Comparative impact of clear aligners versus fixed orthodontic appliances on periodontal health, pain, and quality of life: a systematic review and meta-analysis

Abstract

Objective

Clear aligners have become a popular alternative to fixed appliances because they offer esthetic advantages and potential improvements in periodontal health and pain management while enhancing quality of life (QOL). This systematic review and meta-analysis investigated the effects of clear aligners versus fixed appliances on established outcomes.

Materials and methods

A systematic search was conducted in PubMed, Scopus, Cochrane Library, Embase, and ScienceDirect up to March 2025, along with gray literature and manual searching of key orthodontic journals. The eligible studies consisted of randomized controlled trials and observational studies that evaluated clear aligners against fixed appliances based on the plaque index (PI), gingival index (GI), probing depth (PD), pain intensity, and QOL. Researchers applied mean difference (MD) to PI, GI, and PD, while standardized mean difference (SMD) was used to evaluate pain intensity and QOL. Researchers evaluated heterogeneity using I² and publication bias while performing subgroup analyses centered on treatment duration.

Results

Thirty-two studies were included in the systematic review, of which 28 were included in the meta-analysis. Clear aligners significantly improved periodontal outcomes compared to fixed appliances, as shown by lower PI scores (MD = −0.437, 95% CI: −0.507 to −0.367, p < 0.001), GI scores (MD = −0.233, 95% CI: −0.296 to −0.170, p < 0.001), and PD scores (MD = −0.332, 95% CI: −0.431 to −0.234, p < 0.001). Patients treated with clear aligners experienced less pain than those treated with fixed appliances, particularly during the early treatment phase (SMD = −0.419, p < 0.001). Clear aligners significantly improved the QOF of patients at 1 week (SMD = −0.985, p < 0.001), 1 month (SMD = −0.829, p < 0.001), and end of treatment (SMD = −0.970, p < 0.001) compared with fixed appliances. Low to moderate heterogeneity was observed between groups for pain outcomes, while high heterogeneity was observed for short-term QOF comparisons.

Conclusion

Clear aligners resulted in favorable periodontal indices compared with those of fixed appliances. They also led to less early pain and better QOF than fixed appliances, although these differences were mostly observed at the beginning of treatment. Clinicians should interpret these results cautiously because of heterogeneity, the inclusion of observational evidence, potential publication bias, and small pooled effects.

Introduction

Esthetic concerns have become a key driver for seeking dental care, especially in orthodontics, which has evolved with advanced techniques and devices to enhance micro-, macro-, gingival, and facial esthetics, reflecting a comprehensive approach to improving dental harmony, function, and overall appearance since its establishment as a specialized branch of dentistry [1]. Orthodontic patients seek treatment not only to enhance their dental and facial esthetics but also to boost their social appeal and confidence [2–5]. Malocclusion, recognized by the WHO as a dentofacial anomaly, can impact esthetics, function, and psychosocial well-being, further reinforcing the demand for orthodontic treatment to enhance facial harmony and self-confidence [6, 7].

Defining malocclusion is challenging because perceptions of occlusal issues vary across individuals and cultures and are influenced by aesthetic preferences and functional expectations [8]. Malocclusion commonly arises during the transition to mixed dentition, leading to speech difficulties, eating challenges, facial structural changes, and tongue or cheek biting [9]. This condition is traditionally managed using braces, which are available in various materials, including metal, ceramic, stainless steel, and gold [9, 10]. Conventional metal braces consist of brackets affixed to the teeth and connected by an arch wire that exerts controlled pressure to facilitate alignment but provides minimal cosmetic advantages [11, 12]. Ceramic braces function similarly but are designed to match the natural tooth color for enhanced esthetics [13]. For patients prioritizing discretion, lingual braces offer an alternative by positioning the brackets on the lingual rather than buccal surfaces, which may reduce pain compared to pre-fabricated ones; however, patients often experience greater difficulties with speech and mastication when using lingual appliances [14]. Despite their various advantages, these materials have significant flaws, including poor esthetics and higher modulus of elasticity in stainless steel brackets, fragility and staining in ceramic brackets, lack of stiffness and deformation issues in plastic brackets, mechanical complexity and potential breakage in self-ligating brackets, speech disruption and plaque-related gingival irritation in lingual brackets, reduced accuracy in butterfly systems, and discoloration in brackets [13]. Alternatively, Clear aligners have revolutionized orthodontic treatment since their introduction in 1999, offering a compelling alternative to traditional braces [15]. Their nearly invisible appearance has expanded treatment accessibility, particularly among image-conscious adults [16].

The clinical decision between fixed appliances and clear aligners increasingly relies on evidence-based comparisons of the key outcomes. The evaluation of orthodontic treatment modalities extends beyond traditional measures of occlusal correction to encompass a broader spectrum of clinical and patient-cantered outcomes. The plaque index (PI) serves as a critical measure of oral hygiene maintenance during treatment, quantifying biofilm accumulation, and reflecting the accessibility of surfaces for cleaning [17]. This parameter directly influences the gingival index (GI), which assesses the severity and extent of gingival inflammation through standardized scoring of tissue appearance, contour, and bleeding response to gentle probing [18]. Beyond these clinical parameters, patient-reported outcomes have gained increasing importance in orthodontics. Pain intensity, typically measured using validated visual analog scales (VAS) or numerical rating systems (NRS), captures the sensory and affective dimensions of discomfort throughout the treatment phase [19]. This subjective experience directly influences treatment adherence and satisfaction. Quality of life (QOF) assessment employs comprehensive instruments such as the Oral Health Impact Profile (OHIP-14) or Condition-Specific Quality of Life measures for orthodontic patients to evaluate impacts across functional, psychological, and social domains [20]. Recent randomized clinical evidence has also shown that appliance type can influence oral health-related QOF and patient satisfaction in different ways, with aligner-based approaches showing advantages in psychological disability and appliance appearance, although some functional limitations may persist during treatment [21]. Taken together, these outcome measures represent patient-cantered domains by which orthodontic treatment modalities can be compared. Meta-analyses have been conducted previously comparing these treatment modalities; however, they were focused on evaluating single outcomes or the effectiveness of treatment. Alhafi et al. recently conducted a meta-analysis comparing clear aligners and fixed appliances in terms of treatment quality, treatment duration, and post-treatment stability. This meta-analysis concluded that there were significant heterogeneity and short-term follow-up, which weakened the conclusions that could be made about long-term outcomes [22]. These treatment modalities have been studied but mainly analyzed single outcomes or treatment effectiveness without combining patient experience with periodontal health considerations [23–26]. This study aimed to assess and contrast the effects of clear aligners versus fixed appliances on clinical outcomes and patient-reported results by examining QOF measures, pain perception levels, periodontal health indicators such as probing depth (PD), GI, and PI, and patient discomfort during treatment. The research aimed to integrate findings from randomized controlled trials (RCTs) and observational studies to deliver an exhaustive analysis of the effects of orthodontic treatment methods on measurable clinical outcomes and patients’ subjective experiences, furthermore this research has structured a stratified analysis which includes temporal analysis, GRADE assessment, publication bias assessment being thoroughly conducted and provides a high GRADE certainty assessment which implies the quality of the extracted evidence and briefs upon the clinical recommendations compared to the recent studies like Vasconcelos et al. [27], Jiang et al. [24] and Crego-Ruiz and Jorba-García [28].

