|Year : 2017 | Volume
| Issue : 2 | Page : 133-139
New dimensions in mechanical plaque control: An overview
Arnab Mandal1, Dhirendra Kumar Singh1, Humaira Siddiqui1, Diptajit Das2, Arka Kanti Dey3
1 Department of Periodontics and Oral Implantology, Kalinga Institute of Dental Sciences, Bhubaneswar, Odisha, India
2 Department of Public Health Dentistry, Kalinga Institute of Dental Sciences, Bhubaneswar, Odisha, India
3 Department of Oral and Maxillofacial Surgery, Kalinga Institute of Dental Sciences, Bhubaneswar, Odisha, India
|Date of Web Publication||26-May-2017|
Department of Periodontics and Oral Implantology, Kalinga Institute of Dental Sciences, Campus - 5, KIIT University, Patia, Bhubaneswar - 751 024, Odisha
Source of Support: None, Conflict of Interest: None
Plaque control is the daily removal of dental plaque, oral biofilm and also prevention of their accumulation on the teeth and other parts of oral cavity. Dental plaque is the major etiology of maximum gingival and periodontal diseases. It is also related with various dental problems. Mechanical plaque control is a very effective method to get rid of plaque accumulation in oral cavity. In 3000 BC there was the first toothbrush invented by human beings. With time several modifications came in toothbrushes to make mechanical plaque control more effective in day to day oral hygiene practice. This article emphasizes on the advanced and emerging tools in mechanical plaque control methods in attaining an optimal level of oral hygiene standards and maintenance of oral health.
Keywords: Dental floss, dental plaque, oral irrigation device, plaque control, toothbrushes
|How to cite this article:|
Mandal A, Singh DK, Siddiqui H, Das D, Dey AK. New dimensions in mechanical plaque control: An overview. Indian J Dent Sci 2017;9:133-9
|How to cite this URL:|
Mandal A, Singh DK, Siddiqui H, Das D, Dey AK. New dimensions in mechanical plaque control: An overview. Indian J Dent Sci [serial online] 2017 [cited 2019 Jan 18];9:133-9. Available from: http://www.ijds.in/text.asp?2017/9/2/133/207101
| Introduction|| |
The main aim of periodontal treatment is to achieve the healthy status of periodontium. Dental plaque and oral biofilms are the main causative factors for maximum periodontal diseases. Periodontal therapy helps to achieve reduction in probing depth, bleeding on probing, and helps to maintain or gain clinical attachment level. It also helps to prevent future attachment loss and ensure long-term stability of the periodontal tissues. Along with the clinical improvements, there is ecological shift in the subgingival microbial composition, from a microbial profile related to disease to a profile compatible with health.,,
Setting up of effective programs for the prevention and control of periodontal diseases in both developing and industrialized nations requires a thorough understanding of the various etiological factors that contribute to the initiation and progression of these diseases. Colonization of tooth surfaces by bacteria is recognized as the key etiologic factor in dental caries, gingivitis, and periodontitis. This colonization of microorganism on tooth surface is termed as dental plaque or oral biofilm.,
The term plaque control, on the other hand, refers to the preventive measures aimed at removing dental plaque and preventing it from recurrence. It can be achieved either mechanically or chemically as well as by the combination of two procedures.
The present article is going to provide a meticulous review on routine as well as recent advancements in mechanical plaque control aids.
| Dental Plaque|| |
Dental plaque which is often termed as “Oral biofilm” may be defined as the soft tenacious material found on tooth surfaces that is not readily removed by rinsing with water, but more specifically, it is an organized matrix derived from salivary glycoproteins and extracellular microbial products in the form of a biofilm that forms on the hard, nonshedding surfaces in the mouth.
The most clinically observed plaque commonly seen on the smooth surfaces of the teeth along the gingival margins is termed dentogingival plaque. Plaque may also be found below the gingival margin in the gingival sulcus or in the periodontal pocket, and they are termed as subgingival plaque. Dental plaque plays a dominant role in the causation of both dental caries and periodontal disease. Supragingival plaque is exposed to saliva and to the natural self-cleansing mechanism existing in the oral cavity. However, although such mechanism may eliminate food debris, they do not adequately remove dental plaque. Therefore, the regular oral hygiene practices is a requisite for proper plaque elimination.
| Importance of Plaque Control|| |
Loe et al. in 1965 through experimental gingivitis clearly demonstrated that gingival inflammation consistently follows the buildup of plaque, and that conversely, the removal of plaque can reverse this process. This finding not only demonstrated the central role of supragingival plaque in the development of gingivitis but also showed that mechanical plaque removal of oral hygiene practices can reverse these inflammatory changes.
