Bad teeth may cause diseases of the heart, lung, rheumatoid arthritis, atherosclerosis, and many others. Scientific studies have been linked in recent years, infections of the oral cavity with infective endocarditis, atherosclerosis, myocardial infarction, and stroke. It has been observed that over 90% of patients with heart disease have a gingivitis, and surveys indicate that 40% of patients with inflamed gingiva have serious systemic diseases, the most commonly diabetes, heart disease, or osteoporosis. Scientists have found that to gum disease increase and the risk of Alzheimer's disease - research has shown that people who have them and those who have a lot of teeth have dropped significantly higher risk of developing Alzheimer's disease too. See also: Libby P, et al: Inflammation and atherosclerosis. Circulation, 2002; 105:1135-1143.

There is numerous data available to show link between periodontal dioseases & cardiovascular diseases

In many countries high quality dental care is a luxury rather than routine care. Research tells us that the disadvantaged have poorer health outcomes than general populations. Does anyone know if any studies have focussed on the oral health of say homeless persons and the link to chronic disease burden?  

 I was asked to help a young patient who suffered a stroke due to bleeding into a benign intracranial tumour. He developed absolute trismus, immediately post stroke.There was no fall or trauma to his jaws or facial skeleton. No history of TMJ dysfunction.

He developed wasting of right masseter and temporalis. Corneal reflex was absent. Botox treatment to masseter and temporalis did not improve his condition. Bilateral coronoidotomies and masseter myotomies improved his opening to 4 centimeters.

Despite surgery and vigorous exercises he still not maintaining good mouth opening.

This is a rare case of trismus after stroke.

One interesting link between the oral cavity and stroke lies in the possibility to detect calcified carotid atheroma on the panoramic radiography.Some authors have postulated that dental surgeons that are able to detect such calcifications in at-risk patients could help prevent strokes. 

There have been quite a few papers on the subject. Here are some papers of interest:

Almog DM, Illig KA, Carter LC et al. Diagnosis of non-dental conditions. Carotid artery calficiations on panoramic radiographs identify patients at risk of stroke. N Y State Dent J. 2004;70(8):20-5.

Baumann-Bhalla S, Meier RM, Burow A et al. Recognizing calcifications of the carotid artery on panoramic radiographs to prevent strokes. Schweiz Monatsschr Zahnmed 2012;122(11):1016-29.

Carter LC, Tsimidis K, Fabiano J. Carotid calcifications on panoramic radiography identify an asymptomatic male patient at risk for stroke. A case report. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1998;85(1):119-22.

The exact predictive value of said calcifications has not been fully established yet but remains -I believe- an interesting subject worthy of further research, especially considering the opportunity for prevention of such a serious disease.

In addition to cardiac and stroke issues, there is considerable research linking poor oral hygiene to aspiration pneumonia.

You may be interested in a question I posed a couple weeks ago. Here is the link to that thread.

https://www.researchgate.net/post/How_does_the_salivary_pH_affect_oral_microbial_flora_in_critically_ill_patients?_tpcectx=profile_highlights

Summary:

We discussed how institutionalized patients tend to have poor oral hygiene, as well as the stress of a critical illness and hospitalization. Stress can cause changes in salivary composition. It may also cause low salivary flow rates, but of course medications and immunocompromise play key factors too. Low salivary flow has been linked to low pH (acidic). Less saliva also means less buffering ability by the saliva to normalize pH and kill harmful bacteria. Also, poor oral hygiene leads to more gram-negative bacterial colonization, causing a thick biofilm. This thick biofilm is not penetrable by the salivary properties that kill harmful bacteria. The bacteria's waste or end-products are acidic, further making the mouth acidic. Acids demineralize teeth, and cause more decay and bacterial overgrowth. It is such an interesting but vicious cycle.

These oral microbes are the same ones that make a patient sick with Healthcare Acquired Pneumonia (aka nosocomial pneumonia, Hospital Acquired Pneumonia). Some patients may be getting sick with pneumonia due to micro aspirations of bacteria-laden saliva, and it may be that they do not even have significant dysphagia and food/liquid aspiration to warrant diet modifications. This is a key factor in our bedside swallowing evaluations performed by Speech-Language Pathologists.

https://www.researchgate.net/post/How_does_the_salivary_pH_affect_oral_microbial_flora_in_critically_ill_patients?_tpcectx=profile_highlights

Key article in use of Chlorhexidine gluconate oral rinse in patients undergoing heart surgery showed good prevention of nosocomial infection: DeRiso et al (1996) in Chest, 109: 1556-1561.

More recent research on Chlorhexidine has been not as conclusive, but a problem with the research is that there is no set protocols of oral hygiene. For example, Bellissimo-Rodrigues, et al (2009: Infection Control and Hospital Epidemiology, vol 30, no. 10, 952-958) found little difference between CHG and placebo, but both groups had their teeth brushed before application of rinse. Brushing and applications were done 3 times a day. Just the teeth brushing alone may have reduced pneumonia. The pneumonia rates in placebo group may have been much higher if the patients did not get brushed. Just brushing the teeth alone helps reduce the plaque where the bacteria reside. In reality, do patients really get their teeth brushed 3x/day in the hospitals or nursing facilities? Probably not. Many hospitals do not have written oral hygiene policies (Carson, et al, 2007, of AACN noted that only 56% of nurses surveyed said that their employers had written oral hygiene policies).

Further reading, please see my Dysphagia resource website at link below. See blog section for topics on oral hygiene.

www.swallowstudy.com

A dynamic view on process may give the following interpretation: bad teeth at certain age may serve as an indicator of low income and poor life conditions during the period  before this age, and, after all, namly these  poor life conditions and low income are true causes of bad health.   

Thanks Sumit, Katrina, Kumara, Nathan Alexander, Karen and Vladislav. I appreciate all the useful and high-quality answers, and I believe it will to others who it be read to be interesting and encourage them to further study in this important area of human health.

people  can get accumulation of bacteria and calculus leading to infection and bad breadth .