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Temperature rise in pulpal chamber during fabrication of provisional resinous crowns
Temperature rise in pulpal chamber during fabrication of provisional resinous crowns Jacopo Castelnuovo, DDSaand Anthony H. L. Tjan, Dr Dent, DDS, PhD, b University of Washington School of Dentistry, Seattle, Wash., University of Rome "Tor Vergata" School of Dentistry, Rome, Italy, and Loma Linda University School of Dentistry, Loma Linda, Calif. S t a t e m e n t o f problem. The heat generated during the exothermic polymerization reaction of autopolymetizing resinous materials and the heat generated by ultraviolet lamps during irradiation of photopolymerizing resinous materials could cause pulpal damage when a direct technique is used to fabricate provisional restorations. This could occur if temperature elevations overcome the physiological heat dissipating mechanisms of the dental-periodontal system. P u r p o s e . This in vitro study compared the rise in temperatures in the pulpal chamber during fabrication of provisional complete veneer crowns by direct method with different autopolymerizing and photopolymerizing resins. The effect of curing resinous crowns in different matrices, such as a polyvinyl siloxane impression and a vacuum-formed polypropylene sheet, was also evaluated. Results. The results demonstrated that the amount of heat generated during resin polymerization and transmitted to the pulpal chamber could be damaging to pulpal tissues including odontoblasts. When curing of provisional resinous crowns was performed in the polyvinyl siloxane impression, significantly lower temperatures were recorded compared with curing in the vacuum-formed polypropylene sheet. Conclusions. To prevent pulpal damage, effective cooling procedures are strongly recommended when directly fabricating resinous provisional crowns. (J Prosthet Dent 1997;78:441-6.)
P r o v i s i o n a l restorations are required before definitive restorations are inserted to protect prepared teeth, prevent t o o t h migration with occlusal changes, reduce dentinal sensitivity, and restore function. ~ Dentinal walls exposed during tooth preparation are considered excellent nonconductors 2 because thicker residual dentin has a greater insulating effect necessary to protect pulpal tissues from thermal injuries. The pulp is a low compliance system, according to
Presented before the International Association of Dental Research, San Francisco, Calif., March 1996. aResident, Graduate Prosthodontics, University of Washington; and Associate, Department of Restorative Dentistry, University of Rome "Tor Vergata." bEmeritus Professor and Consultant in Biomaterials Research;Former Professor and Director of Biomaterials Research, Department of Restorative Dentistry, Lorna Linda University. NOVEMBER 1997
Goodis et al., 3 because "it is encased in hard dentinal walls, it consists o f a large a m o u n t o f connective tissue with a small blood supply, and has no possibility o f developing a collateral circulation." For these reasons, the pulp is vulnerable during and after extensive restorative procedures. Pulpal insults can be caused mainly by heat, desiccation, exposure to chemicals, and bacterial infection. Effects o f different harmful procedures are cumulative .4 When fabricating direct provisional resinous crowns, the heat generated by exothermic polymerization reaction of autopolymerizing resins could injure the pulp, a c c o r d i n g to G r a j o w e r et al. 1 and M o u l d i n g and Teplitsky. 5 Goodis et al? reported that visible light-curing units also had a detrimental effect on pulpal tissues because heat was generated during irradiation and there was temperature rise with increased exposure time to light. H e a t can be transferred to the pulp, which THE JOURNAl. OF PROSTHETIC DENTISTRY
441
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CASTELNUOVO A N D ]'JAN
(HEAT SENSOR) Fig. 2. Digital electronic thermometer used to measure temperature rise in pulpal chamber.
DIGITALELECTRONIC! THERMOMETER Fig. 1. Schematic diagram of temperature measuring apparatus.
causes various histopathologic changes, such as burn reactions at the periphery of the pulp including format.ion of" blisters," e ctopic o dontoblasts and their destruction, 2 protoplasm coagulation, 4 expansion of liquid in the dentinal tubules and pulp with increased outward flow from tubules. This process can affect the pulpal vessels and lead to vascular injuries with tissue necrosis. 6 Temperature rises in the pulpal chamber greater than 5.6 ° C are considered unacceptable because of a potential for loss ofpulpal vitality, 7 and this should be considered when fabricating direct provisional resinous crowns. The purpose of this in vitro investigation was to compare thermal changes in the pulpal chamber created by five materials during fabrication of provisional resinous crowns by direct method. Three autopolymerizing resin systems were used: Jet (Lang Dental Mfg. Co. Inc., Wheeling, Ill.), Protemp Garant (Espe Premier Sales Co., Norristown, Pa.), and Splintline (Lang Dental Mfg. Co. Inc.); and two photopolymerizing resinous systems were used: Unifast LC (GC America Inc., Chicago, Ill.) and Provipont (Ivoclar Williams, Amherst, N.Y.). The effects o f polyvinyl siloxane impressions or vacuum-formed polypropylene sheets as matrices were also evaluated. MATERIAL AND
METHODS
An intact extracted human mandibular third molar was prepared for a metal-ceramic complete crown with a 1.5 mm shoulder. The prepared tooth was 4 mm high from the shoulder finish line to the occlusal surface. The root portion was sectioned with a carborundum disk approximately 2 mm below the cementoenamel junction (CEJ) and perpendicular to the long axis of the tooth. An opening was made into the pulpal chamber 442
from the radicular portion of the tooth so that a thermocouple or heat sensor could be inserted. The pulpal chamber was cleaned of remnant pulpal tissues. The root stub was then secured to a acrylic plastic base with an autopolymerizing resin (Trim, H. J. Bosworth Co., Skokie, Ill.). A hole was drilled through the acrylic plastic base to provide entrance for a needle thermocouple into the pulpal chamber (Fig. 1). A silicone heat-transfer compound (Philips E.C.G. Inc., Waltham, Mass.) was injected in the pulpal chamber. This compound facilitated the transfer of heat from the walls of the pulpal chamber to the therm0couple. A thermocouple probe connected to an electronic digital thermometer (Sensortek, Saddle Brook, N.J.) was used to measure thermal changes in the pulpal chamber during fabrication of direct provisional crowns (Fig. 2). Three autopolymerizing and two photopolymerizing resin systems, marketed for provisional restorations, were evaluated in this study (Table I). Except for Protemp Garant (paste-to-paste mixture) and Provipont (pasteto-liquid mixture), all resins were liquid-powder mixtures. Temperature changes were recorded every minute, for a total of 10 minutes for autopolymerizing resins, and for a total of 2 minutes for photopolymerizing resins (according to the manufacturers), when they reached an elastic state. During the following irradiation phase, temperature changes were recorded every 10 seconds for 80 seconds when testing Unifast LC resin, and every 5 seconds for 30 seconds duration when testing Provipont resin. Two experiments were conducted for each system of provisional resin to evaluate the respective effects of two matrices for thermal changes in the pulpal chamber. Measurements were repeated five times for each combination of resin and matrix material and five readings were averaged to determine the mean value in temperature rise. The two matrix materials were addition reaction silicone putty (Reprosil, Caulk Dentsply, Milford, Del.) carried in a lower right disposable plastic tray (Teledyne VOLUME 78 NUMBER 5
CASTELNUOVO AND TJAN
THE JOURNAL OF PROSTHETIC DENTISTRY
Table I. Materials tested Product name
Provipont
Protemp Garant Unifast LC Splintline Jet
Manufacturer
Resin type
Ivoclar Williams Ivoc[ar North America Inc. Amherst, N.Y. Espe Premier Sales Co. Norristown, Pa. GC America Inc. Chicago, I1. Lang Dental, Mfg. Co. Inc. Wheeling, I[. Lang Dental, Mfg. Co. Inc. Wheeling, II.
Batch number
BIS-GMA/UDMA
6541555
BIS-AcryI-Composite
9421
MMA
040842
EMA
Liquid 1122094 Powder 2475PO2 Liquid 1113094 Powder 055PO1
MMA
Table II. Mean and SD maximum temperature rise (°C) in pulp chamber Matrix material Addition silicone
Product name Provipont (E) Provipont (P) Protemp Garant Unifast LC (E) Unifast LC (P) Splintline Jet
Resin
BIS-GMA/U DMA BIS-GMA/UDMA BIS-AcryI-Composite MMA MMA EMA MMA
X
Polypropylene
SD
-0.06 1.7 4.8 -0.7 12.3 7.9 10.6
0.23 1.01 0.17 0.38 1.48 016 0.59
X
SD I
2.7 I 1.71 9.2 3.2 12.3 I 13.3 I 16.4
0.37 1.01 0.49 0.21 1.48 1.21 4.13
(E) = Elastic phase; (P) = photopolymerization. M e a n s c o n n e c t e d by vertical lines are not significantly different.
Getz, Elk Grove Village, Ill.) and a polypropylene sheet (Ultradent Products, Inc., Salt Lake City, Utah ) approximately 0.5 mm thick. For Protemp Garant resin material, the paste-to-paste ratio was automatically proportioned with a special dispenser included in the system. The paste and the liquid of Provipont resin were dispensed with the manufacturer's predosing syringes. The ratios of the liquid-powder resins were standardized on a precision scale: 1 gm of powder and 0.5 gm o f liquid were mixed in a disposable cup for ] 5 seconds. All materials were loaded in each matrix and inserted on the tooth preparation that was coated with a single, thin, brushed-on layer of petrolatum jelly to facilitate removal of a provisional crown. The tooth was preheated in a water bath (VWR Scientific Inc.) set at 37 ° C before insertion of the resin. The water bath resulted in a baseline temperature in the pulpal chamber of approximately 30 ° C. After insertion o f the resin-filled matrix, the crown-tooth preparation assembly was returned to the water bath and the temperature change in the pulpal chamber was recorded. The irradiation phase of Provipont and Unifast LC resinous materials was performed in an incubator set at 37 ° C once the provisional crowns were removed from the matrices and reseated on the prepared tooth. NOVEMBER 1997
After resinous materials had been tested, the tooth was sectioned mesiodistally and buccolingually. The thickness of residual dentin was recorded at various locations with an electronic dial caliper (Mitntoyo, Japan) and calculated; the average dentinal thickness was approximately 3.5 mm. Because of the inequality of variances for both raw and log-transformed data and an interaction between resin system and matrix material, Kruskal-Wallis oneway analysis of variance (A_NOVA) and Mann-Whitney U tests were selected for each matrix and for the two matrices together with a 0.05 level of significance. RESULTS Table II lists the mean values of maximal temperature elevations in the pulpal chamber for the three systems of a u t o p o l y m e r i z i n g resinous materials and the two photopolymerizing resin materials, during both self-curing and fight-curing phases, namely, all specimens cured in two matrix materials during fabrication of provisional resin crowns by direct method. Results are graphically presented in Figure 3. With a vacuum-formed polypropylene matrix, temperature elevations above 13.0 ° C and nearly 17.0 ° C were recorded for Splintline and Jet resinous materials, 443
THE JOURNAL OF PROSTHETIC DENTISTRY
CASTELNUOVO AND TJAN PROTEMP
(E) = Elastic phase; (P) = Photopolymerization
PROTEMP Polyvlnyl siloxane
V-I Polyvlnyl siloxane ~ Polypropylene
T
E
15
M P
E R
.
