Diss. (sammanfattning) Stockholm : Karol. inst. / Härtill 5 uppsatser.

Indiana University-Purdue University Indianapolis (IUPUI) / The luting agent is a crucial factor in the outcome of cemented fixed restorations. A new water-based cement, Ceramir C&B (CM), approved to be marketed in the US, is composed of calcium aluminate and glass ionomer. CM is a luting agent indicated for permanent cementation of cast restorations, all-zirconia or all-alumina crowns, and prefabricated metal and cast dowel and cores. The manufacturer claims that the cement has demonstrated favorable biocompatibility properties when tested in vitro and in vivo and has proven to be bioactive. The objective of this study was to evaluate volumetric dimensional changes and the amount of Ca2+ released by the new luting agent. Twenty specimens of each material, namely calcium aluminate glass ionomer, resin-modified glass ionomer, and two resin luting agents, were fabricated and weighed. The 20 specimens for all materials were divided into four groups (five samples in each group) based on storage conditions: silicone oil at 22°C and 37°C and distilled water at 22°C and 37°C. Using the manufacturers’ instructions for each material, cylindrical specimens were prepared with dimensions of 7 +0.1 mm in diameter and 2 +0.1 mm in height. A 0.01-mg resolution balance was used to determine volumetric dimensional change using an Archimedean equation. Measurements were made 30 minutes after mixing, and at the time intervals of 7 days, 14 days, 21 days, and 30 days, and after total dehydration of the specimen. Chemical analyses of the solutions were performed using atomic absorption spectroscopy to determine the Ca+2 ion concentration. Moreover, the pH values were measured to determine the OH–concentration in the solutions. The results showed that CM had the most expansion among the tested luting agents in distilled water at 22°C and 37°C, and significantly increased at higher temperature. In silicone oil, resin-modified glass ionomer shrank the most and also shrank more with the high temperature. The result of the ion concentration analysis indicated that Ca+2 and OHion release increased with increasing time and also significantly with temperature rise. In conclusion, calcium aluminate-glass ionomer exhibited the most significant dimensional change when stored in water storage. The solubility of the tested luting agents should be evaluated in the future because they were not evaluated in this study. Furthermore, to evaluate the clinical effect of the dimensional changes, the impact on the gap formation at tooth-crown margins should be determined in future work.

Indiana University-Purdue University Indianapolis (IUPUI) / BACKGROUND: Dental erosion is a multifactorial condition that causes irreversible loss of dental hard tissues. Its development is highly influenced by saliva, with higher prevalence in hyposalivatory patients. There is no scientific consensus regarding the restorative treatment of choice for eroded teeth in such highly erosive conditions and to date, this has not been studied under in-vitro conditions. OBJECTIVES: To investigate the effect of erosion on direct tooth-colored restorations and adjacent enamel/dentin under different simulated salivary flow rates. METHODS: Bovine enamel and dentin specimens were prepared (n =16) and restored with the testing restorative materials, resin-composite (Filtek Z250), resin-modified glass ionomer (Fuji II LC), high viscosity glass ionomer cement (Fuji IX), and low viscosity glass ionomer cement (Fuji II).Then, submitted to an in-vitro erosion cycling model simulating different salivary flow rates (normal 0.5 ml/min and low 0.05 ml/min) and dental erosion protocols for 5 days. Surface loss of the restorative material and surrounding enamel/dentin surfaces were analyzed. A mixed-model ANOVAs and Sidak adjustment were used for statistical comparisons (p < 0.05). RESULTS: The surface loss was lower at 0.5 than at 0.05 ml/min, for all tested restorative materials except resin composite. Surface loss was higher in enamel and dentin adjacent to Filtek Z250 compared to Fuji II LC and Fuji IX, with no significant difference in enamel and dentin surface loss adjacent to Filtek Z250 and Fuji II. The restorations surface degradation was significantly lower for Filtek Z250 than for Fuji II, Fuji II LC, and Fuji IX, at both 0.5 and 0.05 ml/min; moreover, the surface loss was significantly lower for Fuji II LC than for Fuji II and Fuji IX, which did not differ from each other. CONCLUSION: Within the limitations of this study, it can be concluded that low salivary flow promoted higher erosive conditions. The use of Fuji II LC and Fuji IX may reduce erosive effects on enamel and dentin adjacent to restoration. Of the materials evaluated, resin-modified glass ionomer restoration may be the most suitable for restoration for patients at higher risk of erosion with low exposure to fluoride.

Indiana University-Purdue University Indianapolis (IUPUI) / Polymerization shrinkage is one of the most significant problems associated with resin-matrix composite. Shrinkage results in contraction stress in the resin, leading to possible debonding in certain areas of the adhesive joint and potentially adversely affecting the bond strength. The reduction in the stress may improve the adaptation of the resin restoration, and decrease the problems that are associated with contraction stress, such as postoperative pain and recurrent caries. Recently, it has been found that varying the inhibitor concentration would reduce the polymerization shrinkage without affecting mechanical properties. In this study, we investigated the effects of varying the initiator and initiator levels on polymerization shrinkage stress, strength, and degree of conversion. An experimental composite was prepared by using a blend of BisGMA: UDMA: TEGMA (1:1:1 weight ratio) with 70 wt% silanated glass fillers. Four levels of inhibitors (BHT 0.0 %, 2%, 6%, 20%) and initiators (CQ 2%, 6%, 20%, 60%) were used (total of 16 combinations). A tensiometer was used to measure the polymerization contraction stress, contraction stress rate and gel time for each resin. FTIR was used to measure the degree of conversion. The flexural strength and flexural modulus were determined using the three-point bending test. Resin-matrix composite with 0.0-percent BHT and 2.0-percent CQ showed the highest contraction stress and stress rate and the shortest gel time, while resin-matrix composite with the 6.0-percent BHT and 6-percent CQ showed the lowest contraction stress and stress rate and the longest gel time. At an extremely high concentrations of CQ (20 percent and 60 percent) and high BHT concentration (20 percent) low degree of conversion values were observed. Overall, from the collected data, group F (2-percent BHT and 6-percent CQ) and G (6-percent BHT and 6-percent CQ) provide the most desirable combination of strength (above 80 MPa) and stress (below 3 MPa) are present as a potential dose combination range of CQ and BHT. In conclusion, the effect of inhibitors and initiators appears to change in different resin formulation. Increasing the levels of both the inhibitor and the initiator decrease the polymerization contraction stress and stress rate, and the impact on the conversion is unpredictable. In this study, we found a decrease in both the conversion value and depth of cure.

Indiana University-Purdue University Indianapolis (IUPUI) / Several studies have found that resin-based amorphous calcium phosphate (ACP) composites can function well for applications that do not require high mechanical demand. Milled tricalcium phosphate (TCP), a new calcium-phosphate-releasing material, is crystalline in nature, suggesting it to be strong. In the present study, we investigated the use of a TCP-filled composite resin as a possible tooth restorative-material. An experimental TCP-based composite was prepared using monomer with a mixture of 34.3 percent by mass of EBPADMA, 34.2 percent by mass of HmDMA, and 30.5 percent by mass of HEMA. TCP fillers were added to the monomer mixture at different levels (30 percent, 40 percent, 50 percent, and 60 percent by weight). A universal testing machine (Sintech Renew 1121; Instron Engineering Corp., Canton, MA) was used to measure the compressive strength and modulus. FTIR was used to measure the degree of conversion. The depth of cure was determined according to the ISO standards for dental resin 4049 using the scrapping technique. Knoop hardness numbers were obtained by a microhardness tester (M-400; Leco Co., St. Joseph, MI). The viscosities of the experimental resin were determined in a viscometer (DV-II+ Viscometer; Brookfield, Middleboro, MA). The data were analyzed using a one-way analysis of variance (ANOVA). A 5-percent significance level was used for all the tests. Resin composites with 30-percent TCP filler showed the highest compressive strength and hardness values. Also, this group showed the lowest degree of conversion. Resin composites with 60-percent TCP filler showed the highest degree of conversion. However, this group showed the lowest compressive strength, depth of cure, and hardness. Resin composites with 50-percent filler showed the highest compressive modulus. Resin composites with 40-percent filler showed higher viscosity values than resin composites with 30-percent filler. In conclusion, increasing the filler level significantly reduced the compressive strength, hardness, and depth of cure, but increased the degree of conversion. Also, resin composites with the lowest filler level (30 percent) had the highest compressive strength, depth of cure, and hardness. From these results, it can be concluded that the experimental TCP-filled resin used in this study cannot be used as restorative material.

