Discussion
This case report has detailed a pleasing overall treatment outcome which
addressed the presenting malocclusion and eliminated the future need for
prosthodontic treatment for the congenitally missing 35 and 45. The
spontaneous eruption of the 38 and 48 into satisfactory clinical
positions further enhanced the treatment outcome from a functional
perspective. The eruption of the 38 and 48 was made possible through
effective mesialisation of the mandibular first and second permanent
molars during the orthodontic treatment. Such mesial movement created
space distal to the mandibular second molars which subsequently created
an unobstructed eruption path for the 38 and 48. Although an argument
could be made for improving the alignment of the 38 and 48 with a second
phase of fixed appliances, this was not desired by the patient. Should
the 38 and/or 48 not erupt further and require removal for any dental
health reason, such removal would be undoubtedly more straightforward
compared to their original pre-treatment position and angulation (Figure
2b). This improvement in angulation and vertical position can be
attributed to the effective orthodontic mesialisation of the mandibular
first and second permanent molars.
The mandibular right second primary molar tooth was not visible
clinically at the initial orthodontic consultation. The pre-treatment
panoramic radiograph was rather confronting as it revealed a severe
submergence of the 85 and its resultant effect upon the succedaneous 45.
This problematic outcome emphasizes the need for routine and periodic
assessment of growing patients. The dentition of a growing patient is as
an individual and dynamic entity which requires all dental practitioners
to be familiar with the eruption sequence of teeth. Any deviation from
the norm should be diagnosed and managed in a timely manner, in order to
preserve dental arch integrity and to avoid negative
outcomes.20 In retrospect, earlier diagnosis of the
infraoccluded 85 (i.e. when this tooth was still in a supragingival
position) would have been ideal and may have completely avoided the
surgical and orthodontic management challenges encountered in the fourth
quadrant.
Congenitally missing premolar teeth are relatively common and are often
associated with both short and long-term clinical dilemmas. Numerous
factors must be carefully considered in the diagnostic and treatment
planning process. It is imperative that every relevant treatment option
be evaluated from the cost-benefit perspective and thoroughly discussed
with the patient as part of the informed consent process.
Maintaining an over-retained primary molar when the succedanenous
premolar is congenitally missing may be a reasonable option for some
individual patients, particularly if the primary molar demonstrates no
sign of infraocclusion, is unrestored, non-mobile and has significant
remaining root structure. Such a tooth may be expected to have a good
long-term prognosis and decent clinical longevity. It has been reported
that after the age of 20 years, retained primary molars display minimal
change with respect to infraocclusion, tipping of adjacent teeth and
root resorption. Therefore, should a primary molar still be present in
the dental arch at 20 years of age, it may have a good prognosis for
long-term survival.21
However, it is difficult to argue that an intact primary tooth would
have superior clinical longevity in comparison to a healthy permanent
tooth. For some patients, it may be advantageous to remove primary
molars and appropriately close the extraction spaces in conjunction with
orthodontic treatment. Such space redistribution may create sufficient
space for third permanent molars to successfully erupt, as demonstrated
in this case report.
Anchorage is defined as a resistance to unwanted tooth
movement22 and anchorage control is a fundamental
principle of contemporary orthodontic treatment.7,23Anchorage can be controlled through the use of intra-oral or extra-oral
devices. The development of non-osseointegrating titanium bone screws
has revolutionised orthodontic anchorage control as they offer a simple,
safe and effective option with reduced patient
compliance.24 These mechanically retained bone screws
are generically referred to as temporary anchorage devices (TADs) and
due to their placement into inter-radicular, mandibular or palatal bone,
their clinical application is also known as skeletal
anchorage.7,22-24
The use of TADs can permit safe, predictable and effective orthodontic
mesialisation of the mandibular first and second permanent molars.
Although such movement can also be achieved through the implementation
of intermaxillary elastics or bite correcting springs, TADs can
significantly reduce the amount of patient compliance required for
challenging tooth movements. With the benefit of hindsight, the authors
concede that the TADs used for this patient may have provided better
indirect anchorage control if rigid wire splinting was used between the
TADs and the mandibular canines or premolar
teeth.25,26 In addition, mesial force applied directly
to the TADs could also have been implemented following uprighting of the
46.27
The mesialisation of first and second permanent molars to provide space
for third molars has been widely discussed in the literature. When a
premolar or a second primary molar is extracted and the remaining
posterior teeth have been moved mesially, the probability of spontaneous
eruption of the third molars does increase.28-33 In
general, the greater the distance of first and second molar
mesialisation, the greater the probability of spontaneous normal
eruption of the third molar teeth.28
Removal of significant alveolar bone was required to extract the
ankylosed 85 and impacted 45. Fortunately, subsequent spontaneous bone
regeneration generally allows bony defects to fill with bone without the
presence of a stimulus or grafting material.34 This
phenomenon also occurs in patients who have had large cysts removed from
the ramus of the mandible. In addition, orthodontic tooth movement
through the area of an alveolar bony defect can further facilitate
regeneration of bone.34 Orthodontic tooth movement can
both stimulate and help maintain bone formation, however, how this
process occurs is not completely understood.35 Two
hypotheses exist with respect to the process of osteogenesis. The first
hypothesis is a bone bending theory as described by Epker and
Frost36,37, which postulates that the flexion of the
alveolar bone creates convexities and concavities which in turn
stimulates osteogenesis and resorption. The second hypothesis is known
as the pressure tension hypothesis.38,39 This
hypothesis relates to the concept of creates pressure and tension areas
that occur within the periodontal ligament as the tooth moves. The
pressure and tension stimulates simultaneous bone resorption and
osteogenesis which then allows for tooth movement. For the patient
described in this case report, the large bony defect which resulted from
surgical removal of the 85 and 45 was completely resolved, and likely
occurred through a combination of normal bone healing and by the
osteogenic effects of orthodontic tooth movement.
In recent times, there has been a resurgence in the technique of tooth
autotransplantation, which refers to the technique of transplanting
embedded, impacted or erupted teeth from one site into another in the
same individual.40 Autotransplantation can provide a
cost-effective and biocompatible solution for adolescent patients with
congenitally missing teeth or significantly compromised teeth when a
suitable donor tooth is available.41 Although
carefully considered individual case selection and surgical skill are
the critical determinants for success, advances in three-dimensional
computed tomography and rapid prototyping have the potential to
significantly reduce the technique sensitivity of the
autotransplantation procedure.41
The patient in this case report was also considered to be a potential
candidate for tooth autotransplantation. The left mandibular third molar
(38) may have eventually become a reasonable donor tooth to replace the
congenitally missing 35. However, the 38 did not demonstrate sufficient
tooth development at the time of the planned removal of the ankylosed 85
and impacted 45 to permit safe autotransplantation under a single
general anaesthetic. The clinicians involved in the management of this
case determined that effective mesialisation of the mandibular molars
would result in a very high likelihood of successful eruption of the 38.
The favourable third molar eruption outcome which was attained with the
orthodontic treatment ultimately justified the clinical decisions made
at the treatment planning stage.
Although restorative implants are increasing in acceptance and
popularity amongst both patients and clinicians, such treatment may not
always represent the most ideal option for compromised or congenitally
missing teeth. Actively growing adolescent patients may also pose
several management issues for future implant
placement.42 Given this patient’s relatively young
age, presence of third molars of suitable morphology and the need for
comprehensive orthodontic treatment, maintaining the over-retained 75
with a view to eventual implant replacement was not considered to be the
ideal option for this individual patient.