Retention of luting agents used for implant-supported restorations: A comparative In-Vitro study.

AIMS: The aim of this study was to compare the retention of different luting agents used with implant-supported restorations. MATERIALS AND METHODS: A total of 90 custom metal frameworks and copings were prepared and divided into six different luting agent groups (n = 15/group): polycarboxylate cement (PC), resin-modified glass-ionomer cement (RMGIC), two self-adhesive resin cements (SARC), copper-ion zinc-phosphate cement (CZPC), and non-eugenol temporary resin cement (TRC). After sandblasting with 50 µm Al2O3, the copings were cemented on frameworks and stored in artificial saliva for 48 h at 37°C and thermocycled between 5-55°C for 37,500 cycles. Samples were subjected to tensile testing by a universal testing machine, and data were statistically analyzed. RESULTS: The differences between the retention values of types of cement were significant (P < 0.05). The maximum retention value was calculated for CZPC (755,12 ± 55 MPa) while the lowest value was for TRC (311,7 ± 61 Mpa). CONCLUSION: Neither of the tested cement had superiority over another to ensuring retention. The types of cement presented were meant to be a discretionary guide for the clinician in deciding the amount of the desired retention between castings and abutments.

The combined effects of salivas and occlusal indicators on occlusal contact forces.

BACKGROUND: Some occlusal detection products are designed for use on dry teeth, but this is not always achieved. Others are suited for dry and wet applications. OBJECTIVE: The objective of this study is to assess the combined effects, on occlusal contact forces, of two previously studied affecting variables-occlusal detection products and saliva. METHODS: We used a full-arch dentiform with three occlusal detection products (an articulating film, an articulation paper and T-Scan) in combination with human (HS) and an artificial saliva. The maxillary arch assembly, weighing ~54 N (the maximum bite force), was lowered onto (occlusion) and lifted off (disclusion) of the mandibular arch through 10 cycles by a mechanical testing machine. The forces and moments acting on the mandibular arch were continuously recorded by a load cell that supported it. RESULTS: The maximum values of Flateral (the in-occlusal plane component of the occlusal contact force) were analysed by occlusion/disclusion separately using one-way ANOVA, with factor for group type to identify the significant effect of salivas on products, effect of products, effect of salivas with products, effect of human saliva. A difference in occlusion and/or in disclusion was considered different. Statistical differences (P < 0.0001) in Flateral were found in: dry product vs product + HS, dry product vs product + artificial saliva (with articulating film and T-Scan) and HS vs product + HS (with articulation paper and T-Scan). CONCLUSION: All products were affected by the salivas, except articulation paper by artificial saliva.

Effects of time and clear aligner removal frequency on the force delivered by different polyethylene terephthalate glycol-modified materials determined with thin-film pressure sensors.

INTRODUCTION: Many factors influence the force changes of clear aligners. The purpose of this study was to identify the various factors that influence the force changes generated by polyethylene terephthalate glycol-modified (PET-G) materials. Therefore, a force measurement system based on a flexible thin-film pressure sensor was established. METHODS: A series of clear aligners with 2 material properties and different activations at the maxillary central incisor, maxillary second premolar, and maxillary permanent first molar was designed and fabricated. The first material was conventional PET-G; the second material was modified PET-G with a higher modulus of elasticity and greater abrasion resistance. Several models, including teeth and aligners, were produced. Then, a force change detection device, including a thin-film pressure sensor, a signal acquisition circuit board, and a computer, was applied to measure changes in the forces delivered by the conventional and modified PET-G materials with increased frequencies of appliance removal. Finally, the forces were repeatedly measured to detect the force changes over 48 hours. RESULTS: The forces of both materials decreased similarly over time. These forces also decreased when the aligner removal frequency increased, but the forces decreased differently. The modified PET-G, with a higher modulus of elasticity and greater abrasion resistance, showed a more stable and lower force change than did the conventional PET-G. CONCLUSIONS: The forces delivered by both materials were within the orthodontic force range. Force changes were apparent when the appliance removal frequency increased. Compared with the conventional material, the modified PET-G material showed better stability. Therefore, the modified PET-G is a promising and applicable material with advantages for both orthodontists and patients.

Effect of Distal Implant Inclination on Dislodging Forces of Different Locator Attachments Used for Mandibular Overdentures: An In Vitro Study.

