|Year : 2020 | Volume
| Issue : 1 | Page : 9-16
Oral and general health status of battery factory workers in Amman, Jordan: Cases presentations and review
Faiez Najeeb Hattab
Visiting Professor, Essen, NRW, Germany
|Date of Submission||08-Dec-2018|
|Date of Acceptance||05-Feb-2020|
|Date of Web Publication||30-Apr-2020|
Dr. Faiez Najeeb Hattab
Visiting Professor, Gerhard-Stötzel, Str., 8, 45139 Essen, NRW
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background: Workers in industrial battery factories frequently exposed to a hazardous working environment that causes adverse effects on their oral and general health. Aim: The aim of this study is to highlight oral and general health status among battery workers exposed to sulfuric acid-lead fumes and mists in the production site. Cases of deteriorated oral health presented. Subjects and Methods: The sample consisted of 24 participants working in the production site and 15 in the nonproduction line matched in age and employment period, acts as controls. Structural questionnaires on oral and general histories had been completed by interviews. Clinical examinations were carried out to assess dental erosion, oral hygiene, periodontal status using the appropriate indices. The data were statistically analyzed. Results: Questionnaires of workers in the production line revealed that more than two-thirds (67%–86%) of the workers had complaints of teeth sensitivity, dry mouth and nose, disturbed sense of taste, burning/itching eyes, and abdominal distress. They exhibited significantly higher scores of dental erosion, poor oral hygiene, and gingivitis compared with the control group (P < 0.05). The general health of the control group was much better than the workers in the production line.Conclusions: The presented cases revealed that unprotected workers in hazardous battery workplace suffer of serious oral and general health problems. These points the need of implementation efficient monitoring and control of acid vapor emission in the workplace coupled with appropriate oral and general health education and care.
Keywords: Acidic workplace, battery workers, Jordan, oral and general health
|How to cite this article:|
Hattab FN. Oral and general health status of battery factory workers in Amman, Jordan: Cases presentations and review. J Interdiscip Dentistry 2020;10:9-16
|How to cite this URL:|
Hattab FN. Oral and general health status of battery factory workers in Amman, Jordan: Cases presentations and review. J Interdiscip Dentistry [serial online] 2020 [cited 2020 Sep 18];10:9-16. Available from: http://www.jidonline.com/text.asp?2020/10/1/9/283540
| Clinical Relevance to Interdisciplinary Dentistry|| |
This study documents that worker's exposed to industrial acid fumes suffer of deteriorated oral and general health status including dental erosion, periodontitis, teeth loss, poor oral hygiene, and hyposalivation. It is important for dental professionals to identify and quantify the worker's needs and plan oral health promotion and treatment for better oral function and an improved quality of life.
| Introduction|| |
Oral health is essential to general health and quality of life. In the workplace, workers may expose to chemical, physical, and biological agents that inflict serious adverse effects on their health and well-being. The oral cavity more frequently exposed to injurious agents than other body organs. One of these agents is the exposure to sulfuric acid-lead fumes and mists (vapor) in industrial battery factories. Car's batteries are composed of six galvanic cells where each cell contains lead (Pb) and lead dioxide (PbO2) plates. The lead plate attached to the negative terminal and lead dioxide plate attached to the positive terminal. The plates submerged in tanks contain electrolyte solution of a mixture of sulfuric acid (35%), water (65%), and charged electrically for several hours. This process referred to as “forming and charging.” The sulfuric ions in the acidic bath trigger a reaction with the lead plates producing hydrogen ions, lead sulfate (PbSO4), sulfur dioxide (SO2), and trioxide (SO3). Sulfur oxides react quickly with air moisture at room temperature producing a fine sulfuric acid-lead vapor. In an open processing system, the vapor frequently evolves in the workplace as it continuously discharges from open containers and may leak from old pipes. The vapor is invisible or cloudy, have a sharp penetrating odor, toxic by inhalation, and extremely corrosive. They are heavier than air, which can deposit in the respiratory airways. The inhalation and ingestion of lead particles generated during forming and charging process is a potent cumulative toxicant that affects virtually every organ in the human body.,
Studies in Western countries of occupational hazards have mainly directed toward the battery industry and to less extent on other acid industrials.,,, Surprisingly, few studies on oral health status of battery factory workers came from developing countries. One study seems available from Arab countries, Tanzania and recently, some from India,,,, with the paucity of data on the general health. Literature reviews of oral/dental status vary greatly among workers in different industrial locations and setup. Gamble et al., reported that almost all battery workers in African countries had dental erosion, whereas only 8%–31% of European, Korean, and Japanese workers exhibited erosion.“ Wiegand and Attin reviewed 18 articles on battery and galvanizing workers. They reported that the prevalence of dental erosion in acid-exposed workers varied greatly, amounting to 26%–100% compared to 0%–80% for controls. Inhalation of acidic vapor induces dental erosion that mostly confined to the labial surfaces of the anterior teeth,,,, while the posterior region shows high incidence of attrition.
