The reliability of standardized flexure strength testing procedures for a light-activated resin-based composite.

OBJECTIVES: To investigate the differences in the reliability of three-point flexure strength (TFS) and bi-axial flexure strength (BFS) data of a dental resin-based composite (RBC) irradiated by a hand-held or an oven light-curing unit (LCU). METHODS: Three-point bar-shaped (25 x 2 x 2 mm3) and bi-axial disc-shaped (12 mm diameter, 2 mm thick) specimens of Filtek Z250 were polymerized utilizing either a hand-held (n = 20) or an oven-LCU (n = 20). The mean TFS and BFS, associated Weibull moduli and degree of conversion (DC) for each curing regime were obtained following 24 h immersion in a light-proof water bath maintained at 37 +/-1 degrees C. RESULTS: A significant decrease in TFS (129 +/- 15 and 127 +/- 13 MPa) compared with BFS (140 +/- 12 and 148 +/- 13 MPa) was identified for specimens irradiated with both LCU types (P < 0.001). The Weibull moduli of TFS data associated with the hand-held--was significantly decreased compared with the oven-LCU since confidence intervals did not overlap (7.5-9.4 and 9.5-10.6, respectively). In contrast, the Weibull moduli of the BFS data associated with either LCU were not significant (11.3-12.4 and 11.3-13.5). A significant decrease in the DC of three-point and bi-axial flexure specimens irradiated with the hand-held compared with the oven-LCU was reported (P = 0.031). CONCLUSIONS: The improved experimental reliability combined with the increased clinical relevance in specimen geometry of disc-compared with bar-shaped specimens may advocate bi-axial flexure testing methodology as the standard to assess the strength of light-activated dental RBCs. The differences in extent of polymerization of RBC specimens cured with either LCU were not consistent with an equivalent dose of light energy density. This phenomenon may be attributed to differences in polymerization efficiency associated with the quantity of useful light energy emitted from the hand-held--compared with the oven-LCU.     

In vitro cuspal deflection and microleakage of maxillary premolars restored with novel low-shrink dental composites.

OBJECTIVES: The development of novel low-shrink resin-based composites (RBCs) may offer a potential reduction in polymerisation shrinkage stresses generated at the tooth/restoration interface compared with current methacrylate RBCs. In vitro cuspal deflection and microleakage of meiso-occlusal-distal (MOD) cavities restored with experimental oxirane and silorane (EXL596 and H1) and methacrylate (Z100 and Filtek Z250) RBCs were assessed. METHODS: Standardised pre-molar MOD cavities were prepared (n = 10) and restored with each material. The flexure of buccal and palatal cusps was recorded 0.1 h following irradiation utilising a differential transformer deflection gauge. Each restored tooth was subjected to a thermocycling regime and microleakage of tooth sections were assessed following 24 h immersion in 0.2% fuschin dye. The degree of conversion (DC) of each RBC material was also assessed using Fourier transform infrared (FTIR) spectroscopy following 0.1, 0.5, 1, 4, 24 and 48 h post-irradiation. RESULTS: A total cuspal deflection was observed for EXL596 (2.5 +/- 0.9 microm) and H1 (6.0 +/- 1.8 microm) compared with Z100 (20.0 +/- 4.7 microm) and Filtek Z250 (16.5 +/- 3.3 microm) following 0.1 h. The cavities restored with EXL596 displayed significantly higher microleakage than any other RBC and H1 exhibited non-significant and significantly decreased microleakage compared with Z100 and Filtek Z250, respectively. The DC of EXL596 and H1 was significantly decreased compared with Z100 and Filtek Z250 following 0.1, 0.5 and 1 h. SIGNIFICANCE: The 'living' polymerisation associated with the novel oxirane and silorane RBCs and the associated decrease in cuspal deflection may suggest a decrease in the magnitude of polymerisation shrinkage stress at the tooth/restoration interface. The decreased DC following 0.1 h of the oxirane compared with the methacrylate RBCs has provided information on the cure rate of cationic and free-radical polymerisation mechanisms, respectively. The inadequate marginal seal of cavities restored with EXL596 would preclude its use as a dental restorative. The reduction in cuspal deflection and decrease in microleakage of cavities restored with H1 compared with Filtek Z250 may be advantageous in terms of marginal integrity following placement. However, the non-significant difference in microleakage between the H1 and Z100 may only present modest decreases in the deleterious effects of shrinkage stress.     

Time-resolved simultaneous measurement of group index and physical thickness during photopolymerization of resin-based dental composite

Light-activated resin-based dental composites are increasingly replacing dental amalgam. However, these materials are limited by inefficient setting reactions as a function of depth that constrain the maximum extent of cure. Insufficient curing can contribute to an overall reduction in biocompatibility of the material. We demonstrate dynamic refractive index measurements of a commercial dental composite throughout cure using spectral domain low coherence interferometry. Our results show a linear relationship between the change in refractive index and polymerization-induced reduction in physical thickness during light-activated curing. This relationship between the optical and physical density demonstrates the potential of this technique as a unique noninvasive tool for measurement of the conversion degree of curing dental composite materials.     

