The change of frontal ramal inclination (FRI) after orthognathic surgery with laterognathism: posteroanterior cephalometric study

Sang-Jin Yu

doi:10.5125/jkaoms.2011.37.1.21

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Yu: The change of frontal ramal inclination (FRI) after orthognathic surgery with laterognathism: posteroanterior cephalometric study

Original Article

J Korean Assoc Oral Maxillofac Surg 2011;37(1):21-29.

Published online: 10 January 2011

DOI: https://doi.org/10.5125/jkaoms.2011.37.1.21

The change of frontal ramal inclination (FRI) after orthognathic surgery with laterognathism: posteroanterior cephalometric study

Sang-Jin Yu

Department of Oral and Maxillofacial Surgery, FOS Dental Clinic, Seoul, Korea

Sang-Jin Yu Department of Oral and Maxillofacial Surgery, FOS Dental Clinic, SM Tower 832 Yeoksam-dong, Gangnam-gu, Seoul, 135-080, Korea. TEL: +82-2-3477-2800 FAX: +82-2-3477-3769 E-mail: sjeenie@hanmail.net

Received 14 October 2010 Revised 20 January 2011 Accepted 10 February 2011

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Introduction

To compare the change in frontal ramal inclination (FRI) in laterognathism after orthognathic surgery.

Materials and Methods

Twenty four patients (10 men, 14 women; mean age, 22.8±5.2 years) with minimal facial canting (≤2 mm) and apparent menton deviation (5.9±2.4 mm) who had been operated on to correct facial asymmetry and skeletal CIII malocclusion, were selected. On a preoperative posteroanterior (PA) cephalogram, the FRI of the deviated side and non deviated side, L1 deviation amounts and menton deviation amounts were measured. The FRI differences between both sides were compared, and the correlations between the measured deviated elements and the FRI differences were analyzed. On a postoperative PA cephalogram, the shifting amount of L1, shifting amount of L7 and FRI of both sides were measured, and the correlations between the shifting elements and the change in FRI were analyzed.

Results

On the preoperative PA cephalogram, the FRI of the non deviated side was significantly greater than those of the deviated side. The differences in FRI, with a menton deviation amount showed a significant correlation. On the postoperative PA cephalogram, the FRI differences between the deviated and non deviated side were decreased significantly and mandibular transverse movement toward central position was noted. The mean shifting amounts of L7 were associated with the amount of change in the deviated side of FRI.

Conclusion

Transverse shifting of the mandible through orthognathic surgery decreases the FRI difference, which showed laterognathism, and improves the facial contour.

Keywords: Frontal ramal inclination (FRI), Laterognathism, Mandibular transverse movement, Orthognathic surgery, Cephalogram

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Fig. 1.

Cephalometric landmarks and measurements used in this study: FRI of deviated side, FRI of non deviated side, amount of menton deviation, amount of U1 deviation, amount of L1 deviation, linear L7 of deviated side, linear L7 of nondeviated side.(FRI: frontal ramal inclination)

Fig. 2.

Diagram of FRI change after parallel shifting of mandibular body.(FRI: frontal ramal inclination)

Fig. 3.

Superimposition of 3-dimensional computed tomography of preoperation and postoperation.

Table 1.

Preoperative deviated amounts in laterognathism

Case	Age/Sex	Deviated site	Amont of Me deviation	Amount of L1 deviation	Amount of U1 deviation	Amount of canting correction	FRI� of non deviated side	FRI� of deviated side	Differential amount of FRI�
1	19.3/F	Rt.	8.0	4.2	2.8	1.5	17.6	10	7.6
2	18/F	Lt.	7.0	4.5	0.5	2.0	11.3	6	5.3
3	27.9/F	Lt.	3.3	1.0	1.0	0.0	11.4	5.8	5.6
4	17.8/F	Lt.	6.5	5.2	2.8	0.0	15.8	6.3	9.5
5	27.4/M	Lt.	5.5	1.2	0.5	0.0	10	1.9	8.1
6	17.7/F	Rt.	5.0	6.8	3.2	0.0	12.2	7	5.2
7	23.8/F	Rt.	1.5	1.5	1.6	1.0	9.5	6.3	3.2
8	30.9/M	Lt.	6.0	3.1	−4.5	−1.0	8.7	0.2	8.5
9	24.9/F	Rt.	9.5	6.2	2.5	2.0	13.1	8	5.1
10	36.4/M	Lt.	7.5	5.5	2.5	1.5	12	4.5	7.5
11	22.6/F	Lt.	7.6	3.8	1.5	0.0	11.7	5	6.7
12	18.8/M	Rt.	6.6	4.5	1.0	1.5	11.5	6.5	5.0
13	25.7/F	Lt.	10.5	6.0	2.3	2.0	16	5.4	10.6
14	18.5/M	Lt.	5.8	4.2	1.5	1.0	8.00	5.00	3.0
15	17.9/F	Lt.	5.2	1.5	0.5	1.0	6.20	−1.0	7.2
16	24.2/F	Lt.	5.7	4.6	0.5	−2.0	14.8	11.7	3.1
17	17/F	Rt.	5.0	5.8	3.2	1.0	14.9	11.5	3.4
18	24.8/M	Lt.	2.6	2.1	1.0	0.0	6.8	3.8	3.0
19	20.8/M	Lt.	3.0	1.5	−2.2	2.0	10	6.4	3.6
20	23/M	Lt.	4.5	5.2	1.2	0.0	4.1	−1.2	5.3
21	19.5/F	Lt.	2.9	3.2	2.9	1.0	12.4	9.2	3.2
22	17.5/F	Lt.	9.7	5.9	1.5	1.0	10.2	2.1	8.1
23	31.2/M	Lt.	4.8	2.6	2.7	−2.0	14.8	9.5	5.3
24	22/M	Lt.	8.9	5.9	4.2	2.0	12.9	3.8	9.1
Mean			5.9	4.0	1.4	0.6	11.5	5.6	5.9
SD			2.4 mm	1.8 mm	1.8 mm	1.2 mm	3.3�	3.5�	2.3�

Table 2.

Postoperative shifting amounts of deviated elements in laterognathism

Case	L1 shifting amount	L7 shifting amount of deviated side	L7 shifting amount of non-deviated side	Mean L7 shifting amount	FRI� of deviated side	FRI� of non deviated side	FRI� change amount of deviated side	FRI� change amount of non deviated side
1	6.5	4.2	4.0	4.1	15.3	15.8	5.3	−1.8
2	5.5	4.0	3.5	3.8	10.1	9.5	4.1	−1.8
3	4.2	2.7	2.0	2.4	9.8	10.5	4.0	−0.9
4	5.5	4.2	3.2	3.7	10.1	14.0	3.8	−1.8
5	3.0	2.8	2.7	2.8	5.5	7.6	3.6	−2.4
6	6.1	4.6	3.6	4.1	12.2	13.1	5.2	0.9
7	1.0	2.9	3.2	3.1	9.1	8.3	2.8	−1.2
8	5.5	4.1	3.6	3.9	5.1	5.8	4.9	−2.9
9	7.0	5.8	5.9	5.9	13.4	10.5	5.4	−2.6
10	6.0	2.9	1.7	2.3	7.5	11.2	3.0	−0.8
11	4.8	3.8	3.8	3.8	9.5	10.2	4.5	−1.5
12	5.0	5.1	4.0	4.6	13.6	13.5	7.1	2.0
13	8.0	6.5	4.5	5.5	12.0	10.5	6.6	−5.5
14	7.7	4.2	3.4	3.8	10.0	6.2	5.0	−1.8
15	3.5	3.0	4.2	3.6	5.9	3.3	6.9	−2.9
16	5.1	3.1	2.9	3.0	15.0	13.4	3.3	−1.4
17	4.5	4.7	4.4	4.6	15.8	13.5	4.3	−1.4
18	3.0	3.0	2.7	2.9	6.1	4.8	2.3	−2.0
19	4.1	4.9	2.3	3.6	12.1	8.7	5.7	−1.3
20	6.1	5.2	3.2	4.2	5.1	5.2	6.3	1.1
21	4.2	2.4	2.7	2.6	13.0	9.8	3.8	−2.6
22	5.4	5.5	5.2	5.4	9.7	8.5	7.6	−1.7
23	3.1	3.5	4.0	3.8	14.5	12.0	5.0	−2.8
24	3.8	3.7	3.0	3.4	8.1	10.5	4.3	−2.4
Mean	4.9	4.0	3.5	3.8	10.4	9.9	4.8�	−1.6
SD	1.6 mm	1.1 mm	1.0 mm	0.9 mm	3.4�	3.2�	1.4�	1.5�

(FRI: frontal ramal inclination, SD: standard deviation)

Table 3.

Comparison of FRI and difference between non deviated side and deviated side in laterognathism (�)

	Non deviated side	Deviated side	Difference	Significance
	Mean±SD	Mean±SD	Mean±SD	Significance
Preoperative FRI�	11.5±3.3�	5.6±3.5�	5.9±2.3�	*

^* P<0.001, paired t-test, FRI: frontal ramal inclination, SD: standard deviation)

Table 4.

Pearson correlation between FRI difference and U1 midline deviation, L1 midline deviation, menton deviation amount in laterognathism (preoperation)

	U1 midline deviation (mm)	L1 midline deviation (mm)	Menton deviation (mm)
Difference of FRI� between deviated and non deviated side	0.058	0.256	0.679^*

^* 0.679: P<0.001, FRI: frontal ramal inclination)

Table 5.

Comparison of FRI after operation (postoperative FRI�- preoperative FRI�)

	Preoperative FRI� Mean±SD	Postoperative FRI� Mean±SD	Difference� Mean±SD	Significance
Non deviated side	11.5±3.3�	9.9±3.2�	−1.6±1.5�	*
Deviated side	5.6±3.5�	10.4±3.4�	4.8±1.4�	*

^* P<0.001, paired t-test, FRI: frontal ramal inclination, SD: standard deviation)

Table 6.

Comparison of FRI and FRI change amount between non deviated side and deviated side after operation (�)

	Non deviated side Mean±SD	Deviated side Mean±SD	Difference Mean±SD	Significance
Postoperative FRI�	9.9±3.2	10.4±3.4	−0.4±2.2	NS
Change amount of FRI� after operation	−1.6±1.7	4.8±1.4	3.1±2	*

^* P<0.001, paired t-test, FRI: frontal ramal inclination, SD: standard deviation, NS: not significant)

Table 7.

Comparison of difference between L1 shifting amount and mean L7 shifting amount after operation

	L1 shifting amount Mean±SD	L7 shifting amount Mean±SD	Difference Mean±SD	Significance
Difference (preoperative distance-postoperative distance)	4.9±1.6	3.8±0.9	1.18±1.36	*

^* P<0.001, paired t-test)

Table 8.

Pearson correlation between FRI changes and L1 shifting amount, L7 shifting amount (deviated site, non deviated site, mean) after operation

	L1 shifting amount (mm)	L7 shifting amount (deviated side, mm)	L7 shifting amount (non deviated side, mm)	Mean L7 shifting amount (mm)
FRI� change of deviated site after operation	0.414^*	0.704^**		0.723^**
FRI� change of non deviated site after operation	−0.056		−0.229	−0.120

FRI: frontal ramal inclination

^* P<0.05

^** P<0.001)

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