Preventive Sheet #2 By Leen

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Preventive Sheet #2 By Leen

Post by Sura on 18/2/2012, 11:47 pm

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Re: Preventive Sheet #2 By Leen

Post by Shadi Jarrar on 13/3/2012, 5:26 am

بسم الله الرحمن الرحيم
14-2-2012
preventive dentistry
Last lecture we started talking about prevention of dental caries and to understand this we should talk about the etiology of dental caries.
Aims of the lecture:
Theories of dental caries and the acidogenic theory
Role of bacteria and the plague
What are the hypothesis relating to how plague causes caries
Host factors
An introduction about the role of diet and sugar

-what is caries?
Simply it is a disease process affecting the mineralized tissue we are talking about enamel ,dentine and cementum(so it is demineralization of these tissues)
-Aetiology?how the damage really occurs?
-Theories of dental caries:
One of the earliest theories was in the 18th-19th century
Started from inside and progressed outwards they thought that it
They thought that it was caused by tooth worms( a being that eats the tooth from inside to outside)and that is not true

Then we know that caries is multifactorial so it involves the
Bacteria,diet,host factors as well
_How does caries occur?( By acid)
Acidogenic theory WD Miller 1890
-acidogenic theory:acid formed by bacteria fermenting sugar of dietary carbohydrate leads to decalcification of the tooth structure in the end it leads to progression of caries
-Animal experiments to support this theory:
There was animal theories to support the acidogenic theory
Kite and colleagues 1950 did experiments on rats by stomach tube vs mouth tube.
Demonstrated that dental caries was caused by the presence of food in the mouth.bcs the rats that were fed by stomach tubes didn’t develop caries.
another Animal experimants:
Orland et al in 1950
They brought two kinds of rats one Is germ free and the other are normal rats and they fed them both by cariogenic diet and they found that:
Germ free rates+cariogenic diet=no caries
Normal rates +cariogenic diet=caries
That shows the importance of bacteria in developing caries then u cant have caries without bacteria.
-Which bacteria responsible for caries?
Cariogenic bacteria ,the charactaristics of these bacteria:
1.acidogenic bcs acid is what causes caries
2.able to produce PH that is low enough to demineralize tooth structure
3.able to survive and continue to produce acid at low PH
4.Adhesive ,so it should stick to the tooth structure.
Eg.
Streptoccoci
Streptococci is the most common and it causes the initiation of caries.
Mutant streptococci group initiation of caries, you took that streptococci mutant is the one that causes caries but that is not exactly right bcs this is a specie and if you look at the actual genetic tree it is a group
Phylogentic tree contains:pyogenic,anglnous,bovis,salfvartus,mitle,mutants(6 groups) and all might cause caries not mutant alone.
Lactobacilli
Rods in shape
Progression of caries,progression in developed caries related to the
Actinomyces
In Caries risk assessment they use these bacteria to know if this person is at high or low risk to develop caries.
Location:
Bacteria responsible for dental caries are not those floating free in the saliva.
What we worry about is the interphase btwn the tooth and the plague, in the stagnation area ,caries forms where plague is in fissures,proximal areas,gingival margins so we don’t worry about the bacteria in saliva what we worry about is bacteria in PLAGUE
Oral plague
-bacteria mostly
-an amorphous matrix
polysaccharide
-leucocytes and desquamated epithelium
WBCs
We cant depend on saliva to remove plague

Hypothesis relating to how plague causes caries:
Hypothesis means either yes or no
-specific
-nonspecific
-ecological
Specific:
Out of the diverce collection of bacteria in plague only a limited type that are enrolled in the disease,so only a specific (certain species) of bacteria, this hypothesis has been rejected bcs it is not only one specie that causes disease
Non specific:
Disease results from the out come of the interactions among all of the component species.
Prevention would be by plague control
This is rejected too,bcs it is not that simple
Ecologic
The disease results from a Shifts in the balance of the resident bacteria m and when the environment becomes supportive of the cariogenic bacteria(that’s when you have caries) and the environment is less supportive(that’s when you have no disease) ,,,,even if you have cariogenic bacteria in the plague in a healthy environment where there is no acid they can actually cause no disease so it doesn’t mean that the presence means a disease,so disease could be controlled by not only by targeting the pathogen but also by interfering with the factors that are responsible in the shifts in the microflora. So there is a balance and if the balance shifts towards bacteria causing disease and then if we can shift the balance back to normal we go to the health state even if the bacteria is there.
Potential cariogenic bacteria can be present in health but that are not clinically revalent .
So here we are talking about ecology and what is happening around the bacteria
Dental plague-Biofilm
Biofilm:well organized ,cooperating community of microorganism what happens here is within the plague we are going to have microorganisms arranged within microcolonies
- are arranged in microcolonies ,groups of bacteria that are together and they are surrounded by a matrix
-microcolonies are surrounded by protective matrix and there is a communication system within the biofilm
Researches are now going on in how they destroy caries as a biofilm bcs biofilm is more resistant to antibiotics and antimicrobial.
How does carries occurs?
Saliva,plague,toothstructure we have 3 environments:
DEMINERALIZATION:
Sugar causes the plague ,the bacteria take the sugar and ferment it,and then you get acid and if it goes below 5.5(critical PH) the hydroxyapetitecristals CA10(PO4)6(OH)2 will be (CA)+2 and( PO4)-4 then these will go from tooth structure to plague and then to saliva.
REMINERALIZATION:
Caries developes in series of demineralization and remineralization so it is not only demineralization
There is a chance for the minerals to go back to the tooth structure ,we have calcium Ca2+ and phosphate (PO4)-3 in the saliva and when the environment allows it it goes back to the plague and simply goes to the hydroxyapetite form ,and if we have floride in the environment (saliva) it can stick to the apetite crystals and form floroapetite Ca10(PO4)6F2 which is more resistant to caries than hydroxyapetite. So we like floride bcs it forms crystals that are more resistance to caries than hydoxyapetite ,we will talk in details about floride later.

