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1 J Dent Hyg Sci Vol. 16, No. 4, 2016, pp RESEARCH ARTICLE Optical Coherence Tomography 를이용한초기치아우식검사 민지현 청주대학교보건의료대학치위생학과 Assessment of Early Dental Caries by Using Optical Coherence Tomography Ji-Hyun Min Department of Dental Hygiene, College of Health Sciences, Cheongju University, Cheongju 28503, Korea The purpose of this study was to assess the correlation between integrated mineral loss (volume % mineral m, ΔZ TMR) determined using transverse microradiography (TMR) and integrated reflectivity (db m, ΔR OCT) determined using optical coherence tomography (OCT) for detecting early dental caries with lesion depth more than 200 m. Sixty tooth specimens were made from sound bovine teeth. They were immersed in a demineralized solution for 20, 30, and 40 days. The ΔR OCT was obtained from the cross-sectional OCT image. The ΔZ TMR was obtained from the TMR image. The correlation between ΔR OCT and ΔZ TMR was examined using Pearson correlation. The Bland-Altman plot was constructed using the ΔR OCT and ΔZ TMR values. A significant correlation between ΔR OCT and ΔZ TMR was confirmed (r=0.491, p=0.003). Moreover, most of the difference between ΔR OCT and ΔZ TMR was included in the error section of the Bland-Altman plot. Therefore, OCT could be used as a substitute for TMR when analyzing mineral loss in early dental caries. Key Words: Early dental caries, Optical coherence tomography, Transverse microradiography 서론 구강내법랑질은탈회 (demineralization) 와재광화 (remineralization) 가반복되며무기질의소실과획득이균형을이루고있다. 그러나이러한순환과정중치면세균막의구성과양, 당의섭취빈도와시간, 타액의성분과흐름, 법랑질의질 (quality), 불소의노출, 개인의면역반응등의복잡한과정이장시간지속되어균형이깨지면무기질이소실되거나획득될수있다 1-6). 치아우식 (dental caires) 은구강내미생물이발효성당질을대사하여생긴각종산 (acid) 으로인해치아무기질이용해되는것을의미하며 3), 치아의붕괴없이무기질소실만일 어나는초기단계에서치아의구조가무너져와동 (cavity) 이형성되는단계를거친다. 초기단계의우식은침습적인의 (invasive) 처치가필요하지않으며무기질의재획득, 즉재광화과정을통해정상치아로의회복이가능하다 2). 따라서초기단계의우식을관리하는것이중요하다고하겠다. 만약초기단계의우식을임상에서쉽게탐지할수있다면더이상의진행을막을수있도록하는예방처치가가능할것이다. 치아우식은전통적으로시진또는촉진, 그리고방사선장비를이용하여탐지하였다. 그러나이러한방법은주관적인평가법으로, 초기우식부위에대해민감도 (sensitivity) 가떨어질수있으며 7,8), 초기우식의심도에따른객관적인수치화가어렵다. 이미초기우식을탐지하고이를심도에따 Received: June 10, 2016, Revised: July 7, 2016, Accepted: July 7, 2016 ISSN (Print) / ISSN (Online) Correspondence to: Ji-Hyun Min Department of Dental Hygiene, College of Health Sciences, Cheongju University, 298 Daeseong-ro, Cheongwon-gu, Cheongju 28503, Korea Tel: , Fax: , jhmin@cju.ac.kr Copyright 2016 by Journal of Dental Hygiene Science This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

