Student Names and

number

: Omid Bafkar

Simon Crilley

Sina Haghiri

Siddhesh Shirpad Saraf

3511706

3395060

3410827

3498252

Subject Code : MANU2211 Assignment 2

Topic Max

Marks

Actual

Marks

Scope & relevance of the project and its significance to the

engineering profession

10

The way in which the project objectives are defined and

formulated

5

The extent and relevance of the investigation 5

The extent to which the techniques and concepts applied were

appropriate

5

The scope, depth and breadth of the project in the context of the

course requirement:

A clearly defined objective or research question

A thorough and comprehensive literature review

A sound methodology that is rigorous, clearly explained

and well documented

Sound conclusions that relate back to the objective or

research question

35

The rigour and thoroughness of the analysis 10

The extent to which the conclusions are justifiable, original and

significant

10

The quality of the presentation

Appearance

Report Cohesion

Communication of Knowledge and Ideas

Reference List

20

Totals 100

Date: 1/10/2014

Abstract

The modern developments in 3D scanning and additive manufacturing (AM) technologies

have made a breakthrough in dental implant designs. Customized root implants can be

produced to the patient’s requirements. These implants are integrated into place by exploiting

the porous structures made possible by additive manufacturing. These structures simulate the

behaviour of trabecular bone and allow bone in-growth. Presented work is the overall

procedure of making a dental root implant and crown assembly by using the 3D scanning and

printing. Dental root dimensions were extracted with respect to its stress-based performance,

stability and osseointegration nature of it, and were justified with several experimental and

finite element studies.

1. Introduction

1.1 Research aims and problems

The aim of this study was to evaluate the requirements and difficulties in producing

trabecular (lattice) metal structures in dental implants, identify optimum design specifications

and assess the availability of proper manufacturing processes to fabricate them. With respect

to the mentioned aspects, a two to one scale of the crown and the dental root implant

assembly was fully designed and fabricated.

1.2 Major milestones

Familiarizing with medical aspects of the task

Justifying design parameters based on respected scientific papers

Crown scanned STL file refinement

Creating trabecular metal structure CAD file

Changing STL format to solid part and vice versa

3D printing of STL file

2. Literature review

A dental root implant is an interface between the bone of the jaw and a dental prosthesis such

as a crown. The materials used should be capable of making a bond with the jawbone. The

dental root implant is executed in many steps including the soft tissue reflection, high speed

and low speed drilling, placement of the implant and tissue adaptation [1].

Figure 1 Scheme of implant-supported prosthesis: (a) drawing of lower jaw with implant-supported prosthesis (b)

transparent view of prosthesis; 1.prosthesis, 2.framework, 3.teeth, 4.oral implants, 5.jawbone, 6.soft tissue, 7.artificial

gums.[2]

The foundation for the present dental implants is a biologic procedure

called “osseointegration”, where biocompatible materials form an intimate bond to the bone

[3]. Modern implants consist of cylinder-shaped or tapered geometries with threads. The

osseointegration technique success is closely related to the bond between living bone and

surface of the artificial implant [4]. Therefore, along with the importance of biocompatible

material, the geometry of this implant root is of great importance. It can enhance the bonding

between implant and bone or affect the stress-based performance of the dental implant [4].

Added to this, it has been found that the surface topology affects osseointegration and a

micro-porous structure greatly aids the process by accelerating it. A micro-porous structure

creates a larger mechanical interlock between bone and implant [5].

Stainless steels, titanium and cobalt–chromium-based alloys have been approved and are

commonly used as implant materials. Less common is magnesium and its alloys, although

their use have increased [6]. Magnesium has inherent beneficial properties including superior

biocompatibility, biodegradability and a lower modulus of elasticity, more closely matched to

bone [7] than other mtallic biomaterials.

Tolochko et al. introduced the requirements of ideal modern root implants as follows in 2002:

ideal dental root shape, sufficient bone in-growth and enough mechanical strength [8]. These

three criteria are addressed, and design specifications are identified in the presented study.

Bone weakening or loss at peri-implant section has become the main factor in the failure of

dental implants, therefore the stress-based performance of the implants have become a

decisive factor in a proper design of the implants. Loading, implant material, geometry,

roughness, adjacent bone and bone-implant interface are important biomechanical factors

affecting stress and strain field. Diameter and length of the interface, along with thread’s

design are the main design parameters that can have major influence on load transfer [4].

Baggi et al. studied different dental implant designs using finite element methods. These

designs are presented in figure 2.

Figure 2 3D solid models of five commercial dental implants[4]

It was concluded that stress peaks are related to maximum implant diameter, where the stress

amount and distribution are mainly influenced by interface length. Moreover, optimum

implant diameter is crucial to achieving homogeneous stress distribution [4].

Figure 3 Von Mises stress contours on the cross-section at y = 0 for single-tooth commercial endosteal implants in molar

mandibular segment[4]

Table 1 geometrical parameters for implants in mm [4]

It was proposed that when diameter is increased, more homogeneous stress distribution and

less stress concentration is achieved at cancellous bone. Moreover, it also results in less stress

around cortical or compact bone. Cancellous is the spongy, weaker part of bone and the other

osseous tissue is cortical, or compact, bone.

Figure 4 various parts of a bone

Baggi et al. deduced that diameter is far more important than length for safe stress

distribution, suggesting overloading risk is greatest around implant neck [4].

Elias et al. studied the effect of shape, size and surface topographies of different implants on

their stability. The stability was evaluated based on factors like insertion torque and removal

torque. It was suggested that by increasing the diameter to 4.5mm, improvement in stability

can be achieved. Moreover, it was concluded that by using thicker and longer implants, low

quality and quantity of bone tissue might be compensated. It was also proposed that, even

though tapered implants have higher primary stability than straight implants, they introduce

higher stresses with respect to cylindrical implant of the same size. Implants were tested at

10mm, 13mm and 15mm lengths and more stability potential was shown by the longest

implant [9].

Mean time Elias et al. estimated that the effect of surface morphology is more significant than

implant shape [9]. Bone suffers more under shear than compressive or tensile forces; so

threaded implants are preferred to transform shear loads to more bearable axial forces for the

interface. The shape of the thread also plays a vital role to optimally reduce the shear force at

the interface [10].

Figure 5 V-thread, square thread, buttress thread and cylindrical (non-threaded) implants [10]

Square thread (either inside thread or outside thread) was suggested by Steigenga et al. as the

best choice to reduce amount of shear force. In this design a larger functional surface is

available when greater number of threads with larger depth are used [10]. This was also

proved to be correct by later studies and it was suggested that 0.60mm pitch gives the optimal

contact area and stress values [11].

Lee et al. recommended porous structure in dental root implants, since it can promote

immobilization of the implant by facilitating mechanical interlocking between implant and

bone, leading to faster osseointegration [12]. Porous metal structure is a connected network

of pores, and designed to enhance bone on-growth and in-growth. Its structure is similar to

cancellous bone [13]. It also has another advantage over solid implants. The classic implants

are typically much stiffer than human bone, for instance the module of elasticity of titanium

is between 80 to 130 GPa, but human bone only ranges from 0.1 to 30 GPa. This mismatch

leads to stress shielding and the implant loosening, resulting in eventual failure; however, the

strength and elasticity of porous structures conform better to the mechanical properties of

trabecular bones [14].

Figure 6 trabecular bone (left) and porous metal structure (right)

By taking into account Baggi’s, Elias’s, Steigenga’s and Lee’s works, a 4.5 mm diameter

cylindrical implant with 15mm length, porous structure in the middle for about 5 mm and

square threads with 0.6 mm pitch was designed. The upper body of the implant was extended

for 4 mm and tapered to further facilitate the assembly of the crown, Similar to classic design

shown in figure 7. The threads in the upper body and the lower body of the implant were

required due to the insertion torque and stability of the implant before complete

osseointegration.

Figure 7 extended upper body of the implant for crown assembly, classic design (right), proposed design (left)

Development of modern computer aided design (CAD), computer aided manufacturing

(CAM), implant material and, particularly the availability of commercialized additive

manufacturing (AM) machines makes the use of designs with porous structures possible.

Selective laser sintering (SLS), direct metal laser sintering (DMLS) and selective laser

melting (SLM) were the AM techniques that have been used successfully for production of

implants with porous metal structures [15]. AM is an advanced manufacturing technology in

which complex geometries are created by consolidating layers of material on top of each

other. In cases of SLS, SLM and DMLS the material is metal powder, which is consolidated

by the use of focused laser beam [2].

