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Temperature rise in the pulp chamber during fabrication of provisional crowns
SECTIONEDITORS
Temperature provisional
rise in the pulp chamber crowns
Anthony H. L. Tjan, Dr.Dent., M. Franklin Godfrey III***
D.D.S.,* Ben E. Grant, D.M.D.,**
during
fabrication
of
and
Loma Linda University, School of Dentistry, Loma Linda, Calif. This study measured and compared thermal changes in the pulp chamber during the fabrication of provisional crowns by direct method using various brands of autopolymerizing resin systems. The effect of curing the crowns in condensation and addition-reaction silicone putty matrices was also evaluated. The results suggested that the amount of heat transferred in the pulp chamber during the curing of resins may be damaging to the dental pulp and odontoblasts. Curing provisional resin crowns in either condensation or addition silicone putty impressions significantly reduced the temperature rise in the pulp chamber. (J PROSTEET DENT 1989;62:622-6.)
P
ulpal injury during fabrication of provisional crowns may result from heat, desiccation, and/or chemical insult. The exothermic reaction that occurs during setting of autopolymerizing resins can coagulate protoplasm, and chemicals may coagulate or dissolve protoplasm. If a significant amount of heat is transferred to the tooth structure, odontoblastic and pulpal changes may OCCUF.~~ 2 An intrapulpal temperature rise of 5.5“ C (10’ F) in rhesus Macaca monkeys caused 15 % of the pulps to lose vitality.3 Heat dissipation may be enhanced by cooling with a water sprati? 5 or by curing the provisional resin crowns in silicone impressions that have a high heat capacity and sufficient thermal conductivity.4 This investigation measured and compared the thermal changes in the pulp chamber by using different materials during the fabrication of provisional crowns by direct method. The following four autopolymerizing provisional resins were used: methyl me&acrylic (Jet, Lang Dental Mfg. Co., Inc., Chicago, Ill.), ethylmethacrylic (Provisional, CADCO Dental Products, Los Angeles, Calif.), vinyl ethylmethacrylic (Trim, H. J. Bosworth Co., Skokie, Ill.), and Bis-acrylic (Protemp, ESPE-Premier, Norristown, Pa.). The effect of curing the crowns in condensation and addition-reaction silicone putty matrices was also evaluated.
MATERIAL
AND
METHODS
An extracted third mandibular human molar was selected and prepared for a complete crown restoration. The
*Professor and Director of Biomaterials Research, Department of Restorative Dentistry. **Professor, Department of Restorative Dentistry. ***Dental student. 1011/14566
622
root portion was sectioned with a Carborundum disk approximately 4 mm below the cementoenamel junctioq and perpendicular to the long axis of the tooth. An opening was made into the pulp chamber in the root portion so that a needle thermocouple (heat sensor) could be inserted into the pulp chamber. The remnant of pulpal tissues was cleaned from the pulp chamber, which was then slightly enlarged. The root stub was affixed to a Plexiglass (Rohm and Haas Co., Philadelphia, Pa.) base using an autopolymerizing acrylic resin (Trim, H.J. Bosworth Co.). A hole was drilled through the Plexiglass base to provide entrance for a needle thermocouple into the pulp chamber. A silicone heat-transfer compound (Philips E.C.G. Inc., Waltham, Mass.) was injected into the pulp chamber. This compound facilitated the transfer of heat from the walls of the pulp chamber to the thermocouple. A thermocouple probe connected to an electronic digital thermometer and an x-y strip-chart recorder (Sensortek, Saddle Brook, N.J.) was used to measure thermal changes in the pulp chamber during the fabrication of provisional, crowns by direct method (Fig. 1). The y-axis recorded the temperature change and the x-axis recorded the timd elapsed. Four brands of autopolymerizing resins formulated for provisional restorations were evaluated in this study. Table I lists the materials tested, the manufacturer, and the batch numbers. Except for the Protemp paste-to-paste mixture, the resins used were monomer-polymer mixtures.’ For each brand of provisional resin, three experiments were conducted to evaluate the respective effect of each of the three matrix or template materials on thermal changes in the pulp chamber. The measurement was repeated five times for each combination of resin and matrix material. The five readings were averaged to determine the mean’ value of the temperature rise. In the first experiment, a small phenolformaldehyde DECEMBER1969
VOLUME02
NUMBER6
,
TEMPERATURE
RISE
IN PULP
CHAMBER
A
SCHEMATIC DIAGRAM OF THE THERMOMETRIC SET.“P
Fig. 1. A, Schematic diagram of thermometric study. B, Temperature-measuring used.
