Linda Wang

Evaluation of the roughness and mass loss of the flowable composites after simulated toothbrushing abrasion

The purpose of this study was to measure mass loss and surface roughness changes of different brands of flowable resin composites after a simulated toothbrushing test. The null hypotheses were that there would be no differences in mass loss and no significant changes in surface roughness after this test and that there would be no correlation between the two variables. The tested materials were Aeliteflo (Bisco), Flow-It (Pentron), Flow-It LF (Pentron), Natural Flow (DFL) and Wave (SDI). Z100 (3M/ESPE) microhybrid and Silux Plus (3M/ESPE) microfilled resin composites were used as control materials. Twelve specimens (5 mm in diameter, 3 mm thick) of each material were prepared according to manufacturers instructions. Toothbrushing abrasion was performed on all specimens from each of the materials using a simulator. The percentage mass loss and surface roughness were assessed before and after 100,000 brushstrokes, using a Sartorius analytical balance of 0.0001 g accuracy and a Hommel Tester T1000, respectively. The measurements of both properties were statistically compared by paired t-test and Tukeys test (p < 0.05). All materials presented a statistically significant mass loss comparing initial and final values, with the exception of Flow-It LF. However, no difference was revealed when comparing the mass loss of the different tested materials. All materials became rougher and Wave presented statistically higher roughness compared to the other resin composites. Flowable resin composites did not seem to be superior to the control groups, and they can be expected to wear by mass loss and to have an increased roughness of surface after toothbrushing action. The anticipated null hypotheses were partially accepted.

In Vitro Effects of Resin Infiltration on Enamel Erosion Inhibition

Resin-based materials that show promising effects for preventing the progression of erosion have been studied. This in vitro study evaluated the effects of applying resin-based materials, including resin infiltration, on previously eroded enamel subjected to erosive challenges. The influence of enamel surface etching prior to application of the material was also studied. Bovine enamel blocks were immersed in hydrochloric acid (HCl), 0.01 M (pH 2.3), for 30 seconds in order to form a softened erosion lesion. The blocks were then randomly divided into nine groups (n=12) and treated as follows: C = control without treatment; Hel = pit & fissure resin sealant (Helioseal Clear); Adh = two-step self-etching adhesive system (AdheSe); Tet = two-step conventional adhesive system (Tetric N-bond); and Inf = infiltrant (Icon). The Helno, Adhno, Tetno, and Infno groups received the same materials without (or with no) surface conditioning. The depth of the materials penetration into softened erosion lesions was qualitatively analyzed using reflection and fluorescence confocal microscopy. After application of the materials, the blocks were immersed in HCl for two minutes; this step was followed by immersion in artificial saliva for 120 minutes four times a day for five days (erosive cycling). Both the enamel alteration and material thickness were analyzed using profilometry, and the results were submitted to Kruskal-Wallis and Dunn tests (p>0.05). Images from the confocal microscopy showed minimal penetration of Adh/Adhno and deep penetration of Inf/Infno into the erosive lesions. The groups Hel, Adh, Inf, Tetno, and Infno resulted in the formation of a layer of material over the enamel, which was effective in inhibiting the progression of erosion. In conclusion, the infiltrant, with or without etching, was able to penetrate and protect the enamel against dental erosion. The other resin-based materials, except for the two-step conventional adhesive, were able to penetrate and inhibit the progression of erosive lesions only when they were applied after enamel etching.

Effect of 2% chlorhexidine digluconate on bond strength of a glass-fibre post to root dentine

