Patient satisfaction with at-home dental bleaching using Vivera or Essix retainers: a randomised clinical trial

Abstract

Background

Smile esthetics have increased the demand for orthodontic treatment and at-home bleaching, yet evidence regarding the performance and patient experience of Vivera^® and Essix retainers as bleaching trays remains limited. This study aimed to compare patient satisfaction during at-home bleaching with 10% carbamide peroxide using Vivera^® and Essix retainers, and to evaluate bleaching efficacy (BE), as well as the risk and intensity of tooth sensitivity (TS) and gingival irritation (GI).

Methods

A randomised, split-mouth, single-blind equivalence clinical trial was conducted with 40 volunteers. Each hemiarch was randomly assigned to either a Vivera^® or Essix retainer. Bleaching was performed for 2 h, three alternate days per week, completing 12 applications over 4 weeks. Satisfaction was measured via a 9-item visual analog scale (VAS, 0–10). BE was assessed using a spectrophotometer (ΔEab, ΔE00, WID) and shade guides (ΔSGU). TS and GI were evaluated using VAS. Statistical analysis included paired Student’s t-test and TOST-P (± 0.09) for satisfaction; paired Student’s t-test for BE; McNemar’s test for TS and GI risk; and paired t-tests for TS/GI intensity (α = 0.05).

Results

After 2 weeks, adaptation, comfort, and overall satisfaction significantly favored Vivera^® (p < 0.01). At 4 weeks, only comfort remained significantly higher for Vivera^® (p = 0.04). BE and GI were similar between retainers (p > 0.05). Although TS risk did not differ significantly (p > 0.05), Vivera^® was associated with lower TS intensity (p = 0.03).

Conclusions

Vivera^® retainers provided greater patient satisfaction, especially in comfort, and were associated with lower TS intensity during at-home bleaching compared to Essix. However, both retainers showed bleaching efficacy.

Trial registration

The study was approved by the University Ethics Committee (protocol code 1601202303323) and registered at ClinicalTrials.gov (Identifier: NCT05835453; date of registration: 04/18/2023).

The trial results have not been publicly disclosed in the trial registry, nor disseminated in the form of a preprint or published articles.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-026-08347-x.

Background

The harmony of the smile, in terms of tooth position and color, is considered an important factor in the overall facial appearance of patients. Consequently, there has been a growing demand for both orthodontic and tooth bleaching treatments [1–3]. In fact, most patients express willingness to undergo tooth bleaching, and many orthodontists recommend it after the completion of orthodontic treatment [4]. Accordingly, a significant increase in patient satisfaction has been reported when tooth bleaching is administered following orthodontic treatment [5].

Among current bleaching techniques, at-home bleaching with low-concentration peroxide gels is considered as the safest and most conservative approach [6, 7]. In this method, patients apply the bleaching gel using individualized trays, which ensure controlled and consistent exposure [8–10].

Whitening outcomes—namely bleaching efficacy, tooth sensitivity, and gingival irritation—are strongly influenced by the concentration, diffusion dynamics, and biological behaviour of the bleaching agent used. For this reason, 10% carbamide peroxide was selected, as it is widely supported by the literature for offering a favourable balance between whitening effectiveness and reduced adverse effects. This concentration provides a slower and sustained release of hydrogen peroxide, producing a gradual diffusion into the enamel and dentin while minimising pulpal irritation and soft‑tissue discomfort. Because of this predictable safety and performance profile, 10% carbamide peroxide is considered the reference standard for tray‑based at‑home bleaching, particularly in studies assessing patient‑centred outcomes [11–13].

Regarding orthodontic treatment, removable clear aligners have increasingly become the modality of choice, especially among adults, due to their clinical effectiveness combined with aesthetic benefits, transparency, ease of hygiene maintenance, and a reduced risk of caries development when compared to traditional orthodontic appliances [14, 15]. Clear aligners, which serve as trays during active orthodontic treatment, have also recently emerged as an alternative to conventional trays for dispensing bleaching agents, offering the dual benefit of orthodontic alignment and bleaching within the same treatment period [16–19].

Another possibility is performing bleaching after orthodontic treatment using orthodontic retainers. Retainers such as Vivera^® (Align Technology Inc., Tempe, AZ, USA) and Essix (Erkoloc-Pro, Erkodent Erich Kopp GmbH, Pfalzgrafenweiler, Germany) share a similar design to that of clear aligners; however, they are generally thicker to ensure greater durability and strength, as their primary function is the long-term stabilization of tooth position [20, 21]. Although both Vivera^® and Essix retainers serve the same clinical purpose, they differ in material properties and manufacturing standardization. Vivera^® retainers are produced through an automated industrial workflow that ensures high dimensional accuracy, consistent fit, and increased durability due to their multilayer polymer composition [22]. In contrast, Essix retainers are typically fabricated chairside by thermoforming single‑layer thermoplastic sheets, followed by manual trimming and finishing [23]. This process introduces greater variability in fit and lower resistance to wear and deformation. These differences in material and fabrication may influence patient‑reported outcomes such as comfort, retention, rigidity, and overall experience during prolonged at‑home bleaching.

