| Tooth root fissures include vertical root fractures and micro-cracks caused by tooth occlusion,root canal treatment,etc.Clinically,the propagation of micro-cracks may lead to vertical root fracture and other periodontal diseases,leading to the need for tooth extraction.Therefore,it is particularly important for early diagnosis and timely treatment of dental micro-cracks.In the early stage of the root fracture,the pathological site is concealed,the early symptoms are atypical,the clinical manifestations are quite different,the disease is difficult to be located,it is easy to be misdiagnosed by missed diagnosis,and the lack of effective treatment means is the current difficult point of clinical diagnosis and treatment.At present,the three-dimensional cone beam computed tomography(CBCT)is the most commonly auxiliary method for diagnosing root fracture.However,CBCT has many limitations: radiation risks,low sensitivity to check root cracks,low resolution(The resolution is greater than 76?m and great diagnostic accuracy for above-30?m fractures)and more artifacts of image.These have a greatly impact on image quality and diagnostic effectiveness.Therefore,it has extremely clinical significance to explore a techniques which has advantages of non-invasive,high-resolution and real-time to detect the internal structure of dental tissues through the inner wall of the root canal.The purpose of this study is to construct a 1310 nm high-speed three-dimensional swept source optical coherence tomography(SS-OCT)system for root canal endoscopic imaging,and to develop an endoscopic probe based on GRIN lens.The combination of the swept optical coherence tomography system and the fiber optic probe is used to study the diagnostic accuracy and clinical application limitations of the SS-OCT system for artificially root micro-fractures.The main research contents and results are as follows:A 1310 nm root canal endoscopic SS-OCT image system has been built.The center wavelength of the swept source is 1310.5 nm,the sweep rate is 100.16 kHz,the wavelength tuning range is 140.1 nm,and the average optical power is 32.8 mW.The interference optical path uses a fiber optical Mach-Zehnder interferometer,which is easy to adjust and is not susceptible to environmental interference.The interference spectr?m signal is acquired by a balanced detector,which can double the system signal-to-noise ratio while suppressing common mode noise.The algorithm process for collecting signals mainly includes subtracting DC term noise,spectral calibration,spectral shaping,dispersion compensation and Fourier transform.The system parameters are as follows: theoretical and experimental longitudinal resolution are 5.4?m and 7.1?m,dynamic range is 62.9dB,and theoretical imaging depth is 6.3mm in air.An optical endoscopic catheter based on GRIN lens technology has been designed and developed.The light guiding portion of the probe is mainly composed of a single mode fiber,a self-focusing fiber and a deflecting prism,which is coupled together by a fiber fusion splicer.The light guide is covered by a spring tube.The function of the spring tube is to drive the fiber to rotate,complete the 360° B-scan.The outermost layer of the probe is covered by a layer of plastic tube for protection and partitioning.Utilizing the constructed three-dimensional swept source optical coherence tomography(OCT)system and cardiovascular endoscopic imaging catheter,we image 46 root section samples with artificial root fractures(width ranges from 8?m to 283?m).It is shown that the system has a diagnostic accuracy as good as 98.3% when the width of root fractures is greater than 30?m.The diagnostic accuracy is 36.3% for fractures smaller than 30?m.For the 25 fracture-free samples the accuracy is 96.0%.Further analysis suggests optimization of the relative position and angle between the catheter and sample slides,as well as 3D reconstruction of images.With these improvements we achieve 100% accuracy for above-30?m fractures and 57.6% accuracy for below-30?m ones.This experiment suggests a promising future for the application of endoscopic OCT in the diagnosis of dental root fractures. |
PDF Full Text Request