Braz J Oral Sci. October-December 2005 - Vol. 4 - Number 15
Effect of different torque levels on the
implant/abutment interface using
castable “UCLA” abutments
Gustavo Augusto Seabra Barbosa1
Paulo Cézar Simamoto Junior2
Alfredo Júlio Fernandes Neto3
Maria da Glória Chiarello de Mattos4
Flávio Domingues das Neves5
1
DDS, MS, PhD Student, School of Dentistry
of Ribeirão Preto, University of Sao Paulo.
Substitute Professor at Department of Fixed
Prosthodontics, Occlusion and Dental
Materials, Federal University of Uberlandia.
2
DDS, MS, PhD Student, Piracicaba Dental
School, State University of Campinas
3
DDS, MS, PhD, Titular Professor at
Department of Fixed Prosthodontics,
Occlusion and Dental Materials, Federal
University of Uberlandia
4
DDS, MS, PhD, Professor at Department of
Dental Materials and Prosthesis at School of
Dentistry of Ribeirão Preto, University of Sao
Paulo
5
DDS, MS, PhD, Assistant Professor at
Department of Fixed Prosthodontics,
Occlusion and Dental Materials, Federal
University of Uberlandia
Abstract
The abutment/implant interface has been reported as a significant factor
on tensile transfer, adverse biological responses or prosthetic restoration
complications. The abutment/implant junction success is directly related
to pre-load attained during torque application. The purpose of this
work was to assess the vertical fit/misfit degree on abutment/implant
interface, when castable “UCLA” type abutments are used on fixed
prosthesis process on implants, after different torque levels
applications. Four three-unit fixed prosthesis were manufactured by
the same laboratory. Torque was applied on the same framework using
initially a 10 Ncm (T1) and later, a 20 Ncm torque level (T2) with a
screwdriver hand Torquimeter. Trough scanning electronic microscope
(SEM), it was obtained two photographs corresponding to mesial and
distal regions of each prosthesis unit, summing 24 assessed regions to
each applied torque value. After submitting the results to statistical
analyses Paired T-Test (p<0.05), a significant difference was seen
between the average vertical fit/misfit degree: T1 = 23.53mm ± 20.20;
T2 = 9.01m ± 11.69 (p=0.000). The misfit degree decrease when applied
manufacturers recommended torques, could decrease mechanical
(loosening or fracture of the screw) complications.
Key Words:
dental implants, prosthetic adjustment, torque
Received for publication: May 24, 2005
Accepted: November 21, 2005
Correspondence to:
Gustavo Augusto Seabra Barbosa
Av: Brasil , 4800, Bl. C; Apt 102 – Umuarama
CEP: 38405-312 – Uberlândia/MG
Phone: (34) 3232-7356
E-mail: [email protected] /
[email protected]
919
Braz J Oral Sci. 4(15):919-922
Effect of different torque levels on the implant/abutment interface using castable “UCLA” abutments
Introduction
The abutment/implant interface has been reported as a
significant factor on stress transfer, adverse biological
response or prosthetic restoration complications1. Michalakis
et al.2 reported two likely complications types inherent to a
misfit of the prosthetic framework: a) biological – increased
load transfer to bone, bone loss, and microflora development
in the micro-gap between implant and abutment3-4; and b)
prosthetics – loosening or fracture of the screw and implant
loss 5.
Due to periodontal ligament absence, implants are incapable
to readily adapt to misfit restorations induced stresses6. It
should than, have a relative precision on fit between
prosthesis and abutments, as also between prosthesis and
implants7, to the implant-supported restorations long term
success 8. However, there’s no perfect fit, and thus, the
clinicians should accept certain misfit level, which doesn’t
affect the bone/implant interface health9. According to early
information about osseointegration, it is considered that an
acceptable fit, values less than 10µm10.
The screw tightening aim to maintain the union between
components. However, during function, micro-gaps could
be formed on the abutment/implant interface due to an
untight abutment fixture, favoring bacterial invasion, as well
as mechanical problems11.
On every implant system the fixture joint system efficiency
depends on several factors: the component design;
connection geometry between implant and abutment;
mechanical adjustment between fixture and its set surface
on abutment; the mechanical and physical component
properties and torque application12.
