Prosthetic misfit of implant-supported prosthesis obtained by an alternative section method.

Abstract

Adequate passive-fitting of one-piece cast 3-element implant-supported frameworks is hard to achieve. This short communication aims to present an alternative method for section of one-piece cast frameworks and for casting implant-supported frameworks.
Three-unit implant-supported nickel-chromium (Ni-Cr) frameworks were tested for vertical misfit (n = 6). The frameworks were cast as one-piece (Group A) and later transversally sectioned through a diagonal axis (Group B) and compared to frameworks that were cast diagonally separated (Group C). All separated frameworks were laser welded. Only one side of the frameworks was screwed.
The results on the tightened side were significantly lower in Group C (6.43 ± 3.24 µm) when compared to Groups A (16.50 ± 7.55 µm) and B (16.27 ± 1.71 µm) (P<.05). On the opposite side, the diagonal section of the one-piece castings for laser welding showed significant improvement in the levels of misfit of the frameworks (Group A, 58.66±14.30 µm; Group B, 39.48±12.03 µm; Group C, 23.13±8.24 µm) (P<.05).
Casting diagonally sectioned frameworks lowers the misfit levels. Lower misfit levels for the frameworks can be achieved by diagonally sectioning one-piece frameworks.

Full text

Page 1

INTRODUCTION
Complete passive fitting of one-piece cast implant sup-
ported frameworks has been hard to achieve according to
reports from the last three decades.1In addition to load bear-
ing capacity, marginal accuracy and clinically acceptable
levels of misfit are crucial factors influencing the clinical
long-term reliability of fixed partial dentures (FPDs).2Misfit
levels of up to 100 ㎛ were once stated as clinically acceptable.3
Laser welding has been used to correct ill-fitting implant-sup-
ported frameworks4and may decrease the strains transferred
to the implant-bone interface.5Previous studies found that laser
welding of implant-supported frameworks is capable of
reducing the prosthetic misfit.4,6-8The diagonal section of
one-piece castings for laser welding reduces the misfit levels
of implant-supported frameworks.9,10Laser welding is also able
to concentrate the laser energy near the welded surface, thus
minimizing distortion of heat-sensitive materials.11
This study aims to evaluate the vertical misfit of three-
unit implant-supported frameworks, cast as one-piece and
later sectioned in its diagonal axis in the attempt to lower the
misfit levels of the one-piece cast frameworks compared to cast
diagonally separated.10The tested null hypothesis was that no
differences would be found between casting one-piece frame-
works and sectioning the one-piece cast frameworks for laser
welding. The misfit levels found for the frameworks that
were cast diagonally separated were used as a parameter for
the improvement in the levels of misfit for the first two
groups.
MATERIALS AND METHODS
This study followed previously described methodology4,12and
used a machined metal matrix with two internal hex cylinder
threaded implants embedded parallel to each other ( � 3.75 mm
× 11 mm, Titamax II Plus, Neodent, Curitiba, PR, Brazil).
Prosthetic misfit of implant-supported prosthesis
obtained by an alternative section method
Rodrigo Tiossi1*, PhD, Hilmo Barreto Leite Falca ̃ ̃o-Filho2, PhD, Fa ′
Renata Cristina Silveira Rodrigues1, PhD, Maria da Gloria Chiarello de Mattos1, PhD, Ricardo Faria Ribeiro1, PhD
′ bio Afra
∧∧nio de Aguiar Ju ′′ nior1, MSc,
1Department of Dental Materials and Prosthodontics, Dental School of Ribeira ̃o Preto, University of Sa ̃o Paulo, Ribeira ̃o Preto,
SP, Brazil, 2Department of Occlusion and Prosthodontics, Dental School of Sobral, University of Ceara′, Sobral, CE, Brazil
PURPOSE. Adequate passive-fitting of one-piece cast 3-element implant-supported frameworks is hard to achieve. This short communica-
tion aims to present an alternative method for section of one-piece cast frameworks and for casting implant-supported frameworks. MATERIALS
AND METHODS. Three-unit implant-supported nickel-chromium (Ni-Cr) frameworks were tested for vertical misfit (n = 6). The frameworks were
cast as one-piece (Group A) and later transversally sectioned through a diagonal axis (Group B) and compared to frameworks that were cast
diagonally separated (Group C). All separated frameworks were laser welded. Only one side of the frameworks was screwed. RESULTS. The
results on the tightened side were significantly lower in Group C (6.43 ± 3.24 ㎛) when compared to Groups A (16.50 ± 7.55 ㎛) and B (16.27
± 1.71 ㎛) (P<.05). On the opposite side, the diagonal section of the one-piece castings for laser welding showed significant improvement
in the levels of misfit of the frameworks (Group A, 58.66±14.30 ㎛; Group B, 39.48±12.03 ㎛; Group C, 23.13±8.24 ㎛) (P<.05). CON-
CLUSION. Casting diagonally sectioned frameworks lowers the misfit levels. Lower misfit levels for the frameworks can be achieved by diag-
onally sectioning one-piece frameworks. [J Adv Prosthodont 2012;4:89-92]
89
KEY WORDS: Dental implants; Implant-supported dental prosthesis; Prosthesis fitting; Prosthodontics; Fixed partial denture; Dental soldering
Corresponding author: Rodrigo Tiossi
Department of Dental Materials and Prosthodontics, Dental School of Ribeira ̃o Preto
- University of Sa ̃o Paulo,
Av. do Cafe ′ , s/n - Monte Alegre, 14040-904 - Ribeira ̃o Preto - SP - Brazil
Tel. 55 16 3602 4046: e-mail, rtiossi@yahoo.com
Received January 26, 2012 / Last Revison May 2, 2012 / Accepted May 7, 2012
ⓒ 2012 The Korean Academy of Prosthodontics
This is an Open Access article distributed under the terms of the Creative Commons
Attribution Non-Commercial License (http://creativecommons.org/licenses/by-
nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction
in any medium, provided the original work is properly cited.
http://dx.doi.org/10.4047/jap.2012.4.2.89
ORIGINAL ARTICLE
J Adv Prosthodont 2012;4:89-92

Page 2

Prosthetic abutments (Mini conical abutments II Plus, Neodent,
Curitiba, PR, Brazil) were screwed to each implant and tight-
ened to 20 Ncm.12All specimens were made using the afore-
mentioned model, which also served as an index for measuring
the accuracy of the casting and soldering procedures.
Plastic cylinders (Mini conical abutment cylinder, Neodent,
Curitiba, PR, Brazil) were screw-retained to each implant and
the cylinders were bonded using acrylic resin (Pattern Resin
LS, GC America Inc., Costa Mesa, CA, USA). A 3-unit
implant-supported FPD framework was then waxed. The
first waxed framework was used as a pattern for the two
groups that were formed (n = 6) and cast in Ni-Cr alloy
(VeraBond II, Aalba Dent. Inc., Cordelia, CA, USA). Group
A was formed by one-piece castings (control group); Group
B used one-piece castings from Group A that were later
transversely sectioned in a diagonal direction in the pontic area9;
and Group C, with the waxed frameworks transversely sectioned
(0.3 mm apart) with surgical blades in a diagonal direction in
the pontic area before casting10(Fig. 1). One-piece frameworks
from group A were sectioned in the pontic with a 0.18 mm thick
diamond disk (Diamond disk #940, Komet USA, Rock Hill,
SC, USA) (Groups B). The two parts of each framework
from groups B and C were laser-welded (Fig. 2) (Desktop Laser,
Dentaurum, Ispringen, Germany) according to settings of
previous study (300 V, pulse duration of 9.0 ms and welding
spot diameter of 0.78 mm).10
Specimens were tested for passive fit by tightening the
screws to 10 Ncm.12The first measurement of the misfit lev-
els between the implant abutment and the FPD framework was
made with one screw tightened. The reading was made on both
tightened and opposite sides. The screw location was changed
for the second reading.4,12Three measurements were per-
formed in an optical microscope (Nikon Corp., Tokyo, Japan)
at 15× magnification at buccal, lingual, and proximal aspects,
totalizing 12 points for each cylinder/condition12so as to sam-
ple all proximal aspects of the cylinder circle.
After all reading procedures, the specimens were coronally
sectioned and submitted to scanning electron microscopy
(SEM) to check the quality of the diagonal welding technique.
ANOVA was applied for one criteria (frameworks' separa-
tion) and the Tukey-Kramer test was used for the comparisons
between the groups (P<.05) when significant differences
were found (JMP 6.0, SAS Institute, Cary, NC, USA).
RESULTS
Table 1 and Fig. 3 present means, standard deviations and
Tukey-Kramer's test results found in this study. With one
screw tightened and on the tightened side, Group C showed sig-
nificantly better results (P<.05). On the opposite side, laser weld-
ed Groups B and C, when compared to Group A, showed sig-
nificantly better passive fitting (P<.05).
Coronally sectioning the diagonally welded frameworks
and submitting to SEM at 50× magnification found a suffi-
ciently welded surface (Fig. 4).
90
Prosthetic misfit of implant-supported prosthesis obtained by an alternative section method
J Adv Prosthodont 2012;4:89-92
Tiossi R et al.
Fig. 1.Framework transversely sectioned with a diagonal direction in the
pontic area.
Fig. 2.Vestibular view of a laser-welded framework.
Table 1.Means (SD) and Tukey-Kramer test results of abutment/frame-
works interfacial gaps (㎛) for all groups and under all reading conditions
Tightened side
GroupsMean (SD)
Tukey-Kramer's test*
Group A 16.50 (7.55)a
Group B16.27 (1.71)a
Group C6.43 (3.24)b
Critical value = 3.25714; P<.05
*Values with different super scripts are significantly different (Tukey-
Kramer test).
Opposite side
Mean (SD)
Tukey-Kramer's test*
58.66 (14.30)a
39.48 (12.03)b
23.13 (8.24)b

