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Essay: Cephalometry

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  • Published: 22 September 2015*
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Cephalometry has been an important tool in orthodontic diagnosis, treatment planning, and evaluation of treatment need and results 1-3; from the time of its introduction by Hofrath4 and Broadbent5 in 1931; and its popularisation by Steiner 6, 7. The conventional cephalometric diagnosis is based on the standardised norms; the population mean and range for separate craniofacial measurements, derived from an untreated sample of subjects with so called ideal or well balanced faces with normal occlusion selected from the same ethnic group. Several methods have been put forth for the craniofacial analysis for different races and ethnic groups8-13. The major drawback of these conventional cephalometric analyses was the use of isolated craniofacial parameters without taking into account their possible interdependence14.
Solow14 introduced the concept of ‘craniofacial pattern’ in 1966 by demonstrating the presence of significant correlation among cephalometric skeletal variables. This concept implies that each cephalometric variable is not independent but guided by the underlying craniofacial pattern, and its deviation more than one standard deviation from the population norm can still be considered acceptable, when a certain correlation with other variables is maintained.
Several attempts have been made to describe combination of acceptable values for different craniofacial facial types15-18. A comprehensive analysis for the assessment of individual craniofacial facial pattern was performed by Segner 19; and he found that the five cephalometric skeletal variables namely SNA, representing maxillary prognathism , SNB, representing mandibular prognathism, NL-NSL, representing maxillary inclination, ML-NSL, representing mandibular inclination, and NSBa, representing the cranial base angle (Figure 1 ) show evidence of correlations with each other. It was also noted that the power of the mathematical correlation among the variables was enhanced because the sella nasion line was shared by all the five variables14.
Segner and Hasund 20constructed the floating norms for the description of sagittal and vertical skeletal relationships for a sample of European adults and represented it in a harmony box 21. The term floating norms means individual norms that vary or float, in accordance with the variations in correlated cephalometric measurements (guiding variables).The harmony box is a graphical box like form, also called a correlation box, patterned primarily after the Bergen cephalometric analysis which was introduced by Hasund et al15. It is a method that describes the individual skeletal pattern by illustrating sagittal and vertical skeletal relationships with the use of floating norms. This graphical representation of cephalometric values aids in assessing whether the facial type of an individual is harmonious or disharmonious and also to determine whether orthognathic, retrognathic or prognathic. It aids in initial diagnosis and for evaluation of treatment objective and effects.
Numerous Studies have been carried out to establish floating norms for different populations; Tollaro et al22 established the floating norms for the Italian children in the deciduous dentition period. Franchi et al23 established the floating norms for the north American adults. Ngarmprasertchai24 and Mahaini25 constructed the floating norms for Thais and Syrians respectively. Marian and Ingrid26 constructed the floating norms for Filipinos.
Comparative cephalometric studies have proven that differences in the craniofacial morphology exist among races and ethnic groups 8-10, 27, 28. Awareness of the normal dentofacial pattern of different ethnic groups of various ages will undoubtedly ensure greater success in orthodontic diagnosis and treatment.
Early diagnosis is needed in order to start treatment at the appropriate time29-31. Some malocclusions are evident during the deciduous dentition period itself, showing a distinct craniofacial pattern32- 34. So the use of floating norms for early diagnosis and treatment planning in the deciduous dentition period and the mixed dentition period should be considered.
The aim of the present study is to provide floating norms for the assessment of the individual craniofacial pattern in the deciduous dentition period for south Indian children, as guidance for early diagnosis and treatment planning.
Material and methods
The study was based on a sample of 50 children (24 males and 26 females) 3 to 6 years of age, who were selected from the schools of Mangalore, India. The subjects were chosen on fulfilling the following criteria:
1) presence of a symmetrical face;
2) presence of normal occlusal relationship i.e. flush terminal plane /mesial step deciduous molar relationship, class 1 deciduous canine relationship, absence of anterior open bite and cross bite;
3) absence of congenitally missing deciduous teeth;
4) absence of proximal caries, or gross carious lesions that could bring migration of teeth ;
5) absence of cleft lip and/or palate, or of craniofacial malformative syndrome.
All subjects were South Indian children with complete deciduous dentition and an ideal occlusion, and with no history of orthodontic treatment. Approval from the ethics committee and parental consent was sought before the interview and clinical examinations were performed; and before cephalograms were obtained.
Lateral standardized cephalograms of each subject were taken using the same x-ray device and by the single technician. The cephalometric films were traced by a single investigator. The landmarks were identified and five angular cephalometric measurements SNA, SNB, NL-NSL, ML-NSL, and NSBa (Figure 1) were obtained. In order to eliminate error each tracing and the recording of the angular measurements to the nearest of 0.5 degree was carried out twice by a single examiner and the mean was used for statistical evaluation. Furthermore, intra-examiner variability was analysed by repeated tracing and recording of the measurements of five cephalograms.
Statistical analysis
All statistical analyses of the data were performed with the use of statistical package for the social sciences program (SPSS package for windows, version 16.0). Systematic errors were tested using the unpaired student’s t-tests. The descriptive statistics (mean, median, range) was calculated for the five cephalometric variables. The association between the cephalometric variables was calculated using the Pearson correlation coefficients, bivariate liner regression analysis, and multiple regression analysis. For all statistical analyses, a confidence level P <0.05 was considered significant.
