Publications by authors named "Lippo V J Lassila"

171 Publications

A Polymer for Application as a Matrix Phase in a Concept of In Situ Curable Bioresorbable Bioactive Load-Bearing Continuous Fiber Reinforced Composite Fracture Fixation Plates.

Molecules 2021 Feb 26;26(5). Epub 2021 Feb 26.

Department of Biomaterials Science and Turku Clinical Biomaterials Centre-TCBC, Institute of Dentistry, Faculty of Medicine, University of Turku, FI-20014 Turku, Finland.

The use of bioresorbable fracture fixation plates made of aliphatic polyesters have good potential due to good biocompatibility, reduced risk of stress-shielding, and eliminated need for plate removal. However, polyesters are ductile, and their handling properties are limited. We suggested an alternative, PLAMA (PolyLActide functionalized with diMethAcrylate), for the use as the matrix phase for the novel concept of the in situ curable bioresorbable load-bearing composite plate to reduce the limitations of conventional polyesters. The purpose was to obtain a preliminary understanding of the chemical and physical properties and the biological safety of PLAMA from the prospective of the novel concept. Modifications with different molecular masses (PLAMA-500 and PLAMA-1000) were synthesized. The efficiency of curing was assessed by the degree of convergence (DC). The mechanical properties were obtained by tensile test and thermomechanical analysis. The bioresorbability was investigated by immersion in simulated body fluid. The biocompatibility was studied in cell morphology and viability tests. PLAMA-500 showed better DC and mechanical properties, and slower bioresorbability than PLAMA-1000. Both did not prevent proliferation and normal morphological development of cells. We concluded that PLAMA-500 has potential for the use as the matrix material for bioresorbable load-bearing composite fracture fixation plates.
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http://dx.doi.org/10.3390/molecules26051256DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7956420PMC
February 2021

Effect of potassium hydrogen difluoride in zirconia-to-resin bonding.

Dent Mater J 2021 Jan 20;40(1):245-252. Epub 2020 Oct 20.

Department of Biomaterials Science and Turku Clinical Biomaterials Centre -TCBC, Institute of Dentistry, University of Turku.

The objective of this study was to compare potassium hydrogen difluoride (KHF) etching for zirconia with commonly used surface roughening and chemical bonding methods (silane, MDP-monomer primer) for resin-based luting cement bonding to zirconia. Zirconia specimens were divided into six groups (n=10) according to surface treatment and bonding procedures, with and without thermocycling (6,000 cycles, 5-55ºC): 1) air-borne particle abrasion with alumina+MDP-monomer (ABP), 2) air-borne particle abrasion with silica-coated trialuminium trioxide+silane (ABPR-S) and 3) KHF etching+silane (ETC). Surface roughness and bond strength (SBS-test) for dry and thermocycled specimens were measured. SBS did not vary statistically between the dry groups, but thermocycling decreased the bond strengths of all the tested methods (p<0.05). After thermocycling, ABP had statistically significantly lower bond strength values compared to ABPR-S and ETC (p<0.05). Etching method with KHF did not provide better bonding capacity to previously introduced and commonly adopted bonding methods.
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http://dx.doi.org/10.4012/dmj.2019-389DOI Listing
January 2021

Midline denture base strains of glass fiber-reinforced single implant-supported overdentures.

J Prosthet Dent 2020 Sep 18. Epub 2020 Sep 18.

Professor, and Chair of Biomaterials Science Department, University of Turku, Turku, Finland; Chief Hospital Dentist, City of Turku, Welfare Division, Turku, Finland.

Statement Of Problem: The fracture incidence of implant-supported overdentures is more frequent in the area of attachment because of stress concentration and denture deformation in this area. How E-glass fiber reinforcement can address this problem is unclear.

Purpose: The purpose of this in vitro study was to evaluate the influence of unidirectional E-glass fiber reinforcement on the mid-line denture base strains of single implant-supported overdentures.

Material And Methods: An experimental acrylic resin cast was constructed with a single implant placed in the mid-line area and a ball attachment screwed to the implant. Twenty-four experimental overdentures were constructed and divided into 4 groups: group AP fabricated from autopolymerizing acrylic resin without fiber reinforcement, group APF fabricated from autopolymerizing acrylic resin with unidirectional E-glass fiber reinforcement running over the residual ridge and the ball matrix, group HP fabricated from heat-polymerized acrylic resin without fiber reinforcement, and group HPF fabricated from heat-polymerized acrylic resin with unidirectional E-glass fiber reinforcement running over the residual ridge and the ball matrix. A biaxial rosette strain gauge was attached to the incisor areas of each overdenture above the attachment level (Ch1, Ch2) and to a multichannel digital strain meter. A static vertical load of 100 N was applied to the first molar area bilaterally by using a universal testing device during strain measurement procedures. The differences in the mean strain and deflection values among the investigated groups were evaluated for statistical significance using 1-way analysis of variance (ANOVA) with the Tukey post hoc multiple comparison (α=.05).

Results: The type of acrylic resin did not have a statistically significant effect on the mean strain values among groups (P=.350), while the reinforcement did significantly affect them (P<.001). The interaction between reinforcement and acrylic resin was not statistically significant (P=.552). Both strain gauge channels in group APF and group HPF recorded significantly lower strain values by almost 50% than those of group AP and group HP (P<.05).

Conclusions: Unidirectional E-glass fiber reinforcement placed over the residual ridge and implant attachment significantly reduced denture base strains and deformation of single implant-supported overdentures.
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http://dx.doi.org/10.1016/j.prosdent.2020.05.018DOI Listing
September 2020

Direct bilayered biomimetic composite restoration: The effect of a cusp-supporting short fiber-reinforced base design on the chewing fracture resistance and failure mode of molars with or without endodontic treatment.

J Mech Behav Biomed Mater 2020 03 24;103:103554. Epub 2019 Nov 24.

Department of Biomaterials Science, Institute of Dentistry, University of Turku, Lemminkäisenkatu 2, 20520, Turku, Finland; Turku Clinical Biomaterials Centre (TCBC), Institute of Dentistry, University of Turku, Itäinen Pitkäkatu 4B, 20520, Turku, Finland.

The aim of this study was to assess the chewing fracture resistance of compromised molars restored with direct composite resin (CR) restorations, with and without a short-fiber reinforcing (short-FRC) base. Wide extension of MOD cavities with removed palatal cusps preparations were simulated on 48 extracted maxillary molars. Five groups (n = 12) were designed: 1. control (intact teeth), 2. non-endodontically treated and 3. endodontically treated teeth with direct CR restorations (GC-Posterior), and 4. non-endodontically treated and 5. endodontically treated teeth with direct biomimetic bilayered restorations. Groups 4 and 5 included an anatomically shaped short-FRC base (everX Posterior), covered with a 2 mm CR layer (GC-Posterior). Restorations were subjected to chewing in water (1.5 Hz), with load of 85 N. Specimens were loaded until fracture or to a maximum of 120 000 cycles. Restorations that survived the chewing cycle were submitted to static load test (post-chewing test). The data were statistically analyzed using two-way ANOVA (p = 0.05) and fracture types with the chi-square test (p = 0.05). Fractures were classified into reparable, possibly reparable or non-reparable. All specimens survived the chewing cycle. The chewing fracture resistance of the direct biomimetic restorations prepared on non-endodontically treated teeth (2889 N) was statistically significantly higher than the direct CR counterparts (1966 N) (p = 0.00015), which was not the case for the groups with endodontically treated teeth (p = 0.257). Inclusion of a short-FRC base also influenced the fracture type resulting in most reparable fractures (67-75% versus 25% for biomimetic and CR groups respectively) (p = 0.054). Anatomically shaped i.e. a cusp-supporting design made of short-FRC base (everX Posterior) improved the chewing fracture resistance and fracture manner of compromised molars regardless of whether they were endodontically treated or not.
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http://dx.doi.org/10.1016/j.jmbbm.2019.103554DOI Listing
March 2020

Effect of Long-Term Brushing on Deflection, Maximum Load, and Wear of Stainless Steel Wires and Conventional and Spot Bonded Fiber-Reinforced Composites.

