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Shock Absorption Capacity of Restorative Materials for Dental Implant Prostheses: An In Vitro Study

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Purpose: To measure the vertical occlusal forces transmitted through crowns made of different restorative materials onto simulated peri-implant bone. Materials and methods: The study was conducted using a masticatory robot that is able to reproduce the mandibular movements and forces exerted during mastication. During robot mastication, the forces transmitted onto the simulated peri-implant bone were recorded using nine different restorative materials for the simulated single crown: zirconia, two glass-ceramics, a gold alloy, three composite resins, and two acrylic resins. Three identical sample crowns for each material were used. Each crown was placed under 100 masticatory cycles, occluding with the flat upper surface of the robot to evaluate the vertical forces transmitted. Two-way analysis of variance was used. Alpha was set at .05. Results: The statistical evaluation of the force peaks recorded on the vertical z-axis showed mean values of 641.8 N for zirconia; 484.5 N and 344.5 N, respectively, for the two glass-ceramics; 344.8 N for gold alloy; 293.6 N, 236 N, and 187.4 N, respectively, for the three composite resins; and 39.3 N and 28.3 N, respectively, for the two acrylic resins. Significant differences were found between materials (P < .0001), except for the comparison between gold alloy and one of the glass-ceramics. Conclusion: Composite and above all acrylic resin crowns were more able to absorb shock from occlusal forces than crowns made of zirconia, ceramic material, or gold alloy.
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Volume 26, Number 6, 2013 549
Implant dentistry has become an increasingly effective
method for correcting edentulism, either partially or
completely. Implant treatments exhibit an overall excel-
lent clinical success rate in the long term.1–4 Despite its
rare occurrence, the reasons for peri-implant bone loss
and implant failure in some patients are not completely
understood. Multifactorial aspects (general health,
bone quality and quantity, surgical procedure, implant
characteristics, parafunctional habits, occlusal over-
loading, medications, bacterial insult, etc) potentially
induce peri-implant bone damage. However, the role
of some of these aspects in reaching and maintaining
osseointegration is controversial.5 Several authors con-
sider occlusal load a crucial factor affecting the dental
implant healing phase and the long-term survival and
success of dental implants.6 –12
In teeth, a semi-elastic connection between the
tooth and bone exists (periodontal tissue), whereas
in implants, a direct and relatively rigid connection
between the bone and implant is achieved if healing
without complications has taken place.13,14 Therefore,
a direct transmission of forces on the peri-implant
bone without any shock-absorbing element is conse-
quent to implant loading.14 It can usually be achieved
by the adaptation capacity of peri-implant bone ar-
chitecture toward changing load conditions.15,16
According to Frost,15,16 within the range of a physi-
ologic loading, bone undergoes its physiologic turn-
over. In mild overloading, below bone’s microdamage
threshold, modeling drifts can begin adding to and/
or reshaping bone. But in the case of a pathologic
overload, bone fractures and bone resorption may oc-
cur.15,16 For these reasons, it appears to be impor tant
to control the forces transmitted on the bone-implant
interface. However, the amount of load defined as
overload has not been quantified because the range
of host physiologic adaptability varies. Overload can
be considered the amount of force that overextends
the host sites adaptation potential.
a
Assistant Professor, Department of Fixed and Implant
Prosthodontics, University of Genoa, Genoa, Italy.
b
Lecturer, Department of Prosthodontics, University of Turin,
Turi n , I ta ly.
c
Lecturer, Department of Health Sciences, Section of Biostatistics,
University of Genoa, Genoa, Italy.
d
Chief and Professor, Department of Fixed and Implant
Prosthodontics, University of Genoa, Genoa, Italy.
Correspondence to: Dr Maria Menini, Department of
Prosthodontics (Pad. 4), Ospedale S. Martino,
L. Rosanna Benzi 10, 16132 Genova, Italy.
Fax: + 39 0103537402. Email: maria.menini@unige.it
©2013 by Quintessence Publishing Co Inc.
Shock Absorption Capacity of Restorative Materials for
Dental Implant Prostheses: An In Vitro Study
Maria Menini, DDS, PhDa/Enrico Conserva, DDSa/ Tiziano Tealdo, DDSa/Marco Bevilacqua, DDSa/
Francesco Pera, DDS, PhDb/Alessio Signori, MScc/Paolo Pera, MD, DDS, PhDd
Purpose: To measure the vertical occlusal forces transmitted through crowns made of
different restorative materials onto simulated peri-implant bone. Materials and Methods:
The study was conducted using a masticatory robot that is able to reproduce the
mandibular movements and forces exerted during mastication. During robot mastication,
the forces transmitted onto the simulated peri-implant bone were recorded using nine
different restorative materials for the simulated single crown: zirconia, two glass-ceramics, a
gold alloy, three composite resins, and two acrylic resins. Three identical sample crowns for
each material were used. Each crown was placed under 100 masticatory cycles, occluding
with the flat upper surface of the robot to evaluate the vertical forces transmitted. Two-way
analysis of variance was used. Alpha was set at .05. Results: The statistical evaluation of
the force peaks recorded on the vertical z-axis showed mean values of 641.8 N for zirconia;
484.5 N and 344.5 N, respectively, for the two glass-ceramics; 344.8 N for gold alloy;
293.6 N, 236 N, and 187.4 N, respectively, for the three composite resins; and 39.3 N and
28.3 N, respectively, for the two acrylic resins. Significant differences were found between
materials (P < .0001), except for the comparison between gold alloy and one of the
glass-ceramics. Conclusion: Composite and above all acrylic resin crowns were more
able to absorb shock from occlusal forces than crowns made of zirconia, ceramic material,
or gold alloy. Int J Prosthodont 2013;26:549–556. doi: 10.11607/ijp.3241
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550 The International Journal of Prosthodontics
Shock Absorption of Restorative Materials
Clinical evidence on the impact of overloading on
peri-implant bone is not available. Only some case re-
ports17–19 and animal studies9,12 , 20 are present. In fact,
clinical trials evaluating overloading are difficult to
design due to ethical reasons. Moreover, it is gener-
ally impossible to identify the reason for peri-implant
bone loss in clinical cases, distinguishing overload-
ing from other potential sources of bone loss. It is the
authors’ opinion that a prudent approach to implant
prosthodontics should be aimed at avoiding the risk
of overloading the implants. In vitro studies21–25 also
demonstrate that off-axial loads increase stress on
the bone-implant interface with respect to axial loads
and may also be responsible for increased resorption
of crestal bone.20
Some authors maintain that the type of material
used for the prosthesis supported by the titanium im-
plant could affect occlusal load.14,26–32 In particular, in
the 1980s, some investigators recommended resilient
occlusal materials such as acrylic resin to reduce the
forces exerted on implants.14,33,34
However, contrasting results on this topic35–38 sug-
gest the need for further investigation. The role of
dental materials in occlusal stress transmission onto
peri-implant bone seems to be especially relevant
over the past few years because of the increasing use
of esthetic but rigid materials, such as glass-ceramic
and zirconia. These materials are reported to have
excellent mechanical and biologic properties,39,40 but
their impact on peri-implant bone and on the whole
masticatory system has not yet been investigated.
The aim of this study was to investigate in vitro the
shock absorption capacity of nine different restor-
ative materials, including both traditional and modern
esthetic materials, using a masticatory robot.
