Duncan J. Wood

Effect of resin matrix composition on the translucency of experimental dental composite resins

OBJECTIVES The purpose of this study was to investigate the effect of the resin matrix composition on the translucency of experimental dental composite resins. METHODS Three types of unfilled resin matrices (TEGDMA-, UDMA- and BisGMA-based) were formulated and light cured. In addition, six different experimental dental composite resins with constant filler loading but varying in the type of monomer and the content of BisGMA were fabricated. Discs of each test material with 15.5mm diameter and 1.0mm thickness were prepared (N=3) and light cured. Total and diffuse transmittance values for each sample were measured using a UV/VIS spectrophotometer with the range of readings from 380 to 700nm. Difference in color was measured using the CIE Lab system. RESULTS Statistical analysis by one-way ANOVA followed by Tukeys test showed that there was no statistically significant difference in transmittance values between the three unfilled resins. However, with the addition of filler, BisGMA-containing composite resins showed significantly higher transmittance values than the UDMA- and TEGDMA-based composite resins. Regression analysis revealed that there was a linear correlation between the percentage of BisGMA in the resin matrix and the total and diffuse translucency. SIGNIFICANCE The amount of BisGMA used in the resin matrix has a significant effect on the translucency of silica filler-containing dental composite resins.

Optical properties of base dentin ceramics for all-ceramic restorations

OBJECTIVES The study was conducted to compare the optical parameters of VM7(®) M-shade base dentin ceramics (VITA, Germany) for all ceramic restorations to the chemical composition across the 3D-MASTER(®) shade system. METHODS Three disc samples, 13 mm diameter and 1.4 mm thickness, were produced for each M-shade following the manufacturers instructions. Each disc was ground and polished to a thickness of 1.0 mm. Spectral light transmittance and reflectance data were recorded in the visible spectrum under the standard illuminant D65 and 2° observer at 10 nm intervals by using a computer-controlled spectrophotometer. Opacity, translucency and opalescence parameters were determined for each sample. RESULTS (1) Spectral transmittance and reflectance in the short-wavelength range systematically decreased with increasing chroma number (M1, M2, M3) when compared within the same value (lightness) group. (2) Spectral transmittance and reflectance decreased systematically across the whole visible spectrum with increasing value group number when compared within the same chroma group. (3) Analysis of relationship between chemical composition and various optical parameters for all the samples showed the significant contribution of ZrO₂ and Y₂O₃ substances to optical properties of the present material. SIGNIFICANCE Systematic variations in optical properties of VM7(®) M-shade base dentin ceramics were observed throughout the 3D-MASTER(®) shade system and were suggested to be caused by the fine structure of the sample which can interfere with shorter wavelengths in the visible spectrum.

Relationship between Color and Translucency of Multishaded Dental Composite Resins

The aim of the present study was to compare the translucency of different shades of two highly aesthetic multilayered restorative composite resins. In total nine shades from Esthet.X and ten shades from Filtek Supreme composite resins were chosen. Discs of each shade were prepared (N = 3) and light-cured. Total and diffuse transmittance values for each sample were measured. Statistical analysis showed that the opaque dentine shades of both composites were the least translucent and the enamel shades had the highest translucency. There was a significant decrease in translucency from A2 to C2 of regular body shades and also from A4 to C4 of opaque dentine shades of Esthet.X composite resin. Grey enamel shade had a significantly higher diffuse translucency compared to clear and yellow enamel shades. There was a significant decrease in translucency from A2B to D2B and also in diffuse translucency from A4D to C6D shades of Filtek Supreme composite resin. It can be concluded that the color of the composite resins tested in this study had a significant effect on their translucency. Information on the translucency of different shades of composite resins can be very useful for the clinicians in achieving optimal esthetic restorative outcome.

Spectral reflectance and color of dentin ceramics for all-ceramic restorations

OBJECTIVE The study was conducted to observe the spectral reflectance curves, and evaluate the color coordinates (CIELAB) of VM7 dentin ceramics (VITA, Germany) across the whole 3D-MASTER shade system. METHODS Three disc samples, 13 mm in diameter and 1.4mm in thickness, were produced for each shade by firing following the manufacturers instructions. Each fired disc was ground to a thickness of 1.0 mm and both faces were polished. Spectral reflectance data in the visible spectrum under the standard illuminant D65 were collected at 1 nm intervals by using a computer-controlled spectrophotometer. Color coordinates, L*, a*, b*, C*, h, in the three-dimensional CIELAB color space were obtained. RESULTS (1) Spectral reflectance in the short-wavelength range systematically decreased with increasing chroma number (M1, M2, and M3) when compared within the same value (lightness) group (1M, 2M, 3M, 4M, and 5M). (2) Spectral reflectance decreased systematically across the whole visible spectrum with increasing value group when compared within the same chroma group. (3) A negative relationship was recognized between lightness (L*) and chromaticity index a* (red-green direction). That is, a* coordinate increases from approximately 1 for the 1M1 sample to approximately 13 for the 5M3 sample, the corresponding lightness systematically decreased from 87 to 69. (4) With increasing a* coordinate, hue angle (h) significantly decreased from 85 degrees for the 1M1 sample to 69 degrees for the 5M3 sample. (5) Lightness apparently increased with increasing hue angle (h) throughout the whole range of the 3D-MASTER shade system. (6) A strong positive relationship between chroma (C*) and chromaticity index b* (yellow-blue direction) was found, demonstrating that the chroma of the present ceramic is mainly controlled by the b* coordinate. SIGNIFICANCE Systematic variations in spectral reflectance and color coordinates of VM7 dentin were observed throughout the 3D-MASTER shade system and were suggested to be caused by the fine structure of the sample which can interfere with shorter wavelengths in the visible spectrum.

The effects of different opacifiers on the translucency of experimental dental composite resins

OBJECTIVE The aim of this study was to evaluate the effects of different opacifiers on the translucency of experimental dental composite-resins. METHODS Three metal oxides that are used as opacifiers were tested in this study: titanium oxide (TiO2), aluminium oxide (Al2O3) and zirconium oxide (ZrO2). Experimental composite-resins were fabricated containing 25wt.% urethane dimethacrylate (UDMA)-based resin matrix and 75% total filler including different concentrations of metal oxides (0, 0.25, 0.5, 0.75 and 1wt.%) blended into silane treated barium-silicate filler. The specimens (15.5mm diameter and 1mm thickness) were light-cured and tested in the transmittance mode using a UV/VIS spectrophotometer at wavelengths from 380 to 700nm under a standard illuminant D65. The color differences (ΔE* ab) between different concentrations of opacifiers were also measured in transmittance mode based on their Lab values. RESULTS Statistical analysis by ANOVA and Tukeys test showed a significant decrease (p<0.05) in light transmittance with the addition of opacifiers to the experimental composite-resins. There was a linear correlation between different concentrations of TiO2 and Al2O3 and total transmittance. Total transmittance was also found to be wavelength dependent. The color differences for the concentrations of 0-1wt.% of the opacifiers were above 1 ΔE* unit, with Al2O3 showing the smallest color shift. SIGNIFICANCE The type and the amount of the opacifiers used in this study had a significant effect on the translucency of the experimental UDMA-based dental composite resins. The most effective opacifier was TiO2, followed by ZrO2 and Al2O3 in decreasing order, respectively.

Fracture resistance of zirconia-composite veneered crowns in comparison with zirconia-porcelain crowns

The objectives were to evaluate the fracture resistance and stress concentration in zirconia/composite veneered crowns in comparison to zirconia/porcelain crowns using occlusal fracture resistance and by stress analysis using finite element analysis method. Zirconia substructures were divided into two groups based on the veneering material. A static load was applied occlusally using a ball indenter and the load to fracture was recorded in Newtons (N). The same crown design was used to create 3D crown models and evaluated using FEA. The zirconia/composite crowns subjected to static occlusal load showed comparable results to the zirconia/porcelain crowns. Zirconia/composite crowns showed higher stress on the zirconia substructure at 63.6 and 50.9 MPa on the zirconia substructure veneered with porcelain. In conclusion, zirconia/composite crowns withstood high occlusal loads similar to zirconia/porcelain crowns with no significant difference. However, the zirconia/composite crowns showed higher stress values than the zirconia/porcelain crowns at the zirconia substructure.

Comparing the optical and mechanical properties of PEKK polymer when CAD/CAM milled and pressed using a ceramic pressing furnace

The aim was to optimise the hot pressing parameters for processing PEKK polymer using a standard ceramic pressing furnace and compare the optical and mechanical properties of pressed samples to PEKK samples produced via CAD/CAM milling. The samples were compared using a spectrophotometer to determine the CIE L*a*b* colour values and ΔE colour difference. A universal testing machine was used for biaxial flexural strength testing and Vickers Hardness machine for measuring the hardness. It was concluded that hot pressed and milled PEKK samples showed no significant difference in the colour values, biaxial flexural strength or hardness.

Characterisation of machinable structural polymers in restorative dentistry

OBJECTIVES To characterise the mechanical properties of the machinable polymers Pekkton® (Cendres-Meteaux, Biel/Bienne, Switzerland), Lava Ultimate® (3MESPE, Seefeld, Germany), Vita Enamic® (Ivoclar Vivadent, Schaan, Liechtenstein) and the ceramic IPS e.Max Press® (Ivoclar Vivadent, Schaan, Liechtenstein). To determine the structural integrity of full coverage crowns fabricated from these materials. METHODS The following tests were conducted: Biaxial flexural strength (BFS) using the piston on 3 balls jig (n=10); Vickers Hardness (VH) 10 indentations per sample with 10kg load & 20s dwell time (n=5); Hygroscopic Expansion Change (HEC) in artificial saliva over 68 days (n=5). Structural Strength (SS) of teeth analogues (n=20) restored with monolithic crowns from the four materials. Mean values and standard deviations for BFS, VH, HEC and SS tests were calculated and compared using one-way ANOVA with post-hoc Tukeys test at a level of 5% significance. RESULTS BFS: IPS e.Max Press® (317MPa±37MPa), Pekkton® (227MPa±18MPa), Lava Ultimate® (145MPa±18MPa) and Vita Enamic® (137MPa±7MPa) with a significance between groups of p<0.0001. VH: IPS e.Max Press® (5064MPa±131MPa), Vita Enamic® (1976MPa±12MPa), Lava Ultimate® (924MPa±27MPa) and Pekkton® (445MPa±21MPa) with a significance between groups of p<0.0001. HEC (%vol change): Pekkton® (0.14%±0.14%), Vita Enamic® (0.38%±0.16%) and Lava Ultimate® (1.06%±0.17%). SS for full-coverage crowns: Pekkton® (2037N±49N no fracture), IPS e.Max Press® (1497N±165N), Lava Ultimate® (1476N±142N) and Vita Enamic® (1127N±108N). SIGNIFICANCE The properties investigated suggest that full coverage monolithic PEKK crowns possess adequate mechanical and physical properties for use in the posterior region of the mouth. These results must be considered alongside other data including clinical studies.

The introduction of digital dental technology into BDS curricula.

The aim of this study was to determine the degree to which digital dental technologies have been introduced into the curricula of UK dental schools. A survey was carried out of all the UK dental schools that teach undergraduate dental students. The survey contained six questions and was designed to determine if digital dental technology techniques or systems were being taught in the curricula, what these techniques were, and whether the school dental laboratories supported these techniques. Sixteen schools were surveyed and 11 replied: a response rate of 69%. Forty-five percent of the schools that replied did not teach digital dental technology in their curriculum. Of the 55% of schools who did teach digital dental technology, 50% gave lectures or demonstrations while the other 50% allowed practical involvement by the student. Two thirds of these stated that not all the students participated in practical usage. Seventy-three percent of the schools that replied had dental laboratories using some, but not all the digital dental technology techniques listed. Eighty percent of the schools that were not teaching digital dental technology said it was because it was not included in the curriculum, and 20% stated it was due to a lack of technical expertise or support.