amilcar chagas freitas júnior , eduardo passos rocha

In: International Journal of Clinical Dentistry ISSN: 1939-5833

Volume 4, Number 1 © 2011 Nova Science Publishers, Inc.

STRESS DISTRIBUTION IN CERAMIC RESTORATIONS

OVER NATURAL TOOTH USING FINITE ELEMENT

ANALYSIS. LITHIUM DISILICATE X ALUMINUM

OXIDE MATERIAL

Amilcar Chagas Freitas Júnior, Eduardo Passos Rocha,

Paulo Henrique dos Santos, Erika Oliveira de Almeida,

Rodolfo Bruniera de Anchieta, Manoel Martín Júnior and

Carlos Marcelo Archangelo

Department of Dental Materials and Prosthodontics,

Araçatuba School of Dentistry,São Paulo State University,

Araçatuba, São Paulo, Brazil

ABSTRACT

Background: Data on stress distribution in tooth-restoration interface with different

ceramic restorative materials are limited. The aim of this chapter was to assess the stress

distribution in the interface of ceramic restorations with laminate veneer or full-coverage

crown with two different materials (lithium dissilicate and densely sintered aluminum

oxide) under different loading areas through finite element analysis.

Materials and Methods: Six two-dimensional finite element models were fabricated

with different restorations on natural tooth: laminate veneer (IPS Empress, IPS Empress

Esthetic and Procera AllCeram) or full-coverage crown (IPS e.max Press and Procera

AllCeram). Two different loading areas (L) (50N) were also determined: palatal surface

at 45° in relation to the long axis of tooth (L1) and perpendicular to the incisal edge (L2).

A model with higid natural tooth was used as control. von Mises equivalent stress (vM)

and maximum principal stress (max) were obtained on Ansys software.

Results: The presence of ceramic restoration increased vM and max in the adhesive

interface, mainly for the aluminum oxide (Procera AllCeram system) restorations. The

full-coverage crowns generated higher stress in the adhesive interface under L1 while the

same result was observed for the laminate veneers under L2.

Conclusions: Lithium dissilicate and densely sintered aluminum oxide restorations

exhibit different behavior due to different mechanical properties and loading conditions.

Correspondence: Amilcar Chagas Freitas Júnior, 1560 Waldir Feliozola de Moraes, Araçatuba, São Paulo, Brasil,

16015-295. # 55(18)91012849. e-mail: [email protected]

Amilcar Chagas Freitas Júnior, Eduardo Passos Rocha et al. 44

Keywords: Ceramics, crowns, biomechanics, finite element analysis.

INTRODUCTION

The physical and structural interaction between a rigid dental tissue as enamel and a

flexible and soft tissue as dentine provides support for chewing load. The knowledge about

this interaction has generated a concerning on biomechanical response of dental tissues to

restorative procedures [1].

Currently, the adhesive technology has demonstrated its efficiency to reestablish

restoration rigidity and preserve remaining dental structure simultaneously [2]. However, the

mechanical behavior of restorative materials still presents some limitations in comparison to

natural enamel considering the partial recovering of crown rigidity [1]. According to this, the

ceramics have been presented as the most appropriate materials [3,4].

In addition, the ceramics have been continuously modified to improve resistance and

eliminate metallic framework. However, mechanical failures are still common with ceramics

since the stress is not properly absorbed by plastics deformation, which generates fractures

and defects especially in the tooth-restoration interface [5-14]. This occurs since ceramics are

brittle materials that failure when the ability to support loading is compromised by defects

[6,15]. So, functional loads applied on ceramic restorations are directly transferred to cement

and supporting structures [5,7,16-18].

The adhesive layer established by the cement allows partial absorption and limits stress

transferring to supporting dental structures, which preserves integrity of tooth-restoration

interface [9]. So, a complete bonding between tooth and ceramic restoration is required [18].

According to this, the chapter of Troédson and Dérand [18] does not indicate any risk to

failure of ceramic restorations properly bonded to remaining dental structure when the other

clinical variables are controlled.

According to this, there are several studies on mechanical properties of ceramics focusing

on flexure, fracture, and fatigue resistances as well as on accuracy of marginal fit [5,17,19-

24]. Some studies also evaluate stress distribution on tooth-restoration interface since this

area is important for treatment success [8,9,14,18,25,26].

However, literature does not present the influence of different restorative systems on

mechanical behavior of a tooth restored with different types of restorations. The studies

generally provide comparisons with other types of restorations [25], between a standard

ceramic and other restorative materials as acrylic resin and/or gold alloy [27-29], or between

metal ceramic and all-ceramic restorations [30].

Additionaly, some studies also evaluate the intensity and direction of loading associated

to the quality of bone tissue [12]. The aim of this chapter was to evaluate the internal stress

distribution on the adhesive interface of a single ceramic restoration in a maxillary central

incisor by two-dimensional finite element analysis. The chapter included different restoration

types (laminate veneer or full-coverage crown) and ceramic systems (IPS Empress, IPS

Empress Esthetic, IPS e.max Press, Procera Laminate and Procera AllCeram) associated to

palatal and inicisal loadings.

Stress Distribution in Ceramic Restorations Over Natural Tooth… 45

MATERIAL AND METHODS

According to anatomical data [31], a buccal-lingual section in the region of the left

maxillary central incisor was used for the two-dimensional (2D) finite element analysis

(FEA). Six models were obtained with the AutoCAD 2006 software (Autodesk Inc.; San

Rafael, CA, USA) varying the restoration type (laminate veneer or full-coverage crown) and

the ceramic restorative material: lithium dissilicate (IPS Empress, IPS Empress Esthetic, IPS

e.max Press) and densely sintered aluminum oxide (Procera AllCeram) (Table 1). The height

(10 mm), the mesio-distal (9 mm) and buccal-lingual (7 mm) distances of coronal portion,

and the root length (12.5 mm) remained constant in all models.

The numerical models included a ceramic restoration cemented on tooth presenting

enamel, dentine and pulp chamber associated to other structures as periodontal ligament,

fibromucosa, cortical and trabecular bone (Figure 1). Each material was characterized by its

elasticity parameters (Table 2). The dimensions of all structures, the characteristics of

supporting and protection periodontium, and the biological width (alveolar ridge, cemento-

enamel junction, connective insertion) remained constant in all models. So, the maxillary

bone was modeled as a spongy center surrounded by a 0.5 mm-thickness layer of cortical

bone and 1.0 mm-thickness layer of mucosa. The dimensions of periodontal ligament,

connective insertion and junctional epithelium presented 0.25 mm, 1.0 mm and 1.0 mm,

respectively [31].

The dimensions of the laminate veneers, which determined the tooth preparation,

remained constant in the models MB1, MB2 and MB3; and were based on each

manufacturer’s instruction: 0.7 mm in thickness in the palatal and buccal surfaces (2.0 mm

palatal extension), 1.0 mm in thickness in the incisal surface for MB1 and MB2, and 2.0 mm

for MB3. A cervical chamfer preparation with 20° of angulation and 0.6 mm of dimension

was established for these models.

Table 1. Description of models and variables


Table 2. Mechanical properties of materials of the models

Figure 1. Representative diagrams of the structures of each model (M) of the study (A, B1, B2, B3, C1,

C2).


For the models with full-coverage crown (MC1 and MC2), the dimensions of the

restorations presented 1.5 mm in thickness in the palatal and buccal surfaces, 2.0 mm in

thickness in the incisal surface, and a 1.0 mm-thickness cervical circular chamfer preparation.

The adhesive cement Variolink II (Ivoclar Vivadent AG, Schaan, Liechtenstein) was

simulated as cement for ceramic restorations considering a cement line with 0.05 mm in

thickness. All materials were considered as homogenous, isotropic and linearly elastic; and

the models were assumed in plane strain. The bonding between the ceramic elements and

tooth by resin cement was considered as perfect in all simulated situations. Each model

exhibited a finite element mesh generated by elements PLANE2, defined by 6 nodes and

presenting 2 degrees of freedom in triangular bodies with displacement with quadratic

behavior (ANSYS 10.0 – ANSYS Inc., Houston, PA, USA). The models exhibited between

18477 (MA) and 18942 (MC1 and MC2) elements and between 37783 (MA) and 38714

(MC1 and MC2) nodes.

As a boundary condition, the zero displacement was considered for the nodes of the

upper region of the cortical bone. All left lateral nodes were fixed on the x-axis. Considering

that the maxillary central incisor may present a maximum force of 555N [35], the value of

50N was assumed for the loading since the chapter is two-dimensional and represents a

segment of the assembly. Thus, two conditions of static and distributed loading (L) were

established: L1 – 45° in relation to the dental long axis in the medium third of the palatal

surface; L2 – vertical loading perpendicular to the incisal edge. Both loading conditions were

applied in the same nodes for each model. For the distributed loading, 5 nodes were used to

receive the load considering that the nodes of each extremity received half of the loading

(Figure 2).

The stress analysis was carried out according to the criterion of von Mises equivalent

stress (vM). vM represents a global combination (directional axis x and y) of the standardized

absolute values of the stress that was generated [8,36]. The individual and general maps of the

structures in each model were obtained according to the areas described in the Figure 3. The

maximum principal stress (max) was individually obtained for each brittle structure, i.e.,

ceramic restoration and cement.

Figura 2. Representative diagrams of the distributed loadings (L1 and L2) assumed in the study. The

approximated view indicates the value of the load applied on each node for each model.


Figure 3. Representative diagram of the areas selected for the detailed analysis of stress distribution in

the restoration-cement-tooth interface in the models restored with laminate veneers (a) and full-

coverage crowns (b). Legend: 1 (buccal cervical region of the interface); 2 (region of the buccal

medium third of the interface); 3 (incisal region of the interface); 4 (region of the palatal medium third

of the interface); 5 (palatal cervical region of the interface). The narrows indicate the region of the

loadings L1 and L2.

RESULTS

The maximum values of vM are presented in Table 3. It was observed that the presence

of restoration (laminate veneer or full-coverage crown) increased the stress in the interface for

all tested conditions. For the loading L1, the full-coverage crowns generated higher stress

concentration than the laminate veneers in comparison to the control model (MA) about 80%

with the IPS e.max Press system (MC1) and 220% with the Procera AllCeram system (MC2).

For the loading L2, the highest values of vM were observed in the models with laminate

veneers with stress increase about 24% in the models MB1 and MB2, and 62% in the model

MB3. The Procera AllCeram system presented higher variation of vM in comparison to the

control model (MA) in all regions for both models restored with laminate veneers or full-

coverage crowns, regardless the loading condition.

Table 4 shows the maximum values of vM for each structure of the adhesive interface

(restoration, resin cement and tooth). It was observed that the highest stress values related to

the ceramic restoration were associated to the Procera AllCeram system, regardless the

restoration type and loading condition.

For the laminate veneers, the maximum value of vM was observed in the region 2 under

loading L1 with both ceramic systems. For the loading L2, maximum value of vM was

exhibited in the region 3 for the IPS Empress system and in the region 2 for the Procera

AllCearm system. However, for the full-coverage crowns, the maximum value of vM was

observed in the region 4 for L1 and in the region 2 for L2, regardless the ceramic material

used.


Table 3. Maximum von Mises stress values (MPa) in the general map for each region

(1, 2, 3, 4 and 5) of the cementation interface

The maximum values of vM for the loading L1, in the resin cement and tooth, were

observed in the region 1 for the models restored with laminate veneers and in the region 5 for

the models restored with full-coverage crowns, regardless the ceramic material. For the

loading L2, the maximum value occurred in the region 1, regardless the restoration type and

material. The value of max (Table 5) demonstrated that the restorations of densely sintered

aluminum oxide (Procera AllCeram system) presented higher stress concentration than the

restorations of lithium dissilicate, regardless the tooth preparation (laminate or full-coverage

crown) and the loading condition (L1 or L2). For the resin cement layer (Table 5), the Procera

AllCeram system also generated the highest values of max for the laminate veneer. However,

for the models with full-coverage crown, the IPS e.max Press system generated higher values

of max in the cement.

DISCUSSION

The maxillary central incisors are important for esthetics and also dynamic of mandibular

movement. During protrusion movement, these teeth protect the posterior teeth that are out of

occlusion during mouth opening. Furthermore, the maxillary and mandibular incisors tear

food, which develops stress that is critical for clinical success of restorations [8].

