Fatigue studies on dental composites and bonding systems

Introduction: Adhesion has become an important concept in modern restorative dentistry. It offers the ability to bond materials to the tooth without invasive tooth preparation. Numerous in-vitro strength tests have been used to determine the bond strength of adhesive systems. However, because the occlusal forces applied to. a restoration are complex, and made up of a combination of forces, no one test can satisfactorily predict the in-vivo behavior of an adhesive system. The majority of bond strength studies have used monotonic tests to assess the bond strength of materials and between the materials and the tooth. These tests are expedient, but do not simulate the cyclic forces that operate in the mouth. Tests that characterize this type of . stress are called fatigue tests. Fatigue can result in wear and fracture of materials or bonds. .Objectives: To investigate fatigue behavior of modern resin composites and resinbonded joints of both metal to enamel and ceramic to enamel. The main approaches to fatigue assessment, 'Fatigue Limit' and 'Fatigue Life'were compared Materials and Methods: Surface effects of fatigue One hundred and eighty samples of two historical composites1-2 and seven modern composites3 - 9 were subjected to 2000 stress cycles between 0 and 120N or 0 and 400N. Surface damage was measured as the diameter of the fatigue scar and subsurface damage was determined by silver nitrate staining. The hardness of both the surface and subsurface was also determined. Fracture Composite to composite Two hundred and twenty composite disks were fabricated using three materials.7 • 9 After one day, one week, four weeks, and twelve weeks, fifty-five specimens of each material were removed from' water and divided into three groups of fifteen and one group of ten. Each group of samples was treated with one of three bonding systems10- 12 before adding a sec~nd increment. For each material, ten samples were subjected to Shear test in a Universal Testing Machine13 (CHS= 50 mmlmin). The fatigue limit test using fifteen samples per group were used to determine the fatigue limit using the staircase method (Draughn 1979). Metal or Ceramic to Enamel (via resin) Three hundred and forty-two discs of Ni/Cr-alloy14 were cast and treated by either sandblasting with aluminium oxide, or by sandblasting followed by electrolytic-etching in HCI. The disks were bonded to etched enamel with one of three dental bonding systems.1S - 17 One hundred and seventy-one ceramic disks were fabricated by sintering ceramic powder.18 One surface of each disk was etched with porcelain etching-gel19 for fifteen minutes and sandblasted with 50 J.Im A120 3. The prepared disks were then divided into three groups and were bonded to etched enamel using one of three dental bonding systems.1S - 17 Ten specimens of each group were sUbjected to a shear bond test (CHS 50 mm/min) and seventeen specimens of each group to a staircase fatigue test to determine the fatigue limit of the bonds. The remaining specimens from each group were placed in the custom made fatigue testing machine and allowed to cycle to failure between 0-20 kg, 0-10 kg or 0-5 kg (n=10 per load). The number of cycles at failure was analysed by Weibull statistics to determine the fatigue life Results: The surface studies in composites indicated that both surface and subsurface damage increased with increasing load. In general, small-particle composites experienced less damage than the large particle materials. At 12 kg, the surface damage was inversely proportional to the surface hardness, whereas at 40 kg, it was proportional to the subsurface hardness. At both loads, subsurface damage was directly proportion to subsurface hardness. For the composite to composite bonds, the fatigue limit values were approximately 30% of the shear bond strength values and the values were significantly different (p<0.01) for all nine groups. For metal to enamel bonds, the fatigue limit (after 5000 cycles) varied between 10.7 and 16.8 MPa compared to 21.3 and 48 MPa for the shear strength. The values for all groups was significantly different (p<0.001). There was no significant correlation between the shear bond strength and the fatigue limit values (Pearson Correlation P<0.01). For all groups, the threshold stress at which the samples equid withstand over one million cycles (fatigue Life) was 2.5 MPa. For ceramic to enamel bonds, the fatigue limit (after 5000 cycles) varied between 11.41 and 13.74 MPa compared to 21.3 and 48 MPa for the shear strength. The values for all groups were significantly differ~nt (p<0.001). There was no significa~t correlation between the shear bond strength and the fatigue limit values (Pearson Correlation P<0.001). For all groups, the threshold stress at which the samples could withstand over one million cycles (fatigue Life) was 2.5 MPa. Conclusion: Fatigue damage to the surface and subsurface of composite was related to the hardness of the material. The values of the fatigue limit were significantly lower than the shear bond strength values. There was no correlation between fatigue limit and shear bond strength. The long term safety limit for resin bonded joints to enamel is 2.5 MPa. Neither the shear test, nor the fatigue limit test was an accurate predictor of the long-term fatigue behaviour of resin-bonded restorations. A fatigue limit test using 100,000 cycles may be a useful predictor of the fatigue life which, in these studies, was half of the fatigue limit at 100, 000 cycles but the only reliable test is to test to failure. The data presented in this thesis indicated that the shear bond strength is not pred!ctor of long term failure. lClearfil Posterior, Cavex. Holland. 20cclusin. ICI. UK. 3Concise, 3M. USA. 4Admira, VOCO, Germany. 5Grandio. VOCO. Germany. 6Grandio Flow, VOCO, Germany. 7Spectrum, Dentsply, Germany. 8Durafill VS, Heraeus Kulzer, Germany. 9Herculite XRV, Kerr, USA. 10Prime&Bond. Dentsply, Germany. 110ptibond solo plus, Kerr, USA. 12BisGMAffEGDMA. 3M ESPE. USA. 13Nene Instruments Ltd.• UK. 14yerabond II, Aalba Dent Inc., USA. 15Calibra with Prime & Bond Resin, Dentsply, Germany. 16Panavia with ED-Primers. Kuraray, Japan. 17Nexus with Optibond Solo Plus Resin, Kerr, USA. 18Vitadur Alpha, VITA Zahnfabrik. Germany. 19Porcelain Etch-it gels, American Dental Supply. USA

