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The Evaluation of Certain Properties of Polymethyl –Methacrylate Powder Treated By Autoclave. An in VitroStudy
•
Dr. Manar N. Y. NazhatSenior in prosthetic dentistry, Al-Salam hospital –Mosul, IRAQProf. Tarik Y.K. BashiCollege of Dentistry, Mosul University, IRAQProf. Dr. Amer A. TaqaDBS. Department, College of Dentistry, Mosul University, IRAQEmail: [email protected]
Introduction
(PMMA) is the resin of choice for the fabrication of denture bases. It has excellent physical properties (Jagger et al., 2002).
Conventional acrylic resin material can be polymerized by autoclave, requires less than 1hr., and utilizes conventional equipment.
Aims Of The Study
1- Study the effect of different curing techniques (by water ˗ bath and by autoclave) on the physical, chemical, and mechanical properties of acrylic resin denture base material.
2- Invistigate the effect of autoclave on some physical, chemical, mechanical properties, and some thermal behavior on the (PMMA) powder by curing in water bath and curing by autoclave.
Review Of Literature
(PMMA) is the material of choice for denture prosthesis due to its desirable properties of excellent aesthetics, and simple processing (Lee et al., 2002 ; Trucker, 1981).
Although several new materials were used, (PMMA) remained the most preffered material of choice for both complete and partial denture prosthesis.
Methods of Curing of (PMMA) :-
1- Conventional water-bath :-
Water - bath processing technique has been the mostconventionally used.
Medium to long cured cycles of more than 7 hrs. produce resin with less residual monomer and optimal mechanical properties (Gugwad and Nagaral, 2010).
2- Microwave :-
A microwave is a device which depends on primaryheating effect by ionizing electromagnetic fields (Quanet al., 1992).
One of the disadvantage is the use of the plastic flask which is expensive and has a tendency to break down after processing several dentures (Ebraheem, 2014).
3- Autoclave :-
An autoclave is a device that is used to sterilize medical and other equipments.
An effective unit contains dry saturated steam, the air should be removed from the chamber by automatic air (Vernon, 2009).
Ming et al., (1996) show that when the acrylic resinpolymerized in autoclave with different pressure andtime, the results show no significant differences between
the autoclave curing and other conventional methods.
Tests Used in the Study :-
1-Transverse Strength Test :-The transverse strength is a combination of
compressive, tensile and shear strength which directly reflect the resistance of a material to fracture. (Lai et al., 2004).
The strength is affected by composition of resin, technique, degree of polymerization, water sorption and also environment of the denture(Unalan et al., 2010).
2- Indentation Hardness Test :-Hardness may be defined as the resistance to the
permanent surface indentation or penetration.
When the resin polymerized in autoclave with different pressure and time, the results no significant differences between the autoclave and conventional polymerization methods (Ming et al., 1996).
3- Surface Roughness Test :-It is influenced by either mechanical or chemical
polishing techniques.(Quirynen et al., 1990).Surface roughness affected by factors such as
polymerization method, material used, and incorporation of fibers into material (Karaagaclioglu, 2008).
4-Tensile Strength Test :-It is defind as the internal induced force that resists
the elongation of a material in a direction of the stresses (Academy of prosthodontics, 2005).
Polymerizing material under pressure can prove itstensile strength and stiffness (Brosh et al.,2002).
5- Water Sorption & Solubility Tests :-Sorption results an increase in weight and swelling
which affect the polymer properties.
Water act as a plasticizer and affects to dimensional stability, internal stresses and crack formation (Tuna et al., 2008).
6- Porosity Test :-The presence of porosity is dependent on the type of
the material and the method of polymerization.
Porosity weakens prosthesis due to accumulation of internal stresses and also lead to wrapage of acrylic denture base. (Keller & Lautenchlager, 1985).
7- Density Test :-Density is the physical property of matter as each
element and compound has a unique density associated with it (O,Brein, 2008).
Low density is one of the criteria of the ideal denturebase material (Ebraheem, 2014).
8- Colour Property Test :-Colour stability is one of the most important clinical
properties for dental materials and its ability to be ableto retain its orginal colour (Goiato et al., 2011).
