Influence of implant-abutment angulations and crown material on stress distribution on central incisor: a 3D FEA

Mohamed I. El-Anwar Khairy E. AL-Azrag Mohamed H. Ghazy Lamia E. Dawood About the authors

Abstract

Aim:

To investigate the effect of implant-abutment angulation and crown material on stress distribution of central incisors. Finite element method was used to simulate the clinical situation of a maxillary right central incisor restored by two different implant-abutment angulations, 15° and 25°, using two different crown materials (IPS E-Max CAD and zirconia).

Methods:

Two 3D finite element models were specially prepared for this research simulating the abutment angulations. Commercial engineering CAD/CAM package was used to model crown, implant abutment complex and bone (cortical and spongy) in 3D. Linear static analysis was performed by applying a 178 N oblique load. The obtained results were compared with former experimental results.

Results:

Implant Von Mises stress level was negligibly changed with increasing abutment angulation. The abutment with higher angulation is mechanically weaker and expected to fail at lower loading in comparison with the steeper one. Similarly, screw used with abutment angulation of 25° will fail at lower (about one-third) load value the failure load of similar screw used with abutment angulated by 15°.

Conclusions:

Bone (cortical and spongy) is insensitive to crown material. Increasing abutment angulation from 15° to 25°, increases stress on cortical bone by about 20% and reduces it by about 12% on spongy bone. Crown fracture resistance is dramatically reduced by increasing abutment angulation. Zirconia crown showed better performance than E-Max one.

Keywords:
finite element analysis; dental implant-abutment design; incisor; materials

Introduction

Dental implant restoration has been widely accepted as one of the treatment modalities to replace missing teeth and restore human masticatory function. The biomechanical properties of the bone-implant interface determine the implant stability. The bone-implant interface properties depend on amount of implant surface in contact with mineralized bone tissue and bone tissue quality around the interface11. Mathieu V, Vayron R, Richard G, Lambert G, Naili S, Meningaud J, et al. Biomechanical determinants of the stability of dental implants: Influence of the bone-implant interface properties. J Biomech. 2014; 47: 3-13.. The interface has a complex biomechanical nature due to (i) its roughness, (ii) the fact that bone is in partial contact with the implant, (iii) adhesion phenomena between bone and the implant and (iv) the time-evolving nature of the interface properties. Therefore, remodeling phenomena of bone tissue around the interface are difficult and highly complicated.

A single tooth implant with crown has greater survival rate than a fixed partial denture (FPD)22. Misch CE. Contemporary implant dentistry. 3rd ed. Saint Louis: Mosby Elsevier; 2008.. The abutment angulation is a mechanical variable in implantology33. Bidez MW, Misch CE. Force transfer in implant dentistry: Basic concepts and principles. J Oral Implantol. 1992; 18: 264-74. that may influence the internal and external structure of bone tissue33. Bidez MW, Misch CE. Force transfer in implant dentistry: Basic concepts and principles. J Oral Implantol. 1992; 18: 264-74.. Thus, the bone behavior is related to the stress and deformation induced on it. The influence of angled abutments on stress is a matter of debate44. Hasan I, Roger B, Heinemann F, Keilig L, Bourauel C. Influence of abutment design on the success of immediately loaded dental implants: Experimental and numerical studies. Med Eng Phys. 2012; 34: 817-25.. It has been widely accepted that increased stress on implants and bone has been associated with the use of angled abutments55. Cavallaro J, Greenstein G. Angled implant abutments: A practical application of available knowledge. J Am Dent Assoc. 2011; 142: 150-8..

The dental implants design is driven by an imitator marketing approach rather than by scientific advances11. Mathieu V, Vayron R, Richard G, Lambert G, Naili S, Meningaud J, et al. Biomechanical determinants of the stability of dental implants: Influence of the bone-implant interface properties. J Biomech. 2014; 47: 3-13.. Clinicians used implants in new applications before research was carried out based on their basic science. Empirical approaches may have some advantages but remain limited when it comes to understand the interaction of the various mechanisms, playing a role in bone healing around an implant11. Mathieu V, Vayron R, Richard G, Lambert G, Naili S, Meningaud J, et al. Biomechanical determinants of the stability of dental implants: Influence of the bone-implant interface properties. J Biomech. 2014; 47: 3-13..

IPS E-max lithium disilicate glass ceramic, a material that provides optimum esthetics, yet has the strength to enable conventional or adhesive cementation. It has a needle-like crystal structure that offers excellent high flexural strength, roughly 360 to 400 MPa and durability, as well as outstanding optical properties. It can be traditionally pressed or contemporarily processed via CAD/CAM technology. Due to its strength and versatility, the material can be utilized for anterior/posterior crowns, inlays/onlays, veneers, thin veneers, telescopic crowns, implant restorations and anterior three units bridgework up to the second premolar (press only)66. Ivoclar Vivadent. IPS e.max lithium disilicate: The future of all ceramic dentistry material science, Practical Applications, keys to success. Mississauga, Ontario: Ivoclar Vivadent. 2009; 2:1-15..

Yttrium-stabilized tetragonal zirconia (Y-TZP) is having increased use in dentistry due to its good mechanical properties. It is currently used as a core material in all-ceramic dental restorations and implant superstructures77. Derand T, Molin M, Kvam K. Bond strength of composite luting cement to zirconia ceramic surfaces. Dent Mater. 2005; 21: 1158-62.. Compared to other dental ceramics, its superior mechanical properties, such as higher strength and fracture toughness, are due to the transformation toughening mechanism, similar to that observed in quenched steel88. Luthardt RG, Sandkuhl O, Reitz B. Zirconia- TZP and alumina-advanced technologies for manufacturing of single crowns. Eur J Prosthodont Restor Dent. 1999; 7: 113-9..

Finite element analysis (FEA) is an accepted and accurate numerical technique used for solving complicated stress analysis problems. It has proven to be a reliable method in dentistry as it provides reliable evaluation of stresses in complex geometries99. El-Anwar MI, Tamam RA, Fawzy UM, Yousief SA. The effect of luting cement type and thickness on stress distribution in upper premolar implant restored with metal ceramic crowns. Tanta Dent J. 2015; 12: 48-55..

In this study, the influence of implant-abutment angulation (15° and 25°) supporting different central incisor crown material on stress distribution was estimated.

Material and methods

Implant fixture (Hexacone HC2 3.7 13 mm) and two abutments (TLA15 HC1, and TLA25 HC1; Dr. Ihde Dental GmbH, Eching, Germany), were modeled using commercial CAD/CAM "AutoDesk Inventor" software version 8.0 (Autodesk Inc., San Rafael, CA, USA). Bone geometry was simplified and simulated as two co-axial cylinders. The inner one represents the spongy bone (14 mm diameter x 22 mm high) filling the internal space of the outer cylinder (1 mm thick shell) that represents cortical bone (16 mm diameter x 24 mm high)1010. El-Anwar MI, El-Mofty MS, Awad AH, El-Sheikh SA, El-Zawahry MM. The effect of using different crown and implant materials on bone stress distribution: a finite element study. Egypt J Oral Maxillofac Surg. 2014; 5: 58-64.-1111. El-Anwar MI, El-Zawahry MM, El-Mofty MS. Load transfer on dental implants and surrounding bones. Aust J Basic Appl Sci. 2012; 6: 551-60.. The crown dimensions were obtained from the anatomical data1212. Nelson SJ, Ash MM. Wheeler's dental anatomy, physiology, and occlusion. 9th ed. Saunders: Elsevier; 2010. of the maxillary right central incisor. The cement layer was designed with a 50 μm thickness.

The geometric models were exported from the CAD/CAM software as several components (SAT and IGES files) to be assembled together in ANSYS version 14.5 environment (ANSYS Inc., Canonsburg, PA, USA). A set of Boolean operations was performed to obtain two FE models, for 15° and 25° abutment angulations.

Element type "Solid 186" (higher order 20 node) was utilized for meshing the model's components, as it has three degrees of freedom (translations in the global directions X, Y and Z).

Complete osseointegration was assumed. In addition isotropic, homogenous, and linearly elastic materials' properties were fed into the finite element (FE) software based on previous studies99. El-Anwar MI, Tamam RA, Fawzy UM, Yousief SA. The effect of luting cement type and thickness on stress distribution in upper premolar implant restored with metal ceramic crowns. Tanta Dent J. 2015; 12: 48-55.

10. El-Anwar MI, El-Mofty MS, Awad AH, El-Sheikh SA, El-Zawahry MM. The effect of using different crown and implant materials on bone stress distribution: a finite element study. Egypt J Oral Maxillofac Surg. 2014; 5: 58-64.
-1111. El-Anwar MI, El-Zawahry MM, El-Mofty MS. Load transfer on dental implants and surrounding bones. Aust J Basic Appl Sci. 2012; 6: 551-60.,1313. AL-Azrag KE. Influence of implant abutment angulations on fracture resistance and stress analysis of different all-ceramic restoration [master's thesis]. Mansoura: Faculty of Dentistry, University of Mansoura, Egypt; 2015. and manufacturer's information (Table 1).

Meshing density was then evaluated and adequate mesh of the models' components was used in the analysis. The number of nodes and elements in each component are in Table 2. Figures 1 and 2a illustrate models' components on ANSYS screen.

Fig. 1:
Modeled and meshed components (implant, screw, GP, abutment, cement layer, crown) screen shots from Inventor / ANSYS screens

Fig. 2:
(a) complete meshed model (b) schematic for load direction

Load of 178 N1414. Helkimo E, Carlsson GE, Hclkimo M. Bite force and state of dentition. Acta Odontol Scand. 1977; 35: 297-303. was applied on each model on the palatal surface of the maxillary right central incisor at oblique directions 45° to the long axis of the implant fixture (Figure 2b)1515. AL-Azrag KI, Ghazy MH, El-Anwar MI, Dawood LE. Influence of implant abutment angulations on fracture resistance and stress analysis of different all-ceramic restoration. Mansoura J Dent. 2014;1:94-9.. The boundary conditions were defined by fixing the lower surface of the cylinder representing cortical bone. Additionally, the implant fixture, abutment, screw, cement-layer, gutta-percha, crown, cortical and spongy bone were assumed to be perfectly bonded together1616. Carvalho MA, Sotto-Maior BS, Del Bel Cury AA, Pessanha Henriques GE. Effect of platform connection and abutment material on stress distribution in single anterior implant-supported restorations: A nonlinear 3-dimensional finite element analysis. J Prosthet Dent. 2014; 112: 1096-102..

The finite element models were verified against previous experimental studies1313. AL-Azrag KE. Influence of implant abutment angulations on fracture resistance and stress analysis of different all-ceramic restoration [master's thesis]. Mansoura: Faculty of Dentistry, University of Mansoura, Egypt; 2015.,1515. AL-Azrag KI, Ghazy MH, El-Anwar MI, Dawood LE. Influence of implant abutment angulations on fracture resistance and stress analysis of different all-ceramic restoration. Mansoura J Dent. 2014;1:94-9., where two groups each of 14 implant-abutment complexes (angled 15° and 25°) were gradually loaded up to failure in a universal testing machine. The FEA results showed very good agreement with experiments' results.

Results

The Von Mises stress distributions and their maximum values were discussed in details. Figure 3 illustrates the increase of maximum value of Von Mises stress with increasing abutment angulation from 15° to 25° on cortical bone, and the stress distribution did not change. On the other hand, spongy bone Von Mises stress distribution with different abutment angulation is in Figure 4, where the spongy bone showed lower values with increasing abutment angulation. Contrarily, crown material change did not affect bone stress.

Fig. 3:
Cortical bone Von Mises stress distribution comparison between (a) 15°, (b) 25° angulated abutment under Zirconia crown

Fig. 4:
Spongy bone Von Mises stress distribution comparison between (a) 15°, (b) 25° angulated abutment under IPS E-Max CAD crown.

From mechanical point of view, the lower-angulated abutment was expected to survive against more loading than the higher-angulated ones. Increasing abutment angulation increases the abutment Von Mises stress and may change its distribution. As indicated in Figure 5, the 15° angulated abutment stress level is about 25% less than the one of the 25 angulated one. Similarly, screw behavior with different abutment angulations indicated higher stress values under the screw head for 25° angulated abutment (Figure 6), which may fail by its head removal, and/or screw bent with load (in the same direction).

Fig. 5:
Abutment Von Mises stress distribution comparison between (a) 15°, (b) 25° angulated abutment under Zirconia crown.

Fig. 6:
Screw Von Mises stress distribution comparison between (a) 15°, (b) 25° angulated abutment under Zirconia crown.

Figure 7, illustrates that the cement layer will suffer more with 15° abutment angulation, about double the Von Mises stress, in comparison with 25° abutment angulation. The location of maximum Von Mises stress was expected to be at the finish line with 15° abutment angulation, and at abutment step with 25° abutment angulation (as crown will tend to slide inward from its original position).

Fig. 7:
Cement layer Von Mises stress distribution comparison between (a) 15°, (b) 25° angulated abutment under IPS E-Max CAD crown.

Comparing the different crown materials investigated in this study, as shown in Figure 8, the place of maximum Von Mises stress of indicated expected crown failure as two similar parts with using vertical cutting plane. Finally, Table 3 compares maximum values of Von Mises stress exerted on all components on the studied models.

Fig.8:
Von Mises stress distribution on different crown materials (a) IPS emax CAD, (b) Zirconia supported by 15° abutment.

Discussion

Nowadays the advantages of monolithic zirconia restorations with an increased mechanical stability made them possible to expand their clinical indications1717. Beuer F, Stimmelmayr M, Gueth JF, Edelhoff D, Naumann M. In vitro performance of full-contour zirconia single crowns. Dent Mater. 2012; 28: 449-56.. Many dentists and patients choose zirconia for its advantages, like high strength similar to metals, high biocompatibility, similar color and translucency to natural teeth and low risk of inflammation due to an unlikely dental plaque in accumulation. In a recent clinical report1818. Marchack BW, Sato S, Marchack CB, White SN. Complete and partial contour zirconia designs for crowns and fixed dental prostheses: a clinical report. J Prosthet Dent. 2011; 106: 145-52., elimination of veneered porcelain on posterior zirconia crowns and fixed dental prostheses was performed for a clinical trial and presented an acceptable esthetic result.

In this study, zirconia crowns showed better performance than the E-Max due to their high rigidity. Thus, better load transfer pattern was expected on the following parts, in comparison with less rigid material (IPS E-Max CAD).

The obtained results in this research matched previous studies' findings, that using low rigidity crown material reduces the stresses generated on the jaw bone (cortical and spongy), that it absorbs more energy from the applied load and transfers less energy to implant-abutment complex and bone1010. El-Anwar MI, El-Mofty MS, Awad AH, El-Sheikh SA, El-Zawahry MM. The effect of using different crown and implant materials on bone stress distribution: a finite element study. Egypt J Oral Maxillofac Surg. 2014; 5: 58-64.. In addition, this finding was proven experimentally1313. AL-Azrag KE. Influence of implant abutment angulations on fracture resistance and stress analysis of different all-ceramic restoration [master's thesis]. Mansoura: Faculty of Dentistry, University of Mansoura, Egypt; 2015., that all zirconia crowns did not fail under 178 N oblique load. Failure occurred in screws supporting angulated abutments whatever the abutment angulation (15° or 25°). About 50% of E-Max crowns failed under load and the other failures occurred in screw.

