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A randomized clinical trial to compare the effectiveness of canine lacebacks with reference to canine tip

¹ University Dental Hospital of Manchester, UK
² St Anne’s Dental Clinic, Lytham St. Anne’s, UK
³ Union St. Orthodontic Practice, Oldham, UK
⁴ Chesterfield Royal Hospital, UK
⁵ University Dental Hospital of Manchester, UK

Dr N. A. Mandall, Orthodontic Unit, Department of Dental Medicine and Surgery, University Dental Hospital of Manchester, Higher Cambridge Street, Manchester M15 6FH, UK. Email: Nicky{at}fs1.den.man.ac.uk.

Abstract

Aim: To assess the effectiveness of canine lacebacks on the proclination of the upper incisors with reference to pre-treatment canine tip.

Study design: Randomized clinical trial.

Sample: Patients receiving upper and lower fixed appliances attending the orthodontic departments of five orthodontic treatment providers. Sixteen patients received canine lacebacks as part of their treatment and 19 patients did not have canine lacebacks.

Method: Patients were randomly allocated to receive canine lacebacks or not receive canine lacebacks. Upper study models were collected at the initial archwire placement and then when the working 0.019 x 0.025-inch stainless steel archwire was placed. The start canine angulation, change in upper incisor proclination/overjet, and any mesial movement of the upper first permanent molars during levelling and aligning was measured with a reflex metrograph.

Statistics: The effect of the use of canine lacebacks on upper incisor proclination and mesial molar movement was assessed using Student t-tests. Regression analysis was used to evaluate any effect of the initial angulation of the canine.

Results: A mean incisor retroclination of 0.5 mm was observed in the canine lacebacks compared with a mean proclination of 0.36 mm when canine lacebacks were not used (P = 0.025). There was no statistically significant difference between groups for mesial movement of upper first molars (P = 0.99). If the canine was more distally inclined at the start of treatment, the incisors was more likely to procline, regardless of whether or not canine lacebacks were used (P = 0.027).

Conclusions: The effect of canine lacebacks on preventing upper incisor proclination at the start of treatment is in the order of 1 mm and their effect on mesial molar movement is insignificant. Canines lacebacks have similar effects that are independent of pre-treatment canine angulation.

Key words: Canine lacebacks, upper incisor proclination, overjet, canine tip, randomized clinical trial

Introduction

The purpose of this study was to compare the effectiveness of canine lacebacks on upper incisor proclination, taking into account the tip of the upper canine at the start of treatment.

One problem that is encountered clinically, when using edgewise appliances is that the incisor may procline during the levelling and aligning phase. Clinical experience suggests that this is associated with the mesial crown tip that is built into the canine bracket, which is exacerbated by any pre-treatment tip of the canine.¹

One method of minimizing this problem is the use of a steel ligature between the canine and the first molar, this is called a laceback. In theory, the laceback will hold the canine crown back and, as a result, the canine root should tip distally as the tip in the bracket is expressed. Despite being a commonly used procedure, a search of the published literature reveals that this has never been examined using a prospective randomized clinical trial.

Therefore, we aimed to investigate the following questions:

1. What are the effects of canine lacebacks on upper incisor proclination?
   
2. Are canine lacebacks effective for all patients or just when the canine tooth is distally tipped?
   

As a result we tested the following null hypothesis.

1. Canine lacebacks do not have an effect on upper incisor proclination.
   
2. The effects of canine lacebacks are not influenced by pre-treatment canine angulation.
   

Sample

The sample size for each group of patients was calculated as n = 11 based on an alpha significance level of 0.05 and a beta of 0.1. This gave a 90 per cent power to detect a difference of 3 mm (±2 mm) of change in overjet during levelling, and aligning between the canine lacebacks groups and control.

The sample of patients was obtained from patients attending for orthodontic treatment at five orthodontic treatment providers. The following inclusion criteria were applied:

• Age 10–16 years at start of treatment.
  
• Premolar extraction cases only
  
• Upper and lower pre-adjusted edgewise appliance (Roth prescription 022 slot)
  
• Upper and lower permanent canines present and erupted
  
• Patient and parent written consent.
  

