European Journal of Orthodontics, 2015, 539–543

doi:10.1093/ejo/cju083
Advance Access publication 29 December 2014

Systematic Review

Periodontal health during clear aligners

treatment: a systematic review
Gabriele Rossini, Simone Parrini, Tommaso Castroflorio,
Andrea Deregibus and Cesare L. Debernardi

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Department of Orthodontics, Dental School, University of Turin, Italy

Correspondence to: Gabriele Rossini, Department of Orthodontics, Dental School, University of Turin, Via Nizza 230, Turin
10125, Italy. E-mail: dr.gabriele.rossini@gmail.com

Summary
Background:  Clear aligner treatment (CAT) has been cited as a safe and comfortable orthodontic
procedure for adult patients. However, the available evidence is scarce.
Objective:  To perform a systematic review of the existing literature in order to assess periodontal
health during CAT.
Search methods and selection criteria:  Pubmed, Pubmed Central, National Library of Medicine’s
Medline, Embase, Cochrane Central Register of Controlled Clinical trials, Web of Knowledge,
Scopus, Google Scholar, and LILACS were searched from January 1945 to September 2014 to
identify all peer-reviewed papers potentially relevant to the review.
Data collection and analysis: After duplicate selection and extraction procedures, the risk of
bias was assessed according to the Centre for Reviews and Dissemination criteria, and a 3-point
grading system, as described by the Swedish Council on Technology Assessment in Health Care
(SBU), was used to rate the methodological quality of the selected papers. A PICOS table was used
for data extraction.
Results:  Five relevant articles were selected from the 1247 identified articles. The level of evidence
was moderate for all the studies. A significant improvement of the periodontal health indexes was
revealed, in particular when CAT was compared to fixed appliances. No periodontal CAT adverse
effects were observed in the selected studies.
Conclusions:  Periodontal health indexes were significantly improved during CAT.The results of this
review should be interpreted with some caution because of the number, quality, and heterogeneity
of the included studies.

Introduction of plaque indexes (PIs) and the decrease in overall oral health con-
ditions in orthodontic patients, especially when treated with fixed
Direct or indirect effects of orthodontic treatments on periodontal
appliances (3–6). The use of removable appliances can minimize the
status and oral health are well known and quite extensively described
orthodontics-related negative effects on periodontal health allowing
in the existing literature (1). The periodontal reaction to an ortho-
patients easier oral hygiene procedures.
dontic appliance depends on several factors, such as host resistance,
In recent years, increasing numbers of adult patients have sought
the presence of systemic conditions, and the amount and composi-
orthodontic treatment and expressed a desire for aesthetic and com-
tion of dental plaque. Lifestyle factors, including smoking, can also
fortable alternatives to conventional fixed appliances (7, 8).
compromise periodontal support. Oral hygiene procedures have a
Clear aligners treatment (CAT) was introduced to answer this
great impact on the periodontal health during orthodontic treatment
requests. Although CAT has been cited as a safe, aesthetic and com-
(2). The existing literature supports the link between the increase
fortable orthodontic procedure for adult patients, only few trials

© The Author 2014. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved.
539
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540 European Journal of Orthodontics, 2015, Vol. 37, No. 5

were focused on its side effects (9, 10). Considering that teeth and Table 1.  Search strategy.
keratinized gingiva are covered almost all day long by aligners, it
Database Search strategy
is important from a clinical perspective to have a sound judgment
regarding the periodontal effects of CAT. Two systematic reviews Pubmed, PMC, Scopus, ((Orthodont* OR Clear) aligner*
were conducted about CAT and were mainly focused on its poten- Web of Knowledge, OR Invisalign) AND (periodont*
tials (11, 12). None of them reported information about the peri- Embase, NLM OR parodont*) AND (health* OR
odontal effects of this kind of orthodontic treatment. (disadvant* OR adverse OR collateral
The present systematic review was undertaken to answer the fol- OR negative OR unfavourable) AND
lowing clinical research question in permanent dentition subjects: (effect* OR outcom*))
LILACS ((Orthodont$ OR Clear) aligner$
• Does CAT produce detrimental effects on periodontal structures? OR Invisalign) AND (periodont$
OR parodont$) AND (health$ OR
(disadvant$ OR adverse OR collateral
Materials and methods OR negative OR unfavourable) AND
(effect$ OR outcom$))
The protocol for this systematic review (CRD42014009982) was
Cochrane Central Register (Orthodontic aligner* or clear aligner*

