RAJIV GANDHI UNIVERSITY OF HEALTH SCIENCES, BANGALORE, KARNATAKA

ANNEXURE II

PROFORMA FOR REGISTRATION OF SUBJECTS FOR DISSERTATION

1 / NAME OF THE CANDIDATE
AND ADDRESS / DR. MITHUN KARAKARADDI
POST GRADUATE STUDENT,
DEPARTMENT OF PROSTHODONTICS, COORG INSTITUTE OF DENTAL SCIENCES,
VIRAJPET-571218, KARNATAKA.
2. / NAME OF THE INSTITUTION / COORG INSTITUTE OF DENTAL SCIENCES,
VIRAJPET-571 218.
3. / COURSE OF THE STUDY & SUBJECT / MASTER OF DENTAL SURGERY, PROSTHODONTICS
4. / DATE OF ADMISSION TO THE COURSE / 25/5/2012
5. / TITLE OF THE TOPIC
AN IN VITRO STUDY TO EVALUATE AND COMPARE THE HARDNESS AND TENSILE BOND STRENGTH OF FOUR DIFFERENT DENTURE LINERS TO A HEAT POLYMERIZED ACRYLIC RESIN FOLLOWING STORAGE IN A DENTURE CLEANSING SOLUTION AND WATER OVER VARYING TIME PERIODS.
6. / BRIEF RESUME OF THE INTENDED WORK:
6.1 NEED FOR THE STUDY:
The use of resilient lining materials is helpful in fabricating removable complete and partial dentures because of their ability to alleviate inflamed mucosa. This results in a more equal distribution of functional load on the denture-bearing tissue. Resilient denture liner materials are applied to the intaglio surface of dentures to achieve more equal force distribution, reduce localized pressure, and improve denture retention by engaging undercuts.
Ideal properties of resilient liners include resiliency, which is desired over a long period of time, and a good bond to the denture base. Resilient liners can be categorized according to their chemical structures as plasticized acrylic resins, using either chemical or heat polymerization, vinyl resins, polyurethane and polyphosphazine rubbers, and silicone rubbers. Two potential problems commonly identified with a denture base incorporating a resilient liner are a failure of the bond between the acrylic resin and resilient liner material and the loss of resiliency of the resilient liner material over time.
This study intends to evaluate the tensile bond strength and hardness of different resilient liners stored under varying duration in a denture cleansing solution and water.
6.2  REVIEW OF LITERATURE:
1. Kawano F, Edward R, Koran A, and Craig G R (1997) conducted a two phase tensile test of the bond strength of six commercial soft denture liners. The soft denture liners investigated were VinaSoft, Prolastic, Flexor, Molloplast-B, Novus, and SuperSoft. The samples were fabricated by processing them (1) against polymerized poly(methyl methacrylate), and (2) against unpolymerized poly(methyl methacrylate).
The soft denture liners were processed according to the manufacturer’s recommendations. The
samples were tested using a Universal Testing Machine. A two-way analysis of variance revealed a significant increase in bond strength when the liners were processed against polymerized poly(methyl methacrylate), except for Novus, which had no change, and VinaSoft, which decreased.
Four of the six liners investigated demonstrated increased bond strength when processed against polymerized poly(methyl methacrylate). It was concluded that bonding can be influenced by the processing method.1
2. Jagger RG, Athel MS, Jagger DC, and Vowles RW (2002) conducted an invitro study to investigate the effect of roughening the denture base surface on the tensile and shear bond strengths of a poly(dimethylsiloxane) resilient lining material (Molloplast-B) bonded to a heat-cured acrylic resin denture base material. These measured bond strengths were compared to those obtained by packing the soft lining material against poly(methylmethacrylate) (PMMA) denture base acrylic resin dough.
Three groups of 10 specimens each were constructed for both tensile and shear tests. In the first group, Molloplast-B was packed against cured PMMA denture base surface. In the second group, Molloplast-B was packed against cured PMMA denture base whose surface had been roughened with an acrylic bur. In a third group, Molloplast-B was packed against PMMA denture base acrylic resin dough. Molloplast-B exhibited significantly higher tensile and shear bond strengths when packed against acrylic resin dough. Roughening the denture base surface prior to the application of Molloplast-B had a statistically significant weakening effect on tensile bond strength compared with the smooth surface and the acrylic resin dough. For the shear bond strength, roughening the surface produced a non significant increase compared with the smooth surface, but the bond was weaker than when packed against acrylic resin dough.
The authors concluded that significant differences in tensile and shear bond strength
were recorded between the three methods used to bond Molloplast-B to denture base material.2
3. Renta C, Garcia R, Leon LT, Oliveira MB, and Cury BD (2003) evaluated the effects of a denture cleanser on weight change, roughness, and tensile bond strength of 2 denture resilient lining materials.
Forty specimens of microwave acrylic resin 30 mm in diameter and 4 mm thick were prepared to verify weight change and surface roughness. The specimens were divided into 4 groups consisting of 10 specimens each, relined with a resilient liner and treated (Polident or tap water). To evaluate tensile bond strength, 12 specimens were used for each group. All specimens were stored in artificial saliva for 15 days, immersed once a day in Polident or tap water, and evaluated at 0 hours and after 24 hours and 7 and 15 days. Roughness was evaluated by use of a profilometer. Weight changes were recorded in milligrams and expressed as the percentage of weight difference between the periods of evaluation. Tensile bond strength was determined with a universal testing machine. The data were submitted to analysis of variance and compared by Tukey’s test.
The authors concluded within the limitations of this in vitro study that, specimens immersed in Polident demonstrated increased weight changes of resilient liners when compared with tap water, but surface roughness and tensile bond strength were unaffected.3
4. Mese A, and Guzel K G, (2008) evaluated the effect of storage duration on the tensile bond strength and hardness of acrylic resin- and silicone-based resilient liners that were either heat- or autopolymerized onto denture base acrylic resin.
