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Review ariticle | DOI: https://doi.org/10.31579/2690-4861/730
*Corresponding Author: Christopher Turner, Specialist in Restorative Dentistry (Rtd) Bath UK.
Citation: Christopher Turner, (2025), Diabetes Mellitus and its Sixth Complication Explained, International Journal of Clinical Case Reports and Reviews, 24(4); DOI:10.31579/2690-4861/730
Copyright: © 2025, Christopher Turner. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Received: 04 March 2025 | Accepted: 07 March 2025 | Published: 24 March 2025
Keywords: diabetes; periodontitis; co-morbidity; professional co-operation
In 1999 Löe described periodontal disease (PD) as the sixth complication of diabetes mellitus (DM) because this latter group of patients has a 3 – 4 times greater risk of developing PD when compared with non-diabetics. This rises to 10 times for smokers.
DM and PD are inter-related, one disease affecting the other and vice versa. The exact mechanism is unclear but may be related to inflammation, blood markers for which are raised in both diseases.
From the medical point of view there are five complications of DM namely cardiac, vascular, renal, ophthalmic and neurological that can be visualised as a simple hub called DM with spokes for the above complications.
However, the research evidence has shown that the severity of all these five complications is worse when patients have active, uncontrolled PD. When PD is treated, there is an improvement in glycaemic control.
These results have led to the conclusion that PD is not a separate complication of DM but a co-morbidity factor acting by: modifying the severity of another disease and modulating the severity of diabetic complications in the manner of a rheostat. A new model is proposed together with a system for doctors and dentists to work together.
There are likely to be wide variations in outcomes depending on both the bacteriological load from mature dental plaque and individual immune responses.
More focussed research is required.
The concept that periodontal disease was the sixth complication of diabetes mellitus (DM) dates back to a paper by the distinguished Scandinavian periodontist Professor Harald Loë in 1999 when he attempted to inform doctors about the increased risk that people living with diabetes had of developing periodontal disease (PD) [1]. In fact, the first description of this was much earlier by Williams in his paper entitled ‘Diabetic Periodontoclasia’ published in 1928 and forgotten [2]. Nearly 100 years later as dentists we still have difficulty persuading too many doctors about this connection. We now know that this risk is about 3-4 times greater than for non-diabetics, rising to 10 times for diabetics who smoke [3].
Pathophysiology
From the medical point of view there are five complications of diabetes mellitus namely, cardiac, vascular, renal, ophthalmic and neurological. We can visualise this simply as a hub called diabetes mellitus with spokes for the above complications (Figure 1).
Where does periodontitis fit in? Is it another spoke? Decidedly not. The evidence is overwhelming that diabetes and periodontitis are interrelated, one disease affecting the other and vice versa [4,5], so the model relationship has to have both diabetes and periodontitis at a much larger hub with an inter-relationship (Figure 2). More importantly, the research evidence has shown that the severity of all these five diabetic complications doctors have to deal with is worse when patients have active, uncontrolled periodontitis. Also, when periodontitis is treated, there is an improvement in glycaemic control [6].
The relationship between DM and PD may be inflammatory in origin. There is a common pathogenesis involving an enhanced inflammatory response at both local and systemic levels7. This is caused by the chronic effects of hyperglycaemia and the formation of advanced glycation end-products that promote the inflammatory response [7]. Levels of C-reactive protein4, tissue necrosis factor [7], and cytokines [8] are raised in both diseases. Polysaccharides in Gram negative bacteria in mature dental plaque are known to stimulate the production of cytokines. Toxic products from these organisms initiate tissue breakdown and increased osteoclastic bone resorption in the periodontium [9]. Osteoclastic activity also increases along with enhanced glycation levels and poor glycaemic control [10], thus stimulating further bone resorption and diminished bone formation in a vicious circle and contributing to the enhanced levels of periodontitis and alveolar bone loss seen in people living with diabetes.
