Dental Resin Composites - Vocabulary Flashcards

Comprehensive vocabulary flashcards covering composite resin composition, curing mechanisms, optical properties, filler technology, and clinical techniques.

Enamel Composition (by weight)

$95\,\%$ mineral, $4\,\%$ organic (protein/matrix), and $1\,\%$ water.

Dentine Composition (by weight)

$70\,\%$ mineral, $20\,\%$ organic (protein/matrix), and $10\,\%$ water.

Enamel Hardness

$300\text{--}500\,\text{KHN}$, making it the hardest tissue in the human body.

Dentine Hardness

$50\text{--}70\,\text{KHN}$.

Hue (Munsell System)

The colour family itself, determined by wavelength (range: R, YR, Y, GY, G, BG, B, PB, P, RP).

Chroma (Munsell System)

The intensity, saturation, or purity of the colour (range: $0\text{--}18$).

Value (Munsell System)

The brightness or total light reflected back (lightness) (range: $0\text{--}10$).

Fluorescence (Dental)

The phenomenon where a material absorbs light at one wavelength and re-emits it at another; dentine fluoresces far more strongly than enamel due to its higher organic content ($20\,\%$ wt matrix).

Metamerism

The optical phenomenon where two objects match under one lighting condition but no longer match under another light with different spectral properties.

Resin Composite Components

The three essential phases of a composite: organic resin matrix, inorganic filler, and coupling agent (silane).

Bis-GMA

Bisphenol A-glycidyl methacrylate; a large base monomer that forms the backbone of the resin matrix and exhibits $7\,\text{vol }\%$ polymerisation shrinkage.

MMA Polymerisation Shrinkage

$22\,\text{vol }\%$, which is significantly higher than Bis-GMA ($7\,\text{vol }\%$) due to MMA's smaller molecular size.

Diluents (Viscosity Controllers)

Monomers such as MMA, EGDMA, and TEGDMA added to thin the viscous base monomer so filler can be loaded and the paste handled.

Inhibitor (Resin Matrix)

Hydroquinone; mops up stray free radicals to prevent premature setting and give shelf life.

UDMA vs Bis-GMA (UDMA Greater Properties)

The four properties where UDMA is greater than Bis-GMA: polymerisation shrinkage, double bond conversion rate, filler loading/toughness, and handling.

Coupling Agent

A chemical link (typically silane) between two materials with no natural affinity—the hydrophilic inorganic glass filler and the hydrophobic organic resin matrix.

γ-MPTS

γ-methacryloxypropyltrimethoxysilane; the primary silane coupling agent used in dental resin composites.

Silane Bonding Mechanism Stages

1. Acid activation (hydrolysis of methoxy groups to silanol), 2. Adsorption (hydrogen-bonding to filler), 3. Condensation reaction (formation of covalent Si–O–Si siloxane bonds), 4. Monolayer formation.

Unsilanated Composite Strength Loss

A $30\,\%$ reduction in compressive strength and fatigue limit when a coupling agent is not used.

Chemical Cure System (Two-Paste)

A self-curing system where an aromatic tertiary amine (activator in catalyst paste) reacts with benzoyl peroxide (initiator in base paste) to produce free radicals.

Camphorquinone

An α-diketone photoinitiator in visible light cure (VLC) composites that absorbs blue light with a peak absorption around $468\text{--}470\,\text{nm}$.

Effective Initiation Wavelength Range (VLC)

$450\text{--}500\,\text{nm}$, with maximum light output at $460\text{--}480\,\text{nm}$.

Recommended Increment Thickness

No more than $2\,\text{mm}$ depth at a time to ensure reliable light penetration and complete cure.

Optimum LED Curing Intensity

$800\text{--}1200\,\text{mW/cm}^2$ in routine practice (with a minimum required threshold of $400\text{--}500\,\text{mW/cm}^2$).

Inverse Square Law (Light Curing)

$\text{Intensity} = 1/d^2$; light intensity falls exponentially as the curing tip moves away from the composite surface.

Oxygen-Inhibited Layer

An unreacted surface layer of methacrylate caused by atmospheric oxygen; necessary between increments for chemical co-polymerisation, but harmful on the final surface.

Glycerine (Dental Application)

Used as an oxygen barrier on the final composite increment surface prior to the final light cure to eliminate the oxygen-inhibited layer.

Clinically Quoted Composite Shrinkage

$2\text{--}3\,\text{vol }\%$ ($2.1\text{--}2.8\,\text{vol }\%$ for $60\text{--}70\,\text{vol }\%$ filled composite).

Cuspal Deflection

Tooth flexure caused by polymerisation contraction stress, clinically manifesting as cracked cusps, enamel cracking (white lines), or biting sensitivity.

Coefficient of Thermal Expansion (CTE)

Methacrylate monomers: $\sim 80\,\text{ppm/}^\circ\text{C}$; Enamel: $\sim 11\,\text{ppm/}^\circ\text{C}$; Glass filler: $\sim 8\,\text{ppm/}^\circ\text{C}$.

Rule of Mixtures (CTE)

Formula $CE_c = V_f CE_f + V_r CE_r$ used to calculate the composite's coefficient of thermal expansion based on volume fractions of filler and resin.

Macrofill Composite

Traditional composite with glass fillers ($10\text{--}20\,\mu\text{m}$) loaded at $70\text{--}80\,\text{wt }\%$ ($60\,\text{vol }\%$); strong but results in a rough surface and dull appearance.

Microfill Composite

Composite containing colloidal silica ($0.01\text{--}0.05\,\mu\text{m}$) at $\sim 50\,\text{wt }\%$; provides high polishability and minimum shrinkage but lower fracture strength.

Nanocomposite

Composite with discrete silica nanoparticles ($2\text{--}20\,\text{nm}$) and zirconia–silica nanoclusters ($0.6\,\mu\text{m}$) at $78\,\text{vol }\%$ loading; balances high strength with high polishability.

Elastic Modulus Comparison (Hybrid vs Tooth)

Hybrid composite: $14\,\text{GPa}$; Dentine: $15\,\text{GPa}$; Enamel: $50\,\text{GPa}$.

Hardness Comparison (Vickers Hardness Number)

Hybrid composite: $90\,\text{VHN}$; Enamel: $350\,\text{VHN}$; Dentine: $60\,\text{VHN}$.