INTRODUCTION:

Lateral cephalometry radiography has become a principal component for the orthodontist in patient treatment. The first practice of cephalometry radiography is began in 1934 by Hofrant from Germany and Broadbent from England for a requirement of research and clinical in orthodontics field for malocclusion study and skeletal difference¹. Cephalometry is the important component in orthodontia science for analysis on growth and development, diagnosis, treatment plan, and evaluation of treatment result². Cephalometry analysis includes in the analysis of dental, skeletal, and soft tissue³. Some cephalometry analysis methods requires a reference plane to measure the cephalometry. Frankfort Horizontal or abbreviated as FH (created in 1882) is to determine the orientation of patient head and continuously practice as a reference plane to nowadays¹.

The most intracranial reference plane that practice in cephalometry radiography is Frankfort Horizontal (FH) line. The first introduction in Frankfort Horizontal line is in anthropology conference in Frankfurt, German in 1884 and may defined as a longitudinal line from left orbit to the porion point. Previously, FH line is considered as a precise horizontal line and applied as a craniometry reference plane for the classification purpose⁴. For the years, FH line and Sella-Nasion line applied as a support for the classification diagnosis of skeletal pattern⁵. Head position during Natural Head Position of NHP that frequently in wrong position⁶ causes the Frankfort Horizontal line become ambiguous horizontal in all cases because of relational deviatio⁷, especially in skeletal discrepancy case⁸. Inaccurate head position in cephalostat rontgen cause a wrong diagnosis⁹.

Basis of considerations to select the Frankfort Horizontal line as a horizontal reference plane consistently become a consideration because the line does not represent the horizontal line of earth surface⁵. Therefore, another reference plane applied as the replacement of Frankfort Horizontal line. This research found many biological variations in facial structure, maxillomandibular relationship, form, and size of dental arch. These biologic variations appear in skeletal anatomy marker location that create a intracranial reference plane. This variation cause inaccuracy in cephalometry result, cause a wrong diagnosis determination and treatment plan².

Some cranial reference plane uses a horizontal line (HOR) as a replacement of Frankfort Horizontal line that become a lateral edge of perpendicular radiography film that generate from Natural Head Position¹⁰. Some researches explain the Natural Head Position (NHP) is a logic reference and become an orientation position for craniofacial morphology evaluation¹¹. Horizontal line or abbreviated as HOR is extracranial reference planes that determined from the physical internal mechanism or a balance of patient head during Natural Head Position (NHP). NHP may defined as a standard for head orientation of individual when the eyes looks a distant object¹². This position is generated when the patient see their own eyes in relaxed situation on the mirror that put in front of the patient.

Cephalogram that derive from patient in Natural Head Position (NHP), lower margin and lateral edge from radiography film is considered as the accurate horizontal and vertical line¹³. A draw of Frankfort Horizontal line compared with the horizontal line of lower margin of radiography film for evaluation either the FH line is parallel with the lower margin of radiography film or deviation is occurring¹⁴. There are five parameters of cephalometry angle measurement that applied the FH line¹⁴, which are (1) antero-posterior maxilla skeletal relation to the cranial base in McNamara analysis (2) anteroposterior mandibula relation to the cranial base in McNamara analysis (3) growth pattern in Tweed analysis (4) incisive proclination of lower jaw in Tweed (5) Facial angle (nasion-pogonion-line) in Ricketts analysis.

METHOD:

This research applied analytical observational method with retrospective approach. The research design is determining the difference of cephalometry line in skeletal pattern diagnosis that caused by a deviation in Frankfort Horizontal line. Deviation in cephalometry value on deviated Frankfort Horizontal line measured by five cephalometry values and applying the true horizontal (HOR) line as alternative reference for a replacement of deviated Frankfort Horizontal line.

Population:

The population in this research is all patients data who receive orthodontic treatment in Dental and Oral Hospital of Airlangga University, Surabaya, Indonesia (RSGM UNAIR) in 2015-2016.

