- Email: [email protected]
Silane to enhance the bond between polymethyl methacrylate and titanium
S i l a n e to e n h a n c e the bond b e t w e e n p o l y m e t h y l m e t h a c r y l a t e and t i t a n i u m Kenneth Michael
B. May, DDS, MS, a Jalani Fox, b E. Razzoog, DDS, MS, MPH, c and Brien
R. Lang, DDS,
MS d
School of Dentistry, The University of Michigan, Ann Arbor, Mich. T h e m a c h i n e d s u r f a c e o f w r o u g h t t i t a n i u m f r a m e w o r k s u s e d in i m p l a n t - s u p p o r t e d , fixed prostheses does not bond well with acrylic resin. Surface pretreatment has b e e n s u g g e s t e d to e n h a n c e t h e r e t e n t i o n o f p o l y m e t h y l m e t h a c r y l a t e to m a c h i n e d t i t a n i u m s u r f a c e s . T h i s s t u d y e v a l u a t e d a n e w b o n d i n g m a t e r i a l ( R o c a t e c ) to d e t e r m i n e i t s e f f e c t on t h e b o n d s t r e n g t h b e t w e e n t i t a n i u m a n d p o l y m e t h y l m e t h a c r y l a t e . T w e n t y r o d - s h a p e d s p e c i m e n s o f g r a d e 2 t i t a n i u m (7.6 x 0.3 cm in d i a m e t e r ) w e r e d i v i d e d i n t o t w o g r o u p s o f 10 s a m p l e s . G r o u p A r e c e i v e d no p r e t r e a t m e n t a n d g r o u p B w a s p r e t r e a t e d w i t h 1 1 0 / z m a l u m i n a air a b r a s i v e a n d the Rocatec material. Heat-cured denture base resin was processed around each t i t a n i u m s a m p l e in a c y l i n d r i c a l s h a p e a p p r o x i m a t e l y 0.9 x 1.5 cm. A S h e l l - N i e l s e n s h e a r t e s t w a s p e r f o r m e d w i t h a u n i v e r s a l t e s t i n g m a c h i n e at a c r o s s h e a d s p e e d o f 0 . 5 m m / m i n u t e to d e t e r m i n e t h e b o n d s t r e n g t h in m e g a p a s c a l s ( M P a ) . G r o u p B s p e c i m e n s ( 2 3 . 8 +_ 1 . 7 8 M P a ) h a d a s h e a r s t r e n g t h 68% g r e a t e r t h a n g r o u p A (16.1 _+ 1.61 M P a ) (p 0 . 0 0 0 1 ) . T h e r e s u l t s o f t h i s s t u d y i n d i c a t e d t h a t s u r f a c e p r e t r e a t m e n t o f g r a d e 2 t i t a n i u m w i t h 1 1 0 um a l u m i n a a i r a b r a s i v e p l u s R o c a t e c b o n d i n g m a t e r i a l s i g n i f i c a n t l y e n h a n c e s t h e s h e a r b o n d s t r e n g t h to P M M A . (J PROSTHET DENT 1 9 9 5 ; 7 3 : 4 2 8 - 3 1 . )
T
h
e
bond between the metal surface of a prosthesis framework and the polymethyl methacrylate (PMMA) base t h a t it supports has been a concern of clinicians. 14 If there is a separation between these two materials, especially at the junction referred to as the finishing line, the cracks or crazing in t h a t area m a y become a haven for microorganisms and plaque, accompanied by staining. Machined t i t a n i u m frameworks (Fig. 1) recently introduced for i m p l a n t - s u p p o r t e d prostheses have demonstrated bonding problems between the machined surface and P M M A . 5 Obviously, any p r e t r e a t m e n t of the framework t h a t prevents debonding would be a significant improvem e n t in a service environment. 6 In an earlier report t h a t examined the bond strength of P M M A to titanium, M a y et al. 7 found that titanium, when p r e t r e a t e d with 110 ~m alumina air abrasive followed by Silicoat S material (clear) (Kulzer and Co., GmbH, Dental,
Study supported by Nobelpharma AB, Inc. This article was derived from a poster presentation at the 72nd general session exhibition of the International Association of Dental Research, Seattle, Wash., March 1994. aAssistant Professor, Department of Prosthodontics. bSummer Research Assistant, Department of Prosthodontics. CAssociate Professor, Department of Prosthodontics. dprofessor and Chair, Department of Prosthodontics. Copyright 1995 | by The Editorial Council of THE JOURNALOF PROSTHETIC DENTISTRY. 0022-3913/95/$3.00 + O. 1 0 / 1 / 6 3 1 0 7
