- Email: [email protected]
Possible role of tensile stress in the etiology of cervical erosive lesions of teeth
TOWNSEND,
non-precious dental castinp alloys. J Oral Rehabil 73325.
14.
1980. ‘0
?I
Prttersen, .2. H., and Jacobsen, N.: Nickel corrosion of non-precious casting alloys and cytotoxic rlfect of nickel jr! : ziro. J Biomed Eng 2:419. 1978. hioffa. J. P.. Guckerq. A. D.. Okawa, M. ‘I‘.. md Lilly, G. I<.: :\n evaluation of non-precious alloys for use with porcelain veneers. Part 11. Industry safety and biocompatibility. .J
75.
PROSTHEI. DEIZ.T 30~432. 1973. ‘7 L..
?i
AND
VERMILYEA
Mofla, J. P., Jenkins, W. A., and Hamilton, J, C.: Five-year clinical evaluation of two base-metal alloys. J Dent Res 60(Special issue A):405, 1981. German, R. M. Wright. D. C., and Gallant, R. F: In vitro tarnish measurements on fixed prosthodontic allovs. J PROSTHET DENT 47599,
26.
GRISWOLD,
1987.
Tuccillo, J. J., and Nielsen. J. P.: Observations of onset of sulfide tarnish on gold base alloys. J PROSTHET DENT 25629, 19’1
Sarkar. K. K.. and Greener, E. Ii.: In N(V) corrosion resistanw of new dental alloys. Biomarer Mrd Devices Artif Organs l:l?l, 1973 ,Idrian, J. (I., and Huget, F;. F.: ‘l’tssue responsr to haw-mrtal tlrnial allow Milit bled 141:748. 1077
Possible role of tensile stress in the etiology of cervical erosive lesions of teeth William
C. Lee, D.D.S., M.A.,*
IInivrrsity
of California,
and W. Stephan
School of Dentistry.
San Francisco,
N
Eakle, D.D.S.** Calif.
oncarious loss of tooth structure in the human dentition can be classified into the three categories of abrasion, attrition, and erosion. Abrasion is the loss of tooth substance through mechanical means such as toothbrushing. Attrition is the loss of structure caused by wear in functional and parafunctional modes, and includes normal mastication and bruxism. Erosion is the loss of tooth structure by chemical or idiopathic processes. Chemical erosions are generally caused by acids from dietary sources, the environment, and the stomach. Idiopathic erosions are usually found in the cervical surfaces of teeth. This article will address the etiology of the idiopathic cervical erosions. Idiopathic cervical lesions are frequently confused with acid erosions and toothbrush abrasions. This is due in part to the variable morphology of the lesions and the lack of understanding of the etiology of the different lesions. A number of investigators have examined the erosive effects of acids from dietary and environmental sources on tooth structure, and some have suggested that erosion may be related to the citrate content of saliva. l-5Subsequent studies 6-Rthat attempted to correlate citrate and citric acid content in the oral environment with the occurrence of erosive lesions in teeth have resulted in some confusion in distinguishing
ROLE OF OCCLUSAL
*Ix~:~urcr. Department oi Resmrative Ikntistry. ** ‘Antant Professor. Department of Restornti\c I)cntistr\
Observations of wedge-shaped cervical lesions may indicate that occlusal stress on teeth is the major factor that initiates these lesions. For lack of better terminology, we will call the lesions cervical erosions to
374
acid erosions, from idiopathic cervical erosions. Acid erosions show tooth structure loss over a wide area with no sharp line angles while idiopathic cervical erosions are generally wedge-shaped defects limited to the cervical area of teeth. Studies by Shulman and Robinson’ showed no correlation between citrate content and occurrence of erosions in human beings. Furthermore, the studies do not explain how citric acid content in the oral fluid can affect one tooth but not the tooth next to it. A number of studies cite toothbrush abrasion as the possible cause of cervical erosions.‘0-12 While some cervical lesions may be produced by abrasion from the brush and dentifrice, others cannot be explained adequately by this process alone. Some lesions probably can be attributed to both cervical erosion and abrasion. A number of other possible etiologic factors have been suggested. Mannerberg’j looked at salivary factors in erosion and suggested that a high mucin content prevented the precipitation of calcium phosphate that repairs minor acid injuries to the enamel. Rost and Brodie’” suggested that cervical erosions might be caused by abrasion from hyperactive oral soft tissues.
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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.
Fig. 2. Proximal view shows teeth functioning along a contact plane. Based on principles of leverage, magnitude of tensile stress on tooth is function of distance between applied force and fulcrum, as indicated by arrows. Faciai view shows morphology of lesion dictated by contact plane. The further applied force is from fulcrum, the greater the region of defect on same side of tooth. Two separate occlusal forces can create two occlusal line angles in cervical lesion.
distinguish them from smooth rounded acid erosions. Studies have shown that eccentric loads applied to the occlusal surfaces of teeth generate stresses that are concentrated in the cervical regions.‘5-‘7 Our hypothesis is that the primary etiologic factor in cervical erosion is the tensile stress caused by mastication and malocclusion, and that the local milieu plays a secondary role in dissolution of the tooth structure to create the lesion.
Types of stress The masticatory system during function places three types of stress on teeth: compressive, tensile, and THE JOURNAL
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shearing stress. Compressive stress is the resistance against compression, tensile stress is the resistance against stretch or elongation, and shearing stress represents the resistance against twisting or sliding.
Physical properties of tooth structure The physical properties of teeth have been me&ured extensively and appear to vary considerably among individuals, from tooth to tooth in the same individual, and even within different locations on the same tooth.1s However, certain physical characteristics can be generalized. Among these is that dentin appears to be 375
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EAKLE
Fig. 3. Stone casts show large wedge-shaped cervical lesion on mandibular first premolar. Adjacent teeth are minimally affected. Occlusal line angle of premolar lesion is skewed to correspond to contact plane with lateral incisor.
substantially stronger than enamel in tension.” “I The high resiliency of dentin enables it to withstand greater deformation without fracture. Enamel moves as a rigid unit, while dentin deforms elastically beneath it. Enamel is made up of three components: a mineral component that comprises the enamel rods, an organic matrix, and water either free or bound. With the electron microscope, enamel rods can be seen to be composed of minute crystallites that are about 40 nm in diameter.” Enamel, although rather hard, is also brittle and can tolerate only a small amount of deformation before it fractures. Its ability to withstand stress depends significantly on the direction of force with respect to the orientation of enamel rods.‘* For example, enamel’s ability to withstand forces that pull the enamel rods from each other (that is, tension) appears to be rather weak. In a study on the frictional behavior and surface failure of enamel, Powers et al.22observed that tensile cracks occurred around enamel rods and through the interprismatic substance. It is a well known fact that surface microcracks seriously weaken brittle materials.
