Effective factors on the number of decayed and filled teeth using the Conway-Maxwell-Poisson count model

Document Type: Original Article(s)


1 Student Research Committee, Shahrekord University of Medical Sciences, Shahrekord, Iran

2 Professor, Modeling in Health Research Center, Shahrekord University of Medical Sciences, Shahrekord, Iran

3 Associate Professor, Department of Epidemiology and Biostatistics, Shahrekord University of Medical Sciences, Shahrekord, Iran

4 Associate Professor, Modeling in Health Research Center, Shahrekord University of Medical Sciences, Shahrekord, Iran


BACKGROUND AND AIM: Recognizing the factors affecting the number of decayed and filled teethhas a major role in oral health. Dental data usually suffer from over-dispersion and excess zero frequencies. The purpose of this study was to use theConway-Maxwell-Poisson (COM-Poisson) model to determine some of the factors affecting the number of decayed and filled teeth.
METHODS: In this cross-sectional study, a sample of 1000 people from a cohort study in Shahrekord City, Iran, aged 35-70 years, was selected through systematic sampling. The data were analyzed using the Bayesian approach through Markov chain Monte Carlo (MCMC) simulation by OpenBUGS. Zero-inflated Poisson (ZIP), COM-Poisson model, and zero-inflated Com-Poisson (ZICMP) model were fitted on the data and compared using the deviance information criterion (DIC).
RESULTS: The mean numbers of decayed and filled teeth were 0.77 ± 1.63 and 4.37 ± 4.62, respectively. The Com-Poisson and ZICMP showed to be better fit for the number of decayed and filled teeth, respectively. Those people who were younger, male, smokers, diabetics, did not floss, and did not use mouthwash had significantly more number of decayed teeth (P < 0.05). Those people who were younger, female, non-diabetics, non-smokers, employed, literate, had less body mass index (BMI), flossed, and got higher score of quality of life had significantly more number of filled teeth (P < 0.05).
CONCLUSION: By controlling such factors as education, BMI, flossing, using mouthwash, smoking, diabetes, and quality of life, we could improve the oral health.


