Objective: This study aimed to analyse dysbiotic changes of periodontal pathogenic bacteria and their relationship with different types of fixed orthodontic appliances in a population located in Northwestern Mexico. Methods: Three groups of patients were identified: a control group without orthodontic appliances (C), a conventional-ligating appliance group (CLA), and a self-ligating appliance group (SLA). Periodontal biofilm samples were collected for DNA extraction to identify the presence and load of Treponema denticola, Prevotella intermedia, and Fusobacterium nucleatum, using a quantitative real-time PCR technique. Results: A total of 92 patients were included. The results showed that F. nucleatum was present in all groups including the control patients (C 96%, CLA 100%, and SLA 67%, respectively). Female participants displayed a higher frequency of periodontal pathogens than males, but males were more affected by F. nucleatum. In addition, the presence of T. denticola and P. intermedia was time-dependent, being more frequent in patients in treatment for longer than 12 months whereas CLA showed 74% and 78% of positive samples and SLA showed 78% and 89%, respectively. F. nucleatum was present in 100% of CLA samples before and after 12 months of treatment and its load was higher in the SLA group after 12 months. Conclusions: Dysbiotic changes that could affect the periodontal tissues were seen in patients wearing orthodontic appliances. The frequency of F. nucleatum was significantly higher in CLA and noted with a greater load in SLA. In addition, female participants showed a higher frequency of periodontal pathogens while male subjects were more affected by F. nucleatum. As expected, treatment for longer than 12 months correlated with a higher frequency of all periodontal pathogens. The results support the concept that dysbiosis leading to periodontal disease can be caused by the rise of a dominant species, instead of the appearance of a new species.

Open bite can be defined as an absence of occlusion, most frequently located in the anterior region of dental arches and its etiology is multifactorial. We present a clinical case of an 8 years and 10 months child presenting an anterior open bite (AOB) with transverse maxillary deficiency caused by tongue thrust during mixed dentition. The malocclusion was corrected by means of a McNamara expander with a palatal crib jointly with the association of speech therapy for tongue repositioning, and otolaryngology to treat adenoid hypertrophy due to its correlation with AOB. The multidisciplinary approach was effective in correcting the malocclusion with stable results after 2 years post-treatment.