A non-optimal ambient temperature is a significant risk factor in public health involving many people. The present research mainly focused on the association between temperature and cardiovascular disease (CVD) mortality and morbidity rates, which, due to colder temperatures, surpass those attributed to higher temperatures(Schneider, Panagiotakos et al. 2008). To our knowledge, researchers have rarely explored the relationship between temperature and oral diseases. Given the direct exposure of the oral cavity to external environments and its sensitivity to temperature fluctuations, it is imperative to quantitatively assess the detrimental effects of non-optimal ambient temperatures on oral health. In this time series study, we probed the association between ambient temperature and oral diseases by leveraging outpatient data from the Affiliated Stomatological Hospital of Guangzhou Medical University, January 1, 2020, and December 31, 2022. Our findings indicated that temperatures below 12–13°C increased the risk of dental caries, periodontitis, pulpitis, periapical periodontitis and TMD. Conversely, temperatures above this threshold showed no pronounced correlation. Further stratified analysis revealed that low temperatures increase the incidence of oral diseases in patients aged ≥ 60 years, especially those aged 60-75years. Our methodology employed a generalized additive model coupled with a distributed lag nonlinear model to explore the correlation between ambient temperature and the incidence of oral diseases in Guangzhou, China. Our results corroborated that low ambient temperatures correlated with a surge in outpatient visits for oral diseases. No discernable association was observed for daily temperatures exceeding 12–13°C. Previous studies have indicated that colder climates can exacerbate the morbidity and severity of inflammation-centric ailments, such as myocarditis, arthritis, and gastroenteritis(Schneider, Panagiotakos et al. 2008, Abasolo, Tobías et al. 2013, Wang, Zhao et al. 2020). Although the exact mechanism remains unclear, inflammatory factors, such as temperature drops, which can alter C-reactive protein levels, fibrinogen levels, and other blood parameters, may be essential for triggering the adverse effects of extreme temperatures (Hampel, Breitner et al. 2010). Schneider's investigation revealed a link between plummeting temperatures and elevated interleukin-6 (IL6) concentrations (Schneider, Panagiotakos et al. 2008), positioning these inflammatory markers as potential catalysts for inflammation-driven malignancies.
Our data indicated that colder temperatures also augment the incidence of oral inflammatory conditions, including dental caries, periodontitis, pulpitis, interstitial periodontitis, and gingivitis.
This study investigated the minimum risk temperature and associated lag patterns for oral diseases. For each outcome, we defined the minimum risk temperature as the temperature correlated with the lowest associated risk. Five diseases exhibit a minimum risk temperature of 12 to 13°C. This observation accentuates the need to enhance public health interventions focused on oral health in colder climes. We concur with the preventive strategies championed by Shanghai(Qian, Gao et al. 2022), which advocate for mitigating prolonged exposure to the cold outdoors, maintaining warmth, residing in spaces with optimal heating, and adopting specific lifestyle alterations, such as consuming warmer beverages (e.g., drinking more hot water). However, our findings did not corroborate the protective effects of mask-wearing against the detrimental impacts of cold temperatures on oral health. This observation is set against 2020 to 2022, when China implemented stringent epidemic control measures, leading to ubiquitous mask usage. It implied that masks may not work to prevent oral disease.
Interestingly, Guangzhou's minimum risk temperature (12–13°C) was greater than that of Shanghai. Furthermore, Shanghai's data indicated that daily temperatures above 7°C had no discernible impact on oral health, marking a notable divergence from our findings. As shown in Fig. 2, the lag patterns show the risks of extremely low temperature generally occurring on the previous 1 day and lasted for 14 days, which is also different from Shanghai’s 7 days. We postulate that these discrepancies might stem from variances in the thermal perceptions of the two populations and the presence of heating facilities in Shanghai, a luxury absent in Guangzhou. Such a lack of heat in Guangzhou might cause residents to face prolonged exposure to colder environments, even if these temperatures are milder than those on Shanghai's coldest days. Another factor is the relationship between seasonality and disease correlation (Chen, Huang et al. 2015, Azzouzi and Ichchou 2020). Shanghai's pronounced four-season climate contrasts with the relatively uniform climate of Guangzhou, potentially accounting for the disparities in observed data between the two cities. Our analyses of lag patterns revealed no significant correlation between extremely low temperatures and several oral conditions, including dental caries, periodontitis, pulpitis, periapical periodontitis, and TMD.