Dental erosion defined as irreversible surface loss of dental hard tissues caused by the chemical acidic process where bacterial action is not involved. Etiology of the condition is multifactorial, caused by chronic exposure of teeth to acids from extrinsic and intrinsic sources with characteristic patterns and distribution of the lesions. In dental erosion, the amount of mineral dissolved from enamel depends on the type of acid (pH, the buffer effect, and dissociation constant) and the length of exposure time. Saliva has been considered the most important biological factor influencing dental erosion prevention due to its ability to act, directly on the erosive agent itself by diluting, clearing, neutralizing and buffering acids, play an important role in reducing the demineralization rate and enhance remineralization by providing calcium, phosphate, and fluoride to eroded enamel and dentin.
The aim of this report is to highlight oral and general status among battery factory workers in Amman city, Jordan. Cases of oral health deterioration in the workers exposed to long-term acid vapor are presented in [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]. No such cases seem been reported in the medical and dental literatures.
|Figure 1: Labial erosion of the maxillary incisors associated with cervical debris accumulation|
Click here to view
|Figure 3: (a) Generalized cervical discolored lesions with heavy debris deposits and notching of the maxillary central incisors and mandibular lateral incisors. Notching of the incisors caused by habitually cracking roasted and salted watermelon seeds. (b) Image shows the position of cracking watermelon seed nut|
Click here to view
|Figure 4: Teeth shows tenacious bluish.green stains deposited on carious lesions with accumulated debris|
Click here to view
|Figure 6: Severe deterioration of oral health in worker spent about 15 year's employment in the production line|
Click here to view
| Subjects and Methods|| |
The study group consisted of 24 participants working in production line (acid workers) and 15 controls working in office and packing services (nonproduction line); matched in age and employment period. Males have been employed in the production line. The worker's age ranged from 29 to 58 (mean 41.6 ± 10.1) years. The mean employment period was 11.3 ± 7.4 (±standard deviation) years. Structural questionnaires completed by interviews and clinical examinations been carried out in the workplace. Consents written/verbal were taken from workers and permission of visiting the workplace was obtained from the factory staff. Data on oral habits, dental and medical histories, symptoms of current health problems, oral hygiene practice, and dietary habits been recorded. Data were statistically analyzed using the Wilcoxon rank-sum test. The clinical oral examination consisted of the assessment of dental erosion, oral hygiene, and periodontal status. Diagnostic criteria and scoring were based on the following indices: Dental erosion index,, Simplified oral hygiene index (OHI-S), and Gingival index. The original OHI-S consisted of two separate components: Debris Index and Calculus Index. Each component allocated on a scale of 0–3 that described the amount of debris or calculus found on preselected tooth surfaces. Clinical examination was carried out under good artificial light using a plane mouth mirror, explorer # 23 (Shepherd's Hook), and periodontal probe. For convenience in this study, debris and calculus indices were combined and presented in three categories with scales ranged from 0 to 6 as follows:
- Scores 0.0–1.2 denote either no soft debris/calculus present or soft debris/supragingival calculus covering less than one-third of the tooth surface
- Scores 1.3–3.0 denote soft debris/supragingival calculus covering one-third of the tooth surface
- Score 3.1–6.0 denote soft debris/supragingival calculus covering more than two-thirds of the tooth surface or a continuous heavy band of subgingival calculus around the cervical portion of tooth.
