American Journal of Orthodontics and Dentofacial Orthopedics
Short CommunicationThe effect of Herbst appliance treatment on the mandibular plane angle: A cephalometric roentgenographic study
Section snippets
Material
The material was comprised of longitudinal data, derived from lateral head films of 80 patients (47 males and 33 females) with Class II malocclusion and treated with the Herbst appliance. The subjects were treated for an average period of 7 months and followed 4.5 to 5 years after therapy. All subjects were treated to a Class I molar relationship. The age of the subjects at start of treatment varied between 10 and 14 years. The appliance design used has been described previously.10
The
Method
The radiographic data were collected at the following times:
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T1 Before treatment
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T2 Start of treatment (insertion of the Herbst appliance)
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T3 After treatment (removal of the Herbst appliance)
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T4 Six months after removal of the Herbst appliance (at the time the occlusion had settled)
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T5 Follow-up (4.5 to 5 years after removal of the Herbst appliance)
On the before treatment head film, the nasion-sella line (NSL) was defined by the anatomic points nasion and sella. The NSL was transferred to all
Statistical methods
For the different variables, the arithmetic mean (M), the standard deviation (SD), the maximum (Max), and minimum (Min) were assessed.
Student's t tests were performed to evaluate the difference in the changes of the ML/NSL when comparing the various observation intervals, the three vertical jaw base relationship groups, and the gender groups. Pearson's correlation coefficients (r) were calculated to assess the interrelations between the pretreatment ML/NSL and its changes during Herbst
Error of the method
For the assessment of the method error in the measurement of the mandibular plane angle, the lateral head films from 10 randomly selected subjects were analyzed twice. The following formula was used for the method error (ME) calculation: Where d is the difference between two measurements of. a pair and n is the number of subjects. The combined method error in defining and transferring the NSL from the first head film to the following films, as well as assessing and measuring the mandibular
Results
The changes in ML/NSL angle for each subject and each observation interval are shown in Fig. 1. A great interindividual variation was present.
At start of treatment when the appliance was placed (T1-T2), the ML/NSL angle
Discussion
In evaluating the results, it should be taken into account that the hyperdivergent and hypodivergent groups were relatively small.
The average changes in the ML/NSL angle for the total subject material showed a characteristic pattern. The increase of ML/NSL at start (T1-T2) was a result of the incisal edge-to-edge construction bite, which leads to a backward autorotation of the mandible. The decrease in ML/NSL from start to after treatment (T2T3) can be attributed to a forward autorotation of
Conclusion
A considerable interindividual variation in the short-term and long-term effects of Herbst appliance treatment on the mandibular plane angle exists. However, Herbst treatment seems not to result in an undesired backward rotation of the mandible.
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2018, American Journal of Orthodontics and Dentofacial OrthopedicsCitation Excerpt :We found a minimal change in the FMPA across the Herbst and Class II control groups at all 3 time points with some individual variations in all groups. This correlates well with previous cephalometric studies examining changes in the FMPA with Herbst treatment.40,41 The anterior displacement of the glenoid fossa is one purported skeletal change induced by the Herbst appliance that is thought to contribute to an increase in the horizontal projection of the mandible.