D. SARAC et al.: EXPERIMENTAL ANALYSIS OF DENTAL-IMPLANT LOAD TRANSFER ...
133–137
EXPERIMENTAL ANALYSIS OF DENTAL-IMPLANT LOAD
TRANSFER IN POLYMETHYL-METHACRYLATE BLOCKS
EKSPERIMENTALNA ANALIZA PRENOSA OBREMENITVE Z
ZOBNIH VSADKOV NA POLIMETIL-METAKRILATNE BLOKE
Dusan Sarac
1
, Nenad Mitrovic
1
, Ivan Tanasic
2
, Zarko Miskovic
1
, Ljiljana Tihacek-Sojic
3
1
University of Belgrade, Faculty of Mechanical Engineering, 11000 Belgrade, Serbia
2
Medical Health Center, Vojvode Misica 231, Obrenovac, 11000 Belgrade, Serbia
3
University of Belgrade, School of Dentistry, Clinic of Prosthodontics, 11000 Belgrade, Serbia
Prejem rokopisa – received: 2018-04-23; sprejem za objavo – accepted for publication: 2018-10-18
doi:10.17222/mit.2018.081
Dental-implant overload can cause bone resorption. Load-transfer characteristics of dental implants are affected by their
macro-design parameters. The goal of this study was to experimentally analyse the load-transfer characteristics of different
dental implants, using polymethyl-methacrylate blocks. Three polymethyl-methacrylate blocks were created, with dimensions
of (68 × 25 × 9) mm. Three dental implants, Nobel ø3.5 mm × 15 mm, Strauman ø4.1 mm × 10 mm and Strauman ø4.8 mm ×
12 mm, were placed in separate blocks. The samples were supported by a three-point-bending set-up and loaded with an axial
force of 600 N. The 3D digital image correlation method was employed for strain and displacement measurements. The highest
displacement and von Mises strain values were found for Strauman ø4.1 mm × 10 mm (p < 0.05), 0.186 mm and 0.596 %,
respectively. The sample of Nobel ø3.5 mm × 15 mm showed the lowest strain values. The sample of Strauman ø4.8 mm × 12
mm (p > 0.05) had similar strain values as Nobel ø3.5 mm × 15 mm. The load transfer during axial loading was primarily
affected by the size of the implant contact surface. The displacement and strain values in the implant vicinity may provide an
insight into the effect of dental-implant design on the load transfer.
Keywords: dental implant, digital image correlation, polymethyl-methacrylate, load transfer
Preobremenitev zobnih vsadkov lahko povzro~i resorpcijo kosti. Zaradi prenosa obremenitve je karakteristika zobnih vsadkov
odvisna od njihovih mikroparametrov oblikovanja. Cilj predstavljene {tudije je bila eksperimentalna analiza karakteristik
prenosa obremenitve razli~nih zobnih vsadkov z uporabo polimetil-metakrilatnih blokov. Avtorji so izdelali tri
polimetil-metakrilatne bloke dimenzij (68×25×9)mm. Tri dentalne vsadke, Nobel ø3,5 × 15 mm, Strauman ø4,1 × 10 mm in
Strauman ø4,8 × 12 mm, so namestili v posamezne bloke. Vzorce so nato podprli s trito~kovno upogibno napravo in jih
obremenili z osno silo 600 N. Za merjenje deformacije in pomikov so uporabili 3D digitalno slikovno korelacijo. Najve~ji
odmik in von Misesovo deformacijo so izmerili pri vsadku Strauman ø4,1 × 10 mm (p < 0,05), 0,186 mm in 0,596 %. Pri vzorcu
Nobel ø3,5 × 15 mm so ugotovili najmanj{e deformacije. Vzorec Strauman ø4,8 × 12 mm (p > 0,05) je imel podobne vrednosti
deformacije kot Nobel ø3,5 × 15 mm. Prenos obremenitve med osnim obremenjevanjem je bil odvisen predvsem od velikosti
kontaktne povr{ine vsadka. Premiki in deformacije v bli`ini vsadkov lahko zagotavljajo vpogled v oblikovanje zobnih vsadkov
glede na prenos obremenitve.
Klju~ne besede: zobni vsadki, korelacija z digitalno sliko, polimetil-metakrilat, prenos obremenitve
1 INTRODUCTION
Dental-implant overload can cause bone resorption
and implant failure.
1,2
It is known that dental-implant
micro-design has a considerable influence on the load
transfer and therefore on the bone resorption and re-
modelling.
3
As a result of continuous research and con-
sumer demand, implant design has been changed.
2
Studies with the goal to resolve the effect of dental-
implant geometry on the load transfer primarily used
numerical techniques.
2,4
A numerical analysis relies on
the assumptions concerning the implant geometry, ma-
terial characteristics and boundary conditions. Therefore,
the numerical analysis needs to be verified with experi-
mental data. Nevertheless, it can provide a great insight
into and a solution to various problems encountered in
dental practice or elsewhere. Dental-implant geometrical
characteristics can be divided into micro- and macro-
design. The micro-design refers to the surface roughness,
while the macro-design refers to the characteristics such
as diameter, length, shape and thread (pitch, depth and
profile). The implant diameter is often described as the
most important factor when the load transfer of a dental
implant is concerned.
5
The length and thread are also
considered important, but are still of the secondary
influence compared to the implant diameter.
5
Over 1300
different dental implant types can be found on the
market.
6
There is no consensus regarding the best dental
implant design.
7
Different acrylate models were used to
analyse the load transfer of implant-supported prostheses
and crown materials.
8,9
It is reported that the strain
measured on the surface of interest can reflect the im-
plant or prosthesis design.
8
The aim of this study is to
employ an experimental acrylate block model and the 3D
digital image correlation (DIC) technique to analyse the
effects of dental-implant macro-design parameters on the
Materiali in tehnologije / Materials and technology 53 (2019) 1, 133–137 133
UDK 620.1:620.172:616.314-77 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 53(1)133(2019)
*Corresponding author e-mail:
dsarac@mas.bg.ac.rs

displacement and strain fields in the vicinity of an
implant during an axial load. DIC can help us determine
a full-field strain and displacements with an accuracy of
0.01 %.
8
An additional goal was to explore the possibi-
lity of using similar models and procedures with larger
groups of dental implants that are already used in dental
practice.
2 EXPERIMENTAL PART
Three different dental implants were used in this
study: NobelSpeadyReplace ø3.5 mm × 15 mm, Strau-
man ø4.1 mm × 10 mm and Strauman ø4.8 mm × 12 mm
(Figure 1). Models of three moulds with interior dimen-
sions of (68 × 25 × 9) mm were created using software
SolidWorks (Dassault Systems, USA). The physical
models of the moulds were manufactured using Ulti-
maker 2+ 3D printers (Ultimaker, Netherlands).
Polylactic acid (PLA) plastic was used as the 3D printing
material. Every mould had a specific groove on the
topside, which corresponded to the implant neck. In this
way, every implant could be fixed in the vertical position
during the process of block casting (Figure 2).
Prior to the PMMA infill, the interior of the moulds
was coated with a thin layer of medical vaseline in order
to prevent PMMA from melting the mould due to its
exothermic polymerization effect. This step also allowed
an easier extraction after the hardening.
Afterwards, liquid PMMA (Triplex Cold, Vivoclar,
Lichtenstein) was poured into the mould openings. The
polymerization lasted for 15 min at a constant tempera-
ture of 40 °C in a UN 30 (Memmert, Germany) heating
oven. Hardened samples were removed from the mould
and marked as N1, S1 and S2 (Table 1). The surface of
interest was painted with a layer of white paint and after-
wards a stochastic layer of black dots was added (Figure
2). The samples were placed on the custom-made holder
of the three-point-bending configuration (Figure 3). A
span length of 48 mm was used in order to mimic a half
arch of the jaw.
8
The strain field and displacement were
measured using 3D optical system Aramis 2M (GOM,
Braunschweig, Germany). The digital image correlation
method is an optical contactless technique for measuring
the full-field strain and displacement.
10
The speckle
pattern enabled the 3D DIC system to measure the
displacement and strain on the sample surface of interest.
For a uniform illumination, a white light source was
used. A system calibration was performed according to
the manufacturer’s instructions.
An axial load of 600 N was applied onto the top of
the implant using an H10K-s universal testing machine
(Tinius Olsen, USA). All implants were loaded without
an abutment. Integrated travel measurement system
positioning was done automatically, limiting the contact
force with the dental implant to a value below 0.5 N.
Every subsequent image was made after a 50-N force in-
crease. During the loading stages, series of consecutive
images were created. The load was considered static.
After reaching the maximum force of 600 N, the model
was unloaded and one additional image of the sample
was created. After the measurements, the images were
exported into the Aramis v6.2.0 (GOM, Germany) soft-
ware. A statistical analysis and data graphical represen-
tation were performed in software R (Vienna, Austria).
D. SARAC et al.: EXPERIMENTAL ANALYSIS OF DENTAL-IMPLANT LOAD TRANSFER ...
134 Materiali in tehnologije / Materials and technology 53 (2019) 1, 133–137
Figure 2: Sample surface with a stochastic pattern (sample S2)
Table 1: Sample details
Sample name
reference
Implant dimensions
(mm)
Manufacturer
N1 ø3.5 × 15 Nobel Biocare
S1 ø4.1 ×10 Strauman
S2 ø4.8 × 12 Strauman
Figure 1: Dental implants: a) Nobel ø 3.5 mm × 15 mm, b) Strauman
ø 4.1 mm × 10 mm, c) Strauman ø 4.8 mm × 12 mm Figure 3: Scheme of the experimental set-up

3 RESULTS
Results were presented in the form of displacement Y
and von Mises strain. However, quantitative differences
remained, so section V0 was placed on the sample sur-
faces, along the longitudinal axis of dental implants
(Figure 3), and data was presented in the form of tables
and comparative diagrams for all the samples. The dis-
placement and strain values used in the statistical
analysis were extracted from the measurement points
along section V0.
Displacement Y for all three samples is presented in
Figure 7. Displacement values were negative as the ver-
tical y axis was directed upwards (Figure 4). The results
showed that displacement values varied between the
samples. Sample N1 showed the lowest displacement
values, while sample S1 had the highest values. The
highest displacement values were generally located on
the block surface, at the marginal level of an implant.
A similar trend was observed for the von Mises strain
values (Figure 8). The highest strain value was found at
the implant neck level, in a range of 0.4–0.6 %, depend-
ing on the sample. The maximum and mean values, as
well as the standard deviation values of displacement Y
and von Mises strain are presented in Tables 2 and 3.
The results were further imported into the R software
for a statistical analysis. Significant differences in the
displacement values along the block height were found
between all three samples, using one-way ANOVA. The
Tukey post-hoc test revealed significant differences (p =
0.000) between the displacement values for all three
samples (Table 4).
Table 4: p-values for displacement and von Mises strain
p-Value
Sample Displacement Mises
N1-S1 0.00 0.00
N1-S2 0.00 0.41
S1-S2 0.01 0.00
Similarly, von Mises strain values were also com-
pared. Significant differences were found between all the
sample combinations (p = 0.000), except for N1 and S2
(p = 0.41) (Table 4).
D. SARAC et al.: EXPERIMENTAL ANALYSIS OF DENTAL-IMPLANT LOAD TRANSFER ...
Materiali in tehnologije / Materials and technology 53 (2019) 1, 133–137 135
Figure 5: Displacements on section V0 for all the samples
Table 2: Vertical displacements along section V0
Displacement (mm)
Sample Mean SD Max
N1 –0.11 0.01 –0.127
S1 –0.16 0.01 –0.186
S2 –0.15 0.00 –0.162
Figure 6: Von Mises strain values on section V0 for all the samples
Table 3: Von Mises strain values along section V0
Mises strain (%)
Sample Mean SD Max
N1 0.21 0.07 0.485
S1 0.37 0.09 0.596
S2 0.24 0.10 0.495
Figure 4: Displacement field on the N1 sample surface

4 DISCUSSION
In this study, 3D digital image correlation was
applied in order to compare the displacement and von
Mises strain in the vicinity of three different dental
implants. This method enables a non-contact measure-
ment of displacement and strain values. It is independent
of the model material, thus overcoming the obstacle of
creating bone models from the materials with birefrac-
tive properties, whose behaviour may not be similar to
that of the bone.
The influence of the dental-implant design was the
subject of many papers, which usually applied numerical
methods to analyse the problem. In experimental studies,
photoelastic methods and strain gauges were mostly
used.
