Assessment of changes in enamel colour following fixed orthodontic therapy using an advanced spectrophotometer: An in vivo study

Abstract

BACKGROUND:

Any manipulation of the surface of natural teeth may result in a variation of their colour. The fixed orthodontic treatment (FOT) is one such procedure which alters the enamel surface during the procedure.

OBJECTIVE:

To clinically evaluate the colour changes in teeth associated with comprehensive FOT (to compare the changes in test and control groups) and to determine the relationship of age and gender on enamel colour due to FOT by using an advanced spectrophotometer.

METHODS:

The selection of sixty patients for the study was done randomly and among these thirty patients who underwent the FOT as the case group, the other thirty patients who did not need FOT, were the control group. The recordings of spectrophotometric data were done in a standardized manner for all patients in the labial circular region of every anterior tooth, following debonding and cleaning operations, and before bracket bonding. The Commission Internationale de l’Eclairage’s L*, a*, and b* (lightness, red/green, and blue/yellow) tooth-type characteristics were used to measure color, and the associated color differences (DE) between the groups were computed. One-way ANOVA (a $<$ 0.05) and the paired $t$ -test were used to evaluate any changes in these color characteristics.

RESULTS:

Fixed orthodontic treatment is associated with changes in colour parameters. L* values decreased ( $P<$ 0.001), while a* and b* values increased ( $P<$ 0.001) at the end of treatment. All measured tooth types showed significant colour change (DE); their mean differences ranged from 1.64 to 2.96 DE units.

CONCLUSIONS:

Fixed orthodontics can change the natural colour of teeth. The CIE colour parameters L*, a*, and b* of natural teeth showed statistically significant differences after debonding the orthodontic appliances. The L* values decreased making the teeth look darker. The adolescent and male patients had more tooth colour changes than the adult and female groups.

Keywords

Fixed appliance orthodontic treatment colour changes in enamel spectrophotometer CIE

1. Introduction

Any manipulation of the surface of natural teeth may result in a variation of their colour. The fixed orthodontic treatment (FOT) is one such procedure which alters the enamel during the procedure. The motive of orthodontic treatment is not only to align the teeth and establish a proper functional occlusion but also to produce a pleasing smile [1]. Orthodontic patients or orthodontists may come across unusual alterations on the surface of enamel, i.e. micro-cracks, fractures, abrasions, and white spots that occur during and after FOT [2, 3, 4]. These negative effects of FOT on enamel have been completely revised. However, the incidence of colour change due to orthodontic bonding has not been extensively studied. There are only a few in vitro studies evaluating the colour changes of tooth enamel during bracket attachment and removal [2, 5, 6, 7, 8]. The results of these studies suggest that some changes in tooth colour are inevitable, but these in vitro tests may not reliably reflect the clinical situation [5]. The in vitro studies mainly depend on the instruments used and their maintenance. These instruments should be maintained properly for better results [9, 10, 11, 12]. Spectrophotometers are one of the advanced instruments used in dentistry for colour assessment and shade matching.

Numerous factors within the oral cavity affect tooth color determination, including ambient illumination, light scattering by surrounding periodontal and gingival tissues [13, 14, 15, 16, 17], and saliva flow rate at rest, which influences tooth hydration [18] as well as the underlying surface’s reflective index. The finished FOT case’s colour aesthetics is very important for visual evaluation [1]. The way light interacts with the enamel surface as seen by the human eye determines the color of teeth [6]. The noticeable alteration in enamel surface color will have an impact on patient satisfaction and clinical efficacy. Both visual inspection and quantitative measurements can be used to evaluate the color characteristics of human teeth [13, 18, 19]. Although it is still the most used technique in dentistry, visual determination – comparing the tooth’s color to a guide – is thought to be quite subjective [13, 18, 19, 20, 21]. However, a variety of factors can impact the consistency of selection and characterization, including age, experience, human eye tiredness, and the intrinsic limits of current color charts. Color descriptions in pictures [19, 22, 23, 24]. Instrument measuring devices are now an additional visual assessment of tooth color due to the widespread requirement for precise color matching in dentistry and the quick advancements in optoelectronic sensors and computer technology [24, 25, 26, 27, 28, 29]. The objective color number is now determined in research and clinical settings using a wide variety of commercial devices, such as spectrophotometers, digital color analyzers, and tristimulus colorimeters [26].