According to Zarone et al. [8] and Troedson and Dérand [13], the stress concentrates on

regions with non-homogenous material distribution, such as regions of adhesive interface of

cementation. So, a tooth-cement-restoration interface with different elasticity modules

represents a fragile point of any restorative system. The fabrication of numerical models

simulating a real or experimental situation accurately is a problem of FEA. The properties in

the tooth-restoration interface, which was considered as homogenous and continuous through

the entire tooth surface in this chapter, are important to determine the stress based on the

perfect bonding between tooth and restoration as it occurs between the structures of higid

natural dentition.

Table 4. von Mises stress values (MPa) for each individual structure observed in each region of the cementation interface


Table 5. Maximum principal stress values (MPa) individualized for each ceramic

restoration and cement for the loading conditions L1 and L2

In the region of cementation interface, the loading L1 generated higher vM in the models

restored with full-coverage crowns while the highest stresses with loading L2 were observed

in the models with laminate veneers. This occurs since the loading L2 was directly applied on

both restoration types while loading L1 determined force appliance only on the full-coverage

crowns, as it was observed in the Figure 3.

Other important aspect was the low value of vM exhibited in MA (control) in

comparison to the models with ceramic restoration (Table 3). This fact was pronounced due

to the linear representation for periodontal ligament, which allowed uniform stress

distribution toward the structures of the model. Probably, a non-homogenous representation

for the periodontal ligament would promote less uniform stress distribution.

For the supporting dental structures, it was observed higher vM concentration in the

region of cervical margin similarly to the results of Troedson and Dérand [13]. This probably

results from the enamel hardness due to its high mineral content. The high E value and the

low stress resistance of this structure determined the fragile properties. However, there is a

low-mineralized and fiber-reinforced biological interface between the enamel and dentine

named enamel-dentine junction (EDJ) that dissipates stress and avoids failure propagation.

So, the EDJ presents reasonable fracture resistance and, considering a resilient subjacent

dentine, it supports enamel integrity preventing fracture during function [10]. The ultimate

tensile strength of the EDJ ranges from 46.9 to 60 MPa [10,24]. So, special attention is

suggested for these regions since the remaining dental structure presents scarce quantity of

enamel after full-coverage crown restoration and reduced dentine support due to the

restoration preparation. Thus, high vM values (39.4 MPa) are generated mainly when the

Procera AllCeram system (MC2) is associated to the loading L1, as it was shown in Table 4.

The present chapter also evaluated the maximum principal stress (max) concentration that

is an appropriate criterion for failure analysis of non-ductile materials; such as enamel,

ceramic and resin cement that present wide variation between the stress or compression


rupture values [1]. So, according to the max values presented in Table 5, the Procera

AllCeram system generated higher stress concentration on the prosthetic restoration for both

laminate veneers and full-coverage crowns. For these max values, a clinical safety margin for

fatigue fracture about 25% of the maximum load for this restorative system should be

considered and not exceeded [18]. However, considering that the adhesive bonding provided

by the cement in the present chapter was defined as ideal, it is suggested that a different

cementation condition increases the stress for each ceramic system [18].

Besides, it is known that the restoration is submitted to repeated stress application below

the resistance supported by the ceramic material. Even under these conditions, the restorative

material may failure after mechanical cycling when the fracture resistance of the material is

measured after cyclic loading. This should be taken into account since Found [37], in 2002,

reported that ceramic systems submitted to static and fatigue loading exhibited similar failures

for the highest stress concentration area.

Figure 4 shows that max was concentrated on the ceramic coping for both restoration

types. This occurred since the ceramic coping exhibits higher E value than the veneering

ceramic of all tested systems, which results in lower stress concentration.

The tooth-restoration bonding was assumed as perfect in the models with ceramic

restoration. The results presented in Table 5 evidenced higher propensity to failure in the

cementation line with the AllCeram system (region 1) in the models restored with laminate

veneer, and with the IPS e.max Press system (region 5) in the models restored with crowns.

Similarly to previous studies [13], it is suggested that the loss of adhesion in the periphery of

cementation interface (cervical margin) is critical for both restoration types; except for the

laminates with the IPS Empress system, which exhibited the max values in the incisal third.