The denture liners investigated were a definitive acrylic resin-based heat-polymerized (Vertex Soft), interim acrylic resin-based autopolymerized (Coe-Soft), definitive silicone-based heat-polymerized (Molloplast- B), and definitive silicone-based autopolymerized (Mollosil Plus) resilient liner. The resilient liners were processed according to manufacturers’ instructions. The
resilient liner specimens for tensile bond strength testing (n=10) were 10 x 10 x 3 mm and were processed between 2 polymethyl methacrylate (PMMA) (Meliodent) blocks (40 x 10 x 10 mm). The resilient liner specimens for hardness testing (n=10) were 20 mm in diameter and 12 mm in height. Specimens were stored for 1 day, 1 week, or 1, 3, or 6 months in water at 37°C. Tensile bond strength was measured in a universal testing machine and hardness was measured using a Shore A durometer. Two-way ANOVA and Tukey HSD tests were used to analyze the data.
Within the limitations of this in vitro study, specimens of resilient liners immersed in water demonstrated significantly lower bond strength values and higher hardness values over time.4
5. Pisani MX, Silva CH, Segundo MA, Macedo AP, and Paranhos HF (2009) conducted an invitro study to investigate the effect of sodium perborate on the bond strength and degree of infiltration between acrylic resin/resilient denture liners.
Three denture liners Elite Soft (Acrylic resin based), Mucopren Soft (Silicon based), Kooliner (Silicon based) were investigated. Twenty specimens (83 x 10 x 10 mm3) of each material were made by processing the denture liners against two polymerized PMMA blocks. Ten specimens for each material were stored in artificial saliva at 37˚C and the other ten specimens were stored in artificial saliva at 37˚C combined with sodium perborate (Corega tabs). All specimens were placed under tension until failure in a Universal Testing Machine at a crosshead speed of 5 mm/min after 7 and 60 days. Failure strength was recorded, and mode of failure was characterized as cohesive, adhesive, or cohesive/adhesive.
For the infiltration tests, ten circular specimens (14-mm diameter x 2-mm thick) of each material were stored in artificial saliva and 0.5% methylene blue at 37˚C, and ten specimens were stored in artificial saliva and 0.5% methylene blue at 37˚C combined with daily immersions for 5 minutes in an effervescent solution of sodium perborate. The degree of infiltration was obtained through photographs and using Software Image Tool after 120 days. For Kooliner, the statistical test did not show a significant difference in the bond strength due to
the influence of the immersion period or to the use of sodium perborate. Elite Soft presented a significant increase in the average tension inversely, the Mucopren suffered a significant decrease in the tension value in the same period. The infiltration percentage was analyzed with
the Kruskal-Wallis, which indicated significant differences between the compared averages for the groups.Comparing the averages of materials, the statistical test did not show significant differences between the control and experimental groups after 120 days.
The authors concluded that the use of sodium perborate did not promote significant alterations in the evaluated properties. Kooliner presented the best results.5
6. Madan N and Datta K. (2012) evaluated the effect of simulated mouth conditions reproduced with thermocycling on the tensile bond strength of two silicone based resilient denture liners with acrylic resin bases.
Two silicone-based soft denture liners (Mollosil - Chairside autopolymerization and Molloplast B - Heat polymerization) were tested. For each liner, 30 specimens with a cross-sectional area of 10 Χ 10 mm and thickness 3 mm were processed between two acrylic blocks (Trevalon). Specimens were divided into a control group that was stored for 24 hours in water at 37°C and a test group that was thermocycled between baths of 5°C and 55°C. Tensile bond strength was determined in a universal testing machine The student t-test was used to determine the significance of the difference in bond strength between the two liners. Comparison of bond strength of control specimens with thermocycled specimens of the liners indicated a significant difference for both Mollosil and Molloplast-B. Comparison between control specimens of both liners and thermocycled specimens of both liners indicated a highly significant difference.
The authors concluded that Heat polymerized resilient denture liner Molloplast-B had higher tensile bond strength than autopolymerizing liner Mollosil regardless of thermocycling. The bond strength of Mollosil increased after thermocycling while that of Molloplast-B decreased
after thermocycling.6
6.3 AIMS AND OBJECTIVES OF THE STUDY
AIM: The aim of this study is to compare the hardness and tensile bond strength of four different denture liners to a heat polymerized acrylic resin following storage in a denture cleansing solution and water over a period of 1 day, 1 week and 1 month.
OBJECTIVES:
1.  To evaluate the tensile bond strength of four different denture liners to a heat polymerized acrylic resin following storage in a denture cleansing solution over a period of 1 day, 1 week and 1 month.
2.  To evaluate the tensile bond strength of four different denture liners to a heat polymerized acrylic resin following storage in water over a period of 1 day, 1 week and 1 month.
3.  To evaluate the hardness of four different denture liners following storage in a denture cleansing solution over a period of 1 day, 1 week and 1 month
4.  To evaluate the hardness of four different denture liners following storage in water over a period of 1 day, 1 week and 1 month
5.  To compare the tensile bond strength of four different denture liners to a heat polymerized acrylic resin following storage in a denture cleansing solution and water over a period of 1 day, 1 week and 1 month.
6.  To compare the hardness of four different denture liners following storage in a denture cleansing solution and water over a period of 1 day, 1 week and 1 month
7.



