Comparison and agreement of visual and instrumental shade matching: an in-vivo evaluation

Dr. Fouda Homsi, DDS, DES, Department of prosthodontics, School of Dentistry, Lebanese University, Beirut, Lebanon.

Elias Smaira, DDS, DU,  Department of prosthodontics, School of Dentistry, Lebanese University, Beirut, Lebanon.

Rita Eid, DDS, DU, Department of prosthodontics, School of Dentistry, Lebanese University, Beirut, Lebanon.

Wiam El Ghoul, BDS, DU, Department of prosthodontics, School of Dentistry, Lebanese University, Beirut, Lebanon.

Abstract

Aim: to evaluate clinically the agreement in shade selection using a traditional Vitapan Classical and the new 3D Master shade guide

Materials and methods: Thirty prosthodontists participated in the study by evaluating clinically the shade of an upper right central maxillary using a visual shade selection guides (Vitapan Classical and 3D Master shade) and compared to an instrumental shade selection system (Easy shade, Vita). The intra-examiner Kappa coefficient (k) and Pearson Chi square test was used to evaluate agreement or no-agreement (α=0.05).

Results: A poor agreement was observed between the visual shade selection and the instrumental values while no significant difference were noted between visual shade selections.

Conclusion: clinical training is advised for visual shade selection especially with the new 3D Master system while instrumental shade selection gave accurate values.

Key words: shade selection, instrumental shade guide, tooth color.

Introduction

Closely matching artificial restorations with natural teeth can be one of the most challenging procedures in restorative dentistry. A key factor is the duplication of the color of the natural tooth, which include the determination of the tooth shade clinically and communication of the selected shade to a dental laboratory technician (1, 2). Esthetically superior restorations are now possible as a result of improvements in dental material properties and the use of layering techniques in fabrication process.

Traditionally, shade selection was performed visually by using a dental shade guide. Various shade guides exist to facilitate the matching process with more accurate results (3, 4). However, visual color determination has been found unreliable and imprecise (5, 6). The perception of color by the bare eye is rather subjective but not objective or even measurable and is therefore felt differently by every individual (7), due to differences in physiological and psychological responses to radiant energy stimulation, experience, environment and lighting conditions (7, 8, 9,10). A phenomenon called metamerism occurs when two colors appear to match under a given lighting condition but have a different spectral reflectance (11, 12). Commercial shade guides don’t cover all range of available shades (13,14) with different batches of one shade guide (15).     Electronic shade selection devices have the potential for more accurate and reliable selection of a tooth color (16, 17,18) since they are not influenced by the visual color determination parameters (19). Currently available electronic shade-matching devices are spectrophotometers colorimeters, digital color analyzers, or combinations of both. Spectrophotometers are useful in the measurement of surface color. A prism disperses white light from a tungsten-filament bulb in the spectrophotometer into a spectrum of wavelength bands between 10 and 20 nm(20).   The amount of light reflected from a specimen is measured for each wavelength in the visible spectrum. Of all devices, a spectrophotometer is the most accurate for absolute color measurement. These instruments have a longer working life than colorimeters and are unaffected by object metamerism (20, 21) Colorimeters are useful in quantifying color differences between specimens. These devices measure tristimulus values according to CIE illuminant and observer conditions (22).

One such instrument is an “intra-oral spectrophotometer” (EasyshadeTM, Vita Zahnfabrik, Bad Säckingen, Germany) with specific modes to identify reference shades from two commercial dental shade guides: the Vita 3D-Master (Vita Zahnfabrik, Bad Säckingen, Germany) and the Vitapan Classical (Vita Zahnfabrik, Bad Säckingen, Germany).

According to Dozic et al(2007) (11)  the intra-oral spectrophotometer, Easyshade, was the most reliable instrument in both in vitro and in vivo circumstances.

While color instrumentation and shade matching procedures have been widely addressed in dental literature, the most popularly used shade guides have not changed much through the last 50 years. The Vita shade guide 3D-Master (3D) was developed with a systematic arrangement for a wide range of natural dentition shades (23). The 3D shade guide is arranged in five discernible value levels with multiple chroma levels, as differentiated from the traditional Vitapan Classical (VC) grouping primarily by hue.

The aim of this clinical study is to evaluate the percent agreement between the human observer using a traditional Vitapan Classical and the new 3D shade guide. The null hypothesis tested was that no significant difference is observed between the uses of both shade guides.

Fig 1 Instrumental shade guide device (easy shade, Vita) and the visual shade guides (Vitapan Classic and 3D-Master, Vita) used in the study.

Materials and Methods

Test subject

An informed consent was obtained from the patient selected to participate in this study, after the approval of the ethical committee at the school of Dentistry at the Lebanese University, Beirut, Lebanon. The inclusion criteria were: patient with one upper right central maxillary  free from caries, restorations, or any dental anomalies (such fluorosis), and that didn’t undergo any orthodontic treatment. The tooth was polished using a slow hand speed hand piece (Sirona Dental System, GmbH, Bensheim, Germany) with disposable brushes and pumice (Garreco, Heber Springs, USA) prior to being measured. Measurements were done according to the manufacturer’s recommendation in the middle third of the tooth.

