Dental Bleaching During Orthodontic Treatment with Aligners

CLINICAL RESEARCH

Dental bleaching during orthodontic treatment with aligners

Luca Levrini, MD, MS Department of Human Sciences, Innovation and Territory (DISUIT), University of Insubria, Italy

Luigi Paracchini, PhD INGEO, Italy

Renata Bakaj, DDS School of Orthodontics, University of Insubria, Italy

Andrada Diaconu, DH Private Practice

Soﬁa Cortese, DH Private Practice

Correspondence to: Prof Luca Levrini Department of Human Sciences, Innovation and Territory (DISUIT), University of Insubria, Via Sant’Abbondio, 12, 22100, Como, Italy; Tel: +39 31 2384311; Email: [email protected]

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Abstract compared with that on teeth 31 and 42 (study teeth, without reservoirs). Objective: The present study was undertaken to de- Results: The FEA results showed that the optimal gel termine the tooth whitening effectiveness of trays distribution is reached when 2 mm3 of gel is applied to with no reservoirs (Invisalign aligners or Vivera retain- the center of the vestibular face of the tooth in the ers used as bleaching trays), initially with a finite ele- tray. As regards the clinical study, there were no rele- ment analysis (FEA) and subsequently with a clinical vant differences of whitening effectiveness between study using spectrophotometry. the teeth with reservoirs and those without. In both Materials and methods: The FEA technique was used cases, the whitening was effective and the patients to determine the ideal distribution of bleaching gel be- were completely satisfied with the results. tween teeth and aligners in vitro. Three sample areas Conclusions: The advantages for patients to receive of gel application on the maxillary central incisors (the dental bleaching during orthodontic treatment with incisal edge, the middle part, and the gingival edge) aligners are evident. The procedure is not time con- were analyzed. Spectrophotometry was used to as- suming and requires less financial expense. Further certain the clinical effectiveness of the bleaching gel clinical studies are required to assess the effectiveness as it related to the results of the FEA. More specifically, of the procedure. the chromatic variation obtained by the bleaching gel on teeth 41 and 32 (control teeth, with reservoirs) was (Int J Esthet Dent 2020;15:44–54)

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Introduction ing gel sealed inside, thus preventing gum irritation and saliva mixing with the gel. The Dental bleaching is often performed during most common disadvantages of this pro- orthodontic treatment as an ancillary procedure are teeth and gum sensitivity due to cedure to obtain better esthetic results. Ac- an uncontrolled and extended treatment cording to the literature, almost 90% of pa- performed autonomously by patients who tients request tooth whitening, and 76% of may desire instant results. orthodontists recommend whitening pro- The most frequently used products are cedures.1 However, only one-third (33%) of carbamide peroxide (10% or 16%) and hy- orthodontists provide in-office whitening, drogen peroxide (10%). Recently, gum and whereas nearly two-thirds (66%) refer pa- teeth sensitivity has been better managed tients to other dental practitioners.1 thanks to thicker peroxide gels that do not It is more common today for tooth soak into the tooth as much as previous whitening to be performed as the ultimate gels, and the use of desensitizers such as end-of-treatment step to obtain optimal es- potassium nitrate and fluoride. Many den- thetic results. However, this is time consum- tists therefore recommend tooth whitening ing and affects the duration of the therapy, home maintenance with a lower-percent- consequently making it more expensive for age bleach that can be kept on the teeth for the patient (additional customized trays longer periods of time. need to be purchased to perform dental Nowadays, progressive orthodontic align- whitening after an orthodontic therapy). On ers are becoming increasingly popular the other hand, using orthodontic aligners among orthodontists and patients. Even or retainers as bleaching trays saves time though in the past aligners were mainly compared with undertaking additional used on adult patients seeking an esthetic bleaching treatment after orthodontic ther- solution for mild malocclusions, they have apy. Also, patients are only charged for the recently become more efficient and can bleaching gel, without having to support ex- also be used for major malocclusions. It tra costs, and the entire procedure out- therefore seems opportune to integrate comes are monitored by the clinician during dental bleaching and aligner treatment op- the scheduled orthodontic visits. tions in the process of care, avoiding the Bleaching can be performed using a need to purchase additional customized wide variety of methods, including in-office trays. Dental bleaching could be performed bleaching and at-home bleaching. The for- on patients simply by using their custom- mer procedure provides fast and immedi- ized aligners without attachments during ately apparent results and takes place under the treatment, instead of buying extra ones carefully monitored conditions that allow for bleaching use only. Additionally, it would for the safe and pain-free use of a relatively also be possible for patients to use their high concentration of bleaching gel. On the customized final retainers (Essix or Vivera) other hand, at-home bleaching is performed as bleaching trays after fixed orthodontics. with a low dosage of bleaching agents by There is no evidence to show that com- patients at home, even though it is neces- monly used trays with reservoirs are better sary for dentists to carefully monitor the than orthodontic aligners or retainers for condition of both the teeth and the gum- tooth whitening purposes. Some reports in line. For this purpose, vinyl trays containing the literature2-4 consider reservoirs to be un- bleaching gel reservoirs are custom fabri- necessary, despite the fact that they are the cated. The objective is to keep the bleach- most common bleaching trays used by pa-

