Journal of Investigative and Clinical Dentistry (2010), 1, 144–150
ORIGINAL ARTICLE Dental Biomaterials
Effect of aluminium oxide particle sandblasting on the artificial tooth–resin bond Rafael Leonardo Xediek Consani, Marina Martorano Richter, Marcelo Ferraz Mesquita, Mario Alexandre Coelho Sinhoreti & Ricardo Danil Guiraldo Department of Prosthodontics and Periodontics, Piracicaba Dental School, State University of Campinas, Piracicaba, Brazil
Keywords acrylic resin, aluminium oxide, artificial tooth, sandblasting, shear bond strength. Correspondence Dr Rafael Leonardo Xediek Consani, State University of Campinas, Piracicaba Dental School, 902 Limeira Avenue, Piracicaba, Sa˜o Paulo, Brazil. Tel: +55-19-2106-5296 Email: [email protected] Received: 24 March 2010; accepted 13 June 2010. doi: 10.1111/j.2041-1626.2010.00027.x
Abstract Aim: The influence of tooth ridge-lap surface sandblasting with aluminium oxide particles was evaluated on the adhesion of artificial teeth to acrylic resins. Methods: Specimens were made with the acrylic resin adhered to teeth (BioCler GII), according to an unmodified surface, glossy surface sandblasted with 50-lm particles and conventional (Classico) or microwaved (Onda Cryl) resin, and a glossy surface sandblasted with 100-lm particles and Classico or Onda Cryl resin. The shear bond test was performed in an Instron machine using a 500-N load cell and cross-speed of 1 mm/min. Results: The analysis of variance revealed significant difference in the tooth– resin shear bond strength for resin, surface treatment, and interaction. For conventional resin, control, 50-, and 100-lm particles showed statistically-different values; for microwaved resin, the control showed less statistical difference when compared to 50- and 100-lm particle treatments; for between resins, only the 100-lm particle treatment showed statistically-different values, with lower values for the microwaved resin. Mixed failures (cohesive in the resin and adhesive) were predominantly observed in all groups. Mixed (cohesive in the tooth and adhesive) or adhesive failures were not observed. Conclusions: Sandblasting with different aluminium oxide particle sizes produced different effects on the shear strength values of the tooth–resin bond.
Introduction Acrylic resin teeth are widely utilized in prostheses processing because of their ability to bond chemically to the denture-base resin due to the chemical similarity of both materials.1,2 However, some studies have shown that the complete prostheses are occasionally repaired due to artificial tooth fracture or failure of the artificial tooth–resin bond,2–5 requiring a new bonding procedure or replacement of the artificial tooth. Failure in the artificial tooth–resin base bond could be caused by accidental falls, excessive stress during chewing, or mechanical fatigue. Poor laboratory technique can also prevent perfect bond of the artificial tooth to denturebase resin, causing subsequent failure. Thus, the artificial 144
tooth ridge-lap surface contaminated by wax residues can produce significantly weaker bonds.1,3,5–7 Besides wax contamination, the degree of a cross-linking monomer added to the artificial tooth and the monomer amount available on the denture-base resin during processing might affect the artificial tooth–resin bond strength.8 Increase of the bond strength between the artificial tooth and denture-base resin involves chemical treatments or mechanical changes on the artificial tooth ridge-lap surface.7,9–14 However, the literature has shown conflicting results with the use of monomers3,15–17 and chemical agents for adhesion.17,18 For the acrylic resin monomer to be effective, it is necessary that the etching treatment softens or dissolves the surface of the ridge lap of the artificial tooth.8 ª 2010 Blackwell Publishing Asia Pty Ltd
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Mechanical retentions on the artificial tooth ridge-lap surface by abrasion or grooving7,13 and aluminium oxide sandblasting11 do not show significantly different results when compared to unmodified surfaces, contrasting with studies which state that such treatments improve the bond strength.9,14,19–21 However, contradictory results reported by various researchers might be due to different methods used in different studies. Different types of artificial teeth and acrylic resins might also contribute to different results.10 The displacement of the artificial tooth from the base of the prosthesis suggests that the chemical adhesion of the artificial tooth was not enough to promote effective bonding with the base resin, or that the artificial tooth was retained on the resin base by a weak mechanical bond due to incorrect laboratory procedures.22 In light of these considerations, it is important to verify the shear bond strength of the artificial tooth–resin bond under the influence of sandblasting of the artificial tooth ridge-lap surface with aluminium oxide particles that are 50 or 100 lm in size. The hypothesis of this in vitro study would be that sandblasting with aluminium oxide particles of different sizes could promote different levels of strength of the artificial tooth–resin bond. Materials and methods Sixty wax rectangular patterns (30 mm in length, 5 mm in height, and 10 mm in width) were traditionally invested into conventional brass flasks (Safrany Metallurgy, Sa˜o Paulo, Brazil) or plastic flasks (Classico Dental Products, Sa˜o Paulo, Brazil) with a type III dental stone (Herodent; Vigodent, Rio de Janeiro, Brazil), proportioned and manipulated following the manufacturer’s recommendations. After the removal of the wax patterns, each stone mold was filled with a layer of laboratory silicone putty (Zetalabor; Zhermack, Rovigo, Italy). Identical BioCler GII P32L (model 3; DentBras Dental Products, Pirassununca, Sa˜o Paulo, Brazil) white, acrylic resin molar teeth (DentBras), with a wax stick (6-mm in diameter and 20-mm in length) attached at the ridge-lap surface, were partially included into the silicone layer, and thus covered with another layer of silicone putty (Zetalabor). After dental stone isolation with petroleum jelly, the flask was filled with type III dental stone (Herodent) and pressed in a hydraulic press (Linea H, Sa˜o Paulo, Brazil) for 1 h. After deflasking, the wax stick was removed from the ridge-lap surface; the artificial tooth was brushed with a solution of liquid detergent (Bombril-Cirio, Sa˜o Paulo, Brazil) to eliminate the wax residues, and rinsed with tap water at room temperature. Samples (Figure 1) were made with the artificial tooth ridge-lap surface attached ª 2010 Blackwell Publishing Asia Pty Ltd
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Figure 1. Specimen for artificial tooth–acrylic resin bonding test.
