TRUE & FALSE QUESTIONS

Embryology

1- The proliferation period begins by fertilization of the ovum till the development of three germ layers2- The embryonic period extends from the beginning of the 5th week of intra-uterine life (3rd wiu) to the end of the 8th wiu. 3- The embryonic period is considered as the second trimester of pregnancy, so any maternal illness specially of viral origin and drug therapy are well known to cause congenital deformities.

4- The fetal period extends from the end of the 8th wiu, until birth. 5- During the embryonic period there is a rapid increase in the overall size of the fetus. 6- The nervous system begins to develop at the 1st week intra uterine life.

7-At the head and neck regions the neural crest cells give rise to all tooth structures except enamel only.8-The stomodeum is separated from the blind end of the foregut by the nasopharyngeal membrane.

9- buccopharyngeal membrane formed by double layers of ectoderm.

10- At 4th week intra uterine life the buccopharyngeal membrane soon breakdown and the stomodeum communicates with the foregut.

11-From the roof of the stomodeum, Rathke's pouch develops and forms the anlage of the posterior lobe of the pituitary glands.

12- The mandibular arch send out a prominence called maxillary process at its distal end, while its proximal extension is called mandibular process.

13-The first branchial arch is covered by ectoderm from out side and lined by endoderm from inside. 14- The cartilage bar of the first arch is called Meckel's cartilage and has an important role in the development of the mandible. 15- The remnants of the posterior portion of Meckel's cartilage forms the mental ossicles.16-The remnants of the middle part of Meckel's cartilage forms the lingula of the mandible.

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17- The stylo-mandibular ligament originates from the fibrous coverage around the Meckel's cartilage.18- The posterior portion of Meckel's cartilage forms the incus and the malleus of the middle ear.19- The muscles of facial expression are derived from the mandibular arch, while the muscles of mastication are derived from the second arch. 20- The branchial arches are supplied by blood vessels originating from the aortic arch. 21-The first arch is supplied by the external and internal carotid arteries, while the second arch is supplied by the facial artery.22- The third arch is supplied by facial artery.23- The sensory nerve that enters the corresponding arch and divide inside the arch is called post-trematic nerve.24-The sensory nerves gets from the nerve of the preceding arch is called post-trematic nerve.25-The first arch is supplied by the mandibular nerve as a pre-trematic nerve and chorda tympani as post-trematic nerve.

26-The third arch is supplied by the glossopharyngeal nerve, while the other arches are supplied by the vagus nerve.

27- The branchial arches are separated by external shallow depression called branchial clefts

28- The branchial arches are separated from the pharyngeal side by shallow depression called pharyngeal pouches. 29-The first branchial cleft is involved in the formation of the Eustachian tube. true30-The second pharyngeal pouch gives rise to the tonsillar fossa and tympanic membrane. 31-development of the face starts at 4th wiu.32-The lower lip developed by the median fusion of the two mandibular prominences.

33-The lateral nasal processes of both sides are separated from the maxillary processes by a groove named nasolacrimal groove.

34- The lateral nasal process gives rise to the philtrum.

35-The mouth orifice is determined by the degree of fusion between the maxillary processes of both sides.

36-The primitive lip and cheeks are invaded by the mesenchymal tissues of the third branchial arch which give rise to the muscles of facial expression.

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37- The mandibular cleft lip is due to failure of union of the mandibular processes at the midline. 38-The maxillary cleft lip results from failure in the proper union of the medial nasal process with the mandibular process.

39- Macrostomia occurs as a result of over union between the maxillary and mandibular processes.40- Transverse facial cleft is the other name of Macrostomia.41-Microstomia results from lack of fusion of the maxillary and mandibular processes, leading to very small mouth.42-Oblique facial cleft resulting from lack of fusion between the medial and lateral nasal processes.

43-Cleft palate is result of lack of union of both palatine processes with each other and with the nasal septum.

44- Vestibular lamina gives rise to oral vestibule.45- The tongue develops from two separate parts which later on fused together in V shape line called foramen ceacum.46- The anterior 2/3 of the tongue is known as papillary portion of the tongue while the posterior 1/3 of the tongue is named lymphoid portion of the tongue.47-The median rhomboid glossitis may be located at the anterior part of the posterior 1/3 of the tongue.48-The posterior part of the post 1/3 of the tongue and the epiglottis originate from the 4th branchial arch.

49- The foramen ceacum represents the opening of a thyroglossal duct.

50- The circumvallate and foliate papillae are supplied by the glossopharyngeal

nerve for taste sensation.

51- The posterior portion of the posterior 1/3 of the tongue and the epiglottis are supplied by the glossopharyngeal nerve for general sensation.

52-The hypoglossal nerve supplies the extrinsic muscles of the tongue only. 53-The extrinsic muscles of the tongue are developed from the occipital

myotomes migrating on the glossopharyngeal nerve.

54- The final tongue papilla developed is the foliate papillae.55- The circumvallate and foliate papillae are the first papillae appears near to the termination of glossopharyngeal nerve.56-The fungiform papillae appear near to the termination of the chorda tympani

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branch of the hypoglossal nerve.57- The first sign in the development of fungiform, circumvallate and foliate papillae is the appearance of taste buds.58-The fungiform papillae are localized at the tip and border of the anterior 1/3

of the tongue.

59-The parotid gland is the last gland develops at 6 wiu at the angle of the

stomodeum between the mandibular and maxillary prominences of both sides.

60-The mandible develops in the lower part of the first branchial arch by intramembranous ossification.

61- The development of the mandible starts by the appearance of ossification center at the bifurcation of the mandibular and incisive nerves.

62- The condylar cartilage appears at 14 miu and continues till the age of 20 years of life.

63- The condylar cartilage gives rise to the condylar head and neck of the mandible.

64-The coronoid cartilage appears at 4 miu and disappears before birth at 6 miu.65- The coronoid cartilage gives rise to the the coronoid process and the anterior part of the ramus to a point as low as the mandibular foramen.66- The most important secondary cartilage for the growth of the mandible is coronoid cartilage. 67- The primary center of the ossification in maxilla appears at the bifurcation of the anterior superior dental nerve and the infra-orbital nerve. 68-Development of maxillary sinus starts at 4 miu as a small depression of the mucosa of the lateral wall of the nasal cavity.69-Growth of the maxilla depends mainly on secondary cartilages. 70-Growth of the Maxilla depends mainly on their bony sutures.71- The sutural growth of the maxilla continues till 15 years of age then become less significant.72-The growth at the maxillary sutures allows shift the maxilla forward and upward.73-The embryonic period characterized by growth.74-Tuberculum impar is a transient structure but contributed to a significant portion of the adult tongue.

75-The symphysial cartilage is independent of the Meckel's cartilage remnants.76-The palatal shelves (palatine processes) are derived from the first branchial arch.

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77- An oblique facial cleft is formed due to the rupture of the buccopharyngeal membrane. 78- The stomodeum is lined by endoderm. 79- The face starts to develop from nine clear outgrowths termed facial prominences.80- The maxillary processes give rise to the middle portion of the upper lip only.

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KEYEmbryology

1- true 21- true 41- false 61- false

2 - false 22- false 42- false 62- false

3- false 23- true 43- true 63- true

4- true 24- false 44- true 64- true

5- false 25- false 45- false 65- true

6- false 26- true 46- true 66- false

7- true 27- true 47- false 67-true

8- false 28- false 48- true 68- true

9- false 29- true 49- true 69- false

10- true 30- false 50- true 70- true

11- false 31- true 51- false 71- false

12- false 32- true 52- false 72- false

13- false 33- true 53- false 73- false

14- true 34- false 54- false 74- false

15- false 35- false 55- true 75- true

16- true 36- false 56- false 76- true

17- false 37- true 57- true 77-false

18- true 38- false 58- false 78- false

19- false 39- false 59- false 79- false

20- true 40- true 60- true 80- false

TOOTH DEVELOPMENT

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1-Odontogenesis of the primary dentition begins between the sixth and seventh week of intrauterine life.2- The first stage of tooth development known as the bud stage.3- The vestibular lamina located lingual to the dental lamina.

4- An oral vestibule is the space between the maxilla and the mandible on one side and the lips and the checks on the other side. 5-The second stage of odontogensis is called the initiation stage.

6-The ectomesenchymal cells condensation just beneath the enamel organ is called dental sac.

7- The connective tissue-beneath-and around the enamel organ and dental papilla forming what is called dental sac (follicle).

8- A basement membrane remains between the bud and the growing underlying ectomesenchyme.

9-The tooth primordium has three components enamel organ, dental papilla and dental lamina.10-The dental organ is ectomesenchymal in origin, while both dental papilla and dental sac are ectodermal in origin. 11-The field model proposes that ectomesenchyme assumes the dominant role in crown pattern formation. 12- The clone model proposes that epithelium assumes the dominant role in crown pattern formation. 13-The third stage of odontogenesis is called the cap stage.

14- The stratum intermedium cells synthesize and secrete glcyosaminoglycans.

15-The lingual extension of the dental lamina is called vestibular lamina.

16-The permanent molars are succedaneous and have no primary predecessors.

17-The permanent molars develop from a posterior extension of the dental lamina.

18-The fourth stage of odontogensis is called the apposition stage.

19-In the bell stage, the connection of dental organ to the dental lamina is elongated forming a lateral dental lamina.

