Originl Article Assocition between orthodontic tretment nd periodontl diseses: Results from ntionl survey Hye-Young Sim ; Hee-Sun Kim b ; D-Un Jung b ; Ho Lee b ; Jeong-Woo Lee c ; Kyungdo Hn d ; Kyoung-In Yun e ABSTRACT Objective: To investigte the ssocition between orthodontic tretment nd periodontitis in ntionlly representtive smple of South Kore. Mterils nd Methods: Dt from the Fifth nd Sixth Koren Ntionl Helth nd Nutrition Exmintion Survey (KNHANES V, VI-1, nd VI-2), conducted from 2012 to 2014, were used in this study. The finl smple size consisted of 14,693 dults ged 19 yers. Logistic regression nlysis ws performed to ssess the ssocition between orthodontic tretment nd periodontitis. Results: The orthodontic tretment group exhibited lower prevlence of periodontitis compred with the nonorthodontic tretment group. The djusted odds rtios for periodontitis in subjects with history of orthodontic tretment compred with those with no history of orthodontic tretment were 0.553, 0.614, nd 0.624, when djusted for vrious confounding vribles (P,.0001). The subjects with periodontitis were of higher ge, body mss index, wist circumference, nd white blood cell counts compred with the subjects without periodontitis regrdless of history of orthodontic tretment. Conclusions: History of orthodontic tretment ws ssocited with decresed rte of periodontitis. (Angle Orthod. 2017;87:651 657.) KEY WORDS: Orthodontics; Periodontitis; Ntionl survey; Cross-sectionl study INTRODUCTION Orthodontic tretment cn improve fcil esthetics nd mstiction through the lignment of teeth. However, dentl cries, tooth discolortion, nd gingivl hyperplsi hve been reported s complictions of this tretment. It is difficult to mintin orl Clinicl Professor, Deprtment of Orthodontics, SMG-SNU Borme Medicl Center, Seoul, Kore. b Clinicl Professor, Deprtment of Dentistry, SMG-SNU Borme Medicl Center, Seoul, Kore. c Reserch Fellow, Deprtment of Dentl Services Mngement nd Informtics, Grdute School of Dentistry, Seoul Ntionl University, Seoul, Kore. d Reserch Fellow, Deprtment of Biosttistics, The Ctholic University of Kore, College of Medicine, Seoul, Kore. e Clinicl Associte Professor, Deprtment of Orl nd Mxillofcil Surgery, The Ctholic University of Kore, Yeouido St. Mry s Hospitl, Seoul, Kore. Corresponding uthor: Dr Kyoung-In Yun, Deprtment of Orl nd Mxillofcil Surgery, The Ctholic University of Kore, Yeouido St. Mry s Hospitl, Seoul, Kore (e-mil: yun_ki@ctholic.c.kr) Accepted: My 2017. Submitted: Mrch 2017. Published Online: July 7, 2017 Ó 2017 by The EH Angle Eduction nd Reserch Foundtion, Inc. hygiene becuse of the presence of orthodontic pplinces, bnds, nd elstics. These conditions my led to plque ccumultion nd chnges in the composition nd type of orl bcteri. 1,2 On the contrry, systemtic review indicted tht there is positive reltionship between mlocclusion nd periodontitis. 3 However, it ws lso reported tht there ws no relible evidence suggesting positive effect of orthodontic tretment on periodontl helth. 3 Some uthors hve reported tht plque nd bleeding indexes improve fter orthodontic tretment. 4 Despite this controversy, periodontl disese is not n bsolute contrindiction for orthodontic tretment. It is possible tht properly ligned teeth contribute to the mintennce or improvement of orl helth. The confusion or debte over the reltionship between orthodontic tretment nd periodontitis my be primrily due to lck of evidence. Moreover, the trget popultion of previous studies did not consist of representtive smples. The current study focused on the ssocition between orthodontic tretment nd periodontitis in ntionlly representtive smple. The hypothesis ws tht orthodontic tretment my be ssocited with decresed prevlence of periodontitis, which ws DOI: 10.2319/030317-162.1 651
