JOCHEN,CAPUTO,ANDMATYAS

application can be based on more discreet factors address specific requirements of patients.

SUMMARY

AND

to

CONCLUSIONS

REFERENCES

This study examined the effect of one-layer and twolayer opaque porcelain applications on the flexural bond strength of three silver-palladium alloys. The results were: 1. There were no significant differences in bond strengths for three alloys between one- or two-layer opaque applications. 2. W-l demonstrated the greatest bond strength of the alloys. 3. Some improvement in bond strength was noted, although not statistically significant, with the one-layer technique for JP-5 and Rx-91 alloys. The results indicated that flexibility, with respect to

Bond strengths oxalate-treated

of luting dentin

D. W. Richardson, D.D.S.,* L. Tao, D. I-I. Pashley, D.M.D., Ph.D.***

bond strength, existed in the selection of the one-layer or two-layer opaque porcelain application.

1. Stein RS, Kuwata M. A dentist and a dental technologist analyze current ceramo-metal procedures. Dent Clin North Am 1977;21:729-49. 2. McLean, JW. The metal-ceramic restoration. Dent Clin North Am 1983;27:747-61. 3. Jochen DG, Caputo AA, Matyas J. Effecte of cooling methods on silverpalladium castings. J PROS= DENT 1988;59:311-4. 4. Jochen DG, Caputo AA, Matyas J. Effect of metal surface treatment on ceramic bond 8trength.J PROSTHETD~~~1986;55:166-8. 5. Matyas J, Caputo AA. Bond strength of spray-opaque porcelain to metal. J Calif Dent Assoc 1982;10:37-9. Reprint requests to: DR. ANGELO A. CAPUTO

SCHOOLOFDENTISTRY uNlVEFW'lYOFCALIFORNIA LosA~~!axs,CA90024

cements to potassium B.D.S.,

M.S.,**

and

MedicalCollegeof Georgia,Schoolof Dentistry, Augusta,Ga. Potassium oxalate is gaining popularity as a dentin treatment to prevent the development of dentin sensitivity. Because treated dentin surfaces are covered with calcium oxalate crystals, the bond strength of cements to oxalate-treated dentin required investigation. This study determined the tensile bond strengths of glass-ionomer, polycarboxylate, and zinc phosphate cements used to cement castings to dentin treated with either water or potassium oxalate. The results indicate that oxalate-treated dentin did not affect the bond strength of glassionomer or polycarboxylate cements, but produced a large decrease in the bond strength of zinc phosphate cement. (J PROSTAET DENT1990;83:418-22.)

s ensitivity is a frequent problem after teeth have been prepared as abutments. Often, during treatment for a fixed partial denture, an abutment may require examination, a provisional restoration may becomedislodged,or the fit of a fixed partial denture may needto be evaluated directly. These procedures require debridement of the abutment tooth, which, in many instances,may causesevere discomfort. Several authorities regard this pain asbeing of hydrodynamic 0rigin.l

This researchwassupportedin part by grantDE06427from the NationalInstitute of DentalResearch andby the MedicalCollegeof GeorgiaDentalResearchCenter. *AssistantProfessor,Departmentof Prcsthodontics. **ResearchFellow,Departmentof Oral Biology. ***Regents’Professor,Departmentof Oral Biology. 10/l/17713

418

The hydrodynamic theory of dental sensitivity wasproposed by Brkmstrom et al.’ This theory states that the movement of dentinal tubule fluid stimulatesnerves in the pulp and/or the pulpal half of the dentin to elicit pain. If the fluid flow through the dentinal tubules is the mechanism involved in the production of dentinal pain, procedures that decreasefluid flow should reduce the sensation of pain. Application of potassium oxaIate tc dentin has been proposedto reduce dentin sensitivity in patients2 It has been shown, in vivo and in vitro, that crystals of calcium oxalate precipitate onto the dentin surface and into the dentin tubules after a sequential application of 30% weight/volume (w/v) dipotassiumoxalate (O-P Laboratories, Augusta, Ga.) for 2 minutes, followed by 3% (w/v) acidic (pH 2) monopotassium-monohydrogenoxalate (O-P Laboratories) for 2 minutes.3l4 Testing of these dentin specimenstreated with potassiumoxalate showeda significant decrease in hydraulic conductance or fluid flow

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1990VOLUME~~

NUMBERQ

BOND

Table

STRENGTH

I.

OF LUTING

CEMENTS

Treatment steps Control

Experimental

1 Air dry 20 set 2 2 Min deionized water 3 Blot dry 4 2 Min deionized water

5 6 7 8

Deionized water rinse Air dry 20 set Affix matrix Inject cement and place swivel 9 Set for 30 min or 24 hr 10 Test tensile bond strength *(w/v).