I
NO Matrix (Photopolymerization)
I~.
~!
lO_
T
•
5-
u (*c) E
t o
Provipent Provipont Protemp Splintline Unifast L C (E)
(P)
Garant
z
=
•
•
•
r
SPLINTLINE
SPLINTUNE
l=;'~,~'~r bne
Poiyvinyl $iloxane
~
Jet
i
•
t
,o
s
0
io
Unif~tst LC
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~p)
MATERIAL =
1
I
I
,
i
•
,
t
•
m
0
1
=
=
i
s
i
7
Fig. 3. Bar graph indicates means and standard deviations of
temperature rise in pulpal chamber with different matrix materials and during irradiation. Matrix
Mean
temp. 1.5rise 1.25..
(°C)
m Polypropylene m Polyvinyl siloxane
10.75
0.50.25,
/.-
\ , ~ ~,
\/
0- 0.25
I \ N ~ " / \I
a
\1/
"
- 0.5- 0.75
.
-1,Jet
Provlp. (b-')
Provlp. (P)
Protemp Splintllne Garant
Unif. (E)
Unlf. (P)
Material
Fig. 4. Graphic representation of statistical interaction between provisional crown materials and matrix materials.
respectively. These values were not statistically different from each other or from temperature changes recorded during photopolymerization of Unifast LC resin material phase performed without matrix. All other temperature changes recorded were significantly different from each other (p < 0.05) except for Provipont during both autopolymerizing and photopolymerizing phases. Negative temperature values were recorded during the autopolymerizing phase of Unifast LC and Provipont resin materials, both cured in a polyvinyl siloxane matrix (Fig. 3). After completion of polymerization by exposure to visible light, Provipont resin material exhibited substantially less temperature increase, when compared with other materials (p < 0.05). Among the autopolymerizing resins, Protemp Garant resin material used with a polyvinyl siloxane impression matrix recorded the least elevation in temperature. The temperatures recorded with a polyvinyl siloxane matrix were consistently and significantly lower than temperatures recorded with a vacuum-formed polypropylene sheet matrix (p = 0.000). An interaction was discovered between provisional resins and matrix materials (Fig. 4). 444
Fig. 5. Temperature rise versus time of Protemp Garant and
Splintline materials. Mean temperature elevations were plotted against time for each provisional resin, for each matrix material, and for both autopolymerizing and photopolymerizing phases (Figs. 5 through 7). Table III lists the removal and intraoral irradiation times suggested by the manufacturers to evaluate, in combination with Figures 5 through 7, the increase in temperature in the pulpal chamber at the moment of removal of provisional crowns from the prepared tooth and after completed intraoral irradiation. When a polypropylene vacuum-formed matrix was used, Jet resinous material recorded a 7.2 ° C rise after 3 minutes; Protemp Garant resinous material exhibited a 8.9 ° C rise after 2 minutes; whereas, Splintline resin material recorded 10.7 ° C after 3 minutes. When the polyvinyl siloxane impression matrix was used, Splintline resinous material disclosed a 7.8 ° C rise after 3 minutes. Unifast LC resin material displayed a 12.3 ° C elevation in temperature after 80 seconds irradiation without a matrix. DISCUSSION According to this in vitro study, the exothermic reaction during polymerization of almost all provisional resins tested could potentially cause pulpal injury. This is true when provisional resinous restorations remain on the preparations during the entire curing process. Clinically, the temperature rise can be controlled by removing and reseating the interim crown on a prepared tooth (reseating technique) as soon as the provisional crown material has reached an elastic state. Moulding and Loney 8 reported that cooling techniques, such as the use of an air-water spray and the removal of the provisional crown from the prepared tooth on initial polymerization of the resin, were effective in limiting temperature rise in the pulpal chamber. This study indicated that most combinations o f autopolymerizing resin and matrix material reached the peak VOLUME 78 NUMBER 5
CASTELNUOVO AND TJAN
*
i
i
THE JOURNAL OF PROSTHETIC DENTISTRY
JET
JET
UNIFAST LC (E)
I~lypro(~rwne
Po]yvln~silo~
pohmmpy~ee
i
4
s
i
r
,
0
I,
,
I
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?
,
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I
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UNIFAST LC (E) PoJyvinytsuoxane
~
o
I
2
i
PROVIPONT (E)
PROVIPONT (E)
PROVIPONT (P)
UNIFAST LC (P)
polypro~lene
Poh/vinyl stloxane
No Matrix
NOMmtrll
T~,p
T~
(el
(¢1
f 0
i
1
3
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2
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0
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IG
IS
~
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Fig. 6. Temperature rise versus time of Jet and Provipont during elastic phase (E) (materials).
