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

Phillip Kia Teng Goh; Hien Nguyen; Richard Olive

doi:10.2478/aoj-2025-0038

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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

Table I.

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

Characteristic	Impacted canine patients	Non-impacted canine controls
n	73	45
Age^a	13.5 (1.6)	13.3 (1.9)
Sex
Male	18 (25%)	12 (27%)
Female	55 (75%)	33 (73%)
Overall treatment time^b	129 (109, 154)	77 (72, 105)

1a Presented as Mean (SD) in years,

1b Presented as Median (Q₁, Q₃) in weeks.

Table II.

Pre-treatment characteristics of patients with impacted canines

	Impacted canine patients
Characteristic	n	%
Treatment factors
Multiple sites
Unilateral impaction	55	75
Bilateral impaction	18	25
Right sided impaction	36	49
Site
Palatal	52	71
Labial/mid-alveolar	21	29
Treatment modality
Orthodontic space opening (OT)	49	67
Surgery from outset (S)	11	15
Orthodontic space opening, mid-treatment surgery (OT + S)	13	18
Radiographic factors
Sector
I	14	19
II	20	27
III	13	17
IV	26	35
Vertical (KPG)
1	9	12
2	46	63
3	14	19
4	4	5
α-angle (°)^a	30.66 (17.22)
β-angle (°)^a	40.04 (16.42)
Vertical (mm)^a,b	14.01 (3.40)
Horizontal (mm)^a,b	8.70 (4.46)

1a Presented as Mean (SD),

1b 23 patients had OPGs without an attached scale to control for magnification, and hence linear measurements presented in this table were only calculated from the remaining 50 patients.

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 – 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.

Table III.

Intra-examiner reliability

Variable	Estimate	95% 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

Table IV.

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

	Estimate	Sth. Error	t value	p-value
(Intercept)	120.021	28.742	4.176	5.868x10⁻⁰⁵ ***
Age	-2.166	2.010	-1.077	0.284
Sex	5.204	7.547	0.690	0.492
Palatal site	43.529	8.856	4.915	3.030x10⁻⁰⁶ ***
Labial/mid-alveolar site	32.115	9.914	3.239	0.002 **

1 Significance codes: 0

1*** 0.001

1** 0.01

1* 0.05 ‘.’ 0.1 ’ ’ 1.

1 The base classes for the regression model characterizing sex is female.

Table V.

Pre-treatment predictors of overall treatment time

Variable	Estimate	Sth. Error	t value	p-value
(Intercept)	134.371	51.545	2.607	0.012 *
Demographic factors
Age	-2.044	3.022	-0.676	0.502
Sex	-0.292	10.692	-0.027	0.978
Treatment factors
Bilateral impaction	15.469	11.953	1.294	0.201
Side	-0.813	8.391	-0.097	0.923
Site	-4.425	15.681	-0.282	0.779
Treatment modality
S	-32.343	17.217	-1.879	0.066.
OT + S	-17.269	15.502	-1.114	0.270
Radiographic factors
Sector
II	1.437	12.352	0.116	0.908
III	-7.786	14.047	-0.554	0.582
IV	-5.056	19.467	-0.260	0.796
Vertical (KPG)
2	35.904	13.782	2.605	0.012*
3	27.976	24.094	1.161	0.251
4	43.922	30.218	1.454	0.152
α-angle (°)	-0.143	0.714	-0.201	0.842
β-angle (°)	0.092	0.689	0.133	0.894
Vertical (mm)	2.391	2.603	0.918	0.363
Horizontal (mm)	-2.959	2.270	-1.304	0.198

1 Significance codes: 0

1*** 0.001

1** 0.01

1* 0.05 ‘.’ 0.1 ’ ’ 1.

1 The base classes for dummy variables characterizing sex, bilateral impaction, side, site, treatment modality, sector classification, and vertical (KPG) classification are as follows: female, unilateral, left-hand side, palatal, orthodontic space opening only, sector I classification, and vertical (KPG) I classification respectively.