PURPOSE: To evaluate the effect of distal implant inclination on axial and nonaxial retentive forces of different Locator attachments used to retain mandibular overdentures. MATERIALS AND METHODS: Four duplicate mandibular edentulous acrylic models received 2 implants in the canine areas with 0°, 5°, 10°, and 20° distal inclinations. Experimental overdentures were connected to the implants with Locator extra light retention (Le), Locator light retention (Ll), and Locator medium retention (Lm). For the 20° model, extended range Locator extra-light retention (Lee) and Locator medium retention (Lem) were used. Axial and nonaxial (anterior, posterior, lateral) retentive forces were measured initially and after 540 cycles of denture insertion and removal. Three-way mixed ANOVA was used to analyze axial and nonaxial retentive forces RESULTS: After wear simulation, 20° angulation showed the highest axial retention for Le and Ll while 5° showed the highest retention for Lm; 0° and 5° showed the highest anterior and posterior retention for Lm; 20° showed the highest lateral retention for Le and Ll. For all implant inclinations, Lm showed the highest axial and nonaxial retention, and Le and Lee showed the lowest retention for 10° and 20° inclined implants, respectively. CONCLUSIONS: Axial and nonaxial retention of Locator attachments for implant-retained overdentures are significantly affected by the degree of distal implant inclination and the type of nylon inserts. Lm is recommended to retain overdentures when implants have 5° or 10° distal inclination, and Le and Ll are recommended with 20° inclination to maintain high axial and nonaxial retention after wear.

Effect of adhesive resin cements on bond strength of ceramic core materials to dentin.

OBJECTIVES: The aim of the present study was to evaluate the effects of self-etch and self-adhesive resin cements on the shear bond strength of ceramic core materials bonded to dentin. MATERIALS AND METHODS: Extracted, caries-free, human central maxillary incisor teeth were selected, and the vestibule surfaces were cut flat to obtain dentin surfaces. Ceramic core materials (IPS e.max Press and Prettau Zirconia) were luted to the dentin surfaces using three self-etch adhesive systems (Duo-Link, Panavia F 2.0, and RelyX Ultimate Clicker) and two self-adhesive resin systems (RelyX U200 Automix and Maxcem Elite). A shear bond strength test was performed using a universal testing machine. Failure modes were observed under a stereomicroscope, and bonding interfaces between the adhesive resin cements and the teeth were evaluated with a scanning electron microscope. Data were analyzed with Student's t-test and one-way analysis of variance followed by Tukey's test (α = 0.05). RESULTS: The type of adhesive resin cement significantly affected the shear bond strengths of ceramic core materials bonded to dentin (P < 0.05). Significant differences were noted between the ceramic core materials when the specimens were luted with self-adhesive resin cements (P < 0.05). The specimens luted with RelyX Ultimate Clicker had the highest shear bond strengths. CONCLUSION: The self-etch adhesive resin cements exhibited better shear bond strength than the self-adhesive resin cements, except for Panavia cement in the IPS e.max Press group. However, shear bond strengths of the self-adhesive resin cements were dependent on the nature of the ceramic core materials.

Fracture resistance force of primary molar crowns milled from polymeric computer-aided design/computer-assisted manufactured resin blocks.

Purpose: To compare fracture resistance force (FRF) and failure types of crowns milled from resin nanoceramic (Lava Ultimate)-, and modified polymethylmethacrylate (PMMA) (Vita computer-aided design (CAD)-Temp)-, and PMMA (Telio CAD)-based CAD/computer-assisted manufactured (CAM) blocks. Materials and Methods: Three experimental groups of 10 milled crowns were arranged: Group-1 (Lava Ultimate), Group-2 (Vita CAD-Temp), and Group-3 (Telio CAD). Crowns were machined in sizes similar to a primary second molar stainless steel crown (SSC) and stored in water at 37°C for 30 days. The crowns were seated on Cr-Co dies. Their FRFs were measured using a universal test machine until fracture. FRFs and failure types were recorded and statistically analyzed (P < 0.05). Results: There were statistically significant differences among the groups for both FRFs and failure types. The sources of significant differences for FRFs and failure types were Group-3 and Group-1, respectively. CONCLUSION: Crowns milled from different chemical structural CAD/CAM blocks may be used for restoration of primary molar teeth.

Effect of application time of maleic acid on smear layer removal and mechanical properties of root canal dentin.

OBJECTIVES: To evaluate the effect of maleic acid (MA) on the cleaning efficacy and mechanical properties of root canal dentine with respect to different time exposure. MATERIALS AND METHODS: One hundred and eighty single-canal premolars were instrumented with rotary-files and then randomly assigned to test groups receiving 7% MA for 30 s, 45 s, 1 min, or 3 min or to control groups treated with 0.9% saline or 17% ethylenediaminetetraacetic acid for 45 s. The micro-hardness, nano-hardness and elastic modules were measured before and after treatment, while the amount of smear and erosion in the coronal, middle and apical thirds in root canal were evaluated by scanning electron microscopy, finally, the fracture strength was assessed by vertical root fracture testing. RESULTS: The efficacy of smear layer removal increased with increasing MA application time. The largest effect was observed at 45 s, even in the apical third, whereas the treatment for 1 min resulted in irreversible erosion of the dentine surface. The micro-hardness and nano-indentation testing confirmed that the micro- and nano-scale mechanical properties were significantly decreased after MA application for 1 min. Furthermore, the specimens treated with MA for 3 min presented the lowest fracture resistance among all groups. In contrast, the 45 s treatment appeared to increase the fracture resistance of the tooth. CONCLUSIONS: The cleaning efficacy and mechanical properties of root canal dentine varied with MA exposure time. The application of MA for 45 s was found to be the most promising for clinical use.

Does the presence of an occlusal indicator product affect the contact forces between full dentitions?

Studies have explored occlusal marking interpretation, repeatability and accuracy. But, when an occlusion detection product is interposed between teeth, direct tooth-tooth occlusal contact relationships are replaced by tooth-material-tooth structures. Thus, the marks cannot reflect the original contacts. This has been shown for single tooth pair contacts. The purpose of this laboratory study was to similarly examine full dentitions. A dentiform was set into Class I centric occlusion with the mandible supported by a load cell. The maxillary arch was guided by precision slides. As the weighted (~52 N) upper assembly was lowered onto and raised off the mandibular arch, the loads on the mandible were measured. With and without (control) occlusal marking material, the steps were as follows: (cleaning - control 1 - material 1) … (cleaning - control 6 - material 6). The six materials were as follows: Accufilm I and II, Rudischhauser Thick and Thin, Hanel Articulating Silk and T-Scan. Then, the six sets of (cleaning - control - material) measurements were repeated with the mandibular assembly shifted, in turn, by 0·1 mm in the Anterior, Posterior, Right and Left directions. The five (Centric and four 0·1 mm shifted) occlusal relationships produced grossly different tooth-tooth (control) load profiles. And, in general, these controls were affected, in different ways, by the marking products. Among the five conventional products, the Rudischhausers fared the worst and the electronic T-Scan was an extreme outlier. Thus, in general, popular occlusal detection products alter the occlusal contact forces, and therefore, their markings cannot characterise the actual occlusion.

Marginal fit and photoelastic stress analysis of CAD-CAM and overcast 3-unit implant-supported frameworks.

STATEMENT OF PROBLEM: Several studies have shown the superiority of computer-assisted design and computer-assisted manufacturing (CAD-CAM) technology compared with conventional casting. However, an advanced technology exists for casting procedures (the overcasting technique), which may serve as an acceptable and affordable alternative to CAD-CAM technology for fabricating 3-unit implant-supported fixed dental prostheses (FDPs). PURPOSE: The purpose of this in vitro study was to evaluate, using quantitative photoelastic analysis, the effect of the prosthetic framework fabrication method (CAD-CAM and overcasting) on the marginal fit and stress transmitted to implants. The correlation between marginal fit and stress was also investigated. MATERIAL AND METHODS: Three-unit implant-supported FDP frameworks were made using the CAD-CAM (n=10) and overcasting (n=10) methods. The frameworks were waxed to simulate a mandibular first premolar (PM region) to first molar (M region) FDP using overcast mini-abutment cylinders. The wax patterns were overcast (overcast experimental group) or scanned to obtain the frameworks (CAD-CAM control group). All frameworks were fabricated from cobalt-chromium (CoCr) alloy. The marginal fit was analyzed according to the single-screw test protocol, obtaining an average value for each region (M and PM) and each framework. The frameworks were tightened for the photoelastic model with standardized 10-Ncm torque. Stress was measured by quantitative photoelastic analysis. The results were submitted to the Student t test, 2-way ANOVA, and Pearson correlation test (α=.05). RESULTS: The framework fabrication method (FM) and evaluation site (ES; M and PM regions) did not affect the marginal fit values (P=.559 for FM and P=.065 for ES) and stress (P=.685 for FM and P=.468 for ES) in the implant-supported system. Positive correlations between marginal fit and stress were observed (CAD-CAM: r=0.922; P<.001; overcast: r=0.908; P<.001). CONCLUSIONS: CAD-CAM and overcasting methods present similar marginal fit and stress values for 3-unit FDP frameworks. The decreased marginal fit of frameworks induces greater stress in the implant-supported system.

Evaluation of Bond Strength, Marginal Integrity, and Fracture Strength of Bulk- vs Incrementally-filled Restorations.

PURPOSE: This study evaluated the effect of application technique and preparation size on the fracture strength (FS), microtensile bond strength (µTBS) and marginal integrity (MI) of direct resin composite restorations. MATERIALS AND METHODS: Conservative (5 × 2 × 2 mm) or extended (5 × 4 × 2 mm) preparations below the cementoenamel junction were performed in 140 human maxillary premolars (n = 70 per group). After adhesive application (XP Bond), half of each group was restored with the bulk technique (one 4-mm increment of Surefill SDR Flow plus one 1-mm horizontal capping layer of TPH3 [Spectrum TPH3 resin composite]) and half incrementally (TPH3 in three horizontal incremental layers, 1.5 to 2 mm each), all using a metal matrix band. After storage (24 h at 37°C), the proximal surfaces of each tooth were polished with Sof-Lex disks. For FS measurement, 60 restorations were mounted in a universal testing machine and subjected to a compressive axial load applied parallel to the long axis of the tooth, running at a crosshead speed of 0.5 mm/min. For µTBS testing, 40 teeth were longitudinally sectioned to obtain resin-dentin bonded sticks from the cavity floor (bonded area: 0.8 mm2). Specimens were tested in tension at 0.5 mm/min. The external marginal integrity of both proximal surfaces was analyzed using SEM of epoxy resin replicas. The µTBS, marginal integrity, and fracture resistance data were subjected to two-way ANOVA, and Tukey's post-hoc test was used for pair-wise comparisons (a = 0.05). RESULTS: Fracture resistance, microtensile bond strength, and marginal integrity values were not statistically significantly affected by application technique or preparation size (p = 0.71, p = 0.82, and p = 0.77, respectively). CONCLUSIONS: The use of a bulk-fill flowable composite associated with a conventional resin composite as a final capping layer did not jeopardize the fracture strength, bond strength to dentin, or marginal integrity of posterior restorations.

Resistance of Hydraulic Calcium Silicate Cements to Dislodgment in Short- and Long-term Assessment.

PURPOSE: To investigate the resistance to dislodgment produced by Biodentine (Septodont) and White-MTA (Angelus) after immersion in phosphate-buffered saline (PBS) for different durations. MATERIALS AND METHODS: Dentin disks 1 ± 0.1 mm thick were obtained from the middle third of the roots of 6 human maxillary canines. On the coronal surface of each dentin disk, four 0.8-mm-diameter holes were drilled. Then the slices were halved using a low-speed saw diamond disk, and the two holes in each half were filled with one of the two tested materials. Each filled half was immersed in PBS solution (pH 7.2) either for 7 days (short term) or 60 days (long term) at 37°C. The push-out test was performed after both time periods. A general linear model (GLM) for repeated measures ANOVA was used to verify the effect of the material and duration of contact with PBS on the push-out strength. The material was considered as the within-subject contrast and the contact duration as the between-subjects effect (p < 0.05). RESULTS: Repeated measures GLM indicated a significant impact of material and time on the push-out strength of the samples (p = 0.000 and p = 0.033, respectively). Biodentine significantly improved the push-out strength compared to MTA at both times (p = 0.000). The lack of significance in the interaction between material and time indicates that PBS immersion positively influenced the push-out values of both tested materials. CONCLUSION: Long-term PBS immersion positively influenced the resistance to dislodgement from dentin of all cements tested. The Biodentine cement provided greater resistance to push-out force than did the MTA.

Accelerated Fatigue Resistance of Thick CAD/CAM Composite Resin Overlays Bonded with Light- and Dual-polymerizing Luting Resins.

PURPOSE: To evaluate the accelerated fatigue resistance of thick CAD/CAM composite resin overlays luted with three different bonding methods. MATERIALS AND METHODS: Forty-five sound human second mandibular molars were organized and distributed into three experimental groups. All teeth were restored with a 5-mm-thick CAD/CAM composite resin overlay. Group A: immediate dentin sealing (IDS) with Optibond FL and luted with light-polymerizing composite (Herculite XRV). Group B: IDS with Optibond FL and luted with dual-polymerizing composite (Nexus 3). Group C: direct luting with Optibond FL and dual-polymerizing composite (Nexus 3). Masticatory forces at a frequency of 5 Hz were simulated using closed-loop servo-hydraulics and forces starting with a load of 200 N for 5000 cycles, followed by steps of 400, 600, 800, 1000, 1200 and 1400 N for a maximum of 30,000 cycles. Each step was applied through a flat steel cylinder at a 45-degree angle under submerged conditions. RESULTS: The fatigue test generated one failure in group A, three failures in group B, and no failures in group C. The survival table analysis for the fatigue test did not demonstrate any significant difference between the groups (p = 0.154). The specimens that survived the fatigue test were set up for the load-to-failure test with a limit of 4600 N. The survival table analysis for the load-to-failure test demonstrates an average failure load of 3495.20 N with survival of four specimens in group A, an average failure load of 4103.60 N with survival of six specimens in group B, and an average failure load of 4075.33 N with survival of nine specimens in group C. Pairwise comparisons revealed no significant differences (p < 0.016 after Bonferroni correction). CONCLUSION: Within the limitations of this in vitro study, it can be concluded that although the dual-polymerizing luting material seems to provide better results under extreme conditions, light-polymerizing luting composites in combination with IDS are not contraindicated with thick restorations.

Effects of Different Radiation Doses on the Bond Strengths of Two Different Adhesive Systems to Enamel and Dentin.

PURPOSE: To evaluate the effects of three different radiation doses on the bond strengths of two different adhesive systems to enamel and dentin. MATERIALS AND METHODS: Eighty human third molars were randomly divided into four groups (n = 20) according to the radiation dose (control/no radiation, 20 Gy, 40 Gy, and 70 Gy). The teeth were sagittally sectioned into three slices: one mesial and one distal section containing enamel and one middle section containing dentin. The sections were then placed in the enamel and dentin groups, which were further divided into two subgroups (n = 10) according to the adhesive used. Three restorations were performed in each tooth (one per section) using Adper Single Bond 2 (3M ESPE) or Universal Single Bond (3M ESPE) adhesive system and Filtek Z350 XT (3M ESPE) resin composite and subjected to the microshear bond test. Data were analyzed using a two-way ANOVA followed by Tukey's test. Failure modes were examined under a stereoscopic loupe. RESULTS: Radiotherapy did not affect the bond strengths of the adhesives to either enamel or dentin. In dentin, the Universal Single Bond adhesive system showed higher bond strength values when compared with the Adper Single Bond adhesive system. More adhesive failures were observed in the enamel for all radiation doses and adhesives. CONCLUSION: Radiotherapy did not influence the bond strength to enamel or dentin, irrespective of the adhesive or radiation dose used.

Microshear Bond Strength of Tri-Calcium Silicate-based Cements to Different Restorative Materials.

PURPOSE: To evaluate the microshear bond strength of tri-calcium silicate-based materials to different restorative materials. MATERIALS AND METHODS: Thirty-five disks of TheraCal LC and Biodentine were fabricated using teflon molds according to manufacturers' instructions. Then the specimens were randomly divided into 7 groups according to the materials applied: Fuji IX, Fuji II, Equia Fil, Vertise Flow, Filtek Bulk Fill Posterior Restorative, Filtek Z250 with Prime&Bond NT and with Clearfil SE Bond. All restorative materials were placed onto the disks using tygon tubes. Following a storage period, the specimens underwent microshear bond strength testing in a universal testing machine, and fracture modes were analyzed. Data were analyzed using one-way ANOVA and Tukey's post-hoc test. RESULTS: For all restorative materials, TheraCal LC showed significantly higher µSBS values compared to Biodentine. GIC based materials showed the lowest µSBS for TheraCal and Biodentine. For Biodentine, Filtek Z250 applied with Prime&Bond NT and Filtek Bulk Fill Posterior Restorative applied with Scotchbond Universal Adhesive exhibited the highest µSBS, while Filtek Z250 applied with Clearfil SE Bond revealed the highest bond strength to TheraCal LC. CONCLUSION: For all restorative materials tested in this study, TheraCal LC showed higher µSBS compared to Biodentine. For both TheraCal LC and Biodentine, the placement of GIC-based materials prior to composite resin restorations might decrease the bond strength. Composite resins applied with self-etching adhesives increased the bond strength of TheraCal LC; however, for Biodentine, application of etch-and-rinse adhesives may improve the adhesion of composite resins.

Fracture Strength of Endodontically Treated Teeth Restored with Composite Overlays with and without Glass-fiber Reinforcement.

PURPOSE: To evaluate the fracture strength and the failure mode of endodontically treated teeth restored with composite resin overlays with and without glass-fiber reinforcement. MATERIALS AND METHODS: A total of 32 extracted molars were divided into four equal groups. In the NFR-NFRC (no foundation restoration, no fiber-reinforced composite) and NFR-FRC (no foundation restoration, fiber-reinforced composite) groups, only a 5-mm-thick composite resin layer sealed the pulp chamber floors, whereas in the FR-NFRC (foundation restoration, no fiber-reinforced composite) and FR-FRC (foundation restoration, fiber-reinforced composite) groups, a 3.0-mm foundation restoration was used. NFR-NFRC and FR-NFRC groups were restored with composite resin overlays, whereas NFR-FRC and FR-FRC groups were restored with fiber-reinforced composite resin overlays. All specimens were subjected to mechanical loading in a computer-controlled masticator and then the fracture resistance was evaluated. Differences in means were compared using two-way ANOVA and Tukey's test. The level of significance was set at ɑ = 0.05. RESULTS: All specimens successfully completed the fatigue test. The least fracture-resistant group was NFR-FRC, exceeded by FR-NFRC, NFR-NFRC, and FR-FRC, in that order, with FR-FRC being the most fracture-resistant group. Statistically significant differences were detected between the pairs NFR-NFRC/FR-FRC (p = 0.001), NFR-FRC/FR-FRC (p = 0.001), and FR-NFRC/FR-FRC (p = 0.001). Eight vertical root fractures occurred in group FR-NFRC, six in group NFR-NFRC, four in group NFR-FRC, and none occurred in group FR-FRC. CONCLUSIONS: Within the limitations of this in vitro study, the incorporation of glass fibers and the presence of a foundation restoration were found to increase the fracture resistance and can favorably influence the fracture mode.

Novel Low-Cost Sensor for Human Bite Force Measurement.

This paper presents the design and development of a low cost and reliable maximal voluntary bite force sensor which can be manufactured in-house by using an acrylic laser cutting machine. The sensor has been designed for ease of fabrication, assembly, calibration, and safe use. The sensor is capable of use within an hour of commencing production, allowing for rapid prototyping/modifications and practical implementation. The measured data shows a good linear relationship between the applied force and the electrical resistance of the sensor. The output signal has low drift, excellent repeatability, and a large measurable range of 0 to 700 N. A high signal-to-noise response to human bite forces was observed, indicating the high potential of the proposed sensor for human bite force measurement.

The effect of cycling deflection on the injection-molded thermoplastic denture base resins.

OBJECTIVE: The aim of this study was to evaluate the effect of cycling deflection on the flexural behavior of injection-molded thermoplastic resins. MATERIALS AND METHODS: Six injection-molded thermoplastic resins (two polyamides, two polyesters, one polycarbonate, one polymethyl methacrylate) and, as a control, a conventional heat-polymerized denture based polymer of polymethyl methacrylate (PMMA) were used in this study. The cyclic constant magnitude (1.0 mm) of 5000 cycles was applied using a universal testing machine to demonstrate plasticization of the polymer. Loading was carried out in water at 23ºC with eight specimens per group (n = 8). Cycling load (N) and deformation (mm) were measured. RESULTS: Force required to deflect the specimens during the first loading cycle and final loading cycle was statistically significantly different (p < 0.05) with one polyamide based polymer (Valplast) and PMMA based polymers (Acrytone and Acron). The other polyamide based polymer (LucitoneFRS), polyester based polymers (EstheShot and EstheShotBright) and polycarbonate based polymer (ReigningN) did not show significant differences (p > 0.05). None of the materials fractured during the loading test. One polyamide based polymer (Valplast) displayed the highest deformation and PMMA based polymers (Acrytone and Acron) exhibited the second highest deformation among the denture base materials. CONCLUSION: It can be concluded that there were considerable differences in the flexural behavior of denture base polymers. This may contribute to the fatigue resistance of the materials.

