Material and methods

In accordance with an institution review board protocol approved by the University of Connecticut, patient records were obtained from 2 orthodontic offices (Dr. Paul Rigali, Wallingford, CT and Dr. Carl Roy, Virginia Beach, VA) that routinely use cone-beam (CB) imaging for diagnostic purposes. Over 3000 patient records (clinical examination records, dental models, photographs, and CBCT scans) were reviewed to select the study sample based on the following inclusion criteria for the subdivision group: (1) complete Class I molar relationship on 1 side of the dental arch with a full-step Class II relationship on the other side; (2) all permanent teeth erupted, including second molars; (3) no malformed or missing teeth, or teeth with extensive restorations or gross decay; (4) no previous orthodontic treatment; (5) no crossbites; (6) no history of facial trauma or medical conditions that might have altered growth; (7) symmetrical spacing or crowding up to 3 mm per arch; (8) age between 10 and 18 years; and (9) no mandibular shift based on the clinical history. The inclusion criteria for the normal occlusion group were as follows: (1) Class I molar relationship on both sides of the dental arch, (2) coincident dental and facial midlines, (3) no clinical dental or skeletal asymmetries, and (4) inclusion criteria 2 through 9 from the subdivision group.

The subdivision and control groups were selected by 2 investigators (P.H.R. and D.S.). The subdivision group consisted of 30 consecutive patients (14 boys, 16 girls), with an average age of 13.99 years (SD, 1.81 years), who came for comprehensive orthodontic treatment with Class II subdivision malocclusions. The control group consisted of 30 consecutive patients (16 boys, 14 girls), with an average age of 14.32 years (SD, 1.67 years), who came for comprehensive orthodontic treatment with normal occlusions.

The 3D scans were acquired before any appliance placement with the patients in maximum intercuspation by using a CBCT unit capable of a full head scan (i-CAT Classic, Imaging Sciences International, Hatfield, Pa). Each volumetric data set was acquired with a 20-second scan time with a 16.0 (diameter) × 22.0 (height) cm field of view at a resolution of 0.4 mm voxels. All images were collected at 120 kVp and 5 mA based on the manufacturer’s specifications. Xoran (i-CAT software, version 2.1.22) was used to reconstruct and export the raw data as a 12-bit-depth digital imaging and communications in medicine (DICOM) file. The DICOM files were imported into Dolphin 3D (version 10.5, Dolphin Imaging, Chatsworth, Calif) for further analysis.

With the Dolphin 3D, the orientation of each 3D volumetric data set was standardized by using the Frankfort horizontal line as the x-axis, the transporionic line as the y-axis, and the midsagittal line as the z-axis ( Fig 1 ). The reference planes were defined by using the volumetric rendering view along with the multiple planar views. A custom analysis was developed, and a total of 34 anatomic landmarks modified from orthodontic cephalometric points were digitized ( Fig 2 , Table I ). The copy-and-paste function of the software was used to export the coordinate data for each defined landmark. The data were then exported into a database (Excel 2007, Microsoft, Redmond, Wash), and orthogonal, linear, and angular measurements were calculated. After the measurements were completed, statistical analyses were calculated with SPSS software (version 14.0.1, SPSS, Chicago, Ill). For convenience of comparison among the Class II subdivision patients, the Class II was set on the right side, which was simply performed by changing the x-coordinates.

Orientation and reference planes used in the study: axial, sagittal, and coronal planes.

Landmarks used in this study in A , right-left profile, B , frontal, and C , SMV views: 1 , Mx1; 2 , Md1; 3 , Mx3R; 4 , Mx3L; 5 , Md3R; 6 , Md3L; 7 , Mx6R; 8 , Mx6L; 9 , Md6R; 10 , Md6L; 11 , ANS; 12 , Me; 13 , Pg; 14 , GlSR; 15 , GlSL; 16 , GlAR; 17 , GlAL; 18 , PoR; 19 , PoL; 20 , CdSR; 21 , CdSL; 22 , CdAR; 23 , CdAL; 24 , CdPR; 25 , CdPL; 26 , GoR; 27 , GoL; 28 , OrR; 29 , OrL; 30 , PNS; 31 , CdLR; 32 , CdLL; 33 , CdMR; 34 , CdML.

Orthogonal measurements from the volumetric image, defined as perpendicular measurements from each 3D landmark to each of the 3D reference planes, were expressed in millimeters ( Fig 3 ). Linear and angular measurements were expressed in millimeters and degrees for the evaluation of dental and dentoalveolar asymmetry ( Fig 4 , Table II ), mandibular morphologic asymmetry ( Fig 5 , Table III ), maxillary angular asymmetry ( Fig 6 , Table III ), and condylar morphologic asymmetry ( Fig 7 , Table IV ). All measurements were made by 1 examiner (D.S.), who was blinded when digitizing the CB images.

Orthogonal measurements in A , frontal view to the sagittal plane ( blue ) and axial plane ( green ); B , SMV view to the sagittal plane ( green ) and coronal plane ( blue ); C , to the coronal plane (profile right and left); D , to the axial plane (profile right and left).

Variables for the evaluation of dental asymmetry. A : 1 , anteroposterior molar differential (mm); 2 , mandibular molar position (mm); B : 3 , overbite (mm, green ); 4, overjet (mm, blue ); C : 5 , midline differential (mm); D : 6 , maxillary arch length (mm); 7 , mandibular arch length (mm).

Variables for the evaluation of mandibular asymmetry: A , frontal; B , SMV; C , sagittal views: 1 , total mandibular length in 3D (mm); 2 , ramus height in 3D (mm); 3 , corpus length in 3D (mm); 4 , total mandibular length in 2D (mm); 5 , ramus height in 2D (mm); 6 , corpus length in 2D (mm); 7 , gonial angle (°); 8 , mandibular plane angle to FH (°); 9 , ramus inclination (°); 10 , dental and chin angulation (°).

Variable for the evaluation of maxillary asymmetry: 1 , palatal plane to the sagittal plane (°).

Variables for the evaluation of condylar asymmetry. A , Frontal; B , SMV; C , sagittal: 1 , M-L diameter of the condylar head in 3D (mm); 2 , anteroposterior diameter of the condylar head in 3D (mm); 3 , superior joint space in 3D (mm); 4 , M-L diameter of the condylar head in 2D (mm); 5 , anteroposterior diameter of the condylar head in 2D (mm); 6 , superior joint space in 2D (mm); 7 , condylar head inclination to the coronal plane (°); 8 , condylar head inclination to the axial plane (°).

Results

In accordance with procedures validated by de Oliveira et al, intrarater reliability for the landmarks used in this study was established by using ICC values. Results, presented in Table V , indicated that the reliability for the landmarks used in this study was generally high for each of the 3 coordinate planes. Intrarater reliability was slightly reduced in the z-plane for the dental measurements.

In the comparison of dental measurements between groups and between sides ( Table VI ), there was a significant anteroposterior molar discrepancy on both sides of the dental arch between groups. The left side (Class I side) of the subdivision group was significantly more Class II by 0.43 mm ( P <0.05) than the left side of the control group. The right side (Class II side) of the subdivision group was significantly more Class II by 4.64 mm ( P <0.01) than the right side of the control group. Similarly, the average molar difference when comparing the differences between the sides of subdivision group and the control group was 4.21 mm ( P <0.01). This measurement was defined as the molar differential, which quantifies the asymmetric molar relationship of the subdivision group, and thus all other results were tested against this variable for correlation.

There was a significant midline difference between the groups ( P <0.01), and the subdivision group showed a significant increase in overjet ( P <0.01). The mandibular molar position was not significantly different when comparing 1 side of the control group to the same side of the subdivision group; however, it was significantly different when comparing the difference between the sides of the control and subdivision groups. Maxillary arch length was decreased on the Class II side in relation to the same side of the control group ( P <0.01), and the difference between the sides of the subdivision and control groups was significant ( P <0.01).

The following dental measurement variables were correlated with the molar differential: midline difference ( P <0.01), overjet ( P <0.01), mandibular molar position difference ( P <0.01), maxillary arch length on the right side ( P <0.05), maxillary arch length difference ( P <0.01), and mandibular arch length on the right side ( P <0.05).

In the comparison of mandibular measurements between groups and between sides ( Table VII ), total mandibular length in 3 dimensions was significantly shorter on the Class II side compared with the same side of the control group ( P <0.05) and when comparing the difference between the sides of the Class II group and the control group ( P <0.01). The difference between right and left ramus heights in the 3D and 2D views was significant between the subject and the control groups ( P <0.01). The difference in corpus length in 2 dimensions between the left and right sides was significant between the subject group and the control group ( P <0.01). The gonial angle was significantly shorter on the Class I and Class II sides of the subdivision group when compared with the same sides of the control group ( P <0.05 and P <0.01). The difference of ramus inclination to the sagittal plane between sides was significant when comparing the subject and control groups. The dental and chin inclinations were also significantly greater in the subdivision group than in the control group ( P <0.05).

The following mandibular variables were correlated with the molar differential: mandibular length in 3 dimensions on the right side ( P <0.05), mandibular length in 3D difference ( P <0.01), ramus height in 3D difference ( P <0.05), ramus height in 2D difference ( P <0.05), corpus length in 2D difference ( P <0.01), gonial angle on the left side ( P <0.05), gonial angle on the right side ( P <0.01), and ramus inclination to the sagittal plane difference ( P <0.05).

In the comparison of maxillary measurements between groups ( Table VII ), there were no statistically significant differences in the angle between the palatal and sagittal planes between the groups. No variables were correlated with the molar differential.

In the comparison of condylar measurements between groups and between sides ( Table VIII ), there were no statistically significant differences with any condylar measurements between groups or between sides. No variables were correlated with the molar differential.

In the comparison of orthogonal measurements with the sagittal plane between groups and between sides ( Table IX ), the maxillary dental midline between the groups was not significantly deviated from the midsagittal plane. The mandibular dental midline was significantly deviated toward the Class II side of the subdivision group when compared with the control group ( P <0.01). The maxillary canine on the Class I side of the subdivision group was significantly more medial than the maxillary canine on the same side of the control group ( P <0.01). The difference in medio-lateral position of the maxillary canine between sides was significant when comparing the Class II and the control groups ( P <0.01). The mandibular canine on the Class I side of the subdivision group was significantly more medial, and the mandibular canine on the Class II side of the subdivision group was significantly more lateral than the mandibular canines on the same side of the control group ( P <0.01). Likewise, the difference in medio-lateral position of the mandibular canines between sides was significant when comparing the Class II and Class I groups ( P <0.01). The maxillary first molar on the Class I side of the subdivision group was significantly more medial than the maxillary first molar on the same side of the control group ( P <0.01). The difference in medio-lateral position of the maxillary first molars between sides was significant when comparing the Class II and Class I groups ( P <0.01). The mandibular first molar on the Class I side of the subdivision group was significantly more medial, and the mandibular first molar on the Class II side of the subdivision group was significantly more lateral than the mandibular first molars on the same side of the control group ( P <0.01). Likewise, the difference in medio-lateral position of the mandibular first molars between the right and left sides was significantly different between the Class II and control groups ( P <0.01).

Table IX

Comparison of orthogonal measurements to the sagittal plane between groups and between sides