652 SIM, KIM, JUNG, LEE, LEE, HAN, YUN tested using multiple regression models. The purpose of this study ws to investigte the ssocition between orthodontic tretment nd periodontitis in ntionlly representtive smple of the South Koren popultion. MATERIALS AND METHODS Study Popultion Dt were obtined from the Fifth nd Sixth Koren Ntionl Helth nd Nutrition Exmintion Survey (KNHANES V, VI-1, nd VI-2), conducted from 2012 to 2014. The KNHANES is ntionwide survey of representtive smple of the South Koren popultion nd is conducted by the Koren Center for Disese Control nd Prevention. This survey ws pproved by the Institutionl Review Bord for Humn Subjects of the Kore Center for Disese Control nd Prevention. Before the survey, ech prticipnt signed n informed consent form. The survey ws composed of helth interviews, helth exmintions, nd nutrition survey. Trined interviewers crried out fce-to-fce interviews with structured questionnire. Trined nd clibrted exminers inspected the prticipnt s physicl sttus. Physicl exmintions nd blood smpling were performed t mobile exmintion center. All dt used in the present study re vilble in public files provided by the Kore Centers for Disese Control nd Prevention nd the Ministry of Helth nd Welfre of Kore. Vribles nd Mesurements Clinicl nd lbortory dt were collected. The eduction level ws clssified s high if the respondent hd finished high school. Individuls with household incomes,25% of the totl equivlized income were clssified in the low-income group. Residentil loction ws divided into two groups (rurl versus urbn). Alcohol intke sttus ws clssified into three groups: nondrinkers, mild-to-moderte drinkers (,30.0 g lcohol/d), nd hevy drinkers (30.0 g lcohol/d). Smoking sttus ws clssified into three groups: nonsmokers, ever-smokers (hve smoked t lest five pcks of cigrettes in their whole lives), nd current smokers (hve smoked t lest five pcks of cigrettes in their whole lives nd still smoke). Occuption ws defined s the prticipnt s self-reported economic ctivity. Regulr physicl exercise ws defined s intense physicl ctivity performed for t lest 20 minutes t time t lest three times week ccording to the Interntionl Physicl Activity Questionnire short form modified for Kore. 5 Blood smples were obtined fter fsting for t lest 8 hours nd ppropritely processed. Serum levels of triglyceride (TG), high-density lipoprotein (HDL), nd fsting blood glucose (FBG) were mesured using Hitchi Automtic Anlyzer 7600 (Hitchi, Tokyo, Jpn) in 2012 nd Hitchi Automtic Anlyzer 7600-210 (Hitchi, Tokyo, Jpn) in 2013 nd 2014. White blood cells (WBCs) were counted using Sysmex XE-2100D (Sysmex, Kobe, Jpn) in 2012, 2013, nd 2014. Dibetes ws dignosed when FBG ws.126 mg/dl or when the individul ws currently using ntidibetic mediction. Hypertension ws defined s systolic blood pressure.160 mm Hg, distolic blood pressure.90 mm Hg, or current use of systemic ntihypertensive drugs. Wist circumference ws mesured t the nrrowest point between the lower border of the rib cge nd the ilic crest. The wist circumference cutoff ws defined s 90 cm in men nd 80 cm in women. Body mss index (BMI) ws clculted s weight in kilogrms divided by height in meters squred. The BMI cutoff ws 23 kg/m 2 for overweight nd 25 kg/m 2 for obesity. 