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DISCUSSION
This study found that casting frameworks separately using
a diagonal section, presented lower misfit values among
groups, though it was not statistically significant in some
cases. Diagonally sectioning one-piece cast frameworks can
promote better fitting results. Complete passivity however can-
not be reported. This finding is consistent with the results found
in previous studies examining the lack of complete passivity
with frameworks, as seen in the results showed in the one-screw
test.4,12
This study focused in the experimental diagonal section
for framework casting and for sectioning one-piece castings
for laser welding. The groups were divided aiming to compare
whether the misfit found for the one-piece castings could
be corrected using the diagonal section. Also, a group cast with
the diagonal section was formed (Group C) so as to provide infor-
mation whether it would be better to cast diagonally sec-
tioned frameworks and whether the diagonal section could be
used to improve the passive fitting of one-piece castings.
The need for a lesser amount of material added to the weld-
ed region for laser welding reduces the volume of metal that
is going to suffer from cooling contraction, thus leading to less
distortions of the welded frameworks.10The diagonal section
of the implant-supported frameworks is expected to provide
a better overlap between the sectioned regions; this feature could
allow for an easier welding procedure, contributing for the reduc-
tion of molten alloy between the welded surfaces. For con-
ventional dental soldering, the parent alloys are soldered
with different types of alloy solder, thus reducing the strength
of the soldered joints and accounting for the failure at the joints
of soldered restorations.13A significant lower misfit level
for the welded frameworks was found in the analysis of data
from the opposite side to the tightened side. Earlier studies found
varying misfit from 10 to 160 ㎛,4,14,15thus validating the
casting and sectioning procedures used in this study. The
levels of misfit that were found in this study were within clin-
ically acceptable ranges (under 100 ㎛).16
The diagonal section of the frameworks allowed for a
smaller joint thickness than that occurring in conventional trans-
versal welding, minimizing horizontal and vertical distor-
tions in the framework position.9These results are in accordance
with another previously published study.10In a study using two
different joint types,17beveled-edged specimens presented
smaller deformation than square-edged surfaces. Laser irradiation
also reached deeper penetration in the beveled-edged specimens.17
It has been suggested that the 'I' design (perpendicularly to the
long axis) or transversal section of joints is not the best sec-
tion for large diameters, because of the limited power supply
of the dental welding machines.18Conversely, the 'X' design,19
may lead to better laser-welded joints. In such design, the cen-
ter is maintained juxtaposed to the sections with thin diame-
ters, permitting deep laser-beam penetration.
Some distortion of the implant-supported frameworks may
occur after the firing cycles required for porcelain application.
Some studies have found that the contributing factors could be
contamination of porcelain to the inner surface of metal cop-
ing and reduction in resilience of metal,20the degassing stage
and the final glaze stage of the porcelain firing cycle.21
However, other studies found that porcelain application had
no effect on casting distortion.22-24No differences were found
for the horizontal fit after porcelain firings between as-cast and
after soldering specimens.25-27
Further studies are necessary to evaluate whether the diag-
onally welded frameworks are capable of providing sufficient
strength to withstand the occlusal forces that the frameworks
are subjected during chewing.
91
Prosthetic misfit of implant-supported prosthesis obtained by an alternative section method
J Adv Prosthodont 2012;4:89-92
Tiossi R et al.
Fig. 3. Means and standard deviations for all groups and under all
reading conditions.
Tightened side Opposite side
80
60
40
20
0
Prosthetic misfit (㎛)
Group A
Group B
Group C
Fig. 4. SEM image of the coronal section of the diagonally welded
framework.

Page 4

CONCLUSION
This study presented a way to minimize framework misfit and
its associated problems by transversely sectioning in a diag-
onal section through the framework before casting and after
one-piece castings. This procedure increased the accuracy of
fit and passivity of the frameworks, thus helping to create a suc-
cessful prosthetic rehabilitation.
ACKNOWLEDGMENTS
The authors thank Neodent (Curitiba, PR, Brazil) for providing
the implants and implant components.
The authors declare that they have no conflict of interest.
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