Publications by authors named "Pekka K Vallittu"

327 Publications

The Effect of Material Type and Location of an Orthodontic Retainer in Resisting Axial or Buccal Forces.

Materials (Basel) 2021 Apr 29;14(9). Epub 2021 Apr 29.

BioCity Turku Biomaterials and Medical Device Research Program, Department of Biomaterials Science, Institute of Dentistry, University of Turku, 20520 Turku, Finland.

The purpose of this study was to investigate the effect of retainer material and retainer position on a tooth to resist movement of the tooth in a simulation model. Bidirectional continuous glass fiber-reinforced composite (FRC) retainers and control retainers of steel wires were tested. The FRC retainers had a polymer matrix of bisphenol-A-glycidyldimethacrylate (bis-GMA) and poly(methylmethacrylate) (PMMA), and it was cured with a photoinitiator system. The retainers were adhered to a lower jaw Frasaco model in two different positions. Resistance against the movement of one tooth was measured from two directions. The average load values within the FRC retainer groups were higher than within the metal retainer groups. The load values for the groups loaded from the axial direction were higher than those loaded from the buccal direction. FRC retainers, which were located 1-2 mm from the incisal edge, showed higher load values than those located 4-5 mm from the incisal edge. There was a significant difference in load values between FRC retainers and metal retainers ( < 0.01). The wire position and the direction of force also had significant effects ( < 0.01). There were no significant differences between metal retainer groups. The results of this study suggest that metal retainers are more flexible, allowing for tooth movements of larger magnitude than with FRC retainers.
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http://dx.doi.org/10.3390/ma14092319DOI Listing
April 2021

Influence of Post-Core and Crown Type on the Fracture Resistance of Incisors Submitted to Quasistatic Loading.

Polymers (Basel) 2021 Apr 2;13(7). Epub 2021 Apr 2.

Turku Clinical Biomaterial Center-TCBC, Department of Biomaterials Science, Institute of Dentistry, University of Turku, 20500 Turku, Finland.

The aim of this paper was to evaluate the fracture resistance and failure type of maxillary incisor teeth, rebuilt with various types of post-core restorations and full crowns made of either direct conventional particulate filler composite (PFC, G-aenial Anterior, GC, Tokyo, Japan) or indirect CAD/CAM restorations (composite Cerasmart 270 and glass ceramic LiSi Block from GC). One hundred ( = 10/group) central incisors were cut and divided into 10 experimental groups restored with different approaches. In approach A, teeth were restored with a core build-up composite (Gradia Core, GC) for a core and full crown of PFC. Approach B had teeth restored using composite core and prefabricated fiber posts, and a complete crown of either PFC or CAD/CAM. Approach C contained teeth restored with a core of short fiber-reinforced composite (everX Flow, GC) and prefabricated fiber posts, and a complete crown of either PFC or CAD/CAM. In approach D, the teeth had a core of short fiber-reinforced composite only, and a complete crown of either PFC or CAD/CAM restorations. The root canals were prepared, and when posts were used, they were luted with either a dual-cure resin cement (LinkForce, GC) or everX Flow. As the control, sound teeth ( = 10) were used. Restorations were quasi-statically loaded until fracture. Failure type was visually investigated. The interface between the fiber post and luting cement was investigated using SEM, before and after completion of the loading test. The data were analyzed by analysis of variance ( = 0.05) followed by Tukey's test. None of the restorative approaches restored the fracture load strength of intact teeth ( < 0.05). Restorations with additional fiber posts (Approaches B and C) had higher load-bearing capacity ( < 0.05) than restorations without fiber posts (Approaches A and D). Restorations that had short fiber-reinforced composite cores with or without fiber posts presented more repairable failures. Using short fiber-reinforced composite as post-luting and core build-up material with conventional fiber posts proved to be a promising method to strengthen severely damaged incisors.
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http://dx.doi.org/10.3390/polym13071130DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8037330PMC
April 2021

The effect of refractive index of fillers and polymer matrix on translucency and color matching of dental resin composite.

Biomater Investig Dent 2021 Apr 1;8(1):48-53. Epub 2021 Apr 1.

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

Objective: When restorative resin composites absorb light from the surrounding tooth structures, it creates a color-match, which is known as 'a chameleon effect'. In this study, series of co-monomer mixtures were prepared with an increasing refraction index (RI) and mixed with glass fillers. The aim of this study was to optimize the mismatch of RI of resin/fillers to create the chameleon effect.

Materials And Methods: BisGMA/TEGDMA resins were prepared with seven different mix fractions from 20 to 80%. Two different series (A&B) of submicron (Ø 0.7 μm) silanized fillers (70 wt%) (A: Schott RI = 1.53, B: Esschem RI = 1.54) were mixed with resins (30 wt%). Disc-shaped specimens (1 mm thickness, Ø10 mm) for each composite combination ( = 3) were prepared and light cured for 20 s. Commercial resin composite (OmniChroma, Tokuyama Dental) was used as control. The translucency parameter (TP) was measured using a spectrophotometer. The color matching abilities of the experimental composites were visually analyzed. Data were statistically analyzed using ANOVA.

Results: The composition of resin and type of fillers had a statistically significant effect on TP values ( < .05). The highest TP values were achieved around 50%-50% fractions of Bis-GMA and TEGDMA for series A and around 60%-40% fraction of Bis-GMA and TEGDMA for series B. Data showed that a high or low fraction of BisGMA resulted in a low translucent composite. Experimental resin composite (80% Bis-GMA) from series A was behaving similarly to Omnichroma in reference to TP values and color matching.

