대한소아치과학회지 28(2) 2001 중합광원과중합시간이복합레진의표면경도에미치는영향 배상만 이광희 김대업 안호영 원광대학교치과대학소아치과학교실 원광치의학연구소 국문초록 플라즈마아크광원을사용하는광중합기를저출력할로겐광원을사용하는전통적인광중합기와비교평가하기위하여, 세종류의복

대한소아치과학회지 28(2) 2001 중합광원과중합시간이복합레진의표면경도에미치는영향 배상만 이광희 김대업 안호영 원광대학교치과대학소아치과학교실 원광치의학연구소 국문초록 플라즈마아크광원을사용하는광중합기를저출력할로겐광원을사용하는전통적인광중합기와비교평가하기위하여, 세종류의복합레진을두께가 2, 3, 4, 5mm인몰드에충전하고레진상면을할로겐광으로 40초간, 플라즈마광으로 3, 6, 9 초간조사한후레진상면과하면의표면미세경도를각각측정하였다. 레진시편상면의표면경도와하면의표면경도간의차이는, 두께 2mm 시편에할로겐광을 40초간조사하였거나플라즈마광을 9초간조사한경우들을제외하고, 모두유의하였다 (P<0.05). 레진시편상면의표면경도는전체실험군들에서서로유의한차이가없었다. 레진시편하면의표면경도는전체적으로보아할로겐광을 40초간조사한군들에서가장높았고플라즈마광의조사시간이감소함에따라감소하였으며레진시편의두께가증가함에따라감소하였다. 이상의결과는복합레진의중합깊이측면에서볼때 3, 6, 9초간조사하는고출력플라즈마광의중합능력이 40초간조사하는저출력할로겐광의중합능력에미치지못함을시사한다. 주요어 : 플라즈마, 할로겐, 광중합, 복합레진, 표면경도 Ⅰ. 서론광중합복합레진은 1970년대에실용화된이후로심미적치과수복의새로운장을열었으며재료와기술이계속진보되어왔다 1). 중합광으로서처음에채택된자외선은인체에대한유해성과복합레진에대한약한투과력등의단점이있었기때문에, 인체에안전하고자외선에비해더짧은시간에더깊이중합할수있는가시광선영역의할로겐광이현재일반적으로사용되고있다 2). 광중합복합레진의최적중합을위하여는와동내레진하면에중합광이도달할수있도록중합광의강도가충분해야하고또레진층의두께가적절해야한다. Fowler 등 3) 은중합광출력감소가중합깊이에미치는영향을경도측정으로평가하였을때레진시편상면의중합은영향을받지않았으나하면은큰영향을받았으며조사시간이짧았을때그영향이더컸다고하였다. Rueggeberg 등 4-6) 은복합레진의광중합에영향을끼치는주된요인은레진의두께이고그다음은중합광의조사시간및강도이며, 레진의두께는 2mm를초과하지말아야한다고하였고, 최소한 400mW/cm 2 의강도를가진광원으로 60초간중합할것을권장하였다. 복합레진을얇은두께의여러층으로나누어충전하는방법은복합레진재료의주된임상적단점인중합수축을최소화할 수있는방법으로서추천되어왔지만 7) 할로겐광으로는한번에 40초이상중합해야하므로전체시술시간이늘어난다는문제점이있었다. 한편, Nomoto 등 8) 은조사광의강도와총조사시간을곱하여산출되는총조사량이일정하면중합의깊이가동일하다고하였으며, 이것은조사광의강도를증가시킴으로써총조사시간을단축할수있음을의미할것이다. 조사광의강도를증가시키는방법으로서할로겐광원보다출력이훨씬강한가시광선파장대의아르곤이온레이저를사용하여짧은시간에복합레진을중합하는기술이연구되었고, 대부분의연구자들이긍정적인결과를보고하였다 9-15). 그러나, 아르곤이온레이저는짧은중합시간의장점에도불구하고가격이매우높기때문에할로겐광중합기에비해실용성이매우낮았다. 최근에개발된플라즈마아크광중합기 (plasma arc light curing unit) 는아르곤이온레이저에비해가격이낮으면서도그에버금가는강한출력을가지고있어서광중합시간을약 3 초까지단축할수있다고선전되고있다. 플라즈마아크광중합기에관한연구보고는출시된기간이짧아아직까지세계적으로희소한편이다. 국내연구에서김 16) 은중합방법과중합시간이치면열구전색재의미세경도와마모도에미치는영향에관한연구에서유사한표면경도를얻기위한중합시간이플라즈마광중합기가할로겐광중합기보다더짧았다고하였다. 국외연구에서 Peutzfeldt 등 17), Roberts 등 18), Ergle과 Rueggeberg 19), 199

J Korean Acad Pediatr Dent 28(2) 2001 Burtscher 등 20), Hofmann 등 21), Munksgaard 등 22) 은여러기준에서볼때플라즈마중합기로 3초간중합하는것이할로겐중합기로 40초간중합한것에미치지못한다고보고하였다. 플라즈마광중합기를사용하는경우복합레진의최적중합시간이 3초보다길더라도할로겐광중합기의 40초중합시간보다훨씬짧다면실용적가치가있을것이다. 또한국내에서일반수복용복합레진을대상으로플라즈마광중합기의중합력을연구할필요성이있었다. 연구목적은복합레진의중합깊이에따른중합후표면경도를측정하는방법으로 3초, 6초, 9초간플라즈마아크광중합기로중합한경우와전통적인방법대로 40 초간할로겐광중합기로중합한경우를비교평가함으로써중합광원과중합시간이복합레진의표면경도에미치는영향을규명하는것이었다. 