Failure analysis and survival rate of post and core restorations under cyclic loading.

AIM: To investigate in a laboratory setting the influence of (i) post material (ii) preparation design and (iii) luting agent on the survival probability of root filled teeth, restored with all-ceramic restorations. METHODOLOGY: The crowns of 80 extracted single-rooted human teeth were removed, and root canal treatment was performed including canal filling with Gutta-percha without sealer (crown-down-pressureless technique). The root fillings were removed and the root canal enlarged with a reamer up to size 110. Prefabricated zirconia (CeraPost) or glass-fibre-reinforced posts (DentinPost) were luted using either Ketac Cem or Panavia F 2.0. A core build-up was applied (Clearfil Photocore), and the teeth were prepared with or without a 2-mm ferrule design (n=10 per experimental group). The prepared teeth were scanned (Cerec 3D) and crowns fabricated. After luting of the crowns (Ketac Cem), teeth were subjected to thermocycling (×4000, 5-55 °C) and cyclic loading (1.5 million cycles, 90 N). After load cycling, the teeth were immersed in methyleneblue solution for 24 h and subsequently sectioned in three segments for a dye penetration test. Kaplan-Meyer analysis was performed to assess the survival probability followed by a Cox regression analysis (α=5%). RESULTS: Teeth prepared using the ferrule design as well as the teeth with DentinPosts exhibited a significantly higher survival probability (P<0.05). The luting agent was of minor importance (P>0.05). Most common failure was debonding of posts (CeraPost) and post fracture (DentinPost). The majority of the teeth showed dye penetration after cyclic loading. CONCLUSIONS: Post material and ferrule design were of paramount importance regarding the survival probability of the post and core restorations using pre-fabricated posts. DentinPosts showed superior results versus CeraPosts.

Surfactant release from hydrophilized vinylpolysiloxanes.

Vinylpolysiloxane impression materials (VPS) exhibit an apolar (hydrophobic) backbone chemistry. Hence, surfactants are added to improve their hydrophilicity for impression-taking in moist environments. However, the mechanisms at the liquid-VPS-interface regarding the surfactant are unknown. We hypothesized that surfactant is leached from the VPS. Four experimental VPS formulations were fabricated containing 0 (control), 1.5, 3, and 5 wt% non-ionic surfactant. Samples were prepared (n = 6) and contact angles determined 30 min after mixing. After 60 sec, droplets were transferred onto the control. Mass spectrometry was used to analyze the droplets. Contact angles were inversely correlated with the surfactant concentration (p < 0.05). Droplets transferred from hydrophilized specimens onto the control showed similar contact angles. Surfactant could be clearly identified inside the droplets from the hydrophilized samples, however, not inside the control. Surfactants reduced the surface tension of the liquid in contact and did not change the surface properties of the VPS itself.

Repairability of cross-linked biopolymers.

Repair of biopolymers is a critical issue, especially with aged restorations. Obtaining a chemical bond to the repair surface might solve this problem. We hypothesized that certain repair liquids are suitable to establish a strong bond to an artificially aged dimethacrylate-based biopolymer for temporary restorations. Specimens made of a self-curing temporary crown-and-bridge material were prepared and thermocycled for 7 days (5000x, 5-55 degrees C). Cylinders made of light-curing composites (n=10) were bonded onto the specimen surface, either after grinding or after the application of 4 different experimental repair liquids (Bis-GMA:TEGDMA mixture=bonding, methylmethacrylate=MMA, bonding & acetone, bonding & MMA). A shear bond strength test was performed 24 hrs after repair. The highest bond strength was obtained with the bonding & acetone liquid (20.1+/-2.2 MPa). The use of MMA significantly affected the bond strength (6.8+/-1.9 MPa). MMA is inadequate as a repair liquid on aged composite-based biopolymers.

Two-year evaluation of restorations of a packable composite placed in UK general dental practices.