Despite the widespread and continually increasing use of clear aligners and orthodontic retainers in contemporary dental practice, scientific evidence supporting their suitability, efficacy, and safety as alternative bleaching trays remains limited [18]. Current literature provides only a small number of investigations addressing this topic, and comparative studies evaluating bleaching effectiveness, tooth sensitivity, and gingival irritation among different retainer designs or materials are notably scarce [8, 19, 24–31]. Moreover, prior research has not evaluated how differences in material and fabrication may influence comfort, fit, tooth sensitivity, or patient-reported satisfaction during bleaching. This persistent gap in the evidence base highlights the need for rigorous, controlled research to guide clinical decision-making and ensure predictable and safe outcomes for patients.

Therefore, the primary objective of this study was to compare patient satisfaction during at-home bleaching treatment using two different types of orthodontic retainers: Vivera^® and Essix in patients that had previously completed orthodontic treatment with clear aligners. Secondary objectives were to evaluate bleaching efficacy, as well as the risk and intensity of tooth sensitivity and gingival irritation during the bleaching protocol. The null hypothesis was that the two retainers are not equivalent with respect to patient satisfaction, with differences exceeding the predefined clinical equivalence margin. The working hypothesis was that both retainers would demonstrate clinical equivalence in patient satisfaction and yield comparable outcomes regarding bleaching efficacy, tooth sensitivity, and gingival irritation.

Methods

This study was a randomised, split-mouth, single-blind and equivalence clinical trial.

Ethics approval and consent to participate

The study was carried out at the private dental clinic (Pamplona, Spain) of the first author between September and December 2023. It was registered in the Clinical Trials Register under the code NCT05835453 (registration date 04/18/23).

This study has been designed, conducted, and reported in accordance with the CONSORT guidelines [32] for clinical trials, ensuring transparency, methodological integrity, and completeness in the presentation of results. The clinical study received ethical approval from the Research Ethics Committee of University Rey Juan Carlos (Madrid, Spain, internal reference number: 1601202303323) and was conducted in accordance with applicable laws and institutional guidelines.

Participants’ privacy rights were fully respected, and informed consent was obtained from each participant prior to their inclusion in the study.

Inclusion and exclusion criteria

Participants over 18 years old, in good general and oral health, wished to undergo at-home bleaching treatment as a complement to their completed orthodontic treatment with Invisalign aligners (Align Technology Inc.) and who were using clear retainers were selected for inclusion. Moreover, their anterior teeth had to be free of carious lesions or periodontal disease, and canines with a saturation of at least A2 or darker according to the Vita Classical scale (VITA Zahnfabrik, Bad Säckingen, Germany) and 15 or less according to the Whiteness Index for Dentistry [33]. Volunteers who had previously undergone at-home bleaching procedure, reported previous tooth sensitivity, continuous use of medications such as analgesics and anti-inflammatories, were pregnant or lactating women, and individuals with habits such as bruxism or smoking were excluded from the study. Criteria for exclusion were also the presence in anterior teeth of fixed orthodontic appliances, attachments, restorations or endodontic treatments, color alterations due to tetracyclines or fluorosis and visible cracks.

Sample calculation

The primary outcome of the study was overall patient satisfaction during at‑home bleaching, assessed using a 10‑cm visual analogue scale (VAS; 0–10) [6]. The sample size calculation was based on a standard deviation of 1.2 reported for patient satisfaction using custom bleaching trays in the upper arch [6], and an equivalence margin (Δ) of 0.9 for the minimally important difference.

Considering a two‑sided alpha level of 5% and 90% statistical power, a total of 39 participants were required. Because the study followed a split‑mouth design, the participant was treated as the statistical unit, with each participant contributing data for both retainer types. To account for potential dropouts, one additional participant was included, resulting in a final target sample of 40 participants.

Randomization and concealment of random sequence

During the first randomisation, each participant was assigned to one of the two groups according to the type of retainer that would always be applied to the right hemiarch (n = 40). The devices assigned were: Vivera^® retainer or Essix retainer. This first randomisation allowed inter-individual variability to be controlled by comparing both devices within the same subject. Given that the study involved the sequential use of both types of retainers on alternate days, a second randomisation was established to control for possible sources of bias linked to the order of use of the retainers: use on Mondays, Wednesdays, and Fridays or use on Tuesdays, Thursdays, and Saturdays. This additional step was considered necessary to avoid effects derived from progressive adaptation to the appliance, variations in behavioral patterns associated with each day of the week, and possible residual effects from the use of one retainer that could influence the response observed with the other device.

The assignments were prepared in opaque, sealed envelopes and numbered sequentially to ensure concealment. Both the random sequence generation and the masking procedure were performed by a person outside the research protocol. The assignment for each participant was revealed only by opening the sealed envelope immediately before delivery of the Vivera^® or Essix retainers.

Blinding

This is a single-blind study, where only the evaluators were unaware of the group assignments as they did not participate in the randomization and implementation process of the study. Considering the procedure for delivering the retainers and explaining their use, neither the operator nor the patient could be blinded.

Bleaching procedure

Two weeks before the start of at-home bleaching, the upper arch of the volunteers was scanned (iTero Lumina; Align Technology Inc.). Moreover, a prophylaxis was performed to remove extrinsic stains using the Air Flow Prophylaxis Master system (EMS, Nyon, Switzerland) with AirflowPlus powder with 14 μm particles (EMS). The STL files were sent to Align Technology Inc. for the fabrication of Vivera^® retainers, which had a thickness of 1.0 mm and a scalloped design.

The same STL files were also used to print the upper arch models from which Essix retainers were fabricated. These retainers were thermoformed using 1.0 mm thick polyethylene terephthalate glycol (PET-G) sheets (Erkoloc-Pro, Erkodent Erich Kopp GmbH, Germany) with a vacuum-forming machine (Erkopress_motion; Erkodent Erich Kopp GmbH) and trimmed to replicate the scalloped finish of Vivera^® retainers.

Once fabricated, they were tested on the participants to confirm complete adaptation and absence of discomfort, minor adjudgments were performed if necessary. Next, 2 syringes of 3 g of 10% carbamide peroxide bleaching gel (Opalescence PF, Ultradent Products, South Jordan, UT, USA) were provided for its application with each type of retainer on the corresponding hemiarch. The same researcher instructed participants to place a small drop of bleaching gel into the compartment corresponding to the buccal surface of each tooth before inserting the retainer. Participants were also advised to remove any excess material after placement. Volunteers were instructed to apply the bleaching gel once a day for 2 h, on three alternate days per week with each retainer. The treatment extended over 4 weeks, although as each retainer was worn on alternate days, the effective application time corresponded to 2 weeks per retainer (12 applications). During the treatment, participants were instructed to brush their teeth with a regular dentifrice free of desensitizing agents, bleaching components, or abrasives. Satisfaction, bleaching efficacy (BE), tooth sensitivity (TS) and gingival irritation (GI) evaluations were only performed on the upper arch.

Patient satisfaction evaluation

The questionnaire used to assess patient satisfaction consisted of nine items structured using a 10-cm visual analogue scale, in line with previous studies [6, 34]. Participants received a diary for each retainer and were asked to record their satisfaction by marking a vertical line across a 10-cm horizontal line with values of 0 and 10 at its ends. They were informed that 0 represented no problem/very good and 10 maximum problems/very bad. The mean value recorded in cm after 2 and 4 weeks of treatment (6 and 12 applications) was used for statistical analysis. Volunteers answered the questionnaire without any intervention from the evaluators and without a time limit for completion.

Evaluation of color change: subjective method

Color was recorded at the baseline and at the end of the treatment. Color assessment through the subjective method was recorded with the VITA Classical color scale ordered by value and the VITA Bleachedguide 3D-MASTER scale (VITA Zahnfabrik, Bad Säckingen, Germany). The color measurement area was in the middle third of the vestibular surface of the upper right and left canines. Color was independently assessed by two blinded examiners using both color scales. Volunteers were evaluated in the same room with the same lighting. In cases where there was a difference of opinion, a consensus was reached in a new evaluation. Color change evaluation was performed through the variation of VITA Scale Units (ΔVSU) organized by value [35].

Evaluation of color change: objective method

For objective evaluation, the VITA Easyshade spectrophotometer (VITA Zahnfabrik) was used. The device was calibrated before each measurement, and recordings were performed simultaneously with the assessments using the color scales. To standardize the color measurements, individual guides were manufactured with blue silicone (Honigum Pro, Putty Soft, DMG Dental, Chemisch-Pharmazeutische Fabrik GmbH, Hamburg, Germany) placed on the anterior maxillary teeth. In each guide, the middle third of the clinical crowns of teeth 13 and 23 were perforated using a circular scalpel (Biopsy Punch, Miltex, York, NJ, USA) with a diameter corresponding to the active tip of the spectrophotometer, ensuring precise and reproducible positioning of the device. The difference between the colors recorded was calculated using the formula CIELab [36]:

Additionally, color change was also calculated using the CIEDE 2000 formula [37]:

and the Whiteness Index for Dentistry (WI_D) [33]:

Tooth Sensitivity (TS) Evaluation

The absolute risk and intensity of TS were evaluated using the VAS (0–10). Volunteers were provided with a TS diary for each retainer, and they were asked to return it after two and four weeks of treatment (corresponding to 6 and 12 applications, respectively). They were instructed to record daily the highest level of TS experienced, even if no pain was present, for both the right and left hemiarches. Volunteers marked the value corresponding to the intensity of their tooth sensitivity on the VAS line in centimeters, as previously described for patient satisfaction [35, 38, 39]. The absence of risk was considered when the patient marked 0, while any value above zero was considered indicative of TS. The highest VAS score recorded during the evaluation period was used to quantify TS intensity. All volunteers received standardized instructions on TS is, its possible short-term acute manifestations, and the importance of accurately recording the outcomes.

Evaluation of Gingival Irritation (GI)

The absolute risk and intensity of GI were evaluated similarly to TS, using the VAS (0–10). Volunteers received a GI diary for each retainer, that was collected after two and four weeks of bleaching. They were informed that 0 was considered no irritation and ten represented severe irritation. Volunteers were asked to record this value daily, even in the absence of symptoms, for both the right and left hemiarches, by marking the intensity of GI with a vertical line on the VAS scale [40]. For risk determination, any value above zero was considered positive. The highest VAS score recorded during the evaluation period was used to determine GI intensity. Volunteers were also instructed on how to identify signs of gingival irritation (burning, itching, or even lesions) and the importance of recording these outcomes.

Statistical analysis

The statistician was blinded to both groups, and the analysis included all participants, following the intent-to-treat protocol. For the primary outcome of patient satisfaction, two one-sided t-tests for paired samples (TOST-P) were performed to verify the equivalence between the study groups at the different evaluation times (± 0.09). This approach includes a right-sided test for the lower satisfaction bound and a left-sided test for the upper bound. The mean difference and the 95% confidence interval (CI) between groups were calculated for each evaluation. For the evaluation of color change, the paired Student’s t-test was used across all scales and evaluation times. The absolute risk of TS and GI was compared using the McNemar test. Odds ratios were calculated, along with confidence intervals (CI) and Spearman’s correlation. The intensity of TS and GI was analyzed using paired Student’s t-test, and Pearson’s correlation was applied to detect differences between groups. All statistical tests were performed with a preset alpha level of 5%.

Results

Eighty-four individuals were examined, and 40 participants were included in the clinical study (Fig. 1). The distribution of participants according to baseline tooth color, gender and age is shown in Table 1. All participants completed the bleaching treatment and no loss during the 2 and 4-week evaluations were recorded (Fig. 1).

Fig. 1.

Flow diagram illustrating the study phases, including enrollment, allocation, and intervention criteria

Table 1.

Baseline characteristics of participants enrolled in the clinical trial

	Retainer (number of participants and hemiarches)
	Vivera® (n = 40)	Essix (n = 40)
Baseline color (SGU; mean ± sd)*	10.4 ± 2.7	10.3 ± 2.5
Gender (female; %)	25 (62.5%)
Mean age (years; female/male)	30.7 / 31

*Abbreviations: SGU Shade guide unit measured by VITA Classical scale

Patient satisfaction evaluation

After two weeks of treatment (6 applications), no significant differences were observed between the two retainers for six of the nine questions (p > 0.10; Table 2). However, three questions showed significant differences related to adaptation (1. Did you adapt well to the tray?; p < 0.01), comfort (4. How was your comfort using the tray, especially in relation to soft tissues such as gums, cheeks, and tongue?; p = 0.01), and overall satisfaction (7. How was your overall satisfaction with using the tray? ); p = 0.01), all favoring the Vivera^® retainer (Table 2). At this 2-week assessment, the mean difference exceeded the previously established equivalence margin of 0.9, indicating that the retainers were not equivalent for these parameters at the first follow-up. After four weeks of bleaching (12 applications), a statistically significant difference persisted only for comfort (p = 0.04; Table 2), again favoring the Vivera^® retainer. However, at this point, the mean difference was below the established equivalence margin of 0.9, indicating that the two retainers could be considered equivalent at the final follow-up.

Table 2.

