CC BY-NC-ND 4.0 · Dental Journal of Advance Studies 2020; 8(03): 102-108
DOI: 10.1055/s-0040-1714322
Original Article

To Establish Cephalometric Floating Norms as a Guide toward Harmonious Cranial Individual Pattern among North Indian Adults

Sanjay Mittal
1  Department of Orthodontics and Dentofacial Orthopedics, Bhojia Dental College and Hospital, Baddi, Himachal Pradesh, India
,
Dipti Chawla
1  Department of Orthodontics and Dentofacial Orthopedics, Bhojia Dental College and Hospital, Baddi, Himachal Pradesh, India
,
Mandeep Bhullar
2  Department of Orthodontics, Bhojia Dental College and Hospital, Baddi, Himachal Pradesh, India
,
Isha Aggarwal
2  Department of Orthodontics, Bhojia Dental College and Hospital, Baddi, Himachal Pradesh, India
,
Tanzin Palkit
1  Department of Orthodontics and Dentofacial Orthopedics, Bhojia Dental College and Hospital, Baddi, Himachal Pradesh, India
,
Sumit Chhatwalia
1  Department of Orthodontics and Dentofacial Orthopedics, Bhojia Dental College and Hospital, Baddi, Himachal Pradesh, India
› Author Affiliations
 

Abstract

Introduction Floating norms put us at ease while diagnosing and establishing a treatment plan for an individual with abnormal skeletal pattern. It uses the variability of the associations among appropriate cephalometric variables and later on the basis of a regression model by combination of both skeletal parameters which are sagittal and vertical and construct a harmony box which make diagnosis straightforward. This study aims to establish floating cephalometric norms for the describing individual craniofacial skeletal pattern among North Indian Adults as an additional diagnostic tool for orthodontic treatment planning.

Materials and Methods The study includes North Indian adults in age range of 17 to 25 years. A total of 30 patients were selected and were subjected to cephalometric evaluation. Various angular measurements viz., SNB (sella-nasion-point B), NL-NSL (maxillary line-nasion sella line), ML-NSL (mandibular line-nasion sella line), N–S–Ba (nasion-sella-basion), SNA (sella-nasion-point A), and ML-NL (mandibular line-maxillary line) were considered for designing harmony box for North Indian adults.

Results The results of the study were subjected to various statistical analyses. SNB served as the independent variable and NL-NSL, NSBa, ML-NSL, ML-NL, and SNA were made the dependent variable due to lesser R2 values in multiple regression analysis. Correlation between some of the variables, such as (SNA–SNB, ML-NSL–NL-NSL, and ML-NSL–ML-NL), in the present North Indian sample showed positive correlation among each other and were statistically significant (p = 0.000). When compared with the other similar studies done previously, least variability was seen with the Segner study and maximum variability was seen with Thilander’s study.

Conclusion The analysis of the individual craniofacial pattern by means of floating norms appears to provide a helpful method in determining the parameters responsible for the skeletal disharmony, thus representing a viable option for additional diagnostic tool in orthodontic and orthopaedic/surgical treatment planning.


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Introduction

Lateral cephalometric analysis has suited as an inseparable segment in diagnosing problems and treatment planning in orthodontics. The target of cephalometric analysis is to approximate the vertical and horizontal relationship of the jaws to the cranial floor and to one another, the relationships of the dentition to their bracing bone, and the outcome of the dentition on the profile. After Broadbent[1] and Hofrath[2] together developed procedures which helped to obtain standardized skull radiographs in 1931, following this a large number of standardized norms using cephalometrics were developed. The principle revolves around the idea that discrepancy in the skeletal frame work of an individual can be detected by comparing its radiographic measurements with that of normal values. Orthodontists benefit from these measurements or norms for diagnosing, treating, and assessing orthodontic problems and their outcomes.[3] [4] [5] The criteria for sampling of individuals for instituting cephalometric norms, involved untreated patients with similar ethnic background, and normal occlusion in a balanced face. The values with their standard deviations gained from cephalometric analysis provided guidelines for diagnosing and treating orthodontic problems. In the conventional cephalometric analysis, no correlation among the various variable is made rather a direct comparison of the values with their normal counter parts is done to evaluate skeletal abnormality. However, it becomes imperative that matching of age, gender, ethnicity is done prior to cephalometric analysis of orthodontic problems among individuals and compare it with norms of similar above-matched variables.[6] Cephalometric norms does not need to depict real situation of craniofacial abnormality but it is important for them to measure diagnostic values. In the study of Solow,[7] “The Pattern of the Craniofacial Associations …” demonstrates correlations among sagittal and vertical variables in cephalometric radiograph, and hence elucidating the concept of “craniofacial pattern.” Consecutively, it can be implied that the values of a patient can lie just at 1 standard deviation (SD) from the population but still it can be considered normal if they are correlated to one another.[8]