Materials and Methods
A masticatory robot able to simulate human chewing
in vitro was used (Fig 1), reproducing three-dimen-
sionally the masticatory movements and loads ex-
erted during mastication, as described in a previous
paper.26
The movable part of the robot is composed of a
Stewart platform and simulates the mandible. The
fixed upper part of the robot simulates the maxilla.
A sensor-equipped base is placed on the moving
platform and records the degree of force being trans-
mitted through the three axes (x, y, and z).
The sensor-equipped base supports a pin that
simulates the implant-abutment system (Fig 2a).
The samples to be tested are placed on the pin and
stressed in the various directions during the robot’s
mastication.
b
Fig 1 (left) Sensor-equipped masticatory robot.
Fig 2 (below) Pin simulating the implant-abutment system
with a ceramic sample crown. (a) A groove was made on the
pin to match a ridge inside the sample crown, so that the crown
would sit precisely on the pin without any possibility of rotation
or other movement during testing. (b) The sample crown has
been inserted onto the pin.
a
Groove
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Volume 26, Number 6, 2013 551
Menini et al
The materials tested were yttrium cation-doped
tetragonal zirconia polycrystals (Procera Zirconia,
Nobel Biocare), a lithium disilicate pressable ceramic
(Empress 2, Ivoclar Vivadent), a low-fusing leucite-
based pressable ceramic (Finesse, Dentsply), a gold
alloy (Ney-Oro CB, Dentsply), a microfilled hybrid
composite resin (Experience, DEI Italia), a microfilled
composite resin (Adoro, Ivoclar Vivadent), a nano-
hybrid composite resin (Signum, Heraeus Kulzer), and
two acrylic resins (Easytemp 2, DEI Italia and Acry
Plus V, Ruthinium) (Table 1).
In total, 27 identical sample crowns were made
(three for each material). The occlusal surfaces were
semispherical in shape (6.5-mm diameter) (Fig 2b).
The main axis of the sample was 11-mm long. The
sample crowns presented a single contact point at the
center of the occlusal surface when occluding with
the flat maxilla of the robot. At this point, the thickness
of the material tested was 5 mm. Each sample was
measured on its main and smaller axes. The material
thickness at the contact point was also measured with
calipers to verify that all crowns were identical.
The specimens tested were chosen at random and
not in a pre-established sequence. Each crown was
placed under 100 chewing cycles with the sample
crown occluding with the flat fixed maxilla of the ro-
bot. The masticatory robot was programmed to follow
a trajectory reproducing human chewing, as described
in the previous paper.26 The masticator traced this
trajectory in all tests described and the movements
were executed independently from generated force.
Vertical loads (kg) transmitted at the simulated
peri-implant bone were recorded using strain gauges
stuck on the sensorized base supporting the simu-
lated implant-abutment system.
With MATLAB 6.1 (MathWorks), the maximum val-
ues of the forces recorded for each masticatory cycle
were highlighted. These values underwent statistical
analysis using SPSS software (version 18.0, IBM). Two-
way analysis of variance (ANOVA) was used to compare
transmitted stresses between the nine materials tested
and across the three sample crowns of each material.
All tests were two-tailed. Alpha was set at .05.
Post hoc comparisons were assessed by means
of the Scheffe test or, alternatively, by means of the
Tamhane test when homogeneity of variances among
materials was not satisfied.
Vertical loads were converted and are found
throughout the paper in Newtons.
Results
The ANOVA found a significant difference between
the forces transmitted using different materials, and
the Scheffe post hoc test was applied. Within the ma-
terials, an internal comparison showed a significant
difference with P < .0001. Only the difference in mean
maximum force between Ney-Oro and Finesse was
not statistically significant (P > .999).
Comparisons within sample crowns made for each
material did not show significant differences, and one
unique mean was reported for each material.
The force transmitted through the simulated im-
plant onto the simulated peri-implant bone by zirco-
nia (mean 641.8 N) was the greatest ( Table 2).
The slope of the curve, representing the force
transmitted onto the peri-implant level, showed that
materials with greater elastic moduli have steeper
peaks compared with other materials, that is, the
maximum force is reached more rapidly.
Table 1 Elastic Moduli of Tested Materials
Material Manufacturer Type of material Elastic modulus (MPa)
Procera Zirconia Nobel Biocare Zirconia 210,000
Empress 2 Ivoclar Vivadent Glass-ceramic 96,000
Ney-Oro CB Dentsply Gold alloy 77,000
Finesse Dentsply Glass-ceramic 70,000
Experience DEI Italia Composite resin 13,000
Adoro Ivoclar Vivadent Composite resin 7,000 ± 500
Signum Heraeus Kulzer Composite resin 3,500
Easytemp 2 DEI Italia Acrylic resin 2,300
AcryPlus V Ruthinium Acrylic resin N/A
N/A = not available.
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552 The International Journal of Prosthodontics
Shock Absorption of Restorative Materials
Discussion
In this investigation, the use of different restorative
materials significantly affected stress transmission on
the simulated peri-implant bone. In fact, more elastic
materials reduced the stress recorded.
The difference in stress transmission between the
gold alloy and one of the two glass-ceramics was the
only difference not statistically significant, presum-
ably because of their similar Young’s moduli (Table 1).
Zirconia and ceramic crowns also showed steeper
peaks of force compared with other materials. These
were considered effects of the different elastic moduli
of the materials tested.
According to Skalak,14 the viscoelastic behavior of
an acrylic resin as occlusal material would be enough
to delay the transmission of force and reduce its peak
compared with materials with greater elastic moduli.
An in vitro study by Gracis et al32 concluded that
the harder and stiffer the material, the higher the
force transmitted onto the implant and the shorter
the rise time. In fact, according to Hooke’s law, the
higher the modulus of elasticity of a material, the less
the material will deform under pressure and the more
likely the force will be transferred through the mate-
rial.41 Conversely, the more resilient the material, the
more easily it will deform under pressure, the longer
the rise time, and the smaller the stress.
However, a review of the literature over the last
20 years demonstrated that many articles refute the
existence of a shock absorption capacity of resilient
dental materials.42–49
Some of these studies have used Instron ma-
chines48 and some have used finite element analysis
(FEA).44,46,47 These studies have several limitations.
They do not accurately reproduce the mandibular
kinematics. Instron machines perform intermittent
movements in only a single plane. They do not repli-
cate the same masticatory cycle that occurs clinically
with mastication.
With regard to FEA, which included a virtual simu-
lation, the validity of the mathematical model is dif-
ficult to estimate objectively, and the assumptions
made in the use of FEA in implant dentistry must be
taken into account when interpreting the results. In
fact, during the modeling process, several simplifica-
tions are necessary (model geometry, material prop-
erties, applied boundary conditions, etc) and greatly
affect the predictive accuracy of FEA.50
An experiment conducted on beagle dogs51 did
not show any clinical, radiographic, or histologic dif-
ferences between peri-implant tissues surrounding
prosthetic restorations made with composite resin
versus those made with ceramic materials. However,
this study did not control the amount of force exerted
onto the implants, and dogs do not replicate human
mastication.
In vivo studies41,43,49 have measured masticatory
forces transmitted through various restorative mate-
rials in patients without finding significant differences
in the results.
This type of test requires that sensors and connect-
ing wires be applied intraorally, which raises several
concerns. For instance, this type of testing may al-
ter the masticatory cycles of the study participants
and therefore may distort the results. Moreover, the
technique is not conducive to studying humans over
long experimental periods, and the masticatory cycles
are not identical. In addition, it is not possible to di-
rectly measure the forces transmitted onto the bone-
implant interface.
