Periodontal Health Status And Treatment Needs Among 12 & 15- Year Old School Children in Shimla, Himachal Pradesh - India

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1 ORIGINAL RESEARCH Periodontal Health Status And Treatment Needs Among 12 & 15- Year Old School Children in Shimla, Himachal Pradesh - India Quick Response Code doi: / Senior Lecture 3 HOD Department of Public Health Dentistry, HP Government Dental College, Shimla, Himachal Pradesh, India. 2 Professor Department of Public Health Dentistry, M.M. College of Dental Sciences and Research, Mullana, Ambala, Haryana, India. Article Info: Received: April 10, 2013 Review Completed: May 8, 2013 Accepted: June 11, 2013 Available Online: October, 2013 ( NAD, All rights reserved for correspondence: drfotedar@rediffmail.com. INTRODUCTION Shailee Fotedar 1, Girish M Sogi 2, Kapil R Sharma 3 ABSTRACT: Background: The understanding of periodontal health and treatment needs of populations with different characteristics is important to establish a reliable baseline data for development of national/regional oral health programmes. Aim: To assess the periodontal status and treatment needs among school children aged 12 and 15 years in Shimla city, Himachal Pradesh, India. Methods: A cross sectional study was conducted on a sample of 1011 school children aged 12 and 15 yrs in Shimla, Himachal Pradesh, India. Information regarding oral hygiene practices was collected by questionnaire. Clinical examination was done as per Community Periodontal Index of Treatment Needs (CPITN) index. The statistical tests used were analysis of variance (ANOVA) and chi-square tests. Results: The prevalence of gingivitis was 75.4% and 57% at 12 and 15 years respectively. Healthy sextants (Code 0) was found to be more frequent in females than males at both the age groups with statistically significant difference at 12 years of age. At both the age groups, higher percentages of children were having healthy sextants in Private schools as compared to Government schools. At 12 years almost two thirds, needed education on oral hygiene measures while at 15 years the need for education was for 57%. Conclusion In this study, at 15 years only 18.8% population had healthy periodontal status and the mean of the healthy sextant is 3.09 which was far away from the goals of WHO for Effective oral health promotion strategies need to be implemented to improve the periodontal health of school children in Shimla city. Key words: Periodontal status, treatment needs, school children, Shimla. Periodontal disease has been defined as a group of lesions affecting the tissues surrounding and supporting the teeth in their sockets. The majority of periodontal diseases can be classified as either gingivitis or periodontitis which occur as a result of the presence of bacterial plaque or calculus on supragingival and subgingival toothsurfaces. 1 INDIAN JOURNAL OF DENTAL ADVANCEMENTS Journal homepage: www. nacd. in

2 Gingivitis - a reversible plaque induced inflammation is a common occurrence in children due to special condition of periodontium and poor oral hygiene. 2 Periodontitis which is bacterially induced, is usually accompanied by gingivitis resulting in irreversible destruction of supporting tissues of the tooth including the alveolar bone. A severe form of periodontitis-aggressive periodontitis, produces destruction of periodontium which is apparent during childhood. 3 Periodontal disease and dental caries are the most common infections affecting human dentition. 4 Gingivitis is common, especially around puberty, affecting over 80% of young children while almost entire population experiences gingivitis, periodontitis or both 5. Periodontal disease occurs at any age and is an extremely slow process. The early stages are around puberty 3,5,6 and unless these early stages are eliminated, degenerative periodontal diseases are inevitable in the latter years of life 6 Hence it is of utmost importance to recognize periodontal problems and treat them in the childhood to accomplish a healthy oral environment in adulthood. Further, a systematic literature review indicated that in majority of studies, improvements in gingival conditions were obtained in short run by oral health promotion initiatives. 7 But for appropriate planning of public dental health services, the knowledge of dental treatment needs of populations with different characteristics is important. The Community Periodontal Index of Treatment Needs (CPITN) developed and proposed by World Health Organisation, has been widely used to determine periodontal treatment needs. 