Fracture Resistance of Roots in Mandibular Premolars Following Root Canal Instrumentation of Different Sizes.

OBJECTIVE: To measure the fracture resistance of mandibular premolar roots following root canal instrumentation with different sizes. METHODS: A total of 100 human permanent mandibular premolars with a straight single canal were decoronated and assigned to 10 groups (n = 10) by block randomisation. In the control group, the roots were uninstrumented, whereas roots in the nine experimental groups were instrumented to different master apical files (MAF) and tapers (MAF/taper): 40/0.05, 45/0.05, 50/0.05, 55/0.05, 60/0.05, 40/0.10, 40/0.15, 45/0.10 and 45/0.15. All roots were subjected to vertical loading until fracture. RESULTS: Fracture load values for instrumented roots were lower than the intact roots of the control group. In 50/0.05, 55/0.05, 60/0.05, 40/0.15 and 45/0.15 groups, the fracture load values were significantly lower than the fracture load value for the control group (P < 0.05) with a 30% decrease. No significant differences in the fracture modes were detected among the 10 groups (P > 0.05). CONCLUSION: Mechanical instrumentation adversely affects the fracture resistance of roots. When the roots of mandibular premolars were instrumented to a MAF equal to or larger than 50 with a taper of 0.05 or to a MAF of 40 or 45 with a taper of 0.15, the fracture load values significantly decreased.

Electrode Placing Sites affect Pulp Vitality Test of Human Incisors and Premolars.

OBJECTIVE: To investigate electric pulp test thresholds at different sites on healthy incisors and premolars and determine appropriate test sites. METHODS: Overall, 47 volunteers aged 20 to 30 years were recruited, and 163 incisors and 140 premolars were tested at several sites with an Electric Pulp Tester. One-way analysis of variance and a Tukey test were used to analyse the threshold values among different tooth types and sites. RESULTS: The lowest threshold value for incisors was identified on the incisal edge. The difference of threshold on the incisal edge and other sites was statistically significant in mandibular incisors. For maxillary premolars and the mandibular second premolar, the lowest response was obtained with the tester tip on the lingual slope of the buccal cusp. For the mandibular first premolar, the response at the lingual slope of the buccal cusp, as the second lowest, was slightly higher than that at the buccal cusp. CONCLUSION: The incisal edge for incisors and the lingual slope of the buccal cusp for premolars was favoured as the optimal sites for electric pulp test.

Comparison of the planning target volume based on three-dimensional CT and four-dimensional CT images of non-small-cell lung cancer.

BACKGROUND AND PURPOSE: To compare positional and volumetric differences of planning target volumes (PTVs) based on axial three-dimensional CT (3DCT) and four-dimensional CT (4DCT) for the primary tumor of non-small cell lung cancer (NSCLC). MATERIALS AND METHODS: Twenty-eight patients with NSCLC underwent 3DCT and 4DCT scans of the thorax during normal free breathing. PTV(vector) was defined on 3DCT using the individual tumor motion vector measured by 4DCT accounting for tumor motion; PTV(4D) was defined on all phases of 4DCT images. In addition, a 7mm margin for microscopic disease and a 3mm setup margin were used for above PTVs, respectively. The differences in target position, volume and coverage between PTV(vector) and PTV(4D) were evaluated for tumors in different lobes, respectively. RESULTS: The median motion vector for tumors located in the upper lobe (group A) and in the middle lower lobe (group B) was 2.8 and 7mm, respectively. The mean centroid shifts between PTV(vector) and PTV(4D) in the LR, AP and CC directions for group A and B were close to zero. The median size ratio of PTV(4D) to PTV(vector) was 0.75 and 0.52 for group A and B. The motion vector showed a significant correlation to the ratio of PTV(4D) to PTV(vector) for group A and B (p=0.008 and 0.003). The median DI of PTV(vector) in PTV(4D) was 69.19% for group A and 51.60% for group B. The median DI of PTV(4D) in PTV(vector) was 98.99% for group A and 99.94% for group B. CONCLUSION: It is necessary to expand the internal margin isotropically in a single direction for 3DCT treatment planning due to the uncertainty of the 3DCT-based target position. The 3DCT-based PTV using individual margins provides a good coverage of the 4DCT-based PTV, meanwhile encompasses relatively large normal tissues, especially for middle and lower lobe tumors. We should be cautious about the use of the individual PTV derived from 3DCT in treatment planning.

