1. Characterization of 8 Popular In-Office Bleaching Systems

A. Chemical Characterization of H2O2
     Tests were conducted to confirm manufacturer's stated H2O2 content and pH, before and after addition of their catalyst, booster, or activator. Each system's percent H2O2 by weight was determined using methods outlined in the U.S. Pharmacopeia Hydrogen Peroxide Concentrate Assay. The pH of each bleach gel before and after addition of its activator was determined using a calibrated Orion 901 pH meter and 3305 surface probe, placed directly into each system's undiluted bleaching gel.
Test Method: U.S. Pharmacopeia Hydrogen Peroxide Concentrate Assay
Test Method: Mixed pH

B. Optical Characterization of Test Lights
     Each light was examined to determine light source type and delivery optics, and compared to a currently popular halogen resin curing light (Optilux 501), which had different mode settings designated for curing and bleaching. The spectral outputs of each test light, plus the control light on both its bleach and cure modes, were measured using a CCD spectrophotometer (S2000) across the range of 350 - 1000 nanometers on the electromagnetic spectrum. This represents measurements within the near-ultraviolet region (300 to 400 nanometers), visible region (400 to 750 nanometers), and near-infrared region (750 to 3000 nanometers).
Test Method: spectral output

Insert Figure 1 and Spectral out put graphs here
Light intensity was measured clinically at the facial surfaces of the 12 anterior teeth of a human subject. To do this, a photocell detector (modified Spring Light Meter 3K) was connected to a voltmeter (Wavetek DM15XL) and calibrated against a research grade radiometer (IL1500 Research Radiometer with SEE033 detector) by varying the distance between the light sources and the detectors over a 2.5 - 11 centimeter range. The resulting voltage and intensity values for each light were curve-fit (TableCurve 2D) to create a calibration curve of voltage vs. intensity. The photocell was then placed on each tooth during the light exposure time and the voltage recorded, and the intensity calculated from the calibration curve. Data were analyzed to determine maximum and average intensity, as well as effect of tooth location on intensity.
Test Method: Intensity on tooth surface

C. In Vivo Gel Temperature
     The temperature of each activated bleach gel was measured clinically on the 12 anterior teeth of five test subjects. To do this, a type K bead thermocouple (TT-K-30) was inserted into the gel and held against the tooth. The gel was applied to a thickness of about one millimeter. The temperature was read on a digital thermometer (Tegam 871A). Temperatures obtained with each gel were recorded without and with use of its accessory light, at times and distances prescribed by each manufacturer. Data were analyzed to determine maximum and average temperatures within the gels.
Test Methods: In-Vivo Gel Temperatures

D. Bleach Light Decomposition of H2O2
     Hydrogen peroxide decomposition by the three lights was determined by measuring the rate of gas release from each bleach gel in the absence and presence of its specific light. The control in these tests was 35% aqueous H2O2 liquid used with the Optilux 501 light on its bleach mode. Freshly mixed bleach gel (0.3 g) was pipetted into a five milliliter quartz cuvette (1-Q-10GL14-S ) and capped with a rubber septum of sufficient tightness to create a seal. A hypodermic thermocouple probe (HYP2) connected to a digital meter (CN 9000) and a hypodermic needle connected to a pressure transducer (PX26) and digital meter (DP25B-S) were inserted into the cuvette through the rubber septum. All junctures between the rubber septum and quartz and metals were subjected previously to overnight internal positive pressure tests to confirm seals. The cuvette was placed into a 35 C water bath to maintain a constant temperature. Pressure readings were recorded each minute for each bleach gel's prescribed contact time, both without and with the system's light positioned at its clinically prescribed distance and time. Each test was repeated three times, and gas pressures were converted to moles of gas and averaged. Rate of gas generation (H2O2 decomposition) was calculated, both without and with use of the light.
Test Method: Bleach Light Decomposition of H2O2

E. Thermal Decomposition of H2O2
     Decomposition rates for each of the three bleach gels, plus 35% aqueous H202 liquid and deionized water controls, were determined using heat conduction calorimetry. Multi-cell, differential, heat-conduction, temperature-scanning calorimeters (model 7707 calorimeter and model 4200 calorimeter) were used.
Test Method: Thermal Decomposition of H2O2