•
The ability of resins to resist colour changes affected by the structure, physical and chemical charactaristics of inorganic fillers present in the resin (Galvao et al., 2010).
9- Melting Point Test :-
The melting point of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure.
The melting point of a pure substance is always higher ofan impure substance (Feistel and Wangner, 2006).
10- Polymerization Shrinkage Test :-Dentures with poor fit are conductive to accelerated
jaw bone atrophy and affect to the retention of the denture in the long time.
The variation in curing technique may not significantly alter the pattern of dimensional behavior due to the decrease in the molecular weight of polymer chains (Sykora and Sutto, 1997).
.
11- Fourier Transform Infrared Spectroscopy (FTIR) Test :-
It is based on infrared absorption and scattering from the inter molecular bonds and they provide the complementory information on the material composition.
Abdul Razzak, (2010) concluded by (FTIR) that raising temperature and extended polymerization time showed improved conversion and lowering monomer release.
12-Degree of Conversion Test :-There is an inverse relationship between the degree
of conversion and the residual monomer(Rueggeberg, 1994; Barcelay et al., 1999).
Water - bath post polymerization treatment increase the degree of conversion and reduced residual monomer content rather than microwave irradiation.
13- Diffrentional Scanning Calometric (DSC)Test :-
It is a thermal technique that measures rate and degree of heat changes in the material as a function of time or temperature (Ebraheem, 2014).
(DSC) has been used for studying setting reactions of dental acrylic resins, and for measuring the (Tg) of acrylic materials (Aydogan et al., 2013).
14- Residual Monomer Analysis by High Performance Liquid Chromatography (HPLC) Test:-
Its important to determine the residual monomer content of the acrylic resin which influences the allergy of acrylic denture (Graig et al., 2000).
Attempts have been made to reduce the residualmonomer content of acrylic resins by using thermoplastic and microwave polymerization rather
than heat technique (Alves et al.,2007).
Materials & Methods
Preparation of the samples :-
The samples in this study were prepared from VertexTM
regular type heat acrylic and divided into two main groups:
1The control groups were cured by water bath and by autoclave.
2The modified groups which modify the powder of acrylic by autoclave . The heat applied is 132 °C and pressure for 4 hr. This powder was also cured by water bath, and by using autoclave.
The modifiied powder before were cured, grinded by sieving for about 5 minutes about 4000 cycle / min. and sieving in a sieve No. 100 micron
•
F i g u r e ( 3 . 1 ) : A u t o c l a v e t y p e H I R A Y A M A - H I C T V E - H U A - 1 1 0
Figure (3.4): Grinding machine (XINGQIAN – XQ500)
Tests used in this study :-1- Transverse Strength Test :-
The total no. of samples was thirty, five in each group, in a bar shaped specimen.
The transverse strength test was performed using a three point bending testing machine. The force required for rupture was recorded and the stress was calculated by equation (Dogan et al., 2008):
S ═ 3.P.L ⁄ 2.b.d2
Figure (3.7): Transverse strength testing specimen dimension
65mm
10mm
2.5mm
2- Indentation Hardness Test :-
Five specimens from each group, and Shore HardnessTest Stand, was used
To minimize the risk of misreading, readings were taken in three different locations and the mean value was taken from each sample subject to minor load and the hardness inspector was calibrated after (15 - 20) seconds .
3- Surface Roughness Test :-
The total no. of samples was eighteen, three in eachgroup,
The method used was to scan a diamond stylus across the surface under constant load and compute the numeric value which measured in µm by using a contact profile meter.
10mm
10mm
2mm
4- Tensile Strength Test :-
Thirty samples were consructed of six groups.
Digital tensile testing machine was used and the samplesgrasped by two arms of machine, forces was applied untilfracture of sample occured in the testing machine.
Vertical alignment of the sample was an important factor for avoiding side loading or bending movements on the sample. Tensile Strength = F (N) / A.
Figure (3.12): Tensile strength Testing specimen dimensions.