[Comparison of overlap ratios of the target volume in different respiratory states with active breathing control for external-beam partial breast irradiation].

OBJECTIVE: To explore the overlap ratio of the target volume in different respiratory statuses of active breath control (ABC) and their differences during external-beam partial breast irradiation (EB-PBI), and from the perspective of target volume overlap to determine the influence of the ABC-assisted breathing condition on intra-fractional target movement of EB-PBI. METHODS: The patients, who received breast-conserving surgery with silver clips marked at the margins of the cavity and were suitable for EB-PBI, were immobilized on the breast bracket to undertake CT simulation assisted by ABC device, six sets of CT simulation images including two sets of image in state of moderate deep inspiration breathing control (mDIBH), two sets of images in state of free breath (FB) and two sets of images in state of deep expiration breathing control (DEBH) were obtained. The six sets of images were transferred to Pinnacle(3) treatment planning system (TPS), then automatic fusion and registration between two sets of mDIBH images, two sets of FB images, two sets of DEBH images and mDIBH image and DEBH image were achieved separately. Thereafter, the overlap ratios of GTV with GTV, CTV with CTV, PTV with PTV were calculated by the Pinnacle(3) TPS. The differences between the overlap ratios of the three kinds of targets in the same registered image and the difference between the overlap ratios of the same kind of target in the different registered images were statistically analyzed using statistical package of SPSS 11.5. RESULTS: Based on mDIBH/mDIBH registration, the overlap ratios of GTV/GTV, CTV/CTV and PTV/PTV were (83.54 ± 11.41)%, (93.00 ± 6.49)%, and (95.26 ± 4.90)%, respectively, and the differences of the overlap ratios between GTV/GTV and CTV/CTV, GTV/GTV and PTV/PTV were all statistically significant (P < 0.05), but statistically not significant between CTV/CTV and PTV/PTV (P > 0.05). Based on FB/FB registration, the overlap ratios of GTV/GTV, CTV/CTV and PTV/PTV were (72.55 ± 29.10)%, (89.36 ± 9.53)% and (92.47 ± 7.25)%, respectively, and the differences of the overlap ratios between GTV/GTV and CTV/CTV, CTV/CTV and PTV/PTV were all not statistically significant (P > 0.05), but statistically significant between GTV/GTV and PTV/PTV (P < 0.05). Based on DEBH/DEBH registration, the overlap ratios of GTV/GTV, CTV/CTV and PTV/PTV were (79.48 ± 22.31)%, (92.83 ± 6.77)% and (95.05 ± 4.81)%, respectively, and the differences of the overlap ratios between GTV/GTV and CTV/CTV (P = 0.000), CTV/CTV and PTV/PTV (P = 0.037), GTV/GTV and PTV/PTV (P = 0.000) were statistically all significant (P = 0.000). The differences of the overlap ratios of GTV/GTV, CTV/CTV, and PTV/PTV (P = 0.000) between mDIBH/mDIBH and DEBH/DEBH, mDIBH/mDIBH and FB/FB, FB/FB and DEBH/DEBH were all statistically significant (P = 0.000), and not statistically significant between mDIBH/mDIBH and mDIBH/DEBH, FB/FB and mDIBH/DEBH. CONCLUSIONS: During the delivering of EB-PBI assisted by ABC, the intra-fractional overlap ratios of the target volume between the same breathing state is increasing in the order of GTV/GTV → CTV/CTV → PTV/PTV. The difference of the overlap ratios of the target volumes between mDIBH and mDIBH, FB and FB, DEBH and DEBH is not significant, and the overlap ratios of PTV/PTV in the three breathing statuses of mDIBH, FB and DEBH reaches a higher level. Therefore, from the perspective of target volume overlap, if the setup error is corrected online before delivering, the necessity of breathing control during delivering of EB-PBI is worthy discussing.