- Email: [email protected]
Relationship of surface area and to the bond strength of etched cast restorations: An in vitro study
EFFECT OF FOUR PRETREATMENT
TECHNIQUES
but not with the different pretreatments. Each metal displayed considerable variation in bond strength with each of the pretreatment techniques. Collectively, the base metal alloys evaluated displayed a disturbing tendency for adhesive failure through the porcelain-metal interface, although this was not universal. Manufacturers and ceramists should develop a specific regime for porcelain bonding for each alloy used. Standardized testing should demonstrate adequate bond strengths with cohesive failure through the body of the porcelains.
6. 7. 8.
9. IO. I I.
REFERENCES 1. Cascone PJ: The effect of thermal properties on porcelain to metal compatibility. J Dent Res 58(A):262, 1969 (Abstr No. 683). 2. Fairhurst CW, Anusavice KJ, Ringle RD, Twiggs SW: Porcelain-metal thermal compatibility. J Dent Res 60~815, 1981. 3. Anusavice KJ, Ringle RD, Morse PK, Fairhurst CW: A thermal shock test for porcelain-metal structures. J Dent Res .59(A):431, 1980 (Abstr No. 654). 4. Miller LL: Framework design in ceramo-metal restorations. Dent Clin North Am 21:4, 1977. 5. Caputo A: Effect of surface preparation on bonding strength of
12. 13.
non-precious and semi-precious alloys. ,J (:alif Dent Assor 6~42. 1978. Shell JS, Nielsen JP: Study of the bond betw em gold alloys and porcelain. J Dent Res 41:1424, 1962. Nalley JN: Chemico-physical analysis and mrcahnical test of the ceramo-metallic complex. Int Dent J 18~309. 1968. Anusavice K,J, Ringle RD, Fairhurst CW: Bonding mechanism evidence in a ceramic non-precious alloy system. J Biomed Mater Res 11:701, 1977. Baran GR: Phase changes in base metal alloys along the metal-porcelain interface. J Dent Res 58~2095, 1979. Kashiwase M: Effect of metal surface preparation on bubbles in metal ceramisn. Shikwa Gakuho 78~117I, ; ‘~78. McLean JW. Seed IE: Bonding of dental porcelain to metal. 11: The base mN:tal alloy/porcelain bond. Br r:rrnm Sot Tram 72~235, 1973 Thompson \, Simonson R, Barrack G: F,tr.hetl Cast Restorations. Chicago, 1983, Quintessence Publications Co. Warpeha WS, Goodkind RJ: Design and :echnique variables affecting fracture resistance of mrtal cerxni(~ restorations. ,J PROSTHETDENT 35:291. 1976.
Ke,hm rc’c/u’\i\ lo: DR. FERIIXXIN DAI’T~Y UNIVERSITY OF SIXTHERN
CALIFORNIA
SCHWJLOF DENTISTRY UNIVERSITY PARK MC-0641 Los I\NC;EI.ES, C.2 90089-0641
ip of surface area and B of ctvd!wd cast study Itsuki Mnrakami,
D.D.S., MS.,* and Gerald M. Barrack, D.D.S.**
New York University,
College
of Dentistry,
New York,
N.Y.
S
ince the introduction of etched cast restorations, a number of studies have been conducted regarding this treatment modality.lm9 Investigations have not focused on the roles of surface area and design parameters affecting retention, however. Incorporation of proximal extension has been recommended to (1) develop a distinct path of insertion and (2) create resistance form.4. lo.” Nevertheless, there has not
Presented before the American College of Prosthodontists meeting, Nashville, Tenn. *Lecturer, Department of Dental Materials Science; Clinical Assistant Professor, Department of Prosthodontics and Occlusion. **Clinical Professor, Department of Prosthodontics and Occlusion. THE JOURNAL
OF PROSTHETIC
DENTISTRY
ken a study conducted to assessthe contribution of the wraparound design for retention or resistance. It is essential to this study to define retention and resistance. “Retention prevents removal of the restoration alag the path of insertion OTlong axis of the tooth preparation. Resistance prevents disiodgment of the restoration by forces directed in an apical or obfque direct&m and prevents any movement of the restoration under occlusal forces.“‘2 ive retainers Lingual cusp coverage for posterioa: has been described but the contributions; of this design and the increase in surface area have not been evaluated. This study evaluated the relationship of surface area and design to retention of etched cast restorations. 539
MURAKAMI
Main groups
primary
groups
A 1
secondary
--E
AND
BARRACK
groups
Al
U
Al
L
A A2U c
A2 A2L P 1 u P 1 PIL
P P2U P 2 -c
P2L
Fig. 1. Sample grouping.
MATERIAL
AND METHODS
Fifty-six human teeth consisting of 28 central and lateral incisors and 28 premolars were used in the study. The anterior teeth formed a main group, group A, and the premolars constituted another main group, group P. Group A was divided into two primary groups, Al and A2, and group P into groups Pl and P2. Each of the four primary groups was subdivided into two secondary groups, for example, Al into AlU and AlL. AlU contained seven maxillary teeth, and AIL consisted of seven mandibular teeth. The remainder of the primary groups (A2, Pl, and P2) were similarly treated (Fig. 1).
Tooth preparation
Fig. 2. Designs Al and A2. Fig. 3. Designs Pl and P2. Fig. 4. Wax-up with a loop.