Methodology

This study was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [29] for conducting this systematic review and meta-analysis and reported using the PRISMA Flow Diagram tool [30]. The study was registered on the International Platform of Registered Systematic Review and Meta-analysis Protocols (INPLASY) under registration number INPLASY 202530100.

Search strategy

Two reviewers (SA and AS) independently searched the PubMed, Scopus, Cochrane Library, Embase, and ScienceDirect databases from inception to March 2025. The gray literature search consisted of ProQuest Dissertations and Theses, along with other sources. Key journals were hand-searched. Key journals included the American Journal of Orthodontics and Dentofacial Orthopaedics, European Journal of Orthodontics, and Angle Orthodontist. The included study designs were RCTs and observational comparative studies that investigated clear aligners compared to fixed appliances. The search strategy used for each database is provided in Table 1. The reference lists of the included studies were searched for other eligible studies. Duplicate records were screened and removed using EndNote 20.2.1 (Clarivate Analytics, Philadelphia, PA, USA).

Table 1.

Search strategy.

Database	Search strategy
PubMed	((“Clear aligners” OR “Invisalign” OR “Removable orthodontic aligners”) AND (“Fixed appliances” OR “Braces” OR “Orthodontic brackets”)) AND ((“Quality of life” OR “Patient satisfaction” OR “Oral health-related quality of life” OR OHIP-14) OR (“Pain perception” OR “Pain intensity” OR “Discomfort” OR “Analgesic use”) OR (“Plaque index” OR “Dental plaque” OR “Oral hygiene” OR “Periodontal health”) OR (“Gingival index” OR “Gingivitis” OR “Gum inflammation”) OR (“Probing depth” OR “Periodontal pocket”))
Science Direct	((“clear aligner*” OR “invisalign*” OR “removable orthodontic aligner*”) AND (“fixed appliance*” OR “orthodontic bracket*” OR “brace*”)) AND ((“quality of life” OR “pain intensity” OR “plaque index” OR “gingival index” OR “probing depth” OR “OHIP-14” OR “periodontal health”)))
Cochrane Library	((“Clear aligners” OR “Invisalign”) AND (“Fixed appliances” OR “Braces”))
Scopus	((“clear aligner*” OR “invisalign*” OR “removable orthodontic aligner*”) AND (“fixed appliance*” OR “orthodontic bracket*” OR “brace*”) AND ((“quality of life” OR “OHIP-14” OR “oral health related quality of life”) OR (“pain perception” OR “pain intensity” OR “discomfort”) OR (“plaque index” OR “periodontal health”) OR (“gingival index” OR “gingivitis”) OR (“probing depth” OR “periodontal pocket”)))
Embase	(‘clear aligner’/exp OR ‘invisalign’/exp OR ‘removable orthodontic appliance’/exp) AND (‘fixed appliance’/exp OR ‘orthodontic bracket’/exp OR ‘brace’/exp) AND ((‘quality of life’/exp OR ‘OHIP-14’) OR (‘pain perception’/exp OR ‘pain intensity’ OR ‘discomfort’) OR (‘plaque index’ OR ‘periodontal health’/exp) OR (‘gingival index’ OR ‘gingivitis’/exp) OR (‘probing depth’ OR ‘periodontal pocket’/exp))

Study selection, data collection and quality appraisal

The researchers implemented the PICO framework as a guideline for their study selection criteria to maintain a structured and rigorous inclusion process for the systematic review. Population (P): Research studies on patients undergoing orthodontic treatment using clear aligners or fixed appliances. All age groups and sexes were included in the study as long as the participants were undergoing orthodontic treatment to correct malocclusions or dental alignment. This review did not consider studies on patients with severe periodontal disease, craniofacial anomalies, or those who underwent orthognathic surgery. Intervention (I): This research focused on clear aligner therapy as the main intervention, which included commercially available systems such as Invisalign, along with other similar removable orthodontic appliances. Comparison (C): The study compared clear aligner therapy with fixed orthodontic devices, including conventional metal braces, self-ligating brackets, and ceramic braces. Research that did not include a direct comparison between clear aligners and fixed appliances did not qualify for inclusion. Outcome (O): Orthodontic patient outcomes were evaluated by measuring QOF and periodontal health indicators (PD, GI, and PI) along with pain perception during treatment. Studies that failed to assess any of these outcomes were excluded from the analyses. The study considered secondary outcomes, including treatment duration and patient-reported discomfort, when these data were available. Study Design: This study included RCTs, cohort studies, and case-control studies. Case-control studies were included in the analysis when they: (1) employed retrospective or prospective matching of orthodontic patients based on key baseline characteristics; (2) clearly defined exposure (type of appliance) and outcomes with standard criteria; and (3) reported objective measurements rather than relying on patient recall. The rationale for inclusion reflects the available evidence base in orthodontic research, where high-quality RCTs remain limited, and well-conducted observational studies provide valuable clinical context. However, the findings from case-control studies were weighted less heavily in the interpretation, with the primary conclusions based on RCTs and prospective cohort evidence. The research omitted Reviews, case reports, expert opinions, and studies that did not clearly define their methodologies were excluded. Studies not written in English were also excluded.

Two reviewers (SA and AS) independently evaluated the papers using EndNote 20.2.1 by examining their titles and abstracts to ensure that they met the inclusion criteria. The two reviewers then independently assessed the full texts of the remaining papers, with conflicts resolved through discussion with the third reviewer. We extracted the following items from the included studies using a piloted Microsoft Excel data extraction sheet: first author, year of publication, study design, sample size, participants’ characteristics, details about the intervention and comparator(s), length of follow-up, domains of outcomes assessed, outcome measurement instrument(s)/scale(s), and numbers needed for the meta-analysis. The finished data extraction sheet for study-level data and meta-analytic inputs is included in the Supplementary Tables S1–S3 for transparency and reproducibility. The research team chose Microsoft Excel for data extraction because of its ability to flexibly organize various categories and filter data, which supported the detailed categorization of the study characteristics and outcomes. The Microsoft Excel data extraction sheet underwent a pre-testing phase with selected studies to verify the uniformity of the data entry procedures and category definitions. The sheet includes the same key categories as the first. The data extraction sheet included special columns that allowed the researchers to systematically document both methodological rigor and potential sources of bias.

The risk of bias was assessed independently by two reviewers using validated study-design-specific tools. RCTs were evaluated using the Cochrane Risk of Bias 2 (RoB 2) tool [31], and non-randomized comparative studies were assessed using the ROBINS-I tool [32]. Each study was judged across the relevant bias domains, and disagreements were resolved through discussion and, when necessary, by consulting a third reviewer. Detailed domain-level judgments and rationale for each judgment are provided in Supplementary Tables S4 and S5. Risk-of-bias visualizations were generated using the Robvis tool.

Statistical analysis

A meta-analysis was conducted using Comprehensive Meta-Analysis statistical software version 3.7. The mean difference (MD) was employed as the measure of treatment effect for continuous outcomes when studies used the same scale; otherwise, the standardized mean difference (SMD) was used. Cochran’s Q statistic, I² statistic and tau² were used to quantify heterogeneity between studies. Given that we anticipated methodological and clinical heterogeneity between studies according to study design, length of follow-up, appliance system used, and method of outcome assessment employed, random-effects models were used to analyze all data whenever possible. Fixed-effect estimates were calculated and inspected where appropriate to determine whether the pooled results were consistent. Pooled effect sizes were reported with 95% confidence intervals (CI), and statistical significance was set at p < 0.05. Subgroup analyses were performed according to the follow-up duration, where possible. Subgroups were defined a priori according to short-term (1 week to 1 month) versus long-term follow-up (≥12 months). Studies were additionally subgrouped by study design or appliance category, where clinically meaningful and sufficient studies existed for subgroup analyses. Publication bias/small-study effects were investigated using funnel plots, Egger’s regression test, Begg’s rank correlation test fail-safe N, and Duval and Tweedie’s trim-and-fill method, where possible.

