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The purpose of this study was to evaluate the stress distribution produced in the dentoalveolar system by a mandibular posterior crossbite appliance used for the correction of mandibular second molars in lingual version. A photoelastic model was fabricated using a photoelastic material (PL-3) to simulate alvelolar bone and ivory-colored resin teeth. The model was observed anteriorly and posteriorly with a circular polariscope and photographically recorded before and after activation of mandibular posterior crossbite appliances. An uncontrolled tipping and an extrusive force were generated when the traction force was applied on the buccal surface of the mandibular second molar. A controlled tipping and an intrusive force were generated when the traction force was applied on the lingual surface of the mandibular second molar. We concluded that to escape the extrusion and uncontrolled tipping that creates occlusal interferences associated with the correction of mandibular second molars in lingual version, the lingual traction force is more useful than the buccal traction force. [ABSTRACT FROM AUTHOR]

The purpose of this study was to evaluate the stress distribution produced in the dentoalveolar system by a maxillary posterior crossbite appliance used for the correction of maxillary second molars in buccal crossbite. A photoelastic model was fabricated using a photoelastic material (PL-3) to simulate alveolar bone and ivory-colored resin teeth. The model was anteriorly and posteriorly observed with a circular polariscope and photographically recorded before and after activation of the maxillary posterior crossbite appliance. An uncontrolled palatal tipping and a rotating force were generated when the traction force was applied on the palatal surface of the maxillary second molar. A controlled tipping and an intrusive force were generated when the traction force was applied on the buccal surface of the maxillary second molar. [ABSTRACT FROM AUTHOR]

The purpose of this study was to identify the potential projection errors of posteroanterior cephalometric radiographs due to head rotation in the vertical Z-axis. For this investigation, 20 human dry skull samples with permanent dentition were collected from the Department of Anatomy in the College of Medicine, Chosun University, Korea. They had no gross asymmetries and were well preserved. Each dry skull was rotated from 0° to ± 10° at 1° intervals. A vertical axis, the Z-axis, was used as a rotational axis for the exposure of 420 posteroanterior cephalometric radiographs. Most of the abscissa values of each landmark showed statistically significant differences in the head rotation from each rotational angle (P < .05), whereas the ordinate values were almost the same in all rotational angles regardless of the head rotation. The abscissa values of each landmark anterior to the vertical rotational axis displaced in the same direction as the head rotation, whereas those of other landmarks posterior to the vertical rotational axis displaced in the opposite direction. The mean differences of the abscissa values, per 1° of head rotation, were larger as the landmark was located further anteroposteriorly from the vertical rotational axis and smaller as the landmark was located nearer the vertical rotational axis. In view of the projection error, a posteroanterior cephalometric radiograph is a more valuable diagnostic tool when it is exposed with no head rotation about the vertical Z-axis. [ABSTRACT FROM AUTHOR]

The purpose of this study was to identify the potential projection errors of lateral cephalometric radiographs due to head rotation in the vertical Z-axis. For this investigation, 17 human dry skull samples with permanent dentition were collected from the Department of Anatomy in the College of Medicine, Chosun University. They had no gross asymmetry and were well preserved. Each dry skull was rotated from 0° to ±15° at 1° intervals. A vertical axis, the Z-axis, was used as a rotational axis to have 527 lateral cephalometric radiographs exposed. The findings were that: (1) angular measurements have fewer projection errors than linear measurements; (2) the greater the number of landmarks on the midsagittal plane that are included in angular measurements, the fewer the projection errors occurring; (3) horizontal linear measurements decrease gradually in length as the rotational angle toward the film increases, whereas a small increase and then decrease of the length occurs as the rotational angle toward the focal spot increases; (4) horizontal linear measurements have more projection errors than vertical linear measurements according to head rotation; and (5) projection errors of vertical linear measurements increase as the distance from the rotational axis increases. In summary, angular measurements of lateral cephalometric radiographs are more useful than linear measurements in minimizing the projection errors associated with head rotation on a vertical axis. [ABSTRACT FROM AUTHOR]