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) / Indirect composites were introduced so that the composites can be cured extraorally to improve the degree of conversion and other material properties. These materials are indicated as long term full coverage dental restorative materials. However the mechanical and physical properties of new Second Generation Indirect Composites for this particular application have not been fully evaluated. The purpose of the study was to compare the appropriateness of the four commercially available laboratory composite resins for application as long term full coverage restorative materials. Water solubility and sorption levels, staining resistance, gloss, surface roughness, wear due to tooth brush abrasion, two-body and three-body wear, fracture toughness and radiopacity of four indirect composite restorative materials; Radica (Dentsply), Sculpture Plus (Pentron), Belleglass-NG (Kerr) and Gradia Indirect (GC America) were determined. The results showed that the four composites differed significantly from each other. Bell eglass-NG and Gradia Indirect showed negative water solubility. All the four groups demonstrated less color stability when exposed to coffee slurry for 3 weeks. Significant decrease in gloss and volume occurred when the omposites were exposed to simulated tooth-brush abrasion. Sculpture Plus v demonstrated lowest abrasion and attrition wear resistance among the four indirect composites. Radica had the highest fracture toughness and radiopacity of all the composites with values close to or less then dentin. In conclusion, different indirect composite systems possessed different mechanical and physical advantages when compared to each other. In general, Belleglass-NG demonstrated superior advantages due to its higher abrasion and attrition wear resistance and stain resistance. This was followed by Radica,Gradia Indirect and Sculpture Plus.

Indiana University-Purdue University Indianapolis (IUPUI) / This study evaluated the color stability of bleach shade composites when activated by a high-intensity quartz tungsten-halogen (QTH) light source after 1 day, 7 days, and 30 days of exposure to different conditions. The color stability of bleach shade composites depends on various factors, namely, the resin material, the shade of the resin material, the storage method, and the storage time.

Indiana University-Purdue University Indianapolis (IUPUI) / Objectives: A new technology has been introduced into the field of dental resin composites that professes to enhance light-curing efficiency. Rapid amplified photopolymerization (RAP) initiator technology has not yet been fully compared with resin composites with conventional initiators such as camphorquinone (CQ). The purpose of this study was to compare and contrast the effects of this novel technology (RAP) on properties of two light-cured resin composites. Flowable (EFQ) and microfilled (ESQ) experimental composites were fabricated and supplied from Tokuyama Dental with (w/RAP) and without RAP (w/o RAP). The flexural strength (MPa) and flexural modulus (MPa) were obtained using a three-point bending apparatus (Sintech Renew 1123, Instron Engineering Corp., Canton, MA). Polymerization stress curves were created using a tensometer (American Dental Association Health Foundation, NIST, Gaithersburg, MD) which were then used to calculate the maximum stress rate. Finally, the degree of conversion was measured using infrared spectroscopy (Jassco FT-IR spectrometer, Model: 4100, Jasco Corporation, Tokyo, Japan). When evaluating the flexural strength, the peak stress for EFQ w/RAP was significantly higher than EFQ w/o RAP (p = 0.0001). This was statistically not significant for the ESQ group, even though ESQ w/RAP did have a higher peak stress then ESQ w/o RAP (p = 0.28). The interaction between resin type and RAP was not significant when evaluating the flexural modulus (p = 0.21). Formulations with RAP had a significantly higher flexural modulus then w/o RAP (p = 0.0001). Experimental resins with RAP had significantly higher maximum stress rates than those w/o RAP when evaluating polymerization stress (p = 0.0001). Finally, groups w/ RAP appeared to have a higher degree of conversion than groups without (p = 0.0057). This study showed that the experimental composites with RAP had greater mechanical properties than those without. Unfortunately, the increase in polymerization stress causes concern clinically due to the chance of leakage at the restoration/tooth interface. One of the main potential disadvantages of this new RAP technology is an increase in the polymerization stress. Deciding if this amount of polymerization stress is clinically acceptable is yet to be accomplished.

