Knowledge differences between general practitioners and orthodontists about Invisalign clear aligner treatment – a cross-sectional survey-based study

ABSTRACT

Purpose

This study investigated the knowledge differences between general practitioners and orthodontists about the Invisalign system.

Materials and methods

A web-based survey regarding 10 Invisalign treatment domains was distributed to 161 orthodontists and 213 general practitioners. The responses were ranked using a Likert-type scale and analysed with the Chi-square test and Bonferroni adjustment.

Results

The response rate was 52.1% for general practitioners and 63.4% for orthodontists. Comparing Invisalign to conventional fixed appliances, orthodontists agreed/strongly agreed that Invisalign aligners are suitable for all types of cases (p = 0.001). Orthodontists also agreed that it causes less tooth discomfort (p = 0.01) and an increased number of attachments can affect its esthetic perception (p = 0.014) but general practitioners opted for the ‘Do Not Know’ option (p ≤ 0.01). General practitioners also responded ‘Do Not Know’ to whether Invisalign treatment finishes in a shorter duration (p = 0.001), achieves all types of tooth movement (p < 0.001) and results in better periodontal health (p = 0.001). Orthodontists were more likely to disagree/strongly disagree that Invisalign treatment results in less tooth root resorption (p = 0.008), better American Board of Orthodontics Objective Grading System and Peer Assessment Rating scores (p < 0.001) and low risk of relapse (p < 0.001), while general practitioners opted for the ‘Do Not Know’ option (p < 0.0001, p < 0.0001 and p < 0.0001, respectively).

Conclusion

Regarding Invisalign treatment, this study found that orthodontists were generally evidenced-based but general practitioners lacked such knowledge, suggesting that general practitioners must be provided with relevant evidenced-based information.

KEYWORDS:

• Clear aligner
• Invisalign
• perception
• orthodontist
• dentist
• dentists

Introduction

Clear aligners have a long history in orthodontics dating back to 1946 when Kesling advocated shape-driven orthodontic tooth movement using thermoplastic tooth positioners to correct tooth malposition [1]. In 1997, Align Technology introduced its ‘Invisalign®’ system, an adoption of Kesling’s concept that uses a sequence of clear plastics [2].

Since its introduction, the Invisalign system has evolved due to advancements in biomaterial design, engineering and biomechanics and it is now capable of full orthodontic therapy [3]. Compared to conventional fixed appliances, Invisalign has clear advantages regarding patients’ comfort and acceptance, easier oral hygiene maintenance and better facial esthetic perception [2,4–6]. Nevertheless, scholars in this area are yet to reach a consensus regarding the clinical effectiveness of Invisalign and whether it can surpass the clinical performance of conventional fixed appliances [7–10].

In recent years, Invisalign advertising has used marketing that supports its application in orthodontic therapy [11,12]. Previous research by the authors of the present study investigated the knowledge of laypeople about Invisalign treatment and whether they were misled by its marketing claims; finding that around 20% of the population know what Invisalign is but a large percentage of those who are familiar with it had misconceptions about its clinical effectiveness [13]. These misconceptions can be explained by Align Technology’s massive marketing campaign across different media outlets and the lack of public access to reliable information that is supported by high-quality evidence. In a continuation of the previous project and since no study has been done on this topic, the current study aims to investigate the knowledge differences between general practitioners and orthodontists about the Invisalign system.

Materials and methods

This study was approved by the Committee of Research Ethics at Qassim University (#23-38-09). Using the Microsoft Forms web-based app (Microsoft Corporation, Washington, United States), we structured an open survey according to the CHERRIES guidelines (supplemental file 1) [14]. Two experienced orthodontists (J.N.A. and N.A.) and one dentist (M.A.) verified the validity and clarity of the survey.

The survey constitutes two main parts, the first of which concerns the participants’ demographics (age range, gender, profession, main workplace and clinical hours per week). The second part begins with gauging each participant’s overall knowledge and perception of Invisalign (ranked with a 10-point visual analogue scale), followed by 10 questions covering eight major Invisalign treatment domains:

1. Appliance case suitability

2. Treatment efficiency

3. Patient discomfort

4. Oral health implications

5. Quality of treatment result

6. Appliance biomechanics

7. Risk of treatment relapse

8. Appliance aesthetic perception

All the questions of Invisalign treatment domains were answered using a 6-point Likert-type scale (0 – Don’t know, 1 – Strongly disagree, 2 – Disagree, 3 – Neutral, 4 – Agree and 5 – Strongly disagree).