The effect of surface preparation and luting agent on bond strength to a zirconium-based ceramic

OBJECTIVES: To investigate the bond strength of modern "self-adhesive" resin cements to a zirconium-based dental ceramic following different surface preparations and storage conditions. METHODS: The surface of zirconium-based ceramic discs (12 x 2 mm) were either left untreated, prepared using alumina grit-blasting or tribochemical treatment. Resin composite cylinders were bonded to ceramic specimens using Panavia-F, RelyX Unicem or Maxcem resin cements. The shear bond strength of specimens (n = 10) was tested "dry," following 24-hour water immersion or a thermocycling regime. RESULTS: For each surface preparation, a significant reduction in bond strength following 24-hour water immersion and thermocycling compared to "dry" storage conditions was identified for both Panavia-F and Maxcem. However, Unicem specimens exhibited statistically similar SBS values for tribochemically-treated specimens stored dry following 24-hour water immersion or thermocycling (11.7 +/- 1.3, 14.1 +/- 6.3 and 11.7 +/- 4.9 MPa, respectively) (p > 0.05). No significant differences in bond strength were identified for Panavia-F or Unicem specimens for any surface preparation following the thermocycling regime (p > 0.05). In contrast, for each surface preparation following thermocycling (p < 0.001), Maxcem exhibited a significant decrease in SBS compared with Panavia-F and Unicem specimens. CONCLUSIONS: The pre-treatment of a zirconium-based ceramic surface with grit-blasting and tribochemical treatment improves the bond strength of resin cements. Following "wet" storage conditions, Panavia-F and Unicem demonstrated superior bond strength compared with Maxcem. Differences in ceramic surface preparation and the chemistry of resin cements will affect the nature of the bonding mechanism and durability of the adhesive layer.     

Two year clinical evaluation of a low-shrink resin composite material in UK general dental practices

Objective

A novel resin composite system, Filtek Silorane (3M ESPE) with reduced polymerization shrinkage has recently been introduced. The resin contains an oxygen-containing ring molecule (‘oxirane’) and cures via a cationic ring-opening reaction rather than a linear chain reaction associated with conventional methacrylates and results in a volumetric shrinkage of ∼1%. The purpose of this study was to review the literature on a recently introduced resin composite material, Filtek Silorane, and evaluate the clinical outcome of restorations formed in this material.

Methods

Filtek Silorane restorations were placed where indicated in loadbearing situations in the posterior teeth of patients attending five UK dental practices. These were evaluated, after two years, using modified USPHS criteria.

Results

A total of 100 restorations, of mean age 25.7 months, in 64 patients, were examined, comprised of 30 Class I and 70 Class II. All restorations were found to be present and intact, there was no secondary caries. Ninety-seven per cent of the restorations were rated optimal for anatomic form, 84% were rated optimal for marginal integrity, 77% were rated optimal for marginal discoloration, 99% were rated optimal for color match, and 93%% of the restorations were rated optimal for surface quality. No restoration was awarded a “fail” grade. No staining of the restoration surfaces was recorded and no patients complained of post-operative sensitivity.

Significance

It is concluded that, within the limitations of the study, the two year assessment of 100 restorations placed in Filtek Silorane has indicated satisfactory clinical performance.     

Dental health of 9–10-year-old mentally retarded children in Eastern Finland

Abstract All 9–10-year-old children in one Finnish county were screened with a standardized set of tasks for their mental performance. 58 verified mentally retarded and 58 randomly selected healthy children were examined for dental and gingival status and level of oral hygiene Comparisons were made between the retarded and the healthy, as well as between subgroups of the retarded. Similar DFS-values, higher DS-values and an inferior level of oral hygiene in terms of VPI were found in mentally retarded when compared with healthy children. No evident difference was found in gingival status (by GBI) between the retarded and the healthy. The mildly or moderately retarded found by the screening and not yet included in special welfare had the highest DFS-scores, the highest prevalence of untreated caries and the poorest gingival health among the retarded.     

Activin inhibition limits early innate immune response in rat kidney allografts—a pilot study

Activins are members of the transforming growth factor‐beta (TGF‐β) superfamily of cytokines. They play critical roles in the onset of acute and chronic inflammatory responses. The aim of this study was to investigate how activin inhibition affects acute kidney injury and inflammation after transplantation. The study was carried out in kidney transplantation and renal ischemia‐reperfusion models in the rat. Soluble activin type 2 receptor (sActRIIB‐Fc) was used to inhibit activin signaling. Transplantation groups were as follows: (i) cyclosporine A (CsA) (ii) CsA + sActRIIB‐Fc, (iii) CsA+ inactive protein control Fc‐G1. IRI groups were as follows: (i) no treatment, (ii) sActRIIB‐Fc. Serum activin B concentration was significantly elevated after transplantation and IRI, whereas activin A was produced locally in renal allografts. Activin inhibition efficiently limited neutrophil, macrophage, and dendritic cell infiltration to the allografts measured 72 h after transplantation. In addition, sActRIIB‐Fc treatment modulated serum cytokine response after transplantation and reduced the early accumulation of fibroblasts in the graft interstitium. In conclusion activin inhibition reduces the innate immune response early after renal transplantation in the rat. It also limits the accumulation of fibroblasts in the graft suggesting that activins may be involved in the fibrogenic signaling already early after kidney transplantation.