Int J Mol Sci 2019 Nov 30;20(23). Epub 2019 Nov 30.

Unit of Orthodontics and Paediatric Dentistry, Section of Dentistry, Department of Clinical, Surgical, Diagnostic and Paediatric Sciences, University of Pavia, 27100 Pavia, Italy.

Fiber-reinforced composite (FRC) retainers are an aesthetic alternative to conventional Stainless Steel splints. They are generally used with a full bonded technique, but some studies demonstrated that they could be managed with a spot bonding technique to significantly decrease their rigidity. In order to propose this FRC spot bonding technique for clinical use, the aim of this study was to evaluate mechanical properties and surface wear of fibers left uncovered. Tests were made by simulating tooth brushing, comparing FRC spot bonding technique splints with stainless steel and FRC traditional technique splints. Specimens were tested both at 0.1 mm of deflection and at maximum load, showing higher values of rigidity for the FRC full bonded technique. After tooth brushing, no significant reduction in values at 0.1 mm deflection was reported, while we found a similar reduction in these values for the Stainless Steel and FRC spot bonding technique at maximum load, and no significant variation for the FRC full bonded technique. SEM images after tooth brushing showed wear for FRC fibers left uncovered, while no relevant wear signs in metal and conventional FRC fibers were noticed. Results showed that FRC spot bonding technique has advantages in mechanical properties when compared to the FRC traditional full bonding technique, also after tooth brushing. However, the surface wear after tooth brushing in the FRC spot bonding technique is considerable and other tests must be performed before promoting this technique for routine clinical use.
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http://dx.doi.org/10.3390/ijms20236043DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6929004PMC
November 2019

Effect of cellulose nanofiber content on flexural properties of a model, thermoplastic, injection-molded, polymethyl methacrylate denture base material.

J Mech Behav Biomed Mater 2020 02 31;102:103513. Epub 2019 Oct 31.

Department of Biomaterials Science and Turku Clinical Biomaterials Centre - TCBC, Institute of Dentistry, University of Turku, Turku, Finland.

Cellulose nanofiber (CNF) made from wood-derived fiber is considered as a potential alternative reinforcing material to conventional fibers. The aim of this study was to investigate the effect of CNF on the flexural properties of CNF-reinforced, injection molded, polymethyl methacrylate (PMMA) denture base material. Test specimens were fabricated from a model thermoplastic denture base resin using the injection molding technique. The resin pellets were mixed with CNF (to obtain different weight percentages 5, 10, 15, and 23 wt%). PMMA without CNF served as the control (0 wt%). Prior to the testing, the test specimens (n = 12/group) were water-immersed at 37 °C water for 50 h. The flexural strengths and moduli of the specimens were determined using three-point bending tests. Statistical evaluation included a one-way analysis of variance and the Student-Newman-Keuls test (α = 0.05). The mean and standard deviation of flexural strengths with the addition of 0, 5, 10, 15 and 23% CNF were 49.4 (±0.7), 56.4 (±1.3), 63.5 (±2.0), 72.0 (±4.7), and 96.8 (±4.0) MPa, respectively. The mean and standard deviation of flexural modulus with the addition of the same concentrations of CNF were 1.31 (±0.02), 1.56 (±0.05), 1.99 (±0.14), 2.40 (±0.15), and 3.96 (±0.08) GPa, respectively. The flexural strengths and moduli of the CNF-reinforced PMMA were significantly higher than those of pure PMMA (p < 0.05). Hence, incorporation of CNF can significantly improve flexural properties of a thermoplastic PMMA denture base material.
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http://dx.doi.org/10.1016/j.jmbbm.2019.103513DOI Listing
February 2020

Biostable glass fibre-reinforced dimethacrylate-based composites as potential candidates for fracture fixation plates in toy-breed dogs: Mechanical testing and finite element analysis.

J Mech Behav Biomed Mater 2019 08 17;96:172-185. Epub 2019 Apr 17.

Department of Biomaterials Science and Turku Clinical Biomaterials Center - TCBC, Institute of Dentistry, University of Turku, Itäinen Pitkäkatu 4B, FI-20520, Turku, Finland; Biomaterial and Medical Device Research Programme - BioCity Turku, Itäinen Pitkäkatu 4B, FI-20520, Turku, Finland.

In toy-breed dogs (bodyweight <5 kg), the fractures of the radius and ulna are particularly common and can be caused by minimal trauma. While fracture fixation using metallic plates is a feasible treatment modality, the excessive stiffness of these devices produces the underloading of the bone which may result in the adverse bone remodelling and complications in the healing of the fracture. In this study, we investigated bisphenol A glycidylmethacrylate -based glass fibre reinforced composites as potential alternatives to metals in the devices intended for the fracture fixation of the distal radius in toy-breed dogs. Four composites with different glass fibre reinforcements were prepared as rectangular specimens and as fracture fixation plates. These were mechanically tested in three-point and four-point bending. There were two controls: polyether etherketone reinforced with short carbon fibres (specimens and plates) and commercially available stainless-steel plates. Finite element simulations were used for the assessment of the behaviour of the plates. For the control stainless steel plate, the bending strength was 1.358 N*m, superior to that of any of the composite plates. The composite plate with the matrix reinforced with continuous unidirectional glass fibres had the bending strength of 1.081 N*m, which is sufficient in this clinical context. For the plates made of polyether etherketone reinforced with carbon fibres, the strength was 0.280 N*m. Similar conclusions on the biomechanical behaviour of the plates could be made solely based on the results of the finite element simulations, provided the geometries and the material properties are well defined.
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http://dx.doi.org/10.1016/j.jmbbm.2019.04.016DOI Listing
August 2019

Fatigue resistance of a simulated single LOCATOR overdenture system.

J Prosthet Dent 2019 Dec 12;122(6):557-563. Epub 2019 Apr 12.

Professor, and Chair of Biomaterials Science Department, University of Turku, Turku, Finland; City of Turku, Welfare Division, Turku, Finland.

Statement Of Problem: The incidence of fracture in a single-implant overdenture base increases in the region adjacent to the fulcrum implant.

Purpose: The purpose of this in vitro study was to evaluate the effect of bidirectional woven electrical glass (E-glass) fiber reinforcements on the fatigue resistance of a simulated single LOCATOR-retained overdenture.

