OB020- Dentine and pulp

Pulp is a source of...

stem cells for tissue

Describe the structure of dentine

Dentine structure • Lining around tubules made of peritubular/intratubular dentine- more mineralised than intertubular dentine Intertubular dentine • Fills the space between tubules • Greater collagen fibre composition than peritubular dentine • Type I collagen fibres arranged perpendicular to the tubule and more loosely distributed • Relatively less mineralised than peritubular dentine Peritubular dentine • Lines the internal surface of the dentinal tubule • Lacks a collagenous fibrous matrix • 15% more mineralised than intertubular dentine so appears more radiopaque • Present in unerupted teeth • Forms at about the same time as intertubular dentine • Occludes the dentinal tubules with age • translucent dentine formation (refractive index become same as intertubular dentine) Can help in forensic dentistry for age estimation

Describe the histology go the pulp

1) Fibrous matrix: o Type I and II collagen fibres, unbundled and randomly dispersed, higher in density around blood vessels and nerves. o Type I collagen is thought to be produced by odontoblasts o Type II (probably produced by the pulp fibroblasts) o Older pulp contains more collagen of both the bundled and diffuse types. 2) Ground substance o proteoglycans, glycoproteins and large amounts of water 3) Odontoblasts comprise the outermost region/layer of the pulp, immediately adjacent to the dentin. o responsible for the secretion of dentine and the formation of dentinal tubules. 4) Fibroblasts of the pulp have demonstrated the ability to degrade collagen as well as form it. 5) Perivascular cells (undifferentiated mesenchymal cells) are present in the pulp and can give rise to odontoblasts, fibroblasts or macrophages. 6) Lymphocytes, plasma cells and eosinophils are other cell types also common in dental pulp

What inflammatory cells present in pulp?

1) T lymphocytes • Normally few in number but increase with inflammation! 2) Macrophages • Found predominantly around central blood vessels and adjacent to odontoblast layer 3) Dendritic antigen presenting cells • Similar distribution to macrophages, but also may be found between odontoblasts and dentine

Describe dentine tubules

• Branch profusely in the periphery near the DEJ • Tubules have lateral processes- connect between tubules allowing the tubules to communicate with each other • However, creates a freely permeable environment for bacteria to get into pulp

Describe circumpulpal dentine

• Bulk of dentine • Uniform in structure, except: Outer surface interglobular Inner surface mineralisation front • Tubules Modified with age by 2o dentine deposition in pulp Modified by disease by tertiary dentine / sclerotic dentine deposition

Describe the chemical properties of dentine

• By weight, it is: 70% inorganic, 20% organic and 10% water • By volume, it is: 50% inorganic, 30% organic and 20% water • Hydroxyapatite crystals- smaller than those in enamel • Organic matrix- similar composition to bone: Collagen fibrils Type 1 (90%); Traces of Type III & V Proteoglycans - Decorin, dermatan sulphate; Glycoproteins - osteonectin, osteopontin; dentine sialoproteins (DSP) Phosphoproteins - Dentine phosphoproteins (DPP) Growth Factors - TGFb; BMPs Lipids

Describe the globular calcification of dentine

• Calcification of dentine begins in small spherical areas. These become larger and fuse with one another to form a calcification front.

Describe the age related changes in pulp

• Cell death results in a decreased number of cells. • Surviving fibroblasts respond by producing more fibrous matrix (increased type I over type II collagen) but less ground substance that contains less water. • So with age the pulp becomes: less cellular more fibrous overall reduction in volume due to the continued deposition of dentin (secondary/reactive)

What are the types of pulp?

• Coronal pulp occupies the crown of the tooth and has six surfaces; occlusal, mesial, distal, buccal, lingual and the floor. • Radicular pulp extends from the cervix down to the apex of the tooth. Molars and premolars exhibit multiple radicular pulps. This pulp is tapered and conical.

What is dentine?

• Dentine is the bulk of the tooth underneath enamel • Covered by enamel at crown and cementum at root • Formed by odontoblasts • Consists of small parallel tubules in a mineralised matrix • Tubules contain: odontoblastic processes, dentinal fluid and nerve endings- so highly sensitised • Formations of it begins during bell stage and continues throughout life

What are primary and secondary curves?

