Influence of different fillers on the properties of an experimental vinyl polysiloxane

Compressive modulus, translucency, and irradiance transmittance of clear PVS materials used for resin injection molding technique

OBJECTIVES

To evaluate the compressive modulus, translucency, and light curing irradiance transmittance of four clear polyvinyl siloxane (PVS) materials used for the injection molding technique at varying thicknesses, and to assess the correlation between color parameters and irradiance transmittance.

MATERIALS AND METHODS

Four clear PVS materials (Exaclear, Clear Bite Matrix, Affinity Crystal, and Memosil 2) were used in this study. Compressive modulus was measured by compressing cylindrical PVS specimens (n = 9; d = 10 mm; t = 6 mm) up to 30% strain using a universal testing machine. For the translucency analysis and irradiance transmittance, specimens (n = 5) were fabricated with five different thicknesses (d = 12 mm and t = 2, 4, 6, 8 and 10 mm). The L*, a, *b* values of specimens were obtained using a CIELab spectrophotometer (CMD-700, Konica Minolta) with calibrated white and black tiles; the translucency parameter was calculated. The same specimens were placed onto a spectrophotometer (MARC Light Collector) to measure irradiance transmitted through the specimens from a light curing unit (Valo Corded, Ultradent). Data were analyzed using analysis of variance (ANOVA) with Tukey post hoc test and the correlation between translucency and irradiance transmittance of materials for each thickness was evaluated using Pearson's correlation.

RESULTS

Compressive modulus differences in PVS materials were significant (one-way ANOVA: df = 3, F = 76.27, p < 0.001); Affinity and Memosil 2 were highest with no significant difference between them (Tukey: t = -1.62; p = 0.382). Clear Bite was higher than Exaclear (Tukey: t = -3.70; p = 0.004). Exaclear was lowest. Translucency decreased with thickness (Two-way ANOVA: df = 3, F = 586.53, p < 0.001; thickness: df = 4, F = 1389.34, p < 0.001). Exaclear was most translucent at all thicknesses. L*, a*, b* values varied by material and thickness (L*: df = 3, F = 1213.32, p < 0.001; a*: df = 3, F = 10766.8, p < 0.001; b*: df = 3, F = 3260.42, p < 0.001). Memosil 2 had lowest b* values. Irradiance transmittance was affected by material and thickness (Two-way ANOVA: df = 4, F = 2388.86, p < 0.001). Exaclear had highest irradiance transmission, surpassing control at >6 mm. Violet/blue irradiance ratio decreased with thickness; Exaclear maintained a constant ratio, indicating preserved violet irradiance. There was a strong positive correlation between translucency and light irradiance (Pearson's r = 0.97, R2 = 0.86-0.96). Radiant exposure analysis suggests adjusting the curing time based on PVS thickness for optimal exposure (10 J/cm2) is achievable within 13-14 s for <2 mm and 21-30 s for 8-10 mm with Clear Bite, Affinity, and Memosil 2; whereas Exaclear requires less time.

CONCLUSIONS

Compressive modulus in clear PVS materials varied by type; Affinity and Memosil 2 demonstrate higher modulus, offering more stability of the clear mold. Translucency and irradiance transmission through clear PVS materials decreased as their thickness increased, yet Exaclear exceled in maintaining high translucency and superior light transmission capabilities. Additionally, there is a strong positive linear correlation between translucency and light irradiance transmittance, offering a method to adjust curing times effectively based on material translucency.

CLINICAL SIGNIFICANCE

The light curing time to adequately polymerize composite through clear impression material may need to be increased, particularly with thicker matrices or less translucent materials.

Effects of Various Disinfection Methods on the Material Properties of Silicone Dental Impressions of Different Types and Viscosities

There is an ongoing search for novel disinfection techniques that are not only effective, cheap, and convenient, but that also do not have adverse effects on the properties of dental impressions. We compared the effects of various methods (UVC, gaseous ozone, commercial solution, and spray) on the dimensional change, tensile strength, and hardness of silicone impressions. Moreover, as a secondary aim, we performed a statistical comparison of the properties of nondisinfected addition (Panasil Putty Soft, Panasil monophase Medium, Panasil initial contact Light) and condensation silicones (Zetaplus Putty and Oranwash L), as well as a comparison of materials of various viscosities (putty, medium-bodied, and light-bodied). Our results revealed that addition silicones had higher dimensional stability, tensile strength, and Shore A hardness compared to condensation silicones. Both traditional (immersion and spraying) and alternative methods of disinfection (UVC and ozone) had no significant impact on the tensile properties and dimensional stability of the studied silicones; however, they significantly affected the hardness, particularly of Oranwash L. Our study demonstrated that, similarly to standard liquid disinfectants, both UVC and ozone do not strongly affect the material properties of most silicones. However, before recommendation, their usefulness for each individual material should be thoroughly evaluated.

Evaluation of setting time, tear strength, dimensional stability and antimicrobial property of silver and titanium nanoparticles incorporated elastomeric impression material

Graph 1: Graph represents the dimensional stability of Group I and Group II samples.Image 1.

Three-dimensional Change of Elastomeric Impression Materials During the First 24 Hours: A Pilot Study

OBJECTIVES

To evaluate the three-dimensional (3D) changes of three elastomeric impression materials using a novel measurement method for the first 24 hours after preparation.

