الفهرس 
Introduction .Only 14 pages are availabe for public view
 |  | from | 139 |  |  |
| | | from | 139 | | |
Abstract
Understanding the optical behavior of a universal resin composite “Omnichroma” and evaluating its ability to mimic the color of the adjacent shade. Using Omnichroma blocker and a model mimicking large esthetic defects to identify the color adjustment potential.
24 single (10mm x 6mm x4mm) and 72 dual (10mm x12mm x 4mm) resin composite blocks were prepared in this study and divided according to two the levels of the study (n=6). Level one: body shade (A1, A2 and A3). Level two: blocker placement (Palatal, Palatal/Proximal, Palatal/Gingival, Palatal/Proximal/Gingival). The blocks were prepared using custom-made rectangular single and dual stainless-steel mold then polished and stored in distilled water for 24 hours before color measurement.
The single blocks were used as control to be able to measure the color difference between Omnichroma (layered over 1 mm Omnichroma blocker) and different esthetic shades separately. The dual blocks examined the color difference when Omnichroma was adjoined to those esthetic shades. Additional surrounding modifications were done to the Omnichroma of the dual block to measure whether there will be an alteration on the color adjustment potential.
Two instrumental methods were utilized to evaluate the color change of Ommichroma clinical spectrophotometry (VITA Easyshade® V;Vita Zahnfabrik, Bad Säckingen, Germany) and digital photography with cross polarized filter.
Color difference (E00) was calculated using the CIEDE2000 formula. Color adjustment potential instrumental (CAP - I) was computed subsequently.
Two-way ANOVA showed a statistically significant difference in the color difference of Omnichroma resin composite for both variables; final shade and blocker placement, as well as both measuring devices. The Color adjustment potential (CAP-I) accordingly showed a statistically significant difference for both variables and measuring devices.
The highest color adjustment potential with a perceivable acceptable E=1.87±0.41 was for the Palatal/ Proximal Gingival (PPG) group in comparison to A3 shade by photographic analysis. The same group had the highest color adjustment potential but with a perceivable unacceptable E= 4.05±0.45 in the spectrophotometric analysis.
On the contrary the best color matching for both shades A1 and A2 was for the Palatal/ Proximal (PP) group in both spectrophotometric and photographic analysis (A1: 4.13±0.05 and 3.55±0.50, A2: 3.70±0.45, 4.38±0.42) respectively. Yet both groups had a perceivable unacceptable E.
All dual specimens showed effective blending which is denoted by a 20% color adjustment potential except A1/PPG group.
Positive correlation between the two measuring devices utilized was shown for both variables of the study using spearman rank correlation. Paired t-test was performed and showed that clinical spectrophotometry readings showed a higher statistically significant difference than digital photography. With a mean of 6.21±2.54 for clinical spectrophotometry and 5.4±2.01 for digital photography with mean difference 0.811±1.26 (p<0.0001).
Within the limitations of this in vitro study, the following conclusion could be suggested:
• The Omnichroma has a good chameleon color pick up which is further enhanced by enclosing it within a tooth-colored environment from all directions.
• The darker the shade the more critical it becomes to enclose the restoration in a tooth-colored environment.
• Although spectrophotometry shows higher numerical values than polarized photography, yet they are both positively correlated.
Clinical recommendation:
According to the manufacturer instructions, the addition of Omnichroma blocker palatally in large anterior esthetic defects is compulsory to avoid the grayness conveyed from the darkness of the oral cavity. Furthermore, corresponding to our results, in case the adjacent is not in direct contact with the part restored or the adjacent is compromised due to discoloration or color mismatch; a proximal blocker is necessary.