Download Mandibular lip bumper treatment and second molar

ORIGINAL ARTICLE
Mandibular lip bumper treatment and second
molar eruption disturbances
Fabrizia Ferro,a Gloria Funiciello,b Letizia Perillo,c and Paolo Chiodinid
Naples, Italy
Introduction: Mandibular lip-bumper (LB) nonextraction treatment, usually started before complete second
molar (M2) eruption, inevitably interacts with the development of the dentition. Yet, its effects on M2 eruption
are still unknown. The first aim of this study was to retrospectively investigate whether LB therapy (260
patients) enhances the risk for M2 ectopic eruptions and impactions in comparison with 135 untreated
subjects. The second aim was to assess, among treated patients (n 5 197), the main potential determinants
of M2 impaction and ectopic eruption. Methods: M2 eruption and impaction were determined on panoramic radiographs. To assess the predictive role of M2 inclination in relation to the first molar, a panoramic radiograph
suitable for this measurement before treatment was required. The data were analyzed by using software (version
8.2, SAS, Cary, NC). Results: LB treatment significantly enhanced M2 impaction and ectopic eruption. Negative
prognostic factors were found. An initial inclination of the M2 greater than 30 was significantly associated with
a higher impaction risk compared with an angulation less than10 . LB treatment duration longer than 2 years increased the risk of ectopic eruptions. Conclusions: While gaining space in the anterior arch, unwanted effects
might be produced in the posterior arch. To be informed about these unplanned events is necessary to better
optimize treatment. (Am J Orthod Dentofacial Orthop 2011;139:622-7)
M
andibular second molar (M2) eruption is
a complex event, requiring the uprighting of
its mesially inclined path, further guided by
the distal root of the first molar (M1) and resorption of
the mandibular anterior ramus.1 Failure of the M2 to
correctly erupt can lead to disturbances from ectopic
eruption to impaction. The latter event is increasing in
normal populations,2 and its multifactorial etiology is
not completely clear.3,4 Among the registered risk
factors, a marked M2 to M1 angulation (.20 ) was
indicated.2 This physical relationship between M1 and
M2 is delicate and requires adequate spacing in the bone.
Hence, both space deficit2,5 and surplus6,7 appear to be
possible factors disturbing the correct eruption of M2.
a
Free Practitioner in Orthodontics, Naples.
Postgraduate student, Department of Dentistry, Orthodontics and Oral Surgery,
Faculty of Medicine and Surgery, Second University of Naples.
c
Associate professor and head, Postgraduate Orthodontic Program, Department
of Dentistry, Orthodontics and Oral Surgery, Faculty of Medicine and Surgery,
Second University of Naples.
d
Researcher, Medical Statistics, Department of Medicine and Public Health,
Faculty of Medicine and Surgery, Second University of Naples.
The authors report no commercial, proprietary, or financial interest in the
products or companies described in this article.
Reprint requests to: Fabrizia Ferro, P.za Santa Maria La Nova, 8, 80134 Napoli,
Italia; e-mail, [email protected].
Submitted, March 2009; revised, June 2009; accepted, July 2009.
0889-5406/$36.00
Copyright Ó 2011 by the American Association of Orthodontists.
doi:10.1016/j.ajodo.2009.07.024
b
622
Because the management of arch spacing belongs to the
orthodontic specialty, its treatments have already been
cited among the hypothetic causes or concauses for
eruption delays, disturbances, and impactions.8,9 The
therapies discussed here are nonextraction treatments
started early, before complete eruption of M2. Indications
for early intervention are usually dental crowding and
biprotrusion correction. In addressing this issue, the most
used device is the mandibular lip bumper (LB), widely
recognized for successfully expanding dental arches in
the transversal, sagittal, and vertical planes.10-13 More
specifically, LBs produce posterior sagittal expansion of
the arch, through distal tipping of the M1,14-16 which
becomes more effective when adding buccal shields.17 If
M1 distal tipping creates mesial space, thus helping crowding resolution, it also reduces distal space, presumably
disturbing the adjustment processes of M1, M2, and
bone spacing, necessary for a physiologic eruption of M2.
