The Effect of Ceramic Thickness and Number of Firings on the Color of Two All-Ceramic Systems Measured by Spectrophotometer

Background: This in vitro study was carried out to evaluate the effects of various veneering dentin ceramic thicknesses and repeated firings on the color of lithium disilicate glass-ceramic (IPS e.max Press) and zirconium-oxide (IPS ZirCAD) all-ceramic systems, measured by clinical spectrophotometers (Easyshade Advance 4.0) . Materials and methods: The 72specimens cube-shaped have the dimension of about 11 mm in width, 14 mm in length, 1mm in thickness, these cores divided into 3 groups according to the type of material each group have (24)core specimens. Each group had been divided into three sub-groups (each having 8 specimens) according to veneering with dentin ceramic thicknesses: as 0.5, 1, or 2 mm (n=8). IPS e.max press and ZirCAD cores group had been veneered with IPS e.max Ceram dentin ceramic shade A2 according to manufacturer’s instructions and the metal group had been veneered with IPS classic dentine ceramic with shade A2 according to manufacturer’s instructions. Repeat firings (3, 5 and 7 times) had been applied on all the specimens. Color differences among ceramic specimens had been measured using a clinical spectrophotometer (VITA Easyshade); the color data had been expressed according the Vita Classic shade guide. Results: The shade of all specimens had been compared inside the subgroups and with the main groups. The percentage of color agreement among the subgroups showed the color of all ceramic systems had been affecting by firing interval, the ceramic thickness and brand of ceramic. The number firings intervals applied on the all ceramic system has a significant effect on the final color, the increase of firing number change the color to a darker and reddish color. The 5th firing interval is the point at which the major color changes happened (darker shade), and in next interval (7th firing) less color changes happened. The thickness of veneering ceramic affected the color significantly. The 0.5 mm specimens in all groups showed the highest percentage of agreement (less color changes) after firing intervals, then the 1mm came and the least percentage of agreement ( highest color changes ) was the 2 mm specimens. The Brand of veneering ceramic and the type of core record a significance difference in color changes when exposed to firing heat. Conclusion: With limit of this study, the final color of the all ceramic system definitely affected by the number of firing cycle exposed to, and the veneering ceramic thickness have a clear effect on the final shade of the all ceramic tested.


INTRODUCTION
All-ceramic restorations are developed rapidly and used widely nowadays; there is a lack of information on the way that the color is affected by manipulation and fabrication procedures.Most all ceramic systems require the application of two layers of ceramic material, such as a core (strong ceramic) and a veneering porcelain (weak ceramic) (1) with different shade, opacity, and thickness, to provide a natural appearance (2,3) .All ceramic restorations without a metal core allow more light transfer within the restoration, this happened by improving the color and translucency of the restoration; however, a perfect esthetic tooth-colored restoration cannot be ensured (4) .The amount of light that is transmitted, absorbed, and reflected depends on, the size of the particles compared to the incident light wavelength and the quantity of crystals within the core matrix, their chemical nature (5) .
The translucency of the Core was also considered as a primary factor in controlling esthetics and a critical consideration in the selection of the materials (6) .Many factors affect the ability of a ceramic system to produce good match with corresponding shade guides, such as condensation techniques, firing temperatures and dentin ceramic layer thickness.The effects of dentin thickness on the color of metal-ceramics were studied, and the researchers reported that a clinically acceptable shade match was influenced by this parameter (7) .A study examining color changes of surface colorants after firing have demonstrated pigment breakdown at firing temperatures (8) .
Hue, Chroma and Value color parameters of metal-ceramic specimens, which were fired 1.68°C and 21°C above the manufacturer's instructions firing temperature, indicated substantial differences in color (9) .Instrumental measurements can quantify color shade and allow communication to be more uniform and precise.Development of advanced computerized colorimeters and spectrophotometers has increased their use in dental applications.Spectrophotometers measure the absorption or transmittance or reflectance factors of an object for one wavelength at a time.

