Week 3

• Oral environment


  • Challenging for long-term clinical performance of dental materials
• Restorative dentistry objective


  • Replace diseased or lost tooth structure
  • Restore teeth for function and appearance
• Requirements for dental materials in oral environment

  • Biocompatible
  • Durable
  • Non-reactive in acid or alkaline conditions
  • Compatible with other materials
  • Esthetically acceptable
  • Tolerable to differing temperatures and forces
• Classification of dental materials by their use

  • Preventive/therapeutic materials
  • Restorative materials
  • Auxiliary materials
• Preventive/therapeutic materials


  • Used to prevent disease or trauma
  • Used for their therapeutic action on the teeth or oral tissue
• Restorative materials


  • Used to repair or replace tooth structure lost to oral disease or trauma
  • Used to change the appearance of the teeth
• Types of restorations


  • Direct: placed immediately and directly into the prepared tooth
  • Indirect: customized tooth replacements, fabricated in the lab
• Auxiliary materials


  Used to fabricate and maintain restorations, directly or indirectly
• Biocompatibility


  • Dental materials must not impede or adversely affect living tissue
  • Materials may be acceptable for use on hard tissue but not on soft tissue
  • Some materials may be therapeutic in small amounts but may be irritating or toxic with longer or larger doses
  • Materials used in the mouth should exhibit no adverse biologic response
• Nickel allergy


  Adverse response may occur from the breakdown of the materials components in the oral environment
• Force


  A push, pull or twist (or a combination of these)
• Stress


  The force (weight) applied at the surface will create stress within the object that tries to resist the weight; if no resistance, the material would be flattened
• Strain


  The amount of change that the force has produced in the object
• Types of forces


  • Compressive (pushing together)
  • Tensile (pulls & stretches)
  • Shearing (slice apart)
• Compressive force


  Pressure applied to compress or condense
• Tensile force


  Pressure applied in opposite directions to stretch an object
• Shearing force


  Pressure applied when two surfaces slide against each other or in a twisting or rotating motion
• Torsion force (torque)


  Twisting force that has tensile & compressive forces
• Stress


  When force is exerted on a tooth, the tooth or material creates resistance to counteract the force
• Strain


  • Distortion or deformation occurring when an object cannot resist stress
  • The amount of change that the force has produced
• Flexural stress


  Compressive forces are placed on the occlusal surface of a bridge bending the bridge downward and tensile forces on the tissue side of the bridge stretch upward in response
• Strength


  • Amalgam and composite resins more closely replicate enamel in compressive strength
  • Porcelain is more likely to fracture under compressive stresses
• Fatigue failure

  • During mastication, stresses occur repetitively over time
  • Repeated stresses resulting in fractures
  • Failures rarely occur in a single-force application
  • They occur when stress is frequently repeated
  • These repeated stresses may produce microscopic flaws that grow over time resulting in fracture
• Moisture/acidity


  • The oral cavity is continually in contact with moisture
  • This moisture varies from acid to alkaline dependent on foods, drinks, medications, and plaque biofilm
  • Many materials that are compatible in a neutral environment may not be compatible in an acidic environment
• Galvanism


  • The result of the presence of dissimilar metals in the mouth along with moisture and acidity
  • The salts of the saliva facilitate the movement of electric current being transmitted between dissimilar metals
  • The current may result in stimulation to the pulp "GALVANIC SHOCK"
• Thermal conductivity


  • The ability of the materials to transmit hot and cold
  • Excellent thermal conductors: METALS
  • Poor thermal conductors: NON-METALS (ceramics, composite resins)
• Thermal expansion


  Dental materials in the mouth are subjected to temperature changes
• Microleakage


  • If the thermal expansion of the restoration does not match the expansion of the tooth, microleakage may occur
  • Continual expansion contraction produces percolation
  • Percolation is the space between the tooth and restoration
  • If the interface is not sealed, fluids and microorganisms can penetrate between tooth structure and restorative materials
• Retention


  • Retention may be secured through mechanical or chemical adhesion
  • Mechanical retention involves the use of undercuts or other projections into which the material is locked in place
• Detection of restorative materials

  • Tactile evaluation of the tooth surface may be the most reliable means of clinical assessment
  • Tracing the enamel surface onto the restoration with the tip of an explorer is the best way to distinguish this difference
  • Illumination and air aids in their identification
  • Sealants may be easily recognized by their smooth, glassy appearance – linear 1-2mm
  • Radiographs are valuable tools for the detection of restorations, especially decay
• Subgingival plaque bacteria and/or their by-products may gain access to distant sites in the body through the circulatory system and may potentially contribute to systemic inflammation. In this way, a dental biofilm infection may contribute to various systemic diseases and conditions
• Scratched surface of gold crowns

  • Due to inappropriate use of polishing agents
• Elasticity


  The resistance of a solid to penetration or indentation
• Stiffness


  The resistance to deformation of a biomaterial, measured by Young's Elastic Modulus
• Proportional limit


  The greatest stress a structure can withstand without permanent deformation
• Resilience


  The resistance of a biomaterial to permanently deform
• Toughness


  The ability of a biomaterial to resist fracture
• Malleability


  The ability for a material to be compressed without breaking
• Ductility


  The amount of dimensional change a material can withstand without breaking
• Fatigue


  Occurs within a material when it is subjected to repeat stresses, can result in sudden failure or fracture