Table VI.

Analysis of multicollinearity

Variable	Generalised VIF	Df	GVIF^(1/(2*Df))
Demographic factors
Age	1.402	1	1.184
Sex	1.258	1	1.122
Treatment factors
Unilateral/bilateral impaction	1.268	1	1.126
Side	1.264	1	1.124
Site	2.242	1	1.497
Treatment modality	3.367	2	1.355
Radiographic factors
Sector	9.296	3	1.450
Vertical (KPG)	3.632	3	1.240
α-angle (°)	10.048	1	3.170
β-angle (°)	9.559	1	3.092
Vertical (mm)	3.680	1	1.918
Horizontal (mm)	5.151	1	2.270

Table VII.

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
Characteristic	n	%	n	%
Age	24	14.5 (1.3)^a	49	13.0 (1.5)^a
Sex
Male	6	25	12	24
Female	18	75	37	76
Multiple sites
Unilateral	17	71	38	78
Bilateral	7	29	11	22
Site^c
Palatal	24	46	28	54
Labial/Mid-alveolar	0	0	21	100
Treatment time^b	136.00 (113.04, 154.82)		128.86 (102.86, 153.14)

1a Results presented as Mean (SD) in years,

1b Results presented as Median (Q₁, Q₃) in weeks,

1c Percentage presented across the row.

Table VIII.

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
Characteristic	n	%	n	%
Age	24	14.5 (1.3)^a	28	13.3 (1.6)^a
Sex
Male	6	25	5	18
Female	18	75	23	82
Multiple sites
Unilateral	17	71	22	79
Bilateral	7	29	6	21
Sector^c
I	0	0	2	100
II	0	0	13	100
III	4	33	8	67
IV	20	80	5	20
Vertical (KPG)^c
1	0	0	4	100
2	14	41	20	59
3	7	64	4	36
4	3	100	0	0
α-angle (°)^a	45.36 (12.21)		25.08 (12.60)
β-angle (°)^a	53.11 (12.03)		35.36 (12.57)
Vertical (mm)^a	15.39 (2.82)		12.69 (3.05)
Horizontal (mm)^a	5.55 (3.45)		10.21 (3.16)
Treatment time^b	136.00 (113.04, 154.82)		129.07 (112.25, 157.18)

1a Results presented as Mean (SD),

1b Results presented as Median (Q₁, Q₃),

1c Percentage presented across the row.

Table IX.

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

Variable	Estimate	Sth. Error	z value	p-value
(Intercept)	-12.343	8.020	-1.539	0.124
Demographic factors
Age	0.551	0.325	1.696	0.090.
Sex	2.249	1.492	1.507	0.132
Treatment factors
Bilateral impaction	0.060	0.951	0.063	0.950
Side	1.500	1.493	1.005	0.315
Radiographic factors
Sector IV	3.215	1.718	1.871	0.061.
Vertical (KPG) 3	-0.447	0.997	-0.448	0.654
α-angle (°)	0.032	0.082	0.390	0.697
β-angle (°)	0.026	0.081	0.326	0.745
Vertical (mm)	-0.071	0.285	-0.250	0.803
Horizontal (mm)	0.141	0.339	0.418	0.676

1 Analysis excludes those patients with a labial/mid-alveolar canine, or patients with a palatal canine located in sector I or II, or vertical (KPG) classification of 1 or 4.

1 Significance codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ’ ’ 1.

1 The base classes for dummy variables characterizing sex, bilateral impaction, side, sector, and vertical (KPG) are as follows: female, unilateral, left-hand side, sector III classification, and vertical (KPG) 2 classification respectively.

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).

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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.

Volume 41 (2025): Issue 1 (January 2025)

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

Figures & Tables

Table I.

Table II.

Figure 1.

Figure 2.

Table III.

Table IV.

Table V.

Table VI.

Table VII.

Table VIII.

Table IX.

Figure 3.

Figure 4.

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