Using the masticatory robot, an attempt was made
to overcome the limitations associated with previ-
ous studies, approximating the three-dimensional
nature of masticatory function by an in vitro model.
The forces were measured by strain gauges attached
to the sensorized base to which the simulated den-
tal implant was screwed; therefore, it was considered
that the forces were recorded at the simulated peri-
implant bone.
Even though non-axial forces seem to be a more
relevant factor for bone maintenance compared with
axial forces, in the present paper, only data regarding
vertical forces have been reported. In fact, previous
papers26,27 showed that the percentage difference
of force using different materials was superimpos-
able on the three axes; data for the three axes were
redundant. For this reason, in the present research,
the sample crowns were left to occlude with a flat
surface and not with the reproduction of the maxilla.
Table 2 Comparison of the Maximum Forces (N)
Transmitted onto the Simulated Peri-implant Bone
Material Mean force (SD)
Difference of force
vs zirconia (%) P
Procera Zirconia 641.8 (6.8)
Empress 2 484.5 (5.5) –24.51
Ney-Oro CB 344.8 (5.7) –46.28
Finesse 344.5 (3.5) –46.32
Experience 293.6 (16.3) –54.25 < .0001
Adoro 236 (4.2) –62.23
Signum 187.4 (6.7) –70.80
Easytemp 2 39.3 (2.3) –93.88
AcryPlus V 28.3 (4.2) –95.59
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Volume 26, Number 6, 2013 553
Menini et al
Occluding with a flat surface, forces on the horizontal
plane were near zero and only data recorded on the
vertical axis were considered for statistical analysis.
The present in vitro setup presents several limita-
tions in simulating the clinical situation. Namely, the
moving platform and the upper part of the robot, sim-
ulating the maxilla, are rigid systems that cannot re-
produce the inherent elasticity of human tissues. The
elastic properties of implant, abutment, and screws
were not properly simulated.
Moreover, no attempt was made to simulate the oral
environment in terms of humidity and temperature.
Comparability of the in vitro and in vivo loading
conditions is limited. Therefore, the absolute values of
force recorded at the peri-implant bone in the present
study cannot be directly correlated to the forces that
would be present in vivo.
It should also be noted that the masticatory system
is provided with protective and self-regulatory mecha-
nisms not simulated in the present in vitro setup. In
fact, natural teeth are equipped with periodontal
mechanoreceptors that signal information about tooth
loads and are involved in the control of human jaw
actions aiming at preventing accidental excessive oc-
clusal loads.52 On the other hand, dental implants lack
periodontal receptors. However, a tactile sensibility at
the level of dental implants (so-called osseopercep-
tion) has been demonstrated and could be responsible
for an implant-mediated sensory-motor control.53
Despite the limits of the present in vitro setup in
simulating the oral implant situation, the attempt was
made to eliminate all possible variables involved. The
standardized in vitro system allowed for fabrication
of identical sample crowns that were all submitted to
identical loading conditions.
A previous paper26 demonstrated that the mas-
ticatory robot is able to reproduce, several times
over, identical masticatory cycles. The paper also
confirmed the precision of the machine during data
collection, therefore validating the reliability of the
method. In fact, the small variations found showed
that the tests are also repeatable and effective under
lengthy testing.
The only variable in the system described was the
material from which the crowns were made, which is
mandatory for a reliable comparison of different mate-
rials. The system was designed to make a comparison
between different materials effective and repeatable.
In the present study, a single crown was tested,
demonstrating a shock absorption potential for acryl-
ic resin. However, contrasting results could be found
using multiunit prostheses.41,44,54,55 In fact, stiff pros-
thetic materials are supposed to distribute the stress
more evenly to the abutments and implants. It is the
authors’ opinion that, in multiunit prostheses, a stiff
substructure (ie, gold alloy) rigidly splinting the im-
plants would be the best option to evenly distribute
loads. The shock absorption capacity of more resil-
ient restorative materials could be used at the lev-
el of the occlusal surface in association with a stiff
substructure.14
The present paper evaluates the shock absorption
capacity of nine restorative materials, including gold
alloy and zirconia, which were not tested in previ-
ous studies.26,27 To the authors’ knowledge, there are
no published studies evaluating the shock absorp-
tion capacity of zirconia. In the last few decades, the
growing patient demand for highly esthetic restora-
tions has led to the development of new all-ceramic
materials such as zirconia.
Zirconia minimizes the dark color transmit-
ted through peri-implant tissues associated with
metal components. Moreover, zirconia restorations
yield higher fracture loads than alumina or lithium
disilicate.56,57
Both the increasing industrial pressure and grow-
ing enthusiasm for attractive esthetic outcomes have
led to the widespread use of all-ceramic restora-
tions and zirconia, even though their impact on the
masticatory system has not been sufficiently tested.
The esthetic characteristics, as well as the biocom-
patibility, and the most common shortcomings of all-
ceramic restorations (brittleness, chipping of the ve-
neering ceramic, fracture strength) have been thor-
oughly investigated for zirconia.40,58 Zirconia is also
considered to have excellent mechanical properties,59
but, so far, the biomechanical consequences of such
a rigid and stiff material in the masticatory system
have not been investigated by the scientific literature.
In fact, zirconia’s elastic modulus and coefficient of
abrasion are much higher than those of natural teeth.
Only a few studies60–62 report assessments of
periodontal or peri-implant tissues around teeth or
implants supporting zirconia restorations after func-
tional loading. To the authors’ knowledge, no clinical
studies report possible consequences at the level of
the antagonist arch or any gnathological consider-
ation. Moreover, to date, the observational period for
the majority of trials on zirconia restorations is quite
short.57
Two systematic reviews on all-ceramic dental
materials and zirconia also underlined the fact that
none of the cited clinical trials took bruxism into ac-
count. More often, such a parafunction figured into
the exclusion criteria. Consequently, the authors
suggested that, since parafunctions were not con-
sidered in any clinical investigation, they should be
regarded as a potential limitation for zirconia-based
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554 The International Journal of Prosthodontics
Shock Absorption of Restorative Materials
restorations.39,6 3 One reason for this suggestion could
be the increased risk of chipping and fracture of
zirconia-based restorations in parafunctional pa-
tients, but evidence is lacking on possible harmful
effects on the masticatory system using zirconia res-
torations when a parafunction is present.
Larsson et al64 noticed that significantly more
porcelain veneer fractures are reported for implant-
supported zirconia fixed dental prostheses when
compared with tooth-supported restorations. One
explanation for this finding could be the role played
by the periodontal ligament, which allows for shock
absorption, sensory function, and tooth movement.
This hypothesis also suggests that the possible harm-
ful effects of zirconia restorations on the masticatory
system would be made worse when dealing with im-
plant-supported restorations in comparison to tooth-
supported restorations. In fact, a shock-absorbing
element is lacking in implant restorations and higher
loads can occur with implant-associated propriocep-
tion loss.52
The choice of the restorative material to be used
in implant restorations should be made in light of
newly introduced concepts of osseosufficiency and
osseoseparation5: as long as the host, the implant,
and the clinical procedures induce and allow for
maintaining osseointegration, an osseosufficiency
state is present. But some patient-related or nonpa-
tient-related factors could induce osseoseparation,
compromising the obtainment or maintenance of
osseointegration. As reported earlier, evidence is
lacking on the role of overloading in peri-implant
bone loss. However, bone has been demonstrated
to be sensitive to loading conditions.65 This suggests
that to control the occlusal loads in implant prosth-
odontics as much as possible, clinicians should aim
to reduce load entity and extra-axial loads. Based on
the present in vitro results, if the aim is reducing load
entity, zirconia is not the proper restorative material
to be used. These findings need to be supported by
clinical trials to investigate their clinical relevance
Conclusion
Within the limitations of this in vitro study, several
conclusions can be drawn. Zirconia, glass-ceramic,
and gold alloy transmitted higher stresses to the
simulated peri-implant bone. In contrast, composite
resin materials were able to significantly reduce the
values of force recorded compared to stiffer materi-
als. In fact, the use of composite resins and acrylic
resins reduced occlusal stress by up to –70.80% and
–95.59%, respectively, compared with zirconia.
