RAJIV GANDHI UNIVERSITY OF HEALTH SCIENCES,
BANGALORE, KARNATAKA.
ANNEXURE – II
PROFORMA FOR REGISTRATION OF SUBJECTS FOR DISSERTATION
Dr. PULKIT CHANDRA,
1.
NAME OF THE CANDIDATE AND
ADDRESS (in block letters)
POST - GRADUATE STUDENT,
DEPARTMENTOF PROSTHODONTICS,
BAPUJI DENTAL COLLEGE AND HOSPITAL,
DAVANGERE - 577004,
KARNATAKA
BAPUJI DENTAL COLLEGE AND HOSPITAL,
2.
NAME OF THE INSTITUTION
DAVANGERE - 577004
MASTER OF DENTAL SURGERY
3.
COURSE OF STUDY AND SUBJECT
IN PROSTHODONTICS INCLUDING CROWN
AND BRIDGE AND IMPLANTOLOGY
4.
DATE OF ADMISSION TO COURSE
27-07-2013
“A
COMPARATIVE
DIFFERENT
5.
TITLE OF THE STUDY
EVALUATION
PROPERTIES
CONVENTIONAL
AND
AUTOPOLYMERIZING
OF
OF
VARIOUS
CROSSLINKED
ACRYLIC
RESINS
COMMERCIALLY AVAILABLE IN INDIA – AN
IN VITRO STUDY”.
1
6.
BRIEF RESUME OF THE INTENDED WORK :
.
6.1: Need for the study:
Auto polymerizing Poly Methyl Methacrylate (PMMA) is the most commonly used material for
repairing and relining of removable partial or complete dentures, for making orthodontic appliances,
acrylic splints, temporary denture bases and impression trays. Their popularity is totally justified due
to the ease of handling, excellent color matching, light weight, cost effectiveness and most
importantly excellent physical and chemical properties.
Acrylic resin complete dentures are susceptible to fracture during periods of clinical use. The
repair of the fractured prosthesis can be accomplished using acrylic resins that are auto polymerized,
heat polymerized or light polymerized. The repair material of choice depends on the following
factors: length of time required for making the repair, transverse strength obtained with the repair
material, and degree to which dimensional accuracy is maintained during the repair.1
In the ever evolving era of research and development, numerous cross linked auto polymerizing
acrylic resins are developed to enhance or customize the properties for clinical and laboratory
procedures as well as for patient use. The addition of different cross linking agents on polymerization
provide a range of cross-linking chain lengths and flexibilities which affects the impact strength,
flexural strength, the tensile strength, modulus of elasticity, water sorption and solubility of the cured
polymer.2 Additionally the cross linking of the polymer of the interstitial matrix is said to provide
craze resistance for the denture bases.3
2
Studies have been conducted on the water sorption and solubility characteristics of auto
polymerizing resins but another very significant parameter which plays a critical role in the reliable
and prolonged functioning of the resin is its ‘Flexural Strength’ and all of these properties in turn are
affected by the sheer presence and the specific type of the ‘Cross Linking Agent’ incorporated in the
resins by the manufacturers.
Effect of cross linking agents on some properties of denture base resins have been investigated
where various cross linking agents have been added externally to the liquids of denture base resins to
improve craze resistance, stiffness and surface hardness and the reports also confirm that addition of
cross linking agents at a high percentage( >15% ) decreases the mechanical properties, eg. Tensile
strength and impact strength.4 Another study has concluded that highly cross linked reline acrylic
resins and the one that contains mainly poly methyl metharylate had higher transverse bend strength
and modulus of elasticity than other reline acrylic resins.5
No literature is available regarding studies which compared the properties of conventional and
cross linked auto polymerizing acrylic resins which are commercially available in India. Hence, this
in-vitro study aims for comparative evaluation of different properties of various conventional and
cross linked auto polymerizing acrylic resins.
