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RAJIV GANDHI UNIVERSITY OF HEALTH SCIENCES,
BANGALORE, KARNATAKA
ANNEXURE II
PROFORMA FOR REGISTRATION OF SUBJECTS
FOR DISSERTATION
DR. JULINE ROSE ANTONY
1.
NAME OF THE CANDIDATE
AND ADDRESS
(in block letters)
POST GRADUATE STUDENT,
DEPARTMENT OF ORTHODONTICS AND
DENTOFACIAL ORTHOPEDICS,
BAPUJI DENTAL COLLEGE AND HOSPITAL,
DAVANGERE - 577 004.
2.
NAME OF THE INSTITUTION
BAPUJI DENTAL COLLEGE AND HOSPITAL,
DAVANGERE-577004
3.
COURSE OF STUDY AND SUBJECT
MASTER OF DENTAL SURGERY IN
ORTHODONTICS AND DENTOFACIAL
ORTHOPEDICS
4.
DATE OF ADMISSION TO COURSE
5.
TITLE OF THE TOPIC
30th MAY 2011
“ASSESSMENT OF PRECISION IN BRACKET
SLOTS AND WIRE DIMENSIONS AND ITS
EFFECT ON 3rd ORDER CLEARANCE AND
EFFECTIVE TORQUE – AN INVITRO STUDY”
6.
BRIEF RESUME OF THE INTENDED WORK :
6.1 Need for the study :
Achieving a satisfactory inclination or torque of the incisors is important for the final
esthetic result. Torque expression depends upon a number of factors including the accuracy of the
size of the bracket slot and arch wire dimensions. Complete torque expression can be achieved by
using an arch wire of appropriate size to fill the bracket slot, however to insert a full size
rectangular arch wire it is necessary that there is a certain amount of play. This means that the
height of the bracket slot must be greater than the height of the arch wire. If there is a large
discrepancy between the bracket slot and the arch wire dimension, the torque expressed will be
inconsistent.
The completely programmed bracket system, created by Andrews , was designed with
the objective of using arches without bends. The MBT system created by McLaughlin, Bennett and
Trevisi modified the torque on the brackets, so that the clinical goals could be attained with the
minimum insertion of bends in the wires, considering the play between the wire and the bracket
slot.
However, in spite of incorporating ideal torque characteristics in the structure of such
brackets, in some cases it is necessary to apply additional or individual torque on some teeth.
Hence a study is needed to assess the precision of the brackets and arch wire dimensions and their
efficiency in producing the required torque in clinical practice.
Research hypothesisDifference in precision of bracket slots’ and wire dimensions has an effect on the
third order clearance and effective torque.
Null hypothesisDifference in precision of bracket slots’ and wire dimensions does not have an
effect on the third order clearance and effective torque.
6.2 Review of literature :
An in-vitro study was conducted to determine the accuracy of different
manufacturer’s dimensions of bracket slots and stainless steel arch wires and compare these
against the tolerance limits. Ten upper central incisor brackets of 0.022 inch from five different
bracket systems were investigated. Bracket slot height was measured with leaf gauges. The height
and width of ten stainless steel arch wires with dimensions 0.019 x 0.022 or 0.020 x 0.025 inches
were measured using a micrometer. The results showed that all measured bracket slot heights were
within the upper and lower tolerance limits. The smallest effective torque loss was 4.50 and the
highest torque loss was 11.7 0. 1
An in-vitro study was conducted in which, slots of five upper left central incisor
brackets from 11 commercially available bracket systems measured in the 0.022-inch (0.5588 mm)
dimension were assessed. Measurements were taken after operator calibration and, a digital readout
was produced. Results indicate that all bracket slots were oversized. Of the 11 bracket system
tested (3M Unitek, Clarity MBT, Victory Series MBT, Discovery Roth, Elegance Plastic Roth,
Mini Mono MBT, Nu-Edge Roth, Mxi Advant-Edge Roth, Damon II SL Roth, Elite Mini OptiMIM Roth and Elite Mini Opti-MIM MBT) three bracket system’s slots were within 5% of their
stated dimensions. The Elegance Plastic slot was parallel sided but oversized by 12%. The Victory
Series slot top was oversized by 6%. The Nu-Edge slot top oversized by 14%. The base of the
Damon slot was oversized by 17%. The Discovery bracket’s slot base was oversized by 24%,
which was the largest recorded variance. This bracket also had a 7% difference between the widths
of the slot top and the base. Inaccurate machining of bracket slot dimensions and the use of
undersized arch wires may directly and adversely affect three-dimensional tooth positioning.2
An in-vitro study was conducted in which effective bracket slot height was estimated
by using a formula that describes the relationship between bracket slot height, wire dimensions,
wire edge bevel and torsional play (third-order clearance). With a torque measuring instrument, the
torsional play was estimated for 10 different brackets (0.018-inch stated slot) of the same
manufacturer and type. With known torsional play, wire dimensions and edge bevel, the bracket
slot height could be calculated. This was performed five times for each bracket. The brackets tested
had a mean slot height of 0.476 +/- 0.003 mm, with a range of 0.470 to 0.481 mm. The method
used to measure bracket slot height seemed to have a high degree of accuracy and is easier to
implement than conventional methods.3
An in-vitro study was conducted to verify the torque precision of metallic brackets
with MBT prescription, using the canine brackets as the representative sample of six commercial
brands. Twenty maxillary and twenty mandibular canine brackets of one of the following
commercial brands were selected: 3M Unitek, Abzil, American Orthodontics, TP Orthodontics,
Morelli and Ortho Organizers. The torque angle, established by reference points and lines, was
measured by an operator using an optical microscope coupled to a computer. The values were
compared to those established by the MBT prescription. The results showed that for the maxillary
canine brackets, only the Morelli torque presented statistically significant difference from the
proposed values . For the mandibular canines, American Orthodontics and Ortho Organizers
presented statistically significant differences from the standards. Comparing the brands, Morelli
presented statistically significant differences in comparison with all the other brands for maxillary
canine brackets. For the mandibular canine brackets, there was no statistically significant
difference between the brands. There are significant variations in torque values of some of the
brackets assessed, which would clinically compromise the buccolingual positioning of the tooth at
the end of orthodontic treatment.4
An in-vitro study was conducted to measure the slot dimensions of 0.022 inch selfligating upper central incisor brackets from six manufacturers using electron microscopy and to
compare them with manufacturers' published dimensions. Six self-ligating upper central incisor
brackets from four manufacturers were imaged with a scanning electron microscope and the slots
heights measured. Intra-operator repeatability and accuracy were determined. All brackets had slot
sizes that were significantly larger (p < 0.05) than the stated 0.022 inch. In most brackets the
distances between the slot walls was generally greater further from the bracket bases. The actual
measurements of upper central incisor self-ligating brackets from six manufacturers were larger
than the manufacturers' stated dimension, and the walls of the slots diverged from the bracket
bases.5
6.3 Objectives of the study :
-To determine the accuracy of different manufacturer’s dimensions of bracket slots
and arch wires.