Stephan Curve
Measuring Cariogenicity




I,ve got the diagram from web pls refer to the slides` diagram as soon as we have it .
If you have glucose rinse the PH is going to go down ,the bacteria produces more and more acid until you reach somewhere below 5.5 but it wont stay down there the PH will slowly increase and this is related to the buffer from saliva and the washing effect of the saliva then slowly it will reach as it was in the beginning which is 7 ( the PH of the plague).
Below the critical PH is where we have demineralization.
When we talk about diet advice we always speaks about the freguency of taking sugar,bcs every time you take sugar you are going to go below the critical PH so if you keeps on taking sugar snacks you are going to have more attacks and no time to be in reminarilization stage.

As you know caries is multifactorial and know we will talk about host factors and one of them is saliva.
Saliva:
What is the role of saliva in caries?
Saliva clears away the cariogenic from the mouth it has a washing effect.
They have done animals experiments to look out the role of saliva in caries as they took the salivary glands from the animals and they saw the increase of the incident of caries which is proportional to the amount of how much the saliva was decreased, that’s why the patients with xerostomia are high risk patients for caries.
Saliva has buffering effect and it is mostly related to the bicarbonate.
The higher the rate of salivary flow the higher the rate of bicarbonate.
High florate with high buffering capacity causes low caries,this is found in Down syndrome(imp) these patients have high periodontal disease but low caries,but we see down syndrome patients with caries but that is bcs nobody takes care of their teeth and their diet.
In saliva we have anibacterials, lysosymes(something? Plz refer to slides) but there is no evidence that these have any role in caries activity.
We have IgG ,IgA but these have little effect on caries.
Tooth supsability is one of the other host factors that play a role.
Enamel Composition:
If we have floride in the enamel we have a crystals that is more resistance to acid so less caries, sometimes we have hypoplastic and hypomineralized enamel and these affect the rate of progression of caries and it would be easier for the destruction to occur bcs we have less enamel. As you know deep and narrow fissures favor retention of plague,more difficult for the plague to be removed so more caries .

The other factor is Diet:
Carbohydrate ( sugars) changed by plague bacteria into acid
Types of sugar:
Classically sucroses is the one that we are worried about ,it is the arch criminal of dental carries,it is the one most likely to cause caries and this is supported by animals experiments
Glucose ,fructose and maltose are similar cariogenicity
Lactose and galactose are less cariogenic
What is the evidence that sugar causes dental carries? there are areas that documented to have low sugar intake and low carries level eg.Alaska,they depends on fish and proteins
Other eg. Island called Tristan du Cunha up to 1930 they depends on vegetables in their diet but when they adopt western diet where they have sugar their caries prevelance increased 8 times.
Other eg. In wars the country usually lack of sugar so they give the families only small amount of sugar and they found that they have decline in the number of caries,but after wars it usually increases
In patient with restriction type of diet like in enzyme deficiency which is called Fructose intolerance these patients cant metabolize fructose and sucrose as well so they cant take any of these sugars and they have low caries.
At the end you have to make a balance between risk factors promoting demineralization and protective factors promoting remineralization.

Qs.what is the role of genetics?
Genetics mostly due to the transmission of bacteria from the mother to the baby,there is genetics in tooth supsuptability as well but mostly it is due to bacteria the earlier they have the bacteria the earlier they will develop caries, but nobody tells me the mother has lots of caries then the child will have a lot too,but mostly it is behavioral (diet,oral hygien)rather than genetics.

Good luck
Leen Qutachi












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Shadi Jarrar
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