8 As there are no earlier studies regarding prevalence and severity of periodontal disease among school children in Shimla city, this study was conducted with the following objectives: To assess the prevalence and severity of periodontal disease among school children aged 12 and 15 years in Shimla city. To compare the periodontal disease levels in Government and Private schools. To establish a reliable baseline data for development of national/regional oral health programmes. Materials and Method: A cross sectional epidemiologic study was conducted among the school going children aged 12 years and 15 years in Shimla city. Ethical approval to conduct the study was obtained from the Institutional Review Board of Himachal Pradesh Government Dental College and Hospital, Shimla. Written consent for the participation of the children in the study was obtained from the Principals of the concerned schools. Sample size and Sampling technique: A two-stage cluster sampling technique was used for obtaining the required sample for the study. For the purpose of the study, Shimla city was arbitrarily divided into 4 geographical regions, which corresponded to the four varying demographic areas of the city: Shimla municipal and 3 Shimla Planning Areas (Dhalli, Tutu and New Shimla). Schools from each region were randomly selected to obtain the desired sample size, such that there was an equal representation from each of the four zones. Under the municipal corporation of Shimla, there were 43 schools (12 Senior Secondary, 24 Secondary and 7 Middle), where the children in age group of 12 and 15 years were available. Out of the 43 schools there were 26 government and 17 private schools as per the data available from the Director of Education, Himachal Pradesh (H.P) in Feb, Total number of school children in the age group of 12 and 15 years were A pilot study was conducted by randomly selecting one government and one private school from the available list of schools. Results from this pilot study were used to calculate the sample size which came out to be 985. For obtaining the required sample size, seven government and five private schools were selected randomly with proportionate representation from each category of schools, i.e., government and private schools, and a total of 1011 subjects was examined over a period of three months April - June Data collection was carried out by one of the authors (FS) trained for clinical examination during several educational and clinical sessions in the department of Public Health Dentistry, Government Dental College Shimla. The author was assisted by a recording assistant. Data regarding general information, oral hygiene practices were obtained through interview and recorded on a proforma. The subjects were examined by a mouth mirror and WHO probe in presence of adequate illumination. (Dunning type III clinical examination) 9 in their respective schools on a comfortable chair. The periodontal examination was performed as per Community Periodontal index of Treatment needs

3 (CPITN). 8 The periodontal indicators assessed were gingival bleeding & calculus for 12 yrs old age group and pockets were not measured as these are indicated for 15 and above 15 yrs. Whereas the periodontal indicators assessed for 15 yrs were gingival bleeding, calculus and periodontal pockets. In this study only six teeth were examined. Second molars were excluded because of high frequency of false pockets. Each sextant was designated as healthy, when no treatment was required Code 0 = TN 0, or X (Missing). In case of gingival bleeding, it was recommended to improve the oral hygiene (Code 1= TN 1). If calculus was detected, oral hygiene instructions were provided and professional cleaning was carried out (Code 2 = TN 2). Presence of 4-5 mm pockets (Code 3), and 6 mm or deeper (Code 4) may or may not need treatment by deep scaling. In these cases, root planning and more complex surgical procedures may be indicated. Intra-examiner reproducibility as determined using Kappa statistic was Five students were randomly selected by asking the teacher to send any five of the students examined the previous day and re-examined the next day to determine intraexaminer reproducibility. Instruments were sterilized by autoclaving at the end of the day s clinical examination. At the site, chemical sterilization was followed. Inclusion criteria: School children (Male and Female) who have completed their twelve and fifteen years of age. Children present on the day of examination. Exclusion Criteria: Children who refused to participate were excluded. Medically compromised children i,e children with systemic diseases or conditions like Papillon lefevre syndrome, cyclic neutropenia, agranulocytosis, Downs syndrome, Hypophosphatasia and leucocyte adherence deficiency because the defect in neutrophil and immune cell function associated with these diseases may lead to in increased susceptibility to periodontitis. A referral was forwarded