Second Exam Text<br>
<br>
<h3>
ODONTOGENIC TUMORS INTRODUCTION<br>

This study set was written for undergraduate and graduate students. It focuses
on the most commonly encountered tumors, omitting the more rare entities. <br>
<br>
As a group, odontogenic tumors are uncommon. The following provides
perspective. At one large university, analysis of 54,534 surgical specimens
from an oral pathology laboratory uncovered 706 odontogenic tumors. The
breakdown was as follows<br>
<br>
78--Ameloblastoma<br>
6---Calcifying epithelial odontogenic tumor<br>
22--0dontogenic adenomatoid tumor<br>
15--Calcifying odontogenic cyst<br>
20--Myxoma<br>
1---Cementoblastoma<br>
11--Cementifying fibroma<br>
54--Cementoma<br>
15--Ameloblastic fibroma<br>
11--Ameloblastic fibro-odontoma<br>
259-Compound odontoma<br>
214-Complex odontoma<br>
        TOTAL=706<br>

<br> 
The term "odontogenic" refers to those tissues in the jaws that form teeth. In
order to understand the histologic features of these tumors, it is necessary to
know how a tooth forms and how normal odontogenic tissues appear
microscopically. <br>
<br>
Teeth differ embryologically from most other organs in that they are derived
from two germ layers. Most organs trace their origin to a single germ layer.
Both ectoderm and mesoderm contribute to the making of a tooth. <br>
<br>
Odontogenesis begins at about the sixth week of development when the embryo is
only a little more than a centimeter long. At each point where a tooth is to be
formed, a cord of basal epithelial cells grows down and penetrates the
underlying mesoderm. The cord of epithelium is called the dental lamina (slide
#1, frame 1). The cells at the deep end of the lamina increase in number and
spread laterally and down to produce a bell-shaped structure called the
enamel-organ (slide # 1, frame 2). <br>
<br>
At this stage something unusual happens. The epithelium exerts an influence on
the mesoderm enclosed in the concavity of the "bell". The mesoderm becomes more
cellular and we say it has become "induced" to become odontogenic connective
tissue (slide #1, frame 3). As a result of this inducement, the mesoderm is now
capable of helping the epithelium form a tooth. This new "odontogenic" mesoderm
is called the dental papilla. (slide # 1, frame 4) <br>
<br>
The interface where the epithelium meets the dental papilla will become the
junction where the enamel joins dentin (DE junction). <br>
<br> 
At the same time the epithelium is inducing the mesoderm, the epithelium is
changing.  Four layers become discernible within the enamel organ. The inner
layer of epithelial cells that abut on the papilla become tall, columnar cells
with their nuclei aligned at one end of the cell, the end away from the
dentinoenamel junction. The cells are aligned in a row (palisaded) and the
nuclei are said to be "polarized" because they have all migrated to one end of
the cell. These columnar cells are the ameloblasts, the cells that will secrete
enamel matrix. They are called the "inner enamel epithelium." Just outside them
on the 44 nuclear" end there is a shallow layer of spindle-shaped cells 2-3
cells deep. This layer is called the stratum intermedium.  Its function is not
known. The long axis of the cells in this layer is parallel to the DE junction
and at a right angle to the long axis of ameloblasts. Outside the stratum
intermedium is a fairly thick area that is less cellular. The cells are
star-shaped (stellate). This area is called the stellate reticulum.  The fourth
and outermost layer of the enamel organ is the outer enamel epithelium. These
layers are all visible in the enlarged circle (slide #1, frame 4). <br>
<br>
As the innermost cells of the enamel organ are differentiating into
ameloblasts, across the DE junction the outermost cells of the dental papillae
are also undergoing change. They too are becoming columnar and palisaded with
polarized nuclei. The nuclei, like those in ameloblasts, become polarized to
the end of the cell farthest from the DE junction. They are tall columnar cells
but are not as tall as ameloblasts. These cells are odontoblablasts. (Because
they are the cells that will soon form dentin, it would make more sense to call