Acknowledgments
The construction of the masticatory robot was financed by the
Ministr y of Instruction, Universit y and Research (MIUR), Italy,
under the auspices of the Research of National Interest Project s
(PRIN, 2002). The authors wish to thank Prof Giambattista Ravera
(Depar tment of Health Sciences, University of Genoa) for the sta-
tistical analysis, dental technician Paolo Pagliari for the labora-
tory support, and engineers Giuseppe Casalino, PhD, Fabio Giorgi,
Tommaso Bozzo, and Enrico Simetti (Depar tment of Informatics
of Systems Theory and Telematics, University of Genoa, Italy). The
authors repor ted no conflicts of interest related to this study.
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Literature Abstract
Identification of risk factors for fracture of veneering materials and screw loosening of implant-supported fixed partial
dentures in partially edentulous cases
The purpose of this retrospective study was to determine the risk factors for fracture of veneering materials and screw loosening of
implant-supported fixed partial dentures. A total of 182 patients had 219 suprastructures inserted. One hundred twenty patients (149
facing suprastructures) were included in a subgroup to investigate the risk factors of fracture of veneering materials, and 81 patients
(92 suprastructures) were included in a subgroup to analyze the risk factors for abutment screw loosening. A Cox proportional haz-
ards regression model was performed to identify the risk factors related to technical complications, and eight factors were regarded
as candidate risk factors. It was suggested that a screw-retained suprastructure was a significant risk factor for fracture of veneering
materials, and connection of suprastructures with natural teeth was a significant risk factor for screw loosening. Further investigations
involving dynamic factors, such as occlusal force and bruxism, should be considered as predictors that may be helpful in studying the
risk factors of fracture of veneering materials and screw loosening.
Noda K, Arakawa H , Maekawa K, Hara ES, Yamaz aki S, Kimura- Ono A , Sonoyama W, Minakuchi H, Matsuka Y, Kuboki T. J Oral Rehabil
2013;40:214–220 . Reprints: Takuo Kuboki, Depar tment of Oral Rehabilitation and Re generative Medi cine, Okayama University, Graduate School
of Medicine, Dentistry and Pharmac eutical Scien ces, Okayama, 700 -8525, Japan. Email: kuboki@md.okayama-u.ac.jp—Arthur S. Sham,
Hong Kong
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... Although high survival rates have been reported, approximately 95% after 5 years in function [3,4,7], implant-supported prostheses have exhibited higher levels of technical complications relative to tooth-supported prostheses, chiefly for Y-TZP reconstructions, which have not been limited to the metallic/Y-TZP framework fracture but mainly involved the integrity of the low-toughness veneering porcelain (K ic : 0.7 MPa m 1/2 for Y-TZP and 1.1 MPa m 1/2 for metal ceramic) [8], with approximately 11-50% reported chipping after 5 years for fixed dental prostheses (FDPs) [3,7]. The rationale for the increased level of technical complications for implant-supported rehabilitations may lie on the absence of periodontal ligament and its inherent micromotion that helps to dampen occlusal forces, as well as mechanoreceptors and their feedback mechanism that differentiate food hardness and consistency [9][10][11]. Hence, technological improvements in the biomaterial science have been concentrated towards the development/improvement of biomechanically favorable restorative systems with occlusal forces dampening features to meet the functional and esthetic demands of dental reconstructions [9,10,[12][13][14][15][16][17]. ...
... The rationale for the increased level of technical complications for implant-supported rehabilitations may lie on the absence of periodontal ligament and its inherent micromotion that helps to dampen occlusal forces, as well as mechanoreceptors and their feedback mechanism that differentiate food hardness and consistency [9][10][11]. Hence, technological improvements in the biomaterial science have been concentrated towards the development/improvement of biomechanically favorable restorative systems with occlusal forces dampening features to meet the functional and esthetic demands of dental reconstructions [9,10,[12][13][14][15][16][17]. Fiber-reinforced composites (FRCs) have emerged as promising systems in several biomedical applications, particularly for their favorable strength-and stiffness-to-weight ratios [15][16][17][18][19]. Dental FRCs are generally composed of a high volume fraction of reinforcement compounds, carbon or glass fibers, bonded to a polymeric matrix by a coupling agent, where the fiber reinforcement bear the loads and increase the energy needed for crack propagation, known as resistance curve (R-curve) behavior, as well as increase the stiffness and strength of the material (: 540−740 MPa, K ic : 9 MPa m 1/2 , E: 30 GPa) [14,15,20]. ...
... Given the typical anisotropic or orthotropic nature of conventional FRC reconstructions properties, the framework dimension and design as well as its three-dimensional position, usu-ally following a structural relationship with occlusal forces distribution through a parallel alignment with the maximum principal stress direction, are key factors to obtain the maximum performance of FRC prostheses [14][15][16][17]19,22]. Moreover, FRC rehabilitations may offer significant clinical advantages due to their lower elastic modulus and increased resilience compared to metallic/Y-TZP rehabilitations, which may favor chewing forces absorption and stress distribution and improve the biomechanical performance of the restorations, particularly for implant-supported reconstructions [9,10,16,17]; as well as favorable cost effectiveness, chemical adhesion to resin composite and resin cement, and easy reparability with conventional in-office direct restorative procedures [14,15,18,21,23]. ...
Article
Objective To characterize the biomechanical performance of fiber-reinforced composite 5-unit implant-supported fixed dental prostheses (FDPs) receiving individually milled crowns by insilico and fatigue analyses. Methods Eighteen implant-supported five-unit fiber-reinforced composite frameworks with an individually prepared abutment design were fabricated, and ninety resin-matrix ceramic crowns were milled to fit each abutment. FDPs were subjected to step-stress accelerated-life testing with load delivered at the center of the pontic and at 2nd molar and 1st premolar until failure. The reliability of the prostheses combining all loaded data and of each loaded tooth was estimated for a mission of 50,000 cycles at 300, 600 and 900 N. Weibull parameters were calculated and plotted. Fractographic and finite element analysis were performed. Results Fatigue analysis demonstrated high probability of survival at 300 N, with no significant differences when the set load was increased to 600 and 900 N. 1st and 2nd molar dataset showed high reliability at 300 N, which remained high for the higher load missions; whereas 1st premolar dataset showed a significant decrease when the reliability at 300 N was compared to higher load missions. The characteristic-strength of the combined dataset was 1252 N, with 1st molar dataset presenting higher values relative to 2nd molar and 1st premolar, both significantly different. Failure modes comprised chiefly cohesive fracture within the crown material originated from cracks at the occlusal area, matching the maximum principal strain location. Significance Five-unit implant-supported FDP with crowns individually cemented in a fiber-reinforced composite framework presented a high survival probability. Crown fracture comprised the main failure mode.