Compressive and tensile stress When occlusion is ideal, the masticatory forces during function are directed primarily along the long axis of the tooth, the forces are dissipated, and minimal distortion of the dentinal and enamel hydroxyapatite crystals results. When occlusion is not ideal, significant lateral forces are generated, which can cause bending of the tooth and create two types of stress on tooth structure (Fig. 1). The first is a compressive stress that is located primarily on the side toward which the tooth is being bent. The second type of stress is a tensile force that acts on the side away from the direction of 376
Fig. 4. Cervical lesions on upper left second premolar and lower left first premolar each show two distinct line angulations on occlusal edge of lesions. Occlusal line angles of lesions on upper canine, premolar, and molar all show different angulations.
bending. For example, if a lingually directed occlusal force is applied on a lower premolar, the lingual portion of the tooth would be compressed while the buccal portion would be stretched. The region under the greatest tensile stress is that closest to the fulcrum, while the regions of greatest compressive stress are the ncclusal contacts, the fulcrum, and the apex of the root. Because both dentin and enamel have high compressive strength, little or no disruption of the crystalline structure results from compression. However, the ability of tooth structure to withstand tension is limited. The tensile force that acts on the tooth may cause disruption of chemical bonds between the hydroxyapatite crystals.
MECHANISM LESIONS
FOR FORMATION
OF
In their study of the enamel surface, Arends et al.” found that small spaces that are filled with water and proteinlike organic material exist between discontinuous crystallites. Liquids and small ions probably can pass through these spaces. As bonds are broken between crystals, additional spaces could be created where small molecules, such as those of water, may penetrate, The action of these small molecules may prevent the reestablishment of chemical bonds between crystalline structures. Subsequent tensile stress of sufficient magnitude would tend to propagate cracks once they are initiated. If this hypothesis is correct, the disrupted crystalline structure SEPTEMBER
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Fig. 5. Lower left tip of buccal cusp. of occlusal forces two distinct line cervical lesion.
CERVICAL
LESIONS
first premolar has wear facets near Facets show two distinct directions acting on tooth that correspond to angulations on occlusal edge of
that results would be more susceptible to chemical dissolution and breakage from physical forces such as friction from brushing, compression, and shearing during mastication and bruxism.
Characteristics of a lesion created by tensile stress A lesion created as a result of tensile stress should possesscertain characteristics. First, the lesion should be at or near the fulcrum. Second, the region of greatest tensile stress concentration would be a wedge-shaped volume at the fulcrum, which is the typical morphology of cervical erosive lesions. Local factors would tend to modify the shape of the lesion, but the overall patterns should be wedge-shaped with sharp line angles. Third, the direction of the lateral force that generates the tensile stress would determine the location of the lesion. For example, if there are two directions of lateral force acting on the same tooth, the created lesion would be a combination of two lesions generated by each of the two forces; that is, the morphology of the lesion would be overlapping of two wedge-shaped volumes. Fourth, the size of the lesion would be directly related to the magnitude and frequency of application of the tensile force. For a given lateral force, the further the lesion is from the fulcrum, the greater is the tensile force generated and therefore the greater the region of tooth structure disruption near the fulcrum (Fig. 2). Occlusal contact is seldom a single point. Instead, opposing teeth function with each other over a surface area. Consequently, the force imposed on a tooth is distributed along the contact plane. The force on any point in the plane of contact is a fixed distance from the fulcrum and is different from any other point within the plane. Occlusal forces on the tooth further from the fulcrum THE JOURNAL
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Fig. 6. Upper right and lower right first molars each show two separate wedge-shaped cervical lesions on facial surface. Two lesions on same tooth correspond to tensile stresses that fulcrum at a point around two roots to leave undisturbed area between.
create greater tensile stress on the tooth structure near the fulcrum. If it is assumed that the amount of tensile force needed to break the chemical bonds that hold the hydroxyapatite crystals together is constant in the same tooth, then the further the lateral force is from the fulcrum, the greater is the tensile force that affects the tooth structure near the fulcrum and therefore the larger the region of disruption. As a result of this effect, lesions of cervical erosion would possessline angles that are dictates of the surface of contact. It is presumed that shearing forces are generated also, and these may play an important but lesser role than tensile stress in the development of cervical lesions.
PATIENT REPORTS Three representative cases chosen from more than 100 whom we examined are presented to illustrate the characteristics of cervical erosions. Patient No. 1 The patient was a 32-year-old man with a Class III malocclusion. The cervical erosion on the lower left first premolar had several points worth noting (Fig. 3). First, the lesion was rather large and the factor(s) that caused the lesion did not seem to affect the adjacent teeth, although there was a smaller lesion on the second premolar. It seems unlikely that the lesion was caused by mechanical means such as brushing. Likewise, factors such as citric acid should not affect only one tooth and leave the adjacent ones intact. Second, the occlusal line angle of the lesion was skewed with respect to the long axis of the tooth. Articulation of the teeth showed contact only between the premolar and the upper lateral incisor. The upper canine was out of occlusion completely. The surface of contact was at the mesial incline of the buccal cusp of the premolar. The occlusal surface contact and the occlusal line angle of the lesion occurred at the same angle, which 377
LEE AND
EAKLE
buccal roots, the tooth structure was undisturbed or disturbed to a lesser extent. Consequently, two separate lesions were created. The lower molar lesions extended well beneath the gingiva where toothbrush bristles would not easily reach.