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Figs 1 and 2 3D models from patients achieved using the iTero Element intraoral scanner.

tients at home. It must be stressed that tigate the best location for gel in the trays these reports do not describe a method without reservoirs in order to obtain optimal protocol and give no indication of the type gel distribution, taking into consideration of gel to use (quantity and physical charac- the tray material and the gel type. The sec- teristics), its placement inside the trays, and ond was a clinical study focusing on the dif- the physical features of the trays them- ferences in effectiveness between gold selves. standard bleaching trays with reservoirs and If the method of the present study proves trays without reservoirs (Invisalign aligners effective and safe for patients, aligner treat- or Vivera retainers). ment could represent an integrative procedure that combines functionality and es- Materials and methods thetics, ie, patients could use aligners to combine the concepts of straight teeth and Finite element analysis (FEA) white teeth, without extra costs or additional treatment time. There should, however, A FEA system was used as a virtual simula- be a focus on the damage that the acidic tion of the chemical and physical behavior bleaching gel might cause to the gums,5 al- of gel (responsible for tooth whitening) though it could be argued that such a tem- placed inside a transparent system (such as porary acidic condition is no more detri- Invisalign aligners or Vivera retainers) be- mental than habitual, long-term poor oral tween the aligners/retainers and the teeth. hygiene or a highly acidic diet. Specific FEA is a type of computer program that uses studies on this aspect need to be conduct- the finite element method to analyze a ma- ed.6 Furthermore, some clinicians believe terial or object to determine how stresses that the contact of the acid on the aligner will affect the material or design. The analy- trays can somehow reduce its efficiency. sis is done by creating a mesh of points in In view of these considerations, and as- the shape of the object that contains infor- suming that active aligners or retainers are mation about the material and the object at useful tools to manage tooth whitening in each point of analysis. For this purpose, a orthodontic patients, two parallel proced- simplified system was devised, taking into ures were performed in this study. The first consideration only eight teeth in the maxilla procedure was a virtual fluid dynamic study on which a three-dimensional (3D) model with a finite element analysis (FEA) to inves- FEA was conducted. For a further refine-

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ment of the FEA, the 3D model of gel, tray, and maxilla was simplified to consider the central incisors only. The simulation con- cerned three different areas of the teeth: the occlusal edge, the middle, and the gingival edge. First, an intraoral scanner (iTero Element) was used to obtain a 3D file of the patient’s impressions. Then, the solid to layer (STL) file, elaborated from the iTero, was pro- 0.000 3.500 7.000 (mm)