them dentinoblasts!) <br>
<br> 
The stage is set for tooth formation.  The dental lamina, having given birth to
the enamel organ, retracts and disappears.  Sometimes small clusters of lamina
cells persist indefinitely in the gingiva and bone surrounding teeth. These
embryonic remnants are called "rests of Serres," in the gingiva and "rests of
Malassez" in the periodontal membrane. They may be one source of tumors and
cysts in adults. <br>
<br>
Slide #2 is a low-power view of a developing tooth. Arrow 1 points to the oral
squamous mucosa. Arrow 2 points to the dental lamina which is almost totally
involuted. Arrow 3 points to the inner enamel epithelium. Arrow 4 points to the
row of odontoblasts and 5 points to the middle of the dental papillae. Arrow 6
pinpoints stellate reticulum and 7 the outer enamel epithelium. The stratum
intermedium cannot be seen at this low magnification. <br>
<br>
Slide #3 is a higher-power view of the previous slide. Arrow 1 points to
stellate reticulum, 2 points to a row of ameloblasts (inner enamel epithelium),
arrow 3 identifies a row of odontoblasts and 4 the middle of the dental
papillae. The clear cleft between ameloblasts and odontoblasts is separation
artifact. <br>
<br>
Slide #4 is a high-power view of the area blocked off in slide #3. Arrows 1 and
2 identify ameloblasts. Arrow 1 is in the cytoplasm and 2 is located in the
vicinity of the nuclei. You can see how the nuclei are displaced to the end of
the cell away from the DE junction. Arrow 7 indicates the separation artifact
that is commonly seen at the DE junction. Arrow 3 identifies the thin zone of
stratum intermedium and arrow 4 is in the stellate reticulum. Cells at arrow 5
are odontoblasts which resemble mirror images of ameloblasts except they are
shorter.  Arrow 6 points to the dental papilla which will eventually become the
dental pulp.  Notice how much the papilla (mesoderm) resembles the stellate
reticulum (ectoderm). <br>
<br>
Dentin is formed first. As soon as a small amount of dentin has been deposited,
the ameloblasts start laying down enamel. <br>
<br>
Earlier it was said that the enamel organ exerts an influence on the underlying
mesoderm that causes the mesoderm to become odontogenic connective tissue which
we call dental papilla. The cells of the papilla nearest the ameloblasts then
differentiate into odontoblasts. This influence has been called "induction."
<br>
<br>
If there is failure of the oral ectoderm so that dental lamina (and the enamel
organ) is not formed, induction doesn't take place. <br>
<br>
There is a genetic condition that illustrates what happens if the ectoderm is
faulty. The condition is known as x-linked hypohidrotic ectodermal dysplasia.
Sweat glands, hair follicles and enamel organs are all of ectodermal origin.
Because of the faulty ectoderm, affected children have diminished hair, few
sweat glands and teeth are abnormally shaped or absent. Slide #5 is the profile
of a 6-year-old boy with this condition. He has no eyebrows nor eyelashes and
his head hair is sparse. Slide #6 shows his lower teeth. At age 6 he should
have about 12 teeth in the lower jaw. He has 5, all of which are abnormally
cone shaped. The other teeth are missing because the ectoderm failed to produce
the normal number of dental laminas. <br>
<br>
Ectodermal dysplasia illustrates failure of ectodermal induction of the
mesoderm. Differentiation of the mesoderm to become dental papilla is dependent
on the presence of a normal lamina and enamel organ. If the papilla were
independent of the enamel organ, in ectodermal dysplasia children would have a
normal complement of teeth, but they would lack enamel. It is clear that the
epithelium determines the shape of the tooth as well as the number of teeth.
<br>
<br>
Brief mention should be made of another event that has been called 44
reciprocal induction" or "induction in reverse." Earlier it was mentioned that
dentin is always laid down before enamel even though ameloblasts differentiate
before odontoblasts. The synthesis of dentin by odontoblasts somehow signals
the ameloblasts to make enamel. The influence that dentin production exerts on
the ameloblasts (to produce enamel) has been called "reciprocal induction".
