- Email: [email protected]
Dentin thickness and ultrasonic heating
aluminum oxide coping to provide support for its all-ceramic crowns. A 0.60-mm coping thickness provides adequate strength and veneering porcelain support for most cases. However, some clinical situations dictate that the coping measure only 0.40 mm, although guidelines restrict these to anterior regions through the premolars. The physical properties of aluminum oxide copings measuring less than 0.60 mm are debated, particularly for use in posterior regions. The relative strengths of a 0.40-mm aluminum oxide coping versus a 0.60-mm coping were compared, along with the effect of various luting agents used for cementation.
Table 1.—Effect of Coping Thickness on Load-tofracture (n = 10 Per Group)
Methods.—Testing required 40 prefabricated grade 2 titanium dies that were premilled to the standard dimensions of a mandibular molar. These were scanned into the Procera CAD/CAM system, then 20 aluminum oxide copings measuring 0.60 mm and 20 measuring 0.40 mm were prepared. The Rely/X Luting and Fuji Plus cements were each used to prepare 10 copings of each thickness. The copings were immediately loaded for 10 minutes, then stored for a week at 100% humidity. The samples were placed in a jig for uniform vertical application of force and loaded to fracture.
the mean load-to-fracture values for the two coping designs. The Procera AllCeram crown system was originally claimed to be able to allow the use of any luting agent and maintain sufficient strength to resist fracture. Even at 0.40-mm thickness, the aluminum oxide coping should be strong enough to be used as a substructure for anterior all-ceramic crowns.
Results.—The mean difference between the 0.40- and the 0.60-mm copings cemented with RelyX Luting cement was 433.50 N (Table 1), which was statistically significant. With the Fuji Plus cement, the mean difference was 892.81 N, also statistically significant. The load-to-fracture values for the thicker copings were higher than those for the thinner copings. Higher load-to-fracture values were achieved for all of the copings cemented with Fuji Plus compared to those done with RelyX Luting cement. Discussion.—The 0.60-mm copings had higher mean load-to-fracture values than the 0.40-mm copings. It should be noted that the force needed to fracture even the thinner copings is significantly higher than the force needed to fracture natural tooth enamel. Choice of luting agent affected
Cement
RelyX Luting RelyX Luting Fuji Plus Fuji Plus
Coping Mean load thickness (mm) to fracture (N)
0.40 0.80 0.40 0.60
451.31 884.82 808.73 1,701.53
SD
Mean diff.
P value
93.22 433.50 <.0002 113.92 171.70 892.81 <.0001 314.01
(Courtesy of Miskinis SB, Snyder M, Sierraaita M, et al: Effect of varying coping thickness on early load-to-fracture strength of Procera AllCeram copings cemented with 2 resin-modified glass-ionomer cements. Quintessence Int 39:501-505, 2008.)
Clinical Significance.—A coping 0.60 mm thick is stronger than one 0.40 mm. However, clinical conditions may require reducing coping thickness to less than the recommended 0.60 mm. Demonstrated here, this loss of strength may be partially compensated for by the choice of luting material. Further load-failure studies are needed.
Miskinis SB, Snyder M, Sierraaita M, et al: Effect of varying coping thickness on early load-to-fracture strength of Procera AllCeram copings cemented with 2 resin-modified glass-ionomer cements. Quintessence Int 39:501-505, 2008 Reprints available from M Snyder, 1011 N University Ave, Ann Arbor, MI 48109; fax: 734-647-2110; e-mail: [email protected]
Devices Dentin thickness and ultrasonic heating Background.—Ultrasonic instruments prove quite useful in removing cemented posts during endodontic treatment. Heat is produced with their use through friction, but the absorption of acoustic ultrasonic energy by the post and the use of coolant flow through the handpiece can moderate the increase in temperature. The intracanal temperature can rise rapidly when ultrasonic instruments are used, with the potential to injure adjacent tissues. Dentin thickness
30
Dental Abstracts
may influence the buildup of heat and its transmission to the periodontal attachment tissues. An investigation looked at root surface temperature changes that occur in thinrooted and thick-rooted teeth having ultrasonic instrumentation with and without irrigation. Methods.—The 24 single-canal teeth had crowns removed and length standardized, then were prepared,
obturated, and cemented with prefabricated posts. The teeth were assigned to a group based on whether they had thick or thin roots. Thermocouples were cemented into place on the external proximal root surfaces next to the ends of the posts. The roots were mounted in plastic molds and immersed in a temperature-controlled water bath. Ultrasonic instruments were applied to the posts with and without irrigation. The external root temperatures were measured over a period of 4 minutes. Results.—Dentin thickness differed significantly between the thin- and thick-rooted specimens. The groups did not differ significantly, however, in the temperature increase that occurred with ultrasonic vibration. The thinand thick-rooted groups had mean temperature increases of 4.92 C and 5.25 C, respectively. When irrigation was used, the temperature increase was significantly lower than when no irrigation was present. Dentin thickness was not related to temperature increase but a relationship was noted between the use of irrigation and the temperature increase.
