Three-dimensional evaluation of changes in lip position from before to after orthodontic appliance removal.

INTRODUCTION: Our objectives were to develop a reproducible method of superimposing 3-dimensional images for measuring soft-tissue changes over time and to use this method to document changes in lip position after the removal of orthodontic appliances. METHODS: Three-dimensional photographs of 50 subjects were made in repose and maximum intercuspation before and after orthodontic appliance removal with a stereo camera. For reliability assessment, 2 photographs were repeated for 15 patients. The images were registered on stable areas, and surface-to-surface measurements were made for defined landmarks. RESULTS: Mean changes were below the level of clinical significance (set at 1.5 mm). However, 51% and 18% of the subjects experienced changes greater than 1.5 mm at the commissures and lower lips, respectively. CONCLUSIONS: The use of serial 3-dimensional photographs is a reliable method of documenting soft-tissue changes. Soft-tissue changes after appliance removal are not clinically significant; however, there is great individual variability.

Biomechanical reevaluation of orthodontic asymmetric headgear.

OBJECTIVE: To investigate the distribution of distal and lateral forces produced by orthodontic asymmetric headgear (AHG) using mathematical models to assess periodontal ligament (PDL) influence and to attempt to resolve apparent inconsistencies in the literature. MATERIALS AND METHODS: Mechanical models for AHG were constructed to calculate AHG force magnitudes and direction using the theory of elasticity. The PDL was simulated by elastic springs attached to the inner-bow terminals of the AHG. The total storage energy (E(t)) of the AHG and the supporting springs was integrated to evaluate the distal and lateral forces produced by minimizing E(t) (Castigliano's theorem). All analytical solutions were derived symbolically. RESULTS: The spring-supported headgear model (SSHG) predicted the magnitude and distribution of distal forces consistent with our data and the published data of others. The SSHG model revealed that the lateral forces delivered to the inner-bow terminals were not equal, and the spring constant (stiffness of the PDL) affected the magnitude and direction of the resultant lateral forces. Changing the stiffness of the PDL produced a greater biomechanical effect than did altering the face-bow design. The PDL spring model appeared to help resolve inconsistencies in the literature between laboratory in vitro experiments and clinical in vivo studies. CONCLUSION: Force magnitude and direction of AHG were predicted precisely using the present model and may be applied to improve the design of AHG to minimize unwanted lateral tooth movement.

Treatment of pain after initial archwire placement: a noninferiority randomized clinical trial comparing over-the-counter analgesics and bite-wafer use.

INTRODUCTION: Pain is a major concern of patients before orthodontic treatment. Currently, the most frequently recommended treatments for pain after archwire placement or appliance adjustment are over-the-counter (OTC) analgesics. Although the overuse of OTC medications and their potential side effects are concerns, particularly for children, no study to date has investigated a nonpharmacologic option for pain management as an alternative for these analgesics. METHODS: A parallel 2-group stratified block randomized clinical trial was designed to assess the pain response of adolescents during the first week after initial archwire placement. The subjects were randomly assigned to 1 of 2 pain management groups: bite wafer (BW) or OTC analgesics. Pain levels were reported on a numerical rating scale. The intensity and unpleasantness of the pain were also assessed. Data were collected at 8 times over a 7-day period. A general linear mixed model with heterogeneous compound symmetry covariance matrix was fitted separately for each outcome. Estimates from the mixed model were used to test a noninferiority hypothesis that the BW group, on average, was not inferior with respect to pain management to the OTC group. RESULTS: The patterns of pain level, intensity, and unpleasantness over time were similar for the 2 groups (P >0.33). Pain management for the BW group as indicated by pain level, intensity, and unpleasantness was not inferior to that of the OTC group (P >0.39). CONCLUSIONS: In adolescents, the BW is a nonpharmacologic option for pain management after orthodontic procedures that is at least as effective as OTC analgesics.

The apparent contact dimension and covariates among orthodontically treated and nontreated subjects.