2. 표면미세경도의측정 Vickers diamond indenter가부착된미세경도측정기 (MXT 70, Matsuzawa, Japan) 를사용하여레진시편의상면과하면의경도를측정하였다. 하중 300gm, 하중속도 0.3mm/sec, acting period 10초로압흔을주고 400배율로크기를계측하여 Vickers Hardness Number를산출하였다. 시편의중앙부위에서일정한값이측정될때까지반복측정하였고 5개시편측정치의평균을각실험군의측정치로하였다. 레진의종류별측정치를하나로통합하여레진시편의두께및중합광원-중합시간에따른 16개실험군별로평균과표준편차를산출하였다. 3. 자료분석 Ⅱ. 재료및방법세종류의복합레진을두께가 2, 3, 4, 5mm인몰드에충전하고레진상면을할로겐광으로 40초간, 플라즈마광으로 3, 6, 9초간조사한후레진상면과하면의표면미세경도를각각측정하였다. 1. 레진시편의제작실험에사용된복합레진은 Z-100(shade A3, 3M, U.S.A.), Tetric Ceram(shade A3, Vivadent, Liechtenstein), SureFil(shade A, Dentsply, U.S.A.) 로서, 각제품의설명서에따르면 Z-100은 1회중합두께가 2.5mm, Tetric Ceram은 1회중합두께가 2.0mm, SureFil은 1회중합두께가 5mm이며, 광중합시간은모두 40초이다. 내경이 4mm, 두께가 2, 3, 4, 5mm인 teflon mold에레진을충전하고레진의상면에플라즈마광중합기 (Flipo, Lokki, France) 로 3, 6, 9초간, 할로겐광중합기 (Optilux 360, Demetron, U.S.A.) 로 40초간중합광을조사하였다 (Table 2). 중합기의 light guide tip은 cover glass의두께만큼시편상부 1mm에위치하였다. 조사광의강도는 Optilux 501 (Demetron, U.S.A.) 에부착된조도계 (radiometer) 로측정하였을때, 플라즈마광은약 1,900mW/cm 2, 할로겐광은약 370mW/cm 2 으로나타났다. 광중합후 1주일동안실온의암소에보관하였다. 레진종류 (3개), 레진시편의두께 (4개), 중합광원및중합시간 (4개) 에따른 48개각실험군당 5개의시편을제작하여총시편수는 240개이었다. 윈도우용 SPSS 9.0을사용하여자료를분석하고분산분석과최소유의차검정및 t검사를통해평균치간차이의유의성을검정하였다. Ⅲ. 성적복합레진의중합깊이를기준으로하였을때 3, 6, 9초간조사한플라즈마광의중합능력이 40초간조사하는저출력할로겐광의중합능력에미치지못하였다 (Table 2). 레진시편상면의표면경도와하면의표면경도간의차이는, 두께 2mm 시편에할로겐광을 40초간조사하였거나플라즈마광을 9초간조사한경우들을제외하고, 모두유의하였다 (P<0.05, 이하유의수준같음 ) (Table 3). 레진시편상면의표면경도는전체실험군들에서서로유의한차이가없었다 (Table 4, 5). 전체적으로보아, 레진시편하면의표면경도는할로겐광을 40초간조사한군들에서가장높았고레진시편의두께가증가함에따라감소하였으며 (Table 4) 플라즈마광의조사시간이감소함에따라감소하였다 (Table 5). 레진시편하면의표면경도의레진두께에따른차이를보면, 할로겐광을 40초조사하였을때레진두께 2mm군과 3mm군간을제외하고레진두께에따른군들간의차이가모두유의하였고 (P<0.05), 플라즈마광을 3, 6, 9초간조사하였을때 4mm군과 5mm군간을제외하고모두유의하였다 (Table 5). 레진시편하면의표면경도의조사광원과조사시간에따른차이를보면, 레진두께 2mm군에서할로겐광 40초군과플라즈마광 3초군간에유의한차이가있었고, 레진두께 3mm군에서할로겐광 40초군과플라즈마광 3초군간, 할로겐광 40초군과플라즈마광 6초군간, 플라즈마광 3초군과플라즈마광 6초군간 Table 1. Light source and curing time Light source Manufacturer Light intensity Curing time Plasma arc light Flipo, Lokki, France c. 1,900 mw/cm 2 3, 6, 9 sec Halogen light Optilux 360, Demetron, USA c. 370 mw/cm 2 40 sec 200

