ORIGINAL CONTRIBUTIONS

Effect of imaging powder andCAD/CAM stone types on themarginal gap of zirconia crowns

ABSTRACT

Objective. To compare the marginal gap using different types of diestones and titanium dies with and without powders for imaging.Methods. A melamine tooth was prepared and scanned using a labora-

Tariq F. Alghazzawi, PhD; Khalid H.Al-Samadani, PhD; Jack Lemons, PhD;Perng-Ru Liu, MS; Milton E. Essig, DMD;Alfred A. Bartolucci, PhD; Gregg M.Janowski, PhD

tory 3-shape scanner to mill a polyurethane die, which was duplicated intodifferent stones (Jade, Lean, CEREC) and titanium. Each die was sprayedwith imaging powders (NP, IPS, Optispray, Vita) to form 15 groups. Ten ofeach combination of stone/titanium and imaging powders were used to millcrowns. A light-bodied impression material was injected into the intagliosurface of each crown and placed on the corresponding die. Each crown wasremoved, and the monophase material was injected to form a monophasedie, which was cut into 8 sections. Digital images were captured using astereomicroscope to measure marginal gap. Scanning electron microscopywas used to determine the particle size and shape of imaging powders andstones.Results. Marginal gaps ranged from mean (standard deviation) 49.32to 91.20 micrometers (3.97-42.41 mm). There was no statistical difference(P > .05) in the marginal gap by any combination of stone/titanium andimaging powders. All of the imaging powders had a similar size and roundedshape, whereas the surface of the stones showed different structures.Conclusions. When a laboratory 3-shape scanner is used, all imagingpowders performed the same for scanning titanium abutments. However,there was no added value related to the use of imaging powder on die stone.It is recommended that the selection of stone for a master cast be based onthe physical properties.Practical Implications. When a laboratory 3-shape scanner is used, theimaging powder is not required for scanning die stone. Whenever scanningtitanium implant abutments, select the least expensive imaging powder.Key Words. Scanner; zirconia; marginal fit; impression; imaging powder.JADA 2015:146(2):111-120

http://dx.doi.org/10.1016/j.adaj.2014.10.006

M argin adaptation is animportant parameter in thelongevity of an indirectrestoration on a natural

tooth because large marginal gaps mayinitiate microleakage1 and plaque depo-sition,2 which can lead to recurrentcaries.3 Generally, increasing the numberof units in a fixed partial denture makesmarginal adaptation to the anchoringteeth a challenge, and it may contributeto larger marginal gaps.4

Microleakage as related to recurrentcaries is not a concern for the adapta-tion of an implant prosthesis to theabutment, but it is imperative to have aprecise adaptation (passive fit), espe-cially for a multiunit prosthesis (implantbars). Misfit may lead to loosening,bending, and fracturing of the prostheticparts as well as increased bone lossaround implants, which will contributeto implant failure.5 Furthermore, themisfit can be exaggerated by higherocclusal forces.6 Fernández and col-leagues7 reported that there was a

Dr. Alghazzawi is a visiting scientist, Department of Materials Science and Engineering, School of Engineering, University of Alabama at Birmingham,Birmingham, AL, and an assistant professor, Department of Prosthetic Dental Sciences, College of Dentistry, Taibah University, Madina, Saudi Arabia.Address correspondence to Dr. Alghazzawi, PO Box 51209, Riyadh, 11543, Saudi Arabia, e-mail drtariq05@gmail.com.Dr. Al-Samadani is an associate professor and vice dean, Graduate Studies and Research, College of Dentistry, Taibah University, Madina, SaudiArabia.Dr. Lemons is a professor, Department of Behavioral & Population Sciences Division of Biomaterials, School of Dentistry, University of Alabama atBirmingham, Birmingham, AL.Dr. Liu is a professor and chair, Department of Restorative Sciences, School of Dentistry, University of Alabama at Birmingham, Birmingham, AL.Dr. Essig is a professor emeritus, Department of Restorative Sciences, School of Dentistry, University of Alabama at Birmingham, Birmingham, AL.Dr. Bartolucci is a professor emeritus, Department of Biostatistics, School of Public Health, University of Alabama at Birmingham, Birmingham, AL.Dr. Janowski is a professor, Department of Materials Science and Engineering, and an associate provost, Assessment and Accreditation, University ofAlabama at Birmingham, Birmingham, AL.

