Pilot in vivo image spectro-photometric evaluation of optical properties of pure enamel and enamel–dentin complex

Abstract

Objectives

The aim of this in vivo study is to investigate the L * a * b *and the opacity (CR) of front teeth by means of an image spectrophotometer and to evaluate the eventual influence of the background color on the results. The second aim is to investigate if there is a relationship between tea, coffee, red wine drinking habits or smoking habits of the test subjects and tooth color.

Methods

A novel image based spectro-photometric approach was developed and applied on a Swiss Army recruits group quantifying L * a * b * of pure enamel as well as of enamel–dentin complex against black and white background together with CR.

Results

When 2 mm thick pure enamel was considered, the values obtained were (mean (SD)) L *(76.3 (3.4)), a *(3.4 (1.2)) and b *(17.2 (2.45)) against white background and L *(63.5 (4.2)), a *(0.8 (1.3)) and b *(10.7 (2.7)) against black background. The opacity (CR) of 2 mm thick pure enamel was (64.4 (0.1)).

When 3 mm thick enamel–dentin complex was considered, the values obtained were L *(79.0 (2.6)), a *(3.9 (1.3)) and b *(20.4 (3.0)) against a white background and L *(74.9 (3.0)), a *(1.8 (1.2)) and b *(16.7 (3.1)) against a black background. The opacity (CR) of 3 mm thick enamel–dentin complex was (87.4 (0.1)).

Significance

The application of this method on a larger group of subjects of different ages may serve as a database for a more exact characterization of optical properties of natural enamel and dentin.

Introduction

The need for imperceptible esthetic restorations is steadily increasing due to the rise of very demanding patients . In modern society, in fact, esthetic is one of the major pillars and dental appearance is an important factor, especially in front teeth. In the modern trend of minimal invasiveness, veneers and crowns are only indicated when acceptable esthetic results cannot be reached by the direct restorative approach, i.e. the use of free-hand bonded composite restorations.

Even if composite resins have proved to give satisfactory results in the hands of excellent practitioners, the invisible restoration is still a chimera for the majority of dentists. Besides the restorations’ shape, a proper color match is of main importance and it is difficult to achieve with today’s composites. There is, in fact, an evident mismatch between shades of available restorative materials and teeth. Furthermore a large part of the available composites still sticks to the Vita shade guide where the shade selection is done by mixing the color information of enamel and dentin. Due to this outdated concept the majority of epidemiologic tooth color studies have been done by measuring the color of the entire tooth. This approach has already been criticized and shade selection based on the separate choice of enamel and dentin color has been proposed . Anyway, no study has, so far, tried to measure in vivo on a larger number of subjects the optical properties of enamel and dentin. The only few available data in this field are, in fact, available from in vitro measurements and limited to a low number of samples.

The aim of this in vivo study is therefore to investigate the L * a * b *, value and opacity (CR) of front teeth by means of an image spectrophotometer and to evaluate the eventual influence of the background color on the results. The second aim is to investigate if there is a relationship between tea, coffee, red wine drinking habits or smoking habits of the test subjects and tooth color.

Materials and methods

62 randomly chosen recruits from the Swiss Army coming from the German Swiss region in the age of 20–21 years gave their written informed consensus for a spectro-photometric analysis and the stone reproduction through a polysiloxane impression of their upper central incisors. Only patients with intact vital upper central incisors without malformations and significant intrinsic colorations, fissures or restorations were included into the study.

After answering a questionnaire on their drinking and smoking habits, their front teeth were cleaned with a 70 RDA toothpaste on a toothbrush (Colgate Total, Colgate-Palmolive, Thalwil, Switzerland).

Spectrophotometer measurements

A calibrated reflectance image spectrophotometer (SpectroShade, Handy Dental Type 713000, Serial No. HDL0090, MHT, Arbizzano di Negar, Verona, Italy) was used in this study. With this device CIE L * a * b * measurements of the entire surface of the central upper incisors of each subject were performed against a white as well as a black background. The device has a build-in aiming routine that enables a reproducible positioning perpendicular to the facial tooth surface to ensure equal measurement conditions for all teeth evaluated. The device is equipped with a D65 light source (6500 K) that is transformed into monochromatic light by means of a grating. This light is splinted in order to have each tooth illuminated simultaneously from two sides at 45° angle. The reflected light is directed at 0° on both the system’s two detector areas (both 18 mm × 13 mm). One detector is a color CCD chip that generates the color video image. The other, black and white, CCD detector records the spectro-photometric data. Polarization filters are used to eliminate surface gloss. The data are stored in a proprietary image file format which is used to create detailed CIE L * a * b * data.

