Pseudo-Class III Malocclusion in an Adolescent
Treated with Mandibular Bone Screws and Bite
Opening to Enhance Late Maxillary Growth
Alex Lin,
Lecturer, Beethoven Orthodontic Center (Left)
Chris H. Chang,
Founder, Beethoven Orthodontic Center
Publisher, Journal of Digital Orthodontics (Center)
W. Eugene Roberts,
Editor-in-Chief, Journal of Digital Orthodontics (Right)
Abstract
History: A 12-year-old female presented with a chief complaint (CC) of anterior crossbite.
Diagnosis: Skeletal Class III (SNA, 77.5°; SNB, 82°; ANB, -4.5°) relationship in centric occlusion (CO) was associated with midface
deficiency, crossbite of the entire dentition except the molars, and lingually inclined lower incisors (L1 to MP, 75.5°). The
Discrepancy Index (DI) was 28.
Treatment: Bone screws were placed in the mandibular buccal shelves to retract the mandibular arch. To enhance adolescent
maxillary growth, the bite was opened at the start of treatment with posterior bite turbos, and Class III elastics were applied.
Left posterior crossbite was corrected with cross elastics. Lower arch retraction was limited by soft tissue impingement in the
retromolar area.
Outcomes: After 25 months of active treatment, a near-ideal profile and occlusal alignment was achieved. The Cast-
Radiograph Evaluation (CRE) was 19. Pink and White esthetic score was 0. There were two discrepancies from ideal: crossbite of
the upper left second molar, and excessive lingual inclination of lower incisors (66.5°).
Conclusions: This case report demonstrated the use of OrthoBoneScrew® (OBS) to resolve skeletal Class III malocclusion in a
growing adolescent. Class III elastics in addition to bite opening for removal of incisal constraint resulted in enhanced anterior
growth expression of the maxilla. A single phase of treatment in the early permanent dentition efficiently resolved a difficult
skeletal Class III malocclusion. (J Digital Orthod 2024;73:26-44; reprinted from J Digital Orthod 2021;61:4-22)
Key words:
Pseudo-Class III, anterior crossbite, late maxillary growth, passive self ligating brackets, mandibular buccal shelf, bone screws
Introduction
Class III malocclusion is defined by Angle1 as a condition in which the relationship of the jaws is abnormal. Compared to normal, all mandibular teeth occlude more mesial by the width of one bicuspid or more. About 5% of ethnic Chinese adolescents are affected by Class III malocclusion.2 Etiology is classified as (a) functional, which is associated with abnormal tongue placement or neuromuscular conditions; (b) skeletal, when the maxilla is underdeveloped and/or mandible is overdeveloped; and (c) dental, due to ectopic palatal eruption of maxillary incisors or the early loss of lower deciduous molars.3 Class III malocclusions of dental origin often involve a substantial functional shift of the mandible to achieve posterior occlusion, so they are defined as pseudo-Class III.4,5 When the mandible is closed in centric relation (CR), the incisors often show an end-to-end relationship, and molars are Class I. When the mandible shifts anteriorly to achieve full posterior occlusion, the molars shift into a Class III occlusion. Pseudo-Class III malocclusion is usually amenable to conservative orthodontic treatment.6 Pseudo-Class III patients with good growth potential are candidates for early intervention.
Typically, the bite is opened and incisal angulations are corrected to resolve the anterior crossbite.3,7-9 Adolescents with midface deficiency may also
benefit from eliminating restraints to maxillary growth. A 5-year cohort study7 was conducted on 25 young Chinese patients with pseudo-Class III
malocclusion treated to a stable result with a 2×4 appliance during mixed dentition. However, 20% of
◼︎Fig. 1: Facial and intraoral photographs at 9y11m
the sample required a second phase of comprehensive fixed appliance therapy, which may be viewed as a psychological and/or financial burden. Introduction of temporary anchorage devices (TADs)10 provided the option for retraction of the entire lower arch. An additional advantage for resolving anterior crossbite during the growing years is facial growth to help resolve the skeletal discrepancy. Enhancing the potential for maxillary growth is a particularly important strategy for pseudo-Class III patients with midface deficiency.
History and Etiology
A relatively immature 9yr-11mo-old female sought orthodontic consultation for an anterior crossbite. Her facial profile was unesthetic due to both midface deficiency and mandibular prognathism (Fig. 1). No contributing medical or dental history was reported.