Copyright ª 2015 American Dental Association. All rights reserved.

JADA 146(2) http://jada.ada.org February 2015 111

TABLE 1

Commercial names and manufacturers of materialsand equipment.MATERIALS/EQUIPMENT COMMERCIAL NAME COMPANY NAME

Materials Jade stone (conventional stone) Whip Mix Corporation

Lean Rock XL5 (CAD/CAMtype IV stone)

Whip Mix Corporation

CEREC stone BC (CAD/CAMtype IV stone)

Sirona Dental Systems GmbH

IPS contrast powder(imaging powder)

Ivoclar Vivadent Inc

Optispray powder(imaging powder)

Sirona Dental Systems GmbH

Vita powder scan powder(imaging powder)

Vident

Polyurethane (master die) Wieland Dental þ TechnikGmbH & Co KG

Argen (monolithic zirconiacrown)

Argen Corporation

Duplicating material (Gingi-Pak,SuperBody 530)

Gingi-Pak, A Division ofBelport Co Inc

Melamine tooth (artificial tooth) Model R861; ColumbiaDentoform Corp

Bard-Parker Aspen Surgical Products

Light body (impression material) Aquasil Ultra LV Smart WettingRegular Set Impression Material,Dentsply International Inc

Monophase (impression material) Aquasil Ultra Monophase SmartWetting Regular Set ImpressionMaterial, Dentsply International Inc

Equipment Three-shape scanner(dental scanner)

Model D900, 3Shape

Parallelometer Parrallel-A-Prep, Dentatus USA Ltd

Third-party milling center Perryman Company Corporate

Roland (milling unit) Roland DGA Corporation

Scanning electron microscope Quanta FEG 650, FEI CorporateHeadquarters

Software Software used to measuremarginal gap

Image-Pro Plus version 7.0 MediaCybernetics Inc

ABBREVIATION KEY. Al: Aluminum. Au: Gold. C: Carbon.CAD/CAM: Computer-aided design and computer-aidedmanufacturing. Cu: Copper. Fe: Iron. K: Potassium. LED:Light-emitting diode. O: Oxygen. Pd: Palladium. SEM: Scan-ning electron microscope or scanning electron microscopy.TiO2: Titanium dioxide. Zn: Zinc.

ORIGINAL CONTRIBUTIONS

strong correlation between the roughness on the mat-ing surfaces of cobalt–chromium alloy abutments andthe microgap width, where the milled abutmentspossessed a connection geometry with defined edgesand a mean roughness of 29 micrometers. Sinteredabutments showed a blurred but functional connectionwith a roughness of 115 mm, and cast abutments showeda connection with a loss of axial symmetry and aroughness of 98 mm. Furthermore, significant differ-ences in the marginal fit of single-implant-retainedcrowns were found among different digitizing tech-niques and the presence of antirotational features.8

Santos and colleagues9 reported that the clip materialand the cross section of the bar framework influencedthe stress distribution in overdentures retained by abar–clip system that could influence vertical misfit.Additionally, there was a higher marginal gap for atitanium abutment with metal framework (79.4 mm)

112 JADA 146(2) http://jada.ada.org February 2015

compared to a zirconia abutmentwith zirconia framework (51.4mm).10 Other studies have devel-oped a method for more accurateorthogonal radiographs11 tomonitor the changes in bonearchitecture associated withprosthetic misfit around theconnection of implant abut-ments, with the intention ofenhancing the longevity of theimplants through a decrease inthe number of failures.

