Round robin test: Wear of nine dental restorative materials in six different wear simulators – Supplement to the round robin test of 2005

Abstract

Objective

The purpose of the present study was to submit the same materials that were tested in the round robin wear test of 2002/2003 to the Alabama wear method.

Methods

Nine restorative materials, seven composites (belleGlass, Chromasit, Estenia, Heliomolar, SureFil, Targis, Tetric Ceram) an amalgam (Amalcap) and a ceramic (IPS Empress) have been submitted to the Alabama wear method for localized and generalized wear. The test centre did not know which brand they were testing. Both volumetric and vertical loss had been determined with an optical sensor. After completion of the wear test, the raw data were sent to IVOCLAR for further analysis. The statistical analysis of the data included logarithmic transformation of the data, the calculation of relative ranks of each material within each test centre, measures of agreement between methods, the discrimination power and coefficient of variation of each method as well as measures of the consistency and global performance for each material.

Results

Relative ranks of the materials varied tremendously between the test centres. When all materials were taken into account and the test methods compared with each other, only ACTA agreed reasonably well with two other methods, i.e. OHSU and ZURICH. On the other hand, MUNICH did not agree with the other methods at all. The ZURICH method showed the lowest discrimination power, ACTA, IVOCLAR and ALABAMA localized the highest. Material-wise, the best global performance was achieved by the leucite reinforced ceramic material Empress, which was clearly ahead of belleGlass, SureFil and Estenia. In contrast, Heliomolar, Tetric Ceram and especially Chromasit demonstrated a poor global performance. The best consistency was achieved by SureFil, Tetric Ceram and Chromasit, whereas the consistency of Amalcap and Heliomolar was poor. When comparing the laboratory data with clinical data, a significant agreement was found for the IVOCLAR and ALABAMA generalized wear method.

Significance

As the different wear simulator settings measure different wear mechanisms, it seems reasonable to combine at least two different wear settings to assess the wear resistance of a new material.

Introduction

In 2005 the results of a round robin test on the wear of dental materials were published . Ten dental materials had been tested with five laboratory wear methods. The results were quite different. When allocating relative ranks to the materials there was only little agreement between the five wear methods. One explanation was that the wear methods follow different wear generating concepts which result in a different ranking of the materials. The test centres used different wear simulators, different forces, different antagonist materials, different number of cycles, with or without thermocycling, etc. Some used abrasive mediums and different methods to evaluate the material loss. ZURICH additionally included 5 h of simulated toothbrushing between the phases as well as storage of the samples in ethanol. Furthermore, some methods showed a low discriminatory power which can be explained by the device that is used in conjunction with the method. Detailed qualification and validation protocols that show that the wear device is qualified and the wear method is validated are not available ; this holds true for all devices that are included in the round robin test.

The laboratory Alabama wear method that has – according to a review on wear – the highest citation frequency in the dental literature was not included in the round robin test at that time . The Alabama wear method is also included in the ISO Technical Specification on the wear by two/three body contact ; three of the other five methods (ACTA, OHSU, Zurich) are also included in the ISO Technical Specification.

The Alabama wear method was developed by Leinfelder and Suzuki and is therefore also called Leinfelder-Suzuki wear method. The method was first published in 1989 and is a modification of a device that has been originally designed by Roulet . Several major modifications were made over the years. In the first publication in 1989, a polyethylene tape was used as intermediate substance, driven by a tape advancing system . The tape was replaced by a slurry of PMMA beads ten years later . The original force was 55 N, which was increased to 75 N ten years later. In the first publication, a stainless steel stylus with 2 mm radius hit the specimen without rotation. In the new method an additional 30° clockwise rotation was integrated as soon as the stylus hits the surface of the specimen which was then called “localized wear”. Additionally, with a new specimen a flat stylus made of polyacetal is brought into contact with the flat specimen; the wear produced by this approach is called “generalized wear”. The materials specimens are incorporated into extracted molars that are trimmed flat. The stylus for generalized wear is made of polyacetal, the one for localized wear is stainless steel. The original publication states that each spring is calibrated with a 200 kg load cell in conjunction with a universal testing machine prior to testing, but no data have been reported with regard to the deviations, the scattering of results and the time intervals of force measurements or the replacement frequency of the spring. Most of the early published data come from the same authors (Leinfelder and/or Suzuki ).

