Effect of biomimetic mineralization on enamel and dentin: A Raman and EDX analysis

ObjectiveTo investigate the effect of an experimental biomimetic mineralization kit (BIMIN) on the chemical composition and crystallinity of caries-free enamel and dentin samples in vitro.MethodsEnamel and dentin samples from 20 human teeth (10 for enamel; 10 for dentin) were divided into a control group without treatment and test samples with BIMIN treatment. Quantitative analysis of tissue penetration of fluoride, phosphate, and calcium was performed using energy-dispersive X-ray spectroscopy (EDX). Mineralization depth was measured by Raman spectroscopy probing the symmetric valence vibration near 960 cm⁻¹ as a marker for crystallinity. EDX data was statistically analyzed using a paired t-test and Raman data was analyzed using the Student’s t-test.ResultsEDX analysis demonstrated a penetration depth of fluoride of 4.10 ± 3.32 μm in enamel and 4.31 ± 2.67 μm in dentin. Calcium infiltrated into enamel 2.65 ± 0.64 μm and into dentin 5.58 ± 1.63 μm, while the penetration depths for phosphate were 4.83 ± 2.81 μm for enamel and 6.75 ± 3.25 μm for dentin. Further, up to 25 μm of a newly mineralized enamel-like layer was observed on the surface of the samples. Raman concentration curves demonstrated an increased degree of mineralization up to 5–10 μm into the dentin and enamel samples.SignificanceBiomimetic mineralization of enamel and dentin samples resulted in an increase of mineralization and a penetration of fluoride into enamel and dentin.     

Influence of halogen irradiance on short- and long-term wear resistance of resin-based composite materials

ObjectiveThe Oregon Health Science University (OHSU) four-chamber oral wear simulator was used to examine the impact of halogen irradiance on the short- and long-term wear behavior of four-methacrylate resin-based composites (RBCs). The hypothesis proposed was that exacerbated wear would occur following the long-term wear of RBCs irradiated under non-optimized irradiance conditions.MethodsDisc-shaped specimens (12.0 ± 0.1 mm diameter and 2.0 ± 0.1 mm height) of each RBC were prepared at irradiances of 650 ± 14, 530 ± 8, 420 ± 14, 350 ± 8, 270 ± 8, 230 ± 14, 190 ± 8, and 150 ± 8 mW/cm², respectively. Short-term three-body wear simulation was carried out for 50,000 cycles and long-term was performed up to 500,000 cycles. The wear facets were analyzed using a non-contact optical profilometer. One-, two-, and three-way analyses of variance (ANOVA) were made at P = 0.05, guided as necessary by Tukeys correction in multiple partial analyses of the mean total volumetric wear and mean maximum wear depth.ResultsFor the short-term wear resistance, the two-way ANOVA identified no significant difference in the mean total volumetric wear (P = 0.188) although the mean total wear depth was identified to be significant (P = 0.024). The long-term wear resistance for the mean total volumetric wear identified significant differences for each RBC at varying irradiances with the number of cycles but not for the mean maximum wear depth.SignificanceThe increased number of ploughing actions of the antagonist on the RBC (long-term) results in increased friction which would be expected to play a major role in the wear process. The significant increase in the mean total volumetric wear, but not the mean maximum wear depth, observed over time which is exacerbated at reduced halogen irradiances emphasizes the arguments of DeLong for the employment of volume for evaluating material loss due to wear following in vitro wear simulation of RBCs.     

Craniofacial growth changes and dental attrition in the primary dentition

Presence of pronounced incisal and occlusal wear in primary dentition is fairly common in children. Several factors are implied, however, the possible correlation of craniofacial growth to the occurrence of severe incisal tooth wear in children has not been described to date. Thus, this study was aimed to find any association between the craniofacial growth changes and the occurrence of severe incisal wear in children.Materials and methodsTwenty-seven sets of series of dental casts and corresponding lateral cephalograms are selected from the archive of Pediatric Dentistry, Department of Tokyo Medical and Dental University Hospital. Samples were divided into two groups based on the extent of incisal wear observed on the primary maxillary anterior teeth: slight attrition (N = 13) and severe attrition (n = 14) groups. Lateral cephalograms at early deciduous dentition at T1 (3.5 ± 0.6 years old) and late deciduous dentition at T2 (6.2 ± 0.6 years old) were manually traced and 17 linear and 22 angular measurements were measured with analyzing software (WinCeph ver.9). Annual growth rate for each sample was calculated to determine any significant difference between samples from two groups.ResultsSignificant horizontal growth of the mandible with both the reduction of anterior tooth height and increase of posterior tooth height were found in the severe attrition group. Reduction of upper incisor angle to FH plane and upper dental arch length were also related with the attrition of teeth.ConclusionsThe incisal tooth wear of deciduous teeth was significantly associated with the craniofacial growth changes.     