The implications and effects of LB use on M2 eruption are yet to be investigated.
The primary aim of this retrospective investigation
was to verify whether LB treatment enhances the risk
of M2 impaction or ectopic eruption in comparison
with untreated subjects.
The secondary aim was to assess, among treated
patients, the main determinants in the development of
impaction or ectopic eruption problems.
Ferro et al
MATERIAL AND METHODS
From 890 patients who consecutively visited an experienced orthodontist from 1982 to 2004, those with
anterior mandibular crowding of 2 mm or more were
collected for this study (n 5 683). Exclusion criteria
were M2 eruption and all possible factors predisposing
or impeding M2 impaction, such as agenesis, dental
inclusions, destroying caries, and previous dental extractions.18 Patients with inadequate documentation or
without a panoramic radiograph for M2 eruption or
impaction diagnosis were excluded (Fig).
Of the 451 remaining subjects, 56 had treatments
other than gingival LBs and were excluded from the investigation. The 260 patients treated with the LB and the
135 who received no therapy were included in the study.
Because of the variety of LB designs, the appliance
was limited to 1 design: the gingival level in the vertical
plane, under the action of the perioral muscles.
Patients could remove the LB by themselves but were
asked to wear it 24 hours a day, taking it out only for
meals. LB treatment duration was individually dictated
by crowding severity and cooperation.
Panoramic radiographs were used for the determination of M2 eruption or impaction. An M2 was considered
erupted once it reached the functional occlusal plane
with its mesial marginal ridge at the same level of the
M1’s distal marginal ridge.
Impaction was diagnosed for molars whose eruption
was interrupted before gingival emergence by physical
barrier or abnormal dental position.19 Even if three quarters of root development already indicated a good maturational stage for eruption, closed apices were necessary for
impaction diagnosis for an easier standardized method.20
Patient age was calculated at the radiographic diagnosis.
To assess the predicting variables, we used a pretreatment panoramic radiograph when the inclination
measurements of M2 to M1 were possible before the
beginning of treatment and M2 eruption.2
Hence, of the 260 treated patients, 197 with a panoramic radiograph suitable for M2 to M1 inclination measurement were further selected. On these tracings, a line
was drawn through the midpoints of the occlusal
surfaces and root bifurcations of both M1 and M2; the
superior anterior angle resulting from the intersection
of M1 and M2’s longitudinal axes indicated the degree
of M2 inclination. Age at the beginning of LB treatment
was also calculated.
All patients gave their consent for data publications.
Statistical analysis
The data were analyzed by using SAS software (version 8.2, SAS, Cary, NC). Continuous variables were
623
expressed as means and standard deviations and compared with unpaired Student t tests. Category variables
were expressed as absolute numbers and percentages
and compared by using the chi-square test. The 2 groups
(treated and control) were compared with multivariate
logistic regression analysis, since a variety of factors
might have acted together and influenced the M2 impaction and ectopic eruption. Results were presented as odds
ratios (OR) with corresponding 95% confidence interval
(CI). For this analysis, the data were summarized at the patient level, defining for each outcome (M2 impaction or
ectopic eruption) a variable that was given the value 1 if
at least 1 tooth (left or right) reached the outcome, and
the value 0 if neither of the 2 teeth reached the outcome.
The covariates were included in the models a priori by
identifying the potential confounders in the comparison
between the 2 groups. Possible differences in patient
follow-ups between the 2 groups were taken into account,
including age at radiographic diagnosis in the model.
For the second aim, generalized estimating equation
logistic regression models were used to identify the main
potential determinants of M2 impaction and ectopic
eruption in the treated group, but using data at the dental level. A generalized estimating equation regression
model was used to account for patient-level clustering.21 Statistical significance was assessed for P \0.05.
RESULTS
The selected treated and untreated groups were similar concerning sex, type of malocclusion, and diagnosis
age. Mean anterior mandibular crowding was more severe in the control group (4.8 mm; SD, 2.1) than in the
treatment group (3.8 mm; SD, 1.3) (Table I).