Material And Methods: Test specimens with a centrally positioned metal housing for a LOCATOR stud attachment were fabricated from autopolymerizing acrylic resin. Specimens for the control group were fabricated without glass fiber reinforcements. The 4L group specimens had 4 layers of E-glass fiber weaves and were divided according to the fiber location into the following 3 subgroups: 4L-A with 4 fiber layers above the metal housing; 4L-N with 4 fiber layers adjacent to the metal housing; and 4L-A+4L-N with 4 fiber layers above and 4 fiber layers adjacent to the housing. Specimens were stored in distilled water for 1 week at 23 °C before cyclic fatigue testing at 10 000 cycles by using a staircase approach (n=12). The results were analyzed with 1-way ANOVA and the Tukey multiple comparisons post hoc analysis (α=.05). A 2-way ANOVA (α=.05) was conducted to detect the effect of fatigue cyclic loading and the position of the fiber layers and their interaction on the fatigue resistance.

Results: The results of the investigated compressive fatigue limits for the test groups were 190 ±15.9 N for the control group, 265 ±15.9 N for the 4L-A subgroup, 220 ±15.9 N for the 4L-N subgroup, and 275 ±15.9 N for the 4L-A+4L-N subgroup. A nonsignificant difference was found for creep values between the control group and reinforced subgroups (P>.05). The postfatigue flexural strength values in the 4L-A and 4L-A+4L-N subgroups were significantly higher than those in the control group (P<.001) and the 4L-N subgroup (P=.004 and P=.005). However, no significant difference was found in postfatigue flexural strength between the control group and the 4L-N subgroup (P=.828).

Conclusions: Placing 4 layers of bidirectional E-glass fiber weaves above the metal housing can increase the fatigue resistance and the postfatigue flexural strength of single LOCATOR-retained overdentures.
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http://dx.doi.org/10.1016/j.prosdent.2018.11.013DOI Listing
December 2019

The effect of smear layer removal on E. faecalis leakage and bond strength of four resin-based root canal sealers.

BMC Oral Health 2018 12 13;18(1):213. Epub 2018 Dec 13.

Department of Clinical Dentistry, Faculty of Health Sciences, UiT The Arctic University of Norway, N-9037, Tromso, Norway.

Background: The aim of the study was to assess bacterial sealability and bonding ability of methacrylate-based Resilon (RS, SybronEndo), Endo Rez (ER, Ultradent Products Inc), and epoxy-based AH Plus (AH, Dentsply/DeTrey), MTA Fill Apex (MTAF, Angelus Soluções Odontológicas) root canal sealers, and the effect of the smear layer removal on the sealability.

Methods: One hundred thirty root segments were instrumented up to apical size #60 and rinsed with 2.5% NaOCl. Half of the roots were rinsed with 5ml 17% EDTA to remove the smear layer. All the roots were filled with AH, ER, MTAF sealers and gutta-percha, or RS with Resilon cones. After storage at 37°C for 7 days the samples were mounted into bacterial leakage assay for 50 days. Another 100 roots were instrumented and rinsed as described above, split longitudinally, cut into the cervical, middle and apical parts. The sealers were injected through the plastic mould on the dentin surface. After 7 days of incubation at 37°C, bond strength was tested using a notched-edge test fixture (Crosshead, Ultradent Products Inc.) and a universal testing machine (Lloyd Instruments).

Results: AH revealed the longest mean time for bacterial resistance by 29.4 and 36.8 days (with and without smear layer, respectively) followed by RS (15.1 and 24.7 days, respectively). The difference between materials was significant (p<0.001). Bond strength values ranged from 0.2± 0.1 to 3.5± 0.7 MPa and increased from the apical to the cervical third. In the apical third, AH showed the highest mean (SD) bond values 1.4 (0.4) MPa and 1.7 (0.6) MPa (with and without smear, respectively, followed by RS, 0.5 (0.1) MPa and 0.8 (0.1) MPa, respectively. The difference between materials was significant (p=0.001).

Conclusion: The effect of the smear layer removal on the sealability was material-dependent.
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http://dx.doi.org/10.1186/s12903-018-0655-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6293555PMC
December 2018

Travel beyond Clinical Uses of Fiber Reinforced Composites (FRCs) in Dentistry: A Review of Past Employments, Present Applications, and Future Perspectives.

Biomed Res Int 2018 22;2018:1498901. Epub 2018 Oct 22.

Unit of Orthodontics and Paediatric Dentistry, Section of Dentistry, Department of Clinical, Surgical, Diagnostic and Paediatric Sciences, University of Pavia, Italy.

The reinforcement of resins with short or long fibers has multiple applications in various engineering and biomedical fields. The use of fiber reinforced composites (FRCs) in dentistry has been described in the literature from more than 40 years. In vitro studies evaluated mechanical properties such as flexural strength, fatigue resistance, fracture strength, layer thickness, bacterial adhesion, bonding characteristics with long fibers, woven fibers, and FRC posts. Also, multiple clinical applications such as replacement of missing teeth by resin-bonded adhesive fixed dental prostheses of various kinds, reinforcement elements of dentures or pontics, and direct construction of posts and cores have been investigated. In orthodontics, FRCs have been used also for active and passive orthodontic applications, such as anchorage units, en-masse movement units, and postorthodontic tooth retention. FRCs have been extensively tested in the literature, but today the advances in new technologies involving the introduction of nanofillers or new fibers along with understanding the design principles of FRC devices open new fields of research for these materials both in vitro and in vivo. The present review describes past and present applications of FRCs and introduces some future perspectives on the use of these materials.
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http://dx.doi.org/10.1155/2018/1498901DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6217899PMC
February 2019

Effect of phytic acid on the setting times and tensile strengths of calcium silicate-based cements.

Aust Endod J 2019 Aug 6;45(2):241-245. Epub 2018 Nov 6.

Department of Biomaterials Science, Turku Clinical Biomaterials Centre - TCBC, Institute of Dentistry, University of Turku, Turku, Finland.

This study aimed to evaluate and compare the effect of 1% phytic acid as a mixing medium on the setting times and diametral tensile strengths of different calcium silicate-based cements. Specimens for four experimental groups (n = 20/each) were fabricated by mixing ProRoot MTA (Dentsply) and Biodentine (Septodont) powders with their original liquids or with 1% phytic acid. Half of the samples in each group were immediately subjected to setting time tests, whereas the remaining half was subjected to the diametral tensile strength test after 3 weeks. When mixed with their original liquids, the setting time of MTA was significantly longer than that of Biodentine (P < 0.05). When mixed with phytic acid, the initial and final setting times of both test materials significantly decreased (P < 0.05). The diametral tensile strength of Biodentine was significantly greater than that of MTA (P < 0.05). However, phytic acid had no effect on this outcome (P > 0.05).
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http://dx.doi.org/10.1111/aej.12314DOI Listing
August 2019

Effect of discontinuous glass fibers on mechanical properties of glass ionomer cement.

Acta Biomater Odontol Scand 2018 31;4(1):72-80. Epub 2018 Jul 31.

Department of Biomaterials Science and Turku Clinical Biomaterials Center-TCBC, Institute of Dentistry, University of Turku, Turku, Finland.

Aim: This study investigated the reinforcing effect of discontinuous glass microfibers with various loading fractions on selected mechanical properties of self-cure glass ionomer cement (GIC).

Method: Experimental fiber reinforced GIC (Exp-GIC) was prepared by adding discontinuous glass microfiber (silane/non-silane treated) of 200-300 µm in length to the powder of self-cure GIC (GC Fuji IX) with various mass ratios (15, 20, 25, 35, and 45 mass%) using a high speed mixing device. Flexural strength, flexural modulus, work of fracture, compressive strength and diametral tensile strength were determined for each experimental and control materials. The specimens ( = 8) were wet stored (37 °C for one day) before testing. Scanning electron microscopy equipped with energy dispersive spectrometer was used to analysis the surface of silanized or non-silanized fibers after treated with cement liquid. The results were analyzed with using multivariate analysis of variance MANOVA.

Results: Fiber-reinforced GIC (25 mass%) had significantly higher mechanical performance of flexural modulus (3.8 GPa), flexural strength (48 MPa), and diametral tensile strength (18 MPa) ( < .05) compared to unreinforced material (0.9 GPa, 26 MPa and 8 MPa). No statistical significant difference in tested mechanical properties was recorded between silanized and non-silanized Exp-GIC groups. Compressive strength did not show any significant differences ( > .05) between the fiber-reinforced and unreinforced GIC.

Conclusion: The use of discontinuous glass microfibers with self-cure GIC matrix considerably increased the all of the studied properties except compressive strength.
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http://dx.doi.org/10.1080/23337931.2018.1491798DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6070992PMC
July 2018

Load-bearing capacity of simulated Locator-retained overdenture system.

J Prosthet Dent 2018 Oct 29;120(4):558-564. Epub 2018 Jun 29.

Professor and Chair of Biomaterials Science Department, University of Turku, and Chief Dentist, City of Turku Welfare Division, Turku, Finland.

Statement Of Problem: Acrylic resin overdenture bases usually fracture because of stress concentrations at the area of the abutments.

Purpose: The purpose of this study was to evaluate the reinforcing effect of bidirectional woven electrical glass (E-glass) fiber weaves with a different number of layers and different locations on the load-bearing capacity of simulated Locator-retained overdenture specimens.

Material And Methods: Test specimens with a centrally located metal housing for a Locator stud attachment were fabricated from autopolymerizing acrylic resin (polymethylmethacrylate based) and reinforced with bidirectional woven E-glass fiber layers. The control group specimens were fabricated without fiber reinforcement. The 2L group had 2 layers of E-glass fiber weaves and was divided according to the fiber location within the specimens as follows: 2L-A subgroup with 2 fiber layers above the metal housing; 2L-N subgroup with 2 fiber layers adjacent to the housing; and 2L-A+2L-N subgroup with 2 fiber layers above and 2 fiber layers adjacent to the housing. The 4L group had 4 layers of E-glass fiber weaves and was divided according to the fiber location as follows: 4L-A subgroup with 4 fiber layers above the housing; 4L-N subgroup with 4 fiber layers adjacent to the housing; and 4L-A+4L-N subgroup with 4 fiber layers above and 4 fiber layers adjacent to the housing. Dry specimens were submitted to a 3-point static loading test, and the mean flexural strength, flexural modulus, and strain values were analyzed with 1-way ANOVA and Tukey post hoc tests (α=.05). Two-way ANOVA was conducted to detect the influence of the number and location of the reinforcing layers (α=.05).

Results: The results revealed a significant difference (P<.001) in flexural strength values between the control group (92.4 ±14 MPa) and the 2 subgroups, 4L-A (116 ±7.3 MPa) and 4L-A+4L-N (117.1 ±6 MPa), with a significant effect only from the number of the reinforcing layers (P<.001) and not the location (P=.153). No significant differences were found with flexural modulus (P=.195) and strain values (P=.174) among the tested groups.

Conclusions: The load-bearing capacity of a Locator-retained overdenture can be significantly increased by placing 4 layers of bidirectional woven E-glass fiber weaves either only above the metal housing or in both locations above and adjacent to the metal.
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http://dx.doi.org/10.1016/j.prosdent.2018.04.009DOI Listing
October 2018

Immediate Repair Bond Strength of Fiber-reinforced Composite after Saliva or Water Contamination.

J Adhes Dent 2018 ;20(3):205-212

Purpose: This in vitro study aimed to evaluate the shear bond strength (SBS) of particulate filler composite (PFC) to saliva- or water-contaminated fiber-reinforced composite (FRC).

Materials And Methods: One type of FRC substrate with semi-interpenetrating polymer matrix (semi-IPN) (everStick C&B) was used in this investigation. A microhybrid PFC (Filtek Z250) substrate served as control. Freshly cured PFC and FRC substrates were first subjected to different contamination and surface cleaning treatments, then the microhybrid PFC restorative material (Filtek Z250) was built up on the substrates in 2-mm increments and light cured. Uncontaminated and saliva- or water-contaminated substrate surfaces were either left untreated or were cleaned via phosphoric acid etching or water spray accompanied with or without adhesive composite application prior applying the adherent PFC material. SBS was evaluated after thermocycling the specimens (6000 cycles, 5°C and 55°C).

Results: Three-way ANOVA showed that both the surface contamination and the surface treatment signficantly affected the bond strength (p < 0.05). Saliva contamination reduced the SBS more than did the water contamination. SBS loss after saliva contamination was 73.7% and 31.3% for PFC and FRC, respectively. After water contamination, SBS loss was 17.2% and 13.3% for PFC and FRC, respectively. The type of surface treatment was significant for PFC (p < 0.05), but not for FRC (p = 0.572).

Conclusion: Upon contamination of freshly cured PFC or semi-IPN FRC, surfaces should be re-prepared via phosphoric acid etching, water cleaning, drying, and application of adhesive composite in order to recover optimal bond strength.
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http://dx.doi.org/10.3290/j.jad.a40515DOI Listing
January 2019

Fracture Strength and Precision of Fit of Implant-Retained Monolithic Zirconia Crowns.

J Oral Implantol 2018 Oct 15;44(5):330-334. Epub 2018 May 15.

1   Department of Prosthetic Dentistry and Stomatognathic Physiology, Institute of Dentistry, University of Turku, Turku, Finland.

New monolithic zirconia materials can be used to fabricate full-contour fixed dental prostheses with the computer-aided design/computer-aided manufacturing (CAD/CAM) method. The aim of this study was to examine the fracture strength and precision of fit of screw-retained monolithic zirconia crowns made directly on implants or by cementing on prefabricated titanium (Ti) bases. Monolithic screw-retained implant crowns (n = 6) were produced by CAD/CAM method using partially (PSZ) and fully stabilized (FSZ) zirconia. Industrially produced zirconia crowns were used as a reference. A lateral incisor study model was made onto an implant replica. Crowns were produced either directly on the implant or through cementing on a prefabricated titanium base (PSZ+Ti, FSZ+Ti). The crowns were tightened to implant replicas with a torque of 35 Ncm. The gap between the replica and the abutment or crown was measured from ×400 scanning electron microscope images for precision of fit. Mechanical testing until failure was completed with a universal testing machine with loading angle of 45°. Statistical analysis was performed (analysis of variance). Mean (±SD) failure loads were 259 ± 23 (PSZ), 140 ± 13 (FSZ), 453 ± 25 (PSZ+Ti), 439 ± 41 (FSZ+Ti), and 290 ± 39 (Procera). Mean (±SD) gap values were 2.2 ± 0.2 (PSZ), 2.5 ± 1.0 (FSZ), 7.0 ± 1.0 (PSZ+Ti), 7.7 ± 1.6 (FSZ+Ti), and 6.7 ± 1.7 (Procera). Monolithic zirconia crowns with a Ti base clearly show higher fracture strengths than the crowns fixed directly on the implant surface. Better marginal fit can be achieved with direct zirconia crowns than with crowns on a titanium base or industrially produced zirconia crowns.
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http://dx.doi.org/10.1563/aaid-joi-D-17-00249DOI Listing
October 2018

Physicochemical properties of discontinuous S2-glass fiber reinforced resin composite.

