- Email: [email protected]
Influence of laboratory variables on the resin bond strength of an etched chrome-cobalt alloy
JOINT
TENSILE
STRENGTH
mum of 42% fresh alloy and the rest once-melted alloy. Each pair of half-dumbbells was assembled and either presoldered or postsoldered using a vacuum-oven and a torch-soldering technique. There was no significant difference in the ultimate tensile strength values between the presoldered and postsoldered joints within the same technique group, but the torch-soldered joints for the same solder were significantly stronger (p <.Ol). It was believed that slow heating and cooling has deleterious effects on the ultimate tensile strength joints (UTS) possibly because of the microstructural changes and the highly oxidizable content of the postsolder used. Another 15 samples cast using once, twice, and three-times remelted parent alloy were presoldered and postsoldered with the torch only. In each of these groups, specimens joined by presolder showed significantly higher strength than those joined by postsolder (ia <.02). Remelting the parent alloy affected the strength differences between the presoldered and postsoldered joints. It was assumed that on remelting, the nature of the parent alloy is changed because some original elements are volatilized and newly formed oxides dissolved into it. Because it contains copper, the postsolder is more affected by this contamination than presolder. The UTS of the parent alloy, as well as that of the presolder and postsolder, were also determined. As expected, the parent alloy possessedthe highest strength and the postsolder, the lowest.
CONCLUSIONS 1. Differences between UTS values of presoldered and postsoldered joints found in one alloy cannot be
generalized and applied to alloys even of the same family of alloys. 2. There were no significant differences in the UTS values of presoldered and postsoldered joints obtained with the use of the same technique. 3. Torch soldering yielded significantly stronger joints than the vacuum-oven soldering technique used. 4. Remelting the parent alloy without adding fresh metal to the melt increased the strength of presoldered joints, while it weakened the postsoldered joints. REFERENCES I.
Mumford G: The porcelain fused to metal restoration. Dent Clin North Am, March 1965, p 241. 2. Mumford G, Ridge A: Dental porcelain. Dent Clin North Am 15:33, 1977. 3. Rasmussen EJ, Goodkind RJ, Gerberich WW: An investigation of tensile strength of dental solder joints. %TPR~STHET DENT 41:418, 1979. 4. Squire BE: The Relative Strength of High and Low Fusing Solder. Thesis, Indiana University, 1971. 5. Stade EH, Reisbick MH, Preston JD: Preceramic and postceramic solder joints. J PROSTHETDENT 34~527, 1975. 6. StafTanou RS, Radke RA, Jendresen MD: Strength properties of soldered joints from various ceramic metal combinations. J PROSTHETDENT 43:31, 1980. 7. Ady B: Effect of solidification time on the microstructure and physical properties of dental gold casting alloys. J Dent Res 45:921, 1966. Re$~rtn~ reyues~ lo:
DR. J. J. Luc MONDAY UNIVERSITYOF MONTREAL FACULTY OF DENTISTRY MONTREAL, QUE. H3C 357 CANADA
Influence of laboratory variables on the resin bond strength of an etched chrome-cobalt alloy Scott C. Dilorenzo,
D.D.S.,* E. Steven Duke, D.D.S., M.&D.,**
and Barry K. Norling,
Ph.D.***
Wilford Hall Medical Center, Lackland AFB, Tex., and University of Texas Health Science Center, Dental School, San Antonio, Tex.
F
ramework design and fabrication of resin-bonded retainers have been modified and improved since the introduction of the concept by Rochette’ in 1973. Improvements in base metal alloys, moderate prepara*Senior resident. **Chief, Restorative Dentistry. ***Chairman. Division of Biomaterials. THE JOURNAL
OF PROSTHETIC
DENTISTRY
tion of tooth surfaces to be covered by retainers, design and surface coverage, and preparation of metal surfaces to accept the bonding resin have significantly improved the viability and acceptance of this treatment modality. Electrolytic etching of metal to receive the bonding resin has significantly increased the bond strength between metal and resin.’ Many variables in the etching process can influence the result. Among these are type of 27
DILORENZO,
Fig.
