Effect of Anti-rotation Devices on Biomechanical Behaviour of Teeth Restored With Cast Post-And-cores.

Effect of anti-rotation devices on biomechanicalbehaviour of teeth restored with cast post-and-cores

L. H. A. Raposo1, G. R. Silva1, P. C. F. Santos-Filho1, P. V. Soares1, P. B. F. Soares1, P. C.Simamoto-Junior2, A. J. Fernandes-Neto3 & C. J. Soares1

1Department of Operative Dentistry and Dental Materials, Biomechanics Group, Federal University of Uberlandia, Minas Gerais,

Brazil; 2Healthy Technical School, Federal University of Uberlandia, Minas Gerais, Brazil; and 3Department of Fixed Prosthodontics

and Dental Materials, Biomechanics Group, School of Dentistry, Federal University of Uberlandia, Minas Gerais, Brazil

Abstract

Raposo LHA, Silva GR, Santos-Filho PCF, Soares PV,

Soares PBF, Simamoto-Junior PC, Fernandes-Neto AJ,

Soares CJ. Effect of anti-rotation devices on biomechanical

behaviour of teeth restored with cast post-and-cores. Interna-

tional Endodontic Journal, 43, 681691, 2010.

Aim To test the hypothesis that the presence of an

anti-rotation device (ARD) and its location can influ-

ence the biomechanical behaviour of root filled teeth

restored with cast post-and-cores and metallic crowns.

Methodology Fifth two bovine incisor roots were

selected and divided into four groups (n = 13): Nd-

without ARD; Bd- buccal ARD; Ld- lingual ARD; BLd-

buccal and lingual ARD. The specimens were restored

with cast post-and-cores and metallic crowns. After a

fatigue process (3 105 50 N), three strain gaugeswere attached on the buccal, lingual and proximal

surfaces and the samples of each group (n = 3) were

submitted to a 0100 N load. Fracture resistance was

assessed in a mechanical testing machine (n = 10).

Strain values and fracture resistance data were anal-

ysed by one-way anova and Tukey Honestly Signifi-

cant Difference (HSD) test (a = 0.05). The failure modewas then evaluated under an optical stereomicroscope.

Bidimensional models of each group were generated for

finite element analysis (FEA) and analysed using the

von Mises criteria.

Results No significant difference in fracture resis-

tance values and fracture modes occurred between the

four groups. The BLd group had higher stress concen-

trations in the buccal dentine and higher strain values

on the proximal surfaces.

Conclusions The anti-rotation devices did not influ-

ence significantly the fracture resistance and fracture

mode. However, the stressstrain values were increased

when the anti-rotation device was prepared on the

buccal and lingual faces concomitantly.

Keywords: anti-rotation device, cast post-and-core,

finite element analysis, fracture mode, fracture resis-

tance, strain gauge test.

Received 20 October 2009; accepted 2 April 2010

Introduction

With the development of endodontic therapy, recovery

and maintenance of severely damaged teeth became

possible. However, there can be a major challenge in

restoring these teeth. Structural loss means that post-

and-cores are often required to maintain the restora-

tion in place (Papa et al. 1993, Morgano & Brackett

1999, Joshi et al. 2001). Root canal preparation results

in dentine removal and increases the risk of fracture

when compared to intact teeth, because the resistance

of root filled teeth is directly related to the amount and

quality of the remaining tooth tissue (Reeh et al. 1989,

Morgano & Brackett 1999, Heydecke et al. 2001). More-

over, the posts do not increase the tooth-restoration

Correspondence: Carlos Jose Soares, Faculdade de Odontologia

Universidade Federal de Uberlandia, Area de Dentstica e

Materiais Odontologicos, Av. Para, no 1720, Campus Umu-

arama, Bloco 2B, Sala 2B-24, CEP: 38405-902, Uberlandia,

Minas Gerais, Brazil (Tel.: +55 34 32182255; fax: +55 34

32182279; e-mail: [email protected]).

doi:10.1111/j.1365-2591.2010.01739.x

2010 International Endodontic Journal International Endodontic Journal, 43, 681691, 2010 681

complex resistance (Sorensen & Martinoff 1984,

Trope et al. 1985, Assif & Gorfil 1994), providing

enough retention and stability only for the prosthesis or

coronal restorative material (Christensen 1996). In

addition, the geometry, extension and mechanical

properties of the post (Caputo & Hokama 1984, Sirimai

et al. 1999, Fokkinga et al. 2006) could have an effect

on dentine stress distribution, reducing the risk of root

fracture.

Posts with mechanical properties similar to dentine,

which may distribute homogenously the stresses

induced by occlusal forces, are favourable in reducing

the likelihood of tooth fracture (Caputo & Hokama

1987, Boschian Pest et al. 2002). However, in

extensive restorative procedures, materials that offer

longevity and avoid subsequent interventions are

commonly chosen by the clinicians. Cast post-and-

cores have been used routinely to restore root filled

teeth with moderate to severe destruction, especially

in single rooted teeth (Ross et al. 1991, Morgano &

Brackett 1999). On the other hand, some forces could

reach the tooth-restoration complex, generating stress

concentrations in this system when the tooth is

under function (Kumagai et al. 1999, Sirimai et al.

1999, Akkayan & Gulmez 2002, Torbjorner &

Fransson 2004, Genovese et al. 2005). These stresses

could be responsible for fractures and subsequent loss

of the tooth (Assif & Gorfil 1994, Pegoretti et al.

2002).

Internal boxes in the mesial and distal faces or in the

greatest bulk of dentine (Tjan & Miller 1984, Hem-

mings et al. 1991) during root canal preparation for

cast post-and-core have been proposed as a way of

dissipating stresses in the longitudinal axis of the tooth

and work as an anti-rotation device (ARD). Shilling-

burg et al. (1997) stated that these devices should be

performed only on the lingual face of incisors with

conical or cylindrical root canals and extensive coronal

destruction.

Destructive mechanical tests, such as fracture tests,

are important for biomechanical analysis of tooth and

restorative materials, as they enhance understanding of

the behaviour of teeth in high loading situations.

However, these tests have limited capacity to clarify the

stressstrain relationship in the tooth-restoration com-

plex (Soares et al. 2006, 2008c). The use of non-

destructive tests, such as strain gauge tests (Ross et al.

1991, Sakaguchi et al. 1991), and finite element

analysis (FEA) (Kishen et al. 2004, Romeed et al.

2004, Jacobsen et al. 2006) is more suitable for

understanding the failure characteristics of the restor-

ative procedures (Ausiello et al. 2001, Lin et al. 2001,

Magne & Belser 2003, Soares et al. 2008b). Several

studies have made comparative investigations using

only FEA (Lin et al. 2001, Pierrisnard et al. 2002,

Magne & Belser 2003, Romeed et al. 2004, Lanza et al.

2005, Jacobsen et al. 2006, Toksavul et al. 2006),

however, this methodology is more representative

when associated with destructive tests (Fennis et al.

2005), or with non-destructive assays such as the

strain gauge test (Palamara et al. 2002, Lertchirakarn

et al. 2003, Soares et al. 2008d).

The aim of this study was to assess ex vivo the

fracture resistance, the strain of the buccal, lingual and

proximal root dentine and the stress distribution of root

filled bovine incisors restored with cast post-and-cores.

The study tested the hypothesis that the presence of

ARDs and their location influences the biomechanical

behaviour of incisors restored with cast post-and-cores

and metallic crowns.

Materials and methods

Tooth selection, preparation and embedding

Fifty-two similar bovine incisor teeth were selected, 40

for fracture resistance and fracture mode evaluation

and 12 for strain measurement tests. External debris

were removed with hand scalers, and teeth were stored

in 0.2% thymol solution (Soares et al. 2007). Teeth of

similar size and shape were selected by crown dimen-

sions after measuring the buccolingual and mesiodistal

widths in millimetres, allowing a maximum deviation

of 10% from the average. The crowns of all the teeth

were sectioned horizontally to the long axis, 15 mm

from the apex, with a water-cooled diamond disk (No.

7020; KG Sorensen, Barueri, SP, Brazil). The roots were

divided into four groups (n = 13): Nd control without

ARD; Bd buccal ARD; Ld lingual ARD; BLd buccal

and lingual ARD.

Root canals were instrumented with size 50 master

apical files (K-files; Dentsply Maillefer, Ballaigues,

Switzerland) in association with 1.0% sodium hypo-

chlorite (Cloro Rio 1.0%; Sao Jose do Rio Preto, SP,

Brazil), filled with gutta-percha and calcium hydrox-

ide-based cement (Sealer 26; Dentsply, Petropolis, RJ,

Brazil). The post space was created initially with a

heated instrument and the residual gutta-percha

was then removed with Gattes-Gliden burs (2, 3, 4,

Dentsply Maillefer), standardizing the post space to

10 mm and preserving 5 mm of root filling at

the apex. Root canal walls were then enlarged with

Anti-rotation devices biomechanics Raposo et al.

International Endodontic Journal, 43, 681691, 2010 2010 International Endodontic Journal682

a 1.5-mm-diameter bur (Largo Peeso Reamer, No. 5,

Dentsply Maillefer).

The selected roots were embedded in self-polymerizing

polystyrene resin (AM 190 Resin; AeroJet, Santo Amaro,

SP, Brazil) to a level 2 mm below the coronal margin.

The periodontal ligament was simulated, using a polye-

ther-based impression material (Impregum Soft; 3M-

ESPE, Saint Paul, MN, USA). To carry out this procedure

root surfaces were dipped into molten wax 2 mm

apically to the coronal surface, resulting in a 0.2 to

0.3mm-thick wax layer. A radiographic film with a

centralized circular hole was used to stabilize teeth for

the embedding procedure. This assembly was placed

with the crown faced down into a hole in a wooden

board leaving the root in a vertical position perpendic-

ular to the supporting radiographic film. Then, a plastic

cylinder (25 mm diameter) was placed around the root

and fixed in position with cyanoacrylate-based adhesive

(Super Bonder; Loctite, Itapev, SP, Brazil) and wax. The

resin was manipulated according to manufacturers

instructions and inserted into the cylinder. After resin

polymerization, the teeth were removed from the cylin-

der and the wax was removed from both root surface and

the cylinder. The impression material was placed into

the resin cylinders, thus the tooth was re-inserted and

the excess of polyether material was removed with a

scalpel blade (Soares et al. 2005).

Anti-rotation device, post-and-core and crown

restoration

The ARDs box preparations were performed in a cavity

preparation machine (Soares et al. 2008a) consisting of

a high-speed handpiece coupled to a mobile base. The

mobile base moves vertically and horizontally with

three precision micrometric heads (152-389; Mitutoyo,

Suzano, SP, Brazil), with a 0.002 mm level of accuracy.

For the preparations, a smooth tapered carbide bur (No.

170; KG Soresen), 1.6 mm diameter and 4.0 mm

depth, was used with its whole active point (Shilling-

burg et al. 1997), following each group designation:

Nd- without ARD; Bd- buccal ARD; Ld- lingual ARD;

BLd- buccal and lingual ARD.

For the cast post-and-core fabrication, pre-fabricated

polycarbonate patterns were used (Nucleojet; Angelus,

Londrina, PR, Brazil). Reline of patterns was carried out

using autopolymerizing acrylic resin in the individual

root canal (Duralay; Reliance Dental Mfg. Co., Worth,

IL, USA) until passive retention was achieved. Subse-

quently, the individual patterns were adjusted in each

respective specimen, standardizing their height at

6.0 mm. The patterns were invested, cast in copper-

aluminium alloy (Cu-Al alloy; Goldent, Sao Paulo, SP,

Brazil) and sandblasted with aluminium oxide particles

(50 lm) under two bars pressure for 10 s (Fig. 1). Priorto cementation, the root canals were cleaned with

distilled water and dried with absorbent paper points

(Dentsply Maillefer). The cast post-and-cores were

cemented with zinc-phosphate cement (Zinc Cement;

SS White, Rio de Janeiro, RJ, Brazil) under a constant

pressure of 50 N for 10 min.

Impressions of the coronal portion of the specimens

were taken with a 2-step technique, using a polyether

impression material (Impregum Soft; 3M-ESPE). After

1 h, the impressions were poured with a type IV dental

stone (Durone IV, Dentsply). A standard crown with a

lingual plateau 1.0 mm in thickness for load applica-

tion was constructed in composite resin (Filtek Z250;

3M-ESPE) and from which a laboratory silicone matrix

was produced (IQ 428 Rubber, Aerojet). Heated liquid

wax (Green wax; Kota Imports, Sao Paulo, SP, Brazil)

was inserted in this matrix, followed by one of the

individual stone casts, resulting in the formation of the

crown wax pattern. The patterns were invested and

cast in nickel-chromium alloy (Kromalit; Knebel, Porto

Alegre, RS, Brazil). The crowns were adjusted and then

cemented with zinc-phosphate cement (Zinc cement, SS

White), under a constant pressure of 50 N for 10 min.

To simulate the fatigue and mechanic deterioration of

the restorative materials (Huysmans et al. 1993, Isidor

et al. 1996, Mannocci et al. 1999, Reagan et al. 1999),

the specimens were submitted to a cyclical loading of

50 N directed at 135 to the lingual elevation of themetallic crowns. At a frequency of 1.25 Hz, 3 105

cycles were undertaken (Isidor et al. 1996, Naumann

et al. 2007) using a fatigue-testing machine (ER-LA-11000;

Figure 1 Experimental groups: Nd- control without ARD; Bd-

buccal ARD; Ld- lingual ARD; BLd- buccal and lingual ARD.

Raposo et al. Anti-rotation devices biomechanics


ERIOS, Sao Paulo, SP, Brazil) with a constant tem-

perature of 37 C in 100% of humidity (Fig. 2).

Strain measurement tests

For strain measurements tests, three strain gauges (PA-

06-060OBG-350LEN; Excel Sensores, Sao Paulo, Brazil)

were fixed on three samples per group, 1.0 mm below

the crown cervical limit of each specimen, two parallel

to the root long axis (one on the buccal root surface

and the other on the lingual root surface) and one

transversely to the root, on the proximal root surface

(Fig. 3). According to the manufacturer, the base

material of these gauges consists of a polyimide and

metal constantan film, with temperature self-compen-

sation for steel. The strain gauge grid had an area of

4.1 mm2 and an electrical resistance of 350 X. Thegauge factor is a proportional constant between elec-

trical resistance variation and strain, and the strain

gauges used for this study had a gauge factor of 2.12

(Santos-Filho et al. 2008, Soares et al. 2008b). For the

strain gauge attachment, the root surface was etched

with 37% phosphoric acid for 15 s (Cond AC 37; FGM,

Joinville, SC, Brazil), rinsed with water and air-dried.

Sequentially, the strain gauges were bonded with a

cyanoacrylate-based adhesive (Super Bonder, Loctite)

and connected to a data acquisition system (AD-

S0500IP; Lynx, Sao Paulo, Brazil). A control specimen,

with three strain gauges attached but not subjected to

load application, was mounted adjacent to the test

tooth as a compensator for temperature fluctuations

because of the gauge electrical resistance or local

environment.

The specimens fitted with strain gauges were sub-

jected to a non-destructive ramp-load from 0 to 100 N

at a cross-head speed of 0.5 mm per min using a

mechanical testing machine (EMIC DL-2000; EMIC,

Sao Jose dos Pinhais, PR, Brazil). The load was applied

at the lingual elevation with a wedge-shaped tip. The

data obtained were transferred to a computer using

specific acquisition, signal transformation and data

analysis software (AqDados 7.02 and AqAnalisys;

Lynx). During load application, one strain value was

recorded for each strain gauge every 0.3 s until a

maximum load was attained. Data for each region

showed normal and homogenous distribution and were

statistically analysed by one-way analysis of variance

(anova) and Tukey Honestly Significant Difference test

(HSD).

Fracture tests

Fracture resistance tests were performed in all speci-

mens using the same compressive design used for the

strain gauge test (Fig. 4). The results were obtained in

Figure 2 Mechanical fatigue: cyclical loading of 50 N directed

at 135 to the lingual elevation of the metallic crowns.

Figure 3 Strain gauges attached to buccal (A) lingual (B) and

proximal (C) faces.

Figure 4 Fracture resistance set up.



Newtons (N) showed normal and homogenous distri-

bution and were submitted to one-way anova and

Tukey HSD tests. For all tests, an alpha level of 0.05

was used. The failed samples were analysed under an

optical stereomicroscope to determine the fracture

mode according to the location of the failure in the

tooth structure (Akkayan & Gulmez 2002, Toksavul

et al. 2006, Naumann et al. 2007). Fractures were

classified as type I, proximal to buccal coronal third

fracture; type II, proximal coronal third fracture; type

III, proximal to buccal medium or apical third fracture

and type IV, proximal medium or apical third fracture

(Fig. 5).

Finite elements analysis

Bidimensional models were created from a longitudinal

cut of one tooth of each experimental groups simulat-

ing the dimensions of the dental structure, using

computer-aided design software (Mechanical Desktop,

AutoCAD 6; Autodesk Inc, San Rafael, CA, USA)

(Soares et al. 2008b). The external outline of the tooth

and its support structures were included in the model.

The data obtained were exported to a software appli-

cation (ANSYS 9.0; ANSYS Inc, Canonsburg, PA,

USA). In this software, the areas corresponding to each

structure were plotted and then meshed with isopara-

metric elements (Plane183). This element is defined by

eight nodes having two degrees of freedom at each

node: translations in the nodal X and Y directions. The

mechanical properties of each structure and materials

used in the analysis are described in Table 1 (Farah

et al. 1975, Ko et al. 1992, Holmes et al. 1996,

Suansuwan & Swain 2001). All tooth structures and

materials used in the models were considered iso-

tropic, elastic, linear and homogeneous. The boundary

conditions were defined with a 10 N load applied at a

135 angle in the centre of the concavity formed onthe lingual face, 1.0 mm bellow the incisal edge,

simulating the load application used on the fracture

resistance test (Lanza et al. 2005). Model displacements

were restricted at the external lateral and top outlines.

Stress distribution analysis was performed by means of

the quantitative association of the main maximum

stress by von Mises criteria. In 10 monitoring points

positioned among the restorative system, the quantita-

tive stress were obtained (Fig. 6).

Results

The one-way anova indicated no significant difference

between the groups in the fracture resistance test

Figure 5 Schematic representation of the failure mode: Type

I- proximal to buccal coronal third fracture; Type II- proximal

coronal third fracture; Type III- proximal to buccal medium or

apical third fracture; and Type IV- proximal medium or apical

third fracture.

Table 1 Mechanical properties of dental structures and

restorative materials

Structure/Material

Youngs

modulus (MPa)

Poissons

ratio

Dentine (Ko et al. 1992) 18600 0.31

Ligament (Holmes et al. 1996) 68.9 0.45

Cortical bone (Ko et al. 1992) 13700 0.30

Cancellous bone (Ko et al. 1992) 1.370 0.30

Gutta-percha (Ko et al. 1992) 6.9 0.45

Zinc-phosphate cement

(Farah et al. 1975)

22000 0.35

NiCr alloy (Suansuwan

& Swain 2001)

203600 0.30

CuAl alloya 109080 0.33

aManufacturers information.

Figure 6 Monitoring points to quantify the von Mises stress

values (MPa).



(P = 0.605). The mean fracture resistance values are

shown in Table 2. Fracture mode distribution is

described in Table 3. Prevalence of types III and IV

(catastrophic fractures) was observed in all groups.

One-way anova revealed no significant difference in

the strain values recorded on the buccal (P = 0.43) and

lingual (P = 0.54) surfaces. However, on the proximal

surface, significant difference between groups was

observed with high strain values for the BLd group,

followed by Bd and Ld groups, and lowest values for Nd

group (Table 4).

Finite element analysis showed greater similarity in

the stress distribution levels within tooth structure

between Nd, Ld and Bd groups, which presented lower

stress concentration into buccal dentine than BLd

group. Bd group showed a stress concentration area on

the buccal face, near to the ARD. The BLd group

presented the higher stresses between all groups

(Fig. 7). In the quantitative analysis, lower stresses

were observed in the Ld and Nd groups, while Bd group

presented a similar pattern to Nd group with higher

stress. The BLd group showed the highest stress

concentration (Fig. 8).

Discussion

The hypothesis of this study was partially supported by

the results. The presence and location of ARDs did not

influence the fracture resistance and fracture mode of

incisors restored with cast post-and-cores. However,

the ARDs influenced the strain values at the proximal

face and the stress distribution within tooth structure,

mainly with its application on the buccal face (Bd) or

simultaneously on the buccal and lingual faces (BLd

group).