1.7500 5.250 cessed by Geomagic (3D Systems) to obtain a 3D file of the dental impressions and a 3D Fig 3 3D solid mesh used for the FEA considering, in particular, a section of the file of the teeth (Figs 1 and 2). The inner sur- central incisor. faces of the tooth tray had an offset of 1 mm compared with the outer surfaces of the patient impressions (Fig 3). Once a 3D file from the scanned two-dimensional (2D) surfaces of the teeth was obtained, a series of as- semblies and matchings were recreated through SolidWorks 2014 SP4 (Dassault Sys- tèmes) in Windows 7 SP1, in order to reach the final phase of the FEA. The aligner with 3D features was created from the outer surfaces of the teeth (Fig 4). During the FEA, two different solid elements were used to mesh the simplified system: tetrahedral solid with 10 nodes and hexahedral solid with 20 nodes. Moreover, contact elements Fig 4 3D models of the mandible and maxilla (gray) and the tray/aligners were used to simulate linking points be- (blue/pink). tween all the parts. The simulation was extended to the chemical-physical features of the materials and the conditions of the loads (on eight teeth, a single load of 300 N was

A: Static structural Time: 1 s used, which is an average value of complex Items: 10 of 11 indicated loads during chewing processes – as shown Fixed Support Force: 150 N Force 2: 150 N in Figure 5) and constraints, with speciﬁc at- Force 3: 300 N Force 4: 300 N tention given to the geometry of solids. Force 5: 300 N Force 6: 300 N A Force 7: 300 N With reference to the gel, the simulation Force 8: 300 N J Force 9: 150 N C considered it as non-Newtonian ﬂuid (its B

I D position is shown in Figure 6). All FEAs were H E conducted by means of NEiFusion 1.2 – 9.1 G F NEiNastran under Windows 7_x64 SP1, 0.000 10.000 20.000 (mm) where 113,483 nodes and 85,686 elements 5.000 15.000 were considered (Figs 5 and 6). Fig 5 Forces (red arrows) and support (blue surface) used to perform the FEA simulation.

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Spectrophotometry Proﬁle of central incisor Position [a] of the gel Position [b]] of the gel Position [c] of the gel Ten patients were selected for the clinical study. For each patient, trays for bleaching AAreaAr = 8.5 mm2 were used with control teeth (teeth 41 and AArea = 8.58 mm2

32; gold standard trays for home bleaching) AreaA = 85m8.58855 mm2 and study teeth (teeth 42 and 31, without reservoirs; Invisalign orthodontic aligners). Geometry Geometry Geometry The inclusion criteria for patient recruit- ment were: 1) age between 18 and 50; 2) no Thickness of the gel = 250 μm Thickness of the gelg = 250 μm Thickness of the gel = 250 μm bleaching treatment in the last 24 months; Thickness of the gel = 350 μm Thickness of the gelg = 350 μm Thickness of the gel = 350 μm 3) no bleeding on probing (BOP); 4) good Thickness of the gel = 650 μm Thickness of the gelg = 650 μm Thickness of the gel = 650 μm general and oral health; and 5) good hygiene conditions with no plaque. The exclu- Fig 6 Central incisor on which the FEA simulation was performed. The sion criteria were: 1) any pharmacologic following have been added to the image: (1) gel position (in zones defined as therapy; 2) cuts, wounds or aphthous le- high position [a], central position [b], and low position [c]); (2) area of distribution 2 sions on the oral mucosa; 3) ascertained of the gel (area = 8.5 mm ); (3) thickness of the gel (first thickness 250 μm, second thickness 350 μm, third thickness 650 μm), which is necessary, together hypersensitivity to active principles of used with the distribution area, to determine the volume (the area for the thickness bleaching agents; 4) fixed orthodontic or was multiplied to determine the volume of the gel used). prosthetic devices; 5) cavities or conserva- tive restorations on teeth 31, 32, 41, and 42; 6) tooth anomalies; and 7) patients who smoke more than 10 cigarettes per day. All cases where the fit between the orthodontic tray and the teeth was not perfect were excluded from the study. The Opalescence PF tooth whitening system was used as a bleaching agent (carbamide peroxide 10%), delivered to each patient in packages of four syringes of 1.2 ml (1.50 g) each. This product contains potassium nitrate and fluorine (110 pmm), which decreases the risk of cavity predisposition and dentinal sensitivity. It also contains wa- ter (20%), which prevents the teeth from de- hydration and relapse discoloration. The trays used for bleaching were In- visalign aligners modified with heated clamps to make the reservoirs on teeth 41 and 32 (Fig 7). Thereafter, a SpectroShade Micro spectrophotometer was implement- ed for color detection, providing both a general and a sectorial evaluation of the color as well as detailed dentinal mapping on the tooth surfaces in order to analyze Fig 7 Control group (teeth 41 and 32) and study group (teeth 31 and 42) created translucency. with heated clamps on Invisalign aligners.

