A comparison of three different methods for the quantification of the in vitro wear of dental materials

Evaluation of wear resistance and surface properties of additively manufactured restorative dental materials

OBJECTIVES

To evaluate the wear resistance of three additively manufactured dental crown materials (NextDent C&B MFH, Saremco print CROWNTEC and Bego VarseoSmile Crown) under two environmental conditions (dry and artificial saliva), two loads (49 N and 70 N) and two surface treatments (polished and glazed).

METHODS

A total of 120 specimens were divided into 24 groups and tested for wear under two loads (49 N and 70 N), surface treatment (polished or glazed), and environment (dry or submerged in artificial saliva). All samples underwent reciprocating wear testing at 1 Hz using a wear simulator, replicating 48 months of In Vivo conditions with a stainless-steel ball as the antagonist. The coefficient of friction (CoF), surface roughness, volumetric and vertical wear loss were measured and statistically analysed. Confocal microscopy assessed the surface properties of crown materials and the antagonists.

RESULTS

The NextDent material demonstrated the most homogenous wear, with relatively low vertical and volumetric loss across all groups (p < 0.004). NextDent and Bego materials performed similarly in artificial saliva regardless of the load type (p > 1.000). The CoF remained below 0.3 for all groups. All groups exhibited significant increases in surface roughness after testing, however, this did not correlate with an increase in the CoF. Confocal analysis revealed material deformities due to load and notable scratch marks on the stainless-steel antagonists.

CONCLUSION

It was found that all investigated addtively manufactured materials can be suggested for provisional use. Both vertical loss and volumetric loss results should be included for material evaluation. CoF and surface roughness should be implemented into wear evaluation.

CLINICAL SIGNIFICANCE

This study highlights the practical value of additively manufactured dental crown materials, particularly for provisional restorations. However, their extended use requires careful consideration of individual patient needs, emphasising the need for judicious clinical application evaluation.

The accuracy and precision of wear testing and wear facet analyses: The two sides of the story

A critical examination of the literature for dental wear publications highlighted three distinct areas, clinical data, laboratory data and the simulation of the clinical situation data. The imprecision of the clinical data values from direct and indirect in vivo methods renders the clinical data compromised at best. Laboratory data showed a focus on finding a correlation between simplistic laboratory abrasive wear resistance studies and established materials science laboratory techniques, but with no actual correlation identified. Replication of the masticatory cycle in the mouth in the form of an oral wear simulator has focussed more on the wear testing devices rather than the wear quantification methods. As a result, the data acquisition variables in the x- and y-planes need to be examined to consider how they can influence the accuracy and precision of the laboratory wear measurements recorded in the dental literature. The current approach was undertaken using the teaching tool outlined in "The First Three Questions".

Antagonist enamel tooth wear produced by different dental ceramic systems: A systematic review and network meta-analysis of controlled clinical trials

OBJECTIVES

The aim of this study was to evaluate the amount of enamel tooth wear induced by different antagonistic ceramic crown materials in the posterior area within a follow-up period up to 24 months in function. A network meta-analysis was performed to assess the effect of the materials on the mean vertical loss (MVL) of the antagonist enamel tooth surface.

DATA

Main search terms used in combination: ceramic, dental materials, metal ceramic, tooth wear and dental enamel.

SOURCES

An electronic search was conducted in PubMed/Medline, Embase, and Cochrane CENTRAL plus hand-searching.

STUDY SELECTION

Eligibility criteria included clinical studies reporting on MVL on antagonist's tooth up to 24 months following the permanent crown placement. From a total of 5697 articles, 7 studies reporting on 261 crowns for 177 subjects with 3 ceramic materials (Lithium disilicate, metal-ceramic, monolithic zirconia) were included. Among all, metal-ceramic and zirconia caused significantly higher enamel tooth wear on antagonist teeth, representing 82.5 µm [54.4; 110.6]) and 40.1 µm [22.2; 58.0]) more MVL than natural teeth group. In contrast, lithium disilicate showed only 5.0 µm [-48.2; 58.1]) more MVL than occurs on opposing natural teeth.

CONCLUSIONS

This systematic review demonstrated that prosthodontic ceramic materials produced significantly more antagonist enamel tooth wear than opposing natural enamel tooth wear, and ceramic material type was correlated to the degree of enamel tooth wear. Additional well-conducted, randomized controlled trials with homogeneous specimens are required due to inadequate sample size and number of the clinical studies included in the analyses.

CLINICAL SIGNIFICANCE

The amount of wear caused by different restorative materials has a high influence on the antagonistic natural teeth and should therefore be evaluated intensively by the dentist.

Digital Volumetric Analysis of CAD/CAM Polymeric Materials after Tooth Brushing

The objective of the study was to evaluate the volumetric wear of four composite materials for CAD/CAM (computer-aided design/computer-aided manufacturing) systems. The materials evaluated were: Cerasmart (CER), Shofu Block HC (SBH), Tetric CAD (TEC) and Brava (BRA). All the samples (n = 40) were subjected to simulated brushing (100,000 cycles). Wear was evaluated by superimposing pre-and post-brushing scans obtained with an intraoral optical scanner (CEREC Primescan; Dentsply Sirona, Germany), which were subsequently imported into the OraCheck software 5.0 (Dentsply Sirona, Germany). The data were analyzed by ANOVA test and Tukey’s HSD test was used for multiple comparisons. Cerasmart showed the least wear after brushing. All the tested materials exhibited mass loss.

Wear Resistance, Color Stability and Displacement Resistance of Milled PEEK Crowns Compared to Zirconia Crowns under Stimulated Chewing and High-Performance Aging

Recently, polyetheretherketone (PEEK) has been introduced to the dental market as a high-performance and chemically inert biomaterial. This study aimed to compare the wear resistance, abrasiveness, color stability, and displacement resistance of zirconia and PEEK milled crowns. An ideal tooth preparation of a first maxillary molar was done and scanned by an intraoral scanner to make a digital model. Then, the prosthetic crown was digitally designed on the CAD software, and the STL file was milled in zirconia (CaroZiir S, Carol Zircolite Pvt. Ltd., Gujarat, India) and PEEK (BioHpp, Bredent GmbH, Senden, Germany) crowns using five-axis CNC milling machines. The wear resistance, color stability, and displacement resistance of the milled monolithic zirconia with unfilled PEEK crowns using a chewing simulator with thermocyclic aging (120,000 cycles) were compared. The antagonist wear, material wear, color stability, and displacement were evaluated and compared among the groups using the Wilcoxon-Mann-Whitney U-test. Zirconia was shown to be three times more abrasive than PEEK (p value < 0.05). Zirconia had twice the wear resistance of PEEK (p value < 0.05). Zirconia was more color stable than PEEK (p value < 0.05). PEEK had more displacement resistance than zirconia (p value < 0.05). PEEK offers minimal abrasion, better stress modulation through plastic deformation, and good color stability, which make it a promising alternative to zirconia crown.

