Comparison of Reproducibility of Nasolabial Angle Constructed by Anatomic point method and Tangent line method

Introduction: Investigators have drawn nasolabial angle using different soft tissue landmarks. This has created confusion among the orthodontic students and clinicians regarding its construction. Objective: To evaluate two commonly used methods of constructing the nasolabial angle in order to establish a single reproducible method. Materials & Method: Lateral cephalograms of 120 patients undergoing orthodontic treatment were obtained from the records of the patients. Soft tissue profile on the lateral cephalograms were traced manually by the principal investigator. All the tracings were photocopied and 6 copies of each tracing were made. Nasolabial angles were constructed and measured on photocopied copies of the tracings first using the anatomic point method and then using the tangent line method by the principal investigator and another investigator independently. Result: The average nasolabial angle values for anatomic point method and tangent line method were found to be 94.32° ± 14.05° and 92.4° ± 14.59° respectively. The intra-class correlation coefficient demonstrated excellent intra-observer and interobserver agreement among the two methods of nasolabial angle construction. Conclusion: Both anatomic point method and tangent line method of nasolabial angle construction have excellent reproducibility in terms of intra-observer and inter-observer agreement. Key-words: anatomic point method, lateral cephalogram, nasolabial angle, tangent line method extraction or non-extraction during orthodontic treatment is also influenced by nasolabial angle.5 Lack of universal definition of nasolabial angle has led to variability in construction of nasolabial angle. Over the years, various investigators6-9 have drawn the nasolabial angle using different soft tissue landmarks. This has created confusion among the orthodontic students and clinicians alike regarding the construction of nasolabial angle. An improperly constructed nasolabial angle can adversely affect orthodontic diagnosis and treatment planning.10 Till date, there are no studies in orthodontic literature comparing the reproducibility of different methods of construction of nasolabial angle. Hence, the primary objective of this study was to evaluate two commonly used methods of construction of the nasolabial angle, namely anatomic point method and tangent line method, in order to establish a single reproducible method. The secondary objective was to assess whether the two methods of construction would lead to significant difference in the values of the angle.