To THE EDITOR: In the October

1991 issue of THE JOURKAL OF PROSTHETIC DENTISTRY, I was misquoted in the article, “Stresses at the dentinoenamel junction of human teeth-a finite element investigation,” by Goel, Khera, Ralston, and Chang. This article demonstrates the relationship between stress concentrations focused at the dentoenamel junction (DEJ) and cervical lesions. In the discussion, the article states that the demonstrable high stresses in the area of the DEJ could contribute to the development of V-shaped notches in the cervical area by mechanical abrasion as suggested by McCoy. This is erroneous. In my article, I implied that what we are actually seeing are classic examples of hard tissue fatigue due to compression failure. The tooth brush has very little to do with this phenomenon. The authors state that compressive occlusal stresses in enamel and dentin are high, but have limited clinical significance. I strongly disagree. In my opinion, high stress at the DEJ is a major etiological factor in the initiation of dental compression syndrome or bruxim. DR. GENE MCCOY IMPLANT AND RECONSTRUCTIVE SUITE 226, Fox PLAZA SAN FRANCISCO, CA 94102

DENTISTRY

REFERENCE. 1. McCoy

6. On the longevity

of teeth. J Oral Implantology

1983;9(2).

Reply To THE EDITOR: Our most sincere thank you to Dr. Gene McCoy for his generously kind words regarding our article, “Stresses at the dentinoenamel junction of human teeth-a finite element investigation.” It was not the intent of the authors to misquote Dr. McCoy. In reality, our own findings and discussion regarding the chipping of cervical enamel due to stress distribution fully concur with his contention. The entire second paragraph of the discussion section is in total agreement with his concept, except that we believe that once the enamel is chipped away, exposing the “soft” dentin, tooth brushing will contribute to the development of the cervical abrasion lesions. With regard to the sentence where Dr. McCoy’s article is referred to, perhaps, a differently worded sentence (“This in turn could expose the softer dentin, which could be mechanically abraded at an accelerated rate by tooth bushing into V-shaped notches in the cervical area such as those observed by Lee and Eakle’O and McCoy.i’“) would have been more appropriate. We regret our poor sentence structure and the impiied misquoting of Dr. McCoy’s article. As regards to the high compressive stresses on the occlusal enamel and dentin and the limited clinical significance, those stresses are at least functional if not physiologic or normal. In addition, there is no evidence that the

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stresses at the DEJ are the “major etiologic factor in the initiation of dental compression syndrome or bruxism.” SATISH C. K~ERA, BDS, DDS, MS College

of Dentistry

University of Iowa Iowa

City,

IA 52242

To THE EDITOR: Bravo! to Kenneth E. Bloodworth and Philip J. Render for their article calling for the development of radiopaque acrylic resins for prostheses (J PROSTHET DENT 1992; 67:121-3). Although rare, inhalation or ingestion of fragments of acrylic resin can be life-threatening since they have the same radiodensity as soft tissues. One resilient denture liner (Novus, Hygenic Corp., Akron, Ohio) uses barium sulfates as the filler to produce a different radiodensity. Unfortunately, dentists and laboratory technicians do not seem to be adequately concerned when informed of the potential for these materials to be seen on radiographs in emergency situations. It is good that Bloodworth and Render have pointed out the magnitude of the situation. In recent years, the National Institute of Dental Research has funded two institutions to develop innovative approaches to the problem (Rawls HR et al. Dent Mater 1990;6:250-55; and Rawls HR et al. J Dent Res 1990; 69(1865):342) using triphenyl bismuth, a soluble nontoxic heavy metal additive. Such developments may help solve this persistent problem. LAWRENCE GETTLEMAN, DMD, MSD UNIVERSITY OF LOUISVILLE SCHOOL OF DENTISTRY DEPARTMENT OF PROSTHODONTICS LOUISVILLE. KY 40292

DENTISTRY

To THE EDITOR: Having recently read the article “Pattern of tooth contacts in eccentric mandibular position in young adults” by Ingervall, Hahner, and Kessi (J PROSTHET DENT 1991;66: 169-76), I am prompted to respond. It is always intriguing to have input from another dental speciality involved with occlusion. Several ideas mentioned prompted questions. In their discussion of the literature, the authors note that most studies have been recorded to an edge-to-edge position of the canines approximately 3 mm lateral to the intercuspal position. They state that: “An eccentric position of this magnitude is probably rarely used during natural function (chewing).” Certainly most clinicans would agree with this, but what about parafunction? Why are many canines faceted? If “on laterotrusion most subjects had group function on the functional side,” then isn’t this contact (probably parafunctional rather than functional) even more significant? It was also interesting that men were selected for this study, based in part on “the fact that no sex differences in tooth contacts have been reported.” It is my clinical experience, and I believe is supported by the literature, that young women have the highest incidence of acute TMJ