Pooling of periodontal outcomes (PI, GI, and PD) was limited to MD and only if these outcomes were reported on similar clinical scales using the same units. The direction of the outcome had to be converted so that negative values consistently indicated better outcomes for clear aligners Table 1. Patient-reported outcomes were pooled using a SMD, as studies reported using various instruments and scoring techniques, such as the VAS, McGill-based measures of pain, OHIP-14, OHRQoL, and OHRQoL-UK. Studies reporting outcomes at multiple follow-ups had their data pooled according to comparable time intervals.

Results

Study characteristics

Figure 1 presents the PRISMA 2020 flow diagram of the study selection. A total of 3890 records were identified through database searches. After the removal of 68 duplicate records and 52 records removed for other reasons, 3770 records remained for screening. Following title and abstract screening, 83 records were excluded, and 3687 reports were retrieved. Of these, 53 reports could not be retrieved, leaving 3634 reports to be assessed for eligibility. After full-text review, 3602 reports were excluded for the following reasons: no measurable outcome (n = 798), unclear methodology or insufficient data (n = 1001), and did not meet the inclusion criteria (n = 1803). Ultimately, 32 studies were included in the systematic review, of which 28 were eligible for the meta-analysis. The main characteristics of the included studies are presented in Table 2, and the detailed extraction sheet and study-level numerical inputs used in the quantitative synthesis are provided in the Supplementary Tables S1–S3. The systematic review incorporated 32 [33–64] studies that offered qualitative insights into the comparison between clear aligners and fixed appliances. The major components of the studies included in this review are listed in Table 2. Twenty-eight studies fulfilled the necessary requirements for meta-analysis, which enabled a statistical combination of treatment effects.

Fig. 1. PRISMA 2020 flow diagram of study selection.

The diagram summarizes the identification, screening, eligibility assessment and inclusion of studies in the systematic review and meta-analysis.

Table 2.

Characteristics of the included studies.

