[ relationship between lower facial height and maxillary and mandibular lengths based on Harvold analysis in Mashhad high school students]

Introduction: at the end of an orthodontic treatment, the coordination between different facial dimensions is very important. The changes in facial height cause changes in other dimensions. In the present study, the relationship between lower third of facial height and maxillary and mandibular lengths was evaluated and compared with the previous studies

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Materials and Methods: in this study, 38 lateral cephalograms of Mashhad high school students aged 16- 19 with mean age of 17 years were selected and traced manually. The profile, occlusal relationship, overjet and overbite in these cases were normal and molar and canine relationships were class I. The data were analysed using SPSS software [version 10] and t-student test was used for analysis

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Results: the findings were as follow: *the relationship between lower third of facial height and both the length of I mandibular base and the length of mandible based on Harvold analysis was significant. *The relationship between the lengths of both the maxilla and anterior cranial base, and lower third of facial height were not significant. *No relationship was found between the length of maxillary base [based on Harvold analysis] and lower third of facial height

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Conclusion: according to this investigation, it is concluded that the length of mandibular base has a significant correlation with the lower third of facial height, but such a correlation does not exist between maxilla and lower third of facial height