Abstract
Aim:
The aim of the present study is to compare the gingival melanin repigmentation after diode laser application and surgical removal done by scraping with Kirkland knife.
Materials and Methods:
This study was a randomized split-mouth study where 10 patients presenting with unattractive, diffuse, dark brown to black gingival discoloration on the facial aspect of the maxillary gingiva were treated by diode laser application and surgical removal and followed up for 3-, 6-, and 9-month intervals.
Results:
The results showed a statistically significant difference in repigmentation between the groups at the interval of 3 months (P = 0.040), but the difference was statistically not significant at 6 months (P = 0.118) and 9 months (P = 0.146). On surgically treated sites, all cases showed repigmentation of the gingiva, but in laser treated, there were two individuals which did not show repigmentation of the gingiva even at the end of 9-month observation time.
Conclusion:
The incidence of repigmentation was slightly less in laser-treated sites as compared to surgical depigmentation although the difference was statistically significant only up to 3 months.
Key words: Diode laser, gingival pigmentation, melanin, repigmentation, surgical removal
INTRODUCTION
Gingival melanin pigmentation is a physiologic condition which does not present any medical problem, but clinicians are often faced with a challenge of achieving gingival esthetics in such cases. Different treatment modalities have shown varying results, and the repigmentation also has been documented to occur. Laser ablation for gingival depigmentation has been recognized as one of the most effective, pleasant, and reliable techniques.
The aim of the present study was to compare the gingival melanin repigmentation after diode laser application and surgical removal with Kirkland knife. In pursuit of achieving this aim, we assessed changes in area of pigmented surface of gingiva, duration of reappearance, and gingival melanin repigmentation postoperatively after 3, 6, and 9 months.
MATERIALS AND METHODS
Ten periodontally healthy controls, aged 18–30 years, having excessive melanin pigmentation of gingiva were selected. The individuals with full complement of teeth, bilateral maxillary facial gingival pigmentation, clinically healthy gingiva, and systemically healthy controls were selected. Pregnant and lactating women, smokers, cases with systemic diseases that have effect on the color of the gingiva, for example, Addison's disease and Peutz–Jeghers syndrome are excluded from the study.
Materials
Surgical instruments [Figure 1] used were mouth mirror, tweezer, surgical gloves, disposable mouth mask, disposable syringes, cotton swabs, sterile gauze pieces, kidney tray, normal saline, suction tip, Kirkland knife [Figure 2], and laser unit [Figure 3] used were laser Console, fiber optic tips, tip initiator kit, surgical handpiece, fiber optic cable of diameter 400 μm, footswitch, AAA batteries (2 packs) for footswitch, protective eye wears, DC power supply, and power cord. Local infiltration employed was local anesthetic solution lignocaine hydrochloride 2% with adrenaline (1:200,000) and periodontal dressing: Coe-pack [Figure 1].
Figure 1.
Armamentarium
Figure 2.
Kirkland knife
Figure 3.
Diode laser unit
Methods
After phase I, periodontal therapy that is scaling was performed with patient education motivation; maxillary arch was randomly divided (as randomized split-mouth design used) into two treatment groups for gingival depigmentation:
Group I: Depigmentation was performed with surgical method (Kirkland knife)
Group II: Depigmentation was performed with diode laser (940 nm).
Presurgical procedures
Preoperative assessment of gingival pigmentation was done by using Dummett oral pigmentation index (DOPI).[1] Distribution of melanin pigmentation in gingiva was recorded in relation to each gingival unit in the maxillary arch of 10 patients (20 quadrants) [Figure 4a and b].
Figure 4.
(a) Preoperative view Group I; (b) Preoperative view Group II
The criteria are as follows:
0 = Pink tissue (no clinical pigmentation)
1 = Mild, light brown tissue (mild clinical pigmentation)
2 = Medium brown or mixed pink or brown tissue (moderate clinical pigmentation)
3 = Deep brown or blue/black tissue (heavy clinical pigmentation).
Surgical procedure
Before operation, the area was dried with sterile cotton. After that, local infiltration anesthesia using 2% lignocaine hydrochloride was administered. The pigmented gingival areas in randomly selected maxillary arch quadrant were scrapped with Kirkland knife [Figure 5a]. All the visible pigmentation was removed exposing underlying connective tissue. Bleeding was controlled by pressure pack with sterile gauze. After the bleeding was stopped, the surgical area was covered with Coe-pack periodontal dressing.