This study adopted a convenient sampling technique, randomly inviting 161 orthodontists and 213 general practitioners to participate in this study. All the invitees were engaged in active clinical duties in Saudi Arabia and were individually approached through emails. The orthodontists recruited for the current study were board certified with at least 5 years of orthodontic clinical practice, while the general practitioners do not provide orthodontic treatments. Two-email reminders were sent 3 weeks apart to each participant who had not yet responded to the survey.

Statistics

Statistical analysis and data representation were conducted using SPSS program for Windows (version 23; SPSS Inc., Chicago, IL). The absolute values and percentages of participants’ responses were calculated. A Chi-square test was used to examine the sample demographics and the relationship between Invisalign treatment domains in relation to participants’ profession. A p value of less than 0.05 was considered statistically significant. Meanwhile, adjusted standardized residuals (z-scores) were used for post hoc comparison with Bonferroni correction for multiple comparisons.

Results

Sample characteristics

A total of 102 (63.4%) orthodontists and 111 (52.1%) general practitioners participated in the study. The majority of participating general practitioners were under 30 years old (84.7%), whereas the majority of orthodontists were between 31 and 40 years (69.6%). Females constitute the majority of general practitioners (58.6%) while males constitute the majority of orthodontists (66.7%). No differences were found between general practitioners and orthodontists in terms of their main working place or clinical hours per week (Table 1).

Table 1. The demographic differences between the participating general practitioners and orthodontists.

Variables		Dentists	Orthodontists	p value
Age	20–30 years	94**	5	<0.0001
	31–40 years	16	71**
	41–50 years	1	18**
	51–60 years	0	8*
Gender	Females	65**	34	<0.001
	Males	46	68**
Main working place	Academic institutions	11	20	n.s.
	Public hospitals	47	30
	Private clinic	53	52
Clinical hours per week	Less than 15 hours	12	9	n.s.
	15–30 hours	18	28
	30–40 hours	43	28
	More than 40 hours	38	37

Statistically significant post hoc differences; *p value < 0.01, **p value < 0.001.

n.s., insignificant Chi-square test at p value 0.05.

Differences in Invisalign treatment knowledge between dentists and orthodontists

The perceived knowledge of Invisalign treatment was statistically different between the two groups (p < 0.001), with orthodontists (8.36 ± 1.36) having a higher perceived knowledge than general practitioners (5.52 ± 2.11). The overall perception of Invisalign treatment compared to conventional fixed appliances was also statistically significant (p = 0.001; Table 2), where general practitioners were more likely than orthodontists to believe that Invisalign can perform better than conventional fixed appliances (p < 0.001).

Table 2. The knowledge differences of general practitioners and orthodontists about the investigated Invisalign treatment domains.

	Dentist						Orthodontist
	Worse		Equal		Better		Worse		Equal		Better		p value
Question # G	31		56		24***		45		51		6		0.001
	Do not know	Strongly disagree	Disagree	Neutral	Agree	Strongly agree	Do not know	Strongly disagree	Disagree	Neutral	Agree	Strongly agree
Question # H1	5	18	58	18	12	0	0	11	37	16	29	9	0.0001
Question # H2	7	5	14	12	46	27	0	5	7	15	44**	31**	n.s.
Question # H3	11**	5	15	26	43	11	0	7	22	33	32	8	0.009
Question # H4	7*	3	11	23	48	19	0	4	9	15	41	33*	0.023
Question # H5	21***	2	6	26	42	14	2	3	17**	32	34	14	0.0005
Question # H6	11**	2	5	20	48	25	0	0	8	17	47	30	0.015
Question # H7	40***	2	10	38	18	3	4	14***	28***	40	16	0	<0.0001
Question # H8	47***	0	5	40	18	1	4	14***	28***	48	8	0	<0.0001
Question # H9	15***	14	37	28	14	3	1	17	46	14	21	3	0.002
Question # H10	28***	5	19	36	19***	4	1	29***	43***	25	2	2	<0.0001
Question # I	4	3	0	7	42	55	0	2	0	8	40	52	n.s.
Question # J	37***	0	10	28	31	5	6	5	12	28	45*	6	<0.0001

Post hoc differences: *, 0.05–0.01; **, <0.01; ***, <0.001.

n.s., insignificant Chi-square test at p value 0.05.

