Days Of Water Storage Research Articles

Release of chlorhexidine digluconate and flexural properties of glass fibre reinforced provisional fixed partial denture polymer

The objective of this study was to determine the flexural properties and the release of chlorhexidine digluconate (CHX) of CHX laced unidirectional E-glass fibre reinforced provisional fixed partial denture polymer. Bar shaped test specimens (3.3 x 10.0 x 65.0 mm) were fabricated from provisional fixed partial denture polymer (mixture of poly[ethylmethacrylate] powder and n-poly[butyl methacrylate] monomer liquid) with E-glass fibre reinforcements. Poly(methyl methacrylate) preimpregnated continuous unidirectional glass fibre reinforcement was laced with CHX. The glass fibre reinforcements were incorporated into the polymer and the polymerised to the form of test specimens. In addition test specimens without CHX in glass fibre reinforcement were made for comparison. Control specimens did not contain glass fibres in the test specimens. Flexural strength and modulus of test specimens (n = 6) was tested with three-point bending test after storing the specimens dry or in water (two weeks). Released CHX was determined with high performance liquid chromatography during 180 days water immersion. In dry conditions, the flexural strength and the modulus of the polymer was 43 MPa and 1.7 GPa, and with glass fibre reinforcement 96 MPa and 3.5 GPa. With the reinforcement laced with CHX, the strength was 92 MPa and the modulus was 3.2 GPa. The water storage of test specimens did not weaken the reinforced polymer. The majority of the CHX released from the glass fibre reinforced polymer during the first days of storage in water. Flexural properties of provisional fixed partial denture polymer were increased using glass fibre reinforcement. The fibre reinforcement that was laced with CHX resulted in similar reinforcing effect.

Adaptation of complete denture bases submitted to chemical polishing

This study evaluated the effect of chemical polishing on the internal adaptation of complete denture bases fabricated with Veracril® resin and polymerized by either the conventional (C) or microwave (M) techniques. Six groups (n=6/group) were tested: 1) C + no polishing (CO); 2) C + chemical polishing (CQ); 3) C + immersion in hot water at 75ºC (CW); 4) M + no polishing (MO); 5) M + chemical polishing (MQ); and 6) M + immersion in hot water at 75ºC (MW). Internal adaptation immediately after the polishing treatment and after 30 days of storage in water at 37ºC was evaluated by weighing a vinyl polysiloxane film reproducing the gap between resin base and metallic master model, using a precision scale. Data were analyzed by ANOVA and Tukey test and paired Student's t test, at a significance level of 0.05. No significant difference in immediate adaptation was found as a function of technique, polishing treatment, or interaction of technique/polishing. After 30 days, adaptation means (g) were: CO=2.46±0.32 a; CQ=3.40±0.23 d; CW=3.14±0.22 c; MO=3.23±0.37 c, d; MQ=3.41±0.47 d; MW=2.81±0.33 b (means followed by different letters are statistically different at alpha=0.05). All groups but group CO had significant increase of misfit over the tested period. The present results suggest that Veracril® resin denture bases submitted to chemical polishing had decrease of internal adaptation in 30 days, although immediate adaptation was not affected.

In vitro shear bond strength of cementing agents to fixed prosthodontic restorative materials