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20-The configuration of the inner enamel epithelium maps out the incisal or occlusal pattern of the crown of the tooth.

21-The point at which inner enamel epithelium differentiation first occurs represents the site of future ADJ.

22-The region where the inner and outer enamel epithelia meet at the rim of the enamel organ is known as cervical loop.

23-The stellate reticulum layer is most fully developed at the cap stages. 24- The cells of stratum intermedium contain much alkaline phosphatase enzyme which essential for dentin maturation.

25- The remnants of the dental lamina and the lateral dental lamina are called epithelial pearls.

26-The peripheral cells of the dental papilla will differentiate into odontoblasts whereas the inner cells are the primordium of the dentin.

27-The final stage of odontogensis is known as apposition stage.

28- The permanent structures seen during the early stages of tooth development are enamel knot, enamel cord and enamel niche.29-Enamel knot are clusters of dividing epithelial cells.

30-The enamel cord is a strand of cells extending form the stratum intermedium into the outer enamel epithelium.

31-The process of root development takes place after the crown is completely formed.

32-The cervical loop is the structure responsible for root development.

33-The function of cervical loop is to map out the root and induce dentin formation in the root area.

34- The remnants of epithelial root sheath of Hertwig are called epithelial rests of Serres. 35- The number of roots that are formed is determined by the number of medial ingrowths at the epithelial diaphragm.

36-Flexion is the union of the root structure of two or more teeth through the cementum only.37- Concrescence commonly occurs in permanent maxillary premolars.

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38- Misplaced enamel formed on the cemental root surface is called enamel pearls. 39- Concrescence is distortion in root (or roots) or crown angulations in a formed

tooth. 40- Flexion is a deviation or bends restricted just to the root portion of the tooth and

less than 90 degrees. 41- Supernumerary roots occurs mainly in the permanent third molars. 42- The dental sac gives rise to periodontal ligament only.43-Primordium for the permanent dentition appears as an extension of dental lamina into the ectomesenchyme lingual to the developing primary tooth germ. 44- The epithelial rests in the periodontal ligament are derived from epithelial root sheath of Hertwing's. 45- The last hard dental tissue to be deposited is bone. 46-The epithelial root sheath of Hertwig disintegrates after odontoblastic differentiation & before dentin matrix deposition. 47- The lateral dental lamina gives rise to permanent teeth. 48- The stratum intermedium lies between outer enamel epithelium & stellate reticulum. 49- The downgrowth of an epithelial thickening buccal to the dental lamina is known as vestibular lamina. 50- The epithelial component of the tooth germ is known as enamel organ. 51- The dental lamina is induced to proliferate into a tooth bud by the ecto-mesenchyme. 52- The stimulus that initiates the actual formation of enamel matrix seems to be the presence of predendtin.53-After the crown of the tooth is formed, the dental papilla is called dentin. 54- A layer of cells that seems to be essential to enamel formation but does not actually secrete the enamel is preameloblast.

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KEY

TOOTH DEVELOPMENT

1- true 13- true 25- true 37- false 49- true

2- false 14- false 26- false 38- true 50- true

3- false 15- false 27- true 39- false 51- true

4- true 16- false 28- false 40- true 52- true

5- false 17- true 29- false 41- true 53- false

6- false 18- false 30- true 42- false 54- false

7- true 19- true 31- true 43- true

8- true 20- true 32- true 44- true

9- false 21- false 33- false 45- false

10- false 22- true 34- false 46- false

11- true 23- false 35- true 47- false12- true 24- false

36- false48- false

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Tooth Eruption1- Tooth eruption continues throughout the whole life span of the tooth.

2- Pre-eruptive phase begins in the cap stage and ends at the beginning of root formation. 3- Increase in width of the jaws: lead to movement of the germs labially and occlusally (bodily movement).4-Increase in height of jaws leads to the occlusal movement (Excentric growth).5-Bodily (drifting) and eccentric growth are the types of movement in pre-eruptive phase.6-Eccentric growth means that the developing tooth germ remains stationary in its place.7- In eccentric growth, bone resorption occurs on the whole crypt wall.

8- Eruptive phase begins by root formation and ends when the tooth reaches the occlusal plane.

9- In extra-osseous stage of eruption, the rate of eruption decelerates.

10-If there are prolonged delays in eruption, ankylosis of tooth to bone can result.

11- Clinically tooth eruption accompanied by discomfort or pain, increased salivation and bleeding.

12-Eruptive path is achieved by the Gubernacular bony canal which is filled with the Gubernacular cord. 13-In a dried skull, holes that identified in the jaws on the labial aspects of the anterior deciduous teeth represents the opening of the Gubernacular canal. 14-Formation of the tooth eruption pathway is a localized, genetically programmed event that does not require pressure from the erupting tooth. 15-Root formation at first causing bone deposition to provide room for the growing root tip.