to the acrylic resin, proportioned and manipulated according to the manufacturer’s instructions, and using the following procedures: (a) unmodified artificial tooth ridge-lap surface; (b) glossy ridge lap sandblasted with 50-lm aluminium oxide particles and Classico resin; (c) glossy ridge lap sandblasted with 100-lm aluminium oxide particles and Classico resin; (d) glossy ridge lap sandblasted with 50-lm aluminium oxide particles and Onda Cryl resin; and (e) glossy ridge-lap surface sandblasted with 100-lm aluminium oxide particles and Onda Cryl resin. The artificial tooth ridge-lap surface was abraded with aluminium oxide particles with a sandblasting device (BioArt Dental Products, Sa˜o Carlos, Sa˜o Paulo, Brazil). The jet of aluminium oxide particles was made on the artificial tooth at an angle of 45, 1 cm away the tooth, for 10 sec. According to manufacturer, BioCler GII is a cross-linked acrylic resin denture tooth based on a polymethylmethacrylate polymer. Classico (conventional) and Onda Cryl (microwaved) pink resins (Classico Dental Products, Brazil) were prepared using a ratio of 35.5 g polymer to 15 mL monomer, according to the manufacturer’s recommendations. The manufacturer claimed that Classico is a conventional acrylic resin based on powder (polymethylmethacrylate copolymer) and liquid (copolymer of methylmethacrylate and ethyl acrylate), and Onda Cryl is a microwaved acrylic resin based on powder (polymethylmethacrylate copolymer and dibutyl phthalate) and liquid (methylmethacrylate monomer and ethylene glycol dimethacrylate). Metallic flasks were placed in traditional clamps after final pressing in a hydraulic press (Linea H) under a load of 1250 kgf for 5 min, and plastic flasks were pressed under a load of 850 kgf for 5 min. For the Classico resin, 30 specimens (n = 10) were conventionally packed, polymerized in a water bath at 74C for 9 h in a polymerizing unit (Termotron, Piracicaba, Sa˜o Paulo, Brazil), and deflasked after bench-flask cooling at room temperature. For the Onda Cryl resin, 30 specimens (n = 10) were conventionally packed; polymerized in a microwave 145
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domestic oven (Continental Domestic Lines, Manaus, Amazonas, Brazil), calibrated at 900 W, under the following conditions: 3 min with 40% potency, 4 min with 0% potency, and 3 min with 90% potency, and then deflasked after bench-flask cooling at room temperature. Afterwards, the resin stick was finished with abrasive stones, and the samples were stored in water at 37C for 24 h. A shear bond test was performed in an Instron machine (Canton, MA, USA), using a 500-N load cell and cross-speed of 1 mm/min. Compressive load was accomplished with a steel knife edge placed on the buccal face of the artificial tooth near to the bond surface margin. The shear bond strength (kgf/cm2) was calculated as a function of the failure load (kgf) and artificial tooth– resin bond area, using the following equation: SBS = F/ pr2, where SBS is the shear bond strength (kgf/cm2), F is the failure load (kgf), and pr2 is the artificial tooth–resin bonding area (p = 3.1416 and r2 = 0.09 cm2; thus, 0.09 · 3.1416 = 0.28 cm2). The results in kgf/cm2 were transformed in MPa by multiplying by the constant 0.098. Data were subjected to two-way ANOVA, considering the following factors: resin, ridge-lap surface sandblasting, and their interactions. Since same factor interactions were significant, differences were subjected to multiple comparison testing (Tukey’s honestly significant difference test at a = 0.05). Observation of the failure mode was under an optical microscope (EMZ-TR; Meiji Thecno, Tokyo, Japan), with ·1.5 magnification.
control, 50-, and 100-lm aluminium oxide particles showed values with statistically-significant difference, with greater value for the 100-lm particle size. Table 3 shows the shear strength means for the artificial tooth–resin bond in relation to resin type and ridgelap surface treatment. For the Classico resin, values with statistically-significant difference were showed by the control, 50-, and 100-lm aluminium oxide particles. For the Onda Cryl resin, the control showed a lower result that was statistically different when compared to the 50- and 100-lm aluminium oxide particle treatments. In the comparison between resins, only the 100-lm particle
Table 2. Shear bond strength means (MPa) and SD in relation to the tooth ridge-lap treatment, regardless of the resin types Treatment
Shear bond strength
Control 50 lm 100 lm
81.80 ± 7.45c 110.79 ± 9.06b 127.13 ±12.35a
Means, followed by different lower case letters, differ significantly by Tukey’s test (P < 0.05). SD, standard deviation. Table 3. Shear bond strength means (MPa) and SD for the Classico and Onda Cryl resins in relation to the aluminium oxide particle size Resin Treatment
Classico
Onda Cryl
Control 50 lm 100 lm
82.55 ± 8.34cA 109.74 ± 7.96bA 137.71 ± 5.75aA
81.04 ± 6.80bA 111.84 ± 10.37aA 116.55 ± 6.36aB
Results Two-way ANOVA (Table 1) revealed significant difference in the artificial tooth–resin shear bond strength for resin (P < 0.00155), ridge-lap surface treatment (P < 0.00001), and interaction (P < 0.00010). The shear strength means of the artificial tooth–resin bond in relation to the ridge-lap surface treatment, independent of the resin types, are shown in Table 2. The
Means, followed by different lower case letters in each column and capital case letter in each row, differ significantly by Tukey’s test (P < 0.05).
Table 1. Results of the two-way ANOVA statistical analysis Variation cause
df
Sum of squares
Mean square
F
P-value
R T R·T Error
1 2 2 54
704.314 21 082.559 1566.761 3248.056
704.314 10 541.279 783.380 60.141
11.709 175.252 13.024
0.00151 0.00001 0.00010
Total
59
26 601. 691
General mean = 106.57; variation coefficient = 7.27%. R, resin; T, treatment.
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(a)
(b)
Figure 2. Predominant fracture modes. (a) Mixed failure (cohesive in resin and adhesive) for the Classico resin/control sample; (b) mixed failure (cohesive in resin and adhesive) for the Classico resin/100-lm particle size and acrylic resin (R).
