Antibiotic Exposure and Dental Health: A Systematic Review

This study followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guidelines (Supplemental Table 5). The review was registered in the PROSPERO database (CRD42020179098).

Medline (PubMed/Ovid), Embase (Ovid; 1946-current), and the Cochrane Library databases were searched in September 2021 using the search strategies listed in Supplemental Materials, Methods. All searches were limited to the English language. Reference lists of included articles were checked. In addition, Pro-Quest Dissertation Abstracts and Thesis database and Google Scholar were searched for gray literature.

Studies were included if they reported antibiotic exposure before 8 years of age (the period of tooth development) and 1 or more of the relevant outcomes (dental caries, intrinsic tooth staining, or developmental defects of enamel) based on visual assessment of the dentition. Developmental defects of enamel with a known etiology such as fluorosis and amelogenesis imperfecta were excluded as outcome measures.²⁹  For the outcomes of dental caries and developmental defects of enamel, only studies using a validated index were included (Supplemental Table 6). As there is no validated tool to measure tetracycline staining, studies using any clearly described method were included.

Two independent investigators (D.R. and G.H.) assessed eligibility of all studies in Covidence (Covidence systematic review software, Veritas Health Innovation, Melbourne, Australia), in a 2-stage screening process; by title and abstract and then by full text. Initial disagreements were resolved by discussion and then by a third independent reviewer (M.S.).

Data on study population, design, type of antibiotic, outcome measurement, and results were extracted from the identified studies by a sole investigator (D.R.) using a standardized extraction form. All data extraction was audited by a second reviewer (G.H.). Odds ratios (OR), P values, and 95% confidence intervals (CIs) were extracted from studies that quantified the risk of caries, developmental defects of enamel, and dental staining with the exposure to antibiotics. If not reported and when possible, the odds ratios and confidence intervals were calculated. All analyses were performed using Stata 16 software (StataCorp. 2019. Stata Statistical Software: Release 16. College Station, TX: StataCorp LLC). Because of heterogeneity and lack of data on covariates, meta-analysis was not considered appropriate.

The studies were assessed for risk of bias according to both the Newcastle Ottawa Scale and Risk Of Bias In Non-randomized Studies - of Exposure tool by a sole investigator (D.R.) (Supplemental Tables 7 and 8) and audited by a second reviewer (M.S.).^30,31  The Newcastle Ottawa Scale was modified to suit the research question (Supplemental Table 9). No studies were excluded on the basis of the bias assessment.

The initial search yielded 1003 articles with 756 articles screened by title and abstract after duplicates had been removed. Overall, 34 were found to be eligible for qualitative analysis (Fig 1). All 34 studies were retrospective cohort studies. A total of 18 studies investigated tetracyclines and/or tetracycline derived antibiotics, 7 investigated amoxicillin only, and 9 did not specify the antibiotic class.

Exposure ascertainment was based on hospital and pharmacy records or patient and parent recall of medication use. The median age at the time of antibiotic exposure was 6 years (range 0–8 years). Outcomes were measured between 24 months to 18 years of age. Sample size varied from 25 to 29 485 participants (Table 1).^3,32 

The methods used to measure and quantify the 3 outcomes (dental caries, enamel defects, and dental staining) varied considerably. A total of 3 different measures were used for caries, 10 for dental staining, and 7 for enamel defects (Supplemental Table 6).^33–35  In addition to detection of tetracycline staining from visual and laboratory analyses, general intrinsic staining was determined by measuring tooth color using a shade guide or spectrometer and applying an arbitrary threshold. The 7 indices used to measure developmental defects of enamel were variations of 2 core validated indices (European Academy of Pediatric Dentistry Criteria for molar-incisor hypomineralization [MIH] and Developmental Defects of Enamel [DDE] Index) (Supplemental Table 6).^36,37 

Eighteen studies investigated tetracyclines and tetracycline derived antibiotics, most of which (n = 16) included dental staining as an outcome. Eleven studies investigated older formulations (e.g., tetracyclines), often at relatively higher doses (from 10 to 38 mg/kg per day), whereas 5 studies investigated the newer formulations (e.g., doxycycline), often at lower dosages (from 2.3 to 6.25 mg/kg per day) (Table 2). Dosage was not reported in 3 studies.^38–40 

Three studies assessed the presence of the characteristic pattern of tetracycline staining from visual inspection and 4 studies used fluorescence of exfoliated or extracted teeth. Four studies used tooth color and shade as a marker of tetracycline staining. The 5 remaining studies used a combination of the above methods or study specific outcome measures based on inherent tooth shade (intrinsic staining).

The studies investigating older formulations of tetracyclines were published between 1962 and 1980 and had a moderate to critical risk of bias, often failing to clearly report the method for measurement of outcomes. Higher doses of tetracyclines were associated with increased presence of dental staining. In 5 studies, doses of ≥20 mg/kg per day with a duration from 5 to 11 days were associated with dental staining, whereas only 1 study of the same dose reported no association.^41–46  The study that reported the strongest association (OR: 11.62, 95% CI 5.96–24.32) evaluated the highest dose for the longest consecutive duration (26.7 mg/kg per day for a mean of 11 days).⁴¹ 

All 5 studies evaluating the relationship between newer formulations of tetracycline (minocycline and doxycycline) and dental staining showed no association. The studies were published between 1998 to 2017 and average dosage ranged from 2.3 to 25 mg/kg per day with a mean duration of 10.7 days.^{17,19,47–49}  Notably, no cases of tetracycline staining were observed in 58 and 78 children at average doses of 2.3 mg/kg per day and 6.25 mg/kg per day, respectively. Although the overall risk of bias varied, there was evidence from 3 low bias studies that doxycycline did not cause intrinsic staining, including tetracycline staining.^17,19,47 

Five studies investigated the relationship between childhood use of tetracycline derived antibiotics and developmental defects of enamel.^{17,40,42,43,50}  Four of these papers provided details regarding dosage (Table 2). Two papers reported contradictory results for tetracycline at doses of 20 mg/kg per day.^42,43  One study with a critical level of bias investigated 40 premature infants with an average treatment duration of 4 days and found higher odds of enamel defects (OR 5.83, 95% CI 0.42–314.48). However, the study did not address the role of prematurity on the relationship.⁴³  In contrast, the other study with a moderate level of bias investigated 160 participants aged 6 to 12 years with an average of 6 days of medication and found no cases of enamel hypoplasia.⁴² 

The 2 studies of newer formulations (doxycycline at 5 mg/kg per day and minocycline at 2.3 mg/kg per day) did not report an increased odds of enamel hypoplasia (OR 0.89, 95% CI 0.38–2.11; OR 0.92, 95% CI 0.2–4.2).^17,50  The findings from these 5 studies are contradictory and preclude clear conclusions but suggest that newer formulations at lower dosages likely do not have an association with developmental defects of enamel.^{17,40,42,43,50} 

Three of the 4 studies of dental caries used the total number of decayed, missing, filled teeth, or surfaces based on visual inspection as a measure of caries prevalence or severity; a single study used radiographic evaluation in addition to a clinical criterion. Tetracycline use at 20 mg/kg per day had no association with the presence of dental caries (OR 1.42, 95% CI 0.34–7.06).⁴⁴  A study of 100 participants found fewer carious tooth surfaces (0.099 ± 0.088) in the exposed group compared with the comparison group (0.146 ± 0.087), however, this study had a serious level of bias because of a lack of confirmation of exposure.³⁸  A similar association was also reported in a study of 86 patients who found a mean of 7.5 (±1.0) carious surfaces in the exposed group compared to a mean of 13.5 (±1.3) in the comparison group.⁴⁰  All 4 studies had high levels of bias, with 1 lacking a comparator group and another reliant upon parent recall for exposure ascertainment and all failing to adjust for confounders, such as socioeconomic status (a major social determinant of dental caries risk).

Seven of the included studies evaluated the effect of amoxicillin on enamel defects and/or dental caries, whereas effects on intrinsic staining were not evaluated (Table 3).

Four studies investigated the relationship between amoxicillin and developmental defects of enamel.^9,51–53  One study found a positive association (OR 7.88, 95% CI 2.43–25.12) between penicillin and developmental defects of enamel in a cohort of 433 with a median age of 7.8 years.⁵¹  This study had a low level of bias and adjusted for relevant confounders, such as fluoride exposure, tooth wear, and age. Conversely 2 studies with a low to moderate risk of bias in populations of 120 and 367 showed a protective association between penicillin (dosage not reported) and developmental defects of enamel with ORs 0.44 (95% CI 0.25–0.77) and 0.07 (95% CI 0.02–0.28).^9,52 

There were 4 studies that investigated the relationship between amoxicillin and dental caries, all with a moderate level of bias.^3,51,54,55  Only 2 studies reported dosage, with 1 being an average of 16 mg/kg per day and the other of 125 mg per day.^54,55  One study with an exposure group of 433 in a population of 7 to 9 year olds found a higher number of carious surfaces in the exposed group (mean 1.46, SD: 0.99) than in the comparison group (0.76, SD: 1.33).⁵¹  Contrastingly, another study of penicillin (125 mg per day) found a lower number of carious surfaces in the exposed group of 6 to 13 year olds (mean 3.55, SD: 0.58) compared with the control group (mean 4.84, SD: 0.32).⁵⁴  A birth cohort study of 29 485 participants found that the number of teeth affected by caries at 2 years of age was on average lower in children who had taken amoxicillin (P < .0001). However, dosage was not provided and odds ratios were unable to be calculated from the data provided, limiting conclusions about effect size.³  This was consistent with a cohort study of 393 participants where amoxycillin doses of 5 to 29 mg/kg per day were found to be protective for dental caries with a mean 0.47 (±0.6) carious surfaces in the exposed group, compared with 1.50 (±0.32) in the comparison group.⁵⁵  Overall, a clear association could not be identified because of the heterogeneity in outcome measures across the studies.