When dental plaque is left, after seven to ten days gingival inflammation ensues and this is the precursor of periodontitis [11].
PD may be thought of as an infection. However, it is not in the true medical sense of the word because it does not meet Koch’s postulates for a single recoverable infective agent. PD is a chronic hyper sensitivity reaction to antigens in mature dental plaque.
Research has shown that when the severity of diabetic complications is compared to periodontal status that for:
Cardiac and Vascular: Poor oral health is associated with atherosclerotic cardiovascular disease. This interaction raises cardiac morbidity fourfold and is associated with chronic infection mediators which may lead to the initiation of endothelial dysfunction [12].
Nephropathy: People on dialysis are at greater risk of developing PD [13]. With severe Periodontitis there is a 2.6 times greater risk of macroglobinaemia and a 4.9 times risk of end stage renal disease [14]. Periodontal management may contribute to the prevention of renal disease [15]. Patients should be screened for periodontitis before acceptance onto dialysis programmes [16].
Neuropathy; Is a microvascular complication associated with xerostomia in 40 per cent of people living with diabetes mellitus [17]. The increased risk of caries goes without saying. There is an inverse relationship between salivary flow and glycated haemoglobin (HbA1c) levels that may be due o disturbances in glycaemic control [18].
Retinopathy: There are few studies of this complication together with PD using different criteria [19,20]. However, an increase in the severity of diabetic retinopathy is associated with the components of periodontal disease [21].
How might this affect the medical model? It is clear that periodontitis is influencing diabetic’s individual responses. It is both
This is a new concept and means that PD should not be regarded as a complication of DM but a co-morbidity factor. Therefore, for optimum treatment of people living with diabetes there has to be both medical and dental contemporaneous input into their care. When both are treated together there may be a synergistic effect [22].
It is expected that there will be wide variations in individual patient responses depending upon the bacteriological load from their plaque, and their immune response.
In summary, the new model shows dentists can help doctors and their diabetic patients but most of the former do not know that, they have not been taught that, and there are too many who see dentists trying to ‘muscle in’ on what is their treatment area. Dentists need to change that and achieve a paradigm shift in thinking with doctors to meet the calls for better interprofessional co-operation in care [23,24].
Defining risk factors for doctors.
The medical gold standard for diabetic monitoring is the serum level of HbA1c, a two to three month retrospective measure. This may be recorded as percentage levels that should be maintained below 6.5%, green on the traffic light method that has been introduced [25,26]. There is an amber band for 6.5 to 8.5% and a red band for greater than 8.5%. More recently these values have been expressed in either mmol/mol or mmol/litre (Table
1). However, previously determined individual targets could be more appropriate for some people with diabetes, particularly those who are frail or lack awareness of hypoglycaemia [27].
| percentage | < 6> | 6.5 – 8.5 | 8.5> |
| mmol/mol | < 48> | 48 – 69 | 69 > |
| mmol/L | < 7> | 7.8 – 10.9 | 10.9 > |
| Risk factor | Low, green | Moderate, amber | High, red |
Table 1: HbA1c levels and medical risks
Defining risk factors for dentists.
Various indices of periodontal health have been described. The measure of choice is the World health Organisation’s Community Periodontal Index of Treatment Need (CPITN) [28]. The mouth is divided into sextants, right and left molars and bicuspids, and incisors and canine teeth for each jaw. The maximum score for each sextant is recorded using the following general guidelines [25,26]:
4* Root furcation involvement or severe periodontal breakdown with an increased risk that teeth will require extraction. The maximum sextant score gives a periodontal risk factor using the traffic light system,0,1,or 2, green, 2* or 3, amber, and 4 0r 4* as red (Table 2). A pro forma has been developed for people living with diabetes to record their results and share them with their respective professional advisors (Table 3)25. This form is freely downloadable at www.chooseabrush.com.
| Highest sextant score | 0 or 1 or 2 | 2* or 3 | 4 or 4* |
| Risk factor | Low, green | Moderate, amber | High, red |
Table 2: Periodontal risk factor
Table 3:
MY DIABETES RESULTS FOR 20……..
