In vitro lifetime of zirconium dioxide-based crowns veneered using Rapid Layer Technology.

Rapid Layer Technology (RLT) uses computer-aided design/computer-aided manufacturing (CAD/CAM) to manufacture a veneer layer that is adhesively bonded to the zirconia framework, avoiding firing steps during the fabrication process and thus preventing build-up of residual stresses. This work studied, using sliding contact fatigue, the in vitro lifetime of restorations produced using RLT compared with restorations produced using conventional veneering techniques. Zirconia copings were veneered with a conventional hand-layering method (VM9) using a fast (n = 16) or a slow (n = 16) cooling protocol, or with RLT. For the latter, the veneers were CAD/CAM fabricated using a feldspathic reinforced-glass (Vitablocs Mark II; n = 16) or a polymer-infiltrated reinforced-glass network (Enamic; n = 16) and adhesively bonded to the zirconia frameworks. Crowns thus obtained were submitted to sliding contact fatigue against a steatite indenter in a chewing simulator until failure. A Kaplan-Meier survival analysis was conducted. None of the hand-layered restorations survived after a 2 × 106 -cycle interval, whereas no fractures in the RLT groups were observed. Vitablocs Mark II veneers survived for a longer testing period (3.5 × 106 cycles) than their Enamic counterparts (2.5 × 106 cycles) owing to their superior wear behavior. The RLT represents an efficient method to veneer zirconia frameworks by reducing processing steps and, more importantly, increasing the lifetime of the restorations.

Mechanical and hydrolytic degradation of an Ormocer®-based Bis-GMA-free resin composite.

OBJECTIVES: The aim of the study was to evaluate the mechanical stability of bisphenol A-glycidyl methacrylate (Bis-GMA) and Ormocer-based resin composites before and after water absorption and to examine water saturation. MATERIAL AND METHODS: Disc-shaped specimens of the Bis-GMA (Grandio SO, Voco) and the Ormocer-based (Admira Fusion, Voco) dental resin composites were produced, stored in water, and weighed after pre-determined times to measure the absorbed water. Bend bars were produced and stored for 24 h in dry conditions as well as in distilled water for 14 days or 60 days at 37 °C. The initial flexural strength (FS) under quasi-static loading and flexural fatigue strength (FFS) under cyclic loading were determined under 4-point bending. Fracture toughness (KIc) of both composites was measured using the single-edge-V-notch-beam (SEVNB) technique after the same storage conditions under 3-point bending. RESULTS: Within the first 14 days, storage conditions did not affect the initial FS of Grandio SO, while a significant drop in initial FS was observed for Admira Fusion after 2 weeks in water and most of the water was absorbed within this time. FFS for the Bis-GMA composite was not reduced before 2 months in water, whereas for the Ormocer®-based composite, there has been a significant decrease in strength after cyclic fatigue already at 2 weeks of water storage. KIc of Admira Fusion decreased significantly after both storage periods, while KIc of Grandio SO decreased only significantly after 2 weeks of water storage. CONCLUSION: All mechanical properties of the Bis-GMA composite were superior to those of the Ormocer®-based material, except water sorption. CLINICAL SIGNIFICANCE: Water storage seems to have a much more pronounced effect on the mechanical properties of Ormocer®-based dental composites in comparison to Bis-GMA-based composites.

Self-adhesive resin cements: pH-neutralization, hydrophilicity, and hygroscopic expansion stress.

OBJECTIVES: The objective of the study was to investigate the relationship between pH-neutralization, hydrophilicity, and free hygroscopic expansion stress of self-adhesive resin cements (SARCs) after storage in artificial saliva. MATERIALS AND METHODS: The SARCs RelyX Unicem Automix 2 (RX2, 3 M ESPE), iCEM (iCEM, Heraeus) and Maxcem Elite (MCE, Kerr) were under investigation in this study. Cylinders (height × diameter, 6 × 4mm) were prepared from each material and stored in artificial saliva (7d at 37 °C). Cylinder height was measured at baseline and after 7 days. After storage, the compression modulus was measured to calculate the free hygroscopic expansion stress. For pH-neutralization and hydrophilicity assessment, disks (height × diameter, 1 × 1.5 mm) were prepared, covered with electrolyte, and monitored over 24 h at 37 °C. Hydrophilicity was assessed using the static sessile drop technique at baseline and at different time intervals up to 24 h. Data were analyzed using one-way ANOVA and post hoc Student-Newman-Keuls test (S-N-K, α = 0.05). RESULTS: After 24 h, RX2 (pH24h 4.68) had a significantly higher (p < 0.05) pH-value than MCE (pH24h 4.2) and iCEM (pH24h 3.23). iCEM showed the significantly highest hydrophilicity (p < 0.05) after 24 h (θ24h 85.02°), while MCE resulted lower (θ24h 113.01°) in comparison with RX2 (θ24h 108.11°). The resulting hygroscopic expansion stress of iCEM (29.15 MPa) was significantly higher (p < 0.05) compared to RX2 (14.5 MPa) and MCE (21.02 MPa). CONCLUSIONS: The material with lowest pH-neutralization capacity displayed higher hydrophilicity after 24 h and higher hygroscopic expansion stress after 7 days compared to those with high pH-neutralization. CLINICAL SIGNIFICANCE: Remnant hydrophilicity due to low pH-neutralization of SARCs could lead to cement interface stress build-up and long-term failure of silicate ceramic restorations.

Are resin composites suitable replacements for amalgam? A study of two-body wear.

OBJECTIVES: Wear resistance is an important property of the dental materials, particularly for large restorations in the posterior regions and for the patients suffering from parafunctional activities. Additionally, the wear resistance of flowable composite resin materials is a clinical concern, although they are popular among dentists because of their easy handling. The aims of the present study were to evaluate the wear resistance of nine composite resins both condensable (G-aenial posterior, Venus, GrandioSO, Tetric EvoCeram, Ceram X duo, Filtek Supreme XTE) and new-generation flowable resin composites (G-aenial Universal Flo, GrandioSO Flow and GrandioSO Heavy Flow) and to compare these results with amalgam. MATERIALS AND METHOD: Eight specimens of each material were subjected to two-body wear tests, using a chewing simulator. The wear region of each material was examined under profilometer, measuring the vertical loss (µm) and the volume loss (mm(3)) of the materials. Additionally, SEM analysis was performed to assess surfaces irregularities. RESULTS: The results showed significant difference of the vertical loss and the volume loss of the examined materials (p < 0.001). Although amalgam had the best wear resistance, two condensable resin composites (GrandioSO, Ceram X duo) and all flowable materials had no significant difference with amalgam. GrandioSO had the highest wear resistance and Filtek Supreme XTE the lowest wear resistance. CONCLUSION: The majority of resin composites had good wear resistance and similar to amalgam. CLINICAL RELEVANCE: Based on the in vitro measurements of two-body wear resistance, the new resin composites could replace amalgam for restorations placed in occlusal stress-bearing regions. New-generation flowable resin materials may also be used in occlusal contact restorations.

Self-adhesive resin cements: adhesive performance to indirect restorative ceramics.

PURPOSE: To evaluate the bonding performance of self-adhesive resin cements to zirconia and lithium disilicate in self- and dual-curing modes before and after thermocycling. MATERIALS AND METHODS: Rectangular bars (3 mm high, 3 mm wide, 9 mm long) were manufactured from zirconia (Vita In-Ceram YZ for inLab, VITA) and lithium disilicate blocks (IPS e.max Press, Ivoclar Vivadent) (n=240 per material). Zirconia bars were sandblasted (35 µm Al2O3, 1.5 bar pressure). Lithium disilicate bars were HF etched (20 s, IPS Ceramic Etching Gel, Ivoclar Vivadent) and silanized with ESPE Sil (3M ESPE). Forty bars of zirconia were luted in twos perpendicular to each other as were 40 bars of lithium disilicate using RelyX Unicem Automix 2 (3M ESPE), G-Cem LinkAce (GC Europe) or Maxcem Elite (Kerr) in self- or dual-curing mode. Half of the specimens from each material were submitted to tensile bond strength (TBS) testing after 24-h storage in distilled water at 37°C, and half underwent TBS testing after thermocycling (5000 cycles, 5°C/55°C, 30-s dwell time). Bond strength values for each bonding substrate were analyzed using one-way ANOVA (Student-Newman- Keuls, α=0.05). RESULTS: On zirconia, dual-curing resulted in significantly (p<0.05) higher tensile bond strengths compared to self-curing, with the exception of RelyX Unicem 2 after thermocycling. Thermocycling significantly (p<0.05) reduced the tensile bond strength of Maxcem Elite to zirconia in both curing modes. The TBS of self-adhesive cements to lithium disilicate showed no significant (p>0.05) difference between the different curing modes and after thermocycling. CONCLUSION: For most of the investigated self-adhesive cements, bond strengths to zirconia were increased by dual curing; this was not true for lithium disilicate. For luting on zirconia with self-adhesive cements, dual curing is strongly recommended in clinical situations.

