In-vitro investigation on suitability of light-cured resins for interocclusal splints : part II: surface hardness

OBJECTIVE

The aim of the present study was to determine the surface hardness of light- and auto-cured resins for the fabrication of occlusal splints employing Vickers hardness measurements.

MATERIALS AND METHOD

In this study we used three auto-polymerized resins (Palapress, Orthocryl, Steady-Resin M) and four light-polymerized resins (Acrylight, Primosplint, Triad Tran- Sheet Colorless and Triad TranSheet Pink). The Vickers hardness measurement was carried out by means of a universal Durimet indenter applying a test load of 50 g for 30 seconds. The light-cured resins were polymerized in a Tagris Power light oven for 10 and 15 minutes each. Three separate test series were carried out (the hardness of plates under optimal conditions and of occlusal splints was measured, and the curing of light-polymerizing materials in layers of varying depth was evaluated). Data underwent statistical analysis via ANOVA and the Scheffé test.

RESULTS

The microhardness determined in each case amounted to values between 10.4 HV 0.5 and 39.3 HV 0.5. The Vickers hardness determined for the plates that had been produced under optimal conditions demonstrated that their surface was significantly (p < 0.05) harder than that of cylinders and splints. The hardness values of the light-cured material Triad TranSheet Pink (39.3 HV 0.5) were significantly higher (p < 0.05) than those of all other resins. In all auto-polymerized resins, the surface hardness of the samples we examined (in the form of plates and splints) was significantly lower (p < 0.05) than that of the light-cured materials Triad TranSheet Pink and Colorless.

CONCLUSION

The results we have obtained so far concerning surface hardness indicate that, in the fabrication of occlusal splints, light-cured resins may represent an alternative to auto-polymerizing materials.

Effect of Low-Level Laser Therapy on Healing of Medial Collateral Ligament Injuries in Rats: An Ultrastructural Study

OBJECTIVE

This study sought to investigate whether low-level laser therapy (LLLT) with a helium-neon (He-Ne) laser would increase fibril diameter of transected medial collateral ligament (MCL) in rats.

BACKGROUND DATA

It has been shown that LLLT can increase ultimate tensile strength MCL healing.

METHODS

Thirty rats received surgical transect to their right MCL, and five were assigned as the control group. After surgery, the rats were divided into three groups: group 1 (n = 10) received LLLT with He-Ne laser and 0.01 J/cm(2) energy fluency per day, group 2 (n = 10) received LLLT with 1.2 J/cm(2) energy fluency (density) per day and group 3 (sham-exposed group; n = 10) received daily placebo laser with shut-down laser equipment, while control group received neither surgery nor LLLT. Transmission electron microscope (TEM) examination was performed on days 12 and 21 after surgery and dimension and density of ligament fibrils were measured. The data were analyzed by Student t-test and Mann-Whitney tests, respectively.

RESULTS

On day 12, the fibril dimension of group 2 and their density were higher than of groups 1 and 3.

CONCLUSION

LLLT with He-Ne laser on incised MCL in rats could not significantly increase fibril diameter and their density in comparison with sham-exposed group.

In vitro and in vivo tissue repair with laser-activated chitosan adhesive

BACKGROUND AND OBJECTIVES

Sutures are currently the gold standard for wound closure but they are still unable to seal tissue and may induce scarring or inflammation. Biocompatible glues, based on polysaccharides such as chitosan, are a possible alternative to conventional wound closure. In this study, the adhesion of laser-activated chitosan films is investigated in vitro and in vivo. In particular we examine the effect of varying the laser power, as well as adding a natural cross-linker (genipin) to the adhesive composition.

STUDY DESIGN/MATERIALS AND METHODS

Flexible and insoluble strips of chitosan films (surface area approximately 34 mm(2), thickness approximately 20 microm) were bonded to sheep intestine using several laser powers (0, 80, 120, and 160 mW) at 808-nm wavelength. The strength of repaired tissue was tested by a calibrated tensiometer to select the best power. A natural cross-linker (genipin) was also added to the film and the tissue repair strength compared with the strength of plain films. The adhesive was also bonded in vivo to the sciatic nerve of rats and the thermal damage induced by the laser assessed 4 days post-operatively.