Dent Mater J 2018 Jan 27;37(1):95-103. Epub 2017 Oct 27.

Department of Biomaterials Science and Turku Clinical Biomaterials Centre -TCBC, Institute of Dentistry, University of Turku.

The objective of this study was to investigate several physicochemical properties of an experimental discontinuous S2-glass fiber-reinforced resin composite. The experimental composite was prepared by mixing 10 wt% of discontinuous S2-glass fibers with 27.5 wt% of resin matrix and 62.5 wt% of particulate fillers. Flexural strength (FS) and modulus (FM), fracture toughness (FT), work of fracture (WOF), double bond conversion (DC), Vickers hardness, volume shrinkage (VS) and fiber length distribution were determined. These were compared with two commercial resin composites. The experimental composite showed the highest FS, WOF and FT compared with two control composites. The DC of the experimental composite was comparable with controls. No significant difference was observed in VS between the three tested composites. The use of discontinuous glass fiber fillers with polymer matrix and particulate fillers yielded improved physical properties and substantial improvement was associated with the use of S2-glass fiber.
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http://dx.doi.org/10.4012/dmj.2017-078DOI Listing
January 2018

Does artificial aging affect mechanical properties of CAD/CAM composite materials.

J Prosthodont Res 2018 Jan 21;62(1):65-74. Epub 2017 Jun 21.

Institute of Dentistry, Department of Biomaterials Science and Turku Clinical Biomaterials Centre - TCBC, Finland; Turku University of Applied Sciences, Turku, Finland.

Purpose: The purpose of this study was to determine the flexural strength and Weibull characteristics of different CAD/CAM materials after different in vitro aging conditions.

Methods: The specimens were randomly assigned to one of the six in vitro aging conditions: (1) water storage (37°C, 3 weeks), (2) boiling water (24h), (3) hydrochloric acid exposure (pH: 1.2, 24h), (4) autoclave treatment (134°C, 200kPa, 12h), (5) thermal cycling (5000 times, 5-55°C), (6) cyclic loading (100N, 50,000 cycles). No treatment was applied to the specimens in control group. Three-point bending test was used for the calculation of flexural strength. The reliability of the strength was assessed by Weibull distribution. Surface roughness and topography was examined by coherence scanning interferometry. Evaluated parameters were compared using the Kruskall-Wallis or Mann-Whitney U test.

Results: Water storage, autoclave treatment and thermal cycling significantly decreased the flexural strength of all materials (p<0.05), whereas HCl exposure or cyclic loading did not affect the properties (p>0.05). Weibull moduli of Cerasmart™ and Lava™ Ultimate were similar with control. Vita Enamic exhibited similar Weibull moduli in all aging groups except the HCl treated group (p>0.05). R values of Cerasmart™ and Lava™ Ultimate were in the range of 0.053-0.088μm in the aged groups. However R results of Vita Enamic were larger than 0.2μm.

Conclusions: Flexural strength of newly developed restorative CAD/CAM materials was significantly decreased by artificial aging. Cyclic loading or HCl exposure does not affect to the flexural strength and structural reliability of Cerasmart™ and Lava™ Ultimate.
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http://dx.doi.org/10.1016/j.jpor.2017.06.001DOI Listing
January 2018

Fracture behavior of single-structure fiber-reinforced composite restorations.

Acta Biomater Odontol Scand 2016 Dec 5;2(1):118-124. Epub 2016 Sep 5.

Turku Clinical Biomaterials Center (TCBC), Institute of Dentistry, University of TurkuTurkuFinland.

The applications of single-structure fiber-reinforced composite (FRC) in restorative dentistry have not been well reported. This study aimed to clarify the static mechanical properties of anterior crown restorations prepared using two types of single-structure FRC. An experimental crown restoration was designed for an upper anterior incisor. The restorations were made from IPS Empress CAD for CEREC (Emp), IPS e.max CAD (eMx), experimental single-structure all-FRC (a-FRC), Filtek™ Supreme XTE (XTE), and commercially available single-structure short-FRC (everX Posterior™) ( = 8 for each material) (s-FRC). The a-FRC restorations were prepared from an experimental FRC blank using a computer-aided design and manufacturing (CAD/CAM) device. A fracture test was performed to assess the fracture load, toughness, and failure mode. The fracture loads were vertically applied on the restorations. The surface micromorphology of the FRC restorations was observed by scanning electron microscopy (SEM). The data were analyzed by analysis of variance ( = .05) followed by Tukey's test. s-FRC showed the highest mean fracture load (1145.0 ± 89.6 N) and toughness (26.2 ± 5.8 Ncm) among all the groups tested. With regard to the micromorphology of the prosthetic surface, local crushing of the fiberglass was observed in s-FRC, whereas chopped fiberglass was observed in a-FRC. The restorations made of short-FRC showed a higher load-bearing capacity than those made of the experimental all-FRC blanks for CAD/CAM. The brittle-like fractures were exhibited in the recent dental esthetic materials, while local crushing fractures were shown for single-structure FRC restorations.
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http://dx.doi.org/10.1080/23337931.2016.1224670DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5433218PMC
December 2016

Light Transmission of Novel CAD/CAM Materials and Their Influence on the Degree of Conversion of a Dual-curing Resin Cement.

J Adhes Dent 2017;19(1):39-48

Purpose: To evaluate the light transmission characteristics of different types, shades, and thicknesses of novel CAD/CAM materials and their effect on the degree of conversion (DC) of a dual-curing resin cement.

Materials And Methods: Square specimens (12 × 12 mm2) of three CAD/CAM materials - GC Cerasmart, Lava Ultimate, Vita Enamic - of different thicknesses (1.00, 1.50, and 2.00 mm, n = 5 per thickness) were irradiated with an LED unit. The amount of transmitted light was quantified. Thereafter, the DC% of the dual-curing resin cement (RelyX Ultimate) was recorded after 15 min using Fourier transform infrared spectroscopy. Statistical analysis was performed using two-way ANOVA followed by the Tukey's HSD post-hoc test at a significance level of p < 0.05. Regression analysis was performed to investigate the correlation between the DC and radiant energy, and the DC and thickness.

Results: Although the type and shade of CAD/CAM material significantly affect transmitted light irradiation (p < 0.0001), degrees of conversion are similar when the CAD/CAM material or material shade were taken into consideration (p > 0.05). Conversely, material thickness significantly affected light transmission (p < 0.0001) and DC (p < 0.0001). Multiple effects of material, shade, and thickness did not significantly affect the evaluated parameters (p = 0.638 for light irradiation; p = 0.637 for DC). Linear regression analysis showed a correlation between delivered energy and DC% results of the Vita Enamic (R² = 0.4169, p < 0.0001).

