Material and methods

The clinical records of consecutively treated patients from 2008 to 2011 were searched to identify appropriate subjects. The patients had undergone level anchorage system treatment at Aichi-Gakuin University Dental Hospital in Nagoya, Japan. A total of 51 subjects met the following inclusion criteria: (1) Angle Class II Division 1 or Class I malocclusion with bimaxillary protrusion, (2) hyperdivergent skeletal pattern, (3) well-aligned maxillary incisors with minimal crowding (≤3.5 mm), (4) full permanent dentition (except for the third molars), and (5) extraction of bilateral maxillary first premolars (with various strategies for the mandibular arch, including nonextraction or extraction of the first or second premolars). All subjects were successfully treated (ie, Class I or full-cusp Class II molar relationship, Class I canine relationship, and adequate overbite and overjet were obtained). The exclusion criteria were (1) poor film quality or incomplete records, (2) patients who received skeletal anchorage in the mandible and midpalatal areas, (3) patients with major rotations or a posterior crossbite, (4) prolonged use of vertical seating elastics during the finishing stage, and (5) patients with congenital malformations, systemic diseases, or syndromic conditions.

The subjects were characterized by maxillary dentoalveolar protrusion and a hyperdivergent skeletal pattern. The treatment plan involved maximum maxillary incisor retraction in addition to vertical dimension control. In these patients, both the anteroposterior and vertical control of the maxillary posterior anchorages were of major importance. The subjects were divided into 2 groups according to the type of maxillary posterior anchorage reinforcement ( Table I ).

The high-pull headgear group included 28 subjects who received traditional anchorage reinforcement with high-pull headgear, conventional transpalatal arch, and interarch elastics. After the initial leveling and aligning in the maxillary arch, maxillary posterior anchorage was reinforced with high-pull headgear, and Class III elastics were used for anchorage preparation to upright the mandibular molars. After stabilization of the mandibular arch, high-pull headgear and Class II elastics were used during the maxillary en-masse retraction. All subjects were instructed to wear the high-pull headgear for 10 to 12 hours per day throughout the treatment period and to record their headgear wear time on daily charts. A force of approximately 250 g on each side was applied at the level of the buccal trifurcation (center of resistance) of the maxillary first molars. The importance of wearing the extraoral appliance as anchorage was explained at the initial stage and reiterated throughout active treatment.

The miniscrew group consisted of 23 subjects who received implantation of 2 self-drilling miniscrews (Induce MS-II; GC Ortholy, Tokyo, Japan; diameter, 1.8 mm; length, 6.0 mm; and Dual-Top Anchor; Jeil Medical, Seoul, Korea; diameter, 2.0 mm; length, 6.0 mm) in the midpalatal suture. The miniscrews were inserted under local anesthesia between the mesiolingual cusps (center of the occlusal surface) of the maxillary first molars and those of the maxillary second molars. To reduce soft-tissue inflammation around the miniscrews, strict instructions regarding oral hygiene were given to the subjects. After 2 weeks of healing, the 2 midpalatal miniscrews were connected with a horizontal 0.030-in stainless steel ligature wire ( Fig 1 ). The horizontal ligature wire provided support where the vertical ligature wires were firmly tied, enabling them to fasten a modified transpalatal arch ( Figs 2 and 3 ). Intrusion was performed with either elastomeric chains or ligature wires from the horizontal ligature wire to the stabilization hook of the modified transpalatal arch. The stabilization hook was used to prevent mesial tipping of the posterior teeth and to apply intrusive force to the posterior teeth. Ideally, the modified transpalatal arch should be positioned 5 to 7 mm from the depth of the palate to prevent impingement of the arch on the tissues when an intrusive force is applied to the maxillary molars. When a long action range of the intrusion action components was needed, the horizontal ligature wire and lingual sheathes of the molar bands were connected with longer elastomeric chains. While the maxillary molars were being intruded, the modified transpalatal arch was also used to prevent palatal tipping of the maxillary molars.

Two midpalatal miniscrews were placed approximately 5 to 8 mm apart in the midpalatal suture and connected with a horizontal 0.030-in stainless steel ligature wire.

