Marketing is heavily directed toward adolescent age groups.  A contemporary example is public school districts contracting with soft drink companies for millions of dollars in exchange for exclusive marketing rights in the schools.  Sales quotas accompany these payments and pressure school administrators to encourage students to consume the soft drinks.  A recent editorial in the Journal of the American Dental Association brings attention to the potential of this marketing technique to increase dental problems such as erosion and caries in the adolescent population.¹⁸

Marketing by the soft drink companies is very successful.  Retail sales in the US are rapidly increasing and totaled over $54 billion in 1997, with a consumption rate of 54 gallons of soft drinks per person per year.¹⁹  This is more than twice the rate in the United Kingdom with approximately 20 gallons per person per year.  With consumption of acidic drinks identified as a risk factor in erosion, this amount of soft drink consumption will likely lead to an increase in prevalence of erosion.²⁰

The erosive potential of beverages does not depend on pH alone.^21,22  Other components of beverages, such as calcium, phosphates, and fluoride, may lessen erosive potential.  Also, factors such as frequency and method of intake of acidic beverages as well as proximity of tooth brushing after intake may influence susceptibility to erosion.  For example, drinking through a straw lessens the contact time of the beverage with the teeth compared to drinking from a cup.²³  Therefore, further investigation is required to clarify the relationship between acidic beverage intake and dental erosion.

Medications that are acidic in nature can also cause erosion via direct contact with the teeth when the medication is chewed or held in the mouth prior to swallowing.  Numerous case reports exist describing extensive erosion secondary to chewing Vitamin C preparations or hydrochloric acid supplements.^24,25,26

Less common sources of extrinsic erosive acids are related to occupational and recreational exposure.  Chromic, hydrochloric, sulfuric and nitric acids have been identified as erosion-causing acid vapors.  They are released into the work environment during industrial electrolytic processes.^{3, 27,28}  However current work safety standards make this type of erosion very rare. Dental erosion has been reported in swimmers who work out regularly in pools with excessive acidity as well as individuals who are occupational wine-tasters.^29,30

Intrinsic Causes
Intrinsic causes, (acid source inside the body), for erosion are gastric acids regurgitated into the esophagus and mouth.  Gastric acids, with pH levels that can be less than 1, reach the oral cavity and come in contact with the teeth in conditions such as gastroesophageal reflux and excessive vomiting related to eating disorders.

The association of gastroesophageal reflux disease (GERD) with dental erosion has been established in a number of studies in adults.^{10,31,32,33,34}  GERD is a common condition, estimated to affect 7% of the adult population on a daily basis and 36% at least one time a month.³⁵  In this condition gastric contents pass involuntarily into the esophagus and can escape up into the mouth.  This is caused by increased abdominal pressure, inappropriate relaxation of the lower esophageal sphincter or increased acid production by the stomach.³⁶  Symptoms of reflux are listed in Table 3.  However, GERD can also be "silent" with the patient unaware of his or her condition until dental changes elicit assessment for the condition.³⁴

Table 3.  Signs and Symptoms of Gastroesophageal Reflux Disease

A thorough health history may reveal elements of the treatment of GERD which may assist dental professionals in the correlation of erosion with this systemic condition.

Treatment of GERD usually begins with head elevation (extra pillows during sleep), dietary modification (avoiding spicy or fatty foods) and the use of antacids.  If this doesn't manage the problem, several medications can be used.  Histamine 2-receptor antagonists such as cimetidine, ranitidine, famotidine, and nizatidine are available over-the-counter as well as in prescription form.  Others, such as cisapride, metoclopramide, and omeprazole, are available in prescription form only.