Conclusion: Reduced light transmission in 2-mm-thick specimens of all CAD/CAM materials indicates that proper curing of the cement beneath CAD/CAM materials should be ensured.
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http://dx.doi.org/10.3290/j.jad.a37722DOI Listing
July 2017

Reinforcing Effect of Glass Fiber-incorporated ProRoot MTA and Biodentine as Intraorifice Barriers.

J Endod 2016 Nov 14;42(11):1673-1676. Epub 2016 Sep 14.

Department of Biomaterials Science and Turku Clinical Biomaterials Centre-TCBC, Institute of Dentistry, University of Turku, Turku, Finland.

Introduction: The purpose of this study was to investigate the fracture resistance of roots by using intraorifice barriers with glass fiber-incorporated ProRoot MTA and Biodentine.

Methods: The diametral tensile strength and compressive strength of ProRoot MTA and Biodentine were determined after incorporation of 5 wt% and 10 wt% alkali resistant (AR) glass fiber powder into both cements. On the basis of higher diametral tensile strength and compressive strength values, ProRoot MTA and Biodentine with 5 wt% AR glass fiber were selected for further testing as intraorifice barriers. The 14-mm-long root specimens obtained from extracted mandibular premolars (n = 60) were prepared with nickel-titanium rotary files and obturated with gutta-percha + AH Plus sealer. After removal of coronal 3 mm of root fillings, the roots were grouped with respect to the intraorifice barrier material (n = 12/group): (1) ProRoot MTA, (2) ProRoot MTA with 5 wt% AR glass fibers, (3) Biodentine, (4) Biodentine with 5 wt% AR glass fibers, and (5) control (no intraorifice barrier). The specimens were loaded vertically at 1 mm/min crosshead speed until vertical root fracture occurred. The data were evaluated statistically by using 2-way analysis of variance and Tukey tests.

Results: Both incorporation of glass fiber and the type of material significantly affected fracture resistance (both P = .002). Roots with glass fiber-reinforced Biodentine barriers showed the highest fracture strength (P = .000).

Conclusions: Incorporation of 5 wt% AR glass fiber can significantly improve the reinforcement effect of ProRoot MTA and Biodentine when used as intraorifice barriers.
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http://dx.doi.org/10.1016/j.joen.2016.08.002DOI Listing
November 2016

Mechanical and structural characterization of discontinuous fiber-reinforced dental resin composite.

J Dent 2016 09 20;52:70-8. Epub 2016 Jul 20.

Department of Biomaterials Science and Turku Clinical Biomaterials Centre-TCBC, Institute of Dentistry, University of Turku, Itäinen Pitkäkatu 4 B, 20520 Turku, Finland; City of Turku Welfare Division, Oral Health Care, Lemminkäisenkatu 2, 20520 Turku, Finland.

Objectives: This study evaluated several fiber- and matrix related factors and investigated different mechanical properties of discontinuous i.e. short fiber-reinforced composite (SFRC) (everX Posterior, eXP). These were compared with three conventional composites, microfilled G-ænial Anterior (GA), nanofilled Supreme XTE (SXTE) and bulk-fill Filtek Bulk-Fill (FBF).

Methods: Fracture toughness (KIC), flexural strength (FS), flexural modulus (FM), compressive strength (CS), diametral tensile strength (DTS), apparent horizontal shear strength (AHSS) and fracture work (Wf) were determined for each composite (n=8) stored dry or in water. SEM analysis of the fiber diameter (df) (n=6) and orientation (n=6) were performed. The theoretical critical fiber length (lfc) and the aspect ratio (l/d) of SFRC were calculated and the volume fraction of discontinuous fibers (Vf%) and the fiber length (lf) of SFRC were evaluated. The results were statistically analyzed with two-way ANOVA (α=0.05).

Results: The mechanical properties of SFRC (eXP) were generally superior (p<0.05) compared with conventional composites. GA had the highest FM (p>0.05), whereas FBF had the highest AHSS (p<0.05). The fiber related properties Vf%, l/d, lf, lfc and df of eXP were 7.2%, 18-112, 0.3-1.9mm, 0.85-1.09mm and 17μm respectively. SEM results suggested an explanation to several toughening mechanisms provided by the discontinuous fibers, which were shown to arrest crack propagation and enable a ductile fracture. Water exposure weakened the mechanical properties regardless of material type. Wf was unaffected by the water storage.

Conclusion: The properties of this high aspect ratio SFRC were dependent on the fiber geometry (length and orientation) and matrix ductility.

Clinical Significance: The simultaneous actions of the toughening mechanisms provided by the short fibers accounted for the enhanced toughness of this SFRC, which toughness value matched the toughness of dentin. Hence, it could yield an inherently uniform distribution of stresses to the hard biological tissues.
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http://dx.doi.org/10.1016/j.jdent.2016.07.009DOI Listing
September 2016

Surface roughness and the flexural and bend strength of zirconia after different surface treatments.

J Prosthet Dent 2016 Oct 5;116(4):577-583. Epub 2016 May 5.

Laboratory Manager, Turku Clinical Biomaterials Centre (TCBC), University of Turku, Turku, Finland; and Senior Lecturer, Turku University of Applied Sciences, Faculty of Health and Well-being, Turku, Finland.

Statement Of Problem: Different surface treatments are commonly used during the fabrication of zirconia fixed dental prostheses. However, such treatments can affect the properties of the zirconia framework material.

Purpose: The purpose of this in vitro study was to determine the effect of different surface treatments on the surface roughness and flexural and bend strength of zirconia.

Material And Methods: Seventy-two zirconia disks (n=8) and 72 zirconia bars (n=8) were sintered and divided into 9 groups for different surface treatments: sintered control, airborne-particle abraded with 50-μm aluminum oxide, airborne-particle abraded with Rocatec soft (30 μm), airborne-particle abraded with Rocatec (105 μm), grinding dry with a micromotor, turbine grinding under water cooling, grinding with silicon carbide paper, diamond paste polishing, and steam cleaning. The biaxial flexural strength of the disks (diameter 19 mm, thickness 1.6 mm) and 3-point bend test of the bars (thickness 2 mm, height 2 mm, length 25 mm) were measured dry at room temperature. One-way ANOVA followed by the Tukey HSD test (α=.05) and Pearson correlation test were used for statistical analysis.

Results: Airborne-particle abrasion and silicon carbide paper grinding increased the flexural and bend strength of zirconia specimens (P<.05). The 3-point bend test gave 20% to 30% higher strength values than the biaxial test, but a strong correlation was shown between the test types. Surface roughness had a statistically significant negative effect on the strength values in the 3-point bend test.

Conclusions: The surface treatments tested affected the strength and surface roughness of zirconia framework material.
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http://dx.doi.org/10.1016/j.prosdent.2016.02.018DOI Listing
October 2016

Wear resistance of injection-molded thermoplastic denture base resins.

Acta Biomater Odontol Scand 2016 Dec 26;2(1):31-37. Epub 2016 Jan 26.

Division of Removable Prosthodontics, Fukuoka Dental CollegeFukuokaJapan.

This study investigated the wear resistance of injection-molded thermoplastic denture base resins using nanoindentation instrument. Six injection-molded thermoplastic denture base resins (two polyamides, two polyesters, one polycarbonate, one polymethylmethacrylate [PMMA]) and a PMMA conventional heat-polymerized denture-based polymer control were tested. Elastic modulus, hardness, wear depth, and roughness were calculated using a nanoindentation instrument. Elastic modulus and hardness of the injection-molded thermoplastic denture base resins were significantly lower than those of the PMMA conventional heat-polymerized denture-based polymer. Wear depth of polycarbonate and PMMA conventional heat-polymerized denture-based polymer were significantly higher than that of other injection-molded thermoplastic denture base resins. The roughness of injection-molded thermoplastic denture base resins was significantly more than that of PMMA conventional heat-polymerized denture-based polymer after testing. Wear resistance of injection-molded thermoplastic denture base was low compared to PMMA conventional heat-polymerized denture-based polymers.
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http://dx.doi.org/10.3109/23337931.2015.1135747DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5433203PMC
December 2016

Physical and chemical properties of an antimicrobial Bis-GMA free dental resin with quaternary ammonium dimethacrylate monomer.

J Mech Behav Biomed Mater 2016 Mar 11;56:68-76. Epub 2015 Nov 11.

Department of Biomaterials Science and Turku Clinical Biomaterials Centre - TCBC, Institute of Dentistry, University of Turku, 20520 Turku, Finland; City of Turku Welfare Division, Oral Health Care, 20520 Turku, Finland.

The objective of this study was to evaluate the antibacterial activity, physicochemical properties of the quaternary ammonium dimethacrylate monomer N,N-bis[2-(3-(methacryloyloxy)propanamido)-ethyl]-N-methylhexadecyl ammonium bromide (IMQ-16) containing diurethane dimethacrylate (UDMA)/tricyclodecane dimethanol diacrylate (SR833s) resin system and compare with bisphenylglycidyl dimethacrylate (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA) resin system. It was hypothesized that the physical and chemical properties of the experimental polymers would be comparable with Bis-GMA/TEGDMA polymer and IMQ-16 monomer could endow the UDMA/SR833s resin with antibacterial activity. Double bond conversion (DC) was measured using Fourier transform infrared spectroscopy (FTIR). Mechanical properties including flexural strength (FS) and flexural modulus (FM) were measured by three-point bending test with bars of 2mm×2mm×25mm. Water sorption (WS) and solubility (WSL) were also investigated. Antibacterial activity of obtained polymers against Streptococcus mutans Ingbitt (S. mutans) was tested through direct contact test (DCT). The presence of antibacterial activity due to soluble components was also investigated by agar diffusion test (ADT). All of the polymers containing IMQ-16 exhibited improvements in WS and WSL, while maintaining equivalent DC and FS relative to the Bis-GMA/TEGDMA control system. Incorporation of 17% and 20% of IMQ-16 into UDMA/SR833s resin reduced the viable counts of S. mutans after incubation on the surface of the materials and produced no inhibition zones around the cured discs in ADT. UDMA/SR833s resin system is promising to formulate an antibacterial polymer with equivalent or even higher physicochemical properties relative to Bis-GMA/TEGDMA formulation. IMQ-16 is capable to endow UDMA/SR833s resin system with significant antibacterial activity when the mass ratio is 17% or 20%.
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http://dx.doi.org/10.1016/j.jmbbm.2015.10.028DOI Listing
March 2016

Mechanical properties, fracture resistance, and fatigue limits of short fiber reinforced dental composite resin.

J Prosthet Dent 2016 Jan 14;115(1):95-102. Epub 2015 Oct 14.

Laboratory Head, Turku Clinical Biomaterials Centre-TCBC, Institute of Dentistry, University of Turku, Turku, Finland.

Statement Of Problem: Cycling masticatory loads decrease the strength of particulate filler composites (PFCs) and initiate the failure process by fatigue. The life expectancy of a composite resin restoration under stress remains difficult to predict.

Purpose: The purpose of this study was to determine the fracture resistance and the compressive fatigue limits (CFL) of anterior crown restorations made of a short-fiber reinforced composite resin (SFC), to investigate selected mechanical properties of the material following standard test methods, and to observe their correlation with the CFL.

Material And Methods: Specimens (n=10) were fabricated either from SFC (everX Posterior, GC Corp) or PFC (G-ænial anterior, GC Corp). The properties investigated were flexural strength (FS), compression strength (CS), diametral-tensile strength (DTS), and single-edge-notched-bend fracture toughness (FT) following ISO standards. Fracture resistance was determined by static load (n=10) and the CFL at 10000 cycles was determined using a staircase approach (n=20), both on anterior composite resin crowns. The results were analyzed with 1-way ANOVA (α=.05) or 2-way ANOVA (α=.05) followed by a Tukey B post hoc test and the Pearson-correlation analysis.

Results: The SFC crowns had higher fracture resistance (954 ±121 N) than the PFC crowns (415 ±75 N) (P<.001) and higher CFL (267 ±23 N) than the PFC crowns (135 ±64 N) (P<.001). SFC revealed also higher FT (2.6 ±0.6 MPa·m(1/2)) than the PFC (1.0 ±0.2 MPa·m(1/2)) (F=69.313, P<.001). A significant correlation was observed only between the FT and the CFL (r(2)=0.899; P<.001).

Conclusions: SFC crowns showed good performance under static and fatigue loading. FT was the only in vitro test method that filtered as a clinically relevant parameter.
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http://dx.doi.org/10.1016/j.prosdent.2015.07.012DOI Listing
January 2016

Load-Bearing Capacity of Fiber-Reinforced Composite Abutments and One-Piece Implants.

Eur J Prosthodont Restor Dent 2015 Jun;23(2):62-9

Fiber-reinforced composites (FRC) can potentially help in a physiologic stress transmission due to its excellent biomechanical matching with living tissues. Novel one-piece FRC implants and abutments with two different fiber orientations were loaded until failure to assess the load-bearing capacity, fracture patterns, and precision of fit. The one-piece FRC implants showed significantly higher load-bearing capacity compared to FRC abutments regardless of the fiber orientation (p < 0.001). For FRC abutments, bidirectional abutments showed significantly higher loads compared to unidirectional abutments (p < 0.001). The type of structure and fiber orientation are strong determinant factors of the load-bearing capacity of FRC implants and abutments.
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June 2015

Three-dimensional finite element analysis of anterior two-unit cantilever resin-bonded fixed dental prostheses.

ScientificWorldJournal 2015 24;2015:864389. Epub 2015 Mar 24.

Department of Restorative Dentistry and Endodontology, Dental School, Ghent University Hospital, Ghent University, De Pintelaan 185/P8, 9000 Gent, Belgium.