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treatment showed values with statistical difference, with a lower value for the Onda Cryl resin. Mixed failures (adhesive, and cohesive in the acrylic resin) were predominantly observed in all groups (Figure 2). Adhesive or mixed (adhesive, and cohesive in the tooth) failures were not observed. Discussion The purpose of this in vitro study was to verify the influence of the ridge-lap surface sandblasting with aluminium oxide particles on the artificial tooth–resin shear bond strength, under effect of the Classico (conventional) and Onda-Cryl (microwaved) acrylic resins. In the current, in vitro study, the research hypothesis that tooth–resin adhesion could be adversely affected by the aluminium oxide particle sandblasting was accepted. The two-way ANOVA revealed significant differences in the shear bond strength for sandblasting with aluminium oxide particles, resin types, and interactions (Table 1). Regardless of other factors, the control, 50-, and 100lm aluminium oxide particle sandblasting showed values with statistically-significant differences (Table 2). Previous work showed that a satisfactory bond could be obtained by a conventional heat processing technique, and mechanical retentions on the artificial tooth ridge lap have failed to increase the bond strength.2 This presumes that the satisfactory bond might be obtained by the conventional technique, and no additional retention on the artificial tooth ridge-lap surface would be necessary. Different types of mechanical retentions did not increase the bond strength between the artificial tooth and resin,7,13 findings that do not corroborate with the data obtained in the current study, in which sandblasting with aluminium oxide particles promotes significant increases in the artificial tooth–resin bond, whatever the resin type. Another significant fact is that the bond strength of the artificial tooth with different amounts of a cross-linking monomer might be differently influenced by the type of mechanical retentions made on the tooth ridge-lap surface,10 and mechanical retention placed within denture teeth might also increase the bond strength of the denture-base resin.23 Wax contamination has been considered the principal cause of weakening the artificial tooth–resin bond, when the tooth is cleaned only with heated water.1 This procedure did not influence of the results of the present study, considering that the artificial teeth were cleaned with a solution of detergent liquid,1 which effectively removed all traces of wax. The findings were coherent with the sandblasting treatments used in the study, in which the ª 2010 Blackwell Publishing Asia Pty Ltd
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main difference was the size of the aluminium oxide particles. Table 3 shows the artificial tooth–resin shear bond strength means, considering the aluminium oxide particle sandblasting (50 and 100 lm) effect in each resin and between resin types. For the Classico resin, there were statistically-significant differences between the control and aluminium oxide particle sizes, with greater values for the 100-lm and lower values for the 50-lm particle sizes, both showing statistical difference. Although there were no values with statistically-significant differences between treatments in both aluminium oxide particles for the Onda Cryl resin, they showed significant differences when compared to the control. When comparing the resins, there were statistically-significant differences only with the 100-lm particles. In the process of abrasion, different particle sizes cause different levels of abrasiveness, and smaller-sized abrasive particles promote a polishing effect on the surface of materials.24 It is possible to presume that the smaller aluminium oxide (50 lm) particles caused the smoothest tooth ridge-lap surface when compared to larger particles (100 lm), which were more effective in creating larger and deeper microroughness on the artificial tooth ridgelap surface. Under this condition, the treatment with the larger particles increased the free surface energy due to the increase of the surface area available for artificial tooth retention, consequently improving the shear bond strength values. This effect was more evident for Classico conventional resin than for Onda Cryl microwaved resin, a result that might presuppose different associations between material compositions and particle sizes, producing different levels of roughness in different types of denture acrylic resins. According to a previous study, greater bond strength was obtained for heat-polymerized denture bases for all teeth types, when compared to microwaved specimens.23 However, acrylic resin polymerized by microwave energy show satisfactory physical properties as the conventional acrylic resin when material processing is considered.25–28 Previous results have suggested that the nature of microwave-polymerized acrylic resins resulted in less interpenetration of the artificial tooth and denture-base networks, showing less amount of cross-linking and leaving less functional groups able to bond.23 In the present study, the effect on the shear strength of the artificial tooth–resin bond was more evident in the Classico conventional resin. This fact promoted different values of shear bond strength between the Classico and Onda Cryl denture-base resins, when the 100-lm particle size was considered. Under these study conditions, it would be permissible to consider that the free surface energy effect caused by sandblasting with smaller particles (50 lm) was 147
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the same for the Classico and Onda Cryl resins, determining bond strength values with statistical similarity. This assumption becomes subject to conflict when it is claimed that conventional and microwaved resins show similar physical properties.25–28 In addition, it is possible to presume that the lower amount of roughness produced by the 50-lm aluminium oxide particles had permitted similar degrees of free surface energy for conventional and microwaved acrylic resins, masking the composition effect of the materials. However, the results were higher than those of the untreated specimens, confirming the increase of the bond strength accomplished by sandblasting. Polymethylmethacrylate resin with a cross-linking monomer is the main chemical composition of the acrylic resin tooth.9 This chemical formulation increases surface hardness and improves the abrasion resistance of the artificial tooth,10 decreasing the bond strength when compared to the artificial tooth without the cross-linking monomer.29,30 As the same artificial tooth type was used for the conventional and microwaved resins, it is possible to assume that the ridge-lap surface hardness was the same for all artificial teeth, and the hardness effect on the bonding was similar for both sandblasting procedures. Although a previous study found that the treatment of the artificial tooth ridge-lap surface with aluminium oxide particles has less effect on the shear strength of the artificial tooth–resin bond when compared to bonding agents,12 the results showed by the current study suggest that the strength of the artificial tooth–conventional resin bond could be considerably increased by mechanical retentions using aluminium oxide sandblasting, mainly when the 100-lm particles were used. Bond strength values of the sandblasted tooth ridge-lap surface were higher than those of the ground surface and control, and the acrylic tooth surface processed with grinding plus sandblasting showed the greatest bond strength between the acrylic tooth and heat-polymerized denture-base resin, when compared to microwavepolymerized resin. It was also claimed that the surface topography type influenced micromechanical retention, emphasizing the advantage of sandblasting treatment in improving bonding.19 These previous findings appear to confirm the advantage of sandblasting as a mechanical method for the prevention of failures in the bonding of teeth to the denture-base resin. In addition, the jet of the abrasive particles can only be directed to the bonding surface to avoid abrasion of other regions of the tooth. In the sandblasting process, to promote abrasion of the labial side of the artificial tooth is necessary to change the position of the tooth, which should not be advisable due to possibility of adding undesirable variables in the process of bonding. The main variables would be the loss of glossiness of the labial 148
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surface and the unnecessary roughness on the area, which are of little significance in obtaining retentive strength in the tooth–resin adhesion, as compared to the ridge-lap surface. Considering that the maximum bite force exerted by the artificial molar tooth established was 7.2 kgf during the chewing of raisins,31 it would be interesting to determine whether the results of the shear strength of the artificial tooth–resin bond obtained in the present study exceed the magnitude of the force necessary for chewing food, such as peanuts, coconut, and raisins, by complete denture wearers. The chewing performance also depends on the geometrical type of notches made on the occlusal pattern of the artificial teeth of the complete denture, with the purpose to increase the chewing efficiency to pulverize raw carrots.32 An analysis of the fracture after the shear bond strength test (Figure 2) showed that the failure of the control group was predominantly mixed (adhesive and cohesive in the resin); however, cohesive failure in the resin and/or mixed failure were observed in the sandblasting groups. Cohesive failure was not observed in the resin tooth. This fact signifies that the cohesive strength of the artificial tooth was greater than the cohesive strength of the resin. This failure mode is most likely due to the lower cohesive strength of the resin, when the complete denture is in use. Conversely, results from the control, grinding, and grinding plus sandblasting treatments associated with heat or microwave-polymerized denture-base materials disclosed combined cohesive fractures (acrylic tooth and denture-base resin) in all tested samples for three brands of acrylic teeth.19 However, the same work showed no adhesive fractures, findings that also support the efficiency of the sandblasting method for bonding artificial teeth to denture acrylic resins. The maximum bite force exerted by complete denture wearers is commonly low (90 N) and showed a great individual variation (range 10–410 N).33 Conversely, changes in denture-bearing mucosa in patients with complete denture process and the negative height of the mandibular alveolar process slightly decreased the bite force,34 whereas severe resorption of the alveolar bone might delay the increase of the maximum bite force in aged patients with the complete denture replaced.35 Under these conditions, it is possible that the artificial tooth displacement of the complete denture base might only occur due to the repeated chewing force (mechanical fatigue), accidental fall during cleaning, or by laboratories that fail to properly bond the artificial tooth and the resin.21 Although attempts were made to characterize the influence of the aluminium oxide particle sandblasting with ª 2010 Blackwell Publishing Asia Pty Ltd
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different sizes of the artificial tooth–resin bond, this study is limited in predicting the effect of other variables. Further studies are necessary to evaluate whether the effect of the bite force might influence the denture-base adaptation and stability, and artificial tooth–resin base bond failure in complete denture wearers. Within the limitations of this study, the following conclusions were drawn: (a) regardless of the resin factor, both aluminium oxide particle sizes improved shear bond strength values when compared to the unmodified teeth; (b) for the Classico resin, both particle size types promoted shear strength values with statistical differences when compared to unmodified artificial teeth, and
References 1 Schoonover IC, Fischer TE, Serio AF, Sweeney WT. Bonding of plastic teeth to heat-cured denture base resins. J Am Dent Assoc 1952; 44: 285–7. 2 Huggett R, John G, Jagger RG, Bates JF. Strength of the acrylic denture base tooth bond. Br Dent J 1982; 153: 187–90. 3 Spratley MH. An investigation of adhesion of acrylic resin teeth to dentures. J Prosthet Dent 1987; 58: 389–92. 4 Darbar UR, Huggett R, Harrison A. Denture fracture––a survey. Br Dent J 1994; 176: 342–5. 5 Cunningham JL, Benington IC. A survey of the pre-bonding preparation of denture teeth and the efficiency of dewaxing methods. J Dent 1997; 25: 125–8. 6 Cunningham JL, Benington IC. A new technique for determining the denture tooth bond. J Oral Rehabil 1996; 23: 202–9. 7 Cunningham JL, Benington IC. An investigation of the variables which may affect the bond between plastic teeth and denture base resin. J Dent 1999; 27: 129–35. 8 Kawara M, Carter JM, Ogle RE, Johnson RR. Bonding of plastic teeth to denture base resin. J Prosthet Dent 1991; 66: 566–71. 9 Vallittu PK. Bonding of resin teeth to the polymethyl methacrylate den-
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were different between them. For the Onda-Cryl resin, there were no significant differences between aluminium oxide particle treatments; both had significant difference when compared with the unmodified artificial teeth; (c) in the comparison between resins, there were only statistically-significant differences with the 100-lm particle size. Acknowledgment The present study was supported by PIBIC/CNPq/UNICAMP at Piracicaba Dental School, State University of Campinas, Piracicaba, Brazil.
ture base material. Acta Odontol Scand 1995; 53: 99–104. Barpal D, Curtis AD, Finzen F, Perry J, Gansly SA. Failure load of acrylic resin denture teeth bonded to high impact acrylic resins. J Prosthet Dent 1998; 80: 666–71. Nishigawa G, Maruo Y, Okamoto M et al. Effect of adhesive primer developed exclusively for heat-curing resin on adhesive strength between plastic artificial tooth and acrylic denture base resin. Dent Mater J 2006; 25: 75–80. Saavedra G, Valandro LF, Leite FPP et al. Bond strength of acrylic teeth to denture base resin after various surface conditioning methods before and after thermocycling. Int J Prosthod 2007; 20: 199–201. Cardash HS, Liberman R, Helft M. The effect of retention grooves in acrylic resin teeth on tooth denture-base bond. J Prosthet Dent 1986; 55: 526–8. Cardash HS, Applebaum B, Liberman R. Effect of retention grooves on tooth-denture base bond. J Prosthet Dent 1990; 64: 492–6. Sorensen SE, Fjeldstad E. Bonding of plastic teeth to acrylic resin denture base materials. J Dent Res 1961; 40: 776. Morrow RM, Matvias FM, Windeler AS, Fuchs RJ. Bonding of plastic teeth to two heat-curing denture base resins. J Prosthet Dent 1978; 39: 565–8.