Table I. Alloys
1. Shear bond loading
tested, manufacturers, ~.-
and etching
Novarex Rexillium III
Generic Gold Co. Wallingford, Conn. Generic Gold Co. Wallingford, Conn. -_-
Table II. Shear bond strength Condition
1 as cast; no agitation 2 as cast; agitation 3 fired; no agitation 4 fired; agitation 111 1 as cast; no agitation 2 as cast; agitation 3 fired; no agitation 4 fired; agitation
NORLING
to surface of alloy.
conditions Time
IN HNOA:MeOH (6:4)
200 mA/cm*
7 min
10% H,SO,
300 m.4 /cm2
3 min
- --..
results. Mean Strength (MPa)
parallel
AND
Current density
SD
15.1 15.4 16.4 13.6
4.8 2.8 4.8 3.8
20.7 20.3 20.2 22.2
4.2 7.0 5.6 7.4
alloys used, etching electrolyte, current density during etching, agitation of electrolyte during etching, repeated firing of the metal during porcelain buildup, and surfaces to be etched. All can have an effect on the resin-metal bond strength.3-’ The greatest success with etching base metal alloys has been with those that contain nickel-chrome-beryllium.6 Prompted by the potential health hazards of nickeland beryllium-containing alloys,’ a number of chromecobalt base metal alloys have been introduced for fabricating resin-bonded retainers. Although a study by Thompson et al” suggested proper etching conditions for a new chrome-cobalt alloy, minimal research has been reported on the ability to bond resin to these alloys or on 28
resin material
Electrolyte
Manufacturer
Alloy
Novarex Group Group Group Group Rexillium Group Group Group Group
of composite
DUKE,
~--
--
---_- -... ._ .____
the possible influence of various laboratory variables. Therefore, the purposes of this investigation were to further examine the resin bond strength of a chromecobalt alloy and to determine if electrolyte agitation or porcelain firing influences this bond strength. MATERIAL
AND METHODS
The alloys used in this study, their manufacturers, electrolyte, current density, and etch time are listed in Table I. The electrolytes and current densities are those recommended by the manufacturer. Rexillium III was used as the control alloy because of its extensive use for retainers and the amount of research with this alloy in terms of developing adequate resin bond strength. A recently introduced chrome-cobalt alloy (Novarex), which is recommended for use with resin-bonded retainers, eliminates both nickel and beryllium and was studied as an alternate. Forty tabs of each of the two alloys were cast 10 mm square by 0.5 mm thick using techniques recommended by the manufacturers. This resulted in 10 specimens per test group to examine the two variables, acid agitation, and porcelain firing. The four test groups for each alloy were group No. 1, as cast with no acid agitation; group No. 2, as cast with acid agitation; group No. 3, porcelain fired, no acid agitation; and group No. 4, porcelain fired with acid agitation. Group Nos. 3 and 4 of Novarex and Rexillium III IANUARY
19%
VOLUME
55
NUMBER
1
BOND
STRENGTH
OF ETCHED
CR-CO
ALLOY
defined in terms of what is necessary to achieve clinical success. Recommendations have been that the metalresin strength should be two times as great as the enamel-resin bond strength made arbitrarily.6 This is based on the so-called weak link concept that the enamel-resin interface will fail first. Based on reported shear bond strengths of approximately 10 mPa for composite resin to ename1,6r9both alloys tested in this study appear to be adequate in terms of bond strength. Although resin-metal bond strength is important, the development of proper preparation form in terms of proximal wrapping and resistance form is important if acceptable clinical results are to be achieved. The importance of electrolyte agitation during the electrolytic procedure and the influence of porcelain firing on metal-resin bond strength was not found to be a factor as previously reported.4,5 When Novarex specimens were subjected to the firing cycles, an excessive oxide film that was never totally removed by cleaning with hydrochloric acid developed after etching. The recommendation has been made that treatment with a 5% ammonium hydroxide solution before etching will overcome this phenomenon with a similar chrome-cobalt alloy.6 Inhibition of the oxide film may improve the bond strengths with Novarex alloy and should be investigated further.