to the parents of the children in need of dental care. At the conclusion of the survey, an oral health education session and tooth brushing demonstration was conducted in each classroom. The data collected was analyzed by Statistical Package for Social Sciences (SPSS) package 13. The statistical tests used were analysis of variance (ANOVA) as appropriate for continuous variables and chi-square tests for categorical data. A level of p < 0.05 was considered statistically significant and p < was taken as highly statistically significant. Results: Of the total study population 49.2% were in the 12 years age group and 50.8% were in the 15 years age group. Among the 12 year age group there were 322 (64.8%) males and 175 (35.2%) females while in the 15 year age group there were 304 (59.2%) males and 210 (40.8%) females. Among the 12 year age group 46.1% of children were in Government schools and 53.9% of children were in Private schools whereas in the age group of 15 years 48.6% of the children were in Government schools and 51.4% were in Private schools (Table 1). Table 2 shows distribution of subjects according to oral hygiene practices. 100% of the children in private schools used toothbrush and tooth paste as compared to Government schools (95.4% used tooth brush and 93.6% used tooth paste) and the difference was statistically significant, p < The frequency of brushing twice a day was statistically higher in private schools than Government schools (Table 3). There was significant age difference (p value < 0.05) regarding CPITN scores. The percent of children with healthy component of gingiva was higher at 15 years of age than 12 years. Higher percentage of children had calculus at 15 years as compared to 12 years. At the age of 12 years, healthy periodontal tissues existed only in 14.1% of subjects. The highest score in this age group was for gingival bleeding (75.4%) while as at the age of 15 years, 57.0 % had a score of 1 (bleeding gums), 18.9% had healthy periodontium, 18.7% had a score of 2, 5.4% had a score of 3 and no one had a score of 4.(Table 4) A significant difference was found in the CPITN in terms of gender (p value < 0.05) at the age of 12 yrs. Healthy sextants (Code 0) was found to be more frequent in females than males at both the age groups. (Table 4) At both the age groups, higher percentages of children were having healthy sextants in Private schools as compared to Government schools. At 12 yrs there was statistically higher percentage of children having calculus in Government schools as compared to private. (Table 4)

4 The average number of sextants affected for each student was higher at 12 yrs of age as compared to 15 yrs. In this study the at the age of 15 years, there was a significant correlation between frequency of brushing and CPITN scores but at the age of 12 years, the positive correlation between frequency of brushing and CPITN scores could not reach the statistical significance. The mean number of healthy sextants was higher in children who brush twice a day when compared to those who brush once a day at both the age groups. At 12 yrs almost two thirds, needed education on oral hygiene measures and 10.5% needed scaling and polishing. There was no need for treatment in 14.1% of subjects. At 15 yrs there was no treatment need for 18.8%, need for education was for 57%, scaling and polishing for 18.6% and scaling and root planning for 5.4%. At the age of 12 yrs, the need for scaling and polishing was statistically higher in Government school. Discussion: A cross sectional study was carried out to assess the prevalence and treatment needs of periodontal disease among school children in Shimla city, Himachal Pradesh India. The 12 and 15 age groups were chosen for this study, as these are global monitoring ages for disease trends. The present study sample consisted of schoolchildren. In, Himachal Pradesh, India schools are classified as either private or government depending on the source of their funding. Government schools are funded by the government and tuition fees are subsidized while private schools are funded by individual and high tuition fees are charged. Here the type of school a child attends depends on the environment where the child lives and the parent s social economic status. Most children from high and middle social economic family status attend private schools while children from low income family status attend government schools. The major reason for this difference in the choice of school is economic condition. The present study sample consisted of schoolchildren from both government and private schools in Shimla city in order to have representative of children from all the social, economic and cultural communities. Regarding oral health services there is one government dental school, one government dental care unit and few private dental clinics in the city to provide oral health care services to the population of Shimla. At both the age groups around 97% of population claimed to use tooth brush and tooth paste for cleaning their teeth. At the age of 12 years, 35.6% used to brush twice a day which is less than 77% given by Peterson 10 and 55.6% given by Cesar Mexia de Almeida 11. This study indicates the children are aware of oral hygiene but lack complete formal education on oral hygiene practices. The frequency of brushing twice was more common in private schools as compared to Government schools which was also reported by Mahesh Kumar, 12 Tanni 13 and Petersen. 14 In the present study as the frequency of brushing increased prevalence and severity of periodontal diseases decreased which is in line with other studies and can be explained by significant co relation between plaque retention and gingival inflammation. 15 Only 11% of the children had visited a dentist before the present examination at the age of 12 yrs and around 17% of the children at 15 years. The children at 15 years showed higher proportion of healthy gingiva as compared to 12 years. At the age of 12 years, gingivitis was the main finding in about 75% of children which was also reported by Peterson 14 and Mahesh Kumar, 12 Abid 16 but is less than 85% as reported by Dhar, 17 Addy 18 and higher than 35% as reported by Bandara. 19 The higher proportion of gingival bleeding may be due to exfoliation and tooth-eruption processes, which contribute to a higher accumulation of bacterial plaque. 20 It can also be due to pubertal periods. Gingivitis has been associated with puberty on account of hormonal changes. The potentiated gingival reaction creates an environment in the gingival sulcus, which in the long run paves the way for the development of more severe form of periodontitis. Several authors have reported peak form of gingivitis around 9-14 years of age. 21 Periodontal status was worse among males than females. This finding is in line with the findings of Mahesh Kumar 12, Kanli 22,Saed Maulamie, 23 Al- Ansari, 24 Walter, 25 Tanni 26,27 but opposite to the one reported by Saha and Sarkar 28 This can be explained by the fact that females are more conscious of their appearance; including their oral hygiene which is reflected from the present study by the more frequent toothbrushing among females than males. The overall high prevalence of gingivitis at both the age groups may be due to ineffective oral hygiene measures. As the present study showed that about 97% used tooth brush, but the gingivitis present in most of the school children reflects irregular brushing methods which can be due to inadequate brushing time, ineffective brushing technique or

5 both factors or it may also be possible that some of the children did not brush as they claim. Data collected through interview have limitations, so over reporting is possible regarding use of tooth brushing. In the present study, it was found that the children in private schools had significantly higher proportion of healthy gingiva as compared to Governmenrt at 12 yrs which was also reported by Tani 26 and Mahesh Kumar. 12 This can be explained by better awareness of oral health among children in private schools as compared to Government schools, which create positive attitude towards oral health. Due to better socio economic conditions in private school children, the means already exist to maintain reasonably good periodontal condition throughout life, using simple forms of personal and professional care. This explanation can be seen in this study as more children from private schools brush their teeth twice daily compared to Govt. schools. Comparative studies of the populations from the developing countries and developed countries suggested that periodontal diseases were associated with nutritional deficiencies. Periodontal disease progresses more rapidly in undernourished populations as the role of nutrition in maintaining an adequate immune response may explain this observation 29. The present study did not reveal any significant difference between the children showing clinical symptoms of general malnutrition and those of wellnourished children which is also supported by Ramjford etal. 30 The treatment need for most of this population is covered by education, the necessity for the mobilization of efforts towards information and education on oral health and oral hygiene measures becomes very important. The treatment need TN 2a (scaling and polishing) and TN 2b (scaling and root planning) is indicated for 10% at 12 yrs and 20% at 15 yrs. The limitation of the present study was that the socioeconomic status of the subjects could not be correlated with periodontal