16-pre- eruptive phase begins after the tooth has reached its functional position in the occlusal plane and continues through the whole life of the tooth.

17-The occlusal wear is compensated by continued bone deposition around the apex of the tooth.18-The interproximal wear is compensated by a process known as mesial drift.

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19- The vascular pressure theory supposes the existence of cushion- hammock ligament, running across the base of the socket to provide a fixed base for the growing root to react against.20-Periodontal ligament traction theory proposed that the cells and fibers of the periodontal ligament pull the tooth into occlusion.

21-Vascular pressure theory supposes that a local increase in tissue fluid pressure in the periapical region is sufficient to move the tooth. 22- The premature loss of a deciduous tooth occasionally leads to delayed eruption of its permanent successor.

23-Impaction is a fusion of cementum to alveolar bone due to cellular changes in the periodontal ligament caused by trauma and other pathologies.

24-The ankylosed tooth appears submerged in relation to adjacent teeth that continue to erupt.

25- The ankylosis most commonly affects mandibular primary central incisor. 26-Ankylosis can lead to increase loss of arch length.

27-Impaction is a cessation of eruption of a tooth. 28-The second premolars are particularly prone to impaction because they erupt last, when the least room is available. 29-The upper canine is impacted frequently because of its late eruption.

301-Ectopic eruption is eruption of a developing tooth beyond the range of the normal eruption date. 31- Eruption of the maxillary third molar in the maxillary sinus represents an eccentric eruption.

32- Eruption hematoma is a bluish, opaque asymptomatic swelling overlays an erupting tooth due to the accumulation of blood in the follicular sac around the eruption crown.

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KEYTooth Eruption

1- true 12- true 23- false

2- false 13- false 24- true3- false 14- true

25- false4- true 15- false 26- true5- true 16- false

27- true 6- false 17- false

28- false7- false 18- true

29- true

8- false 19 false30- false

9- false20- true

31-false

10- true21- true

32- true

11- false22- false

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SHEDDING

1- The neural elements remain in the pulp until shedding is completed. 2- Remnants of deciduous teeth are most frequently found in the canine-premolar region.3- Shedding is the pathological elimination of the deciduous teeth.

4- The anterior deciduous teeth are often shed with much of their pulp chamber intact.

5- The permanent incisors and canines develop labial to the deciduous teeth and erupt in an occlusal and vestibular direction.

6- The resorption of the roots of the deciduous molars often begins early on their inner surface facing the inter-radicular septum.

7- The premolar tooth germs move apical to the deciduous molars to relieve the pressure on the roots of the overlying deciduous molars.

8-The resorption of permanent molars may proceed far up into the coronal dentin and occasionally some areas of the enamel may be destroyed.

9-The process of tooth resorption is continuous; there periods of resorption and periods of rest and repair.

10-The resorption of the hard dental tissues of deciduous teeth is achieved by highly specialized multinucleated cells called osteoclasts.

11-Odontoclasts are derived from blood circulating monocytes.

12-Odontoclasts are found on a shallow hollowed out depressions or bays called Howship's lacunae.

13-Odontoclast cells have been detected in the root canals and pulp chambers of resorbing deciduous incisors.

14-Odontoclasts are able to resorb all hard dental tissues including cementum, dentin and on occasions enamel.

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15-The tooth sheds with some pulpal tissue intact except that neural elements seem to be missing.

16-the pulp plays an active role in the shedding process.

17-Loss of the periodontal ligament fibers is abrupt, and cell death in this region occurs without inflammation.

18-Shedding of teeth is programmed developmental event.

19-Pressure from the erupting permanent molars plays a role in the shedding of deciduous dentition.20-Retained deciduous teeth are most often the upper lateral incisor.

21-The most frequently remnants are found in the region of premolars because their roots are widely divergent.

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KEYSHEDDING

1- false 12- true

2- false 13- false

3- false 14- true

4- true 15- true

5- false 16- false

6- true 17- true

7- true 18- true

8- false 19- false

9- false 20- true

10- false 21- true

11- true

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ENAMEL

1- The ameloblasts having ruffled borders are protective ameloblasts.2-Maturative ameloblasts are characterized by having a distal cell membrane with many infoldings.3-Incremental lines are a result of variation in crystal orientation.4-Enamel tufts are seen in thick decalcified sections. 5- Organic components of enamel are primarily removed from enamel by secretoryameloblasts.6- The main difference between the rod and the interrod region is crystal orientation.7- The striae of Retzius would be seen as concentric rings in a horizontal section of the crown.8-The extensions from secretory ameloblast cells that give structure to enamel rods are called Tomes' fibers.9- Striae of Retzius are due to rhythmic apposition of enamel. 10- Enamel is formed of 96% organic materials and water& 4% minerals. 11- Cross striations in enamel result from abrupt change in environment before and after birth.12- The prism sheath results from abrupt change in crystals orientation.13- The complex arrangement of rods over the cusps of teeth is termed prismless enamel.14- Prismless enamel is less mineralized than prismatic enamel.15- The predominant organic portion of enamel is calcium.16-Developmental enamel lamellae are type B enamel lamellae.17-Enamel prism of the cusp tip passes in twisted course.18- The predominant organic portion of developing enamel is Enamelin. 19-The enamel lines fissures, grooves and pits.

