Objectives: To compare microarchitecture parameters of bone samples scanned using micro-CT (mCT) to those obtained by using CBCT. Methods: A bone biopsy trephine bur (3 3 10 mm) was used to remove 20 cylindrical bone samples from 20 dry hemimandibles. Samples were scanned using mCT (mCT 35; SCANCO Medical, Brüttisellen, Switzerland) with a voxel size of 20 mm and CBCT (3D Accuitomo 170; J. Morita, Kyoto, Japan) with a voxel size of 80 mm. All corresponding sample scans were aligned and cropped. Image analysis was carried out using BoneJ, including the following parameters: skeleton analysis, bone surface per total volume (BS/TV), bone volume per total volume (BV/TV), connectivity density, anisotropy, trabecular thickness and spacing, structure model index, plateness and fractal dimension. Pearson and Spearman correlation coefficients (R) were calculated. CBCT values were then calibrated using the slope of the linear fit with the mCT values. The mean error after calibration was calculated and normalized to the standard deviation of the mCT values. Results: R-values ranged between 0.05 (plateness) and 0.83 (BS/TV). Correlation was significant for both Spearman and Pearson's R for 8 out of 16 parameters. After calibration, the smallest normalized error was found for BV/TV (0.48). For other parameters, the error range was 0.58-2.10. Conclusions: Despite the overall correlation, this study demonstrates the uncertainty associated with using bone microarchitecture parameters on CBCT images. Although clinically relevant parameter ranges are not available, the errors found in this study may be too high for some parameters to be considered for clinical application.

Objective: To evaluate the effect of exposure parameters and voxel size on bone structure analysis in dental CBCT. Methods: 20 cylindrical bone samples underwent CBCT scanning (3D Accuitomo 170; J. Morita, Kyoto, Japan) using three combinations of tube voltage (kV) and tube currentexposure time product (mAs), corresponding with a CT dose index of 3.4 mGy: 90 kV and 62 mAs, 73 kV and 108.5 mAs, and 64 kV and 155 mAs. Images were reconstructed with a voxel size of 0.080 mm. In addition, the 90 kV scan was reconstructed at voxel sizes of 0.125, 0.160, 0.200, 0.250 and 0.300 mm. The following parameters were measured: bone surface (BS) and bone volume (BV) per total volume (TV), fractal dimension, connectivity density, anisotropy, trabecular thickness (Tb. Th.) and trabecular spacing (Tb. Sp.), structure model index (SMI), plateness, branches, junctions, branch length and triple points. Results: For most parameters, there was no significant effect of the kV value. For BV/TV, "90 kV" differed significantly from the other kV settings; for SMI, "64 vs 73 kV" was significant. For BS/TV, fractal dimension, connectivity density, branches, junctions and triple points values incrementally decreased at larger voxel sizes, whereas an increase was seen for Tb. Th., Tb. Sp., SMI and branch length. For anisotropy and plateness, no (or little) effect of voxel size was seen; for BV/TV, the effect was inconsistent. Conclusions: Most bone structure parameters are not affected by the kV if the radiation dose is constant. Parameters dealing with the trabecular structure are heavily affected by the voxel size. Dentomaxillofacial Radiology (2015Radiology ( ) 44, 20150078. doi: 10.1259 Cite this article as: Pauwels R, Faruangsaeng T, Charoenkarn T, Ngonphloy N, Panmekiate S. Effect of exposure parameters and voxel size on bone structure analysis in CBCT. Dentomaxillofac Radiol 2015; 44: 20150078.

The molecular control of tooth development is different between the maxilla and mandible, contributing to different tooth shapes and locations; however, whether this difference occurs in human permanent teeth is unknown. The aim of this study was to investigate and compare the transcriptome profiles of permanent maxillary and mandibular posterior teeth. Ten participants who had a pair of opposing premolars or molars extracted were recruited. The RNA obtained from cultured dental pulp stem cells underwent RNA-sequencing and qRT-PCR. The transcriptome profiles of two opposing premolar pairs and two molar pairs demonstrated that the upper premolars, lower premolars, upper molars, and lower molars expressed the same top-ranked genes, comprising FN1, COL1A1, COL1A2, ACTB, and EEFIA1, which are involved in extracellular matrix organization, immune system, signal transduction, hemostasis, and vesicle-mediated transport. Comparative transcriptome analyses of each/combined tooth pairs demonstrated that PITX1 was the only gene with different expression levels between upper and lower posterior teeth. PITX1 exhibited a 64-fold and 116-fold higher expression level in lower teeth compared with their upper premolars and molars, respectively. These differences were confirmed by qRT-PCR. Taken together, this study, for the first time, reveals that PITX1 is expressed significantly higher in mandibular posterior teeth compared with maxillary posterior teeth. The difference is more evident in the molars compared with premolars and consistent with its expression pattern in mouse developing teeth. We demonstrate that differences in lower versus upper teeth gene expression during odontogenesis occur in permanent teeth and suggest that these differences should be considered in molecular studies of dental pulp stem cells. Our findings pave the way to develop a more precise treatment in regenerative dentistry such as gene-based therapies for dentin/pulp regeneration and regeneration of different tooth types.

Objective : Given the anatomical and locational differences between the maxillary and mandibular teeth, it is possible that there are differences in gene expression patterns of dental pulp cells within those teeth. This study evaluates and compares the gene expression profiles of the maxillary and mandibular human teeth with the aim of finding differences in gene expression patterns of dental pulp cells by RNA-Sequencing technique. Methods : The upper and lower premolar and molar teeth obtained from the same participant were employed. Two pairs of opposing premolar teeth and two pairs of opposing molar teeth were isolated, cultured, and subjected for RNA sequencing. RNA-Seq Alignment and RNA-Seq Differential Expression were used to analyze gene expression profile. Quantitative RT-PCR was performed to confirm the result obtained from RNA-Sequencing. Results : RNA sequencing demonstrated that 19,372 genes out of 27,914 in total were expressed. The top expression genes were FN1, COL1A1, COL1A2, ACTB and EEF1A1. In DPSCs of posterior teeth (premolar and molar), only PITX1 gene had a significant higher expression (exhibiting 26.47 or 89-fold change) in the lower teeth compared to the upper teeth (64-fold change in premolar teeth and 116-fold change in molar teeth). Conclusion : We showed that PITX1 gene had a significant higher expression in the lower teeth compared to the upper teeth and this difference in PITX1 level was more evident in the molars compared to premolars.