Thekra.doc J Bagh College Dentistry Vol. 27(1), March 2015 Effect of different Restorative Dentistry 92 Effect of different palatal vault shapes and woven glass fiber reinforcement on dimensional stability of high impact acrylic denture base [part II] Shnay M. Atiyah, B.D.S., H.D.D. (1) Thekra I. Hamad, B.D.S., M.Sc., Ph.D. (2) ABSTRACT Background: Change in palatal vault shape and Reinforcement of high impact acrylic denture base resin may in turn affect the dimensional accuracy of acrylic resin and affecting the fitness of the denture. The aim of study is to evaluate the effect of fiber reinforcement for high-impact acrylic resin denture base with different palatal vault shapes on linear dimensional change and effect of palatal vault shapes on linear dimensional changes of non- reinforced and fiber reinforced high impact denture base acrylic resin Material and method: Three different palatal vault shapes were prepared on standard casts using CNC (computer numerical control) machine. 60 samples of heat polymerized high impact acrylic resin maxillary denture base were fabricated onto each definitive cast according to manufacturer instruction. Samples divided into three main experimental groups represented the three different palatal vault shapes (20 samples for each main group); 1st rounded 2nd U-shaped and the 3rd groups V-shaped. Each main group divided into two subgroups (10 samples for each subgroup) representing non fiber reinforced high impact acrylic group as a control and the fiber reinforced high impact acrylic. The measurements of linear dimensional changes of denture bases done at two stages, 1st 24 hour after polymerization and 2nd measurement done after one month storage in distilled water at room temperature. Results and conclusion: Linear dimensional changes of high impact acrylic denture base not affected by glass fiber reinforcement p-value in all reference lines ≥ 0.05, while topographical change in maxillary vault shapes effects on the linear dimensional changes in woven glass fiber reinforced high impact acrylic denture base p-value < 0.05. Key words: High impact acrylic resin, topographical change in vault, woven glass fiber reinforcement. (J Bagh Coll Dentistry 2015; 27(1):92-95). INTRODUCTION Most fractures of maxillary dentures are caused by a combination of fatigue and impact which is reported more in case where maxillary denture base oppose the mandibular natural teeth. The fracture of denture bases when dropped is due to impact force and authors have suggested that repeated flexing from chewing ultimately fatigues the denture in the mouth, in most situations, fractures occur in the midline of the maxillary dentures (1, 2). Considering only the strength though the incorporation of fillers like rubber and fibers to heat-cured poly methyl methacrylate resin improves the impact strength and fatigue resistance (3), improvement may in turn affect some of the properties of heat-cured poly methyl methacrylate resin such as dimensional accuracy, dimensional stability, water sorption, and affecting the fitness of the denture (4). High- impact acrylic denture base is made by the heat- cured dough method; Impact resistance arises from the incorporation of rubber phase into the beads during their suspension polymerization (5), An alternative of the direct addition of elastomers is the use of acrylic/elastomer copolymers. These are, typically, methyl methacrylate-butadiene or (1)Master student. Department of Prosthodontics. College of Dentistry, University of Baghdad. (2)Assistant Professor . Department of Prosthodontics. College of Dentistry, University of Baghdad. methyl methacrylate-butadiene styrene copolymers which are now available in certain commercial products. (6) Dimensional changes caused by water uptake are influenced by the storage period and may compensate the polymerization shrinkage to a certain extent (7). However, after 3 weeks of storage in water, no further significant dimensional changes were observed (8). The aim of study is to evaluate the effect of fiber reinforcement for high-impact acrylic resin denture base with different palatal vault shapes on linear dimensional change and effect of palatal vault