Shnay.doc J Bagh College Dentistry Vol. 26(4), December 2014 Effect of different Restorative Dentistry 90 Effect of different palatal vault shapes and woven glass fiber reinforcement on dimensional stability of high impact acrylic denture base [Part I] 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.This study evaluated tostudy the effect of fiber reinforcement for high-impact acrylic resin denture base with different palatal vault shapes on adaptation or gap space between the denture base and the stone cast and compare with non-fiber reinforcement and effect of palatal vault shapes on adaptation 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 gap-space 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: Dimensional changes of high impact acrylic denture base not affected by glass fiber reinforcement p-value for all reference pointes ≥ 0.05, while topographical change in maxillary vault shapes effects on the gap-space in non-fiber reinforced high impact acrylic denture base p-value < 0.05 in point one, four, and seven. Key words: High impact acrylic resin, topographical change in vault, woven glass fiber reinforcement. (J Bagh Coll Dentistry 2014; 26(4):90-94). الخالصھ الكلریك ویؤثر بالتالي على ثبوتیھ الطقمدعم االكلریلك عالي الصدمات المستخدم في قاعده الطقم ممكن ان یؤثر على االستقرار البعدي للراتنج ا: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 ثم یستنسخ القالب الحجري باستعمال ماده السلیكون الخاص للحصول , تعمال جھاز النحتبالكومبیوتر الرقميتم تحضیرثالثھ اشكال من القحف للفك العلوي باس:المواد والطرق المستعملھ ): عینھ لكل طریقھ 60(لقیاس التغییر باالبعاد . عینھ قاعده طقم علوي من ماده االكلریك عالي الصدمات تحضر لكل قالب صخري حسب تعلیمات المنشاء . 60 قالب صخر 06على 20ولكل مجموعھ , -uوحرف v-وشكل حرف,ثم العینات تقسم الى ثالث مجموعات رئیسیھ حسب شكل القحف وھي الدائري . یس مسافھ الفراغ بین القالب الحجري وقاعده الطقم تق كریلك عالي الصدمات غیر المدعم والمجموعھ الفرعیھ مجموعھ فرعیھاالولى تستخدم اال): عینات لكل مجموعھ فرعیھ 10(ثم كل مجموعھ رئیسیھ تقسم لمجموعتین فرعیتین, عینھ ساعھ من 24المرحلھ االولى بعد :كل القیاسات لمسافھ الفراغ بین القالب الحجري وقاعده الطقم تقاس لمرحلتین . الثانیھ تستخدم االكلریلك عالي الصدمات المدعم بااللیاف الزجاجیھ .یوم من حفظ العینات بالماء المقطر بدرجھ حراره الغرفھ 30الطبخ والمرحلھ الثانیھ للقیاس تتم بعد وتغییر شكل القحف یؤثر على مسافھ الفراغ الموجود بین , مسافھ الفراغ بین القالب الحجري وقاعده الطقم في االكریلك عالي الصدمات التتأثر بالدعم من االلیاف الزجاجیھ :النتائج ات تغییر شكل القحف یؤثرعلى مسافھ الفراغ في الراتنج االكریلك عالي الصدمات الغیر مدعم بینما الیؤثر على الراتنج االكریلك عالي الصدمباالضافھ . القالب الصخري وقاعده الطخم المدعم بااللیاف الزجاجیھ لكن تغییر شكل القحف یؤثر في مسافھ الفراغ في االكریلك عالي , متغییرومسافھ الفراغ الموجود بین القالب الحجري وقاعده الطقم الیتاثرباستعمال الیاف الزجاج الداع :االستنتاج الصدمات 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 (1)Master student. Department of Prosthodontics. College of Dentistry, University of Baghdad. (2)Assistant Professor . Department of Prosthodontics. College of Dentistry, University of Baghdad. 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 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). J Bagh College Dentistry Vol. 26(4), December 2014 Effect of different Restorative Dentistry 91 MATERIAL 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 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). Table 1: Research methodology and grouping of the samples 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 bases. 