Table
I.
device
Materials tested
Product
name
Manufacturer
Jet
Resin
Lang Dental Mfg. Co. Inc. Chicago, Ill. CADCO Dental Products Los Angeles, Calif. H.J. Bosworth Co. Skokie, Ill. ESPE-Premier Norristown, Pa.
Provisional Trim Protemp
type
Mixing proportions (gm of powder to liquid)
Mixing time (see)
PMMA
1:0.5
15
PR’MA
1:0.5
15
PR’MA
1:0.5
15
*
20
Bis-GMA composite
Batch
No.
Liq. 070783 Pwd. 070186 Liq. 8556 Pwd. 5028 Liq. 070787-474 Pwd. 070287-73 Cat. 00260019 Base 0078
R’ is an alkyl group larger than methyl. *Proportioning
device
provided
by manufacturer.
resin cylinder was used as the matrix in which the provisional crown was cured. This material has a low heat conductivity (6.00016° C/mm) and thus a high insulating value.‘j This material was expected to produce a maximum heat transfer into the tooth structure. The two other ma-
(Bisico, Batch No. 80087075, Pulp Dent Corp, Brookline, Mass.) and addition-reaction silicone putty (Express, Batch No. 6ED8 for catalyst and No. 6 X 42 for base, 3M Dental Products, St. Paul, Minn.). The powder:liquid ratio of the provisional resins was
trix
materials
standardized
THE
JOURNAL
were condensation-reaction OF PROSTHETIC
DENTISTRY
putty
silicone
by weighing
each
portion
on a precision
scale.
623
TJAN,
MAXIMUM 20 ;
TEMp
AND
GODFREY
RISE IN PULP CHAMBER
MMA m
GRANT,
VMA
Eakelite
Bis-GMA m
Fig. 2. Graph depicts maximum temperature rise in Provisional; VMA, Trim; and BIS-GMA, Protemp.
pulp
Addition
chamber; MMA, Jet; EMA,
Table II. Mean maximum temperature rise (” C) in pulp chamber Matrix Bakelite Product
name
Jet Provisional Trim Protemp
Code
MMA
EMA VMA Bis-GMA
i
19.1 10.8 18.8 10.7
Condedsation
silicone
Addition
silicone
SD
Ti
SD
ii
SD
4.27 1.57 3.49 0.73
11.2 8.2 11.8 5.8
1.87 0.44 2.01 0.24
10.3 7.12 9.1 4.2
0.10
For the monomer-polymer resins, 1 gm of powder and 0.5 gm of liquid were mixed in a disposable paper cup for 15 seconds, loaded into the matrix, and inserted onto the tooth preparation. The paste resin was also weighed for accurate proportion. Before insertion of the resin, the tooth preparation had been preheated in an incubator (VWR, Model 1540, San Francisco, Calif.) set at 37” t- 1” C. However, in this study the baseline temperature of the pulp chamber was raised only to approximately 30’ C despite efforts to duplicate oral temperature. After insertion of the resinfilled matrix, the crown preparation assembly was returned to the incubator and the temperature change in the pulp chamber was recorded. After completion of the experiment, the tooth preparation was sectioned faciolingually and mesiodistally, and the thickness of the dentin wall at various locations was measured with a dial caliper (Kori, Seiki Mfg. Co. Ltd., Japan). The average thickness was approximately 4 mm.
624
material
’
0.63
1.69 0.38
The data were analyzed with two-way analysis of variance (ANOVA). Duncan’s multiple range test was used to compare group means. A statistical software package (SPSS/PC+, SPSS, Inc., Chicago, Ill.) was used for the analyses.