shapes on linear dimensional changes of non-reinforced and fiber reinforced high impact denture base acrylic resin. MATERIALS AND METHODS The study involves preparation of 60 samples of heat polymerized high impact acrylic resin maxillary denture base without artificial teeth onto definitive casts according to the recommendations of manufacturer, the samples divided into three main experimental groups represented the three different palatal vaults shapes (20 samples for each main group); 1st rounded, 2nd U-shaped and the 3rd groups V- shaped. Each main group divided into two subgroups (10 samples for each subgroup) representing the non-fiber reinforced high impact J Bagh College Dentistry Vol. 27(1), March 2015 Effect of different Restorative Dentistry 93 acrylic group (NF group) and the fiber reinforced high impact acrylic (WF group) (table 1). According to cross-arch forms three casts with different palatal vault shapes were prepared by carving palatal vault of standard cast using CNC machine (Computer Numerical Control). According to anatomical land marks on the upper master cast four reference points (A, B, C, &D) were chosen and prepared using stainless steel round hand piece bur (018 size) (figure 1). Point (A) was marked in the center of incisive papillary region, points (B) and (C) were marked in the right and left anterior of maxillary tuberosity, and point (D) was marked in the fovea palatine area (Fig.2). Denture base without reinforcement preparation For denture base preparation in three different palatal vault shapes in non-fiber reinforced groups (NFO, NFU, and NFV) heat polymerized high impact acrylic powder and liquid was placed in clean, dry porcelain jar and mixed according to manufacturer instruction 10ml/21gm W/P ratio, mixing time 30 second until the monomer and polymer were thoroughly companied, the jar sealed and the mixture left for 5min at room temperature 22C° (±2) until reaching the dough stage. The resin removed from the jar, rolled and packed into the mold of each flask. Denture bases with glass fiber reinforcement preparation Reinforced high impact acrylic include groups WFO, WFU and WFV, woven type glass fibers were shaped to provide 2mm shorter border than the boundaries of acrylic resin bases (9). Also a study recommended that woven glass fiber reinforcement should be placed on the tensile side of the specimens under loading resulted in considerably higher flexural strength and flexural modulus values (10). As result, in clinical situations the fiber reinforcement in complete maxillary denture base should be close to the oral surface of the denture and perpendicular to the midline; so two layers of high impact acrylic resin precisely prepared to encase the woven glass fibers by using 2 and 3mm thickness record base. Finally for or all specimens (fiber reinforced and non- fiber reinforced high impact denture base) pressed in the hydraulic press under the load of 100 Bar for 5 min. the flasks then placed in clamp and immersed in water bath 70°C for 90 min then the temperature raised to100°C for 30 min according to manufacturer instruction. After curing the flask was left to cool on bench for three hours (11). The samples detached from their corresponding casts and are kept in distilled water to be measured at two periods. The first measurement after one day (24h) then the second measurement done after one month storage in distilled water (12,13), and Measurement of linear dimensional change performed by measuring the distance between the reference points as follow AB, AC, AD, and BC (Fig. 2) using digital microscope at magnification 10X (Fig. 3). Table 1: Research methodology and grouping of the samples Fig. 1: Three maxillary casts with different palatal vault shapes each cast with four reference points (A, B, C, and D) Fig. 2: Denture bases of high impact acrylic with four reference points Fig. 3: Measurement of linear dimensional changes using digital microscope J Bagh College Dentistry Vol. 27(1), March 2015 Effect of different Restorative Dentistry 94 RESULTS Mean difference between two measuring interval calculated (24hours and 30 days immersion in distilled water) for all lines, Standard deviation was