were treated to four firing cycles in an Ultramat (Unitek Corp., Monrovia, Calif.) furnace at 920” C to simulate the application of porcelain. Electrolytic etching of the specimens was carried out using Ultra-Etch (Tri-Dynamics Corp., New Brunswick, N. J.) electroetching equipment. The 80 specimens were attached to stainless steel electrodes. The backs and sides of the tabs were covered with wax leaving l2 cm of the as-cast and porcelain-fired metals exposed for etching. The specimens were air abraded with 50 pm aluminum oxide, washed with distilled water, and dried. The specimens were etched at the specified current densities and times, Group Nos. 1 and 2 received no agitation during etching. After etching, all specimens were cleaned in 18% hydrochloric acid for 10 minutes in an ultrasonic bath and rinsed in distilled water. A stereomicroscope was used to view the specimens at x50 magnification to ensure etching had occurred. Composite resin was applied to the metal specimens to test bond strengths in the following manner. Teflon (Du Pont Co., Wilmington, Del.) tubes, 6 mm wide by 10 mm high, were positioned in the center of each tab. An unfilled resin bonding agent (3M Dental Products, St. Paul, Minn.) was placed into the tubes followed by the injection of a composite resin (Silar, 3M Dental Products). When the composite resin was completely set, the Teflon tubes were removed, and the specimens were stored in distilled water at 37” C. Shear bond strength of the composite resin was tested at 7 days using an Instron universal testing machine (Instron Corp., Canton, Mass.) with a strain rate of 0.5 mm/min. The metal tabs were placed in a fixture that directed load force on the composite resin cylinders parallel to the metal surface (Fig. 1). The force required to dislodge the composite resin from the metal tab was recorded as the shear bond strength.
1. The mean shear bond strength of a composite resin to Rexillium III was found to be greater than that of Novarex. 2. The variable of porcelain firing was not found to influence the composite resin shear bond strength of either Rexillium III or Novarex. 3. Agitation of the electrolyte during etching did not influence composite resin shear bond strengths for either alloy.
RESULTS
REFERENCES
The results of the shear bond testing for the eight groups of specimens is shown in Table II. The greatest bond strengths were found with the four groups using the Rexillium III alloy. A three-way analysis of variance of the results determined that only the variable of type of alloy significantly (It < .OOl) influenced bond strength. Agitation of electrolyte solutions and firing of the alloy did not influence the resulting bond strength of either alloy. A post hoc Bonferroni t-test was performed on the individual groups of specimens and demonstrated no significant (p < .OS) difference among group Nos. 1 to 4 for either Novarex or Rexillium III.
DISCUSSION The minimum bond strength between the composite resin and an etched-metal retainer has never been THE JOURNAL
OF PROSTHETIC
DENTISTRY
CONCLUSIONS
Rochette AL: Attachment of a splint to enamel of lower anterior teeth. J PROSTHET DENT 30:418, 1973. 2. McLaughlin G: Composite bonding of etched metal anterior splints. Compendium Continuing Educ Dent 2~279, 1981. 3. Del Castillo E, Thompson VP: Electrolytically etched nonprecious alloys: Resin bond and laboratory variables. J Dent Res Gl(Special issue):186, 1982 (Abstr No. 64). 4. Thompson VP: Electrolytic etching modes of various nonprecious alloys for resin bonding. J Dent Res Gl(Special issue):186, 1982 (Abstr No. 65). 5. Al-Shamary A, Meiers J, Mayclin T, Jensen M: Bond strengths of etched metal-to-enamel: Effects of different etching times. J Dent Res 62(Special issue):221, 1983 (Abstr No. 465). 6. Simonsen R, Thompson VP, Barrack G: Etched Cast Restorations: Clinical and Laboratory Techniques. Chicago, 1983, Quintessence Publishing Co, Inc. 7 Council on Dental Materials, Instruments, and Equipment: Biological effects of nickel-containing dental alloys. J Am Dent Assoc 104~501, 1982. 1.
29
DILORENZO,
8.
9.
AND
NORLING
Thompson VP, Grolman K, Liao R: Electrolytic etching 01 Co-G alloys for resin bonded restoration. .J Dent Res 63(Special issue):320, 1984 (Abstr No. 1346). Livaditis CJ, Thompson VP: Etched castings: An improved retentive mechanism for resin-bonded retainers. J PROYTHET DWI 47:52, 1982.