Anterior groups. The teeth in group Al were prepared with a V-shaped cingulum rest and an esthetically designed proximal extension. Group A2 received a cingulum rest without a proximal extension and served as a control (Fig. 2). The preparation for Al was similar to type A4 described by Yamashite,13 and followed the design principles recommended by Simonsen et al.‘O The design in A2 resembled YamashitaW type A3, associated with a specific number of clinical failures. Posterior groupa. Group Pl was prepared with one rest including a proximal extension covering the lingual and proximal surfaces and served as a control. Group P2 was designed with two rests, a proximal extension, and lingual cusp coverage (Fig. 3). The rests differed from
540
removable partial denture tooth preparation they were placed with a more acute angle.‘O
because
Procedures Each tooth was embedded in a cylinder of tray acrylic resin with the long axis parallel to the cylinder. The teeth were then prepared by one dentist as described. The prepared surfaces were lubricated and wax patterns were fabricated directly on the teeth. A loop was included in the wax-up for later testing (Fig. 4). The
NOVEMBER
1986
VOLUME
56
NUMBER
5
BOND STRENGTH OF ETCHED CAST RESTORATIONS
Table I. Bonding surface area (X) and shearing force (Y) for anterior groups
-._
Specimen number Group
1
2
3
4
5
6
7
Mean
SD
cv
Al u
X Y
1.02 183
0.785 124
0.786 122
0.790 179
0.850 153t
0.870 193
0.659 101t
0.823 150.7
0.110 35.7
0.134 0.237
L
X Y
0.475 120
0.619 127
0.464 116
0.565 67
0.488 151t
0.488 97
0.422 74t
0.503 107.4
0.0666 29.9
0.132 0.279
U
X Y
0.452 123’
0.480 111
0.460 131
0.515 133
0.476 119
0.495 100
0.455 99
0.476 116.6
0.0230 13.8
0.0483
X Y
0.241 81’
0.297 63
0.239 88
0.288 111
0.286 58
0.265 49
0.241 62t
0.265 73.1
0.0252 21.4
0.0951 0.293
cv
A2
L
0.118
X = cm2, Y = lb; SD = standard deviation; CV = coefficient of variation. *Partial coronal fracture. tTotal coronal fracture below the gingival finishing line.
Table II. Bonding surface area (X) and shearing force (Y) for posterior groups Specimen number Group
1
2
3
4
5
6
7
Meitn
SD
PI U
X Y
0.586 108’
0.687 98’
0.679 93
0.703 145*
0.698 100
0.562 88
0.472 72
0.627 100.6
0.0886 22.6
0.141 0.225
L
X Y
0.560 98
0.466 94
0.489 78
0.562 88’
0.552 93’
0.497 74
0.345 75
0.496 86.7
0.0767 9.91
0.155 0.116
U
X Y
0.951 112*
0.918 235*
1.03 203*
1.08 144
0.878 103
1.01 103
0.928 193t
0.971 156.1
0.0714 54.0
0.0735 0.346
L
X Y
0.517 117t
0.588 169t
0.528 163
0.508 108
0.585 114
0.541 110
0.519 136
0.541 131.0
0.0328 25.7
0.0606 0.196
P2
X = cm*; Y = lb; SD = standard deviation; CV = coefficient of variation. *Partial coronal fracture. +Total coronal fracture below the gingival finishing line.
patterns were invested in a phosphate-bondedinvesting material (High-Span, J.F. Jelenko and Co., Armonk, N.Y.), burned out in a furnace at 16OO”F,and cast in a Ni-C&e alloy (Litecast B, Williams Goid Refining Co., Buffalo, N.Y.) with an induction casting machine (Electromatic Induction Casting Machine, Howmedica, Chicago, Ill.). After the casting, the restorations were inspectedand adjwted on the teeth for fit. Surface areas of the specimenswere calculated by using lead foil.” This step was performed to assessthe appropriate currents for etching the alloy and to statistically analyze the relation-
ship of the surface area to force required to displace the h 50 restorations. The restoratio in a hrn alumina particles and solution of nine parts of 10%sulfuric acid to one part of methanol, by using a direct current power supply (Oxy-Etch, Oxy Dental, HiPside, N.J.). Currents wem regulated at 200 mA/emz, and in for 6 minutes. The restorau~nswere cleanedin an uftrasonic bath in 18%hydrochb&c acid for 5 minntos tu removethe gmssdebris, followed by 10 more minutes of eIear&ngin a fresh solution of 18%hydrochloric acid. A&qt~@ etching was establishedin the castingsby observationand a test of 541
MURAKAMI
FIRER,
N
I-
In
q
a;
Isi
a;
a
5Q.
AND
BARRACK
Is .
CM.
Fig. 5. Relationship of surface area to retention.
capillary action. lo Various castings were randomly selected and inspected under a scanning electron microscope (Super IIIA, International Scientific Instruments, Milpitas, Calif.) to verify an etched surface. Tooth enamel was etched with a 37% orthophosphoric acid for 60 seconds, rinsed in tap water for 15 seconds, and air-dried for bonding. The bonding procedures were performed by using a composite luting resin, Conclude (3M Co., St. Paul, MN). Before bonding, an unfilled resin (Concise Enamel Bond Resin, 3M Co.) was applied to the etched metal surface, and a dentin bonding agent, Scotchbond (3M Co.), was applied to the enamel to increase the wetability. The prepared specimen were stored in water at room temperature for 36 to 48 hours and subjected to tensile loading with a cross head speed of .02m/min in an Instron Universal testing machine (Instron Corp., Canton, Mass.). Before testing, a metal hook was embedded in the bottom of the acrylic resin cylinder. The testing was performed with two S-shaped hooks interposed between the grips of the Instron machine and the specimen to allow self-alignment of the specimen.
Statistical analyses The data are presented in Tables I and II and the relationship of surface area to retention is described in 542
Fig. 5. Anterior and posterior groups were analyzed separately because of the difference in geometry. Three statistical techniques were used to analyze the data.’ One-way analyses of variance (ANOVA) were performed on secondary groups. When significant differences were detected by ANOVA, Student-Newman-Keuls multiple comparisons were performed to identify them.2 Sample correlation coefficients were computed and the relationship between surface area and force was determined.3 One-way analyses of covariance (ANOCVA) were performed for the two main groups.15A confidence level of 95% was used.
RESULTS The resutls of one-way ANOVA for the bond strength are listed in Tables III and IV. In groups A and P, significant differences were evident (p < .002 for group A and p < .002 for group P).
