J Indian Prosthodont Soc. 2013 Dec.
The success of the dental restorations largely depends on its esthetics, although various literature reviews recommend that anterior teeth midline be placed coinciding the facial midline, the amount of acceptable deviation between facial and dental midline has not been fully investigated. To observe the acceptable deviation between the dental and facial midline. Facial photographs of 200 students aged about 18–30 years of both sexes, without any missing teeth, with complete alignment of anterior teeth, were selected and scanned on to computer screen. Using specialized programme, the crown width of the central incisor in the mouth and on photograph was ensured constant. The distance between the facial midline, (obtained by bisecting intercanthal line) and the mesial surfaces of the central incisors were read on the computer. 44.4 % Boys and 55 % of Girls showed deviation between dental and facial midline in the range of 0–1 mm. while, 54 % of boys and 33 % of girls showed deviation of the dental and facial midline in the range 1–2 mm. 37 % of boys and 8 % of girls showed deviation of dental midline with facial midline with the range of 2–3 mm. 80 % of the study population showed maxillary and mandibular dental midlines never coincide. Majority of the study population showed deviation between facial midline and anterior teeth midline within the range of 0–1 mm.
The term “Esthetic” is used to connote that some thing seen is pleasant. Over the centuries as artists have developed the management of esthetic process into principles of visual perception, they have enabled to create scenes of intense vitality, beauty, depth and realism all on a 2D canvas . As dental restorations are subjected to the same perceptual process, understanding of perceptual principle can eliminate confusion in achieving the realm of esthetics and maintaining esthetic harmony [1, 2]. Dentist who understands the principles of visual perception can fabricate the restoration with confidence to meet, the esthetic demands subtly and wisely without violating the principles of reality [3, 4].
The study of the relationships existing between different objects is made visible by the contrast in color, line and texture. This is called Composition . The ordering of, a part of composition to give the individual total effect of the “whole” is called Unity. Unity exists in two types: Static unity and dynamic unity. The regular geometric shapes, such as snowflakes and crystals, exhibit static unity . Plants and animals exhibit dynamic unity. Repetitions of shape, color and line are cohesive forces . Success of a dentist lies in making use of these static cohesive forces to fabricate prosthesis, to suit a living dynamic human being . Consider an instance, where anterior teeth placement is done on the unchanging curve of a circle . The resulting denture gives a dull dead appearance, immediately noticeable in a living dynamic mouth as something abnormal . The objective of a dentist is to provide dynamic and not static unity. Dentogenic factor helps us in achieving this [6–8].
The term “Dentogenic” means, the art, practice and techniques used to achieve esthetic goals in dentistry [8, 9]. Lombardi noted that proper location of the dental midline was necessary for stability of the dental composition as improper placement of the midline would produce tension that make the viewer feel that the line must move to its proper place to produce stability & permanence [3, 5]. Various complete denture textbooks [3, 7, 9, 10] recommend that the mesial surfaces of maxillary central incisors be in contact with the imaginary vertical line that bisects the face. Anatomical landmarks like, incisive papilla, labial frenum, tubercle of upper lip have been used to estimate the position of the central incisor for complete denture prostheses. Using tubercle of the upper lip as the midline of the face, Latta [11, 12] found that in 70 % of 100 patients the average distances of the mid-palatal suture, nasopalatine papilla and labial frenum were less than 1 mm from the midline and the range may vary as much as 5.5 mm. Tjan  suggested that, an imaginary line dividing the middle lobe of the upper lip could be used to establish the facial midline, as it is closer to the mouth compared to other landmarks. Miller  suggested that center of the philtrum should be considered as the most reliable guide to the facial midline.
Because no human face is symmetrical, there can be no hard and fast rule for determining the facial midline . The artistic judgment of the individual clinician therefore must be used. Since the amount of deviation of the anterior tooth midline from the facial midline that is noticeable to a viewer is unknown, the purpose of this investigation was to determine the observable deviation between the anterior tooth and facial midlines in a limited sample of dentate subjects confining to a specific area and age group.
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