On the question that asked whether Invisalign is suitable for treating all types of malocclusions, responses were statistically significant between the two groups (p < 0.001). Orthodontists were more likely than general practitioners to agree or strongly agree that Invisalign is suitable for treating all types of malocclusions (p = 0.001). This study also found a group-related difference on whether Invisalign treatment finishes in a shorter duration (p = 0.009), achieves all types of tooth movement (p = 0.002) and results in better periodontal health (p = 0.015) compared to conventional fixed appliances; general practitioners were more likely than orthodontists to opt for the ‘Do Not Know’ option for the three questions (p = 0.001, p < 0.001 and p = 0.001, respectively). However, there were no statistical differences between the two groups in their knowledge of whether Invisalign treatment results in fewer appointments than conventional fixed appliances (p = 0.087).

Another group-related difference was observed on whether Invisalign treatment can cause less tooth root resorption than conventional fixed appliances (p < 0.001), where orthodontists disagree (p = 0.008) while general practitioners opted for the ‘Do Not Know’ option (p < 0.0001). A group-related difference was similarly observed on whether Invisalign treatment can cause less tooth discomfort than conventional fixed appliances (p = 0.023), with orthodontists strongly agreeing (p = 0.01) and general practitioners opting for the ‘Do Not Know’ option (p = 0.01).

A significant group difference was observed on whether the treatment results obtained by Invisalign have a better Peer Assessment Rating (PAR) index (p < 0.0001) or American Board of Orthodontics Objective Grading System (ABO-OGS) index scores (p < 0.0001). For the two questions, orthodontists were more likely to disagree or strongly disagree (p < 0.001), while general practitioners opted for the ‘Do Not Know’ option (p < 0.0001).

The question regarding whether the risk of relapse of Invisalign treatment is less than conventional fixed appliances was statistically significant between the two groups (p < 0.0001). Orthodontists were more likely to disagree or strongly disagree (p < 0.001), while general practitioners agreed (p < 0.001) or chose the ‘Do Not Know’ option (p < 0.0001).

Almost all the participating general practitioners and orthodontists believed that patients perceived Invisalign appliances as more esthetic than conventional fixed appliances (p = 0.402). However, when asked if the number of attachments of Invisalign treatment was increased (p < 0.0001), orthodontists agreed that this would affect patients’ esthetic perception (p = 0.014) while general practitioners chose the ‘Do Not Know’ option (p < 0.0001).

Discussion

Clear aligners have grown in popularity in recent years, where Invisalign is the most widely used brand. This study investigated general practitioners’ and orthodontists’ knowledge of Invisalign treatment. Apart from the importance of patient cooperation in clear aligner treatment, a low-to-moderate risk of bias literature indicates that clear aligners present challenges in optimal movement of teeth with short clinical crowns, correcting severe deep bite and premolar extraction cases, correcting diastemas and dental crowding of more than 5 mm, and achieving optimal root parallelism, torque control and occlusal contacts [15–20].

Furthermore, the present study also found that, unlike general practitioners, orthodontists agreed or strongly agreed that Invisalign aligners can treat all types of malocclusions. Clear aligners are well-suited for mild to moderate non-extraction cases [7–10]. However, due to their inherent mechanical limitations, clear aligners should be used with extra care in treating difficult cases, especially when tooth extraction is required [10,15–17]. Nonetheless, recently published studies demonstrated that clear aligners, compared to conventional fixed appliances, are capable to treat severe orthodontic cases, such as Class I and II crowding cases with or without first premolar extraction or cases requiring orthognathic surgery [21–23]. This can explain the positive response of orthodontists in the current study regarding the ability of clear aligners to treat all types of malocclusions. On the other hand, this study found that general practitioners were more likely than orthodontists to believe that the overall performance of Invisalign aligners is better than conventional fixed appliances. This result contrasts with previous literature and indicates that general practitioners were overestimating the treatment effects of clear aligners compared to orthodontists.

