Comparison of prevalence of anterior and posterior crossbites in primary and high school students in Mashhad

Introduction:
Anterior and posterior crossbites are observed in orthodontic patients more frequently than other malocclusions. The purpose of this study was to the determine the prevalence of anterior crossbite and posterior crossbite (unilateral & bilateral) in primary and high school students in Mashhad and comparing the results with each other.
Materials and Methods:
In this cross sectional study the data collection method was clinical observation and a form for recording the data.
In this study 2956 students including 2050 primary school students (1030 boys and 1020 girls) with the age range of 7-12 years and also 906 high school students (490 boys and 416 girls) with the age range of 15-18 years were selected in random cluster sampling. Statistical analysis was done using SPSS software (Fisher's exact test in two-by-two cross tabulations).
Results:
1-The prevalence of posterior crossbite in primary school students was 6.9% and in high school students was 5.2%. The difference was not significant.
2-The prevalence of posterior crossbite in boys in primary school was 7.8% and in high school boys was 8.4%. The difference was not significant.
3-The prevalence of posterior crossbite in girls in primary school was 6% and in high girls was 1.4%. The difference was significant.
4-The prevalence of bilateral posterior crossbite in primary school students was 0.87% and in high school students was 1.6%. Unilateral posterior crossbite in primary school students was 6% and in high school students was 3.5%. The difference in unilateral crossbite was significant.(P-v=0.006)
5-In general, the prevalence of anterior crossbite in primary school students was 6.5% and in high school students was 5.4%.The difference was not significant.
6-The prevalence of anterior crossbite in primary school boys was 7.8% and in high school boys was  8.6%. The difference was not significant.
7-The prevalence of anterior crossbite in primary school girls was 5.3% and in high school girls was 1.6%. The difference was significant. (P-v=0.002)
Conclusion:
In this study anterior and posterior crossbites in primary school students were more than high school students. The difference was not significant.
Unilateral crossbite was more frequent in primary school students than high school students. The difference was significant.
Bilateral posterior crossbite in high school boys was more than primary school boys but in high school girls was less than primary school girls. Anterior and posterior crossbite in high school girls decreased and in high school boys increased significantly compared to primary school students.