20- After destruction of enamel by caries or injury, neither the body nor the dentist can restore the enamel tissue.

21-Enamel is extremely hard because of its high mineral content.22- The permeability is the property that enables enamel to withstand the mechanical forces applied during tooth functioning. 23-Enamel of permanent teeth is softer than that of deciduous teeth.

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24-Enamel hardness is greatest at the surface and decreases gradually towards the dentino-enamel junction.25- The hardness is greater towards the cervical line and decreases at the cusp and incisal edges. 26- Dentin is less mineralized and less brittle and be necessary as a support for enamel.

27-Enamel has a certain degree of permeability. The main pathway is from outer layer of enamel to the saliva.

28-By volume, mature enamel is composed of 88-90 % inorganic material and 10-12 % organic material and water.

29- The mineral content decreases at the surface than at dentino-enamel junction.30-Enamel crystals are extremely long, relative to their thickness, and are highly oriented. 31-Fluoro-apatite is 20% more soluble than hydroxyapatite which means that it is

much less susceptible to demineralization.32- Because fluoride ions help killing cavity-causing bacteria. So, it used as topical

application of fluorides on the teeth to minimize caries.33- Spread of caries seems to be prevented or reduced by areas of enamel rich in

protein content.34- 90% of the developing enamel proteins are a heterogeneous group of low-

molecular weight hydrophobic proteins known as Enamelin. 35- In the mature enamel, enamelin predominates. 36- Stippled material secreted by secretory ameloblasts.37-Tomes' processes interdigitate with the surface of the forming enamel giving it a picket fence appearance. 38- Tomes' fibers determine the orientation of the newly formed enamel hydroxyapatite crystals and responsible for the rod structure of enamel.

39- Transitional stage is a brief reorganization stage between enamel secretion and maturation.40- During the transitional stage, the overall number of ameloblasts is reduced by as much as 50%.by programmed cell death (apoptosis).41- During maturative stage there is selective withdrawal of enamel proteins, mainly enamelin and water.42 - The maturative ameloblasts are either ruffled-ended (20 % of maturation ameloblasts) or smooth-ended (80 %). 43- Maturative ameloblast yielding three complete modulations per day.

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44-In the ruffled-ended ameloblasts the distal junctions are leaky and the proximal are tight.45- The reduced dental epithelium protects the enamel from being in contact with connective tissue cells in the dental sac.46- The reduced dental epithelium and the oral epithelium are joined to form the dento-gingival junction of the erupting tooth.47- Human enamel forms at a rate of 10 microns per day.

48- Secretory ameloblasts release small isolated drops of unmineralized enamel proteins called stippled material.

49- Final prismatic enamel layer the crystals are arranged parallel to each other and perpendicular to the surface.

50- Tertiary maturation is characterized by gradual completion of mineralization to reach the 96 % of the total weight of enamel.51- During the maturation process, amelogenins and ameloblastins are removed leaving enamelins and tuftelin in the mature enamel. 52-Once tooth enamel is formed, the mineralization is never decreased by any physiologic process within the tooth.

53-Histological structure of enamel could be described in decalcified sections only. 54-Under the cusp tip and incisal ridges, the course of the rods is more complicated where they become twisted and braided together and it is called gnarled enamel.

55-Hunter-Schreger bands are an optical phenomenon, viewed by oblique reflected light under the low power of the microscope.

56- Hunter-Schreger bands are found in the outer two thirds of the enamel.

57- Cross striations appear as dark lines 2.5- 6 microns apart. They represent weekly increment of growth. 58- Brown striae of Retzius overlying the cusps do not reach the surface unless there is some enamel loss due to attrition. 59-The base for the formation of striae of Retzius is supposed to be as a result of daily rhythm in enamel production.60- Neonatal line mainly appears in deciduous teeth and permanent molars and may be associated with increased caries susceptibility.61-The quality of the prenatal enamel is better than that of the post natal enamel due to the more protected condition and constant nutrition.62-Enamel spindle results from some Tomes' processes during the early stages of enamel formation pushed themselves between the pre-ameloblasts.