Sample:

The sample of this research is all male and female patients data that consists of cephalogram and the status is fulfilled these criteria:

· The roentgenogram result is produced by a similar cephalostat machine

· A standard quality on roentgenogram result

· The patient is between 18 to 40 years old

· The patient is never perform an orthodontic treatment previously

· A proper facial profile

· No craniofacial malformation or face disorder

· No history or no oral habits occurrence

Simple random sampling practiced in this research. Cephalometry from the sample that comply the criteria will achieve a manual tracing. If there are two structure images, then the reference point putted in the middle of the images. Points determination performed by two different-operators to avoid an error of point settlement and measurement. The measurement will practice again after one week with the another operator to get an accurate measurement.

Classification of research variable and operational definition of research variable:

The variables classification of this research are:

1. Independent Variable

a. Frankfort Horizontal (FH) Line

b. True Horizontal (HOR) Line

2. Dependent Variable

a. The angle between Frankfort Horizontal line with the lower margin of radiography film

b. Cephalometry value that determined from five parameters are:

1. Maxilla antero-posterior skeletal relationship to the cranial base in McNamara analysis

2. Mandibular anteroposterior relationship to the cranial base in McNamara analysis

3. Growth pattern in Tweed analysis

4. Lower jaw incisive inclination in Tweed analysis

5. Facial angle (Nasion-Pogonion line) in Ricketts analysis

Procedure:

Re-drawn cephalogram sample in tracing paper, determine the cephalometry point, and calculate the linear and angular measurement. Generally, the tracing procedure performs in soft tissue profile, external cranial, cranial base, inner edge of cranium, ear rods, maxilla and the inner structure include nasal bone, fisura pterygomaxillary, edge of lateral orbital, infraorbital ridge, and mandible includes lower jaw incisive. The tracing result continued by manual analysis and determining the Frankfort Horizontal (FH) line and true horizontal (HOR) line. True horizontal (HOR) line draws in parallel tracing paper with cephalogram lower margin and perpendicular on lateral edge of cephalogram.

Then, the result of Frankfort Horizontal (FH) line compared with true horizontal (HOR) line to asses either the FH line is parallel with lower margin of radiography film or deviation occurs. Next, the assessment result grouped into two groups, which are the cephalogram group with normal Frankfort Horizontal line and cephalogram group with deviated Frankfort Horizontal line.

Five parameters of cephalometry will determined the cephalometry value. Five parameters of cephalometry constantly practice in true horizontal (HOR) as a replacement of FH either in normal FH line or deviated FH line. All measurement performs by two different-operators and the measurement result re-measure by similar operator within interval of one week.

Figure 2.7. Cephalometry Discrepancy Measurement with Frankfort Horizontal (FH) Line and True Horizontal (HOR) Line with Five Parameters of Cephalometry 1. A distance of point A from Nasion perpendicular line of FH and HOR ;2. A distance of Pogonion from Nasion perpendicular of FH and HOR; 3. Angle of FH and HOR to the mandibular plane; 4. Incisive axis angle of RB to the FH and HOR; 5. Angle between Nasion-Pogonion.

Remarks: Frankfort Horizontal (FH) Line :

True Horizontal (HOR) Line :

Result And Analysis of Data:

Aims of this research are to evaluate with cephalometry deviation of Frankfort Horizontal (FH) line, comparing the result of five parameters of cephalometry with FH line and true horizontal (HOR) line, and the application of true horizontal (HOR) line as the alternative of FH line substitution to the cephalometry value decision.

Determining result for an occurrence of deviation on Frankfort Horizontal (FH):

In order to determining the deviation, Frankfort Horizontal line measured by creating a parallel Frankfort Horizontal with the lower margin of radiographic film.

From 104 samples (Table 5.1), 49 samples with angle inclination of FH line with lower margin of radiographic film is between -2^o to 2^o and called as control group and 55 samples with inclination of angle inclination of FH line with lower margin of radiographic film is less than -2^o and more than 2^o and called as study group. Inclination of Frankfort Horizontal angle between -2° to 2° is considered or reflected as a truly horizontal line. Inclination Frankfort Horizontal angle that less than -2° and more than 2° is consider or reflected as a deviated Frankfort Horizontal and can not consider to be a horizontal line¹⁴.