examined for mean difference and subjected to statistical analysis (t- test, and ANOVA test). t-test for linear dimensional changes estimated between non- reinforced and reinforced high impact acrylic in Rounded, U-shaped, and V-shape maxillary vault shapes for four lines (table1). ANOVA test for linear dimensional changes affected by change in maxillary vault shape for all lines estimated between reference points in reinforced and non- reinforced high impact acrylic denture base. And when the difference was found to be statistically significant LSD test (least significant difference test) was used for examining differences between each 2 groups. DISCUSSION In the present study it was revealed that water storage of 30 days and fiber reinforcement have no significantly effect on the linear distance between references points marked on high impact acrylic resin bases in all experimental groups and this is agreed with others (14-16). ANOVA test revealed highly significant difference in AC line, and significant difference in AD line, while no significant difference in both AB and BC lines (table 2). Consequently the difference in oral anatomy appear to have a significant effect to the size of the discrepancy level of fiber reinforced high impact acrylic denture base, and this is accepted with the study of Mehmet et al. (17). It may be due to that distribution of linear dimensional changes of fiber reinforced high impact acrylic denture base affected by change in palatal vault shape and not equally distributed. As conclusions 1. Linear dimensional changes of high impact acrylic denture bases stored for 30 days in distal water not affected by woven glass fiber reinforcement. 2. Topographical changes in maxillary vault shape not effect on linear dimensional change of high impact acrylic denture base. 3. Topographical changes in maxillary vault shape effect on linear dimensional changes of woven glass fiber reinforcement of high impact acrylic denture base. Table 2: Linear dimensional changes in different palatal vault shapes between non-reinforced and fiber reinforced high impact acrylic denture base Studied groups No-fiber With fiber t-test No. Mean difference ±SD No. Mean difference ±SD t Sig. (mm) (mm) p-value O -S ha pe AB 10 0.1 0.03 10 0.11 0.03 0.71 0.49 Non sig. AC 10 0.1 0.04 10 0.13 0.04 1.53 0.14 Non sig. AD 10 0.13 0.04 10 0.12 0.04 0.32 0.75 Non sig. BC 10 0.12 0.02 10 0.13 0.02 1.42 0.17 Non sig. U -S ha pe AB 10 0.09 0.01 10 0.12 0.05 0.78 0.578 Non sig. AC 10 0.21 0.01 10 0.18 0.04 0.77 0.452 Non sig. AD 10 0.13 0.03 10 0.15 0.02 0.73 0.475 Non sig. BC 10 0.12 0.02 10 0.13 0.02 0.58 0.388 Non sig. V -S ha pe AB 10 0.13 0.06 10 0.13 0.03 0.75 0.94 Non sig. AC 10 0.29 0.03 10 0.25 0.04 0.38 0.7 Non sig. AD 10 0.14 0.04 10 0.19 0.04 1.73 0.09 Non sig. BC 10 0.21 0.03 10 0.13 0.02 0.8 0.43 Non sig. REFERENCES 1. Johnston EP, Nicholls, Smith PE. Flexural fatigue of 10 commonly used denture base resin. J Prosth Dent 1981; 46(5):478-483. 2. Sung-Hun K, David CW. The effect of reinforcement with woven E-glass fibers on the impact strength of complete dentures fabricated with high-impact acrylic resin. J Prosth Dent 2004; 91:274-80. 3. Uma MB, Patil KG, Nagaraj KR, Shweth K. Comparative analysis of flexural strength of conventional polymethyl methacrylate resin, high impact resin and glass fiber reinforced resin-an in vitro study. Indiana J Dental Sci 2013; 5(4): 77-9. 4. Ranganath LM, Shet RGK, Rajesh AG, Sathish. The Effect of Fiber Reinforcement on the Dimensional Changes of Poly Methyl Methacrylate Resin after Processing and after Immersion in Water: An in vitro Study. The Journal of Contemporary Dental Practice 2011;12(4):305-317 5. O Brain WJ. Dental Materials and Their Selections. 3rd ed. Quintessence Publishing Co.; 2002. 6. McCabe JF, Walls AWG. Applied Dental Materials. 