Even though additive manufacturing has the capability to produce far more complex

geometries in comparison with traditional manufacturing, the possibility of manufacturability

still depends on specific design guidelines. These guidelines relate to heat transfer, inclination

angle, minimum size or thickness and more, which usually result in the cost and time

consuming process of use of support materials [16, 17]. Even though circle has the most area

to facilitate the osseointegration, the elliptical holes were substituted, after the primary

design, in order to minimize the need for support structure.

3. Methodology

In order to achieve this goal the following steps were taken:

An actual replica of the tooth with one to two scale was scanned by 3D scanner

Figure 8 the tooth model to be scanned (left) and the 3D scanner (right)

The STL file was produced by using VXelement software.

Figure 9 Scanned tooth before refinement

The STL file was manipulated in order to modify its clashes and problems

Figure 10 Refinement of STL file in Geomagic

This task was done in Geomagic in the following steps:

Import the STL file into the magic

Orient the file by orientation optimizer

Using fix tab and fix wizard

Automatic fix

Smoothing feature

Scenes tab > machine library >selecting machine

Scene> new scene > select machine type

Generate support

Modifying file from support parameter page and selecting the support profile type

Save the support file and give it a name

Finally save the file with magic file format which is *.magics

An extensive literature review was performed and best viable dental root implant design

was identified

This task was done by reviewing more than 15 scientific papers from well-respected

journals like: Journal of the Mechanical Behaviour of Biomedical Materials, Journal of

Materials Design and Applications, Implant dentistry and Journal of Dental Sciences. In

this process the optimum design parameters were extracted, and justified. The major

challenge in this process was the medical nature of the task.

A CAD file of the dental root was created

The CAD file was built with Solidworks software, based on design specifications

extracted from the literature.

Bottom cylinder was designed through an extrusion of a circle

The top cylinder was created with the same procedure, followed by a conical

tapering

Threads were introduced. The spiral (helix) sketch was developed around the

cylinder, followed by sweep cut along it.

Fillets were added to the bottom and top surfaces

Through the design of a polygon sketch on the top surface of bottom cylinder,

and extruding it after make it a pattern the honeycomb or porous structure was

fabricated.

The holes were subtracted from the design in order to develop an optimum

design for bone in-growth.

A plane was made from the right view, on that plane an ellipse was created,

and was expanded with a linear pattern in the X-Z axes.

The ellipse sketch was extrude cut through the structure.

This process was repeated on Y-Z axes.

Figure 11 cross section of dental root implant with circle holes (left), elliptical holes in the 2nd design (right)

Even though additive manufacturing has the capability to produce far more complex

geometries in comparison with traditional manufacturing, the possibility of

manufacturability still depends on specific design guidelines. These guidelines relate

to heat transfer, inclination angle, minimum size or thickness and more, which usually

result in the cost and time consuming process of use of support materials [16, 17]

The STL file of the crown was transformed to a solid model.

This task was done by Solidworks in the following steps:

Geomagic-Capture plugin for Solidworks was downloaded to export

Geomagic file to Solidcworks

Mesh file was oriented by mesh tool

Coordinate system alignment

Repairing the intersected triangles, non-manifold edges, freestanding

triangles(noise), tunnels or double layered constructs, spike edges, spike

vertices

Extract freeform surface from regions

Knit surfaces into one

Thicken the surface to create a solid part

Figure 12 crown solid model made in Solidworks

The CAD model of the crown was modified and the root CAD file was deducted from

it to make the assembly possible

Figure 13 CAD model of crown, ready for assembly

Two solid models were assembled together

Figure 14Crown and root implant assembly (circle holes)

Two STL files were created for crown and root implant

The STL file could be directly exported from solidworks.

The last step, parts fabrication

4. Discussion

The optimum design parameters will vary, taking the characteristics and dimensions of the

patient’s jaw into account and may depend on the position of the root in mandibular or

maxillary bone sectors. Available room, damaged bone, proximity of another implant are all

factors that have to be considered before choosing the right implant. Each study showed that

creating as large as possible contact surface between bone and implant, has led to greater

success.