RESULTS

Chitosan adhesives successfully repaired intestine tissue, attaining a maximum repair strength of 14.7+/-4.3 kPa (n = 30) at the laser power of 120 mW. The chitosan-genipin films achieved lower repair strength (9.1+/-2.9 kPa). The laser caused partial demyelination of axons at the site of operation, but the myelinated axons retained a normal morphology proximally and distally.

CONCLUSIONS

The chitosan adhesive effectively bonded to tissue causing only localized thermal damage in vivo, when the appropriate laser parameters were selected.

Effect of Surface Conditioning on Adhesion of Glass Ionomer Cement to Er,Cr:YSGG Laser-Irradiated Human Dentin

OBJECTIVE

This study aimed to show the effect of dentin conditioner on the bond strength of glass ionomer cement to Er,Cr:YSGG-laser-irradiated dentin compared to conventional bur-prepared dentin.

BACKGROUND DATA

Glass ionomer cement bonds to tooth structure via direct chemical bonding without using any adhesive system. To improve the adhesion of this material, pretreating the dentin surface with a conditioner is recommended. Recently, lasers for tooth drilling have been used for cavity preparation, especially the Er,Cr:YSGG laser. However, there is a lack of research on the bond strength of glass ionomer cement to conditioned Er,Cr:YSGG-laser-irradiated dentin.

METHODS

Extracted human teeth were divided into eight experimental groups and prepared by using either Er,Cr:YSGG laser or a conventional bur. In half of these two groups, the relevant conditioner was applied on the dentin before building up with glass-ionomer cement. After 24 h, all teeth were sectioned, and the microtensile bond strength was determined. The mode of failure was observed, and the fractured surfaces were examined by scanning electron microscopy (SEM).

RESULTS

The use of conditioner was found to significantly affect bond strength for laser-prepared samples (analysis of variance [ANOVA], p < 0.05). Failure analysis showed no adhesive failures in the laser-prepared teeth, and this suggests an effective bond between glass ionomer cement and Er,Cr:YSGG laser-cut dentin.

CONCLUSION

To obtain the maximum retention of a glass ionomer restoration to Er,Cr:YSGG laser-irradiated dentin, the results of this study confirm that pretreatment of the laser-prepared dentin with dentin conditioner is advantageous.

[Viability of murine 3T3 fibroblasts on the poly(methyl methacrylate) surface modified by constant UV irradiation]

Poly(methyl methacrylate) (PMMA) is commonly applied both in dentistry (bone cement) and in ophthalmology (contact lens, intraocular implants). High adhesion of fibroblasts to bone cement is desirable but keratoprosthesis (intraocular lens--IOL) should be characterized by good transparency and indicate no cells adhesion. Some earlier reports show that sterilization and modification of surface properties of some polymers can be achieved by UV-irradiation which causes a serious physicochemical change in polymer materials to depth of 4 microm. In present studies the surface of PMMA films (30 microm) was continuously irradiated with monochromatic UV-light at 254 nm in varied time intervals. The viability of murine 3T3 fibroblasts cultivated by 12 hours on the surfaces of the non-exposed and the UV-irradiated PMMA in relation to the control fibroblast cell line cultured on the surface of borosilicate glass was estimated with standard fluorescence microscopy procedure. It was found, that 3T3 fibroblasts are highly sensitive to the chemical changes of irradiated surface of PMMA, i.e. increase of surface hydrophilicity and oxidation degree accompanied by decrease of polymer molecular mass and increase of free monomer fraction as determined on the results of contact angle measurements and attenuated total reflection infrared spectra. The percentage of living 3T3 fibroblast cells was 87% after cultivation on the untreated virgine PMMA and only 47% after cultivation on the polymer which was pre-irradiated by 72 h. No further changes in fibroblasts viability (47%) was observed in cultures developed on PMMA after 96 h of its introductory permanent irradiation. However, a period of 48 h of such constant UV-irradiation was quite optimal to obtain a specific modification of PMMA surface leading to significantly increased viability of cultured 3T3 fibroblasts up to the 94%.