Means and standard deviations for patient satisfaction questions related to retainer use, measured on a 0–10 Visual Analog Scale (VAS)

Questionnaire	Follow-up	Groups		Mean difference (95% CI)	Equivalence	p-value (**)
		Vivera	Essix		[p-value*]
1. Did you adapt well to the retainer?	2-week	0.4 ± 0.8	1.5 ± 1.9	1.1 (0.3 to 1.8)	No; p > 0.05	< 0.01
	4-week	0.3 ± 0.6	0.7 ± 1.4	0.3 (-0.1 to 0.7)	Yes; p < 0.001	0.12
2. Was it easy to talk to the retainer?	2-week	0.6 ± 1.0	0.6 ± 0.7	-0.0 (-0.2 to 0.2)	Yes; p < 0.001	0.92
	4-week	0.5 ± 0.8	0.4 ± 0.6	-0.0 (-0.3 to 0.2)	Yes; p < 0.001	0.72
3. Was it easy to swallow liquids and saliva?	2-week	0.4 ± 0.6	0.5 ± 0.6	0.1 (-0.0 to 0.2)	Yes; p < 0.01	0.22
	4-week	0.4 ± 0.6	0.4 ± 0.6	0.0 (-0.0 to 0.1)	Yes; p < 0.001	0.35
4. How was your comfort using the retainer, especially in relation to soft tissues such as gums, cheeks and tongue?	2-week	0.5 ± 0.9	1.5 ± 2.1	1.0 (0.3 to 1.8)	No; p > 0.05	0.01
	4-week	0.4 ± 0.7	0.9 ± 1.4	0.4 (0.0 to 0.9)	Yes; p < 0.001	0.04
5. Was it easy to maintain the retainer’s hygiene?	2-week	0.4 ± 0.7	0.4 ± 0.5	-0.0 (-0.2 to 0.1)	Yes; p < 0.001	0.58
	4-week	0.4 ± 0.7	0.3 ± 0.5	-0.1 (-0.2 to 0.1)	Yes; p < 0.001	0.27
6. What do you think about the aesthetics of the retainer?	2-week	0.7 ± 1.3	0.6 ± 0.9	-0.1 (-0.4 to 0.2)	Yes; p < 0.001	0.51
	4-week	0.6 ± 1.0	0.5 ± 0.9	-0.1 (-0.3 to 0.1)	Yes; p < 0.001	0.38
7. How was your overall satisfaction with using the retainer?	2-week	0.6 ± 1.0	1.6 ± 2.3	1.1 (0.3 to 1.9)	No; p > 0.05	0.01
	4-week	0.4 ± 0.7	0.8 ± 1.4	0.4 (-0.1 to 0.8)	Yes; p < 0.001	0.10
8. How was the retainer’s strength and durability?	2-week	0.5 ± 0.9	0.6 ± 1.4	0.1 (-0.1 to 0.4)	Yes; p < 0.001	0.41
	4-week	0.4 ± 0.8	0.3 ± 0.5	-0.1 (-0.2 to 0.0)	Yes; p < 0.001	0.10
9. How was the retainer?	2-week	0.7 ± 1.3	1.1 ± 1.8	0.4 (-0.1 to 1.0)	Yes; p < 0.001	0.12
	4-week	0.5 ± 0.9	0.4 ± 0.6	-0.0 (-0.3 to 0.2)	Yes; p < 0.001	0.84

* p-value for equivalence using TOST-P methodology; That is p < 0.05 implies that the two groups had equivalent means

** Paired t-test

Color evaluation

Baseline color values (SGU) were comparable between the two groups (Table 1). Once the bleaching treatment was concluded, both groups showed a statistically significant bleaching effect, as measured by both subjective and objective methods. The color change was approximately 6 units on the Vita Classical scale, 7 units on the Vita Bleached guide scale, 9 units for ∆E_ab, 6 units for ∆E₀₀, and 27 units for the WI_D (Table 3). However, no statistically significant differences were found between both retainers (p > 0.05; Table 3).

Table 3.

