Objective To observe the value of self-made improved cone-beam CT(CBCT)fixation components for maxillofacial scanning.Methods CBCT fixation components(chin rest,temporal clamp)equipped by Planmeca ProMax 3D Mid dental panoramic X-ray system were modified to obtain improved CBCT fixation components,including improved chin rest,temporal clamp and occipital retention band.Totally 571 patients who underwent maxillofacial CBCT examinations for dental-related diseases were retrospectively enrolled,including 288 cases(group A)underwent scanning by a junior technician using original chin rest+original temporal clamp(component 1,n=78,A1 subgroup),modified chin rest+original temporal clamp(component 2,n=74,A2 subgroup),original chin rest+original temporal clamp+occipital retention band(component 3,n=68,A3 subgroup)or modified chin rest+original temporal clamp+occipital retention band(component 4,n=68,A4 subgroup),while the rest 283 cases(group B)underwent scanning by a senior using the above components,respectively,and were taken as B1(n=72),B2(n=69),B3(n=73)and B4(n=69)subgroups.The incidence of motion artifacts were compared among A2/B2,A3/B3,A4/B4 subgroups and A1/B1 subgroups.Results Compared with A1+B1 subgroups,the overall motion artifacts rate in A4+B4 subgroups decreased from 17.33％(26/150)to 8.03％(11/137)(P=0.019),while in A2+B2 subgroups(13.29％[19/143])and A3+B3 subgroups(9.93％[14/141])did not significantly decrease(P=0.337,0.067).In group A,no statistical difference of motion artifacts rate was found between A 2(17.57％[13/74])or A3(13.24％[9/68])subgroups and A1 subgroup(23.08％[18/78])(P=0.399,0.127),while the motion artifacts rate in A4 subgroup(10.29％[7/68])was lower than that in A1 subgroup(23.08％[18/78])(P=0.041).In group B,no significant difference of motion artifacts rates was found between B2,B3 or B4 subgroups(8.70％[6/69],6.85％[5/73],5.80％[4/69])and B1 subgroup(11.11％[8/72])(P=0.632,0.369,0.258).Conclusion Self-made improved CBCT fixation components could effectively secure patients' head and reduce motion artifacts in maxillofacial CBCT.

Objective To observe the value of self-made improved cone-beam CT(CBCT)fixation components for maxillofacial scanning.Methods CBCT fixation components(chin rest,temporal clamp)equipped by Planmeca ProMax 3D Mid dental panoramic X-ray system were modified to obtain improved CBCT fixation components,including improved chin rest,temporal clamp and occipital retention band.Totally 571 patients who underwent maxillofacial CBCT examinations for dental-related diseases were retrospectively enrolled,including 288 cases(group A)underwent scanning by a junior technician using original chin rest+original temporal clamp(component 1,n=78,A1 subgroup),modified chin rest+original temporal clamp(component 2,n=74,A2 subgroup),original chin rest+original temporal clamp+occipital retention band(component 3,n=68,A3 subgroup)or modified chin rest+original temporal clamp+occipital retention band(component 4,n=68,A4 subgroup),while the rest 283 cases(group B)underwent scanning by a senior using the above components,respectively,and were taken as B1(n=72),B2(n=69),B3(n=73)and B4(n=69)subgroups.The incidence of motion artifacts were compared among A2/B2,A3/B3,A4/B4 subgroups and A1/B1 subgroups.Results Compared with A1+B1 subgroups,the overall motion artifacts rate in A4+B4 subgroups decreased from 17.33％(26/150)to 8.03％(11/137)(P=0.019),while in A2+B2 subgroups(13.29％[19/143])and A3+B3 subgroups(9.93％[14/141])did not significantly decrease(P=0.337,0.067).In group A,no statistical difference of motion artifacts rate was found between A 2(17.57％[13/74])or A3(13.24％[9/68])subgroups and A1 subgroup(23.08％[18/78])(P=0.399,0.127),while the motion artifacts rate in A4 subgroup(10.29％[7/68])was lower than that in A1 subgroup(23.08％[18/78])(P=0.041).In group B,no significant difference of motion artifacts rates was found between B2,B3 or B4 subgroups(8.70％[6/69],6.85％[5/73],5.80％[4/69])and B1 subgroup(11.11％[8/72])(P=0.632,0.369,0.258).Conclusion Self-made improved CBCT fixation components could effectively secure patients' head and reduce motion artifacts in maxillofacial CBCT.

Objective: To compare the effect of different scanning parameters of cone beam computed tomography (CBCT) on displaying trabecular microstructure in the anterior region of the mental foramen of the mandible, and to provide a basis for the rational selection of CBCT scanning parameters. Methods: This study was approved by the Ethics Committee of the Affiliated Stomatological Hospital, Medical School of Nanjing University. An in vitro study was conducted using CBCT (ProMax 3D Mid) to scan eight dry human mandibular specimens with five scanning protocols: Group A: 90 kV/6.3 mA, Group B: 90 kV/8.0 mA, Group C: 90 kV/10.0 mA, Group D: 75 kV/8.0 mA, and Group E: 60 kV/8.0 mA, resulting in a total of 40 CBCT images. Entrance surface dose (ESD) and computed tomography dose index (CTDI) under different scanning conditions were recorded. The original CBCT images were imported into the image analysis software (Hiscan Analyzer) to measure four trabecular bone microstructural parameters in the region of interest of the mandible: trabecular thickness (Tb.Th), trabecular number (Tb.N), trabecular space (Tb.Sp), and bone volume/tissue volume (BV/TV). A total of 108 CBCT images were retrospectively collected from clinical implant patients using any of the 90 kV/6.3 mA, 90 kV/8.0 mA, or 90 kV/10.0 mA scanning conditions, and the above four parameters of the region of interest of the mandible were also measured. SPSS 26.0 software was used to compare the differences in the four trabecular bone microstructural parameters between the CBCT images of the mandibular specimens in vitro and clinical patients in vivo. Results: The in vitro study results showed that reducing the tube voltage and tube current would lead to a decrease in the ESD and CTDI. When the tube voltage was maintained at 90 kV and the tube current was changed, BV/TV, Tb.N, and Tb.Th values increased with the increase of tube current; Tb.Sp values decreased with the increase of tube current, but there was no statistically significant difference in the four bone morphological parameters (P > 0.05). When the tube current was maintained at 8.0 mA and the tube voltage was altered, BV/TV and Tb.N decreased with the increase of tube voltage, Tb.Sp values increased with the increase of tube voltage, and BV/TV, Tb.N, and Tb.Sp showed statistically significant differences (P < 0.05). In clinical patients undergoing CBCT scanning, when the tube voltage was 90 kV and the tube current was different (6.3, 8.0, 10.0 mA), there was no statistically significant difference in the four bone morphological parameters (P > 0.05). Conclusions In this study, when the tube voltage was fixed at 90 kV, there was no difference in the trabecular microstructure of the anterior region of the mandible when the tube current was increased. When CBCT scanning of clinical patients needs to show the trabecular microstructure of the anterior region of the mandible, the tube current can be appropriately reduced to decrease the radiation dose received by the patient. Thus, it is recommended to use the parameters 90 kV and 6.3 mA for CBCT scanning.