disease as it was not possible to assess because the children could not be relied upon for this information and the collection of this information from the school was not feasible. Conclusion and Recommendations: This study reports a high prevalence of gingivitis, especially at 12 yrs. The proportion of children with healthy periodontium ranged from 14.1 percent among twelve-year-olds to 18.9 percent at year old. Oral hygiene instructions, however, was the most prevalent treatment need followed by prophylaxis. In this study, at 15 yrs 18.8% population had healthy periodontal tissues and the mean of the healthy sextant is 3.09 which was far away from the goals of WHO for 2010 (that all at 15 yrs should have 5-6 mean healthy sextants by the year 2010). To improve the periodontal health of children in Shimla, the following recommendations are given. 1. Educating parents on the importance of dental care practices in children from an early age, possible risk factors for periodontal disease and the value of dental prophylactic visits in reducing oral health problems. 2. Proper techniques of tooth brushing and flossing must be explained and demonstrated on models in schools and health centers. 3. Children readily accept the advice of teachers. Hence training programs and workshops on dental health education for teachers should be organized. Other than imparting knowledge the teachers should also supervise activities of toothbrushing and flossing during schooltime. 4. Secondary prevention programs be introduced later, depending upon the availability of resources. Acknowledgement: The author would like to thank Mrs. Kusum Chopra, Statistician, without whose valuable input this work would not have been possible. TABLE 1. Distribution of 12yr and 15 yr old school children according to age, gender and school in Shimla, H.P- India. Distribution of subjects according to age and gender Age Male Female Total N % N % N % 12 Yrs % % % 15 Yrs % % % Total % % %

6 Distribution of subjects according to schools Age Schools Male Female Total N % N % N % 12 Yrs Govt % % % Private % % % Total % % % 15 Yrs Govt % % % Private % % % Total % % % TABLE 2. Distribution of 12yr and 15 yr old school children according to oral hygiene practices in Shimla, H.P- India. Distribution of subjects according to oral hygiene practices at 12 years Sex Sub- Cleaning Habits Material used Frequency of brushing School jects Tooth Finger Tree Tooth Tooth Other Once a Twice a Not even brush stick paste powder day day day once a Day N % N % N % N % N % N % N % N % N % M F Total Distribution of subjects according to oral hygiene practices at 15 years M F Total Distribution of subjects according to oral hygiene practices & school category Govt Private Total P value < 0.001* P value < 0.001* P value < 0.001* Test used- Chi square *- Statistically significant TABLE 3 CPITN scores in relation to age, gender, schools among 12yr and 15 yr old school children in Shimla, H.P-India. CPITN Scores in relation to gender and schools at 12 yrs Gender/School CPITN score Total P Value 0(Healthy) 1(Bleeding) 2(calculus Male 39(12.1%) 248(77.1%) 35(10.8%) 322(100%) <0.05* Female 31(17.7%) 127(72.4%) 17(9.9%) 175(100%) Total 70(14.1%) 375(75.4%) 52(10.5%) 497(100%) Govt. School 13(16.6%) 186(51.0%) 30(58.8%) 229(100%) <0.001* Private School 65(83.4%) 180(49.0%) 23(41.2%) 268(100%) Total 78(100%) 366(100%) 53(100%) 497(100%)

7 CPITN Scores in relation to gender and schools at 15 yrs Gender/School CPITN score Total P Value (Shallow 4 (Deep (Healthy) (Bleeding) (calculus) pocket) pocket) Male 55(18.1%) 174(57.5%) 58(19.0%) 17(5.4%) 0 304(100%) >0.05* Female 42(20.0%) 119(56.6%) 38(18.1%) 11(5.3%) 0 210(100%) Total 97(18.9%) 293(57.0%) 96(18.7%) 28(5.4%) 0 514(100%) Govt. School 35(14%) 133(53.2%) 62(24.8%) 20(8%) 0 250(100%) >0.05* Private School 75(28.4%) 138(52.1%) 44(16.5%) 8(3.0%) 0 264(100%) Total 110(21.4) 271(52.7) 106(40%) 28(5.4%) 0 Test used- Chisquare*- Statistically signific Age Table 4. Mean score of the sextants for each periodontal indicator according to age and brushing frequency among 12yr and 15 yr old school children in Shimla,H.P-India. Mean score of the sextants according to age CPITN SCORE 0(Healthy) 1(bleeding) 2(calculus) Shallow pockets Deep pockets N Mean N Mean N Mean N Mean N Mean S.D S.D S.D S.D S.D 12 yrs yrs Table 4. Mean score of the sextants for each periodontal indicator according to age and brushing frequency among 12yr and 15 yr old school children in Shimla, H.P-India. Mean score of the sextants according to brushing frequency Age Frequency N 0 (Healthy) 1 (bleeding) 2 (calculus) Shallow Deep P value pocket pocket Mean S.D Mean S.D Mean S.D Mean S.D Mean S.D 12 yrs once a day > 0.05 Twice a day yrs once a day < 0.05* Twice a day Test used- ANOVA *- Statistically significant TABLE 5. Treatment needs according to age and school category Treatment need as per Age Age No. of No Education Scaling and p-value subjects treatment Polishing 12 yrs (15.7%) 368(74.0%) 51(10.3%) > yrs (21.2%) 302(58.8%) 103(20.0%)

