Materials Science Hardness and Wear Testing

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Questions and Answers

What characterizes fatigue failure in materials?

Crack propagation occurs only at high stress levels.

It can happen at stresses well below tensile strength. (correct)

It occurs without any repeated stress cycles.

Cracks never form in areas of low stress concentration.

Which method is NOT a recognized hardness testing method?

Fischer (correct)

Rockwell

Vickers

Knoop

The term 'viscoelastic behavior' refers to which of the following?

Permanent deformation after load removal.

Resistance of a material to flow without any deformation.

Time-dependent deformation and relaxation of materials. (correct)

Immediate recovery of materials without time dependency.

Which factor does NOT influence creep in materials?

Humidity Signup and view all the answers

What is true about dilatant materials?

They tend to have increasing viscosity with increasing shear rate. Signup and view all the answers

What defines the setting time of a dental material?

The total time required for the material to achieve its intended properties. Signup and view all the answers

Which of the following is NOT a factor in stress relaxation?

Temperature fluctuations Signup and view all the answers

How can corrosion wear be best described?

It is a combination of mechanical and chemical wear processes. Signup and view all the answers

What is a characteristic of catastrophic failure in fatigue failure?

It happens rapidly once a critical crack size is reached. Signup and view all the answers

Why are resin modified glass ionomer cement (GIC) sealants considered less effective over time compared to resin-based sealants?

They lose a significant portion within a few months to years. Signup and view all the answers

Which method is crucial to prevent saliva contamination during resin sealant application?

Field isolation through suction and absorbent materials. Signup and view all the answers

What characteristic of white sealants contributes to their usability during clinical procedures?

They are filled and easier to detect during application and review. Signup and view all the answers

What should be done to ensure effective bonding when etching the enamel surface?

Avoid saliva contamination after rinsing. Signup and view all the answers

In which situation should GIC based sealants be utilized according to established guidelines?

When treatment is needed under non-optimal conditions. Signup and view all the answers

What is the approach suggested to avoid failures due to overfilling of sealants?

Aim for a minimum bulk that just fills the valleys and grooves. Signup and view all the answers

What primarily causes the imbalance of oral flora leading to multifactorial oral disease?

Presence of fermentable dietary carbohydrates Signup and view all the answers

Which of the following best describes erosion in dental health?

Chemical loss not involving bacterial action Signup and view all the answers

What is the primary factor causing tooth abrasion?

Frictional wear from contact with non-tooth objects Signup and view all the answers

Which condition is characterized by a cervical V-shaped enamel defect without a history of abrasion?

Abfraction Signup and view all the answers

Which of the following is considered an intrinsic acid source?

Gastric acid Signup and view all the answers

What type of wear is referred to as functional wear due to masticatory forces?

Attrition Signup and view all the answers

Which term describes the lack of enamel due to a quantitative defect?

Hypoplasia Signup and view all the answers

What are the two primary sources of environmental acid exposure affecting dental health?

Gastric acid and acid fumes Signup and view all the answers

Which of the following types of wear results from parafunctional activities?

Attrition Signup and view all the answers

Which dental condition is likely multifactorial and associated with abfraction?

Erosion and abrasion Signup and view all the answers

What is the primary effect of ozone at a concentration of 2200ppm on microorganisms in carious lesions?

It kills 99% of them Signup and view all the answers

Which of the following treatments utilizes impacting abrasive particles to remove hard substances from teeth?

Air abrasion Signup and view all the answers

Which of these statements about pit and fissure sealants is NOT true?

They completely remove plaque from pits. Signup and view all the answers

What is the main advantage of the painless and noiseless treatment provided by ozone for carious lesions?

It improves patient comfort during dental procedures. Signup and view all the answers

In the application of hard tissue lasers, which of these skills is emphasized as necessary?

Precision hand control Signup and view all the answers

What is a significant disadvantage of air prophylaxis units in dental procedures?

They can cause soft tissue trauma if uncontrolled. Signup and view all the answers

When were the concepts of chemo-mechanical caries removal developed?

1970s Signup and view all the answers

What is a potential downside of using ozone treatment on patients?