Sample preparation:
Group A(Zirconia based all ceramic system): Twopresented Y-TZP block (IPS e.maxZirCad, IvoclarVivadent, Schaan, Liechtenstein)were divided to specimens (dimensions: 1.4-1.5 mm in height, 15.5mm in width,19mm in length).Then the specimens were sintered in furnace (InFireHTC speed sintering furnace, Sirona) According to the cycle recommended by manufacturer.After sintering, approximately 25% shrinkage was occurred in zirconia specimens.After sintering, the dimensions of specimens was about (11.7 mm in width, 14.3 mm in length, 1 in height), Then(24) zirconia core specimens were divided randomly to three subgroups according to the veneering ceramic thickness added, each subgroup contains (8) specimens.These subgroups are: Group A1: Zirconia core of 1 mm and veneering ceramic thickness 0.5 mm.Group A2: Zirconia core of 1 mm and veneering ceramic thickness 1 mm.Group A3: Zirconia core of 1 mm and veneering ceramic thickness 2 mm.All specimens were cleaned with water for (10) minutes in a digital ultrasonic cleaner (model cd-4820\china), and air dried.A Liner was applied to all specimens by using a brush to create an even layer (7) .Then Zirliner was fired in calibrated porcelain furnace (P3000, Ivoclarvivodent, Schaan, Liechtenstein) according to the manufacturer's recommendations.Then the ceramic (IPS e.max Ceram dentine A2) was added incrementally onto the customize-made stainless steel mold (on one of the surfaces of the Zirconia) by using brush, the excess liquid sucked off with paper tissue, the veneering procedure was continued until the mold completely filled.Because of the volumetric shrinkage during firing of porcelain, the rings of the custom made mold designed larger in size to compensate the shrinkage and achieve the exact thickness needed.Eight samples of each thickness (0.5mm, 1mm and 2 mm) of veneering ceramic prepared.Firing of ceramic\dentin was performed in a calibrated porcelain furnace (p 3000, Ivoclar Vivadent, Schaan, Liechtenstein) according to the manufacturer's recommendations.The same firing cycle repeated 3 times before the first shade test and 2 firing cycles added after each testing procedure (5 and 7 firings).

Group B (e.maxPress all ceramic system):
Twenty four Specimens prepared by cut the thermoforming sheet (Forplast, Roko), have dimensions of about (1mm thickness, 10 mm width,10 mm length) for the single specimen.All specimens attached to wax minor sprus, using blue wax wire, each four minor sprus attached to a major connector (Major spru).Investing was carried out with IPS Press VEST Speed (speed investment).Burn-out (wax elimination) technique used, the investment ring was removed from the burnout oven to the pressing furnace (P 3000\ Ivoclar vivadent) without cooling it.Then the pressing procedure achieved with e.mac press ingots After cooling to room temperature the ring was broken by using plaster knife and cutting disc with care.All the specimens were cleaned from the investment remnants and the reacting layer was removed by immersing them in IPS e.max Press Invex Liquid for (10-30 min) and washed with water the sandblasted.The same procedure used of applying veneering ceramic in the zirconia group used in the e.max group and for the same thicknesses achieved.
Then (24) e.max core specimens were divided randomly to three subgroups according to the veneering ceramic thickness added, each subgroup contains (8) specimens.These subgroups are: Group B1: e.max press core of 1 mm and veneering ceramic thickness 0.5mm.Group B2:e.max press core of 1 mm and veneering ceramic thickness 1 mm.Group B3: e.max press core and veneering ceramic thickness 2 mm.

Group C (porcelain fused to metal system) control group:
Twenty four specimens prepared by cut the thermoforming sheet (For-plast, Roko), in dimensions of about (1mm thickness , 10 mm width, 10 mm length ) for the single specimen.The same steps used of spruing in the e.max press group.Then the usual steps of preparing and casting metal cores done (Investing, wax elimination ,casting , recovery of casting, finishing , oxide treatment , sandblasting , First opaque application and firing and Second opaque firing) .To obtain the desired dimensions of veneering ceramic, the same custom made mold is used in the same method of specimens of zirconia and e.max.Then (24) core specimens were divided randomly to three subgroups according to the veneering ceramic thickness added, each subgroup contains (8) specimens.subgroups Group C1 and veneering ceramic thickness Group C2 ( and veneering ceramic thickness 1mm Group C3 and veneering ceramic thickness

Color test
All the specimens were measured 3 times the firing firings).Each type of specimens certain temperature as instructions.

