الفهرس 
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Abstract
This study was conducted to compare the bactericidal effect of photodynamic therapy using Diode laser (650 nm) and non-coherent light (480 nm) in young permanent teeth as well as the effect of time of exposure on the effectiveness of photodynamic therapy.
A total of 90 mandibular first permanent molars were selected from children with ages ranging from 7 to 9 years old who were patients attending the out patient clinic of the Pediatric Dentistry Department, Faculty of Dentistry, Ain Shams University.
These teeth were selected having occlusal caries not involving buccal or lingual surfaces and having the base of the cavity in dentine.
The molars were divided according to the type of light used for the activation of the photosensitizer and according to the time of exposure into six groups (15 molars each):
group I ( 1 min of diode laser), group II ( 2 min of diode laser), group III ( 3 min of diode laser), group IV ( 1 min of non-coherent light ), group V (2 min of non-coherent light), and group VI ( 3 min of non-coherent light).
The cavities were excavated and a preoperative standardized sample of carious dentine was collected. A DROP of MB dye was applied into the cavity using a sterile plastic syringe then the cavity was exposed
involving buccal or lingual surfaces and having the base of the cavity in dentine.
The molars were divided according to the type of light used for the activation of the photosensitizer and according to the time of exposure into six groups (15 molars each):
group I ( 1 min of diode laser), group II ( 2 min of diode laser), group III ( 3 min of diode laser), group IV ( 1 min of non-coherent light ), group V (2 min of non-coherent light), and group VI ( 3 min of non-coherent light).
The cavities were excavated and a preoperative standardized sample of carious dentine was collected. A DROP of MB dye was applied into the cavity using a sterile plastic syringe then the cavity was exposed
to the source of light for activation of the dye and the time of exposure predetermined according to each group.
A second carious dentine sample was collected from the same point of the first then the cavity was completed and restored.
Microbiological sampling and processing was done in an anaerobic atmosphere followed by aerobic atmosphere at 37º C after being cultured on mitis salivarius agar.
The colony forming units of S mutans were counted preoperatively and postoperatively. Results were statistically analyzed to compare between them for each tooth and to compare between groups.
The results of the study revealed that the best killing percentage (85.6%) was achieved when diode laser was applied for 3 min while the least killing percentage (38.8%) happened when diode laser was applied for 1 min only.