Indiana University-Purdue University Indianapolis (IUPUI) / A provisional restoration must fulfill biologic, mechanical, and esthetic requirements. These prostheses should provide comfort, pulp protection, positional stability, occlusal function, hygiene access, esthetics, strength and retention. Methyl-methacrylate acrylic has assumed many appli¬cations in the field of restorative dentistry. However, the material still has deficiencies, such as polymerization shrinkage, pulpal damage associated with exothermic polymerization and susceptibility to fracture. Bis-GMA composites, Bis-acryl composites and visible light-cured urethane dimethacrylate resins have been developed to address these issues. The purpose of this study was to compare the mechanical properties of provisional restorations made from composite resins (Protemp Plus, Luxatemp Solar, Radica, Protemp Crown) to those made of the traditional methacrylate resins (Jet, Snap, High Impact). Six groups of samples, two groups from methacrylate and four groups from composite based materials, were fabricated. Samples from each group were evaluated for microhardness (n=10), flexural strength and flexural modulus (n=20) according to ISO 4049, and fracture toughness (n=20) according to ISO 13586. From each of the six groups, ten samples were tested for flexural strength, flexural modulus and fracture toughness and 5 samples were tested for microhardness. These tests were done after storing at 37°C in a distilled water solution for 7 days followed by thermal cycling (2500 cycles, 5-55°C, 45 s. dwell). Identical sets of samples from each group were used as controls; these were tested after storing for 24 hours in dry conditions. The results were analyzed by two-way ANOVA with material type and aging conditions as the two main variables. Significance level was set at p=0.05. For flexural strength and flexural modules, the higher values were obtained for Radica. Protemp plus (7 days) and Radica (24h) had the highest fracture toughness value. Protemp crown showed the highest surface hardness. The mechanical properties of composite resin were superior.

Indiana University-Purdue University Indianapolis (IUPUI) / Background: Interim restoration for a lost anterior tooth is often needed for temporary esthetic and functional purposes. Materials for interim restorations usually have less strength than ceramic or gold and can suffer from fracture. Several approaches have been proposed to reinforce interim restorations, among which fiber reinforcement has been regarded as one of the most effective methods. However, some studies have found that the limitation of this method is the poor polymerization between the fibers and the composite resin, which can cause debonding and failure. 64 Purpose: The purpose of this study was to investigate the effects of different polymerization methods as well as fiber types on the mechanical behavior of fiberreinforced composite resin. Material and Methods: A 0.2-mm thick fiber layer from strip fibers or mesh fibers embedded in uncured monomers w as fabricated with polymerization (two-step method) or without polymerization (one-step method), on top of which a 1.8-mm composite layer was added to make a bar-shape sample, followed by a final polymerization. Seventy-five specimens were fabricated and divided into one control group and four experimental groups (n=15), according to the type of glass fiber (strip or mesh) and polymerization methods (one-step or two-step). Specimens were tested for flexural strength, flexural modulus, and microhardness. The failure modes of specimens were observed by scanning electron microscopy (SEM). Results: The fiber types showed significant effect on the flexural strength of test specimens (F = 469.48; p < 0.05), but the polymerization methods had no significant effect (F = 0.05; p = 0.82). The interaction between these two variables was not significant (F = 1.73; p = 0.19). In addition, both fiber types and polymerization steps affected the flexural modulus of test specimens (F = 9.71; p < 0.05 for fiber type, and F = 12.17; p < 0.05 for polymerization method). However, the interaction between these two variables was not significant (F = 0.40; p = 0.53). Both fiber types and polymerization steps affected the Knoop hardness number of test specimens (F = 5.73; p < 0.05 for polymerization method. and F = 349.99; p < 0.05 for fiber type) and the interaction between these two variables was also significant (F = 5.73; p < 0.05). SEM images revealed the failure mode tended to become repairable while fiber reinforcement was 65 existed. However, different polymerization methods did not change the failure mode. Conclusion: The strip fibers showed better mechanical behavior than mesh fibers and were suggested for use in composite resin reinforcement. However, different polymerization methods did not have significant effect on the strength and the failure mode of fiber-reinforced composite

Indiana University-Purdue University Indianapolis (IUPUI) / The purpose of this study is to further investigate the effect of using six different light source types with different light output intensities on the parameters of a mathematical model that predicts the DOC in VLDC’s. In this equation: D = Dp In(E0/Ec), D is the depth of cure in millimeters, E is the curing energy in J/cm2, Ec is the critical curing energy for the composite to reach a gel layer, and Dp is a characteristic coefficient. Three LED and three halogen dental curing units with different light output intensities were used to cure three shades (B1, A3, D3) of a hybrid resin composite. The exposure duration was at the intervals of 10, 20, 30, and 40 seconds for each sample setting. ISO scraping technique was performed to measure the depth of cure of each sample. Regression analysis was used to assess the fit of the proposed mathematical model D = Dp In(E0/Ec) to the experimental data obtained in this study. 72 For all the shade-light combinations; A3, B1, and D3 had significantly different regression lines (P < 0.05) with significantly higher Dp and Ec for B1 than A3 and D3. The only exceptions were for the Ec values between B1 and D3 in Allegro, Astralis 5, and Visilux 2 groups; and the Ec between A3 and B1 in Allegro group. The Dp and Ec parameters didn’t show significant differences between A3 and D3 shades in all the groups. Also, most of the significant differences for Dp values occurred in the B1 shade-light combinations; however, none of the D3 shade-light combinations showed significant differences for Dp. Several factors play combined influential effects on the kinetics of polymerization and depth of cure in VLDC’s. The shade has a more dominant effect on both parameters Dp and Ec than the curing light type or source output intensity. As we cure lighter shades “B1,” the effect of using different lights with different output intensities on the two parameters Dp and Ec will be greater and more significant than for darker shades “A3 or D3.” The clinical significance drawn from this study is that clinicians should recognize that using curing lights w/ increased output intensities doesn’t absolutely increase the DOC of VLDC’s especially with the darker shades.

