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Physical-Mechanical Properties of Dental Biomaterial物理力學性能 (Types of…
Physical-Mechanical Properties of Dental Biomaterial物理力學性能
Strian/ Deformation 應變
is a measure of deformation
representing the displacement between particles in the body relative to a reference length表示體內顆粒之間相對於參考長度的位移
change in length per unit length when stress is applied施加應力時每單位長度的變化
may be elastic, plastic or both
Strain(ε)= Deformation/Original length
Hooke's Law胡克定律 (Elasticity)
within the limits of elasticity the “strain produced in a body is directly proportional to stress在彈性範圍內，”體內產生的應變與應力成正比“
STRESS / STRAIN = a constant, {Also called elastic modulus }
The stress at which a material ceases to obey Hooke's Law is known as the Proportional Limit.比例極限
Proportional limit
greatest stress that a material will tolerate承受 without a deviation from the proportionality of stress to strain沒有偏離應力與應變的比例
no permanent deformation happens在此之下不會發生永久變形。
Elastic limit/ Yield limit
maximum stress that a material will tolerate without permanent deformation.
Stress 應力
defined by mechanical stress
force divided by the perpendicular cross sectional area over which the force is applied.力除以施加力的垂直橫截面積
Stress= Force (N)/Area (mm2)
[Force per unit area] (Mpa)]
physical quantity that expresses the internal forces內力 that particles of a continuous material (bulk) exert on each other.
連續材料（體積）顆粒相互施加的內力（內力）的物理量。
Type
Simple
compression
shorten or compress
shear stress
sliding or twisting
Application of shear force may produce elastic shear strain or plastic shear strain.
tesile stress
Tensile stress is always accompanied by tensile strain
elongate
complex
Flexural stress
Produced by bending forces over the dental appliance.
single or two-point bending stress.
Type of forces applied
Axial
Compressive
tensile
Non Axial
shear
Torsion
Bending
Introduction
Properties of Materials
Biological
antimicrobial 抗菌
biocompatibility生物相容性
Physical
thermal
electrical
volumetric體積
mechanical properties 機械
replace missed teeth or for caries treatment
ceramic
polymers
metals
composite複合材料
cement水泥
Failure or success potential of any prosthesis假體/restoration修復體 is dependent upon the mechanical properties of materials.
Material response
Elastic : reversible on force removal.
Plastic: Irreversible / non-elastic.
Mechanical properties
need to be considered together
are expressed in terms of:
Stress
Strain
Restorative material
Strong enough to resist biting forces without fracture
Rigid (stiff) to maintain their shape under load
Analysis for Stress/Strain curve “Elastic Modulus”
stiffness and flexibility
far from the long axis the material is flexible; Moduli (E’) is lower
If it is far from the long axis and the elastic region is very small, Moduli (E’) is lower and the material is plastic
If longitudinal portion of the curve is closer to the long axis, the material is stiff (rigid) & not flexible and the Moduli (E’) is high
toughness and brittleness
brittle脆性
rigidity
break without defamation
ex: glass
tough material 韌性
Plasticity
break with deformation
If material fractures after a long concave portion of the curve, it donates that the material is tough & ductile 材料堅韌且具有韌性
Strong and weaken
longitudinal portion of curve is long, it means that the material is strong.
longitudinal portion is short the material is weak.
Hence from the analysis of the stress strain curve it is possible to have an idea about the properties of a material通過對應力應變曲線的分析，可以了解材料的特性
Types of Elastic Modules
value of the constant depends on
material
type of stress
Young's modulus {E} (The ratio of stress to the longitudinal strain)縱向應變的比率
E= STRESS / STRAIN = a constant
For shearing forces it is called Shear modulus {S}
For forces affecting the volume of the object it is called the Bulk modulus {K}
is the relative stiffness or rigidity of a material.
