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An important part in the evaluation of dental aesthetics for digital smile design is the selection of tooth shapes based on patients' facial characteristics. For patients with a square face, a tooth with an 80% width-to-length ratio would be more appropriate, the acceptable interval for this relation being evaluated to 70 - 85% [6]. The dimensional relationship for different teeth, or the corellation between teeth and the dental arch form involves the golden proportion. A useful rule guiding proportion is 1-2-3-4-5: the lateral is 2/3 of the central and the canine 4/5 of the lateral. Finally, contact inter-proximal areas can be moved restoratively up to the root of the adjacent teeth. Digital Smile Design is dedicated to the full face photographs of the patients; this allows the clinician to plan the restorations only in two dimensions. A set of profile photos that include the virtual placement for the future occlusion plane of the prosthetic restoration is not usually part of the common aesthetic analysis, but can be relevant in the evaluation of the prosthetic rehabilitations' functionality. A three dimensional preview can be a very useful instrument for clinicians in order to obtain aesthetic and functional prosthetic dental rehabilitations. Methods & Materials Ten elderly patients were selected for this study. An extra- and intra-oral set of photographs, from different angles, is performed for each patient, using a standard camera "Fujifilm Finepix S7000", with a fixed focal length lens and manual focus setting. Four additional artificial light sources, a tripod and a retractor for soft perioral tissues were used. From our experience, the necessary number of photos in this system is of 20-60. The photographs were taken by continuously moving the camera around the subject from a distance of 1.2 m. We performed three shooting sessions, each of 20 photos (exposure time: 1/25, manual focus setting, ISO 200, fixed focal length 47 mm, from an approximately 35° angle between the incidences, on two transversal planes: one at the mention level and the other on the bipupilar line). In order to obtain a correct stitch of the photos, we marked various anatomic points: menton, subnasion, glabella, trichion, gonion, zygion, labial commissures, external angle of the eye, earlobe, back of the neck. The aim was to obtain three-dimensional personalized models of the head and neck, in different circumstances (mouth closed and light lip contact; dental arches slightly apart and a light smile; dental arches slightly apart and a retractor for perioral soft tissues). As an example, for B.V., female, 72 years old, we applied the method introduced by Dr. Christian Coachman, using the photos taken in the frontal perspective, in order to obtain an adequate D.S.D. (Digital Smile Design), as shown in Fig. 1. These processed photographs were stitched to the other 19 photos, derived from eccentric perspectives, in order to obtain a tridimensional personalized model of the head and neck, using available software packages such as "Autodesk 123D Catch" (Fig. 2). Fig. 1. D.S.D. offers an aesthetic and functional 2D preview of the final prosthetic rehabilitation Fig. 2. The recordings are collected and processed with "Autodesk 123D Catch" Software and thus 3D personalized models of the head and neck are obtained. Results The captures derived from lateral perspectives, belonging to the tridimensional personalized models, were processed to obtain the aesthetic preview of the final restoration, taking into account some specific details: the occlusal plane parallel to Camper's plane, the concavity of Spee occlusal curve, the relation between the width and the height of the teeth, dental and facial harmony. Fig. 3. An aesthetic and functional preview of the prosthetic rehabilitation is obtained from frontal and lateral perspectives - selected from the 3D personalized models of the head. Conclusions A relevant preview in prosthetic rehabilitations for elderly patients can be obtained using tridimensional computerized personalized models, which offer better possibilities compared to the bi-dimensional planning. The 3D aesthetic preview can be considered a useful and valuable instrument in the complex process of obtaining a correct aesthetic diagnosis and treatment; it also offers elderly patients better circumstances to assess the final aesthetic results of the suggested prosthetic rehabilitations. The current limitations of the presented method consist in partial discontinuity between different processed frames selected from the 3D personalized models. Bibliography
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