Material and methods

The subjects consisted of 46 Japanese women who were diagnosed with mandibular prognathism and underwent single-jaw mandibular setback surgery with either SSRO (25 patients; mean age, 25.1 ± 5.6 years) or IVRO (21 patients; mean age, 24.2 ± 5.2 years), and had presurgical and postsurgical orthodontic treatment with the multi-bracket system ( Table I ). All subjects were randomly selected from the files of patients with jaw deformations registered between 2000 and 2006 in the Kyushu University Hospital at Fukuoka, Japan. Patients who either underwent bimaxillary surgery or had a craniofacial anomaly were excluded. No asymmetry patients were included in the study. The 46 patients were randomized to undergo either SSRO or IVRO according to an adaptive random-assignment procedure.

Maxillary premolars were extracted in 11 subjects who had SSRO and in 8 subjects in the IVRO group to eliminate maxillary crowding and reduce maxillary incisor proclination for decompensation. In the mandibular arch, incisor alignment and proclination were accomplished without extractions, except in 2 patients in the IVRO group with severe crowding. Semirigid fixation was used in the SSRO operation with 2 mono-cortical titanium screws (15.0 and 17.0 mm) on each side. The average amount of mandibular setback at Point B was 8.1 ± 3.1 mm in the SSRO group. IMF was postoperatively maintained for 13.6 ± 1.3 days. No osseous fixation was used in the IVRO group, but it was used in the IMF procedure until a mean of 21.5 ± 3.4 days after surgery. The average amount of mandibular setback at Point B was 10.4 ± 3.8 mm in the IVRO group.

The control group consisted of 30 volunteer women (mean age, 25.1 ± 5.6 years) with normal visual harmony of the facial and skeletal profile, and normal dental Class I occlusion, and normal overbite and overjet. The mean of the peer assessment rating index was 3.63 (SD, 2.93) in the control group, and the mean body mass index was 20.1 (SD, 1.8). All subjects in the volunteer group were healthy, with no craniofacial anomalies. They were recruited with the approval of the institutional ethics committee; their informed consent was obtained.

Lateral cephalometric radiographs were taken by a standardized technique with the mandible in the habitual occlusal position, the lips and tongue relaxed, and the cephalostat in the Frankfort horizontal. A lateral cephalogram was taken for each patient at the start of the presurgical orthodontic treatment (T1), immediately after surgery (T2), and after the postsurgical treatment (T3).

Sella was used as the origin, and a horizontal line passing through sella parallel to the Frankfort horizontal plane was used as the x-coordinate in the analyses. A line perpendicular to the x-axis passing through sella was defined as the y-coordinate.

All cephalograms were traced on acetate paper by the same investigator (T.K.) to eliminate any interexaminer variability. The conventional cephalometric measurements and the coordinates of the reference points ( Figs 1 and 2 ) were calculated by using a cephalometric analysis software program (version 5, WinCEPH, Rise, Sendai, Japan). The measurements of the pharyngeal airway morphology and the hyoid bone position represented 4 linear variables and an angular variable. The width of the PAS was measured in the sagittal plane at 3 levels: nasopharynx (PP1-PNS), oropharynx (PP2-UV), and the region of minimal airway space at the base of the tongue (PP3-Tb).

Lateral cephalometric landmarks and lines used in the PAS and hyoid bone: N , nasion; S , sella; ANS , anterior nasal spine; PNS , posterior nasal spine; PNSp , point of intersection of ANS-PNS line with a line from H perpendicular to ANS-PNS line; B , Point B; UV , the most adjacent point on the soft palate to the posterior pharyngeal wall; UT , the lowest point on the soft palate; PP1 , the point of intersection of the line joining ANS and PNS and the posterior pharyngeal wall; PP2 , the most adjacent point from the uvula to the posterior pharyngeal wall; PP3 , the most adjacent point from the back of the tongue to the posterior pharyngeal wall; Tb , the most posterior point of the back of the tongue; H , the most superior and anterior point of the hyoid bone; Cv2ip , the inferoposterior point of the second cervical vertebrae; Cv2tg , the tangent point of the superoposterior extremity of the second cervical vertebrae.

