Evaluation of adverse physiological events during Invisalign® treatment: part 2

Drs. Bridgette Jones Brooks, Bryan Keith Blankenship, and Jared Stasi continue their exploration of the literature regarding clear aligners as compared to traditional braces

Introduction

The aim of this study is to review the appropriate literature concerning adverse physiological events experienced by patients being treated with Invisalign^® appliances and comparing this literature to that of patients’ adverse physiological events when undergoing fixed orthodontic appliance therapy. Part 1 discussed various areas of treatment, efficacy, effectiveness, and oral hygiene, including orofacial pain/discomfort, periodontal health, dental caries and demineralization, and interproximal reduction (IPR) adjunct in Invisalign therapy and its impact upon oral health. Read part 1 here: https://orthopracticeus.com/ce-articles/evaluation-of-adverse-physiological-events-during-invisalign-treatment-part-1/.

Part 2 of this article will continue with the discussion and findings of the individual studies and some conclusions regarding orofacial pain, periodontal health, and caries/demineralization.

Discussion and findings: Orofacial pain

“A comparison of treatment impacts between Invisalign aligner and fixed appliance therapy during the first week of treatment”¹

This study was a prospective longitudinal cohort study involving adult orthodontic patients. The purpose of this study was to evaluate through survey and diary entries the differences in quality of life impacts between subjects treated with Invisalign aligners and those with fixed appliances during the first week of orthodontic treatment. Overall, Invisalign patients reported less of a quality-of life decrease during the first week of treatment, and fixed appliance patients reported more analgesic use.

The findings of this study are pertinent to the orthodontic practitioner in that the practitioner gains knowledge as to how to relay information and expectations to the patient regarding initial quality of life changes due to orthodontic treatment. Few studies are of this nature and evaluate the first 7 days of treatment. Limitations of this study include the subjective nature of individual pain perception and inability to apply results toward treatment after the first week.

“Adult patients’ adjustability to orthodontic appliances. Part I: a comparison between Labial, Lingual, and Invisalign”²

This study was a prospective longitudinal study that examined the adult patient’s perception of recovery after insertion of three types of orthodontic appliances: buccal, lingual and Invisalign. The purpose of this study was to evaluate through survey with visual analog scale the differences in pain perception and recovery between the three different types of orthodontic appliances. Overall lingual appliances were associated with the worst perceived pain and oral disturbances. Invisalign as well as buccal appliances were less than lingual in these categories and similar in perceived levels to each other.

The findings of this study are pertinent to the orthodontic practitioner in that the practitioner gains knowledge as to how to relay information and expectations to the patient regarding expected pain during treatment and between different the three studied treatment options. Few studies compare different pain perceptions between the three treatment options as well as analgesic use. Limitations of this study include the subjective nature of individual pain perception and possibly standardization of complexity of the presenting malocclusion for treatment as the practitioner is likely to exclude certain treatment options based upon complexity of perceived treatment.

“Analysis of pain level in cases treated with Invisalign aligner: comparison with fixed edgewise appliance therapy”³

This study was a prospective longitudinal study that examined the adult patient’s perception of pain during treatment with edgewise or Invisalign appliances. The study also identified common sources of pain associated with Invisalign treatment. The aim of this study was to evaluate and compare the difference in the level of pain using the visual analog scale (VAS) between cases treated with the edgewise appliance and Invisalign. Overall Invisalign may offer less pain in comparison to edgewise appliances specifically after adjustments. Most pain associated with Invisalign was found to be deformation of the tray.

The findings of this study are pertinent to the orthodontic practitioner in that the practitioner gains knowledge as to how to relay information and expectations to the patient regarding expected pain during treatment and between the two studied treatment options. Several studies have attempted to determine which treatment option delivers the least pain. Present studies have conflicting results as to which appliance results in less pain. Limitations of this study include the subjective nature of individual pain perception and possibly standardization of complexity of the presenting malocclusion for treatment, as the practitioner is likely to exclude certain treatment options based upon complexity of perceived treatment.