Discussion.—The risk for thermally induced damage to the periodontium is minimized by using irrigation with ultrasonic instrumentation. Temperature increase was not related to the thickness of the dentin.
Clinical Significance.—The temperature increase at the surface of teeth with both thick and thin dentin walls undergoing ultrasonic post removal was within the 10 C safety range when water irrigation was used.
Horan BB, Tordik PA, Imamura G, et al: Effect of dentin thickness on root surface temperature of teeth undergoing ultrasonic removal of posts. J Endod 34:453-455, 2008 Reprints available from GG Goodell, 12214 Hollow Tree Ln, Fairfax, VA 22030; e-mail: [email protected]
Ultrasonic abrasion system Background.—With our improved understanding of the caries process and physiological response of tooth structure plus better adhesive dental materials, dental treatment has been modernized to focus on preservation of tooth structure rather than the removal of carious tissues. Only softened, carious, and irreversibly demineralized tissue needs to be removed, so more conservative measures are possible. Chemical vapor deposition (CVD) has permitted us to create dental diamond tips that can be joined to ultrasonic appliances. The manufacturing process is not the same as for conventional tips, with processing carried out in a reactor that permits the diamonds to adhere to a metal rod securely enough to be able to withstand ultrasound’s vibratory effect. The new tips have a continuous diamond film with no metal binder between crystals. Teeth are therefore not contaminated by metal ions, which are present in the binder matrix of convention tips. CVD tips are highly resistant to cutting and exhibit both efficiency in cutting and longevity. An in vitro comparison was performed, matching cavity preparations in primary and permanent molars performed with high-speed rotary (HR) or ultrasonic abrasion (UA) systems. Methods.—The two systems were compared on the basis of topography and presence of the smear layer. Fourteen molars, divided into seven primary and seven
permanent teeth, underwent preparation using HR or UA systems. Results.—The HR system produced regular layers of enamel and dentin even when there were grooves and microfractures on the enamel surfaces. The UA system produced more irregular surfaces in the enamel and dentin, with a granular and wavy aspect but no enamel microfractures. Both produced an intense smear layer that partially or completely obliterated the dentinal tubules. The amount of smear layer produced was similar whether the teeth were primary or permanent. Discussion.—Tooth type and surface were not the determining factors in differentiating the two systems. The HR and UA systems both permitted dense smear layer formation that completely or at least partially obscured the dentinal tubules. The HR system produced a thicker, more disorganized smear layer than the UA system. The UA system would cause less discomfort for the patient, with limited noise, vibration, sensation of pressure, and heat. Further study should focus on whether the ‘‘soft’’ smear layer UA produces is easier to remove than the thicker layer produced by HR. Also remaining to be studied is whether the inner topography would produce better bonding of restorative materials in teeth, primary or permanent.
Volume 54
Issue 1
2009
31
Table 1.—Effect of Coping Thickness on Load-tofracture (n = 10 Per Group)
Methods.—Testing required 40 prefabricated grade 2 titanium dies that were premilled to the standard dimensions of a mandibular molar. These were scanned into the Procera CAD/CAM system, then 20 aluminum oxide copings measuring 0.60 mm and 20 measuring 0.40 mm were prepared. The Rely/X Luting and Fuji Plus cements were each used to prepare 10 copings of each thickness. The copings were immediately loaded for 10 minutes, then stored for a week at 100% humidity. The samples were placed in a jig for uniform vertical application of force and loaded to fracture.
the mean load-to-fracture values for the two coping designs. The Procera AllCeram crown system was originally claimed to be able to allow the use of any luting agent and maintain sufficient strength to resist fracture. Even at 0.40-mm thickness, the aluminum oxide coping should be strong enough to be used as a substructure for anterior all-ceramic crowns.
Results.—The mean difference between the 0.40- and the 0.60-mm copings cemented with RelyX Luting cement was 433.50 N (Table 1), which was statistically significant. With the Fuji Plus cement, the mean difference was 892.81 N, also statistically significant. The load-to-fracture values for the thicker copings were higher than those for the thinner copings. Higher load-to-fracture values were achieved for all of the copings cemented with Fuji Plus compared to those done with RelyX Luting cement. Discussion.—The 0.60-mm copings had higher mean load-to-fracture values than the 0.40-mm copings. It should be noted that the force needed to fracture even the thinner copings is significantly higher than the force needed to fracture natural tooth enamel. Choice of luting agent affected
Cement
RelyX Luting RelyX Luting Fuji Plus Fuji Plus
Coping Mean load thickness (mm) to fracture (N)
0.40 0.80 0.40 0.60
451.31 884.82 808.73 1,701.53
SD
Mean diff.
P value
93.22 433.50 <.0002 113.92 171.70 892.81 <.0001 314.01
(Courtesy of Miskinis SB, Snyder M, Sierraaita M, et al: Effect of varying coping thickness on early load-to-fracture strength of Procera AllCeram copings cemented with 2 resin-modified glass-ionomer cements. Quintessence Int 39:501-505, 2008.)
Clinical Significance.—A coping 0.60 mm thick is stronger than one 0.40 mm. However, clinical conditions may require reducing coping thickness to less than the recommended 0.60 mm. Demonstrated here, this loss of strength may be partially compensated for by the choice of luting material. Further load-failure studies are needed.
Miskinis SB, Snyder M, Sierraaita M, et al: Effect of varying coping thickness on early load-to-fracture strength of Procera AllCeram copings cemented with 2 resin-modified glass-ionomer cements. Quintessence Int 39:501-505, 2008 Reprints available from M Snyder, 1011 N University Ave, Ann Arbor, MI 48109; fax: 734-647-2110; e-mail: [email protected]
Devices Dentin thickness and ultrasonic heating Background.—Ultrasonic instruments prove quite useful in removing cemented posts during endodontic treatment. Heat is produced with their use through friction, but the absorption of acoustic ultrasonic energy by the post and the use of coolant flow through the handpiece can moderate the increase in temperature. The intracanal temperature can rise rapidly when ultrasonic instruments are used, with the potential to injure adjacent tissues. Dentin thickness
30
Dental Abstracts
may influence the buildup of heat and its transmission to the periodontal attachment tissues. An investigation looked at root surface temperature changes that occur in thinrooted and thick-rooted teeth having ultrasonic instrumentation with and without irrigation. Methods.—The 24 single-canal teeth had crowns removed and length standardized, then were prepared,
obturated, and cemented with prefabricated posts. The teeth were assigned to a group based on whether they had thick or thin roots. Thermocouples were cemented into place on the external proximal root surfaces next to the ends of the posts. The roots were mounted in plastic molds and immersed in a temperature-controlled water bath. Ultrasonic instruments were applied to the posts with and without irrigation. The external root temperatures were measured over a period of 4 minutes. Results.—Dentin thickness differed significantly between the thin- and thick-rooted specimens. The groups did not differ significantly, however, in the temperature increase that occurred with ultrasonic vibration. The thinand thick-rooted groups had mean temperature increases of 4.92 C and 5.25 C, respectively. When irrigation was used, the temperature increase was significantly lower than when no irrigation was present. Dentin thickness was not related to temperature increase but a relationship was noted between the use of irrigation and the temperature increase.
Discussion.—The risk for thermally induced damage to the periodontium is minimized by using irrigation with ultrasonic instrumentation. Temperature increase was not related to the thickness of the dentin.
Clinical Significance.—The temperature increase at the surface of teeth with both thick and thin dentin walls undergoing ultrasonic post removal was within the 10 C safety range when water irrigation was used.
Horan BB, Tordik PA, Imamura G, et al: Effect of dentin thickness on root surface temperature of teeth undergoing ultrasonic removal of posts. J Endod 34:453-455, 2008 Reprints available from GG Goodell, 12214 Hollow Tree Ln, Fairfax, VA 22030; e-mail: [email protected]
Ultrasonic abrasion system Background.—With our improved understanding of the caries process and physiological response of tooth structure plus better adhesive dental materials, dental treatment has been modernized to focus on preservation of tooth structure rather than the removal of carious tissues. Only softened, carious, and irreversibly demineralized tissue needs to be removed, so more conservative measures are possible. Chemical vapor deposition (CVD) has permitted us to create dental diamond tips that can be joined to ultrasonic appliances. The manufacturing process is not the same as for conventional tips, with processing carried out in a reactor that permits the diamonds to adhere to a metal rod securely enough to be able to withstand ultrasound’s vibratory effect. The new tips have a continuous diamond film with no metal binder between crystals. Teeth are therefore not contaminated by metal ions, which are present in the binder matrix of convention tips. CVD tips are highly resistant to cutting and exhibit both efficiency in cutting and longevity. An in vitro comparison was performed, matching cavity preparations in primary and permanent molars performed with high-speed rotary (HR) or ultrasonic abrasion (UA) systems. Methods.—The two systems were compared on the basis of topography and presence of the smear layer. Fourteen molars, divided into seven primary and seven
permanent teeth, underwent preparation using HR or UA systems. Results.—The HR system produced regular layers of enamel and dentin even when there were grooves and microfractures on the enamel surfaces. The UA system produced more irregular surfaces in the enamel and dentin, with a granular and wavy aspect but no enamel microfractures. Both produced an intense smear layer that partially or completely obliterated the dentinal tubules. The amount of smear layer produced was similar whether the teeth were primary or permanent. Discussion.—Tooth type and surface were not the determining factors in differentiating the two systems. The HR and UA systems both permitted dense smear layer formation that completely or at least partially obscured the dentinal tubules. The HR system produced a thicker, more disorganized smear layer than the UA system. The UA system would cause less discomfort for the patient, with limited noise, vibration, sensation of pressure, and heat. Further study should focus on whether the ‘‘soft’’ smear layer UA produces is easier to remove than the thicker layer produced by HR. Also remaining to be studied is whether the inner topography would produce better bonding of restorative materials in teeth, primary or permanent.
Volume 54
Issue 1
2009
31