COMPARING SELLA TURCICA SHAPES AND DIMENSIONS IN SKELETAL CLASSES I, II AND III BIMAXILLARY PROTRUSION PATIENTS IN A NIGERIAN POPULATION

BACKGROUND: Bimaxillary protrusion is a common type of malocclusion seen in Africans with marked protrusion of the maxillary and mandibular incisors and an increased procumbency of the lips. Management involves cephalometric radiographic evaluation and comparison with other structures within the skull. The sella turcica is one of these radiographic landmarks used in determining orthodontic parameters for management. The shape and dimensions in these patients may be affected as a result of the bimaxillary protrusion. OBJECTIVE : The aim of this study was to evaluate sella turcica shapes and dimensions in skeletal classes I, II and III bimaxillary protrusion patients in a Nigerian population STUDY

respectively.Six shapes of sella turcica were identified with the normal shape most prevalent in bimaxillary protrusion skeletal class II (52.4%) and absent in the oblique anterior wall shape in bimaxillary protrusion skeletal Class III.The double contour shape was also absent in bimaxillary protrusion skeletal classes I and III.The mean length (9.932±2.14mm),depth (6.96±1.88mm)and diameter (9.30±1.41mm)were determined.The dimensions of the sella turcica were longest in class III with mean values of 10.67mm ± 0.577 (length), 7.83mm ±2.466 (depth) and 10.0mm ±1.732 respectively.CONCLUSION: Bimaxillary protrusion patients exhibit a mean interincisal angle of 100.16°; various shapes of the sella turcica also exist for bimaxillary protrusion classes I, II and III respectively.

KEY WORDS: Bimaxillary protrusion, skeletal class, sella turcica
Bimaxillary protrusion is a common orthodontic problem seen amongst Africans and those of African ancestry and also among 1-3.

Asians
It is characterized by protrusive upper and lower incisors and an increased 2 procumbency of the lips and is a common problem seen amongst orthodontic patients in skeletal protrusion and pattern While studies found a variation in the shape in the 6 three skeletal classes , there appear to be limited data comparing the shape, dimensions and skeletal classes in bimaxillary protrusion classes II and III There however appear to be no studies in our environment comparing bimaxillary protrusion in the three skeletal classes with the dimension of the sella turcica.The aim of this study therefore was to compare bimaxillary protrusion in skeletal classes I, II and III with sella turcica shapes and dimensions in a Nigerian population

MATERIALS AND METHODS
A total number of 107 patients who were clinically diagnosed with bimaxillary protrusion were selected.Cephalometric radiographs were taken and the following inclusion criteria used: Only radiographs with the clearest reproduction of the sella turcica and the incisal teeth were analyzed.

Tracing of sella turcica
The contour of the sella turcica was traced manually on matte acetate paper 0.003 inches thick using a 0.05 mm lead pencil placed over the printed image.Morphological shapes were identified as described by Axelsson et 8 al.

Measurement of sella turcica dimensions
The linear measurements of length, depth, and diameter were done using the method described by Silverman9.The following were determined as below: • Length: The distance between the tuberculum sella to the tip of the dorsum sella.
• Depth: Was determined by a perpendicular line drawn from the tuberculum sella to the tip of the dorsum sella to the deepest point on the floor of the sella turcica.
• D i a m e t e r : T h i s w a s d o n e anteroposteriorly with a line drawn from the tuberculum sella to the most posterior point on the posterior wall of the sella turcica.

Determination of Orthodontic indices
Cephalometric analysis was also carried out

RESULT
This study had a total number of 64 participants with 28 (43.8%)male and 36 (56.2%) female.The mean interincisal angle was 100.16 ±7.004.Table 1 shows the mean frequency distribution of the interincisal angle and sella turcica dimensions.Figure 1 demonstrates the incisal angle in bimaxillary protrusion skeletal classes II and III on cephalometric radiographs.
A normal shape of the sella turcica was seen in 42 (65.6%).Females exhibited the highest number in the normal shape in 23 (35.9%).The double contour shape was absent in females and the irregular dorsum sellae shape was absent in males.Figure 2 shows the association between sella turcica shape and gender.Bimaxillary protrusion was most prevalent in a normal sella turcica shape in skeletal classes I, II and III in 28 (43.8%),33 (51.6%) and 3 (4.7%)respectively.Table 2 demonstrates the association between sella turcica shapes amongst the skeletal classes with bimaxillary class II exhibiting the highest number with 22 (52.4%) in a normal sella turcica shape.

FIGURE 1: CEPHALOMETRIC RADIOGRAPHS SHOWING BIMAXILLARY PROTRUSION IN SKELETAL CLASSES II AND III WITH AN INTERINCISAL ANGLE OF 90° AND 99° RESPECTIVELY
The age of the study participants was grouped into three: 12-15-years (n=23), 16-25-years (n=28) and 26-30-years (n=13).Table 3 shows a one way analysis of variance between the various age groups and sella turcica dimensions The dimensions of the sella turcica were longest in class III with mean values of 10.67mm ±0.577 (length), 7.83mm ±2.466 (depth) and 10.0mm ±1.732 respectively.This was however not statistically significant.The association between bimaxillary protrusion in the three skeletal classes and sella turcica dimensions is demonstrated in figure 3.

