In vitro performance of an autocured universal adhesive system in bonding to dentin.

BACKGROUND: The successful integration of resin-based dental adhesives significantly impacts restorative dentistry, providing efficient and aesthetically pleasing caries treatments. Among various adhesives, one-step self-etching adhesives (1-SEAs) have gained popularity due to their simplicity and short application time. However, concerns have been raised regarding their bonding performance and marginal adaptation characteristics, which differ from two-step self-etching adhesives (2-SEAs) and three-step etch-and-rinse adhesives. Additionally, light-cured bonding materials may encounter challenges in deep cavities and inaccessible areas, necessitating extended light irradiation time. Autocured bonding materials are a potential solution, but limited comparative studies have been conducted on their performance. METHODS: In this in vitro study, we evaluated a new autocured universal bonding material (Bondmer Lightless 2) and compared the results with recent light-cured bonding materials. Microshear bond strength (µSBS) tests were performed on 25 human molars using five different combinations of adhesives and composite resins: Bondmer Lightless 2 with Estelite Bulk Fill Flow (BE group), Bondmer Lightless 2 with a prototype composite resin (BO group), Prime&Bond Universal with SDR flow + (PS group), Scotchbond Universal with Filtek Bulk Fill (SF group), and G-Premio Bond with Gracefil BulkFlo (GG group). The bond strengths and failure modes were assessed using a universal testing machine and scanning electron microscope (SEM), respectively. Marginal adaptation was evaluated using swept-source optical coherence tomography (SS-OCT) and confocal laser scanning microscopy (CLSM) on 40 sound bovine maxillary incisors. RESULTS: The µSBS test showed no significant differences in bond strength among the tested groups. Most failure modes were observed at the bond interface between the adhesive and the dentin. The autocured bonding material demonstrated significantly higher marginal adaptation (SI%) than PS, SF, and GG. The CLSM images corresponded with gaps observed in the SS-OCT images, indicating improved marginal sealing in the autocured group. CONCLUSIONS: The new autocured universal bonding material exhibited comparable bond strength to a conventional light-cured material while demonstrating a superior marginal adaptation level. This finding suggested that the autocured material could be a valuable alternative, especially when extended light irradiation would pose a challenge. Further clinical studies would be warranted to evaluate the performance of the autocured bonding material in actual restorative dental practice.

Fostering globally competent dental students through virtual team-working, problem-solving and person-centred multi-disciplinary care planning.

Background/purpose: : Development and acquisition of communication, logical thinking, team-building, critical appraisal, critical thinking and person-centred multi-disciplinary care planning must be considered as skill sets and global core competencies for a dental professional. Therefore, an international online study course to foster undergraduate dental students' skill sets in these areas was established and this study aimed to report the perceptions of participants. Materials and methods: An international online course consisting of three levels pertaining to the school year was delivered to dental undergraduates of Japan and Thailand from September to December in 2021. An online questionnaire survey was conducted to obtain feedback from the participants and assess the implementation of the course. Results: In total, 64 responses were obtained from students who participated in all the assigned online sessions and completed the questionnaire (a response rate of 88%). More than 95% of students from each level felt that the programme increased their motivation to study clinical dentistry, and was beneficial for their future and made them appreciate the importance of participating in international exchange. The ratio of favourable respondents was more than 90% with a 95% confidence interval. Conclusion: Fostering globally competent dental students is important and the acquisition of necessary skill sets could be enhanced through international virtual team-working, problem-solving and person-centred multi-disciplinary care planning activities. These are beneficial for undergraduate dental student training so that they graduate with a broader global perspective and an appreciation of the importance of delivering person-centred culturally sensitive dental care.

Addition of metal chlorides to a HOCl conditioner can enhance bond strength to smear layer deproteinized dentin.

