This clinical study evaluated factors related to root resorption before (T1) and after (T2) orthodontic treatment. Ninety-six subjects between 9 and 34 years (34 males and 62 females) who had been treated using fixed appliances for at least 1 year and who had panoramic radiographs at T1 and T2 were selected. The relationship between root resorption at T1 and T2, with regard to gender, age, extraction versus non-extraction patterns, specific teeth and treatment duration was investigated. No statistically significant differences in root resorption were found in relation to gender. Significant differences in root resorption (P = 0.000, P < 0.01) and also in treatment duration (P = 0.036, P < 0.05) were noted between the extraction and non-extraction groups; extraction and treatment duration correlated with T2 mean root resorption. Patient age correlated with root resorption of the upper incisors at T1 and T2. Using multiple regression analysis, age and duration of treatment were found to be more associated with root resorption than with extractions; the presence of root resorption at T1 was associated with T2 root resorption, especially of the anterior teeth.

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Sucrose has long been regarded as the most cariogenic carbohydrate. However, why sucrose causes severer dental caries than other sugars is largely unknown. Considering that caries is a polymicrobial infection resulting from dysbiosis of oral biofilms, we hypothesized that sucrose can introduce a microbiota imbalance favoring caries to a greater degree than other sugars. To test this hypothesis, an in vitro saliva-derived multispecies biofilm model was established, and by comparing caries lesions on enamel blocks cocultured with biofilms treated with sucrose, glucose and lactose, we confirmed that this model can reproduce the in vivo finding that sucrose has the strongest cariogenic potential. In parallel, compared to a control treatment, sucrose treatment led to significant changes within the microbial structure and assembly of oral microflora, while no significant difference was detected between the lactose/glucose treatment group and the control. Specifically, sucrose supplementation disrupted the homeostasis between acid-producing and alkali-producing bacteria. Consistent with microbial dysbiosis, we observed the most significant disequilibrium between acid and alkali metabolism in sucrose-treated biofilms. Taken together, our data indicate that the cariogenicity of sugars is closely related to their ability to regulate the oral microecology. These findings advance our understanding of caries etiology from an ecological perspective.Dental caries, one of the most prevalent diseases occurring on tooth hard tissues, is driven by a disequilibrium in the oral microbial community that is termed dental biofilm 1-3 . Dental biofilm is a highly organized polymicrobial structure on tooth surfaces 4 and is enmeshed in an extracellular matrix whose major component is extracellular exopolysaccharides (EPS) 5 . By metabolizing dietary fermentable carbohydrates, microorganisms within the dental biofilm generate organic acids (e.g., lactic acid). When acid production exceeds the neutralizing capacity of both alkali-producing bacteria and saliva, the low pH caused by acid accumulation within the dental biofilm initiates demineralization of tooth hard tissues 4,6-11 . Meanwhile, the acidic environment favors the growth of acidic/ aciduric species but not alkali-producing bacteria, which in return prompts the progression of dental caries and the formation of tooth cavities 2,7,10,11 .There is a consensus that carbohydrates, especially dietary sugars, determine whether caries develops or not 12 . Three variables of sugar consumption, the amount, frequency and sugar type, are closely related to caries progression 13,14 , as studies showed that individuals frequently taking large amounts of specific sugars experienced greater caries severity relative to those with a lower intake 15,16 . In addition to serving as bacterial metabolism substrates for energy production, sugars also affect the formation and properties of dental biofilms. For example, oral bacteria use sugars to synthesize EPS 17 , while EPS enhance the adherence of biof...