Abstract

The aim of this study was to evaluate the stress distribution of platform switching implants using a photoelastic method. Three models were constructed of the photoelastic resin PL-2, with a single implant and a screw-retained implant-supported prosthesis. These models were Model A, platform 5.0 mm/abutment 4.1 mm; Model B, platform 4.1 mm/abutment 4.1 mm; and Model C, platform 5.00 mm/abutment 5.00 mm. Axial and oblique (45°) loads of 100 N were applied using a Universal Testing Machine (EMIC DL 3000). Images were photographed with a digital camera and visualized with software (AdobePhotoshop) to facilitate the qualitative analysis. The highest stress concentrations were observed at the apical third of the 3 models. With the oblique load, the highest stress concentrations were located at the implant apex, opposite the load application. Stress concentrations decreased in the cervical region of Model A (platform switching), and Models A (platform switching) and C (conventional/wide-diameter) displayed similar stress magnitudes. Finally, Model B (conventional/regular diameter) displayed the highest stress concentrations of the models tested.

Introduction

The final goal of oral rehabilitation with osseointegrated implants is to create an optimal prosthetic restoration surrounded by stable bone, with a natural gingival architecture, ensuring functional and esthetic harmony. The lack of postoperative bone resorption around the implant collar constitutes a vital factor in stabilizing the papillae and obtaining a harmonious dental neck line in relation to neighboring teeth.15 

Bone resorption around the implant neck is frequently observed after loading and appears to depend on both biological and mechanical factors, such as biological width, bacterial microleakage, location of the inflammatory conjunctival tissue area,610 cervical area stress concentration, location of the implant/abutment joint,4 and micromovement.4,11 Some clinical, histological, and retrospective studies2,4 have shown that crestal bone loss around dental implants can be prevented by applying platform switching. In a standard protocol, implants are rehabilitated with abutments of the same diameter. The platform switching technique uses prosthetic components that are undersized relative to the diameter of the implant platform.2,9,12 

Mechanical and biological principles of platform switching have been theorized for how bone loss can be minimized.2,12 First, with the increased surface area created by the exposed implant seating surface, the amount of crestal bone resorption necessary to expose a minimum amount of implant surface to which the soft tissue can attach is reduced.2,9,12 Second, and perhaps more important, by repositioning the implant-abutment junction (IAJ) inward and away from the outer edge of the implant and adjacent bone, the overall effect of the abutment inflammatory cell infiltrate (ICT) on surrounding tissue may be reduced, thus decreasing the resorptive effect of the abutment ICT on crestal bone. As a consequence, the reduced exposure and confinement of the platform-switched abutment ICT may result in a reduced inflammatory effect within surrounding soft tissue and crestal bone.6,8,13 

The biological benefits and clinical efficacy of the platform switching technique have been demonstrated by numerous studies.4,9,10,1316 However, the biomechanics of this technique have been researched only minimally.17,18 Evaluation of the mechanical factors and their influence on bony tissue preservation is of great importance. One method used for such study is photoelasticity, which allows prediction of the mechanical response of a photoelastic model when load is applied.19 Thus, the aim of this study was to evaluate the stress distribution of platform switching implants using a photoelastic method.

Materials and Methods

Using a wax block simulating a mandibular bone portion, a mold was constructed using duplication silicone (Sapeca, Bauru, São Paulo, Brazil). This matrix was then poured with dental stone type IV (Durone, Dentsply, Petrópolis, Rio de Janeiro, Brazil). An analogue implant (Conexão Sistemas de Prótese Ltda, Arujá, São Paulo, Brazil) was inserted into the dental stone blocks with a dental surveyor, corrected the seating of the implant (Figure 1) (Conexão Sistemas de Prótese Ltda), and was verified; then another mold was obtained with the implants correctly positioned. The photoelastic resin (PL-2, Vishay, Micro-Measurements Group Inc, Raleigh, NC) was manipulated according to the manufacturer's instructions. The mold was poured with resin and placed under a pressure of 40 lbf/in2 (to remove the internal bubbles), thereby producing 3 photoelastic models (Table).

Figure 1–3

Figure 1,. Dental stone models with implant analogues and photoelastic models with implants. Figure 2,. Dental stone models with single crowns (NiCr). Figure 3 . Universal testing machine (EMIC DL-3000).