Porcelain glazing
surface texture after reduction
Maya Zalkind, D.M.D.,* Suzi Lauer,** and Noah Stem, D.M.D., Hebrew University-Hadassah School of Dental Medicine, Jerusalem, Israel
all the available restorative materials, the gingiva responds best to restorations made of porcelain. This is explained by the ability of porcelain to attain a smooth, polished surface.’ Restorations with a smooth surface, such as those of porcelain, greatly impede the accumulation of plaque and thus reduce the incidence of gingival infiammation.2*3 Another advantage of porcelain restorations is their esthetic appearance. This is attributable to the surface texture of the restoration, which is characterized by reflection and absorption of light rays. Such a desirable effect is achieved only if the surface of the restoration is optimally smooth.’ Adjustment of porcelain restorations in the mouth may be required for correction of occlusion or contour. This procedure is done at chairside with different abrasive instruments. After reduction, there is again a need to create a smooth surface and thus restore this advantage of porcelain. To obtain a smooth surface on the finished restoration, both dentist and technician should choose the most desirable instrument for final adjustment of the porcelain. The aim of this investigation was to examine the degrees of roughness of porcelain after subjecting it to abrasive techniques and to natural (self) glazing. The use of an aluminum oxide sandblast after reduction produced the most desirable natural glaze. MATERIAL
AND
and natural
M&D.***
Fig. 1. Porcelain sample in porcelain mold. Table I. Grinding instruments and surface roughness after reduction and after natural
glaze
Surface roughness After reduction with grinding instruments
Instrument New diamond stone Used diamond stone Carbide stone Dura white Shofu stone Sandpaper disk Control sample Aluminum oxide powder following reduction with a new diamond stone
After natural daze
+t+++t +++++ ++++
+++++ ++++ ttt
++t i-i ++t+
-t t i + --
METHODS
Following the manufacturer’s instructions, 35 samples of porcelain (Vita Zahnfabrick, Bad Sackingen, W. *Lecturer, Departmen of Oral Rehabilitation. ‘*Certified Dental Technician, Department of Oral Rehabilitation. “‘Associate Professor and Director, Fixed Prosthodontirs
30
DUKE,
Germany) were prepared in a porcelain mold (J. F. Jelenko Co., New Rochelle, N. Y.) (Fig. 1). The final glaze of the porcelain was obtained by natural glaze (self-glaze). The natural glaze is produced by the final firing in air. This procedure is considered superior to the overglaze method.‘.’ JANUARY
1986
VOLUME
55
NUMBER
1
TENSILE
STRENGTH
mum of 42% fresh alloy and the rest once-melted alloy. Each pair of half-dumbbells was assembled and either presoldered or postsoldered using a vacuum-oven and a torch-soldering technique. There was no significant difference in the ultimate tensile strength values between the presoldered and postsoldered joints within the same technique group, but the torch-soldered joints for the same solder were significantly stronger (p <.Ol). It was believed that slow heating and cooling has deleterious effects on the ultimate tensile strength joints (UTS) possibly because of the microstructural changes and the highly oxidizable content of the postsolder used. Another 15 samples cast using once, twice, and three-times remelted parent alloy were presoldered and postsoldered with the torch only. In each of these groups, specimens joined by presolder showed significantly higher strength than those joined by postsolder (ia <.02). Remelting the parent alloy affected the strength differences between the presoldered and postsoldered joints. It was assumed that on remelting, the nature of the parent alloy is changed because some original elements are volatilized and newly formed oxides dissolved into it. Because it contains copper, the postsolder is more affected by this contamination than presolder. The UTS of the parent alloy, as well as that of the presolder and postsolder, were also determined. As expected, the parent alloy possessedthe highest strength and the postsolder, the lowest.
CONCLUSIONS 1. Differences between UTS values of presoldered and postsoldered joints found in one alloy cannot be
generalized and applied to alloys even of the same family of alloys. 2. There were no significant differences in the UTS values of presoldered and postsoldered joints obtained with the use of the same technique. 3. Torch soldering yielded significantly stronger joints than the vacuum-oven soldering technique used. 4. Remelting the parent alloy without adding fresh metal to the melt increased the strength of presoldered joints, while it weakened the postsoldered joints. REFERENCES I.
Mumford G: The porcelain fused to metal restoration. Dent Clin North Am, March 1965, p 241. 2. Mumford G, Ridge A: Dental porcelain. Dent Clin North Am 15:33, 1977. 3. Rasmussen EJ, Goodkind RJ, Gerberich WW: An investigation of tensile strength of dental solder joints. %TPR~STHET DENT 41:418, 1979. 4. Squire BE: The Relative Strength of High and Low Fusing Solder. Thesis, Indiana University, 1971. 5. Stade EH, Reisbick MH, Preston JD: Preceramic and postceramic solder joints. J PROSTHETDENT 34~527, 1975. 6. StafTanou RS, Radke RA, Jendresen MD: Strength properties of soldered joints from various ceramic metal combinations. J PROSTHETDENT 43:31, 1980. 7. Ady B: Effect of solidification time on the microstructure and physical properties of dental gold casting alloys. J Dent Res 45:921, 1966. Re$~rtn~ reyues~ lo:
DR. J. J. Luc MONDAY UNIVERSITYOF MONTREAL FACULTY OF DENTISTRY MONTREAL, QUE. H3C 357 CANADA
Influence of laboratory variables on the resin bond strength of an etched chrome-cobalt alloy Scott C. Dilorenzo,
D.D.S.,* E. Steven Duke, D.D.S., M.&D.,**
and Barry K. Norling,
Ph.D.***
Wilford Hall Medical Center, Lackland AFB, Tex., and University of Texas Health Science Center, Dental School, San Antonio, Tex.
F
ramework design and fabrication of resin-bonded retainers have been modified and improved since the introduction of the concept by Rochette’ in 1973. Improvements in base metal alloys, moderate prepara*Senior resident. **Chief, Restorative Dentistry. ***Chairman. Division of Biomaterials. THE JOURNAL
OF PROSTHETIC
DENTISTRY
tion of tooth surfaces to be covered by retainers, design and surface coverage, and preparation of metal surfaces to accept the bonding resin have significantly improved the viability and acceptance of this treatment modality. Electrolytic etching of metal to receive the bonding resin has significantly increased the bond strength between metal and resin.’ Many variables in the etching process can influence the result. Among these are type of 27
DILORENZO,
Fig.
Table I. Alloys
1. Shear bond loading
tested, manufacturers, ~.-
and etching
Novarex Rexillium III
Generic Gold Co. Wallingford, Conn. Generic Gold Co. Wallingford, Conn. -_-
Table II. Shear bond strength Condition
1 as cast; no agitation 2 as cast; agitation 3 fired; no agitation 4 fired; agitation 111 1 as cast; no agitation 2 as cast; agitation 3 fired; no agitation 4 fired; agitation
NORLING
to surface of alloy.
conditions Time
IN HNOA:MeOH (6:4)
200 mA/cm*
7 min
10% H,SO,
300 m.4 /cm2
3 min
- --..
results. Mean Strength (MPa)
parallel
AND
Current density
SD
15.1 15.4 16.4 13.6
4.8 2.8 4.8 3.8
20.7 20.3 20.2 22.2
4.2 7.0 5.6 7.4
alloys used, etching electrolyte, current density during etching, agitation of electrolyte during etching, repeated firing of the metal during porcelain buildup, and surfaces to be etched. All can have an effect on the resin-metal bond strength.3-’ The greatest success with etching base metal alloys has been with those that contain nickel-chrome-beryllium.6 Prompted by the potential health hazards of nickeland beryllium-containing alloys,’ a number of chromecobalt base metal alloys have been introduced for fabricating resin-bonded retainers. Although a study by Thompson et al” suggested proper etching conditions for a new chrome-cobalt alloy, minimal research has been reported on the ability to bond resin to these alloys or on 28
resin material
Electrolyte
Manufacturer
Alloy
Novarex Group Group Group Group Rexillium Group Group Group Group
of composite
DUKE,
~--
--
---_- -... ._ .____
the possible influence of various laboratory variables. Therefore, the purposes of this investigation were to further examine the resin bond strength of a chromecobalt alloy and to determine if electrolyte agitation or porcelain firing influences this bond strength. MATERIAL
AND METHODS
The alloys used in this study, their manufacturers, electrolyte, current density, and etch time are listed in Table I. The electrolytes and current densities are those recommended by the manufacturer. Rexillium III was used as the control alloy because of its extensive use for retainers and the amount of research with this alloy in terms of developing adequate resin bond strength. A recently introduced chrome-cobalt alloy (Novarex), which is recommended for use with resin-bonded retainers, eliminates both nickel and beryllium and was studied as an alternate. Forty tabs of each of the two alloys were cast 10 mm square by 0.5 mm thick using techniques recommended by the manufacturers. This resulted in 10 specimens per test group to examine the two variables, acid agitation, and porcelain firing. The four test groups for each alloy were group No. 1, as cast with no acid agitation; group No. 2, as cast with acid agitation; group No. 3, porcelain fired, no acid agitation; and group No. 4, porcelain fired with acid agitation. Group Nos. 3 and 4 of Novarex and Rexillium III IANUARY