The marginal gap can beaffected by several other factors.For example, better marginal fitvalues were obtained for zirconia-based and lithium disilicatecrowns when milled with anEverest computer-aided designand computer-aided manufac-turing (CAD/CAM) techniquecompared to the CEREC inLabsystem.12 Katsoulis and col-leagues13 reported that CAD/CAM titanium bars had a higherprecision of fit than zirconia barsand soldered gold bars. Asavapa-numas and Leevailoj14 reportedthat tooth preparation with a 5-millimeter abutment finish linecurvature for ceramic restorations(Cercon and Lava zirconia cop-ings) exhibited greater marginalgap width values compared to 3-mm and 1-mm abutment finishline curvatures. A supragingivalmargin design was recommended

to reduce the degree of finish line curvature of theabutment teeth. However, there was no statistical dif-ference in the marginal fit of e.max crowns fabricated bypressing when compared to a CAD/CAM fabricationtechnique.15 Additionally, there was a comparablemarginal fit in the CAD/CAM-generated 4-unit zirconiafixed dental prostheses fabricated from either a digitalimpression (Lava COS system) or a conventionalimpression (polyether impression of the master modelwith Impregum).16

ADVANCED SETTINGSThe properties of the die interface are specified under Advanced Settings.

(1) Cement gap is the amount of offset in the area of the margin line.(2) Extra cement gap is the amount of offset in the upper part of the interface.

1

1

2

2

4

3

3

4

Figure 1. The offset areas at margin line and the upper area of interface during designing of dental restoration.Comp.: Composition. Dist.: Distance. mm: Millimeters.

ORIGINAL CONTRIBUTIONS

With advanceddental scanners, themaster die can be scan-ned and the restorationor pattern milled from asolid block of ceramic,metal, or resin. Thistechnology may savetime in the fabricationof the restorationbecause there is norequirement for manualprocessing of wax pat-terns with subsequentcasting or pressing ofceramic to the die.Additionally, it has beendocumented that thedigital impression canbe a substitute for aconventional impres-sion.17 The manufac-turers of conventionaldental scanners recom-mend the application ofimaging powder to

TABLE 2

Classification of experimental groupsaccording to powder and die materialto form 15 groups (10 samples pergroup) to fabricate 150 zirconiacrowns.DIE MATERIAL POWDER TYPE ABBREVIATION OF DIE

MATERIAL/POWDER TYPE

CEREC Stone No powder CER/NP

CEREC Stone IPS contrast powder CER/IPS

CEREC Stone Optispray powder CER/Opti

CEREC Stone Vita powder CER/Vita

Lean RockXL5 Stone

No powder Lean/NP

Lean RockXL5 Stone

IPS contrast powder Lean/IPS

Lean RockXL5 Stone

Optispray powder Lean/Opti

Lean RockXL5 Stone

Vita powder Lean/Vita

Jade Stone No powder Jade/NP

Jade Stone IPS contrast powder Jade/IPS

Jade Stone Optispray powder Jade/Opti

Jade Stone Vita powder Jade/Vita

Titanium IPS contrast powder Ti/IPS

Titanium Optispray powder Ti/Opti

Titanium Vita powder Ti/Vita

enhance the reflectivity of a traditional stone. In thisregard, a special CAD/CAM stone has been released inthe dental market as an alternative to the technique ofspraying an imaging powder directly on conventionalstone. Studies of the laboratory 3-shape scanner (modelD900) using a blue light-emitting diode (LED) lightwith multiple cameras have shown more detailedcolored images where the scan of the master cast,composed of any stone material, did not necessitate theuse of imaging powder, except for titanium abutments.

However, marginal adaptation has not been sys-tematically investigated relative to the effects of sprayingpowder on conventional stone, special CAD/CAMstone, or a combination of both stone and powder.Furthermore, many propose that there is a tremendousneed to have a passive fit of a multiunit prosthesis ontitanium abutments, and thus a possible need exists forspraying with imaging powders before scanning. Re-views indicate that the effect of powder compositionand particle shape on the marginal gap has not beenstudied in detail, especially when considering implantabutments.

One of the most common chemical compounds inthe composition of imaging powder is titanium dioxide(TiO2), which is an opaque powder that reflects lightand minimizes the light scattering from the substrate.Studies have shown that both the imaging powderand substrate might affect marginal integrity, andone study reported that there was a difference in the

JADA 146(2) http://jada.ada.org February 2015 113

Lingual Surface

Monophase Die Mesial SurfaceDistal Surface

Buccal Surface1 2

3

4

56

7

8

Figure 2. The locations of the marginal gap measurements: 2 measurements per surface (mesial, distal, buccal,and lingual) for the total of 8 measurements per sample.