6 Metbolic syndrome ws defined ccording to the Americn Hert Assocition/Ntionl Hert, Lung, nd Blood Institute Scientific Sttement criteri for Asins. 7 Specificlly, metbolic syndrome ws dignosed when greter thn or equl to three of the following criteri were met: (1) wist circumference 90 cm in men or 80 cm in women, (2) fsting TG 150 mg/dl or use of lipid-lowering mediction, (3) HDL-C,40 mg/dl in men or,50 mg/dl in women or use of cholesterollowering mediction, (4) blood pressure 130/85 mm Hg or use of ntihypertensive mediction, nd (5) FBG 100 mg/dl or current use of ntidibetic mediction. History of orthodontic tretment ws ssessed by yes or no questionnire. Periodontitis Periodontl helth ws evluted ccording to the World Helth Orgniztion community periodontl index (CPI). 8 Ech CPI score rnged from 0 to 4: helthy periodontl conditions (CPI ¼ 0), gingivl bleeding (CPI ¼ 1), clculus nd bleeding (CPI ¼ 2), shllow periodontl pocket of 3.5 to,5.5 mm (CPI ¼ 3), or deep periodontl pocket of 5.5 mm (CPI ¼ 4). Periodontl pocket depth ws mesured t six sites (mesiobuccl, midbuccl, distobuccl, distolingul, midlingul, nd mesiolingul sites) of ech tooth with CPI probe. Periodontitis ws defined s CPI vlue of 3 or 4, indicting tht t lest one site hd.3.5- mm pocket. 9,10 The eight molrs nd the upper right nd lower left centrl incisors were exmined by 30 (2012 KNHANES), 33 (2013 KNHANES), nd 21 (2014 KNHANES) trined nd clibrted dentists. Trining ws performed to stndrdize the survey nd minimize
ASSOCIATION BETWEEN ORTHODONTICS AND PERIODONTITIS 653 errors in the mesurement of periodontl probing depths. Ech exminer ws trined using dentl models nd simultion of the orl helth exmintion with humn subjects. They were lso provided field trining, reproducing exmintions, nd periodic clibrtion. Relibility of exmintion ws confirmed by specilists commissioned by the Ministry of Helth nd Welfre of Kore. The interexminer mens of the Kpp vlue were 0.69 in 2012, 0.70 in 2013, nd 0.79 in 2014. 11 13 Sttisticl Anlyses All survey nlyses included the smpling weights, strt, nd clusters becuse KNHANES is strtified multistge clustered probbility design. All dt were expressed s men 6 stndrd error or percentge. Logistic regression nlyses were performed to ssess odds rtios (ORs) nd 95% confidence intervls (CIs), which were used to determine the ssocition between orthodontic tretment nd periodontl disese. Regression nlyses were performed in ccordnce with KNHANES sttisticl guidelines. ORs nd CIs were estimted fter djustment for potentil confounders. Three multiple regression models were used. Model 1 ws djusted for ge nd sex. Model 2 ws djusted for ge, sex, income, eduction, lcohol intke, smoking, regulr exercise, BMI, nd WBC count. Model 3 ws djusted for ge, sex, income, eduction, lcohol intke, smoking, regulr exercise, BMI, WBC count, dibetes, hypertension, metbolic syndrome, nd tooth brushing times per dy. All dt were nlyzed using SAS softwre version 9.2 for Windows (SAS Institute Inc, Cry, NC). Results were considered significntly different when P,.05. RESULTS A totl of 23,625 subjects prticipted in the periodontl disese questionnire nd exmintions (8057 prticipnts in 2012, 8018 in 2013, nd 7550 in 2014). The prticiption rte ws 80.0% in 2012, 79.3% in 2013, nd 77.8% in 2014. Prticipnts ged,19 yers (5244 prticipnts) nd ptients with missing vlues in the helth ssessment or questionnires (3689 prticipnts) were excluded from the current nlysis. As result, the finl smple size for the present study ws 14,693. Tble 1 shows the generl chrcteristics