Durable bonding to fixed prosthodontic restorations is desirable; however, little information is available on the strength of the bond between different cements and fixed prosthodontic restorative materials. This study determined the shear-bond strength of cementing agents to high-gold-content alloy castings and different dental ceramics: high-strength aluminum oxide (Procera AllCeram), leucite-reinforced (IPS Empress), and lithium disilicate glass-ceramic (IPS Empress 2). Prepolymerized resin composite cylinders (5.5 mm internal diameter, n=20) were bonded to the pretreated surfaces of prosthodontic materials. High-gold-content alloy and high-strength aluminum oxide surfaces were airborne-particle-abraded, and pressable ceramics were hydrofluoric acid-etched and silanized prior to cementing. The cementing agents tested were a zinc-phosphate cement (Fleck's zinc cement), glass ionomer cements (Fuji I, Ketac-Cem), resin-modified glass ionomer cements (Fuji Plus, Fuji Cem, RelyX Luting), resin cements (RelyX ARC, Panavia F, Variolink II, Compolute), and a self-adhesive universal resin cement (RelyX Unicem). Half the specimens (n=10) were tested after 30 minutes; the other half (n=10) were stored in distilled water at 37 degrees C for 14 days and then thermal cycled 1000 times between 5 degrees C and 55 degrees C prior to testing. Shear-bond strength tests were performed using a universal testing machine at a constant crosshead speed of 0.5 mm/min. Statistical analysis was performed by multifactorial analysis of variance taking interactions between effects into account. For multiple paired comparisons, the Tukey method was used (alpha=.05). In a 3-way ANOVA model, the main factors substrate, cement, time, and all corresponding interactions were statistically significant (all P <.0001). In subsequent separate 1-way or 2-way ANOVA models for each substrate type, significant differences between cement types and polymerizing modes were found (all P <.001). None of the cement types provided the highest bonding values with all substrate types. After 14 days of water storage followed by thermal cycling, only the self-adhesive universal resin cement (RelyX Unicem) and 2 of the resin cements (Panavia F and Compolute) exhibited strong bond strengths to specific prosthodontic materials. In contrast, zinc-phosphate, glass ionomer, and resin-modified glass ionomer cements showed the lowest values of all tested cementing agents after 14 days of water storage followed by thermal cycling.

The effect of six years of water storage on resin composite bonding to human dentin.

The aim of this in vitro study was to evaluate dentin bond strength and marginal adaptation of direct resin composite fillings after different storage times. Three hundred sixty cavities were prepared in discs of freshly extracted human third molars and filled with resin composites. Multistep self-etching adhesives (Syntac Classic, A.R.T. Bond, both with and without total etching), three-step etch-and-rinse adhesives (Scotchbond Multi-Purpose Plus, EBS), and two-step etch-and-rinse adhesives (Prime and Bond 2.0, Syntac Single-Component) were used for bonding. After 1, 90, and 2190 days of water storage and 24 h thermocycling (1150 cycles), push-out testing was performed. From the 6-year group, replicas were made after 1 day, 90 days, and 1, 2, 3, 4, 5, and 6 years, and examined regarding marginal adaptation under an SEM (x 200 magnification). In all groups under investigation, push-out bond strengths remained stable after 90 days; however, the strengths significantly decreased after 6 years of water storage. The two-step systems exhibited lower bond strengths than three-step systems after 6 years. Marginal analysis revealed a significant loss regarding the percentage of perfect margins having been stable after 2 years for the three-step etch-and-rinse systems. Overall, the older three-step systems proved to be more effective than the simplified adhesives Syntac Single-Component and Prime and Bond 2.0 with regard to bond strength and marginal adaptation.

Reducing the negative effects of chemical polishing in acrylic resins by use of an additional cycle of polymerization