Two hundred and thirty-four teeth of 468 surfaces been examined for tooth erosion. Erosive lesions recorded on the labial and palatal surfaces of the maxillary anterior teeth. The oral hygiene status (using OHI-S) was assessed on six tooth surfaces, which are the facial surfaces of the teeth 16, 11, 26, and 31 and the lingual surfaces of the teeth 36, 46 (FDI notation). Each tooth surface was divided horizontally into gingival, middle, and incisal thirds. The surface area covered by debris was recorded by running the side of an explorer along the tooth surface. The gingival condition scored on the mesial, distal, buccal, and lingual aspects of the following selected teeth: 16, 11, 26, 36, 31, and 46. Periodontal probes used to assess the bleeding potential of the gingival tissues. The number of tooth aspects scored for oral hygiene and gingival status was 936 each.
Diagnostic criteria and scoring
- Dental erosion. The criteria used for dental erosion were to determine the extent of loss of dental hard tissue's loss. (0) No loss of enamel surface characteristics; (1) Loss of enamel surface characteristics; (2) Faceting or convexity in enamel; (3) Loss of enamel exposing dentin to less than one-third of the surface; (4) Loss of enamel exposing dentin for more than one-third of the surface or pulp visible through the dentin
- Oral hygiene index. The combined debris and calculus indices were presented in three categories. (0) No debris or stain/calculus; (1) Soft debris/calculus covering not more than one-third of the tooth surface; (2) Soft debris/calculus covering more than one-third of the tooth surface; (3) Soft debris/calculus covering more than two-thirds of the exposed tooth surface or a continuous heavy band of subgingival calculus
- Gingival health. The gingival index used to score gingival health as follows: (0) Normal gingiva; (1) Mild inflammation: slight change in color, slight edema. No bleeding on probing; (2) Moderate inflammation: redness, edema, and glazing. Bleeding on probing; (3) Severe inflammation: marked redness and edema, ulceration. Tendency to spontaneous bleeding.
| Results|| |
The oral screening questions included: oral hygiene practice, diet, dry mouth, tooth pain/sensitivity, bleeding gum, chewing, taste, habits, etc., Questions on general health contained: any health problems, pains, stomach discomfort, eye problems, strain, anxiety, nervousness, dermatitis/skin itching, headaches, nausea, vomiting, smell, dental care, and medical care. The general and oral symptoms expressed by workers in the production line are tabulated in [Table 1]. More than two-thirds (67%–86%) of the acid workers had a complaint of teeth sensitivity, dry mouth and nose, disturbed sense of taste, burning/itching eyes, and abdominal distress. More than half (56%–64%) of the workers had headaches, disturbed sense of smell, bleeding gum, and burning/itching skin. They complained a loss of appetite, metallic taste, coughing, weakness, fatigue, nervous irritability, muscle, and joint pain. The severity of symptoms directly related to the duration of acid exposure and long-term employment. Poor oral hygiene was obvious. Only 14% of the workers brushed their teeth daily and no other oral hygiene adjunct been used.
|Table 1. Percentages of general and oral health problems in Jordanian and oral condition in Indian battery workers at the production line|
Click here to view
Dietary and smoking habits
The most frequent dietary habit was the daily intake of sweetened tea in 82% of workers and to less extent the intake of soft drinks and fruit juices. Consumption of acidic fruits and spicy foods was uncommon practice. More than half of the workers (58%) were cigarette smokers who had smoked for several years. Very few (12%) had visited the dental clinic during the past year, mainly for tooth extraction. The majority (69%) of acid workers believed that their problems are related to the unsafe work environment.
Clinical examination showed that 79.2% (19 out of 24) of the study group had dental erosion in which 25% had a Grade 2 of the index scoring, 37.5% had a Grade 3, and 16.7% had a Grade 4. Only 20.8% exhibited Grade 0 (no visible enamel changes). Of the 15 control group, 46.7% had minor erosion, whereas the rest had Grade 0 erosion. In both groups, erosion mainly confined to the labial surfaces of the maxillary incisors in workers who had no history of gastric problems or vomiting [Figure 1].
Two-thirds (66.7%) of the study group had scores ranged between 3.1 and 6.0, the rest had scored of 1.3–3.0. None was free of debris, stain, or calculus. In the control group, 73.3% had scores ranged from 1.3 to 3.0 and the rest had scores 0.0–1.2. OHI-S scores in acid workers were significantly higher than the control group (P< 0.05).