90mm
10mm
3mm
5- Water Sorption & Solubility Tests :-
Sixty samples prepared, ten in each group.The samples were dried in air for 15 seconds at 37°C
until their weight was constant, this result was recorded as (m1). The samples were then immersed in distilled water for one week, removed, and weight, this result was recorded as (m2).
The samples were placed in the desiccator and drieduntil the final constant mass was recorded (m3). Thevolume of samples (V) was calculated by multiplying(length x width x thickness).
To calculate water sorption (Wsp) and solubility (Wsl) the following equations (1) and (2) were used (Podyoski, 2010) :
Wsp = m2─ m1 ⁄ V (1)
(2)Wsl = m2─ m3 ⁄ V
6- Porosity Test :-Sixty samples were prepared, ten from each group
The samples were dried in a desiccator.
With samples dried, two weights made, one with samplesin air and other immediately immersed in distilled water.
There were then weighetd at regular intervals until a constant mass reached indicating a state of water saturation for a 30 days.
The samples were removed from water and excess water was removed and weighted, in air and with immediately immersed in distilled water.
The porosity calculations were made using the following equations (Keller and Lautenchlager, 1985; Oliveira et al., 2003).
VS = ms ─ ms⁄
⁄Vd = md ─ md ⁄ ρw
⁄ ρw
(1)
(2)
% Porosity = ( VS ─ Vd ) x 100 ⁄ Vd (3)
Figure (3.15): Elecric sessitive balance up to 0.0001 gm.
7- Density :-Two samples of (PMMA) powder were used and
divided in 2 groups.Group 1- contain powder that is not treated by autoclaveGroup 2- contain powder which was modified by autoclave.
From each group, a sample of 2.5 gm powder of acrylic and placed inside a graduated glass cylinder then vibrated by the dental vibrator device for 2 minutes, then the volume was recorded for groups (1 & 2).The density was calculated according to the following
formula (Slowinnski et al., 2011):-
D = M / V
8- Colour Property Test :-Total no. of samples was thirty, five in each group.
Measurments were done by Vita Easy shade device toobtain the base line L*, a*, b* values
The total colour change :-
∆E = ] (∆L*)2+ (∆a*)2+(∆b*)2]½.
∆E = ](L2*- L1*) + (a2*- a1*) + (b2*- b2*)]½.
(1)
(2)Magnitude of the difference between two colours in specified condition, referred to as delta ∆E.
9- Melting Point Test :-Several grains of (PMMA) of 5 samples from each
group.
The device used in this study for measuring the meltingpoint is electrothermal melting piont device.
10- Polymerization Shrinkage Test :-Thirty samples were fabricated in both control and
modified groups. Six measurments distances (AB, BC, CD, AD, AC & BD).
The dimensional changes in the polymerization of the acrylic samples were calculated by this formula (Baydas et al., 2003).
Dimensional Changes
= 𝑨𝑩 ² + 𝑩𝑪 𝟐 + 𝑪𝑫 𝟐
+𝑨𝑫 𝟐
+𝑨𝑪 𝟐 + (𝑩𝑫)²
Polymerization shrinkage % determined by dimensionalchanges.
11- Fourier Transform Infrared Spectroscopy (FTIR) Test :-
A sample size of 1 mg was used in each group, samples
dried in a dry - oven for 12 hrs at 70 °C, the powder isplaced in the sample beam to obtain the chart of wavelength absorbed and transmitted in the wide range from(500 - 4000 nm) region (Aydogan et al.,2013)
12- Degree of Conversion Test :-
Eighteen specimens were prepared, three specimensfrom each type of group. All specimens were treated inthe same method for (FTIR) test.
By taking the ratio between the two absorbances of each sample, the fraction of unreacted double bonds could be calculated from the formula (Abdul Razzak, 2010)
DC % = [ 1-𝑨𝒃𝒔(𝑪=𝑪)/𝑨𝒃𝒔 𝑪=𝑶 𝒑𝒐𝒍𝒚𝒎𝒆𝒓
𝑨𝒃𝒔 𝑪=𝑪 / 𝑨𝒃𝒔 𝑪=𝑶 𝒎𝒐𝒏𝒐𝒎𝒆𝒓[ X 100 %
Where DC = degree of conversion
Abs = absorbance.
