Background: The aim of this study was to examine the effect of self-etch primer (SEP) application on the bond failure rate of a mandibular bonded lingual retainer over 24 months.

Materials and Methods: After the removal of the orthodontic appliances, the lingual retainers, which were made of six-stranded stainless steel wire 0.0215 inches in diameter, wiil bent and bond onto the lingual surface of all mandibular anterior teeth. The study will performed using a split-mouth design. In the study group, the SEP will be administired to the teeth's lingual surfaces. In the control group, they will etch using 37% phosphoric etchant liquid gel. After etching, the primer wiil be applied. The adhesive resin was applied and the lingual retainer was fitted. The patients will be re-valuated over 24 months. The first bond failures and the amount of adhesive remaining on the tooth will be recorded as the adhesive remnant index (ARI) scores.

The chi-square test will be used to compare the bond failure rates and ARI scores between the groups. The survival rates of the retainers will be estimated using the Kaplan-Meier test. The significance level will P < 0.05.

Inclusion Criteria:

1. Individuals who will continue to the retention phase after fixed orthodontic treatment,
2. Presence of all mandibular incisor and canine teeth,
3. Good oral hygiene,
4. No caries,
5. No fractures,
6. Healthy periodontal condition,
7. No restorations,
8. No previous bonded retainer,
9. No traumatic parafunctional habits such as bruxism.

Exclusion Criteria:

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