This research aimed to compare treatment effects of functional appliances between children with and without morphologic deviations in the upper spine and analyze associations between Atlas dimensions and the short- and long-term treatment effects.
Sixty-eight prepubertal or pubertal children (35 boys and 33 girls; mean age, 11.47 ± 1.39 years) treated with Class II functional appliances were included. Lateral cephalograms were taken at pretreatment (T1), postfunctional appliance treatment (T2), and after retention at postpuberty (T3). Upper spine morphology and Atlas dimensions were evaluated at T1. T1-T2 and T1-T3 lateral cephalograms were superimposed using a structural method. Changes in the jaws were compared with multiple linear regression analysis between children with and without deviations in the upper spine. Associations between the changes and Atlas dimensions were analyzed by partial correlation.
Children with morphologic deviations in the upper spine showed significantly more backward rotation of the mandible ( P <0.01) and increased inclination of the jaws ( P <0.05, P <0.01) from T1-T2 and significantly smaller condylar growth ( P <0.01) from T1-T3 compared with children without the deviations. Atlas height was significantly associated with vertical and rotational changes in the mandible ( P <0.01) from T1-T2 and condylar growth ( P <0.05) from T1-T2 and T1-T3.
Morphologic deviations in the upper spine and low Atlas height were significantly associated with smaller condylar growth induced by functional appliances in the long term. Upper spine morphology and the Atlas dimension may be valuable in phenotypic differentiation in children with Class II malocclusion for optimal treatment outcome.
Long-term condyle growth was smaller in children with deviations in the upper spine.
In the short term, they also had more backward rotation of the mandible.
Vertical and rotational changes in the jaws did not differ significantly between groups.
Atlas height was associated with vertical and rotational changes of the mandible in the short term.
Upper spine morphology and Atlas dimension may be valuable phenotypic differentiation.
Functional appliances have been widely used for growth modification treatment in growing children with Class II malocclusion. It is generally agreed that functional appliances are effective in improving skeletal relationships in the short term, but it is still discussed with regard to long-term skeletal effects because of individual variations to the same treatment approach.
It has been reported that mandibular growth patterns can affect the treatment outcome of functional appliances in Class II malocclusion. Some studies have found that pretreatment craniofacial variables, such as condylar angle or lower anterior facial height, are associated with the treatment outcome of functional appliances and thereby could be used to predict the growth. However, craniofacial morphology may not be considered a reliable predictor in children as it undergoes constant changes before puberty.
Recent studies have found that upper spine morphology and Atlas dimensions are significantly associated with craniofacial morphology and growth prediction signs by Björk. , , Children with morphologic deviations in the upper spine or decreased Atlas dimension presented significantly more backward growth prediction signs by Björk than children without morphologic deviations in the upper spine or increased Atlas dimensions respectively. , The results suggested that the upper spine morphology is valuable for predicting jaw growth and rotation and may be included in orthodontic diagnosis and treatment planning for children. , So far, no studies have examined upper spine morphology or Atlas dimension in association with longitudinal growth changes in children treated with Class II functional appliances.
Therefore, the aims of the present study were to (1) to compare treatment outcomes of functional appliances between children with and without morphologic deviations in the upper spine and (2) analyze associations between Atlas dimensions and the short- and long-term treatment outcome.
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 ).
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 ).
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.
When normality of distribution was assessed with the Shapiro-Wilk W-test, all the variables were normally distributed. Skeletal and rotational changes in the jaws from T1-T2 and T1-T3 were compared between children treated with Z- and E-activators using a t test beforehand. As the changes in the jaws between the children treated with the Z- and E-activators were not significantly different, except for mandibular inclination at T2 and maxillary rotation at T3, the children treated with the Z- and the E-activators were pulled in the following analysis.
At baseline, CVM stage and treatment timing were compared between children with and without morphologic deviations in the upper spine by Chi-square test. Craniofacial morphology and Atlas dimensions at pretreatment and skeletal and rotational changes in the jaws from T1-T2 and T1-T3 were compared between children with and without morphologic deviations in the upper spine using a t test. For the changes in the jaws from T1-T2 and T1-T3, possible effects of age, sex, ethnicity, appliance type, treatment timing, and duration were adjusted with multiple linear regression analysis.
Associations between the initial Atlas dimensions and the skeletal/rotational changes in the jaws from T1-T2 and T1-T3 were analyzed by partial correlations, adjusted for possible effects of age, sex, ethnicity, appliance type, treatment timing, and duration.
Of the total population, 36.8% had morphologic deviations in the upper spine, at least 1 fusion deviation, or posterior arch deficiency ( Table I ).
|Upper spine morphology||n||%|
|Normal upper spine||43||63.2|
|Any upper spine deviations||25||36.8|
|Posterior arch deficiency||17||25.0|
|More than 1 deviation||4||5.9|
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 ).
|Characteristics||No deviation (n = 43)||Upper spine deviations (n = 25)||P|
|Atlas dimensions (mm)|
|Cranial base angle (°)|
|Sagittal dimensions (°)|
|Vertical dimensions (°)|
|Mandibular form (°)|
|ILs to NL (°)||116.91||5.34||117.71||8.37||NS|
|ILi to ML (°)||99.76||6.35||97.56||7.10||NS|