Nanda and Ghosh[9] stated that there can still be individual variations existing, despite matching of ethnic group and race while evaluating and comparing cephalometric norm for the concurrent population. Furthermore, individual’s facial type has more importance as compared with isolated measured angle or line. Di Paolo et al[10] emphasized that locating the area of the skeletal dysplasia in cephalometric analysis has much more importance than merely detecting the skeletal abnormality.

Fundamentals of orthodontics are based on an optimal description of patient skeletal pattern concurrent with associated malocclusion, especially in patients whose treatment plan involve orthognathic surgery or functional orthopaedic jaw therapy.

One of the first attempts to enumerate combinations of acceptable values pertaining to craniofacial measurements were made by Steiner,[11] who used the ANB (point A-nasion-point B) angle as a “guiding variable” to assess the position of the lower incisors. The ANB angle was also employed by Tweed[12] as a guiding variable to modify the norm values of his diagnostic triangle. Hasund and Boe[13] modified Steiner’s analysis by means of floating norms,” they recommended positioning of the lower incisors, based on the guiding variables ANB, ML-NL (inclination of the mandibular plane to the palatal plane), and the N angle (the angle formed by the tangent to the bony chin passing through B-point and the mandibular plane).

Floating norms, thus are individual norms that vary (float) in accordance with the variations of correlated measurements (guiding variables). Järvinen[14] developed floating norms for ANB angle by using a regression analysis with SNA and ML-NSL (the inclination of mandibular plane to the nasion sella line) as independent variables. Finally, a comprehensive individual craniofacial patterns analysis was performed by Segner[15] and Hasund,[16] who constructed floating norms in a sample of European adults based on vertical and sagittal skeletal relationships. In their method, they used SNA, SNB, NL-NSL, ML-NSL, and NSBa for craniofacial measurements. Moreover, interdependence between two cephalometric variables in their technique was elucidated by linear correlation coefficient “r” (Segner and Hasund). Segner and Hasund have been credited with the concept of harmony box, and nowadays it is used widely with some modifications as a Segner–Hasund harmony box (Segner and Hasund). The notion of harmony box is, when cephalometric values lie within the harmony schema for suitable population group (correlating values alongside SD), the subject is considered with harmonious skeletal pattern and this is the mechanism of harmony box determining the facial type. Any value of a parameter that is lying away from the schema of the harmony box can be predicted to be the causative agent for the facial disharmony. Henceforth harmony box became an efficient and effective tool that could be used to detect and locate skeletal dysplasia in the craniofacial complex.

The floating norms have invariably become an inherent part of diagnostic arsenal in the field of orthodontics. In 1998, Franchi et al[17] conducted a study that established floating norms among population from North America. Ngarmprasertchai[18] and Mahaini[19] evaluated Thais and Syrians population and established floating norms among them. Tollaro and coworkers[20] evaluated southern European children with complete primary dentition to formulate floating norms among them. Lavergne and Gasson[21] also presented floating norms for facial patterns of young children using cephalometric classification.

Malocclusion displays a more comprehensive picture once skeletal pattern and dento alveolar evaluation has been done while making an orthodontic diagnosis. Here the importance lies while evaluating skeletal pattern, the measurements need to be accurate as in nature a case of skeletal dysplasia might depict considerable dental compensation. Additionally, a dental problem that look quite similar to the previously discussed situation might require a completely different methods of intervention with similar skeletal pattern especially in cases requiring orthognathic surgery. Interventions implemented by the operator do not provide much options in changing the position of the jaws, henceforth a norm guidance is especially useful in these cases. Population serves to be the first norm used.

