Volume 33 Issue 2 Article 4

January 2021

Unilateral Premolar Crossbite and Atypical Extraction Case

Treated with Clear Aligner
Ting-Fen Chang
Taipei Veterans General Hospital, National Yang Ming Chiao Tung University

Tzu-Ying Wu
Section of Orthodontics, Department of Stomatology, Taipei Veterans General Hospital, Taipei, Taiwan;
School of Dentistry, National Yang Ming Chiao Tung University, Taiwan

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Recommended Citation
Chang, Ting-Fen and Wu, Tzu-Ying (2021) "Unilateral Premolar Crossbite and Atypical Extraction Case
Treated with Clear Aligner," Taiwanese Journal of Orthodontics: Vol. 33: Iss. 2, Article 4.
DOI: 10.38209/2708-2636.1101
Available at: https://www.tjo.org.tw/tjo/vol33/iss2/4

This Case Report is brought to you for free and open access by Taiwanese Journal of Orthodontics. It has been
accepted for inclusion in Taiwanese Journal of Orthodontics by an authorized editor of Taiwanese Journal of
Orthodontics.
Unilateral Premolar Crossbite and Atypical Extraction Case Treated with Clear
Aligner

Abstract
A unilateral buccal crossbites can be observed in adult patients with skeletal asymmetry and crowded
dentition. This case report describes the orthodontic treatment with clear aligners for a 57-year-old
female with chin deviation, lower dentition crowding and a unilateral complete buccal crossbite in right
premolars. Mandibular single incisor extraction was planned to relieve crowding and the crossbite was
resolved by intrusion of upper premolar and uprighting of lower premolar with clear aligners in combined
with inter-arch elastic. The entire treatment was completed within 20 months and the treatment result
showed good vertical control. This case report demonstrates that clear aligners can be considered as an
effective, esthetic, and comfortable tool for premolar crossbite correction, when the treatment sequence
on ClinCheck® was designed properly. Also, one incisor extraction was a good option in specific case,
especially when anterior Bolton discrepancy are larger than normal.

Keywords
Clear aligner; Unilateral buccal crossbite; Single lower incisor extraction

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License.

Cover Page Footnote

Conflicts of intrerst: The authors have declared they have no conflicts of interest.

This case report is available in Taiwanese Journal of Orthodontics: https://www.tjo.org.tw/tjo/vol33/iss2/4

CASE REPORT

Unilateral Premolar Crossbite and Atypical Extraction

Case Treated with Clear Aligner

Ting-Fen Chang a,b, Tzu-Ying Wu a,b,*

a
Section of Orthodontics, Department of Stomatology, Taipei Veterans General Hospital, Taipei, Taiwan
b
School of Dentistry, National Yang Ming Chiao Tung University, Taiwan

ABSTRACT

A unilateral buccal crossbites can be observed in adult patients with skeletal asymmetry and crowded dentition. This
case report describes the orthodontic treatment with clear aligners for a 57-year-old female with chin deviation, lower
dentition crowding and a unilateral complete buccal crossbite in right premolars. Mandibular single incisor extraction
was planned to relieve crowding and the crossbite was resolved by intrusion of upper premolar and uprighting of lower
premolar with clear aligners in combined with inter-arch elastic. The entire treatment was completed within 20 months
and the treatment result showed good vertical control. This case report demonstrates that clear aligners can be
considered as an effective, esthetic, and comfortable tool for premolar crossbite correction, when the treatment sequence
on ClinCheck® was designed properly. Also, one incisor extraction was a good option in specific case, especially when
anterior Bolton discrepancy are larger than normal. Taiwanese Journal of Orthodontics 2021;33(2):68e76

Keywords: Clear aligner; Unilateral buccal crossbite; Single lower incisor extraction

INTRODUCTION crowding is thought to be relate to late mandibular

growth.2 Sometimes, stripping or one incisor
extraction could be an alternative treatment option.
C omplete buccal crossbite is defined as
palatal cusp of the maxillary tooth opposing This case report illustrated a good indication for one
lower incisor extraction.
to the buccal side of the mandibular tooth. Its
prevalence is 0.4e2.7% in adults.1 Complete
CASE REPORT
buccal crossbite can occur unilaterally or bilater-
ally, and unilateral complete buccal crossbite may A 57-year-old female presented with a chief
be accompanied by a midline discrepancy. The complaint of mandibular teeth crowding progres-
sively with aging. She also complaint about difficult
etiology of complete buccal crossbite may
oral hygiene maintain, especially the lingual tilted
comprise skeletal discrepancy in transverse premolar.
aspect, or malaligned dentition due to tooth size
arch length discrepancy.2 Clinical examination
Disocclusion is an important step during cross-
bites correction. Compared to bite turbo and The extraoral examination revealed that she had
occlusal splint, clear aligner is considered as a more lower facial asymmetry with 5 mm deviation of
esthetic and comfortable bite raiser. This article pogonion point to her right side. The upper dental
describes the treatment of a unilateral premolar midline was coincident with her facial midline, but
buccal crossbite in adult with the clear aligners lower dental midline was deviated to the right side
combined with auxiliary appliances. about 4 mm. The patient had straight profile with
Mandibular incisor crowding is a general phe- normal infraorbital prominent (Figure 1). As for
nomenon in adult patient.3 Late lower incisor intraoral examination, normal overjet and overbite,

Received 29 March 2021; revised 10 May 2021; accepted 5 June 2021.

