Keywords
ceramometal - digital impression - internal accuracy - press-on ceramic - sintered
metal
Introduction
Ceramometal restorations have been successfully utilized for restoring damaged teeth
owing to the aesthetic ceramic veneering on a durable metal substructure.[1] Construction of ceramometal restoration comprises of two steps; metal substructure
fabrication and ceramic veneering. Predominately, nonnoble alloys are frequently used
due to their superior mechanical properties, biocompatibility, and lower cost compared
with others. The cobalt-chromium alloys are selected for patient sensitive to nickel.[1]
[2] Nonnoble metal substructures are conventionally fabricated through the lost-wax
technique, which is a considerably sensitive technique and inferior castability, more
than noble metals, owing to their high melting temperature and little ductility.[3] Thus, some accumulating errors from the casting processes are unavoidable. Lately,
computer-aided design and computer-aided manufacturing (CAD-CAM) technology has allowed
for the fabrication of metal substructures through a milling process by using data
designed with CAD software.[4]
[5]
[6] The systems are capable of producing better accuracy and reliability of restorations
from milling presintered alloy blank, however, it requires producing at a qualified
milling center, which is costly.[7] Milling the partially sintered powder alloy offers a simpler process but needs further
sintering to achieve the fully sintered alloy, which consumes less time and cost.
The mechanical properties of the sintered alloy were proved to be comparable to the
hard-milled alloy.[8]
[9] Through CAD-CAM it is now possible to fabricate wax pattern to be further invested
and cast or pressed for coping. The accuracy of the sintered metal substructure is
probably related to the omission of waxing, investing, and casting processes in the
conventional casting method.[10] Nevertheless, limitations of laser scanners in the CAD systems to reproduce sharp
edges were reported.[8]
Veneering the metal substructure with ceramic can be accomplished either by conventional
layering or pressed-on methods. To achieve favorable esthetic and clinical results
demands a skilled dental technician. On using the layering method, the ceramic slurry,
made from mixing ceramic powder with modeling liquid, is stacked and overbuilt to
compensate for firing shrinkage. During the process, the metal substructure is subjected
to a series of ceramic firing cycles and exposed to a variety of high-temperature
treatments relative to each ceramic layer applied. Thus, metal copings may get affected
and undergo distortion.[11] The press-on technique enables easier producing ceramometal restorations by pressing
the melted ceramic onto the metal substructure.[12] This technique avoids multiple ceramic firings and results in achieving precise
anatomical form and occlusion of the restorations to the opposing tooth. Better distribution
of crystalline phases in the glass matrix minimizes ceramic firing shrinkage and provides
better internal accuracy.[12]
Internal accuracy is defined as the distance between the intaglio surface of the restoration
and the prepared tooth surface, which is considered an essential part of the long-term
success of fixed restoration. It is significantly influenced by the accuracy of the
fabrication process. Improper internal fit provokes microbacteria to spread through
the gap, which potentially causes dental caries and periodontal disease that precedes
restoration failure.[13] Excessive internal gap induces tensile stresses at the intaglio surface of the restoration
while deforming the luting cement upon cyclic load triggers, chipping of veneering
ceramic and decreases fracture strength.[14] Conversely, insufficient cement space can impede the proper seating of the restoration[15] and potentially cause a larger gap upon cementation, which leads to biological complications.[16] The distortion of the ceramometal restoration probably increased after ceramic veneering,
firings, and glazing, which perhaps prevented the internal adaptation of restorations
to abutment.[3]
[17]
[18] However, dimensional changes mostly occur during the cooling process.[3]
[19] This is possibly related to the substructure design, fabrication technique, type
of alloy, shrinkage of ceramic, and the coefficient of thermal expansion difference
between alloy and ceramic.[1]
[2]
[3]
[6]
[12]
[20] Some studies reported the porcelain firing cycle effect on internal accuracy,[21]
[22] while others did not.[12]
[17] The consistent internal fit facilitates seating and also maintains retention or
resistance of restoration.[17]
[23]
[24] Up to the present time, there is no consensus on the clinically acceptable internal
accuracy for fixed dental restoration. An internal gap of 50 to 100 μm was suggested
for conventional types of cement,[25] whereas 200 to 300 μm for adhesive types of cement. The largest internal gap appeared
at the occlusal area,[13] with an acceptable range from 100 to 200 μm was stated.[26] Yet, a suitable internal gap is required to promote acceptable fit and ensure clinical
reliability.[14]
The impact of ceramometal fabrication techniques on internal adaptation is a crucial
concern for dentists.[1]
[11]
[24] Both the sintered metal substructure and the press-on ceramic veneering method are
promising future of restoration.[5]
[6]
[11] Nevertheless, there was limited information on the internal accuracy of ceramic
veneer sintered alloy related to ceramic veneering methods, as well as limited connection
to practicing processes.[11] Hence, this in vitro study intended to assess the internal accuracy of ceramometal crowns fabricated from
four metal substructure fabrication techniques, veneered with two ceramic veneering
methods, and measured at five stages of fabrication, at 18 sites of restoration, with
the research design relevant to clinical practice processes. The null hypothesis was
that the internal accuracy of the ceramometal crown not being significantly affected
by the difference in metal substructure fabrication techniques, ceramic veneering
methods, stages of restoration fabrication, sites of restoration, and their interactions.
Conventional ceramometal crowns based on traditional fabricated cast metal veneered
with conventional porcelain layering served as a control group.
Materials and Methods
The sample size was estimated by G*power 3.1 software (Heinrich-Heine-Universität,
Düsseldorf, Germany) using the values from the previous study,[27] power of test = 0.9, and an α error = 0.05 as shown in [Equation 1].
where Zα
= normal standard deviation = 1.96 (α error = 0.05), Zβ
= normal standard deviation = 1.28 (β error = 0.1), µ
1–µ
2 = differences of mean between tested groups = 5, and s = standard deviation (s
1 = 5, s
2 = 2).
The calculated sample size was 12 specimens/group used for this investigation.
Fabrication Master Model
A typodont maxillary first premolar (Frasaco, Tettnang, Germany) was prepared for
the ceramometal crown with diamond rotary instruments (Khon Kaen University Preparation
Kit 1918, Jota, Ruthi, Switzerland) and high-speed handpiece (KaVo, Biberarch, Germany).
The preparation was designed for 1.5 mm identical axial and anatomical occlusal reduction,
a 1.2-mm smooth continuous chamfer finishing line located 0.5 mm above the cemento-enamel
junction with a round internal line angle, and 10 degrees total occlusal convergence
angle ([Fig. 1A-1]). The prepared tooth was duplicated with polyvinyl siloxane (PVS) impression material
(Silagum, DMG, Hamburg, Germany) and poured with pattern resin (Duralay, Reliance,
Alsip, Illinois, United States). The resin pattern was invested in the casting ring
using phosphate bonded investment (Ceramvest Hi-Speed; Protechno, Girona, Spain) to
transform to cast metal through the process of loss wax technique. The investment
mold was burnt-out in a furnace (EWL-5645, Kavo) and cast with nonnoble metal alloy
(d.SIGN 30, Ivoclar Vivadent, Schaan, Liechtenstein) using a centrifuged casting apparatus
(Fornax, Bego, Bremen, Germany). The metal casting specimens were divested and sandblasted
with 110 μm aluminum oxides (Al2O3) abrasive (Korox, Bego) in a sandblasting machine (Vario, Renfert, Hilzingen, Germany)
to remove the remaining residue. The sprues were cut with Al2O3 cutting disk (Shofu, Kyoto, Japan), and the cast was finished with Dura-Green Stone
burs (Shofu), polished with gold polishing kit (Shofu), and ultrasonically cleaned
with the distilled water for 15 minutes in a cleansing machine (Vitasonic, Vita Zahnfabrik,
Bad Sackingen, Germany) to remove the remaining Al2O3 particle and cleaned with streaming machine (Touchsteam, Kerr, Brea, California,
United States) to eliminate the grease residues. The metal tooth abutment was positioned
at the central portion of the metal base (width × length × thick = 3 × 4 × 3 cm) and
used as a master model in this investigation ([Fig. 1A-2]).
Fig. 1 (A) A typodont maxillary first premolar was prepared (1), replicated to a cast metal
die, positioned on the metal base model (2), which was used for fabrication of four
types of metal substructures including cast metal with traditionally impressed tooth
[CmTt], sintered metal with digitally impressed tooth [SmDt], sintered metal with
digitally impressed stone model [SmDm], and cast metal with digitally milled wax [CmDw]
(3). (B) The intaglio surface of the ceramic (P) veneer metal (M) crown was filled with a
light viscosity silicone impression material, placed onto the master die (Tm), and
constantly loaded (L) in apical direction (1, 2). (C) The silicone replica (R) was picked up with regular viscosity silicone impression
material using split mold metal cap (Sc) and cap stabilizer (Cs) (1) for further sectioning
in mesial-distal (Me–Di) and buccal-lingual (Bu–Li) directions using razor blades
(Rb) (2). (D) The internal accuracy was determined at gingival (G), gingiva-axial (Ga), axial
(A), axio-occlusal (Ao), and occlusal (O) location of the buccal (Bu), lingual (Li),
mesial (Me), and distal (Di) sites.
Fig. 2 The metal die was traditionally impressed (Tt) to fabricate 48 stone models. Twenty-four
standard tessellation language (STL) files were generated from digitally impressed
metal tooth (Dt), designed, milled wax (Dw) copings to fabricate cast copings (Cm)
upon the CmDw technique. Twenty-four STL files were generated by Dt, designed, milled
presintered copings, and sintered to derive sintered metal (Sm) copings upon the SmDt
technique. Twenty-four STL files were generated by digitally impressed stone models
(Dm), designed, milled presintered copings, and sintered to reach for sintered metal
(Sm) copings upon to SmDm technique. Twenty-four stone dies were manually carved for
wax copings to fabricate cast metal (Cm) copings upon the CmTt technique. All metal
copings were randomly veneered with ceramic by either ceramic layering (Pl) or ceramic
press-on (Pp) technique.
Fabrication of Metal Substructure
Fabrication of Metal Substructure
Single ceramometal crowns were evaluated for internal accuracy. A total of 96 metal
substructures were fabricated with a standard thickness of 0.3 mm with narrow metal
collars all around the margin and designated into four main groups: cast metal constructed
from the traditionally impressed tooth (CmTt), cast metal constructed from digitally
milled wax (CmDw), sintered metal constructed from the digitally impressed tooth (SmDt),
and sintered metal constructed from the digitally impressed model (SmDm) ([Fig. 2]). All substructures were subjected to degassing and opaque application fired according
to the manufacturer's instructions. These groups were further subgrouped according
to the method of ceramic veneering into conventional layered and press-on. Evaluation
of internal accuracy was carried out at different stages of fabrication; after metal
substructure construction, after degassing, after opaque application, after veneering,
and lastly after glazing, respectively. All laboratory processes for the fabrication
of ceramic veneered metal were blindly performed by one well-qualified dental technician
who is capable of performing both digital and conventional fixed prosthesis, followed
the standardized protocols, and conducted in the professional dental institute under
the blind supervision of the Professor of Prosthodontics belonging to the institute.
The metal substructure fabrication techniques were described as follows.
Cast Metal (Cm) Constructed from Traditionally Impressed Tooth (Tt) [CmTt Technique]
Twenty-four traditional impressions of the master die (Tt) were performed by the double-mixed,
one-step impression technique using a light viscosity (syringe type) and putty-soft
(tray type) PVS impression material (Silagum, DMG) with a customized autopolymerizable
resin (Formatray, Kerr) trays and then poured the impression with type IV dental stone
(Vel-Mix, Kerr) to fabricate 24 stone models and dies. The hardening solution (Bredent,
Senden, Germany) was applied to the stone casts. Two coats of red color die spacer
(Durolan, DFS, Riedenburg, Germany) (10 µm thickness per coat application as specified
by the manufacturer) were applied on the stone dies with 0.5 mm clearance from the
finishing line of the abutments to reach an equivalent thickness of 20 μm and let
dry for 60 seconds. Twenty-four wax pattern copings were fabricated with standardized
control for identical shape and thickness through a wax-dipping method using the blue
inlay casting wax (Kerr). Then, the sculpting wax was added to thin areas by an electric
wax carver (SJK 110, Bonew, California, United States), finalized margin with cervical
red wax (GEO Crowax, Renfert, Germany), controlled shape of wax pattern coping with
jig, verified wax coping of a thickness of 0.3 mm with a wax caliper (Unique Dental
Supply, Concord, Ontario, Canada), and transformed to cast metal (Cm) substructures
using nonnoble metal alloy (d.SIGN 30, Ivoclar Vivadent, comprising Co 66.2%, Cr 30.1%,
Ga 3.9%, Nb 3.2%, Mo 5%, and Si, Fe, Mn < 1%, and Si, B, Fe, Al, Li < 1%) through
the loss wax technique as previously described to derive for 24 CmTt copings (n = 24).
Cast Metal (Cm) Constructed from Digitally Milled Wax (Dw) [CmDw Technique]
Twenty-four digital impressions of the master die were obtained by scanning with a
confocal microscopy-based intraoral scanner (TRIOS 5, 3Shape A/S, Copenhagen, Denmark)
to produce standard tessellation language (STL) files to be used in designing substructures
with the CAD software (Ceramill Mind v2.7.05, Amann Girrbach, Koblach, Austria) by
setting marginal discrepancy for 0 mm, thickness of 0.3 mm, and 20 µm simulated die
spacer starting 0.5 mm away from the finishing line of the prepared abutment. The
intended data were assigned to a 5-axis CAM-milling instrument (Ceramill Motion 2;
Amann Girrbach) for milling 24 digitally milled wax (Dw) copings from the hard wax
blank (Ceramill Wax, Amann Girrbach) for further fabrication of 24 CmDw copings (n = 24) by means of loss wax technique as previously described.
Sintered Metal (Sm) Constructed from Digitally Impressed Tooth (Dt) [SmDt Technique]
Twenty-four digital impressions of the master die (Dt) were obtained by scanning with
an intraoral scanner (TRIOS 5, 3Shape A/S) to produce STL files, and used for designing
substructures with the CAD software (Ceramill Mind v2.7.05, Amann Girrbach), with
the previous identical design, but setting 15% larger than required. The proposed
data were assigned to mill the presintered Co-Cr alloy blank (Sm, Ceramill Sintron,
Amann Girrbach, comprising Co 66%, Cr 28%, Mo 5%, and Si, Fe, Mn < 1%) in a CAM-milling
device (Ceramill Motion 2; Amann Girrbach) to produce presintered metal copings and
further sintered to derive for 24 SmDt copings (n = 24).
Sintered Metal (Sm) Constructed from Digitally Impressed Model (Dm) [SmDm Technique]
Twenty-four conventional stone models and dies were fabricated as previously described.
The digital impressions of the stone models (Dm) were obtained by scanning with a
cast scanning machine (Ceramill Map-400; Amann Girrbach) to produce STL files and
used for designing substructures with the CAD software (Ceramill Mind v2.7.05, Amann
Girrbach), with the previous identical design, but setting 15% larger than required.
The intended data were assigned to a CAM-milling device (Ceramill Motion 2; Amann
Girrbach) to produce presintered metal copings from Co-Cr presintered alloy blank
(Sm, Ceramill Sintron, Amann Girrbach) and further sintered to derive for 24 SmDm
copings (n = 24).
The sintered metal coping for both were further sintered at 1,300°C for 6 hours in
an argon gas chamber of the furnace (Ceramill Argotherm-2, Amann Girrbach) for both
SmDt and SmDm
Surface Preparation of Metal Substructure
Surface Preparation of Metal Substructure
The surface of metal substructures was prepared by grinding with stone bur (coral
stones, Shofu) in a unique path at 20,000 revolutions per minute speed and then blasted
with 110 μm Al2O3 (Korox, Bego) using 2 bar pressure for 10 seconds in a sandblaster unit (Vario, Renfert)
with placing the tip at 10 mm away from the substructure. The samples were ultrasonically
cleaned in the distilled water for 30 minutes and then steam-cleaned for 15 seconds.
All metal substructures were heat treated in the furnace (Programat, Ivoclar Vivadent)
to oxidize the metal surface by degassing process (D) as following the manufacturer's
instruction.
Opaque Ceramic Application
Opaque Ceramic Application
The A3 paste opaque ceramic (IPS Inline, Ivoclar Vivadent) was smeared to all metal
copings and fired twice as stated by the company's firing instruction in the ceramic
furnace (Programat, Ivoclar Vivadent) to derive for the 0.1-mm thickness of opaque
layer. The first opaque ceramic layer was sparsely smeared and fired. The second opaque
ceramic layer was completely applied over the first layer and fired to achieve an
eggshell appearance surface. Each type of metal substructure was randomly allocated
into two subgroups to be veneered with ceramic either by conventional ceramic layering
(Pl) or ceramic press-on (Pp) technique ([Fig. 2]).
Conventional Ceramic Layering Technique
Conventional Ceramic Layering Technique
The samples were veneered with ceramic with Pl technique to the desired shape and
thickness. A creamy uniformity of A3 dentine porcelain (IPS InLine, Ivoclar Vivadent)
was spread over the opaque surface, condensed with an ultrasonic condensing machine
(Ceramosonic, Unitek, Osaka, Japan) to generate crown contour, and fired in the ceramic
furnace (Programat, Ivoclar Vivadent) according to the manufacturer's instructions.
The dentine ceramic was permitted for two applications to derive the final contour
of 1.2 mm thickness, using a jig to control an anatomical crown contour, and finally
glazed.
Ceramic Pressed-On Technique
Ceramic Pressed-On Technique
The samples were coated with the modeling wax (Geo Classic, Renfert) for 1.2 mm thickness
to fabricate the anatomical crown contour, attached the sprue to the wax portion,
invested in the silicone investing ring, using a phosphate bonded investment (IPS
PressVEST Speed; Ivoclar Vivadent), and burned out in the furnace according to the
manufacturer's instruction. After the completion of the burned-out process, the investment
mold was relocated to a pressed oven (EP 500, Ivoclar Vivadent) for the porcelain
pressing (Pp) process, using A3 porcelain ingots (IPS InLine PoM, Ivoclar Vivadent).
After the pressed process was accomplished, the divestment process was performed by
blasting with 110 µm Al2O3 abrasive (Korox, Bego) with a pen blaster (Vario, Renfert) by setting the blasting
tip at 20 mm far from the crown surface, with 4 bars pressure, for 10 seconds. Once
the pressed ceramic became visible, the pressure was reduced to 1.5 bars, and gently
blasted the ceramic surface. A diamond disk (Kerr) was used to separate the sprues
from the crown. Then, the samples were finished, polished, and glazed.
Evaluation Internal Accuracy
Evaluation Internal Accuracy
All samples were evaluated for internal accuracy on the same master die. The silicone
replica method was used to assess the internal accuracy of restoration to the master
die (Tm) on the master metal model.[1]
[28] The internal accuracy was measured by a single operator, based on blind investigation,
at each stage of restoration fabrication including as-cast (As) metal coping, degassing
(De), opaquing (Op), body contouring (Co), and glazing (Gl). The intaglio surface
of the metal coping was inspected under a widefield zoom stereo-microscope (Carl Zeiss,
Oberkochen, Germany) to confirm free of residue particles before evaluating the internal
gap for every stage. The intaglio surface of the restoration was covered with a light
viscosity PVS material (Silagum, DMG), positioned on the Tm, together with constantly
loaded for 50 Newton (N) in the vertical direction until the PVS material completely
polymerized ([Fig. 1B]).[29] Upon removal of the restoration from the Tm, a skinny layer of silicone replica
(R) was left adhering on the Tm, representing the discrepancy between restoration
and Tm ([Fig. 1C-1]). A regular viscosity PVS material (Reprosil, Dentsply Sirona, Charlotte, North
Carolina, United States) was applied into the split mold metal cap (C) and seated
on the master metal model by keeping in place the cap stabilizer (Cs) to pick up the
replica and further injected a regular viscosity PVS material (Reprosil, Dentsply
Sirona) to the internal surface to stabilize the R as a sandwiching method. The R
was longitudinally sectioned by super thin razor blades (Gillette, Boston, Massachusetts,
United States) through the center of the replica in buccal (Bu)–lingual (Li) and mesial
(Me)–distal (Di) directions ([Fig. 1C-2]), leading to four sections of silicone replica used for measuring the internal gap
at gingival (G), gingiva-axial (Ga), axial (A), axio-occlusal (Ao), and occlusal (O)
location of the buccal (Bu), lingual (Li), mesial (Me), and distal (Di) sites, yielding
18 measurements for each stage by using the polarized light microscope (Eclipse LV100pol,
Nikon, Melville, New York, United States) at ×30 magnification. Each measurement was
repeated three times, and performed by a single examiner with 89% intraexaminer agreement.
The thickness of the silicone replica between the metal coping and the internal surface
of the tooth abutment was measured, analyzed by Image J software (U.S. National Institutes
of Health, Bethesda, Maryland, United States), and was defined as the internal accuracy
([Fig. 1D]).[2]
Statistical Analysis
The internal gap data were analyzed with statistics software (SPSS/PC V-26, IBM, Armonk,
New York, United States). The data were examined for normality using the Shapiro–Wilk
test and for the homogeneity of the variances using the Levene's test. Since the data
met the assumptions for an analysis of variance (ANOVA), a comparison of the measured
adjustments was analyzed using multifactorial ANOVA to conclude the statistically
significant difference in internal accuracy of the ceramometal restorations upon different
substructure fabrication techniques, ceramic veneering methods, stages of fabrication,
and sites of restoration. Post hoc Bonferroni multiple comparisons were applied to
justify differences among groups at a 95% level of confidence.
Results
The means internal accuracy for ceramometal restorations related to different metal
substructure fabrication techniques, stages of restoration fabrication, methods of
ceramic veneering, and sites of restoration were presented ([Table 1] and [Fig. 3]). Multifactorial ANOVA confirmed significantly different internal accuracy of restoration
upon various substructure fabrication techniques, stages of restorative fabrication,
methods of ceramic veneering, and sites of restoration (p < 0.05). When interacting factors were taken into account, significant differences
were detected between the substructure fabrication techniques and the methods of ceramic
veneering, between the substructure fabrication techniques and sites of restoration,
between the substructure fabrication techniques and stages of restoration fabrication,
between the methods of ceramic veneering and the sites of restoration, between the
methods of ceramic veneering and the stages of fabrication, together with between
the substructure fabrication techniques, methods of ceramic veneering, and the sites
of restoration (p < 0.05). However, no significant differences in internal accuracy were detected between
the sites of restoration and the stages of fabrication, and among other three and
four factors interaction (p > 0.05) ([Table 2]).