Dental erosion associated with GERD also occurs in children and may be an initial finding in this gastric condition.^37,38  GERD in children can occur from infancy through the teenage years.  Table 3 lists common symptoms of GERD in children, which differ from that of adults.  Several studies have reported erosion of primary and permanent teeth in children with GERD, though not to the extent of that in adult patients with GERD.³⁹  This may be in part due to careful avoidance of acidic foods and beverages on the part of the parents.  There is a high incidence of GERD in children with cerebral palsy, which coupled with the tendency for bruxism, places them at particular risk for tooth wear.⁴⁰

Chronic, excessive vomiting has long been recognized as causing erosion of the teeth.  The patient with an eating disorder such as anorexia nervosa or bulimia is the classic example. The problem was first reported by Hellstrom and Hurst in 1977.^41,42  Many reports and reviews have been published on the topic since that time.⁴³  Although erosion caused by vomiting typically affects the palatal surfaces of the maxillary teeth, it is also common for individuals with eating disorders to consume large amounts of acidic beverages and fresh fruits.  This results in another source of acid exposure, primarily affecting the labial surfaces of the teeth.  In addition, treatment for bulimia may include use of antidepressants or other psychoactive medications that may cause salivary hypofunction.  Therefore, the cause of erosion cannot be reliably determined from its location.⁴⁴ 

Erosion associated with alcoholism is caused by frequent vomiting.^44,45  Other causes of vomiting that may cause erosion include gastrointestinal disorders such as peptic ulcers or gastritis, pregnancy, drug side effects, diabetes or nervous system disorders.

Saliva as a Modifying Factor
Buffering capacity of saliva refers to its ability to resist a change in pH when an acid is added to it.  This property is largely due to the bicarbonate content of the saliva which is in turn dependent on salivary flow rate. Bicarbonate concentration also regulates salivary pH.  Therefore, there is a relationship between salivary pH, buffering capacity and flow rate, with pH and buffer capacity increasing as flow rate increases.⁴⁸

Normally, when an acid enters the mouth, whether from an intrinsic or extrinsic source, salivary flow rate increases, along with pH and buffer capacity.  Within minutes, the acid is neutralized and cleared from the oral cavity and the pH returns to normal.  Patients with erosion were found to have lower salivary buffer capacity when compared with controls in several studies.^31,32,45,49  In other studies, low whole salivary flow rates in patients with erosion were determined to be the major difference.^20,49,50  Therefore, salivary function is an important factor in the etiology of erosion.  Since many common medications and diseases can lower salivary flow rate, it is important to assess these salivary characteristics when evaluating a patient with erosion.

Risk Factors
Given the numerous possible etiologies of erosion, it is important clinically to assess which risk factors a patient may have.  Table 4 lists risk factors that have been determined by various studies.  In a study conducted in Finland in which 106 erosion cases (defined by strict criteria) were compared with 100 randomly selected controls, the results indicated that when citrus fruits were consumed more than twice a day, this was associated with an erosion risk 37 times greater than in those who consume citrus fruits less frequently.²⁰  Consumption of sports drinks weekly or soft drinks daily increased the erosion risk by 4 times, compared to those who did not consume these beverage types.  Vomiting once a week or more, symptoms of gastroesophageal reflux and a low unstimulated whole salivary flow rate (<0.1 mL/min) were also significant risk factors.

Table 4.  Risk Factors for Dental Erosion
(Adapted from Jarvinen, 1991²⁰)

Presently, there are no longitudinal studies of patients with erosion.  However, two recent studies raise the possibility of an inherent susceptibility to erosion.  In a study of 14-year old children, horizontal wear of the maxillary anterior teeth predicted the continuing wear of these teeth at 18 years of age.⁵¹  In a similar longitudinal study of 223 orthodontically treated cases, orthodontic casts obtained during childhood years were compared with adult records.⁵²  Statistical analysis indicated that tooth wear could be predicted in the adult stage from wear observed on the deciduous teeth.  Although the authors considered bruxism as the possible common etiologic mechanism, the scoring system for tooth wear was very similar to that of erosion, raising the question that erosive factors could have been the etiologic mechanism for tooth wear.

It is important to keep in mind when interpreting results of these studies that factors yet to be identified may modify the susceptibility a given individual has for erosion.  These factors may include characteristics of saliva, tooth enamel constitution, and microenvironments within the oral cavity related to fluid/food bolus movement.