Although studies to determine the cephalometric floating norms in various region of the world have been largely quite frequent but conversely no Indian study has been performed till date to establish cephalometric floating norms. Thus it was realized that there is a need to establish the cephalometric floating norms in a representative sample of North Indian young adults who will be useful for orthodontic diagnosis and treatment planning of North Indian population.


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Objectives

The aim of the present study was to (1) present cephalometric floating norms for describing individual craniofacial skeletal pattern among North Indian adults as an additional diagnostic tool for orthodontic treatment planning, and (2) compare these cephalometric floating norms with other norms presented in similar studies.


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Materials and Methods

The present cross-sectional, cephalometric study was conducted in the Department of Orthodontics and Dentofacial Orthopedics, Bhojia Dental College and Hospital, Baddi, Himachal Pradesh. Various cephalometric measurements were done in this analytical study to establish the cephalometric floating norms for North Indian adults.

The patients included in this study were of North Indian origin. They were recruited from undergraduate students, postgraduate students, hospital staff of Bhojia Dental College, Baddi. The age range of these patients was 17 to 25 years.

After explaining the nature and purpose of the study to all the patients, informed consent was obtained. Only those patients who agree to participate and allow their radiographs to be taken were included in the study.

Each individual’s basic information about name, age, origin, history of facial trauma, and previous orthodontic treatment was taken and those patients satisfied the following criteria were included in the study:

  • North Indian ancestry, while noting the ancestry, it will be ascertained that patient and their parents and grandparents (two generations) are original inhabitants of North.

  • Well-balanced profile (assessed by three investigators) and Angle’s class-I occlusion with normal overjet and overbite.

  • No or minor crowding or spacing.

  • All the teeth up to second molars except the third molars erupted.

  • No history of previous orthodontic or prosthodontics treatment.

  • No history of plastic or orthognathic surgery.

  • No history of facial trauma.

  • Absence of congenital anomalies such as cleft lip or palate.

  • Good state of health and no history of any medical disorder.

A minimum of 30 patients were selected for present study to develop cephalometric floating norms in North Indian adults.

Patients were asked to bite in centric occlusion and lips in repose with natural head orientation, so that lateral cephalogram of each patient could be made. The cephalometric film was evaluated and traced for Landmarks[22] such as sella (S), nasion (N), point A (A), point B (B), anterior nasal spine (ANS), posterior nasal spine (PNS), menton (Me), basion (Ba), and planes,[22] such as sella–nasion plane, palatal plane, mandibular plane, and following angular measurements by a single investigator ([Fig. 1]). Each value was measured twice and the average was used for further analysis.

Zoom Image
Fig. 1 Cephalometric landmarks, planes, and angles.

Cephalometric Angles

  1. SNA: its an angle formed between the sella nasion plane and a line connecting the nasion to point A.

  2. SNB: the angle formed between the sella nasion plane and a line connecting the nasion to point B.

  3. S-N-Ba: its an angle formed between the sella nasion plane and a line connecting the basion point to sella.

  4. NL-SNL: the angle formed by intersection of sella nasion plane and the palatal plane.

  5. NL-ML: the angle formed by intersection of palatal plane and mandibular plane.

  6. NL-SNL: the angle formed by intersection of sella nasion plane and the mandibular plane.


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The Harmony Box

Bergen cephalometric analysis g iven by Hasund et al[13] acts as the basis for Segner and Hasund’s harmony box and it outlined individuals’ skeletal features and marked initial stage in establishing floating norms. The floating norms were established for often used vertical and sagittal measurements by using the sanctioned norms of Bjork which were shown in the Bergen box.