2 J Dent Hyg Sci Vol. 16, No. 4, 2016 라수치화하여결과를제시하는다양한장비들이시판되고있다 9-11). 그중최근광간섭단층영상기 (optical coherence tomography, OCT) 를이용한초기우식탐지및심도평가가능성에대해많은연구가이루어지고있다 12-17). OCT는 1991년도에처음개발되었으며, 백색광간섭계 (white-light interferometry) 또는저가간섭간섭계 (low coherence interferometry) 의원리와공초점현미경 (confocal microscopy) 의원리를조합한영상기기이다 18). 기본적으로마이켈슨간섭계 (Michelson interferometry) 의시스템을가지며, 안과학 (ophthalmology) 영역에서활발히활용되고있다 19). OCT 를이용하면실시간으로생체조직내부의미세구조를비접촉방식으로고해상도영상을관찰할수있으며, 초기치아우식도비파괴적으로단층 (cross section) 에대해관찰이가능하다 12,13,20). 게다가초기치아우식평가의 gold standard로여겨지는횡단미세방사선법 (transverse microradiography, TMR) 과상관성이높은것으로확인되었다 21,22). 그러나 200 m 이상의깊은법랑질초기우식과의상관성에대한연구는부족한실정이다. 따라서본연구의목적은 200 m 이상의깊이를가지는법랑질초기우식병소에서병소의심도를의미하는 TMR의 integrated mineral loss (volume % mineral m, ΔZ TMR) 와 OCT에서이와상응하는 integrated reflectivity (db m, ΔR OCT) 를구하여둘간의상관성을확인해보고자하였다. Fig. 1. Bland-Altman plot between integrated mineral loss (volume % mineral m, ΔZ TMR) and integrated reflectivity (db m, ΔR OCT). The line in the center indicates the mean difference between ΔZ TMR and ΔR OCT. The two dotted lines indicate plus or minus 1.96 times the standard deviation from the mean between ΔZ TMR and ΔR OCT. TMR: transverse microradiography, OCT: optical coherence tomography. 연구대상및방법 1. 시편제작치아시편은건전한우치영구치의전치를이용하여제작하였다. 저속핸드피스 (Lasungmedice, Incheon, Korea) 를이용하여 6 4 mm의크기로치아를절단하여, 레진에매몰하였다. 이후 1,200 grit까지 silicon carbide paper (Allied High Tech Products, Rancho Dominguez, CA, USA) 를이용하여편평하고매끄럽게치아시편표면을연마하였다. 노출된치아면에 2 4 mm의창 (window) 이형성되도록내산성바니쉬를도포하였다 (Fig. 1). 200 m 이상의다양한깊이를가지는병소를인공적으로형성하기위해서 37 o C의배양기에저장된탈회용액에각 20개씩의시편을 20일, 30일, 40일간침적하였다. 탈회용액은 21일째에한차례교환하였다. 탈회용액은 ph 4.8의 lactic acid gel로수산화인회석 (hydroxyapatite) 에대해 50% 포화상태이며, 1% carbopol (Carbopol ETD 2050 polymer; The Lubrizol Corporation, Wickliffe, OH, USA) 이포함되어있었다. 탈회이후에는모든시편을철저히세척후치아의측면, 법랑질과상아질층이확인될수있도록 diamond saw (Techcut 4; Allied High Tech Products) 를이용하여치아시편을절단하였다. 2. OCT 촬영및이미지분석본연구에서사용한 OCT는 spectral domain OCT (SD-OCT prototype; LG Electronics, Seoul, Korea) 였다 12). OCT를통한이미지영상은치아시편의측면이노출되도록절단한면에최대한가깝게 probe를위치시켜촬영을진행하였다. 이미지의폭과높이는각각 5.3 mm, 3.2 mm였다. OCT의 probe와치아시편표면간에는 4 mm의거리가있었으며, backscattered light의강도 (intensity) 에대한 B-scan 영상을획득했다. 이미지내치아표면에서부터우식병소최하방까지의 backscattered light의강도를각화소 (pixel) 에서흑백명암의값으로 Image J software (public domain developed by National Institutes of Health, Bethesda, MD, USA) 를이용하여얻었다. 이후화소의명암값이 0에서 100까지가되도록재구성하였으며, 이값을세로축으로하고우식병소의깊이를가로축으로하는그래프를그렸다. TMR의경우와마찬가지로 OCT 영상에서도세로축의명암값을무기질함량으로가정하였으며, 세로축에서 89% 의값을정상치아의무기질함량으로가정하였다. 이후치아표면에서부터 89의명암값과만나는 x축의거리까지를컴퓨터프로그램 (Ori- 258