Restoration of endodontically treated teeth with major hard tissue loss - influence of post surface design on pull-out bond strength of fiber-reinforced composite posts.

AIM: The aim was to evaluate the influence of post surface design and luting system on bond strength of quartz-fiber-reinforced composite posts (QFRCPs) luted to root canal dentin. MATERIALS AND METHODS: Single-rooted bovine teeth (n = 650) were randomly assigned (13 groups, n = 50), sectioned, endodontically treated, filled, and post space (length 8 mm) prepared. Custom-made plain-surfaced fiber posts (PSXRO) and (both RTD) macroretentive Macro-Lock Post Illusion X-RO (MLXRO) were inserted into the post spaces using six luting systems: Ketac Cem (KC), Fuji Plus (FP), RelyX Unicem, Multilink Primer_Multilink, Sealbond Ultima_CoreCem, and LuxaBond_LuxaCore Z. As control, a titanium post was cemented with KC. After water storage (24 h, 37°C), pull-out test was performed, followed by failure mode assessment. Bond strength was calculated in MPa and analyzed using anova, Dunnett-T3-test, and Student's t-test with Bonferroni correction. RESULTS: Post design and luting system significantly influenced the bond strength [MPa] (P < 0.05). Compared with the control 4.3 (1.5), all test groups exhibited higher bond strengths (P < 0.05), except for group PSXRO/KC 4.2 (1.0). The remaining bond strengths were PSXRO: FP 8.6 (1.5), RelyX Unicem 10.4 (3.4), Multilink Primer_Multilink 12.7 (3.0), SealBond Ultima_CoreCem 12.7 (3.0), LuxaBond_LuxaCore Z 15.7 (2.5), and MLXRO: KC 7.2 (2.2), FP 13.4 (2.5), RelyX Unicem 9.2 (2.9), Multilink Primer_Multilink 12.5 (4.5), SealBond Ultima_CoreCem 13.7 (4.6), LuxaBond_LuxaCore Z 20.6 (2.2). The bond strengths of MLXRO were higher than those of PSXRO when luted with KC, FP, and LuxaBond_LuxaCore Z (P < 0.05). CONCLUSION: The post surface design and luting system selection influenced the bond strength of conventionally and adhesively luted QFRCPs to bovine root canal dentin.

Influence of attachment and bone loss on the mobility of incisors and canine teeth.

OBJECTIVE: The purpose of this clinical study was to evaluate the correlation between tooth mobility (TM), crown-to-root ratio (CRR) and clinical attachment loss (CAL) in periodontally-compromised participants. MATERIALS AND METHODS: While slowly biting on a load cell, the mobility of the upper incisors and canine teeth of 20 volunteers was measured using a photogrammetric measurement technique. An automated software program recorded the force-related three-dimensional TM at 3-N intervals. CAL was assessed clinically and CRR values were assessed radiographically. For each contralateral pair of teeth (central, lateral incisor, canine) and for each main level of force, the Pearson product-moment correlation coefficient between TM and CRR and between TM and CAL was computed. Correlations were considered statistically significant at p < 0.05. RESULTS: Statistically significant positive correlations were found between TM and CRR for incisors and canines for each main level of force, whereas canines had the lowest correlation. Statistically significant positive correlations were also found between TM and CAL for the central and lateral incisors at each main level of force. Canines showed no significant correlation between CAL and TM, regardless of force level. CONCLUSION: The loss of attachment and bone seem to have more influence on the mobility of incisors than canines.

Influence of adhesive point dimension and splint type on splint rigidity--evaluation by the dynamic Periotest method.

AIM: To evaluate the influence of adhesive point dimension and splint type on the rigidity of wire-composite splints in vitro. MATERIALS AND METHODS: A custom-made artificial model was used. The two central incisors served as injured teeth (degrees of loosening III and II) and the two lateral incisors as non-injured teeth (physiological mobility). Horizontal and vertical tooth mobilities were investigated before and after splinting with the Periotest(®) method; the percent change was taken as the relative splint effect. Teeth were splinted with three types of wire-composite splints: Dentaflex (0.45 mm), Strengtheners (0.8 × 1.8 mm), and Dentaflex completely covered with composite. Four adhesive point dimensions (2, 3, 4, and 5 mm) were evaluated. Normal distribution was tested with the Kolmogorov-Smirnov test. Differences were evaluated with the anova and post hoc tests for pair-wise comparisons. Significance level was set at 0.05. RESULTS: The adhesive point dimension did not influence splint rigidity, in general ( P  = 0.288). Significant effects were found in non-injured teeth with the Dentaflex ( P  < 0.001) and in injured teeth with the Strengtheners ( P  < 0.001). The Strengtheners splint rigidity increased significantly with increasing adhesive point dimensions. The three splints showed significantly different effects at 5-mm adhesive point dimension ( P  < 0.001). CONCLUSION: Splint rigidity for injured teeth was influenced by adhesive point dimension only when splinting with Strengtheners. We recommend adapting splint rigidity by selecting different wires and reducing the adhesive point dimension to a minimum. Dentaflex can be used for flexible splinting, Strengtheners, and composite covered Dentaflex for rigid splinting.

Restoration of endodontically treated teeth with major hard tissue loss--bond strength of conventionally and adhesively luted fiber-reinforced composite posts.

AIM: To evaluate the influence of the luting system on the pull-out bond strength of conventionally and adhesively luted fiber-reinforced composite posts (FRCPs). MATERIAL AND METHODS: One hundred extracted bovine teeth (Di 3) were endodontically treated and randomly assigned to nine test groups and one control group (n = 10) according to luting system. After preparing the post cavities (8 mm), the custom-made FRCPs were inserted using conventional glass-ionomer cement (Ketac Cem), resin-reinforced glass-ionomer cement (Meron Plus and Fuji Plus), self-adhesive resin cement (RelyX Unicem and BisCem), self-conditioning adhesive and resin cement [Multilink Primer + Multilink and AdheSE + DC Activator + MultiCore Flow, or etch-and-rinse adhesive and resin cement (SealBond Ultima + CoreCem, and LuxaBond + LuxaCore Z). As a control, custom-made titanium posts were inserted with Ketac Cem. After water storage (37°C, 24 h, dark), the pull-out test was performed, followed by failure mode evaluation. The data were statistically analyzed (α = 0.05) using analysis of variance and the Dunnett T3 post hoc test. RESULTS: Luting system type and identity significantly influenced bond strength (P < 0.001); the bond strengths of all luting systems except Ketac Cem, MeronPlus, and BisCem were significantly higher than the control (4.4 ± 1.1 MPa). RelyX Unicem (12.0 ± 3.0 MPa) and LB + LCZ (14.8 ± 2.3 MPa) generated the highest bond strengths. The clinical application was demonstrated by restoring a traumatized tooth with extensive coronal destruction and thin root canal walls, using a FRCP combined with direct composite build-up. CONCLUSION: Luting system selection significantly influenced the bond strength of conventionally and adhesively luted FRCPs to bovine root canal dentin.

Influence of preliminary etching on the stability of bonds created by one-step self-etch bonding systems.

We evaluated the effects of preliminary etching of dentine on the stability of the bond created by one-step self-etch adhesives under different storage conditions. Adper Easy Bond (3M ESPE) and iBond Self-Etch (iBond SE; Heraeus Kulzer) were applied with an etch-and-rinse (i.e. after preliminary phosphoric acid etching for 15 s) or a self-etch approach. Resin-dentine bonded specimens were sectioned perpendicularly to the adhesive interface according to the 'non-trimming technique'. Beams were stored in artificial saliva for 24 h, 6 months, or 1 yr at 37°C, or in 10% NaOCl for 5 h at room temperature, and then stressed until failure; the microtensile bond strengths were calculated. Interfacial nanoleakage of additional teeth was evaluated using light microscopy or transmission electron microscopy. Adper Easy Bond showed higher bond strength than iBond SE, regardless of the dentine treatment. Similar microtensile bond strength results were obtained for teeth subjected to artificial ageing in 10% NaOCl for 5 h at room temperature and for teeth stored in artificial saliva for 6 months at 37°C. The additional etching step increased the microtensile bond strength for Adper Easy Bond and iBond SE. This study supports the use of one-step adhesives on etched dentine because of the increased bond strength compared with their application onto smear-layer-covered dentine, regardless of storage conditions.

Rigidity evaluation of quartz-fiber splints compared with wire-composite splints.

AIM: To evaluate the influence of reinforcement material on in vitro dental splint rigidity. MATERIALS AND METHODS: A custom-made artificial model was used. The central incisors simulated 'injured' teeth with increased mobility, and the lateral incisors served as 'uninjured' teeth with physiologic mobility. The Periotest and Zwick methods were used to assess horizontal and vertical tooth mobility before and after splinting, and relative splint effect (SpErel) was calculated. Teeth 12-22 were splinted using two wire-composite splints (WCS), WCS1 (Dentaflex 0.45mm), and WCS2 (Strengtheners 0.8×1.8mm) as well as four quartz-fiber splints, QS1 (Quartz Splint UD 1.5mm), QS2 (Quartz Splint Rope 1.5mm), QS3 (Quartz Splint Woven 2.5mm), and QS4 (dry fibers 667 tex). The influence of the splint type was evaluated using anova, Tukey range, and the Dunnett-T3 test (α=0.05). To test the influence of initial tooth mobility, the t-test was applied (α=0.05). RESULTS: Reinforcement materials significantly influenced splint rigidity (P<0.05). The horizontal and vertical SpErel of WCS1 compared with WCS2 and QFSs1-4 was statistically significant (P<0.05). Significant differences were found when comparing the horizontal SpErel of WCS2 with WCS1 and QSs1-4 (P<0.05). SpErels of the 'injured' and 'uninjured' teeth showed significant differences (P<0.05). CONCLUSION: WCS1 is flexible compared with the more rigid WCS2 and QSs1-4. Initial tooth mobility influences SpErel. The flexible WCS1 can be recommended for splinting dislocation injuries whereas the semi-rigid/rigid WCS2 and QS1-4 can be used for horizontal root fractures and alveolar process fractures. The QS1-4 provide good esthetic outcome.

Influence of Simulated Oral Conditions on Different Pretreatment Methods for the Repair of Glass-Ceramic Restorations.

PURPOSE: The present study investigated the influence of simulated intraoral conditions (increased temperature and humidity) on two different surface pretreatment methods to repair a lithium-disilicate glass-ceramic (LDS). MATERIALS AND METHODS: A total of 540 rectangular lithium-disilicate glass-ceramic bars were manufactured (3 x 7 x 9 mm; IPS e.max CAD, Ivoclar Vivadent). Further specimen preparation was performed in an incubator with controlled relative humidity (RH) and temperature to simulate three different environmental settings: laboratory conditions (LC, n = 180, 23°C, 50% RH), rubber-dam conditions (RC, n = 180, 30°C, 50% RH) or oral conditions (OC, n = 180, 32°C, 95 ± 5% RH). One-third of the bars under each condition (n = 60) were grit blasted (GBL) with alumina (35 µm at 1 bar pressure for 10 s and a working distance of 4 ± 1 cm) and primed (60 s, Monobond Plus, Ivoclar Vivadent). Another third (n = 60) were pretreated with a self-etching glass-ceramic primer (MEP, Monobond Etch & Prime, Ivoclar Vivadent). One group without surface pretreatment (n = 60, NoPT) served as a control. All pretreated surfaces were coated with Heliobond (Ivoclar Vivadent). Two bars from the same pretreatment method were luted perpendicular to each other with a resin composite to form a square adhesion area of 9 mm2 (TetricEvo Ceram, Ivoclar Vivadent), and light cured for 20 s on each side (1200 mW/cm2, Bluephase 20i, Ivoclar Vivadent). All specimens were stored for 24 h in distilled water at 37°C. Half of the specimens from each environmental setting and pretreatment method (n = 15) were thermocycled (TC, 5000 cycles, 5/55°C, 30-s dwell time), and tensile bond strength (TBS) testing was performed for all groups using an x-bar rope-assisted set-up. Data were statistically analyzed using two-way ANOVA (a = 0.05) with Bonferroni adjustment. RESULTS: Regardless of the environmental and storage conditions (24 h or TC), MEP showed a significantly higher mean TBS than GBL. A decrease in TBS was recorded in specimens under OC compared to RC and LC for both pretreatment methods independent of the storage condition. No significant difference in mean TBS was found between RC and LC within the MEP pretreatment group for the 24 h stored and thermocycled specimens. For all MEPs and GBLs, TC reduced the mean TBS in all environmental conditions. The NoPT groups showed no adhesion regardless of environmental or storage conditions. CONCLUSIONS: Increased temperature and high humidity significantly reduced TBS. However, MEP was less sensitive to environmental influences than GBL, which makes it a promising candidate for intraoral ceramic repair. These findings suggest that clinical intraoral repair of lithium-disilicate glass-ceramics should be performed using a rubber-dam, primarily when using GBL.

Preparation and filling of small oval root canals: influence of file system and sealer.

OBJECTIVE: To carry out a morphometric analysis of small oval root canals prepared with different instruments (part 1) and filled with different sealers (part 2). METHOD AND MATERIALS: Ninety extracted mandibular incisors with small oval root canals were instrumented with Self-Adjusting File (n = 45), XP-endo Finisher (n = 15), GentleFile (n = 15), or Reciproc (n = 15). All groups of part 1 were filled with AH Plus (n = 15 each). For part 2 (including group Self-Adjusting File/AH Plus) teeth instrumented with Self-Adjusting File were additionally filled with GuttaFlow Bioseal (n = 15) or Total Fill BC sealer (n = 15). All sealers were placed with a lentulo and filled with master point and additional points. Serial cuts were made at 1-mm intervals up to 10 mm. Total root canal area, percentage of gutta-percha filled area (PGFA), sealer, voids, and debris were evaluated using interactive image analysis software. RESULTS: Preparation with Reciproc caused significantly wider canals than with Self-Adjusting File, GentleFile, or XP-endo Finisher, but also resulted in the greatest PGFA and lowest percentage of sealer (P ≤ .05). Following XP-endo Finisher, the significantly greatest percentage of debris (30%) was found 1 mm from the apex (P ≤ .05). Regarding different sealers, only minor differences were found (GuttaFlow Bioseal: less percentage of sealer at 2 and 3 mm levels [P ≤ .05]). CONCLUSION: Within the limits of this study Reciproc caused the greatest substance loss, but also the most favorable PGFA. The apical debris accumulation with XP-endo Finisher needs further investigation. The sealers under investigation performed equally well.

Evaluation of wear behavior of dental restorative materials against zirconia in vitro.

OBJECTIVES: To evaluate two-body wear (2BW) and three-body wear (3BW) of different CAD/CAM and direct restorative materials against zirconia using a dual-axis chewing simulator and an ACTA wear machine. METHODS: 3 CAD-CAM resin-based composite or polymer infiltrated ceramic network blocs, 1 lithium disilicate CAD-CAM ceramic (LS2), 3 direct resin composites, amalgam and bovine enamel were tested. For 2BW, 8 flat specimens per material were produced, grinded, polished, stored wet (37 °C, 28d) and tested (49 N, 37 °C, 1,200,000 cycles) against zirconia. For 3BW, specimens (n = 10) were stored accordingly, and tested against a zirconia antagonist wheel (3Y-TZP, d = 20 mm, h = 6 mm; 200,000 cycles, F = 15 N, f = 1 Hz, 15% slip) in millet seed suspension. Wear resistance was analysed in a 3D optical non-contact profilometer, measuring vertical wear depth and volume loss for 2BW and mean wear depth and roughness (Ra) for 3BW. Vickers hardness (15 s, HV2) was measured. Statistical analysis was performed using non-parametric tests (Mann-Whitney-U test, p < 0.05). RESULTS: 2BW and 3BW have a different impact on material surfaces. Similar wear resistance was observed for direct and indirect resin based materials with analogous filler configurations in both methods. Bovine enamel exhibited the best wear resistance in 2BW, but the least wear resistance in 3BW against zirconia. Regarding 2BW, a direct/indirect composite material pair of the same manufacturer showed the significantly highest mean volume losses (2.72/2.85 mm³), followed by LS2 (1.41 mm³). LS2 presented the best wear resistance in 3BW (mean wear depth 2.85 µm), combined with the highest mean Vickers hardness (598 MPa). No linear correlation was found between Vickers hardness and both wear testing procedures. The zirconia antagonists showed no recordable signs of wear. SIGNIFICANCE: Dental restorative materials behave differently in 2BW and 3BW laboratory testing. Vickers hardness testing alone cannot hold for a correlation with wear behavior of materials. Micromorphological investigation of material composition can reveal insights in wear mechanisms related to variations in filler technologies.

Professional brushing study comparing the effectiveness of sonic brush heads with manual toothbrushes: a single blinded, randomized clinical trial.

The aim of this study was to evaluate the plaque removal efficacy of four toothbrushes: the Philips Sonicare Elite with medium and mini brush heads, the Elmex Sensitive, and the American Dental Association (ADA) reference toothbrush. This study was a randomized, controlled, investigator-blinded, four-brush crossover design study, which examined plaque removal following a consecutive repeated use. All brushes were used on each participant in a randomly assigned quadrant of the mouth. A total of 90 subjects participated in the study. Prior to the experiment, they received a professional prophylaxis and were requested to refrain from toothbrushing for 48 h. Teeth were professionally brushed consecutively for 10 to 90 s per quadrant. A Turesky-modified Quigley Hein Index score was assessed at baseline and after each brushing interval by one blinded investigator. Results showed reduction of mean plaque scores for all brushes with time from 10 to 90 s. After 30 s (2-min whole mouth equivalent) of brushing, the Sonicare brushes cleaned 19, the ADA brush 16, and the Elmex Sensitive 10 of in average 28 tooth surfaces. With time, the number of additional cleaned surfaces decreased. Time is an important variable in the evaluation of plaque-removing efficacy since absolute efficacy increases with time and differs per toothbrush. No differences could be found between the two brush heads of the Sonicare.

Strength and wear resistance of a dental glass-ionomer cement with a novel nanofilled resin coating.

PURPOSE: To evaluate the influence of different resin coating protocols on the fracture strength and wear resistance of a commercial glass-ionomer cement (GIC). METHODS: A new restorative concept [Equia (GC Europe)] has been introduced as a system application consisting of a condensable GIC (Fuji IX GP Extra) and a novel nanofilled resin coating material (G-Coat Plus). Four-point fracture strength (FS, 2 x 2 x 25 mm, 14-day storage, distilled water, 37 degrees C) were produced and measured from three experimental protocols: no coating GIC (Group 1), GIC coating before water contamination (Group 2), GIC coating after water contamination (Group 3). The strength data were analyzed using Weibull statistics. Three-body wear resistance (Group 1 vs. Group 2) was measured after each 10,000 wear cycles up to a total of 200,000 cycles using the ACTA method. GIC microstructure and interfaces between GIC and coating materials were investigated under SEM and CLSM. RESULTS: The highest FS of 26.1 MPa and the most homogenous behavior (m = 7.7) has been observed in Group 2. The coated and uncoated GIC showed similar wear resistance until 90,000 cycles. After 200,000 wear cycles, the coated version showed significantly higher wear rate (ANOVA, P< 0.05). The coating protocol has been shown to determine the GIC fracture strength. Coating after water contamination and air drying is leading to surface crack formation thus significantly reducing the FS. The resin coating showed a proper sealing of GIC surface porosities and cracks. In terms of wear, the coating did not improve the wear resistance of the underlying cement as similar or higher wear rates have been measured for Group 1 versus Group 2.

Development of new artificial models for splint rigidity evaluation.

AIM: We developed two versions of an artificial model and assessed their suitability for splint rigidity evaluation. These models allowed the simulation of traumatically loosened teeth and the use of the acid-etch technique for splint application. MATERIALS AND METHODS: A straight and half-round arch bar model with bovine tooth facets were manufactured. Using the Periotest method, tooth mobility was evaluated before (PTVpre) and after (PTVpost) splinting. Two types of previously investigated wire-composite splints, WCS1 (Dentaflex 0.45 mm; Dentaurum) and WCS2 (Strengthens 0.8 × 1.8 mm; Dentaurum), were applied (n = 10) to each model. The relative splint effect (SpErel = ΔPTV/PTVpre) was calculated, and the working times for the models and splints were evaluated. Student's t-test and the Mann-Whitney U-test were employed with Bonferroni correction for multiple hypotheses. RESULTS: When comparing the relative splint effect of the 'injured' central incisors between the models within one splint type, differences were only found for tooth 21 (WCS2; P < 0.008); for comparisons of splints within one model type, differences were detected for both incisors and model types (P < 0.008). With the straight model, significantly less working time was necessary (P < 0.05). CONCLUSION: Using these models for in vitro splint rigidity evaluation, the splints can be applied with the acid-etch technique and tooth mobility can be individually adjusted. WCS1 is considered flexible compared to the more rigid WCS2. The results from the straight and the round model were predominantly closely related to each other. In terms of working time, the straight model is superior to the round model.

Influence of wire extension and type on splint rigidity--evaluation by a dynamic and a static measuring method.