Fig. 7. Temperature rise versus time of Unifast LC material during elastic phase (E) and of Provipont and Unifast LC materials during irradiation (P).
temperature before or at removal time suggested by manufacturers for a specific provisional crown resin. Therefore, for those combinations, the reseating technique would be ineffective for controlling temperature changes if the manufacturers' recommended times are followed. Different results may have been recorded with the use of air and water coolants during the setting process. Clinically, these procedures are effective in preventing pulpal insult from excessive heat. 9,1°However, in clinical conditions, the elevations in temperature are also reduced by presence of the periodontal ligament 6,n and other organic structures, such as protoplasmic extensions of cells in dentinal tubules. ~° Pulpal and osseous circulation are also effective in heat dissipation. 6,n Therefore caution is advised when interpreting data from an in vitro study. Because of its insulating effect residual dentinal thickness is a critical factor in the protection of pulpal tissues from thermal injuries. This comparative study was performed with the same specimen to standardize dentinal thickness that can be highly variable for different teeth before and after tooth preparation has been completed. Clinically, the amount of heat transferred to the pulp cannot be predicted, so it is important to perform routinely effective cooling procedures during polymerization of resinous materials, regardless of the thickness of residual dentin. There is always the possibility of exothermic reaction with resinous materials. This generated heat can cause pulpal injury with a direct method for fabrication of interim resinous restorations. Zach and Cohen 7 reported i5% of irreversible pulpal damage in monkeys for temperature elevations of 5.6 ° C, 60% for temperature elevations of 11° C, and 100% for temperature elevations of i6.6 ° C. Even though their experimental setting was different from this in vitro study and pulpal reactions were analyzed in monkeys, their results can be suggested as a baseline for potential histopathologic changes in pulpal tissues when the temperature
Table III. Provisional crown removal time and intraoral irradiation time suggested by manufacturers
NOVEMBER
1997
Material
Crown removal time
Irradiation time
(min.)
(sec.)
Jet
3
P r o v i p o n t (E)
2
--
P r o v i p o n t (P)
--
30
--
Protemp Garant
2
--
Splintline
3
--
Unifast LC (E)
2
Unifast LC (P)
-
-80
(E) = Elastic phase; (P) : photopolymerization.
rise exceeds 5.6 ° C. Excessive heat is detrimental to pulpal tissues. To avoid pulpal damage, indirect techniques have been recommended for fabrication of provisional crowns.4 In this study, when Provipont and Unifast LC resinous materials were used with a polyvinyl siloxane matrix, the temperature elevation was exclusively the result of the visible light-curing units. This was because the heat generated during the autopolymerizing phase of these materials was totally absorbed by the matrix as demonstrated by the negative temperatures recorded. When those same materials were used with a vacuum-formed polypropylene matrix, a slight temperature increase was recorded during autopolymerizing, but remained below the "critical" value of 5.6 ° C. Therefore, when visible light is applied with a curing unit to complete polymerization of the resin, the heat generated would not result in a cumulative, harmful effect on the pulp. To quantify the temperature elevation for these dual-curing resins, it may be considered only the heat generated during the photopolymerizing phase, because it is only after photoactivation that the resinous provisional crown is completed. 445
THE JOURNAL OF PROSTHETIC DENTISTRY
Visible light-curing units can cause pulpal damage with temperature elevation in the pulpal chamber during irradiation. The pulpal deterioration is directly proportional to exposure time to the light and inversely proportional to residual dentinal thickness? When temperature elevations are expected to be similar to those recorded in this study when ultraviolet (UV) lamps are used, the concomitant use of an air spray is recommended. The consistently lower temperature elevations and the negative temperature values recorded when the addition silicone impression was used as a matrix are in agreement with previous findings 1° and confirm the heatadsorbing properties of this material. Additional testing is suggested to evaluate temperature elevations when an acrylic resin shell is relined by direct method. This study simulated the clinical situation of restoring a single tooth. The amount of heat generated during polymerization of resinous materials is proportional to the volume of material used; therefore higher temperatures should be expected when restoring multiple units and replacing missing teeth with provisional fixed partial dentures, Protemp Garant resinous material exhibited acceptable thermal behavior, was easy to manipulate, and cost-effective. Nevertheless, Provipont resinous material was more technique-sensitive and some of the resinous crowns were remade because of tearing during removal from matrices before irradiation. CONCLUSIONS
CASTELNUOVO AND TJAN
Provipont resinous material resulted in the least temperature rise followed by Protemp Garant resinous material with a polyvinyl siloxane matrix, whereas Jet, Splinfline, and Unifast LC resinous materials used with the polypropylene matrix created the highest temperatures. In clinical settings, cooling procedures that use air/water sprays are essential to prevent pulpal damage. REFERENCES 1. Grajower R, Shaharbani S, Kaufman E. Temperature rise in pulp chamber during fabrication of temporary self-curing resin crowns. J Prosthet Dent 1979;41:535-40. 2. Robinson HB, Lefkowitz W. Operative dentistry and the pulp. j Prosthet Dent 1962;12:985-1001. 3. Goodis HE, White JM, Andrews J, Watanabe LG. Measurement of temperature generated by visible light-cure lamps in an in-vitro model. Dent Mat 1989;5:230-4. 4. Langeland K, Langeland LK. Pulp reactions to crown preparation, impression, temporary crown fixation and permanent cementation. J Prosthet Dent 1965;15:129-43. 5. Moulding MB, Teplitsky PE. Intrapulpa[ temperature during direct fabrication of provisional restorations. Int J Prosthodont 1990;3:299-304. 6. Nyborg H, Br~innstr6m M. Pulp reaction to heat. J Prosthet Dent 1968;19:605-12. 7. Zach L, Cohen C. Pulp response to externally applied heat. Oral Surg Oral Med Oral Pathol 1965;19:515-30. 8. MouldingMB, Loney RW. The effect ofcooling techniques on intrapulpal temperature during direct fabrication of provisional restorations. Int J Prosthodont 1991 ;4:332-6. 9. Zach L, Cohen C. Thermogenesis in operative techniques: comparison of four methods. J Prosthet Dent 1962;12:977-84. 10. Tjan AHL, Grant B, Godfrey M Ill. Temperature rise in the pulp chamber during fabrication of provisional crowns. J Prosthet Dent 1989;62:622-6. 11. White M, Fagan M, Goodis HE. Intrapulpal temperatures during pu}sed Nd:yag laser treatment of dentin in vitro. J Periodonto[ 1994;65:255-9. Reprint requests
Temperature elevations in the pulpal chambers during fabrication of provisional resinous crowns by the direct method were recorded in vitro. Curing provisional resinous crowns with the use o f a polyvinyl siloxane impression as a matrix significantly reduced temperature increases in the pulpal chamber compared with a vacuum-formed polypropylene matrix.