Since there is a direct link between plaque and gingivitis and as it is determined that the best way of preventing periodontal disease is by implementing optimal plaque control measures, it will be appropriate to consider the temporal influences. The clinical and subclinical effects of unhindered plaque accumulation over a timeline from a healthy baseline show that it takes 48 h to produce signs of gingival inflammation. Gingival health is maintained when plaque gets removed more frequently or at an interval of 48 h. However, where the time was extended, gingival inflammation ensued. The conclusion that can be drawn from this finding is that to prevent gingivitis from developing, an individual need only meticulous removal of plaque from their teeth every 2 days.
Hence, to maintain a healthy oral environment, most preventive measures are directed toward the elimination of plaque and on the minimization of its effects.
| Classification of Mechanical Plaque Control Aids|| |
We already know about the common mechanical plaque control aids that function with the aim of day-to-day oral hygiene maintenance. These include:
- Chewing sticks 
- Neem stick
- Mango leaves
- Miswak stick.
- Depending on type of bristle used
- Depending on the function
- Manual toothbrush
- Powered toothbrush.
- Single headed
- Double headed
- Triple headed.
- Depending on diameter of bristles
- Depending on number of tufts present
- Dental floss/tape
- Twisted; Nontwisted
- Bonded; Nonbonded
- Waxed; Unwaxed
- Thick; Thin
- Floss/Knitting yarn combinations
- Monofilament floss
- Manual floss
- Powered floss.
ToothpicksWooden tipsRubber tips.
- Cone shaped
- Cylindrical shapes
- Small insert with reversible handle
- Brushes with wire handle
- Single-tufted marginal
- Multitufted interdental.
This review article will focus on the current advancement in toothbrushes along with other mechanical plaque control aids such as interdental floss and oral irrigation devices.
| 21ST Century-the Era of Smart Toothbrushes|| |
Since the time of invention till the present day, toothbrushes have been continuously improved to promote healthier teeth. The modern, manual toothbrush helps to clean teeth more effectively than traditional instruments such as fingers, sticks, and twigs. As a result of continuous research and development, recently more advanced toothbrushes such as electric rotation-oscillation, sonic, and solar-powered toothbrushes have been invented. These advanced toothbrushes do not just restrict their functions of scrubbing teeth with a plastic handle; they also promote better oral healthy with less effort using their additional cleaning mechanisms.
The first electric toothbrush came much later and was first introduced in the 1960's which has been introduced as an alternative to manual method of tooth brushing. Frederick Wilhelm, a Swedish clockmaker, patented the earliest tooth brushing device in 1855. The powered toothbrushes are provided with a brush head capable of a variety of motions driven by a power source. Powered brushes were first introduced with a back and forth action. Subsequent development has lead to the evolution of rotary action brushes, and more recently higher frequency vibration brushes. In general, the brush heads of powered toothbrushes tend to be more compact than those of conventional, manual brushes. The bundles of bristles are arranged either in rows or in a circular pattern mounted in a round head. Bristles are also arranged as more compact single tufts which facilitate interproximal cleaning and brushing in less accessible area of the mouth. Although mechanical plaque removal with a manual toothbrush remains the primary method of maintaining good oral hygiene for the majority of the population, due to the increasing interest in powered toothbrushes, their effectiveness in comparison to manual toothbrushes has been brought into question. Silverman et al. in 2004 did a comparative study among 4–5-year-old children for the evaluation of plaque removal efficacy between powered and manual toothbrushes. There was no clinically meaningful difference found between any of the toothbrushes tested during either of the trials with regard to plaque removal or improvement in gingival health. A meta-analysis by Vibhute and Vandana in 2012 compared the efficacy of manual and powered brushes in relation to the removal of plaque and gingival health. There was no statistically significant difference between powered and manual brushes. Although there are no significant differences in plaque removal efficacy of powered toothbrushes in comparison to manual toothbrushes, but such toothbrushes have been found to be effective in persons not highly motivated to oral health care, including children and adults. In addition, such toothbrushes can be effective in patients with limited manual dexterity [Figure 1].
The ultrasonic toothbrush is a manual toothbrush, in which a Piezoelectric ultrasonic emitter is embedded in the brush head. The ultrasonic emitter is driven by a power supply located in the handle that operates at 1.6 MHz. The plaque destroying power of ultrasound and the deep, gentle cleansing wave action of sonic vibration penetrate the gumline to a depth of 5 mm. This results in the destruction of the periodontal pathogen. Studies have shown that the effect of such toothbrushes on the oral hygiene status and stain removing efficacy is better in comparison to manual toothbrushes. Emmi-dent ® is the first ultrasonic toothbrush that was provided with its nonabrasive nano-bubble toothpaste. It worked motionlessly as an ultrasonic rather than an electronic toothbrush which reduced plaque and lowered risk for periodontal disease. It is also beneficial in destroying bacteria, removal of stains of coffee, wine, nicotine, and food. The teeth returned to their natural white color within days. It also worked under braces, cleaning, and removing stains. It is gentle for children. It also cleans gingival pockets where even dental floss cannot reach. It is gentle enough to use immediately after oral surgery, including implants, avoiding damage to teeth, and gums and is painless on sensitive teeth and gums.,
Ultraviolet-sterilized toothbrush system
Toothbrushes are rapidly contaminated with different microorganisms representing a possible cause of infection or reinfection, especially in the periodontal patients under therapy, and these microorganisms may originate not only from the oral cavity but also from the environment where the toothbrushes are stored. Procedures for the decontamination of toothbrushes would prevent the risks of reinfection or infection by other pathogenic microorganisms from the environment. The ultraviolet (UV), sterilized toothbrush system concept, is helpful for those who have habit of keeping everything clear and germ-free. On an average, 10,000,000 bacteria live on a toothbrush. In the UV-sterilized toothbrush system, UV base help to sterilize the toothbrush whenever it is placed and can hold up to a quartet of UV pods to keep a small family's toothbrushes safe and bacteria free whenever they are not in use. Toothbrushes have color-coding. Recently, few studies indicated the use of UV light as the most effective household method to sanitize the toothbrushes after contamination. Furthermore, due to the ease of use, these techniques may increase compliance in toothbrush bacterial decontamination , [Figure 2].
Ionic toothbrush works on the principle of polarity that every element in nature has a positive or a negative charge. Use of devices with ionic action in the oral cavity is not a new concept. The terms iontophoresis, electrophoresis, and electrolyzing have been used in dentistry for many years. The ionic toothbrush is only slightly larger than the manual toothbrush, with replaceable brush heads. It works on the principle of changing surface charge of tooth to repel plaque even from inaccessible areas of teeth. The bonding between the pellicles and bacteria is mediated by Ca 2+ bridge formation. The anions supplied by the lithium battery inhibits the bonding between the bacteria and Ca 2+ and prevents the bacteria from adsorbing to the pellicles. Hence, the plaque accumulation is reduced because the above-mentioned anions continuously supplied from the tips of the bristles of the ionic toothbrushes prevent the mild electrostatic bonding between the bacteria itself. The important ionic exchange, along with the normal mechanical action of the bristles on the tooth surface, enhances plaque removal [Figure 3].
Deshmukh et al. in 2006 conducted a clinical study to evaluate the effectiveness of an ionic toothbrush on oral hygiene status. There was a significant reduction in plaque index and gingival index scores as well as there was no soft-tissue trauma following the use of ionic toothbrushes. This result shows that such as manual toothbrushes ionic toothbrushes are equally helpful for regular and long-term use.
Singh et al. in 2011 conducted a study to clinically assess and compare the efficacy of the sonic and ionic toothbrushes among 22 individuals. From their study, it was concluded that though the sonic toothbrush was insignificantly superior to the ionic toothbrush, both the toothbrushes are clinically effective in removing plaque and improving the gingival conditions.,
Dentinal hypersensitivity is one of the most common complications that affect patients both in day-to-day life as well as after periodontal therapy. It has been shown that Nd:YAG lasers can block depolarization of rapidly conducting A-β fibers, and such laser radiation can block an action potential conduction in a simulated intradental nerve. More recently, low-level laser therapy (LLLT) has gained attention as a new method to control pain. LLLT is reported to increase blood supply, and the recovery of dental tissues was promoted when irradiated with lasers. Laser toothbrushes are an improved version of the modern toothbrush that emits red (635 nm) light in the visible spectrum produced by a diode laser inside the toothbrush powered with an AA battery. The LLLT with the help of such toothbrushes help to reduce dentinal hypersensitivity. Another advantage of using laser in toothbrush is that the patient can use it at home, which is cost-effective, less time-consuming and easily used by patients [Figure 4].