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THE J O U R N A L OF PROSTHETIC DENTISTRY
Friedrichshorf, Germany), had a 60 % increase in the shear bond strength between the t i t a n i u m and the heat-cured P M M A . Recently, Guggenberger 9 reported t h a t Rocatec material (ESPE, G m b H & Co., Seefeld/Oberbay, Germany), a surface p r e t r e a t m e n t bonding agent, increased the shear bond strength between P M M A and the surface of a cast alloy. Rocatec bonding agent was applied to the alloy surface as a thin layer in three steps. 6 In the first step, Rocatec-Pre abrasive cleanser was used to create a m a t t e finish on the alloy surface. An adhesive bonding material (Rocatec-Plus) was then applied as a thin coating on the surface of the alloy to provide a chemically reactive surface. Finally, a silane coupling agent (Rocatec-Sil), a silicium organic adhesive mediator with functional methacrylic groups, was applied to provide the bond with veneering materials such as PMMA. The Rocatec system has been suggested as a method that may eliminate the debonding problem experienced with machined t i t a n i u m castings. This investigation was initiated to test the null hypothesis t h a t there is no difference in shear bond strength between P M M A and untreated titanium or t i t a n i u m treated with 110 #m alumina air abrasive and the Rocatec (clear) system. METHODS
AND
MATERIAL
Twenty grade 2 titanium rods, 7.6 x 0.3 cm in diameter, were divided into two groups of 10 samples each. An area of approximately 1 cm was isolated at one end of each rod for testing the bond strength of heat-processed PMMA. Pink baseplate wax was applied to the test area on 10 of the rods in a symmetric cylinder shape 1.2 x 1.7 cm in diam-
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THE J O U R N A L OF P R O S T H E T I C D E N T I S T R Y
F i g . 1. Example of i m p l a n t - s u p p o r t e d machined titanium framework.
F i g . 2. Packing P M M A and Rocatec bonding m a t e r i a l - t r e a t e d titanium rod in denture flask. eter. The 10 rods with the wax p a t t e r n were invested in five denture flasks with two specimens per flask. After flasking, the wax was removed in boiling water. This procedure provided molds for processing acrylic resin to all test specimens. T h e rods were grouped for testing according to surface pretreatments. Group A received no treatment, and group B was p r e t r e a t e d with 110 ttm alumina air abrasive plus the Rocatec (clear) material. T h e bond strengths were evaluated in an earlier study by use of air abrasive and P M M A ,
MAY 1995
and no significant differences were found between the bond shear strength for titanium and P M M A when treated or not treated with air abrasive. 7 T h e air abrasive t r e a t m e n t (60 psi for 2 minutes per specimen) was uniformly applied to the i cm area test site on each rod. All Rocatec applications were applied by the same commercial dental laboratory. A heat-cured P M M A material (Lucitone CH Caulk, Milford, Del.) was processed around the titanium rods in the test site according to the manufacturer's recommendations (Fig. 2). The specimens were deflasked and cleaned,
429
THE J O U R N A L OF P R O S T H E T I C D E N T I S T R Y
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30
pretreatment, was 16.1 + 1.61 MPa. T h e values for group B, the samples p r e t r e a t e d with 110 ttm alumina air abrasive and Rocatec bonding material, were 23.8 _+ 1.78 M P a (Fig. 3). A one-way ANOVA demonstrated a significant difference in bond strength between the two groups (p 0.0001) (Table I).