LB treatment started at a mean age of 10 years and
lasted 28 months on average (range, 7-75 months). At
each visit, the LB was kept gingival in the vertical plane,
and a distance of 1 to 2 mm from the incisor was kept in
the sagittal plane. Activations reflected the patient’s
tolerance and perception of esthetics.
During follow-up, of the 395 analyzed patients, 20
exhibited M2 impaction. More specifically, M2 impaction was associated with LB treatment (18 patients; 9
bilaterally) in comparison with the control group (2 patients, 1 bilaterally; Table I).
According to the multivariate analysis, the risk for M2
impaction in the treated patients was 9.0 times (95% CI,
1.8-45.2) higher than in the control group adjusted for
sex, age at radiographic diagnosis, crowding, and Angle
class malocclusion. Also, age at radiographic diagnosis
and initial anterior crowding were significantly associated with M2 impaction in the multivariate analysis
(Table II).
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Ferro et al
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Fig. Flow chart.
In the pooled sample, with the exclusion of bilateral
impactions (385 subjects), ectopic eruptions occurred
in 43 subjects, without a preference side, but with
a more frequent distal inclination. Most significantly, ectopic eruption prevalence was increased by treatment:
41 patients (16.4%) vs 2 untreated subjects (1.6%)
(Table I). In the multivariate analysis, the OR of treatment was 18.5 (95% CI, 4.1-82.4) compared with the
control group. Furthermore, the increased incidence of
ectopic eruption was correlated with age at radiographic
diagnosis (Table II).
Inherently to the second aim, the study was conducted on 394 molars of 197 treated patients, for
whom 22 impactions and 42 ectopic eruptions were
found (Table III). M2 initial inclination greater than
30 was significantly associated with a higher impaction
risk compared with an angulation less than 10 .
LB treatment duration longer than 2 years increased
the risk of ectopic eruptions by 2.6 times (95% CI, 1.06.5) in comparison with shorter LB therapies (Table III).
DISCUSSION
Nonextraction treatment with the LB has been recognized to successfully correct anterior crowding both in
the short term12 and the long term.22-24 These
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successful LB results are unanimously ascribed to the
functional expansion of the mandibular arch and the
prevention of mesial migration of M1.
Although the early creation of enough space in the
anterior part of the arch is usually considered a priority
to save the premolars, less attention is sometimes given
to what happens distally in the arch.
Nonextraction treatment consequences on thirdmolar (M3) impaction have already been reported by
literature, but data on M2s are lacking.25
The primary aim of this study was to retrospectively
investigate the effects of nonextraction treatment with
the mandibular LB on the M2 eruption process and,
more specifically, on ectopic eruption and impaction
events.
To reach this goal, 260 patients treated with gingival
LBs were compared with 135 untreated subjects. Both
groups were carefully selected to obtain more
evidence-based information for the orthodontic specialty. The 2 compared samples were similar for most
features, but not for crowding, which was more severe
in the control group.
The impaction incidence in our untreated subjects
was 1.4% (Table I); ie, it was similar to the increasing
tendency registered in recent years.2 Since no patients
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Ferro et al
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Table I. Characteristics of the selected patients
Clinical and demographic characteristics
Male, n (%)
Crowding in mm, mean (SD)
Crowding .4 mm, n (%)
Angle class of malocclusion, n (%)
I
II
III
Impaction and eruption
Age at radiographic diagnosis in years, mean (SD)
Impaction, n (%)
Bilateral
Unilateral
None
Ectopic eruption, n (%)y
Bilateral
Unilateral
None
Characteristics of 197 treated patients and additional information
Male, n (%)
Crowding in mm, mean (SD)
Age at start of treatment in years, mean (SD)
Treatment duration .2 years, n (%)
Age at radiographic diagnosis in years, mean (SD)
M2 inclination (394 molars)
\10 , n (%)
10 -20 , n (%)
21 -30 , n (%)
.30 , n (%)
Treated
(n 5 260)
Control
(n 5 135)
92 (35.4)
3.8 (1.3)
84 (32.3)
58 (43.0)
4.8 (2.1)
62 (45.9)
50 (19.2)
194 (74.6)
16 (6.2)
34 (25.2)
89 (65.9)
12 (8.9)
13.4 (1.5)
13.8 (2.1)
9 (3.5)
9 (3.5)
242 (93.1)
1 (0.7)
1 (0.7)
133 (98.5)
15 (6.0)
26 (10.4)
210 (83.7)
1 (0.8)
1 (0.8)
132 (98.5)
P value
0.141
\0.001
0.008
0.187
0.071
0.065*
\0.001z
73 (37.1)
3.8 (1.4)
10.2 (1.1)
99 (50.3)
13.4 (1.5)
188 (47.7)
129 (32.7)
52 (13.2)
25 (6.4)
*Test trend, P 5 0.027; yEvaluated only on patients without bilateral impaction; zTest trend, P \0.001.