... Static (clenching) and dynamic forces (chewing, swallowing, and eccentric bruxism) occur in the masticatory system [10][11][12][13][14][15]. The literature shows that forces are transferred to a lesser or greater extent to the peri-implant area [16] depending on whether the applied force is static or dynamic [17][18][19][20][21][22][23][24]. Moreover, the results in recent publications showed that static loading, compared with dynamic loading, caused increased stress, which proves the need of transient analysis of dental implants [25,26]. ...
... Dynamic forces and the impact of the moving mandible against the maxilla are transferred very differently in single and multiple implant-supported prostheses, depending on the material that the prostheses are made from. Rigid materials, such as zirconia, ceramics, and metals, generate higher dynamic forces [17,[19][20][21] than other materials used in veneering prosthetic frameworks (composites, hybrid composites, or resins) or in prosthetic framework manufacturing (carbon fiber, fiberglass, or polyether-ether-ketone (PEEK)), which absorb and dissipate the impact energy with lower dynamic forces [28][29][30][31][32][33][34][35][36][37][38][39][40]. ...
... Gracis [19] recorded the impact force transmitted by a steel ball rolled along a slope to discs made from different materials. Menini [17,20], used strain gauges to design a device that applied oscillating movements to monolithic prostheses of different materials (gold, zirconia, ceramics, composites, and resins) against an upper dental arch made of a Co-Cr alloy. The force transferred to the crowns (made from different materials) by the simulation of the mandibular movements was recorded. ...
Article
Full-text available
In the literature, many researchers investigated static loading effects on an implant. However, dynamic loading under impact loading has not been investigated formally using numerical methods. This study aims to evaluate, with 3D finite element analysis (3D FEA), the stress transferred (maximum peak and variation in time) from a dynamic impact force applied to a single implant-supported prosthesis made from different materials. A 3D implant-supported prosthesis model was created on a digital model of a mandible section using CAD and reverse engineering. By setting different mechanical properties, six implant-supported prostheses made from different materials were simulated: metal (MET), metal-ceramic (MCER), metal-composite (MCOM), carbon fiber-composite (FCOM), PEEK-composite (PKCOM), and carbon fiber-ceramic (FCCER). Three-dimensional FEA was conducted to simulate the collision of 8.62 g implant-supported prosthesis models with a rigid plate at a speed of 1 m/s after a displacement of 0.01 mm. The stress peak transferred to the crown, titanium abutment, and cortical bone, and the stress variation in time, were assessed.
... Studies have shown contradictory results regarding the transmission of loads toward the supporting tissues by the different restorative materials used for crown manufac ture. [27][28][29][30] Menini et al. performed a simulation in order to measure the occlusal forces transmitted by different materials to the periimplant bone tissue and concluded that the use of softer materials, such as resin or acrylic, re duces the forces by up to 70.8% and 95.6%, respectively. 27 However, in the present study, only materials for permanent restorations were compared, and the results showed a dif ference of 75.5% between the highest and the lowest values of the area of strain distribution around the implant with load 1, and 19.8% with load 2. The G6 crowns made of lithium disilicate presented the highest strain values in terms of area and number of pixels of the colors for both applied loads. ...
... [27][28][29][30] Menini et al. performed a simulation in order to measure the occlusal forces transmitted by different materials to the periimplant bone tissue and concluded that the use of softer materials, such as resin or acrylic, re duces the forces by up to 70.8% and 95.6%, respectively. 27 However, in the present study, only materials for permanent restorations were compared, and the results showed a dif ference of 75.5% between the highest and the lowest values of the area of strain distribution around the implant with load 1, and 19.8% with load 2. The G6 crowns made of lithium disilicate presented the highest strain values in terms of area and number of pixels of the colors for both applied loads. Other authors compared stress distribution in lithium disilicate ceramic and other ceramic materi als, and reported that lithium disilicate ceramic crowns showed higher stress values under vertical loading. ...
Article
Full-text available
Background: Various ceramic materials have been used for esthetic rehabilitation with implants, but the issues regarding the dissipation of masticatory loads are not well understood. Objectives: This in vitro quasi-static study aimed to evaluate with the photoelasticity test the dissipation of stress around dental implants with regard to different rehabilitation materials. Material and methods: A photoelastic model was elaborated in resin, where a conical Morse-tapered implant was inserted. On the abutments (1 per crown), 6 single crowns were prepared using different materials to form 6 groups: feldspathic ceramic (G1); chrome-cobalt alloy covered with ceramic (G2); hybrid ceramic (G3); zirconia covered with ceramic (G4); zirconia (G5); and lithium disilicate (G6). Axial loads of 100 N (load 1) and 300 N (load 2) were applied in the center of the crowns, and photoelastic images were captured and analyzed. The total area of stress dissipation was measured for each group. Then, a computational program was developed to measure the number of pixels of the colors generated in each group. Two image sizes were analyzed - total image and crestal image. Results: Counting the numbers of pixels of the colors in the total images showed that G6 > G4 > G5 > G1 > G2 > G3 when load 1 was applied. When load 2 was applied, the sequence was G6 > G4 > G1 > G3 > G2 > G5. In the evaluation of the crestal area, the obtained results were G4 > G5 > G1 > G3 > G2 > G6 with load 1 and G5 > G1 > G2 > G6 > G4 > G3 with load 2. Conclusions: Within the limitations of this in vitro quasi-static study, the findings indicate that the zirconia crown (G5) presented higher stress in the crestal images, while the lithium disilicate crown (G6) presented higher stress in the total images.
... Since the forces applied in the masticatory process and eccentric bruxism are dynamic, it is important not only to study the mechanical behavior of the restorative materials in static forces, but also to know the mechanical behavior produced by dynamic forces. The rehabilitation materials used in the oral cavity could absorb impacts that may vary according to their mechanical properties [10,[40][41][42]. Therefore, the evaluation of the mechanical behavior of the most widely-used materials in implant supported rehabilitations becomes a key issue. ...
... Our study demonstrated that more stress is transferred to the bone when stiffer materials (metal and/or ceramic) are used in implant supported rehabilitations and, conversely, more flexible materials transfer less stress to the implant connection. These relationships between materials' elastic properties and the dynamic force transmission are in accordance with the findings of different authors [10,[40][41][42][43]. ...
Article
Full-text available
Statement of problem. Previous peri-implantitis, peri-implant bone regeneration, or immediate implant placement postextraction may be responsible for the absence of cortical bone. Single crown materials are then relevant when dynamic forces are transferred into bone tissue and, therefore, the presence (or absence) of cortical bone can affect the long-term survival of the implant. Purpose: the purpose of this study is to assess the biomechanical response of dental rehabilitation when selecting different crown materials in models with and without cortical bone. Methods: several crown materials were considered for modeling six types of crown rehabilitation: full metal (MET), metal-ceramic (MCER), metal-composite (MCOM), peek-composite (PKCOM), carbon fiber-composite (FCOM), and carbon fiber-ceramic (FCCER). An impact-load dynamic finite-element analysis was carried out on all the 3D models of crowns mentioned above to assess their mechanical behavior against dynamic excitation. Implant-crown rehabilitation models with and without cortical bone were analyzed to compare how the load-impact actions affect both type of models. Results: numerical simulation results showed important differences in bone tissue stresses. The results show that flexible restorative materials reduce the stress on the bone and would be especially recommendable in the absence of cortical bone. Conclusions: this study demonstrated that more stress is transferred to the bone when stiffer materials (metal and/or ceramic) are used in implant supported rehabilitations; conversely, more flexible materials transfer less stress to the implant connection. Also, in implant-supported rehabilitations, more stress is transferred to the bone by dynamic forces when cortical bone is absent.