	Author (year)	Study design	Sample size	Age/participant descriptor	Intervention	Comparator	Follow-up duration/assessment time points	Outcomes measured	Outcome scale/instrument	Main findings
1	Almasound et al. [33]	Prospective observational study	n = 64	26.00 ± 7.31 years	Invisalign aligners	Passive self- ligating fixed appliances	7 days	Pain perception using VAS	VAS	The aligners reported significantly lower pain than the fixed appliances group in the first week of treatment
2	Antonio-Zancajo et al. [34]	Prospective observational study	n = 120	30.0 ± 7.5 years	Invisalign aligners	Conventional, low- friction brackets and lingual brackets	14 days	Pain assessed using McGill questionnaire and oral health- related quality of life (OHIP-14)	VAS, OHIP-14, McGill questionnaire	Least pain was noted in the lingual brackets group. Invisalign aligners has slightly lower pain when compared to conventional brackets
3	Azaripour et al. [35]	Observational study	n = 100	Invisalign: 31.9 ± 13.6 years and Fixed orthodontic appliances: 16.3 ± 6.9 years	Invisalign aligners	Fixed orthodontic appliances	Invisalign: 12.6 ± 7.4 months and Fixed orthodontic appliances: 12.9 ± 7.2 months	Gingival health and patient satisfaction	GI, modified sulcus bleeding index, approximal PI, modified PI	Patients in the Invisalign group had better gingival health and greater satisfaction
4	Bollen et al. [36]	Randomized controlled trial	n = 51	34 years (range, 19–55)	Sequential removable orthodontic appliances (aligners)	Fixed orthodontic appliances	14 days	Rate of treatment completion	Peer assessment rating and need for extractions	2- week activation of aligners led to higher completion rates. Complex cases required additional aligners or fixed appliances
5	Borsato et al. [37]	Randomized controlled trial	n = 40	Orthodontic aligner: 23.63 ± 5.62 years and Fixed appliances: 20.91 ± 4.35 years	Orthodontic aligners	Fixed appliances	12 months	OHIP-14 questionnaire at various time points	OHIP-14	Aligners have less impact on the quality of life of subjects in first month, there was no difference noted after six months
6	Casteluci et al. [38]	Randomized controlled trial	n = 39	Orthodontic aligner: 23.63 ± 5.62 years and Fixed appliances: 20.75 ± 4.77	Orthodontic aligners	Fixed appliances	6 months	Intensity of pain using the VAS scale, anxiety and hypervigilance	VAS	Pain was noted to be mild in both groups. It was noted to be higher during the first week with different perception of pain patterns between the groups
7	Chhibber et al. [39]	Randomized controlled trial	n = 71	15.6 ± 4.3 years	Clear aligners and self- ligating brackets	Elastomeric ligated brackets	18 months	PI, periodontal bleeding index and GI	PI, GI, and PBI	No significant difference was noted in oral hygiene among the groups
8	Alcon et al. (2021)	Prospective observational study	n = 140	29.36 ± 9.80 years	Invisalign aligners	Fixed brackets	12 months	Pain assessed using the VAS	VAS	Significant differences in pain between the groups in most months except 8th
9	Abbate et al. [41]	Randomized controlled trial	n = 50	10–18 years	Invisalign aligners	Fixed orthodontic appliances	12 months	PD, PI, periodontal microbiology, bleeding on probing	PD, PI, BOP, full mouth plaque score, and full mouth bleeding score	The intervention group had lesser bleeding on probing, lower PD and lower PI
10	Alfawal et al. [42]	Randomized controlled trial	n = 44	24.22 ± 2.99 years	Clear aligners	Fixed appliances	6 months	OHIP-14 questionnaire	OHIP-14	Adults in the aligners group had better quality of life and notably shorter duration of treatment
11	Flores-Mir et al. [43]	Observational study	n = 122	26 and 35 years	Invisalign aligners	Fixed appliances	22 months	Quality of life of the patients and satisfaction	DIDL dimensions, Doctor-patientrelationship Situationalaspects Dentofacial improvement Psychosocialimprovement Dentalfunction	The Invisalign group showed better satisfaction
12	Fujiyama et al. [44]	Observational study	n = 145	EG: 26.45 ± 5.45 years; IG: 26.64 ± 5.69 years; EIG: 25.24 ± 6.51 years	Invisalign aligners	Fixed edgewise appliances	7 days	Pain levels using VAS and discomfort	VAS	Patients in the Invisalign group have lesser pain than patients in edgewise appliances group
13	Gao et al. [45]	Observational study	n = 110	adult patients 18–40 years	Clear aligners	Fixed appliances	14 days	Pain perception using VAS, OHRQoL and anxiety	VAS, OHRQoL	Clear aligners group reported lesser pain, anxiety and enhanced quality of life than the other group
14	Hennessy et al. [46]	Randomized controlled trial	44	26.4 ± 7.7 years	Clear adults	Fixed labial appliances	11.3 months	Mandibular incisor proclination	Cephalometric change, Quick Ceph System	No significant difference noted between the groups
15	Karkhanechi et al. [47]	Prospective observational study	42	34 ± 7.18 years	Clear aligners	Fixed appliances	12 months	Periodontal indices	PI, GI, BOP, and PD	Fixed appliances group showed worser periodontal indices compared to clear aligners group over 12 months. Clear aligneres has good hygiene.
16	Levrini et al. [48]	Prospective observational study	77	24.3 years (range from 16 to 30)	Invisalign aligners	Fixed appliances	3 months	Overall periodontal health	PCR procedures of the biofilm collected	Invisalign aligners showed better periodontal health compared to fixed appliances. Aligners also had lower biofilm mass
17	Leyva et al. [49]	Randomized controlled trial	28	Median age 28 years; range, 18–52 years	Invisalign aligners	Fixed appliances	18 months	Quality of life and periodontal health	PI, PD, OHIP-14, OQLQ-22 and NRS-10 questionnaires	Adults in the aligners group showed better quality of life and periodontal health
18	Lin et al. [50]	Randomized controlled trial	66	Invisalign: 26.7 (IQR: 9.8) years; Braces: 25.9 (IQR: 16.6) years	Invisalign aligners	Fixed appliances	Invisalign: 1.7 years (IQR: 0.7); Braces: 1.3 years (IQR: 0.7)	Case quality using ABO- OGS scores and duration of treatment	ABO- OGS	Aligners reported to take longer time but had final outputs similar to fixed appliances group
19	Melo et al. [51]	Randomized controlled trial	40	orthodontic aligner 23.60 ± 5.65 years; Fixed appliances: 20.56 ± 4.51 years	Orthodontic aligners	Fixed appliances	6 months	Assessment of speech production	speech production, VAS	Speech was impacted by aligners initially but it was resolved in 30 days. In both groups, self-perceived difficulties with speech were noted
20	Miethke and Brauner [52]	Prospective observational study	60	39.6 years	Invisalign aligners	Fixed lingual appliances	4 weeks	Periodontal indices were assessed	GI, PBI, PI,PD	Periodontal health was comparatively better in the Invisalign aligners group
21	Miethke and Vogt [53]	Prospective observational study	60	30.1 years (18 and 51)	Invisalign aligners	Fixed orthodontic appliances	4 weeks	Periodontal indices were assessed	GI, modified PI, modified PBI, andsulcus PD	Periodontal health was comparatively better in the Invisalign aligners group
22	Miller et al. [54]	Prospective observational study	60	Invisalign aligners 38.0 ± 12.4 years. Fixed appliances 28.6 ± 8.7 years	Invisalign aligners	Fixed appliances	7 days	Levels of pain, quality of life and use of analgesics	VAS, Geriatric Oral Health Assessment Index	Lower pain and better quality of life was noted in Invisalign aligners group
23	Pereira et al. [55]	Randomized controlled trial	38	22.08 years	Orthodontic aligners	Fixed appliances	6 months	Frequency of anxiety, facial pain, stress and awake bruxism	level of anxiety by the State-Trait Anxiety Inventory, stress by the Perceived Stress Scale, catastrophising related to pain and degree of hypervigilance by the Pain Vigilance and Awareness Questionnaire, and the presence of facial pain evaluated by the DC/TMD.	There was no significant difference in the frequency of awake bruxism noted between the two groups
24	Shalish et al. [56]	Prospective observational study	68	18–60years	Invisalign aligners	Fixed lingual appliances and fixed buccal appliances	14 days	Adaptation period, pain and quality of life	OHRQoL questionnaire, VAS	More pain and dysfunction were noted with lingual appliances. Adaptation was faster and symptoms were lesser with aligners
25	Silva et al. [57]	Randomized controlled trial	32	Clear Aligners: 9.33 ± 1.01 years; Fixed appliances: 9.65 ± 0.8 years	Clear aligners	2 × 4 fixed appliances	8 months	White spot lesions, PI, duration of treatment, incisor irregularity index and arch time	incisor irregularity index, treatment time, arch width, perimeter, length, size and shape, incisorlevelling, incisor mesiodistal angulation, PI, and white spot lesion formation (InternationalCaries Detection and Assessment System index)	Efficacy and efficiency was found to be similar in both groups
26	Tunca et al. [58]	Randomized controlled trial	60	Fixed orthodontic: 21.3 ± 3.37; clear aligners: 23.65 ± 6.58 years	Clear aligners	Fixed appliances	21 days	Pain assessment using VAS, OHRQoL-UK, anxiety levels and OHIP-14	VAS, OHIP-14, OHRQoL-UK, OHRQoL	The initial pain was noted to be lower with aligners but on long term, there were no differences noted between the two groups in terms of quality of life or anxiety
27	White et al. [59]	Randomized controlled trial	41	Adults	Clear aligners	Fixed appliances	7 days	Discomfort and pain assessed using VAS, use of analgesic and disturbances with sleep	VAS	Lesser discomfort and pain was noted with aligners and use of analgesic was also found to be lower in the aligners group
28	Withayanukonkija et al. [60]	Randomized controlled trial	40	Clear aligners: 21.69 ± 6 2.67 years; Fixed appliances: 21.85 ± 6 2.71 years	Clear aligners	Fixed appliances with mini screw	6 months	Molar intrusion, max bite force, root resorption	Lateral cephalograms, cone-beam computed tomography, and maximum bite force,	There was impoved bite force with aligners and they led to lesser root resorption and intrusion
29	Zamora-Martinez et al. [61]	Prospective observational study	120	37.4 ± 14.6 years	Clear aligners	Lingual braces, metal braces and esthetic braces	19.6 ± 4.7 months	OHIP-14	OHIP-14	Aligners showed least reduction in the quality of life of the subjects
30	Dubey et al. [62]	Prospective observational study	100	Not disclosed	Removable appliances	Fixed appliances	not disclosed	GI and PI	PI and GI	The indices and oral hygiene was better in removable appliances group than in fixed appliances group
31	Petti et al. [63]	Prospective observational study	30	7-to-15-years	Removable appliances	Fixed appliances	7 months	Periodontitis and gingivitis risk, microbial composition and PI	gingivitis (bacterial count evaluated with light microscope, percentage of Gram-negative rods) and periodontitis (motile rod and spirochete percentages, presumptive Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis prevalence)	Microbial counts were higher in fixed appliances group showing higher risk for periodontitis and gingivitis
32	Rego RO et al. [64]	Observational study (case controlled)	48	Fixed appliances: 14.5 ± 1.7 years; 9.6 ± 1.5 years	Removable appliances	Fixed appliances	cross sectional	Microbial analysis, PD, PI, GI and DMFT	PI, GI, number of decayed, missing and filled teeth, probing pocket depth and DMFT	There were no clinical differences between the two groups, but the fixed appliances group showed higher counts of microbes.

VAS Visual Analog Scale, OHIP-14 Oral Health Impact Profile-14, PI Plaque index, GI gingival index, PD Probing depth, PBI Papillary bleeding index, BOP Bleeding on probing, PCR Polymerase Chain Reaction, DMFT Decayed, Missing, and Filled Teeth, OHRQoL Oral Health-Related Quality of Life, OHRQoL-UK United Kingdom Oral Health Related Quality of Life measure, DC/TMD Diagnostic Criteria for Temporomandibular Disorders, OQLQ-22 Orthognathic Quality of Life Questionnaire, NRS-10 Numeric Rating Scale—10, ABO-OGS American Board of Orthodontics-Objective Grading System, DIDL Dental Impact on Daily Living.