TABLE 3

Mean, standard deviation, and 95%confidence intervals of mean for15 experimental groups.GROUP* MEAN

(MICROMETERS)STANDARDDEVIATION

LOWER95%MEAN

UPPER95%MEAN

CER/NP 58.08 15.25 47.17 68.99

CER/IPS 91.20 39.10 63.23 119.17

CER/Opti 65.64 23.56 48.79 82.50

CER/Vita 71.69 31.17 49.39 93.99

Lean/NP 63.46 21.75 47.90 79.02

Lean/IPS 62.29 19.29 48.48 76.09

Lean/Opti 64.45 19.41 50.57 78.33

Lean/Vita 76.12 23.26 59.48 92.76

Jade/NP 58.81 13.44 49.19 68.42

Jade/IPS 66.68 21.64 51.21 82.16

Jade/Opti 76.54 42.41 46.21 106.88

Jade/Vita 49.43 10.15 42.17 56.69

Ti/IPS 84.22 38.37 56.77 111.66

Ti/Opti 63.13 7.83 57.53 68.74

Ti/Vita 60.84 3.97 58.00 63.68

* See Table 2 for group definitions.

ORIGINAL CONTRIBUTIONS

marginal gap when Vita imaging powder was sprayedon a natural tooth and resin die.18 Another studyshowed that marginal adaptation was not affected bydifferent brands of imaging powders.19

The objectives of this study were to comparethe marginal gap of conventional stone to specialCAD/CAM stones with no use of imaging powder;study the effect of different imaging powders on the

114 JADA 146(2) http://jada.ada.org February 2015

marginal gap of tita-nium and a selectedstone; and study theeffect of the same im-aging powder on themarginal gap with atitanium die and diff-erent die stones. Thehypotheses were asfollows: there is a dif-ference in the marginalgap between conven-tional stone and specialCAD/CAM stoneswithout the use of im-aging powders; there isan effect of differenttypes of imaging pow-ders on the marginalgap of titanium andthe same stone type;and there is an effect of

the same imaging powder type on the marginal gap oftitanium and different types of stones.

METHODSSample preparation and fabrication. A melaminemandibular left first molar was prepared for placementof zirconia crowns using a parallelometer to ensureaccurate replication of the preparation parameters. Thepreparation design included a 1.0-mm rounded shoul-der around the entire circumference, an occlusogingivalheight of 4 mm, and a 12� total convergence angle. Anocclusal reduction of 1.5 mm was prepared in the areaof the occlusal surface. The prepared melamine toothwas scanned and designed using a laboratory 3-shapescanner (model D900) to mill a resin die using poly-urethane material with the Roland milling machine tofabricate a polyurethane master die. The commercialnames of all materials and equipment used in this study,along with the corresponding manufacturers, are listedin Table 1.

The polyurethane die was duplicated into 3 typesof stone dies and one titanium die. The stone dies wereduplicated by creating a mold of the original milledpolyurethane die and then pouring the mold using theprescribed die stone. The titanium die was milled bya third-party milling center using the raw STL file. Eachdie was then scanned with the 3-shape scanner. Thedental restoration was designed to be a fully contouredcrown with 35 mm offset in the area of the margin lineand 65 mm offset in the upper area of the interface,as illustrated in Figure 1. The dies were scanned againafter spraying with a uniform method: the opaquingpowder was sprayed to obtain a uniform layer with anoptimal thickness of 32 mm to visualize the internal line

TYPE OF DIE MATERIAL

MEA

N M

AR

GIN

AL

GA

P (

MIC

RO

MET

ERS)

No Powder IPS Contrast Powder

Optispray Powder Vita Powder

Lean RockCEREC Stone Jade Stone Titanium0

10

20

30

40

50

60

70

80

90

100

Figure 3. The combination effect of different imaging powders and die materials on the mean marginal gaps.The error bars signify the upper and lower 95% confidence intervals.

