A Transparent, Highly Stretchable, Autonomous Self-Healing Poly(dimethyl siloxane) Elastomer.

An innovative self-healing polydimethylsiloxane (PDMS) elastomer, namely, PDMS-TFB, is reported by incorporating the reversibly dynamic imine bond as the self-healing points into the PDMS networks. The PDMS-TFB elastomer features good optical transmittance (80%) in full visible light region, high stretchability (≈700%), and excellent autonomous self-healing ability at room temperature. Surprisingly, the self-healing behavior can take place in water and even at a temperature as low as -20 °C in air, showing a promising outlook for broader applications. As a proof-of-concept, this study demonstrates the use of the PDMS-TFB elastomer for preparing anticorrosion coating and adhesive layer, and also the use of such an elastomer to be the platform for fabricating the flexible interconnector and chemical sensor. Remarkably, no significant difference is observed between the pristine and healed samples. Taking full advantage of these unique properties, it is anticipated that such a PDMS-TFB elastomer shows wide applications in the fields of materials science, electronics, biology, optics, etc.

A comparison of the accuracy of polyether, polyvinyl siloxane, and plaster impressions for long-span implant-supported prostheses.

PURPOSE: The purpose of this study was to compare the capacity of different impression materials to accurately reproduce the positions of five implant analogs on a master model by comparing the resulting cast with the stainless steel master model. The study was motivated by the knowledge that distortions can occur during impression making and the pouring of casts and that this distortion may produce inaccuracies of subsequent restorations, especially long-span castings for implant superstructures. MATERIALS AND METHODS: The master model was a stainless steel model with five implant analogs. The impression materials used were impression plaster (Plastogum, Harry J Bosworth), a polyether (Impregum Penta, 3M ESPE), and two polyvinyl siloxane (PVS) materials (Aquasil Monophase and Aquasil putty with light-body wash, Dentsply). Five impressions were made with each impression material and cast in die stone under strictly controlled laboratory conditions. The positions of the implants on the master model, the impression copings, and the implant analogs in the subsequent casts were measured using a coordinate measuring machine that measures within 4 µm of accuracy. RESULTS: Statistical analyses indicated that distortion occurred in all of the impression materials, but inconsistently. The PVS monophase material reproduced the master model most accurately. Although there was no significant distortion between the impressions and the master model or between the impressions and their casts, there were distortions between the master model and the master casts, which highlighted the cumulative effects of the distortions. The polyether material proved to be the most reliable in terms of predictability. The impression plaster displayed cumulative distortion, and the PVS putty with light body showed the least reliability. CONCLUSIONS: Some of the distortions observed are of clinical significance and likely to contribute to a lack of passive fit of any superstructure. The inaccuracy of these analog materials and procedures suggested that greater predictability may lie in digital technology.

Evaluation of accuracy of casts of multiple internal connection implant prosthesis obtained from different impression materials and techniques: an in vitro study.

Movement of impression copings inside the impression material using a direct (open tray) impression technique during clinical and laboratory phases may cause inaccuracy in transferring the 3-dimensional spatial orientation of implants intraorally to the cast. Consequently, the prosthesis may require corrective procedures. This in vitro study evaluated the accuracy of 3 different impression techniques using polyether and vinyl polysiloxane (VPS) impression material to obtain a precise cast for multiple internal connection implants. A reference acrylic resin model with 4 internal connection implants was fabricated. Impressions of the reference model were made using 3 different techniques and 2 different impression materials. The study consisted of 24 specimens divided into 6 groups of 4 each. Impressions were poured with ADA type IV stone (Kalrock, Kalabhai Karson Pvt Ltd, Mumbai, India). All casts were evaluated for the positional accuracy (mm) of the implant replica heads using a profile projector. These measurements were compared to the measurements calculated on the reference resin model, which served as a control. Data were analyzed with 2-way analysis of variance (ANOVA) followed by Bonferroni multiple comparison procedures to evaluate group means. The results revealed significant difference for anterior implant distance between the 2 impression materials (P < .01) and also among the 3 different techniques (P < .05). The lowest mean variation was found with the polyether impression material and the splinted technique. For posterior implants, the results suggested no significant difference between the 2 impression materials (P ≥ .05). Although results were not statistically significant, the polyether impression material showed the lowest mean variation as compared to the VPS impression material. However, there was a significant difference among the 3 different techniques (P < .05). Among the 3 different techniques, the lowest mean variation between 2 posterior implants was found in the splinted technique. Casts obtained from impression techniques using square impression copings splinted together with autopolymerizing acrylic resin prior to the impression procedure were more accurate than casts obtained from impressions with nonmodified implant impression copings and with airborne particle-abraded, adhesive-coated copings. Casts obtained from polyether impression material were more accurate than casts obtained from vinyl polysiloxane impression material.

The effect of one-step vs. two-step impression techniques on long-term accuracy and dimensional stability when the finish line is within the gingival sulcular area.

PURPOSE: To evaluate the effect of two putty-wash impression techniques on the long-term accuracy and dimensional stability of poly(vinyl siloxane) (PVS) in the gingival sulcus area. MATERIALS AND METHODS: Impressions were taken from a master cast to simulate molar crown preparation. A space around the abutment served as the gingival sulcus. Fifteen impressions using the one- and two-step impression techniques were taken using Express Regular, Express Fast, and President impression materials with custom trays. Using a Toolmaker's microscope, the long (LD) and short distances (SD) of the abutment and the planar distance between two parallel lines (PL) at the circumference of the cast were taken at 0.5, 2, 24, 48, 72, 96, 120, and 144 hours after mixing. ANOVA was performed, with the discrepancy between the distances of the impressions and the master cast as the dependent variable. RESULTS: The differences when different materials and impression techniques were used were significant (p < 0.001) for LD, SD, and PL, as was the interaction between the material, time, and technique (p < 0.001). SD discrepancies were higher than those of LD for all materials and times. The two-step impression technique was more accurate, with smaller discrepancies than the one-step impression technique. For all materials, the PL discrepancy was deemed acceptable (less than 0.5%) for all tested times. President had higher discrepancies than the other materials. CONCLUSIONS: When using the two-step putty-wash impression technique, pouring of the impressions may be postponed up to 30 hours; however, when using the one-step impression technique, pouring should be performed within 2 hours.

Safe human exposure limits for airborne linear siloxanes during spaceflight.

BACKGROUND: Low molecular weight siloxanes are used in industrial processes and consumer products, and their vapors have been detected in the atmospheres of the Space Shuttle and International Space Station. Therefore, the National Aeronautics and Space Administration (NASA) developed spacecraft maximum allowable concentrations (SMACs) for siloxane vapors to protect astronaut health. Since publication of these original SMACs, new studies and new risk assessment approaches have been published that warrant re-examination of the SMACs. OBJECTIVE: To reevaluate SMACs published for octamethyltrisiloxane (L3) for exposures ranging from 1 hour to 180 days, to develop a 1000-day SMAC, and to expand the applicability of those values to the family of linear siloxanes. METHODS: A literature review was conducted to identify studies conducted since the SMACs for L3 were set in 1994. The updated data were reviewed to determine the sensitive toxicity endpoints, and current risk assessment approaches and methods for dosimetric adjustments were evaluated. RESULTS: Recent data were used to update the original 1-hour, 24-hour, 30-day, and 180-day SMACs for L3, and a 1000-day SMAC was developed to protect crewmembers during future exploration beyond Earth orbit. Group SMACs for the linear siloxane family, including hexamethyldisiloxane (L2), L3, decamethyltetrasiloxane (L4), and dodecamethylpentasiloxane (L5), were set for exposures of 1-hour to 1000 days. CONCLUSION: New SMACs, based on acute pulmonary and neurotoxicity at high doses only achievable with L2 and potential liver effects following longer-term exposures to L2 and L3, were established to protect crewmembers from the adverse effects of exposure to linear siloxanes.

Accuracy of three implant impression techniques with different impression materials and stones.

The purpose of this study was to compare the accuracy of casts made using three different impression techniques to obtain an accurate definitive cast for fabrication of multiple-implant prostheses. Twelve experimental groups were formed combining the following conditions: three impression techniques, two impression materials, and two cast materials. The main effects of the three factors were analyzed by three-way analysis of variance using the full factorial general linear model between factors. The results showed that there were no significant differences in mean values for the transferred dimensions between the control and experimental groups. None of the measurements in the horizontal plane of the definitive casts demonstrated significant differences among the impression techniques with different impression and cast materials (P > .01).