Visual shade selection

Thirty prosthodontists (men and women, with a mean age of 37.5years) with an average practice experience of 10 years participated to this study. All examiners were tested for color deficiencies (Farnsworth test, panel D15 desaturated). Two shade guide systems were chosen: the Vitapan Classical (VC) and the Vita 3D-Master (3D) (Vita Zahnfabrik, Bad Säckingen, Germany). The VC was ordered into the four common shade groups- A,B,C and D as the testers were familiar with it. None of the investigators had any experience with the 3DM and thus 1 day training was conducted 3 days before the investigation started.

The patient examination was performed in a lightened area by daylight fluorescent tubes of 36W/5,000K each (Just Normlicht, 73235 Weilheim/Teck, Germany). The illumination of the tested area was done at 45° angle using two reflectors cases (Kaiser, RB 5004, Buchen, Germany). The walls of the operatory in which shade selection was performed were neutral gray and the personal clothing of the patient was covered with a grey coat. The patient was requested to remove her make-up and to brush her teeth to eliminate any soft deposit.

Clinicians were requested to select the shade that was most congruent in color with natural tooth to be matched, starting with the VC then with the 3DM with 15 minutes of time interval between both shade guides. A time limit of 10 seconds was imposed for each assessment.

Instrumental shade selection

Shade measurement was obtained using VITA Easy Shade (VES) (VITA, Zahnfabrik Bad Sachingen, Germany) (Fig 1). The VES consists of a base unit and a hand piece connected by PVC stainless steel monocoil fiberoptic cable. The hand piece contains a fiberoptic probe assembly for illuminating and receiving light from a tooth, multiple spectrometers and microprocessors for communication with the base unit.

Cross contamination was controlled using provided polyurethane infection control shield. Calibration of the machine was performed according to the manufacturer’s recommendation after applying the shield, and the machine was adjusted on a single tooth area mode. When measuring the shade, the tip of the probe was held at 90 deg in contact with the tooth surface as recommended. The VES base unit displays the results of the measurements as compared to the system of the Vita Classic shade guide and 3D-Master shade guide.

This measurement was performed by an independent examiner and checked by a second procedure to ensure measurements errors. Data was recorded for both systems (VC and 3D) and used as basis for comparison.

The intra-examiner Kappa coefficient (k) was calculated as previously described (24). Each observer shade selection was recorded as a visual (VC and 3D)-instrumental “agreement or non-agreement” based on the instrumental shade identification (control). Pearson Chi square test was performed with level of significance at α=0.05,and SPSS software used for statistical analysis.

Fig 2 matching and no matching frequency between visual shade selection using Vitapan Classic (VLV) and 3D-Master (V3DM)

Results

A poor agreement was observed between the visual shade selection and the instrumental values (k=0.19) and p= 0.0001 (Table 1). When comparing the values selected by the 30 examiners in both visual shade selection (VC and 3D) there was no difference (P>0.05) (Fig 2)

When the results for the two shade guides (VC and 3D) were grouped and analyzed, there was no significant difference between the two shade guides (P>0.05)

Symmetric Measures
		Value	Asymp. Std. Error(a)	Approx. T(b)	Approx. Sig.
Measure of Agreement	Kappa	-0.050437956	0.1817045	-1.742753592	0.081376666
N of Valid Cases		30

Table 1 agreement measurement using the intra-examiner Kappa coefficient (k) between the visual shade selection and the instrumental values.

Discussion

Data of the present study support the rejection of the null hypothesis that no difference exists between visual and instrumental shade matching.

Previous studies reported that visual shade determination independent of the type of shade guide used remains a very challenging procedure (25-27). The Vita 3D-Master guide is associated with a high intrarater repeatability (8) and success in achieving acceptable color match (28). The 3D shade guide design presents a new viewing arrangement for value and chroma with 26 shades rather than the familiar 16 VC shades (29). The observers in this study were not familiar with the 3D shade guide even so there was no significant difference between both visual determinations, this may be explained by the color science principles followed by the specialists even when using the VC shade guide.  Other study reported significant improvement in agreement and intrarater repeatability when a 3D shade guide was used,wich was not in agreement with the results of the present study(30 , 31 ).

Several studies showed that instrumental shade determination was more accurate than the visual shade evaluation (32, 33,34), while others reported no significant difference between both techniques (35). In the present investigation there was no agreement between the instrumental and visual shade determination, even so the VES used showed very high accuracy (36), this might be explained by the amount of light that is reflected back into the instrument from the surface being targeted. Consequently, positioning of the probe is reported to be critical, for this reason an experienced operator performed the evaluation (29). Illumination is essential to minimize errors in color evaluation (37), as in the present study a standardized lighting was used for both instrumental and visual determination.   

Further in-vitro and in-vivo studies should be conducted in order to validate the results obtained in this study and try to find an accurate process to achieve accurate shade selection.

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