Shade test by
The specimens were placed over a surface of fifty white A4 papers, to ensure a complete wh background especially for the transparent specimens (e.max cores).The Easyshade Advance 4.0 device was turned on, calibrated and the option average reading was selected.captures were taken and the result of the average shade was recorded B 3, A2, etc.).

Shade test Easyshade Advance 4.0 results: Group veneering ceramic thickness
The results of this group (table 1) showed a relatively high percentage of agreement when comparing the samples inside the group after each firing interval, happened after firing.

Color test
All the specimens were measured 3 times the firing interval ( firings).Each type of specimens certain temperature as instructions.

Shade test by Easyshade
The specimens were placed over a surface of fifty white A4 papers, to ensure a complete wh background especially for the transparent specimens (e.max cores).The Easyshade Advance 4.0 device was turned on, calibrated and the option average reading was selected.captures were taken and the result of the average shade was recorded for each specimen like (A 3.5, B 3, A2, etc.).

Shade test Easyshade Advance 4.0 results: Group A1 ( Zirconia core with 0.5mm veneering ceramic thickness
The results of this group (table 1) showed a relatively high percentage of agreement when comparing the samples inside the group after each firing interval, which happened after firing.
: Shade results of group A1 (Zirconia core with ceramic thickness 0.5 mm) 1. Percentage of agreement between the 3 firing is 100 %.The specimens were placed over a surface of fifty white A4 papers, to ensure a complete wh background especially for the transparent specimens (e.max cores).The Easyshade Advance 4.0 device was turned on, calibrated and the option average reading was selected.captures were taken and the result of the average for each specimen like (A 3.5,

Shade test Easyshade Advance 4.0 results: Zirconia core with 0.5mm veneering ceramic thickness):
The results of this group (table 1) showed a relatively high percentage of agreement when comparing the samples inside the group after each which means less color changes happened after firing.All the specimens were measured 3 times after 3 firings, 5 firings and 7 firings).Each type of specimens was fired at a the manufacturer Advance 4.0 The specimens were placed over a surface of fifty white A4 papers, to ensure a complete wh background especially for the transparent specimens (e.max cores).The Easyshade Advance 4.0 device was turned on, calibrated and the option average reading was selected.Four to five captures were taken and the result of the average for each specimen like (A 3. fired at a the manufacturer The specimens were placed over a surface of fifty white A4 papers, to ensure a complete white background especially for the transparent specimens (e.max cores).The Easyshade Advance 4.0 device was turned on, calibrated and the Four to five captures were taken and the result of the average for each specimen like (A 3.5,

Zirconia core with 0.5mm
The results of this group (table 1) showed a relatively high percentage of agreement when comparing the samples inside the group after each means less color changes Shade results of group A1 (Zirconia and 5 th and 7 th and 7 th

Group ceramic thickness
relatively low percentage of agreement when comparing the samples inside the group after each firing interval, which happened especially after the 7 results showed a different color changes behavior from the less veneering ceramic thickness 0.5mm (Group A1).Table 1.Percentage of agreement between the 3 firing is 75 %.
2. Percentage of agreement between the 3 firing is 0 %. 3. Percentage of agreement between the 5 firing is 25 %.

Group A ceramic thickness
relatively low percentage of agreement when comparing the samples inside the group after each firing interval, which means much color changes, happened esp results showed a different color changes behavior from the less veneering ceramic thickness 0.5mm and 1 mm June 2016

Group A2 (Zirconia core with ceramic thickness
The results of this group (table 2) showed a relatively low percentage of agreement when comparing the samples inside the group after each firing interval, which happened especially after the 7 results showed a different color changes behavior from the less veneering ceramic thickness 0.5mm (Group A1).

