Dental restoration interfaces can present failures, known as marginal microleakage. These failures are extremely difficult to diagnose and can develop into recurrent caries if left untreated. The most common tool used for diagnostic imaging in dentistry, X-ray, is not able to visualize micrometric structures. Evaluation of dental restoration in a non-invasive way is a very desirable tool for clinical practice. We present an in vivo study applying Optical Coherence Tomography (OCT) to detect failures at the enamel-dental restoration interface in a clinical setting.