Our data revealed a stronger association between cold temperatures and oral diseases in patients older than 60 years, even though these stratified observations were not statistically significant. We speculated that this trend could be attributed to the inherent attributes of elderly people. Older individuals are more susceptible to other chronic conditions, and exhibit diminished resilience. The manifestations of untreated or partially treated oral conditions become more pronounced when the body's defenses wane (Ferrucci and Fabbri 2018, Wang, Chen et al. 2019). Moreover, challenges in thermoregulation among older individuals due to difficulties in free fatty acid mobilization, increased visceral fat, decreased physical activity, and challenges in maintaining core body temperature during cold stress(Azzouzi and Ichchou 2020) increase susceptibility. Such insights stress the importance of enhancing oral care interventions for this age group, including improved public oral consultation services, strengthened oral health education, and measures to ensure warmth.
Oral diseases, including dental caries, pulpitis, and periodontitis, pivot to a crucial pathogenic mechanism: disequilibrium between the host and the oral microbiota. Several mechanisms suggest how low temperatures might influence oral diseases. First, direct exposure of the oral cavity to a cold environment can induce significant temperature fluctuations within the mouth. This abrupt change can disrupt the oral microbial community. When the ecological balance of the oral microbiota is perturbed, it can precipitate a range of oral diseases(Roberts and Darveau 2015, Mira, Simon-Soro et al. 2017). Second, cooler ambient temperatures can incite an inflammatory response. Specifically, colder conditions can trigger the substantial release of stress hormones such as adrenaline, noradrenaline, and cortisol. These hormones, in turn, can inhibit the secretion of proinflammatory cytokines (Eimonte, Eimantas et al. 2021, Eimonte, Paulauskas et al. 2021). Third, colder ambient temperatures can compromise the body's immune defenses (Brazaitis, Eimantas et al. 2014). A weakened immune system due to low temperatures can heighten an individual's susceptibility to oral diseases. Nevertheless, while these mechanisms provide some insight, the intricate interplay of cold temperatures on oral diseases warrants more comprehensive investigation.
Our findings also illuminate the relationship between low temperatures and TMD, a prevalent ailment in the oral and maxillofacial domains. This multifactorial condition is caused by a spectrum of factors, encompassing muscle hyperactivity or dysfunction, trauma, hormonal fluctuations, and joint alterations(Gauer and Semidey 2015). Deciphering the role of low temperatures in its etiology requires further scrutiny.
Several limitations exist in our study. However, time series analyses, which are intrinsically ecological, preclude adjustments for individual-level risk factors, such as transient dietary behaviors. Nonetheless, such factors are unlikely to skew the results appreciably in time series evaluations, as their prevalence within specific cohorts remains relatively stable over time or can be modulated by integrating a time-smoothing function in the mode(Davalos, Luben et al. 2017). Moreover, specific individual determinants, such as socioeconomic metrics and oral hygiene practices, might act as confounders, but our dataset lacked these parameters. Employing ambient temperature as a surrogate for individual oral temperature might introduce inaccuracies, potentially leading to an underestimation of the effects of ambient temperature on oral health(Gasparrini and Armstrong 2010). Pinpointing the precise onset of oral conditions poses another challenge, potentially misaligning environmental exposure data with health metrics. Given our study's confinement to Guangzhou, extrapolating our findings to a broader demographic might be limited. Hence, future endeavors encompassing multiple cities and spanning longer durations are pivotal to validate our conclusions.