11
Both techniques have some limitations. Strain
gauges provide localized measurements, while the
photoelastic technique provides only qualitative data and
requires an application of birefractive materials. There is
only a limited number of experimental studies that com-
pare dental-implant designs. Pellizzer et al. compared
five different dental-implant designs using photoelastic
models.
1
They reported that the presence of a specific
thread type affects the load transfer and stress on the
contact surface, although the parameters like implant
diameter and length were not commented on. A similar
analysis was conducted by Cehreli et al.
9
Through ex-
perimental results, they concluded that a greater implant
diameter contributes to a lower stress and strain in the
block model in the vicinity of an implant.
The most obvious differences between samples N1
and S2 were found in the diameter and length. The
diameter of the sample-S2 implant was 27 % larger and
it was 20 % shorter. The implant diameter was shown to
be the primary parameter of influence when the load
transfer was taken into consideration.
12
On the surfaces of interest, differences in the axial
displacement and von Mises strain values were observed
between the samples. Nobel ø3.5 mm × 15 mm (in N1)
showed the lowest displacement and strain values, while
the highest values were observed for Strauman ø4.1 mm
× 10 mm (S1). The vertical displacement seemed to be
more affected by the implant length and the thread
characteristics or by their combined effect in the form of
a greater contact surface. The thread pitch was the
smallest for the N1 implant, which entailed the highest
thread density and a greater contact surface than those of
the Strauman implants. These conditions caused reduced
displacement and strain values. The implant contact
surface is one of the main parameters, affecting the
values of stress and strain in its vicinity. Additionally, the
N1 implant neck exhibited micro-threads that bonded
better with the crestal bone and transformed the shear
load into compression. This presents an advantage be-
cause the bone and PMMA should be loaded in com-
pression whenever possible.
13
This feature is also found
to promote the bone formation in the crestal area.
14
In
this case, this feature is not as significant as when found
in a bone due to the bone’s ability to osseointegrate.
Nevertheless, it seems that the presence of microthreads
leads to a better bonding with the acrylate block when
compared with a strictly rough surface.
A similar result was reported for photoelastic models
where the highest strain was found in the cervical third
of the block.
1,15
It was not observed that the diameter size
played a crucial role during the loading process.
Numerous studies reported that the implant diameter was
the most notable when lateral loads were applied.
16,17
But
the strain patterns for the axial and lateral loading are
different.
5
During the axial loading, the implant length is
considered to be more important, especially in a
cancellous bone.
16
Although this model was not made of
a cancellous bone, its modulus of elasticity was 2 GPa,
which was close to the cancellous modulus of elasticity
that is around 1.4 GPa.
18
This difference is less notable
when compared with the cortical bone elasticity modulus
(14 GPa).
18
Although no abutments were attached to the
implants, it was reported that during the axial loading,
the load transfer was very similar to these two cases, but
only when an axial load was applied.
15
The acquired results lead to the same conclusion.
When determining the optimal design of dental implants,
the values of mechanical strain and stress can point
toward the most important parameters. Sometimes the
parameters like implant diameter, length, shape, surface
and thread should not be evaluated only individually as
their combined effect should be examined as well. This
simplified jaw-bone model can be applied to many dental
implants available on the market.
6
The results found on
the surface of interest reflect the effects of dental-im-
plant design and loading conditions. This model can
provide an additional insight into the biomechanical
influence of dental-implant design on the load-transfer
characteristics.
5 CONCLUSIONS
The goal of this study was to evaluate the load
transfer of dental implants under an axial load onto the
surrounding structure. The implant length in combina-
tion with a large contact surface can provide a more
optimal load transfer during the axial loading. Acrylate
models can be applied to different implant types to
experimentally detect and compare the effects of implant
geometries on the surrounding area. A combined effect
of geometrical parameters should also be taken into con-
sideration. Future research should explore the applica-
tion of lateral loads in similar settings.
Acknowledgement
This research was supported by the Ministry of
Education, Science and Technological Development of
the Republic of Serbia within Projects TR35031,
D. SARAC et al.: EXPERIMENTAL ANALYSIS OF DENTAL-IMPLANT LOAD TRANSFER ...
136 Materiali in tehnologije / Materials and technology 53 (2019) 1, 133–137

TR35040, III41006 and III45009, which we gratefully
acknowledge.
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