Midterm


Unit 1: Properties and Terminology


Coefficient of thermal expansion:

  • Definition: change in volume in relation to change in temperature

    • No dental material expands or contracts exactly like tooth structure

    • Leads to microleakage and percolation

  • Microleakage: seeping of fluids into the tooth/restoration interface

  • Percolation: fluids moving in and out of the interface due to temperature fluctuation

Galvanism

  • When 2 different metals contact in a wet environment (saliva), an electrical current is generated

Viscosity

  • Ability to flow

    • thick → flows POORLY (impression material)

    • thin → flows easily (etch for sealants)

Polymerization

  • definition: hardens liquid into solid durable materials

    • 2 types: auto-polymerization (chemical/self-cure) or photo-polymerization

Stress vs. strain

  • Stress-force within an object when a load is applied

  • Strain- change in length or shape

    • CANNOT have one without the other

Elasticity

  • An object deforms under stress and then returns to its original position

    • Modulus of elasticity: the stiffness (higher the modulus, the stiffer the material)

Wettability

  • Affinity of a liquid for a solid, as indicated by the spreading of a drop

  • Measured by the contact angle

    • Low contact angle = good wetting

    • High contact angle = poor wetting

  • Factors Affecting Wetting:

    • Surface energy of material→ attracts or repels

      • Impurities: debris, air bubbles, water, saliva; surface roughness

Difference between inlay, on-lay, and crown

  • inlay: fills the center of the tooth between cusps

  • on-lay: extends over one or more cusps

  • crown: caps entire visible portion of the tooth

Blacks classification of caries

  • Class I

    • pits or fissures

    • occlusal surfaces of premolars and molars

    • facial and lingual surfaces of molars

    • lingual surfaces of maxillary incisors

  • Class II

    • proximal surfaces of premolars and molars

  • Class III

    • proximal surfaces of incisors and canines that DO NOT involve incisal edges

  • Class IV

    • proximal surfaces of incisors and canines that do involve incisal edges

  • Class V

    • cavities in cervical 1/3 of the facial or lingual surfaces

  • Class VI

    • cavities in the incisal edges of anterior teeth and the cusp tips of posterior teeth

Indirect and direct restorations

  • Indirect: dental restorations made outside of the mouth (crown and bridges)

  • Direct: dental restorations cured directly in the mouth (amalgam and composite)

Sealants

Purpose of Sealants

  • physical barrier to decay by sealing surface

Role of etch and chemical makeup

  • Role: Etching enamel creates micro-pores in enamel that become a retention mechanism (resin tags) → over-manipulation will break down micro-pores

  • Makeup: composed of 37% phosphoric acid

Difference between self-cure and polymerized sealants

  • Auto-polymerized or chemical cure or self-cure

    • 2 equal parts (drops) mixed; polymerization will begin (the hardening process)

    • Setting time: about 2 minutes

  • Visible light-cured or photo-polymerized

    • Blue light to polymerize material (halogen)

    • Curing time: 20 seconds

Common errors in placement of sealants

  • Improper technique is the major cause of failure or early loss of sealants

    • Contamination (saliva, water, oil-laden compressor air, etc.)

    • do NOT over manipulate to prevent air bubbles

  • Patient Causes:

    • Teeth with frank caries

    • Well-coalesced pits and fissures

    • Uncooperative patient

Appropriate patient selection for sealants (teeth numbers, age, anatomy)

Patient Assessment:

  • Moderate to high caries risk

  • Risk assessment form

  • Incipient caries within the enamel (controversial)

  • Pits & fissures anatomically susceptible to decay

  • decay occurs during 1st year AFTER eruption → protect susceptible teeth as soon as possible

Placement Guidelines:

  • Fully erupted tooth→ no operculum present

  • Decay history regardless of age

  • Diet recommendation

Composition of Sealants: BPA

  • Composition of sealants: bis-GMA (bisphenol A glycidyl dimethacrylate)

    • similar to composite resin (less viscous)

