#23 What I Learned Today

Introduction to Operative Dentistry

No lecture; we had an exam and a rubber dam isolation practical. However, I don't want to leave you empty handed, so here is some bonus content on the physiological characteristics of enamel!

General and Oral Histology

Enamel is formed from ameloblasts, which differentiate from inner enamel epithelium of the enamel organ. This differentiation occurs to the cells on the other side of the basement membrane, adjacent to the dental papilla cells. The ameloblasts begin to deposit enamel shortly after odontoblasts begin depositing dentin (layering process in both is referred to as apposition).

Enamel is one of the hardest substances in the human body, and consists of rods made of hydroxyyapatite (HAP) crystals from calcium and phosphates. Also find some proteins called alemogenin, ameloblastin, and enamelin

You commonly see six different life stages in ameloblasts:

1. morphogenic: begin to see IEE cells differentiate into pre-ameloblasts
2. organizing: odontoblasts sectrete growth factors which leads to further differentiation into columnar secretory cells, or ameloblasts.
3. formative: basement membrane between ameloblasts and odontoblasts disappears, and enamel crystals are secreted along mantle dentin to form the DEJ
4. secretory: ameloblasts secrete enamel from Tomes' processes and move away from DEJ
5. maturative: ameloblasts undergo structural changes. These include the loss of the Tomes' processes, and the ameloblasts are no longer able to secrete enamel.
6. protective/desmolytic: ameloblasts collapse to form the reduced enamel epithelium
   

At the maturative stage, the cells function in increasing the mineralization of the enamel rods up to a content level of ~96%. This development process is important for both dentist and patient to know because it is the reason why enamel is nonvital and cannot be self-repaired (not including arrested enamel lesions) after removal.

Enamel rods are arranged in rows that extend from the DEJ to the outer surfaces. They form 'S' like paths, with the most oblique angles (as compared to the DEJ) occuring towards the incisal edge. Clinically, this is important, as isolated enamel rods, or parts of enamel rods are brittle and break easily. The strength of the enamel is dependent on the dentin support underneath.