[Table 2] shows 45.8% of the study group had a score 3, 33.3% had score 2, and 20.8% had score 1. No acid workers had healthy gingiva. Collectively, 79.1% of the acid workers had scores 2 and 3, whereas 53.3% of the controls had those scores. The difference was statistically significant (P = 0.01).
|Table 2: Gingival index scores in workers in the production line and control group in Jordanian and Indian battery workers at Kanpur city|
Click here to view
Other distinct observations in the study group were the following:
- Almost one-third (29%) had extensive caries [Figure 2]
- Generalized cervical discolored lesions with debris deposits [Figure 3]a
- Notching of the maxillary central incisors and mandibular lateral incisors, [Figure 3]a caused by habitually cracking roasted and salted watermelon seed nuts [Figure 3]b
- Dense blue-green stains and debris are mainly deposited on maxillary anterior teeth with underlying carious lesions [Figure 4]
- Large calculus builds on the mandibular anterior teeth [Figure 5]
- General and oral health deterioration increased with prolonged working period [Figure 6].
The general and oral health of the control group was considerably better than of the study group. They were more educated and health concerned.
| Discussion|| |
Sulfuric acid is the most commonly used industrial chemicals. The world annual production of sulfuric acid is over 250 million tones. In the United States alone, more than 40 million tons of sulfuric acid used each year. Between 60% and 70% of the sulfuric acid is used in the fertilizer industry to convert phosphate rock to phosphoric acid. It has been estimated that between 60,000 and 70,000 people are employed globally in lead battery manufacturing; many of these workers lives in the developing world. Battery factory workers often exposed to harmful sulfuric acid-lead vapor created by the forming and charging processes. Chronic overexposure to lead may result in severe damage of body systems involving blood-forming, nervous, urinary, and fertility.,, The threshold of detectable exposure to acid fumes and mists in human beings is at the level of 0.5–0.7 mg/m. Concentrations <1 mg/m may undetected by odor, taste, or irritation. It has been reported that inhalation at concentrations of 1.0–2.0 mg/m irritates the nose, throat, eyes, skin, and lungs. Reports on battery factories indicated that acid fumes concentration varied from <1 to >5 mg/m at different locations.,, Much higher fumes levels of 8.0 mg/m, and 16 mg/m, have been found in some factories. Currently, international bodies have set recommendations to lessen the occurrence of occupational hazards to workers at sulfuric industries. Based on animal studies, the European Commission on occupational exposure limits for sulfuric acid (2007) concluded, “Long-term exposure to the sulfuric acid mists should be maintained <0.1 mg/m." In US, the Occupational Safety and Health Administration have suggested 1 mg/m as legal limit for sulfuric acid exposure.
Earlier study in the UK (1961) showed among 63 battery workers, 46% had enamel erosion and 41% had dentin erosion. Tuominen et al. conducted a survey on 68 study group exposed to high concentrations of sulfuric acid fumes in Tanzania fertilizer factories. They found that 63.2% had dental erosion, whereas for controls was 37.7% (P< 0.005). Petersen and Gormsen evaluated the oral condition in a modern battery factor in Germany, where workers were exposed to sulfuric acid's vapor in the workplace of 0.4–4.1 mg/cm. They observed that 31% of workers had dental erosion, mostly in the front teeth and 92% by attrition in posterior teeth. Suyama et al. reported that among 40 battery factory workers in Japan, 20% exhibited dental erosion in the anterior mandibular teeth. The prevalence of erosion rose from 42.9% for a working period of 10–14 to 66.7% for a period of over 20 years and increased proportionally to sulfuric acid air density.
