10.59987/ads/2018.2.77-83
Introduction: Oxidizing agents which are used as tooth whitening agents can induce an oxidative stress, a situation that initiates some systemic diseases. This clinical study aims to evaluate the effect of ascorbic acid (vitamin c) on urinary level of an oxidative stress biomarker during the athome tooth whitening period. Material and methods: Thirty healthy patients who requested for the tooth whitening were involved in this trial. Specified bleaching trays were fabricated for both arches after making an impression. Each participant was given two syringes containing 15% carbamide peroxide gel and instructed to apply it for 6 h per night for 14 consecutive nights. Patients were divided into two equal groups. In the experimental group, the patients applied two tablets containing 500 mg of vitamin C every night along with the tooth whitening period. Urine samples were obtained in the morning before the study was started and were repeated in 5, 10, 15th days and five days after the expiration of the bleaching period. TBARS test was employed to evaluate the urinary level of malondialdehyde (MDA) as an oxidative stress biomarker. Data were analyzed by means of independent sample t-test and repeated measurement analysis. Results: Twenty-nine subjects completed the study. The MDA level increased during the bleaching period in both groups; however, the difference was not significant (P&gt;0.05). In addition, the ascorbic acid application could not present a significant difference in the MDA level (P= 0.34). Conclusion: The application of 15% carbamaide peroxide did not significantly elevate the oxidative stress biomarker in human urine (IRCTID: IRCT2012113011618N1).
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Annali di stomatologia
vitamin C
The effect of vitamin C on urinary level of an oxidative stress biomarker during at-home tooth bleaching process: a randomized double blinded clinical trial
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Original Article
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H. S. Mohammadipour 
2018
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The effect of vitamin C on urinary level of an oxidative stress biomarker during at-home tooth bleaching process: a randomized double blinded clinical trial
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                                                                                                   Original article



    The effect of vitamin C on urinary level of an
    oxidative stress biomarker during at-home tooth
    bleaching process: a randomized double blinded
    clinical trial




                                                                                                li
                                                                                              na
    Majid Akbari1 DDS, MS                                     along with the tooth whitening period. Urine sam-
    Atefeh Nemati-Karimooy2,3 DDS, MS                         ples were obtained in the morning before the study
    Seyed Isaac Hashemy4,5 PHD                                was started and were repeated in 5, 10, 15th days
    Hamideh Sadat Mohammadipour2,3 DDS, MS                    and five days after the expiration of the bleaching




                                                                                            io
                                                              period. TBARS test was employed to evaluate the
                                                              urinary level of malondialdehyde (MDA) as an ox-
    1 Professor of Restorative Dentistry, Department of       idative stress biomarker. Data were analyzed by




                                                                        az
    Restorative and Cosmetic Dentistry, School of             means of independent sample t-test and repeated
    Dentistry, Mashhad University of Medical Sciences,        measurement analysis.
    Mashhad, Iran                                             Results: Twenty-nine subjects completed the
    2 Assistant Professor of Restorative Dentistry, Depart-   study. The MDA level increased during the
                                                              bleaching period in both groups; however, the dif-




                                                                      rn
    ment of Restorative and Cosmetic Dentistry, School of
    Dentistry, Mashhad University of Medical Sciences,        ference was not significant (P>0.05). In addition,
    Mashhad, Iran                                             the ascorbic acid application could not present a
    3 Dental Research Center, Mashhad University of           significant difference in the MDA level (P= 0.34).




                                                        te
    Medical Sciences, Mashhad, Iran                           Conclusion: The application of 15% carbamaide
    4 Department of Biochemistry, Faculty of Medicine, Ma-    peroxide did not significantly elevate the oxida-
    shhad University of Medical Sciences, Mashhad, Iran       tive stress biomarker in human urine (IRCTID:
                                                      In
    5Addiction Research Centre, Faculty of Medicine, Ma-      IRCT2012113011618N1).
    shhad University of Medical Sciences, Mashhad, Iran
                                                              Key words: ascorbic acid, at-home tooth bleach-
                                                              ing, oxidant and antioxidant, oxidative stress, vit-
    Corresponding author:                                     amin C.
                               ni

    Hamideh Sadat Mohammadipour
    Department of Restorative and Cosmetic Dentistry,
    Mashhad University of Medical Sciences                    Introduction
                             io


    Vakil-Abad Blvd, Mashhad 91735, Iran
    Tel.: +989153213271                                       Discolored anterior teeth are perceived as a great es-
    Fax: +985138829500                                        thetic problem by most patients. Tooth whitening or
                           iz



    E-mail: Mohammadipourh@mums.ac.ir;                        bleaching is a very conservative method which em-
    hm_7264@ yahoo.com                                        ploys oxidizing agents to achieve a lighter and more
                                                              desirable tooth color. During the course of bleaching,
            Ed




                                                              long-chain pigmented molecules oxidize and split into
    Summary                                                   smaller, lighter ones with the release of carbon, water
                                                              and oxygen (1).
    Introduction: Oxidizing agents which are used as          The bleaching of vital teeth can be accomplished by
    tooth whitening agents can induce an oxidative            either in-office or at-home technique of which the
    stress, a situation that initiates some systemic          second method is performed by the patients them-
 IC




    diseases. This clinical study aims to evaluate the        selves. The at-home bleaching method has created
    effect of ascorbic acid (vitamin c) on urinary level      an easy performing, safe and low cost bleaching
    of an oxidative stress biomarker during the at-           technique that is available to all socioeconomic class-
    home tooth whitening period.                              es of the patients. During this procedure, carbamide
C




    Material and methods: Thirty healthy patients who         peroxide, a combination of hydrogen peroxide as an
    requested for the tooth whitening were involved in        effective tooth whitening agent and urea, are com-
    this trial. Specified bleaching trays were fabricated     monly applied in a custom-fit tray for a few minutes to
    for both arches after making an impression. Each          several hours each day, with regards to peroxide con-
©




    participant was given two syringes containing 15%         centration and manufacturer recommendations. Al-
    carbamide peroxide gel and instructed to apply it         though strong evidences supported the effectiveness
    for 6 h per night for 14 consecutive nights. Pa-          of this method, nevertheless, it has lower clinical con-
    tients were divided into two equal groups. In the         trol compared to in-office one (2).
    experimental group, the patients applied two              A number of concerns over systemic side effects of
    tablets containing 500 mg of vitamin C every night        the bleaching agents have been raised because the

    Annali di Stomatologia 2018;IX (2):77-83                                                                       77
    M. Akbari et al.


    patient may have swallowed these oxidizing com-               ments. The null hypothesis was that, the ascorbic
    pounds which inevitably come in contact with their            acid did not affect the urinary level of the MDA as a
    teeth and soft tissues for a long time especially dur-        marker of oxidative stress.
    ing night. Genotoxicity, cytotoxicity, and carcinogenic-
    ity of the tooth whitening materials have been report-
    ed by many previous animal studies (3-9). They indi-          Material and methods
    cated that hydrogen peroxide might act as a promoter




                                                                                                     li
    and ingestion of carbamide peroxide in a dose-de-             Study population




                                                                                                   na
    pendent manner, induced acute mucosa ulcerations              Participants in this randomized double-blind clinical
    in rats’ stomach. Notwithstanding, multiple exposures         trial were selected from dental students with undesir-
    to hydrogen peroxide might reduced food consump-              able tooth discoloration complaint in Mashhad Dental
    tion, weight gain, and result to changes in blood chem-       School (the second biggest city in Iran). Thirty (19 fe-
    istry (5). The presence of adenoma and duodenum car-          males and 11 males) healthy volunteers signed a de-




                                                                                                 io
    cinoma alongside hyperplasia was reported following           tailed informed consent and this investigation was ap-
    the ingestion of 0.1 and 0.4% (w/v) of hydrogen perox-        proved by the Ethical Board of Mashhad University of
    ide solution for 8 weeks in rats (5-7). Timblin et al. (10)   Medical Sciences (Approval number: 901092).




                                                                            az
    presented an increase over-expression of proto-onco-          The subjects with any of the following criteria were
    gen c-jun protein in human tracheal epithelial cells.         excluded from this assay:
    However, the International Agency for Research on             1. Participants who had previous anterior restora-
    Cancer (IARC) has concluded that there is no clear evi-            tions, tooth decay, exposed root surfaces, broken




                                                                          rn
    dence in animal and human experiments for the car-                 teeth, enamel erosions or poor oral hygiene that
    cinogenicity of hydrogen peroxide (11).                            needs further treatments.
    Certainly, oxidizing agents such as tooth bleaching           2. Participants who experienced the tooth whitening
    compounds can disturb oxidant-antioxidant body bal-                procedures or they used antioxidant drugs (vita-




                                                           te
    ance in favor of oxidants and can induce a potentially             min C and vitamin E supplements) in the past six
    harmful challenge known as “oxidative stress”, which               months.
    has a potential in damaging cell structures, alters           3. Patients who are suffering from systemic or enzy-
                                                         In
    their functions and contributes in several pathological            matic disorders that disturb oxidant-antioxidant
    conditions and common diseases (12,13). One of the                 balance and smokers due to synergic oxidant with
    most important outcomes from the oxidant damage is                 the bleaching agents.
    lipid peroxidation (13). Lipid peroxides are unstable         4. Women who are pregnant or lactating mothers.
    and decompose to form a group of reactive carbonyl            5. Volunteers with temporomandibular disorders or
                              ni

    compounds like malondialdehide (MDA) (14), which                   having para-function habits like broxism and
    can be quantified with thiobarbituric acid-reactive                clenching contraindicated for the at-home tooth
    substances test (TBARS) (15). A recent study con-                  bleaching method.
                            io


    ducted by Akbari et al. (16) regarding the systemic
    side effects of the bleaching agents on human health          Bleaching procedure
    showed that these agents have the potential to dis-           To produce an accurate negative mold, alginate im-
                          iz



    turb the body balance and induce the oxidative                pressions (Bayer, Leverkusen, Germany) were ob-
    stress. They revealed that the serum concentrations           tained from both arches for each participant. There-
    of the MDA, total antioxidant capacity (TAC), and pro-        after, casts were poured with dental stone powder
           Ed




    oxidant-antioxidant balance (PAB) were increased              (Tara, Kheyzaran, Isfahan, Iran) and were trimmed to
    significantly after the tooth bleaching period.               a horseshoe shape with no palatal or tongue sec-
    Aside body’s defense, exogenous antioxidants as               tions, without damaging tooth surfaces and gingival
    therapeutic adjuncts may well improve the inherent            margins. To incorporate reservoir spaces, several
    human antioxidant capacity and overcome the oxida-            layers of nail polish were applied on labial tooth sur-
    tive damages. Considering the effectiveness of an-            faces of stone casts. The bleaching trays were fabri-
 IC




    tioxidant vitamins like vitamin C on the oxidative            cated with 0.035 inch vacuum formed sheets utilizing
    stress induced diseases such as Alzheimer disease             a vacuum tray-forming machine (Ultravac; Ultradent
    (17) and atherosclerosis (13) and its effective role in       Products Inc., South Jordan, USA). Subsequently,
    inhibiting lipid peroxidation (15), it may be necessary       the trays were trimmed to form scalloped borders on
C




    to equip the human body with a variety of external            2 mm far away from the gingival margins. Two 3-ml
    origin antioxidants in order to counter balance harm-         syringes of 15% carbamide peroxide gel (Opales-
    ful effects of the tooth whitening oxidants (12).             cence, Ultradent Products Inc., South Jordan, USA)
    To the best of our knowledge, no study has been car-          were given to each participant. The patients were in-
©




    ried out on humans regarding the effect of ascorbic           structed to place adequate amount of the bleaching
    acid on tooth bleaching induced oxidative stress. This        agent into the tray to cover the facial surfaces of the
    clinical trial was carried out to investigate whether the     teeth which are visible during laughing and speaking.
    oxidative stress following at-home bleaching could be         To obtain maximum benefits of the product and pa-
    reduced by shifting pro-oxidant-antioxidant balance in        tient compliance, participants were asked to wear
    favor of antioxidants via the use of vitamin C supple-        bleaching trays for at least 6 h per night (according to

    78                                                                                Annali di Stomatologia 2018;IX (2):77-83
    The effect of vitamin C on urinary level of an oxidative stress biomarker during at-home tooth bleaching process:
    a randomized double blinded clinical trial

    the manufacturer’s instruction) for 2 weeks. After the          Results
    loaded tray is seated, the patients were instructed to
    gently remove any excess of the bleaching material              Twenty-nine participants (19 females and 10 males)
    with a tissue or a brush. They were cautioned to dis-           completed the two-week study period. One of the par-
    continue the use of bleaching agents in the situations          ticipants was excluded from the evaluation as a result
    of tooth hypersensitivity or gingival problems and              of low cooperation, and no adherence to the study
    alert research team immediately.                                protocol. None of the participants who completed the




                                                                                                        li
    In the end, the volunteers were randomly assigned in            study reported any signs of tooth hypersensitivity or




                                                                                                      na
    equal numbers to one of the two treatment groups.               gingival irritation.
    The randomization process was carried out by a third            Table 1 presents the mean, standard deviation and
    person who was not involved in the research proto-              minimum and maximum value of the MDA in both
    col. In the experimental group, patients were instruct-         control and intervention groups between five sam-
    ed to chew two tablets containing 500 mg of vitamin             pling intervals.




                                                                                                    io
    C (Sunkist, Sunkist Growers, USA) before using the              The Kolmogorov Smirnow test demonstrated that the
    bleaching tray every night along with the tooth                 MDA concentration was normally distributed in all
    whitening procedure. Participants were reminded by              measurements (P>0.05).




                                                                              az
    a research operator through telephone to take their             According to repeated measurement analysis, the uri-
    daily doses of the ascorbic acid. In the control group,         nary concentration of the MDA in both groups gradu-
    no drug was prescribed. The whole procedure was                 ally increased during the study period that suddenly
    clarified by an expert operator for each participant to         subsided at the final sample session (Fig. 1), howev-




                                                                            rn
    increase adherence to the protocol. Neither the oper-           er, no significant difference presented between these
    ator nor the statistician knew the group allocation,            five sample sessions in each of the control and ex-
    both were blinded to the protocol.                              perimental groups (P value= 0.7 and 0.66, respec-
                                                                    tively). Furthermore, this analysis showed no signifi-




                                                          te
    Urine sample                                                    cant difference in the MDA concentration during study
    One milliliter of participants’ morning urine was taken         period between two groups (P value= 0.86).
    on days 0, 5, 10, 15 and 20 of the study. The first             Independent sample t-test showed no significant dif-
                                                        In
    sample was collected in the morning before the initia-          ference between two groups on the baseline with oth-
    tion of bleaching procedure and was continued every             er sampling sessions (P value= 0.79, 0.80, 0.81 and
    five days until the final sample which was gathered             0.34, respectively).
    five days after the expiration of the whitening period.         The data regarding the comparison of the urinary
    Regarding sequencing sample collection, the sam-                concentration of the MDA between the first and other
                               ni

    ples were refrigerated at -80°C with no special treat-          sampling intervals are presented in Table 2.
    ment, according to commercial kit recommendation
    until initiating the assay.
                             io


                                                                    Discussion
    Thiobarbituric Acid Reactive Substances (TBARS)
    Assay                                                           The findings of the current research could not reveal
                           iz



    To evaluate the effect of ascorbic acid on the urinary          a significant increase in the MDA concentration in
    level of the MDA, as a product of lipid peroxidation as         urine samples during the tooth bleaching procedure
    well as an index of the oxidative stress, TBARS test            (P=0.7). Literally, this study has been designed to
            Ed




    (Cayman Chemical, Ann Arbor, MI, USA, Item Num-                 protect tooth bleaching volunteers from the systemic
    ber 10009055) was used based on an established                  side effects of the whitening agents by vitamin C sup-
    method (18). The pink colored MDA-TBA adduct was                plementation, based on a recent study, which was
    formed by the reaction of MDA and thiobarbituric acid           carried out by the same investigators who indicated
    (TBA) under high temperature (90-100°C) and acidic              that the serum concentrations of the MDA, total an-
    conditions. The absorbance of the MDA-TBA complex               tioxidant capacity (TAC), and prooxidant-antioxidant
 IC




    was read at 532 nm and the concentration of the                 balance (PAB) were increased significantly after the
    MDA in samples was calculated using a standard                  tooth bleaching period (16). Although this study could
    curve.                                                          not reveal similar results, monitoring of the MDA con-
                                                                    centration from onset to end of the study period
C