A spectrophotometer was used in our investigation. Accurate color measuring is possible with this equipment [24]. The three color characteristics used to determine color ratings are lightness (L), red/green hue (a), and yellow/blue hue (b). These parameters are based on the Commission Internatinale de l’Eclairage. This technique is the most widely used color measurement system because it gives digital data that is closely linked to the actual visual reaction. The colour space diagram produced by CIELAB can be used to describe this system. The quantitative relationships between colours on three axes are represented by the CIELAB colour system, often known as CIE L* a* b*: The chroma coordinates are a* and b*, while the brightness is represented by the L* value. L* is shown on the vertical axis of a color space diagram, with values ranging from 0 (black) to 100 (white). The red-green component of a color is represented by the a* value, where the red and green values are denoted by the values a* (positive) and Àa* (negative), respectively. Plotting the blue and yellow components as b* (negative) and b* (positive) values, respectively, on the b* axis. The plane’s center is achromatic or neutral. The chroma (C*), or color saturation, is represented by the distance from the central axis [30, 31].

This prospective clinical study aimed to assess the color changes in teeth after fixed orthodontic treatment, compare the color changes between test and control groups, and use a spectrophotometer to ascertain the impact of age and gender on the color of enamel caused by FOT. The null hypothesis formulated that Commission Internationale de l’Eclairage (CIE) color criteria L*, a*, and b* (lightness, red/green, and blue/yellow) for natural teeth before and after orthodontic treatment would be the same.

2. Materials and methods

The prospective clinical study was conducted on 60 patients visiting the Department of Orthodontics and Dentofacial Orthopaedics, King Khalid University, College of Dentistry, Abha, Saudi Arabia. There were two groups of patients:

The test group had thirty patients [14 female and 16 males; age range, 13–26 years (adults over 17 and adolescents under 17)] who needed orthodontic treatment and consecutive 30 patients who did not need FOT with similar age and gender were included as an untreated control group. The sample size was decided based on the previous similar study conducted by Murat T. and Yeşim K., [32] where they assessed 25 patients in the study, we included 30 in the test and 30 in the control group.

Inclusion criteria

(1) without any previous orthodontic treatment; (2) required fixed orthodontic treatment; (3) permanent teeth; (4) mild or no dental crowding ( $<$ 4 mm); (5) absence of caries, decalcifications, or restored teeth under examination; (6) signed informed consent form by the patient or the parent to participate in this study.

Exclusion criteria

(1) mentally unfit; (2) tobacco chewing or smoking habits and drinking tea or coffee more than 3 cups; (3) history of trauma; (4) systemic diseases; (5) developmental disturbances; (6) attrition or abrasion.

The study was conducted after clearance from the Ethical Committee of the College of Dentistry, King Khalid University (SRC/ETH/2018-19/128). Informed consent was obtained from all patients or their guardians. The duration of treatment for all patients was 18 to 24 months.

Figure 1.

Flowchart of the study.

Figure 2.

Spectrophotometer-Vita Easyshade Advance used in study.

Patients’ data were recorded in an organized manner before and after orthodontic treatment, as shown in the flowchart (Fig. 1). For the visual examinations, each subject was assessed by a single, qualified researcher under similar lighting conditions. In the dentist’s practice, the same fluorescent bulb was used to standardize the timing of patient data recording to the morning. After using a fluoride-free paste to clean and polish every tooth, they were thoroughly washed with water. Teeth are kept wet to prevent discolouration from drying out. The tooth color was assessed both before and after treatment using a Vita Easyshade Compact spectrophotometer (Vita Zahnfabrik, Germany) (Fig. 2). This tool offers precise colour measurement. The lateral incisors, canines, and upper and lower central incisors were the teeth under investigation. Three separate Vita Easy color recordings were made for each tooth under study.