DISCUSSION
Fig. 7. A, Facial view of molar shows production of two separate cervical lesions as tensile stressesproduce fulcruming about each of two buccal roots. B, Proximal view of molars in function demonstrates production of cervical lesion in region of tooth under tensile stress. appeared to be consistent with the theory that tensile force was the primary factor in the etiology of the lesion. Patient
No. 2
.A M-year-old man with a Class II malocclusion presented with cervical erosive lesions in a number of teeth. The lesions of interest were those of the upper left second premolar and the lower left first premolar (Fig. 4). Unlike Patient No. 1, the lesions on these teeth had two distinct line angulations on the occlusal edge of the lesions. It is unlikely that brushing or acid alone caused such unusual defects. However, the shape was consistent with the concept that tensile stresses from two directions were responsible for the lesions. In effect, the lesions represented two wedge-shaped defects on the same tooth. The wear facets on the lower premolar were clearly visible near the tip of the buccal cusp (Fig. 5) and showed two distinct directions of occlusal forces acting on the tooth. F’urthermore, the lesions on the upper first and second premolars and the first molar all showed different angulations, a fact explainable by the tensile stress concept. Patient
No. 3
A 4.5year-old woman presented with numerous wear facets on her teeth, which indicated problems of bruxism. Seven substantial cervical erosive lesions and several small ones were located on the cervical buccal regions of the posterior teeth. Of particular interest were the lesions on the upper right first molar and the lower right first molar (Fig. 6). The lesions consisted of two distinct and separate wedgeshaped defects that appeared to occur only in the molar teeth with the highest incidence among first molars. These unusual
dual defectscan also be explained by the tensile stresstheory. Each of the lesions on the same tooth correspond to the fuicruming effect of the roots of the tooth (Fig. 7). For the upper molar, the defects would be causedby the tensile stress created as a result of the fulcrum points that correspond to the two buccal roots, Because there is no fulcrum between th’e
378
A number of hypotheses have been proposed to explain the etiology of cervical erosive lesions. These include mechanical abrasions such as brushing, chemical dissolution by acids, intrinsic weakness of tooth structure in the cervical surface, and traumatic occlusion. Neither the abrasion nor the chemical dissolution hypothesis accounts for the frequently localized effect of cervical erosions. It is difficult to explain how these processescan often cause a lesion on one tooth and not the adjacent tooth. Neither hypothesis can explain the varied morphology
and location
of the lesions in the
patients described. At present, there is no evidence that intrinsic weakness existed in the region where the lesions developed. Brady and Woodyz3 suggested that occlusal stress and collagen/apatite interaction in dentin may explain the development of angular lesions. However, no satisfactory mechanism has been proposed that explains how traumatic occlusion and bruxism can produce cervical erosions. Although tensile stress is proposed as the initiating factor in the etiology of cervical erosions, multiple factors affect the developmental process. Some of these factors are abrasion from toothbrushing, acids in oral fluid, the presence of fluoride
in teeth and oral fluid,
the presence of adjacent teeth that affect bending of the tooth
under
tensile
stress, and the alignment
and
anatomy of teeth. The contributory role of toothbrush abrasion is likely to vary depending on the lesion. Tooth structure that has been disrupted by tensile stress may be susceptible to frictional wear, but only where accessible. This is not to imply that toothbrush abrasion cannot produce similar cervical lesions, but it cannot explain the varied morphology and location of all wedge-shaped cervical lesions. Certain lesions, such as those in upper anterior teeth of older patients, may indeed be abrasive in origin. The presence of plaque may contribute to the acidity of oral fluid. Acidity, whether from plaque, diet, stomach, or other sources, may have a significant contributory role in the dissolution of tooth substance, particularily that which has been disrupted by tensile stress. The presence of fluoride in teeth and in oral fluid may affect the development of cervical erosions by decreasing the solubility of tooth structure and thus slowing the development of the lesions after the interprismatic bonds are broken. In that regard, it would be interesting to examine the prevalence and rate of SEPTEMBER
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progression of cervical erosions in fluoridated and nonfluoridated populations. The effectiveness of topical fluoride treatments on cervical erosions has been examined, In a 5-month study, Xhonga et a1.24found that the topical applications of 33.33% sodium fluoride had no effect on the rate of progression of cervical erosions. However, they did not consider their results to be conclusive and suggested a longer term study. In another study conducted over 1 year, Xhonga and Sognnaes25used fluorides and sealants to treat cervical erosions and observed only a minimal amount of protection. Because of the morphology of occlusal surfaces (buccal and lingual inclined planes and fossae) most forces generated during functional and parafunctional jaw movements are directed along the long axis of teeth or in a buccolingual direction. The presence of adjacent teeth can help to direct forces buccolingually. When third molars are absent, second molars do not develop erosions on their distal surfaces because the major forces are directed axially or buccolingually; and the adjacent first molar prohibits mesial bending of the tooth, which would be necessary to generate tensile stresses on the distal surface. The alignment and anatomy of a tooth may play a significant role in determining how susceptible it is to tensile stress. Furthermore, they may dictate where the maximum stress concentrates on a tooth. In the upper molars, cervical erosions usually develop in the mesiobuccal regions. Perhaps the lingual cusp, because it is more to the mesial portion of the tooth, concentrates the stress mesially. Traumatic occlusion in itself may not generate a significant tensile stress. Depending on the direction of the applied force and the alignment and anatomy of a tooth, occlusal trauma may produce mainly compressive stress and thus require a greater force than would tensile stress to cause the disruption of tooth structure. In lateral movements of the mandible, the canines play a significant protective function in disclusion of the posterior teeth. In dentitions that lack canine disclusion, lateral forces are transmitted to the posterior teeth, which may lead to the development of cervical erosions in teeth that are under tensile stress. In bruxism where canine disclusion eventually may be lost, the potential for the development of cervical erosions exists. Indeed, reports seem to indicate that there is a high frequency of cervical lesions in patients who brux.26,27The relationship of canine disclusion to the prevalence of cervical erosions remains to be examined. The tensile stress-induced cervical erosion theory provides a feasible explanation for a puzzling phenomenon. In a study of 10,000 extracted teeth, Sognnaes et a1.28reported an 18% incidence of cervical lesions. Even THE JOURNAL
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if only a fraction of these teeth requires treatment, cervical lesions still would constitute a significant problem economically. To the present time, treatment of these lesions has been largely empirical. With the tensile stress concept, a rational approach to treatment of cervical erosions could be planned and tested. SUMMARY A tensile stress hypothesis for the etiology of idiopathic cervical erosions of human teeth is presented. It is proposed that when occlusion is not ideal, lateral forces cause the teeth to bend. The tensile stresses created during bending disrupt the chemical bonds of the crystalline structures of enamel and dentin. Small molecules may enter between the crystals and prevent the reestablishment of the chemical bonds. As a result, the disrupted tooth structure is more susceptible to loss through dissolution and abrasion and results in the development of the typically wedge-shaped lesions. Patients with lesions typical of hundreds examined by the authors were presented to illustrate the concept. The possible consequences of the proposed hypothesis were discussed. The hypothetical conclusions made in this article will be tested by experimentation. REFERENCES 1. Gortner, R. A., Restarski, J. S., Bieri, J. G, and McCay, C. M.: Factors influencing the destructive eifects of acidic beverages on the teeth of white rats and tamsters. Arch Biochem 8~405, 1945. 2. Stafne, E. C., and Lovestedt, S. A.: Dissolution of tooth substance by lemon juice, acid beverages and acids from some other sources. J Am Dent Assoc 34~586, 1947. 3. Elsbury, W. B.: Hydrogen-ion concentration and acid erosion of the teeth. Br Dent J 93:177, 1952. 4. Larsen, M. J.: Degrees of saturation with respect to apatites in fruit juices and acidic drinks. Stand J Dent Res 83:13, 1975. 5. McClure, F. J., and Ruzicka, S. J.: The destructive effect of citrate vs. lactate ions on rats’ molar tooth surfaces, in viva. J Dent Res 25:1, 1946. 6. Zipkin, I., and McClure, F. J.: Salivary citrate and dental erosion. J Dent Res 28:613, 1949. I. Ericsson, Y.: Investigations on the occurrence and significance of citric acid in the saliva. J Dent Res 32:850, 1953. 8 Fuller, J. L., and Johnson, W. W.: Citric acid consumption and the human dentition. J Am Dent Assoc 95:80, 1977. 9 Shulman, E., and Robinson, H. B. G.: Salivary citrate content and erosion of teeth. J Dent Res 27:541, 1948. 10 Radentz, W. II., Barne, G. P., and Cutright, D. E.: A survey of factors possibly associated with cervical abt,asion of tooth surfaces. J Periodontol 47:148, 1976. 11 Bergstrom, J., and Lavstedt, S.: An epidemiologic approach to toothbrushing and dental abrasion. Community Dent Oral Epidemiol 7:57, 1979. 12 Hollinger, J. O., and Moore, E. M.: Hard tissue loss at the cementoenamel junction: A clinical study. J NJ Dent Assoc, Fall 1979, p 27. 13. Mannerberg, F.: Salivary factors in cases of erosion. Odont Revy 14~156, 1963. 14. Rest, T., and Brodie, A. G.: Possible etiologic factors in dental erosion. J Dent Res 40~385, 1961.
379
LEE AND
Thresher, R. W., and S&to, G. E.. The stress analysis of human teeth. J Biomech 6:443, 1973. S&a, L. G., Shillingburg, H. T.. and Kerr, P. A.: Finite element analysis of dental structures-Axisymmetric and plane stress idealizations. J Biomed Mater Res 9:237, 1975. Yettram, A. L.. Wright, K. W. J., and Pickard, H. M.: Finite element stress analysis of the crowns of normal and restored teeth. ~J Dent Res 55:1004, 1970. Phillips, R. W.: Skinner’s Science ot Dental Materials, ed 7. Philadelphia, 1973. W. B. Saunders Co., pp 49-51. Craig, R., Peyton, F., and Johnson, D.: Compression properlies of enamel, dental cements and gold. J Dent Res 40:936. 1961. Bowen, R., and Rodriguez, M.. Tensile strength and modulus of elasticity of tooth structure and several restorative materials J Am Dent Assoc 64~378, 1962. hrends, J.: Schuthof, J., and Jongebloed. W. I,.: Mineral properties of the outer tooth surface. in Leach, S. A., editor: Dental Plaque and Surface Interactions in the Oral Cavity. Cheshire, England, 1979, Imperial Chemical Industries Ltd., pp 251-272. Powers, J. M., Craig, R. G., and Ludema, K. C.: Frictional behavior and surface failure of human t-name]. J Dent Re\ 52:1x27, 1971.
23. 24.
2s
16 27. 28
EAKLE
Brady, J. M., and Woody, R. D.: Scanning microscopy of cervical erosion. J Am Dent Assoc 94:726, 1977. Xhonga, F. A., Wolcott, R. B., and Sognnaes, R. F.: Clinical measurements of dental erosion progress. J Am Dent Assoc 84:577. 1972. Xhonga, F A., and Sognnaes, R. F.: Dental erosion: Progress of erosion measured clinically after various fluoride applications J Am Dent Assoc 87:1223, 1973. Xhonga, F. :I.. Bruxism and irs effect on the teeth. J Oral Rehabil 4~65. 1977 Xhonga, F. A, and Van Herle, A.: The influence of hyperthyroldism on dental erosions. Oral Surg 36~349, 1973. Sognnaes. R. F., Wolcott, R. B., and Xhonga, F. A.: Erosionhke patterns occurring in association with other dental conditwn$. J Am Dent Assoc 84:571, 1972.
Gingival tissue response to rotary curettage Fred W. Kamansky, D.D.S.,* Thomas R. Tempel, D.D.S., M.S.Ed.,** and Arthur C. Post, D.D.S., M.Ed.*** Walter
Reed Army Medical Center, Washington, D.C.
T
he management of gingival tissues during subgingival preparation of teeth for fixed prostheses varies in the technique used and the degree of effectiveness. High-frequency electrosurgery and lateral gingival tissue displacement achieved with a variety of chemically treated retraction cords are now the most common methods for tissue management of prepared teeth. One approach to gingival tissue management during fixed prosthodontic procedures is rotary gingival curettage. This technique? uses a specially designed rotary diamond instrument to remove a portion of the inner epithelial lining of the gingival sulcus during the
I‘hr opinions or assertions herein are the private views of the authors ,ind are not to be construed as official or as reflecting the views of ~hc I.~.$. Departments of the Army, Naby. or Defense. Subrnittrd in partial fulfillment of the requirements of the Fixed i’rosthodontirs Rrsidenc) Program. Walter Reed .4rmy Medical (:entrr, Washington. D.C “! Zrxnmander (DC:) USN; Prosthodontirs Dept.. Branch Dental (:linic NDC, N.4S North Island. San Diego. C.4. **Colone!, DC. LrSA, 1.1 S. Army Hospital, \C’orzburg. West t Germany. *‘*Formerly, Colonel. DC, USA; Augsburg, West Germany; prescntly, Colonel, DC, 17% (retired). fInqrah,+m. R. Perconal communication. 1978
380
placement of the finish line on tooth preparations. Tupac and Neacy’ conducted a study on dogs to compare cord gingival displacement with the rotary gingitage technique. They found no significant difference clinically or histologically between the two methods.
Amsterdam* suggested the use of rotary curettage in conjunction with the preparation of teeth for fixed prostheses. However, he observed that the rotating diamond instrument provided questionable tactile guidance while locating the position of the rotary instrument in the gingival sulcus during the procedure. The rate of healing of the gingival tissues after a surgical curettage procedure is relevant to the rotary curettage technique. Moskow3 reported that complete coverage of the debrided tissue with epithelium was seen within 7 days after gingival curettage on dogs. Blass and Lite4 found microscopically that complete healing was seen within 10 days after curettage on a healthy patient. Although complete healing of the gingiva can be predicted after rotary curettage, the human clinical application of the procedure could have collateral factors that affect the ultimate clinical response. The SEPTEMBER
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non-precious dental castinp alloys. J Oral Rehabil 73325.