◼︎Fig. 2: Pre-treatment facial and intraoral photographs at 12y9m
Clinical examination revealed a concave facial profile, lower lip protrusion, anterior crossbite, and lingual crossbite of left molars. Buccal segments were Class I on the right and Class III on the left. An edge-to-edge incisal relationship was noted when the mandible was guided to CR. Intraoral examination revealed all primary molars and both primary upper canines were present. Early intervention therapy with 2×4 appliances or rapid palatal expansion (RPE) was proposed, but the deep Curve of Spee and anterior deepbite suggested that a second phase of orthodontic therapy would be required. To control
the financial impact, the family preferred only one phase of treatment: comprehensive management after the permanent buccal segments erupt. The patient was recalled three years later at 12y9m of age for a follow-up orthodontic evaluation (Fig. 2). The malocclusion remained stable as the buccal
segments erupted. Overjet was -3mm, overbite was 6mm, and there was a full-cusp-Class III relationship in CO. In CR, the incisors were end-toend with asymmetric buccal segments: Class I right and end-on-Class III left. There was no significant crowding in either arch.
Panoramic (Fig. 3) radiography was within normal limits (WNL). Lateral cephalometric radiographs (Fig. 4) revealed decreased inclination of the incisors in
both arches and a relatively straight profile when the patient was in CR. The decreased SNA angle (77.5°) contributed to midface deficiency. Some
maxillary growth potential was expected, so comprehensive orthodontic treatment was indicated to correct the anterior crossbite (Fig. 5).
◼︎Fig. 3: Pre-treatment panoramic radiograph
◼︎Fig. 4: Cephalometric radiograph in the CO (left) and CR (right) positions. See text for details.
Pseudo-Class III Malocclusion in an Adolescent Treated with Mandibular Screws and Bite Opening JDO 73
29
◼︎Fig. 5: Pre-treatment dental models (casts)
Diagnosis
Facial:
• Facial Convexity: Concave (-3° G-Sn-Pg’)
• Lip Protrusion: Retrusive upper and protrusive
lower lip (-2.5mm/1mm to the E-line)
Skeletal:
• Sagittal Relationship:
– Mild Skeletal Class III at CO (SNA 77.5°, SNB 82°,
ANB -4.5°)
– Skeletal Class I at CR (ANB -1°)
• Mandibular Plane Angle: WNL (SN-MP 33.5°,
FMA 26.5°)
Dental:
• Occlusion: Class III molar relationship
• Overjet: -3mm
• Lower incisor: Retrusive (L1-NB 1.5mm), decreased
axial inclination (L1-MP 75.5°)
• Crossbite: All teeth except left molars
American Board of Orthodontics (ABO) Discrepancy
Index (DI): 28.
Treatment Objectives
1. Level and align both arches.
2. Open the bite, and rotate the mandible posteriorly.
3. Encourage growth of the maxilla with passive
self-ligating (PSL) appliances and Class III elastics.
4. Protract the upper incisors and retract the lower
incisors to correct anterior cross-bite.
5. Optimize occlusal contacts with archwire
finishing and posterior vertical elastics.
Treatment Plan
The objective for full fixed appliance treatment was
to resolve the pseudo-Class III malocclusion, retract
the lower arch, and protract the upper dentition.
Three options were considered:
1. Non-extraction therapy to retract the lower arch
with bilateral anchorage provided by the
◼︎Table 1: Cephalometric summary
mandibular buccal shelf (MBS) OrthoBoneScrew® (OBS) (iNewton, Inc., Hsinchu City, Taiwan) bilaterally
2. Differential space closure following extraction of upper second premolars (U5s) and lower first premolars (L4s) that utilizes MBS OBS anchorage
3. Achieve ideal alignment with two-jaw orthognathic surgery.
First Option: directly addresses the anterior crossbite of the pseudo-Class III malocclusion. Bilateral MBS OBSs are required to retract the lower dentition to correct the anterior crossbite. This option is minimally invasive but it requires an extended treatment time.
Second Option: efficient for anterior crossbite management, but closing extraction spaces in the absence of crowding may compromise incisal axial
inclinations and complicate posterior lingual crossbite correction.