13-Diffrentional Scanning Calorimetric Test (DSC) :-
Samples devided into 6 groups
A sample size of 4 mg was used in each study group, (Tg) of each sample in the study groups was evaluated by (DSC) in a nitrogen atmosphere with a heating rate of 10°C / min. up to 250 °C (Aydogan et al., 2013).
14- Residual Monomer Test by (HPLC) :-
Eighteen samples were prepared.
A sample of 50 mg was dissolved in 1 ml of acetone and then 10 ml of methanol was added to the solution to precipitate the polymer (HPLC) analysis was performed using liquid charomatography (Mohamed et al.,2008).
Statistical Analysis :-The following statistical methods were analyzed to
asses the results :-
1Descripitive Statistical analysis including, Mean,Standerd Deviation and, Duncan᾿s Multiple Rangetests were used.
2 One way analysis of variance (ANOVA).
Results & Discussion
1-Transverse Strength Test :-
The descriptive statistics revealed a significant difference between control groups and of modified groups.
The presence of heat and pressure may affect to the polymeric chains and change in structure which cause enhancing the transverse strength of modified group.
1 •Table(4.2): F–test by ANOVAtable of Transverse Strengthresults.
Sum of
Squaresdf Mean
SquareF P-value
BetweenGroups 4659.173 5 931.835 248.825 0.000*
WithinGroups 89.878 24 3.745
Total 4749.052 29*Significant difference at P ≤ 0.05. df: degree offreedom
F i g ur e (4.1): M e a n , S t a nd e r d D e v i a t i on a n d D unc a n ᾿ s M ul t i p l e T e s t of
T r a ns v e r s e s t r e ng t h test of acyl ic s t udy g r oups .
1 2 0
1 0 0
80
60
40
20
0
A A 1 B B 1 C C 1
Tra
nsv
erse
Stre
ngt
h
N/m
m2
The presence of porosities, and internal voids often concentrated stresses in the matrix and formation of microcracks under loading (Ming et al., 1996).
2- Indentation Hardness Test :-
A significant difference between groups.
Conventional heat cured is leading to the formation ofa partial cross linked aliphatic polymer chains giving theacrylic higher hardness (Antonio, 2000).
The treated acrylic powder with autoclave had a
plasticizing effect on acrylic particles which lead to a
decrease in hardness value.
65
80
75
70
85
60
A A 1 B B1 C C 1
Fig ure (4.3): M e a n , S tanderd Deviat ion a nd Dunca n᾿ s Mult iple Test
of Indentat ion Hardness Tes t of acryl ic s tudy groups.
Ind
en
tati
on
Har
dn
ess
in
Kg/
mm
2
Table (4.8): F – test by ANOVA table of Indentation Hardness results.
Sum of
Squar
es
df Mean
Squa
re
F P-
value
BetweenGroups 616.084 5 123.217 10.525 0.000
*
WithinGroups 280.957 24 11.707
Total 897.042 29*Significant difference at P ≤ 0.05. df: degree of freedom
3- Surface Roughness Test :-
A non - significant difference between groups. The surface roughness of acrylic resin was not affected by polymerization methods and without adverse effects on the surface roughness of the material.
1.4
1.2
1
0.8
0.6
0.4
0.2
0A A1 B B1 C C1
Figure (4.4): Mean, Standerd Deviation and Duncan᾿s Mutiple Range
of Surface Roughness Test of acrylic study groups.
Surf
ace
Ro
ugh
ne
es
µm
Table (4.10): Descriptive Statistics of Surface Roughness results.
Groups N Mean Std.
Deviat
ion
Std.
Err
or
Minimum Maximum
A 3 1.19267 .404181 0.233354 0.929 1.658
A1 3 0.98367 0.026502 0.015301 0.965 1.014
B 3 1.25033 0.336898 0.194508 0.626 1.626
B1 3 0.96600 0.076374 0.044095 0.878 1.015
C 3 0.98500 0.109494 0.063217 0.868 1.085
C1 3 0.96833 0.090185 0.052068 0.875 1.055
4-Tensile Strength Test :-
A significant difference between groups. The value may be related to degree of polymerization and crystalline nature as well as less voids within materials which agree with John et al., (2001), who reported that presence of voids which assocaited with polymerization shrinkage due to excess monomer applied during procedure.
