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. Author manuscript; available in PMC: 2012 Mar 1.
Published in final edited form as: J Oral Maxillofac Surg. 2011 Jan 13;69(3):754–762. doi: 10.1016/j.joms.2010.11.013

Orthopedic Correction of Growing Hyperdivergent, Retrognathic, Patients with Miniscrew Implants

Peter H Buschang 1, Roberto Carrillo 2, P Emile Rossouw 3
PMCID: PMC3046301  NIHMSID: NIHMS253398  PMID: 21236539

Abstract

Traditional orthodontic treatments do not adequately address the skeletal problems of retrognathic, hyperdivergent, Class II adolescents; the few approaches that do require long-term patient compliance. This paper introduces a novel approach using miniscrew implants (MSIa) and growth to treat retrognathic hyperdivergent adolescents. Nine consecutive patients were evaluated at the start of treatment (13.2 ±1.1 years of age) and again at the end of the orthopedic phase (after 1.9 ±0.3 years). Each patient had two MSIs placed in either side of the palate. Coil springs (150 g) extended from the MSIs to a RPE, which served as a rigid segment for intruding the maxillary premolar and molars. Two additional MSIs were placed between the first mandibular molars and second premolars; coil spring (150 g) extended from the MSIs to hold or intrude the mandibular molars. Prior to treatment, the patients exhibited substantial and significant mandibular retrusion (Z-score=−1.0), facial convexity (Z-score=0.7), and hyperdivergence (Z-score=1.6). Treatment produced consistent and substantial orthopedic effects. The chin was advanced an average of 2.4 mm, the SNB angle increased by 2.1°, the mandibular plane angle decreased 3.9°, and facial convexity decreased by approximately 3.2°. Questionnaires showed that this treatment approach was not painful or uncomfortable; the majority of the patients indicated that they were very likely to recommend the treatment to others. Treatment was accomplished by titrating the amount of orthodontic intrusion performed based on the individuals’ growth potential.

Introduction

Growing individuals with Class II malocclusions comprise a large segment of the population requiring orthodontic treatment for both esthetic and functional reasons. Approximately 15% of untreated adolescents in the United States have Class II malocclusion.1,2 Treatment is necessary to correct the malocclusion and to straighten the profile, which tends to be convex. Among Caucasian, convex profiles are among the least favored, while straighter profiles with prominent chins are the most favored.3 Changing retrusive profiles to straighter, less retruded profiles, significantly increases attractiveness. 4 Individuals with Class II malocclusion also have functional deficits and impaired masticatory function,5,6 which have been directly related to their malocclusion.7

Class II patients often have retrognathic mandibles and hyperdivergent growth tendencies, which make them among the most difficult to treat orthodontically. The skeletal problems associated with Class II’s are primarily mandibular; the mandible becomes retrusive and hyperdivergent throughout childhood and adolesence.8,9 Importantly, Class II patients with hyperdivergent tendencies have additional morphological characteristics, the correction of which make treatment more difficult, including excessive anterior and posterior dentoalveolar heights, open bites, increased lower face heights, steeper mandibular planes and larger gonial angles.10–19

To address the myriad of problems associated with hyperdivergent Class II patients, forward mandibular rotation must be incorporated into any treatment plan attempting to address the skeletal dysmorphology. Björk and Skieller’s landmark studies were among the first to show that true forward rotation (as defined by Solow and Houston20) is associated with greater chin projection, reductions in the gonial angle, redirection of condylar growth and control of vertical eruption.21–22 True mandibular rotation has repeatably been shown to be the most important determinant of the anteroposterior position of the chin in untreated23 and treated subjects.24,25

Current orthodontic treatment approaches for growing hyperdivergent Class II’s do not control rotation and therefore, cannot adequately address the skeletal dysmorphology. Because vertical control is especially difficult for hypdivergent patients,18 established treatment mechanics often impede improvements of the profile.26–29 The most common orthodontic treatment approaches for hyperdivergent Class II’s produce mainly dental corrections. LaHaye et al.25 recently showed that the three most common treatment approaches for such patients (head-gear with extractions, head-gear without extractions, and the Herbst appliance) corrected the Class II malocclusions, but not consistently improve the chin projection or hyperdivergent tendencies. The literature clearly shows that traditional treatment approaches to Class II hyperdivergent patients have little or no effect on the mandible (Table 1).

Table 1.

