In vitroand clinical evaluation of optical tooth whitening toothpastes

Abstract

Objectives

To measure tooth whitening effects delivered immediately after brushing with silica-based toothpastes containing either blue covarine or a combination of blue covarine and FD&C Blue No. 1 in vitro and in vivo .

Methods

Salivary pellicle coated human extracted teeth were brushed with either a slurry of a toothpaste containing blue covarine (BC) or a formulation containing a matched level of blue covarine and FD&C Blue No.1 (BC + D). The colour of the specimens were measured in vitro using a colorimeter, before and after brushing and changes in CIELAB and tooth Whiteness Index (WIO) values calculated. In a double-blind cross-over clinical study, subjects brushed with BC toothpaste, a toothpaste containing increased levels of blue covarine (BC + ) or BC + D toothpaste and tooth colour changes were measured with a digital image analysis system.

Results

The in vitro study demonstrated that BC + D gave a significantly (p = 0.002) greater change in WIO value than BC. Clinical results showed that BC, BC+ and BC + D gave a significant increase in WIO (p < 0.0001) from baseline. The WIO change was significantly greater when brushing with BC + D toothpaste than with either toothpaste BC (p < 0.0001) or BC+ (p < 0.05).

Conclusions

Toothpastes containing blue covarine or a combination of blue covarine and FD&C Blue No. 1 gave a statistically significant improvement in tooth whiteness immediately after brushing in both in vitro and clinical studies. In addition, the toothpaste containing both blue covarine and FD&C Blue No. 1 gave statistically significant greater tooth whitening from baseline than the blue covarine containing toothpastes.

Clinical significance

The silica-based toothpastes containing blue covarine or a combination of blue covarine and FD&C Blue No. 1 evaluated in the current study gave significant tooth whitening benefits immediately after one brush.

Introduction

Whitening toothpastes are designed for daily use and are typically formulated to provide enhanced physical and chemical tooth cleaning ability, using a range of ingredients, in order to effectively remove and prevent extrinsic stains . There is a wealth of published data supporting their safety and demonstrating various degrees of tooth whitening efficacy . For example, the use of perlite as a cleaning and polishing agent has been added to both silica- and calcium carbonate-based toothpaste formulations to give enhanced extrinsic stain removal versus non-whitening toothpaste formulations, without causing an increase in abrasive wear towards enamel and dentine .

It was hypothesised that a thorough understanding of colour science and its application to teeth would provide new technical insights and offer breakthrough technology for tooth whitening . The Commission International De l’Eclairage (CIE) in 1976 defined a three-dimensional colour space (CIELAB) which gives a representation for the perception of colour stimuli. The three axes are L*, a* and b*, where the L* represents a measure of the lightness of the object and the a* and b* represent the colour on the red-green and yellow-blue axes respectively . The perception of tooth colour is recognised to be a complex phenomenon and the visual assessment of tooth colour can be influenced by many factors. These include the ambient lighting, tooth mineral content, presence of extrinsic and intrinsic stains, experience of assessor and lip colour . Insights into the perception of tooth colour following tooth whitening with peroxide based vital tooth bleaching products indicate that the yellow-blue shift (b*) in tooth colour is the most important factor for self-perceptual tooth whitening . For example, Gerlach et al. investigated the subjective first-person response following hydrogen peroxide tooth bleaching and reported that the subjective responses to whiteness improvement and satisfaction were significantly correlated with changes in b* values but not L* and a* values. Other tooth bleaching studies confirm that the reduction in yellowness (b*) is an important factor for tooth whitening .

These optical principles were applied in the development of a silica-based toothpaste containing the pigment blue covarine . The toothpaste deposits blue covarine onto the tooth surface during brushing which gives a yellow to blue hue colour shift to the teeth. This reduction in yellowness makes the teeth appear whiter immediately after brushing, as confirmed in several in vitro and clinical studies .

Further investigation and development of the blue optical approach for tooth whitening has identified an effective combination of the blue covarine pigment with FD&C Blue No. 1. The aims of the current work are to compare, after one brushing, the tooth whitening effects of silica-based toothpastes containing blue covarine at two different concentrations and a silica-based toothpaste containing a combination of blue covarine and FD&C Blue No. 1. The null hypothesis is that a toothpaste containing blue covarine and FD&C Blue No. 1 is not superior to a toothpaste containing blue covarine alone in terms of improvement in tooth whiteness after one brushing.

Materials and methods

In vitro study

Extracted human anterior teeth, obtained for research purposes according to the Human Tissue Act procedures and with informed consent, were mounted in acrylic resin blocks by embedding the roots into cold-cure acrylic resin (Simplex Rapid, Kemdent, Wiltshire, UK). Any remaining exposed dentine was sealed with two coats of nail varnish (No. 7, Colour Lock™ Nail Enamel, Boots plc, Nottingham, UK). The enamel surfaces were then cleaned with a prophylaxis paste (Clean Chemical Sweden AB, Sweden) to ensure removal of extrinsic stain. The specimens were placed in sterilised (gamma irradiated) whole human saliva for two hours to allow a pellicle to form. The baseline colour of each tooth was measured using a Minolta CR321 chromameter (Minolta Camera Co. Ltd., Japan) in the CIELAB mode. Five separate measurements of the labial surface were taken and the mean baseline colour parameters calculated.

The specimens (n = 8) were randomly assigned to the test products which were either a silica-based toothpaste containing blue covarine (BC) or a silica-based toothpaste containing a matched level of blue covarine and FD&C Blue No. 1 (BC + D).

The teeth specimens were brushed for 1 min with a flat-trim toothbrush and a 1:2 slurry of toothpaste: water. The specimens were then rinsed with water and their colour re-measured. Changes in CIELAB tooth colour parameters were calculated as follows:

ΔL* = L*(t) − L*(0)
Δa* = a*(t) − a*(0)
Δb* = b*(t) − b*(0)

Where L*(t) and L*(0) are L* values after water rinsing for time t and pre-brushing values respectively with similar definitions for a*(t), a*(0), b*(t) and b*(0). In addition, whiteness values based on a previously described tooth whiteness index (WIO) were determined at each time point and mean changes in WIO calculated.

Clinical study

This was a double blind, randomised, three product, cross-over design study. The objective of the study was to measure the change in tooth colour and tooth whiteness immediately after brushing with either a silica-based toothpaste containing blue covarine (BC), a silica-based toothpaste containing a matched level of blue covarine and FD&C Blue No. 1 (BC + D) or a silica-based toothpaste containing an increased level of blue covarine and no FD&C Blue No.1 (BC + ).

The protocol for the study was reviewed and approved by an Independent Ethics Committee of the Shanghai Clinical Research Centre. Male and female subjects in good general health aged 18-65 were accepted onto the study. Subjects had to have two suitable natural upper central incisors (no caps, crowns, veneers, cracks, gum recession or restorations on the distal, mesial, buccal or incisal edges). Subjects with teeth too white or too dark (1M1/2, 2M1 and 3M1 from VITA 3D MASTER tooth guide) were not included. In addition, the teeth had to be free of extrinsic stain and free of intrinsic stain ( e.g. tetracycline, fluorosis). Smokers and chewers of tobacco were not included in the study. Informed consent from subjects was obtained.

The study involved four visits to the study site ( Fig. 1 ). At each test session, subjects had images taken of two upper central incisors, before and immediately after brushing with 1.5 g (±0.1 g) toothpaste for 90 s and water rinsing (5 ml for 5 s) using a non-contact camera-based digital imaging system (DIS) . From these images, the tooth colour parameters CIELAB and WIO values were determined.

Fig. 1
Overview of clinical study.

The outcome variable per subject was defined as the average of the two parameter values measured on the two upper central incisor teeth. The two parameters were checked for differences to ensure reproducibility. Paired t-tests were used to test for significant differences between the pre-images and “immediately after” post-images for each colour parameter and each product. Between test groups differences were assessed using mixed model analysis of variance suitable for crossover studies. Separate models were fitted to post-images for each colour parameter. Each model included a random effect for subject and fixed effects for product and pre-images. Pair-wise treatment comparisons were performed using Contrast analysis at the 5% significance level.

Materials and methods

In vitro study

Extracted human anterior teeth, obtained for research purposes according to the Human Tissue Act procedures and with informed consent, were mounted in acrylic resin blocks by embedding the roots into cold-cure acrylic resin (Simplex Rapid, Kemdent, Wiltshire, UK). Any remaining exposed dentine was sealed with two coats of nail varnish (No. 7, Colour Lock™ Nail Enamel, Boots plc, Nottingham, UK). The enamel surfaces were then cleaned with a prophylaxis paste (Clean Chemical Sweden AB, Sweden) to ensure removal of extrinsic stain. The specimens were placed in sterilised (gamma irradiated) whole human saliva for two hours to allow a pellicle to form. The baseline colour of each tooth was measured using a Minolta CR321 chromameter (Minolta Camera Co. Ltd., Japan) in the CIELAB mode. Five separate measurements of the labial surface were taken and the mean baseline colour parameters calculated.

The specimens (n = 8) were randomly assigned to the test products which were either a silica-based toothpaste containing blue covarine (BC) or a silica-based toothpaste containing a matched level of blue covarine and FD&C Blue No. 1 (BC + D).

The teeth specimens were brushed for 1 min with a flat-trim toothbrush and a 1:2 slurry of toothpaste: water. The specimens were then rinsed with water and their colour re-measured. Changes in CIELAB tooth colour parameters were calculated as follows:

ΔL* = L*(t) − L*(0)
Δa* = a*(t) − a*(0)
Δb* = b*(t) − b*(0)

Where L*(t) and L*(0) are L* values after water rinsing for time t and pre-brushing values respectively with similar definitions for a*(t), a*(0), b*(t) and b*(0). In addition, whiteness values based on a previously described tooth whiteness index (WIO) were determined at each time point and mean changes in WIO calculated.

Clinical study

This was a double blind, randomised, three product, cross-over design study. The objective of the study was to measure the change in tooth colour and tooth whiteness immediately after brushing with either a silica-based toothpaste containing blue covarine (BC), a silica-based toothpaste containing a matched level of blue covarine and FD&C Blue No. 1 (BC + D) or a silica-based toothpaste containing an increased level of blue covarine and no FD&C Blue No.1 (BC + ).

The protocol for the study was reviewed and approved by an Independent Ethics Committee of the Shanghai Clinical Research Centre. Male and female subjects in good general health aged 18-65 were accepted onto the study. Subjects had to have two suitable natural upper central incisors (no caps, crowns, veneers, cracks, gum recession or restorations on the distal, mesial, buccal or incisal edges). Subjects with teeth too white or too dark (1M1/2, 2M1 and 3M1 from VITA 3D MASTER tooth guide) were not included. In addition, the teeth had to be free of extrinsic stain and free of intrinsic stain ( e.g. tetracycline, fluorosis). Smokers and chewers of tobacco were not included in the study. Informed consent from subjects was obtained.

The study involved four visits to the study site ( Fig. 1 ). At each test session, subjects had images taken of two upper central incisors, before and immediately after brushing with 1.5 g (±0.1 g) toothpaste for 90 s and water rinsing (5 ml for 5 s) using a non-contact camera-based digital imaging system (DIS) . From these images, the tooth colour parameters CIELAB and WIO values were determined.

Jun 17, 2018 | Posted by in General Dentistry | Comments Off on In vitroand clinical evaluation of optical tooth whitening toothpastes
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