Dental Biomaterials I Physical Properties PDF

Course Title: Dental Biomaterials I Course Code:DBM011 Physical Properties F A C U L T Y O F D e n t i s t r y T h e F u t u r e S t a r t s H e r e S p r i n g 2 0 2 4 Topics to be covered Mass related properties - Density vs Sp...

Course Title: Dental Biomaterials I Course Code:DBM011 Physical Properties F A C U L T Y O F D e n t i s t r y T h e F u t u r e S t a r t s H e r e S p r i n g 2 0 2 4 Topics to be covered Mass related properties - Density vs Specific gravity Thermal properties Heat of fusion vs Latent heat of fusion Specific heat vs heat capacity Thermal conductivity vs Thermal diffusivity Coefficient of thermal expansion and contraction Optical properties Light (nature of light – light & interfaces – luminescence) Color (parameters – factors affecting color appearance) Electrical properties Electromotive force Electrochemical corrosion Other properties Water sorption - Solubility -Setting time -Shelf life Mass related properties Density Specific gravity mass per unit volume of the material Ratio of the mass of a particular body to the mass of an equal volume of water. Unit= gm/cm3 density of water is 1 gram/cm3at 4oC Clinical significance 1. Casting 2. Denture base retention  Thermal properties Heat of fusion vs Latent heat of fusion  Thermal properties Heat of fusion vs Latent heat of fusion Heat of fusion Latent Heat of fusion Heat in calories or joules required to convert l gram of a Heat in calories or joules released when converting l gram material from the solid to the liquid state at the melting of a material from the liquid to solid state at the melting temperature. temperature.  Thermal properties Specific heat vs Heat capacity Specific heat (Cp) Heat capacity quantity of heat needed to raise the temperature of 1 gm of Heat required to raise the whole object by 1 C the substance 1◦ C. Unit: Joules/ gram degree Celsius J/g ᴼC  Thermal properties Specific heat vs Heat capacity Clinical significance Heat required for melting during Casting  Thermal properties Thermal conductivity Vs Diffusivity Coefficient of thermal conductivity (K) quantity of heat in calories or joules passing per second through a body of 1 cm thickness and 1 cm2 cross – sectional area, when the temperature difference is 1 C. The units are: Cal / sec / cm 2 / (C / cm) or Watt per meter degree Kelvin (W/mK).  Thermal properties Thermal conductivity Vs Diffusivity Clinical significance Base under restorations Denture base materials  Thermal properties Thermal conductivity Vs Diffusivity Thermal diffusivity (Δ) the measure of transient heat-flow.  Thermal properties Coefficient of thermal expansion and contraction The linear coefficient of thermal expansion (α) the change in length per unit length of a material for a 1 C change in temperature  Thermal properties Coefficient of thermal expansion and contraction Clinical significance Close matching of thermal expansion is very important at any interface like: Dental restoration and tooth structure (avoid marginal percolation) Porcelain and metal in porcelain fused to metal PFM Artificial teeth in denture  Thermal properties Coefficient of thermal expansion and contraction Clinical significance Dental casting Wax expansion and contraction Type of investment to compensate shrinkage for accurate casting Optical properties  Optical properties Light Nature of light: continuous waves of electromagnetic radiation or, according to the quantum theory, as a discrete stream of particles of electromagnetic energy known as photons. Origin of Light: a. Thermal (hot substances) as the sun and the hot metals. b. Electrical as in fluorescent lamps. c. Chemical as fluorescence and phosphorescence A "vertically polarized" electromagnetic wave of wavelength λ has its electric field vector E (red) oscillating in the vertical direction. The magnetic field B (or H) is always at right angles to it (blue), and both are perpendicular to the direction of propagation (z)  Optical properties Interaction of light with interfaces  Optical properties Interaction of light with interfaces Reflection Reflection Diffuse reflection (Rough) Specular reflection (smooth) Clinical significance Finishing and polishing of restorations is very crucial to avoid dull appearance Optical properties Color  Optical properties Interaction of light with interfaces Transmission Transmission Smooth transmission (transparent) Diffuse transmission (translucent) No transmission {reflection or absorption} (Opaque)  Optical properties Transparent, translucent, Opaque Transparent Translucent Opaque  Optical properties Transparent, translucent, Opaque Transparent Translucent Opaque Opacity is a property of the material that prevents the passage of light through it. Objects cannot be seen through opaque materials.  Optical properties Interaction of light with interfaces Scattering Opacifiers or scattering centers Clinical significance Voids in restorations acts opacifiers Adding scattering fillers in composite to control its translucency  Optical properties Interaction of light with interfaces Refraction Refractive index  Optical properties Luminescence Phosphorescence Delayed remission of light Fluorescence Immediate remission of light Sound human teeth emit fluorescent light with the greatest intensity in the blue region (450 nm) when excited by ultraviolet radiation (365nm).  Optical properties Color Color parameters Hue Chroma Value  Optical properties Color Hue Dominant wavelength Primary colors RGB Secondary colors CMY Complementary colors  Optical properties Color Chroma Color intensity  Optical properties Color Value amount of gray in the color(Lightness and darkness) The most important color parameter. Why? Dimensions of color (parameters) 1-Hue (tonality): This indicates the dominant wavelength of the observed luminous radiation observed (e.g. red, green, blue, yellow…). 2- Chroma (saturation): This refers to the amount of dye that the color contains. (saturation of the colour) 3- Value (luminosity): This expresses the amount of light that makes up the color ranging from a maximum value: white, and a minimum value: black. (lightness and darkness) Primary colors Blue, green and red are primary colors. Combining suitable proportions of lights of the three primary colors results in white. Secondary colors Each secondary color – cyan, magenta or yellow results from the combination of two primary colors  Complementary colors Two colors are complementary to each other when their combination results in white, eg. yellow is the complementary color of blue.  Factors affecting colour appearance Source: 1- Colour content (metamerism) 2- Surroundings Object: 1- Color reflectance and transmittance 2- Translucency 3- Surface finish(smooth or rough) Observer: 1- Color response: sensetivity 2- Color vision: colour blindness 3- Colour fatigue 4- Optical illusion  Optical properties Factors affecting color appearance Source Color content (metamerism) Different sources have different color contents. Example: Incandescent light has color content different from that of fluorescent light. The change in color matching of two objects under different light sources is called metamerism. Surroundings They modify the type of light reaching the object. A yellow wall, by absorbing some of the blue light emitted by the source, imparts more yellow component to the resultant illumination. Colors of walls, clothing and lips contribute to the color of light incident on the teeth.  Optical properties Factors affecting color appearance Object Color reflectance and transmittance: This is dependent on the relative amount of each color reflected or transmitted by the object. Translucency: high translucency gives a lighter color appearance. Surface finish : The relative amount of light reflected determines the gloss or shininess. A high gloss lightens color appearance.  Optical properties Factors affecting color appearance Observer Color response (Eye sensitivity) : Eye response varies among individuals. The human eye response varies with wavelength. It is most sensitive in the green color region. Color vision and blindness: Color blindness is the inability to distinguish certain colors. It is a hereditary disease, more in males than in females. Optical illusion:A color appears darker against a light background and lighter against a dark background. Color fatigue :Constant stimulus of one color decreases the response to that color. A complementary color image persists after removal of the stimulus.(constat exposure to blue light, makes you see objects more yellow) Measurement of color  Optical properties Shade selection Shade selection Principles of shade selection 1- Teeth to be matched must be clean 2- Remove bright colors from the field of view (Makeup, bright gloves, neutral operatory walls) 3- View patient at eye level 4- Evaluate shade under multiple light source 5- Make shade comparisons at start of the appointment 6- should be made quickly to avoid eye fatigue  I-Non electronic shade selection The usual shade estimation technique is based on comparing the color of the tooth to an artificial guide and checking which of the samples of the guide is most similar to the examined tooth. Disadvantages Liability to human errors. Organization of shade guides in different ways. Shade guides A) Vita Classic Traditional guide that is most commonly used is the Vita Classic which is organized by groups of : Hues: A, B, C, D. Chroma &Value: are noted from 1 to 4 in the Vita guide. Classic guide would be organized as-follows: B1, A1, A2, D2, B2, C1, C2, D4, D3, A3, B3, A3.5, B4, C3, A4, C4. (on the basis of lightness (value) , instead of tonality (hue) because our eyes are more sensitive to the value) B) Vitapan 3D- Master Recently, shade guides are based on luminosity (=value= Lightness) of the colors and not according to tonality (hue), due to the fact that our eye is sensitive to minute changes in brightness (value). Value gives indication about tooth vitality. The grouping is by luminosity (value), decreasing from 1 to 5 Groups are divided into subgroups according to chromatic saturation, increasing from 1 to 3. It is then determined whether within these groups the medium color tone M is maintained, or whether it moves towards yellow L or red R. (2M3)  II-Electronic color measurements To avoid the great subjectivity during color measurement process in the clinic, a series of electronic devices designed to facilitate and make the process of color measurement more objective more precise, reliable and repeatable.  The VITA Easyshade It is cordless (Portable) Delivers instant shade measurements in both VITA 3D-Master and VITA Classical shades. Lightweight Having rechargeable batteries. Having transparent infection control coverages. Measures a basic overall tooth shade or separates the tooth into cervical, middle and incisal areas, depending on our preference.  Other properties Water sorption Adsorption + ABsorption It amount of water adsorbed on the surface and absorbed into the body of the material Clinical significance Dimensional changes in hydrocolloid impression Acrylic resin denture base  Other properties Solubility and disintegration Solubility and disintegration are measured gravimetrically by the suspension of two disk 20 mm in diameter 1 mm in thickness for 24 hrs or longer in water at 37OC. The units are percent mass loss or mgm/cm 2.  Other properties Setting time Time required for a material to set or harden from a plastic or fluid state, it does not indicate the completion of the reaction, which may continue for much longer time. Working time: it is the time during which the materials is workable Shelf life : Shelf life is a term applied to the time before general deterioration and change in quality of materials during storage.