The aim of this study was to evaluate the influence of different framework materials on biomechanical behaviour of anterior two-unit cantilever resin-bonded fixed dental prostheses (RBFDPs). A three-dimensional finite element model of a two-unit cantilever RBFDP replacing a maxillary lateral incisor was created. Five framework materials were evaluated: direct fibre-reinforced composite (FRC-Z250), indirect fibre-reinforced composite (FRC-ES), gold alloy (M), glass ceramic (GC), and zirconia (ZI). Finite element analysis was performed and stress distribution was evaluated. A similar stress pattern, with stress concentrations in the connector area, was observed in RBFDPs for all materials. Maximal principal stress showed a decreasing order: ZI>M>GC>FRC-ES>FRC-Z250. The maximum displacement of RBFDPs was higher for FRC-Z250 and FRC-ES than for M, GC, and ZI. FE analysis depicted differences in location of the maximum stress at the luting cement interface between materials. For FRC-Z250 and FRC-ES, the maximum stress was located in the upper part of the proximal area of the retainer, whereas, for M, GC, and ZI, the maximum stress was located at the cervical outline of the retainer. The present study revealed differences in biomechanical behaviour between all RBFDPs. The general observation was that a RBFDP made of FRC provided a more favourable stress distribution.
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http://dx.doi.org/10.1155/2015/864389DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4387912PMC
July 2016

The effect of short fiber composite base on microleakage and load-bearing capacity of posterior restorations.

Acta Biomater Odontol Scand 2015 Jan 14;1(1):6-12. Epub 2015 Apr 14.

Department of Biomaterials Science, Turku Clinical Biomaterials Centre, TCBC, Institute of Dentistry, University of TurkuTurkuFinland.

: To determine the marginal microleakage of Class II restorations made with different composite base materials and the static load-bearing capacity of direct composite onlay restorations. : Class II cavities were prepared in 40 extracted molars. They were divided into five groups ( = 8/group) depending on composite base material used (everX Posterior, SDR, Tetric EvoFlow). After Class II restorations were completed, specimens were sectioned mid-sagitally. For each group, sectioned restorations were immersed in dye. Specimens were viewed under a stereo-microscope and the percentage of cavity leakage was calculated. Ten groups of onlay restorations were fabricated ( = 8/group); groups were made with composite base materials (everX Posterior, SDR, Tetric EvoFlow, Gradia Direct LoFlo) and covered by 1 mm layer of conventional (Tetric N-Ceram) or bulk fill (Tetric EvoCeram Bulk Fill) composites. Groups made only from conventional, bulk fill and short fiber composites were used as control. Specimens were statically loaded until fracture. Data were analyzed using ANOVA ( = 0.05). : Microleakage of restorations made of plain conventional composite or short fiber composite base material showed statistically ( < 0.05) lower values compared to other groups. ANOVA revealed that onlay restorations made from short fiber-reinforced composite (FRC) as base or plain restoration had statistically significant higher load-bearing capacity (1593 N) ( < 0.05) than other restorations. : Restorations combining base of short FRC and surface layer of conventional composite displayed promising performance related to microleakage and load-bearing capacity.
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http://dx.doi.org/10.3109/23337931.2015.1017576DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5433219PMC
January 2015

Preparation of antibacterial and radio-opaque dental resin with new polymerizable quaternary ammonium monomer.

Dent Mater 2015 May 2;31(5):575-82. Epub 2015 Mar 2.

Department of Biomaterials Science, Institute of Dentistry and Biocity Turku Biomaterial Research Program, University of Turku, Lemminkäisenkatu 2, Turku 20520, Finland; Turku Clinical Biomaterials Centre-TCBC, University of Turku, Itäinen Pitkäkatu 4 B, Turku FI-20520, Finland; Institute of Dentistry, University of Turku, Turku 20520, Finland; City of Turku Welfare Division, Oral Health Care, Turku 20101, Finland.

Objective: A new polymerizable quaternary ammonium monomer (IPhene) with iodine anion was synthesized and incorporated into Bis-GMA/TEGDMA (50/50, wt/wt) to prepare antibacterial and radio-opaque dental resin.

Methods: IPhene was synthesized through a 2-steps reaction route, and its structure was confirmed by FT-IR and (1)H-NMR spectra. IPhene was incorporated into Bis-GMA/TEGDMA (50/50, wt/wt) with a series of mass fraction (from 10 wt.% to 40 wt.%). Degree of monomer conversion (DC) was determined by FT-IR analysis. Polymerization shrinkage was determined according to the variation of density before and after polymerization. The flexural strength, modulus of elasticity, and fracture energy were measured using a three-point bending set up. Radiograph was taken to evaluate the radio-opacity of the polymer. A single-species biofilm model with Streptococcus mutans (S. mutans) as the tests organism was used to evaluate the antibacterial activity of the polymer. Bis-GMA/TEGDMA resin system without IPhene was used as a control group.

Results: FT-IR and (1)H-NMR spectra of IPhene revealed that IPhene was the same as the designed structure. ANOVA analysis showed that when mass fraction of IPhene was more than 10 wt.%, the obtained resin formulation had lower DC, polymerization shrinkage, FS, and FM than control resin (p<0.05). Polymers with 20 wt.% and 30 wt.% IPhene had higher fracture energies than control polymer (p<0.05). IPhene containing samples had higher radio-opacity than control group (p<0.05), and radio-opacity of IPhene containing sample increased with the increasing of IPhene mass fraction (p<0.05). Only polymers with 30 wt.% and 40 wt.% of IPhene showed antibacterial activity (p<0.05).

Significance: IPhene could endow dental resin with both antibacterial and radio-opaque activity when IPhene reached 30 wt.% or more. Though sample with 30 wt.% of IPhene had lower FS and FM than control group, its lower volumetric shrinkage, higher fracture energy, higher radio-opacity, and antibacterial activity still made it having potential to be used in dentistry.
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http://dx.doi.org/10.1016/j.dental.2015.02.007DOI Listing
May 2015

Oxygen inhibition layer of composite resins: effects of layer thickness and surface layer treatment on the interlayer bond strength.

Eur J Oral Sci 2015 Feb 31;123(1):53-60. Epub 2014 Dec 31.

Department of Biomaterials Science and Turku Clinical Biomaterials Centre-TCBC, Institute of Dentistry, University of Turku, Turku, Finland.

An oxygen inhibition layer develops on surfaces exposed to air during polymerization of particulate filling composite. This study assessed the thickness of the oxygen inhibition layer of short-fiber-reinforced composite in comparison with conventional particulate filling composites. The effect of an oxygen inhibition layer on the shear bond strength of incrementally placed particulate filling composite layers was also evaluated. Four different restorative composites were selected: everX Posterior (a short-fiber-reinforced composite), Z250, SupremeXT, and Silorane. All composites were evaluated regarding the thickness of the oxygen inhibition layer and for shear bond strength. An equal amount of each composite was polymerized in air between two glass plates and the thickness of the oxygen inhibition layer was measured using a stereomicroscope. Cylindrical-shaped specimens were prepared for measurement of shear bond strength by placing incrementally two layers of the same composite material. Before applying the second composite layer, the first increment's bonding site was treated as follows: grinding with 1,000-grit silicon-carbide (SiC) abrasive paper, or treatment with ethanol or with water-spray. The inhibition depth was lowest (11.6 μm) for water-sprayed Silorane and greatest (22.9 μm) for the water-sprayed short-fiber-reinforced composite. The shear bond strength ranged from 5.8 MPa (ground Silorane) to 36.4 MPa (water-sprayed SupremeXT). The presence of an oxygen inhibition layer enhanced the interlayer shear bond strength of all investigated materials, but its absence resulted in cohesive and mixed failures only with the short-fiber-reinforced composite. Thus, more durable adhesion with short-fiber-reinforced composite is expected.
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http://dx.doi.org/10.1111/eos.12167DOI Listing
February 2015