Table

1 Air dry 20 set 2 2 Min 30% (w/v)* dipotassium oxalate 3 Blot dry 4 2 Min 3% (w/v) monopotassium monohydrogen oxalate 5 Deionized water rinse 6 Air dry 20 set 7 Affix matrix 8 Inject cement ma place swivel 9 Set for 30 min or 24 hr 10 Teat tensile bond strength

Weight/volume.

II.

Acrvlic

Cementstested Cement

Durelon Flecks Extraordinary Cement Fuji Ionomer (type 1)

type

Polycarboxylate Zinc phosphate Glass ionomer

P/L (gm/gm)

1.0/l 2.411 1.411

through the dentin compared with control specimens. Subsequent challenge of the oxalate-treated dentin surfaces with 6 % citric acid produced no significant changes in the decreased hydraulic conductance.4 Thus, after application of potassiumoxalate, a layer of calcium oxalate crystals is deposited that decreasesfluid flow acrossthe dentin and is resistant to acid challenge.As the dentin surface is often literally covered with calcium oxalate crystals after useof potassiumoxalate asa surfacetreatment, a potential problem is the possiblereduction in bond strength of an artificial crown cementedto dentin. This study determined the tensile bond strength of three luting agentsusedto cementartificial crownsto dentin that had beentreated with potassiumoxalate solutions.A comparison wasmade between the bond strengths of cements to dentin treated with oxalates and controls treated with deionized water.

MATERIAL

AND

METHODS

Crown segments of human third molar teeth were cemented to clear acrylic resin blocks. These resin blocks served to maintain the position of the teeth. The crown segmentswere made by removing the enamel in a plane parallel to the occlusalsurfaceof the tooth. The teeth were then sectionedat the level of the cementoenameljunction, thus producing a flat crown segment (Fig. 1). By use of 320&t Sic sandpaper(Buehler Ltd., Lake Bluff, Ill.) on

JOURNAL

Tooth

Fig. 1. Schematic showstooth segmenton acrylic resin block. Cylindrical nylon matrix wasusedto retain the cement. A double wire loop was embeddedin the cement.

Material

THE

Cement Matrix Dentin

OF

PROSTHETIC

DENTISTRY

an Ecomet III (Buehler Ltd.) circular grinding machine, a uniform smearlayer was applied to the specimenswith a force of 500 gm and a rotating speedof 103rpm for 15 seconds. The teeth were then stored in phosphate buffered saline(PBS) until tested. Oncea smearlayer wasproduced, if a specimenwasnot usedfor testing during a 24-hour period, a new smearlayer wascreated. The dentin surfaceof eachspecimenwasair-dried for 20 seconds(Table I). Control specimensreceived deionized water for 2 minutes; experimental specimensreceived 30% (w/v) dipotassium oxalate for 2 minutes. The specimens were then blotted dry. Control specimensthen received deionized water for 2 minutes; experimental specimensreceived 3 % (w/v) monopotassium-monohydrogenoxalate for 2 minutes. The specimenswere then rinsed with deionized water and air-dried for 20 seconds. A cylindrical nylon matrix (Fig. 1) with an internal area of 0.1 cm2and 3 mm high was fixed to the dentin surface with clear adhesive tape. The cementslisted in Table II were then mixed according to the indicated proportions. Durelon (Premier Dental Products, Norristown, Pa.) cement wasmixed within a 30-secondperiod on a paper pad supplied by the manufacturer. Flecks Extraordinary (M&y, Clift Forge, Va.) cement was completely mixed within 90 secondson a room-temperature glassslabby use of the incremental powder incorporation technique. Fuji Ionomer, Type I (G-C Dental Industrial Corp., Tokyo, Japan) cement wasmixed within 30 secondson a paper pad supplied by the manufacturer. The cementswere loaded into a Centrix Mark I (Centrix, Inc., Stratford, Conn.) syringe and ejected onto the dentin surface within the confines of the nylon matrix to fill the matrix with cement. A swivel was then suspendedover the matrix so that a portion of the swivelwasembeddedwithin the cement (Fig. 1). 419

RICHARDSON,

Table

III.