Tumors mimic normal tissue from which they are derived. Odontogenic tumors that
make both enamel and dentin will always make dentin first. It should be
possible for a tumor to make dentin alone or both dentin and enamel, but it
should be impossible for a tumor to make only enamel. <br>
<br>
Before the individual odontogenic tumors are presented, a few comments are in
order concerning tumors and the tissue in which they grow. <br>
<br>
All tissues depend on a supply of nutrients. Like a smart general, the body
keeps its supply lines short. No cell, with the possible exception of
chondrocytes, is far removed from the nourishment of blood. <br>
<br>
There is evidence that tumor cells secrete factors (tumor-derived angiogenic
factors) that leak into the surrounding tissue inducing fibroblasts and blood
vessels to proliferate. Fibroblasts form a scaffolding that provides structural
support for tumor cells. New blood vessels assure that tumor cells will never
be far removed from a blood supply. Thus, a tumor provides for its own
survival. <br>
<br>
        The proliferation of supporting connective tissues (chiefly fibroblasts
and blood vessels) is called the "stroma" of the tumor. <br>
<br>
So the usual tumor consists of two populations of cells: a neoplastic group and
non-neoplastic supporting stroma. Presumably, if one could take all the
neoplastic cells from the stroma, the stroma would fade away. <br>
<br>
In some cases, however, such as ameloblastic fibroma of the jaws and
fibroadenoma of the breast, the stromal cells also become neoplastic so that
both populations are neoplastic. <br>
<br> 
CLASSIFICATION OF ODONTOGENIC TUMORS (Slide #7) <br>
<br>
A.      Tumors that histologically mimic the epithelial portion of the tooth
germ (dental lamina and enamel organ) but which exhibit no inductive effect on
mesoderm. <br>
<br>
----1.      Ameloblastoma<br>
----2.      Odontogenic adenomatoid tumor<br>
----3.      Calcifying epithelial odontogenic tumor (Pindborg) <br>
<br>
B.      Tumors that histologically mimic odontogenic epithelium and mesoderm
and therefore exhibit induction and in some cases, reciprocal induction. <br>
<br>
----1.     Ameloblastic fibroma<br>
----2.      Ameloblastic fibro-dentinoma<br>
----3.      Ameloblastic fibro-odontoma<br>
----4.      Odontoma, compound and complex<br>
<br>
C.      Tumors that histologically mimic odontogenic mesoderm. <br>
<br>
----1.      Odontogenic Myxoma<br>
----2.      Odontogenic Fibroma<br>
----3.      Cementoblastoma (true cementoma) <br>
<br>
AMELOBLASTOMA<br>
<br> 
This is the most common of the three epithelial odontogenic tumors. It affects
males and females equally. This tumor avoids the extremes of life, the mean
ages of patients is between 35-45 years of age. <br>
<br>
The tumor is usually asymptomatic in the early stages. Expansion of overlying
bone is often the first sign. Pain or numbness are infrequently seen. <br>
<br>
Approximately 90% of ameloblastomas are found in the mandible, the remainder in
the maxilla. Within the mandible the posterior portions the molar-ramus are
most often involved. <br>
<br>
Radiographically the classic appearance is a multilocular radiolucency. The
terms "honeycomb" and "soapbubble" appearance are often used. This tumor may
also be unilocular or unicystic (one cavity). As the tumor enlarges, the roots
of nearby teeth may be pushed out of normal alignment and drift in the tumor.