This study also found no differences between general practitioners and orthodontists on the question of whether Invisalign treatment can result in a shorter treatment duration or involves a fewer number of visits than conventional fixed appliances. In terms of the treatment duration and number of visits for Invisalign and conventional fixed appliances, previous meta-analyses have shown contradictory and insignificant results [9,20,24]. However, a recent randomized clinical trial by Lin et al. [25] showed a longer treatment duration (approximately 4.8 months) with Invisalign clear aligners than conventional fixed appliances for mild malocclusions, while a recent retrospective study found Invisalign aligners and conventional fixed appliances resulted in a similar treatment duration for adults with severe deep bite [26].

In this study, compared to general practitioners, orthodontists strongly agreed that Invisalign treatment causes less discomfort than conventional fixed appliances. This is in line with the findings of a recent limited-evidence systematic review, which suggested that patient discomfort was reduced in the first few days of clear aligner treatment versus conventional fixed appliances, but no noticeable differences were found thereafter [4].

Concerning the risk of root resorption, orthodontists in the current study disagreed that this occurs less with Invisalign treatment than conventional fixed appliances, while general practitioners chose the ‘Do Not Know’ option. The literature regarding the incidence of root resorption in aligners compared to conventional fixed appliances is contradictory but showed that apical root resorption can be less with clear aligners than with conventional fixed appliances [27–29]. However, the evidence in these studies can be considered low-quality and did not properly control some important risk factors for root resorption, such as the patient’s genetic predisposition towards apical resorption, force magnitude of fixed appliances, treatment mechanics and duration, tooth movement distance, tooth measurement errors and patient compliance [28,30–32].

Concerning the quality of the Invisalign treatment result, orthodontists compared to general practitioners disagreed or strongly disagreed that it results in better PAR or ABO-OGS index scores than conventional fixed appliances. Previous meta-analyses had shown that the treatment quality of clear aligners (rated using the ABO-OGS index) was worse than conventional fixed appliances [9,33,34]. While a recent study found similar ABO scores for Invisalign and fixed appliances for simple Class I cases [25], previous studies reported no differences in PAR scores [9,26].

The present study also showed that orthodontists are more likely to disagree or strongly disagree that the risk of treatment relapse with clear aligners is less than with conventional fixed appliances, while general practitioners agreed. In agreement with the participating orthodontists, a recently published overview of systematic reviews and meta-analyses reported clear aligners to have a higher relapse tendency 1–3 years posttreatment than conventional fixed appliances with a moderate level of evidence [29].

Both general practitioners and orthodontists in the current study also believed that Invisalign appliances were more esthetically perceived by patients than conventional fixed appliances, which are in line with previous literature [6,35–38]. Moreover, when asked whether an increased number of attachments could affect patients’ esthetic perception of the appliance, orthodontists agreed while general practitioners chose the ‘Do Not Know’ option. The orthodontists’ perception in the current study aligns with a previous study, which showed that the increase in clear aligner attachments could compromise its esthetic attractiveness [35].

The current study’s results should be interpreted with caution due to several limitations. First, while this study’s response rate for general practitioners and orthodontists can be deemed adequate, it might suffer from selection bias. Second, there were age differences between dentists and orthodontists in the current study. Specifically, 84.7% of general practitioners were between 20 and 30 years, while 69.6% of orthodontists were between 31 and 40 years (Table 1). The age distribution differences between general practitioners and orthodontists could have affected the knowledge differences of Invisalign system, thus the study result interpretations. Third, because this study focused only on Saudi Arabian practitioners, this may have influenced the results together with other limitations such as educational backgrounds and clinical experience. Therefore, the study findings cannot be generalized to other regions or assumed to be true for practitioners in countries other than Saudi Arabia.

Conclusions

• The response rate was 52.1% for general practitioners and 63.4% for orthodontists.

• The current study found that orthodontists were generally evidence-based regarding Invisalign treatment, while general practitioners lacked such knowledge.

• The study therefore suggests that there is an urgent need to provide general practitioners with evidence-based information about Invisalign treatment.

Author contributions

M. Alsultan contributed to methodology, formal analysis, investigation, data acquisition and writing – original draft.

J. N. Alqefari contributed to methodology, formal analysis, Investigation, data acquisition and writing – original draft.

N. Almotairy contributed to conceptualization, methodology, validation, investigation, resources, writing – original draft, writing – review & editing, visualization and project administration.

Ethical approval

This study was approved by the Committee of Research Ethics at Qassim University (#23-38-09).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplemental material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/27705781.2024.2366747