Later, modifications to the original methods reported by Leinfelder and Suzuki were introduced to increase the reproducibility and reliability of the overall method. In an effort to move away from placing test specimens in extracted human teeth, a standardized cavity in a stainless steel custom fixture was used for positioning the tests materials in the wear simulator. To eliminate variations due to the wear of the acetal generalized wear stylus an identically shaped flattened stainless steel was introduced . For localized wear, a custom antagonist fixture was used that could accommodate a stainless steel ball bearing with a radius of 2.387 mm was used in place of the original hardened steel cone-shaped stylus. The original hardened steel localized antagonist tip surface degraded with use altering the surface finish of the stylus. Using ball bearings facilitates a cost-effective way to provide a new, standardized antagonist for each test specimen and each experiment trial .

The aim of the present study was to submit the same dental materials that were included in the round robin test published in 2005 to the Alabama wear method and to compare the results to the other five methods with the same statistical methodology. Therefore, this publication is a supplement to the 2005 publication; Section 2 as well as Section 5 are abbreviated and the reader is asked to consult the first publication.

Materials and methods

The selected materials were the same as in the first phase of the round robin test except for Targis 130 °C. As the oven that cured Targis specimens at a temperature of 130 °C was no longer available, this material had to be excluded. However, Targis specimens cured at 95 °C were included. Except for two materials (belleGlass and Targis) batches other than the ones used in the first phase of the round robin test (2002–2003) had to be used since the batch was not longer available or had already expired. Table 1 lists the materials with their batch numbers of the first and second phase of the round robin test.

Table 1
List of materials, manufacturer, type of material, processing and batch-number.
Material Manufacturer Type of material Processing Batch 2003 Batch 2008
Amalcap Plus Ivoclar Vivadent Amalgam Mixing C25527 J14154
Empress TC1 Ivoclar Vivadent Leucite reinforced ceramic Pressing C35146 G17472
belleGlass enamel KerrLab Fine particle hybrid composite Polymerization by heat and light 911422 911422
Chromasit S4 Ivoclar Vivadent Microfilled composite Polymerization by heat and pressure C15082 K15062
Estenia Enamel E2 Kuraray Hybrid composite Polymerization by heat and light 202CA 00020B/E2
Heliomolar 210 B Ivoclar Vivadent Microfilled composite Polymerization by light 29157 K30118
SureFil Shade Dentsply Fine particle hybrid composite Polymerization by light 990615 051013
Targis Incisal S1 Ivoclar Vivadent Fine particle hybrid composite Polymerization by heat and light C05051 C05051
Tetric Ceram 210 Ivoclar Vivadent Fine particle hybrid composite Polymerization by light C16761 G08104

The materials were produced in the same way as in the first phase. They were produced at Ivoclar by one operator, coded with numbers and sent to the test centre so that the centre was not aware which material they were testing.

ALABAMA wear method

The ALABAMA wear method was carried out at the Center for Oral Health Research at Creighton University (Omaha, USA) using three Leinfedler-Suzuki wear simulators that were thoroughly calibrated before testing the specimens. The materials were submitted to both generalized wear testing using a flat surface stainless steel stylus and localized wear using a stainless steel ball bearing. Specimens for both wear models were placed in a water bath with slurry of PMMA beads (average particle size 44 μm). Each generalized and localized specimen was surface scanned with the Proscan 2000 non-contact optical profilometer (Scantron Industrial Products, Ltd, Taunton, England) using a S38/3 sensor with a depth of field of 3000 μm. Proscan and ProForm software were used for quantification of material changes between the “before” and “after” surface profiles.