This review encompasses 32 studies, summarized in the expanded characteristics table (Table 2), which includes the study design, sample size, participant age, appliance type, follow-up duration, outcomes measured, and instruments or scales used for outcome assessment. Of these, 17 were RCTs, providing high-quality evidence, whereas the remaining 15 were prospective and observational studies. The participant pool varied from children to adults, with sample sizes spanning 28–145 individuals.

The interventions predominantly involved clear aligners (Invisalign, orthodontic aligners, or clear aligners), whereas the comparators included fixed labial appliances, self-ligating brackets, lingual braces, and traditional metal appliances. Three studies also included removable appliances for comparison.

The outcomes assessed were diverse in the included studies. Pain perception and discomfort were the most frequently evaluated using VAS and validated questionnaires, such as the OHIP-14 and McGill pain scale. Multiple studies have reported that aligners are associated with reduced pain, particularly in the initial treatment stages. Periodontal health indices, including PI, bleeding on probing, and PD, were also common outcomes, with aligners generally showing better oral hygiene and reduced periodontal inflammation compared to fixed appliances. QOF and patient satisfaction were frequently explored, favoring aligners in the early treatment phase. A few studies have addressed treatment efficiency, root resorption, speech impact, and microbial analysis. The study-level numerical inputs used in the quantitative synthesis are also provided in the Supplementary Table S2 to support reproducibility.

Evidence suggests that clear aligners offer better short-term comfort, improved periodontal outcomes, and higher patient satisfaction with no significant compromise in treatment efficacy. However, differences in follow-up duration, study designs, and outcome measures highlight the need for standardized methodologies in future comparative orthodontic research.

Risk of bias

Randomized controlled trials

The traffic light plots in Fig. 2 show the risk of bias assessment for the included RCTs across the five domains. The results indicate that most studies demonstrated a low risk of bias for D3 (missing data) and D4 (outcome measurement), as shown by the predominance of the green circles in the summary figure. This suggests that the studies had adequate follow-up and minimized measurement errors, ensuring that the reported outcomes were reliable and reflective of true intervention effects. However, some domains showed moderate risks or concerns, particularly D1 (randomization process) and D2 (deviations from intended interventions), which could introduce potential confounding factors and reduce internal validity. Several studies, including those by Alfawal et al. [42], Chhibber et al. [39], Hennessy et al. [46], Tunca et al. [58], and White et al. [59], exhibited concerns or moderate risk due to issues with the randomization process. These concerns likely stemmed from inadequate allocation concealment or improper sequence generation, which may have compromised the comparability of the intervention groups in this study. Additionally, deviations from the intended interventions (D2) were observed, particularly in Tunca et al. [58], which raises concerns about protocol adherence and intervention fidelity. Although these biases do not completely invalidate the results, they necessitate cautious interpretation, particularly when assessing the efficacy of treatments. Despite these limitations, outcome measurement and reporting biases (D4 and D5) were generally low, reinforcing the reliability of the primary and secondary endpoint assessments in these trials. Nevertheless, to improve future clinical trials, researchers should prioritize rigorous randomization methods, enhanced blinding strategies, and transparent reporting of results. Addressing these biases will help strengthen the evidence synthesis in systematic reviews and meta-analyses, ultimately leading to more robust and generalizable conclusions in evidence-based medicine. Detailed study-level RoB 2 domain judgments and supporting justifications are presented in Supplementary Table S4.

Fig. 2. Risk of bias assessment for randomized controlled trials.

The figure presents the RoB 2 traffic-light plot for randomized controlled trials included in the review. Each row represents an individual study and each column represents a risk-of-bias domain.

Non-randomized cohort studies

The risk of bias assessment for the included non-randomized controlled trials (non-RCTs) revealed varying levels of bias across the different domains (Fig. 3). While several studies exhibited a low risk of bias, others were rated as having moderate to serious concerns, particularly in the domains of confounding (D1), missing data (D5), and selection of reported results (D7). Fujiyama et al. [44], Rego et al. [64], and Zamora-Martínez et al. [61] were the most notable contributors to high bias. Fujiyama et al. [44] and Rego et al. [64] were both rated as having serious bias in D1 (confounding) and D5 (missing data), suggesting inadequate control for baseline differences and substantial missing data, which could impact the validity of their findings. Similarly, Zamora-Martínez et al. [61] received a serious bias rating for D7 (selection of reported results), indicating the potential selective reporting of outcomes that could distort the overall evidence base. Additionally, Almasoud [33], Antonio-Zancajo et al. [34], Dubey et al. [62], and Flores-Mir et al. [43] showed moderate concerns in confounding (D1) and missing data (D5), highlighting potential limitations in study design and data completeness. Gao et al. [45] and Miller et al. [54] had uncertainty in D6 (outcome measurement), reflecting possible issues in outcome assessment. Given these variations, the findings of studies with moderate-to-serious bias should be interpreted with caution. Detailed ROBINS-I domain judgments and supporting justifications for each included non-randomized study are presented in Supplementary Table S5.

Fig. 3. Risk of bias assessment for non-randomized studies.

The figure presents the ROBINS-I traffic-light plot for non-randomized comparative studies included in the review. Each row represents an individual study and each column represents a bias domain, including confounding, participant selection, intervention classification, deviations from intended interventions, missing data, outcome measurement and selection of reported results.

GRADE assessment

The certainty of the evidence for each pooled outcome was evaluated using the GRADE approach. The certainty of the evidence ranged from moderate to high. Pain intensity and QoL were considered to have moderate certainty because publication bias and/or inconsistency raised concerns about these outcomes. In contrast, the GI and PD had high-certainty evidence. The PI showed moderate-to-high certainty, depending on the domain of concern (risk of bias and publication bias). The GRADE evidence profiles with explanations of the downgrading reasons for each domain are presented in Supplementary Table S6.

Pain scores

Figure 4 depicts a meta-analysis comparing pain intensity between fixed appliances and clear aligners, with a subgroup analysis based on the treatment duration. Pain outcomes were synthesized using SMD because the included studies used different pain instruments and assessed pain at multiple follow-up intervals; therefore, data were grouped by comparable time points before pooling. The SMD of −0.419 suggests that clear aligners are associated with lower pain intensity than fixed appliances. This negative value indicates a small-to-moderate effect size favoring aligners in reducing pain perception during orthodontic treatment. Heterogeneity, measured by I², varied across the subgroups, indicating differences in the study outcomes. The overall I² value of 23.5% suggests low-to-moderate heterogeneity, implying reasonable consistency among the included studies. However, certain subgroups, such as the 1-week and 2-week durations, showed higher heterogeneity (I² = 42.1% and 69.9%, respectively), likely due to variations in pain assessment methods, sample sizes, or treatment protocols. Among the major contributing studies, Casteluci et al. [38] appeared repeatedly across different time points, demonstrating consistent findings. Similarly, Tunca et al. [58] and White et al. [59] contributed significantly to the overall findings. Notably, studies with shorter durations, such as 1 and 2 weeks, showed a greater negative SMD, reinforcing the idea that clear aligners provide early pain relief compared with fixed appliances. Clinically, this analysis underscores the advantages of clear aligners in reducing pain, particularly during the initial treatment. This information can guide orthodontists in treatment planning, especially for patients with lower pain tolerance. However, individual patient responses and other treatment factors should be considered when making clinical decisions.

