dental anatomy tooth microstructure and pulp morphology exam #6

what are the four tooth structure types?

1. enamel

2. dentin

3. cementum

4. pulp

what are the hard tissues of teeth?

enamel, dentin, cementum

what is the soft tissue of teeth?

pulp

what is enamel?

highly mineralized tissue covering the anatomical crown of a tooth

what is the hardest tissue in the body?

enamel

what is the composition of enamel?

inorganic salts 95-97%

organic matter 1%

water 2-4%

what makes up the inorganic matrix of enamel?

calcium, phosphate, calcium carbonate, magnesium phosphate, calcium fluoride

what makes up the majority of the inorganic matrix of enamel?

calcium and phosphate - join to form calcium hydroxyapatite

how does enamel formation begin?

with ameloblasts secreting the amelogenin protein in the embryonic tooth buds

what do amelogenins form?

nanospheres (18-20 nanometer structures)

what is the function of nanospheres?

regulate the formation and organization of tooth enamel by controlling the crystalline growth

amelogenins also self assemble to form what?

extra-cellular matrix within which the crystals of mineralization start to form

what is the structure of enamel?

the crystals are hexagonal prisms arranged at right angles to the surface of the tooth

what has the hardness of enamel been compared to?

stainless steel alloy

what is the purpose of the hardness of enamel?

helps the tooth resist wear and makes it more resistant to decay than dentin or cementum

compared to diamond and tungsten carbide, where does enamel rank on the hardness scale?

eighth

what does it mean if enamel or dentin is soft?

it is diseased

what can affect the solubility of enamel?

presence of alkalis and acids

what ions decrease solubility of enamel?

sodium, calcium, phosphates

what increases the solubility of enamel?

acids - lemon juice, vinegar, sports drinks, sodes

nature tries to saturate the saliva with what to help protect the teeth?

sodium, calcium, and phosphate ions (with less saliva, there is no saturation and less protection)

true or false: enamel cannot repair itself

true

___________ _______ of enamel can remineralize if the surface is not cavitated

incipient caries

what can be helpful if the patient has areas of enamel that are partially demineralized?

fluoride varnishes, rinses, toothpastes, and gels

what ions enhance the precipitation of calcium and phosphate ions from the saliva and make the remineralized enamel more resistant to decay?

fluoride ions (fluorapatite as opposed to hydroxyapatite)

______ _______ can be observed clinically as intact, but discolored spots

arrested lesions

what do arrested lesions look like?

usually brown or black - change in color is believed to be due to trapped organic debris and/or metallic ions within the enamel

arrested lesions are _______________ and are resistant to subsequent _________

remineralized; caries

where do arrested lesions occur mainly?

pits and grooves (may be restored for esthetic reasons)

tensile strength of enamel is _______

low - causes enamel to be brittle and require dentinal support

restorative preparations must be extended to areas of _______ support

dentinal (leaving little unsupported enamel)

what may reduced salivary flow lead to?

tooth decay problems due to lack of natural cleansing and lack of available calcium and phosphate ions for remineralization

what is the color of enamel?

translucent white, but at times appears yellowish due to reflection of the color of the underlying dentin

what characteristic of enamel is very helpful in the flow of food?

smooth enamel surface - makes enamel somewhat self-cleansing and helps prevent food from sticking to its surface

what is the ability of light to pass through an object?

translucency

the reproduction of the "enamel" can be very important when making _________ __________

esthetic restorations

dentists sometimes wait to take the _______ shade for a crown until after the preparation is finished

dentin

the enamel is thickest on the _________ and ________ surfaces of the permanent teeth

incisal; occlusal

what is dentin?

the hard tissue which forms the main body of the tooth

what does the dentin surround?

pulp cavity

dentin is covered by the ________ in the anatomical crown and by ________ in the anatomical root

enamel; cementum

true or false: dentin may not repair itself

false, it may, it is a specialized connective tissue

what are the physical properties of dentin?

significantly softer than enamel, but harder than cementum or bone

________ becomes harder with increasing age

dentin

the hardness of dentin averages about _________ that of enamel

1/5

what is the composition of dentin?

inorganic salts 65-75%

organic matter 20-30%

water 5%

what are the functions of dentin?