UNLABELLED: The apparent contact dimension (ACD), a determinant of dental esthetics, has been purported to exhibit an esthetic relationship termed the "50:40:30" rule, implying that in an esthetic smile, the ACD between the central incisors, central and lateral incisors, and lateral incisor and canine would be 50, 40, and 30% of the height of a central incisor, respectively. This study assessed the existence of this proportion using casts of orthodontically treated (N = 40) and nontreated (N = 27) subjects deemed to possess excellent occlusion. Covariates studied included tooth size, tooth shape, tip, and torque. The average ACD proportions in this study, relative to the height of an ipsilateral central incisor, were found to be 49, 38, and 27% between the central incisors, central and lateral incisors, and the lateral incisor and canine, respectively. The ACD exhibited a positive correlation (p < 0.05) with the height of the clinical crown and a negative correlation (p < 0.05) with the width/height ratios of the corresponding teeth. No statistically significant correlations were evident between the ACD with the shape of the clinical crown, tip, and torque. However, the tip and torque did exhibit a statistically significant (p < 0.05) correlation with the height of the clinical crown. This study is the first to validate the existence and proportions of the ACD. CLINICAL SIGNIFICANCE: This study validates the existence of the ACD and quantifies the relationship of the ACD with tooth size, tooth shape, mesiodistal crown angulation (tip), and labiolingual crown inclination (torque) among subjects deemed to possess excellent occlusion and alignment. This quantifiable "ideal" and its correlation with the other determinants of dental esthetics may be used in conjunction with various evidence-based paradigms in the esthetic appraisal of the maxillary anterior teeth.

Accuracy of measurements of mandibular anatomy in cone beam computed tomography images.

OBJECTIVES: Cone beam computed tomography (CBCT) images of ideally positioned and systematically mispositioned dry skulls were measured using two-dimensional and three-dimensional software measurement techniques. Image measurements were compared with caliper measurements of the skulls. STUDY DESIGN: Cone beam computed tomography volumes of 28 skulls in ideal, shifted, and rotated positions were assessed by measuring distances between anatomic points and reference wires by using panoramic reconstructions (two-dimensional) and direct measurements from axial slices (three-dimensional). Differences between caliper measurements on skulls and software measurements in images were assessed with paired t tests and analysis of variance (ANOVA). RESULTS: Accuracy of measurement was not significantly affected by alterations in skull position or measurement of right or left sides. For easily visualized orthodontic wires, measurement accuracy was expressed by average errors less than 1.2% for two-dimensional measurement techniques and less than 0.6% for three-dimensional measurement techniques. Anatomic measurements were significantly more variable regardless of measurement technique. CONCLUSIONS: Both two-dimensional and three-dimensional techniques provide acceptably accurate measurement of mandibular anatomy. Cone beam computed tomography measurement was not significantly influenced by variation in skull orientation during image acquisition.

Accuracy of measurements of mandibular anatomy and prediction of asymmetry in panoramic radiographic images.

OBJECTIVES: Measurements of ideally positioned and systematically mis-positioned skulls were used to evaluate errors in linear measurements and symmetry ratios made with panoramic X-ray images. METHODS: Digital panoramic images of 30 skulls placed in ideal, shifted and rotated positions, were assessed by measuring distances between anatomic points and fiducial references. Differences between photographic measurements (control) and radiographic measurements were compared. Horizontal measurements included a 20 mm wire and the distance from gonion to mental foramen (G-MF). Vertical distances measured included a 40 mm wire, condyle to sigmoid notch length, and condyle to gonion (posterior mandibular height or PMH). A relative symmetry ratio comparing the difference between right and left PMH was also calculated. Distances measured in panoramic images were corrected using the left vertical wire distance or the panoramic unit's stated magnification factor (1.25x). RESULTS: Greatest differences were noted for horizontal measurements and shifted skull positions. Use of an arbitrary magnification correction was consistently less accurate than use of an internal calibration and resulted in general underestimation of actual dimensions. Measures of PMH varied significantly from expected values for each of the three skull positions (P<0.005). Panoramic accuracy for detecting asymmetry was 67% for ideal, 70% for rotated, and 47% for shifted skull positions when an internal reference was used. CONCLUSIONS: Panoramic radiographs should be used with caution in making absolute measurements or relative comparisons. Even when internal fiducial calibration for image distortion of anatomy is used, measurements such as those assessing posterior mandibular facial symmetry may be unreliable.