    • fluoride- or non-fluoride releasing

    • clear, tinted, or opaque

    • filled or unfilled

  • Concerns stemmed from reports that resin-based materials may be exposed to xenoestrogens (mimic estrogen → affects reproductive tissues)

  • A recent study supported by ADA reported that BPA released orally may not be absorbed systemically, or the quantity absorbed is below detectable levels

resin material

  • resin-based, moisture-tolerant sealant

    • advanced acid-integrating chemistry that is activated by moisture

    • retention rate is higher than glass ionomer sealants

  • Preventive resin restoration (PRR)

    • caries suspected → fissure opened with bur → caries is removed → filled with composite → place sealant

sealant placement

  • 1. Prepare surface → remove debris from tooth with pumice, air polishing, or toothbrushing with hydrogen peroxide

    • IMPORTANT: Do NOT have oil or fluoride in the agent used, so it’s ideal to place before prophy and fluoride

  • 2. Rinse thoroughly

  • 3. Isolate

  • 4. Dry tooth for 10 seconds or more

  • 5. Apply etch

    • liquid etch: gently dab with a brush or cotton pellet

    • Gel: distribute with explorer and DO NOT DISTURB

  • 6. Remove etch and rinse for 30 seconds

  • 7. Re-isolate and dry for 20-30 seconds

  • 8. Check for chalky appearance

  • 9. Apply sealants

    • DO NOT extend beyond the etch area → results in microleakage and sealant failure

    • Air bubbles form from poor flow, over-manipulation, or filler amount

  • 10. Cure for 20-40 seconds (polymerize sealants)

  • 11. Evaluate with articulating paper and remove markings afterwards

  • 12. Floss interproximal spaces

  • 13. Rinse and record

Whitening

materials used for vital tooth whitening

  • oxidizing agents:

    • hydrogen peroxide

    • carbamide peroxide

  • NOTE: 3% hydrogen peroxide is approximately = to 10% carbamide peroxide (STRONGER)

Restorations:

  • do NOT whiten with treatment

description of custom trays

  • fabricated from a model

    • applies gel to tray and insert over teeth

side effects of whitening

  • taste of whitening gel

  • gingival irritation

  • uneven tooth whitening

  • splotchy appearance during initial stages of whitening treatment

  • tooth hypersensitivity

Reducing Sensitivity

  • potassium nitrate (KN03) formulation in tray or toothpastes    

    • have patient place sensitivity toothpaste containing 5% KNO3 1 week before initiating whitening in tray that will be used for 30 min a day

oxidation

  • Free radicals in oxygen oxidize stains

Rigid and Hydrocolloid Impression Materials


Nonelastic or Rigid Materials

  • NOTE: rigid material cannot be used where undercuts exist

Aqueous = Hydrocolloids

  • Hydrocolloids

    • “Hydro”: water-based

    • “Colloid”: particles suspended in a medium

    • 2 phases: liquid (sol) and semi-solid (gel)

      • Sol → Gel state (chemical)

      • Sol ⇄ Gel state (thermal)

Aqueous Elastomeric: Flexible

  • alginate: IRREVERSIBLE hydrocolloid

    • sol (liquid) → gel (semi-solid) via chemical reaction

  • agar: REVERSIBLE hydrocolloid

    • sol (liquid) ⇄ gel (semi-solid) via thermal reaction

  • SETTING REACTION: gelation

alginate mixing procedure

  • Place water in a flexible bowl FIRST, then add powder

  • Mix against the side of the bowl (stropping)

  • Mix for 1 minute

  • Load tray and seat in mouth (mandibular first)

  • Remove 2 to 4 minutes after gelation (loss of tackiness)

    • Regular set: gel in 3-4 minutes

    • Fast set: gel in 1-2 minutes

  • Remove with a snap to avoid permanent deformation (distortion)

  • Disinfect according to manufacturer’s directions

Water Temperature Regarding Alginate

  • Water temperature controls the rate of the setting reaction

    • warm water → sets faster

    • cooler water → sets slower

Alginate Considerations/Disadvantage

  • Due to imbibition and syneresis, alginate impressions MUST be poured immediately!!!

    • imbibition: absorption of water (swelling)

    • syneresis: loss of water (shrink)

  • If unable to pour immediately, store at 100% humidity for less than 1 hour (humidor)

Alginate Preparation:

  • Must be disinfected according to the manufacturer’s recommendations before pouring

    • Blood or debris on impression → rinse under water, then disinfect

alginate indication

  • Indication:

    • One of the most widely used materials to study models, impressions for dentures, partial dentures, night guards, whitening trays, fluoride trays

    • NOT as accurate as agar → rounds off sharp angles (NOT GOOD impressions for crowns, bridges, and in-lays/on-lays)

agar indications and restrictions

  • Indications: High accuracy; suitable for crowns and bridges

  • Equipment: Requires 3-chamber water bath, water-cooled trays, and tubing (expensive)

    • 1. boiling bath (212 F for at least 10 minutes) that changes to sol

    • 2. Storage bath (150 F) that keeps material until ready to be used

    • 3. Conditioning bath (110 F) fill tray and place in bath for 15 minutes (gelation)

      • Cool with water at 13 C for 3 minutes

  • Preparation: be prepared in advance (boiling, storing, tempering); SUBJECTED to imbibition and syneresis

  • Restriction: initial expense and poor tear strength

Gypsum Study Models

Difference between casts, dies, and models

Study model: used for observation and treatment planning

  • 3-dimensional record

  • Study of occlusal relationships

  • Study of tooth size, position, shape & arch

  • present conditions

  • Visual aid for patient education

  • Legal record for insurance, legal suits, and forensics

2. Cast: replica of more than one tooth (quadrant or arch) used for fabrication of a restoration or appliance

  • Partial denture

  • Whitening tray

  • Space maintainer

  • Ortho retainer

3. Die: replica of a single tooth used to fabricate an inlay, onlay, crown, or bridge

Types of Gypsum

  • Gypsum products differ in physical characteristics based on the calcination process used

    • Calcination: a heating process that drives water off to create gypsum products (Calcium sulfate hemihydrate)

  • Chemically: all products are alike

  • Gypsum is a mineral mined from the earth (Calcium sulfate dihydrate)

Difference between plaster, stone, and improved stone

Property

Plaster

Stone

High-Strength Stone / Die Stone

Calcination Process

Heated at atmospheric pressure

Calcinated under pressure

Calcined with calcium chloride solution

Hemihydrate Type

Beta hemihydrate

Alpha-hemihydrate

Modified alpha-hemihydrate


Particle Characteristics

Rough, random, and porous

More regular, less porous

Very dense, cuboidal with reduced surface area

Relative Strength & Cost

Weakest and least expensive

Stronger and more expensive than plaster

Strongest and most expensive

Color

Usually white

Usually yellow

Comes in different colors

Primary Uses / Applications

Used where strength is not required: study models, whitening trays

Casts for denture and partial denture construction

Die construction for inlays, onlays, crowns, and bridges

Water / Powder Ratio (IMPORTANT)

50ml water/100g powder

30ml water/100g powder

24ml water/100g powder

Setting Expansion

Expands the most (0.2% – 0.3%)

0.08% – 0.10%

Expands the least (0.05% – 0.07%)

Proper mixing of gypsum

  • Measure water and powder for optimum properties

    • Adding too much water or stone will WEAKEN the final product, which DECREASES strength

  • Sift powder INTO water

  • Mix by swiping sides of bowl w/spatula; avoid incorporating air

  • A homogeneous mix is obtained in 1 minute

Setting Time for Gypsum

  • Two intervals: working or initial setting time

  • Working time:

    • Start of mix until material thickens

    • Indicated by loss of surface gloss

    • Do not manipulate after initial set or mixture is weakened

  • Setting time:

    • Start of mix until hardened and removed from impression

    • 45-60 minutes (risk of fracture if removed early)