• Dentine tubules- these are odontoblast processes • Dentinal tubules in the crown of the tooth follow a S-shaped course • They get squeezed into smaller and smaller space within pulp cavity- called primary curve • Pattern of pathway of tubules means that conditions such as caries can spread further than you think Secondary curves • Subtle changes in primary curve= secondary curve • Can give an appearance of a line crossing the dentine- called contour lines of Owen • Usually present at the junction of 1o and 2o dentine

What is interlobular dentine?

• Found just below Mantle zone in crown or Granular Layer of Tomes in root. • Area of less calcified areas of dentine appear as irregularly shaped crescents Result of uneven fusion of the mineralisation front; thus, no calcification • Tubules pass through but peritubular dentin is absent in these areas

What is predentine?

• Initially laid down dentine matrix before mineralization • The innermost layer of the dentine • The mineralising front-globular or linear • Width 10-40 μm • Thicker in young teeth

What are the clinical implications of the pulp-dentine complex?

• Living pulp is required to maintain dentine integrity and tooth sensitivity • Inflammation of the pulp due to caries causes high fluid content and swelling: compression of nerve fibres on the walls of the pulp cavity and pain • Mechanical injury of dentine (including drilling or trauma) may induce pain transmitted by the nerve fibres, and tertiary dentin formation by the odontoblasts • Severe damage or infection of pulp may require its removal and filling of the pulp chamber and root canal (root canal treatment: Endodontics)

Describe the regional variations in dentine

• Mantle dentine= first part of dentine laid down by odontoblasts. It is right next to enamel • Bulk of dentine= circumpulpal dentine • Root- hyaline and granular layer- dentine in roots • Predentine= initial deposition before dentine becomes mineralised

Describe the contents of dentine tubules

• Odontoblast process • Afferent nerve terminals • Antigen presenting cells • Dentinal fluid

Describe the mineralisation of dentine

• Organic matrix laid down by odontoblasts • Calcium transported through odontoblast to area of calcification • Calcium becomes crystalline in dentine after deposition onto collagen fibrils DPPs (unique to Dentine) thought to play a role in this • As matrix deposition and mineralisation continue, a zone of calcification will nearly always be visible • Linear and globular mineralisation occurs Linear - deposition by apposition onto existing calcified areas Globular - deposition occurs in spheres (calcospherites)

Describe the physical properties of dentine

• Pale yellow in colour • Harder than bone and cementum but softer than enamel • Permeable- due to dentine tubules

Describe the hyaline layer and granular layer of Tomes

• Periphery of the dentine in the root • Hypo-mineralised in comparison to circumpulpal dentine • Dentinal tubules branch more profusely and loop back creating air spaces in ground sections or incomplete fusion of calcospherites • Internal reflection of transmitted light

What incremental lines associated with matrix deposition and mineralisation

von Ebners lines • Daily alterations in the formation of dentine, seen as banding along the dentinal tubules • Perpendicular to the dentinal tubules. • 4 μm in width in cuspal region, 2 μm in root dentine

What clinical implications of dentine are there?

• Permeability of dentine: When dentine is exposed (dental trauma, caries) substances from external environment can reach dental pulp through dentinal tubules - pulpitis • Response to external stimuli: Stimuli not strong enough to destroy the pulp can stimulate production of tertiary dentine by odontoblasts as a protective barrier • Sensitivity of dentine: Exposed dentine is often painful (sensitive): when dentinal fluid moves it compresses nerve endings on dentinal tubules transmitting sense of pain Teeth are one of the few body structures that perceive only the modality of pain Three theories to explain this phenomenon 1. Direct innervation theory 2. Transduction theory 3. Hydrodynamic theory

What are odontoblasts?