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emitting diode (LED) technology, which ac- quires dental images and visualizes them on the display, analyzing the general color of the tooth and the chromatic mapping with reference to the incisal edge, the middle part, and the cervical area of the tooth. Col- or measurements were obtained through a 0.000 5.000 10.000 (mm) light source which generated the entire visi- 2.500 7. 500 ble spectrum of light. The image of the illu- minated area was reflected on a black-and- white sensor CCD positioned at the end of the optic system that could register data from 400 to 700 nm of the visible spectrum. The system CIE L*, a*, b* was used to calculate the acquired chromatic data, 0.000 5.000 10.000 (mm) 2.500 7. 500 where L* indicates the clarity of the color on a scale from 1 (black) to 100 (white) and corresponds to the value; a* indicates the amount of green and red on a scale from -a (green) to +a (red) and represents the chro- ma; and b* indicates the quantity of blue and yellow on a scale from -b (blue) to +b 7,8 0.000 5.000 10.000 (mm) (yellow) and represents the shade. Using 2.500 7. 500 the following formula, it was possible to compute the color difference ʘ( E) of two Fig 8 Stress distribution, according to the theory of non-Newtonian fluids, on elements acquired by the spectrophotom- the vestibula aspect of the maxilla. This distribution will depend on the position of eter: ʘE = (ʘL2 + ʘa2 + ʘb2)1/2, where ʘL is the gel and the quantity (amount expressed in terms of volume, as described in the difference between the two values of L; Figure 5). ʘa is the difference between the two values of a; and ʘb is the difference between the two values of b. ʘE indicates the difference of the general color of two samples and is expressed as the distance of two points in The correct bleaching application on the the space of color, being therefore an ob- trays was shown to the patients, who were jective evaluation.9 CIELAB parameters were asked to put the gel on the center of the performed and used for the tooth color vestibular crown of the clear aligner, using analysis on the incisal edge, in the middle, about 2 mm3 of the product for teeth 31 and and on the cervical part of the teeth at T0 42, and about 4 mm3 for teeth 32 and 41. (before whitening treatment) and T1 (10 days Patients were asked to wear the whitening after whitening treatment). A two-sided trays while sleeping (around 8 h) for 10 con- t test of the two separate samples was per- secutive days. After 10 days (end of the formed to verify the bleaching effectiveness treatment), color detection was performed and compare the two techniques used in and photographs were taken. the study. The differences observed were The color was detected by the spectro- considered significant when they resulted in photometer. This device works with light a 98.5% confidence level.

