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JAE HYUN PARK, DMD, MSD, MS, PHDKIYOSHI TAI, DDS, PHDMASATO TAKAGI, DDS, PHD

Open-Bite Treatment Using Maxillary and Mandibular Miniplates

Dr. Tai Dr. TakagiDr. Park

Dr. Park is an Associate Professor and Chair, Postgraduate Orthodontic Program, Arizona School of Dentistry & Oral Health, A.T. Still University, 5835 E. Still Circle, Mesa, AZ 85206, and an Adjunct Professor, Graduate School of Dentistry, Kyung Hee University, Seoul, South Korea; e-mail: [email protected]. Dr. Tai is a Visiting Adjunct Assistant Professor, Postgraduate Orthodontic Program, Arizona School of Dentistry & Oral Health, A.T. Still University, and an Adjunct Professor, Graduate School of Dentistry, Kyung Hee University. Drs. Tai and Takagi are in the private practice of orthodontics in Okayama, Japan.

in open-bite patients or when en masse distaliza-tion is required—because they allow efficient tooth movement without the need for removal and reinstallation.4,5

Conventional therapies for the correction of skeletal open bite10,11 have included high-pull head-gear,12 fixed appliances such as the Multiloop Edgewise Arch Wire (MEAW),13 tongue cribs,14 posterior bite blocks,15 posterior magnets,16 and vertical elastics.17 All of these rely on patient com-pliance and are less effective in adult patients. More severe cases of anterior open bite have tradi-tionally required orthognathic surgery. As an al-ternative, several authors have recently had success in treating open bite with skeletal anchorage from TADs.18 This article shows how an open bite with a canted palatal plane can be treated with a com-bination of maxillary and mandibular miniplates.

The development of temporary anchorage de-vices (TADs) has offered new options for treat-

ing orthodontic problems such as anterior open bite by means of molar intrusion, Class II malocclusion by maxillary molar distalization, Class III maloc-clusion by maxillary protraction or mandibular distalization, deep bite by anterior intrusion, and spacing from missing posterior teeth with mesial-ization.1-7 The slightly lower reported success rate of miniscrews (about 86.5%8) compared to mini-plates (91-96%5,9) is due to the tendency of mini-screws to loosen when orthodontic force is ap-plied.9 On the other hand, the ease of insertion and removal of miniscrews under local anesthesia gives them an advantage over miniplates, which require flap-raising surgery for insertion and re-moval. Still, there are certain clinical situations in which miniplates may be preferable—for example,

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399VOLUME XLIX NUMBER 6

Fig. 1 21-year-old male patient with crowded Class I occlusion, 7.5mm overjet, and 2.5mm open bite before treatment.

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7.5mm overjet and a 2.5mm open bite. The maxil-lary dental midline was coincident with the facial midline, but the mandibular dental midline was deviated by about 2mm to the right. The patient displayed two different occlusal planes in the man-dibular arch, with a downward tilt in the anterior segment (except for the right lateral and left central

Case Report

A 21-year-old male presented with concerns about his anterior open bite. Intraoral examination found severe mandibular crowding and moderate maxillary crowding (Fig. 1). He had Class I molar and canine relationships on both sides, with a

TABLE 1CEPHALOMETRIC ANALYSIS

Japanese Pre- Post- One Year Norm treatment Treatment Post-Treatment

SNA 82.0° 78.5° 78.1° 78.6°SNB 80.0° 72.3° 74.6° 74.9°ANB 2.0° 6.2° 3.5° 3.7°Wits appraisal +1.1mm +8.9mm +1.8mm +2.8mmSN-MP 34.0° 39.8° 35.0° 35.0°FH-MP 28.2° 33.1° 27.6° 27.7°Lower facial height 55.0% 59.0% 58.6% 58.2%U1-SN 104.0° 106.9° 104.0° 102.4°U1-NA 22.0° 28.4° 25.9° 23.8°IMPA 90.0° 104.6° 99.6° 99.4°L1-NB 25.0° 36.7° 29.2° 29.3°U1/L1 124.0° 108.7° 121.4° 123.2°Upper lip to E-line 1.2mm 2.5mm 0.4mm 0.2mmUpper lip to E-line 2.0mm 4.6mm 1.8mm 1.0mm

TABLE 2CONE-BEAM COMPUTED TOMOGRAPHY

LATERAL CEPHALOMETRIC DATA

Norm Pretreatment Post-Treatment

RightU1/PP 31.0mm 35.2mm 36.0mmU6/PP 24.6mm 29.3mm 26.7mmL1/MP 44.2mm 46.1mm 47.2mmL6/MP 32.9 mm 39.3mm 38.5mm

LeftU1/PP 31.0mm 35.1mm 35.6mmU6/PP 24.6mm 27.4mm 26.6mmL1/MP 44.2mm 47.2mm 47.4mmL6/MP 32.9mm 40.7mm 38.3mm


Park, Tai, and Takagi

incisors) and an upward tilt in the posterior re-gions. He was observed to have a tongue-thrust habit, with a forced opening of the lips when swal-lowing.19

A panoramic radiograph showed that all third molars were present. The lateral cephalogram revealed the presence of two palatal planes, and cone-beam computed tomography (CBCT) con-firmed a canted palatal plane with the palatal vault higher on the left side than on the right. Lateral cephalometric analysis (Table 1) indicated a skel-

etal Class II (ANB = 6.2°) with a hyperdivergent growth pattern (SN-MP = 39.8°) and proclined upper and lower incisors (U1-SN = 106.9°, IMPA = 104.6°). Because of the retrognathic mandible, the lips were protrusive, ahead of the E-line.

