Utilizing Digital Subtraction Technology To Identify The True Fracture Lines And Artifacts For Endodontically Treated Teeth With Subtle Vertical Root Fractures

[Objective] The aim of this study was to find the subtle true root facture lines in endodontically treated teeth on cone-beam computed tomography(CBCT)images using digital subtraction radiography and evaluate the effect of width of fracture line on the identification using CBCT.[Methods] 32 endodontically treated teeth with suspected Vertical root fractures(VRF)from 30 patients were collected from December 2016 to March 2019.All patients were performed CBCT scan and evaluated the presence or absence of fracture lines;all teeth were extracted due to diagnosis of VRF or severe bone loss.The teeth were immediately subjected to micro-CT scan in vitro,and the Image J was used to measure the width of fracture lines on micro-CT images.Fracture lines on micro-CT images were considered as the gold standard.A digital subtraction software(DSS)was designed and developed,the true fracture lines on the micro-CT images were marked on the CBCT images to identify how many hypodense fracture lines were the true ones,and these teeth were divided as CBCT positive VRF teeth.Digital subtraction was performed as following: 1.The CBCT and micro-CT images were matched and overlapped;2.The true Fracture lines on the micro-CT images were marked and the micro-CT images were subtracted;3.The marked FL was left on the CBCT image to identify the true one or the streak artifacts.If all CBCT images for one tooth were recorded as positive,the tooth was finally evaluated as CBCT positive.Based on this method,the 32 teeth were divided into CBCT positive or CBCT negative.The inside point(IP)and outside point(OP)were selected and the width of IP and OP were measured on micro-CT images.The difference of width of Fracture lines between CBCT positive group and negative group and the difference of IP and OP were compared using independent sample t-test.The features of the true fracture lines were also analyzed and summarized in this study.[Results] Of the 32 teeth,23 teeth were CBCT negative(71.87%)and 9 teeth were CBCT positive(28.13%).For CBCT positive teeth,the width of OP and IP were 121.58±4.09μm and 126.41±4.84μm;for CBCT negative group,the width of OP and IP were 106.45±2.87μm and 107.34 ±2.96μm.The T test showed significant differences of width of fracture lines between CBCT positive and negative groups(P < 0.05),and no significant differences was found between OP and IP(P>0.05).The Tiny V-shape defects,irregular(not so straight and so sharp)hypodense line,and not center on the filling materials were found to be the features of true fracture line on the CBCT images.Of the 9 CBCT positive teeth,tiny V-shape defect were observed for 7 teeth(77.78%),irregular(not so straight and so sharp)hypodense line was found for 8 teeth(88.89%).Tiny V-shape defects and irregular(not so straight and so sharp)hypodense line were found to be the features of true fracture line on the CBCT images.[Conclusion] Most hypodense lines on CBCT images were artifacts secondary to the presence of root canal filling materials for endodontically treated teeth with subtle vertical root fracture.Wider fracture lines are easier being found on CBCT images for endodontically treated VRF teeth.