19%
VOLUME
55
NUMBER
1
BOND
STRENGTH
OF ETCHED
CR-CO
ALLOY
defined in terms of what is necessary to achieve clinical success. Recommendations have been that the metalresin strength should be two times as great as the enamel-resin bond strength made arbitrarily.6 This is based on the so-called weak link concept that the enamel-resin interface will fail first. Based on reported shear bond strengths of approximately 10 mPa for composite resin to ename1,6r9both alloys tested in this study appear to be adequate in terms of bond strength. Although resin-metal bond strength is important, the development of proper preparation form in terms of proximal wrapping and resistance form is important if acceptable clinical results are to be achieved. The importance of electrolyte agitation during the electrolytic procedure and the influence of porcelain firing on metal-resin bond strength was not found to be a factor as previously reported.4,5 When Novarex specimens were subjected to the firing cycles, an excessive oxide film that was never totally removed by cleaning with hydrochloric acid developed after etching. The recommendation has been made that treatment with a 5% ammonium hydroxide solution before etching will overcome this phenomenon with a similar chrome-cobalt alloy.6 Inhibition of the oxide film may improve the bond strengths with Novarex alloy and should be investigated further.
were treated to four firing cycles in an Ultramat (Unitek Corp., Monrovia, Calif.) furnace at 920” C to simulate the application of porcelain. Electrolytic etching of the specimens was carried out using Ultra-Etch (Tri-Dynamics Corp., New Brunswick, N. J.) electroetching equipment. The 80 specimens were attached to stainless steel electrodes. The backs and sides of the tabs were covered with wax leaving l2 cm of the as-cast and porcelain-fired metals exposed for etching. The specimens were air abraded with 50 pm aluminum oxide, washed with distilled water, and dried. The specimens were etched at the specified current densities and times, Group Nos. 1 and 2 received no agitation during etching. After etching, all specimens were cleaned in 18% hydrochloric acid for 10 minutes in an ultrasonic bath and rinsed in distilled water. A stereomicroscope was used to view the specimens at x50 magnification to ensure etching had occurred. Composite resin was applied to the metal specimens to test bond strengths in the following manner. Teflon (Du Pont Co., Wilmington, Del.) tubes, 6 mm wide by 10 mm high, were positioned in the center of each tab. An unfilled resin bonding agent (3M Dental Products, St. Paul, Minn.) was placed into the tubes followed by the injection of a composite resin (Silar, 3M Dental Products). When the composite resin was completely set, the Teflon tubes were removed, and the specimens were stored in distilled water at 37” C. Shear bond strength of the composite resin was tested at 7 days using an Instron universal testing machine (Instron Corp., Canton, Mass.) with a strain rate of 0.5 mm/min. The metal tabs were placed in a fixture that directed load force on the composite resin cylinders parallel to the metal surface (Fig. 1). The force required to dislodge the composite resin from the metal tab was recorded as the shear bond strength.
1. The mean shear bond strength of a composite resin to Rexillium III was found to be greater than that of Novarex. 2. The variable of porcelain firing was not found to influence the composite resin shear bond strength of either Rexillium III or Novarex. 3. Agitation of the electrolyte during etching did not influence composite resin shear bond strengths for either alloy.
RESULTS
REFERENCES
The results of the shear bond testing for the eight groups of specimens is shown in Table II. The greatest bond strengths were found with the four groups using the Rexillium III alloy. A three-way analysis of variance of the results determined that only the variable of type of alloy significantly (It < .OOl) influenced bond strength. Agitation of electrolyte solutions and firing of the alloy did not influence the resulting bond strength of either alloy. A post hoc Bonferroni t-test was performed on the individual groups of specimens and demonstrated no significant (p < .OS) difference among group Nos. 1 to 4 for either Novarex or Rexillium III.
