There is no pulp necrosis or calcific metamorphosis of pulp induced by orthodontic treatment: biological basis

Abstract

To biologically explain why the orthodontic treatment does not induce pulp necrosis and calcific metamorphosis of the pulp, this paper presents explanations based on pulp physiology, microscopy and pathology, and especially the cell and tissue phenomena that characterize the induced tooth movement. The final reflections are as follows: 1) the orthodontic movement does not induce pulp necrosis or calcific metamorphosis of the pulp; 2) there is no literature or experimental and clinical models to demonstrate or minimally evidence pulp alterations induced by orthodontic movement; 3) when pulp necrosis or calcific metamorphosis of the pulp is diagnosed during orthodontic treatment or soon after removal of orthodontic appliances, its etiology should be assigned to concussion dental trauma, rather than to orthodontic treatment; 4) the two pulp disorders that cause tooth discoloration in apparently healthy teeth are the aseptic pulp necrosis and calcific metamorphosis of the pulp, both only induced by dental trauma; 5) the concussion dental trauma still requires many clinical and laboratory studies with pertinent experimental models, to increasingly explain its effects on the periodontal and pulp tissues.

Full text

© 2018 Dental Press Journal of Orthodontics Dental Press J Orthod. 2018 July-Aug;23(4):36-4236
Alberto Consolaro1,2, Renata Bianco Consolaro3
How to cite: Consolaro A, Consolaro RB. There is no pulp necrosis or calcic
metamorphosis of pulp induced by orthodontic treatment: biological basis. Den-
talPress J Orthod. 2018 July-Aug;23(4):36-42.
DOI: https://doi.org/10.1590/2177-6709.23.4.036-042.oin
Submitted: May 18, 2018 - Revised and accepted: May 29, 2018
» The authors report no commercial, proprietary or financial interest in the products
or companies described in this article.
Contact address: Alberto Consolaro
E-mail: consolaro@uol.com.br
There is no pulp necrosis or calcific metamorphosis of
pulp induced by orthodontic treatment:
biological basis
orthodontic insight
1
Universidade de São Paulo, Faculdade de Odontologia de Bauru (Bauru/SP, Brazil).
2
Universidade de São Paulo, Faculdade de Odontologia de Ribeirão Preto, Programa
de Pós-graduação em Odontopediatria (Ribeirão Preto/SP, Brazil).
3
Centro Universitário de Adamantina (Adamantina/SP, Brasil).
To biologically explain why the orthodontic treatment does not induce pulp necrosis and calcic metamorphosis of the pulp,
this paper presents explanations based on pulp physiology, microscopy and pathology, and especially the cell and tissue phe-
nomena that characterize the induced tooth movement. The nal reections are as follows: 1) the orthodontic movement
does not induce pulp necrosis or calcic metamorphosis of the pulp; 2) there is no literature or experimental and clinical
models to demonstrate or minimally evidence pulp alterations induced by orthodontic movement; 3) when pulp necrosis
or calcic metamorphosis of the pulp is diagnosed during orthodontic treatment or soon aer removal of orthodontic ap-
pliances, its etiology should be assigned to concussion dental trauma, rather than to orthodontic treatment; 4) the two pulp
disorders that cause tooth discoloration in apparently healthy teeth are the aseptic pulp necrosis and calcic metamorphosis
of the pulp, both only induced by dental trauma; 5) the concussion dental trauma still requires many clinical and laboratory
studies with pertinent experimental models, to increasingly explain its eects on the periodontal and pulp tissues.
Keywords: Dental concussion. Tooth movement. Orthodontics. Pulp necrosis. Calcic metamorphosis of the pulp.
DOI: https://doi.org/10.1590/2177-6709.23.4.036-042.oin
Para fundamentar biologicamente por que o tratamento ortodôntico não induz necrose pulpar e metamorfose cálcica da
polpa, apresentou-se explicações com base na siologia, microscopia e patologia pulpar, bem como, e principalmente, nos
fenômenos celulares e teciduais que caracterizam a movimentação dentária induzida. As reexões nais foram: 1) o movi-
mento ortodôntico não induz necrose pulpar ou metamorfose cálcica da polpa; 2) não há literatura e modelos experimen-
tais e clínicos que comprovem ou minimamente evidenciem alterações pulpares induzidas pelo movimento ortodôntico;
3)quando a necrose pulpar ou metamorfose cálcica da polpa for diagnosticada durante o tratamento ortodôntico ou logo
após a remoção dos aparelhos ortodônticos, a sua etiologia deve ser atribuída ao traumatismo dentário do tipo concussão, e
não ao tratamento ortodôntico; 4)as duas doenças pulpares que levam ao escurecimento coronário em dentes aparentemente
hígidos são a necrose pulpar asséptica e a metamorfose cálcica da polpa, ambas induzidas exclusivamente pelo traumatismo
dentário; 5)o traumatismo dentário do tipo concussão requer, ainda, muitos estudos clínicos e laboratoriais, com modelos
experimentais pertinentes, para fundamentar cada vez mais os seus efeitos sobre os tecidos periodontais e pulpares.
Palavras-chave: Concussão dentária. Movimentação dentária. Ortodontia. Necrose pulpar. Metamorfose cálcica da polpa.