Tribology of Medical Devices

Importance of tribology in a number of medical devices and surgical instruments is reviewed, including artificial joints, artificial teeth, dental implants and orthodontic appliances, cardiovascular devices, contact lenses, artificial limbs and surgical instruments. The current focus and future developments of these medical devices are highlighted from a tribological point of view, together with the underlying mechanisms

Effect of composite surface treatment and aging on the bond strength between a core build-up composite and a luting agent

Objective The purpose of this study was to assess the influence of conditioning methods and thermocycling on the bond strength between composite core and resin cement. Material and Methods Eighty blocks (8×8×4 mm) were prepared with core build-up composite. The cementation surface was roughened with 120-grit carbide paper and the blocks were thermocycled (5,000 cycles, between 5°C and 55°C, with a 30 s dwell time in each bath). A layer of temporary luting agent was applied. After 24 h, the layer was removed, and the blocks were divided into five groups, according to surface treatment: (NT) No treatment (control); (SP) Grinding with 120-grit carbide paper; (AC) Etching with 37% phosphoric acid; (SC) Sandblasting with 30 mm SiO2 particles, silane application; (AO) Sandblasting with 50 mm Al2O3 particles, silane application. Two composite blocks were cemented to each other (n=8) and sectioned into sticks. Half of the specimens from each block were immediately tested for microtensile bond strength (µTBS), while the other half was subjected to storage for 6 months, thermocycling (12,000 cycles, between 5°C and 55°C, with a dwell time of 30 s in each bath) and µTBS test in a mechanical testing machine. Bond strength data were analyzed by repeated measures two-way ANOVA and Tukey test (α=0.05). Results The µTBS was significantly affected by surface treatment (p=0.007) and thermocycling (p=0.000). Before aging, the SP group presented higher bond strength when compared to NT and AC groups, whereas all the other groups were statistically similar. After aging, all the groups were statistically similar. SP submitted to thermocycling showed lower bond strength than SP without thermocycling. Conclusion Core composites should be roughened with a diamond bur before the luting process. Thermocycling tends to reduce the bond strength between composite and resin cement

