Orthodontics and root resorption. Part 1

Abstract

The first article in this series of two aims to outline the biological processes which form the basis of orthodontically-induced inflammatory root resorption (OIIRR). It will also provide an overview of patient-related factors associated with OIIRR.

Full text

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Orthodontic Update October 2010
Orthodontics and Root
Resorption Part 1
Abstract: The first article in this series of two aims to outline the biological processes which form the basis of orthodontically-induced
inflammatory root resorption (OIIRR). It will also provide an overview of patient-related factors associated with OIIRR.
Clinical Relevance: This paper reviews the current evidence, in particular the patient-related aetiological factors, so that practitioners are
aware and can inform patients of these risks and, if possible, minimize the extent to which it occurs.
Ortho Update 2010; 3: 102–106
Christopher S Barker, BChD, MFDS RCS(Ed), Specialist Registrar in Orthodontics, Farnaz Parvizi, MPhil, BDS, FDS RCS(Eng), MOrth RCS(Ed),
Senior Registrar (FTTA) in Orthodontics, Child Dental Health, Bristol Dental Hospital, Frank Weiland, DMD, PhD, Specialist Practitioner
in Orthodontics, Department of Orthodontics, University Dental School, Vienna, Austria, Jonathan R Sandy, PhD, MOrth RCS, FDS RCS,
FMedSci, Professor and Honorary Consultant in Orthodontics and Anthony J Ireland, PhD, MSc, BDS, FDS RCS, MOrth RCS, Consultant in
Orthodontics, Royal United Hospitals, Bath Reader in Orthodontics, Child Dental Health, Bristol Dental School, Bristol, UK.
External apical root resorption
(EARR) stimulated by orthodontic
forces is known as orthodontically-
induced inflammatory root resorption
(OIIRR) and is a common complication of
orthodontic treatment. This association
has been recognized for many years and
it is known that some resorption occurs
in almost every patient who undergoes
orthodontic treatment. The prevalence
of OIIRR is such that it is seen in 90% of
patients under treatment. In most cases,
this is clinically insignificant.1 During a
course of orthodontic treatment, root
resorption results in an average loss of
around 1.5 mm per anterior tooth2 and has
been found to be severe (where at least
one tooth is affected by resorption greater
than 5 mm) in 5%3 of adults and 2%2 of
adolescents. When orthodontic forces are
applied, a local periodontal inflammatory
process is induced. This inflammation,
which is essential for tooth movement, is
the fundamental component of the root
resorption process and causes remodelling
of both cementum and dentine of
the roots.4 During periods of relative
quiescence, the cementum undergoes
repair such that, for most teeth in most
patients, the changes in root length are so
small as to be difficult to detect and are
often clinically insignificant5 (Figure 1).
Brezniak and Wasserstein4
describe three degrees of OIIRR:
 Cemental or surface resorption with
remodelling. In this process, only the outer
cemental layers are resorbed and these are
later regenerated or remodelled.
 Dentinal resorption with repair. In this
process, the cementum and the outer layers
of the dentine are resorbed and usually
repaired with cementoid material. The final
shape of the root after this resorption may
or may not be identical to the original form.
 Circumferential apical root resorption.
In this process, full resorption of the
hard tissue components of the root apex
occurs and root shortening is evident
on radiographs. When the root loses
apical material beyond the cementum no
regeneration is possible.
Animal studies have
demonstrated that OIIRR is a part of what
is known as the hyaline zone elimination
process. Hyalinization occurs in the
periodontal ligament where the force
applied is above capillary blood pressure.
The affected tissues undergo aseptic
necrosis and send signals to macrophage
like cells, which then begin to remove this
tissue. Hyaline zone elimination is initiated
at its periphery, where the blood supply
to the periodontal ligament exists. During
this process of elimination, the nearby
outer surfaces of the root consisting of the
cementoblast layer covering the cementoid,
can be damaged leading to exposure of the
underlying, highly mineralized, cementum.
The resorption process continues until no
hyaline tissue is present and/or the force
level within the ligament decreases (Figures
2 and 3).
Categories of root resorption
Root resorption can be
categorized based on radiographic root
morphology and has been described by
several authors.6-7
Levander and Malmgren7
devised a classification which is as follows:
 Grade 1: indicates an irregular root
outline;
 Grade 2: < 2 mm root resorption (minor);
 Grade 3: > 2 mm root resorption (severe);
 Grade 4: resorption > one-third of root
length (extreme).
 Occasionally, Grade 0 is added to this
classification to indicate no resorption
(Figure 4).
Aetiological factors
Christopher S Barker Farnaz Parvizi, Frank Weiland, Jonathan R Sandy and Anthony J Ireland