JULY

1992

VOLUME

68

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1

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dysfunction. This may not be related to tooth contact difference alone, but must in some way be related to occlusal parafunctional abuse. Shouldn’t women be investigated too? Naturally I was most interested in the “clinical implications” drawn by the authors of this study. They state that: “These varying types of tooth contact patterns should be of no concern with respect to mandibular dysfunction, as no association between the pattern of tooth contact and dysfunction has been found in this or in similar studies.” And further, “the practice of prophylactically eliminating occlusal interferences on the nonfunctional side may be questioned, as patients tend to adapt to this type of occlusion. It may be wise to accept the existing pattern of tooth contacts and only consider occlusal adjustment if mandibular dysfunction develops.” Dentistry should consider it a great blessing that the body’s adaptive ability can accept a less than ideal occlusion. However, it has been my clinical experience that individuals with acute TMJ dysfunction often have occlusal problems such as contact on the nonfunctioning side. Further, that complete treatment including the elimination of these contacts aids markedly in the restoration of patient comfort and health. Why not before the acute problem? As an analogy, in restorative dentistry we often observe poor or inadequate restorations that for the moment are not destructive or even symptomatic. Should they be left untouched? Investigations of occlusal states, such as this report, seem to be focused on proving that all occlusions are all right until they are acutely involved or disabled. The continued supervision of these occlusions until the need for intervention reminds me of closing the barn door after the horse has escaped. Having studied skull material from some earlier cultures, I was amazed at the radical bony changes in some TMJs. Can we consider this adaptive? If not, then when is intervention best accomplished? An analogy of an automobile wheel misalignment comes to mind. In this case the tire will adjust with irregular wear but the problem remains. If the auto is run long and hard enough, the tire will fail. Surely the prophylatic balancing of automobile wheels is universally accepted. Finally, I’m sure that if we were to inform a patient experiencing acute TMJ syndrome that occlusal adjustment might well have minimized this problem, then they would ask why we had not implemented this treatment before the problem surfaced. After all, we often end treatment of TMJ dysfunction at some point with a type of occlusal adjustment. My concern is an apparent dichotomy between clinical research and clinical practice. Hopefully, future studies will effectively meld the two. JAMES D.LYTLE,DDS 121 WM. HOWARD TAFT ROAD CINCINNATI, OH 45219

THE

JOURi’iAL

OF PROSTHETIC

DENTISTRY

Reply To THE EDITOR: I agree with many of the comments of Dr. Lytle in his letter. It is certainly true that mandibular positions outside the normal,functional range can be used (and frequently are) during parafunction. As far as I know, no studies have compared the tooth contact patterns between the sexes. I agree with Dr. Lytle that young women are in the lead with regard to acute TMJ dysfunction. This could have many explanations and, although I think a difference in tooth contact patterns between the sexes unlikely, it would be of interest to evaluate. In our study, we found no relation between the type of tooth contact pattern (group function or canine protection) and symptoms and signs of mandibular dysfunction, in agreement with the conclusions of many recent studies on this topic. The question of prophylactically eliminating an occlusal interference is very controversial. It is true that patients having mandibular dysfunction (acute TMJ dysfunction) may improve after elimination of occlusal interference. This is, however, no proof of the need to eliminate such contacts in all patients. It is a fact that the vast majority of individuals with occlusal interference have no problems. The critical question seems to be how an individual uses and adapts to an interference. This is the concept of a physiologic occlusion in contrast to a nonphysiologic occlusion, as described by Mohl et a1.l There seems to be a growing consensus that the constitution of an individual and his capacity to react to stress are more important in the etiology of mandibular dysfunction than occlusal factors. After all, occlusal grinding is an irreversible procedure that can prove to be unnecessary because of small continuing changes of the occlusion and that may even be harmful if it creates an exaggerated occlusal consciousness in the patient. The ideal solution would be if the occlusion was continuously supervised by the dentist, who made therapeutic intervention only when needed. In his letter, Dr. Lytle uses the examples of inadequate restorations and an automobile wheel misalignment to justify the prophylactic elimination of occlusal interference. It could, however, equally well be objected that not all heart defects or cases of spinal cord scoliosis, for example, are surgically corrected-only when absolutely necessary. DR. BENGT~NGERVALL DEPARTMENT OF ORTHODONTICS UNIVERSITY OF BERN FREIBURGSTRASSE 7 CH-3010 BERN SWITZERLAND

REFERENCES 1. Mohl N, et al. A textbook ing Co, Inc, 1988.

of occlusion. Chicago: Quintessence

Publish-

Pattern of tooth contacts in eccentric mandibular position in young adults.

To THE EDITOR: In the October 1991 issue of THE JOURKAL OF PROSTHETIC DENTISTRY, I was misquoted in the article, “Stresses at the dentinoenamel junct...
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