Roots of teeth may be partially resorbed. <br>
<br>
Slide #8 illustrates early mandibular expansion in a patient with
ameloblastoma, slide #9 is a more advanced case. Radiographs labeled 10, 11,
12, 13, 14, and 15 are all ameloblastomas. Slides # 10 and # 11 are small
tumors and illustrate the soapbubble appearance. Slides #12 and #13 are more
advanced tumors and slide #14 is a large tumor. Slide #15 illustrates a
unicystic tumor. Unicystic ameloblastomas occur at a younger age (second and
third decades) and approximately 75% occur in the molar ramus region. They can
easily be confused with a dentigerous cyst radiographically. <br>
<br>
The histology of ameloblastmoa is variable.  Slide #16 is a low-power view in
which one can see islands of epithelium separated by stroma composed of fibrous
connective tissue. Slide # 17 is a higher magnification of a single island of
epithelium surrounded by stroma. One can see the tendency of the outermost
cells of the island to become palisaded thus mimicking ameloblasts of the
enamel organ. Just inside the outer layer, the cells resemble stellate
reticulum. The middle of the island is more eosinophilic because the central
cells have undergone differentiation into squamous epithelium (squamous
metaplasia) and have formed keratin. This commonly occurs in ameloblastomas.
Rarely an ameloblastoma will undergo so much squamous differentiation that
squamous cells dominate histology. Such a tumor is referred to as an
"acanthomatous" ameloblastoma. Slide #18 is a high-power view of a portion of a
single island of tumor tissue. The peripheral columnar cells, the tumor
equivalent of ameloblasts, are easily seen. The fibrous stroma adjacent to the
island is "non-induced." <br>
<br>
A histologic subtype of ameloblastoma referred to as granular cell
ameloblastoma is illustrated in slides #19 and #20. The latter is the
high-power view. Instead of cells resembling ameloblasts and stellate
reticulum, they appear as large cells with small nuclei and abundant pink,
granular cytoplasm. Though few cases have been reported, there is a hint this
type tumor may be more aggressive. <br>
<br>
Ameloblastomas lack a capsule. Fingers and islands of tumor cells extend
outward from the main body of the tumor into surrounding marrow spaces. Thus
the tumor is always larger than it appears on radiographs. Metastasis from
ameloblastoma is a rarity, but they are locally aggressive tumors. Surgical
resection is the treatment of choice. <br>
<br>
Simple curettage is usually followed by recurrence.  Radiation therapy is used
as adjunctive treatment or in those tumors not amenable to surgery.  The extent
of surgery varies with the size of the lesion. Small tumors may be totally
removed along with a block of surrounding normal bone. Surgeons call this an
"en-bloc" procedure. Slide #21 is a photograph of a gross specimen removed
en-bloc. Larger tumors may require removing a larger segment of bone. Slide #22
is a photograph of the gross specimen in which a large portion of the jaw was
resected. Slide #23 is a post-surgical film of such a procedure in which the
resected bone was replaced with a metal mesh tray filled with normal marrow
(from the iliac crest). Slide #24 is a cross-section of a mandibular
ameloblastoma. Bone is greatly expanded. White areas are solid tumor. Cystic
spaces which are often formed in this tumor appear as empty cavities. <br>
<br>
Unicystic ameloblastoma typically require a more conservative enucleation with
only a 10% recurrance rate reported. <br>
<br>
Ameloblastomas are derived from 4 sources: The remnants of Hertwig's epithelial
root sheath known as "rests of Malassez." These rests appear as small clusters
of cells within periodontal membrane. These rests are illustrated in slide #25.
(The solid area is tooth root.) (2) The epithelial lining of cysts is thought
to be the source of some ameloblastomas. Slide #26 shows what appears to be a
typical dentigerous cyst around a mandibular third molar. Microscopic
examination of this lesion revealed it was an ameloblastoma. Such tumors have
been referred to as "cystic ameloblastomas" (3) Basal cells of oral epithelium
may rarely give rise to ameloblastoma. These tumors appear as a mass on the
surface of bone in the gingiva and are known as "peripheral" ameloblastoma. 