Ko et al. in 2014 and Yaghini et al. in 2015 tested the efficacy and the safety of a low-level laser-emitting toothbrush on the management of dentinal hypersensitivity and concluded that the use of the low-level laser-emitting toothbrush is a safe and effective treatment option for the management of dentinal hypersensitivity.,
Such types of toothbrushes are meant for one-time use and are found to be very effective in maintaining oral hygiene regime in cases of travelers, children and elderly patients, hospital patients, and any other persons that lacks manual dexterity.
A chewable toothbrush is a miniature plastic molded toothbrush that can be used when no water is available. They tend to be very small, but should not be swallowed and should be disposed of after use. They are most commonly available from bathroom vending machines and composed of xylitol, flavoring aqua, and polydextrose. Other types of disposable toothbrushes include those that are a small breakable plastic ball of toothpaste on the bristles which can be used without water and prove to be quite handy to travelers. These brushes should be used between the teeth, to swivel from left to right and then, the tongue need to be used to move the brush around the mouth similar to the way one would use chewing gum [Figure 5].
Myoken et al. in 2005 investigated the effectiveness of the chewable toothbrush in a care-dependent elderly population and concluded that chewing the brush results in the removal of a significant amount of plaque.
Bezgin et al. in 2015 also conducted a pilot study on the effectiveness of chewable brush in removing plaque in children and found no adverse clinical signs or symptoms caused by the toothbrushes. From this study, it was concluded that chewable brush may be an appropriate oral hygiene adjunct for school children, including children with disabilities.,,
Tooth towelettes are being marketed as a method of plaque removal when tooth brushing is not possible. Their use is not meant to replace a daily tooth brushing regimen. Finger brushes are mounted on the index finger of the brushing hand, and the agility and sensitivity of the finger are used to clean the teeth. Consequently, the pressure with which they are applied can be well controlled because the finger can actually feel the tooth and gingival surfaces and helps in positioning the brush for more effective scrubbing. However, the plaque removal efficacy of such brushes, in particular proximal plaque reduction is less than a regular manual toothbrush.
Foam brushes resemble a disposable soft sponge soaked in chlorhexidine on a stick. They have been dispensed to hospital patients for intraoral cleansing and refreshing since the 1970s. They are used in particular for oral care in medically compromised and immunocompromised patients to reduce the risk of oral and systemic infection.
| Powered Flossing Devices|| |
Dental floss is the mostly widely recommended tool for removing plaque from proximal surfaces. Dental floss as an adjunct to tooth brushing has a significant effect in the reduction of plaque and parameters of gingival inflammation, in adults with periodontal disease. However, at the same time, manual flossing is a very technique sensitive procedure that requires patient knowledge and awareness. To overcome such issues, powered flossing has been introduced.
Powered flossing devices are one of the recent advancements in mechanical plaque control. They consist of battery operated nylon tip that slip easily between teeth and is very gentle to the gums. They are very effective in cases of patients wearing orthodontic appliances. Shibly et al. in 2001 conducted a study comparing powered flossing device (Waterpik power floss ®) with that of manual dental floss. From the study, they concluded that in case of oral hygiene maintenance powered floss are equally effective as manual floss  [Figure 6].
| Oral Irrigation Devices|| |
A dental water jet or water flosser or oral irrigator (OI) is an electric device that delivers a pulsating stream of fluid (containing chlorhexidine, stannous fluoride, iodine solution, antibiotics like 5% tetracycline hydrochloride) through controlled pressure which is aimed at the removal of interdental and subgingival plaque biofilm on tooth surfaces to reduce inflammation as an adjunct to tooth brushing. The devices may be power or nonpower driven and depending on the type of application; they are designed for both professional as well as patient applied home irrigation. Waterpik ® oral irrigation device is one of such devices consisting of a reservoir and a handle with replaceable tips. The tip design varies according to the purpose for which they are being used.
