C M Um

Publications (14)9.22 Total impact

• Article: A new method to measure the polymerization shrinkage kinetics of light cured composites.

  I B Lee, B H Cho, H H Son, C M Um
  [show abstract] [hide abstract]
  ABSTRACT: This study was undertaken to develop a new measurement method to determine the initial dynamic volumetric shrinkage of composite resins during polymerization, and to investigate the effect of curing light intensity on the polymerization shrinkage kinetics. The instrument was basically an electromagnetic balance that was constructed with a force transducer using a position sensitive photo detector (PSPD) and a negative feedback servo amplifier. The volumetric change of composites during polymerization was detected continuously as a buoyancy change in distilled water by means of the Archimedes' principle. Using this new instrument, the dynamic patterns of the polymerization shrinkage of seven commercial composite resins were measured. The polymerization shrinkage of the composites was 1.92 approximately 4.05 volume %. The shrinkage of a packable composite was the lowest, and that of a flowable composite was the highest. The maximum rate of polymerization shrinkage increased with increasing light intensity but the peak shrinkage rate time decreased with increasing light intensity. A strong positive relationship was observed between the square root of the light intensity and the maximum shrinkage rate. The shrinkage rate per unit time, dVol%/dt, showed that the instrument can be a valuable research method for investigating the polymerization reaction kinetics. This new shrinkage-measuring instrument has some advantages that it was insensitive to temperature changes and could measure the dynamic volumetric shrinkage in real time without complicated processes. Therefore, it can be used to characterize the shrinkage kinetics in a wide range of commercial and experimental visible-light-cure materials in relation to their composition and chemistry.
  Journal of Oral Rehabilitation 05/2005; 32(4):304-14. · 1.53 Impact Factor
• Article: A new resin matrix for dental composite having low volumetric shrinkage.

  Y Kim, C K Kim, B H Cho, H H Son, C M Um, O Y Kim
  [show abstract] [hide abstract]
  ABSTRACT: The applications of dental restorative composite resins containing 2,2 bis [4-(2-hydroxy-3-methacryloyloxy propoxy) phenyl] propane (Bis-GMA), as a base resin, and triethylene glycol dimethacrylate (TEGDMA), as a diluent, are often limited in dentistry due to the relatively large amount of volumetric shrinkage that occurs during the curing reaction. In this study, various new resin matrices were examined for use as dental composites in order to reduce the amount of volumetric shrinkage that occurs in dental composites as a result of curing. Bis-GMA derivatives were synthesized by substituting methyl groups for hydrogen on the phenyl ring. The derivatives of TEGDMA with different chain lengths or reactive groups were also examined. The molecular structural changes in the TEGDMA derivatives were not effective in reducing the level of volumetric shrinkage. The resin matrix containing a Bis-GMA derivative and TEGDMA showed a reduced amount of volumetric shrinkage in proportion to the number of methyl groups on the phenyl rings. Polymerization with a mixture of Bis-GMA, its derivatives and a diluent is a promising strategy for obtaining a polymer with a low amount of volumetric shrinkage. A comparison of the volumetric shrinkage of dental composites containing Bis-GMA, TMBis-GMA (2,2-bis[3,5-dimethyl, 4-(2-hydroxy-3-methacryloyloxy propoxy) phenyl] propane)), and TEGDMA with that prepared from a Bis-GMA and TEGDMA mixture showed that the volumetric shrinkage reduction in the new resin was approximately 50%. Furthermore, the mechanical strength of the former was higher than that of the latter.
  Journal of Biomedical Materials Research Part B Applied Biomaterials 08/2004; 70(1):82-90. · 2.15 Impact Factor
• Article: Thermal analysis on the cure speed of dual cured resin cements under porcelain inlays.

  I B Lee, C M Um
  [show abstract] [hide abstract]
  ABSTRACT: The reaction kinetics of five commercial dual cured resin cements (Bistite, Dual, Scotchbond, Duolink and Duo) were investigated when cured under varying thicknesses of porcelain inlays by chemical or light activation. The effect of the porcelain disc on the rate of polymerization of dual cured resin cement during light exposure was evaluated using thermal analysis, thermogravimetric analysis and differential scanning calorimetry. Inorganic filler weight %, the heat of cure (Delta H), the maximum rate of heat output and the peak heat flow time were measured when the polymerization reaction occurred by chemical cure only or by light exposure through 1, 2 and 4-mm thick porcelain discs. In 4-mm thick porcelain discs, the exposure time was varied from 40 to 60 s to investigate the effect of the exposure time on polymerization reaction. Cure speed by light exposure was 5--20 times faster than by chemical cure. The dual cured resin cements differed markedly in their sensitivity to light and chemical activation. The peak heat flow time increased by 1.51, 1.87 and 3.24 times as light cure was carried out through 1, 2 and 4-mm thick porcelain discs, respectively. Exposure times recommended by the manufacturers were insufficient to compensate for the attenuation of light by the 4-mm thick porcelain disc.
  Journal of Oral Rehabilitation 03/2001; 28(2):186-97. · 1.53 Impact Factor
• Article: Color differences between resin composites and shade guides.