Available online 9 August 2021.

* Corresponding author. No. 201, Sec. 2, Shipai Rd., Beitou Dist., Taipei City, 112063, Taiwan. Fax: þ02 28742375.
E-mail address: wu_3793@yahoo.com.tw (T.-Y. Wu).

https://doi.org/10.38209/2708-2636.1101
2708-2636/© 2021 Taiwan Association of Orthodontist. This is an open access article under the CC-BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Taiwanese Journal of Orthodontics T.-F. CHANG, T.-Y. WU
2021;33(2):68e76 CLEAR ALIGNER FOR PREMOLAR CROSSBITE

Figure 1. Pre-treatment facial photographs revealed 5 mm right deviation of mandible on pogonion point and straight facial profile with normal
infraorbital prominence.

and bilateral Class III molar relationship were Angle's Class III malocclusion with complete buccal
noted. Elongated tooth #15 and lingual tilted tooth crossbite of right second premolars and increased
#45 were resulting in a unilateral complete buccal anterior Bolton ratio (83%).
crossbite at right side (Figure 2). There was mild
crowding in the maxillary arch and severe crowding Treatment objectives and plan
in the mandibular arch. A large anterior Bolton ratio
of 83% was recorded, which may be due to a Our treatment goal was to address the patient's
mandibular dental excess of 2.5 mm (Figure 3). chief complaint of mandibular crowding. Since the
The panoramic radiograph findings included mild patient was satisfied with the size and shape of her
localized bone loss, teeth #11, #18, #38 were missing, current prosthesis in upper anteriors, the Bolton
and tooth #28 was highly impacted (Figure 4). Tooth ratio had to be corrected by managing the tooth
#11 was restored with 3-unit porcelain fused to proportion of lower anterior. Therefore, one
metal ill-fitting bridge for more than 30 years. mandibular incisor and right mandibular third
Cephalometric analysis indicated that the patient molar extraction were planned to relieve anterior
presented Class I skeletal pattern, normal mandib- and posterior crowding in lower arch.
ular plane angle and retroclined maxillary incisors Since the anterior Bolton ratio was 83%, tooth #41
(Table 1). was selected to be extracted in this case. The ante-
rior Bolton ratio after tooth #41 extraction was 74%.
Diagnosis As for posterior crowding at right side, distalization
of the mandibular right first and second molars was
The patient had straight profile, skeletal Class I planned. A diagnostic 3D digital setup was made for
jaw relationship, normal mandibular plane angle, interview and discussion with the patient (Figure 5).

Figure 2. Pre-treatment intraoral photographs showed 4 mm right deviation of lower dental midline, elongated tooth 15 and lingual tilted tooth 45
resulting in a unilateral complete buccal crossbite at right side.

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CLEAR ALIGNER FOR PREMOLAR CROSSBITE 2021;33(2):68e76

Figure 3. Pre-treatment digital models in different views. The anterior Bolton ratio was 83%.

Figure 4. a. Pre-treatment panoramic radiograph showed mild localized bone loss. b. Pre-treatment lateral cephalogram demonstrated a Class I
skeletal pattern, normal mandibular plane angle and retroclined maxillary incisors.

Treatment progress
Table 1. Comparison between pre- and post-treatment cephalometric
analysis.
Before clear aligner treatment, teeth #41, #48 were
Skeletal Pre-treatment Post-treatment
extracted. Teeth #31, #42 were then receiving root
SNA 80.5 80.5
axis adjustment with sectional fixed appliance
SNB 77.5 77.0
ANB 3.0 3.5 (0.022-in. standard brackets with sectional 0.016 NiTi
SN-MP 34.5 34.5 wire) while waiting for maxillary anterior provi-
LAFH 74.0 mm 74.0 mm sional bridge fabrication. After 3 months of local
Dental treatment, the angulation of teeth #31, #42 was
U1-NA 5.0 mm 3.0 mm
improved (Figure 6). Digital impression was taken
U1-SN 94.0 94.0
L1-NB 6.5 mm 7.0 mm with a 3Shape TRIOS 3® intraoral scanner (3Shape
L1 MP 105.0 92.5 A/S, Copenhagen, Denmark) when provisional
Soft Tissue bridge was delivered.
Upper lip-E line 1 mm 1 mm A three-dimensional virtual planning of tooth
Lower lip-E line 2 mm 2 mm
movement was performed through ClinCheck®
software (©Invisalign, US) (Figure 7). Invisalign
Clear aligner was considered for esthetic, comfort, Comprehensive Package with 32 aligners were
convenience, and a useful tool for disocclusion scheduled, the treatment was started with the lower
when cross-bite correction. The patient chose clear anterior extraction space closure and tooth #47 dis-
aligner for easier oral hygiene maintain and better talization. Vertical rectangular attachments were
social esthetics. placed over teeth #31, #42 to achieve better root axis