DISCUSSION The minimum bond strength between the composite resin and an etched-metal retainer has never been THE JOURNAL
OF PROSTHETIC
DENTISTRY
CONCLUSIONS
Rochette AL: Attachment of a splint to enamel of lower anterior teeth. J PROSTHET DENT 30:418, 1973. 2. McLaughlin G: Composite bonding of etched metal anterior splints. Compendium Continuing Educ Dent 2~279, 1981. 3. Del Castillo E, Thompson VP: Electrolytically etched nonprecious alloys: Resin bond and laboratory variables. J Dent Res Gl(Special issue):186, 1982 (Abstr No. 64). 4. Thompson VP: Electrolytic etching modes of various nonprecious alloys for resin bonding. J Dent Res Gl(Special issue):186, 1982 (Abstr No. 65). 5. Al-Shamary A, Meiers J, Mayclin T, Jensen M: Bond strengths of etched metal-to-enamel: Effects of different etching times. J Dent Res 62(Special issue):221, 1983 (Abstr No. 465). 6. Simonsen R, Thompson VP, Barrack G: Etched Cast Restorations: Clinical and Laboratory Techniques. Chicago, 1983, Quintessence Publishing Co, Inc. 7 Council on Dental Materials, Instruments, and Equipment: Biological effects of nickel-containing dental alloys. J Am Dent Assoc 104~501, 1982. 1.
29
DILORENZO,
8.
9.
AND
NORLING
Thompson VP, Grolman K, Liao R: Electrolytic etching 01 Co-G alloys for resin bonded restoration. .J Dent Res 63(Special issue):320, 1984 (Abstr No. 1346). Livaditis CJ, Thompson VP: Etched castings: An improved retentive mechanism for resin-bonded retainers. J PROYTHET DWI 47:52, 1982.
Porcelain glazing
surface texture after reduction
Maya Zalkind, D.M.D.,* Suzi Lauer,** and Noah Stem, D.M.D., Hebrew University-Hadassah School of Dental Medicine, Jerusalem, Israel
all the available restorative materials, the gingiva responds best to restorations made of porcelain. This is explained by the ability of porcelain to attain a smooth, polished surface.’ Restorations with a smooth surface, such as those of porcelain, greatly impede the accumulation of plaque and thus reduce the incidence of gingival infiammation.2*3 Another advantage of porcelain restorations is their esthetic appearance. This is attributable to the surface texture of the restoration, which is characterized by reflection and absorption of light rays. Such a desirable effect is achieved only if the surface of the restoration is optimally smooth.’ Adjustment of porcelain restorations in the mouth may be required for correction of occlusion or contour. This procedure is done at chairside with different abrasive instruments. After reduction, there is again a need to create a smooth surface and thus restore this advantage of porcelain. To obtain a smooth surface on the finished restoration, both dentist and technician should choose the most desirable instrument for final adjustment of the porcelain. The aim of this investigation was to examine the degrees of roughness of porcelain after subjecting it to abrasive techniques and to natural (self) glazing. The use of an aluminum oxide sandblast after reduction produced the most desirable natural glaze. MATERIAL
AND
and natural
M&D.***
Fig. 1. Porcelain sample in porcelain mold. Table I. Grinding instruments and surface roughness after reduction and after natural
glaze
Surface roughness After reduction with grinding instruments
Instrument New diamond stone Used diamond stone Carbide stone Dura white Shofu stone Sandpaper disk Control sample Aluminum oxide powder following reduction with a new diamond stone
After natural daze
+t+++t +++++ ++++
+++++ ++++ ttt
++t i-i ++t+
-t t i + --
METHODS
Following the manufacturer’s instructions, 35 samples of porcelain (Vita Zahnfabrick, Bad Sackingen, W. *Lecturer, Departmen of Oral Rehabilitation. ‘*Certified Dental Technician, Department of Oral Rehabilitation. “‘Associate Professor and Director, Fixed Prosthodontirs
30
DUKE,
Germany) were prepared in a porcelain mold (J. F. Jelenko Co., New Rochelle, N. Y.) (Fig. 1). The final glaze of the porcelain was obtained by natural glaze (self-glaze). The natural glaze is produced by the final firing in air. This procedure is considered superior to the overglaze method.‘.’ JANUARY
1986
VOLUME
55
NUMBER
1