Fatigue studies on dental composites and bonding systems

Introduction: Adhesion has become an important concept in modern restorative dentistry. It offers the ability to bond materials to the tooth without invasive tooth preparation. Numerous in-vitro strength tests have been used to determine the bond strength of adhesive systems. However, because the occlusal forces applied to. a restoration are complex, and made up of a combination of forces, no one test can satisfactorily predict the in-vivo behavior of an adhesive system. The majority of bond strength studies have used monotonic tests to assess the bond strength of materials and between the materials and the tooth. These tests are expedient, but do not simulate the cyclic forces that operate in the mouth. Tests that characterize this type of . stress are called fatigue tests. Fatigue can result in wear and fracture of materials or bonds. .Objectives: To investigate fatigue behavior of modern resin composites and resinbonded joints of both metal to enamel and ceramic to enamel. The main approaches to fatigue assessment, 'Fatigue Limit' and 'Fatigue Life'were compared Materials and Methods: Surface effects of fatigue One hundred and eighty samples of two historical composites1-2 and seven modern composites3 - 9 were subjected to 2000 stress cycles between 0 and 120N or 0 and 400N. Surface damage was measured as the diameter of the fatigue scar and subsurface damage was determined by silver nitrate staining. The hardness of both the surface and subsurface was also determined. Fracture Composite to composite Two hundred and twenty composite disks were fabricated using three materials.7 • 9 After one day, one week, four weeks, and twelve weeks, fifty-five specimens of each material were removed from' water and divided into three groups of fifteen and one group of ten. Each group of samples was treated with one of three bonding systems10- 12 before adding a sec~nd increment. For each material, ten samples were subjected to Shear test in a Universal Testing Machine13 (CHS= 50 mmlmin). The fatigue limit test using fifteen samples per group were used to determine the fatigue limit using the staircase method (Draughn 1979). Metal or Ceramic to Enamel (via resin) Three hundred and forty-two discs of Ni/Cr-alloy14 were cast and treated by either sandblasting with aluminium oxide, or by sandblasting followed by electrolytic-etching in HCI. The disks were bonded to etched enamel with one of three dental bonding systems.1S - 17 One hundred and seventy-one ceramic disks were fabricated by sintering ceramic powder.18 One surface of each disk was etched with porcelain etching-gel19 for fifteen minutes and sandblasted with 50 J.Im A120 3. The prepared disks were then divided into three groups and were bonded to etched enamel using one of three dental bonding systems.1S - 17 Ten specimens of each group were sUbjected to a shear bond test (CHS 50 mm/min) and seventeen specimens of each group to a staircase fatigue test to determine the fatigue limit of the bonds. The remaining specimens from each group were placed in the custom made fatigue testing machine and allowed to cycle to failure between 0-20 kg, 0-10 kg or 0-5 kg (n=10 per load). The number of cycles at failure was analysed by Weibull statistics to determine the fatigue life Results: The surface studies in composites indicated that both surface and subsurface damage increased with increasing load. In general, small-particle composites experienced less damage than the large particle materials. At 12 kg, the surface damage was inversely proportional to the surface hardness, whereas at 40 kg, it was proportional to the subsurface hardness. At both loads, subsurface damage was directly proportion to subsurface hardness. For the composite to composite bonds, the fatigue limit values were approximately 30% of the shear bond strength values and the values were significantly different (p<0.01) for all nine groups. For metal to enamel bonds, the fatigue limit (after 5000 cycles) varied between 10.7 and 16.8 MPa compared to 21.3 and 48 MPa for the shear strength. The values for all groups was significantly different (p<0.001). There was no significant correlation between the shear bond strength and the fatigue limit values (Pearson Correlation P<0.01). For all groups, the threshold stress at which the samples equid withstand over one million cycles (fatigue Life) was 2.5 MPa. For ceramic to enamel bonds, the fatigue limit (after 5000 cycles) varied between 11.41 and 13.74 MPa compared to 21.3 and 48 MPa for the shear strength. The values for all groups were significantly differ~nt (p<0.001). There was no significa~t correlation between the shear bond strength and the fatigue limit values (Pearson Correlation P<0.001). For all groups, the threshold stress at which the samples could withstand over one million cycles (fatigue Life) was 2.5 MPa. Conclusion: Fatigue damage to the surface and subsurface of composite was related to the hardness of the material. The values of the fatigue limit were significantly lower than the shear bond strength values. There was no correlation between fatigue limit and shear bond strength. The long term safety limit for resin bonded joints to enamel is 2.5 MPa. Neither the shear test, nor the fatigue limit test was an accurate predictor of the long-term fatigue behaviour of resin-bonded restorations. A fatigue limit test using 100,000 cycles may be a useful predictor of the fatigue life which, in these studies, was half of the fatigue limit at 100, 000 cycles but the only reliable test is to test to failure. The data presented in this thesis indicated that the shear bond strength is not pred!ctor of long term failure. lClearfil Posterior, Cavex. Holland. 20cclusin. ICI. UK. 3Concise, 3M. USA. 4Admira, VOCO, Germany. 5Grandio. VOCO. Germany. 6Grandio Flow, VOCO, Germany. 7Spectrum, Dentsply, Germany. 8Durafill VS, Heraeus Kulzer, Germany. 9Herculite XRV, Kerr, USA. 10Prime&Bond. Dentsply, Germany. 110ptibond solo plus, Kerr, USA. 12BisGMAffEGDMA. 3M ESPE. USA. 13Nene Instruments Ltd.• UK. 14yerabond II, Aalba Dent Inc., USA. 15Calibra with Prime & Bond Resin, Dentsply, Germany. 16Panavia with ED-Primers. Kuraray, Japan. 17Nexus with Optibond Solo Plus Resin, Kerr, USA. 18Vitadur Alpha, VITA Zahnfabrik. Germany. 19Porcelain Etch-it gels, American Dental Supply. USA.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Variables related to materials and preparing for bond strength testing irrespective of the test protocol