Conclusions: Including fillers with RI of 1.53 into BisGMA/TEGDMA resin with RI of 1.524 resulted in composite resin providing a good color match with surrounding structure 'chameleon effect'.
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http://dx.doi.org/10.1080/26415275.2021.1906879DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8018547PMC
April 2021

Impact of Fast High-Intensity versus Conventional Light-Curing Protocol on Selected Properties of Dental Composites.

Materials (Basel) 2021 Mar 12;14(6). Epub 2021 Mar 12.

Department of Biomaterials Science, Turku Clinical Biomaterial Center-TCBC, Institute of Dentistry, University of Turku, 20500 Turku, Finland.

To study the influence of fast high-intensity (3-s) and conventional (20-s) light curing protocols on certain physical properties including light-transmission and surface wear of two nano-hybrid composite resins (Tetric PowerFill and Essentia U) specifically designed for both curing protocols. According to ISO standards, the following properties were investigated: flexural properties, fracture toughness and water sorption/solubility. FTIR-spectrometry was used to calculate the double bond conversion (DC%). A wear test using a chewing simulator was performed with 15,000 chewing cycles. A tensilometer was used to measure the shrinkage stress. Light transmission through various thicknesses (1, 2, 3 and 4 mm) of composite resins was quantified. The Vickers indenter was utilized for evaluating surface microhardness (VH) at the top and the bottom sides. Scanning electron microscopy was utilized to investigate the microstructure of each composite resin. The light curing protocol did not show a significant ( > 0.05) effect on the mechanical properties of tested composite resins and differences were material-dependent. Shrinkage stress, DC% and VH of both composite resins significantly increased with the conventional 20 s light curing protocol ( < 0.05). Light curing conventional composite resin with the fast high-intensity (3-s) curing protocol resulted in inferior results for some important material properties.
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http://dx.doi.org/10.3390/ma14061381DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8000385PMC
March 2021

Universal Adhesive for Fixed Retainer Bonding: In Vitro Evaluation and Randomized Clinical Trial.

Materials (Basel) 2021 Mar 10;14(6). Epub 2021 Mar 10.

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

This study aims to assess the efficacy of a universal adhesive (Scotchbond Universal, 3M ESPE) (SB) in total-etch mode, compared to a traditional orthodontic primer (Transbond XT Primer, 3M ESPE) (XT Primer), to perform bonding of orthodontic fixed retainers along with the Transbond XT Light Cure Adhesive Paste (3M ESPE). For the in vitro study, a round section wire (Ortosmail Krugg) was bonded using XT Primer for 20 bovine incisors (Group 1) and SB for other 20 (Group 2). Samples were debonded in a universal testing machine applying a tangential force to specimens (crosshead speed of 1 millimeter per minute). Shear bond strength (SBS) and adhesive remnant index (ARI) scores were calculated. For the in vivo study, 100 patients needing upper and lower canine-to-canine fixed retainers after orthodontic treatment were randomly assigned to two groups of 50 participants each, i.e., group 1 (retainer bonding with XT Primer) and group 2 (retainer bonding with SB). Over two years, examinations were carried out monthly, and detachments were registered by considering the teeth and arches affected. In vitro, no statistically significant differences in SBS and ARI scores were demonstrated between the two groups, both showing a mean bond strength of about 12 MPa and major frequency of ARI "2" (>50% remnant adhesive on the enamel). Conversely, a significantly lower failure rate over 2 years was assessed clinically for group 2 in both arches. Independently of the adhesive and arch, incisors reported a significantly higher failure rate than canines. Scotchbond Universal used in total-etch mode could be a valid alternative to the traditional orthodontic Transbond XT Primer.
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http://dx.doi.org/10.3390/ma14061341DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7999612PMC
March 2021

Fatigue failure of anterior teeth without ferrule restored with individualized fiber-reinforced post-core foundations.

J Mech Behav Biomed Mater 2021 Jun 3;118:104440. Epub 2021 Mar 3.

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

Objectives: The aim was to explore the survival of extensively damaged anterior teeth without ferrule restored with different fiber-reinforced composite (FRC) post-core foundations and composite crowns.

Materials And Methods: Sixty extracted upper central incisors were decoronated and randomly divided into four groups (n = 15). After endodontic treatment, the specimens were restored with different individualized fiber-reinforced post-core foundations as follows: control group (CTRL): multiple unidirectional FRC-post + dual-cure composite-core, PFC: multiple unidirectional FRC-post + packable short fiber-reinforced composite (SFRC), BPFC: Bioblock technique with only packable SFRC, BFFC: Bioblock technique with only flowable SFRC. After core build-up, the teeth were finalized with adhesively luted CAD/CAM composite crowns. Cyclic isometric loading (5 Hz) was applied at 100 N for 5000 cycles, and then 200 N and 300 N for 15,000 cycles each in a fluid chamber. The specimens were loaded until fracture occurred or when a total of 35,000 cycles were reached. Kaplan-Meyer survival analysis was conducted, followed by pairwise log-rank post hoc comparisons (Mantel-Cox).

Results: The survival rates of the control (8279 cycles) and PFC (6161 cycles) were significantly higher compared to BPFC (3223 cycles) and BFFC (2271 cycles) (p < 0.05). Regarding fracture pattern, nearly all specimens fractured in a restorable manner.

Conclusions: For restoring extensively damaged anterior teeth, multiple unidirectional FRC posts are recommended.

Clinical Relevance: Although different FRC post/core systems are available for the restoration of damaged root canal treated anterior teeth, multiple unidirectional FRC posts tend to be a good option when the ferrule is missing.
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http://dx.doi.org/10.1016/j.jmbbm.2021.104440DOI Listing
June 2021

Fracture-behavior of CAD/CAM ceramic crowns before and after cyclic fatigue aging.

Int J Prosthodont 2021 Feb 23. Epub 2021 Feb 23.

