A light microscopic and ultrastructural examination of calcified dental tissues of horses: 3. Dentine.

This research investigates the microscopic structure of dentine (the hard, dense, bony tissue forming the bulk of a tooth) in horses. Through detailed examination, the study reveals how dentinal tubules extend from the amelodentinal junction to the pulp, and how their number and diameter increase, particularly in secondary dentine.

Ultrastructural examinations of equine dentine

• The study initially focuses on documenting the ultrastructure of the dentine in horse teeth, which is a complex microanatomy consisting of dentinal tubules, primary curvatures, and varying densities of hard dental material known as dentine.
• The research finds that these dentinal tubules extend from the amelodentinal junction (the area where enamel and dentine meet) and angle towards the pulp, a soft part inside the tooth.

Distribution of Dentinal Tubules

• The number of dentinal tubules within each unit area was observed to significantly increase from the amelodentinal junction towards the pulp cavities.
• This increase was particularly notable in regular secondary dentine, a layer of dentine that contributes to the growth of teeth after they have initially formed. However, irregular secondary (tertiary) dentine, which forms in response to stimuli such as damage or disease, contained no dentinal tubules.
• These tubules house odontoblast processes, which are elongated cells responsible for the formation of dentine. These processes appear to extend as far as the amelodentinal junction.
• Nevertheless, due to the probable loss of integrity during specimen preparation, odontoblasts were seldom found in regular secondary dentine.

Peritubular Dentine

• In primary dentine, the first layer of dentine to be formed, dentinal tubules are surrounded by significant amounts of denser dentine known as peritubular dentine.
• The diameter of this peritubular dentine was found to increase from the amelodentinal junction towards the junction of primary and secondary dentine.
• The location of the dentinal tubule within the peritubular dentine varied at different dentinal sites.
• Peritubular dentine was present only in the primary dentine layer and was observed to be encircled by a thin layer of less dense dentine termed as intertubular dentine.
• When acid etched, or treated with a special substance to reveal the finer structures, this peritubular dentine gave the dentine a honeycomb appearance near the junction of primary and secondary dentine—offering a visual aid for identifying these structures in future research or clinical settings.