Alterations of human acellular tissue matrix by gamma irradiation: Histology, biomechanical property, stability,in vitro cell repopulation, and remodeling

AlloDerm, a processed acellular human tissue matrix, is used in a number of surgical applications for tissue repair and regeneration. In the present work, AlloDerm serves as a model system for studying gamma radiation-induced changes in tissue structure and stability as well as the effect of such changes on the cell-matrix interactions, including cell repopulation and matrix remodeling. AlloDerm tissue matrix was treated with 2-30 kGy gamma irradiation at room temperature. Gamma irradiation reduced the swelling of tissue matrix upon rehydration and caused significant structural modifications, including collagen condensation and hole formation in collagen fibres. The tensile strength of AlloDerm increased at low gamma dose but decreased with increasing gamma dosage. The elasticity of irradiated AlloDerm was reduced significantly. Calorimetric study showed that gamma irradiation destabilized the tissue matrix, resulting in greater susceptibility to proteolytic enzyme degradation. Although gamma irradiation did not affect in vitro proliferation of fibroblast cells, it promoted tissue degradation upon cell repopulation and influenced synthesis and deposition of new collagen.

Laser welding of cast titanium and dental alloys using argon shielding

PURPOSE

This study investigated the effect of argon gas shielding on the strengths of laser-welded cast Ti and Ti-6Al-7Nb and compared the results to those of two dental casting alloys.

MATERIALS AND METHODS

Cast plates of Ti, Ti-6Al-7Nb, gold, and Co-Cr alloy were prepared. After polishing the surfaces to be welded, two plates were abutted and welded using Nd:YAG laser at a pulse duration of 10 ms, spot diameter of 1 mm, and voltage of 200 V. Five specimens were prepared for each metal by bilaterally welding them with three or five spots either with or without argon shielding. The failure load and percent elongation were measured at a crosshead speed of 1.0 mm/min.

RESULTS

The factor of argon shielding significantly affected the failure load and elongation of the laser-welded specimens. The failure loads of argon-shielded laser-welded CP Ti and Ti-6Al-7Nb were greater compared with the failure loads of specimens welded without argon shielding for both three- and five-spot welding. Regardless of argon shielding, the failure loads of the laser-welded gold alloy were approximately half that of the control specimens. In contrast, the failure loads of the nonshielded laser-welded Co-Cr alloy were greater. The percent elongations positively correlated with the failure loads.

CONCLUSIONS

The use of argon shielding is necessary for effective laser-welding of CP Ti and Ti-6Al-7Nb but not for gold and Co-Cr alloy.

Ultrasonically set glass polyalkenoate cements for orthodontic applications

There is an accepted clinical requirement for a luting cement that can be command set upon satisfactory placement of an orthodontic appliance onto dentition. This work evaluates the suitability of ultrasound, imparted from a dental scaler, as a potential mechanism for achieving this. The net setting times and subsequent compressive strengths of a range of commercial and experimental glass polyalkenoate cements (GPCs) were evaluated, using modified ISO 9917 methods, when set both chemically and by ultrasound. The ultrasound was applied to the GPC through an orthodontic brace. It was possible to command set GPCs by the application of five to ten seconds of ultrasound; the exact time required being dependent upon the composition of the GPC in question. The compressive strengths of these cements can be improved by around 90% with the command set when the optimum PAA molecular weight and tartaric acid content is employed.

In-vitro investigations on suitability of light-cured resins for interocclusal splints: part I: mechanical properties

OBJECTIVE

It was the aim of the present study to investigate the material properties of different resins and their suitability for the fabrication of occlusal and intermaxillary splints.

MATERIAL AND METHOD

We subjected auto-polymerized resins (Palapress, Orthocryl, Steady-Resin M) and light-polymerized resins (Acrylight, Primosplint, Triad TranSheet Colorless and Pink) to investigation. The Targis Power light oven was used to polymerize the light-cured resins. After the auto-polymerized resins had been mixed by hand and filled into the forms, they were polymerized for 15 minutes in a high-pressure polymerization machine (Palamat) at 2 bar. The parameters examined were flexural strength, water adsorption, and polymerization shrinkage. Tests carried out according to DIN EN ISO 1567 served to determine flexural strength, flexural modulus, and water adsorption. Polymerization shrinkage was determined via the buoyancy test.

RESULTS

The resins' flexural strength ranged from 60 to 101 MPa. Flexural moduli lay between 1.3 and 5.3 GPa. The water adsorption noted in light-cured resins amounted to 2.1-4.6 mass percent. Palapress and Steady-Resin displayed the lowest water adsorption with 2.0 mass percent. The light-polymerized resins revealed significantly less shrinkage (p < 0.05) than the autopolymerized resins tested in this study.