Figure 1–3

Figure 1,. Dental stone models with implant analogues and photoelastic models with implants. Figure 2,. Dental stone models with single crowns (NiCr). Figure 3 . Universal testing machine (EMIC DL-3000).

Table

Models used in the study

Models used in the study
Models used in the study

Three screw-retained implant-supported prostheses (UCLA abutment) were constructed with a nickel/chrome (NiCr) alloy (Figure 2). The crowns were screwed onto the implant of the photoelastic model with a torque of 20 N. Each model was placed in a circular polariscope (Figure 3). Axial (0°) and oblique (45°) loads of 100 N were applied at fixed points on the occlusal surface of all crowns with a Universal Testing Machine (EMIC-DL 3000, São José dos Pinhais, Paraná, Brazil), which was programmed to transmit the load for a period of 10 seconds.

The stress patterns (photoelastic fringes) resulting from force application in the photoelastic models were photographed by a digital camera (Nikon D80, Nikon Corporation, Tokyo, Japan), and subsequently transferred to a computer graphics software (AdobePhotoshop, Adobe Systems, San Jose, Calif) for visualization.20 For qualitative analysis, the area around each implant was arbitrarily divided into 3 zones, corresponding to the coronal, middle, and apical third of each implant.

Photographic records were analyzed by 2 investigators, who observed and compared stress patterns to determine the relative stress magnitudes and locations. Qualitative analysis followed the method outlined by Caputo and Standlee,19 where the number and proximity of the fringes to each other was proportional to the stress magnitude and concentration, respectively.

Results

Before loading, all specimens were free from any stress pattern, such that all stress patterns observed were the direct result of the occlusal load applied to the implants.

Axial load

Figures 4, 5, and 6 show that the stress distribution patterns were similar for all models, with stress concentration at the middle to apical third, and the highest stress concentrations were at the apical level. In Models B and C, stress was concentrated from the middle third to the apical portion of the implant, but in Model A (Figure 4), the stress was more centralized at the apical area. Stress concentration at the coronal third was absent in Model A, in contrast with Models B and C (Figures 5 and 6), where stress was concentrated at the first threads of the implants.

Figure 4–9

Figure 4,. Axial load on Model A—platform switching. Figure 5,. Axial load on Model B—conventional/regular diameter. Figure 6,. Axial load on Model C—conventional/wide diameter. Figure 7,. Oblique load on Model A—platform switching. Figure 8,. Oblique load on Model B—conventional/regular diameter. Figure 9 . Oblique load on Model C—conventional/wide diameter.

Figure 4–9

Figure 4,. Axial load on Model A—platform switching. Figure 5,. Axial load on Model B—conventional/regular diameter. Figure 6,. Axial load on Model C—conventional/wide diameter. Figure 7,. Oblique load on Model A—platform switching. Figure 8,. Oblique load on Model B—conventional/regular diameter. Figure 9 . Oblique load on Model C—conventional/wide diameter.

We observed a larger number of fringes in Model B compared with the other models, and the stress concentration was higher at the apical level. Models A and C had the same number of fringes. However, the fringes were more broadly distributed in Model C (Figure 6), indicating a lower stress concentration compared with Model A. The number of photoelastic fringes revealed stress magnitudes of Model B > Model A > Model C.

Oblique load

Analysis of the models subjected to oblique loads (Figures 7, 8, and 9) revealed that the stress concentration patterns were similar for all 3 models. Stress was observed in the cervical and middle thirds (distal region) and in the apical portion of the implants. The highest stress concentrations were located at the apex of the implant on the contralateral side of load application in all 3 models.

In Models A and B (Figures 7 and 8), the photoelastic fringes were in close proximity, corresponding to higher stress concentration, and were located at the apex of the implant in the mesial region. In Model C (Figure 9), the stress concentration was lower. Model B exhibited the greatest number of fringes, and the number of fringes was similar between Models A and C. The order of stress magnitude in the models was Model B > Model A > Model C.

The pattern of the fringes when models were under oblique load application was different from that under axial loads. In oblique loads, the number of fringes increased, and they were in much closer proximity, corresponding to higher stress concentration.

Discussion

Analysis when the axial load was applied showed that Model A (platform switching) presented a stress distribution pattern that differed from that of the other models, with more centralization of stresses at the implant apex. This result can be explained by the load concentration at the IAJ,14 which purportedly transfers the stress to a more centralized position.12,2 This theory of centralization was verified by Maeda et al17 through finite element analysis, which revealed that stress concentrations on a platform switching implant are located at the center of the implant-abutment joint (at the level of the implant screw).

Consistent with previous studies,2,4,9,10,12 the stress concentrations in Model A decreased at the cervical region. This altered the horizontal position of the microgap in the IAJ, resulting in a reduced horizontal component of bone loss after abutment connection. From a biological standpoint, this change decreases bone loss in the cervical area. Similar findings have been observed in histological, histomorphometric,1,13 clinical,2,4,9,10 and retrospective studies.14,16,21 Finite element analyses17,18 have also verified that the stress concentration is lower or absent at the cervical region of platform switching implants compared with standard implants.

Compared with Model C, where the stress magnitude was lower and more dissipated, Model B displayed higher stress concentrations. This difference in stress concentration was due to the increased surface of the wide-diameter implants. Ding et al21 found that use of wider implants increases the area of the bone-implant contact surface, allowing engagement of a maximal amount of bone and theoretical improvement of stress distribution in the surrounding bone. Several additional studies using various methods to compare regular and wide-diameter implants found better biomechanical behavior among the wide-diameter implants.2123 

All models showed higher magnitudes and stress concentrations when an oblique load was applied. An oblique force is less favorable than an axial load for stress distribution along the implant. Mathematical analyses24,25 have shown that oblique force application on the crown surface produces lateral force components, creating moments on the implant and thus producing higher stress concentrations.

Comparison of Models A and C revealed decreasing stress concentrations at the cervical and middle thirds of Model A. This observation also was noted by Liu et al18 in a study using 3-dimensional finite element analysis to compare the platform switching technique vs a standard protocol. Investigators found that the platform switching design improved stress distribution and decreased maximum stresses in peri-implant bone around the implant cervix.

The platform switching technique is a simple and viable technique14,9,1316 that does not increase implant treatment costs. This technique is an effective way to control circumferential bone loss around dental implants, although it has been tested by few biomechanical studies. The present study verified the favorable biomechanical behavior of the platform switching technique and found no significant differences between wide-diameter and platform switching implants with respect to the magnitude of stress.

