Dental Materials Lecture: Oral Environment & Properties

DH 267: Dental Materials Chapters 1, 2, & 3 Oral Environment + Physical and Mechanical Properties References: Eakle, W. S., & Bastin, K. G. (2021). Dental Materials: Clinical Applications for Dental Assistants and Dental Hygien...

DH 267: Dental Materials Chapters 1, 2, & 3 Oral Environment + Physical and Mechanical Properties References: Eakle, W. S., & Bastin, K. G. (2021). Dental Materials: Clinical Applications for Dental Assistants and Dental Hygienists (4th ed.). Elsevier Inc.  Learning Objectives Recognize at least three reasons a dental hygienist should have knowledge of dental materials Define key terms associated with the oral environment and physical and mechanical properties of dental materials Differentiate between various key concepts associated with dental materials Recognize governing bodies for dental materials and their approval process Identify classifications of dental materials and list characteristics of each Why do hygienists need to know about dental materials?  Agencies Responsible for Standards ADA FDA ○ Class I ○ Class II ○ Class III International Organization for Standardization  Dental Materials Classifications: Preventative/therapeutic materials Restorative materials (indirect and direct) Permanent Temporary (provisional) Intermediate Auxiliary materials Examples: Preventative: sealants, fluoride Restorative: fillings, crowns Auxiliary: wax, alginate, stone  What can we observe about the gingiva Dental materials must in the image below? have biocompatibility. We aim to avoid: Post-op sensitivity Hypersensitivity Irritation Toxicity These reactions are referred to as an adverse response.  Oral Environment and Patient Considerations  Force, Stress, & Strain What is force (aka load) and why do we care about it? Force  Stress  Strain A. Tensile Force B. Compressive Force C. Shearing Force  Torsion (torque)- twisting force; both compressive and tensile Flexure- aka bending force; compressive, tensile and shearing combined Stress results to resist force; measured in psi or Mpa Strain- amount of change force produces in an object Stress-strain curve-  Fracture toughness- energy needed to fracture material Ultimate strength- point of fracture Resilience- energy needed to permanently deform a material Fatigue Failure- resulting fracture from repeated stress causing small flaws over time  Creep- small change(s) in shape from continuous compressive force Stress relaxation- like creep; slow decrease in force over time Stress concentration- stress focused around defects  Moisture and Acid Solubility (low is desirable) Water sorption (undesirable) Corrosion (undesirable)  Galvanism Phenomenon of electrical current transmission via electrolyte solution between two dissimilar metals. Galvanic shock- stimulates tooth pulp *Electrical conductivity- metals conduct electricity well, while polymers/ceramics conduct poorly  Temperature Dimensional change- expanding with heat/contracting with cold Coefficient of thermal expansion (CTE)- measurement of change in volume/length in relation to temperature Percolation- repeated shrinking/expanding + oral fluids entering the gaps Thermal conductivity- rate of heat flow through material over time Exothermic reaction- chemical reaction that produces heat  Retention Retention - ability to maintain position without displacement under stress Achieved through mechanical, chemical adhesion, or bonding of materials (p. 16) Bonding: acid etch  rough surface  bonding material “locks” into place  Factors Affecting Bond Strength Wetting- degree a liquid adhesive can spread over a surface Wettability determined by contact angle between liquid & surface Low contact angle = better wetting vs. High contact angle = poor wetting Viscosity- resistance of liquid to flow Can affect wetting and film thickness High viscosity = poor flow, low viscosity = good flow Film thickness- minimal thickness of material Surface characteristics Cleanness, moisture, texture, etc.  Microleakage Can affect longevity of restorations Fluids/microbes leak into interface causing recurrent caries, stain, sensitivity Interface- space between tooth and restoration  Esthetics & Color Hue- dominant color Chroma- intensity of color Value- light vs. dark Transparent  light goes through Opaque  light doesn’t go through Physical and Mechanical Properties of Dental Materials  Primary Bonds Primary = strongest, involve sharing or transferring of electrons Covalent bonds Two nonmetal atoms sharing outer shell electrons Ionic bonds Electron given up by one atom and accepted by another Metallic bonds Electrons shared by all atoms in the material (sea of electrons)  Secondary Bonds AKA van der Waals forces No sharing or transferring of electrons Weaker than primary bonds N S Forces of attraction in alike molecules Created by dipoles Dipole- electrons unequally shared between atoms causing (+) and (-) charged ends Ex: Hydrogen bonds (dipole-dipole forces), permanent dipoles, temporary dipoles  States of Matter Gas Weakest attraction Liquid Stronger attraction than gas, weaker than solid Solid Strongest attraction Crystalline solids- ordered, specific arrangement (3D cube) Amorphous solids- irregular patterns (dry ice, polymers)  Physical Properties & Related Terms Melting/boiling point- aid in identifying material, some do not melt or boil but decompose Vapor pressure- measure of liquid’s tendency to evaporate (high vapor pressure evaporates faster at room temp.) Density- amount/mass in a given volume Viscosity- resistance of liquid to flow Thermal conductivity- rate of heat flow through material over time Thermal expansion- measurement of change in volume/length in relation to temperature (CTE) Color  Mechanical Properties & Related Terms Hardness- resistance of a solid to wear and abrasion, measured by severity of indentation Stress- object resisting force Strain- amount of change force produces in an object Fatigue- repeated stresses over time causing failure Ultimate strength- amount of stress on material at time of break Toughness- ability of material to absorb energy without fracture Ductility- pulling or stretching under tensile stress Malleability- ability to handle compressive forces Durability- ability of material to withstand damage due to pressure or wear Abrasion resistance- ability to withstand friction, scraping, or  Mechanical Properties & Related Terms (cont.) Elasticity- non-permanent deformation and material recovers completely Elastic limit- material does not return to original shape Plastic deformation- permanent deformation Young’s modulus- measures resistance of material to being deformed Stiffness- lack of elasticity Resilience- amount of energy a material can absorb without permanent deformation Toughness- ability of material to absorb energy without fracture  Mixing Mixing time- time to achieve homogeneous mix Working time- mixing to hard (time to move fast!) Initial set time- end of working time Final set time- conclusion of reaction from mixing, permanent state of material results  Materials Metals Metallic bonds; characterized by high thermal cond., ductile, opacity, and luster (amalgam, implants, crowns, bridges) Ceramics Ionic bonds; characterized by strength (yet brittle), insulators, high melting point, low thermal cond., chemical rx break old bonds/form new, sometimes transparent (crowns, veneers) Polymers Long chains of repeating covalent bonds; characterized by great strength in one direction, cross links in chains = stiff, strong material (denture base + teeth, temp. crown)  Materials (cont.’d) Composites Made of 2+ different materials (polymer + ceramic fiberglass), materials act as a team; Property lacking in one is enhanced by the other(s), lightweight and strong Colloids Not true solutions; mix of gases, liquids, solids; one material suspended in another Emulsions 2 liquids that do not blend (think oil/water)  Detecting Restorations Tactile sense Light Drying Magnification Radiographs Questions & Final Thoughts Quiz 1 due before next class (see due date in Sakai) Review Alginate Instructions and Alginate Video listed in Resources tab under DH 268 before lab tomorrow; come prepared to lab to take your first impression! Bring Dexter to lab tomorrow Reminder: NO CLASS MONDAY (MLK Jr Day) Recommendations: Review Learning objectives from chapters Test your knowledge with review ?s at end of chapters