The tension needed to maintain two parts of the same
junction tightly united, either under static or dynamic
conditions, is referred as preload13. Surface imperfections
lead to friction rising and to decreasing of such pre-load.
Increasing the same is due to screw take off and consequent
tightening 13-14 . During abutment screw tightening, a
compressive strength is generated to keep implant and
abutment surfaces in touch. This joint success is directly
related to attained pre-load during torque and for this preload maintenance with time. The fixture untightening, as also
the pre-load reduction to critical levels, can compromise the
joint stability, making a clinical failure more powerful15.
Regarding to the screw tightening, some authors report that
increasing the torque applied on screws, the compression
between the facing surfaces is also increased, producing a
greater stability on the joint16.
In one study comparing the micro-leakage level on abutment/
implant interface of five implant systems, varying the torque
between 10 Ncm and 20 Ncm, the authors observed significant
differences on micro-leakage between applied torques. There
was a significant decrease when the torque was near to
recommended values17.
920
Due to a great misfit presented by UCLA abutment, this study
aims to evaluate the vertical fit/misfit degree on abutment/
implant interface, when using castable “UCLA” type
abutments, with different torque levels.
Material and Methods
Four three unit fixed prosthesis were manufactured from a
metallic matrix with three compatible Brånemark implants
(3,75x10mm) (Conexão Sistemas de Prótese, Sao Paulo, SP,
Brazil). Those were made of castable UCLA type abutments
(Conexão Sistemas de Prótese, Sao Paulo, SP, Brazil), with
nickel-chrome alloy (Verabond II, Albadent Inc., USA). The
frameworks were united with conventional solder method.
They were placed on the matrix, first with 10 Ncm torque
(screwdriver hand Torquimeter, Conexão Sistemas de Prótese,
Sao Paulo, SP, Brazil) (Treatment 1 – T1) so the first analyze
could be done, using the scanning electronic microscopy
(SEM, LEO 435 VP, GERMANY), at a x500 magnification.
Later, the same frameworks were placed, with a 20 Ncm torque
(Treatment 2 – T2), to the last analyze.
For each framework “dental unit”, two images were obtained,
one mesial and other distal, making a total of 24 images. The
images were printed using a laser printer (Laser Jet 1500L,
Hewlett Packard, USA). From the printed photos, a ruler was
built with the micrometers scale existing on the lower portion
of the images, by a rule of three.
Tracing a line paralleled to the implant platform and other
parallel to lower surface of the abutment the vertical fit/misfit
value can be obtained, if it’s present. Looking for a better
view of the results, the measurement site received a number
(Table 1). Factors as visual accuracy, view angle, light and
professional experience, were described by Kan et al.18, as
the factors that could interfere on the accurate determination
of misfit. To minimize those interference factors, three
examiners were trained to the measurements. Statistical
processing was done using the SPSS data program (SPSS/
PC for Windows Inc., Chicago, IL). Parametric statistical test
were used, with the Paired T- test for paired samples. A pvalue less than 0.05 was considered statistically significant.
Results and Discussion
The three examiners mean values for vertical misfit after two
torque levels apply (T1 and T2) are expressed in µm, on
Table 2. As showed on table 2, all misfit values were larger
when 10 Ncm load was applied, decreasing, in some cases,
more than 35µm after applied torques of 20 Ncm load (as
show regions 13 and 19, table 2). After 20 Ncm torque
application sixteen analyzed regions presented values less
than 10µm and figures 1 and 2 exemplify the best fit obtained
with this torque level. The statistical analysis (Paired Ttest) presented significant difference in the vertical fit among
the two levels of applied torques (p=0.000), being lower when
used 20 Ncm.
Braz J Oral Sci. 4(15):919-922
Effect of different torque levels on the implant/abutment interface using castable “UCLA” abutments
Table 2. The three examiners average for vertical misfit, in µm.
Table 1. Regions of mensuration.