Means, standard deviations, and mean differences (95% CI) in color change between baseline and week 4

Color evaluation tool	Groups		Mean difference (95% CI)	p -value*
	Vivera®	Essix
VITA Classical (ΔSGU)	6.5 ± 2.3	6.8 ± 3.0	0.2 (-0.7 to 1.2)	0.58
VITA Bleachedguide (ΔSGU)	7.6 ± 2.9	7.4 ± 2.9	-0.2 (-0.8 to 0.4)	0.48
CIELAB (ΔEab)	8.6 ± 3.5	9.3 ± 3.2	0.7 (-0.2 to 1.6)	0.11
CIEDE (ΔE00)	5.5 ± 2.2	6.0 ± 2.3	0.5 (-0.0 to 1.1)	0.06
Whiteness Index for Dentistry (WID)	26.3 ± 8.5	27.2 ± 9.3	0.9 (-0.5 to 2.3)	0.20

*Paired t-test

Tooth Sensitivity (TS) Evaluation

The absolute risk of participants suffering TS was 80% for Vivera^® retainer and 85% for Essix group, with no statistically significant difference between them (p = 0.41; Table 4). Regarding TS intensity, no significant differences were observed after two weeks of treatment (p = 0.07; Table 5). In contrast, at the four-week follow-up, significantly higher TS was reported in the Essix group (p = 0.03; Table 5). This difference was also confirmed in the worst-case scenario analysis, when the highest value of TS reported each participant during bleaching was considered (p = 0.03; Table 5).

Table 4.

Matched tabulation of absolute risk of tooth sensitivity risk for both groups, odds ratio and 95% Confidence Interval (CI)

		Essix			Odds ratio (95% CI)
		Positive	Negative	Total
Vivera®	Positive	30	2	32	0.70 (0.2 to 2.2)
	Negative	4	4	8
	Total	34	6	40

Mc Nemar’s test (p = 0.41); Spearman correlation between paired data (r = 0.49; p-value = 0.001)

Table 5.

Means, standard deviations, mean differences (95% CI), and correlation coefficients for tooth sensitivity intensity in both groups

Main factor time	Groups		Mean difference (95% CI)	p-value*	Correlation coefficient[p-value]
	Vivera®	Essix
2-week	0.8 ± 2.3	1.3 ± 1.7	0.5 (-0.0 to 1.0)	0.07	0.46; p = 0.003
4-week	1.0 ± 1.7	1.2 ± 2.1	0.3 (0.0 to 0.5)	0.03	0.93; p < 0.001
Worst overall scenario	1.3 ± 1.7	1.8 ± 2.3	0.5 (0.1 to 1.0)	0.03	0.76; p < 0.001

*Paired t-test

Gingival Irritation (GI) evaluation

GI was reported by 67.5% of participants using Vivera^® retainers and 70% of those undergoing bleaching with Essix retainers, with no statistical differences observed (p = 0.65; Table 6). Regarding the intensity of GI, no significant differences were observed between both groups (p > 0.05; Table 7), including in the overall worst-case scenario (p > 0.05; Table 7), regardless of the evaluation time.

Table 6.

Matched tabulation of absolute gingival irritation risk for both groups, odds ratio and 95% Confidence Interval (CI)

		Essix			Odds ratio (95% CI)
		Positive	Negative	Total
Vivera®	Positive	25	2	27	0.89 (0.3 to 2.3)
	Negative	3	10	13
	Total	28	12	40

Mc Nemar’s test (p = 0.65); Spearman correlation between paired data (r = 0.71; p-value < 0.001)

Table 7.

Means and standard deviations of intensity of gingival irritation for both groups and mean difference (95% Confidence Interval [CI]) and correlation coefficient values

Main factor time	Groups		Mean difference (95% CI)	p-value*	Correlation coefficient [p-value]
	Vivera®	Essix
2-week	0.9 ± 1.5	0.5 ± 0.6	0.3 (-0.1 to 0.8)	0.09	0.46; p = 0.002
4-week	0.5 ± 1.2	0.4 ± 0.6	0.1 (-0.1 to 0.3)	0.39	0.87; p < 0.001
Worst overall scenario	1.1 ± 1.8	0.6 ± 0.7	0.4 (-0.0 to 0.9)	0.05	0.65; p < 0.001

*Paired t-test

Discussion

Tooth whitening is a highly sought-after procedure, particularly following the completion of orthodontic treatment. At this stage, it is common practice to use the clear aligner or retainers’ trays for the application of bleaching agents [24]. Building on this approach, Align Technology Inc. has introduced a system that combines Vivera^® retainer with a 10% carbamide peroxide at-home whitening treatment. Nevertheless, Essix retainers remain the standard appliance used during the retention phase in many clinical settings [23]. Since participants are already accustomed to prolonged use of these devices, it is relevant to assess their level of satisfaction when using retainers for tooth whitening, as this can significantly influence their overall perception of the treatment [41]. To the extent of authors’ knowledge, the present randomised clinical trial is the first to compare patient satisfaction with at-home dental bleaching using Vivera^® and Essix retainers.