Changes (deg) of SNA, SNB, and MPA for traditional headgear non-extraction and extraction treatments

Non-extraction Treatments Extraction Treatment
Reference SNA SNB MPA SNA SNB MPA
LaHaye et al25 −2.0 0.4 0.6 −3.7 0.6 0.6
Haralabakis et30 −1.5 0.7 −0.4 - - -
Gandini et al31 −2.1 0.8 −0.3 - - -
Bishara32 −0.6 0.8 −1.4 - - -
Hubbard et al33 −2.1 −0.4 0.1 - - -
Luppanapornlarp & Johnson34 −1.4 −0.3 0.7 −1.8 −0.1 −0.2
Paquette et al35 −1.5 0.2 −2.0 −2.3 −1.8 0.3
Congiolosi et al36 −1.1 0.5 −0.3
Brown37 (HPHG) −0.7 −0.2 0.9 −0.1 0.5 −0.3
Brown37 (CPHG) −0.9 0.1 0.8 −1.2 −0.1 0.7
Taner-Sarisoy et al38 - - - −1.2 −0.3 0.1
Bishara et al39 - - - −2.3 −0.2 −1.4
Average −1.4 0.3 −0.1 −1.8 −0.2 −0.1
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In contrast, vertical pull chin cup appliances are effective in producing true anterior mandibular rotation and decreasing the anterior facial height.44–42 For example, young patients treated with anterior-pull chin-cup therapy show twice as much forward movement of the chin, and almost three times as much true mandibular forward rotation, than matched controls.42 Such findings support the notion that rotation is the key mechanism in treating hyperdivergent Class II’s. However, vertical pull chin cup depends heavily on patient compliance, which makes treatment results unpredictable.

Currently, surgery is the most effective approach for treating moderate-to -severely hyperdivergent Class II patients. While case studies have shown more spectacular results, the existing cohort studies evaluating maxillary impaction have shown clinically significant increases of the SNB angle(0.4–2.6°),43–45 decreases in the mandibular plane angle (3.4–3.5°),43,45 and decreases in gonial angulation (0.2–1.6°), 43,45 all of which address the underlying skeletal problems. However, LeFort surgical procedures are substantially more expensive than orthodontics alone and can only be performed on non-growing individuals.

With the incorporation of fixed anchorage devices, patient compliance has been almost eliminated and force magnitudes can be better controlled.46 Of all the fixed anchorage devices, miniscrew implants (MSIs) are the least invasive, most conservative in terms of placement and removal, the most flexible with respect to implantation site, and the least expensive. MSIs are also esthetically more acceptable than extraoral appliances and they are especially well suited for non-compliant patients.

While miniscrew implants have been used for various orthodontic treatments, there is only limited information available on their use as anchorage for intrusive mechanics in growing patients The existing studies, which pertain to adults (Table 2), have shown 1.7–3.3° decreases in the mandibular plane angle, 1.6–3.7 mm decreases in lower face height, 1.8–3.4 mm and 0.1–1.3 mm of upper and lower molar intrusion, respectively, and 1.5–1.8° decreases in the SNB angle.47–50 However, these findings provide no guidelines for growing adolescents, who comprise most of the orthodontic cases being treated, and who might be expected to respond differently to treatment than adults.

Table 2.

Summary statistics for hyperdivergent adults treatment with intrusion of teeth with miniscrew implants

N MPA (°) SNB (°) U6PP (mm) L6MP (mm) Gonial Angle (°) ANS-Me (mm)
Erverdi et al47 10 −1.7 +1.8 −2.6 −0.1 (NS) ------ ------
Kuroda et al48 10 −3.3 +1.5 −2.3 −1.3 −0.3 (NS) ------
Xun et al49 12 −2.3 +1.6 −1.8 −1.2 −1.0 (NS) −1.6
Akay et al50 10 −3.0 +1.6 −3.4 ------ ------ −3.7
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NS=no statistically significant change

The fact that miniscrew implants make it possible for orthodontists to apply forces more effectively is important because it allows the application of light forces produce intrusion, thereby reducing the potential of root resorption. Our experimental and histological studies have shown that light forces and miniscrews can be used to intrude multiple multiradicular teeth (segmental intrusion) without significant root resorption.51–53

The foregoing, prospective, feasibility study was designed to evaluate the skeletal and dental effects of intruding segments of teeth in a controlled fashion using miniscrew implants. By intruding maxillary and mandibular teeth in a controlled fashion, we expected to produce mandibular forward rotation and remodeling changes that address both the skeletal and dental problems associated with growing Class II hyperdivergent patients.

Study Design

The sample consists of nine consecutive patients (8 ♀ and 1 ♂) recruited during screenings held at the Graduate Orthodontic Clinic of Baylor College of Dentistry. The patients met the following selection criteria:

Inclusion Criteria

  1. Early permanent dentition (premolars and permanent canines emerged)

  2. Lower anterior facial height greater than age and sex specific mean values (based on reference data reported by Riolo et al.54)

  3. Retrognathic mandible with the SNB angle being 1 SD or more below age and sex specific values (based on reference data reported by Riolo et al.54)

  4. End-on or greater bilateral Class II canine and/or molar relationships

Exclusion Criteria

  1. Inability to attain acceptable hygiene levels before starting orthodontic treatment.

  2. Second molars fully erupted into occlusion (the mesial marginal ridge of all second molars should be at least 2 mm apical to the distal marginal ridge of the first molar).

IRB approval was obtained and all of the subjects have been recruited into the study. The overall study included 20 patients; the present preliminary report pertains to the nine patients for whom complete pre- and post-treatment records have been obtained.

The appliances used for skeletal anchorage were IMTEC (IMTEC Corporation; Ardmore, OK) miniscrew implants (1.8 × 8 mm). Sentalloy® coil springs (GAC international, Bohemia, NY) were used to intrude and hold the posterior teeth; each spring was calibrated using a gram force gauge (Correx, Haag-Streit, Switzerland) to deliver a constant force of approximately 150 g. A rapid palatal expander (RPE) (Variety SP, Dentaurum, Germany) was used to hold the premolars and molars as a rigid segment during intrusion. Fixed orthodontic appliances (0.018 Slot, SPEED Industries, Canada) were used to complete the orthodontic phase of treatment.

After approximately two months of treatment and retention, the RPE was sealed, and the two maxillary MSI’s were placed in the parasagital region of the palate mesial to the first molars. Vertically, the MSIs were placed where the palatal roof and lingual walls meet (Figure 1A). The patients rinsed with clorhexidine (Peridex, Zila Pharmaceuticals, Inc, Fort Collins, CO ) for 30 seconds immediately before MSI insertion, and 2 or 3 times per day for the next 3–5 days. Each patient was previously anesthetized using topical anesthesia followed by local infiltration of ¼ cartidrge of lidocaine with epinephrine. A periodontal probe was used to puncture the palatal tissues in the parasaggital region mesial to the maxillary first molar. Once firm contact with the cortical bone had been made, the tissue thickness at the implantation site was assessed. Using a manual contraangle, each miniscrew (1.8 mm × 8 mm) was inserted perpendicular to the cortical bone following the palate’s anatomy. They were inserted without a pilot hole or a tissue punch. Both MSI’s were immediately loaded with an intrusive force of 150 g using calibrated Sentalloy® coils that extended directly to the RPE frame between the first molar and second premolar, following the protocol previously described.55

Figure 1.

Figure 1

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A) Maxillary and B) mandibular appliances used for the mini-screw implant treatment.

The sites for the mandibular MSIs were prepared by bonding brackets to diverge the roots between the first molars and second premolars. The objective was to widen the site for MSI insertion using a 0.016×0.022 stainless steel wire. After approximately one month, a periapical radiograph was taken to evaluate the increase of interradicular space attained. If the space was determined to be sufficient for implant placement, the patient was scheduled for MSI insertion; if not, adjustments were made to further widen the implant site. The lower MSIs were placed following the same clorhexidine rinse protocol used for the maxillary MSIs. The mandibular MSIs were also placed without pilot holes and tissue punch. A double insertion technique was used in order to insert the MSIs at an angle, with the head of the screw positioned at the level of the mucogingival junction (Figure 2). The lower MSIs were loaded immediately using calibrated 150g coils, following the same protocol as in the maxilla. The lower molars bands were prepared for insertion of a removable lower lingual arch, if needed to control molar torque. Lingual arches were only installed in a few of the cases, especially those who mandibular teeth were actively intruded.

Figure 2.

Figure 2

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A) Buccal view location of mandibular MSIs, B) frontal view showing insertion angle.

To prevent their extrusion while intruding the posterior teeth, the upper anterior teeth (canine to canine) were not initially bonded with fixed appliances. They were bonded once the upper anterior teeth made contact with the lower teeth, which prevented them from interfering with mandibular autorotation.

Periodontal health was closely monitored during intrusion. The need for the patients to maintain proper hygiene was emphasized throughout treatment. Importantly, there was a temporary shortening of the clinical crowns of the teeth that had been intruded (Figure 3); there was also some tissue bulging, especially on the palate. This was deemed to be temporary gingival overgrowth that disappeared in all cases after intrusion had been stopped and the teeth had been held in place for 2–3 months.

Figure 3.