Figure 5.
(a) Surgical procedure; (b) Diode laser application
Laser procedure:
After administration of local infiltration anesthesia, melanin-pigmented gingiva was ablated by gallium aluminum arsenide diode laser device (EPIC™) with a wavelength of 940 nm at 1 W power [Figure 5b]. The semiconductor diode laser was emitted in a continuous wave mode and was operated in a contact method using a flexible fiber optic delivery system of diameter 400 μm. The delivery of laser light was controlled manually with the help of a footswitch. The fiber optic tip was used in a gentle brush stroke over the hyperpigmented area. Remnants of the ablated tissue were removed using sterile gauze dampened with saline. The procedure was performed from a cervicoapical direction in all the pigmented areas in the quadrant. Coe-pack, periodontal dressing was placed following the procedure.
Postoperative assessment
Patients were recalled at the 7th day postoperatively to observe healing. Observations for clinical reappearance of melanin pigmentation and its intensity was recorded on completion of 3, 6, and 9 months postoperatively again with the help of DOPI index [Figure 6a and b, 7a and b and 8a and b.
Figure 6.
(a) Group I after 3 months; (b) Group II after 3 months
Figure 7.
(a) Group I after 6 months; (b) Group II after 6 months
Figure 8.
(a) Group I after 9 months; (b) Group II after 9 months
The data thus obtained were tabulated and analyzed statistically as shown from Tables 1–7 and Graphs 1–4.
Table 1.
Mean pigmentation scores of all the individuals at different time intervals in Group I (surgically treated)
Table 7.
Comparative analysis of gingival repigmentation at different time intervals between the groups (N par tests: Mann-Whitney test)
Graph 1.
Mean pigmentation scores of all the individuals at different time intervals in Group I (surgically treated). Preop: Preoperative, mths: Months
Graph 4.
Mean change in gingival repigmentation and standard deviation at different time intervals within Group I and Group II
RESULTS
The continuous data recorded were written in the form of its mean and standard deviation (SD). As data were skewed, Mann–Whitney U-test was used for statistical analysis of the two groups. For comparison of time-related variables, Wilcoxon signed-rank test was used. All the statistical tests were two-sided and were performed at a significance level of α = 0.05 (i.e., P ≥ 0.05 – not significant; P < 0.05 – significant; P < 0.001 – highly significant). Analysis was conducted using SPSS Statistics (Statistical package for the social sciences, version 20.0, for windows OS).
Tables 1 and 2 with Graphs 1 and 2 depict DOPI scores of all the individuals recorded preoperatively and then at the intervals of 3, 6 and 9 months postoperatively which were seen to range from 1.13 to 3.00, 0.25 to 0.37, 0.25 to 1.75, and 0.25 to 1.75, respectively, in Group I and 1.13 to 2.87, 0.00 to 0.87, 0.00 to 1.50, and 0.00 to 1.50, respectively, in Group II with baseline of 0.00 for both the groups.
Table 2.
Mean pigmentation scores of all the individuals at different time intervals in Group II (laser treated)
Graph 2.
Mean pigmentation scores of all the individuals at different time intervals in Group II (laser treated). Preop: Preoperative, mths: Months
Table 3 and Graph 3 depicts the mean gingival repigmentation scores and SD at different time intervals in both the groups. The mean and SD values preoperatively, at baseline and at 3, 6, and 9 months was 1.84 ± 0.586, 0.000 ± 0.000, 0.474 ± 0.342, 0.574 ± 0.443, and 0.648 ± 0.457, respectively, in Group I and 1.76 ± 0.622, 0.000 ± 0.000, 0.251 ± 0.287, 0.389 ± 0.465, and 0.451 ± 0.450, respectively, in Group II.
Table 3.
Mean gingival pigmentation scores and standard deviation at different time intervals in both groups
Graph 3.
Mean gingival pigmentation scores and standard deviation at different time intervals in both groups. Preop: Preoperative, mths: Months
Table 4 and Graph 4 show mean change in gingival repigmentation at different time intervals within groups. The mean change and SD from baseline to 3 months was 0.474 ± 0.342 and 0.251 ± 0.287; from baseline to 6 months was 0.574 ± 0.443 and 0.389 ± 0.465; from baseline to 9 months was 0.648 ± 0.457 and 0.451 ± 0.450, respectively, for Group I and II. These values show that there was repigmentation of gingiva at 3, 6, and 9 months after therapy in both the groups. The mean change and SD from 3 to 6 months was 0.100 ± 0.131 and 0.138 ± 0.233; from 3 to 9 months was 0.174 ± 0.158 and 0.200 ± 0.232; from 6 to 9 months was 0.070 ± 0.104 and 0.060 ± 0.090, respectively, for Group I and II. These values show that there was repigmentation of gingiva between each time interval between both the groups.
Table 4.
Mean change in gingival repigmentation and standard deviation at different time intervals within Group I and Group II
Wilcoxon signed-rank test was performed for comparative analysis of mean change in gingival repigmentation at different time intervals within the groups, presented in Table 5. Group I showed statistically highly significant change in gingival repigmentation from baseline to 3 months (P = 0.005), baseline to 6 months (P = 0.005), and baseline to 9 months (P = 0.005) but statistically significant from 3 to 6 months (P = 0.042) and 3–9 months (P = 0.011) whereas the results were statistically not significant from 6 to 9 months (P = 0.068). Group II shows statistically significant change in gingival pigmentation from baseline to 3 months (P = 0.017), baseline to 6 months (P = 0.011), baseline to 9 months (P = 0.011), and 3–9 months (P = 0.027) whereas the results were statistically not significant from 3 to 6 months (P = 0.068) and 6–9 months (P = 0.059).
Table 5.
Comparative analysis of mean change in gingival repigmentation at different time intervals within the groups (Wilcoxon signed ranks test)
Table 6 shows comparative analysis of mean change in gingival repigmentation at different time intervals between the groups. The change in pigmentation was statistically significant between the groups of baseline to 3 months (P = 0.040) whereas it was statistically not significant from baseline to 6 months (P = 0.118) and baseline to 9 months (P = 0.146). Furthermore, the comparison of mean change in pigmentation between the groups was statistically not significant from 3 to 6 months (P = 0.901), 3–9 months (P = 0.817), and 6–9 months (P = 0.830).
Table 6.
Comparative analysis of mean change in gingival repigmentation at different time intervals between the groups
Mann–Whitney U-test was performed for comparative analysis of gingival repigmentation at different time intervals between the groups as shown in Table 7. The results showed a statistically significant difference in repigmentation between the groups at the interval of 3 months (P = 0.040), but the difference was statistically not significant at 6 months (P = 0.118) and 9 months (P = 0.146).
DISCUSSION
Gingival hyperpigmentation is a major concern for a large number of patients and many a times forces the patient to seek cosmetic treatment.[2] Attempts have been made in the past to remove this pigmentation by different procedures such as gingivectomy, scalpel surgical technique, electrosurgery, and cryosurgery with variable results regarding the reappearance of pigmentation.[3,4,5]
A patchy repigmentation was observed at the end of 3 months in Group I and II which was in accordance with the study done by Singh V et al., (2012) in which they reported partial recurrence of gingival pigmentation in six out of eight patients after gingivectomy at 1- and 4-month interval.[6] Grover et al. noted repigmentation after 3 months in 20 individuals and found more repigmentation with scalpel technique as compared to diode laser application.[7] Bergamaschi et al. stated that permanent results cannot be offered when gingival depigmentation procedures are performed for cosmetic reasons.[8] These results are in contradiction with some studies in which repigmentation was found to be absent after 3 months.[9,10] Similarly, 6 months after the treatment, a gradual increase in mean pigmentation score was observed, but the intensity of repigmentation was very mild as compared to the preoperative intensity. These results partially comply with the study done by Bhardwaj et al. in which both techniques were used over 7 patients at 20 sites in anterior maxillary and mandibular gingiva. After 6 months of follow up, repigmentation was found in one of the knife-treated sites, but no reoccurrence was found in diode laser-treated sites.[11] However, repigmentation after 6 months was also found to be completely absent in some studies.[3,12,13]
At the end of 9-month study period, the repigmentation was observed in all the cases in Group I, but in Group II, two cases did not show any repigmentation. These results show that although the pigmentation did reappear at the end of 9 months, it was still significantly less than the preoperative observations in both the groups. It was seen as very small spots, dots, or streaks of very mild intensity as compared to dark continuous bands of heavy or moderate intensity preoperatively. These results are in accordance with the study done by Kaur et al. on twenty patients treated for gingival hyperpigmentation (surgical removal). After 9 months of follow-up period, repigmentation was observed in 75% of the cases. About 5 cases showed no repigmentation in any of the segments.[4] Gupta et al. evaluated the effect of surgical scraping and electrosurgery in 15 patients for reoccurrence of pigmentation of gingiva. After 9-month follow-up period, repigmentation was observed in 7 cases. The reoccurrence of gingival pigmentation was more on surgically treated sites.[2] However, these results are in contradiction with the studies who reported the absence of repigmentation even after 9 months of follow-up.[14,15,16,17] Furthermore, some authors have reported pigmentation to remain absent for longer than 9 months, for instance, Perlmutter and Tal reported the case of one patient in whom gingival repigmentation occurred 7 years after removal of gingival tissues.[5]
There may be various reasons for the repigmentation in the present study. The most important may be the migration and activity of melanocytic cells from the surrounding areas. Active melanocytes from adjacent pigmented tissues migrate to the treated areas, causing reoccurrence of pigmentation.[12,18,19] Melanocytes have a reproductive self-maintaining system of cells.[20] Another reason may be the melanocytes which are left during surgery. These may become activated and start synthesizing melanin. Ginwalla et al. also attributed the repigmentation to the left out melanocytes.[21]
When the two groups were compared, the mean repigmentation score was less in the diode laser group at all time intervals although the difference was statistically significant at 3 months only (P = 0.040) [Table 7]. These findings show that the repigmentation was lesser in cases treated with laser as compared to knife-treated sites up to 3 months of interval, but at 6 and 9 months, the results were statistically comparable. These results are in accordance with the studies who also reported the reoccurrence of pigmentation with both the treatment modalities.[6,7,10,22,23] On an average, the epithelium of vestibular gingiva is 0.30 ± 0.07 mm thick, and the required depth of epithelial dissection for treating gingival pigmentation must be more than 0.31 mm deep.[24,25] Therefore, as per the results of our study, the use of Kirkland knife for gingival depigmentation might not have been able to completely eliminate cells from the basal cell layer that contribute to melanin reappearance, while laser, which has been seen to penetrate up to 0.50 mm, may have penetrated to the required depth for better removal of melanin pigmentation in comparison to surgical method.[26] However, at 6 and 9 months, the two treatment modalities showed comparable results with respect to reappearance of pigmentation which indicates that the melanocytes may have repopulated the treated sites from adjacent tissues. Soliman et al. discussed the use of soft-tissue diode laser in the treatment of oral hyperpigmentation and found that some underlying melanocytes were not sufficiently affected by the heat to be destroyed which causes repopulation of melanocytes at treated areas causing repigmentation of gingiva.[27] Furthermore, Azzeh et al. stated that because of the presence of rete pegs in oral epithelium, ablation of the epithelium at the same level may not remove all melanocytes which repopulate the treated area and cause repigmentation.[28]
Gingival hyperpigmentation is seen as a genetic trait in some populations and is more appropriately termed physiologic or racial gingival pigmentation. It has also been suggested that although pigmentation under normal conditions is genetically determined, its particular distribution in the mouth may be the result of secondary influences and perhaps environmental factors. High levels of oral melanin pigmentation are normally observed in individuals of African, East-Asian, or Hispanic ethnicity.[4] In the present study, most of the patient's facial complexion was dark or wheatish or brown. Various authors have stated that the color of the gingiva is comparable to the facial complexion, due to the activity of melanocytes present.[29,30,31,32,33] Physiologic pigmentation is probably genetically determined, but, as suggested by Dummett, the degree of pigmentation is partially related to mechanical, chemical, and physical stimulation.[30] Kaur et al. observed that all (100%) the 3 patients with dark complexion had repigmentation, whereas 12 (85.71%) out of 14 wheatish- or brown-complexioned patients had repigmentation after surgery except 3 fair-complexioned patients.[4] Ponnaiyan et al. observed that dark-skinned individuals had heavy gingival pigmentation whereas fair-skinned individuals had mild pigmentation.[32] These statements may be employed to the above findings even for repigmentation cases with different facial complexions and the possible reason may be the rate of melanogenesis, which is genetically maintained and higher in dark-complexioned patients as compared to light-complexioned cases.[34] This relationship of duration and intensity of repigmentation with the complexion of person or race must be taken into consideration while comparing the results of various studies done in different races. Although the results of this study are encouraging even with small sample size and short-term study period, further research with longer period of clinical observations, along with histological studies to observe the causes of repigmentation are needed. Furthermore, research should focus on finding a solution for preventing recurrence that necessitates repeated depigmentation to eliminate the unsightly pigmented gingiva.