Conclusions

  1. Stress concentrations decreased in the cervical region of the platform switching implant.

  2. Models A (platform switching) and C (conventional/wide-diameter) displayed similar stress magnitudes.

  3. Model B (conventional/regular diameter) displayed the highest magnitude and stress concentration.

Abbreviations

     
  • IAJ

    implant-abutment junction

  •  
  • ICT

    inflammatory cell infiltrate

References

References
1
Hermann
,
F.
,
H.
Lerner
, and
A.
Palti
.
Factors influencing the preservation of the periimplant marginal bone.
Implant Dent
2007
.
16
:
165
175
.
2
Gardner
,
D. M.
Platform switching as a means to achieving implant esthetics.
N Y State Dent J
2005
.
71
:
34
37
.
3
Hermann
,
J. S.
,
D.
Buser
,
R. K.
Schenk
, et al
.
Biologic width around titanium implants: a physiologically formed and stable dimension over time.
Clin Oral Implants Res
2000
.
11
:
1
11
.
4
Calvo Guirado
,
J. L.
,
M. R.
Saez Yuguero
,
G.
Pardo Zamora
, et al
.
Immediate provisionalization on a new implant design for esthetic restoration and preserving crestal bone.
Implant Dent
2007
.
16
:
155
164
.
5
Priest
,
G. F.
The esthetic challenge of adjacent implants.
J Oral Maxillofac Surg
2007
.
65
(
7 suppl 1
):
2
12
.
6
Quirynen
,
M.
and
D.
van Steenberghe
.
Bacterial colonization of internal part of two-stage implants: an vivo study.
Clin Oral Implants Res
1993
.
4
:
158
161
.
7
Ericsson
,
I.
,
L. G.
Persson
,
T.
Berglundh
, et al
.
Different types of inflammatory reactions in peri-implant soft tissues.
J Clin Periodontol
1995
.
22
:
255
261
.
8
King
,
G. N.
,
J. S.
Hermann
,
J. D.
Schoolfield
, et al
.
Influence of the size of the microgap on crestal bone levels in non-submerged dental implants: a radiographic study in the canine mandible.
J Periodontol
2002
.
73
:
1111
1117
.
9
Chiche
,
F. A.
The concept of platform-switching.
J Parodontologie & d'Implantologie Orale (JPIO)
2005
.
1
:
30
36
.
10
Degidi
,
M.
,
G.
Iezzi
,
A.
Scarano
, et al
.
Immediately loaded titanium implant with a tissue-stabilizing/maintaining design (‘beyond platform switch’) retrieved from man after 4 weeks: a histological and histomorphometrical evaluation: a case report.
Clin Oral Implants Res
2008
.
19
:
276
282
.
11
Duyck
,
J.
,
H. J.
Rønold
,
H.
Van Oosterwyck
, et al
.
The influence of static and dynamic loading on marginal bone reactions around osseointegrated implants: an animal experimental study.
Clin Oral Implants Res
2001
.
12
:
207
218
.
12
Lazzara
,
R. J.
and
S. S.
Porter
.
Platform switching: a new concept in implant dentistry for controlling postrestorative crestal bone levels.
Int J Periodontics Restorative Dent
2006
.
26
:
9
17
.
13
Becker
,
J.
,
D.
Ferrari
,
M.
Herten
, et al
.
Influence of platform switching on crestal bone changes at non-submerged titanium implants: a histomorphometrical study in dogs.
J Clin Periodontol
2007
.
34
:
1089
1096
.
14
Hürzeler
,
M.
,
S.
Fickl
,
O.
Zuhr
, et al
.
Peri-implant bone level around implants with platform-switched abutments: preliminary data from a prospective study.
J Oral Maxillofac Surg
2007
.
65
(
7 suppl 1
):
33
39
.
15
Baumgarten
,
H.
,
R.
Cocchetto
,
T.
Testori
, et al
.
A new implant design for crestal bone preservation: initial observations and case report.
Pract Periodontics Aesthet Dent
2005
.
17
:
735
740
.
16
Calvo Guirado
,
J. L.
,
A. J.
Ortiz Ruiz
,
G.
Gómez Moreno
, et al
.
Immediate loading and immediate restoration in 105 expanded-platform implants via the Diem System after a 16-month follow-up period.
Med Oral Patol Oral Cir Bucal
2008
.
13
:
E576
E581
.
17
Maeda
,
Y.
,
J.
Miura
,
I.
Taki
, et al
.
Biomechanical analysis on platform switching: is there any biomechanical rationale?
Clin Oral Implants Res
2007
.
18
:
581
584
.
18
Liu
,
X. J.
,
Z. Y.
Li
, and
H. B.
Xia
.
Influence of implant-abutment connection mode on stress distribution in peri-implant bone.
Zhonghua Kou Qiang Yi Xue Za Zhi
2008
.
43
:
50
53
.
19
Caputo
,
A. A.
and
J. P.
Standlee
.
Biomechanics in Clinical Dentistry
.
Chicago, Ill
Quintessence Publishing Company
.
1987
.
20
da Silva
,
E. F.
,
E. P.
Pellizzer
,
J. V.
Quinelli Mazaro
, et al
.
Influence of the connector and implant design on the implant-tooth-connected prostheses.
Clin Implant Dent Relat Res
2010
.
12
:
254
262
.
21
Ding
,
X.
,
X. H.
Zhu
,
S. H.
Liao
, et al
.
Implant–bone interface stress distribution in immediately loaded implants of different diameters: a three-dimensional finite element analysis.
J Prosthodont
2009
.
18
:
393
402
.
22
Himmlová
,
L.
,
T.
Dostálová
,
A.
Kácovský
, et al
.
Influence of implant length and diameter on stress distribution: a finite element analysis.
J Prosthet Dent
2004
.
91
:
20
25
.
23
Holmgren
,
E. P.
,
R. J.
Seckinger
,
L. M.
Kilgren
, et al
.
Evaluating parameters of osseointegrated dental implants using finite analysis—a two-dimensional comparative study examining the effects of implant diameter, implant shape, and load direction.
J Oral Implantol
1998
.
24
:
80
88
.
24
Rangert
,
B.
,
T.
Jemt
, and
L.
Jörneus
.
Forces and moments on Branemark Implants.
Int J Oral Maxillofac Implants
1989
.
4
:
241
247
.
25
Weinberg
,
L. A.
Atlas of Tooth- and Implant-Supported Prosthodontics
.
Chicago, Ill
Quintessence Publishing Company
.
2003
.