NAME…………………………………………………DOB…………
Doctors – HbA1c, this should be below 6.5%
Risk Factor: less than 6.5% low; 6.5-8.5%, medium; 8.5% or more high, or
Less than 48mmol/mol,low;48-70mmol/mol,medium; 70mmol/mol or more,high
Less than 7.8mmol/l, low; 7.8-10.9 mmol/L, medium: more than 10.9 mmol/L high
Date HbA1c……………… Risk level…………
Previous results
Date HbA1c……………… Risk level…………
Dentists: The Basic periodontal examination
Date………………….. Highest score……..
Risk Factor 0,1,2 low; 2*-3 medium; 4 or 4* high
Previous results
Date………………….. Highest score……..
Risk Factor 0,1,2 low; 2*-3 medium; 4 or 4* high
Notes. These numbers range from 0 to 4*. The maximum score in each sextant is recorded.
2* Pockets of less than 3.5mm. Presence of sub-gingival calculus indicating a need for professional mechanical plaque removal.
4* Root furcation involvement or severe periodontal breakdown with an increased risk that teeth will require extraction.
© Dr C Turner, 2022, 2024. Reference: Brit dent J 233: 1, 2022.
See www.chooseabrush.com to down load this form
Doctors need to understand basic facts about periodontitis and record which of their patients is receiving dental care and advise those who are not that they are at greater risk of developing PD and that when PD is treated their blood sugar levels can be better controlled [29,30].
Dentists should revise their medical history questionnaire [31] to include questions about type 1 or type 2 DM. What medications are being taken because some type 2 diabetics do need insulin injections in addition to oral medication. and about hypo or hyper glycaemic episodes requiring hospitalisation. They may have a medical emergency to deal with.
However, the medical gold standard for diabetic monitoring is the glycated haemoglobin level, the HbA1c. So, the HbA1c level is a most important addition to the medical history. Each patient may know, or you may have to ask their doctor.
In our recent study, asking this question in general dental practice these are the results [32]:
Most patients, 84 per cent were type 2. Analysing their HbA1c results showed that 40 per cent were in the green zone, 20 per cent amber, 12 per cent red and 28 per cent did not know. The study also identified 9 per cent of patients who were not attending for annual review by their doctors. The importance here is that as the HbA1c increases, bringing PD under control becomes harder.
Fortunately, periodontitis is both a treatable and preventable disease with good clinical outcomes when detected at an early stage. Prevention depends on daily efficient and effective plaque control by patients33. When plaque is left in situ for 7 to 10 days inflammation results [11]. In relation to the other costs of care for the main diabetic complications, dental treatment is relatively cheap and can be cost-effective.
Where these is bone loss between teeth limited and gingivae the most efficient way to remove plaque is by using interdental brushes. These are made in a variety of diameters by different manufacturers some of whom have a limited size range [34]. For ideal results in individual prescription for the correct diameter brush for each space is essential as in one study every pattern of bone loss and therefore brush diameter requirement was individual [33].
When few sizes are suggested, plaque will always be left behind contributing to the bacteriological load, periodontal disease will continue and diabetic complications are less likely to be limited.
PD is not the sixth complication of DM. It modifies and modulates the severity of diabetic complications. This means that both diseases should be treated concurrently and that dentists and their teams have a very important role to play together with doctors.
The glycated haemoglobin results, HbA1c are essential for dentists. The higher the score the more difficult it is to control periodontal disease.
Risk results need to be shared between doctors and dentists. A form has been developed for patients themselves to show their respective professional advisors.
This can be downloaded at www.chooseabrush.com.
Dentists need to be more proactive, teach and work with doctors who may not know about the increased risk that their patients living with DM have for PD.
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