Anchorage reinforcing appliances in the miniscrew group: A, a modified transpalatal arch with distally extending arms to control the posterior teeth ( a , 1 stabilization hook; b , 2 anchorage hooks); B, the maxillary molars were controlled both anteroposteriorly and vertically with the modified transpalatal arch, which was supported by 2 midpalatal miniscrews.

A, Lateral cephalometric radiograph; B, schematic diagram ( a , 1 stabilization hook; b , 2 anchorage hooks; red line , horizontal ligature wire; blue lines , vertical ligature wires): the modified transpalatal arch was ligated at 2 anterior anchorage hooks and at 1 posterior stabilization hook with the vertical ligature wires.

All midpalatal miniscrews achieved primary stability. However, 3 (1 in each of 3 subjects) of the 46 total midpalatal miniscrews became mobile during the en-masse retraction, for a success rate of 93.48%. In the failed cases, a hairpin-shaped wire was bent to fit the head part of the remaining sound miniscrew passively; this provided support instead of a horizontal ligature wire. Treatment was continued with 1 remaining sound miniscrew. Therefore, the failed cases can be considered to have had a limited influence on the results.

All subjects were treated with preadjusted edgewise appliances, 0.018 × 0.025-in slot, level anchorage system prescription brackets (3M Unitek, Monrovia, Calif). We applied the same treatment protocol in both groups with 1 exception: the method of anchorage reinforcement. After the initial leveling and aligning in the maxillary arch, stabilizing transpalatal arches were needed to control the posterior segments. Therefore, we added stabilizing (conventional or modified) transpalatal arches in both groups. Maxillary posterior anchorage was reinforced with high-pull headgear or miniscrew-supported modified transpalatal arches in each group. Once the clinicians were satisfied that the anchorage reinforcement was secure, the bilateral maxillary first premolars were extracted. In both groups, 6 maxillary anterior teeth were retracted on a 0.017 × 0.025-in nickel-titanium archwire with 0.010 × 0.036-in stainless steel closed-coil springs that were stretched two-thirds of the distance from the maxillary first molars to the crimpable hooks located mesial to the canines. Gable bends of 45° were placed in the extraction sites to prevent tipping of the maxillary incisors lingually during the en-masse retraction. When the extraction space measured 2 to 3 mm, a 0.018 × 0.025-in stainless steel archwire with keyhole loops was used for root control in the extraction sites, torque control of the maxillary anterior teeth, and final space closure. The keyhole loops were activated 1 mm at a time. Anchorage reinforcement was continued until the extraction space was closed. When the mandibular arch was stabilized and the maxillary canines were in a Class I relationship with the mandibular canines, the patients were instructed to stop wearing the high-pull headgear, or the midpalatal miniscrews were disconnected from the modified transpalatal arch. Stabilizing (conventional or modified) transpalatal arches were also removed in both groups. In the finishing phase, after removing only the posterior segments of the 0.018 × 0.025-in stainless steel finishing archwires, laced posterior vertical elastics were applied for better interdigitation of the occlusion; these remained in place for 2 to 3 weeks at the most.

Lateral cephalometric radiographs, obtained routinely within 1 month before treatment and immediately after removal of the fixed appliances, were taken in centric occlusion. The images were then hand-traced on matte cephalometric acetate tracing film by the orthodontists in charge (M.T., M.S., M.K.) and verified by another orthodontist (K.M.). Tracings were made through the midpoints between the right and left structures, and the measurements were adjusted to eliminate radiographic magnification. All radiographs were taken anonymously by obscuring any patient data.

To evaluate changes between the pretreatment and posttreatment data and to compare treatment changes between the 2 groups, skeletal and dental changes were calculated according to the method described by Pancherz. In several recent studies, the dentofacial morphology of subjects with maxillary dentoalveolar protrusion was compared using the Pancherz cephalometric analyses. The Pancherz approach comprises sagittal occlusal analysis and vertical occlusal analysis ; the use of these 2 methods enables differentiation between sagittal and vertical dentofacial problems, as well as associated changes. The cephalometric landmarks and reference lines for Pancherz’s sagittal, vertical, and angular analyses are shown in Table II and Figures 4 through 6 .

