THE TOOTH SHADE MATCHING ABILITY AMONG DENTAL PROFESSIONALS: A COMPARATIVE STUDY (2024)

Abstract

Keywords: Shade selection, Shade guide, Dental professionals

INTRODUCTION

Perception of colour which is a complex phenomenonis considered an important part of aesthetic dentistryand an essential goal for a dentist who wants to choosetoothshade correctly to meet the demands of patientsfor satisfactory restorations.^1,2 Any slight change in thecolour of a restoration may lead to a significantcosmetic problem and makes the prosthesis lookartificial and unacceptable to the patient.^3,4 Perceptiondepends on the three entities namely the light source,the object and the detector (human eye).⁵ Despite thefairly high knowledge of proper shade selectionprocedures among the dental practitioners⁶understanding the colour and appearance of teeth is adifficult task. There are many factors such as lightingconditions, translucency, opacity, light scattering, surfacetexture, gloss with the human eye and brain influencingthe overall perceptibility and acceptability of toothcolour. The very first step to achieving good clinicaloutcome in aesthetic dentistry is the ability to correctlyidentify the tooth colour we need to imitate and thematerial that most closely matches it, as well as, thecorrect, conveyance of this information to thelaboratory.⁷

However, there are many challenges that the cliniciansface, which makes it difficult in selecting the correcttooth shade and influence the outcome of toothcolouredextra-coronal restorations.⁵ One of suchfactors is metamerism in which an object present withdifferent colour when viewed under differentconditions such as light source, instruments, geometricangle to mention a few. The perceived colour of atooth is affected by its reflecting ability which in turnis influenced by the source of light.^8-9 More so, thetranslucency of enamel and the polychromatic natureof dentine together produce complex depth of shadethat is not easy to characterize.¹⁰ Consequently, thedistribution of shade guides on the CommissionInternationale de l'Eclairage (CIELAB) colour spaceis not uniform, hence, the entire range of natural toothshade is not covered.¹¹ Fatigue, personality, gender andcolour defects are other human physiological factors that affect visual tooth matching.¹² Tooth colourmeasurement can either be done subjectively by theoperator through the use of shade guides, orobjectively by placing a device which technologicallyperforms the role of an observer while eliminatingthe effect of negative visual illusion, to deliver exactand reproducible information.¹³ One of such devicesis spectrophotometer.

Spectrophotometer is a sophisticated device that hasseveral configurations which measures the spectralreflectance of an object. It is a form of photometerfor measuring light intensity, it tends to measure thewave length as a function of the colour.¹⁴ Aspectrophotometer possesses a white light source eithera tungsten-filament bulb or LED lamp which create alight output of wavelength between 400 and 700 nm.The light passes through a prism and emerges into aspectrum of wavelength bands between 10 and 20nm, gets to the object, which may reflect, pass, or scatter,as the object selectively absorbs the differentwavelengths of light in varying amounts. The volumeof light emitted from or transmitted through the objectis measured for each wavelength band in the visiblespectrum. The detector converts the intensity of thelight at a particular wavelength into an electrical signalthat is amplified and displayed on the screen of thedevice. These measurements are usually converted toa corresponding shade tab on shade guide. However,there are newer form of spectrophotometer that hasmonochromators and photodiodes that can measurethe reflectance curve of an object’s colour every 10nm or even less.¹⁵ Based on measurement geometrySpectrophotometer can be classified into two typesnamely: entire tooth surface measurement and spotmeasurement while showing some differences in theangle of irradiance/reflection, lighting sensors, andfilters.¹⁶

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

The most common system for visual selection of toothcolour is the Munsell colour system; the parametersused 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 beobtained is the chroma with tabs that are close to themeasured value but are of increasing intensity ofcolour. Chroma ranges from achromatic or grey to ahighly saturated colour. Hue is obtained last by matchingwith colour tabs of the “value” and “chroma” alreadydetermined. Hue is measured on a scale of 2.5 to 10in 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 performedvisually using dental shade guides also known as colourstandards, which is a tab of different hues that servesto determine a tooth shade accurately. To avoid theproblems of metamerism these shades guide are madeof porcelain materials.¹⁷ Different types of colourstandards (shade guides) are used in dentistry,depending on their purpose and the tissue for whichthey are intended. These include tooth shade guides,shade guides for oral soft-tissues and shade guides forfacial prostheses commonly known as dental, gingivaland facial shade guides, respectively. The first shadeguide was introduced by Vita Zahnfabrik in 1956.⁴Thereafter, various shade guides have been introducedwhich include VITA classic shade guide, Chromascope,Hayashi shade guide, Clark shade guide, Vitapan 3D-Mastershade guide, Spectatone amongst others. VITAclassical shade guide is the most popular and one ofthe most commonly used shade guide. It consists of16 tabs that are arranged into four groups accordingto the hue.⁴