Figure 3

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Maxillary first molar clinical crown height A) before and B) during active orthodontic intrusion

After the required amount of posterior intrusion had been attained, or when the maxillary anterior and posterior occlusal planes had been leveled, the RPE was removed and fixed orthodontic appliances were bonded onto all of the maxillary posterior teeth. After the RPE was removed, a transpalatal arch (TPA) was fitted to the maxillary first molars to hold the transverse dimension and prevent any unwanted torque of the posterior teeth. The maxillary and mandibular MSI’s remained in place until full treatment was completed. They held the vertical dimension of the posterior teeth using an 0.010 in stainless steel ligature tied to the palatal sheath in the maxilla and to the archwire mesial to the first molar band in the mandible.

Treatment Results and Discussion

The subjects were 13.2 ±1.1 years old at the start of treatment. The orthopedic phase of treatment lasted for an average of 1.9 ±0.3 years; the shortest and longest treatment durations were 1.4 and 2.5 years, respectively. Longer treatment time were required for patients who had impacted canines (N=2) and extractions (N=2).

Of the 54 MSI that have been placed so far, only two have failed (Table 3), with one failure in each jaw. A failure was defined as an MSI that was unable to hold the force of the coil spring or steel ligature without noticeable mobility of its head. This resulted in an success rate of 96.3%, which is considerable higher than previously reported for miniscrew implants, and more closely approximates the success rates of endosseous implants.

Table 3.

Numbers of implants placed, the number that failed, and the relative stability of the miniscrew implants used in the present study

# Placed # Failed % Stability
Maxilla 32 1 96.9%
Mandible 22 1 95.4%
Total 54 2 96.3%
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Prior to treatment, patients presented with greater mandibular retrusion (SNB= 73.8°; Z-score= −1.0), greater facial convexity (N-A-Pg = 9.2°; Z-score= 0.7) and substantially more hyperdivergence (MPA=43.3°; Z-score=1.6) than exhibited by untreated controls. They also had substantially larger gonial angles (Ar-Go-Me=134°; Z-score= 1.4) than controls.54

The treatments produced consistent and substantial effects, which were statistically significant despite the small size of the sample (Table 4). The chin moved forward an average of 2.4 mm; the maximum anterior movement of the chin was 7.1 mm. The SNB angles increased by 2.1 ±1.3°and the mandibular plane angle decreased an average of 3.9 ±1.8°. Hard- and soft tissue facial convexities decreased by approximately 3.2°, and the gonial angle decreased by 2.4 ±1.8°.

Table 4.

Orthopedic changes of nine consecutive Class II hyperdivergent adolescents treated with miniscrew implants

Units Minimum Mean Standard Deviation Maximum Probability of Changes
Pg_hor mm −0.7 2.4 2.3 7.1 .020
SNB deg −0.1 2.1 1.3 4.2 .002
MPA deg −1.0 −3.9 1.8 −6.5 .001
HT Convexity deg 1.3 −3.2 2.4 −6.1 .007
ST Convexity deg −0.9 3.15 2.9 8.7 .017
Gonial Angle deg 0.8 −2.4 1.8 −5.3 .018
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Cranial base superimpositions showed positive orthopedic treatment results for all but one of the females, who was 12.2 years of age at the start of her non-extraction treatment (Figure 4A). She showed only limited amounts of growth, and her lower molars erupted by approximately the same amount that the upper molars were intruded, which explains why she did not display the forward rotation and chin projection that was planned for. Approximately half of the remaining subjects exhibited forward rotation and anterior chin projection with little or no growth. The positive treatment effects that they exhibited were due primarily to intrusion of the upper molars and either relative intrusion (i.e. holding the vertical dimension) (Figure 4B) or actual intrusion (Figure 4C) of the lower molars. The remaining subjects showed positive treatment effects due to good growth, intrusion of the upper molar, and intrusion or relative intrusion of the lower molars. For example, a 13 year-old female treated for 1.7 years with extractions showed a substantial decrease in her mandibular plane angle and over 5 mm of chin projection (Figure 4D). Due to her good growth potential, she actually needed less intrusion of her upper molars and only relative intrusion of the lower molars.

Figure 4.

Figure 4

Figure 4

Figure 4

Figure 4

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Figure 4A. Changes between 12.2–13.5 years of age for a female patient (#1) treated nonextraction.

Figure 4B. Changes between 13.7–15.8 years of age for a female patient (#3) treated with extractions.

Figure 4C. Changes between 14.2–15.9 years of age for a female patient (#4) treated with extractions.

Figure 4D. Changes between 13.0–14.7 fora female patient (#4) treated with extractions.