(4)  Rests of Serres may be a potential source of  ameloblastoma. <br>
<br>
 
Exceedingly rare cases of ameloblastomas become dysplastic with histologic
features associated with malignancy. These tumors are known as ameloblastic
carcinoma or malignant ameloblastomas. <br>
<br>
The tumors are uniformly aggressive, frequently recur and may metasize to lymph
nodes and lungs. <br>
<br>
ODONTOGENIC ADENOMATOID TUMOR (O.A.T.) <br>
(Adenomatoid Odontogenic Tumor) <br>
<br>
In a review of 111 cases, the age range was 5 to 53 years; mean age was 17.8
years. This is a tumor of teenagers and young adults. Two-thirds of the
patients were female and 65% were in the maxilla. The anterior portion of the
jaws is the most common site, 76% are in the cuspid-incisor area. <br>
<br>
The most common presenting symptom is a painless swelling of the affected jaw.
Extraoral swelling does occur but only in advanced tumors. <br>
<br>
Radiographically this tumor often masquerades as a dentigerous cyst; associated
with the crown of an unerupted tooth.  All are unilocular with a sharply
circumscribed border. Most tumors are purely radiolucent but occasional O.A.T.
will have calcifications that may be seen on the radiograph. Slides #27 and #28
are typical. Each is associated with an unerupted tooth and the resemblance to
dentigerous cyst is apparent. Slide #29 is a larger O.A.T. The medial borders
are marked with double arrows and the unerupted cuspid tooth with which this
tumor was associated in labeled "X".  "O" is a lateral incisor displaced by the
tumor and the lateral most arrow designates the outer aspect of the tumor.
Careful examination reveals small spots of calcification within the tumor
visible in the vicinity of the cuspid cusp. Slide #30 is a lateral oblique film
of the mandible. A huge O.A.T. occupies the body of the mandible with a
bicuspid tooth visible at the inferior pole. Slide #31 is the gross tumor seen
in slide #30. The tumor has been transected. It has a capsule around it and the
tooth is at the left lateral pole. <br>
<br>
Low-magnification of the histologic features are seen in slide #32. A portion
of the capsule is seen at the right margin, the balance is tumor tissue.
Rounded balls of cells can be seen; they are surrounded by a network of cords
of tumor cells. Slide #33 is a higher magnification of a ball of tumor cells,
they are referred to as rosettes. The X is at the center of the rosette and the
arrow identifies a small necklace of spindle cells which usually surround the
rosettes. It has been suggested these spindle cells are the tumor equivalent of
stratum intermedium of the enamel organ. Slide #34 a is low magnification that
illustrates two rosettes which have formed duct-like structures, slide #35
shows a duct. In three dimentions, these ducts are actually globes. They appear
to be rosettes in which the central cells have disappeared. Why a tumor should
form such a structure is unknown; there is no equivalent structure formed in
normal tooth formation. <br>
<br>
Though the tumor has a thick fibrous connective tissue capsule, there is sparse
stroma within the tumor. The areas of dystrophic calcification that may be seen
on the radiograph are not illustrated in your photomicrograph. Slide #36 shows
a small "smudge" of eosinophilic material often seen in this tumor.  Its
composition is unknown.  Some authors contend it is atypical dentin, others
believe it to be enamel matrix. From a theoretic standpoint, it cannot be
enamel. Since the tumors shows no "induction" of mesoderm, there can be no
"reciprocal induction" necessary to the formation of enamel matrix. <br>
<br>
Conservative treatment such as curettage is the treatment of choice. The tumor
easily shells out due to the capsule. Recurrence of an O.A.T. has not been
recorded. <br>
<br>
CALCIFYING EPITHELIAL ODONTOGENIC TUMOR (CEOT) <br>
<br>
Recognized as a specific tumor in 1955, the CEOT is a rare lesion constituting
less than 1% of all odontogenic tumors. Jens Pindborg, a Danish oral
pathologist, is credited with first reporting this tumor and it often is called
"Pindborg tumor." <br>
<br>
The vast majority of these tumors are located in the molar-premolar region of
the mandible. There is no sex predilection and the mean age is around 40 with a
very wide range. Most lesions are asymptomatic. <br>
<br>
The radiographic characteristics are variable, ranging from those that are
purely radiolucent to those that are radiodense. Early lesions are usually
radiolucent and unilocular but tend to become multilocular as the tumor grows.