Third Option: corrects the skeletal discrepancy, but occlusal relationships deteriorate because the molars are Class I in CR prior to treatment. Extensive
orthodontics is required to align the dentition once the skeletal discrepancy is corrected. This option is undesirable because (1) surgical intervention is not necessary; (2) It is highly invasive; and (3) surgical correction of the jaws complicates orthodontic finishing.
After a discussion of the three options with the patient and her parents, the first option was preferred because it was expected to deliver a
near ideal dentofacial result in a minimally invasive manner.
Treatment Progress
PSL appliances (Damon Q®, Ormco Corporation, Brea, CA) were initially bonded on all lower teeth, and a 0.014-in CuNiTi archwire was engaged. Hightorque brackets were chosen for the anterior teeth, i.e., low-torque brackets positioned upside down to avoid loss of torque during retraction of the lower arch (Fig. 6). After one month of lower arch leveling and aligning, PSL brackets were bonded on the upper dentition utilizing low torque brackets on the incisors to resist Class III mechanics. Glass ionomer cement (GC Fuji II®, GC America, Alsip, IL) was applied to the occlusal surfaces of the lower first
molars (bite turbos) to open the bite for correction of the anterior crossbite (Fig. 7). Early light short Class III elastics (Parrot 5/16-in 2-oz, Brea, CA) were
used for five months to correct the anterior crossbite (Fig. 8). Once the anterior crossbite was resolved, the buccal occlusions was Class I (Fig. 9), so
the glass ionomer bite turbos were removed. In the tenth month, 0.016×0.025-in stainless steel archwires were placed in both arches, and Class III
elastics were increased to Fox 1/4-in 3.5-oz (Ormco, Brea, CA) to reinforce the anterior crossbite correction. Upper archwire adjustment increased
the root-palatal torque on the upper incisors and expanded the arch. In the 16th month of treatment, an OBS was inserted in each MBS to retract the
l ower a rc h . Computer i zed tomography documented that each OBS was buccal to the roots of the respective molars and well-anchored in the cortical plate (Fig. 10). Extra-alveolar insertion of a MBS OBS is crucial for en masse movement of the mandibular dentition without tooth root interference as the arch is retracted. The OBSs were removed in the 22nd month when it was evident that the brackets of the lower second molars were embedded in the retromolar soft tissues (Fig. 11). This complication limited the amount of lower arch retraction. By the next appointment, all crossbites were corrected except for the left posterior segment. Buttons were placed on the lingual side of LL4, LL5, UL6 and UL7 to attach cross elastics (Fig. 12). A panoramic
radiograph revealed problems with root parallelism that required bracket repositioning. Figs. 13 and 14
◼︎Fig. 6:
Low-torque brackets were placed upside-down on lower
incisors. See text for details.
◼︎Fig. 7:
Occlusal view of bite turbos constructed at two months (2M) by
placing glass ionomer cement on the occlusal surfaces of the
lower first molars. See text for details.
◼︎Fig. 8:
Frontal view of bite turbos placed on lower first molars at two
months (2M) into treatment to open the bite. Class III elastics are
used to to retract the lower arch. See text for details.
◼︎Fig. 9:
Cephalometric radiograph exposed at 5 months into treatment
(5M). Notice the crossbite was corrected and buccal segments
were Class I. See text for details.
◼︎Fig. 10:
CBCT slices in the 16th month show the E-A insertion of
mandibular shelf bone screws on the right (upper) and left
(lower) sides.
◼︎Fig. 11:
Retraction of the lower arch with Class III elastics resulted in the
lower second molar brackets embedded into retromolar soft
tissue in the 22nd month (22M). See text for details.
◼︎Fig. 12:
Crossbite at the left posterior region was corrected with cross
elastics in the 23rd month (23M).
are panels of intraoral occlusal photographs showing treatment progress in the maxillary and mandibular arches, respectively. Immediately after
the fixed appliances were removed, a mandibular 3-3 lingual retainer was bonded in place.