Group A3 (Zirconia core with ceramic thickness
The results of this group (table relatively low percentage of agreement when comparing the samples inside the group after each firing interval, which means much color changes, happened especially after the results showed a different color changes behavior from the less veneering ceramic thickness 0.5mm and 1 mm (Group A1

Zirconia core with ceramic thickness):
The results of this group (table 2) showed a relatively low percentage of agreement when comparing the samples inside the group after each firing interval, which means much color changes, happened especially after the 7 results showed a different color changes behavior from the less veneering ceramic thickness 0.5mm

Shade results of group A core with ceramic thickness 1 mm)
1. Percentage of agreement between the 3 2. Percentage of agreement between the 3

Percentage of agreement between the 5 (Zirconia core with ceramic thickness):
The results of this group (table relatively low percentage of agreement when comparing the samples inside the group after each firing interval, which means much color changes, ecially after the results showed a different color changes behavior from the less veneering ceramic thickness 0.5mm (Group A1 and Group A2 Shade results of group A3 (Zirconia core with ceramic thickness 2 mm) The effect

Zirconia core with 1mm veneering
The results of this group (table 2) showed a relatively low percentage of agreement when comparing the samples inside the group after each means much color changes, happened especially after the 7 th firing.These results showed a different color changes behavior from the less veneering ceramic thickness 0.5mm Shade results of group A2 (Zirconia core with ceramic thickness 1 mm) 1. Percentage of agreement between the 3 2. Percentage of agreement between the 3

Percentage of agreement between the 5 (Zirconia core with 2mm veneering
The results of this group (table 3) showed a relatively low percentage of agreement when comparing the samples inside the group after each firing interval, which means much color changes, ecially after the 5 th firing.These results showed a different color changes behavior from the less veneering ceramic thickness 0.5mm and Group A2).The effect of mm veneering

Shade results of group A3 (Zirconia
The results of this group (table 2) showed a relatively low percentage of agreement when comparing the samples inside the group after each means much color changes, firing.These results showed a different color changes behavior from the less veneering ceramic thickness 0.5mm

Group B ceramic thic
The results of this group (table 4) showed a relatively high percentage of agreement when comparing the samples inside the subgroup after each firing interval and in comparing with other subgroup , which means less color changes happened after there is a between the Zirconia core specimens and the e.max core specimens that have the same veneering ceramic thickness and brand during the same firing cycles , that make the core ma real effecting factor on color of all ceramic system .Table 4 core with veneering ceramic thickness 0.5 1. Percentage of agreement between the 3 firing is 87.5 %.

Percentage of agreement betwe
firing is 75 %.
3. Percentage of agreement between the 5 firing is 62.5 %.

Group B2 (e.max core with 1mm veneering ceramic thickness):
The results of this group (table 5) showed a relatively low percentage of agreement when comparing the samples firing cycle inside the sub much color changes, happened especially after the 5 th firing that agree with showed a different color changes behavior from the less veneerin e.max core h College Dentistry

Restorative Dentistry
Percentage of agreement between the 3 firing is 25 %. 2. Percentage of agreement between the 3 firing is 12.5 %. 3. Percentage of agreement between the 5 firing is 87.5 %.
B1 (e.max core with 0.5mm veneering ceramic thickness): The results of this group (table 4) showed a relatively high percentage of agreement when comparing the samples inside the subgroup after each firing interval and in comparing with other subgroup , which means less color changes happened after firing .there is a different color changes behavior between the Zirconia core specimens and the e.max core specimens that have the same veneering ceramic thickness and brand during the same firing cycles , that make the core ma real effecting factor on color of all ceramic system

Group B2 (e.max core with 1mm veneering ceramic thickness):
The results of this group (table 5) showed a relatively low percentage of agreement when comparing the samples firing cycle inside the sub much color changes, happened especially after the firing that agree with showed a different color changes behavior from the less veneering ceramic thickness 0.5mm e.max core (Group B1).

Restorative Dentistry
Percentage of agreement between the 3 2. Percentage of agreement between the 3 3. Percentage of agreement between the 5

(e.max core with 0.5mm veneering
The results of this group (table 4) showed a relatively high percentage of agreement when comparing the samples inside the subgroup after each firing interval and in comparing with other subgroup , which means less color changes firing .theresults also showed that different color changes behavior between the Zirconia core specimens and the e.max core specimens that have the same veneering ceramic thickness and brand during the same firing cycles , that make the core ma real effecting factor on color of all ceramic system Shade results of group B1 (e.max core with veneering ceramic thickness 0.5 mm) 1. Percentage of agreement between the 3 2. Percentage of agreement between the 3

