A novel approach for treatment of skeletal Class II malocclusion: Miniplates-based skeletal anchorage

Introduction

The objective of this study was to evaluate the effect of a new approach—bimaxillary miniplates-based skeletal anchorage—in the treatment of skeletal Class II malocclusion compared with untreated subjects.

Methods

The study (miniplates) group comprised 28 patients (14 boys, 14 girls) with skeletal Class II malocclusion due to mandibular retrusion, with a mean age of 11.83 years. After 0.017 × 0.025-in stainless steel archwires were placed in both arches, 4 miniplates were fixed bilaterally, 2 in the maxillary anterior areas and 2 in the mandibular posterior areas, and used for skeletal treatment with elastics. Twenty-four Class II untreated subjects (11 boys, 13 girls), with a mean age of 11.75 years, were included as controls. Skeletal and dental changes were evaluated using pretreatment and posttreatment or observational lateral cephalometric radiographs. The treatment changes were compared with the growth changes observed in the control group using independent t tests.

Results

Compared with the minimal changes induced by growth in the control group, the skeletal changes induced by miniplates were more obvious. The mandibular length increased significantly (3 mm), and the mandible moved forward, with a significant restraint in the sagittal position of the maxilla ( P <0.001). The overjet correction (−4.26 mm) was found to be a net result of skeletal changes (A-Y-axis = −1.18 mm and B-Y-axis = 3.83 mm). The mandibular plane was significantly decreased by 2.75° ( P <0.001).

Conclusions

This new technique, bimaxillary miniplates-based skeletal anchorage, is an effective method for treating patients with skeletal Class II malocclusions through obvious skeletal, but minimal dentoalveolar, changes.

Highlights

  • Bimaxillary miniplate-based skeletal anchorage was used for skeletal Class II malocclusion.

  • Miniplates were fixed in the anterior maxilla and the posterior mandible.

  • Elastics were used to apply bilateral pull force.

  • Compared with controls, the miniplates had a growth-enhancing effect on the mandible.

  • Compared with controls, the miniplates had a restricting effect on the maxilla.

  • This is an effective method for treating skeletal Class II malocclusion.

A Class II malocclusion is one of the most common problems in orthodontics. It accounts for approximately one third of the patients seeking orthodontic treatment. About 37% of Syrian and 20% of Egyptian schoolchildren have this malocclusion. Several studies have stated that a Class II skeletal pattern is caused by a mandibular deficiency in most patients.

Treatment of mandibular deficiency can be achieved by growth modification through stimulation of mandibular growth and inhibition of maxillary growth. For this purpose, appliances such as extraoral headgears and removable or fixed functional appliances may be used.

Evidence on the efficiency of removable functional appliances is controversial. Some researchers have reported favorable treatment effects on mandibular growth, either as an increase in mandibular length or as effective condylar growth. Others found that these appliances have no significant effect on the mandible. This debate extends to the effect of these appliances on the maxilla; some studies found a restriction effect, whereas others disputed this. However, the dentoalveolar effects, including proclination of the mandibular labial dentition and retroclination of the maxillary labial dentition, are much more agreed upon.

The same applies for fixed functional appliances; with greater dentoalveolar than skeletal effects. Collectively, evidence from systematic reviews and meta-analyses states that neither removable nor fixed functional appliances produce pure skeletal changes; instead, the effects are mainly dentoalveolar.

The revolution in using the skeletal-anchorage aids in orthodontics has helped to overcome the limitations of conventional orthodontic techniques. Miniplates have been used to intrude molars and for orthopedic correction of skeletal Class III malocclusions. Skeletal Class II correction using miniplates has been reported in the literature. The authors affixed single-jaw miniplates in the mandibular symphysis to support a fixed functional appliance (the forsus fatigue resistant device) that was attached on the other end to the maxillary first molars. They reported correction of a skeletal Class II malocclusion but still had the fixed functional appliance supported to the dentition on 1 arch.

Here we introduce a new technique that aims at providing bimaxillary skeletal anchorage; it may lead to more favorable skeletal changes and reduce the bulkiness of the appliance. Therefore, the aim of this prospective clinical trial was to evaluate the effect of this new approach for the treatment of skeletal Class II malocclusion with mandibular deficiency in growing subjects using bimaxillary miniplates-based skeletal anchorage compared with untreated Class II subjects.

Material and methods

This technique was registered as a patented technique at the World Intellectual Property Organization in 2012 under number WO2012096633 at: patentscope.wipo.int/search/en/detail.jsf?docId=WO2012096633&recNum=1&maxRec=2&office=&prevFilter=&sortOption=Pub+Date+Desc&queryString=Al-Domaini+Abdulsalam&tab=PCT+Biblio .

