Compound structures Flashcards
As a bioengineer, how do they see teeth?
A highly sophisticated functional microstructure that is not yet fully understood
Such a structure, if damaged cannot be properly be repaired with today’s technologies
What is a compound system?
Number of different materials coming together synergistic effect - when combine, greater than individual materials
What is the compound system that makes up a tooth?
Enamel - hard and translucent, can be brittle
Dentine - softer, porous, tough not brittle, supports enamel
PDL - bounces back to shape, active suspension system, responds to loading, active proprioceptive mechnism - this fails in bruxism and epilepsy
Alveolar bone
Pulp - moisture and innervation
Stomatognathic musculature
What is the elastic modulus of enamel compared to dentine?
E - 85 Gpa - more brittle
D - 15 Gpa - more resillient
What is the fracture strength of enamel compared to dentine?
Enamel - 10Mpa
Dentine - 50 Mpa
What is the compressive strength of enamel compared to dentine?
E - 4000 Mpa
D - 300 Mpa
What needs to be done when restoring compound systems?
restore Structure Restore Form and colour/shade Resist functional/ parafunctional forces Resist ware and degradation Resist static and dynamic fatigue
How do we aim to restore the compound structure of teeth by? (3 ways)
Using compound systems made up of components with desireable properties
By careful bio-mechanical design considerations
By using an effective and reliable adhesive interface assembly
What are the relavent properties of restorative materials?
Elastic modulus Compressive strength Flexural strength Fracture toughness Coefficient of thermal expansion Hygroscopic expansion Wear behaviour Fatigue behaviour
The tooth has a coefficient of thermal expansion of 10ppm degrees C, Composite has a coefficient of thermal expansion of 50ppm degrees C. What can this cause to happen?
This can cause the composite to expand more and fracture the tooth
What is the strength of the bone of the composite to the tooth?
26mpa
What is a composite material
A single entity containing 2 or more constituent phases e.g. dental composites
What do composite fillers do?
Alters the propertied and behaviour of the material Reduced polymerisation shrinkage Limits fracture propagation Increases wear resistance Improves optical properties
What is the need for compound structures
To restore compound structure
To compensate for inadequate properties in otherwise useful materials
To utilise materials with different properties
To create a system which utilises the most desirable property of each desirable material
What are examples of compound systems?
Enamel bonded to dentine Composites bonded to ionomers Beta quartz inserts in composites Porcelain bonded to metal Porcelain bonded to alumina Glas infiltrated ceramic crowns Porcelain-acrylic metal dentures
How can you join materials in a compound system?
Specific adhesion Micromechanical adhesion Mechanical interlocking Moulding around base material Casting against second material Welding Soldering Adhesives
What are the desirable benefits of the compound structure?
Complementary properties e.g aesthetics vs strength
Mechanical protection
Adhesion
What are the unavoidable drawbacks of material interactions?
Electromechanical corrosion
Mismatched thermal expansion coefficiet - interface damage
Unstable dimensional form
What properties are needed for a dentine replacement?
Low elastic modulus Adhesive Resilient to absorb shocks Fluoride-releasing resistant to degradation
What propertied are needed for an enamel replacement?
High elastic modulus Tooth-coloured Reliable bonding mechanism High strength Abrasion matched to enamel Resistance to mechanical fatigue Resistance to static fatigue
What are the bio-mechanical design considerations for restoring teeth?
Block form e.g. plastic restoration - doesn’t withstand load very well
Shell form e.g. crown
Laminate form e.g. porcelain veneer/dentine bonded crown - alone weak, need to be bonded for strength
What is the key to success when restoring a compound system?`
Match the restorative system to the remaining substrate by the appropriate choice of compound system and appropriate design construct
Compensate for inadequacies of materials properties by design construct and vice versa
Effective and reliable adhesive assembly
Materials vs design
Gold shell crown vs adhesive porcelain crown
Gold shell crown - ductile and easily deformed, 360 degree wrap prevents deformation
Adhesive porcelain crown - brittle and easily fractured if deformed, adequate bulk prevents deformation
How can you get effective and predictable adhesive assembly? What needs to be considered?
Strength of the bond to the restorative substrate
Strength of the bond to the tooth
Durability of the chemistry
Cohesive strength of the component materials
Resistance of the lute to the surface degradation and wear