14.
1980. ‘0
?I
Prttersen, .2. H., and Jacobsen, N.: Nickel corrosion of non-precious casting alloys and cytotoxic rlfect of nickel jr! : ziro. J Biomed Eng 2:419. 1978. hioffa. J. P.. Guckerq. A. D.. Okawa, M. ‘I‘.. md Lilly, G. I<.: :\n evaluation of non-precious alloys for use with porcelain veneers. Part 11. Industry safety and biocompatibility. .J
75.
PROSTHEI. DEIZ.T 30~432. 1973. ‘7 L..
?i
AND
VERMILYEA
Mofla, J. P., Jenkins, W. A., and Hamilton, J, C.: Five-year clinical evaluation of two base-metal alloys. J Dent Res 60(Special issue A):405, 1981. German, R. M. Wright. D. C., and Gallant, R. F: In vitro tarnish measurements on fixed prosthodontic allovs. J PROSTHET DENT 47599,
26.
GRISWOLD,
1987.
Tuccillo, J. J., and Nielsen. J. P.: Observations of onset of sulfide tarnish on gold base alloys. J PROSTHET DENT 25629, 19’1
Sarkar. K. K.. and Greener, E. Ii.: In N(V) corrosion resistanw of new dental alloys. Biomarer Mrd Devices Artif Organs l:l?l, 1973 ,Idrian, J. (I., and Huget, F;. F.: ‘l’tssue responsr to haw-mrtal tlrnial allow Milit bled 141:748. 1077
Possible role of tensile stress in the etiology of cervical erosive lesions of teeth William
C. Lee, D.D.S., M.A.,*
IInivrrsity
of California,
and W. Stephan
School of Dentistry.
San Francisco,
N
Eakle, D.D.S.** Calif.
oncarious loss of tooth structure in the human dentition can be classified into the three categories of abrasion, attrition, and erosion. Abrasion is the loss of tooth substance through mechanical means such as toothbrushing. Attrition is the loss of structure caused by wear in functional and parafunctional modes, and includes normal mastication and bruxism. Erosion is the loss of tooth structure by chemical or idiopathic processes. Chemical erosions are generally caused by acids from dietary sources, the environment, and the stomach. Idiopathic erosions are usually found in the cervical surfaces of teeth. This article will address the etiology of the idiopathic cervical erosions. Idiopathic cervical lesions are frequently confused with acid erosions and toothbrush abrasions. This is due in part to the variable morphology of the lesions and the lack of understanding of the etiology of the different lesions. A number of investigators have examined the erosive effects of acids from dietary and environmental sources on tooth structure, and some have suggested that erosion may be related to the citrate content of saliva. l-5Subsequent studies 6-Rthat attempted to correlate citrate and citric acid content in the oral environment with the occurrence of erosive lesions in teeth have resulted in some confusion in distinguishing
ROLE OF OCCLUSAL
*Ix~:~urcr. Department oi Resmrative Ikntistry. ** ‘Antant Professor. Department of Restornti\c I)cntistr\
Observations of wedge-shaped cervical lesions may indicate that occlusal stress on teeth is the major factor that initiates these lesions. For lack of better terminology, we will call the lesions cervical erosions to
374
acid erosions, from idiopathic cervical erosions. Acid erosions show tooth structure loss over a wide area with no sharp line angles while idiopathic cervical erosions are generally wedge-shaped defects limited to the cervical area of teeth. Studies by Shulman and Robinson’ showed no correlation between citrate content and occurrence of erosions in human beings. Furthermore, the studies do not explain how citric acid content in the oral fluid can affect one tooth but not the tooth next to it. A number of studies cite toothbrush abrasion as the possible cause of cervical erosions.‘0-12 While some cervical lesions may be produced by abrasion from the brush and dentifrice, others cannot be explained adequately by this process alone. Some lesions probably can be attributed to both cervical erosion and abrasion. A number of other possible etiologic factors have been suggested. Mannerberg’j looked at salivary factors in erosion and suggested that a high mucin content prevented the precipitation of calcium phosphate that repairs minor acid injuries to the enamel. Rost and Brodie’” suggested that cervical erosions might be caused by abrasion from hyperactive oral soft tissues.
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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.
Fig. 2. Proximal view shows teeth functioning along a contact plane. Based on principles of leverage, magnitude of tensile stress on tooth is function of distance between applied force and fulcrum, as indicated by arrows. Faciai view shows morphology of lesion dictated by contact plane. The further applied force is from fulcrum, the greater the region of defect on same side of tooth. Two separate occlusal forces can create two occlusal line angles in cervical lesion.
distinguish them from smooth rounded acid erosions. Studies have shown that eccentric loads applied to the occlusal surfaces of teeth generate stresses that are concentrated in the cervical regions.‘5-‘7 Our hypothesis is that the primary etiologic factor in cervical erosion is the tensile stress caused by mastication and malocclusion, and that the local milieu plays a secondary role in dissolution of the tooth structure to create the lesion.
Types of stress The masticatory system during function places three types of stress on teeth: compressive, tensile, and THE JOURNAL
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shearing stress. Compressive stress is the resistance against compression, tensile stress is the resistance against stretch or elongation, and shearing stress represents the resistance against twisting or sliding.
Physical properties of tooth structure The physical properties of teeth have been me&ured extensively and appear to vary considerably among individuals, from tooth to tooth in the same individual, and even within different locations on the same tooth.1s However, certain physical characteristics can be generalized. Among these is that dentin appears to be 375
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Fig. 3. Stone casts show large wedge-shaped cervical lesion on mandibular first premolar. Adjacent teeth are minimally affected. Occlusal line angle of premolar lesion is skewed to correspond to contact plane with lateral incisor.
substantially stronger than enamel in tension.” “I The high resiliency of dentin enables it to withstand greater deformation without fracture. Enamel moves as a rigid unit, while dentin deforms elastically beneath it. Enamel is made up of three components: a mineral component that comprises the enamel rods, an organic matrix, and water either free or bound. With the electron microscope, enamel rods can be seen to be composed of minute crystallites that are about 40 nm in diameter.” Enamel, although rather hard, is also brittle and can tolerate only a small amount of deformation before it fractures. Its ability to withstand stress depends significantly on the direction of force with respect to the orientation of enamel rods.‘* For example, enamel’s ability to withstand forces that pull the enamel rods from each other (that is, tension) appears to be rather weak. In a study on the frictional behavior and surface failure of enamel, Powers et al.22observed that tensile cracks occurred around enamel rods and through the interprismatic substance. It is a well known fact that surface microcracks seriously weaken brittle materials.