Anterior
groups
Results of multiple comparisons (Table V) indicated that the designs with an increased surface area performed significantly better when maxillary teeth (AlU) were compared with other maxillary teeth (A2U), and mandibular teeth (AlL) with other mandibular teeth (A2L). Within the same design, AlU and A2U performed NOVEMBER
1986
VOLUME
56
NUMBER
5
BOND
STRENGTH
OF ETCHED
CAST RESTORATIONS
Table III. Analysis of variance for anterior groups (unit: pound)
Table V. Multi.ple comparisons for anterior groups (unit: pound)
Source of variation
df
SS
MS
F
A2L
AIL
A2U
AlU
Treatment Error Total
3 24 27
21353.3 16913.7 38267.0
7117.75 704.738
10.0999
73.1
107.4
116.6
150.7
SE = 10.0; line indicates nonsignificance
p < .0002
Table VI. Multiple comparisons for posterior groups (unit: pound)
Table IV. Analysis of variance for posterior groups (unit: pound) Source of variation
df
SS
MS
F
Treatment Error Total
3 24 27
20786.4 25122.0 45908.4
6928.81 1046.75
6.6194
significantly better than their mandibular counterparts, and A2L.
Posterior groups Maxillary and mandibular teeth with lingual cusp coverage exhibited significantly higher values (P2U > PlU; P2L > P2L). Results of multiple comparisons are exhibited in Table VI. Within the same design, however, differences between maxillary and mandibular teeth (PIU versus PlL; P2U versus P2L) were not statistically significant. Correlation coefficients were computed for eight secondary groups, four primary groups, two main groups, and the entire sample. The groups were then tested (Tables VII and VIII). Although the secondary groups did not display linearity, the primary groups, except P2, exhibited significant linearity. With group A, group P, and the combination of groups A and P, significant linearity was observed at 99.9% confidence level. Although graphical appearances of best-fit regression lines varied considerably within secondary groups, group A, group P, and the entire sample resembled one another.
Analysis of covariance Primary groups in group A and in group P were subjected to an analysis of covariance that takes into account variations in surface area. Results from the covariant analysis in Tables IX and X indicated that in groups Al and A2 the adjusted means were equal. The adjusted mean of 137 lb for groups P2 was significantly greater than group Pl, 99.8 lb, at the surface area of 0.756 cm2 (P2) and 0.561 cm* (Pl).
DISCUSSION The fracture of human teeth presented a problem that was encountered by H&gins et a1.16Partial fractures THE JOURNAL
PlU
P2L
P2U
85.7
100.6
131.0
156.1
SE = 12.2; lines indicate nonsignificance
p < ,002
AlL
PlL
OF PROSTHETIC
DENTISTRY
observed in group A occurred within the incisal third of the tooth crown. However, in group P2, the typical partial fracture was restricted to the lingual cusp, A total fracture was defined as occurring below the gingival finishing line of .the preparation (Tables I and II). This factor needs to be addressed in future research, because etched cast restorations require human teeth rather than metal dies. Results of statistical analyses denote several points. A proximal extension design for anterior teeth proved more advantageous for maxillary and mandibuztlr teeth alike. The mean from group AlL, 73.1 lb, the lowest in group A, was higher than the mean of 57.6 lb for three-quarter crowns with incisal and proximal grooves reported by Lorey and Myers,14 who used metal dies for the testing. The design for premolars with iingual cusp coverage was more retentive in maxillary and mandibular teeth. The mean exhibited by the group of maxillary premolars with lingual cusp coverage was 156.1 lb. Conversely, Potts et al.” reported a mean of 92 lb for premolar three-quarter corwns using metal dies. Other investigators who used human molars reported mean forcesof 70 lb,18 81.6 lb19 and 112 lbzOto displace complete crowns. The larger the surface area, the greater the retention,‘4* 21 evidenced by the equation, Y = 115 + 128(X - 0.588), through the regression analysis of 56 specimens. However, the total intraoral force in pounds associated with a particular design is the primary factor. Increased surface area has been shown to predictably contribute to retention; therefore perforated retainers would not be desirable, because of compromised retention. How much force can a restoration tolerate? Howell and Manly22 reported the highest mean oral forces of 54 lb for maxillary incisors and 103 lb for maxillary premolars. Most of the specimens in this study tolerated 543
MURAKAMI
AND
BARRACK
Table VII. Test of linearity for secondary groups Y Y Y Y Y Y Y Y
AIU AIL A2U A2L PlU PIL P2U P2L
= = = = = = = =
150.7 107.4 116.6 73.1 100.6 86.7 156.1 131.0
+ + + + + +
244 48.4 90.6 20.7 164 78.0 18.7 249
(X (X (X (X (X (X (X (X
-
r
P
rs = .7519 r5 = .1077 rS = .I512 rS = -.0244 r) = .6433 rS = .6040 rS = -.0247 rs = .3054
>.05 >.05 >.05 >.05 >.05 >.05 >.05 >.05
Range of X
Regression line*
Group
0.659 0.422 0.452 0.239 0.472 0.345 0.878 0.508
0.823) 0.503) 0.476) 0.265) 0.627) 0.496) 0.971) 0.541)
5 5 5 5 5 5 5 5
X X X X X X X X
5 5 5 5 5 c 5 5
1.02 0.619 0.515 0.297 0.703 0.562 1.08 0.588
X = cm2; Y = lb; r = correlation coefficient. *A total line.”
Table VIII. Test of linearity for primary groups, main groups, and the entire sample Regression line*
Group Y Y Y Y Y Y Y
Al A2 PI P2 A P A+P
= = = = = = =
129 94.9 93.1 144 112 118 115
+ + + + + + +
192 29.8 128 28.0 161 68.0 128
(X (X (X (X (X (X (X
-
r
Range of X
0.663) 0.371) 0.561) 0.756) 0.517) 0.659) 0.588)
0.422 0.239 0.345 0.508 0.239 0.345 0.239
5 5 5 c 5 5 5
X X x X X X X
5 5 5 5 5 5 5
r12 = rlI = rll = rlz = rzh = rz6 = rS4=
1.02 0.515 0.703 1.08 1.02 1.08 1.08
P <.Ol <.Ol CO1 >.05 COO1 <.OOl <.OOl
.7129 .7809 .6886 .3054 .7862 .5577 .6557
X = cmz; Y = lb; r = correlation coeffkient. *A common line.lz
Table IX. Analysis of covariance for anterior groups (unit: pound*): Al vs. A2 Source of variation Equality of adjusted means Zero slope Error Equality of slopes Error
df
ss
MS
F
D
1 1 25 1 24
583.199 16040.1 14032.6 310.318 13772.2
583.199 16040.1 561.304 310.318 571.760
1.0390 28.5765
> .3100 <.OOOl
.5427
> .4600
[Adjusted mean] (unit: pound) Group
N
Group mean
Adjusted mean
Standard error
Al A2
14 14
129.1 94.9
105.6 118.4
7.71 7.71
Table X. Analysis of covariance for posterior groups (unit: pound*): I?1 vs. P2 Source of variation Equality of adjusted means Zero slope Error Equality of slopes Error
df
ss
MS
F
P
1 1 25 1 24
7338.34 3817.10 24290.0 492.374 23797.7
7338.34 3817.10 971.602 492.374 991.570
7.5528 3.9287
< .0111 > .0580
0.4966
> .4800
[Adjusted mean] (unit: pound)
544
Group
N
Group mean
Adjusted mean
Standard error
Pl P2
14 14
93.1 143.6
99.8 137.0
8.97 8.97
NOVEMBER
1986
VOLUME
56
NUMBER
5
BOND
STRENGTH
OF ETCHED
CAST RESTORATIONS
these limits. Since the experiments were performed under ideal conditions, which is not always possible, it is necessary to exhaust all measures to attain maximum retention. Major variables determining the successof etched cast restorations are (1) surface area, (2) quality of enameletching and moisture control, (3) quality of alloyetching, and (4) accuracy of fit of a casting. Clinical and laboratory procedures can control the variables for a successful etched cast restoration. Certain aspects of an etched cast restoration still remain unexplored. Although wraparound or proximal extension has been purported to enhance resistance,” it ,was not the intent of this study to prove or disprove it. The effects of circumference (wraparound), grooves, or both, on resistance would be subject for future research.
CONCLUSIONS
REFERENCES
2.
Rochette AL: Attachment of a splint to enamel of lower anterior teeth. J PRCXSTHET DENT 30~418, 1973. Howe DF, Denehy GE: Anterior fixed partial dentures utilizing the acid-etch technique and a cast metal framework. J PROSTHET DENT 37:28,
1977.
3. Thompson VP, Livaditis GJ, Del-Castillo E: Resin bond to electrolytically etched nonprecious alloys for resin-bonded prosthesis. J Dent Res (Spec. Issue A); 1981 (Abstr No. 265). 4. Livaditis GJ, Thompson VP: Ethced casting: An improved retentive mechanism for resin-bonded retainers. J PROSTHET DENT 47:52,
5.
1982.
Eshleman JR, Moon PC, Douglas HB, Stall M: Retentive strength of acid-etched fixed prosthesis. J Dent Res 60:349,1981 (Abstr No. 153).
THE JOURNAL
OF ‘PROSTHETIC
7.
DENTISTRY
Williams VD, Den&y GE, Thayer KE, Boyer DB: Acid-etch retained cast metal prostheses: A seven year retrospective study. J Am Dent Assoc 10&629, 1984. Eshleman JR, Moon PC, Barnes RF: Clinical evaluation of cast metal resin-bonded anterior fixed partial dentures. J PROSTHET DENT 5:761,
8.
9. 10.
11.
12.
13. 14.
The findings of this study suggested the following: 1. A design with proximal coverage for incisors provided a significant advantage because of increased surface area. 2. Lingual cusp coverage for premolars enhanced the bond strength significantly with the combined effect of increased surface area and improved design. 3. A linear relationship exists between the surface area and the force required to displace specimens. 1.
6.
15. 16. 17.
1984.
Meiers JC, Jensen ME, May&n T: Effect of surface treatments on the bond strength of etched-metal resin-bonded retainers. J PROSTHET DEIVT 53~185, 1985. Love CD, Breitman JB: Resin retention by immersion-etched alloy. J PROSIHET DENT 53~623, 1985. Simonsen R, Thompson VP, Barrack GM: Etched Cast Restorations: Clinical and Laboratory Techniques. Chicago, 1983, Quintessence Pub1 Co. Wood M, Thompson VP: Anterior etched cast resin-bonded retainers: An overview of design, fabrication and clinical use. Compendium Cont Ed Dent 4~3, 1983. Shillingburg Jr HT, Hobo S, Whitsett LD: Fundamentals of Fixed Prosthodontics, ed 2. Chicago, 1981, Quintessense Pub1 co, p 79. Yamashita A: A Dental Adhesive and Its Clinical Applications. Tokyo, 1983, Quintessence Pub1 Co, pp 86-91 (in Japanese). Lorey RE, Myers GE: The retentive qualities of bridge retainers. J Am Dent Assoc 76~568, 1968. Snedecor GW, Cochran WG: Statistical Methods, ed 7. Ames, Iowa, 1980, Iowa State Univ Press, pp 185, and 369. Hudgins JL, Moon PC, Knap RF: Particle-roughened resinbonded retainers. J PR~~THET DENT 53471, 1985. Potts RG, Shillingburg Jr HT, Duncanson MG: Retention and resistance of preparations for cast restorations. J PROSTHET DENT 43~303, 1980.
Eames WB, G’Neal SJ, Monteiro J, Miller C, Roan Jr JD, Cohen KS: Techniques to improve the seatings of castings. J Am Dent Assoc %432, 1978. 19. Vermilyea SG, Kuffler MJ, Huget EF: The effects of die relief agent on the retention of full coverage castings. J PWSTHET
18.
DENT 50~207, 1983.
20. 21.
22.
Hembree Jr J:H, Cooper Jr EW: Effects of die relief on retention of cast crowns and inlays. J Oper Dent 4:104, 1979. Kaufman EG, Coelho DH, Colin L: Factors influencing the retention of cemented gold castings. J PROSTHET DENT 11:487, 1961. Howell HA, Manly RS: An electronic strain gauge for measuring oral forces. J Dent Res 27:705, 1948.
Refirint requests to: DR. GERALD M. BARRACK NEW YORK UNIVERSITY COLLFASE OF DENTISTRY NEW YORK, NY 10010
545
TECHNIQUES
but not with the different pretreatments. Each metal displayed considerable variation in bond strength with each of the pretreatment techniques. Collectively, the base metal alloys evaluated displayed a disturbing tendency for adhesive failure through the porcelain-metal interface, although this was not universal. Manufacturers and ceramists should develop a specific regime for porcelain bonding for each alloy used. Standardized testing should demonstrate adequate bond strengths with cohesive failure through the body of the porcelains.
6. 7. 8.
9. IO. I I.
REFERENCES 1. Cascone PJ: The effect of thermal properties on porcelain to metal compatibility. J Dent Res 58(A):262, 1969 (Abstr No. 683). 2. Fairhurst CW, Anusavice KJ, Ringle RD, Twiggs SW: Porcelain-metal thermal compatibility. J Dent Res 60~815, 1981. 3. Anusavice KJ, Ringle RD, Morse PK, Fairhurst CW: A thermal shock test for porcelain-metal structures. J Dent Res .59(A):431, 1980 (Abstr No. 654). 4. Miller LL: Framework design in ceramo-metal restorations. Dent Clin North Am 21:4, 1977. 5. Caputo A: Effect of surface preparation on bonding strength of
12. 13.
non-precious and semi-precious alloys. ,J (:alif Dent Assor 6~42. 1978. Shell JS, Nielsen JP: Study of the bond betw em gold alloys and porcelain. J Dent Res 41:1424, 1962. Nalley JN: Chemico-physical analysis and mrcahnical test of the ceramo-metallic complex. Int Dent J 18~309. 1968. Anusavice K,J, Ringle RD, Fairhurst CW: Bonding mechanism evidence in a ceramic non-precious alloy system. J Biomed Mater Res 11:701, 1977. Baran GR: Phase changes in base metal alloys along the metal-porcelain interface. J Dent Res 58~2095, 1979. Kashiwase M: Effect of metal surface preparation on bubbles in metal ceramisn. Shikwa Gakuho 78~117I, ; ‘~78. McLean JW. Seed IE: Bonding of dental porcelain to metal. 11: The base mN:tal alloy/porcelain bond. Br r:rrnm Sot Tram 72~235, 1973 Thompson \, Simonson R, Barrack G: F,tr.hetl Cast Restorations. Chicago, 1983, Quintessence Publications Co. Warpeha WS, Goodkind RJ: Design and :echnique variables affecting fracture resistance of mrtal cerxni(~ restorations. ,J PROSTHETDENT 35:291. 1976.
Ke,hm rc’c/u’\i\ lo: DR. FERIIXXIN DAI’T~Y UNIVERSITY OF SIXTHERN
CALIFORNIA
SCHWJLOF DENTISTRY UNIVERSITY PARK MC-0641 Los I\NC;EI.ES, C.2 90089-0641
ip of surface area and B of ctvd!wd cast study Itsuki Mnrakami,
D.D.S., MS.,* and Gerald M. Barrack, D.D.S.**
New York University,
College
of Dentistry,
New York,
N.Y.
S
ince the introduction of etched cast restorations, a number of studies have been conducted regarding this treatment modality.lm9 Investigations have not focused on the roles of surface area and design parameters affecting retention, however. Incorporation of proximal extension has been recommended to (1) develop a distinct path of insertion and (2) create resistance form.4. lo.” Nevertheless, there has not
Presented before the American College of Prosthodontists meeting, Nashville, Tenn. *Lecturer, Department of Dental Materials Science; Clinical Assistant Professor, Department of Prosthodontics and Occlusion. **Clinical Professor, Department of Prosthodontics and Occlusion. THE JOURNAL
OF PROSTHETIC
DENTISTRY
ken a study conducted to assessthe contribution of the wraparound design for retention or resistance. It is essential to this study to define retention and resistance. “Retention prevents removal of the restoration alag the path of insertion OTlong axis of the tooth preparation. Resistance prevents disiodgment of the restoration by forces directed in an apical or obfque direct&m and prevents any movement of the restoration under occlusal forces.“‘2 ive retainers Lingual cusp coverage for posterioa: has been described but the contributions; of this design and the increase in surface area have not been evaluated. This study evaluated the relationship of surface area and design to retention of etched cast restorations. 539
MURAKAMI
Main groups
primary
groups
A 1
secondary
--E
AND
BARRACK
groups
Al
U
Al
L
A A2U c
A2 A2L P 1 u P 1 PIL
P P2U P 2 -c
P2L
Fig. 1. Sample grouping.
MATERIAL
AND METHODS
Fifty-six human teeth consisting of 28 central and lateral incisors and 28 premolars were used in the study. The anterior teeth formed a main group, group A, and the premolars constituted another main group, group P. Group A was divided into two primary groups, Al and A2, and group P into groups Pl and P2. Each of the four primary groups was subdivided into two secondary groups, for example, Al into AlU and AlL. AlU contained seven maxillary teeth, and AIL consisted of seven mandibular teeth. The remainder of the primary groups (A2, Pl, and P2) were similarly treated (Fig. 1).
Tooth preparation
Fig. 2. Designs Al and A2. Fig. 3. Designs Pl and P2. Fig. 4. Wax-up with a loop.