Table 5.1 Inclination of Angle on Frankfort Horizontal Line

Fh Angle Inclination With Lower Margin of Radiographic Film	Total
Between -2° to 2°	49
Less than -2° and more than 2°	55

Deviation distribution of Frankfort Horizontal (FH) line inclination to HOR based on sex:

According to Table 5.2 and from 104 samples, mean and Standard Deviation (SD) from female is 2.07 with SD 3.17 and male is 1.26 and SD 2.73.

Table 5.2 Distribution of Deviation on FH Line Inclination to The True Horizontal (HOR) Based on Sex

Sex	N	Min.	Max.	Mean	SD	SE
Female	81	-4.00	9.00	2.07	3.17	0.35
Male	23	-4.00	6.00	1.26	2.73	0.57
Total	104	-4.00	9.00	1.89	1.89	0.30

Result of descriptive test:

Table 5.3.1. shows the first parameter, distance from point A to the line that across the N point and perpendicular with FH line. The first parameter mean± SD 3.52±4.52 and mean on true horizontal (HOR) line is ±SD 3.53±4.60. The second parameter is a distance from Pogonion point to the line that across the N point and perpendicular with FH line. The second parameter mean is ± SD 11.57±4.52 and the mean of True Horizontal (HOR) line is ±SD 11.54±7.69. The third parameter is angle between mandibular line and the FH line. The third parameter ±SD mean is 34.40±9.27 and true horizontal (HOR) mean±SD is 34.58±9.04. The fourth parameter is angle between incisive inclination lower jaw and FH line. The fourth parameter ±SD mean is 52.01±10.23 and true horizontal (HOR) mean±SD is 51.96±9.93. The Fifth parameter is angle between N-Pogonion and the FH line. The fifth parameter ± SD mean is 83.78±4.94 and true horizontal (HOR) mean ± SD is 83.56±4.66.

Table 5.3.1 Description for Control Group (Angle FH Line Between -2° to 2° With Lower Margin of Radiographic Film)

Parameter	N	MIN.	MAX.	MEAN±SD
N to Point A – FH	49	-11.00	12.00	3.52±4.52
HOR	49	-9.00	14.00	3.53±4.60
N to Pog – FH	49	-9.00	30.50	11.57±4.52
HOR	49	-8.00	30.50	11.54±7.69
MA - FH	49	14.00	74.00	34.40±9.27
HOR	49	15.00	74.00	34.58±9.04
LI - FH	49	30.00	75.25	52.01±10.23
HOR	49	32.50	77.25	51.96±9.93
N – Pog to FH	49	70.25	94.00	83.78±4.94
HOR	49	70.25	95.00	83.56±4.66

Table 5.3.2 explains the first parameter or a distance from point A to the line that across point N and perpendicular with FH line, the mean±SD is 3.01±3.72 and true horizontal (HOR) mean±SD is -0.48±4.609. The second parameter, a distance from point in Pogonion to the line that across point N and perpendicular with FH line mean is ± SD is 12.82±47.36 and the true horizontal (HOR) mean ± SD is 9.18±7.41. The third parameter is angle between mandibular line and the FH line. The third parameter ± SD mean is 33.04±6.36 and true horizontal (HOR) mean ± SD is 29.45±6.16. The fourth parameter is angle between incisive inclination lower jaw and FH line. The fourth parameter ± SD mean is 53.01±9.92 and true horizontal (HOR) mean ± SD is 56.60±9.77. The fifth parameter is angle between N-Pogonion and the FH line. The fifth parameter ± SD mean is 83.52±4.22 and true horizontal (HOR) mean ± SD is 87.09±4.74.

Table 5.3.2 Description for Study Group (Angle FH Line is Less than -2° and More Than 2° With Lower Margin of Radiographic Film)

Parameter	N	Min.	Max.	Mean±Sd
N to Point A – FH	55	-3.00	14.50	3.01±3.72
HOR	55	-9.00	11.50	-0.48±4.69
N to Pog – FH	55	0.00	28.50	12.82±7.36
HOR	55	-6.00	25.50	9.18±7.41
MA - FH	55	20.00	45.00	33.04±6.36
HOR	55	15.25	41.00	29.45±6.16
LI - FH	55	33.50	76.00	53.01±9.92
HOR	55	36.50	80.00	56.60±9.77
N – Pog to FH	55	74.50	95.50	83.52±4.22
HOR	55	77.50	97.50	87.09±4.74

Kolmogorov-Smirnov Test Result:

This research applied data normality test with Kolmogorov-Smirnov test because the sample is > 30.