AIMnTo assess the immediate influence of dentine bonding systems (DBS) associated with 2% chlorhexidine digluconate (CHX) on glass-fibre post-bond strength to root dentine, in terms of coronal, middle and apical thirds.nnnMETHODOLOGYnSixty bovine roots were root filled and randomly assigned to 1 of 6 groups (nxa0=xa010): SBMP (3-step etch-and-rinse system, Scotchbond Multi-Purpose), SB (2-step etch-and-rinse system, Single Bond 2), SE (2-step self-etching system, Clearfil SE Bond) and SBMP-CHX, SB-CHX and SE-CHX, respectively, associated with CHX. For all groups, a glass-fibre post was luted with a dual-cure resin cement, RelyX ARC. After 7-day storage, specimens were subjected to the push-out test. Failure modes were analysed under optical microscopy (40x). Bond strength values were statistically analysed by two-way anova and Bonferroni tests (Pxa0<xa00.05).nnnRESULTSnThe effect of DBS was significant (Pxa0<xa00.05), and SE reached higher bond strength in comparison with the other DBS tested. CHX association did not show improvement with any DBS (Pxa0>xa00.05); rather, it negatively affected SE, which was detected for all thirds. There was no difference between thirds (Pxa0>xa00.05), except for the SE-CHX, which presented lower values for the apical third (Pxa0<xa00.05). Adhesive cement/dentine adhesive failure was predominant for all groups. CHX did not influence the failure mode for any DBS (Pxa0>xa00.05).nnnCONCLUSIONSnThe performance of the dentine bonding systems was material dependent. CHX did not improve immediate bond strength; however, CHX negatively affected the bond strength of the self-etching system, especially in the third apical.

Role of chlorhexidine in bond strength to artificially eroded dentin over time.

PURPOSEnTo assess the long-term effect of a 2% aqueous chlorhexidine (CHX) solution on bond strength to artificially eroded dentin compared to sound dentin.nnnMATERIALS AND METHODSnFlat mid-coronal dentin surfaces of extracted third molars (n = 28) were subjected only to grinding with a 600-grit SiC paper for 1 min (sound dentin S, n = 14) or additionally to erosive pH cycling with a cola-based soft-drink (eroded dentin E, n = 14). After acid etching, rinsing, and air drying, S and E were rehydrated with 1.5 μl of 2% CHX (S2%, n = 7; E2%, n = 7) or of distilled water (control SC, n = 7; EC, n = 7). Composite buildups were incrementally constructed with Filtek Z350 following Adper Single Bond 2 application. Specimens were sectioned into beams, which were subjected to microtensile testing immediately or after 6 or 12 months of aging. Fractured surfaces were observed under a digital microscope (50X magnification). Microtensile bond strength (μTBS) (MPa) was analyzed by three-way ANOVA and Tukeys tests (α = 0.05) and failure mode by the Kruskal-Wallis test (α = 0.05).nnnRESULTSnCompared to sound dentin, eroded dentin was consistently related to lower μTBS. Immediately and after 12-month aging, the effect of CHX was insignificant, but it was significant after 6-month aging, when it conserved the bond strength to both eroded and sound dentin. The percentage of adhesive and mixed failures were equivalent, and significantly more frequent than cohesive failures, whether in dentin or in composite.nnnCONCLUSIONnThe 2% CHX effect on bond strength conservation to both eroded and sound dentin was not found to be persistent.

Comparative In Vitro Effect of TiF4 to NaF and Potassium Oxalate on Reduction of Dentin Hydraulic Conductance

Dentin hypersensitivity (DH) is related to an increase in dentin permeability. This study tested the effect of titanium tetrafluoride (TiF4) compared with sodium fluoride (NaF) and potassium oxalate gel on reducing hydraulic conductance (Lp) from the perspective of diminishing dentin permeability. The Lp of the dentin disks (1.0 ± 0.2 mm) was evaluated using Flodec. The maximum Lp values of each disk were taken after phosphoric acid etching (15 seconds) and randomly allocated to seven groups (n=8) according to the treatments. The minimum (smear layer) and the maximum (after acid etching) Lp values were recorded. Treatments were performed for 4 minutes as follows: 1) NaF varnish 2) and solution (2.45% F, pH 5.0), 3) TiF4 varnish and 4) solution (2.45% F, pH 1.0), 5) 3% potassium oxalate gel, 6) free fluoride varnish (placebo, pH 5.0), 7) and no treatment (control). The Lp after each treatment was assessed. Samples were exposed to an erosive challenge (6% citric acid, pH 2.1, 1 minute), and the final Lp was recorded. The data were statistically analyzed using repeated measures two-way analysis of variance (p<0.05). All treatments were effective in reducing dentin Lp compared with the control immediately after the application. However, only potassium oxalate and NaF varnish significantly differed from placebo varnish (p<0.0001). The same results were found after the erosive challenge. Therefore, the TiF4 was less effective than the NaF varnish and potassium oxalate gel in reducing dentin permeability. Using this experimental model, both NaF varnish and potassium oxalate gel reduced the Lp similarly to the presence of smear layer.

Evaluation of weight loss and surface roughness of compomers after simulated toothbrushing abrasion test

This study aimed at analyzing the compomers wear by an in vitro toothbrushing abrasion test. The null hypotheses tested were that there would be no differences in weight loss and no significant changes in surface roughness of the compomers after this test. The utilized commercial brands were Dyract (Dentsply), Dyract AP (Dentsply), Compoglass F (Vivadent), Freedom (SDI), F2000 (3M ESPE), which were compared to the two resin composites Z100 (3M ESPE) and Silux Plus (3M ESPE). Ten cylindrical specimens for each commercial brand were prepared with 5mm diameter and 3mm thickness. An appropriate machine with soft bristle tips containing dentifrice solution and deionized water was used. A total of 100,000 brushing cycles were performed. The amount of weight loss was measured by the percentage alteration between the initial (before toothbrushing) and final weight (after toothbrushing), measured by a Sartorius analytical balance. The surface roughness change was determined by the percentage difference between initial and final means after 5 tracings by a T 1000 Hommel Tester roughness meter on the specimens surfaces before and after toothbrushing abrasion test. The statistical analysis (Students paired t-test, ANOVA and Tukey, á=0.05) showed that all materials presented statistically significant weight loss and roughness increase after abrasion test. All compomers presented higher weight loss than resin composites. Freedom and Dyract AP presented the lowest weight loss among compomers. F2000 presented the worst abrasion resistance, without statistical differences with Dyract. For roughness changes, Dyract, Dyract AP, Z100, Compoglass F and Silux Plus showed the lowest surface roughness alteration, in increasing order, without statistical differences between them. Freedom was the statistically roughest material of the study.

Influence of 2% chlorhexidine digluconate on bond strength of a glass-fibre post luted with resin or glass-ionomer based cement

OBJECTIVESnThis study evaluated the influence of 2% chlorhexidine digluconate (CHX) on the bond strength (BS) of a glass-fibre post to the root canal, regarding the cements (dual-cured resin or resin-modified glass-ionomer cement), the root thirds and the time of storage.nnnMETHODnEighty bovine roots were selected and endodontically treated, before being randomly assigned to the following groups according to the luting protocol: ARC (RelyX ARC); ARC+CHX; RL (RelyX Luting 2); and RL+CHX. After 24 h of luting, the roots were sliced to obtain 1 mm-thick slices. Half of each group was submitted to either 7-day or 6-month storage in artificial saliva (n=10). The specimens were subjected to push-out tests with a crosshead speed of 0.5 mm/min. The data were analysed with four-way ANOVA and Tukeys test (P≤0.05). The failure modes were analysed with a digital microscope (50× and 200×).nnnRESULTSnARC yielded a significantly higher BS compared to RL (P<0.001). Despite CHX exerted a significant effect; it depends on the interaction with the luting cement and time (P<0.001). Thus, CHX decreased the values of BS to those of ARC after 6 months (P<0.001). On the 7th day of storage, the ARC+CHX presented higher BS to the cervical and middle thirds compared to RL+CHX (P=0.012). Time solely was not a significant factor (P=0.081). Adhesive cement-dentine type and mixed failures were predominant modes for the ARC groups. For the RL groups, the main failures were adhesive cement-post and mixed modes.nnnCONCLUSIONSnGlass-fibre posts luted with RelyX ARC dual-cure resin cement exhibited higher BS than those luted with RelyX Luting 2 resin-modified glass-ionomer cement. Furthermore, CHX was not effective to improve the BS and negatively affected the BS of RelyX ARC after 6 months of storage.nnnCLINICAL SIGNIFICANCEnThe use of chlorhexidine solution seems not to improve the bond strength of fibre posts to root canals, disregarding the composition of the luting cement.

56-month clinical performance of Class I and II resin composite restorations.