Our results show that during the first two weeks of bleaching, participants reported greater satisfaction with the Vivera^® system, particularly regarding retainer adaptation, comfort and overall satisfaction. These differences decreased after 4 weeks of treatment, although Vivera^® retainers continued to outperform Essix retainers in terms of overall satisfaction. Consequently, the working null hypothesis was rejected. Regarding bleaching efficacy, tooth sensitivity, and gingival irritation, both orthodontic retainers yielded comparable outcomes.

Specifically, participants indicated that they perceived the adaptation to be superior with Vivera^® retainers compared to Essix after two-week use, suggesting a more precise fit. This perception may be related to its CAD-based design process, which employs 3D digital scanning and model fabrication to achieve more accurate adaptation to dental morphology [42].

Moreover, during the first two weeks, participants reported that Vivera^® retainers were more comfortable, particularly in relation to soft tissues such as gums, cheeks, and tongue. This greater initial comfort may be attributable to the accurate trimming process of these retainers, which is fully automated, and machinery guided [22]. After trimming, the edges are polished or smoothed, typically via tumbling, buffing or fine trimming, to minimize irritation to the gingival tissues [43, 44]. Finally, the edge finish of each retainer is inspected before packaging. In contrast, Essix retainers were manually trimmed to simulate the Vivera^® design and then carefully polished and checked in the participants. However, this process is less precise and may explain why participants perceived these differences [43], which eventually disappeared over time. It is worth noting that, in our study, participants used the bleaching trays during the day, which may have influenced their perception of comfort. Unlike nighttime use, daytime wear involves greater interaction with normal oral functions such as speech, swallowing, and saliva production [45]. This conscious exposure may heighten participants’ sensitivity to potential discomfort, including pressure points, irregular tray edges, or interference with soft tissues [45]. In this context, the perception of adaptation and comfort becomes especially relevant, as any irritation is more noticeable during routine daily activities [46]. This factor may partly explain the differences in initial satisfaction observed between the systems evaluated. Participants reported greater overall satisfaction with Vivera^® retainers compared to Essix retainers, not only during the initial two weeks of use but also after completing the bleaching protocol.

Although participants were not blinded to the type of retainer used, the potential influence of this factor was mitigated by several aspects of the study design. To reduce expectation‑related bias, both retainers were presented as clinically accepted and routinely used options. Moreover, the randomized crossover design ensured that each participant acted as their own control, thereby reducing inter‑individual variability and strengthening internal validity. Additionally, it is important to consider that these participants had previously undergone orthodontic treatment with the Align system. This familiarity could have influenced initial perceptions [47]. Nevertheless, when analyzing the values reported by the participants for the individual items of the questionnaire, patient satisfaction remained high. This result is noteworthy, since previous studies have reported that the use of removable retainers can interfere with speech and increase salivation, particularly during the initial adaptation period [42, 48, 49], which could negatively affect patient satisfaction. This finding may be partially explained by the fact that, in the present study, patient satisfaction was assessed during the bleaching treatment. Considering that bleaching therapy significantly enhances self-esteem and quality of life [50, 51], this factor may have contributed to the higher levels of patient satisfaction observed in our study. Actually, a closer analysis of the patient satisfaction scores revealed a decrease in all items with the prolongation of the treatment (4 weeks), although the differences observed were below the established equivalence margin.

However, it is worth mentioning that adaptation, comfort, and overall satisfaction during the first two weeks of treatment are fundamental for motivating participants to properly complete the entire protocol, especially considering that this procedure is performed at home without direct clinical supervision. Therefore, the use of retainers appears to be a valid alternative for at-home bleaching treatment, with Vivera^® retainers showing more favorable outcomes.

Regarding BE, both Vivera^® and Essix retainers achieved equivalent results after the completion of treatment. They are also aligned with previous studies validating the use of clear aligners as effective trays for at-home bleaching treatments [17, 19]. Moreover, the agent used in this study, 10% carbamide peroxide, has been shown to be clinically effective for tooth whitening, especially when applied consistently over several weeks. While results may take longer to appear compared to higher concentrations, this formulation offers an excellent balance of efficacy, safety, and patient tolerance with lower sensitivity and adverse effects [13], even when used for only 2 h [52], as in the present study.