Remineralization effectiveness of the PAMAM dendrimer with different terminal groups on artificial initial enamel caries in vitro

ObjectiveDisruption of the demineralization–remineralization balance could trigger the development of dental caries, making it challenging for enamel to “self-heal”. Thus, extrinsic assistance is needed to restore enamel lesions and stop undermining progression. The aim of this study was to investigate enamel remineralization in a simulated oral environment via poly (amino amine) (PAMAM) dendrimers quantitatively.MethodsBovine enamel specimens were shaken in demineralization solution (pH 4.5, 37 °C, 50 rpm/min) for 72 h to create initial enamel carious lesions. The subsurface-demineralized specimens were then divided into four groups: enamel treated with PAMAM-NH₂, enamel treated with PAMAM−COOH, enamel treated with PAMAM−OH, and enamel treated with deionized water. The treated specimens underwent subsequent 12-day pH cycling. Enamel blocks were analyzed by transverse microradiography (TMR), surface microhardness testing and scanning electron microscopy (SEM) before and after demineralization and pH cycling.ResultsGroups treated with PAMAM dendrimers showed lower lesion depth and less mineral loss, attained more vertical-section surface microhardness recovery, and adsorbed more mineral deposits (p < 0.05). The enamel lesion remineralization values of PAMAM-NH₂, PAMAM-COOH, and PAMAM-OH groups were 76.42 ± 3.32%, 60.07 ± 5.92% and 54.52 ± 7.81%, respectively.SignificanceIn conclusion, PAMAM with different terminal groups could induce enamel remineralization, among which PAMAM-NH₂ showed the most prominent competence, followed by PAMAM-COOH and PAMAM-OH, in that order.     

In vitro enamel erosion and abrasion-inhibiting effect of different fluoride varnishes

ObjectiveTo investigate the erosion and abrasion inhibiting effect of CPP-ACP/NaF and xylitol/NaF varnishes.MethodsBovine enamel samples (n = 40) were exposed to the following treatments (n = 10): NaF varnish (Duraphat^®, positive control); CPP-ACP/NaF varnish (MI varnishTM); xylitol/NaF (Profluorid^®) or distilled and deionized water (MilliQ^®, negative control). The samples were submitted for 3 days to 4 cycles/day of erosion (5 min in Sprite Zero) and 2 cycles of abrasion/day after the first and last erosive challenge, with a toothbrush machine and slurries of a placebo toothpaste for 15 s (50 strokes/s). Among the cycles and after the last daily cycle, the specimens remained in artificial saliva. The change in the enamel surface was evaluated by using 3D non-contact optical profilometry with surface roughness (Ra and Sa values) and tooth structure loss (TSL) measurements. Scanning electron microscopy (SEM) assessed the enamel topographic characteristics. Differences in the Ra, Sa and TSL among treatments were tested using one-way ANOVA followed by the Tukey test.ResultsAll varnishes promoted better results for Ra and Sa values than the negative control (p = 0.0001), without difference among them (p > 0.05). However, CPP-ACP/NaF varnish stimulated fewer TSL (7.09 ± 0.70 μm) compared to NaF varnish (10.33 ± 1.36 μm, p = 0.002), xylitol/NaF varnish (9.96 ± 0.41 μm, p = 0.007) and the negative control (18.38 ± 3.32 μm, p = 0.0001).ConclusionA single-application of fluoride topical varnishes was effective in reducing enamel wear. The CPP-ACP/NaF varnish had the best effect against enamel loss from an erosion-abrasion challenge.     