DISCUSSION
Malocclusion is prevalent amongst the three skeletal classes and also in bimaxillary protrusion which is a common orthodontic 1-5 problem in our environment .This study identified bimaxillary protrusion to be prevalent in all three skeletal classes.While dimensions This present study demonstrated a mean length of the sella turcica in bimaxillary protrusion as 10.05±2.029mm.This is at 7 variance with other studies where the mean length was 8.67±2.94mm.The values recorded from this current study of the mean depth and diameter of the sella turcica in bimaxillary protrusion patients was 7.05±1.759mmand 9.41±1.889mm.When 7 compared with the other study , the difference was also at variance with the results from this current study.Variations in dimensions of the sella turcica have been identified across ethnic lines and could be the factor 5-8 attributable for this differences .This study identified three age groups and skeletal pattern and sella turcica shapes but this current studied correlated sella turcica shapes in bimaxillary protrusion patients in the three skeletal classes.The findings from this study revealed the highest prevalence of a normal sella turcica shape in the three skeletal classes.While these other 5-7, 15 studies identified a normal shape as most prevalent which is in agreement with this study, theirs did not differentiate the prevalence for skeletal classes I, II and III bimaxillary protrusion.This study revealed skeletal class III bimaxillary protrusion in only two shapes namely, the normal and in the 6, 7, 15 sella turcica bridge.While other studies identified a sella turcica bridge in 7.9%, 9.2% and 2.8% respectively, this finding was not in agreement with the results of this study where a prevalence of 12.5% was seen.This is probably due to the fact that some studies limit bimaxillary protrusion to a skeletal class [12][13][14]16.

I or II relationship
The most predominant variation in shape from other 5-8.studies was the oblique anterior wall This study however demonstrated this shape in 9.4% which is far below the number recorded 5-8.

in other studies
While other studies correlated the sella turcica shapes to skeletal 5, 6. class I, II and III normal patients This study correlated only sella turcica shapes in bimaxillary protrusion cases in the three skeletal patterns hence the possible reason for the variation.

CONCLUSION:
The mean dimensions of the sella turcica in bimaxillary protrusion differs from those of normal patients.The prevalence of sella turcica bridge in bimaxillary protrusion was 12.5% .While the Skeletal class I bimaxillary protrusion did not record the double contour shape, the Skeletal class II bimaxillary protrusion recorded the six shapes of the sella turcica.The Skeletal class III bimaxillary protrusion did not exhibit shapes in the oblique anterior wall, the double contour shape, irregular dorsum sellae and the pyramidal shape.
e n v i r o n m e n t C e p h a l o m e t r i c radiographs have been used to determine the severity of the protrusion with measurements 1-3.varying for different ethnicities The upper and lower incisors are easily identifiable on the cephalometric radiograph and an interincisal angle of 108-116°signifies a INTRODUCTION Consultant Orthodontist/Associate Professor, Department Of Preventive Dentistry, University Of Benin Teaching Hospital and University of Benin, Nigeria formed from the junction of two lines (a perpendicular drawn along the long axis of 1 the upper and lower incisors) .Cephalometric evaluation also utilizes various anatomic landmarks and the identification of the midpoint of the sella turcica is important in determining the 1, 4, 5.
Caucasians identified skeletal class II patterns as being more prevalent in patients with bimaxillary 2, protrusion there appear to be few Nigerian 1, 4 studies on this subject.A Nigerian study by 4 Isiekwe identified skeletal class I pattern as being more prevalent in patients with bimaxillary protrusion.Other studies correlated the sella turcica and skeletal classes and identified a significant difference in the diameter of the sella turcica in skeletal 5.

FIGURE 2 :
FIGURE 2: ASSOCIATION BETWEEN SELLA TURCICA SHAPE AND GENDER demonstrated values for Nigerians with bimaxillary protrusion of ≤ 107°, this current study agreed with this finding with a mean interincisal angle value of 100.16 ±7.004°.Other studies on bimaxillary protrusion however did not evaluate the association between the interincisal angle and sella turcica 5, 6.

TABLE 2 :
ASSOCIATION BETWEEN SELLA TURCICA SHAPES AND BIMAXILLARY PROTRUSION CLASSES I, II AND III

Comparing Sella Turcica Shapes and Dimensions In Skeletal Classes I, II And III Bimaxillary Protrusion Patients In A Nigerian Population Ibom Medical Journal Vol.11 No.2 August, 2018 analysed
this with the sella turcica dimensions.The results revealed no significant differences in all age groups studied.Also, the mean length, depth and diameter from this study were close to the