Nevertheless, our results showed a high incidence of TS in all participants, independent of the retainer used, even with the application of a 10% carbamide peroxide formulation. Although the incidence was high, the intensity of TS was very low, as previously reported [53]. The higher intensity of dentin hypersensitivity observed in participants using Essix retainers at the 4-week assessment may have several explanations. First, this finding may be partially influenced by the age range of the participants, as dentin hypersensitivity tends to increase with age due to cumulative dentin exposure and progressive enamel thinning [54]. However, even when considering this individual factor, a consistent pattern associated with the type of retainer emerged. Structural differences between the two retainers provide an additional clinical explanation [55]. Vivera^® retainers are industrially manufactured using a multilayer polymer and a standardized trimming and finishing process, resulting in greater precision, uniformity, and stability of fit. This improved adaptation may reduce localized pressure on dental tissues and promote a more homogeneous distribution of the bleaching agent, thereby decreasing the likelihood of sensitivity and enhancing comfort during treatment. In contrast, Essix retainers, fabricated manually in the clinic using a different thermoplastic material, tend to show greater variability in edge trimming, rigidity, and adaptation to the tooth surface. Such variations may create localized pressure points or areas where bleaching gel accumulates, which is consistent with the lower comfort and higher sensitivity reported by participants using Essix retainers. Overall, these findings indicate that the selection of the retainer used as a bleaching tray has clinically relevant implications for the patient’s experience, beyond individual factors such as age. Devices offering a more accurate and stable fit may improve treatment tolerance, reduce dentin hypersensitivity, and ultimately enhance adherence and satisfaction during at-home bleaching procedures.

Regarding GI, no significant differences were observed between the groups treated with Vivera^® and Essix retainers, either in terms of frequency or intensity of reported symptoms. Notably, despite differences in marginal fit precision were found between the two types of retainers in our study, this did not result in increased GI, unlike TS, where significant differences were observed [53]. This finding supports the notion that the fit and marginal adaptation of the retainer may have a greater influence on TS than on the response of the surrounding soft tissues. Furthermore, current evidence supports the use of customized trays with 10% carbamide peroxide as a safe and well-tolerated technique, provided that the recommended application times are followed and gel overflow onto gingival tissues is prevented [56].

One limitation of the present study is the absence of an objective and standardised assessment of whitening tray fit accuracy. Although both types of retainers were manufactured in accordance with strict clinical and laboratory protocols, equivalent fit between them cannot be unequivocally ensured. This variability may have influenced the level of comfort reported by patients. However, it is unlikely to have affected the whitening efficacy, as no significant differences in bleaching outcomes were observed between the groups.

Although the sample size was sufficient to detect significant differences in variables such as satisfaction and TS, it may not be representative of larger or more diverse populations. This limits the generalisability of the findings and constitutes an additional constraint of the study.

Furthermore, the results are specific to the two types of retainers evaluated and therefore cannot be extrapolated to other commercially available retainers. Variations in material composition, thickness, and manufacturing processes may influence the fit, comfort, and clinical performance of different products.

The evaluation period was restricted to four weeks; thus, neither the long‑term stability of the bleaching results nor the potential emergence of delayed adverse effects could be assessed. Finally, as the whitening protocol consisted of a 10% carbamide peroxide gel applied for two hours daily over two weeks, these findings cannot be generalised to other concentrations, formulations, or application regimens.

Conclusions

Despite both Vivera^® and Essix retainers proved to be equally effective for at-home bleaching with 10% carbamide peroxide, Vivera^® retainers were associated with higher patient satisfaction, particularly regarding adaptation, comfort, and overall experience. Although tooth sensitivity and gingival irritation were common in both groups, their intensity was generally very low, with significantly higher tooth sensitivity intensity values reported for Essix after four weeks. However, these subjective findings should be interpreted with caution due to the impossibility of blinding participants to the type of retainer used.

Abbreviations

BE

Bleaching efficacy

TS

Tooth sensitivity

GI

Gingival irritation

VAS

Visual analog scale

PET-G

Polyethylene terephthalate glycol

WI_D

Whiteness index for dentistry

TOST-P

Two one-sided t-tests for paired samples

CI

Confidence intervals

SGU

Shade guide unit measured by VITA Classical scale

Authors’ contributions

JI performed clinical treatments and collected the data. JI also contributed to funding acquisition, data analysis, and the writing of the original draft. IG contributed to funding acquisition and participated in data analysis and drafting of the original manuscript. TSC was responsible for the methodological design and conducted the formal data analysis, as well as the review and editing of the original manuscript. MWF contributed to the methodological design of the study. NE and VF were responsible for reviewing and editing the original manuscript. AL and LC contributed to funding acquisition and were responsible for the conceptualization and supervision of the project, as well as for writing, reviewing, and editing the original manuscript.

Funding

This work has been funded by Align Technology Align Inc., Switzerland GMBH through an Article 60 Project from Rey Juan Carlos University (project code 2023/SART60-138944).

Data availability

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

The study was conducted in accordance with the Declaration of Helsinki and approved by the Research Ethics Committee of University Rey Juan Carlos (Madrid, Spain, internal reference number: 1601202303323). Written informed consent was obtained from all participants prior to inclusion.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.