Studies have found that human eye is capable ofdetecting even small differences, while other authorshave mentioned that the human evaluation of toothshade is unreliable.¹⁸ Traditional visual tooth shadeselection is characterized by high intra-examinervariability and unpredictability, due to the numeroussubjective factors that affect colour selection.¹⁹ Theconsistency and reliability of visual shade matching aretherefore questionable. The perception of colourdifference seems to be learned trait although thepersonality of the patient can also have influence onthis. Therefore, this present study focused oncomparing the shade matching skill amongst the dentalprofessionals, and assesses the inter-examiner reliabilityof the visual shade selection. Furthermore, the shadeselected subjectively by the professionals werecompared with spectrophotometer; an objective formof shade assessment.

MATERIALS AND METHOD

This was designed as a cross sectional study involvingconventional visual tooth shade selection. Twenty fourpatients with 26 teeth that presented for porcelain fusedto metal crown fabrication of anterior teeth andpremolars were included in the study using convenientsampling. Patient with teeth discoloration and thosethat have had orthodontic treatment done were excluded from the study. Ethical approval wasobtained from the ethical committee of the UniversityCollege Hospital/University of Ibadan with ethicalnumber UI/EC/17/0507. Patients were asked toundergo scaling and polishing a week before the shadeselection procedure was done to remove any extrinsicstain. Also, patients brushed for one minute just beforethe shade selection to remove any accumulated plaque.Visual shade selection was done for each patient usingVITA classical shade guide by three categories of dentalprofessionals; a specialist restorative dentist(consultant), a dental surgery intern (house officer) anda dental surgery technician (dental nurse). The onlineIshihara’s colour chart test was used to test theexaminers and patients for colour vision prior to theshade selection to rule out any visual defect that couldaffect the outcome of the colour matching. Theexaminers were calibrated before the commencementof the shade matching. Shade was matched under adaylight colour-corrected light device (Corrected dentallight, Bremadent Premier (Bristol) LTD, Walthanshn,London E177PJ) with correlated colour temperatureof 5500k.

Shade selection was carried out by each examiner atseparate times. Patient was positioned upright on thedental chair with the head firmly positioned in theheadrest. Coloured eye glasses were removed as wellas coloured make up (such as lipstick) in female patientsand patient’s cloth was covered with grey bib. Theexaminer positioned him/herself at a distance of about28 to 33cm from the patient while taking the shade.The comparison of tooth colour with shade tabs wasnot viewed for more than 7 seconds each time to avoidfatigue.²¹ Shade of the middle third of tooth was takenwith the teeth well hydrated using a jet of clean water.The shade guide was moistened with water to mimicthe tooth that is constantly bathed with saliva in themouth and was thoroughly disinfected with methylatedspirit after each shade selection in each patient. Shadeguide tab labels were covered and assigned three digitID numbers (code) by the primary investigator, withthe code clearly written on it. The order in which thetarget shade tabs were arranged was randomized foreach shade matching session. The examiners recordedthe code for whatever shade they selected, this was toblind the examiners and prevent them from guessingthe shade based on the pre-knowledge of the shadecommonly selected for a particular tooth. Shade guideteeth were placed close to the tooth to be matched,above or below it (not by the side to avoid binoculareffect). Each examiner recorded the shade (i.e. thecoded number) he or she selected on a piece of paperand placed it in an envelope next to the operatorychair. The investigator collected the envelopes after allexaminers had finished shade matching. Any two orthree identical shade selected by the examiners wastaken as the final shade selected. When none of thethree shades for the three examiners was identical, thepatient was asked to pick the shade he/she felt wasthe best match out of the three shades, and that wasused as the final shade for the restoration fabrication.Shade selection was also done by the investigator usingVita easyshade advance V spectrophotometer (VasaDenticity Private Limited. Ghitorni, Delhi, India) thatwas calibrated according to the manufacturerspecification. The shades selected by visual andinstrumental method were recorded.

Data were entered into personal computer spreadsheet and analysis was done using IBM SPSS Statisticsfor Windows, Version 23.0. Armonk, NY: IBM Corp.Normalcy of the data was assessed using Kolmogorov-Smirnov test and found to be normally distributed.Descriptive statistics including frequency, mean andstandard deviation were used to report parametersfor each method of shade selection analysed in thestudy. Inter-examiner reliability was measured usingCohen’s Kappa coefficient. Statistical significance wasplaced at p ≤0.05

RESULT

Nine (37.5%) males and 15 (62.5%) femalesparticipated in the study (Figure ​(Figure1).1). The mean age ±SDof the participants was 39.9 ± 18.47 years. The dentalsurgery technician and the house officer agreed onshades selected in 2 (7.7%) teeth out of the 26 teeth.The dental surgery technician and consultant selectedthe same shade for 6 (23.1%) teeth while the houseofficer and consultant did so for 8 (30.8%) teeth. Thethree examiners agreed on shades selected for only 1(3.8%) tooth. While in eleven (11) (42.3%) cases, allthe three visual selections differed. Inter-examinerreliability measured with Cohen's Kappa coefficientwas 0.11 (Table ​(Table11)

In the final toothshade selection process, among the26 teeth, only one (3.8%) had the same shade selectedusing both the conventional visual and spectrophotometricshade methods. This indicates poor agreementbetween the two methods of shade selection (Table ​(Table2).2). Shades selected by the consultant matched that ofthe spectrophotometer in 3 of the 26 teeth (11.5%)being the best. The dental surgery technician matchedin only 1 (3.8%), while shades selected by the houseofficer did not agree with that of the spectrophotometerin any of the teeth. (Table ​(Table33)

DISCUSSION

Shade guides remain the most popular options fortooth colour selection despite the recent advances inshade matching instruments to reduce variability.²⁰ Oneof the most important factors in the determinationof tooth colour is a clinician’s colour perception.²¹ Evenfor a dentist with colour vision, matching of toothshade is complicated by the individual’s own differencesin colour observation.²⁰

This study found a very low (3.8%) inter-examineragreement in shade selection by the 3 examiners. Theinter-examiner reliability measured with Cohen’s Kappacoefficient was 0.¹¹. This very low inter-examineragreement may be due to the disparity in experienceand training of the three examiners in the study. Thisis however, different from the results of study by Paulet al.,²² in which the three examiners using visual shadeselections matched in 8 of the 30 patients (26.6%).Similarly, Gehrke et al.,²³ in their own study of 40 casesreported that all the three human examiners obtainedthe same shade in 22.5% of the cases. Furthermore,Paul et al.,²⁴ reported that 2 out of 10 (20%) cases ofshade evaluated in all three visual shade selectionmatched. Individual differences and personality of theevaluators of visual shade selection in the various studiesmay account for the variation in the results. Theseresults, nevertheless, pointed to the fact that visual shadeselection is highly subjective and not very reliable.

Comparing the shade selected by each of the threeexaminers using the conventional visual method with the final shade selected by the use of spectrophotometer,it was observed that the level of agreementbetween the shade selected by the three examiners usingconventional method and the spectrophotometer wasgenerally low. This was similar to that of Meireles etal.,²⁵ who in their study found that the agreementbetween visual assessment by the examiners and digitalspectrophotometer was also low. On the contrary,Guan et al.,²⁶ using extracted teeth observed a positivecorrelation between the digital spectrophotometer andvisual assessment methods of tooth colour. Thisdifference may be attributed to condition of the testedextracted teeth (in vitro) which was different from theteeth used in the current study (in vivo) which were intheir normal physiological environment. However, theconsultant had higher agreement of 11.5% followedby the dental surgery technician with 3.8% match whilethe shade selected by the house officer did not matchthat of spectrophotometer in any of the cases. Thehigher percentage by the dental surgery technician whencompared with the house officer may be as a resultof length of years of experience in the clinical practice.This finding was in variant with the study of Moodleyet al.,²⁷ that reported a better agreement of the shadeselected by the 2 operators in their study with that ofspectrophotometer.

In colour science, the influence of the level ofexperience and professional training is controversial;some authors have reported positive effects whileothers see no significant differences.^28,29,30,31 This currentstudy found that the house officer and the consultanttended to select more same shade than the dentaltechnician. However, the shade selected by the houseofficer did not match any of the spectrophotometer.This may be as a result of experience coupled withthe kind of training the dentists had received on shadeselection in school at one point or the other. Della etal.²⁸, reported that there was correlation between visualinstrumentagreement and the experience of theoperators. This finding was further supported by somestudies^32,33,34,35, that emphasised the fact that training incolour and experience have impact on the shadematching ability. Furthermore, Alshiddi et al.,29 reportedthat trained students were able to assess tooth shadebetter than untrained students. Pimentel and Tiossi30also reported that a successful tooth shade selectionrelies on adequate knowledge of colour science andcontrol of the variables that influence the visual colourassessment. Contrarily, Udijak et al.,³¹ claimed there isno role of previous knowledge and experience indental shade matching.

CONCLUSION

1. Within the limitation of this study, it was foundthat Inter-examiner reliability was very low in theconventional visual shade selection. However,experience and training in colour science and shadeselection may play a role in correct tooth shadeselection.

2. There is need to lay emphasis on training in colourscience at undergraduate level

REFERENCES