Ivoclar Vivadent-Method (IVOCLAR)

After processing and before testing, the specimens ( n = 8) were kept dry at a temperature of 37 °C for 24 h. The samples were mounted in a chewing simulator that is commercially available by Willytec (SD Mechatronik, Germany). Antagonists are made by pressed IPS Empress ceramic (Ivoclar Vivadent) which was glazed two times at a temperature of 870 °C. The diameter of the antagonist is 2.36 mm at a height of 600 μm measured from the tip of the antagonist. A weight of 5 kg had been put on each vertical bar. The sliding movement has been fixed at 0.7 mm. The frequency of the antagonist movement was 1.6 Hz. A total of 120,000 cycles of unidirectional antagonist movements have been carried out. Thermocycling with a frequency of 320/120,000 cycles has been included in the wear setting with a temperature difference between 5 °C and 55 °C. After completing the wear generating procedure, replicas were made with white super hard plaster (Fuji Superhard rock, GC Corporation, Japan). The plaster replicas have been analyzed by means of a commercially available laserscanner device (Laserscan 3D, Willytec, Germany) and the appropriate Match 3D software . The volumetric (IVVOL) as well as the maximal vertical loss (IVVERT) (1% percentile) have been calculated by the software.

Zurich-Method (ZURICH)

After processing and before testing the samples ( n = 8) were kept in water at a temperature of 36.5 °C for 2 weeks. This method has been described elsewhere in detail . With a load of 49 N and a frequency of 1.7 Hz the palatal cusps cut out of similar upper molars pushed against the surface of the specimens ( n = 6) that were mounted on a rubber socket at 45° angle allowing the antagonist to glide over the surface of the test specimen. The test specimens were kept in water with exchanged temperature according to a thermocycling protocol (3000× 5 °C/55 °C). After 120,000, 240,000, 640,000, and 1,200,000 cycles of loading the samples were submitted to a toothbrushing device with a slurry of toothpaste for 30 min, 30 min, 100 min, and 140 min resp. . Additionally, at the end of the first phase (120,000 cycles) the samples were put into a solution of 75% ethanol for 20 h to simulate the chemical degradation. After each thermomechanical sequence, the maximal vertical loss of both the specimens (occlusal contact area OCA) and the antagonists as well as the vertical loss in the contact free area (CFA) were calculated by using a computerized 3D-scanner . The scanner is driven by step motors which scan the object in 1 μm steps in the z -direction and in 100 μm steps in the xy -direction . In each test sequence six different materials have been submitted to wear which were randomly allocated to the six test chambers.

OHSU-Method (OHSU)

This method has been described elsewhere in detail . In principle, enamel cusps were forced into contact with the specimens through a layer of food like slurry (mixture of poppy seeds and PMMA beads). The enamel cusps were drilled out of human upper molars of similar shape giving them a spherical shape of a diameter of 10 mm. The enamel stylus were polished with 600 grit and 1000 grit silicon carbide slurry and polished with 5 μm aluminium oxide paste and then ultrasonically cleaned for 1 min. Before mounting the specimens ( n = 10) in the wear simulator, they were kept in water for 24 h at 37 °C. First the cusp was forced with a load of 50 N on the surface, sliding across a linear path of 8 mm producing abrasive wear. At the end of each path, a static load of 80 N was applied to produce localized attrition wear. For a whole test sequence 100,000 cycles at 1 Hz with unidirectional movements were run. The mean vertical loss of the abrasion and attrition wear facets were measured with a profilometry device at 10 defined tracks. The values of tracks 4–6 correspond to the abrasion wear (OHSUABR) and the tracks 8–9 to the attrition wear facet (OHSUATT).

Munich-Method (MUNICH)

For this method, a prototype of the wear simulator used for the Ivoclar Vivadent method has been used but with the configuration according to a pin-on-block-design allowing the test specimens ( n = 8) gliding under permanent contact to the spherical antagonist (Degusit aluminium oxide, 5 mm diameter) at a linear distance of 8 mm and a vertical load of 50 N. After processing and before testing the samples ( n = 8) were kept in physiological sodium chloride solution at room temperature for 7 days. During the chewing simulation the samples were rinsed with distilled water at 37 °C. At 10,000, 30,000, and 50,000 double cycles (bidirectional forth- and back-movement), replicas have been made with white plaster (Fuji Superhard rock, GC Corporation, Japan). The volumetric loss of the wear facet has been determined on the plaster models with the Laserscan 3D device described above (Willytec, Germany). In each test sequence eight different materials have been submitted to wear which were randomly allocated to the eight test chambers.

ACTA-Method (ACTA)

Two metal wheels rotate in different directions with about 15% difference in the circumferential speed while having near contact . The test specimens ( n = 24 and n = 28 resp.) are placed on the circumference of the wheel while the other wheel serves as antagonist. The force with which the two wheels come together was adjusted to 15 N. The wheels were placed in a slurry of white millet seeds in a buffer solution. After 50,000, 100,000 and 200,000 cycles the maximal vertical loss of the test specimens was measured with a profilometry device.

Materials and methods

The selected materials were the same as in the first phase of the round robin test except for Targis 130 °C. As the oven that cured Targis specimens at a temperature of 130 °C was no longer available, this material had to be excluded. However, Targis specimens cured at 95 °C were included. Except for two materials (belleGlass and Targis) batches other than the ones used in the first phase of the round robin test (2002–2003) had to be used since the batch was not longer available or had already expired. Table 1 lists the materials with their batch numbers of the first and second phase of the round robin test.

Table 1
List of materials, manufacturer, type of material, processing and batch-number.
Material Manufacturer Type of material Processing Batch 2003 Batch 2008
Amalcap Plus Ivoclar Vivadent Amalgam Mixing C25527 J14154
Empress TC1 Ivoclar Vivadent Leucite reinforced ceramic Pressing C35146 G17472
belleGlass enamel KerrLab Fine particle hybrid composite Polymerization by heat and light 911422 911422
Chromasit S4 Ivoclar Vivadent Microfilled composite Polymerization by heat and pressure C15082 K15062
Estenia Enamel E2 Kuraray Hybrid composite Polymerization by heat and light 202CA 00020B/E2
Heliomolar 210 B Ivoclar Vivadent Microfilled composite Polymerization by light 29157 K30118
SureFil Shade Dentsply Fine particle hybrid composite Polymerization by light 990615 051013
Targis Incisal S1 Ivoclar Vivadent Fine particle hybrid composite Polymerization by heat and light C05051 C05051
Tetric Ceram 210 Ivoclar Vivadent Fine particle hybrid composite Polymerization by light C16761 G08104

The materials were produced in the same way as in the first phase. They were produced at Ivoclar by one operator, coded with numbers and sent to the test centre so that the centre was not aware which material they were testing.

ALABAMA wear method

The ALABAMA wear method was carried out at the Center for Oral Health Research at Creighton University (Omaha, USA) using three Leinfedler-Suzuki wear simulators that were thoroughly calibrated before testing the specimens. The materials were submitted to both generalized wear testing using a flat surface stainless steel stylus and localized wear using a stainless steel ball bearing. Specimens for both wear models were placed in a water bath with slurry of PMMA beads (average particle size 44 μm). Each generalized and localized specimen was surface scanned with the Proscan 2000 non-contact optical profilometer (Scantron Industrial Products, Ltd, Taunton, England) using a S38/3 sensor with a depth of field of 3000 μm. Proscan and ProForm software were used for quantification of material changes between the “before” and “after” surface profiles.

Ivoclar Vivadent-Method (IVOCLAR)

After processing and before testing, the specimens ( n = 8) were kept dry at a temperature of 37 °C for 24 h. The samples were mounted in a chewing simulator that is commercially available by Willytec (SD Mechatronik, Germany). Antagonists are made by pressed IPS Empress ceramic (Ivoclar Vivadent) which was glazed two times at a temperature of 870 °C. The diameter of the antagonist is 2.36 mm at a height of 600 μm measured from the tip of the antagonist. A weight of 5 kg had been put on each vertical bar. The sliding movement has been fixed at 0.7 mm. The frequency of the antagonist movement was 1.6 Hz. A total of 120,000 cycles of unidirectional antagonist movements have been carried out. Thermocycling with a frequency of 320/120,000 cycles has been included in the wear setting with a temperature difference between 5 °C and 55 °C. After completing the wear generating procedure, replicas were made with white super hard plaster (Fuji Superhard rock, GC Corporation, Japan). The plaster replicas have been analyzed by means of a commercially available laserscanner device (Laserscan 3D, Willytec, Germany) and the appropriate Match 3D software . The volumetric (IVVOL) as well as the maximal vertical loss (IVVERT) (1% percentile) have been calculated by the software.

