Influence of tooth surface roughness and type of cement on retention of complete cast crowns

Influence of tooth surface roughness and type of cement on retention of complete cast crowns M o h a m m e d F. Ayad, BDS, M S c D , a Stephen F. Rosenstiel, BDS, M S D , b and M i r f a t Salama, BDS, M S c D , PhD c College of Dentistry, The Ohio State University, Columbus, Ohio; and College of Dentistry, University of Tanta, Tanta, Egypt

Statement o f Problem. Bond strength of luting cements to dentin is a critical consideration for success of cast restorations.

Purpose o f Study. This study determined the relationship between surface characteristics of teeth prepared for complete cast crowns and retention of respective cemented restorations. Material and Methods. Ninety artificial crowns were cast for standardized complete crown tooth preparations accomplished with the use of a milling machine on extracted human teeth. Diamond, tungsten carbide finishing, and cross
The retention of luting cements has been reported extensively in the literature. 1,2However, it has been demonstrated that retention o f artificial crowns varied not only with mechanical properties o f luting medium 3 but also with the geometric relationship of the prepared tooth surface 4 and definitive restoration. 5 These factors can influence stress distribution within the interposed cement layer, 6 the bonding efficiency o f cement to both surfaces, and durability o f the cement including the long-term resistance to mechanical deterioration. The two primary adhesive mechanisms o f dental cements are mechanical interlocldng and physicochemical

~Visiting Scholar, Section of Restorative and Prosthetic Dentistry, School of Dentistry,The Ohio State University. bAssociate Professorand Chairman,Section of Restorativeand Prosthetic Dentistry,School of Dentistry,The Ohio State University. CLecturer,Section of Restorativeand Prosthetic Dentistry,Collegeof Dentistry, University of Tanta. 116

THE JOURNAL OF PROSTHETIC DENTISTRY

bonding. 7 Zinc phosphate cement is a luting agent that adheres by mechanical interlocldng to irregularities in the tooth and casting? Glass ionomer cements attain their adhesion primarily through physicochemical bonding. An actual ionic chemical reaction occurs between calcium o f the hydroxyapatite and carboxyl ions o f a polyacrylic acid. 9 It has been claimed that Panavia-EX resin cement adheres chemically and mechanically to tooth structures.l° Previous research 9,11 has reported different retentive values for castings with the use of different cements, but most investigations have n o t included the entire t o o t h surface condition. Ayad et al) 2 reported a statistically significant relationship between the area o f dentin available for bonding and retention of the casting and concluded that surface roughness o f tooth preparation that encourages mechanical interlocldng o f cement may enhance retention and reduce the need for additional retentive measures. VOLUME 77 NUMBER2

AYAD, ROSENSTIEL, AND SALAMA

THE JOURNAL OF PROSTHETIC DENTISTRY

C

~

T~th Preparation~imensions (ram)

b a

3,5

b 6

c

2 d~

7

2

e

f

g

1.2!

2,2

2.4

4,6

*Convergenceangle (degree)

-8 m m

Fig. 3. Longitudinal cross-section of master tooth weparation for complete crowns. Fig. 1. Rotary instruments for tooth preparations

Table I. Rotary instruments for tooth preparations of complete

crowns (n = 30 for each group) Rotary Abbreviation instrument

Description

Catalog No.

Diamond*

D

Round end taper course grit

6856 L-016

Finishing* Tungsten carbide*

F C

12-fluted round end taper Cross-cutround end fissure

H375 R-016 H 33 R-0] 6

*BrasselerInc., Savannah,Ga.

MATERIAL

Fig. 2. Milling machine for tooth preparations of complete crowns.

The purpose o f this study was to compare the influencc o f the surface roughness o f dentin preparcd with diamond stones and finishing or cross-cut carbide burs on retention o f complete cast crowns cemented with zinc phosphate cemcnt, glass ionomcr cement, and an adhesive resin cement. FEBRUARY 1997