OBJECTIVES: To evaluate the effect of smear layer deproteinization using hypochlorous acid (HOCl) with/without metal chlorides (SrCl2 and ZnCl2) on the microtensile bond strength (µTBS) of two simplified adhesives to dentin. METHODS: Human dentin surfaces with a standardized smear layer were pretreated using a 105 ppm HOCl solution with/without SrCl2 (0.05 M, 0.1 M, 0.2 M, 0.4 M) or ZnCl2 (0.05 M, 0.1 M, 0.2 M) for 5 s, 15 s, or 30 s. After the deproteinizing solution was washed out with water for 5 s, 15 s, or 30 s, pretreated surfaces were bonded with one-step self-etch adhesive Bond Force II or universal adhesive Clearfil Universal Bond Quick, and µTBS was measured after 24 h. Additionally, the deproteinizing effects of HOCl solutions with/without the metal chlorides were compared by measuring changes in the amide:phosphate ratio using attenuated total reflection Fourier transform infrared spectroscopy. Statistical analysis was performed using multifactor ANOVA, Tukey's post hoc tests and t-tests (p < 0.05). RESULTS: Pretreatment with pure HOCl for 15 s and 30 s significantly decreased the amide:phosphate ratio (p < 0.05), indicating effective deproteinization, but the µTBS of both adhesives increased significantly only if HOCl was washed out for 30 s (p < 0.05). Increasing the concentrations of metal chlorides enabled shortening of the wash-out time down to 5 s while maintaining the improved µTBS (p < 0.05). The deproteinizing effect of HOCl was not significantly altered by the addition of metal chlorides (p > 0.05). SIGNIFICANCE: The effectiveness of smear layer deproteinization using HOCl can be improved by the addition of metal chlorides, as their increasing concentration allowed to shorten the wash-out time from 30 s down to 5 s.

Smear layer deproteinization with NaOCl and HOCl: Do application/wash-out times affect dentin bonding of one-step self-etch adhesives?

This study investigated the influence of application/wash-out times of sodium hypochlorite (NaOCl) and hypochlorous acid (HOCl) on dentin bond strength of one-step self-etch adhesives (1-SEAs). Human coronal dentin discs with a standardized smear layer were pretreated with 6% NaOCl or 100 ppm HOCl for 5 s, 15 s, or 30 s, and washed out with water for 5 s, 15 s or 30 s with or without the application of Clearfil DC Activator (CDA). No pretreatment was used as a control. The discs were bonded with a 1-SEA (Bond Force II or Clearfil Universal Bond Quick) and microtensile bond strength (µTBS) was measured after 24 h. Pretreatment with NaOCl for 15 s and 30 s significantly decreased µTBS (p<0.05), irrespective of wash-out time. The application of CDA recovered µTBS but did not outperform the control group. Conversely, pretreatment with HOCl for 15 s and 30 s followed by 30 s wash-out time significantly increased µTBS of 1-SEAs (p<0.05), regardless of CDA application.

Sodium p-Toluenesulfinate Enhances the Bonding Durability of Universal Adhesives on Deproteinized Eroded Dentin.

The effects of deproteinization using sodium hypochlorite (NaOCl) and the subsequent application of an antioxidant (sodium p-toluenesulfinate, STS) onto the bonding durability of universal adhesives on eroded dentin were investigated. Untreated sound dentin served as the control, whereas eroded dentin, which had been prepared by pH-cycling in 1% citric acid and a remineralization solution, was either untreated, deproteinized with a 10% NaOCl gel or deproteinized with the 10% NaOCl gel and subsequently treated with an STS-containing agent. The dentin surfaces were bonded using a universal adhesive (Clearfil Universal Bond Quick, Scotchbond Universal or G-Premio Bond), and the micro-tensile bond strength (µTBS) test was performed after 24 h or 10,000 thermal cycles. The µTBS data were statistically analyzed using a three-way ANOVA and Tukey's HSD post hoc tests. The lowest µTBS was measured on untreated eroded dentin (p < 0.001). Deproteinization of eroded dentin resulted in µTBS similar to untreated sound dentin (p > 0.05), but the highest µTBS was obtained if deproteinization was followed by the application of STS. Thermocycling significantly decreased µTBS in all groups (p < 0.001), except for STS-treated deproteinized eroded dentin (p > 0.05). This indicated that deproteinization, followed by the application of STS, could enhance the bonding durability of universal adhesives on eroded dentin.