RESULTS Table II presents the mean values of the maximum temperature rise in the pulp chamber for four types of autopolymerizing resins cured in three matrix materials during fabrication of the provisional crowns by direct technique. These mean values of temperature rise are graphed in Fig. 2. With phenolic resin (Bakelite) asa matrix, a temperature increase approaching 20’ C was recorded with Jet (methyl methacrylic resin) and Trim (vinyl ethylmethacrylic resin). Protemp resin, with addition or condensation silicone putty as the matrix, produced the least increase in temper-
DECEMBER
1989
VOLUME
62
NUMBER
6
TEMPERATURE
RISE
IN PULP
CHAMBER
TIME
Methylmethacrylate
(Jet)
TIME -
Vinylethylmethacrylate
0
TIME
(Trim)
Bis.GMA
Gil
Composite
(Protemp)
Fig. 3. Temperature rise versus time of four materials tested. Note initial decrease in temperature caused by contact with cold mixture of resin. A, Jet (methyl methacrylate); B, Provisional (ethylmethacrylate); C, Trim (vinyl ethylmethacrylate); D, Protemp (BIS-GMA-based).
* Table
III. Source
Summary of ANOVA Sum of square*
of variation
Main effects Provisional materials Matrix a-Way interactions Provisional/matrix Explained Residual Total
DF
JOURNAL
OF PROSTEETIC
DENTISTRY
F
Signif.
of F
378.085 149.483 219.646 139.545
5 3 2 6
75.617 49.828 109.823 23.257
3.839 2.530 5.575 1.181
0.004 0.064 0.006 0.327
517.630 1378.843 1896.473
11 70 81
47.057 19.698 23.413
2.389
0.014
ature. However, statistical analyses indicated no significant differences among the four autopolymerizing resins used in this study (Table III). Use of either addition or condensation silicone putty as r a matrix for making provisional restorations significantly reduced the temperature rise in the pulp chamber, compared with use of phenolic resin (p < 0.006). No interaction was found between autopolymerizing resins and matrix materials. In addition, no significant differences were found between values for condensation and addition sili* cone putty. The temperature rise plotted against time is depicted in Fig. 3 for each material tested.
THE
Mean square
A sudden decrease in temperature was measured when the preheated tooth came in contact with the cold, freshly mixed resin. The temperature in the pulp chamber then steadily increased to peak value in 8 to 12 minutes.
DISCUSSION The results of this study suggest the possibility of thermal damage to dental pulp and odontoblasts during the setting of provisional resins. However, caution is advised when interpreting results from an in vitro investigation. In clinical situations, dentin is usually vital and contains protoplasmic extensions of cells. The different properties of 625
TJAN,
the organic structure in the tubules of vital and nonvital teeth and the effect of circulation of dentinal fluids must be considered. The condition and quality of the pulpal vascular structures may determine the degree of damage from thermal trauma.2 In addition, the thickness of the residual dentin with its poor thermal conductivity is a critical factor in reducing thermal transfer to the pulp. The thermal conductivity of dentin is only 0.0015° C/cm.7 Damage to vital cells can occur even though the thermocouple records no significant rise in temperature.8 Biologic reactions cannot be measured with a thermocouple or thermography. The actual damage to the pulp and/or odontoblasts can be assessedaccurately only by a well-designed histologic study. If fabrication of provisional restorations by direct technique is preferred, precautionary measures must be used to minimize temperature increase of the tooth structure from the exothermic reaction of the resins. The temperature rise may be reduced by using air and water coolant or irrigating the restorations with cool water and by using a matrix material that can dissipate the heat rapidly. The results of this study are in agreement with the finding of Grajower et a1.4that silicone putty reduced temperature increase in the pulp chamber. The temporary restoration may be removed, cooled in water, and then reinserted into the tooth preparation several times during polymerization.7 It is not prudent to use a direct technique for making provisional restorations when the remaining dentin is at a minimum or when the tooth has been severely damaged by caries that may have caused some degree of inflammation of the pulp. The same tooth was used throughout this thermometric study to standardize the thickness of the residual dentin and the thermal conductivity because these variables affect the rate of heat flow through the dentin. This relationship may be represented by a modified equation from thermodynamics:g H=
- td D where His the quantity of heat flowing through the dentin per unit time, K is the thermal conductivity of dentin, A is the surface area of the tooth exposed to the resin, D is the thickness of the residual dentin, and ts - ti is the temperature difference. This equation indicates that the flow of heat through the dentin is directly proportional to the thermal conductivity and inversely proportional to the thickness of the residual dentin.
626
KA
02
GRANT,
AND
GODFREY
The amount of heat produced by the exothermic reaction of provisional resins appears to be dependent on the amount of material used. A larger amount of material obviously generates more heat during polymerization and a proportionally higher temperature increase to the tooth.
