Journal of Environmental and Public Health Table 1: Prevalence of skeletal ﬂuorosis (SF) among children in a coal-burning endemic ﬂuorosis area, Zhijin, Guizhou, China, 2004. Gender n Boys 830 Girls 786 Total 1,616 Number examined SF cases detected Prevalence (%) 188 70 8.4§ 182 52 6.6 370 122 7.5 §Boys were 1.48 times as likely as girls to be diagnosed with skeletal ﬂuorosis (OR = 1.48, 95% CI: 0.96–2.30; P = .0764). Diagnoses were made according to the Chinese standards for Radiological Diagnosis of Skeletal Fluorosis, published by the Chinese Department of Health on November 26, 1999 (professional standard number: WS 192-1999). The Chinese standard is line with the international standard ﬁrst propose by Roholm in 1937, then modiﬁed by Singh and Jolly in 1970. Diagnosed cases were divided into three grades mild, moderate, and severe and four types: constrictive, raritas, mixed, and soft. The grade of SF was further deﬁned using radiographic characteristics from hyperostosis, osteopenia, and turn over of bone. Detailed descriptions on 33 criteria for grading were illustrated in Appendix A of the WS 192- 1999. 2.4.2. Deﬁnition of Skeletal Fluorosis Type. Constrictive type SF is characterized by a thickening of bone trabeculae in the pelvis. Bone spots, dense patches, and os in os phenomenon in the pelvic region are also observed with this type of SF. Children with constrictive type may also have multiple growth retardation lines in the long bones of their legs or lateral line-shaped shadows in the compact bone trabeculae in the leg metaphysis [17]. Raritas type SF shows less thickening of the bone trabeculae in the pelvis; bone trabeculae are thinning or rare in the metaphysis of the legs. Cortical bone thickening and lower densities in the tibioﬁbular region also characterize raritas type. With raritas type, strip microtubule lucency lines are increasingly visible. Mixed type SF is diagnosed when constrictive and raritas types exist at the same time. Soft type SF is characterized by lower density of the bony structure, thickening of bone trabeculae, raritas, and veil construction. With soft type, tibia bones may be abnormally curved. Pelvic deformity and os in os phenomenon in the abdominal vertebra are also associated with soft type SF. 2.4.3. Deﬁnition of Dental Fluorosis. Dean’s Scale was used to assign and record a dental ﬂuorosis index score for each child [15]. DF classiﬁcations for this investigation included normal, questionable, very mild, mild, moderate or severe. Normal teeth appeared smooth and glossy with a white translucent surface. A few white specks on tooth enamel were classiﬁed as questionable. In contrast, DF appeared as opaque white areas on the tooth surface. Moderate cases typically aﬀected the entire tooth surface and a brown stain may have been present. In severe cases, the entire tooth surface was aﬀected, enamel pitting was present, and brown staining was evident. Prevalence of DF was based upon index scores of very mild to severe. Index scores were assigned ordinal values 3 Figure 1: X-ray for a 7-year old boy. as follows: normal or questionable = 0, very mild = 1, mild = 2, moderate = 3, and severe = 4. 2.5. Statistical Analysis. SPSS 11.5 (SPSS Inc., Chicago, Ill, USA) was used for all data management and analysis. Chi- square tests were used to assess the statistical signiﬁcance of observed diﬀerences in disease prevalence or SF type according to gender or age. Odds ratios (ORs) and 95% conﬁdence intervals (CIs) were calculated for all2x2 bivariate associations. Chi-square tests were also used to assess the observed diﬀerences and a linear trend in disease grade by gender. All reported P-values are two-sided and P < .05 was considered statistically signiﬁcant. 3. Results Table 1 depicts SF detection rates by gender. Among the 370 high-risk children, 122 were diagnosed with SF. Data collected from the sampled children (1616) were used to estimate the current prevalence of SF in the study population. In this severe endemic ﬂuorosis area, the prevalence of SF among children ages 7 to 16 years from indoor burning of coal was 7.5%. In addition, boys were 48% more likely to be diagnosed compared to girls, although the higher proportion was of marginal signiﬁcance (OR = 1.48, 95% CI: 0.96–2.30; P = .0764). Table 2 illustrates SF detection rates by gender and age. Older children (12–16 years) were signiﬁcantly more likely to be diagnosed with SF compared to younger children (OR = 1.84, 95% CI: 1.17–2.90; P = .0082). Table 3 describes the distribution of SF type and grade among the aﬀected children. Constrictive type was the most common form of SF in Zhijin County, aﬀecting 74 (60.7%) children. Raritas and mixed-type SF accounted for 39 cases (32.0%); soft type was the least common form of the disease. SF type did not appear to diﬀer according to gender. Of the 122 SF cases, 111 (91.0%) were classiﬁed as mild or moderate in severity. Severe SF was diagnosed in 8 boys and 3 girls. Two of these children, both 7 years old, had severe skeletal deformities (X-shaped or O- shaped legs, Figures 1