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Figure 1 Sagittal sections through Carnegie stage 22 (right) and 23 (left) human embryos

showing the formation of the palate. At stage 22 the tongue occupies the common oronasal

cavity, whereas at stage 23 the tongue is depressed and the forming palate intervenes between theoral and nasal cavities.

Figure 2 Coronal sections through Carnegie stage 22 (left) and 23 (right) human embryos

showing the formation of the palate. The palatal shelves are independent on either side of thetongue and depress it as the shelves extend toward the midline.

Figure 3 Human embryo at 62 days. The entire embryo has been stained with alizarin red, which

preferentially stains mineralized bone, to show the membranous bones forming in associationwith the skull and face.

Figure 4 Rat embryo at 16 days stained with alizarin red (to show bone) and alcian blue (to

show cartilage). No ossification is detectable at this stage.

Figure 5 Rat embryo at 17 days stained with alizarin red (to show bone) and alcian blue (toshow cartilage). Note the membranous bone formation lateral to Meckels cartilage and the

formation of the condylar cartilage.

Figure 6 Rat embryo at 19 days. Mandible stained with alizarin red (to show bone) and alcian

blue (to show cartilage) showing the primary (Meckels) and secondary (condylar, coronoid,angular, and alveolar) cartilages associated with the membranous bone forming the body of the

mandible.Figure 7 Coronal section through a developing embryo. A number of developmental features are

apparent. The tongue is easily identified. Note Meckels cartilage and intramembranous

ossification of the forming mandible lateral to it. The forming mandible is growing alveolarplates to surround a bud stage tooth germ. In the developing upper jaw, a cap stage can be seen.

Figure 8 Late cap stage of tooth development. The forming tooth is undergoing

histodifferentiation, and the dental papilla and dental follicle can be clearly distinguished. Note

the enamel knot.Figure 9 Bud stage of tooth development. Note the accumulation of ectomesenchymal cells

around the epithelial bud.Figure 10 High-power view of a developing tooth bud.Figure 11 Early cap stage of tooth development. The enamel organ is expanding, but folding is

just beginning.

Figure 12 Early cap stage of tooth development. The enamel organ is undergoinghistodifferentiation, and the dental papilla and dental follicle can be clearly distinguished. Note

the enamel knot.

Figure 13 Late cap stage of tooth development. The enamel organ has folded, producing a

concavity into which the ectomesenchymal cells of the papilla accumulate. Intramembranousbone formation has initiated around the developing tooth crown.

Figure 14 High magnification of a late cap stage tooth organ. Note the difference in structural

appearance between the inner and outer dental epithelia and the concentration ofectomesenchymal cells facing the inner dental epithelium.

Figure 15 Cap stage tooth bud. The enamel knot is an accumulation of epithelial cells on the

internal aspect of the inner dental epithelium.Figure 16 The enamel cord is a condensation of epithelial cells that extends from the inner to the

outer dental epithelium.

Figure 17 Bell stage of tooth development. The primary tooth has acquired its final shape but

not its final size.

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Figure 18 High-power view of the four layers of the enamel organ. (Courtesy P. Tambasco de

Oliveira.)

Figure 19 Bell stage of tooth development. Both dentinogenesis and amelogenesis have begun(dentin,pink; enamel,purple) at the cusp tip. Note collapse of the stellate reticulum where

mineralized matrix has been formed.

Figure 20 Bell stage of tooth development. Both dentinogenesis and amelogenesis have begun(dentin, pink; enamel, purple) at the cusp tip. Crown pattern formation has folded the inner

dental epithelium upward to bring the ameloblasts close to the blood vessels situated outside the

outer dental epitheliumthe so-called collapse of the stellate reticulum.Figure 21 Forming root. Hertwig epithelial root sheath (HERS) is present at the leading root

edge.

Figure 22 Body of the mandible. The outer layers consist of compact bone, between which is a

supporting network of trabecular bone.Figure 23 Phase-contrast micrograph of woven bone. Note the random organization of the

refringent collagen fibrils.

Figure 24 Ground section of lamellar bone. The osteon represents the basic structural unit. It

consists of concentric lamellae that form a cylinder of bone with a vascular canal, the Haversiancanal, at its center.

Figure 25 Lamellar bone visualized by phase-contrast microscopy. Note the concentric lamellaethat form the osteon.

Figure 26 Interstitial lamellae (fragments of preexisting concentric lamellae) are interspersed

between osteons, and circumferential lamellae enclose the outer and inner aspects of bone.Figure 27 Osteocytes are entrapped within bone. These cells reside in lacunae, and their

processes in interconnecting canaliculi (arrows) form an extensive network.

