WALL,
CONCLUSION This study corroborates the findings of Sorensen et a1.3 and further demonstrates that required folds in platinum foil substantially increase marginal discrepancies around luted porcelain veneers. However, these discrepancies are apparently smaller than those that are created when the porcelain veneer is fabricated on a refractory die. REFERENCES 1. Phillips RW. Skinner’s science of dental materials. 8th ed. Philadelphia: WB Saunders, 1982521. 2. American Dental Association. Dentists desk reference. 1st ed. Chicago, 1981:81.
An evaluation of smear layer agents a.fter tooth preparation Ali
Zaimoglu,
University
DDS,
of Ankara,
PhD,a
Faculty
and
A. Kevser
of Dentistry,
Aydin,
REISBICK,
AND
ESPELETA
3. Sorensen JA, Strutz D, Materdomini D, Torres TJ. Porcelain veneer marginal fidelity. Platinum foil vs refractory die technique [Abstract]. J Dent Res 1989;68:200. 4. Tay WM. Effects of some finishing techniques on cervical margins of porcelain laminates. Quintessence Int 1987;18:559. 5.. Rosenstiel SF, Land MF, Fnjimoto J. Complete ceramic crown fabrication, Contemporary fixed prosthodontics. St. Louis: CV Mosby, 1988:416. Reprint requests to: DR. J. GREGORY WALL THE OHIO STATE UNIVERSITY COLLEGE OF DENTISTRY 305 W. 12~~ AVE. COLUMBUS. OH 43210
with various DDS,
desensitizing
PhDb
Ankara, Turkey
According to hydrodynamics, any agent blocking the dentinal tubules reduces the flow of fluids and diminishes hypersensitivity. The properties of the desensitizing agents that sponsor tubular occlusion and the barrier efficiency resulting from the interaction of the smear layer with test materials were examined with the scanning electron microscope and energy-dispersive x-ray microanalysis. Selected dentinal desensitizing was accomplished with burnishing procedures, cavity varnish, calcium hydroxide, and topical fluoride. Subjective evaluations were also recorded chnically after tooth preparation. This investigation indicated that the smear layer did not protect against zinc phosphate cement, and that cavity varnish prevented the formation of the smear plugs. The smear layer and plugs were basically composed of calcium and phosphorus, the major ingredients of dentin. (J PROSTHET DENT 1992;68:460-7.)
D.
rfferent approaches related to the control of dentinal sensitivity after tooth preparation have been extensively reported, namely mechanical abrasives and surface medications.l-lo Despite these measures, sensitivity is encountered during cementation of castings, particularly in young people having numerous dentinal tubules with wide diameters. The coronal dentin of most young patients remains more sensitive to all external stimuli.lr Although the precise mechanism of pain transmission within the dentin is subject to speculation, there are currently three main theories. These are: (1) the direct nerve endings theory, (2) the odontoblast-receptor theory, and (3) the hydrodynamic theory.12vI3 The first theory suggested the existence of nerve endings in the dentin with a pulpal origin that can be directly stimaProfessor, Department bProfessor, Department 10/l/37847
450
of Prosthodontics. of Prosthodontics.
1. SEM of specimens in the control group. Age group 20 to 30 years. (Original magnification X2000.)
Fig.
SEPTEMBER
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LAYER
Fig. 2,. SEM of specimens in the control group. Age group 20 to 30 years. (Original nification X1000.)
ulated. Various physiologic studies have indicated that there were nerves in the most pulpal portion of the dentin, but rarely at the periphery. l2 According to the second theory, the odontoblast transferred stimuli to the nerve endings in the pulp through its process within the dentinal tubules.12, I3 A special functional relationship exists between the odontoblastic processes and the nerve fibers, so that together they constitute a receptor complex. The intratubular fibers appear in scanning electron microscopy (SEM) as collagen fibers and not odontoblastic processes. Therefore if the odontoblastic processes do not occupy the entire length of the dentinal tubules, dentinal hypersensitivity cannot be adequately explained based on the odontoblastreceptor concept.r2 The third theory is the most plausible and suggests that the stimulus is transmitted to the pulp by the hydrodynamic movement of fluids in the dentinal tubules.13 If the hydrodynamic theory for pain transmission was valid, occlusion of the patent dentinal tubules would be essential for treatment.5, l3 This treatment would control the flow of fluids in the tubules.13 In prosthodontics, the pressures that are generated during cementation of castings and mastication are transferred to the fluid in dentin. According to Pashley,l* there is a danger that the cement will enter the dentinal tubules before it sets, displacing an equal volume of dentinal fluid in the pulp. This could be responsible for the pain that unanesthetized patients experience during cementation of crowns and could plausibly explain the hydrodynamic theory. This investigation determined the properties of the commonly used desensitizing treatments that occlude the dentinal tubules and compared the barrier efficiency of the smear layer to specific test materials.
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Table
I. Treatment
mag-
groups
I Control group (conventional tooth preparation with dia-
mond bum) II Zinc phosphate cement* III Burnishing group (sandpaper disk + rubber phosphate cement) IV Cavity varnish? + zinc phosphate cement V Ca(OH)z + zinc phosphate cement VI Sodium fluoride+ + zinc phosphate cement
point + zinc
*Lumicon, Bayer Dental Division, Leverkusen, Germany. tCavi-Line, Cavity Lining Agent, Caulk Dentsply, Milford, Del. $Base Fluorogel, Base Chemical Division, Ankara, Turkey.