Results
No systematic errors were found. No statistically significant differences between males and females were found for any of the cephalometric variables, so the data were pooled.
Table 1 shows the mean, standard deviation (SD) and ranges for the five cephalometric variables. Resulting linear correlation coefficients ( r ) between the cephalometric variables are shown in Table 2. All correlations between the five variables were significant at the .001, .002 and .05 levels. Linear regression equations with corresponding r2 and the standard error (SE) of the estimates are reported in Table 3; and illustrated in Figure 2 as the floating norms in a graphical box-like form or harmony box, with SNA as the independent variable and NL-MSL, NSBa, ML-NSL and SNB each as the dependent variables according to the method of Segner19. The multiple correlation coefficients R, the adjusted R2 and the SE of the estimate when predicting one of the five measured variables from the remaining four by means of a multiple regression analysis are shown in Table 4, and illustrated in Figure 3 as the range of accepted variability or harmony schema.
DISCUSSION
Sakamoto35, Antonio et al36 and several others have recommended an early orthodontic or orthopedic approach to different type of malocclusions, for which early diagnosis and treatment planning is essential. Cephalometric norms have been established mostly for the adults, for different races and ethnic groups, still individual variation exists37, 38. An isolated measured angle or line should not be considered, but rather should be described in relation to the background of the individual’s facial type39.
Most of the cephalometric studies have been done on Caucasian adults, the present study was undertaken to establish floating norms for South Indian children. The comparison between the values for some cephalometric variables (SNB, ML-NSL) in our deciduous dentition sample and in Tollaro’s22 deciduous dentition sample was statistically significant (student’s t- test, P<0.05). This further justified the investigation into craniofacial skeletal pattern in the South Indian children, to provide a discreet tool for early diagnosis and treatment planning. From the comparison of the cephalometric variables means of our study and Tollaro’s 22(SNB and ML-NSL), it may be deduced that the Italian populations display a larger mandibular prognathism than the Indian population.
This study provides floating norms in the form of a harmony box and schema to describe the individual craniofacial pattern among South Indian children in the deciduous dentition period. The harmony box (fig 1) presented as a graphical box is the outcome of the pattern of associations among the examined cephalometric variables. The cephalometric variables SNA and SNB determine the sagital relationship of the maxilla and the mandible respectively to the cranial base. The three facial types namely retrognathic, orthognathic, and prognathic based on the ANB value, obtained as the difference between SNA and SNB, is presented in the harmony box. In the upper zone of the harmony box, SNA and SNB values are below the mean values given in Table 1, with a corresponding ANB value of 0 to 4 degrees. This area describes the facial type as retrognathic. In the middle zone, SNA and SNB values agree with the mean values in Table 1, with an ANB value of 2 to 6 degrees; and describe the facial type as orthognathic. In the lower zone, SNA and SNB values are above the established mean values; here the facial type is described as prognathic.
Generally, the greater the cranial base angle, the more retrognathic the face becomes, and smaller the cranial base angle, more prognathic the face becomes25.These facts are confirmed in this study also, in Figure 1, the retrognathic zone displays greater values of ML-NSL, NL-NSL, and NSBa, and in the prognathic zone, the ML-NSL, NL-NSL, and NSBa values are decreased. The cephalometric variables NL-NSL and MN-NSL determine the vertical relationship of the maxilla and the mandible to the cranial base respectively.
The harmony schema with the horizontal line or the harmony line in the middle is shown in Figure 2. The horizontal harmony line connects the mean values of the five correlated cephalometric variables. The range of accepted variability allowed for the horizontal line was derived by computing the SE, when one of the cephalometric variables is predicted from the other four by multiple regression analysis(Table 4); and is represented as the harmony schema. The range is narrower for SNA and SNB, and wider for the remaining three variables. The harmony schema represents the degree of variability allowed among the five correlated cephalometric measurements in describing a harmonious face. A harmonious combination from a correlation point of view would not necessarily require the values to lie on a perfectly straight horizontal line19.
To assess an individual’s craniofacial pattern, an acetate paper with the harmony schema for the specific population traced on it could be shifted to include all or most of the five cephalometric variables of that individual plotted on the harmony box. An individual whose all-cephalometric values fall inside the harmony schema is said to display a harmonious skeletal pattern. Moreover, based on the zone occupied by the schema the individuals facial type can be defined as orthognathic and harmonious, prognathic and harmonious, and retrognathic and harmonious. On the other hand a disharmonious pattern may be presented if any of the variable lie outside the schema, and this also reveals the variable that causes the disharmony.
Cephalometric floating norms are an adjunctive tool that can be used with ease to detect and locate skeletal dysplasia in the craniofacial complex. At present, it is widely used as a valuable adjunct in orthodontic diagnosis and treatment planning26. It aids in determining the individual facial type whether orthognathic, prognathic or retrognathic and whether the face is harmonious or disharmonious.
Conclusion
The present study provides cephalometric floating norms for the assessment of individual craniofacial pattern among the south Indian children in the deciduous dentition period. Further investigation should provide floating norms for population specific samples for various racial or ethnic groups in the different age groups.

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