Approximately one-half are associated with an unerupted tooth. Many have the
radiographic appearance of a dentigerous cyst. <br>
<br> 
Slide #37 is a lateral oblique x-ray of a large honeycombed tumor that fills
the body of the mandible; tumor borders are indistinct and an unerupted tooth
is visible at the inferior pole of the tumor. <br>
<br>
The histologic features of CEOT are illustrated in slides #38, #39 and #40. In
slide #38 (low power) the upper portion is dominated by a large sheet of tumor
cells. Pale stroma is seen in the lower portion of the slide. Within the stroma
(arrow, slide #38) there is a Pale, homogeneous eosinophilic material of
controversial nature. The most prevalent theory is that the material amyloid.
<br>
<br>
Slide #39 is a medium magnification. Variation in size of tumor cell nuclei may
now be seen, and a purple calcified body is seen just off center. This
calcified structure is thought to be calcified amyloid and the radiographic
appearance of the tumor varies with the amount of calcification. Scant
calcification results in a tumor that is radiolucent whereas extensive
calcification produces a predominately radiodense lesion. Concentric
calcifications are known as Lisegang rings. <br>
<br>
Slide #40 is a high-power photomicrograph. One of the histologic hallmarks of
this tumor is the variation in size and shape of tumor nuclei, readily seen in
this slide. Nucleoli are also greatly enlarged. Intercellular bridges connect
adjacent cells; this lends a "squamoid" appearance to the tumor. <br>
<br>
From a histologic standpoint, CEOT does not have an odontogenic appearance.
There are no cells that resemble ameloblasts', stellate reticulum or dental
papilla. <br>
<br>
Surgical removal of the tumor, enucleation or resection is the treatment.
Recurrence rate appears to be about 20%. The atypical epithelial cells may
histologically suggest a malignancy, but CEOT behaves as a benign lesion.
<br> 
<br>
AMELOBLASTIC FIBROMA<br>
<br>
This is a tumor of children and teens, although they occasionally occur in
adults. There is no sex preference and the mean age of patients is
approximately 12 years. The mandible molar region is the most common site and
like many odontogenic tumors, the usual symptom is painless swelling of the
affected jaw. <br>
<br>
Radiographically the ameloblastic fibroma presents as a unilocular or
multilocular radiolucency. The tumor may be associated with an unerupted tooth.
Slide #41 illustrates a small tumor, overlying the crown of a lower molar
tooth. <br>
<br>
This tumor has a limiting capsule and seldom recurs following curettage. <br>
<br>
The histologic features of ameloblastic fibroma are distinctive. Slide #42 is a
low magnification. A portion of the thick fibrous connective tissue capsule is
seen on the left. The tumor appears as thin cords and islands of epithelium
embedded in a stroma of primitive mesoderm. Slide #43 magnifies the previous
slide. Some of the epithelial cords have enlarged and exhibit peripheral
palisading of columnar cells with the central areas resembling stellate
reticulum. The stroma is cellular, collagen poor and rich in mucopolysaccharide
ground substance. The primitive mesodermal tissue resembles dental papillae.
Slide #44 illustrates the stroma at high power. A small portion of epithelium
is seen in the upper right comer. In some ameloblastic fibromas, the epithelium
never opens up to form large islands.  Such a tumor is seen in slides #45 and
#46, in which the epithelium appears as narrow cords of small, round cells.
<br>
<br>
As we ascend the ladder of increasing differentiation of odontogenic tumors,
the ameloblastic fibroma is the earliest tumor on which induction of the
mesoderm has occurred. This explains why the stroma resembles dental papillae.