8 Treatment need as per Age Age No. of No Education Scaling and p-value subjects treatment Polishing Govt (9.8%) 345(72.0%) 87(18.6%) >0.05 Private (26.4%) 325(61.1%) 67(12.5%) Test used-chi square References 1. Carranza FA. Clinical Periodontology. 10 th ed. Philadelphia: W B Saunders Company; p Pourheshami S, Motlagh M, Khainaki G. Prevalance and Intensity of gingivitis among 6-10 yrs Old Elemantary School Children in Tehran, Iran. J.Med. Sci 2007;7(5): Carranza F, Glickman.Clinical Periodontology (7 th ed). Philadelphia,WB Saunders Company Brown LJ, Brunelle JA, Kingman A. Periodontal status in the United States , prevalence, extent & demographic variation.j Dent Res. 1996;75: WHO Technical Report Series 621: Epidemiology,etiology & Prevention of periodontal diseases;who Geneva Sidney Finn.Clinical Pedodontics (4rth ed).philadelphia, WB Saunders Company Watt RG, MarinhoVC. Does oral health promotion improve oral hygiene and gingival health? Periodontal ;37: Cutress T W, Ainamo J, S ardo Inferri J. The Community Periodontal Index of Treatment Needs procedure for population groups and individuals. Int Dent J. 1987;37: Dunning JM. Principles of Dental Public Health.4rth ed. Harward University Press:1986; Petersen PE, Hoerup N, Poomviset N, Prommajan J, Watanapa A. Oral health status and oral health behaviour of urban and rural schoolchildren in Southern Thailand. Int Dent J 2001 Apr; 51(2): Almeida CM, Petersen PE, André SJ, Toscano. A Changing oral health status of 6- and 12-year-old schoolchildren in Portugal. Community Dent Health 2003 Dec;20(4): Mahesh Kumar P, Joseph T, Varma RB, Jayanthi M. Oral health status of 5 years and 12 years school going children in Chennai city - An epidemiological study. J Indian Soc Pedod Prev Dent 2005;23(1): Tanni DQ. Caries prevalence and periodontal treatment needs in public and private school pupils in Jordan. Int Dent J 1997 Apr; 47(2): Petersen PE, Wierzbicka M, Szatko F, Dybizbanska E, Kalo I. Changing oral health status and oral health behaviour of school children in Poland. Community Dent Health 2002 Dec; 19(4): Kurt A, Rosenzwe G, Anselm L. Oral diseases in Yushiva students. J Dent Res.1961; 5: Abid A. Oral health in Tunisia. Int Dent J 2004 Dec; 54(6 Suppl 1): Dhar V, Jain A, Van Dyke TE, Kohli A. Prevalence of gingival diseases, malocclusion and fluorosis in school-going children of rural areas in Udaipur district. J Indian Soc Pedod Prev Dent. 2007Apr-Jun;25(2): Addy M, Dummer PMH, Hunter ML et.al. The effect of toothbrushing frequency, toothbrushing hand, sex and social class on the incidence of plaque, gingivitis and pocketing in adolescents; a longitudinal study. Community Dent Health 1990;7: Bandara KMW. Oral health status of students at the ages of years in Southern Highlands Province of Papua New Guinea. PNG Med J 1997 Sep-Dec; 40(3-4): Hugoson A, Koch G, Rylander H. Prevalence and distribution of gingivitis-periodontitis in children and adolescents. Epidemiological data as a base for risk group selection. Swed Dent J 1981;5(3): Mattson L. Factors influencing the susceptibility to gingivitis during childhood:a review. Int J of Pediatric Dent 1993;3: Kanli A, Kanbor O, Dural S, Derman O. Effects of Oral health behaviors & socio-economic factors on a group of Turkish adolescents. Quintessence Int, 2008 Jan;39(1): Saied- Moallemi Z, Virtamen JI, Vehkalanti MM. School based intervention to promote pre adolescents gingival health: a community trial. Commnity Dent Oral Epidemiol, 2009 Dec; 37(6): Al Ansari JM, Honkola S. Gender Differences in oral health knowledge & behavior of the health science college students in Kuwait. J Allied Health, 2007;36(1): Walter MH, Worunuk JI, Tan HK. Oral health related quality of life & its association with sociodemographic & Clinical findings in 3 Northern Outreach Clinics. J Can Dent Assoc 2007 March;73(2): Tanni QD, Al-wahadni AM, Al-Omari,M. The effect of frequency of toothbrushing on oral health of year olds. J Irish Dent Asso.2003; 49: Taani QD. Relationship of socioeconomic background to oral hygiene, gingival status and dental caries in children. Quintessence Int 2002;33: Saha, Sarkar. Prevalence and severity of dental caries and oral hygiene status in rural and urban areas of Calcutta. J Indian Soc Pedod Prev Dent 1996; 14: Russell AL.Geographic Distribution & Epidemilogy of Periodontal diseases. Geneva.World Health Organisation:1960.(WHO/DH/33/34). 30. Ramjford SP,Emslie RD, Greene JC, Held AJ. Epidemiological studies of Periodontal diseases. Am J Public Health.1968;58: