1. external root resorption during orthodontic - vn

So sánh ngoại tiêu cuống ở răng đã điều trị tủy và răng đối bên trong chỉnh nha

J. M. Llamas-Carreras1, A. Amarilla1, E. Solano1, E. Velasco-Ortega2, L. Rodrı´guez-Varo3 & J. J. Segura-Egea4

Khoa chỉnh nha 1; 2Nha khoa toàn diện; 3Nha chu; và 4Nội nha, Trường RHM, Đại học Seville, Seville, Spain

Llamas-Carreras JM, Amarilla A, Solano E, VelascoOrtega E, Rodrı

´guez-Varo L, Segura-Egea JJ. So sánh ngoại tiêu cuống ở răng đã

điều trị tủy và răng đối bên trong chỉnh nha . Tạp chí nha khoa quốc

tếl, 43, 654–662, 2010.

Tóm tắt

Mục tiêu: Xác định ngoại tiêu cuống (ERR) (hệ quả trong chỉnh nha) có tương đồng giữa răng đã điều trị tủy và răng vẫn còn tủy sống hay không.

Phương pháp nghiên cứu: Tham gia nghiên cứu có 77 bệnh nhân, tuổi trung bình 32.7 ± 10.7, đã có một răng điều trị tủy trước khi hoàn thành điều trị chỉnh nha có gắn band/mắc cài ít nhất 1 năm. Với mỗi bệnh nhân đều được chụp phim toàn cảnh kĩ thuật số trước và sau điều trị để xác định mức độ ngoại tiêu cuống (PRR), tính bằng tỉ lệ tiêu cuống trên răng đã điều trị so với răng đối bên vẫn còn tủy sống. Các phương pháp phân tích: Quy luật student, ttest, anova và hồi qui logistic được sử dụng để xác định ý nghĩa thống kê.

Kết quả PRR (mức độ ngoại tiêu cuống) là 1.00 ± 0.13, cho thấy rằng không có sự khác biệt mang ý nghĩa thống kê về mức độ tiêu cuống trên răng đã điều trị tủy so với răng đố bên ở tất cả bệnh nhân tham gia. Phân tích hồi qui logistic đa biến gợi ý rằng PRR tăng cao hơn ở nhóm răng cửa khi so sánh giữa các răng (P = 0.0014; tỉ suất chăng = 6.2885, C.I. 95% = 2.0–19.4), và cao hơn ở phụ nữ khi so sánh về giới (P = 0.0255; tỉ suất chăng = 4.2, C.I. 95% = 1.2–14.6). Kết luận: Không có sự khác biệt đáng kể giữa số lượng hay mức độ giữa răng đã điều trị tủy và răng đối bên vẫn còn tủy sống trong quá trình chỉnh nha.

Từ khóa: tiêu chóp chân răng, nội nha, chỉnh nha

Lời mở đầu

Tiêu cuống là sự mất mô răng (ví dụ xương hay ngà răng) do kết quả của quá trình odontoclastic (clastic: describes a type of rock consisting of broken pieces of other rock). Phân loại tiêu cuống theo vị trí so với bề mặt cuống gồm có ngoại tiêu và nội tiêu. Ngoại tiêu cuống (ERR) có thể phân loại tiếp gồm: tiêu bề mặt, tiêu viêm, tiêu thay thế, tiêu cổ răng, tiêu chóp thoáng qua (?) (transient apical breakdown) (Patel & Pitt Ford 2007).

Tiêu bề mặt (tiêu sữa chữa) là một loại của ERR gây nên trong quá trình phẫu thuật, do sang chấn cơ học hay lực ép quá mức từ răng ngầm hay u (Andreasen et al. 1993). Bề mặt bị tổn thương sẽ bị loại bỏ bởi đại thực bào và TB hủy xương theo sau là quá trình sửa chữa hình thành nên xương răng mới và dây chằng nha chu (PDL) (Andreasen & Andreasen 2007).

ERR thường xuyên xảy ra sau những tổn thương mạn tính tác động lên PDL như quá trình chỉnh nha, sang chấn khớp cắn, sức ép từ các nang phát triển/u hạt quanh cuống và răng mọc sai vị trí (Andreasen 1985). Khi những yếu tố này được loại bỏ, quá trình sửa chữa sẽ bắt đầu, đây là điển hình của quá trình tiêu sửa chữa When the trauma and/or pressure is stopped, spontaneous healing takes place, which is the typical feature of repair-related resorption (Andreasen et al. 1993).

Sự di chuyển răng trong chỉnh nha dựa trên việc áp dụng lực làm tái cấu trúc PDL và xương ổ răng. Đặc điểm mô học đặc trưng của quá trình này là tiêu PDL ở phía nén cùng với việc hình thành vùng không tế bào ở đây do sự hoạt động của hủy cốt bào làm tiêu xương ổ răng lân cận, phía căng có sự bồi xương của tạo cốt bào (Abuabara 2007). Thay đổi cục bộ do lực chỉnh nha gây nên có tất cả những đặc điểm của viêm: sưng, nóng, đỏ, đau và suy giảm chức năng (Stedman 1982). Quá trình viêm này tuy rất cần thiết cho sự di chuyển răng nhưng cũng đồng thời khởi động quá trình tiêu cuống (Bosshardt et al. 1998). Yếu tố có vẻ kích hoạt sự tiêu cuống cũng như tiêu xương là các cytokines. TB miễn dịch thoái ra khỏi mao mạch vào vùng PDL sau đó tương tác với các tế bào tại chỗ bằng cách sản xuất một loại các phân tử tín hiệu (Ja¨ger et al. 2005). Mô khoáng hóa bị bộc lộ sẽ bị hủy cốt bào đi

International Endodontic Journal, 43, 654–662, 2010 ª 2010 International Endodontic Journal 654

Orthodontics and external root resorption Llamas-Carreras et al.

tới, khởi đầu quá trình tiêu. Tuy nhiên, nếu không có sự kích thích liên tục từ các tế bào này (do lực chỉnh nha) thì quá trình này sẽ kết thúc một cách tự nhiên.

ERR là vấn đề liên quan đến quá trình chỉnh nha và có thể xảy ra ở giai đoạn đầu của quá trình điều trị (Abuabara 2007). Tiêu cuống do chỉnh nha được xếp vào tiêu bề mặt hay tiêu viêm thoáng qua (Andreasen & Andreasen 2007). Về hình thái LS và trên XQ, đặc điểm tiêu cuống này là từ hơi cùn hoặc tròn cuống cho đến tiêu chóp lớn (Hamilton & Gutmann 1999).

Mức độ ERR khác nhau ở các báo cáo, giá trị trung bình trong khoảng từ 0.5 - emm (Hamilton & Gutmann 1999). Mirabella & A˚ rtun (1995) báo cáo tần số tiêu chóp nặng từ 5 – 18%. Nghiên cứu của Killiany (1999) cho thấy tiêu cuống > 3mm có tần số 30%, còn >5mm thì tần số là 5%

Nguyên nhân cụ thể của ERR trong quá trình chỉnh nha chưa được hiểu rõ, nhưng nó thường liên quan đến những lực lớn, lực ấn hoặc lực nghiêng (Kaley & Phillips 1991, Vardimon et al. 1991). Các yếu tố liên quan tới ERR có thể được chia thành yếu tố cơ học và sinh học (Brezniak & Wasserstein 1993). Sau đây lực cơ học: The following are amongst the mechanical factors: extensive tooth movement, root torque and intrusive forces, movement type, orthodontic force magnitude, duration and type of force (Harris et al. 1997). The biological factors include the following: genetic susceptibility, systemic factors (hormone unbalance), teeth agenesis and medication intake (Brezniak & Wasserstein 1993, Harris et al. 1997, Levander et al. 1998). It is therefore not surprising to find terms such as individual susceptibility, genetics, and systemic factors being discussed when damage is evident after otherwise successful orthodontic treatment (Owman-Moll et al. 1995, Killiany 1999). Levander & Malmgren (1988) indicated that teeth with blunt or pipette-shaped roots of maxillary central incisors were at greater risk for ERR than teeth with normal root form.

With a multitude of studies identifying the role of orthodontics for ERR on teeth with vital pulps, the issue of root filled teeth and ERR is important (Hamilton & Gutmann 1999). Is the extent of ERR, that may occur during orthodontic treatment, the same on teeth with vital pulps as root filled teeth? In animal models neither Mattison et al. (1984) nor Mah et al. (1996) found significant differences between ERR of root filled and teeth with vital pulps when both were subjected to orthodontic forces. On the contrary, Spurrier et al. (1990) studied 43 patients who had one or more root filled teeth treated teeth before

orthodontic treatment and who exhibited signs of apical root resorption after treatment. The contralateral incisors with vital pulps served as controls. Results showed that incisors with vital pulps resorbed to a significantly greater degree than incisors that had been root filled. Finally, Mirabella & A˚ rtun (1995), in a sample of 39 pairs of contralateral teeth with and without root canal treatment in 36 patients, found that there was significantly less resorption in root filled teeth.

The purpose of this study was to compare, in the same patient, the ERR associated with orthodontic treatment in teeth with vital pulps and contralateral teeth with root filling. The null hypothesis was that there is no difference between root resorption in root filled teeth and their control teeth with vital pulps.

Materials and methods

Sample

The subjects for this study were 77 patients (21 men and 56 women), aged 32.7 ± 10.7 years, who had one root filled tooth before orthodontic treatment. The scientific committee of the Dental Faculty approved the study, and all the patients gave written informed consent. Of the 77 patients selected, 36.4% (28) had Class I, 44.2% (34) had Class II (24 Division 1, 10 Division 2) and 19.5% (15) Class 3 occlusions.

Inclusion criteria

The patients included in this study had completed multiband/bracket orthodontic therapy, with duration of active treatment exceeding 1 year (26.8 ± 8.9 months). In order that a comparison of the amount and severity of root resorption could be made, each patient selected had some degree of resorption evident by the end of active treatment. All endodontic therapy had been completed before orthodontic band placement. The contralateral tooth had never had invasive pulp therapy, although


Llamas-Carreras et al. Orthodontics and external root resorption

the extent to which either tooth may have been traumatized was not known.

Exclusion criteria

Teeth with fractured or otherwise mutilated roots and teeth with radiological signs of periapical pathosis in the pre-treatment radiography (Periapical Index score of 3, 4 or 5) (Ørstavik et al. 1986) were excluded. Patients with obvious incisal-edge changes were also excluded from the study. Pre-treatment and posttreatment orthodontic study casts were evaluated to ensure incisal integrity throughout the active treatment period.

Radiographic examination and evaluation

For each patient, digital panoramic radiographs, taken before and after orthodontic treatment, were used. Two trained radiology assistants using a digital orthopantomograph machine (Promax, Planmeca, class 1, type B, 80 KHz; Planmeca, Helsinki, Finland) took the panoramic radiographs. The same radiology assistant and panoramic machine were used for the two radiographs of each patient. A mirror and horizontal and vertical light guides, incorporated into the machine, facilitated standardization of head positioning. Images were obtained using the Dimaxis Pro 3.1.1 program (Planmeca Group). In all cases radiographs were of good quality, showing the entire corono-apical length of measured teeth with the apex clearly defined. Digital panoramic images were displayed in a 17¢¢ Plug-andPlay model monitor using a NVIDIA Riva TNT 2 model 64 graphic card with 32 bit quality colour and 1280 · 1024 pixels resolution (120 ppp) in a room with subdued light.

Measurements were made before and after orthodontic treatment using Adobe Photoshop CS software. The reference points and lines for measurements are shown in Fig. 1. First, radiographs were standardized by measuring the greatest distance from incisal/oclusal edge to cementoenamel junction on each patients in pre-treatment and post-treatment radiographs. Thus, crown lengths in

the initial and final radiographs were calculated in the root filled tooth (CEi and CEf) and in its contralateral tooth with vital pulp (CVi and CVf) (Fig. 2). Secondly, root lengths in the initial and final radiographs were also calculated in the root filled tooth (REi and REf) and its contralateral tooth with vital pulp (RVi and RVf) measuring the distance from cementoenamel junction to the line between both root apexes.

From these values, tables were constructed for resorption in millimetres. To allow intrapatient standardization, root resorptions in the root filled tooth (RRE) and contralateral tooth with vital pulp ( RRV ) were calculated (Fig. 3). Then, the proportion of root resorption (PRR) for each patient was calculated as follows: PRR = RRE/RRV.

Statistical analysis

Student’s t-test, anova and logistic regression analysis were applied. The level for statistical significance was set at P < 0.05.

Error analysis

The same clinician, an experienced orthodontist ( LL-C), performed all measurements. To assess intra-examiner reliability, 10 randomly selected patient radiographs were measured on three separate occasions at 1- week intervals to determine the reliability (j = 0.82). Variance from original measurements ranged from 0.00 to 0.33 mm. The mean error was 0.27 mm for the measurement of the root filled teeth and 0.15 mm for the control measurement.

Results

The characteristics of the patients, orthodontic treatments, proportion of root resorption (PRR), and mean and standard deviation of the total sample are listed in Table 1. Thirty-seven of the 77 (48.0%) exhibited aFigure 1 Reference points and lines for measurements.

ª 2010 International Endodontic Journal International Endodontic Journal, 43, 654–662, 2010 656


Figure 2 Calculation of the crown and root lengths in the initial and final radiographs in the root filled tooth (crown: CEi and CEf, root: REi and REf) and its contralateral vital tooth ( crown :

CVi and CVf, root: RVi and RVf).

INITIALS REFERENCE POINTS FINAL REFERENCE POINTS

Ei1 Incisal/oclusal edge of RFT before orthodontic treatment

Ef1 Incisal/oclusal edge of RFT after orthodontic treatment

Ei2 Amelo-cemental junction of RFT before orthodontic treatment

Ef2 Amelo-cemental junction of RFT tooth after orthodontic treatment

Ei3 Line between root apices of RFT before orthodontic treatment

Ef3 Line between root apices of RFT after orthodontic treatment

Vi1 Incisal/oclusal edge of VCT tooth before orthodontic treatment

Vf1 Incisal/oclusal edge of VCT tooth after orthodontic treatment

Vi2 Amelo-cemental junction of VCT before orthodontic treatment

Vf2 Amelo-cemental junction of VCT after orthodontic treatment

Vi3 Line between root apices of VCT before orthodontic treatment

Vf3 Line between root apices of VCT after orthodontic treatment

RFT: root filled tooth. VCT: vital contralateral tooth.

Crown Endodontically initial (CEi) |Ei2 Ei1|

Root Endodontically initial (REi) |Ei3 Ei2|

Crown Endodontically final (CEf) |Ef2 Ef1|

Root Endodontically final (REf) |Ef3 Ef2|

Crown Vital initial (CVi) |Vi2 Vi1|

Root Vital initial (RVi) |Vi3 Vi2|

Crown Vital final (CVf) |Vf2 Vf1|

Root Vital final (RVf) |Vf3 Vf2|

CEi

RRE = – RRf ×

CEf

CVi

RRV = – RVf ×

CVf

Figure 3 Calculation of the standardized root resorption. RR endo, standardized root resorption in the root filled tooth; RR vital, standardized root resorption in the contralateral vital tooth.

PRR > 1, showing greater resorption of their root filled teeth than their contralateral control. In 36 patients (46.7%) the control teeth with vital pulps resorbed to a greater extent (P > 0.05). The mean and standard deviation of PRR were 1.00 ± 0.13, indicating that, in the total sample, there was no significant differences between the amounts of root resorption in the root filled teeth and its contralateral control teeth with vital pulps.

Sample distribution by tooth type is showed in Table 2. PRR was significantly higher in incisors compared to canines (P = 0.0061). Multivariate logistic regression was run with gender (0 = men; 1 = women), age (year), treatment length (months), type of treatment (0 = without extractions; 1 = with extractions), and tooth type (0 = not incisor; 1 = incisor) as independent

International Endodontic Journal, 43, 654–662, 2010 ª 2010 International Endodontic Journal

VCT

RFT

657

REi

RVi


explanatory variables, and ‘PRR’ (dichotomized: 0 = PRR < 1; 1 = PRR > 1) as the dependent variable (Table 3). The analysis suggested that tooth type (B coefficient = 1.8393; P = 0.0031) was a factor associated significantly with greater resorption of the root filled teeth than the controls. Gender (B coefficient = 1.0483; P = 0.0873) was marginally significant. Age (P = 0.4396), treatment length (P = 0.53.71) and treatment type (P = 0.8502) were not associated with PRR and were eliminated from the analysis. A refined multivariate logistic regression analysis including only tooth type and gender as explanatory variables(Table 4), suggested that PRR was significantly greater in incisors (P = 0.0014; odds ratio = 6.2885, C.I. 95% = 2.0–19.4), compared to other teeth, and in women (P = 0.0255; odds ratio = 4.2, C.I. 95% = 1.2–14.6), compared to men.

Discussion

In this study, pre- and post-treatment tooth lengths of the maxillary and mandibular teeth were measured on panoramic radiographs of 77 subjects. Previous studies have also used panoramic radiographs in assessing ERR during orthodontic movement (Brin et al. 2003, Armstrong et al. 2006, Pandis et al. 2008). In general, extra-oral radiographs are considered less accurate than periapical radiographs in studying the extent of

ERR. The use of panoramic films to measure pre- and post-treatment root resorption may overestimate (Sameshima & Asgarifar 2001) or underestimated (Dudic et al. 2009) the amount of root loss after orthodontic tooth movement. However, Katona (2006) questioned the validity of the periapical films in accurately depicting ERR because of errors from the variability in tooth shape.

It has been demonstrated that an important source of error associated with panoramic radiographs is head positioning with respect to tilting. Stramotas et al. (2002) concluded that linear measurements on panoramic radiographs taken at different times are sufficiently accurate if the occlusal plane is positioned similarly on the two occasions and the extent of tilting does not exceed 10. In this study, the same radiology assistant and panoramic machine were used for all radiographs, and a mirror, and

horizontal and vertical light guides, incorporated into the machine, facilitated standardization of head positioning. Moreover, the objective was to compare the ERR in both teeth groups rather than to determine the absolute values of root lost.

The measurement of root resorption in this study has been performed taking into account the length of the crown. Thus, root resorption was calculated as ‘standardized root resorption’, being a more accurate measure than those used in other studies ( Armstrong et al. 2006, Pandis et al. 2008).

This study revealed that, although in 48% of patients ERR in root filled teeth was greater than controls, in the total sample there were not significant differences between the amounts of root resorption in the root filled teeth and their contralateral teeth with vital pulps.

Root resorption occurring during orthodontic treatment was the same on teeth with vital pulps as on teeth with previous root canal treatment has been studied previously. Weiss (1969) reported no significant difference in the amount of root resorption between vital and non-vital teeth when both were subjected to orthodontic forces. However, the power of this study was low because the sample consisted of only eighteen patients who had completed orthodontic therapy. A sample of this size is usually considered too small for statistical significance.



Table 1 Characteristics of the patients and orthodontic treatments, and proportion of root resorption ( PRR )

Table 1 ( Continued )

Patient

Age

(year)

Gender

(M; F)

Treatment length (months)

Tooth type PRR

55 45 F 23 CI 1.08

56 27 F 16 PM 1.0857 34 F 24 M 1.0958 30 F 38 M 1.1059 43 F 42 LI 1.1160 27 F 22 M 1.1161 31 M 17 CI 1.1262 18 M 24 CI 1.1263 24 F 26 CI 1.1364 24 F 51 CI 1.1365 36 F 22 M 1.1466 17 F 26 M 1.1467 47 F 30 LI 1.1468 25 F 32 CI 1.1469 14 F 20 CI 1.1570 31 F 24 M 1.1771 10 M 40 CI 1.1772 24 F 51 LI 1.1973 14 M 27 CI 1.1974 52 M 22 LI 1.1975 37 F 19 CI 1.2076 47 F 25 LI 1.2277 33 F 18 LI 1.34Total 33 ± 11 21M/56F 27 ± 9 – 1.00 ± 0.13

CI, central incisor; CA, canine, M, molar, PM, premolar; LI, lateral incisor.

Wickwire et al. (1974) in a retrospective study reviewed 45 orthodontic patient case histories that contained 53 root filled teeth. They found that appeared to be greater radiographic evidence of root resorption in the root filled teeth compared to those with vital pulps. On the contrary, Spurrier et al. (1990) studied 43 patients who had one or more root filled teeth before orthodontic treatment and exhibited signs of apical root resorption after orthodontic treatment. In this study, contralateral incisors with vital pulps served as controls. The results showed that incisors with vital pulps resorbed to a significantly greater degree than incisors that had been root filled. Mirabella & A˚ rtun (1995) reported that there was significantly less resorption in root filled teeth in a sample of 39 pairs of teeth with and without endodontic treatment in 36 patients.

Huettner & Young (1955) evaluated the root structure of monkey teeth with both


Patient

Age

(year)

Gender

(M; F)

Treatment length (months)

Tooth type PRR1 32 M 34 CI 0.77

2 24 M 20 CI 0.793 16 M 33 CI 0.804 21 M 37 M 0.805 17 F 13 CI 0.816 46 F 37 CI 0.827 27 F 16 CA 0.828 41 F 30 CA 0.829 24 F 28 PM 0.85

10 31 F 22 CI 0.8611 30 F 38 CI 0.8612 41 F 30 CA 0.8713 49 F 12 CA 0.8714 33 F 20 M 0.8715 27 F 16 PM 0.8816 53 M 21 M 0.8817 19 F 25 PM 0.8918 40 F 46 M 0.8919 41 F 20 CA 0.8920 12 F 33 M 0.8921 43 F 41 M 0.9022 24 F 27 M 0.9023 24 F 25 PM 0.9024 16 M 29 M 0.9125 44 F 24 CA 0.9126 43 F 41 PM 0.9127 23 F 27 LI 0.9128 28 F 24 LI 0.9229 24 F 27 M 0.9230 38 M 22 M 0.9331 45 F 37 CA 0.9432 53 M 21 M 0.9533 42 F 13 CA 0.9634 26 F 16 M 0.9735 52 M 22 M 0.9736 41 F 30 PM 0.9837 30 M 21 CI 1.0038 30 M 21 LI 1.0039 27 F 22 M 1.0040 46 F 24 M 1.0041 39 F 29 CI 1.0242 38 M 22 LI 1.0343 39 F 29 LI 1.0344 47 F 29 CA 1.0345 39 F 29 CI 1.0346 38 M 22 CI 1.0347 34 F 24 PM 1.0448 37 F 19 LI 1.0549 27 F 26 M 1.0550 34 F 19 PM 1.0551 29 M 17 CI 1.0552 31 M 39 CI 1.0653 30 M 51 M 1.0654 45 F 22 M 1.07


vital and non-vital pulps (root canal treatment) following orthodontic movement and observed similar root resorption in both groups.

The results of this study are in accordance with previous studies carried out in animal models, such asOverall model fit: v2 = 14.0188; df = 2; P = 0.0009.

those of the in vivo study developed by Mattison et al. (1984) on cats showing no significant difference between ERR in root filled or in teeth with vital pulps when both were subjected to orthodontic forces. However, that study was an animal study carried out over a 4-month treatment period. This may have been too brief a time for significant differences to become apparent.

This study is also in agreement with the finding of Mah et al. (1996) evaluating the effectiveness of orthodontic forces in moving root filled teeth and the degree of ERR that may occur in the ferret animal model. These investigators found greater loss of cementum after tooth movement in root filled teeth than in teeth with pulps, but without significant differences in radiographic root length. The root filled teeth also showed more resorption lacunae than teeth with vital pulps, but the small difference in incidence between active (orthodontically) root filled teeth and inactive root filled teeth was not statistically significant. This suggests that the incidence of resorption lacunae may be related to non-vitality and probably the

presence of periradicular pathosis rather than orthodontic forces.

In this study, multivariate logistic regression analysis indicated that root resorption was significantly greater in root filled teeth compared to their control teeth with vital pulps in women (P = 0.0255; odds ratio = 4.2 , C.I. 95% = 1.2–14.6). On the contrary, Spurrier et al. (1990) reported that, when the sample was subdivided by gender, no significant difference in the amount of root resorption of the root filled teeth was evident, but the male patients exhibited a greater degree of change in the control teeth (P < 0.02). This different result could be attributed to the type of teeth included in the study: the study of Spurrier et al. only analyzed incisors but this study included all teeth types. Previous studies have reported inconclusive results. Phillips (1955) and Sameshima & Sinclair (2001) found no difference in the incidence or severity of resorption between male and female patients, but Newman (1975) found female patients to be more susceptible to ERR during orthodontic movement.

Multivariate logistic regression analysis also revealed that tooth type was an explanatory variable statistically associated with greater ERR in root filled teeth (P = 0.0014; odds ratio = 6.2885, C.I. 95% = 2.0 – 19.4). Thus, the PRR (resorption in root filled tooth/ resorption in


Table 2 Sample distribution by tooth type, age (years), gender (male/female), cause of root canal treatment (TI, tooth injury; TD, tooth decay), treatment length (months) and proportion of root resorption ( PRR )Tooth type Number (%) Age (year) Gender Cause Length* PRR

Incisor 35 (45.5) 31.0 ± 10.6 14/21 TI 27.5 ± 9.3 1.04 ± 0.14

Canine 9 (11.7) 41.9 ± 6.3** 0/9 TD 23.4 ± 8.7 0.90 ± 0.07Premolar 9 (11.7) 30.3 ± 8.2 0/9 TD 24.9 ± 7.8 0.95 ± 0.09Molar 24 (31.2) 32.7 ± 11.7 7/17 TD 27.6 ± 8.9 0.99 ± 0.10Total 77 (100) 32.7 ± 10.6 21/56 – 26.7 ± 8.8 1.00 ± 0.13

*P > 0.05; **P < 0.05.PRR: incisor vs canine: unpaired t-test (two-tailed) = P value equals 0.0061.PRR: incisor vs pre-molar: unpaired t-test (two-tailed) = P value equals 0.0751.

Table 3 Multivariate logistic regression analysis of the influence of the independent variables gender (0 = male; 1 = female), age (year), treatment length (months), type of treatment (0 = without extractions; 1 = with extractions), and tooth type (0 = not incisor; 1 = incisor) on the dependent variable ‘proportion of root resorption (PRR)’ (0 = PRR < 1; 1 = PRR > 1)

Independent variables B P Odds ratio

C.I. 95%

Inf. limit

C.I. 95 %

Sup. limit

Gender 1.0483 0.0873 2.8527 0.8577 9.4887

Age 0.0190 0.4396 1.0192 0.9713 1.0694Treatment length )0.0193 0.5371 0.9809 0.9225 1.0429Treatment type 0.1151 0.8502 1.1220 0.3398 3.7046Tooth type 1.8393 0.0031 6.2924 1.8625 21.2588

Overall model fit: v2 = 12.5987; df = 5; P = 0.0274.

Table 4 Multivariate logistic regression analysis of the influence of the independent variables gender (0 = male; 1 = female) and tooth type (0 = not incisor, 1 = incisor) on the dependent variable ‘proportion of root resorption (PRR)’ (0 = PRR < 1 ; 1 = PRR > 1)

Independent variables B P Odds ratio

C.I. 95%

Inf. limit

C.I. 95 %

Sup. limit

Gender 1.4279 0.0255 4.1701 1.1909 14.6014

Tooth type 1.8387 0.0014 6.2885 2.0364 19.4199


contralateral vital tooth) during orthodontic movement was greater in incisors compared to the others tooth types. Two considerations are relevant in relation to this result. (i) This result could be attributed to the greater amount of resorption that orthodontic movement causes in maxillary incisors, compared to other tooth types, as reported by Sameshima & Sinclair (2001). Remington et al. (1989) reported that the maxillary incisors underwent root resorption more frequently and to a greater degree than the rest of the teeth during orthodontic treatment. This could be because of their less root surface area. (ii) Moreover, the pathology that motivated the root canal treatment also could explain this result. In this study, all root filled incisors were treated endodontically because of dental injury: all incisors had been traumatized previously. On the contrary, all other teeth (canines, pre-molars and molars) were root filled teeth because of pulp/periapical pathosis as a consequence of tooth decay. Hamilton & Gutmann (1999) concluded that if a previously traumatized tooth exhibits resorption, there is a greater chance that orthodontic tooth movement will enhance the resorption process. If a tooth has been severely traumatized (intrusive luxation/avulsion), there may be a greater incidence of resorption with tooth movement. These two considerations explain the greater ERR in incisors that emphasize the significance of differences between non-vital and vital teeth.

Conclusions

There was no significant difference in the amount or severity of external root resorption during orthodontic movement between root filled teeth and their contralateral healthy controls. However, the PRR (resorption in root filled tooth/resorption in contralateral vital tooth) during orthodontic movement was greater in incisors compared to others tooth types.

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