Ethical approval
The project was approved by the relevant ethical committees and all patients were treated according to the Declaration of Helsinki.²

Random allocation method
Randomization was carried out by throwing an unweighted dice. A restricted randomization method was used in blocks of 12 to ensure that equal numbers of patients were allocated to each of the two groups. The treatment allocation was then concealed in envelopes labelled with the study identification number.

When the patient was consented to enter the study and registered, a telephone call was made to research assistant, who then revealed whether the patient (the unit of randomization) would or would not receive canine lacebacks. During the trial, the operator could not be blind to whether canine lacebacks were used. However, the examiner carrying out the model outcome measurements did not know whether canine lacebacks were used or not.

Interventions and their timing
The planned interventions were placement of canine lacebacks in the test group and no canine lacebacks in the control group. All patients were therefore treated identically, apart from the named interventions according to the following protocol:

• 0.009-inch ligature wire was used for all canine lacebacks, placed from the hook on the first permanent molar band to the permanent canine bracket in a figure of eight in each quadrant.
  
• Archwire sequence 016-inch NiTi, 0.018 x 0.025-inch NiTi, 0.019 x 0.025-inch stainless steel.
  
• Canine lacebacks were adjusted as necessary at each appointment, so that there was enough tension in the ligature wire but the laceback was passive. The canine laceback was replaced if broken.
  

Outcome measures
The outcome measures to be assessed in the trial were change in proclination of the upper incisors and any mesial movement (loss of anchorage) of the upper first permanent molars.

Patient records
An upper study model was collected at the initial archwire placement and again when the 0.019 x 0.025-inch stainless steel archwire was placed.

Measurement method
Measurements were recorded using a reflex metrograph.³ This is a three-dimensional plotter. The principle of the reflex metrograph is that a tiny moveable light is adjusted to coincide with a point on the model, and a computer programme calculates distances, angles, and angles between planes. The measurements that were recorded were:

1. A lateral point on a right and left palatal rugae, which were joined to construct a rugae line going across the arch.
   
2. The upper incisor proclination was measured as the distance perpendicular from the rugae line to the most prominent incisal edge (Figure 1).
   
3. The right and left molar position was measured as the distance perpendicular from the rugae line to the buccal grooves of the first molars.
   
4. The start canine tip was assessed by measuring the angle between a line of best fit of the right and left upper occlusal plane, and the long axis of the right and left canine, respectively.
   

View larger version (30K): [in this window] [in a new window]   Fig. 1 Profile of a randomized clinical trial to evaluate the effect of canine lacebacks on upper incisor proclination / overjet change during initial levelling and aligning.

Method error
Observer bias was reduced by ensuring that the examiner was blind to whether the patient had received canine lacebacks or not. All models were measured in a random order so that the same patient’s start and completion of trial models were not measured consecutively.

Random error may have occurred or error in locating the measurement landmarks. This was addressed by taking each measurement three times and calculating an average. The error associated with the alginate impression technique and model preparation has been shown to have a 97 per cent coefficient of reliability.⁶

Examiner calibration and reliability
The examiner was calibrated for the reflex metrograph using four metal calibration cubes of different sizes. The exact measurements of the cubes were determined by the engineering department, University of Manchester, who constructed them. Reliability of the measurements was assessed by re-measuring all the study models at least 1 week later.

Statistics
The following data were analysed with the Student t-test.

• Examiner calibration
  
• Assessment of pre-treatment equivalence.
  
• Comparison of the change in upper incisor proclination and mesial movement of upper first permanent molars between the canine lacebacks group and control group.
  
• Comparison of patients who completed the study and drop-outs.
  

Intra-class correlation coefficients were used to assess intra-examiner reliability.

Multiple linear regression analysis was used to assess the effect of canine lacebacks and canine tip (and any interaction between these independent variables) on the change in overjet (dependent variable).

Results

Examiner calibration and reliability
Table 1 contains data on examiner calibration for the calibration blocks and Table 2 shows reliability for the repeated measurements of the study casts. This reveals that adequate levels of calibration and reliability were achieved.

