Introduction
Various types of appliances have been tried by the orthodontist for retraction of maxillary anterior teeth in extraction cases.1 The main goal of retraction of anterior teeth in extraction cases is to keep the vertical dimension stable so as not to allow downward and backward rotation of mandible. If mandibular plane angle opens during treatment for subjects with skeletal class II malocclusion having retrognathic mandible, it may appear more retrog- nathic with downward and backward rotation of mandible. In vertical grower, downward and backward rotation of mandible may also exaggerate open bite thus worsening the aesthetics. Any unfavourable changes in post treatment mandibular angle affects aesthetics and balance Premolar extractions are routinely done during fixed orthodontic treatment for improving the profile of the patient. Orthodontic mechanics should be such as so not to alter the mandibular angle in adult patients undergoing all 1st premolar extraction.
The aim of this study was to compare changes in mandibular rotation following fixed ortho- dontic treatment on subjects who have undergone extraction of all first premolars.
Sample selection
Sample selection was done solely on the pre-treatment criteria and pre-treatment records. The study was retrospective in nature thus the samples were selected only after the completion of treatment.
Material and Methods
The sample consisted of pre and post cephalogram of 25 subjects (13 females and 12 males) aged 18-25 years.
Exclusion criteria
No other method was used for retraction such as headgears.
Patient who have undergone orthodontic treatment previously.
Orthognathic surgery.
Lateral cephalogram were taken from record files of the patient’s lateral cephalogram was taken from the same machine (planmeca proline XC) in department of Oral medi cine and Radiology (using panoramic x-ray machine planmeca proline XC) exposed at 68.0kV 5mA for a exposure time of 23.0 seconds(Figure 1). The subjects were placed at a distance of 60 inches. Soft copy of lateral cephalogram was taken by copying it into a CD rom. Nemoceph (dental studio v6.0) software was used for tracing and analysing the lateral cephalogram. The size of headfilm used was 8 X 10 inches.
Lateral cephalograms were taken using standard protocols. Lateral cephalogram was taken in natural head position with lips relaxed and teeth in centric occlusion. Soft copies of lateral cephalograms were transferred to a computer loaded with planmeca software from where the digital lateral cephalogram was saved in bitmap file and taken into a CD ROM.
The soft copies of all the lateral cephalograms was transferred to nemotec software program (dental studio NX version 6.0).(Figure 2)
Calibration of image: image calibration was done by identifying the cross hairs 10mm apart on lateral cephalogram using the calibration tool of the (nemotec) software. Identification of landmarks was done after using image enhancement feature of the software like brightness, contrast adjustment and magnification were used to identify individual cephalometric landmarks as precisely as possible. The landmarks were marked using the inbuilt touchpad of the laptop. This was done for both pre and post treatment cephalogram. Following landmarks were used in the study:-
The reference points taken on the lateral cephalogram for this study included: (Figure 3)
Nasion (N): The most anterior point on the frontonasal suture in midsagittal plane
Sella (Se): Midpoint of the cavity of sella turcica
Porion (Po): The most superiorly positioned point of the external auditory meatus.
Orbitale (Or): Lowest point on the inferior rim of the orbit
Gonion (Go): A constructed point on the intersection of lower and posterior mandibular border.
Menton (Me): Lowest point on the mandible.
Gnathion (Gn): A midpoint located between the anterior (pogonion) and inferior (men ton) points of the bony chin.
Following four planes were used in the analysis. (Figure 4)
Mandibular plane (tweed) : a tangent was drawn to the lower border of the mandible Mandibular plane (steiner): A line drawn from gonion to gnathion.
Frankfort horizontal plane: a plane connecting lower border of the orbit and superior point on the auditory meatus.
S-N plane: a plane formed by connecting the centre of sella turcica and point nasion.
Parameters used to assess the changes included anterior face height (N-Me) and posterior face height (Se-Go) (fig5). Angular measurements taken in the study includes FMA, SN- GoGN (fig4). The anterior and posterior face height was taken to deduce the facial growth pattern using Jaraback ratio.
Observation and Results
The changes in various parametres have been summarised in Table 1.
Mean difference of SN-GoGn (0.15±0.07), FMA(0.23±0.52), Anterior facial height (0.18±0.01) and posterior height(0.45±0.01) and Jarabak ratio (0.47±0.01) did not show statistically significant difference pre and post treatment (Table 1). Assessment of pre and post treatment results do not show any alteration in mandibular if proper mechanics is followed during retraction in premolar extraction cases.
Table 1
Sample size distribution of group I and group II
|
Sample |
Group I (control) |
Group II (study) |
|
Maxillary study model (N=50) |
n=25 |
n=25 |
Table 2
Depicts the statisticsfor the orientation, length strength and shape of left and right side of palatalrugae (I-IV) in group I
Table 0
Table 0
Table 0
Table 3
Depicts the statistics for the orientation, length strength and shape of deviated and non-deviated side of palatal rugae (I-IV) In Group II)
Table 0
Table 0
Table 0
Discussion
This study was aimed to assess the relationship between changes in mandibular plane angle before and after treatment in cases with premolar extraction. Brodie2 stated that the facial pat- terns once established did not change much. Bishara 3 in his study concluded that differences among facial types were more pronounced at adulthood. Studies have shown that the growth changes of the facial tissues, although not completed, occurred predominantly before the age of 18 years, hence samples included subjects above 18 years. The results of present study stated that vertical dimension did not alter significantly from pre to post treatment in subjects who had undergone premolar extraction. Staggers,4 Beit, 5 Sharma,6 Al-Nimri,7 Kim8 and Ko- cadarel9 showed no significant increase in vertical dimension between premolar exrtraction and no extraction cases. According to these authors extraction did not result in collapse of vertical dimension when compared with non-extraction cases. For present study there was no alteration in mandibular plane angle in extraction cases. Similar to present study, Alhajeri- K,10 reported a non-significant decrease in SN GoGn when compared to post treatment rec- ords. He also reported contradictory result for anterior facial height which showed significant increase in this study whereas it was non-significant in the present study. Aras A. et al.,11 re- ported no significant alteration in mandibular plane related in subjects with skeletal open bite who had undergone all 1st premolar extraction. Dwivedi et al.,12 reported significant increase in mandibular plane angle in post treatment tracing in subjects with hyperdivergent growth pattern.
Though sample was mixed in present study but we achieved no significant difference in man- dibular rotation between pre and post treatment. Thus it can be suggested that appropriate mechanism as per growth pattern must be followed so as to keep vertical dimension stable and prevent distortion of facial aesthetics.
Further studies must be directed in larger sample size divided as per growth pattern to ob- serve changes between pre and post treatment.
Conclusion
No significant alteration in SN-GoGn angle and FMA was observed from pre to post.
Changes in facial height (anterior and posterior) was insignificant between pre and post treatment
No significant alteration was seen in Jarabak’s ratio between pre and post treatment.
It can be suggested that appropriate mechanics as per growth rotation must be followed to keep vertical dimension stable.