Effect of photo-thermal acceleration on in-office bleaching.

The purpose is to evaluate the effect of photo-thermal acceleration on in-office bleaching efficiency using a bleaching agent without photocatalysts in vitro. Artificially discolored bovine lower incisors were prepared, and the mixed in-office bleaching material contained hydrogen peroxide 23% was applied by following treatment for 10 min: high-(HI group) and low-intensity LED lights (LI group), oven at 38 °C (OV group), and room temperature at 23 °C (RT group). Color was measured before and after bleaching and color difference (∆E*) was calculated. The data were statistically analyzed using a two-way ANOVA and Tukey's post hoc test. The temperature change (∆T) of applied bleaching agent in HI and LI groups was measured using a thermography and was analyzed using a T test. The bleaching procedures were repeated 6 times. Irradiation in the HI group resulted in the highest ΔE, followed by the LI group whose ΔE was significantly lower. Both irradiated modes exhibited higher ΔE compared to non-irradiated OV and RT groups which were not significantly different from each other. The average temperature rise of bleaching agents in HI and LI groups after 10 min irradiation was 15.00 °C and 11.80 °C, respectively. The effect of photo-thermal acceleration was proved for an in-office bleaching agent without photocatalysts in vitro.

Effect of smear layer deproteinization with chemo-mechanical caries removal agents on sealing performances of self-etch adhesives.

OBJECTIVES: To evaluate the sealing performance of self-etch adhesives (SEA) after smear layer deproteinization with chemo-mechanical caries removal agents (CRA) to enamel and dentin cavity walls in comparison with 6% NaOCl smear layer deproteinizing. METHODS: Eighty extracted bovine incisors with tapered cylindrical cavities (2.5 mm upper diameter, 1.5 mm lower diameter, 2 mm depth) at the cemento-enamel junction were randomly divided into four pre-treatment groups; no treatment (control), Papacarie (papain enzyme-based CRA), Carisolv (NaOCl-based CRA), and 6% NaOCl. After pretreatment, G-Bond Plus (GBP, one-step SEA) or Clearfil SE Bond 2 (CSE, two-step SEA) was applied to the pre-treated cavity, and then filled with a flowable resin composite (Clearfil Majesty ES Flow). Gap formations at the enamel and dentin lateral walls, and on the dentin cavity floor were investigated using swept-source optical coherence tomography (SS-OCT) after 24-h water storage at 37 °C. Deproteinizing effects of the tested agents on smear layer-covered enamel and dentin were quantified by changes in the amide:phosphate ratio using ATR-FTIR analysis. RESULTS: Papacarie significantly reduced gap formation with both self-etch adhesives at all locations, compared to the control group (p < 0.05). In contrast, increased gap formation was observed with Carisolv and NaOCl. In most groups, CSE exhibited significantly lower gap formation than GBP (p < 0.05). ATR-FTIR revealed a significant decrease in the amide:phosphate ratio for all the deproteinizing agents (p < 0.05). CONCLUSIONS: Chemo-mechanical CRAs could effectively remove the organic phase of enamel and dentin smear layer. The papain enzyme-based gel Papacarie could improve the sealing performance of the self-etch adhesives to both enamel and dentin.

The combined effect of light-illuminating direction and enamel rod orientation on color adjustment at the enamel borders of composite restorations.