                                                                    showed the gradual elevation of the MDA that sud-
    Statistical analysis                                            denly decreased in the final sample session which
                                                                    was taken five days after the expiration of the whiten-
    The normality of data distribution was examined by              ing period. Thus, it cannot entirely rule out the proba-
©




    Kolmogorov Smirnov test. The difference of the MDA              bly tooth bleaching induced oxidative damage. To
    values between the five measurements was carried                clarify different outcomes between these two studies,
    out using repeated measurements and Independent                 the Authors need to emphasize on some points. Ini-
    sample test. SPSS version 11.5 software (SPSS,                  tially, the difference between these two experiments
    Chicago, IL, USA) was used for statistical analysis             may be attributed to the kind of samples that were
    while level of statistical significance was set at 0.05.        taken for the oxidative stress assay. The evaluation

    Annali di Stomatologia 2018;IX (2):77-83                                                                             79
    M. Akbari et al.


    Table 1. The mean, standard deviation, minimum and maximum value of the MDA in both groups between five sampling
    intervals.

    !Sampling intervals                     Study groups       ! Mean±SD              ! Min            ! Max

        First                              !Control            ! 0.072±0.011           0.059            0.104




                                                                                                  li
                                                                                                na
                                           !Intervention       ! 0.074±0.008           0.063            O.092

                                           !Total              ! 0.073±0.009           0.059            0.104

    !Second                                !Control            ! 0.074±0.013           0.059            0.109




                                                                                              io
                                           !Intervention       ! 0.074±0.013           0.059            0.112

                                           !Total              ! 0.074±0.013          ! 0.059           0.112




                                                                        az
        Third                              !Control            ! 0.076±0.017           0.059            0.114

                                           !Intervention       ! 0.076±0.011           0.057            0.102
    !




                                                                      rn
                                           !Total              ! 0.076±0.015           0.057            0.114

    !Fourth                                !Control            ! 0.080±0.017           0.051            0.106




                                                         te
                                           !Intervention
                                                       In      ! 0.080±0.017           0.063            0.111

                                           !Total              ! 0.080±0.017           0.051            0.111

    !Fifth                                 !Control            ! 0.077±0.011           0.065            0.112
    !
                                           !Intervention       ! 0.073±0.012           0.058            0.101
                              ni

                                           !Total              ! 0.075±0.011           0.058            0.112
                            io
                          iz
                Ed
 IC
C




    Figure 1. Repeated measurement analysis of the groups.

    of oxidative stress biomarkers in human serum sam-        hardly be traced in situations with minute quantities in
©




    ples is more popular than that of urine. On the other     human serum. In fact, the current research was de-
    hand, ethical consideration did not permit researchers    signed to monitor oxidant status during the bleaching
    to take five blood samples for the duration of 20 days    period and after its expiration, as a multiple time se-
    (one blood sample in each five days). Moreover, it        ries method in response to the limitation of the previ-
    was determined that urinary level of the MDA is sig-      ous study with no evaluation of oxidant changes after
    nificantly lower than that of blood (19, 20) and can      the bleaching period, so as to determine the time


    80                                                                            Annali di Stomatologia 2018;IX (2):77-83
    The effect of vitamin C on urinary level of an oxidative stress biomarker during at-home tooth bleaching process:
    a randomized double blinded clinical trial


    Table 2. The comparison of the urinary concentration of MDA between first with other sampling intervals.

    Comparisons                                Study groups     ! Number                ! Mean ± SD                  P-value
      First compared with second               !Intervention    ! 14                    ! 0.0002±0.013               0.793
    ! interval




                                                                                                             li
                                               !Control         ! 15                    ! -0.0015±0.020
    ! First compared with third interval       !Intervention    ! 14                    -0.0022±0.013                0.809




                                                                                                           na
                                               !Control         ! 15                    ! -0.0040±0.022
    ! First compared with fourth interval      !Intervention    ! 14                    ! -0.0059±0.017              0.819
                                               !Control         ! 15                    ! -0.0075±0.019




                                                                                                         io
    ! First compared with fifth interval       !Intervention    ! 14                    ! 0.0010±0.013               0.343
                                               !Control         ! 15                    ! -0.042±0.015




