Material and methods

The sample size of each group was calculated based on an alpha significance level of 0.05 and a beta of 0.2 to achieve power of 80% to detect a mean difference of 1.5 mm between the groups, with an estimated standard deviation of 1.73 mm, according to Pedrin et al. The sample size calculation showed that 22 patients in each group were needed. The sample size of this study comprised 30 patients in each group.

To obtain 30 patients of both sexes for the treated group, 1 operator (M.A.C.) examined 1482 subjects in the city of Bauru, São Paulo, Brazil, under written authorization of their parents and school supervisors. The subjects were consecutively selected according to the following criteria: children between 6 and 10 years of age with Angle Class I malocclusions, anterior open bite equal to or greater than 1 mm, and the maxillary and mandibular permanent central incisors fully erupted. Full eruption in young children is difficult to determine. Therefore, children in the first transition period were considered to be eligible for treatment when the maxillary lateral incisors were beginning to erupt and the maxillary central incisors still showed an open bite. Children with tooth agenesis, loss of permanent teeth, crowding, maxillary constriction, or posterior crossbites were excluded from this stu dy. Oral habits were not evaluated. The treated group consisted of 30 patients with Angle Class I malocclusion with initial mean anterior open bite of −3.93 mm. All patients were treated by 1 operator (M.A.C.) under a senior supervisor.

The control group consisted of 30 untreated patients with Angle Class I malocclusion with an initial mean anterior open bite of −3.93 mm obtained from the files of the orthodontic department at the University of São Paulo, Bauru Dental School, Brazil ( Table I ). This sample had no treatment and was previously selected according to the same criteria as above. Informed written consent was obtained from the parents, allowing their children to participate in this research. This research project was approved by the ethics committee of the University of São Paulo, Bauru Dental School, Brazil. The initial mean cephalometric characteristics of both groups are shown in Table II . At the pretreatment stage, both groups were at stage 1 of cervical vertebrae maturation, which is the period before the peak in skeletal maturity, according to the classification of Baccetti et al.

The protocol used in the treated group was Nogueira lingual bonded spurs associated with high-pull chincup therapy for 12 months. These appliances were bonded on the palatal and lingual surfaces of the maxillary and mandibular central incisors by using Concise Orthodontic Chemical Curing Adhesive (3M Unitek, Monrovia, Calif). The bonded spurs were sharpened with a carborundum disk before installation, according to the prescription of Haryett et al and Justus. The bonded spurs were positioned in the cervical and incisal portions of the maxillary and mandibular incisors, respectively, to prevent possible future occlusal interferences ( Figs 1 and 2 ).

Bonded spurs gingivally placed on the palatal aspects of the maxillary central incisors.

Bonded spurs apically placed on the lingual aspects of the mandibular central incisors.

A high-pull chincup delivering 450 to 550 g of force per side was used. All patients were instructed to wear the chincup 14 to 16 hours a day for 12 months. To improve patient compliance with treatment, booklets were given to the parents, and they were instructed to record the number of hours of appliance usage every day.

Cephalometric data were obtained from lateral cephalograms taken at pretreatment and after 12 months of treatment with bonded spurs associated with high-pull chincup therapy for the treated group and at a comparable time period for the control group.

Cephalometric tracings and landmark identifications were made on acetate paper by 1 investigator (M.A.C.) for each group and then digitized with an AccuGrid XNT (model A30TLF digitizer; Numonics, Montgomeryville, Pa) for both groups ( Figs 3 and 4 ). These data were stored on a computer and analyzed with Dentofacial Planner software (version 7.02; Dentofacial Planner, Toronto, Ontario, Canada) that corrected the image magnification factors of the groups, which was 9.5%.

Cephalometric points: S , Sella; N , nasion; A , subspinale; B , supramentale; Pog , pogonion; Me , mentalis; Go , gonion; Gn , gnathion; Co , condylion; ANS , anterior nasal spine; PNS , posterior nasal spine; Is , edge of the maxillary incisor; UIA , apex of the maxillary incisor; Ii , edge of the mandibular incisor; LIA , apex of the mandibular incisor; UMT , mesiobuccal cusp of the maxillary first molar; LMT , mesiobuccal cusp of the mandibular first molar; Ar , articulare.