Consolaro A, Consolaro RB
© 2018 Dental Press Journal of Orthodontics Dental Press J Orthod. 2018 July-Aug;23(4):36-42
37
orthodontic insight
INTRODUCTION: HOW TO SEARCH FOR
WHAT TO READ AND WHO TO LISTEN TO
ABOUT THIS SUBJECT?
The search for biological and clinical basis of pulp al-
terations induced by orthodontic forces is almost always
conducted using keywords as “pulp”, “pulp changes”,
“pulp pathologies”, “pulp biology”, “Endodontics” and
other keywords related to the pulp. Similarly, when ask-
ing someone on the “possible changes, opinions, dog-
mata and beliefs” on the eect of orthodontic treatment
on the pulp tissues, it is very common to search for who
putatively investigates and researches the pulp biology
and diseases – almost always, endodontists. This occurs
because, simply put, there seems to be a logical direct
relationship with the dental pulp.
However, if we want to find researches to achieve
basis and search for specialists to whom we should
listen, we should search for those who specifically in-
vestigate the periodontal ligament, because the orth-
odontic movement is an exclusive phenomenon of the
periodontal ligament, rather than of the dental pulp.
Textbooks of Endodontics and Dental Traumatology
rarely discuss the biology of orthodontic movement,
which occurs in several texts of Periodontology.
To deeply understand why the dental pulp is not
affected by orthodontic movement, there is the need
to deepen into periodontal biology and changes, since
the pulp does not participate in tooth movement.
THE ACTIVE ORTHODONTIC FORCES ARE
NECESSARILY LIGHT AND MODERATE
The orthodontic movement is achieved by the
application of forces on the tooth, promoting a bio-
logical stirring of periodontal ligament cells, known
as cellular stress, which may evolve to a mild initial
inflammation for some hours or days,
1
characterized
by a mild inflammatory exudate and incipient inflam-
matory infiltrate (Figs 1 to 4).
The orthodontic forces are very light in any situ-
ation, because the goal is to induce these phenomena
of cellular stress and periodontal ligament inflamma-
tion in the periodontal ligament, which represents a
membranous structure of only 0.25mm – which cor-
responds to the thickness of a paper leaf – formed by
specialized fibrous connective tissue.
1,2
Besides being very light and moderate, the forc-
es applied on the tooth over the periodontal liga-
ment are dissipating, i.e. they gradually reduce in
intensity and disappear in 2 to 7 days, allowing
periodontal reorganization, with return to normal-
ity between 10 to 15 days after the activation of
orthodontic appliances.
1
Figure 1 - Microscopic aspects of rat molar
root in axial or transverse section, revealing
the root structures, including the pulp, alveo-
lar bone and periodontal ligament (HE, 10X
magnification).
bone periodontal
ligament
cement
dentin
dental pulp

© 2018 Dental Press Journal of Orthodontics Dental Press J Orthod. 2018 July-Aug;23(4):36-4238
There is no pulp necrosis or calcific metamorphosis of pulp induced by orthodontic treatment: biological basisorthodontic insight
of the periodontal space, which is narrowed by the
tooth compression on its structures.
1
This phenom-
enon is stimulated by the chemical mediators released
by the compressed and hypoxic cells in the periodon-
tal ligament.
After 7 to 10 days, there are nearly no active forc-
es moving the teeth in which the orthodontic forces
were applied. After this period, the periodontal phe-
nomena are predominantly reparative, to reorganize
the normality of tissues, preparing them to receive
another cycle of forces.
Since the first minutes, it is not possible to break
the vascular and neural bundles that cross the peri-
odontal ligament and penetrate into the apical fora-
men to nourish the pulp tissue with blood.
3
There
are no sudden orthodontic movements that might
promote partial or total lesions in the blood vessels
responsible for the pulp blood supply.
THE SEVERE OR HEAVY ORTHODONTIC
FORCES ARE UNABLE TO MOVE THE TEETH
Since the first moment, the orthodontic forces are
dissipating and tend to disappear after 5 to 7 days,
in a gradual and decreasing process regarding their
intensity.
Immediately, the orthodontic force applied on
the tooth is reduced or partly dissipated by two
mechanisms:
1. The liquids and gel represented by the ex-
tracellular matrix are displaced to the marrow and
perivascular spaces, partially cushioning the effects
of the orthodontic forces applied. This represents
a physiological mechanism of the periodontal liga-
ment to cushion the heavy masticatory forces.
1,2
Considering that this applies to the occlusal loads,
which are very intense and incomparably extreme
or heavy, by deduction it may be inferred that they
apply even more to orthodontic forces, which are
extremely light or moderate.
2. Usually, the orthodontic forces applied are re-
duced in 20 to 30% almost immediately after appli-
cation, because the alveolar bone crest, which sup-
ports the tooth to be moved, undergoes a deflection
or deformation due to its elastic or plastic capacity
1
.
Thealveolar bone tissue is thin and, alike any bone
tissue, it presents a high ratio of organic components,
liquids and cells.
Over 10 to 12 hours, several clasts or osteoclasts
appear on the periodontal bone surface, which initi-
ate the process of bone resorption and enlargement
Figure 2 - Microscopic aspects, at greater
magnification, of the same rat molar root in
axial or transverse section of Figure 1, reveal-
ing the root structures, including the pulp,
alveolar bone and periodontal ligament (HE,
40X magnification).
periodontal
ligament
cementoblasts
bone
vases
osteoblasts
fibroblasts
vases
cement
dentin

Consolaro A, Consolaro RB
© 2018 Dental Press Journal of Orthodontics Dental Press J Orthod. 2018 July-Aug;23(4):36-42
39
orthodontic insight
The orthodontic movement of a tooth requires an
alive or biologically viable periodontal ligament, that
may receive and nourish the clasts that will promote
bone resorption on the periodontal surface of the
tooth socket (Figs 1 to 4). Without vessels with blood
supply, without extracellular matrix and mediators,
there are no tools necessary for tooth movement in
the bone (Figs 5 and 6).
Figure 3 - Microscopic aspects of rat molar
root, in axial section, after 4 days under mod-
erate orthodontic forces that induced the re-
lease of mediators to stimulate the clastic ac-
tivity on the periodontal bone surface. In this
situation, tooth movement occurs slowly, and
the forces dissipate without inducing changes
in the vascular and neural bundles that pen-
etrate into the pulp via the apical foramen
(HE,25X magnification).
Figure 4 - Microscopic aspects of rat molar
root presented in Figure 3, at greater magnifi-
cation, in axial section, after 4 days under mod-
erate orthodontic forces. The image reveals
the activity of clasts and other cells, thanks
to the maintenance of periodontal structures,
without hyalinization (HE, 40X magnification).
periodontal
ligament
cementoblasts
clasts and bone resorption
bone
bone
fibroblasts
cement
dentin
moderate force
periodontal ligament
cementoblasts
clasts and bone resorption
vases
bone
fibroblasts
cement
dentin
moderate force