Figure 28 High magnification of an osteon showing its concentric lamellae, the centrally located

Haversian canal, and the osteocyte lacunae interspersed among the lamellae.Figure 29 Intramembranous bone formation in the region of the future mandible; plump-looking

osteoblasts line forming bone surfaces.

Figure 30 The presence of numerous osteoclasts associated with this trabecula of embryonicbone suggests that it is being turned over rapidly.

Figure 31 Trabecular bone. All the cell types associated with bone can be recognized in this

micrograph.Figure 32 Osteocytes are usually found within the calcified matrix but can also be present within

osteoid (asterisks).

Figure 33 Histochemical detection of tartrate-resistant acid phosphatase activity, a marker for

osteoclasts in the primary spongiosa of the rat tibia growth plate.Figure 34 Human osteoclasts stained for tartrate-resistant acid phosphatase. Note the presence of

multiple nuclei in these cells.

Figure 35 Endochondral ossification in the rat tibia growth plate. The section is stained with vonKossa's stain to reveal mineral distribution (black deposits).

Figure 36 Mineral deposition starts in the calcification zone of the growth plate.

Figure 37 High magnification of mineralized cartilage in the growth plate. Note that mineral(black deposits) is only present in the longitudinal septae.

Figure 38 Light micrograph of intramembranous bone formation in the rat calvarium. The first

step is condensation of ectomesenchymal cells between the skin and developing brain.

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Figure 39 As intramembranous bone formation progresses, ectomesenchymal cells differentiate

into osteoblasts that form woven cancellous bone.

Figure 40 Cross section of the cartilage model of a digit. Before the start of intramembranousbone formation, alkaline phosphatase activity appears in the connective tissue surrounding the

anlage (perichondrium) and periosteum in areas of vascular invasion.

Figure 41 Vascular invasion of the cartilage model of a digit. Alkaline phosphatasepositivecells from the periosteum accompany the vascular elements and accumulate at the center of

ossification.

Figure 42 The center of ossification of the cartilage model of a digit in longitudinal section.Alkaline phosphatase activity is present both in the center of ossification and the periosteum.

Figure 43 Section showing the hard and soft tissues of the tooth.

Figure 44 Tooth bud at the stage when both enamel and dentin formation begins.

Figure 45 Incisal tip of a tooth just before the start of the enamel layer formation.Figure 46 A and B, Early crown stage of tooth development. Dentin (D) and enamel (E) have

begun to form at the crest of the folded inner dental epithelium (incisal tip). There is a reduction

in the amount of stellate reticulum (SR) in the region where matrix deposition has occurred. Note

the developmental gradient in cell differentiation from the tip toward the cervical portion of thetooth crown.Am, Ameloblasts; Od, odontoblasts; ODE, outer dental epithelium; SI, stratum

intermedium;PD, predentin.Figure 47 Secretory stage amelogenesis. Tomes processes jut into enamel and in certain species

in a "picket fence" appearance. The line at the base of the ameloblasts represents the proximal

cell web (pcw), and that at the apex, the distal cell web (dcw).Figure 48 Histologic section of a decalcified tooth along the slope of the cusp showing an incisal

to cervical gradient in enamel maturation. As maturation progresses, enamel matrix is lost and

mineral content increases. Almost mature enamel (top right) appears whitish because mineral has

been removed and there is very little matrix left in this area. Note the striae of Retzius andmorphology of maturation stage ameloblasts (no Tomes process).

Figure 49 Maturation stage of amelogenesis. A, Smooth-ended ameloblasts. Note that the three

other layers of enamel organ have amalgamated together to form a highly infolded and vascularlayer, the papillary layer. Ameloblasts undergo modulation, a process by which their apexes

alternate between a smooth-ended border (A) and a ruffle-ended border (B).

Figure 50 Once enamel is completely mature, the enamel organ forms the reduced dentalepithelium. At this stage, ameloblasts are no longer distinguishable.

Figure 51 Mature enamel. In decalcified preparation, the fully calcified enamel is completely

removed, leaving behind the space it occupied. Note also that the enamel organ on the cuspal

aspect of the tooth has reorganized into a reduced dental epithelium in which individual celllayers cannot be distinguished.

