Lecture 5- Dentine and Pulp (Part 2) PDF

Dentine and the pulp (Part 2) Pulp structure, histology, function By the end of this lecture, you should be able to: Identify the major cellular and structural features of the dental pulp Outline the three major hypotheses used to explain the mechanisms of dentine sensitivity Describe the immune res...

Dentine and the pulp (Part 2) Pulp structure, histology, function By the end of this lecture, you should be able to: Identify the major cellular and structural features of the dental pulp Outline the three major hypotheses used to explain the mechanisms of dentine sensitivity Describe the immune responses of the dentine-pulp complex Enamel Dental pulp Dentine and the pulp are part of the same developmental and functional unit Dentine is deposited along the walls of the pulp by the odontoblasts, which reside in the pulp. The structure and histology of the pulp are linked with development and function of dentine à need to understand them both! Pulp Dentine Dental pulp- the basics The pulp performs three key functions: Production, maintenance, and repair of dentine (odontoblasts) Sensitivity (nociception and proprioception) Immune response (defense against pathogens) Histology of the pulp reflects these functions… Ten Cate’s Oral Histology (8th Edition); Fig. 8-6 Dental pulp- the basics Histology of the pulp (4 regions from periphery to center of pulp): Odontoblastic zone Cell-free zone of Weil Cell-rich zone Pulp core Major cell types and structures found in the pulp: Odontoblasts Fibroblasts Undifferentiated ectomesenchymal cells Dental pulp stem cells Inflammatory cells Nerves Lymph vessels Blood vessels Dental pulp- the basics Odontoblasts Histology of the pulp (4 regions from periphery to center of pulp): Dentine 1. The odontoblastic zone Forms the outer periphery of the pulp Odontoblasts line the walls of the pulp and produce the predentine, which mineralizes into mature dentine Odontoblasts are typically long, columnar cells, but may be flatter in more apical (rootward) regions of the pulp These cells provide the link between the pulp and the dentine via the odontoblast processes within the dentine tubules Odontoblasts Prede ntine Dental pulp- the basics Histology of the pulp (4 regions from periphery to center of pulp): 2. Cell-free zone of Weil Rich in blood capillaries and nerves (will become important when discussing dentine’s sensitivity) Cell-free zone Dental pulp- the basics Histology of the pulp (4 regions from periphery to center of pulp): 3. Cell-rich zone A region rich in fibroblasts (the main cell type found in this zone) These cells form and maintain the pulp matrix (collagen types I and III, ground substance) Undifferentiated ectomesenchymal cells are also found here These cells may give rise to new odontoblasts or fibroblasts depending on the stimulus Cell-rich zone Dental pulp- the basics Histology of the pulp (4 regions from periphery to center of pulp): 3. Cell-rich zone A region rich in fibroblasts (the main cell type found in this zone) These cells form and maintain the pulp matrix (collagen types I and III, ground substance) Undifferentiated ectomesenchymal cells are also found here These cells may give rise to new odontoblasts or fibroblasts depending on the stimulus Ten Cate’s Oral Histology (8th Edition); Fig. 8-39 Dental pulp- the basics Histology of the pulp (4 regions from periphery to center of pulp): 4. Pulp core Contains the principal vascular network (blood vessels), which enters the pulp via the apical foramen Lymph vessel network Pulp core Dental pulp- the basics Histology of the pulp (4 regions from periphery to center of pulp): 4. Pulp core Contains the principal vascular network (blood vessels), which enters the pulp via the apical foramen Lymph vessel network Ten Cate’s Oral Histology (8th Edition); Figs. 8-55, 8-59 Dental pulp- the basics Nerves and vasculature enter the pulp through a hole at the root apex: the apical foramen. Ten Cate’s Oral Histology (8th Edition); Fig. 1-1 Innervation of the pulp and dentine: the plexus of Raschkow Dentine The dental pulp is richly innervated Nerves enter the pulp through the apical foramen These are sensory afferent nerves of the trigeminal nerve (fifth cranial nerve) ts s la ob t on d O Pulp Silver stain of a human tooth- shows the nerves stained black Innervation of the pulp and dentine: the plexus of Raschkow Dentine Nerves branch as they extend coronally to form a large network in the cell-free zone. Here the nerves form the plexus of Raschkow This nerve plexus is primarily situated in the cell-free zone of the pulp… …however, some nerve endings extend into the odontoblastic layer and even into the dentine tubules Odon tobla st s Plex us o f Ra schk ow Pr ed en tin e Closeup of the plexus of Raschkow and small number of nerve endings entering dentine tubules (arrowhead) The source of dentine sensitivity: 3 hypotheses How can dentine be such a sensitive tissue to temperature, changes in osmolarity, and physical stimuli? No concrete answer, but there are three hypotheses, based on the histology of the dentine and pulp, as well as several experiments Ten Cate’s Oral Histology (8th Edition); Fig. 8-66 The source of dentine sensitivity: 3 hypotheses Hypothesis 1 Sensitivity is due to stimulation of nerve endings that are found within the dentine tubules Support: Some nerve endings do extend into the dentine tubules Against: Relatively few tubules contain nerve endings and sensitivity does not depend on the stimulation of these particular nerves to cause discomfort Ten Cate’s Oral Histology (8th Edition); Figs. 8-63. 8-66 The source of dentine sensitivity: 3 hypotheses Hypothesis 2 The odontoblasts are the receptors of stimuli and are coupled with nerves in the pulp Support: Odontoblast processes extend into the dentine à to act as receptors? Against: Not clear if odontoblasts can send signals to nerves in the pulp, and no clear indication of a synaptic connection between nerves and odontoblasts Ten Cate’s Oral Histology (8th Edition); Figs. 8-63. 8-66 The source of dentine sensitivity: 3 hypotheses Hypothesis 3 Hydrodynamic theory: fluid movement through the tubules is sensed by the free nerve endings in the plexus of Raschkow. Support: dentine tubules are fluidfilled, fluid exits through exposed dentine tubules naturally (when dried, more fluid is lost, leading to more pain) Explains why pain can be induced from heat, mechanical probing, hypertonic solutions, dehydration (all of which would move fluid within the tubules) Ten Cate’s Oral Histology (8th Edition); Figs. 8-63. 8-66 Immune responses of the pulp Innervation and the continued presence of odontoblasts and other cells make the pulp-dentine complex very responsive to environmental stimuli Dental caries progression is slowed by closure of dentine tubules Attrition can stimulate sclerotic dentine production Larger physical or bacterial stimuli can trigger tertiary dentine production Dead dentine tracts- tubules that may contain bacteria Infilled dentine tubules give this tooth a glassy appearance Ten Cate’s Oral Histology (8th Edition); Figs. 8-30 Abnormalities of the pulp Pulp stones: mineralizations within the dental pulp, possible causes include disease, developmental abnormalities Pulp stone Relatively common and can form from a variety of host tissues (pulp collagen bundles, epithelial cells, blood thrombi) By the end of this lecture, you should be able to: Identify the major cellular and structural features of the dental pulp Outline the three major hypotheses used to explain the mechanisms of dentine sensitivity Describe the immune responses of the dentine-pulp complex