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Dental Embryology
 The development of the teeth initiates from the oral
epithelium, beginning at 40 days of intrauterine life.
In the first stage, or bud stage, there is an invagination
into the mesenchyme of the jaw that gives rise to the tooth bud or primordial
tooth. The following tissues can be
differentiated in the next stage: the inner enamel epithelium and the outer
enamel epithelium, which form a cap over the dental papilla. The dentin starts to form from outside in,
initially from the cells of the inner enamel epithelium and subsequently from
the differentiation of the cells of the dental papilla (the odontoblasts). After the first layer of dentin is organised,
the cells of the external dental epithelium (now the ameloblasts) begin to move
outwards, forming the dental enamel; the crown stage has started.
Finally, the dental pulp forms in the dental papilla and the
support tissues (the cement, the periodontal ligament and the alveolar bone) in
the dental follicle (cate T.
Histologia Orl, desamollo, estructura y function. 2nd edición.
Buenos Aires: Editorial Médica Panamericana, 1986) (Lindhe J. Tratado de
periodontia clinica e implantología oral. Tercera edición. Rio de Janeiro:
Editora Guanabara Koogan S. A. 1999).
Temporary Dentition
The temporary dentition is formed of twenty teeth, the 10
upper and 10 lower; these are called: central incisors, lateral incisors,
canines, first molars and second molars.
The first teeth begin to appear between the fourth and sixth months of
life, and start to be replaced between 6 and 7 years of age, approximately.
The principal differences with the permanent dentition
include their size (the temporary teeth are smaller), colour and resistance to
caries (they are more bluish-weight and less resistant due to their lower level
of calcification), and sensitivity, which is lower due to the smaller number of
nerve terminals.
Another difference is that separations between the teeth
(diastema) are usually present in the temporary dentition due to the larger
size that the new teeth will have (cate T. Histologia Orl, desamollo, estructura y function. 2nd
edición. Buenos Aires: Editorial Médica Panamericana, 1986)(Figón ME, Garino
RR. Anatomía odontológica functional y aplicada. Seunda edición. Buenos Aires:
El Ateneo, 1992).
Chronology of the
eruption of the primary teeth:
Sequence
|
Tooth
|
Eruption
|
|
|
Upper
|
Lower
|
1
|
Central
|
10
months
|
8
months
|
2
|
Lateral
|
11
months
|
13
month
|
3
|
1st
molar
|
16
months
|
16
months
|
4
|
Canine
|
19
months
|
20
months
|
5
|
2nd
molar
|
29
months
|
27
months
|
(click on images to enlarge)
Permanent Dentition
The permanent dentition is formed by 32 teeth, 16 upper and
16 lower; these are called: central incisors, lateral incisors; canines; 1st
premolars; 2nd premolars; and 1st, 2nd and 3rd
molars. These teeth usually complete their eruption with the appearance of the
canines at thirteen or fourteen years of age and, later, at eighteen years of
age or older, the 3rd molars appear.
The permanent dentition in women usually presents a mounded
form of the individual teeth and more harmonic angles whereas, in men, the angles
are more marked and the free borders are flatter (Figón ME, Garino RR. Anatomía odontológica functional y
aplicada. Seunda edición. Buenos Aires: El Ateneo, 1992) (Ash M. Ramfjord S.
Oclusión .Cuarta edición. México: Mc Graw-Hill Interamericana, 1996).
Chronology of the
eruption of the permanent teeth:
Tooth
|
Eruption
(age in years)
|
|
Upper
|
Lower
|
1st
molar
|
6
¼
|
6
|
Central
incisor
|
7
¼
|
6
¼
|
Lateral
incisor
|
8
¼
|
7
½
|
1st
premolar
|
10
¼
|
10
½
|
2nd
premolar
|
11
|
11
¼
|
Canine
|
11
½
|
10
½
|
2nd
molar
|
12
½
|
12
|
3rd
molar
|
20
|
20
|
Dental Caries,
Responsible Factors
Dental caries is the most common disease of the human
race. It is a demineralization of the
tooth as a result of the action of organic acids derived from the metabolism of
carbohydrates by the bacterial flora.
A classification of the factors involved in the onset of
dental caries includes: primary factors that interact together, such as the
diet, the tooth and the bacteria, together with the time factor; there are
additional secondary factors, such as the position of the tooth, its
composition, a salivary factor, age, systemic causes and race; and tertiary
factors, such as social class, education, knowledge and habits (Urzua Araya I. Stanke Celis F. Nuevas
estrategias en cariología, factores de riesgo y tratamiento. Chile: Editores
Iván Urzua Araya, Felipe Stanke Celis, 1999) ( Riethe M. Atlas de profilaxis de
la caries y tratamiento conservador. Barcelona: Salvat editors, S.A. 1990)
Stages of Caries
Caries may be classified in 2 manners. From the point of
view of the clinical course of the caries, they may be active or of rapid
progression, chronic or of slow progression, or rampant caries that affect
almost all the teeth and progress rapidly.
They may otherwise be classified according to the tissue involved: first
degree affecting the enamel; second degree affecting the enamel and dentin;
third degree affecting the enamel, dentin and pulp; fourth degree when
periapical changes are present; and fifth degree when there is dental root
disease (Barrancos Mooney
J.Operatoria dental, técnica y clinica. Buenos Aires: Editorial Médica
Panamericana, 1993) (Urzua Araya I. Stanke Celis F. Nuevas estrategias en
cariología, factores de riesgo y tratamiento. Chile: Editores Iván Urzua Araya,
Felipe Stanke Celis, 1999)(Preconc. Dra. Bordoni N, Dra. Doño R. Dra. Miraschi
C. Organización Panamericana de la Salud, 1992).
Root Canal Therapy - Endodontic Treatment
Endodontic treatment consists of the partial or total
removal of the dental pulp that, for some reason, whether due to bacterial
colonisation or trauma, cannot adequately carry out its function.
The opening or approach to the pulp cavity differs according
to each individual tooth, and this is very important for good access to the
root canals.
The elimination of the dental pulp or its remnants and the
decontamination of the dentin wall may be performed manually or with mechanical
devices.
After cleaning the root canals, they are usually sealed with
gutta percha and different types of endodontic cement (Maisto OE. Endodoncia. Cuarta edición. Argentina:
Mundi, 1984)(Cohen Burns. Endodoncia, los caminos de la pulpa. 5ta. Edición.
México: Editorial Médica Panamericana, 1995).
Dental Trauma
In cases of trauma, the consequences for the tooth may
differ depending basically on the intensity of the trauma. Dental fracture due to trauma may or may not
affect the dental pulp, or the trauma may leave it exposed. In other cases, the tooth may be luxated and
return to its position either spontaneously or with external aid, or it may be
completely avulsed.
In the case of pulp exposure, endodontic treatment is
usually required, with a later reconstruction of the crown by whatever method
is indicated. If luxation occurs, the
tooth should be repositioned and splinted for a certain time. If the tooth is avulsed, its replacement may
be attempted if it has not been contaminated.
The avulsed tooth may be preserved in saline solution, milk
or even in the patient's mouth, until it is reinserted (Andreasen JO. Andreasen FM, Bakland LK, Flores MT:
Traumatic Dental Injuries. A Manual. Copenhaguen: Munksgaard, 1999) (Blomlof L,
Milk and saliva as possible storage media for traumatically exarticulated teeth
prior to replantation. Swed. Dent J. 1981; Suppl 8: 1-26).
Impacted Third Molar
The third molar is the tooth that presents the highest index
of impaction of the whole dental arch.
The reason for this is usually lack of the space that is
required for its eruption. The
indications for extraction (exodontias) include a lack of space for eruption,
an abnormal position of the tooth, pericoronitis, caries, or the presence of
cysts. Extraction is contraindicated
when sufficient space is available for eruption of the tooth, if the patient's
state of health is compromised, or in teeth that have shown no symptoms despite
being impacted for 30 to 35 years (Koemer KR, Tilt LV, Johnson KR. Atlas color de cirugía oral menor.
Barcelona: Editorial Espaxs, 1995).
Consequences of Tooth
Loss
The loss of a tooth gives rise to a significant
disequilibrium in the masticatory system.