MATERIAL
AND METHODS
A total of 54 freshly extracted intact human teeth were selected for this study, using the three age groups of 20 to 30 years, 30 to 40 years, and 40 to 50 years. The test materials were selected using the criteria established by Grossmani and included approaches such as burnishing, cavity varnish, calcium hydroxide [Ca(OH)z], and topical sodium fluoride. After conventional tooth preparation, the treatments listed in Table I were applied to these teeth. Acrylic resin crowns were prepared for all the teeth except for the controls. During cementation, the acrylic resin crowns were inserted on the prepared teeth with pressure that was sustained until the cement had set. A groove was prepared on the palatal surface of the crown with fine diamond bum from the palatal to the facial surface. The tooth was then sectioned longitudinally in halves by exerting pressure between the thumb and forefinger on the mesial and distal surfaces. The halves were recovered
451
Fig. 3. Energy dispersive x-ray microanalysis (EDXA) the superficial smear layer in the control group.
of
Fig. 5. SEM of the specimen in Fig. 4 from the second group. (Original magnification X2000.)
Fig. 4. SEM of the second group. Age group 20 to 30 years. (Original magnification X5000.)
without disturbing the facial surfaces, mounted on a metal holder, and sputter-coated with gold before evaluation with the SEM and energy-dispersive x-ray microanalysis (EDXA). The dentinal tubules on the facial surfaces of the teeth were examined with the SEM (Cambridge Stereoscan S4-10, Cambridge, England; and JEOL JSM-840A, Japan Electron Optics Limited, Tokyo, Japan) and photographs were made between 1000 and 8000 power magnification. In addition, the components of the selected areas were determined by EDXA (Tracer, Northern TN-5502 Series EDS x-ray microanalysis system, Tracer, USA, Elk Grove Village, Ill.) and the clinical evaluations were recorded.
RESULTS Control group The number and diameter of dentinal tubules diminished during aging, and was verified upon SEM evaluation.
452
Fig. 6. SEM of the second group. Age group 20 to 30 years. (Original magnification X5000.)
In control specimens without a desensitizing agent, it was observed that no distinct grinding debris entered the dentinal tubules (Fig. 1). However, the superficial smear layer was noted in all specimens (Fig. 2). Microanalysis of the superficial smear layer revealed that the smear was composed of calcium and phosphorus, the major components of dentin (Fig. 3).
Zinc phosphate
cement
group
Zinc phosphate cement was directly applied after preparation in the second group. The presence of extremely long plugs was evident, although infrequently, in the age group
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Fig. 7. SEM of the second group. Age group 20 to 30 years. (Original
magnification
X8000.)
Fig. 9. SEM of the third group. Age group 20 to 30 years. (Original
Fig.
8. EDXA
group
The SEM of the burnishing procedures in the age group of 20 to 30 years revealed the formation of certain “fingerlike” smear plugs at the large tubular apertures (Figs. 9 and 10). Photomicrographs of specimens of the same age are seen in Fig. 11. The smear plugs in particles were observed at the tubular apertures in the 30- to 40-year group (Fig. 12). There is a possibility that smear plugs were displaced from the other tubules during the sectioning of the teeth. In the 40- to 50-year group, the superficial smear layers ex-
THE
JOURNAL
OF PROSTHETIC
X5000.)
of the plug in Fig. 7.
of 20 to 30 years (Fig. 4), and the entire length of the same plug is evident in Fig. 5. A long, dense, homogeneous plug was also seen in another specimen of this group (Fig. 6). A photomicrograph produced from the specimens of the same age group is clearly displayed in Fig. 7, while an x-ray dispersive spectrum of the plug in Fig. 7 demonstrated calcium and phosphorus in varying proportions (Fig. 8). Calcium and phosphorus peaks were higher than in the control group, but at the same time only traces of zinc were noted.
Burnishing
magnification
DENTISTRY
Fig. 10. SEM of the third group showing another characteristic
region. (Original
magnification
X5000.)
tended into the dentinal tubules like fingers, progressed, and then fractured (Fig. 13). An x-ray dispersive spectrum of the plug as seen in Fig. 11 disclosed that the calcium peak was lower than the phosphorus peak, and this deviated from the control (Fig. 14).
Cavity grow
varnish
+ zinc phosphate
cement
The test material of cavity varnish plus zinc phosphate cement appeared as a cancellous structure without smear plugs because of its occluding property (Fig. 15). Radio-
453
ZAIMOGLU
AND
AYDIK
11. SEM of specimens in the third group. Age group 20 to 30 years. (Original magnification X3300.)
Fig.
13. SEM of specimens in the third group. Age grolUP 49 to 50 years. (Original magnification X4500.)
Fig.
Fig.
12. SEM of specimens in the third group. Age group 30 to 40 years. (Original magnification X4000.)
14. EDXA of the plug in Fig. 11.
Fig.
graphic microanalysis was not required in this fourth group because the same details were observed in the microradiographs of the other age groups. Ca(OH),
+ zinc phosphtate
cement
group
The dense plugs were not evident in dentinal tubules in the fifth group to which a slurry of calcium oxide (CaO) plus sterile water was applied before the cement. The plugs were in particles for the ‘LO-to 30-year group (Fig. 16), and similar details were noted in the specimens of the other age groups. The smear plug is clearly present in Fig. 17, produced from the 20- to 30-year group. An x-ray dispersive spectrum of this plug revealed that the phosphorus peak was lower than the calcium peak (Fig. 18). Zinc was also minutely present in the media. 454
Topical cement
sodium group
fluoride
+ zinc phosphate
Circular precipitations were observed in the dentinal tubules of the 20- to 30-year group (Fig. 19), and in the dense smear plugs for some of the specimens of the 30- to 40-year group (Fig. 20). According to the x-ray dispersive spectrum of the specimens in the ZO- to 30 year group, the calcium and phosphorous produced dentinal plugs that existed in approximately equal portions (Fig. 21). The patients with applied cavity varnish did not experience sensitivity after preparation or during cementation. A reduction in sensitivity was noted in the fifth and sixth groups, while it was less in the third group than in the latter groups. DISCUSSION The term “smear layer” is commonly used to describe the grinding debris remaining on the dentin after tooth prep-
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Fig. 15. SEM of the fourth group. Age group 20 to 30 years. (Original magnification X2200.)
