Estimation of alveolar crest height using routine periapical dental radiographs

Root proximity is a major factor for screw failure in orthodontic anchorage

INTRODUCTION

The purpose of this study was to evaluate root proximity as a risk factor for the failure of miniscrews used as orthodontic anchorage.

METHODS

We used dental radiographs and 3-dimensional computed tomography images to examine 216 titanium screws in 110 patients. Each screw was classified according to its proximity to the adjacent root. Category I, the screw was absolutely separate from the root; category II, the apex of the screw appeared to touch the lamina dura; and category III, the body of the screw was overlaid on the lamina dura. If the orthodontic force could be applied to the screw for 1 year (or until completion of orthodontic treatment), we recorded the screw anchorage as a success.

RESULTS

The screws had a high success rate--above 80%. Screws placed in the maxilla had a significantly higher success rate than those in the mandible. There was a significant correlation between success rate and root proximity. There were significant differences in the success rates between categories I and II, I and III, and II and III. Although screws in all 3 categories in the maxilla and categories I and II in the mandible showed high success rates above 75%, screws in category III in the mandible had a low success rate of 35%.

CONCLUSIONS

The proximity of a miniscrew to the root is a major risk factor for the failure of screw anchorage. This tendency is more obvious in the mandible.

Applicability of an image analysis system in alveolar bone loss measurement

Clinical and epidemiological studies in the field of periodontics and endodontics often utilize radiographs to monitor or measure the changes in bone structure and density. Periodontal bone loss or gain can be quantified on a radiograph by measurement of the distance between the bottom of the bony pocket and the apical contour of the involved tooth. The objective of this investigation was to study the accuracy of an image analysis system (IAS) to measure changes in height of the interproximal crest on radiographs. Artificial bone lesions were introduced in a dissectioned part of a human mandible. The distances between crest and apices were measured with a micrometer (MM). Radiographs were produced with horizontal and vertical deviations of 10 degrees. The radiographs were digitized and processed by computer. The landmarks in the digital image were enhanced mathematically and by histogram-based thresholding. The depth of the introduced defect was increased 6 times, followed by the measurement procedure. The IAS produced measurements of crown-apex distances with an accuracy of 0.066 to 0.358 mm. Repeated crest height measurements were recorded with an accuracy of 0.112 to 0.184 mm. Both the histogram-based binarization and the ellipse-fitting type of contour detection could be applied precisely. Misangulation errors during radiographic exposure of 10 horizontal or vertical did not statistically significant influence the IAS-measurements. The IAS can be applied in clinical trials and follow-up studies.