... However, its lower modulus of elasticity made it a suitable material for implant supported restorations. (41)(42)(43) On the other hand, according to the current study; it was found that an increase in occlusal thickness of v.enamic to 1.5mm lead to fracture resistance increase to be insignificantly different from e.max at the same occlusal thickness. This result is agreed with Menini M and Conserva E. (43) , they have explained that resin-based materials and composites have higher shock absorbing capacity than ceramics. ...
... (41)(42)(43) On the other hand, according to the current study; it was found that an increase in occlusal thickness of v.enamic to 1.5mm lead to fracture resistance increase to be insignificantly different from e.max at the same occlusal thickness. This result is agreed with Menini M and Conserva E. (43) , they have explained that resin-based materials and composites have higher shock absorbing capacity than ceramics. (20,21) This was in agreement with findings by Kok et al. (29) who found higher fracture values for materials with a lower modulus of elasticity. ...
... Occlusal overload occurs if the functional and/or parafunctional loads exceed the mechanical strength of prosthesis, implant components or implant, or the biological tolerance of the osseointegrated interface, resulting in structural or biological damage. 27,28 All occlusal loading will be absorbed by the implant-bone interface as there is only minor shock absorption mechanism that reduces the impact of such loading. 29 Occlusal loading generally produces a mechanical stimulus that may be crucial for establishing and maintaining osseointegration. ...
Article
Full-text available
This case report documents a non‐plaque‐induced marginal bone loss around an osseointegrated implant. The loss of osseointegration, most likely caused by overload and/or suboptimal distribution of occlusal loading, may be reversed when the loading is reduced by optimally transmitting stress forces to the implant‐to‐bone interface and surrounding bone. Limited crestal bone width and a history of ridge augmentation may make peri‐implant supporting bone vulnerable to occlusal overload. In such cases, the prosthetic restoration should be planned with particular focus on reducing and optimizing the occlusal load.
... These results could be explained by PEEK's cushioning effect, the fact that the low modulus of elasticity of PEEK copings could have absorbed more energy from the functional occlusal loads than PFM ones, and transferred less energy to the supporting structures. Therefore, PEEK might absorbed the occlusal forces, and thus decreased its effect on the bone implant interface (28,29). ...
Article
Full-text available
Purpose: to compare the clinical and radiographic outcomes of PEEK and PFM implant supported crowns. Methods: This study was designed as randomized controlled study. Twenty-three single implants in posterior region were restored randomly either with PFM or PEEK crowns. Peri implant soft tissue parameters were evaluated using the modified plaque index (mPI), bleeding on probing (BOP), probing depth (PD), modified gingival index (mGI), and crestal bone loss was measured (CBL). Clinical data were collected at crown delivery, after 6 months, and after one year of function. Results: there was no statistical significant difference between the mean of the modified plaque index (mPI), bleeding on probing (BOP), probing depth (PD), modified gingival index (mGI) in the two groups, while the mean crestal bone loss was statistically less in PEEK group than that of the PFM one. Conclusion: PEEK implant supported crowns appeared to reduce the amount of CBL in the posterior region. Regarding the peri-implant soft tissue parameters both PEEK and PFM crowns showed comparable results.
... Implant dentistry has become an increasingly prevalent and effective treatment option for the management of partial or complete edentulism, with an overall excellent long-term clinical success rate [1,2]. However, several authors consider occlusal load during the implant healing phase and stress distribution patterns critical factors affecting the long-term success of dental implants [3,4]. Since implants are in direct contact with bone due to the absence of the periodontal ligament of natural teeth, they do not have the same elastic buffering mechanisms and their biomechanical behavior is different [5][6][7]. ...
Article
Objectives To evaluate the force absorption capacity of implant supported restorations utilizing different CAD-CAM materials for the fabrication of crowns and customized abutments. Methods 80 titanium inserts were scanned to design customized abutments and crowns. The specimens were divided into four groups (n = 20/material): (Z): zirconia, (P): PEEK, (V): VITA Enamic, and (E): IPS e.max. Each group was subdivided into two subgroups according to customized abutment material: (Z) zirconia, and (P) for PEEK. For the assessment of force absorption, all specimens were loaded in a universal testing machine, applied loads curves were collected from the machine’s software, and resulting loads curves were collected from forcemeter below the assembly. The slopes of all curves were analyzed using Two-way multivariate analysis of variance with pairwise comparisons using Tukey Post Hoc test (p < 0.05). Results The curve progression of the applied and resulting forces varied among the investigated materials for each specimen. For zirconia abutments, ZZ showed the highest slope values of the applied and resulting force curves, followed by EZ, VZ, and PZ demonstrating statistically significant differences (P < .001). As for PEEK abutments, ZP and EP showed the least slope values, followed by PP then VP demonstrating statistically significant differences (P < .001). For Zirconia and e.max crowns, using PEEK abutments significantly increased slope loss. As for PEEK and Vita Enamic crowns changing abutment material did not significantly affect slope loss. Significance Combining rigid crown materials with less rigid abutments might enhance their force absorption capacity. However, with less rigid crown materials a stiff substructure might be mandatory to preserve their force absorption behavior.
... Two different aesthetic veneering materials were employed: metal-ceramic in the first group treated (Group 1) and metal-composite in the cohort of patients treated more recently (Group 2). In fact, the prosthodontic protocol applied by the authors changed following their studies on the shock-absorption capacity of restorative materials [39]. Cantilevered extensions were avoided and a careful occlusal control was performed at prosthesis delivery. ...
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The present post-trial follow-up investigated the influence of titanium implants with different surface treatments on clinical behavior of soft and hard peri-implant tissues. Each of the 18 included patients received at least two adjacent implants: one control implant with a dual acid- etched (DAE) surface in their apical portion and a machined coronal part, and one test implant with a DAE surface up to its coronal portion. Peri-implant bone level change (BLC), probing depth (PD), bleeding on probing (BOP) and plaque index (PI) were recorded. A total of 42 implants was inserted. The mean follow-up period was 9.3 years (range: 5–16 years) and there were six dropouts. No implant failed. Moderate crestal bone remodeling occurred during the first year after implant insertion, with lower bone loss next to test implants compared to control ones (0.80 vs. 1.39 mm; p = 0.002). This difference was also detected at the 5- (p = 0.011), 6- (p = 0.008) and 7-year follow- up appointment (p = 0.027). No statistically significant differences were found in bone resorption between implants rehabilitated with ceramic vs. composite resin veneering material. No statistically significant differences were detected between test and control implants for BOP, PI, and PD at any time point. The results of the present study suggest that DAE surfaces reduce peri-implant bone loss in the initial phase of healing compared to machined surfaces, while they do not significantly affect soft peri-implant tissue and bone maintenance in the long-term. In conclusion, the minimally rough surfaces favour peri-implant bone maintenance and their effect is greater in the first year post implant insertion.