Statement of problem The chemical polishing of dentures and orthodontic appliances is an efficient and time-saving technique. However, the process may adversely affect the physical properties of resin. Purpose This study evaluated the effect of an additional polymerization cycle in a microwave or water bath on the physical properties of an autopolymerized acrylic resin submitted to chemical polishing. Material and methods Control groups comprised acrylic resin specimens submitted to mechanical (group 1) and chemical (group 2) polishing. Experimental groups comprised chemically polished specimens submitted to an additional cycle of polymerization in a microwave at 450 W for 3 minutes (group 3) or in a hot water bath at 65° C for 1 hour (group 4). For the residual monomer test, 10 standardized half-disc specimens (30 × 3 mm) were fabricated for each of the test groups, and daily ultraviolet spectrophotometric (206 nm) analyses were assessed for 13 days (μg/cm 2). For transverse strength and internal Knoop hardness (KH) tests, 10 (65 × 10 × 2.5 mm) and 5 (32 × 10 × 2.5 mm) specimens were fabricated for each test group, respectively. Internal Knoop hardness (kg/mm 2) was assessed at depths of 100, 700, and 1500 μm. Transverse strength (MPa) was measured with a 3-point bending test in a universal testing machine with a 10-kg load cell at a crosshead speed of 5 mm/min. The data were analyzed with 1-way analysis of variance, and the means were compared with Student’s t test and Tukey-Kramer intervals ( P<.05). Results At the end of the first day of the test, all groups showed significantly different residual monomer levels ( P<.05). The groups in order of decreasing residual monomer were: group 2 (1315.7 ± 225.5 μg/cm 2), group 3 (848.2 ± 150.4 μg/cm 2), group 4 (295.1 ± 81.6 μg/cm 2), and group 1 (136.6 ± 45.5 μg/cm 2). After 13 days of water storage, the lowest residual monomer levels were recorded for group 1 (4.6 ± 1.6 μg/cm 2). There were no significant differences among group 2 (11.3 ± 3.1 μg/cm 2), group 3 (9.6 ± 1.5 μg/cm 2), and group 4 (12.3 ± 1.7 μg/cm 2). Group 1 demonstrated the highest transverse strength (78.1 ± 6.1 MPa); the other groups were not significantly different from each other. All groups exhibited lower KH values at the 100-μm depth than at 700- and 1500-μm depths. At the latter depths, group 4 specimens demonstrated the highest hardness values (18.0 ± 0.5 and 18.8 ± 0.7 kg/mm 2, respectively). Conclusion Within the limitations of this study, additional polymerization with hot water reduced residual monomer content of chemically polished acrylic resins on the first day. Although additional polymerization increased the internal hardness of the material, however, it did not recover the transverse strength that was decreased by the chemical polishing.

SEM and TEM analysis of water degradation of human dentinal collagen.

Recently several long-term studies have reported evidence of the hydrolytic degradation of collagen fibrils based on fractured surface observations after bond testing. Those studies suggested that one cause of the decline in the bond strength was the degradation of the collagen fibrils within the bonds. However, one concern has been raised that the dentinal collagen fibrils may be stable in water that does not contain oral bacteria or enzymes. Therefore, the present study aimed to clarify the micromorphological change in naked collagen fibrils after 500 days of water storage. To prepare exposed collagen fibrils, sectioned and polished human dentin surfaces were acid conditioned for 15 s with the use of two commercially available acid conditioners: All-Etch (10% phosphoric acid) and Uni-Etch (32% phosphoric acid) (Bisco, Inc.). Those specimens were stored in distilled water at 37 degrees C for 1 day (control) for 500 days. After the storage periods, the samples were examined with the use of SEM and TEM. Under SEM and TEM examination, micromorphological alterations (disarrangement of collagen web, widening the interfibrillar space, and the thinning diameter of collagen fibrils) were found in the specimens after 500 days in water.

Effect of a heat-treatment on the linear dimensional change of a hard chairside reline resin

Statement of Problem. Little data are available regarding the effect of heat-treatments on the dimensional stability of hard chairside reline resins. Purpose. The objective of this in vitro study was to evaluate whether a heat-treatment improves the dimensional stability of the reline resin Duraliner II and to compare the linear dimensional changes of this material with the heat-polymerized acrylic resin Lucitone 550. Material and Methods. The materials were mixed according to the manufacturer's instructions and packed into a stainless steel split mold (50.0 mm diameter and 0.5 mm thickness) with reference points (A, B, C, and D). Duraliner II specimens were polymerized for 12 minutes in water at 37° C and bench cooled to room temperature before being removed from the mold. Twelve specimens were made and divided into 2 groups: group 1 specimens (n=6) were left untreated, and group 2 specimens (n=6) were submitted to a heat-treatment in a water bath at 55° C for 10 minutes and then bench cooled to room temperature. The 6 Lucitone specimens (control group) were polymerized in a water bath for 9 hours at 71° C. The specimens were removed after the mold reached the room temperature. A Nikon optical comparator was used to measure the distances between the reference points (AB and CD) on the stainless steel mold (baseline readings) and on the specimens to the nearest 0.001 mm. Measurements were made after processing and after the specimens had been stored in distilled water at 37° C for 8 different periods of time. Data were subjected to analysis of variance with repeated measures, followed by Tukey's multiple comparison test (P<.05). Results. All specimens exhibited shrinkage after processing (control, −0.41%; group 1, −0.26%; and group 2, −0.51%). Group 1 specimens showed greater shrinkage (−1.23%) than the control (−0.23%) and group 2 (−0.81%) specimens after 60 days of storage in water (P<.05). Conclusion. Within the limitations of this study, a significant improvement of the long-term dimensional stability of the Duraliner II reline resin was observed when the specimens were heat-treated. However, the shrinkage remained considerably higher than the denture base resin Lucitone 550. (J Prosthet Dent 2002;88:611-5.)

Alteração dimensional linear de resinas para bases de próteses polimerizadas com microondas

A proposta deste estudo foi comparar as alterações dimensionais de 3 resinas submetidas à polimerização com os seguintes ciclos: 1) banho d’água em 73ºC durante 12 horas - ciclo longo, 2) banho d’água durante 3 horas - ciclo curto, 3) energia de microondas por 3 minutos a potência de 500 W, após armazenamento em água destilada a 37 ± 2ºC durante 30 dias. As resinas usadas foram Clássico, Lucitone 550 e Acron MC. As resinas Clássico e Lucitone 550 foram submetidas aos três ciclos, enquanto a resina Acron-MC somente ao ciclo 3. Amostras medindo 65,0 x 10,0 x 3,0 mm e com marcas iguais em três pontos eqüidistantes foram confeccionadas a partir da inclusão de matrizes de aço em gesso-pedra tipo III. Foram confeccionados 21 corpos-de-prova para cada combinação resina/ciclo de polimerização e que foram submetidos a 3 leituras para cada posição (A e B), com o auxílio do microscópio de mensuração (precisão de 0,001 mm), imediatamente após a polimerização e depois do período de imersão em água por 30 dias. Os resultados mostraram que todas as resinas, independendo do ciclo a que tenham sido submetidas e das medidas avaliadas, apresentaram expansão dimensional após terem sido mantidas em água; a composição da resina interferiu na expansão dimensional mais do que o ciclo de polimerização ao qual as resinas foram submetidas; a resina convencional, quando polimerizada com energia de microondas, apresentou alteração dimensional semelhante à resina desenvolvida para a polimerização em microondas.

Reply to the discussion of the paper “Durability of the hydrated limestone-silica fume Portland cement mortars under sulphate attack”

The authors thank Dr. B. Mather for his interest in our paper and for his comments, which we find most helpful. We feel that we should try to clarify some things. Our experiments were performed with industrial, blended Portland cement produced in the Croatian Cement Works, with 30 percent mass blast furnace slag and the 28-day strength class of 45 MPa, marked PC30z45s according to the Croatian standard HRN.B.C1.011-conforming to the European cement standard EN 197.1:cement type: CE II-S, strength class 42, 5. Table 2 lists the potential mineralogical composition (the Bogue calcularion) of cements used. In ad-dition to this, the C_3A content of the cement clinker is 10.5°~o mass, according to Bogue. Many studies have dealt with the ettringite formation mechanism and the damage mechanism associated with ettringite formation in hardened mortar/concrete. We agree with the statement in Dr. Mather's discussion that the mech-anism of the ettringite formation is the result of complex, long-term processes, in which the cement composition, the concentration conditions and pH values in the pore solution, and ambient effects play important roles. Various study re-sults show that the ettringite formed at high pH values is probably microcrystalline (Type II according to Mehta) and less stable, and can therefore gradually dissolve in the pore liquid of a moist concrete and recrystallize in the voids, cracks, or contact zones. As a rule, the occurrence of ettringite crystals in concrete cracks is only a consequence, and seldom the cause, of the cracks. Fig. 6 shows that after the 120-day immersion in Na_2S0_4 solution, the scanning electron microscopy (SEM) of mortar containing 8 percent mass of silica fume detected large, long-needle ettringite crystals (Type I as defined by Mehta) in pores. Based on the experimental results, given in our paper, we have con-cluded that this type of ettringite crystal, formed under condi-tions of low calcium hydroxide concentration, resulting from silica fume addition to the cement mixture, is not expansive. The same photomicrograph also shows a couple of cracks transecting the void, as Dr. Mather points out. In our opinion, however, microcracks observed in Fig. 6 have only resulted from the effect of the high vacuum in the specimen chamber of the SEM. Artefacts (specimen changes, cracks) caused by the method preparation and the effects of high vacuum in the sample chamber are typical and only occur in a conventional high vac-uum scanning electron microscope (conventional SEM), as have been reported by Moser and Stark. The investigations also confirm that any information associated with contraction of the hardened cement paste observed with conventional SEM is to be regarded with caution. The sulphate performance was examined using the ASTM C 452-68 mortar bar expansion test. In conformance to this standard, we did not incorporate additional gypsum into the mortar mix and the expansion difference was measured after 28 days of water storage and thereafter every 30 days within a 6-month period of sulphate immersion. The initial length mea-surements of mortar were carried out by means the length com-parator after the 28-day water storage. We agree with Dr. Mather that the ASTM C 425-68 method applies only to Port-land cement. It is for this reason that we have used only a part of this test, as described, but not emphasized in section 1.2. (Test methods) of our paper, and have adjusted it for testing the sulphate resistance of blended cement (i.e., the Portland ce-ment-silica fume-limestone systems). The experimental pro-cedure used corresponds to the ASTM C 1012-84, for both plain Portland cements and blended cements or composite ce-ments, as Dr. Mather has suggested.