A dual energy micro-CT methodology for visualization and quantification of biofilm formation and dentin demineralization

ObjectiveThe aim of this study was to induce artificial caries in human sound dentin by means of a microcosm model using human saliva as source of bacteria and to apply a novel dual-energy micro-CT technique to quantify biofilm formation and evaluate its demineralization potential.DesignEight sound third molars had the occlusal enamel removed by cutting with a diamond disk and five cylindrical cavities (±2 mm diameter; ±1.5 mm depth) were prepared over the dentin surface in each specimen (n = 40 cavities). After sterilization, each specimen received the bacterial salivary inoculum obtained from individuals without any systemic diseases presenting dentin caries lesions and were incubated in BHI added of with 5% sucrose for 96 h to allow biofilm formation. After that, two consecutive micro-CT scans were acquired from each specimen (40kv and 70kv). Reconstruction of the images was performed using standardized parameters. After alignment, registration, filtering and image calculations, a final stack of images containing the biofilm volume was obtained from each prepared cavity. Dentin demineralization degree was quantified by comparison with sound dentin areas. All data were analyzed using Shapiro-Wilk test and Spearman correlation using α=5%.ResultsDual-energy micro-CT technique disclosed biofilm formation in all cavities. Biofilm volume inside each cavity varied from 0.30 to 1.57 mm³. A positive correlation between cavity volume and volume of formed biofilm was obtained (0.77, p < 0.01). The mineral decrease obtained in dentin was high (± 90%) for all cavities and all demineralized areas showed mineral density values lower than a defined threshold for dentin caries (1.2 g/cm³).ConclusionDual-energy micro-CT technique was successful in the quantification of a microcosm human bacterial biofilm formation and to quantify its demineralization potential in vitro.     

High-translucent yttria-stabilized zirconia ceramics are wear-resistant and antagonist-friendly

ObjectivesTo evaluate two-body wear of three zirconia ceramics stabilized with 3, 4 and 5 mol% yttria and to compare their wear behavior with that of a lithium-disilicate glass-ceramic.MethodsSixteen rectangular-shaped specimens made from three grades of zirconia ceramics and a lithium-disilicate glass-ceramic were polished and dynamically loaded in a chewing simulator (2 kg vertical load, 2.1 Hz) under water at 90 °C for 1.2 × 10⁶ cycles (about 7 days) in the ball-on-plate mode against steatite antagonists. Surface roughness was measured before and after wear testing. Wear tracks were scanned with a non-contact 3D profilometer and super-impositions were used to determine wear loss of the antagonists. Wear surfaces were imaged by SEM. XRD and micro-Raman spectroscopy were used to characterize phase transformation and stress status in the worn and unworn areas of the zirconia ceramics.ResultsIndependent of fracture toughness, strength and aging-susceptibility, the three zirconia ceramics showed a similar and limited amount of wear (∼10 μm in depth) and were more wear-resistant than the lithium-disilicate glass-ceramic (∼880 μm in depth). Abrasive wear without obvious cracks was observed for all investigated zirconias, whereas the glass-ceramic with a lower fatigue threshold and high susceptibility to surface dissolution exhibited significant abrasion, fatigue and corrosion wear. All three zirconia ceramics yielded a lower antagonist wear than the glass-ceramic and no significant differences were found between the zirconia ceramics.SignificanceIn the context of this study, high-translucent zirconia ceramics stabilized with a higher yttria content, recently introduced in the dental field, were as wear-resistant and antagonist-friendly as conventional high-strength zirconia and suitable for monolithic restorations.     

Influence of bonding surface and bonding methods on the fracture resistance and survival rate of full-coverage occlusal veneers made from lithium disilicate ceramic after cyclic loading

ObjectivesThe purpose of this laboratory study was to evaluate the influence of bonding method and type of dental bonding surface on fracture resistance and survival rate of resin bonded occlusal veneers made from lithium disilicate ceramic after cyclic loading.MethodsFourty-eight extracted molars were divided into three groups (N = 16) depending on the preparation: within enamel, within dentin/enamel or within enamel/composite resin filling. Lithium disilicate occlussal veneers were fabricated with a fissure-cusp thickness of 0.3–0.6 mm. Restorations were etched (5% HF), silanated and adhesively luted using a dual-curing luting composite resin. Test groups were divided into two subgroups, one using a only a self-etching primer, the other additionally etching the enamel with phosphoric acid. After water storage (37 °C; 21 d) and thermocycling (7500 cycles; 5–55 °C), specimens were subjected to dynamic loading in a chewing simulator (600,000 cycles; 10 kg/2 Hz). Surviving specimens were loaded until fracture using a universal testing machine.ResultsAll specimens survived artificial aging, several specimens showed some damage. ANOVA revealed that enamel etching provided statistically significantly (p ≤ 0.05) higher fracture resistance than self-etching when bonding to enamel and dentin. Self-etching provided statistically significant (p ≤ 0.05) higher fracture resistance for the enamel-composite group than for the enamel group. Enamel etching provided statistically significant (p ≤ 0.05) higher fracture resistance for the enamel and dentin group than for groups enamel and enamel-composite.SignificanceEtching enamel improved the fracture resistance of occlusal veneers when bonding to dentin and enamel and increased the survival rate when bonding to enamel.     

