Dentistry, as a distinct field within healthcare, focuses on the prevention, diagnosis, and treatment of diseases affecting the oral cavity. It plays a crucial role in overall systemic well-being.^[1] For this purpose, dental professionals perform a wide range of procedures that expose them to various occupational hazards.^[2,3] Exposure to chemical substances is an important group of occupational hazards among dentists. The exposure to these substances can lead to adverse outcomes, such as contact dermatitis, allergic reactions, pneumoconiosis, reproductive complications, and other toxic effects.^[4]

Previous studies have tried to identify and evaluate the exposure to chemical substances among dentists. Picard et al. conducted a review on occupational exposures to chemicals among dentists. They found that most health assessments focused on mercury, followed by nitrous oxide (N₂O), methacrylate compounds, and silica.^[5] Anjum et al. also, in a review, investigated the occupational hazards among dentists. The identified chemical substances included caustics (hydrogen peroxide, and formaldehyde), organic (resins, solvents, and gases), inorganic (mercury toxicity), and latex glove allergy (contact dermatitis).^[6] Naryal et al., in a comprehensive review, examined chemical occupational hazards in dentistry. They concluded that the dentists are exposed to mercury, powdered natural rubber latex (NRL), disinfectants, methyl methacrylate, metal alloys, silica, and N₂O.^[7] Nagpal et al. evaluated the mercury exposure and health of dental personnel. They observed that dental professionals may be associated with low-level, long-term exposure to occupational mercury.^[8] However, given the wide variety of materials used in dentistry, a comprehensive assessment is required. On the other hand, because of changes in procedures as well as the implementation of control measures, chemical exposures may alter over time. Gustavsson et al. investigated time trends of occupational exposure to chemicals in Sweden. They found that exposure to some chemical agents has changed over time, suggesting alterations in well-controlled working conditions.^[9] Kauppinen et al. also examined the trends of occupational exposure to chemical agents in Finland between 1950 and 2020. They observed that there is a reduction in inhalation exposure to most chemicals since 1970.^[10] Given that these temporal changes have not been investigated among dentists, this study aimed to evaluate changes in chemical exposure levels and control measures in general dental offices in Isfahan, Iran, from 2001 to 2023.

A repeated cross-sectional study was performed in 2001 and 2023 using a researcher-made checklist.

Table 1 represents the statistical distribution of demographic characteristics among dentists in 2001 (n = 184) and 2023 (n = 250). There was a difference in sample size between 2001 and 2023. It is due to the increase in the number of dental offices in 2023 compared to 2001. However, to eliminate the effect of this difference, the relative frequency for the parameters in each year was reported. Based on the results, most of the participants in 2001 had work experience of 5–10 years (40.8%), gender of male (75%), and worked in a dental office in a building with multiple floors (94.6%). Most of the participants in 2023 also had an age range higher than 50 years (37.6%), work experience more than 20 years (42.8%), and gender of male (70.8%), and worked in a dental office in a building with multiple floors (91.2%). Among demographic variables, there was a significant difference in the work experience of participants between 2001 and 2023 (P < 0.001).

Table 2 reports the statistical distribution of exposure time characteristics among dentists in 2001 (n = 184) and 2023 (n = 250). The results showed that most participants in 2001 had career lengths of 5–10 years (40.8%), work duration per day of more than 6 h (43.5%), and work frequency per week of 4–6 days (83.2%). Most participants in 2023 had career lengths of more than 20 years (42.8%), work duration per day of more than 6 h (57.6%), and work frequency per week of 4–6 days (70.4%). As a result, the career length and work duration per day have significantly increased among participants in 2023 compared to those in 2001 (P < 0.001). While work frequency per week has not significantly changed among participants in 2023 compared to those in 2001 (P = 0.060).

Tables 3-5 represent the statistical distribution related to type and consequences of exposure to chemicals used in prosthetics, endo, and restorative operations and infection control among dentists in 2001 (n = 184) and 2023 (n = 250). The results indicated that 22 chemical substances were used in most dental offices in 2001, and 14 chemical substances were applied in most dental offices in 2023.

Among chemicals used in prosthetics, the use of dental cements’ liquid, plasticized acrylic resin soft liner, Speedex impression set, and alginate has significantly increased in 2023 compared to those in 2001 (P < 0.001). Use of chloroform solvent also did not change between 2001 and 2023 (P = 0.699), whereas the use of other chemical substances has significantly decreased in 2023 compared to those in 2001 (P < 0.004).