CONCLUSION
The repigmentation was found to be less in diode laser-treated sites (up to 3 months) as compared to Kirkland knife-treated sites. Both the procedures did not result in any postoperative complication and the gingiva healed uneventfully. Surgical method is recommended in consideration of being simple, easy to perform, and laser ablation for gingival depigmentation has been recognized as one of the most effective, pleasant and reliable techniques that offers bloodless, painless, and sterile field with better patient compliance and satisfaction.
Financial support and sponsorship
This study was financially supported by Department of Periodontology, Guru Nanak Dev Dental College and Research Institute, Sunam, Punjab, India.
Conflicts of interest
There are no conflicts of interest.
REFERENCES
- 1.Dummett CO, Gupta OP. Estimating the epidemiology of oral pigmentation. J Natl Med Assoc. 1964;56:419–20. [PMC free article] [PubMed] [Google Scholar]
- 2.Gupta G, Kumar A, Khatri M, Puri K, Jain D, Bansal M, et al. Comparison of two different depigmentation techniques for treatment of hyperpigmented gingiva. J Indian Soc Periodontol. 2014;18:705–9. doi: 10.4103/0972-124X.147404. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Almas K, Sadig W. Surgical treatment of melanin-pigmented gingiva; An esthetic approach. Indian J Dent Res. 2002;13:70–3. [PubMed] [Google Scholar]
- 4.Kaur H, Jain S, Sharma RL. Duration of reappearance of gingival melanin pigmentation after surgical removal – A clinical study. J Indian Soc Periodontol. 2010;14:101–5. doi: 10.4103/0972-124X.70828. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5.Perlmutter S, Tal H. Repigmentation of the gingiva following surgical injury. J Periodontol. 1986;57:48–50. doi: 10.1902/jop.1986.57.1.48. [DOI] [PubMed] [Google Scholar]
- 6.Singh V, Bhat S, Kumar S, Bhat M. Comparative evaluation of gingival depigmentation by diode laser and cryosurgery using tetrafluoroethane: 18-months follow-up. Clin Adv Periodontics. 2012;2:129–34. [Google Scholar]
- 7.Grover HS, Dadlani H, Bhardwaj A, Yadav A, Lal S. Evaluation of patient response and recurrence of pigmentation following gingival depigmentation using laser and scalpel technique: A clinical study. J Indian Soc Periodontol. 2014;18:586–92. doi: 10.4103/0972-124X.142450. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 8.Bergamaschi O, Kon S, Doine AI, Ruben MP. Melanin repigmentation after gingivectomy: A 5-year clinical and transmission electron microscopic study in humans. Int J Periodontics Restorative Dent. 1993;13:85–92. [PubMed] [Google Scholar]
- 9.Tanuja P, Butchi BK, Krishna M. Laser-assisted crown lengthening and gingival depigmentation to enhance aesthetics - A case report. Ann Essen Dent. 2011;3:56–9. [Google Scholar]
- 10.Hegde MN, Hegde N, Bhat R. Gallium arsenide aluminium lasers in the value addition of smile. Sch J Med Case Rep. 2014;2:593–6. [Google Scholar]
- 11.Bhardwaj A, Uppoor AS, Naik DG. A comparative evaluation of management of melanin pigmented gingiva using a scalpel and laser. J Interdiscip Dent. 2014;4:135–9. [Google Scholar]
- 12.Tal H, Landsberg J, Kozlovsky A. Cryosurgical depigmentation of the gingiva. A case report. J Clin Periodontol. 1987;14:614–7. doi: 10.1111/j.1600-051x.1987.tb01525.x. [DOI] [PubMed] [Google Scholar]
- 13.Kathariya R, Pradeep AR. Split mouth de-epithelization techniques for gingival depigmentation: A case series and review of literature. J Indian Soc Periodontol. 2011;15:161–8. doi: 10.4103/0972-124X.84387. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 14.Roshna T, Nandakumar K. Anterior esthetic gingival depigmentation and crown lengthening: Report of a case. J Contemp Dent Pract. 2005;6:139–47. [PubMed] [Google Scholar]