Figure 52 Indicator dyes can be used to detect regional variations in pH along the maturing enamel

of rat incisors that correspond to the modulation cycle of ameloblasts. (Courtesy C. E. Smith.)Figure 53 Ground section viewed by contrast-phase microscopy. In a longitudinal section of the

tooth, the striae of Retzius are seen as a series of dark lines extending from the dentinoenamel

junction toward the tooth surface and capping its tip.Figure 54 Striae of Retzius manifest on the surface of the tooth as a series of grooves called

perikymata.

Figure 55 Striae of Retzius manifest on the surface of the tooth as a series of wavelike grooves,

or Hunter-Schreger bands, as seen in a decalcified section of maturing enamel.

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Figure 56 Transmitted light image of ground section showing the alternating orientation of a

group of rods in the region of Hunter-Schreger bands.

Figure 57 Phase-contrast microscopic image of the longitudinal ground section of a calcifiedtooth.

Figure 58 Transmitted light image of cross-sectional ground section of a tooth showing a

lamella and concentric lines/bands representing the striae of Retzius.Figure 59 Ground section of a tooth showing the disposition of striae of Retzius and of enamel

tufts at the dentinoenamel junction.

Figure 60 High magnification of the dentinoenamel junction.Figure 61 Enamel tufts resemble tufts of grass in ground section.

Figure 62 Ground sections permit ready visualization of the scalloped appearance of the

dentinoenamel junction. Also note the complex trajectory of the enamel rods in the inner enamel.

Figure 63 Enamel spindles represent odontoblast processes trapped in enamel.Figure 64 Odontoblast differentiation and initial dentin formation. An acellular zone separates

the undifferentiated cells of the dental papilla from the differentiating ameloblasts. The

preodontoblasts gradually develop into tall and polarized cells with their nucleus away from the

matrix; they deposit at the interface with ameloblasts.Figure 65 Higher magnification of the acellular zone separating differentiating odontoblasts and

ameloblasts.Figure 66 The first secretory products of odontoblasts accumulate as an unmineralized layer,

predentin, that gradually mineralizes to form mantle dentin.

Figure 67 Thicker fibers of collagen (arrowheads) originate from between odontoblasts andextend into the forming mantle predentin. These fibers are referred to as von Korffs fibers.

Figure 68 Mineralization foci appear in the initial matrix deposited by odontoblasts. These foci

eventually grow and coalesce to form the mantle dentin.

Figure 69 Primary dentin. Odontoblasts border the pulp chamber and line the predentin surface.Below the odontoblasts is a cell-free zone followed by a cell-rich zone.

Figure 70 Ground section of dentin stained to demonstrate dentin phosphophoryn (mauve). Note

its absence from mantle and reparative dentin. (Courtesy Takagi Y, Sasaki S:J Oral Pathol15:463, 1986.)

Figure 71 Undemineralized section of the mature dentin-pulp complex. The vascularity of the

pulp is evident. The cell-free zone of Weil can be clearly seen beneath the odontoblast layer.Figure 72 Tooth section stained to demonstrate the nerves of the pulp. Note the plexus beneath

the odontoblast layer.

Figure 73 Histologic preparation illustrating the transformation of predentin into mineralized

dentin along a linear mineralization front (arrows).Figure 74 Globular mineralization results in an irregular mineralization front (arrows) at the

predentin-dentin interface.

Figure 75 Odontoblasts have apical processes that remain in the matrix they form.Figure 76 Silver-stained section illustrating the globular nature of the mineralization front.

Figure 77 Interglobular dentin represents unmineralized matrix regions resulting from imperfect

globular mineralization.Figure 78 Ground section of dentin showing the dentinal tubules in which the odontoblast

processes run.

Figure 79 The junction between primary and secondary dentin is characterized by a change in

the direction of dentinal tubules (arrowheads).

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Figure 80 Cellular cementum. Cementocytes have extensive cell processes that point toward the

root surface. This calcified ground section shows the lacunae and canaliculi that accommodate

the cementocyte bodies and processes, respectively.Figure 81 Pulp stone (false). Note the concentric layers of matrix and the absence of cells. Its

proximity to dentin surface suggests that it may eventually become embedded in it (attached pulp

stone).Figure 82 Ectopic calcification. Illustrated here is a free pulp stone; it is not attached to dentin.

Note the concentric layering of its matrix, which reflects a phasic growth pattern. (Courtesy P.

Tambasco de Oliveira.)Figure 83 A tooth and mandible cut in the sagittal plane. (Courtesy P. Tambasco de Oliveira.)

Figure 84 Histologic preparation illustrating the tissues supporting and investing the tooth.

These consist of cementum, periodontal ligament, alveolar bone, and that part of the gingiva

facing the tooth.Figure 85 The undersurface of a developing root. The apical foramen is still widely open and

will close when root formation is completed.