Cephalometric landmarks and reference lines for the sagittal measurements. The sagittal skeletal and dental changes were analyzed by constructing a reference grid based on 2 reference planes: the maxillary occlusal line ( OLs ) and the occlusal line perpendicular ( OLp ), obtained from the pretreatment lateral cephalogram. This reference grid was used for all sagittal measurements between the OLp and the cephalometric landmarks. The reference grid from pretreatment was transferred to the posttreatment radiographs by superimposition on the SN line with the sella as the registering point.

Cephalometric landmarks and reference lines for the vertical measurements. The vertical measurements included OLs , NL , and ML . OLs was obtained from the pretreatment radiograph and transferred by superimposition on the anterior cranial base to the posttreatment radiographs. The vertical movements of the maxillary molars and incisors were determined by measuring the distance to the NL.

Cephalometric landmarks and reference lines for the angular measurements. Angular measurements were used to identify angular changes in the dentofacial complex.

Results

There were no statistically significant differences in initial ages and treatment durations between the 2 groups ( P >0.05) ( Table I ). The effect of any residual growth and treatment periods on treatment changes could be expected to be similar.

Pretreatment differences in the variables for the groups are shown in Table III . For the sagittal measurements, A-OLp, Is-OLp, and Ms-OLp were used to compare the anteroposterior amounts of skeletal and dental changes according to maxillary posterior anchorage. These parameters represented the anteroposterior position of the maxillary base, the maxillary central incisor, and the maxillary first permanent molar, respectively. The pretreatment anteroposterior position showed no significant differences between the 2 groups ( P >0.05). The pretreatment axial inclination of the maxillary incisor showed no significant difference ( P >0.05). However, overjet, molar relationship, jaw relationship, and ANB angle were significantly greater in the miniscrew group. These results suggested that this group would have greater anteroposterior discrepancies in skeletal and dental relationships. For the vertical measurements, an independent t test showed no significant differences for any variable between the groups.

Table IV shows the skeletal and dental changes in each group and compares the changes between the groups. For each cephalometric parameter, changes between pretreatment and posttreatment in each group are listed and compared with the associated P values, as determined by the paired-samples t test. An increase in the measurement was expressed as a positive value; a decrease was expressed as a negative value. Positive values indicated extrusion, mesial movement, or crown anterior and root posterior angular changes; negative values indicated intrusion, distal movement, or crown posterior and root anterior angular changes.

