Incisor Mandibular Plane Angle ( IMPA) in Normodivergent Individuals


J. Insira Sarbeen, Dr. Saravana Pandian

Saveetha Dental College, Chennai

*Corresponding Author E-mail :



Aim: To determine gender variation in the incisor mandibular plane angle (IMPA) which include in Dravidian population. Materials and method: 50 cephalometric normal class 1 individuals group A ( 30 males), group B (20 females) manual cephalometric tracing to be done. Test to compare two groups. Background: The study of cephalometric norms has been a part of orthodontic treatment for more than half a century. Steiner, Downs, Ricketts, Margolis, Tweed, Coben, Mc Namara, Ann Arbor and Sassouni have developed cephalometric analyses and corresponding norms. All these investigators formed an opinion that normal measurements for one group should not also be considered normal for other racial groups. Reason : Cephalometric analysis aids in proper diagnosis and treatment planning of a orthodontic patients, norms for particular racial groups helps in more accurate diagnosis and treatment planning.







Incisor mandibular plane angle ( IMPA) was constructed by drawing a line through apex and incisal edge of mandibular incisor, extending it to intercept Frankfort and mandibular planes thus forming the triangle. Cephalometric radiographs and cephalometric analyses aids in orthodontic diagnosis procedures and also allows accurate evaluations of different types of malocclusion in patients with respect to their skeletal relation. Tweed’s Facial Triangle is a method that helps in diagnosis, classification and prognosis. The difference in craniofacial characteristics among ethnical and racial groups had been described in many studies which mentioned the normal mean values for each specific group. Thus normal measurements for one group should not also be considered normal for other groups. Black patients have more protruded upper jaw with relation to the cranial base and also they have more inclined upper and lower incisors than White patients [1].


The process of judgment of an existent problem is called diagnosis and depends on the largest possible quantity of collected data. The orthodontic diagnosis of malocclusion also depends on early correct detection and it is a fundamental point for the treatment planning. Therefore, the establishment of any orthodontic treatment is marked by the identification of present abnormalities, and similar problems are frequently systematised for convenience purposes. This procedure, called classification, has always been one of the great challenges in the history of Orthodontics. Angle1 (1907) classified the malocclusions based on occlusal relationships, considering the first permanent molar as the "key" of occlusion [2]. It has been stated that the position of mandibular incisors is the most important key in diagnosis and treatment planning. In today's multicultural society, racial and ethnic differences are assuming an increasing level of importance [3].Cephalometrics can be utilised to describe, compare and classify the nature of orthodontic problems. Different analyses and their corresponding norms have been formulated by various authors to interpret the diagnostic data that the lateral cephalogram provides [4]. This study aimed to determine gender variation in the incisor mandibular plane angle (IMPA) in the Dravidian population.



Cephalometric’s of normal class 1 individuals of group of 50 that includes both males and females were calculated. The  IMPA values were measured using protractor from the cephalometric tracing which was done. The data has been collected and statistical analysis were done.



Following data were collected and average were calculated for both males and females.

( Table 1and graph 1).


Table 1: IMPA values of males and females








Graph 1: graphical representation of IMPA value of both male and female


According the data collected the difference in IMPA value of male and female is 0.53 in the population. There is no statistical difference between males and females.



The values which were obtained for the current study differ from those established by Tweed, who stated that ultimate facial aesthetics and balance are achieved only when lower incisors are vertically positioned on the basal bone with IMPA at 90+/- 5,  thus disagreeing with our present results, where IMPA showing a mean value of 101.265 difference. Results showed that there is a greater dental protrusion and a more convex facial profile. Determining IMPA values are important for orthodontic treatment planning. There is no sexual dimorphism.



As we compared with small group of population there is no statistical significance between the male and female so future studies can be done with high population to know the values and to differentiate between male and female that helps in orthodontic diagnosis and treatment planning.



1.        Tweed CH.  Was the development of the diagnostic facial triangle as an accurate analysis based on fact or fancy?  Am J Orthod 1962; 48: 823-40.

2.        Craniofacial analysis of the Tweed Foundation in Angle Class II, division 1 malocclusion. Análise craniofacial da Fundação Tweed na maloclusão Classe II, divisão 1 de AnglePaulo César TukasanI; Maria Beatriz Borges de Araújo MagnaniII; Darcy Flávio NouerIII; Paulo Roberto Aranha NouerIV; João Sarmento Pereira NetoII; Ivana Uglik Garbui. Braz. oral res. vol.19 no.1 São Paulo Jan./Mar. 2005. 42005000 100013.

3.        Craniofacial structure of Japanese and European-American adults with normal occlusions and well-balanced face. Kuniaki Miyajima, James A. McNamara, Jr., Tetsushi Kimura, Satoru Murata, and Tetsuo lizuka, Nagoya, Japan, and Ann Arbor,  American Journal of Orthodontics and Dentofacial Orthopedics October 1996.

4.        Tweeds analysis of Nepalese people, P Bhattarai and RM Shrestha Dental Sciences and Hospital- Nepal Medical College Teaching Hospital, Jorpati, Kathmandu, Kantipur Dental College, Kathmandu, Nepal, Nepal Med Coll J 2011; 13(2): 103-106.




Received on 28.06.2016             Modified on 02.07.2016

Accepted on 05.07.2016           © RJPT All right reserved

Research J. Pharm. and Tech 2016; 9(10):1621-1622.

DOI: 10.5958/0974-360X.2016.00322.X