Table 5.4.1 shows data normality test with Kolmogorov-Smirnov test. All parameters value in control group with FH line or True Horizontal (HOR) line have significant value more than 0.05. The value explain all data in each parameter with FH line or True Horizontal (HOR) line is distributed normally.

Table 5.4.1 Kolmogorov-Smirnov Test for Control Group

Parameter	P-Value (Sig)
N to Point A – FH	0.74
HOR	0.85
N to Pog – FH	0.97
HOR	0.98
MA - FH	0.32
HOR	0.12
LI - FH	0.42
HOR	0.99
N – Pog to FH	0.49
HOR	0.97

Table 5.4.2 shows data normality test with Kolmogorov-Smirnov test. All parameters value in study group with FH line or True Horizontal (HOR) line have significant value more than 0.05. The value explain all data in each parameter with FH line or True Horizontal (HOR) line is distributed normally.

Table 5.4.2 Kolmogorov-Smirnov Test in Study Group

Parameter	P-Value (Sig)
N to Point A – FH	0.70
HOR	0.52
N to Pog – FH	0.89
HOR	0.94
MA - FH	0.73
HOR	0.96
LI - FH	0.52
HOR	0.51
N – Pog to FH	0.96
HOR	0.71

Discrepancy test between Frankfort Horizontal (FH) line and True Horizontal (HOR) line (paired t-test):

After Kolmogorov-Smirnov test with all data is distributed normally, then continued by the Paired T-Test to determine the significant difference between FH line and True Horizontal (HOR) line.

Table 5.5.1 is the analysis result on five parameters of cephalometry in control group. The first parameter is a distance from point A to the line that across the N point and perpendicular with FH line or True Horizontal (HOR) line with significant value is 0.96 or the value is more than p<0.05 value. Therefore, there is no a significant difference between the application of FH line or True Horizontal (HOR). The second parameter is the distance from point in Pogonion to the line that across point N and perpendicular with FH line or True Horizontal (HOR) line with significant value is 0.92 or the value is more than p < 0.05 value. Therefore, there is no a significant difference between the application of FH line or True Horizontal (HOR). The third parameter is the angle between mandible line with FH line or True Horizontal (HOR) with significant value is 0.84 or the value is more than p < 0.05 value. Therefore, there is no a significant difference between the application of FH line or True Horizontal (HOR). The fourth parameter is the angle between incisive inclination lower jaw with FH line or True Horizontal (HOR) with significant value is 0.83 or the value is more than p < 0.05 value. Therefore, there is no a significant difference between the application of FH line or True Horizontal (HOR). The fifth parameter is the angle between N-Pogonion line with FH line or True Horizontal (HOR) with significant value is 0.66 or the value is more than p < 0.05 value. Therefore, there is no a significant difference between the application of FH line or True Horizontal (HOR).

Table 5.5.1 Paired T-Test for Control Group

Parameter	Mean±Sd	Mean Deviation	P-Value (Sig)
N to Point A – FH	3.52±4.53	-0.01	0.96
N to Point A – HOR	3.53±4.61	-0.01	0.96
N to Pog – FH	11.56±8.16	0.02	0.92
N to Pog – HOR	11.54±7.69	0.02	0.92
MA - FH	34.40±9.27	0.04	0.84
MA –HOR	34.36±9.03	0.04	0.84
LI - FH	52.01±10.23	0.04	0.83
LI –HOR	51.96±9.93	0.04	0.83
N – Pog to FH	83.78±4.94	-0.81	0.66
N – Pog - HOR	83.86±4.66	-0.81	0.66

