To THE EDITOR: In regard to the article “Comparison of weight reduction in different designsof solid and hollow obturator prostheses,” by Drs. Wu and Schaaf (J PROSTHET DENT 1989;62:214-7),useful general guidelinesare provided for estimating a reduction of weight, dependent on defect size and classof maxillectomy defect, when a hollow-bulb obturator is usedinstead of a solid obturator. The maxillofacial prosthodontist interested in (1) a more definitive comparison of weight reduction afforded by a given technique of bulb construction, or (2) determination of a specific reduction in weight of a completed clinical prosthesisincorporating a hollow bulb (in comparisonwith a like restoration of solid design), can do so readily using the following procedure. 1. Drill an opening 2 to 3 mm in diameter through the highest point of the hollow bulb. 2. Usinga pipette or calibrated syringe, fill the bulb with distilled water, being careful to avoid entrapment of air bubbles. Record in cubic centimeters the volume of water required to fill the bulb. 3. Multiply the recorded volume of water (in cubic centimeters) by 1.17, the accepted average density of polymethyl methacrylate denture resin.l The resulting figure representsan accurate estimateof the weight in gramsthat would have been added if the restoration had been constructed as a solid prosthesis. If polyvinyl acrylic resin is usedfor the prosthesis,substitute the number 1.29 (the accepted average density of polyvinyl acrylic resin denture basematerial)l into the calculation. 4. Drain the water from the bulb. Dry the cavity thoroughly, and repair the accesshole with autopolymerizing denture resin. W. 0. RAMSEY, D.D.S. THE UNIVERSITY OF MARYLAND BALTIMORE COLLEGE OF DENTAL SURGERY DENTAL SCHOOL 666 WEST BALTIMORE ST. BAL’NMORE, MD 21201-1586
REFERENCE 1. Craig G. Restorative
dental materials.
St Louis: CV Mosby Co, 1985;470.
Reply To THEEDITOR: I appreciate Dr. Ramsey’srecommendedmethod to calculate the weight reduction between solid and hollow obturators by multiplying the recorded volume by the averagedensity of polymethyl methacrylate resin. The density of the monomeris 0.945 g&cc, and the polymethyl methacrylate is 1.16 to 1.18l or 1.19.2
602
Some factors may affect the density of the polymethyl methacrylate. For example: 1. The monomer-polymer ratio. The more polymer used,the lower is the shrinkage.2 2. The porosity. Porosities result from too rapid rate of heating, insufficient mixing of monomer and polymer, and insufficient pressureduring polymerization.2 3. The polymethyl methacrylate particles of various manufacturers may have a slight variation in density. If we adopt Dr. Ramsey’smethod, a pilot study of density control of a specific polymethyl methacrylate under specific conditions probably is necessary. YN-LOW H. WV, B.D.S., M.S. UNIVERSITY OF CALIFORNIA SANFRANCISCO SCHOOL OF DENTISTRY
SAN FRANCISCO CA, 94143-0758
REFERENCES 1. Craig G. Restorative dental materials. St Louis: CV Mosby Co, 1986470. 2. Phillips RW. Skinner’s science of dental materials. 8th ed. WB Saunders Co, 1986;1’74, 184, 197-9.