Because of the increasing awareness of occupational hazards, several studies on the oral health of battery industry workers in different cities of India were recently published. Among 138 battery factory workers in Mandideep, Agrawal et al. found that 74% of the workers at the production line had dental erosion compared to 37.7% of the controls (P< 0.05). The study group had tooth sensitivity by 57.6% and oral hygiene practice by 33% compared to 11.3% and 63% of the controls, respectively. Raj et al. examined 600 battery workers in Chennai city and reported that oral symptoms and dental erosion among the study group was significantly greater than the control group (P< 0.001). Kundu et al. conducted a study on 1400 workers in twenty battery factories at the Ghaziabad city. They reported highly significant prevalence of dental erosion, gingival bleeding, and periodontal pockets among workers in the production line compared with the controls (P< 0.001). Khurana et al. found out of the 47 battery factory workers in Kanpur city, 84.9% had dental erosion. In a study among 800 battery industry workers in Baddi city, Bansal et al. showed that the prevalence of dental erosion in battery workers was 48.6%, with the labial surfaces of the maxillary anterior teeth were the most affected. Almost 28.3% of the workers were using anti-sensitive toothpastes due to tooth hypersensitivity. Yusuf et al. examined 800 workers at the production line of 24 battery factories in Moradabad. They found that 49.5% of the study groups had dental erosion compared to 4.4% among the controls, with enamel (19.9%), dentinal (21.4), and pulpal erosions (8.2%). Kumar et al. examined 200 battery factory workers in and 200 workers from another factory in Bengaluru city. The prevalence of dental erosion among the studied group was significantly higher (39.5%) than the control group (11.5%) with 2–3 erosion index scores were 3.8 times more than in the controls. Vianna et al. observed that Brazilian workers exposed to acid mists were at risk of developing oral mucosal lesions and periodontal tissue changes.
The factory, in which this study conducted, lacks the essential safety and protection measures including:
- Monitoring system of acidic fume's concentration in the workplace
- Efficient ventilation and exhaust systems
- Personal protective equipment such as protective respiratory masks, safety goggles or face shield, rubber gloves, and skin protection
- Medical and dental care services
- Educational measures.
The outcome of this study suggests that the severity of general and oral problems in workers at the production line relates to the high concentration of acid fumes evolves in the workplace, prolonged working period and exposure time, poor oral hygiene, lack of health knowledge, and negligence of healthcare. Workers in the study group were of low socioeconomic status and of inadequate nutritional requirements. They often go uncared due to their stressful working conditions and long working hours. It has been reported that wearing personal protective respiratory masks in acid's factories was significantly had less dental erosion. Workers in an aluminum plant who used a safety-mask during duty reduced the inhalation of fluoride to 30%–40% compared to those who did not use any mask.
This study pointed that heavy accumulation of debris, poor oral hygiene, reduced salivary flow, frequent intake of sweetened tea, smoking, and other harmful habits makes the teeth of the study group more susceptible to caries and periodontal disease. The predilection of maxillary front teeth to erosion suggests a direct action of acid mists on teeth that exposed during mouth breathing, probably due to chronic nasal problems caused by inhaled fumes. Halitosis could attribute to sulfide produced by oral bacteria in poor oral hygiene. It has been documented that aging, smoking, enamel defects, low salivary flow rate, and neglected oral hygiene are causative factors in tooth discoloration. Metallic dental stains were evident in industrial workers exposed to iron, manganese, silver (black); lead, mercury (blue-green); copper, nickel (green); chromic acid fumes (deep orange). This study add that exposure to sulfuric-lead vapor in battery manufacturing produced bluish-green dental stains [Figure 4] caused by lead sulfide evolved while forming and charging process.
In this study, the prevalence of sensitive teeth, dry mouth, and gingivitis among the study group was three times and the dental erosion 2.6 times more than those found in the German workers. The oral symptoms of Jordanians workers compared to the Indians are in [Table 1] and [Table 2]. Accumulate evidence suggests that exposures to the acid environment affect periodontal health and induce mucosal ulceration. This event may attribute to direct acid mists insult on cellular histophysiologies and functional activity by inhibiting the phagocyte activity of neutrophils, disrupting the oral immunity system and impairing tissue turnover and healing process. The olfactory and gustatory receptors in the upper respiratory tract are particularly sensitive to hazardous agents. Inhaled acid fumes may lead to atrophic changes in smell and taste buds' receptors, as evident in the present study and others.
| Conclusions|| |
This study showed that workers in the battery industry suffer of general and oral health problems. The chronic overexposure of acid fumes and mists in workplaces with the lack of safety and protection measures is the principal causative factor of health deterioration in the workers. This alarms occupational health authorities particularly in the developing countries to implement effective and mandatory measures included:
- Surveillance and control of acid emission in the workplace
- Installing effective ventilation and exhaust systems
- Mandatory use of personal protective equipment
- Implementing safety measures of acid handling and processing
- Educating workers on occupational hazards and healthcare
- Provide medical and dental care services.
