RAJIV GANDHI UNIVERSITY OF HEALTH SCIENCES,

BANGALORE, KARNATAKA.

ANNEXURE – II

PROFORMA FOR REGISTRATION OF SUBJECTS FOR DISSERTATION

1. NAME OF THE CANDIDATE

AND ADDRESS

(In Block Letters)

DR. NEHA ARORA

POST GRADUATE STUDENT,

DEPARTMENT OF PROSTHODONTICS,

BAPUJI DENTAL COLLEGE AND HOSPITAL,

DAVANGERE – 577004,

KARNATAKA.

2. NAME OF THE INSTITUTION BAPUJI DENTAL COLLEGE AND HOSPITAL,

DAVANGERE.

3. COURSE OF THE STUDY AND

SUBJECT

MASTER OF DENTAL SURGERY

IN PROSTHODONTICS INCLUDING CROWN AND

BRIDGE AND IMPLANTOLOGY.

4. DATE OF ADMISSION TO

COURSE

30-05-2012

5. TITLE OF THE TOPIC “ COMPARATIVE EVALUATION OF THE

FLEXURAL STRENGTH, FLEXURAL MODULUS

AND IMPACT STRENGTH OF A HEAT CURE

DENTURE BASE RESIN ON INCORPORATION

OF 2% DIMETHYLDIOCTYL AMMONIUM

BROMIDE”-AN IN VITRO STUDY

BRIEF RESUME OF THE INTENDED WORK:

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6.

6.1

NEED FOR THE STUDY:

The use of a dental prosthesis is indispensable for functional and esthetic rehabilitation of

edentulous patients. Disinfection protocol is mandatory in Prosthodontics because saliva

harbors many microorganisms which have a potential to cause harm to the human body.

Denture base acrylic resin is easily colonized by oral endogenous bacteria and Candida spp.and

eventually by extra-oral species.1 Literature reveals that the management of Candida–associated

microbial lesions relies on denture cleaning and disinfection, appropriate denture wearing

habits, and prescription of topical or systemic antifungal agents.2,3,4 However, the incidence of

relapse of the infection is high, and it is often difficult to obtain patient compliance.1

It has been proved that 2% quaternary ammonium compound act as an effective antiseptic when

combined with acrylic resin samples towards bacterial and fungal suspensions.1 However, the

authors identified no study that has reported the effect of respective compound on properties of

a denture base resin. The disinfection of dental prosthesis by incorporation of antiseptic should

be capable of rapid inactivation of pathogenic microorganisms, without causing any adverse

effect on denture base resin.

Impact strength is an important parameter, as it can reflect the contact force required to cause

fracture in a denture under situations such as accidental dropping. Flexural strength and

modulus of elasticity are other important mechanical properties. High flexural strength is

crucial to denture wearing success, as alveolar resorption is gradual and irregular process that

leaves tissue-borne prostheses unevenly supported. As a foundation, the acrylic resin materials

should exhibit a high proportional limit to resist plastic deformation and also exhibit fatigue

resistance to endure repeated masticatory loads.

The International Standards Organization specification for denture base polymers (ISO 1567)5

stipulates that transverse deflection must be between 1mm and 2.5 mm for forces of 15 N and

35 N, and between 2 mm and 5 mm for forces of 15 N and 50 N. Hence, the aim of this in vitro

study is to evaluate and compare the mechanical properties of a heat cure denture base resin on

incorporation of 2% Quaternary Ammonium compound.

6.2 REVIEW OF LITERATURE:

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Authors conducted a study on the effects of incorporation of chlorhexidine acetate on some

physical properties of polymerized and plasticized acrylics. It concluded that hardness and

modulus of elasticity measurements were significantly reduced for heat and cold cured acrylics

containing chlorhexidine acetate.6

A study done by authors to evaluate the effect of long-term disinfection immersion on flexural

properties of denture base resin and concluded that there was no significant change in the

modulus of rupture and modulus of elasticity for trevalon specimens after a 7 day immersion

period in disinfectant solution and modulus of rupture for homopolymer was significantly

affected when the specimens in alcohol-based disinfectant were compared to the control group.7

Authors conducted a study to evaluate the flexural strength and modulus, water sorption,

solubility and color stability on addition of phosphate group in 10% and 20% by volume into

liquid monomer and concluded that E-20 exhibited the lowest flexural strength and modulus,

highest sorption and solubility and no significant changes for color stability and staining were

noted.8

A study was conducted to evaluate the antimicrobial activity of acrylic resins containing

different percentages of silver-zinc anti-microbial zeolites and to assess whether the addition of

zeolites alters the flexural and impact strength of denture bases and concluded that a significant

antimicrobial activity was observed at 2.5% but decrease in flexural strength was also noted.9

A study done by authors to evaluate the effect of incorporation of the antimicrobial monomer

MUPB containing 0.3% w/w and 0.6%w/w on the hardness, roughness, flexural strength and

color stability of a denture base material and concluded that 0.6% MUPB reduced the flexural

strength. Hardness and surface roughness, however are not affected at 0.3% or 0.6%.10

6.3 OBJECTIVES OF THE STUDY:

1. To evaluate the flexural strength, modulus of elasticity and impact strength of a heat cure

denture base resin without incorporation of 2% quaternary ammonium compound.