Tensile bond strengths of hard chairside reline resins as influenced by water storage.

Due to gradual resorption of the edentulous ridge bone, removable prostheses often require denture base relines to improve fit and stability. This research evaluated the bond strength between one heat-cured acrylic resin (Lucitone 550(R)) and two hard chairside reline resins, after two different periods of storage in water (50 h and 30 days). The bond strength was evaluated using a tensile test. The mode of failure, adhesive or cohesive, was also recorded. The results submitted to the Kruskal-Wallis test indicated that the highest tensile strengths were achieved with intact Lucitone 550(R) denture base resin in both periods of storage in water. After 50 h of storage in water, Duraliner II(R) reline material exhibited the highest bond strength to the denture base resin. After 30 days of storage in water, Duraliner II(R) reline resin demonstrated a significant reduction in adhesion, showing lower tensile bond strength than Kooliner(R) material. Both hard chairside reline materials failed adhesively across Lucitone 550(R) denture base resin, in both periods of time.

Surface roughness and bond strength of enamel to composite

Objectives: The aim of the study was to assess the influence of pretreating enamel by different rotary instruments on shear-bond strength of composite to enamel after the acid etch technique. Methods: Ninety human enamel specimens with transversely and longitudinally sectioned prisms were ground flat, and half of the enamel area of each specimen was prepared with one of the eight different rotary instruments: a 120 μm diamond bur, three finishing diamonds (30, 15 and 8 μm), two tungsten carbide finishing instruments (8- and 30-fluted) and two stones (Dura green and Dura white). The other half of the enamel area was left untreated. Enamel roughness was measured by laser-stylus profilometry. Two cylinders filled with the hybrid composite Pertac® were adhesively fixed on each enamel surface, one on the prepared side and the other on the untreated side. After seven days of water storage, shear-bond strength was measured with a Universal testing machine. Results: R z values of the treated enamel surfaces were between 4.14 and 17.75μm. The shear-bond strength data varied between 16.8 and 29.4 MPa and were similar for transversely and longitudinally orientated prisms. The different roughness data had no significant influence on shear-bond strength of composite to enamel. Additional SEM investigation showed that the surface geometry caused by the rotary instruments largely persisted after acid etching. Significance: With regard to shear-bond strength, there was no advantage in using a special bur for finishing enamel surfaces prior to the acid etch technique. Burs causing extreme roughness should not be used for this purpose.