TAO,

AND

PASHLEY

Resultscompared with other studies Bond

Investigator

Finger5 PeddyG Hinouraet al.8 Richardson* Finger5 Peddys Negm7 Hinouraet al.8 Richardson* Ghanet al? Richardson*

Material

strength

ii

Fuji Ionomer(I) Fuji Ionomer(I) Fuji Ionomer(II) Fuji Ionomer(I) Durelon Durelon Durelon Durelon Durelon Mizzy-ZnPOd Mizzy-ZnP04

Superscript numbers

SEM

2.39 2.49

1.06 5.5 1.55 0.81 1.23 3.64 2.31 2.17 1.10 1.18 0.74

1.27 2.25 3.29 4.49 3.20 2.17 2.89 0.36 0.86

indicate reference citation. bracket are not statistically significantly different ignated type of Fuji glass ionomer used. *Richardson et al., this report, 24 hr.

(MPa)

(6) (12) (10) (17) (6) (11) (11) (10) (13) (40) (22)

Numbers connected by at p < 0.05. I and II des-

can’s multiple range test at the p < 0.05 level of significance.

RESULTS Fig.

2. Schematic of testing device. The shadedportion

represents container that received the lead shot. Insert showsflat crown segmentpositionedto test tensilestrength of cements. The cementswere allowedto set for either 30 minutes or 24 hours, after which time the tensile bond strength of the cement/dentin interface was tested. Those specimens tested after 24 hourswerestored in PBS at 37’ C. The resin blocks holding the specimenswere mounted in a holding stand so that the long axis of the tooth wasparallel to the table top. A wire was attached to the swivel that was embedded into the cement. A plastic bucket was suspended from the other end of the wire (Fig. 2). When activated, No. 9 lead shot flowed at a rate of 0.89 kglmin into the suspendedbucket. When the ultimate tensile strength was reached,the suspendedbucket fell, depressinga platform. The depressedplatform triggered a switch that stoppedthe flow of shot to the bucket. This testing device was calibrated to an Instron machine (Instron Corp. Canton, Mass.). Samplestested with both the Instron machine and the simpledevice were not statistically different. Tensile bond strength wascalculatedby weighingthe shot-plastic bucket combination and dividing by the internal diameter of the plastic matrix (0.10 cm2) to expressthe bond strength in kg/cm2 units. The results were statistically evaluated with a two-way analysisof variance (material versustreatment) and Dun-

420

The results are shown in Tables III and IV. All dentin surfaceswere covered with a 320-grit Sic-created smear layer. Treatment of the dentin surface with water before the application of glassionomer cement (Fuji Ionomer, Type I) yielded bondstrengthsof 1.42 + 0.65MPa (N = 10) at30minutesbut2.25 + 0.62MPaafter 24hours(p < 0.05). Pretreatment of the dentin with the oxalates increasedthe 30-minute bond ‘strengthsof the glassionomer cement to 2.41 + 0.64MPa (N = 13), avalue significantly higher than that of the water treatment group (p < 0.05). Oxalate treatment had no effect on the 24-hour bond strengths. Using polycarboxylate cement (Durelon, ESPE GmbH) pretreatment with water gave30-minute bond strengthsof 2.78 +- 0.91 MPa (N = 15) and 24-hour bond strengths of 2.89 +- 1.10MPa. Pretreatment of the dentin surface with the oxalates produced bond strengths of 3.43 +- 1.06 and 3.38 ? 0.84 MPa at 30 minutes and 24 hours, which were not statistically different from the water-treatment group. Treatment of dentin with oxalateshad no effect on the 30minute bond strengths of zinc phosphatecement (controls 0.76 +- 0.65 versus treated 0.86 f 0.74, Table IV). However, the 24 hour bond strength of zinc phosphatecement fell to near zero in the oxalate-treatment group (Table IV). The glassionomer cementsin both the water (control) and oxalate (experimental) groups produced higher bonds strengths than did the zinc phosphate cements(p < 0.05), but the bonds were lower than those produced with polycarboxylate cements (p < 0.05). The bonds produced by the polycarboxylate cementswerestatistically significantly higher than those produced by zinc phosphatecementsor

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glass ionomer cement after water treatment (p < 0.05) but they did not differ from the bonds produced by glass ionomer cement after oxalate treatment.

Table

IV.