aration. It is composed of the fused residue of the mineralized dentinal matrix, cavity debris, and possibly of scattered bacteria.16,17 The smear layer occluded the tubule apertures or entered the dentinal tubules as a plug in several specimens. SEM photomicrographs (Figs. 1 and 2) of the control group demonstrated that this layer occluded the orifices of dentinal tubules d.uring the superficial formation and prevented fluid movement in the tubules, arresting the hydrodynamics.3: 14,lo, ig In conventional preparations, the absence of the smear layer in tubular apertures can be attributed to the preparation of water with pressure plus superficial cutting. This condition was also evident for the dentinal tubules at the same level as the sectioned surface. The pH of zinc phosphate cement is acid before it sets. Pashley14 reported that the zinc phosphate cement removed portions of the smear layer during cementation and pulpal irritation resulted from the movement of fluid rather than because of the acidity of the cement. The pain resulted from the displacement of an equal volume of dentinal fluid into the pulp by cement entering the dentinal tubules before setting. In certain specimens it was clearly demonstrated that extremely long, dense, and homogeneous plugs existed in dentinal tubules when zinc phosphate cement was applied, especially in the 20- to 30-year age group (Figs. 4 through 7). Pashley14 believed that zinc phosphate cement may also enter these tubules as organic and inorganic constituents to produce the smear layer. Our findings confirmed Pashley’s theory, but these formations in the form of plugs were rarely observed. The x-ray dispersive spectrum corroborated that the major components of “the plug” were calcium and phosphorus (Fig. 8). The phosphorus peak was higher than that of the control (Fig. 3) and some zinc was
THE
JOURNAL
OF PROSTHETIC
DENTBTRY
16. SEM of the fifth group. Age group 20 to 30 years. (Original magnification X5000.)
Fig.
1’7. SEM of specimens in the fifth group. Age group 20 to 30 years. (Original magnification x6500.)
Fig.
also identified in the media. Although this condition indicated that the plug resembled the natural structure of dentin, the fact that the proportion of phosphorus was higher than in the control implied that phosphorus entered the tubules in a manner similar to zinc. According to various investigators,3, 6,7 the tubules appeared occluded and certain “peritubular dentin groups” were observed when fine abrasives such as diamond disks and silicon carbides were used after preparation. Pashley et a1.6stated that more debris appeared in the dentinal tubules because of pressure and the dentinal permeability was diminished by burnishing. In this investigation, the dentinal tubules were occluded with more plugs than other groups that were occluded by burnishings (Figs. 9 through 13). The sensitivity was not entirely eliminated in the bur-
455
ZAIMOGLU
Fig.
18. EDXA
AND
AYDIN
of the plug in Fig. 17.
Fig. 20. SEM of the sixth group. Age group 30 to 40 years. (Original magnification X4500.)
Fig. 19. SEM of the sixth group, Age group 20 to 30 years. (Original magnification x1600.)
nishing group. This subjective finding may be attributed to the following: (1) The burnishing procedure would not be performed at the contact surfaces of the prepared teeth. (2) Long smear plugs entering the dentinal tubules may be responsible for the pain, according to the hydrodynamic theory. The dentinal plug mimics the natural structure of dentin and the proportion of the phosphorous is higher than that of calcium (Fig. 14). This condition may be attributed to the point analysis, but an explanation of a high concentration of phosphorus is difficult. The thickness and permeability of cavity varnishes for occluding the orifices of dentinal tubules are variable,14 and as the solvent evaporates, it leaves a film that protects the underlying tooth structure. 2o Cavity varnishes are commonly applied in a thin layer to protect the treated surface from the irritation of acids or the newly placed cement.20, ‘l Cavi-Line (Caulk-Dentsply Inlternational, Milford, Del.) is a cavity lining agent that can be used as a cavity varnish on the prepared teeth. The SEM findings (Fig. 15) of this test group revealed that Cavi-Line prevented the smear plugs 456
Fig.
21. EDXA
of the plug in the sixth test group.
from entering the dentinal tubules. This successful finding may be attributed to a quick isolation of cavity varnish in a thin layer without the formation of a plug. There was no need for x-ray microanalysis in the fourth test group because the dentinal plugs were absent. Calcium hydroxide is a common ingredient in current bases and liners, and offers pulpal protection by reducing the dentinal permeability and stimulating irregular secondary dentin.lO Brannstromz2 believed that Ca(OH)s reinforced the remaining smear layer in the outer apertures of dentinal tubules and Ca(OH)s also encouraged the formation of less permeable dentin by mineralizations Warfvinge et al.rO observed that a water slurry of Ca(OH)e did not extend into dentinal tubules, but protein microprecipitation existed within these tubules. Our specimens that were treated with Ca(OH)z presented an appearance similar to the specimens of Warfvinge et al.l” The plugs were diversely observed in various specimens either as particles (Fig. 16) or as homogeneous formations that possessed a designated length (Fig. 17). An x-ray dispersive spectrum SEPTEMBER
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of this group confirmed the presence of the major components of dentin (Fig. 18). Sodium fluoride was proposed as a dentinal desensitizing agent by various investigators.23-26 The reduced sensitivity has been attributed to an intratubular precipitate and to the elevation in the resistance of the dentin to acid decalcification.5s 24,26,27It has been hypothesized that topical fluoride will sponsor the formation of a fluoride hydroxyapatite5 and mechanically block the tubules, affecting the transmission of stimuli.5, 24 Circular precipitations (Fig. 19) and the dense smear plugs (Fig. 20) were observed in the specimens belonging to the sixth group. X-ray microanalysis of these plugs demonstrated a spectrum characteristic of the dentin (Fig. 21), with the proportions of calcium and phosphorous almost identical. This was verified by point analysis.
