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Treatment duration for impacted maxillary canines: A comparison between surgical exposure and conservative non-surgical orthodontic space opening Cover

Treatment duration for impacted maxillary canines: A comparison between surgical exposure and conservative non-surgical orthodontic space opening

Australasian Orthodontic Journal
Volume 41 (2025): Issue 1 (January 2025)
By: Phillip Kia Teng Goh,  Hien Nguyen and  Richard Olive  
Open Access
|Dec 2025

Figures & Tables

Figure 1.

OPG and reconstructed OPG measurements – linear and angular measures (1) α-angle (°): Angulation of the canine according to the angle formed by the long axis of the impacted maxillary canine, and a line bisecting the central incisor axes (2) β-angle (°): Angulation of the canine according to the angle formed by the long axis of the impacted maxillary canine, and the long axis of the adjacent lateral incisor. (3) Vertical (mm): Absolute distance from the occlusal plane, measured perpendicularly from the canine cusp tip to the occlusal plane (defined as the plane connecting the mesiobuccal cusp of the upper first permanent molar, and the disto-incisal edge of the upper central incisor on the same side). (4) Horizontal (mm): Absolute distance from the mid-sagittal plane, measured perpendicularly from the line bisecting the central incisor axes and the canine cusp tip.
OPG and reconstructed OPG measurements – linear and angular measures (1) α-angle (°): Angulation of the canine according to the angle formed by the long axis of the impacted maxillary canine, and a line bisecting the central incisor axes (2) β-angle (°): Angulation of the canine according to the angle formed by the long axis of the impacted maxillary canine, and the long axis of the adjacent lateral incisor. (3) Vertical (mm): Absolute distance from the occlusal plane, measured perpendicularly from the canine cusp tip to the occlusal plane (defined as the plane connecting the mesiobuccal cusp of the upper first permanent molar, and the disto-incisal edge of the upper central incisor on the same side). (4) Horizontal (mm): Absolute distance from the mid-sagittal plane, measured perpendicularly from the line bisecting the central incisor axes and the canine cusp tip.

Figure 2.

OPG and reconstructed OPG measurements – Sector and Vertical (KPG). Vertical (KPG): The vertical component of the KPG index categorises the perpendicular distance of the canine cusp tip to the occlusal plane, relative to the central incisor (after Kau, Pan, Gallerano et al. 2009).29 Grade 0: Canine cusp tip is in the proper vertical position. Grade 1: Cusp tip is in the coronal region. Grade 2: Cusp tip lies in a horizontal plane adjacent to the cervical third of the incisor root. Grade 3: Cusp tip lies in a horizontal plane adjacent to the middle third of the incisor root. Grade 4: Cusp tip lies in a horizontal plane adjacent to the apical third of the incisor root. Grade 5: Cusp tip is supra-apical to the incisor root. Sector: The sector classification categorises the horizontal displacement of the canine cusp tip, relative to the lateral incisor (after Lindauer et al. 1992’s modification28 to Ericson and Kurol’s original classification). Sector I: canine cusp tip is distal to the distal outline of the lateral incisor root. Sector II: canine cusp tip is mesial to the distal outline of the lateral incisor root, but distal to the long axis of the lateral incisor. Sector III: canine cusp tip is mesial to the long axis of the lateral incisor, but distal to the mesial outline of the lateral incisor root. Sector IV: canine cusp tip is mesial to the mesial outline of the lateral incisor root.
OPG and reconstructed OPG measurements – Sector and Vertical (KPG). Vertical (KPG): The vertical component of the KPG index categorises the perpendicular distance of the canine cusp tip to the occlusal plane, relative to the central incisor (after Kau, Pan, Gallerano et al. 2009).29 Grade 0: Canine cusp tip is in the proper vertical position. Grade 1: Cusp tip is in the coronal region. Grade 2: Cusp tip lies in a horizontal plane adjacent to the cervical third of the incisor root. Grade 3: Cusp tip lies in a horizontal plane adjacent to the middle third of the incisor root. Grade 4: Cusp tip lies in a horizontal plane adjacent to the apical third of the incisor root. Grade 5: Cusp tip is supra-apical to the incisor root. Sector: The sector classification categorises the horizontal displacement of the canine cusp tip, relative to the lateral incisor (after Lindauer et al. 1992’s modification28 to Ericson and Kurol’s original classification). Sector I: canine cusp tip is distal to the distal outline of the lateral incisor root. Sector II: canine cusp tip is mesial to the distal outline of the lateral incisor root, but distal to the long axis of the lateral incisor. Sector III: canine cusp tip is mesial to the long axis of the lateral incisor, but distal to the mesial outline of the lateral incisor root. Sector IV: canine cusp tip is mesial to the mesial outline of the lateral incisor root.