25
2O
DISCUSSION a. 3E 15 10
5
0
Group A
Group B
F i g . 3. Means and s t a n d a r d deviations, group A, no treatment; group B, p r e t r e a t m e n t with 110 ttm alumina-air abrasive plus Rocatec bonding material (Significant difference at p 0.01.)
and the acrylic resin was finished with a Levin jeweler's lathe to create a 0.9 • 1.5 cm cylindrical shape. A digital dial gauge was used to measure the dimensions of all of the specimens and to ensure consistency in the contact area between the metal and the acrylic resin. The specimens were stored in distilled water between processing and investing procedures and ~vere removed from the water storage only for finishing procedures. Each specimen was k e p t in water storage for a m i n i m u m of 24 hours before the specimens were invested in die stone. The remaining exposed metal of each rod specimen was invested in die stone to support the samples during shear testing. To minimize any influence of the die stone on the shear values, a thin coat of pink baseplate wax was applied to the exposed metal parts of the rods before they were invested in die stone. T h e invested specimens were allowed to stand at room t e m p e r a t u r e for 24 hours before testing. The Shell-Nielsen 1~ shear test was performed by use of a universal testing machine (Instron Corp., Canton, Mass.). The specimens were loaded at a crosshead speed of 0.5 m m / m i n u t e to determine the force in newtons (N) required to break the bond of titanium to PMMA. The bond strengths were calculated as megapascals (MPa) for each specimen. Means and s t a n d a r d deviations were calculated for each test group. The d a t a were analyzed with a one-way analysis of variance (ANOVA). The Scheffe F-test was used to compare the u n t r e a t e d group with the pretreated group at p ~ .05. II RESULTS The mean shear bond strength and standard deviation (SD) for group A, the samples t h a t did not receive
430
Commercially pure titanium and t i t a n i u m alloys are used to make frameworks for implant-supported prostheses (Fig. 1). Failure of the bond at the P M M A - t i t a n i u m interface can result in prosthetic failures and create spaces between the metal and P M M A where oral debris, microorganisms, and stains can accumulate. 2' 3 A poor bond between a titanium framework and P M M A may compromise the quality of the prosthesis and potentially place patients at risk for infection from opportunistic microorganisms. In this study, the bond strength of P M M A bonded to chemically pure grade 2 titanium that was pretreated with Rocatec was evaluated for the purpose of enhancing the bond between these two prosthodontic materials. The mean shear bond strength of P M M A bonded to tit a n i u m in the untreated group was 16.1 _+ 1.61 M P a and was significantly lower t h a n the mean shear bond strength of the Rocatec group (23.8 + 1.78 MPa). Titanium pret r e a t e d with alumina air abrasive and Rocatec bonding material produced a mean shear bond strength that was 7.7 M P a higher than the mean of the untreated group. This 68% increase in mean shear bond strength represents a considerable improvement in the bond between these two materials (Fig. 3). Rocatec appears to be a hybrid bonding system t h a t uses m e c h a n i c a l (embedded silane) and chemical (reactive groups and methacrylic groups) retention mechanisms t h a t function together to enhance retention of the veneering materials. Each step in the Rocatec system is exacting and requires specific protocols; however, they can be learned easily. The use of various opaquing materials with Rocatec bonding material and the possibility of an adverse effect on bonding still should be investigated. Other factors t h a t could influence the bond, such as variations in the surface morphology of the framework and the thickness of the Rocatec material, also need to be studied. In addition, it would be of interest to know where the failure occurs, between the metal and the Rocatec material or the P M M A and the Rocatec material. These variables will be addressed in future studies. CLINICAL
IMPLICATIONS
This study d e m o n s t r a t e d t h a t premachined substructures fabricated from chemically pure grade 2 titanium t h a t received a surface p r e t r e a t m e n t consisting of 110 #m alumina air abrasive plus Rocatec bonding material will withstand higher shear forces at the t i t a n i u m - t o - P M M A interface than will u n t r e a t e d substructures.
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THE JOURNAL OF PROSTHETIC DENTISTRY
T a b l e I. O n e - w a y A N O V A o f t e s t g r o u p s A a n d B Source
DF
Sum square
Mean square
F-test
P-value
Between Within Total
1 18 19
293.301 51.845 345.146
293.301 2.880
101.832
0.0001 *
9Significant at level of p < 0.01.