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registered in the International Prospective Register of Systematic of Controlled Clinical trials or Invisalign) AND (periodont*
Review (http://www.crd.york.ac.uk/PROSPERO/). OR parodont*) AND (health* OR
On 25 September 2014, a systematic search in the medical lit- (adverse effect* or collateral effect*
erature produced between January 1945 and September 2014 was or negative effect* or unfavo$rable ef-
performed to identify all peer-reviewed papers reporting possible fect* or collateral outcom* or negative
periodontal effects of CAT. In order to retrieve lists of potential outcom* or unfavo$rable outcom* or
papers to be included in the review, the search strategy illustrated disadvant*))
in Table  1 was used in the following databases: Pubmed, Pubmed
Central, National Library of Medicine’s Medline, Embase, Cochrane
Central Register of Controlled Clinical trials, Web of Knowledge, Table 2.  Study selection criteria.
Scopus, Google Scholar, and LILACS. Inclusion criteria Exclusion criteria
Title and abstract (TIAB) screening was performed to select articles
for full text retrieval. Prospective original studies Studies on patients with genetic
The inclusion and exclusion criteria for admittance in the system- on human subjects with syndrome and severe facial
atic review were based on the type of study, were dependent on the permanent dentition malformations
clinical research questions, and are reported in Table  2. The refer- Studies on orthodontic Studies with surgical-orthodon-
treatment with clear aligners tic techniques
ence lists of these articles were perused, and references related to the
Studies that included clear Case reports
articles were followed up.
descriptions of the materials
Duplicate papers were removed and the studies were selected and applied technique
for inclusion independently by two of the authors (G.R. and S.P.). Reviews
Disagreements were solved by discussion between all the authors. Abstracts
The ‘PICO’ approach was used to extract data from the Author debates
selected papers independently and in duplicate by two review Summary articles
authors (S.P. and G.R.). The acronym PICO stands for Population Studies with less than 10
(Participants), Intervention (or Exposure for observational studies), patients
Comparator, and Outcomes. For the purposes of this systematic Studies on animals
review, the PICO format was modified in the PICOS one, where ‘S’
stands for study design (Table 3) (13). The authors of the selected 1. Grade A (High level of evidence): randomized controlled trials (RCTs)
papers were contacted in case of missing information about sample or prospective study with a well-defined control group; presence of
selection and characteristics of their studies. defined diagnosis and endpoints; well-described diagnostic reliability
The primary outcome included the periodontal effects of CAT tests and reproducibility tests; blinding outcome assessment.
evaluated on the basis of periodontal indexes variations detected 2. Grade B (Moderate level of evidence): same criteria as grade
during CAT. The secondary outcome included the eventual CAT A except for the blinding outcome assessment.
orthodontic movements with detrimental effects on dental and peri- 3. Grade C (Low level of evidence): articles that do not meet the
odontal structures. criteria of grade A and B.
According to the CRD (Centre for Reviews and Dissemination,
University of York) and to the PRISMA (Preferred Reporting Items SBU tool permitted to assess the level of the available evidence of the
for Systematic Reviews and Meta-Analyses) statements, evaluation systematic review accordingly to the following classification:
of methodological quality gives an indication of the strength of evi-
1. Strong: at least two studies of level ‘A’.
dence provided by the study because flaws in the design or in the
2. Moderate: one study of level ‘A’ and at least two studies of level ‘B’.
conduction of a study can result in biases (19, 20). However, no sin-
3. Limited: at least two studies of level ‘B’.
gle approach for assessing methodological soundness is appropriate
4. Scarce: fewer than two studies of level ‘B’.
to all systematic reviews (20). A 3-point grading system, described
by the Swedish Council on Technology Assessment in Health Care
(SBU) and the CRD, was used to rate the methodological quality of Results
the selected papers (Table 3) (19, 21). Articles were graded according The search strategy yielded five relevant publications. Four studies
to the SBU criteria as follow: were prospective non-randomized and one study was prospective
G. Rossini et al. 541

Table 3.  PICOS table.