Zurich-Method (ZURICH)

After processing and before testing the samples ( n = 8) were kept in water at a temperature of 36.5 °C for 2 weeks. This method has been described elsewhere in detail . With a load of 49 N and a frequency of 1.7 Hz the palatal cusps cut out of similar upper molars pushed against the surface of the specimens ( n = 6) that were mounted on a rubber socket at 45° angle allowing the antagonist to glide over the surface of the test specimen. The test specimens were kept in water with exchanged temperature according to a thermocycling protocol (3000× 5 °C/55 °C). After 120,000, 240,000, 640,000, and 1,200,000 cycles of loading the samples were submitted to a toothbrushing device with a slurry of toothpaste for 30 min, 30 min, 100 min, and 140 min resp. . Additionally, at the end of the first phase (120,000 cycles) the samples were put into a solution of 75% ethanol for 20 h to simulate the chemical degradation. After each thermomechanical sequence, the maximal vertical loss of both the specimens (occlusal contact area OCA) and the antagonists as well as the vertical loss in the contact free area (CFA) were calculated by using a computerized 3D-scanner . The scanner is driven by step motors which scan the object in 1 μm steps in the z -direction and in 100 μm steps in the xy -direction . In each test sequence six different materials have been submitted to wear which were randomly allocated to the six test chambers.

OHSU-Method (OHSU)

This method has been described elsewhere in detail . In principle, enamel cusps were forced into contact with the specimens through a layer of food like slurry (mixture of poppy seeds and PMMA beads). The enamel cusps were drilled out of human upper molars of similar shape giving them a spherical shape of a diameter of 10 mm. The enamel stylus were polished with 600 grit and 1000 grit silicon carbide slurry and polished with 5 μm aluminium oxide paste and then ultrasonically cleaned for 1 min. Before mounting the specimens ( n = 10) in the wear simulator, they were kept in water for 24 h at 37 °C. First the cusp was forced with a load of 50 N on the surface, sliding across a linear path of 8 mm producing abrasive wear. At the end of each path, a static load of 80 N was applied to produce localized attrition wear. For a whole test sequence 100,000 cycles at 1 Hz with unidirectional movements were run. The mean vertical loss of the abrasion and attrition wear facets were measured with a profilometry device at 10 defined tracks. The values of tracks 4–6 correspond to the abrasion wear (OHSUABR) and the tracks 8–9 to the attrition wear facet (OHSUATT).

Munich-Method (MUNICH)

For this method, a prototype of the wear simulator used for the Ivoclar Vivadent method has been used but with the configuration according to a pin-on-block-design allowing the test specimens ( n = 8) gliding under permanent contact to the spherical antagonist (Degusit aluminium oxide, 5 mm diameter) at a linear distance of 8 mm and a vertical load of 50 N. After processing and before testing the samples ( n = 8) were kept in physiological sodium chloride solution at room temperature for 7 days. During the chewing simulation the samples were rinsed with distilled water at 37 °C. At 10,000, 30,000, and 50,000 double cycles (bidirectional forth- and back-movement), replicas have been made with white plaster (Fuji Superhard rock, GC Corporation, Japan). The volumetric loss of the wear facet has been determined on the plaster models with the Laserscan 3D device described above (Willytec, Germany). In each test sequence eight different materials have been submitted to wear which were randomly allocated to the eight test chambers.

ACTA-Method (ACTA)

Two metal wheels rotate in different directions with about 15% difference in the circumferential speed while having near contact . The test specimens ( n = 24 and n = 28 resp.) are placed on the circumference of the wheel while the other wheel serves as antagonist. The force with which the two wheels come together was adjusted to 15 N. The wheels were placed in a slurry of white millet seeds in a buffer solution. After 50,000, 100,000 and 200,000 cycles the maximal vertical loss of the test specimens was measured with a profilometry device.

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Nov 28, 2017 | Posted by in Dental Materials | Comments Off on Round robin test: Wear of nine dental restorative materials in six different wear simulators – Supplement to the round robin test of 2005
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