Article
The effectiveness of dimple surface texturing via picosecond pulsed laser processing for reducing wear loss was investigated using two types of titanium alloys, β-type Ti–29Nb–13Ta-4.6Zr (TNTZ) and α+β-type Ti–6Al–4V ELI (Ti64). The two alloys showed different modes of wear against zirconia. As the sliding distance increased, the wear loss was observed to increase for Ti64, but not necessarily for TNTZ. The wear debris of Ti64 acted as abrasive particles, but that of TNTZ easily adhered to the surface, and the adhered wear debris turned into a hard wear-protective layer. Therefore, the dependence of wear loss on the sliding distance for these two titanium alloys could be attributed to the difference in the roles of wear debris between each titanium alloy and zirconia. Further, depending on this difference in wear mode, the effect of dimple surface texturing on the wear was found to be different in Ti64 and TNTZ. As the dimples can trap the wear debris, they are effective for reducing wear in Ti64 but are detrimental in TNTZ.
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To compare the biological, technical and aesthetic outcomes of single implant-supported all-ceramic versus metal-ceramic crowns. Thirty-six patients with premolar agenesis were randomly treated with 38 all-ceramic (AC) and 37 metal-ceramic (MC) implant-supported single-tooth restorations. A quasi-randomisation of consecutively included restorations in patients with one or more implants was used, i.e. a combination of parallel group (for 13 patients with one restoration) and split-mouth (for 23 patients with ≥2 restorations). All patients were recalled for baseline and 1-year followup examinations. Biological and technical outcomes, including complications, were clinically and radiographically registered. The Copenhagen Index Score and visual analogue scale (VAS) score were used to assess professional and patient-reported aesthetic outcomes, respectively, by blinded assessors. One-year after loading, no patient dropped out and no implant failed, though one MC restoration had to be remade. The marginal bone loss was not significantly different between AC and MC restorations (AC: mean 0.08 mm, SD 0.25; MC: mean 0.10 mm, SD 0.17). Seven out of 10 inflammatory reactions were registered at AC restorations. Two technical complications, one loss of retention and one chipping of veneering porcelain were recorded at two metal-ceramic crowns. The marginal adaptation of the all-ceramic crowns was significantly less optimal than the metal-ceramic crowns (P = 0.014). The professional-reported colour match of all-ceramic crowns was significantly better than metal-ceramic crowns (P = 0.031), but other aesthetic parameters as well as the VAS scores demonstrated no statistically significant difference between AC and MC restorations. Marginal bone loss and the aesthetic outcomes were not significantly different between AC and MC restorations in this short-term follow-up study, though inflammatory reactions in the peri-implant mucosa as well as less optimal marginal adaptation were more frequently registered for all-ceramic compared to the metal-ceramic crowns.
Article
This literature review summarizes research with the aim of providing dentists with evidence-based guidelines to apply when planning treatment with osseointegrated implants. Peer-reviewed literature published in the English language between 1969 and 2003 was reviewed using Medline and hand searches. Topics reviewed include systemic host factors such as age, gender, various medical conditions, and patient habits, local host factors involving the quantity and quality of bone and soft tissue, presence of present or past infection and occlusion, prosthetic design factors, including the number and arrangement of implants, size and coatings of implants, cantilevers and connections to natural teeth, and methods to improve outcomes of implant treatment in each category. The review demonstrated that there is no systemic factor or habit that is an absolute contraindication to the placement of osseointegrated implants in the adult patient, although cessation of smoking can improve outcome significantly. The most important local patient factor for successful treatment is the quality and quantity of bone available at the implant site. Specific design criteria are provided, including guidelines for spacing of implants, size, materials, occlusion, and fit. Limitations in the current body of knowledge are identified, and directions for future research are suggested.
Article
A study was conducted to investigate the hypothesis that mechanical loading of implants and the consequent stress and strain fields influence bone modeling and remodeling at the bone-implant interface. Two implants ad modum Brånemark were placed in each of 20 canine tibiae, allowed to heal for I year, and then subjected to a controlled loading protocol. Implants in the left limb were loaded in axial tension with a triangular waveform (300 N maximum, 10 N minimum, 330 N/s) for 500 cycles per day for 5 consecutive days; implants in the right limb served as unloaded controls. Twelve weeks after loading, polished undecalcified thick sections were examined with light and scanning electron microscopy to provide bone modeling and remodeling data, including the surface area of periosteal and endocortical modeling, the percentage of mineralized tissue in the bone threads, and the frequency of occurrence of preloading and postloading fluorochrome bone labels. Also, a three-dimensional finite element model was developed to investigate the strain state in the bone near loaded implants. The morphometric data were statistically analyzed in terms of individual load-control pairs and showed the following trends for loaded implants: (1) a net bone loss near the coronal portion of the implant, (2) a smaller percentage of mineralized tissue in the cortex, and (3) a decreased frequency of occurrence of postloading fluorochrome bone label in the cortex adjacent to the implant. The finite element model indicated regions of high strain on the periosteal surface adjacent to the loaded implants. The results support the premise that the bone loss observed around the neck of the loaded implants at 12 weeks postloading was a consequence of bone modeling and remodeling secondary to bone microdamage caused by the loading protocol. This scenario, as well as certain other features of the bone response at the interfaces, can be interpreted in light of existing bone modeling and remodeling theories that relate bone activities and mechanical loading. When considering any load-bearing implant in bone, it is important to understand not only the mechanics of stress transfer at the interface, but also the biological response of the interfacial tissues to these stresses. The ability to maintain a healthy bone-implant interface is widely believed to be critical to the survival of the implant. JOMI on CD-ROM, 1994 Mar (345-360): Mechanical Loading of Brånemark Implants Af… Copyrights © 1997 Quinte… 1 Although success rates for most dental implant designs are good, implant failure is often characterized by minor to massive bone loss, implant mobility, and the inability of the implant to perform its intended function.2 The importance of mechanical factors in dental implant failure cannot be overlooked given the increased incidence of component fracture,3,4 coronal bone resorption,5 and fixture loss6 in situations of compromised prosthetic reconstruction and long-term loading. The exact nature of the mechanical stimuli resulting in bone destruction or deposition and the biological response to such stimuli has yet to be established. The objective of this study was to investigate interfacial bone response to implant loading in a controlled model system and to examine the response of the interfacial tissues in terms of general bone modeling and remodeling concepts. The bone biology literature has used the terms bone modeling and bone remodeling nearly interchangeably to describe almost all types of bone growth and turnover. Recent publications7,8 have distinguished between the two terms and have given separate definitions, which will be adopted here. Bone modeling has been defined as the deposition or removal of bone from bone surfaces. Modeling produces an overall change in the size or shape of the bone via activation followed by either formation or resorption. Bone remodeling, however, involves activation followed by a sequence of bone resorption and formation that results in the formation of a secondary osteon within the existing bone tissue. A remodeling cycle rarely alters gross bone architecture or size.
Article
Although the favorable mechanical properties of zirconium oxide-based ceramics have increased the acceptance of fixed dental prostheses for use in the posterior regions of the mouth in recent years, there are few clinical studies documenting the longevity of these restorations. Furthermore, certain complications must be resolved before the material is used more extensively. The purpose of this randomized prospective study was to evaluate the clinical performance of zirconia (Lava) 3-unit posterior fixed dental prostheses. Twenty 3-unit fixed dental prostheses were placed in 17 participants to replace a second premolar or a first molar. Eleven were placed in the maxilla and 9 in the mandible. All abutment teeth were prepared with a chamfer finish line of 0.8 to 1 mm, and frameworks were prepared with the Lava system. Restorations were cemented with a resin cement. Two calibrated examiners independently evaluated the fixed dental prostheses 1 week (baseline) and 1, 2, and 3 years after placement with the California Dental Association quality evaluation system. The periodontal parameters: the gingival index, plaque index, margin index, and the probing depths of abutment teeth and contralateral teeth were assessed. Data were analyzed by using descriptive statistics and the Wilcoxon signed-rank test (α=.05). All fixed dental prostheses were rated satisfactory after 3 years, and no fracture of the framework was observed during the observation period. One fixed dental prostheses was lost because of a biological complication at the 3-year examination, and a small degree of chipping of the veneering ceramic was observed in 2 participants. No significant differences among the periodontal parameters of the test and control teeth were observed except for the margin index. The results of a 3-year evaluation suggest that posterior zirconia 3-unit fixed dental prostheses are a reliable treatment.