Results Achieved
After 25 months of active treatment, this difficult malocclusion (DI = 28) was treated to an optimal alignment (CRE = 19) with an excellent Pink and White esthetic score of zero (see worksheets at the end of this case report). Two discrepancies from an ideal outcome were noted: (1) lingually tipped lower incisors (L1 to MP 66.5°), and (2) lingual crossbite of the UL7. Post-treatment panoramic and lateral cephalometric radiographs are shown in Figs. 15 and 16, respectively. Although the UL7 was in crossbite, the occlusion was stable at the end of treatment (Fig. 17). After the functional shift was corrected, the facial profile was improved and buccal segments were in Class I occlusion. Superimposition of the pretreatment and posttreatment cephalometric tracings reveal the late facial growth, dentofacial orthopedic changes of the maxilla, and posterior rotation of the mandible (Fig. 18). Fig. 19 is a panel of post-treatment facial and intraoral photographs. Assessment of specific objectives:
◼︎Fig. 13:
Maxillary occlusal views of treatment progress in months (M) and the mandibular archwire progression are shown from the start of
treatment (0M) to twenty-three months (23M).
◼︎Fig. 14:
Mandibular occlusal views of treatment progress in months (M) and the mandibular archwire progression are shown from the start of
treatment (0M) to twenty-three months (23M).
◼︎Fig. 15: Post-treatment panoramic radiograph
◼︎Fig. 16: Post-treatment cephalometric radiograph
◼︎Fig. 17: Post-treatment dental models (casts)
Pseudo-Class III Malocclusion in an Adolescent Treated with Mandibular Screws and Bite Opening JDO 73
35
Maxilla (all three planes):
• A-P: Increased
• Vertical: Maintained
• Transverse: Maintained
Mandible (all three planes):
• A-P: Decreased
• Vertical: Increased
• Transverse: Maintained
Maxillary Dentition
• A-P: Protraction of incisors and molars
• Vertical: Extrusion of molars
• Inter-molar Width: Decreased
Mandibular Dentition
• A-P: Retraction of incisors and molars • Vertical: Maintained
• Inter-molar/Inter-canine Width: Increased/
Maintained Facial Esthetics
• Upper and lower lip: Retraction of both lips
Final Evaluation of Treatment
Clinical examination revealed an improved facial profile as the maxilla grew forward and the mandible rotated posteriorly. The inclination of the maxillary incisors was corrected to resolve the anterior crossbite and eliminate the CO-CR functional shift. The molars were extruded and the inter-molar width of the maxillary arch was decreased as the upper molars were protracted while the lower arch was retracted. Both lips were retracted relative to the E-line as the mandible rotated posteriorly. Dental alignment and esthetics were near ideal. The only significant discrepancies were crossbite of the upper left second molar and decreased axial inclination of the lower incisors. Two-year follow-up evaluation documented the stability of the final occlusion (Fig. 20). Neither relapse of the anterior crossbite nor excessive mandibular growth were noted.
Discussion
Managing adolescents with pseudo-Class III malocclusion requires diagnostic acumen to
◼︎Fig. 18:
Superimposition of the pre-treatment (black) and post-treatment (red) cephalometric tracings shows the dentofacial effects of treatment.
distinguish between a true skeletal Class III relationship as opposed to a pseudo-Class III with a functional shift. Correct timing for the intervention
is designed to maximize the treatment response while minimizing the burden on the patient. MBS OBSs provide E-A anchorage to conservatively
resolve both the skeletal and pseudo-Class III components of a malocclusion.
Diagnosis
Pseudo-Class III malocclusion can be challenging to diagnose and treat. Skeletal Class III patients may have a mandibular length (Co-Gn) that is 3-6mm
longer than for Class I subjects.4 On the other hand, pseudo-Class III patients often have a mandible of average length, which results in a Class I buccal
◼︎Fig. 19: Post-treatment facial and intraoral photographs
◼︎Fig. 20: Intraoral photographs taken 2 years after treatment was completed
segments with edge-to-edge incisal contact in CR. Mandibular protrusion into an exaggerated anterior crossbite is required for the posterior
segments to occlude. Abnormal occlusal posture may contribute to an undesirable inclination of the incisors. Clinicians may overlook the functional and
dental compensations associated with a pseudo- Class III malocclusion, and inappropriately refer the patient for orthognathic surgery as a skeletal Class
III problem. To correctly diagnose pseudo-Class III malocclusion, Lin devised the 3-ring diagnosis system (Fig. 21), which is composed of three
diagnostic steps: 11,12
• Profile: If the patient has an acceptable
(orthognathic) facial profile when the mandible
is in the CR position, conservative orthodontic
therapy is indicated.