Factors for setting time

  • Increase setting time → sets slower

    • Higher W/P ratio

  • Decrease setting time → sets faster

    • Lower W/P ratio

Pouring the Impression

  • Use vibrator to flow gypsum material through the disinfected impression

    • Prevents air bubbles, which create voids

  • Start in first tooth imprint and flow around to last tooth imprint

Strength

  • Wet strength: while free water is still present

  • Dry strength: when excess water is no longer present

Storage

  • affected by moisture

  • Stored in air-tight containers

  • Moisture contamination can cause faster or slower setting reactions

characteristics of polysiloxanes, polyvinyl siloxane, polyethers, and polysulfides

Cements, Bases, and Liners

1. Primary Function & Indications

  • Dental Cements:

    • Used for luting (attaching restorations to teeth like a glue), including crowns, inlays, on lays, veneers, and orthodontic brackets

    • Used as temporary restorations for emergency care, time management, pain relief, diagnosis, or managing rampant caries

  • Liners: pulp protection that’s used against chemical irritation

    • used for pulp-capping or near pulp-capping.

  • Bases: Placed under restorations providing thermal protection before placing an amalgam) and mechanical support (supporting the condensing of an amalgam restoration)

2. Thickness & Mechanical Support

  • Dental Cements (Luting): Prepared to a thin film thickness controlled by particle size so that restorations seat properly, minimizing open margins and recurrent decay.

  • Liners: Applied as a very thin layer (< 0.5 mm)

    • too weak for mechanical support and too thin to provide thermal insulation.

  • Bases: Thicker and stronger than liners

3. Material Properties & Clinical Considerations

  • Liners:

    • Calcium Hydroxide (Dycal): A common liner material with a high pH (about 11) that stimulates secondary dentin formation by "shocking" the tooth.

    • Note: Liner use is decreasing in dentistry

  • Bases:

    • Zinc Oxide-Eugenol (ZOE): Provides an obtundent/palliative (pain-reducing) effect with a neutral pH of 7 (least irritating), is bacteriostatic, and offers low thermal diffusivity. However, eugenol inhibits polymerization and must not be used under composites.

    • Zinc Phosphate: Very strong with low solubility, but has a low pH during setting that makes it irritating to the pulp; therefore, a liner must be placed first when using zinc phosphate as a base.

    • Glass Ionomer / Resin-Modified Glass Ionomer: Can function as a luting agent, restoration, base, or liner. It bonds chemically to tooth structure, releases fluoride (anticariogenic), and exhibits high strength and low solubility.

    • Zinc Polycarboxylate: Used as a base or permanent cement; it bonds chemically to tooth structure and is biocompatible (less acidic to the pulp), but is not as strong and exhibits moderate solubility.

4. Mixing Consistency & Powder/Liquid (P/L) Ratios

  • Luting / Primary Consistency: Uses a lower P/L ratio to achieve a fluid consistency. When lifted with a spatula, luting mixes of zinc phosphate and ZOE string 1 inch from the slab, while glass ionomer luting mixes string to 1/2 inch.

  • Secondary Consistency (Bases): Uses a higher P/L ratio to produce greater strength and a thicker consistency. For ZOE and zinc phosphate bases, powder is added until the material reaches a thick, putty-like consistency that can be rolled into a ball.

-properties of glass ionomers

-eugenol

  • weak acid derived from oil of cloves

  • obtundent/palliative: reduces irritation

  • antibacterial

  • inhibits polymerization (DO NOT used with composite)

-zinc oxide: Eugenol

  • multi-purpose cement

    • low strength

  • Produces:

    • unreinforced ZOE-temp cement

    • reinforced ZOE-temp restoration, base, intermediate restoration (IRM)

    • liners

-calcium hydroxide (dycal)

  • common liner material with a high pH (about 11) that stimulates secondary dentin formation by "shocking" the tooth.

  • Note: Liner use is decreasing in dentistry

ratios of bases

ratios of liners