Table 1
Mean internal accuracy (μm) of cast (Cm) and sintered (Sm) metals constructed from
traditional (Tt), digitally impressed tooth (Dt), digitally impressed model (Dm),
and digitally milled wax (Dw) techniques, veneered with porcelain by layering (Pl)
or press-on (Pp) method at as-cast (As), degassing (De), opaquing (Op), body contouring
(Co), and glazing (Gl) stage at gingival (G), gingiva-axial (Ga), axial (A), axio-occlusal
(Ao), and occlusal (O) location of the buccal (Bu), lingual (Li), mesial (Me), and
distal (Di) sites
|
Metal
|
Veneer
|
Stage
|
Site
|
|
BuG
|
BuGa
|
BuA
|
BuAo
|
Obl
|
LiAo
|
LiA
|
LiGa
|
LiG
|
MeG
|
MeGa
|
MeA
|
MeAo
|
Odl
|
DiAo
|
DiA
|
DiGa
|
DiG
|
|
CmTt
|
Pl
|
As
|
56.9
|
69
|
75
|
108.4
|
116.9
|
111
|
74.6
|
69.8
|
59.6
|
58.2
|
72.8
|
73.9
|
104.5
|
116.5
|
103.8
|
75.2
|
73.5
|
60.7
|
|
CmTt
|
Pl
|
De
|
71.1
|
82.9
|
86
|
127.9
|
137.2
|
130.2
|
85.3
|
84.3
|
72.5
|
73.8
|
87.2
|
83.2
|
124.9
|
137.2
|
124.3
|
85.8
|
88.3
|
75.8
|
|
CmTt
|
Pl
|
Op
|
72.9
|
85.2
|
88
|
130.3
|
140.4
|
132.7
|
87.2
|
86.2
|
74.5
|
75.8
|
88.7
|
84.8
|
126.7
|
140.1
|
126.6
|
87.7
|
90.2
|
77.9
|
|
CmTt
|
Pl
|
Co
|
77.3
|
90.1
|
91.6
|
135
|
145.6
|
136.9
|
90.4
|
89.9
|
78.8
|
79.8
|
92.7
|
88.2
|
131.5
|
145.6
|
131.2
|
90.8
|
93.92
|
81.8
|
|
CmTt
|
Pl
|
Gl
|
78.1
|
91.2
|
93
|
136.8
|
147.8
|
138.8
|
91.8
|
91.1
|
79.9
|
81.1
|
93.9
|
89.7
|
133.1
|
146.8
|
132.6
|
92.7
|
95.4
|
82.9
|
|
CmTt
|
Pp
|
As
|
58.7
|
69.1
|
74.7
|
110.2
|
117.4
|
110.5
|
74.7
|
70.9
|
59.3
|
61.3
|
69.8
|
77.3
|
109.4
|
117.5
|
109.2
|
75.9
|
70.9
|
60.1
|
|
CmTt
|
Pp
|
De
|
71.9
|
83.2
|
85.5
|
130.7
|
140
|
131.2
|
85.9
|
84.1
|
72.25
|
74.4
|
83.1
|
88.2
|
129.4
|
140.2
|
128.6
|
87
|
84.2
|
72.8
|
|
CmTt
|
Pp
|
Op
|
73.8
|
84.8
|
86.7
|
133.6
|
143.2
|
134.2
|
87.8
|
86
|
74.1
|
75.8
|
85.2
|
89.7
|
132.6
|
143.7
|
130.9
|
88.8
|
86.4
|
74.5
|
|
CmTt
|
Pp
|
Co
|
71.3
|
83.2
|
85.6
|
131.6
|
140.5
|
131.9
|
86.2
|
85.1
|
71.6
|
72.8
|
83.2
|
88.1
|
130.5
|
141.1
|
128.4
|
87.4
|
85.4
|
72.3
|
|
CmTt
|
Pp
|
Gl
|
73.5
|
85.3
|
87.7
|
134.6
|
144
|
134.8
|
87.8
|
87
|
73.9
|
74.9
|
85.1
|
90.1
|
133.7
|
144.4
|
131.2
|
89.3
|
87.6
|
74.5
|
|
CmDw
|
Pl
|
As
|
61.6
|
85.8
|
78.4
|
126.7
|
134.2
|
126.6
|
78.8
|
87.2
|
61.6
|
62.8
|
88.7
|
81.5
|
123.8
|
134.3
|
123.8
|
84.3
|
91.7
|
65.2
|
|
CmDw
|
Pl
|
De
|
74.8
|
98.3
|
88.8
|
147.3
|
155.2
|
146.2
|
90.5
|
100.2
|
74.5
|
75.5
|
101
|
91.6
|
144.2
|
155.3
|
143.8
|
94.5
|
103
|
78.2
|
|
CmDw
|
Pl
|
Op
|
76.9
|
100.8
|
90.9
|
150.6
|
158.3
|
149.2
|
92.2
|
102.2
|
76.7
|
77.4
|
103.2
|
93.4
|
147.3
|
158.6
|
146.4
|
96.2
|
105.3
|
80.5
|
|
CmDw
|
Pl
|
Co
|
80.9
|
106.1
|
95.7
|
156.6
|
164.6
|
156.2
|
96.1
|
106.3
|
80.6
|
81.7
|
108.5
|
97.4
|
154.2
|
164.6
|
152
|
99.9
|
109.3
|
84.2
|
|
CmDw
|
Pl
|
Gl
|
82.2
|
106.8
|
96.8
|
158.1
|
166.8
|
156.9
|
97.2
|
107.3
|
81.8
|
83.2
|
109.9
|
98.5
|
155.4
|
166.8
|
153.4
|
101.4
|
110.7
|
85.1
|
|
CmDw
|
Pp
|
As
|
64.2
|
85.8
|
78.2
|
126.2
|
130.8
|
128.6
|
79.5
|
87.2
|
63.3
|
67.8
|
88.9
|
79.5
|
121.7
|
131.1
|
121.2
|
79.7
|
89.8
|
67.2
|
|
CmDw
|
Pp
|
De
|
77.1
|
98.5
|
87.8
|
146.6
|
150.2
|
149.9
|
88.9
|
99.8
|
75
|
80
|
102
|
89.4
|
142.5
|
151.8
|
141.1
|
90.1
|
102.3
|
79.3
|
|
CmDw
|
Pp
|
Op
|
78.8
|
100.6
|
89.7
|
149.2
|
153.6
|
152.6
|
90.5
|
101.8
|
76.9
|
82
|
104.6
|
91.3
|
145.3
|
155.2
|
143.3
|
91.8
|
104.2
|
81.2
|
|
CmDw
|
Pp
|
Co
|
76.5
|
99.3
|
88.1
|
146.3
|
150.2
|
150.1
|
89.1
|
99.8
|
74.3
|
79.7
|
103.2
|
89.9
|
142.8
|
151.8
|
141.2
|
90.6
|
102.6
|
79.2
|
|
CmDw
|
Pp
|
Gl
|
79
|
101.8
|
89.7
|
149.3
|
153.3
|
150
|
90.9
|
102
|
76.8
|
82.5
|
105.2
|
91.5
|
145.2
|
155.9
|
143.8
|
92.5
|
104.2
|
81.2
|
|
SmDt
|
Pl
|
As
|
36.5
|
59.2
|
60.8
|
112.2
|
119.8
|
114.4
|
69.3
|
63.6
|
40.7
|
40.1
|
64
|
71.4
|
100.1
|
120.7
|
100.2
|
72.2
|
62.9
|
40
|
|
SmDt
|
Pl
|
De
|
47.9
|
71.7
|
69.4
|
131.3
|
139.1
|
133.5
|
77.9
|
75.6
|
49.2
|
48.9
|
77.1
|
80.3
|
119.2
|
139.5
|
120.2
|
83
|
76.2
|
48.4
|
|
SmDt
|
Pl
|
Op
|
49.4
|
73.9
|
71.8
|
134.1
|
142.3
|
135.8
|
80
|
77.8
|
51.1
|
50.6
|
79.2
|
82.3
|
121.8
|
142.5
|
122.8
|
84.8
|
78.3
|
49.9
|
|
SmDt
|
Pl
|
Co
|
53.9
|
78.5
|
76.2
|
138.9
|
148.5
|
141.3
|
84.2
|
82.2
|
54.9
|
54.7
|
83.8
|
86.6
|
127
|
149
|
128
|
88.6
|
82.2
|
53.5
|
|
SmDt
|
Pl
|
Gl
|
55.1
|
79.8
|
77.7
|
140.9
|
150.0
|
142.8
|
85.8
|
83.6
|
56
|
55.9
|
85.2
|
88
|
128.6
|
150.5
|
129.6
|
90.2
|
83.7
|
54.8
|
|
SmDt
|
Pp
|
As