the higher the molecule, the higher the stiffness
彈性模量可視為衡量材料產生彈性變形難易程度的指標,其值越大,使材料發生一定彈性變形的應力也越大,即材料剛度越大。
The lower the strain for a given stress, the greater the elastic modulus and therefore the stiffness
unit
Giganewtons/mm2 = (GPa)十億帕斯卡
Newtons/mm2 = (MPa)百萬帕斯卡
Pascal: kn/m2
單位用到有用到 GPa 的話比較強。
Wear strength
Loss of material due to contact between two surfaces
Bond strength
Testing the chemical or mechanical adhesion of restorative and bonding agents
bond strength between two dental materials
Eithertensile(microtensile)orshear(micro-shear)
Utimate strength
The point at which the maximum load for a sample is achieved .
beyond this point , elongation of the sample continues but the force being exerted decrease
S= F/ A
Fracture strength
it does give an indication of the needed thickness (cross section) of the restorations before failure
The Ultimate strength: the maximum that a material can tolerate before failure (tension or compressive).
the stress at which the material fractures
Ductutility and Malleability
Malleability 可鍛性
Gold is the most ductile and malleable pure metal, followed by silver
bility of a material to be hammered or rolled into thin sheets without fracturin材料被錘擊或捲成薄片而不會破裂的能力
Ductility 韌性
The ability of a material to be plastically deformed.
Toughness vs Resilience
resilience
also defined as the maximum energy
that can be absorbed within the elastic limit, without creating a permanent distortion
the ability of a material to absorb energy when it is deformed elastically, and release that energy upon unloading
toughness
the maximum amount of energy a material can absorb before fracturing
Toughness tends to be small for brittle materials, because elastic and plastic deformations allow materials to absorb large amounts of energy.
Hardness
Knoop hardness number 是我們在牙科裡面最常用的!!!
In metallurgy and mostly in all other disciplines, hardness is defined as resistance to indentation.對壓痕的抵抗力
In mineralogy, relative hardness of a substance is based upon its ability to resist scratching.
<重要> Enamel is more hardness than dentine!!!!!
鑽石是最 Hardness 的物質
Zinc- polycarboxylate cements we used for cementation.
Rheology Viscosity(流變黏度)
Rheology流變學
the study of the flow of matter
primarily in a liquid state, but also as 'soft solids' or solids
Newtonian fluids
whose viscosity is independent of shear rate
The viscosity of these materials will remain a constant no matter how fast they are forced to flow through a pipe or channel.
Gases, water and many common liquids can be considered Newtonian in ordinary conditions and contexts. (also isotropic as their mechanical properties are the same along any direction)
Non- newtonian fluids
most commonly, the viscosity of non-Newtonian fluids is dependent on shear rate or shear rate history非牛頓流體的粘度取決於剪切速率或剪切速率歷史
Thixotropic liquids觸變性液體
hat become less viscous over time when shaken, agitated, or otherwise stressed
Shear thinning liquids, whose viscosity decreases with the rate of shear stress
Rheopectic liquids流變液體
become more viscous over time when shaken, agitated, or otherwise stressed
Shear thickening liquids, whose viscosity increases with the rate of shear stress.
補充:牛頓流體意味著不論流體所受的力如何,流體都能繼續流動,例如,水就是一種牛頓流體,因為不管它攪拌得多快,它都能繼續表現出流體的性質。這與非牛頓流體不一樣,在非牛頓流體中,只要一攪拌,後面就會出現一個「洞」,或導致流體變得稀薄,黏度的下降使它流動得更多。
viscosity(黏性)
the resistance of a fluid to flow
Viscosity is influenced by the friction between neighbouring particles in a fluid (Composite with fillers帶填料的複合材料)粘度受流體中相鄰顆粒之間的摩擦的影響
The higher the molecular weightthe higher the
viscosity.
Solubility and Absorption
solubility
dissolved material in fluid (μg/mm3)
biggest for cements水泥
absorption
describes as absorption of a liquid by a solid (μg/mm3)
biggest for resins樹脂
Water sorption in unfilled resins is >2%