Currently, the ameliorated Segner–Hasund harmony box is universally used as a beneficial adjunct in the diagnosis and treatment planning in orthodontics. It explains the craniofacial pattern demonstrating the vertical and sagittal skeletal relationships individually by using the floating norms. Also, it describes the types of facial pattern in patients and determining the face whether it is balanced or unbalanced. This box classifies skeletal profile into multiple zones, such as retrognathic, orthognathic, and prognathic zones, here ANB value serves as the basis of the individual’s skeletal profile. A harmony line of an individual is a horizontal line joining the values of various cephalometric variables plottted inside the box. Cephalometric values of an individual lying inside the perspective shows a balanced or harmonious skeletal pattern. Although any value lying outside the perspective is the variable that causes facial disharmony.

Thus, the present study was intended to develop cephalometric floating norms, as well as harmony box, for the North Indian adults.


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Data Collection and Analysis

Using a 0.5-mm lead pencil, tracing of lateral cephalograms was done manually by operator. Precautions were taken, so that no stray light was encountered, for accurate identification of the cephalometric landmarks. All the angular measurements were obtained to the nearest of 0.5 by protractor and ruler.


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Method Error

To determine error of radiographic measurements, retracing and remeasuring of 10 films selected randomly from the total sample was done at an interval of 3 weeks. The interclass correlation coefficient was found to be highly significant.


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Data Analysis

Data were analyzed for descriptive statistics of all cephalometric measurement and the statistical examination of the recorded data comprised of the following:

  • Calculation of correlation coefficient.

  • Bivariate linear regression analysis.

  • Multiple linear regression analysis.


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Results

Descriptive statistics for all the cephalometric measurements and the multiple regression analysis, R, the adjusted R 2, and the standard error of the estimate while predicting one of the six measured variables from the remaining five are given in [Table 1].

Table 1

Descriptive statistics and standard error of estimate by means of multiple regression analysis

Cephalometric variables

Mean

SD

SE

Min.

Max.

R 2

SE

Abbreviations: Ba, basion; Max., maximum; Min, minimum; ML-NSL, mandibular line-nasion sella line; ML-NL, mandibular line-maxillary line; N, nasion; NL-NSL, maxillary line-nasion sella line; N-S-Ba, nasion-sella-basion; S, sella; SD, standard deviation; SE, standard error; SNA, sella-nasion-point A; SNB, sella-nasion-point B.

SNA

83.833

4.0712

0.7433

78.5

97.0

0.433

3.37

SNB

80.433

3.6477

0.6660

75.0

90.0

0.900

1.27

NL-NSL

7.450

2.8987

0.5292

0.0

13.0

0.802

1.45

N-S-Ba

131.300

4.7463

0.8666

124.0

141.0

0.420

3.95

ML-NSL

27.017

6.2346

1.1383

13.0

40.0

0.883

2.35

ML-NL

20.450

4.6782

0.8541

12.5

31.0

0.662

2.99

[Fig. 2] illustrates harmony box with the regression results, here SNB acts as the independent variable, while the other three variables were considered as the dependent variable, these were plotted according to Segner’s method. Variable that shows the highest R 2 value in multiple regression analysis and also correlates with other variables is taken as the independent variable, here SNB serves as an ndependent variable.

Zoom Image
Fig. 2 Harmony box. Ba, basion; ML-NSL, mandibular line-nasion sella line; ML-NL, mandibular line-maxillary line; N, nasion; NL-NSL, maxillary line-nasion sella line; N-S-Ba, nasion-sella-basion; S, sella; SNA, sella-nasion-point A; SNB, sella-nasion-point B.

[Table 2] illustrates comparison with other studies using independent t-test. On comparison with Segner’s[15] study, only parameter SNA showed statistical difference, with Franchi’s[17] North American population, parameter S–N–Ba and ML-NSL display a statistical difference, with Bjork’s[23] study, three out of six parameters, that is, SNA, ML-NSL, ML-NL showed statistical significance. Maximum difference was seen with Thilander’s[24] study in which parameters SNA, SNB, ML-NSL, and ML-NL were found to be statistically significant.