Among chemicals used in endo and restorative operations, the use of mercury amalgam powder has significantly increased in 2023 compared to that in 2001 (P = 0.008). The use of eugenol also did not change between 2001 and 2023 (P = 0.156), whereas the use of other chemical substances has significantly reduced in 2023 compared to those in 2001 (P < 0.010).

Among chemicals used in infection control, the use of sodium hypochlorite has significantly increased in 2023 compared to 2001 (P < 0.001). While the use of other chemical substances has significantly decreased in 2023 compared to those in 2001 (P < 0.028).

In 2001, skin effects were more frequently self-reported consequences among individuals exposed to acid etch material, latex, alkaline dental X-ray developer, acidic dental X-ray fixer, bathroom soap, mercury amalgam powder, and sodium hypochlorite. Moreover, respiratory effects were more frequently self-reported consequences among people exposed to formocresol, formalin, self-cure acryl, varnish solvent (ether), chloroform solvent, alkaline dental X-ray developer, mercury amalgam powder, and sodium hypochlorite. In 2023, skin effects were more frequently self-reported consequences among persons exposed to latex and micro 10 disinfectant, and respiratory effects were more frequently self-reported consequences among individuals exposed to sodium hypochlorite.

Table 6 represents the statistical distribution of control measures among dentists in 2001 (n = 184) and 2023 (n = 250). The findings revealed that professional control measures, including education, personal protective equipment, engineering control, and several solutions, have significantly improved in 2023 compared to those in 2001 (P < 0.001). Furthermore, the use of gloves and masks has also significantly increased in 2023 compared to those in 2001 (P < 0.001). However, ventilation status has not significantly changed in 2023 compared to that in 2001 (P = 0.137).

Exposure to chemicals is one of the most important health concerns in dentistry. Although several studies have examined some of these exposures, there is a need for a comprehensive investigation. Moreover, exposure to chemicals in dentists has altered over time because of changes in procedures, consumables, and control measures. The present study aimed to investigate the changes in chemical exposure and control measures in dental offices in Isfahan city, Iran, from 2001 to 2023.

On exposure time characteristics of dentists, the results of the present study showed that career length and work duration per day have significantly increased among participants in 2023 compared to those in 2001. While work frequency per week has significantly decreased among dentists in 2023 compared to that in 2001. In terms of exposure time, the increase in career length among dentists may lead to more experience in the use of chemicals and implementation of control measures.^[11] Furthermore, although their duration (working hours per day) has increased, the frequency (number of working days per week) has decreased. The sum of these agents can affect the exposure to chemicals.^[12]

On exposure type and control measures, the results indicated that 22 chemical substances were used in most dental offices in 2001, and 14 chemical substances were applied in most dental offices in 2023. Although the use of some chemicals has increased or unchanged, the use of most chemicals has decreased. The results of some studies on temporal changes of exposure to occupational chemicals show that exposure levels of most chemicals have decreased over time.^[9,10] Furthermore, the results of the present study showed that professional control measures, including education, personal protective equipment, engineering control, and several solutions, have significantly improved in 2023 compared to those in 2001. Hence, the use of gloves and masks has significantly increased in 2023 compared to 2001. These improvements are consistent with reduced exposure potential. However, direct exposure measurements or incident health outcomes were not assessed. This can be because of replacing less hazardous materials with more hazardous materials, implementing stricter control measures, developing advances in dental materials and technologies, increasing employee awareness, and implementing updated national and international regulations and guidelines. For example, the use of developer/fixer chemicals and mercury amalgam has likely declined due to digital radiography and amalgam phase-downs. Technology adoption, regulatory shifts, and market availability are introduced as drivers of substitution for various materials. The extensive implementation of digital radiography, encompassing advanced sensors and imaging software, has significantly reduced reliance on traditional film-based processing methods.^[13] In addition, international agreements like the Minamata Convention on mercury have encouraged the reduction of dental amalgam containing mercury.^[14] On a commercial scale, the broader accessibility, enhanced efficacy, and greater patient preference for mercury-free restorative options – such as resin composites and glass ionomer cements – have further driven this shift in the dental profession.^[15] Moreover, Petrović et al. recommended several preventive strategies to reduce occupational diseases among dental technicians. These strategies include the design of standardized and optimal workplace conditions, use of local and general ventilation systems, design of workstations equipped with appropriate tools, and use of suitable personal protective equipment.^[16] Lajolo et al. also emphasized that sufficient awareness is essential for the execution of effective preventive strategies in oral healthcare professionals.^[17] Furthermore, it should be noted that the increased awareness can be partly due to the coronavirus disease 2019 (COVID-19) pandemic. The results of several studies performed by Khader et al.,^[18] Mustafa et al.,^[19] and Princeton et al.^[20] show that the COVID-19 pandemic has increased the knowledge, attitudes, and awareness of dentists about infection control and preventive measures. The results of a study performed by Taha et al. showed that some patients avoid the treatment in some dental offices due to perceived cross-infection risk and concerns about the methods used by the dentists to sterilize dental instruments.^[21] These findings are consistent with the results obtained in the present study.

