Rap bardwell

BLEACHING
In vitro evaluation of tooth
colour modifications using
differing hydrogen peroxide
concentrations
By David Bardwell DMD, MS, Aikaterini Papathanasiou, DDS & Simone Deliperi, DDS
Much of bleaching is still an unknown sci-
techniques include the dentist-prescribed in-office booster, ence. In this study, the authors look at
the home-applied tray delivery system, or a combination of products on the US market and evaluate
the two. The in-office bleaching technique employs a 15- the effects of different levels of hydrogen
35% hydrogen peroxide bleaching agent (heated or non- peroxide on tooth colour modification
heated), while the dentist prescribed home-applied tech- nique most commonly uses a 10 or 15% carbamide perox- One of the fastest growing areas of cosmetic dentistry ide gel. The very slow response to NGVB in some cases today is the management of the discoloured and/or (Barghi, 1998) and patients’ demand for faster methods, hypoplastic dentition. Bleaching is the most conservative have pushed the clinician to look for easier, more rapid treatment for discoloured teeth compared to resin-bond- ed composites, porcelain veneers and crowns. Tooth The advantage of the in-office procedure is that it does bleaching has become dentistry’s most popular aesthetic not require patient compliance and immediate results may treatment.The exact mechanism of action is not complete- be seen. The disadvantage is the chairtime and cost to the ly understood, but theorised. Hydrogen peroxide diffuses patient, as this procedure usually requires multiple visits.
through the organic matrix of the enamel and dentine The introduction of very high intensity plasma arc lights (Bowles et al 1987, 1986; Fuss et al, 1989). Because the rad- and argon lasers in the market are a result of this increas- icals have unpaired electrons, they are extremely electro- ing demand. However, no study to date has demonstrated phylic and unstable and will attack most other organic mol- ecules to achieve stability, generating other radicals. These The authors are based at Tufts
radicals can react with most unsaturated bonds, resulting in University School of Dental
disruption of electron conjugation and a change in the Medicine, Boston, USA. David
absorption energy of the organic molecules in tooth enam- Bardwell DMD, MS is Director of
el. Simpler molecules that reflect less light are formed, cre- Postgraduate Esthetic Dentistry,
ating a successful whitening action. This process occurs and is an associate clinical
when the oxidising agent (hydrogen peroxide) reacts with professor of Restorative
organic material in the spaces between the inorganic salts Dentistry in the Divisions of
both Fixed and Removable
in tooth enamel (Goldstein and Garber, 1995).
Prosthodontics and Operative
Since the introduction of carbamide peroxide for home Dentistry. Aikaterini
bleaching (Haywood & Heymann, 1989; Haywood, 1992) Papathanasiou, DDS is an
approximately 12 years ago, continued development of assistant professor of
new techniques and materials with improved properties Restorative Dentistry. Simone
have occurred (Garber, 1997; Settembrini et al, 1998) Deliperi, DDS is a visiting
spurning greater case acceptance amongst clinicians. Safety instructor of Restorative
and effectiveness of Nightguard Vital Bleaching (NGVB) has Dentistry at Tufts University
been widely reported in several studies (Leonard et al, School of Dental Medicine
2001; Ritter et al, 2001; Haywood et al, 1994). Acceptable RESTORATIVE & AESTHETIC PRACTICE VOLUME 4 NO. 6 JULY 2002 BLEACHING
TABLE 1:VITA VALUE ORDER
has demonstrated encouraging results (Barghi, 1998; Kugel by value order (lightest to darkest) and all shades will be et al, 1997; Papathanasiou et al, 2001). The use of a more recorded. A relative number was assigned to each Vita stable and less caustic hydrogen peroxide bleaching mater- shade (B1-1, A1-2, B2-3, etc., as seen in Table 1). Shades ial, along with concomitant use of 10% carbamide peroxide were selected by three independent evaluators precali- containing fluoride and potassium nitrate may help to satis- brated at 85% reliability.Teeth were removed from physio- fy patients’ increasing demand to achieve whiter teeth logic saline and cleaned with a prophycup and prophypaste faster with more predictable results. Finally, current bleach- without fluoride. After being rinsed and air-dried, all teeth ing methods can offer a conservative, efficient, and eco- were exposed to hydrogen peroxide. Group I samples nomical approach to changing the colour of one’s teeth.
were exposed to 7.5% hydrogen peroxide (Table 3), Group MATERIALS AND METHODS
TABLE 2: MEAN SHADE CHANGE
40 freshly extracted caries-free human teeth were used in this in-vitro evaluation. All teeth were scaled before being stored in physiologic saline. Teeth were randomly divided into four groups of ten. Each tooth was coded with the Group III
group and specimen numbers. All samples were evaluated for initial shade according to the Vita shade guide arranged Figures 1 & 2: Before and after bleaching - note shade change
Figures 3 & 4: Bleaching on tetracycline-stained teeth
RESTORATIVE & AESTHETIC PRACTICE VOLUME 4 NO. 6 JULY 2001 TABLE 3: GROUP I SAMPLES EXPOSED TO 7.5% HYDROGEN PEROXIDE
Baseline
II to 15% hydrogen peroxide (Table 4), Group III to 25% When all test groups were compared, utilising the hydrogen peroxide (Table 5) and Group IV to 35% hydro- Kruskal-Wallis One Way Anova analysis, a p level of >0.1 was calculated, confirming no significant difference between All bleaching materials were applied on the buccal/facial surfaces of the teeth, limiting it to enamel only, for 30 min- Results of this study showed no significant difference in utes for three consecutive days. All specimens were stored tooth colour modification when utilising these four different in saline between treatments. After each whitening session, concentrations of hydrogen peroxide (7.5%, 15%, 25% and shade evaluation was conducted for each tooth and 35%).Results of all treated samples yielded an average recorded, in the same manner as performed initially.
change in shade of 4.7±2.6 for Group I, 6.7±2 for Group II, Statistically analysis was employed to evaluate results.
5.1±1.4 for Group III and 6.6±2.1 for Group IV. Shade All groups were compared to determine if statistical differ- changes were determined from the number of shade changes on the Vita Shade Guide when arranged in value order. Statistical analysis utilising the Kruskal-Wallis ANOVA STATISTICAL ANALYSIS
revealed no statistically significant difference (p>0.10) Statistical analysis was employed to evaluate the mean between all groups. In conclusion, the results of this study shade change when all groups were compared showed no significant difference in tooth colour modifica- TABLE 4: GROUP II SAMPLES EXPOSED TO 15% HYDROGEN PEROXIDE
Baseline
RESTORATIVE & AESTHETIC PRACTICE VOLUME 4 NO. 6 JULY 2002 BLEACHING
TABLE 5: GROUP III SAMPLES EXPOSED TO 25% HYDROGEN PEROXIDE
Group III
Baseline
tion when utilising the four different concentrations of hydrogen peroxide (7.5%, 15%, 25% and 35%).
NGVB using 10% CP has become the standard for home bleaching and has been demonstrated to be safe and DISCUSSION
effective when appropriately administered (Haywood, 35% hydrogen peroxide has been the standard for bleach- 1992; Haywood, 1994; Li, 1998; Swift & Perdigao, 1998; ing of discoloured teeth for many years.
Leonard et al, 2001; Ritter et al, 2001). Conversely, issues of Tooth bleaching procedures became widely available safety and effectiveness are still controversial when higher with the 1989 introduction of dentist prescribed concentrations (greater than 10% CP) are used. Numerous Nightguard vital bleaching (NGVB) (Haywood & Heymann, brands of differing HP concentrations are now available in 1989). Since then, bleaching popularity has increased expo- the market; with lower concentrations being used for den- nentially with numerous products available in the market tist prescribed home bleaching, and higher concentrations containing differing concentrations of either carbamide (CP) or hydrogen peroxide (HP). Dentists can choose to This in vitro study evaluated the effectiveness of differ- bleach teeth using 5-22% CP and 1-10% HP home bleach- ing HP concentrations with regard to tooth lightening. Four ing products, 15-35% HP in office bleaching materials and, different concentrations were tested in this study. 7.5% HP as of late, 15% HP and 35% CP waiting room tooth whiten- (which can be equated to 20% CP) was the lowest con- TABLE 6: GROUP IV SAMPLES EXPOSED TO 35% HYDROGEN PEROXIDE
Baseline
RESTORATIVE & AESTHETIC PRACTICE VOLUME 4 NO. 6 JULY 2001 centration used. It was chosen as a starting point due to which may result in increased tooth sensitivity. Moreover, one product presently found readily available to dentists in Weiger et al (1993) and Price et al (2000) stated that the today’s market (Day White- Discus Dental). Secondly 15% greater the HP concentration, the more acidic the pH of HP (which can be equated to 44% CP) was developed by the bleaching solution. Morphological alterations in enamel, Dentsply/Professional for dentist-prescribed waiting room dentine and cementum are common when teeth are sub- use (Illumine - Dentsply Professional) (Papathanasiou, jected to pH’s lower than 5.2 (Weiger et al, 1993; Driessens 2001). Next, 25% HP (not present in any product on the et al, 1986; Rotstein & Friedman, 1991). Peroxides may also market that this author is aware of) was considered an increase microleakage (Crim, 1992; Barkhordar, 1997; intermediate concentration that deserved consideration.
Bardwell, 2000) and reduce tensile and shear bond strength Finally, 35% HP, presently the most popular chairside con- (Stokes et al, 1992; Garcia-Godoy et al, 1993; Titley et al, centration used for in office bleaching, (OpalesceneXtra - 1993; Perdigao et al, §998) and which may be time and Ultradent; Hi Lite - Shofu) (Garber, 1997; Barghi, 1998) was dose dependent. Some controversy does exist in the inter- national literature with respect to peroxide concentration The results of this study indicated that there was no and pH. Are varied concentrations and/or pH responsible statistically significant difference between the four groups for these alterations? Future investigation is needed to when teeth where exposed to differing concentrations of answer these questions, and to better understand the influ- HP for 30 minutes in three consecutive days. Even though ence of HP on tooth structure and restorative materials.
not statistically significant, the individual tooth colour mod- ifications may be significant from a clinical point of view. An CONCLUSION
increasing number of patients are asking for dramatic tooth This in vitro investigation helps us understand the effective- colour modifications in only a few days. This may be ness of differing HP concentrations with regard to tooth achieved by using a combination of in office and home bleaching, utilising 15% (Group II) and 35% (Group IV) HP • 7.5% HP was less effective in producing tooth whitening to boost the home bleaching program. This study demon- than 15%, 25%, 35% HP, but can represent an alternative to strated that teeth in groups II and IV yielded greater light- ening than those in I and III. Average change in II and IV • 15 and 35% HP produced the greater tooth colour mod- were two shades lighter than those in group I and 1.5 ification and may be considered materials of choice in shades lighter than those in Group III. At the time of this writing we have no explanation for this result. It may be • 25% HP was not as effective as 15 and 35% HP. Due to hypothesised that there is more than one range of effec- its higher concentration and lower effectiveness it might tiveness with respect to concentrations in which HP is sup- not be indicated in-office bleaching.
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This project was funded in part by a Grant from
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uation of carbamide peroxide and hydrogen peroxide whitening RESTORATIVE & AESTHETIC PRACTICE VOLUME 4 NO. 6 JULY 2001

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