L * a * b * values on white ( L * 96.6; a * −0.7; b * 2.6) and black ( L * 0.4; a * 0.1; b * −0.1) background were then recorded and also converted into Yxy values to obtain information about opacity as well. The mathematic formulas used for these calculations are described in Table 1 .

Table 1
Formulas used for the calculations of Yxy , and contrast ratio (CR) out of CIE L * a * b * measurements.

Tooth shape determination

A vinyl polysiloxane impression (Express fast set light body, 3M ESPE Dental Products, St Paul, MN, USA) of upper front teeth was taken and poured with plaster to enable registration of 3D tooth dimensions. The oro-facial thickness and the length of the tooth were measured on the model by using a dental calliper.

Opacity determination

Areas of pure enamel with 2 mm thickness were identified by comparing optical data of the MHT device in gloss mode ( Fig. 1 ) with the plaster models, where a digital calliper was used to measure their thickness in oro-facial direction. Once the area detected, CIE L * a * b * measurements were performed on the corresponding SpectroShade images with white and black background. Areas of 3 mm tooth thickness consisting of an equal amount of enamel and dentin according to Shillingburg and Scott Grace were then detected and CIE L * a * b * values on white and black background were obtained through the same methodology as described for enamel. No direct measurements on pure dentin samples were possible due to the absence of exposed dentin in intact young teeth.

Fig. 1
Vision of a upper right central of the gloss mode and normal mode obtained with the spectrophotometer SpectroShade MHT.

The CIE L * a * b * values of enamel and enamel–dentin were used to calculate opacity. CIE L * a * b * values of 2 mm thick enamel and 3 mm thick enamel–dentin complex with white and black background were then converted to Yxy scale to obtain contrast ratio (CR) values.

An exhaustive description of the whole methodology was reported in a preceding publication .

Materials and methods

62 randomly chosen recruits from the Swiss Army coming from the German Swiss region in the age of 20–21 years gave their written informed consensus for a spectro-photometric analysis and the stone reproduction through a polysiloxane impression of their upper central incisors. Only patients with intact vital upper central incisors without malformations and significant intrinsic colorations, fissures or restorations were included into the study.

After answering a questionnaire on their drinking and smoking habits, their front teeth were cleaned with a 70 RDA toothpaste on a toothbrush (Colgate Total, Colgate-Palmolive, Thalwil, Switzerland).

Spectrophotometer measurements

A calibrated reflectance image spectrophotometer (SpectroShade, Handy Dental Type 713000, Serial No. HDL0090, MHT, Arbizzano di Negar, Verona, Italy) was used in this study. With this device CIE L * a * b * measurements of the entire surface of the central upper incisors of each subject were performed against a white as well as a black background. The device has a build-in aiming routine that enables a reproducible positioning perpendicular to the facial tooth surface to ensure equal measurement conditions for all teeth evaluated. The device is equipped with a D65 light source (6500 K) that is transformed into monochromatic light by means of a grating. This light is splinted in order to have each tooth illuminated simultaneously from two sides at 45° angle. The reflected light is directed at 0° on both the system’s two detector areas (both 18 mm × 13 mm). One detector is a color CCD chip that generates the color video image. The other, black and white, CCD detector records the spectro-photometric data. Polarization filters are used to eliminate surface gloss. The data are stored in a proprietary image file format which is used to create detailed CIE L * a * b * data.

L * a * b * values on white ( L * 96.6; a * −0.7; b * 2.6) and black ( L * 0.4; a * 0.1; b * −0.1) background were then recorded and also converted into Yxy values to obtain information about opacity as well. The mathematic formulas used for these calculations are described in Table 1 .

Nov 30, 2017 | Posted by in Dental Materials | Comments Off on Pilot in vivo image spectro-photometric evaluation of optical properties of pure enamel and enamel–dentin complex
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