Anti-rotation devices have been described as impor-

tant means to avoid dislodgment of cast posts-and-cores

in teeth with round root canals (Tjan & Miller 1984,

Hemmings et al. 1991, Shillingburg et al. 1997). Pre-

vious studies, concluded that this class of devices could

indeed increase the torsion resistance of teeth submit-

ted to these forces (Tjan & Miller 1984, Hemmings et al.

1991, Joshi et al. 2001) and improve stress distribution

over the restorative system (Shillingburg et al. 1997).

Despite the fact of the fracture resistance of root filled

teeth being proportional to the remaining structure

(Assif & Gorfil 1994), the tooth loss caused by the ARD

preparation did not affect the fracture resistance of

incisor roots. This probably occurred because of the low

sensitivity of the fracture resistance test, which is not

capable of measuring adequately the influence of such

small alterations.

Despite significant differences on the proximal

strains, the results of this region were lower than the

buccal and lingual ones. This occurred probably

because of the core and crown major supporting area,

which is located mainly at the buccal and lingual faces

of the root, instead of the proximal sites, where the

dentinal support for the metallic components is con-

siderably reduced. This can result in high strain values

in the referred areas during the specimen loading. The

reduced amount of dentine of the proximal regions and

the ARD preparation could explain the differences in

the strain values between groups. The fracture mode

analysis showed failures starting mainly on the prox-

imal faces, continuing normally towards the buccal

face. The removal of sound tooth structure in the

preparation of the anti-rotation increased dentine

strain, favouring higher strains on the proximal site.

However, strain gauge method records the strains on a

surface just before these forces dissipate throughout the

whole body. Consequently, strains that occur inside a

body with load application reach higher values than

those measured on its surface.

The post inserted into the root canal modifies the

tooth stressstrain distribution (Assif & Gorfil 1994).

Under loading, stress will concentrate in the more rigid

material in a system with materials that present

different stiffness. A cast post-and-core presents differ-

ent mechanical properties when compared to a

non-metallic post system and to the inner dentine

(Pierrisnard et al. 2002, Toksavul et al. 2006). The

Table 2 Mean fracture resistance values (SDs) and results of

Tukey Honestly Significant Difference (HSD) test (n = 10)

Groups Fracture resistance (N) Tukey Categorya

Nd 708.6 (110.1) A

Bd 716.8 (217.3) A

Ld 766.9 (270.0) A

BLd 823.80 (221.9) A

aTukey categories with same uppercase letters are not statisti-

cally significant from each other (P < 0.05)

Table 3 Fracture mode distribution among the groups

Fracture type

Group I II III IV

Nd 1 0 5 4

Bd 0 0 6 4

Ld 0 0 4 6

BLd 1 1 4 4

Total (%) 5% 2.5% 47.5% 45%



stiffness imposed on the root by the metallic post does

not allow the root structure to flex and consequently

increases the stress concentration along the whole

system. On this way, the stress primary distributed to

the root periphery concentrate inside the regions where

the micro-dislodgment is restricted as in the dentine-

cement-post interfaces (Genovese et al. 2005, Lanza

et al. 2005). The collapse of the interface induces

dissipation of the energy accumulated in the metallic

post to the dentine. This could explain the strains

observed on the proximal surface, predominantly when

anti-rotations devices are used on the buccal and

lingual faces. Strain values on proximal surfaces seem

to be particularly more important when comparing the

fracture resistance and fracture mode. This tensile

strain starts inside the root canal and can spread

through the cracks leading to catastrophic fractures of

the structure (Santos-Filho et al. 2008).

In a normal occlusion, the dentine exhibits consid-

erable flexibility to elastic strains, withstanding several

forces applied from different angles (Kishen et al. 2004,

Naumann et al. 2007). However, these forces could

exceed the dentine strength as well as the proportional

limit, and fracture may occur (Kishen et al. 2004).

Besides the metallic post stiffness, root canal dentine is

arranged radially and the stress tends to be parallel to

the tubules direction, generating a wedge effect and

consequent root failures. Catastrophic fractures (types

III and IV) occurred in all groups, mainly in the Bd

group samples. This probably happened because of the

load applied on the lingual face, which concentrates

compressive stresses on the buccal face (Assif & Gorfil

1994), increasing the fractures on this region. FEA

showed a high stress concentration on the buccal

dentine in the BLd model. The increase in the volume of

the metallic post may explain this behaviour. This

finding did not have a direct effect on the fracture

resistance. However, as shown previously, this could

explain the highest strain values on the proximal

surface during strain gauge tests verified on this group.

Table 4 Mean values and standard deviations of strain values (lS) for the groups, maximum loading of 100 N

Buccal Lingual Proximal

Groups lS

Tukey

Categorya lS

Tukey

Categorya lS

Tukey

Categorya

Nd 549.9 (74.2) A 346.9 (263.6) A 125.5 (16.5) B

Bd 386.5 (216.1) A 333.7 (159.9) A 144.9 (16.5) AB

Ld 562.5 (266.2) A 472.9 (380.4) A 133.9 (65.9) AB

BLd 345.4 (145.9) A 363.7 (110.3) A 311.5 (244.7) A

aTukey categories with same uppercase letters are not statistically significant to each other into the same region (P = 0.0001).

Figure 7 von Mises stress values (MPa):

Nd control without anti-rotation device

(ARD); Bd buccal ARD; Ld lingual

ARD; BLd buccal and lingual ARD.



The fracture resistance values of all groups are higher

than the incident anterior forces of the oral cavity,

quoted in the literature between 27.8 and 65.3 N

(Kumagai et al. 1999). In addition, the failures that

occur in restorative procedures involving cast post-and-

cores are frequently related to fractures because of the

mechanical fatigue of the system, caused by the forces

concentrated out of the long axis of the tooth (Torbjorner

& Fransson 2004). Consequently, a well planned and

developed prosthesis with favourable biomechanics is

crucial to the longevity of root filled teeth. To conserve

intact dental structure, ARDs should only be realized

when really necessary. Moreover, the lingual face should

be the unique region of choice because of the lower

strains and stress values were observed on this area.

This study was conducted in laboratorial conditions

and it presents some intrinsic limitations, such as the

static loading and absence of thermal cycling. Despite

using bovine teeth, several studies show large accep-

tance of these teeth for laboratory investigations

because of its similarity to human dentine and

geometric root configuration (Schilke et al. 2000,

Fonseca et al. 2008). Additionally, as bovine teeth

have greater availability, it is possible to standardize

specimen size and shape (Santos-Filho et al. 2008,

Soares et al. 2008c), which is essential when obtaining

comparable results as deformation and fracture resis-

tance are dependent on tooth geometry.

The FEA analysis also had limitations, such as the

bidimensional models and the materials assumed as

being elastic and isotropic. The linear elastic analysis is

also another limitation, because the periodontal liga-

ment and interfaces behaviour differently when anal-

ysed using non-linear analysis. However, the

combination of non-destructive (strain gauge) and

destructive experimental mechanical tests (fracture

resistance) with numerical analyses (FEA) can be

effective in predicting the biomechanical behaviour of

dental restorative procedures. FEA using 3D models is

recommended, as it allows anatomic alterations and

devicesample contact to be shown with greater

accuracy (Soares et al. 2008b). Further clinical evalu-

ations, taking into account the remaining dentine

thickness and the presence and location of ARDs,

Figure 8 von Mises stress distribution quantitative analysis.



would be of benefit. In addition, the use of restorative

materials that could resemble the mechanical behav-

iour of sound teeth should be incorporated into the

clinical choices when indicated.

Conclusions

Within the limitations of this laboratory study, the

following conclusions were drawn:

1. The presence and location of an ARD did not affect

significantly the fracture resistance and fracture mode

of tooth restored with cast post-and-core;

2. Higher strains were observed on the proximal

surface of teeth in the presence of ARDs. The associ-

ation of buccal and lingual ARDs produced the highest

strains;

3. Lower stresses were observed when the ARD was

positioned on the lingual face; despite higher stress

concentrations being observed when this feature was

positioned concomitantly on the buccal and lingual

faces.

Acknowledgements

This study was supported by the Research Support

Foundation of the State of Minas Gerais (FAPEMIG\

Brazil).

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Effect of Anti-rotation Devices on Biomechanical Behaviour of Teeth Restored With Cast Post-And-cores.

Documents

cast post

group n

rotation device ard

fracture modes

fracture resistance

biomechanics group

bld group

fracture resistance