For the investigation of consequences due to chemical exposure, the information on skin and respiratory effects was collected through self-reported assessment from dentists. In 2001, skin effects were more frequently self-reported among individuals exposed to acid etch material, latex, alkaline dental X-ray developer, acidic dental X-ray fixer, bathroom soap, mercury amalgam powder, and sodium hypochlorite. Acidic substances cause coagulation necrosis, which results in cytotoxic effects. Alkaline substances generally exhibit greater toxicity than acids, because of their capacity to cause irreversible protein denaturation and tissue injury.^[22] These agents can provoke skin irritation, such as itching, rashes, or hives, as well as allergy symptoms.^[23] Because soap is often alkaline, it can deplete the skin’s natural oils, which potentially lead to breakouts, inflammation, and irritation.^[24] Contact with amalgam has also been linked to the development of dermatitis.^[25] Sodium hypochlorite is recognized as an irritant, and there are documented reports of allergic contact dermatitis due to exposure to this substance.^[26] Moreover, based on the results of the present study, respiratory effects were more frequently self-reported among people exposed to formocresol, formalin, self-cure acryl, varnish solvent (ether), chloroform solvent, alkaline dental X-ray developer, mercury amalgam powder, and sodium hypochlorite. Formocresol, as a pulpotomy agent in dental procedures, is recognized as a chemical substance with carcinogenic potential and well-documented risks.^[27] Formalin acts as an irritant to the eyes, skin, and respiratory system. Inhalation of its vapors may result in bronchial constriction and pulmonary edema.^[28] Contact with acrylic compounds is linked to the development of asthma and other respiratory disorders.^[29] Exposure to ether can cause irritation of the respiratory mucosa, which leads to laryngeal spasms.^[30] Inhalation of chloroform vapors may provoke irritation of the respiratory tract.^[31] Alkaline substances can diminish vigorous inspiratory efforts during respiratory failure.^[32] Respirable amalgam powder with mercury may adversely affect respiratory function.^[33] Inhalation of sodium hypochlorite can irritate the airways and lead to pulmonary edema.^[34] The results of the present study indicated that in 2023, skin effects were more frequently self-reported among individuals exposed to latex and micro 10 disinfectant, and respiratory effects were more frequently self-reported among people exposed to sodium hypochlorite. The skin and respiratory effects due to exposure to latex and sodium hypochlorite were explained. On micro 10 disinfectants, exposure to these substances can be associated with skin dryness, irritation, and itching.^[35] Several studies also introduced some chemical exposures. Lajolo et al. introduced some chemical hazards among dental hygienists, including exposure to NRL, composite resins, acrylic resins, and mercury.^[17] Naryal et al. concluded that hazardous chemicals used in clinical dentistry included mercury, powdered NRL, disinfectants, methyl methacrylate, metal alloys, silica, and N₂O.^[7] In the study of Lindbohm et al. also, chemicals with high exposure rates in dentistry included mercury amalgam, polymethylmethacrylate, organic solvents, and disinfectant.^[36] Most of these exposures in the present study were observed.

As a limitation, the data were collected through self-reported assessments, not chemical or clinical tests. Moreover, the study was performed with a cross-sectional design, not a longitudinal design. However, the sample size was calculated based on the study population in 2001 and 2023, and an attempt was made to select appropriate samples from the population through simple random sampling. Moreover, it was tried that the differences were decreased through inclusion criteria, including the presence of a dentist in the office, office location within Isfahan, and the willingness of the dentists to cooperate in the research. The exclusion criteria also included inaccuracy in completing the checklist. Furthermore, data related to age in 2001 was not available.

This study showed that the use of most chemical substances in dental offices decreased in 2023 compared with 2001. Moreover, professional control measures, including education, personal protective equipment, and engineering controls, improved substantially over time. Hence, these changes have been accompanied by a reduction in self-reported effects. These findings can be used by policymakers to perform regular monitoring of chemical use, plan the implementation of control measures, and strengthen occupational health regulations for the continued adoption of safer materials and technologies in dental practice. Moreover, the results are useful for dentists who are encouraged to maintain and enhance the implementation of effective control measures and to substitute hazardous substances with safer alternatives.