Effects of oxalate treatment on tensile bond

strengths Bond (MPa)

DISCUSSION The retention of restorations by zinc phosphate cement is primarily due to mechanical interlocks between irregularities in the restorative materials and the dentin. Polycarboxylate and glass ionomer cements both adhere to dentin. During testing, most of the bonds exhibited adhesive failure at the dentin surface instead of cohesive failure within the material. The lowest bond strengths were found with zinc phosphate cement, the highest with polycarboxylate cement, and glass ionomer cements had intermediate strengths. Our results (Table III) were not statistically different from those of other investigators.5-g To the extent that polycarboxylate cement bonds are the result of chemical bonding to dentin in addition to mechanical bonding, it was thought that oxalate treatment of the dentin surface might lower the bond strength of polycarboxylate cements.1° That oxalate treatment did not reduce the bond strength of polycarboxylate cement may indicate that the calcium oxalate crystals that are produced on dentin as a result of treatment with these oxalate solutions may provide sites for chemical bonding of polycarboxylate cements.4 If that speculation is true, it also suggests that the calcium oxalate crystals must be rather firmly bound to the dentin surface. These crystals may adhere to the dentin tightly, increasing surface roughness and allowing for more mechanical retention. Until careful scanning electron microscopic studies are conducted on both sides of the failed bonds of these cements, such suggestions, although interesting, remain speculative. Because most cements are acidic before setting, they have the potential to solubilize at least the surface of the smear layer.4 Some manufacturers are recommending treatment of the dentin surface with polyacrylic acid before application of glass ionomer cements. Although such treatments increase bond strengths of glass ionomer cements they also remove smear layers. If the cement is torn at the margin before it sets or if it is lost in any other manner, the dentinal tubules will be open and sensitive. Oxalic acid is the only acid that we are aware of that decreases dentin permeability. 3,4 The second oxalate solution, monopotassium monohydrogen oxalate, is acidic (approximately pH 2) and may have increased the early bond strengths of the glass ionomer cement by its acid etching action. Oxalate treatments of dentin cover the surface with crystals of calcium oxalate. 4,l1 Several investigators have increased the strength of bond to enamel or dentin by producing crystal growth on the surface.12 The use of oxalates on abutment teeth after crown preparation should make such surfaces more resistant to dietary- and plaque-generated acids during the time the preparations are under tem-

THE

JOURNAL

OF PROSTHETIC

DENTISTRY

strengths of samples

30 min Cements

x

24 hr

SEM

N

:

SEM

N

1.42 2.41

0.65 0.64

10 13

2.25 2.30

0.80 0.59

17 10

2.78 3.43

0.91 1.06

15 13

2.89 3.38

1.10 0.84

13 14

0.76 0.72

0.65 0.30

11 12

0.86 0.18

0.74 0.12

22 23

treatment

with both oxalate

Glassionomer Control

OX-TX Polycarboxylate Control

OX-TX Zinc phosphate Control

OX-TX OX-TX, Sequential

solutions.

porary restorations.4,l1 These teeth should also be less sensitive to thermal, tactile, and osmotic stimuli. Although most cement bond strengths are measuredafter 24 hours of storage in water, the early bond strengths are of considerableclinical interest. That is why we tested early or 30-minute bond strengths as well as those developed after 24 hours. The effect of oxalate treatment of dentin on the 24-hour bond strength of zinc phosphatecement wasunexpected. That the 30-minute bond strengths were normal and the 24-hour bond strengths were zero suggeststhat the differenceswas due to a delayed or slow reaction. Perhaps oxalate treatment increasesthe solubility of the cement at the cement-dentin interface. The results clearly indicate that dentists usingoxalate to prevent dentin sensitivity under temporary crownsshould not lute castingswith zinc phosphate cement. Overall, the use of oxalatesasa dentin treatment to prevent sensitivity before and after cementation looks promising. Double-blind clinical trials of its efficacy seemwarranted.

CONCLUSION Within the conditions of this study, several conclusions can be made. 1. The sequentialapplication of 30% (w/v) dipotassium oxalate for 2 minutes and 3% (w/v) monopotassiummonohydrogen oxalate for 2 minutes significantly enhanced the tensile bond strength of Fuji Ionomer luting cement to dentin at 30 minutes but waswithout affect at 24 hours. 2. The sequentialapplication of the oxalate solutionsfor 2 minutes has no significant effect on the tensile bond strength of Durelon luting cementsto dentin at either 30 minutes or 24 hours. 3. The sequential application of the oxalate solutions lowered the 24-hour bond strength of zinc phosphate

421

RICFIARDSON,TAO,ANDPASALEY

cement. The use of zinc phosphate cement is contraindicated on oxalate-treated dentin surfaces. We thank Shirley Johnston for her secretarial assistance in the preparation of this manuscript. REFERENCES 1. Briinnstrijm M, Linden LA, Yhgtrbm A. The hydrodynamics of the dental tubule and of pulpal fluiuid: a discussion of its significance in relation to dental eensitivity. Caries Rea 1967;1:310-7. 2. Greenhill J, Paehley D. The effect of desensitizing agents on the hydraulic conductance of human dentin in vitro. JDent Res 1981;60:68698. 3. Paehley DH. Dentin permeability, dentin sensitivity, and treatment through tubules occlusion. J Endodont 1986;12:465-74. 4. Paehley D, Galloway S. The effect of oxalate treatment on the smear layer of ground surfaces of human dentin. Arch Oral Biol 1985;30: 131-l. 5. Finger W. Evaluation

of glass ionomer luting cements. Stand J Dent Res

1983;91:143-9.