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63- Enamel spindles are most common beneath cusps where most crowding of odontoblasts would have occurred.

64-Enamel lamellae are always unmineralized. They are narrower, longer and less common than enamel tufts.

65- Developmental type A lamellae are hypo mineralized. They never extend to dentin .66- Non developmental lamellae or cracks occur before amelogenesis is completed.

67-Type B lamella is a crack occurs in the enamel before the tooth eruption due to a stimulus on the enamel surface causing its fracture.68-Type B lamella is a crack occurs in the enamel after the tooth eruption while it is functioning in the oral cavity.

69-Dentino-enamel junction is less curved on the lateral surfaces.

70-The convexities of the scallops of the DEJ are directed towards the enamel. 71- The outer prismless enamel is 20-100 microns of newly erupted deciduous teeth and 20-70 microns of newly erupted permanent teeth. 72-Rodless enamel may be lost rapidly by abrasion, attrition and erosion in erupted teeth.

73- Perikymata are numerous near the cusp region and nearly disappear at the cervical region. 74- Rod-end markings are deepest in the cervical region and shallowest near the occlusal and incisal surfaces.75- Afibrillar cementum occurs in 30 % of cases.76- Attrition is the physiological wearing away of the tooth hard substance as a result of tooth to tooth contact.77-The wear rate of enamel is nearly 8 micrometers a year from normal factors.

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KEYENAMEL

1- false 12- true 23-false 34- false 45- true 56- false 67- true

2- true 13- false 24True 35- true 46- true 57- false 68- false3- false 14- false 25- false 36- false 47- false 58- true 69- true4- false 15- false 26-true 37- true 48- false 59- false 70- false5- false 16- false 27- false 38- false 49- false 60- false 71- true

6- true 17- true 28- true39- true 50- false 61- true 72- true

7- true 18- false 29- false 40- true 51- true 62- false 73- false8- false 19- true 30- true 41- false 52- true 63- true 74- false

9- true 20- true 31- false 42 – false 53- false 64- false 75- false

10- false 21- true 32- true 43- true 54- true 65- true 76- true

11- false 22- false 33- true 44- false 55- true 66- false 77- true

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Dentinogenesis & Dentin Structures

1- Enamel is highly mineralized tissue that forms the bulk of the tooth.

2-Two major properties distinguish dentin from enamel: First, dentin is sensitive. Second, dentin is formed throughout life.

3-Dentin is slightly harder than bone and is less hard than cementum. 4-On radiographs, dentin appears more radioopaque than enamel and more radio-lucent (lighter) than pulp. 5-Mature dentin couldn't be seen either in ground or decalcified sections. 6- The collagen of dentin comprises over 90% of the organic matrix. The principle collagen fibril is type II collagen.7-The odontoblasts are highly specialized connective tissue cells that differentiate from the peripheral cellular layer of the dental papilla.8-Secretory odontoblasts exhibit alkaline-phosphatase and Ca-ATPase activity along their plasma membranes. 9- The resting odontoblast doesn't produce dentin. 10-In resting odontoblasts, there are increase in number and size of lysosomes and

phagosomes.

11- In Mantle dentin, ground substance is incorporated with some pre-existing ground substance of the cell free zone.12- ''Mantle dentin'' varying in width from 200-300 µm. The large collagen fibrils

(0.1-0.2 mm in diameter) aggregate in the cell free zone. 13- The collagen fibrils of mantle dentin are aligned at right angles to the basal

lamina,while in the mantle dentin of the root they are parallel to it. 14- The circumpulpal dentin is the basic structure of dentin and forms its bulk. 15- The collagen fibers of circumpulpal dentin are smaller in diameter (0.05Mm) and

are more closely packed and interwoven with each other.16- The fibers of circumpulpal dentin are present parallel or oblique angles to the

tubules.

17- Odontoblastic transduction theory contends that a dental stimulus excites the odontoblastic process which then transmits the excitation to the adjacent nerve plexus.

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18-The matrix vesicles are rich in calcium and phosphate ions but not contain alkaline phosphatase enzyme.

19-The sclerosis slows down an advancing carious process, so it may help to prolong pulp vitality.

20- The function of matrix vesicles is to provide a special micro-environment in which the first hydroxyappatite crystals can form.

21-the presence of matrix vesicles is limited to mantle and circumpulpal dentin. 22-Linear calcification founds in secondary dentin.23-Globular calcification (calcospherite) usually presents in circumpulpal dentin formed just below mantle dentin.24-In the rest of the circumpulpal dentin, a combined pattern of calcification occurs with a globular phase alternating with a linear phase. 25-The concavity of the primary curvatures of dentinal tubules nearest the pulp chamber faces root ward.26-The "secondary curvatures" result from the spiral track taken by the odontoblast during its course from the outer dentin surface to the pulp.27-Each dead tract is surrounded and isolated by a narrow zone of reparative dentin.

