- Email: [email protected]
Macro- and microtopographical examination and quantification of CAD-CAM composite resin 2- and 3-body wear
RESEARCH AND EDUCATION
Macro- and microtopographical examination and quantification of CAD-CAM composite resin 2- and 3-body wear Carolin Stöckl, BSc,a Rüdiger Hampe, Dipl-Ing (FH), MSc,b Bogna Stawarczyk, PD Dr Rer Biol Hum Dip-Ing (FH), MSc,c Miriam Haerst, Dr Dipl-Ing,d and Malgorzata Roos, PD Dr Phile Computer-aided design and ABSTRACT computer-aided manufacturing Statement of problem. The selection of an appropriate restorative material based on wear (CAD-CAM) allows highly behavior is important for the long-term success of a dental restoration. For computer-aided design precise fabrication of dental resand computer-aided manufacturing (CAD-CAM) composite resins, information about their wear torations. Due to the progress resistance and wear mechanism is scarce. in software and milling technolPurpose. The purpose of this in vitro study was to compare the 2- and 3-body wear of CAD-CAM ogies, chairside CAD-CAM use composite resins with that of lithium disilicate ceramic and to develop analysis software. has increased, with demand for Material and methods. Flat specimens were prepared from the following CAD-CAM composite metal-free esthetic options resins: Cerasmart (CS), SHOFU Block HC (SH), Katana Avencia (KA), Brilliant Crios (BC), an 1-4 contributing to the trend. experimental composite resin (EXP), and lithium disilicate ceramic IPS e.max CAD (REF). The Novel composite resin matespecimens underwent 2-body wear (50 N, 5/55 C, 400 000 cycles) opposed by human enamel rials have been developed antagonists. Specimen wheels were prepared with each material on each wheel for 3-body wear with a millet slurry (15 N, 15% slip, 200 000 cycles). All specimens were digitized by using a for dental CAD-CAM applicadedicated laser scanner. Analysis software was developed to calculate macrotopographical tions5 with improved machinexamination of volume loss. The microtopography of the surfaces was examined by using ability and less chipping than scanning electron microscopy. For data analysis, the Kruskal-Wallis test with the Tukey-Kramer 6 ceramics. Manufacturers claim post hoc test and the 1-sample Wilcoxon test were used (a=.05). improved restoration quality Results. After 2-body wear simulation, SH and KA presented higher volume loss than the other for CAD-CAM composite resin CAD-CAM materials. For 3-body wear, REF had lower volume loss than CS, SH, or BC. In addition, blocks compared with manually BC led to higher volume loss than EXP. The patterns of 2- and 3-body wear were different. polymerized (laboratory or Conclusions. The ceramic showed good global wear resistance. The volume loss of the CAD-CAM chairside) composite resins composite resins differed and depended on the material. The 2- and 3-body wear test methods because of increased polymeritended to differ with regard to volume loss. Examination of the worn surfaces revealed different zation. CAD-CAM generated mechanisms acting in 2- and 3-body wear test. (J Prosthet Dent 2018;-:---) composite resin restorations show fewer voids than direct placement composite resin show wear behavior comparable to that of natural dentirestorations7 and have similar or better mechanical proption, with clinical wear rates in the range of 15 to 29 mm per erties and color stability than dental glass ceramics.8-11 year.12 Patients with parafunctional habits show increased Wear behavior is an important aspect of all dental tooth wear of more than 140 mm per year.13 Together with restorative materials. Ideally, restorative materials should secondary caries and fracture, wear has been identified as a
a
Graduate student, Institute of Medical and Polymer Engineering, Faculty of Mechanical Engineering, Technical University, Munich, Germany. Research Fellow of Dental Material Unit, Department of Prosthodontics, Ludwig-Maximilians-University, Munich, Germany. Scientific Head of Dental Material Unit, Department of Prosthodontics, Ludwig-Maximilians-University, Munich, Germany. d Adjunct Professor, Institute of Medical and Polymer Engineering, Faculty of Mechanical Engineering, Technical University, Munich, Germany. e Senior Statistician, Department of Biostatistics, Epidemiology, Biostatistics and Prevention Institute, University of Zurich, Zurich, Switzerland. b c
THE JOURNAL OF PROSTHETIC DENTISTRY
1
2
Volume
Clinical Implications An important aspect of all dental restorative materials is their wear behavior. Some but not all novel CAD-CAM composite resins seem to be wear resistant alternatives to ceramics for dental CAD-CAM restorations.
chief reason for the failure of direct composite resin restorations.14,15 CAD-CAM composite resins have high fatigue and wear resistance and can withstand clinically applied forces well.11,16-18 The reduced wear of the enamel antagonist compared with that of ceramics is another advantage of composite resins.11,18 In contrast with other mechanical properties, wear is not a material property but a system property of the tribological system.19 Consequently, no single generally accepted wear test method exists. A combination of at least 2 different wear test simulations is recommended to assess the wear resistance of materials.19-22 In principle, the methods used can be divided into tribological systems with mainly 2- or 3-body wear. Mastication simulation is an established method for simulating 2-body wear.18,22-25 For 3-body wear simulation, the Academic Centre for Dentistry Amsterdam (ACTA) wear machine has also been used.22,26 To analyze the wear properties of dental restorative materials, suitable quantitative evaluation models should be applied. Optical 3-dimensional (3D) scanning or tactile 3D scanning are the most suitable methods for the accurate and reproducible examination of volume loss.27 The importance of visualization and graphical processing of the macrotopographical information provided by scans has been emphasized.28,29 Heintze23 reported a close relationship between vertical and volume loss and stated that it is reasonable to measure only a single variable. Notwithstanding the vigorous development of graphic facilities, the authors are unaware of an analysis of both macrotopographical features and wear volume estimations. The purpose of this study was to determine the wear behavior of 5 CAD-CAM composite resins by using the commonly used methodologies of 2-body wear by using a mastication simulator and 3-body wear by using an ACTA machine and then compare the results with those of a lithium disilicate ceramic. One goal was to develop new software to analyze the digital scan data provided by an optical 3D scanner. Complementary to the quantification of volume loss, the worn surfaces were analyzed topographically by using scanning electron microscopy (SEM) to assess the wear mechanisms. The tested null hypotheses were that the 2- and the 3-body wear test methods would show comparable tendencies concerning
THE JOURNAL OF PROSTHETIC DENTISTRY
-
Issue
-
volume loss among the different material groups and that the CAD-CAM materials would show comparable wear behavior for the 2- and 3-body wear test methods. MATERIAL AND METHODS Each material group (Table 1) in each wear test method consisted of 12 specimens. The specimens were fabricated, and the worn specimens were digitized by a trained operator (C.S.). For 2-body wear, the material specimens were cut (thickness, 2 mm) from CAD-CAM blocks under water cooling (Secotom-50; Struers GmbH), using the following parameters: speed of 2200 rpm; feed rate of 0.09 mm/s for all composite resins and 0.07 mm/s for the lithium disilicate. The lithium disilicate was then crystallized at a final temperature of 840 C under vacuum according to the manufacturer’s instructions (Programat EP 5000; Ivoclar Vivadent AG). All specimens were embedded in acrylic resin (Scandiform/ScandiQuick; Scan-DIA, Struers GmbH) and polished with silicon carbide (SiC) paper in 4 steps up to P4000 under constant pressure and water cooling (Tegramin-20; Struers GmbH). The specimens were stored for 14 days in distilled water at 37 C before wear testing. Extracted human teeth were obtained from dentists in the Munich area. After extraction, the teeth were stored in a 0.5% chloramine solution (Chloramine-T; Sigma-Aldrich Laborchemikalien GmbH) at room temperature for 7 days and then in distilled water at 5 C for a maximum of 6 months.30 After the mesiobuccal cusps were sectioned, the teeth were embedded in stainless steel molds with dental amalgam (Dispersalloy; Dentsply Sirona). A shape congruent spherical cusp of 3 mm in diameter with 40 mm and 8 mm grit was generated by using a bench drill (BT-BD 1020 D; Einhell Germany AG). The specimens were mounted in a mastication simulator (CS-4; SD Mechatronik GmbH) (Fig. 1). For the simulation, a vertical load of 50 N at 1.2 Hz was applied for 400 000 cycles with a sliding movement of 0.7 mm; they were thermocycled between 5 C and 55 C with a dwell time of 60 seconds for 2000 cycles. For 3-body wear, 6 specimen wheels were prepared. With 12 cavities in a wheel, 2 specimens of each material were placed on 1 wheel. Specimens of the same material were positioned diametrically opposed. To prepare the cavities, 12 slices of each material were cut (thickness, 5 mm) from CAD-CAM blocks under water cooling (Secotom-50; Struers GmbH). The lithium disilicate was crystallized. The wheels were airborne particle abraded (110-mm alumina powder, 200 kPa, Basic Quattro; Renfert GmbH) and silanated (ESPE Sil; 3M ESPE). Custom tray material (Omnident GmbH) was used to cement the material specimens into the cavities. After removing any Stöckl et al
-
2018
3
Table 1. Materials tested Manufacturer
Lot No. Shade and Block Sizes
Product Name
Abbreviation
Cerasmart
CS
GC Europe NV
Composition
SHOFU Block HC
SH
SHOFU Inc
Katana Avencia Block
KA
Kuraray Noritake Dental Inc
000115 14L/A2 LT
Organic part: UDMA, TEGDMA Inorganic part: filler content: 62wt% aluminum oxide (20 nm), SiO2 (40 nm)
Brilliant Crios
BC
Coltène AG
G93044 A2 HT 14
Organic part: crosslinked methacrylates Inorganic part: filler content (71 wt%) silica and barium glass
1407311 A2 LT 14L
Organic part: Bis-MEPP, UDMA, DMA Inorganic part: filler content 71wt% silica (20 nm) and barium glass (300 nm)
111501 A2 LT M
Organic part: UDMA, TEGDMA Inorganic part: filler content 61wt% silica powder, fumed silica, zirconia silicate
Experimental Composite EXP
Ivoclar Vivadent AG
b.28923 HAT A2/C14
Organic part: resin composite Inorganic part: 80wt% nanoparticles
IPS e.max CAD
Ivoclar Vivadent AG
T44670 HAT A3/B 40
Lithium disilicate crystals (Li2Si2O5) embedded in a glassy matrix
REF
Bis-MEPP, 2,2-bis-(4-(2-methacryloxyethoxy)phenyl)propane; DMA, dimethacrylate; TEGDMA, triethylene glycol dimethacrylate; UDMA, urethane dimethacrylate.
Figure 1. Human enamel antagonist and tested material in chamber of mastication simulator.
excess material and after prepolymerization for 55 seconds at 400 to 500 nm wavelength (Quick curing light; Ivoclar Vivadent AG), the final polymerization was ensured by light irradiation by using a wavelength between 370 and 500 nm for 180 seconds (bre.Lux Power Unit; bredent GmbH & Co, KG). The wheels were rounded on a lathe under water cooling using diamond disks (speed, 500 rpm; feed motion, 0.08 mm) and stored for 14 days in distilled water at 37 C. The abrasive slurry was mixed (International Organization for Standardization/Technical Specification 14569 standard21) and contained 150 g millet, 1 g sodium azide, and 220 mL deionized water. The millet grains were milled for 5 seconds (MKM 6000; Robert Bosch Hausgeräte GmbH). The wheels were placed in the testing device (ACTA 3; Willytec GmbH) (Fig. 2). The specimen wheel and the antagonistic stainless-steel wheel rotated in different directions with 15% difference in circumferential speed while having no direct contact. The force which pressed the wheels together was adjusted to 15 N. The angular frequency of Stöckl et al
Figure 2. Antagonist wheel and wheel with tested materials.
the specimen wheel was set to 1 Hz. The speed of the antagonistic wheel was calculated separately for each run from the following equations21: dPK ×f PK ×p ; v PK = 60
(1)
where vPK=circumferential speed of specimen wheel (mm/s); dPK=diameter of specimen wheel (mm); fPK=frequency of specimen wheel (1/min) and fA =
vA
p×dA
×60=
0:85v PK ×60; p×dA
(2)
where fA=frequency of antagonist wheel (1/min); vA=circumferential speed of antagonist wheel (mm/s); dA=diameter of antagonist wheel (mm) A wear-in of 60 000 cycles was carried out before the simulation. The wear simulation was conducted with 200 000 cycles and with the same parameters as the wear-in process. A new millet slurry was used for each run but was not refreshed within a run in order to have a THE JOURNAL OF PROSTHETIC DENTISTRY
4
Volume
-
Issue
-
Figure 3. A, Material of 2-body-wear scan. B, With region of interest inside. C, With region of interest outside. D, Post-cutoff area. Scratches visible in A on left and right were placed intentionally as marks on all specimens. Table 2. Median (IQR) for volume loss for all material groups together with results of Kruskal-Wallis and 1-sample Wilcoxon test
Material Groups*
2-Body-Wear Specimens (P<.001)†
3-Body-Wear Specimens (after wear-in) (P<.001)†
CS
0.31ab (0.15)
1.84b (1.31)
SH
0.49b (0.21)
1.40b (1.14)
KA
0.64b (0.13)
0.84ab (1.36)
BC EXP REF
a
2.31bc (0.55)
a
0.76ab (0.65)
a
0.13a (0.62)
0.22 (0.08) 0.14 (0.19) 0.20 (0.12)
*Except for REF under 3-body-wear conditions, all materials revealed significant volume loss. † Different superscript letters indicate significant differences among tested groups.
robust test procedure with a low number of steps and to minimize variation between the cycles. A dedicated laser scanner (LAS-20; SD Mechatronik GmbH) with a horizontal resolution of 40 mm, and a vertical resolution of 0.8 mm was used for digitization. In the macrotopographical approach, the volume loss (mm3) was quantified by applying a geometric approach programmed in R software (R Foundation for Statistical Computing; Vienna).31 Given the scan of a 2-body wear specimen (Fig. 3A), 2 disjointed regions of interest (ROI) were set, ROI(inside) (Fig. 3B) and ROI(outside) (Fig. 3C). The ROI(inside) was chosen to completely THE JOURNAL OF PROSTHETIC DENTISTRY
include the area with the wear hollow. A multiple regression on the ROI(outside) modeled its geometric properties (inclination and curvature). Predicted values for ROI(inside) and residuals were subsequently computed. A cutoff based on reference residuals was applied, leaving a postcutoff area for volume estimation (Fig. 3D). For 3-body wear, volume loss estimates were obtained by numerical integration based on the postcutoff area and curvature-adjusted residuals. The final volume loss was adjusted for baseline wear by subtracting the volume loss at baseline from the volume loss after wear simulation. For baseline scans with missing volume estimations, the values were imputed by the corresponding sample median. All scans were evaluated by one statistician (M.R.) to ensure the unity of approach and quality. Median and interquartile range (IQR) were computed for descriptive statistics. The Kruskal-Wallis test together with the Tukey-Kramer post hoc test were used to identify differences in volume loss among the tested groups. The 1-sample Wilcoxon test was applied to evaluate the volume loss within each test group (IBM SPSS Statistics v23.0; IBM Corp, and R Foundation for Statistical Computing) (a=.05). Stöckl et al
-
2018
5
Figure 4. Scanning electron microscope images (original magnification ×200 [left], ×1500 [middle], and ×5000 [right]) of selected material specimens after 2-body wear. Acronyms indicate test materials. White scale bars refer to 100 mm, 10 mm, and 5 mm. BC, Brilliant Crios; CS, Cerasmart; EXP, experimental composite resin; KA, Katana Avencia; REF, lithium disilicate ceramic IPS e.max CAD; SH, SHOFU Block HC.
Stöckl et al
THE JOURNAL OF PROSTHETIC DENTISTRY
6
Volume
-
Issue
-
Figure 5. Scanning electron microscope images (original magnification ×50) for antagonists of selected antagonist specimens after 2-body wear. Acronyms are indicating counterpart materials. White scale bars refer to 500 mm. BC, Brilliant Crios; CS, Cerasmart; EXP, experimental composite resin; KA, Katana Avencia; REF, lithium disilicate ceramic IPS e.max CAD; SH, SHOFU Block HC.
To analyze the wear patterns, SEM images (×50 magnification for antagonists and ×200, ×1500, ×5000 magnification for materials) were made (JSM-6390; JEOL Ltd) at 10-kV acceleration voltage with a variable working distance of between 7 and 9 mm. Cleaned specimens had been stored for 7 days in a desiccator and sputter coated with gold to a thickness of 7.5 mm (SCD005; Bal-Tec AG). RESULTS For 2-body wear, volume loss varied with the tested materials (P<.001) (Table 2). Generally, all CAD-CAM materials presented significant volume loss after mastication simulation compared with baseline (P<.001). SHOFU Block HC (SH) and Katana Avencia (KA) showed higher volume loss than Cerasmart (CS), Brilliant Crios (BC), experimental composite resin (EXP), and lithium disilicate ceramic IPS e.max CAD (REF). For 3-body wear, the CAD-CAM materials presented statistically significant differences in volume loss (P<.001) (Table 2). REF had lower volume loss than CS, SH, and BC. In addition, BC showed higher volume loss than EXP. A significant volume loss was found (P<.012) after 3-body wear simulation for all materials, with the exception of REF. Mastication simulation led to wear patterns with abrasion grooves produced by sliding movements (Fig. 4). At ×200 magnification, CS, SH, and KA revealed a rough, worn surface with deep grooves, whereas BC and EXP showed smooth surfaces with shallow grooves. THE JOURNAL OF PROSTHETIC DENTISTRY
At this low magnification, no scratches were detected for REF. At ×5000 magnification, plastic deformations of CS along the abrasion grooves became visible, and irregularly shaped, uncovered fillers smaller than 0.5 mm and pits of the same dimension were observed. For SH, a shattered surface and fracture blocks were apparent at ×5000 magnification. At ×200 magnification, KA showed deep furrows with a shattered surface at the ground (at ×5000 magnification). Some loose debris were also visible. The SEM analysis of BC revealed irregularly splintered fillers, holes, and pits at ×1500 and ×5000 magnification. The size of the fillers varied widely. The worn surface of EXP showed smooth insular areas at ×200 magnification and shallow micropits with rough ground at ×1500 magnification; short microploughing tracks were detected at ×5000 magnification. Also at ×5000 magnification, raised insular zones surrounded by rougher areas including shallow pits were apparent on the REF surface. The antagonists of CS, SH, and KA showed scratches induced by sliding movement during the mastication simulation (Fig. 5), whereas BC, EXP, and REF antagonists had a smoother surface appearance without deep scratches. For 3-body wear, depressions and waves were clearly seen on all materials. Figure 6 presents SEM images of each material at magnifications of ×200, ×1500, and ×5000. At the REF surface, grinding tracks from specimen preparation are visible, which indicates low 3-body wear. At ×5000 magnification, irregularly shaped fillers of CS and BC and holes of the same size as the fillers were Stöckl et al
-
2018
7
Figure 6. Scanning electron microscope images (original magnification ×200 [left], ×1500 [middle], and ×5000 [right]) of selected material specimens after 3-body wear. Acronyms indicate test materials. White scale bars refer to 100 mm, 10 mm, and 5 mm. BC, Brilliant Crios; CS, Cerasmart; EXP, experimental composite resin; KA, Katana Avencia; REF, lithium disilicate ceramic IPS e.max CAD; SH, SHOFU Block HC.
Stöckl et al
THE JOURNAL OF PROSTHETIC DENTISTRY
8
visible (Fig. 6, lines 1 and 4). On the surface of SH and EXP, rounder shaped structures (both spheres and holes [Fig. 6, lines 2 and 5]) of different sizes were detected. These structures were bigger than the fillers of the respective material. For KA and REF (Fig. 6, lines 3 and 6), none of these structures were visible. DISCUSSION The longevity of dental materials is affected by wear. In this study, dental CAD-CAM composite resins were macro- and microtopographically examined. A new script in R software was programmed to calculate volume loss.31 The procedure applied numerical integration based on postcutoff area and residuals adjusted for the specimens’ geometry. For both 2- and 3-body wear, a post hoc power analysis revealed that the sample size of 12 in each group had a 99% power to detect the difference in means between the reference material and the material with the highest effect. The sample size for wear evaluation was sufficient. The best global performance in the 2-body wear test methods was achieved by the experimental composite resin and the lithium disilicate. For 2-body wear, BC and CS also belonged to the group of higher wear resistant materials. SH and KA, the composite resins with the lowest filler content and a brittle matrix containing triethylene glycol dimethacrylate (TEGDMA), had the highest volume loss. The relationship between volume loss in 2-body wear and TEGDMA content has been reported previously.18 In contrast to poor resistance against 2-body wear, KA performed well in the 3-body wear test. Here, BC was the material with the highest volume loss. The CAD-CAM materials with fillers in the low nanoscale range performed best in the 3-body wear test and had results comparable to the reference lithium disilicate. The presence of small filler particles is beneficial for wear resistance.32 Mitra et al33 also stated that nanofilled composite resins showed better resistance in 3-body wear testing than microfilled and microhybrid composite resins. Oliveira et al34 reported that fine, dispersed fillers might have strengthened the resin matrix, protecting the organic matrix from wear. Furthermore, only a small volume can be displaced due to the wear process. The hypothesis that the 2- and 3-body wear test methods provide comparable volume loss for the different materials was rejected. In addition to determining volume loss, studies should include morphological analyses to explore the wear mechanism.27 Microtopographical analysis of the worn surfaces can help visualize the wear mechanisms, which are material, shape, and size changing effects of the friction processes. Different wear mechanisms lead to different microscopic phenomena, which can be detected by analyzing the wear patterns of the tribologically THE JOURNAL OF PROSTHETIC DENTISTRY
Volume
-
Issue
-
stressed surface.19 The wear patterns found in the present study showed differences between 2- and 3-body wear. In previous studies where the wear behavior of direct placement composite resins was evaluated, the same observation was described.22,26 The principle mechanisms of 2-body wear were abrasion and surface fatigue. After 2-body wear, the surface appearance varied widely among the different material groups. The surfaces of the enamel antagonists from the material groups with higher volume loss (CS, SH, KA) showed deep scratches. These scratches corresponded to those seen on the surfaces of the respective material specimens. All scratches were in the sliding direction and represented a typical wear pattern for abrasion. Groups BC, EXP, and REF had smoother surfaces after 2-body wear than SH or KA. The pits with their rough surfaces and the surface cracks indicated surface fatigue as the wear mechanism. Particularly for REF, surface fatigue was the principal wear mechanism. The CAD-CAM composite resins showed evidence of abrasion and surface fatigue. The dominant wear mechanism for 3-body wear was hydroabrasive erosion. As observed in the SEM analysis, the inorganic fillers of the CAD-CAM composite resins were not directly stressed but were displaced when the matrix was worn. The shape of the fillers mainly influenced the appearance of the surface after wear simulation. EXP contains 80% nanofillers but also contains larger clusters with high wear resistance, which might have contributed to the good performance of this material. The clusters seen in the SEM analysis are probably firmly bonded to the surrounding polymer matrix. In 3-body wear, they withstood the hydroabrasive erosion and behaved like compact particles. In 2-body wear, the clusters were abraded and the SEM images showed smooth insular areas. The second null hypothesis, that the materials would show comparable wear behavior for the 2- and 3-body wear methods, was rejected. In vivo wear mechanisms are complex and differ from patient to patient.20 Even though it has been claimed, the authors are unaware of scientific evidence that results in in vitro simulations correspond to clinical situations.23 A laboratory test, even with sophisticated wear testers, can only indicate how the tested materials will perform clinically. To predict the typical clinical wear resistance of a material, wear tests with different wear conditions are necessary.21 The geometric method used for macrotopographical examination and quantification provided many advantages. The files from the scanner were in text format and were easily processed in R software. The volume loss quantification was unified and repeatable for all specimens. In the case of missing information, the approach could be combined with an imputation step. The method is broadly applicable not only for flat but also for tall or curved specimens. The geometric approach has the Stöckl et al
-
2018
potential to be extended to the automatic analysis of differences in registered scans. The functions in R can be obtained from the authors upon request. A critical aspect may be the independent evaluation of scans of the same specimen at baseline and after 3-body wear simulation. The 2 scans were not aligned, so the volume loss had to be quantified independently. CONCLUSIONS Within the limitations of this in vitro study, the following conclusions were drawn: 1. Both of the wear test methods provided different volume losses among the materials. 2. The CAD-CAM materials showed different levels of wear for the 2- and 3-body wear tests. 3. The microtopographic examination provided supplemental information concerning the failure mechanisms of the different materials. REFERENCES 1. Miyazaki T, Hotta Y, Kunii J, Kuriyama S, Tamaki Y. A review of dental CAD/ CAM: current status and future perspectives from 20 years of experience. Dent Mater J 2001;28:44-56. 2. Fasbinder DJ, Dennison JB, Heys D, Neiva G. A clinical evaluation of chairside lithium disilicate CAD/CAM crowns: a two-year report. J Am Dent Assoc 2010;141:10-4. 3. Magne P. Composite resins and bonded porcelain: the postamalgam era. J Calif Dent Assoc 2006;34:135-47. 4. Poticny DJ, Klim J. CAD/CAM in-office technology: innovations after 25 years for predictable, esthetic outcomes. J Am Dent Assoc 2010;141:5-9. 5. Fasbinder DJ. Chairside CAD/CAM: an overview of restorative material options. Compend Contin Educ Dent 2012;33:50. 52-8. 6. Chavali R, Nejat AH, Lawson NC. Machinability of CAD-CAM materials. J Prosthet Dent 2017;118:194-9. 7. Harada A, Nakamura K, Kanno T, Inagaki R, Örtengren U, Niwano Y, et al. Fracture resistance of computer-aided design/computer-aided manufacturing-generated composite resin-based molar crowns. Eur J Oral Sci 2015;123:122-9. 8. Nakamura K, Harada A, Inagaki R, Kanno T, Niwano Y, Milleding P, et al. Fracture resistance of monolithic zirconia molar crowns with reduced thickness. Acta Odontol Scand 2015;73:602-8. 9. Stawarczyk B, Ender A, Trottmann A, Özcan M, Fischer J, Hämmerle CH. Load-bearing capacity of CAD/CAM milled polymeric three-unit fixed dental prostheses: effect of aging regimens. Clin Oral Investig 2012;16: 1669-77. 10. Stawarczyk B, Sener B, Trottmann A, Roos M, Ozcan M, Hämmerle CH. Discoloration of manually fabricated resins and industrially fabricated CAD/ CAM blocks versus glass-ceramic: effect of storage media, duration, and subsequent polishing. Dent Mater J 2012;31:377-83. 11. Stawarczyk B, Özcan M, Trottmann A, Schmutz F, Roos M, Hämmerle C. Two-body-wear rate of CAD/CAM resin blocks and their enamel antagonists. J Prosthet Dent 2013;109:325-32. 12. Lambrechts P, Braem M, Vuylsteke-Wauters M, Vanherle G. Quantitative in vivo wear of human enamel. J Dent Res 1989;68:1752-4. 13. Ahmed KE, Whitters J, Ju X, Pierce SG, MacLeod CN, Murray CA. Clinical monitoring of tooth wear progression in patients over a period of one year using CAD/CAM. Int J Prosthodont 2017;30:153-5.
Stöckl et al
9
14. Ferracane JL. Resin-based composite performance: are there some things we can’t predict. Dent Mater 2013;29:51-8. 15. Da Rosa Rodolpho PA, Cenci MS, Donassollo TA, Loguercio AD, Demarco FF. A clinical evaluation of posterior composite restorations: 17-year findings. J Dent 2006;34:427-35. 16. Ankyu S, Nakamura K, Harada A, Hong G, Kanno T, Niwano Y, et al. Fatigue analysis of computer-aided design/computer-aided manufacturing resinbased composite vs. lithium disilicate glass-ceramics. Eur J Oral Sci 2016;124: 387-95. 17. Kassem AS, Atta O, Et.-Mowafy O. Fatigue resistance and microleakage of CAD/ CAM ceramic and composite molar crowns. J Prosthodont 2012;21:28-32. 18. Stawarczyk B, Liebermann A, Eichberger M, Güth JF. Evaluation of mechanical and optical behavior of current esthetic dental restorative CAD/CAM composites. J Mech Behav Biomed Mater 2015;55:1-11. 19. Czichos H, Habig KH. Tribologie-handbuch. 4th ed. Wiesbaden: Friedr Vieweg & Sohn Verlag; 2015. p. 13-160. 20. Heintze SD, Barkmeier WW, Latta MA, Rousson V. Round robin test: wear of nine dental restorative materials in six different wear simulatorsdsupplement to the round robin test of 2005. Dent Mater 2011;27:1-9. 21. International Organization for Standardization. ISO/TS 14569-2. Dental materialsdguidance on testing of wear. Part 2. Wear by two- and/or threebody contact. Geneva: International Organization for Standardization; 2001. Available at: http://www.iso.org/iso/store.htm. 22. Heintze SD, Zappini G, Rousson V. Wear of ten dental restorative materials in five wear simulatorsdresults of a round robin test. Dent Mater 2005;21:304-17. 23. Heintze SD. How to qualify and validate wear simulation devices and methods. Dent Mater 2006;22:712-34. 24. Heintze SD, Cavalleri A, Forjanic M, Zellweger G, Rousson V. A comparison of three different methods for the quantification of the in vitro wear of dental materials. Dent Mater 2006;22:1051-62. 25. Wimmer T, Huffmann A, Eichberger M, Schmidlin P, Stawarczyk B. Twobody-wear rate of PEEK, CAD/CAM resin composite and PMMA: Effect of specimen geometries, antagonist materials and test set-up configuration. Dent Mater 2016;32:127-36. 26. Osiewicz A, Werner A, Pytko-Polonczyk J, Roeters F, Kleverlaan C. Contactand contact-free wear between various resin composites. Dent Mater 2015;31:134-40. 27. DeLong R. Intra-oral restorative materials wear: rethinking the current approaches: how to measure wear. Dent Mater 2006;22:702-11. 28. Demant CH, Streicher-Abel B, Garnica C. Industrial image processing. Visual quality control in manufacturing. 2nd ed. Berlin: Springer; 2013. p. 1-24. 29. Szeliski R. Computer vision. Algorithms and applications. Berlin: Springer; 2011. p. 1-26. 30. International Organization for Standardization. ISO/TS 11405. Dentistryd testing of adhesion to tooth structure. Geneva: International Organization for Standardization; 2015. Available at: http://www.iso.org/iso/store.htm. 31. R Foundation for Statistical Computing. A language and environment for statistical computing; R Foundation for Statistical Computing: Vienna, Austria, 2010. Available online: http://www.R-project.org. Accessed June 15, 2016. 32. Turssi CP, Ferracane JL, Vogel K. Filler features and their effects on wear and degree of conversion of particulate dental resin composites. Biomaterials 2005;26:4932-7. 33. Mitra SB, Wu D, Holmes BN. An application of nanotechnology in advanced dental materials. J Am Dent Assoc 2003;134:1382-90. 34. De Oliveria GU, Mondelli RFL, Rodrigues MC, Franco EB, Ishikiriama SK, Wang L. Impact of filler size and distribution on roughness and wear of composite resin after simulated toothbrushing. J Appl Oral Sci 2012;20:510-6. Corresponding author: Rüdiger Hampe Department of Prosthodontics, Dental School Ludwig-Maximilians-University Munich Goethestrasse 70 80336 Munich GERMANY Email: [email protected] Copyright © 2017 by the Editorial Council for The Journal of Prosthetic Dentistry.
THE JOURNAL OF PROSTHETIC DENTISTRY
Macro- and microtopographical examination and quantification of CAD-CAM composite resin 2- and 3-body wear Carolin Stöckl, BSc,a Rüdiger Hampe, Dipl-Ing (FH), MSc,b Bogna Stawarczyk, PD Dr Rer Biol Hum Dip-Ing (FH), MSc,c Miriam Haerst, Dr Dipl-Ing,d and Malgorzata Roos, PD Dr Phile Computer-aided design and ABSTRACT computer-aided manufacturing Statement of problem. The selection of an appropriate restorative material based on wear (CAD-CAM) allows highly behavior is important for the long-term success of a dental restoration. For computer-aided design precise fabrication of dental resand computer-aided manufacturing (CAD-CAM) composite resins, information about their wear torations. Due to the progress resistance and wear mechanism is scarce. in software and milling technolPurpose. The purpose of this in vitro study was to compare the 2- and 3-body wear of CAD-CAM ogies, chairside CAD-CAM use composite resins with that of lithium disilicate ceramic and to develop analysis software. has increased, with demand for Material and methods. Flat specimens were prepared from the following CAD-CAM composite metal-free esthetic options resins: Cerasmart (CS), SHOFU Block HC (SH), Katana Avencia (KA), Brilliant Crios (BC), an 1-4 contributing to the trend. experimental composite resin (EXP), and lithium disilicate ceramic IPS e.max CAD (REF). The Novel composite resin matespecimens underwent 2-body wear (50 N, 5/55 C, 400 000 cycles) opposed by human enamel rials have been developed antagonists. Specimen wheels were prepared with each material on each wheel for 3-body wear with a millet slurry (15 N, 15% slip, 200 000 cycles). All specimens were digitized by using a for dental CAD-CAM applicadedicated laser scanner. Analysis software was developed to calculate macrotopographical tions5 with improved machinexamination of volume loss. The microtopography of the surfaces was examined by using ability and less chipping than scanning electron microscopy. For data analysis, the Kruskal-Wallis test with the Tukey-Kramer 6 ceramics. Manufacturers claim post hoc test and the 1-sample Wilcoxon test were used (a=.05). improved restoration quality Results. After 2-body wear simulation, SH and KA presented higher volume loss than the other for CAD-CAM composite resin CAD-CAM materials. For 3-body wear, REF had lower volume loss than CS, SH, or BC. In addition, blocks compared with manually BC led to higher volume loss than EXP. The patterns of 2- and 3-body wear were different. polymerized (laboratory or Conclusions. The ceramic showed good global wear resistance. The volume loss of the CAD-CAM chairside) composite resins composite resins differed and depended on the material. The 2- and 3-body wear test methods because of increased polymeritended to differ with regard to volume loss. Examination of the worn surfaces revealed different zation. CAD-CAM generated mechanisms acting in 2- and 3-body wear test. (J Prosthet Dent 2018;-:---) composite resin restorations show fewer voids than direct placement composite resin show wear behavior comparable to that of natural dentirestorations7 and have similar or better mechanical proption, with clinical wear rates in the range of 15 to 29 mm per erties and color stability than dental glass ceramics.8-11 year.12 Patients with parafunctional habits show increased Wear behavior is an important aspect of all dental tooth wear of more than 140 mm per year.13 Together with restorative materials. Ideally, restorative materials should secondary caries and fracture, wear has been identified as a
a
Graduate student, Institute of Medical and Polymer Engineering, Faculty of Mechanical Engineering, Technical University, Munich, Germany. Research Fellow of Dental Material Unit, Department of Prosthodontics, Ludwig-Maximilians-University, Munich, Germany. Scientific Head of Dental Material Unit, Department of Prosthodontics, Ludwig-Maximilians-University, Munich, Germany. d Adjunct Professor, Institute of Medical and Polymer Engineering, Faculty of Mechanical Engineering, Technical University, Munich, Germany. e Senior Statistician, Department of Biostatistics, Epidemiology, Biostatistics and Prevention Institute, University of Zurich, Zurich, Switzerland. b c
THE JOURNAL OF PROSTHETIC DENTISTRY
1
2
Volume
Clinical Implications An important aspect of all dental restorative materials is their wear behavior. Some but not all novel CAD-CAM composite resins seem to be wear resistant alternatives to ceramics for dental CAD-CAM restorations.
chief reason for the failure of direct composite resin restorations.14,15 CAD-CAM composite resins have high fatigue and wear resistance and can withstand clinically applied forces well.11,16-18 The reduced wear of the enamel antagonist compared with that of ceramics is another advantage of composite resins.11,18 In contrast with other mechanical properties, wear is not a material property but a system property of the tribological system.19 Consequently, no single generally accepted wear test method exists. A combination of at least 2 different wear test simulations is recommended to assess the wear resistance of materials.19-22 In principle, the methods used can be divided into tribological systems with mainly 2- or 3-body wear. Mastication simulation is an established method for simulating 2-body wear.18,22-25 For 3-body wear simulation, the Academic Centre for Dentistry Amsterdam (ACTA) wear machine has also been used.22,26 To analyze the wear properties of dental restorative materials, suitable quantitative evaluation models should be applied. Optical 3-dimensional (3D) scanning or tactile 3D scanning are the most suitable methods for the accurate and reproducible examination of volume loss.27 The importance of visualization and graphical processing of the macrotopographical information provided by scans has been emphasized.28,29 Heintze23 reported a close relationship between vertical and volume loss and stated that it is reasonable to measure only a single variable. Notwithstanding the vigorous development of graphic facilities, the authors are unaware of an analysis of both macrotopographical features and wear volume estimations. The purpose of this study was to determine the wear behavior of 5 CAD-CAM composite resins by using the commonly used methodologies of 2-body wear by using a mastication simulator and 3-body wear by using an ACTA machine and then compare the results with those of a lithium disilicate ceramic. One goal was to develop new software to analyze the digital scan data provided by an optical 3D scanner. Complementary to the quantification of volume loss, the worn surfaces were analyzed topographically by using scanning electron microscopy (SEM) to assess the wear mechanisms. The tested null hypotheses were that the 2- and the 3-body wear test methods would show comparable tendencies concerning
THE JOURNAL OF PROSTHETIC DENTISTRY
-
Issue
-
volume loss among the different material groups and that the CAD-CAM materials would show comparable wear behavior for the 2- and 3-body wear test methods. MATERIAL AND METHODS Each material group (Table 1) in each wear test method consisted of 12 specimens. The specimens were fabricated, and the worn specimens were digitized by a trained operator (C.S.). For 2-body wear, the material specimens were cut (thickness, 2 mm) from CAD-CAM blocks under water cooling (Secotom-50; Struers GmbH), using the following parameters: speed of 2200 rpm; feed rate of 0.09 mm/s for all composite resins and 0.07 mm/s for the lithium disilicate. The lithium disilicate was then crystallized at a final temperature of 840 C under vacuum according to the manufacturer’s instructions (Programat EP 5000; Ivoclar Vivadent AG). All specimens were embedded in acrylic resin (Scandiform/ScandiQuick; Scan-DIA, Struers GmbH) and polished with silicon carbide (SiC) paper in 4 steps up to P4000 under constant pressure and water cooling (Tegramin-20; Struers GmbH). The specimens were stored for 14 days in distilled water at 37 C before wear testing. Extracted human teeth were obtained from dentists in the Munich area. After extraction, the teeth were stored in a 0.5% chloramine solution (Chloramine-T; Sigma-Aldrich Laborchemikalien GmbH) at room temperature for 7 days and then in distilled water at 5 C for a maximum of 6 months.30 After the mesiobuccal cusps were sectioned, the teeth were embedded in stainless steel molds with dental amalgam (Dispersalloy; Dentsply Sirona). A shape congruent spherical cusp of 3 mm in diameter with 40 mm and 8 mm grit was generated by using a bench drill (BT-BD 1020 D; Einhell Germany AG). The specimens were mounted in a mastication simulator (CS-4; SD Mechatronik GmbH) (Fig. 1). For the simulation, a vertical load of 50 N at 1.2 Hz was applied for 400 000 cycles with a sliding movement of 0.7 mm; they were thermocycled between 5 C and 55 C with a dwell time of 60 seconds for 2000 cycles. For 3-body wear, 6 specimen wheels were prepared. With 12 cavities in a wheel, 2 specimens of each material were placed on 1 wheel. Specimens of the same material were positioned diametrically opposed. To prepare the cavities, 12 slices of each material were cut (thickness, 5 mm) from CAD-CAM blocks under water cooling (Secotom-50; Struers GmbH). The lithium disilicate was crystallized. The wheels were airborne particle abraded (110-mm alumina powder, 200 kPa, Basic Quattro; Renfert GmbH) and silanated (ESPE Sil; 3M ESPE). Custom tray material (Omnident GmbH) was used to cement the material specimens into the cavities. After removing any Stöckl et al
-
2018
3
Table 1. Materials tested Manufacturer
Lot No. Shade and Block Sizes
Product Name
Abbreviation
Cerasmart
CS
GC Europe NV
Composition
SHOFU Block HC
SH
SHOFU Inc
Katana Avencia Block
KA
Kuraray Noritake Dental Inc
000115 14L/A2 LT
Organic part: UDMA, TEGDMA Inorganic part: filler content: 62wt% aluminum oxide (20 nm), SiO2 (40 nm)
Brilliant Crios
BC
Coltène AG
G93044 A2 HT 14
Organic part: crosslinked methacrylates Inorganic part: filler content (71 wt%) silica and barium glass
1407311 A2 LT 14L
Organic part: Bis-MEPP, UDMA, DMA Inorganic part: filler content 71wt% silica (20 nm) and barium glass (300 nm)
111501 A2 LT M
Organic part: UDMA, TEGDMA Inorganic part: filler content 61wt% silica powder, fumed silica, zirconia silicate
Experimental Composite EXP
Ivoclar Vivadent AG
b.28923 HAT A2/C14
Organic part: resin composite Inorganic part: 80wt% nanoparticles
IPS e.max CAD
Ivoclar Vivadent AG
T44670 HAT A3/B 40
Lithium disilicate crystals (Li2Si2O5) embedded in a glassy matrix
REF
Bis-MEPP, 2,2-bis-(4-(2-methacryloxyethoxy)phenyl)propane; DMA, dimethacrylate; TEGDMA, triethylene glycol dimethacrylate; UDMA, urethane dimethacrylate.
Figure 1. Human enamel antagonist and tested material in chamber of mastication simulator.
excess material and after prepolymerization for 55 seconds at 400 to 500 nm wavelength (Quick curing light; Ivoclar Vivadent AG), the final polymerization was ensured by light irradiation by using a wavelength between 370 and 500 nm for 180 seconds (bre.Lux Power Unit; bredent GmbH & Co, KG). The wheels were rounded on a lathe under water cooling using diamond disks (speed, 500 rpm; feed motion, 0.08 mm) and stored for 14 days in distilled water at 37 C. The abrasive slurry was mixed (International Organization for Standardization/Technical Specification 14569 standard21) and contained 150 g millet, 1 g sodium azide, and 220 mL deionized water. The millet grains were milled for 5 seconds (MKM 6000; Robert Bosch Hausgeräte GmbH). The wheels were placed in the testing device (ACTA 3; Willytec GmbH) (Fig. 2). The specimen wheel and the antagonistic stainless-steel wheel rotated in different directions with 15% difference in circumferential speed while having no direct contact. The force which pressed the wheels together was adjusted to 15 N. The angular frequency of Stöckl et al
Figure 2. Antagonist wheel and wheel with tested materials.
the specimen wheel was set to 1 Hz. The speed of the antagonistic wheel was calculated separately for each run from the following equations21: dPK ×f PK ×p ; v PK = 60
(1)
where vPK=circumferential speed of specimen wheel (mm/s); dPK=diameter of specimen wheel (mm); fPK=frequency of specimen wheel (1/min) and fA =
vA
p×dA
×60=
0:85v PK ×60; p×dA
(2)
where fA=frequency of antagonist wheel (1/min); vA=circumferential speed of antagonist wheel (mm/s); dA=diameter of antagonist wheel (mm) A wear-in of 60 000 cycles was carried out before the simulation. The wear simulation was conducted with 200 000 cycles and with the same parameters as the wear-in process. A new millet slurry was used for each run but was not refreshed within a run in order to have a THE JOURNAL OF PROSTHETIC DENTISTRY
4
Volume
-
Issue
-
Figure 3. A, Material of 2-body-wear scan. B, With region of interest inside. C, With region of interest outside. D, Post-cutoff area. Scratches visible in A on left and right were placed intentionally as marks on all specimens. Table 2. Median (IQR) for volume loss for all material groups together with results of Kruskal-Wallis and 1-sample Wilcoxon test
Material Groups*
2-Body-Wear Specimens (P<.001)†
3-Body-Wear Specimens (after wear-in) (P<.001)†
CS
0.31ab (0.15)
1.84b (1.31)
SH
0.49b (0.21)
1.40b (1.14)
KA
0.64b (0.13)
0.84ab (1.36)
BC EXP REF
a
2.31bc (0.55)
a
0.76ab (0.65)
a
0.13a (0.62)
0.22 (0.08) 0.14 (0.19) 0.20 (0.12)
*Except for REF under 3-body-wear conditions, all materials revealed significant volume loss. † Different superscript letters indicate significant differences among tested groups.
robust test procedure with a low number of steps and to minimize variation between the cycles. A dedicated laser scanner (LAS-20; SD Mechatronik GmbH) with a horizontal resolution of 40 mm, and a vertical resolution of 0.8 mm was used for digitization. In the macrotopographical approach, the volume loss (mm3) was quantified by applying a geometric approach programmed in R software (R Foundation for Statistical Computing; Vienna).31 Given the scan of a 2-body wear specimen (Fig. 3A), 2 disjointed regions of interest (ROI) were set, ROI(inside) (Fig. 3B) and ROI(outside) (Fig. 3C). The ROI(inside) was chosen to completely THE JOURNAL OF PROSTHETIC DENTISTRY
include the area with the wear hollow. A multiple regression on the ROI(outside) modeled its geometric properties (inclination and curvature). Predicted values for ROI(inside) and residuals were subsequently computed. A cutoff based on reference residuals was applied, leaving a postcutoff area for volume estimation (Fig. 3D). For 3-body wear, volume loss estimates were obtained by numerical integration based on the postcutoff area and curvature-adjusted residuals. The final volume loss was adjusted for baseline wear by subtracting the volume loss at baseline from the volume loss after wear simulation. For baseline scans with missing volume estimations, the values were imputed by the corresponding sample median. All scans were evaluated by one statistician (M.R.) to ensure the unity of approach and quality. Median and interquartile range (IQR) were computed for descriptive statistics. The Kruskal-Wallis test together with the Tukey-Kramer post hoc test were used to identify differences in volume loss among the tested groups. The 1-sample Wilcoxon test was applied to evaluate the volume loss within each test group (IBM SPSS Statistics v23.0; IBM Corp, and R Foundation for Statistical Computing) (a=.05). Stöckl et al
-
2018
5
Figure 4. Scanning electron microscope images (original magnification ×200 [left], ×1500 [middle], and ×5000 [right]) of selected material specimens after 2-body wear. Acronyms indicate test materials. White scale bars refer to 100 mm, 10 mm, and 5 mm. BC, Brilliant Crios; CS, Cerasmart; EXP, experimental composite resin; KA, Katana Avencia; REF, lithium disilicate ceramic IPS e.max CAD; SH, SHOFU Block HC.
Stöckl et al
THE JOURNAL OF PROSTHETIC DENTISTRY
6
Volume
-
Issue
-
Figure 5. Scanning electron microscope images (original magnification ×50) for antagonists of selected antagonist specimens after 2-body wear. Acronyms are indicating counterpart materials. White scale bars refer to 500 mm. BC, Brilliant Crios; CS, Cerasmart; EXP, experimental composite resin; KA, Katana Avencia; REF, lithium disilicate ceramic IPS e.max CAD; SH, SHOFU Block HC.
To analyze the wear patterns, SEM images (×50 magnification for antagonists and ×200, ×1500, ×5000 magnification for materials) were made (JSM-6390; JEOL Ltd) at 10-kV acceleration voltage with a variable working distance of between 7 and 9 mm. Cleaned specimens had been stored for 7 days in a desiccator and sputter coated with gold to a thickness of 7.5 mm (SCD005; Bal-Tec AG). RESULTS For 2-body wear, volume loss varied with the tested materials (P<.001) (Table 2). Generally, all CAD-CAM materials presented significant volume loss after mastication simulation compared with baseline (P<.001). SHOFU Block HC (SH) and Katana Avencia (KA) showed higher volume loss than Cerasmart (CS), Brilliant Crios (BC), experimental composite resin (EXP), and lithium disilicate ceramic IPS e.max CAD (REF). For 3-body wear, the CAD-CAM materials presented statistically significant differences in volume loss (P<.001) (Table 2). REF had lower volume loss than CS, SH, and BC. In addition, BC showed higher volume loss than EXP. A significant volume loss was found (P<.012) after 3-body wear simulation for all materials, with the exception of REF. Mastication simulation led to wear patterns with abrasion grooves produced by sliding movements (Fig. 4). At ×200 magnification, CS, SH, and KA revealed a rough, worn surface with deep grooves, whereas BC and EXP showed smooth surfaces with shallow grooves. THE JOURNAL OF PROSTHETIC DENTISTRY
At this low magnification, no scratches were detected for REF. At ×5000 magnification, plastic deformations of CS along the abrasion grooves became visible, and irregularly shaped, uncovered fillers smaller than 0.5 mm and pits of the same dimension were observed. For SH, a shattered surface and fracture blocks were apparent at ×5000 magnification. At ×200 magnification, KA showed deep furrows with a shattered surface at the ground (at ×5000 magnification). Some loose debris were also visible. The SEM analysis of BC revealed irregularly splintered fillers, holes, and pits at ×1500 and ×5000 magnification. The size of the fillers varied widely. The worn surface of EXP showed smooth insular areas at ×200 magnification and shallow micropits with rough ground at ×1500 magnification; short microploughing tracks were detected at ×5000 magnification. Also at ×5000 magnification, raised insular zones surrounded by rougher areas including shallow pits were apparent on the REF surface. The antagonists of CS, SH, and KA showed scratches induced by sliding movement during the mastication simulation (Fig. 5), whereas BC, EXP, and REF antagonists had a smoother surface appearance without deep scratches. For 3-body wear, depressions and waves were clearly seen on all materials. Figure 6 presents SEM images of each material at magnifications of ×200, ×1500, and ×5000. At the REF surface, grinding tracks from specimen preparation are visible, which indicates low 3-body wear. At ×5000 magnification, irregularly shaped fillers of CS and BC and holes of the same size as the fillers were Stöckl et al
-
2018
7
Figure 6. Scanning electron microscope images (original magnification ×200 [left], ×1500 [middle], and ×5000 [right]) of selected material specimens after 3-body wear. Acronyms indicate test materials. White scale bars refer to 100 mm, 10 mm, and 5 mm. BC, Brilliant Crios; CS, Cerasmart; EXP, experimental composite resin; KA, Katana Avencia; REF, lithium disilicate ceramic IPS e.max CAD; SH, SHOFU Block HC.
Stöckl et al
THE JOURNAL OF PROSTHETIC DENTISTRY
8
visible (Fig. 6, lines 1 and 4). On the surface of SH and EXP, rounder shaped structures (both spheres and holes [Fig. 6, lines 2 and 5]) of different sizes were detected. These structures were bigger than the fillers of the respective material. For KA and REF (Fig. 6, lines 3 and 6), none of these structures were visible. DISCUSSION The longevity of dental materials is affected by wear. In this study, dental CAD-CAM composite resins were macro- and microtopographically examined. A new script in R software was programmed to calculate volume loss.31 The procedure applied numerical integration based on postcutoff area and residuals adjusted for the specimens’ geometry. For both 2- and 3-body wear, a post hoc power analysis revealed that the sample size of 12 in each group had a 99% power to detect the difference in means between the reference material and the material with the highest effect. The sample size for wear evaluation was sufficient. The best global performance in the 2-body wear test methods was achieved by the experimental composite resin and the lithium disilicate. For 2-body wear, BC and CS also belonged to the group of higher wear resistant materials. SH and KA, the composite resins with the lowest filler content and a brittle matrix containing triethylene glycol dimethacrylate (TEGDMA), had the highest volume loss. The relationship between volume loss in 2-body wear and TEGDMA content has been reported previously.18 In contrast to poor resistance against 2-body wear, KA performed well in the 3-body wear test. Here, BC was the material with the highest volume loss. The CAD-CAM materials with fillers in the low nanoscale range performed best in the 3-body wear test and had results comparable to the reference lithium disilicate. The presence of small filler particles is beneficial for wear resistance.32 Mitra et al33 also stated that nanofilled composite resins showed better resistance in 3-body wear testing than microfilled and microhybrid composite resins. Oliveira et al34 reported that fine, dispersed fillers might have strengthened the resin matrix, protecting the organic matrix from wear. Furthermore, only a small volume can be displaced due to the wear process. The hypothesis that the 2- and 3-body wear test methods provide comparable volume loss for the different materials was rejected. In addition to determining volume loss, studies should include morphological analyses to explore the wear mechanism.27 Microtopographical analysis of the worn surfaces can help visualize the wear mechanisms, which are material, shape, and size changing effects of the friction processes. Different wear mechanisms lead to different microscopic phenomena, which can be detected by analyzing the wear patterns of the tribologically THE JOURNAL OF PROSTHETIC DENTISTRY
Volume
-
Issue
-
stressed surface.19 The wear patterns found in the present study showed differences between 2- and 3-body wear. In previous studies where the wear behavior of direct placement composite resins was evaluated, the same observation was described.22,26 The principle mechanisms of 2-body wear were abrasion and surface fatigue. After 2-body wear, the surface appearance varied widely among the different material groups. The surfaces of the enamel antagonists from the material groups with higher volume loss (CS, SH, KA) showed deep scratches. These scratches corresponded to those seen on the surfaces of the respective material specimens. All scratches were in the sliding direction and represented a typical wear pattern for abrasion. Groups BC, EXP, and REF had smoother surfaces after 2-body wear than SH or KA. The pits with their rough surfaces and the surface cracks indicated surface fatigue as the wear mechanism. Particularly for REF, surface fatigue was the principal wear mechanism. The CAD-CAM composite resins showed evidence of abrasion and surface fatigue. The dominant wear mechanism for 3-body wear was hydroabrasive erosion. As observed in the SEM analysis, the inorganic fillers of the CAD-CAM composite resins were not directly stressed but were displaced when the matrix was worn. The shape of the fillers mainly influenced the appearance of the surface after wear simulation. EXP contains 80% nanofillers but also contains larger clusters with high wear resistance, which might have contributed to the good performance of this material. The clusters seen in the SEM analysis are probably firmly bonded to the surrounding polymer matrix. In 3-body wear, they withstood the hydroabrasive erosion and behaved like compact particles. In 2-body wear, the clusters were abraded and the SEM images showed smooth insular areas. The second null hypothesis, that the materials would show comparable wear behavior for the 2- and 3-body wear methods, was rejected. In vivo wear mechanisms are complex and differ from patient to patient.20 Even though it has been claimed, the authors are unaware of scientific evidence that results in in vitro simulations correspond to clinical situations.23 A laboratory test, even with sophisticated wear testers, can only indicate how the tested materials will perform clinically. To predict the typical clinical wear resistance of a material, wear tests with different wear conditions are necessary.21 The geometric method used for macrotopographical examination and quantification provided many advantages. The files from the scanner were in text format and were easily processed in R software. The volume loss quantification was unified and repeatable for all specimens. In the case of missing information, the approach could be combined with an imputation step. The method is broadly applicable not only for flat but also for tall or curved specimens. The geometric approach has the Stöckl et al
-
2018
potential to be extended to the automatic analysis of differences in registered scans. The functions in R can be obtained from the authors upon request. A critical aspect may be the independent evaluation of scans of the same specimen at baseline and after 3-body wear simulation. The 2 scans were not aligned, so the volume loss had to be quantified independently. CONCLUSIONS Within the limitations of this in vitro study, the following conclusions were drawn: 1. Both of the wear test methods provided different volume losses among the materials. 2. The CAD-CAM materials showed different levels of wear for the 2- and 3-body wear tests. 3. The microtopographic examination provided supplemental information concerning the failure mechanisms of the different materials. REFERENCES 1. Miyazaki T, Hotta Y, Kunii J, Kuriyama S, Tamaki Y. A review of dental CAD/ CAM: current status and future perspectives from 20 years of experience. Dent Mater J 2001;28:44-56. 2. Fasbinder DJ, Dennison JB, Heys D, Neiva G. A clinical evaluation of chairside lithium disilicate CAD/CAM crowns: a two-year report. J Am Dent Assoc 2010;141:10-4. 3. Magne P. Composite resins and bonded porcelain: the postamalgam era. J Calif Dent Assoc 2006;34:135-47. 4. Poticny DJ, Klim J. CAD/CAM in-office technology: innovations after 25 years for predictable, esthetic outcomes. J Am Dent Assoc 2010;141:5-9. 5. Fasbinder DJ. Chairside CAD/CAM: an overview of restorative material options. Compend Contin Educ Dent 2012;33:50. 52-8. 6. Chavali R, Nejat AH, Lawson NC. Machinability of CAD-CAM materials. J Prosthet Dent 2017;118:194-9. 7. Harada A, Nakamura K, Kanno T, Inagaki R, Örtengren U, Niwano Y, et al. Fracture resistance of computer-aided design/computer-aided manufacturing-generated composite resin-based molar crowns. Eur J Oral Sci 2015;123:122-9. 8. Nakamura K, Harada A, Inagaki R, Kanno T, Niwano Y, Milleding P, et al. Fracture resistance of monolithic zirconia molar crowns with reduced thickness. Acta Odontol Scand 2015;73:602-8. 9. Stawarczyk B, Ender A, Trottmann A, Özcan M, Fischer J, Hämmerle CH. Load-bearing capacity of CAD/CAM milled polymeric three-unit fixed dental prostheses: effect of aging regimens. Clin Oral Investig 2012;16: 1669-77. 10. Stawarczyk B, Sener B, Trottmann A, Roos M, Ozcan M, Hämmerle CH. Discoloration of manually fabricated resins and industrially fabricated CAD/ CAM blocks versus glass-ceramic: effect of storage media, duration, and subsequent polishing. Dent Mater J 2012;31:377-83. 11. Stawarczyk B, Özcan M, Trottmann A, Schmutz F, Roos M, Hämmerle C. Two-body-wear rate of CAD/CAM resin blocks and their enamel antagonists. J Prosthet Dent 2013;109:325-32. 12. Lambrechts P, Braem M, Vuylsteke-Wauters M, Vanherle G. Quantitative in vivo wear of human enamel. J Dent Res 1989;68:1752-4. 13. Ahmed KE, Whitters J, Ju X, Pierce SG, MacLeod CN, Murray CA. Clinical monitoring of tooth wear progression in patients over a period of one year using CAD/CAM. Int J Prosthodont 2017;30:153-5.
Stöckl et al
9
14. Ferracane JL. Resin-based composite performance: are there some things we can’t predict. Dent Mater 2013;29:51-8. 15. Da Rosa Rodolpho PA, Cenci MS, Donassollo TA, Loguercio AD, Demarco FF. A clinical evaluation of posterior composite restorations: 17-year findings. J Dent 2006;34:427-35. 16. Ankyu S, Nakamura K, Harada A, Hong G, Kanno T, Niwano Y, et al. Fatigue analysis of computer-aided design/computer-aided manufacturing resinbased composite vs. lithium disilicate glass-ceramics. Eur J Oral Sci 2016;124: 387-95. 17. Kassem AS, Atta O, Et.-Mowafy O. Fatigue resistance and microleakage of CAD/ CAM ceramic and composite molar crowns. J Prosthodont 2012;21:28-32. 18. Stawarczyk B, Liebermann A, Eichberger M, Güth JF. Evaluation of mechanical and optical behavior of current esthetic dental restorative CAD/CAM composites. J Mech Behav Biomed Mater 2015;55:1-11. 19. Czichos H, Habig KH. Tribologie-handbuch. 4th ed. Wiesbaden: Friedr Vieweg & Sohn Verlag; 2015. p. 13-160. 20. Heintze SD, Barkmeier WW, Latta MA, Rousson V. Round robin test: wear of nine dental restorative materials in six different wear simulatorsdsupplement to the round robin test of 2005. Dent Mater 2011;27:1-9. 21. International Organization for Standardization. ISO/TS 14569-2. Dental materialsdguidance on testing of wear. Part 2. Wear by two- and/or threebody contact. Geneva: International Organization for Standardization; 2001. Available at: http://www.iso.org/iso/store.htm. 22. Heintze SD, Zappini G, Rousson V. Wear of ten dental restorative materials in five wear simulatorsdresults of a round robin test. Dent Mater 2005;21:304-17. 23. Heintze SD. How to qualify and validate wear simulation devices and methods. Dent Mater 2006;22:712-34. 24. Heintze SD, Cavalleri A, Forjanic M, Zellweger G, Rousson V. A comparison of three different methods for the quantification of the in vitro wear of dental materials. Dent Mater 2006;22:1051-62. 25. Wimmer T, Huffmann A, Eichberger M, Schmidlin P, Stawarczyk B. Twobody-wear rate of PEEK, CAD/CAM resin composite and PMMA: Effect of specimen geometries, antagonist materials and test set-up configuration. Dent Mater 2016;32:127-36. 26. Osiewicz A, Werner A, Pytko-Polonczyk J, Roeters F, Kleverlaan C. Contactand contact-free wear between various resin composites. Dent Mater 2015;31:134-40. 27. DeLong R. Intra-oral restorative materials wear: rethinking the current approaches: how to measure wear. Dent Mater 2006;22:702-11. 28. Demant CH, Streicher-Abel B, Garnica C. Industrial image processing. Visual quality control in manufacturing. 2nd ed. Berlin: Springer; 2013. p. 1-24. 29. Szeliski R. Computer vision. Algorithms and applications. Berlin: Springer; 2011. p. 1-26. 30. International Organization for Standardization. ISO/TS 11405. Dentistryd testing of adhesion to tooth structure. Geneva: International Organization for Standardization; 2015. Available at: http://www.iso.org/iso/store.htm. 31. R Foundation for Statistical Computing. A language and environment for statistical computing; R Foundation for Statistical Computing: Vienna, Austria, 2010. Available online: http://www.R-project.org. Accessed June 15, 2016. 32. Turssi CP, Ferracane JL, Vogel K. Filler features and their effects on wear and degree of conversion of particulate dental resin composites. Biomaterials 2005;26:4932-7. 33. Mitra SB, Wu D, Holmes BN. An application of nanotechnology in advanced dental materials. J Am Dent Assoc 2003;134:1382-90. 34. De Oliveria GU, Mondelli RFL, Rodrigues MC, Franco EB, Ishikiriama SK, Wang L. Impact of filler size and distribution on roughness and wear of composite resin after simulated toothbrushing. J Appl Oral Sci 2012;20:510-6. Corresponding author: Rüdiger Hampe Department of Prosthodontics, Dental School Ludwig-Maximilians-University Munich Goethestrasse 70 80336 Munich GERMANY Email: [email protected] Copyright © 2017 by the Editorial Council for The Journal of Prosthetic Dentistry.
THE JOURNAL OF PROSTHETIC DENTISTRY