Figure 3.

Empirical cumulative distribution function with Dvoretzky-Kief-er-Wolfowitz-Massart simultaneous confidence bounds, demonstrating the treatment times for patients treated with an impacted canine (blue) and without an impacted canine (red).
Empirical cumulative distribution function with Dvoretzky-Kief-er-Wolfowitz-Massart simultaneous confidence bounds, demonstrating the treatment times for patients treated with an impacted canine (blue) and without an impacted canine (red).

Figure 4.

Empirical cumulative distribution function with Dvoretzky-Kief-er-Wolfowitz-Massart simultaneous confidence bounds, demonstrating the treatment times for patients treated with orthodontic space opening alone (red), or surgical exposure (either from the outset or after initial orthodontic space opening – blue).
Empirical cumulative distribution function with Dvoretzky-Kief-er-Wolfowitz-Massart simultaneous confidence bounds, demonstrating the treatment times for patients treated with orthodontic space opening alone (red), or surgical exposure (either from the outset or after initial orthodontic space opening – blue).

Effect of site of canine impaction on treatment time, as compared to controls without an impacted canine

EstimateSth. Errort valuep-value
(Intercept)120.02128.7424.1765.868x10−05 ***
Age-2.1662.010-1.0770.284
Sex5.2047.5470.6900.492
Palatal site43.5298.8564.9153.030x10−06 ***
Labial/mid-alveolar site32.1159.9143.2390.002 **

Pre-treatment characteristics of patients with an impacted canine (palatal or labial/mid-alveolar), stratified according to the requirement for surgical exposure

Surgical exposure (from outset, or after orthodontics)Orthodontics only
Characteristicn%n%
Age2414.5 (1.3)a4913.0 (1.5)a
Sex
 Male6251224
 Female18753776
Multiple sites
 Unilateral17713878
 Bilateral7291122
Sitec
 Palatal24462854
 Labial/Mid-alveolar0021100
Treatment timeb136.00 (113.04, 154.82)128.86 (102.86, 153.14)

Analysis of multicollinearity

VariableGeneralised VIFDfGVIF^(1/(2*Df))
Demographic factors
 Age1.40211.184
 Sex1.25811.122
Treatment factors
 Unilateral/bilateral impaction1.26811.126
 Side1.26411.124
 Site2.24211.497
 Treatment modality3.36721.355
Radiographic factors
 Sector9.29631.450
 Vertical (KPG)3.63231.240
 α-angle (°)10.04813.170
 β-angle (°)9.55913.092
 Vertical (mm)3.68011.918
 Horizontal (mm)5.15112.270

Pre-treatment characteristics of patients with impacted canines, and patients without impacted canines (controls)

CharacteristicImpacted canine patientsNon-impacted canine controls
n7345
Agea13.5 (1.6)13.3 (1.9)
Sex
  Male18 (25%)12 (27%)
  Female55 (75%)33 (73%)
  Overall treatment timeb129 (109, 154)77 (72, 105)

Intra-examiner reliability

VariableEstimate95% CI
Sector-0.087-0.236, 0.062
Vertical (KPG)0.000-0.153, 0.153
α-angle (°)-0.374-0.983, 0.236
β-angle (°)0.109-0.966, 1.183
Vertical (mm)0.070-0.077, 0.216
Horizontal (mm)0.052-0.099, 0.204

