Novel dental composite resin derived from rice husk natural biowaste: A systematic review and recommendation for future advancement.

OBJECTIVES: This review aimed to summarize contemporary evidence related to dental composite resin derived from rice husk biowaste and its potential future advancement. This review paper included the techniques for synthesis, characterization, and preparation of rice husk composite resin. Focus was also given to the flexural strength and modulus, compressive strength, wear rate, hardness, surface roughness, color stability, polymerization shrinkage, degree of conversion, and their application onto root canal treated teeth. MATERIAL AND METHODS: A search of English peer-reviewed literature (January 1960-February 2021) was conducted from electronic databases (PubMed Central, Cochrane, LILACS, Science Direct, Web of Science, SIGLE, EMBASE, EBSCO, Medline, and Google Scholar). RESULTS: 11 articles and a book section were finally selected for qualitative analysis. Studies concluded that the physicomechanical properties and the color stability of rice husk dental composites showed comparable results to conventional dental composites. Incorporation of zirconia nanopowder into rice husk dental composite increased the compressive strength and hardness values, associated with lower shrinkage, a high degree of conversion, and improved fracture strength when applied on root canal treated teeth. CONCLUSIONS: Due to its low cost, eco-friendliness, and acceptable clinical performances, rice husk dental composite resin can be considered as an alternative to conventional composites. CLINICAL SIGNIFICANCE: Dental composite resin derived from rice husk silica demonstrated excellent performance, which could potentially substitute currently available composite resins. This review will give new insight to clinicians and researchers on the usage of natural biowaste mass in the field of dental restorative materials.

New Experimental Zirconia-Reinforced Rice Husk Nanohybrid Composite and the Outcome of Its Surface Roughness and Microhardness in Comparison with Commercialized Nanofilled and Microhybrid Composite Resins.

BACKGROUND: An ideal composite resin should demonstrate smooth surface after polishing and high hardness value to provide long-term success. Thus, this study aimed to compare the surface roughness and microhardness of new experimental zirconia-reinforced rice husk nanohybrid composite (Zr-Hybrid) with commercialized nanofilled (Filtek-Z350-XT) and microhybrid composite (Zmack-Comp) resins before and after artificial ageing. METHODS: One hundred and eighty standardized disc samples were prepared, of which ninety samples each were used for surface roughness and microhardness test, respectively. They were divided equally into: Group 1 (Filtek-Z350-XT), Group 2 (Zmack-Comp), and Group 3 (Zr-Hybrid). For surface roughness test, all samples were polished with aluminium oxide discs and further subdivided into aged and unaged subgroups, in which composite samples in aged subgroups were subjected to 2500 thermal cycles. Next, all the samples were subjected to surface roughness test using a contact stylus profilometer. As for microhardness test, all the aged and unaged samples were tested using a Vickers hardness machine with a load of 300 kgf for 10 s and viewed under a digital microscope to obtain microhardness value. Data were analyzed using two-way ANOVA followed by post hoc Tukey's honestly significant difference and paired sample t-test with significance level set at P = 0.05. RESULTS: In both the aged and unaged groups, Zr-Hybrid showed statistically significantly lower surface roughness (P < 0.05) than Filtek-Z350-XT and Zmack-Comp, but no statistically significant difference was noted between Filtek-Z350-XT and Zmack-Comp (P > 0.05). A similar pattern was noted in microhardness test, whereby Zr-Hybrid showed the highest value (P < 0.05) followed by Filtek-Z350-XT and lastly Zmack-Comp. Besides, significant differences in surface roughness and microhardness were noted between the aged and unaged groups. CONCLUSION: Zr-Hybrid seems to demonstrate better surface roughness and microhardness value before and after artificial ageing.

Dislodgement resistance and adhesive pattern of different endodontic sealers to dentine wall after artificial ageing: an in-vitro study.

To compare the dislodgement resistance and the adhesive pattern of four different endodontic sealers to root dentine walls. Ninety lower premolars were assigned to five groups (n = 18), Group 1: no sealer (control); Group 2: EndoRez (ERZ); Group 3: Sealapex (SPX); Group 4: EndoSeal MTA (ESA) and Group 5: BioRoot RCS (BRS). They were instrumented up to size 30 taper 0.06 and obturated using single cone technique with matched-taper gutta-percha cones and one of the mentioned sealers. Six teeth from each group were then randomly subjected to 100, 1000 and 10,000 thermocycles, respectively. 1 mm slice of mid root region, measuring 6 mm from the apical foramen was prepared and subjected to push-out test under a Universal Testing Machine. Adhesive patterns of sealers were assessed using a stereomicroscope at 20 × magnification and classified using a new system. Statistical analyses were performed using two-way ANOVA, complemented by Tukey HSD and Chi-square tests. ESA and BRS showed significantly higher (p < 0.05) push-out bond strength, followed by SPX, ERZ and lastly the control, but no significant difference was noted between ESA and BRS (p > 0.05) at 100, 1000 and 10,000 thermocycles, respectively. Both ESA and BRS exhibited a significant higher rate (p < 0.05) of Type 3 and Type 4 adhesive patterns as the thermocycles increased. ESA and BRS demonstrated higher bond strength and better adhesive pattern to root dentine wall than SPX and ERZ, especially after artificial ageing.