METHODS AND MATERIALS

Three impression materials consisting of a low-viscosity polyvinyl siloxane (PVS) (Aquasil LV, Dentsply Sirona, Charlotte, NC, USA) and two vinyl polyether silicone (VPES) materials consisting of a light body (EXA'lence LB, GC America, Alsip, IL, USA) and monophase (EXA'lence Monophase, GC America) materials were used in this study. All materials were prepared following manufacturer's recommendations with approximately 1-2 millimeters of material placed on the measurement pedestal of a calibrated noncontact, video imaging based, volumetric change measuring device (AcuVol ver 2.5.9, Bisco, Schaumburg, IL, USA). Data collection was initiated immediately, with measurements made every 30 seconds for 24 hours. Each material was evaluated 10 times (n=10). Evaluated parameters included were 24-hour mean shrinkage, mean shrinkage at time of recommended first pour, mean shrinkage between recommended first pour and 24 hours, mean maximum shrinkage, and the time of maximum shrinkage. Mean data, both within and between each group, was evaluated using Kruskal-Wallis/Dunn's tests at a 95% level of confidence (α=0.05).

RESULTS

All three materials were found to have significant differences (p<0.001) in volumetric shrinkage over 24 hours. Aquasil LV and EXA'lence LB polymerization shrinkage rates were statistically similar all through the 24-hour evaluation (p=0.92). All three materials demonstrated similar (p=0.19) shrinkage between 10 and 15 minutes after preparation, while between 5 and 16 hours both EXA'lence Monophase and low-viscosity materials demonstrated similar polymerization shrinkage values (p=0.22). EXA'lence Monophase demonstrated significantly greater 24-hour mean shrinkage (p<0.008) as well as shrinkage between recommended first pour time and 24 hours (p=0.003) than Aquasil LV and EXA'lence LB. EXA'lence Monophase demonstrated significantly greater (p=0.002) shrinkage at the recommended time of first pour as compared to Aquasil LV and EXA'lence LB that displayed similar shrinkage (p=0.89). Furthermore, all materials demonstrated increasing polymerization shrinkage values that reached a maximum between 16 for Aquasil LV and 20 hours for EXA'lence LB, after which some relaxation behavior was observed. However, EXA'lence Monophase did not display any relaxation behavior over the 24-hour evaluation.

CONCLUSIONS

Under the conditions of this study, volumetric polymerization shrinkage was observed for one polyvinyl siloxane (PVS) and two vinyl polyether silicone (VPES) materials for up to 24 hours. All impression materials exhibited fast early volumetric shrinkage that continued past the manufacturer's recommended removal time. Dimensional change behavior was not uniform within or between groups; resultant volume change between the manufacturer recommended pouring time and 24 hours might represent up to from 20% to 30% of the total material shrinkage. It may be prudent to pour elastomeric impressions at the earliest time possible following the manufacturer's recommendations.

Investigation of dental elastomers as oral mucosa simulant materials

Objective

To measure mechanical properties of dental soft liners in tensional stress to identify their suitability as human oral mucosa simulant materials.

Methods

Eleven different dental elastomers were subjected to tensile testing to obtain their tensile strength and elastic moduli (n = 15/group) according to the ISO‐527 method. Fractured surfaces of one specimen per sample group were examined under the light microscope and scanning electron microscope (SEM). Energy‐dispersive X‐ray spectroscopy (EDS) was performed for the elemental analysis or chemical characterization of each sample group. The obtained data were quantitatively and qualitatively analysed. They were also statistically analysed using SPSS version 25.

Results

The tensile strength of dental elastomers ranged from 0.43 MPa (±0.09) to 7.41 MPa (±1.11) and had statistically significant differences between tested groups (p = 0.001). Vertex soft heat‐cure soft liner, GC impression silicones and Silagum soft liners were found to have tensile strengths close to that of the oral mucosa reported by previous studies. SEM analysis revealed that the elastomers with higher filler contents showed rough fractured surface with plucking of particles after tensile fracture.

Conclusion

This is the first study assessing the suitability of dental elastomers as human oral mucosa simulant materials which can be used for in vitro, mathematical modeling and finite element analysis (FEA) to study masticatory force distribution in oral mucosa. Out of 11 studied, six (Vertex Soft, GC heavy and Light body, Molloplast B, Algin X Ultra and Exaclear) dental elastomers showed similar mechanical properties to the Theil embalmed gingival tissues. Vertex Soft, GC Light body, and Molloplast B may be used for the majority of oral mucosal model when considering tensile strength as the primary factor for mechanical stimulation.

Characterization and Biodegradability of Rice Husk-Filled Polymer Composites

The fabrication of affordable biodegradable plastics remains a challenging issue for both the scientific community and industries as mechanical properties and biodegradability improve at the expense of the high cost of the material. Hence, the present work deals with fabrication and characterization of biodegradable polymer with 40% rice husk waste filler and 60% polymer-containing mixture of polybutylene succinate (PBS) and poly butylenes adipate-Co-terephthalate (PBAT) to achieve good mechanical properties, 92% biodegradation in six months, and competitive pricing. The challenge in incorporating high amounts of hydrophilic nature filler material into hydrophobic PBS/PBAT was addressed by adding plasticizers such as glycerol and calcium stearate. The compatibilizers such as maleic anhydride (MA) and dicumyl peroxide (DCP) was used to improve the miscibility between hydrophobic PBS/PBAT and hydrophilic filler material. The component with the formulation of 24:36:40 (PBS/PBAT/TPRH) possessed the tensile strength of 14.27 MPa, modulus of 200.43 MPa, and elongation at break of 12.99%, which was suitable for the production of molded products such as a tray, lunch box, and straw. The obtained composite polymer achieved 92% mass loss after six months of soil burial test confirming its biodegradability.