A controlled clinical trial of the effects of the Twin Block and Dynamax appliances on the hard and soft tissues

Eur J Orthod. 2007 Jun;29(3):272-82. doi: 10.1093/ejo/cjm004. Epub 2007 Apr 24.


The aim of this controlled trial was to identify and quantify skeletal, soft tissue and dental changes during treatment, and immediately post-treatment with Twin Block (TB) or Dynamax appliance using the techniques of three-dimensional (3D)optical surface laser scanning, cephalometric, and clinical measurements. Sixty-two Caucasian subjects, 36 males aged 11-14 years and 26 females aged 10-13 years were enrolled in the study. The patients were placed in two groups, matched for gender and age and subsequently allocated randomly for treatment with either a TB or Dynamax appliance. Active treatment lasted 9 months followed by 3 months' post-treatment observation. Laser scanning and clinical measurements were taken at 3-monthly intervals and final cephalometric records after 12 months. Statistical analysis was performed using Wilcoxon's matched-pairs signed-rank tests. The non-compliance rates were the same for both groups (9 per cent), but a greater incidence of breakages was found in the Dynamax group. The TB was found to produce slightly more antero-posterior skeletal change, median ANB reduction, TB=2 degrees, Dynamax 1.1 degree (P=0.006), and similar forward movements of the chin and was associated with larger increases in the vertical facial dimension, median total anterior face height increase; TB=3.2 mm, Dynamax = 2.8 mm (P=0.03). The soft tissue vertical cephalometric increases were 3.6 mm with the TB, 2.0 mm with the Dynamax (P=0.036), and with laser scanning 5.05 and 2.6 mm, respectively, a difference which is likely to be more clinically relevant. The median post-treatment changes in soft tissue pogonion were -0.65 mm in the TB and +0.22 mm in the Dynamax group. The optical surface scanning mark and measure system is a valid method for quantifying soft tissue changes.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Adolescent
  • Cephalometry
  • Child
  • Face / anatomy & histology*
  • Face / diagnostic imaging
  • Facial Bones / anatomy & histology
  • Facial Bones / diagnostic imaging
  • Female
  • Humans
  • Male
  • Malocclusion, Angle Class II / diagnostic imaging
  • Malocclusion, Angle Class II / therapy*
  • Orthodontic Appliances*
  • Orthodontics, Corrective / instrumentation*
  • Orthodontics, Corrective / methods
  • Prospective Studies
  • Radiography
  • Statistics, Nonparametric
  • Vertical Dimension