Orthodontist need to closely and continuously monitor these cases to determine if they are exhibiting the desired treatment changes. This is done clinically by evaluating changes in interarch dental and overbite/overjet relationships. If growth or intrusion are occurring, the case should exhibit a shift of the molar and premolar relationships from Class II to Class I (Figure 5). If such a shift is not evident within 4–6 months, then the orthodontist should plan on greater amounts of intrusion of the upper, and perhaps, even intrusion of the lower molars. In actively growing individuals, it is usually sufficient to intrude the upper posterior teeth and hold the lower posterior teeth in place so as to prevent them from erupting.

Figure 5.

Figure 5

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Clinically assessment of treatment effects A) on the day of RPE cementation, B) after 5 months of active intrusion (2 months with maxillary MSI and 5 months of mandibular MSIs), C) at debond. Note deepening of the bite and Class II correction associated with autorotation of the mandible.

Subjective Self-Assessments

When the patients were initially asked about each of the appliances that were to be used, they substantially overestimated the amounts of pain that they expected to have with each appliance (Table 5). Approximately 36% 45% and 50% of the patients expected braces, expanders, and MSIs, respectively, to be be moderately or very painful. At the end of treatment, none of the patients reported that MSIs were either moderately or very painful; about 8% reported that braces were moderately painful and 17% felt that the expanders were moderately or very painful.

Table 5.

Pretreatment (PreTx) and post-treatment (PostTx) percentages of subjects reporting pain and discomfort associated with braces, expanders, and miniscrew implants, along with post-treatment percentages of how much they would recommend their treatment to friends and family

How painful are the appliances?
Not at all Somewhat Moderately Very
PreTx PostTx PreTx PostTx PreTx PostTx PreTx PostTx
Braces 22.7 58.3 40.9 33.3 22.7 8.3 13.6 0
Expander 27.3 41.7 27.3 41.7 31.8 8.3 13.6 8.3
MSIs 9.1 91.7 40.9 8.3 13.6 0 36.4 0
How uncomfortable are the appliances?
Not at all Somewhat Moderately Very
Braces 4.5 8.3 36.4 83.3 27.3 8.3 13.6 0
Expander 22.7 16.7 22.7 50.0 27.3 25.0 27.3 8.3
MSIs 4.5 66.7 36.4 25.0 27.3 8.3 31.8 0
How much would you recommend your treatment to your friends and family?
Not at all Somewhat Moderately Very Much Extremely
 0 16.7 25.0 16.7 41.7
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The patients also initially overestimated the amounts of discomfort that they associated with each of the appliances, especially for the MSIs and expanders. Approximately 59% of the patients thought that the MSIs would be moderately or very uncomfortable; 55% thought that the expanders would be moderately or very uncomfortable, and; 41% felt that the braces would be moderately or very uncomfortable. After treatment, only 8% of the patients thought that the MSIs and braces were uncomfortable; none reported them to be very uncomfortable. Approximately 25% and 8% thought that the expanders were moderately and very uncomfortable, respectively.

Perhaps most important, the majority of the patients indicated that they would recommend the treatment that they had received to their friends and relatives. Approximately 17% said they would recommend the treatment “very much” and 42% said that they would recommend it “extremely much”. No-one said that they would not recommend the treatment.

Conclusions

These preliminary results indicate that our novel approach is effective for addressing the primary skeletal treatment objectives of growing hyperdivergent, retrognathic, patients (Figure 6). Major orthopedic changes were produced, including substantial advancement of the chin and autorotation of the mandible, along with decreases in the gonial angle, all of which combined to reshape the mandible and improve facial profile. The treatment was accomplished by titrating the amount of orthodontic intrusion performed based on the individuals’ growth potential. This treatment approach was not painful or uncomfortable; the majority of the patients indicated that they were very likely to recommend the treatment to others.

Figure 6.

Figure 6

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Treatment and growth related mandibular rotation, producing orthopedic effects that reshape the mandible and improve facial profile

Acknowledgments

This research was funded by NIDCR RFA-DE-06-007. We express our thanks to the Drs. Robert Gallagher, Monte Collins, J. Moody Alexander, and C. Moody Alexander for donated their cases, particularly to Dr. Phillip Campbell for helping to complete the sample.

Footnotes

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Contributor Information

Peter H. Buschang, Department of Orthodontics, Baylor College of Dentistry, Texas A&M University Health Science Center, Dallas, Texas.

Roberto Carrillo, Department of Orthodontics, Baylor College of Dentistry, Texas A&M University Health Science Center, Dallas, Texas.

P. Emile Rossouw, Department of Orthodontics, University of North Carolina, Chapel Hill, NC.

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