Light Cure Principles Flashcards
How does photoinitiator get activated
Hit by visible light and absorbs a photon. Absorbed energy of photon changes molecular structure to form free radical
What is conversion rate of composite resin
About 70%
What is the active time for a free radical in polymerisation reaction
0.1-1s
How may termination in polymerisation of cr occur
Activated photoinitiator reacts with another
Monomer reacts with activated end of polymer chain instead of another monomer
Coinitator in polymerisation in cr
Tertiary amine which does not absorb light. Interacts with photoinitiator to produce reactive species
Why is halogen lamp energy inefficient
5% of total energy is visible light. Continuous spectrum narrowed by filters
What is the lifespan of the halogen lamp
100 hours, consecutive degradation of bulb
What is a disadvantage of led
Narrow emission spectrum, can only polymerise materials with absorption between 440 and 480nm (hence must use camphorquinone as photoinitiator)
How much energy needed for cr curing
24 joules (LED: 20s at 2000mW)
How far should light tip be from composite surface for curing
6mm
What is step curing
10s at low intensity
Increased power output at 700mw/cm2
No unanimous proof for marginal adaptation
What is soft start polymerisation
Start at low energy level and increase to final power density exponentially
Some reduction of polymerisation stress in class v cavities
What is pulse delay light cure
Initially irradiated with short pulses of light energy, wait 3 min, final polymerisation at high intensity for 30s
Low degree of polymerisation at cavity floor
What happens if you underpolymerise material
Inferior physical and mechanical properties
Higher solubility
Loss of retention
Excess wear and softness
Poor colour stability, increases susceptibility to stain