Table 2

Independent t-test for comparison among various studies (p < 0.05)

Parameters

North Indian adult

Mean ± SD

Segner’s sample

Mean ± SD

Franchi et al—North American

Mean ± SD

Bjork

Mean ± SD

Thilander

Mean ± SD

Abbreviations: Ba, basion; ML-NSL, mandibular line-nasion sella line; ML-NL, mandibular line-maxillary line; N, nasion; NL-NSL, maxillary line-nasion sella line; N-S-Ba, nasion-sella-basion; S, sella; SD, standard deviation; SNA, sella-nasion-point A; SNB, sella-nasion-point B.

a,bDenotes significant values.

SNA

83.83 ± 4.07

82.13 ± 3.50

(0.029a)

82.98 ± 3.48

(0.260)

82 ± 3.50

(0.020a)

82.23 ± 3.17

(0.039a)

SNB

80.43 ± 3.64

80.51 ± 3.36

(0.909)

80.37 ± 3.21

(0.925)

79 ± 3.50

(0.071)

78.95 ± 2.89

(0.034a)

NL-NSL

7.45 ± 2.9

7.60 ± 3.26

(0.779)

7.33 ± 0.26

(0.822)

8 ± 3

(0.307)

7.29 ± 2.75

(0.456)

N–S–Ba

131.30 ± 4.75

131.22 ± 4.73

(0.927)

128.36 ± 5.13

(0.002b)

31 ± 4.5

(0.732)

130.14 ± 4.54

(0.191)

ML-NSL

27.02 ± 6.23

28.20 ± 5.91

(0.908)

30.07 ± 0.37

(0.012a)

33 ± 6

(0.000b)

31.42 ± 4.89

(0.001a)

ML-NL

20.45 ± 4.68

20.50 ± 5.80

(0.307)

25 ± 6

(0.000b)

24 ± 4.72

(0.000b)


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Discussion

The present study provides cephalometric floating norms that are derived from and are specific for a North Indian adult sample. It is always preferable to compare the cephalometric values of a given patient with a norm extrapolated from his or her racial or ethnic group. In fact, the comparisons between the values for some of the cephalometric variable (SNA) in the present North Indian sample and Segner’s Middle European sample were statistically significant (Student’s t-test p<0.05). For example, SNA angle was significantly greater in North Indian adults than in Middle Europeans. On comparing with another study by Franchi et al in North American population, parameter S–N–Ba displayed a statistical difference at 0.002; while ML-NSL showed statistical difference at p < 0.012. When compared with Bjork’s study, three out of six parameters, that is, SNA, ML-NSL, and ML-NL showed statistical significance at 0.020, 0.000, and 0.000, respectively. Lastly with Thilander’s study four parameters (SNA, SNB, ML-NSL, and ML-NL) displayed statistical difference at 0.039, 0.034, 0.001, and 0.000. Differences can be a result of different geographical area, ethnicity. All sample for comparison consisted of an ideal occlusion group except for the Bjork and Thilander samples which consisted of cross-sectional population group.

The graphical box ([Fig. 2]) is the outcome of associations among the examined cephalometrics variables. Individual harmony line is a horizontal line connecting various variables present inside the harmony box of an individual displaying harmonious skeletal features. The line may lie at the center of the box and therefore the subject is labeled as harmonious and orthognathic. In majority of instances, this central line represents the mean values for different variables.

Additionally, line lying superior to the box, the patient is considered harmonious but retrognathic. To maintain an ideal occlusion and an acceptable craniofacial balance, both the maxilla and the mandible will be required to move downward and backward with respect to cranial base. Conversely, when the line lies inferior to the box, the patient is classified as harmonious and prognathic, and both the maxilla and the mandible will show an upward and forward inclination relative to cranial base.

A range of accepted variability is allowed for any individual and is represented by the standard error of the estimate of the multiple regression analysis ([Table 2]). Angles SNB and NL-NSL presented with a narrower range, while for the remaining variables, the range was wider. The variability estimates of the range can be shifted to any individual “horizontal harmony line” when evaluating the craniofacial characteristics of a given patient.