<br>
<br>
It has been suspected that some ameloblastic fibromas undergo further
maturation because otherwise typical ameloblastic fibromas will sometimes be
found to contain dentin. Such tumors have been designated "ameloblastic
fibro-dentinoma." <br>
<br>
Further differentiation mimicking the development of a tooth would be an
ameloblastic fibroma that produces both dentin and enamel. This tumor is called
an ameloblastic fibro-odontoma. <br>
<br>
While this concept of maturation of ameloblastic fibromas appears logical, some
research refutes this and supports the idea that ameloblastic fibromas do not
mature. <br>
<br>
ODONTOMA<br>
<br>
Odontomas are the most common odontogenic tumor and represent the highest
degree of odontogenic differentiation. In most tumors mature ameloblasts and
odontoblasts secrete enamel and dentin that dominate the tumors. In the
majority of odontomas, the tumor so faithfully mimics normal odontogenesis
forming tooth-like structures. This variety is known as compound odontoma.
Other odontomas are composed of enamel and dentin but in a disorderly
arrangement so there is no resemblance to teeth.  This type is referred to as a
complex odontoma. <br>
<br>
 
All authors agree the tumor is seen chiefly in teens and young adults with most
cases discovered between the ages of 10-30. All regions of the jaw are
affected. Compound tumors are, more common and favor the cuspid-incisor area.
Complex odontomas are found more often in the premolar-molar area. Most are
located above the crowns of unerupted teeth. (One or more odontomas may occur
in Gardner's syndrome, an inheritable condition characterized by intestinal
polyps, multiple osteomas and fibromas and cysts of the skin. The intestinal
polyps occur chiefly in the colon and show a high rate of malignant change.)
<br>
<br>
Compound odontomas are among the most easily diagnosed tumors; radiographs are
virtually pathognomonic. Compound odontomas are illustrated in slides #47-50.
Slide #47 is a small, incipient lesion. Multiple tooth-like structures are
easily seen in slides #48, #49, and #50. Slide #51 is a picture of teeth
removed from an odontoma. Slide #52 is a photomicrograph of a compound tumor.
The resemblance to teeth is obvious. The 'X' is in the pulp of a "tooth" and
arrow 1 points to dentin and arrow 2 to enamel matrix. Slides #53 and #54 are
complex tumors; the tumor in #53 has also formed a dentigerous cyst which is
the radiolucent portion. The combination of cyst and tumor associated with an
unerupted tooth is not rare. The tumor in slide #54 is about a large as they
come. Although benign, its sheer size creates a problem. <br>
<br>
Slides #55 and #56 illustrate the microscopic aspects of a complex tumor. Slide
#55 is low-power and one can see the tumor consists of a mixture of calcified
tissues bearing no resemblance to teeth. Slide #56 is a higher-power view.  The
two more deeply stained prongs are dentin and the pale matrix is enamel.  Slide
#57 illustrates a complex odontoma associated with the crown of an unerupted
lower second molar tooth. Complex odontomas often have "a frayed margin or
sunburst appearance" that may mimic the radiographic features of osteogenic
sarcoma. <br>
<br>
The treatment of odontomas is surgical removal. Most odontomas have a limited
growth potential. Once the predetermined size is reached, growth stops. Such
lesions behave more like developmental abnormalities or hamartomas than true
neoplasms. Once removed, they do not recur. <br>
<br>
As previously noted some odontogenic tumors with histologic features of an
ameloblastic fibroma also produce enamel and dentin and are called ameloblastic
fibro-odontomas. <br>
<br>
ODONTOGENIC MYXOMA<br>
<br>
The myoma is a benign tumor composed of a loose myxoid fibrous tissue that is
similar to the dental papilla or primitive mesenchymal tissue. Since similar
tumors are not usually found in other parts of the body, the tumor is
designated as an odontogenic neoplasm. <br>
<br>
The myxoma is rare, with the typical presentation being a multilocular
radiolucency with indistinct borders. They are most commonly diagnosed in the
second and third decades with the posterior mandible being a slightly more
common site than the maxilla. These tumors may be aggesssive in their behavior
destroying considerable bone, and in the maxilla invading the antrum.
