Dental Materials : Basics
Introduction to Dental Materials
Overview of the Lecture
- The channel "Easy Dentistry" aims to simplify dental topics for better understanding.
- Today's lecture focuses on the history of dental materials and the structure of matter, emphasizing the importance of physics and chemistry in dentistry.
Historical Context
- Gold was historically used as a restorative material for tooth loss, dating back to 700-500 BC.
- The era of modern dentistry began in 1728 with Peary Forcher's book "The Surgeon Dentist," marking significant advancements in dental practices.
- Notable developments include porcelain teeth introduced by Nicholas Dubois D. Chammant in 1792 and single porcelain teeth by G. Fonzi between 1806-1808.
Evolution of Dental Materials
Key Innovations
- Gutta Parcha, a common root canal filling material, was first introduced in India in 1842 and became widely used by 1847.
- In 1855, vulcanite was adopted as a denture base material, later replaced by celluloid in 1869.
Establishment of Standards
- The American Dental Association (ADA) was established following research initiated by the US Army and conducted by the National Bureau of Standards starting in 1920.
- International organizations like FDI and ISO were also formed to set specifications for dental materials globally.
Understanding Matter: Structure and Forms
Basic Concepts
- Matter exists in three forms: solid, liquid, and gas; these states are influenced by energy levels.
Energy Transitions
- Heat energy is required for transitions between states: solid to liquid requires heat; liquid to gas requires additional heat; cooling reverses these processes.
Interatomic Bonds
- The strength of mutual attraction between atoms varies across states: strongest in solids, weaker in liquids, and weakest in gases.
Types of Bonds
- Interatomic bonds are categorized into primary (ionic, covalent, metallic bonds) and secondary (van der Waals forces), essential for understanding material properties.
Chemical Bonds and Their Properties
Ionic and Covalent Bonds
- Sodium is positively charged while chlorine is negatively charged, forming an ionic bond, a simple type of chemical bond.
- A covalent bond involves the sharing of two valence electrons; for instance, in methane, carbon shares its four valence electrons with hydrogen to stabilize.
Metallic Bonds
- Metals conduct heat and electricity due to the presence of free electrons that can move easily when energy is applied.
- The outermost shield of electrons in metal atoms can be easily removed, leading to a positively charged ion as inner electrons remain bonded to the nucleus.
Electron Cloud and Attraction
- Removed outer shield electrons form an electron cloud or electron gas, which creates electrostatic attraction between this cloud and the positive ions, holding metal atoms together as solids.
Secondary Bonds: Van der Waals Forces
Nature of Secondary Bonds
- Unlike ionic and covalent bonds (chemical), secondary bonds like Van der Waals forces are more physical in nature.
- These forces arise from dipole formation within symmetric atoms where electron accumulation leads to negative polarity at one end and positive polarity at another.
Attraction Between Dipoles
- The attraction occurs between the positive pole of one atom and the negative pole of another atom, resulting in what are known as Van der Waals forces.
Thermal Expansion Concepts
Kinetic Energy and Vibration
- The thermal energy of matter correlates with atomic kinetic energy at a given temperature; atoms vibrate constantly within a crystal structure.
- When heat is applied, atomic vibration amplitude increases, leading to greater interatomic spacing which results in thermal expansion.
Crystalline vs. Non-Crystalline Structures
Crystalline Structures
- A crystal features an orderly arrangement where each atom is positioned similarly; these structures may result from primary or secondary bonds.
- There are 14 types of crystal lattices; metals used in dentistry predominantly exhibit a cubic system arrangement.
Non-Crystalline Structures
- Non-crystalline or amorphous structures have random atomic arrangements; for example, waxes display such randomness.
- These solids are referred to as supercooled liquids, reflecting their liquid-like properties despite being solid.
Understanding Stress and Strain
Interatomic Distance Dynamics
- The distance between two atoms is termed interatomic distance; if forced closer together, they repel due to similar charges.
Equilibrium Position
- When attractive forces equal repulsive forces between atoms, it establishes a normal equilibrium position.
Stress and Strain Definitions
- Displacing force on atoms is called stress; any change in dimension resulting from this stress is termed strain.
Diffusion Factors
Influences on Diffusion Rate
- The rate of diffusion depends on temperature—higher temperatures increase diffusion rates. Other influencing factors include:
- Size of the atom,
- Interatomic bonding,
- Lattice imperfections.
Understanding Surface Tension in Dental Materials
Concept of Surface Tension
- Surface tension is a crucial concept in the properties of dental materials, representing the cohesive forces among atoms within a lattice structure.
- Atoms within a lattice are equally attracted to each other; however, surface atoms experience unequal attraction, leading to tension on the surface due to their exposure.
Reduction of Surface Tension
- To alleviate surface tension, surface atoms bond with external atoms, a process known as adhesion. Higher surface tension correlates with increased adhesion.
Wetting Phenomenon
- Wetting refers to the ability of fluids to occupy spaces between solid surfaces, facilitating adherence. This is essential for effective bonding between two solid surfaces.
- For instance, placing polished glass surfaces together shows minimal adhesion until water is introduced, which enhances contact and makes separation difficult.
Contact Angle and Adhesion
- The contact angle measures how well an adhesive wets an adherent; a zero-degree angle indicates complete spreading and strong adhesion.
- When flooring is applied to tooth surfaces, it reduces surface energy and consequently decreases debris adherence, lowering dental caries incidence.
Factors Affecting Adhesion in Dental Structures
- Fluorine reduces surface energy and adhesion levels, contributing to lower rates of dental caries. Secondary caries can develop around restorations due to differences in enamel and dentine composition.
- Variations in organic and inorganic content between enamel and dentine create challenges for adhesive bonding; adhesives may bond effectively with one but not the other.
Challenges in Dental Material Application
- A monolayer of water on tooth surfaces hinders wetting and thus affects adhesion quality. Effective dental materials must displace or react with this fluid for optimal bonding.
Quiz Time: Assess Your Understanding
- Questions posed include:
- What nature are Van der Waal forces? (Chemical or Physical?)
- Does an increase in surface energy indicate strong or weak adhesion?
- If adhesives completely flow over adherents, what would be the contact angle?
The next lecture will cover physical properties of dental materials. Please subscribe for updates!