“Discomfort associated with Invisalign and traditional brackets: a randomized, prospective trial”⁴

This study was a prospective randomized equivalence two-arm parallel trial. This study examined the adult patient’s perception of pain with visual analog scale during treatment with traditional fixed orthodontic appliances or Invisalign. Overall, Invisalign may offer less pain in comparison to traditional orthodontic appliances specifically after adjustments. The intensity of pain appeared to decrease over time after the 2-month time frame. Patients treated with traditional appliances may also consume more analgesics in comparison to patients treated with Invisalign.

The findings of this study are pertinent to the orthodontic practitioner in that the practitioner gains knowledge as to how to relay information and expectations to the patient regarding expected pain during treatment and between the two studied treatment options. Several studies have attempted to determine which treatment option delivers the less pain. Present studies have conflicting results as to which appliance results in less pain. Limitations of this study include the subjective nature of individual pain perception and that patients treated with either appliance in comparison are not identical or “twins.” Pain perception was identified after adjustments for the traditional group, but it is unclear how the patients in the Invisalign were tracked or instructed to change trays. Consistently changing trays over time may allow for increased pain threshold in comparison to adjustments with traditional appliances. This study was also self-reported to not be registered.

Discussion and findings: Periodontal health

“Braces versus Invisalign^®: gingival para-meters and patients’ satisfaction during treatment: a cross-sectional study”⁵

This study was a cross-sectional study involving adult orthodontic patients. The purpose of this study was to evaluate differences in oral hygiene and patient satisfaction between subjects treated with Invisalign aligners and those with fixed appliances. Reports about the effects of aligner treatment on oral hygiene and gingival conditions are minimal and conflicting.

The findings of this study are pertinent to the orthodontic practitioner in that the practitioner gains knowledge as to how to relay information and expectations to the patient regarding changes in oral health due to orthodontic treatment. The findings suggest Invisalign and fixed appliances have similar plaque measurements, but that fixed appliances demonstrated a worse gingival condition. One primary limitation in this study is propensity for examiner bias. Due to obvious visual differences between Invisalign and fixed appliances, one clinical examiner can be prone to selection bias. A better but likely unrealistic study would suggest removal of all indications as to what treatment was occurring, such as removing all fixed appliances and attachments prior to clinical exam. Limitations of this study also include the subjective nature of oral hygiene. Patients in the fixed appliance group were on average 15 years younger than the Invisalign group, 16 years of age and 31 years of age respectively. Patients were controlled for initial oral hygiene, but better parameters should have been implemented to track and standardize daily oral hygiene differences such as duration and quality of daily oral hygiene maintenance. Older individuals may be more personally and financially invested in treatment outcomes, suggesting Invisalign patients may be more attentive to oral hygiene maintenance than adolescent counterparts. Additionally, complex hormonal changes are often occurring during the average age range of the fixed appliance group (16) in which plaque may unequally exacerbate gingival response in comparison.

“A comparison of the periodontal health of patients during treatment with the Invisalign system and with fixed lingual appliances”⁶

This study was a prospective longitudinal concomitant trial of two groups of consecutive patients. The purpose of this study was to evaluate periodontal health of patients during treatment with the Invisalign system or fixed lingual appliances. The findings of this study are pertinent to the orthodontic practitioner in that the practitioner gains knowledge as to how to relay information and expectations to the patient regarding oral health changes due to orthodontic treatment. Relatively few studies evaluate the differences between fixed lingual appliances and Invisalign. Limitations of this study include the subjective nature of oral hygiene maintenance and quality of self-care. It is unclear if the examiners were standardized to perform the clinical exams, and due to the visual differences of each treatment modality, observers may be prone to examiner bias.

“Periodontal health during clear aligners treatment (CAT): a systematic review”⁷

The purpose of the study was to perform a systematic review of the existing literature in order to assess periodontal health during clear aligner therapy. The findings of this study are pertinent to the orthodontic practitioner in that the practitioner gains knowledge as to how to relay information and expectations to the patient regarding oral health changes due to orthodontic clear aligner therapy treatment. Relatively few studies, five in this review, have successfully evaluated periodontal health during clear aligner treatment. Most of the studies presented with methodological problems: bias and confounding variables, lack of adequate blinding procedures, and absence of proper randomization methods. Thus, conclusions with a moderate level of evidence could be drawn from the review process.