대한소아치과학회지 28(2) 2001 Table 2. Surface hardness of composite resins cured by halogen or plasma light Specimen Light source Vickers Hardness Number thickness & curing time N Top Bottom Mean 2mm Halogen 40sec 15 30.27±9.74 26.40±7.68 28.33± 8.84 Plasma 3 15 25.68±7.23 18.21±9.15 21.95± 8.95 Plasma 6 15 27.23±6.73 21.97±6.96 24.60± 7.24 Plasma 9 15 28.16±5.44 23.90±6.67 26.03± 6.36 3mm Halogen 40sec 15 28.94±6.57 22.26±5.73 25.60± 6.94 Plasma 3 15 26.73±7.82 11.26±5.28 19.00±10.23 Plasma 6 15 26.66±5.99 17.68±5.49 22.17± 7.26 Plasma 9 15 28.28±5.30 19.16±5.95 23.72± 7.22 4mm Halogen 40sec 15 27.48±6.81 15.18±6.05 21.33± 8.90 Plasma 3 15 25.50±6.29 5.42±0.73 15.46±11.12 Plasma 6 15 27.32±4.64 7.71±3.43 17.51±10.74 Plasma 9 15 27.88±5.08 10.30±3.76 19.09± 9.96 5mm Halogen 40sec 15 25.35±6.60 9.65±4.02 17.50± 9.62 Plasma 3 15 25.22±7.01 4.90±0.00 15.06±11.42 Plasma 6 15 26.54±7.04 5.39±0.82 15.96±11.83 Plasma 9 15 26.84±6.58 7.11±2.24 16.97±11.13 Totals Halogen 40sec 60 28.01±7.58 18.37±8.75 23.18± 8.48 Plasma 3 60 25.78±6.95 9.95±7.49 17.87±10.72 Plasma 6 60 26.94±6.02 13.18±8.33 20.07±10.00 Plasma 9 60 27.79±5.52 15.12±8.33 21.46± 9.49 Mean±SD; Values less than 5.0 (lower limit of measurement) were considered as 4.9 Table 3. Significance of difference in hardness between top and bottom 2mm 3mm 4mm 5mm Totals H40 NS P 3 P 6 P 9 NS t-test, 2-tailed * : P<0.05; NS : Not Significant Table 4. Significance of difference in hardness between resin thickness groups Halogen 40sec Plasma 3sec Plasma 6sec Plasma 9sec Top Bottom Mean Top Bottom Mean Top Bottom Mean Top Bottom Mean 2mm a* a a a b a a b a a b a 3 a a a a c ab a c ab a c a 4 a b b a a b a a bc a a b 5 a c b a a b a a c a a b F 1.169 22.959 9.140 0.129 20.692 2.877 0.060 41.365 5.359 0.204 36.522 6.553 Sig 0.330 0.000 0.000 0.943 0.000 0.039 0.980 0.000 0.002 0.893 0.000 0.000 * : Values in columns having the same letter were not significantly different (P>0.05) by the LSD test 201

J Korean Acad Pediatr Dent 28(2) 2001 Table 5. Significance of difference in hardness between light source and curing time groups 2mm 3mm 4mm 5mm Totals Top Bottom Mean Top Bottom Mean Top Bottom Mean Top Bottom Mean Top Bottom Mean H40 a* a a a a a a a a a b a a b a P 3 a b a a c b a b b a a a a c b P 6 a ab b a b ab a bc ab a a a a a bc P 9 a a b a ab a a c ab a c a a a ac F 0.994 3.037 3.418 0.460 10.199 3.631 0.502 16.702 1.771 0.218 12.666 0.289 1.418 11.006 6.157 Sig 0.402 0.036 0.020 0.711 0.000 