of the subjects in this survey. The prevlence of periodontitis ws lower in the orthodontic tretment group compred with the nonorthodontic tretment group (9% vs 44%). The subjects with periodontitis were of higher ge, BMI, wist circumference, nd WBC count compred with the subjects without periodontitis regrdless of orthodontic tretment. In the nonorthodontic tretment group, the subjects with periodontitis exhibited higher rtes of dibetes, hypertension, nd metbolic syndrome. However, in the orthodontic tretment group, the subjects with periodontitis did not show higher prevlence of dibetes. The subjects with periodontitis showed higher rtes of smokers regrdless of orthodontic tretment. In the orthodontic tretment group, household income level ws not ssocited with prevlence of periodontitis, unlike the nonorthodontic tretment group. Frequency of tooth brushing nd use of n interdentl brush nd floss were not ssocited with periodontitis in the orthodontic tretment group. Tble 2 shows the ssocitions between orl hygiene hbits nd orthodontic tretment. The orthodontic tretment group showed lower rtes of chewing nd speking difficulties nd higher rtes of hving hd professionl orl exmintion within 1 yer compred with the nonorthodontic tretment group. The subjects with orthodontic tretment exhibited more frequent tooth brushing nd felt tht their orl helth sttus ws bove norml. Generlly, the orthodontic tretment group showed lower prevlence of periodontitis compred with the nonorthodontic tretment group in ll ge groups (Figure 1). The orthodonticlly treted dults my hve come from higher socioeconomic sttus to begin with, which would hve influenced the results s this is significnt fctor in dult periodontl helth. However, considering confounding fctors including income nd eduction level, the orthodontic tretment group lso showed lower prevlence of periodontitis compred with the nonorthodontic tretment group (Tble 3). The djusted ORs were 0.553 (model 1), 0.614 (model 2), nd 0.624 (model 3) in the orthodontic tretment group (P,.0001). DISCUSSION This study investigted the ssocition between orthodontic tretment nd periodontitis in ntionlly representtive smple of the Koren popultion. The results of this study indicted tht orthodontic tretment is ssocited with decresed prevlence of periodontitis. Periodontitis ws less prevlent in the orthodontic tretment group. To the best of our knowledge, this is the first study to exmine the reltionship between orthodontic tretment nd periodontitis in the generl popultion. The effect of orthodontic tretment on prevlence of periodontitis hs been debted. Recently, the importnce of periodontl helth hs incresed s the number of dult orthodontic ptients hs incresed. The reltionship between orthodontic tretment nd periodontitis hs been widely studied. Mny clinicl studies hve reported tht plque ccumultion nd
654 SIM, KIM, JUNG, LEE, LEE, HAN, YUN Tble 1. Demogrphic Chrcteristics of the Study Popultion (N ¼ 14,693) Nonperiodontitis (n ¼ 9752) Orthodontic Tretment (No) Periodontitis (n ¼ 4157) P Nonperiodontitis (n ¼ 716) Orthodontic Tretment (Yes) Periodontitis (n ¼ 68) P Age, y (men 6 SD) 42.96 6 0.24 54.49 6 0.31,.0001 30.17 6 0.38 40.07 6 1.34,.0001 Mle sex (%) 46.2 (0.6) 59.5 (0.8),.0001 39.1 (2.2) 54.8 (7.2).0373 Eduction (%),.0001.0076 Elementry school or less 12.8 (0.5) 28.7 (1) 0.6 (0.3) 3.8 (1.7) Middle school 8.1 (0.3) 14.5 (0.7) 1.1 (0.4) 3.3 (2) High school 41.7 (0.7) 34.3 (1) 44.2 (2.4) 50.2 (6.9) University or higher 37.4 (0.8) 22.5 (1) 54.1 (2.4) 42.7 (6.7) Household income (%),.0001.3225,25% 12.6 (0.6) 20.8 (1) 5.9 (1.1) 5.2 (2.7) 25%~50% 25.8 (0.8) 27.1 (1) 22.5 (2) 23.3 (5.5) 50%~75% 30.2 (0.8) 27 (1) 32.5 (2.1) 21.6 (5.4).75% 31.4 (1) 25.1 (1.2) 39.1 (2.4) 49.9 (7.5) Smoking (%),.0001.0035 Nonsmoker 63.5 (0.6) 46.3 (0.9) 71.9 (2.1) 47.4 (7.2) Ex-smoker 15.2 (0.4) 22.6 (0.8) 9.7 (1.3) 18.1 (6) Current smoker 21.2 (0.6) 31 (0.9) 18.4 (1.8) 34.5 (7.4) Alcohol consumption (%),.0001.6922 Nondrinker 23.1 (0.6) 28.6 (0.9) 13.2 (1.4) 12.3 (4.7) Mild to moderte-drinker 68.6 (0.6) 60.1 (1) 79.2 (1.7) 76.6 (6.4) Hevy drinker 8.3 (0.4) 11.3 (0.6) 7.5 (1.2) 11.1 (5.3) Plce, urbn (%) 84.4 (1.5) 75.5 (2.3),.0001 90.8 (1.7) 71.1 (6.8),.0001 Occuption (yes, %) 62.5 (0.6) 65.4 (1).0093 60.1 (2.4) 67.7 (6.5).2994 Frequency of tooth brushing per dy (%),.0001.1791 1 8.4 (0.4) 15.3 (0.7) 4.1 (0.9) 3.8 (2.4) 2 36.9 (0.6) 43.3 (0.9) 27.6 (2) 39.5 (6.8) 3 54.8 (0.6) 41.4 (1) 68.2 (2) 56.8 (6.9) Use of interdentl brush (yes, %) 23.3 (0.6) 11.8 (0.6),.0001 32.6 (2.1) 29 (6.8).624 Use of floss (yes, %) 19 (0.6) 18.1 (0.8).3658 24.1 (1.9) 28 (6.5).5481 Professionl orl exmintion within 26.8 (0.6) 26.5 (0.9).8123 38.7 (2.1) 27.4 (6.5).1257 1 yer (yes, %) Self-reported orl helth sttus (%),.0001,.0001 Good 14.9 (0.5) 10.4 (0.5) 21 (1.9) 11.8 (4.1) Moderte 44.9 (0.7) 32.6 (0.9) 47.9 (2.2) 29.2 (5.9) Bd 40.3 (0.7) 57 (1) 31.1 (2) 59 (6.6) White blood cell count (310 9 /L) b 5.84 (5.79 5.88) 6.2 (6.13 6.27),.0001 5.92 (5.78 6.06) 6.29 (5.96 6.65).0421 Body mss index, kg/m 2 (men 6 SD) 23.63 6 0.05 24.37 6 0.07,.0001 22 6 0.17 23.92 6 0.46,.0001 Wist circumference, cm (men 6 SD) 80.03 6 0.16 83.72 6 0.21,.0001 75.2 6 0.48 81.64 6 1.23,.0001 Number of remining teeth 25.83 6 0.06 23.85 6 0.11,.0001 25.97 6 0.09 24.96 6 0.38.0093 Regulr exercise within week (yes, %) 40.3 (0.7) 35.7 (0.9),.0001 41.8 (2.2) 48 (6.9).3628 Dibetes (yes, %) 6.1 (0.3) 16.8 (0.7),.0001 1.3 (0.5) 4 (2.5).0994 Hypertension (yes, %) 20.7 (0.6) 38.9 (1),.0001 4.3 (0.8) 15.2 (4.6).0002 Metbolic syndrome (yes, %) 22.8 (0.6) 40.1 (1),.0001 7.4 (1.1) 28.6 (6.7),.0001 Vlues re presented s the men 6 stndrd error for continuous vribles or s the proportion (stndrd error) for ctegoricl vribles. Ex-smokers hve smoked t lest five pcks of cigrettes in their whole lives; current smokers hve smoked t lest five pcks of cigrettes in their whole lives nd smoke currently; mild-to-moderte drinkers drink,30.0 g lcohol/d; hevy drinkers drink 30.0 g lcohol/d. b Log trnsformtion ws performed to obtin P vlues, nd the vlue represents the geometric men (95% confidence intervl). gingivitis incresed during orthodontic tretment. 14 16 The composition nd types of orl bcteri were ltered s result of orthodontic tretment. 1,17,18 Recent niml studies suggested tht orthodontic tooth movement hd synergistic effect on periodontitis by incresing the presence of IL-1b nd TNF-. 19 DNA probe nlysis reveled tht periodontl pthogens incresed fter 6 months of orthodontic tretment but decresed to the level of pretretment fter 12 months of therpy. 20 In tht study, the uthors hypothesized tht the fixed pplinces my provide some dvntges for periodontl pthogens only during the initil stge of orthodontic tretment. 20 One long-term study showed tht pocket depths were not significntly different between subjects with history of orthodontic tretment nd nonorthodontic control group. 21 This study lso showed tht the gingivl index ws higher in the control group. Another popultionbsed longitudinl study found tht periodontl ttchment loss nd gingivl recession ws not significntly different between the orthodontic tretment group nd nonorthodontic tretment group. 22 The current study