SUMMARY
AND
CONCLUSIONS
The temperature rise in the pulp chamber during the fabrication of provisional resin crowns by direct method was measured in an in vitro investigation. The results suggested that the amount of heat transferred to the pulp, chamber during the polymerization of the resins may be sufficient to cause thermal damage to the dental pulp and odontoblasts. However, caution should be exercised in predicting clinical consequence from results of an in vitro study without identifying the biologic environment. Curing provisional resin crowns in either addition or, condensation silicone putty impressions significantly reduced the temperature rise in the pulp chamber. Although Protemp resin produced the lowest temperature increase, no statistically significant differences were found among the four brands of provisional resins tested. REFERENCES 1. Langeland K, Langeland LK. Pulp reactions to crown preparation, impression, temporary crown fixation, and permanent cementation. J PR~.WHET DENT 1965;16:129-42. Nyborg H, Briinnstriim J. Pulp reaction to heat. J PROSTHET DENT 1968;19:605-12.
Zach L. Cohen G. Thermogenesis in operative techniques, comparisons of four methods. J PR~~THET DENT 1962;12:977-84. Grajower R, Shaharbani S, Kaufman E. Temperature rise in pulp, chamber during fabrication of temporary self-curing resin .crowns. J PR~WHET DENT 1979;41:535-40. 5. Kaiser DA. Accurate acrylic resin temporary DENT 1978;39:158-61. 6. Morrison RT, Boyd RN. Organic chemistry.
restorations.
J PROSTHET
3rd ed. Boston: Allyn and Bacon Inc, 1976:1027-37. 7. Craig RG. Restorative dental materials. 7th ed. St Louis: CV Mosby Co, 1985:48,506. 8. Seltzer S, Bender IB. The dental pulp. 2nd ed. Philadelphia: JB ’ Lippincott Co, 1975203. 9. Mucci JF, Stearns RL. The fundamentals of physics and chemistry. 1st ed. Columbus: CE Merrill Publishing Co, 1968:3&Y403. Reprint requests to: DR. ANTHONY H. L. TJAN SCHOOL OF DENTISTRY LOMA LINDA UNIVERSITY LOMA LINDA, CA 92350
DECEMBER
1989
VOLUME
62
NUMBER
6
Temperature provisional
rise in the pulp chamber crowns
Anthony H. L. Tjan, Dr.Dent., M. Franklin Godfrey III***
D.D.S.,* Ben E. Grant, D.M.D.,**
during
fabrication
of
and
Loma Linda University, School of Dentistry, Loma Linda, Calif. This study measured and compared thermal changes in the pulp chamber during the fabrication of provisional crowns by direct method using various brands of autopolymerizing resin systems. The effect of curing the crowns in condensation and addition-reaction silicone putty matrices was also evaluated. The results suggested that the amount of heat transferred in the pulp chamber during the curing of resins may be damaging to the dental pulp and odontoblasts. Curing provisional resin crowns in either condensation or addition silicone putty impressions significantly reduced the temperature rise in the pulp chamber. (J PROSTEET DENT 1989;62:622-6.)
P
ulpal injury during fabrication of provisional crowns may result from heat, desiccation, and/or chemical insult. The exothermic reaction that occurs during setting of autopolymerizing resins can coagulate protoplasm, and chemicals may coagulate or dissolve protoplasm. If a significant amount of heat is transferred to the tooth structure, odontoblastic and pulpal changes may OCCUF.~~ 2 An intrapulpal temperature rise of 5.5“ C (10’ F) in rhesus Macaca monkeys caused 15 % of the pulps to lose vitality.3 Heat dissipation may be enhanced by cooling with a water sprati? 5 or by curing the provisional resin crowns in silicone impressions that have a high heat capacity and sufficient thermal conductivity.4 This investigation measured and compared the thermal changes in the pulp chamber by using different materials during the fabrication of provisional crowns by direct method. The following four autopolymerizing provisional resins were used: methyl me&acrylic (Jet, Lang Dental Mfg. Co., Inc., Chicago, Ill.), ethylmethacrylic (Provisional, CADCO Dental Products, Los Angeles, Calif.), vinyl ethylmethacrylic (Trim, H. J. Bosworth Co., Skokie, Ill.), and Bis-acrylic (Protemp, ESPE-Premier, Norristown, Pa.). The effect of curing the crowns in condensation and addition-reaction silicone putty matrices was also evaluated.
