3D Printing and the Advent of Digital Dentistry
How often have we admired a bewitching smile and yearned for the same? The dental industry harnesses the fact that many a battle can be won with an enticing smile. With the advent of a fast life and flawed diet patterns, problems in dental hygiene loom large. But, with the advancements in dental sciences, owning a beautiful smile is no longer a distant dream.
Problems such as Gingivitis (gum disease) and tooth decay are major causes of tooth loss. Bridges, which are cemented to the teeth adjacent the gap, and dentures, which are like a detachable set of teeth, are common solutions to the problem of missing teeth. However their efficacy is limited in comparison to the use of dental implants.
Dental implants are titanium posts which are firmly fixed into the jaw bone and eventually fuse with the surrounding bone to give a completely natural experience. With these, patients wouldn’t have to chew awkwardly or constantly adjust a misaligned denture. Implants usually consist of three parts: The titanium fixture, an abutment and the visible crown. The titanium interfaces with the bone and serves as the root of the tooth. The abutment is the equivalent of the neck region of the tooth and simply serves the function of connecting the implant to the crown and finally the crown, is the pearly white portion that we show off to the world.
Structure of Dental Implants:
Dental implants are much like natural teeth; rooted in the jaw bone, strong, and fit in the mouth snug as they do. Unlike dentures, there is no hassle of removing them to cleanup. Creating a bridge between teeth requires the enamel from the adjacent teeth to be scraped off and sometimes may result in dental decay. On the contrary, other than the cost factor and the healing period associated with it, there isn’t much of a downside to dental implants.
With the burgeoning demand for dental implants, the industry is exploring different manufacturing processes. The traditional method of manufacturing begins with turning a Titanium rod to the required diameter, following which threads are cut on the external as well as internal surfaces using a specialized lathe. The external threads serve to hold the implant in place in the jaw bone while the internal threads mesh with the abutment. The so produced implant is anodized to increase porosity of the outer surfaces. Additional surface treatments are done to remove lubricants and other oil used during the manufacturing process and to make sterilize the implant. To produce the crown, an impression of the teeth is taken and a plaster mould is made. There are a couple of ways that we can proceed from here. One of the methods used is to machine Ceramic or Metal to obtain the required shape.
Additive Manufacturing/3D Printing is a highly advantageous alternative to the traditional method. It involves fusing layers, one on top of another, to produce the shape that is obtained from a CAD file. The CAD file is generated from Scanned data of the jaw impression made from the mould obtained from the dentist.
The software decomposes the component as a number of connected layers and generates something called GCODE that communicates to the machine to follow a particular path.
Some of the commonly used methods are:
An ultraviolet laser traces out layer by layer on a bed of photosensitive material. The material then forms polymer chains in the shape of each predetermined slice. An elevator raises the bed by the distance between consecutive layers. The result is a complete component. No finishing, no more working. Just an implant tailored to the need of the patient.
Polyjet / Multijet Printing:
The Polyjet/Multijet technology differs from Stereolithography in that it uses a binding fluid instead of a laser. It is very similar to inkjet printing, instead of spraying ink onto paper, PolyJet 3D Printers jet layers of curable liquid photopolymer onto a build tray.
Selective Laser Sintering (SLS):
Laser Sintering can be used with metals as well as thermoplastics. If used with metals, it is called Direct Metal Laser Sintering (DMLS) and in the case of thermoplastic powders, the term used is Selective Laser Sintering (SLS). Direct metal laser sintering is facilitated by a Ytterbium fiber laser and is used to fuse metals together to form components in an inert atmosphere. Being more dense, metals require a support material. The use of a secondary material becomes unnecessary in the case of SLS.
DMLS, is the process preferred for dental implants. The material of choice being Titanium has a property of fusing with bone which justifies its usage in implants. The particular property is called osseointegration. The titanium core of the implant and surrounding bone tissue has different Young’s modulus. This leads to stresses on the implant when they are loaded and affects fixation. If all the stress is taken by the implant called stress shielding which leads to bone resorption or even fretting . To compensate for the loss, a variable porosity is imparted to the implant, perpendicular to its long axis. Also compared to other metals, Titanium has a closer Young’s modulus compared to the bone. This further improves its integration with the bone. Bone cells migrate into pores interconnected by tunnel like structures to form an interlocked network. In traditionally manufactured implants a surface coating is used to enhance surface porosity. Additive manufacture obviates any such extra coating. The implants produced by these methods are given an increased surface porosity.
For producing the crown, usually an impression of the patients teeth is made and a mould is made with dental plaster. The model is then scanned and using CAD a 3D Model of the crown is generated such that it meshes with the adjoining tooth flawlessly.
The part is then 3D Printed in wax, and a silicone mould is made out of it. Using the mould we can get part produced in different materials of our choice. Alternatively the part can also directly be 3D printed in metal using DMLS and then finished.
If such technology was not used, this requires a highly skilled workforce, and it would only increase costs, now that’s not just a pain in your mouth but your pockets also.
3D printing also has several other advantages over traditional methods. If the implant is integrated to the abutment and printed as a single part, the risk of bacterial growth in crevices is highly reduced. The cost incurred by 3D printing implants is lower since it precludes the use of surface treatment. The implants are personalized to the need of the patient, are accurately shaped and compatible. The biological benefits include better diffusion of fluids and nutrients between the implant and tissue and consequently better healing and osseointegration.
The other advantage is that you had to use 5 axis machines for milling the metal parts to get complex geometries manufactured.
In light of its bounteous advantages, 3D printing is becoming a sought after option in the dental industry. By 2018, the dental implant and prosthetic market in the US is projected to reach $6.4 billion and the market for dental implants in Europe and the US is estimated to grow to $4.2 billion by 2022, according to AAID (American Academy of Implant Dentistry). Reports by Persistence Market Research predict a compound annual growth rate of 9.7% in the dental implant market from 2014 to 2020. South Korea, China and India are rapidly growing markets.
‘Dentcare’, Asia’s largest dental prostheses fabricator, for example, heavily uses additive manufacturing to meet the industry’s demands.
The popularity of implants has grown beyond the dental industry. Implants are being used in orthopaedics — complete hip replacements, elbow replacements, facial reconstruction (zygomatic implants), fixation of the spine and of tiny bones are being carried out using titanium implants which is opening up larger frontiers for the science of additive manufacturing. To give some perspective, the first titanium dental implant was placed by Brånemark in 1965, who was then, the Professor of Anatomy at Gothenburg University in Sweden. He has been cited many times as the Father of modern dental implants. We have come a long way since then, and the technology will only get better.
Special Thanks To:
- Shilpa Vijayakumar, Final Year Engineering Student who helped us write the article.
- Dr. Arvind Nagaraj, Postgraduate student (MDS).
- REALIZ3D Team.