Lecture 6- Dentine and Pulp (Part 3) PDF

Dentine and the pulp (Part 3) Dentinogenesis By the end of this lecture, you should be able to: Identify the origins of the dentine and pulp from tooth bud to mature tooth Describe the major steps involved in odontoblast maturation Describe the major steps involved in dentine matrix secretion Descri...

Dentine and the pulp (Part 3) Dentinogenesis By the end of this lecture, you should be able to: Identify the origins of the dentine and pulp from tooth bud to mature tooth Describe the major steps involved in odontoblast maturation Describe the major steps involved in dentine matrix secretion Describe the major steps involved in dentine mineralisation Distinguish between different incremental and non-incremental lines found in dentine The development of the dental tissues Dentine and pulp development involves the following cell layers and types. By the end of this lecture, you should know where these structures are located at different stages of tooth development, their roles in tooth development, their appearance, etc. Ten Cate’s Oral Histology (8th Edition); Fig. 5-35 Tooth development- a quick reminder Bud stage (~8th week of embryonic development) Cap stage (~9-10th week of embryonic development) Bell stage (~11th week of embryonic development) Dentine and pulp development Bud stage (~8th week of embryonic development) Enamel organ Ectomesenchyme condensation Dentine and pulp development Enamel organ Cap stage (~8th week of embryonic development) Dental papilla (ectomesenchyme) Dentinogenesis 1. Odontoblast differentiation Occurs in the dental papilla, along the boundary between the epithelial cells of the enamel organ and the ectomesenchymal cells of the dental papilla (some of which will become the odontoblasts) Ten Cate’s Oral Histology (8th Edition); Fig. 8-11 Dentinogenesis 1. Odontoblast differentiation Undifferentiated cells of the dental papilla (ectomesenchyme) are attracted to the boundary by signalling molecules and growth factors originating from the epithelial cells of the developing enamel organ Ten Cate’s Oral Histology (8th Edition); Fig. 8-11 Dentinogenesis 1. Odontoblast differentiation The epithelial cells orient themselves relative to the boundary with the enamel organ Ectomesenchymal cells rapidly enlarge and divide Ten Cate’s Oral Histology (8th Edition); Fig. 8-11 Dentinogenesis 1. Odontoblast differentiation The ectomesenchymal cells adjacent to the epithelial boundary are influenced by the growth factors and signalling molecules of the epithelial cells. These ectomesenchymal cells elongate and develop organelles for protein synthesis. Ten Cate’s Oral Histology (8th Edition); Fig. 8-11 Dentinogenesis 1. Odontoblast differentiation The ectomesenchymal cells closest to the boundary with the cells of the enamel organ elongate, polarize, and differentiate into odontoblasts, which will secrete the dentine matrix. Ten Cate’s Oral Histology (8th Edition); Fig. 8-11 Dentinogenesis 2. Dentine matrix production ***Begins BEFORE enamel matrix production Odontoblasts secrete the mantle predentine matrix (type III collagen- von Korff’s fibers) Odontoblasts Predentine Ten Cate’s Oral Histology (8th Edition); Fig. 8-10 Dentinogenesis 2. Dentine matrix production As odontoblasts increase in size during dentinogenesis, they begin secreting type I collagen fibrils of the circumpulpal predentine These fibrils are oriented parallel to the secretory surface (unlike the vK fibers) Odontoblasts Predentine Ten Cate’s Oral Histology (8th Edition); Fig. 8-10 Dentinogenesis 2. Dentine matrix production Odontoblasts do not become entombed in the collagen matrix they produce. They leave behind a cellular extension (the odontoblast process) in the matrix, leading to the formation of a dentine tubule. Odontoblast process Odontoblasts Ten Cate’s Oral Histology (8th Edition); Fig. 8-15 Dentinogenesis Predentine 2. Dentine matrix production The unmineralized, collagen-rich predentine matrix always separates the odontoblast layer from the mineralised dentine. The mineralization front lags behind à so how does it mineralise? Odontoblasts Dentinogenesis 3. Dentine mineralisation- mantle dentine Odontoblasts secrete matrix vesicles containing phosphate-sequestering enzymes and proteins to promote hydroxyapatite crystal growth These act