17 Adeyemi AA, Lyons MF, Cameron DA. The acrylic tooth-denture base bond: effect of mechanical preparation and surface treatment. Eur J Prosthodont Res Dent 2007; 15: 108– 14. 18 Cunningham JL. Shear bond strength of resin teeth to heat-cured and lightcured denture base resin. J Oral Rehabil 2000; 27: 312–6. 19 Chung KH, Chung CY, Chung CY, Chan DCN. Effect of pre-processing surface treatments of acrylic teeth and bonding to the denture base. J Oral Rehabil 2008; 35: 268–75. 20 Consani RLX, Mesquita MF, Zampieri MH, Mendes WB, Consani S. Effect of simulated disinfection by microwave energy on the impact strength of the tooth/acrylic resin adhesion. Open Dent J 2008; 2: 13–7. 21 Consani RLX, Manesco IM, Mesquita MF, Correr-Sobrinho L, Sinhoreti MAC. Effect of microwave treatment on the shear bond strength of denture tooth/acrylic resin. J Adhesion 2008; 84: 937–48. 22 Zuckerman GK. A reliable method for securing anterior denture teeth in denture bases. J Prosthet Dent 2003; 89: 603–7. 23 Schneider RL, Curtis ER, Clancy JM. Tensile bond strength of acrylic resin denture teeth to a microwave- or heat-processed denture base. J Prosthet Dent 2002; 88: 145–50.
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24 Anusavise KJ. Phillips’ science of dental materials. Philadelphia, WB Saunders, 2003: 273–315, 663–680. 25 Levin B, Sanders JL, Reitz PV. The use of microwave energy for processing acrylic resins. J Prosthet Dent 1989; 61: 381–3. 26 Reitz PV, Sanders JL, Levin B. The curing of denture acrylic resins by microwave energy. Physical properties. Quintessence Int 1985; 8: 547– 51. 27 Truong VT, Thomasz FGV. Comparison of denture acrylic resins cured by boiling water and microwave energy. Aust Dent J 1988; 33: 201–4.
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28 Wallace PW, Graser GN, Myers ML, Proskin HM. Dimensional accuracy of denture resin cured by microwave energy. J Prosthet Dent 1991; 66: 403–9. 29 Clancy JM, Boyer DB. Comparative bond strengths of light-cured, heatcured, and autopolymerizing denture resins to denture teeth. J Prosthet Dent 1989; 61: 457–62. 30 Suzuki S, Sakoh M, Shiba A. Adhesive bonding of denture base resins to plastic denture teeth. J Biomed Mater Res 1990; 24: 1091–103. 31 Howell AH, Brudevold F. Vertical forces used during chewing of food. J Dent Res 1950; 29: 133–6.
32 Kapur KK, Soman S. The effect of denture factors on masticatory performance. IV. Influence of occlusal pattern. J Prosthet Dent 1965; 15: 662–70. 33 Tzakis MG, Osterberg T, Carlsson GE. A study of some masticatory functions in 90-year old subjects. Gerodontology 1994; 11: 25–9. 34 Lassila V, Holmlund I, Koivumaa KK. Bite force and its correlations in different denture types. Acta Odontol Scand 1985; 43: 127–32. 35 Muller F, Heath MR, Ott R. Maximum bite force after the replacement of complete dentures. Gerodontology 2001; 18: 58–62.
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ORIGINAL ARTICLE Dental Biomaterials
Effect of aluminium oxide particle sandblasting on the artificial tooth–resin bond Rafael Leonardo Xediek Consani, Marina Martorano Richter, Marcelo Ferraz Mesquita, Mario Alexandre Coelho Sinhoreti & Ricardo Danil Guiraldo Department of Prosthodontics and Periodontics, Piracicaba Dental School, State University of Campinas, Piracicaba, Brazil
Keywords acrylic resin, aluminium oxide, artificial tooth, sandblasting, shear bond strength. Correspondence Dr Rafael Leonardo Xediek Consani, State University of Campinas, Piracicaba Dental School, 902 Limeira Avenue, Piracicaba, Sa˜o Paulo, Brazil. Tel: +55-19-2106-5296 Email: [email protected] Received: 24 March 2010; accepted 13 June 2010. doi: 10.1111/j.2041-1626.2010.00027.x
Abstract Aim: The influence of tooth ridge-lap surface sandblasting with aluminium oxide particles was evaluated on the adhesion of artificial teeth to acrylic resins. Methods: Specimens were made with the acrylic resin adhered to teeth (BioCler GII), according to an unmodified surface, glossy surface sandblasted with 50-lm particles and conventional (Classico) or microwaved (Onda Cryl) resin, and a glossy surface sandblasted with 100-lm particles and Classico or Onda Cryl resin. The shear bond test was performed in an Instron machine using a 500-N load cell and cross-speed of 1 mm/min. Results: The analysis of variance revealed significant difference in the tooth– resin shear bond strength for resin, surface treatment, and interaction. For conventional resin, control, 50-, and 100-lm particles showed statistically-different values; for microwaved resin, the control showed less statistical difference when compared to 50- and 100-lm particle treatments; for between resins, only the 100-lm particle treatment showed statistically-different values, with lower values for the microwaved resin. Mixed failures (cohesive in the resin and adhesive) were predominantly observed in all groups. Mixed (cohesive in the tooth and adhesive) or adhesive failures were not observed. Conclusions: Sandblasting with different aluminium oxide particle sizes produced different effects on the shear strength values of the tooth–resin bond.