© 2018 Dental Press Journal of Orthodontics Dental Press J Orthod. 2018 July-Aug;23(4):36-4240
There is no pulp necrosis or calcific metamorphosis of pulp induced by orthodontic treatment: biological basisorthodontic insight
When the forces are very severe or heavy, due to
accidental or intentional application of forces that
compress the periodontal ligament to an extent
enough to occlude the periodontal blood vessels, the
cells migrate to neighboring areas to the site of anoxia
(Figs 5 and 6).
The orthodontic movement never occurs suddenly!
This sudden characteristic is observed in dental trau-
Figure 5 - Microscopic aspects of rat molar
root presented in axial section after 4 days un-
der heavy orthodontic forces, which induced
hyalinization of a segment of periodontal liga-
ment. In this situation there is no tooth move-
ment, because the clasts are unable to resorb
the bone on the periodontal surface (HE, 10X
magnification).
periodontal
ligament
dental pulp
bone cement
clasts
periodontal hyalinization
dentin
heavy
forces
Figure 6 - Microscopic aspects of the same rat
molar root of Figure 5, at greater magnifica-
tion, in axial section after 4 days under heavy
orthodontic forces, which induced hyaliniza-
tion of a segment of periodontal ligament.
In this situation there is no tooth movement,
because the clasts are unable to resorb the
bone on the periodontal surface (HE, 40X
magnification).
periodontal ligament
bone
cement
periodontal hyalinization
dentin
heavy
forces

Consolaro A, Consolaro RB
© 2018 Dental Press Journal of Orthodontics Dental Press J Orthod. 2018 July-Aug;23(4):36-42
41
orthodontic insight
ma,
4
not in orthodontic movement. The orthodontic
movement and dental trauma promote completely dif-
ferent tissue changes, even though both are caused by
forces, which are yet entirely dierent concerning their
intensity, duration and eld of action. In the area where
heavy forces act on the periodontal ligament, there will
remain only the extracellular matrix, without cells nor
blood vessels with blood supply, which will be occlud-
ed. Atthis site, the clasts are unable to resorb the alveo-
lar bone and it is impossible to enlarge the periodontal
space and achieve tooth movement. Microscopically,
these areas that only present extracellular matrix, with-
out cells, are named hyaline areas, or the process is iden-
tied as periodontal hyalinization (Figs 5 and 6).
That is to say: if the forces are not light or mod-
erate, there is no tooth movement;
1,3
i.e., severe or
heavy forces do not allow orthodontic tooth move-
ment. Therefore, if heavy forces are applied by pro-
fessionals without proper orthodontic training, the
risk of pulp necrosis and calcific metamorphosis of
the pulp is reduced to zero.
ORTHODONTIC MOVEMENT AND DENTAL
TRAUMA: THEY ARE NOT COMPARABLE
Once again: the orthodontic movement never
occurs suddenly! This sudden characteristic is ob-
served in dental trauma, not in orthodontic move-
ment. Theorthodontic movement and dental trauma
promote completely different tissue changes, even
though both are caused by forces, which are yet en-
tirely different concerning their intensity, duration
and field of action.
Similarly, since the pulp alterations supposedly as-
signed to orthodontic treatment are actually related
to dental trauma, it is pertinent to investigate the
literature or question investigators of dental trauma
about this issue.
Dental concussion is the type of dental trauma that
may lead to silent aseptic pulp necrosis and calcific
metamorphosis of the pulp.
1,3,4
During orthodontic
treatment, if there is aseptic pulp necrosis or calcific
metamorphosis of the pulp, it may be surely stated
that the cause was dental concussion.
The forces of dental trauma induce sudden move-
ments of teeth in the socket, possibly damaging the
vascular and neural bundles that penetrate into the
apical foramen to nourish the pulp tissues.
4
As previously mentioned in this paper, the orthodon-
tic forces are dissipating, and the eective occurrence of
tooth movement requires light or moderate forces. The
intense forces cause hyalinization of the periodontal liga-
ment and do not allow the tissue and cellular phenomena
that characterize the tooth movement.
When specialists and investigators of dental trau-
ma are questioned on the periodontal and pulp ef-
fects of dental concussion, their responses are usually
evasive. The literature about dental concussion and
its tissue effects is still underestimated in the field of
dental traumatology, which understandably still fo-
cuses on experimental models of fracture, luxation,
avulsion and replantation.
One reason is the clinical relevance of these most
severe types of dental trauma. Another reason is the
difficulty to establish clinical and laboratory experi-
mental models to reproduce dental concussion, con-
sidering its incipience and subtility.
4
Dental concussion is the type of dental trauma
that does not immediately induce clinical changes af-
ter a knock on the affected teeth, and some cases only
present mild painful symptomatology or discomfort
for some hours, which disappear spontaneously.
The patient that suffers a concussion does not
consciously remind the dental trauma and will rarely
report it during an anamnesis after some months or
years. The chief complaint of the patient that suf-
fered concussion will only appear after some months
or years, with discoloration of the tooth crown.
3
The coronal discoloration of apparently healthy
teeth may only be caused by two pulp pathologies,
both induced by the same cause — dental trauma,
especially concussion —, namely: aseptic pulp ne-
crosis and calcific metamorphosis of the pulp.
3,5,6
TWO EXAMPLES OF MORPHOLOGICAL
EVIDENCES IN HUMANS AND ANIMALS
In 2000, Valadares Neto
7
microscopically ana-
lyzed the dentin-pulp complex and external root
surfaces of human teeth of twelve teenagers, ex-
tracted after rapid maxillary expansion, and com-
pared them to the teeth of other three teenagers not
submitted to tooth movement. The following could
be concluded about the dentin-pulp complex:
1. There was no dentin and pulp alteration, evaluating
the immediate response and aer 120 days of retention.

© 2018 Dental Press Journal of Orthodontics Dental Press J Orthod. 2018 July-Aug;23(4):36-4242
There is no pulp necrosis or calcific metamorphosis of pulp induced by orthodontic treatment: biological basisorthodontic insight
2. There was no dentin and pulp alteration, con-
sidering two (0.45mm) and four (0.9mm) daily acti-
vations of the expanding screw.
3. The rapid maxillary expansion using a modi-
fied Haas expander was considered a biologically safe
procedure for the dentin-pulp complex.
It should be highlighted that the forces employed
in rapid maxillary expansion were sufficiently intense
to hyalinize the buccal periodontal ligament and pre-
clude the tooth movement. Despite the severe orth-
odontic forces applied on the teeth, there were no
microscopic pulp alterations.
In 2005, Consolaro
8
described the tooth move-
ment in 39 rats, with periods of 1 to 7 days, using
the model initially developed by Heller and Nanda,
9
recognized worldwide as the most employed in stud-
ies on this subject. The study analyzed pulp tissues,
8,10
compared to those of teeth of other 9 animals not sub-
mitted to tooth movement. It was concluded that in-
duced tooth movement did not promote morphologi-
cal alterations in the dental pulp detectable by light
microscopy, either degenerative or inflammatory.
Frequently, due to the methodological limitations
of studies on the pulp or due to the experimental
model employed, studies attempt to detect alterations
in molecular oxygenation, as well as biochemical and
enzymatic changes, in orthodontically moved pulps,
yet the results are not visible and associated with de-
tectable morphological alterations, and even less mi-
croscopically.
11
In nearly all studies on photomicrographs, the
dental pulps of orthodontically moved teeth are mor-
phologically normal.
CONCLUDING REMARKS
1. The orthodontic movement does not induce
pulp necrosis or calcific metamorphosis of the pulp.
2. There is no literature nor experimental and clini-
cal models that demonstrate or minimally evidence
pulp alterations induced by orthodontic movement.
3. When pulp necrosis or calcific metamorphosis
of the pulp is diagnosed during orthodontic treat-
ment or soon after removal of orthodontic appliances,
its etiology should be assigned to concussion dental
trauma, rather than to orthodontic treatment.
4. The two pulp pathologies that cause coronal
discoloration in apparently intact teeth are aseptic
pulp necrosis and calcific metamorphosis of the pulp,
both exclusively induced by tooth movement.
5. The concussion dental trauma still requires fur-
ther clinical and laboratory studies using pertinent
experimental models, to provide more information
on its effects on the periodontal and pulp tissues.
REFERENCES
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Maringá: Dental Press; 2012.
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Quintessence; 1988.
3. Consolaro A. Biopatologia da polpa e do periápice. Maringá: Dental Press;
2018.
4. Queiroz AF, Hidalgo MM, Consolaro A, Panzarini SR, França AB, PiresWR,
et al. Calcific metamorphosis of pulp after extrusive luxation. Dent
Traumatol. 2018. In press.
5. Consolaro A. Tratamento ortodôntico não promove necrose pulpar. Dental
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[dissertação]. Goiania (GO): Universidade Federal de Goiás; 2000.
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à movimentação dentária induzida em ratos. [dissertação]. Bauru (SP):
Universidade de São Paulo; 2005.
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