                                                                                 az
    needed for the human body to completely recover                    health risk with the tooth bleaching agents have
    from the oxidative stress. Also in a previous study                largely diminished (22). It was reported that the fre-
    (16), 9% hydrogen peroxide was used as the whiten-                 quency of genetic mutation induced by 10% car-
    ing agent, but in this study, relying on long, success-            bamide peroxide is relatively similar to a physiological




                                                                               rn
    ful clinical application, the 15% carbamide peroxide               saline control (23). Sometimes other ingredients in
    was utilized which released about 5% hydrogen per-                 the bleaching gels such as carbopol or glycerin may
    oxide. Finally, the participants of this study were se-            be responsible for the poisoning rather than the
    lected from dental students who strictly adhered to                bleaching agent itself (4). In spite of this, salivary per-
    the described bleaching protocol. Furthermore, the
    whole procedure was completely described for each
    patient by an expert clinician and the patients try to
                                                                 te    oxidase as a body enzymatic equipment rapidly de-
                                                                       composes large amount of hydrogen peroxide in the
                                                                       oral cavity (22). It has been determined that the oral
                                                               In
    follow the treatment instructions immediately. The                 cavity is capable of decomposing more than 29 mg of
    well educated participants used the proper amount of               hydrogen peroxide per minute, whereas for a night
    the bleaching agents and removed excess on tray                    guard bleaching of both arches using 10% carbamide
    borders to minimize leakage, gingival irritation and               peroxide, the total hydrogen peroxide exposure dose
                                ni

    swallowing. This was based on previous obtained                    was estimated to be approximately 3.5 mg (24).
    facts which emphasized that the at-home bleaching                  On the other hand, the in vitro studies that have fre-
    procedure should be carried out with high ethical                  quently emphasized the carcinogenicity, mutagenicity
                              io


    standards and under full professional supervision, in              and teratogenicity of H2O2 (6-9) could not be repro-
    order to decrease potential systemic side effects (5).             duced in vivo due to inappropriate design, conduct
    There is concern regarding the possible adverse ef-                and assessment of the results (24). The overall data
                            iz



    fects of the at-home bleaching agents by swallowing                on bleaching studies accumulated over the last 20
    a minute quantity and absorption through the gas-                  years also confirmed the results of the present study,
    trointestinal tract or local absorption through the gin-           which concluded that the use of low concentrations of
            Ed




    gival, especially when they are applied with no dental             hydrogen peroxide is still safe (25-28).
    supervision (21). The probably systemic side effects               In the current study, due to the ability of well-de-
    of hydrogen peroxide are dependent on the amount                   signed trays to make precise contact with the teeth
    and the concentration of its compounds ingested. Ac-               with no gingival exposure, no participant dropout was
    cording to the study of Dahl et al. (5), accidental in-            reported due to gingival irritation or tooth hypersensi-
    gestion of 35% hydrogen peroxide has resulted in fa-               tivity. Indeed, the gingival irritation which has been
 IC




    tal or near-fatal poisonings. Nevertheless, it is not a            reported by the at-home bleaching method that used
    major concern as regards carbamide peroxide which                  low concentration of carbamide peroxide in custom
    yields lower concentration of hydrogen peroxide (2).               made trays is more likely attributed to an ill-fitting tray
    In addition, Cherry et al. (3) indicated acute toxicolog-          rather than the bleaching agent itself (29).
C




    ical effects of ingested 35% carbamide peroxide in fe-             Although several in vitro studies have reported
    male rats. However, they reported that commercial                  promising findings about the use of different antioxi-
    products containing 10 or 15% carbamide peroxide                   dant agents for treatment and/or prevention of the ox-
    showed milder symptoms than 35% carbamide perox-                   idative damages caused by hydrogen peroxide (30-
©




    ide concentration.                                                 32), the present study investigators indicated that the
    Unfortunately, in each of the previous cases that re-              vitamin C supplementation did not significantly re-
    ported toxic, fatal or near fatal effects of hydrogen              duce the urinary level of the MDA as a marker of ox-
    peroxide, the amount of hydrogen peroxide swal-                    idative stress following the tooth bleaching procedure
    lowed was unknown. Considering the dosage and ap-                  with 15% carbamide peroxide (P=0.66), thus the null
    plication mode, concerns with potential systemic                   hypothesis could not reject. Literally, obtained results