CONCLUSIONS 1. The smear layer evident after tooth preparation did not protect against zinc phosphate cement. 2. Mechanical burnishing of dentin should not be performed because of the accumulation of microorganims and their products in the tubules, the increase of plugs entering the tubules, and the pain related to the hydrodynamic mechanism. 3. The cavity varnishes prevented the formation of smear plugs, but diminished dsntinal hypersensitivity. This treatment also created bright and smooth surfaces, so the problem of crown retention should be examined separately. 4. Ca(OH)s and topical fluoride treatments allowed the formation of smear plugs, and these applications were effective in treating hypersensitivity. Ca(OH)s and topical fluoride treatments have been used successfully as desensitizing agents for years, and did not adversely affect retention. 5. Direct cementation with zinc phosphate cement can cause pain in patients, so many dentists apply desensitizing agents before the direct cement application. When the findings were reviewed, it was evident that the desensitizing agents, except for cavity varnish, were incapable of preventing the smear plugs. However, the treatment materials did not create the composition of smear plugs. 6. The results of x-ray microanalysis indicated that the smear layer and plugs were composed mainly of calcium and phosphorus, the major structural elements of dentin. REFERENCES 1. Cuhadaroglu 1973.
THE
JOURNAL
i. Kuron-koprii
protezi.
OF PROSTHETIC
DENTISTRY
Ankara:
Ayyildiz
Matbaasi,
2. Gangarosa LP, Park NH. Practical considerations in iontophoresis of fluoride for desensitizing dentin. J PROSTHET DENT 197&39:173-S. 3. Gwinnett AJ. Smear layer, morphological considerations. Oper Dent 1984;3:3-12. 4. Johnston JF, Phillips RW, Dykema RW. Modern practice in crown and bridge prosthodontics. 1st ed. Philadelphia: WB Saunders Co, 1971. teeth. Part II. Treatment. J PROSTHET 5. Krauser JT. Hypersensitive DENT 1986;56:307-11. 6. Pashley DH, Leibach JG, Homer JA. The effects of burnishing NaF/kaolin/glycerin paste on dentin permeability. J Periodont 1987; 5819-23. 7. Pashley DH, Livingston MJ, Reeder OW, Homer J. Effects of the degree of tubule occlusion on the permeability of human dentine in vitro. Arch Oral Biol 1978;23:1127-33. cav8. Tjan AHL, Grant BE, Nemetz H. The efficacy of resin-compatible ity varnishes in reducing dentin permeability to free monomer. J PROSTHET DENT 1987;57:179-84. 9. Tylman SD. Theory and practice of crown and fixed partial prosthodontics (bridge). 6th ed. St. Louis: The CV Mosby Co, 1970. 10. Warfvinge J, Rose11 B, Hedstrijm KG. Effect of calcium hydroxide treated dentine on pulpal responses. Int Endodont J 1987;20:183-93. 11. Zaimoglu L, Sayan NB. Digin farkli bdlgelerinde dentin kanal sayisinin saptanmasi ye bunun yag ile iliskisinin tesbiti. HU Dis Hek Fak Derg 1985;9:245-60. teeth. Part I. Etiology. J PROSTHET DENT 12. Krauser JT. Hypersensitive 1986;56:153-6. 13. Uygun H. Dentin agiri duyarliligi. Hii Dig Hek Fak Derg 1987;11:136-8. considerations. Oper Dent 14. Pashley DH. Smear layer physiological 1984;(suppl 3):13-29. 15, Grossman L. A systematic method for the treatment of hypersensitive dentin. J Am Dent Assoc 1935;22:592-602. 16. Cotton WR. Smear layer on dentin. Oper Dent 1984;(suppl 3):1-2. 17. Meryon SD, Tobias RS, Jakeman KJ. Smear removal agents: a quantitative study in viva and in vitro. J PROSTHET DENT 1987;57:174-9. 18 Pashley DH, Michelich V, Kehi T. Dentin permeability: effects of smear layer removal. J PROSTHET DENT 1981;46:531-7. 19 Welch FH, Eick JD. A method to reduce or prevent postoperative sensitivity with posterior composite resin restorations. Quintessence Int 1986;17:667-76. 20 Bayirli GS, Sirin $. Restoratif tedavi. Istanbul: Tq M&baa&, 1985. 21. Horn HR. Practical considerations for successful crown and bridge therapy. Philadelphia: WB Saunders Co, 1976. 22. Brannstrom M. Smear layer: pathological and treatment considerations. Oper Dent 1984;(suppl 3):35-42. 23. Hoyt WH, Bibby BF. The use of sodium fluoride for desensitizing dentin [Abstract]. J Dent Res 1943;22:208. 24. Tal M, Oron M, Gedalia I, et al. X-ray difraction and scanning electron microscope investigations of fluoride-treated dentine in man. Arch Oral Biol 1976;21:285-90. 25. Carlo GT, Ciancio SG, Seyrek SK. An evaluation of iontophoretic application of fluoride for tooth desensitization. J Am Dent Assoc 1982; 105452.4. 26. Kofoglu S, Akbay T. Topikal Bi-fluorun k&dentin hassasiye-tindeki etkinliginin scanning elektron mikroskobu ile aragtirilmasi. HU Dig Hek Fak Derg 1988;12:125-8. 27. Ehrlich J, Hochman N, Gedalia I, et al. Residual fluoride concentrations and scanning electron microscopic examination of root surfaces of human teeth after topical application of fluoride in viva. J Dent Res 1975;54:897-900.
