Bioresorbable polymers bring a smile to patients and dentists

Dentistry and periodontal surgery have been at the forefront of the development and use of bioresorbable biomaterials for several decades, with a wider range of products and applications than in any other medical field. Bioresorbable biomaterials have now largely replaced the use of traditional non-degradable materials in almost all dental fields, including sutures, implants, grafts, and drug delivery systems. The ability to manufacture products that have specific mechanical and degradation properties suited to specific dental applications, without triggering any inflammatory, immune, or toxic reaction, has proven incredibly useful in the medical setting.¹

Bioresorbable polymers are metabolized and excreted by the body leaving no toxic traces behind. In many situations their use avoids the need for secondary interventions to remove implanted material once healing has been achieved, thus avoiding unnecessary costs, patient discomfort and potential surgical complications.

Although the benefits and use of biomaterials in dentistry is relatively well established, the potential for further growth is enormous. The global market for dental materials is estimated to be around $7.25 billion in 2023, with the U.S. alone accounting for about $1 billion. Within this market, dental barrier membranes are expected to show the highest level of growth; sales of resorbable dental membranes in the U.S. are currently about seven times those of non-resorbable membranes ($176 million vs $25 million) and continue to grow annually.²

Biomaterials are also fueling new applications for 3D printing technology, the medical use of which was pioneered by dental implants in the 1990s. The vast majority of structures used by dentists and faciomaxillary surgeons can be made using 3D printing, including prosthodontics, periodontics, endodontics, and temporomandibular joints (TMJ). Many long-standing dental challenges, such as replacing damaged TMJ discs, have been resolved using 3D printing.

Despite the many applications of bioresorbable materials in dentistry, there are still many unmet needs and there is considerable on-going research to look for new and better ways to use this technology. PLGA (polylactic-co-glycolic acid), for example, is one of the most widely used bioresorbable polymers and it is approved by the FDA in the U.S. and EMA in Europe. PLGA has potential in scaffolds, membranes, microparticles, nanoparticles and gels to aid bone fixation and regeneration. It also provides a vehicle for the delivery of antimicrobials, pharmaceuticals and vaccines in implants, disks, and dental films. Many human and animal studies are currently looking at various aspects of these and other dental uses.

Manufacturing synthetic bioresorbable polymers with different mechanical and biological properties is a job for experts in chemical synthesis. Evonik has been producing a range of bioresorbable polymers under the tradename RESOMER® for more than 30 years. This portfolio of semi-crystalline and amorphous polymers has a proven heritage of efficacy, biocompatibility, and safety, and has been used in a wide range of medical devices for orthopedic, spine, cardiovascular, and wound healing applications, as well as dental uses. This includes providing biomaterials for devices such as interference screws, suture anchors, fracture plates, vascular closures, stents, sutures, ligating clips and dental membranes and scaffolds.

The breadth and versatility of the RESOMER® portfolio means that Evonik can match the properties and characteristics required for specific dental applications. The expertise and experience developed during 30 years of commercial production has put Evonik in a strong position to help manufacturers develop specific dental products for existing and emerging unmet needs in the dental market.

The RESOMER® portfolio includes bioresorbable polymers based on polylactide, poly(lactide-co-PEG), polycaprolactone, polydioxanone, polyglycolide or composites. Each product has precise mechanical and chemical properties, including strength and elasticity, with degradation timelines ranging from one month to more than four years. As well as standard products such as RESOMER® Filament and powders, the portfolio can be customized to meet specific needs and made to order in the form of filaments, powders, tubes, granules and films. Whether the finished product requires high strength and modulus, or flexibility and elongation, RESOMER® can be precisely tuned to the specific need.

The recent launch of a range of polyglycolide-based innovative bioresorbable polymers has opened up a new range of possibilities for medical textile applications. These polymers combine strength with rapid degradation and are particularly suited to wound healing applications, including those based on homopolymer (PGA), copolymer (PGLA) and block copolymer (PGA-CL and PGA-TMC). They are available in standard and custom compositions in a semi-crystalline form and optimized for easy processing into monofilaments or multi-filaments. They are also available in colorless and violet grades and can be configured to precisely degrade as required.

Suture anchors, interference screws and dental devices can all benefit from the inclusion of bioresorbable polymer technology. Bone fixation devices have been found to perform much better if they include calcium phosphate-based additives which confer beneficial osteoconductive properties. The inclusion of a poly (L-lactide) with 25 percent hydroxyapatite additive or poly (L-co-D,L-lactide) with 30 percent ß-tricalcium phosphate additive can give a degradation timeline up to more than three three years, and promotes faster healing and patient recovery.

The company has a vast database of biomechanical information on its products which means that it can offer a bespoke service for biodevices fulfilling different biological functions. For example, tensile strength depends on the ratio of PLA and PGA polymers used. The speed at which these resorbable polymers are broken down by proteolytic enzymes is also kept on the database.

Barrier membranes are central components of the form and function of a healthy mouth, teeth, and gums. They are a key component of healing and regeneration to restore healthy function after disease or injury. Commercially available dental barrier membranes are designed to retain bone grafting materials, exclude epithelium and connective tissue from entering into sites of desired bone and ligament regeneration, or a combination of these reasons. When trying to restore lost bone around teeth or implants, or in larger areas of the jaw affected by trauma or disease, there is often inadequate gingival tissue to cover the membranes, leading to membrane exposure, extensive membrane contamination and procedural failure, which is unacceptable.

Bioresorbable polymers offer an opportunity to develop materials that can be used to enhance guided tissue regeneration (GTR) to repair periodontal defects, and guided bone regeneration (GBR) to prevent gum tissue from growing into bone cavity for tooth extraction or implant replacement. As mentioned earlier, dental barrier membranes are expected to be the fastest growing sector of the dental market in the next few years.

Evonik continues to develop new, innovative additions to the RESOMER® portfolio which offer unique performance in dental applications. Next generation malleable RESOMER® with chair-side handling properties is one example. This patented product can be used to produce non-sticky beads that can be easily shaped but will hold that shape without load. It can also be used for highly flexible membranes with strength similar to collagen dental membranes, but which maintain their strength and shape in wet conditions. In vitro the material degrades in six months and has excellent biocompatibility and no cytotoxicity.

Over the past 30 years 3D printing – or additive manufacturing (AM) – has had a profound impact by making personalized medical treatments possible in a number of medical fields. The first 3D printed hearing aid and dental implants in the 1990s were followed by numerous other medical applications including transplant organ (1999), prosthetic limb (2008), blood vessel (2009), lower jaw implant (2012), resorbable dental membrane implant (2015), and the first resorbable bone graft (2020).

Being able to manufacture complex implants with precise internal design that are tailormade for individual patients is revolutionizing the development of biomaterials for scaffolds in implant dentistry. Not surprisingly, significant advances continue to be made in terms of printers, processes and, of course, materials.

Material selection is a critical aspect of 3D printing if the desired result is to be achieved. To date, the development of suitable materials has been the rate-limiting step which has prevented the technology from being more widely applicable. Evonik recently launched RESOMER® Filament, a series of bioresorbable materials of different grades that enable higher resolution printing with Fused Filament Fabrication (FFF) technology – arguably the most popular 3D printing technology.

The company is the first in the world to supply a full portfolio of medical grade powder, granule- and filament-based bioresorbable polymers for 3D printing used in medical settings. RESOMER® PrintPowder is a range of free-flowing powders that are optimized for high resolution printing on Selective Laser Sintering (SLS) equipment. In 2015, a large periodontal osseous defect was treated for the first time with a patient-specific scaffold, produced using SLS 3D printing. The scaffold remained covered for 12 months, exhibiting a 3 mm gain of clinical attachment and partial root coverage.

FFF and SLS 3D printing using bioresorbable polymers are ideal for use where medical applications require high compressive strength or complex geometries. Additional RESOMER® bioresorbable options for 3D printing applications include granules for use with freeformer and bioplotter technologies. Evonik offers a range of 3D printing services to support the testing and scale-up of medical applications alongside its bioresorbable polymers.

Smart polymers can change shape or other properties in response to external stimuli such as heat, pH, moisture, or magnetic fields. They have been extensively used in the fabrication of medical devices. Shape memory polymers (SMP) have received substantial attention due to their capability to remember and restore their original shape. SMPs have made it possible to progress from 3D printing to 4D printing by adding time as the 4th dimension in printing medical implants. 4D printing not only allows for minimally invasive surgery but also for the tissue to regenerate between open cells in the printed architecture³.  Evonik’s patented shape memory RESOMER® can change shape at body temperature which is convenient for minimally invasive surgery and implants. It can also be used for 4D printing.

Dental devices manufactured using bioresorbable polymers eliminate the need for the surgical removal of implants, thus saving time and costs, while improving patient comfort and convenience. The growing range of synthetic bioresorbable polymers with different mechanical and biological properties is continuing to expand the possibilities for the use of bioresorbable devices in dentistry. The ability to customize the strength, elasticity and rate of degradation of devices means that biomaterials have the potential to replace virtually all traditional dental implants, grafts, scaffolds, etc. The increasing use of 3D and, more recently, 4D printing means that this technology now has the potential to be tailored to truly individual patient needs.  

The future prospects for bioresorbable dental devices are very exciting. As the range of available bioresorbable polymers continues to expand, the market for innovative biodevices in dentistry and many other fields of medicine will continue to grow.

_{[1] Conte, R. et al (2018) Bioresorbable polymers in dental tissue engineering and regeneration, AIMS Materials Science 5(6): 1073-1101}

_{[2] 2017 US Dental Barrier Membrane Market Drived by Increased Use of Resorbable Membranes – iDataresearch.com}

_{[3] Miao, Shida. et al (2017) 4D printing of polymeric materials for tissue and organ regeneration,  Materials Today  20(10): 577-591,  https://doi.org/10.1016/j.mattod.2017.06.005}