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Spectrophotometry A spectrophotometer (Fig. 5) is a sophisticated analytical optical instrument consisting of a stable and precise light source and light detector (photo detector) capable of measuring discrete colors or wavelengths with a 1 nm resolution measured between the ultraviolet and infrared wavelengths within the visible light spectrum. True colors, shades and optical properties can be reproducibly quantified by a spectrophotometer, which engineers and scientists use to characterize optical ceramic and dental ceramic materials by measuring the transmission, reflection and absorption of light as a function of wavelength. The latest digital dental shade-taking systems use a simplified spectrophotometer to quantify tooth shades. Determining Shade Ceramic crown & bridge restorations are fabricated to the desired shade and esthetic detail based typically on a standardized shade guide system, such as the VITA Classical Shade Guide or VITA 3D-Master Shade Guide. The VITA Classical Shade Guide was introduced in 1956 and is considered the gold standard for dental tooth shade quantification. This guide classifies dental shades into 16 different shade guide tabs. The VITA 3D-Master Shade Guide introduced in the 1990s is based on the earlier Munsell color space and the CIELAB colorimetry system. The VITA 3D-Master Shade Guide tabs are categorized by value, hue and chroma colorimetry parameters. The dentist and dental laboratory technician use the shade guide tabs to determine the appropriate tooth shade by visually comparing the shade guide tabs against the patient’s tooth and against the ceramic dental restoration — in ambient background lighting. This method, although common, is inherently subjective, dependent on myriad variations arising from ambient light interactions and color sensitivity of the human eye. Figure 5: PerkinElmer Lambda 35 UV/VIS Spectrophotometer with <strong>Labs</strong>phere RSA-PE-20 Reflectance Spectroscopy Accessory Color and the Human Eye The eye detects three primary colors: red, green and blue. The optical focal plane is the retina, which contains two kinds of light detection sites: rods and cones. Rods make up the majority of light sensors in the retina. They are extremely sensitive to light intensity variation, but are not color-sensitive. Cones are sensitive to specific colors — or rather the electromagnetic wavelengths that are responsible for color vision. Cones consist of three primary lengths attuned to specific colors or wavelengths: long (L-cones), medium (M-cones) and short (S-cones). L-cones detect red colors at a peak wavelength of 565 nm, while M-cones detect green colors at a peak of 540 nm and S-cones detect blue colors at a peak of 440 nm. The majority of these retinal cones are of the long and medium variety. The superpositioning of the three different color signals results in a peak sensitivity to light wavelength at 550 nm. The human brain can perceive the continuum of visible colors between blue (the shortest wavelength the retina is sensitive to at 400 nm) and red (the longest light wavelength the retina is sensitive to at 700 nm). Except for red, green and blue, color is a perception, a result of the brain processing the additive intensities of the three primary colors detected by the cones. Visible Light and the Electromagnetic Spectrum The color-related esthetics of natural dentition and dental ceramic materials result from the interaction of light with the material in the visible part of the electromagnetic spectrum (400–700 nm). This visible range, of course, represents only a small portion of the larger electromagnetic spectrum, which includes ultraviolet rays, X-rays, and gamma rays smaller than 400 nm in wavelength; and near-infrared, infrared, microwaves, radio waves, and longwaves larger than 700 nm in wavelength (Fig. 4). Wavelengths that fall within the visible electromagnetic spectrum are expressed in nanometer units, where 1 nm equals one billionth of a meter (1 nm=1x10 -9 m). Expressed in colors, the visible electromagnetic spectrum ranges from violet (400 nm) to red (700 nm). As described earlier, the human eye is most sensitive to the yellow-orange color at a wavelength of 550 nm. Dielectrics <strong>Dental</strong> ceramic materials such as veneering porcelains and alumina/zirconia crown & bridge frameworks are electrically insulating materials commonly known as dielectrics. Dielectric materials are generally comprised of inorganic oxides, such as silicon dioxide (SiO 2 ), zirconium dioxide (ZrO 2 ), titanium dioxide (TiO 2 ) and many others. Additionally, the calcium phosphate of natural dentition and polymer materials such as composites are typically dielectrics consisting also of inorganic nitrides and some carbides. 52 – www.inclusivemagazine.com –
Refraction and Permittivity The refractive index (n) of a material can be defined as the ratio of the speed of light (c) propagating in a vacuum to the velocity of light (v) propagating in that material, expressed as n=c/v. l1 The refractive index is a function of permittivity, which is the measure of the resistance that is encountered when forming an electric field in a medium. More specifically, permittivity is determined by a material’s ability to polarize in an applied alternating electric field. Dielectric materials are susceptible to this polarization from the electric field component of the propagating electromagnetic waves. The relative permittivity (ε r ) of a dielectric material is determined by its composition, crystal structure and the applied electromagnetic field wavelength or frequency. In nonmagnetic dielectric materials, the refractive index is equal to the square root of its relative permittivity (expressed as n= ε r ). 12 The index of refraction for some common dental materials can be compared to that of natural dentition in Figure 1. Transmission vs. Reflection When visible light interacts with dielectric dentition and dental ceramic materials, wavelengths are either transmitted, reflected or absorbed, the sum of these values equaling the incident light source energy. This can be expressed as 1=T+R+A, where T is the value of transmission, R is the value of reflection and A is the value of absorption. A schematic of optical material-light interaction is shown in Figure 6. The optical esthetics of dental ceramics are based on the wavelength dependence of light reflected from the ceramic restoration and the depth perception of transmitted light. An observer’s eye will see light reflected from the ceramic. This reflected light is comprised of first (initial) surface reflection, and also light partially transmitting from the dental ceramic and reflecting from a second interface or lightscattering surface. Additionally, backlighting of the ceramic is transmitted through the material. The observer’s visual perception is based on the summation of these optical reflections and transmissions that result from interaction with the restorative ceramic material. Light Interaction in Dielectric Materials The wavelength dependence of light interaction with dielectric materials is a complex phenomenon. Light-dielectric material interaction ranges from light scattering from material porosity on the order of the effective wavelength (Mie theory) to quantum mechanical interaction with light and the crystalline order and atomic structure of the ceramic. 12–18 Additionally, light scattering caused by birefringence (double refraction) is the driving force behind recent research into optically transparent nanocrystalline ceramic materials. Birefringence is caused by anisotropic crystalline index of refraction, as found in non-symmetric crystal structures — typically noncubic or strained. This results in the refractive index being different for various crystallographic plane orientations with respect to the direction of light propagation (Fig. 7). Figure 6: Optical material schematic Crystal orientation 2 Crystal orientation 3 Crystal orientation 4 Crystal orientation 1 Figure 7: Birefringence light-scattering model Hue – A color, as it corresponds to the dominant wavelength in the visible electromagnetic spectrum. Value – A level of brightness, ranging from black (low value) to white (high value). Chroma – The intensity or purity of a color, combining hue and saturation. Translucency – The amount of light that transmits through a material. Opacity – The lack of light transmitting through a material. Spectrophotometry – Measuring the relative intensities of light in different parts of a spectrum. Superpositioning – A principle stating that, for all linear systems, the net response at a given place and Glossary Light scattering caused by different indexes of refraction from different zirconia crystal orientations time caused by two or more stimuli is the sum of the responses that would have been caused by each stimulus individually. Dielectric – A nonconductor of direct electric current. Refractive Index – The ratio of the speed of light (electromagnetic radiation) in a vacuum to the velocity of light in another medium (material). Permittivity – The ability of a material to store electrical potential energy under the influence of an electric field. Birefringence – The refraction of light in an anisotropic material in two slightly different directions to form two rays. Anisotropic – Having unequal physical properties along different axes. – Understanding Zirconia Crown Esthetics and Optical Properties – 53
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Inclusive® Restorative Driven Impl
Page 3: Contents 6 15 From Intraoral Scan t
Page 6 and 7: Contributors ■ Bradley C. Bockhor
Page 8 and 9: From Intraoral Scan to Final Custom
Page 10 and 11: Figure 4: Healing abutments at six
Page 12 and 13: Figure 15: iTero virtual scan (Alig
Page 14 and 15: Figure 25: 4-unit BruxZir Solid Zir
Page 17 and 18: Implant Q&A: An Interview with Dr.
Page 19 and 20: Not only are we maintaining the bon
Page 21: BB: If you go that route — four i
Page 24 and 25: For proper prosthetic function, zir
Page 26 and 27: On the abutment, there were three a
Page 28: Finite element analysis (FEA) provi
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Page 33 and 34: Clinical Delivery The following pro
Page 35: Delivery of a Screw-Retained BruxZi
Page 39 and 40: Figure 1: Preoperative digital trea
Page 41 and 42: Figure 8: Inclusive Mini Implant Im
Page 43 and 44: Figure 16: Wax rim delivered on cas
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Page 47 and 48: Implant-retained overdentures can o
Page 49 and 50: Figure 2: Sagittal MPR view with ma
Page 52 and 53: Understanding Zirconia Crown Esthet
Page 56 and 57: The key to increasing light transmi
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