Five relevant articles were selected from the 1,247 identified articles. The level of evidence was moderate for all the studies. A significant improvement of the periodontal health indexes was revealed, in particular when CAT was compared to fixed appliances. No periodontal CAT adverse effects were observed in the selected studies.

Periodontal health indexes were significantly improved during CAT. Limitations of the study are the number, quality, and heterogeneity of the included studies.

“Ultrastructure and morphology of biofilms on thermoplastic orthodontic appliances in ‘fast’ and ‘slow’ plaque formers”⁸

This study was a scanning electron microscopy investigation involving adult orthodontic patients. Fifty-six Chinese male/female volunteers (aged 19-39 years) were screened for their plaque-forming rate using the plaque percentage index (PPI) coupled with digital photography and computer-based image analysis, after a period of 48 hours of abstinence from oral hygiene procedures. Eleven volunteers (seven males/four females) representing the lowest and highest ends of the plaque formation spectrum were chosen as slow and fast plaque formers, respectively.

The findings of this study are pertinent to the orthodontic practitioner in that the practitioner gains knowledge as to how to relay information and expectations to the patient regarding potential oral health changes due to orthodontic treatment specifically with clear aligner treatment. The orthodontic practitioner can also inform patients about their own oral health maintenance. Additionally, patients can be directed with the cleaning of aligners as well as direction as to where on the aligner to specifically target during daily cleaning. Few studies have researched biofilm accumulation and differences in composition between slow and fast plaque formers. Limitations of this study may be the differences in chemical composition of different proprietary aligner systems which may influence plaque formation and adherence.

“Periodontal health status in patients treated with the Invisalign^® system and fixed orthodontic appliances: a 3 months’ clinical and microbiological evaluation”⁹

This study was a prospective longitudinal study involving adult and non-adult orthodontic patients. Seventy-seven patients were recruited for this study, 52 females and 25 males with an age range of 16-30. The findings of this study are pertinent to the orthodontic practitioner in that the practitioner gains knowledge as to how to relay information and expectations to the patient regarding potential oral health changes due to orthodontic treatment specifically when comparing fixed appliances with clear aligner treatment. The orthodontic practitioner can also inform patients about their own oral health maintenance and possible increased attention to thoroughness for patients with fixed appliances.

The Invisalign^® group showed better results in terms of periodontal health and total biofilm mass compared to the fixed orthodontic appliance group. A statistically significant difference (P < 0.05) at the T2 in the total biofilm mass was found between the two groups. Some limitations of this present study are potential for bias due to one examiner performing all clinical exams with easily distinguishable treatment types. The mean age of patients was 24.3, but the mean age of each group of patients was not reported. This could possibly lead to irregularities between the two groups. Adult patients may be more motivated to assist in their own oral health maintenance as they are likely also financially invested in the treatment and self-motivated to approve their appearance. Patients in late teenage years often have hormonal changes that are also associated with increased gingival inflammatory response when plaque accumulates. Traditionally younger patients are also more likely to be treated with fixed appliances rather than Invisalign. Invisalign patients are often more esthetically driven and may exhibit better oral hygiene maintenance.

“Which orthodontic appliance is best for oral hygiene? A randomized clinical trial”¹⁰

The aim of this prospective randomized clinical trial was to compare the effects of clear aligners, self-ligated brackets, and elastomeric-ligated brackets on patients’ oral hygiene during active orthodontic treatment. There was no evidence of any significant difference in the oral hygiene levels among clear aligners, self-ligated brackets, and conventional (elastomeric-ligated) brackets after 18 months of active orthodontic treatment. Overall, there was not enough evidence to reject the null hypothesis that the type of orthodontic appliance has no effect on periodontal health. This study had two calibrated examiners perform all clinical exams. The examiners could not be blinded to the type of appliances being used to treat the patient, so this could be a potential area of bias. From previous studies, it can be confirmed that some patients also form plaque at different amounts and rates than others, and therefore, this could lead to potential flaws as not all patients can be realistically standardized.

This study does afford the orthodontic practitioner knowledge to present to patients concerned about oral health in relation to different orthodontic treatment options.

