acific Coast Society of Orthodontists Bulletin Summer 2018 - 32

Special Section

Let's Talk About That

RETENTION

MP: I strongly believe in the evidence-based
orthodontic theories that suggest we should not
violate the mandibular intercanine width, but it
is important to distinguish between expansion
and uprighting when the canines are tipped lingually. In a meta-analysis, Burke et al. support the
concept of maintaining the original intercanine
width.5 During treatment, intercanine width
expands by 0.8 to 2.0 mm, but it tends to constrict by 1.2 to 1.9 mm during post retention. You
can upright them and gain width without expansion. Due to the increased popularity of nonextraction and fast treatments that certain
companies promote, clinically we see a lot more
relapse and other periodontal-related issues,
including unstable occlusion.
PT: Numerous types of bonded retainers are currently being used and marketed. The lingual bar
with bonded pads for the canines appears to be
used less often in favor of various types of wires
bonded to the lingual of each individual tooth.
Outside of individual preferences, what advantages and disadvantages have been shown in
studies with these different types?
MP: Today, bonded retainers are being used routinely for retention. They can be as thick as a
0.030" to 0.32" SS lingual bar bonded only to the
canines or a multistranded 0.0195" or 0.0215" SS
wire bonded to all lingual surfaces, from two to
six teeth, and even eight in extraction cases.
There are also other variations of fixed retainers
such as multilooped 0.20" SS wires, glass fiber
reinforced composites, and others. The retention
protocol should take into consideration the initial
malocclusion, patient habits, age, growth pattern, and other factors that might have an effect.
Although they are easier for patients to keep
clean than when individual teeth are bonded,
canine-only bonded retainers have a higher incidence of tooth movement. According to the literature, fixed retainers bonded to individual teeth
with 0.0215" five-strand SS wires allow physiologic tooth movement and thus are less likely to
break than solid, more rigid wires are.6

32

PT: How do the results compare between the
three most common methods of retention
(Hawley, Essix, fixed) for maintaining correction?
MP: In a randomized controlled study, Tynelius et
al. found that from a clinical perspective, it was
evident that all three retention methods had
equal ability to retain treatment results during
the first year.1 In a comparison study of Hawley
vs. vacuum-formed retainers, Rowland et al.
found that vacuum-formed retainers were more
effective than Hawley retainers after six months.7
In other studies, Gill et al. showed that full-time
and part-time wear of an Essix had the same
results.8 On the other hand, bonded retainers
have a better ability to hold the mandibular incisors in the first six months post-treatment than
do vacuum-formed retainers.9
PT: Patients are always asking, "How long do I
have to wear retainers?" What does the literature
say about this?
MP: Maintaining teeth in their corrected positions after orthodontic treatment can be
extremely challenging. Relapse is the result of
teeth moving towards their original malocclusion, but changes may also occur as a normal
part of the growth process and function. Because
relapse is unpredictable, it should be presumed
that every patient has the potential for long-term
changes. As part of informed consent, patients
need to be fully aware of their commitment to
wear retainers for as long as they want to keep
their teeth straight. There is currently insufficient
high-quality evidence on the best type of retention regimen, so each clinician's approach to
retention will be dictated by personal clinical
experience and expertise with different retainers,
and also on their patients' expectations and circumstances.10
In 1934 Oppenheim stated, "Retention is one of
the most difficult problems in orthodontics; in
fact, it is the problem."11 Decades later, we are
still struggling with the same issue!

PCSO Bulletin  Summer 2018



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