Implementation of oral hygiene, general health education, and nutritional supplementation helps to improve the quality of life.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
The authors would like to thank John Wiley and Sons for permitting reuse part of data from our previous publication (Int Dent J 2001;51(3):169-174).
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
World Health Organization. Lead Poisoning and Health. Geneva: World Health Organization; 2017.
Gamble J, Jones W, Hancock J, Meckstroth RL. Epidemiological-environmental study of lead acid battery workers. III. Chronic effects of sulfuric acid on the respiratory system and teeth. Environ Res 1984;35:30-52.
Wiegand A, Attin T. Occupational dental erosion from exposure to acids: A review. Occup Med (Lond) 2007;57:169-76.
Amin WM, Al-Omoush SA, Hattab FN. Oral health status of workers exposed to acid fumes in phosphate and battery industries in Jordan. Int Dent J 2001;51:169-74.
Tuominen ML, Tuominen RJ, Fubusa F, Mgalula N. Tooth surface loss and exposure to organic and inorganic acid fumes in workplace air. Community Dent Oral Epidemiol 1991;19:217-20.
Khurana S, Jyothi C, Dileep CL, Jayaprakash K. Oral health status of battery factory workers in Kanpur city: A cross-sectional study. J Indian Assoc Public Health Dent 2014;12:80-87. DOI: 10.4103/2319-5932.140254. [Full text]
Petersen PE, Gormsen C. Oral conditions among German battery factory workers. Community Dent Oral Epidemiol 1991;19:104-6.
Hattab FN, Yassin OM. Etiology and diagnosis of tooth wear: A literature review and presentation of selected cases. Int J Prosthodont 2000;13:101-7.
Smith BG, Knight JK. An index for measuring the wear of teeth. Br Dent J 1984;156:435-8.
Greene JC, Vermillion JR. The simplified oral hygiene index. J Am Dent Assoc 1964;68:7-13.
Loe H, Silness J. Periodontal disease in pregnancy. I. prevalence and severity. Acta Odontol Scand 1963;21:533-51.
Singamsetty B, Gollapalli PK. A study on health profile of workers in a battery factory with reference to lead toxicity: Six months study. Int J Comm Med Public Health 2017;4:1519-25.
Canadian Centre for Occupational Health and Safety. Battery Acid, Sulphuric Acid. CAS Registry No.: 7664-93-9. Canadian Centre for Occupational Health and Safety; 2017.
Suyama Y, Takaku S, Okawa Y, Matsukubo T. Dental erosion in workers exposed to sulfuric acid in lead storage battery manufacturing facility. Bull Tokyo Dent Coll 2010;51:77-83.
Malcolm D, Paul E. Erosion of the teeth due to sulphuric acid in the battery industry. Br J Ind Med 1961;18:63-9.
Occupational Safety and Health Administration. Sulfuric Acid Exposure Limit and Health Effects. CAS# 7664-93-9. Occupational Safety and Health Administration; 2008.
Bansal M, Singh S, Bector A, Dogra M. Effect of dental erosion on oral health among employees of battery-manufacturing units in Baddi, Himachal Pradesh, India. J Educ Health Promot 2018;7:26.
Kumar A, Puranik MP, Sowmya KR, Rajput S. Impact of occupational dental erosion on oral health-related quality of life among battery factory workers in Bengaluru, India. Dent Res J (Isfahan) 2019;16:12-7.
Vianna MI, Santana VS, McKelvey W. Periodontal health and oral mucosal lesions as related to occupational exposure to acid mists. Community Dent Oral Epidemiol 2005;33:341-8.
Kim HD, Douglass CW. Associations between occupational health behaviors and occupational dental erosion. J Public Health Dent 2003;63:244-9.
Ehrnebo M, Ekstrand J. Occupational fluoride exposure and plasma fluoride levels in man. Int Arch Occup Environ Health 1986;58:179-90.
Hattab FN, Qudeimat MA, Al-Rimawi HS. Dental discoloration: An overview. J Esthet Dent 1999;11:291-310.
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2]