  H S Kim, C M Um
  [show abstract] [hide abstract]
  ABSTRACT: The color of manufacturers' shade guides was compared with the color of the actual resin composites. Five light-activated resin composite products were evaluated. Resin specimens and shade guides of same thickness were measured with a spectrophotometer. Color differences (delta E* values) were more than perceptible in all products. The mean delta E* values were least in Z100 and greatest in Herculite XR. Generally, the L* and b* values of the shade guides were higher than those of the resin composites. Some colors showed color differences greater than the acceptable level.
  Quintessence international 09/1996; 27(8):559-67. · 0.76 Impact Factor
• Article: Survey of amalgam and composite restorations in Korea.

  I A Mjör, C M Um
  [show abstract] [hide abstract]
  ABSTRACT: A small scale survey amongst general dental practitioners in Korea aimed to discover the reasons for placement or replacement of restorations. Material used and cavity type were recorded as was the age of restorations to be replaced, where known. Comparisons with data from the USA, Scandinavia, the UK and Italy provide the basis for observations on the reasons for longevity of restorations.
  International Dental Journal 09/1993; 43(4):311-6. · 0.96 Impact Factor
• Article: Bond strength of glass-ionomer cement and composite resin combinations.

  G Oilo, C M Um
  [show abstract] [hide abstract]
  ABSTRACT: The tensile bond strength to dentin was measured for three glass-ionomer cement and composite resin combinations: two light-curing glass-ionomer cements (Vitrebond and XR-Ionomer) and one traditional glass-ionomer cement (Ketac-Bond), two adhesive systems (Scotchbond, and XR-Bonding System), and a corresponding composite resin. The bond strength of this "sandwich" was also compared with that of the same cements used in bulk. Vitrebond showed a significantly higher bond strength in bulk than did the other two cements. Of the sandwiches, the XR-Ionomer and XR-Bond combination showed a bond strength significantly higher than that of the Vitrebond and Scotchbond or Ketac-Bond and Scotchbond combination. The fracture of the bond was mainly adhesive for Vitrebond, cohesive for XR-Ionomer when used in bulk and adhesive-cohesive when used in a sandwich, and cohesive for Ketac-Bond.
  Quintessence international 10/1992; 23(9):633-9. · 0.76 Impact Factor
• Article: The effect of early water contact on glass-ionomer cements.

  C M Um, G Oilo
  [show abstract] [hide abstract]
  ABSTRACT: The purpose of this study was to observe the effect of immersion in water at 3, 5, 7, and 10 minutes after mixing on the surface of three regular and one light-curing glass-ionomer cements by measuring penetration of a methylene blue solution. Early solubility of these cements was also measured and compared with that of a zinc phosphate and a polycarboxylate cement. A blue-stained zone was observed in all glass-ionomer cements, but an inner, opaque zone was observed in only two of the regular glass-ionomer cements. Extending the time between start of mixing and immersion in water decreased the width of both zones in all cements and markedly lowered the loss of substance from the surface of regular glass-ionomer cements. However, time after mixing had no or only a limited effect on the loss of substance from the light-curing glass-ionomer cement, the zinc phosphate cement, or the polycarboxylate cement.
  Quintessence international 04/1992; 23(3):209-14. · 0.76 Impact Factor
• Article: Staining of resin-based veneering materials with coffee and tea.

  C M Um, I E Ruyter
  [show abstract] [hide abstract]
  ABSTRACT: Two light-activated, and three heat-polymerized, resin-based veneering materials were exposed to boiled coffee, filtered coffee, or tea at 50 degrees C and evaluated for color stability. Specimens immersed in distilled water in the dark at 37 degrees C for 4 months were also assessed. One of the light-activated, resin-based veneering materials underwent intrinsic discoloration during the long-term immersion both in distilled water and in the staining solutions. The discoloration of the other materials by tea was mainly due to surface adsorption of the colorants. Discoloration by coffee was due to adsorption, and also to absorption of colorants by two of the materials investigated. This absorption and penetration of colorants into the organic phase of the veneering materials were probably due to compatibility of the polymer phase with the yellow colorants of coffee.
  Quintessence international 06/1991; 22(5):377-86. · 0.76 Impact Factor
• Article: [Scanning electron microscopic study of dispersal amalgams].

  C M Um
  Taehan Ch'ikkwa Uisa Hyŏphoe chi 02/1988; 26(1):65-71.
• Article: [An experimental study of the interface between plated cemented pins and amalgams].

  B H Cho, C M Um
  Taehan Ch'ikkwa Uisa Hyŏphoe chi 04/1987; 25(3):273-87.
• Article: [The interface of repaired amalgam].

  C M Um
  Taehan Ch'ikkwa Uisa Hyŏphoe chi 04/1986; 24(3):277-82.
• Article: [X-ray diffraction analysis of dental amalgams].

  C M Um, Y H Kim
  Taehan Ch'ikkwa Uisa Hyŏphoe chi 04/1985; 23(3):229-35.
• Article: [The contact surface between amalgam and pins].

  C M Um
  Taehan Ch'ikkwa Uisa Hyŏphoe chi 05/1984; 22(4):323-8.
• Article: [History of dental amalgam].

  S C Kim, Y G Sunoo, Y H Kim, C M Um
  Ch'ikwa Kijae Hakhoe chi. The Journal of the Korea Research Society for Dental Materials 01/1973; 6(1):11-4.