|Year : 2017 | Volume
| Issue : 4 | Page : 239-244
Effect of first premolar extraction on point A, point B, and pharyngeal airway dimension in patients with bimaxillary protrusion
Sunilkumar Nagmode1, Prasad Yadav2, Manali Jadhav3
1 Prof., Department of Orthodontics, SMBT Dental College and Hospital, Ahmednagar, Maharashtra, India
2 Former PG Student, Department of Orthodontics, SMBT Dental College and Hospital, Ahmednagar, Maharashtra, India
3 Second Year PG Student, Department of Orthodontics, SMBT Dental College and Hospital, Ahmednagar, Maharashtra, India
|Date of Submission||14-Mar-2017|
|Date of Acceptance||21-Jul-2017|
|Date of Web Publication||12-Oct-2017|
Department of Orthodontics, SMBT Dental College and Hospital, Amrutnagar, Ghulewadi, Sangamner, Ahmednagar - 422 608, Maharashtra
Source of Support: None, Conflict of Interest: None
Objective: The aim was to determine the effect of first premolar extraction on point A, point B and pharyngeal airway dimension in patients with bimaxillary protrusion. Materials and Methods: The following study included pre- and post-orthodontic treatment cephalograms of thirty bimaxillary protrusion patients. First premolars were extracted and all the cases were treated with maximum anchorage. Cephalometric radiographs were used to measure the changes in point A, point B, and pharyngeal airway dimensions. Pre- and post-treatment variables comparison was done using paired t-test and study of relationship between soft- and hard-tissue variables was carried out using linear regression equation. Results: In the results, there was a statistically significant increase in upper airway space (P < 0.05) and reduction in upper adenoid thickness (P < 0.05), tongue length (P < 0.05), and inferior airway space (P < 0.05). Retraction of mean point A and soft tissue point A (sA) was 3.3 mm (P < 0.001) and 2.1 mm (P < 0.001) and mean point B and soft tissue point B (sB) was 3.8 mm (P < 0.001) and 2.6 mm (P < 0.001), respectively. Between retraction of point A and soft tissue point A (r = 0.9594, t = 101.84, P< 0.01) and point B and soft tissue point B (r = 0.9102, t = 83.246, P< 0.01) a significant degree of correlation was seen to exist, along with lips retraction, retraction of the skeletal and soft tissue points A and B contributed to the decrease in hard and soft-tissue convexity. Conclusions: Upper airway space was increased which may be caused by lymphoid mass regression. Inferior airway space was reduced with the extraction of the first premolars for the treatment of bimaxillary protrusion. Retraction of Sa and Sb was brought about by retraction of skeletal point A and point B. Skeletal points and overlying corresponding soft tissue points showed nearly proportionate changes.
Keywords: Point A, point B, premolar extractions, soft tissue point A, soft tissue point B
|How to cite this article:|
Nagmode S, Yadav P, Jadhav M. Effect of first premolar extraction on point A, point B, and pharyngeal airway dimension in patients with bimaxillary protrusion. J Indian Orthod Soc 2017;51:239-44
|How to cite this URL:|
Nagmode S, Yadav P, Jadhav M. Effect of first premolar extraction on point A, point B, and pharyngeal airway dimension in patients with bimaxillary protrusion. J Indian Orthod Soc [serial online] 2017 [cited 2018 Jul 17];51:239-44. Available from: http://www.jios.in/text.asp?2017/51/4/239/216654
| Introduction|| |
Bimaxillary protrusion is stated as a condition in which the upper and lower incisors are proclined and protrusive, which results in increased lip procumbency. It is visible in almost every ethnic group although African–American and Asian populations frequently show this feature. Many patients with bimaxillary protrusion seek orthodontic treatment to reduce the procumbency because of the negative perception of protrusive dentition and lips.
The underlying cause of bimaxillary protrusion is multifactorial and includes genetic component along with environmental factors such as mouth breathing, tongue thrust, lip sucking habits, and tongue volume. In a study reported by Keating, bimaxillary protrusion was found to be associated with shorter posterior cranial base, a longer and more prognathic maxilla and a mild Class II skeletal pattern. A smaller upper and posterior face height, diverging facial planes, and a procumbent soft tissue profile with low lip line seen in Caucasians was also shown by him. The main aim behind the orthodontic treatment of bimaxillary protrusion is to retract the maxillary and mandibular incisors with the resultant reduction in soft tissue procumbency and convexity which is brought about by extracting the four first premolars followed by the retraction of anterior teeth using maximum anchorage mechanics.
