A competing risk model for bond strength data analysis

Evaluating the advancements in a recently introduced universal adhesive compared to its predecessor

Background/purpose

The dental adhesive market is constantly evolving to meet the demands of dentists and patients, but new products and upgrades should be rigorously evaluated before being used in clinical practice. This study investigated the physicomechanical properties and dentin bonding efficacy of a newly upgraded universal adhesive compared to its predecessor.

Materials and methods

Twenty-four molars were divided into four groups (n = 6/group) based on adhesive (new vs. predecessor) and application mode [self-etch (SE) vs. etch-and-rinse (ER)] for evaluating their dentin microtensile bond strength (μTBS), failure pattern, and bonding interface. Additional thirty-six molars' crowns were perpendicularly sectioned to obtain flat mid-coronal dentin discs. The opposing dentin surfaces of each disc received contrasting treatments (new/predecessor adhesive applied in SE/ER mode), resulting in six interventions. The bonded discs (n = 6/intervention) were used to assess the adhesives' survival probability employing a double-sided μTBS test. The other physicomechanical properties examined were adhesives' oxygen inhibition layer (OIL), viscosity, hardness, elastic modulus, degree of conversion (DC), and in-situ DC.

Results

Both adhesive versions showed similar μTBS (P > 0.05), failure pattern (P > 0.05), and survival probability (P > 0.008). ER mode promoted resin tag formation and exhibited a slender adhesive layer for both adhesives. The newer adhesive version showed a thinner adhesive layer in general with narrower OIL (P < 0.001), less viscosity (P < 0.001), higher hardness (P < 0.05), elastic modulus (P < 0.05), DC (P < 0.001), and in-situ DC (P < 0.001).

Conclusion

While the newly updated adhesive had superior physicomechanical properties with more fluidity, its dentin bonding efficacy and survival probability were comparable to its predecessor.

Bond strength of bulk-fill resin composites

 Aim: Evaluating the resin-dentin bond strength of Class II conventional and bulk-fill composite restorations, using different cavity sizes before and after aging. Methods: Seventy-five human molars were distributed into groups according to the buccolingual width of the cavities, conservative (n=25) and extended (n=50). They were divided according to the restorative material: conventional (Z100/control group) or bulk-fill resin composites (Filtek Bulk Fill/FBF; Tetric N Ceram Bulk Fill/TNCBF; Filtek Bulk Fill Flow/FBFF; Surefill SDR flow/SDR). The restored teeth were sectioned on sticks (n=50 per restorative materials + width cavities group), half were stored in Water/Ethanol 75% for 30 days and the other half were submitted to the immediate microtensile bond strength (μTBS) test. Data were analyzed applying the Three-Way Analysis of Variance (ANOVA), Bonferroni test, test t, and Weibull analyses (p<0.05). Results: SDR and FBF presented lower μTBS values for extended preparation when compared to the conservative preparation, before aging. After aging, only for the FBFF, a decrease in the μTBS values was observed. Comparing the μTBS values, before and after aging, the SDR demonstrated lower μTBS values after aging when the conservative cavity was used. A decrease in the μTBS values was observed for the Z100, the FBF and, the FBFF, after aging, when the extended cavity was used. Conclusion: The effect of cavity preparation and aging on the resin-dentin of Class II is material dependent. Most of the bulk-fill resin composites evaluated presented a similar performance to the conventional resin composites for all the conditions of this study.

Novel predictive tools and therapeutic strategies for patients with initially diagnosed glottic cancer in the United States

OBJECTIVE

The objective of this study is to identify valuable prognostic factors, build clinical prediction nomograms, and recommend the optimal therapeutic strategy for patients with initially diagnosed glottic cancer.

METHODS

Patients were extracted from the SEER database. Cox regression analyses, survival analyses, an internal validation, the propensity score analysis, and the competing risk analysis were performed.

RESULTS

Nine overlapped factors were considered as valuable prognostic factors. Furthermore, nomograms were established for clinical prediction models to assess the 1-, 3-, and 5-year overall survival (OS) and cancer-specific survival (CSS). C-indexes, receiver operating characteristic curves, calibration curves, and decision curve analyses proved that nomograms showed better predictive accuracy, ability, and prognostic value compared to the American Joint Committee on Cancer stage. For patients in stage I, primary site surgery alone would acquire best OS and CSS. For patients in stage II, primary site surgery and/or radiation would gain better OS and CSS. For patients in stage III, radiation plus chemotherapy or primary site surgery (alone or plus radiation) would acquire better OS and CSS. Moreover, for patients in stage IV, primary site surgery plus radiation would gain better OS and CSS.

CONCLUSIONS

Nomograms could be useful for patients' counseling and guide therapeutic decision-making. Primary site surgery alone may likely be the optimal therapy for stage I glottic cancer, and primary site surgery and/or radiation may be the recommended therapy for stage II glottic cancer. The combination treatment would be the preferred choice for advanced-stage (stage III & IV) glottic cancer, and the role of chemotherapy needs to be further explored.

Influence of central and peripheral dentin on micro-tensile bond strength estimated using a competing risk model

The bonding performance of dental adhesives is most frequently evaluated using the micro-tensile bond strength (μTBS) test. Despite lacking evidence, peripheral specimens are often discarded to avoid regional variability. This study, therefore, examined whether μTBS to central and peripheral dentin differed. Dentin surfaces of extracted human molars were bonded with various self-etch adhesives, built up with a resin composite, cut into beams, and stressed in tension. Failure mode was classified as adhesive, cohesive in dentin, or other using scanning electron microscopy. Since cohesive failures in dentin were frequent and could confound μTBS results, the data from central/peripheral dentin were analyzed using a Weibull competing risk (CR) model distinguishing failure modes, and its outcomes were compared to a conventional failure mode non-distinguishing Weibull model. Based on the strength data of cohesively failed specimens, the CR model also estimated the strength of dentin. For comparison, the ultimate tensile strength (UTS) of dentin was measured in both regions. The conventional model suggested that peripheral μTBS was higher than central μTBS. Conversely, the CR model disclosed no significant difference in μTBS between the regions but indicated a higher strength of peripheral dentin. This finding was confirmed by UTS measurements, and further supported by the significantly higher incidence of cohesive failures in central dentin. Therefore, peripheral specimens can be used in the μTBS test as well as central ones, but a CR model should be used for statistical analysis if cohesive failures in dentin are frequent, as the strength of peripheral dentin is higher.