• Shuffle
    Toggle On
    Toggle Off
  • Alphabetize
    Toggle On
    Toggle Off
  • Front First
    Toggle On
    Toggle Off
  • Both Sides
    Toggle On
    Toggle Off
  • Read
    Toggle On
    Toggle Off
Reading...
Front

Card Range To Study

through

image

Play button

image

Play button

image

Progress

1/48

Click to flip

Use LEFT and RIGHT arrow keys to navigate between flashcards;

Use UP and DOWN arrow keys to flip the card;

H to show hint;

A reads text to speech;

48 Cards in this Set

  • Front
  • Back

3 Calcified tissues of the mouth

1) Enamel, 2) Dentin, 3) Cementum
Role of enamel
Resists wear in mastication and protects dentin/tooth
Qualities of enamel
Hard but brittle; The most Highly calcified and hardest tissue in the body: about 96% mineral by weight, 1% protein and 3% water
What happens if water missing from enamel? Protein?
If enamel has no water, it will crack.]; [If enamel has no protein, the enamel becomes weaker and more brittle
Enamel vs dentin
Enamel is ACELLULAR vs dentin is CELLULAR
What us constantly occurring in enamel?
Remineralization and demineralization
How hard is enamel?
On average, enamel hardness is ~3-4 GPa. (GPa = 10^9 N/m^2). But outer enamel surface is as high as 5.5-6 GPa (FLUORIDE-RICH ENAMEL) while some interior region could be < 3 GPa.; * Enamel is usually harder at occlusal and cuspal areas and less hard near the DEJ
Another name for enamel rods
Enamel prisms
Enamel rods
Made of nanocrystals of materials; Extend from DEJ to the enamel surface; We chew in a direction perpendicular to enamel rods
Enamel etching
Phosphoric acid dissolves crystals in prisms to roughen surface for better binding due to increased surface area; Frosty appearance
Type I Etching
Interior of rods is eaten away faster than boundary of rods. So you end up with higher boundary elevation and lower interior rods.
Type II Etching
Boundary of rods is etched away faster than interior of rods
Dentin
Forms bulk of tooth; Softer but tougher than enamel; Dentinal tubules
Odontoblast
Cells in the pulp that give rise to a cytoplasmic extension traversing the thickness of dentin; Odontoblastic processes occupy the dentinal tubules
Composition of dentin
Calcium Phosphate mineral called 50% apatite by volume, 30% organics (mainly collagen Type I), and 20% fluids (similar to plasma); Has tubules
Dentin apatite
Contains more carbonate (~5%) than in enamel (3%); Has higher solubility than enamel apatite, and are more susceptible to acid challenges
Another reason why dentin more susceptible to caries
Highly porous so more surface area to attack; Once caries penetrates the DEJ, it can spread rapidly.
Lumen of dentinal tubules
lined by a highly mineralized cuff of PERITUBULAR DENTIN of ~0.5 to 1µm thick. It contains mostly apatite crystals and little organic matrix/collagen. It is whitish in color and is a hard shell.
Intertubular dentin
consists of a matrix of collagen reinforced by apatite. It makes up most of the volume of dentin.
Tubule Density
# of tubules/area; tubule density is LOWER near the DEJ (bigger area) and HIGHER near the pulp (smaller area)
Percent Tubule Area
(the area of the tubule openings / total area of dentin); Tubules have small diameter and there is wider total dentin area at DEJ
Diameter, Tubule Density, and Percent Tubule Area at DEJ vs toward pulp
Diameter, Tubule Density, and Percent Tubule Area increase moving toward the pulp; *The number of tubules is the same near DEJ or near Pulp, but the % tubule area is different. Each tubule is continuous, going from pulp to DEJ. The percent tubule area is different because there is a smaller surface area near the pulp. Also each tubule becomes larger and larger as it approaches the pulp.
Hardness of dentin at DEJ vs toward pulp
Near DEJ: Dentin is stronger, tougher, and harder; Near the pulp: Dentin is more highly porous; thus weaker and softer.
Dentin Smear Layer
During cavity preparation when dentin is cut or abraded by dental instruments, a smear layer is formed. It covers dentin surface and obscures tubule lumens.
Purpose of Dentin Acid etching
