Lennart Forsten

Resin-modified glass ionomer cements: Fluoride release and uptake

The aim was to study the short- and long-term fluoride release from resin-modified glass ionomer cements (GIC). The aim was also to determine the effect of fluoride treatment of 9-month-old specimens, consistency of the mix, and pH of the environment on the fluoride release. GIC test specimens were continually exposed to running water, and the fluoride release was measured periodically by storing the specimens in 5 ml deionized water for 1 week and measuring the fluoride content of the solution. After 24 h, 1 month, 9 months, and 11 months in running water four of the six resin-modified GICs released as much as or more fluoride than the auto-curing GIC tested for comparison. Fluoride treatment after 9 months also increased the fluoride release of these four brands, as was the case with the conventional GIC. At 24 h and 1 month two of the resin-modified GICs released smaller amounts of fluoride than the other materials, and the fluoride treatment used on those had no or only a minimal effect. Thin consistency of a mix resulted in higher fluoride release for one resin-modified material than a thick mix. Low pH increased the fluoride release for all materials.

Transverse and Bond Strength of Restorative Resins

One silicate, one acrylic resin, and five manually and two mechanically mixed composite resins were studied. The strength was tested by three point loading on rectangular specimens (2 × 2 × 12 mm) 24 hours after storage in water. The lateral thirds of the bond strength specimens consisted of old and the central third of newly added material. The transverse strength of the strongest composite resin was five times higher than that of the silicate cement, two times higher than that of the acrylic resin and of the weakest composite, but one third of the average strength of amalgam. There were no differences in strength between manual and mechanical mixing of the silicate cement or between using flow and brush technique for the acrylic resin. Using the recommended ratio of the base to catalyst paste of a composite resulted in the highest strength value compared with the strength when the amount of either base or catalyst paste was doubled. Varying the time of the ultrahigh-speed mixer for one composite did not...

Sealing of preventively enlarged fissures.

The occlusal fissures of 156 permanent first molars in 63 children, 7--8 years of age, were sealed with a chemically polymerizing material (Delton). Deep and narrow fissures were opened up with a pointed diamond before etching and sealing. The treatment was performed by untrained dental students. The patients were called back for treatment every 6 months. 2/3 of the patients were followed up for a period of 2 1/2 years. After that period the retention of sealants was 93% (74 sealants) in ground deep fissures and 88% (28 sealants) in unground shallow fissures.

The alkaline and antibacterial effect of seven Ca(OH)2 liners in vitro.

The alkaline effect of seven Ca(OH)2 liners was studied, using extractions with unbuffered 0.9% NaCl solutions and buffered bacterial growth media. The antibacterial effect was studied by cultivating Streptococcus mutans in the presence of liner specimens. All liners made the NaCl solutions strongly alkaline (pH greater than 10), although MPC and Reolite released much less Ca than did Dycal, Life, Procal, Renew, and Reocap-E. The weaker alkaline effect of MPC and Reolite was shown by the extractions with the growth media. Consequently, these two liners were not able to prevent the growth of Str. mutans. No growth was observed in the presence of the other five liners, and the media remained alkaline during the 12-h incubation period. Regrowth of the bacteria grown in the presence of these effective liners showed that only Dycal could be considered bactericidal, whereas the four other liners acted bacteriostatically.

Curing depth of visible light-activated composites

Three composites, two microfilled (Heliosit and Silux) and one macrofilled (Prisma-Fil), were exposed to visible light from three different light units. The depth of the cure was estimated by measuring the length of the test specimen after removing the uncured material. The macrofilled composite cured to a greater depth than the microfilled materials. The curing depth of Heliosit was lower, of Silux about the same, and of Prisma-Fil higher than the values of curing depth given by the manufacturers. The shade of the pastes influenced the curing depth of the macrofilled more than that of the microfilled composites. Doubling the exposure time increased the curing depth by about 1/3. Exposure through tooth substance reduced the curing depth by at least 1/3. The curing effectivity of Prisma-Lite was slightly greater than that of Heliomat and the 3M unit.

Marginal leakage and consistency of the composite resin material in etched cavities.

The purpose of the study was to evaluate the degree of adaptation of undiluted and diluted composite resin to etched enamel walls with and without an intermediary resin. Cavities (O = 2 mm) were drilled in extracted teeth and the walls were etched with phosphoric acid. Fillings were made of Concise composite resin, without applying an intermediary resin (1), after applying the resin layer (2), after diluting the mix with one (3) or two (4) drops of catalyst resin but without an intermediary resin, and after diluting the mix and applying the resin layer (5). The fillings were ground flush with the tooth surface and the teeth were cycled thermally between two dye solutions baths. The marginal penetration of the dye was evaluated by measuring the discoloured portion of the margin at different depths using a stereomicroscope. The restorations with an intermediary resin (2 and 5) exhibited significantly less leakage than fillings without the intermediary layer (1, 3 and 4). When no resin layer was applied the dilution of the mix seemed to reduce the leakage compared with undiluted material but the differences were not statistically significant. The results indicate the advantage of using an intermediary resin with etching even when the composite is diluted.

Effect of a Ca(OH)2 solution and a chlorhexidine based detergent on the microbial activity of human carious teeth

Occlusar carious lesions from human molars, preserved in continuous humidity after extraction, were removed using conventional clinical techniques. Bacteriological samples were taken after rinsing the cavity with water only, after experimentally infecting the cavity and after treating uninfected cavities either with a saturated Ca(OH)2 solution or with a chlorhexidine based detergent. The samples were cultivated on blood agar plates aerobically and anaerobically. Cavities rinsed with water only showed very sparce bacterial growth. After experimental infection the growth was significant, but decreased radically after treatment with the test materials. In order to describe the effect of the two test materials on the microbial enzyme activity in infected dentin, cryostat sections of 10 micrometer were prepared from undermineralized carious dentin fragments excavated from freshly extracted human teeth. Conventional histochemical techniques were applied to demonstrate the aminopeptidase activity in the sections using N-L-leucyl-2-naphthylamide as a substrate. The aminopeptidase activity of carious dentin was inhibited totally with the Ca(OH)2 solution, whereas the chlorhexidine based detergent had no effect on the enzyme activity.

The influence of precondensation mercury content on the transverse strength of amalgams.

The purpose of this investigation was to study the influence of changing the precondensation mercury content (initial mercury content) on the early and final transverse strength of different amalgams. The material consisted of five conventional lathe cut alloys, two of which were zinc free, of one dispersion strengthened and one spherical alloy and of three lathe cut preamalgamated alloys. The amalgam was mixed with mercury using three different alloy-mercury ratios. Thus the precondensation mercury content of Mix I was about 50 per cent, of Mix II about 54 and of Mix HI about 59 per cent for all amalgams except the spherical brand. Rectangular amalgam test pieces, measuring 2 × 2 × 12 mm, were condensed by hand using a load of about 17 kg/cm2. The transverse strength test was performed either after one hour or one week using three point loading. The results show that for some of the amalgams an increase of the precondensation mercury content resulted in a slight reduction of the early strength. Furthermo...