Pre-treatment predictors of overall treatment time

VariableEstimateSth. Errort valuep-value
(Intercept)134.37151.5452.6070.012 *
Demographic factors
 Age-2.0443.022-0.6760.502
 Sex-0.29210.692-0.0270.978
Treatment factors
 Bilateral impaction15.46911.9531.2940.201
 Side-0.8138.391-0.0970.923
 Site-4.42515.681-0.2820.779
 Treatment modality
  S-32.34317.217-1.8790.066.
  OT + S-17.26915.502-1.1140.270
Radiographic factors
 Sector
  II1.43712.3520.1160.908
  III-7.78614.047-0.5540.582
  IV-5.05619.467-0.2600.796
 Vertical (KPG)
  235.90413.7822.6050.012*
  327.97624.0941.1610.251
  443.92230.2181.4540.152
 α-angle (°)-0.1430.714-0.2010.842
 β-angle (°)0.0920.6890.1330.894
 Vertical (mm)2.3912.6030.9180.363
 Horizontal (mm)-2.9592.270-1.3040.198

Pre-treatment predictors for the need for surgical exposure of an impacted canine

VariableEstimateSth. Errorz valuep-value
(Intercept)-12.3438.020-1.5390.124
Demographic factors
 Age0.5510.3251.6960.090.
 Sex2.2491.4921.5070.132
Treatment factors
 Bilateral impaction0.0600.9510.0630.950
 Side1.5001.4931.0050.315
Radiographic factors
 Sector IV3.2151.7181.8710.061.
 Vertical (KPG) 3-0.4470.997-0.4480.654
 α-angle (°)0.0320.0820.3900.697
 β-angle (°)0.0260.0810.3260.745
 Vertical (mm)-0.0710.285-0.2500.803
 Horizontal (mm)0.1410.3390.4180.676

Pre-treatment characteristics of patients with a palatally impacted canine, stratified according to the requirement for surgical exposure

Surgical exposure (from outset, or after orthodontics)Orthodontics only
Characteristicn%n%
Age2414.5 (1.3)a2813.3 (1.6)a
Sex
 Male625518
 Female18752382
Multiple sites
 Unilateral17712279
 Bilateral729621
Sectorc
 I002100
 II0013100
 III433867
 IV2080520
Vertical (KPG)c
 1004100
 214412059
 3764436
 4310000
α-angle (°)a45.36 (12.21)25.08 (12.60)
β-angle (°)a53.11 (12.03)35.36 (12.57)
Vertical (mm)a15.39 (2.82)12.69 (3.05)
Horizontal (mm)a5.55 (3.45)10.21 (3.16)
Treatment timeb136.00 (113.04, 154.82)129.07 (112.25, 157.18)

Pre-treatment characteristics of patients with impacted canines

Impacted canine patients
Characteristicn%
 Treatment factors
  Multiple sites
   Unilateral impaction5575
   Bilateral impaction1825
  Right sided impaction3649
  Site
   Palatal5271
   Labial/mid-alveolar2129
  Treatment modality
   Orthodontic space opening (OT)4967
   Surgery from outset (S)1115
   Orthodontic space opening, mid-treatment surgery (OT + S)1318
Radiographic factors
  Sector
   I1419
   II2027
   III1317
   IV2635
  Vertical (KPG)
   1912
   24663
   31419
   445
 α-angle (°)a30.66 (17.22)
 β-angle (°)a40.04 (16.42)
 Vertical (mm)a,b14.01 (3.40)
 Horizontal (mm)a,b8.70 (4.46)
DOI: https://doi.org/10.2478/aoj-2025-0038 | Journal eISSN: 2207-7480 | Journal ISSN: 2207-7472
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Language: English
Page range: 392 - 405
Submitted on: Aug 1, 2024
|
Accepted on: Nov 1, 2025
|
Published on: Dec 26, 2025
Published by: Australian Society of Orthodontists Inc.
In partnership with: Paradigm Publishing Services
Publication frequency: 1 issue per year
Related subjects:
Medicine,
Basic medical science,
Basic medical science, other

© 2025 Phillip Kia Teng Goh, Hien Nguyen, Richard Olive, published by Australian Society of Orthodontists Inc.
This work is licensed under the Creative Commons Attribution 4.0 License.

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