Evaluating upper lip changes during smiling and at rest in Indian population.

CONTEXT: Smile aesthetics is one of the major goals to be achieved after orthodontic mechanotherapy as it visibly displays the results of orthodontic treatment. Although orthodontic retainers aid in maintaining post-treatment occlusion, soft tissue function and aesthetics, appropriate knowledge of smile changes with age can help orthodontists to obtain stable and aesthetically appealing treatment results. AIM: To assess and quantify soft tissue changes in the upper lip in vertical dimension at both repose and maximum smiling and to evaluate changes occurring with the smile index and upper lip with age and sex in subjects of Indian origin. SETTINGS: Department of Orthodontics and Dentofacial Orthopaedics, Army College of Dental Sciences, Secunderabad, Telangana, India. DESIGN: Observational study. METHODS AND MATERIALS: A total of 160 volunteers (80 males and 80 females) selected and were divided into 4 groups according to age and were further divided into 2 sub-groups according to gender. Thirteen measurements of relaxed and smiling upper lip were taken with a calibrated metal ruler and divider directly on the subjects. STATISTICAL ANALYSIS USED: Analysis of variance (ANOVA) was done followed by post hoc test to determine which groups were significant from others. Levene's test was done to assess equality of variance and t-test for equality of means was done. RESULTS: Statistically significant results were obtained in between groups and sub-groups for parameters like smile index, upper lip elevation while smiling and smile pattern in males and females changing with increase in age. CONCLUSIONS: High smile patterns with more vertical smile are more common among females and low smile patterns are more common among males. With age, the smile tends to be more horizontal in both genders.

Stress distribution patterns in mini-implant and bone in the infra-zygomatic crest region at different angulations: A finite element study.

PURPOSE: To evaluate, using the finite element method (FEM), von Mises stress patterns produced both in a mini-implant (MI) and the infra-zygomatic crest region (IZC) at different placement angles and force magnitudes. MATERIAL AND METHODS: FEM modeling of an infra-zygomatic crest MI, of dimensions 2 mm × 12 mm, was designed and placed in the IZC bone. The MI was inserted at 50°, 60°, 70°, 80°, and 90° angulations to the IZC surface. Simulated orthodontic forces of magnitudes 8, 9, 10, 11, and 12 oz were applied to the MI head. Von Mises stress and magnitude both in the MI and surrounding bone were measured. RESULTS: Von Mises stress in the MI and bone was maximum at 90°. Least stresses were observed at 50° and 60° angulations. As force magnitude increased, von Mises stress increased linearly. Maximum stresses in the MI and bone were observed when loads were 12 oz and minimum stresses were observed at 8 oz. CONCLUSION: To achieve optimum primary stability, angles of insertion between 50° and 60° are recommended in the IZC region. Highest von Mises stress values were detected in the MI, followed by cortical and cancellous bone. Also, loading force between 8 and 12 oz exerted stresses below the tolerable threshold of bone and MI. Hence, proper placement of MI in IZC using these findings might provide better biomechanical stability during retraction and may help in preserving the bone-implant interface.

Finite element analysis of dental implant as orthodontic anchorage.

AIM: The purpose of this three-dimensional (3D) finite element study was to investigate orthodontic loading simulation on a single endosseous implant and its surrounding osseous structure, to analyze the resultant stresses and to identify the changes in the bone adjacent to the implant following orthodontic loading. MATERIALS AND METHODS: Two models were constructed using finite element method consisting of endosseous dental implant and the surrounding bone. In the first model, the contact between the implant and the bone was simulated showing no osseointegration, while the second model showed 100% osseointegration. Simulated horizontal loads of 20 N, at 90° from the long axis, were applied to the top of the implant. The study simulated loads in a horizontal direction, similar to a distalmesial orthodontic movement. RESULTS: In the first model, the stress was mainly concentrated at the neck of the implant and at the closest surrounding bone. In the second model, the stress was chiefly concentrated at the neck of the implant at the level of the cortical superficial bone. The stresses decreased in the cancellous bone area. On the implant, the highest stress concentration was at the first cervical thread decreasing uniformly to the apex. The stress distribution on the mesial and distal sides showed that the maximum compressive stress was localized mesially and the maximum tensile stress distally. If both models are compared, it can be observed that the stresses were less and more evenly distributed in model 1 (initial stability) than in model 2 when osseointegration was assumed. CONCLUSION: A lack of bony support for the implant represents an unfavorable situation from biomechanical point of view that should be considered and solved. As clinical problems mostly occur at the marginal bone region (bacterial plaque accumulation, overcontoured abutments, infections, osseous defects), attention should be focused on this region. CLINICAL SIGNIFICANCE: When osseointegrated implants are primarily used as anchorage for orthodontic purposes and then as fixed prosthesis, the functional and structural union of titanium to bone should be preserved.

Apical force distribution due to orthodontic forces: a finite element study.

AIM: This finite element study was conducted to calculate the distribution of stresses in the periodontal ligament when various orthodontic forces were applied, with emphasis on the effect on root apex. MATERIALS AND METHODS: An in vitro finite element method was used to construct a three-dimensional finite element model of a maxillary central incisor, its periodontal ligament and alveolar bone was constructed on the basis of average anatomic morphology. To this model, five types of orthodontic forces namely tipping, bodily movement, intrusion, extrusion and rotations were applied at various points on the crown of the tooth model. After the application of the forces, initial stress and initial displacements of the periodontal ligament were evaluated. The principal stress obtained on the periodontal ligament due to various orthodontic loadings on the maxillary central incisor was analyzed using ANSYS 10 finite element software. RESULTS: It showed that the greatest amount of relative stress at the apex of maxillary central incisor occurred with intrusion, extrusion and rotation. Bodily movement and tipping forces produce stress concentrated at the alveolar crest and not at the root apex. CONCLUSION: Clinical implications of this study suggest that if the clinician is concerned about placing heavy stresses on the root apex, then vertical and rotational forces must be applied with caution. CLINICAL SIGNIFICANCE: If heavy stresses are to be placed on the root apex, then vertical and rotational forces must be applied with caution during orthodontic therapy.