Figure 3.

Representative clinical image showing the use of the Spectrophotometer on the patient and its location on the tooth surface.

Each color parameter (L, a, and b) were recorded. The average value of three consecutive measurements for each tooth is used to determine the color of the tooth before and after treatment. The sterile tip of the intraoral device, or mouthpiece, is held perpendicular to each tooth’s buccal surface during the color measurement process. A uniform circular area is included in spectrophotometric colorimetry, and it is located in the middle third of each tooth’s buccal surface (Fig. 3). Before every session, the gadget was calibrated on the included whiteboard. The identical internal light at the probe tip of the gadget illuminates each tooth during the measurement. To prevent variations in the amount of light emanating from the internal light source, calibration is required. Cotton rollers and a saliva ejector were utilized to regulate moisture during the assessment. The designated tooth quadrants for traditional acid etching were etched for 15 seconds using 37% phosphoric acid (3M ESPE, Seefeld, Germany), followed by a 15-second water rinse and a dry, compressed air oil-free drying process. An extremely thin coating of paint from Transbond. Then, using Transbond XT glue (3M Unitek), metal orthodontic brackets (0.022 $\times$ 0.028 inch, Roth Systems; GAC International, Bohemia, NY, USA) were affixed. As directed by the manufacturer, the excess resin was scraped off and the bracket was cured for 10 seconds per tooth using a curing lamp (Biolux, CFON 1163; BIO-ART Dental Equipment, Sao Carlos, Brazil). Every patient receiving orthodontic treatment must practice good oral hygiene. During therapy, avoid using mouthwash containing chlorhexidine to avoid discoloration and yellowing of teeth. The fixed orthodontic appliances will be taken out and any leftover adhesive will be cleaned up after orthodontic therapy is finished. The same operator (M) visually evaluated the extent of resin removal. After polishing the teeth using a paste devoid of fluoride, they are thoroughly cleaned with water. Using the difference in L, a, and b values before and after orthodontic treatment, the color difference (DE) of each group was computed using the following formula:

DE is equal to $[(L1-L2)^{2}+(a1-a2)^{2}+(b1-b2)^{2}]^{1/2}$

Before and after therapy are indicated by the subscript letters 1 and 2, respectively. Three individuals were removed from the trial due to poor oral hygiene and gingival hypertrophy linked to the development of white spot lesions. Five patients in the control group did not show up. As a result, the study sample was reduced to 52 patients (27 cases and 25 controls). Before therapy, the patients’ ages ranged from 13 to 26 years old, with an average age of 18 years and 7 months. They are separated into two categories: adults (over 17) and adolescents (less than 17). The evaluation was done on canines, lateral and central incisors of the maxilla and mandible. Three weeks before the commencement of the study, the evaluation was conducted to guarantee the consistency of color measurements among examiners. Twenty-seven patients were chosen randomly after the corrective period, and the same practitioner reexamined them one week later (before to beginning orthodontic treatment).

Statistical analysis

The statistical analysis was carried out utilizing SPSS software version 17.0) (SPSS Inc., Chicago, IL, USA). Descriptive statistics, such as mean and standard deviation, were computed for every variable. To find variations in every tooth color characteristic before and after treatment, a paired $t$ -test was employed. To assess the difference in tooth color between age groups and between sexes, independent $t$ -tests were employed. Groupwise comparison was done using one-way ANOVA. $P<$ 0.05, was considered significant.