- 15.Kumara Ajeya EG, Avinash JL, Rajiv NP, Galgali Sushama R. Split mouth gingival depigmentation using blade and diode laser – A case report. Ann Dent Res. 2011;1:91–5. [Google Scholar]
- 16.Gupta G. Management of gingival hyperpigmentation by semiconductor diode laser. J Cutan Aesthet Surg. 2011;4:208–10. doi: 10.4103/0974-2077.91256. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 17.Aggarwal A, Bala D, Arora S, Walia MS, Malhan S. Treatment of gingival hyperpigmentation with diode laser-An esthetic approach. Ind J Dent Sci. 2012;2:61–2. [Google Scholar]
- 18.Dummett CO, Bolden TE. Post surgical clinical repigmentation of the gingiva. Oral Surg Oral Med Oral Pathol. 1963;16:353–65. [Google Scholar]
- 19.Farnoosh AA. Treatment of gingival pigmentation and discoloration for esthetic purposes. Int J Periodontics Restorative Dent. 1990;10:312–9. [PubMed] [Google Scholar]
- 20.Hirobe T. Role of keratinocyte-derived factors involved in regulating the proliferation and differentiation of mammalian epidermal melanocytes. Pigment Cell Res. 2005;18:2–12. doi: 10.1111/j.1600-0749.2004.00198.x. [DOI] [PubMed] [Google Scholar]
- 21.Ginwalla TM, Gomes BC, Varma BR. Surgical removal of gingival pigmentation. (A preliminary study) J Indian Dent Assoc. 1966;38:147–50. [PubMed] [Google Scholar]
- 22.Anoop S, Abraham S, Ambili R, Mathew N. Comparative evaluation of gingival depigmentation using scalpel and diode laser with 1 year follow-up. Int J Laser Dent. 2012;2:87–91. [Google Scholar]
- 23.Doshi Y, Khandge N, Byakod G, Patil P. Management of gingival pigmentation with diode laser: Is it a predictive tool? Int J Laser Dent. 2012;2:29–32. [Google Scholar]
- 24.Schroeder HE. Differentiation of Human Oral Stratified Epithelia. Basel: Karger; 1981. pp. 33–156. [Google Scholar]
- 25.Lin YH, Tu YK, Lu CT, Chung WC, Huang CF, Huang MS, et al. Systematic review of treatment modalities for gingival depigmentation: A random-effects poisson regression analysis. J Esthet Restor Dent. 2014;26:162–78. doi: 10.1111/jerd.12087. [DOI] [PubMed] [Google Scholar]
- 26.Convissar RA. Principles and Practice of Laser Dentistry. St. Louis: Mosby; 2010. pp. 27–52. [Google Scholar]
- 27.Soliman MM, Al Thomali Y, Al Shammrani A, El Gazaerly H. The use of soft tissue diode laser in the treatment of oral hyper pigmentation. Int J Health Sci (Qassim) 2014;8:133–40. doi: 10.12816/0006079. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 28.Azzeh MM. Treatment of gingival hyperpigmentation by erbium-doped: Yttrium, aluminum, and garnet laser for esthetic purposes. J Periodontol. 2007;78:177–84. doi: 10.1902/jop.2007.060167. [DOI] [PubMed] [Google Scholar]
- 29.Oluwole D, Elizabeth D. Gingival tissue color related with facial skin and acrylic resin denture base color in a Nigerian population. Afr J Biomed Res. 2010;13:107–11. [Google Scholar]
- 30.Dummett CO. Physiologic pigmentation of the oral and cutaneous tissues in the Negro. J Dent Res. 1946;25:421–32. doi: 10.1177/00220345460250060201. [DOI] [PubMed] [Google Scholar]
- 31.Jones J, McFall WT., Jr A photometric study of the color of health gingiva. J Periodontol. 1977;48:21–6. doi: 10.1902/jop.1977.48.1.21. [DOI] [PubMed] [Google Scholar]
- 32.Ponnaiyan D, Jegadeesan V, Perumal G, Anusha A. Correlating skin color with gingival pigmentation patterns in South Indians – A cross sectional study. Oral Health Dent Manag. 2014;13:132–6. [PubMed] [Google Scholar]
- 33.Steigmann S. The relationship between physiologic pigmentation of the skin and oral mucosa in Yemenite Jews. Oral Surg Oral Med Oral Pathol. 1965;19:32–8. doi: 10.1016/0030-4220(65)90212-4. [DOI] [PubMed] [Google Scholar]
- 34.Billingham RE. Dendritic cells. J Anat. 1948;82:93–109. [PMC free article] [PubMed] [Google Scholar]
