A systematic review uncovers links between maternal smoking and tooth defects in children, from missing teeth to enamel damage, while calling for stronger research to confirm the risks.
Study: The association between maternal smoking during pregnancy and dental development in offspring: a systematic review. Image credit: HenadziPechan/Shutterstock.com
A recent systematic review in the journal Evidence-Based Dentistry explored the association of various dental anomalies with maternal smoking during pregnancy (MSDP). MSDP has an adverse impact on fetal health and development. In Australia, one in 12 women reported smoking during pregnancy in 2021, despite its association with preterm birth, low birth weight, miscarriage, and ectopic pregnancy.
Introduction
Defects in tooth development can affect both appearance and function, potentially reducing the quality of life. Genetic and environmental factors, including MSDP, can disrupt tooth development at the molecular level. The effects range from total tooth non-formation to defective tooth formation.
Teeth begin to develop around the sixth week of gestation and continue through the first year of life. This process, called odontogenesis, includes the formation of the tooth layers, called enamel, dentine, and cementum, around the neurovascular tooth pulp. Tooth eruption begins at around 8.6 months, with the milk teeth, the last erupting around 28 months.
The permanent teeth erupt between 6 and 12 years, although the roots continue to develop for an additional 2-3 years. Mineralization of the crowns occurs by one year for the milk teeth, and at around 8-9 years for permanent teeth, except for the wisdom teeth.
Any disruption of these processes affects the shape and number of teeth or their enamel formation. The exact association between defective dentition and MSDP is unclear, and inconsistent findings from different studies prompted the current research.
The researchers reviewed observational studies from six databases, finding 17 that examined tooth development abnormalities associated with MSDP. The outcomes of interest included molar incisor hypomineralisation (MIH) vs other enamel defects (other than MIH), missing teeth, dental eruption, and short root anomaly.
Smoking during pregnancy varied from smoking at any point, trimester-specific exposure, or first-trimester exposure, and from daily to occasional exposure or exposure for part of the pregnancy. The number of cigarettes smoked was reported in only two studies, while most studies provided a yes or no response.
Study findings
Most of the studies found that MSDP was potentially associated with tooth development abnormalities, including enamel defects, hypodontia, and short root anomalies. However, the findings related to MIH were mixed and inconsistent. Some studies have shown an association, while others have not. This contrasts with other reviews, possibly due to the inclusion of more recent studies in this review.
Other enamel defects, missing teeth, and short root anomalies were associated with MSDP in several studies, while no consistent association was found with tooth eruption patterns. MSDP was linked to reduced tooth number in a dose-dependent manner, supporting the possibility of a causal relationship.
Mechanistically, MSDP might trigger oxidative stress and hypoxia of the placenta. Both passive and active maternal smoking may adversely affect neural crest cells, which are responsible for tooth formation, potentially resulting in hypodontia or a reduction in tooth number.
This could be further exacerbated by chronic nicotine-induced hypoxia in the fetus, impacting proper dental development as well as mineralization. Disrupted ameloblast function (enamel-forming cells) has been observed in animal studies, suggesting a possible mechanism for enamel defects.
However, tooth eruption does not appear to be affected, perhaps because it is a more complex process with many more inputs. While the results show inconsistent associations with eruption, the evidence was rated as of very low quality. While most studies found no association, at least two reported statistically significant links between MSDP and early tooth eruption in offspring.
Short root anomaly was shown to be more common in the offspring of mothers who smoked, based on findings from a single study.
The review encompassed developmental outcomes across the spectrum of tooth development; however, the studies themselves were too diverse to provide high-quality data in all areas.
The overall quality of evidence was rated as low or very low due to methodological heterogeneity, reliance on self-reported data, limited adjustment for confounders, and inconsistent findings across studies. The authors emphasize the need for well-designed prospective studies. Future research should use objective biomarkers instead of self-reported data, report specific timing and dose of smoking, and better adjust for confounders.
Conclusions
According to the review, MSDP may be associated with abnormal development of the teeth in children. Both the number of teeth and enamel development appear to be potentially affected by smoking exposure in pregnancy.
There is also limited and inconsistent evidence of an association with MIH and early eruption; however, the findings are inconsistent.
The strength of these conclusions is limited by the low or very low quality of the evidence, and further high-quality, well-controlled studies are needed to clarify the risk of MSDP on dental development in offspring.
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