Table 5.5.2 is the analysis result on five parameters of angle in study group. The first parameter is a distance from point A to the line that across the N point and perpendicular with FH line or True Horizontal (HOR) line with significant value is 0.00 or the value is less than p < 0.05 value. Therefore, there is a significant difference between the application of FH line or True Horizontal (HOR). The second parameter is the distance from point in Pogonion to the line that across point N and perpendicular with FH line or True Horizontal (HOR) line with significant value is 0.00 or the value is less than p < 0.05 value. Therefore, there is a significant difference between the application of FH line or True Horizontal (HOR). The third parameter is the angle between mandible line with FH line or True Horizontal (HOR) with significant value is 0.00 or the value is less than p < 0.05 value. Therefore, there is a significant difference between the application of FH line or True Horizontal (HOR). The fourth parameter is the angle between incisive inclination lower jaw with FH line or True Horizontal (HOR) with significant value is 0.00 or the value is less than p < 0.05 value. Therefore, there is a significant difference between the application of FH line or True Horizontal (HOR). The fifth parameter is the angle between N-Pogonion line with FH line or True Horizontal (HOR) with significant value is 0.00 or the value is less than p < 0.05 value. Therefore, there is a significant difference between the application of FH line or True Horizontal (HOR).

Table 5.5.2 Paired T-Test for Study Group

Parameter	Mean±Sd	Mean Deviation	P-Value (Sig)
N to Point A – FH	3.01±3.71	3.56	0.00
N to Point A – FH	-0.48±4.69	3.56	0.00
N to Pog – FH	12.82±7.36	3.64	0.00
N to Pog – HOR	9.18±7.41	3.64	0.00
MA - FH	33.04±6.36	3.59	0.00
MA –HOR	29.45±6.16	3.59	0.00
LI - FH	53.01±9.92	-3.58	0.00
LI –HOR	56.59±9.77	-3.58	0.00
N – Pog to FH	83.52±4.22	-3.56	0.00
N – Pog - HOR	87.09±4.74	-3.56	0.00

DISCUSSION:

This research determining an occurrence of deviation in Frankfort Horizontal (FH) line. Aims of this research is to evaluate line deviation with cephalometry study, comparing the the result of five parameters of cephalometry measurement by Frankfort Horizontal (FH) line and True Horizontal (HOR) line, and the application of HOR as the alternative of replacement on FH for the decision of cephalometry value. The research practice the cephalometry photo from pre-treatment of orthodontic patient in Dental and Oral Hospital of Airlangga University, Surabaya, Indonesia (RSGM UNAIR) in 2015-2016. The sample is following these research criteria.

There are 104 cephalometry photo samples in this research. There are 49 patients with normal Frankfort Horizontal (FH) line or parallel, with the angle is between -2° to 2° with lower margin of radiographic file. There are 55 patients with Frankfort Horizontal (FH) line with deviation occurrence and the angle is less than -2° and more than > 2° with lower margin of radiographic film. Line selection where the anatomy is stable has become a growing debate since the early development of cephalometry radiography. During the massive application of these two reference planes, Frankfort Horizontal (FH) line and S-N line, there are remarkable variation in inclination. This variation cause the orthodontists to re-thinking on the application of the line in cephalometry diagnosis and determining the treatment plan¹.

From 104 cephalogram samples, there are only 20 samples with parallel Frankfort Horizontal (FH) line to the true horizontal (HOR) line. The result of this research is similar with Ramirez¹⁵. From 145 samples, there is only 5 patients with parallel Frankfort Horizontal (FH) line to the true horizontal (HOR)¹⁵. This great significant variation that found in Frankfort Horizontal (FH) line when applied as intracranial reference plane lead the application of extracranial reference plane as the true horizontal (HOR) line¹⁰.

According to Table 5.2 and from 104 total samples, the average of angle inclination for Frankfort Horizontal (FH) line to the true horizontal (HOR) line is 1.89°. The value is bigger in female (2.07°) than a male (1,26°). Bjerin report found an inclination difference for Frankfort Horizontal (FH) line to the true horizontal (HOR) line and the value is 4.6¹⁶. According to the Lundstrom et. al. research to 79 kids in England, there are statistical differences on the angle that formed between Frankfort Horizontal (FH) line to the true horizontal (HOR) line in natural head position (NHP) and the difference is 2.6° for boys and 4.1° for girls sample¹⁷. The patient head position in cephalostat is considered have specific relevance because would cause a incorrect diagnosis, especially lead to the maxilla and mandible position^9,18. Miss interpretation is usually caused by a mistake on head posture in sagittal direction (flexion and extension) because the cephalostat machine restricts the rotation movement and head inclination movement. Possibility exception, this case would caused by asymmetric external auditory canal or from asymmetric cephalostat¹⁹. A mistake that cause by head rotation would not significantly cause a distortion in cephalometry measurement. Gron conclude that the rotation from 5° would cause measurement error effect ²⁰.

