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considered a scomplex cavity when three or more surfaces are involved. Compound and complex cavities may include one or both of the proximal surfaces as well as portions of the facial and lingual surfaces. When caries attack the proximal surfaces of posterior teeth, the cavity preparation must also include preparation of the occlusal surfaces. Cavities may be classified according to the location where the carious lesion begins. Caries frequently start in the developmental pits and fissures of the teeth. These areas are deeper than the surrounding tooth substance and are nearly impossible to clean thoroughly, creating ideal conditions for bacterial plaque formation. Locations of pit and fissure caries can be located in any of the following areas: Lingual pits of maxillary incisors Lingual grooves and pits of maxillary molars Occlusal surfaces of posterior teeth Facial grooves and pits of mandibular molars Pits occurring in areas because of irregularities in the formation of enamel Smooth surface cavities can be found on all teeth on the proximal surfaces, and gingival one-third of the facial and lingual surfaces. STEPS IN CAVITY PREPARATION After the dentist decides which tooth or teeth to restore, the anesthesia is administered and the rubber dam placed. If you are well prepared, the steps in the cavity preparation should proceed smoothly without delay, and the patient will be more at ease and confident. Watch closely during the procedure and be ready to irrigate and aspirate as needed, as well as, pass the instruments and material to the doctor when needed. The initial cavity preparation generally is done using the high-speed handpiece and a variety of rotary instruments. Cavity Design The design of the cavity preparation for either a tooth with initial caries or replacement restoration is based on the location of the caries, the amount and extent of the caries, the amount of lost tooth structure, and the restorative material to be used. Some basic principles should be considered when preparing a cavity preparation. The dentist must establish an outline form, which determines the overall shape of the preparation along the cavity margins of the restoration and the tooth surfaces. The outline form is determined by the size and shape of the carious lesion and by the need for a suitable design that will hold a restoration firmly in place. Usually, the dentist is able to visualize the shape of the completed cavity before cutting the preparation by viewing the extent of the caries on the radiograph and examining the tooth and soft tissues. Removal of Remaining Caries Carious dentin not removed during the design of the cavity preparation is removed by using either round burs or spoon excavators. When the dentin has a firm feel with the explorer, removal of the tooth structure should cease, even if stained dentin remains. Finishing the Enamel Walls and Margins The last cutting step in the preparation of the cavity is finishing the enamel walls. This is a process of angling, beveling, and smoothing the walls of the cavity preparation to achieve the best marginal seal possible between the restorative material and tooth structure. The dentist may use burs, diamond stones, or hand-cutting instruments (chisels, hoes, hatchets, and gingival margin trimmers) to complete the walls by removing loose or unsupported enamel to create the strongest possible enamel wall. Cleansing the Cavity The final step in cavity preparation is cleansing the cavity. This includes the removal of accumulated debris, drying the cavity, and final inspection before placing restorative materials. All debris must be removed from the cavity, especially on the margins, because deposits left on them subsequently dissolve, resulting in a leak that invites recurrent caries. Irrigating the cavity preparation with warm water usually removes all debris. Stubborn particles of debris may be removed with a small cotton pellet dampened with water or hydrogen peroxide. Following irrigation and aspiration to remove the debris, the cavity must be dried thoroughly with pressurized air from the 3-way syringe or dry cotton pellets. 4-23


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