The effect of accelerated aging on the color stability and translucency of novel zirconia reinforced rice husk dental composite resin in different infusion media / O efeito do envelhecimento acelerado na estabilidade de cor e translucidez de uma nova resina composta de casca de arroz reforçada com zircônia em diferentes meios de infusão

Objective: To compare the color stability and translucency of aged and unaged experimental zirconia reinforced rice husk nanohybrid composite resin (Zr-Hybrid) with a commercialized nanofilled and a microhybrid composite resin after immersion in four different infusion media. Material and Methods: Three groups of standardized disc-shaped composite resin with 80 samples per group were prepared as follow: Group 1 (Filtek-Z350-XT), Group 2 (Zmack-Comp), and Group 3 (Zr-Hybrid). Each group was further subdivided into aged (n=40) and unaged (n=40) groups. Initial color measurements were taken using a digital spectrophotometer based on CIE L*a*b* color system. Samples in aged subgroup were subjected to 2500 thermal cycles. Subsequently, all samples were immersed in four different types of infusion media (n=10): T1 - Distilled water, T2 - Soft drink, T3 - Tea and T4 - Coffee. After 15 days, color measurements of all samples were measured again. Data were analyzed using two-way ANOVA followed by Bonferroni and paired sample t-tests with a significance level set at P=0.05. Results: Unaged Zr-Hybrid showed comparable color change to Zmack-Comp and Filtek-Z350-XT (P=0.181), but aged Zr-Hybrid demonstrated the lowest color change (P<0.001). Zr-Hybrid exhibited the lowest translucency value (P<0.001), but no significant color and translucency changes (P=0.051 and P=0.069, respectively) were observed between unaged and aged Zr-Hybrid. Soft drink had the greatest effect (P<0.001) on color change, while coffee showed the greatest effect (P<0.001) on translucency. Conclusion: Although Zr-Hybrid showed greater opacity, it still retained its color stability and translucency after accelerated aging compared to commercialized microhybrid and nanofilled composite resins. All infusion media caused discoloration and affected the composite resins' translucency. (AU)

Objetivo: Comparar a estabilidade de cor e translucidez de uma resina composta nanohíbrida de casca de arroz reforçada com zircônia experimental envelhecida e não envelhecida (Zr-Hybrid) com uma resina composta comercial nanoparticulada e microhíbrida após a imersão em quatro meios de infusão diferentes. Material e Métodos: Três grupos de resina composta em forma de disco padronizado com 80 amostras por grupo foram preparados da seguinte forma: Grupo 1 (Filtek-Z350-XT), Grupo 2 (Zmack-Comp) e Grupo 3 (Zr-Hybrid). Cada grupo foi subdividido em grupos de envelhecimento (n = 40) e não envelhecimento (n = 40). As medições iniciais de cor foram feitas usando um espectrofotômetro digital baseado no sistema de cores CIE L * a * b *. As amostras do subgrupo envelhecido foram submetidas a 2500 ciclos térmicos. Posteriormente, todas as amostras foram imersas em quatro tipos diferentes de meios de infusão (n = 10): T1 - Água destilada, T2 - Refrigerante,T3 - Chá e T4 - Café. Após 15 dias, as medições de cor de todas as amostras foram medidas novamente. Os dados foram analisados usando ANOVA dois fatores seguido por Bonferroni e testes t pareados com nível de significância estabelecido em P = 0,05. Resultados: O grupo Zr-Hybrid não envelhecido mostrou uma mudança de cor comparável a Zmack-Comp e Filtek-Z350-XT (P = 0,181), mas o grupo Zr-Hybrid envelhecido demonstrou a menor mudança de cor (P <0,001). Zr-Hybrid exibiu o menor valor de translucidez (P <0,001), mas nenhuma mudança significativa de cor e translucidez (P = 0,051 e P = 0,069, respectivamente) foram observadas entre Zr-Hybrid não envelhecido e envelhecido. O refrigerante teve o maior efeito (P <0,001) na mudança de cor, enquanto o café apresentou o maior efeito (P <0,001) na translucidez. Conclusão: Apesar do grupo Zr-Hybrid tenha mostrado maior opacidade, ele ainda manteve sua estabilidade de cor e translucidez após envelhecimento acelerado em comparação com resinas compostas micro-híbridas e nanoparticuladas comercializadas. Todos os meios de infusão causaram descoloração e afetaram a translucidez das resinas compostas (AU)

Fracture strength of endodontically treated lateral incisors restored with new zirconia reinforced rice husk nanohybrid composite.