A tooth remains in its position thanks to the support given by
neighbouring teeth, the antagonist tooth and contact with the tongue and
cheeks. When a tooth is lost, the
posterior tooth begins to deviate forwards and the anterior tooth backwards,
and the opposing tooth begins to extrude.
This leads to the loss of the point of contact of the teeth, generating
gingival and periodontal problems between neighbouring teeth.
In this way, dental loss that started with a single tooth
extends to the other teeth )(Figón
ME, Garino RR. Anatomía odontológica functional y aplicada. Seunda edición.
Buenos Aires: El Ateneo, 1992).
Restoration of Caries
of the Enamel and Dentin
The dentin and the enamel present different physical
characteristics and, therefore, when restoring a tooth, a material should be
chosen that can replace the lost tissue in the best possible manner.
Glass ionomers have physical characteristics similar to
those of dentin, and are therefore usually chosen to replace this tissue; this
technique, commonly called the "sandwich" technique, uses composite resins to
substitute the lost enamel. The
composite resin is formed of ceramic particles in an organic matrix and,
depending on the size and the relative proportion of the particles, provides
similar physical characteristics to the enamel (Hidalgo Lostaunau RC, Técnica Sandwich con acondicionamiento
ácido selective empleando ionómeros de alta viscosidad y resinas de
nanorelleno. Endoroot.com
http://www.endoroot.com/estetica/articulos/tecnicasandwich.html) (Schwartz J. y
col. Reducing microleakage with the glass ionomer resin sandwich technique.
Oper Dent 1990: 15: 1286-92).
 
Amalgam
The silver, copper and mercury amalgam is the tooth
restoration material that has been most widely used to date. This is due to its excellent cost/benefit
ratio and it is therefore very likely that even though more modern and aesthetic
dental restoration materials exist, this material will continue to be used for
a long time. A large quantity of copper
has been added to the classic amalgams, eliminating the gamma 2 phase that led
to a higher susceptibility of the amalgam to corrosion. For this reason, the amalgam alloys currently
used are called non-gamma 2. The amalgam
is inserted into the cavity as a paste, compacted, remodelled and, after
hardening, polished (Riethe M.
Atlas de profilaxis de la caries y tratamiento conservador. Barcelona: Salvat
editors, S.A. 1990)
 
Dental Bridge
The dental bridge is a prosthetic solution to replace one or
several absent teeth. Nowadays this
device is used less frequently due to the excellent results obtained with
dental implants. A bridge is composed of:
a0 the crowns fixed on to the tooth remnants; b0 the pontic span; and c0 the
connectors that unite the bridge to the crowns.
The number of teeth that can be replaced by a single bridge is
calculated using Ante's law, which states that the surface area of the teeth to
be replaced must be equal to or less than the surface area of the abutment
teeth. Different designs exist for the
support of the pontic span on the gum, and these depend on the objective to be
achieved, which may be aesthetic or functional (Shillingburg H, HoboS, Whitsett L. Fundamentals of fixed
prosthodontics. Tercera edición. Berlin: Quintessence Publishing Co Inc.,
1997)(Lang MP, Siegrist Guldener BE. Atlas de prótesis de coronas y puentes.
Planificación sinóptica de tratamiento. Barcelona: Masson S.A. 1995).
Pericoronitis
Pericoronitis is the inflammation that occurs in the gum
around a tooth that has still not fully erupted.
This situation is usually most common in the lower third
molars, although it can occur with any tooth in the mouth.
The gum forms a pericoronal pouch or sac in which food
remnants and microorganisms accumulate, leading to an inflammation of the
gum. The area usually becomes
haemorrhagic and very sensitive to
swallowing or even to opening and closing the mouth. Lymph node changes are sometimes observed in
the floor of the mouth and in the neck.
Repetitive pericoronitis is often one of the indications for the
extraction of a third molar (Carranza
Newman. Periodontologia clinica. Octava edición. México DF: McGraw-Hill
Interamricana editors, S.A. de C.V. México DF, 1998)(marsh P, Martin MV. Oral
Microbiology.4ta. ed. Great Britain: Wright, 1999) (Aspectos microbiológicos de
la pericoronitis. Acta odontológica Venezolana 2005;43(1). http://www.actaodontologica.com/43_1_2005/aspectos_microbiologicos_pericoronitis.asp).
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