Resin bonding can be compared to making a sandwich with the tooth on one side and the restoration on the other, a layer of bonding resin is applied to either side and a filled resin (composite) placed in between. The materials to be bonded may be either ceramic, metal or composite. These may be formed by various methods such as casting, pressing, sintering or machining. In the case of metals and ceramics there is no requirement to age the surfaces prior to bonding whereas with composites, a number of studies have attempted to age the composite substrate in order to mimic the situation of bonding new composite to old composite in the mouth. It is normal to prepare the bonding surfaces of the teeth and restoration prior to the application of the bonding resin. This normally involves a combined physical and chemical approach (e.g. sandblasting + silanation). Having prepared the surfaces the testpiece is assembled. The assembly protocol may attempt to mimic the clinical situation, which is relatively uncontrolled, or attempt to control variables such as the precise location of the restoration and the “seating force”. Having completed the assembly the testpiece may be aged prior to testing. In vitro aging is a function of time and environment plus additional features such as thermal or mechanical cycling. This paper considers these factors; but is limited to preparation of the restoration side of the sandwich

Comparison of Shear Bond Strength, Fatigue Limit and Fatigue Life in resin-bonded metal to enamel bonds

Objective To compare the Shear Bond Strength (SBS) of resin-bonded metal/enamel bonds with the Fatigue Limit and Fatigue Life of identical joints. Methods 285 discs of Ni/Cr-alloy (dia 5 mm × 4 mm) were cast and treated by either (1) Sandblasting with aluminium oxide or (2) Sandblast + 15 min electrolyticetch in HCl. The discs were bonded to etched enamel (37% HPO4/30 s) using 3 bonding systems. Ten discs of each group were subjected to a shear bond test (SBT) in a Universal Testing Machine5 (CHS = 50 mm/min). Seventeen discs of each group were used to determine the Fatigue Limit using the Staircase method (5000 cycles, 4 kg increment). Further batches of 10 discs were subjected to cyclic loads of either 5, 10, or 20 kg to determine the number of cycles at failure (Fatigue Life). The SBS and Fatigue Limit results were compared by correlation analysis. The Fatigue-Life cycles were compared by Weibull analysis to determine the β (reliability) and α (number of cycles) coefficients for the 3 loads. Results For all materials and treatments, the Fatigue-Limit results were much lower than the SBS and there was no correlation between the values (r = 0.49, p = 0.18). The Fatigue Limit for the samples using 5000 cycles ranged from 10.7 to 16.1 MPa. In the Fatigue-Life study, the stress at which the samples were reliably able to withstand more than 1million cycles (β > 5) was 2.5 MPa. Conclusion The Fatigue Limit of the bonds was much lower than the SBS and there was no correlation between the two values. In this study the Fatigue Limit was not a good predictor of the long term Fatigue-Life failure of the specimens

Contemporary denture base resins: Part 1

Provision of partial and complete dentures constructed from resin is commonplace and a satisfactory outcome requires the consideration of the properties of the resin, the oral tissues and prosthodontic principles. Conventional acrylic resin has been widely adopted as a popular denture base material since the 1930s. In this first of a two-part series, the benefits and shortcomings of acrylic resin are discussed alongside contemporary ‘enhancements’ to the material which can improve its properties. In the second part of the series, flexible and other alternative denture base resins, soft-linings, adverse effects of denture base materials and maintenance will be discussed. Clinical Relevance: Knowledge of contemporary denture base resin systems will help to achieve optimal outcomes in removable prosthodontics. </jats:p

Determination of surface and subsurface fatigue damage in dental composites

Dental filling materials are subjected to cyclic compression in the mouth. Nine resin-based composite filling materials were subjected to 2000 compression cycles between either 0 and 12 kg, or 0 and 40 kg. Surface deformation was measured as the diameter of the compression scar and surface microhardness determined by a Vickers’ microhardness test at 4 sites around the scar. Subsurface damage was stained with silver nitrate and the area of stain determined by image analysis software. Subsurface microhardness was measured at 4 sites around the stained zone. Surface deformation at 12 kg was inversely proportional to the surface microhardness at 12 kg. At both loads subsurface damage was directly proportional to the subsurface microhardness. Samples with small filler particles experienced less subsurface damage than those with larger particles. Silver nitrate staining was found to be a useful method for identifying subsurface damage

Contemporary denture base resins: Part 2

Provision of partial and complete dentures constructed from resin is commonplace and a satisfactory outcome requires the consideration of the properties of the resin, the oral tissues and prosthodontic principles. This second of a two-part series examines the advantages and disadvantages of flexible nylon denture base resins, which have found popularity for the provision of partial dentures. Adverse effects of denture base resins are examined and the benefits and shortcomings of softliners are explored. Chairside adjustment and polishing, and denture hygiene are also discussed. Clinical Relevance: Knowledge of contemporary denture base resin systems will help to achieve optimal outcomes in removable prosthodontics. </jats:p