AND METHODS

Ninety extracted, intact human molar teeth o f similar size were collected and stored in distilled water at room temperature (23 o C). The roots of all teeth were notched for anchorage with a separating disk, and then the teeth were prepared to simulate clinical preparations for complete crowns. Each tooth was aligned vertically in an individual polymeric tube and embedded with epoxy resin (Epoxide Resin, Leco Corp., St. Joseph, Mich.)within 2 mm o f the cementoenamel junction. A dental surveyor was used to position the long axis o f each tooth parallel to the tube. Mounted teeth were stored in an atmosphere o f 100% humidity except at the time o f embedding, tooth preparation, impression, cementation, and removal o f the crown. The teeth wcrc randomly assigned to three groups of 30 according to the rotary instruments used iTable I). The three rotary instruments were chosen for the tooth preparations because o f close similarities in taper, diameter, and tip configuration (Fig. 1). The teeth wcrc prepared to receive complete cast crowns by flattening the occlusal surface to the depth o f the central groove to expose the dentin. The reduced occlusal surface was examined with a 19-power stereoscopic microscope (SMZ-1, Nikon Inc., Garden City, N.Y.). Additional reduction was completed to remove any remaining enamel. Occlusal reduction was oriented in a direction perpendicular to the axis o f the polymeric 117

THE JOURNAL OF PROSTHETIC DENTISTRY

AYAD, ROSENSTIEL, A N D SALAMA

Table II. Luting cements Cement

Abbreviation

Manufacturer

Zinc phosphate cement Glass-ionomer cement (Ketac-Cem Aplicap) Panavia-EX cement

ZP GS

Fleck's, Mizzy, Inc., Cherry Hill, N.J. ESPE-Premier Sales Corp., Norristown, Pa.

Powder: D39 05791; X231

PA

J. Morita USA Inc., Tustin, Calif.

64279

tube. Axial reduction was standardized by using a milling machine (model F1, Degussa AG, Frankfurt am Main, Germany) modified to produce replicas guided by a stylized metal master tooth preparation for a complete crown (Fig. 2). An aluminum fixture was used to attach a stylus to the superior fixed part o f the machine. The stylus taper, diameter, and tip shape were machined to the same dimensions as the rotary instruments and fixed at a known distance from the "cutting tools." A movable X-Y table on the milling machine supported another fixture that secured embedded specimens at the same distance from the master tooth preparation for a complete crown (Fig. 3). The apparatus operated similar to a hardware store key cutter. Teeth were prepared by moving the table and t o o t h assembly past the fixed portion o f the machine after the tool and stylus tips were centered above the occlusal surfaces o f both the t o o t h and the master die. All tooth preparations were initially rough cut with a diamond and then refined or "finalized" with the randomly assigned instruments. The depth o f tooth preparation was limited by a track o f the stylus along the master die. The length o f the tooth preparation was controlled by the working height setting of the milling machine. A chamfer margin was formed as the negative image o f the round-ended tapered rotary instruments. A new rotary instrument was used for each tooth, and a continuous water jet was directed at the rotary instruments. After the axial reduction, an occlusal groove was machined with a tapered fiat-ended diamond (TwoStriper, Abrasive Technology Inc., Westerville, Ohio) to develop an occlusal surface with a configuration that closely simulated actual tooth preparation. A single mix technique was used to make impressions o f the prepared teeth with a polyvinyl siloxane (Examix, GC America Inc., Chicago, Ill.), and the impressions were cast with type IV die-stone (Jade stone, Whip Mix Corp., Louisville, Ky.). A cylindrical wax pattern (Gator Wax, Whip Mix Corp.) was made for each die with a brass split mold with four tapered projections for orientation. Each wax pattern was designated with a code number corresponding to the tooth from which it was derived, so that each pattern could be identified. The patterns were invested with phosphate bonded investment (Cera-fina, Whip Mix Corp.) and cast with an ADA type III dental gold alloy (Ney-Oro-B2, Ney Co., Bloomfield, Conn.). Investing and casting protocol was established by pilot testing to produce crowns that seated well on the stone dies and 118

Lot No.