Table II. Results of multivariate logistic regression on impaction and ectopic eruption on treated and control subjects
Impaction
(yes/no 5 20/375)
Treatment, yes vs no
Sex, male vs female
Age at radiographic diagnosis in years
Crowding in mm
Angle class of malocclusion
I (reference)
II
III
Ectopic eruption
(yes/no 5 43/342)
OR (95% CI)
9.0 (1.8-45.2)
0.8 (0.3–2.1)
1.3 (1.0–1.7)
1.3 (1.0–1.8)
P value
0.007
0.653
0.048
0.047
OR (95% CI)
18.5 (4.1–82.4)
1.9 (0.9–3.6)
1.3 (1.0–1.6)
1.1 (0.9–1.4)
1.0
1.0 (0.3–3.1)
1.9 (0.3-11.4)
0.432
0.519
1.0
1.6 (0.6–4.2)
1.9 (0.4–8.8)
P value
\0.001
0.073
0.020
0.329
0.589
0.702
OR, Odds ratio; CI, confidence interval.
referred to M2 impaction as the reason for their orthodontic visit, this finding can be considered to reflect
a real increasing trend in the population.
Impaction incidence in the treated patients was
7.0%, higher than in the control group (Table I), with
an adjusted OR of 9.0 (95% CI, 1.8-45.2) derived from
the multivariate analysis (Table II).
This finding might be correlated with the LB design
that we used. As is well known, different vertical positions of the LB (at the incisal edge, at the third middle
of the incisor crown, at the gingival and subgingival
levels) are suggested to produce different results, both
at the incisors and the molars. In particular, a molardistalizing effect, rather than a tipping effect, should
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626
Table III. Results of multivariate generalized estimating equation regression model on impaction and ectopic
eruption of teeth of 197 treated subjects
Impaction
(yes/no 5 22/394)
M2 inclination, \10 (reference)
10 -20
21 -30
.30
Sex, male vs female
Age at radiographic diagnosis in years
Age at start of treatment in years
Crowding in mm
Treatment duration, .2 y vs #2 y
OR (95% CI)
1.00
1.5 (0.5–4.6)
1.2 (0.2–6.3)
10.6 (2.6–43.3)
0.7 (0.2–2.3)
0.7 (0.4–1.1)
1.3 (0.8–2.0)
1.1 (0.7–1.6)
2.1 (0.6–7.1)
Ectopic eruption
(yes/no 5 42/372)
P value
0.458
0.851
0.001
0.568
0.125
0.274
0.705
0.253
OR (95% CI)
1.00
1.2 (0.5–2.5)
1.6 (0.5–4.7)
3.0 (0.7–13.9)
2.0 (0.8–4.6)
0.9 (0.6–1.4)
1.3 (0.9–1.7)
1.1 (0.9–1.5)
2.6 (1.0–6.5)
P value
0.696
0.412
0.154
0.117
0.665
0.107
0.279
0.044
OR, Odds ratio; CI, confidence interval.
be expected when using a gingival LB rather than an incisal LB. Yet, a cephalometric investigation on 110 subjects, treated in the mixed dentition with a gingival LB,
showed significant distal tipping on the mandibular
plane.16 It is possible that a subgingival LB might produce a greater molar-distalizing effect, thus protecting
the M2 from impaction.
