gms | German Medical Science

GMS Hygiene and Infection Control

Deutsche Gesellschaft für Krankenhaushygiene (DGKH)

ISSN 2196-5226

Health promotion through structured oral hygiene and good tooth alignment

Gesundheitsförderung durch strukturierte Mundhygiene und gute Zahnstellung

Review Article

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  • corresponding author Axel Kramer - Institute of Hygiene and Environmental Medicine, University Medicine Greifswald, Greifswald,Germany
  • Christian Splieth - Preventive & Pediatric Dentistry, University Medicine Greifswald, Greifswald, Germany

GMS Hyg Infect Control 2022;17:Doc08

doi: 10.3205/dgkh000411, urn:nbn:de:0183-dgkh0004118

Published: May 10, 2022

© 2022 Kramer et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License. See license information at


Aim: Periodontal diseases and caries are two of the most common forms of chronic degenerative diseases, with consequences not only for the oral cavity manifesting as tooth loss, orofacial pain and xerostomia, but also with effects on the cardiovascular system and, in the elderly, on the pneumonia rate. This can be prevented or controlled by structured oral hygiene.

Method: Based on a systematic literature search in PubMed, the possibilities for ensuring structured oral hygiene are analyzed.

Results and conclusion: Limiting the consumption of sugary meals and beverages, regular removal of food debris – supplemented by sugar-free chewing gum if desired – and preventing plaque formation by brushing with fluoridated toothpastes, using dental floss and interdental brushes after meals, serve to prevent or control gingivitis, periodontitis and caries. In the long term, the development of periodontitis-associated cardiovascular diseases and, in the elderly, the risk of pneumonia can probably be reduced.

Antiseptic rinsing of the oral cavity is an important supplement to prevent periodontitis, especially in cases of limited ability to perform mechanical biofilm removal, but also for the prevention of respiratory infections.

Proper functional tooth alignment is important for optimal mechanical cleaning to prevent plaque accumulation. If correction of misaligned teeth is possible with the use of removable aligners instead of fixed orthodontic appliances, these are to be preferred because of the better accessibility for mechanical hygiene measures.

Keywords: periodontitis, gingivitis, caries, systemic effects, prevention, oral hygiene, aligner


Zielsetzung: Parodontopathien und Karies zählen zu den häufigsten Formen chronisch degenerativer Krankheiten mit Auswirkungen nicht nur in der Mundhöhle mit Zahnverlust, orofazialen Schmerzen und Xerostomie, sondern auch auf das kardiovaskuläre System und im Senium auf die Pneumonierate. Dem muss durch strukturierte Mundhygiene entgegengewirkt werden.

Methode: Auf der Grundlage einer systematischen Literaturrecherche in PubMed sollten die Möglichkeiten zur Gewährleistung einer strukturierten Mundhygiene analysiert werden.

Ergebnisse und Schlussfolgerungen: Die Einschränkung des Konsums zuckerhaltiger Mahlzeiten und Getränke, die regelmäßige Entfernung von Speiseresten, ggf. ergänzt durch Kaugummikauen, und die Verhinderung der Plaquebildung durch Zähneputzen mit fluoridhaltigen Zahnpasten, Anwendung von Zahnseide und Interdentalbürsten nach den Mahlzeiten dienen der Verhinderung von Gingivitis, Parodontopathien und Karies. Langfristig kann dadurch vermutlich auch mit Periodontitis assoziierten systemischen Erkrankungen vorgebeugt werden.

Insbesondere bei eingeschränkter Fähigkeit zur Durchführung der mechanischen Biofilmentfernung, aber auch zur Prävention respiratorischer Infektionen, ist die antiseptische Spülung der Mundhöhle eine wichtige Ergänzung zur Prävention der Periodontitis.

Eine gute, funktionale Zahnstellung erleichtert die mechanische Reinigung zur Verhinderung der Plaqueakkumulation. Sofern mit dem Einsatz von Alignern anstelle festsitzender kieferorthopädischer Apparaturen die Stellungskorrektur möglich ist, sind diese wegen der besseren Zugängigkeit für mechanische Hygienemaßnahmen zu bevorzugen.