In vitro mechanical property comparison of four resins used for fabrication of provisional fixed restorations

Purpose. This study recorded and compared the flexural elastic moduli and moduli of rupture of four materials (Provipont DC resin, Triad provisional restorative material, Jet acrylic resin, and a 50:50 mixture of Jet acrylic resin and orthodontic resin) used to make provisional restorations. Material and methods. Thirty-nine identical 63 × 10 × 3 mm specimens were made from each of the four materials. After 24 hours, 30 days, and 60 days of water storage at 37° C (13 specimens each), standard three-point bend tests were conducted on an Instron universal testing machine at a crosshead speed of 0.5 cm/minute. Stress strain curves were generated, and values for the flexural elastic moduli and moduli of rupture were calculated. Data were subjected to two-way and one-way analyses of variance (α = 0.05). Results. Provipont DC resin exhibited significantly higher flexural elastic moduli and moduli of rupture values at the 24-hour test time. However, Provipont DC resin exhibited the greatest decrease in these values over time. (J Prosthet Dent 1998;80:158-62.)

Relative Importance of Neutral Lipids and Glycogen as Energy Stores in Dauer Larvae of Two Entomopathogenic Nematodes, Steinernema carpocapsae and Steinernema feltiae

The infectivity of Steinernema carpocapsae dauer larvae (infective juveniles) remained nearly constant up to 60 days of storage in water at 25°C and then declined rapidly over the next 30 days. Few individuals remained infective after 120 days. Concurrent measurements showed that the mean neutral lipid content of individual S. carpocapsae declined to about 10% of initial levels after 60 days, and staining of individual nematodes with Oil Red O indicated that the population was almost homogeneous for low levels of neutral lipids. In contrast, the mean glycogen content of S. carpocapsae only declined significantly between 60 and 90 days of storage. These results show that the decline in infectivity in S. carpocapsae is correlated primarily with the decline in glycogen reserves and suggests that glycogen is the key late energy store in aged infective juveniles. In contrast, Steinernema feltiae dauer larva showed a much more gradual decline in infectivity over a 150- to 180-day storage period with a concurrent decline in neutral lipids, whereas glycogen levels declined up to 90 days of storage and then remained nearly constant. Thus, unlike S. carpocapsae, neutral lipids remain an important energy store in S. feltiae during storage, although glycogen also appears to be important, at least initially.

Unrestricted linear dimensional changes of two hard chairside reline resins and one heat-curing acrylic resin

The selection and use of hard chairside reline resins must be made with regard to dimensional stability, which will influence the accuracy of fit of the denture base. This study compared the dimensional change of two hard chairside reline resins (Duraliner II and Kooliner) and one heat-curing denture base resin (Lucitone 550). A stainless steel mold with reference dimensions (AB, CD) was used to obtain the samples. The materials were processed according to the manufacturer's recommendations. Measurements of the dimensions were made after processing and after the samples had been stored in distilled water at 37°C for eight different periods of time. The data were recorded and then analyzed with analysis of variance. All materials showed shrinkage immediately after processing ( p < 0.05). The only resin that exhibited shrinkage after 60 days of storage in water was Duraliner II; these changes could be clinically significant in regard of tissue fit.

Linear dimensional variability of three denture base resins after processing and in water storage

It has been shown that denture base resins shrink during curing and expand during storage in water. This investigation measured and compared linear dimensional changes of three denture base resins that occurred during processing and after storage in water for 30, 60, and 90 days. Triad, Accelar 20, and Lucitone 199 long and short-cured resins were studied, and it was found that Accelar 20 resin exhibited the least curing shrinkage and Lucitone 199 resin short-cured exhibited the most. However, no significant differences occurred between the groups. After 90 days of water storage, the only resin that exhibited a shrinkage from the processed state was Accelar 20. All of the expansion or shrinkage changes were so small that they were not statistically significant and should not be clinically detectable.

The effect of carbon graphite fiber reinforcentent on the strength of provisional crown and fixed partial denture resins

This study compared the moduli of elasticity of three provisional crown and fixed partial denture resins. Eighteen specimens of each resin were reinforced with carbon graphite fibers and 18 resin specimens from each group contained no fibers. Six specimens of each resin, with and without fibers, were tested within 6 hours of fabrication, after 30 days, and after 60 days of water storage. The mean moduli of elasticity of all the resins increased significantly with fiber incorporation. Water storage did not have a significant effect on the moduli of elasticity of the resins tested.