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①Class I: lesions occur in pits and fissures on the facial, lingual, and occlusal surfaces of molars and premolars, and, less often, the lingual surfaces of maxillary anterior teeth (most frequently lateral incisors, less frequently central incisors, rarely canines).②Class II: lesions occur on the proximal surfaces of the posterior teeth (molars and premolars). If a proximal surface of a posterior tooth is involved in a restoration, it is a Class II restoration③Class III: lesions occur on the proximal surfaces of anterior teeth (central and lateral incisors and canines). Class III cavities do not involve an incisal angle.④Class IV: lesions occur on the proximal surfaces of anterior teeth when the incisal angle requires restoration. The angle may have to be removed because of its fragility or for proper placement of the restoration, or it may have been fractured by trauma. ⑤Class V: lesions occur on smooth facial and lingual surfaces in the gingival third of teeth. This class begin close to the gingiva and may involve a cementum or dentinal surface as well as the enamel⑥Class VI: lesions are pit or wear defects on the incisal edges of anterior teeth or the cusp tips of posterior teeth
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outline the mechanisms of plaque formation.The attachment , growth , removal and reattachment of bacteria to the tooth surface is a continuous and dynamic process. However, several distinct processes can be recognized.Absorption of salivary proteins and glycoproteins, together with some bacterial molecules, to the tooth surface to form a conditioning film(the acquired pellicle).Long-range(>E0nm), non-specific interaction of microbial cell surfaces with the acquired pellicle via van der Waals attractive forces.Shorter-range(A0-B0nm) interactions, in with the interplay of van der Waals attraction forces and electrostatic repulsion produces a weak area of attraction that can result in reversible to the surface.Irreversible adhesion can occur if specific inter-molecular interactions take place between adhesions on the cell surface and receptors in the acquired pellicle.Secondary or late-colonisers attach to primary colonizers (coaggregation), also by specific inter-molecular interactions.Cell division of the attached cells to produce confluent growth, and a biofilm.
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