The current composition of dental amalgam is 40% to 70% silver, 12% to 30% tin, and 12% to 24% copper, with the quantitative ranges reflecting variations in the manufacturing processes. Trace amounts of indium, palladium, and zinc may also be included in the mixture [4]. The combination of these metals is useless as a restorative dental material unless they are combined with mercury, which creates a pliable restorative material that can be condensed into cavity preparations and that hardens soon after its placement. Mercury comprises about 42% to 45% of the total weight of the combined amalgam alloy [5].

The debate about the safety of dental amalgam restorations is a global one. Norway, Denmark, and Sweden have all banned the use of dental amalgam due to their concerns about the impact of mercury on patients and have labeled it an environmental toxin [9]. It is unclear if the actions of these countries will set a precedent for other countries (such as the United States) to enact similar legislation and ban the use of dental amalgam as a restorative material.

There is no doubt that the debate about the safety of dental amalgam will continue. To date, studies have not found scientific evidence demonstrating the use of dental amalgam is a precipitating factor in the development of systemic disease, but research is ongoing. Dentists should be forthright in discussing the use of dental amalgam as a restorative material with their patients. Alternative restorative materials, such as composites, gold, and porcelain, also have their limitations, advantages, and disadvantages. Patients should be informed that these alternatives are more expensive than dental amalgam and that insurance reimbursement is variable. An open exchange of scientifically based information about the safety of dental amalgam among members of the dental profession, the allied health professions, and the public is in the best interest of all.

Fluoridated water works both topically and systemically to reduce the potential for teeth to develop carious lesions. Systemic fluorides are ingested directly through the consumption of fluoridated water, foods, or beverages. Fluoride dietary supplements in pill, tablet, or liquid form are also considered systemic fluorides.

As a result of their analysis, the HHS changed its recommendation to a target concentration of 0.7 mg per liter of water for all fluoridated water supplies across the United States [20,21]. This level of fluoride was deemed sufficient to reduce the incidence of dental caries while minimizing the risk of dental fluorosis.

As with any ingested substance, there are levels at which chronic fluoride ingestion can be associated with adverse effects. The maximum allowable concentration of fluoride in community water systems, also known as the maximum contaminant level (MCL), is 4.0 mg/liter [20]. This level is nearly six times the recommended level for community water systems. Ingestion of fluoride at the MCL for a long period of time can lead to the development of dental and skeletal fluorosis [22]. The most common adverse effect associated with the long-term ingestion of fluoride in excess of 2 mg/liter is dental fluorosis [20,23]. Mild forms of dental fluorosis feature small white spots or streaks in the dental enamel (i.e., mottled enamel). Severe forms of dental fluorosis feature brown or black pits in the enamel. These are not carious lesions but may require composite restorations, as surface pitting will enhance the retention of plaque and increase the potential for the development of caries. In more severe cases, all the enamel may be damaged [24]. A study published by the Centers for Disease Control and Prevention found that approximately 23% of the U.S. population between 6 and 49 years of age had some form of dental fluorosis; 16.0% had very mild fluorosis, 4.8% had mild fluorosis, 2.0% had moderate fluorosis, and less than 1% had severe fluorosis [25]. An additional 16.5% were classified as having questionable or possible dental fluorosis. This same study found that the rates of dental fluorosis among adolescents (12 to 15 years of age) significantly increased between 1986–1987 and 1999–2004. Skeletal fluorosis is characterized by pain and stiffness in major joints and an increased risk for fractures. This condition is extremely rare in the United States [20].

As with any ingested substance, there are levels at which chronic fluoride ingestion can be associated with adverse effects. The maximum allowable concentration of fluoride in community water systems, also known as the maximum contaminant level (MCL), is 4.0 mg/liter [20]. This level is nearly six times the recommended level for community water systems. Ingestion of fluoride at the MCL for a long period of time can lead to the development of dental and skeletal fluorosis [22]. The most common adverse effect associated with the long-term ingestion of fluoride in excess of 2 mg/liter is dental fluorosis [20,23]. Mild forms of dental fluorosis feature small white spots or streaks in the dental enamel (i.e., mottled enamel). Severe forms of dental fluorosis feature brown or black pits in the enamel. These are not carious lesions but may require composite restorations, as surface pitting will enhance the retention of plaque and increase the potential for the development of caries. In more severe cases, all the enamel may be damaged [24]. A study published by the Centers for Disease Control and Prevention found that approximately 23% of the U.S. population between 6 and 49 years of age had some form of dental fluorosis; 16.0% had very mild fluorosis, 4.8% had mild fluorosis, 2.0% had moderate fluorosis, and less than 1% had severe fluorosis [25]. An additional 16.5% were classified as having questionable or possible dental fluorosis. This same study found that the rates of dental fluorosis among adolescents (12 to 15 years of age) significantly increased between 1986–1987 and 1999–2004. Skeletal fluorosis is characterized by pain and stiffness in major joints and an increased risk for fractures. This condition is extremely rare in the United States [20].