Moderately high recurrence rates are reported if a complete resection is not
performed.  Partial mandibulectomy or maxillectomy may be necessary in large
tumors. <br>
<br>
Radiographically these are totally radiolucent lesions, multilocular and often
expansite. The remaining bone trabeulae left in the areas of resorption often
have a "wispy" or reticulated spider web like appearance. <br>
<br>
Slides #58 and #59 illustrate the multilocular pattern of myxoma. They may also
be unilocular as seen in slide #60. Teeth may be separated and drift in the
tumor or roots may be partially resorbed. <br>
<br>
Microscopically, myxoma is composed of young fibroblasts that are more devoted
to the synthesis of mucopolysaccharide ground substance than to the production
of collagen fibers. For this reason, tumor cells lie in a collagen-poor,
mucopolysaccharide-rich stroma. Mucopolysaccharides stain poorly with routine
stains so that the tumor cells lie in a pale background. Nuclei of tumor cells
are usually spindle shaped or angulated. Some cells may have several sharp
cytoplasmic projections lending a star (stellate) shaped appearance. Slides #61
and #62 are low and high-power photomicrographs of myxoma. <br>
<br>
ODONTOGENIC FIBROMA<br>
<br>
Since this is a very rare odontogenic tumor, there will be a limited
discussion. It is a benign tumor of the jaws that has a predilection for the
anterior maxilla and is more common in females. It is a benign tumor of mature
fibrous connective tissue (not loose myxoid tissue as in the odontogenic
myxoma) that contains widely scattered cords and nests of odontogenic
epithelium. Despite the unencapsulated borders surgical curettage results in a
very low recurrence rate.  The lesions as expected are totally radiolucent and
may cause root resorption of adjacent teeth.  These lesions may mimic
periapical pathology of pulpal origin. A radiograph of an odontogenic fibroma
is illustrated in slide #63. <br>
<br>
CEMENTOBLASTOMA (TRUE CEMENTOMA) <br>
<br>
Cementoblastoma is a tumor of cementoblasts that occurs most commonly in teens
and young adults. There is no apparent sex predilection. Eighty percent of all
cases are in the molar-premolar region of the jaws. <br>
<br>
Clinically, this lesion may produce expansion of the jaw. Pain is sometimes
present. The tumor does not usually impair tooth vitality. <br>
<br>
Radiographically this tumor is distinctive. It grows as a radiodense mass
attached to the root of a tooth. A halo of radiolucency surrounds the mass and
tooth root may be partially resorbed. Slide #64 is a before and after view of a
cementoblastoma. Slide #65 is an extracted tooth with tumor attached and #66 is
an x-ray taken after extraction. <br>
<br>
This tumor does not exhibit the 3 stages of growth seen in simple cementomas;
it does not progress from a radiolucent to a radioplaque lesion. <br>
<br>
Occasionally cementoblastoma will display a peripheral sunray or sunburst
pattern which may be mistaken radiographically for osteogenic sarcoma. (This
may also occur in complex odontomas.) <br>
<br>
Histologically the dense material is a rather solid mass of cementum attached
to the root with scant tumor stroma. Tumor cells in the radiolucent zone may
exhibit enlarged and hyperchromatic nuclei and one must guard against
over-diagnosing this tumor as a sarcoma.  Slide #67 is a cementoblastoma.  The
acellular material which dominates the upper half of the slide is cementum. A
small rim of normal bone (arrow) is seen at the periphery. Sandwiched between
is the cellular zone. Shrinkage artifact separates the cementum from the
cellular zone. <br>
<br>
Treatment is conservative surgical excision, including the involved tooth. <br>
<br>
ODONTOGENIC HAMARTOMA<br>
<br>
A non-neoplastic developmental overgrowth of tissue native to the area is
referred to as a hamartoma. Slide #68 and #69 illustrate children with small
nodules on the gingiva, which consist of developmental malformation of dental
tissues referred to as "odontogenic hamartoma." <br>
<br>
Microscopically they consist of small foci of odontogenic mesoderm (papilla)
and frequently have small cords and islands of odontogenic epithelium. Slides
#70 and #71 illustrate these features. These nodules have very limited growth
potential, seldom achieving a size beyond those shown here. <br>
<br>
Treatment is excision. <br>
<br>