الفهرس 
Introduction .Only 14 pages are availabe for public view
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Abstract
Occlusal pit and fissures are highly caries susceptible due to their surface’s complex morphology. This is especially true for erupting teeth that are in the enamel maturation process and their anatomic characteristics cause difficulty in access for cleansing procedures.
Pit and fissure sealants have proved to be an effective method in reducing the rate of occlusal caries on posterior teeth by forming a barrier between the tooth surface and the oral environment.
Thus, The present study aimed at evaluating and comparing the effect of various enamel preparation techniques; 37% phosphoric acid etching, self-etching adhesive and Er:YAG laser treatment before application of a fluoridated resin-based pit and fissure sealant on caries-free premolars in regard to SBS, microleakage and penetration depth.
Seventy-two freshly extracted premolars for orthodontic reasons with deep pits and fissures were included in the study. Teeth were cleaned from any gross debris and scaled with ultra-sonic scaler and stored in distilled water and divided randomly into three equal groups (n=24), group I was pretreated with conventional acid etching (n=12 for SBS and n= 12 for microleakage and penetration depth), group II was pretreated with self-etching adhesive(n=12 for shear bond strength test and n= 12 for microleakage and penetration depth), and group III was pretreated with ER: YAG laser(n=12 for shear bond strength test and n= 12 for microleakage and penetration depth), before the application of a fluoride-releasing resin-based pit and fissure sealant.
For SBS testing:
Roots of all teeth were cut 2 mm below the cementoenamel junction. The crowns were then bisected longitudinally in mesiodistal direction with a water-cooled diamond disc in low-speed handpiece, providing 36 buccal tooth halves (12 buccal tooth halves for each subgroup)
After All subgroups pretreated as previously explained, a cylindrical transparent gelatin tube (Foley Catheter) with an internal diameter of 3 mm and height of 4 mm was placed on the treated enamel to ensure standardization of the sealant size and shape during application. Then pit and fissure sealant was applied into the tube and was cured according to manufactures’ instructors. Then, the tube was removed.
then, the prepared samples were kept in 37°C distilled water for 24 hours before testing.
Each specimen was placed into a Universal Testing Machine (LLOYD Instruments, Ametek, UK) and chisel edge was placed on the fissure sealant loaded to the bonding surface, running at a crosshead speed of 1 mm/min till the fracture occurred. The force required to fracture the specimen was recorded in Newtons and was converted to MPa using the following formula: Megapascal (MPa) = Newton (N)/connection surface area (mm²).
For microleakage and penetration depth testing:
A total of 36 premolars were selected, cleaned and divided into three groups. After each group pretreated as previously explained, one DROP of a resin based sealant was applied on occlusal surface of samples.
All samples were subjected to thermal cycles in water baths at a temperature range between 5°C and 55°C. The duration of each bath was 30 s with a 10 s transfer time. The thermal cycles were repeated 500 times.
After thermocycling, the apices of the specimens were sealed with sticky wax and the surface of each specimen was covered by a double layer of nail polish applied 1mm away of tooth and sealant conjunction. The varnish was applied to avoid dye penetration to other parts of the tooth.
Then all samples were immersed in 2% methylene blue dye solution for 24 hours at room temperature to allow dye penetration into gaps between the enamel and sealant then rinsed under running water to remove excess solution. The samples were then sectioned in a buccolingual direction into two halves in a vertical plane parallel to the long axis of the tooth. Sealant microleakage and penetration depth were evaluated for all groups using stereomicroscope.
SBS and microleakage results showed significant difference between different groups while there was no significant difference between group (I) conventional acid etching group and group (II) self-etching adhesive and there was no significant difference between group (II) self-etching adhesive and group (III) Er: YAG laser treatment.
Conventional acid etching showed the highest SBS values and the least microleakage scores while Er:YAG laser treatment group showed the least SBS values and the highest microleakage scores.
Penetration depth results showed no significant difference among all groups, where all groups showed penetration to full fissure depth.