Group B2 (e.max core with 1mm veneering
The results of this group (table 5) showed a relatively low percentage of agreement when comparing the samples after the 3 firing cycle inside the subgroup, which means much color changes, happened especially after the firing that agree with (11) .These results showed a different color changes behavior from g ceramic thickness 0.5mm (Group B1).
Percentage of agreement between the 3 rd and 5 2. Percentage of agreement between the 3 rd and 7 3. Percentage of agreement between the 5 th and 7

(e.max core with 0.5mm veneering
The results of this group (table 4) showed a relatively high percentage of agreement when comparing the samples inside the subgroup after each firing interval and in comparing with other subgroup , which means less color changes the results also showed that different color changes behavior between the Zirconia core specimens and the e.max core specimens that have the same veneering ceramic thickness and brand during the same firing cycles , that make the core material a real effecting factor on color of all ceramic system Shade results of group B1 (e.max core with veneering ceramic thickness 0.5 1. Percentage of agreement between the 3 rd and 5 en the 3 rd and 7 3. Percentage of agreement between the 5 th and 7

Group B2 (e.max core with 1mm veneering
The results of this group (table 5) showed a relatively low percentage of agreement when after the 3 rd and the 5 group, which means much color changes, happened especially after the .These results showed a different color changes behavior from g ceramic thickness 0.5mm with and 5 th and 7 th and 7 th

(e.max core with 0.5mm veneering
The results of this group (table 4) showed a relatively high percentage of agreement when comparing the samples inside the subgroup after each firing interval and in comparing with other subgroup , which means less color changes the results also showed that different color changes behavior between the Zirconia core specimens and the e.max core specimens that have the same veneering ceramic thickness and brand during the terial a real effecting factor on color of all ceramic system Shade results of group B1 (e.max core with veneering ceramic thickness 0.5 and 5 th and 7 th and 7 th

Group B2 (e.max core with 1mm veneering
The results of this group (table 5) showed a relatively low percentage of agreement when and the 5 th group, which means much color changes, happened especially after the .These results showed a different color changes behavior from with Table 1.Percentage of agreement between the 3 firing is 12.5 %.
2. Percentage of agreement between the 3 firing is 12.5 %.
3. Percentage of agreement between the 5 firing is 100 %.

Group B3 ( ceramic thickness):
zero samples inside the group after firing also zero when comparing the samples af 3 rd color changes, happened especially after the 5 firing when increasing the firing till 7 agreement between the samples after the 5 the 7 different color changes behavior from the less veneering ceramic thickness 0.5mm and 1 mm (Group group with same veneering ceramic Table 6 1. Percentage of agreement between the 3 firing is 0 %. 2. Percentage of agreement between the 3 firing is 0 %. 3. Percentage of agreement between the 5 firing is 100 %.

June 2016
Table 5: Shade results of group B core with ceramic thickness 1 mm) 1. Percentage of agreement between the 3 firing is 12.5 %.
2. Percentage of agreement between the 3 firing is 12.5 %.
3. Percentage of agreement between the 5 firing is 100 %.

Group B3 ( emax ceramic thickness):
The results of this group (table zero percentage of agreement when comparing the samples inside the group after firing interval, the percentage of agreement was also zero when comparing the samples af rd and the 7 th color changes, happened especially after the 5 firing and there is no changes happened in color when increasing the firing till 7 agreement between the samples after the 5 the 7 th firing cycles) fferent color changes behavior from the less veneering ceramic thickness 0.5mm and 1 mm (Group B1 and Group group with same veneering ceramic

Shade results of group B core with ceramic thickness 1 mm)
1. Percentage of agreement between the 3 firing is 12.5 %. 2. Percentage of agreement between the 3 firing is 12.5 %. 3. Percentage of agreement between the 5 firing is 100 %.

emax core with 2mm veneering ceramic thickness):
The results of this group (table percentage of agreement when comparing the samples inside the group after interval, the percentage of agreement was also zero when comparing the samples af th firing cycle, color changes, happened especially after the 5 and there is no changes happened in color when increasing the firing till 7 agreement between the samples after the 5 firing cycles).These results showed a fferent color changes behavior from the less veneering ceramic thickness 0.5mm and 1 mm 1 and Group B2) and even from Zirconia group with same veneering ceramic Shade results of group B2 (e.max core with ceramic thickness 2 mm) 1. Percentage of agreement between the 3 2. Percentage of agreement between the 3

Percentage of agreement between the 5
ing is 100 %.