    Annali di Stomatologia 2018;IX (2):77-83                                                                                   81
    M. Akbari et al.


    from the in vitro studies cannot necessarily be extra-        noted that this paper was extracted from thesis num-
    polated to the clinical situation. It seems that the          ber 493.
    amount of antioxidant delivered to cultured cells in
    the in vitro studies was much higher than the level of
    antioxidant reached in the extracellular fluid after oral     Conflict of interest
    administration of 500 mg of ascorbic acid (30-32).
    In the clinical setting, the achieved outcomes on pro-        The Authors of this manuscript clarify that they have




                                                                                                             li
    tective antioxidant role of vitamin C administration are      no proprietary, financial, or other personal interest of




                                                                                                           na
    conflicting. In spite of the study of Harats et al. (33)      any sort which has been used in this study.
    who determined the effective role of vitamin C against
    oxidative stress in smokers, two other studies in which
    the diets of smokers were supplemented with the vita-         References
    min C could not significantly reduce plasma TBARS




                                                                                                         io
    levels (34, 35). These findings are in line with the re-      1.    Zimmerli B, Jeger F, Lussi A. Bleaching of nonvital teeth. A
                                                                        clinically relevant literature review. Schweiz Monatsschr Zah-
    sults of Padayatty et al. (13) who reported that al-
                                                                        nmed. 2010;120:306-320.
    though diet rich in fruits and vegetables is associated




                                                                              az
                                                                  2.    Dhillon JS, Narula NB, Kansal N, Kaur A. Tooth Whitening-
    with lower risk of cardiovascular disease and cancer,               A Review. Indian Journal of Dental Sciences. 2011;3(5).
    it is not clear if vitamin C contributes to these benefits.   3.    Cherry DV, Bowers DE, Jr., Thomas L, Redmond AF. Acute
    In addition, they concluded that the vitamin C treat-               toxicological effects of ingested tooth whiteners in female rats.
    ment in humans could not change oxidation biomark-                  J Dent Res. 1993;72:1298-1303.




                                                                            rn
    ers or clinical outcomes which completely confirmed           4.    Dahl J, Becher R. Acute toxicity of carbamide peroxide and
    the outcome of this study. In the field of vitamin C                a commercially available tooth-bleaching agent in rats. J Dent
    supplementations, the unique study of Nyyssönen et                  Res. 1995;74:710-714.
                                                                  5.    Dahl JE, Pallesen U. Tooth bleaching-a critical review of the
    al. (35) is of particular interest presented a significant




                                                           te
                                                                        biological aspects. Crit Rev Oral Biol Med. 2003;14:292-304.
    increase in plasma TBARS after regular and slow re-           6.    Ito A, Watanabe H, Naito M, Naito Y. Induction of duodenal
    lease of vitamin C and the Authors could not find any               tumors in mice by oral administration of hydrogen peroxide.
    logical etiology for this phenomenon.                               Gann. 1981;72:174-175.
                                                         In
    The present study concluded that the night guard              7.    Ito A, Watanabe H, Naito M, et al. Correlation between in-
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                                                                        peroxide in mice. . Hiroshima Daigaku Genbaku Hoshanou
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                            io


                                                                        terization of gastroduodenal lesions in mice given con-
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    and debates over the systemic risks of bleaching may          10.   Timblin CR, Janssen YW, Mossman BT. Transcriptional
                          iz



    arise periodically. Thus, further clinical research is              activation of the proto-oncogene c-jun by asbestos and
                                                                        H2O2 is directly related to increased proliferation and trans-
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                                                                        1995;55:2723-2726.
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                                                                        tioxidant: evaluation of its role in disease prevention. J Am
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                                                                        Coll Nutr. 2003;22:18-35.
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                                                                  14.   Wang LH, Tsai AL, Hsu PY. Substrate binding is the rate-
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    ascorbic acid on tooth bleaching induced oxidative            15.   Huang HY, Appel LJ, Croft KD, et al. Effects of vitamin C and
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    Acknowledgements                                                    ing induce systemic oxidative stress in healthy patients? Aust
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    a randomized double blinded clinical trial

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    Annali di Stomatologia 2018;IX (2):77-83                                                                                             83
