For the past decade, great effort has been directed toward the introduction and development of shape-memory materials. Basically, these materials are designed in finite dimensions, stored temporarily in a second dimension under specific heat or force, and then converted into a third permanent dimension.
This technique has been developing, thanks to advances in material science and better understanding of polymerization reactions and crosslinking. The 4-D printing technique has some common features with shape memory. However, it eliminates the temporization phase of fabrication.1
4-D printing is the process of fabricating objects with self-folding properties of 3-D printable ingredients, each with different physical properties and responses to physical stimuli over time. In other words, the final object of 4-D printing is a structured hybrid of materials (eg plastics). Each of these materials provides a different amount and direction of elongation, so the final object keeps moving over time.
Motion, or elongation, could be in response to thermal, electrical, or magnetic stimuli; radiation; or humidity, which is the major stimulus in the oral cavity and will have a significant effect on future 4-D printing applications.2
Self-folding objects could have functional use in dentistry, surgery, and medicine. Innovative motile objects may revolutionize the medical industry in light of the wide applicability of such materials. Designed and tailored for individual patients, prostheses could be programmed to adapt with aging and daily activities.3,4
Prosthetic heart valves have been designed with programmed movement behavior to correspond with blood flow. The amount of blood passing through the valve is subject to increase and decrease, based on blood pressure. Unlike standardized 3-D-printed valves, 4-D-printed valves can cope with such changes in blood pressure.
4-D printing can present motile objects, which can be exploited to provide some cushion effect. In orthopedics, this could be turned into joint implants where motile discs replace standard plastic discs to give the cushion action in knees, hips, ankles, and shoulder joints as well as in spines.
Dental Applications of 4-D Printing
In dentistry, 4-D printing could have a variety of uses based on its motile nature, which could be turned into functional use. Humidity is always changing in the mouth, which could initiate the folding of 4-D-printed objects and keep them continuously folding.
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| 4-D printed dental restorative material could possess motile characteristics to compensate for dimensional changes and setting shrinkage. This favorable property could help to avoid marginal leakage. |
For example, they could be used as functional appliances in orthodontics. Dental discrepancies could be corrected with smart, movable, and removable appliances that keep moving overtime. A variety of such uses could be achieved, such as arch-expansion appliances and bite-raising devices.
Meanwhile, fixed orthodontics could be enhanced with smartly moving ligatures and wires that move teeth in the desired direction, with the desired force over time, hopefully with atraumatic bone and periodontal ligament responses.
Removable dentures also could be designed from a tailored mix of materials particularly for each patient considering dentition, arrangement of occlusion forces, ages, eating and drinking habits, coexisting medications, or medical conditions that could cause dry mouth or excessive salivation, as well as daily activities.
Filling materials could be customized to undergo permanent movement and fashioned to override the drawbacks related to dimensional changes that have long been encountered by dental practitioners with the existing materials in market.
Furthermore, 4-D printing could be exploited to enhance skeletally developed temporomandibular joint disorders. Fabricated smart materials could be injected or surgically inserted into the joint space.
Tissue-culture engineering currently uses 3-D printing to make scaffolds for living cells or stem cells for transplantation procures. 4-D printing could enhance these processes as the scaffolds become motile to ensure the delivery of stem cells to the target areas to perform a specific function.5
And in implant dentistry, 4-D printing could further improve the ongoing research into creating a completely 3-D-printed tooth, enabling either the cushioning base for the delivered implants to move in harmony with the surrounding periodontium (see the figure). Or, researchers could fabricate an overall 4-D-printed dental implant with motile properties simulating those of natural teeth.6
References
- Shape memory polymers with high and low temperature resistant properties. Xinli Xiao, Deyan Kong, Xueying Qiu, Wenbo Zhang, Yanju Liu, Shen Zhang, Fenghua Zhang, Yang Hu, Jinsong Leng. Sci Rep. 2015; 5: 14137.
- Active Printed Materials for Complex Self-Evolving Deformations. Dan Raviv, Wei Zhao, Carrie McKnelly, Athina Papadopoulou, Achuta Kadambi, Boxin Shi, Shai Hirsch, Daniel Dikovsky, Michael Zyracki, Carlos Olguin, Ramesh Raskar, Skylar Tibbits. Sci Rep. 2014; 4: 7422.
- Emerging Applications of Bedside 3D Printing in Plastic Surgery. Michael P. Chae, Warren M. Rozen, Paul G. McMenamin, Michael W. Findlay, Robert T. Spychal, David J. Hunter-Smith. Front Surg. 2015; 2: 25.
- Multi-shape active composites by 3D printing of digital shape memory polymers. Jiangtao Wu, Chao Yuan, Zhen Ding, Michael Isakov, Yiqi Mao, Tiejun Wang, Martin L. Dunn, H. Jerry. Qi Sci Rep. 2016; 6: 24224.
- Engineering a Biocompatible Scaffold with Either Micrometre or Nanometre Scale Surface Topography for Promoting Protein Adsorption and Cellular Response. Xuan Le, Gérrard Eddy Jai Poinern, Nurshahidah Ali, Cassandra M. Berry, Derek Fawcett. Int J Biomater. 2013; 2013: 782549.
- Griffith uses 3d tissue engineering to revolutionise dental disease. Louise Durack. March 30, 2016.
Hosamuddin Hamza obtained his BDS from the Faculty of Dental and Oral Medicine, Cairo University, in 2005. Since then, he has dedicated his career to scientific and medical research work. In 2012, he joined the orthopedic department at October 6 University in Cairo as a research assistant and worked under direct supervision of the head of the department, Professor Mahmoud A. Hafez. He has published a number of studies in orthopedics, 3-D printing, and dental technology. He also serves as an R&D specialist at K Line GmbH (www.kline-europe.de) with plenty of research activities in computer-aided orthodontics and the clear aligners industry.
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