g , c u r i n g a n d c o n t o u r i n g : After matrix placement, etching and adhesive placement, the composite is inserted into the cavity using hand instrument or syringe (gun).
  • F i n al c o n t o u r i n g a n d p oli s h i n g o f t h e c o m p o s i t e
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