TABLE 4

ORIGINAL CONTRIBUTIONS

angles of the preparationand to define the cavosur-face margin.20 To ensureaccuracy and uniformpowder distribution, thecannula tip of the disper-sant was held 1 cm fromthe die surface at a 45�angle to the long axis ofthe die while slowlydispensing the powder in arotating manner to avoidclumping. This ensuredeven distribution, resultingin a uniform opacity of thedie surfaces, as well asuniformity of the cavosur-face margin and the inter-secting planes of thepreparation. The visualcriteria of homogenousopaqueness, along withdefined margins and lineangles, were confirmed byan optical scan of the finalpowder application untilan image was obtained thatwas focused and clear, withvisible corners and mar-

Two-way analysis of variance analysisof marginal gap by die stone andimaging powder.*SOURCE DF† TYPE III

SUM OFSQUARES

MEAN SQUARE F VALUE PVALUE

Stone 3 1557.900161 519.300054 0.81 .4924‡

Powder 3 4812.445257 1604.148419 2.49 .0627‡

SOURCE DF SQUARES MEAN SQUARE F VALUE PVALUE

Model 6 6504.54791 1084.09132 1.68 .1293

Error 143 92113.63373 644.15128

CorrectedTotal

149 98618.18164

* Marginal gap assessed by die stone for 4 levels (CER, Lean, Jade, Ti)and imaging powder for 4 levels (NP, IPS, Opti, Vita).

† DF: Degree of freedom.‡ No statistical difference among the 15 groups.

gins, without powder dark areas or spike, using 3different types of imaging powders to form 15 groups (10samples per group), except for the titanium die, whichwas not scanned without the use of imaging powder.The digital file of each optical impression was trans-ferred to the Roland milling unit, and 150 monolithiczirconia crowns were milled from presintered blocks,then sintered according to the manufacturer’s instru-ctions. The distributions of the 15 groups using acombination of 3 types of die stones and the titaniumdie with 3 types of imaging powders are illustrated inTable 2.

Replica technique and gap measurement. The pre-pared tooth had a uniform defined cavosurface marginand 12� of taper for relative parallelism of the axialwalls in order to comply with acceptable clinical stan-dards for resistance form. The crowns were milled witha thin die spacer thickness of 35 mm. The fit of eachcrown on the corresponding die was verified using 2different colors (green and blue) of pinpoint permanentmarkers. The blue marker was used to mark a point onthe die of the corresponding crown on the buccal side,and the green marker was used in the same way on thelingual side. A light-bodied impression material wasinjected into the intaglio surface of each crown, and therestoration was then positioned on the correspondingdie with the same procedure as that described in the

literature14,21,22 to control the amount of injected ma-terial into the intaglio surface of the crown. The crownwas loaded with a force of 50 Newtons directed alongthe occlusal aspect for 5 minutes (the setting time of themonophase impression material) and positioned toalign exactly with the predetermined reference points

JADA 146(2) http://jada.ada.org February 2015 115

Figure 4. Scanning electron microscopy images for the microstructure of different imaging powders(1000�) and stones (10,000�). The IPS contrast powder (A), Optispray powder (B), and Vita powder (C)have rounded particles with similar particle size. However, the CEREC stone (D) has particles bondedtogether, whereas Lean Rock stone (E) and Jade stone (F) have long crystals.

ORIGINAL CONTRIBUTIONS

on the buccal and lingual surfaces. This was then fol-lowed by full seating of the zirconia crowns on theirrespective dies by using a digital caliper to stabilize thecrown until the distance between the crown and diecould not be changed, and a tine of a sharp explorerwas used to ensure complete seating of the cervicalinterfacial crown–die margins while confirming theexact alignment of the previously placed referencemarks, so as to thereby control the amount of light-bodied impression expressed at the margins for all

116 JADA 146(2) http://jada.ada.org February 2015

samples of the study. Aftercomplete polymerization of thelight body material, the crownwas removed from the corre-sponding die. The light bodymaterial, which represented themarginal misfit, remainedattached to the intaglio surface ofthe crown. Monophase impres-sion material was then injectedon top of the light body in thecrown. The monophase die wasthereby fabricated and separatedfrom the crown after completepolymerization. The monophasedie was sectioned perpendicularto its surface with a sharp No. 25Bard-Parker blade into 8 sec-tions: 2 buccal, 2 lingual, 2mesial, and 2 distal (Figure 2).The blade was changed every5 samples to maintain thesharpness of the blade for precisecutting of the monophase die.Digital images of each section ofthe monophase die werecaptured using a stereomicro-scope at �40 magnification. Im-age analysis software was used tomeasure the marginal gap oneach image. Therefore, a total of8 measurements were made foreach crown, then averaged toobtain the mean marginal gapvalues.