However, we should consider to the head position control that would not independently will prevent systematically error, such as X-Ray magnification or other technical error possibility (anode characteristic, quality of X-Ray film or random error that related to the structure identification, the measurement itself or the experience and operator capability²¹. When natural head position (NHP) observation, angulation of conventional intracranial reference plane has great variation for each individual. In Caucasoid and non-Caucasoid population, the variation of this line is between 25° to 36° with standard deviation is close to 5° to 6°²².

Alternative research for other line leads to true horizontal (HOR) line during natural head position (NHP) that shows a better stability. Moreover, true horizontal line would describe the facial profile and dentofacial of individual as seen in actual condition¹⁰. The result of this research explore a cephalometry value in a deviated Frankfort Horizontal (FH) to the true horizontal (HOR) line and the value cause a mistake in determining the skeletal pattern diagnosis of the patient. The first parameter is a distance from point A to the line that across the N point and perpendicular with Frankfort Horizontal (FH) line. The first parameter mean is ± SD 3.01±3.72 and the mean of True Horizontal (HOR) line is ± SD -0.48±4.609. The maxilla is normal in the measurement with Frankfort Horizontal (FH) line but the maxilla becomes retrognathia in True Horizontal (HOR) measurement. The second parameter is a distance from Pogonion point to the line that across the N point and perpendicular with Frankfort Horizontal line. The second parameter mean is ± SD 12.82±47.36 and the mean of True Horizontal (HOR) line is ± SD 9.18±7.41. The third parameter is angle between mandible line and the Frankfort Horizontal line. The third parameter ± SD mean is 33.04±6.36 and true horizontal (HOR) mean ± SD is 29.45±6.16. The fourth parameter is angle between incisive inclination lower jaw with Frankfort Horizontal line. The fourth parameter ± SD mean is 53.01±9.92 and true horizontal (HOR) mean ± SD is 56.60±9.77. The fifth parameter is angle between N-Pogonion line with the Frankfort Horizontal line. The third parameter ± SD mean is 83.52±4.22 and true horizontal (HOR) mean ± SD is 87.09±4.74.

Some mistakes is frequently occur during the determining of growth pattern cases and the cephalometry description of the patient shows the growth pattern tends to vertical direction that caused by an additional of angle. This angle is formed by a deviated Frankfort Horizontal (FH) line and mandible line²³. Aim of independent T-Test for two groups is for a cephalometry value comparison in Frankfort Horizontal (FH) line and true horizontal (HOR) line in determining the statistical differences. For the study group, the angle in Frankfort Horizontal (FH) line with true horizontal (HOR) is less than -2° and more than 2°. When the comparison of five cephalometry parameters between Frankfort Horizontal and true horizontal (HOR), value in all parameters is significant 0.00 or less than p 0.05. Therefore, there is a significant difference between the application of Frankfort Horizontal (FH) line and true horizontal (HOR) .

CONCLUSION:

According on the results of the research that has been done, it can be concluded that there is inclination deviation in Frankfort line when the patient is in Natural Head Position (NHP). The inclination difference in Frankfort line cause a different value in cephalometry. If the inclination value is significant then an incorrect diagnosis will be high and the inaccurate in treatment plan for orthodontic case. The True Horizontal (HOR) would applied as a replacement of Frankfort line for Frankfort line with inclination angle is between -2° to 2° to the horizontal plane or lower margin of radiographic film in determining the cephalometry value.

RECOMMENDATION:

Further research is required to determine more homogeneous criteria or determining the difference of skeletal malocclusion class.

CONFLICT OF INTEREST:

The authors have no conflicts of interest regarding this investigation.

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Received on 23.04.2022 Modified on 06.09.2022

Research J. Pharm. and Tech 2023; 16(4):1843-1850.

DOI: 10.52711/0974-360X.2023.00302