The findings of this study (and others) are pertinent to the orthodontic practitioner in that the practitioner gains knowledge as to how to relay information and expectations to the patient regarding initial quality of life changes due to orthodontic treatment.

Discussion and findings: Caries

“A case of severe caries and demineralization in a patient wearing an Essix-type retainer”¹¹

This study was a case report on an 18-year-old male patient. Consequently, this study does not carry a high level of evidence. Nevertheless, the reported patient had previously been orthodontically treated. The patient was wearing Essix retainers for roughly 20 hours per day and reported infrequent removal other than to eat. The patient also reported having multiple carbonated sugary beverages per day. The full coverage of the Essix retainer allowed beverages to pool within the retainer. Normally the oral environment would thoroughly cleanse these beverages from tooth surfaces; however, due to the full coverage nature of the retainer, this could not occur. The patient had extensive generalized caries that went undiagnosed due lack of regular office visits with his dentist. This case report is a valuable example for the orthodontic patient and practitioner. It is of extreme importance that the patient be informed of proper wear and care instructions for all Essix-type retainers as well as clear aligners.

“Dental health assessed after interproximal enamel reduction: Caries risk in posterior teeth”¹²

This study was a retrospective cohort study clinical comparison with control. Forty-three consecutive patients aged 19 to 71 with IPR accomplished 4 to 5 years ago as part of orthodontic treatment were examined radiographically. Overall there was no evidence to suggest mesiodistal enamel reduction within suggested limits will cause harm to the teeth and supporting structures. Caries were found in only three patients treated with interproximal reduction.

Some limitations of this study are related to the methods of examiner standardization. There was mention of only one dentist examiner who detected caries intraorally and by radiograph. There was only one examiner mentioned reading radiographs which is subject to intra-examiner bias. There was no mention of how the single examiner was calibrated. Additionally, interproximal caries detection by explorer and light by a single examiner is subject to much variation and subjectivity.

“Caries risk after interproximal enamel reduction”¹³

This study was a retrospective cohort study. Forty patients treated with air rotor stripping were examined clinically 12 months after orthodontic treatment concluded. The study found that there is no significant risk of caries with ARS. Additionally, fluoride was suggested to have minimal-to-no benefit in patients that had ARS done. The orthodontic practitioner can apply this gained knowledge to treatment modalities and assurance to patients. Control trials were suggested for further research on application of fluoride.

One limitation of this study was the use of a single examiner for all radiographic and clinical examination although the examiner was calibrated. Further investigation on the application of fluoride after ARS would be suggested.

“Dental health assessed more than 10 years after interproximal enamel reduction (IPR) of mandibular anterior teeth”¹⁴

This study was a retrospective cohort study. Sixty-one patients had stripping (enamel reduction) of all six anterior teeth on the mesial and distal surfaces greater than or equal to 10 years prior. The results were compared to a reference group of sixteen students. The study found that no carious lesions were noted, no evidence of root pathology, the distance between roots were significantly greater in patients who had stripping of the anterior teeth, and 59 of the patients experienced no sensitivity with temperature differences. No iatrogenic damage was noted. Overall irregularities of the incisors were minimal.

With having 10 years as a follow-up to the study, results also show the irregularity index of 0,67 (DS 0.64). This study appears to have validity and a foundation for support of the null hypothesis.

“Atomic force microscopy analysis of enamel nanotopography after interproximal reduction”¹⁵

This study measured the differences in roughness of enamel surfaces treated with interproximal reduction using different reduction techniques and reduction tools.  The roughness was measured using atomic force microscopy and analyzed the enamel nanotopography of treated enamel.  Results would be as expected in that diamond coated burs resulted in the roughest enamel, while enamel treated with Sof-Lex™ Discs (3M) after the enamel reduction resulted in a smoother than untreated enamel. Range of roughness from highest to lowest are a result of the following: Larger Grit Medium Diamond Burs > Medium Strips > Fine Diamond Burs > Fine Strips and Mesh Discs = Fine Strips and Curved Discs > Control Surface > Sof-Lex Discs (Entire Series).