3 민지현 :OCT 를이용한초기치아우식검사 ginpro 9.0; OriginLab, Northampton, MA, USA) 을이용하여적분하여 ΔR OCT 를구하였다. (IBM Co., Armonk, NY, USA) 을이용하였으며, 유의수준은 p<0.05를기준으로검정하였다. 3. TMR 촬영및분석치아시편을측면으로절단하여노출된면에대해 TMR 촬영을할수있도록, 그부위의치아를절단하여 100 m 의 slice가될수있도록 silicon carbide paper (Allied High Tech Products) 를이용하여편평하게연마 (grinding) 하였다. 시편을얇게제작하는이과정에서 20일, 30일, 40일간탈회한각 20개시편중각각 9개, 10개, 7개의시편 ( 총 26개 ) 소실이있었다. 이후 100 m로제작한 slice와 aluminium step wedge를 20 kv, 15 ma의 Cu-K radiation (X-ray generator PW 1830; Philips, Amedo, The Netherlands) 에 18초간노출했다 23). 획득된필름은현상, 정착 (Korectol E; Fujifilm, Tokyo, Japan) 과정을거쳤다. TMR에서얻어진필름은현미경 (Optiphoto; Nikon, Tokyo, Japan) 으로관찰하여 8-bit 디지털영상 (digital images) 으로표준화된상태하에서캡쳐하여이미지파일을획득하였다. 이후각시편마다치아표면에서부터병소깊이까지의무기질함량의윤곽 (mineral content profile) 을얻어, 치아표면 (0) 에서부터병소깊이까지의적분값, 즉 ΔZ TMR 을이전연구의방법에따라컴퓨터프로그램 (OriginPro 9.0) 을이용하여구하였다 23). 4. 통계분석 ΔZ TMR 과 ΔR OCT 간의평균값의차이는 paired t-test를통해확인하였으며, 탈회시간에따른 ΔZ TMR 과 ΔR OCT 의평균값간의차이는 ANOVA 분석으로검정하였다. 또한 ΔZ TMR 과 ΔR OCT 간의상관성은 Pearson correlation을통해확인하였으며, 이후 gold standard인 ΔZ TMR 과 OCT에서구한 ΔR OCT 간의오차를확인하기위해 Bland-Altman plot을그렸다. 모든통계분석은 PASW Statistics ver 결과 ΔZ TMR 의평균값은 14,236.66±3, vol% m였으며, ΔR OCT 의평균값은 10,366.26±2, db m로 ΔZ TMR 이 ΔR OCT 보다평균적으로 1.42배컸다. ΔZ TMR 과 ΔR OCT 의평균값간에 20일간탈회를진행한군에서는유의한차이가없었으나, 30일 (p=0.002) 과 40일 (p<0.001) 간탈회를진행한군에서는유의한차이가확인되었다. 또한탈회기간에따른평균 ΔZ TMR 값간에는유의한차이가확인되었으나 (p<0.001), 평균 ΔR OCT 값간에는유의한차이가없었다 (p=0.413, Table 1). ΔZ TMR 과 ΔR OCT 간에유의한상관관계가확인되었으며 (r=0.491, p=0.003), Bland-Altman plot에서도 TMR과 OCT의두측정방법으로구해진 ΔZ TMR 과 ΔR OCT 값간의차이가거의대부분오차구간내에있는것이확인되어두측정방법간의오차가적은것으로확인되었다 (Fig. 1). 고찰 TMR은초기우식병소의무기질밀도 (mineral density) 조사에 gold standard 장비로알려져있다. TMR 분석에서는얇은치아 slice에방사선을조사하여높은해상도의법랑질영상을취득한다. 이때 TMR의소프트웨어에는 aluminum stepwedge에대비하여 calibration이되어있어, 치아 slice 를촬영하면그영상의회색도 (gray level) 에따라무기질함량 (mineral content) 값을자동적으로산출하는원리를가진다. 본연구에서조사한 TMR의무기질소실 (ΔZ TMR) 정도의값은병소의깊이 ( m) 뿐만아니라무기질함량이반영된값으로서의미가있다 24). 또한이전연구에서는낮은깊이의 Table 1. The Values of ΔZ TMR and ΔR OCT according to the Groups Group ΔZ TMR ΔR OCT p-value c Demineraliztionfor 20 days 10,491.66±2, a 9, ±3, a Demineraliztionfor 30 days 14,581.33±2, b 10,894.53±2, a Demineraliztionfor 40 days 16,667.65±2, b 11,198.83±2, a <0.001 p-value < Values are presented as mean±standard deviation. TMR: transverse microradiography, OCT: optical coherence tomography. a,b Values with the same letter superscripts are not significant in Scheffé s multiple-comparison test at =0.05. c p-value was obtained from paired t-test between integrated mineral loss (volume % mineral m, ΔZ TMR) and integrated reflectivity (db m, ΔR OCT) values. 259