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Results Table 1 Values of L*, a*, and b* before and after the bleaching treatment in the control group (teeth 41 and 32)

FEA Control group L* a* b* with reservoir The results of the FEA in vitro study showed Before 71.2 3.6 16.0 three different scenarios of total gel defor- After 73.9 2.8 13.1 mation according to the different analyzed Difference +2.7 -0.8 -2.9 areas. The optimal situation was 2 mm3 of Significance (t test) 0.007 0.08 0.001 gel volume placed in the center of each tooth in the tray. This specific circumstance Confidence level 99.3 92 % 100% allowed for the bleaching gel to flow through the tray homogeneously, evenly Table 2 Values of L*, a*, and b* before and after the bleaching treatment in the distributing across the tooth surfaces and study group (teeth 42 and 31) preventing the gel from pouring out of the tray contours to cause gingival sensitivity. Study group L* a* b* without reservoir The second scenario was 6 mm3 of gel volume placed into the incisal edge of the tray; Before 71.8 3.2 16.2 this situation presented the risk of the gel After 74.0 2.8 13.8 spreading uncontrollably into the whole Difference +2.2 -0.4 -2.4 3 tray. The third scenario was 2 mm of gel Significance (t test) 0.005 0.243 0.014 volume placed near the gum, which was Confidence level 99.5 75.6 % 99.9% the worst condition for gel deformation because an homogeneous distribution across the tooth surfaces was not obtained; also, Table 3 ʘE general difference in color between the two samples there was a high risk of the gel spilling onto ̪(ZLWKUHVHUYRLU 4.0 the gums to cause sensitivity, decreasing the bleaching effectiveness( Fig 8). ̪E without reservoir 3.5 Difference -0.5 Spectrophotometry Significance (t test) 0.1133 Confidence level 88.7 Except for some cases of hypersensitivity and dysgeusia (which was spontaneously recovered), there were no side effects caused by the bleaching treatments for any (L*) and a reduction in the amount of green of the patients, and in no case was it neces- red (a*). Table 3 shows the data in relation to sary to interrupt the treatments. Tables 1 ʘE, representing the measurements of col- and 2 show the results of L*, a*, b* acquired or differences betweenT 0 (before bleach- from the spectrophotometry on the teeth, ing) and T1 (at the end of the bleaching with and without the reservoir. Both the treatment). The average value of ʘE on the techniques resulted in a significant decrease teeth that underwent bleaching with reser- of shade b*, which corresponds to a varia- voirs (control group) was 4, whereas the av- tion in the shade of the tooth. This results in erage value of ʘE for the teeth treated with- a whitening effect that, according to the lit- out reservoirs (study group) was 3.5. Both erature,7 is highly satisfactory to patients. procedures were proven valid in terms of Both with and without the reservoir, there bleaching effectiveness because the ʘE was an increase in the clarity of the color could be perceived with the naked eye.10

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When the two methods were compared, a The present study showed that there are difference of 0.5 in the ʘE value was detect- no clinical differences in effectiveness be- ed in favor of the technique with the reser- tween the two methods, although there are voir, but this difference was not statistically more advantages to using aligners. The significant. bleaching technique with aligners is less time consuming for both the dental hygien- Discussion ist and the patient and is consequently less expensive. A smaller amount of bleaching In patients treated with aligners or fixed gel is required in the aligners (without reser- appliances, it is possible to perform profes- voirs), and it was shown that 2 mm3 of gel sional tooth whitening in two basic ways: placed on the center of the teeth within the with a high concentration of hydrogen per- aligners is enough to spread out onto the oxide (35%) at the dental office or by taking whole surface without pouring out and additional impressions of the dental arches causing gingival sensitivity. Also, performing and then using at-home whitening trays dental whitening during the orthodontic with reservoirs and a low concentration of treatment improves the patient’s self-es- gel (10% carbamide peroxide). In both cas- teem and provides psychological and social es, additional materials and chair time are benefits, as is shown from the surveys that required because, when a patient desires a were taken during the study. dental bleaching at the end of treatment, During the in vitro studies it was ob- the orthodontist takes two dental impres- served that the general gel deformation sions: one for the retention trays and anoth- was due to differing pressures applied to er for the whitening trays. the tray; what was considered were the in- It is proposed that the trays for Invisalign tensity of the force function, the point of aligners or Vivera retainers be used as tools application, and the direction of the force. for tooth whitening during an orthodontic These forces derive from chewing process- treatment and its follow up by using at-home es and the interplay between the maxilla tooth whitening gel at a medium concentra- and mandible. It could be argued that the tion in the tooth–tray interface. In the pres- pressure points in active aligners could ent study, it was hypothesized and clinically change this force system, and consequent- shown that this procedure may guarantee ly affect the gel deformation and distribu- teeth whitening similar to the at-home pro- tion. While this argument is certainly rea- fessional whitening kits with trays equipped sonable, the present clinical study showed with a reservoir (gold standard) in an effec- no difference in effectiveness between the tive, safe, and inexpensive procedure. active aligners and the common (passive) Provided that this method is safe and whitening trays with reservoirs. Therefore, it does not damage the gums, it is certainly ef- can be stated that gel distribution is mostly fective because the patient can supervise influenced by its chemical and physical fea- the level of whitening at home until the teeth tures, volume, thickness, and point of appli- reach the desired color, while professional cation on the tooth tray. Other influencing monitoring of the procedure is guaranteed factors are tooth typology, the surface ge- by the orthodontist during the scheduled ometry of the teeth, and the chemical-phys- visits. Moreover, it is an inexpensive option ical characteristics of the constitutive ma- because patients do not need to buy extra terial of the tray. trays; instead, they are only charged for the The use of bleaching gel with aligners at syringes containing the bleaching gel. the beginning of an orthodontic therapy

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when the teeth are crowded is not recom- Instead of bleaching gel, other materials mended because crowding could influence could be used to meet patients’ needs and the fit of the tray. Moreover, it is advisable cosmetic requests while using Invisalign not to use aligners with attachments as they aligners or Vivera retainers. For instance, a could obstruct the optimal gel distribution fluoride or casein therapy could be per- across the tooth surfaces. The proposed formed during orthodontic treatment to re- method is not viable if there are attach- duce the risk of tooth decalcification and ments on the teeth because they would subsequently improve the overall treatment. form a barrier between the enamel and the Further studies are necessary to ascertain bleaching gel, causing a differential whiten- the best conditions for the optimal distribu- ing effect on the tooth surface. For this rea- tion of these substances. son, it is only possible to perform dental Some clinical precautions should be fol- bleaching with this method during ortho- lowed to prevent tooth and gum sensitivity, dontic treatment with aligners that do not eg, the use of hydrogen peroxide at medi- require attachments (such as the first or the um concentrations, and prescribing a de- last ones), after the removal of the attach- sensitizing substance for 7 to 10 days after ments or with Vivera retainers. the bleaching therapy. An important factor to consider for the In conclusion, the present study de- correct execution of this procedure is the scribed a technique to determine the mini- accurate fitting of the teeth in the aligners; mum amount of bleaching gel and its best all areas of the teeth should be in direct location in aligners used as whitening trays. contact with the aligner, especially at the This technique could also be used for other gingival margins. This aspect should be tak- substances of clinical utility. The study also en into consideration when performing showed that gold standard whitening trays end-of-treatment dental bleaching. with reservoirs are no more effective for the When a clinician provides a lingual re- purposes of bleaching than custom-made tainer in order to avoid relapse, dental aligners. The authors suggest the usage of bleaching could be performed using the last this versatile method to reduce both time orthodontic aligner prior to the removal of and costs for the dental office and thep a- the contact areas between the retainer and tient while reducing treatment time and the aligner. This could allow for the possibil- guaranteeing a better overall orthodontic ity of using the last orthodontic aligner in treatment. the mandibular arch and the Vivera retainer in the maxillary arch to perform dental Clinical relevance bleaching, even during the years following the end of orthodontic treatment. Dental bleaching with clear aligners is effec- It is essential that the clinician verifies the tive and reduces treatment time and costs excellent fit of the orthodontic tray to the for both the dental office and the patient. teeth and also to the gingival margin con- Dental bleaching with clear aligners guar- tour before suggesting this dental bleaching antees a better overall orthodontic treat- treatment method. ment.

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