• Polarised columnar cells with single process extending into dentine tubules • Form continuous lining at junction between pulp and dentine • Responsible for the formation of dentine • In adult teeth secrete secondary and tertiary/ reactionary dentine • Contribute to protection of the pulp

Describe dentinogenesis

• Primary All dentine until tooth eruption Can become translucent with age (increased deposition of peritubular dentine occludes tubule) Physiological changes particularly in root and used in forensic dentistry to age patient • Secondary Begins after eruption - often as tooth comes into occlusion Structurally similar to 1o dentine but with fewer tubules In time will reduce pulp chamber and root canal size • Tertiary produced in response to external stimuli (attrition, caries, cavity preparation, microleakage around restorations, trauma). It has a protective role. Reactionary dentine Reparative dentine • Sclerotic Formed in response to external challenge Appears translucent - due to increased mineralisation Tubules filled in to block ingress of bacteria in caries • Dead Tracts Empty tubules following death of odontoblast or retraction of process

Describe the functions of the pulp

• Primary function= providing vitality to the tooth Loss of the pulp following a root canal) does not mean the tooth will be lost. The tooth then functions without pain but, it has lost the protective mechanism that pulp provides. • Other functions: • Inductive: very early in development the future pulp interacts with surrounding tissues and initiates tooth formation. • Formative: the odontoblasts of the outer layer of the pulp organ form the dentin that surrounds and protects. • Protective: pulp responds to stimuli like heat, cold, pressure, operative cutting procedures of the dentin, caries, etc.. A direct response to cutting procedures, caries, extreme pressure, etc., involves the formation of reactive dentine by the odontoblasts. Formation of sclerotic dentin, in the process of obliterating the dentinal tubules, is also protective to the pulp, helping to maintain the vitality of the tooth

What is dental pulp?

• Pulp mirrors shape of tooth • Is a specialised connective tissue of tooth • Occupies pulp chamber and root canal • Active throughout life and maintains health of dentine through odontoblast layer • Functionally and structurally associated to dentine • Provides sensation (nerve endings) and blood supply (nutrients and immune cells)

Describe the neural supply to the pulp

• Several large nerves enter the apical foramen of each molar and premolar with single ones entering the anterior teeth • These nerves have two primary modalities: 1) Autonomic Nerve Fibres Only sympathetic autonomics fibres are found in the pulp. fibres extend from the neurons whose cell bodies are found in the superior cervical ganglion at the base of the skull They are unmyelinated fibres Travel with the blood vessels. They innervate the smooth muscle cells of the arterioles and therefore function in regulation of blood flow in the capillary 2) Afferent (Sensory) Fibres maxillary and mandibular branches of the fifth cranial nerve terminate in the central pulp send out small individual fibres that form the subodontoblastic plexus just under the odontoblast layer free nerve endings near the odontoblasts good at transmitting pain stimuli from heat, cold or pressure

Describe the composition of pulp

• Unmineralised oral tissue composed of soft connective tissue, vascular, lymphatic and nervous elements • Majority of pulp (75-80%) is water. • No inorganic component in normal dental pulp- pulp stones, found pathologically within the pulp cavity of aging teeth • Pulp chambers of molar teeth are approximately 4x larger than those of incisors. • Developmentally and functionally, pulp and dentine are closely related. Both are products of the neural crest-derived connective tissue that formed the dental papilla

What is tertiary dentine?

• laid down in response to irritation or damage to the overlying dentine and/or enamel. • Also called reparative, reactionary, response, and osteodentine dentine • has irregularly arranged and few dentinal tubules. • With aging or severe damage, tertiary dentine can totally obliterate the pulp cavity

Describe the vascular supply to the pulp

• small arterioles enter the pulp via the apical foramen • ascend through the radicular pulp of the root canal • branch out peripherally to form a dense capillary network immediately under - and sometimes extending up into - the odontoblast layer • Small venules drain the capillary bed and eventually leave as veins via the apical foramen. • pulpal vessel walls are very thin as the pulp is protected by a hard-unyielding sheath of dentin. • The capillaries exhibit numerous pores, reflecting the metabolic activity of the odontoblast layer. • Blood flow is more rapid in the pulp than in most areas of the body and the blood pressure is quite high. • Arterio-venous anastomoses are frequent in the pulp