Angular changes and their rates in concurrence to developmental stages of the mandibular second premolar.

In the early developmental stage of the mandibular second premolar (MnP2), it is not unusual to find the tooth extremely angulated to the lower border of the mandible, as seen in the panoramic roentgenogram. On eruption, the tooth, in most cases, is close to being upright. However, impaction or other types of malocclusions due to its ectopic eruption are not rare. This study follows the angular changes of the MnP2 during development. Two hundred two panoramic roentgenograms of 101 patients were retrospectively analyzed. All patients had two sequential films with a minimal time interval of nine months. Each MnP2 was traced, and its developmental stage as well as its angulation to the lower border of the mandible was registered. We found that normally more MnP2 are distally (56.5%) than mesially (25%) inclined. There is a statistically significant difference in the inclination of the teeth during their development from stage D to stage F (D = 75.17 degrees +/- 15.25 degrees, E = 79.35 degrees +/- 12.18 degrees, F = 83.38 degrees +/- 10.79 degrees). The average amount of total angular change rate of the MnP2s from stage D to stage G is 0.09 +/- 0.25 degrees/mo, and the absolute angular change rate is 0.19 +/- 0.25 degrees/mo.

The accuracy of the cementoenamel junction identification on periapical films.

In the study of orthodontically induced inflammatory root resorption, many researchers use the cementoenamel junction (CEJ) as a bisecting reference point to measure the amount of root shortening. The accuracy of the identification of the CEJ point might affect the conclusions of those studies. This study aims to find the effects of angular changes between the tooth and the film on the validity and reproducibility of identifying three different CEJ points, ie, the most apical CEJ point between the crown and the root, the most mesial CEJ point, and the most distal CEJ point. An extracted maxillary central incisor was placed in a special jig and radiographed at four different tooth to film angulations. Eight examiners were asked to identify the buccal and palatal CEJ, whereas six examiners were asked to identify the mesial and distal CEJ points, all on a computer monitor. The distances between the identified points and the apex were computed and compared with the actual ones. The angular changes between the tooth and the film did have a statistically significant effect on the identification of some of these CEJ points. The difference was significant on the identification of the buccal and palatal points but not on the mesial and the distal ones.

The use of an individual jig in measuring tooth length changes.

The parallel periapical radiographic technique hides several problems that might affect the image seen on the film. To overcome these problems a special jig with an external wire attached to the tooth surface and parallel to its long axis was suggested. This study examines the accuracy of using an external object for measuring root length differences due to angular changes between the tooth and the film. The rule of three was used for all calculations as a compensating formula. A human central incisor was placed in a special jig. Two different wire lengths (11.8 +/- 0.1 mm and 16 +/- 0.1 mm) were attached to the tooth in six different ways. The tooth was radiographed at four different film to tooth angulations. The tooth and wire lengths were measured on the model itself and directly on the scanned film on a computer monitor. The results reveal that a wire, placed nine mm from the crown and parallel to the long axis of the tooth was the best jig for accurately measuring tooth length changes. Neither palatal nor buccal metal wires, intimately attached to the crown of the tooth, can serve as a tool to measure tooth length changes. The study could not find a way to skip the need for a cephalometric radiograph to verify the parallelism between the wire and the long axis of the tooth for this matter.

A comparison of three methods to accurately measure root length.

Measuring the severity of root shortening after orthodontic treatment is a common problem in the dental fields as well as in litigation, legislation, and the ethics arena. The most common method to evaluate root length shortening is by using periapical radiographs. Surprisingly, root elongation after orthodontic treatment in adult patients was reported in the past. The aims of this study were to measure the effects of angular changes between the tooth and the film on the length of the image of a tooth model, to compare three methods to accurately measure root length in different films, and to find the most accurate reference points on the tooth for calculating root lengths. Five amalgam dots were placed on an acrylic model of a maxillary central incisor: ie, most apical, most incisal, mesial CEJ, distal CEJ, and most apical CEJ on the buccal side. The tooth model was placed in a special jig and radiographed at four different film-to-tooth angulations. Root and crown lengths were measured on both the model itself and on a computer monitor displaying the image that resulted from scanning the film into the computer. The results revealed that angular changes between the tooth and the film affect the measured tooth length. The midpoint between the mesial CEJ point and the distal CEJ point (median CEJ) was the best reference point for measuring root length. This was true when the calculations were done with the rule-of-three formula.

Pathognomonic cephalometric characteristics of Angle Class II Division 2 malocclusion.

The Class II division 2 (Class II/2) malocclusion as originally defined by E.H. Angle is relatively rare. The orthodontic literature does not agree on the skeletal characteristics of this malocclusion. Several researchers claim that it is characterized by an orthognathic facial pattern and that the malocclusion is dentoalveolar per se. Others claim that the Class II/2 malocclusion has unique skeletal and dentoalveolar characteristics. The present study describes the skeletal and dentoalveolar cephalometric characteristics of 50 patients clinically diagnosed as having Class II/2 malocclusion according to Angle's original criteria. The study compares the findings with those of both a control group of 54 subjects with Class II division I (Class II/1) malocclusion and a second control group of 34 subjects with Class I (Class I) malocclusion. The findings demonstrate definite skeletal and dentoalveolar patterns with the following characteristics: (1) the maxilla is orthognathic, (2) the mandible has relatively short and retrognathic parameters, (3) the chin is relatively prominent, (4) the facial pattern is hypodivergent, (5) the upper central incisors are retroclined, and (6) the overbite is deep. The results demonstrate that, in a sagittal direction, the entity of Angle Class II/2 malocclusion might actually be located between the Angle Class I and the Angle Class II/1 malocclusions. with unique vertical skeletal characteristics.