Year : 2009 | Volume
: 27 | Issue : 4 | Page : 202--204
The effect of posterior bite-plane on dentoskeletal changes in skeletal open-bite malocclusion
S Emami Meibodi1, SAR Fatahi Meybodi2, AH Samadi3,
1 Department of Orthodontics, Islamic Azad University, Tehran, Iran
2 Department of Orthodontics, Tehran University of Medical Sciences, Tehran, Iran
3 Private Practice, Tehran, Iran
S Emami Meibodi
Apartment 8, No.5, Jalinus Alley, Yarmohammadi Alley, Kolahdouz St., Shariati Ave., Tehran
With regard to the vertical problem of skeletal open-bite malocclusion, this study was undertaken to evaluate the effect of upper posterior bite-plane on the dentoskeletal changes of skeletal open-bite malocclusion. The material consisted of 23 patients, with skeletal open-bite in mixed dentition period. The patients were treated by upper removable posterior bite plane appliance. Before and after treatment lateral cephalogram were obtained. Certain angular and linear variables were measured. The pre-treatment and post-treatment measurements were compared using paired t-test to evaluate the significance of the results. There were significant changes in vertical incisor overlap following treatment with upper posterior bite plane. Increase of PFH, Jaraback index, UAFH/LAFH ratio were significant .There was significant decrease in SN-MP angle. The dentoalveolar heights of the upper and lower anterior segment were increased as well as the distance of the lower molars to mandibular plan. Only the maxillary first molar height did not change.
|How to cite this article:|
Meibodi S E, Fatahi Meybodi S, Samadi A H. The effect of posterior bite-plane on dentoskeletal changes in skeletal open-bite malocclusion.J Indian Soc Pedod Prev Dent 2009;27:202-204
|How to cite this URL:|
Meibodi S E, Fatahi Meybodi S, Samadi A H. The effect of posterior bite-plane on dentoskeletal changes in skeletal open-bite malocclusion. J Indian Soc Pedod Prev Dent [serial online] 2009 [cited 2013 May 22 ];27:202-204
Available from: http://www.jisppd.com/text.asp?2009/27/4/202/57653
Skeletal open-bite is one of the most difficult malocclusions to treat. The morphologic pattern usually consists of excessive vertical height in maxillary dentoalveolar portion,  and the absence of over-bite in anterior segment of dental arches.  Kelly et al have reported the prevalence of this malocclusion in 3.5% of white American children and 16.5% of African-Americans,  while a prevalence of 3.5% in patients aged 8 to 17 is reported by Proffit et al.  In an investigation it was shown that among patients suffering from skeletal open-bite, 41% had a Cl II Div 1 malocclusion  which was created due to improper growth pattern, inheritance or oral habits. , If left untreated, several unfavorable sequela would be encountered such as posterior cross-bite, anterior facial height excess and facial disproportion, and lip incompetency ,,,,,,, and orthodontic treatment could become so difficult that orthognathic surgery would be inevitable.
Vertical chin-cup, high pull head-gear, vertical elastics, functional appliances and skeletal anchorage have been proposed for treatment. ,,,, Among the treatment protocols is growth modification, recruitment of growth remained, which consists of early treatment of vertical dimension during mixed dentition period by restraining vertical alveolar growth with a functional appliance. Posterior bite plane, which could be considered a simple functional appliance, could be used for this purpose. Some believe that forward and upward rotation of mandible achieved by this appliance is beyond that of fixed orthodontic appliances. ,, Regarding controversies existing about this appliance, this study was undertaken to evaluate the effect of posterior bite plane on dentoskeletal characteristics in skeletal open-bite.
Materials and Methods
Twenty three patients (13 girls and 10 boys), aged 9.5 ± 1 years, who were referred to an academic center and a private clinic in Tehran were selected based on the following criteria: mixed dentition period, vertical growth pattern with SN-MP > 36°, anterior open-bite > 1 mm, lack of history of orthodontic treatment, trauma and dentofacial syndromes. All the patients were treated with a posterior bite plane, which consisted of a simple removable maxillary Hawley appliance with occlusal acrylic plate from distal of first permanent molar to mesial of first deciduous molar that vertically exceeded the freeway space by 2 mm. The minimum treatment period was 8 months. The pre- and post-treatment lateral cephalograms were obtained, traced and the following measurements were done with an accuracy of 0.5 mm for linear measurements or 0.5° for angular measurements [Figure 1]: SN-MP, AFH, PFH, Jaraback index, UAFH/LAFH. In order to evaluate the vertical position of dentition, the distance of central incisor edge (1 for upper incisor, /1 for lower incisor) and mesial cusp of first permanent molar (6 for upper molar, /6 for lower molar) to palatal plan (PP) or mandibular plan (MP) for respective jaw were measured. All the parameters were re-measured for the 10 randomly selected cases; since the difference between 2 was not significant, the first measurements were considered for statistical analysis by paired t-test.
SN-MP was significantly decreased, where as PFH, Jaraback index and UAFH/LAFH were significantly increased; change in AFH was insignificant [Table 1].
Regarding vertical dimension of dentition, all the measurements increased significantly unless those related to upper molar (6-PP) where the changes were insignificant [Table 2].
This study showed that the posterior bite plane as a removable appliance caused the SN-MP to decrease significantly; since AFH had not changed while PFH increased, it seems that the appliance made the soft tissue and muscles to stretch, induced the growth in posterior region and mandibular rotation upwardly. Significant increase in UAFH/LAFH confirms anterior rotation of mandible and decrease of LAFH.
Significant increase in mandibular and maxillary anterior dentoalveolar height indicates that one of the reasons that caused the open-bite to close was the eruption of anterior teeth. In the upper first molar region, dentoalveolar height did not undergo any increase (and even slightly decreased); the conclusion is that the posterior-bite plane inhibited the eruption of upper molars and dentoalveolar growth, which are among the most important factors in vertical growth. As for lower first molar, the dentoalveolar height increased; although it may seem the contrary, the appliance did not inhibit its eruption.
Stellzig  found that in open-bite patients, bite block caused the vertical growth to decrease and Jaraback index to increase. He declared that bite block would stimulate the masticator muscles consistently, and produce an intrusive force against the posterior segment. In our study, decrease in SN-MP and increase in Jaraback index also indicate vertical growth inhibition; but dentoalveolar height increased in mandible while remaining constant in maxilla.
Kuster  declared that bite block would produce intrusive forces on upper and lower molars; by means of electromyography he observed increased activity in the temporalis and masseter muscles in the beginning of the treatment, which remained constant thereafter. He considered the eruption of anterior segment as the cause of open-bite closure, the same observation we had encountered.
Mavropoulos  studied the effect of bite plane in growing mice and declared that the major mechanism of open-bite closure was anterior rotation in mandible, posterior segment intrusion and increase in mandibular growth. He also stated that the functional appliance displaced the mandible, stretched the surrounding soft tissue and exerted forces to dentoskeletal structures directly or indirectly. He believed that the appliances that open the bite can influence the mandibular morphology and observed changes in mandibular plan, occlusal plan and coronoid process length.
The results of this study revealed that with posterior bite plane therapy during mixed dentition period in patients suffering from skeletal open-bite, one could inhibit the posterior maxilla to grow vertically and with anterior mandibular rotation due to growth in posterior face, disharmony would be relieved, saving patient from future complex orthodontic treatment or even orthognathic surgery.
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