Nine studies (Table 4) evaluated the dental effects of any antibiotic exposure by either combining several antibiotics into a single exposure group, or without specifying the antibiotic formulations.^2,56–63  Out of 4 studies with low to moderate bias focused on MIH, a common developmental defect, 3 found a positive association with MIH prevalence. In contrast, none of the 3 studies with low to moderate risk of bias that investigated developmental defects of enamel in general (as opposed to MIH specifically) reported an association.^57,61,64 

To our knowledge, this is the first systematic review to investigate early childhood antibiotics and 3 dental outcomes (caries, enamel defects, and dental staining). We included evidence from 34 studies. Tetracyclines at higher dosages (≥ 20 mg/kg per day) were associated with dental staining; these doses are not currently recommended. There were conflicting results both between early childhood antibiotics and dental caries and between early childhood antibiotic use and MIH.

There was no evidence that newer tetracycline-related formulations (doxycycline, minocycline), nor other antibiotic classes, were associated with adverse dental outcomes. Our findings are in keeping with other systematic reviews of doxycycline that concluded that median treatment durations up to 10 days had negligible effects on tooth staining.^18,27,28,65  The change in formulation from tetracycline to doxycycline included removal of the hydroxyl group at C-6.⁶⁶  This resulted in an inherent change on calcium binding capacity (doxycycline 19% vs tetracycline 39.5%) with doxycycline, therefore, less likely to result in the ion complexes that cause intrinsic staining.²⁷  This change combined with more recent studies on safety of doxycycline has also prompted the American Academy of Pediatrics 2021 Red Book to recommend use of doxycycline for less than 21 days regardless of age.⁶⁷ 

A previous systematic review reported an association between antibiotic use and developmental defects of enamel (MIH) but lacked data on dosage and the age of antibiotic administration, so it was not possible to ascertain if exposure occurred during tooth calcification.⁶⁸  Notwithstanding, the findings are in keeping with the current study. No studies evaluating enamel defects have determined if the effect on dentition is because of the antibiotic itself or the underlying illness.^57,69–71  Therefore, until any risk of MIH has been quantified through prospective studies with data on any dose response relationship, the treatment of infections with antibiotics outweighs any putative MIH risk.

We were unable to draw clear conclusions regarding the effect of early childhood antibiotics on dental caries because of the heterogeneity of outcome measures. Previous studies have reported an increase in risk of dental caries from early childhood antibiotic use.³  This is in contrast to data from patients with cystic fibrosis, who have prolonged cumulative antibiotic exposure from early childhood and in whom there is a lower risk of dental caries.^2,5,6 

This study has a number of strengths, including assessment of 3 different dental outcomes for the first time. Two bias tools were used to assess all papers, which was done in duplicate using a number of databases and at several time points. Most of the studies in this systematic review have methodological limitations. All studies rely on retrospective data, and several did not adjust for potential confounders, such as socioeconomic status and age. The previous data on tetracycline-derived antibiotics and dental staining is largely from the 1960s and 1970s, and data quality is limited. The introduction of standardized reporting guidelines (such as STROBE) has improved the quality and reduced bias.⁷² 

Limitations include the lack of standardized and validated outcome measures (for tooth staining in particular) that made comparison between studies difficult. Although validated outcome measures were used for both developmental defects of enamel and caries, several different indices were used (Supplemental Table 6). A validated index for tetracycline staining is hard to develop because of the low prevalence of staining. This systematic review applied causal inference using observational data to evaluate the effect of early childhood antibiotic use on dental outcomes. Such analyses are powerful and increasingly common; there are inherent biases and challenges to answering causal questions from observational research.⁷³  General associations between any exposures to antibiotics and dental health without specific doses may provide a signal of an association but are limited in providing causal insights. Further studies with prospective longitudinal cohorts of patients with quantification of dosages would provide more complete evidence to inform clinical practice.

Despite the limitations of the existing, largely retrospective data, we found no evidence that currently used antibiotics at currently recommended doses before 8 years of age was associated with later dental effects of tooth staining, developmental defects of enamel, or caries. Newer formulation tetracyclines (doxycycline and minocycline) at currently recommended doses do not cause long term dental effects. There is conflicting evidence for the relationship between antibiotic use and other dental outcomes (caries and enamel defects). Further well-designed prospective longitudinal cohort studies are needed to determine this relationship using standardized outcomes with adjustment for confounders, together with biological sampling and microbiome analysis, are warranted.

DDE

developmental defects of enamel

MIH

molar-incisor hypomineralisation