0.015 0.682 0.000 0.157 0.884 0.000 0.834 0.238 0.000 0.000 * : Values in columns having the same letter were not significantly different (P>0.05) by the LSD test 에각각유의한차이가있었으며, 레진두께 4mm군에서할로겐광 40초군과플라즈마광 3초군간, 할로겐광 40초군과플라즈마광 6초군간, 할로겐광 40초군과플라즈마광 9초군간, 플라즈마광 3초군과플라즈마광 9초군간에각각유의한차이가있었고, 레진두께 5mm군에서는플라즈마광 3초군과플라즈마광 6 초군간을제외하고나머지군들간에모두유의한차이가있었다 (Table 5). Ⅳ. 고찰복합레진의중합광은먼저레진의중합유도가가능한파장범위에속해야하고다음으로충분한강도를가져야한다. Nomoto 23) 는 410~550nm 범위의빛이레진의중합을일으키며가장효율적인파장은 470nm이고가장적절한파장은 450~490nm의범위에있다고하였다. 연구에사용된플라즈마광중합기 Flipo는제품설명서에따르면 380 520nm의파장영역을가지며그중 50% 가 440 510nm에집중되어있고정점은 475nm인청색광을내는것으로되어있다. Hofmann 등 21) 은플라즈마아크광중합의적합성은복합레진이함유하고있는 photoinitiator에달려있다고하였다. Photoinitiator로서 camphoroquinone만함유한레진의경우에, 플라즈마아크광으로 3초간두번중합한경우에중에너지 (550mW/cm 2 ) 가시광선으로중합한경우와표면경도가대등하였으나더짧은파장 (370~450nm) 을흡수하는 photoinitiator를함께함유하고있는레진의경우에는가시광선으로중합한경우보다열등한결과를낳았다. 연구에사용된플라즈마광의강도는 1,900mW/cm 2 으로서할로겐광의강도 370mW/cm 2 의약 5배에해당하였다. 조사광의강도와총조사시간을곱하여산출되는총조사량이일정하면중합의깊이가동일하다고한 Nomoto 등 8) 의이론을따른다면플라즈마광의적절한중합시간은할로겐광의최소중합시간 40초의약 5분의 1인 8초이상이될것이다. 이것은고강도의플라즈마광이라하더라도 3초의중합시간은최적의중합을일으키기에는너무짧으며이연구에서설정한 9초에가까워야한다는것을시사한다. 그러나, 조사광의강도와조사시간외에 도플라즈마광과할로겐광의파장대분포가다르다는점과중합기전이상이할가능성등기타요인들도고려하여야한다. 할로겐광의문제점중의하나는할로겐전구의임상적수명은약 40~110시간으로제한되어있으며시간이경과함에따라중합효율이감소한다는것이다 24-28). Solomon과 Osman 29) 은치과진료실에서사용되는광중합기를검사한결과, 사용자의 100% 가주관적만족을표시하였으나, 실제로는 45.7% 가적정강도 300mW/cm 2 에미치지못하였다고보고하였다. 반면에, 플라즈마아크전구는교환이필요없고시간의경과에따라출력이감소되지않는특성이있으므로중합광의강도를유지하는측면에서장점을가진다. 복합레진의광중합에서중합광선의광원에따른중합의질을비교평가하기위하여흔히사용되는방법은중합깊이 (depth of cure) 의측정으로서, 중합깊이는다양한방법으로측정될수있다 30). 중합깊이를측정하기위하여 ISO 4049에제시된 scrape test 31) 는중합되지않은레진을술자가긁어내는방법으로서단순하고정성적인 pass/fail 검사이며술자의주관적판단에따르고재현도즉신뢰도가낮다는단점이있다고평가되었다 32). Harrington과 Wilson 33) 의방법은 1,250g 하중의침 ( ) 이레진에침투한깊이를측정하는 penetrometer를사용하는것으로서, scrape test보다는객관적이고신뢰도가높으나역시일정한기준에맞춘정성적검사이다. 정량적방법으로는이연구에서사용한방법과같이다양한두께의레진시편상면에중합광을조사한후레진상면과하면의표면미세경도를측정하여상대적으로비교하는것이많이사용되고있다. Kanca 34-36) 는레진시편을여러조건으로중합한다음시편의상면과하면의경도차이를조사한실험에서노출시간을증가시키고광원과의거리가짧을수록경도차이가작다고하였다. Rueggeberg 등 4-6) 은레진의광중합에영향을끼치는주된요인은레진의두께로서, 2mm 이상의레진두께에서는중합이불완전하고광강도와조사시간의변화에매우민감하므로레진의두께는 2mm를초과하지말아야하며, 1mm 두께의레진층을 400mW/cm 2 이상의강도를가진광원으로 60초간중합해야한다고하였다. 저자의연구성적에서, 레진두께가 2mm인경우에할로겐광 40초군과플라즈마광 9초군은모두레진상면과 202

