The CONSORT statement will be used as a guide for this study. This work will be a parallel
group study, randomized, with active control, with an allocation ratio of 1: 1.
This study was submitted to the Research Ethics Committee of the Pontifical Catholic
University of Minas Gerais. Participants will be recruited in the Master's Degree in
Orthodontics at PUC Minas, based on inclusion criteria.
Interventions:
Palatal expanders of the HYRAX type, with bands on the first permanent molars or second
deciduous molars will be used for patients in both groups. The hooks for the use of Class III
elastics will be welded on the vestibular of the upper molar bands. In the experimental
group, the expander will be anchored mesially and bilaterally in mini-implants, in a
technique known as rapid maxillary expansion assisted by mini-implants (MARPE). The control
group will be active, with conventional dento-mucus-supported HYRAX expanders. All expanders
will be manufactured by the same orthodontic technician.
Both groups will be treated with maxillary protraction with a Petit-type face mask at night
(12 hours a day). The direction of the elastics for the maxillary traction force will be
between 15˚ to 30˚ below the occlusal plane, providing a force between 400 and 500 g per
side. During the day (12 hours a day), patients will use a lower expansion plate with an
occlusal stop, which will be activated once a week (0.25 mm), with hooks in the region of the
lower canines for the use of Class III elastics. size 3/16 "(150g). The time-frame of the
experiment will be 6 months.
Results (primary and secondary) The primary outcome will be the degree of anterior movement
of the maxilla after treatment). Secondary outcomes will be changes in other cephalometric
variables and treatment time.
Conical beam computed tomography (CBCT) will be performed at the beginning and at the end of
the treatment. Teleradiographies will be extracted from the CFFCs and cephalometric
measurements will be obtained by the investigator (V.E.) using the Dolphin Image software
(Austin, USA). Traditional cephalometric measurements will be used to describe the changes
before and after treatment.
Calculation of the sample size As no study in the orthodontic literature used the same
protocol used in this study, the sample size will be estimated by G * Power (version 3.0.8),
with 95% power; significance level of 5%; two-tailed. For point A, sagittal movements of 2.6
+/- 1.5 mm in the RME group and 5.8 +/- 2.3 mm in the RME group with constriction, a minimum
sample size of 11 in each group will be necessary to detect a significant difference between
groups. For ANS, sagittal movements of 2.1 +/- 1.3 mm in the RME group and 4.8 +/- 2.5 mm in
the RME group with constriction, a minimum sample size of 16 in each group will be necessary
to detect a significant difference between groups. Therefore, 16 will be the minimum sample
size for each group. The sample size will be increased by 40%, resulting in 22 patients for
each group, in case there is a withdrawal or the need to use a different protocol.
Randomization (random number generation, allocation hiding, implementation) Patients will be
recruited and allocated to the control group (RME) or the intervention group (MARPE)
according to the sequence of participation. Simple randomization will be applied.
Blinding The blinding of investigators or participants will not be possible because the
expanders in the two groups will be different. Operators and patients will easily know which
group they are in. However, blinding will be used during cephalometric analysis. All image
exams will be hidden by opaque tape and replaced with research numbers and then mixed
together before analysis. The investigator will not know the clustering of the CT scans,
which will look similar.
Statistical analysis (primary and secondary results, subgroup analyzes) All statistical
analyzes will be performed using the software (version 18.0; PASW Statistics, Chicago,
Illinois). Descriptive statistics will include the means and standard deviations of age,
total treatment time, maxillary prostration time, cephalometric values and changes in values
in each group. The 1-sample Kolmogorov-Smirnov test will be used to test the normality of
distributions for all times and differences in cephalometric values. Independent t-tests will
be used to compare the two groups, including total treatment time, protraction time and
changes in cephalometric values; the t-tests will be used for the values that show "equality
of variances not assumed" between the groups (SNA and Nasio perpendicular). The level of
significance will be 0.05, with two-tailed test.
Error of the Method All locations and measurements of the points will be checked twice
carefully at the end of the initial plots and measurements. Not all images will be traced
twice. However, to evaluate the tracing errors, 20 scans will be chosen at random. Plots,
locations and measurements will be made twice, two weeks apart and then subjected to the
Dahlberg formula. The error of the method will be determined by the Dahlberg formula, where n
= 20 and d will be the difference between the measurements in 2 moments.