OBJECTIVES: To evaluate the influence of wire dimension and wire length on the splint rigidity of wire-composite splints in vitro. MATERIALS AND METHODS: A custom-made artificial model was used. The central incisors simulated 'injured' teeth with increased mobility, and the lateral incisors and canines served as 'uninjured' teeth with physiological mobility. To assess horizontal and vertical tooth mobility before and after splinting, the Periotest and Zwick methods were applied. Teeth 13-23 were splinted using wire-composite splint 1 (WCS1; Dentaflex 0.45 mm) and wire-composite splint 2 (WCS2; Strengtheners 0.8 × 1.8 mm). Splint length was varied by successively shortening the wire. The influence of wire dimension was tested using t-test and Wilcoxon-Mann-Whitney test with the Bonferroni-Holm procedure (α = 0.05). To test the influence of wire length, anova and Kruskal-Wallis tests as well as Tukey range and Wilcoxon test with Bonferroni-Holm procedure were applied (α = 0.05). RESULTS: Wire dimension significantly influenced splint rigidity (P < 0.05). The wire length significantly influenced the splint rigidity of WCS1 in the horizontal dimension and WCS2 in the horizontal and vertical dimensions (P < 0.05). Splint rigidity was significantly reduced when splinting only 'injured' teeth compared with splints including 'uninjured' adjacent teeth (P < 0.05). No differences were found between splints including one or two 'uninjured' teeth on each side (P > 0.05). CONCLUSION: WCS1 is flexible compared with the more rigid WCS2. The wire length influences the rigidity. To ensure adequate fixation and reduce the risk of enamel damage during splint removal, the splint should include only one 'uninjured' tooth bilaterally.

In vitro splint rigidity evaluation--comparison of a dynamic and a static measuring method.

OBJECTIVES: The aim of this in vitro study was to investigate a dynamic and static tooth mobility assessment method in terms of reproducibility and correlation. MATERIALS AND METHODS: A custom-made artificial model was used. The central incisors simulated 'injured' teeth with increased mobility, and the lateral incisors served as 'uninjured' teeth with physiological mobility. To assess tooth mobility, three consecutively repeated measurements were taken, in the vertical and horizontal dimensions before and after splinting, using the Periotest method as well as the Zwick universal testing machine. Reproducibility of the measurements was tested using anova and the Bonferroni post hoc test (α = 0.05). Correlation was analysed using Spearman's rank correlation (α = 0.05). RESULTS: No significant differences were found when comparing the three consecutively taken Periotest values and the vertical Zwick values (P > 0.05). In the horizontal dimension, the first Zwick values differed from the second and third values (P < 0.05). Only a few random correlations (P < 0.05) were found when comparing the two assessment methods. Horizontal and vertical measurements within one method did not correlate (P > 0.05). CONCLUSIONS: The Periotest and vertical Zwick values are highly reproducible. The measurements of the two methods do not correlate; therefore, a conversion of Periotest values into metric displacement data is not feasible. The two methods provide different valuable information about tooth mobility. The Periotest method describes the damping characteristics of the periodontal ligament while the Zwick method reveals quantitative metric values.

Viscosity and stickiness of dental resin composites at elevated temperatures.

OBJECTIVE: To investigate the influence of pre-heating different classes of dental resin composites on viscosity and stickiness at five different temperatures. METHODS: Six flowable, five conventional packable, and one thermo-viscous bulk-fill resin composites were heated up to 54°C in a plate-plate rheometer to determine their complex viscosity. Normal force measurements were carried out for the six packable materials to determine the unplugging force and unplugging work (stickiness) over the same temperature range. Data were analyzed using Kolmogorov-Smirnoff test, one-way ANOVA and Tukey Post Hoc test with α=0.05 as level of significance. RESULTS: At 23°C packable composites showed viscosity between 6.75 and 19.14kPas, while flowable composites presented significantly lower viscosities between 1.31 and 2.20kPas. Pre-heating led to a drop of 30-82% in the viscosity of packable materials. The thermo-viscous material dropped to the level of flowables at 45 and 54°C thus behaving as a packable composite at room temperature with flowable-like viscosity at higher temperatures. No statistically significant differences for viscosity were observed among flowable composites at any temperature. The unplugging force decreased for packable composites, while their unplugging work generally increased at elevated temperature. At 23°C unplugging force was measured between 7.50 and 19.18N, while pre-heating up to 54°C led to values between 2.9 and 6.2N. Regarding unplugging work at 23°C the calculated values were between 3.0 and 8.9×10-3J and at 54°C between 8.8 and 13.0×10-3J. SIGNIFICANCE: Pre-heating significantly reduced viscosity of highly viscous resin composites, while no influence was shown for flowable composites. In general stickiness, measured as unplugging work, increased at elevated temperatures. The thermo-viscous material showed low viscosity comparable to flowable composites at 45 and 54°C, yet its stickiness did not increase significantly compared to the values at 23°C.