3. Results

Table 1
Descriptive statistics of test and control group

	$N$	Minimum	Maximum	Mean	Std. deviation
Test group
l1	27	83.37	86.68	85.18	0.72
l2	27	80.17	83.93	82.22	1.01
l1_l2	27	$-$ 5.25	$-$ 0.73	$-$ 2.96	0.89
a1	27	0.58	1.39	0.86	0.22
a2	27	1.64	4.12	2.51	0.96
a1_a2	27	0.38	3.44	1.65	0.99
b1	27	25.90	28.07	27.59	0.54
b2	27	28.46	32.18	29.70	1.18
b1_b2	27	0.76	4.87	2.11	1.23
DE	27	1.08	28.01	9.54	6.59
Control group
l1	25	82.00	86.68	84.73	1.10
l2	25	82.00	85.89	84.56	1.04
l1_l2	25	$-$ 1.38	0.89	$-$ 0.17	0.64
a1	25	0.58	1.57	0.90	0.28
a2	25	0.66	2.15	0.99	0.34
a1_a2	25	$-$ 0.53	0.78	0.09	0.23
b1	25	26.40	28.60	27.74	0.46
b2	25	26.52	28.71	27.75	0.50
b1_b2	25	$-$ 1.08	0.27	0.02	0.24
DE	25	0.00	1.03	0.27	0.31

Table 2

Paired sample $t$ -test for control and test group

Paired samples $t$ -test for control group
	Paired differences					$t$	df	Sig. (2-tailed)
	Mean	Std. deviation	Std. error mea	95% confidence interval of the difference
				Lower	Upper
l1–l2	0.17	0.64	0.13	$-$ 0.09	0.44	1.36	24.00	0.19
a1–a2	$-$ 0.09	0.23	0.05	$-$ 0.18	0.00	$-$ 2.03	24.00	0.05
b1–b2	$-$ 0.02	0.24	0.05	$-$ 0.12	0.08	$-$ 0.33	24.00	0.74
Paired samples $t$ -test for test group
	Paired differences					$t$	df	Sig. (2-tailed)
	Mean	Std. deviation	Std. error mea	95% confidence interval of the difference
				Lower	Upper
l1–l2	2.96	0.89	0.17	2.61	3.31	17.21	26.00	0.00^*
a1–a2	$-$ 1.65	0.99	0.19	$-$ 2.04	$-$ 1.26	$-$ 8.67	26.00	0.00^*
b1–b2	$-$ 2.11	1.23	0.24	$-$ 2.59	$-$ 1.62	$-$ 8.89	26.00	0.00^*

^*p< 0.05-significant.

Table 3

One-way ANOVA for test and control group

	DE	Sum of squares	df	Mean square	$F$	Sig.
Test group	Between groups	858.68	3	286.227	24.258	0^*
	Within group	271.381	23	11.799
	Total	1130.061	26
Control group	Between groups	0.841	3	0.28	3.951	0.022
	Within group	1.491	21	0.071
	Total	2.332	24

^*p< 0.05-significant.

Figure 4.

Graph showing the mean L, a, b for Pre and Post-treatment and colour differences (DE) for test and control group.

Figure 5.

Graph showing the mean L, a, b for Pre and Post-treatment and colour differences (DE) based on gender for the test and control group.

Figure 6.

Graph showing the mean L, a, b for Pre and Post-treatment and colour differences (DE) based on age for test and control group.

The duration of treatment for patients was 18 to 24 months. Treatment time was not recorded as a statistical assessment variable because there was no discernible difference in treatment duration across patients. The L*, a*, and b* color parameters had mean pretreatment values of 85.18 $\pm$ 0.72, 0.85 $\pm$ 0.22, and 27.59 $\pm$ 0.53 respectively. The L*, a*, and b* color parameters had mean post-treatment values of 82.2 $\pm$ 1.01, 2.50 $\pm$ 0.96, and 29.69 $\pm$ 1.18, respectively (Table 1). The color parameters revealed statistically significant alterations following orthodontic treatment when comparing the pre-and post-treatment data (Tables 2 and 3). The mean a* and b* values increased by 1.64 and 2.1 units, respectively, whereas the mean L* value decreased by 2.98 units ( $P<$ 0.001). The color parameters L*, a*, and b* had mean pretreatment values of 84.73 $\pm$ 1.10, 0.89 $\pm$ 0.27, and 27.73 $\pm$ 0.46 in the control group, respectively. The color parameters L, a, and b had mean post-treatment values of 84.55 $\pm$ 1.04, 0.98 $\pm$ 0.33, and 27.75 $\pm$ 0.50, in that order (Fig. 4). The mean a* and b* values increased by 0.9 and 0.2 units, respectively, but the mean L* value declined by 0.18 units ( $P<$ 0.001). There was no statistical significance in these findings. There was a notable variation in color between the case and control groups (cases 9.53 $\pm$ 6.5, controls 0.26 $\pm$ 0.31). Following fixed orthodontic treatment, significant color changes were observed in all examined teeth. Every variation in tooth color was measured. Comparing men and women, mean L* values decreased by 3.18 and 2.62 units, and mean a* and b* increased by 2.10, 0.97, 2.39, and 1.68 units, respectively. The mean tooth colour difference between male and female subjects was DE 7.45 $\pm$ 1.86 units and 2.32 $\pm$ 0.70 units, respectively. The results showed that tooth colour changes in male patients were statistically more pronounced than in female patients (Fig. 5). Comparing the age, youth, and adult groups, the mean L* values reduced by 3.49 and 2.46 units, respectively ( $P<$ 0.001), and the mean values of a* and b* increased by 2.33 and 2.46 units. The mean difference in tooth colour between adolescents and adults was DE 13.99 $\pm$ 6.70 and 5.39 $\pm$ 2.66 units. The results indicated that changes in tooth colour in adolescents were statistically more pronounced than in adults (Fig. 6).

4. Discussion

Focusing on the underlying scientific concepts of colour is crucial for aesthetic dentistry since it places multiple demands on the artistic ability of both the dentist and the technician. Incorporating proper colour enhances aesthetics and gives the restoration a more appealing, natural appearance. The relationship between changes in tooth colour and fixed orthodontic treatments remains challenging. Inadequate information is available regarding colour changes. Till recent times, the related studies conducted were not done on patients and had given controversial results. Few studies suggested that the procedure of bonding and debonding will not play a major role in the colour of teeth in bovine or human enamel [7, 8]. It is important to analyze the impact of FOT on changes in enamel colour. Owing to the absence of stimulation in the oral cavity, in vitro study results are typically cautiously interpreted. The main advantage that in vivo studies have over in vitro research is that the former are more appropriate for examining the study’s overall effects. The present study examined the impact of FOT on tooth color by contrasting it with a control group. Consequently, the outcomes unequivocally show how varied the color changes of natural teeth can be following extensive orthodontic treatment with fixed therapy. CIE color parameters L*, a*, and b* of natural teeth showed statistically significant alterations when orthodontic appliances were removed, rejecting the null hypothesis.

When compared to the control group, there were statistically significant changes in the study’s observations on color parameters following fixed orthodontic treatment. In the experimental group, the average L* value declined by 0.18 and the average values of a* and b* grew by 1.64 and 2.10, respectively, whereas the average L* value decreased by 2.98 units. expanded by 0.2 and 0.9 units. These findings are in line with those of other researchers who have noted an increase in a* and b* values and a drop in L* values. These findings demonstrate that in clinically noticeable color changes, teeth typically get darker and more reddish-yellowish [5, 6, 17, 31, 33].

According to Paul et al., a change in L* value of less than 2.0 units was deemed non-clinically noticeable and clinically acceptable [8]. Due to the teeth becoming darker in our study, the L* value was over this threshold and clinically relevant; nevertheless, in the control group, the L* value was well-accepted clinically. A clinically noticeable difference is visible above the usual value of the clinical detection limit of color comparison, which has been set at 3.7 units of color change [31, 34]. The color of tooth enamel may vary as a result of fixed orthodontic treatment for several etiological reasons. The surface roughness and structural makeup of dental enamel may be impacted by several variables. A change in tooth color can be caused by various factors, including enamel surface roughness. The teeth’s ability to disperse light may be impacted by this roughness [35, 36]. Enamel surface roughness can be caused by debonding methods or adhesive removal operations [31, 36], or by etching the enamel because acid dissolves the enamel prism [37]. The irreversible penetration of adhesive resin, which can reach 30 to 50 mm into tooth enamel, is another factor that might cause discoloration [35]. The light-scattering components may be impacted by this penetration, which can alter dental enamel’s refractive index. As previously mentioned [38], parameter L* is mostly impacted by this phenomenon. Furthermore, the colour of dental enamel may be impacted by the discolouration of these plastic labels [5]. Food stains may adhere to the surface or orthodontic appliances may corrode, causing discolouration [39, 40]. According to reports, these sites influence how the b parameter changes in the yellow direction [40].

Then, considering the length of the treatment – another crucial consideration – might make more sense. The length of the treatment ranged between 18 and 24 months in our study, and it was not taken into account as a variable in the analysis. This suggests that more investigation is required to look at the effects of treatment duration and tooth color evaluation following bond removal during the retention period. Because the resin is still present and will become increasingly discolored.

According to this study, male patients experience a 7.45 $\pm$ 1.86 and 2.32 $\pm$ 0.70 unit tendency to change the color of their teeth after receiving fixed orthodontic treatment, respectively. However, as females often practice better oral hygiene than males do and are consequently more prone to dental alterations, this gender difference may be attributed to variations in eating habits or oral hygiene quality between male and female patients. Vibrance. Furthermore, it has been noted that male patients exhibit a greater tendency than female patients to have tooth enamel demineralization; this finding may be partially attributed to oral hygiene practices and enamel infiltration, as well as the likelihood of discoloration and demineralization in male patients relative to female patients [41, 42].

After receiving fixed orthodontic treatment, this study revealed that adolescents tended to experience greater color changes than adults, with DE values of 13.99 $\pm$ 6.70 units and 5.39 $\pm$ 2.66 units, respectively. This can be explained by the fact that young patients’ enamel is more porous, and their teeth are more vulnerable to acid assault than those of adults [43, 44].

Limitations of the study included the small sample size. Also, due consideration should be given to the other habits of patients as only smoking and the number of tea and coffee consumed daily were included in the study, other habits like the use of the type of toothpaste and frequency of brushing, treatment with bleaching agents and presence of endogenous tooth discolouration should also be considered. It is recommended that in a future study with a large sample size an investigation into the impact of different treatment phases on tooth color, should be conducted. In addition, different techniques of bonding and debonding should be assessed and a longer period of follow-up is recommended.

5. Conclusion

The fixed orthodontic treatment is related to considerable changes in tooth colour. A spectrophotometer is a beneficial device to assess the colour change following the orthodontic treatment. There was a significant colour change after fixed orthodontic treatment and more pronounced in males. Following fixed orthodontic treatment, adolescents displayed more color changes than adults. This outcome could be the result of bonding, abrasion, and cleaning operations. Leaving persistent iatrogenic effects on tooth enamel. The leftover adhesive that is discoloured externally, alterations brought about by orthodontic tooth movement in the teeth and pulp tissue.

Footnotes

Acknowledgments

The authors extend their appreciation to the Deanship of Research and Graduate Studies at King Khalid University for funding this work under grant through Small group Research number RGP1/298/45.

Conflict of interest

None to report.

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Assessment of changes in enamel colour following fixed orthodontic therapy using an advanced spectrophotometer: An in vivo study

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSIONS:

Keywords

1. Introduction

2. Materials and methods

Inclusion criteria

Exclusion criteria

Statistical analysis

Table 1 Descriptive statistics of test and control group

5. Conclusion

Footnotes

Acknowledgments

Conflict of interest

References

Table 1
Descriptive statistics of test and control group