Occlusal Alejandro

accuracy Peregrina,

6. Peddy M. The bond strength of polycarboxylic acid cements to dentin: effect of surface modification and time after extraction. Au& Dent J 1981;26:178-80. 7. Negm N, Cenbe E, Grant A. Factors affecting the adhesion of polycarboxulate cement to enamel and dentin. J PFIOSTHIW DENT 1981;45:40510.

8. Hinoura K, Morre BK, Phillips RW. Influence of dentin surface treatment on the bond strengths of dentin-lining cements. Oper Dent 1986;11:147-54. 9. Chan K, Svare C, Horton D. The effect of varnish on dentinal bonding strength of five dental cements. J PROSTHET DENT 1976;35:403-6. 10. Beech DR. Improvements in the adhesion of polyacrylate cements to human dentine. Br Dent J 1973;135:442-5. 11. Chan DCN, Jensen ME. Dentin permeability to phosphoric acid: effect of treatment with bonding resin. Dent Mater 1986;2:251-6. 12. Maijer R, Smith DC. A new surface treatment for bonding. J Biomed Mater Res 1979;13:9’?5-85. Reprint requests to: DR. DAVID H. PASHLEY SCHOOL OF DENTISTRY MEDICAL COLLECE OF GEORGIA AUGUSTA, GA 30912-1129

of casts made and articulated

differently

D.D.S., M.S.,* and M. H. Reisbick, D.M.D., M.S.**

University of Missouri-Kansas City, School of Dentistry, Kansas City, MO., and The Ohio State University, College of Dentistry, Columbus, Ohio This study evaluated the occlusal accuracy of gypsum casts constructed from irreversible hydrocolloid and selected nonaqueous elastomeric materials. Master metal casts were attached to a vertically moving apparatus that allowed their occlusal surfaces to produce repeatable contacts. Impressions were made with irreversible hydrocolloid, polysulfide, and vinylsiloxane. Resulting maxillary casts were mounted with a constant positioning device and mandibular casts were mounted with zinc oxide-eugenol paste records or by maximum intercuspation. Four specific master occlusal contacts were compared with contacts generated from the mounted gypsum casts; a perfect score was 40 (four contacts X 10 casts). A chi-square linear model for category data was used to compare groups. Results indicated that casts made from irreversible hydrocolloid should not be articulated with the use of a zinc oxide-eugenol paste but are best articulated by using maximum intercuspation (32/40 contacts). (J PROSTHET DENT 1990;63:422-6.)

I

rreversible hydrocolloid is often used for making. diagnostic and preliminary casts. However, the material hasseveralimportant shortcomings,namely lack of surface detail registration,l deleterious surface interaction with certain gypsum products,2t3 and greater permanent set

Presented at the American and International Association for Dental Research meeting, Montreal, Canada, and the Carl 0. Boucher Prosthodontic Conference, Columbus, Ohio. *Assistant Professor, Department of Fixed Prosthodontics and Occlusion, University of Missouri-Kansas City, School of Dentistry. **Professor and Chairperson, Section of Restorative and Prosthetic Dentistry, The Ohio State University, College of Dentistry. 1011117707

422

(distortion) than reversible hydrocolloid or nonaqueous elastomericmaterials.4-7Despite theseshortcomings,dentists often use casts made from alginate (irreversible hydrocolloid) impressionsto opposetype IV gypsumtooth dies when making cast restorations. This study evaluated the occlusalaccuracy of articulated gypsumcastsmade from irreversible hydrocolloid and selected elastomeric nonaqueousimpression materials oriented by using two different clinical methods.

MATERIALS

AND

METHODS

Master maxillary and mandibular metal casts(Columbia Dentoform Corp., New York, N.Y.) were mounted on a vertical moving device that allowed their occlusalsurfaces to produce repeatable contacts (Fig. 1). One operator selectedfour occlusalcontacts (Fig. 2) marked with articulating ribbon and a second operator made all of the [email protected]@O

VOLUME83

NUMBER4

Bond strengths of luting cements to potassium oxalate-treated dentin.

Potassium oxalate is gaining popularity as a dentin treatment to prevent the development of dentin sensitivity. Because treated dentin surfaces are co...
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