Even though many factors may affect the overall success rate and optimum design of the

implant, one thing is certain: trabecular metal structures have the potential to change the

future for bone implants, not only in dentistry. These structures aid the osseointegration that

has been found integral to successful implantations. Further development of additive

manufacturing techniques and the availability of specialized commercial 3D printing

machines, play vital roles in its future success, as 3D printing works well to create porous

structures; however, the optimum porous structure is not understood yet. Fast manufacturing

of customized dental root implant in a short amount of time may be a possible and affordable

option in a few years, through maturing additive manufacturing and 3D scanning

technologies. Specialized optimisation software for calculating the best possible root implant

design is still the missing piece of the puzzle.

5. Conclusion

An assembly of dental crown and dental root implant was fabricated by the use of 3D

scanning, computer aided design and additive manufacturing. The optimum design was made

in order to achieve the best root shape, bone in-growth and mechanical properties. This was a

cylindrical, threaded implant with as long a length and as wide a diameter as practicable, with

square threads. This was justified by previous studies on stress-based performance and

stability of implants. The potential of trabecular metal structure to revolutionise bone implant

was discussed and the role of modern additive manufacturing technologies and the ideal

candidates were introduced.

References

1. Parr, G.R., Tissue-integrated prostheses: Osseointegration in clinical dentistry: Per-Ingvar Branemark, MD, Ph. D., George A. Zarb, DSS, MS, FRCD (C), and Thomas Albrektsson, MD, Ph. D. Chicago, 1985, Quintessence Publishing Company, Inc. 350 pages, illustrated, indexed. Price $88.00. 1985, Mosby.

2. Kruth, J., et al., Digital manufacturing of biocompatible metal frameworks for complex dental prostheses by means of SLS/SLM. Virtual Prototyping and Rapid Manufacturing-Advanced research in virtual and Rapid Prototyping, Taylor & Francis, London, 2005: p. 139-146.

3. Brånemark, P.-I., et al., Intra-osseous anchorage of dental prostheses: I. experimental studies. Scandinavian Journal of Plastic and Reconstructive Surgery and Hand Surgery, 1969. 3(2): p. 81-100.

4. Baggi, L., et al., Stress-based performance evaluation of osseointegrated dental implants by finite-element simulation. Simulation Modelling Practice and Theory, 2008. 16(8): p. 971-987.

5. Çelen, S. and H. Özden, Laser-induced novel patterns: As smart strain actuators for new-age dental implant surfaces. Applied Surface Science, 2012. 263(0): p. 579-585.

6. Staiger, M.P., et al., Magnesium and its alloys as orthopedic biomaterials: A review. Biomaterials, 2006. 27(9): p. 1728-1734.

7. Savalani, M.M., C.C. Ng, and H.C. Man. Selective Laser Melting of Magnesium for Future Applications in Medicine. in Manufacturing Automation (ICMA), 2010 International Conference on. 2010.

8. Tolochko, N., et al., Dental root implants produced by the combined selective laser sintering/melting of titanium powders. Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials Design and Applications, 2002. 216(4): p. 267-270.

9. Elias, C.N., et al., Influence of implant shape, surface morphology, surgical technique and bone quality on the primary stability of dental implants. Journal of the Mechanical Behavior of Biomedical Materials, 2012. 16(0): p. 169-180.

10. Steigenga, J.T., et al., Dental implant design and its relationship to long-term implant success. Implant dentistry, 2003. 12(4): p. 306-317.

11. Lee, C.-C., et al., Effects of implant threads on the contact area and stress distribution of marginal bone. Journal of Dental Sciences, 2010. 5(3): p. 156-165.

12. Lee, W.H. and C.Y. Hyun, XPS study of porous dental implants fabricated by electro-discharge-sintering of spherical Ti–6Al–4V powders in a vacuum atmosphere. Applied Surface Science, 2006. 252(12): p. 4250-4256.

13. zimmer, http://www.zimmerdental.com/tm. 14. Hsu, H.-C., et al., Processing and mechanical properties of porous Ti–7.5Mo alloy. Materials &

Design, 2013. 47(0): p. 21-26. 15. Chen, J., et al., Design and manufacture of customized dental implants by using reverse

engineering and selective laser melting technology. The Journal of Prosthetic Dentistry, (0). 16. Leary, M., et al., Optimal topology for additive manufacture: A method for enabling additive

manufacture of support-free optimal structures. Materials & Design, 2014. 63(0): p. 678-690.

17. Strano, G., et al., A new approach to the design and optimisation of support structures in additive manufacturing. The International Journal of Advanced Manufacturing Technology, 2013. 66(9-12): p. 1247-1254.