8.

/ MATERIALS AND METHODS
7.1  Source of the data:
Heat cured denture base specimens of standard size and four commercially available resilient liner materials of which 2 types of acrylic resin based and 2 types of silicone based liners will be used.
Water.
Commercially available denture cleansing solution.
Universal testing machine will be used for testing the tensile bond strength of specimens.
Shore A durometer tester will be used for testing the hardness of the specimens.
7.2  Method of data collection
The study consists of eight groups of ten specimens each for evaluation of tensile bond strength.
Group 1: Heat polymerized acrylic based resilient liner immersed in denture cleansing solution.
Group 2: Autopolymerized acrylic based resilient liner immersed in denture cleansing solution.
Group 3: Heat polymerized silicone based resilient liner immersed in denture cleansing solution.
Group 4: Autopolymerized silicone based resilient liner immersed in denture cleansing solution.
Group 5: Heat polymerized acrylic based resilient liner immersed in water.
Group 6: Autopolymerized acrylic based resilient liner immersed in water.
Group 7: Heat polymerized silicone based resilient liner immersed in water.
Group 8: Autopolymerized silicone based resilient liner immersed in water.
The study consists of eight groups of ten specimens each for evaluation of hardness.
Group 1: Heat polymerized acrylic based resilient liner immersed in denture cleansing solution.
Group 2: Autopolymerized acrylic based resilient liner immersed in denture cleansing solution.
Group 3: Heat polymerized silicone based resilient liner immersed in denture cleansing solution.
Group 4: Autopolymerized silicone based resilient liner immersed in denture cleansing solution.
Group 5: Heat polymerized acrylic based resilient liner immersed in water.
Group 6: Autopolymerized acrylic based resilient liner immersed in water.
Group 7: Heat polymerized silicone based resilient liner immersed in water.
Group 8: Autopolymerized silicone based resilient liner immersed in water.
For the tensile test, ten rectangular specimens with cross-sectional area of 10mmx10mm will be prepared for each group using a heat-polymerized polymethylmethacrylate (PMMA) denture base material. PMMA plates will be made by investing two brass dies (10mm×10mm×40mm) with a 3-mm-thick brass spacer in between them (to create space for resilient liner) in a conventional denture flask. All dies and spacers will be prepared to the same dimensions to standardize the shape of the denture base blocks and the thickness of the resilient denture liners. Specimens for testing tensile bond strength will be fabricated by processing the resilient denture liners between two polymerized PMMA blocks. After polymerization, the specimens will be removed from the flask and trimmed with a sharp blade. Four groups of specimens will be stored in denture cleansing solution at 37°C for 1 day, 1 week and 1 month and four groups of specimens will be stored in water at 37°C for 1 day, 1 week and 1 month. The specimens will be placed under tension until failure in a universal testing machine.