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The aetiological factors
associated with OIIRR are complex and
multifactorial and can include patient-
related and treatment-related factors.1
Patient-related factors
Age
Most studies have not
found a consistent association between
chronological age and OIIRR.8 However,
Linge and Linge2 demonstrated that the
degree of root resorption observed in
patients undergoing treatment before
the age of 11 is less, perhaps due to the
preventive effect of the pre-dentine
layer on the underdeveloped roots. They
also suggested that resorption could be
avoided if tooth movement was completed
before the roots were fully developed.
Orthodontic tooth movement of immature
roots does not prevent root development
but these roots may not develop to their
true potential and have been found to be
shorter.9
Gender
There does not seem to be a
consistent association between gender
and OIIRR. Baumrind et al10 found a
greater prevalence of OIIRR in men than
in women in a group of adult orthodontic
patients. Conversely, Kjaer found a greater
prevalence of OIIRR in girls than in boys.11
Ethnicity
Sameshima and Sinclair’s12
Figure 1. (a) Pre-treatment DPT. (b) Mid-treatment DPT showing extensive root resorption in the labial
segments. (Courtesy of Mr Scott Deacon.)
a
b
Figure 2. Histological section of tooth exhibiting
root resorption.
Figure 3. Macroscopic identification of resorption lacunae occurring during orthodontic treatment and
a detailed view using confocal laser-scanning microscopy. From Weiland F. Constant versus dissipating
forces in or thodontics: the effect on initial tooth movement and root resorption. Eur J O rthod 2003; 25: 335-
342. Courtesy of Prof. F Weiland and reprinted with the permission of Oxford University Press.

