COLOR PERCEPTION

TOP ABSTRACT COLOR PERCEPTION PATIENTS, MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION REFERENCES

 
People vary in their ability to detect small differences in color between two objects.^1–3 Color perception also might differ for the same person under varying conditions.³ Moreover, once observers detect a color difference between two objects, their opinions might differ considerably in regard to the degree of this difference.⁴

Instrumental color measurement in dentistry assists in shade selection via intraoral optical electronic determination of a target color during fabrication of a restoration.⁵ However, application of technology that quantifies color and color difference is not yet a common practice in dental clinics. Previous research has not shown a positive correlation between instrumental and visual assessment of color differences in regard to matching crown pairs in all dimensions of color space.⁵ Acceptability thresholds were found to depend on chromaticity. Observers were more critical of crowns in which color differed in redness as opposed to crowns that differed to the same extent in yellow color.¹

Factors affecting shade matching. Many factors affect the process of shade matching, including the light source, the patient’s clothing and makeup, inherent inconsistencies of commercial shade guides and vague orders on the laboratory prescription form.⁶ Research also has demonstrated that dental personnel who have impaired color vision make significantly more errors in the process of shade matching.⁷ Therefore, some authors have suggested that dentists consult an assistant for a second opinion during the shade selection process.^8–10 Mollon¹¹ conducted a study and reported that women generally are more capable than men in the shade selection and color matching process. This may be because more deficiencies in color vision are recorded for men than for women.¹²

Consequently, selecting the proper porcelain shade and matching restorations to the natural dentition continue to be challenges for the restorative dentist. The process of shade selection is an art in which the dentist and patient should collaborate. Dentists may consider changing a restoration because they believe the color does not match that of the adjacent teeth, even though the color difference might not be noticeable to the patient. Involving the patient in the shade selection process likely will improve his or her satisfaction with the final outcome. To date, patient satisfaction with shade matching or patient input into the shade selection process has not been appraised carefully in the dental literature.

Assessment of patient and clinician. In this study, we investigated patients’ assessment of how accurately the shade of their PFM crown or fixed bridge matched the adjacent natural dentition, by having them rate the restoration as poor, satisfactory or good. We then compared this rating with that of a prosthodontist, who assessed the shade match of each restoration under the same controlled conditions (Figures 1 through 3). The frequency of agreement between the patient and the prosthodontist in this assessment was determined and the results were analyzed for statistical significance. The null hypotheses for this study were as follows:

View larger version (75K): [in this window] [in a new window]   Figure 1. Comparison of a porcelain-fused-to-metal restoration on tooth no. 9 with adjacent natural tooth no. 10. The patient’s rating was satisfactory and the prosthodontist’s rating was poor.

View larger version (93K): [in this window] [in a new window]   Figure 2. Comparison of a porcelain-fused-to-metal restoration on tooth no. 7 with adjacent natural tooth no. 6. The patient’s rating was poor and the prosthodontist’s rating was poor.

View larger version (100K): [in this window] [in a new window]   Figure 3. Comparison of a porcelain-fused-to-metal restoration on tooth no. 10 with adjacent natural tooth no. 11. The patient’s rating was good and the prosthodontist’s rating was satisfactory.

– There is no statistically significant difference in the perception of shade match of PFM restorations between patients and the prosthodontist.

– There is no statistically significant difference between men and women in regard to their perception of shade match of restorations.

– There is no statistically significant difference in the patient’s perception of shade match between restorations placed by a prosthodontist or placed under the supervision of a prosthodontist and those placed by a general practitioner.

	PATIENTS, MATERIALS AND METHODS

TOP ABSTRACT COLOR PERCEPTION PATIENTS, MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION REFERENCES

 
Two hundred twelve patients who had at least one PFM restoration (that is, crown, cantilever bridge or fixed bridge) were selected in a convenience sample from patients visiting the Department of Restorative Dentistry at Jordan University of Science and Technology, Irbid, for a routine examination. Inclusion criteria were as follows: one fixed restoration was evaluated per patient, as long as he or she had one or more sound adjacent teeth that were free from obvious facial discoloration.

Participants ranged in age from 19 through 76 years, with a mean age of 39.5 years (standard deviation = 13.0 years). The majority of patients (80 percent) were between 20 and 40 years old. One hundred eight (51 percent) of the patients were female and 104 (49 percent) were male. One hundred twenty-nine of the restorations had been placed in private practice, while the remaining 83 were placed at the dental school at Jordan University of Science and Technology.

The restorations were located in the mouth as follows: 16 (7.5 percent) were in anterior mandibular teeth; two (0.94 percent) were in anteroposterior mandibular teeth; 28 (13.2 percent) were in anteroposterior maxillary teeth; 75 (35.4 percent) were in anterior maxillary teeth; 48 (22.7 percent) were in posterior mandibular teeth; and 43 (20.3 percent) were in posterior maxillary teeth.

One of us (R.A.) asked patients to express their degree of satisfaction regarding how well the shade of their restoration matched that of the adjacent natural teeth; they could rate the match as poor (that is, obvious color mismatch), satisfactory (that is, acceptable blend to the adjacent natural dentition, but a color difference could be detected) or good (that is, good blend to the adjacent natural dentition). A value of 0, 1 or 2 was assigned, respectively, to each category.

Immediately after we obtained the patient’s assessment, a prosthodontist (A.A.-W.) evaluated the shade match of the fixed PFM restoration to the adjacent teeth according to the same rating system. The prosthodontist (who was tested with the Farnsworth-Munsell 100-hue test and Farnsworth’s D15 test to rule out inherent color deficiencies) performed all of the evaluations and was blinded to the patients’ assessments. Standard conditions used for evaluating shade match included color-corrected lighting and having the patient seated in an upright position with his or her mouth at the prosthodontist’s eye level.

Statistical analysis. We used Kendall’s tau-b statistic¹³ to measure the strength of the association between the shade satisfaction rating of the patient and that of the prosthodontist, as measured on an ordinal scale (that is, poor, satisfactory and good). The weighted statistic for ordinal data¹⁴ was used as a measure of agreement between the patient and the prosthodontist. The question of whether a significant difference in shade-match perception existed between patients and the evaluating prosthodontist was addressed using a test of symmetry.¹³ Potential differences between the distributions of perceptions of patients and the prosthodontist were further examined via the Stuart-Maxwell ² test of marginal homogeneity.¹⁵

Variables associated with patient satisfaction. In addition, we examined the level of patient satisfaction with respect to the following variables: sex, treatment setting (that is, private dental office or hospital) and clinician who placed the restoration (that is, general practitioner, prosthodontist or student). We used the Cochran-Mantel-Haenszel ² test¹³ to consider whether the distribution of ordinal patient ratings differed according to the particular characteristic (for example, treatment setting). (This is a mean score test that uses the integer scores [0, 1 and 2] to denote the set of possible responses [poor, satisfactory and good].)

An alternative approach to scoring the ordered responses, called ridit analysis,^15,16 also was used; this method compares patterns of ratings in the subgroups (defined by the particular characteristic of interest) with the overall distribution of scores. Because the results were identical to those obtained using the integer scores, these data are not presented.

	RESULTS

TOP ABSTRACT COLOR PERCEPTION PATIENTS, MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION REFERENCES

 
Our analysis of the observed frequencies for shade-match satisfaction indicated that there was a highly significant but modest correlation (Kendall’s tau-b = .55, P < .001) between patients’ and the prosthodontist’s ratings. The patient and prosthodontist assigned the same rating in only 91 (42.9 percent) of the 212 cases. The level of agreement, as measured by the weighted , was similarly modest, with a value of 0.33 (95 percent confidence interval, 0.25 to 0.41); values reflect levels of agreement adjusted for expected agreement due only to chance. Kappa coefficients of 0.4 to 0.8 generally are considered to indicate moderate agreement. A coefficient equals 0 when the agreement equals that expected by chance, whereas the closer the value is to 1, the greater the agreement between the two ratings.

The data provided strong evidence that patients rated shade match differently from the prosthodontist (P < .0001 by symmetry test), and the distribution of shade ratings provided by patients was significantly more positive than that provided by the prosthodontist (Stuart-Maxwell ² test of marginal homogeneity = 62.2 with 2 degrees of freedom, P < .0001).

Ratings of patients and prosthodontist. These results indicate that although there was a positive correlation between the patients’ and the prosthodontist’s ratings, the overall level of agreement was not strong, with patients tending to rate the shade match significantly better than did the prosthodontist. Patients rated 103 (48.6 percent) of the 212 restorations as good, while the prosthodontist assigned a good rating to only 57 restorations (26.8 percent). Patients rated 79 (37.3 percent) of the restorations as satisfactory and, similarly, the prosthodontist rated 77 (36.3 percent) of the restorations as satisfactory. Finally, patients rated only 30 (14.2 percent) of the restorations as poor, while the prosthodontist rated 78 (36.8 percent) of the restorations as poor.

Using the Cochran-Mantel-Haenszel mean score statistics, we did not find any sex differences in the distribution of shade-match ratings (Table 1) (P = .88). However, the data strongly support differences in patients’ ratings associated with classification of the clinician (Table 2, P < .0001). Furthermore, there did not appear to be significant differences in the distribution of patients’ ratings when the procedures were performed by a prosthodontist or by undergraduate dental students (P = .65). However, patients’ ratings tended to be lower when procedures were performed by general practitioners than when they were performed by prosthodontists (P = .005) or students (P = .0001). We should note that the latter pairwise differences remained significant even after adjusting for multiple comparisons according to the standard Bonferroni method (overall type I error = .01).

	DISCUSSION

TOP ABSTRACT COLOR PERCEPTION PATIENTS, MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION REFERENCES

The results of this study suggest that differences in patients’ ratings were associated with various factors, including treatment location and the clinician placing the restoration. Patients were more satisfied with the color of PFM restorations placed by a prosthodontist or a student under the prosthodontist’s supervision than with the color of restorations placed by a general practitioner. This may be a result of the prosthodontist’s experience or the patient’s perception of quality. This also directly relates to the finding that patients rated PFM restorations placed in a hospital or academic setting as more satisfactory compared with those placed in private practice.

Hospital vs. private practice setting. These findings might be due to the fact that in a hospital or academic center, more people are involved in the process of selecting shades, or the findings might reflect the public’s opinion of the institution’s quality. The higher shade-match ratings attributed to restorations made and fitted in the hospital setting might be related to the benefit of having a controlled academic supervisory environment, in-house laboratory support and a strict scientific approach to fixed prosthodontics within the dental school. A higher rating by patients for restorations placed by dental students might have resulted from patients being defenders of dental students (they may have believed, erroneously, that students were being graded on the basis of patients’ ratings).

Pokorny¹² reported more color vision differences for men than for women. Wasson and Schuman¹⁷ examined 150 dental personnel. The results of their study showed that 9.3 percent of the men and none of the women exhibited color-vision defects. Research done by Davison and Myslinski⁷ and Yorty and colleagues¹⁸ showed that dental personnel with deficiencies in color perception made significantly more errors in hue and chroma selection than did personnel whose vision was normal.

The examining prosthodontist in this study had no color-perception defects, as determined by a medical examination, but no color test was performed on the patients. Although we did not screen patients for color-perception defects, we assume that the incidence of color blindness in these patients follows that of the general population in Jordan, where the allelic frequencies of the color vision gene deficiency were found to be 0.087 in men, 0.003 in women and 0.016 in the total population.¹⁹ In our study, however, no differences were found between men and women in the distribution of shade-match ratings.

Culpepper³ found disagreement between dentists in regard to shade matching for the same tooth, and individual dentists could not duplicate their shade selections on different days. The present study compared patients’ opinions with those of one practitioner, rather than comparing agreement among practitioners. The results show that patients are not always in agreement with the clinician in regard to shade-matching decisions. These findings support our belief that patients’ involvement in shade selection and their satisfaction with the outcome are important to achieving the best esthetic results.

Shade selection is highly affected by viewing conditions, such as light source, wall color, the amount of sunlight, the patient’s clothing and makeup, and the viewing angle of the tooth.⁶ In our study, both patients and the examiner conducted the test at the same visit under the same controlled conditions, using a color-corrected light source.

Importance of patient satisfaction. To minimize the problem of shade mismatch of PFM restorations, the dentist should not forget that patient satisfaction is an important goal. Furthermore, a systematic method for shade determination, which includes input from both the clinician and the patient, as suggested by Sorensen and Torres, ⁶ always should be followed.

Although the use of one rater may limit the generalizability of our study results, we hoped that this design would provide a measure of internal consistency and precision. Our use of one clinician in this study reflects most clinical settings, in which one dentist selects the restoration shades for patients.

	CONCLUSION

TOP ABSTRACT COLOR PERCEPTION PATIENTS, MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION REFERENCES

 
Patients’ satisfaction with the selected shade of a PFM restoration is an important factor to consider, and the opinion of the patient may differ from that of the practitioner. This study demonstrated that patients were less critical of shade matches than was the evaluating prosthodontist. We did not find any correlation between satisfaction with the shade match and the sex of the patient. In addition, this study demonstrated that patients were more satisfied with the shade of restorations placed by a prosthodontist or by a student under the supervision of a prosthodontist in a hospital or academic center. Future studies might include a panel of evaluators who rate all of the shade matches.