In other words, regardless the crown material, the increased abutment angulation resulted in increasing the lateral stresses exerted on the whole assembly rather than the apical stresses. Lateral stress increases may affect the screw of the abutment, as it represents the weakest component of the whole assembly. These results were in full agreement with those found by Ellakwa et al.1919. Ellakwa A, Raj T, Deeb S, Ronaghi G, Martin FE, Klineberg I. Influence of implant abutment angulations on the fracture resistance of overlaying CAM-milled zirconia single crowns. Aust Dent J. 2011; 56:132-40. as their results assessed the effect of three implant abutment angulations and three core thicknesses on the fracture resistance of overlaying CAM milled zirconia, and found that the 30° implant abutment angulation significantly reduced the fracture resistance of the overlaying CAM milled zirconia single crowns.

In addition, the cervical areas are the most critical on the abutments due to the force concentration that may be a reason for failures, i.e. increasing the abutment angulation had a negative influence on the fracture load.

Former experimental studies1313. AL-Azrag KE. Influence of implant abutment angulations on fracture resistance and stress analysis of different all-ceramic restoration [master's thesis]. Mansoura: Faculty of Dentistry, University of Mansoura, Egypt; 2015.,1515. AL-Azrag KI, Ghazy MH, El-Anwar MI, Dawood LE. Influence of implant abutment angulations on fracture resistance and stress analysis of different all-ceramic restoration. Mansoura J Dent. 2014;1:94-9. showed different modes of failure for the 15° and 25° implant abutment angulations with IPS E-max CAD crowns. About half the specimens had screw fracture and the other half had crown fracture. This was assigned to the fact that the flexural strength of IPS E-Max CAD crown (460 MPa) is near to that of titanium screw (500 MPa). On the other hand, zirconia crowns have flexural strength of 900-1400 MPa, which is superior to the titanium screw.

The fractures in the ceramic crowns typically occurred at the cervical portion of the abutment and at the screw. According to previous studies2020. Kerstein RB, Radke J. A comparison of fabrication precision and mechanical reliability of two zirconia implant abutments. Int J Oral Maxillofac Implants. 2008; 23: 1029-36.

21. Adatia ND, Bayne SC, Cooper LF. Fracture resistance of yttria-stabilized zirconia dental implant abutments. J Prosthodont. 2009; 18: 17-22.
-2222. Nothdurft FP, Doppler KE, Erdelt KJ, Knauber AW, Pospiech PR. Fracture behavior of straight or angulated zirconia implant abutments supporting anterior single crowns. Clin Oral Invest. 2011; 15: 157-63., these abutment areas have the highest stress concentrations due to levering effects.

Using angulated abutments with different types of restorative materials to construct the overlaying crowns are significant factors in determining the amount and distribution of stresses loaded onto the superstructure and implant under functional forces2323. Brunski JB. Biomechanics of oral implants: future research directions. J Dent Educ. 1988; 52: 775-87..

Most FE models in dental researches99. El-Anwar MI, Tamam RA, Fawzy UM, Yousief SA. The effect of luting cement type and thickness on stress distribution in upper premolar implant restored with metal ceramic crowns. Tanta Dent J. 2015; 12: 48-55.-1010. El-Anwar MI, El-Mofty MS, Awad AH, El-Sheikh SA, El-Zawahry MM. The effect of using different crown and implant materials on bone stress distribution: a finite element study. Egypt J Oral Maxillofac Surg. 2014; 5: 58-64.,2424. Deepa RH, Surendra Kumar GP, Satish Babu CL, Shetty S, Jnandev KR, Rohit P, et al. Influence of occlusal forces on stress distribution on preloaded dental implant abutment screw: A finite element analysis. Int J Oral Implant Clin Res. 2013; 4: 16-23. assumed perfect bond between assembled model components to simulate natural condition, in addition to assuming linear, static and isotropic material properties.