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investigations into root resorption found
that there was a difference between
races, with Hispanic patients experiencing
significantly more OIIRR than White or Asian
patients. White patients tended to have less
OIIRR than Asians, although this was not
statistically significant
Medical history
There is not a strong association
between OIIRR and general health. Chronic
asthmatic patients have an increased
incidence of maxillary root resorption
(although not statistically significant),
perhaps as a result of the close proximity of
the apices to the inflamed maxillary sinus.13
Other investigators have named hormonal
deficiencies, such as hypothyroidism, as
risk factors, but this is not conclusive.14
There have been some anecdotal reports
of the effects of hyperparathyroidism on
root resorption with no consistent effects
described. Goultschin et al15 described
a case of an adult patient that showed
extensive external and internal root
resorption much like Figure 5. Midgett
et al.16 conducted an animal experiment
on beagle dogs with an induced state of
hyperparathyroidism. They found that
tooth movement in the experimental group
was quicker and related this to increased
bone turnover and decreased bone density.
There was no mention of an increase in root
resorption in these dogs.
Family history
There is a wide variation in
the extent of OIIRR between individuals
treated with the same mechanics and this
has led to the suggestion of a genetic
component to EARR. This was investigated
by Harris et al17 who conducted a study
into 103 full sibling pairs. They concluded
that there was a high genetic susceptibility
between siblings with an estimate of EARR
heritability of 70% for maxillary central
incisors and mandibular molars (but not
mandibular incisors). Although there is
very little the orthodontist can control
regarding the genetic component to OIIRR,
this information may be of use in alerting
the clinician to the possibility of increased
OIIRR in siblings of patients who have been
known to experience severe OIIRR.
Types of malocclusion
Patients with an acceptable
overjet and Class I occlusion at the
beginning of treatment are significantly
less likely to develop severe root resorption.
This probably reflects the smaller amounts
of tooth movement, particularly of the
maxillary incisors.
Class III cases are over-
represented in the group with severe root
resorption, perhaps owing to an increased
chance that proclined maxillary incisors
moving forward in compensation for Class
III skeletal relationship will have their roots
forced against the palatal cortical plate.5
Proffit18 suggests that some
malocclusions cause undesirable ’jiggling’
of the teeth once the teeth are in occlusion.
Such patients may have shortened roots
prior to treatment and are subsequently
at a higher risk of root resorption during
treatment, possibly due to uneven loading
of the periodontium.
Habits may also have a role in
the extent of root resorption. Odenrick
and Brattström19 found increased root
resorption prior to, and after, orthodontic
treatment in nail-biters. This could be
attributed to increased pressures on the
periodontium for sustained periods. This
may also be true of digit habits.
Tooth type and series
The teeth that most commonly
undergo root resorption, as a consequence
of orthodontic treatment, are the maxillary
lateral incisors and the maxillary central
incisors, followed by the mandibular
incisors and the distal root of the first
permanent molars.1,20 Sameshima and
Sinclair12 found that OIIRR affected single-
rooted teeth to a greater extent (Figure
6). This is confirmed in the investigations
by Mirabella and Årtun3 who found a
relationship between the amount of
resorption and increased tooth length and
reduced tooth width, thus the lateral incisor
having a narrow width would be more
susceptible.
Root form and morphology
In 1988, Levander and
Malmgren suggested that the degree
of root resorption in teeth with blunt or
pipette-shaped roots was significantly
higher than in teeth with normal root
lengths (Figure 7)7. However, more
recently, from a systematic review of
relevant randomized trials, Weltman
and co-workers1 have been unable to
demonstrate an association between teeth
with roots of unusual morphology and
increased susceptibility to moderate and
severe root resorption.
Dental anomalies
Associations between anomalies
of dental form and root resorption have
Figure 4. Categories of root resorption modified from Levander and Malmgren.7
Figure 5. Extensive external and internal root
resorption in a patient with hyperparathyroidism.

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long been suspected because of the
polygenic inheritance patterns of these
anomalies and the heritability of external
apical root resorption. Investigations into
the association of dental anomalies, such
as developmentally absent teeth, peg-
shaped or diminutive lateral incisor, dens
invaginatus, taurodontism, ectopic eruption
and abnormally short-rooted teeth with
increased OIIRR, have revealed that there
are no statistically significant differences
with control groups.21
Trauma
It has been reported that
movement of teeth which have undergone
a traumatic injury, including those which
are endodontically treated, previously
avulsed or luxated, suffer a greater
frequency of root resorption.22–23 The
types of root resorption most frequently
associated with such teeth are progressive
inflammatory resorption and replacement
resorption (ankylosis). Malmgren et al24
reported that teeth that have undergone
slight or moderate trauma, and where the
periodontal ligament is intact, are not at a
greater risk of root resorption as a result of
orthodontic treatment. This is supported
by more recent studies.25–26 There is even a
suggestion that there may be a ’protective’
effect of endodontically treated teeth
with possibly less OIIRR.3,27 Interestingly,
those traumatized teeth which show root
resorption prior to treatment tend to
undergo more resorption during treatment.
The evidence linking previous trauma (with
no signs of root resorption) and unusual
root morphology with root resorption
during orthodontic treatment is weak.
Conclusions
This first article has discussed
patient-related factors which may be
associated with orthodontically-induced
inflammatory root resorption. It highlights
the need for good patient assessment
and family history as there does appear
to be convincing evidence of a genetic
susceptibility to OIIRR, but individual
variation makes it difficult to predict the
likelihood or extent of root resorption
that might arise as a result of orthodontic
treatment. It is therefore important to try
and identify those factors which might
contribute to root resorption in order
to minimize their potential effect, and
patients must be advised of the risk of root
resorption before starting treatment, as
part of the process of informed consent.
The second article will outline
the current evidence on the effects of
different orthodontic treatment mechanics
on the susceptibility and extent of OIIRR.
Acknowledgements
We would like to thank Scott
Deacon for the use of his images for Figure
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