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3D Printing - An Advancing Forefront in Imprinting the Inner Dimensions of Tooth with Precision
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This article was originally published by Informatics Publishing and was migrated to Scientific Scholar after the change of Publisher.
Abstract
3D printing is rooting itself as a promising digital technology in the field of dentistry. Emergence of this recent advanced digital science has opened up new perspectives for design and production of 3D models quickly and automatically. The concept of utilizing this technology is to improvise the standards of the treatment provided to the patients, due to more precision and less technique sensitive outcomes. It works on the concept of additive manufacturing, which has its advantages in contrast to the subtractive manufacturing process. It is important to have knowledge about the different 3D printing modalities available as it is not only an upcoming technology in dentistry but also one which is emerging with myriad applications which offer better predictable results in areas of preoperative diagnostic planning, clinical handling and follow up. This article provides an overview on the method and applications of 3D printing with focus primarily in the field of Operative Dentistry and Endodontics.
Keywords
3D (Dimensional) Printing
CAD (Computer Aided Design)
Guided Endodontics
Rapid Prototyping
1. Introduction
The dental profession has experienced an enormous technological growth during the past few years. 3D printing is paving its way as an emerging technology with a wide range of applications and vast opportunities in the dental field and is expected to grow exponentially in the next few years. Digitalization through 3D printing is a remarkable advancement in the field of dentistry that facilitates to provide treatment that is customized to an individual patient. Thus this technology ensures precision in terms of quality and quantity making it preferable in this modern era.
3D printing is a method which uses 3 dimensional CAD data sets for producing 3D physical models1. Also referred to as “additive manufacturing” it is the method of fabricating materials of choice namely, metal/polymer/resins, in incremental or serial layers using CAD/CAM (Computer Aided Design/Computer Aided Manufacturing) digital scans for the dual purpose of designing a product and for controlling the manufacturing process. Based on the production method used it can be mentioned to as rapid prototyping, solid free form, computer automated or layered manufacturing1.
The procedure involves giving input to the computer through 3D CAD data which materializes the design by additive deposition of the material of choice to give final shape to the desired model. The first ever use of 3D printing in dentistry was in 19992.
3D printing having its application in aerospace, art and design, is now becoming a subject of great interest in medical and dental fields as well3. In particular the medical field utilizes 3D printing for surgical planning, prosthetics and generation of graspable 3D objects2.
It is also used for reconstruction of complex organs with intricate 3D microstructure, restoration of 3D anatomic defects in craniomaxillofacial complex caused by pathoses such as cancer, trauma or congenital defects4.
2. What are the Benefits of 3D Printing?
A few of the recent software programs enable designing of a restoration/study model or guided template which is then subsequently printed in the material chosen based on the area of application. These 3D objects enable clinicians to study through reconstruction, the patient’s jaw or tooth morphology on the table top. This enables efficient case analysis, preoperative planning, guided operative procedures and facilitates productive preclinical training methods. Anything that can be manufactured through dental laboratory can be done digitally, potentially and more consistently at a reduced cost and time.
3. Role of 3D Printing Technology in Dentistry
Its variant applications in dentistry include: Fabrication of 3D printed restorations, composite and ceramic esthetic inlays and onlays, guided Endodontic interventions, invisalign Orthodontic braces, Orthodontic surgical case evaluation and handling, crown and denture prosthesis, customized myofunctional appliances and customized facial and dental implants. A second revolution can be experienced in dental device manufacturing when layered fabrication techniques reach the point of being able to produce a high quality dental prosthesis5.
4. What are the Methods of 3D Printing?
The various 3D printing processes currently available are4,6 :
Stereolithography.
Fused deposition modelling.
Selective laser sintering.
Photopolymer jetting.
Powder binder printer.
3D plotting or direct writes bioprinting.
4.1 Stereolithography
Stereolithography is a form of additive manufacturing that converts liquid material into solid parts, layer by layer by curing them using a light source through photopolymerization. The materials used must be photo curable to initiate the photo cross linking. These include acrylics, epoxies, fabrication of titanium dental implants etc2,4.
4.2 Fused Deposition Modeling
It utilizes thermoplastic materials which are deposited in molten form. The basic structure of the machine included the presence of nozzles through which the material is deposited in layer by layer after which the layers are fused together4,6.
FDM (Fused Deposition Modeling) uses biocompatible polymers, bioactive glass composites7, PMMA Poly (Methyl Methacrylate)8. Its applications include bone tissue engineering9, craniofacial defects8,10 etc.
4.3 Selective Laser Sintering
Scanning laser sinters metal powder layer by layer in cold built chambers as build platform descends. The variety of materials used is titanium, cobalt chrome, stainless steel. It has its applications in areas which require high fracture toughness and mechanical strength which includes manufacturing metallic implants that facilitate bone ingrowths and regeneration2,4.