to:
DR. JACOPOCASTELNUOVO VIA ARCHIMED~
No. 185 00197 ROME ITALY
Copyright © 1997 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/97/$5.00 + O. 10/1/82835
Bound volumes available to subscribers Bound volumes of The Journal of Prosthetic Dentistry are available to subscribers (only) for the 1997 issues from the publisher at a cost of $76.00 ($89.00 international) for Vol. 77 (January-June) and Vol. 78 (July-December). Shipping charges are included. Each bound volume contains a subject and author index, and all advertising is removed. Copies are shipped within 30 days after publication of the last issue in the volume. The binding is durable buckram with the journal name, volume number, and year stamped in gold on the spine. Volumes 75 and 76 are also available. Payment must accompany all orders. Contact Mosby-Year Book, Inc., Subscription Services, 11830 Westline Industrial Drive, St. Louis, MO 63146-3318, USA; phone (800)453-4351, or (314)453-4351. Subscriptions m u s t be in force to qualify. Bound volumes are n o t available in place of a regular Journal subscription.
446
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P r o v i s i o n a l restorations are required before definitive restorations are inserted to protect prepared teeth, prevent t o o t h migration with occlusal changes, reduce dentinal sensitivity, and restore function. ~ Dentinal walls exposed during tooth preparation are considered excellent nonconductors 2 because thicker residual dentin has a greater insulating effect necessary to protect pulpal tissues from thermal injuries. The pulp is a low compliance system, according to
Presented before the International Association of Dental Research, San Francisco, Calif., March 1996. aResident, Graduate Prosthodontics, University of Washington; and Associate, Department of Restorative Dentistry, University of Rome "Tor Vergata." bEmeritus Professor and Consultant in Biomaterials Research;Former Professor and Director of Biomaterials Research, Department of Restorative Dentistry, Lorna Linda University. NOVEMBER 1997
Goodis et al., 3 because "it is encased in hard dentinal walls, it consists o f a large a m o u n t o f connective tissue with a small blood supply, and has no possibility o f developing a collateral circulation." For these reasons, the pulp is vulnerable during and after extensive restorative procedures. Pulpal insults can be caused mainly by heat, desiccation, exposure to chemicals, and bacterial infection. Effects o f different harmful procedures are cumulative .4 When fabricating direct provisional resinous crowns, the heat generated by exothermic polymerization reaction of autopolymerizing resins could injure the pulp, a c c o r d i n g to G r a j o w e r et al. 1 and M o u l d i n g and Teplitsky. 5 Goodis et al? reported that visible light-curing units also had a detrimental effect on pulpal tissues because heat was generated during irradiation and there was temperature rise with increased exposure time to light. H e a t can be transferred to the pulp, which THE JOURNAl. OF PROSTHETIC DENTISTRY
441
THE JOURNAL OF PROSTHETIC DENTISTRY
CASTELNUOVO A N D ]'JAN
(HEAT SENSOR) Fig. 2. Digital electronic thermometer used to measure temperature rise in pulpal chamber.
DIGITALELECTRONIC! THERMOMETER Fig. 1. Schematic diagram of temperature measuring apparatus.
causes various histopathologic changes, such as burn reactions at the periphery of the pulp including format.ion of" blisters," e ctopic o dontoblasts and their destruction, 2 protoplasm coagulation, 4 expansion of liquid in the dentinal tubules and pulp with increased outward flow from tubules. This process can affect the pulpal vessels and lead to vascular injuries with tissue necrosis. 6 Temperature rises in the pulpal chamber greater than 5.6 ° C are considered unacceptable because of a potential for loss ofpulpal vitality, 7 and this should be considered when fabricating direct provisional resinous crowns. The purpose of this in vitro investigation was to compare thermal changes in the pulpal chamber created by five materials during fabrication of provisional resinous crowns by direct method. Three autopolymerizing resin systems were used: Jet (Lang Dental Mfg. Co. Inc., Wheeling, Ill.), Protemp Garant (Espe Premier Sales Co., Norristown, Pa.), and Splintline (Lang Dental Mfg. Co. Inc.); and two photopolymerizing resinous systems were used: Unifast LC (GC America Inc., Chicago, Ill.) and Provipont (Ivoclar Williams, Amherst, N.Y.). The effects o f polyvinyl siloxane impressions or vacuum-formed polypropylene sheets as matrices were also evaluated. MATERIAL AND
METHODS
An intact extracted human mandibular third molar was prepared for a metal-ceramic complete crown with a 1.5 mm shoulder. The prepared tooth was 4 mm high from the shoulder finish line to the occlusal surface. The root portion was sectioned with a carborundum disk approximately 2 mm below the cementoenamel junction (CEJ) and perpendicular to the long axis of the tooth. An opening was made into the pulpal chamber 442
from the radicular portion of the tooth so that a thermocouple or heat sensor could be inserted. The pulpal chamber was cleaned of remnant pulpal tissues. The root stub was then secured to a acrylic plastic base with an autopolymerizing resin (Trim, H. J. Bosworth Co., Skokie, Ill.). A hole was drilled through the acrylic plastic base to provide entrance for a needle thermocouple into the pulpal chamber (Fig. 1). A silicone heat-transfer compound (Philips E.C.G. Inc., Waltham, Mass.) was injected in the pulpal chamber. This compound facilitated the transfer of heat from the walls of the pulpal chamber to the therm0couple. A thermocouple probe connected to an electronic digital thermometer (Sensortek, Saddle Brook, N.J.) was used to measure thermal changes in the pulpal chamber during fabrication of direct provisional crowns (Fig. 2). Three autopolymerizing and two photopolymerizing resin systems, marketed for provisional restorations, were evaluated in this study (Table I). Except for Protemp Garant (paste-to-paste mixture) and Provipont (pasteto-liquid mixture), all resins were liquid-powder mixtures. Temperature changes were recorded every minute, for a total of 10 minutes for autopolymerizing resins, and for a total of 2 minutes for photopolymerizing resins (according to the manufacturers), when they reached an elastic state. During the following irradiation phase, temperature changes were recorded every 10 seconds for 80 seconds when testing Unifast LC resin, and every 5 seconds for 30 seconds duration when testing Provipont resin. Two experiments were conducted for each system of provisional resin to evaluate the respective effects of two matrices for thermal changes in the pulpal chamber. Measurements were repeated five times for each combination of resin and matrix material and five readings were averaged to determine the mean value in temperature rise. The two matrix materials were addition reaction silicone putty (Reprosil, Caulk Dentsply, Milford, Del.) carried in a lower right disposable plastic tray (Teledyne VOLUME 78 NUMBER 5
CASTELNUOVO AND TJAN
THE JOURNAL OF PROSTHETIC DENTISTRY
Table I. Materials tested Product name
Provipont
Protemp Garant Unifast LC Splintline Jet
Manufacturer
Resin type
Ivoclar Williams Ivoc[ar North America Inc. Amherst, N.Y. Espe Premier Sales Co. Norristown, Pa. GC America Inc. Chicago, I1. Lang Dental, Mfg. Co. Inc. Wheeling, I[. Lang Dental, Mfg. Co. Inc. Wheeling, II.
Batch number
BIS-GMA/UDMA
6541555
BIS-AcryI-Composite
9421
MMA
040842
EMA
Liquid 1122094 Powder 2475PO2 Liquid 1113094 Powder 055PO1
MMA
Table II. Mean and SD maximum temperature rise (°C) in pulp chamber Matrix material Addition silicone
Product name Provipont (E) Provipont (P) Protemp Garant Unifast LC (E) Unifast LC (P) Splintline Jet
Resin
BIS-GMA/U DMA BIS-GMA/UDMA BIS-AcryI-Composite MMA MMA EMA MMA
X
Polypropylene
SD
-0.06 1.7 4.8 -0.7 12.3 7.9 10.6
0.23 1.01 0.17 0.38 1.48 016 0.59
X
SD I
2.7 I 1.71 9.2 3.2 12.3 I 13.3 I 16.4
0.37 1.01 0.49 0.21 1.48 1.21 4.13
(E) = Elastic phase; (P) = photopolymerization. M e a n s c o n n e c t e d by vertical lines are not significantly different.
Getz, Elk Grove Village, Ill.) and a polypropylene sheet (Ultradent Products, Inc., Salt Lake City, Utah ) approximately 0.5 mm thick. For Protemp Garant resin material, the paste-to-paste ratio was automatically proportioned with a special dispenser included in the system. The paste and the liquid of Provipont resin were dispensed with the manufacturer's predosing syringes. The ratios of the liquid-powder resins were standardized on a precision scale: 1 gm of powder and 0.5 gm o f liquid were mixed in a disposable cup for ] 5 seconds. All materials were loaded in each matrix and inserted on the tooth preparation that was coated with a single, thin, brushed-on layer of petrolatum jelly to facilitate removal of a provisional crown. The tooth was preheated in a water bath (VWR Scientific Inc.) set at 37 ° C before insertion of the resin. The water bath resulted in a baseline temperature in the pulpal chamber of approximately 30 ° C. After insertion o f the resin-filled matrix, the crown-tooth preparation assembly was returned to the water bath and the temperature change in the pulpal chamber was recorded. The irradiation phase of Provipont and Unifast LC resinous materials was performed in an incubator set at 37 ° C once the provisional crowns were removed from the matrices and reseated on the prepared tooth. NOVEMBER 1997
After resinous materials had been tested, the tooth was sectioned mesiodistally and buccolingually. The thickness of residual dentin was recorded at various locations with an electronic dial caliper (Mitntoyo, Japan) and calculated; the average dentinal thickness was approximately 3.5 mm. Because of the inequality of variances for both raw and log-transformed data and an interaction between resin system and matrix material, Kruskal-Wallis oneway analysis of variance (A_NOVA) and Mann-Whitney U tests were selected for each matrix and for the two matrices together with a 0.05 level of significance. RESULTS Table II lists the mean values of maximal temperature elevations in the pulpal chamber for the three systems of a u t o p o l y m e r i z i n g resinous materials and the two photopolymerizing resin materials, during both self-curing and fight-curing phases, namely, all specimens cured in two matrix materials during fabrication of provisional resin crowns by direct method. Results are graphically presented in Figure 3. With a vacuum-formed polypropylene matrix, temperature elevations above 13.0 ° C and nearly 17.0 ° C were recorded for Splintline and Jet resinous materials, 443
THE JOURNAL OF PROSTHETIC DENTISTRY
CASTELNUOVO AND TJAN PROTEMP
(E) = Elastic phase; (P) = Photopolymerization
PROTEMP Polyvlnyl siloxane
V-I Polyvlnyl siloxane ~ Polypropylene
T
E
15
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.
I
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I~.
~!
lO_
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,
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=
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temperature rise in pulpal chamber with different matrix materials and during irradiation. Matrix
Mean
temp. 1.5rise 1.25..
(°C)
m Polypropylene m Polyvinyl siloxane
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.
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Provlp. (P)
Protemp Splintllne Garant
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Material
Fig. 4. Graphic representation of statistical interaction between provisional crown materials and matrix materials.
respectively. These values were not statistically different from each other or from temperature changes recorded during photopolymerization of Unifast LC resin material phase performed without matrix. All other temperature changes recorded were significantly different from each other (p < 0.05) except for Provipont during both autopolymerizing and photopolymerizing phases. Negative temperature values were recorded during the autopolymerizing phase of Unifast LC and Provipont resin materials, both cured in a polyvinyl siloxane matrix (Fig. 3). After completion of polymerization by exposure to visible light, Provipont resin material exhibited substantially less temperature increase, when compared with other materials (p < 0.05). Among the autopolymerizing resins, Protemp Garant resin material used with a polyvinyl siloxane impression matrix recorded the least elevation in temperature. The temperatures recorded with a polyvinyl siloxane matrix were consistently and significantly lower than temperatures recorded with a vacuum-formed polypropylene sheet matrix (p = 0.000). An interaction was discovered between provisional resins and matrix materials (Fig. 4). 444
Fig. 5. Temperature rise versus time of Protemp Garant and
Splintline materials. Mean temperature elevations were plotted against time for each provisional resin, for each matrix material, and for both autopolymerizing and photopolymerizing phases (Figs. 5 through 7). Table III lists the removal and intraoral irradiation times suggested by the manufacturers to evaluate, in combination with Figures 5 through 7, the increase in temperature in the pulpal chamber at the moment of removal of provisional crowns from the prepared tooth and after completed intraoral irradiation. When a polypropylene vacuum-formed matrix was used, Jet resinous material recorded a 7.2 ° C rise after 3 minutes; Protemp Garant resinous material exhibited a 8.9 ° C rise after 2 minutes; whereas, Splintline resin material recorded 10.7 ° C after 3 minutes. When the polyvinyl siloxane impression matrix was used, Splintline resinous material disclosed a 7.8 ° C rise after 3 minutes. Unifast LC resin material displayed a 12.3 ° C elevation in temperature after 80 seconds irradiation without a matrix. DISCUSSION According to this in vitro study, the exothermic reaction during polymerization of almost all provisional resins tested could potentially cause pulpal injury. This is true when provisional resinous restorations remain on the preparations during the entire curing process. Clinically, the temperature rise can be controlled by removing and reseating the interim crown on a prepared tooth (reseating technique) as soon as the provisional crown material has reached an elastic state. Moulding and Loney 8 reported that cooling techniques, such as the use of an air-water spray and the removal of the provisional crown from the prepared tooth on initial polymerization of the resin, were effective in limiting temperature rise in the pulpal chamber. This study indicated that most combinations o f autopolymerizing resin and matrix material reached the peak VOLUME 78 NUMBER 5
CASTELNUOVO AND TJAN
*
i
i
THE JOURNAL OF PROSTHETIC DENTISTRY
JET
JET
UNIFAST LC (E)
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Fig. 6. Temperature rise versus time of Jet and Provipont during elastic phase (E) (materials).
Fig. 7. Temperature rise versus time of Unifast LC material during elastic phase (E) and of Provipont and Unifast LC materials during irradiation (P).
temperature before or at removal time suggested by manufacturers for a specific provisional crown resin. Therefore, for those combinations, the reseating technique would be ineffective for controlling temperature changes if the manufacturers' recommended times are followed. Different results may have been recorded with the use of air and water coolants during the setting process. Clinically, these procedures are effective in preventing pulpal insult from excessive heat. 9,1°However, in clinical conditions, the elevations in temperature are also reduced by presence of the periodontal ligament 6,n and other organic structures, such as protoplasmic extensions of cells in dentinal tubules. ~° Pulpal and osseous circulation are also effective in heat dissipation. 6,n Therefore caution is advised when interpreting data from an in vitro study. Because of its insulating effect residual dentinal thickness is a critical factor in the protection of pulpal tissues from thermal injuries. This comparative study was performed with the same specimen to standardize dentinal thickness that can be highly variable for different teeth before and after tooth preparation has been completed. Clinically, the amount of heat transferred to the pulp cannot be predicted, so it is important to perform routinely effective cooling procedures during polymerization of resinous materials, regardless of the thickness of residual dentin. There is always the possibility of exothermic reaction with resinous materials. This generated heat can cause pulpal injury with a direct method for fabrication of interim resinous restorations. Zach and Cohen 7 reported i5% of irreversible pulpal damage in monkeys for temperature elevations of 5.6 ° C, 60% for temperature elevations of 11° C, and 100% for temperature elevations of i6.6 ° C. Even though their experimental setting was different from this in vitro study and pulpal reactions were analyzed in monkeys, their results can be suggested as a baseline for potential histopathologic changes in pulpal tissues when the temperature
Table III. Provisional crown removal time and intraoral irradiation time suggested by manufacturers
NOVEMBER
1997
Material
Crown removal time
Irradiation time
(min.)
(sec.)