Frequency of intake and amount of fluoride in milk for remineralisation of artificial caries on enamel and dentine: Ex vivo/in situ study

ObjectivesThis study analysed the effect of frequency of intake and amount of fluoride in milk on the remineralisation of artificial enamel and dentine caries lesions ex vivo/in situ.Materials and methodsPre-demineralised bovine enamel and dentine slabs were randomly allocated into 5 groups and fixed in removable appliances used by subjects for 7 days in each phase. Each treatment comprised milk containing 2.5 ppm fluoride daily (T1), or every other day (T2), 5.0 ppm F daily (T3), or every other day (T4) or no treatment (T5).ResultsEnamel alterations were quantified by surface hardness recovery (%SHR) and transversal microradiography (TMR), and in dentine by TMR only. Data were analysed by ANOVA and Tukey’s test (p < 0.05). For enamel, the highest %SHR was found for T1 and T3 compared to control, without significant differences between them. All groups showed positive values of ΔΔZ − T1 (247.3 ± 198.5); T2 (110.9 ± 303.2); T3 (226.0 ± 299.2); T5 (5.0 ± 288.0), except T4 (−274.5 ± 407.3). For dentine, the only group that presented remineralisation was T2 (350.0 ± 657.5).ConclusionsFluoridated milk daily seems to have higher remineralising effect on enamel than its use every other day. Dentine, does not seem to benefit from daily use of fluoridated milk.     

Diagnostic guide enabling distinction between taphonomic stains and enamel hypomineralisation in an archaeological context

ObjectiveMolar Incisor Hypomineralisation (MIH) is a structural anomaly that affects the quality of tooth enamel and has important consequences for oral health. The developmentally hypomineralised enamel has normal thickness and can range in colour from white to yellow or brown with or without surface breakdown. The possibility of finding MIH in ‘ancient populations' could downplay several current aetiological hypotheses (e.g., dioxin derivatives, bisphenols, antibiotics) without excluding the possible multifactorial aspect of the anomaly. In an archaeological context, chemical elements contained in the burial ground can stain teeth yellow or brown and therefore might create a taphonomic bias. The purpose of the present study is to test a proposed diagnostic guide enabling determination of the pathological or taphonomic cause of enamel discolouration and defects that resemble MIH present on ‘ancient teeth'.DesignTwo sample groups including MIH discoloration (n = 12 teeth) from living patients, taphonomic discoloration (n = 9 teeth) and unknown discoloration (n = 2 teeth) from medieval specimens were tested. Three non-destructive methods—Raman spectroscopy, X-ray micro-computed tomography and X-ray fluorescence were utilised.ResultsHypomineralised enamel has decreased mineral density (p < 0.0001) and increased phosphate/β-carbonate ratio (p < 0.01) compared to normal enamel whereas relative concentrations of manganese, copper, iron and lead are similar. In taphonomic discoloration, relative concentrations of these elements are significantly different (p < 0.05) to normal enamel whereas mineral density and Raman spectra profile are comparable.ConclusionsEnamel hypomineralisation can be distinguished from taphonomic staining in archaeological teeth.     

