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significance of lateral forces to the
development of dental abfractions©
Author: Brian Palmer, D.D.S.
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For many years, practicing dentists have accepted the theory that
hard-bristled toothbrushes coupled with improper brushing technique cause
abfractions. This article proposes
another explanation. Based on
twenty-seven years of private clinical practice, a review of the literature and
personal observation of hundreds of historical human skulls, this author raises
a hypothesis that abfractions are caused by tongue thrusts, and other lateral
forces secondary to malocclusions resulting from oral cavity changes associated
with bottle feeding and the use of pacifiers in infants.
The dental profession took a giant step backward when it accepted as a
scientifically supported theory that tooth brushing was the cause of gingival
notching of teeth. Many dental
schools still teach this erroneous concept.
This article proposes an alternative theory, that traumatic forces are
the cause of notches and erosion of teeth around the area of the gingival
of past research and literature
The works by Dr. W. D. Miller
in the late 1800s and early 1900s,
seem to be the earliest review in English of the erosion-abrasion issue as
it relates to tooth brushing and dentifrices.
Miller discussed wasting away of the tooth at the neck as “very often
taking a form as though produced by a three-cornered file (pp2).”
Possible causes of wasting away mentioned
in the literature at that time included: toothbrushes, alkalis, acids, friction
of folds of the mucous membrane, exfoliation, acid secretions of the mucous
membrane, electrolytic action, defective development, and rubbing of partial
clasps, among others. Ingredients
used in toothpastes at that time included: pumice, oyster shells, precipitated
calcium carbonate, prepared chalk, and cigar ashes.
The results of Dr. Miller’s two years work on the etiology of erosion
were published in 1907 when he announced his belief that erosion was caused by
weak acids or gritty tooth powders, or by both, assisted by the toothbrush.
He seemed to be convinced that the toothbrush was the main factor.
From his investigations, Miller deduced that wasting of the teeth was for
the most part a purely mechanical process in which the chief and often only
factor concerned was the toothbrush in conjunction with tooth powder.
He believed lingual wasting was due to friction of artificial plates or
clasps. He also concluded that
acids alone could never produce wasting.
In 1914, G. V. Black,
the “Father of Modern Dentistry” and witness to
Dr. Miller’s experiments, did not believe that the brush could produce the
kind of wasting to the hard tissue of the teeth that Miller described.
some cases it has appeared as though the brush might be responsible for injury
to the teeth near the gum margin, but other cases where the brush had not been
used at all are so nearly like these as to show that the injury had not been
done by severe brushing (pp.157).”
The works by S. C. Miller
in 1950 appear to be the first in the literature that
stated that traumatic and lateral forces by the tongue, lips, and cheeks were
contributors to gingival recession.
In 1965, Glickman,
stated that susceptibility to recession was
influenced by many factors, such as the position of teeth in the arch, the angle
of the root in the bone, and the mesio-distal curvature of the tooth surfaces.
In 1974 Brodie
demonstrated erosion-like patterns occurred in
acrylic dentures and teeth. Brodie
noted and suspected that individuals with erosion-like lesions tended to be of
the nervous type, exhibiting bruxism and tension and perhaps psychosomatic
conditions. In 1972, Sognnaes et al.
examined a random sample of about 10,000 extracted
teeth. About 1,700 teeth (18%) had
typical patterns of erosion-like lesions. They
noted that erosion patterns did not occur exclusively on surfaces that were
exposed to obvious physical factors such as the abrasive action of a toothbrush.
Instead, lesions were found on the lingual surfaces of the teeth and on
regions that were inaccessible to friction from tooth brushing.
In 1975, Volpe et al.
did a long-term supervised, double-blind human
clinical study and concluded that factors other than dentifrice abrasivity
played an important role in tooth wear. Sangnes
found that of 533 patients examined, 45% had
wedge-shaped defects in the cervical area of one or several teeth.
The various tooth brushing techniques did not seem to influence the
development of such lesions. Yettram
used engineering principles and studied forces
applied within a tooth when external loads were placed on it.
Using the "Finite Mathematical Element Stress Analysis," they
were able to determine the stress loads in teeth during various tests.
They explained why abfractions could occur even gingival to the margins
of crowns. They found the amount of
load placed on the teeth was the key factor.
Radentz et al.
found there was no relationship between cervical
abrasion and tooth brushing technique, tooth brushing frequency, brand of
dentifrice, brand of toothbrush, and/or salivary pH.
In addition, there was no relationship between the prevalence of cervical
abrasion and race or hand dexterity. Alexander’s
research was based on attaching toothbrushes to a
machine. It was concluded that
brush design, brushing frequency, and brushing pressure all affect the degree of
cervical abrasion on patients with good oral hygiene habits.
In this author’s opinion, the assumptions drawn from Alexander’s
scientific research were inappropriate. Granted,
notching or ditching will occur when conditions are purposefully set up as in
that study, much the same as will flowing of water over a period of time create
the Grand Canyon.
Lee and Eakle
described lateral forces as the cause of the
breakdown of tooth structure. Their
illustration (Fig.1) was the first and best
illustration to date as to what occurred during lateral force loading.
In 1983, McCoy
proposed that bruxing produced most of the
destructive forces on tooth structure, and recommended removal of lateral forces
by reshaping teeth. McCoy
discussed vertical and horizontal forces as related
to "Dental Compression Syndrome.” McCoy
stated that vertical forces were less harmful because they provided axial
stimulation to the teeth and bone. Horizontal
forces, however, were extremely damaging, because they subjected teeth and bone
to torquing and off-loading. These
forces caused further damage by exposing the condyles to unwanted lateral
forces, thus constantly preventing them from assuming their natural positions in
their fossae. Grippo
coined the term abfraction.
He stated that abfractions were the pathologic loss of both enamel and
dentin caused by biomechanical loading forces.
The forces could be static, as in swallowing and clenching, or cyclic, as
in chewing. The abfractive lesions
were caused by flexure and ultimate material fatigue of susceptible teeth at
locations away from the point of loading. The
breakdown was dependent on the magnitude, duration, direction, frequency, and
location of the forces.
The work of Lee, Eakle, McCoy and Grippo should have alerted more
dentists that the toothbrush is not the cause of notching.
It is appalling that the toothbrush is still being accused, and still
being taught in dental schools, as the major cause of these notches.
For over twenty years, this author has focused on the evaluation of
notching and the collapse of the oral cavity and the airway. This private clinical experience, combined with a review of
the literature and a personal observation of approximately 600 human skulls, has
led the author to conclude that a person with an abfraction has either a
damaging lateral force caused by an occlusal disharmony, or a damaging lateral
force caused by a tongue thrust.
lateral forces caused by occlusion.
described the requirements for a stable occlusion.
These included: 1) Having stable stops on all teeth when the condyles
were in centric relation, 2) Having anterior guidance in harmony with border
movements of the envelope of function, and 3) disclusion of all posterior teeth
in protrusive and excursive movements, including posterior teeth on the
non-working (balancing) and working side.
If a tooth has an abfraction, the occlusal loading on the tooth can be
tested in centric occlusion and in excursive movements with occlusal marking
paper. There is a good chance the
tooth with the abfraction will have a heavy marking on one of the inclines of a
cusp. This damaging lateral force
produces stress lines in the tooth and results in tooth breakdown as explained
by Lee and Eakle.
suggested that to resolve the problem, the tooth
needed to be reshaped. A word of
caution about reshaping (equilibrating): once one tooth is equilibrated, the
dentist must be prepared to possibly equilibrate the entire mouth, because once
the pressure is taken off one tooth, the patient may then feel pressure on other
This same treatment of equilibration can often resolve sensitive teeth
problems. To prevent Class V
abfractive restorations from falling out, one needs to treat the cause of the
abfraction before restoring it. Heymanet
found a statistically significant association in
retention failure of restorations when related to tooth flexure.
lateral force caused by a tongue thrust.
If the patient does not have heavy markings on the inclines, then the
patient is probably a tongue thruster or deviate swallower.
For the purpose of this article, a "normal swallow" is a
swallow that is initiated with the tip of the tongue starting in the area of the
maxillary anterior papilla, then with a peristaltic-like action, pressing up
against the roof of the maxilla, forcing the bolus (saliva or food) posteriorly
and finally down the throat. The
tip of the tongue remains in the area of the anterior papilla during the entire
swallow. Within the context of this
article, any other swallow is a "tongue thrust" or "deviate
swallow.” The tongue should not
press with any force into, against, or between any teeth during the swallow.
A visual examination of the area of the abfraction with the teeth
together and lips slightly parted, can reveal whether the tongue is pushing into
the tooth, or saliva bubbles are visible coming between the interproximal
spaces. Tongue thrusting can also be the result of large tongues and
congested or obstructing airways.
Reputed American orthodontist, Dr. Harry W. Tepper, appreciated and
understood the importance of the action of the tongue in treating orthodontic
cases. Dr. Tepper treated several
thousands of patients over 40 years of practice.
Just a simple four-page article by Dr. Tepper
can be used to introduce his important concepts.
If these concepts were understood and practiced by all dentists,
especially orthodontists, there would be minimal failures of restorations and
relapses in orthodontics. In his
article Tepper stated that the correction of the tongue thrust should be an
integral part of treatment in dentistry, particularly in orthodontics. He stated that the major causes for malocclusion, like narrow
arches, crowded bites and maxillary protrusions, were usually brought about by
an interference of the normal swallowing process by the use of artificial
nursing. Tepper explained that the
initial insertion of the large and elongated rubber nipple was a basic cause for
tongue malfunction. This author
agrees with that statement.
If the key requirements of occlusion are not met, or if lateral tongue
forces traumatize teeth, then the following can occur:
Loosening of teeth
Excessive wear of teeth
Change in alignment of teeth
Bone breakdown and bone loss
Broken or destroyed restorations
Non-bacterial, non-plaque related gingival recession
Opening of contacts
Any combination of the above.
Depending on varying conditions, any or all of the above can occur over
time. Factors such as the over-all
health of the individual, the health of the surrounding bone and tissue, oral
hygiene habits, personality of the individual, stress level of the individual,
strength of masticatory and peri-oral musculature, et cetera, all contribute to
the degree of the response and subsequent breakdown.
Not all teeth respond in the same way, but with time, teeth may even
Abfractions are a modern malady; contemporary anthropologists are
unfamiliar with modern day abfractions. Notches
noted by anthropologists are usually found on the interproximal surfaces of
teeth. These interproximal notches
are usually attributed to strands of sinew having been passed between the teeth.
In 1884, Dr. W. D. Miller
examined all the skulls in the Berlin anatomical
museum, but did not succeed in finding a single case of indisputable wasting.
He quoted other works by Zahnarzt Stieren of Wiesbaden, S. P. Mummery of
London, and Dr. Grevers of Amsterdam, all of whom had had similar findings.
Miller attributed the lack of wasting of teeth in early skulls to the
fact that pre-industrialized races cared for their teeth by using a twig as a
This author has evaluated approximately 600 human skulls from a variety
of historic time periods. The first
collection of skulls evaluated by this author was at the University of Kansas
Medical Center. These 210 skulls
were believed to be old skulls from India, a culture that predominately
breastfed until recently. Of those
210 skulls, only four (approximately two percent) showed signs of malocclusion.
One skull had an asymmetrical jaw and three others had slight open bites.
Two of the skulls with slight open bites showed signs of beginning
abfractive lesions. In another
study of 20 prehistoric skulls, some dating back 70,000 years, in the
anthropology department at Kansas University, no abfractions were noted.
During this author’s research of ancient skulls at the Smithsonian
Institution in Washington, D.C., staff anthropologists were intrigued to see the
handful of extracted teeth with abfractions with which this author presented
them. At that time, the anthropologists at the Smithsonian with
whom this author talked to, were only aware of one tooth in their collection of
historic teeth that had an abfraction on a buccal or lingual surface.
They had set it aside as being special.
One quick look at the tooth showed a severe wear facet on one of its
Figure 4a shows the
mandibular bicuspid seen in figure 3, in the mouth.
The dark spot above the abfraction that can help identify the tooth can
be seen in both figures. Most of the abfraction was subgingival, making it impossible
for a toothbrush to reach. The
tooth had an extensive periapical abscess due to a pulpal exposure caused by the
The causes of tongue thrusts, malocclusions, and a collapsing of the oral
Noxious habits such as excessive thumb sucking, blanket sucking, etc.
Infant feeding using improperly designed baby bottles and nipples.
Macroglossia (large tongue).
Grossly enlarged tonsils/adenoids and obstructed airways.
Facial-skeletal growth abnormalities.
Central nervous system dysfunction affecting facial muscles.
Refined sugars and poor nutrition as described by Dr. Weston Price.
When anthropologists in the future examine the skulls from our culture,
what will they deduce about abfractions from this era?
This author has observed that abfractions rarely occur in skulls older
than 200 years. Why 200 years?
The precursors to modern baby bottles and nipples were invented in Italy
between 1770 and 1800 AD.
The major causes of the increase in malocclusions and
abfractions in present modern cultures involve the use of bottle-feeding,
pacifiers, and excessive noxious infant habits such as thumb and finger sucking.
Toothbrushes cannot get much softer than they already are; yet people
continue to have notches, even with instructions to lighten the forces and to
brush in a circular manner. This
author concludes that abfractions are not due to brushing, but rather to
traumatic lateral forces placed on teeth as a result of a malocclusion or a
This author’s research has also led him to predict with a reasonable
degree of confidence, that the above causes of abfractions are also the same
factors that contribute to the collapse of the airway and to the development of
snoring and obstructive sleep apnea. According
to Kushida et al.,
characteristics of malocclusions such as high
palates, narrow maxillary and mandibular arches, and overjet, have a high
sensitivity and specificity (t-test was p<.0001) for predicting which people
might be candidates for having snoring and obstructive sleep apnea problems.
Dentists need to understand the importance of obstructive sleep apnea, a
serious medical condition. An
examination for sleep apnea can be quickly done during a regular dental
examination. If the condition is
suspected, a referral to a qualified physician for further evaluation would be
warranted. This author will cover
apnea in another article.
FOR FURTHER RESEARCH
Several unanswered questions could provide interesting topics for further
investigation. For example, a more
extensive comparative study of the abfraction rate in modern versus historic
skulls would provide additional information.
Longitudinal studies that look at individual factors involved in the
causation of abfractions would provide information of use.
Finally, controlled studies that isolate individual factors, such as
excessive pacifier use, that lead to malocclusion and abfractions would assist
dentists in determining the cause of their patients’ problems.
This author hopes that a research facility or someone just starting in
practice, will take these hypotheses and test them experimentally.
Acknowledgments: This author
wishes to thank Cheryl Hall Harris for assistance in organizing and developing
the material, Nicole Bernshaw and Joan Gilson for their assistance, and Ann Mary
Corry for procuring previously published studies supporting this research.
1. Miller WD. Experiments and observations on the wasting of tooth tissue variously designated as erosion, abrasion, chemical abrasion, denudation, etc. Dental Cosmos 1907;XLIX:1-23.
2. Black GV. Operative dentistry: the pathology of the hard tissues of the teeth. London. Medico-Dental Publ Co; 1914:39-59,157.
3. Miller SC. Textbook of periodontia. Phila: Blakiston Co; 1950:63.
4. Glickman I. Clinical periodontology. Phila: WB Saunders; 1965:101-3.
5. Brodie A, Sognnaes RF. Erosionlike denture markings possibly related to hyperactivity of oral soft tissue. J Am Dent Assoc 1974;88:1012-7.
6. Sognnaes R, Wolcott R, Xhonga F. Dental erosion: erosion-like patterns occurring in association with other dental conditions. J Am Dent Assoc 1972;84:571-82.
7. Volpe A, Mooney R, Zumbrunnen C, Stahl D, Goldman H. A long term clinical study evaluating the effect of two dentifrices on oral tissue. J Periodontol 1975;46:113-8.
8. Sangnes G, Gjermo P. Prevalence of oral soft and hard tissue lesions related to mechanical toothcleansing procedures. Community Dent Oral Epidemiol 1976;4:77-83.
9. Yettram A, Wright K, Pickard H. Finite element stress analysis of the crowns of normal and restored teeth. J Dent Res 1976;55:1004-11.
10. Radentz WH, Barnes GP, Cutright DE. A survey of factors possibly associated with cervical abrasion of tooth surfaces. J Periodontol 1976;47:148-54.
11. Alexander JF, Saffir AJ, Gold W. The measurement of the effect of toothbrushes on soft tissue. J Dent Res 1977;56:722-7.
12. Lee WC, Eakle WS. Possible role of tensile stress in the etiology of cervical erosive lesions of teeth. J. Prosthet Dent. 1984;52:374-80.
13. McCoy G. On the longevity of teeth. J. Oral Implant. 1983;II:249-67.
14. McCoy G. Examining the role of occlusion in the function and dysfunction of the human mastication system. Dental Focus (Korean J of Dent) 1995;15:10-15.
15. Grippo JO. Abfraction: a new classification of hard tissue lesions of teeth. J Esth Dent. 1991;3:14-8.
16. Dawson PE. Evaluation, diagnosis, and treatment of occlusal problems. St. Louis: CV Mosby; 1989:1-91.
17. Heymann HO, Sturdevant JR, Bayne S, Wilder AD, Sluder TB, Brunson WD. Examining tooth flexure effects. J Am Dent Assoc. 1991;122:41-7.
18. Tepper HW. Tongue thrust correction in one easy lesson. Functional Orthod 1986;March/April:40-43.
19. Price WA. Nutrition and physical degeneration - a comparison of primitive and modern diets and their effects. Los Angeles: Amer Acad of Applied Nutrition; 1948.
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Kushida C, Guilleminault C, Ahmed O Jr, Clerk AA. Clinical prediction of
obstructive sleep apnea by a morphometric model. Presented at 10th Annual
Conference of the Assoc of Prof Sleep Societies (APSS). Washington D.C., June
significance of lateral forces to the development of dental abfractions
1. Lateral forces create cervical regions of tension and
compression, as indicated by arrows. The magnified section depicts disruption of
chemical bonds between enamel rods. Small
molecules enter between hydroxyapatite crystals and prevent reestablishment of
bonds to make crystals more susceptible to breakage and chemical dissolution.
Reprinted with permission. (Lee
W, Eakle W. Possible role of tensile stress in the etiology of cervical erosive
lesions of teeth. J. Prosthet Dent. 1984.)
2. Serious consequences of abfractions.
(a) Note various angulations in the abfractions.
The toothbrush could not have caused these abfractions.
(b) Hygiene better but weakened lower incisor fractured off.
(c) Strong lateral force on the teeth from the thrust of the tongue.
3. Comparison of an abfraction on a bicuspid, seen quite
frequently in contemporary dental practices, to the only tooth found in the
Smithsonian collection at the time of my study, to have an abfraction.
Note flat occlusal incline where molar had been traumatized.
Same bicuspid as in figure 3 prior to extraction.
Dark dot above the notch identifies the tooth as being the same tooth in
both figures. Note that most of the
notch is subgingival. A toothbrush
could not have caused this abfraction. Note
tongue thrusting into adjacent space and cusp-tip to cusp-tip occlusion of
bicuspid to maxillary canine. Figure
3b demonstrates the possibly consequence of an abfraction – an abscessed