Lateral cephalometric measurements used in the PAS and hyoid bone: 1 , OPT/NSL: craniocervical angulation at the uppermost part of the cervical spine; 2 , PP1-PNS: the distance from PNS to PP1, representing the nasopharyngeal airway space; 3 , PP2-UV: the distance from UV to PP2, representing the oropharyngeal airway space; 4 , PP3-Tb: the shortest distance between the base of the tongue and the posterior pharyngeal wall; 5 , PNSp-H: the distance from the palatal plane to the hyoid bone.

A random sample of 20 cephalometric tracings was selected and digitized to assess the measurement errors. The measurements of the coordinates were completed twice on 2 separate occasions, 4 weeks apart, by the same investigator. The mean values measured on each occasion were compared by using paired t tests to detect any systematic errors. The error variance was calculated according to Dahlberg’s formula. The error analyses found no significant differences between any paired measurements ( Table II ). All x and y coordinates had accidental errors smaller than 1.0 mm.

The Student t test was used to compare the mean differences in the x and y coordinates, and the linear and angular measurements among the 2 Class III groups (SSRO and IVRO) and the control group by using the JMP statistical software package (release 6.0, SAS Institute, Cary, NC). Any statistically significant differences in the cephalometric coordinates and variables between T1 and T3 were determined by paired t tests. Differences with P values less than 0.05 were considered statistically significant.

Results

No significant differences were identified, except for an average amount of mandibular setback at T3 and the duration of IMF between the SSRO and IVRO groups, as shown in Table I ( P <0.05 and P <0.001, respectively). The cephalometric parameters showed similar maxillomandibular relationships as denoted by the SNA, SNB, and FMA in the 2 patient groups.

Comparisons of the mean values and standard deviations of the hard-tissue variables between the 3 observation periods are presented in Table III . The SNB angle in both the SSRO and IVRO groups decreased significantly after surgery. At the postoperative stage, the SNB angle in the SSRO group appeared to be stable but was significantly decreased in the IVRO group ( P <0.001). The FMA showed posterior (clockwise) rotation after surgery in both the SSRO and IVRO groups ( P <0.05 and P <0.001, respectively). There were no significant postoperative changes in the SSRO group, whereas a significant increase of FMA was found in the IVRO group ( P <0.001).

The SSRO and IVRO groups’ measurements of the width of the PAS, the distance from palatal plane to the hyoid bone (PNSp-H) and the craniocervical angulations at the uppermost part of the cervical spine (OPT/NSL) at T1, T2, and T3 were compared and are presented in Table IV . One significant difference in the distance from the back of the tongue to the posterior pharyngeal wall (PP3-Tb) was observed between the SSRO and IVRO groups at the presurgical stage ( P <0.05).

Table V shows the comparisons among the SSRO, IVRO, and control groups and the comparisons in measurements at each treatment stage of the PAS and hyoid bone. The distances from the uvula to the posterior pharyngeal wall (PP2-UV) and PP3-Tb in the Class III group were significantly greater than those in the control group at T1 ( P <0.05 and P <0.001, respectively).

Significant differences were noted in the PNSp-H at T2, which was larger in the SSRO and IVRO groups than in the controls ( P <0.001). The PNSp-H significantly increased between T1 and T2 in the SSRO and IVRO groups ( P <0.001). In contrast, the linear measurement of PP2-UV significantly decreased ( P <0.01 and P <0.001, respectively). A significant decrease in the PP3-Tb was observed in the IVRO group ( P <0.01).

The PNSp-H of the SSRO group was significantly larger than in the control group at T3 ( P <0.05). The PNSp-H at T2 significantly decreased from T2 to T3 ( P <0.01 and P <0.001, respectively) in the SSRO and IVRO groups. The PP3-Tb significantly decreased in the SSRO group ( P <0.05), whereas significant decreases were also found at the PP2-UV ( P <0.05) and PP3-Tb ( P <0.01) in the IVRO group.

