3D Morphological Measurements of Dental Casts with Occlusal Relationship using Microfocus X-ray CT

Spatial and angular alterations in the dental arch after premature loss of primary molars: Immediate and 9-month computed tomography evaluation

BACKGROUND

Contemporary imaging methods and quickly advancing technologies have increased the number of diagnostic tools available in medicine and orthodontics. The current study aimed to determine three-dimensional (3D) space changes that occurred after the extraction of either the maxillary or mandibular primary molars during the mixed dentition period.

MATERIALS AND METHODS

The present study was a longitudinal split-mouth study with a study group and a control group. The sample consisted of 20 children aged between 6 and 9 years. Clinical examination, radiological analysis, and 3D digital images of the plaster casts were used sequentially to gather all the data. The dental cast measurements recorded were arch width, arch length, hemi-perimeter, dental space at the extraction site, and angulation of the first permanent molar. The children were recalled for follow-up after 9 months, and all dental cast measurements were repeated using nondestructive 3D computed tomography software. For repeated measurements, the test applied was a paired t-test, and for independent samples, the test was a Student's t-test.

RESULTS

A significant decrease in arch width (P = 0.001), arch length (P < 0.001), hemi-perimeter (P < 0.001), D-space (P < 0.001), and E-space (P = 0.001) was observed following extraction. A significant increase in angulation measurements was observed (P = 0.001).

CONCLUSION

The study revealed a comparative reduction in mandibular arch width, a reduction in arch length in both the maxilla and the mandible, a reduced hemi-perimeter of dental arches, loss of dental extraction space, and a change in angulation of the erupted first permanent molars following premature loss of the primary molar.

Crown shape of maxillary molars with delayed eruption

The purpose of this study was to explore the crown shapes of maxillary molars with delayed eruption (DEMo1) at the position distal to the maxillary second premolar. Included teeth erupted later than the average for the maxillary first molar eruption in Japanese females (6.58 ± 0.67 years) by more than two standard deviations. Crown shapes of 12 four-cusped left DEMo1 teeth were compared with those of 25 four-cusped left maxillary first molars (U6n) and 25 four-cusped left maxillary second molars (U7n) from different patients with normal eruption. Seven landmarks were established on the reference plane containing the mesiobuccal, distobuccal and mesiolingual cusp tips of the molars; the origin was defined as the center of gravity of these three points. According to the obtained discriminant function (percentage of correct classifications, 84%), five DEMo1 teeth were classified as U6n and the other seven as U7n. The DEMo1 teeth were also classified into two subgroups, the U6n-close and U7n-close groups, according to the location of the distolingual cusp tip. These results suggest that DEMo1 teeth could include U6 and U7 with delayed eruption or could be an intermediate between U6 and U7, according to their crown shapes.

Investigation of the effects of storage time on the dimensional accuracy of impression materials using cone beam computed tomography

PURPOSE

The storage conditions of impressions affect the dimensional accuracy of the impression materials. The aim of the study was to assess the effects of storage time on dimensional accuracy of five different impression materials by cone beam computed tomography (CBCT).

MATERIALS AND METHODS

Polyether (Impregum), hydrocolloid (Hydrogum and Alginoplast), and silicone (Zetaflow and Honigum) impression materials were used for impressions taken from an acrylic master model. The impressions were poured and subjected to four different storage times: immediate use, and 1, 3, and 5 days of storage. Line 1 (between right and left first molar mesiobuccal cusp tips) and Line 2 (between right and left canine tips) were measured on a CBCT scanned model, and time dependent mean differences were analyzed by two-way univariate and Duncan's test (α=.05).

RESULTS

For Line 1, the total mean difference of Impregum and Hydrogum were statistically different from Alginoplast (P<.05), while Zetaflow and Honigum had smaller discrepancies. Alginoplast resulted in more difference than the other impressions (P<.05). For Line 2, the total mean difference of Impregum was statistically different from the other impressions. Significant differences were observed in Line 1 and Line 2 for the different storage periods (P<.05).

CONCLUSION

The dimensional accuracy of impression material is clinically acceptable if the impression material is stored in suitable conditions.

Influence of filler on bite impression material in transillumination method for occlusal examination

The purpose of this present study was to investigate the influence of material filler and RGB values' fluctuation on creating a calibration curve, which indicates the relationship between material thickness and transmitted light brightness using the transillumination method. Creating the calibration curves were carried out through the following three methods; 1) the conventional method creates the calibration curve with a formula of thickness, 2) the maximum value method, with samples of a specified thickness, and 3) the actual value method, with a microscope. Furthermore, the reliability of each curve was verified via scanned artificial tooth data. In addition, the characteristics of light decrement were investigated. From our results, it was suggested that the filler diameter must be considered when the calibration curve is created using the bite impression material with a filler. In addition, it was suggested that the RGB values' fluctuation did not influence the calibration curve.

Direct 3-D morphological measurements of silicone rubber impression using micro-focus X-ray CT

Three-dimensional computer models of dental arches play a significant role in prosthetic dentistry. The microfocus X-ray CT scanner has the advantage of capturing precise 3D shapes of deep fossa, and we propose a new method of measuring the three-dimensional morphology of a dental impression directly, which will eliminate the conversion process to dental casts. Measurement precision and accuracy were evaluated using a standard gage comprised of steel balls which simulate the dental arch. Measurement accuracy, standard deviation of distance distribution of superimposed models, was determined as +/-0.050 mm in comparison with a CAD model. Impressions and casts of an actual dental arch were scanned by microfocus X-ray CT and three-dimensional models were compared. The impression model had finer morphology, especially around the cervical margins of teeth. Within the limitations of the current study, direct three-dimensional impression modeling was successfully demonstrated using microfocus X-ray CT.