Purpose: To evaluate the fracture behavior of monolithic crowns made of lithium disilicate (IPS e.max CAD, Ivoclar Vivadent; and Initial LiSi Block, GC) and zirconia-reinforced lithium silicate (Celtra Duo, Dentsply Sirona; and Suprinity, VITA) materials before and after cyclic fatigue aging.

Materials And Methods: Four groups (n = 22 per group) of CAD/CAM-fabricated maxillary incisor crowns were produced. All crowns were luted on metal dies with an adhesive dual-curing resin cement (G-CEM LinkForce [GC]). Half of the crowns in each group (n = 11) were statically loaded to fracture without aging. The remaining half were subjected to cyclic fatigue aging for 120,000 cycles (F = 220 N) and then loaded statically to fracture. Fracture mode was then visually examined. Scanning electron microscopy and energy-dispersive spectroscopy were used to evaluate the microstructure of the CAD/CAM ceramic materials. The data were statistically analyzed with two-way analysis of variance followed by Tukey honest significant difference (HSD) test (α = .05).

Results: Before cyclic aging, there was no statistically significant difference in load-bearing capacity among the four groups (P = .371). After cyclic aging, the load-bearing capacity significantly decreased for all groups (P = .000). While the e.max CAD blocks had significantly higher load-bearing capacity (1,061 ± 94 N) than both monolithic ceramic crowns (P < .05), no significant difference was obtained compared to the Initial LiSi Block group (920 ± 140 N) (Tukey HSD P = .061).

Conclusion: The mechanical performance of monolithic ceramic crowns fabricated from lithium disilicate was better than zirconia-reinforced lithium silicate after cyclic fatigue aging.
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http://dx.doi.org/10.11607/ijp.7207DOI Listing
February 2021

Flexural strength and flexural modulus of fiber-reinforced, soft-liner retained implant overdenture.

Int J Prosthodont 2021 Feb 12. Epub 2021 Feb 12.

Purpose: To compare the flexural strength and flexural modulus of soft liner-retained overdentures to ball-and-socket-retained overdentures, as well as to evaluate the effect of using glass fiber as a reinforcement material for soft liner-retained overdentures on such mechanical properties.

Materials And Methods: A total of 80 overdenture specimens were fabricated and divided equally into four groups (n = 20 each): specimens with a metal matrix (group 1); a silicone soft liner matrix (group 2); reinforced with one bundle of unidirectional glass fiber sticks placed above the silicone soft liner matrix (group 3); and reinforced with four layers of bidirectional Stick Net glass fiber weaves placed above the silicone soft liner matrix (group 4). Half of the specimens from each group were stored in water at room temperature (23°C ± 1°C) for 24 hours, while the other half were stored in water at 37°C for 30 days before being subjected to a static 3-point loading test.

Results: After 1 day of water storage, the flexural strength and flexural modulus values of groups 1, 3, and 4 were not significantly different from each other (P = .788, P = .084), but were significantly higher than group 2 (P < .05). Water storage for 30 days significantly decreased the flexural strength and modulus values of group 1 only (P < .001) and not the other three groups (P >.05).

Conclusion: After 30 days of water storage, the flexural strength and flexural modulus values of overdentures retained with a metal housing were not significantly different from those of overdentures retained with a silicone soft liner housing. Placing uni- and bidirectional glass fiber reinforcement above soft liner matrices increases the fracture resistance of a soft liner-retained overdenture.
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http://dx.doi.org/10.11607/ijp.6677DOI Listing
February 2021

The Viability and Growth of HaCaT Cells After Exposure to Bioactive Glass S53P4-Containing Cell Culture Media.

Otol Neurotol 2021 Feb 12. Epub 2021 Feb 12.

Department of Otorhinolaryngology-Head and Neck Surgery Department of Medical Biochemistry and Genetics, Institute of Biomedicine BioCity, Turku Biomaterials Research Program, Turku Clinical Biomaterials Centre - TCBC Department of Biomaterials Science and Turku Clinical Biomaterials Centre - TCBC, Institute of Dentistry, University of Turku City of Turku Welfare Division, Oral Health Care Department of Pathology Department of Dermatology, Turku University Hospital and University of Turku FICAN West Cancer Research Laboratory, University of Turku and Turku University Hospital, Turku, Finland.

Hypothesis: Bioactive glass (BG) S53P4 reduces the viability of epidermal keratinocyte-derived immortalized cell line, HaCaT in sufficient concentrations in vitro.

Background: Although used in mastoid obliteration surgery, there is no data available on whether BG S53P4 granules have an inhibitory or excitatory effect on keratinocytes, found in normal skin and ear cholesteatoma in vivo.

Methods: HaCaT cell cultures were incubated with a direct BG S53P4 granule contact. Microscopic evaluation of the cultures was performed and interleukin-6 (IL-6) and -8 (IL-8) concentrations were measured from the medium samples. In addition, BG granules were incubated in two cell culture media for 6 days and the pure media were used in confluent HaCaT cultures preceding cell viability assay. Finally, a scratch assay test was performed to reveal the possible BG effect on HaCaT cultures.

Results: Eight to ten cell thick layers of dead HaCaT cells were noticed after a 2-day BG granule contact. With a BG concentration of 2.5%, IL-6 and IL-8 concentrations were smaller compared with the control group without BG after 2 days' incubation. Overall, HaCaT cell viability decreased when BG was incubated in keratinocyte growth medium, but did not change in Dulbecco's modified Eagle's medium. In a scratch assay test, cell regrowth in the scratch area was notable in cultures without BG.

Conclusions: BG S53P4 seems to have an inhibitory effect on HaCaT cell growth. Although further studies are needed, this observation seems advantageous for cholesteatoma treatment.
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http://dx.doi.org/10.1097/MAO.0000000000003057DOI Listing
February 2021

Correction to: Fracture resistance and marginal gap formation of post-core restorations: influence of different fiber-reinforced composites.

Clin Oral Investig 2021 May;25(5):3339-3340

Department of Biomaterials Science and Turku Clinical Biomaterials Center - TCBC Institute of Dentistry, University of Turku, Itäinen Pitkäkatu 4 B, FI-20520, Turku, Finland.

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http://dx.doi.org/10.1007/s00784-021-03798-8DOI Listing
May 2021

Behaviour of different bioactive glasses incorporated in polydimethylsiloxane endodontic sealer.

Dent Mater 2021 02 10;37(2):321-327. Epub 2021 Jan 10.

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

Objectives: The aim of this study was to analyze the behavior of different bioactive glass fillers (BAGs) embedded in a polydimethylsiloxane matrix of an endodontic sealer.

Methods: Three different endodontic sealers were fabricated using S53P4, 45S5 and 18-06 glass fillers. Endodontic sealer Guttaflow Bioseal consisting of polydimethylsiloxane (PDMS) matrix was used as base of the experimental sealers. Behaviors of different glass fillers leaching from polymer matrix was studied in vitro for 14 days by measuring static ion dissolution profiles of Si, Na, Ca and P -ions. In addition, pH of the simulated bodyfluid (SBF) was monitored during the 14 days and all the sealer samples was examined with SEM/EDX analysis on the surface. Identical but non-glass filler containing polydimethylsiloxane-based sealer was used as a control material.

Results: By the time point of 24 h sealer with 45S5 had released twice as much of Si-ions compared to sealer with S53P4. No statistical differences of Na, Ca and P -ions dissolution were observed in the first 168 h for any groups whereas concentrations of Ca and P -ions decreased with 45S5 significantly after 336 h. Highest pH was measured for sealers with glass filler 45S5 and S53P4 (7.64-7.65). Visible mineral precipitation was observed only on sealer surfaces after 336 h' time period with groups of 45S5 and S53P4. However, presence of calcium and phosphorus oxides was confirmed only with 45S5.

Significance: Bioactive glass type 45S5 outperforms S53P4 and 18-06 by acting more dynamically in vitro set-up.
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http://dx.doi.org/10.1016/j.dental.2020.11.013DOI Listing
February 2021

Fatigue behavior of endodontically treated premolars restored with different fiber-reinforced designs.

Dent Mater 2021 03 19;37(3):391-402. Epub 2021 Jan 19.

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

Objectives: The aim was to investigate the fatigue survival and marginal-gap inside the root-canal of endodontically treated (ET) premolars reinforced by various fiber-reinforced post-core composites (FRCs). Moreover, composite-curing at different depths in the canal was evaluated.

Methods: 170 intact upper-premolars were collected and randomly divided into ten groups (n = 15). One group served as control (intact-teeth). After endodontic procedure standard MO cavities were prepared and restored with different post-core fiber-reinforced materials and designs. Three-group (A1-A3) were restored with either packable and flowable short fiber-reinforced composite (SFRC) core or conventional composite-core. Two-group (B1-B2) were restored with SFRCs as short post (3 mm) and core. Four-group (C1-C4) were restored with SFRCs as post (6 mm) and core with or without unidirectional FRC posts (individually-made or conventional). After completing the restorations, teeth from Group C1-C4 (n = 5/group) were sectioned and stained. Specimens were viewed under a stereo-microscope and the percentage of microgaps within the root-canal was calculated. Fatigue-survival was measured using a cyclic-loading machine in the rest of the specimens.

Results: Application of flowable SFRC as luting-core material with individually-made FRC post (Group C3) did not differ from intact-teeth regarding fatigue-survival (p > 0.05). The rest of the groups produced significantly lower survival (p < 0.05) compared to intact-teeth. Post/core restorations made from packable SFRC (Group C1) had a lower microgap (19.1%) at the examined interphase in the root-canal than other groups.

Significance: The restoration of ET premolars with the use of individually-made FRC post and SFRC as luting-core material showed promising achievement regarding fatigue-resistance and survival.
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http://dx.doi.org/10.1016/j.dental.2020.11.026DOI Listing
March 2021

Evaluation of the mechanical properties and degree of conversion of 3D printed splint material.

J Mech Behav Biomed Mater 2021 03 13;115:104254. Epub 2020 Dec 13.

Department of Biomaterials Science and Turku Clinical Biomaterials Centre-TCBC, Institute of Dentistry, University of Turku, Itäinen Pitkäkatu 4B (2nd Floor), FI-20520, Turku, Finland.

Objective: To evaluate the effect of post-curing method, printing layer thickness, and water storage on the mechanical properties and degree of conversion of a light-curing methacrylate based resin material (IMPRIMO® LC Splint), used for the fabrication of 3D printed occlusal splints and surgical guides.

Methods: 96 bar-shaped specimens were 3D printed (Asiga MAX), half of them with a layer thickness of 100 μm (Group A), and half with 50 μm (Group B). Each group was divided in three subgroups based on the post-curing method used: post-curing with light emitting diode (LED) and nitrogen gas; post-curing with only LED; and non-post-curing. Half of the specimens from each subgroup were water-stored for 30 days while the other half was dry-stored (n = 8). Flexural strength and flexural modulus were evaluated. Additional specimens were prepared and divided in the same way for surface hardness (n = 96), fracture toughness, and work of fracture (n = 96). Five specimens were selected from each subgroup for evaluating the degree of conversion (DC). Data were collected and statistically analyzed with 1-way, 2-way ANOVA, and Tukey post-hoc analysis (α = 0.05).

Results: The 2-way ANOVA showed that the post-curing method and water storage significantly affected the investigated mechanical properties (P < 0.001). The 1-way ANOVA revealed a statistically significant difference among the tested groups on the investigated properties (P < 0.001). After water storage, the 100 μm subgroup post-cured with only LED showed higher flexural strength (51 ± 9) than the 50 μm and 100 μm subgroups that were post-cured with LED in addition to nitrogen gas atmosphere (38 ± 5, 30 ± 3) (p < 0.05). The 50 μm subgroup post-cured with only LED showed the highest significant flexural modulus values (1.7 ± 0.08) (p < 0.05). However, the 50 μm subgroup post-cured with LED plus nitrogen showed significantly higher surface hardness values (p < 0.05) among the investigated groups. The non-post-cured subgroups showed the lowest values, which were significantly different from the other subgroups (p < 0.05).

Conclusion: The post-curing method, water storage, and printing layer thickness play a role in the mechanical properties of the investigated 3D Printed occlusal splints material. The combination of heat and light within the post-curing unit can enhance the mechanical properties and degree of conversion of 3D printed occlusal splints. Flexural strength and surface hardness can increase when decreasing printing layer thickness.
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http://dx.doi.org/10.1016/j.jmbbm.2020.104254DOI Listing
March 2021

Corrigendum to "Biomechanical aspects of reinforced implant overdentures: A systematic review" [J. Mech. Behav. Biomed. Mater. 91 (2019) 202-211].

J Mech Behav Biomed Mater 2021 Feb 16;114:104199. Epub 2020 Nov 16.

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

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http://dx.doi.org/10.1016/j.jmbbm.2020.104199DOI Listing
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

Bilayered composite restoration: the effect of layer thickness on fracture behavior.

Biomater Investig Dent 2020 2;7(1):80-85. Epub 2020 Jun 2.

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

By combining the increased toughness of a resin composite reinforced with discontinuous fibers and the surface wear resistance of a particulate filler composite (PFC), a bilayered composite technique was recently introduced. This study aimed to evaluate the effect of the thickness of the overlaying PFC placed over a fiber-reinforced composite (FRC) core, on the fracture-behavior of direct crown restorations. Six groups of posterior crown restorations ( = 8/group) were fabricated having a discontinuous FRC-core (everX Flow) and a layer of surface PFC (Essentia U) with various thicknesses (0.5, 1.0, 1.5, 2.0 mm), with the remaining thickness of the bilayered being 6 mm. Control groups were only made of PFC or FRC materials. Restorations were statically loaded until fracture. Failure-modes were visually examined. Data were analyzed using ANOVA ( = .05) and regression analysis. The regression analysis showed that by decreasing the thickness of PFC layer, the load bearing capacity of restorations increased linearly (R=0.7909). ANOVA revealed that crown restorations made only from everX Flow composite had significantly higher load-bearing capacities (3990 ± 331 N) ( < .05) among all the groups tested. With regard to the failure-mode analysis, crowns that had a FRC core material of everX Flow revealed delamination of the PFC surface composite from the core. Crowns which were made only of PFC i.e. with no fiber reinforcement, showed a crushing-like fracture pattern. Restorations combining a thick FRC-core and a thin surface layer of PFC (0.5-1 mm), displayed promising performance related to fracture-behavior and load-bearing capacity.
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http://dx.doi.org/10.1080/26415275.2020.1770094DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7521310PMC
June 2020

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

Effect of Short-Term Aging on the Flexural Strength of a Novel Experimental CAD/CAM Fiber-Reinforced Composite Material: A Pilot Study.

Int J Prosthodont 2020 Sep/Oct;33(5):523-526

Purpose: To investigate the three-point flexural strength of a novel CAD/CAM fiber-reinforced composite (FRC) material following different aging conditions.

Materials And Methods: The specimens were randomly assigned to one of five groups based on aging condition: (1) control (no treatment); (2) short-term water storage; (3) thermal degradation with autoclaving; (4) chemical degradation with hydrochloric acid; and (5) chemical degradation with citric acid (n = 10 per group). The specimens in the control group received no treatment. Following each treatment protocol, the three-point bending test was used to calculate the flexural strength. Data were statistically analyzed (α = .05), and scanning electron microscopy (SEM) analysis of the specimens was conducted.

Results: No significant differences in flexural strength were observed among the groups (P = .199). In addition, no distinct morphologic differences were detected in the SEM images of the specimens.

Conclusion: The flexural strength of this novel CAD/CAM FRC material was unaffected by different aging methods.
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http://dx.doi.org/10.11607/ijp.6428DOI Listing
September 2020

Characterization of restorative short-fiber reinforced dental composites.

Dent Mater J 2020 Dec 7;39(6):992-999. Epub 2020 Aug 7.

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

The aim was to evaluate and compare certain physical properties including surface-wear of five commercial short fiber-reinforced composites (SFRCs; Alert, NovaPro-Flow, NovaPro-Fill, everX Flow and everX Posterior). The following properties were examined according to ISO: flexural strength, flexural modulus, fracture toughness, water sorption. Degree of conversion was determined by FTIR-spectrometry. A wear test was conducted with 15,000 chewing-cycles using a chewing-simulator. Polymerization shrinkage-stress was measured using tensilometer. SEM was used to evaluate the microstructure of SFRCs. everX Flow exhibited the highest fracture toughness (2.8 MPa m) and the lowest wear depth (20.4 µm) values (p<0.05) among the SFRCs tested. NovaPro Fill (141.5 MPa) and everX Flow (147 MPa) presented the highest flexural strength values (p<0.05). everX Flow showed the highest shrinkage-stress value (5.3 MPa) while other SFRCs had comparable values. The use of SFRCs in dentistry can be advantageous, but special attention should be given to the selection of the materials.
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http://dx.doi.org/10.4012/dmj.2019-088DOI Listing
December 2020

Physicochemical properties of dimethacrylate resin composites with comonomer of Hexa/Tri-ethylene glycol bis(carbamate-isoproply-α-methylstyrene).

J Mech Behav Biomed Mater 2020 08 1;108:103832. Epub 2020 May 1.

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

New photocurable "Phene" like monomers Hexaethylene glycol bis(carbamate-isoproply-α-methylstyrene) (HE-Phene) and Triethylene glycol bis(carbamate-isoproply-α-methylstyrene) (TE-Phene) were synthesized and incorporated into Bis-GMA/TEGDMA with the aim of reducing polymerization shrinkage without detriment to the physical and handling properties of the resin composites. Phene like monomers (HE/TE-Phene) were synthesized through a one-step reaction route, and their structures were confirmed by FT-IR and H-NMR spectra. HE/TE-Phene were incorporated into Bis-GMA/TEGDMA (50/50,wt/wt) with a series of mass fraction (from 0 wt.% to 40 wt.%). Experimental resin composites were prepared by mixing 29 wt.% of resin matrix to 71 wt.% of particulate-fillers. Degree of conversion (DC) was determined by FT-IR analysis. The volumetric shrinkage (VS) was calculated as a buoyancy change in distilled water by means of the Archimedes principle. Polymerization shrinkage-stress (SS) was measured using the tensilometer technique. The flexural strength (FS), modulus (FM), and fracture toughness (FT) were measured using a three-point bending setup. Viscosity was analyzed with a rotating disk rheometer. Water sorption and solubility were also measured. ANOVA analysis showed that DC (after 40 s), VS, and SS were in a trend of decreasing with the increasing of HE/TE-Phene concentration. In general, the experimental resin composites had comparable FT, FS and FM (p > 0.05) when the mass fraction of HE/TE-Phene in resin matrix was not more than 30 wt.%. The overall tested properties prove that including HE/TE-Phene up to 30 wt.% into Bis-GMA/TEGDMA resin could be potentially useful in the formulation of low-shrinkage resin composites.
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http://dx.doi.org/10.1016/j.jmbbm.2020.103832DOI Listing
August 2020

Biomaterial and implant induced ossification: in vitro and in vivo findings.

J Tissue Eng Regen Med 2020 08 8;14(8):1157-1168. Epub 2020 Jul 8.

International Clinical Research Center of St. Anne's University Hospital Brno, Brno, Czech Republic.

Material-induced ossification is suggested as a suitable approach to heal large bone defects. Fiber-reinforced composite-bioactive glasses (FRC-BGs) display properties that could enhance the ossification of calvarial defects. Here, we analyzed the healing processes of a FRC-BG implant in vivo from the perspective of material-induced ossification. Histological analysis of the implant, which was removed 5 months after insertion, showed the formation of viable, noninflammatory mesenchymal tissue with newly-formed mineralized woven bone, as well as nonmineralized connective tissue with capillaries and larger blood vessels. The presence of osteocytes was detected within the newly generated bone matrix. To expand our understanding on the osteogenic properties of FRC-BG, we cultured human adipose tissue-derived mesenchymal stromal cells (AD-MSCs) in the presence of two different BGs (45S5 and S53P4) and Al O control. AD-MSCs grew and proliferated on all the scaffolds tested, as well as secreted abundant extracellular matrix, when osteogenic differentiation was appropriately stimulated. 45S5 and S53P4 induced enhanced expression of COL2A1, COL10A1, COL5A1 collagen subunits, and pro-osteogenic genes BMP2 and BMP4. The concomitant downregulation of BMP3 was also detected. Our findings show that FRC-BG can support the vascularization of the implant and the formation of abundant connective tissue in vivo. Specifically, BG 45S5 and BG S53P4 are suited to evoke the osteogenic potential of host mesenchymal stromal cells. In conclusion, FRC-BG implant demonstrated material-induced ossification both in vitro and in vivo.
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http://dx.doi.org/10.1002/term.3056DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7496445PMC
August 2020

Surface dissolution and transesterification of thermoset dimethacrylate polymer by dimethacrylate adhesive resin and organic catalyst-alcohol solution.

Dent Mater 2020 05 6;36(5):698-709. Epub 2020 Apr 6.

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

Objectives: To evaluate transesterification based dissolution of dimethacrylate and epoxy polymers, the former containing ester groups. Polymer substrates were treated with an adhesive resin (Stick™ Resin) and an organic catalyst-alcohol solution (ethylene glycol and triazabicyclodecene). The surface was chemically and nanomechanically analyzed with Fourier Transform-Infrared (FTIR) spectroscopy, surface profile peak (R) and nanohardness and modulus of elasticity.

Methods: A total of 100 specimens each of light-cured dimethacrylate polymer and heat-cured diepoxy polymer were prepared. 20 specimens were randomly selected and used as control group (0s). The remaining specimens were randomly divided into 40 each for treatment with an Stick™ resin and ethylene glycol+triazabicyclodecene. Within each group the 40 specimens were randomly subdivided into 20 each for treatment at 5min and 24h, with 10 specimens for FTIR and nanohardness and modulus of elasticity, and the other 10 for SEM and surface R analyses.

Results: Dimethacrylate polymer showed a reduction in the nanohardness and modulus of elasticity, R values and SEM also showed significant topographical changes after being treated with either Stick™ resin or ethylene glycol+triazabicyclodecene, whereas epoxy resin substrate did not. FTIR analyses affirmed changes in the intensity of ester groups.