Inhibition of enamel mineral loss by fissure sealant: An in situ study

ObjectivesThis study evaluated the effect of fluoride and non-fluoride sealants on hardness decrease (HD) and marginal adaptation (MA) on enamel substrates after cariogenic challenge.MethodsOcclusal enamel blocks, from human third molars, were randomly divided into six groups (n = 12), according to occlusal fissures condition (S – sound; C – caries-like lesion; CF – caries-like lesion + topical fluoride) and sealants (F – FluroShield; H – Helioseal Clear Chroma). Lesion depths were 79.3 ± 33.9 and 61.3 ± 23.9 for C and CF groups, respectively. Sealants were placed on occlusal surface and stored at 100% humidity (37 °C; 24 h/d). HD was measured by cross-sectional microhardness analysis at the sealant margin distances: ?1 (under sealant), 0 (sealant margin), 1, 2 (outer sealant). Sealant MA was observed by polarized light microscopy and scored according to: 0 – failure (no sealant MA or total sealant loss); 1 – success (sealant MA present). MA and HD were analysed by ANOVA-R and mixed model analysis, respectively.ResultsFor HD (ΔS), F values (6900.5 ± 3686.6) were significantly lower than H values (8534.6 ± 5375.3) regardless of enamel substrates and sealant margin distances. Significant differences were observed among sealant margin distances: ?1 (5934.0 ± 3282.6) < 0 (8701.5 ± 6175.7) = 1 (8473.2 ± 4299.4) = 2 (7761.5 ± 4035.1), regardless of sealant and substrate. MA was similar for all groups (p ≥ 0.05).ConclusionMA was not affected by sealant type or substrate condition, whereas enamel HD was favourably impacted by fluoride in the sealant. In addition, sealants were more effective as a physical barrier than as its chemical potency in reducing enamel HD.Clinical significanceSealing with a fluoride material is a recommended procedure to prevent caries of occlusal permanent molars in high-caries-risk patients, even though those exhibiting white spot lesions, since the enamel hardness decrease when fluoride sealant was used in vitro.     

Optimization of calcium concentration of saliva with phosphoryl oligosaccharides of calcium (POs-Ca) for enamel remineralization in vitro

ObjectivePhosphoryl oligosaccharides of calcium (POs-Ca) are highly soluble calcium source made from potato starch. The aim of this study was to investigate the optimal concentrations of POs-Ca for the remineralization of subsurface enamel lesions in vitro.DesignDemineralized bovine enamel slabs (n = 5) were remineralized in vitro for 24 h at 37 °C with artificial saliva (AS) containing 0–0.74% POs-Ca to adjust the Ca/P ratio to 0.4–3.0, then sectioned and analysed by transversal microradiography (TMR). The data were analysed by Scheffe's post hoc test. The Ca/P ratio with most remineralization was used to investigate the effect of calcium on enamel remineralization (n = 11). The demineralized slabs were treated with AS with calcium-chloride- (CaCl₂-) or POs-Ca with an identical calcium content, and sectioned for TMR and wide-angle X-ray diffraction (WAXRD) analyses to evaluate the local changes in hydroxyapatite (HAp) crystal content. The data were analysed using the Mann–Whitney U-test.ResultsThe highest mineral recovery rate resulted from addition of POs-Ca to adjust the Ca/P to 1.67. At this ratio, the mineral recovery rate for AS containing POs-Ca (24.2 ± 7.4%) was significantly higher than that for AS containing CaCl₂ (12.5 ± 11.3%) (mean ± SD, p < 0.05). The recovery rate of HAp crystallites for AS containing POs-Ca (35.7 ± 10.9%) was also significantly higher than that for AS containing CaCl₂ (23.1 ± 13.5%) (p < 0.05). The restored crystallites were oriented in the same directions as in sound enamel.ConclusionsPOs-Ca effectively enhances enamel remineralization with ordered HAp at a Ca/P ratio of 1.67.     

Influence of dentin pretreatment with 2.5% titanium tetrafluoride on inhibiting caries at the tooth-restoration interface in situ

ObjectiveInvestigate the effects of dentin pretreatment with 2.5% titanium tetrafluoride (TiF₄) aqueous solution followed by two-step self-etching (CLE/Clearfil SE Bond) and one-step self-etching adhesive systems (SBU/Single Bond Universal) on carious lesion inhibition at the tooth-restoration interface using an in situ model.DesignSixty-four cavities at the enamel-dentin junction of dental fragments were randomly distributed according to groups (n = 16): 1) TiF₄ + CLE; 2) TiF₄ + SBU; 3) CLE; 4) SBU. Cavities were restored using resin composite, and placed in intraoral palatal devices used by 16 volunteers for 21 days, to induce caries formation in situ. The fragments were then ground-flat to perform Knoop microhardness tests. Nine indentations were performed on each enamel and dentin substrate, subjacent to the restoration. Analysis of variance and Tukey’s test were applied.ResultsEnamel: groups receiving TiF₄ dentin pretreatment (regardless of adhesive system and tooth-restoration interface distance) presented higher hardness means at a depth of 25 μm from the outer tooth surface (p < 0.0001). Dentin: groups receiving CLE presented higher means when applying TiF₄ pretreatment, whereas groups restored with SBU presented higher means without pretreatment (p = 0.0003).ConclusionsDentin pretreatment with TiF₄ inhibited demineralization of the enamel interface in situ, regardless of the adhesive, and TiF₄ pretreatment followed by CLE application showed higher potential for inhibiting dentin demineralization at the interface.     