대한소아치과학회지 28(2) 2001 하면간에경도의유의한차이가없었으나플라즈마광 3초군과 6초군에서는유의한차이가있었다. 이것은일반적으로권장되는 1회광중합을위한레진층의두께인 2mm의경우에도플라즈마광 3초나 6초의중합은레진하면의불완전한중합을일으킬수도있음을시사한다. 또한, 저자의연구성적에서, 레진상면의경도는군간에유의한차이가없었으나레진하면의경도는레진의두께가증가할수록뚜렷하게감소하였고특히플라즈마 3초군은할로겐광 40 초군에비해매우낮은경도를보였다. 다만플라즈마 9초군은레진두께가 2mm와 3mm일경우할로겐광 40초군과대등한성적을나타냈다. Tanoue 등 37,38), Matsumura 등 39) 은보철용복합레진을휴대용할로겐광중합기와기공용 xenon광중합기로각각중합하였을때할로겐광이더깊은중합을일으켰다고하였다. 김 16) 은열구전색재에서유사한표면경도를얻기위한중합시간이플라즈마광중합기가할로겐광중합기보다더짧았다고하였으나두께 1mm의시편을사용하였기때문에두께의영향은없었다고생각된다. Peutzfeldt 등 17) 은 3초간플라즈마광중합의중합깊이는 40 초간의할로겐광중합에비해얕았다고하였으며중합된깊이가 4mm 미만이었으므로이중절반이적절하게중합되었다고가정하면 2mm를초과하지않게레진을축성해야한다고하였다. Roberts 등 18) 은플라즈마광으로 3초간중합한레진은할로겐광으로 40초간중합한레진에비해시편의상하면경도가모두낮았다고하였으며, Ergle과 Rueggeberg 19) 도 3초간플라즈마광으로중합한경우에아르곤레이저나할로겐광으로중합한경우보다레진의경도가유의하게낮았다고하였다. Burtscher 등 20) 은최소한 3회의플라즈마광중합이레진의완전한중합에필요하였다고하였고, Hofmann 등 21) 은플라즈마광으로 3초간두번중합한경우에중에너지 (550mW/cm 2 ) 가시광선으로중합한경우와비교해서표면경도가대등하였다고하였다. Munksgaard 등 22) 은플라즈마광으로중합된복합레진에서용리 ( ) 된단량체의양이할로겐광중합군에비해 4배많았다고하였다. 한편, 고강도중합광을조사할때복합레진중합과관련하여발생하는다른문제들이존재한다. 가장큰것은복합레진고유의문제인중합수축이고강도중합광에의해더커짐으로써수복물의변연적합도를악화시키고미세누출을증가시킬수있다는점이다 40-44). 이에대한해결책중의하나로서광중합을처음시작할때에는저출력으로조사하고그후에고출력으로조사하는 2단계중합방법 (soft-start polymerization) 이제안되고있다 45-50). Pires 등 51) 은레진표면에서광조사기의말단을 10mm 떨어지게하면표면의강도는약 50% 로감소하므로 2 단계중합장치가내장되어있지않은중합기도정확하게취급한다면 2단계중합광으로중합할수있다고하였다. 총괄하여볼때, 복합레진의두께또는깊이의증가에따른레진하면의적절한중합여부측면에서볼때저자의연구결과는 3초간의플라즈마광중합이 40초간의할로겐광중합에미 치지못한다는선학들의연구결과와일치하며, 강도가매우높은고출력광중합기의경우에도충분한조사시간이필요하다는것을강조한다. 저자의연구결과에근거하여본다면레진의두께가 3mm 이내인경우에는플라즈마광을 3초간 3회즉 9초간조사함으로써할로겐광을 40초간조사하는것과대등한중합을일으킬수있다고할수있다. 플라즈마광중합기에대한정확한평가를위해서는저자의연구방법외의다른접근방법들을사용한연구들이수행될필요가있다고사료된다. Ⅴ. 결론플라즈마아크광원을사용하는광중합기를저출력할로겐광원을사용하는전통적인광중합기와비교평가하기위하여, 세종류의복합레진을두께가 2, 3, 4, 5mm인몰드에충전하고레진상면을할로겐광으로 40초간, 플라즈마광으로 3, 6, 9 초간조사한후레진상면과하면의표면미세경도를각각측정하였다. 1. 레진시편상면의표면경도와하면의표면경도간의차이는, 두께 2mm 시편에할로겐광을 40초간조사하였거나플라즈마광을 9초간조사한경우들을제외하고, 모두유의하였다 (P<0.05). 2. 레진시편상면의표면경도는전체실험군들에서서로유의한차이가없었다. 3. 레진시편하면의표면경도는전체적으로보아할로겐광을 40초간조사한군들에서가장높았고플라즈마광의조사시간이감소함에따라감소하였으며레진시편의두께가증가함에따라감소하였다. 참고문헌 1. Fortin D, Vargas MA : The spectrum of composites: new techniques and materials. J Am Dent Assoc 131(Suppl):26-30, 2000. 2. Tirtha R, Fan PL, Dennison JB, Powers JM : In vitro depth of cure of photo-activated composites. J Dent Res 61:1184-1187, 1982. 3. Fowler CS, Swartz ML, Moore BK : Efficacy testing of visible-light-curing units. Oper Dent 19:47-52, 1994. 4. Rueggeberg FA, Caughman WF, Curtis JW, Davis HC : Factors affecting cure at depths within lightactivated resin composites. Am J Dent 6:91-95, 1993. 5. Rueggeberg FA, Caughman WF, Curtis JW Jr, Davis HC : A predictive model for the polymerization of photo-activated resin composites. Int J Prosthodont 7:159-166, 1994. 203

