A local infectious lesion that may cause pathologic changes elsewhere in the body, even in organs situated far from the original site of infection, is called an infectious focus. In oral radiographs, intrabony foci, such as periapical periodontitis lesions, vertical bone loss defects and furcation lesions, can be detected, but no foci that involve soft tissue only. The noxious effect of oral infections upon the general health status and their associations with general diseases have been observed and suspected since the beginning of this century (Äyräpää 1902). There are several known mechanisms whereby an infectious focus can cause damage at distant sites, but some unknown ones may still exist. A periapical periodontitis lesion in a lower molar can perforate the mandibular lingual cortical bone, with pus oozing into the floor of the mouth under m. mylohyoideus and into the mediastinum, resulting in Ludwig"s angina, a life-threatening condition even nowadays (Äyräpää 1902, Moncada et al. 1978, Garatea-Grego & Gay-Escoda 1991). Dental plaque may be aspirated, and oral bacteria (especially anaerobic periodontopathogens) can in this way cause pneumonia. This is a special hazard to institutionalized or hospitalized elderly in a poor state of health or to immunosuppressed patients (Greenberg et al. 1982, Limeback 1988, Rams & Slots 1992, Christensen et al. 1993, Finegold et al. 1993). Non-oral respiratory pathogens are also able to colonize dental plaque, which then acts as a reservoir of these bacteria, seeding them to the lungs. (Scannapieco et al. 1992, Scannapieco and Mylotte 1996, Fourrier et al. 1998). Bacteria themselves may pass into the bloodstream from oral foci, and they have been found to cause very serious infections, such as endocarditis, pyelonephritis and brain abscessses (Rams & Slots 1992, Nieminen et al. 1993, DeStefano et al. 1993, Navazesh & Mulligan 1995, Beck et al. 1996, Grau et al. 1997, Meurman 1997). The bacteria themselves need not even leave the foci to be detrimental for general health. Their toxins circulating in blood may cause fever, often termed in the medical practice as "fever of unknown origin", for the causative focus itself may be completely asymptomatic (Katz et al. 1992, Rams & Slots 1992). A similar phenomenon is "metastatic inflammation" manifesting most often in the eye as uveitis or iritis. It is caused by an overreactive immunologic host response against the bacteria present in the foci, bacterial parts, or bacterial toxins (Torabinejad et al. 1983, Kettering & Torabinejad 1984, Bloch-Michel 1985, Brummer & van Wyk 1987, Rams & Slots 1992). Elevated levels of IgE and an increased prevalence of systemic allergies have also been associated with the presence of periapical periodontitis lesions (Kettering & Torabinejad 1984, Brummer & van Wyk 1987). The presence of oral foci has been associated with an increased frequency of exacerbations in Crohn"s disease (Halme et al. 1993). Furthermore, eradication of oral foci has been observed to ameliorate the symptoms of severe arthritis in some cases (Meurman 1997).
Oral infections, as well as other infections and inflammations have been associated with increased risk of myocardial infarction and brain infarction in young and middle-aged subjects (Syrjänen et al. 1989, Valtonen 1991, Mattila 1993, Nieminen et al. 1993, DeStefano et al. 1993, Beck et al. 1996, Grau et al. 1997). The exact pathogenic mechanism whereby the focal infections inflict their hazardous systemic effects on those conditions is still obscure. However, it has been suggested that infections and inflammations increase the blood leukocyte count, circulating fibrinogen and other blood coagulation factors, which, in turn, may lead to heart and brain infarctions. (Syrjänen et al. 1989, Valtonen 1991, Mattila 1993, Kweider et al. 1993, Beck et al. 1996, Meurman 1997). Bacterial lipopolysaccharide endotoxins and host-produced inflammatory cytokines may also play a role in the formation of atheromas and thus lead to infarctions (Loesche 1994, Herzberg & Meyer 1996, Beck et al. 1996, Meurman 1997). Myocardial infarction is a common cause of death, and an association between death from coronary heart disease and oral infections has been observed: Beck et al. (1996), in a study cohort of 1,147 men, aged 21 to 80 years at the baseline and followed up for 18 years, found mean radiographic periodontal attachment loss of more than 20% of the root length to be associated with a twofold increase in fatal heart attacks. The age-adjusted odds ratio was 2.2, the 95% confidence interval 1.3-3.9, and odds ratio adjusted for age, and known risk factors for cardiovascular disease was 1.9, with a 95%, confidence interval of 1.1-3.4. Clinical probing depth was also associated with cardiovascular disease, as the percentage of all teeth having more than 3 mm probing depth showed an age-adjusted odds ratio of 3.6, the 95% confidence interval being 1.5-8.5, the highest risk ratio that has been observed between oral infections and cardiovascular disease (Beck et al. 1996).
DeStefano et al. (1993), also found an association between clinically diagnosed periodontal pockets and death risk (OR 1.5, confidence interval 1.3-1.7) in a sample of 9,760 subjects aged 25-74 years. This association was most pronounced in young and middle-aged men aged 25-49 years (OR 2.1, confidence interval 1.2-3.6). The number of carious teeth had no association with the risk of death. In addition, they found edentulism to be associated with increased death risk in young and middle-aged men (OR 2.6, confidence interval 1.3-5.1). The mortality rates in the edentulous and dentate groups in the present study did not differ (Table 4, V). This may reflect the homogeneity and relatively good state of health of the present study group as a whole. The effect of edentulism may, on the other hand, be most pronounced in younger subjects, or that some other factors, possibly ones related to life-style and socioeconomic status and leading to edentulism at young age, may also precipitate early death.