9th ed. Oxford: Blackwell publishing; 2008. J Bagh College Dentistry Vol. 27(1), March 2015 Effect of different Restorative Dentistry 95 Table 3: Linear changes for all lines in three different palatal vaults shapes (Rounded, U-shaped and V-shaped) in non-reinforced and reinforced high impact acrylic denture base Studied groups ANOVA No fiber With fiber No. Mean Difference (mm) F-test p-value No. Mean Difference (mm) F-test p-value AB O-Shape 10 0.1 1.13 0.34 Non sig. (p≥0.05) 10 0.11 0.25 0.78 Non sig (p≥0.05) U-Shape 10 0.1 10 0.12 V-Shape 10 0.13 10 0.13 AC O-Shape 10 0.01 2.62 0.09 Non sig (p≥0.05) 10 0.13 10.7 0.000 Highly sig. (p<0.01) U-Shape 10 0.21 10 0.18 V-Shape 10 0.29 10 0.25 AD O-Shape 10 0.13 0.4 0.67 Non sig (p≥0.05) 10 0.12 3.86 0.03 Sig (p<0.05) U-Shape 10 0.13 10 0.15 V-Shape 10 0.14 10 0.19 BC O-Shape 10 0.11 0.39 0.39 Non sig (p≥0.05) 10 0.13 0.01 0.89 Non sig. (p≥0.05) U-Shape 10 0.12 10 0.13 V-Shape 10 0.21 10 0.13 7. Miessi AC, Goiato MC, dos Santos DM, Dekon SF, Okida RC. Influence of storage period and effect of different brands of acrylic resin on the dimensional accuracy of the maxillary denture base. Braz Dental J 2008; 19: 204-8. 8. Peroz I,Manke P, Zimermann E. Polymerization shrinking of prosthetic plastic materials in a variety of manufacturing processes [in German] ZWR. 1990; 99: 292-6 9. Vallittu PK. Flexural strength of acrylic resin polymers reinforced with unidirectional and woven glass fiber. J Prosth Dent 1999; 81(3): 318-26. 10. Katja KN, Lippo VL, Pekka KV. The Static Strength and Modulus of Fiber Reinforced Denture Base Polymer. Dental Materials 2005; 21:421-8 11. Al-Khafaji AM. The effect of four different cooling procedures on the dimensional stability of microwave- activated acrylic resin at different time interval. J Bagh Coll Dentistry 2011; 23(2): 1-5. 12. Duymus ZY, Yanikoglu ND. Influence of a thickness and processing method on the linear dimensional change and water sorption of denture base resin. Dent Mater J 2004; 23 (1):8-13. 13. Vurakkara V. An in-vitro study to evaluate the effect of thickness of different heat cured acrylic denture base materials on water sorption, linear dimensional change and warpage. Dissertation, Rajiv Gandhi University of Health Sciences, Bangalore, Karnataka, 2006. 14. Rafael LX, Marcelo FM, Mario AC, Simonides C. Influence of the deflasking delay time on the displacements of maxillary denture teeth. J Appl Oral Sci 2003;11(4):332-6 15. Consani RLX, Mesquita MF, Consani S, Correr- Sobrinho L, Sousa-NetoMD. Effect of water storage on tooth displacement in maxillary complete dentures. Braz Dent J 2006; 17:53-57. 16. Henrik V. The effect of processing methods and acrylic resin on the accuracy of maxillary dentures and toothless denture bases: An in vitro study. Quint Int 2011; 42 (8): 669-77. 17. Mehmet D, Demet A, Ali Riza T, Mslim B, Halila P. Effect of different palatal vault shapes on the dimensional stability of glass fiber-reinforced heat- polymerized acrylic resin denture base material. Eur J Dentistry 2012; 6:70-8. الخالصھ یھ الطقمدعم االكلریلك عالي الصدمات المستخدم في قاعده الطقم ممكن ان یؤثر على االستقرار البعدي للراتنج االكلریك ویؤثر بالتالي على ثبوت:المقدمھ صدماتھو بحث تاثیر الیاف االزجاج الداعمھ وتاثیر تغییر شكل القحف على االستقرار البعدي للطقم العلوي المصنوع من راتنج االكلریك عالي ال :الھدف من الدراسھ ج ري باس تعمال م اده الس لیكون الخ اص ث م یستنس خ القال ب الح , ت م تحض یرثالثھ اش كال م ن القح ف للف ك العل وي باس تعمال جھ از النحتب الكومبیوتر الرقم ي :المواد والطرق المس تعملھ تقیس التغیر بالبع د الطولی او الخط ي . عینھ قاعده طقم علوي من ماده االكلریك عالي الصدمات تحضر لكل قالب صخري حسب تعلیمات المنشاء 60.قالب صخري60للحصول على ث م ك ل مجموع ھ رئیس یھ تقس م لمجم وعتین , عین ھ 20ولك ل مجموع ھ , -uوح رف v-ح رفوش كل ,تقس م العین ات ال ى ث الث مجموع ات رئیس یھ حس ب ش كل القح ف وھ ي ال دائري . مجموعھ فرعیھاالولى تستخدم االكریلك عالي الصدمات غیر المدعم والمجموعھ الفرعیھ الثانیھ تس تخدم االكلریل ك ع الي الص دمات الم دعم ): عینات لكل مجموعھ فرعیھ 10(فرعیتین یوم من حفظ العینات بالم اء المقط ر بدرج ھ 30ساعھ من الطبخ والمرحلھ الثانیھ للقیاس تتم بعد 24المرحلھ االولى بعد :ات للبعد الطولي تقاس لمرحلتین كل القیاس. بااللیاف الزجاجیھ .حراره الغرفھ باالض افھ تغیی ر ش كل القح ف الی ؤثر عل ى . الیؤثر باالبع اد الخطی ھ ایض ا وتغییر شكل القحف , االبعاد الخطیھ في االكریلك عالي الصدمات التتأثر بالدعم من االلیاف الزجاجیھ:النتائج الراتنج االكریلك عالي الصدمات المدعم بااللیاف الزجاجیھ .ات المدعم بالیاف الزجاجلكن تغییر شكل القحف یؤثر على االبعاد الخطیھ في االكلریلك علي الصدم, تغییر باالبعاد الخطیھ الیتاثرباستعمال الیاف الزجاج الداعم :االستنتاج