The effect
Shade results of group B2 core with ceramic thickness 1 mm) 1. Percentage of agreement between the 3 2. Percentage of agreement between the 3

Percentage of agreement between the 5 core with 2mm veneering
The results of this group (table 6) showed a percentage of agreement when comparing the samples inside the group after the 3 rd and the interval, the percentage of agreement was also zero when comparing the samples af firing cycle, which means much color changes, happened especially after the 5 and there is no changes happened in color when increasing the firing till 7 times (100 agreement between the samples after the 5 .These results showed a fferent color changes behavior from the less veneering ceramic thickness 0.5mm and 1 mm and even from Zirconia group with same veneering ceramic thicknesses.

Shade results of group B2 (e.max core with ceramic thickness 2 mm)
1. Percentage of agreement between the 3 2. Percentage of agreement between the 3

Percentage of agreement between the 5
The effect of (e.max core with ceramic thickness 1 mm) 1. Percentage of agreement between the 3 rd and 5 th 2. Percentage of agreement between the 3 rd and 7 th 3. Percentage of agreement between the 5 th and 7 th core with 2mm veneering ) showed a percentage of agreement when comparing the and the 5 th interval, the percentage of agreement was also zero when comparing the samples after the means much color changes, happened especially after the 5 th and there is no changes happened in color (100% of agreement between the samples after the 5 th and .These results showed a fferent color changes behavior from the less veneering ceramic thickness 0.5mm and 1 mm and even from Zirconia thicknesses. Shade results of group B2 (e.max core with ceramic thickness 2 mm) 1. Percentage of agreement between the 3 rd and 5 th 2. Percentage of agreement between the 3 rd and 7 th 3. Percentage of agreement between the 5 th and 7 th of Group C1 control group (metal core with 0.5mm veneering ceramic thickness): The results of this group (table 7) showed 100 percentage of agreement when comparing the samples inside the group after each firing interval, which means no color firing.The comparison between the group C1 and groups A1, B1 showed that porcelain fused to metal system is not sensitive to firing.
3. Percentage of agreement between the 5 firing is 100 %.

Group C2 veneering ceramic
The results of this group (table 8) showed a relatively high percentage of agreement when comparing the samples inside the group after each firing interval, which means happened after firing.The results of this group (table 7) showed 100 percentage of agreement when comparing the samples inside the group after each firing interval, which means no color firing.The comparison between the group C1 and groups A1, B1 showed that porcelain fused to metal system is not sensitive to firing.
: Shade results of group A1 (Zirconia core with ceramic thickness 0.5 mm) 1. Percentage of agreement between the 3 firing is 100 %. 2. Percentage of agreement between the 3 firing is 100 %. 3. Percentage of agreement between the 5 firing is 100 %.

Group C2 control group veneering ceramic th
The results of this group (table 8) showed a relatively high percentage of agreement when comparing the samples inside the group after each firing interval, which means happened after firing.The results of this group (table 7) showed 100 percentage of agreement when comparing the samples inside the group after each firing interval, which means no color changes happened after firing.The comparison between the group C1 and groups A1, B1 showed that porcelain fused to metal system is not sensitive to firing.The results of this group (table 7) showed 100 percentage of agreement when comparing the samples inside the group after each firing interval, changes happened after firing.The comparison between the group C1 and groups A1, B1 showed that porcelain fused to metal system is not sensitive to firing.
Shade results of group A1 (Zirconia core with ceramic thickness 0.5 mm) of agreement between the 3 rd and 5 2. Percentage of agreement between the 3 rd and 7 3. Percentage of agreement between the 5 th and 7

(metal core with 1mm
The results of this group (table 8) showed a relatively high percentage of agreement when comparing the samples inside the group after each color changes, Shade results of group C2 (metal core with ceramic thickness 1 mm) 1. Percentage of agreement between the 3 rd and 5 2. Percentage of agreement between the 3 rd and 7 3. Percentage of agreement between the 5 th and 7

Group C1 control group (metal core with
The results of this group (table 7) showed 100 percentage of agreement when comparing the samples inside the group after each firing interval, changes happened after firing.The comparison between the group C1 and groups A1, B1 showed that porcelain fused to Shade results of group A1 (Zirconia and 5 th and 7 th and 7 th

(metal core with 1mm
The results of this group (

Group C3 control group ( veneering ceramic thickness
The results of this group (table zero percentage of agreement when comparing the samples inside the group after interval and after 3 means the most dramatically happened after a different color changes behavior from the less veneering ceramic thickness 0.5mm and 1 mm (Group C1 and Group groups (Zirconia and e.max).