This propensity to failure deserves special attention regardless the region since defects in

the cementation line decrease the physical properties, resistance, rigidity, and color stability;

and increases water absorption [14]. This issue is important since a proper cementation line

may partially absorb deformation of restorative system and limit the stress intensity

transferred to the remaining dental tissues, which provides restoration longevity [9].

Figure 4. Maximum principal stress distribution (σmax) in MC2 under loading L1.


CONCLUSIONS

The presence of ceramic restoration (laminate veneer or full-coverage crown) increased

the vM and max in the supporting structures toward the interface in comparison to the non-

restored natural tooth;

Lithium dissilicate and densely sintered aluminum oxide restorations present different

behavior due to different mechanical properties and loading conditions;

Aluminum oxide restorations (Procera AllCeram) generated the highest vM and max

values in the entire region of adhesive interface for both laminate veneers and full-coverage

crowns;

The full-coverage crowns generated higher stress in the adhesive interface under L1

while the same result was observed for the laminate veneers under L2.

ACKNOWLEDGMENTS

This chapter was supported by the Fundação de Amparo à Pesquisa do Estado de São

Paulo (FAPESP #2006/02336-2).

REFERENCES

[1] Magne P, Belser U. Bonded porcelain restorations in the anterior dentition: A

biomimetic approach. 1st ed., Quintessence Publishing Co, Chicago, 2002.

[2] MacPherson LC, Smith BG. Reinforcement of weakened cusps by adhesive restorative

materials: an in vitro study. Br. Dent. J. 1995;178:341-4.

[3] Reeh ES, Ross GK. Tooth stiffness with composite veneers: a strain and finite element

evaluation. Dent. Mater. 1994;10:247-52.

[4] Magne P, Douglas WH. Porcelain veneers: dentin bonding optimization and biomimetic

recovery of the crown. Int. J. Prosthodont. 1999;12:111-21.

[5] Albakry M, Guazzato M, Swain MV. Biaxial flexural strength, elastic moduli, and x-

ray diffraction characterization of three pressable all-ceramic materials. J. Prosthet.

Dent. 2003;89:374-80.

[6] Blatz MB, Sadan A, Kern M. Resin-ceramic bonding: a review of the literature. J.

Prosthet. Dent. 2003;89:268-74.

[7] Kim B, Zhang Y, Pines M, Thompson VP. Fracture of porcelain - veneered structures

in fatigue. J. Dent. Res. 2007;86:42-6.

[8] Zarone F, Sorrentino R, Apicella D, Valentino B, Ferrari M, Aversa R et al. Evaluation

of the biomechanical behavior of maxillary central incisors restored by means of

endocrowns compared to a natural tooth: a 3D static linear finite element analysis.

Dent. Mater. 2006;22:1035-44.

[9] Ausiello P, Apicella A, Davidson CL. Effect of adhesive layer properties on stress

distribution in composite restorations – a 3D finite element analysis. Dent. Mater.

2002;18:295-303.


[10] Giannini M, Soares CJ, Carvalho RM. Ultimate tensile strength of tooth structures.

Dent. Mater. 2004;20:322-9.

[11] Hikita K, Van Meerbeek B, De Munck J, Ikeda T, Van Landuyt K, Maida T et al.

Bonding effectiveness of adhesive luting agents to enamel and dentin. Dent. Mater.

2007;23:71-80.

[12] Papavasiliou G, Kamposiora P, Bayne SC, Felton DA. Three-dimensional finite

element analysis of stress-distribution around single tooth implants as a function of

bony support, prosthesis type, and loading during function. J. Prosthet. Dent.

1996;76:633-40.

[13] Troedson M, Dérand T. Shear stresses in the adhesive layer under porcelain veneers. A

finite element method study. Acta Odontol. Scand. 1998;56:257-262.

[14] Tunc EP. Finite element analysis of heat generation from different light-polymerization

sources during cementation of all-ceramic crowns. J. Prosthet. Dent. 2007;97:368-74.

[15] Fischer H, Dautzenberg G, Marx R. Nondestructive estimation of the strength of dental

ceramic materials. Dent. Mater. 2001;17:289-95.

[16] Chai J, McGivney GP, Munoz CA, Rubenstein JE. A multicenter longitudinal clinical

trial of a new system for restorations. J. Prosthet. Dent. 1997;77:1-11.

[17] Rizkalla AS, Jones DW. Mechanical properties of commercial high strength ceramic

core materials. Dent. Mater. 2004;20:207-12.

[18] Troedson M, Dérand T. Effect of margin design, cement polymerization, and angle of

loading on stress in porcelain veneers. J. Prosthet. Dent. 1999;82:518-524.

[19] Anusavice KJ. Degradability of dental ceramics. Adv. Dent. Res. 1992;6:82-9.

[20] Att W, Kurun S, Gerds T, Strub JR. Fracture resistance of single-tooth implant-

supported all-ceramic restorations: an in vitro study. J. Prosthet. Dent. 2006;95:111-6.

[21] Att W, Kurun S, Gerds T, Strub JR. Fracture resistance of single-tooth implant-

supported all-ceramic restorations after exposure to the artificial mouth. J. Oral

Rehabil. 2006;33:380-6.

[22] Cattel MJ, Knowless JC, Clarke RL, Lynch E. The biaxial flexural strength of two

pressable ceramic systems. J. Dent. 1999;27:183-96.

[23] Höland W, Schweiger M, Frank M, Rheinberger V. A comparison of the microstructure

and properties of the IPS Empress2 and the IPS Empress glass-ceramics. J. Biomed.

Mater. Res. 2000;53:297-303.

[24] Addison O, Fleming GJ. The influence of cement lute, thermocycling and surface

preparation on the strength of a porcelain laminate veneering material. Dent. Mater.

2004;20:286-92.

[25] Lin CL, Chang CH, Wang CH, Ko CC, Lee HE. Numerical investigation of the factors

effecting interfacial stresses in an MOD restored tooth by auto-meshed finite element

method. J. Oral Rehabil. 2001;28:517-25.

[26] Cattaneo PM, Dalstra M, Melsen B. The finite element method: a tool to study

orthodontic tooth movement. J. Dent. Res. 2005;84:428-33.

[27] Çiftçi Y, Canay S. Stress distribution on the metal framework of the implant-supported

fixed prosthesis using different veneering materials. Int. J. Prosthodont. 2000;14:406-

11.

[28] Stegaroiu R, Kusakari H, Nishiyama S, Miyakawa O. Influence of prosthesis material

on stress distribution in bone and implant: a 3-dimensional finite element analysis. Int.

J. Oral Maxillofac. Implants. 1998;13:781-90.


[29] Wang TM, Leu LJ, Wang J, Lin LD. Effects of prosthesis materials and prosthesis

splinting on peri-implant bone stress around implants in poor-quality bone: a numeric

analysis. Int. J. Oral Maxillofac. Implants. 2002;17:231-7.

[30] Sevimay M, Usumez A, Eskitascioglu G. The influence of various occlusal materials on

stresses transferred to implant-supported prostheses and supporting bone: a three-

dimensional finite-element study. J. Biomed. Mater. Res. B Appl. Biomater.

2005;73:140-7.

[31] Sicher H, Dubrul EL. Oral Anatomy. 8th ed., Ishiyaku Euroamerica, St Louis, 1988.

[32] Ko CC, Chu CS, Chung KH, Lee MC. Effects of posts on dentin stress distribution in

pulpless teeth. J. Prosthet. Dent. 1992;68:421-7.

[33] Atmaram GH, Mohammed H. Estimation of physiologic stresses with a natural tooth

considering fibrous PDL structure. J. Dent. Rest. 1981;60:873-7.

[34] Farah JW, Craig RG, Merqueh KA. Finite element analysis of a mandibular model. J.

Oral Rehabil. 1988;15:615-24.

[35] Tortopidis D, Lyons MF, Baxendale RH, GilmourWH. The variability of bite force

measurement between sessions in different positions within the dental arch. J. Oral

Rehabil. 1998;25:681-6.

[36] Williamson LJR, Fotos PG, Goel VK, Spivey JD, Rivera EM, Khera SC. A three-

dimensional finite-element stress analysis of an endodontically prepared maxillary

central incisor. J. Endodon. 1995;21:362-7.

[37] Found MS. Experimental techniques and design in composite materials. 4th ed., A.A.

Balkema Publishers, Lisse, 2002.

amilcar chagas freitas júnior , eduardo passos rocha

Documents