Fig ure (4 .13): M e a n , S tanderd Deviat ion a nd Dunca n᾿ s Mult iple
R a ng e of M o dul us of Elast ic ity results of acryl ic s tudy groups.
0
20 0
15 0
10 0
50
25 0
A A1 B B1 C C 1
Mo
du
lus
ofE
last
icit
y M
Pa
Table (4.14): F-test by ANOVA table of Tensile Strenght results.
Sum of
Squar
es
df Mean
Squa
re
F P-value
BetweenGroups 3353.787 5 670.757 62.234 0.000*
WithinGroups 258.673 24 10.778
Total 3612.460 29*Significant difference at P ≤ 0.05. df: degree of freedom
5- Water Sorption & Solubility Tests :-
A significant difference between all groups in water sorption which may be due to the presence of voids that lead to diffusion of ionic molecules of water between the polar bonds of acrylic resin.
Table (4.23): F -test by ANOVA table of Water Sorption results.
Sum of
Squaresdf Mean
SquareF P-value
BetweenGroups 62.766 5 12.553 4.239 0.003*
WithinGroups 159.916 54 2.961
Total 222.682 59
*Significant difference at P ≤ 0.05. df: degree of freedom
Figure (4.20): Mean, Standerd Deviation and Duncan᾿s Multiple Range of Water
Sorption result in acrylic samples groups.
4
3
2
1
0
7
6
5
A A1 B B1 C C1W
ater
Sorp
tio
n m
g /
cm3
A non – significant difference between all groups in water solubility test due to the small amount of residual monomer released. Water solubility may be due to a decrease in the potential sites of water exchange occur and related to the leach of soluble materials like residual monomer and plasticizers.
Figure (4.21): Mean, Standerd Deviation and Duncan᾿s Multiple Range of Water
Solubility results of acrylic sample groups.
1
0
4
3
2
6
5
A A1 B B1 C C1
Wat
er
solu
bili
tym
g/cm
3
Table (4.26): F -tset by ANOVAtable of Water Solubilityresults.
Sumof
Squ
ares
df Mean
Squ
are
F P-value
Between Groups 10.904 5 2.181 0.610 0.693
WithinGroups 193.163 54 3.577
Total 204.066 59
6- Porosity Test :-A non significant difference between all groups which may be
related to polymer processing temp. higher than 74°C.Density of the acrylic , pressure in polymerization wasconsidered to minimize porosity.
(PMMA) monomer has a high vapor pressure. Processing temp. beyond 100.3°C causes vaporation of monomer which
produces porosity in the final set material.
Figure (4.22): Mean, Standerd Deviat ion a nd Duncan᾿s Multiple Ra ng e of
porosity results of acryl ic s tudy groups.
1.2
1
0.8
0.6
0.4
0.2
0A A 1 B B 1 C C 1
Po
rosi
ty
%
Table (4.28): Discripitive Statistics of Porosity results.
Grou
ps
N Mean Std.
DeviationStd.Error Mini
mu
m
Maxi
mu
m
A 10 1.020790 0.4422391 0.1398483 0.3158 1.6670
A1 10 0.839650 0.2051769 0.0648826 0.4667 1.1818
B 10 0.990570 0.3158792 0.0998898 0.5333 1.5466
B1 10 0.897870 0.2451328 0.0775178 0.5385 1.3333
C 10 0.876950 0.4013481 0.1269174 0.4282 1.6250
C1 10 0.697150 0.2510358 0.0793845 0.4111 1.2677
7-Density Test :-T- Test revealed a significant difference between
the powder of control and modified groups and decrease in its weight due to thermal effect and change in particle size, this finding is agreement with AL - Saraj (2014) who reported that thermal effect lead to enhanced the nucleation process, change particle size and decrease density of acrylic
•7
Table (4.31): T-Test of Density results.
Grou
pN Mean Std.