DISCUSSION
The effect of veneering ceramic brand on shade and reflection Two types of veneering ceramic (IPS classic dentine ceramics and IPS e.max Ceram dentine) used in this study, the metal group veneered with IPS classic have a different behavior of color changes from the e.max and Zirconia groups veneered with IPS e.max Ceram which they are undergo a relatively similar behavior of changes .that is mean color shade and even the reflection value affected by the veneering ceramic brand , IPS e.max Ceram is glass ceramic filled with fluorapatite crystals which does not contain feldspar or leucite that make it more translucent and the IPS classic (metal ceramic) is a feldspar is more opaque .These differences in optical properties affect the results of this study that is agreed with Antonson (11) .

Group C3 control group (metal veneering ceramic thickness
The results of this group (table percentage of agreement when comparing the samples inside the group after and after 3 rd and 7 th the most dramatically the 5 th firing.These results showed a different color changes behavior from the less veneering ceramic thickness 0.5mm and 1 mm 1 and Group C2) groups (Zirconia and e.max).

Shade results of group C2 (metal core with ceramic thickness 2 mm)
1. Percentage of agreement between the 3rd and 5th firing is 0 %. 2. Percentage of agreement between the 3rd and 7th firing is 0 %.
Percentage of agreement between the 5th and 7th firing is 100 %.

The effect of veneering ceramic brand on shade and reflection
Two types of veneering ceramic (IPS classic dentine ceramics and IPS e.max Ceram dentine) used in this study, the results showed that the metal group veneered with IPS classic have a different behavior of color changes from the e.max and Zirconia groups veneered with IPS e.max Ceram which they are undergo a relatively similar behavior of changes .that is mean color shade and even the reflection value affected by the veneering ceramic brand , IPS e.max Ceram is glass ceramic filled with fluorapatite crystals which does not contain feldspar or leucite that make it more translucent and the IPS classic ) is a feldspar is more opaque .These differences in optical properties affect the results of this study that is Heffernan (5) The effect metal core with 2mm veneering ceramic thickness): The results of this group (table 9) showed a percentage of agreement when comparing the samples inside the group after 3 rd and 5 th firing interval, the most dramatically changes firing.These results showed a different color changes behavior from the less veneering ceramic thickness 0.5mm and 1 mm 2) and from groups (Zirconia and e.max).results showed that the metal group veneered with IPS classic have a different behavior of color changes from the e.max and Zirconia groups veneered with IPS e.max Ceram which they are undergo a relatively similar behavior of changes .that is mean color shade and even the reflection value affected by the veneering ceramic brand , IPS e.max Ceram is glass ceramic filled with fluorapatite crystals which does not contain feldspar or leucite that make it more translucent and the IPS classic

Shade results of group C2 (metal
) is a feldspar-based ceramic which is more opaque .These differences in optical properties affect the results of this study that is (5) , Uludag The effect of core with 2mm ) showed a percentage of agreement when comparing the and 5 th firing firing interval, which in color firing.These results showed a different color changes behavior from the less veneering ceramic thickness 0. results showed that the metal group veneered with IPS classic have a different behavior of color changes from the e.max and Zirconia groups veneered with IPS e.max Ceram which they are undergo a relatively similar behavior of changes .that is mean color shade and even the reflection value affected by the veneering ceramic brand , IPS e.max Ceram is glass ceramic filled with fluorapatite crystals which does not contain feldspar or leucite that make it more translucent and the IPS classic based ceramic which is more opaque .These differences in optical properties affect the results of this study that is (10) and of