ASSOCIATION BETWEEN ORTHODONTICS AND PERIODONTITIS 655 Tble 2. Assocition Between Orl Hygiene Hbits nd Orthodontic Tretment No (n ¼ 13,752) Orthodontic T Yes (n ¼ 782) P Dily frequency of tooth brushing,.0001 1 10.3 (0.3) 4.1 (0.8) 2 38.6 (0.5) 28.6 (1.8) 3 51.1 (0.6) 67.3 (1.9) Professionl orl exmintion 26.7 (0.5) 37.8 (2.0),.0001 within the pst yer (yes, %) Chewing difficulty (yes, %),.0001 Discomfort 20.8 (0.4) 9.9 (1.2) Minor problem 16.1 (0.4) 15.2 (1.6) No problem 63.1(0.5) 75.0 (1.9) Speking difficulty (yes, %).0003 Discomfort 8.1 (0.3) 3.7 (0.8) Minor problem 10.4 (0.3) 9.4 (1.2) No problem 81.4 (0.4) 86.9 (1.4) Self-reported orl helth sttus,.0001 Good 13.6 (0.4) 20.3 (1.8) Moderte 41.5 (0.6) 46.4 (2.1) Bd 44.9 (0.6) 33.3 (2.0) Vlues re presented s the men 6 stndrd error for continuous vribles or s the proportion (stndrd error) for ctegoricl vribles. Figure 1. Prevlence of periodontitis by ge groups between ptients with nd without history of orthodontic tretment. found tht periodontitis tended to be less prevlent in the orthodontic tretment group. Some interesting results were found in the present study. Ptients with periodontitis exhibited higher WBC counts, incresed BMI, nd greter incidence of dibetes, hypertension, nd metbolic syndrome thn subjects without periodontitis. These findings were similr to those of previous studies. 23,24 These helth sttes my lso be relted to socioeconomic sttus. The reltionship between periodontitis nd socioeconomic position such s eduction nd income hs been reported since the 1960s. 25 Periodontitis ws less common in the subjects with higher levels of eduction nd income. 25,26 However, household income ws not ssocited with periodontitis in the orthodontic tretment group in this study. This my be due to reltively lower proportion in the lowest income group in the orthodontic tretment group becuse of the high cost of orthodontic tretment. Plque control hbits such s frequency of tooth brushing nd the use of n interdentl brush nd floss were not ssocited with prevlence of periodontitis in the orthodontic tretment group, unlike in the nonorthodontic tretment group. It my be suggested tht the subjects with periodontitis in the orthodontic tretment group try to mintin good orl hygiene. It ws lso found tht the orthodontic tretment group tended to hve lower prevlence of periodontitis compred with the nonorthodontic tretment group in ll ge groups. This suggests tht orthodontic tretment hd preventive effect on periodontitis. According to these results, there re severl possible explntions for the ssocition between orthodontic tretment nd periodontitis. First, the lower prevlence of periodontitis in the orthodontic tretment group my be ssocited with tooth lignment. In fct, it hs been observed tht crowded or tipped teeth re difficult to clen. Orthodontic tretment my help ptients clen their teeth nd fcilitte orl helth cre. Previous studies hve shown tht the plque nd gingivl indexes of crowded teeth were significntly higher thn tht of noncrowded teeth. 27,28 Also, the number of periodontl pthogens in crowded teeth ws found to be greter thn the number in noncrowded teeth. 29 Orthodontic uprighting of tipped teeth my lso eliminte plque-retentive res nd reduce periodontl pocket depths on mesil surfces. 