Deviation
Std.Error
Meant df P-
value
A 3 0.646933 0.0008386 0.0004842 10.263 4 0.001*
A1 3 0.601933 0.0075481 0.0043579
*Significant difference at P ≤ 0.05. df:degreeFigure (4.23 ): T-Test results of acrylic study groups.
0.65
0.64
0.63
0.62
0.61
0.6
0.59
0.58
0.57
Control Group Modification
Den
sity
gm
/cm
3
8- Colour Property Test :-
A non significant difference between all groups in (∆E) of colour property test.
The monomer conc. was responsible for colour changesassociated with porosity caused by over heating .
This finding is in agree with Madhyastha and Kotain, (2013) who found the colour stability was influenced by the type of materials, methods of cure, and leaching of monomer.
Table (4.48): F - test by ANOVA of Colour Difference (∆E) results.
Sumof
Squaresdf Mean
SquareF P-value
BetweenGroups 4.561 5 0.912 1.008 0.435
WithinGroups 21.722 24 0.905
Total 26.283 29
F i g u r e ( 4 . 2 9 ) : M e a n , S t a n d e r d D e v i a t i o n a n d D u n c a n ᾿ s M u l t i p l e
r a n g e r e s u l t s o f c o l o u r d i f f e r e n c e ( ∆ E ) o f a c r y l i c s t u d y g r o u p s .
4
3 . 5
3
2 . 5
2
1 . 5
1
0 . 5
0A A 1 B B 1 C C 1
Co
lou
rD
iffe
ren
ce
(∆E
)
9- Melting Point Test :-
A significat difference between all groups.
The finding of results may be due to the different in the density of sample.
The higher the quantity of components of thematerial is lower the melting point (Tylor, 1994).
Table (4.51): F - test by ANOVA of Melting point results.
Sum of
Squar
es
df Mean
Squa
re
F P-value
BetweenGroups 268.400 5 53.680 2.668 0.047*
WithinGroups 482.800 24 20.117
Total 751.200 29*Significant difference at P ≤ 0.05. df: degree of freeom
Figure (4.30): Mean, Standerd deviation and Duncan᾿s Multiple Range of
Melting point results of acrylic study groups.
292
290
288
302
300
298
296
294
A A1 B B1 C C1
Me
ltin
gP
oin
tC
10-Polymerization Shrinkage Test :-
A non significant difference between all groups.
This finding may be due to the type of curing cycle and different coeffecient of gypsum and acrylic resin which affects the residual monomer content.
Table (4.53): Descripitive Statistics of Polymerization Shrinkage results.
Groups N Mean Std.
DeviationStd.Error Mini
mu
m
Maxi
mu
m
A 5 6.251480 4.3760532 1.9570305 1.4697 11.2290
A1 5 5.178660 0.6983465 0.3123100 4.2371 5.8948
B 5 7.213020 2.7929391 1.2490403 5.1175 11.5765
B1 5 7.064500 1.1863378 0.5305464 5.2911 8.6134
C 5 8.533660 1.4583795 0.6522071 6.2055 10.0616
C1 5 8.226300 1.3651397 0.6105090 5.9349 9.2656
9
8
7
6
5
4
3
2
1
0A A1 B B1 C C1
Figure (4.31): Mean, Standerd deviation and Duncan᾿s Multiple Range of
Polymerization Shrinkage results of acrylic study groups.
Po
yme
riza
tio
nSh
rin
kage
%
Jorge et al., (2003) reported that, total heat in fast polymerization cycles, could exceed the boiling point of the monomer causes internal porosities that affect the polymerization shrinkage and dimensional accurey.
The curing of polymer by autoclave decreased monomer released, internal porosities and changed the (Tg) of the polymer.
11-Fourier Transform Infrared Spectroscopy (FTIR) Test:-
The results showed no changes in the chemicalstructure of the modified groups.
When the (C = C) bond was decreased in its height the amount of residual monomer decreased and this finding agree with Ebraheem, (2014) who reported that the height of (C = C) bond indicates the residual monomer polymer group.
12-Degree of Conversion Test :-
A non significant difference between all groups.
The polymerization time and the temp. affect the residual monomer of polymer. Above (Tg) of polymer, the monomer had a better ability to polymerize due to higher molecular chain motions and this is as in the modified groups.
