Sealant materials are typically employed in dentistry in order to prevent the development of cavities on the teeth. They prevent bacterial adhesion to enamel, thus arresting the development of demineralization and of caries. In this study, the critical zone of the interface between different sealant materials and the results of the dental work for the teeth processed were investigated ex vivo using swept source (SS) optical coherence tomography (OCT). Optical inspection and X-ray investigation revealed no defects, while SS-OCT proved capable to asses exactly the position, the nature, and the dimensions of each type of these defects. Specifically, different failures were targeted into the structure of pit and fissure sealants, including bubbles, internal cracks, structural defects of sealant material, and structural defects of enamel, with uncovered sealant material and enamel/sealant interface (marginal integrity and marginal adaptation of dental sealant). The investigation of the possible types of defects that may appear into this dental interface was thus accomplished - for the dental practitioner.