CLASS 4                                 

       COMPOSITE RESTORATIONS

A class 4 restoration restores incisal tooth structure on anterior teeth.  Incisal tooth structure is lost from caries, trauma or wear.  Small incisal chips are left alone, esthetically recontoured  or restored with composite based on esthetic evaluation.   Esthetic recontouring reshapes enamel with burs or sandpaper disks to improve appearance.  Large defects that exposed dentin should be restored to avoid pulpal trauma and excessive dentin wear.

A composite restoration of incisal tooth structure receives direct force.  Failure occurs from intracomposite fracture, separation of bonded interfaces or fracture of supporting tooth structure.  Force intensity, duration, frequency and direction verses restoration strength determines success or failure of a restoration.  Direction of forces are lateral, rotational, downward, and pulling upward resulting in tensile, shear and compressive failure.  Preparation design, material selection and placement technique are critical to success.

Class 4 restorations have no tooth backing so they show the back of the mouth when viewed from the facial.  The back of the mouth is a dark area because it receives no light.  Composite must block out this darkness or a restoration appears darker.  The more translucent a material the more darkness shows through.  Placement of opaque or dentin composite covered with translucent composite achieves a natural looking restoration that is not influenced by this darkness.  Blending composite color to tooth color is further achieved by proper composite selection, placement and preparation design.  

Bonding to enamel and dentin provides strength to hold composite onto tooth structure, minimize microleakage and sensitivity.  Removal of caries often creates areas of mechanical locking that aids retention.  Strength of enamel bonding is increased by beveling across enamel rods.  A longer bevel or chamfer preparation creates more surface area for strength and provides a long gradual show through of tooth structure for better color transition.  A translucent outer layer of composite provides a chameleon effect picking up and showing through surrounding tooth color. 

Caries and weak tooth structure is removed.  Bevels are created on the facial surface.  Lingual and incisal bevels are avoided as direct force breaks thin composite or thin tooth structure.  Extension of a restoration to lingual tooth structure is used if mechanical retention to resist lingual force is required.  Enamel and dentin bonding is done to maximize interface strength and seal dentin tubules.  Acid is placed on enamel for 15 to 30 seconds.  Acidity is neutralized so only 10 microns of enamel is removed.  Inorganic structure dissolves quicker than organic structure and a porous, honeycomb surface is created.  Acid is placed on dentin for 10 to 15 seconds to remove the smear layer created by debris from tooth preparation.  Long exposure to acid removes collagen fibers and leaves a bare dentin surface.

A lingual wall of dentin or opaque composite is created to block darkness from the back of the mouth.  Translucent or enamel composite is placed on the facial surface providing the translucent effect seen on natural teeth. Incisal composite or tints provide final detail as required by the restorative situation.  Finishing burs, polishing points, cup and wheels, sandpaper disks, sandpaper or diamond strips, and polishing pastes are used for final surface shaping, contouring and texturing.

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