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Authors : Dr. Manisha Kamal , Dr. Ajit Rohilla , Dr. Mahesh  Goel.


This retrospective cephalometric study compares the facial heights produced in 10 patients treated with twin block appliance in the department of Orthodontics, PGIDS, Rohtak. The average age for the twin block appliance therapy in patients was 11-13 years with a definite inclusion and exclusion criteria. The total treatment with twin block appliance was 10-12 months inclusive of active and retentive phase. At the end of the retentive phase the post treatment cephalometric facial height were measured and compared with the pre treatment cephalometric facial height and it was found to be statistically significant.


Functional appliance therapy has become an increasingly popular method of correcting class 11 malocclusion, with appliances such as bionator, frankel 2, activator, the fixed and removable types of herbst appliance1. Another functional appliance system that has shown increased use during the last decade is the twin block appliance. The twin block appliance was developed by William .J. Clark of fife, Scotland, for use in the correction of class 11 malocclusion   characterized in part by mandibular skeletal retrusion.2

Lund and Sandler3, conducted a prospective clinical trial in which they compared patients treated with twin block appliance with control sample and it was found that the treated group demonstrated an increase in the mandibular length with slight inhibition of forward maxillary growth. The upper molars were distalized in the twin block group, some proclination   of lower incisors was there and lingual tipping of upper incisors was noted as well.

Very few studies  had compared the facial height facial heights in the pretreatment and post treatment twin block patients. Accordingly the purpose of the present study is to compare the facial heights in the pre treatment and post treatment group

Aims and Objectives

  1. The present study was conducted with the aim and objective to compare the facial   heights in the pre and post treatment   patients treated with the twin block appliance.
  2. To compare the   jarabak ratio in the pre and the post treatment   groups.

Material and method

The cephalometric records of 10 patients before and after the completion of twin block therapy treated by me in the department of Orthodontics PGIDS, Rohtak   were used for the study . The   patients   who were treated with the   twin block therapy had

       Inclusion criteria:

  1. Skeletal class 11 molar relationship   (ANB > 4 degrees ) .
  2. Mandibular retrognathy ( SNB < 78 degrees ) .
  3. Overjet > 5mm .
  4. SN-GoGn – (30-35 degrees) .
  5. Minimum  crowding   in the dental  arches.
  6. Bilateral  class 11 molar  and canine relationship.
  7. Patient with CVMI 2 or CVMI 3

Exclusion  criteria:

  1. No history of orthodontic treatment
  2. Congenitally missing or extracted permanent teeth ( except third molars )
  3. Posterior cross bites
  4. Severe   facial   asymmetries.
  5. Systemic   diseases   that may  affect  orthodontic  treatment results.

 All the   patients  were given  standard twin block appliance and the patients had undergone active phase for around 6-8 months followed by a retentive phase of 2-3 months. All the patients had class 1 or super class 1 molar relationship   at the end of twin block   phase of treatment

For those patients undergoing twin block treatment with mild to moderate overjets at the beginning of treatment, the appliances were constructed from bite registrations taken with the incisors in an end   to end position. In cases where pretreatment over jet exceeded 6 to 7 mm, the bite registration  was done step wise. The bite registration was allowd for 5-7 mm of vertical opening in the regions of posterior bite blocks for control vertical development of molars and premolars   through selective removal of acrylic   during treatment. All patients involved in the study were asked to wear the appliance 24 hours a day. After completion of the retentive phase that was nearly after 10-12 months , the pre treatment and the post treatment cephalogram were taken and   tracings were done to calculate the linear measurements.

Observations and Results

Showing comparison of PFH in pretreatment vs. post-treatment

Pre PFH (n=10)

Post PFH (n=10)

Statistical significance



<0.01 significant

Showing comparison of AFH in pretreatment vs. post-treatment

Pre AFH (n=10)

Post AFH (n=10)

Statistical significance



<0.05 significant

Showing comparison of ratio in pretreatment vs. post-treatment

Pre AFH (n=10)

Post AFH (n=10)

Statistical significance



<0.01 significant

Showing sexwise comparison of various parameters in pretreat. vs. post-treat.
  Male (n=6) Female (n=4) Statistical significance
Age 12.5±0.836 12.5±0.577 >0.05 N.S.
Pre PFH 71.16±6.14 70.5±7.76 >0.05 N.S.
Post PFH 78.16±6.40 72.5±5.68 >0.05 N.S.
Pre AFH 102.16±5.03 105.75±6.02 >0.05 N.S.
Post AFH 108.91±2.49 105.75±5.90 >0.05 N.S.
Pre Ratio 69.66±5.25 66.54±3.94 >0.05 N.S.
Post ratio 71.74±5.44 67.55±3.25 >0.05 N.S.


Control of the vertical dimension is one of the proposed benefits of the twin block appliance . It is believed that the acrylic bite blocks either can inhibit molar eruption in patients for whom an increase in facial height is undesirable   or can be modified   to allow posterior dental eruption   in situations   when increasing facial height   is primary goal of treatment. Indeed Clark has stressed   selective removal of acrylic to allow an increase in the vertical dimension as an important component of twin block therapy.

In the present study all patients of class 11   who had   short anterior facial heights were taken and the posterior acrylic bite blocks were trimmed   during treatment   in an attempt to increase the vertical dimension. There   was an significant increase in the   anterior facial height .This was similar to the results of the study done by Mc.Namara et al .

The anterior facial height and posterior facial height increased by 3 mm and 3.5 mm respectively . Significant increase were observed in the jarabak ratio which is the posterior facial height divided by anterior facial height percentage4.


  1. Linda  Ratner Toth    Treatment  effects  produced  by  twin  block  appliance  and  the  FR-2  appliance  compared  with  untreated  class  11   Am J Orthod Dentofacial Orthop 1999; 116:597-609
  2. Asli Baysal, Tancan Uysal : Dento skeletal  effects  of  twin blocl  and  herbst  appliances  in  patients  with  class 11  division 1  mandibular  retrognathy  Europ. J of Orthod. 2013 :22 (3):207-210
  3. Mills CM, McCulloch KJ  Treatment effects of the twin block appliance: a cephalometric study. Am J Orthod Dentofacial Orthop. 1998;114 (1):15-24.
  4. Antanas Sidlauskas Clinical Effectiveness of the Twin Block Appliance in the treatment of Class  11  division  1  malocclusion.
  5. Stomatologija, Baltic Dental and Maxillofacial Journal, 7:7-10, 2005
More references are available on request.

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