It is highly irritating to eyes and lungs. Signup and view all the answers

What unintended benefit was observed from using sodium hypochlorite in root canal treatments?

It helps in dissolving carious dentine. Signup and view all the answers

Which of the following options describes the role of pit and fissure sealants in dental health?

They serve as a barrier against food and bacteria. Signup and view all the answers

What is the significance of a sudden decrease in plaque pH after a glucose rinse?

It suggests increased acid production by plaque. Signup and view all the answers

Which type of caries occurs primarily in infants due to prolonged exposure to sugary liquids?

Rampant caries Signup and view all the answers

What distinguishes soft dentin from firm dentin?

Soft dentin has a low mineral content and is easily excavated. Signup and view all the answers

What defines a carious lesion that is described as 'arrested'?

It has stopped progressing and remains inactive. Signup and view all the answers

What is the role of remineralization in caries management?

It aims to restore the mineral content of early lesions. Signup and view all the answers

Which of the following statements about visual detection aids is true?

Using a wet field helps in diagnosing white spot lesions. Signup and view all the answers

What defines hard dentin in the context of dental caries?

It represents the deepest zone of a caries lesion. Signup and view all the answers

Which factor is not directly related to the management of caries in Minimal Invasive Dentistry (MID)?

Initiation of aggressive restorative treatments Signup and view all the answers

Which of the following components is proven to be superior to fluoride for enamel surface remineralization?

Casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) Signup and view all the answers

What is a unique characteristic of caries that reaches the dentin-enamel junction (DEJ)?

The dentin pulp responds with formation of tertiary dentin. Signup and view all the answers

Study Notes

Hardness Testing Methods

Different methods of hardness testing exist depending on the indenter's shape.
Common tests include Vickers, Knoop, Brinnell, and Rockwell.

Fatigue Wear

Characterized by crack initiation, crack propagation, and catastrophic failure.
Crack initiation takes place at a high stress concentration point.
Crack propagation occurs gradually with each stress cycle.
Catastrophic failure occurs quickly when the crack reaches a critical size.

Fatigue Failure

Structures can fail at stresses below the material's tensile strength when exposed to repeated stress cycles.
Fatigue failure occurs at low loads with no outward visible signs.

Corrosion Wear

Occurs primarily in oral environments due to combined mechanical and chemical attacks.
Abrasion-erosion lesions are a common example.

Creep

Occurs when materials undergo permanent deformation under sustained or cyclic loading for a period of time.
Factors impacting creep include applied load, temperature, and time.

Surface Contact Angle

The angle between the surface of a material and a liquid droplet in contact with it.
Influences the wetting and adhesion properties of materials.

Elastic and Plastic Behaviour

Elastic behaviour exhibits instantaneous and full recovery after load removal.
Plastic behavior retains deformation after load removal.

Viscoelastic Behaviour

Deformation in materials, particularly polymers, can be time-dependent.
Recovery after loading can be complete (elastic) or incomplete (viscous).

Stress Relaxation

The reduction of stress in a material under constant strain.
The rate of stress relaxation is crucial in orthodontic elastic bands.
Latex bands have a constant relaxation rate while plastic bands exhibit variable relaxation.

Viscoelasticity in Dental Materials

Viscoelastic behavior is important when removing elastic impression materials from undercuts.
Permanent distortion during removal depends on force magnitude and duration.
Force magnitude depends on elastic modulus, material thickness, and undercut depth.
Distortion can be represented as time x force.

Rheological Properties

Describe the deformation behavior of materials under stress.
Elasticity and viscoelasticity theory explains rheology in solids and elastomers.
Viscosity, the resistance of a fluid to flow, explains the rheology of liquids and pastes.

Rheological Behaviour and Shear Rate

Dilatant: Viscosity increases with increasing shear rate (shear thickening).
Newtonian: Shear stress is directly proportional to shear rate, and viscosity remains constant.
Pseudoplastic: Viscosity decreases with increasing shear rate (shear thinning).

Rheological Behaviour of Dental Materials

Non-setting materials generally experience reduced viscosity with increasing temperature.
Conversely, setting materials exhibit increased viscosity with rising temperature.
Viscosity increases during the setting process until manipulation becomes impossible.
Working time is the time from mixing to reaching the point of unmanageability.
Setting time is the time from mixing until the desired initial properties are achieved.

Damage to Teeth

Caries (Preventable): Biofilm-mediated, chronic disease caused by dietary carbohydrates and oral microbial imbalance.
Non-Carious: Irreversible loss of tooth surface not caused by caries or trauma.

Non-Carious Damage

Tooth Wear: Attrition (tooth-to-tooth contact), Abrasion (tooth-to-non-tooth contact), Abfraction (cervical v-shaped enamel-dentin defect).
Developmental Defects: Hereditary (Amelogenesis imperfecta, Dentinogenesis imperfecta) and Non-hereditary (Hypoplasia, Hypomineralization).
Trauma: Accidental and non-accidental.

Causes of Erosion

Intrinsic acid (gastric acid) - involuntary.
Extrinsic acid (dietary-acidic foods and drinks).
Environmental (acid fumes).

Mechanical Wear: Tooth to Tooth Contact

Functional: Normal chewing.
Parafunctional: Habits like bruxism.
Proximal wear: Resulting from physiological tooth movements.

Abrasion

Mechanical/frictional wear caused by contact between teeth and non-tooth surfaces.
Caused by habits like nail biting, bottle opening, stripping wire, and chewing abrasive materials.

Abfraction

Cervical wedge-shaped enamel or dentin wear, attributed to masticatory stress concentrated in the cervical area.
Likely a multifactorial process involving erosion and toothbrush abrasion.

Stephan's Curve

Shows a sudden reduction in plaque pH following glucose rinse, returning to normal within 30-60 minutes.
Net demineralization occurs below a critical pH of 5.5.
Mature plaque metabolizes fermentable carbohydrates, producing acid.

Progression of Caries/Caries Balance

A dynamic equilibrium between demineralization and remineralization processes.
Affected by factors like diet, oral hygiene, and fluoride exposure.

Rampant Caries

Accelerated caries with multiple carious lesions.
Occurs in infants (nursing bottle caries), teenagers/youth (cariogenic diet, recreational drugs), and adults (xerostomia).

Arrested Caries

Caries lesions that have stopped progressing.
Enamel lesions: White lesions can be arrested and potentially reversed with proper oral hygiene.
Dentin lesions: Can be arrested but not reversed.

Enamel Caries

Subsurface demineralization causes enamel prism porosities (white spot lesions).
White spot lesions can be remineralized with proper oral hygiene and fluoride exposure.
Enamel caries progresses as an inverted cone towards the dentino-enamel junction (DEJ).
Active white spot lesions are smooth, frosty white, and non-cavitated.
Arrested lesions have smooth, shiny surfaces.
Porous lesions can become stained, forming brown spot lesions.
Advanced lesions become rough and prone to cavitation.

Caries at the DEJ

Caries histologically reaches the DEJ before cavitation.
The pulp responds with a translucent dentin zone and tertiary dentin formation.
The lesion extends laterally and penetrates the dentinal tubules.

Caries in Dentin

Visibly creates a gray shadow/opacity.
Triggers pulpal response to hot, cold, and sweet stimuli.
Active caries: Dentin appears moist, matte, rough, and soft.
Arrested caries: Dentin appears shiny, hard, and scratchy.

Soft Dentin/Infected Dentin

Outer carious dentin, characterized by bacterial contamination.
Low mineral content and irreversibly denatured collagen.
Does not self-repair.
Easily excavated with hand and rotary instruments.

Firm Dentin/Affected Dentin

Inner carious dentin with demineralized intertubular dentin.
Transparent appearance.
Softer than normal dentin.
Can be remineralized.
Resistant to hand excavation and only removed by exerting pressure.
Transition zone between soft and firm dentin has a leathery texture.

Hard Dentin

Deepest zone of a caries lesion, including sound normal dentin.
Hard, resistant to penetration by a blunt explorer.
Removed only by a bur or a sharp cutting instrument.