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7

7.1

2. To evaluate the flexural strength, modulus of elasticity and impact strength of a heat cure

denture base resin with incorporation of 2% quaternary ammonium compound.

3. To compare the flexural strength, modulus of elasticity and impact strength of a heat cure

denture base resin with and without incorporation of 2% quaternary ammonium compound.

RESEARCH HYPOTHESIS (H1): There will be alteration in mechanical properties of a

heat cure denture base resin on incorporation of 2% Quaternary Ammonium Compound.

NULL HYPOTHESIS (H0): There will be no alteration in mechanical properties of a heat

cure denture base resin on incorporation of 2% Quaternary Ammonium Compound.

MATERIALS AND METHODS:

SOURCE OF DATA:

All the materials will be collected/ purchased through scientific chemical/ dental suppliers.

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7.2

7.3

Specimens will be prepared in the Department of Prosthodontics, Bapuji Dental College and

Hospital, Davangere and data will be obtained from laboratory based studies.

SAMPLE SIZE DETERMINATION:

Based on the information available from the previous studies, a sample size is determined

using the formula,

Sample size ( n ) = 2× t ² × s ²

d ²

where,

t = theoretical value of ‛t’ distribution with a 95% confidence.

= 2.13

Level of significance = 5%

Power of the study = 1 - β

= 1 - 0.20 = 0.80

= 80%

s = pooled standard deviation

= 10

d = minimum expected difference in the zone (from previous studies)8,10

= 8 mm

n = 2× 2.13× 2.13 ×10 ×10

8× 8

= 14 ≈ 15

Therefore, the sample size is 15 for evaluating flexural strength and flexural modulus and 15 for

evaluating impact strength i.e. sample size for each group is 30, thereby total number of sample

will be 60.

MATERIALS:

Material Manufacturer

1.Trevalon (Heat-polymerized acrylic resin) Dentsply

5

7.4

(A)

(B)

2.Quaternary Ammonium Compound TCI, Japan

3.Azo-bis-iso-butyro-nitryl Paras Polymers & Chemicals, Rajasthan

METHOD OF COLLECTION OF DATA:

GROUPING:

For the purpose of study, a total of 60 test specimens will be prepared and divided into 2

groups:

Grouping Sample Size(To evaluate Flexural

Strength & Modulus of Elasticity)

Sample Size(To evaluate Impact

Strength)

Group 1 (Control) 15 15

Group 2 (Experimental) 15 15

PREPARATION OF TEST SPECIMENS:

TO EVALUATE FLEXURAL STRENGTH, MODULUS OF ELASTICITY AND IMPACT

STRENGTH:

According to ADA specification no.12 for flexural strength and flexural modulus test, a

rectangular steel block measuring 65mm in length, 2.5 ± 0.03 mm in thickness and 10 ± 0.03

mm in width and for impact strength test, a rectangular steel block fabricated in accordance

with ISO179:2000 will be used to create uniform mould spaces in gypsum in a custom

fabricated maxillofacial metal flask and replica blocks of test specimens will thus be

produced.5,11

All the test specimens will be prepared using a commercially available heat

polymerized acrylic resin i.e. (TREVALON).

Heat polymerized acrylic resin will be manipulated according to manufacturer’s

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(C)

(D)

instructions.

For group 1(control), test specimen manipulation will be done conventionally. For

group 2(experimental), test specimen manipulation will be done directly by mixing

homogenously Quaternary Ammonium Compound with polymer of an acrylic resin in

concentration of 2% (powder/ powder) and then Azo-bis-iso-butyro-nitryl is added in

concentration of 0.05% by weight to act as an initiator in the polymerization of an antiseptic

(Quaternary Ammonium Compound) with a heat cure acrylic resin.1 After reaching the

dough stage, mixture will be packed and processed in accordance with manufacturer’s

recommendations.8

PROCESSING OF THE SPECIMENS:

Specimens shall be processed according to the following schedule:

The flasked specimens held in clamp, will be processed by step-up curing cycle on

immersion in water at73±1 ° C for one and half hour followed by 100 °C for 30 minutes.