Significance: Ester group containing dimethacrylate polymer showed a reduction in NMP within 5min of exposure to the treatment agents with softening by solution ethylene glycol+triazabicyclodecene associated to the reduction of ester groups in the polymer structure by transesterification. Epoxy polymer without ester groups was not affected by surface softening with treatment agents. Adhesive resin caused surface swelling.
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http://dx.doi.org/10.1016/j.dental.2020.03.005DOI Listing
May 2020

Effects of Different Polishing Protocols and Curing Time on Surface Properties of a Bulk-fill Composite Resin.

Chin J Dent Res 2020 ;23(1):63-69

Objective: To determine the effects of different polishing protocols and curing times on the surface roughness (SR), surface gloss (SG) and surface hardness (SH) of a bulk-fill composite resin (BCR).

Methods: A total of 30 block-shaped specimens (40 mm long × 10 mm wide × 2 mm thick) were made from Filtek Bulk-Fill composite resin and divided into two groups (n = 15) according to curing time (10 and 40 seconds). Each group was subdivided into five groups (n = 3) according to the polishing protocol: laboratory polishing with different silicon paper grits (G1:1200) → (G2:2400) → (G3:4000). Chairside polishing was performed using a series of Sof-Lex spiral (G4) and Jiffy Polisher (G5) points. The SR was measured by a surface profilometer. A Vickers indenter was used to test the SH, and a glossmeter was used to determine the SG at 60 degrees. The SR, SG and SH were quantified before and after polishing. A scanning electron microscopy (SEM) evaluation was then performed.

Results: The curing time did not affect the surface properties of the BCR (P > 0.05). Significant differences in SR (ranging from 0.1 to 2 μm) and SG (ranging from 20 to 90 GU [gloss unit]) were found according to the type of polishing protocol (P < 0.05). The SH values following different polishing protocols were significantly higher (ranging from 82 to 95 VH [Vickers hardness]) than the polishing values obtained before the polishing protocols (P < 0.05).

Conclusion: The tested chairside polishing protocols presented lower SG and higher SR values than the laboratory polishing protocols.
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http://dx.doi.org/10.3290/j.cjdr.a44337DOI Listing
April 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

Fatigue resistance of metal-free cantilever bridges supported by labial laminate veneers.

J Mech Behav Biomed Mater 2020 03 13;103:103596. Epub 2019 Dec 13.

Adhesive Dentistry Research Group, Department of Restorative Dentistry and Cardiology, Institute of Dentistry, University of Turku, Turku, Finland; Turku University Hospital, TYKS, Turku, Finland.

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http://dx.doi.org/10.1016/j.jmbbm.2019.103596DOI Listing
March 2020

Assessment of CAD-CAM polymers for digitally fabricated complete dentures.

J Prosthet Dent 2021 Jan 14;125(1):175-181. Epub 2020 Feb 14.

Professor, Department of Biomaterials Science and Director of Turku Clinical Biomaterials Centre - TCBC, Institute of Dentistry, University of Turku and City of Turku Welfare Division, Oral Health Care, Turku, Finland; Visiting Professor, Dental Health Department, College of Applied Medical Sciences, King Saud University, Riyadh, Saudi Arabia.

Statement Of Problem: Information on the mechanical properties of the materials used for manufacturing computer-engineered complete dentures is scarce.

Purpose: The purpose of this in vitro study was to evaluate the mechanical properties of 3 prepolymerized polymethyl methacrylate (PMMA) resins used in the fabrication of computer-aided design and computer-aided manufacturing (CAD-CAM) milled complete dentures (CDs), as well as 2 denture base polymers used for conventionally fabricated CDs.

Material And Methods: Three CAD-CAM materials were evaluated: Degos Dental L-Temp, IvoBase CAD, and Zirkonzahn Temp Basic Tissue. Two materials used for conventionally manufactured dentures were also included as controls (Palapress and Paladon 65). Each material type was sectioned into bars for flexural strength, nanohardness, elastic modulus, and surface microhardness evaluation (n=8/material). Half of the specimens were stored in water for 30 days, while the other half was dry-stored. A 2-way ANOVA was conducted to detect the effect of material and storage on the evaluated properties (α=.05). Linear contrasts were conducted to compare the differences among the 3 types of CAD-CAM material and the conventional ones.

Results: Material type and storage had a significant influence on the flexural strength, nanohardness, elastic modulus, and surface hardness of the materials investigated (P<.001). The post hoc Scheffé test for flexural strength revealed a nonsignificant difference in the interaction between Degos L-Temp and Paladon (P=1.000). In terms of nanohardness, no difference was found when comparing Palapress with Paladon, as well as IvoBase CAD with Zirkonzahn Temp Basic (P=1.000). A nonsignificant interaction in terms of surface hardness was also found between IvoBase CAD and Palapress (P=.575).

Conclusions: The tested materials showed variation in their mechanical properties, with satisfactory behavior of the CAD-CAM materials. However, the results obtained when testing the materials used for the conventional fabrication of complete dentures suggest that their use might still be advisable.
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http://dx.doi.org/10.1016/j.prosdent.2019.12.008DOI Listing
January 2021

The effect of polishing protocol on surface gloss of different restorative resin composites.

Biomater Investig Dent 2020 3;7(1):1-8. Epub 2020 Jan 3.