4.4 Photopolymer Jetting
This utilizes light cure resin materials which are laid on a stationary platform and has dynamic print head which cures the materials. The materials that can be printed are resins, waxes for casting and silicon rubber material. Applications include implant drill guides and manufacture of indirect orthodontic bracket splints2.
4.5 Powder Binder Printers
It is form of modified ink jet head which is used for printing. It utilizes liquid droplets which is usually water used to print onto powder commonly done for plaster of Paris. It is built by incremental process2.
4.6 3D Plotting/Direct Write Bioprinting
It is used to create soft tissue scaffolds, 3 Dimensional ceramics, polymers, hydrogels4,11. This does not involve the use of thermoplastics and can be operated at room temperature. Materials that can be used are alginate, fibrin, collagen, PLGA Poly (Lactic Co-Glycolic Acid) and TCP (Tri Calcium Phosphate)4,12.
5. Applications in Operative Dentistry and Endodontics
Digital technology and 3D printing have significantly elevated the rate of success and improvised the quality and precision of dental operative work13.
In addition, for the dentist, it will affect clinical practice on how quickly and efficiently one will be able to operate; for the dental lab support team, it will affect the marketing strategy to clients and for the patient it will affect which dentist he chooses - the one who has adopted this new technology that allows for more comfortable diagnosis and faster results or one who still uses more traditional methods.
5.1 3D Printing as an Effective Tool in Reconstruction of 3D Models
With the advent of 3D printing in dentistry one can take a 3D image of the teeth and upload to a computer software program which can be accessed and the desirable model can be adjusted or altered as per the needed requirement and can be printed within a couple of hours. This model can be held by hand as a hard copy replicate of the area of interest for superior observation.
5.2 3D Printing as an Effective Denovo Method in Preclinical Training
Bench practice of instrumentation with various printed teeth would help the student discover and improve clinical skills in contrast to the current use of extracted teeth used for learning purposes. Due to the limited availability of the extracted teeth, multiple model tooth copies can be printed from any selected micro CT (Computed Tomography) scan for use among the dentists and dental trainees as well. Also the use of these 3D printed tooth models can help to recreate conditions that mimic pulp stones, internal and external root resorptive defects, dens –in-dente and many more anomalies which will help them visualize, improvise and advance in the science and art of Endodontics14.
One important application of 3D printing in dentistry is creating digital scans of full or partial arches into durable plastic model casts. This reduces the effort and inconvenience to the operator as well as to the patient in using impression materials for recording impressions followed by fabrication of casts with stone14.
5.3 3D Printing as an Effective Tool in Fabrication of Tooth Restorations
Utilization of 3D printing technology for tooth fillings will reduce the treatment costs in comparison to an all ceramic/ CAD-CAM (Computer Aided Design/Computer Aided Manufacturing) restoratives and decrease the technique sensitivity of placement of the restorative material. It can be used to restore a complex cavity involving multiple surfaces that cannot be restored directly. The following are the steps to fabricate a 3D printed restoration15:
Tooth preparation according to the cavity prepared, it can be two or three surface preparations.
Scanning of the preparation and uploading the data on the computer.
Printing the filling with appropriate material of choice of restoration.
Finally cementation of the prepared 3D filling into the scanned cavity with suitable adhesive material.
The current problem associated with 3D printing restorative materials is that the most commonly used methacrylates like BisGMA (bisphenol A-Glycidyl Methacrylate), UDMA (Urethane Dimethacrylate)16 used in clinical practice are loaded with glass fillers where as the ones that are used in 3D printing machines are devoid of these filler particles, thus compromising the mechanical properties of the 3D printed composites making them inferior to the contemporary resin materials17. Hence in order to improve their mechanical properties the filler particles are to be incorporated and research is being carried out in this direction.
Another limitation to be addressed is the adhesive compatibility of the 3D printable composite resins with current resin based adhesive systems when bonded to the enamel and dentin substrate and further studies are required to gain a better understanding.
Dentists can also print objects such as custom made trays for in office bleaching of vital teeth which duplicate higher accuracy, precision of fit and ease of placement15.
3D printed guides and models help the clinician in esthetic treatment planning and also aid them in minimal intervention and skill acquisition18.
5.4 3D Printing as an Effective Tool in Reconstuction of Tooth Models to Assist in Endodontic Treatment of Atypical Anterior Tooth
There have been reported cases of atypical anterior tooth, where a physical tooth model was fabricated to guide the treatment procedure favourably. A translucent tooth model was built carrying the information regarding the internal root canal structure through a 3 step process:
Data collection through CBCT (Cone Beam Computed Tomography) scanning.
Virtual modelling by image processing.
Manufacturing through 3D printers.