After completion of heating schedule, the flask shall be bench cooled in air at room temperature

for 30 minutes.8 After deflasking, the specimens will be retrieved and the excess is trimmed

with tungsten carbide bur and finished using silicon carbide paper carefully.

The specimens of both groups measuring standard dimensions will be selected and stored in

distilled water at 37 ±1°C for 7 days immediately before testing the mechanical properties.10

METHOD FOR MEASURING MECHANICAL PROPERTIES:

TO MEASURE FLEXURAL STRENGTH AND MODULUS OF ELASTICITY:

The specimens will be subjected to the three point bending test under a universal testing

machine (Tinius Olsen company, model H5KS, U.S.A.). At the point of fracture, the amount

of force and deflection will be recorded.10

Flexural strength (FS) will be calculated using the formula,

FS = 3PI

2b h ²

where, FS = flexural strength in MPa (N/mm2).

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(E)

7.5

P = maximum load applied at fracture in (N)

I = distance between the supporting wedges (span length) in mm.

b = width of the transverse test specimen in mm.

h = thickness of the transverse test specimen in mm.

Modulus of elasticity (E) will be calculated using the formula,

E =PI ³

4 bh ³ d

where, E = elastic modulus in MPa.

d = deflection of transverse test specimen in mm.

TO MEASURE IMPACT STRENGTH:

The specimen will be subjected under Charpy type Impact tester to measure the impact energy

required to fracture the specimen.

The impact strength (IS) will be calculated using the following formula11

IS= E c(hb)

where, Ec = corrected absorbed energy (KJ).

h = specimen thickness (m).

b = width below the notch (m).

STATISTICAL ANALYSIS:

The data obtained from the tests will be tabulated and subjected to statistical analysis.

Unpaired ‛t’ test will be used to compare Flexural strength, Modulus of elasticity and Impact

strength between control and experimental group.

DOES THE STUDY REQUIRE ANY INVESTIGATION OR INTERVENTIONS

BRIEFLY TO BE CONDUCTED ON PATIENTS OR OTHER HUMANS OR

ANIMALS? IF SO, PLEASE DESCRIBE.

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7.6

8.

Not Applicable.

HAS ETHICAL CLEARANCE BEEN OBTAINED FROM YOUR INSTITUTION IN

CASE OF 7.3?

Not Applicable.

LIST OF REFERENCES:

1. Pesci –Bardon C, Fosse T, Serre D, Madinier I .In vitro antiseptic properties of an

ammonium compound combined with denture base acrylic resin. Gerodontology 2006

Jun;23(2):111-6.

2. Wilson J. The aeitology, diagnosis and management of denture stomatitis. Br Dent J

1998 Oct 24;185(8):380-4.

3. Holmstrup P, Axell T. Classification and clinical manifestations of oral yeast

infections. Acta Odontol Scand 1990 Feb;48(1):57-9.

4. Budtz-Jörgenson E. Etiology, pathogenesis, therapy, and prophylaxis of oral yeast

infections. Acta Odontol Scand 1990 Feb;48(1):61-9

5. International Organization for Standards. International Standard ISO 1567,2nd ed.

Denture base polymers .Geneva: International Organization for Standards,1988.

6. Addy M, Handley R The effects of incorporation of chlorhexidine acetate on some

physical properties of polymerized and plasticized acrylics. J Oral Rehabil 1981

Mar;8(2):155-63.

7. Asad T, Watkinson AC, Huggett R. The effect of disinfection procedures on flexural

properties of denture base acrylic resins. J Prosthet Dent 1992 Jul;68(1):191-5.

8. Dhir G, Berzins DW, Dhuru VB, Periathamby AR, Dentino A. Physical properties of

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denture base resins potentially resistant to Candida adhesion. J Prosthodont 2007 Nov-

Dec;16(6):465-72.

9. Casemiro LA, Gomes Martins CH, Pires-de- Souza FdeC, Panzeri H. Antimicrobial and

mechanical properties of acrylic resins with incorporated silver-zinc zeolites-

part1.Gerodontology 2008 Sep;25(3):187-94.

10. Regis RR , Zanini AP, Della Vecchia MP, Silva-Lovato CH, Oliveira Paranhos HF,de

Souza RF.Physical properties of an acrylic resin after incorporation of an antimicrobial

monomer.J Prosthodont 2011Jul;20(5):372-379.

11. ISO 179:2000. Plastics -Determination of Charpy impact strength. 3rd ed. Geneva:

International Organization Standardization; 2000.

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