Introduction Acrylic resin teeth are widely utilized in prostheses processing because of their ability to bond chemically to the denture-base resin due to the chemical similarity of both materials.1,2 However, some studies have shown that the complete prostheses are occasionally repaired due to artificial tooth fracture or failure of the artificial tooth–resin bond,2–5 requiring a new bonding procedure or replacement of the artificial tooth. Failure in the artificial tooth–resin base bond could be caused by accidental falls, excessive stress during chewing, or mechanical fatigue. Poor laboratory technique can also prevent perfect bond of the artificial tooth to denturebase resin, causing subsequent failure. Thus, the artificial 144
tooth ridge-lap surface contaminated by wax residues can produce significantly weaker bonds.1,3,5–7 Besides wax contamination, the degree of a cross-linking monomer added to the artificial tooth and the monomer amount available on the denture-base resin during processing might affect the artificial tooth–resin bond strength.8 Increase of the bond strength between the artificial tooth and denture-base resin involves chemical treatments or mechanical changes on the artificial tooth ridge-lap surface.7,9–14 However, the literature has shown conflicting results with the use of monomers3,15–17 and chemical agents for adhesion.17,18 For the acrylic resin monomer to be effective, it is necessary that the etching treatment softens or dissolves the surface of the ridge lap of the artificial tooth.8 ª 2010 Blackwell Publishing Asia Pty Ltd
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Mechanical retentions on the artificial tooth ridge-lap surface by abrasion or grooving7,13 and aluminium oxide sandblasting11 do not show significantly different results when compared to unmodified surfaces, contrasting with studies which state that such treatments improve the bond strength.9,14,19–21 However, contradictory results reported by various researchers might be due to different methods used in different studies. Different types of artificial teeth and acrylic resins might also contribute to different results.10 The displacement of the artificial tooth from the base of the prosthesis suggests that the chemical adhesion of the artificial tooth was not enough to promote effective bonding with the base resin, or that the artificial tooth was retained on the resin base by a weak mechanical bond due to incorrect laboratory procedures.22 In light of these considerations, it is important to verify the shear bond strength of the artificial tooth–resin bond under the influence of sandblasting of the artificial tooth ridge-lap surface with aluminium oxide particles that are 50 or 100 lm in size. The hypothesis of this in vitro study would be that sandblasting with aluminium oxide particles of different sizes could promote different levels of strength of the artificial tooth–resin bond. Materials and methods Sixty wax rectangular patterns (30 mm in length, 5 mm in height, and 10 mm in width) were traditionally invested into conventional brass flasks (Safrany Metallurgy, Sa˜o Paulo, Brazil) or plastic flasks (Classico Dental Products, Sa˜o Paulo, Brazil) with a type III dental stone (Herodent; Vigodent, Rio de Janeiro, Brazil), proportioned and manipulated following the manufacturer’s recommendations. After the removal of the wax patterns, each stone mold was filled with a layer of laboratory silicone putty (Zetalabor; Zhermack, Rovigo, Italy). Identical BioCler GII P32L (model 3; DentBras Dental Products, Pirassununca, Sa˜o Paulo, Brazil) white, acrylic resin molar teeth (DentBras), with a wax stick (6-mm in diameter and 20-mm in length) attached at the ridge-lap surface, were partially included into the silicone layer, and thus covered with another layer of silicone putty (Zetalabor). After dental stone isolation with petroleum jelly, the flask was filled with type III dental stone (Herodent) and pressed in a hydraulic press (Linea H, Sa˜o Paulo, Brazil) for 1 h. After deflasking, the wax stick was removed from the ridge-lap surface; the artificial tooth was brushed with a solution of liquid detergent (Bombril-Cirio, Sa˜o Paulo, Brazil) to eliminate the wax residues, and rinsed with tap water at room temperature. Samples (Figure 1) were made with the artificial tooth ridge-lap surface attached ª 2010 Blackwell Publishing Asia Pty Ltd
Effect of sandblasting on artificial teeth
Figure 1. Specimen for artificial tooth–acrylic resin bonding test.
to the acrylic resin, proportioned and manipulated according to the manufacturer’s instructions, and using the following procedures: (a) unmodified artificial tooth ridge-lap surface; (b) glossy ridge lap sandblasted with 50-lm aluminium oxide particles and Classico resin; (c) glossy ridge lap sandblasted with 100-lm aluminium oxide particles and Classico resin; (d) glossy ridge lap sandblasted with 50-lm aluminium oxide particles and Onda Cryl resin; and (e) glossy ridge-lap surface sandblasted with 100-lm aluminium oxide particles and Onda Cryl resin. The artificial tooth ridge-lap surface was abraded with aluminium oxide particles with a sandblasting device (BioArt Dental Products, Sa˜o Carlos, Sa˜o Paulo, Brazil). The jet of aluminium oxide particles was made on the artificial tooth at an angle of 45, 1 cm away the tooth, for 10 sec. According to manufacturer, BioCler GII is a cross-linked acrylic resin denture tooth based on a polymethylmethacrylate polymer. Classico (conventional) and Onda Cryl (microwaved) pink resins (Classico Dental Products, Brazil) were prepared using a ratio of 35.5 g polymer to 15 mL monomer, according to the manufacturer’s recommendations. The manufacturer claimed that Classico is a conventional acrylic resin based on powder (polymethylmethacrylate copolymer) and liquid (copolymer of methylmethacrylate and ethyl acrylate), and Onda Cryl is a microwaved acrylic resin based on powder (polymethylmethacrylate copolymer and dibutyl phthalate) and liquid (methylmethacrylate monomer and ethylene glycol dimethacrylate). Metallic flasks were placed in traditional clamps after final pressing in a hydraulic press (Linea H) under a load of 1250 kgf for 5 min, and plastic flasks were pressed under a load of 850 kgf for 5 min. For the Classico resin, 30 specimens (n = 10) were conventionally packed, polymerized in a water bath at 74C for 9 h in a polymerizing unit (Termotron, Piracicaba, Sa˜o Paulo, Brazil), and deflasked after bench-flask cooling at room temperature. For the Onda Cryl resin, 30 specimens (n = 10) were conventionally packed; polymerized in a microwave 145
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domestic oven (Continental Domestic Lines, Manaus, Amazonas, Brazil), calibrated at 900 W, under the following conditions: 3 min with 40% potency, 4 min with 0% potency, and 3 min with 90% potency, and then deflasked after bench-flask cooling at room temperature. Afterwards, the resin stick was finished with abrasive stones, and the samples were stored in water at 37C for 24 h. A shear bond test was performed in an Instron machine (Canton, MA, USA), using a 500-N load cell and cross-speed of 1 mm/min. Compressive load was accomplished with a steel knife edge placed on the buccal face of the artificial tooth near to the bond surface margin. The shear bond strength (kgf/cm2) was calculated as a function of the failure load (kgf) and artificial tooth– resin bond area, using the following equation: SBS = F/ pr2, where SBS is the shear bond strength (kgf/cm2), F is the failure load (kgf), and pr2 is the artificial tooth–resin bonding area (p = 3.1416 and r2 = 0.09 cm2; thus, 0.09 · 3.1416 = 0.28 cm2). The results in kgf/cm2 were transformed in MPa by multiplying by the constant 0.098. Data were subjected to two-way ANOVA, considering the following factors: resin, ridge-lap surface sandblasting, and their interactions. Since same factor interactions were significant, differences were subjected to multiple comparison testing (Tukey’s honestly significant difference test at a = 0.05). Observation of the failure mode was under an optical microscope (EMZ-TR; Meiji Thecno, Tokyo, Japan), with ·1.5 magnification.