3
6.2 : Review of Literature:
The authors in a study added eight different cross linking agents to the monomer component of a
linear PMMA denture base resin in various concentrations and they found out that the Impact
resistance of the notched specimens generally decreased with increasing concentration of cross
linking agent. The impact resistance of reverse notch specimens generally increased with low
concentrations of cross linking agent; with higher concentration of the cross linking agent the impact
resistance continued to increase with the addition of four cross linking agents (TEGDMA;PEG 600
DMA;1,10-DMGDMA;EBADMA), decreased with three of them(EGDMA;DVB; TMPTMA) while
it remained constant with one of them(1,6-HMGDMA). The authors also reported that the
concentrations of the cross linking agents is usually not more than15%. At this level the polymer’s
susceptibility to solvent crazing is significantly reduced but not eliminated. Higher concentrations of
these agents are avoided because of their observed effect in reducing tensile strength and impact
strength.6
The authors in a study on four different cross linking agents found out that the increase in the
number of (CH2-CH2-O) units promoted flexibility in the material which resulted in a higher Impact
strength but an increase in the chain length and flexibility led to a decrease in the transverse bend
strength and ultimate tensile strength. A significant increase in impact strength with 20% TEGDMA
and continued to increase with 40%, however the impact strength slightly decreased with 60% of both
TEGDMA and PEG 600 DMA. The slight increase of tensile strength with low concentrations of
EGDMA reported by Wollff (1962) and Causton (1972) was also observed in this study when 10%
EGDMA was added. This increase of tensile strength remained constant with up to 40% and then
decreased slightly with 60% concentrations.2
4
The authors in a study compared the properties of highly cross linked self-curing acrylic resins
with those of conventional non cross-linked materials and the heat polymerizing denture base resins.
They found out that the highly cross linked reline acrylic resins and the one that contains mainly poly
methyl methacrylate and methyl methacrylate had higher Transverse Bend Strength and Modulus of
Elasticity than other reline acrylic resins. Highly cross linked reline acrylic resins had significantly
lower water sorption than non-cross linked reline acrylic resins and the heat polymerized denture base
material. Most reline acrylic resins had significantly higher solubility than heat polymerizing denture
base material.5
In another study the authors studied the effect of six different cross linking agents on the transverse
bending properties, water sorption and solubility of HEMA based resin. They concluded that increase
in the concentration of the cross linking agents increased the strength and rigidity till a certain
percentage (about 50%) above which the values level out or begin to fall. Water absorption drops with
increasing cross linking agent over the whole range of concentrations. Solubility tends to show a
small decrease initially (up to 40%) , followed by a noticeable increase as cross linking concentration
is increased.7
In a study authors investigated the material property changes of 2 new resilient denture lining
materials that represent 2 different curing modes : auto polymerization and conventional laboratory
processing and concluded that sorption values for the Laboratory Processed and Auto Polymerized
products were statistically equivalent after 6 months and after 1 year of water storage and at all time
intervals after 1 week, significantly lower resin solubility was recorded for the Auto polymerized
product than for the Laboratory Processed product.8
5
The authors in a study evaluated the influence of water absorbed in denture base resin on the bond
strength and resistance to cyclic thermal stresses of auto polymerizing resins bonded to the denture
base resin and found out that the bond strength of auto polymerizing resin to the denture base resin
were not significantly influenced by the water content of denture base resin but were significantly
influenced by the resin type, thermal cycling and surface treatment.9
The authors in a study to evaluate the effectiveness of different post polymerization methods on the
properties of removable orthodontic appliance resins concluded that fracture toughness and Vikers
hardness of the resins slightly increased after curing. Heat as a secondary curing method decreases
water uptake of the resins used for removable orthodontic appliances.10
Another recent study evaluated the impact strength of a denture base resin (Lucitone 550—L) and
four reline resins (Tokuyama Rebase II—T; Ufi Gel Hard—U; New Truliner—NT, and Kooliner—
K), both intact and in a reline combination (L/L,L/T, L/U, L/NT, and L/K) and concluded that thermo
cycling reduced the impact strength.11
6.3 : Objectives of the Study:
1. To evaluate the flexural strength, modulus of elasticity, water sorption and solubility of
conventional and cross linked auto polymerizing acrylic resins commercially available in India.
2. To compare the flexural strength, modulus of elasticity, water sorption and solubility of
conventional and cross linked auto polymerizing acrylic resins commercially available in India.
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7.
MATERIALS AND METHODS:
7.1 Source of data:
All the materials will be collected / purchased through scientific chemical/dental suppliers and
specimens will be prepared in the Department of Prosthodontics, Bapuji Dental College & Hospital,
Davangere and data will be obtained from laboratory based studies.
MATERIALS TO BE USED IN THE STUDY:
CONVENTIONAL
SN.
MATERIAL
MANUFACTURER
CROSS LINKING AGENT
1.
RR COLD CURE
DPI
--
2.
RR
DENTSPLY
--
3.