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J Korean Acad Pediatr Dent 28(2) 2001 Abstract INFLUENCE OF LIGHT SOURCE AND CURING TIME ON SURFACE HARDNESS OF RESIN COMPOSITES Sang-Man Bae, D.D.S., M.S.D.. Kwang-Hee Lee, D.D.S., M.S.D., Ph.D., Dae-Eup Kim, D.D.S., M.S.D., Ph.D., Ho-Young Ahn, D.D.S., M.S.D. Department of Pediatric Dentistry, College of Dentistry, Wonkwang Dental Research Institute Wonkwang University The purpose of study was to compare the plasma arc light with the halogen light in compostie resin curing. Three composite resin materials(z-100, 3M, USA; Tetric Ceram, Vivadent, Liechtenstein; SureFil, Dentsply, USA) were filled in the teflon molds (4mm in diameter and 2, 3, 4, 5mm in thickness) and cured with either the conventional low-intensity light curing unit with a halogen lamp (Optilux 360, Demetron, U.S.A.) for duration of 40 seconds or with the high-intensity light curing unit with a plasma arc lamp (Flipo, Lokki, France) for duration of 3, 6, and 9 seconds. The intensity of halogen light was about 370mW/cm 2 and that of plasma light was about 1,900mW/cm 2. After one week, the surface hardnesses of both the top and the bottom of the resin samples were measured with a microhardness tester(mxt70, Matsuzawa, Japan). There were significant differences in the hardness between the top and the bottom of the resin samples except the 2mm thickness samples cured by halogen light for 40s or by plasma light for 9s. There was no significant difference between the hardness values of the top surfaces of the thickness groups. The hardness values of the bottom surfaces decreased as the curing time decreased and as the thickness of resin samples increased, and the three kinds of resin composites showed similar patterns. The results suggest that the halogen light for 40 seconds might be able to cure greater depth of resin composites than the plasma light for 3, 6, or 9 seconds. Key words : Plasma, Halogen, Light-curing, Composite resin, Surface hardness 206