The Water Flosser's mechanisms of action are centralized to its effectiveness. The two main physical features of water bossing action include pulsation and pressure. Pressure is essentially regulated by pulsation. A combination of these two actions causes disruption of bacterial activity, expulsion of subgingival bacteria, and the removal of loosely lodged debris and food particles. Clinical effectiveness has been demonstrated in the 50–90 psi (pounds of pressure per square inch) range. These levels reject what both healthy and inflamed tissues can comfortably handle without tissue damage , [Figure 7].
Rosema et al. in 2011conducted a study to compare the effectiveness of an OI with a prototype jettip or a standard jet tip to floss as adjunct to daily tooth brushing on gingival bleeding. From the study, it was concluded that when combined with manual tooth brushing the daily use of an OI, either with prototype or standard jet tip, is significantly more effective in reducing gingival bleeding scores than the use of dental floss, as determined within the limits of this 4-week study design.
| Modification of Other Interdental Cleaning Aids|| |
Interdental brushes were introduced in the 1960s as an alternative to wood sticks. The interdental brush consists of soft nylon filaments twisted into a fine stainless steel wire. Since the metal wire causes discomfort to the patients with sensitive root surfaces for such patients, the use of plastic-coated metal wires may be recommended. The support wire is continuous or inserted into a metal/plastic handle. Interdental brushes are manufactured in different sizes and forms. The most common forms are cylindrical or conical/tapered (like a Christmas tree). The length of the bristles in cross section should be tailored to the interdental space. Appropriate interdental brushes are currently available for the smallest to the largest interdental space which ranges from 1.9 to 14 mm in diameter. Interdental brushes are frequently recommended by dental professionals to patients with sufficient space between their teeth.
While using, the brush should be inserted gently between the teeth and should not be forced into space. Then the brush is to be moved full length, back and forth a few times until the entire tooth surface gets properly cleaned. The brush can be rinsed with water and reused later on. When the filaments are worn out the brushes need to be replaced.
An end-tufted brush is a type of toothbrush used specifically for cleaning along the gum line adjacent to the teeth. The bristles are usually shaped in a pointed arrow pattern to allow closer adaptation to the gums. The single tuft or group of small tufts may be from 3 to 6 mm in diameter and may be flat or tapered. The handle may be straight or contra-angled. An end-tufted brush is ideal for cleaning specific difficult-to-reach areas, such as between crowns, bridgework and crowded teeth. End-tufted brushes may also be used around fixed orthodontic appliances such as braces  [Figure 8].
| Conclusion|| |
Mechanical plaque control is the most important way to get rid from daily plaque accumulation. With continuously developing lifestyle, methods of mechanical plaque control are also getting advanced day-by-day. There was a time when people used to clean their teeth with chewing sticks which later on got modified to manual toothbrushes, and now, there is the era of advanced plaque control methods such as, powered toothbrush, ultrasonic brushes, ionic brushes, chewable toothbrushes, laser toothbrushes, end-tufted toothbrushes, powered flossing devices for interdental plaque control and oral irrigation devices for pan-oral plaque control. Conventional mechanical plaque control aids such as manual toothbrush, chewing sticks, and dental flosses require manual dexterity and are time-consuming whereas recent advancements are more accurate and less time-consuming. These advanced devices should be included in routine mechanical plaque control measures. Further developments are going on and the day is not very far when plaque can be controlled more easily, effectively, and accurately within the seconds of time.
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Conflicts of interest
There are no conflicts of interest.
| References|| |
Socransky SS, Haffajee AD. Dental biofilms: Difficult therapeutic targets. Periodontol 2000 2002;28:12-55.
Teles RP, Haffajee AD, Socransky SS. Microbiological goals of periodontal therapy. Periodontol 2000 2006;42:180-218.
Faveri M, Mayer MP, Feres M, de Figueiredo LC, Dewhirst FE, Paster BJ. Microbiological diversity of generalized aggressive periodontitis by 16S rRNA clonal analysis. Oral Microbiol Immunol 2008;23:112-8.
Feres M, Faveri M, Figueiredo LC, Teles R, Flemmig T, Williams R, et al
. Non-surgical periodontal therapy: Mechanical debridement, antimicrobial agents and other modalities. J Int Acad Periodontol 2015;17 1 Suppl:21-30.