Effects of different pre-treatment methods on the shear bond strength of orthodontic brackets to demineralized enamel.

OBJECTIVE: To compare the effects of different treatment methods used for the enamel damage, on the shear bond strength (SBS) and fracture mode of orthodontic brackets. MATERIALS AND METHODS: Freshly-extracted 140 premolars were randomly allocated to seven groups: Group I was considered as the control of other groups. The remaining groups were exposed to demineralization. In group II, brackets were directly bonded to the demineralized enamel surface. CPP-ACP paste (GC Tooth Mousse), fluoride varnish (Bifluorid 12), microabrasion with a mixture prepared with 18% hydrochloric acid and fine pumice powder, microabrasion with an agent (Opalustre) and resin infiltrant (Icon®) were applied in Groups III, IV, V, VI and VII, respectively. The specimens were tested for SBS and bond failures were scored according to the Adhesive Remnant Index (ARI). Analysis of variance and Tukey tests were used to compare the SBS of the groups. ARI scores were compared with G-test. The statistical significance was set at p < 0.05 level. RESULTS: Statistically significant differences were found among seven groups (F = 191.697; p < 0.001). The SBSs of groups I (mean = 18.8 ± 2.0 MPa) and VII (mean = 19.1 ± 1.4 MPa) were significantly higher than the other groups. No statistically significant difference was found between groups IV (mean = 11.5 ± 1.2 MPa) and V (mean = 12.6 ± 1.5 MPa). The differences in ARI scores of the groups were statistically significant (p < 0.01). CONCLUSIONS: All demineralization treatment methods improve bonding to demineralized enamel. Resin infiltrant application after demineralization showed similar bond strength values as intact enamel.

Comparison of fracture loads of CAD/CAM and conventionally fabricated temporary fixed dental prostheses after different aging regimens.

This study evaluated the fracture loads of different threeunit fixed dental prostheses (FDPs) for temporary restorations. In total, three CAD/CAM materials (VITA CADTemp [CT], Telio CAD [TC], and ZENO ProFix [ZP]) and two chairside materials (Protemp 4 [PT], and Dentalon Plus [DP]) were used for the fabrication of the FDPs. Sixteen FDPs were fabricated from each material in an anatomical shape and stored in 0.9% NaCl solution at 37°C for 14 days. Thereafter, one half of the specimens from each group (n = 8) were additionally mechanically and thermally loaded (240,000 chewing cycles, 50 N, 5°/55°C, 2,100 thermal cycles). Fracture loads were measured and data analyzed using two- and one-way ANOVA, followed by Scheffé's post hoc test. ZP showed the highest mean fracture loads, regardless of the aging regime. Significantly lowest values were identified for DP and TC within the non-thermal loaded group, and for PT and CT within the thermal loaded group. No negative impact of aging regimes could be observed.

Evaluation of shear bond strength, penetration ability, microleakage and remineralisation capacity of glass ionomer-based fissure sealants.

AIM: The aim of this study was to evaluate the bond strength, penetration ability, microleakage, and remineralisation capacity of glass ionomer-based fissure sealant materials. MATERIALS AND METHODS: In this study, three glass ionomer-based fissure sealants were evaluated (Fuji Triage, Fuji VII EP, and GCP Glass Seal). A dye-penetration test was performed to evaluate microleakage under a stereomicroscope. The materials were applied to occlusal tooth surfaces, and bucco-lingual sections (1 mm width) were assessed to evaluate the penetration ability. Shear bond strength of tested materials was assessed using a universal testing machine. Finally, the remineralisation capacities of the materials were evaluated with EDS. RESULTS: The Fuji Triage exhibited the lowest microleakage and unfilled area proportion (p<0.05). The highest shear bond strength was calculated with Fuji VII EP (p<0.05). The fluoride content for all treatment groups was significantly different when remineralisation values were compared to demineralisation (p<0.05). CONCLUSION: Both the Fuji Triage and Fuji VII EP yielded compatible and satisfactory results and all fissure sealants used in this study are sufficient as anti-caries agents.