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

The purpose of this study was to determine the effects of different polishing protocols on the surface gloss (SG) of different commercial dental resin composites (RCs). A total of 147 block-shaped specimens (40 mm length × 10 mm width × 2 mm thick) were made from conventional RCs (G-aenial Ant. and Flo X), bulk-fill RC (Filtek Bulk Fill), fluoride-releasing RCs (BEAUTIFIL II, ACTIVA-Restorative) and discontinuous microfiber-reinforced RCs (Alert and everX Flow). Each group was subdivided into seven subgroups ( = 3), according to polishing protocol: Laboratory-machine polishing with different siliconcarbide paper grits (G1: 320) → (G2: 800) → (G3: 1200) → (G4: 2000) → (G5: 4000). Chairside-hand polishing using a series of Sof-Lex spiral (G6) and abrasive polishing points (G7). Glossmeter was used to determine the SG at 60° incidence angle. SG was measured before and after polishing. Three-dimensional (3 D) noncontact optical profilometer and scanning electron microscopy (SEM) analysis were performed. Data were analyzed using ANOVA ( = .05). Significant differences in SG (ranged 3-93 GU) were found according to the type of polishing protocol and RC ( < .05). Specimens polished with 4000 grit paper showed the highest SG (93 GU) values among all the groups tested. The tested chairside-hand polishing protocols presented lower SG values than laboratory-machine polishing (4000 silicon paper grit) and unpolished surfaces.
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http://dx.doi.org/10.1080/26415275.2019.1708201DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6968704PMC
January 2020

Priming and bonding metal, ceramic and polycarbonate brackets.

Biomater Investig Dent 2019 6;6(1):61-72. Epub 2019 Nov 6.

Institute of Dentistry, University of Turku, Turku, Finland.

To investigate if primers can be used to modify bonding characteristics of orthodontic brackets. Stainless steel, zirconia-alumina ceramic and polycarbonate brackets were bonded to enamel with and without universal and bracket material specific primers on the bracket base. Orthodontic adhesive cement (Transbond™XT) was used for bonding. The primers in each group ( = 10) were silane based (RelyX™ Ceramic Primer) and universal primer (Monobond Plus) for ceramic and metal brackets, and adhesive resin (Adper™ Scotchbond™ Multi-Purpose Adhesive) and composite primer (GC Composite Primer) for polycarbonate brackets. Controls with no primer were used for all bracket types. Teeth with bonded brackets were stored in distilled water in 37 °C for 7 days and debonded with static shear loading. Debonding forces were recorded and analyzed with ANOVA. Adhesive remnant index (ARI) was determined and enamel damage examined. The bond strength without primers was 8.14 MPa (±1.49) for metal, 21.9 MPa (±3.55) for ceramic and 10.47 MPa (±2.11) for polycarbonate brackets ( < .05). Using silane as primer increased the bond strength of ceramic brackets significantly to 26.45 MPa (±5.00) ( < .05). ARI-scores were mostly 2-3 (>50% of the adhesive left on the enamel after debonding), except with silane and ceramic brackets, ARI-score was mostly 0-1 (>50% of the adhesive left on the bracket). Debonding caused fractured enamel in four specimens with ceramic brackets. Bond strength was highest for ceramic brackets. Silane primer increased bond strength when used with ceramic brackets leading to enamel fractures, but otherwise primers had only minor effect on the bond strength values.
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http://dx.doi.org/10.1080/26415275.2019.1684823DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6964778PMC
November 2019

Incorporation of cellulose fiber in glass ionomer cement.

Eur J Oral Sci 2020 02 28;128(1):81-88. Epub 2020 Jan 28.

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

This study investigated the effect of discontinuous cellulose microfibers with various loading fractions on selected physical properties of glass polyalkenoate (glass ionomer) cement (GIC). Fiber-reinforced GIC (Exp-GIC) was prepared by adding discontinuous cellulose microfiber (with an average length of 500 μm) at various mass ratios (1, 2, 3, 4, and 5 mass%) to the powder of conventional GIC (GC Fuji IX) using a high-speed mixing device. Fracture toughness, work of fracture, and compressive strength were determined for each experimental and control material. The specimens (n = 6) were wet stored (37°C for 1 d) before testing. A scanning electron microscope equipped with an energy dispersive spectroscope was used to examine the surface of fibers after treatment with cement liquid. Data were analyzed using ANOVA. The Exp-GIC (5 mass%) specimen had statistically significantly higher fracture toughness (0.9 MPa.m ) than unreinforced material (0.4 MPa.m ). On the other hand, Exp-GIC with 1 mass% displayed the highest compressive strength (116 MPa) among all tested groups. The use of discontinuous cellulose microfibers with conventional GIC matrix considerably increased the toughening performance compared with the particulate GICs used.
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http://dx.doi.org/10.1111/eos.12668DOI Listing
February 2020

Dual-curing resin cement with colour indicator for adhesively cemented restorations to dental tissues: Change of colour by curing and some physical properties.

Saudi J Biol Sci 2020 Jan 28;27(1):395-400. Epub 2019 Oct 28.

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

The study was aimed to investigate a color indicator containing dual curing resin composite luting cement and to plot the color change to the time of solidification of the cement. In addition some physical properties were studied. Specimens were made of a dual-cure resin cement (Maxcem Elite™ Chroma, Kerr, Orange, CA, USA) and polymerized by autopolymerization only, or with light initiated polymerization. A spectrophotometer was used to quantify the color change of the cement as plotted with the curing time. The efficacy of the curing process was studied by measuring water sorption and the ultimate flexural properties of the cement. The results showed that the flexural strength of cement after autopolymerization was 27.3 MPa and after light initiated polymerization 48.1 MPa. Young's modulus of bending was 2089.3 MPa and 3781.5 MPa respectively for the same cement samples. Water sorption after two weeks for the autopolymerization cement samples was -1.12 wt% and for the light initiated polymerization samples 0.56 wt%. Non-parametric Spearman's correlation was measured for autopolymerized cement samples between variables for color and solidification load (N), which showed a strong correlation between curing process and color change (p < 0.05). There was a correlation between the color change and degree of monomer conversion of the dual curing resin composite luting cement which contained a color indicator system for polymerization reaction. The study also suggested that autopolymerization only resulted in suboptimal polymerization of the cement. By additional light curing considerably higher flexural properties were obtained.
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http://dx.doi.org/10.1016/j.sjbs.2019.10.009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6933191PMC
January 2020