The Dental cosmos . anical operation. The second requires an accurate knowledge THE MANAGEMENT OF ENAMEL MARGINS. 355 of the cause of caries, and of the conditions under which that causebecomes active ; coupled with close insight into conditions favorableor unfavorable, present and prospective. It is only in recent yearsthat we have known the cause of caries of the teeth ; and therefore itis only now, we might almost say, that we are beginning to be able toapply effectively this knowledge to the prevention of recurrence ofcaries about our fillings. It is through this line of study and practice
The Dental cosmos . anical operation. The second requires an accurate knowledge THE MANAGEMENT OF ENAMEL MARGINS. 355 of the cause of caries, and of the conditions under which that causebecomes active ; coupled with close insight into conditions favorableor unfavorable, present and prospective. It is only in recent yearsthat we have known the cause of caries of the teeth ; and therefore itis only now, we might almost say, that we are beginning to be able toapply effectively this knowledge to the prevention of recurrence ofcaries about our fillings. It is through this line of study and practicethat the best progress of the immediate future is promised. Large may now turn our attention to the lines best suited for enamelmargins in large cavities in the upper incisors. In these the initialpenetration has been ordinarily near the labio-lingual center of theproximate surface and near the junction of the incisive and middlethird, the particular point varying with the position of the proxi- Fig. Lingual surfaces of the central incisors, a, and b, b, lingual grooves; c, c, distal marginalridges; h, mesial marginal ridges; d, d, lingual ridges; e, e, e, linguo-gingival grooves;/, f,central division of linguo-gingival grooves. In each there is a cavity with margins cut nearlyto the lingual grooves. The line of the margins should be on the line of the grooves. mate contact, which is much closer to the cutting-edge in bell-crowned teeth than in those with thick necks. The spread of cariesin the dentine has usually been primarily in the middle third of thelength of the crown, and with a much greater tendency toward the gin-gival than toward the occlusive portion of the tooth. Therefore manycases are found in which the dentine of the middle third of the tooth hasbeen destroyed to a considerable depth with extension to the lingual andlabial surfaces, while sufficient dentine still remains in the incisive thirdto support the angle of the tooth. In these cases it is
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