MATERIAL
AND
METHODS
An extracted third mandibular human molar was selected and prepared for a complete crown restoration. The
*Professor and Director of Biomaterials Research, Department of Restorative Dentistry. **Professor, Department of Restorative Dentistry. ***Dental student. 1011/14566
622
root portion was sectioned with a Carborundum disk approximately 4 mm below the cementoenamel junctioq and perpendicular to the long axis of the tooth. An opening was made into the pulp chamber in the root portion so that a needle thermocouple (heat sensor) could be inserted into the pulp chamber. The remnant of pulpal tissues was cleaned from the pulp chamber, which was then slightly enlarged. The root stub was affixed to a Plexiglass (Rohm and Haas Co., Philadelphia, Pa.) base using an autopolymerizing acrylic resin (Trim, H.J. Bosworth Co.). A hole was drilled through the Plexiglass base to provide entrance for a needle thermocouple into the pulp chamber. A silicone heat-transfer compound (Philips E.C.G. Inc., Waltham, Mass.) was injected into the pulp chamber. This compound facilitated the transfer of heat from the walls of the pulp chamber to the thermocouple. A thermocouple probe connected to an electronic digital thermometer and an x-y strip-chart recorder (Sensortek, Saddle Brook, N.J.) was used to measure thermal changes in the pulp chamber during the fabrication of provisional, crowns by direct method (Fig. 1). The y-axis recorded the temperature change and the x-axis recorded the timd elapsed. Four brands of autopolymerizing resins formulated for provisional restorations were evaluated in this study. Table I lists the materials tested, the manufacturer, and the batch numbers. Except for the Protemp paste-to-paste mixture, the resins used were monomer-polymer mixtures.’ For each brand of provisional resin, three experiments were conducted to evaluate the respective effect of each of the three matrix or template materials on thermal changes in the pulp chamber. The measurement was repeated five times for each combination of resin and matrix material. The five readings were averaged to determine the mean’ value of the temperature rise. In the first experiment, a small phenolformaldehyde DECEMBER1969
VOLUME02
NUMBER6
,
TEMPERATURE
RISE
IN PULP
CHAMBER
A
SCHEMATIC DIAGRAM OF THE THERMOMETRIC SET.“P
Fig. 1. A, Schematic diagram of thermometric study. B, Temperature-measuring used.
Table
I.
device
Materials tested
Product
name
Manufacturer
Jet
Resin
Lang Dental Mfg. Co. Inc. Chicago, Ill. CADCO Dental Products Los Angeles, Calif. H.J. Bosworth Co. Skokie, Ill. ESPE-Premier Norristown, Pa.
Provisional Trim Protemp
type
Mixing proportions (gm of powder to liquid)
Mixing time (see)
PMMA
1:0.5
15
PR’MA
1:0.5
15
PR’MA
1:0.5
15
*
20
Bis-GMA composite
Batch
No.
Liq. 070783 Pwd. 070186 Liq. 8556 Pwd. 5028 Liq. 070787-474 Pwd. 070287-73 Cat. 00260019 Base 0078
R’ is an alkyl group larger than methyl. *Proportioning
device
provided
by manufacturer.
resin cylinder was used as the matrix in which the provisional crown was cured. This material has a low heat conductivity (6.00016° C/mm) and thus a high insulating value.‘j This material was expected to produce a maximum heat transfer into the tooth structure. The two other ma-
(Bisico, Batch No. 80087075, Pulp Dent Corp, Brookline, Mass.) and addition-reaction silicone putty (Express, Batch No. 6ED8 for catalyst and No. 6 X 42 for base, 3M Dental Products, St. Paul, Minn.). The powder:liquid ratio of the provisional resins was
trix
materials
standardized
THE
JOURNAL
were condensation-reaction OF PROSTHETIC
DENTISTRY
putty
silicone
by weighing
each
portion
on a precision
scale.