30 32 Second, occlusl conditions my hve contributed to the lower prevlence of periodontitis in the orthodontic tretment group in this study. Trumtic occlusion hs Tble 3. Adjusted Odds Rtios (95% Confidence Intervl) for Periodontitis According to Orthodontic Tretment Model 1 Model 2 Model 3 Orthodontic tretment 0.553 (0.414 0.74) 0.614 (0.452 0.836) 0.624 (0.455 0.854) P,.0001 P,.0001 P,.0001 Model 1 ws djusted for ge nd sex. Model 2 ws djusted for ge, sex, income, eduction, lcohol intke, smoking, regulr exercise, body mss index, nd white blood cell counts. Model 3 ws djusted for ge, sex, income, eduction, lcohol intke, smoking, regulr exercise, body mss index, white blood cell counts, dibetes, hypertension, metbolic syndrome, nd dily frequency of tooth brushing.
656 SIM, KIM, JUNG, LEE, LEE, HAN, YUN been considered s one of the detrimentl fctors in periodontl disese. A popultion-bsed cross-sectionl study showed tht nonworking side contcts were ssocited with incresed ttchment loss. 31 Some retrospective studies indicted tht occlusl discrepncies between initil contct nd centric occlusion, centric reltion, nd working nd blncing contcts re ssocited with periodontl disese. 33,34 Teeth with occlusl discrepncies exhibited deeper periodontl pockets but did not increse in probing depth fter occlusl tretment. 34 Third, it my be supposed tht improved plque control hbits nd periodontl therpy before orthodontic tretment my provide positive long-term effects on the mngement of periodontl helth. Recently, orthodontists hve become more interested in periodontl disese nd mintennce becuse of the incresing number of dult orthodontic ptients. Regulr orl helth checkups during orthodontic tretment my be helpful for motivting ptients nd crete more interest in mintining periodontl helth. The min strength of the present study ws tht it included ntionlly representtive smple of Korens with sufficient power for investigtion of n ssocition between orthodontic tretment nd periodontitis. Also, sttisticl djustments were performed to minimize the effects of confounding fctors such s socioeconomic sttus nd periodontl plque control methods. To the best of our knowledge, this is the first study to exmine the ssocition between orthodontic tretment nd periodontitis in the generl popultion. Limittions The results should be interpreted with some cution becuse there re some limittions. First, it is difficult to generlize these results on globl scle becuse this helth survey ws conducted in only one Asin country nd reltively smll number of people were included in the orthodontic tretment group. Second, s in other cross-sectionl studies, it is not possible to explin the cuse-nd-effect reltionship between orthodontic tretment nd reduction in the prevlence of periodontitis. Future well-controlled longitudinl studies re needed to clrify the cusl reltionships between orthodontic tretment nd reducing periodontitis. Third, in the present study, periodontl helth ws evluted ccording to the CPI. This index hs some limittions, lthough it hs been widely used to evlute the periodontl helth nd tretment needs of popultions. 35 This index is bsed on the ssumption tht periodontl disese progresses hierrchiclly. Thus, the teeth with scores of 3 or 4 re ssumed to hve clculus or bleeding. 35 However, ll teeth with deep periodontl pockets do not hve clculus. CONCLUSIONS Orthodontic tretment is ssocited with decresed prevlence of periodontitis. Future well-controlled longitudinl studies re needed to clrify the cusl reltionships between orthodontic tretment nd reduced prevlence of periodontitis. 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