Automatic measurement of mandibular cortical bone width on cone-beam computed tomography images.

OBJECTIVE: The computed tomography cortical index (CTCI), computed tomography mandibular index (CTMI), and computed tomography index (inferior) [CTI(I)] are indexes obtained from cone-beam computed tomography images for the assessment of the mandibular cortex quality for implant planning or osteoporosis. However, cross-sectional image reconstruction for the measurements is labor-intensive. This study aimed to develop and evaluate a method to automatically reconstruct cross-sectional images and measure the cortex width in all areas inferior to the mental foramen (MF). METHODS: Seventy-one women (mean age: 52.4 years; range: 20-78 years) were enrolled. They were divided into four age and CTCI groups, including females younger (FY) and females older (FO) than 50 years (C1: normal, C2: mild/moderate erosion, and C3: severe porosity). Automatic and manual measurements of CTMI and CTI(I) were compared, and the inter- and intraobserver agreements were assessed using the intraclass correlation coefficient (ICC). The relationships between CTMI or CTI(I) and CTCI were also assessed. RESULTS: The mean processing times for reconstruction and measurements were 31.9 s and 1.22 s, respectively. ICCs for the comparison of automatic and manual measurements were 0.932 and 0.993 in the C1 and C2/C3 groups, respectively. Significant differences in CTMI and CTI(I) were observed between the FY or the FO-C1 and FO-C3 groups (p < 0.05). CONCLUSION: The automatic and manual measurements showed a strong agreement. The new method could drastically reduce routine clinical workload. Additionally, our method enables the measurement of the cortex width in all the mandibular bones inferior to the MF.

[Estimation of effective dose to salivary glands at examination of the oral and maxillofacial region].

The salivary glands and the oral mucosa were included in the determination of effective doses of radiography in the new ICRP (International Commission on Radiological Protection) recommendations. These changes will likely result in an upward reassessment of the effective dose during oral and maxillofacial radiographic examination. We measured the dose received by many organs and calculated the effective doses using the guidelines in ICRP Publications 103 and 60. For this study, we used intraoral radiography (incisor, canine, premolar, molar, maxillary, and mandibular areas) and panoramic radiography. The two levels of effective doses were compared. As a result, exposure during intraoral radiography ranged from 4 to 8 microSv and that during panoramic radiography ranged from 16 microSv in Publication 103. Effective doses in Publication 103 were higher than those in Publication 60. The dose was 1.6-4.5 times higher in intraoral radiography and 2.2 times higher in panoramic radiography. In conclusion, the salivary glands markedly influenced the value of the effective doses of radiography in this study.

New weighting factor of weighted CTDI equation for PMMA phantom diameter from 8 to 40 cm: A Monte Carlo study.

PURPOSE: The weighted computed tomography dose index (CTDIw ) uses measured CTDI values at the center and periphery of a cylindrical phantom. The CTDIw value is calculated using conventional, Bakalyar's, and Choi's weighting factors. However, these weighting factors were produced from only 16- and 32-cm-diameter cylindrical phantoms. This study aims to devise new weighting factors to provide more accurate average dose in the central cross-sectional plane of cylindrical phantoms over a wide range of object diameters, by using Monte Carlo simulations. METHODS: Simulations were performed by modeling a Toshiba Aquilion ONE CT scanner, in order to compute the cross-sectional dose profiles of polymethyl methacrylate (PMMA) cylindrical phantoms of each diameter (8-40 cm at 4-cm steps), for various tube voltages and longitudinal beam widths. Two phantom models were simulated, corresponding to the CTDI100 method and the method recommended by American Association of Physicists in Medicine (AAPM) task group 111. The dose-computation PMMA cylinders of 1 mm diameter were located between the phantom surfaces and the centers at intervals of 1 mm, from which cross-sectional dose profiles were calculated. By using linear least-squares fits to the obtained cross-sectional dose profiles data, we determined new weighting factors to estimate more accurate average doses in the PMMA cylindrical phantoms by using the CTDIw equation: CTDIw = Wcenter ・ CTDIcenter + Wperiphery ・ CTDIperiphery . In order to demonstrate the validity of the devised new weighting factors, the percentage difference between average dose and CTDIw value was evaluated for the weighting factors (conventional, Bakalyar's, Choi's, and devised new weighting factors) in each calculated cross-sectional dose profile. RESULTS: With the use of linear least-squares techniques, new weighting factors (Wcenter = 3/8 and Wperiphery = 5/8 where Wcenter and Wperiphery are weighting factors for CTDIcenter and CTDIperiphery ) were determined. The maximum percentage differences between average dose and CTDIw value were 16, -12, -8, and -6% for the conventional, Bakalyar's, Choi's, and devised new weighting factors, respectively. CONCLUSIONS: We devised new weighting factors (Wcenter = 3/8 and Wperiphery = 5/8) to provide more accurate average dose estimation in PMMA cylindrical phantoms over a wide range of diameter. The CTDIw equation with devised new weighting factors could estimate average dose in PMMA cylindrical phantoms with a maximum difference of -6%. The results of this study can estimate the average dose in PMMA cylindrical phantoms more accurately than the conventional weighting factors (Wcenter = 1/3 and Wperiphery = 2/3).

Regional brain activity during jaw clenching with natural teeth and with occlusal splints: a preliminary functional MRI study.

OBJECTIVE: The purpose of this study was to investigate regional brain activity during jaw clenching with natural teeth and with two types of occlusal splints using functional magnetic resonance imaging (fMRI). METHODS: Sixteen healthy volunteers were enrolled in this study. Blood oxygenation level-dependent (BOLD) fMRI signals were compared under three conditions: during clenching with natural teeth, with a soft splint, and with a hard splint. For each condition, 30-second jaw clenching followed a 60-second rest, and was repeated three times, with intervening 30-second rests. SPM 8 was used for the fMRI analysis. RESULTS: Blood oxygenation level-dependent signals during clenching with natural teeth increased in BA44, 45, and the cerebellum. Blood oxygenation level-dependent signals increased in those areas and in BA17, 18 during clenching with a soft splint. Use of the hard splint increased the BOLD signals in BA6 and BA20, 37 in addition to the areas previously mentioned. Blood oxygenation level-dependent signals in the left BA6, the left BA20, 37, and the right BA44, 45 were significantly higher during clenching with a hard splint than with natural teeth. These regions are associated with motor coordination, memory, and cognition, respectively. CONCLUSION: Jaw clenching with a hard splint caused activity in the widest brain regions, including the associated area with motor coordination.

[Comparison of absorbed and effective dose from two dental cone beam computed tomography scanners].

OBJECTIVE: This research compared the field of view with the tissue absorbed dose and effective doses using the two dental cone beam computed tomography (CBCT) scanners. MATERIALS AND METHODS: Two CBCT devices, an Alphard VEGA and 3DX multi-image micro CT MCT-1, were used. Measurements were made using an Alderson RANDO phantom and thermoluminescence dosimeters (TLDs). The calculation of the effective dose was carried out according to ICRP Publication 60 and 103. RESULTS: The effective doses for Alphard VEGA D mode, I mode, P mode, and C mode were 86, 238, 413, and 323 µSv, respectively. The effective doses using 3DX for the maxillary incisor, maxillary molar, mandibular incisor, mandibular molar, TMJ, and mandibular molar scout images were 27, 30, 48, 60, 14, and 1 µSv, respectively. CONCLUSIONS: Both Alphard VEGA and 3DX values revealed salivary gland and oral mucosa doses much higher than those required for other tissues. It is necessary to select a small mode suitable in order to realize optimization.