Examination of corrosion effects on orthodontic brackets under simulated gastroesophageal reflux disease (GERD) – an in-vitro study

The aim of this study was to investigate the surface roughness and ion release of stainless steel brackets (N=180, upper central incisor) after corrosion under simulated Gastroesophageal Reflux Disease. The effects of different pHs and durations were evaluated. Brackets were randomly divided into 3 main groups and 15 subgroups (n=12). The pH solutions forming the main groups were: simulating severe (pH 1.5) and moderate (pH 3.0) forms of gastric regurgitation and artificial saliva (pH 7.0) as the control group. Each pH group was divided into subgroups according to the brackets' elapsed times in the solutions (30 minutes, 12 hours, 24 hours, a week, a month). All of the specimens were kept in an incubator, at specified times. The average surface roughness of bracket slots was examined with optical profilometer. Inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the metal ions (Fe, Ni, Cr) released to the solutions from brackets. Before immersions, initial surface roughness (ISR) of each braket slot was measured. After immersions, final surface roughness (FSR) and the difference of FSR-ISR of each bracket slot were examined, and the results were compared statistically in all main pH groups and time subgroups. Also, ion release at 30 minutes, 24 hours and 1 month were examined and the results were compared statistically in all main pH groups and specified time subgroups. When the pH groups were evaluated in terms of FSR at different time intervals, the statistically significant difference in all pH groups firstly occured after 24 hours (p=0.0001). The FSR-ISR was statistically significant in all main pH groups and time subgroups (p=0.0001). As the acidity of the environment and the immersion time increased, increased corrosion of brackets was observed. The highest FSR, FSR-ISR and ion release were found in pH 1.5 group at 1 month. pH 7.0 group's ion release at all time subgroups (except 30 minutes for Ni) was found to be lower than gastric solutions. Ion release from the brackets occurred in all pH groups at all time intervals, but the amounts of ion release were below the toxic limits.