To THE EDITOR: In the article “A provisional restorative technique for laminate veneer preparations” (J PROSTHET DENT 1989;62:139-42),the authors describea technique to make provisional veneers. May I suggestsomeremarks: 1. Do the dimpleson me&al and distal axial walls create incidenceson the esthetic aspectof the definitive laminate veneer (the total thicknessat the dimples’level should be at least twice the thickness,0.5 mm, of the veneer to allow them to play someretentive role)? 2. In step 6, the surface of the tooth is prepared with a dental sealant to inhibit penetration of the acrylic resin monomer. This precaution is important. However, what about the inhibitive effect of this samesealanton the etching and bonding agent usedto bond the definitive veneer? How can the sealant be completely removed before etching? 3. Which cementing agent is used by the authors? All cementsdo not stand without sufficient mechanicalretentions (in this case,in the palatolabial direction). I suggestanother method for provisional laminate veneers: 1. Do not provide mechanicalretentions in the preparations. 2. Make the provisional veneer in light-cured composite resin. 3. Bond the provisional veneer in the following manner: A, Etch a 2 mm diameter circle in the center of the tooth surface or etch a line around the tooth approximately 0.5 mm wide at 1.5 mm inside the border and approximately 0.5 mm large. B, Usethe bonding agent to be usedfor the
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definitive veneer sparcely and only on the etched surface. C, Deposit a small amount of bonding composite resin on the same surface and apply the provisional veneer firmly before a light-cure. In this manner, the provisional veneer is really bonded, but provisionally. And it does not interfere in the bonding protocol of the definitive veneer. NGUYEN Luu
BAO
70 RUE DU PERE CORENTIN PARIS 75014 FRANCE
Reply To THE EDITOR:
I concur with Dr. Bao that another method is neededto retain the provisional restoration for the provisional laminate veneer. My present technique is to make the provisionalrestoration asdescribedin the article, but I bond the provisional veneer to a small etched area with an autopolymerizing, unfilled Bis-GMA resin such as a pit and fissure sealant. The autopolymerizing resin is necessary sincethe light-cured resin apparently doesnot completely polymerize through the acrylic resin interface. My bonding technique for the provisional laminate is as follows: 1. Make the preoperative impression. 2. Do not add mechanicalretention to the laminate veneer preparation. 3. Wet the impressionwith resin and uniformly coat with acrylic resin powder as previously described.
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4. Reposition the impressionon the teeth. 5. Let the impressionset 6 to 8 minutes until complete polymerization has occurred. 6. Remove the impression and easeout the cured shell from the impression. 7. Scissorsmay be usedto trim. 8. Reseatthe shell on the teeth. 9. Trim with a high-speedinstrument. 10. Spot etch a segmentof enamel2 mm by 2 mm near the incisal edge. 11. Cement with a small amount of autopolymerizing pit and fissure sealant. 12. Coat with a resin glaze. 13. To place the definitive veneer, remove the provisional veneer with a pointed instrument, 14. Identify and remove any retained resin from the tooth preparation with a bur. Any under-contouring that results is distal to the finish line. 15. Place and bond the definitive veneer in the customary manner. This technique bondsthe acrylic resinprovisional veneer with autopolymerizing Bis-GMA resin to the tooth.’ The technique supports the time- and cost-savingadvantages as previously described. DEAN A. ELLEDGE,
D.D.S.,
M.S.
SCHOOL OF DENTISTRY UNIVERSITY OF MISSOURI KANSAS CITY, MO 64108
REFERENCE 1. Elledge DA, Mixeon laminate veneers 1990,21:15-8.
JM, Cowan RD, Honrath G. Predicting esthetics of without tooth preparation. Quintessence Int
603
REFERENCE 1. Craig G. Restorative
dental materials.
St Louis: CV Mosby Co, 1985;470.
Reply To THEEDITOR: I appreciate Dr. Ramsey’srecommendedmethod to calculate the weight reduction between solid and hollow obturators by multiplying the recorded volume by the averagedensity of polymethyl methacrylate resin. The density of the monomeris 0.945 g&cc, and the polymethyl methacrylate is 1.16 to 1.18l or 1.19.2
602
Some factors may affect the density of the polymethyl methacrylate. For example: 1. The monomer-polymer ratio. The more polymer used,the lower is the shrinkage.2 2. The porosity. Porosities result from too rapid rate of heating, insufficient mixing of monomer and polymer, and insufficient pressureduring polymerization.2 3. The polymethyl methacrylate particles of various manufacturers may have a slight variation in density. If we adopt Dr. Ramsey’smethod, a pilot study of density control of a specific polymethyl methacrylate under specific conditions probably is necessary. YN-LOW H. WV, B.D.S., M.S. UNIVERSITY OF CALIFORNIA SANFRANCISCO SCHOOL OF DENTISTRY
SAN FRANCISCO CA, 94143-0758
REFERENCES 1. Craig G. Restorative dental materials. St Louis: CV Mosby Co, 1986470. 2. Phillips RW. Skinner’s science of dental materials. 8th ed. WB Saunders Co, 1986;1’74, 184, 197-9.
To THE EDITOR: In the article “A provisional restorative technique for laminate veneer preparations” (J PROSTHET DENT 1989;62:139-42),the authors describea technique to make provisional veneers. May I suggestsomeremarks: 1. Do the dimpleson me&al and distal axial walls create incidenceson the esthetic aspectof the definitive laminate veneer (the total thicknessat the dimples’level should be at least twice the thickness,0.5 mm, of the veneer to allow them to play someretentive role)? 2. In step 6, the surface of the tooth is prepared with a dental sealant to inhibit penetration of the acrylic resin monomer. This precaution is important. However, what about the inhibitive effect of this samesealanton the etching and bonding agent usedto bond the definitive veneer? How can the sealant be completely removed before etching? 3. Which cementing agent is used by the authors? All cementsdo not stand without sufficient mechanicalretentions (in this case,in the palatolabial direction). I suggestanother method for provisional laminate veneers: 1. Do not provide mechanicalretentions in the preparations. 2. Make the provisional veneer in light-cured composite resin. 3. Bond the provisional veneer in the following manner: A, Etch a 2 mm diameter circle in the center of the tooth surface or etch a line around the tooth approximately 0.5 mm wide at 1.5 mm inside the border and approximately 0.5 mm large. B, Usethe bonding agent to be usedfor the
MAY 1999
VOLUME
68
NUMBER
5
READERS’
ROUND
TABLE
definitive veneer sparcely and only on the etched surface. C, Deposit a small amount of bonding composite resin on the same surface and apply the provisional veneer firmly before a light-cure. In this manner, the provisional veneer is really bonded, but provisionally. And it does not interfere in the bonding protocol of the definitive veneer. NGUYEN Luu
BAO
70 RUE DU PERE CORENTIN PARIS 75014 FRANCE
Reply To THE EDITOR:
I concur with Dr. Bao that another method is neededto retain the provisional restoration for the provisional laminate veneer. My present technique is to make the provisionalrestoration asdescribedin the article, but I bond the provisional veneer to a small etched area with an autopolymerizing, unfilled Bis-GMA resin such as a pit and fissure sealant. The autopolymerizing resin is necessary sincethe light-cured resin apparently doesnot completely polymerize through the acrylic resin interface. My bonding technique for the provisional laminate is as follows: 1. Make the preoperative impression. 2. Do not add mechanicalretention to the laminate veneer preparation. 3. Wet the impressionwith resin and uniformly coat with acrylic resin powder as previously described.
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
4. Reposition the impressionon the teeth. 5. Let the impressionset 6 to 8 minutes until complete polymerization has occurred. 6. Remove the impression and easeout the cured shell from the impression. 7. Scissorsmay be usedto trim. 8. Reseatthe shell on the teeth. 9. Trim with a high-speedinstrument. 10. Spot etch a segmentof enamel2 mm by 2 mm near the incisal edge. 11. Cement with a small amount of autopolymerizing pit and fissure sealant. 12. Coat with a resin glaze. 13. To place the definitive veneer, remove the provisional veneer with a pointed instrument, 14. Identify and remove any retained resin from the tooth preparation with a bur. Any under-contouring that results is distal to the finish line. 15. Place and bond the definitive veneer in the customary manner. This technique bondsthe acrylic resinprovisional veneer with autopolymerizing Bis-GMA resin to the tooth.’ The technique supports the time- and cost-savingadvantages as previously described. DEAN A. ELLEDGE,
D.D.S.,
M.S.
SCHOOL OF DENTISTRY UNIVERSITY OF MISSOURI KANSAS CITY, MO 64108
REFERENCE 1. Elledge DA, Mixeon laminate veneers 1990,21:15-8.
JM, Cowan RD, Honrath G. Predicting esthetics of without tooth preparation. Quintessence Int
603