Quality of the
evidence (SBU
Author (ref.) Study design Population Intervention Comparison Outcomes grading system)

Miethke and Vogt Prospective study 60 patients (43 M Orthodontic Orthodontic Modified B
(14) and 17 F, age range: treatment with treatment with PI*
18–51 years, mean age: fixed appliance clear aligners
Modified GI
30.1 years): 30 patients
PBI
fixed appliance and 30
patients clear aligners SPD
Miethke and Prospective study 30 patients with lingual Orthodontic Orthodontic Modified B
Brauner (15) appliance (age range: treatment with treatment with PI*
16–48 years, mean age: lingual fixed clear aligners Modified
39.6 years) appliance (from the GI*
previous 2005 PBI*

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study) SPD*
Low et al. (16) Prospective study 11 patients (7 M and Clear aligner Clear aligner PPI B
4 F, age range: treatment of treatment of
19–39 years) slow plaque fast plaque
formers patients formers
patients
Karkhanechi et al. Prospective study 42 patients: 22 fixed Orthodontic Orthodontic PI* B
(17) appliance (6 M and treatment with treatment with
16 F, mean age: fixed appliance clear aligners BoP*
34 ± 7.18 years, age
GI*
range: 18–44 years)
and 20 clear aligners
PPD*
(8 M and 12 F, mean
age: 28 ± 6.86 years, age BANA score
range: 18–44 years)
Levrini et al. (18) Prospective RCT 30 patients (9 M Orthodontic Untreated Modified B
and 21 F, mean age: treatment with control group PI*
25.1 ± 4.6 years): clear aligners PPD*
10 fixed appliance, and with fixed
BoP*
10 clear aligners, and appliance
Compliance
10 control Class I 
malocclusion with Biofilm
Little’s Index from 1 to 3 mass*

BANA, N-benzoyl-dl-arginine-beta-naphthylamide; BoP, bleeding on probing; GI, gingival index; PBI, papillary bleeding index; PI, plaque index; PPD, probing
pocket depth; PPI, plaque percentage index; SPD, sulcus probing depth; VAS, visual analog scale.
*P < 0.05.

randomized (14–18). The article selection process is illustrated in the Effects of interventions
PRISMA Flow Diagram (Figure 1). Five studies (one RCT and four prospective Clinical Controlled
Sample size in individual studies ranged from 11 to 60 subjects Trials) analyzed the CAT effects on periodontal health (14–18). All
with a total of 173 subjects. Mean age at the start of CAT in the the selected studies analyzed Invisalign (Align Technology, San Jose,
evaluated samples ranged from 16 to 51 years. California, USA) treatments.
From a methodological point of view, the selected papers Levrini et al. in their RCT recorded periodontal indexes from 3
used different procedures to detect treatment effects: four studies groups of patients (10 treated with CAT, 10 treated with fixed buccal
observed periodontal indexes variations, while one study collected appliances, and 10 not-treated subjects) and evaluated the total bio-
biofilm samples from aligners surfaces in order to analyze its ultras- film mass and the bacterial population in the collected plaque sam-
tructure and morphology. ples (18). Significantly better values of PI [odds ratio (OR): 0.09/95%
Four studies performed a comparison between groups, confidence interval (CI): 0.05–0.15, P  <  0.001], bleeding on prob-
while one study used the analyzed cases as own control group ing (BoP; OR: 0.20/95% CI: 0.11–0.36, P < 0.001), probing pocket
(14–18). depth (PPD; P = 0.002), and amount of biofilm mass (P = 0.003) were
found in the CAT sample. Miethke et al. in their 2005 and 2007 stud-
Quality analysis ies compared periodontal indexes from patients treated with clear
According to the SBU tool, the quality of the collected evidences was aligners or fixed buccal or fixed lingual appliances (30 patients for
moderate (grade B) in all the five studies (14–18). Thus, conclusions each group) (14, 15). Significant differences were found for PI (differ-
with a limited level of evidence could be drawn from the review pro- ence: 0.2) between CAT and fixed buccal appliance group (P < 0.05).
cess. The most important sources of bias were the absence of clues Significant differences for PI (difference: 0.5), gingival index (GI; dif-
about randomization procedures and the lack of adequate blinding ference: 0.4), papillary bleeding index (PBI; difference: 0.2), and sulcus
procedures. The quality grading of the selected papers is shown in probing depth (T3 difference: 0.2) were observed between CAT and
PICOS Table (Table 3). fixed lingual appliance group (P < 0.05). Karkhanechi et al. evaluated
542 European Journal of Orthodontics, 2015, Vol. 37, No. 5

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Figure 1.  Flow chart according to the PRISMA Statement, from Moher et al. (20).

periodontal indexes variations between patients treated with fixed sample selection, while in one study a proper control group was not
appliances (22 patients) and patients treated with clear aligners (20 available (16). Therefore, the results should be interpreted with cau-
patients) after 6 weeks, 6  months, and 12  months from therapy tion. Incomplete reporting of outcomes was investigated according
beginning (17). Significant differences between CAT and fixed appli- to the Cochrane Collaboration guidelines (19). Results showed com-
ances for PI after 6 months (P < 0.001) and 12 months (P < 0.001), plete and reliable data reports among the sample. A  meta-analysis
BoP after 12 months (P < 0.05), GI after 6 months (P < 0.01) and of the results of the studies was planned. However, due to the high
12 months (P < 0.01), and PPD after 6 weeks (P = 0.012), 6 months heterogeneity (I2 > 75%), meta-analysis was omitted as suggested by
(P < 0.021), and 12 months (P < 0.003) were revealed. Low et al., the Cochrane Collaboration (19).
who collected and analyzed biofilm samples from clear aligners sur- A systematic review by Bollen et al. stated the absence of reliable
faces of 56 volunteers, did not find any significant variation of the evidence about the effects of orthodontic treatment on periodontal
plaque percentage index during treatment (16). health (22). Furthermore, other systematic reviews by van Gastel et al.
and Talic focused on plaque retention as the main risk factor for peri-
odontal diseases after orthodontic treatment, confirmed that ortho-
Discussion dontic treatment itself does not increase the incidence of periodontal
The present review evaluated the existing literature related to the pathologies (2, 23). However, oral hygiene procedures have a great
periodontal effects of CAT. impact on the periodontal status of orthodontic patients (2). In this sys-
Five prospective studies, of which only one was randomized, tematic review, the five selected studies (one RCT and four prospective
were included in the review process. Despite the widespread use of CCTs) analyzed the influence of CAT on periodontal health (14–18).
CAT, there is still a lack of strong evidence about the type and entity Four studies assessed a statistically significant reduction (P < 0.05) of
of periodontal effects. Accordingly to the SBU tool, the evidence PI in CAT patients with respect to fixed (lingual and/or buccal) appli-
emerging from the selected papers is of moderate level. The analysis ances patients (14, 15, 17, 18). Other periodontal indexes, as GI, PBI,
of possible sources of bias revealed the lack of some methodological BoP, and PPD, were analyzed in these studies (15, 17, 18). In each
features: a very strong limitation of all studies was the absence of study and for each parameter, a significant improvement during CAT
proper blinding procedures, as well as the lack of information about was obtained with respect to fixed appliance treatment.
G. Rossini et al. 543

As widely stated in the scientific literature, the most important 6. Al-Anezi, S.A. (2014) Dental plaque associated with self-ligating brackets
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the orthodontic treatment of patients with compromised periodontal
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14. Miethke, R.R. and Vogt, S. (2005) A comparison of the periodontal health
Considering all the results of this systematic review, strong lim- of patients during treatment with the Invisalign system and with fixed
itations come from the heterogeneity and the low number of the orthodontic appliances. Journal of Orofacial Orthopaedics, 66, 219–229.
selected studies, as well as multiple sources of bias that decreased the 15. Miethke, R.R. and Brauner, K. (2007) A Comparison of the periodontal
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R.G., Craig, R.G. and Cisneros, G.J. (2013) Periodontal status of adult
1. Most of the studies presented with methodological problems:
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bias and confounding variables, lack of adequate blinding proce-
one year of active orthodontic therapy. The Angle Orthodontist, 83, 146–51.
dures and absence of proper randomization methods. Thus, con- 18. Levrini, L., Abbate, G.M., Migliori, F., Orrù, G., Sauro, S. and Caprioglio, A.
clusions with a moderate level of evidence could be drawn from (2013) Assessment of the periodontal health status in patients undergoing
the review process. orthodontic treatment with fixed or removable appliances. A microbiological
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3. A significant decrease of periodontal indices (GI, PBI, BoP and CRD’s Guidance for Undertaking Reviews in Health Care. Centre for
PPD) during CAT was observed in the analyzed sample of patients. Reviews and Dissemination, University of York, York.
20. Moher, D., Liberati, A., Tetzlaff, J. and Altman, D.G.; PRISMA Group.
(2009) Preferred reporting items for systematic reviews and meta-analy-
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