Another possible cause suggested for M2 impaction is
incorrect fitting of first molar bands.8,9 We wondered
whether replacing M1 bands with direct bonding would
have facilitated M2 eruption. Nevertheless, further
studies on this issue are needed.
In disagreement with previous data, the type of malocclusion and sex did not correlate with impaction in our
study.26,27 On the other hand, the positive association
found with anterior crowding strengthened our
expectations of also finding a posterior space deficit,
when there is already anterior crowding.
The statistically significant association with age at
radiographic diagnosis should be considered with caution, since the definition for impaction included closed
apices, inevitably delaying the age at which patients
are diagnosed.
Interestingly, LB treatment disturbed the whole M2
eruption process.
Although our ectopic eruption percentage without
treatment (1.6%) confirmed previous data in a normal
population, LB treatment most significantly increased
the number of M2 ectopic eruptions (16.4%, Table I),
with an adjusted OR of 18.5 (95% CI, 4.1-82.4, Table
II) when compared with the control group.9
On diagnostic panoramic radiographs, ectopic molars showed a distal inclination more frequently than
a mesial inclination. This might be due to the continuous LB action and the presence of mesially inclined
M3s.
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No sex differences were found, as already reported in
a normal population.9
As expected, radiographic eruption timing significantly influenced the final M2 position in the arch.
Delayed-erupting M2s in crowded malocclusions are
reasonably more at risk for ectopic eruptions, because
of space competition with M3s.
Inherently to our secondary aim—to assess the potential determinants of M2 ectopic eruption and impaction
in treated patients—our findings supported the importance of the delicate physical relationship between
M1s and M2s. For an initial M2 inclination less than
30 , the M2 had a good chance to erupt normally.
Greater than 30 , an association with impaction was instead found (Table III). The initial inclination of the M2
offered useful pretreatment information concerning impaction risk, independently of molar angulation
changes. These are in general associated with LB design
choice and were not investigated in our study.
On the contrary, M2 inclination did not affect M2 ectopic eruptions, which were instead associated with
treatment durations over 2 years. It is probable that muscle and mechanical pressures produced by wearing the
LB over a longer period disturbed the M2’s correct eruption path by further reducing distal space in already
crowded arches. Most of the arch expansion produced
by the LB has recently been found to occur within 300
days.28 For this reason, longer treatments should be discouraged to also reduce ectopic eruptions, the correction
of which would in any case require additional orthodontic intervention.
This study highlighted the increased risk of M2 ectopic eruptions and impactions after nonextraction
treatment with a LB. In particular, M2 impaction was
significantly associated with pretreatment M2 to M1
inclination greater than 30 .
American Journal of Orthodontics and Dentofacial Orthopedics
Ferro et al
In this study, ectopic eruptions were favored by
delayed eruption patterns but might be limited by M3
germectomies. Also, orthodontists should work more efficiently to reduce treatment durations, which, according to this study, were also associated with M2 ectopic
eruptions. To address this issue, the building of young
patients’ willingness to cooperate steadily also becomes
a key factor for treatment effectiveness. An alternative to
make up for lack of cooperation is to tie in the LB.
An ideal treatment with no unwanted side effects
does not exist, but acknowledging both risk factors and
undesired events can be fundamental. The price to pay
to avoid premolar extractions might be a higher risk for
M2 impaction and ectopic eruption. However, having several alternatives for the recovery of impacted molars can
be reassuring.6,29
The limitations of this study were its observational
nature and lack of randomization, which did not allow
a proper assessment of the cause-and-effect relationship
between LB treatment and M2 eruption disturbances.
But retrospective clinical observations are often necessary to start future prospective research.
CONCLUSIONS
This investigation showed the following.
1.
2.
Mandibular LB treatment affected eruption on the
whole, significantly increasing both M2 impactions
and ectopic eruptions in comparison with the untreated group. Initial anterior crowding favored impaction.
Negative predictive factors included pretreatment
molar inclination greater than 30 for impaction,
as well as LB treatment longer than 2 years for ectopic eruptions.
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