An individual with cephalometric values within the range of harmony box is considered as harmonious, though it still can be classified as orthognathic, prognathic, or retrognathic. Here the individual horizontal harmony line is the line that is best adapted to the individual’s cephalometric values. Now if any of the cephalometric variable is lying outside the harmony box, it indicated deviation form the harmonious relationship and hence can easily be discerned as the culprit for skeletal disharmony.

Cephalometric floating norms are intended for initial diagnosis and for evaluation of treatment effects. Due to the correlations among the six measurements in the graphical box, every reassessment of therapeutic results will describe not only the modifications of the target variables but also the newly established craniofacial pattern.

Various steps ([Fig. 3B]) for the procedure are as follows:

Zoom Image
Fig. 3 (A) Cephalometric tracing of AT (patient)’ and (B) diagnosis for AT. Ba, basion; ML-NSL, mandibular line-nasion sella line; ML-NL, mandibular line-maxillary line; N, nasion; S, sella; SNA, sella-nasion-point A; SNB, sella-nasion-point B.
  • Measure the six variables on the patient’s cephalogram and mark the values within the graphical box.

  • Identify on the SNA column, the SNA values corresponding to the other five variables in that patient. Draw a horizontal line connecting each of the individual value on the SNB, NL-NSL, N-S-Ba, ML-NSL, and ML-NL columns to the SNA column. Calculate the average value for the six values now on the SNA column and mark it on the SNA column (harmony point).

  • Photocopy the range together with the harmony line on a piece of transparent acetate paper.

  • Place the transparent acetate with the range and the harmony line on the graphical box, so that the harmony line is positioned on the harmony point.

  • Any value falling outside the box indicates a deviation from a harmonious craniofacial pattern.


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Case Example

The cephalometric values of AT (patient), a 19-year-old female, is shown in [Fig. 3A]. The small unfilled rectangle in the SNA column ([Fig. 3B]) represents the harmony point (78.5 degrees), that is, the guiding point for the location of the individual harmony line. The patient presents five out of six measurements outside the range. Although the patient is harmonious, the individual harmony line lies outside the box in the upper half. This relationship classifies the patient as retrognathic. deviation from a harmonious craniofacial pattern are located in the sagittal position of the mandible (SNB) and in the inclination of the mandibular plane in relation to the cranial base (ML-NSL). Although both maxilla and mandible are retruded; however, mandible in relation to maxilla is deficient and the mandibular plane is tilted downward and backward. Consequently, a diagnosis of high-angle mandibular retrognathism can be made.


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Conclusion

Analyzing individual craniofacial pattern by means of floating norms helps us in determining which parameter(s) is the culprit for the skeletal disharmony, thus it presents as a viable additional diagnostic tool in planning orthopedic/surgical treatment. However, it would not be valid based on cephalometric data given by floating norms to suggest specific surgical decisions in patient with abnormal skeletal pattern. Other important relationships, such as static and functional soft tissue relationships to the facial skeleton, the function of the occlusion and the temporomandibular joint, and the patient’s chief complaint and psychosocial concerns should be taken into account in this respect.


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Conflict of Interest

None declared.


Address for correspondence

Dipti Chawla, MDS
Department of Orthodontics and Dentofacial Orthopedics, Bhojia Dental College and Hospital
Baddi, Himachal Pradesh 173205
India   

Publication History

Publication Date:
05 August 2020 (online)

© .

Thieme Medical and Scientific Publishers Private Ltd.
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Zoom Image
Fig. 1 Cephalometric landmarks, planes, and angles.
Zoom Image
Fig. 2 Harmony box. Ba, basion; ML-NSL, mandibular line-nasion sella line; ML-NL, mandibular line-maxillary line; N, nasion; NL-NSL, maxillary line-nasion sella line; N-S-Ba, nasion-sella-basion; S, sella; SNA, sella-nasion-point A; SNB, sella-nasion-point B.
Zoom Image
Fig. 3 (A) Cephalometric tracing of AT (patient)’ and (B) diagnosis for AT. Ba, basion; ML-NSL, mandibular line-nasion sella line; ML-NL, mandibular line-maxillary line; N, nasion; S, sella; SNA, sella-nasion-point A; SNB, sella-nasion-point B.