623
TJAN,
MAXIMUM 20 ;
TEMp
AND
GODFREY
RISE IN PULP CHAMBER
MMA m
GRANT,
VMA
Eakelite
Bis-GMA m
Fig. 2. Graph depicts maximum temperature rise in Provisional; VMA, Trim; and BIS-GMA, Protemp.
pulp
Addition
chamber; MMA, Jet; EMA,
Table II. Mean maximum temperature rise (” C) in pulp chamber Matrix Bakelite Product
name
Jet Provisional Trim Protemp
Code
MMA
EMA VMA Bis-GMA
i
19.1 10.8 18.8 10.7
Condedsation
silicone
Addition
silicone
SD
Ti
SD
ii
SD
4.27 1.57 3.49 0.73
11.2 8.2 11.8 5.8
1.87 0.44 2.01 0.24
10.3 7.12 9.1 4.2
0.10
For the monomer-polymer resins, 1 gm of powder and 0.5 gm of liquid were mixed in a disposable paper cup for 15 seconds, loaded into the matrix, and inserted onto the tooth preparation. The paste resin was also weighed for accurate proportion. Before insertion of the resin, the tooth preparation had been preheated in an incubator (VWR, Model 1540, San Francisco, Calif.) set at 37” t- 1” C. However, in this study the baseline temperature of the pulp chamber was raised only to approximately 30’ C despite efforts to duplicate oral temperature. After insertion of the resinfilled matrix, the crown preparation assembly was returned to the incubator and the temperature change in the pulp chamber was recorded. After completion of the experiment, the tooth preparation was sectioned faciolingually and mesiodistally, and the thickness of the dentin wall at various locations was measured with a dial caliper (Kori, Seiki Mfg. Co. Ltd., Japan). The average thickness was approximately 4 mm.
624
material
’
0.63
1.69 0.38
The data were analyzed with two-way analysis of variance (ANOVA). Duncan’s multiple range test was used to compare group means. A statistical software package (SPSS/PC+, SPSS, Inc., Chicago, Ill.) was used for the analyses.
RESULTS Table II presents the mean values of the maximum temperature rise in the pulp chamber for four types of autopolymerizing resins cured in three matrix materials during fabrication of the provisional crowns by direct technique. These mean values of temperature rise are graphed in Fig. 2. With phenolic resin (Bakelite) asa matrix, a temperature increase approaching 20’ C was recorded with Jet (methyl methacrylic resin) and Trim (vinyl ethylmethacrylic resin). Protemp resin, with addition or condensation silicone putty as the matrix, produced the least increase in temper-
DECEMBER
1989
VOLUME
62
NUMBER
6
TEMPERATURE
RISE
IN PULP
CHAMBER
TIME
Methylmethacrylate
(Jet)
TIME -
Vinylethylmethacrylate
0
TIME
(Trim)
Bis.GMA
Gil
Composite
(Protemp)
Fig. 3. Temperature rise versus time of four materials tested. Note initial decrease in temperature caused by contact with cold mixture of resin. A, Jet (methyl methacrylate); B, Provisional (ethylmethacrylate); C, Trim (vinyl ethylmethacrylate); D, Protemp (BIS-GMA-based).
* Table
III. Source
Summary of ANOVA Sum of square*
of variation
Main effects Provisional materials Matrix a-Way interactions Provisional/matrix Explained Residual Total
DF
JOURNAL
OF PROSTEETIC
DENTISTRY
F
Signif.
of F
378.085 149.483 219.646 139.545
5 3 2 6
75.617 49.828 109.823 23.257
3.839 2.530 5.575 1.181
0.004 0.064 0.006 0.327
517.630 1378.843 1896.473
11 70 81
47.057 19.698 23.413
2.389
0.014
ature. However, statistical analyses indicated no significant differences among the four autopolymerizing resins used in this study (Table III). Use of either addition or condensation silicone putty as r a matrix for making provisional restorations significantly reduced the temperature rise in the pulp chamber, compared with use of phenolic resin (p < 0.006). No interaction was found between autopolymerizing resins and matrix materials. In addition, no significant differences were found between values for condensation and addition sili* cone putty. The temperature rise plotted against time is depicted in Fig. 3 for each material tested.
THE
Mean square
A sudden decrease in temperature was measured when the preheated tooth came in contact with the cold, freshly mixed resin. The temperature in the pulp chamber then steadily increased to peak value in 8 to 12 minutes.