liquid: 31 052893

tooth preparations with minimal force and could not be rocked or rotated. No die spacer was used in this study. Castings were recovered from investment, cleaned in piclding solution (Jel-Pac, J.F. Jelenko Co., Armonk, N.Y.), and air-abraded with S0 ~am aluminum oxide for 10 seconds and a contraangle microetcher (Microetcher, erc-er, Danville Engineering, Danville, Calif.) at 60 psi. The internal surface o f each casting was inspected with a 20-power stereomicroscope, and minute nodules were removed with a half-round bur in slow-speed straight handpiece. After necessary adjustment, castings were passively fit to their dies but were not noticeably loose or unstable. Artificial crowns o f each group were randomly assigned to three subgroups o f 10 each according to the cement listed in Table II. Cements were mixed according to each manufacturer's specifications. Zinc phosphate cement was mixed incrementally for 2 minutes on an 18 ° to 20 ° C glass slab. The p o w d e r / l i q u i d ratio (0.5 g m / 0 . 3 ml) was established to provide a mix that formed a 20 to 25 mm "string" o f cement when pulled from the glass slab after mixing. Panavia-EX resinous cement was mixed for 60 seconds with a powder dispensed in proportion to two drops o f the liquid. The prescribed coating material was applied to inhibit air during polymerization. Glass ionomer cement was activated for 2 seconds and mixed for 10 seconds in an amalgamator (Silamat, Vivadent, Amherst, N.Y.). A stiff brush was used to coat the inner surface (intaglio) o f each crown with an even thickness of cement. Each crown was seated with finger pressure and use o f a slight back and forth axial rotation until engagement o f the occlusal groove. A dynamic 98 N load was applied from a force gauge (Chatillon LTC, Greensboro, N.C.) through an orangewood stick placed transversely on the occlusal surface o f the artificial crown (Fig. 4). The opposite end o f the loaded stick was subjected to horizontal and vertical movement for 20 seconds, suggested by Rosenstiel and Gegauff, 13 and the force was maintained for 10 minutes. Excess cement was then removed, and specimens were stored for 24 hours in 100% humidity at 37 ° C before they were thermocycled at 1500 cycles between 5 ° C and 55 ° C with 1 minute dwell times. The treated specimens were then returned to their original storage condition for 2 hours before retention o f each crown was measured. Retention was measured by applying a force sufficient to dislodge the crown from the tooth with a universal VOLUME 77 NUMBER2

AYAD, ROSENSTIEL, A N D SALAMA

THE JOURNAL OF PROSTHETIC DENTISTRY

400

372.9

Z

312.8

300

308.5

298,9

351"~348"~~

L ~ A

265.c

0 0

K×

x ",,'-.\\\'G

213"~201. 6

200

x\\\N'q

=l

x v x -: :-.\\\\'q ~vv, ¢ v X 2 N\\\NN

100 K X ~ ) ,-..\\\\-,

0

!v~? -.----~.

Zinc phosphate Glass ionomer

Panavia-EX

Luting cements Fig. 5. Mean differences among luting cements for each rotary instrument. Horizontal lines connect values that are not

significantly different at p < 0.001.

~-~ 4 0 0

~ 0

308.~ ,,1/I/I

300

"0

i 200

Fig. 4. Chatillon force gauge for cementation of artificial crown.

Source of variation

df

MS

F value

Model Burs Cement Roughness x cement Error

8 2 2 4

373.920 249.026 1037.554 104.550

25.782 17.260 71.540 7.209

81

14.503

C

'k////l /////i /I1H1/1/ I1 1 ,,,,,, ,,.,,,

7///// //,'//, ///H~

.m

Table III. ANOVA procedure for the dependent variable retention

372.9

351.6

z

i/////,

10o

,H///,

',(,~Z,(,'

p <0.001 <0.001 <0.001 <0.001

Diamond

Finishing

Carbide

Rotary instruments Fig. 6. Mean differences among rotary instruments for each luting cement. Horizontal lines connect values f o r luting cement that are not significantly different at e~= 0.05.

dr, Degreesof freedom MS, meansquare;p, probabilities.

RESULTS testing machine model 4204, Instron Corp., Canton, Mass.). With a 1000 N load cell and 0.5 m m / m i n crosshead speed, the tensile load was applied until separation occurred. The polymeric tubes were drilled to allow attachment to the Instron machine. The crown was attached to the upper component o f the Instron machine with a flat metal plate that engaged ears on occlusal surface like a bayonet m o u n t while chains linked the plate to the machine. This fixture ensured that the removal force was aligned in the long axis o f the preparation. The Instron machine was operated at control mode. Means and SDs were calculated for each group, and results were compared by a two-way analysis o f variance (ANOVA) and Tukey's Studentized range test at 5% level o f significance. FEBRUARY 1997

The ANOVA results in Table III demonstrate a statistically significant difference between cements and burs and between cement-bur combinations (p < 0.001). Figs. 5 and 6 illustrate the mean differences for each rotary instrument and luting cement separately. The data indicate that castings on t o o t h preparations finalized with finishing burs had lower retention, and higher retention was found for tooth preparations finished with carbide burs with all different types o f cements. Retention o f cast crowns cemented with zinc phosphate cement on tooth preparations finalized with carbide burs (312.8 N) was improved by 46% to 55% compared with retention on t o o t h preparations completed with diamond rotary instruments (223.9 N) or finisht 79