Compressive and tensile stress When occlusion is ideal, the masticatory forces during function are directed primarily along the long axis of the tooth, the forces are dissipated, and minimal distortion of the dentinal and enamel hydroxyapatite crystals results. When occlusion is not ideal, significant lateral forces are generated, which can cause bending of the tooth and create two types of stress on tooth structure (Fig. 1). The first is a compressive stress that is located primarily on the side toward which the tooth is being bent. The second type of stress is a tensile force that acts on the side away from the direction of 376
Fig. 4. Cervical lesions on upper left second premolar and lower left first premolar each show two distinct line angulations on occlusal edge of lesions. Occlusal line angles of lesions on upper canine, premolar, and molar all show different angulations.
bending. For example, if a lingually directed occlusal force is applied on a lower premolar, the lingual portion of the tooth would be compressed while the buccal portion would be stretched. The region under the greatest tensile stress is that closest to the fulcrum, while the regions of greatest compressive stress are the ncclusal contacts, the fulcrum, and the apex of the root. Because both dentin and enamel have high compressive strength, little or no disruption of the crystalline structure results from compression. However, the ability of tooth structure to withstand tension is limited. The tensile force that acts on the tooth may cause disruption of chemical bonds between the hydroxyapatite crystals.
MECHANISM LESIONS
FOR FORMATION
OF
In their study of the enamel surface, Arends et al.” found that small spaces that are filled with water and proteinlike organic material exist between discontinuous crystallites. Liquids and small ions probably can pass through these spaces. As bonds are broken between crystals, additional spaces could be created where small molecules, such as those of water, may penetrate, The action of these small molecules may prevent the reestablishment of chemical bonds between crystalline structures. Subsequent tensile stress of sufficient magnitude would tend to propagate cracks once they are initiated. If this hypothesis is correct, the disrupted crystalline structure SEPTEMBER
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Fig. 5. Lower left tip of buccal cusp. of occlusal forces two distinct line cervical lesion.
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first premolar has wear facets near Facets show two distinct directions acting on tooth that correspond to angulations on occlusal edge of
that results would be more susceptible to chemical dissolution and breakage from physical forces such as friction from brushing, compression, and shearing during mastication and bruxism.
Characteristics of a lesion created by tensile stress A lesion created as a result of tensile stress should possesscertain characteristics. First, the lesion should be at or near the fulcrum. Second, the region of greatest tensile stress concentration would be a wedge-shaped volume at the fulcrum, which is the typical morphology of cervical erosive lesions. Local factors would tend to modify the shape of the lesion, but the overall patterns should be wedge-shaped with sharp line angles. Third, the direction of the lateral force that generates the tensile stress would determine the location of the lesion. For example, if there are two directions of lateral force acting on the same tooth, the created lesion would be a combination of two lesions generated by each of the two forces; that is, the morphology of the lesion would be overlapping of two wedge-shaped volumes. Fourth, the size of the lesion would be directly related to the magnitude and frequency of application of the tensile force. For a given lateral force, the further the lesion is from the fulcrum, the greater is the tensile force generated and therefore the greater the region of tooth structure disruption near the fulcrum (Fig. 2). Occlusal contact is seldom a single point. Instead, opposing teeth function with each other over a surface area. Consequently, the force imposed on a tooth is distributed along the contact plane. The force on any point in the plane of contact is a fixed distance from the fulcrum and is different from any other point within the plane. Occlusal forces on the tooth further from the fulcrum THE JOURNAL
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Fig. 6. Upper right and lower right first molars each show two separate wedge-shaped cervical lesions on facial surface. Two lesions on same tooth correspond to tensile stresses that fulcrum at a point around two roots to leave undisturbed area between.
create greater tensile stress on the tooth structure near the fulcrum. If it is assumed that the amount of tensile force needed to break the chemical bonds that hold the hydroxyapatite crystals together is constant in the same tooth, then the further the lateral force is from the fulcrum, the greater is the tensile force that affects the tooth structure near the fulcrum and therefore the larger the region of disruption. As a result of this effect, lesions of cervical erosion would possessline angles that are dictates of the surface of contact. It is presumed that shearing forces are generated also, and these may play an important but lesser role than tensile stress in the development of cervical lesions.
PATIENT REPORTS Three representative cases chosen from more than 100 whom we examined are presented to illustrate the characteristics of cervical erosions. Patient No. 1 The patient was a 32-year-old man with a Class III malocclusion. The cervical erosion on the lower left first premolar had several points worth noting (Fig. 3). First, the lesion was rather large and the factor(s) that caused the lesion did not seem to affect the adjacent teeth, although there was a smaller lesion on the second premolar. It seems unlikely that the lesion was caused by mechanical means such as brushing. Likewise, factors such as citric acid should not affect only one tooth and leave the adjacent ones intact. Second, the occlusal line angle of the lesion was skewed with respect to the long axis of the tooth. Articulation of the teeth showed contact only between the premolar and the upper lateral incisor. The upper canine was out of occlusion completely. The surface of contact was at the mesial incline of the buccal cusp of the premolar. The occlusal surface contact and the occlusal line angle of the lesion occurred at the same angle, which 377
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buccal roots, the tooth structure was undisturbed or disturbed to a lesser extent. Consequently, two separate lesions were created. The lower molar lesions extended well beneath the gingiva where toothbrush bristles would not easily reach.