Fig. 4. Forest plot comparing pain outcomes between clear aligners and fixed appliances.

The figure shows the pooled standardized mean difference in pain intensity between clear aligners and fixed orthodontic appliance with subgrouping according to treatment duration.

Plaque index

Figure 5 depicts a meta-analysis of the effect of fixed appliances versus clear aligners on PI, with a subgroup analysis based on study type (RCTs vs. non-RCTs). Only studies reporting PI on clinically comparable scales were pooled, and the direction of effect was standardized such that lower scores favored clear aligners. The overall pooled estimate for the difference in means was −0.437 (95% CI: −0.507 to −0.367), indicating that clear aligners were associated with a lower PI than fixed appliances. This negative value suggests a reduction in plaque accumulation in patients using clear aligners. Heterogeneity analysis revealed moderate variations across studies. The I² value for non-RCTs was 39.88%, indicating moderate heterogeneity, whereas RCTs showed no heterogeneity (I² = 0). Study design subgrouping was performed to explore whether the observed effect differed between randomized and observational evidence; the total between-group heterogeneity (Q = 1.416, p = 0.234) suggests that differences in study type did not significantly influence the overall effect. Among the major contributing studies, Dubey et al. [62] and Miethke and Brauner [52] strongly supported the trend favoring clear aligners, with effect sizes of −0.39 and −0.61, respectively. In the RCT subgroup, Silva et al. [57] and Leyva et al. [49] reported larger reductions in PI (−0.85 and −0.71, respectively), strengthening the conclusion that clear aligners lead to improved oral hygiene. This finding has important clinical implications. Given that plaque buildup causes dental caries and periodontal disease, patients who use clear aligners might experience improved oral health outcomes compared with those who use fixed appliances. The necessity of oral hygiene training is especially crucial for patients undergoing fixed orthodontic treatment, as they may require additional interventions to control plaque successfully.

Fig. 5. Forest plot comparing plaque index between clear aligners and fixed appliances.

The figure shows the pooled mean difference in plaque index between clear aligners and fixed orthodontic appliances, with subgrouping according to study design.

Gingival index

Figure 6 depicts a meta-analysis of the effect of fixed appliances versus clear aligners on GI, summarizing the findings of seven studies. Pooling was limited to studies that reported the GI on comparable scales, and the direction of effect was aligned so that lower gingival inflammation scores favored the clear aligners. The pooled estimate for the difference in means was −0.233 (95% CI: −0.296 to −0.170), indicating that clear aligners were associated with a significantly lower GI than fixed appliances, suggesting that patients with clear aligners experience less gingival inflammation. The heterogeneity analysis showed a Q-value of 3.33 (p = 0.766) with an I² of 0%, indicating no significant heterogeneity among the included studies. This suggests consistency across studies, reinforcing the reliability of the pooled estimates. Among the key contributing studies, Rego et al. [64] reported an effect size of −0.23 with strong statistical significance (p < 0.001), supporting the finding that clear aligners reduce gingival inflammation. Miethke and Brauner [52] also contributed notably, with an effect size of −0.30, reinforcing this overall trend. Karkhanechi et al. [47] reported a larger reduction (−0.48), highlighting the potential clinical benefit of aligners in improving gingival health. Clinically, this finding is significant because gingival inflammation is a major concern in orthodontic treatment. Fixed appliances can make oral hygiene maintenance challenging, leading to increased plaque accumulation and subsequent periodontal inflammation. Clear aligners are removable, allowing for better oral hygiene and potentially reducing the risk of gingivitis. These results emphasize the importance of patient education on oral hygiene practices, particularly for those using fixed appliances, to minimize gingival complications during orthodontic treatment.

Fig. 6. Forest plot comparing gingival index between clear aligners and fixed appliances.

The figure shows the pooled mean difference in gingival index between clear aligners and fixed orthodontic appliances.

Probe depth

The meta-analysis in Fig. 7 evaluated the effects of fixed appliances on PD against clear aligners by integrating the results of eight different studies. Only studies reporting PD in comparable units were combined, and the direction of the effect was aligned so that lower PD values favored clear aligners. The pooled estimate for the difference in means was −0.332 (95% CI: −0.431 to −0.234), indicating that clear aligners were associated with significantly lower PD than fixed appliances. The heterogeneity analysis revealed a Q-value of 4.98 (p = 0.663) and an I² of 0%, suggesting minimal variability among the included studies. This consistency strengthens the reliability of the pooled effect size and indicates that the studies reported similar findings regarding the effect of orthodontic treatment on PD. Among the most influential studies, Abbate et al. [41] reported the largest effect size (−0.70, p = 0.001), suggesting a notable reduction in PD with aligner use. Miethke and Brauner [52] and Karkhanechi et al. [47] also contributed significantly, with effect sizes of −0.39 and −0.30, respectively. These findings reinforce the conclusion that clear aligners may offer periodontal benefits compared with fixed orthodontic appliances. Clinically, this study highlights the potential advantages of using clear aligners to maintain periodontal health. Fixed appliances make oral hygiene maintenance more difficult, leading to plaque accumulation and increased PD, which are indicative of early periodontal diseases. Clear aligners are removable, allowing for better plaque control and potentially lowering the risk of periodontal complications, thereby emphasizing the need for proper oral hygiene during orthodontic treatment.

Fig. 7. Forest plot comparing probing depth between clear aligners and fixed appliances.

The figure shows the pooled mean difference in probing depth between clear aligners and fixed orthodontic appliances.

Quality of life

Figure 8 compares clear aligners and fixed appliances for their effect on the QOF during treatment of varying durations. Because various validated questionnaires were used to assess QOF outcomes, pooling was performed using SMD, and individual QOF outcomes were grouped according to similar follow-up durations before the meta-analysis. Overall, the SMD favored clear aligners (−0.850, 95% CI: −0.973 to −0.727, p < 0.001). Outcomes were stratified by the follow-up period because it was hypothesized that patients’ experiences with orthodontic appliances would differ over time. Participants responded favorably to clear aligners, reporting greater adaptation and lower discomfort with the appliances throughout treatment, which is reflected by the negative SMDs throughout most follow-up times. Clear aligners were preferred early on, with statistically significant differences at 1 week (SMD = −0.985), 10 days (SMD = −0.895), and 1 month (SMD = −0.829) (p < 0.001). Patients continued to experience some QOL benefit at the end of treatment (SMD = −0.970, 95% CI: −1.410 to −0.520, p < 0.001), but the effect was no longer significant at 12 months (SMD = −0.531, 95% CI: −1.178 to 0.116, p = 0.108), indicating that patients may notice fewer differences in QOL between the two treatments as time progresses. Heterogeneity was moderate-to-high, with I² = 74% at 1 week and lower as the follow-up length increased.

Fig. 8. Forest plot comparing quality of life between clear aligners and fixed appliances.

The figure shows the pooled standardized mean difference in quality-of-life outcomes between clear aligners and fixed orthodontic appliances with subgrouping according to follow up duration.