Minimal Invasive Dentistry (MID)

Focuses on early detection and minimal intervention to restore damaged tooth structure.
Emphasizes management of risk factors rather than solely relying on restorative treatment.

Caries Detection and Diagnostic Aids

Visual and clinical methods: Mirror, probe, magnification (loupes, headlight), wet/dry field, caries detecting dyes.
Radiographs: Intraoral (bitewing, periapical), extraoral (OPG).
Optical/trans illumination: Intraoral cameras, LED cameras, FOTI, laser, QLF systems.
Tooth separators.

Principles of Caries Management in MID

Disease control by reducing cariogenic bacteria.
Remineralization of early lesions.
Minimize tooth structure removal.
Use of dental materials to preserve tooth structure.

International Caries Detection and Assessment System (ICDAS)

A standardized system for classifying and assessing caries lesions.
Uses visual and tactile criteria for diagnosis.

ICCMS Risk Factors

Factors that contribute to an individual's risk of developing caries.
Include dietary habits, oral hygiene practices, fluoride exposure, and genetics.

Caries Treatment

Non-invasive: Oral hygiene instruction, topical fluoride, fissure sealants, varnish.
Micro-invasive: Pit and fissure sealants.
Selectively invasive: Partial caries removal.
Invasive: Conventional preparations and restorations.

Prevention

Non-invasive and preventive approaches.
Fluoride: Promotes enamel remineralization.
Casein phosphopeptide-amorphous calcium phosphate (CPP-ACP): Effective for remineralization.
Xylitol: Suppresses cariogenic bacteria and promotes beneficial bacteria.
Dental ozone: Antibacterial and remineralization properties.

Dental Ozone

Indications: Primary root carious lesions and primary pit and fissure carious lesions.
Advantages: Kills microorganisms, oxidizes caries, speeds up remineralization, whitens discolored caries, reduces treatment time, painless, noiseless, no allergic reactions, removes organic debris, minimal resistance development.
Contraindications: Highly irritating to eyes and lungs.

MID: Alternatives to Rotary Instruments

Minimally invasive techniques for caries removal.
Air abrasion: Impacts abrasive particles in a stream of air or air-water.
Hard tissue laser: Precision tool for accessing enamel and dentin caries.
Chemo-mechanical caries removal: Uses chemical agents to dissolve carious dentin.

Pit and Fissure Sealants

Low viscosity plastic materials applied to occlude pits and fissures, preventing caries development.
Act as a physical barrier and eliminate the cariogenic environment.

Pit and Fissure Sealant Application Techniques

Acid etch: Removes plaque and creates a microsurface for better sealant adhesion.
Field isolation: Essential to prevent contamination during application.
Pit and fissure preparation: Not typically needed for complete occlusion.
Complete sealing: Critical for optimal protection.
Minimal sealant application: Avoid bulky overfilled sealants.

GIC-Based Pit and Fissure Sealants

Contain fluoride for enhanced caries protection.
Adhere under moist conditions.
Lower retention rate compared to composite resins.

Resin Sealants

Flow readily, adhere strongly, and withstand masticatory forces.
Offer good resistance to wear and tear.
Available in both clear and opaque versions.

Steps in Pit and Fissure Sealant Restoration

Clean and dry the tooth surface.
Acid etch the enamel for 15-30 seconds.
Rinse and dry thoroughly.
Apply sealant material without trapping air.
Light cure the sealant for 20 seconds per application.
Check for complete sealing and smooth surfaces.

Light-Cured Resin Sealant Clinical Procedure

Clean the tooth with pumice or prophy paste.
Rinse and dry.
Acid etch for 15 seconds.
Rinse and dry.
Apply the sealant.
Light cure for 20 seconds.
Inspect for complete sealing.

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Description

Explore the various methods of hardness testing and the concepts of fatigue and corrosion wear in materials. This quiz covers key aspects such as Vickers and Rockwell tests, along with the mechanisms of crack formation and creep behavior in materials. Test your knowledge on how these properties affect material performance and longevity.