To close the anterior open bite and relieve crowding, we recommended extraction of the four first premolars. When the patient declined extrac-tion of teeth other than the third molars, we de-cided to plan for nonextraction treatment with miniplate anchorage. According to the CBCT

Fig. 2 Progress of open-bite closure after 20 months of treatment.

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premolars (Fig. 2). This system produced bodily intrusion while preventing buccal tipping of the maxillary posterior dentition. Lingual torque was added to the archwire as needed. To avoid poste-rior buccal tipping during the intrusion, a lower 3D Lingual Arch*** was placed.

Interproximal reduction was performed on the lower anterior teeth during the finishing stage to improve the anterior interocclusal relationship (Fig. 3). Light posterior and anterior box elastics were worn at night to settle the occlusion.

All appliances were removed after 34 months of treatment. Fixed lower 3-3 and upper 2-2 retain-ers were bonded, and wraparound removable re-tainers were also delivered. Because the patient showed slight gingival recession at the lower right central incisor, he was referred to a periodontist for a gingival graft.

images, the lower first molars were extruded and the lower central incisors were lower than the lower lip, even though they were extruded com-pared to normal values (Table 2). The upper first molars and central incisors were also extruded compared to the norms, but because the upper central incisal edges were in the proper vertical position at rest (about 4mm below the lip line on the lateral cephalogram20), we focused our me-chanics more on intrusion of the posterior teeth than on extrusion of the anterior teeth.

The four third molars were extracted, and full fixed .022" preadjusted appliances* were placed for leveling and alignment. Both arches were leveled with continuous archwires, from .014" nickel titanium up to .019" × .025" beta titanium.

After six months of treatment, “Y”-shaped anchor plates** were implanted in the zygomatic buttresses and “T”-shaped” anchor plates** in the mandibular buccal bone on both sides, using monocortical screws. For skeletally anchored in-trusion of the posterior teeth,4,5 extension arms were soldered to a transpalatal arch to engage elastomeric chains from lingual buttons on the

*Unitek Miniature Twin, 3M Unitek, Monrovia, CA; www. 3Munitek.com.**Orthoanchor SMAP, Dentsply-Sankin, Tokyo, Japan; www.dentsply-sankin.com***Registered trademark of RMO, Inc., Denver, CO; www. rmortho.com.

Fig. 3 Finishing stage after 24 months of treatment.



Fig. 4 A. Patient after 34 months of treatment. B. Superimposition of pre- and post-treatment cephalomet-ric tracings.

A

A

B

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Fig. 5 Left side (A) and right side (B) lateral cone-beam computed tomography measurements before and after treatment.

B

A



Post-treatment records demonstrated that the Class I molar and canine relationships were main-tained, while satisfactory overbite and overjet were achieved (Fig. 4A). The panoramic radiograph showed acceptable root parallelism, except be-tween the lower left canine and first premolar. There were no significant signs of bone resorption, although the anterior teeth demonstrated some signs of apical root resorption.

Cephalometric analysis confirmed intrusion of the posterior dentition and slight extrusion of the anterior dentition (Fig. 4B, Table 1), as well as sig-nificant skeletal changes (ANB = 3.5°, SN-MP = 35°). The maxillary incisors were normally inclined (U1-SN = 104°); the mandibular incisors were im-proved but still proclined (IMPA = 99.6°). These dental and skeletal changes contributed to a correc-tion of the anterior open bite and an improvement in the profile and smile esthetics. CBCT showed a canted palatal plane with little change from the relationship before treatment (Fig. 5, Table 2).

Twelve months later, the results had remained stable (Fig. 6).

Discussion

Although a dental anterior open bite typi-cally manifests as a normal craniofacial pattern, with undererupted anterior teeth and an inadequate curve of Spee in the mandibular arch, a skeletal anterior open bite is generally associated with a deficient posterior facial height, an excessive ante-rior facial height and lower anterior facial height, a steep mandibular plane angle, a deficient SN-PP angle, and an excessive gonial angle and PP-GoGn angle, with either normally erupted or overerupted anterior teeth.21 Our patient did show a skeletal anterior open-bite tendency in terms of a steep mandibular plane, excessive posterior eruption, and downward and backward rotation of the mandible, but he also displayed an inadequate mandibular curve of Spee due to the dental open-bite tendency, possibly as a result of his tongue-thrust habit.