DISCUSSION
Fig. 7. A, Facial view of molar shows production of two separate cervical lesions as tensile stressesproduce fulcruming about each of two buccal roots. B, Proximal view of molars in function demonstrates production of cervical lesion in region of tooth under tensile stress. appeared to be consistent with the theory that tensile force was the primary factor in the etiology of the lesion. Patient
No. 2
.A M-year-old man with a Class II malocclusion presented with cervical erosive lesions in a number of teeth. The lesions of interest were those of the upper left second premolar and the lower left first premolar (Fig. 4). Unlike Patient No. 1, the lesions on these teeth had two distinct line angulations on the occlusal edge of the lesions. It is unlikely that brushing or acid alone caused such unusual defects. However, the shape was consistent with the concept that tensile stresses from two directions were responsible for the lesions. In effect, the lesions represented two wedge-shaped defects on the same tooth. The wear facets on the lower premolar were clearly visible near the tip of the buccal cusp (Fig. 5) and showed two distinct directions of occlusal forces acting on the tooth. F’urthermore, the lesions on the upper first and second premolars and the first molar all showed different angulations, a fact explainable by the tensile stress concept. Patient
No. 3
A 4.5year-old woman presented with numerous wear facets on her teeth, which indicated problems of bruxism. Seven substantial cervical erosive lesions and several small ones were located on the cervical buccal regions of the posterior teeth. Of particular interest were the lesions on the upper right first molar and the lower right first molar (Fig. 6). The lesions consisted of two distinct and separate wedgeshaped defects that appeared to occur only in the molar teeth with the highest incidence among first molars. These unusual
dual defectscan also be explained by the tensile stresstheory. Each of the lesions on the same tooth correspond to the fuicruming effect of the roots of the tooth (Fig. 7). For the upper molar, the defects would be causedby the tensile stress created as a result of the fulcrum points that correspond to the two buccal roots, Because there is no fulcrum between th’e
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A number of hypotheses have been proposed to explain the etiology of cervical erosive lesions. These include mechanical abrasions such as brushing, chemical dissolution by acids, intrinsic weakness of tooth structure in the cervical surface, and traumatic occlusion. Neither the abrasion nor the chemical dissolution hypothesis accounts for the frequently localized effect of cervical erosions. It is difficult to explain how these processescan often cause a lesion on one tooth and not the adjacent tooth. Neither hypothesis can explain the varied morphology
and location
of the lesions in the
patients described. At present, there is no evidence that intrinsic weakness existed in the region where the lesions developed. Brady and Woodyz3 suggested that occlusal stress and collagen/apatite interaction in dentin may explain the development of angular lesions. However, no satisfactory mechanism has been proposed that explains how traumatic occlusion and bruxism can produce cervical erosions. Although tensile stress is proposed as the initiating factor in the etiology of cervical erosions, multiple factors affect the developmental process. Some of these factors are abrasion from toothbrushing, acids in oral fluid, the presence of fluoride
in teeth and oral fluid,
the presence of adjacent teeth that affect bending of the tooth
under
tensile
stress, and the alignment
and
anatomy of teeth. The contributory role of toothbrush abrasion is likely to vary depending on the lesion. Tooth structure that has been disrupted by tensile stress may be susceptible to frictional wear, but only where accessible. This is not to imply that toothbrush abrasion cannot produce similar cervical lesions, but it cannot explain the varied morphology and location of all wedge-shaped cervical lesions. Certain lesions, such as those in upper anterior teeth of older patients, may indeed be abrasive in origin. The presence of plaque may contribute to the acidity of oral fluid. Acidity, whether from plaque, diet, stomach, or other sources, may have a significant contributory role in the dissolution of tooth substance, particularily that which has been disrupted by tensile stress. The presence of fluoride in teeth and in oral fluid may affect the development of cervical erosions by decreasing the solubility of tooth structure and thus slowing the development of the lesions after the interprismatic bonds are broken. In that regard, it would be interesting to examine the prevalence and rate of SEPTEMBER
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progression of cervical erosions in fluoridated and nonfluoridated populations. The effectiveness of topical fluoride treatments on cervical erosions has been examined, In a 5-month study, Xhonga et a1.24found that the topical applications of 33.33% sodium fluoride had no effect on the rate of progression of cervical erosions. However, they did not consider their results to be conclusive and suggested a longer term study. In another study conducted over 1 year, Xhonga and Sognnaes25used fluorides and sealants to treat cervical erosions and observed only a minimal amount of protection. Because of the morphology of occlusal surfaces (buccal and lingual inclined planes and fossae) most forces generated during functional and parafunctional jaw movements are directed along the long axis of teeth or in a buccolingual direction. The presence of adjacent teeth can help to direct forces buccolingually. When third molars are absent, second molars do not develop erosions on their distal surfaces because the major forces are directed axially or buccolingually; and the adjacent first molar prohibits mesial bending of the tooth, which would be necessary to generate tensile stresses on the distal surface. The alignment and anatomy of a tooth may play a significant role in determining how susceptible it is to tensile stress. Furthermore, they may dictate where the maximum stress concentrates on a tooth. In the upper molars, cervical erosions usually develop in the mesiobuccal regions. Perhaps the lingual cusp, because it is more to the mesial portion of the tooth, concentrates the stress mesially. Traumatic occlusion in itself may not generate a significant tensile stress. Depending on the direction of the applied force and the alignment and anatomy of a tooth, occlusal trauma may produce mainly compressive stress and thus require a greater force than would tensile stress to cause the disruption of tooth structure. In lateral movements of the mandible, the canines play a significant protective function in disclusion of the posterior teeth. In dentitions that lack canine disclusion, lateral forces are transmitted to the posterior teeth, which may lead to the development of cervical erosions in teeth that are under tensile stress. In bruxism where canine disclusion eventually may be lost, the potential for the development of cervical erosions exists. Indeed, reports seem to indicate that there is a high frequency of cervical lesions in patients who brux.26,27The relationship of canine disclusion to the prevalence of cervical erosions remains to be examined. The tensile stress-induced cervical erosion theory provides a feasible explanation for a puzzling phenomenon. In a study of 10,000 extracted teeth, Sognnaes et a1.28reported an 18% incidence of cervical lesions. Even THE JOURNAL
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if only a fraction of these teeth requires treatment, cervical lesions still would constitute a significant problem economically. To the present time, treatment of these lesions has been largely empirical. With the tensile stress concept, a rational approach to treatment of cervical erosions could be planned and tested. SUMMARY A tensile stress hypothesis for the etiology of idiopathic cervical erosions of human teeth is presented. It is proposed that when occlusion is not ideal, lateral forces cause the teeth to bend. The tensile stresses created during bending disrupt the chemical bonds of the crystalline structures of enamel and dentin. Small molecules may enter between the crystals and prevent the reestablishment of the chemical bonds. As a result, the disrupted tooth structure is more susceptible to loss through dissolution and abrasion and results in the development of the typically wedge-shaped lesions. Patients with lesions typical of hundreds examined by the authors were presented to illustrate the concept. The possible consequences of the proposed hypothesis were discussed. The hypothetical conclusions made in this article will be tested by experimentation. REFERENCES 1. Gortner, R. A., Restarski, J. S., Bieri, J. G, and McCay, C. M.: Factors influencing the destructive eifects of acidic beverages on the teeth of white rats and tamsters. Arch Biochem 8~405, 1945. 2. Stafne, E. C., and Lovestedt, S. A.: Dissolution of tooth substance by lemon juice, acid beverages and acids from some other sources. J Am Dent Assoc 34~586, 1947. 3. Elsbury, W. B.: Hydrogen-ion concentration and acid erosion of the teeth. Br Dent J 93:177, 1952. 4. Larsen, M. J.: Degrees of saturation with respect to apatites in fruit juices and acidic drinks. Stand J Dent Res 83:13, 1975. 5. McClure, F. J., and Ruzicka, S. J.: The destructive effect of citrate vs. lactate ions on rats’ molar tooth surfaces, in viva. J Dent Res 25:1, 1946. 6. Zipkin, I., and McClure, F. J.: Salivary citrate and dental erosion. J Dent Res 28:613, 1949. I. Ericsson, Y.: Investigations on the occurrence and significance of citric acid in the saliva. J Dent Res 32:850, 1953. 8 Fuller, J. L., and Johnson, W. W.: Citric acid consumption and the human dentition. J Am Dent Assoc 95:80, 1977. 9 Shulman, E., and Robinson, H. B. G.: Salivary citrate content and erosion of teeth. J Dent Res 27:541, 1948. 10 Radentz, W. II., Barne, G. P., and Cutright, D. E.: A survey of factors possibly associated with cervical abt,asion of tooth surfaces. J Periodontol 47:148, 1976. 11 Bergstrom, J., and Lavstedt, S.: An epidemiologic approach to toothbrushing and dental abrasion. Community Dent Oral Epidemiol 7:57, 1979. 12 Hollinger, J. O., and Moore, E. M.: Hard tissue loss at the cementoenamel junction: A clinical study. J NJ Dent Assoc, Fall 1979, p 27. 13. Mannerberg, F.: Salivary factors in cases of erosion. Odont Revy 14~156, 1963. 14. Rest, T., and Brodie, A. G.: Possible etiologic factors in dental erosion. J Dent Res 40~385, 1961.