as “seeds” for matrix mineralization. Ten Cate’s Oral Histology (8th Edition); Fig. 8-17 Dentinogenesis sp o c l ca es t i r he 3. Dentine mineralisation- mantle dentine Odontoblasts secrete matrix vesicles containing phosphate-sequestering enzymes and proteins to promote hydroxyapatite crystal growth These act as “seeds” for matrix mineralization. Ten Cate’s Oral Histology (8th Edition); Figs. 8-20, 8-35, 8-54 Dentinogenesis Globular (calcospheric) Fast mineralisation 3. Dentine mineralisation- circumpulpal dentine Linear Odontoblasts can continue to produce matrix vesicles that locally mineralize dentine matrix (calcospheric mineralization) But they also appear to pump mineral ions into the matrix directly (linear mineralization) Slow mineralisation Changes in dentine deposition rates Incremental growth lines Dentine is deposited for many years following tooth eruption (not the case for enamel). Fluctuations in odontoblast activity over this time produces incremental growth lines that are observable in the dentine. What do these lines signify? Changes in dentine deposition rates Incremental growth lines Dentine is deposited for many years following tooth eruption (not the case for enamel). Fluctuations in odontoblast activity over this time produces incremental growth lines that are observable in the dentine. What do these lines signify? Changes in dentine deposition rates Incremental growth lines Dentine is deposited for many years following tooth eruption (not the case for enamel). Fluctuations in odontoblast activity over this time produces incremental growth lines that are observable in the dentine. What do these lines signify? Changes in dentine deposition rates Incremental growth lines Tetracycline labeling shows dentine preserves a daily record of growth Lines of von Ebner: daily variations in dentine production Daily changes in metabolism? Sleep/awake cycles? Incremental line widths in humans ~4-5 µm suggest that dentine matrix is deposited at this rate à this is variable depending on age and region of the tooth! Represent structural variations in the collagenous matrix, not the hydroxyapatite crystals. Emken et al. (2021) Journal of Anatomy 239: 1207-1220 Changes in dentine deposition rates Incremental growth lines Andresen lines: multi-day incremental lines spaced 6-10 days apart Weekly changes in metabolism? Some other biorhythm? Tetracycline labeling experiments used to show Andresen lines are long-period (multi-day) lines. Represent structural variations in the collagenous matrix, not the hydroxyapatite crystals. Emken et al. (2021) Journal of Anatomy 239: 1207-1220 Changes in dentine deposition rates Incremental growth lines Andresen lines: multi-day incremental lines spaced 6-10 days apart Weekly changes in metabolism? Some other biorhythm? Tetracycline labeling experiments used to show Andresen lines are long-period (multi-day) lines. Represent structural variations in the collagenous matrix, not the hydroxyapatite crystals. Dean (2000)- Chapter 9 in “Development, Function and Evolution of Teeth” (Dr. LeBlanc’s favourite tooth book) Dentine in ground section Changes in dentine deposition rates Incremental growth lines Lines of von Ebner and Andresen lines in ground and paraffin sections Wouldn’t be preserved if they were variations only in the crystal orientations of the dentine à paraffin sections don’t contain hydroxyapatite of the dentine! Dentine in paraffin section Changes in dentine deposition rates Non-incremental growth lines Countour lines of Owen: supra-daily, non-rhythmic variations in dentine production Physiological changes (e.g., illness) Variations in nutrition (e.g., malnutrition) Birth (neonatal line) Can be caused by coincidence of secondary curvatures of dentine tubules during dentinogenesis, and/or hypomineralisation à causes might be multiple! https://quizlet.com/306415201/nbde-clinical-considerations-toothmorphology-and-anomolies-flash-cards/ By the end of this lecture, you should be able to: Identify the origins of the dentine and pulp from tooth bud to mature tooth Describe the major steps involved in odontoblast maturation Describe the major steps involved in dentine matrix secretion Describe the major steps involved in dentine mineralisation Distinguish between different incremental and non-incremental lines found in dentine