COMPOSITE TECHNIQUE SMILE DESIGN COMPANIES/MATERIALS MATERIAL SCIENCE
Composites are indicated for Class 1, class 2 and class 5 defects on premolars and molars. Ideally, an isthmus width of less than one third the intercuspal distance is required. This requirement is balanced against forces created on remaining tooth structure and composite material. Forces are analyzed by direction, frequency, duration and intensity. High force occurs with low angle cases, in molar areas, with strong muscles, point contacts and parafunctional forces such as grinding and biting finger nails.
Composite
is strongest in compressive strength and weakest in shear, tensile and modulus
of elasticity strengths. Controlling forces by preparation design and
occlusial contacts can be critical to restorative success. Failure of a
restoration occurs if composite fractures, tooth fractures, composite debonds
from tooth structure or microleakage and subsequent caries occurs. A
common area of failure is direct point contact by sharp opposing cusps.
Enamelplasty that creates a three point contact in fossa or flat contacts is
often indicated.
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In the case above, large interproximal defects require contoured bands to produce convex surfaces for ideal contacts. Occlusial forces on marginal ridges would cause fracture so contact is minimal and dispersed to avoid fracture.
Tooth preparation requires adequate access to remove caries, removal of caries, elimination of weak tooth structure that could fracture, beveling of enamel to maximize enamel bond strength, and extension into defective areas such as stained grooves and decalcified areas. Matrix systems are placed to contain materials within the tooth and form proper interproximal contours and contacts. Selection of a matrix system should vary depending on the situation (see web pages contacts and contours in this section).
Enamel and dentin bonding is completed. Composite shrinks when cured so large areas must be layered to minimize negative forces. Generally, any area thicker than two millimeters requires layering. In addition, cavity preparation produces multiple wall defects. Composite curing when touching multiple walls creates dramatic stress and should be avoided.
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Above a small occlusial lesion and a small interproximal lesion are restored on a first bicuspid. Access is gained to the interproximal area through the distal marginal ridge using a small rounded bur such as a 330 or diamond bur. Extension through the central groove eliminates the defective groove and occlusial caries. A tofflemire band is placed and tightened to adapt to tooth structure shape. Tooth structure is acid etched with the band in place and bonding accomplished. The matrix confines materials within the prepared tooth structure. A gingival layer of composite is placed and light cured. A final occlusial layer is placed and light cured.
The matrix is removed but the wedge is left in place to keep slight separation for finishing. A marginal ridge occlusial embrasure is formed with a sandpaper disk or flame shaped finishing bur. The occlusial is shaped with a rounded bur such as a 245 from the facial. The bur is placed into the mesial pit area and moved distally while be sure the bur does not cross the central groove. Remaining tooth structure show proper inclination and contours. The bur stops at the distal pit and the process is repeated from the lingual approach. The bur is placed into the distal pit again, however, it is approaching from the distal. It is moved lingual and facial to form the inside of the marginal ridge. Refinement of the grooves and pit areas are done with a shape ended bur such as a flame shaped finishing bur. The surface is then polished with rubber points, cups, wheels and polishing pastes.
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In the case above, the first and second molars have defective amalgam restorations, interproximal caries and cracking of the marginal ridges. A wood wedge is placed in the mesial interproximal to protect the rubber dam. A matrix band is placed in the distal interproximal to utilize a sliding band technique (see section of the website on contacts). The first molar has a defective amalgam, caries and a distal marginal ridge crack removed. The second molar has a defective amalgam, caries and cracked mesial and distal marginal ridges removed.
Preparation of the first molar results in a large mesial box and loss of existing contact. The distal box requires crack removal and no extension to the buccal and lingual that would result in significant tooth loss. To establish proper contours and contact area on the mesial a precontoured, unilateral matrix is placed with a wooden wedge and matrix holder. The holder and wooden wedge combine to separate teeth to compensate for the width of a matrix when it is removed. The wooden wedge is place with little force initially so the matrix shape is not distorted but still held firmly. Tooth separation is not done at this stage except for force form the matrix holder. A first layer of composite is placed on the gingival floor and light cured after bonding procedures. The wooden wedge is now progressively pushed to cause tooth separation. The matrix shape does not distort because the first layer of composite holds the shape.
The distal marginal ridge is matrixed by the sliding band technique. The band is placed prior to preparation and moved in a buccal or lingual direction as damage occurs from the bur. If a matrix is not placed prior to tooth preparation, matrix placement is difficult or impossible without tooth separation. Matrix holders or wooden wedges are necessary only when the preparation becomes large enough to extend past the buccal, lingual or gingival aspects of the contact. Final layers of composite are placed and shaped with composite instruments and light cured. Matrix bands are removed and finishing accomplished.
A marginal ridge occlusial embrasure is formed with a sandpaper disk or flame shaped finishing bur. The occlusial is shaped with a rounded bur such as a 245 from the facial. The bur is placed into the mesial pit area and moved distally while be sure the bur does not cross the central groove. Remaining tooth structure show proper inclination and contours. The bur stops at the distal pit and the process is repeated from the lingual approach. The bur is placed into the distal pit again, however, it is approaching from the distal. It is moved lingual and facial to form the inside of the marginal ridge. Refinement of the grooves and pit areas are done with a shape ended bur such as a flame shaped finishing bur. The surface is then polished with rubber points, cups, wheels and polishing pastes. A surface resin sealer is placed and light cured to seal cracks created from finishing.
