| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
School of Dentistry, St Chad's Queensway, Birmingham. B4 6NN, UK
 |
Abstract |
|---|
 Top Abstract IntroductionAims of studyMethodsResultsDiscussionReferences |
|---|
Key words: Brackets, Recycling
|
Introduction |
|---|
|
TopAbstractIntroductionAims of studyMethodsResultsDiscussionReferences |
|---|
).
It is probable that the main impetus towards recycling is financial, since some straightwire
brackets
cost
more than £3.00 each. However, when recycled brackets are used in the mouths of
patients it is
crucial that the clinician has assurance that they are as good as new. This presents quite a
challenge
since new straightwire orthodontic brackets are manufactured to very tight specifications. The
definitive
`A' Company Straight-Wire® brackets (Opident Ltd, Butterfield Dental
Centre,
Acorn Business Park, Keighly Road, Skipton, North Yorkshire BD23 2UE, UK) are investment
cast
from plastic patterns. The mould leaves a small depression in each casting into which the slot is
milled in
a separate procedure. During manufacture an individual bracket may be examined up to seven
times.
Slot-to-base angle and slot wall parallelism are assessed optically, and slot size is checked using
`Go/No-Go' gauges. A tolerance level of 0.2-0.5 degrees is claimed for tip and
torque
angulations, and this has been supported by independent research (Tan, 1991). Less
than 1 in 1000 brackets sent to a recycling company has been found to have
manufacturing flaws (Matasa, 1990).
The tendency to require brackets of ever more complex shapes has lead to the replacement of milling by casting as a manufacturing technique, although slots may be milled into castings as a secondary operation as described above. Cast brackets are somewhat softer than those produced by milling from cold drawn steel and they are therefore more susceptible to damage during clinical usage.
Brackets may be damaged in several ways:
). ). Although such a high force might easily deform the
wings of a
bracket it
is more likely that a bonded bracket would be dislodged from the tooth. ). There is some evidence that commercial
recycling
may
increase the chances of bracket corrosion (Maijer and Smith, 1986). ) reported slot closure, base distortion, and damage
to
tie wings. Several types of instrument have been used to remove brackets from teeth at the end of treatment.
Bracket removing pliers (Figure 1), which apply a force across the
bracket
base
were used by 66 per
cent of American orthodontists in a survey by Gorelick (1979).
|
; Graber
and Vanardsdall, 1994; Zarrinnia et al., 1995). The
use
of pliers in this way inevitably
produces distortion of the bracket wings so that the
brackets are less suitable for recycling than those debonded using other methods.
Ligature cutters applied across the base of a bracket cause bending, and consequent fracture
within the
resin or at the resin/enamel interface. This method is considered by some to be the safest,
although it
has the disadvantage that the distorted bracket cannot be reused (Bennett et al.,
1984).
Others have expressed concern that enamel damage may be caused by the beaks of
ligature cutters used in this way (Oliver, 1988).
The Lift-Off Debonding Instrument (LODI; Figure 2) has a wire loop that
engages beneath a tie-wing
and applies a shear force when the handles are squeezed. This method has been considered to
produce
no damage and is recommended if recycling is a consideration (McGuinness, 1992).
|
|
Aims of study |
|---|
|
TopAbstractIntroductionAims of studyMethodsResultsDiscussionReferences |
|---|
|
Methods |
|---|
|
TopAbstractIntroductionAims of studyMethodsResultsDiscussionReferences |
|---|
All patients were treated with 0.022-inch slot `A' Company upper and lower Straight-Wire® appliances, finishing on 0.019 x 0.025-inch rectangular stainless steel archwires. All brackets were bonded using Right On® (TP Orthodontics, 2 Bruntcliffe Way, Morley, Leeds LS27 OJG, UK) adhesive after etching for 30 seconds. At the conclusion of treatment, appliances were removed from alternate patients using either bracket-removing pliers or the LODI. Using random allocation for the first upper quadrant to be debonded, contralateral upper and lower quadrants were debonded with the finishing archwire in place. The wires were then removed before the two remaining quadrants were debonded. This split mouth technique produced four experimental groups (Table 1).
|
Differences in the proportions of brackets that fitted test archwires in the four groups were evaluated using the Chi-squared test.
|
Results |
|---|
|
TopAbstractIntroductionAims of studyMethodsResultsDiscussionReferences |
|---|
2= 6.38, P < 0.05).
|
2= 30.745, P< 0.001). A breakdown of the numbers of test archwires of each size that failed to fit the bracket slot of each tooth type is shown as Table 3. Canine brackets were most often affected by slot closure and 69 (54 per cent) did not accommodate the 0.021 x 0.025-inch test wire. Thirty-six per cent of all brackets with slot closure to this extent were from canines.
|
2=0.906, P> 0.05). Distortion of the base was seen on 25 (9.7 per cent) of brackets debonded using bracket removing pliers (Figure 3). No base distortion was associated with use of the LODI.
|
|
|
Discussion |
|---|
|
TopAbstractIntroductionAims of studyMethodsResultsDiscussionReferences |
|---|
). From 13th June 1998, regulations
were further tightened since devices now require a CE (Conformite Europeenne) marking to
indicate
that
the product conforms to Medical Devices Directive 93/42/EEC.
In the course of bracket recycling, old adhesive is removed by heat or chemical solvents, after
which
the brackets are cleaned and repolished. The aim of the process must be to produce a bracket,
which
is to all intents and purposes as good as new so that it can be rebonded to enamel to produce a
bond of
adequate strength (Postlethwaite, 1992).
