Dental Biomaterials I - Physical Properties

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Questions and Answers

What is defined as the mass per unit volume of a material?

Density (correct)

Weight

Volume

Mass

Which property measures the ability of a material to transfer heat?

Heat of fusion

Specific heat

Thermal conductivity (correct)

Thermal diffusivity

Why are materials with low density important for the upper denture?

They enhance aesthetic appearance.

They ensure better retention. (correct)

They provide structural support.

They reduce cost.

What does the co-efficient of thermal conductivity (K) measure?

Heat transfer in a unit cube Signup and view all the answers

What happens during the casting of molten alloys with low density?

Higher pressure is required. Signup and view all the answers

Which of the following contributes to discomfort when metallic filling materials are close to the pulp?

High thermal conductivity Signup and view all the answers

What physical property describes the heat required to change a material's state without changing its temperature?

Latent heat of fusion Signup and view all the answers

Which property affects how materials expand as they heat up?

Thermal expansion coefficient (α) Signup and view all the answers

Which type of materials typically have low specific heat?

Metals Signup and view all the answers

What does thermal diffusivity indicate in materials?

Rate of reaching thermal equilibrium Signup and view all the answers

Why is it important for dental restorations to have a polished surface?

To achieve specular reflection of light Signup and view all the answers

What is the refractive index defined as?

The speed of light in a vacuum divided by the speed of light in any medium Signup and view all the answers

What type of reflection occurs when light strikes a perfectly smooth surface?

Specular reflection Signup and view all the answers

What is the primary consequence of high thermal diffusivity in dental materials?

High thermal shock risk Signup and view all the answers

What is the nature of light defined as?

A beam of photons Signup and view all the answers

What happens to light rays when they are subjected to scattering?

They are redirected in different directions Signup and view all the answers

What is the linear coefficient of thermal expansion (α)?

The change in length per unit length for a 1°C change in temperature Signup and view all the answers

Why is matching the coefficient of thermal expansion important in dentistry?

To prevent marginal leakage and maintain a good seal Signup and view all the answers

What effect does high thermal conductivity in metallic denture base materials have?

It maintains tissue health and prevents hot substance ingestion Signup and view all the answers

What is the significance of melting temperature in dentistry?

It influences the choice of casting machinery and investment materials Signup and view all the answers

What is meant by the heat of fusion?

The amount of heat required to convert a solid to a liquid Signup and view all the answers

What is specific heat?

The ratio of heat absorbed to change temperature of a certain mass Signup and view all the answers

What does crazing refer to in the context of dental materials?

The surface cracking of artificial teeth Signup and view all the answers

What is a consequence of marginal leakage in restorative dentistry?

It can lead to recurrent caries and hypersensitivity Signup and view all the answers

What is a key characteristic of laser light regarding its wave structure?

All waves are in phase. Signup and view all the answers

Which of the following mediums can EITHER solid, liquid, OR gas be used for laser light production?

Any physical state can be used to produce laser light. Signup and view all the answers

Which clinical application of laser is NOT mentioned?

Bone regeneration. Signup and view all the answers

What does 'chroma' refer to in the Munsell color system?

Degree of saturation or strength of a color. Signup and view all the answers

Which dimension of color correlates with the dominant wavelength?

Hue. Signup and view all the answers

What is NOT a characteristic of laser light?

Diffused. Signup and view all the answers

What should be done to achieve accurate color matching?

Use daylight as one of the light sources. Signup and view all the answers

Which of the following best describes the 'value' dimension in color perception?

How bright or dark a color appears. Signup and view all the answers

What is the main characteristic of transparent materials?

They allow light to pass with little distortion. Signup and view all the answers

Which property of materials allows some light to pass but does not allow objects to be clearly seen through them?

Translucency Signup and view all the answers

What describes the phenomenon where materials emit light immediately after being excited by ultraviolet light?

Fluorescence Signup and view all the answers

What term is used to describe materials that prevent any passage of light?

Opaque materials Signup and view all the answers

Which color materials absorb all light colors and appear black?

Black color materials Signup and view all the answers

What is the significance of fluorescence in human teeth?

It contributes to brightness and a vital appearance. Signup and view all the answers

Which process allows materials to glow in the dark after being exposed to light?

Phosphorescence Signup and view all the answers

What is the process that uses light amplification by stimulated emission of radiation known as?

Laser Signup and view all the answers

What is metamerism?

The change in color matching of two objects under different light sources. Signup and view all the answers

Which shade guide is known to consist of 16 tabs divided into groups A, B, C, and D?

VITA Classical Signup and view all the answers

What is the primary purpose of a dental shade guide?

To match tooth colors with artificial restorations. Signup and view all the answers

In the context of shade matching, what is an isomeric pair?

Two objects that are color matched under all light sources. Signup and view all the answers

What method involves taking a photograph of shade guide teeth next to patient teeth?

Photocolorimetry Signup and view all the answers

What is the maximum number of shades in the VITA SYSTEM 3D-MASTER shade guide?

26 Signup and view all the answers

Which of the following shade guides includes bleach shades?

Chromoscop Signup and view all the answers

What characteristic does the shade guide known as Vitapan 3D Master utilize?

Hue is marked using numerical and alphabetical combinations. Signup and view all the answers

Study Notes

Dental Biomaterials I - Lecture 5: Physical Properties of Dental Materials

Physical properties are based on laws of physics (mass, heat, light, electricity, energy, force, and other phenomena).
Mechanical properties are a subgroup of physical properties dealing with force.
This chapter provides a brief overview. More detailed discussions will use these properties to describe the characteristics of specific dental materials.

Density is the mass per unit volume of a material.
Units: gm/cm³ and pound/in³
Clinical Importance in Dentistry:
- Upper dentures require low-density materials for retention.
- Low-density molten alloys during casting require higher pressure to fill the mold cavity.

II - Thermal Properties

Thermal Conductivity: the ability of a material to transfer heat.
- Heat transfer is slower in materials with low thermal conductivity than in materials with high conductivity.
Coefficient of Thermal Conductivity (k): the amount of heat transported in one second across a unit cube when one face is hotter than the other.
Thermal Coefficient of Expansion (α): the change in length per unit length of a material for a 1°C change in temperature.
Melting and Freezing Temperature: the temperature at which a material melts into a liquid state or freezes into a solid state. Important in dentistry:
- Casting metals and alloys determines the melting machine and investment material selection.
Heat of Fusion: amount of heat (joules or calories) needed to change 1 gram of a substance from solid to liquid state.
Specific Heat: amount of heat in calories needed to increase the temperature of 1 gram of a substance by 1°C.
- Metals have low specific heat; non-metals have high specific heat.
- Low specific heat of dental gold alloys means less prolonged heating during casting is needed.
Thermal Diffusivity: the rate at which a material goes from non-uniform temperature to thermal equilibrium (uniform temperature). Important in Dentistry:
- High thermal diffusivity in gold or amalgam restorations may cause thermal shock (due to high thermal conductivity and low specific heat).

III - Optical Properties

Optics is the study of light, sight, and vision (including color).
- Restorative dentistry aims to restore the color and appearance of natural teeth.
Nature of Light:
- Light is a beam of photons.
- Color is the wavelength of light.
Production of light:
- Thermal (e.g., the sun, hot metal)
- Electrical (e.g., passing electric current through inert gas like neon)
- Chemical (e.g., fluorescence, phosphorescence)
Interaction of Light and Matter:
- Reflection (specular and diffuse)
  - Specular reflection occurs on smooth surfaces (e.g., mirrors), reflecting light in one direction.
  - Diffuse reflection occurs on rough surfaces, reflecting light in all directions.
  - Smooth, polished surfaces of restorations are desirable for specular reflection.
- Refraction (change in the direction of light as it enters a different medium)
- Scattering (light is redirected and attenuated due to obstructions like inclusions within a material)
  - Opacifiers added to composite materials, air bubbles in restorations, cause scattering.
Properties of materials in relation to light transmission and absorption:
- Transparency: allows light to pass through without distortion (e.g., glass).
- Translucency:allows some light through while scattering or reflecting the rest (e.g., tooth enamel, porcelain).
- Opacity: prevents light from passing through (e.g., opaque materials).
Luminescence (fluorescence and phosphorescence): emission of light after absorbing electromagnetic radiation
- Immediate emission (fluorescence): objects glow after excitation.
- Delayed emission (phosphorescence): objects continue to glow after the excitation source is removed.
- Teeth emit fluorescent light when excited by UV light.
Laser (Light Amplification by Stimulated Emission of Radiation):
- A device that uses stimulated emission of light to produce high-intensity, monochromatic, and coherent light.
- A special type of light that can be produced by solid, liquid or gas mediums excited by high-energy. Characteristics of laser light: monochromatic, coherent (same speed), collimated (parallel). Various types of lasers exist (e.g., CO2, Argon, Diode lasers).
Clinical applications of lasers:
- Surgery (tissue removal, regeneration, coagulation)
- Initial carious lesions removal
- Composite curing
- Endodontics
- Filling pits and fissures (hydroxyapatite)
Laboratory applications of lasers:
- Welding (joining alloys)
- Sintering (ceramics)

IV - Color

Color perception (vision):
- For objects to be seen, they reflect or transmit light from an external source.
- Light from objects is focused on the retina and converted into nerve impulses that are transmitted to the brain.
- Cone cells in the retina are responsible for color vision.
- Defects in color sensing receptors can result in various types of color blindness.
Color definition and dimensions: Munsell color system (three dimensions)
- Hue: name of the color (e.g., red, blue, green) related to the dominant wavelength
- Chroma/Saturation: intensity or strength of the color
- Value: lightness or darkness of the color
Light source and color appearance:
- Metamerism: Change in color matching between objects under different light sources (e.g., daylight vs. laboratory light)
  - Metameric pairs: Two objects match in color under one light source, but not under another. Isomeric pair- color match under all light sources
Shade color matching:
- Dental shade guides consist of color standards mimicking natural teeth.
- Used to match artificial restorations to natural tooth color.
- Methods for shade matching: Photocolorimetry, Chair-side colorimeter.
- Popular shade guides: VITA Classical, Chromoscop, VITA 3D-Master.

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Description

This quiz explores the physical properties of dental materials, detailing mass-related properties like density and their clinical importance in dentistry. Additionally, it covers thermal properties, including thermal conductivity and their implications for material selection. Prepare to test your knowledge on the fundamental aspects relevant to dental biomaterials.