CONCLUSIONS
1. S i g n i f i c a n t d i f f e r e n c e s in s h e a r b o n d s t r e n g t h w e r e d e m o n s t r a t e d w h e n t e s t s p e c i m e n s were t r e a t e d w i t h R o c a t e c b o n d i n g m a t e r i a l ; h e n c e , t h e null h y p o t h e s i s m u s t be r e j e c t e d . 2. T h e m e a n s h e a r b o n d s t r e n g t h b e t w e e n t i t a n i u m a n d P M M A was 23.8 M P a w h e n t r e a t e d w i t h t h e R o c a t e c syst e m (group B), c o m p a r e d w i t h t h e m e a n s h e a r b o n d s t r e n g t h o f 16.1 M P a for t h e u n t r e a t e d t i t a n i u m surface (group A). 3. S u r f a c e p r e t r e a t m e n t o f g r a d e - 2 w r o u g h t t i t a n i u m alloy w i t h 110 ~ m a l u m i n a air a b r a s i v e a n d R o c a t e c b o n d ing m a t e r i a l i n c r e a s e d t h e b o n d s h e a r s t r e n g t h b y 68% w h e n t h e s u r f a c e was v e n e e r e d w i t h c o n v e n t i o n a l h e a t - a c tivated PMMA.
This study was supported by Nobelpharma AB, Inc. Travel support was provided through a Faculty Grant Award from the Office of the Vice Provost for Academic and Multicultural Affairs, The University of Michigan. A special thanks to Dr. John Wataha for his assistance in setting up the statistical analysis of the research data; also, Dr. Warren Wagner and Mr. Edward Dootz in the department of Biologic and Material Sciences for their assistance in the design of the research project. A special thanks to Dr. Valerie Lee for her assistance in the preparation of the manuscript.
MAY 1995
REFERENCES
1. McCracken WL. Denture bases and stress breakers. Partial denture construction. 2nd ed. ,qt Louis: CV Mosby, 1964:218-37. 2. Craig RG. Prosthetic application of polymers. Restorative dental materials. 8th ed. St Louis: CV Mosby, 1989:509-59. 3. Jacobson TE. The significance of adhesive denture base resin. Int J Prosthodont 1989;2:163-72. 4. Krol AJ, Jacobson TE, Finzen FC. Denture base design. Removable partial denture design. Outline syllabus. 4th ed. San Rafael: Indent 1990;107-11. 5. Jemt T, Linden B. Fixed implant-supported prostheses with welded titanium frameworks. Int J Periodont Rest Dent 1992;12:177-83-4. 6. Rocatec-System. Information for use. Seefeld/Oberbay, Germany: ESPE, Fabrik pharmazeutischer Praparate GmbH & Co. 7. May KB, Russell MM, Razzoog ME, Lang BR. The shear strength of polymethyl methacrylate bonded to titanium partial denture framework material. J PROSTHETDENT 1993;70:410-3. 8. Silicoater. Technique and operating instructions. Hamburg, Germany: Kulzer & Co. 9. Guggenberger R. Rocatec system--adhesionby tribochemical coating. Dtsch Zahnarztl Z 1989;44:874-6. 10. Shell JS, Nielsen JP. Study of the bond between gold alloys and porcelain. J Dent Res 1962;44:1424-37. ll. Feldman D, Gagnon J, Hofmann R, Simpson J. Interactive statistics and graphics package. Abacus Concepts Inc. Calabasas, Calif."Brain Power Publishing Inc., 1986. Reprint requests to:
DR. KENNETHB. MAY DEPARTMENTOF PROSTHDONTICS SCHOOLOF DENTISTRY UNIVERSITYOF MICHIGAN ANN ARBOR,MI 48109-1078
431
B. May, DDS, MS, a Jalani Fox, b E. Razzoog, DDS, MS, MPH, c and Brien
R. Lang, DDS,
MS d
School of Dentistry, The University of Michigan, Ann Arbor, Mich. T h e m a c h i n e d s u r f a c e o f w r o u g h t t i t a n i u m f r a m e w o r k s u s e d in i m p l a n t - s u p p o r t e d , fixed prostheses does not bond well with acrylic resin. Surface pretreatment has b e e n s u g g e s t e d to e n h a n c e t h e r e t e n t i o n o f p o l y m e t h y l m e t h a c r y l a t e to m a c h i n e d t i t a n i u m s u r f a c e s . T h i s s t u d y e v a l u a t e d a n e w b o n d i n g m a t e r i a l ( R o c a t e c ) to d e t e r m i n e i t s e f f e c t on t h e b o n d s t r e n g t h b e t w e e n t i t a n i u m a n d p o l y m e t h y l m e t h a c r y l a t e . T w e n t y r o d - s h a p e d s p e c i m e n s o f g r a d e 2 t i t a n i u m (7.6 x 0.3 cm in d i a m e t e r ) w e r e d i v i d e d i n t o t w o g r o u p s o f 10 s a m p l e s . G r o u p A r e c e i v e d no p r e t r e a t m e n t a n d g r o u p B w a s p r e t r e a t e d w i t h 1 1 0 / z m a l u m i n a air a b r a s i v e a n d the Rocatec material. Heat-cured denture base resin was processed around each t i t a n i u m s a m p l e in a c y l i n d r i c a l s h a p e a p p r o x i m a t e l y 0.9 x 1.5 cm. A S h e l l - N i e l s e n s h e a r t e s t w a s p e r f o r m e d w i t h a u n i v e r s a l t e s t i n g m a c h i n e at a c r o s s h e a d s p e e d o f 0 . 