introduction, structure of matter, principles of adhesion in dm

INTRODUCTION : 

STRUCTURE OF MATTER & PRINCIPLES OF ADHESION INTRODUCTION

INTRODUCTION : 

INTRODUCTION Early Period : Greek & Romans – Bridges 700 to 500 B.C. Medieval & Early Modern Develop, Little progress till 1500 A.D. 1600 -1840 – foundation of Science of Dentistry 16 th century – limited knowledge of dentistry Modern Dentistry – 1728 PIERRE FAUCHARD

BRIEF REVIEW : 

BRIEF REVIEW Plaster Models – in Wax impression – Phillip Ptaff 1792 Nicholas Dubois de chamant – Porcelain teeth 1826 – Taveau – Silver + Mercury – Amalgam Silver Paste 1842 – 47 – Gutta Percha was discovered & used as RCF 1855 – Vulcanite – for Ivory dentures 1869 – Celluloid 1937 – Acrylic Resin

Slide 4: 

G V Black – 1895 Studies in Amalgam 1919 – U S Army – National Bureau of Standard Specification of Amalgam – Dr. Wilmer Sounder ADA – Physical & Chemical Properties of Materials Clinical Significance & some Specifications International Standards Value of particular DM can be guaged 49 ADA Specifications

Slide 5: 

1976 – Food & Drug Administration of US – to protect public from hazardous & ineffective devices International Standards – Federation Dentaire Internationale [FDI] - International Standards Organisation {ISO} FDI – DM – substance / combination of substances prepared &/or presented for use in dentistry Preventive, Corrective & restorative types Replacement of tooth – Esthetics & Restoration of Function

AIM : 

AIM Basic – Chemical & Physical properties of DM {Manipulation of DM by the dentist} Sound educational background Art & Science Generate Curiosity “WHY”

OBJECTIVES : 

OBJECTIVES Understand evolution of& development Explanation purpose of course of DM to personnel Knowledge of physical 7 chemical properties Knowledge of bio-mechanical requirements Laying standards / specification Search for newer / better material Understand & evaluate claims made by manufacturer

STRUCTURE OF MATTER : 

STRUCTURE OF MATTER Material Properties to be considered (for DM) 1. BIOCOMPATIBILITY (whether material can be used intraorally) 2. PHYSICOCHEMICAL Properties 3. HANDLING CHARACTERISTICS (ease of handling) 4. AESTHETICS (relating to beauty / study of beauty & artistic taste) 5. ECONOMY (cost effectiveness)

Slide 9: 

To understand DM – Basic Knowledge of “Matter” (short review) B’coz behavior of DM – depends on atomic structure (ceramic, plasticizer, metal) Atoms & Molecules are held together by “ATOMIC INTERACTIONS”

Change of State : 

Change of State SOLID LIQUID GAS Heat of Vaporization : when water boils ‘quantity of energy ’ needed to transform Liquid to Vapour Amount of heat needed to evaporate 1 gm of liquid to vapour (at given temp & pressure) Ex:- 540 cal. of heat is reqd to vaporize 1 gm of H2O (at 100 *C & pressure of 1 atom) Melting Temp. Heat of Vaporization Latent heat of Fusion

KINETIC ENERGY : 

KINETIC ENERGY Gaseous state possesses more KE than does the Liquid state If the KE of liquid decreases sufficiently when temp is decreased, 2nd Transformation in state may occur Liquid can change to solid KE is released (in form of heat) when Liquid freezes Latent Heat of Fusion 1gm of H2O freezes, 80 cal. Of heat is released 1 gm of solid is changed to liquid – input of energy is reqd For Metals – the temp. at which Change occurs is k/as Melting Temperature There is Mutual Attraction between Atoms/Molecules ----- INTERATOMIC BONDS

INTERATOMIC BONDS : 

INTERATOMIC BONDS Forces that hold atoms together – Cohesive forces Primary – Ionic, Covalent & Metallic Secondary – Hydrogen bonding & Van der Waal’s forces Ionic Bonds : Simple Chemical type, resulting from Mutual attraction of +ve & -ve charges Ex: Na+, Cl- Ionic Bonding exists in certain crystalline phases of DM – Gypsum , Phosphate cements

INTERATOMIC BONDS : 

INTERATOMIC BONDS Covalent Bonds : 2 valence electrons are shared by adjacent atoms Ex: Hydrogen molecule, H- H Other is Dental Resins(hydrocarbon chain) , Silicone Metallic Bonds: Ex: Pure gold Gold atoms can easily donate electrons (gas of free electrons) Ability to donate & recover electrons So, structure is responsible for excellent electrical & thermal conductivity

INTERATOMIC SECONDARY BONDS : 

INTERATOMIC SECONDARY BONDS Do not share electrons, but there are charge variations (molecule/atom groups) induce Polar forces that attract the Molecules HYDROGEN BONDING : Ex: Attached to Oxygen atom are 2 Hydrogen atom Ex: Sorption of H2O by synthetic dental resins VAN DER WAAL’S Forces : form basis of Dipole Attraction. In inert gas – electron field is constantly fluctuating so charge becomes momentarily +ve & -ve Fluctuating dipole created will attract other similar dipoles – such forces are quite weak

Interatomic Bond Distance & Bonding Energy : 

Interatomic Bond Distance & Bonding Energy Bond Distance : Limiting factor which prevents atoms / molecules from approaching each other too closely If Distance reduces – Repulsion If Distance increases – Attraction If forces of Attraction increases – Interatomic space decreases Bonding Energy: Energy can be defined as a force integrated over a distance Thermal Energy: KE of atoms/molecules at a given temp. atoms are is constant state of vibration If higher the temp. greater the amplitude so, greater is the KE/ Internal Energy. Gross effect is expansion – k/as Thermal Expansion

Crystalline Structure : 

Crystalline Structure Atoms are bonded by Primary / Secondary forces, Na+ attract Cl- results in regularly spaced configuration – Space Lattice/ Crystal. Any arrangement of atoms such that every atom is situated similar to every atom

Non Crystalline Structure : 

Non Crystalline Structure Waxes – may solidify as amorphous materials such that the molecules are distributed at random. Glass – its atoms tends to develop a short order instead of long range order (Crystalline Structure) Ordered arrangement of glass is more/less locally interspersed with a considerable no. of disordered units because this arrangement is typical of liquids: such solids (glass)are sometimes called Supercooled Liquids

Glass Transition Temperature : 

Glass Transition Temperature The temp. at which there is an abrupt increase in the thermal expansion coefficient, indicating increased molecular mobility is called Glass Transition Temperature(Tg) It is characteristic of the particular glassy structure. Also k/as Glass Temperature

Diffusion : 

Diffusion In Gases & Liquid is well-known Atoms/Molecules diffuse in solid state as well . Average KE of vibration over the entire crystal is related to temp. Diffusion rate varies which atom size, interatomic/ intermolecular bonding lattice imperfections of similar phenomena Diffusion in Crystalline structure at room temp. is very low. At increased temp. prop. of metals may be changed radically by atomic diffusion Diffusion in Non-crystalline structure may occur at rapid rate (b.coz of disordered structure) Diffusion Coefficient ‘D’ Defined as Amount of Diffusion that takes place across a given unit area

ADHESION & BONDING : 

ADHESION & BONDING In complete denture retention – Adhesion between Denture & Saliva & Soft tissue Plaque , Calculus ---- to Tooth structure 2 substances brought into Intimate contact, one adhere to the other, this Force is Adhesion : In / When Unlike molecules are attracted {Cohesion: In / When Like molecules are attracted} Material / film produced for Adhesion is Adhesive (fluid/semiviscous is best) Material to which it is applied is Adherend

Slide 21: 

In Mechanical bonding there is Strong attachment, ex – Screws, Bolts, Undercuts Internal surface of Crown / Post with cement irregularities with Air abrasion Enamel Acid Etching – Phosphoric Acid (10-20 secs) forms minute pores – resin flows into pores Increased /improved Mechanical Retention – Decreased Marginal Leakage, Stains, Secondary Caries & Irritation of Pulp

Principles of Adhesion : 

Principles of Adhesion Surface Energy Wetting Contact Angle of Wetting () Surface Energy At surface of lattice, energy is greater (outermost atoms are not equally attracted) increase in energy per unit area of surface is referred to as Surface Energy/ Tension With gold, bonding forces are Secondary type With silver, bonding forces are Primary/Chemical type – when pri.bonding is involved the Adhesion is Chemisorption Greater Surface energy – greater capacity of Adhesion

Principles of Adhesion : 

Principles of Adhesion Wetting Liquid must flow easily over entire surface & adhere to solid Contact Angle of Wetting (8)