control, 50-, and 100-lm aluminium oxide particles showed values with statistically-significant difference, with greater value for the 100-lm particle size. Table 3 shows the shear strength means for the artificial tooth–resin bond in relation to resin type and ridgelap surface treatment. For the Classico resin, values with statistically-significant difference were showed by the control, 50-, and 100-lm aluminium oxide particles. For the Onda Cryl resin, the control showed a lower result that was statistically different when compared to the 50- and 100-lm aluminium oxide particle treatments. In the comparison between resins, only the 100-lm particle
Table 2. Shear bond strength means (MPa) and SD in relation to the tooth ridge-lap treatment, regardless of the resin types Treatment
Shear bond strength
Control 50 lm 100 lm
81.80 ± 7.45c 110.79 ± 9.06b 127.13 ±12.35a
Means, followed by different lower case letters, differ significantly by Tukey’s test (P < 0.05). SD, standard deviation. Table 3. Shear bond strength means (MPa) and SD for the Classico and Onda Cryl resins in relation to the aluminium oxide particle size Resin Treatment
Classico
Onda Cryl
Control 50 lm 100 lm
82.55 ± 8.34cA 109.74 ± 7.96bA 137.71 ± 5.75aA
81.04 ± 6.80bA 111.84 ± 10.37aA 116.55 ± 6.36aB
Results Two-way ANOVA (Table 1) revealed significant difference in the artificial tooth–resin shear bond strength for resin (P < 0.00155), ridge-lap surface treatment (P < 0.00001), and interaction (P < 0.00010). The shear strength means of the artificial tooth–resin bond in relation to the ridge-lap surface treatment, independent of the resin types, are shown in Table 2. The
Means, followed by different lower case letters in each column and capital case letter in each row, differ significantly by Tukey’s test (P < 0.05).
Table 1. Results of the two-way ANOVA statistical analysis Variation cause
df
Sum of squares
Mean square
F
P-value
R T R·T Error
1 2 2 54
704.314 21 082.559 1566.761 3248.056
704.314 10 541.279 783.380 60.141
11.709 175.252 13.024
0.00151 0.00001 0.00010
Total
59
26 601. 691
General mean = 106.57; variation coefficient = 7.27%. R, resin; T, treatment.
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(a)
(b)
Figure 2. Predominant fracture modes. (a) Mixed failure (cohesive in resin and adhesive) for the Classico resin/control sample; (b) mixed failure (cohesive in resin and adhesive) for the Classico resin/100-lm particle size and acrylic resin (R).
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treatment showed values with statistical difference, with a lower value for the Onda Cryl resin. Mixed failures (adhesive, and cohesive in the acrylic resin) were predominantly observed in all groups (Figure 2). Adhesive or mixed (adhesive, and cohesive in the tooth) failures were not observed. Discussion The purpose of this in vitro study was to verify the influence of the ridge-lap surface sandblasting with aluminium oxide particles on the artificial tooth–resin shear bond strength, under effect of the Classico (conventional) and Onda-Cryl (microwaved) acrylic resins. In the current, in vitro study, the research hypothesis that tooth–resin adhesion could be adversely affected by the aluminium oxide particle sandblasting was accepted. The two-way ANOVA revealed significant differences in the shear bond strength for sandblasting with aluminium oxide particles, resin types, and interactions (Table 1). Regardless of other factors, the control, 50-, and 100lm aluminium oxide particle sandblasting showed values with statistically-significant differences (Table 2). Previous work showed that a satisfactory bond could be obtained by a conventional heat processing technique, and mechanical retentions on the artificial tooth ridge lap have failed to increase the bond strength.2 This presumes that the satisfactory bond might be obtained by the conventional technique, and no additional retention on the artificial tooth ridge-lap surface would be necessary. Different types of mechanical retentions did not increase the bond strength between the artificial tooth and resin,7,13 findings that do not corroborate with the data obtained in the current study, in which sandblasting with aluminium oxide particles promotes significant increases in the artificial tooth–resin bond, whatever the resin type. Another significant fact is that the bond strength of the artificial tooth with different amounts of a cross-linking monomer might be differently influenced by the type of mechanical retentions made on the tooth ridge-lap surface,10 and mechanical retention placed within denture teeth might also increase the bond strength of the denture-base resin.23 Wax contamination has been considered the principal cause of weakening the artificial tooth–resin bond, when the tooth is cleaned only with heated water.1 This procedure did not influence of the results of the present study, considering that the artificial teeth were cleaned with a solution of detergent liquid,1 which effectively removed all traces of wax. The findings were coherent with the sandblasting treatments used in the study, in which the ª 2010 Blackwell Publishing Asia Pty Ltd
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main difference was the size of the aluminium oxide particles. Table 3 shows the artificial tooth–resin shear bond strength means, considering the aluminium oxide particle sandblasting (50 and 100 lm) effect in each resin and between resin types. For the Classico resin, there were statistically-significant differences between the control and aluminium oxide particle sizes, with greater values for the 100-lm and lower values for the 50-lm particle sizes, both showing statistical difference. Although there were no values with statistically-significant differences between treatments in both aluminium oxide particles for the Onda Cryl resin, they showed significant differences when compared to the control. When comparing the resins, there were statistically-significant differences only with the 100-lm particles. In the process of abrasion, different particle sizes cause different levels of abrasiveness, and smaller-sized abrasive particles promote a polishing effect on the surface of materials.24 It is possible to presume that the smaller aluminium oxide (50 lm) particles caused the smoothest tooth ridge-lap surface when compared to larger particles (100 lm), which were more effective in creating larger and deeper microroughness on the artificial tooth ridgelap surface. Under this condition, the treatment with the larger particles increased the free surface energy due to the increase of the surface area available for artificial tooth retention, consequently improving the shear bond strength values. This effect was more evident for Classico conventional resin than for Onda Cryl microwaved resin, a result that might presuppose different associations between material compositions and particle sizes, producing different levels of roughness in different types of denture acrylic resins. According to a previous study, greater bond strength was obtained for heat-polymerized denture bases for all teeth types, when compared to microwaved specimens.23 However, acrylic resin polymerized by microwave energy show satisfactory physical properties as the conventional acrylic resin when material processing is considered.25–28 Previous results have suggested that the nature of microwave-polymerized acrylic resins resulted in less interpenetration of the artificial tooth and denture-base networks, showing less amount of cross-linking and leaving less functional groups able to bond.23 In the present study, the effect on the shear strength of the artificial tooth–resin bond was more evident in the Classico conventional resin. This fact promoted different values of shear bond strength between the Classico and Onda Cryl denture-base resins, when the 100-lm particle size was considered. Under these study conditions, it would be permissible to consider that the free surface energy effect caused by sandblasting with smaller particles (50 lm) was 147
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the same for the Classico and Onda Cryl resins, determining bond strength values with statistical similarity. This assumption becomes subject to conflict when it is claimed that conventional and microwaved resins show similar physical properties.25–28 In addition, it is possible to presume that the lower amount of roughness produced by the 50-lm aluminium oxide particles had permitted similar degrees of free surface energy for conventional and microwaved acrylic resins, masking the composition effect of the materials. However, the results were higher than those of the untreated specimens, confirming the increase of the bond strength accomplished by sandblasting. Polymethylmethacrylate resin with a cross-linking monomer is the main chemical composition of the acrylic resin tooth.9 This chemical formulation increases surface hardness and improves the abrasion resistance of the artificial tooth,10 decreasing the bond strength when compared to the artificial tooth without the cross-linking monomer.29,30 As the same artificial tooth type was used for the conventional and microwaved resins, it is possible to assume that the ridge-lap surface hardness was the same for all artificial teeth, and the hardness effect on the bonding was similar for both sandblasting procedures. Although a previous study found that the treatment of the artificial tooth ridge-lap surface with aluminium oxide particles has less effect on the shear strength of the artificial tooth–resin bond when compared to bonding agents,12 the results showed by the current study suggest that the strength of the artificial tooth–conventional resin bond could be considerably increased by mechanical retentions using aluminium oxide sandblasting, mainly when the 100-lm particles were used. Bond strength values of the sandblasted tooth ridge-lap surface were higher than those of the ground surface and control, and the acrylic tooth surface processed with grinding plus sandblasting showed the greatest bond strength between the acrylic tooth and heat-polymerized denture-base resin, when compared to microwavepolymerized resin. It was also claimed that the surface topography type influenced micromechanical retention, emphasizing the advantage of sandblasting treatment in improving bonding.19 These previous findings appear to confirm the advantage of sandblasting as a mechanical method for the prevention of failures in the bonding of teeth to the denture-base resin. In addition, the jet of the abrasive particles can only be directed to the bonding surface to avoid abrasion of other regions of the tooth. In the sandblasting process, to promote abrasion of the labial side of the artificial tooth is necessary to change the position of the tooth, which should not be advisable due to possibility of adding undesirable variables in the process of bonding. The main variables would be the loss of glossiness of the labial 148
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surface and the unnecessary roughness on the area, which are of little significance in obtaining retentive strength in the tooth–resin adhesion, as compared to the ridge-lap surface. Considering that the maximum bite force exerted by the artificial molar tooth established was 7.2 kgf during the chewing of raisins,31 it would be interesting to determine whether the results of the shear strength of the artificial tooth–resin bond obtained in the present study exceed the magnitude of the force necessary for chewing food, such as peanuts, coconut, and raisins, by complete denture wearers. The chewing performance also depends on the geometrical type of notches made on the occlusal pattern of the artificial teeth of the complete denture, with the purpose to increase the chewing efficiency to pulverize raw carrots.32 An analysis of the fracture after the shear bond strength test (Figure 2) showed that the failure of the control group was predominantly mixed (adhesive and cohesive in the resin); however, cohesive failure in the resin and/or mixed failure were observed in the sandblasting groups. Cohesive failure was not observed in the resin tooth. This fact signifies that the cohesive strength of the artificial tooth was greater than the cohesive strength of the resin. This failure mode is most likely due to the lower cohesive strength of the resin, when the complete denture is in use. Conversely, results from the control, grinding, and grinding plus sandblasting treatments associated with heat or microwave-polymerized denture-base materials disclosed combined cohesive fractures (acrylic tooth and denture-base resin) in all tested samples for three brands of acrylic teeth.19 However, the same work showed no adhesive fractures, findings that also support the efficiency of the sandblasting method for bonding artificial teeth to denture acrylic resins. The maximum bite force exerted by complete denture wearers is commonly low (90 N) and showed a great individual variation (range 10–410 N).33 Conversely, changes in denture-bearing mucosa in patients with complete denture process and the negative height of the mandibular alveolar process slightly decreased the bite force,34 whereas severe resorption of the alveolar bone might delay the increase of the maximum bite force in aged patients with the complete denture replaced.35 Under these conditions, it is possible that the artificial tooth displacement of the complete denture base might only occur due to the repeated chewing force (mechanical fatigue), accidental fall during cleaning, or by laboratories that fail to properly bond the artificial tooth and the resin.21 Although attempts were made to characterize the influence of the aluminium oxide particle sandblasting with ª 2010 Blackwell Publishing Asia Pty Ltd
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different sizes of the artificial tooth–resin bond, this study is limited in predicting the effect of other variables. Further studies are necessary to evaluate whether the effect of the bite force might influence the denture-base adaptation and stability, and artificial tooth–resin base bond failure in complete denture wearers. Within the limitations of this study, the following conclusions were drawn: (a) regardless of the resin factor, both aluminium oxide particle sizes improved shear bond strength values when compared to the unmodified teeth; (b) for the Classico resin, both particle size types promoted shear strength values with statistical differences when compared to unmodified artificial teeth, and
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32 Kapur KK, Soman S. The effect of denture factors on masticatory performance. IV. Influence of occlusal pattern. J Prosthet Dent 1965; 15: 662–70. 33 Tzakis MG, Osterberg T, Carlsson GE. A study of some masticatory functions in 90-year old subjects. Gerodontology 1994; 11: 25–9. 34 Lassila V, Holmlund I, Koivumaa KK. Bite force and its correlations in different denture types. Acta Odontol Scand 1985; 43: 127–32. 35 Muller F, Heath MR, Ott R. Maximum bite force after the replacement of complete dentures. Gerodontology 2001; 18: 58–62.
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