Material and methods

A total of 68 prepubertal or pubertal children (35 boys and 33 girls; mean age, 11.47 ± 1.39 years) with Class II malocclusion were included. Thirty-six children (21 boys and 15 girls; mean age, 11.81 ± 1.46 years) treated with a combined high-pull headgear–activator (Z-activator) and 32 children (14 boys, 18 girls; mean age, 11.10 ± 1.23 years) treated with a modified Andresen activator (E-activator) were systematically collected from 2008 to 2015 from the Orthodontic section at the Institute of Odontology, Copenhagen University, Denmark and from the Orthodontic Department of Seoul National University Dental Hospital, South Korea.

The inclusion criteria were as follows: (1) no previous orthodontic treatment, (2) lateral cephalograms available at pretreatment (T1); postfunctional appliance (T2); and more than 1-year retention after the functional appliance treatment at postpuberty, followed either with or without fixed appliances (T3); (3) sagittal jaw relationship: Subspinale-Nasion-Supramentale (Ss-N-Sm) larger than 4.5°; (4) overjet larger than 5 mm; (5) prepubertal or pubertal stage at T1 assessed by cervical vertebral maturation (CVM) method (cervical stage [CS] 1-CS4), and (6) postpubertal stage (CS5-CS6) at T3. Exclusion criteria were as follows: (1) fixed appliance treatment with extractions, Class II elastics and other fixed Class II devices after the functional appliance, and (2) craniofacial syndromes or general diseases.

The children were treated with 2 functional appliance types: Z-activator with a high-pull headgear (force vector going between the center of resistance of the nasomaxillary complex and maxillary dentition) and E-activator without a headgear. In both appliances, a construction bite was taken at an anterior edge-to-edge bite with an opening about 2 mm between the central incisors. The children in both groups were instructed to wear the appliance daily for 14 hours during the evening and night. Appliances and compliance were checked every 8 weeks until Class I molar relationship and proper overjet was achieved. After the active treatment, the children were recalled regularly until the postpubertal stage. If needed, a fixed appliance treatment was performed during the period.

The study was approved by the Danish Data Protection Agency (no. 2015-57-0121) and the ethical committee of Seoul National University Dental Hospital, South Korea (institutional review board no. 207/08-16).

When power analysis was performed using variables, such as condylar growth and sagittal jaw changes from previous studies, ^, at least 17 and 33 children with and without upper spine morphologic deviations were required respectively to have sufficient power (80%) to identify statistically significant differences at the 5% level of significance.

Lateral cephalograms were taken at T1, T2, and T3, in the centric occlusion and the standard mirror position.

For the Danish children, the lateral cephalograms were taken with a Philips MEDIO 30 CP x-ray tube (Philips, Eindhoven, Netherlands) with a film to focus distance of 180 cm and film-to-median plane distance of 10 cm. The constant linear enlargement was 5.6%. For the Korean patients, the lateral cephalograms were taken with Asahi CX-90 SP (Toshiba, Tokyo, Japan) with a film to focus distance of 150 cm and a film to the median plane distance of 15 cm. The constant linear enlargement was 10%. Correction for the constant linear enlargement was made for both groups.

Upper cervical spine morphology was visually assessed on pretreatment lateral cephalograms, and upper spine deviations were classified into 2 categories: fusion and posterior arch deficiency, as described by Sandham. Children with either fusion or posterior arch deficiency were categorized as with morphological deviations of the upper spine , and children with neither fusion nor posterior arch deficiency were categorized as without morphological deviations of the upper spine ( Fig 1 ). ^{, ,} Atlas dimensions according to Huggare, including the height of the posterior neural arch at the slimmest part, ^, were measured on pretreatment lateral cephalograms using TIOPS 2005 (version 2.12.4 Total Interactive Orthodontics Planning System; TIOPS, Copenhagen, Denmark) ( Fig 2 ).

Upper spine morphology according to Sandham: A, normal upper spine morphology; B and C, upper spine deviation. P, posterior arch deficiency; F, fusion of the second and the third cervical spine at articular facet; O, occipitalization of the Atlas and the occipital bone.

Atlas dimensions. DAH , dorsal arch height; PNAH, posterior neural arch height; AP , anteroposterior dimension.

The skeletal maturation stage was visually assessed by the CVM method on lateral cephalograms. Children were categorized into 2 groups according to treatment timing. Children treated with the functional appliances before the pubertal growth peak was categorized as the early treatment group and children treated during the growth peak as the late treatment group . As the pubertal growth peak occurs between CS3 and CS4, the CVM stage from CS1 to CS3 at T2 was considered as the early treatment group and from CS4 to CS5 as the late treatment group.