1. supports the enamel

2. poor thermal conductivity

3. transmits sensory information

why is dentin supporting the enamel important?

loss of underlying dentin requires special consideration in preparation design

what is the purpose of dentin having poor thermal conductivity?

reduces trauma from normal thermal stimuli; provides a fairly thick wall of insulation around the pulp

excessive _______ from dental procedures has killed many teeth

heat (make sure you have adequate water with high speed drill)

how does the dentin transmit sensory information?

the fibers within the dentinal tubules are responsible for the conduction of stimuli

ideally a material of very ______ thermal conductivity would be highly desirable because it protects the _________ cells from too much heat or cold

low; pulpal

on large or deep preparations, what should the dentist place to protect the patient from sensitivity to heat or cold?

a base/liner

what is more susceptible to the carious process and why?

dentin because it is less densely calcified

inflammation of the pulp involves swelling, which cannot occur within the rigid ________ walls; as a result, __________ _________ may occur

dentinal; pressure necrosis

what permits the placement and retention of restorations in the teeth?

plastic adaptability of dentin (restorations that are placed in enamel only may not be retained)

what measures how much materials expand and contract with changes in temperature?

coefficient of thermal expansion

what happens from a dental material that expands too much?

will cause teeth to crack

what happens from a dental material that does not expand enough?

will leave a space between the filling and tooth structure

what is the layer of hard, bonelike tissue which covers the anatomical root of a tooth?

cementum

how is the cementum joined to the bone?

by the periodontal ligament (only way it is connected)

what is the function of cementum?

provides a protective covering to the dentin of the anatomical root

what is the composition of cementum?

inorganic salts 55%

organic matter 30-35%

water 15%

what is cementum?

protective covering of the dentin on the anatomical root

what is the color of cementum?

has a yellowish color

the layer of cementum on the root is relatively ______

thin

where is cementum very thin?

next to the cervical line (about the thickness of a page of paper or 50-100 micrometers thick)

how hard is cementum?

softer than both enamel and dentin

the cementum overlaps the enamel in _______ of cases

60%

in _______ of the cases, the cementum meets the enamel at a sharp junction

30%

in the remaining ______ of the cases, the enamel and cementum do not meet, leaving the dentin exposed at the cervical line

10%

what is the soft connective tissue found in the central portion of the tooth entirely surrounded by dentin?

pulp tissue

what is the living soft tissue that occupies the pulp cavity?

pulp

what surrounds the pulp cavity?

dentin

what does the pulp contain?

the tooth's nutrient supply in the form of blood vessels, as well as the nerve supply

the pulp transmits _______ ________

sensory stimuli

the walls of the pulp cavity are lined with ____________, which are responsible for dentin formation

odontoblasts

the pulp is subject to _____________

inflammation (pain, which can progress to abscess, which can progress to the pulp's death)

what are the two types of inflammation of the pulp?

1. reversible

2. irreversible (need root canal)

how can the pulp be removed?

by endodontic procedures

on badly broken down teeth, what may be seated in a pulp canal (after root canal therapy) to help build up the tooth to normal contours

cast or prefabricated posts

what are the four main functions of pulp tissue?

1. formation of dentin

2. nutrition

3. sensation

4. defense and protection

what is the process of dentin formation and what is it a function of?

dentinogenesis; odontoblasts (cells that have differentiated from the peripheral portion of the pulp)

what are the four types of dentin?

1. primary physiologic dentin

2. secondary physiologic dentin

3. tertiary (reparative) dentin

4. reactionary (sclerotic) dentin

what type of dentin is laid down only during tooth formation?

primary physiologic dentin

when does production of primary physiologic dentin end?

when root development is complete (approximately 3 years post eruption)

what type of dentin is only produced after complete formation of the tooth and is formed as long as the tooth is vital (amount and rate variable)?

secondary physiologic dentin

what type of dentin is formed in response to a noxious stimulus, such as caries, and is a defensive action?

tertiary (reparative) dentin

when tertiary dentin is formed, what is happening with odontoblasts?

original odontoblasts have undergone apoptosis and a new group of secondary odontoblasts have differentiated from cells in the pulp

what type of dentin is formed by odontoblasts that have survived a noxious stimulus or mild irritation?

reactionary (sclerotic) dentin

what type of dentin results from aging?

physiologic sclerotic dentin

what does secondary dentin form in response to?

normal physiological activities throughout life

what does reparative (tertiary) dentin form in response to?

irritants such as bruxing or clenching, erosion, trauma, and dentinal caries

what makes up the nutrition that maintains pulp vitality?

blood and lymph vessels in pulp tissue that enter the tooth mainly through the apical foramen, some auxiliary supply through periodontal membrane

what tissue in the pulp is responsible for pain and all other sensory functions of the teeth?

sensation

pulp is capable of responding through __________, resulting in __________ differentiation and __________ dentin

inflammation; odontoblast; reparative

what is the pulp cavity?

the entire central space in the dentin, both root and crown, which contains the pulp tissue of a vital tooth

what does the outline of the pulp cavity generally correspond to?

external contour of the tooth

what is the pulp chamber?

portion of the pulp cavity located in the anatomical crown

what is the pulp canal?

portion of the pulp cavity located in the anatomical root, apical to the pulp chamber (aka root canals)