OBJECTIVES: To investigate the effect of light-illuminating direction (from composite or enamel side) on color adjustment at the coronal and cervical enamel borders in composite restorations. MATERIALS AND METHODS: Forty cylindrical holes (3.0-mm diameters) were prepared in bovine enamel disks (1.0-mm thickness). After application of a one-step self-etch adhesive, one of four resin composites (Estelite Asteria, EA; Estelite Pro, EP; Kalore, KA; Clearfil Majesty ES-2 Premium, MJ) was restored in the holes. After 24-h storage, the colors (L*, C*, or h* values) at the restored enamel disks over a black background were measured in a black box using a CIE XYZ camera, spotted with D65 standard illuminant either from coronal or cervical side at 45°/0° geometry. The color shifting rate was calculated at the coronal and cervical enamel borders of the composite restorations, and analyzed by three-way ANOVA with Dunnett's T3 and t test for post hoc analysis (p < 0.05). RESULTS: The light-illuminating directions significantly affected the L* shifting rate at the cervical enamel border in EP and MJ (p < 0.05), and the C* shifting rate at the coronal enamel border in EA, EP, and MJ (p < 0.05). CONCLUSIONS: The color appearance at the border of the composite restoration was influenced by the light-illuminating direction in conjunction with the enamel rod orientation in the coronal or cervical enamel border. CLINICAL RELEVANCE: The line-of-vision angle would affect the perception of color adaptation at the enamel borders in the composite restorations.

Stress distribution in tooth resin core build-ups with different post-end positions in alveolar bone level under two kinds of load directions.

This study aimed to evaluate influence of different post-end positions in alveolar bone level on stress distributions in resin-core build-up tooth under different load directions. Three-dimensional mathematical models of a root-filled mandibular premolar tooth were constructed. Resin post and core were built-up with six post lengths: 0, 1, 2, 3, 4, and 6 mm. Finite element analysis calculated stress distributions with oblique load of 400 N to buccal cusp 45 degree from buccal side or from lingual side. The 3 mm-post length (post-end position equal to cancellous bone level) caused highest equivalent stress of post-end compared with the shorter or longer post length. When change of load direction, the direction of maximum shear stress became completely opposite at mesiodistal cervical edge of core-part without a change of the magnitude. Changing shear stress direction would increase risk of debonding at mesiodistal cervical edge.

The influence of elastic moduli of core materials on shear stress distributions at the adhesive interface in resin built-up teeth.

This study aimed to investigate shear stress distributions in resin built-up teeth using resin composites of varying elastic moduli (E), with or without fiber posts. Three-dimensional mathematical models of a root-filled mandibular premolar tooth were constructed. Resin post and cores were built-up with resin composites of three different E: 12,000, 18,000 and 24,000 MPa, with or without fiber posts. Finite element linear analysis was performed to calculate shear stress distributions at bonding interface between resin core and dentin. Regardless of fiber post insertion, the shear stress on the cervical surface of resin core decreased as the E of resin composites increased. Insertion of fiber posts increased the shear stress on the post surface of resin core, with increases in the E of resin composites. In conclusion, using resin core materials with higher E decreased the shear stress at cervical interface between resin core and dentin regardless of fiber post insertion.

[Symmetrical bilateral epidural hematoma after head injury in the mid parietooccipital region: case report].

The authors presented a patient with acute symmetrical bilateral epidural hematomas, which are rare but life threatening. A 72-year-old male accidentally fell from the roof at a height of about 3 meters and hit his head against the ground. He was transferred to the emergency ward in our hospital. On admission, he was alert and had no neurological deficits. Skull X-ray film revealed a depressed fracture in the mid parietoocipital region and bilateral linear fractures extending from the parietal regions to the temporal regions. CT scan showed symmetrical bilateral epidural hematomas in the both parietotemporal regions. His consciousness deteriorated to be drowsiness about one hour after admission. An additional CT scan revealed enlargement of the both epidural hematomas and impending tentorial herniation. Therefore, an emergency operation was called for. For rapid decompression of the brain, bilateral craniotomies were carried out simultaneously by the two neurosurgeon-groups involved and bilateral epidural hematomas were also simultaneously removed. Injury of both of the middle meningeal arteries was revealed to be the cause of the bilateral epidural hematomas. Clinical course after operation was uneventful and the patient was discharged without any neurological deficit. Simultaneous bilateral craniotomies and removal of the epidural hematomas would have contributed to obtaining the good result in this patient.