Wear of monolithic zirconia against different CAD-CAM and indirect restorative materials

STATEMENT OF PROBLEM

The wear of monolithic zirconia against enamel has been widely studied, but how zirconia affects different opposing restorative materials is not clear.

PURPOSE

The purpose of this in vitro study was to investigate the depth of wear and volumetric loss of different restorative materials opposed by monolithic zirconia.

MATERIAL AND METHODS

Sixty-six Ø10×3-mm specimens (n=11) were fabricated from monolithic zirconia, zirconia reinforced ceramic, lithium disilicate ceramic, feldspathic ceramic, ORMOCER, and ceramic optimized polymer. A 2-body pin-on-disk wear test was performed by using monolithic zirconia pins. The specimens were scanned with a noncontact profilometer after the tests. The scan parameters were a frame size area of 1.5×1.5 mm, frequency of 400 Hz, and scan sensitivity of 2 μm. After the evaluation of depth and volume loss, the specimens were analyzed with a scanning electron microscope. The Kruskal-Wallis test was used to analyze the differences in wear values across the specimen groups, and pairwise comparison tests were performed with a post hoc test (α=.05).

RESULTS

Maximum depth of wear was 257.55 ±18.88 μm for lithium disilicate ceramic, 295.36 ±14.46 μm for zirconia reinforced ceramic, 421.82 ±214.49 μm for ORMOCER, 333.73 ±79.09 μm for ceramic optimized polymer, 146.27 ±22.86 μm for feldspathic ceramic, and 41.55 ±5.04 μm for monolithic zirconia. The depth of wear was not significantly different among lithium disilicate, zirconia-reinforced ceramic, ORMOCER, and ceramic optimized polymer (P<.05). However, the depth of wear of monolithic zirconia and feldspathic ceramic was less than that of other materials (P<.001). Volume loss of lithium disilicate was 1.68 ±0.25 mm³, 1.08 ±0.35 mm³ for zirconia reinforced ceramic, 4.29 ±2.91 mm³ for ORMOCER, 2.46 ±0.63 mm³ for resin ceramic, 1.07 ±0.09 mm³ for feldspathic ceramic, and 0.19 ±0.02 mm³ for monolithic zirconia. Feldspathic ceramic and monolithic zirconia had significantly less volume loss than the other groups (P<.001), and the difference between them for volume loss was statistically insignificant (P>.05).

CONCLUSIONS

The tested ceramic-based materials had favorable wear resistance compared with the tested composite resin-based ones. However, the ceramics tended to crack formation than the composite resins.

Dental implant-abutment fracture resistance and wear induced by single-unit screw-retained CAD components fabricated by four CAM methods after mechanical cycling

STATEMENT OF PROBLEM

Computer-aided design and computer-aided manufacturing (CAD-CAM) methodologies allow the fabrication of custom dental implant abutments with a variety of materials and techniques. Studies on the mechanical strength of such components and the wear induced at their coupling interface during mechanical cycling are sparse.

PURPOSE

The purpose of this in vitro study was to measure the wear patterns at the hexagonal platform of dental implants induced by the installation and mechanical cycling of custom abutments fabricated by using 4 different CAD-CAM methods and to determine the compressive static resistance of the implant-abutment combinations.

MATERIAL AND METHODS

A CAD software program was used to design a custom abutment for a single-unit screw-retained external hexagon dental implant crown. The same design file was used to manufacture with 4 CAM methods (N=40): milling and sintering of zirconium dioxide (ZO), cobalt-chromium (Co-Cr) sintered by selective laser melting (SLM), fully sintered machined Co-Cr alloy (MM), and machined and sintered agglutinated Co-Cr alloy powder (AM). Prefabricated titanium abutments were used as a control (TI). Each abutment was installed onto a dental implant (4.1×11 mm), and the specimens were mechanically aged (1 million cycles, 2 Hz, 100N, 37 °C). After mechanical cycling, the hexagonal connection of the dental implants was examined with a scanning electron microscope (SEM), and unused dental implants (NI) were examined as a control (n=10). The images were analyzed with a software program to quantify the areas that showed wear. The implant-abutment combinations were reassembled and submitted to a compression test (1mm/min) with a universal testing machine. The data obtained were submitted to 1-way ANOVA (α=.05).

RESULTS

The mean ±standard deviation fracture load (N) of the specimens of each group were 1005 ±187 (ZO), 1074 ±123 (SLM), 1033 ±109 (MM), 1019 ±149 (AM), and 923 ±129 (TI). These values were statistically similar (P=.213). The mean ±standard deviation wear of the implants in squared-pixels were 1.1 ±0.38×10⁵ (ZO), 2.0 ±0.29×10⁵ (SLM), 1.0 ±0.38×10⁵ (MM), 1.1 ±0.27×10⁵ (AM), 1.1 ±0.33×10⁵ (TI), and 0.51 ±0.29×10⁵ (NI). The results indicated that, although significantly higher than those in in the control group (NI), the wear values found in the groups TI, ZO, MM, and AM were significantly lower than in the SLM group (P<.001).

CONCLUSIONS

The CAD-CAM abutments presented the same mechanical fracture load and wear measurements as the TI group, except for the SLM material, which showed increased wear. The failure mode from the load bearing test was the fracture of the abutments for the ZO group. The implants permanently deformed or fractured for the metal abutment groups.

In vitro wear of (resin-coated) high-viscosity glass ionomer cements and glass hybrid restorative systems

OBJECTIVES

The aim of the present study was to investigate the volumetric abrasive wear of a high-viscosity glass ionomer cement (hvGIC; Equia Fil) and a glass hybrid restorative system (ghRS; Equia Forte), each being recommended as amalgam alternatives. Both materials were applied with or without their respective resinous coating, and were compared with a conventional GIC (Ketac Fil) and a hybrid composite resin (CR; G-ænial Posterior).