Clinical Tests
A. Color Assessment Method
     The Vitapan 3D-Master Shade Guidem was selected as the method of tooth color assessment in this study. It was used per its manufacturer's instructions. A visual method of color assessment was selected because clinically cosmetic tooth lightening is a phenomenon perceived by the human eyes. The Vitapan 3D-Master Shade Guide was selected because it theoretically has the following improvements over other shade guides: 1) it is based on natural color of human teeth rather than on restorative material colors; 2) it provides for separate reading of the three variables of tooth color (value or grayness, chroma or intensity of color, and hue or color, which for teeth is variations of yellow and red) which allows improved repeatability and agreement in color assessment; 3) representations of value and chroma are evenly placed; and 4) the color samples on the guide cover the color space for teeth. In addition, the Vitapan 3D-Master Shade Guide assigns value and chroma numbers that indicate specific positions on the three-dimensional color grid. Hue is designated by letter assignments L, M, R which represents yellow, medium, and red.
Three researchers used the Vitapan 3D-Master Shade Guide to independently judge tooth color. Insert Fig 5 photo All candidates received flour of pumice polishing performed by the same clinician to remove extrinsic stains before initial shades were taken by the three color judges. Tooth colors were taken on each potential subject's 12 anterior teeth on the cervical half and the incisal half by each researcher. Cervical and incisal grades were averaged for each tooth. Test subject's average tooth color, across their 12 anterior teeth, was calculated and recorded. Based on these calculations, 3 test groups were developed and defined as light, medium, and more profound yellow/orange discoloration. The definitions were as follows: light yellow/orange had a value and chroma sum of 4.0; medium yellow/orange had a value and chroma sum of 4.5; and more profound yellow/orange had a value and chroma sum of 5.0. These designations were used to provide each system with similarly discolored teeth.

The following parameters were standardized for all shade evaluations throughout the study: 1) location (the same operatory, overhead lights, no use of the operating light, natural light from outdoors blocked); 2) light (color corrected F32T8/Vision, 5,550 Kelvin overhead lights); and 3) patient position (the same programmed setting on the same patient chair). Tooth dehydration during the shade taking procedures was avoided by allowing the subjects to close their oral cavity frequently throughout the process and forgoing use of isolation or lip and cheek retractors.

B. Test Subject Selection
     Potential test subjects were screened as outlined above for presence of yellow/orange tooth discoloration. Additional inclusion criteria for test subjects were: 1) age of at least 18 years; 2) no tetracycline or fluorosis staining; 3) no prior tooth bleaching; 4) not pregnant or lactating; 5) non-smokers; 6) available for long-term recalls; 7) no restorations on facial surfaces of the12 anterior teeth; 8) good general health; 9) no active orthodontics; 10) no carious lesions; 11) all 12 anterior teeth vital; and 12) fit into the study's color stratification groups. Informed consent was secured from all potential subjects before procedures were performed.

C. Bleaching Protocol
     Subject's teeth were bleached following each manufacturer's directions, using a split arch protocol (see Figure 7), where centrals, laterals, and canines on one side received bleach gel plus light, and contralateral teeth received bleach gel only using the same bleach gel contact time, but no light, thus allowing contralateral teeth within each subject to serve as controls. Characteristics randomized for each subject included: 1) side of arch to receive light (left or right), 2) order of bleach gel application (canine to central or central to canine), 3) order of arch treatment (upper or lower arch to receive bleach gel application first), and 4) order of treatment type (light with bleach gel or bleach gel only). Light and no-light treatments were performed during the same appointment. The same isolation procedures were used for all patients. Tooth dehydration during the bleach treatment was avoided by thoroughly covering all teeth not then under treatment with cotton gauze moistened with tap water which was re-moistened as needed throughout the procedure and was always covered with regular weight aluminum foil molded to arch contour to block all light. Only one side of the oral cavity was treated at a time and all isolation was removed between treatments, which allowed subjects to rinse and close their oral cavity for several minutes. The opposite side was then isolated with the same procedures described above to maintain hydration and isolation from light.
Following are the different step-by-step protocols used with each of the three systems according to their specific manufacturer's directions. LumaArch system required three, seven-minute applications of its H2O2 gel. The bleach was dispensed as liquid H2O2 that was hand mixed with fumed silica powder, which included a chemical catalyst. The system used its own special light that was positioned per manufacturer's directions to illuminate the upper and lower teeth simultaneously for each of the eight-minute applications. Opalescence Xtra Boost required four, 15-minute applications of its H2O2 gel. The bleach was dispensed as H2O2 gel in one syringe that was joined to a second syringe containing pH booster and contents of the two syringes were mixed back and forth to obtain a homogeneous mix. For this study, the Optilux 500 resin-curing light with a ten-millimeter light guide was used to illuminate the light treated teeth for 30 seconds per tooth for each of the four gel applications. Zoom required three, 20-minute applications of its H2O2 gel. The H2O2 and activator were dispensed from a dual barrel syringe fitted with an auto-mix tip. The system used its own special light with spacer bars that established distance from the oral cavity and upper and lower arches were illuminated simultaneously for each 20-minute application.
Shades of each of the 12 anterior teeth on all 15 subjects were evaluated as outlined above before treatment, immediately after treatment, and one week later. Initial value and chroma numbers were subtracted from one week recall value and chroma numbers to calculate change in value and chroma. Changes in hue were recorded using the shade guide's letter designations. Data on each subject's no-light side vs. light treated side were analyzed using the General Linear Model (GLM) and Tukey's HSD multiple comparison test (a = 0.05). Each subject's contralateral teeth served as controls, and comparisons were made of before treatment shade vs. after treatment shade on each tooth type to determine if the bleach treatment lightened the teeth and if the use of accessory lights produced color change beyond use of the bleach gels alone.
For assessment of sensitivity, subjects were contacted following treatment, and daily until pain was no longer reported. Subjects also completed questionnaires with questions on sensitivity that were given immediately following treatment and returned at the one week recall appointment.

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