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Taiwanese Journal of Orthodontics T.-F. CHANG, T.-Y. WU
2021;33(2):68e76 CLEAR ALIGNER FOR PREMOLAR CROSSBITE

Figure 5. a. A diagnostic 3D digital setup of teeth #41 and #48 extraction. b. Superimposition of pretreatment model (Yellow) and diagnostic setup
model (Green).

control. In the upper arch, we planned to expand reciprocal anchorage. Inter-arch and intra-arch
bilateral premolar to gain 0.5 mm space for tooth #15 elastics (3M Unitek, 3.5 oz. force, 1/4-inch lumen
intrusion. The attachment on teeth #14 and #16 were size) were used for cross-bites correction, tooth de-
used as anchorage to support tooth #15 intrusion. rotation and space closure. The crisscross inter-arch
In the lower arch, sequential distalization of teeth elastic from the button on buccal cervical side of
#47 and #46, as well as sequential mesialization of tooth #14 to the lingual button on tooth #45 was used
teeth #43 and #44 were planned to create space for for tooth #45 uprighting. The intra-arch elastics from
tooth #45. The tooth movement planning was using the button on buccal cervical side of tooth #44 to the

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CLEAR ALIGNER FOR PREMOLAR CROSSBITE 2021;33(2):68e76

Figure 6. a. Pre-treatment radiography revealed divergent roots angulation adjacent to the extraction site. b. Adjustment the angulation of teeth #31
and #42 with fixed appliance. c. Radiography taken after 3M of local treatment showed parallel roots of teeth #31 and #42.

Figure 7. Virtual planning of tooth movement was performed through ClinCheck® software. a. Treatment plan. b. Superimposition of tooth
movement.

precision cut over tooth #32 facilitated the de-rota- removed, and the patient was instructed to wear
tion movement of tooth #44 and space closure be- Essex-type retainers all day.
tween teeth #44 and #43 (Figure 8).
At the last month, 0.022-in braces with Treatment result
0.022  0.028-in SSW stabilizing wires were put over
bilateral lower posterior area, 0.016-in NiTi wire From the extraoral view, the patient had more
with 0.022 braces were put at upper right side to harmonious lateral facial profile (Figure 10). Intra-
maintain vertical position of tooth #15, and buttons orally, the problems of crowding and the complete
with vertical elastics at upper left side were used to buccal cross-bites over right side had been solved,
achieve better intercuspitation (Figure 9). After 20 and the periodontal condition was maintained
months of entire treatment, all appliances were (Figure 11). The molars and canines were

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Taiwanese Journal of Orthodontics T.-F. CHANG, T.-Y. WU
2021;33(2):68e76 CLEAR ALIGNER FOR PREMOLAR CROSSBITE

Figure 8. a. Inter-arch and intra-arch elastics were used to facilitate cross-bites correction, tooth de-rotation and space closure. b. lower occlusal view
of stage 16 at the 12th month.

Figure 9. The intraoral photographs showed sectional nickel-titanium alloy round wires were used to maintain alignment on posterior area, and
intermaxillary up-and-down elastics to settle the posterior occlusion in the 19th month. The Upper and lower anterior teeth were covered with aligner
by 12hr per day.

Figure 10. Post-treatment facial photographs revealed harmonious facial profile.

maintained at the left side for Bolton ratio consid- the teeth after uprighting and result in clockwise
eration but improved at the right side (Figure 12). rotation of mandible and anterior open bite. More-
Panoramic radiograph showed acceptable root over, unilateral crisscross elastics may cause
parallelism of lower incisors adjacent to the extrac- occlusal plane canting. Therefore, using mini-screw
tion space (Figure 13). Posttreatment cephalometric as an anchorage to provide intrusion force had been
analysis (Table 1) and superimposition (Figure 14) widely reported in treatment of unilateral complete
revealed retraction of lower lip, retraction of lower buccal crossbite.4e6
anterior teeth and distalization of tooth #46. In this case, the complete buccal crossbite was due
to severe lingual tilting of tooth #45 and supra-
DISCUSSION eruption of tooth #15. The vertical overlap of tooth
#45 and tooth #15 was about 2 mm. Therefore, we
When dealing with unilateral complete buccal
designed intrusion of tooth #15 first, and tooth #45
crossbite, bite raisers combined with inter-arch
was uprighted and intruded in frog pattern (2 stages
crisscross elastic are commonly used. With
for uprighting and 2 stages for intrusion in turns).
adequate occlusal clearance, the over tilted maxil- The uprighting movement was combined with
lary and mandibular teeth could possibly pass
inter-arch crisscross elastic. In order to provide
through each other by inter-arch crisscross elastics.
better retention during elastics wearing, a vertical
However, the vertical force from elastic may extrude