Variable	Normal occlusion (n = 30)		Class II subdivision (n = 30)		P	Mean difference	Pearson correlation with molar differential	P
	Mean	SD	Mean	SD
Dental
Mx1 (x) to the sagittal plane (mm)	–0.11	0.51	–0.29	0.88	0.322	0.19	–0.108	0.410
Md1 (x) to the sagittal plane (mm)	–0.11	0.56	–2.45	1.17	0.000 †	2.34	–0.784	0.000 †
Mx3 (x) to the sagittal plane (mm)
Left side normal/Class I side subdivision	16.94	0.98	15.96	1.17	0.009 †	0.98	–0.302	0.019 ∗
Right side normal/Class II side subdivision	16.96	1.22	17.36	1.39	0.238	–0.40	0.212	0.104
Difference (left – right)	–0.02	1.11	–1.40	2.07	0.002 †	1.38	–0.403	0.001 †
Md3 (x) to the sagittal plane (mm)
Left side normal/Class I side subdivision	12.23	0.92	10.54	1.48	0.000 †	1.69	–0.522	0.000 †
Right side normal/Class II side subdivision	12.48	1.08	14.23	1.56	0.000 †	–1.75	0.591	0.000 †
Difference (left – right)	–0.25	1.46	–3.69	2.16	0.000 †	3.44	–0.683	0.000 †
Mx6 (x) to the sagittal plane (mm)
Left side normal/Class I side subdivision	25.41	1.21	24.34	1.69	0.007 †	1.07	–0.254	0.050
Right side normal/Class II side subdivision	25.16	1.41	25.05	1.70	0.786	0.11	0.063	0.632
Difference (left – right)	0.25	1.13	–0.71	1.54	0.008 †	0.96	–0.346	0.007 †
Md6 (x) to the sagittal plane (mm)
Left side normal/Class I side subdivision	23.01	1.01	21.81	1.82	0.003 †	1.20	–0.289	0.000 †
Right side normal/Class II side subdivision	22.73	1.26	23.97	1.63	0.002 †	–1.24	0.476	0.000 †
Difference (left – right)	0.29	1.07	–2.15	1.86	0.000 †	2.44	–0.620	0.000 †
Midface
ANS (x) to the sagittal plane (mm)	–0.16	0.48	–0.40	0.89	0.193	0.24	–0.244	0.060
PNS (x) to the sagittal plane (mm)	–0.22	0.54	–0.13	0.43	0.447	–0.10	0.104	0.428
Or (x) to the sagittal plane (mm)
Left side normal/Class I side subdivision	33.61	2.20	33.90	2.09	0.595	–0.30	0.089	0.499
Right side normal/Class II side subdivision	33.66	2.67	34.11	2.49	0.500	–0.45	0.072	0.585
Difference (left – right)	–0.05	1.70	–0.21	1.85	0.734	0.16	0.003	0.983
Mandible
Me (x) to the sagittal plane (mm)	0.11	0.68	–2.31	1.60	0.000 †	2.42	–0.653	0.000 †
Pg (x) to the sagittal plane (mm)	0.20	0.67	–2.25	1.58	0.000 †	2.45	–0.663	0.000 †
Go (x) to the axial plane (mm)
Left side normal/Class I side subdivision	43.72	2.49	42.17	3.26	0.043 ∗	1.55	–0.229	0.079
Right side normal/Class II side subdivision	43.24	2.97	42.90	2.62	0.643	0.34	–0.072	0.583
Difference (left – right)	0.48	1.89	–0.73	2.35	0.032 ∗	1.21	–0.218	0.095
CdS (x) to the sagittal plane (mm)
Left side normal/Class I side subdivision	47.64	2.72	47.40	3.63	0.779	0.23	–0.058	0.658
Right side normal/Class II side subdivision	47.82	2.38	47.32	2.93	0.471	0.50	–0.099	0.453
Difference (left – right)	–0.19	1.81	0.08	2.54	0.642	–0.27	0.035	0.791
CdL (x) to the sagittal plane (mm)
Left side normal/Class I side subdivision	55.88	2.84	55.46	3.54	0.614	0.42	–0.060	0.649
Right side normal/Class II side subdivision	56.43	3.15	55.20	3.15	0.134	1.24	–0.175	0.180
Difference (left – right)	–0.55	1.56	0.26	2.19	0.102	–0.82	0.190	0.146
CdM (x) to the sagittal plane (mm)
Left side normal/Class I side subdivision	38.41	1.74	38.57	2.92	0.797	–0.16	–0.019	0.885
Right side normal/Class II side subdivision	39.04	2.00	38.40	2.32	0.257	0.64	–0.165	0.206
Difference (left – right)	–0.62	1.28	0.18	2.16	0.087	–0.80	0.173	0.146
CdA (x) to the sagittal plane (mm)
Left side normal/Class I side subdivision	45.69	2.21	45.84	3.12	0.831	–0.15	0.009	0.943
Right side normal/Class II side subdivision	47.03	2.58	46.16	2.66	0.201	0.87	–0.171	0.192
Difference (left – right)	–1.34	1.47	–0.32	2.25	0.041 ∗	–1.02	0.243	0.061
CdP (x) to the sagittal plane (mm)
Left side normal/Class I side subdivision	48.77	2.22	48.58	3.54	0.804	0.19	–0.049	0.707
Right side normal/Class II side subdivision	49.68	2.63	48.36	3.11	0.083	1.31	–0.223	0.087
Difference (left – right)	–0.90	1.51	0.22	2.23	0.026 ∗	–1.12	0.257	0.047 ∗
Temporal
GlS (x) to the sagittal plane (mm)
Left side normal/Class I side subdivision	47.04	2.42	47.14	3.49	0.901	–0.10	–0.024	0.856
Right side normal/Class II side subdivision	46.80	2.05	46.96	2.78	0.801	–0.16	0.000	0.998
Difference (left – right)	0.24	1.54	0.18	2.22	0.898	0.06	–0.037	0.777
GlA (x) to the sagittal plane (mm)
Left side normal/Class I side subdivision	43.04	2.38	43.59	2.74	0.413	–0.55	0.091	0.492
Right side normal/Class II side subdivision	44.77	2.55	44.00	2.57	0.249	0.77	–0.159	0.225
Difference (left – right)	–1.73	1.52	–0.42	2.65	0.022 ∗	–1.32	0.285	0.027 ∗
Po (x) to the sagittal plane (mm)
Left side normal/Class I side subdivision	45.15	2.44	45.24	2.73	0.893	–0.09	–0.029	0.826
Right side normal/Class II side subdivision	45.50	2.45	45.51	2.27	0.991	–0.01	–0.017	0.896
Difference (left – right)	–0.35	1.66	–0.27	2.20	0.869	–0.83	–0.018	0.893

For unpaired structures, a negative value indicates that the landmark is to the right of the sagittal plane.

For paired structures, each listed value is the distance to the sagittal plane.

For the difference, a negative value indicates that the right structure was located more lateral than the left structure.

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. Self-ligating brackets: Looking back and going forward
2. Correction
3. Posttreatment tooth movement: For better or for worse
4. Retainer wear and compliance in the first 2 years after active orthodontic treatment
5. Three-dimensional ultrasound diagnostics of tongue posture in children with unilateral posterior crossbite
6. It’s time we listened to our teeth: The SoundBite hearing system

Stay updated, free dental videos. Join our Telegram channel

Join