Table IV

Comparison of treatment changes between the groups

Parameter	Headgear group							Miniscrew group							Headgear group vs miniscrew group
	Pretreatment		Posttreatment		Difference	P value	Significance ∗	Pretreatment		Posttreatment		Difference	P value	Significance ∗	P value	Significance †
	Mean	SD	Mean	SD				Mean	SD	Mean	SD
Sagittal measurements
Overjet (mm)	4.86	3.52	3.07	0.66	−1.79	0.012	‡	6.85	3.06	3.04	1.83	−3.80	0.000	¶	0.047	‡
Molar relationship (mm)	−2.54	2.38	−2.23	2.64	0.30	0.371	NS	−0.04	1.88	−0.28	3.34	−0.24	0.645	NS	0.364	NS
Position of maxillary base (mm)	79.13	4.05	79.14	4.11	0.02	0.935	NS	79.80	4.16	79.20	3.89	−0.61	0.002	§	0.033	‡
Position of mandibular base (mm)	82.11	5.27	82.98	5.52	0.88	0.105	NS	79.70	7.74	79.78	8.07	0.09	0.831	NS	0.254	NS
Jaw relationship (mm)	−2.98	3.84	−3.84	4.42	−0.86	0.083	NS	0.11	4.60	−0.59	5.38	−0.79	0.118	NS	0.806	NS
Position of maxillary central incisor (mm)	92.02	4.52	87.52	4.33	−4.50	0.000	§	92.98	3.77	86.11	4.52	−6.87	0.000	¶	0.003	§
Position of mandibular central incisor (mm)	87.16	5.83	84.45	4.35	−2.71	0.000	¶	86.13	4.77	83.07	4.64	−3.07	0.000	¶	0.697	NS
Maxillary central incisor relationship to A-point (mm)	12.89	2.95	8.38	2.77	−4.52	0.000	¶	13.17	2.37	6.91	2.22	−6.26	0.000	¶	0.016	‡
Mandibular central incisor relationship to Pg (mm)	5.05	3.70	1.46	3.61	−3.59	0.000	¶	6.43	5.64	3.28	4.76	−3.15	0.000	¶	0.606	NS
Position of maxillary first permanent molar (mm)	58.75	3.88	62.38	4.16	3.63	0.000	¶	60.57	4.54	61.41	4.80	0.85	0.034	‡	0.000	¶
Position of mandibular first permanent molar (mm)	61.29	5.14	64.61	5.41	3.32	0.000	¶	60.61	4.96	61.70	5.48	1.09	0.073	NS	0.004	§
SNA (°)	81.36	2.74	81.02	2.73	−0.34	0.004	§	82.63	3.11	82.02	2.79	−0.61	0.012	‡	0.253	NS
SNB (°)	77.55	3.98	77.36	3.98	−0.20	0.407	NS	75.54	3.36	75.26	3.65	−0.28	0.212	NS	0.792	NS
ANB (°)	3.80	2.11	3.66	2.17	−0.14	0.565	NS	7.09	2.26	6.76	2.18	−0.33	0.214	NS	0.609	NS
Angulation of maxillary central incisor (°)	108.32	11.58	100.32	10.05	−8.00	0.001	¶	105.61	12.44	96.30	9.31	−9.30	0.001	¶	0.683	NS
Angulation of mandibular central incisor (°)	98.93	6.67	95.55	8.71	−3.38	0.030	‡	102.41	7.07	100.39	9.41	−2.02	0.235	NS	0.543	NS
Interincisal angle (°)	114.18	9.57	127.43	8.54	13.25	0.000	¶	111.65	13.03	124.33	9.12	12.67	0.001	¶	0.880	NS
Vertical measurements
Overbite (mm)	1.93	2.15	1.57	0.49	−0.36	0.386	NS	2.39	3.80	1.65	0.57	−0.74	0.373	NS	0.677	NS
Lower facial height (mm)	73.77	4.39	74.46	4.74	0.70	0.123	NS	75.76	7.08	75.26	7.13	−0.5	0.188	NS	0.047	‡
Position of maxillary central incisor (mm)	31.34	2.72	31.89	3.38	0.55	0.072	NS	32.85	3.05	31.30	3.53	−1.54	0.023	‡	0.005	§
Position of maxillary first permanent molar (mm)	25.48	2.12	26.20	2.02	0.71	0.001	¶	25.22	2.60	23.91	2.60	−1.30	0.000	¶	0.000	¶
Position of mandibular central incisor (mm)	46.68	2.60	44.86	3.19	−1.82	0.000	¶	48.00	3.36	45.39	4.47	−2.61	0.000	¶	0.181	NS
Position of mandibular first permanent molar (mm)	37.11	2.60	38.89	2.58	1.79	0.000	¶	37.54	3.05	39.07	3.23	1.52	0.000	¶	0.466	NS
Nasal plane angle (°)	10.25	3.07	10.34	3.09	0.09	0.259	NS	8.83	3.24	8.89	3.05	0.07	0.328	NS	0.818	NS
Mandibular plane angle (°)	37.41	6.27	37.05	7.06	−0.36	0.337	NS	39.46	8.11	38.65	8.28	−0.80	0.021	‡	0.374	NS
Maxillary occlusal plane angle (°)	20.39	4.55	22.63	5.30	2.23	0.001	¶	22.39	5.59	25.52	6.47	3.13	0.014	‡	0.496	NS
Mandibular occlusal plane angle (°)	16.55	5.60	19.05	5.24	2.50	0.010	§	17.59	7.08	22.02	6.60	4.43	0.001	¶	0.177	NS

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