  1. Harada S, Akhter R, Kurita K, Mori M, Hoshikoshi M, Tamashiro H, et al. Relationships between lifestyle and dental health behaviors in a rural population in Japan. Community Dent Oral Epidemiol 2005; 33(1): 17-24.
  2. Pitts NB, Zero DT, Marsh PD, Ekstrand K, Weintraub JA, Ramos-Gomez F, et al. Dental caries. Nat Rev Dis Primers 2017; 3: 17030.
  3. Nishikawara F, Nomura Y, Imai S, Senda A, Hanada N. Evaluation of cariogenic bacteria. Eur J Dent 2007; 1(1): 31-9.
  4. Correa-Faria P, Daher A, Freire MDCM, de Abreu MHNG, Bonecker M, Costa LR. Impact of untreated dental caries severity on the quality of life of preschool children and their families: a cross-sectional study. Qual Life Res 2018; 27(12): 3191-8.
  5. Meurman JH, Sanz M, Janket SJ. Oral health, atherosclerosis, and cardiovascular disease. Crit Rev Oral Biol Med 2004; 15(6): 403-13.
  6. Lamster IB, Lalla E, Borgnakke WS, Taylor GW. The relationship between oral health and diabetes mellitus. J Am Dent Assoc 2008; 139 Suppl: 19S-24S.
  7. Hessari H, Vehkalahti MM, Eghbal MJ, Murtomaa HT. Oral health among 35- to 44-year-old Iranians. Med Princ Pract 2007; 16(4): 280-5.
  8. Li LW, Wong HM, McGrath CP. Longitudinal association between obesity and dental caries in adolescents. J Pediatr 2017; 189: 149-54.
  9. Vergnes JN, Boucher JP, Lelong N, Sixou M, Nabet C. Discrete distribution based on compound sum to model dental caries count data. Caries Res 2017; 51(1): 68-78.
  10. Jahani Y, Eshraghian R, Foroushani M, Nourijelyani A, Mohammad K, Shahravan K, et al. Effect of socio-demographic status on dental caries in pupils by using a multilevel hurdle model. Health 2013; 5(7): 1110-6.
  11. Conway R, Maxwell WL. A queuing model with state dependent service rate. Journal of Industrial Engineering 1962; 12: 132-6.
  12. Shmueli G, Minka TP, Kadane JB, Borle S, Boatwright P. A useful distribution for fitting discrete data: Revival of the Conway–Maxwell–Poisson distribution. J R Stat Soc Ser C Appl Stat 2005; 54(1): 127-42.
  13. Choo-Wosoba H, Levy SM, Datta S. Marginal regression models for clustered count data based on zero-inflated Conway-Maxwell-Poisson distribution with applications. Biometrics 2016; 72(2): 606-18.
  14. Khaledifar A, Hashemzadeh M, Solati K, Poustchi H, Bollati V, Ahmadi A, et al. The protocol of a population-based prospective cohort study in southwest of Iran to analyze common non-communicable diseases: Shahrekord cohort study. BMC Public Health 2018; 18(1): 660.
  15. Poustchi H, Eghtesad S, Kamangar F, Etemadi A, Keshtkar AA, Hekmatdoost A, et al. Prospective Epidemiological Research Studies in Iran (the PERSIAN Cohort Study): Rationale, objectives, and design. Am J Epidemiol 2018; 187(4): 647-55.
  16. Eghtesad S, Mohammadi Z, Shayanrad A, Faramarzi E, Joukar F, Hamzeh B, et al. The PERSIAN Cohort: Providing the evidence needed for healthcare reform. Arch Iran Med 2017; 20(11): 691-5.
  17. Sellers KF, Raim A. A flexible zero-inflated model to address data dispersion. Comput Stat Data An 2019; 99(C): 68-80.
  18. Chanialidis C, Evers L, Neocleous T, Nobile A. Efficient Bayesian inference for COM-Poisson regression models. Stat Comput 2018; 28(3): 595-608.
  19. Spiegelhalter DJ, Best NG, Carlin BP, Van Der Linde A. Bayesian measures of model complexity and fit. J R Stat Soc Series B 2002; 64(4): 583-639.
  20. Hescot P. The new definition of oral health and relationship between oral health and quality of life. Chin J Dent Res 2017; 20(4): 189-92.
  21. Habicht JP. Health for All by the Year 2000. Am J Public Health 1981; 71(5): 459–61.
  22. Furuta M, Ekuni D, Irie K, Azuma T, Tomofuji T, Ogura T, et al. Sex differences in gingivitis relate to interaction of oral health behaviors in young people. J Periodontol 2011; 82(4): 558-65.
  23. Ahmadi A, Sahaf R, Rashedi V, Akbari Kamrani AA, Shati M, Delbari A. Relationship between oral health and demographic characteristics in retired elderly people in Iran. Salmand Iran J Ageing 2019; 13(4):452-63. [In Persian].
  24. Gao YB, Hu T, Zhou XD, Shao R, Cheng R, Wang GS, et al. Dental caries in Chinese elderly people: Findings from the 4th National Oral Health Survey. Chin J Dent Res 2018; 21(3): 213-20.
  25. Yonekura S, Usui M, Murano S. Association between numbers of decayed teeth and HbA1c in Japanese patients with type 2 diabetes mellitus. Ups J Med Sci 2017; 122(2): 108-13.
  26. Ide R, Mizoue T, Ueno K, Fujino Y, Yoshimura T. Relationship between cigarette smoking and oral health status. Sangyo Eiseigaku Zasshi 2002; 44(1): 6-11. [In Japanese].
  27. Millar WJ, Locker D. Smoking and oral health status. J Can Dent Assoc 2007; 73(2): 155.