Acid etching removes smear layer (which would hinder dentin bonding), opens tubules for infiltration by bonding agent, creates micromechanical interlocks, and enhances bonding
What occurs during Dentin Acid etching
Tubule lumen widens as peritubular dentin is preferentially removed since it is mostly mineral, forming funnel-shaped openings; (External) Mineral on collagen fibril is dissolved with progressive demineralization, revealing the typical banded repeat pattern of Type I collagen fibril
What role do collagen fibrils play in bonding?
Desirable to have the bonding agent infiltrate and impregnate the collagen fiber network layer, so when it is light-cured, the polymerized adhesive resin is interlocked with collagen fibers to achieve a strong bonded interface; We want to Keep the collagen fiber of dentin moist so the fiber scaffold is available for better bonding.
Transparent Dentin
forms under caries infected dentin layer.; Results when tubules become filled with mineral, which changes the refractive index of the tubules and produces a translucent or transparent zone; These precipitated mineral inside the tubules are more RESISTANT TO ACID ETCHING, which makes BONDING MORE DIFFICULT.
What else can cause transparent dentin?
bruxism or aging (exposed root dentin becomes transparent as the tubules are filled).
3 Basic Types of materials
Polymers, Ceramics (brittle but hard), and Metals (tough)
Polymers
deforms a lot with small force applied
Ceramics
Only deform a little, even with heavy force
What kind of material are collagen fibers?
Organic/polymeric materials
What kind of material are minerals?
ceramic materials
Dentin matrix
a combination of organic and ceramics materials, where the surfaces of collagen fibers are covered by minerals, making it stronger and more stiff
Polymerization shrinkage
Resin materials can shrink a few % in volume away from tooth surface when light cured, stressing the bonds and producing micro-fracture interface where food and bacteria can go.
Modulus of elasticity
Stiffness of material; ex: Enamel has a higher modulus of elasticity than dentin
Flexural strength
Force required to fracture a material ÷ cross section dimension of the material; DENTIN has greater flexural strength because enamel fractures more easily even though it is harder
Where do cracks in the tooth stop?
Cracks happen in the enamel, but stopped at DEJ. Cracks do not propagate into dentin; *DEJ acts as a protective layer
Characteristics of DEJ
highly interlocked and very rough, scalloped shape with concavity toward enamel; Molars have larger scallops than anterior teeth; Although collagen is absent from enamel, collagen fibers cross the DEJ from dentin into enamel to further integrate the 2 tissues
Cementum
Cover the dentin of the tooth root; provides connection to alveolar bone via the periodontal ligament
Periodontal ligament (PDL)
attaches the cementum of tooth root to alveolar bone socket. The collagen fibers of the ligament are grouped into bundles.; * PDL is like a double-sided tape, bonding to tooth surface on one side and bone surface on the other side.
Subsurface damage in cavity preparation for Orientation I
Machining along buccal or lingual sides perpendicular to interface results in occlusal damage
Subsurface damage in cavity preparation for Orientation II
Machining on occlusal surface results in axial damage
Micro-crack
tend to be surrounding the enamel rods (tend to propagate along boundaries between enamel rods since the rod is harder than the interface itself), although some cracks do occur within rods
Relationship between crack length and diamond particle size of the bur
Crack length is linearly proportional to the diamond particle size
Griffin Strength relation
Measures strength of prepared enamel based on crack lengths; S = (1 / α) KIC /(c1/2), where c is the crack length, KIC is the enamel fracture toughness, and α is the crack geometry factor.
Effect of finishing with finer burs on strength of enamel

Strength of prepared enamel is higher when finishing with fine and superfine bur, giving you stronger interface and longer lasting prep. Lowest strength seen in enamel prepared with coarse bur ONLY, with no finer finishing.