Reprintrequeststo: DR. A. KEVSER AYDIN KIRA~I SOKAK No: 13/15 06570 MALTEPE, ANKARA TURKEY
457
CONCLUSION This study corroborates the findings of Sorensen et a1.3 and further demonstrates that required folds in platinum foil substantially increase marginal discrepancies around luted porcelain veneers. However, these discrepancies are apparently smaller than those that are created when the porcelain veneer is fabricated on a refractory die. REFERENCES 1. Phillips RW. Skinner’s science of dental materials. 8th ed. Philadelphia: WB Saunders, 1982521. 2. American Dental Association. Dentists desk reference. 1st ed. Chicago, 1981:81.
An evaluation of smear layer agents a.fter tooth preparation Ali
Zaimoglu,
University
DDS,
of Ankara,
PhD,a
Faculty
and
A. Kevser
of Dentistry,
Aydin,
REISBICK,
AND
ESPELETA
3. Sorensen JA, Strutz D, Materdomini D, Torres TJ. Porcelain veneer marginal fidelity. Platinum foil vs refractory die technique [Abstract]. J Dent Res 1989;68:200. 4. Tay WM. Effects of some finishing techniques on cervical margins of porcelain laminates. Quintessence Int 1987;18:559. 5.. Rosenstiel SF, Land MF, Fnjimoto J. Complete ceramic crown fabrication, Contemporary fixed prosthodontics. St. Louis: CV Mosby, 1988:416. Reprint requests to: DR. J. GREGORY WALL THE OHIO STATE UNIVERSITY COLLEGE OF DENTISTRY 305 W. 12~~ AVE. COLUMBUS. OH 43210
with various DDS,
desensitizing
PhDb
Ankara, Turkey
According to hydrodynamics, any agent blocking the dentinal tubules reduces the flow of fluids and diminishes hypersensitivity. The properties of the desensitizing agents that sponsor tubular occlusion and the barrier efficiency resulting from the interaction of the smear layer with test materials were examined with the scanning electron microscope and energy-dispersive x-ray microanalysis. Selected dentinal desensitizing was accomplished with burnishing procedures, cavity varnish, calcium hydroxide, and topical fluoride. Subjective evaluations were also recorded chnically after tooth preparation. This investigation indicated that the smear layer did not protect against zinc phosphate cement, and that cavity varnish prevented the formation of the smear plugs. The smear layer and plugs were basically composed of calcium and phosphorus, the major ingredients of dentin. (J PROSTHET DENT 1992;68:460-7.)
D.
rfferent approaches related to the control of dentinal sensitivity after tooth preparation have been extensively reported, namely mechanical abrasives and surface medications.l-lo Despite these measures, sensitivity is encountered during cementation of castings, particularly in young people having numerous dentinal tubules with wide diameters. The coronal dentin of most young patients remains more sensitive to all external stimuli.lr Although the precise mechanism of pain transmission within the dentin is subject to speculation, there are currently three main theories. These are: (1) the direct nerve endings theory, (2) the odontoblast-receptor theory, and (3) the hydrodynamic theory.12vI3 The first theory suggested the existence of nerve endings in the dentin with a pulpal origin that can be directly stimaProfessor, Department bProfessor, Department 10/l/37847
450
of Prosthodontics. of Prosthodontics.
1. SEM of specimens in the control group. Age group 20 to 30 years. (Original magnification X2000.)
Fig.
SEPTEMBER
1992
VOLUME
68
NUMBER
3
EVALUATION
OF SMEAR
LAYER
Fig. 2,. SEM of specimens in the control group. Age group 20 to 30 years. (Original nification X1000.)
ulated. Various physiologic studies have indicated that there were nerves in the most pulpal portion of the dentin, but rarely at the periphery. l2 According to the second theory, the odontoblast transferred stimuli to the nerve endings in the pulp through its process within the dentinal tubules.12, I3 A special functional relationship exists between the odontoblastic processes and the nerve fibers, so that together they constitute a receptor complex. The intratubular fibers appear in scanning electron microscopy (SEM) as collagen fibers and not odontoblastic processes. Therefore if the odontoblastic processes do not occupy the entire length of the dentinal tubules, dentinal hypersensitivity cannot be adequately explained based on the odontoblastreceptor concept.r2 The third theory is the most plausible and suggests that the stimulus is transmitted to the pulp by the hydrodynamic movement of fluids in the dentinal tubules.13 If the hydrodynamic theory for pain transmission was valid, occlusion of the patent dentinal tubules would be essential for treatment.5, l3 This treatment would control the flow of fluids in the tubules.13 In prosthodontics, the pressures that are generated during cementation of castings and mastication are transferred to the fluid in dentin. According to Pashley,l* there is a danger that the cement will enter the dentinal tubules before it sets, displacing an equal volume of dentinal fluid in the pulp. This could be responsible for the pain that unanesthetized patients experience during cementation of crowns and could plausibly explain the hydrodynamic theory. This investigation determined the properties of the commonly used desensitizing treatments that occlude the dentinal tubules and compared the barrier efficiency of the smear layer to specific test materials.
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Table
I. Treatment
mag-
groups
I Control group (conventional tooth preparation with dia-
mond bum) II Zinc phosphate cement* III Burnishing group (sandpaper disk + rubber phosphate cement) IV Cavity varnish? + zinc phosphate cement V Ca(OH)z + zinc phosphate cement VI Sodium fluoride+ + zinc phosphate cement
point + zinc
*Lumicon, Bayer Dental Division, Leverkusen, Germany. tCavi-Line, Cavity Lining Agent, Caulk Dentsply, Milford, Del. $Base Fluorogel, Base Chemical Division, Ankara, Turkey.