Indiana University-Purdue University Indianapolis (IUPUI) / Background: Since the introduction of glass ionomer cements (GICs) in the 1970s, many attempts have been made to improve them and expand their application in restorative dentistry. Recently, GC America introduced a new glass ionomer restorative system called EQUIA. The manufacturer claims that this material has improved wear resistance by coating the surface of high-strength GIC with a nano-filled resin coating. Objective: The objective of this study was to measure the wear resistance and hardness of EQUIA and to compare it to other current restorative materials. Materials and Methods: Four different materials were used in this study: EQUIA, Fuji IX GP Extra, Fuji II LC and Z-100. Six specimens of each material were made and then tested in a toothbrush abrasion machine for 20,400 cycles, after which the amount of volume loss was calculated. Eight specimens of each material were made and tested in a three-body Alabama wear testing machine under a load of 75 N for 400,000 cycles. Four surface profiles were obtained from each specimen and volume loss was calculated using computer software. Five specimens of each material were made and Knoop microhardness was determined by using the mean of the three values from the top surface of the specimen. Results of each test were collected and compared with the other materials using one-way analysis of variance (ANOVA) at a significance level of 0.05. Results: Wear-resistance results showed that EQUIA has wear-resistance values comparable to composite resin and higher values than those for the high-strength GIC. The results also showed that Fuji II LC had the highest wear among all tested materials. Microhardness results showed that EQUIA has significantly lower microhardness than Fuji IX GP Extra and Z-100. Conclusion: Based on the results of the present study, it can be concluded that coating the surface of glass ionomer restorations with a nano-filled resin coat results in increasing the wear resistance and decreasing the microhardness of the material. Within the limitations of this study, EQUIA has comparable wear resistance to composite resin.

Indiana University-Purdue University Indianapolis (IUPUI) / The use of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP), normally employed as a framework for all-ceramic restorations, has now started to be used without any veneering ceramics in patients with parafunctional activities. The aims of this study were to evaluate the influence of Y-TZP surface roughness on the wear behavior (volume/height loss) against glass-based ceramics (i.e., IPS Empress CAD and IPS e.max CAD, Ivoclar-Vivadent). Thirty-two Y-TZP full-contour zirconia (Ardent®) sliders (ϕ=2 mm, 1.5 mm in height) were milled in a CAD/CAM unit and sintered according to the manufacturer instructions. Sliders were embedded in brass holders using acrylic resin and then randomly allocated into 2 groups according to the surface treatment (n=16): G1-as-machined and G2-glazed (Diazir®). Empress and e.max antagonists were cut into tabs (13×13×2 mm) wet-finished and also embedded in brass holders. Two-body pin-on-disc wear testing was performed at 1.2 Hz for 25,000 cycles under a 3-kg load. Non-contact profilometry was used to measure antagonist height (μm) and volume loss (mm3). Qualitative data of the testing surfaces and wear tracks were obtained using SEM. Statistics were performed using one- and two-way ANOVAs (α=0.05). The results indicated that G1 yielded significantly higher mean roughness values (Ra=0.83 μm, Rq=1.09 μm) than G2 (Ra=0.53 μm, Rq=0.78 μm). Regarding antagonist loss, G1 caused significantly less antagonist mean height and volume loss (68.4 μm, 7.6 mm3) for Empress than G2 (84.9 μm, 9.9 mm3) while no significant differences were found for e.max. Moreover, Empress significantly showed lower mean height and volume loss than e.max (p<0.0001). SEM data revealed morphological differences on wear characteristics between the two ceramics against Y-TZP. Within the limitations of this study, e.max wear was not affected by Y-TZP surface roughness. However, Empress wear was greater when opposing glazed Y-TZP. Overall, based on our findings, surface glazing on full-contour Y-TZP did not minimize glass-ceramic antagonist wear when compared with as-machined group.