The aim of this study is to assess if there are significant differences in the failure rate of stainless steel and ceramic brackets. For this study, patients will be enrolled and divided into two groups, according to the type of brackets (stainless steel or ceramic) used for orthodontic treatment. Failure rates will be recorded every month for 12 months and survival analysis will be performed, together with skeletal and space analysis.

This clinical trial aims to investigate if there are differences in the failure rates of stainless steel and ceramic orthodontic brackets. Patients willing to start orthodontic fixed therapy and recruited for the study will be asked to sign the informed consent. Parents will sign the consent for underage patients. After that, patients will be divided into two groups:

• Group MET: stainless steel brackets will be bonded on the vestibular surfaces of teeth.
• Group CER: ceramic brackets will be bonded on the vestibular surfaces of teeth. The following sequence of archwires will be adopted for the first six months: 0.012-in Niti, 0.014-in Niti, 0.016-in NiTi, 0.018 SS Australian, 0.020 SS Australian, 0.017X0.025-in NiTi, 0.019X0.025-in SS. The failure rates of the brackets will be recorded each month for 12 months. Each failed bracket will be recorded once. For each patient, pre-treatment lateral cephalometric radiograph and study models will be used to measure ANB angle, Wits, Skeletal Class, dento-alveolar discrepancy and Little Index at the beginning of the treatment. Bond failures will be recorded together with the archwire engaged at the moment of the failure.

Sample size Sample size was calculated with the following assumptions: ability to detect a clinically relevant difference of 4.935% in the failure rates (primary outcome) of the two groups with an alfa = 0.05 and power = 80%. The assumptions were based on findings of a previous study with an expected value of 12.08% for the first group at the end of 12 months of therapy. Therefore, 800 brackets (40 patients) per group were required for the study.

Statistical analysis Statistical analysis will be conducted with R software (R version 3.1.3, R Development Core Team, R Foundation for Statistical Computing, Wien, Austria). Fisher exact test will be performed to evaluate the differences between the failure rates of the two groups, between anterior and posterior sites and between upper and lower arches. Kaplan-Meier survival analysis of the bond failures will be performed among the 12 months of the study. Linear regressions will be calculated to assess the effects on bond failure of the skeletal and dental variables collected before the bonding procedure. Significance for all statistical tests will be predetermined at P<0.05.

Inclusion Criteria:

• patients willing to begin fixed multibracket therapy with metallic or ceramic brackets;
• full permanent dentition;
• enamel integrity, absence of traumatic or carious lesions, no pretreatment procedure performed with chemical agents;
• no previous orthodontic treatment with fixed vestibular appliances.

Exclusion Criteria:

• patients suffering from systemic diseases;
• patients taking medications that could alter periodontal conditions (NSAIDS, steroids, etc.);
• patients with low compliance;
• patients unable to give informed consent;
• presence of congenital enamel defects;
• extractions for orthodontic reasons;
• oral/orthognathic surgery.

Data will be available upon motivated request to Principal Investigator