Figure 86 Forming root. Hertwig epithelial root sheath is present only on the advancing root

edge.Figure 87 Histologic section through an elongating root. The apical foramen is widely open and

delimited by a slight inward inflection of Hertwig epithelial root sheath, called the diaphragm.Figure 88 Histologic section of the advancing root edge in a rat molar during acellular extrinsic

fiber cementum (AEFC) formation. In the rat, Hertwig epithelial root sheath (HERS) is still

present when radicular dentin calcifies.Figure 89 Periodontal tissues. Note the presence of epithelial cell rests of Malassez along the

root surface.

Figure 90 Remnants of Hertwig epithelial root sheath persist in the periodontal ligament (PDL)

as clusters of cells called epithelial rests of Malassez (ERM). Cb, Cementoblast; Cc,cementocyte; CIFC, cellular intrinsic fiber cementum.

Figure 91 Light micrograph of a porcine forming root. Epithelial cell rests of Malassez (ERM)

are present in the periodontal ligament (PDL) close to the surface of acellular extrinsic fibercementum (AEFC) and sometimes appear as relatively long strands of cells.

Figure 92 In a tangential section to the tooth surface, the epithelial cell rests of Malassez appear

to form a network.Figure 93 Epithelial cell rests of Malassez. Note the abundance of heterochromatin in the nuclei.

Figure 94 Collagen fiber bundles (arrows) pass between cementoblasts and insert into

cementum.

Figure 95 Section of a human tooth extracted for orthodontic reasons. The periodontal ligamenthad been destroyed during extraction, but cementoblasts and fiber fringes extending between

them are still visible.

Figure 96 In ground sections, the granular layer of Tomes process (GLT) appears as a regioncontaining dark polymorphic structures at the interface between dentin and cementum, here of

the acellular extrinsic fiber variety (AEFC).

Figure 97 Ground section showing the transition between acellular extrinsic (AEFC) and cellularintrinsic (CIFC) fiber cementum. Note the lacunae occupied by cementoblasts in cellular

cementum.

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Figure 98 In some cases, cementum overlaps enamel at its cervical extremity. This cementum is

generally of the acellular afibrillar variety; in a porcine specimen, the overlapping cementum is

of the cellular variety, particular to this animal species.Figure 99 Phase-contrast image of the cementoenamel junction. In some cases, cementum and

enamel do not abut, leaving a region of exposed dentin (arrow) between them that may lead to

tooth sensitivity. (Courtesy P. Tambasco de Oliveira.)Figure 100 Phase-contrast image of cementoenamel junction. In the majority of cases cementum

and enamel meet end to end (arrow) along the cervical margin of the crown. (Courtesy P.

Tambasco de Oliveira.)Figure 101 Low-power view of the tooth support tissues.

Figure 102 Periodontal tissues. Note the longitudinal lines in cementum resulting from its

appositional deposition.

Figure 103 The periodontal ligament is a highly cellular and vascular connective tissue.Figure 104 A, Histologic section of periodontal tissues examined by transmitted light.AEFC,

Acellular extrinsic fiber cementum. B, Same section examined by polarized light, which allows

for readily seen striations in the cementum layer and the lamellar organization of the bone.

(Courtesy P. Tambasco de Oliveira.)Figure 105 Acellular extrinsic fiber cementum (AEFC). Some histologic stains allow

visualization of both a longitudinal layering (successive layers of cementum) and a fibrous fringeat the surface of the cementum.

Figure 106 Appositional growth lines in cellular intrinsic fiber cementum (CIFC).

Figure 107 Histologic section stained to highlight the fibrous component of the periodontalligament.

Figure 108 Specially prepared section to demonstrate oxytalan fibers in the periodontal

ligament.

Figure 109 Histologic preparation of alveolar bone examined by transmitted light microscopy.Periodontal ligament fiber bundles insert into the bone lining the alveolar socket, giving it the

name bundle bone. The inserted fibers are referred to as Sharpeys fibers. (Courtesy P. Tambasco

De Oliveira.)Figure 110 Root resorption. The lost dentin has essentially been replaced by cellular cementum,

on top of which acellular cementum has formed.

Figure 111 Periodontium. The surface of the alveolar bone shows many osteoclasts, indicatingthat it is undergoing remodeling.

Figure 112 The transseptal ligament (part of the gingival ligament) is situated just below the

junctional epithelium and extends from the cementum of one tooth, over the alveolar crest, to the

cementum of an adjacent tooth.Figure 113 Micrograph of the globular organization of salivary glands.

