Vol.1, No.4, 263-268 (200
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9) Health
Openly accessible at/HEAL H
New insights in understanding dental caries and
periodontal disease: the avalanche model
Peter Gaengler1, Ljubisa Markovic1, Dagmar Norden2, Rainer A. Jordan1
1Department of Operative and Preventive Dentistry, University of Witten/Herdecke, Witten, Germany; peter.gaengler@uni-wh.de
2Ordination, Rheinstraße 1826382 Wilhelmshaven, Germany
Received 12 October 2009; revised 10 November 2009; 13 November 2009.
Biology is based on evolution; therefore, eu-
cariotes like plants, animals and human beings
are living in harmony with their procariote an-
cestors. If this is obviously the normal way of
life, then pathobiology follows the same basic
principles. The highly complex harmony of the
living world may be disrupted, and a punctuated
disease starts which is different from the health
equilibrium. To reflect this biological archetype
on the main diseases in dentistry - caries and
periodontitis - the avalanche model is being
proposed based on scientific and clinical evi-
dence. This way of argumentation does influ-
ence the strategic planning of preventive and
curative programmes in dental research as well
as in daily practise.
Keywords: Dentistry; Dental Caries; Etiology;
Model; Pathology; Periodontal Disease
The role of dental caries as a health related sociological
phenomenon goes back to the 10th millenium BC, at the
end of the last ice age, when raising temperatures in the
flood plains of the fertile crescent allowed the cultivation
of wild corn [1]. As a consequence, the fundamental
change from a nomadic hunting-gathering way of life to
settled farming and agriculture in man took place [2].
The development of the grinding stone was an important
milestone during the continuous process of refining food.
Consequently, the highly abrasive and fibre rich food of
the prehistoric population was being more and more
replaced by a soft diet consisting of pastries and pasta. In
the 2nd millennium BC, increasing incidence of dental
caries - though on a low level - inspired the creation of
the very first etiologic model for tooth decay in human
history: the concept of the tooth worm causing caries
and periodontal disease. Paleoantropologic examination
of skulls showed a low prevalence of dental caries (Pa-
ganelli C. Dental caries frequency in adult egyptian
mummies. Personal communication. Valdaora, 2006) less
than 10% [3] increasing up to 25% in medival times [3].
During the transatlantic slave trade and the beginning of
the industrial processing of cane sugar in North America
and Europe, dental caries prevalence went up to 50%
reaching a frequency of almost 100% in all industrialised
countries today [4]. Sociologically, the dramatic increase
and spread of dental caries in human society can be seen
as a consequence of civilisation and industrialisation in
food production. From a functional point of view, it
seems to be a consequence of the absence of masticatory
abrasion and tribological attrition caused by dramatic
changes in diet [5]. Thus, non-opened fissures and
proximal sites show the highest rates of affection, when
no longer exposed to abrasive and attritional wear. These
presumptions are supported by comparative odontology.
Extended occlusal wear far into the dentine core, a pulp
chamber becoming smaller by forming tertiary dentine
and the dentition drifting mesially by flattening the
proximal contacts were shown to be a natural pattern of
function in omnivorous dentitions, i.e. in dentitions of
wild living boars and primates showing hardly any tooth
decay [6]. The Witten Dental Caries study showed fur-
ther strong correlation between tooth wear and dental
caries experience in man [7]. Based on phylogenetic
findings, it is supposed that a thick enamel cover and a
spacious pulp lumen in omnivorous species represents
an equifinality - a common characteristic in open sys-
tems converging to a dynamic equilibrium - in which the
pulp is a spaceholder for replacement with tertiary den-
tine to compensate the decreasing thickness of enamel
and dentine caused by attrition and abrasion [8].
Clinical observations have shown that caries and perio-
dontal diseases have a chronic-cumulative character and
no continuous way of progression. They lead to the con-
P. Gaengler et al. / HEALTH 1 (2009) 263-268
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Figure 1. Biomineralisation consequences of the pathogenesis of dental caries diseases
according to the concept of progression and stagnation. Comparison of factors con-
tributing to either bursts of disease progression or to long-lasting periods of stagnation.
MC = stem cell; T = T lymphocyte; B = B lymphocyte; P = plasma cell; L = lympho-
cyte. [21]
cept of a destructive periodontal disease pathogenesis
with different types of progression showing characteris-
tic episodes of activity and inactivity [9]. Corresponding
dynamics in caries progression with episodes of demin-
eralisation and remineralisation have already been
pointed out since the 1960s [10,11]. Consequently,
knowledge from both cariology and periodontology was
then consolidated to one robust pathogenetic Concept of
Progression and Stagnation of Dental Caries and Perio-
dontitis noticing epidemiologic, historic, immunologic,
odontologic, physiologic and sociologic perceptions [12]
(Figures 1,2). The initial stages of the diseases,
pre-caries as the first detectable mineral deficite and
gingivitis are reversible and therefore, they are at least
partly underlying a principle of progression and remis-
sion. In dental caries, the highly complex “ion whip”
contributes to loss and uptake of calcium and phosphate
ions in enamel and exposed dentine and cementum. This
is a lifelong ongoing equilibrium, and bursts of prevail-
ing demineralisation activity with the consequence of
pre-caries and clinical caries lesions are rather occa-
sional episodes.