Schlüsselwörter: Periodontitis, Gingivitis, Karies, systemische Auswirkungen, Prävention, Mundhygiene, Aligner


Periodontal diseases and caries are among the most common forms of inflammatory and infectious diseases and one of the most common forms of chronic degenerative disease [1], [2]. With increasing life expectancy, the number of people with chronic diseases, immune deficiencies and impairments leading to multimorbidity and need for long-term care is increasing. With increasing age, the risk of diseases of the oral cavity involving the periodontium and the teeth also increases. Different periodontal diseases resulting in tooth loss affect the well-being, psychological condition, social relationships and physical health. The quality of life is positively associated with a higher number of teeth and the chewing function they provide, greater number of occlusal pairs, implant-supported overdentures, and the short dental arch concept, but negatively associated with xerostomia, orofacial pain, and poor chewing ability [3]. However, subjectively perceived esthetics in the oral and facial region is also important for the quality of life and psychosocial well-being [4]. Due to growing evidence on the importance of the oral cavity for health and well-being, the maintenance and promotion of oral-cavity health are gaining importance beyond the improvement of the local situation in the oral cavity. In terms of health policy, it is crucial to start preventing gingivitis, periodontitis, caries, and ensuring good tooth position by beginning oral care in early childhood rather than at the onset of problems.

Considering the current state of knowledge on the interrelationship between the health of the oral cavity and the effects on the rest of the organism, the following highlights ways to maintain oral-cavity health.


Based on a systematic literature search in PubMed, the possibilities of ensuring structured oral hygiene are analyzed with following search criteria: Periodontitis, gingivitis, caries, combined with prevention, oral hygiene, periodontitis-associated cardiovascular diseases, periodontitis-associated pneumonia, systemic effects of oral health, senescence and oral health, influencing factors on oral health, fixed orthodontic appliances, wafer-thin, aligner, combined with oral health, antiseptic mouth rinse oral health.


Influence of pregnancy and senescence on oral cavity health

Pregnancy is associated with an increased caries and periodontal risk. By constructing a cariogram, it is possible to identify risk factors for the development of caries as a basis for intensified prevention [5]. Thus, intensified oral hygiene measures are advisable.

With increasing age, physiological, hormonal and cellular changes occur. In principle, all cells can be affected by aging processes. If, for example, the number of T lymphocytes decreases, this results in an increased susceptibility to infection. Furthermore, the capacity of the immune system is reduced by unfavorable lifestyle factors, such as smoking, alcohol consumption, inactivity, and unhealthy diet, whereas regular physical activity is associated with an improvement in the immune response even at older ages [6]. An important feature of senescence is the transformation of somatic cells into a “senescence-associated phenotype” associated with the production of inflammatory mediators [7]. In the context of aging, the chronic burden of inflammatory mediators (interleukins, acute phase proteins, etc.) is called “inflammaging” [8].

Association of oral cavity health with systemic diseases

Observational studies support the hypothesis of a weak association between periodontitis and cardiovascular disease (CVD). However, whether poor periodontal health causes CVD is still unclear. Masi et al. [9] concluded that cardiovascular prevention begins in the oral cavity. Furthermore, periodontal microbes are associated with atherosclerosis, hypertension, and dyslipidemia, but again, causality is still unproven [10].

Epidemiologic studies suggest an association between oral health and pneumonia in older people in outpatient or inpatient medical care. Of seniors living independently at home, 13% were hospitalized for pneumonia within 10 years. Approximately 22% of the disease burden can be explained by high plaque levels and limited physical mobility, independent of other confounding variables [11]. These data underscore the importance of oral hygiene [12].

There is also an association between periodontitis and metabolic as well as psychiatric diseases, probably based on inflammatory processes [13].

Prevention of periodontitis and caries

Oral hygiene

In addition to subjective well-being, the objective of oral hygiene is to maintain an intact mucous membrane, a plaque-free tongue, the dental status and supple lips. Inadequate care can lead to dehydration, rhagades, aphthae, damage to the teeth, mucositis, gingivitis, periodontitis, parotitis, and possibly also to descending respiratory infections and cardiovascular side effects. Especially at risk are disabled patients, seniors, patients undergoing chemotherapy or radiotherapy, and immunosuppressed patients.

Caries-protective nutrition [14] and consistent, structured oral hygiene [15] will counteract the risk of microbially maintained inflammation in the oral cavity, including systemic side effects emanating from it [16]. Oral hygiene includes regular removal of food debris and mechanical removal of biofilm for plaque prevention, with the aim of preventing gingivitis, periodontitis and caries [14], [15]. In the long term, this is likely to prevent systemic disease, as periodontal inflammation exacerbates systemic inflammation [10], [13]. Intensified oral hygiene (toothbrushing, supragingival scaling) has been shown to permanently improve oral inflammatory status and slow periodontal deterioration in patients with type 2 diabetes [17]. If patients are unable to perform oral hygiene adequately, care takers should be instructed and trained to guarantee standard oral hygiene procedures.

For prophylaxis of caries, gingivitis and periodontitis, with maintenance of the physiological oral cavity flora, at least twice-daily toothbrushing with a fluoridated toothpaste using an electric toothbrush, if possible [18], is effective, provided the gums are intact. Brushing only once a day has a lower caries-preventive effect [19], [20]. There is no epidemiological evidence on the optimal brushing duration. The only evidence is that 1-minute toothbrushing removes an average of 27% of plaque, and 2-minute toothbrushing removes 41% of plaque [21]. A longitudinal cohort study demonstrated an association between the frequency of toothbrushing and the development of new carious lesions in children aged 6–10 years [22]. Toothbrushing should be renewed after 8 to12 weeks. The use of dental floss and interdental brushes of different thicknesses for the interdental spaces additionally prevents the accumulation of biofilm. Brushes angled in the bristle area facilitate cleaning of the posterior teeth. Dentures, fixed orthodontic appliances and aligners should be included in oral hygiene. It is important to practice an effective brushing technique with a systematic approach [14]. Particularly in cases of increased caries risk during pregnancy and diseases with altered oral cavity flora, tooth cleaning after every meal is especially important, if possible in conjunction with the use of dental floss. Unfortunately, brushing teeth in the morning and evening is not universal practice. Brushing teeth is especially important before going to bed, because the reduced saliva flow at night enhances bacterial reproduction and attacks on the tooth enamel.

In additional to fluoridated toothpaste, fluoridated table salt should be used [14]. In cases of increased caries risk, e.g., during pregnancy, it is advisable to use toothpastes with increased fluoride concentration or fluoride varnishes, gels or antiseptic mouthrinses to remineralize the enamel [14], [23].

If tooth cleaning is supplemented by antiseptic mouth rinses, which is particularly useful if the ability to perform mechanical biofilm removal is limited, active ingredients with the risk of developing resistance, including the risk of cross-resistance to antibiotics, should not be used. This applies to the antiseptic agents chlorhexidine digluconate [24], [25] and triclosan [26], [27], commonly used in mouthrinses, whereas essential oils are not known to develop resistance [28], [29]. Regular antiseptic oral cavity rinsing (2–3 times daily) additionally reduces the frequency and severity of infections during epidemic or pandemic periods of respiratory infections, demonstrated for influenza and COVID-19 [30], [31].

The number of sugary meals and snacks, including sugary drinks, should be kept to a minimum. Food and beverages without free sugars are to be preferred, especially in between meals. Regular chewing of sugar-free chewing gum can help prevent caries and is therefore particularly useful after meals [14].

Ensuring good tooth alignment

Good tooth alignment improves function and self-cleaning and support effective oral hygiene, because mechanical tooth cleaning can only be effective where it reaches the tooth. Preventing biofilm formation in the interdental spaces is crucial for the long-term prevention of periodontitis. There are indications that the orthodontic treatment of malocclusions possibly could coincide with a reduced risk of compromised oral health [32] and periodontitis prevalence [33]. To restore good, functional tooth position, fixed orthodontic appliances or wafer-thin, transparent removable dental splints that rest on the teeth (so-called aligners) can be used. The disadvantage of fixed appliances is the difficulty in ensuring oral hygiene due to numerous surfaces that are difficult to reach [34]. In contrast, aligners facilitate oral hygiene [35] and have been shown to significantly improve periodontal health indices, although the strength of evidence from studies is moderate [36], [37], [38], [39]. However, the indication for aligners must be carefully considered, as not all tooth movements are possible with aligner therapy. For buccolingual inclination of the maxillary and mandibular incisors with mild to moderate tooth misalignment, results comparable to those of fixed appliances can be achieved [37]. When comparing results with aligners vs fixed braces, both were effective, with aligners having the advantage of segmented movement of the teeth and, depending on the malocclusion, shortened treatment time; however, aligners were not as effective as braces in establishing adequate occlusal contacts and controlling the torque of the teeth [40]. In conclusion, aligners are not a full substitute for orthodontic treatment in childhood and adolescence, but when used as indicated, they improve the guarantee of good dental hygiene and thus contribute to tooth preservation. Their use should therefore be reviewed, particularly in cases of incipient periodontitis.


The aim of oral hygiene is tooth preservation by dental health maintenance or its restoration in case of caries, using home and individual professional dental prophylaxis. In the long term, the development of periodontitis-associated cardiovascular diseases and, in the elderly, the risk of pneumonia can probably be reduced.


Competing interests

The authors declare that they have no competing interests.


The authors received no funding.


Kassebaum NJ, Smith AGC, Bernabé E, Fleming TD, Reynolds AE, Vos T, Murray CJL, Marcenes W; GBD 2015 Oral Health Collaborators. Global, Regional, and National Prevalence, Incidence, and Disability-Adjusted Life Years for Oral Conditions for 195 Countries, 1990-2015: A Systematic Analysis for the Global Burden of Diseases, Injuries, and Risk Factors. J Dent Res. 2017 04;96(4):380-7. DOI: 10.1177/0022034517693566 External link
Billings M, Holtfreter B, Papapanou PN, Mitnik GL, Kocher T, Dye BA. Age-dependent distribution of periodontitis in two countries: Findings from NHANES 2009 to 2014 and SHIP-TREND 2008 to 2012. J Clin Periodontol. 2018 06;45 Suppl 20:S130-S148. DOI: 10.1111/jcpe.12944 External link
van de Rijt LJM, Stoop CC, Weijenberg RAF, de Vries R, Feast AR, Sampson EL, Lobbezoo F. The Influence of Oral Health Factors on the Quality of Life in Older People: A Systematic Review. Gerontologist. 2020 07;60(5):e378-e394. DOI: 10.1093/geront/gnz105 External link
Larsson P, Bondemark L, Häggman-Henrikson B. The impact of oro-facial appearance on oral health-related quality of life: A systematic review. J Oral Rehabil. 2021 Mar;48(3):271-81. DOI: 10.1111/joor.12965 External link
Rivera KB, González López BS, Sánchez Vargas LO, Alanís Tavira J, Bermeo Escalona JR. Evaluation of caries risk factors associated with pregnancy. CIENCIA ergo-sum. 2019;26(3):1-11. DOI: 10.30878/ces.v26n3a5 External link
Simpson RJ, Lowder TW, Spielmann G, Bigley AB, LaVoy EC, Kunz H. Exercise and the aging immune system. Ageing Res Rev. 2012 Jul;11(3):404-20. DOI: 10.1016/j.arr.2012.03.003 External link
von Kobbe C. Cellular senescence: a view throughout organismal life. Cell Mol Life Sci. 2018 Oct;75(19):3553-3567. DOI: 10.1007/s00018-018-2879-8 External link
Franceschi C, Zaikin A, Gordleeva S, Ivanchenko M, Bonifazi F, Storci G, Bonafè M. Inflammaging 2018: An update and a model. Semin Immunol. 2018 12;40:1-5. DOI: 10.1016/j.smim.2018.10.008 External link
Masi S, D’Aiuto F, Deanfield J. Cardiovascular prevention starts from your mouth. Eur Heart J. 2019 04;40(14):1146-8. DOI: 10.1093/eurheartj/ehz060 External link
Merchant AT, Virani SS. Evaluating Periodontal Treatment to Prevent Cardiovascular Disease: Challenges and Possible Solutions. Curr Atheroscler Rep. 2017 Jan;19(1):4. DOI: 10.1007/s11883-017-0640-7 External link
Azarpazhooh A, Leake JL. Systematic review of the association between respiratory diseases and oral health. J Periodontol. 2006 Sep;77(9):1465-82. DOI: 10.1902/jop.2006.060010 External link
Juthani-Mehta M, De Rekeneire N, Allore H, Chen S, O'Leary JR, Bauer DC, Harris TB, Newman AB, Yende S, Weyant RJ, Kritchevsky S, Quagliarello V; Health ABC Study. Modifiable risk factors for pneumonia requiring hospitalization of community-dwelling older adults: the Health, Aging, and Body Composition Study. J Am Geriatr Soc. 2013 Jul;61(7):1111-8. DOI: 10.1111/jgs.12325 External link
Makkar H, Reynolds MA, Wadhawan A, Dagdag A, Merchant AT, Postolache TT. Periodontal, metabolic, and cardiovascular disease: Exploring the role of inflammation and mental health. Pteridines. 2018 Feb;29(1):124-63. DOI: 10.1515/pteridines-2018-0013 External link
Deutsche Gesellschaft für Zahnerhaltung (DGZ); Deutsche Gesellschaft für Zahn-, Mund- und Kieferheilkunde (DGZMK). Kariesprophylaxe bei bleibenden Zähnen – grundlegende Empfehlungen. S2k-Leitlinie 2016. Registernummer 083-021. AWMF; 2016. Available from: External link
Deutsche Gesellschaft für Parodontologie (DG PARO); Deutsche Gesellschaft für Zahn-, Mund- und Kieferheilkunde (DGZMK). Häusliches chemisches Biofilmmanagement in der Prävention und Therapie der Gingivitis. S3-Leitlinie, 2018, Amendment Dezember 2020, Registernummer 083-016. AWMF; 2018. Available from: External link
Quagliarello V, Ginter S, Han L, Van Ness P, Allore H, Tinetti M. Modifiable risk factors for nursing home-acquired pneumonia. Clin Infect Dis. 2005 Jan;40(1):1-6. DOI: 10.1086/426023 External link
Lee HK, Choi SH, Won KC, Merchant AT, Song KB, Jeong SH, Lee SK, Choi YH. The effect of intensive oral hygiene care on gingivitis and periodontal destruction in type 2 diabetic patients. Yonsei Med J. 2009 Aug;50(4):529-36. DOI: 10.3349/ymj.2009.50.4.529 External link
Yaacob M, Worthington HV, Deacon SA, Deery C, Walmsley AD, Robinson PG, Glenny AM. Powered versus manual toothbrushing for oral health. Cochrane Database Syst Rev. 2014 Jun;(6):CD002281. DOI: 10.1002/14651858.CD002281.pub3 External link
Hellwig E, Schiffner U, Schulte A, Koletzko B, Bergmann K, Przyrembel H. S2K-Leitlinie Fluoridierungsmaßnahmen zur Kariesprophylaxe. Register Nr. 083-001. AWMF; 2013.
Marinho VC, Higgins JP, Sheiham A, Logan S. Fluoride toothpastes for preventing dental caries in children and adolescents. Cochrane Database Syst Rev. 2003;(1):CD002278. DOI: 10.1002/14651858.CD002278 External link
Slot DE, Wiggelinkhuizen L, Rosema NA, Van der Weijden GA. The efficacy of manual toothbrushes following a brushing exercise: a systematic review. Int J Dent Hyg. 2012 Aug;10(3):187-97. DOI: 10.1111/j.1601-5037.2012.00557.x External link
Maserejian NN, Tavares MA, Hayes C, Soncini JA, Trachtenberg FL. Prospective study of 5-year caries increment among children receiving comprehensive dental care in the New England children's amalgam trial. Community Dent Oral Epidemiol. 2009 Feb;37(1):9-18. DOI: 10.1111/j.1600-0528.2008.00437.x External link
Duckworth RM, Maguire A, Omid N, Steen IN, McCracken GI, Zohoori FV. Effect of rinsing with mouthwashes after brushing with a fluoridated toothpaste on salivary fluoride concentration. Caries Res. 2009;43(5):391-6. DOI: 10.1159/000239753 External link
Kampf G. Chlorhexidine Digluconate. In: Kampf G, editor. Antiseptic Stewardship: Biocide Resistance and Clinical Implications. Cham: Springer International Publishing; 2018. p. 429-534. DOI: 10.1007/978-3-319-98785-9_13 External link
Cieplik F, Jakubovics NS, Buchalla W, Maisch T, Hellwig E, Al-Ahmad A. Resistance Toward Chlorhexidine in Oral Bacteria – Is There Cause for Concern? Front Microbiol. 2019;10:587. DOI: 10.3389/fmicb.2019.00587 External link
McNamara PJ, Levy SB. Triclosan: an Instructive Tale. Antimicrob Agents Chemother. 2016 12;60(12):7015-6. DOI: 10.1128/AAC.02105-16 External link
Zeng W, Xu W, Xu Y, Liao W, Zhao Y, Zheng X, Xu C, Zhou T, Cao J. The prevalence and mechanism of triclosan resistance in Escherichia coli isolated from urine samples in Wenzhou, China. Antimicrob Resist Infect Control. 2020 10;9(1):161. DOI: 10.1186/s13756-020-00823-5 External link
Yap PS, Yiap BC, Ping HC, Lim SH. Essential oils, a new horizon in combating bacterial antibiotic resistance. Open Microbiol J. 2014;8:6-14. DOI: 10.2174/1874285801408010006 External link
Fierascu RC, Fierascu IC, Dinu-Pirvu CE, Fierascu I, Paunescu A. The application of essential oils as a next-generation of pesticides: recent developments and future perspectives. Z Naturforsch C J Biosci. 2020 Jul;75(7-8):183-204. DOI: 10.1515/znc-2019-0160 External link
Kramer A, Eggers M. Prevention of respiratory viral infections by virucidal mucosal antisepsis among medical staff and in the community. Hyg Med. 2020;45(9):1-9.
Kramer A, Eggers M, Exner M, Hübner NO, Simon A, Steinmann E, Walger P, Zwicker P. Recommendation of the German Society of Hospital Hygiene (DGKH): Prevention of COVID-19 by virucidal gargling and virucidal nasal spray – updated version April 2022. GMS Hyg Infect Control. 2022 [in press].
Bock NC, Saffar M, Hudel H, Evälahti M, Heikinheimo K, Rice DPC, Ruf S. Langfristige Effekte einer kieferorthopädischen Klasse-II-Behandlung auf die Mundgesundheit Long-term effects of Class II orthodontic treatment on oral health. J Orofac Orthop. 2018 Mar;79(2):96-108. DOI: 10.1007/s00056-018-0125-5 External link
Sim HY, Kim HS, Jung DU, Lee H, Lee JW, Han K, Yun KI. Association between orthodontic treatment and periodontal diseases: Results from a national survey. Angle Orthod. 2017 Sep;87(5):651-7. DOI: 10.2319/030317-162.1 External link
Ren Y, Jongsma MA, Mei L, van der Mei HC, Busscher HJ. Orthodontic treatment with fixed appliances and biofilm formation--a potential public health threat? Clin Oral Investig. 2014 Sep;18(7):1711-8. DOI: 10.1007/s00784-014-1240-3 External link
Kim K, Jung WS, Cho S, Ahn SJ. Changes in salivary periodontal pathogens after orthodontic treatment: An in vivo prospective study. Angle Orthod. 2016 Nov;86(6):998-1003. DOI: 10.2319/070615-450.1 External link
Rossini G, Parrini S, Castroflorio T, Deregibus A, Debernardi CL. Periodontal health during clear aligners treatment: a systematic review. Eur J Orthod. 2015 Oct;37(5):539-43. DOI: 10.1093/ejo/cju083 External link
Levrini L, Mangano A, Montanari P, Margherini S, Caprioglio A, Abbate GM. Periodontal health status in patients treated with the Invisalign(®) system and fixed orthodontic appliances: A 3 months clinical and microbiological evaluation. Eur J Dent. 2015 Jul-Sep;9(3):404-10. DOI: 10.4103/1305-7456.163218 External link
Robertson L, Kaur H, Fagundes NCF, Romanyk D, Major P, Flores Mir C. Effectiveness of clear aligner therapy for orthodontic treatment: A systematic review. Orthod Craniofac Res. 2020 May;23(2):133-42. DOI: 10.1111/ocr.12353 External link
Jiang Q, Li J, Mei L, Du J, Levrini L, Abbate GM, Li H. Periodontal health during orthodontic treatment with clear aligners and fixed appliances: A meta-analysis. J Am Dent Assoc. 2018 Aug;149(8):712-20.e12. DOI: 10.1016/j.adaj.2018.04.010 External link
Ke Y, Zhu Y, Zhu M. A comparison of treatment effectiveness between clear aligner and fixed appliance therapies. BMC Oral Health. 2019 01;19(1):24. DOI: 10.1186/s12903-018-0695-z External link