Assessment of cortical bone microdamage following insertion of microimplants using optical coherence tomography: a preliminary study

Abstract

Objectives: The study was done to evaluate the efficacy of optical coherence tomography (OCT), to detect and analyze the microdamage occurring around the microimplant immediately following its placement, and to compare the findings with micro-computed tomography (μCT) images of the samples to validate the result of the present study.

Methods: Microimplants were inserted into bovine bone samples. Images of the samples were obtained using OCT and μCT. Visual comparisons of the images were made to evaluate whether anatomical details and microdamage induced by microimplant insertion were accurately revealed by OCT.

Results: The surface of the cortical bone with its anatomical variations is visualized on the OCT images. Microdamage occurring on the surface of the cortical bone around the microimplant can be appreciated in OCT images. The resulting OCT images were compared with the μCT images. A high correlation regarding the visualization of individual microcracks was observed. The depth penetration of OCT is limited when compared to μCT.

Conclusions: OCT in the present study was able to generate high-resolution images of the microdamage occurring around the microimplant. Image quality at the surface of the cortical bone is above par when compared with μCT imaging, because of the inherent high contrast and high-resolution quality of OCT systems. Improvements in the imaging depth and development of intraoral sensors are vital for developing a real-time imaging system and integrating the system into orthodontic practice.

Keywords: Optical coherence tomography; Microimplant; Cortical bone; Micro-computed tomography.

Fig. 1

Representative images of microimplant insertion onto the cortical bone surface Microimplant was inserted at an angle of 90° (a) and 45° (b) to the cortical bone surface

Fig. 2

SS-OCT system schematic diagram Schematic representation of the 1300 nm swept-source optical coherence tomography (SS-OCT) system used for the experiment

Fig. 3

2D and 3D images of the control area imaged using SS-OCT system (a) 2D OCT image of the bone sample, with the arbitrary location of implant placement. (b) En face image obtained at 100 µm from the bone surface. (c) 3D OCT image of the control surface, which was an orthogonally sectioned view of internal structural variations. (d) 3D image along with orthogonal section planes with en face. Angulations of 90° and 45°, shown in (a), give a representative arbitrary placement of microimplants

Fig. 4

Representative 2D and 3D SS-OCT images of an implant inserted at 45° to the cortical bone surface (a) An added representative camera photograph of the implant mounted in a bone. (b) A 3D image with sectional planes in all three directions. (c, d) 2D OCT images show the cross-section of the sample along with the orthodontic implant. (e, f) En face images at 100 and 50 µm depth, respectively. Red arrows shown in the images indicate the location of microcracks around the microimplant. The red dotted arrows indicate the direction of implant insertion on to the bone

Fig. 5

Representative 2D and 3D SS-OCT images of an implant inserted at 90° to the cortical bone surface (a) An added representative camera photograph of the implant mounted in a bone. (b) A 3D image with sectional planes in all three directions. (c, d) 2D OCT images show the cross-section of the sample along with the orthodontic microimplant. (e, f) En face images at 50 and 100 µm depth, respectively. Red arrows shown in the images indicate the location of microcracks around the microimplant. The red dotted arrows indicate the direction of implant insertion onto the bone

Fig. 6

A-scan plot analysis and microcrack and microdamage identifications for en face OCT images of 90^° and 45^° angulated insertions of microimplants on the cortical bone surface (a) and (b) are the en face OCT images of the 45° and 90° angulated microimplant OCT images, respectively. (c) and (d) are the horizontal A-scan plots obtained from (a) and (b), respectively. Similarly, (e) and (f) are the vertical A-scan plots obtained from (a) and (b), respectively. Their corresponding crack is identified in their A-scan plots. The direction of obtained A-scan is represented by black and red arrows in the en face images. Also, the precise location at which the A-scan in the OCT images was obtained is represented with black and red dotted lines for their respective horizontal and vertical directions, respectively. A clear representative crack in the en face images of 45° and 90° angulated microimplant OCT images is shown as red box. The inset images at the top right region in (a) and (b) are the magnified areas, which are represented by a red box region in their respective en face images. Clear and distinct microcracks around the bone-implant interface are represented in the inset indicated by a white arrow. In the A-scan plots (e, f), the red box regions correspond to the indicated microcracks in the respective inset images

Fig. 7

Representative 2D and 3D μCT images of a microimplant inserted to the cortical bone surface at 45° (a, c, e) and 90° (b, d, f) angulations (a, b) 3D images showing cortical and trabecular bone. (c, d) 2D μCT images showing the cross-section of the sample along with the microimplant. (e, f) En face images at 100 μm depth. Red arrows indicate the location of microcracks around the microimplant

Fig. 8

Comparisons of images obtained from OCT and μCT 2D (a) and en face (c) images of the bone sample scanned with OCT. 2D (b) and en face (d) images of the bone sample scanned with μCT. Presentation of bone debris (1) and micro-elevations (2) seen around the microimplant on the OCT (e) and μCT (f) images. Red arrows indicate the occurrences of microcracks around the microimplant. Inset images are magnified areas representative of red box regions in (a‒d)