No mention of fluoride use or any other treatment post enamel reduction or polishing.  Due to the nanotopography, a careful consideration of test subjects should have been considered. Teeth can vary even within a subject and have multifactorial items to be considered such as oral hygiene, enamel wear, age, and nutritional resultant wear. The article stated strict exclusions in the methods which enhanced the results and conclusions of the project.

“Air-rotor stripping and enamel demineralization in vitro”¹⁶

This was an in vitro study evaluating the effect of air-rotor stripping of enamel. An in vitro caries model was used to assess the susceptibility to demineralization. Air-rotor stripping was performed on one surface of each extracted tooth with enamel reduction of 0.5 mm.  These teeth were then introduced to demineralizing gel for various lengths of time and evaluated using microradiography and computerized image analysis (double window technique). Each abraded surface of all time frames resulted in a greater depth of demineralization and less mineral density. A second experiment using fluoride on the abraded surface showed a reduction of lesion penetration on abraded and control surfaces.  This study demonstrates the negative effect and increased susceptibility of demineralization to air-rotor stripping of interproximal surfaces. However, it was not a longitudinal study, and long-term effects were not studied.

Conclusion

Orofacial pain

Four studies were included in this literature review. Of the four studies, three were in agreement that Invisalign caused less pain than fixed appliances. However, in one study, there was not a statistical difference between Invisalign and the fixed appliance groups. Increased analgesic use was attributed to the fixed appliance group in two of the three studies that reported analgesic use. Significant potential for bias and limitations of the subjective nature of pain require a cautious approach to accepting or rejecting the null hypothesis. In conclusion, more studies should be accomplished specifically randomized controlled studies.

Periodontal health

Five studies were included in this literature reviewed evaluating periodontal health. One study concluded the plaque formation was similar in Invisalign and Fixed Appliance groups but that gingival health was worse in the Fixed Appliance group. A second study concluded that the plaque formation was significantly lower for the Invisalign group in comparison to the fixed appliance group but that periodontal health was not statistically different. A third study concluded that periodontal health was significantly better in the Invisalign group than the orthodontic appliance group. There were significant potential biases and methodological limitations in these studies previously mentioned that lead to a cautious acceptance of the results. Specifically, group demographics, variance in oral hygiene between groups, use of single examiners, and absence of blinding could be problematic to assume a high level of evidence is supported by these studies. A systematic review was included in this literature review. Five studies were included of the 1,247 that met search criteria. The conclusion of the systematic review was that periodontal health was significantly better in the clear aligner group compared to the fixed appliance group. The authors of the systematic review acknowledged that “most of the studies presented with methodological problems: bias and confounding variables, lack of adequate blinding procedures and absence of proper randomization methods. Thus, conclusions with a moderate level of evidence could be drawn from the review process.”

A randomized control trial was included in this review that concluded there “was not enough evidence to reject the null hypothesis that the type of orthodontic appliance has no effect on periodontal health.” This study likely has the highest level of evidence of the included studies for this literature review. The two examiners were calibrated in this study but could not be blinded to types of treatment being performed which may allow for potential bias. In conclusion, there is conflicting evidence as to which type of orthodontic treatment, Invisalign versus fixed orthodontic appliances, demonstrates better periodontal health. Further randomized control studies are needed. We cannot accept nor reject the null hypothesis that there are no differences in periodontal health experienced by patients who are orthodontically being treated with Invisalign as compared to traditional fixed appliances.

Caries/Demineralization

Six studies were included for evaluation of caries and demineralization susceptibility due to interproximal reduction during orthodontic treatment. One study had only a single subject, and therefore had no validity or statistical significance. The type of enamel removal and whether the enamel was polished after IPR had a significant impact on the outcome of caries and demineralization susceptibility. A 10-year study was included, which has the longevity and support to validate the null hypothesis. The remaining studies with statistical significance further clarify these results. Overall, the studies agree that demineralization can occur; however, with proper interproximal reduction, post-reduction polishing, and a fluoride treatment, the susceptibility of caries and demineralization are minimal to none. Therefore, the null hypothesis and the experimental hypothesis are supported.

Acknowledgments

The authors would like to extend their appreciation to Dr. Harish Parihar (the biostatistician) and Dr. John Stockstill, Professor and Director of Dental Research at the Georgia School of Orthodontics, for their valuable guidance and contributions to this article.