P. Gaengler et al. / HEALTH 1 (2009) 263-268
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Figure 2. Biomineralisation consequences of the pathogenesis of periodontal diseases according to the
concept of progression and stagnation. Comparison of factors contributing to either bursts of rapid
disease progression with periodontal pocket formation or to long-lasting periods of stagnation. T = T
lymphocyte; B = B lymphocyte. [21]
In periodontal diseases, there are alternating short
lasting activities of destruction (with localised immu-
nological breakdowns) and long-lasting episodes of
equilibria. From a structural biological point of view,
progression means loss of connective tissue and bacterial
penetration through the wall of leucocytes, stagnation
means replacement of connective tissue and build-up of
the wall of leucocytes.
Irregularity in biological behaviour as a principle has
already been discussed in evolutionary theories in the
1970s as an alternative to phyletic gradualism of Dar-
win’s theory of evolution, and it was later described as a
general biological principle [13,14]. Phyletic gradualism
proceeds on the assumption of long-term continuous
transformation of genetic material in the majority of a
population without basic episodes of stagnation. Palae-
ontological evidence for this stepwise transformation of
slightly different forms in a common evolutionary chain
could never be found. The conceptual basis for the al-
ternative theory of punctuated equilibria is based on this
assumptions: a) geographic isolation as a precondition
for a genetic process of transformation and b) a homoeo-
static equilibrium with rare and temporally compressed
changes in the gene pool alternating with long episodes
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Figure 3. Initial white spot lesion (teeth 43 and 45)
and brown spot lesion (tooth 47) in a young female pa-
tient, (a) start of non-invasive treatment with the daily
bioavailability of fluoride by F-containing dentifrice
and F tablets (1 mg p.d.), (b) clinical control over 5
years demonstrating reversals of the white spot lesions
in canine and premolar and decreased but stable molar
lesion. (courtesy of Dr. T. Lang, Witten, Germany).
Figure 4. Periodontal condition in a young HIV-
seropositive patient undergoing Highly-active Anti-
retroviral Therapy, (a) before periodontal treatment
with black triangles especially between incisors as a
result of chronic marginal periodontitis triggered by
necrotising ulcerative bursts, (b) 16 month after con-
servative treatment and a strict supportive periodontal
programme with a “creeping attachment”.
of stasis. The theory especially implies so-called punctu-
ated equilibria during the early stages of speciation,
while dramatic changes in the environmental conditions
are taking place. If this is indeed a general biological
principle, then one could try to apply this to pathobiol-
ogy. Punctuationalism applied to oral medicine, then,
also means, periodontal disease is a pathologic event in
limited dental sites and not in the entire dentition despite
the all-over presence of plaque; just like caries, that is
rarely seen as a generalised event but showing age-re-
lated peaks. In palaeontology, the postulation of favour-
able environmental conditions for punctuations is met by
geographic separation from the mother-species; in hu-
man life sciences by a locally different immunologic
host reactivity [15]. The concept of pulpal reaction [16]
in particular takes up the theory of biologic equilibria, as
it compares pattern of pulpal reactions on dental caries
progression with different functional periods of the den-
tition. The concept of a multifactorial disease [17] goes
even one step further assuming biofilms to be a physiol-
ogic phenomenon, and demineralisations to be a simple
reflection to multifactorial disturbances in a physiologic
balance between the natural biofilm and all (wet) smooth
surfaces. The dynamic character of dental caries and
periodontal diseases has recently emphazised in the
concept of cyclical progression [18]. Knowledge from
microbiology confirms this view, as only 10% of all cells
in human beings are mammalian; the vast amount are
procaryotes, mainly bacteria. In the oral cavity, more
than 20,000 genetically differentiable bacterial species
were recently analyzed. They usually diversify in several
clones, of which eventually one is pathogenic. As a re-
sult, many organic systems basically live in a state of
symbiosis or commensalism with their microorganisms
[19]. Recently, Mogens Kilian et al. suggested a scenario
that commensal streptococci gradually evolved from a
pathogen by genome reduction. Their study provided
insight into the evolutionary history that resulted in ge-
netically closely related streptococci with very high (S.
pneumoniae) or no pathogenic potential of commensal
species [20]. The comprehensive model of progression
and stagnation was extended by these realisations from
palaeontology and contemporary theories of evolution,
from cellular biology, microbiology, and cariology to
suggest the avalanche model of dental caries and perio-
dontal diseases:
“[Punctuated equilibrium means] for the main infec-
tious diseases in dentistry, caries and periodontitis, a
promotion of the concept of progression and stagnation,
when rapid punctuated bursts disrupt prolonged dormant
episodes of stagnation: the macroorganism, which is
otherwise living in balance with its microorganisms,
reacts with an acute burst of demineralisation and/or
inflammation - the episode of punctuation. This is an
avalanche model, where different punctuated episodes
(sun, snow, wind, hazardous snowboarder) initiate an
avalanche in an otherwise highly complex system” [21].
It would make sense to look at very few clinical exam-
ples to demonstrate the snowballing character of the
avalanche caries progression model. Despite a complex
variety of etiological components, the development of
white spot lesions per time and per tooth mainly on
smooth surfaces of dental enamel is well documented as
the only evident clinical risk factor for progression or
remission of subclinical pre-caries or initial caries into a
surface lesion. This is also reflected in modern caries
detection and assessment systems [22]. Otto Backer
Dirks clearly demonstrated in a rather simple way that
initial lesions may undergo remineralisation and, there-
fore, being arrested (10). This could be shown in longi-
tudinal studies assessing caries over an eight year period
[23]: even under highly controlled clinical conditions in-
cluding oral health education and bioavailability of topical
fluoride, one third of initial smooth surface caries lesions
were found to turn into superficial cavities (Figure 3).
As with avalanches in winter mountains it is hard to
say that a single factor of lesion progression is responsi-
ble for cavity formation, and it could easily be asked: is
the shift in bacterial activity due to quorum sensing re-
sponsible, is the change in host responses due to saliva
factors responsible, is temporary overload of low mo-
P. Gaengler et al. / HEALTH 1 (2009) 263-268
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Openly accessible at
lecular carbohydrates responsible, is insufficient oral
hygiene responsible, or is any other factor causing pro-
gression responsible? It could also be looked at the in-
fluence of drug-induced hyposalivation as one of the
main factors of root caries progression in the elderly [24].
Seemingly, it is a well-known scenario in patients at-
tending for their routine dental check-ups to see indi-
viduals under antihypertensive and/or tranquilizing
medication to develop hidden approximal or root dentine
lesions within a very short time after decades of robust
caries inactivity. Is the causative factor just the hy-
posalivation when a change in food intake and oral hy-
giene within the last few months is rather unlikely? An-
other issue is the susceptibility to secondary caries in
teeth with long-term performing composite restorations
with obvious marginal leakage: eighteen years old fill-
ings were followed-up for another two years, and despite
slightly increasing surface deterioration no secondary
caries at the wide gaps was micromorphologically de-
tected [25]. Plaque control at these sites was rather poor,
alimentary regime stressed a slight cariogenic influence,
but the avalanche did not occur.
Per Axelsson, Birgitta Nyström and Jan Lindhe fol-
lowed-up 357 subjects maintained in a preventive pro-
gramme for 3, 6, 15 and finally 30 years [26]. The clini-
cal outcome clearly demonstrated: only 21 teeth were
lost due to progressive periodontitis or due to dental car-
ies, and it was evident that the exposure of patients to a
highly individualised maintenance programme in only
one private dental practice provided by the same dental
hygienist was mainly contributing to disease stagnation.
Undeniably, the influence of various factors may have
slowed down the progression of the disease, but man-
agement with a strict preventive programme retarded
tooth loss dramatically, and the avalanche in most cases
did not occur. On the other hand, it is also clinically and
microbiologically well documented that bacterial shift
due to systematic antibiotic treatment regimes may lead
to outbursts of deep pocket periodontal abscesses [27].
This is obviously the result of an overgrowth of antibi-
otic resistant anaerobic pathogens turning a long-lasting
stable periodontal disease into progressive deep pockets
rapidly. Risky snowboarding with antibiotics, though,
may be that fundamental change in environmental com-
mensalism condition to initiate a punctuated equilibrium.
Finally, the prevalence of oral manifestations in HIV-
seropositive showed necrotising ulcerative periodontitis,
erythematous candidiasis and oral hairy leucoplakia to
be significantly associated with the HI-viral load [28].
Again, only one factor - like the famous risky snow-
boarder – out of the complex host response was contrib-
uting to severe disease progression and an avalanche
(Figure 4).
Dentistry is a medical discipline. Therefore, biomedical
principles in their uniqueness in the living world should
be applied to dental problems and solutions. The mam-
malian life is mainly characterised by symbiosis and
harmony of our “own” (eucaryotic) cells and of the
neighborhood (procaryotic) cells, communicating to
each other by signal molecules until – the avalanche
goes down. This is a rare punctuated episode. And the
whole dental care armamentarium should be concen-
trated to these episodes. Rather often we do not know
what is the real cause for a given individual burst. Nev-
ertheless, our preventive programmes and treatment
strategies are powerful and effective bringing back the
harmony disrupted by the avalanche.
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