Studies by Miller et al. [54] (−1.347, 95% CI: −1.726 to −0.969, p < 0.001) and Gao et al. [45] (−1.131, 95% CI: −1.534 to −0.729, p < 0.001) contributed significantly to the overall effect size, reflecting a stronger preference for clear aligners in the short term. In contrast, Borsato et al. [37] showed a smaller effect size at 12 months (−0.531, 95% CI: −1.178 to 0.116, p = 0.108), suggesting that QOF differences may diminish over extended treatment durations. Clinically, these findings emphasize that clear aligners offer superior short-term QOF benefits compared to fixed appliances, likely because of reduced pain, better esthetics, and ease of removal. However, long-term outcomes should be considered when selecting a treatment option. This study highlights the need for individualized treatment planning that balances QOF with treatment efficacy and cost.

Publication bias

Publication bias was explored visually using funnel plots (Fig. 9) and statistically using Egger’s regression test, Begg’s rank correlation test, fail-safe N, and trim and fill analyses. Evidence of asymmetry was more apparent for some outcomes than for others, particularly for pain, whereas other outcomes showed limited or no clear evidence of small-study effects. For pain, Egger’s test indicated substantial bias with an intercept of −3.61087 (95% CI: −5.21790 to −2.00384, t = 4.74058, p = 0.00019), while Begg’s test also showed significant correlation (Kendall’s tau = −0.59146, p = 0.00069). The fail-safe N was 273, suggesting a robust result but also highlighting the need for cautious interpretation of the results. PI demonstrated a similar pattern, with a fail-safe N of 357, and Egger’s and Begg’s tests confirming asymmetry (Egger’s intercept: −0.91033, 95% CI: −2.21465 to 0.39398, p = 0.14883; Begg’s tau = −0.29091, p = 0.21291). The GI had a fail-safe N of 82, and Begg’s test showed moderate bias (tau = −0.38095, p = 0.22956), although Egger’s test was not significant. The probe depth had a lower fail-safe N (67), with Egger’s test showing no substantial bias (intercept = 0.08509, p = 0.91570); however, trim and fill suggested two missing studies. QoL, with the highest fail-safe N (898), showed minimal bias (Egger’s intercept = −0.13114, p = 0.89575), and trim-and-fill confirmed no missing studies. While the Duval and Tweedie trim-and-fill analysis did not detect missing studies for most outcomes, probe depth had an imputed estimate of −0.34843 (−0.44414, −0.25273), suggesting a possible bias. The presence of publication bias, particularly for pain and PI, suggests an overestimation of treatment effects due to the absence of smaller, nonsignificant studies with negative results. These biases highlight the importance of including unpublished and gray literature in future research. Despite bias concerns, the high fail-safe N values indicate that the findings were stable. Clinically, the results should be interpreted cautiously, ensuring that treatment decisions consider the potential influence of selective reporting and small-study effects. Future studies should aim to include comprehensive data to enhance the reliability of meta-analytic conclusions. Overall, these findings suggest that publication bias may have influenced the magnitude of effect for some outcomes, especially pain-related outcomes, and therefore the pooled estimates should be interpreted cautiously

Fig. 9. Funnel plots assessing publication bias and small-study effects across pooled outcomes.

A Pain, B plaque index, C quality of life, D probing depth, and E gingival index.

Discussion

Our comprehensive meta-analysis revealed compelling evidence favoring clear aligners across all five critical outcome measures, suggesting that they provide superior patient comfort and periodontal health benefits. QOF assessments demonstrated a significant advantage for aligners (SMD, −0.85; 95% CI, −0.973 to −0.727; p < 0.001), with particularly pronounced benefits during the early treatment phases. Similarly, periodontal health indicators consistently favored aligners, with reduced PD (MD: −0.332, 95% CI: −0.431 to −0.234), lower GI scores (MD: −0.233, 95% CI: −0.296 to −0.170), and decreased plaque accumulation (MD: −0.437, 95% CI: −0.507 to −0.367). Pain intensity measures likewise demonstrated a modest but significant advantage for aligners (SMD: −0.419), with the greatest differences observed during the initial stages of treatment. Importantly, the consistency of these findings across multiple studies, reflected by low heterogeneity in periodontal parameters (I² = 0% for PD and GI), strengthens the reliability of our conclusions. However, the publication bias assessment indicated possible small-study effects for some outcomes, particularly pain, which may have led to overestimation of the pooled effect size and should be considered when interpreting the strength of these findings.

However, these findings should be interpreted with caution. Although statistically significant differences were observed across several outcomes, the included evidence base comprised a substantial proportion of observational studies in addition to randomized trials, which increases the possibility of selection bias and residual confounding factors. Variability in the study design, follow-up duration, oral hygiene instructions, appliance systems, and outcome measurement methods may have also influenced the pooled estimates. In addition, the publication-bias assessment suggested possible small-study effects for some outcomes, particularly pain-related outcomes, which may have contributed to the overestimation of treatment benefits.

The pooled meta-analytic findings demonstrated statistically significant improvements in clinical periodontal and patient-reported outcomes favoring aligner therapy; however, its clinical significance remains nuanced. For PD, the pooled MD of –0.332 mm, although statistically robust, represents a minor change relative to established periodontal thresholds (≤3 mm healthy, 4–5 mm mild disease, and ≥6 mm severe). This modest reduction likely lacks a meaningful individual-level clinical impact but may indicate beneficial population-level trends. Similarly, for GI, a pooled MD of –0.233 (95% CI: –0.296 to –0.170) equates to roughly an 8% improvement on the 0–3 scale; however, its clinical importance remains uncertain without a defined minimal clinically important difference for orthodontic contexts. The PI demonstrated a pooled MD of –0.437, translating to an approximate 15% reduction, suggesting improved hygiene efficacy, although possibly influenced by study-specific hygiene protocols. Importantly, statistical significance does not necessarily imply a clinical significance. Although the pooled reductions in the GI and PD favored clear aligners, the absolute magnitude of these differences was modest, and their direct clinical relevance should be interpreted cautiously. Nevertheless, the publication bias analyses suggested that some pooled effects, particularly for pain-related outcomes, may have been influenced by small-study effects, and the magnitude of benefit may therefore be overestimated.

Patient-centered outcomes have stronger clinical implications than other outcomes. Pain reduction (SMD: –0.419) corresponded to a small-to-moderate effect, likely denoting the difference between “mild” and “very mild” discomfort, which is clinically relevant given the influence of pain on adherence to treatment. QOF improvements (SMD: –0.985 at 1 week) indicated a large, meaningful benefit favoring aligners, emphasizing enhanced early treatment comfort and satisfaction in the aligner group. These subgroup patterns support the importance of follow-up duration as a clinically relevant effect modifier when comparing clear aligners and fixed appliances; however, the interpretation of our results is constrained by confounding factors. Variability in oral hygiene protocols, compliance monitoring, baseline periodontal health, and plaque biofilm composition likely affected PI and GI outcomes more than appliance type. Moreover, heterogeneity in follow-up duration may reflect transient treatment phases rather than stable effects. Collectively, while aligners show modest biological and clear perceptual advantages, clinical interpretation should consider the contextual and behavioral confounders.