28-Dentin located between the dentinal tubules is called "intra-tubular dentin".

29- Intratubular dentin contains little amount of collagen. It is about 40% more mineralized than intertubular dentin.

30- External stimulus accelerates inter-tubular dentin formation that eventually may obliterate the tubules spaces.

31- Peritubular dentin will be seen as translucent rings in ground sections.

32-Inter-globular dentin is the area of hypomineralized dentin where globular zones of mineralization have failed to fuse within mature dentin.

33-Inter-globular dentin is seen most frequently in the mantle dentin. 34-In the inter-globular dentin, the tubules run uninterrupted through the interglobular areas.

35- Tomes' granular layer is a transient feature of the root dentin immediately

adjacent to cementum.

36- Tomes' granular layer do not follow any incremental pattern and usually smaller

than interglobular dentin.

37-The dentinal tubules do not cross through Tomes' granular layer.

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38- Incremental lines of Von-Ebner run parallel to the dentinal tubules.

39- Contour line of Owen may results from a coincidence of the secondary curvatures between neighboring dentinal tubules.

40- Neonatal line could be seen in all deciduous teeth as well as in the mesio lingual cusp of the first permanent molar.

41-Regular secondary dentin develops by odontoblasts before root formation is completed.

42-Irregular secondary dentin (Reparative dentin) is produced only by those cells directly affected by the stimulus.

43- The dentin with no tubules at all named "atubular dentin". While the dentin with trapped forming cells named "vasodentin".

44- Sclerotic dentin is characterized by calcification of dentinal tubules, where the odontoblastic processes undergo fatty degeneration and then calcification.

45-In transparent dentin, the most likely source of the calcium salts is the fluid of "dental lymph" within the tubules.

46- Sclerotic dentin appears translucent when viewed by transmitted light while with reflected light these areas appear white.47-Dentin areas characterized by degenerated odontoblastic processes have been called "dead tracts".

48-Dead tracts may be caused in some teeth by the death of odontoblasts crowded in narrow pulpal horns.

49- Fluid or hydrodynamic theory proposes that dentin contains nerve endings, which respond when dentin is stimulated.

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KEYDentinogenesis & Dentin Structures

1- false 11- true 21- false 31-true 41- false

2- true 12- false 22- false 32- true 42- true

3- false 13- true 23- true 33- false 43- false4- alse 14- true 24- true 34- true 44- true5- false 15- true 25- false 35- false 45- true

6- false 16- false 26- true 36- true 46- false

7- true 17- true 27- false 37- true 47- true

8- true 18- false 28- false 38- false 48- true

9- false 19- true 29- true 30- true 49- false10- true 20- true 30- false 40- true

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Cementum Structure and Cementogenesis

1-Cementogenesis comprises both matrix formation and mineralization.2- The inner dental epithelium will induce the neighboring cells of the dental papilla to differentiate into ameloblasts. 3-When the epithelial root sheath of Hertwig will loss its continuity, its cells become the epithelial rests of Serres. 4- The cells entrapped in the mineralized cementum are referred to as cementoblasts and occupy lacunae.

5-cellular cementum has the same mineral content than acellular cementum.

6-The Sharpey's fibers of cellular cementum generally retain an unmineralized core. 7-The Sharpey's fibers in cellular cementum exhibit a more complete degree of mineralization.

8-Sharpey's fibers are derived from periodontal fibers, which are not classifiable in their original location.

9- The mineral content of cementum once formed changes significantly with age. While that of the root dentin shows no change in mineral content with age.

10-Acellular afibrillar cementum covers minor areas of the enamel, particularly at the cementoenamel junction.

11- Cementum hyperplasia is characterized by the presence of Sharpey’s fibers. 12- Acellular afibrillar cementum consists of a mineralized matrix, which contains neither collagen fibrils nor embedded cells.

13- Acellular afibrillar cementum plays an important role in tooth attachment.

14-acellular extrinsic fiber cementum has significant function in tooth anchorage to the surrounding bone through numerous Sharpey’s fibers inserting into it.15- The furcations of human teeth are covered with thick cementum layers before

they emerge into the oral cavity.16- Impacted and erupted teeth without antagonists appear to have thinner cementum

layers than fully erupted and functioning teeth.17- Over-compression of the periodontal ligament causes root resorption.

18-An increase of cementum in a non-functioning tooth or in an embedded tooth, this is called cementum hypertrophy.

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19- Cementum is unique in that it is avascular, does not undergo continuous remodeling like enamel, but continues to grow in thickness throughout life.

37-More cementum is formed apically and in the furcations areas of multi-rooted teeth than cervically.