|
40.1
|
62.9
|
61.3
|
112.2
|
119.5
|
112.4
|
63.8
|
64
|
40.2
|
40.6
|
66.2
|
67.8
|
101.1
|
119.3
|
102.6
|
69.5
|
66.4
|
41.7
|
|
SmDt
|
Pp
|
De
|
48.4
|
74.8
|
71.2
|
129.5
|
138.1
|
130.2
|
73.4
|
76.1
|
48.4
|
49.9
|
77.5
|
78
|
116.5
|
137.9
|
119.3
|
80.3
|
79.1
|
50.8
|
|
SmDt
|
Pp
|
Op
|
50.4
|
76.8
|
77.3
|
132.3
|
140.9
|
133.1
|
75.5
|
78.5
|
50.3
|
51.9
|
79.7
|
79.9
|
119.2
|
140.6
|
122
|
81.8
|
81.1
|
52.5
|
|
SmDt
|
Pp
|
Co
|
40.8
|
74.8
|
71.1
|
129.5
|
137.2
|
119.6
|
79.7
|
78.3
|
50.4
|
48.2
|
75.2
|
73.8
|
130.6
|
136.9
|
116.6
|
77.6
|
77.3
|
49.9
|
|
SmDt
|
Pp
|
Gl
|
50.6
|
77.3
|
73.5
|
132.2
|
140.6
|
133.4
|
75.9
|
78
|
50.9
|
52.3
|
80
|
79.5
|
120.1
|
140.3
|
122.6
|
82.2
|
81.2
|
53.1
|
|
SmDm
|
Pl
|
As
|
38.9
|
63.2
|
63.4
|
118.2
|
123.8
|
119.5
|
62.3
|
64.6
|
40.8
|
42.9
|
65.3
|
66.7
|
108
|
122.6
|
108.8
|
67.2
|
64.4
|
41.5
|
|
SmDm
|
Pl
|
De
|
47.3
|
75.2
|
73.7
|
135.2
|
144.1
|
135.7
|
72.7
|
76.6
|
49
|
51.4
|
77.1
|
76.5
|
124.5
|
143.8
|
127.1
|
78.1
|
76.3
|
50.1
|
|
SmDm
|
Pl
|
Op
|
49
|
76.8
|
75.7
|
138.1
|
147.3
|
138.7
|
74.4
|
78.2
|
50.7
|
53.2
|
78.8
|
78.9
|
127.5
|
147.1
|
130
|
79.9
|
78.1
|
51.3
|
|
SmDm
|
Pl
|
Co
|
53.3
|
80.5
|
79.9
|
142.7
|
152.9
|
143.6
|
78.3
|
81.8
|
54.3
|
57.2
|
82.8
|
82.5
|
131.8
|
152.4
|
134.2
|
83.5
|
81.9
|
55.2
|
|
SmDm
|
Pl
|
Gl
|
54.9
|
81.7
|
81.4
|
145.1
|
154.8
|
145.7
|
79.6
|
83.3
|
55.8
|
58.6
|
84.4
|
84.2
|
134
|
154.3
|
135.8
|
84.9
|
83.6
|
56.8
|
|
SmDm
|
Pp
|
As
|
39.8
|
67.8
|
65.4
|
118.2
|
124.8
|
120
|
64.4
|
66.1
|
40.5
|
40
|
66.6
|
67.7
|
108.6
|
124.2
|
110.5
|
65.2
|
53.8
|
38.8
|
|
SmDm
|
Pp
|
De
|
47.7
|
80.2
|
74.8
|
137.7
|
144.2
|
139
|
74.5
|
77.2
|
48.8
|
47.7
|
77.1
|
77.5
|
128
|
143.9
|
129.5
|
75
|
75.2
|
46.8
|
|
SmDm
|
Pp
|
Op
|
49
|
82.1
|
76.6
|
140.2
|
147.2
|
141.7
|
76.2
|
78.9
|
50.2
|
49.3
|
78.8
|
79.8
|
130
|
146.9
|
132
|
77.1
|
77.2
|
48.6
|
|
SmDm
|
Pp
|
Co
|
46.6
|
79.6
|
73.2
|
137.3
|
143.5
|
139.1
|
74.4
|
76.9
|
47.6
|
46.9
|
76.8
|
78
|
127.3
|
143.4
|
128.8
|
75.2
|
75
|
46.1
|
|
SmDm
|
Pp
|
Gl
|
49.1
|
81.8
|
75.2
|
140.3
|
146.3
|
142.2
|
76.4
|
79.1
|
50.1
|
49.2
|
79.7
|
80.4
|
130.8
|
146.7
|
131.6
|
77.4
|
77.8
|
48.8
|
Fig. 3 Mean internal accuracy at different sites [gingival (G), gingiva-axial (Ga), axial
(A), axio-occlusal (Ao), and occlusal (O) location of the buccal (Bu), lingual (Li),
mesial (Me), and distal (Di) surface] of ceramic veneered (A) cast metal constructed from traditional loss wax (CmTt), (B) cast metal of the digitally impressed wax (CmDw), (C) sintered metal of digitally impressed tooth (SmDt), and (D) sintered metal of digitally impressed model (SmDm) techniques, with either ceramic
layering (Pl) or ceramic press-on (Pp) at as-cast (As), degassing (De), opaquing (Op),
body contouring (Co), and glazing (Gl) stages.
Table 2
Analysis of variance (ANOVA) of internal accuracy at different sites of ceramic veneer
metal substructures constructed from different techniques with different veneering
methods upon various stages of fabrication
|
Source
|
SS
|
df
|
MS
|
F
|
p
|
|
Corrected model
|
8690094.324
|
719
|
12086.362
|
182.755
|
0.001
|
|
Intercept
|
78906147.426
|
1
|
78906147.426
|
1193120.795
|
0.001
|
|
Substructure
|
566193.110
|
3
|
188731.037
|
2853.756
|
0.001
|
|
Stage
|
410275.035
|
4
|
102568.759
|
1550.917
|
0.001
|
|
Ceramic
|
12376.884
|
1
|
12376.884
|
187.148
|
0.001
|
|
Site
|
7464066.605
|
17
|
439062.741
|
6638.962
|
0.001
|
|
Substructure * Ceramic
|
1157.590
|
3
|
385.863
|
5.835
|
0.001
|
|
Substructure * Site
|
169578.567
|
51
|
3325.070
|
50.278
|
0.001
|
|
Substructure * Stage
|
1795.834
|
12
|
149.653
|
2.263
|
0.007
|
|
Ceramic * Site
|
2010.522
|
17
|
118.266
|
1.788
|
0.024
|
|
Ceramic * Stage
|
21168.211
|
4
|
5292.053
|
80.020
|
0.001
|
|
Site * Stage
|
28827.965
|
68
|
423.941
|
6.410
|
1.000
|
|
Substructure * Ceramic * Site
|
9974.445
|
51
|
195.577
|
2.957
|
0.001
|
|
Substructure * Ceramic * Stage
|
114.923
|
12
|
9.577
|
.145
|
1.000
|
|
Substructure * Site * Stage
|
1204.666
|
204
|
5.905
|
.089
|
1.000
|
|
Ceramic * Site * Stage
|
642.664
|
68
|
9.451
|
.143
|
1.000
|
|
Substructure * Ceramic * Site * Stage
|
707.302
|
204
|
3.467
|
.052
|
1.000
|
|
Error
|
523783.250
|
7920
|
66.134
|
|
|
|
Total
|
88120025.000
|
8640
|
|
|
|
|
Corrected total
|
9213877.574
|
8639
|
|
|
|
Abbreviations: df, degree of freedom; F, F-ratio; MS, mean square; SS, sum of squares.
Post hoc Bonferroni multiple comparisons showed significant differences in the internal
accuracy of restorations upon different factors tested ([Tables 3] and [4]). The internal discrepancy of ceramometal restorations as a factor of the substructure
fabrication techniques indicated that the CmDw (108.15 ± 30.6 µm) exhibited a significantly
greater internal gap than that constructed from the CmTt (97.11 ± 26.86 µm), SmDm
(89.42 ± 35.57 µm), and SmDt (87.58 ± 32.9 µm), respectively (p < 0.05) ([Fig. 4A] and [Table 3A]). The internal discrepancy of ceramometal restorations as a factor of stages of
fabrication revealed a significant difference in the internal gap among As (82.22 ± 28.34 µm),
De (99.5 ± 33.01 µm), Op (96.2 ± 32.17 µm), Co (101.51 ± 33.23 µm), and Gl (98.4 ± 32.64 µm)
stages (p < 0.05) ([Fig. 4A] and [Table 3B]). The internal discrepancy of ceramometal restorations as a factor of ceramic veneering
methods demonstrated a significantly larger internal gap upon veneering with conventional
layering (Pl) (96.76 ± 32.99 µm) compared to the pressed-on veneering (Pp) (94.37 ± 32.28 µm)
methods (p < 0.05) ([Fig. 4A] and [Table 3C]). The statistics also indicated significantly better internal accuracy upon the
metal substructures fabricated from sintered metal (Sm, 88.50 ± 34.27 µm) compared
to cast metal (Cm, 102.63 ± 29.31 µm) (p < 0.05) ([Fig. 4A] and [Table 3D]). The internal discrepancy of ceramometal restorations as a factor of sites of restoration
demonstrated a significantly larger internal gap from the gingival (G), axial (A),
gingivo-axial (Ga), axio-occlusal (Ao), and occlusal (O) locations, respectively,
for both buccal (Bu), lingual (Li), mesial (me), and distal (Di) sites (p < 0.05). Nevertheless, no significant difference in internal discrepancy of restoration
was found between BuG-LiG, MeG-DiG, BuA-LiA, BuGa-LiGa-MeA-DiA, MeGa-DiGa, MeAo-DiAo,
BuAo-LiAo, and O sites of Bu-Li and Me-Di directions (p > 0.05) ([Fig. 4B] and [Table 3E]). Post hoc Bonferroni multiple comparisons signified significant differences in
internal accuracy upon the different combinations of substructure fabrication techniques
and methods of ceramic veneering (p < 0.05), except between CmDwPl–CmDwPp, CmTtPl–CmTtPp, SmDmPl–SmDmPp–SmDtPl, and SmDtPl–SmDtPp–SmDwPp
groups (p > 0.05) ([Fig. 4C] and [Table 4A]). Bonferroni multiple comparisons signified a significant difference in internal
accuracy upon the different combination of stages of restoration fabrication and methods
of ceramic veneering (p < 0.05), except between AsPl–AsPp, DePl–DePp–OpPl–OpPp–CoPp–GlPp, and CoPl–GlPl groups
(p > 0.05) ([Fig. 4C] and [Table 4B]). Bonferroni multiple comparisons signified significant difference in internal accuracy
between the combination of substructure fabrication techniques and stages of restoration
fabrication (p < 0.05), except between CmTtAs–SmDtAs–SmDmAs groups, CmTtDe–CmTtOp–CmTtCo–CmTtGl
groups, SmDtDe–SmDtOp–SmDtCo–SmDtGl–SmDmDe–SmDmOp–SmDmCo–SmDmGl–CmDwAs groups, and
CmDwDe–CmDwOp–CmDwCo–CmDwGl groups (p > 0.05) ([Fig. 4D] and [Table 4C]).
Table 3
Post hoc Bonferroni multiple comparisons of internal accuracy of ceramic veneer alloy
as a factor of (A) substructures constructed from (cast: Cm; sintered: Sm) metal upon
different techniques (traditional: Tt; digitally impressed tooth: Dt; digitally impressed
model: Dm; and digitally milled wax: Dw), (B) stages of fabrication (as-cast: As;
degass: De; opaquing: Op; body contouring: Co; glazing: Gl), (C) ceramic veneering
methods (layering: Pl; Press-on: Pp), (D) alloys (cast: Cm; sintered: Sm), and (E)
sites (at gingival: G; gingiva-axial: Ga; axial: A; axio-occlusal: Ao; and occlusal:
O locations of the buccal: Bu; lingual: Li; mesial: Me; distal: Di surface)
|
(A) As a factor of substructures
|
(B) As a factor of fabrication stages
|
(C) As a factor of ceramic
|
|
Substructure
|
CmTt
|
SmDt
|
SmDm
|
CmDw
|
Stage
|
As
|
De
|
Op
|
Co
|
Gl
|
Ceramic
|
Pl
|
Pp
|
|
CmTt
|
1
|
0.001
|
0.001
|
0.001
|
As
|
1
|
0.001
|
0.001
|
0.001
|
.001
|
Pl
|
1
|
0.001
|
|
SmDt
|
|
1
|
0.001
|
0.001
|
De
|
|
1
|
0.001
|
0.001
|
.001
|
Pp
|
|
1
|
|
SmDm
|
|
|
1
|
0.001
|
Op
|
|
|
1
|
0.001
|
.001
|
(D) As a factor of alloys
|
|
CmDw
|
|
|
|
1
|
Co
|
|
|
|
1
|
.001
|
Alloy
|
Cm
|
Sm
|
|
Gl
|
|
|
|
|
1
|
Cm
|
1
|
0.001
|
|
|
Sm
|
|
1
|
|
(E) As a factor of sites
|
|
Site
|
Bu
|
O
|
Li
|
Me
|
O
|
Di
|
|
G
|
Ga
|
A
|
Ao
|
O
|
Ao
|
A
|
Ga
|
G
|
G
|
Ga
|
A
|
Ao
|
O
|
Ao
|
A
|
Ga
|
G
|
|
Bu
|
G
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
1
|
0.030
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.022
|
|
Ga
|
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
0.190
|
1
|
.001
|
0.001
|
0.004
|
1
|
0.001
|
0.001
|
0.001
|
1
|
0.001
|
0.001
|
|
A
|
|
|
1
|
0.001
|
0.001
|
0.001
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
|
Ao
|
|
|
|
1
|
0.001
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
|
O
|
O
|
|
|
|
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
|
Li
|
Ao
|
|
|
|
|
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
|
A
|
|
|
|
|
|
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
0.013
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
|
Ga
|
|
|
|
|
|
|
|
1
|
0.001
|
0.001
|
1
|
1
|
0.001
|
0.001
|
0.001
|
1
|
0.048
|
0.001
|
|
G
|
|
|
|
|
|
|
|
|
1
|
0.014
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.913
|
|
Me
|
G
|
|
|
|
|
|
|
|
|
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
1
|
|
Ga
|
|
|
|
|
|
|
|
|
|
|
1
|
0.071
|
0.001
|
0.001
|
0.001
|
0.022
|
1
|
0.001
|
|
A
|
|
|
|
|
|
|
|
|
|
|
|
1
|
0.001
|
0.001
|
0.001
|
1
|
0.017
|
0.001
|
|
Ao
|
|
|
|
|
|
|
|
|
|
|
|
|
1
|
0.001
|
1
|
0.001
|
0.001
|
0.001
|
|
O
|
O
|
|
|
|
|
|
|
|
|
|
|
|
|
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
|
Di
|
Ao
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
1
|
0.001
|
0.001
|
0.001
|
|
A
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
1
|
0.016
|
0.001
|
|
Ga
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
1
|
0.001
|
|
G
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
1
|
Table 4
Post hoc Bonferroni multiple comparisons of internal accuracy of ceramic veneer alloy
as a function of (A) the interaction of substructures (cast: Cm; sintered: Sm) metal
constructed from different techniques (traditional: Tt; digitally impressed tooth:
Dt; digitally impressed model: Dm; and digitally milled wax: Dw) and ceramic veneering
methods (layering: Pl; Press-on: Pp), (B) the interaction of stages of fabrication
(as-cast: As; degass: De; opaquing: Op; body contouring: Co; glazing: Gl) and ceramic
veneering methods, and (C) the interaction of substructures constructed from different
techniques and stages of fabrication
|
(A) As an interaction of substructures and ceramic
|
(B) As an interaction of stage of fabrication and ceramic
|
|
Sub*Por
|
CmTt
|
SmDt
|
SmDm
|
CmDw
|
Stage*Por
|
As
|
De
|
Op
|
Co
|
Gl
|
|
Pl
|
Pp
|
Pl
|
Pp
|
Pl
|
Pp
|
Pl
|
Pp
|
Pl
|
Pp
|
Pl
|
Pp
|
Pl
|
Pp
|
Pl
|
Pp
|
Pl
|
Pp
|
|
CmTt
|
Pl
|
1
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
As
|
Pl
|
1
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
|
Pp
|
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
Pp
|
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
|
SmDt
|
Pl
|
|
|
1
|
0.842
|
1
|
1
|
0.001
|
0.001
|
De
|
Pl
|
|
|
1
|
1
|
1
|
1
|
0.001
|
1
|
0.001
|
1
|
|
Pp
|
|
|
|
1
|
0.043
|
1
|
0.001
|
0.001
|
Pp
|
|
|
|
1
|
1
|
1
|
0.010
|
1
|
0.001
|
1
|
|
SmDm
|
Pl
|
|
|
|
|
1
|
1
|
0.001
|
0.001
|
Op
|
Pl
|
|
|
|
|
1
|
1
|
0.016
|
1
|
0.005
|
1
|
|
Pp
|
|
|
|
|
|
1
|
0.001
|
0.001
|
Pp
|
|
|
|
|
|
1
|
0.018
|
1
|
0.005
|
1
|
|
CmDw
|
Pl
|
|
|
|
|
|
|
1
|
0.052
|
Co
|
Pl
|
|
|
|
|
|
|
1
|
0.001
|
1
|
0.028
|
|
Pp
|
|
|
|
|
|
|
|
1
|
Pp
|
|
|
|
|
|
|
|
1
|
0.001
|
1
|
|
Gl
|
Pl
|
|
|
|
|
|
|
|
|
1
|
0.010
|
|
Pp
|
|
|
|
|
|
|
|
|
|
1
|
|
(C) As an interaction of substructure and stage of fabrication
|
|
Sub*Stage
|
CmTt
|
SmDt
|
SmDm
|
CmDw
|
|
As
|
De
|
Op
|
Co
|
Gl
|
As
|
De
|
Op
|
Co
|
Gl
|
As
|
De
|
Op
|
Co
|
Gl
|
As
|
De
|
Op
|
Co
|
Gl
|
|
CmTt
|
As
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
0.147
|
1
|
0.066
|
0.008
|
0.001
|
1
|
0.105
|
0.002
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
|
De
|
|
1
|
1
|
1
|
1
|
0.001
|
0.001
|
0.037
|
0.024
|
1
|
0.001
|
0.023
|
0.035
|
1
|
1
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
|
Op
|
|
|
1
|
1
|
1
|
0.001
|
0.001
|
0.001
|
0.004
|
0.023
|
0.001
|
0.001
|
0.022
|
0.100
|
0.015
|
0.003
|
0.009
|
0.001
|
0.001
|
0.001
|
|
Co
|
|
|
|
1
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
0.032
|
0.001
|
0.001
|
0.002
|
0.012
|
0.028
|
0.114
|
0.017
|
0.001
|
0.001
|
0.001
|
|
Gl
|
|
|
|
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.019
|
0.003
|
1
|
0.038
|
0.002
|
0.001
|
|
SmDt
|
As
|
|
|
|
|
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
|
De
|
|
|
|
|
|
|
1
|
1
|
1
|
1
|
0.001
|
1
|
1
|
1
|
0.153
|
0.713
|
0.001
|
0.001
|
0.001
|
0.001
|
|
Op
|
|
|
|
|
|
|
|
1
|
1
|
1
|
0.001
|
1
|
1
|
1
|
1
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
|
Co
|
|
|
|
|
|
|
|
|
1
|
1
|
0.001
|
1
|
1
|
1
|
1
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
|
Gl
|
|
|
|
|
|
|
|
|
|
1
|
0.001
|
1
|
1
|
1
|
1
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
|
SmDm
|
As
|
|
|
|
|
|
|
|
|
|
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
|
De
|
|
|
|
|
|
|
|
|
|
|
|
1
|
1
|
1
|
1
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
|
Op
|
|
|
|
|
|
|
|
|
|
|
|
|
1
|
1
|
1
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
|
Co
|
|
|
|
|
|
|
|
|
|
|
|
|
|
1
|
1
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
|
Gl
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
1
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
|
CmDw
|
As
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
1
|
0.001
|
0.001
|
0.001
|
0.001
|
|
De
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
1
|
1
|
1
|
1
|
|
Op
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
1
|
1
|
1
|
|
Co
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
1
|
1
|
|
Gl
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
1
|
Fig. 4 Internal accuracy as a function of (A) substructure fabrication techniques [cast metal constructed from the traditional
impressed tooth (CmTr), sintered metal constructed from the traditional impressed
model (SmDt), sintered metal constructed from the digitally impressed model (SmDm),
and cast metal constructed from digitally impressed wax (CmDw)], stages of fabrication
(as-cast: As; degassing: Ds; opaquing: Op; body contouring: Co; glazing: Gl), ceramic
veneering method (layering: Pl; Press-on: Pp), alloy types (cast metal; Cm, sinter
metal; Sm), (B) sites [gingival (G), gingiva-axial (Ga), axial (A), axio-occlusal (Ao), and occlusal
(O) location of the buccal (Bu), lingual (Li), mesial (Me), and distal (Di) surface],
(C) interaction of substructure fabrication techniques with ceramic veneering methods,
interaction of stages and ceramic veneering methods, and (D) interaction of substructure fabrication techniques and stages of fabrication.
Discussion
Although carefully prepared tooth abutments as well as a well-controlled process of
restoration construction, imprecision remains between the restorations and the prepared
abutments, which predisposes to caries and periodontal disease.[13] The more precisely the fit of the restoration adapts to the prepared tooth, the
smaller the internal gap displays, the slighter the cement film is bared to oral fluid,
as well as the better the retentive and the resistance to dislodgement of the restoration.
This study partially rejected the null hypothesis as there were significant differences
in internal accuracy of ceramometal crown upon metal substructure fabrication techniques,
stages of restoration fabrication, methods of ceramic veneering, sites of restoration,
and two factors interaction except for sites and stages of restoration fabrication.
However, no significant differences in the internal accuracy of ceramometal crown
upon three- and four-factor interaction were found, except only the interaction of
substructure fabrication technique, ceramic veneering methods, and site of restoration.
Hence, the alternative hypothesis was partially confirmed. However, the internal gap
for all the studied groups was less than 200 μm at the occlusal region and less than
100 μm at other regions, which is considerably accepted for internal misfit limit.[1]
[25]
[26]
The metal substructures fabricated either from CmTt or CmDw techniques exhibited less
internal accuracy than those fabricated either from SmDt or SmDm techniques, which
were consistent with other studies.[1]
[3]
[4]
[20] This could be attributed to the conventional lost wax cast technique, which is a
complex, sensitive, nonreproducible method, and requires high skill of dental technician
to achieve a precise fit of restoration. The internal discrepancy of metal substructures
constructed from the CmTt technique is primarily associated with the dimensional accuracy
of the conventional processes in the construction of the restoration including the
traditional impression technique of the prepared tooth (Tt), dimensional accuracy
of the stone model, and investing material together with the solidification shrinkage
volume of metal upon casting that directly influenced the restorations fit.[29] The internal discrepancy of the CmDw technique demonstrated a higher internal discrepancy
than the CmTt technique, which is probably related to the milled wax substructure
that additionally increases error accumulation in this process.[22] This was supported by other studies that reported the internal accuracy of the wax
coping produced by hand carving was more precise than the wax coping produced by digitally
milled wax.[5]
[8] The study indicated that metal substructure produced from sintered metal (Sm) provided
better internal accuracy than cast metal (Cm). This study was in agreement with other
previous studies.[4]
[7]
[9] The metal substructures constructed from the digital impression procedure either
from the intraoral scanner for making a digital impression of the prepared tooth or
the laboratory scanner for performing a digital impression of the stone die of the
stone model were both designed for the copings using a three-dimensional software
program and then milled the presintered metal blank with a CAM milling machine. These
techniques do not involve the process of lost wax and for that reason, the stable
dimensions seem to be achieved. Although fully sintered metal substructures must involve
the shrinkage of powder metal upon sintering, the compensation was planned during
CAD-designed substructures, which is considerably negligible.[6] The digital impression process normally creates somewhat rounded borders related
to the resolution for each scanner, which probably causes an early contact of restoration
at the axial-occlusal edges and causes a larger internal gap. The process of digital
impression-taking usually makes the overshooter peak around the edges of the target
and causes a higher internal inaccuracy.[10] This occurrence was expressed in every single CAD-CAM that involves digital impressions.[6] The cloud points gained from the digitally scanned process were converted into a
continuously smooth surface depending on the proficiency of the designed software.
