Thirty-nine children, 20 boys and 19 girls aged on average 9.3 years, in the phase of mixed dentition, initially participated in the study. The children were divided into two groups, 28 subjects with posterior crossbite (posterior crossbite group) and 11 with no occlusal changes (control group). The children were selected at the Screening Office of the Preventive and Interceptor Orthodontic Clinic of the Dental School and at the Mouth Breather Center (CERB) and at the Otorhinolaryngology service of the University Hospital, School of Medicine of Ribeirão Preto, University of São Paulo. The study was approved by the Research Ethics Committee (protocol number 6443/2007) and all persons responsible for the children gave written informed consent to participate.

Inclusion criterion for the crossbite group was the presence of unilateral or bilateral crossbite involving the deciduous canines and molars and the first permanent molars, with an indication of orthodontic treatment, with no restrictions regarding respiratory condition or other associated malocclusions. The inclusion criteria for the control group were absence of occlusal changes, being in the mixed dentition phase, no history of orthodontic and/or orthopedic treatment, and no restrictions regarding respiratory condition.

Exclusion criteria were presence of genetic syndromes, congenital and acquired dentofacial deformities, tooth decay a history of neurological treatment and of orthodontic and/or functional orthopedic treatment, and orofacial myofunctional treatment performed before or during the study.

The 28 children of the posterior crossbite group were treated while participating in all initial stages of the study, but seven of them did not participate in the final exam after palatal expansion and were excluded from the sample. Thus, the crossbite group was reduced to 21 children, 14 of them with unilateral posterior crossbite associated with anterior open bite and 4 with bilateral crossbite. Descriptive data and statistical analysis according to age are presented in Table 1.

Evaluation of the upper airways was performed in the Service of Otorhinolaryngology, consisting of anterior rhinoscopy and nasofibroscopy (pediatric flexible fibroscope Pentax FNL – 10RP2, 3.4 mm) for the measurement of adenoid size. Ten of the 21 children in the crossbite group (47.62%) showed 10%–50% obstruction of the cavum, 6 (28.58%) showed 50%–70% obstruction and 5 (23.80%) 70%–100% obstruction. Seven of the 11 control children (63.64%) showed 10%–50% obstruction of the cavum, 2 (18.18%) showed 50%–70% obstruction and 2 (18.18%) 70%–100% obstruction.

Complete orthodontic documentation (lateral and occlusal cephalometric radiographies, study models, intraoral photographs and extraoral front and profile photographs) was requested for diagnosis and planning of dental treatment. After the individual study of each orthodontic documentation, a dental mucous-supported orthodontic appliance — modified Haas expander9 was prepared. The orthodontic procedures were performed by two dentists, one of them an orthodontics specialist responsible for the installation and adaptation of all appliances. The procedure was finalized by over correction of the uni or bilateral posterior crossbite, taking care for the bite not to cross in a contrary manner. The appearance of a diastema was also noted between the upper central incisors, which was confirmed radiographically with the opening of the median palatal suture in all cases. After this process, which lasted about 15 days, the screw was locked with photopolymerizable resin and the appliance was left in place for containment, without activation, for a period of 180 days for fiber reorganization and bone neoformation in the median palatal suture.14

Videofluoroscopy evaluation was performed by the same investigator before the installation of the appliance and 5-months, on average, after its removal. During this time, the stabilization of occlusion was controlled by the orthodontist.

A Philip instrument, model BV Pulsera was used. The images were recorded ona Philips DVD + RW using a recorder coupled to the Medical DVD Recorder, MDVDR – 100 instruments. During the exam, the children sat comfortably on a chair in erect posture wearing a lead apron for radiologic protection. The videofluoroscopic images were capured at a rate of acquisition of 30 frames per second in the lateral and anteroposterior view, with an anterior limit at the lips and a posterior limit at the vertebrae. Mean time of exposure to radiation was 2.0 min for each exam. The images were analyzed using a Vegas Pro.0 image editing software (Sony) that permitted frame by frame analysis and time recording in seconds.

Two Bono® Nestlé cookies were offered to each child (one in a lateral view and the other in an anteroposterior view). Each cookie weighed 11 g and was shaped as a chocolate-flavored mini-pie with Bariogel® 100% barium sulfate (Cristália laboratory, Itapirica, SP, Brazil). The children were instructed to eat the cookies in the usual manner and their natural mastication and swallowing behavior was investigated.

The variables assessed were oral preparatory transit time, oral swallowing transit time, number of cycles and masticatory frequency. For the investigation of preparatory oral transit time and of oral swallowing transit time we considered the definition of the swallowing phases proposed by Logemann.15 The author considered the oral preparatory phase as the period of preparation of the food bolus corresponding to mastication, and the oral phase of swallowing as the time of propulsion of the food bolus.

For the measurement of oral preparatory transit time (seconds) we considered the time from the first movement of bolus capture to bolus organization, and for the measurement of oral transit time we considered the time from the beginning of bolus propulsion to the point when the last portion of the contrasted bolus passes the base of the tongue and crosses the mandible (Fig. 1).

Figure 1.

(A) Beginning of the oral preparatory phase; (B) bolus organization; (C) final oral phase.

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Masticatory frequency was calculated as number of masticatory cycles per total time of bolus trituration, in seconds.16 Time started to be counted at the beginning of food cutting, ending with the final chewing stroke before the complete organization of the food bolus. The count of number of cycles and the masticatory frequency were considered by analysis in the anteroposterior view (Fig. 2).

Figure 2.

(A) Food cutting; (B) bolus trituration (right side).

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The SPSS statistical package, version 17.0, was used for all analyses and the level of significance was set at p < 0.05. The Student t-test was used for group comparisons regarding all variables studied. The paired t-test was used to compare the crossbite group before and after RME and the unpaired t-test was used for comparison of the crossbite group and the control group. The p-values were adjusted using the false discovery rate method to control the multiple comparisons.17