The film thickness of the resin cement might significantly affect the short- and long-term bond strengths. It was reported that greater resin cement film thickness (100 ìm vs. 50 ìm) resulted in lower bond strength of resin materials to lithium disilicate ceramics1313. AL-Azrag KE. Influence of implant abutment angulations on fracture resistance and stress analysis of different all-ceramic restoration [master's thesis]. Mansoura: Faculty of Dentistry, University of Mansoura, Egypt; 2015.. Another study2525. Gehrke P, Dhom G, Brunner J, Wolf D, Degidi M, Piattelli A. Zirconium implant abutments: fracture strength and influence of cyclic loading on retaining-screw loosening. Quintessence Int. 2006; 37: 19-26. showed that the zirconia bond strengths were significantly reduced with thicker (100 ìm) resin cement layer. Thus, in this study the film thickness was considered to be 50 μm.

Finally, the results of this study were in agreement with literature33. Bidez MW, Misch CE. Force transfer in implant dentistry: Basic concepts and principles. J Oral Implantol. 1992; 18: 264-74. when abutments with 0, 15°, and 25° angulations were evaluated in the maxilla by 3D FEM. That concluded to the superiority of abutments with less-angulation than 25°, which increased stresses on the peri-implant region and demonstrated higher stress concentration on the opposite side of loading with angulated abutments.

Within the limitations of this study, the following conclusions can be drawn:

  1. 1- Implant Von Mises stress level was negligibly changed with increased abutment angulation, which indicated good implant-abutment complex design.

  2. 2- Abutment with higher angulation is mechanically weaker and is expected to fail at lower load level in comparison with steeper one.

  3. 3- Screw used with abutment angulation of 25° will fail at lower (about one-third) of the failure load of similar screw used with abutment angulated by 15°.

  4. 4- Cement layer placed above the 15° angulated-abutment will fail at lower load than that one placed on the 25° angulated-abutment, as it rests on smaller area of abutment lowest surface.

  5. 5- Bone (cortical and spongy) is insensitive to crown material. Increasing abutment angulation from 15° to 25°, increased stress on cortical bone by about 20%, and reduced it by about 12% on spongy bone.

  6. 6- More rigid crown material (zirconia), showed better distribution of load on the following parts, in comparison with less rigid material (IPS E-Max CAD).