Lateral cephalograms which have been used to study airway dimensions can identify the commonly used landmarks of the airway structures. Extraction of first premolar teeth in a group of patients with bimaxillary protrusion who may have different airway dimension may change dimensions of the upper airway. It is extremely essential to know about the changes in the relationship of soft tissues to skeletal and dental structures which actually affect the treatment outcome with orthodontic tooth movement since the objective of treating bimaxillary protrusion cases is to obtain an esthetically superior profile and harmonious lip relationship. The purpose of this study was to study the results of fixed orthodontic treatment with extraction of first premolar teeth in patients with a bimaxillary protrusion on pharyngeal airway dimensions and to relate the skeletal point A and point B changes with the soft tissue points A and B.
| Materials and Methods|| |
Ethical approval was obtained from the SMBT Institutional review committee. Before and after treatment lateral cephalograms of 30 adults having Class I bimaxillary protrusion treated at the Department of Orthodontics, in our Institute were selected for this study.
Sample selection criteria included:
- Minimum age 16 years
- Class I molar, canine and premolar relationship
- Well-aligned arches with no or minimal crowding
- Upper and lower lips with protrusion
- Before and after treatment radiographs with better hard- and soft-tissue outlines
- Patient presenting with medical history of pharyngeal pathology or nasal obstruction, obstructive sleep apnea, snoring, adenoidectomy, and tonsillectomy were not included
- Treatment includes fixed orthodontic appliance using maximum anchorage and maximal retraction of anterior teeth.
For each cephalogram, 21 landmarks for sagittal airway measurements were identified. Definition of different points and measurements used is shown in [Table 1] and [Figure 1]. All cephalometric measurements were performed manually using a ruler to the nearest 0.1 mm so that the linear distance between the two points can be measured, making the measurements and protractor to the nearest 0.5° to measure the angular measurements.
For point A and point B changes a constructed plane joining the points porion and orbitale-Frankfort horizontal (FH) plane, drawn at an downward angle of 7° to SN plane through point “S” was considered. It was referred to as a plane that is modified and denoted by “FH.” FH perpendicular was constructed perpendicular to the FH plane through point sella-”S” and denoted by “FHp.” The linear measurements were carried out from FHp plane to skeletal and soft tissue points A and B [Figure 2] and [Table 2].
|Figure 2: Cephalometric landmarks, measuements, and reference planes. (1) AFHp, (2) BFHp, (3) ssFHp, (4) siFHp, (5) SNA, (6) SNB, (7) ANB, (8) IIA, (9) IMPA, (10) U1SN, (11) sella nasion and gonion gnathion, (12) TU1FHp, (13) AU1FHp, (14) TL1FHp, (15) AL1FHp, (16) IsFHp, (17) IiFHp|
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The cephalometric values of pretreatment and posttreatment cephalograms were evaluated using paired t-test. Mean and the standard deviation are calculated [Table 3]. Significance was predetermined at 0.05 levels. A linear regression analysis was used to predict changes in the soft tissue points A and point B.
|Table 3: Means and standard deviations of pre- and post-treatment measurements for soft tissues and airways dimensions (n=30)|
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| Results|| |
In the present study, we observed that there was an increase in the measured upper airway thickness and a decrease in upper adenoid thickness. Tongue length was reduced. Similarly, there was a decrease in the measured inferior airway space.
Cephalometric measurements for point A and B
As a result of retraction of incisors, the mean point A was retracted and mean sA was retracted. Similarly, the point B was retracted and sB was retracted. Angle SNA and angle SNB were reduced. The angle formed by the difference by joining points sella, nasion and point A and sella, nasion and point B, i.e., ANB angle and the angle between sella nasion and gonion gnathion did not show any significant changes. The mean interincisal angle was increased. The IMPA was decreased. The tip of the upper incisor and the tip of the lower incisor were retracted. Apices of upper and lower incisors showed retraction following treatment. The upper and lower lips were retracted. The changes in the above parameters were statistically significant [Table 4].
|Table 4: Comparison of mean and standard deviation values of skeletal and soft tissue point A and point B changes following orthodontic treatment from pretreatment to posttreatment (n=30)|
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| Discussion|| |
This study is retrospective in nature and determined the effect of premolar extraction as a part of fixed orthodontic treatment on the pharyngeal airway dimensions and point A, point B in bimaxillary protrusion patients.
The dimensions of the pharyngeal airway may be influenced by the effect of growth. It has been noticed that between 6 and 9 years and between 12 and 15 years more changes occurred in the soft tissue measurements of the posterior pharyngeal wall., This study considered the minimum age to be 16 years so as to make sure that the oropharyngeal structures had reached the adult size and the effect from growth would not affect the results.
The mean increase in the measured upper airway thickness was 1.20 mm and this improvement in upper airway thickness, i.e., nasopharyngeal airway space may not be related to retraction-extraction orthodontic therapy as the above may be due to lymphoid mass regression in the nasopharynx that is natural phenomenon in adolescents. The mean decrease in the measured inferior airway space was 0.40 mm and this was the important finding concerning airway dimensions. A study of Germec-Cakan et al. which reported that superior airway space and middle airway space increased in the minimum anchorage group also supported the above-given observations. On the other hand, the middle airway space and the inferior airway space were reduced in maximum anchorage group. The difference between the two groups was demonstrated by mesial molar movement after resolution of anterior crowding which on average was 3 mm in the minimum anchorage group. The increased posterior tongue space and the superior and middle airway dimensions have been found to be caused by the mesial molar movement. They found that the tongue space might have reduced and resulted in significant reduction of middle airway space and inferior airway space which was around 3 mm after significant incisor retraction. Similarly, in this study, all the cases were treated with maximum anchorage, and we found that the inferior airway space was reduced. After studying the relation between the amount of incisor retraction and reduction in airway size it was observed that mainly the changes occurred in the antero-posterior direction. The tongue shifted posteriorly, and there was a reduction of anterior boundary of the oral cavity and its contents. Thus, the adaptation of the tongue is responsible for reducing velopharyngeal, and glossopharyngeal airway and hence, the association between the movement of anterior teeth and the decrease in pharyngeal airway at the soft palate and tongue level is clearly explained.
In a study done by Wang et al. and Bhatia et al., they observed that the velopharyngeal, glossopharyngeal, and hypopharyngeal airway size was decreased with the retraction of incisors in bimaxillary protrusive adult patients treated with the extraction of four premolars similar to our findings. Furthermore, they concluded that the treatment resulted in narrowing of pharyngeal airway size. Similarly, Hang  in his study showed that obstructive sleep apnea was effectively resolved with re-opening of four extraction spaces that provided space for the tongue and opened airway space, which was previously reduced by the retraction of anteriors. However our results differed from the result of a study done by, Valiathan et al. which showed that oropharyngeal airway volume was not affected as a result of extraction of four premolars with incisor retraction.
The other important finding in this study was tongue length that was reduced significantly (mean reduction = 5.60 mm). The restriction of the tongue after bimaxillary proclination treatment is considered to be the main cause of relapse and space reopening, and the reduction in the tongue length thus matches the expectations. In this group, there was no significant change in the hyoid bone position. This matched with the findings reported previously.
In this study, it was noticed that following incisor retraction there was a relationship between retraction of skeletal point A (A) and soft tissue point A (sA) and point B (B) and soft tissue point (sB). The changes in the lip positions at the bases were found to be caused with the backward movement of the skeletal points A and B and the soft tissue overlying these osseous points that followed them. The upper lip was slightly higher in relation to the lower lip. This was in contrast to the findings of LaMastra, where skeletal point A moved back by 2.34 mm, soft tissue point A moved back by 1.75 mm, skeletal point B moved back by 1.89 mm, soft tissue point B moved back by 1.73 mm. This difference could be traced to the difference in the amount of tooth movement in the maxilla and mandible in Class II Division I cases unlike Class I bimaxillary protrusion cases in this study.
The clinical importance of this study is that the clinician must position the incisors in the most esthetic position by initial up-righting and some bodily movement. The reciprocal movement of the roots of anterior teeth labially during treatment should be avoided. Thus, it is necessary to maintain the root positions and retract the incisors in this malocclusion group. The labial movement of the roots increases the skeletal convexity due to the forward movement of the skeletal points which could cause undesirable treatment results. The decrease in the dimensions of pharyngeal airway and its effect on breathing during sleep are necessary to be taken into consideration. The posture of the tongue and oral space are the crucial factors to be taken into account for fixed orthodontic treatment with bicuspid extractions.
As suggested by many previous studies regarding the reliability of lateral cephalograms in the evaluation of pharyngeal airway, their use is justified in this study. Airway being a three-dimensional structure, lateral cephalograms has a disadvantage of providing only a linear dimension of the airway. The airway needs to be studied in three-dimensions so that its different parts can be evaluated as they behave independently. Thus, 3D CBCT studies are preferred over lateral cephalograms considering their superiority. Further studies may be aimed at long-term effects of orthodontic treatment on pharyngeal airway using CBCT but it will expose the patients to unnecessary radiation exposure and may not be justified for them, hence being a limitation of this study.
| Conclusions|| |
- Upper and lower first premolar extraction for the treatment of bimaxillary protrusion reduces the inferior airway space
- Lymphoid mass regression, a natural phenomenon in adolescents may be responsible for the increase in upper airway space
- Retraction of skeletal points A and B lead to retraction of sA and sB
- Lip retraction and retraction of the skeletal and soft tissue points A and B reduced the soft tissue convexity and enhanced the soft tissue profile
- Nearly proportionate changes in the skeletal and soft tissue points A and B were seen with comparatively increased response in the upper lip than the lower one.
We would like to thank the administration of SMBT Dental College and Hospital, Sangamner, Maharashtra for permitting us to undertake this study. We also would like to acknowledge the postgraduate students of the Department of Orthodontics and Dentofacial Orthopedics for their support during the study.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4]