Garcia et al. (1998) found, in a sample of 804 dentate men (mean age 42 years), followed for over 25 years, that radiographically diagnosed mean alveolar bone loss and clinically diagnosed periodontal pockets had a statistically significant association with the death risk (OR 1.9, confidence interval 1.3-2.7 and OR 1.7, confidence interval 1.1-2.8, respectively). The number of remaining teeth had little effect on the death risk.
The mean alveolar bone loss in the previous studies can be compared with the extent of horizontal bone loss in the present study, OR 1.8, confidence interval 0.9-3.8, and the difference did not quite reach the 95% significance level, probably because of the limited sample size. In the present study, the number of carious teeth and the number of furcation lesions showed an inverse relationship to the risk of death, but it was not statistically significant. (V, Fig"s 1 and 2, Table 5). In the present dentate study group, increased all-cause mortality was associated with periodontal infrabony extending to the middle third of the roots or deeper, age-and sex-adjusted OR 2.2, 95% confidence intervals 1.0-4.7, figures comparable with those observed in previous studies. Mortality was also slightly increased in the subjects who had 5-14 infrabony pockets, moderate to advanced horizontal bone loss, or apical periodontitis lesions, and along with the pooled sum of all the potentially infectious findings, but the 95% significance level was not attained, again most probably due to the limited sample size.
Of the present 293 radiographed subjects, 54 (18.4%) died within the four year follow-up, and 32 of them (59.3%) were dentate. The sample is thus very small for an epidemiological study of death risk, and one must be careful in making conclusions on the basis of the findings. However, it would be tempting to interpret the results of these previous studies and the present one as indicating a causal relationship between the observed oral findings and the increased death risk. But Joshipura et al. (1996) found no association between self-reported periodontal disease and coronary disease and sudden death in a sample of 44,119 male health professionals. The fact that no associations were found in this study may reflect the unreliability of the method used (self-reporting, a questionnaire study), or a possible influence of the selected study cohort. A causal relationship between oral infectious foci and death has been observed in cases where an oral infection has directly spread into vital areas (Äyräpää 1902, Moncada et al. 1978, Garatea-Grelgo & Gay-Escoda 1991). Also, the poor oral hygiene and the resulting dental plaque accumulation in the hospitalized and institutionalized elderly in a poor general condition have been associated with aspiration pneumonia, and pneumonia is one of the most common causes of death in these groups (Greenberg et al. 1982, Limeback 1988, Rams & Slots 1992, Christensen et al. 1993, Finegold et al. 1993). Furthermore, there is another possible explanation for the association between the observed oral foci and clinical periodontal findings and the increased death risk in the elderly: the presence of clinically probed deepened periodontal pockets and radiographically observed infrabony pockets, horizontal bone loss and periapical periodontitis lesions may be indicators of deteriorated physical condition, manual dexterity or capacity to carry out adequate oral hygiene. Possible non-utilisation of professional dental services may also play a role in the development of oral foci in these elderly. The many diseases that the elderly suffer from and various medications they use may often cause hyposalivation, which negatively affects oral health (Närhi 1994, Pajukoski et al. 1997). Psychological factors caused by negative life-events may aggravate existing periodontitis. The effect of negative life-events on periodontitis may be due to less active oral hygiene, decreased salivary flow (caused by medication or the psychologic disturbance itself) or possible immunologic factors. Although tobacco smoking, a well-known risk factor for periodontitis (and cardiovascular disease), increased in association with negative life-events in one study, the association between negative life-events and periodontitis remained significant even after smoking was taken into account in the statistics. (Croucher et al. 1997). In elderly men, anxiety has been associated with fatal myocardial infarction (OR 3.2, 95% confidence interval 1.3-8.1) and sudden death (OR 5.7, 95% confidence interval 1.3-26.1) (Kawachi et al. 1994). Anger has also been associated with an increased risk of cardiovascular disease in elderly men (OR 3.2 for heart attack, 95% confidence interval 0.9-5.6) (Kawachi et al. 1996).
Deteriorated physical, cognitive and sensory functional capabilities go hand in hand with a poor functional dental status and an increased risk of death (Österberg et al. 1990). Deteriorated physical condition which manifests as various disabilities in daily life has, indeed, been found to be prognostic of death in an extensive follow-up study of community-dwelling elderly, of whom 531 died within one year (Guralnik et al. 1991). The deterioration of the dental status and the consequent loss of teeth has been found to be an indicator of deteriorating physical condition in a sample 1,029 75-year-olds from Finland, Denmark and Sweden (Österberg et al. 1995). Poor functional dental status was also associated with an impaired quality of life and increased death risk also in a population of 1,137 70- to 75-year-olds in Brescia, Italy (Appollonio et al. 1997).
Because of the complex interrelationships between the various risk factors and indicators of the increased mortality, it has not been possible to demonstrate absolutely certain causal relationships between oral infectious foci and death. However, the results of the studies so far undertaken strongly suggest that such causal connections may exist.