Mark G. Hans

Reliability and accuracy of cone-beam computed tomography dental measurements

INTRODUCTION Dental measurements are an integral part of the orthodontic records necessary for proper diagnosis and treatment planning. In this study, we investigated the reliability and accuracy of dental measurements made on cone-beam computed tomography (CBCT) reconstructions. METHODS Thirty human skulls were scanned with dental CBCT, and 3-dimensional reconstructions of the dentitions were generated. Ten measurements (overbite, overjet, maxillary and mandibular intermolar and intercanine widths, arch length available, and arch length required) were made directly on the dentitions of the skulls with a high-precision digital caliper and on the digital reconstructions with commercially available software. Reliability and accuracy were assessed by using intraclass correlation and paired Student t tests. A P value of < or = 0.05 was used to assign statistical significance. RESULTS Both the CBCT and the caliper measurements were highly reliable (r >0.90). The CBCT measurements tended to slightly underestimate the anatomic truth. This was statistically significant only for compounded measurements. CONCLUSIONS Dental measurements from CBCT volumes can be used for quantitative analysis. With the CBCT images, we found a small systematic error, which became statistically significant only when combining several measurements. An adjustment for this error allows for improved accuracy.

Accuracy and reliability of cone-beam computed tomography for measuring alveolar bone height and detecting bony dehiscences and fenestrations

INTRODUCTION The purpose of this study was to evaluate the accuracy and reliability of cone-beam computed tomography (CBCT) in the diagnosis of naturally occurring fenestrations and bony dehiscences. In addition, we evaluated the accuracy and reliability of CBCT for measuring alveolar bone margins. METHODS Thirteen dry human skulls with 334 teeth were scanned with CBCT technology. Measurements were made on each tooth in the volume-rendering mode from the cusp or incisal tip to the cementoenamel junction and from the cusp or incisal tip to the bone margin along the long axis of the tooth. The accuracy of the CBCT measurements was determined by comparing the means, mean differences, absolute mean differences, and Pearson correlation coefficients with those of direct measurements. Accuracy for detection of defects was determined by using sensitivity and specificity. Positive and negative predictive values were also calculated. RESULTS The CBCT measurements showed mean deviations of 0.1 +/- 0.5 mm for measurements to the cementoenamel junction and 0.2 +/- 1.0 mm to the bone margin. The absolute values of the mean differences were 0.4 +/- 0.3 mm for the cementoenamel junction and 0.6 +/- 0.8 mm for the bone margin. The sensitivity and specificity of CBCT for fenestrations were both about 0.80, whereas the specificity for dehiscences was higher (0.95) and the sensitivity lower (0.40). The negative predictive values were high (>or=0.95), and the positive predictive values were low (dehiscence, 0.50; fenestration, 0.25). The reliability of all measurements was high (r >or=0.94). CONCLUSIONS By using a voxel size of 0.38 mm at 2 mA, CBCT alveolar bone height can be measured to an accuracy of about 0.6 mm, and root fenestrations can be identified with greater accuracy than dehiscences.

Image distortion and spatial resolution of a commercially available cone-beam computed tomography machine

INTRODUCTION Our objective was to evaluate images produced by a commercially available cone-beam computed tomography (CBCT) machine (i-CAT model 9140-0035-000C, Imaging Sciences International, Hatfield, Pa) for measurement and spatial resolution (ie, the ability to separate 2 objects in close proximity in the image) for all settings and in all dimensions. METHODS A custom phantom containing 0.3 mm diameter chromium metal markers approximately 5 mm apart in 3 planes of space was developed for analyzing distortion and measurement accuracy. This phantom was scanned in the CBCT machine by using all 12 commercially available settings. The distance between the markers was measured 3 times on the 3-dimensional images by using a Digital Imaging and Communications in Medicine (DICOM) viewer and was also measured 3 times directly on the phantom with a fine-tipped digital caliper. A line-pair phantom was used to evaluate spatial resolution. Thirty evaluators analyzed images and assigned a resolution from 0.2 to 1.6 mm according to the separation of the line pairs. RESULTS There were no statistically significant differences among the 3-dimensional images for any setting, in any dimension, or in images divided by thirds in terms of measurement accuracy. Comparison of the CBCT measurements to the direct digital caliper measurements showed a statistically significant difference (P <0.01). However, the absolute difference was <0.1 mm and is probably not clinically significant for most applications. The worst spatial resolution found was 0.86 mm. Spatial resolution was lower at faster scan times and larger voxel sizes. CONCLUSIONS This CBCT machine has clinically accurate measurements and acceptable resolution.

Upright and supine cephalometric evaluation of obstructive sleep apnea syndrome and snoring subjects.

Specific craniofacial characteristics are reported to occur with obstructive sleep apnea syndrome (OSAS). The purpose of this study was to determine whether craniofacial morphology differs between subjects with OSAS and heavy snorers, and to investigate how change in posture from upright to lying down affects the upper airway passage. Lateral head radiographs of ten persons diagnosed with OSAS(AHI > 50) and ten snorers matched for age, height and weight without any history of daytime sleepiness, doctor-diagnosed OSAS, and no evidence of significant desaturation on overnight oximetry were obtained in both upright seated and awake supine positions. The posterior superior pharyngeal space in both the OSAS and snorers was reduced when changing from upright to supine posture (p < or = 0.05). Significant differences in cranial base alignment, ramus width relative to the middle-cranial fossa, position of the maxilla relative to the cranial base in the seated position (P < or = 0.01) were noted between subjects with OSAS and subjects with snoring and less severe apnea. In addition, differences in the posterior superior pharyngeal space, tongue length, tongue to intermaxillary area ratio and hyoid position (p < or = 0.05) were demonstrated both in the upright and in the supine positions (p < or = 0.05) in the OSAS compared to the snoring group. These results suggest that anatomic factors may predispose some snorers to develop OSAS. Measurements made from awake supine position lateral head radiographs revealed no additional differences between OSAS and snoring subjects when compared to measurements made on radiographs taken in the upright position.

Influence of CBCT exposure conditions on radiation dose

BACKGROUND Cone-beam computed tomography (CBCT) has been changing the way dental practitioners use imaging. The radiation dose to the patient and how to effectively reduce the dose is still not completely clear to most users of this technology. OBJECTIVE The objective of this study was to quantitate the change in radiation dose when using different CBCT settings. METHODS A CBCT machine was modified to allow different setting combinations. The variables consisted of 4 different mA choices (2, 5, 10, and 15), 2 kVp choices (100 and 120), and 3 fields of view (6 inches, 9 inches, and 12 inches). A radiation phantom with 10 thermoluminescent dosimeters (TLD) was used to measure radiation dose. One specific setting (15 mA, 120 kVp, and 12-inch FOV) was scanned 3 times to determine consistency. RESULTS The CBCT showed less than 5% variance in radiation dose values. An overall reduction in dose of about 0.62 times was achieved by reducing the kVp from 120 to 100. When reducing the field size the dose decreased 5% to 10%, while for organs that escaped the direct beam the reduction was far greater. CONCLUSIONS A reduction in radiation dose can be achieved by using the lowest exposure settings and narrow collimation.

Cephalometric assessment in obstructive sleep apnea

It is reported that some specific craniofacial characteristics are associated with obstructive sleep apnea syndrome (OSAS). To test this finding, the present study developed and assessed the feasibility of a craniofacial index score (CIS) in differentiating patients with OSAS from habitual snorers. Anthropometric measurements and lateral head radiographs were obtained on 24 male and 4 female patients with OSAS who had physician-diagnosed OSAS (respiratory disturbance index (RDI) >20), and 25 male and 5 female habitual snorers (RDI <20). Thirteen cephalometric and four anthropometric measure- ments were used in a discriminant model to construct the CIS. The model was able to correctly classify 82.1% of the OSAS group and 86.7% of the snoring group. In addition, variables that were related to the soft tissues, hyoid bone to mandibular plane, Body Mass Index, and soft palate length had the highest predictive value. These findings indicate that a CIS constructed from cephalometric and anthropometric measurements can be used to identify subjects with and without OSAS.

Buccal cortical bone thickness for mini-implant placement.

INTRODUCTION The thickness of cortical bone is an important factor in mini-implant stability. In this study, we investigated the buccal cortical bone thickness of every interdental area as an aid in planning mini-implant placement. METHODS From the cone-beam computed tomography scans of 30 dry skulls, 2-dimensional slices through every interdental area were generated. On these, cortical bone thickness was measured at 2, 4, and 6 mm from the alveolar crest. Intraclass correlation was used to determine intrarater reliability, and analysis of variance (ANOVA) was used to test for differences in cortical bone thickness. RESULTS Buccal cortical bone thickness was greater in the mandible than in the maxilla. Whereas this thickness increased with increasing distance from the alveolar crest in the mandible and in the maxillary anterior sextant, it behaved differently in the maxillary buccal sextants; it was thinnest at the 4-mm level. CONCLUSIONS Interdental buccal cortical bone thickness varies in the jaws. There appears to be a distinct pattern. Knowledge of this pattern and the mean values for thickness can aid in mini-implant site selection and preparation.

Comparison of two dental devices for treatment of obstructive sleep apnea syndrome (OSAS)

Previous case reports have indicated dental devices can be an effective nonsurgical treatment for snoring and obstructive sleep apnea. This pilot study evaluated the effectiveness of two intraoral devices in reducing the Respiratory Disturbance Index (RDI) and Epworth Sleepiness Scale (ESS) scores in a group of 24 adult volunteers with a history of loud snoring. Subjects were randomly assigned to two groups. Twelve subjects were fitted with a dental device designed to increase vertical dimension and protrude the mandible (device A). The other 12 subjects received a different device designed to minimally increase vertical opening without protruding the mandible (device B). Unattended home sleep monitoring (Edentrace II Digital Recorder, Edentech Corp.) was used to compute RDI at two time periods: (T0) before using any dental device and (T1) while using a dental device 2 weeks after the initial delivery date. The mean RDI and ESS scores at T0 for subjects in the device A group were 35.6 +/- 28.4 and 12.0 +/- 3.9, respectively. Means for the same measures at T1 were 21.1 +/- 21.4 and 8.2 +/- 4.0. For subjects in the device B group, means for RDI and ESS scores at T0 were 36.5 +/- 43.7 and 13.0 +/- 4.5, the means at T1 were 46.8 +/- 47.0 and 12.5 +/- 5.7. The effectiveness of the two devices was estimated by comparing the difference in RDI scores from T0 to T1 for the 10 subjects who were using device A and completed the study and the 8 subjects who were using device B and completed the study. Six subjects withdrew for various reasons. From T0 to T1, device A reduced RDI scores in 9 of 10 subjects, with a mean reduction in RDI of 14.5 (p < or = 0.05) and in ESS score of 3.8 (p < or = 0.005). Device B showed no change or an increased RDI score in 8 of 8 subjects. Seven of the eight subjects who showed no improvement in RDI with device B were then fitted with device A. Four of these seven subjects showed a reduction in RDI and five showed a reduction in ESS after using device A for 2 weeks. The mean reduction in RDI and ESS was 2.4 +/- 19.8 and 2.4 +/- 3.0, respectively. Hence, we conclude that a dental device that advances the mandible and increases the vertical dimension to open the upper airway is more effective in reducing the number of apneic and snoring events during sleep than one which does not.

Image quality produced by different cone-beam computed tomography settings.

INTRODUCTION The aim of this study was to evaluate image quality at different cone-beam computed tomography settings and 3 fields of view. METHODS A Hitachi CB MercuRay (Hitachi Medical Systems, Tokyo, Japan) was modified to allow different setting combinations. The variables consisted of 4 milliampere settings (2, 5, 10, and 15 mA), 2 kilovolt (peak) settings (100 and 120 kV[p]), presence or absence of a copper filter, and 3 fields of view (6, 9, and 12 in). Thirty-two scans were taken on a cadaver head and 16 scans on a dry skull. The groups were divided by field of view, and the images were ranked by at least 30 judges. Diagnostic quality was addressed in a questionnaire. Descriptive statistics and rankings were calculated with Excel 2003 (Microsoft, Redmond, Wash) and the Friedman and Wilcoxon signed rank tests with SPSS software (version 14.0.1; SPSS, Chicago, Ill). RESULTS The presence or absence of a filter showed significant differences (P <.006) in 2 pairs of the 9-in field of view. Variation in kilovolt (peak) settings showed significant differences (P <.006) in the 6-in 5-mA images with a filter. Altering the milliampere settings showed significant differences (P <.008) in the 6- and 12-in groups. The 9-in group showed significant differences between 2 mA and 10 and 15 mA. Overall, the 6-, 9-, and 12-in images had diagnostic quality 56%, 99%, and 99% of the time, respectively. CONCLUSIONS Presence or absence of a filter and the kilovolt (peak) setting did not affect overall image quality. Images taken at lower milliampere settings showed good diagnostic quality.

Mini-implant anchorage for the orthodontic practitioner.

Mini-implant-enhanced anchorage has become a popular concept in orthodontics over the past years. Although these systems are routinely used in university settings, there is some reservation because of lack of information in private practices. This article will introduce the concept of mini-implant anchorage to the orthodontic practitioner.