5 m m / m i n u t e to d e t e r m i n e t h e b o n d s t r e n g t h in m e g a p a s c a l s ( M P a ) . G r o u p B s p e c i m e n s ( 2 3 . 8 +_ 1 . 7 8 M P a ) h a d a s h e a r s t r e n g t h 68% g r e a t e r t h a n g r o u p A (16.1 _+ 1.61 M P a ) (p 0 . 0 0 0 1 ) . T h e r e s u l t s o f t h i s s t u d y i n d i c a t e d t h a t s u r f a c e p r e t r e a t m e n t o f g r a d e 2 t i t a n i u m w i t h 1 1 0 um a l u m i n a a i r a b r a s i v e p l u s R o c a t e c b o n d i n g m a t e r i a l s i g n i f i c a n t l y e n h a n c e s t h e s h e a r b o n d s t r e n g t h to P M M A . (J PROSTHET DENT 1 9 9 5 ; 7 3 : 4 2 8 - 3 1 . )
T
h
e
bond between the metal surface of a prosthesis framework and the polymethyl methacrylate (PMMA) base t h a t it supports has been a concern of clinicians. 14 If there is a separation between these two materials, especially at the junction referred to as the finishing line, the cracks or crazing in t h a t area m a y become a haven for microorganisms and plaque, accompanied by staining. Machined t i t a n i u m frameworks (Fig. 1) recently introduced for i m p l a n t - s u p p o r t e d prostheses have demonstrated bonding problems between the machined surface and P M M A . 5 Obviously, any p r e t r e a t m e n t of the framework t h a t prevents debonding would be a significant improvem e n t in a service environment. 6 In an earlier report t h a t examined the bond strength of P M M A to titanium, M a y et al. 7 found that titanium, when p r e t r e a t e d with 110 ~m alumina air abrasive followed by Silicoat S material (clear) (Kulzer and Co., GmbH, Dental,
Study supported by Nobelpharma AB, Inc. This article was derived from a poster presentation at the 72nd general session exhibition of the International Association of Dental Research, Seattle, Wash., March 1994. aAssistant Professor, Department of Prosthodontics. bSummer Research Assistant, Department of Prosthodontics. CAssociate Professor, Department of Prosthodontics. dprofessor and Chair, Department of Prosthodontics. Copyright 1995 | by The Editorial Council of THE JOURNALOF PROSTHETIC DENTISTRY. 0022-3913/95/$3.00 + O. 1 0 / 1 / 6 3 1 0 7
428
THE J O U R N A L OF PROSTHETIC DENTISTRY
Friedrichshorf, Germany), had a 60 % increase in the shear bond strength between the t i t a n i u m and the heat-cured P M M A . Recently, Guggenberger 9 reported t h a t Rocatec material (ESPE, G m b H & Co., Seefeld/Oberbay, Germany), a surface p r e t r e a t m e n t bonding agent, increased the shear bond strength between P M M A and the surface of a cast alloy. Rocatec bonding agent was applied to the alloy surface as a thin layer in three steps. 6 In the first step, Rocatec-Pre abrasive cleanser was used to create a m a t t e finish on the alloy surface. An adhesive bonding material (Rocatec-Plus) was then applied as a thin coating on the surface of the alloy to provide a chemically reactive surface. Finally, a silane coupling agent (Rocatec-Sil), a silicium organic adhesive mediator with functional methacrylic groups, was applied to provide the bond with veneering materials such as PMMA. The Rocatec system has been suggested as a method that may eliminate the debonding problem experienced with machined t i t a n i u m castings. This investigation was initiated to test the null hypothesis t h a t there is no difference in shear bond strength between P M M A and untreated titanium or t i t a n i u m treated with 110 #m alumina air abrasive and the Rocatec (clear) system. METHODS
AND
MATERIAL
Twenty grade 2 titanium rods, 7.6 x 0.3 cm in diameter, were divided into two groups of 10 samples each. An area of approximately 1 cm was isolated at one end of each rod for testing the bond strength of heat-processed PMMA. Pink baseplate wax was applied to the test area on 10 of the rods in a symmetric cylinder shape 1.2 x 1.7 cm in diam-
VOLUME 73
NUMBER 5
MAY ET AL
THE J O U R N A L OF P R O S T H E T I C D E N T I S T R Y
F i g . 1. Example of i m p l a n t - s u p p o r t e d machined titanium framework.
F i g . 2. Packing P M M A and Rocatec bonding m a t e r i a l - t r e a t e d titanium rod in denture flask. eter. The 10 rods with the wax p a t t e r n were invested in five denture flasks with two specimens per flask. After flasking, the wax was removed in boiling water. This procedure provided molds for processing acrylic resin to all test specimens. T h e rods were grouped for testing according to surface pretreatments. Group A received no treatment, and group B was p r e t r e a t e d with 110 ttm alumina air abrasive plus the Rocatec (clear) material. T h e bond strengths were evaluated in an earlier study by use of air abrasive and P M M A ,
MAY 1995
and no significant differences were found between the bond shear strength for titanium and P M M A when treated or not treated with air abrasive. 7 T h e air abrasive t r e a t m e n t (60 psi for 2 minutes per specimen) was uniformly applied to the i cm area test site on each rod. All Rocatec applications were applied by the same commercial dental laboratory. A heat-cured P M M A material (Lucitone CH Caulk, Milford, Del.) was processed around the titanium rods in the test site according to the manufacturer's recommendations (Fig. 2). The specimens were deflasked and cleaned,
429
THE J O U R N A L OF P R O S T H E T I C D E N T I S T R Y
MAY ET AL
30
pretreatment, was 16.1 + 1.61 MPa. T h e values for group B, the samples p r e t r e a t e d with 110 ttm alumina air abrasive and Rocatec bonding material, were 23.8 _+ 1.78 M P a (Fig. 3). A one-way ANOVA demonstrated a significant difference in bond strength between the two groups (p 0.0001) (Table I).
25
2O
DISCUSSION a. 3E 15 10
5
0
Group A
Group B
F i g . 3. Means and s t a n d a r d deviations, group A, no treatment; group B, p r e t r e a t m e n t with 110 ttm alumina-air abrasive plus Rocatec bonding material (Significant difference at p 0.01.)
and the acrylic resin was finished with a Levin jeweler's lathe to create a 0.9 • 1.5 cm cylindrical shape. A digital dial gauge was used to measure the dimensions of all of the specimens and to ensure consistency in the contact area between the metal and the acrylic resin. The specimens were stored in distilled water between processing and investing procedures and ~vere removed from the water storage only for finishing procedures. Each specimen was k e p t in water storage for a m i n i m u m of 24 hours before the specimens were invested in die stone. The remaining exposed metal of each rod specimen was invested in die stone to support the samples during shear testing. To minimize any influence of the die stone on the shear values, a thin coat of pink baseplate wax was applied to the exposed metal parts of the rods before they were invested in die stone. T h e invested specimens were allowed to stand at room t e m p e r a t u r e for 24 hours before testing. The Shell-Nielsen 1~ shear test was performed by use of a universal testing machine (Instron Corp., Canton, Mass.). The specimens were loaded at a crosshead speed of 0.5 m m / m i n u t e to determine the force in newtons (N) required to break the bond of titanium to PMMA. The bond strengths were calculated as megapascals (MPa) for each specimen. Means and s t a n d a r d deviations were calculated for each test group. The d a t a were analyzed with a one-way analysis of variance (ANOVA). The Scheffe F-test was used to compare the u n t r e a t e d group with the pretreated group at p ~ .05. II RESULTS The mean shear bond strength and standard deviation (SD) for group A, the samples t h a t did not receive
430
