THE TOOTH SHADE MATCHING ABILITY AMONG DENTAL PROFESSIONALS: A COMPARATIVE STUDY

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G.E. Adebayo, O.S. Gbadebo, M.D. Ajayi

Department of Restorative Dentistry, Faculty of Dentistry, College of Medicine, University of Ibadan/University College Hospital, Ibadan, Nigeria

Abstract

Background: Shade matching presents a complex and multidimensional process that involves the cognitive ability of the operator. Hence, dental professionals need to have high shade matching skill.

Method: This was a cross sectional study involving conventional visual tooth shade selection by three categories of dental professionals. Twenty four patients that met the selection criteria were included in the study and Ethical approval duly obtained. Visual shade selection using vital classical shade guide was done by calibrated 3 categories of the dental professionals. Data collected was analysed using IBM SPSS with statistical significance placed at p <0.05

Objective: To compare the shade matching ability among three categories of dental professionals and assess the inter-examiner reliability of the visual shade selection.

Results: There were 9 (37.5%) male and 15 (62.5%) female participants with mean age ±SD of 39.9 ± 18.47 years. In the shade selection, the dental surgery technician and the house officer agreed in 2 (7.7%) teeth, dental surgery technician and consultant in 6 (23.1%) teeth while the house officer and consultant did so for 8 (30.8%) teeth. The three examiners agreed on shades selected for only 1 (3.8%) tooth. Inter-examiner reliability was 0.11. Shades selected by the consultant matched that of the spectrophotometer in 3 of the 26 teeth (11.5%) being the best.

Conclusion: Inter-examiner reliability was very low in the conventional visual shade selection. Experience and training in colour science and shade selection may play a role in correct tooth shade selection.

Keywords: Shade selection, Shade guide, Dental professionals

Introduction

Perception of colour which is a complex phenomenon is considered an important part of aesthetic dentistry and an essential goal for a dentist who wants to choose toothshade correctly to meet the demands of patients for satisfactory restorations.^1,2 Any slight change in the colour of a restoration may lead to a significant cosmetic problem and makes the prosthesis look artificial and unacceptable to the patient.^3,4 Perception depends on the three entities namely the light source, the object and the detector (human eye).⁵ Despite the fairly high knowledge of proper shade selection procedures among the dental practitioners ⁶ understanding the colour and appearance of teeth is a difficult task. There are many factors such as lighting conditions, translucency, opacity, light scattering, surface texture, gloss with the human eye and brain influencing the overall perceptibility and acceptability of tooth colour. The very first step to achieving good clinical outcome in aesthetic dentistry is the ability to correctly identify the tooth colour we need to imitate and the material that most closely matches it, as well as, the correct, conveyance of this information to the laboratory.⁷

However, there are many challenges that the clinicians face, which makes it difficult in selecting the correct tooth shade and influence the outcome of toothcoloured extra-coronal restorations^.5 One of such factors is metamerism in which an object present with different colour when viewed under different conditions such as light source, instruments, geometric angle to mention a few. The perceived colour of a tooth is affected by its reflecting ability which in turn is influenced by the source of light.^8-9 More so, the translucency of enamel and the polychromatic nature of dentine together produce complex depth of shade that is not easy to characterize.¹⁰ Consequently, the distribution of shade guides on the Commission Internationale de l’Eclairage (CIELAB) colour space is not uniform, hence, the entire range of natural tooth shade is not covered.¹¹ Fatigue, personality, gender and colour defects are other human physiological factors that affect visual tooth matching.¹² Tooth colour measurement can either be done subjectively by the operator through the use of shade guides, or objectively by placing a device which technologically performs the role of an observer while eliminating the effect of negative visual illusion, to deliver exact and reproducible information.¹³ One of such devices is spectrophotometer.

Spectrophotometer is a sophisticated device that has several configurations which measures the spectral reflectance of an object. It is a form of photometer for measuring light intensity, it tends to measure the wave length as a function of the colour. ¹⁴ A spectrophotometer possesses a white light source either a tungsten-filament bulb or LED lamp which create a light output of wavelength between 400 and 700 nm. The light passes through a prism and emerges into a spectrum of wavelength bands between 10 and 20 nm, gets to the object, which may reflect, pass, or scatter, as the object selectively absorbs the different wavelengths of light in varying amounts. The volume of light emitted from or transmitted through the object is measured for each wavelength band in the visible spectrum. The detector converts the intensity of the light at a particular wavelength into an electrical signal that is amplified and displayed on the screen of the device. These measurements are usually converted to a corresponding shade tab on shade guide. However, there are newer form of spectrophotometer that has monochromators and photodiodes that can measure the reflectance curve of an object’s colour every 10 nm or even less.¹⁵ Based on measurement geometry Spectrophotometer can be classified into two types namely: entire tooth surface measurement and spot measurement while showing some differences in the angle of irradiance/reflection, lighting sensors, and filters.¹⁶

Over the years, the traditional way of selecting tooth shade has been through visual observation by the unaided eye.^12,13 This is done by the operator visually comparing the tooth colour with standard shade guides (tabs of several hues and chroma) and choosing the one he/she perceives to be the best or closest match.^14,15

The most common system for visual selection of tooth colour is the Munsell colour system; the parameters used are the triads of value, chroma and hue. Value (lightness) is determined first by selecting a tab thatclosely matches the lightness or darkness of the colour, which spans between white and black.¹⁶ Next to be obtained is the chroma with tabs that are close to the measured value but are of increasing intensity of colour. Chroma ranges from achromatic or grey to a highly saturated colour. Hue is obtained last by matching with colour tabs of the “value” and “chroma” already determined. Hue is measured on a scale of 2.5 to 10 in increments of 2.5 for each of the 10 colour families (red, R; yellow-red, YR; yellow, Y; green-yellow, GY; green, G; blue-green, BG; blue, B; purple-blue, PB; purple, P; red-purple, RP).¹⁷

Tooth colour matching is most commonly performed visually using dental shade guides also known as colour standards, which is a tab of different hues that serves to determine a tooth shade accurately. To avoid the problems of metamerism these shades guide are made of porcelain materials.¹⁷ Different types of colour standards (shade guides) are used in dentistry, depending on their purpose and the tissue for which they are intended. These include tooth shade guides, shade guides for oral soft-tissues and shade guides for facial prostheses commonly known as dental, gingival and facial shade guides, respectively. The first shade guide was introduced by Vita Zahnfabrik in 1956.⁴ Thereafter, various shade guides have been introduced which include VITA classic shade guide, Chromascope, Hayashi shade guide, Clark shade guide, Vitapan 3DMaster shade guide, Spectatone amongst others. VITA classical shade guide is the most popular and one of the most commonly used shade guide. It consists of 16 tabs that are arranged into four groups according to the hue.

Studies have found that human eye is capable of detecting even small differences, while other authors have mentioned that the human evaluation of tooth shade is unreliable.¹⁸ Traditional visual tooth shade selection is characterized by high intra-examiner variability and unpredictability, due to the numerous subjective factors that affect colour selection.¹⁹ The consistency and reliability of visual shade matching are therefore questionable. The perception of colour difference seems to be learned trait although the personality of the patient can also have influence on this. Therefore, this present study focused on comparing the shade matching skill amongst the dental professionals, and assesses the inter-examiner reliability of the visual shade selection. Furthermore, the shade selected subjectively by the professionals were compared with spectrophotometer; an objective form of shade assessment.