Influence of marginal configuration and porcelain addition on the fit of In-Ceram crowns.

The fit of In-Ceram copings and crowns was investigated in a laboratory study. Two methods were used, one a direct sectioning technique and the other a cement analogue technique using addition-cured polyvinylsiloxane impression material. The former method involved 40 crowns cemented and sectioned on their respective electroformed silver dies. For the second method, 80 analogues were embedded and sectioned. All measurements were made using a Reflex microscope. This showed In-Ceram crowns and copings to fit well with marginal openings and ranging from 1 to 63 microns and a mean of 19 microns. No significant difference in fit was found between chamfer margins and shoulder margins. The addition of porcelain to the In-Ceram coping and repeated firing cycles involved in building a crown did not alter the fit. It is concluded that In-Ceram crowns fit well in comparison to other crown types.

Influence of dimensional stability of impression materials on the probability of acceptance of a prosthetic restoration.

The accuracy of rubber impression materials was evaluated by taking impressions of a steel model, pouring it with stone and comparing certain measurements between steel and stone models. It is assumed that acceptance is achieved when the difference in measurements is within permissible limits, defined by clinical criteria. A mathematical formulation of these criteria will lead to the concept of probability of acceptance. The probability is affected when the limits are changed. The particular case of satisfying two acceptance criteria that contain variables which are not statistically independent is considered, leading to the application of the bivariate normal distribution in the evaluation of acceptance probability.

Medical-purpose elastic materials based on siloxane rubbers and items made from them.

Vulcanization of the unsaturated siloxane rubbers with silicon hydrides of various structure (organohydrosiloxanes, organohydrosilazanes, organohydrosilanes) was investigated for the purpose of creating biologically-compatible materials with a high complex of medical and engineering properties. The effect of the silicon hydride structure on the vulcanization process and properties of the produced rubbers was identified. The basis sanitary and hygienic indices of rubbers were studied. A wide range of medical-purpose items was manufactured using the developed compounds.

Vinyl polysiloxane impression materials: a status report. Council on Dental Materials, Instruments, and Equipment.

Results of investigations of vinyl polysiloxanes indicate that they produce highly accurate impressions, have excellent elastic recovery, minimal permanent deformation, and adequate tear strength. A number of vinyl polysiloxanes are certified by the American Dental Association. All of these materials provide clinically acceptable results. Advantages of using the vinyl polysiloxanes include the ability of the impression to be poured up after 1 hour or 1 day, or for some products, after 1 week without significant loss of accuracy; the possibility of repouring the impression a second time and producing an accurate cast; the impression materials are available in several viscosities allowing flexibility in choosing an impression technique; and they can be immersed in recommended disinfectants without affecting the accuracy of the impression. The disadvantages of using the vinyl polysiloxanes include a difficulty in lengthening the working time of products without retarders and a high surface tension making it difficult to wet the impression when pouring up a stone cast. Hydrophilic materials appear to facilitate the casting of the impressions with stone. The automixing devices seem to provide convenience without sacrificing the quality of the impression and are currently available for several products. As with all elastomeric impression materials, proper handling is necessary to ensure the best results. The vinyl polysiloxanes seem to be an excellent choice of impression materials for many clinical situations.

The influence of temperature on some physical properties of dental composites.

In this study diametral tensile strength and microhardness of composites were investigated in relation to various temperatures during curing. It has been demonstrated that temperatures elevated up to 60 degrees C can improve the mechanical properties considerably. Also the stability of the resin system in aggressive environments was improved due to more efficient cross-linking. Thermal analysis of the material showed an endothermic reaction between 60 and 70 degrees C that is believed to be responsible for the initiation of the extra cross-linking. Heating of composite fillings during clinical use is suggested.

Biological evaluation of biomaterials for cardiovascular applications: some current results.

The proper biologic evaluation of biomaterials for blood-contacting applications must include considerations of hemorheologic parameters, species-related differences, and damages to the reticuloendothelial system. Although there are no materials currently available that are completely blood compatible, several smooth-surfaced polymers are quite tolerable in the physiological environment. These include chemically grafted polyacrylamide hydrogels, glow-discharge polymers of silica-free hexamethldisiloxane, and ethyl cellulose perfluorobutyrate.