MATERIAL
AND METHODS
A total of 54 freshly extracted intact human teeth were selected for this study, using the three age groups of 20 to 30 years, 30 to 40 years, and 40 to 50 years. The test materials were selected using the criteria established by Grossmani and included approaches such as burnishing, cavity varnish, calcium hydroxide [Ca(OH)z], and topical sodium fluoride. After conventional tooth preparation, the treatments listed in Table I were applied to these teeth. Acrylic resin crowns were prepared for all the teeth except for the controls. During cementation, the acrylic resin crowns were inserted on the prepared teeth with pressure that was sustained until the cement had set. A groove was prepared on the palatal surface of the crown with fine diamond bum from the palatal to the facial surface. The tooth was then sectioned longitudinally in halves by exerting pressure between the thumb and forefinger on the mesial and distal surfaces. The halves were recovered
451
Fig. 3. Energy dispersive x-ray microanalysis (EDXA) the superficial smear layer in the control group.
of
Fig. 5. SEM of the specimen in Fig. 4 from the second group. (Original magnification X2000.)
Fig. 4. SEM of the second group. Age group 20 to 30 years. (Original magnification X5000.)
without disturbing the facial surfaces, mounted on a metal holder, and sputter-coated with gold before evaluation with the SEM and energy-dispersive x-ray microanalysis (EDXA). The dentinal tubules on the facial surfaces of the teeth were examined with the SEM (Cambridge Stereoscan S4-10, Cambridge, England; and JEOL JSM-840A, Japan Electron Optics Limited, Tokyo, Japan) and photographs were made between 1000 and 8000 power magnification. In addition, the components of the selected areas were determined by EDXA (Tracer, Northern TN-5502 Series EDS x-ray microanalysis system, Tracer, USA, Elk Grove Village, Ill.) and the clinical evaluations were recorded.
RESULTS Control group The number and diameter of dentinal tubules diminished during aging, and was verified upon SEM evaluation.
452
Fig. 6. SEM of the second group. Age group 20 to 30 years. (Original magnification X5000.)
In control specimens without a desensitizing agent, it was observed that no distinct grinding debris entered the dentinal tubules (Fig. 1). However, the superficial smear layer was noted in all specimens (Fig. 2). Microanalysis of the superficial smear layer revealed that the smear was composed of calcium and phosphorus, the major components of dentin (Fig. 3).
Zinc phosphate
cement
group
Zinc phosphate cement was directly applied after preparation in the second group. The presence of extremely long plugs was evident, although infrequently, in the age group
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Fig. 7. SEM of the second group. Age group 20 to 30 years. (Original
magnification
X8000.)
Fig. 9. SEM of the third group. Age group 20 to 30 years. (Original
Fig.
8. EDXA
group
The SEM of the burnishing procedures in the age group of 20 to 30 years revealed the formation of certain “fingerlike” smear plugs at the large tubular apertures (Figs. 9 and 10). Photomicrographs of specimens of the same age are seen in Fig. 11. The smear plugs in particles were observed at the tubular apertures in the 30- to 40-year group (Fig. 12). There is a possibility that smear plugs were displaced from the other tubules during the sectioning of the teeth. In the 40- to 50-year group, the superficial smear layers ex-
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X5000.)
of the plug in Fig. 7.
of 20 to 30 years (Fig. 4), and the entire length of the same plug is evident in Fig. 5. A long, dense, homogeneous plug was also seen in another specimen of this group (Fig. 6). A photomicrograph produced from the specimens of the same age group is clearly displayed in Fig. 7, while an x-ray dispersive spectrum of the plug in Fig. 7 demonstrated calcium and phosphorus in varying proportions (Fig. 8). Calcium and phosphorus peaks were higher than in the control group, but at the same time only traces of zinc were noted.
Burnishing
magnification
DENTISTRY
Fig. 10. SEM of the third group showing another characteristic
region. (Original
magnification
X5000.)
tended into the dentinal tubules like fingers, progressed, and then fractured (Fig. 13). An x-ray dispersive spectrum of the plug as seen in Fig. 11 disclosed that the calcium peak was lower than the phosphorus peak, and this deviated from the control (Fig. 14).
Cavity grow
varnish
+ zinc phosphate
cement
The test material of cavity varnish plus zinc phosphate cement appeared as a cancellous structure without smear plugs because of its occluding property (Fig. 15). Radio-
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11. SEM of specimens in the third group. Age group 20 to 30 years. (Original magnification X3300.)
Fig.
13. SEM of specimens in the third group. Age grolUP 49 to 50 years. (Original magnification X4500.)
Fig.
Fig.
12. SEM of specimens in the third group. Age group 30 to 40 years. (Original magnification X4000.)
14. EDXA of the plug in Fig. 11.
Fig.
graphic microanalysis was not required in this fourth group because the same details were observed in the microradiographs of the other age groups. Ca(OH),
+ zinc phosphtate
cement
group
The dense plugs were not evident in dentinal tubules in the fifth group to which a slurry of calcium oxide (CaO) plus sterile water was applied before the cement. The plugs were in particles for the ‘LO-to 30-year group (Fig. 16), and similar details were noted in the specimens of the other age groups. The smear plug is clearly present in Fig. 17, produced from the 20- to 30-year group. An x-ray dispersive spectrum of this plug revealed that the phosphorus peak was lower than the calcium peak (Fig. 18). Zinc was also minutely present in the media. 454
Topical cement
sodium group
fluoride
+ zinc phosphate
Circular precipitations were observed in the dentinal tubules of the 20- to 30-year group (Fig. 19), and in the dense smear plugs for some of the specimens of the 30- to 40-year group (Fig. 20). According to the x-ray dispersive spectrum of the specimens in the ZO- to 30 year group, the calcium and phosphorous produced dentinal plugs that existed in approximately equal portions (Fig. 21). The patients with applied cavity varnish did not experience sensitivity after preparation or during cementation. A reduction in sensitivity was noted in the fifth and sixth groups, while it was less in the third group than in the latter groups. DISCUSSION The term “smear layer” is commonly used to describe the grinding debris remaining on the dentin after tooth prep-
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Fig. 15. SEM of the fourth group. Age group 20 to 30 years. (Original magnification X2200.)