Table VI shows the horizontal and vertical changes of the landmarks of the PAS and the hyoid bone. The UV, Tb, and H in the SSRO and IVRO groups were in significantly more anterior positions than in the control group at T1 ( P <0.01 and P <0.001).

Table VI

Horizontal and vertical changes (mm) of landmarks in the PAS and hyoid bone at the 3 times in the control and Class III groups

	Control (n = 30)		SSRO (n = 25)											IVRO (n = 21)
			T1			T2				T3				T1			T2				T3
Landmark	Mean	SD	Mean	SD		Mean	SD		T1-T2	Mean	SD		T2-T3	Mean	SD		Mean	SD		T1-T2	Mean	SD		T2-T3
Horizontal
H	10.3	6.8	17.3	5.4	‡	12.6	8.1	NS	¶	14.6	5.6	†	#	17.7	8.3	‡	15.2	9.6	∗	§	12.7	6.9	NS	#
PP1	−7.7	3.1	−7.0	3.7	NS	−7.7	2.9	NS	NS	−8.1	3.1	NS	NS	−7.5	3.9	NS	−6.9	3.8	NS	NS	−7.6	3.2	NS	NS
PP2	−12.7	3.5	−11.8	4.3	NS	−12.5	4.2	NS	NS	−13.0	3.8	NS	NS	−11.4	4.2	NS	−11.4	5.0	NS	NS	−12.0	4.0	NS	NS
PP3	−16.3	5.0	−13.5	5.4	∗	−16.8	7.1	NS	¶	−15.6	5.3	NS	NS	−13.8	6.8	NS	−14.6	7.5	NS	NS	−15.7	6.1	NS	NS
UV	−3.2	3.2	0.2	4.1	‡	−2.0	4.2	NS	¶	−3.0	4.2	NS	NS	1.0	5.1	‡	−1.7	5.7	NS	¶	−3.5	4.2	NS	#
Tb	−6.5	4.8	−2.1	5.2	†	−5.1	5.7	NS	¶	−5.2	4.6	NS	NS	−1.0	6.8	‡	−3.4	7.4	∗	‖	−6.2	5.6	NS	∗∗
Vertical
H	−106.8	7.3	−107.9	6.4	NS	−115.5	6.7	‡	¶	−110.4	5.94	∗	††	−105.6	4.8	NS	−111.7	†	†	¶	−107.8	6.6	NS	∗∗
PP1	−45.2	3.3	−45.3	4.4	NS	−45.3	4.7	NS	NS	−45.4	4.25	NS	NS	−44.6	3.4	NS	−45.0	3.2	NS	§	−44.4	3.2	NS	#
PP2	−65.5	5.1	−66.8	5.5	NS	−66.4	5.9	NS	NS	−67.3	6.07	NS	NS	−64.5	5.3	NS	−65.9	5.1	NS	§	−65.4	6.3	NS	NS
PP3	−87.2	5.5	−91.7	5.7	†	−94.8	7.9	‡	¶	−91.0	6.89	∗	††	−88.3	6.2	NS	−90.2	6.8	∗	§	−87.8	6.2	NS	#
UV	−67.6	4.7	−68.3	4.8	NS	−68.7	5.2	NS	NS	−68.9	5.61	NS	NS	−66.9	4.5	NS	−67.6	4.6	NS	NS	−67.1	5.8	NS	NS
Tb	−88.9	5.2	−92.7	5.5	†	−96.6	7.5	‡	¶	−92.2	6.61	∗	††	−89.8	5.3	NS	−91.4	6.1	NS	§	−89.1	5.5	NS	#

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

1. Authors’ response
2. White spot lesions: Prevention and treatment
3. Editor’s Comment and Q&A
4. Ortodoncia lingüal: Procedimientos y aplicación clínica
5. Martensitic transformation of austenitic stainless steel orthodontic wires during intraoral exposure
6. Identification and prevention of digital forgery in orthodontic records

Stay updated, free dental videos. Join our Telegram channel

Join