Axelsson P, Albandar JM, Rams TE. Prevention and control of periodontal diseases in developing and industrialized nations. Periodontol 2000 2002;29:235-46.
Claydon NC. Current concepts in toothbrushing and interdental cleaning. Periodontol 2000 2008;48:10-22.
Axelsson P, Odont D. Concept and practice of plaque-control. Pediatr Dent 1981;3:101-13.
Menon L, Ramamurthy J. New vistas in plaque control. IOSR J Dent Med Sci 2014;13:64-8.
Loe H, Theilade E, Jensen SB. Experimental gingivitis in man. J Periodontol 1965;36:177-87.
Sumant G, Benna G, Bhongade L. Oral health status of young adults using indigenous oral hygiene methods. Stomatol India1992;5:17-23.
Scutt JS, Swann CJ. The first mechanical toothbrush? Br Dent J 1975;4:139-52.
Silverman J, Rosivack RG, Matheson PB, Houpt MI. Comparison of powered and manual toothbrushes for plaque removal by 4- to 5-year-old children. Pediatr Dent 2004;26:225-30.
Vibhute A, Vandana KL. The effectiveness of manual versus powered toothbrushes for plaque removal and gingival health: A meta-analysis. J Indian Soc Periodontol 2012;16:156-60.
] [Full text]
Vandana KL, Penumatsa GS. A comparative evaluation of an ultrasonic and a manual toothbrush on the oral hygiene status and stain removing efficacy. J Indian Soc Pedod Prev Dent 2004;22:33-5.
Sharma K, Sangwan A. Era of smart toothbrushes. Adv Hum Biol 2013;3:2. [Full text]
Gujjari SK, Gujjari AK, Patel PV, Shubhashini PV. Comparative evaluation of ultraviolet and microwave sanitization techniques for toothbrush decontamination. J Int Soc Prev Community Dent 2011;1:20-6.
Deshmukh J, Vandana KL, Chandrashekar KT, Savitha B. Clinical evaluation of an ionic tooth brush on oral hygiene status, gingival status, and microbial parameter. Indian J Dent Res 2006;17:74-7.
] [Full text]
Singh G, Mehta DS, Chopra S, Khatri M. Comparison of sonic and ionic toothbrush in reduction in plaque and gingivitis. J Indian Soc Periodontol 2011;15:210-4.
] [Full text]
Ko Y, Park J, Kim C, Park J, Baek SH, Kook YA. Treatment of dentin hypersensitivity with a low-level laser-emitting toothbrush: Double-blind randomised clinical trial of efficacy and safety. J Oral Rehabil 2014;4:523-31.
Yaghini J, Mogharehabed A, Safavi N, Mohamadi M, Ashtiju F. Evaluation of the effect of low level laser therapy toothbrush in treatment of dentin hypersensitivity. J Lasers Med Sci 2015;6:85-91.
Bezgin T, Dag C, Ozalp N. How effective is a chewable brush in removing plaque in children? A pilot study. J Pediatr Dent 2015;3:41-5. [Full text]
Lang NP, Lindhe J. Textbook of Clinical Periodontology and Implant Dentistry. 6th
ed. The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK: John Wiley & Sons; 2015.
Shibly O, Ciancio SG, Shostad S, Mather M, Boardman TJ. Clinical evaluation of an automatic flossing device vs. Manual flossing. J Clin Dent 2001;12:63-6.
Bhaskar SN, Cutright DE, Gross A, Frisch J, Beasley JD 3rd
, Perez B. Water jet devices in dental practice. J Periodontol 1971;42:658-64.
Selting WJ, Bhaskar SN, Mueller RP. Water jet direction and periodontal pocket debridement. J Periodontol 1972;43:569-72.
Rosema NA, Hennequin-Hoenderdos NL, Berchier CE, Slot DE, Lyle DM, van der Weijden GA. The effect of different interdental cleaning devices on gingival bleeding. J Int Acad Periodontol 2011;13:2-10.
Van der Weijden GA, Slot DE. Interdental oral hygiene: The evidence. Multi-Disciplinary Management of Periodontal Disease. Ch. 3: Asian Pacific Society of Periodontology; Hong Kong 2012. p.1-18.
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]