CONCLUSION

Our results demonstrate that the light-cured resins-with the exception of Acrylight -easily match and even exceed the material properties of the cold-polymerized resins regarding flexural strength, flexural modulus, water adsorption and polymerization shrinkage. The light-cured resins examined thus seem suitable for use as splint material.

The effect of light-curing source and mode on microtensile bond strength to bovine dentin

PURPOSE

The purpose of this study was to evaluate the effects of different light-curing techniques on the microtensile bond strength of hybrid and packable resin composite to dentin. The null hypotheses were that different light-curing techniques do not affect the adhesion of resin composites to tooth structure and that different resin composites do not have a similar bond to dentin.

MATERIALS AND METHODS

One hundred four box-shaped buccal preparations were made and dentin/enamel adhesive was applied according to the manufacturer's instructions (Single Bond 3M ESPE). A hybrid resin composite (Filtek Z250, A2, 3M ESPE) or a packable resin composite (Solitaire 2, A2, Heraeus Kulzer) were inserted in bulk and polymerized using one of these techniques (n = 13): (a) Soft-start (SS) using a halogen lamp (QTH); (b) LED low intensity; (c) Plasma arc (PAC) curing for 6 s for packable resin composite and 3 s for the hybrid resin composite; (d) Conventional (C) QTH curing for 40 s. Afterwards, specimens were thermocycled 1,000 times between 5 degrees C and 55 degrees C in tap water, and were sectioned into beams with a rectangular cross-sectional area of approximately 1 mm2. Microtensile bond strength testing was performed using a universal testing machine at a crosshead speed of 0.5 mm/min.

RESULTS

Bond strength means +/- (SD) in MPa were: Filtek Z250: SSQTH = 17.9 (5.4); LED = 17.9 (6.4); PAC = 16.8 (6.8); CQTH = 16.1 (4.6). Solitaire 2: SSQTH = 12.4 (6.4); LED = 15.5 (4.3); PAC = 16.2 (4.4); CQTH = 13.8 (5.7). The data were structured in a split-plot design and analyzed by a two-way ANOVA and Tukey's tests (alpha = 0.05).

CONCLUSION

The light-curing method did not significantly affect bond strengths. However, the bond strengths of the packable resin composite were significantly lower than those of the hybrid resin composite for all polymerization techniques, suggesting that the restorative material itself might be a more critical factor in adhesion than the curing method.

In situ formation of blends by photopolymerization of poly(ethylene glycol) dimethacrylate and polylactide

Blends of cross-linked poly(ethylene glycol) dimethacrylate (PEGDMA) and poly(d,l-lactide) (PLA) were prepared by mixing photoactive PEGDMA (molecular mass: 875 g/mol) and PLA, and subsequently photopolymerizing the mixture with visible light. The effects of PLA molecular mass and mass fraction on the rheological properties of the PEGDMA/PLA mixtures, and on the degree of methacrylate vinyl conversion (DC), as well as blend miscibility, microstructure, mechanical properties, in vitro swelling behavior, and cell responses were studied. PLA-2K (molecular mass: 2096 g/mol) and PLA-63K (molecular mass: 63 000 g/mol) formed miscible and partially miscible blends with cross-linked PEGDMA, respectively. The addition of the PLA-2K did not affect the immediate or post-cure (>24 h) DC of the PEGDMA upon photopolymerization. However, the addition of PLA-63K decreased the immediate DC of the PEGDMA, which can be increased through extending the curing time or post-curing period. Compared to the cross-linked neat PEGDMA and PLA-2K/PEGDMA blends, PLA-63K/PEGDMA blends were significantly stronger, stiffer, and tougher. Both types of blends and the cross-linked PEGDMA swelled when soaked in a phosphate buffered saline (PBS) solution. The attachment and spreading of MCT3-E1 cells increased with increasing PLA-63K content in the blends. The facile and rapid formation of PEGDMA/PLA blends by photopolymerization represents a simple and efficient approach to a class of biomaterials with a broad spectrum of properties.

Near infrared laser-tissue welding using nanoshells as an exogenous absorber

BACKGROUND AND OBJECTIVE

Gold nanoshells are a new class of nanoparticles that can be designed to strongly absorb light in the near infrared (NIR). These particles provide much larger absorption cross-sections and efficiency than can be achieved with currently used chemical chromophores without photobleaching. In these studies, we have investigated the use of gold nanoshells as exogenous NIR absorbers to facilitate NIR laser-tissue welding.