Indiana University-Purdue University Indianapolis (IUPUI) / The purpose of this study was 1) To determine the impact of eliminating or delaying the photo-activation procedure on the polymerization contraction stress (PCS)and degree of conversion (DC) of a dual-cured resin luting agent, and 2) To determine the amount of delay in photo-initiation of the dual-cured resin cements that can achieve a reduced PCS value with the highest possible DC. The amount of PCS and DC of a dual-cured resin luting agent was determined using a tensometer and ATR spectroscopic technique, respectively. Photo-activation delay in seven tested groups was 0 min, 2 min, 4 min, 6 min, 8 min, 10 min and no photoactivation. Five samples for each group were tested. There were two hypotheses for this study: 1) A significant decrease in the amount of PCS associated with delayed photo-activation, and 2) A significant increase in DC associated with delayed photo-activation.The PCS of the chemical-cure luting agent had significantly lower value than all of the light-cure groups. For the light-cure groups, those with a 4-min delay had higher PCS than those with delays of 0 min, 2 min, 6 min, 8 min, and 10 min. The zero (0)-min and 2-min delay had higher PCS than the 6-min, 8-min, and 10-min delay; and the 6-min delay had higher PCS than the 8-min and 10-min delay. The PCS decreased 0.086 MPa per minute of delay. The DC of the chemical-cure luting agent had significantly lower value than the 2-min, 4-min, 6-min, 8-min, and 10-min delaylight cure. For the light-cure groups, 0-min delay had a lower DC than the 2-min, 4-min, 6-min, 8-min, and 10-min delay; 2-min delay had lower DC than 4-min, 6-min, 8-min, and 10-min delay. The 4-min and 6-min delay had lower DC than the 8-min and 10-min delay; and the 8-min delay had a lower degree of conversion by peak area than the 10- minute delay. The DC increased 0.021 per minute of delay. Extending the stress relief period of the dual-cured luting agents by delaying light activation has a significant impact on PCS and DC values. There was significant decrease in PCS with the delayed light curing of the resin luting agent. Significant increase in DC was noticed when light activation was delayed in the dual-cured resin luting agents.

Indiana University-Purdue University Indianapolis (IUPUI) / Background: A silorane based resin composite, Filtek LS restorative, has been introduced to overcome the polymerization shrinkage of the methacrylate based resin composite. The repair of resin composite may hold clinical advantages. Currently, there is no available information regarding the repair potential of silorane resin composite with either silorane or methacrylate based resin composite. Objectives: The purpose of this study was to compare the repaired microtensile bond strength of aged silorane resin composite using different surface treatments and either silorane or methacrylate based resin composite. Methods: One hundred and eight silorane resin composite blocks (Filtek LS) were fabricated and aged by thermocycling between 8oC and 48oC (5000 cycles). A control (solid resin composite) and four surface treatment groups (no treatment, acid treatment, aluminum oxide sandblasting and diamond bur abrasion) were tested. Each treatment group was randomly divided in half and repaired with either silorane resin composite (LS adhesive) or methacrylate based resin composite (Filtek Z250/Single Bond Plus). Specimens were 12 blocks and 108 beams per group. After 24 hours in 37oC distilled water, microtensile bond strength testing was performed using a non-trimming technique. Fracture surfaces were examined using an optical microscopy (20X) to determine failure mode. Data was analyzed using Weibull-distribution survival analysis. Results: Aluminum oxide sandblasting followed by silorane or methacrylate based resin composite and acid treatment with methacrylate based resin composite provided insignificant differences from the control (p>0.05). All other groups were significantly lower than the control. Failure was primarily adhesive in all groups. Conclusion: Aluminum oxide sandblasting produced comparable microtensile bond strength compared to the cohesive strength of silorane resin composite. After aluminum oxide sandblasting, aged silorane resin composite can be repaired with either silorane resin composite with LS system adhesive or methacrylate based resin composite with methacrylate based dentin adhesive.

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.