The craniofacial morphology at pretreatment and the skeletal and rotational changes in the jaws after functional appliance treatment (T1-T2) and after more than 1-year retention (T1-T3) were analyzed digitally by TIOPS 2005 ( Figs 3-5 ). ^, The series of lateral cephalograms were superimposed on the stable structures, the structural method according to Björk. Stable anatomic structures in the anterior cranial base were used as reference structures when the vertical, sagittal, and rotational changes in the jaws were analyzed. The nasion-sella line at the baseline was transferred to the following lateral cephalograms as a reference line (NSL ^ref ) ( Fig 4 ). The maxilla and the mandible were separately superimposed on the stable anatomic structures in the maxilla and mandible (T1-T2 and T1-T3), respectively, and a reference line was marked on the maxilla (maxilla ^ref ) and the mandible (mandible ^ref ) of the series of lateral cephalograms. The angles between NSL ^ref and maxilla ^ref and between NSL ^ref and mandible ^ref were measured to analyze the rotation of the maxilla and the mandible, respectively ( Fig 4 ). The condylar growth was measured as a linear distance from condylion at T1 (Cd ^ref ) to condylion (Cd) at T2 or T3 when the 2 sets of lateral cephalograms were superimposed on the stable structures of the mandible ( Fig 5 ).

Cephalometric landmarks.

Illustration of superimposition on the stable structures in the anterior cranial base between 2 stages. NSL ^ref , nasion-sella line at T1 transferred to the following lateral cephalogram as a reference line when the 2 sets are superimposed on the stable structures in the anterior cranial base; maxilla ^ref , a reference line drawn in the maxilla when the 2 sets are superimposed on the stable structures in the maxilla; mandible ^ref , a reference line drawn in the mandible when the 2 sets are superimposed on the stable structures in the mandible.

Illustration of superimposition on the stable structure in the mandible between 2 stages. Cd ^ref , condylion at T1.

The reliability of the craniofacial and upper spine morphology and CVM methods was evaluated by remeasuring 25 randomly selected sets after 1 month, as reported previously. ^{, ,} All the analyses were performed by 1 author (E.O), and the upper spine morphology was evaluated together with another author (L.S). For the craniofacial analysis, the method errors according to Dahlberg ranged from 0.14 to 2.12, and the reliability coefficients according to Houston were 0.76-0.99. The reliability of the CVM method (κ = 0.91) ^, and the upper spine morphology (κ = 0.82) was excellent.

Results

Of the total population, 36.8% had morphologic deviations in the upper spine, at least 1 fusion deviation, or posterior arch deficiency ( Table I ).

At baseline, the maturation stage and craniofacial morphology were not significantly different between the children with and without morphologic deviations in the upper spine. However, Atlas dimensions (dorsal arch height, P <0.01; anteroposterior dimension, P <0.01) were significantly smaller in children with morphologic deviations in the upper spine compared with children without deviations in the upper spine ( Table II ).

Table II

Craniofacial characteristics between children with and without upper spine morphologic deviation at T1

Characteristics	No deviation (n = 43)		Upper spine deviations (n = 25)		P
	n	%	n	%
CVM stage					NS
CS1	7	16.3	8	32.0
CS2	16	37.2	11	44.0
CS3	13	30.2	4	16.0
CS4	7	16.2	2	25.0
Treatment timing					NS
Early treatment	20	46.5	16	64.0
Late treatment	23	53.5	9	36.0

 

	Mean	SD	Mean	SD	P
Age (y)	11.65	1.36	11.17	1.42	NS
Atlas dimensions (mm)
DAH	8.52	1.53	7.20	1.99	∗
PNAH	4.02	0.79	3.70	0.81	NS
AP dimension	45.14	3.17	43.07	2.78	∗
Cranial base angle (°)
N-S-Ba	133.03	5.30	133.17	5.03	NS
Sagittal dimensions (°)
Ss-N-Sm	6.37	1.38	6.49	1.28	NS
Ss-N-Pg	5.59	1.86	5.92	1.59	NS
S-N-Ss	80.85	2.54	80.18	3.44	NS
S-N-Pg	75.27	2.69	74.27	3.82	NS
Vertical dimensions (°)
NL/ML	25.67	4.36	26.54	5.78	NS
NSL/NL	8.33	3.09	8.94	3.83	NS
NSL/ML	34.01	5.18	35.47	6.86	NS
Mandibular form (°)
ML/Rlar	120.41	6.61	120.55	7.61	NS
ML/MBLar	19.89	2.89	19.45	2.94	NS
Dental
Overjet (mm)	8.45	2.13	9.09	2.26	NS
Overbite (mm)	3.64	1.99	3.33	1.77	NS
ILs to NL (°)	116.91	5.34	117.71	8.37	NS
ILi to ML (°)	99.76	6.35	97.56	7.10	NS

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