aration. It is composed of the fused residue of the mineralized dentinal matrix, cavity debris, and possibly of scattered bacteria.16,17 The smear layer occluded the tubule apertures or entered the dentinal tubules as a plug in several specimens. SEM photomicrographs (Figs. 1 and 2) of the control group demonstrated that this layer occluded the orifices of dentinal tubules d.uring the superficial formation and prevented fluid movement in the tubules, arresting the hydrodynamics.3: 14,lo, ig In conventional preparations, the absence of the smear layer in tubular apertures can be attributed to the preparation of water with pressure plus superficial cutting. This condition was also evident for the dentinal tubules at the same level as the sectioned surface. The pH of zinc phosphate cement is acid before it sets. Pashley14 reported that the zinc phosphate cement removed portions of the smear layer during cementation and pulpal irritation resulted from the movement of fluid rather than because of the acidity of the cement. The pain resulted from the displacement of an equal volume of dentinal fluid into the pulp by cement entering the dentinal tubules before setting. In certain specimens it was clearly demonstrated that extremely long, dense, and homogeneous plugs existed in dentinal tubules when zinc phosphate cement was applied, especially in the 20- to 30-year age group (Figs. 4 through 7). Pashley14 believed that zinc phosphate cement may also enter these tubules as organic and inorganic constituents to produce the smear layer. Our findings confirmed Pashley’s theory, but these formations in the form of plugs were rarely observed. The x-ray dispersive spectrum corroborated that the major components of “the plug” were calcium and phosphorus (Fig. 8). The phosphorus peak was higher than that of the control (Fig. 3) and some zinc was
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16. SEM of the fifth group. Age group 20 to 30 years. (Original magnification X5000.)
Fig.
1’7. SEM of specimens in the fifth group. Age group 20 to 30 years. (Original magnification x6500.)
Fig.
also identified in the media. Although this condition indicated that the plug resembled the natural structure of dentin, the fact that the proportion of phosphorus was higher than in the control implied that phosphorus entered the tubules in a manner similar to zinc. According to various investigators,3, 6,7 the tubules appeared occluded and certain “peritubular dentin groups” were observed when fine abrasives such as diamond disks and silicon carbides were used after preparation. Pashley et a1.6stated that more debris appeared in the dentinal tubules because of pressure and the dentinal permeability was diminished by burnishing. In this investigation, the dentinal tubules were occluded with more plugs than other groups that were occluded by burnishings (Figs. 9 through 13). The sensitivity was not entirely eliminated in the bur-
455
ZAIMOGLU
Fig.
18. EDXA
AND
AYDIN
of the plug in Fig. 17.
Fig. 20. SEM of the sixth group. Age group 30 to 40 years. (Original magnification X4500.)
Fig. 19. SEM of the sixth group, Age group 20 to 30 years. (Original magnification x1600.)
nishing group. This subjective finding may be attributed to the following: (1) The burnishing procedure would not be performed at the contact surfaces of the prepared teeth. (2) Long smear plugs entering the dentinal tubules may be responsible for the pain, according to the hydrodynamic theory. The dentinal plug mimics the natural structure of dentin and the proportion of the phosphorous is higher than that of calcium (Fig. 14). This condition may be attributed to the point analysis, but an explanation of a high concentration of phosphorus is difficult. The thickness and permeability of cavity varnishes for occluding the orifices of dentinal tubules are variable,14 and as the solvent evaporates, it leaves a film that protects the underlying tooth structure. 2o Cavity varnishes are commonly applied in a thin layer to protect the treated surface from the irritation of acids or the newly placed cement.20, ‘l Cavi-Line (Caulk-Dentsply Inlternational, Milford, Del.) is a cavity lining agent that can be used as a cavity varnish on the prepared teeth. The SEM findings (Fig. 15) of this test group revealed that Cavi-Line prevented the smear plugs 456
Fig.
21. EDXA
of the plug in the sixth test group.
from entering the dentinal tubules. This successful finding may be attributed to a quick isolation of cavity varnish in a thin layer without the formation of a plug. There was no need for x-ray microanalysis in the fourth test group because the dentinal plugs were absent. Calcium hydroxide is a common ingredient in current bases and liners, and offers pulpal protection by reducing the dentinal permeability and stimulating irregular secondary dentin.lO Brannstromz2 believed that Ca(OH)s reinforced the remaining smear layer in the outer apertures of dentinal tubules and Ca(OH)s also encouraged the formation of less permeable dentin by mineralizations Warfvinge et al.rO observed that a water slurry of Ca(OH)e did not extend into dentinal tubules, but protein microprecipitation existed within these tubules. Our specimens that were treated with Ca(OH)z presented an appearance similar to the specimens of Warfvinge et al.l” The plugs were diversely observed in various specimens either as particles (Fig. 16) or as homogeneous formations that possessed a designated length (Fig. 17). An x-ray dispersive spectrum SEPTEMBER
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of this group confirmed the presence of the major components of dentin (Fig. 18). Sodium fluoride was proposed as a dentinal desensitizing agent by various investigators.23-26 The reduced sensitivity has been attributed to an intratubular precipitate and to the elevation in the resistance of the dentin to acid decalcification.5s 24,26,27It has been hypothesized that topical fluoride will sponsor the formation of a fluoride hydroxyapatite5 and mechanically block the tubules, affecting the transmission of stimuli.5, 24 Circular precipitations (Fig. 19) and the dense smear plugs (Fig. 20) were observed in the specimens belonging to the sixth group. X-ray microanalysis of these plugs demonstrated a spectrum characteristic of the dentin (Fig. 21), with the proportions of calcium and phosphorous almost identical. This was verified by point analysis.