The mean patient age at the start of the trial was 13.7 years (SD = 1.8) and the sample consisted of 13 boys and 22 girls. The malocclusion types consisted of incisor Class I (n = 15), Class II division 1 (n = 14), Class II division 2 (n = 4) and Class III (n = 2). The mean change in upper incisor proclination was an increase of 0.36 mm (SD = 1.1 mm) when canine lacebacks were not used and a decrease of 0.50 mm (SD = 1.1 mm) when canine lacebacks were used.

Table 3 shows data on changes incisor proclination and mean mesial movement of upper first molars. Data analysis revealed that the use of lacebacks resulted in a statistically significant reduction in incisor proclination (P = 0.025), but had no statistically significant effect on mesial molar movement (P = 0.99).

Discussion

This was the first randomized clinical trial of the effects of canine lacebacks. As a result, there is no relevant literature to compare with the results of this study. Nevertheless, we can conclude that canine lacebacks have an effect and they cause some retroclination of upper incisors and prevent increase in overjet during the initial aligning phase of Edgewise fixed appliance treatment. However, it should be emphasized that this effect is small and may not be of clinical significance. Furthermore, if the canine was distally tipped, the overjet was still likely to increase regardless of the use of canine lacebacks.

We should consider if the findings of this study have implications for clinical practice. When an operator interprets the results of a clinical trial they need to consider if the benefits of an intervention outweigh the risks and costs of using that intervention. Certainly, placing canine lacebacks is an easy procedure that does not carry any risk to the patient, apart from occasional soft tissue trauma. However, the benefits do not appear to be worthwhile. As a result, we can suggest from our findings that upper canine lacebacks are not of benefit, as a routine procedure, even if the canines are distally angulated.

Deficiencies of this investigation
Ideally, we would have liked to measure the effects of lacebacks on the lower arch, in addition to the upper dentition. However, there are no points in the mandible that we can use as fiducial points. The only alternative would be to use cephalograms; however, this is unlikely to gain ethical committee approval, as the additional radiation exposure could not be justified.

The sample size calculation was based on an expected difference in overjet of 3 mm between the test and control groups. In the absence of published literature on which to base our calculation, a value of 3 mm was chosen to reflect what might be a clinically significant effect of canine lacebacks. Since the study detected a statistically significant effect of lacebacks around 1 mm, this suggests that the sample size had enough power to detect a difference of less than 3 mm between groups. However, as we previously suggested, a 1 mm effect on overjet may not be clinically significant.

Conclusions

The effect of canine lacebacks on preventing an increase in upper incisor proclination at the start of treatment is in the order of 1 mm and their effect on mesial molar movement is insignificant. Canines lacebacks are similarly effective for patients with mesially inclined, upright or distally angulated upper canines.

Acknowledgments

Dr D. Bearn for his help in writing the reflex metrograph programme.

References

1 McClaughlin R. Chapter 2 In Orthodontic Treatment Mechanics and the Pre-adjusted Appliance. Wolfe 1993.

2 World Health Organization. Declaration of Helsinki. Br Med J 1996; 313: 1448–9.[Free Full Text]

3 Butcher G. The reflex optical plotter. Br Dent J 1981; 151: 304.[CrossRef][Medline]

4 Van der Linden F. Changes in the position of posterior teeth in relation to rugae points. Am J of Orthod 1978; 74: 142–61.

5 Hoggan BR, Sadowsky C. The use of palatal rugae for the assessment of antero-posterior tooth movements. Am J Orthod Dentofacial Orthop 2001; 119: 482–8.[CrossRef][Medline]

6 O’Brien KD, Lewis DH, Shaw WC, Combe E. A clinical trial of aligning archwires. Eur J Orthod 1990; 12: 380–4.[Abstract/Free Full Text]

Received June 5, 2002; accepted November 23, 2001

This article has been cited by other articles:

				B. S. Khambay, S. McHugh, and D. T. Millett Magnitude and reproducibility of forces generated by clinicians during laceback placement J. Orthod., December 1, 2006; 33(4): 270 - 275. [Abstract] [Full Text] [PDF]

				R. Irvine, S. Power, and F. McDonald The effectiveness of laceback ligatures: A randomized controlled clinical trial J. Orthod., December 1, 2004; 31(4): 303 - 311. [Abstract] [Full Text] [PDF]

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