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COMPLEX CASES

Restoration of complex cases changes tooth color, position or shape.  Treatment options include adding composite or tooth reduction. There are two major limitations to treatment results.  First, tooth structure which emerges from the gingiva can not be moved laterally, forward or back.  Second, tooth reduction must leave enough supporting structure to support a restoration and resist force.

Projected tooth position, shape and color is visualized in the mind, by wax ups on models or intraoral composite build up.  Analysis of existing tooth position, color and shape are compared to projected tooth position, color and shape and treatment planning is done.

Composite veneering, diastema closure, tooth rotation, tooth tipping, restoration of lost tooth structure and changing tooth dimensions are the most common techniques used to change tooth color, position or shape.  Addition of composite to tooth structure increases tooth size and therefore, can require tooth reduction to make room for composite placement.  Tooth structure that is outside of the projected tooth position is reduced.  The amount of tooth reduction is determined by original tooth position in relation to the desired position, color of tooth structure and thickness of composite materials required to block out tooth color, quality of remaining tooth structure and remaining restorations.

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 is lateral, rotational, downward, and pulling upward resulting in tensile, shear and compressive failure.  Preparation design, material selection and placement technique are critical resist force and therefore, success.

Caries removal and extension of tooth dimensions interproximally or incisally produces areas of restoration with no tooth backing. These restorations 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 darkness or a restoration appears darker.  Placement of opaque material or dentin shades covered with translucent material achieves natural looking restorations that are not influenced by this darkness.

Caries and weak tooth structure are removed.  Diamond burs reduce and shape remaining tooth structure to accept a restoration leaving a rough surface for improved bond strengths..   

Bonding to enamel and dentin provides strength to hold composite onto tooth structure, minimizes microleakage and reduces sensitivity.  Removal of caries often creates areas of mechanical locks 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 color for better color transition.  Blending composite color to tooth color is further achieved by proper composite selection, placement and preparation design.  A translucent outer layer of composite provides a chameleon effect showing through tooth color.

Enamel and dentin bonding is done to maximize interface strength.  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 such that 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.  Dentin bonding areas are light cured prior to composite placement to stabilize collagen fibers.  

Bonding resin is applied in a thin layer achieved by placing a small amount with a brush or blowing excess away.  Bonding resin does not require light curing prior to composite placement.  Not precuring a bonding agent allows easier surface wetting by composite.  

Composite restores class 3, class 4 and diastema areas first.  If required, a sublayer of composite and/or opaquer is used to block out improper tooth color.  Composite is rolled into a ball.  The ball is placed on the facial surface resulting in a point contact  When the ball is pressed with a finger, it spreads and contacts tooth structure without trapping air.  Shaping with instruments using a tapping motion minimizes sticking of the instrument to composite.  Composite is shaped as close to final contours as possible and light cured. 

Shaping and polishing is done with burs, sandpaper disks, rubber wheels, points, cups, and polishing pastes.  Composite shaping, contouring and texturing require different techniques depending on the desired result.  (See the section on contouring, shaping and texturing of this website)

 

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COMPOSITE TECHNIQUE    SMILE DESIGN     COMPANIES/MATERIALS    MATERIAL SCIENCE