A recent review on clinical studies published on the performance of posterior composite restorations that were recalled at least up to 24-months reported that the overall failure rates for studies conducted between 2006-2016 was 13.13% and the two main reasons for failure in these two decades remained the same, i.e. secondary caries (25.68% - 29.47%) and composite fracture (28.84% - 39.07%). In in vitro studies, secondary caries has been attributed to interfacial gap or marginal defect both of which are consequences of polymerization contraction stresses. However, to date no clinical study has been able to directly establish a link between these stresses (and its consequences) to secondary caries. World Dental Federation (FDI) and United States Public Health Service (USPHS) clinical assessment criteria are the two main systems used to evaluate dental restorations in clinical trials. Both systems are designed to evaluate different properties of a restoration and properties pertaining to marginal integrity has been reported to be the most frequent properties investigated of a resin composite restoration. The grading descriptions for these properties are subjective and the discrimination between grading and between properties (especially between marginal stains and secondary caries) are problematic. Reasons to the lack of such a link is the discriminative deficiency of the clinical visual evaluation systems, the FDI and USPHS assessment criteria, and the ethical dilemma of restoration removal to assess for presence or absence of secondary caries. It has been long acknowledged that an objective clinical measuring tool and new clinical study designs for secondary caries is needed to further the understanding of secondary caries initiation and progression and how these relates to the marginal integrity of dental restorations. This brings forth the need of a sensitive yet clinically applicable assessment method for interfacial debonding and demineralization. Optical coherence tomography (OCT) is an optical, nondestructive and clinically- applicable technique that uses near infra red-light waves to provide cross-sectional images of structures. It is regarded as a standard-of-care equipment in ophthalmology and its clinical application has recently expanded to cardiology and dermatology. In dentistry, it has been used intra-orally in clinical trials to detect and quantify enamel demineralization and to detect mucosal and submucosal lesions. Optical coherence tomography and has been used to assess the performance of dental adhesives in a 12-month in vivo trial on non-carious cervical lesion. The authors reported that OCT outcome measures detected significant differences between groups while visual assessments did not. Hence supplementing the two visual assessment techniques with OCT outcome measures is expected to increase the sensitivity of short term interfacial debonding and demineralization changes. The aim of the study is to compare the short-term marginal integrity of two preparation techniques for Class I composite restoration using two visual assessment techniques, the FDI World Dental Federation and US Public Health Service assessment criteria. In addition, Optical Coherence Tomography (OCT) will be used to assess the marginal integrity of the restoration.