THE JOURNAL OF PROSTHETIC DENTISTRY

AYAD, ROSENSTIEL, AND SALAMA

Panavia-EX resinous cement on tooth preparations completed with carbide burs. The least mean bond strength (201.6 N) was recorded with crowns cemented with zinc phosphate cement on tooth preparations that had been completed with finishing burs. Tukey's Studentized range test revealed no significant difference for retention o f crowns cemented with zinc phosphate cement when used with tooth preparations completed with diamond or finishing burs. However, the retentive strength o f tooth preparations refined with carbide burs was statistically greater (p < 0.05). Glassionomer and Panavia-EX cements recorded no significant difference among the three tested groups of rotary instruments for tooth preparations. A comparison among luting cements for each finishing bur indicated significant differences among all three cements for finishing burs. However, a difference was found only between Panavia-EX and the other two cements for tungsten carbide burs. Zinc phosphate cement was significantly lower than the other two cements with diamond rotary instruments. DISCUSSION

Fig. 7. SEM of prepared teeth. (Original magnification x200

[left] and x1000 [right].) A, Carbide bur. Galling pattern on dentinal surface; grooves demonstrated mean depth of approximately 25 pm and distance between ridges 150 lam. B, Finishing bur and smoother surface. C, Diamond rotary instrument; fine grooves running within deeper grooves with mean depth of 15 [am and distance between ridges of nearly 100 IJm.

ing burs (201.6 N). A similar comparison for crowns cemented with Panavia-EX resinous cement and glass ionomer cement revealed no significant difference between groups. Comparisons between experimental groups in this study revealed that the greatest mean retentive strength (372.9 N) was recorded for cast crowns cemented with 120

Numerous factors can affect the long-term success o f dental cast restorations. This investigation has documented that both selection of luting cement and type of bur used to finish t o o t h preparations are essential in achieving suitable retention for complete cast crowns. This study substantiated the differences in retention that were attributable to both choice of rotary instrument and luting cement. Zinc phosphate cement is a nonadhesive conventional cement but is a reliable, successful luting agent. The luting of zinc phosphate cement is achieved mainly from mechanical interlocldng. The greatest retentive strength of the cement was achieved by finishing t o o t h preparations with cross-cut carbide burs that created a horizontal ridge and groove surface pattern (Fig. 7, A). This study supported the findings of Oilo and Jorgensen 14 and Witwer et al. is A possible explanation for the influence o f increased roughness on the retention o f zinc phosphate could be that more cement floated into and hardened in undercuts where it required compression or shear fracture before the cement failed. Smooth surface tooth preparations (Fig. 7, B) that were completed with finishing burs had lower retentive values, but tooth preparations created with diamond rotary instruments (Fig. 7, C) recorded moderate retention values. Gorodovsky and Zidan 16 reported no significant difference in retention between glass ionomer and zinc phosphate cements. This study has verified that glass ionomer cements attained their total retentive strength with mechanical interlocldng and physicochemical bonding. Regardless o f the nature o f dentinal surface roughness, this factor was only a minimal influence on the retentive strength o f glass i o n o m e r cement. Glass VOLUME 77 NUMBER2

AYAD, ROSENSTIEL, A N D SALAMA

ionomer cement also recorded significantly greater retention with smooth dentinal surfaces than zinc phosphate cement. The reasons for this cement having the greatest retentive strength with tooth preparations completed with diamond rotary instrument remained elusive. However, the difference in the smear layer was an incidental consequence o f tooth preparation with rotary instruments (Fig. 7). Panavia-EX resinous cement is claimed to adhere chemically and mechanically to tooth substance and dental alloys.17 This study indicated greater retentive values for Panavia-EX cement with different types of rotary instruments than for zinc phosphate cement, and the difference was statistically significant (p < 0.05). H o w ever, no significant difference was recorded with glass ionomer cement for tooth preparations completed with diamond rotary instruments. Moreover, Panavia-EX cement showed no significant difference in retention to dentinal surfaces prepared with different rotary instruments. The superiority of the retentive bond strength of Panavia-EX resinous cement may be attributed to the capability o f the cement to wet the involved surfaces or the actual compressive strength of the cement. CONCLUSIONS The following conclusions were drawn from this investigation. 1. Optimal retention of artificial crowns with zinc phosphate cement was recorded with tooth preparations completed with carbide burs. Cross-cut carbide burs improved retention ofcomplcte cast crowns cemented with zinc phosphate cement by 46% to 55% compared with tooth preparations completed with diamond stones or finishing burs. If finishing burs are selected to refine tooth preparations, an alternative retentive feature should be considered. 2. The rotary instrument used for tooth preparation did not have a significant difference on retentive strength of either glass ionomer cement or Panavia-EX resinous ce m e n t .

3. In this study, Panavia-EX resinous cement provided greater tensile resistance to dislodgment of the casting and more strength regardless o f type of instrumentation selected to finish the tooth preparations.

FEBRUARY 1997

THE J O U R N A L OF PROSTHETIC DENTISTRY

We thank Brasseler Dental Rotary Instruments, AbraSive Technology Inc., for supplying the tools and Ney Co. for supplying the cast ing alloy. Luting cements were contributed by J. Morita USA Inc., and ESPE-Premier Sales Corp. We also thank Dr. Robe~rt Seghi and Professor Emeritus Julian Woelfel for editorial suggesticns.

REFERENCES 1. Dahl BL, Oilo G. Retentive properties of luting cements: an in vitro inves tigation. Dent Mater 1986;2:17-20. 2. Walls AW, McCabe JF, Murray JJ. Factors influencing the bond strength between glasspolya[kenoate (ionomer) cements and dentine! ] Oral RehabiI 1988;15:537-47. 3. Rosenstiel SF, Gegauff AG. Mixing variables of zinc phos'phate cement and their influence on the seating and retention of completle crowns. Int Prosthodont 1989;2:138-42. 4. Felton DA, Kanoy BE, White JT. The effect of surface roughness of crown preparations on retention of cemented castings. J P!rosthet Dent 1987;58:292-6. 5. Ayad MF, Rosenstiel SF. Improvement of the retention and t~arginal adap ration of extracoronal restorations [abstract]. J Dent Res 1995;74:29. 6. Juntavee N, Millstein PL. Effect of surface roughness and cement space on crown retention. J Prosthet Dent 1992;68:482-6. 7. Tjan AH, Sarkissian R. Effect of preparation finish on retention and fit of complete crowns. J Prosthet Dent 1986;56:283-8. 8. Phillips RW. Skinner's Science of dental materials. 8th ed. Philadelphia: W8 Saunders, 1982:455. 9. McComb D. Retention of castings with glass ionomer cement, l Prosthet Dent 1982;48;285-8. 10. Rosenstiel SF, Land MF, Fujimoto J. Contemporary fixed prosthodontics. 2nd ed. St Louis: Mosby, 1995:618-30. 11. Ayad MF, Rosenstiel SF, Mirfat S. Assessment of retention and marginal seating of cemented cast crowns [abstract]. J Dent Res 19916;75:50. 12. Ayad MF, Rosenstiel SF, Hassan MM. Surface roughness 0f dentin after tooth preparation with different rotary instrumentation. J 16rosthet Dent 1996; 75:122-8. 13. Rosenstiel SF, Gegauff AG. Improving the cementation of domplete cast crowns: a comparison of static and dynamic seating methods. J Am Dent Assoc 1988;117:845-8. 14. Oilo G, Jorgensen KD. The influence of surface roughness on the retentive ability of two dental luting cements. J Oral Rehabil 1978;5:377-89. 15. Witwer DJ, Storey RJ, von Fraunhofer JA. The effects of surface texture and grooving on the retention of cast crowns. J Prosthet Dent 19~36;56:421-4. 16-; Gorodovsky S, Zidan O. Retentive strength, disintegration, and marginal qu~tlity of luting cements. J Prosthet Dent 1992;68:269-74. 17. Wada T. Development of a new adhesive material and its properties in adhesive prosthodontics. 1st ed. Niimegen, the Netherlands: Eurosound Drukkerij BV, 1986:9 20. Reprint requests to: DR. STEPHENROSENSTIEL THE OHIO STATEUNIVERSITY,COLLEGEOE DENTISTRY

305 W. I2TH AVE. COLUMBUS, OH 43210-1241 Copyright © 1997 by The Editorial Council of The Journal of Prbsthetic Den tistry. 0022-3913/97/$5.00 + 0. 10/1/79107

121