Objective This study evaluated the 56-month clinical performance of Class I and II resin composite restorations. Filtek P60 was compared with Filtek Z250, which are both indicated for posterior restorations but differ in terms of handling characteristics. The null hypothesis tested was that there is no difference in the clinical performance of the two resin composites in posterior teeth. Material and Methods Thirty-three patients were treated by the same operator, who prepared 48 Class I and 42 Class II cavities, which were restored with Single Bond/Filtek Z250 or Single Bond/Filtek P60 restorative systems. Restorations were evaluated by two independent examiners at baseline and after 56 months, using the modified USPHS criteria. Data were analyzed statistically using Chi-square and Fishers Exact tests (a=0.05). Results After 56 months, 25 patients (31 Class I and 36 Class II) were analyzed. A 3% failure rate occurred due to secondary caries and excessive loss of anatomic form for P60. For both restorative systems, there were no significant differences in secondary caries and postoperative sensitivity. However, significant changes were observed with respect to anatomic form, marginal discoloration, and marginal adaptation. Significant decreases in surface texture were observed exclusively for the Z250 restorations. Conclusions Both restorative systems can be used for posterior restorations and can be expected to perform well in the oral environment.

Penetration of resin-based materials into initial erosion lesion: A confocal microscopic study.

The application of resin‐based materials is an alternative of treatment for eroded lesions. Nevertheless, there are no studies about the penetration of these materials into eroded lesion, which might affect its adhesion. Therefore, this study evaluated the penetration of four resin‐based materials, with and without enamel etching. By using an in vitro protocol, types of treatment were studied at five levels (AdheSE®, Tetric N‐Bond®, Single Bond 2®, Helioseal Clear®, Icon®) and types of enamel etching in two levels (with and without). Materials were stained with 0.02 mg/mL ethanolic solution of tetramethylrhodamine isothiocyanate. Bovine enamel samples (4 × 4 mm) were immersed in 0.01 M HCl, pH 2.3, for 30 seconds to produce initial eroded lesions. Afterward, the materials were applied on half of sample enamel surface following the manufacturers instructions. On the other half of sample, the materials were applied without etching the enamel. Materials penetration into the enamel was assessed by Confocal Laser Scanning Microscopy on reflection and fluorescence modes. The penetration depth (PD) was measured using ImageJ software. Data were analyzed by two‐way ANOVA and Tukey test (Pu2009<u20090.05). Regardless of the material, etched enamel resulted in higher PD than non‐etched (Pu2009<u20090.05). Icon® showed the highest PD in enamel followed by Helioseal Clear® (Pu2009<u20090.05), with significant difference between them (Pu2009<u20090.05) and no difference was found among AdheSE®, Tetric N‐Bond®, and Single Bond 2® (Pu2009>u20090.05). It can be concluded that prior enamel etching increased the materials penetration into eroded enamel and the Icon®—infiltrant presented highest penetration. Microsc. Res. Tech. 79:72–80, 2016.

In situ effect of enamel salivary exposure time and type of intraoral appliance before an erosive challenge

ObjectivesThis study tested the effect of enamel salivary exposure time prior to an acid challenge (30xa0min, 1, 2, or 12xa0h) and type of intraoral appliance (palatal or mandibular) on initial erosion.MethodsAfter initial surface hardness evaluation, enamel blocks (nxa0=xa0340) were randomly divided into groups and volunteers (nxa0=xa020). The control group was not exposed to saliva previously to the erosive challenge. The volunteers wore palatal and mandibular appliances simultaneously. After salivary exposure, the blocks were subjected to acid exposure by immersion in hydrochloric acid (0.01xa0M, pHxa02.3) for 30xa0s. Then, the enamel surface hardness was evaluated. Data were analyzed using ANOVA, Kruskal–Wallis and Tukey’s test (pxa0<xa00.05).ResultsNo difference was observed on percent surface hardness change (% SHC) in the enamel blocks between the types of intraoral appliances. Exposure to saliva for 30xa0min and 1xa0h promoted similar enamel resistance to the erosive attack, which was similar to the control group for both appliances. Blocks exposed to saliva for 2xa0h showed less hardness loss when compared to 30xa0min. Keeping the blocks in saliva during 12-h overnight resulted in similar percentage of enamel hardness loss compared to 2xa0h.ConclusionsA 2-hour in situ exposure to saliva is adequate to promote partial protection against initial erosive lesions, independently of the type of intraoral appliance used.Clinical significanceThis finding will help researchers in the development of erosion studies, which will provide information for dentists to offer a better treatment for erosion.