Another possible area of controversy is the link between fluoride exposure and intelligence quotient (IQ). Several studies have explored this relationship, and patients may have questions about the safety of fluoride, especially for children or while pregnant. A 2019 Canadian study of 512 mother-child pairs compared IQ in offspring of women living in areas with fluoridated water to those living in areas with non-fluoridated water. In this study, a 1-mg higher daily intake of fluoride among pregnant women was associated with a 3.66 lower IQ score in offspring at 3 to 4 years of age [28]. These findings were consistent with findings from other studies in India and Mexico [29,30]. Studies over the last three years have consistently linked fluoride exposure in pregnancy with adverse neurodevelopmental effects in offspring [31,32,33].

Bacterial ingress from necrotic pulpal tissues and from periodontal pockets is the usual source of odontogenic infections. Empiric antibiotic therapy should be used when a patient with an odontogenic infection develops an elevated body temperature, lymphadenopathy, trismus (i.e., difficulty opening the mouth), dysphagia (i.e., difficulty swallowing), and/or cellulitis (the extension of the infection into the contiguous tissues, the borders of which are ill-defined and the surface texture indurated). Other indications for empiric antibiotic therapy are periodontal abscesses, pericoronitis, and acute necrotizing ulcerative gingivitis [37]. This is not an all-inclusive list, as the patient's overall medical history, immune status, and age should also be considered when making the decision to prescribe an antibiotic.

Nausea and vomiting of pregnancy ("morning sickness") occurs in about 75% of pregnancies [50]. It usually begins between the fourth and eighth week of pregnancy and though it usually resolves before 20 weeks, it may continue through the duration of the pregnancy for some women [51]. The long-term regurgitation of acidic gastric contents can lead to the erosion and loss of enamel. Patients who have this problem should be instructed to first rinse their mouths with a neutralizing solution of 1 teaspoon of baking soda to 8 ounces of water to remove any acidic residue from the teeth. Patients who do not rinse before brushing their teeth with toothpaste will essentially be burnishing the acidic residue onto the enamel surface, enhancing the erosive effects. Continued erosion of enamel can lead to exposure of dentin, with subsequent development of tooth sensitivity. Patients may be prone to avoid brushing and flossing sensitive areas, with a consequent accumulation of plaque that can increase the risk of caries and periodontal problems. Desensitizing toothpastes or fluoride varnishes can relieve this sensitivity for minor areas of exposed dentine, but larger areas of erosion will require restoration.

Prescribing and administering medications for pregnant patients should be done with concern for both maternal and fetal safety. The FDA has established pregnancy drug risk categories according to drugs' effects on reproduction and pregnancy [52]. The safest medications that have been tested in pregnant women are category A drugs. However, due to possible risks to maternal and fetal health, drug trials rarely include pregnant women, and there are only a few medications that fall into this category. Category B medications have been found to have no fetal risk in animal studies, or more rarely, have been proven safe in women despite evidence of increased risks in animal studies. Medications for which increased risk of harm to mother or fetus cannot be ruled out are referred to as category C, while medications with evidence of negative effects are category D. Any medications that are contraindicated during pregnancy are considered category X.

Rapid cell division and organ development occurs between the second and eighth week of pregnancy. During this time, the fetus is most susceptible to the effects of stress and teratogens. Approximately 50% to 75% of all spontaneous abortions (miscarriages) occur during this period [57]. Dental treatment should be limited to basic periodontal prophylaxis, if needed, and emergency treatment of traumatic injuries, acute odontogenic infections, and/or pain of dental origin. Radiographs should only be done if required for diagnosis of an emergent dental problem. This is also an excellent time to educate patients about the importance of oral hygiene and the challenges that they may face during pregnancy.

A number of changes in the oral cavity have been associated with pregnancy, including caries, perimylolysis, tooth mobility, xerostomia, pregnancy granuloma, and ptyalism/sialorrhea [58]. Perhaps most commonly, the hormonal changes that occur during pregnancy have been linked with gingivitis. Approximately 60% to 75% of women will develop pregnancy gingivitis [59]. This can range from mild to severe gingival inflammation that can develop despite meticulous oral hygiene and the absence of chronic irritants such as plaque and calculus. Shifts in hormone levels may cause changes in the established microbiota, with overgrowth of certain bacteria species, increases in the ratio of bacterial anaerobes to aerobes, and changes in the proportions of Prevotella intermedia, Prevotella melaninogenicus, and Porphyromonas gingivalis [58,60,61]. Pre-existing subclinical gingivitis may become exacerbated during pregnancy to the point that clinical signs become apparent, including swelling, redness, bleeding, and tenderness [62]. These signs may begin to be noticeable in the second trimester and peak around the eighth month. Anterior teeth may be more apparently involved than the posterior. Mouth breathing is a potential exacerbating factor. A woman who has poor oral hygiene runs the risk of even greater gingival problems, although gingivitis can develop in women with no changes in their plaque-management behavior. Postpartum studies have shown that after delivery, the mother's level of gingivitis decreases as the constituency of the microbiota changes back to approximate its prepregnancy status. With the inflammation comes an increase in tooth mobility. Xerostomia is also reported in a high percentage of patients.

