Damaging lateral forces

Damaging lateral forces caused by occlusion.
Dawson 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 that 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 described by Lee and Eakle. McCoy suggested that to resolve the problem, the tooth needed to be reshaped. To prevent Class V abfractive restorations from falling out, however, one needs to treat the cause of the abfraction before restoring it. Not surprisingly, Heyman et al. found a statistically significant association in retention failure of restorations when related to tooth flexure.

Damaging lateral force caused by abnormal tongue activity.
If the patient does not have heavy markings on the inclines, then the patient may have abnormal activity of the tongue. 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, that continues 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 considered to be the result of abnormal tongue activity. 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 patient’s teeth together and lips slightly parted, can reveal whether the tongue is pushing into the tooth, or if salivary bubbles are visible coming between the interproximal spaces (also a sign of abnormal tongue activity). Note the abnormal position of the tongue during swallowing in. Tongue thrusting can also be the result of large tongues and congested or obstructed airways.

Reputed American orthodontist, Harry W. Tepper , appreciated and understood the importance of the action of the tongue in treating orthodontic cases. Tepper treated several thousands of patients over 40 years of practice. 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 a number of events deleterious to dental health 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

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.

The hypothesis is basically simple, and easily tested in any dental office. Abfractions are not generally found on teeth of calm, non-stressed individuals with a natural and ideal (non-crowded, non-ortho) Class I occlusion. These individuals with a non-crowded natural Class I occlusion will normally have a good cuspid rise during lateral excursions. With cuspid rise, the loading forces of the excursive movement will be directed onto the cuspid. Abfractions are frequently found, however, on cases where mal-aligned cuspids cause initial lateral guidance forces to be exerted on the lingual incline of the buccal cusp of the first maxillary bicuspid (or whichever tooth bears the initial lateral guiding force of excursion). An abfraction can be commonly found on any tooth that has an exceptionally heavy occlusal marking on an inclined plane. Abfractions are also found quite frequently on patients with slight anterior open bites for the same reason — guidance coming from the bicuspids, rather than the cuspid. The open bite is usually the result of an abnormal motor action of the tongue. If damaging lateral forces are not obvious during excursive motions, then one needs to evaluate the position and motion of the tongue as described above.

Abfractions are rarely seen on teeth from prehistoric cultures and lesions that are found can usually be explained by the customs of that culture. Examples include interproximal notching or grooving from a cultural custom of passing sinew between the teeth; smooth wear facets on the buccal surface on the first mandibular molar of some Eskimo teeth (due to the custom of placing a bone through the cheek, which rubbed on the molar); pointed teeth resulting from the custom of some African cultures of filing their teeth. McEvoy et al. noted cervical lesions in two prehistoric populations. These authors, however, stated the ancient lesions were smaller and had rougher surfaces than the modern lesions under discussion. This study did not examine either the customs or the diet of the two populations.

CONCLUSION
Toothbrushes cannot get much softer than they already are, yet people continue to develop notches on their teeth, despite instructions from dentists to lighten the forces and to brush in a circular manner. Such instructions reflect the early and inaccurate findings of 100-year-old research. This author hypothesizes, however, that abfractions do not result from brushing at all, but rather from traumatic lateral forces placed on the teeth as a result of a malocclusion or abnormal tongue activity, both of which stem from feeding conditions and training of the oral muscles begun during infancy. By embracing the findings and clear implications of current research, dental practitioners can do much to assure that the serious dental health issues related to the symptoms of abfractions will be more adequately addressed in the future.