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CLEAR ALIGNER FOR PREMOLAR CROSSBITE 2021;33(2):68e76

Figure 11. Post-treatment intraoral photographs showed the previous crowding and the complete buccal cross-bites over right side had been solved,
and the periodontal condition was maintained.

Figure 12. Post-treatment digital models in different views. The anterior Bolton ratio was 74%.

Figure 13. a. Post-treatment panoramic radiograph showed acceptable root parallelism of the lower incisors adjacent to the extraction space. b. Post-
treatment lateral cephalogram.

rectangular attachment was designed on buccal instructed to eat with aligner during crossbite
surface of tooth #45. Clear aligner is a more conve- correction. Furthermore, the bite block effect pro-
nient and comfortable bite raiser compared to glass vided by the aligner's thickness could be used to
ionomer or resin bite turbos, and our patient was optimize vertical control and prevent bite openings

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Taiwanese Journal of Orthodontics T.-F. CHANG, T.-Y. WU
2021;33(2):68e76 CLEAR ALIGNER FOR PREMOLAR CROSSBITE

Figure 14. Pre-treatment (black line) and post-treatment (red line) superimpositions revealed retraction of lower lip, retraction of lower anterior teeth
and distalization of tooth #46 (sloid line).

which may result from inter-arch elastics use. With case, tooth #41 was outside the natural arch and
proper mechanics design, the complete buccal closest to the crowding with least healthy gingival
crossbite in this case was corrected within 10 condition. Therefore, it became the candidate for
months with clear aligners treatment, and the ver- extraction. In addition, tooth #41 extraction in this
tical dimension was maintained without any screw case would decrease the amount of tooth movement
anchorage. and diminish the risk of anchorage loss. Concerning
Single-lower-incisor extraction is not a standard the risk of bone loss and gingival recession for one
approach to most of malocclusions in orthodontic incisor extraction, we started to close the space
treatment, but in certain clinical condition, it can be immediately after atraumatic extraction of tooth #41
a choice to facilitate mechanics, preserve peri- to avoid the ridge atrophy. Also, we monitored the
odontal health and maintain the facial profile. Canut soft tissue response and reinforced oral hygiene
had suggested that single-lower-incisor extraction is during space closure frequently. Finally, there was
indicated in four types of clinical situations: (1) still some loss of the interdental papillae between
anomalies in the number of anterior teeth, (2) tooth teeth #31 and #42.
size anomalies, (3) ectopic eruption of incisors and According to literature review, root control and
(4) mild Class III malocclusions.7 Our patient had rotation movement are the most challenging or-
mild Class III malocclusion, Bolton ratio discrep- thodontic tooth movement when treating with clear
ancy, well-aligned upper arch, and crowded lower aligner.10,11 Miller et al. reported the first lower
arch. Since the patient was 57-year-old, and the incisor extraction case treated with the Invisalign®
posterior occlusion was quite stable, to minimize system, tipping rather than bodily movement of
total treatment time, maintain original occlusion on adjacent teeth into the extraction site was found
left side, and try to find space for lower anterior from post-treatment panoramic radiography.12 In
crowding relief were our treatment goals. Therefore, the present case, the root angulation adjacent to the
finishing at three incisors is an alternative option. extraction site was divergent at the beginning
The decision of which incisor to be extracted de- (Figure 6), which is not favorable for space closure in
pends on several considerations, including the clear aligner treatment. Therefore, to reduce the
periodontal condition, restorability, mesiodistal total treatment time, we used sectional fixed appli-
width and the location of incisor.8 The lateral incisor ance to adjust axis of teeth #31, #42 before oral scan.
is usually the preferred tooth rather than central On the other hand, de-rotation of a cylindric tooth,
incisor, since the black triangle would be more such as canine and premolar, is the least predictable
obvious when extraction the central incisor.9 In this movement. Simon et al. reported an average

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CLEAR ALIGNER FOR PREMOLAR CROSSBITE 2021;33(2):68e76

accuracy of 37.5% for premolar de-rotation even experience and prevalence of malocclusion traits in an Ice-
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