Closing the interincisal distance by more than 5mm with orthodontic tooth movement alone is difficult.22 Orthodontists have clearly benefited from the advent of TADs, particularly in severe

open-bite cases with borderline indications for surgery. Various authors have shown successful molar intrusion using miniplates in such pa-tients.3,22 Miniplates are especially useful in cor-recting severe open bite because they allow intru-sive forces as high as 500g per side to be applied,23 without the need for reinstallation or the risks associated with surgery5,6 (Table 3).

Skeletal open bite often requires the align-ment of two occlusal planes, such as an anterior plane with an upward tilt and a posterior plane with a downward tilt, almost always involving extruded molars and premolars.13,30 Arriola-Guillén and Flores-Mir reported greater lower molar height in their Class II group compared to the control group,31 indicating that intrusion of both upper and lower molars would benefit such open-bite pa-tients. In the case shown here, by intruding the upper and lower molars at the same time, we were able to align two different occlusal planes in the mandibular arch. The lower anterior segment was also extruded, however, because it was already below the lip line before treatment.

There are only a few published reports on the stability of open-bite treatment. In a meta-analysis, Greenlee and colleagues reported long-term suc-cess rates greater than 75% for the correction of anterior open bites by both surgical and nonsurgi-cal methods.32 Sugawara and colleagues noted a 30% relapse rate one year after anterior-open-bite treatment using miniplates as anchorage for man-dibular molar intrusion.33 Lee and Park found a 10.36% relapse rate for intruded maxillary mo-lars.34 Our patient showed stable results 12 months after debonding, but that may be at least partly attributable to the control of his tongue-thrust hab-it. Baek and colleagues, who recently evaluated the three-year post-treatment stability of anterior open-bite correction in adults by orthodontic intrusion of posterior teeth with miniscrew anchorage, re-ported that 80% of the total relapse of the intruded upper first molars occurred during the first year of retention.35 They concluded that the use of an ap-propriate retention protocol during this period would significantly improve long-term stability.ACKNOWLEDGMENT: We thank Ms. Ki Yoon Chung for her help with the literature review.

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Fig. 6 Follow-up records taken 12 months after debonding.



TABLE 3COMPARISON OF MINISCREWS AND MINIPLATES

Miniscrews Miniplates

Success rate 86.5%.8 91-96%.5,9

Healing time before loading

Zero to two weeks.24 • Immediate loading is possible.24 Generally two weeks

for soft-tissue healing.25

One to eight weeks.9 • Generally three weeks for soft-tissue healing; no

osseo integration needed.5 Although immediate loading is possible, orthodontic force application is usually de-layed for three weeks for resolution of postoperative fa-cial swelling, soft-tissue healing, and reinstitution of oral hygiene procedures.5

Loading time period

Two to 20 months.9 Three months to two years.9

Anatomical considerations

Sites with thick cortical bone are favorable.25,26

• Mandible: buccal side of posterior region.25

• Maxilla: midpalatal suture area (or paramedian palatal area).25

Because bone density is usually high in the posterior mandible, midpalatal suture, and paramedian palatal ar-eas, self-tapping method is recommended.24

Soft-tissue thickness is also important in determining the length of screws to use.25

• Area of attached gingiva coronal to mucogingival junc-tion is recommended to reduce soft-tissue impinge-ment, patient discomfort, tissue hypertrophy, and microjiggling.25,26

Must consider interradicular distance26 and numbers, po-sitions, and parallelism of proximal roots (use panoramic or periapical radiographs or cone-beam computed tomo-graphy for this purpose).25

Avoid or consider other anatomical structures such as ar-teries, veins, maxillary sinus, nasal cavity, mandibular ca-nal, mental foramen, incisive canal, and greater palatine nerve.25-27

At least 2mm of cortical bone thickness for anchor plate.5

• Mandible: lateral cortex in most locations except adja-cent to mental foramen.5

• Maxilla: zygomatic buttress and piriform rim (lateral wall of maxilla is too thin).5

Advantages Surgical procedure (flap) not required.Ease of removal.9

Little risk of bone trauma.24

Immediate loading.24

Fewer restrictions regarding insertion sites compared to miniscrews (less dependent on the anatomy of muco-gingival tissue); stable anchorage applicable to most areas.9,28

More reliable under higher (orthopedic) forces.6

Fixation screws of bone plates are mostly placed sub-apically, where bone quality is adequate, to allow tooth movement without obstruction or risk of injuring adjacent roots during placement.29

Drawbacks, complications, and risks

Lack of initial stability in cases of inadequate cortical bone thickness.8,9

Injury to adjacent structures (periodontal ligament, roots, nerves, blood vessels, or sinus).8,9

Mucosal inflammation, infection, and soft-tissue hypertrophy.8,9

Root perforation.9

Loss of stability (prone to loosening).9

Miniscrew fracture (can be avoided by using screws 2mm or more in diameter).25

Need for surgical procedure (insertion and removal).9

Mild-to-moderate facial swelling after placement proce-dure.5

Difficulty of adapting miniplates to bony contour.7

Mild mucosal inflammation, infection, and gingival reces-sion.9

Loosening.9

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