This procedure can also steer to some impreciseness. However, the process of milling
presintered metal blank is quite soft, seems easy, is not prone to establish internal
cracking, and has less stress accumulation on the presintered substructure.[1]
[7]
[20] The internal accuracy of sintered metal substructures was comparable with either
the presintered metal constructed from the STL file derived from digitally impressed
tooth or digitally impressed model. This is probably related to the preciseness of
the prepared tooth and the stone die was comparable. The result was consistence with
other studies that found no significant difference between the digital impression
of the prepared tooth and the prepared stone die.[30] Furthermore, the study signified that the restoration constructed from sintered
metal revealed superior internal fit than those constructed from cast metal as supported
by other studies.[4]
[7]
[9]
Concerning the stages of restoration fabrication, the internal accuracy of the restoration
was affected by the sequential stages of fabrication. Before veneering with ceramic,
the Sm copings revealed superior internal preciseness than the Cm copings as supported
by other studies.[1]
[2] A significant increasing internal gap of restorations upon as-cast to degassing,
opaquing, contouring, and glazing process was evidenced, which corresponded with other
studies.[1]
[11]
[18]
[21] The greatest increasing internal gap was found after the degassing process. Metal
substructures exposed to extremely high temperatures during the porcelain firing stage
possibly produce dimensional distortion and finally decrease the preciseness of the
restoration. The result of this study corresponded with other studies that stated
the greatest distortion of ceramic veneered metal occurs during the degassing stage.[11]
[18]
[21] This study used nonnoble metal alloy for fabricated metal substructure because of
low cost, biocompatibility, resistance to corrosion, and stable in biological environments.
However, the inherited disadvantage of nonnoble metal alloy is the thick oxide layer
formation on the surface upon the degassing process. The degassing process took place
at an elevated temperature and could cause the grain growth of the deformed crystals
and was postulated to cause greater internal discrepancy upon degassing due to the
composition of metal substructure as confirmed by other studies.[17]
[21] The increase in internal gap after sequential ceramic sintering generally influenced
by numerous factors, for example, the ceramic firing shrinkage, the coefficient of
thermal expansion (CTE) of metal (Cm = 14.5 × 10−6K−1, Sm = 14.5 × 10−6K−1), and ceramic (Pl = 12.9 ± 0.5 × 10−6K−1, Pp = 13.2 ± 0.5 × 10−6K−1), and the residual stresses generated from multiple firing processes. The CTE differences
of Pl to both alloys were slightly larger than the CTE differences of Pp to those
alloys. This probably induced higher residual stress on the layering system than the
press-on system, and caused a larger internal gap for the layering groups compared
to the pressed-on groups, as supported by other studies.[1]
[5] However, this study indicated that internal discrepancies occurred after ceramic
veneering, ceramic firing shrinkage as a causative factor in the internal misfit,
were not primary factors in distortion as in agreement with other studies.[1]
[15]
[22]
The ceramic veneering methods could generate different internal discrepancies of metal-ceramic
restorations, which exhibited less internal distortion upon veneering with pressable
ceramics. The internal accuracy of restoration veneered with pressed-on ceramic (Pp)
was better than restoration veneered with conventional layering ceramic (Pl), which
was supported by other studies.[12]
[22]
[23] This might be the effect of the number of ceramic firing cycles. The conventional
ceramic veneering technique normally requires more firing cycles and higher skillfulness
of dental technicians than the pressed-on techniques during the dentine porcelain
contouring process. The press-on ceramic veneering technique requires full contour
wax-up of the restoration on the substructure and then replaces it with pressed ceramic.
This technique also eliminates technical errors from the porcelain firing process
and multiple firings in conventional ceramic layering, thus reducing accumulated internal
discrepancies.[23] Increased internal gap was reported from contamination of ceramic at the intaglio
surface of metal substructure upon ceramic layering, while this event never occurred
in the press-on technique.[22]
A larger internal gap was exhibited at the occlusal region than at the axio-occlusal,
axial, gingiva-axial, and gingival locations, respectively. This is probably associated
with the configuration of the restoration shrinkage through the processes of fabrication
that are exhibited in three dimensions. The characteristics of firing shrinkage occur
toward the center of the restoration and cause inaccuracy on the occlusal and proximal
sites more than on the other sites as other reports.[19]
[24] There are many techniques for evaluating internal accuracy of restorations such
as direct viewing, cement thickness measurement, cone-beam computed tomography, and
silicone replica technique.[28] This study uses the silicone replica technique because it provides several advantages
of the measuring process without destroying the specimen, repeating the measurement,
high reliability, and precision.[14]
[28] Nevertheless, the color of the silicone replica should be extremely different from
the color of the pick-up silicone used for sandwiching replica to mitigate error during
evaluation of the internal gap. Since this study used the prepared premolar size metal
tooth abutment that has the preparation conforming with the geometry of the tooth,
thus the locations of the internal accuracy were assigned at 18 sites on the bucco-lingual
and mesio-distal direction to eliminate the confounding effect from sectioning silicone
replica upon other sites. Thus, it is suitable for the evaluation of internal accuracy
at different stages of fabrication in this study.
Since ceramic veneer sintered metal is comparatively new and rapidly utilized in clinical
practice, there are several techniques to derive for final restorations. The information
on the accuracy of restoration in this experiment founded on the systematized circumstances
concerning the study design, metal substructure fabrication techniques, ceramic veneering
methods, method of evaluation, and experimental implementation providing realistically
important scientific value for dentists in decision-making for dental reconstruction
using digital approached ceramic veneer metal restoration in their dental practices.
Nevertheless, upon the study's limitations, sintered metal substructures either fabricated
from digitally impressed tooth or digitally impressed stone model, whether ceramic
veneering by layering or press-on methods, provided better internal accuracy than
cast metal substructures either fabricated from traditional lost wax or digitally
milled wax, even if ceramic veneering by layering or press-on technique. However,
the operator and the equipment calibration need to be considered, which could influence
the results. Nevertheless, all techniques described in the study satisfied precise
internal fit and were clinically acceptable for the fabrication of ceramic veneer
metal restorations for oral reconstruction.[14]
[25]
[26] Still, the effects of different types of dental cement and the potential impact
of internal accuracy of ceramometal restoration on the long-term clinical use need
to be further investigated.
Conclusion
This study confirmed that the internal accuracy of ceramometal restorations was significantly
affected by the different metal substructure fabrication techniques, ceramic veneering
methods, sequential stages of restoration fabrications, and sites of restorations.
Sintered metal substructures either fabricated from digitally impressed tooth (SmDt)
or digitally impressed stone models (SmDw) achieved better internal accuracy than
cast metal substructures either fabricated from traditional lost wax (CmTt) or digitally
milled wax (CmDw). Ceramic press-on metal substructure generated better internal accuracy
than the conventional ceramic layering method. A continued increase in internal inaccuracies
of ceramic veneer metal through the sequential restorative fabrication processes was
addressed, with the greatest increasing internal inaccuracies occurring during the
degassing process and sequential ceramic sintering. Higher internal inaccuracies were
exhibited more on the occlusal and axio-occlusal sites than on the other sites. Nevertheless,
the ceramic veneered metal restoration fabricated in this study has shown clinically
acceptable internal accuracy. The study suggests fabricating ceramometal restoration
with a sintered metal substructure and veneered with a ceramic press-on technique
to derive suitable internal accuracy for restorative reconstruction.