PROBASE
COLD
POLYMER
IVOCLAR VIVADENT
TETRAMETHYLENE
SR TRIPLEX
COLD
POLYMER
IVOCLAR VIVADENT
(NON- CROSSLINKED)
CROSS-LINKED
4.
DIMETHACRYLATE
TABLE N0 - 1
7
ETHYLENE
DIMETHACRYLATE
7.2 Method of collection of data (including sampling procedure, if any) :
a) Sample Size:
Based on the available information from previous studies, sample size was determined as follows:
Z 1-α/2 = 1.96 for α = 0.05
Z 1-β = 0.84 for β = 0.2 i.e. 80% power
δ = Expected difference to be detected between the two groups. It was kept as 3 based on previous
studies.
S2 = pooled standard deviation of 2 groups.
S1 = 2.30, S2 = 5.54
S2= 17.99
2
Alpha error (%) = 5
Using the formula12 , N = 2 x Z 1-α/2 + Z 1-β
x S2
δ0
Number needed (n) = 32 in each group
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b) Methodology:
Measuring the Flexural strength and Modulus of Elasticity:
The sizes of the test specimens will be 64x10x2.5mm. Each specimen for measuring Flexural
Strength will be stored in distilled water at 370C for 50 hours before testing. The specimens will be
subjected to the three point bending test using a Universal Testing Machine. At the point of fracture,
the amount of force will be recorded in accordance with ISO specification no. 1567 for denture base
polymers.5
Measuring the Water Sorption and Solubility:
The size of the test specimens will be 50mm diameter and 0.5mm thickness. Specimens will be dried
in the desiccators in the oven at 370C and after the specimens reached constant mass they will be
immersed in distilled water at 370C for seven days. After this period the samples will be weighed and
reconditioned to constant mass. Water sorption and solubility will be calculated in micrograms per
cubic millimeter in accordance with ISO specification 1567 for denture base polymers.5
C) Statistical Analysis:
The data obtained from the study will be subjected to appropriate statistical analysis. For comparison
with multiple groups, ANOVA will be used.
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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
7.4: Has ethical clearance been obtained from your institution in case of 7.3?
Ethical clearance certificate has been obtained and attached.
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8.
LIST OF REFERENCES:
1. Ellakwa AE, El- Sheikh. Effect of chemical disinfectants and repair materials on the
transverse
strength
of
repaired
heat
polymerized
acrylic
resins.
J. Prosthodont 2006; 15:300-5.
2. S.Caycik, R.J.Jagger. The effect of cross linking chain length on mechanical properties of a
dough moulded poly methyl methacrylate resin. Dent Mat May 1992; 8;153-157.
3. Jagger RG, Huggett R. The effect of cross linking on sorption properties of a denture base
material. Dent Mat 1990; 6:276-8.
4. Arima T, Murata H, Hamada T. The effects of cross linking agents on the water sorption
and solubility characteristics of denture base resin. J. Oral Rehabilitation 1996; 23:476-80.
5. Arima T, Murata H, Hamada T. Properties of highly cross-linked autopolymerizing reline
acrylic resins. J. Prosthet Dent 1995; 73:55-9.
6. C.A.Price. The effect of cross linking agents on the impact resistance of a linear Poly methyl
methacrylate denture base polymer. J. Dent Res July 1986 65(7); 987-992.
7. T.Arima, T.Hamada, J.F.Mccabe. The effects of cross linking agents on some properties of
HEMA based resins. J. Dent Res Sept 1995; 74(9); 1597-1601.
8. G.R. Parr, F.A. Rueggeberg. In vitro hardness, water sorption and resin solubility of
laboratory-processed and auto polymerized long term resilient denture liners over one year of
storage. J. Prosthet Dent 2002; 88L:139-44.
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9. H Minami, S Suzuki, Y minesaki, H Kurashige, T Tanaka. In vitro evaluation of the influence of
repairing condition of denture base resin on the bonding of auto polymerizing resins. J. Prosthet Dent
2004; 91:164-70.
10. A Faltermeier, M Rosentritt, D Mussig. Acrylic removable appliances: Comparative
evaluation of different post polymerization methods. Am J Orthod Dentofacial Orthop
2007; 131:301. E16 -316.22.
11. Ana L Machado1. et al. Impact strength of denture base and reline acrylic resins: An invitro study.
J. Dent Biomech 2012.Vol 3.
12. B. Zhong. How to calculate sample size in randomized controlled trial? J. Thorac Dis 2009; 1:51-4.
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