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 were 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). Fig. 1: Maxillary cast with denture base sectioned through two imaginary lines with a precision rotary microtome The samples deflasked with their corresponding stone cast and sectioned in two positions, first the specimens were sagittal sectioned with a precision rotary microtome in an anteroposterior direction along the imaginary line passing through the midline. A second frontal cross section prepared and its perpendicular to the sagittal section (12,113) (fig 1). The cutting was made on a fixer table under constant water cooling.Four reference points were marked along the resin base/stone cast interface in sagittal section which corresponded to [anterior maxillary ridge (1), anterior part of vault area (2), middle of the vault area (3), posterior termination of vault area (4) ] (4) and three reference points were marked at frontal cross section which represent the posterior palatal border gap area measurement which corresponded to[ slop of posterior ridge (5), posterior maxillary ridge (6), middle of buccal vestibule (7) ](fig 2) (13-16). Then the prepared acrylic specimens were kept in plastic containers containing distilled water.To determine the adaptation or interfacial gap between high impact acrylic resin bases and the stone casts after water storage a digital microscope used under magnification power of 200X. The total seven reference points at each specimen were J Bagh College Dentistry Vol. 26(4), December 2014 Effect of different Restorative Dentistry 92 measuredat two periods first 24 hours after polymerization process and storage in distilled water. A second measurement was performed after the storage in distilled water for 30 days (17). Fig. 2: Total seven reference points for adaptation measurement RESULTS Mean difference between two measuring interval calculated (24 hours and 30 daysimmersion in distilled water) for all reference points, Standard deviation was examined for mean difference and subjected to statistical analysis (t- test, and ANOVA test).t-test for gap space dimensional changes estimatedbetween non- reinforced and reinforced high impact acrylic in Rounded, U-shaped, and V-shape maxillary vault shapes for seven reference points. The t-test result reveals non-significant difference in all reference points ANOVA test for gap space dimensional changes affected by change in maxillary vaultshape for all reference points in reinforced and non-reinforced high impact acrylic denture base.When the difference wasfound to be statistically significant LSD test (least significant difference test) was used for examining differences between each 2 groups Table 2: Gap space (Adaptation) of non-reinforced and fiber reinforced high impact acrylic denture base in different palatal vault shapes Studied groups No-fiber With-fiber Comparison No. Mean Difference (mm) ±SD No. Mean Difference (mm) ±SD t-test p-value Sig. O -S ha pe 1 10 0.01 0 10 0.01 0 0.08 0.93 NS 2 10 0.012 0 10 0.013 0 0.55 0.58 NS 3 10 0.015 0 10 0.017 0 0.57 0.57 NS 4 10 0.01 0 10 0.016 0 0.32 0.74 NS 5 10 0.014 0 10 0.015 0 0.24 0.8 NS 6 10 0.009 0 10 0.012 0 0.28 0.82 NS 7 10 0.01 0 10 0.01 0 1.33 0.19 NS U -S ha pe 1 10 0.015 0 10 0.015 0.01 0.06 0.94 NS 2 10 0.014 0 10 0.016 0.01 0.99 0.33 NS 3 10 0.016 0 10 0.017 0.01 0.24 0.81 NS 4 10 0.012 0 10 0.016 0 1.55 0.14 NS 5 10 0.015 0 10 0.015 0 0.14 0.88 NS 6 10 0.009 0 10 0.012 0 1.23 0.23 NS 7 10 0.01 0 10 0.012 0 0.22 0.82 NS V -S ha pe 1 10 0.006 0 10 0.008 0 1.41 0.17 NS 2 10 0.01 0 10 0.016 0 2.1 0.05 NS 3 10 0.017 0 10 0.016 0 0.39 0.69 NS 4 10 0.018 0 10 0.018 0 0.02 0.98 NS 5 10 0.018 0 10 0.019 0 0.45 0.65 NS 6 10 0.009 0 10 0.012 0 1.62 0.12 NS 7 10 0.01 0 10 0.011 0 0.16 0.87 NS J Bagh College Dentistry Vol. 26(4), December 2014 Effect of different Restorative Dentistry 93 Table 3: Gap space change in reference points in three different palatal vaults shapes (Rounded, U-shaped and V-shaped) in non- reinforced and fiber 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 Point 1 O-Shape 10 0.01 3.41 0.048 Sig P<0.05 10 0.01 2.67 0.087 Non Sig P≥0.05 U-Shape 10 0.015 10 0.015 V-Shape 10 0.015 10 0.008 Point 2 O-Shape 10 0.012 0.89 0.42 Non Sig P>0.05 10 0.013 1.48 0.24 Non Sig P≥0.05 U-Shape 10 0.014 10 0.016 V-Shape 10 0.01 10 0.016 Point 3 O-Shape 10 0.015 0.31 0.73 Non sig. P>0.05 10 0.017 1.48 0.98 Non Sig. P≥0.05 U-Shape 10 0.016 10 0.017 V-Shape 10 0.017 10 0.016 Point4 O-Shape 10 0.01 6.05 0 Highly Sig. p≤0.00 10 0.016 0.01 0.99 Non Sig. P≥0.05. U-Shape 10 0.013 10 0.016 V-Shape 10 0.018 10 0.018 Point 5 O-Shape 10 0.014 1.65 0.21 Non Sig. P≥0.05. 10 0.015 0.99 0.385 Non Sig. P≥0.05. U-Shape 10 0.015 10 0.015 V-Shape 10 0.019 10 0.02 Point 6 O-Shape 10 0.009 0.006 0.994 Non-sig. 10 0.012 0.031 0.97 Non-sig. P≥0.05. U-Shape 10 0.009 10 0.012 V-Shape 10 0.009 10 0.012 Point 7 O-Shape 10 0.019 9.13 0.001 Highly Sig. p≤0.00 10 0.015 1.69 0.202 Non Sig. P≥0.05. U-Shape 10 0.01 10 0.011 V-Shape 10 0.01 10 0.011 DISCUSSION The result demonstrated that fiber impregnation into high impact acrylic resin bases does not affect the magnitude of interfacial gap between the base and the stone cast surface, after 30 days of water storage (table 1). This finding is similar with the statement of Polat et al. (18) who reported that the dimensional stability of conventional acrylic resin denture base material not affected with fiber reinforcement.The study also revealed that the smallest dimensional discrepancies were found in the regions corresponding to the crests of the alveolar ridges (point 1 and point 6), these two points have smaller mean difference value than the values found in the median region of the palate (point 1, 3, and 4), and this result agreed with Rizzatti- Barbosa et al. (19), who found that the smallest dimensional discrepancies were found in the regions corresponding to the crests of thealveolar ridges immediately after resin base removal, this result may be due to that palatal region more affected by stress release and from processing pressure on these area. The results of gap-space changes in different palatal vault shape in non-reinforced high impact acrylic denture base revealed significant difference in points (1, 4, and 7) (table 2). It seemed that change in palatal vault shape and difference of the type of tissues in the posterior area near post-dam area may cause a large discrepancy in gap space in high impact acrylic denture base resin this is in agreement with the results of Chen et al. (20), who found that an increase in dimensional changes in the posterior area of the palate for most dentures analyzed after 30 days of water storage. The conclusions that can be drawn from this study are: 1. Gap-space change of high impact acrylic denture base stored for 30 days in distal water not affected by woven glass fiber reinforcement. 2. Topographical changes in maxillary vault shape effect on gap-space dimensional changes of high impact acrylic denture base. 3. Topographical changes in maxillary vault shape not effect on gap-space dimensional change of woven glass fiber reinforcement of high impact acrylic denture base. 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