Table (4.56): Descripitive Statistics of Degree of Conversion results.
Groups N Mean Std.
Deviation
Std.
Err
or
Mini
mu
m
Maxi
mu
mA 3 90.11833 0.980086 0.565853 88.995 90.799
A1 3 90.78967 0.856109 0.494275 90.228 91.775
B 3 89.16433 0.624443 0.360522 88.655 89.861
B1 3 91.68800 3.511778 2.027526 88.959 95.650
C 3 91.77933 0.618636 0.357170 91.065 92.139
C1 3 93.11833 0.985715 0.569103 92.155 94.125
94
93
92
91
90
89
88
87A A1 B B1 C C1
Figure (4.38) : Mean, Standerd Deviation and Duncan᾿s Multiple
Range results of Degree of Conversion of acrylic study groups.
De
gree
of
Co
nve
rsio
n%
13-Differential Scanning Calomateric (DSC) Test:-
The powder of control groups showed broad endothermic peak. The powder of modified groups showed a change in thermal behavior.
The thermal behavior of both groups have changes between them and an increase in (Tg) may be due to the polymerization of the residual monomer or decomposition of the benzoyl peroxide,.
.14-Residual MonomerTest By Using (HPLC) :-
A significant difference between all groups.
Curing cycles with a temperature under 100 °C produced polymers with higher residual (MMA) content than those produced with a prolonged curing period at 100 °C.
Figure (4.45): Mean, Standerd Deviation and Duncan᾿s Multiple Range results of
Residual Monomer by (HPLC) of acrylic study groups.
0.2
0.25
0.3
0.35
0.4
A A1 B B1 C C1
Res
idu
al M
on
om
er b
y (
HP
LC)
F i g ur e ( 4 . 5 4 ) : C a l i br a t i on c ur v e of r e s i dua l m o n o m e r c onc e nt r a t i o n 5 % .
y = 3 0 6 8 . 8 x + 5 1 8 8 . 5R² = 0 . 9 7 4 4
5 0 0 0 0
4 0 0 0 0
3 0 0 0 0
2 0 0 0 0
1 0 0 0 0
0
9 0 0 0 0
8 0 0 0 0
7 0 0 0 0
6 0 0 0 0
0 5 1 0 1 5 2 0 2 5 3 0
a
a
)a
The cross - linking agents of the acrylic resins mayalso affect the residual monomer content, a rigid polymer structure hinders the conversion of the (MMA) monomers especially at curing temperature lower than the glass transion temperature.
In this study, the modified curing types had a great influence in reducing the residual monomer content which is in agreement with many reseachers who reported similar findings by Mohamed et al., 2008.
Conclusions & Suggestions
Conclusions :-Within the limitation in this vitro study,, we concluded
the following :-
-The autoclave processing technique might be a good alternative to the conventional water - bath in the curing of acrylic resin of all study groups.
-The treatment of acrylic powder by autoclave has a significant difference in transverse strength,tensile strength and modulus of elasticity of all study groups.
- The treatment of acrylic powder by autoclave has asignificant decrease in hardness value in group (B1).
-The treatment of acrylic powder by autoclave has nosignificant difference in surface roughness, water solubility, porosity and polymerization shrinkage of all
study groups.
-The density of acrylic resin was decreased when treated the powder of acrylic resin by autoclave.
- The treatment of acrylic powder by autoclave a nonsignificant difference in colour change.
- The treatment of acrylic resin with autoclave has a significant difference in residual monomer in all study groups.
- The treatment of acrylic powder with autoclave changed its thermal behavior.
Suggestions :-
The study comes with the following suggestions
-Studying the impact strength, compressive strength and creep of the treated powder of acrylic with autoclave.
- Studying the biocompatibility of the treated powderof acrylic with autoclave
-Curing the modified powder with autoclave by microwave in different times and powers, then measuring the physical, chemical and mechanical properties of it.
-Evaluating the physical and chemical properties of modified acrylic resin by autoclave curing in different times and temperature.
- Improvement the conventional prosthetic acrylicresins and modified acrylic by nano technology.