The effect of magnesium hydroxide-containing dentifrice using an extrinsic and intrinsic erosion cycling model

ObjectiveTo evaluate, in vitro, the effect of Mg(OH)₂ dentifrice, and the influence of the number of experimental days, on the extrinsic (citric acid –CA) and intrinsic (hydrochloric acid –HCl) enamel erosion models.DesignHuman enamel slabs were selected according to surface hardness and randomly assigned to 3 groups (n = 9) as follows: non-fluoridated (negative control), NaF (1450 ppm F- positive control) and Mg(OH)₂ (2%) dentifrices. The slabs were daily submitted to a 2-h period of pellicle formation and, over a period of 5 days, submitted to cycles (3×/day) of erosive challenge (CA 0.05 M, pH = 3.75 or HCl 0.01 M, pH = 2 for 30 s), treatment (1 min −1:3 w/w of dentifrice/distilled water) and remineralization (artificial saliva/120 min). Enamel changes were determined by surface hardness loss (SHL) for each day and mechanical profilometry analysis. Data were analyzed by two-way ANOVA followed by Tukey’s test to % SHL and one-way ANOVA to profilometry (p < 0.05).ResultsThe number of experimental days influenced the erosion process for the two types of erosion models (p < 0.001). Mg(OH)₂-containing dentifrices were effective in reducing enamel extrinsic acid erosion as determined by % SHL (p < 0.001) when compared to the control group, being better than positive control (p < 0.001); however, the dentifrices were not effective for the intrinsic model (p = 0.295). With regards to surface wear, no statistically significant differences were found among the groups for CA (p = 0.225) and HCl (p = 0.526).ConclusionThe findings suggest that Mg(OH)₂ dentifrices might protect enamel against slight erosion, but protection was not effective for stronger acid erosion.     

Experimental composites containing quaternary ammonium methacrylates reduce demineralization at enamel-restoration margins after cariogenic challenge

ObjectiveThis study evaluated the influence of experimental composites containing quaternary ammonium monomers (QAM) at different concentrations and alkyl chains on demineralization at enamel-composite margins after cariogenic challenge.MethodsStandardized 4 × 4 mm cavities were cut into 35 bovine enamel blocks, which were randomly divided into seven groups (n = 5) and restored with the following experimental composites and commercial materials: (G12.5) – 5% dimethylaminododecyl methacrylate (DMADDM) with a 12-carbon alkyl chain (G12.10) – 10% DMADDM, (G16.5) – 5% dimethylaminohexadecyl methacrylate (DMAHDM) with a 16-carbon alkyl chain (G16.10) – 10% DMAHDM, (CG) – control group (without QAM), (GZ250) – commercial composite (Filtek Z250^®), and (GIC) – glass ionomer cement (Maxxion R^®). After restorative procedures, initial microhardness was measured and experimental composites were subjected to Streptococcus mutans biofilm formation for 48 h. After cariogenic challenge, the samples were washed and microhardness was reassessed. A 3D non-contact profilometer was used to determine surface roughness and enamel demineralization was assessed by micro-CT. Microhardness results were analyzed by the Kruskal–Wallis and Mann-Whitney tests and micro-CT results were analyzed by Tukey’s HSD test (95% confidence interval).ResultsNone of the materials could prevent mineral loss at the enamel-restoration margins. The addition of 10% DMAHDM yielded the lowest, albeit statistically significant, mineral loss (p < 0.05). 3D non-contact profilometry showed enamel surface roughness modification after biofilm exposure. The CG had the highest roughness values. Micro-CT analysis revealed mineral loss, except for GIC.SignificanceThe addition of 10% QAM with a 16-carbon chain in experimental composites reduced mineral loss at the enamel-restoration margins after cariogenic challenge.     

Impact of high-speed sintering,layer thickness and artificial aging on the fracture load and two-body wear of zirconia crowns

ObjectiveTo investigate the impact of high-speed sintering, layer thickness and artificial aging in a chewing simulator on the fracture load (FL) and two-body wear (2BW) of 4Y-TZP crowns.Methods4Y-TZP crowns (Ceramill Zolid HT+, Amann Girrbach AG) in three different layer thicknesses (0.5, 1.0, 1.5; N = 192, n = 64/group) were manufactured using CAD/CAM technology and sintered at 1580 °C (high-speed sintering) or 1450 °C (control group). Specimens were polished in two-steps and bonded to standardized CoCr abutments with Multilink Automix (Ivoclar Vivadent). 2BW after 6000 thermo- and 1,200,000 chewing-cycles employing enamel antagonists was determined using best fit machining. FL was tested before and after artificial aging. Univariate ANOVAs, post hoc Scheffé, unpaired t-, Kruskal–Wallis- and Mann–Whitney-U-test were computed (p < 0.05).ResultsHigh-speed sintering resulted in less 2BW of the zirconia than the control group (p = 0.013). High-speed sintering (p = 0.001–0.006) and an increase in layer thickness (p < 0.001–0.012) resulted in higher FL values, while artificial aging led to a reduction of FL (p < 0.001).SignificanceAs high-speed sintering resulted in less two-body wear of the zirconia and comparable or even higher fracture load results than the control group, this cost- and time efficient alternative presents promising mechanical results.     

Fabrication and characterization of remineralizing dental composites containing calcium type pre-reacted glass-ionomer (PRG-Ca) fillers

ObjectiveTo fabricate and characterize dental composites with calcium type pre-reacted glass-ionomer (PRG-Ca) fillers.MethodsPRG-Ca fillers were prepared by the reaction of calcium fluoroaluminosilicate glass with polyacrylic acid. Seven dental composites were produced from the same organic matrix (70/30 wt% Bis-GMA/TEGDMA), with partial replacement of barium borosilicate (BaBSi) fillers (60 wt%) by PRG-Ca fillers (wt%): E0 (0) – control, E1 (10), E2 (20), E3 (30), E4 (40), E5 (50) and E6 (60). Enamel remineralization was evaluated in caries-like enamel lesions induced by S. mutans biofilm using micro-CT. The following properties were characterized: degree of conversion (DC%), roughness (Ra), Knoop hardness (KHN), flexural strength (FS), flexural modulus (FM), water sorption (W_sp), water solubility (W_sl), and translucency (TP). Data were analyzed to one-way ANOVA and Tukey’s HSD test (α = 0.05).ResultsAll composites with PRG-Ca induced enamel remineralization. E0 and E1 presented similar and highest DC% than E2 = E3 = E4 = E5 = E6. Ra and KHN were not influenced by PRG-Ca fillers (p < 0.05). The higher the content of PRG-Ca, the lower FS, FM and TP (p < 0.05). W_sp increased linearly with the content of PRG-Ca fillers (p < 0.05). E6 presented the highest W_sl (p < 0.05), while the W_sl of the other composites were not different from each other (p > 0.05).SignificanceIncorporation of 10–40 wt.% of PRG-Ca fillers endowed remineralizing potential to dental composites without jeopardizing the overall behavior of their physicochemical properties. Dental composites with PRG-Ca fillers seems to be a good alternative for reinforcing the enamel against caries development.     

Three-body wear of 3D printed temporary materials

ObjectiveThe aim of this study was to investigate the three-body wear of different additively manufactured temporary materials, one temporary PMMA material for CAD/CAM milling and one resin-based composite for direct restorations as a control group by using an ACTA machine.MethodsSpecimens (n = 8) of the 3D printing materials 3Delta temp, NextDent C&B, Freeprint temp were additively manufactured by DLP 3D printer. Postprocessing was carried out according to the manufacturer's specifications. Telio CAD were cut out of blocks, Tetric EvoCeram was applied directly and light cured. Three-body wear was simulated with an ACTA machine. Data were statistically analysed (ANOVA, post hoc test: Tukey, p < 0.05). The worn surfaces of the specimens were examined with a FE-SEM.ResultsThe average mean wear was 50 ± 15 μm for Tetric EvoCeram < 62 ± 4 μm for 3Delta temp < 236 ± 31 μm for Telio CAD < 255 ± 13 μm for NextDent C&B < 257 ± 24 μm for Freeprint temp. After 200,000 cycles, the wear and wear rates for Tetric EvoCeram and 3Delta temp were significantly lower than those for the other materials. SEM revealed that 3Delta temp has a higher filler proportion than the other 3D printing materials but less than Tetric EvoCeram.SignificanceThe filler content influences the wear behaviour of additively manufactured materials as well as dental restorative composite materials. While most 3D printing materials have a low inorganic filler load, which qualifies the materials for temporary use only, one 3D printing material has an optimized composition that would qualify the material for longer clinical service time if wear is considered as the outcome variable.     