Scanning electron micro-scopy. Scanning electron micro-graphs (SEM) were obtainedusing a high-vacuum mode ona Quanta SEM device with anaccelerating voltage of 30 kilo-volts. The samples were fixed toaluminum sample holders andthen sputter coated with gold–palladium. The sputter coaterused was a Denton Vacuum

Desk II sputtering system. This was done to determinethe particle size and shape for each imaging powderand stone. Energy-dispersive spectroscopy was con-ducted for elemental analysis of each imaging powder.

Statistical analysis. No power analysis was per-formed, and the sample size was based on the previousliterature.23

Means, standard deviations, and 95% confidenceintervals of the mean of the 15 specimens for eachcombination of stone type and powder were calculated.

Figure 5. Scanning electron microscopy images for the microstructure of the titanium die at 2different magnifications: 1000� (A) and 10,000� (B). The titanium die has a typically metallicmachined surface.

ORIGINAL CONTRIBUTIONS

The primary data analysis used a2-factor analysis of variancemodel, including main effectterms for stone, with 4 levels(CER, Lean, Jade, Ti) and pow-der, with 4 levels (NP, IPS, Opti,Vita). If the hypothesis wasrejected at the .05 level, then thepost hoc test was used to test thepairwise comparisons to deter-mine which groups were statisti-cally different from one anotherat P ¼ .05. The software used wasSAS version 9.3 (SAS Institute,Cary, NC).

RESULTSMeans, standard deviations, and

upper and lower 95% confidence intervals for the meanvalues of the margin gaps for the 15 groups are shown inTable 3 and Figure 3. Marginal gaps ranged from mean(SD) 49.32 to 91.20 mm (3.97-42.41 mm). There were nosignificant main effects or interactions (P > .05) in2-way analysis of variance analysis. No post hoc testswere performed because the initial results were notsignificant (Table 4).

The SEM micrographs of the imaging powders andstone surfaces are shown in Figure 4. The imagingpowder particles had a similar size and a rounded shape.In all cases, an organic carrier was present. The surfaceof the stones showed different structures; the CERECstone surface showed particles bonded together, but thesurfaces of the Lean and Jade stones showed longacicular crystals. The titanium look like typicallymetallic machined surfaces (Figure 5).

Energy-dispersive spectroscopy (Figure 6) of the3 imaging powders showed that many different ele-ments (titanium, oxygen, potassium, gold, palladium,iron, copper, and zinc) were present in their compo-sitions. The gold and palladium were due to thesample coating for SEM examination. Trace elementsmay have been due to the organic carrier or theanalysis substrates. However, the IPS contrast powderwas predominately titanium (48.98 weight percent [wt%]) and oxygen (48.31 wt%), whereas Optispraypowder and Vita powder both contained a lowerpercentage of titanium (Optispray powder ¼ 11.62 wt%, Vita powder ¼ 13.38 wt%) and oxygen (Optispraypowder ¼ 16.49 wt%, Vita powder ¼ 18.03 wt%)with larger amounts of aluminum (Optispraypowder ¼ 27.47 wt%, Vita powder ¼ 24.49 wt%). Itis likely that the particles in the IPS contrast powderare TiO2 and that the other powders are composed ofan aluminium-titanium-oxygen (Al-Ti-O)combination.

DISCUSSIONThe combinations of different imaging powders, diestone materials, and the titanium die used in this studyresulted in the construction of zirconia crowns withclinically acceptable margins (below 100 mm), which issimilar to that of laboratory-fabricated restorations andconsistent with values reported in other studies.14,15

However, the mean marginal gaps obtained in thisstudy were different compared to other studies becauseof the difference in the accuracy of the scanner, millingequipment, uniformity and thickness of the powderspray, setting expansion of the stones, and method ofdetermining the gap width.

Effect of no spray on different die stones. There wasa difference in the apparent particle shape between the3 stone types as shown in the SEM images; Jade andLean stones showed long acicular crystals, and theCEREC stone showed particles bonded together. Theparticles bonded together would be expected to scatterless light, whereas the long acicular crystals wouldscatter more light. However, the 3-shape scanner uses4 cameras, which are claimed to have the ability todetect both low and high light-scattering rates equallyfrom different stones and to have a similar resolution onthe detector. This study showed statistically insignificant(P > .05) marginal gap differences between the variousstone dies. Therefore, there was no statistical differencein the marginal gaps when different stone types werescanned without imaging powders, regardless of thestone type. Also, the particle shape of the stone die hadno effect on the results of the measurements of therespective marginal gaps. The hypothesis was that thereis an effect of the same imaging powder type on themarginal gap of different types of stones. Therefore, thishypothesis was rejected.

Effect of the same imaging powder on different diestones. When different stone dies were sprayed with

JADA 146(2) http://jada.ada.org February 2015 117

0.00

0.0K

1.5K

3.0K

4.5K

6.0K

7.5K

9.0K

10.5K

12.0K

13.5K

15.0K

A1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00

K L

Ti L

Fe L

O K

Cu L Al K Au M

K Kα

K Kβ

Ti Kβ

Fe KβFe Kα

Ti Kα

Cu Kβ Au LαCu Kα

Pd Lβ2

Pd Lβ

Pd Lα

Lsec: 30.0 0 Cnts 0.000 keV Det: Apollo XL-SDD Det Reso

B0.00

0.0K

1.3K

2.6K

3.9K

5.2K

6.5K

7.8K

9.1K

10.4K

11.7K

13.0K

1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00

Ti L

Fe L

O K

C K

Cu L

Zn L

Al K

Au MTi Kβ

Fe KβFe Kα

Ti Kα

Cu Kβ Au LαCu KαZn KβZn Kα

Pd Lβ2

Pd Lβ

Pd Lα

Lsec: 30.0 0 Cnts 0.000 keV Det: Apollo XL-SDD Det Reso

C0.00

0.0K

1.1K

2.2K

3.3K

4.4K

5.5K

6.6K

7.7K

8.8K

9.9K

11.0K

1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00

Ti LFe L

O K

C K

Cu L

Zn L

Al K

Au MTi Kβ

Fe KβFe Kα

Ti Kα

Cu Kβ Au LαCu KαZn KβZn Kα

Pd Lβ2

Pd Lβ

Pd Lα

Lsec: 30.0 0 Cnts 0.000 keV Det: Apollo XL-SDD Det Reso

Figure 6. A. IPS Contrast powder. B. Optispray powder. C. Vita powder. Different imaging powders have differentelemental composition in which IPS contrast powder has more titanium and oxygen elements but Optispray andVita powders have more aluminum element. Al: Aluminum. Au: Gold. C: Carbon. Cu: Copper. Fe: Iron. K: Potas-sium. keV: Kiloelectronvolt. O: Oxygen. Pd: Palladium. Ti: Titanium. Zn: Zinc.

ORIGINAL CONTRIBUTIONS

118 JADA 146(2) http://jada.ada.org February 2015

specific imaging pow-der, similar marginalgaps were attained withdifferent combinationof powders and stonedies. These were notaffected by differentscattering rates fromthe stone materials un-der the powder. Theconstant marginal gapmay have occurredbecause the 3-shapescanner used the blueLED, which could giverise to higher scatteringeffect with less pene-tration depth. There-fore, the scattering ratewas more affected bythe surface layer(sprayed imaging pow-der) regardless of thedie material under-neath. The hypothesiswas that there is a dif-ference in the marginalgap between conven-tional stone and specialCAD/CAM stoneswhen sprayed withspecific imaging pow-der. Therefore, this hy-pothesis was rejected.However, Costa andcolleagues18 reporteddifferent results whenoptical impressionswere made using aCEREC 3-D camerawith different condi-tions. In that study,a thin layer of TiO2

powder (CERECpowder–Vita) wasapplied directly to thesurface of the preparedtooth, and the sameimaging powder wassprayed on a resin die(polyvinylsiloxaneKwikkModel Scan).There was a statisticaldifference in themean marginal gapbetween the former

ORIGINAL CONTRIBUTIONS

(111.6 � 34.0 mm) and the latter group (161.4 � 37.6 mm).The difference in the marginal gap between the 2 groupswas attributed to inconsistent powder thickness uponspraying the dies.

Effect of different imaging powders on the same diestone. The composition (titanium, oxygen, and alumi-num), optical properties of minor elements, and the formof titanium (TiO2 and Al-Ti-O) of each imaging powderwere not associated with the scattering rate, most likelybecause of the blue LED induced by the 3-shape scanner.The results obtained in this study were in agreement withthe findings of Cook and Fasbinder,19 who reported thatthere was no statistical difference in the marginal fit(marginal gap ¼ 58 � 6 mm to 67 � 18 mm) when epoxyresin dies were sprayed with 2 different imaging powders(Optispray and Vita powders) and the digital impressionswere recorded using an LED CEREC AC/BlueCam unit.The insignificant differences in themarginal gapmost likelyoccurred due to the blue LED.Thehypothesiswas that thereis an effect of different types of imaging powders on themarginal gap of the same stone type. Therefore, this hy-pothesis was also rejected.

Effect of different imaging powders on titaniumdies. Metals by nature are normally reflective; therefore,the titanium die in this experiment was not scannedwithout the use of imaging powder to avoid hazy, ill-defined images. There was no statistical difference in themeasurements of the marginal gaps of the zirconiacrowns when the titanium die was sprayed with the 3types of imaging powder. The hypothesis that there is aneffect of different imaging powders on themarginal gap oftitanium dies was therefore rejected. Obtaining compa-rable marginal gaps between different imaging powderscan occur as a result of low penetration depth associatedwith the blue LED, which is emitted by the 3-shapescanner. This would have occurred regardless of the ti-tanium dies underneath. Furthermore, the mean mar-ginal gap was not affected by the integration of the type ofimagingpowder and the titaniumdie beneath the powder.

When a 3-shape scanner was used to scan titaniumabutments for the fabrication of implant bars and fixedpartial dentures, we found that cost is really the onlyfactor to be considered when selecting the imagingpowder for spraying titanium abutments. Further, re-sults show that the type of stone (CAD/CAM specialstone or conventional stone) will not affect marginaladaptation when the 3-shape scanner is used for scan-ning stone dies. Additionally, the type of imagingpowder will not affect the marginal gap of the same diestone. Therefore, the selection of a stone product shouldbe based on its physical properties (compressivestrength, initial setting time, working time, settingexpansion) and the desired color preference to differ-entiate the diagnostic cast from the master cast.

A limitation of our study applies to a specific labo-ratory method we used: scanning a master model made

from an impression. Clinicians want to eliminate theneed for an impression. Future research will investigatemarginal gap measurements after cementation to tita-nium and zirconia dies combined with aging of zirconiarestorations to study the effect of tetragonal to mono-clinic transformation (due to aging) on the marginal gap.

CONCLUSIONSWithin the limitations of this study, which utilized a3-shape scanner (model D900), there was no effect ofcomposition, optical properties, or form of titanium(TiO2 and Al-Ti-O) in different imaging powders on themarginal gaps of zirconia crowns as measured on atitanium die as well as on conventional and specialCAD/CAM die stones. The selection of imaging powderwhen scanning titanium abutments using a 3-shapescanner should be based only on cost. The selectionof stone material when scanning master dies using a3-shape scanner should be based on the physicalproperties, color, and cost. n

Disclosure. None of the authors reported any disclosures.

This experiment was supported in part by the Deanship of Research,Taibah University, Madina, Saudi Arabia, and Matt Winstead, CDT, vicepresident of Oral Arts Dental Labs, Huntsville, AL.

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