STUDY DESIGN/MATERIALS AND METHODS

Gold nanoshells with peak extinction matching the NIR wavelength of the laser being used were manufactured and suspended in an albumin solder. Optimization work was performed on ex vivo muscle samples and then translated into testing in an in vivo rat skin wound-healing model. Mechanical testing of the muscle samples was immediately performed and compared to intact tissue mechanical properties. In the in vivo study, full thickness incisions in the dorsal skin of rats were welded, and samples of skin were excised at 0, 5, 10, 21, and 32 days for analysis of strength and wound healing response.

RESULTS

Mechanical testing of nanoshell-solder welds in muscle revealed successful fusion of tissues with tensile strengths of the weld site equal to the uncut tissue. No welding was accomplished with this light source when using solder formulations without nanoshells. Mechanical testing of the skin wounds showed sufficient strength for closure and strength increased over time. Histological examination showed good wound-healing response in the soldered skin.

CONCLUSIONS

The use of nanoshells as an exogenous absorber allows the usage of light sources that are minimally absorbed by tissue components, thereby, minimizing damage to surrounding tissue and allowing welding of thicker tissues.

Effect of cross-linking on the microstructure and mechanical properties of ultra-high molecular weight polyethylene

Ultra-high molecular weight polyethylene is a semicrystalline polymer, which means that a portion of the molecules is in a solid crystalline phase and the remaining portion is in a rubbery amorphous phase. Varying the polymer chemistry in the two phases can alter the mechanical properties of the material. When highly cross-linked polyethylene is formed, the cross-links occur in the amorphous but not the crystalline region. Remelting after irradiation-induced cross-linking neutralizes the free radicals that are caused by irradiation but also decreases the amount of crystallinity. Decreased crystallinity can contribute to a decrease in mechanical properties. Annealing below the melt temperature after irradiation retains a higher level of crystallinity. However, heating below the melt temperature does not neutralize irradiation-induced free radicals that can then react with oxygen, causing oxidative degradation. Newer "second-generation" highly cross-linked polyethylenes have been developed that are annealed below the melt temperature, but use either a pharmacologic antioxidant, mechanical deformation, or sequential low-dose irradiation and annealing treatments rather than heating above the melt point to neutralize residual free radicals. High-pressure treatment at elevated temperatures also can increase crystallinity. However, increased crystallinity is associated with an increase in modulus and contact stress, which can increase wear. Although cross-linking ultra-high molecular weight polyethylene can reduce wear, currently available highly cross-linked polyethylenes also decrease mechanical properties when compared with conventional ultra-high molecular weight polyethylene, so that use of these materials in total knee arthroplasty may contribute to mechanical failure of the bearing surface.

Effect of microwave disinfection on the hardness and adhesion of two resilient liners

STATEMENT OF PROBLEM

Microwave irradiation has been suggested for denture disinfection. However, the effect of this procedure on the hardness and bond strength between resilient liners and denture base acrylic resin is not known.

PURPOSE

This study evaluated the effect of water storage time and microwave disinfection on the hardness and peel bond strength of 2 silicone resilient lining materials to a heat-polymerized acrylic resin.

MATERIAL AND METHODS

Acrylic resin (Lucitone 199) specimens (75 x 10 x 3 mm) were stored in water at 37 degrees C (2 or 30 days) before bonding (n = 160). The resilient lining materials (GC Reline Extra Soft and Dentusil) were bonded to the denture base and divided into the following 4 groups (n = 10): Tests performed immediately after bonding (control); specimens immersed in water (200 mL) and irradiated twice, with 650 W for 6 minutes; specimens irradiated daily for 7 total cycles of disinfection; specimens immersed in water (37 degrees C) for 7 days. Specimens were submitted to a 180-degree peel test (at a crosshead speed of 10 mm/min) and the failure values (MPa) and mode of failure were recorded. Pretreatment and posttreatment hardness measurements (Shore A) of the resilient materials were also performed. Three-way analysis of variance, followed by the Tukey HSD test, was performed (alpha = .05).

RESULTS

The analysis revealed that, for all conditions, the mean failure strengths of GC Reline Extra Soft (0.95-1.19 MPa) were significantly higher ( P < .001) than those of Dentusil (0.45-0.50 MPa). The adhesion of the liners was not adversely affected by water storage time of Lucitone 199 or microwave disinfection. All peel test failures were cohesive. There was a small but significant difference ( P < .001) between the pretreatment (34.33 Shore A) and posttreatment (38.69 Shore A) hardness measurements.

CONCLUSION

Microwave disinfection did not compromise the hardness of either resilient liners or their adhesion to the denture base resin Lucitone 199.

Photomediated crosslinking of C6-cinnamate derivatized type I collagen

Synthesis and characterization of cinnamated Type I collagen and its related mechanical properties after photomediated crosslinking were investigated in detail. Using an EDC/NHS conjugation method, collagen was chemically modified to incorporate a photosensitive cinnamate moiety. The cinnamated collagen was fully characterized by 1H NMR, UV-vis, and circular dichroism (CD) spectroscopy, as well as by rheological and mechanical analyses. Cinnamated collagens with varying degrees of derivatization retained collagen triple helical structure. The rheological spectra of collagen solutions demonstrate that the storage modulus decreases with increasing cinnamate content, owing to a decrease in physical crosslinking. The kinetics of the crosslinking process in both hydrated gels and dry films were monitored by UV-vis spectroscopy and confirmed that crosslinking was complete within 60 min of irradiation. The uniaxial stress-strain behavior of crosslinked collagen films, including Young's modulus and ultimate tensile strength, was comparable to values reported for glutaraldehyde-crosslinked monomeric collagen films. These data demonstrate that derivatization of collagen with photosensitive cinnamate moieties provides a facile route for solid-state crosslinking, thereby improving the mechanical properties of collagen and enhancing the potential applicability of collagen-based materials in tissue engineering and drug delivery.

Effects of Laser Irradiation on Tensile Strength of Bovine Dentin

OBJECTIVE

The purpose of the present study was to investigate the tensile strengths of dentin after laser irradiation using three kinds of dental lasers to elucidate the laser-irradiation effect on dentin properties.

BACKGROUND DATA

Different kinds of laser devices have been developed in dentistry. The characteristics of each laser are determined by its original wavelength; however, one common feature is to generate heat in irradiated tissues, and such heat possibly affects dentin collagen, which contributes to tensile strength of the tissues.

MATERIALS AND METHODS

Er:YAG, CO2, and diode (GaAlAs) lasers were used to irradiate bovine dentin. Subsequently, tensile test specimens were made from the irradiated dentin and tensile tests were conducted. The tensile strengths were analyzed using the paired-t test and Weibull analysis. Irradiated dentin was also observed transversally using light microscopy.

RESULTS

The tensile strengths of the lased dentin and the control group for the Er:YAG, CO2, and diode lasers were 73.1 and 78.5, 70.3 and 74.3, and 64.3 and 71.0 MPa, respectively. The tensile strength of the dentin had a tendency to decrease with laser irradiation. Weibull analysis indicated that the laser influence was different among the three kinds of laser apparatuses and seemed to correspond to the depths the laser beam reached, which were suggested by light microscopy observation.

CONCLUSION

Laser irradiation could possibly decrease dentin tensile strength, which suggests the importance of careful use of laser for hard tissue treatment, considering its energy-transforming characteristics.

Microwave irradiated collagen tubes as a better matrix for peripheral nerve regeneration

Collagen is one of the best materials used for nerve guide preparation due to its biocompatibility and desirable tensile strength. In this work, we have compared regeneration and functional reinnervation after sciatic nerve resection with bioresorbable crosslinked collagen guides in 10 mm gap. The crosslinking was carried out either with glutaraldehyde (GTA) or microwave irradiation (MWI). The multilayered collagen membrane used for nerve guides are prepared by lamellar evaporation technique. Functional evaluations of the regenerated nerves were performed by measuring the sciatic functional index (SFI), nerve conduction velocity (NCV), and electromyography (EMG). Transmission electron microscopic studies showed growth of axonal cable with fewer myelinated axons, Schwann cells and more unmyelinated axons present in the case of group treated with uncrosslinked collagen tubes after 1 month of implantation. However, we have observed more myelinated axons in the case of autograft, GTA, and MWI crosslinked collagen tube implants across the gap of 1 cm after the same period of implantation. Smaller myelinated fiber diameter was observed in the case of GTA crosslinked collagen tube group when compared with the autograft and MWI collagen tube groups. There were more myelinated axons during the 3rd and 6th months postoperatively using these conduits as substantiated by light microscopic studies of the regenerated nerve. The conduction velocity and recovery index improved significantly after 5 months reaching the normal values in the autograft and MWI crosslinked collagen groups compared to GTA and uncrosslinked collagen tubes.

Influence of composite restorative materials and light-curing units on diametrical tensile strength

The aim of this study was to evaluate the diametrical tensile strength (DTS) of three light-curing photo-activated composites with two different light curing units (LCU). Three types of dental restorative composites were used in this study: micro filled A110 (3M Espe); P60 (3M Espe) for posterior restorations, and micro-hybrid Charisma (Heraeus-Kulzer). The two LCUs were: halogen light (HAL) (Degulux, Degussa) and blue light emitting diode (LED) (Ultrablue, DMC). Resin composite specimens were inserted incrementally into a Teflon split mold meas-uring 3 mm in depth and 6 mm in internal diameter, and cured using either LCU (n = 10). Specimens were placed into a dark bottle containing distilled water at 37°C for 7 days. DTS tests were performed in a Universal Testing Machine (0.5 mm/min). Data were submitted to two-way ANOVA and Tukey's test. Results were (MPa): A110/HAL: 276.50 ± 62.94ª; A110/LED: 306.01 ± 65.16ª; P60/HAL: 568.29 ± 60.77b and P60/LED: 543.01 ± 83.65b; Charisma/HAL: 430.94 ± 67.28c; Charisma/LED: 435.52 ± 105.12c. Results suggested that no significant difference in DTS was obtained with LCUs for the same composite. However, resin composite restorative materials presented different DTS.

Mechanical properties of light-cured composites polymerized with several additional post-curing methods

This study determined the microhardness and diametral tensile strength of two hybrid resin composites submitted to conventional light curing, which were post-cured with different methods, and compared these data with the same data collected from one indirect resin composite. Two hybrid composites (TPH Spectrum and Filtek P60) and an indirect one (Solidex) were used. Conventional composites were polymerized with 1) conventional light curing for 40 seconds. Additional curing methods were applied with 2) laboratory multi-focal light curing for seven minutes, 3) microwave curing for five minutes at 500W, 4) oven curing for 15 minutes at 100 degrees C, 5) autoclave curing for 15 minutes at 100 degrees C and (6) were polymerized only with a laboratory light curing unit in three increments for three minutes and post-polymerized for seven minutes. The Solidex group was done following the manufacturers' instructions only. Diametral tensile strength and Knoop hardness tests were applied for all groups of five samples. Data were compared using ANOVA, Tukey and Student t-tests (p < 0.05). Post-curing methods increased the Knoop hardness and diametral tensile strength of conventional composites. In general, Filtek P60 showed higher hardness and diametral tensile strength values than TPH Spectrum resin. The Indirect resin composite showed poorer mechanical properties than conventional composites.

Effects of x-ray irradiation on material properties

With a new commercial sterilisation technique about to enter the market, this article details a study that compared the effects of existing electron-beam irradiation with X-ray irradiation on different types of plastics commonly used in the manufacture of medical devices. The results are evaluated here.

Microtensile Bond Strength Analysis of Different Adhesive Systems and Dentin Prepared with High-Speed and Er:YAG Laser: A Comparative Study

OBJECTIVE

The aim of this study was to evaluate the bond strength of two adhesive systems (Single Bond and Clearfil SE Bond) subjected or not to a thermocycling procedure and applied to cavities prepared either with high-speed diamond bur or Er:YAG laser.

BACKGROUND DATA

One of the possible applications of dental lasers includes increasing the quality of bond strength.

METHODS

This in vitro study was carried out using a microtensile test on 16 bovine teeth, divided into eight groups. Cavities were prepared on superficial dentin of the medium portion of the buccal surface. After application of adhesive systems, composite restorations were performed at 5-mm height. After 24 h, four groups of teeth were immersed in water, and the other four were thermocycled. Bonded specimens were sectioned into serial 1x1-mm beams, which were subjected to a microtensile test. Final values of bond strength were measured, expressed in MPa, and statistically analyzed.