References

  • 1
    Mathieu V, Vayron R, Richard G, Lambert G, Naili S, Meningaud J, et al. Biomechanical determinants of the stability of dental implants: Influence of the bone-implant interface properties. J Biomech. 2014; 47: 3-13.
  • 2
    Misch CE. Contemporary implant dentistry. 3rd ed. Saint Louis: Mosby Elsevier; 2008.
  • 3
    Bidez MW, Misch CE. Force transfer in implant dentistry: Basic concepts and principles. J Oral Implantol. 1992; 18: 264-74.
  • 4
    Hasan I, Roger B, Heinemann F, Keilig L, Bourauel C. Influence of abutment design on the success of immediately loaded dental implants: Experimental and numerical studies. Med Eng Phys. 2012; 34: 817-25.
  • 5
    Cavallaro J, Greenstein G. Angled implant abutments: A practical application of available knowledge. J Am Dent Assoc. 2011; 142: 150-8.
  • 6
    Ivoclar Vivadent. IPS e.max lithium disilicate: The future of all ceramic dentistry material science, Practical Applications, keys to success. Mississauga, Ontario: Ivoclar Vivadent. 2009; 2:1-15.
  • 7
    Derand T, Molin M, Kvam K. Bond strength of composite luting cement to zirconia ceramic surfaces. Dent Mater. 2005; 21: 1158-62.
  • 8
    Luthardt RG, Sandkuhl O, Reitz B. Zirconia- TZP and alumina-advanced technologies for manufacturing of single crowns. Eur J Prosthodont Restor Dent. 1999; 7: 113-9.
  • 9
    El-Anwar MI, Tamam RA, Fawzy UM, Yousief SA. The effect of luting cement type and thickness on stress distribution in upper premolar implant restored with metal ceramic crowns. Tanta Dent J. 2015; 12: 48-55.
  • 10
    El-Anwar MI, El-Mofty MS, Awad AH, El-Sheikh SA, El-Zawahry MM. The effect of using different crown and implant materials on bone stress distribution: a finite element study. Egypt J Oral Maxillofac Surg. 2014; 5: 58-64.
  • 11
    El-Anwar MI, El-Zawahry MM, El-Mofty MS. Load transfer on dental implants and surrounding bones. Aust J Basic Appl Sci. 2012; 6: 551-60.
  • 12
    Nelson SJ, Ash MM. Wheeler's dental anatomy, physiology, and occlusion. 9th ed. Saunders: Elsevier; 2010.
  • 13
    AL-Azrag KE. Influence of implant abutment angulations on fracture resistance and stress analysis of different all-ceramic restoration [master's thesis]. Mansoura: Faculty of Dentistry, University of Mansoura, Egypt; 2015.
  • 14
    Helkimo E, Carlsson GE, Hclkimo M. Bite force and state of dentition. Acta Odontol Scand. 1977; 35: 297-303.
  • 15
    AL-Azrag KI, Ghazy MH, El-Anwar MI, Dawood LE. Influence of implant abutment angulations on fracture resistance and stress analysis of different all-ceramic restoration. Mansoura J Dent. 2014;1:94-9.
  • 16
    Carvalho MA, Sotto-Maior BS, Del Bel Cury AA, Pessanha Henriques GE. Effect of platform connection and abutment material on stress distribution in single anterior implant-supported restorations: A nonlinear 3-dimensional finite element analysis. J Prosthet Dent. 2014; 112: 1096-102.
  • 17
    Beuer F, Stimmelmayr M, Gueth JF, Edelhoff D, Naumann M. In vitro performance of full-contour zirconia single crowns. Dent Mater. 2012; 28: 449-56.
  • 18
    Marchack BW, Sato S, Marchack CB, White SN. Complete and partial contour zirconia designs for crowns and fixed dental prostheses: a clinical report. J Prosthet Dent. 2011; 106: 145-52.
  • 19
    Ellakwa A, Raj T, Deeb S, Ronaghi G, Martin FE, Klineberg I. Influence of implant abutment angulations on the fracture resistance of overlaying CAM-milled zirconia single crowns. Aust Dent J. 2011; 56:132-40.
  • 20
    Kerstein RB, Radke J. A comparison of fabrication precision and mechanical reliability of two zirconia implant abutments. Int J Oral Maxillofac Implants. 2008; 23: 1029-36.
  • 21
    Adatia ND, Bayne SC, Cooper LF. Fracture resistance of yttria-stabilized zirconia dental implant abutments. J Prosthodont. 2009; 18: 17-22.
  • 22
    Nothdurft FP, Doppler KE, Erdelt KJ, Knauber AW, Pospiech PR. Fracture behavior of straight or angulated zirconia implant abutments supporting anterior single crowns. Clin Oral Invest. 2011; 15: 157-63.
  • 23
    Brunski JB. Biomechanics of oral implants: future research directions. J Dent Educ. 1988; 52: 775-87.
  • 24
    Deepa RH, Surendra Kumar GP, Satish Babu CL, Shetty S, Jnandev KR, Rohit P, et al. Influence of occlusal forces on stress distribution on preloaded dental implant abutment screw: A finite element analysis. Int J Oral Implant Clin Res. 2013; 4: 16-23.
  • 25
    Gehrke P, Dhom G, Brunner J, Wolf D, Degidi M, Piattelli A. Zirconium implant abutments: fracture strength and influence of cyclic loading on retaining-screw loosening. Quintessence Int. 2006; 37: 19-26.

Publication Dates

  • Publication in this collection
    Oct-Dec 2015

History

  • Received
    15 Nov 2015
  • Accepted
    13 Dec 2015
Faculdade de Odontologia de Piracicaba - UNICAMP Avenida Limeira, 901, 13414-903 - Piracicaba - SP, Tel.: 55 19 2106 5706, Fax: 55 19 2106 5218 - Piracicaba - SP - Brazil
E-mail: brjorals@fop.unicamp.br