AUTHOR: Gayle B. McCombs, RDH, MS
AUDIENCE: Dentists, dental hygienists, dental assistants, oral health care professionals
ABSTRACT: The emergence of low temperature atmospheric pressure plasma (LTAPP) is becoming a groundbreaking field of research for treating a myriad of medical and dental conditions. Novel advances in dental technology are often sporadic; therefore, the discovery of the biological effects of plasma—which are suitable for oral applications—has been a major finding. PlasmaDent, the term applied to plasma technology and plasma pharmacology in dentistry, represents a major paradigm shift from chemical- to molecular-based medium in order to treat various oral conditions. Although in its infancy, the success of plasma in medicine and other industries lays the foundation for highly promising applications in dentistry. The following is an overview of plasma science and what is possible for the future of dentistry.
At the completion of this course, the participant should be able to:
1. Explain the basic characteristics of plasma science.
2. Discuss the potential applications of plasma in dentistry.
3. Debate the pros and cons of plasma technology.
4. Describe the characteristics that make plasma technology well suited for dental applications.
5. Appreciate the importance of new technology in dentistry.
CLINICAL CATEGORY: Preventive
CE ACTIVITY: Online/Self-Instructional
TOTAL CREDITS: 2 CE Credits
TOTAL COST: $20.00
PUBLISH DATE: July 2013
EXPIRATION DATE: July 2016
COURSE CONTENT: The information and opinions contained in this CE course are those of the author, and do not necessarily reflect the views of The Richmond Institute for Continuing Dental Education, or its affiliates. Any brand or product name mentioned throughout this course should not be inferred as an endorsement of any kind by the aforementioned parties. In addition, The Richmond Institute does not warrant or make any representations concerning the accuracy or reliability of the materials on this website, or any site(s) that are linked to richmondinstitute.com.
CONFLICT OF INTEREST: Gayle B. McCombs, RDH, MS does not have a financial arrangement or affiliation with any corporate organization offering financial support or grant monies for this continuing dental education program, nor does she have a financial interest in any commercial product(s) or service(s) discussed in this program. The Richmond Institute for Continuing Dental Education is a division of Young Innovations, Inc. It is dedicated to ensuring that its continuing dental education programs are intended for the sole purpose of education and do not serve as an endorsement for any product(s) or service(s), including those of the sponsoring company.
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SCORING: To earn credit for completing a course from The Richmond Institute for Continuing Dental Education, participants must earn an overall score of 80% or above on the associated exam before receiving a certificate that confirms CE accreditation. (*NOTE: There is no limit to the number of times a participant may re-take the exam in order to obtain this passing score). All courses that are published on this site are categorized as self-instructional—which means participants must complete the course on their own time and submit the accurate payment in order to earn CE credit.
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LIMITED KNOWLEDGE RISK: The information provided in this course may not be comprehensive enough for implementation into professional dental practice. It is highly recommended that additional information be attained once the course is completed to establish greater proficiency on the topic at hand.
The Richmond Institute for Continuing Dental Education is an ADA CERP Recognized Provider. ADA CERP is a service of the American Dental Association to assist dental professionals in identifying quality providers of continuing dental education. ADA CERP does not approve or endorse individual courses or instructors, nor does it imply acceptance of credit hours by boards of dentistry. Concerns or complaints about a CE provider may be directed to the provider or to ADA CERP at www.ada.org/goto/cerp.
PLASMADENT: BREAKTHROUGH TECHNOLOGY FOR DENTAL HYGIENE AND DENTISTRY
Dental professionals currently rely on mechanical and chemical interventions to treat and manage a number of oral conditions. Procedures such as scaling and root debridement, caries removal, and the application of chemotherapeutic agents are commonplace, and have been for many years. Breakthroughs in dental technology and treatment modalities may be infrequent, but the emergence of the multi-disciplinary field of plasma (or PlasmaDent) opens the door to a new therapeutic approach.
When most people hear the word “plasma”, they think of blood components—yet there are many other forms of plasma that have a wide-range of implications. Low temperature atmospheric pressure plasma (LTAPP), also known as cold or non-thermal plasma, is a relatively new medium that has the potential to replace or augment traditional oral therapies.1,2 The concept of LTAPP is unknown to most dental professionals, even though plasma technology has steadily advanced in several other industries (including medicine). The biological properties and effects of plasma are clinically relevant for a number of oral applications. For example, research suggests that plasma has the ability to kill bacterial cells without harming the surrounding healthy cells, and may exhibit therapeutic properties that can boost wound healing and enhance tissue regeneration.3,4 Given the current state of knowledge, this course provides insight into the potential applications that plasma has for the dental industry.
Plasma—referred to as the fourth state of matter—comprises approximately 99% of the universe. In nature, plasma is commonly associated with the stars and lightening, while the remainder of the universe consists of ordinary matter such as solids, liquids, and gases (Figure 1). The boundary between gas and plasma is often blurred, but plasma possesses unique properties that are unlike those of solids, liquids, or gases. First of all, plasma does not have a defined shape or a definitive volume unless enclosed in a container, or formed into configurations like plumes or beams. The plasma discharge produced can then take on different shapes (wide, narrow) and colors (blue, white, green) depending on factors such as type of gas used (e.g. argon, helium) and flow rate. Typically, plasma emissions generated for dental applications resemble a narrow “glowing” blue/white mass (Figure 2).
Plasmas are classified as either thermal (hot) or non-thermal (cold). If plasma is nearly fully ionized, it is referred to as “hot”; if only a small fraction of the gas molecules are ionized (e.g. 1%), then it is referred to as “cold.” Thermal plasmas exist at thousands of degrees Celsius, and require pressure and a significant power source in order to operate. Non-thermal plasmas, on the other hand, are artificially generated, and can operate with ambient air (room temperature) and much less power. For example, thermal applications include surface etching, cauterization and sterilization where high heat is necessary. On the other hand, non-thermal applications would be used for intraoral procedures where high heat is intolerable.
Plasma can be activated by applying an electrical field (heat or electricity) to a gas, which produces energetic electrons and ions that facilitate highly reactive chemistry. Plasma exhibits strong oxidative properties through the generation of chemically reactive oxygen species (ROS)—such as, for example, hydrogen peroxide (H2O2). As a result, bacteria have been found unable to cope in the hostile environment created by plasma, and therefore die very quickly. 2-6
Laboratory studies have demonstrated that plasma has the ability to inactivate or kill bacteria, viruses, and fungi without adversely affecting the surrounding healthy cells. The oxygen-based active species in plasma play a critical role in its germicidal effects. The causative agents are short-living species called radicals that are highly reactive and affect only the targeted area. The germicidal action of plasma depends on several factors, such as: power, type and composition of gases, flow rate, exposure time, configuration of plasma, as well as the type and concentration of the cell.5
The physics of plasma are complex and multifaceted, yet due to its unique characteristics, the potential for growth in the healthcare arena is enormous. Plasma research is slowly emerging as an innovative, multidisciplinary field; nevertheless, regulations and guidelines need to be established in order to substantiate the safety and efficacy of impending devices and therapies.
PLASMA IN NON-HEALTHCARE ARENAS
Industrial applications of thermal and non-thermal plasmas have been expanding into non-healthcare arenas for years. For instance, plasma technology is currently used in the manufacturing of neon and fluorescent tubes, semiconductors and televisions. Other examples include surface etching, welding, and plating or coating to provide corrosive resistance and thermal insulation for certain materials. Plasma technology is also employed in the food industry to increase product safety by killing pathogens that are commonly associated with foodborne illnesses, such as: Listeria spp., E. coli strains, and Salmonella. Moreover, large volume plasma systems provide three unique capabilities in the food industry to ensure overall safety:
1) deposition of barrier coating for packaging
2) product treatment to remove organic contaminants
3) decontaminating surface areas such as: counters, cutters, and conveyors
The growth of plasma research in food science has increased tremendously over the past few years and is expected to continue as consumer demands for safety and quality increase.
PLASMA IN THE BIOMEDICAL FIELD
The discovery of plasma’s biological effects—coupled with the growth in nano-technology—has spurred tremendous interest in the biomedical field. In the l990s, the field of plasma medicine was introduced to the scientific community; however, the first International Conference on Plasma Medicine (ICPM) was not held until 2007. Since that inaugural meeting, there has been a dramatic interest in biomedical applications.
There are a variety of biomedical challenges and conditions being researched that show potential in dentistry. Researchers are currently studying plasma’s germicidal effect on a variety of pathogenic microorganisms that are associated with hospital-acquired infections, antibiotic-resistant bacteria, and prion diseases, just to name a few.6-9 Plasma-assisted devices are also under investigation in a number of areas, including: wound healing and tissue regeneration (i.e. burns and ulcers), treatment of dermatological diseases and skin rejuvenation, treatment of certain cancers, and the inactivation a wide range of pathogenic microorganisms associated with common diseases and environmental challenges.
Since the early 2000s, much effort has been dedicated to non-thermal plasma devices in healthcare. Implications for plasma are wide-ranging, although not without challenges (Table 1). Biomedical applications are of particular interest because plasma displays many therapeutic and germicidal properties, while being non-invasive, non-chemical, and non-corrosive (Table 2). In order for LTAPP to gain traction in dentistry, plasma-assisted devices will need to be designed to meet unique equipment challenges and varying conditions that are specific to the oral cavity.
PLASMA IN DENTISTRY
Currently, there is significant interest in the use of plasma in the practice of dentistry.10-12 PlasmaDent, represents a paradigm shift from mechanical and chemical therapies to molecular-based technology. Although research on plasma-enhanced dental applications is scant, there is significant potential since this medium operates under the threshold of tissue damage and exhibits therapeutic and germicidal properties.13
Research suggests that LTAPP is effective in the inactivation of a myriad of environmental and oral pathogenic microorganisms that are common in dentistry.14,15 For instance, plasma emitting devices are under investigation for a variety of dental applications, including: hand sanitation, the inactivation of pathogens associated with caries, periodontal diseases, root canal infections, and peri-implantitis, in addition to tooth whitening, and surface modification (Figure 3). Moreover, pivotal studies have revealed that plasma is effective in killing bacteria within biofilms, which has substantial implications in dentistry.16-18
Although the exact mechanism of action is not clearly understood, it is hypothesized that LTAPP exposure disturbs or destroys the bacterial cell wall and damages the DNA, thus inactivating the microorganism.3,5,15,16 According to current research, LTAPP offers a plausible alternative to treating various oral conditions without being harmful to adjacent healthy tissues. Future applications of LTAPP in dentistry are highly desirable, considering the challenges that currently persist in clinical practice.
THE PLASMA PENCIL
The small hand held device called the plasma pencil (PP), which is about the size of a power toothbrush and resembles a miniature light saber, has the capacity to kill bacteria. The PP, developed at Old Dominion University by Laroussi and colleagues in the late 1990s, is being studied to determine its germ-killing capabilities on a wide array of microorganisms.19-21 The PP generates a non-thermal focused plume in the form of chemically reactive, small plasma “bullets.” The PP plume can be directed into microscopic crevices and around angles, which makes this device ideal for many intra oral applications (Figure 3). Currently, the PP is being studied as a medium for killing bacteria associated with dental caries and periodontal infections, as well as tooth whitening. Further refinement of the PP would include interchangeable tips that connect to a portable table top unit and provide multiple functionalities, from inactivating bacteria to lightening teeth.
STERILIZATION AND DISINFECTION
Plasma-based sterilization is a reality, yet this technology is not widely used. Contemporary sterilization methods that include steam, dry heat, ultraviolet light or chemicals (such as ethylene oxide) are not only slow, expensive, and energy inefficient, but can also be caustic to certain heat sensitive materials, and may be toxic to humans and the environment. In an effort to develop new approaches to sterilization and disinfection, plasma technologies are now being explored. Plasma inactivation has already been confirmed for the following pathogenic microorganisms22-25:
- Escherichia coli
- Pseudomonas aeruginosa
- Salmonella typhimurium
- Aspergillus niger
- Penicillium citrinum
- Geobacillus stearothermophilus
- Staphylococcus aureus
- Staphylococcus epidermidis
- Bacillus atrophaeus
- Micrococcus luteus
- Bacillus cereus
The germicidal effects of plasma—based on the principle of charged particles, free radicals, and radiation—operates differently from traditional sterilization methods. The reactive species and radicals (e.g., O, OH, HO2, H2O2, 03) generated in plasma are capable of degrading organic compounds and inactivating microorganisms by affecting the outermost membrane of the bacterial cell wall.23 Plasma-based sterilization is a non-toxic, non-thermal, and non-corrosive “dry” system, which uses gases that have no germicidal properties of their own. The potential to rapidly inactivate harmful microorganisms in infectious waste, liquids, water systems, and instruments with non-thermal, non-chemical means is motivating research in this area. The germicidal effects of plasma at the cellular and sub-cellular levels are in need of further investigation; however, the stimulus to explore this domain is clear.
Despite advances in oral disease science and oral health strategies, dental caries remains a worldwide public health problem. Typical methods for management and treatment of dental caries include the use of fluorides, mechanical biofilm removal, and elimination of infected tooth structure. In the search for minimally invasive techniques, an alternate approach for caries management may be to remove infected tissues and destroy the key causative agent, while leaving healthy adjacent tissue intact. To minimize tooth structure removal, a caries detection solution was developed, which selectively stains caries affected dentin; however, bacteria remaining in the dentin tubules continues to be a concern for secondary caries. The fact that LTAPP is germicidal, can reach around corners, and is able to penetrate into microscopic crevices and canals suggests that this medium is well-suited to assist in caries management.
Various devices are under investigation to evaluate the effects of plasma on caries causing bacteria. Results from numerous studies show that exposing S. mutans to LTAPP for various time intervals demonstrates significant bacterial inactivation in a matter of seconds.26-32 Although plasma-assisted devices would not replace traditional rotary instruments to remove infected hard tissues, it may help in the prevention and control of dental caries by inactivating the remaining bacteria and minimizing tissue removal, without exposing pulp to unnecessary thermal threats. The need to move beyond in vitro investigations is essential in order to validate existing findings and test applications under challenging intra-oral conditions.
Post-treatment bacterial infections represents a serious challenge in endodontics, but the prevention of these infections could be reduced with the use of intra-canal plasma sterilization. Numerous plasma devices are being studied as an alternative to traditional wet intra-canal sterilization, such as sodium hypochlorite, since the action of LTAPP relies on dry “plasma chemistry” rather than mechanical, wet chemical, or pharmacological agents.32-39 Studies show that plasma-based devices were able to emit a very narrow plasma plume into root canals, which were effective in killing E. faecalis—the primary bacteria associated with root canal failures. A plasma device developed for root canal sterilization is highly desirable as a “dry”, non-caustic germicidal medium that can reach into commonly inaccessible or convoluted microscopic areas. Further research is needed to optimize the extent to which plasma reaches into the canal, and its killing capacity on other associative bacteria.
Mechanical and chemical modalities are the gold standard of periodontal therapy, yet in the search for less invasive, non-chemical therapies, plasma could be a plausible alternative. Foundational work has been conducted to determine the germicidal effect of LTAPP on Porphyromonas gingivalis—the periodontal pathogen strongly associated with periodontal disease. Research has shown that exposure to LTAPP can inactivate P. gingivalis.40 Mahasneh and colleagues found a statistically significant difference in bacterial zones of inhibition after 5-, 7-, 9-, and 11-minute intervals of LTAPP exposure compared to the unexposed bacteria (p<0.0001), thus supporting the dose response germicidal characteristic of plasma.
The lasting effects of plasma exposure and penetration capabilities are still inconclusive; however, research confirmed that plasma can penetrate biofilms and effectively inactivate one of the main causative oral pathogens associated with periodontal disease.Expanding research into human testing is needed to validate the evidence gathered in the presence of saliva, gingival crevicular fluid, calculus, and other various states of the disease. The potential for non-invasive, site-specific, non-chemical methods to treat periodontal disease may lessen reliance on antibiotics and antimicrobials, which is another growing concern in the healthcare industry. Plasma-assisted devices may someday be available to augment or replace traditional mechanical and chemical periodontal therapies.
The chemical and physical properties of plasma-material surface interactions are complex, nevertheless, plasma surface modification, plasma-spraying, and plasma-coating are quite common in other industries. Plasma-based technology has the potential to modify surfaces to enhance adhesion and increase surface bonding, as well as inhibit bacterial adhesion, and boost the host-to-implant response. Numerous investigations are looking into the plasma-coating of biomaterials that are relevant to dentistry.41-48 Considering the time it takes to develop and test new biomaterials, efforts dedicated to plasma surface modification can shorten the time needed to develop new techniques. For example, plasma treated titanium implants showed enhanced osseointegration of bone-to-implant contact, which improved the interaction between connective tissue and the bone itself.46 Similar research demonstrated that the application of plasma actually altered dentin surface chemistry, which improved osteoblast spreading.47 These plasma regimes may improve cell-surface interaction, and directly affect the migration and proliferation of osteoblasts, as well as enhance implications for periodontal regeneration and implant success.
Plasma surface engineering may also have potential in dentistry by providing an antibacterial coating to minimize both microbial adhesion and colonization for a number of metal and non-metal dental materials, particularly titanium.45-46 A problem with many devices are device-related infections (DRI) that arise when bacteria attach to and proliferate the surface. One example of combating DRI in ophthalmology, for example, was the emergence of plasma surface treatments used by companies like Bausch & Lomb to provide non-fouling, extended wear contacts.44
Non-fouling surfaces have implications for improving oral care by reducing microbial adhesion and proliferation on implants, dentures, orthodontic appliances and mouth guards, to name a few. Additionally, plasma surface modification of biomaterials and tooth structures (enamel and dentin) has vast implications. Specifically, plasma-treated surfaces have shown to improve the bond strength of composites materials used in restorative dentistry.41,42 The potential to increase the longevity of dental restorations, improve dental implant outcomes, enhance periodontal therapy, augment or replace current etching and bonding agents, and improve overall dental care is possible with plasma technology.
Tooth whitening (bleaching) is the most requested cosmetic procedure in dentistry today. Whitening procedures include in-office, professionally dispensed, and over-the-counter (OTC) protocols. Utilizing hydrogen or carbamide peroxide agents can produce transient side effects, such as tooth sensitivity and gingival irritation. Power- and laser-assisted bleaching techniques enhance the whitening process over a shorter period of time with the use of an accelerator (light, heat or laser), but they may increase the overall side effects. It is thought that a heated bleaching agent may penetrate deeper into the dental hard tissues, which may help explain why the activation-bleaching method is more effective. The release of hydroxyl-radicals from peroxide is accelerated by the rise in temperature, which most likely is the main mechanism of action for increasing whitening efficacy. Similarly, the reactive oxygen species (ROS) generated by LTAPP at the plasma tooth interface is considered to be fundamental in plasma-assisted whitening.
Concerns over length of transient side effects, procedure time, and chemical and thermal insults have propelled researchers to investigate other whitening alternatives. Numerous plasma devices are currently being studied to evaluate their effects on tooth whitening. In vitro studies suggest that the use of LTAPP improves the whitening capabilities without causing thermal damage or altering surface morphology.49-54 For instance, in a study by Claiborne et al., results showed that there was a significant difference in lightness after exposing teeth to LTAPP and H202 gel versus H202 gel alone in as little as 10 minutes.54 Pan and colleagues demonstrated that plasma-assisted whitening exceeded traditional H2O2 gel treatment in a 20 minute period, and that the treatment did not significantly affect the micro-hardness of tooth enamel.51
Utilizing plasma to enhance tooth whitening and remove surface proteins is in its infancy, but significant progress is being made. The potential for a chemical-free, non-thermal whitening procedure is desirable as an adjunct or alternative to existing techniques. The challenge of reducing chair time and minimizing the reapplication of whitening gels is also critical in order to limit current side effects. LTAPP enhanced whitening, with or without added gels or solutions, may someday be the gold standard in whitening.
Plasma is cutting edge technology. Through interdisciplinary partnerships in medicine, dentistry, physics, engineering, chemistry, and biology, PlasmaDent is evolving into a dynamic field of research. The accumulated knowledge gained in industry and medicine now lays the foundation for unique plasma applications in dentistry. Plasma chemistry is complex, but the shift from mechanical and chemical approaches to a molecular-based medium in order to manage oral diseases is certainly desirable. Plasma has been shown to be effective in wet and dry environments, which is advantageous in the presence of saliva, blood and gingival crevicular fluids. Numerous studies have also demonstrated plasma’s ability to inactivate pathogenic microorganisms, particularly those associated with dental caries, periodontal diseases and endodontic failures. Given the popularity of tooth whitening, plasma-enhanced tooth whitening research is likely to surge as well. Moreover, the limitation of certain tooth-material and material-material interactions will likely propel interest in plasma surface modification.
The future of plasma in dentistry is significant, albeit new discoveries and the corroboration of foundational research is needed to grow this science to its full potential. Tremendous progress has been made in the interdisciplinary field of plasma giving rise to numerous PlasmaDent applications. Looking toward a rapid, effective, non-thermal, chemical-free alternative to prevent, treat and manage oral conditions, the characteristics of LTAPP are ideal. Certainly, there are challenges to be met, but LTAPP may someday be as indispensable to dental professionals as ultrasonics are to daily practice.
Based on known physical and biological properties of plasma, it is worthwhile to speculate that a number of dental applications are possible, yet fundamental principles of how plasma influences cells and effect time needs further investigation. A few years ago, PlasmaDent was just speculation, but plasma-assisted dental devices will unquestionably be available in the future to augment or replace existing technologies and therapies–the untapped potential of plasma in dentistry is limitless.
The field of plasma medicine and PlasmaDent are in early development; however, of particular interest to the readers may be the first Plasma Medicine book published to help understand plasma physics and the potential biomedical uses of plasma, as well as the Journal of Plasma Medicine and Clinical Plasma Medicine.
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