A randomized clinical trial to assess the sagittal effects of Transforce transverse appliance (TTA) and NiTi palatal expander (NPE) on skeletal class II malocclusion in growing patients during retention phase - A cephalometric study using a historical control group

Abstract

Objectives: To evaluate and compare the skeletal changes during the retention period after expansion with "Transforce Transverse lingual or palatal Appliance®" (TTA) and "NiTi Palatal Expander®" (NPE) in growing subjects with class II division 1 malocclusion and to compare these changes with a matched historical control.

Subjects and methods: A unicentric two arm, parallel randomized clinical trial with additional historical control group was conducted over a period of six years. The subjects in the age group of 9-13 years were screened and recruited as they reported. The inclusion criteria were: late mixed/early permanent dentition, class II or end on molar relationship, posterior transverse inter-arch discrepancy 4-8mm, overjet≥5mm, cephalometrically ANB>4° and CVMI stage CS2-CS3. Subjects were randomly allocated to two study groups (SG), TTA and NPE using block randomization. Appliances in both SG were managed and followed by a single clinician with equal standards of care. The lateral cephalograms in digital form were obtained at the beginning of the treatment (T1), post-expansion (T2) and after ten months retention period (T3). Linear positional change>1mm and angular change>0.75° were considered as a clinically significant change. Due to the ethical reasons a historical control of ten patients (CG) comparable to the SG for age and inclusion criteria was used to rule out the growth changes on serial lateral cephalograms. All Cephalometric measurements were done by a single operator blinded for the group allocation. Operator's measurement error was estimated. The study was single-blinded in regard to statistical analysis. Inter-group comparisons between SG were made by using an unpaired Student's t-test. ANOVA with post-hoc analysis was used for comparison among the study and control groups.

Results: A total of 36 subjects were recruited, 18 in each SG. Average time required to achieve the desired expansion in the TTA and NPE group was 13.6 weeks and 9.8 weeks respectively. The TTA group showed significant increase in SNB (1.54±0.33°) when compared with the control group (0.53±0.37°) and with the NPE group (0.74±0.29°) (P<0.0001). Significant differences were observed when post-retention changes in SNB, ANB, Wits appraisal, and N perpendicular to Pogonion, were compared among the three groups (ANOVA, P<0.0001). Tukey's multiple comparison showed that these mandibular sagittal changes were significantly greater in the TTA group than in NPE and the control group (P=<0.007, Bonferroni corrected value).

Conclusion: Cephalometrically significant sagittal advancement of mandible took place after expansion with TTA and NPE compared to untreated control. TTA appears to be more efficient for the sagittal positional changes than the NPE. Additional studies with larger samples are warranted to elucidate individual variations in skeletal response to the expansion protocol with these appliances.

Keywords: Class II malocclusion, maxillary transverse discrepancy; Maxillary expansion; NiTi palatal expander; Palatal expansion technique; TransForce.