RESULTS

Results were as follows: G1 (26.281 +/- 5.454 MPa); G2 (10.965 +/- 3.714 MPa); G3 (18.549 +/- 6.113 MPa); G4 (14.295 +/- 3.806 MPa); G5 (18.225 +/- 5.701 MPa); G6 (5.588 +/- 2.211 MPa); G7 (18.256 +/- 3.819 MPa); and G8 (15.423 +/- 4.714 MPa).

CONCLUSIONS

Self-etching adhesive system (SE) produced more stable bond strength results than the system that indicates total etching (SB). For dentin prepared at high speed, the total etching adhesive system was more indicated, whereas Er:YAG laser-preparation dentin was not influenced by the adhesive system. The thermocycling procedure could negatively affect microtensile bond strength of both adhesive systems, being more deleterious to SB than to SE.

Influence of indocyanine green staining on the biomechanical properties of porcine anterior lens capsule

PURPOSE

Indocyanine green (ICG) has recently been introduced in cataract surgery to stain the anterior lens capsule for better visualization of the capsulorhexis. The aim of the current in vitro study was to examine the effect of ICG staining on the biomechanical strength of the anterior porcine lens capsule.

METHODS

Two parallel, 8 mm anterior lens capsule strips were prepared from each of 65 porcine postmortem eyes. ICG staining combined with white light exposure of 0.5, 1, 3, and 30 min duration was conducted. Unstained, nonilluminated and 0.1% glutaraldehyde-treated specimens were used as controls. Biomechanical stress-strain measurements were performed using an automated material tester. The absorption spectrum of the 0.5% ICG solution and the emission spectrum of the light source were controlled.

RESULTS

After ICG staining combined with at least 3 min light exposure, a significant increase of stress (31%) at 25% strain and a significant decrease (7%) in ultimate strain was found. Without light exposure, there was no such effect, suggesting a light-dependent process. After 30 min of 0.1% glutaraldehyde treatment, there was a similar increase in stress (322%) at 25% strain and a decrease (47.6%) in ultimate strain.

CONCLUSIONS

ICG staining of the lens capsule causes a significant increase in elastic stiffness and a reduction in ultimate extensibility, thereby facilitating a smooth continuous capsulorhexis. The effect is due to a photosensitizing effect of ICG, leading to collagen cross-linking.

Mechanical properties of UV irradiated rat tail tendon (RTT) collagen

The mechanical properties of RTT collagen tendon before and after UV irradiation have been investigated by mechanical testing (Instron). Air-dried tendon were submitted to treatment with UV irradiation (wavelength 254 nm) for different time intervals. The changes in such mechanical properties as breaking strength and percentage elongation have been investigated. The results have shown, that the mechanical properties of the tendon were greatly affected by time of UV irradiation. Ultimate tensile strength and ultimate percentage elongation decreased after UV irradiation of the tendon. Increasing UV irradiation leads to a decrease in Young's modulus of the tendon.

Effect of type of polymerization on different properties of dental composites

The aim of this study is to assess the influence of plasma lamps on the properties of the composites compared to the influence of conventional polymerization. Vickers hardness tests, three-point bending tests, and measurement of the shrinkage marginal gap by scanning electron microscopy were carried out on three resin composites (Tetric Ceram, Z-100 and Inten-S) irradiated with to lamps (Flipo) plasma and Astralis 7 halogen lamps). With a 3-second exposure, the results of Vickers hardness and resistance to flexion (excepting values for Z-100) were lower for the composites cured by the Flipo plasma lamp, than after 40-second curing by the conventional halogen lamp (Astralis 7), notably at a depth of 3 mm. With a 5-second exposure the results of Vickers hardness and resistance to flexion obtained using the plasma lamp approached those obtained by using the halogen lamp. Whatever the polymerization protocol used, the measurements of the gap between the tooth and the filling are very similar except for Z-100/Astralis 7, for which shrinkage results are more important. For any one resin composite and lamp used, the shrinkage values obtained at a depth of 4 mm are twice higher than those obtained at the surface. In conclusion, for a 3-second exposure the level of polymerization obtained by plasma curing is lower than the one obtained by halogen curing, particularly in depth. On the other hand, 5-second plasma curing results recommends the use of this kind of lamp.