Introduction. At the microscopic level, enamel rods are the main structural components of dental enamel. The orientation of enamel rods is the main factor that predetermines the differences of the mechanical properties of dental enamel in different parts of the tooth crown. The predisposition of certain surfaces of the tooth crown to the development of caries is also associated with enamel rods orientation. However the full characteristic of enamel rods arrangement in different parts of the dental crown has still not been definitely established.
Aim. To study the arrangement of enamel rods on the vestibular, lingual and aproximal surfaces of the molar crown in the deep, middle and surficial layers of enamel.
Materials and methods. In thin sections of twenty permanent human molars, which were made in two different planes, the average values of tilt angles of enamel rods to enamel-dentin junction were determined in the deep, middle and surficial layers of enamel at the vestibular, lingual and aproximal surfaces of crowns using polarizing microscopy. The one-way ANOVA, followed by the Newman–Keuls test was used to compare the obtained data.
Results. In our research was revealed that the primary portions of enamel rods, which are located in the deep layers of tooth enamel are always oriented to the occlusual surfaces. The direction of the rods to tooth root was not revealed in any of the investigated portions of molar’s crown.
We distinguished two main variants of enamel rods orientation within tooth enamel: straight-lined and arc-shaped (the direction of the top of the arc could be different). We determined the orientation of rods as straight-lined if there were no statistical differences between the values of tilt angles of enamel rods to enamel-dentin junction in the middle and surfacial layers of enamel. And the orientation was determined as arc-shaped if such differences were found.
By the straight-lined type of orientation are characterized all parts of lingual surface of the tooth crown. The same type of enamel rods orientation occurs at the middle third of both vestibular and aproximal surfaces. Arc-shaped variant of orientation with the top of the arc directed to the occlusial surface of the crown is typical for the upper third of vestibular and aproximal surfaces. And, finally, the arc-shaped variant of orientation with the top of the arc directed to the tooth root occurs at lower third of vestibular and aproximal surfaces of molar’s crown.