These findings align with previous investigations, offering a more comprehensive perspective. In addition, Alam et al. [65] reported that Invisalign and fixed appliances showed broadly similar overall efficacy for orthodontic tooth movement, although Invisalign was associated with a shorter treatment duration, supporting the importance of distinguishing treatment effectiveness from patient-centered advantages such as comfort and QOF [65]. Cardoso et al. [66] previously documented reduced pain with aligners, although our analysis provides greater granularity in terms of temporal patterns. Similarly, while Jiang et al. [24] reported improved periodontal outcomes with aligners, our study is the first to simultaneously analyze all four outcome domains within a single framework. Interestingly, our QoL results suggest diminishing differences over extended treatment periods (12-month SMD: −0.531, p = 0.108), an important nuance not captured in the previous study by Miller et al. [54]. Conversely, Tamer et al. [15] found no significant differences in patient comfort between modalities in complex cases, diverging from our findings and highlighting the need for malocclusion-specific analyses in future studies to confirm our findings. Similarly, Jaber et al. [67] found no significant difference in the overall ABO-OGS treatment effectiveness between clear aligners and fixed appliances in extraction-based Class I severe crowding cases, although fixed appliances showed better occlusal contacts and a higher proportion of successful cases, underscoring the importance of case complexity when interpreting the comparative outcomes [67]. Overall, this integrated analysis provides clinicians with robust evidence to inform treatment decisions while acknowledging that long-term efficacy and case complexity remain critical considerations, alongside patient-centered and periodontal advantages.

Interestingly, Jiang et al. [24] found that clear aligners resulted in better periodontal health than fixed appliances, with significant reductions in the PI (MD = −0.p3, 95% CI: −0.85 to −0.20, P = 0.001), GI (MD = −0.p7, 95% CI: −0.37 to −0.17, P < 0.001), and PD (MD = −0.p5, 95% CI: −0.67 to −0.03, P = 0.03). Our study similarly demonstrated superior periodontal outcomes with clear aligners but also assessed pain and QOL using the SMD. While Jiang et al. [24] raised concerns about bias and false-positive results, our findings further reinforce the benefits of using a clear aligner.

Li et al. [23] demonstrated that clear aligners resulted in significantly lower pain levels than fixed appliances at 3 days (MD = −0.97, 95% CI: The study found significant lower pain levels for clear aligners compared to fixed appliances at 3 days (MD = −0.p7, 95% CI: −1.52 to −0.43, P = 0.0005) and 4 days (MD = −0.p9, 95% CI: −0.98 to −0.20, P = 0.003) but not at other time points. Our investigation revealed lower pain levels when using clear aligners, which coincides with these results. Additionally, Li et al. [23] reported elevated oral health-related quality of life (OHRQoL) scores in clear aligners patients at 1 week (MD = −10.88, P < 0.0p001), 1 month (MD = −6.27, P < 0.00001) p and 6 months (MD = −4.19, P < 0.00001). Our data confirmed that clear aligners significantly improved OHRQoL, demonstrating their benefits in terms of comfort and adaptation to treatment. This study had multiple limitations that require recognition. Variability in the study design, along with differences in the sample size and follow-up duration across the included studies, may have resulted in heterogeneity in the findings. The application of strict statistical methods did not completely eliminate inconsistencies in our findings. Our study examined key periodontal parameters and patient-reported outcomes but did not conduct a comprehensive analysis of long-term periodontal stability and relapse, which restricts the applicability of our findings. The majority of studies included in the review were observational and featured a small number of RCTs, which could have led to selection bias and impacted the quality of evidence. Owing to the different clear aligner systems and treatment protocols used across studies, it was challenging to draw a universal conclusion for all aligner systems. To reinforce and validate our findings we require future RCTs that are well-designed and feature extended follow-up periods, and our research stands out from the several recent systematic reviews by considering and addressing various aspects like stratified analysis, temporal analysis (1 week, 1 month, 6 months, 12 months), GRADE assessment, comprehensive publication bias assessment (Egger, Begg, Trim-and-fill), risk of bias tools (RoB 2 for RCTs and ROBINS-I tool assessed observational or cohort studies), high quality of extracted evidence implied by high GRADE assessment and focusing on multidimensional, evidence based decision framework as clinical recommendations, whereas other recent studies like Vasconcelos et al. [27], Jiang et al. [24] and Crego-Ruiz and Jorba-García [28] are mixed and integrated reviews but are not meta-analysis with no or limited temporal analysis breakdown, no GRADE assessment, no detailed publication bias and with limited clinical recommendations.

Future research should focus on several key areas to enhance the understanding of periodontal health outcomes of clear aligner therapy. First, well-designed RCTs with larger sample sizes and longer follow-up periods are required to provide stronger evidence of the long-term effects of clear aligners on periodontal health. Second, studies should investigate the effects of different aligner materials and wear protocols on plaque accumulation, gingival inflammation, and PD. Third, future research should explore patient adherence and oral hygiene behaviors in clear aligner users compared to those with fixed appliances, as compliance is critical for periodontal outcomes. Fourth, advanced imaging techniques, such as three-dimensional periodontal assessments, can provide more precise measurements of periodontal changes. Finally, studies examining the economic and patient-centered aspects, including cost-effectiveness and QOF over extended treatment durations, would help optimize treatment recommendations for various patient populations. Unlike earlier reviews that analyzed isolated outcomes or included a limited number of trials, our meta-analysis provides an updated and comprehensive evidence. By integrating both objective periodontal metrics and subjective patient-reported measures within a single statistical model and including newly published randomized trials up to 2025, this study addresses unresolved clinical questions and provides a more holistic view of the outcomes of aligners versus fixed appliances.

This review has some limitations. First, although RCTs were included, a substantial proportion of the evidence was derived from observational studies, which are more susceptible to selection bias, confounding, and differences in baseline patient characteristics than RCTs. As a result, residual confounding cannot be excluded, particularly for outcomes that may be influenced by patient motivation, oral-hygiene behavior, and case selection. Second, variability in appliance systems, oral hygiene instructions, follow-up duration, and outcome measurement methods may have contributed to heterogeneity across studies. Third, some outcomes were assessed using different patient-reported instruments, which required pooling through a SMD and may have reduced direct clinical comparability. Finally, the publication bias assessment suggested possible small study effects for some outcomes. Therefore, although the overall evidence favors clear aligners for several short-term outcomes, these findings should be interpreted cautiously. This raises the possibility that some favorable estimates for clear aligners, especially for short-term patient-reported outcomes, may be larger than the true underlying effects.

Future research should prioritize adequately powered long-term RCTs with standardized periodontal, pain, and QOF assessments to clarify whether the observed short-term advantages of clear aligners persist over time and translate into meaningful clinical benefits.

Conclusion

Clear aligners were associated with better periodontal indices, lower early pain scores, and better short-term QOF outcomes than fixed appliances. However, these results should be interpreted with caution because of the heterogeneity between studies, incorporation of observational evidence, and potential publication bias. Additionally, some statistically significant differences were small, and it is unclear whether they are clinically meaningful. More long-term RCTs with consistent outcome reporting are required.

Author contributions

Kanwalpreet Kaur: Conceptualization, metodology, writing—review and editing. Syed Altafuddin Quadri: Conceptualization, metodology, writing—original draft preparation. Ravinder S Saini: Investigation, resources, supervision, project administration, funding acquisition. Mario Alberto Alarcón-Sánchez: Validation, formal analysis, writing—review and editing. Artak Heboyan: Validation, formal analysis, writing—original draft preparation.

Funding

The authors extend their appreciation to the Deanship of Scientific Research at King Khalid University for funding this work through a Small Group Research Project under grant number RGP1/331/44.

Data availability

The data supporting the findings of this study are available from the corresponding author upon reasonable request.

Competing interests

The authors declare no competing interests.

Supplementary information

The online version contains supplementary material available at 10.1038/s41405-026-00450-z.