-To calculate the torque play and effective torque produced by the interaction between
the afore said brackets and arch wires.
-To compare the results obtained to the nominal torque, as prescribed by the
manufacturer.
7.
MATERIALS AND METHODS
7.1. Source of the data:
Ten upper central incisor brackets of MBT prescription with nominal 0.022” slots and
ten 0.019” x 0.025” and 0.021” x 0.025” stainless steel arch wires from three different
manufacturers will be investigated. They will be collected from the respective company outlets.
MANUFACTURER
BRACKETS (inches)
STAINLESS STEEL ARCHWIRE
(inches)
3M-Unitek
0.022
0.019 x 0.025 and 0.021 x 0.025
American Orthodontics
0.022
0.019 x 0.025 and 0.021 x 0.025
Dentaurum
0.022
0.019 x 0.025 and 0.021 x 0.025
7.2. Method of collection of data:
Determination of sample sizeFor the study, sample size is determined by fixing α at 5% and β at 20% .Thus power
of the study is (1- β) = 80%. The data required to calculate the sample size was obtained from my
key article. To detect a minimum difference of 0.003 mm between the three systems of orthodontic
brackets and arch wires, the following formula was employed.
Sample size= ( Zα + Zβ)2 x 2 x S2
(d) 2
Where Zα = 1.96 for α =5%
Zβ = 0.84 for β= 20%
S = 0.002mm
d = 0.003mm
Therefore the sample size = (1.96+0.84) 2x2x(0.002)2
(0.003) 2
= 6.96 = 7
Hence I will be using 10 specimens of brackets and arch wires each for a particular
manufacturer.90 specimens, that is 30 specimens (10 brackets per manufacturer) of brackets with
60 specimens of 0.019” x 0.025” and 0.021” x 0.025” arch wires (10 wires per manufacturer for a
particular dimension) will be tested. Both the brackets and arch wires are made of stainless steel.
The arch wires used will be of rectangular cross section.
Method of study:
The height of the bracket slot is determined using a “Nikon profile projector V12”.
The breadth and height of the arch wire is measured using a Mahr micrometer and the accuracy is
evaluated. The same are then substituted in a trigonometric equation1 to obtain the torque play. The
brackets will then be placed on acrylic plates that serve as templates. Holes will be made in these
plates (7 mm in diameter by 4 mm deep) and lines will be demarcated to guide positioning of the
brackets. To fix the brackets, the holes will be filled with starch based modelling clay so that half
of the bracket in profile would be inserted while the other half will be exposed for the assessment.
Then incorporated torque of the bracket will be measured using “Nikon profile projector V12”. The
effective torque is then derived by subtracting the torque play from the incorporated torque. The
results will then be compared to the nominal torque, as prescribed by the manufacturers.
Statistical Analysis :
The values obtained will be statistically analyzed using the following tests :
- One way ANOVA will be used for multiple group simultaneous comparison.
- Post-hoc Tukey’s test will be used for group wise comparisons.
7.3 Does the study require any investigations or interventions to be conducted on patients or
other humans or animals? If so, please describe briefly
No. And there is no conflict of interest between the different manufacturers.
7.4 Has ethical clearance been obtained from your institution in case of 7.3?
Yes , and the clearance from the ethical committee is attached.
8.
LIST OF REFERENCES :
1. Astrid Joch, Margit Pichelmayer, Frank Weiland. Bracket slot and arch wire
dimensions: manufacturing precision and third order clearance. Journal of orthodontics
2010,Vol.37, 241-9.
2. Cash AC, Good SA, Curtis RV, McDonald F. An evaluation of slot size in orthodontic
brackets. Are standards as expected? Angle Orthod. 2004 Aug;74(4):450-3.
3. Meling TR, Odegaard J, Seqner D. On bracket slot height : A methodologic study
Am J Orthod Dentofacial Orthop. 1998 Apr;113(4):387-93.
4. Alessandra Motta Streva, Flavo Augusto Cotrim – Ferreira, Daniela Gamba Garib,
Paulo Eduardo Guedes Carvalho. Are torque values of pre adjusted brackets precise?
J Appl Oral Sci : I-V.
5. Bhalla NB, Good SA, McDonald F, Sherriff M, Cash AC. Assessment of slot sizes in
self-ligating brackets using electron microscopy. Aust Orthod J. 2010 May; 26(1):38-41.