Retrospective analysis on the repair vs. replacement of composite restorations

ObjectiveOur retrospective study aimed to assess the impact of repairs on the longevity of anterior and posterior direct composite restorations and to compare longevity of repaired and replacement restorations.MethodsPatient records were retrospectively screened for anterior and/or posterior composite restorations with 2+ surfaces placed in permanent teeth between 2000 and 2015. During follow-up, repaired and replaced restorations were assessed and mean annual failure rates (mAFR) calculated. Outcome was considered in three levels: Success (no further intervention), survival 1 (first repair = survival, second repair = failure) and survival 2 (more than one repair = survival, all surfaces repaired = failure). Statistical analysis was performed using Kaplan–Meier statistics, log-rank tests, and multi-variate Cox-regression analyses with shared frailty (p < 0.05).Results8542 initial restorations placed in 3239 patients were included (4.7 ± 4.4 years follow-up, 2.5 ± 0.7 surfaces). Longevity of initial restorations was prolonged by repair(s) (after 10 years: success: 68.3%, mAFR: 3.7%; survival 1: 77.3%, mAFR: 2.5%; survival 2: 80.4%, mAFR: 2.2%; p < 0.001). 616 repaired restorations (4.9 ± 4.2 years follow-up, 3.5 ± 1.0 surfaces) and 264 replacement restorations (5.6 ± 4.1 years follow-up, 3.0 ± 0.8 surfaces) were analyzed. Success of repaired restorations amounted to 43.4% after 10 years (mAFR: 8.0%), further repair(s) prolonged survival (survival 1: 65.7%, mAFR: 4.1%; survival 2: 74.8%, mAFR: 2.9%; p < 0.001). Success of replacement restorations amounted to 48.6% after 10 years (mAFR: 7.0%), repair(s) prolonged survival (survival 1: 67.4%, mAFR: 3.9%, p = 0.044; survival 2: 74.1%, mAFR: 3.0%, p = 0.003).SignificanceRepairs are suitable to increase the survival of restorations; repaired restorations last as long as replacements.     

Sodium fluoride effect on erosion–abrasion under hyposalivatory simulating conditions

ObjectivesTo investigate the effect of fluoride (0, 275 and 1250 ppm F; NaF) in combination with normal and low salivary flow rates on enamel surface loss and fluoride uptake using an erosion–remineralization–abrasion cycling model.DesignEnamel specimens were randomly assigned to 6 experimental groups (n = 8). Specimens were individually placed in custom made devices, creating a sealed chamber on the enamel surface, connected to a peristaltic pump. Citric acid was injected into the chamber for 2 min followed by artificial saliva at 0.5 (normal flow) or 0.05 (low flow) ml/min, for 60 min. This cycle was repeated 4×/day, for 5 days. Toothbrushing with abrasive suspensions containing fluoride was performed for 2 min (15 s of actual brushing) 2×/day. Surface loss was measured by optical profilometry. KOH-soluble fluoride and enamel fluoride uptake were determined after the cycling phase. Data were analysed by two-way ANOVA.ResultsNo significant interactions between fluoride concentration and salivary flow were observed for any tested variable. Low caused more surface loss than normal flow rate (p < 0.01). At both flow rates, surface loss for 0 was higher than for 275, which did not differ from 1250 ppm F. KOH-soluble and structurally-bound enamel fluoride uptake were significantly different between fluoride concentrations with 1250 > 275 > 0 ppm F (p < 0.01).ConclusionsSodium fluoride reduced enamel erosion/abrasion, although no additional protection was provided by the higher concentration. Higher erosion progression was observed in low salivary flow rates. Fluoride was not able to compensate for the differences in surface loss between flow rates.