4 J Dent Hyg Sci Vol. 16, No. 4, 2016 법랑질초기우식병소또는치근우식병소에대해 TMR과 OCT 간의상관성에대해조사한경우가대부분이었다 21,22,25). 그러나본연구에서사용한시편은 20일에서 40일까지법랑질에탈회를진행하여 m에서 m의범위의깊은병소깊이를가지고있었다 (data not shown). TMR 분석은초기우식병소의무기질밀도조사에대한정확성은높으나, 분석을위해서는시편을절단해야하며, 약 100 m의 slice로제작해야만한다. 이과정에많은노력이소요될뿐만아니라정교한작업실패로인해시편의소실이있을수있다 26). 본연구에서도초기 60개의인공탈회시편을제작하였으나, TMR 촬영을위해시편을 100 m의 slice로제작중에 26개의시편소실이발생하였다. 또한 TMR 분석은시편을파괴해야하므로동일병소의무기질변화에대해종적인추적이불가능하다. 한편 OCT를이용하면비파괴적으로높은해상도의실시간생체영상획득이가능하다 18,27). 초기우식병소에대해 OCT를활용하면병소의단층영상 (cross-sectional image) 을얻을수있으며, 이는 TMR 또는편광현미경 (polarized light microscopy) 에서제공하는초기우식병소의단층영상과매우흡사하다. 이전연구에서는편광현미경과 OCT에서측정한각각의법랑질초기우식병소깊이간에 0.64에서 0.83의상관계수를확인하였으며 20,25,28), ΔZ TMR 과 ΔR OCT 간에는 ), 편광현미경에서구한 ΔZ과 ΔR OCT 간에는 0.76의상관계수를확인하였다 (p<0.05) 28). 본연구에서도 ΔZ TMR 과 ΔR OCT 간의유의한상관관계가확인되었으며 (r=0.491, p=0.003), Bland-Altman plot에서오차구간내에둘간의차이가확인되었다. 따라서 TMR을대신하여 OCT를초기우식병소의정성분석및정량분석에이용할수있을것으로생각된다. 본연구결과에서 20일, 30일, 40일의탈회기간에따라 TMR로측정하여얻은결과값인 ΔZ TMR 에서는유의한차이가확인되었으나 (p<0.001), OCT로측정하여얻은 ΔR OCT 에서는유의한차이가없었다 (p=0.413). 이는시편에인공탈회를형성시탈회용액을 21일에교체하여 20일탈회한치아와 30일과 40일탈회한치아간탈회량에상당한차이를형성하였는데, 이러한차이가초기치아우식탐지의 gold standard로여겨지는 TMR에서는정밀하게확인되었으나, OCT에서는유의한차이가확인되지않은것으로생각된다. 본연구의제한점은실제사람치아에형성된초기우식병소가아닌우치에인공적으로형성한초기우식병소를이용하여분석하였다는것이다. 그러나사람치아와조성이비슷한우치를연구에이용하였으며, 치아표면의소실이없는 치아우식병소를사용하였다. 본연구결과, ΔZ TMR 과 ΔR OCT 간의유의한상관관계를확인하였으며 (r=0.491, p=0.003), Bland-Altman plot에서도 ΔZ TMR 과 ΔR OCT 간의차이가오차구간내에확인되었다. 따라서 TMR을대신하여 OCT 를활용하면비파괴적으로초기우식병소조직의단층영상확인이가능하다. 뿐만아니라, 치과임상에서 OCT를활용하면초기우식병소의탐지및모니터링, 그리고초기우식병소의심도파악이가능하며, 이에따른처치방법의결정을효과적으로할수있을것으로생각된다. 요약 TMR은초기우식평가의 gold standard로여겨지나시편을파괴하여야만시편의무기질밀도를확인할수있는실험법이다. 그러나 OCT는비파괴적인검사법으로임상에서도초기우식을확인하는데사용하므로본연구에서는 200 m 이상의깊은법랑질초기우식에서의 OCT와 TMR에서구한 integrated mineral loss값간의상관성을확인하고자하였다. 200 m 이상의깊이를갖는인공초기우식병소를제작하여 TMR (ΔZ TMR) 과 OCT (ΔR OCT) 에서구한 integrated mineral loss를각각구하여상관성분석을시행하였으며 Bland-Altman plot을그려두값간의오차분석을시행하였다. ΔR OCT 과 ΔZ TMR 간에는유의한상관성이확인되었으며 (r=0.491, p=0.003), Bland-Altman plot 상에서도 ΔZ TMR 과 ΔR OCT 값간의차이가거의대부분오차구간내에있는것이확인되어두측정방법간의오차가적은것으로확인되었다. 따라서치과임상에서 OCT를활용하면초기우식병소의탐지및모니터링그리고초기우식병소의심도파악이가능할것으로여겨진다. 감사의글 이논문은 학년도에청주대학교보건의료과학연구소가지원한학술연구조성비 ( 특별연구과제 ) 에의해연구되었음. 본연구성과를얻기위해많은가르침을주시고지원을아끼지않으신연세대학교치과대학김백일교수님과 Iwate Medical University School of Dentistry의 Daisuke Inaba 교수님께깊은감사의말씀을드립니다. References 1. Aoba T, Fejerskov O: Dental fluorosis: chemistry and 260

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untitled Journal of Korean Academy of Oral Health 2014 March 38(1):10-16 http://dx.doi.org/10.11149/jkaoh.2014.38.1.10 Original Article QLF-D 와 OCT 를이용한초기인공우식병소의변화탐지 구혜민 1,2,3, 김보라 1,2,3, 강시묵 1,2,3, 정중호 4, 권호근