METHODS

78 standardized occlusal Class I cavities were restored with the various materials (n = 13 per group). Before and after chewing simulation (30,000 cycles at 40 N), each sample underwent optical scanning procedures (Omnicam). A comparison of the total wear using a fluorescence-aided identification technique (OraCheck) followed, and differences (α = 5%) between groups were compared by means of MANOVA.

RESULTS

Regarding the wear rates of hvGIC and ghRS, no differences could be observed (p > .050), and this was not affected by the resinous coating. All hvGIC and ghRS restorations showed significantly higher abrasive wear than CR (p < .001), while the conventional GIC displayed a significant underperformance compared with any other material (p < .001).

CONCLUSIONS

Resinous coating of hvGIC or ghRS does not appear to exert an effective long-term protection against advanced abrasive wear. Compared to the conventional GIC showing a considerable substance loss, both hvGIC and ghRS materials revealed an improved abrasion resistance, but clearly failed to meet the excellent values of the CR.

CLINICAL SIGNIFICANCE

Occlusal loading should be carefully considered when using hvGIC or ghRS as amalgam (or composite resin) alternatives for the restoration of posterior teeth.

Novel methodology for measuring intraoral wear in enamel and dental restorative materials

Objectives

To test the hypotheses that (a) the chairside/handheld dental scanner combined with a metrology software will measure clinical wear in vivo in agreement with measurements from X‐ray computed microtomography and; (b) polished monolithic zirconia does not cause accelerated wear of opposing enamel.

Materials and methods

Thirty single crowns were randomized to receive a monolithic zirconia or metal‐ceramic crown. Two non‐restored opposing teeth in the same quadrants were identified to serve as enamel controls. After cementation, quadrants were scanned using an intraoral dental scanner. Patients were recalled at 6‐months and 1‐year for re‐scanning. Scanned images were compared using a metrology software to determine maximum vertical wear of teeth. The accuracy of the scanning measurements from this new method was compared with X‐ray computed microtomography (micro‐CT) measurements. Statistical analysis was performed using Mann–Whitney U test to determine significant differences between wear of enamel against zirconia, metal‐ceramic or enamel. Linear regression analysis determined agreement between measurements obtained using intraoral scanning and micro‐CT.

Results

Regression analysis demonstrated that there is a quantitative agreement between depth and volume measurements produced using intraoral scanning and the micro‐CT methodologies. There was no significant difference between the wear of enamel against polished monolithic zirconia crowns and enamel against enamel.

Conclusions

Intraoral scanning combined with a matching software can accurately quantify clinical wear to verify that monolithic zirconia exhibited comparable wear of enamel compared with metal‐ceramic crowns and control enamel. Agreement between the intraoral scanner and the micro‐CT was 99.8%. Clinical Trials.gov NCT02289781.

Wear resistance of 3D-printed denture tooth resin opposing zirconia and metal antagonists

STATEMENT OF PROBLEM

Additive manufacturing technology can be used for denture bases and also denture teeth. Therefore, the mechanical properties of 3D-printed resin denture teeth should be evaluated.

PURPOSE

The purpose of this in vitro study was to compare the wear resistance of 3D-printed denture tooth resin with that of conventionally prefabricated denture teeth.

MATERIAL AND METHODS

Eighty substrate specimens were prepared with 5 kinds of resin denture teeth: 3D-printed denture tooth resin (DENTCA denture tooth resin; DENTCA, Inc), Artic 6 (Kulzer GmbH), Preference (Candulor AG), Premium 6 (Kulzer GmbH), and Surpass (GC Corp). The 3D-printed denture tooth specimens were made of methacrylate-based photopolymerized resin by stereolithography 3D printing. Antagonistic surfaces were made from zirconia by milling and from cobalt-chromium (Co-Cr) alloy by 3D printing and casting. The specimens were loaded at 49 N for 30 000 cycles under thermocycling conditions in a mastication simulator. Wear resistance was measured by calculating the volume of substance lost. Wear surface characteristics were observed by using a scanning electron microscope (SEM). Two-way ANOVA was used to analyze the data (α=.05).

RESULTS

The influence of the resin denture teeth and the type of antagonist were both statistically significant. The wear volume loss of the 3D-printed denture tooth resin was higher than that of Artic 6 and Preference when opposing the zirconia and the metal antagonists (P<.05). The 3D-printed denture tooth resin did not show a significant difference from Premium 6 with the zirconia and the metal antagonists or Surpass with the zirconia antagonist. From the SEM images, the specimens of the 3D-printed denture tooth resin showed a relatively smooth surface with the zirconia antagonist and exhibited cracks when opposed by the metal antagonist.

CONCLUSIONS

The results suggest that 3D-printing by using resin materials provides adequate wear resistance for denture tooth use.

Comparative Evaluation of Mechanical Properties and Wear Ability of Five CAD/CAM Dental Blocks

This study compares the mechanical properties and wear ability of five CAD/CAM (computer-aided design/computer-aided manufacturing) millable dental blocks. All the discs, including Amber Mill Hybrid, Vita Enamic, Katana Avencia, Lava Ultimate, and Amber Mill, were cut in dimensions of 1.2 mm in thickness and 12 mm in diameter, polished to a machined surface, and immersed in distilled water for seven days. Vickers hardness was measured and the indentations were observed using microscope. The discs were brushed under a 150 g load. Mean surface roughness (Ra) and topography were determined after 100,000 cycles. Finally the biaxial flexure strength of the discs was measured and the broken surfaces were observed using scanning electron microscopy (SEM). The data was subjected to Weibull analysis. All data were analyzed by one-way analysis (ANOVA). The results of Vickers hardness are shown as: Amber Mill > Vita Enamic > Amber Mill Hybrid > Lava Ultimate > Katana Avencia. Katana Avencia showed the highest volume percentage reduction and the roughest surface after toothbrushing. The biaxial flexural strength is shown as: Amber Mill > Katana Avencia > Lava Ultimate > Amber Mill Hybrid > Vita Enamic. All the tested materials exhibited varying degrees of mass loss and surface roughness. The properties of the composite materials are related to the filler content, filler volume, and polymerization methods.

Wear Characteristics of Dental Ceramic CAD/CAM Materials Opposing Various Dental Composite Resins

The aim of this study was to evaluate the wear properties of opposed dental ceramic restorative CAD/CAM materials and several posterior direct restorative composite resins. Three kinds of dental ceramics CAD/CAM materials (monolithic zirconia, lithium disilicate, leucite) and four dental composite resins—that is, MI Gracefil, Gradia Direct P, Estelite Σ Quick, and Filtek Supreme Ultra—were used in this study. For each of the 12 groups (three ceramics × four composite resins), five each of a canine-shaped ceramic specimen and a cuboidal shape opposing composite resin were prepared. All of the specimens were tested in a thermomechanical loading machine (50 N, 100,000 cycles, 5/55 °C). Wear losses of ceramic specimens and composite resin specimens were evaluated using a three-dimensional profiling system and an electronic scale, respectively. Statistical analyses were performed using the Kruskal–Wallis test and Mann–Whitney U test with Bonferroni’s correction. Zirconia showed significantly less volumetric loss than lithium disilicate or leucite regardless of composite resin type (p > 0.05/3 = 0.017), and that Estelite Σ Quick showed significantly more weight loss than Filtek Supreme Ultra, MI Gracefil, or Gradia Direct P regardless of ceramic type (p > 0.05/6 = 0.083). Zirconia showed less volumetric loss than lithium disilicate or leucite. Some composite resins opposing ceramics showed considerable weight loss.

Whitening toothpastes effect on nanoparticle resin composite roughness after a brushing challenge: An in vitro study

Background

Nowadays, the use of whitening toothpastes is a common habit, especially among young adults, due to aesthetic appeal. On the other hand, little is known regarding the effects of brushing with those newly dentifrices on wear properties of resin composites.

Material and Methods

Thirty specimens of nanoparticle composite resin were fabricated and stored in distilled water for 24 h at 370C. After this, the roughness analysis was performed and submitted to the simulated brushing technique using three types of toothpastes: conventional (GI), and two with whitening effect (GII and GIII) for a period of 15 days, with 2 brushing sessions per day for 2 minutes each. The final surface roughness was analyzed after completing all the brushing cycles and stereoscopic images were taken for each group. The data was analyzed by one-way ANOVA and Tukey-test post hoc for intergroup comparison and the T-test for dependent samples as well (α = 0.05).

Results

However showing an increase of roughness for all groups after the brushing cycles (p = 0.01), no statistically significant differences among the groups after simulated brushing was verified (p = 0.17). Yet, just some cracks of the stereoscopic images were shown, demonstrating no distinct visual effects among the studied groups.

Conclusions

After simulated brushing with the whitening toothpastes, similar degree of roughness was verified on the composite resin tested. Key words:Composite resin, toothpastes, whitening.

Wear of dental materials: Clinical significance and laboratory wear simulation methods -A review

This review focusses on tribological aspects of teeth during function, the clinical significance of wear, wear of natural teeth and restorative materials and laboratory methods to simulate wear of restorative materials. Ceramic, metal alloy and amalgam show low material wear, whereas resin-based materials demonstrate substantial wear in the long term. The clinical wear shows a high variability with the patient factor accounts for about 50% of the variability. Wear as such seldomly compromises the function of the stomatognath system or individual teeth and is in most cases an esthetic problem. Particles that are ingested due to attrition and abrasion wear may pose a health risk to the patient, especially those from composite resin materials. However, systematic clinical studies on that issue are not available. For laboratory research many wear simulation devices and methods have been developed but only few are validated and have a moderate correlation with clinical wear.

Comprehensive analysis of laserscanner validity used for measurement of wear

OBJECTIVES

The aims of this study were to test the hypotheses that (a) a laserscanner used for measuring maximum depth and volume loss will yield the same results as a surface profilometer; (b) the surface roughness will affect the maximum depth and volume loss measured with the laserscanner; (c) analytical results using the laserscanner from multiple operators have no more than 10% inter-rater difference and; (d) replicating samples using either stone or impression material is an accurate method for measuring wear using the laserscanner.

MATERIALS AND METHODS

The volume and maximum depth of indentations from fine, medium and rough burs on glass-ceramic disks were measured using two devices, a surface profilometer (Dektak II, Veeco) and a 3D Laserscanner (LAS-20, SD Mechatronik). Replicates of the indentations made from polyvinysiloxane impression material and gypsum were also measured.

RESULTS

Comparison of profilometer and laserscanner readings using ceramic disks demonstrated a mean error of 13.61% for depth and 25.32% for volume. Replication errors were minimal (2.6% for impression, 2.5% for stone). Surface profilometer data for volume measurements revealed a difference of 6.1% for impression and 6.5% for stone compared with ceramics. However, when measurements for replicates were compared between laserscanner and surface profilometer, depth had a mean error of 74% for impression and 51% for stone. Volume differences of 78% for impression and 44% for stone were recorded.

CONCLUSION

This work demonstrated that the laserscanner was a convenient device for measuring wear but there is a need to validate the accuracy of the measurements.

Wear Resistance of 3D Printing Resin Material Opposing Zirconia and Metal Antagonists

3D printing offers many advantages in dental prosthesis manufacturing. This study evaluated the wear resistance of 3D printing resin material compared with milling and conventional resin materials. Sixty substrate specimens were prepared with three types of resin materials: 3D printed resin, milled resin, and self-cured resin. The 3D printed specimens were printed at a build angle of 0° and 100 μm layer thickness by digital light processing 3D printing. Two kinds of abraders were made of zirconia and CoCr alloy. The specimens were loaded at 5 kg for 30,000 chewing cycles with vertical and horizontal movements under thermocycling condition. The 3D printed resin did not show significant difference in the maximal depth loss or the volume loss of wear compared to the milled and the self-cured resins. No significant difference was revealed depending on the abraders in the maximal depth loss or the volume loss of wear. In SEM views, the 3D printed resin showed cracks and separation of inter-layer bonds when opposing the metal abrader. The results suggest that the 3D printing using resin materials provides adequate wear resistance for dental use.

Macro- and microtopographical examination and quantification of CAD-CAM composite resin 2- and 3-body wear

STATEMENT OF PROBLEM

The selection of an appropriate restorative material based on wear behavior is important for the long-term success of a dental restoration. For computer-aided design and computer-aided manufacturing (CAD-CAM) composite resins, information about their wear resistance and wear mechanism is scarce.

PURPOSE

The purpose of this in vitro study was to compare the 2- and 3-body wear of CAD-CAM composite resins with that of lithium disilicate ceramic and to develop analysis software.

MATERIAL AND METHODS

Flat specimens were prepared from the following CAD-CAM composite resins: Cerasmart (CS), SHOFU Block HC (SH), Katana Avencia (KA), Brilliant Crios (BC), an experimental composite resin (EXP), and lithium disilicate ceramic IPS e.max CAD (REF). The specimens underwent 2-body wear (50 N, 5/55°C, 400 000 cycles) opposed by human enamel 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 dedicated laser scanner. Analysis software was developed to calculate macrotopographical examination of volume loss. The microtopography of the surfaces was examined by using scanning electron microscopy. For data analysis, the Kruskal-Wallis test with the Tukey-Kramer post hoc test and the 1-sample Wilcoxon test were used (α=.05).

RESULTS

After 2-body wear simulation, SH and KA presented higher volume loss than the other CAD-CAM materials. For 3-body wear, REF had lower volume loss than CS, SH, or BC. In addition, BC led to higher volume loss than EXP. The patterns of 2- and 3-body wear were different.

CONCLUSIONS

The ceramic showed good global wear resistance. The volume loss of the CAD-CAM composite resins differed and depended on the material. The 2- and 3-body wear test methods tended to differ with regard to volume loss. Examination of the worn surfaces revealed different mechanisms acting in 2- and 3-body wear test.

In Vitro Investigation of Wear of CAD/CAM Polymeric Materials Against Primary Teeth

The aim of the study was to evaluate the effects of polymeric computer-aided design/computer-aided manufacturing CAD/CAM materials on antagonistic primary tooth wear. Five CAD/CAM polymeric materials were examined: Vipi Block Monocolor (VBM), Yamahachi polymethylmethacrylate (PMMA) (YAP), Mazic Duro (MZD), Vita Enamic (ENA), and Pekkton (PEK). All of the specimens were tested in a thermomechanical loading machine with the primary canine as the antagonist (50 N, 1.2 × 10⁵ cycles, 1.7 Hz, 5/55 °C). The wear losses of the antagonist tooth and the restorative materials were calculated using reverse modelling software and an electronic scale. VBM and ENA showed significantly higher antagonist tooth wear than PEK (p < 0.05), but there was no significant difference observed among VBM, YAP, MZD, and ENA (p > 0.05). PEK showed the largest value in both material volumetric and weight losses. In terms of material volumetric losses, there was no significant difference between all of the groups (p > 0.05). In terms of material weight losses, PEK was significantly larger than ENA (p < 0.05), but there was no significant difference between VBM, YAP, MZD, and ENA (p > 0.05). Volumetric and weight losses of materials showed similar wear behaviour. However, the wear patterns of antagonists and materials were different, especially in PEK.

Nanoclay-Reinforced Glass-Ionomer Cements: In Vitro Wear Evaluation and Comparison by Two Wear-Test Methods

Glass ionomer cement (GIC) represents a major transformation in restorative dentistry. Wear of dental restoratives is a common phenomenon and the determination of the wear resistance of direct-restorative materials is a challenging task. The aim of this paper was to evaluate the wear resistance of novel glass ionomer cement by two wear-test methods and to compare the two wear methods.The wear resistance of a conventional glass ionomer cement (HiFi Advanced Health Care Kent, UK) and cements modified by including various percentages of nanoclays (1, 2 and 4 wt %) was measured by a reciprocating wear test (ball-on-flat) and Oregon Health and Sciences University's (OHSU) wear simulator. The OHSU wear simulation subjected the cement specimens to three wear mechanisms, namely abrasion, three-body abrasion and attrition using a steatite antagonist. The abrasion wear resulted in material loss from GIC specimen as the steatite antagonist forced through the exposed glass particles when it travelled along the sliding path.The hardness of specimens was measured by the Vickers hardness test. The results of reciprocation wear test showed that HiFi-1 resulted in the lowest wear volume 4.90 (0.60) mm³ (p < 0.05), but there was no significant difference (p > 0.05) in the wear volume in comparison to HiFi, HiFi-2 and HiFi-4. Similarly, the results of OHSU wear simulator showed that the total wear volume of HiFi-4 1.49 (0.24) was higher than HiFi-1 and HiFi-2. However, no significant difference (p > 0.05) was found in the OHSU total wear volume in GICs after nanoclay incorporation. The Vickers hardness (HV) of the nanoclay-reinforced cements was measured between 62 and 89 HV. Nanoclay addition at a higher concentration (4%) resulted in higher wear volume and wear depth. The total wear volumes were less dependent upon abrasion volume and attrition volume. The total wear depths were strongly influenced by attrition depth and to some extent by abrasion depth. The addition of nanoclay in higher wt % to HiFi did not result in significant improvement in wear resistance and hardness. Nonetheless, wear is a very complex phenomenon because it is sensitive to a wide number of factors that do not necessarily act in the same way when compared using different parameters.

An approach to understanding tribological behaviour of dental composites through volumetric wear loss and wear mechanism determination; beyond material ranking

OBJECTIVE

To investigate the fundamental wear mechanisms of six resin-based composite (RBC) formulations during short-term in vitro wear testing.

MATERIALS

RBC materials were condensed into rectangular bar-shaped specimens and light irradiated using the ISO 4049 specimen manufacture and irradiation protocol. Wear testing (n=10 specimens for each RBC) was performed on a modified pin-on-plate wear test apparatus and wear facets were analysed for wear volume loss using a white light profilometer. The wear tested RBC specimens and their corresponding antagonists were analysed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), respectively to determine the wear mechanism.

RESULTS

Data generated using the profilometer showed variations in the mean total wear volume (mm³) between the RBCs tested (p<0.05). Abrasive wear was evident in all RBCs investigated with varying degrees of damage. Material transfer/deposition of the filler particles on the corresponding antagonists was evident in two RBC materials (Filtek Supreme and Kalore) indicative of a further adhesive wear mechanism.

CONCLUSION

It is proposed that the approach employed to use a combination of measurement and analytical techniques to quantify the wear facet volume (profilometry), wear trough (SEM) and material transfer (EDS) provides more useful information on the wear mechanism and the tribology of the system rather than relying on a simple wear ranking for the RBC materials as is routinely the case in dental research studies.

Comparison of four monolithic zirconia materials with conventional ones: Contrast ratio, grain size, four-point flexural strength and two-body wear

OBJECTIVES

To test the mechanical and optical properties of monolithic zirconia in comparison to conventional zirconia.

MATERIALS AND METHODS

Specimens were prepared from: monolithic zirconia: Zenostar (ZS), DD Bio ZX(2) hochtransluzent (DD), Ceramill Zolid (CZ), InCoris TZI (IC) and a conventional zirconia Ceramill ZI (CZI). Contrast ratio (N=75/n=15) was measured according to ISO 2471:2008. Grain sizes (N=75/n=15) were investigated with scanning electron microscope. Four-point flexural strength (N=225/n=15/zirconia and aging regime) was measured initially, after aging in autoclave or chewing simulator (ISO 13356:2008). Two-body wear of polished and glazed/veneered specimens (N=108/n=12) was analyzed in a chewing simulator using human teeth as antagonists. Data were analyzed using 2-/1-way ANOVA with post-hoc Scheffé, Kruskal-Wallis-H, Mann-Whitney-U, Spearman-Rho, Weibull statistics and linear mixed models (p<0.05).

RESULTS

The lowest contrast ratio values were found for ZS and IC and CZ. IC showed the largest grain size followed by DD and CZI. The smallest grain size was observed for ZS followed by CZ. There was no correlation between grain size and contrast ratio. The aging regime showed no impact on flexural strength. All non-aged and autoclave-aged specimens showed lower flexural strengths than the control group CZI. Within groups aged in chewing simulator, ZS showed significantly lower flexural strength than CZI. CZI showed higher material and antagonist wear than monolithic polished and glazed groups. Glazed specimens showed higher material and antagonist loss compared to polished ones. There was no correlation between roughness and wear.

CONCLUSIONS

Monolithic zirconia showed higher optical, but lower mechanical properties than conventional zirconia.

Applications of Light Amplification by Stimulated Emission of Radiation (Lasers) for Restorative Dentistry

Light amplification by stimulated emission of radiation (laser) has been used widely in a range of biomedical and dental applications in recent years. In the field of restorative dentistry, various kinds of lasers have been developed for diagnostic (e.g. caries detection) and operative applications (e.g. tooth ablation, cavity preparation, restorations, bleaching). The main benefits for laser applications are patient comfort, pain relief and better results for specific applications. Major concerns for using dental lasers frequently are high cost, need for specialized training and sensitivity of the technique, thereby compromising its usefulness particularly in developing countries. The main aim of this paper is to evaluate and summarize the applications of lasers in restorative dentistry, including a comparison of the applications of lasers for major restorative dental procedures and conventional clinical approaches. A remarkable increase in the use of lasers for dental application is expected in the near future.

Are resin composites suitable replacements for amalgam? A study of two-body wear

OBJECTIVES

Wear resistance is an important property of the dental materials, particularly for large restorations in the posterior regions and for the patients suffering from parafunctional activities. Additionally, the wear resistance of flowable composite resin materials is a clinical concern, although they are popular among dentists because of their easy handling. The aims of the present study were to evaluate the wear resistance of nine composite resins both condensable (G-aenial posterior, Venus, GrandioSO, Tetric EvoCeram, Ceram X duo, Filtek Supreme XTE) and new-generation flowable resin composites (G-aenial Universal Flo, GrandioSO Flow and GrandioSO Heavy Flow) and to compare these results with amalgam.

MATERIALS AND METHOD

Eight specimens of each material were subjected to two-body wear tests, using a chewing simulator. The wear region of each material was examined under profilometer, measuring the vertical loss (μm) and the volume loss (mm(3)) of the materials. Additionally, SEM analysis was performed to assess surfaces irregularities.

RESULTS

The results showed significant difference of the vertical loss and the volume loss of the examined materials (p < 0.001). Although amalgam had the best wear resistance, two condensable resin composites (GrandioSO, Ceram X duo) and all flowable materials had no significant difference with amalgam. GrandioSO had the highest wear resistance and Filtek Supreme XTE the lowest wear resistance.

CONCLUSION

The majority of resin composites had good wear resistance and similar to amalgam.

CLINICAL RELEVANCE

Based on the in vitro measurements of two-body wear resistance, the new resin composites could replace amalgam for restorations placed in occlusal stress-bearing regions. New-generation flowable resin materials may also be used in occlusal contact restorations.

Initial sliding wear kinetics of two types of glass ionomer cement: a tribological study

The aim of this work was to characterize the initial wear kinetics of two different types of glass ionomer cement used in dentistry (the conventional glass ionomer cement and the resin-modified glass ionomer cement) under sliding friction after 28-day storing in distilled water or Ringer's solution. Sliding friction was applied through a pin-on-disk tribometer, in sphere-on-plane contact conditions, under 5 N normal load and 120 rotations per minute. The test lasted 7500 cycles and replicas were performed at 2500, 5000 and 7500 cycles. A profilometer was used to evaluate the wear volume. Data were analysed using Student's t-test at a significant level of 5%. There is no statistical significant difference between the results obtained for a given material with the maturation media (P > 0.05). However, for a given maturation medium, there are significant statistical differences between the data obtained for the two materials at each measurement (P < 0.0001). The wear rates of both materials decrease continuously during the running-in period between 0 and 2500 cycles. After 2500 cycles, the wear rate becomes constant and equal for both materials. The resin matrix contained in the resin-modified glass ionomer cement weakens the tribological behaviour of this material.

Volumetric wear of various orthotic appliance materials

The purpose of this study was to compare the resistance to wear of six commonly used orthotic appliance materials. These materials were: SR Ivocap (Ivoclar Vivadent, Inc., Amherst, NY), Eclipse (Dentsply International, York, PA), ProBase (Ivoclar Vivadent), Valplast (Valplast International Corp., Oceanside, NY), Impak (CMP Industries LLC, Albany, NY), and Clearsplint (Astron Dental Corp., Lake Zurich, IL). Twelve cylindrical specimens of each material were fabricated per manufacturer instructions. Occlusal wear was simulated in a custom-made wear simulator with each specimen receiving four wear scars in a two-body wear simulation using a 1.5 mm tungsten-carbide tipped stylus at 40 newtons for 2500 cycles at 1 Hz, while immersed in 37 degrees C distilled water (n = 48). The specimens were evaluated before and after wear testing using a three-dimensional (3D) noncontact profilometer (Proscan 2000, Scantron Corp., Eagan, MN). A mean change in volume was determined for each orthotic material. Results found that Clearsplint material displayed the greatest amount of volume loss/wear, while SR Ivocap, Eclipse, and ProBase materials had the least amount of wear. Valplast and Impak performed more moderately. Based upon this wear knowledge, practitioners are able to more reliably choose the appliance material necessary for their various patients.

Surface characterization of current composites after toothbrush abrasion

The present study was designed to evaluate the surface roughness and the gloss of current composites before and after toothbrush abrasion. We assessed forty dimensionally standardized composite specimens (n=8/group) from five composites: two nanohybrids (i. e., IPS Empress Direct Enamel and IPS Empress Direct Dentin), two microhybrids (i. e., Clearfil AP-X and Filtek Z250) and one organically modified ceramics (Admira). All of the specimens were polished with 4000-grid silicon carbide papers. Surface roughness was measured with a profilometer and gloss was measured with a glossmeter before and after powered toothbrush abrasion with a 1:1 slurry (dentifrice/tap water) at 12,000 strokes in a toothbrush simulator. There was a significant increase in the surface roughness and a reduction in gloss after toothbrush abrasion in all of the composites except Clearfil AP-X (p<0.05). Simple regression analysis showed that there was not an association between the surface roughness and the gloss (R(2)=0.191, p<0.001).

Three years in vivo wear: core-ceramic, veneers, and enamel antagonists

OBJECTIVES

Test the hypotheses that there are equivalent wear rates for enamel-versus-enamel and ceramic-versus-enamel, analyzing the in vivo wear of crown ceramics, their natural enamel antagonists, and the corresponding two contralateral teeth; and, that bite force does not correlate with the wear.

METHODS

A controlled, clinical trial was conducted involving patients needing full coverage crowns opposing enamel antagonists. Bite forces were measured using a bilateral gnathodynamometer. Single-unit restorations of metal/ceramic (Argedent 62, Argen Corp/IPS d.SIGN veneer); or, core-ceramic/veneer from either, Empress2/Eris, or e.max Press core/e.max Ceram glaze (ceramics: Ivoclar Vivadent, USA) were randomly assigned, fabricated and cemented. Impressions were made of the ceramic crowns, as well as each maxillary and mandibular quadrant at one week (baseline) and one, two and three years. Resulting models were scanned (3D laser scanner). Maximum wear was calculated by superimposing baseline with annual images.

RESULTS

There were a total of thirty-six crowns required for thirty-one patients. Each restoration had three associated enamel teeth: crown, (1) antagonist, (2) contralateral and (3) contralateral-antagonist. SAS PROC MIXED (α=0.05) indicated no statistical significance for mean maximum wear among crown ceramics, enamel antagonists and contralaterals. However, enamel wear was statistically significant in relation to intraoral location (p=0.04) and among years (p<0.02). Analyzed alone, the enamel contralateral-antagonist exhibited significantly greater wear (p<0.001). Considering all wear sites, there was no correlation with bite force (p=0.15).

SIGNIFICANCE

The ceramics and their antagonists exhibited in vivo wear rates within the range of normal enamel. Future studies should examine the wear implications of the contralateral-antagonist enamel.

In vitro performance of full-contour zirconia single crowns

OBJECTIVES

Zirconia based restorations exhibited high failure rates due to veneering-porcelain fractures. Milling to full-contour might be an alternative approach for zirconia restorations. The aim of this study was to evaluate full-contour zirconia crowns in terms of light-transmission, contact wear (restoration and antagonist) and load-bearing capacity. Powder build-up veneered zirconia substructures and CAD/CAM-veneered zirconia substructures served as controls.

METHODS

Four different kinds of crowns were fabricated on 12 metal dies: zirconia substructure with powder build-up porcelain (veneering technique), zirconia substructure with CAD/CAM generated veneering (sintering technique), full-contour zirconia glazed (glazed full-contour) and full-contour zirconia polished (polished full-contour). All crowns had the same dimensions. After light-transmission was measured the crowns were cemented on the corresponding metal dies. The specimens were loaded according to a special wear method in the chewing simulator (120,000 mechanical cycles, 5 kg load, 0.7 mm sliding movement, 320 thermocycles). Wear of the restoration and the antagonist were measured. All specimens were loaded until failure. One-way ANOVA and a LSD post-hoc test were used to compare data at a level of 5%.

RESULTS

Polished full-contour showed significantly higher light transmission than the other groups (p=0.003; ANOVA). Polished full-contour exhibited significantly less contact wear at the restoration (p=0.01; ANOVA) and higher contact wear at the antagonist (p=0.016; ANOVA) compared to the other groups. Glazed full-contour zirconia showed similar contact wear at the antagonist compared to veneering technique (p=0.513, post-hoc LSD). Crowns with conventional veneering showed significantly lower load-bearing capacity (p<0.001; ANOVA).

SIGNIFICANCE

Milling zirconia to full-contour with glazed surface might be an alternative to traditionally veneered restorations.

Wear resistance of experimental titanium alloys for dental applications

The present study evaluated microstructure, microhardness and wear resistance of experimental titanium alloys containing zirconium and tantalum. Alloys were melted in arc melting furnace according to the following compositions: Ti-5Zr, Ti-5Ta and Ti-5Ta-5Zr (%wt). Hemispheres and disks were obtained from wax patterns that were invested and cast by plasma. Microstructures were evaluated using optical microscopy and X-ray diffraction (XRD) analysis and also Vickers microhardness was measured. Hemispherical samples and disks were used for 2-body wear tests, performed by repeated grinding of the samples. Wear resistance was assessed as height loss after 40,000 cycles. The data were compared using ANOVA and post-hoc Tukey test. Ti-5Zr presented a Widmanstätten structure and the identified phases were α and α' while Ti-5Ta and Ti-5Ta-5Zr presented α, β, α' and α" phases, but the former presented a lamellar structure, and the other, acicular. The microhardness of Ti-5Zr was significantly greater than other materials and cp Ti presented wear resistance significantly lower than experimental alloys. It was concluded that wear resistance was improved when adding Ta and Zr to titanium and Zr increased microhardness of Ti-5Zr alloy.

Enamel loss and adhesive remnants following bracket removal and various clean-up procedures in vitro

This study evaluated the enamel loss and composite remnants after debonding and clean-up. The tested null hypothesis is that there are no differences between different polishing systems regarding removing composite remnants without damaging the tooth surface. Brackets were bonded to 75 extracted human molars and removed after a storage period of 100 hours. The adhesive remnant index (ARI) was evaluated. The clean-up was carried out with five different procedures: 1. carbide bur; 2. carbide bur and Brownie and Greenie silicone polishers; 3. carbide bur and Astropol polishers; 4. carbide bur and Renew polishers; and 5. carbide bur, Brownie, Greenie and PoGo polishers. Silicone impressions were made at baseline (T0) and after debonding (T1) and polishing (T2) to produce plaster replicas. The replicas were analysed with a three-dimensional laser scanner and measured with analytical software. Statistical analysis was performed with the Kruskal-Wallis test and pairwise Wilcoxon tests with Bonferroni-Holm adjustment (α = 0.05). Enamel breakouts after debonding were detectable in 27 per cent of all cases, with a mean volume loss of 0.02 mm(3) (±0.03 mm(3)) and depth of 44.9 μm (±48.3 μm). The overall ARI scores was 3 with a few scores of 1 and 2. The composite remnants after debonding had a mean volume of 2.48 mm(3) (±0.92 mm(3)). Mean volume loss due to polishing was 0.05 mm(3) (±0.26 mm(3)) and the composite remnants had a mean volume of 0.22 mm(3) (±0.32 mm(3)). There were no statistically significant differences in volumetric changes after polishing (P = 0.054) between the different clean-up methods. However, sufficient clean-up without enamel loss was difficult to achieve.

