To assess the current status of patients with dental metal allergies in Japan. This study analyzed dental metal allergy in 1225 patients (1:3 male to female ratio; average age 53.0 ±16.5 years), including 300 who were scheduled to undergo dental implant surgery, between 2006 and 2016. For diagnosis of metal allergy, patch tests using metal allergens were performed. Additionally, when necessary, metal element analysis of dental alloys was performed in the mouths of some patients using an X-ray fluorescence analyzer for those who exhibited positive reactions. Among 925 patients (i.e., excluding those scheduled to undergo dental implant surgery [n=300]), nearly one-half (44.0%) exhibited a positive response to any metal element in the patch test. The positivity rates were as follows: nickel (22.5%); palladium (14.8%); and zinc (11.5%). Almost one-half (42.3%) of the patients had diseases associated with metal allergy. Among patients who exhibited a positive reaction to any metal element in the patch test, more than two-thirds (67.9%) had dental alloys containing the positive metal element(s). One-half (55.6%) of the patients who underwent treatment to remove the metal experienced improvement in symptoms. In patients who underwent patch testing as an implant preoperative examination, several (2.7%) exhibited a positive reaction to titanium. Dental metals, including nickel, palladium and zinc, which are indispensable to dental treatment in Japan, had high positivity rates in patch testing, and one-half of the patients improved following removal of the metal. Additionally, there were several patients with allergy to titanium.

This study aimed to determine the salivary factors that influence salivary bacterial counts and the microbiome composition in children and young adults. This cross-sectional study included 382 patients who visited the dental clinic in Hiroshima University Hospital. All participants underwent a saliva test and were divided into high- and low-bacterial-count groups based on the median bacterial count. Salivary factors and clinical variables, including the total number of teeth and plaque control record, were analyzed to determine their association with salivary bacterial counts. Furthermore, a comprehensive analysis of microbiome diversity and composition was performed using 16S rRNA sequencing. Univariate and multivariate analyses identified stimulated saliva volume (SSV) and plaque control record as independent factors influencing salivary bacterial counts. Principal coordinate analysis revealed a significant decrease in beta diversity in the high-bacterial-count group. LEfSe analysis revealed Prevotella, Veillonella, Megafaella, Selenomonas, and TM7X as the 5 most abundant bacteria. The relative abundance of the 35 KEGG pathways exhibited significant differences. Furthermore, Prevotella and Veillonella were strongly associated with 25 functional pathways. Oral hygiene instruction is necessary even for children and young adults with relatively adequate SSV to maintain a healthy oral microbiome.