Commercially pure titanium and t i t a n i u m alloys are used to make frameworks for implant-supported prostheses (Fig. 1). Failure of the bond at the P M M A - t i t a n i u m interface can result in prosthetic failures and create spaces between the metal and P M M A where oral debris, microorganisms, and stains can accumulate. 2' 3 A poor bond between a titanium framework and P M M A may compromise the quality of the prosthesis and potentially place patients at risk for infection from opportunistic microorganisms. In this study, the bond strength of P M M A bonded to chemically pure grade 2 titanium that was pretreated with Rocatec was evaluated for the purpose of enhancing the bond between these two prosthodontic materials. The mean shear bond strength of P M M A bonded to tit a n i u m in the untreated group was 16.1 _+ 1.61 M P a and was significantly lower t h a n the mean shear bond strength of the Rocatec group (23.8 + 1.78 MPa). Titanium pret r e a t e d with alumina air abrasive and Rocatec bonding material produced a mean shear bond strength that was 7.7 M P a higher than the mean of the untreated group. This 68% increase in mean shear bond strength represents a considerable improvement in the bond between these two materials (Fig. 3). Rocatec appears to be a hybrid bonding system t h a t uses m e c h a n i c a l (embedded silane) and chemical (reactive groups and methacrylic groups) retention mechanisms t h a t function together to enhance retention of the veneering materials. Each step in the Rocatec system is exacting and requires specific protocols; however, they can be learned easily. The use of various opaquing materials with Rocatec bonding material and the possibility of an adverse effect on bonding still should be investigated. Other factors t h a t could influence the bond, such as variations in the surface morphology of the framework and the thickness of the Rocatec material, also need to be studied. In addition, it would be of interest to know where the failure occurs, between the metal and the Rocatec material or the P M M A and the Rocatec material. These variables will be addressed in future studies. CLINICAL
IMPLICATIONS
This study d e m o n s t r a t e d t h a t premachined substructures fabricated from chemically pure grade 2 titanium t h a t received a surface p r e t r e a t m e n t consisting of 110 #m alumina air abrasive plus Rocatec bonding material will withstand higher shear forces at the t i t a n i u m - t o - P M M A interface than will u n t r e a t e d substructures.
VOLUME 73
NUMBER 5
MAY ET AL
THE JOURNAL OF PROSTHETIC DENTISTRY
T a b l e I. O n e - w a y A N O V A o f t e s t g r o u p s A a n d B Source
DF
Sum square
Mean square
F-test
P-value
Between Within Total
1 18 19
293.301 51.845 345.146
293.301 2.880
101.832
0.0001 *
9Significant at level of p < 0.01.
CONCLUSIONS
1. S i g n i f i c a n t d i f f e r e n c e s in s h e a r b o n d s t r e n g t h w e r e d e m o n s t r a t e d w h e n t e s t s p e c i m e n s were t r e a t e d w i t h R o c a t e c b o n d i n g m a t e r i a l ; h e n c e , t h e null h y p o t h e s i s m u s t be r e j e c t e d . 2. T h e m e a n s h e a r b o n d s t r e n g t h b e t w e e n t i t a n i u m a n d P M M A was 23.8 M P a w h e n t r e a t e d w i t h t h e R o c a t e c syst e m (group B), c o m p a r e d w i t h t h e m e a n s h e a r b o n d s t r e n g t h o f 16.1 M P a for t h e u n t r e a t e d t i t a n i u m surface (group A). 3. S u r f a c e p r e t r e a t m e n t o f g r a d e - 2 w r o u g h t t i t a n i u m alloy w i t h 110 ~ m a l u m i n a air a b r a s i v e a n d R o c a t e c b o n d ing m a t e r i a l i n c r e a s e d t h e b o n d s h e a r s t r e n g t h b y 68% w h e n t h e s u r f a c e was v e n e e r e d w i t h c o n v e n t i o n a l h e a t - a c tivated PMMA.
This study was supported by Nobelpharma AB, Inc. Travel support was provided through a Faculty Grant Award from the Office of the Vice Provost for Academic and Multicultural Affairs, The University of Michigan. A special thanks to Dr. John Wataha for his assistance in setting up the statistical analysis of the research data; also, Dr. Warren Wagner and Mr. Edward Dootz in the department of Biologic and Material Sciences for their assistance in the design of the research project. A special thanks to Dr. Valerie Lee for her assistance in the preparation of the manuscript.
MAY 1995
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DR. KENNETHB. MAY DEPARTMENTOF PROSTHDONTICS SCHOOLOF DENTISTRY UNIVERSITYOF MICHIGAN ANN ARBOR,MI 48109-1078
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