Jet
3
P r o v i p o n t (E)
2
--
P r o v i p o n t (P)
--
30
--
Protemp Garant
2
--
Splintline
3
--
Unifast LC (E)
2
Unifast LC (P)
-
-80
(E) = Elastic phase; (P) : photopolymerization.
rise exceeds 5.6 ° C. Excessive heat is detrimental to pulpal tissues. To avoid pulpal damage, indirect techniques have been recommended for fabrication of provisional crowns.4 In this study, when Provipont and Unifast LC resinous materials were used with a polyvinyl siloxane matrix, the temperature elevation was exclusively the result of the visible light-curing units. This was because the heat generated during the autopolymerizing phase of these materials was totally absorbed by the matrix as demonstrated by the negative temperatures recorded. When those same materials were used with a vacuum-formed polypropylene matrix, a slight temperature increase was recorded during autopolymerizing, but remained below the "critical" value of 5.6 ° C. Therefore, when visible light is applied with a curing unit to complete polymerization of the resin, the heat generated would not result in a cumulative, harmful effect on the pulp. To quantify the temperature elevation for these dual-curing resins, it may be considered only the heat generated during the photopolymerizing phase, because it is only after photoactivation that the resinous provisional crown is completed. 445
THE JOURNAL OF PROSTHETIC DENTISTRY
Visible light-curing units can cause pulpal damage with temperature elevation in the pulpal chamber during irradiation. The pulpal deterioration is directly proportional to exposure time to the light and inversely proportional to residual dentinal thickness? When temperature elevations are expected to be similar to those recorded in this study when ultraviolet (UV) lamps are used, the concomitant use of an air spray is recommended. The consistently lower temperature elevations and the negative temperature values recorded when the addition silicone impression was used as a matrix are in agreement with previous findings 1° and confirm the heatadsorbing properties of this material. Additional testing is suggested to evaluate temperature elevations when an acrylic resin shell is relined by direct method. This study simulated the clinical situation of restoring a single tooth. The amount of heat generated during polymerization of resinous materials is proportional to the volume of material used; therefore higher temperatures should be expected when restoring multiple units and replacing missing teeth with provisional fixed partial dentures, Protemp Garant resinous material exhibited acceptable thermal behavior, was easy to manipulate, and cost-effective. Nevertheless, Provipont resinous material was more technique-sensitive and some of the resinous crowns were remade because of tearing during removal from matrices before irradiation. CONCLUSIONS
CASTELNUOVO AND TJAN
Provipont resinous material resulted in the least temperature rise followed by Protemp Garant resinous material with a polyvinyl siloxane matrix, whereas Jet, Splinfline, and Unifast LC resinous materials used with the polypropylene matrix created the highest temperatures. In clinical settings, cooling procedures that use air/water sprays are essential to prevent pulpal damage. REFERENCES 1. Grajower R, Shaharbani S, Kaufman E. Temperature rise in pulp chamber during fabrication of temporary self-curing resin crowns. J Prosthet Dent 1979;41:535-40. 2. Robinson HB, Lefkowitz W. Operative dentistry and the pulp. j Prosthet Dent 1962;12:985-1001. 3. Goodis HE, White JM, Andrews J, Watanabe LG. Measurement of temperature generated by visible light-cure lamps in an in-vitro model. Dent Mat 1989;5:230-4. 4. Langeland K, Langeland LK. Pulp reactions to crown preparation, impression, temporary crown fixation and permanent cementation. J Prosthet Dent 1965;15:129-43. 5. Moulding MB, Teplitsky PE. Intrapulpa[ temperature during direct fabrication of provisional restorations. Int J Prosthodont 1990;3:299-304. 6. Nyborg H, Br~innstr6m M. Pulp reaction to heat. J Prosthet Dent 1968;19:605-12. 7. Zach L, Cohen C. Pulp response to externally applied heat. Oral Surg Oral Med Oral Pathol 1965;19:515-30. 8. MouldingMB, Loney RW. The effect ofcooling techniques on intrapulpal temperature during direct fabrication of provisional restorations. Int J Prosthodont 1991 ;4:332-6. 9. Zach L, Cohen C. Thermogenesis in operative techniques: comparison of four methods. J Prosthet Dent 1962;12:977-84. 10. Tjan AHL, Grant B, Godfrey M Ill. Temperature rise in the pulp chamber during fabrication of provisional crowns. J Prosthet Dent 1989;62:622-6. 11. White M, Fagan M, Goodis HE. Intrapulpal temperatures during pu}sed Nd:yag laser treatment of dentin in vitro. J Periodonto[ 1994;65:255-9. Reprint requests
Temperature elevations in the pulpal chambers during fabrication of provisional resinous crowns by the direct method were recorded in vitro. Curing provisional resinous crowns with the use o f a polyvinyl siloxane impression as a matrix significantly reduced temperature increases in the pulpal chamber compared with a vacuum-formed polypropylene matrix.
to:
DR. JACOPOCASTELNUOVO VIA ARCHIMED~
No. 185 00197 ROME ITALY
Copyright © 1997 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/97/$5.00 + O. 10/1/82835
Bound volumes available to subscribers Bound volumes of The Journal of Prosthetic Dentistry are available to subscribers (only) for the 1997 issues from the publisher at a cost of $76.00 ($89.00 international) for Vol. 77 (January-June) and Vol. 78 (July-December). Shipping charges are included. Each bound volume contains a subject and author index, and all advertising is removed. Copies are shipped within 30 days after publication of the last issue in the volume. The binding is durable buckram with the journal name, volume number, and year stamped in gold on the spine. Volumes 75 and 76 are also available. Payment must accompany all orders. Contact Mosby-Year Book, Inc., Subscription Services, 11830 Westline Industrial Drive, St. Louis, MO 63146-3318, USA; phone (800)453-4351, or (314)453-4351. Subscriptions m u s t be in force to qualify. Bound volumes are n o t available in place of a regular Journal subscription.
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