• Class: Buccal segments at or near a Class I
relationship in CR is a favorable indication for
nonsurgical correction. This diagnostic step can
be interpreted liberally because osseous
anchorage devices (TADs) can compensate for
many dental alignment problems.6
• Functional Shift: The present patient had an
edge-to-edge incisor relationship when the
mandible was guided into the CR position, i.e,.
about a 2mm CO→CR functional shift.
◼︎Fig. 21:
The 3-ring diagnosis system for pseudo-Class III malocclusion
(Dr. Lin Jin-Jong)
All three diagnostic criteria (Fig. 21) favored conservative orthodontic treatment without orthognathic surgery. However, the severity of the problem required opening the bite to produce posterior rotation of the mandible. In addition, treating the patient in the early permanent dentition resulted in a desirable forward growth of the maxilla.
Anterior Crossbite Correction
To provide clearance for anterior crossbite correction, glass ionomer cement (bite turbos) were placed on the occlusal surfaces of lower molars.13 High torque brackets were selected for the lower incisors to resist retraction mechanics and Class III elastics. In contrast, low torque brackets were bonded on the upper anterior teeth to prevent flaring due to the anterior component of force for the Class III elastics. In retrospect, the high torque brackets for the lower incisors with the specified archwire sequence failed to correct or even maintain the axial inclinations of the lower incisors (Fig. 18; Table 1). This problem is related to the limit on lower arch retraction due to soft tissue impingement in the retromolar area (Fig. 11). Attempting to correct lower incisor root angulation with additional root lingual torque in the brackets or archwire may have resulted in relapse of the anterior crossbite.
Treatment Timing
Maxillary growth is helpful for correcting pseudo-Class III relationships that are associated with midface deficiency.7 Use of RPE14 and/or 2×4 appliances in mixed dentition takes advantage of maxillary growth.7 Many anterior crossbites corrected in the mixed dentition require no further orthodontic treatment unless there are dental alignment problems such as crowding. Pseudo-Class III patients with a deepbite and exaggerated lower Curve of Spee are difficult to resolve with 2×4 appliances and/or RPE in the mixed dentition. Although it may increase the financial and psychological burden for the patient and family, Phase I early intervention in the mixed dentition may require arch leveling and alignment prior to correction of the anterior crossbite.
Furthermore, Phase II therapy is often required to achieve a stable result. If resolving the entire malocclusion with one stage of treatment is the priority for the family, comprehensive treatment should be delayed until the early permanent dentition (~12yr of age). MBS OBS anchorage is effective for retraction of the entire lower arch to manage Class III malocclusion. Similar mechanics are also effective for pseudo-Class III problems in adults with no growth potential,6 but maxillary growth in younger patients enhances the facial outcome.15,16 Thus, for optimal facial esthetics, treatment in the mixed or early permanent dentition is preferable.15 With adequate clearance for anterior crossbite correction provided by posterior bite turbos, light short elastics and passive self-ligating brackets17 deliver a continuous light mechanics to encourage anterior growth of the maxilla. This growth response was important for an optimal facial outcome for the present patient because of the pretreatment maxillary deficiency (SNA 77.5°) (Figs. 18 and 19; Table 1). Growth is not as important for patients with an ideal SNA prior to treatment. Dental compensations can be corrected at any age, but a favorable growth response requires intervention during the growing years. This case report demonstrates the advantage for treating pseudo-Class III malocclusion in an adolescent with PSL system and MBS OBS anchorage.
Residual Posterior Crossbite
Despite the correction of the anterior crossbite, the upper left second molar erupted into lingual crossbite. In retrospect, this problem was preventable with more posterior archwire expansion during treatment.
◼︎Fig. 22: Facial and intraoral photographs at 4 years post-treatment document the current condition of the patient.
Conclusions
Differential diagnosis of an anterior crossbite is essential for distinguishing a pseudo-Class III malocclusion that is amenable to conservative correction. Unlike a skeletal Class III relationship which requires complete growth of the mandible for predictable treatment, correction of pseudo-Class III is indicated during the growing years. Although the anterior crossbite of a pseudo-Class III is correctable in adults, a young growing patient with a midface
deficiency usually achieves an enhanced facial outcome.
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