2 .
Percentage of agreement between the 3 firing is 87.5 %. 3. Percentage of agreement between the 5 firing is 87.5 %. ): metal core of 1 mm veneering ceramic thickness 0.5mm.control group): metal core of 1 mm veneering ceramic thickness 1mm (control group): metal core of 1 mm veneering ceramic thickness 2 mm.All the specimens were measured 3 times interval ( 3 firings, 5 firings and 7 firings).Each type of specimens certain temperature as the manufacturer Easyshade Advance 4.0 Zirconia core with ceramic thickness 0.5 mm) 1. Percentage of agreement between the 3 2. Percentage of agreement between the 3 3. Percentage of agreement between the 5 subgroup contains (8) specimens.These metal core of 1 mm 0.5mm.metal core of 1 mm veneering ceramic thickness 1mm.metal core of 1 mm 2 mm.

5 ,
Shade test Easyshade Advance 4.0 results:Zirconia core with 0.5mmThe results of this group (table1) showed a relatively high percentage of agreement when comparing the samples inside the group after each means less color changes Shade results of group A1 (Zirconia core with ceramic thickness 0.5 mm) 1. Percentage of agreement between the 3 rd and 5 2. Percentage of agreement between the 3 rd and 7 3. Percentage of agreement between the 5 th and 7 These metal core of 1 mm metal core of 1 mm metal core of 1 mm after 3 firings, 5 firings and 7

1 .of 1 .
Percentage of agreement between the 3 rd and 5 th 2. Percentage of agreement between the 3 rd and 7 th 3. Percentage of agreement between the 5 th and 7 th mm veneering ) showed a relatively low percentage of agreement when comparing the samples inside the group after each firing interval, which means much color changes, firing.These results showed a different color changes behavior from the less veneering ceramic thickness 0.5mm Shade results of group A3 (Zirconia core with ceramic thickness 2 mm) Percentage of agreement between the 3 firing is 25 %. 2. Percentage of agreement between the 3 firing is 12.5 %. 3. Percentage of agreement between the 5 firing is 87.5 %.

Table 4 :
Shade results of group B1 (e.max core with veneering ceramic thickness 0.5 1. Percentage of agreement between the 3 firing is 87.5 %. 2. Percentage of agreement betwe firing is 75 %.3. Percentage of agreement between the 5 firing is 62.5 %. Shade results of group A1 (Zirconia core with ceramic thickness 0.5 mm) of agreement between the 3 2. Percentage of agreement between the 3 3. Percentage of agreement between the 5 control group (metal core with 1mm thickness): The results of this group (table 8) showed a relatively high percentage of agreement when comparing the samples inside the group after each firing interval, which means no happened after firing.Shade results of group C2 (metal core with ceramic thickness 1 mm) 1. Percentage of agreement between the 3 2. Percentage of agreement between the 3 3. Percentage of agreement between the 5 Group C1 control group (metal core with 0.5mm veneering ceramic thickness):

core with ceramic thickness 2 mm) 1 .
Percentage of agreement between the 3rd and 2. Percentage of agreement between the 3rd and Percentage of agreement between the 5th and The effect of veneering ceramic brand on Two types of veneering ceramic (IPS classic dentine ceramics and IPS e.max Ceram dentine) 5mm and 1 mm and from the other Shade results of group C2 (metal core with ceramic thickness 2 mm) 1. Percentage of agreement between the 3rd and 2. Percentage of agreement between the 3rd and Percentage of agreement between the 5th and The effect of veneering ceramic brand on Two types of veneering ceramic (IPS classic dentine ceramics and IPS e.max Ceram dentine)

Table 6 : Shade results of group B2 (e.max core with ceramic thickness 2 mm)
3. Percentage of agreement between the 5 ing is 100 %.

Table 8 core with ceramic thickness 1 mm)
h College

Table 8 : Shade results of group C2 (metal core with ceramic thickness 1 mm)
h

Table 1 .
Percentage of agreement between the 3rd and 5th firing is 0 %. 2. Percentage of agreement between the 3rd and 7th firing is 0 %.

Table 9 : Shade results of group C2 (metal core with ceramic thickness 2 mm)
1. Percentage of agreement between the 3rd and 5th firing is 0 %. 2. Percentage of agreement between the 3rd and 7th firing is 0 %. 3. Percentage of agreement between the 5th and 7th firing is 100 %.