Z250 composite

Blocks approximately 10 × 2 mm with the enamel at least 500-μm thick were prepared from bovine incisors. Composite discs at least a mm thick were prepared from Z250 composite (3M, Minneapolis, MN) by sectioning a block of the cured composite. Layers between 400–800 μm thick of GrenGloo™ (Ormco, Orange, CA) composite were applied to the bovine blocks as shown in Figure 1 for the composite removal samples. The Ortho Solo™ (Ormco) adhesive, and 37% phosphoric acid etchant were used according to the manufacturer’s instructions. Grengloo™ composite changes color and appears green below body temperature. This helps to identify any residual composite missed by the laser. It also has similar composition to other standard composites such as Z250.

Extracted molars and premolars that contained composite were collected (CHR approved) from oral surgeons in the San Francisco area (n=9) and sterilized with gamma radiation. Criteria for selection included size and visibility of composite, and amount of decay near the composite.
In addition to collecting extracted teeth with composite restorations, sound teeth were selected and placed together in mounting stone to simulate interproximal contacts. The selected teeth in groups of two (n=7) were arranged by position (upper or lower jaw, distal or mesial, left or right side) and orientation (lingual-buccal) and mounted together as they would be positioned in the mouth. Class II preparations were then drilled on one of the teeth for each set of two teeth using high-speed dental burrs and filled with Z250 composite (3M, Minneapolis, MN). All samples were then stored in a moist environment of 0.1% thymol to maintain tissue hydration and prevent bacterial growth. In Figure 1, depth composition 2-D images taken with a Keyence VHX-1000 digital microscope are shown for two teeth with composite restorations. The top image shown has stain in the pit and fissures but since histology was not performed for this study we cannot determine whether the tooth is carious.