21-Cementum has been shown to be impermeable from both the dentin and the periodontal ligament side.

22-Cementum contains 45% to 50% inorganic substances and 55% to 50% organic materials.

23-Under the light microscope two types of cementum can be differentiated: the acellular and the cellular cementum.

24-The cementum is usually covered by a zone of cementoid tissue 3-4 microns wide in acellular cementum and is thinner in cellular cementum.

25- Over compression of the periodontal ligament can result in the physiologic resorption of cementum and dentin.

26-Increase in the thickness of cementum does not enhance the strength of attachment of the individual fibers.

27-cementocytes cells have processes directed toward the pulp to provide nutrition for the cementum.

28-cementocytes present in the superficial layers show definite signs of degeneration such as cytoplasmic clumping and vesiculation.

29- The number of cells that become incorporated in cementum is proportional to the rate of cementum deposition.

30-Incremental Lines of Salter are highly mineralized areas with less collagen and more ground substance.31-The incremental lines are roughly parallel to the long axis of the root.32- The cellular cementum is formed at a faster rate than the acellular cementum and so, the incremental lines are closer in acellular cementum.33- In 60% of all teeth, cementum meets the cervical end of enamel in a relatively

sharp line.34-In about 60% of the teeth cementum overlaps the cervical end of enamel for a short distance. 35- Cementum is markedly thicker on the mesial than on the distal root surface, indicating a relationship to mesial drift.

- 27 -

38-Hypercementosis is an abnormal thickening of cementum.

39-cementum hypertrophy is increase of cementum in good function teeth to permit more periodontal fibers to be attached to the tooth.

- 28 -

KEYCementum Structure and Cementogenesis

1- true 11- false 21- false 31- true

2- false 12- true 22- true 32- true

3- false 13- false 23- true 33- false

4- false 14- true 24- false 34- true

5- false 15- true 25- false 35- false

6- true 16- false 26- true 38- true7- false 17- true 27- False 39- true8- true 18- false 28- false

9- false 19- false 29- true

10- true 37- true 30- true

- 29 -

Periodontal ligament

1- The width of PDL ranges from 1.05-1.69 mm.

2- The PDL is formed from dental sac shortly after root development begins.3- The connective tissue fibers are mainly collagenous. The main types of collagen in the PDL are types I and III. More than 70 % of the periodontal collagen is type I.

4- The intercellular spaces of the PDL contain fibers and cells.

5- The oblique group running from the cementum in an oblique direction to be inserted into the bone apically.

6- Synthetic cells include: fibroblasts, odontoblasts and cementoblasts only. 7- Periodontal nerve fibers are myelinated and unmylenated.

8- In PDL there are two types of nerve endings.

9- The PDL through aging shows decreases in vascularity.

10- mechanoreceptors are responsible for localization of pain on the teeth.

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KEY

Periodontal ligament

1- false 3- true 5- false 7- false 9- true2- true 4- false 6- false 8- false 10- false

- 31 -

Bone structure

1- The cytoplasm of the osteoblasts is rich in vesicular structures.

2- Type II and type III collagen are the principal collagen in the mineralized bone.

3- Incremental lines are hypermineralized.

4- All the bones of the body are covered externally by a membrane of specialized dense connective tissue called periosteum.

5- The periosteum consists of three layers: The outer layer known as vascular layer, The inner layer known as osteogenic and the intermediate layer known as cambium layer.

6- Bundle bone is generally described as containing more intrinsic collagen fibrils than lamellar bone and exhibiting a fine fibered texture.

7- Radiographically, bundle bone appears more radioluscent than lamellated bone.

- 32 -

KEY

Bone structure

1- false 5- false

2- false 6- false

3- false 7- false

4- false

- 33 -

THE TEMPROMANDIBULAR JOINT

1- The Temporomandibular joint is a unilateral fibrous articulation between the mandible and the temporal bone.

2- The development of the joint starts at 3 W.I. U.

3- Meckel's cartilage provides the skeletal support for the development of the lower jaw and extents from the midline upward and ventrally, where it terminates incus & malleus cartilages.

4- The articular surface of the condyle is strongly concave in the antroposterior direction and slightly convex postero-laterally.

5- Only the articular eminence forms the cranial articulation of the TMJ.

6- The fossa is extremely concave while the articular eminence is convex.

7- In general, the tempromandibular ligament restricts displacement of the mandible in different planes except backward with the head of the condyle slipping in front of the eminence.

8- The fibers of inner layer of the eminence are at right angle to the bony surface, while fibers of outer layer are oblique to the surface.

- 34 -

KEY

THE TEMPROMANDIBULAR JOINT

1- false 5- false

2- false 6- false

3- false 7- false

4- false 8- false

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