It is in the interests of both patient and orthodontist that a reused bracket should not have been adversely affected by clinical use, including the debond procedure and, subsequently, by the recycling process. Even small distortions of tie wings could affect the fit of archwires and in-built values of tip and torque, and the problem may be compounded, since the damage would not become apparent until relatively late in treatment. It is possible that round aligning arches up to 0.016 inch in diameter would engage into quite badly distorted brackets to produce satisfactory initial realignment of displaced teeth, and the difficulties produced by small, but important distortions would only be seen when attempts were made to fit rectangular arches of 0.018 x 0.025 inch and above.
The need to replace a bracket at this relatively late stage of treatment is particularly galling, since it is difficult to place the new bracket with sufficient precision to avoid the need to drop down the archwire sequence as far as a flexible aligning wire to permit correct slot engagement. In consequence treatment time may be extended by 2-3 months.
Table 3 shows the numbers of brackets in each group that were fully engaged by test archwires of various sizes. Since the brackets all had 0.022-inch slots when new, failure of each size of test arch to fit represented slot closure of from 0.006 inch for the 0.016 x 0.022-inch wire to 0.001 inch for the 0.021 x 0.025-inch test wire. For each wire size the greatest proportion of fit failures was found in quadrants debonded using bracket-removing pliers with the archwire removed before debonding. Significantly more brackets in this group failed to accommodate a test wire of each size than did brackets in the other three groups, except when the 0.021 x 0.025-inch wire was used (P< 0.01).
In the present study all treatments were finished on 0.019 x 0.025-inch archwires. Following debond 36 (7.1 per cent) of the total 507 brackets would not have accommodated an archwire of similar size had they been reused. Thirty of the 36 brackets were from quadrants debonded using bracket-removing pliers with the archwire removed before debond. The results, therefore, suggest that if bracket-removing pliers are to be used and bracket recycling is contemplated, the archwire should be left in place at the time of debond.
The most severe test of bracket slot closure was the 0.021 x 0.025-inch wire and the greatest numbers of fit failures were found in association with this wire. This is not surprising, since a slot closure of only one-thousandth of an inch would be enough to prevent fit of a wire of this size. Around half of the brackets debonded using pliers failed to accommodate the largest test wire and having the 0.019 x 0.025-inch archwire in situ at the time of debond made no difference. When the LODI was used with the archwire in place, significantly more brackets were distorted by one-thousandth of an inch than when the archwire was removed before debond. It is possible that the support afforded to the brackets by the 0.019 x 0.021-wire meant that the LODI had to pull more forcefully on a tie wing in order to produce dislodgment of the bracket from the tooth.
The presence of wear facets in the slot bases of many brackets must have been due to contact between the bracket and archwire. The shiny facets showed up clearly against the matt cast surface of the bracket when viewed under the microscope. They suggest that, even with an accurately designed rectangular slot system, actual archwire/bracket contact takes place over a very small area, generally at one or both ends of the slot. The significance of this observation in terms of friction is a topic that will be the subject of further study.
|
References |
|---|
|
TopAbstractIntroductionAims of studyMethodsResultsDiscussionReferences |
|---|
Bennett, G. S., Shen, C. and Waldron, J. M. (1984) The effects of debonding on the enamel surface,Journal of Clinical Orthodontics , 18, 330 –334.
Coley-Smith, A. and Rock, W. P. (1997) Bracket recycling—Who does what?British Journal of Orthodontics , 24, 172 –174.[Abstract]
Department of Health, Medical Devices Agency (1995) The Reuse of Medical Devices Supplied for Single Use Only,Device Bulletin MDA DB 9501, Medical Devices Agency, Department of Health, London.
Gorelick, L. (1979) Bonding, the state of the art: a national survey,Journal of Clinical Orthodontics , 13, 39 –53.
Graber, T. M. and Vanardsdall, R. L. (1994) Orthodontics, Current Principles and Techniques, 2nd edn, Mosby Year Book Inc., London.
Lavelle, C. L. B. (1988) Applied Oral Physiology, 2nd edn, Butterworth, London.
Maijer, R. and Smith, D. C. (1986) Biodegradation of the orthodontic bracket system,American Journal of Orthodontics , 90, 195 –198.
Matasa, G. C. (1989) Pros and cons of the reuse of direct-bonded appliances, American Journal of Orthodontics, 96, 72 –76.
Matasa, G. C. (1990) Flaws in bracket manufacturing,Journal of Clinical Orthodontics , 14, 149 -152.
Matasa, G. C. (1995) Attachment corrosion and its testing,Journal of Clinical Orthodontics , 29, 16 –23.
McGuinness, N. J. P. (1992) Prevention in orthodontics: a review,Dental Update , 19, 168 –175.[Medline]
Oliver, R. G. (1988) The effect of different methods of bracket removal on the amount of residual adhesive,American Journal of Orthodontics , 93, 196 –200.
Postlethwaite, K. M. (1992) Recycling bands and brackets,British Journal of Orthodontics , 19, 157 –164.[Abstract]
Tan, G. M. Y. (1991) The effects of debonding on slot dimensions and base torque angle in new and clinically used brackets, MSc Thesis, University of London.
Zarrinnia, K., Eid, N. M. and Kehoe, M. J. (1995) The effect of different debonding techniques on the enamel surface: an in vitro study,American Journal of Orthodontics , 108, 284 –293.
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