Anterior groups. The teeth in group Al were prepared with a V-shaped cingulum rest and an esthetically designed proximal extension. Group A2 received a cingulum rest without a proximal extension and served as a control (Fig. 2). The preparation for Al was similar to type A4 described by Yamashite,13 and followed the design principles recommended by Simonsen et al.‘O The design in A2 resembled YamashitaW type A3, associated with a specific number of clinical failures. Posterior groupa. Group Pl was prepared with one rest including a proximal extension covering the lingual and proximal surfaces and served as a control. Group P2 was designed with two rests, a proximal extension, and lingual cusp coverage (Fig. 3). The rests differed from
540
removable partial denture tooth preparation they were placed with a more acute angle.‘O
because
Procedures Each tooth was embedded in a cylinder of tray acrylic resin with the long axis parallel to the cylinder. The teeth were then prepared by one dentist as described. The prepared surfaces were lubricated and wax patterns were fabricated directly on the teeth. A loop was included in the wax-up for later testing (Fig. 4). The
NOVEMBER
1986
VOLUME
56
NUMBER
5
BOND STRENGTH OF ETCHED CAST RESTORATIONS
Table I. Bonding surface area (X) and shearing force (Y) for anterior groups
-._
Specimen number Group
1
2
3
4
5
6
7
Mean
SD
cv
Al u
X Y
1.02 183
0.785 124
0.786 122
0.790 179
0.850 153t
0.870 193
0.659 101t
0.823 150.7
0.110 35.7
0.134 0.237
L
X Y
0.475 120
0.619 127
0.464 116
0.565 67
0.488 151t
0.488 97
0.422 74t
0.503 107.4
0.0666 29.9
0.132 0.279
U
X Y
0.452 123’
0.480 111
0.460 131
0.515 133
0.476 119
0.495 100
0.455 99
0.476 116.6
0.0230 13.8
0.0483
X Y
0.241 81’
0.297 63
0.239 88
0.288 111
0.286 58
0.265 49
0.241 62t
0.265 73.1
0.0252 21.4
0.0951 0.293
cv
A2
L
0.118
X = cm2, Y = lb; SD = standard deviation; CV = coefficient of variation. *Partial coronal fracture. tTotal coronal fracture below the gingival finishing line.
Table II. Bonding surface area (X) and shearing force (Y) for posterior groups Specimen number Group
1
2
3
4
5
6
7
Meitn
SD
PI U
X Y
0.586 108’
0.687 98’
0.679 93
0.703 145*
0.698 100
0.562 88
0.472 72
0.627 100.6
0.0886 22.6
0.141 0.225
L
X Y
0.560 98
0.466 94
0.489 78
0.562 88’
0.552 93’
0.497 74
0.345 75
0.496 86.7
0.0767 9.91
0.155 0.116
U
X Y
0.951 112*
0.918 235*
1.03 203*
1.08 144
0.878 103
1.01 103
0.928 193t
0.971 156.1
0.0714 54.0
0.0735 0.346
L
X Y
0.517 117t
0.588 169t
0.528 163
0.508 108
0.585 114
0.541 110
0.519 136
0.541 131.0
0.0328 25.7
0.0606 0.196
P2
X = cm*; Y = lb; SD = standard deviation; CV = coefficient of variation. *Partial coronal fracture. +Total coronal fracture below the gingival finishing line.
patterns were invested in a phosphate-bondedinvesting material (High-Span, J.F. Jelenko and Co., Armonk, N.Y.), burned out in a furnace at 16OO”F,and cast in a Ni-C&e alloy (Litecast B, Williams Goid Refining Co., Buffalo, N.Y.) with an induction casting machine (Electromatic Induction Casting Machine, Howmedica, Chicago, Ill.). After the casting, the restorations were inspectedand adjwted on the teeth for fit. Surface areas of the specimenswere calculated by using lead foil.” This step was performed to assessthe appropriate currents for etching the alloy and to statistically analyze the relation-
ship of the surface area to force required to displace the h 50 restorations. The restoratio in a hrn alumina particles and solution of nine parts of 10%sulfuric acid to one part of methanol, by using a direct current power supply (Oxy-Etch, Oxy Dental, HiPside, N.J.). Currents wem regulated at 200 mA/emz, and in for 6 minutes. The restorau~nswere cleanedin an uftrasonic bath in 18%hydrochb&c acid for 5 minntos tu removethe gmssdebris, followed by 10 more minutes of eIear&ngin a fresh solution of 18%hydrochloric acid. A&qt~@ etching was establishedin the castingsby observationand a test of 541
MURAKAMI
FIRER,
N
I-
In
q
a;
Isi
a;
a
5Q.
AND
BARRACK
Is .
CM.
Fig. 5. Relationship of surface area to retention.
capillary action. lo Various castings were randomly selected and inspected under a scanning electron microscope (Super IIIA, International Scientific Instruments, Milpitas, Calif.) to verify an etched surface. Tooth enamel was etched with a 37% orthophosphoric acid for 60 seconds, rinsed in tap water for 15 seconds, and air-dried for bonding. The bonding procedures were performed by using a composite luting resin, Conclude (3M Co., St. Paul, MN). Before bonding, an unfilled resin (Concise Enamel Bond Resin, 3M Co.) was applied to the etched metal surface, and a dentin bonding agent, Scotchbond (3M Co.), was applied to the enamel to increase the wetability. The prepared specimen were stored in water at room temperature for 36 to 48 hours and subjected to tensile loading with a cross head speed of .02m/min in an Instron Universal testing machine (Instron Corp., Canton, Mass.). Before testing, a metal hook was embedded in the bottom of the acrylic resin cylinder. The testing was performed with two S-shaped hooks interposed between the grips of the Instron machine and the specimen to allow self-alignment of the specimen.
Statistical analyses The data are presented in Tables I and II and the relationship of surface area to retention is described in 542
Fig. 5. Anterior and posterior groups were analyzed separately because of the difference in geometry. Three statistical techniques were used to analyze the data.’ One-way analyses of variance (ANOVA) were performed on secondary groups. When significant differences were detected by ANOVA, Student-Newman-Keuls multiple comparisons were performed to identify them.2 Sample correlation coefficients were computed and the relationship between surface area and force was determined.3 One-way analyses of covariance (ANOCVA) were performed for the two main groups.15A confidence level of 95% was used.
RESULTS The resutls of one-way ANOVA for the bond strength are listed in Tables III and IV. In groups A and P, significant differences were evident (p < .002 for group A and p < .002 for group P).
Anterior
groups
Results of multiple comparisons (Table V) indicated that the designs with an increased surface area performed significantly better when maxillary teeth (AlU) were compared with other maxillary teeth (A2U), and mandibular teeth (AlL) with other mandibular teeth (A2L). Within the same design, AlU and A2U performed NOVEMBER
1986
VOLUME
56
NUMBER
5
BOND
STRENGTH
OF ETCHED
CAST RESTORATIONS
Table III. Analysis of variance for anterior groups (unit: pound)
Table V. Multi.ple comparisons for anterior groups (unit: pound)
Source of variation
df
SS
MS
F
A2L
AIL
A2U
AlU
Treatment Error Total
3 24 27
21353.3 16913.7 38267.0
7117.75 704.738
10.0999
73.1
107.4
116.6
150.7
SE = 10.0; line indicates nonsignificance
p < .0002
Table VI. Multiple comparisons for posterior groups (unit: pound)
Table IV. Analysis of variance for posterior groups (unit: pound) Source of variation
df
SS
MS
F
Treatment Error Total
3 24 27
20786.4 25122.0 45908.4
6928.81 1046.75
6.6194
significantly better than their mandibular counterparts, and A2L.
Posterior groups Maxillary and mandibular teeth with lingual cusp coverage exhibited significantly higher values (P2U > PlU; P2L > P2L). Results of multiple comparisons are exhibited in Table VI. Within the same design, however, differences between maxillary and mandibular teeth (PIU versus PlL; P2U versus P2L) were not statistically significant. Correlation coefficients were computed for eight secondary groups, four primary groups, two main groups, and the entire sample. The groups were then tested (Tables VII and VIII). Although the secondary groups did not display linearity, the primary groups, except P2, exhibited significant linearity. With group A, group P, and the combination of groups A and P, significant linearity was observed at 99.9% confidence level. Although graphical appearances of best-fit regression lines varied considerably within secondary groups, group A, group P, and the entire sample resembled one another.
Analysis of covariance Primary groups in group A and in group P were subjected to an analysis of covariance that takes into account variations in surface area. Results from the covariant analysis in Tables IX and X indicated that in groups Al and A2 the adjusted means were equal. The adjusted mean of 137 lb for groups P2 was significantly greater than group Pl, 99.8 lb, at the surface area of 0.756 cm2 (P2) and 0.561 cm* (Pl).
DISCUSSION The fracture of human teeth presented a problem that was encountered by H&gins et a1.16Partial fractures THE JOURNAL
PlU
P2L
P2U
85.7
100.6
131.0
156.1
SE = 12.2; lines indicate nonsignificance
p < ,002
AlL
PlL
OF PROSTHETIC
DENTISTRY
observed in group A occurred within the incisal third of the tooth crown. However, in group P2, the typical partial fracture was restricted to the lingual cusp, A total fracture was defined as occurring below the gingival finishing line of .the preparation (Tables I and II). This factor needs to be addressed in future research, because etched cast restorations require human teeth rather than metal dies. Results of statistical analyses denote several points. A proximal extension design for anterior teeth proved more advantageous for maxillary and mandibuztlr teeth alike. The mean from group AlL, 73.1 lb, the lowest in group A, was higher than the mean of 57.6 lb for three-quarter crowns with incisal and proximal grooves reported by Lorey and Myers,14 who used metal dies for the testing. The design for premolars with iingual cusp coverage was more retentive in maxillary and mandibular teeth. The mean exhibited by the group of maxillary premolars with lingual cusp coverage was 156.1 lb. Conversely, Potts et al.” reported a mean of 92 lb for premolar three-quarter corwns using metal dies. Other investigators who used human molars reported mean forcesof 70 lb,18 81.6 lb19 and 112 lbzOto displace complete crowns. The larger the surface area, the greater the retention,‘4* 21 evidenced by the equation, Y = 115 + 128(X - 0.588), through the regression analysis of 56 specimens. However, the total intraoral force in pounds associated with a particular design is the primary factor. Increased surface area has been shown to predictably contribute to retention; therefore perforated retainers would not be desirable, because of compromised retention. How much force can a restoration tolerate? Howell and Manly22 reported the highest mean oral forces of 54 lb for maxillary incisors and 103 lb for maxillary premolars. Most of the specimens in this study tolerated 543
MURAKAMI
AND
BARRACK
Table VII. Test of linearity for secondary groups Y Y Y Y Y Y Y Y
AIU AIL A2U A2L PlU PIL P2U P2L
= = = = = = = =
150.7 107.4 116.6 73.1 100.6 86.7 156.1 131.0
+ + + + + +
244 48.4 90.6 20.7 164 78.0 18.7 249
(X (X (X (X (X (X (X (X
-
r
P
rs = .7519 r5 = .1077 rS = .I512 rS = -.0244 r) = .6433 rS = .6040 rS = -.0247 rs = .3054
>.05 >.05 >.05 >.05 >.05 >.05 >.05 >.05
Range of X
Regression line*
Group
0.659 0.422 0.452 0.239 0.472 0.345 0.878 0.508
0.823) 0.503) 0.476) 0.265) 0.627) 0.496) 0.971) 0.541)
5 5 5 5 5 5 5 5
X X X X X X X X
5 5 5 5 5 c 5 5
1.02 0.619 0.515 0.297 0.703 0.562 1.08 0.588
X = cm2; Y = lb; r = correlation coefficient. *A total line.”
Table VIII. Test of linearity for primary groups, main groups, and the entire sample Regression line*
Group Y Y Y Y Y Y Y
Al A2 PI P2 A P A+P
= = = = = = =
129 94.9 93.1 144 112 118 115
+ + + + + + +
192 29.8 128 28.0 161 68.0 128
(X (X (X (X (X (X (X
-
r
Range of X
0.663) 0.371) 0.561) 0.756) 0.517) 0.659) 0.588)
0.422 0.239 0.345 0.508 0.239 0.345 0.239
5 5 5 c 5 5 5
X X x X X X X
5 5 5 5 5 5 5
r12 = rlI = rll = rlz = rzh = rz6 = rS4=
1.02 0.515 0.703 1.08 1.02 1.08 1.08
P <.Ol <.Ol CO1 >.05 COO1 <.OOl <.OOl
.7129 .7809 .6886 .3054 .7862 .5577 .6557
X = cmz; Y = lb; r = correlation coeffkient. *A common line.lz
Table IX. Analysis of covariance for anterior groups (unit: pound*): Al vs. A2 Source of variation Equality of adjusted means Zero slope Error Equality of slopes Error
df
ss
MS
F
D
1 1 25 1 24
583.199 16040.1 14032.6 310.318 13772.2
583.199 16040.1 561.304 310.318 571.760
1.0390 28.5765
> .3100 <.OOOl
.5427
> .4600
[Adjusted mean] (unit: pound) Group
N
Group mean
Adjusted mean
Standard error
Al A2
14 14
129.1 94.9
105.6 118.4
7.71 7.71
Table X. Analysis of covariance for posterior groups (unit: pound*): I?1 vs. P2 Source of variation Equality of adjusted means Zero slope Error Equality of slopes Error
df
ss
MS
F
P
1 1 25 1 24
7338.34 3817.10 24290.0 492.374 23797.7
7338.34 3817.10 971.602 492.374 991.570
7.5528 3.9287
< .0111 > .0580
0.4966
> .4800
[Adjusted mean] (unit: pound)
544
Group
N
Group mean
Adjusted mean
Standard error
Pl P2
14 14
93.1 143.6
99.8 137.0
8.97 8.97
NOVEMBER
1986
VOLUME
56
NUMBER
5
BOND
STRENGTH
OF ETCHED
CAST RESTORATIONS
these limits. Since the experiments were performed under ideal conditions, which is not always possible, it is necessary to exhaust all measures to attain maximum retention. Major variables determining the successof etched cast restorations are (1) surface area, (2) quality of enameletching and moisture control, (3) quality of alloyetching, and (4) accuracy of fit of a casting. Clinical and laboratory procedures can control the variables for a successful etched cast restoration. Certain aspects of an etched cast restoration still remain unexplored. Although wraparound or proximal extension has been purported to enhance resistance,” it ,was not the intent of this study to prove or disprove it. The effects of circumference (wraparound), grooves, or both, on resistance would be subject for future research.
CONCLUSIONS
REFERENCES
2.
Rochette AL: Attachment of a splint to enamel of lower anterior teeth. J PRCXSTHET DENT 30~418, 1973. Howe DF, Denehy GE: Anterior fixed partial dentures utilizing the acid-etch technique and a cast metal framework. J PROSTHET DENT 37:28,
1977.
3. Thompson VP, Livaditis GJ, Del-Castillo E: Resin bond to electrolytically etched nonprecious alloys for resin-bonded prosthesis. J Dent Res (Spec. Issue A); 1981 (Abstr No. 265). 4. Livaditis GJ, Thompson VP: Ethced casting: An improved retentive mechanism for resin-bonded retainers. J PROSTHET DENT 47:52,
5.
1982.
Eshleman JR, Moon PC, Douglas HB, Stall M: Retentive strength of acid-etched fixed prosthesis. J Dent Res 60:349,1981 (Abstr No. 153).
THE JOURNAL
OF ‘PROSTHETIC
7.
DENTISTRY
Williams VD, Den&y GE, Thayer KE, Boyer DB: Acid-etch retained cast metal prostheses: A seven year retrospective study. J Am Dent Assoc 10&629, 1984. Eshleman JR, Moon PC, Barnes RF: Clinical evaluation of cast metal resin-bonded anterior fixed partial dentures. J PROSTHET DENT 5:761,
8.
9. 10.
11.
12.
13. 14.
The findings of this study suggested the following: 1. A design with proximal coverage for incisors provided a significant advantage because of increased surface area. 2. Lingual cusp coverage for premolars enhanced the bond strength significantly with the combined effect of increased surface area and improved design. 3. A linear relationship exists between the surface area and the force required to displace specimens. 1.
6.
15. 16. 17.
1984.
Meiers JC, Jensen ME, May&n T: Effect of surface treatments on the bond strength of etched-metal resin-bonded retainers. J PROSTHET DEIVT 53~185, 1985. Love CD, Breitman JB: Resin retention by immersion-etched alloy. J PROSIHET DENT 53~623, 1985. Simonsen R, Thompson VP, Barrack GM: Etched Cast Restorations: Clinical and Laboratory Techniques. Chicago, 1983, Quintessence Pub1 Co. Wood M, Thompson VP: Anterior etched cast resin-bonded retainers: An overview of design, fabrication and clinical use. Compendium Cont Ed Dent 4~3, 1983. Shillingburg Jr HT, Hobo S, Whitsett LD: Fundamentals of Fixed Prosthodontics, ed 2. Chicago, 1981, Quintessense Pub1 co, p 79. Yamashita A: A Dental Adhesive and Its Clinical Applications. Tokyo, 1983, Quintessence Pub1 Co, pp 86-91 (in Japanese). Lorey RE, Myers GE: The retentive qualities of bridge retainers. J Am Dent Assoc 76~568, 1968. Snedecor GW, Cochran WG: Statistical Methods, ed 7. Ames, Iowa, 1980, Iowa State Univ Press, pp 185, and 369. Hudgins JL, Moon PC, Knap RF: Particle-roughened resinbonded retainers. J PR~~THET DENT 53471, 1985. Potts RG, Shillingburg Jr HT, Duncanson MG: Retention and resistance of preparations for cast restorations. J PROSTHET DENT 43~303, 1980.
Eames WB, G’Neal SJ, Monteiro J, Miller C, Roan Jr JD, Cohen KS: Techniques to improve the seatings of castings. J Am Dent Assoc %432, 1978. 19. Vermilyea SG, Kuffler MJ, Huget EF: The effects of die relief agent on the retention of full coverage castings. J PWSTHET
18.
DENT 50~207, 1983.
20. 21.
22.
Hembree Jr J:H, Cooper Jr EW: Effects of die relief on retention of cast crowns and inlays. J Oper Dent 4:104, 1979. Kaufman EG, Coelho DH, Colin L: Factors influencing the retention of cemented gold castings. J PROSTHET DENT 11:487, 1961. Howell HA, Manly RS: An electronic strain gauge for measuring oral forces. J Dent Res 27:705, 1948.
Refirint requests to: DR. GERALD M. BARRACK NEW YORK UNIVERSITY COLLFASE OF DENTISTRY NEW YORK, NY 10010
545