CONCLUSIONS 1. The smear layer evident after tooth preparation did not protect against zinc phosphate cement. 2. Mechanical burnishing of dentin should not be performed because of the accumulation of microorganims and their products in the tubules, the increase of plugs entering the tubules, and the pain related to the hydrodynamic mechanism. 3. The cavity varnishes prevented the formation of smear plugs, but diminished dsntinal hypersensitivity. This treatment also created bright and smooth surfaces, so the problem of crown retention should be examined separately. 4. Ca(OH)s and topical fluoride treatments allowed the formation of smear plugs, and these applications were effective in treating hypersensitivity. Ca(OH)s and topical fluoride treatments have been used successfully as desensitizing agents for years, and did not adversely affect retention. 5. Direct cementation with zinc phosphate cement can cause pain in patients, so many dentists apply desensitizing agents before the direct cement application. When the findings were reviewed, it was evident that the desensitizing agents, except for cavity varnish, were incapable of preventing the smear plugs. However, the treatment materials did not create the composition of smear plugs. 6. The results of x-ray microanalysis indicated that the smear layer and plugs were composed mainly of calcium and phosphorus, the major structural elements of dentin. REFERENCES 1. Cuhadaroglu 1973.
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i. Kuron-koprii
protezi.
OF PROSTHETIC
DENTISTRY
Ankara:
Ayyildiz
Matbaasi,
2. Gangarosa LP, Park NH. Practical considerations in iontophoresis of fluoride for desensitizing dentin. J PROSTHET DENT 197&39:173-S. 3. Gwinnett AJ. Smear layer, morphological considerations. Oper Dent 1984;3:3-12. 4. Johnston JF, Phillips RW, Dykema RW. Modern practice in crown and bridge prosthodontics. 1st ed. Philadelphia: WB Saunders Co, 1971. teeth. Part II. Treatment. J PROSTHET 5. Krauser JT. Hypersensitive DENT 1986;56:307-11. 6. Pashley DH, Leibach JG, Homer JA. The effects of burnishing NaF/kaolin/glycerin paste on dentin permeability. J Periodont 1987; 5819-23. 7. Pashley DH, Livingston MJ, Reeder OW, Homer J. Effects of the degree of tubule occlusion on the permeability of human dentine in vitro. Arch Oral Biol 1978;23:1127-33. cav8. Tjan AHL, Grant BE, Nemetz H. The efficacy of resin-compatible ity varnishes in reducing dentin permeability to free monomer. J PROSTHET DENT 1987;57:179-84. 9. Tylman SD. Theory and practice of crown and fixed partial prosthodontics (bridge). 6th ed. St. Louis: The CV Mosby Co, 1970. 10. Warfvinge J, Rose11 B, Hedstrijm KG. Effect of calcium hydroxide treated dentine on pulpal responses. Int Endodont J 1987;20:183-93. 11. Zaimoglu L, Sayan NB. Digin farkli bdlgelerinde dentin kanal sayisinin saptanmasi ye bunun yag ile iliskisinin tesbiti. HU Dis Hek Fak Derg 1985;9:245-60. teeth. Part I. Etiology. J PROSTHET DENT 12. Krauser JT. Hypersensitive 1986;56:153-6. 13. Uygun H. Dentin agiri duyarliligi. Hii Dig Hek Fak Derg 1987;11:136-8. considerations. Oper Dent 14. Pashley DH. Smear layer physiological 1984;(suppl 3):13-29. 15, Grossman L. A systematic method for the treatment of hypersensitive dentin. J Am Dent Assoc 1935;22:592-602. 16. Cotton WR. Smear layer on dentin. Oper Dent 1984;(suppl 3):1-2. 17. Meryon SD, Tobias RS, Jakeman KJ. Smear removal agents: a quantitative study in viva and in vitro. J PROSTHET DENT 1987;57:174-9. 18 Pashley DH, Michelich V, Kehi T. Dentin permeability: effects of smear layer removal. J PROSTHET DENT 1981;46:531-7. 19 Welch FH, Eick JD. A method to reduce or prevent postoperative sensitivity with posterior composite resin restorations. Quintessence Int 1986;17:667-76. 20 Bayirli GS, Sirin $. Restoratif tedavi. Istanbul: Tq M&baa&, 1985. 21. Horn HR. Practical considerations for successful crown and bridge therapy. Philadelphia: WB Saunders Co, 1976. 22. Brannstrom M. Smear layer: pathological and treatment considerations. Oper Dent 1984;(suppl 3):35-42. 23. Hoyt WH, Bibby BF. The use of sodium fluoride for desensitizing dentin [Abstract]. J Dent Res 1943;22:208. 24. Tal M, Oron M, Gedalia I, et al. X-ray difraction and scanning electron microscope investigations of fluoride-treated dentine in man. Arch Oral Biol 1976;21:285-90. 25. Carlo GT, Ciancio SG, Seyrek SK. An evaluation of iontophoretic application of fluoride for tooth desensitization. J Am Dent Assoc 1982; 105452.4. 26. Kofoglu S, Akbay T. Topikal Bi-fluorun k&dentin hassasiye-tindeki etkinliginin scanning elektron mikroskobu ile aragtirilmasi. HU Dig Hek Fak Derg 1988;12:125-8. 27. Ehrlich J, Hochman N, Gedalia I, et al. Residual fluoride concentrations and scanning electron microscopic examination of root surfaces of human teeth after topical application of fluoride in viva. J Dent Res 1975;54:897-900.
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