OBJECTIVE: The aim of this study was to assess the clinical performance at two years of 100 Solitaire 2 restorations placed in five United Kingdom dental practices by members of a practice-based research group. METHOD AND MATERIALS: Restorations were assessed after two years by a trained evaluator and the dental practitioner who had placed the material, for anatomic form, marginal adaptation, surface roughness, gingival condition and the presence or absence of secondary caries. In addition, the patients completed a questionnaire requesting details of the comfort and performance of the Solitaire 2 restoration(s). RESULTS: A total of 88 (58 Class II and 30 Class I) restorations of Solitaire 2 placed in 49 patients (mean age 43 years) were assessed. Twelve restorations could not be evaluated because of patient unavailability for the dates of the examinations. Two Class II restorations (2%) had failed by the time of the two-year evaluation and the remaining 86 restorations were found to be intact with no secondary caries. A high percentage of optimal scores were recorded for anatomic form and surface roughness. The colour match of two restorations (2%) was recorded as an obvious mismatch, but otherwise no unacceptable scores were recorded. CONCLUSIONS: After two years of clinical service a high proportion (96%) of the Solitaire 2 restorations that were available for re-examination, placed in general dental practice settings, were found to be performing satisfactorily.

Rewetting strategies for bonding to dry dentin with an acetone-based adhesive.

PURPOSE: The objective of this study was to investigate the effect of rewetting agents on bonding to etched and air-dried dentin. MATERIALS AND METHODS: For shear bond strength testing (SBS), the proximal surfaces of 90 molars were ground on wet SiC paper to prepare them for resin composite bonding with Gluma One Bond (Heraeus Kulzer, Germany). Dentin cavities were cut (Ø 3.5 mm, 1.5 mm deep) in 60 molars and restored with Gluma One Bond/Charisma for evaluation of the marginal performance (MGW). The adhesive was applied on acid-etched and rinsed dentin after the following pretreatment techniques: A: moist; B: 15 s air dried; C through F: 15 s air dried, followed by 30 s rewetting with C: water; D: 35% HEMA; E: Gluma Primer; F: 5% glutardialdehyde; G through J: as C through F, but followed by 15 s air drying. SBS data were analyzed with ANOVA and Tukey's test, and MGW with Kruskal-Wallis and Mann-Whitney U-test (alpha = 0.05). RESULTS: Shear bond strengths of groups A and B were 20.3 and 1.1 MPa, respectively. The Tukey ranking of SBS results was [A=C=D=E] > [C=D=E] > [C=D=I] > H > [F=J] > [B=G]. Groups A, C, D, E, H, and I with 3 or 4 gap-free restorations each showed no differences in MGW (p > 0.05). In contrast, no gap-free specimens were found in groups B, F, G, or J, and marginal gaps were significantly larger (p < 0.05). CONCLUSION: Rewetting of dried dentin with water, 35% HEMA, or Gluma Primer resulted in effective bonding. Excessive drying after rewetting had no compromising effect on adhesion in the HEMA- and GLUMA-primed groups, whereas the water and glutardialdehyde-treated groups showed poor bonding.

Practitioner variability effects on dentin bonding with an acetone-based one-bottle adhesive.

PURPOSE: The objective of this study was to investigate the effect of operator variability on the marginal performance of resin composite restorations bonded with an acetone-base one-bottle adhesive in standardized dentin preparations. MATERIALS AND METHODS: Five general practitioners were recruited for this trial. In the first group, each dentist received six extracted human teeth with dentin preparations (Ø 3.5 mm, 1.5 mm deep), cut in flatground proximal dentin, and original packages of Gluma One Bond adhesive and Charisma resin composite (Heraeus-Kulzer, Werheim, Germany) including instructions for use. For the second group, the operators were orally instructed, emphasizing the importance of the moist technique, before they received another six teeth for restoration with the same materials. Finally, a third group of six preparations was restored in order to evaluate a possible training effect. The restored teeth were stored in a hygrophor prior to removal of excess material and microscopic determination of the maximum marginal gap width (MGW). Statistical analyses were performed with the Kruskal-Wallis and Wilcoxon tests at p < 0.05. RESULTS: Apart from two samples, preparation margins in the first test group showed gaps between 1 and 12 microns. In the second and third groups, 15 and 16 restorations were gap free, respectively. Significant interoperator variation was found in the first group only. Marginal performance of group 1 restorations was significantly inferior to groups 2 and 3, which were not different (p = 0.79). CONCLUSION: Application of the one-bottle adhesive is technique-sensitive and requires meticulous attention to the instructions.