LOCAL
REGIONS
Mesial of right upper premolar
Distal of right upper premolar
Mesial of first right upper molar
Distal of first right upper molar
Mesial of second right upper molar
Distal of second right upper molar
Mesial of left upper premolar
Distal of left upper premolar
Mesial of first left upper molar
Distal of first left upper molar
Mesial of second left upper molar
Distal of second left upper molar
Mesial of right inferior premolar
Distal of right inferior premolar
Mesial of first right inferior molar
Distal of first right inferior molar
Mesial of second right infeior molar
Distal of second right infeior molar
Mesial of left inferior premolar
Distal of left inferior premolar
Mesial of first left inferior molar
Distal of first left inferior molar
Mesial of second left inferior molar
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Distal of second left inferior molar
24
Torque Level
Regions
T1
10NCm
T2
20NCm
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
27.5
55
23.3
5
10
13.3
30
2.5
10
10
9.1
50
65
5
22.5
30
25
5
65
50
2.5
5
35
15
30
8
5
2.5
10
5
0
0
0
5
30
30
0
0
0
0
0
27.5
25
0
0
23.3
24
9.1
0
Fig.1. Vertical misfit after 10 Ncm torque application.
Fig. 2. Absence of the misfit in the same abutment, after 20 Ncm
torque application
In the present study, a misfit until 10µm was concerned as
clinically acceptable10, because an absence of perfect fit
between abutment and implant9.
A relative precision on the fit between prosthesis and
abutment, as well as prosthesis and implant7, is important for
the long term success of implant-supported restorations1,8.
Because of the absence ligament between bone and implants
the restorations misfit could induce stresses on the marginal
bone6. An abutment-implant interface misfit could produce
mechanical and biological problems2-5,11.
Factors such as torque application were described like
important characteristics for the efficiency of screw junction
on implant systems12. The casting process could change the
mechanical performance and structural properties of the
contacting surfaces during screws tightening, changing
either, the frictional resistance value of the applied torque12.
921
Braz J Oral Sci. 4(15):919-922
Effect of different torque levels on the implant/abutment interface using castable “UCLA” abutments
It could also compromise the junction stability, increasing to
possibility of clinical failure15. In the present study, when the
castable UCLA and the casting process were used, the fit
degree was significantly modified in relation to torque level.
The present study observed a significant difference on fit
degree between abutment/implant interface related to the
screw applied torque. When applying different torque levels
(10 and 20 Ncm), a lower misfit was observed when 20 Ncm
was used. In this torque level, sixteen regions presented
values clinically acceptable (less than 10µm), while 10 Ncm
torque level presented thirteen regions with larger values
than 10µm (table 2). Jörnéus et al. 16 observed that when
increasing the applied torque level on screws, the
compression between the contacting surfaces also increases
producing a greater stability on the junction and lower misfit.
Screwed junctions with torques exceeding the recommended
present lower micromovement, without apparent system
commitment 11,14. However, it agrees in part with such
affirmative since in the situation of 10 Ncm torque greater
misfit were observed. Nonetheless, applying torque greater
than recommended can produce an exacerbated stress on
screws. Still on the presence of a misfit in which the tow
faces (implant platform and abutment base) are not in ideal
contact and hence it can’t have contact by load apply. This
screw will experience its maximum loading, thus decreasing
its life-span19. On a static analyze, with the screw tightening
besides the manufacturers recommended levels it can
obtaining a more stable junction decreasing the problems
with screw loosening14.
On another study varying torques between 10 Ncm and 20
Ncm, the authors observed that fluids and small molecules
have the capacity of penetrating the abutment/implant
interface of all studied systems. However, there are significant
differences on micro-leakage between the 10 Ncm and 20
Ncm torques, decreasing significantly when the torque was
near to the recommended values17. In the present study, a
lower misfit is observed when applying manufacturers
recommended torques (20 Ncm), and it could difficult the
microorganisms penetration on abutment/implant interface,
decreasing the potential of biological risks to restorations.
According to the results obtained in this study, the
application of appropriate torques can decrease implant/
abutment misfit, and thus could decrease mechanical
(loosening or fracture of the screw) complications.
Acknowledgments
Conexão Sistemas de Prótese LTDA;
Professor Elliot Watanabe Kitajima from the ESALQ (Escola
Superior de Agricultura “Luiz de Queiroz”).
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