This prospective study was conducted at the outpatient clinic, Department of Orthodontics, Faculty of Dentistry, Damascus University, in Damascus, Syria. It was approved by the faculty scientific board (9-1-15/09/2009/1358). All participants and their parents were informed about the study procedures and the potential benefits or complications. Informed consent was signed by at least 1 parent.

The inclusion criteria were (1) chronologic age range, 10 to 13 years; (2) skeletal Class II Division 1 (ANB, ≥5°); (3) deficient mandible with a normal or protruded maxilla; (4) convex facial profile (NAPg, ≥190°); (5) skeletal age just before the pubertal growth spurt according to the cervical vertebrae maturational index ; (6) average or vertical pattern of growth; (7) buccal segment relationship, greater than or equal to half unit Class II molar and canine relationships; (8) overjet, greater than or equal to 5 mm; (9) no history of orthodontic treatment; (10) no clinical signs and symptoms of temporomandibular disorders; and (11) healthy subjects with no history of trauma, surgical procedure in the craniofacial area, chronic medication, or systemic disease.

Based on the above criteria, 28 participants (14 boys, 14 girls) were included in the treatment (miniplates) group. The sample size was calculated to detect a clinically significant increase in mandibular length of not less than 3 ± 1 mm after 8 months of active treatment. A conservative (underestimated) correlation of 0.5 between pretreatment and posttreatment measurements was considered. The value of significance and the power of the study were set at 0.05 and 0.9, respectively. A 2-tailed paired t test was proposed for the above calculation using the G*Power program (version 3.1.2).

All patients were treated by an author (A.A.A.). For each participant, a pretreatment (T1) lateral cephalometric radiograph (Cranex D model PP1; Soredex, Tuusula, Finland) was taken. Both arches were bonded with 0.018 × 0.022-in preadjusted edgewise multibracket appliances (MBT prescription). The archwire sequence increased progressively to reach 0.017 × 0.025-in stainless steel, which was cinched back distal to the first molars in both arches. After alignment and leveling, a second lateral cephalometric radiograph (T2) was taken for each participant to represent the prefunctional phase record.

In preparation for the skeletally anchored orthopedic treatment, titanium miniplates (Jeil Medical, Seoul, South Korea) were surgically fitted to the maxilla and the mandible. Each jaw received 2 miniplates surgically placed under local anesthesia. The mandibular miniplates were placed in the posterior buccal area inferior to and between the distal root of the mandibular first molar and the mesial root of the mandibular second molar above the external oblique ridge ( Fig 1 , A ). The maxillary miniplates were placed in the anterior labial area with the arm centered slightly distal to the lateral incisor. The distal hole was positioned 4 to 5 mm above the apical area of the maxillary canines, and the mesial hole was placed 2 to 3 mm from the nasal pyriform aperture ( Fig 1 , B ). Each miniplate was fixed with 3 self-drilling titanium screws (2-mm diameter × 6-mm length). The miniplates were placed in the right side first and then in the left side with 10 to 14 days between the 2 surgeries.

Fig 1
A, Miniplates inserted in the mandibular posterior area; B, miniplates inserted in the maxillary anterior area.

Twenty days from the intrabony fixation, the miniplates were loaded. The participants were taught how to wear the elastics between the hooks of the maxillary miniplates and the hooks of the mandibular miniplates of the corresponding side. They were instructed to wear the elastics full time except at mealtimes and to change them every 12 hours ( Fig 2 ). The miniplates were loaded by gradually increasing the force levels in accordance with the protocol applied for bone-anchored maxillary protraction by De Clerk et al. A force of 450 g in each side was achieved after gradual progression for easy patient adaptation and for stability of the miniplates in the following order: 250 g per side for the first 3 weeks followed by 350 g per side for the next 3 weeks to reach 450 g per side for the rest of the functional treatment phase. Once Class I molar and canine relationships and overjet of 1 to 3 mm were achieved, a third lateral cephalometric radiograph (T3) was taken for each participant and considered the postfunctional record. Thereafter, the patients were instructed to continue wearing the elastics during sleep as retention for the achieved results. Treatment continued until proper finishing was achieved.

Fig 2
A, The miniplates after the healing period; B, application of the intermaxillary elastic; C, finishing to Class I molar and canine relationships.

To evaluate the treatment changes, the images at T2 and T3 were compared. Twelve linear and 11 angular cephalometric measurements were used ( Fig 3 ). The main reference lines used in this context were the H- and Y-axes. Both lines are projected from the SN line, which is easily identified and reproducible since it is in the midsagittal plane away from overlapping facial structures. Intraexaminer reliability of the readings was assessed with measurements made twice within 2 weeks.

Fig 3
A, Linear measurements used in the study (millimeters): 1 , A-Y axis; 2 , Ar-Go; 3 , Go-Me; 4 , Co-Go; 5 , Co-Pog; 6 , Pog-Y axis; 7 , B-Y axis; 8 , S-Go; 9 , N-Me; 10 , overjet; and 11 , overbite. B, Angular measurements used in the study (degrees): 1 , SNA; 2 , SNB; 3 , ANB; 4 , SNPog; 5 , NAPog; 6 , ArGoMe; 7 , SN-PP; 8 , SN-GoMe; 9 , U1-SN; 10 , L1-GoMe; and 11 , U1-L1.

Data for the untreated control group were obtained from a previous study conducted on a clinically matching sample. The control group included preobservational and postobservational cephalometric images (equivalent to T2 and T3, respectively) of 24 participants. In addition to fulfilling the inclusion criteria, extreme emphasis was directed toward clinically matching the control group to the miniplates group as closely as possible regarding race, age, sex, observational period, and skeletal maturity. All subjects in this group were orthodontically treated after the observational period.

Statistical analysis

Data were analyzed using SPSS software (version 21; IBM, Armonk, NY). The means and standard deviations of pretreatment (T2), and posttreatment or observation measurements (T3) and of treatment or observation changes were presented for both groups. All variables were tested for normal distribution using the Kolmogorov-Smirnov test. When the data were not normally distributed, the within and between groups comparisons were done by nonparametric tests, Wilcoxon signed rank tests, and Mann-Whitney U tests, respectively. Dependent and independent t tests, respectively, were the corresponding tests for normally distributed data. A P value of <0.05 was considered significant.

Results

The miniplate group comprised 26 participants; 2 participants discontinued follow-up visits and were dropouts. These 26 participants were successfully treated with multibracket appliances and skeletally anchored devices to Class I molar and canine relationships, and overjet was reduced to normal. No miniplates failed during this functional orthodontic treatment.

The initial alignment and leveling phase lasted for an average of 7 months followed by a functional phase for an average of 9 months. The average age of the miniplate group at T2 was 11.83 ± 0.85 years. The corresponding average age of the controls at the beginning of the observational period was 11.75 ± 0.75 years ( Table I ).

Table I
Mean ages of the study and control groups before (T2) and after skeletal treatment or observation (T3) and mean follow-up period
Miniplates, mean (SD) Control, mean (SD) P value
T2/T3
T2 T3 T2 T3
Boys age (y) (n = 14/11) 12.16 (0.97) 12.91 (0.89) 12.27 (0.6) 13.02 (0.63) 0.878/0.886
Girls age (y) (n = 12/13) 11.46 (0.73) 12.21 (0.75) 11.37 (0.57) 12.48 (0.6) 0.884/0.894
Total (n = 26/24) 11.83 (0.85) 12.58 (0.87) 11.75 (0.75) 12.5 (0.76) 0.893/0.894
Mean follow-up period (mo) 8.96 (0.82) 9 (0.83) 0.899

High values of intraexaminer reliability were reported; the intraclass correlation coefficient ranged from a minimum of 0.883 for overjet to a maximum of 0.990 for ArGo and NAPog.

The outcomes evaluated were categorized into maxillary skeletal, mandibular skeletal, horizontal and vertical intermaxillary relationships, and dental variables. The initial measurements of both groups along with the results of independent t tests are presented in Table II . With the exception of the A-Y axis, ANB, SNPP, ArGoMe, LiGoMe, and overjet, the other variables were significantly different between the 2 groups.

Table II
Pretreatment or observation skeletal and dental measurements (T2)
Measurements Miniplates Control P value
Pretreatment measurements Preobservation measurements
Mean SD Mean SD
Maxillary measurements
A-Y axis (mm) 61.91 4.55 62.03 4.64 0.925
Mandibular measurements
ArGo (mm) 41.27 4.46 46.19 3.26 <0.001
GoMe (mm) 65.53 2.95 69.19 3.27 <0.001
CoGo (mm) 50.85 4.35 44.69 3.27 <0.001
CoPog (mm) 102.63 4.56 108.14 3.92 <0.001
Pog-Y axis (mm) 47.42 4.92 53.45 4.64 <0.001
B-Y axis (mm) 48.67 4.60 52.23 4.64 0.011
Sagittal jaw relationship
SNA (°) 80.79 1.60 82.34 1.85 0.001
SNB (°) 73.83 1.41 75.75 1.69 <0.001
ANB (°) 7.10 1.69 6.60 1.22 0.321
SNPog (°) 74.42 1.36 76.75 1.69 <0.001
NAPog (°) 194.02 2.89 192.05 3.55 0.025
Vertical jaw relationship
SGo (°) 69.97 4.49 63.67 3.68 <0.001
NMe (°) 114.29 5.01 110.04 5.43 0.006
SGo/NMe 61 2 58 4 0.001
ArGoMe (°) 125.94 4.50 125.96 5.26 0.988
SNPP (°) 7.10 2.57 8.11 1.82 0.298
SNGoMe (°) 39.77 3.98 31.75 2.64 <0.001
Dental relationship
U1SN (°) 103.73 2.47 106.76 3.77 0.002
L1GoMe (°) 96.00 4.82 96.26 5.42 0.815
U1L1 (°) 120.33 6.16 116.24 5.60 0.018
Overjet (mm) 6.68 1.08 6.78 1.12 0.8
Overbite (mm) 1.10 1.19 3.58 1.12 <0.001

Mann Whitney U test unless otherwise specified; independent t test.

Similarly, means and standard deviations of all outcomes of the pretreatment and posttreatment or observational measurements along with the results of paired t tests are presented in Table III . Means and standard deviations of the treatment or observational changes for both groups, and the differences between the groups for the same outcomes, are presented in Table IV . The net results of the effect of the miniplates consider the natural growth in the control group.

Table III
Means and standard deviations of before (T2) and after treatment or observation skeletal and dental measurements (T3)
Measurement Miniplates P value Control P value
Pretreatment measurements Posttreatment measurements Preobservation measurements Postobservation measurements
Mean SD Mean SD Mean SD Mean SD
Maxillary measurements
A-Y axis (mm) 61.91 4.55 61.00 4.44 <0.001 62.03 4.64 62.30 4.65 0.003
Mandibular measurements
ArGo (mm) 41.27 4.46 44.25 4.68 <0.001 46.19 3.26 46.91 3.68 0.001
GoMe (mm) 65.53 2.95 67.44 3.06 <0.001 69.19 3.27 69.91 3.68 0.001
CoGo (mm) 50.85 4.35 53.58 4.30 <0.001 44.69 3.27 45.39 3.72 0.001
CoPo (mm) 102.63 4.56 105.63 4.34 <0.001 108.14 3.92 109.04 3.79 <0.001
Pog-Y axis (mm) 47.42 4.92 51.83 5.43 <0.001 53.45 4.64 54.34 4.55 0.002
B-Y axis (mm) 48.67 4.60 52.81 4.68 <0.001 52.23 4.64 52.54 4.72 0.002
Sagittal jaw relationship
SNA (°) 80.79 1.60 79.38 2.04 0.001 82.34 1.85 82.59 1.82 0.073
SNB (°) 73.83 1.41 76.73 1.63 <0.001 75.75 1.69 76.30 1.82 0.01
ANB (°) 7.10 1.69 3.10 1.11 <0.001 6.60 1.22 6.30 0.88 0.147
SNPog (°) 74.42 1.36 77.29 1.20 <0.001 76.75 1.69 77.33 1.92 0.002
NAPog (°) 194.02 2.89 187.46 3.05 <0.001 192.05 3.55 190.85 3.63 <0.001
Vertical jaw relationship
SGo (mm) 69.97 4.49 72.40 4.21 <0.001 63.67 3.68 64.48 4.15 0.41
NMe (mm) 114.29 5.01 114.23 4.90 0.699 110.04 5.43 111.26 5.26 <0.001
SGo/NMe 61 2 63 2 <0.001 58 4 58 4 0.786
ArGoMe (°) 125.94 4.50 124.33 4.16 <0.001 125.96 5.26 127.43 5.99 <0.001
SNPP (°) 7.10 2.57 8.02 2.59 <0.001 8.11 1.82 8.34 1.99 0.1
SNGoMe (°) 39.77 3.98 37.52 4.01 <0.001 31.75 2.64 32.25 2.51 0.051
Dental relationship
U1SN (°) 103.73 2.47 102.58 2.43 <0.001 106.76 3.77 107.17 3.70 0.053
LiGoMe (°) 96.00 4.82 94.73 3.34 0.011 96.26 5.42 96.73 5.34 0.095
U1L1 (°) 120.33 6.16 124.90 5.46 <0.001 116.24 5.60 116.01 5.62 0.389
Overjet (mm) 6.68 1.08 2.42 0.54 <0.001 6.78 1.12 6.66 1.17 0.194
Overbite (mm) 1.10 1.19 2.58 0.90 <0.001 3.58 1.12 3.45 1.13 0.016
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Dec 12, 2018 | Posted by in Orthodontics | Comments Off on A novel approach for treatment of skeletal Class II malocclusion: Miniplates-based skeletal anchorage
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