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Thresher, R. W., and S&to, G. E.. The stress analysis of human teeth. J Biomech 6:443, 1973. S&a, L. G., Shillingburg, H. T.. and Kerr, P. A.: Finite element analysis of dental structures-Axisymmetric and plane stress idealizations. J Biomed Mater Res 9:237, 1975. Yettram, A. L.. Wright, K. W. J., and Pickard, H. M.: Finite element stress analysis of the crowns of normal and restored teeth. ~J Dent Res 55:1004, 1970. Phillips, R. W.: Skinner’s Science ot Dental Materials, ed 7. Philadelphia, 1973. W. B. Saunders Co., pp 49-51. Craig, R., Peyton, F., and Johnson, D.: Compression properlies of enamel, dental cements and gold. J Dent Res 40:936. 1961. Bowen, R., and Rodriguez, M.. Tensile strength and modulus of elasticity of tooth structure and several restorative materials J Am Dent Assoc 64~378, 1962. hrends, J.: Schuthof, J., and Jongebloed. W. I,.: Mineral properties of the outer tooth surface. in Leach, S. A., editor: Dental Plaque and Surface Interactions in the Oral Cavity. Cheshire, England, 1979, Imperial Chemical Industries Ltd., pp 251-272. Powers, J. M., Craig, R. G., and Ludema, K. C.: Frictional behavior and surface failure of human t-name]. J Dent Re\ 52:1x27, 1971.
23. 24.
2s
16 27. 28
EAKLE
Brady, J. M., and Woody, R. D.: Scanning microscopy of cervical erosion. J Am Dent Assoc 94:726, 1977. Xhonga, F. A., Wolcott, R. B., and Sognnaes, R. F.: Clinical measurements of dental erosion progress. J Am Dent Assoc 84:577. 1972. Xhonga, F A., and Sognnaes, R. F.: Dental erosion: Progress of erosion measured clinically after various fluoride applications J Am Dent Assoc 87:1223, 1973. Xhonga, F. :I.. Bruxism and irs effect on the teeth. J Oral Rehabil 4~65. 1977 Xhonga, F. A, and Van Herle, A.: The influence of hyperthyroldism on dental erosions. Oral Surg 36~349, 1973. Sognnaes. R. F., Wolcott, R. B., and Xhonga, F. A.: Erosionhke patterns occurring in association with other dental conditwn$. J Am Dent Assoc 84:571, 1972.
Gingival tissue response to rotary curettage Fred W. Kamansky, D.D.S.,* Thomas R. Tempel, D.D.S., M.S.Ed.,** and Arthur C. Post, D.D.S., M.Ed.*** Walter
Reed Army Medical Center, Washington, D.C.
T
he management of gingival tissues during subgingival preparation of teeth for fixed prostheses varies in the technique used and the degree of effectiveness. High-frequency electrosurgery and lateral gingival tissue displacement achieved with a variety of chemically treated retraction cords are now the most common methods for tissue management of prepared teeth. One approach to gingival tissue management during fixed prosthodontic procedures is rotary gingival curettage. This technique? uses a specially designed rotary diamond instrument to remove a portion of the inner epithelial lining of the gingival sulcus during the
I‘hr opinions or assertions herein are the private views of the authors ,ind are not to be construed as official or as reflecting the views of ~hc I.~.$. Departments of the Army, Naby. or Defense. Subrnittrd in partial fulfillment of the requirements of the Fixed i’rosthodontirs Rrsidenc) Program. Walter Reed .4rmy Medical (:entrr, Washington. D.C “! Zrxnmander (DC:) USN; Prosthodontirs Dept.. Branch Dental (:linic NDC, N.4S North Island. San Diego. C.4. **Colone!, DC. LrSA, 1.1 S. Army Hospital, \C’orzburg. West t Germany. *‘*Formerly, Colonel. DC, USA; Augsburg, West Germany; prescntly, Colonel, DC, 17% (retired). fInqrah,+m. R. Perconal communication. 1978
380
placement of the finish line on tooth preparations. Tupac and Neacy’ conducted a study on dogs to compare cord gingival displacement with the rotary gingitage technique. They found no significant difference clinically or histologically between the two methods.
Amsterdam* suggested the use of rotary curettage in conjunction with the preparation of teeth for fixed prostheses. However, he observed that the rotating diamond instrument provided questionable tactile guidance while locating the position of the rotary instrument in the gingival sulcus during the procedure. The rate of healing of the gingival tissues after a surgical curettage procedure is relevant to the rotary curettage technique. Moskow3 reported that complete coverage of the debrided tissue with epithelium was seen within 7 days after gingival curettage on dogs. Blass and Lite4 found microscopically that complete healing was seen within 10 days after curettage on a healthy patient. Although complete healing of the gingiva can be predicted after rotary curettage, the human clinical application of the procedure could have collateral factors that affect the ultimate clinical response. The SEPTEMBER
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