A customized guide jig was fabricated to get a safe and precise working path to the root canal and follow up after few months reported complete healing of the periapical region with no clinical signs and symptoms19. The fabrication of such 3D models help to analyze in a life size manner the anomalous defects better.
5.5 3D Printing as an Effective Tool in Guided Endodontics
3D printed virtual templates were utilized to gain guided access to root canals and various in vitro research studies concluded that accurate access cavity preparation up to apical third of the root could be obtained through 3D template guided Endodontic procedures20. This would especially be useful for clinicians to apply when faced with challenging canal morphologies. A 3D guided access stent which is digitally designed to fit each particular tooth could pave the way to minimally invasive endodontic access and minimize the chances of iatrogenic errors.
5.6 3D Printing as an Effective Tool in Guided Implant Surgery
High accuracy can be achieved through 3D printed templates for guided implant surgery when used as alternatives to laboratory manufactured templates21. The guides offer better precision of placement of the implant, when compared with free hand placement which is fully dependent on the clinician’s skill and experience. Also the cost effectiveness and time saving fabrication of the guides is an added bonus in addition to 3D data analysis and interpretation which ensures more predictable results.
5.7 3D Printing as an Effective Tool in Tooth Transplantation Procedures
The clinical application of computer aided rapid prototyping for tooth transplantation works on the fabrication of a duplicate form of the donor tooth, which is obtained prior to the extraction, by taking a 3D image with real dimensions of the donor tooth from a CT (Computed Tomography) high speed scan to fabricate a life sized resin model of the tooth. This procedure would help in minimizing the extra oral time during the surgical procedure, which in turn maintains healthy periodontal ligament cells in the donor tooth for successful tooth transplantation22.
5.8 3D Printing as an Effective Tool in the Repair of Bony/Soft Tissue Defects
The repair of defects caused by accidents, surgery or birth can be done by fabricating 3D scaffolds of various geometric shapes through customized tissue engineering. Rapid prototyping or solid free-form fabrication techniques are very useful in designing customized scaffolds. Poly (ethylene oxide) and poly (ethylene glycol) dimethacrylate photopolymerisable hydrogels were used to fabricate scaffolds which resulted in constructs that were comparable with soft tissues in terms of elasticity and high cell viability which was achieved along with high density constructs23.
5.9 3D Printing as an Effective Tool in Dental Pulp Regeneration
The pulp tissue can be replaced by utilizing a 3D cell printing technique. An ink jet device is used to recreate the structure of pulp tissue by dispensing layers of cells that are suspended in hydrogel. This helps us to precisely position cells and this mimics the natural pulp tissue of the tooth. In order to mimic the pulp of natural tooth a systematic positioning of cells is required that includes positioning of the odontoblastic cells at the periphery and fibroblasts with in the core with a supportive network of vascular and neural cells. However careful orientation of the cells is required, and research is in focus to in vivo create a functional tissue like pulp24,25.
6. Future: New Generation Reprap 3D Printers
The RepRap 3D printers are self-replicating manufacturing machines initiated by Dr. Adrian Bower in 200426 in an attempt to replace the conventional laboratory procedures. These printers utilize Cartesian robots, which can move along x, y, z axis and can precisely deposit the appropriate quantities of thermoplastic polymers. These printers require digital information by CAD (Computer Aided Design/Computer Aided Manufacturing) and then objectify the provided input by applying additive manufacturing technology called fused filament fabrication27. It has limited application usually for reconstruction of study models for orthodontic purposes and reconstruction of skeletal defects28.
7. Future: 4D Printing
The main concept of 4D printing is to create 3D printed models that can undergo spontaneous shape transformation as a process of adapting to the oral environment in response to thermal or moisture changes. This can be achieved by mixing various materials in a proportionate pattern and quantity each with known strain and shrinkage properties. 4D printing could produce restorative materials that are self-adjustable spontaneously without further intervention from the dentist that could avoid micro leakage and overhangs at the margins. Hence it may help produce materials with better fit and retention qualities than conventional or 3D printed materials29. This offers a whole new promising scope to improve the standard of quality dental care to the patients.
8. Conclusion
3D printing could establish itself as a milestone in the field of dentistry due to its efficacy, accuracy, potency and minimal time consumption in the fabrication process. Its utility in treatment planning and analysis of treatment outcomes improvises the quality of treatment provided by the dentist to the patient enhancing the patient satisfaction. As 3D printing is an additive manufacturing process the amount of material wastage can be effectively reduced. Another advantage of this technology is that each computer data file is a permanent record of the object being printed and this data can be stored. Hence it is possible to reproduce multiple copies of the same object when desired. However, like every newly invented technology 3D printing has its own challenges to overcome such as cost, lack of trained personnel and limited choice of materials that are biocompatible. Hence more research is required in this field to establish itself as a reliable technology and studies should be directed to observe clinical treatment outcomes employed by 3D printed objects.
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