Angular and linear measurements: 1 , SNA angle; 2 , Co-A line; 3 , SNB angle; 4 , Ar-Go line; 5 , Ar.GoMe angle (angle between Ar-Go and Go-Me lines); 6 , Co-Gn line; 7 , ANB angle; 8 , SN.GoGn angle (angle between S-N and Go-Gn lines, or mandibular plane angle); 9 , SN.PP angle; 10 , NS.Gn angle (angle between N-S and S-Gn lines); 11 , AFH (distance between N and Me); 12 , PFH (distance between S and Go); 13 , lower anterior face height (distance between ANS and Me); 14 , overbite (distance between the incisal edges of the maxillary and mandibular central incisors, perpendicular to the occlusal plane); 15 , U1.NA (angle between upper incisor long axis and NA line); 16 , U1-NA (distance between the most anterior point of the maxillary central incisor and the NA line; positive value was assigned when the structure was posterior to the line); 17 , U1-PP (perpendicular distance between the maxillary central incisor and the palatal plane); 18 , U6-PP (perpendicular distance from the maxillary first molar mesial point to the palatal plane); 19 , L1.NB (angle between the mandibular incisor long axis and the NB line); 20 , L1-NB (distance between the most anterior point of the mandibular central incisor and the NB line; a positive value was assigned when the structure was posterior to the line); 21 , L1-GoMe (perpendicular distance from the tip of the mandibular incisor to the GoMe line); 22 , L6-GoMe (perpendicular distance from the mandibular first molar mesial point to the GoMe line).

For the error study, 40 cephalograms from the 2 groups were randomly selected and remeasured by the same investigator (M.A.C.) after 1 month, following the guidelines suggested by Baumrind et al. Random errors were calculated with Dahlberg’s formula, and systematic errors were evaluated with dependent t tests. The random errors for linear measurements ranged from 0.33 mm for overbite to 0.81 mm for Ar-Go, and from 0.48° for NS.Gn to 1.62° for U1.NA for angular measurements. The systematic errors were significant for only 3 variables: lower anterior face height, L1-GoMe, and L6-GoMe ( Fig 4 ).

Results

There was no significant intergroup difference for the initial and final ages ( Table I ).

There were no significant differences between the 2 groups for sex distributions.

No significant differences were found between the initial characteristics of the treated and control groups, with the exception of Co-A, which was smaller for the control group (75.84 ± 2.91 mm) compared with the treated group (77.38 ± 2.9 mm).

Descriptive statistics regarding the mandibular plane angle, ANB, and the amount of initial overbite of the groups are described in Table II .

During treatment, there were a significantly greater decrease of the gonial angle, an increase in overbite, palatal tipping of the maxillary incisors, and vertical dentoalveolar development of the maxillary and mandibular incisors in the treated group ( Table III ).

Table III

Comparison of treatment changes between the treated and control groups

Variable	Treated group		Control group		P
	Mean	SD	Mean	SD
Maxillary component
SNA (°)	−0.33	1.60	0.18	1.98	0.27
Co-A (mm)	1.53	1.53	1.49	1.74	0.94
Mandibular component
SNB (°)	−0.0	1.29	0.33	1.73	0.40
Ar-Go (mm)	−0.28	1.45	0.25	1.95	0.23
Ar.GoMe (°)	−1.23	2.13	0.22	1.62	<0.01 ∗
Co-Gn (mm)	1.64	1.40	2.14	1.49	0.19
Maxillomandibular component
ANB (°)	−0.33	1.21	−0.16	1.62	0.65
Vertical component
SN.GoGn (°)	0.01	1.76	−0.29	2.06	0.55
SN.PP (°)	0.21	1.26	−0.22	2.16	0.35
NS.Gn (°)	0.23	1.35	−0.45	1.81	0.10
AFH (mm)	1.67	1.40	1.64	2.01	0.93
PFH (mm)	0.68	1.23	0.78	1.46	0.77
LAFH (mm)	1.05	1.05	0.89	1.45	0.64
Overbite (mm)	5.23	1.69	1.98	1.41	<0.0001 ∗
Maxillary dentoalveolar component
U1.NA (°)	−3.86	5.29	0.00	4.65	<0.01 ∗
U1-NA (mm)	0.29	1.34	0.55	1.89	0.53
U1-PP (mm)	3.16	1.13	1.39	0.85	<0.0001 ∗
U6-PP (mm)	0.90	0.95	0.66	1.14	0.38
Mandibular dentoalveolar component
L1.NB (°)	−1.29	3.81	0.28	3.04	0.08
L1-NB (mm)	0.70	1.08	0.48	0.90	0.40
L1-GoMe (mm)	3.30	0.75	1.43	0.72	<0.0001 ∗
L6-GoMe (mm)	0.75	0.61	0.54	0.58	0.19

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