Figure 114 Lobule of a salivary gland showing the presence of both serous and mucous acini.

Figure 115 Salivary gland section stained to demonstrate mucous acini.Figure 116 Seromucous demilunes capping mucous acini in the sublingual gland.

Figure 117 Salivary gland immunostained to demonstrate actin in the contractile myoepithelial

cells.Figure 118 Parotid gland. Connective tissue septae divide the serous acini into lobules.

Figure 119 Higher-magnification view of parotid gland lobule.

Figure 120 Submandibular gland. This mixed gland contains both serous and some mucous

acini.

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Figure 121 Higher magnification of the submandibular gland in Figure 120. Striated ducts and

mucous acini with serous demilunes can be seen.

Figure 122 Monkey mandible in sagittal section showing the two primary molars in function andthe partially erupted first molar. Note the position of the permanent premolar tooth germs

between the resorbing roots of the deciduous molars.

Figure 123 The gubernacular canal overlying the crypt of an erupting permanent incisor. Thecanal is filled with soft connective tissue and an epithelial strand, which is the remnant of the

dental lamina.

Figure 124 Odontoclasts resorbing dentin.Figure 125 Erupting molar. Both the reduced dental epithelium, overlying the enamel space in

this demineralized section, and the oral epithelium have begun to proliferate into the intervening

connective tissue as it breaks down.

Figure 126 Erupting tooth. The reduced dental organ and overlying tissues reorganize as thetooth is about to protrude into the oral cavity.

Figure 127 Erupting molar. Fusion of the reduced dental epithelium and the oral epithelium has

occurred to form the beginning of an epithelial-lined canal.

Figure 128 The mucogingival junction (arrows) can be readily seen in a healthy dentition.Figure 129 The junctional epithelium attaches the gingiva to the tooth surface.

Figure 130 The dentogingival junction. Junctional, sulcular, and keratinized gingival epitheliumcan all be distinguished.

Figure 131 Higher magnification of the gingiva. Note the various fiber groups in the gingival

ligament.Figure 132 Free gingiva. The sulcular epithelium is not keratinized, whereas that of the exposed

gingival surface is keratinized.

Figure 133 The interdental papilla is the part of the gingiva that fills the space between two

adjacent teeth.Figure 134 Attached gingiva. Note the thick layer of keratin.

Figure 135 Mucogingival junction. Keratinized gingiva (right) and nonkeratinized mucosa (left)

are shown.Figure 136 Masticatory mucosa covering the hard palate.

Figure 137 Attached gingiva. This masticatory mucosa has no distinct submucosa. The collagen

fibers of the lamina propria attach directly and firmly to the periosteum of the alveolar bone.Figure 138 Palate. The lamina propria consists of a dense connective tissue. Fat can be found in

some regions of the submucosa.

Figure 139 Sagittal section through the tongue. The dorsal surface is covered by a specialized

keratinized and nonkeratinized mucosa, whereas the ventral surface shows a thinner,nonkeratinized epithelium. Filiform papillae cover the entire anterior part of the tongue.

Figure 140 Specialized mucosa of the tongue. Filiform papillae cover the anterior dorsal portion

of the tongue.Figure 141 Low-power view of a circumvallate papilla. The papilla is surrounded by a deep

circular groove into which open the ducts of minor salivary glands.

Figure 142 Taste buds line the lateral walls of circumvallate papillae.Figure 143 Specialized mucosa. Taste bud at the junction of the hard and soft palates.

Figure 144 Keratinized epithelium of the skin just below the vermillion zone of the lip.

Sebaceous glands and hair follicles are present within the dermis.

Figure 145 Block dissection of a human temporomandibular joint.

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Figure 146 Section through the rat temporomandibular articulation.

Figure 147 Temporomandibular articulation. The condylar cartilage undergoes typical

endochondral ossification.Figure 148 Lateral view of bones of the temporomandibular joint. (From Liebgott B: The

anatomical basis of dentistry, ed 2,St. Louis, 2001, Mosby.)

Figure 149 Mandibular fossa and articular eminence of temporal bone. A, Lateral aspect. B,Inferior aspect of the base of the skull. (From Liebgott B: The anatomical basis of dentistry, ed 2,

St. Louis, 2001, Mosby.)

Figure 150 Internal features of the temporomandibular joint. A, Sagittal section. B, Coronalsection. (From Liebgott B: The anatomical basis of dentistry, ed 2, St. Louis, 2001, Mosby.)

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