Two-body wear of artificial acrylic and composite resin teeth in relation to antagonist material

STATEMENT OF PROBLEM

Wear resistance is one of the most important physical properties of artificial resin teeth, and its dependence on the antagonist material has not been clearly established.

PURPOSE

The purpose of this in vitro study was to investigate the wear resistance of representative artificial resin teeth in relation to antagonist material.

MATERIAL AND METHODS

Twenty-four standardized specimens were prepared for each of 8 tooth types representative of anterior and posterior artificial acrylic and composite resin teeth (Gnathostar, SR Orthosit PE, Condyloform II NFC, SR Postaris DCL, SR Vivodent PE, VITA Physiodens, SR Antaris DCL, Bioplus), for a total of 192 specimens. Each specimen was prepared to a diameter of 5 mm and a thickness of 2 mm on the buccal/facial tooth surfaces. The specimens were then polished and subjected to simulated mastication (50 N, 1.2 x 10(5) cycles, 1.2 Hz) using a pin-on-block design and additional thermocycling (600 cycles, 5/55 degrees C, 2 min/cycle). Three antagonists (artificial resin teeth, steel, steatite) were prepared, and 8 specimens per tooth type were tested for each antagonist. Vertical substance and volume loss were analyzed using cast replicas and an optical 3-dimensional (3-D) surface profilometer, as well as scanning electron microscopy. Data were analyzed using 2- and 1-way ANOVA and the Games-Howell test (alpha=.05).

RESULTS

For both vertical substance and volume loss, significant differences were found for the various antagonists. Lowest overall mean values (SD) for vertical substance and volume loss were measured for artificial tooth antagonists (26 (10) microm to 95 (46) microm, 1.5 (1.5) microm(3) to 10.5 (9) microm(3)), and the highest values were measured for steatite antagonists (95 (23) microm to 723 (168) microm, 8 (4) microm(3) to 245 (109) microm(3)). Intermediate mean values (SD) for vertical substance and volume loss were measured for steel antagonists (118 (88) microm to 205 (120) microm, 9 (7) microm(3) to 28 (24) microm(3)). Using artificial teeth and steel antagonists, few significant differences in wear resistance were found between the various resin teeth. In contrast, significant differences were observed with steatite antagonists.

CONCLUSIONS

The use of steatite antagonists allowed for significantly better differentiation of wear behavior between various artificial teeth than the use of artificial resin teeth or steel antagonists.

Three-year randomised clinical trial to evaluate the clinical performance, quantitative and qualitative wear patterns of hybrid composite restorations

The aim of the study was to compare the clinical performance, quantitative and qualitative wear patterns of conventional hybrid (Tetric Ceram), micro-filled hybrid (Gradia Direct Posterior) and nano-hybrid (Tetric EvoCeram, TEC) posterior composite restorations in a 3-year randomised clinical trial. Sixteen Tetric Ceram, 17 TEC and 16 Gradia Direct Posterior restorations were placed in human molars and evaluated at baseline, 6, 12, 24 and 36 months of clinical service according to US Public Health Service criteria. The gypsum replicas at each recall were used for 3D laser scanning to quantify wear, and the epoxy resin replicas were observed under scanning electron microscope to study the qualitative wear patterns. After 3 years of clinical service, the three hybrid restorative materials performed clinically well in posterior cavities. Within the observation period, the nano-hybrid and micro-hybrid restorations evolved better in polishability with improved surface gloss retention than the conventional hybrid counterpart. The three hybrid composites showed enamel-like vertical wear and cavity-size dependant volume loss magnitude. Qualitatively, while the micro-filled and nano-hybrid composite restorations exhibited signs of fatigue similar to the conventional hybrid composite restorations at heavy occlusal contact area, their light occlusal contact areas showed less surface pitting after 3 years of clinical service.

Wear of composite resin veneering materials and enamel in a chewing simulator

OBJECTIVES

The purpose of this in vitro study was to evaluate the wear of six composite resins for the veneering of crowns compared with the wear of human and bovine enamel, tested in a dual-axis chewing simulator.

METHODS

Eight specimens of six different composite resins (Targis I+II, Solidex, BelleglassHP, Estenia, Solidex) and of human and bovine enamel were prepared. Steatite ceramic balls served as antagonistic specimens. Specimens were dynamically loaded in a dual-axis chewing simulator with 49 N up to 1,200,000 loading cycles with additional thermal cycling between 5 and 55 degrees C. After 120,000, 240,000, 480,000, 840,000 and 1,200,000 loading cycles, an impression of the specimens' surface and the antagonistic specimen was taken using a polyvinylsiloxane impression material. The substance loss at the surface was measured with computer-aided laser profilometry. Data were analyzed using ANOVA and the Tukey test.

RESULTS

The wear of the ultra fine compact filled composite resins Solidex and BelleglassHP was not statistically significantly different from that of human enamel. The other composite resins and bovine enamel showed a wear statistically significantly higher than human enamel.

SIGNIFICANCE

Comparing six composite resins for the veneering of crowns, ultra fine compact filled composite resins BelleGlassHP and Solidex showed a wear not significantly different from the wear of human and bovine enamel.

Synthesis and characterization of dimethacrylate monomer with high molecular weight for root canal filling materials

A new dimethacrylate monomer 9,9'-bis[4-(2'-hydroxy-3'-methacryloyloxy-propoxy)phenyl] fluorene (3) with a molecular weight of 634 was synthesized in 51.4% yield by addition of a glycidyl ether group to 9,9'-bis(4-hydroxyphenyl) fluorene (1) by the reaction of compound 1 with epichlorohydrin, and then introducing the methacrylate moiety by the reaction of the epoxy group with methacrylic acid. The structure of monomer 3 was confirmed by FT-IR, (1)H-NMR, mass spectra and elemental analysis.