Mandibular Response After Maxillary Orthopedic Expansion in Class II Growing Subjects
Condition: Malocclusion, Angle Class II; Malocclusion
MeSH terms: Malocclusion; Malocclusion, Angle Class II; Overbite
Study type: Interventional

Summary: 
      the effectiveness of RME (Rapid Maxillary Expander) on the sagittal dental or skeletal
      parameters is still controversial because very little has been written regarding the behavior
      of antero-posterior mandibular changes in Class II growing subjects who underwent RME as the
      phase 1 treatment intervention. The reported significant occlusal improvement could be
      attributed to other reasons, ie, skeletal growth or the use of additional appliances during
      transition from mixed to permanent dentition. Moreover, the majority of the studies show some
      limits: they are not randomized, they are not prospective, and they have no control group or
      they use patients from growth studies as a source for the control group. The primary
      objective of the present investigation was to conduct a pilot randomized controlled trial
      (RCT) evaluating the changes in the antero-posterior mandibular position induced by bonded or
      banded RMEs compared with an untreated Class II control group
    

Detailed description: 
      Class II malocclusions are commonly observed in orthodontic patients. During treatment
      planning among the several dento-skeletal pattern combinations of Class II malocclusion, it
      is important to consider the maxillary transverse deficiency, which is often overlooked.

      it has been showed showed an underlying posterior interarch transverse discrepancy of 3 to 5
      mm in subjects in early mixed dentition with Class II malocclusions without posterior
      crossbites in centric occlusion. When these Class II patients are asked to posture their
      lower jaw forward in a Class I molar relationship, this transverse discrepancy (ie, maxillary
      constriction) can be observed clinically. It was postulated that in these subjects the
      mandible is kept in a distal position relative to centric relation because the constricted
      maxilla is holding it back. The presence of a primitive transverse discrepancy between the
      dental arches induces a backward position of the mandible, as the occlusal goal is to obtain
      the highest number of functional contacts.

      As reported by several authors, widening the maxilla with rapid maxillary expansion often
      leads to spontaneous forward posturing of the mandible during the retention period. The
      orthopedic expansion removes occlusal interferences, allowing the mandible to posture
      forward, thus improving the sagittal relationships. The mandibular arch acts as a ''foot''
      that moves forward after the ''shoe'' is widened.

      However, the effectiveness of RME on the sagittal dental or skeletal parameters is still
      controversial because very little has been written regarding the behavior of antero-posterior
      mandibular changes in Class II growing subjects who underwent RME as the phase 1 treatment
      intervention. The reported significant occlusal improvement could be attributed to other
      reasons, ie, skeletal growth or the use of additional appliances during transition from mixed
      to permanent dentition. Moreover, the majority of the studies show some limits: they are not
      randomized, they are not prospective, and they have no control group or they use patients
      from growth studies as a source for the control group.

      Considering that it was not possible to estimate from previous studies the standard deviation
      to be used for sample size calculation of the main trial with special regards to type of
      intervention and observation intervals, the primary objective of the present investigation
      was to conduct a pilot randomized controlled trial (RCT) evaluating the changes in the
      antero-posterior mandibular position induced by bonded or banded RMEs compared with an
      untreated Class II control group.

      To evaluate the sagittal mandibular response induced by RME therapy in mixed dentition
      patients with Class II malocclusion, comparing the effects of bonded RME and banded RME with
      a matched untreated Class II control group

      This is a single center, prospective 3-arm parallel group randomized clinical trial with a
      1:1:1allocation ratio. 30 (thirty) of subjects are planned. Each subject in the treated
      groups will be treated with a Rapid Maxillary Expander (RME), bonded or banded respectively.
      Subjects will be assigned to the groups in random order. Evaluations will be taken at
      baseline and at the end of the retention period/follow up (for a total of 12 months).
      Subjects who meet all inclusion criteria and none of the exclusion criteria will be entered
      into the study.

      Allocation of patients to the three groups in a 1:1:1 ratio was determined by a
      computer-generated randomization list using Rv.0.1 software and by a block size of 4. Then,
      the allocation information (randomization results) was concealed in opaque and sealed
      envelopes by the statistician.

      The study was blinded in regard of the statistical analysis. Data were recorded and blinded
      for the statistician: blinding was obtained by eliminating from the elaboration file every
      reference to patient group assignment

      To determine the reliability of the method 15 radiographs chosen at random were traced and
      digitized by the same investigator on 2 separate occasions at least one month apart. A paired
      t-test was used to compare the two measurements (systematic error). The magnitude of the
      random error was calculated by using the method of moment's estimator (MME). Exploratory
      statistics revealed that not all cephalometric variables were normally distributed
      (Kolmogorov-Smirnov test) with equality of variances (Levene's test).Kruskal-Wallis test or
      ANOVA with Tukey's post-hoc tests were used to compare the T2-T1 changes in the three groups.
      All changes were considered significant at P<0.05. All statistical computations were
      performed with Statistical Package for the Social Sciences software (Version 12, Chicago,
      IL)..

      10 randomized subjects will be included in the treated group 1, 10 randomized patients will
      be included in the treated group 2 and 10 randomized patients will be used as untreated
      control group.

      The baseline age was 8.1 ± 0.6 years (range 6.6-9.1 years).

      Sample size for this pilot trial was calculated according to the method proposed by Whitehead
      et al. For a standardized effect size of 1 (a clinically relevant change of 2.0 mm with a
      combined Standard Deviation of 2.0 mm derived from Guest et al.) for the 8 primary outcome
      variable Pogonion to Nasion perpendicular, a sample size of 10 subjects per group was
      required for a Type I error rate of 5% and a power of 80%.
    

Intervention name(s): Bonded RME (Rapid Maxillary Expander) appliance; Banded RME (Rapid Maxillary Expander) appliance
Intervention type(s): Device; Device
Intervention description(s): The expansion screw was activated 1 quarter of a turn per day (0.25 mm per turn) until the palatal cusps of the maxillary posterior teeth approximated the lingual cusps of the mandibular posterior teeth.
The expander was kept in place as a passive retainer for 8 months. After expander removal, patients were followed without performing any additional treatment for 4 months.; The expansion screw was activated 1 quarter of a turn per day (0.25 mm per turn) until the palatal cusps of the maxillary posterior teeth approximated the lingual cusps of the mandibular posterior teeth.
The expander was kept in place as a passive retainer for 8 months. After expander removal, patients were followed without performing any additional treatment for 4 months.
Allocation: Randomized
Intervention model: Parallel Assignment
Intervention model description: prospective 3-arm parallel group randomized clinical trial with a 1:1:1 allocation ratio
Masking: None (Open Label)
Primary purpose: Treatment
Keywords: Rapid maxillary expansion; Mandibular response; Class II malocclusion; Growing subjects