DISCUSSION The results of this study suggest the possibility of thermal damage to dental pulp and odontoblasts during the setting of provisional resins. However, caution is advised when interpreting results from an in vitro investigation. In clinical situations, dentin is usually vital and contains protoplasmic extensions of cells. The different properties of 625
TJAN,
the organic structure in the tubules of vital and nonvital teeth and the effect of circulation of dentinal fluids must be considered. The condition and quality of the pulpal vascular structures may determine the degree of damage from thermal trauma.2 In addition, the thickness of the residual dentin with its poor thermal conductivity is a critical factor in reducing thermal transfer to the pulp. The thermal conductivity of dentin is only 0.0015° C/cm.7 Damage to vital cells can occur even though the thermocouple records no significant rise in temperature.8 Biologic reactions cannot be measured with a thermocouple or thermography. The actual damage to the pulp and/or odontoblasts can be assessedaccurately only by a well-designed histologic study. If fabrication of provisional restorations by direct technique is preferred, precautionary measures must be used to minimize temperature increase of the tooth structure from the exothermic reaction of the resins. The temperature rise may be reduced by using air and water coolant or irrigating the restorations with cool water and by using a matrix material that can dissipate the heat rapidly. The results of this study are in agreement with the finding of Grajower et a1.4that silicone putty reduced temperature increase in the pulp chamber. The temporary restoration may be removed, cooled in water, and then reinserted into the tooth preparation several times during polymerization.7 It is not prudent to use a direct technique for making provisional restorations when the remaining dentin is at a minimum or when the tooth has been severely damaged by caries that may have caused some degree of inflammation of the pulp. The same tooth was used throughout this thermometric study to standardize the thickness of the residual dentin and the thermal conductivity because these variables affect the rate of heat flow through the dentin. This relationship may be represented by a modified equation from thermodynamics:g H=
- td D where His the quantity of heat flowing through the dentin per unit time, K is the thermal conductivity of dentin, A is the surface area of the tooth exposed to the resin, D is the thickness of the residual dentin, and ts - ti is the temperature difference. This equation indicates that the flow of heat through the dentin is directly proportional to the thermal conductivity and inversely proportional to the thickness of the residual dentin.
626
KA
02
GRANT,
AND
GODFREY
The amount of heat produced by the exothermic reaction of provisional resins appears to be dependent on the amount of material used. A larger amount of material obviously generates more heat during polymerization and a proportionally higher temperature increase to the tooth.
SUMMARY
AND
CONCLUSIONS
The temperature rise in the pulp chamber during the fabrication of provisional resin crowns by direct method was measured in an in vitro investigation. The results suggested that the amount of heat transferred to the pulp, chamber during the polymerization of the resins may be sufficient to cause thermal damage to the dental pulp and odontoblasts. However, caution should be exercised in predicting clinical consequence from results of an in vitro study without identifying the biologic environment. Curing provisional resin crowns in either addition or, condensation silicone putty impressions significantly reduced the temperature rise in the pulp chamber. Although Protemp resin produced the lowest temperature increase, no statistically significant differences were found among the four brands of provisional resins tested. REFERENCES 1. Langeland K, Langeland LK. Pulp reactions to crown preparation, impression, temporary crown fixation, and permanent cementation. J PR~.WHET DENT 1965;16:129-42. Nyborg H, Briinnstriim J. Pulp reaction to heat. J PROSTHET DENT 1968;19:605-12.
Zach L. Cohen G. Thermogenesis in operative techniques, comparisons of four methods. J PR~~THET DENT 1962;12:977-84. Grajower R, Shaharbani S, Kaufman E. Temperature rise in pulp, chamber during fabrication of temporary self-curing resin .crowns. J PR~WHET DENT 1979;41:535-40. 5. Kaiser DA. Accurate acrylic resin temporary DENT 1978;39:158-61. 6. Morrison RT, Boyd RN. Organic chemistry.
restorations.
J PROSTHET
3rd ed. Boston: Allyn and Bacon Inc, 1976:1027-37. 7. Craig RG. Restorative dental materials. 7th ed. St Louis: CV Mosby Co, 1985:48,506. 8. Seltzer S, Bender IB. The dental pulp. 2nd ed. Philadelphia: JB ’ Lippincott Co, 1975203. 9. Mucci JF, Stearns RL. The fundamentals of physics and chemistry. 1st ed. Columbus: CE Merrill Publishing Co, 1968:3&Y403. Reprint requests to: DR. ANTHONY H. L. TJAN SCHOOL OF DENTISTRY LOMA LINDA UNIVERSITY LOMA LINDA, CA 92350
DECEMBER
1989
VOLUME
62
NUMBER
6