By the second trimester, fetal organ formation is complete, so some elective dental procedures may be performed at this time. The increasing fetal size and weight during the second trimester can place pressure on the inferior vena cava and compromise the return of blood to the heart when the patient is in a supine position. This can lead to maternal hypotension, decreased cardiac output, and loss of consciousness. Turning the patient on her left side will relieve the fetal weight against the inferior vena cava and allow the resumption of the appropriate blood flow. Radiographs should only be taken if absolutely necessary.

Atheromas are small, patchy thickenings that develop on the inner lining of arteries and subsequently protrude into the arterial lumen. These plaques can impede and ultimately stop the flow of blood. Platelets can collect on these atheromatous lesions and further impede the flow of blood by forming a thrombus (a stationary blood clot). If the thrombus detaches and travels through the bloodstream, it can lodge anywhere in the vascular network. Studies show that 40% of atheromatous lesions contain antigens produced in response to periodontal pathogens [75]. P. gingivalis can stimulate platelet aggregation, a component of atheromas and thrombi [76]. It has also been suggested that these periodontal pathogens can infiltrate the vascular endothelium and directly cause dysfunction, inflammation, and atherosclerosis [77]. One study suggests that having a better understanding of the periodontal pathogens coupled with proper examination of the oral cavity may aid in the early diagnosis and treatment of systemic diseases and conditions [78].

Both diabetes and periodontal disease share a common pathogenesis that involves enhanced inflammatory response at the local and systemic levels. This inflammatory response is mainly caused by the chronic effects of hyperglycemia and specifically the formation of biologically active glycated proteins and lipids [86,89]. Patients with diabetes, especially uncontrolled diabetes, are at an increased risk for impaired healing, and the periodontal pocket can experience persistent inflammation and bacterial infection in patients with periodontal disease, which can be made worse by this impaired healing [88,90]. Loss of teeth because of aggressive periodontitis may also occur [90].

In addition to vasoconstriction, endothelial dysfunction is correlated with aggregation of platelets, a proinflammatory state characterized by the accumulation of leukocytes and coagulation products on the endothelium. Fibrinolysis is decreased, and thrombosis is increased. As the secretion of prostacyclin and nitric oxide induce vasoconstriction, plasma cytokine and prothrombin factors levels increase. This makes the plasma markedly procoagulant and antifibrinolytic, promoting atherosclerosis [90]. The Insulin Resistance Atherosclerosis Study also demonstrated that chronic hyperglycemia was positively associated with increased intimal-medial wall thickness [89]. These changes in both the microvascular and macrovascular systems lead to reduced vascular reactivity and increased production of glycation end products [91]. The accumulation of advanced glycation end products in the gingival tissues is generally responsible for the oral complications of diabetes. In fact, individuals with poorly controlled diabetes have a two- to three-fold increase in the prevalence of oral lesions and periodontal disease.

While smokeless tobacco eliminates the risks of secondhand and thirdhand smoke to bystanders, it remains highly addictive and harmful to users. Nicotine from smokeless tobacco is absorbed more slowly through the oral mucosa, compared with the rapid systemic absorption and distribution from cigarette smoke [103]. However, the effects of nicotine absorbed through the oral mucosa are more protracted. Although the route of absorption varies, the potential for addiction remains the same.

From 2017 to 2018, adolescent use of e-cigarettes increased from 11.7% to 20.8%, making it the number one form of tobacco used among youth. The rate increased again in 2019 to 27.5%, but decreased in 2020 to 19.6% [107]. In 2018, the FDA issued more than 1,300 warnings and fines to retailers who illegally sold e-cigarette products to minors [108]. In 2020, the FDA banned mint- and fruit-flavored e-cigarette cartridges in an effort to halt uptake among children [109].

Because e-cigarettes have been used in the United States for a relatively short period, the long-term effects on oral and systemic health are not totally clear. Elimination of exposure to tar is a benefit for e-cigarette use. However, the chemicals that are inhaled while using e-cigarettes are associated with known health hazards. Nicotine remains a highly addictive compound regardless of its source. People who use e-cigarettes can experience nicotine withdrawal symptoms if they discontinue the use of the device. One study demonstrated that formaldehyde, a known carcinogen, can be produced during the vaping process, with the potential for the user and bystanders to inhale vapor that contains the carcinogen [110]. In general, e-cigarettes cannot be considered a safe alternative to cigarette smoking.

As compared to decades ago, dental health has improved across the United States, which is primarily attributed to fluoridation of water and toothpaste and greater awareness of optimal oral hygiene. However, rural areas have a variety of factors that continue to contribute to poorer oral health in this population [130]: