The significance of lateral forces to the
development of dental abfractions^© 

Author: Brian Palmer, D.D.S.

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ABSTRACT

             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. 

INTRODUCTION

             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 margin. 

Review of past research and literature

             The works by Dr. W. D. Miller ¹ 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).” ¹   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, ² 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.  Black stated:

“In 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 ³ 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, ⁴ 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 ⁵ 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. ⁶ 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. ⁷ 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 and Gjermo ⁸ 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 et al. ⁹ 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. ¹⁰ 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 ¹¹ 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 ¹² 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 ¹³ proposed that bruxing produced most of the destructive forces on tooth structure, and recommended removal of lateral forces by reshaping teeth.  McCoy ¹⁴ 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 ¹⁵ 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. 

Damaging lateral forces caused by occlusion.  Dawson ¹⁶ 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. ¹²   McCoy ¹³ 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 teeth.

             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 al. ¹⁷ found a statistically significant association in retention failure of restorations when related to tooth flexure. 

Damaging 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 ¹⁸ 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:   

 1) Abfractions 

 2) Sensitive teeth 

 3) Loosening of teeth 

 4) Excessive wear of teeth 

 5) Change in alignment of teeth

 6) Bone breakdown and bone loss 

 7) Broken or destroyed restorations

 8) Non-bacterial, non-plaque related gingival recession

 9) Opening of contacts

10) 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 fracture (Fig.2). 

Skull Studies

             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 ¹ 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 toothbrush.

             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 cusps (Fig.3).  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 abfraction (Fig.4b). 

             The causes of tongue thrusts, malocclusions, and a collapsing of the oral cavity include:

1) Noxious habits such as excessive thumb sucking, blanket sucking, etc.

2) Use of pacifiers.

3) Infant feeding using improperly designed baby bottles and nipples.

4) Ankylosed tongues.

5) Macroglossia (large tongue).

6) Grossly enlarged tonsils/adenoids and obstructed airways.

7) Facial-skeletal growth abnormalities. 

8) Central nervous system dysfunction affecting facial muscles. 

9) Refined sugars and poor nutrition as described by Dr. Weston Price. ¹⁹ 

DISCUSSION

             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. ²⁰ 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 tongue thrust.

             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., ²¹ 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. 

IMPLICATIONS 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.   

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REFERENCES

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.

20.     Fildes V. Breast bottles & babies: a history of infant feeding. Edinburgh: Edinburgh University Press; 1986:325.

21.     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 1996. 

Illustrations for:  The significance of lateral forces to the development of dental abfractions

Fig. 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.) 

Fig. 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.  

Fig. 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. 

Fig. 4.  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 tooth.