Article
The aim of this study was to compare the survival rates and biologic and technical complications of three-unit metal-ceramic posterior fixed dental prostheses (FDPs) with those obtained with zirconia frameworks. Thirty-seven patients in need of 40 three-unit posterior FDPs were included in this study. The FDPs were randomly assigned to 20 zirconia and 20 metal-ceramic restorations. Abutment preparation guidelines consisted of a 1-mm-wide circumferential chamfer, axial reduction of 1 mm, and occlusal reduction of 1.5 to 2 mm. At baseline and 1, 2, 3, and 4 years after cementation, success of both types of restorations was evaluated. The restorations were assessed using the California Dental Association's assessment system. Periodontal parameters were assessed by determining the Plaque Index (PI), Gingival Index (GI), Marginal Index (MI), and pocket depth of the abutment and control teeth. Statistical analysis was performed by applying Wilcoxon rank sum and Wilcoxon signed-rank tests. Patients were examined after a mean observation period of 50 ± 2.4 months. The survival rates for metal-ceramic and zirconia restorations were 100% and 95%, respectively. One biologic complication in a zirconia FDP was observed at the 3-year follow-up. No fractures of the zirconia or metal frameworks were observed. Restorations from both groups were assessed as satisfactory. Minor chipping of the veneering ceramic was observed in 2 zirconia FDPs after 4 years. No significant differences were observed between abutment and contralateral teeth for either type of restoration or within the groups with regard to PI, GI, and pocket depth. Zirconia-based FDPs demonstrated a similar survival rate to metal-ceramic FDPs after medium-term clinical use.
Article
The purpose of this study was to compare clinical, radiographic and histological differences around titanium oral implants loaded with either acrylic-veneered metal or ceramo-metal fixed prostheses. Five beagle dogs were used in this investigation. At the beginning of the study, all mandibular premolars and first molars were extracted. After 3 months of healing, 2 Brånemark implants were installed on each side of the mandibles. Three months later, abutments were inserted on each implant and a daily oral hygiene regime was initiated. One month after abutment connection, the implants on one side of the mandible were restored with an acrylic-veneered metal fixed prosthesis, whereas, on the other side a ceramo-metal fixed prosthesis was inserted. The prostheses were constructed in occlusion with the maxillary first molars. The following clinical parameters were measured around each implant at this time (i.e., baseline), and thereafter, at monthly intervals up to 5 months: Plaque Index; Gingival Index; implant mobility (using the Periotest®); probing depth and clinical attachment level (using the Florida Probe®). In addition, standardized radiographs were taken at baseline and 5 months after insertion of the prostheses and evaluated by subtraction radiography. Another Brånemark fixture was installed on each side of the mandibles 3 months before the end of the study. These implants remained unloaded and submerged for the entire study period. Five months after prosthesis insertion, the animals were killed, and implants with their supporting peri-implant tissues were processed for histological evaluation. Analyses of the clinical, radiographic and histometric parameters revealed no significant differences between the acrylic-veneered and ceramometal loaded implants. All clinical and radiographic parameters remained stable over time. Histological comparison of the alveolar bone height levels around both loaded groups with those from the unloaded, submerged implants revealed that a similar and slight loss of bone height (approximately 0.6 mm) occurred on the loaded groups following abutment connection. It was concluded that both acrylic-veneered metal and ceramo-metal suprastructures appear to be suitable for the restoration of endosseous oral implants. Additional long-term studies in humans, however, are needed evaluating both types of implant-supported prostheses, in a variety of clinical conditions. before final restorative recommendations are made.
Article
Objectives: The purpose of this clinical study was to describe outcome variables of all-ceramic and metal-ceramic implant-supported, single-tooth restorations. Materials and methods: A total of 59 patients (mean age: 27.9 years) with tooth agenesis and treated with 98 implant-supported single-tooth restorations were included in this study. Two patients did not attend baseline examination, but all patients were followed for 3 years. The implants supported 52 zirconia, 21 titanium and 25 gold alloy abutments, which retained 64 all-ceramic and 34 metal-ceramic crowns. At baseline and 3-year follow-up examinations, the biological outcome variables such as survival rate of implants, marginal bone level, modified Plaque Index (mPlI), modified Sulcus Bleeding Index (mBI) and biological complications were registered. The technical outcome variables included abutment and crown survival rate, marginal adaptation of crowns, cement excess and technical complications. The aesthetic outcome was assessed by using the Copenhagen Index Score, and the patient-reported outcomes were recorded using the OHIP-49 questionnaire. The statistical analyses were mainly performed by using mixed model of ANOVA for quantitative data and PROC NLMIXED for ordinal categorical data. Results: The 3-year survival rate was 100% for implants and 97% for abutments and crowns. Significantly more marginal bone loss was registered at gold-alloy compared to zirconia abutments (P = 0.040). The mPlI and mBI were not significantly different at three abutment materials. The frequency of biological complications was higher at restorations with all-ceramic restorations than metal-ceramic crowns. Loss of retention, which was only observed at metal-ceramic crowns, was the most frequent technical complication, and the marginal adaptations of all-ceramic crowns were significantly less optimal than metal-ceramic crowns (P = 0.020). The professional-reported aesthetic outcome demonstrated significantly superior colour match of all-ceramic over metal-ceramic crowns (P = 0.015). However, no significant differences in the other aesthetic parameters at various restoration materials were registered. After 3 years, the patient-reported outcome variables at different restoration materials were not significantly different. Conclusion: The biological outcomes at the zirconia and metal abutments were comparable. All-ceramic crowns demonstrated better colour match, but higher frequency of marginal discrepancy compared to metal-ceramic crowns. Generally, the patients noticed no difference in aesthetic outcome of all-ceramic and metal-ceramic restorations.
Article
Evidence is limited on the efficacy of zirconia-based fixed dental prostheses. The purpose of this systemic review was to assess zirconia-based FDPs in terms of survival and complications. Searches performed in PubMed databases were enriched by hand searches to identify suitable publications. The keywords used were: "zirconia" and "fixed dental prosthesis," "zirconia" and "crown," "zirconia" and "fixed partial denture" and "humans," "zirconia" and "crown" and "humans," "crown" and "all-ceramics," and "fixed partial denture" and "all-ceramics". Titles and abstracts were read to identify literature that fulfilled the inclusion criteria. Only peer reviewed clinical studies published in the English language from January 1999 through June 2011 were included. Twelve clinical studies based on zirconia, framework design, and porcelain veneering technique met the inclusion criteria. Of the studies identified, 1 was a randomized clinical study with 3-year follow-up results; the others were cohort prospective studies. Clinical complications included chipping of veneering porcelain, abutment failure, and framework fracture. One study investigated pressed ceramics as the veneering material and found no chipping of veneering porcelain after 3 years. Short term clinical data suggest that zirconia-based fixed dental prostheses may serve as an alternative to metal ceramic fixed dental prostheses in the anterior and posterior dentition.