The object of this study was to compare the microleakage between various composite resin systems of multistep, one-bottle, and self-etching systems using electrical conductivity.
After making class V cavities (4×3×1.5 mm around CEJ), they were bulk filled with three kinds of resins of A3. Teeth were storaged in a saline solution for one day, after then, they were finished and polished using Sof-Lex system. Another stress of thermocycling was made for 500 times from 5° to 55℃ with each dwelling time of 10 seconds. Electrical conductivity (microamphere, µA) was checked four times: before and after cavity preparation, after filling, after thermocycling.
One-way ANOVA and 95% Scheffe Post Hoc test was used for checking any statistical difference among groups. Another 95% Paired Samples T-test was also used for estimating any significant difference within group after cavity filling or thermocycling.
The results were as follows:
Every specimen showed various range of microleakage after filling. There was, however, no difference between composite resin systems. All composite resin systems showed marked increase in microleakage with a thermocycling (p<0.05), there was, however, no difference between composite resin systems. Although there was no significant difference between groups (p=0.078), one-bottle and self-etching systems seemed to be unstable than multistep system.
Within the limits of this study, it was concluded that much more consideration should be needed when using thermally unstable one-bottle and self-etching systems that have multi-advantages from simplified step. More studies will be needed to solve these kinds of problems.
Mechanical properties and microleakage of two composites [conventional hybrid type DenFil (VERICOM Co., Anyang, Korea) / micro matrix hybrid type Esthet X (Dentsply Caulk, Milford, DE, U.S.A.)] were evaluated to assess whether variable light intensity curing is better than conventional curing technique.
Curing was done for 40 seconds in two ways of 2 step soft-start technique and 5 step ramping technique. Three kinds of light intensities of 50, 100, 200 mW/cm2 were initially used for 10, 20, 30 seconds each and the maximum intensity of 600 mW/cm2 was used for the rest of curing time in a soft-start curing technique. In a ramping technique, curing was done with the same initial intensities and the light intensity was increased 5 times with the same rate to the maximum intensity of 600 mW/cm2.
After determining conditions that showed no different mechanical properties with conventional technique, Esthet X composite was filled in a class V cavity, which dimension was 4×3×1.5 mm and cured under those conditions.
Microleakage was evaluated in two ways of dye penetration and maximum gap estimation through SEM observation. ANOVA and Spearman's rho test were used to confirm any statistical significance among groups.
The results were as follows:
Several curing conditions of variable light intensities resulted in the similar mechanical properties with a conventional continuous curing technique, except conditions that start curing with an initial light intensity of 50 mW/cm2, Conventional and ramping techniques were better than soft-start technique in mechanical properties of microhardness and compressive strength. Soft-start group that started curing with an initial light intensity of 100 mW/cm2 for 10 seconds showed the least dye penetration. Soft-start group that started curing with an initial light intensity of 200 mW/cm2 for 10 seconds showed the smallest marginal gap, if there was no difference among groups. Soft-start technique resulted in better dye-proof margin than conventional technique (p=0.014) and ramping technique(p=0.002). There was a very low relationship(p=0.157) between the methods of dye penetration and marginal gap determination through SEM evaluation.
From the results of this study, it was revealed that ramping technique would be better than conventional technique in mechanical properties, however, soft-start technique might be better than conventional one in microleakage.
It was concluded that much endeavor should be made to find out the curing conditions, which have advantages of both aspects or to solve these kinds of problems through a novel idea of polymerization.
The purpose of this study is to evaluate the polymerization ability of three different light sources by microhardness test. Stainless steel molds of 1, 2, 3, 4 and 5 mm in thickness of 7 mm in diameter were prepared. The hybrid composite Z100 was packed into the hole of the mold and curing light was activated for designated time. Three different light sources, conventional halogen, light emitting diode, and plasma arc, were used for curing of composite. Two different curing times applied; one is to follow the manufacturer's recommendation and the other is to extend the curing time of LED and plasma arc for balancing the light energy with halogen. Immediately after curing, the Vickers hardness was measured at the bottom of specimen.
The results were as follows.
The composite cured with LED showed equal to higher microhardnesss than halogen. The composite was cured with plasma arc by manufacturer's recommendation showed lowest microhardness at all thickness. However, when curing time was extended, microhardness was higher than the others.
In conclusion, this study suggested that plasma arc needs properly extended curing time.
The purpose of this study was to investigate the frequency of 7 putative pathogens in endodontic infections. The specimens were collected from infected pulpal tissue of patients who were referred for root canal treatment to the department of conservative dentistry, Chosun University. Samples were collected aseptically using a barbed broach and a paper point. The cut barbed broaches and paper points were transferred to an eppendorf tube containing 500 ml of 1 X PBS. DNAs were extracted from the samples by direct DNA extraction method using lysis buffer (0.5% EDTA, 1% Triton X-100). Identification of 7 putative pathogens was performed by PCR based on 16S rDNA. The target species were as follows: