Hindawi

BioMed Research International

Volume 2021, Article ID 5699962, 16 pages
https://doi.org/10.1155/2021/5699962

Review Article
Biomechanics in Removable Partial Dentures: A Literature
Review of FEA-Based Studies

Mohammed A. Mousa ,1,2 Johari Yap Abdullah ,3 Nafij B. Jamayet ,4

Mohamed I. El-Anwar ,5 Kiran Kumar Ganji,6 Mohammad Khursheed Alam ,6
and Adam Husein 1
1
Prosthodontic Unit, School of Dental Sciences, Universiti Sains Malaysia, 16150 Kubang Kerian, Kelantan, Malaysia
2
Department of Prosthetic Dental Sciences, College of Dentistry, Jouf University, Sakakah, Jouf, Saudi Arabia
3
Craniofacial Imaging and Additive Manufacturing Laboratory, School of Dental Sciences, Universiti Sains Malaysia,
16150 Kubang Kerian, Kelantan, Malaysia
4
Division of Restorative Dentistry, School of Dentistry, International Medical University, Bukit Jalil, Jalan Jalil Perkasa 19,
57000 Kuala Lumpur, Malaysia
5
Mechanical Engineering Department, National Research Centre, Giza, Egypt
6
Department of Preventive Dentistry, College of Dentistry, Jouf University, Sakakah, Saudi Arabia

Correspondence should be addressed to Mohammed A. Mousa; dr.mohammed.assayed@gmail.com,

Mohammad Khursheed Alam; dralam@gmail.com, and Adam Husein; adamkck@usm.my

Received 1 July 2021; Revised 23 July 2021; Accepted 30 July 2021; Published 27 August 2021

Academic Editor: Vincenzo Iorio Siciliano

Copyright © 2021 Mohammed A. Mousa et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The present study was aimed at reviewing the studies that used finite element analysis (FEA) to estimate the biomechanical stress
arising in removable partial dentures (RPDs) and how to optimize it. A literature survey was conducted for the English full-text
articles, which used only FEA to estimate the stress developed in RPDs from Jan 2000 to May 2021. In RPDs, the retaining and
supporting structures are subjected to dynamic loads during insertion and removal of the prosthesis as well as during function.
The majority of stresses in free-end saddle (FES) RPDs are concentrated in the shoulder of the clasp, the horizontal curvature of
the gingival approaching clasp, and the part of the major connector next to terminal abutments. Clasps fabricated from flexible
materials were beneficial to eliminate the stress in the abutment, while rigid materials were preferred for major connectors to
eliminate the displacement of the prosthesis. In implant-assisted RPD, the implant receive the majority of the load, thereby
reducing the stress on the abutment and reducing the displacement of the prosthesis. The amount of stress in the implant
decreases with zero or minimal angulation, using long and wide implants, and when the implants are placed in the first molar area.

1. Introduction sidered a cost-effective treatment option in partially edentu-

lous patients, compared to fixed and implant-retained
The main objective of removable partial dentures (RPDs) is restorations [3]. Although there was no worldwide meta-
to provide prosthetic rehabilitation of missing teeth and asso- analysis report about the prevalence of patients wearing
ciated structures, with avoidance of further loss of remaining RPD, up to the authors’ knowledge, there was an agreement
teeth. RPDs are indicated (in terms of aesthetic and mastica- that the number of partial edentulism is increasing in the
tory efficiency) when the edentulous span is extensive, hori- United States and the United Kingdom [4–6], with more
zontally and vertically, to be treated with conventional fixed prevalence in female patients [7]. In Brazil, Kennedy class I
dental restoration because of the excessive resorption that was the most prevalent lower edentulism, while Kennedy
may happen following extraction [1, 2]. RPDs are still con- class III was the most frequent maxillary one [7]. 13% of
2 BioMed Research International

the United Kingdom population was reported wearing RPDs, sponding prostheses virtually without the need to get ethical
while 6% wear complete dentures [8, 9]. As per the men- approval [38]. FEA can be performed by achieving the per-
tioned reports, RPDs still provide realistic and predictable sonal data from laser scanning, Cone Beam Computerized
treatment options, and therefore, all efforts should be done Tomography (CBCT), Magnetic Resonance Imaging (MRI)
to design adequate prostheses that serve efficiently with no or even simulating the design using available computer-
or minimal damage. aided engineering software. This is followed by customized
The prosthetic management of partially edentulous segmentation, specifying the properties of the materials, get-
patients with RPDs remains to face challenges due to varie- ting the model, meshing it, loading that model, and, finally,
ties of factors including dental factors, patient’s factors, and getting the solution to the problem (Figure 1) [33, 35, 39].
factors related to the prosthesis itself [10–12]. Components Introduction of nonlinear contact analyses in FEA has solved
of the prosthesis are subjected to stress and, at the same time, the soft tissue behavior, problems of sliding, prediction of the
can produce stresses in the supporting structures as well [13]. deflection and permanent deformation of clasp arms, and the
Abutment teeth, as supporting and retaining structures to the friction phenomena that happen between the prosthesis and
prosthesis, are subjected to stress during function, insertion, abutment teeth and at the proximal contact surfaces between
and removal of the prosthesis. If this stress exceeded their adjacent teeth [40, 41]. Figure 2 shows the problems that FEA
natural resistance, this may result in resorption in the sup- can solve in dentistry.
porting alveolar bone, loss of the abutment, and, eventually, Although the study of biomechanical stress developed in
failure of the prosthesis [14, 15]. In the same way, the free- RPDs using FEA is rapidly expanding, there was no broad
end saddle prostheses are subjected to stress during function, review in the literature, up to the best of authors’ knowledge,
resulting in bone resorption, loss of the support, and loss of concerned with the collection of the stress developed in RPDs
stability of prostheses, which necessitate a frequent replace- and how to minimize it. The purpose of the present review
ment [16, 17]. Implant-assisted RPDs showed welcomed treat- was to identify the distribution of the biomechanical stress
ment modalities compared with the conventional RPDs, in in components of RPD and their supporting structures, to
terms of preserving supporting structures, optimizing the elaborate the causes of this stress, and to optimize prostheses
retention and stability of the prostheses, improvising the design in order to reduce this stress, from the point of per-
chewing efficiency, and improving the quality of patient life spective of FEA studies. The disparate themes and data make
[18–21]. On the other hand, the implant does not show the this study unsuited to be in the form of an ordinary system-
same tolerance of the natural tooth to the different kinds of atic review or meta-analysis study.
occlusal force which, if it exceeded its limit, may result in bone
resorption around the implant or even fracture of the implant
itself [22, 23]. The occlusal considerations, design of the pros- 2. Strategy of the Literature Search
thesis, implant length, diameter, and macro- and micro-
surface texture of the implant, bone quantity, and patient fac- This study is a part of a PhD research protocol approved by
tors, play a major role in the survival of implants [24–26]. the Human Research Ethics Committee of Universiti Sains
The biomechanics of oral structures and prosthetic resto- Malaysia (HREC/USM) with JEPeM Code: USM/JE-
ration used in dentistry highly influence the long-term suc- PeM/21030222. An electronic search was conducted by using
cess of dental treatment. Therefore, it was crucial to “Google Scholar, Saudi Digital Library (SDL), PubMed, Sco-
investigate the biomechanical interaction between support- pus, and Web of Science (WOS)” database research tools.
ing structures and the overlying prosthesis, in order to con- The keywords used for the present study were chosen to be
trol it, to preserve the remaining structures and to maintain more general (“finite element analysis”, “implant-assisted
the prosthesis working adequately [27, 28]. RPD”, and “removable partial denture”) to allow extraction
Measurement of stress in abutment teeth, implants and of all relevant data. The initial search was done in “Google
surrounding structures, and prostheses has been performed Scholar” by the first 3 authors (M.A.M., J.A., N.J.), “SDL”
using diversities of methods including analytical, numerical, by (M.A.M., K.K.G.), “PubMed and Scopus” by (M.K.A.,
and experimental methods [29]. Experimental methods such M.E.), and “WOS” by (J.A., A.H.). The titles and abstracts
as electrical strain gauges can provide point-to-point precise of the data sources were screened over nearly one month.
quantitative measurement to the stress distribution in in vivo When an article was found relevant to the objective of our
and in vitro scenarios [30], while photoelasticity can provide study, its references were screened for further studies that
a full-field qualitative measurement of the same kind of stress meet the inclusion criteria. The search was done to find
[31]. Each technique of experimental methods has its advan- answers for the question “what are the factors contributing
tages and limitations, which make it necessary to use two or to the development of the biomechanical stress in RPDs
more methods to identify the stress and strain in any area and how to minimize it?” Table 1 shows the inclusion
of interest [31, 32]. and exclusion criteria of the present review. All picked
Finite element analysis (FEA), as a numerical method, articles were collected, the required data were extracted,
has been approved as a proficient way of providing qualita- and duplicated articles were excluded from the study.
tive and quantitative mathematical data of the biomechanics Although there are different software programs, techniques
of different dental prostheses and their supporting structures are currently available for performing FEA studies; how-
[33–37]. The main advantage of FEA is the capability to work ever, FEA is a numerical process with reproducible data
with complex situations (or defects) and creating their corre- of the same quality.
BioMed Research International 3

A B C D E

F G H I

Figure 1: The workflow steps of finite element analysis.

Minimum (negative)
principal stress
(Compressive force)

Uses of
Retention Deflection
FEA in
(Force of removal) (Displacement)
Dentistry

Maximum (positive)
principal stress
(Tensile force)

Figure 2
4 BioMed Research International

Table 1: Inclusion and exclusion criteria.

Inclusion criteria Exclusion criteria

1. Only studies that used FEA 1. Experimental and in vivo studies
2. Full-text studies 2. Letter to editor or conference studies
3. From Jan 2000 to May 2021 3. Before Jan 2000 or after May 2021
4. Only in English or translated papers 4. Other than English or not translated studies
5. Only studies conducted on RPD 5. The studies conducted in removable complete or fixed restoration

3. Results and Discussion focused on the influence of different RPD designs and mate-
rials in the development of the stress and how to manage it.
During the selected times, 8258 articles were surveyed. Out of To be more convenient to readers, the findings have been cat-
these articles, 8178 were excluded based on screening of the egorized under the main titles “Identification areas of stress
title and abstract (as they do not relate to the objectives of concentration and deflection in RPDs” and “Factors affecting
the current review), while 44 articles were finally recruited the biomechanical stress in RPDs”.
for this study [17, 21, 36, 42–82]. The initial causes of exclu-
sion of articles were the articles worked on complete, maxil- 3.1. Areas of Stress Concentration in RPDs. Although there
lofacial, fixed, and non-FEA methods. Figure 3 shows the was a shortage in the literature regarding the identification
prevalence of conducted English studies that used FEA in of stress distribution in tooth-supported RPDs, FES scenarios
RPDs in the last 20 years. It shows an increase in publications got much interest regarding this interest. It was found that
of FEA studies in 2020 compared to 2008 and before (except the terminal abutment shows a concentration of the stress
2018, which showed zero publications). The results were in the apical and distal side [42], while the residual ridge
extracted and grouped to identify the targeted problem and shows the main stress concentration at the occlusal and lin-
how to solve it. Among the selected articles, 14 studies have gual side when the saddle is short [36], and both of the mesial
reported the influence of different retainer designs [44, 55– and distal area when the saddle is long [43]. The most com-
67], while seven studies measured the influence of different mon areas of FES RPD components subjected to stress dur-
designs and materials of major connectors [66, 69–74], and ing function of the prosthesis include; the minor and major
the studies concerned with implant-assisted RPD were ten connector lingual to the terminal abutment, the horizontal
articles [17, 43, 55, 76–82]. The results were broad-covering curvature of the gingival approaching clasp [44], and the
with heterogeneous and disparate data, which made it not shoulder of the Aker and back action clasp (Figure 4) [45,
compatible to be a meta-analysis or systematic review. For 46]. However, the proper design of the prosthesis makes the
this, a form of narrative review has been chosen for the cur- stress concentration be within the yield strength of the Co-
rent research. Cr alloy, which results in an extension of the survival rate
There is no disput about the fact that the long-term suc- of the clasp to 5.5 years [45, 46].
cess of RPDs is directly proportional to the extent of control In implant-assisted RPDs, the stress is concentrated
of various stresses induced by them on the supporting struc- evenly around the implant if they were fully implant-
ture. This concept is emphasized by a long history of evalua- retained [21]. In the case the scenario was FES RPDs, the
tion of each type of stress and suggesting the optimal design stress is mainly concentrated in the mesial side of the implant
and materials for bringing them to the physiologic limits of [49, 50], while the stress in abutments and residual ridges is
the supporting structure [28]. According to the literature, significantly decreased regardless of the position, length, or
the stress from the RPD components arises from either an width of the implant used [47, 48].
accurately designed and fabricated prostheses or prostheses
with inaccurate design or fault fabrication. The stress arising 3.2. Displacement and Deflection in RPDs. The displacement
from an accurately designed prosthesis is affected by prosthe- induced by RPD mainly results from the deflection of the
sis (or prosthodontist) factors and patient’s factors. The fac- prosthesis, which was affected by mechanical properties of
tors relating to the prosthesis include major connector the base materials and the length of the saddle. As the rigidity
designs, retainer designs, locations of the occlusal rest, prop- of the major connector increases, the defection of the denture
erties of denture material, extension of edentulous saddles, base materials decreases, while the stress in abutments and
and the presence or absence of implant/s. The factors related implant increases. The displacement of FES RPD is concen-
to the patient include age, ridge shape and form, occlusal trated in the posterior part (distal) of the saddle of the pros-
force, and type of torque on the prosthesis. The stress arises thesis. As the saddle length increases, the displacement
from inaccurately designed prosthesis including thickness increases [43, 51]. To minimize the adverse effect of long
of the framework of the prosthesis, design of the major con- FES RPDs on supporting structures, implant-assisted RPD
nector, thickness of the occlusal rest, and selection of the would be considered [52, 53]. Upon using implant-assisted
materials [27, 28]. As all FEA studies assumed that the RPD, the displacement of the prosthesis significantly
designed prostheses are optimal, regarding the design and decreases regardless of the length, position, width, or inclina-
materials, and well fitted on their model, the current review tion of the implant [50, 54].
BioMed Research International 5

Number of FEA studies

12

10

0
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 May-21

Figure 3: The graph shows the number of FEA studies conducted on RPDs from 2000 to May 2021.

3 1

Areas show
maximum
stress in RPD

4 2

Figure 4: The portions of RPD components that receive the maximum stress.

3.3. Factors Affecting the Biomechanical Stress in cumferential clasps, a formula was introduced to optimize
Conventional RPDs. To overcome adverse effects of biome- the length and width of the clasp. According to this formula,
chanical stress in RPDs and decrease the stress on the the clasp should be a half-round shape with W2/W1 = 0:6
supporting structures, a variety of different approaches have and T/L = 0:5 to express the least stress, while W1 is the
been advocated in the FEA literature. width of the clasp at the base, W2 is the width of the clasp
at the tip, T is the thickness, and L is the length [56]. More
3.3.1. Design of Retention. The retention of conventional flexible materials were introduced to substitute the Co-Cr
RPDs is mainly gained from the adjacent teeth and underly- materials as well. Among these materials, titanium alloys,
ing tissues. There are different types of retainer systems such gold alloys, polyetheretherketones (PEEK), polyamides,
as occlusal approaching clasps, gingival approaching clasps, polyoxymethylenes, and acetal resin are examples [55, 57].
rigid and nonrigid attachment systems, telescopic crowns, Clasps made from polyamides, followed by polyoxymethy-
and implant/s. Table 2 shows that the studies evaluated the lenes, were found to produce the least amount of stress on
different retainer designs and their influences on the stress abutment teeth compared to clasps made of Co-Cr and tita-
and displacement of RPDs. niums, regardless of the depth they engage [55]. In the same
For bounded saddles, although the circumferential Co-Cr respect, the clasp made of acetal resin results in less stress
clasp showed the maximum force of removal, maximum when compared with the Co-Cr clasp, despite the retention
rigidity, and highest stability to the prostheses, it exhibits not being comparable between Co-Cr and acetal resins [57].
the maximum stress on the abutment teeth [55]. Moreover, In FES RPDs, there are diversities of retainer designs that
the clasp arms are subjected to stress that concentrated at can be used. Gingival approaching clasps as a most used
the junction of arms and the body of minor connector, which retainers for FES RPD received the most interest in the liter-
may result in loss of efficiency or even fracture of the clasp ature. When compared with Aker, reverse Aker, and embra-
[46]. The magnitude of the stress depends on the depth of sure clasp, the I-bar clasp (of the same material) shows a less
undercut, the length of the clasp, and the material of con- distal displacement and stress in PL of abutment teeth when
struction [55]. To decrease the stress arising in Co-Cr cir- engaged in a 0.01-inch undercut, while the embrasure clasp
6 BioMed Research International

Table 2: Studies reporting the influence of different retainer designs on stress and displacement of conventional RPD.

Reported dependent
Type of The examined independent Materials used in variable
Authors Outcome
prosthesis variable the denture Displacement
Stress
deflection
(i) I-bar clasp design could demonstrate
Richert
Optimizing the length of I-bar optimal mechanical properties as long as
et al. 2021 FES RPD Co-Cr √ —
clasp the length of horizontal and vertical arms
[60]
did not exceed 6 mm length
(i) The stress was concentrated at the
shoulder of the circumferential clasp in
Six materials: all models
(i) Polyamide (ii) The highest stress was reported in Co-
18 3D designs of Aker clasps, (ii) Cr with 0.75 mm, while the lowest stress
Tribst et al. with different materials, within Polyoxymethylene √ and force of was reported in polyamide, regardless of
BS RPD √
2020 [55] 0.25, 0.5, and 0.75 mm (iii) PEEK removal depths of undercuts
undercuts (iv) Gold alloy (iii) Polyamide showed the lowest forces
(v) Titanium (Ti– of removal, followed by
6Al–7Nb) Co-Cr polyoxymethylene, while Co-Cr showed
the highest removal force followed by
titanium
(i) The maximum stress concentration
was located at the base of the clasp
(ii) The stress concentration increased
when the thickness of the material
72 3D models of PEEK clasps increased
Peng et al. (i) PEEK √ and force of
— with different thickness/width √ (iii) PEEK clasp showed higher flexibility
2020 [63] (ii) Co-Cr removal
ratios when compared with Co-Cr clasp
(iv) PEEK clasp with a ratio of
width/thickness at the tip 2.70/1.69,
1.50/1.13, or 1.75/1.53 was considered an
optimal clasp to 0.5 mm undercut
(i) The stress was concentrated at the
Co-Cr base shoulder of the clasps but on the inner
Resin clasp with 6 areas of denture with two surface
Yamazaki
Mandibular blocked-out undercut with 0.50 thermoplastic √ and force of (ii) No significant differences were
et al. 2019 √
FES RPD & 0.75 mm on the buccal surface resin clasps removal reported between the two types of resin
[64]
of the main abutment (i) Polyester (iii) The retention of thermoplastic clasps
polyamide depends on the position and depth of
undercut rather than the material itself
(i) The highest stress was reported in the
Co-Cr clasp compared with the acetal
Reddy
Mandibular 2 Aker clasps, with two different (i) Co-Cr √ and force of resin
et al. 2016 √
BS RPD materials, in 0.25 mm undercut (ii) Acetal resin removal (ii) The force of removal of acetal resin
[57]
was significantly lesser than that of the
Co-Cr
(i) RPI clasp shows lower stress
concentration in the buccal and apical
region and areas of the cortical bone
supporting the abutment tooth when
compared with Aker and embrasure
Nakamura (i) 1 Aker and 1 reverse Aker
Mandibular clasps
et al. 2014 (ii) 1 embrasure clasp Co-Cr √ √
FES RPD (ii) Embrasure clasp expressed slightly
[58] (iii) 1 I-bar clasp
lesser vertical displacement compared
with RPI and Aker clasps, while RPI
showed significantly lesser distal
displacement followed by embrasure and
Aker clasps
(i) The maximum stress concentration
(i) Co-Cr
9 3D models of the I-bar clasp of was located at the horizontal curvature of
Oyar et al. (ii) Titanium (Ti–
— three different materials and √ — the clasp and was reported in the Co-Cr
2012 [44] 6Al–7Nb)
three modified tips specimen, while the gold alloy specimen
(iii) Gold alloy
showed the minimum stress
BioMed Research International 7

Table 2: Continued.

Reported dependent
Type of The examined independent Materials used in variable
Authors Outcome
prosthesis variable the denture Displacement
Stress
deflection
(ii) There is a direct relationship between
lengths of the horizontal arm and
development of stresses in the arms of the
clasp
(i) Both attachments showed similar
stress distribution in the alveolar bone
and PL, but with more concentration in
the case of rigid attachment
(ii) Compared with the rigid attachment,
Wang et al. Mandibular Rigid and nonrigid precision
Ni-Cr √ — the nonrigid attachment resulted in
2011 [67] class II attachment (ERA attachment)
higher stress in the mesial and distal end
of the residual ridge when subjected to
axial loads; however, the opposite was
true regarding buccolingual and
mesiodistal loads
(i) Reverse Aker clasp put more stress in
abutment teeth compared with
(i) Reverse Aker embrasure and back action clasps
Aoda et al. Mandibular
(ii) Embrasure Co-Cr √ √ (ii) Reverse Aker provided higher stability
2010 [59] FES RPD
(iii) Back action and lesser deflection to the denture
compared with embrasure and back
action clasps
(i) The stress was concentrated in the
inner surface of both half-round and
round wires, in the part of the arm
located above the height of contour of
Evaluation of round and half- abutment teeth
Sandu et al. Maxillary
round clasps with 9 diameters Stainless steel √ √ (ii) Regarding the displacement, the clasp
2010 [62] FES RPD
(from 0.5 to 1.3 mm) for each arm with half-round shape (with a
diameter of 1 mm) showed a similar
displacement to the clasp arm with round
shape (with a diameter between 0.6 and
0.7 mm)
The circumferential clasp with half-
Judy 2009 Optimizing the width & length round shape and formula W2/W1 = 0:6
FES RPD Co-Cr √ —
[56] of the circumferential clasp arm and T/L = 0:5 showed the least stress
concentration
(i) I-bar clasp with thin and wide arm,
taper 0.020-0.023, and radius of curvature
Sato et al. Evaluation of the I-bar clasp
FES RPD Co-Cr √ √ of 2.75–3.00 exhibited less stress
2001 [61] with 6 widths & lengths
compared with the thicker or shorter
ones
FES: free-end saddle; BS: bounded saddle; Co-Cr: cobalt-chromium; Ni-Cr: nickel chromium; PEEK: polyetheretherketone; W2: the width of the clasp at the tip;
W1: the width of the clasp at the base; T: thickness; L: length; PL: periodontal ligaments.

shows lesser vertical displacement (tissue ward) in the same ble area to stress concentration in the RPI system is located
undercut depth [58]. Reverse Aker brings more load on the in the inner surface of the retentive clasp arm and the area
main abutment but also shows higher stability and lesser just above the vertical projection of the horizontal arm [62].
deflection in the prosthesis in the same undercut depth To optimize the length and width of the I-bar clasp arm, a
[59]. The RPI system was found to produce stress and at thinner and wider arm with a taper of 0.02-0.03 and radius
the same was subjected to stress and deformations as well. of 2.75-3.00 mm was advocated to reduce the stress in the
The stress is concentrated in the neck of the retentive arm abutment tooth [61]. It was found that the optimal length
(just before the retentive tip) and at the horizontal curvature of horizontal and vertical arms should not exceed 6 mm to
of the clasp [44, 55]. The magnitude of stress depends on optimize the biomechanical stress within the clasp [60]. More
many factors: the thickness and width of clasp arms, the taper flexible materials were compared with Co-Cr to optimize the
and radii of the retentive arm, the shape and curvature of the stress on the abutment in FES RPD scenarios such as gold
horizontal approach arm, and the vertical distance between alloys, titanium alloys, stainless clasps, PEEK, and the use
retentive tip and horizontal axis [60, 61]. The most vulnera- of resin clasps (polyesters and polyamides) [62–65]. PEEK
8 BioMed Research International

Table 3: Studies reporting the influence of different designs of the major connector on the stress and displacement of conventional RPD.

Reported dependent
Type of The examined independent Materials used variable
Authors Outcome
prosthesis variable in the denture Displacement
Stress
deflection
(i) In both models, the
maximum stress has been shown
Two materials on the slopes of the maxillary
(i) Co-Cr arch
Rodrigues et al. Maxillary Two 3D models of two different (ii) (ii) The maximum displacement
√ √
2021 [74] class I materials Thermoplastic has been shown on the crest of
nylon (flexible the residual alveolar ridge
denture) (iii) The Co-Cr showed the least
stress and displacement
compared with nylon
(i) The lowest stress in the PDL
3 materials of the abutment and framework
Chen et al. Mandibular Three models for three different (i) Co-Cr was reported with PEEK
2019 [66] class I materials (ii) Ti alloy (ii) PEEK has exhibited the
(iii) PEEK highest displacement of the ridge
and mucosa
(i) The maximum distal
displacement was reported in the
wide and shallow palate, while
maximum buccal displacements
Five 3D models of different were higher in the deep palate
Hallikerimath Maxillary
palatal vaults (average, wide, Co-Cr — √ (ii) Maximum vertical
et al. 2015 [72] class II RPD
narrow, deep, and shallow) displacement was higher in the
average model
(iii)The deflection was lesser in
the narrow palate compared to
the other palatal shapes
(i) APPS showed the lowest
deflection compared with CPP
and PS
(ii) For APPS, the maximum
deflection was reported in the
occlusal rest responding to load
Different Six 3D models of 3 different
with anteroposterior direction
Bhojaraju et al. scenarios of maxillary MC (PS, CPP, APPS)
Co-Cr — √ and the anterior part of buccal
2014 [69] maxillary with different scenarios of
slope regarding vertical direction
RPD Kennedy classification
(iii) For CPP, the maximum
deflection has been reported in
the occlusal rest regarding
anteroposterior load and the
buccal slope and crest of the
ridge regarding vertical force
(i) The PB with a regular width
showed the maximum deflection
and displacement compared
with the other forms
Four 3D models of U-shape PB (ii) The double-thickness U-
Ramakrishnan (regular, increasing the width, shape MC exhibited the lowest
Maxillary
& Singh 2010 adding posterior PS, and Co-Cr √ √ stress followed by wide U-shape
class IV
[71] duplicating the thickness to MC
1 mm) (iii) The highest stress on the
palate and teeth has been shown
in double thickness as well
(iv) The lowest stress on the
palate and mucosa has been
BioMed Research International 9

Table 3: Continued.

Reported dependent
Type of The examined independent Materials used variable
Authors Outcome
prosthesis variable in the denture Displacement
Stress
deflection
reported in the scenario of wide
MC
(i) In all tested MC models, the
narrow model has reported the
Three lowest displacement when
materials were compared with the basic, wide,
used: and shallow palates, which
Five 3D models of different
Takanashi Maxillary (i) Co-Cr exhibited the maximum
palatal vaults (basic, wide, — √
et al. 2009 [73] class II (ii) Titanium displacement
narrow, deep, and shallow)
(Ti–6Al–7Nb) (ii) In the deep palate model, the
(iii) Gold alloy Ti MC with a width of 11 mm
(type IV) and gold MC with a width of
9 mm showed similar
displacement to the basic model
(i) The maximum displacement
has been shown in all models at
the posterior edge of the saddle
(ii) Vertical and buccal
displacements were inversely
In 13 3D models, 11 of them
proportional to the width of the
show PS MC with different AP
Eto et al. 2002 Maxillary major connector. As the major
widths at the midlines, 1 design Co-Cr — √
[70] class II RPD connector increased, the
for APPB, and lastly, horseshoe
displacement decreased
PS with 7 mm
(iii) APPB and wide PS exhibited
the lowest buccal displacement
compared with horseshoes,
which showed the maximum
displacement (least rigidity)
FES: free-end saddle; AP: anteroposterior; PS: palatal strap; APPS: anteroposterior palatal strap; APPB: anteroposterior palatal bar; CPP: complete palatal plate;
MC: major connector; Ti: titanium.

was proven as an attractive option to replace the Co-Cr due connectors should be rigid to provide an equal distribution
to the minimum stress on the PL of the abutments and at of load and prevent stress concentration in supporting struc-
the same time showed adequate retention [63, 66]. To opti- tures. The prosthesis with a highly rigid major connector is
mize the retention of the PEEK clasp in a 0.01-inch undercut, associated with less deflection during function [69]. The
the ratio width/thickness at the tip shall be 1.50/1.13, deflection of the prosthesis results in unequal distribution
1.75/1.53, or 2.70/1.69 [63]. of the stress in the underlying structures, which leads to
Rigid and nonrigid attachments are considered efficient inflammation and resorption of the residual ridge [69]. The
retainers to FES RPD with no visible metal components. stress developed in supporting structures depends on the
Use of nonrigid attachment results in less stress in the main material of fabrication, design and thickness of the used
abutment but on the other hand brings more stress to the major connector, and the shape of the palate [66]. The ante-
supporting ridge. The concentration of the stress in the ridge roposterior palatal strap design was found to be the most
was obvious in the mesial and distal area of the saddle [67]. rigid design compared with different designs such as com-
plete palatal plate, posterior palatal strap, and, lastly,
3.3.2. Occlusal Rest Position. The occlusal rest position shows horseshoe-shaped major connector, which showed the lowest
a role in stress distribution in abutment teeth and RPD rigidity [69, 70]. To increase the rigidity and to reduce the
framework. Putting the occlusal rest on the distal side of internal stres in of horseshoe-shaped major connectors, a
the terminal abutment was found to improve the stress distri- double thickness was advocated. This modification, however,
bution in these teeth and stiffen the metal frameworks and can deliver higher stress on the underlying mucosae and PL
acrylic resin denture bases by 66% when compared with the [71]. The shape of the palate also influences the stress and
occlusal rest placed on the mesial side of the same abut- displacement of the major connector [72, 73]. The narrow
ment [68]. palate shows the least displacement in the major connector
comparing the wide and shallow palate [72, 73]. The flexible
3.3.3. Design of Major Connectors. While the retentive arm of framework materials are always associated with less stress in
retainers should be fabricated from flexible materials, major the major connector, but more displacement on the ridge is
10 BioMed Research International

Table 4: Studies reporting the biomechanical stress and displacement in implant-assisted removable partial denture with different designs.

The reported dependent

The examined independent variable
Authors Type of prosthesis variable Outcome
Length Width Location Inclination Attachment Stress Deflection
(i) M1 at
the 1st (i) The highest stress
molar concentration in the
Four 3D models (ii) M2 at implant has been reported
Tribst of conventional
the 2nd in the implants of M2
et al. 2020 and ISRPD class — —
[55] II mod 2 with 3 molar followed by M3
different designs (iii) M3 2 (ii) The implant in the 1st
implants at molar region received less
the 1st and stress as in M1 and M3
2nd molars
(i) The implant located in
the premolar area
exhibited the highest
displacement in the
(i) M1
posterior region, while the
implants
opposite happened when
located at
the implant was located in
Two 3D models of the
Messias the molar area
mandibular class I premolar
et al. 2019 — — — — √ — (ii) The stress was more
IARPD in 2 area
[76] concentrated in the part of
different locations (ii) M2 at
the major connector next
the
to abutment teeth
premolar
(iii) More stress on the
area
posterior part of the saddle
was shown when the
implant was located in the
premolar area
Three
different
locations
(i) M1 at When the implant was
Ortiz- Two 3D models of the 2nd located in the 1st molar
Puigpelat mandibular class I molar area, less displacement
— — — — √ —
et al. 2019 IARPD in 2 (ii) M2 at and minimum stress at the
[77] different locations the 1st implant and the metal
framework were reported
molar
(iii) M3 at
the 2nd
premolar
(i) In the conventional
RPD, the maximum stress
was reported at the
anterior (premolar) and
2 implants posterior (2nd molar) areas
One model for (ii) There was a reduction
Andrei were placed
conventional and
et al. 2015 — — bilaterally — — √ √ in the maximum stress at
IARPD for Co-Cr
[43] in the 2nd the same area in IARPD
mandibular class I
molar area compared with the
conventional RPD
(iii) The lateral
displacement was high at
the distal edge of both
BioMed Research International 11

Table 4: Continued.

The reported dependent

The examined independent variable
Authors Type of prosthesis variable Outcome
Length Width Location Inclination Attachment Stress Deflection
prostheses but with a
higher value in the
conventional RPD than in
IARPD
(i) M1 at
the 2nd
As the implant was placed
molar area more anteriorly, more
Three 3D models, (ii) M2 at stress was concentrated in
Memari
one for class II the 1st the terminal abutment,
et al. 2014 — — — — √ —
IARPD in 3 molar area reaching its maximum
[17]
different locations (iii) M3 at value when the implant
the 2nd was located next to the
terminal abutment
premolar
area
(i) In all IARPD designs,
there was a clear diminish
in the displacement when
compared with the
conventional RPD
(ii) In IARPD, the lowest
displacement has been
The
exhibited in an implant
implant
Five models: located in the middle of
location:
(i) Natural the residual ridge and then
(i) Distal
Cunha (ii) Conventional the distal area of the ridge,
(2nd molar)
et al. 2008 (iii) IARPD (3 — — — — √ √ while the mesial location
(ii) Middle
[80] models) Co-Cr of the implant showed the
(1st molar)
mandibular class lowest stress in the
(iii) Mesial
II terminal abutment
(1st
(iii) The mesially placed
premolar)
implant showed the
highest stress value in the
internal thread of the
implant followed by the
middle and then the distal
area, which showed the
least stress
(i) The stress on the
terminal abutment was the
least with an implant of
10 × 3:5 and then 10 × 3 in
Six 2D models One the 1st molar area,
(i) Natural implant in compared with implants
El-Okel
(ii) Conventional the 6th and of 10 × 3:5 and 10 × 3, at
and 3&
(iii) IARPD (4 10 mm one implant — — √ — the 2nd molar area
Elnady 3.5 mm
models) Co-Cr in the 7th (ii) The highest stress has
2013 [79]
mandibular class molar been recorded in the
II region
implant of 10 × 3 and
located in the 2nd molar
area, while the lowest
stress has been recorded in
the implant of 10 × 3 and
12 BioMed Research International

Table 4: Continued.

The reported dependent

The examined independent variable
Authors Type of prosthesis variable Outcome
Length Width Location Inclination Attachment Stress Deflection
located in the 1st molar
area
(i) Increasing the
inclination of the implant
has shown increase in the
(i) M1-3 at stress in the implant to
Six 3D models of
(i) M1-3 0°, 10°,and reach the maximum in
IARPD with two
Fayaz (7 mm) 1st molar 15° M6, while the stress in the
lengths and 3 4 mm — √ —
2015 [81] M4-6 area M4-6 at 0°, terminal abutment
different
(10 mm) 10°, and 15°, decreased to the minimum
inclinations
respectively (ii) As the length of the
implant increased, the
stress on the abutment
decreased
(i) Adding an implant to
assist RPD led to a
4 models significant reduction in the
Six 3D models of with displacement of the
natural, different prostheses
de Freitas
conventional, and inclinations (ii) The stress around the
Santos 2nd molar
IARPD — — were used: — √ √ apex of the terminal
et al. 2011 region
mandibular class (0°, 5°, 15°, abutment in all models
[82]
II with 4 different and 30°) in a with implants has shown
angles mesial better distribution in 0°
direction and 5° compared to 15°
and 30°, which showed the
highest stress
M: model; IARPD: implant-assisted removable partial denture.

recorded [66, 73, 74]. Table 3 shows that the studies evalu- amount of stress, which may lead to the frequent fractures
ated the influences of major connectors on the stress and of this part of acrylic around the attachment. This is mainly
deflection of RPDs. Table 3 shows also the lack of literature due to the mismatch of the distribution of stress between
in evaluation of stress developed in the different designs of the acrylic bases and the base metal framework as the stresses
mandibular major connectors. developed in the metal frameworks mainly concentrated in
the major and minor connectors away from the attachment
3.3.4. Splinting of the Abutment Teeth. Teeth with reduced area, while the occlusal load transfers directly to the acrylic
periodontal support are considered inadequate abutments materials around the attachment [49].
for retention and support of RPDs, especially RPDs with dis- The stress developed on the abutment, implants, and
tal extension scenarios. However, splinting two or more denture base materials varies according to the implant loca-
reduced periodontally supported teeth was beneficial for ade- tion, inclination, diameter, and type of applied load. Table 4
quate stress distribution and reduction of the anterior dis- shows the influences of implant designs on the development
placement of these teeth. Splinting more than three teeth of stress and displacement.
around the arch was more beneficial as it can provide a curve
for resistance to the buccolingual displacement [75]. 3.4. Factors Affecting Stress Developed in Implant-
Assisted RPDs
3.3.5. Use of the Implant Approach. Implant-assisted RPDs
were advocated for FES scenarios to provide a substantial 3.4.1. Implant Location. Implant locations were found to
increase in retention of the RPD as well as reduction of the have direct influences on the development of stress in abut-
stress in the abutments and residual ridges. According to ments and residual ridge. When the implant is placed more
the implant-assisted RPD concept, the implant and sur- anteriorly (the premolar area), the stress on the implant
rounding bone (especially the cancellous) receive the major- became maximum, the stress on the abutment teeth became
ity of the stress, while abutments receive minimal stress and minimum, and the displacement distally became maximum.
the displacement of the prosthesis becomes minimal [21, On the other hand, when the implant is placed more posteri-
47–49]. On the other hand, the acrylic base of the prosthesis orly (the 2nd molar area), the stress on the abutment teeth
over the abutment of the implant receives a significant becomes considerably high and more displacement is
BioMed Research International 13

reported at the mesial side of the residual ridge. Placement of Data Availability
the implant in the first molar area has been proven to have
the lowest stress in the implant, lowest stress in abutment All data are available within the manuscript.
teeth, and lowest stress in the distal side of the residual ridge
[17, 55, 76–79]. Conflicts of Interest
3.4.2. Length and Diameter of the Implant. The length and There are no conflicts of interest.
diameter of the implant influence the displacement and stress
in abutment teeth, denture supporting structures, and bone Authors’ Contributions
surrounding the implant. Long implants were found to
decrease the stresses in abutments and minimize the stress All authors had the same contribution in data collection,
in the surrounding bone, especially the cancellous one [81]. annotation, and manuscript preparation in this study.
Similarly, the wide implants were found to decrease the
displacement of the prostheses, decrease the stresses in References
abutments, and minimize the stress in both cortical and can-
cellous bone [79]. [1] M. A. Mousa, E. Lynch, M. G. Sghaireen, A. M. Zwiri, and
O. A. Baraka, “Influence of time and different tooth widths
3.4.3. Implant Angulation. Different angulations of implants on masticatory efficiency and muscular activity in bilateral
were evaluated to estimate their influences on the develop- free-end saddles,” International Dental Journal, vol. 67, no. 1,
ment of stress in abutments and implants [81, 82]. The incli- pp. 29–37, 2017.
nations of the implant result in the improvement of stress in [2] M. A. Mousa, S. Patil, and E. Lynch, “Masticatory efficiency
abutment teeth but increase it on the bone surrounding the and muscular activity in removable partial dental prostheses
with different cusp angles,” The Journal of Prosthetic Dentistry,
implant to reach its maximum extent with angulation of 15°
vol. 117, no. 1, pp. 55–60, 2017.
[81] and 30° [82].
[3] B. Shrestha, B. B. Basnet, and G. Adhikari, “A questionnaire
Even though the FEA has been used in the estimation of
study on the impact on oral health-related quality of life by
stresses in RPDs for 20 years, still lack of FEA studies in the conventional rehabilitation of edentulous patient,” BDJ Open,
literature exists. The lack is mainly regarding the estimation vol. 6, no. 1, 2020.
of stresses in different designs of RPDs (especially the [4] S. D. Campbell, L. Cooper, H. Craddock et al., “Removable
bounded and anterior edentulism), different designs of man- partial dentures: the clinical need for innovation,” The Journal
dibular major connectors, use of short and narrow implants, of Prosthetic Dentistry, vol. 118, no. 3, pp. 273–280, 2017.
and use of different systems of attachments. [5] L. F. Cooper, “The current and future treatment of edentu-
lism,” Journal of Prosthodontics, vol. 18, no. 2, pp. 116–122,
4. Conclusion 2009.
[6] P. Preshaw, A. Walls, N. Jakubovics, P. Moynihan, N. Jepson,
Within the limitation of the present study, the following can and Z. Loewy, “Association of removable partial denture use
be concluded: with oral and systemic health,” Journal of Dentistry, vol. 39,
no. 11, pp. 711–719, 2011.
(1) Implants in implant-assisted RPDs receive the major- [7] E. P. Pellizzer, D. A. F. Almeida, R. M. Falcón-Antenucci,
ity of the dynamic load. The magnitude of the load D. M. I. K. Sánchez, P. R. J. Zuim, and F. R. Verri, “Prevalence
decreases with zero or minimal angulations of the of removable partial dentures users treated at the Aracatuba
implant, using long and wide implants, and when Dental School – UNESP,” Gerodontology, vol. 29, no. 2,
the implant is placed in the first molar area pp. 140–144, 2012.
[8] J. G. Steele and I. O’Sullivan, Executive summary: Adult Dental
(2) Stress in FES RPDs are concentrated in the shoulder Health Survey, NHS Health and Social Care Information Cen-
of the clasp, the minor connector of the mesial rest, tre, 2009, http://contentdigitalnhsuk/catalogue/PUB01086/
and the part of major connector next to the terminal adul-dent-heal-surv-summ-them-exec-2009-rep2pdf.
abutment [9] J. G. Steele, E. T. Treasure, I. O'Sullivan, J. Morris, and J. J.
Murray, “Adult Dental Health Survey 2009: transformations
(3) Clasps with flexible arms decrease the stress in abut- in British oral health 1968-2009,” British Dental Journal,
ment teeth, while the rigid major connector decreases vol. 213, no. 10, pp. 523–527, 2012.
the displacement and stresses in the residual ridge [10] C. D. Lynch, “Successful removable partial dentures,” Dental
Update, vol. 39, no. 2, pp. 118–126, 2012.
(4) The distal occlusal rest stiffens the framework and
[11] B. Benso, A. C. Kovalik, J. H. Jorge, and N. H. Campanha,
decreases the stress on the terminal abutment
“Failures in the rehabilitation treatment with removable par-
(5) Resilient attachments put less stress in abutments but tial dentures,” Acta Odontologica Scandinavica, vol. 71, no. 6,
increase the stress in the residual ridge, especially the pp. 1351–1355, 2013.
posterior part of the saddle [12] H. N. H. Alsharif, K. K. Ganji, M. K. Alam et al., “Periodontal
Clinical Parameters as a Predictor of Bite Force: A Cross- Sec-
(6) A lack of FEA studies covering many aspects of dif- tional Study,” BioMed Research International, vol. 2021, Arti-
ferent designs of RPDs exists cle ID 5582946, 8 pages, 2021.
14 BioMed Research International

[13] M. Bhathal, J. Batra, G. Attresh, and S. Sambyal, “A review on [28] R. D. Phoenix, D. R. Cagna, and C. F. DeFreest, Stewart's clin-
stresses-induced by removable partial dentures,” International ical removable partial prosthodontics, Quintessence Chicago,
Journal of Contemporary Dental & Medical Reviews, vol. 2015, 2003.
2015. [29] W. G. Assunção, V. A. Ricardo Barão, L. F. Tabata, É. A.
[14] L. Costa, C. do Nascimento, V. O. P. de Souza, and V. Pedrazzi, Gomes, J. A. Delben, and P. H. dos Santos, “Biomechanics
“Microbiological and clinical assessment of the abutment and studies in Dentistry,” Journal of Craniofacial Surgery, vol. 20,
non-abutment teeth of partial removable denture wearers,” no. 4, pp. 1173–1177, 2009.
Archives of Oral Biology, vol. 75, pp. 74–80, 2017. [30] A. A. Pesqueira, M. C. Goiato, H. G. Filho et al., “Use of stress
[15] R. C. S. Rodrigues, A. C. L. Faria, A. P. Macedo, M. G. C. de analysis methods to evaluate the biomechanics of oral rehabil-
Mattos, and R. F. Ribeiro, “Retention and stress distribution itation with implants,” Journal of Oral Implantology, vol. 40,
in distal extension removable partial dentures with and with- no. 2, pp. 217–228, 2014.
out implant association,” Journal of Prosthodontic Research, [31] K. Ramesh and S. Sasikumar, “Digital photoelasticity: recent
vol. 57, no. 1, pp. 24–29, 2013. developments and diverse applications,” Optics and Lasers in
[16] J. D. Jones, I. Turkyilmaz, and L. T. Garcia, “Removable partial Engineering, vol. 135, p. 106186, 2020.
dentures–treatment now and for the future,” Texas Dental [32] J. P. M. Tribst, A. M. O. Dal Piva, and A. L. S. Borges, “Biome-
Journal, vol. 127, p. 365, 2010. chanical tools to study dental implants: a literature review,”
[17] Y. Memari, A. Geramy, A. Fayaz, S. Rezvani Habib Abadi, and Brazilian Dental Science, vol. 19, no. 4, pp. 5–11, 2016.
Y. Mansouri, “Influence of implant position on stress distribu- [33] S. Trivedi, “Finite element analysis: a boon to dentistry,” Jour-
tion in implant-assisted distal extension removable partial nal of Oral Biology and Craniofacial Research, vol. 4, no. 3,
dentures: a 3D finite element analysis,” Journal of Dentistry, pp. 200–203, 2014.
vol. 11, no. 5, pp. 523–530, 2014. [34] W. M. S. al Qahtani and M. I. el-Anwar, “Advanced computa-
[18] R. G. Bassetti, M. A. Bassetti, and J. Kuttenberger, “Implant- tional methods in bio-mechanics,” Open Access Macedonian
assisted removable partial denture prostheses: a critical review Journal of Medical Sciences, vol. 6, no. 4, pp. 742–746, 2018.
of selected literature,” The International Journal of Prostho- [35] M. Mousa, N. Jamayet, E. Lynch, and A. Husein, “Biomechan-
dontics, vol. 31, no. 3, pp. 287–302, 2018. ical stress in removable complete dental prostheses: a narrative
[19] M. G. Sghaireen, K. C. Srivastava, D. Shrivastava et al., “A review of finite element studies,” Journal of International Oral
CBCT based three-dimensional assessment of mandibular Health, vol. 12, pp. 413–419, 2020.
posterior region for evaluating the possibility of bypassing [36] H. Suenaga, J. N. Chen, W. Li et al., “Validate mandible finite
the inferior alveolar nerve while placing dental implants,” element model under removable partial denture (RPD) with
Diagnostics, vol. 10, no. 6, p. 406, 2020. In Vivo pressure measurement,” Applied Mechanics and Mate-
[20] M. Sato, Y. Suzuki, D. Kurihara, H. Shimpo, and C. Ohkubo, rials, vol. 553, pp. 322–326, 2014.
“Effect of implant support on mandibular distal extension [37] M. A. Mousa, J. Y. Abdullah, N. B. Jamayet, M. K. Alam, and
removable partial dentures: relationship between denture sup- A. Husein, “Biomechanical stress in obturator prostheses: a
porting area and stress distribution,” Journal of Prosthodontic systematic review of finite element studies,” BioMed Research
Research, vol. 57, no. 2, pp. 109–112, 2013. International, vol. 2021, Article ID 6419774, 12 pages, 2021.
[21] J. W. Eom, Y. J. Lim, M. J. Kim, and H. B. Kwon, “Three- [38] S. Mohammed and H. Desai, “Basic concepts of finite element
dimensional finite element analysis of implant-assisted remov- analysis and its applications in dentistry: an overview,” Journal
able partial dentures,” The Journal of Prosthetic Dentistry, of Oral Hygiene & Health, vol. 2, no. 5, 2014.
vol. 117, no. 6, pp. 735–742, 2017.
[39] T. H. Farook, M. A. Mousa, and N. B. Jamayet, “Method to
[22] D. M. Daubert, B. F. Weinstein, S. Bordin, B. G. Leroux, and control tongue position and open source image segmentation
T. F. Flemmig, “Prevalence and predictive factors for peri- for cone- beam computed tomography of patients with large
implant disease and implant failure: a cross-sectional analysis,” palatal defect to facilitate digital obturator design,” Journal of
Journal of Periodontology, vol. 86, no. 3, pp. 337–347, 2015. Oral and Maxillofacial Surgery, Medicine, and Pathology,
[23] S. Vervaeke, B. Collaert, J. Cosyn, E. Deschepper, and H. De vol. 32, no. 1, pp. 61–64, 2020.
Bruyn, “A multifactorial analysis to identify predictors of [40] R. Kanbara, Y. Nakamura, K. T. Ochiai, T. Kawai, and
implant failure and peri-implant bone loss,” Clinical Implant Y. Tanaka, “Three-dimensional finite element stress analysis:
Dentistry and Related Research, vol. 17, pp. e298–e307, 2015. the technique and methodology of non-linear property simu-
[24] S. Raikar, P. Talukdar, S. Kumari, S. K. Panda, V. M. Oommen, lation and soft tissue loading behavior for different partial den-
and A. Prasad, “Factors affecting the survival rate of dental ture designs,” Dental Materials Journal, vol. 31, no. 2, pp. 297–
implants: a retrospective study,” Journal of International Soci- 308, 2012.
ety of Preventive & Community Dentistry, vol. 7, no. 6, [41] A. A. Mahmoud, N. Wakabayashi, and H. Takahashi, “Predic-
pp. 351–355, 2017. tion of permanent deformation in cast clasps for denture pros-
[25] S. Cakarer, F. Selvi, T. Can et al., “Investigation of the risk fac- theses using a validated nonlinear finite element model,”
tors associated with the survival rate of dental implants,” Dental Materials, vol. 23, no. 3, pp. 317–324, 2007.
Implant Dentistry, vol. 23, no. 3, pp. 328–333, 2014. [42] T. Ohashi, Y. Sato, T. Sasaki, H. Itoh, and M. Sato, “Prediction
[26] O. Boboeva, T. G. Kwon, J. W. Kim, S. T. Lee, and S. Y. Choi, of stress distribution in mandibular bone treated with distal-
“Comparing factors affecting dental-implant loss between age extension partial denture using finite element analysis,” Jour-
groups: a retrospective cohort study,” Clinical Implant Den- nal of the Japanese Society for Experimental Mechanics, vol. 6,
tistry and Related Research, vol. 23, no. 2, pp. 208–215, 2021. pp. 269–274, 2006.
[27] A. B. Carr and D. T. Brown, McCracken's Removable Partial [43] O. Andrei, C. Dăguci, M. Ţierean, T. Farcaşiu, C. Farcaşiu, and
Prosthodontics-e-Book, Elsevier Health Sciences, 2010. L. Tănăsescu, “Compared stress levels of removable partial
BioMed Research International 15

dentures with attachments with and without distal three-dimensional finite element analysis,” Journal of Clinical
implants—a finite element analysis,” in 2015 E-Health and and Diagnostic Research: JCDR, vol. 10, p. ZC13, 2016.
Bioengineering Conference (EHB), Iasi, Romania, 2015. [58] Y. Nakamura, R. Kanbara, K. T. Ochiai, and Y. Tanaka, “A
[44] P. Oyar, C. Soyarslan, G. Can, and E. Demirci, “Finite element finite element evaluation of mechanical function for 3 distal
analysis of stress distribution on modified retentive tips of bar extension partial dental prosthesis designs with a 3-
clasp,” Computer Methods in Biomechanics and Biomedical dimensional nonlinear method for modeling soft tissue,” The
Engineering, vol. 15, no. 6, pp. 609–613, 2012. Journal of Prosthetic Dentistry, vol. 112, no. 4, pp. 972–980,
[45] L. Sandu, N. Faur, and C. Bortun, “Finite element analysis of 2014.
stress distribution in the cast clasps, direct retainers of a [59] K. Aoda, I. Shimamura, Y. Tahara, and K. Sakurai, “Retainer
removable partial denture,” Timisoara Medical Journal, design for unilateral extension base partial removable dental
vol. 53, pp. 264–266, 2003. prosthesis by three-dimensional finite element analysis,” Jour-
[46] L. Sandu, N. Faur, and C. Bortun, “Finite element stress anal- nal of Prosthodontic Research, vol. 54, no. 2, pp. 84–91, 2010.
ysis and fatigue behavior of cast circumferential clasps,” The [60] R. Richert, A. A. Alsheghri, O. Alageel et al., “Analytical model
Journal of Prosthetic Dentistry, vol. 97, no. 1, pp. 39–44, 2007. of I-bar clasps for removable partial dentures,” Dental Mate-
[47] F. R. Verri, E. P. Pellizzer, J. A. Pereira, P. R. J. Zuim, and J. F. rials, vol. 37, no. 6, pp. 1066–1072, 2021.
Santiago Júnior, “Evaluation of bone insertion level of support [61] Y. Sato, K. Tsuga, Y. Abe, S. Asahara, and Y. Akagawa, “Finite
teeth in class I mandibular removable partial denture associ- element analysis on preferable I-bar clasp shape,” Journal of
ated with an osseointegrated implant: a study using finite ele- Oral Rehabilitation, vol. 28, no. 5, pp. 413–417, 2001.
ment analysis,” Implant Dentistry, vol. 20, no. 3, pp. 192– [62] L. Sandu, F. Topală, and S. Porojan, “Stress distribution in
201, 2011. retentive arms of combination clasps used on premolars,”
[48] C. M. Rocha and S. M. Arndt, “Bone remodeling response dur- Journal of Applied Biomaterials and Biomechanics, vol. 8,
ing mastication on free-end removable prosthesis–a 3D finite no. 2, pp. 76–81, 2010.
element analysis,” in SIMULIA Customer Conference, 2010. [63] T.-Y. Peng, Y. Ogawa, H. Akebono, S. Iwaguro, A. Sugeta, and
[49] R. Shahmiri, J. M. Aarts, V. Bennani, R. Das, and M. V. Swain, S. Shimoe, “Finite-element analysis and optimization of the
“Strain distribution in a Kennedy class I implant assisted mechanical properties of polyetheretherketone (PEEK) clasps
removable partial denture under various loading conditions,” for removable partial dentures,” Journal of Prosthodontic
International Journal of Dentistry, vol. 2013, 11 pages, 2013. Research, vol. 64, no. 3, pp. 250–256, 2020.
[50] Y. Liu, Y.-N. Zhang, K. Sasaki, and X.-D. Chen, “Influence of loca- [64] T. Yamazaki, N. Murakami, S. Suzuki et al., “Influence of
tion of osseointegrated implant on stress distribution in implant block-out on retentive force of thermoplastic resin clasps: an
supported longitudinal removable partial dentures: 3- in vitro experimental and finite element analysis,” Journal of
dimensional finite element analysis,” International Journal of Clin- Prosthodontic Research, vol. 63, no. 3, pp. 303–308, 2019.
ical and Experimental Medicine, vol. 12, pp. 10399–10410, 2019. [65] M. Bahrami, B. Shakeri, and M. Memarian, “Investigating the
[51] V. Patrnogić, A. Todorović, M. Šćepanović, K. Radović, stress distribution applied to edentulous ridge from polyamide
J. Vesnić, and A. Grbović, “Free-end saddle length influence and cobalt-chrome removable-partial-dentures using three-
on stress level in unilateral complex partial denture abutment dimensional finite-element-analysis,” Journal of Dentomaxil-
teeth and retention elements,” Vojnosanitetski Pregled, lofacial, vol. 9, pp. 1–8, 2020.
vol. 70, no. 11, pp. 1015–1022, 2013. [66] X. Chen, B. Mao, Z. Zhu et al., “A three-dimensional finite ele-
[52] R. Shahmiri and R. Das, “Finite element analysis of implant- ment analysis of mechanical function for 4 removable partial
assisted removable partial denture attachment with different denture designs with 3 framework materials: CoCr, Ti-6Al-
matrix designs during bilateral loading,” The International 4V alloy and PEEK,” Scientific Reports, vol. 9, pp. 1–10, 2019.
Journal of Oral & Maxillofacial Implants, vol. 31, no. 5, [67] H.-y. Wang, Z. Y-m, D. Yao, and C. J-h, “Effects of rigid and
pp. e116–e127, 2016. nonrigid extracoronal attachments on supporting tissues in
[53] R. Shahmiri and R. Das, “Finite element analysis of implant- extension base partial removable dental prostheses: a nonlin-
assisted removable partial dentures: framework design consid- ear finite element study,” The Journal of Prosthetic Dentistry,
erations,” The Journal of Prosthetic Dentistry, vol. 118, no. 2, vol. 105, no. 5, pp. 338–346, 2011.
pp. 177–186, 2017. [68] R. Shahmiri, R. Das, J. M. Aarts, and V. Bennani, “Finite ele-
[54] T. Nogawa, M. Saito, N. Murashima, Y. Takayama, and ment analysis of an implant-assisted removable partial denture
A. Yokoyama, “Influence of rigidity of retainers on dynamic during bilateral loading: occlusal rests position,” The Journal of
behavior of implant-supported removable partial dentures,” Prosthetic Dentistry, vol. 112, no. 5, pp. 1126–1133, 2014.
International Journal of Implant Dentistry, vol. 6, no. 1, [69] N. Bhojaraju, J. Srilakshmi, and G. Vishwanath, “Study of
pp. 60–69, 2020. deflections in maxillary major connectors: a finite element
[55] J. P. M. Tribst, A. M. de Oliveira Dal Piva, A. L. S. Borges et al., analysis,” The Journal of Indian Prosthodontic Society,
“Effect of different materials and undercut on the removal vol. 14, no. 1, pp. 50–60, 2014.
force and stress distribution in circumferential clasps during [70] M. Eto, N. Wakabayashi, and T. Ohyama, “Finite element
direct retainer action in removable partial dentures,” Dental analysis of deflections in major connectors for maxillary
Materials, vol. 36, no. 2, pp. 179–186, 2020. RPDs,” The International Journal of Prosthodontics, vol. 15,
[56] H. Judy, “Studying the effect of circumferential clasp arm no. 5, pp. 433–438, 2002.
design on stress distribution using three-dimensional finite [71] H. Ramakrishnan and R. G. Singh, “Three-dimensional finite
element analysis,” MDJ, vol. 6, pp. 55–60, 2009. element analysis of the stress distribution pattern in the design
[57] J. C. Reddy, S. B. Chintapatla, N. K. Srikakula et al., “Compar- modifications of U-shaped palatal major connector,” Indian
ison of retention of clasps made of different materials using Journal of Dental Research, vol. 21, no. 4, pp. 506–511, 2010.
16 BioMed Research International

[72] R. Hallikerimath, H. D. Mallikarjun, V. Patil, and V. S. Kumar,

“Evaluation of deflection in single palatal strap major connec-
tor as influenced by different shapes of palatal vault: a three-
dimensional finite element study,” Journal of International
Oral Health, vol. 7, p. 53, 2015.
[73] T. Takanashi, I. Shimamura, and K. Sakurai, “Influence of
width and depth of palatal vault on rigidity of palatal strap: a
finite element study,” Journal of Prosthodontic Research,
vol. 53, no. 2, pp. 95–100, 2009.
[74] M. T. Rodrigues, B. H. Harshitha Gowda, and B. Alva, “Stress
distribution in tooth supported removable partial denture fab-
ricated using two different materials: a 3-dimensional finite
element analysis,” Materials Today: Proceedings, 2021.
[75] H. Sasaki, Y. Takayama, M. Saito, K. Mizuno, M. Goto, and
A. Yokoyama, “Effects of splinting on displacement of maxil-
lary canines as abutments of removable partial dentures: a
finite element analysis,” Prosthodontic Research & Practice,
vol. 6, no. 3, pp. 159–165, 2007.
[76] A. Messias, P. Nicolau, F. Guerra, A. Amaro, L. Roseiro, and
M. A. Neto, “Implant-assisted removable partial dentures in
mandibular Kennedy class I patients: the impact of implant
positioning,” in Mediterranean Conference on Medical and
Biological Engineering and Computing, Springer, 2019.
[77] O. Ortiz-Puigpelat, A. Lazaro-Abdulkarim, J. M. de Medrano-
Rene, J. Gargallo-Albiol, J. Cabratosa-Termes, and
F. Hernandez-Alfaro, “Influence of implant position in
implant-assisted removable partial denture: a three-
dimensional finite element analysis,” Journal of Prosthodon-
tics, vol. 28, no. 2, pp. e675–e681, 2019.
[78] T. Ohyama, S. Nakabayashi, H. Yasuda, T. Kase, and
S. Namaki, “Mechanical analysis of the effects of implant posi-
tion and abutment height on implant-assisted removable par-
tial dentures,” Journal of Prosthodontic Research, vol. 64, no. 3,
pp. 340–345, 2020.
[79] A. El-Okel and A. O. Elnady, “Influence of location and dime-
ter of osseointegrated implants associated with distal extension
removable partial dentures: (a finite element analysis),” Egypt
Dental Journal, vol. 59, pp. 1–10, 2013.
[80] L. D. Cunha, E. P. Pellizzer, F. R. Verri, and J. A. Pereira, “Eval-
uation of the influence of location of osseointegrated implants
associated with mandibular removable partial dentures,”
Implant Dentistry, vol. 17, no. 3, pp. 278–287, 2008.
[81] A. Fayaz, A. Geramy, Y. Memari, and Z. Rahmani, “Effects of
length and inclination of implants on terminal abutment teeth
and implants in mandibular CL1 removable partial denture
assessed by three-dimensional finite element analysis,” Journal
of Dentistry, vol. 12, pp. 739–746, 2015.
[82] C. M. de Freitas Santos, E. P. Pellizzer, F. R. Verri, S. L. de
Moraes, and R. M. Falcon-Antenucci, “Influence of implant
inclination associated with mandibular class I removable par-
tial denture,” The Journal of Craniofacial Surgery, vol. 22,
no. 2, pp. 663–668, 2011.