BACKGROUND: This study aimed to compare the fracture strength, fracture pattern and type of fracture of endodontically treated maxillary lateral incisors restored with new zirconia reinforced rice husk nanohybrid composite. MATERIAL AND METHODS: Eighty mature permanent maxillary lateral incisors from patients age range of 30-60 years with single canal were selected and randomly divided into: Group 1 - RCT + nanofilled composite (Filtek), Group 2 - RCT + microhybrid composite (Zmack), Group 3 - RCT + new nanohybrid composite (Zr-Hybrid) and Group 4 - Intact teeth (control). Standardized mesio-palatal-distal cavity was prepared, and endodontic treatment was carried out using crown-down technique until size 30, tapered 0.04. Obturation was completed using single cone technique with gutta-percha and AH plus sealer. Cavity access was restored with respective composite resins. Next, teeth were stored in incubator for 24 hours and subdivided into aged and unaged subgroups. Teeth in aged subgroups were subjected to 2500 thermal cycles for 5ºC, 37ºC and 55ºC with 30 seconds dwell time and 5 seconds transfer time. After that, root surfaces of teeth were covered with silicone-based material and placed in boxes filled with acrylic until the cemento-enamel-junction (CEJ) level. They were then tested under Universal Testing Machine until fracture occurred. Samples were then viewed under Leica microscope to determine the fracture pattern and type of fracture. Data analyzed using One-way ANOVA complimented by post hoc Tukey HSD and paired sample T test for fracture strength. Fracture pattern and type of fracture were analyzed using Chi-square test. Level of significance was set at p<0.05. RESULTS: Significant differences were observed (p<0.05) with Group 3 demonstrating the highest fracture strength followed by Group 4, Group 1 and lastly Group 2 in both aged and unaged subgroups respectively. A significant decreased in fracture strength was noted in Group 1 and Group 2 (p<0.05) as number of thermocycle increased but no significant differences were noted in Group 3 and Group 4 (p>0.05). Besides, Group 3 and Group 4 showed higher rate of favorable fracture pattern, followed by Group 1 and lastly Group 2. Most favorable fracture pattern was noted to exhibit horizontal fracture type (86.36%), whereas most unfavorable fracture pattern exhibited vertical fracture type (77.78%). CONCLUSIONS: Endodontically treated teeth restored with new zirconia reinforced rice husk nanohybrid composite (Zr-Hybrid) demonstrated higher fracture strength than commercialized composite resins especially after artificial ageing. Zr-Hybrid showed similar fracture pattern to those of intact teeth with higher rate of horizontal fracture type. Key words:Fracture strength, fracture pattern, composite resin, rice husk, Zirconia.

Polymerization Shrinkage and Degree of Conversion of New Zirconia-Reinforced Rice Husk Nanohybrid Composite.

OBJECTIVES: This study aimed to compare the polymerization shrinkage and degree of conversion of new zirconia-reinforced rice husk nanohybrid composite with commercialized microhybrid and nanofilled composites. MATERIALS AND METHODS: Overall, 180 samples were used for polymerization shrinkage (buoyancy and optical methods) and degree of conversion tests in which they were divided into Group 1, nanofilled composite (Filtek-Z350- XT; 3M ESPE, St Paul, MN 55144-1000, USA), Group 2, microhybrid composite (Zmack-Comp), and Group 3, nanohybrid composite (Zr-Hybrid). Polymerization shrinkage test was performed using buoyancy and optical methods. For buoyancy method, samples were weighed in air and water to calculate the shrinkage value, whereas, for optical method, images of nonpolymerized samples were captured under a digital microscope and recaptured again after light-cured to calculate the percentage of shrinkage. Degree of conversion was tested using Fourier-transform infrared spectroscopy spectrometer. STATISTICAL ANALYSIS: Data were analyzed using one-way analysis of variance complemented by post hoc Dunnett's T3 test for polymerization shrinkage and Tukey's honestly significant difference test for degree of conversion. Level of significance was set at p < 0.05. RESULTS: Group 3 demonstrated similar polymerization shrinkage with Group 1, but lower shrinkage (p < 0.05) than Group 2 based on buoyancy method. However, optical method (p < 0.05) showed that Group 3 had the lowest shrinkage, followed by Group 1 and lastly Group 2. Besides, Group 3 showed a significantly higher degree of conversion (p < 0.05) than Group 1 and comparable conversion value with Group 2. CONCLUSIONS: Zirconia-reinforced rice husk nanohybrid composite showed excellent shrinkage and conversion values, hence can be considered as an alternative to commercially available composite resins.

Modeling the Growth of Bacteria Streptococcus sobrinus Using Exponential Regression

Abstract Objective: To build an exponential regression model based on parameter estimation. Material and Methods: We developed a simple mathematical model to simulate the growth of bacteria and the exponential growth is often used to model population growth as such cell growth while the exponential decay is portraying a declining or decreases in the size of the population. An exponential regression method was used to fit the data and estimate growth parameter values Streptococcus sobrinus using statistical software SPSS version 20. Results: Based on the results of the parameter estimates, which is constant are 83.039 and b1 is 0.005 while R-square is 0.952. According to the R-Square results obtained, the model is good and appropriate. Conclusion: The model can be used to find the potential biological parameters, which may be able to predict the treatment outcome. This study helps researchers to understand the specific growth rate(s), which can be used to best grow the organism.