Comparison of the bond strength of stainless steel orthodontic brackets bonded to crown porcelains.

BACKGROUND: The bond strengths and mode of failure of stainless steel orthodontic brackets bonded to the newer all-ceramic crown systems has not been fully investigated. OBJECTIVES: To compare the shear-peel bond strengths and modes of failure of stainless steel Begg orthodontic brackets bonded to all-ceramic crown systems (Finesse, Empress II) and a conventional feldsphatic crown porcelain (Vita Omega 900). METHODS: Fifteen flat-surface discs of three crown porcelains (Finesse, Vita Omega 900, Empress II) were made and mounted in acrylic moulds. The discs were pumiced, etched with phosphoric acid, primed with silane, and a flat stainless steel Begg bracket bonded to each disc with a chemical cure composite resin (Unite Bond). The discs were stored for one week in water and debonded with a sheer-peel load in an Instron uniaxial testing system with a crosshead speed of 0.5 mm/min. The composite remnants on the ceramic surfaces were classified using the Adhesive Remnant Index (ARI). RESULTS: The bond strength of Finesse (15.03 +/- 1.90 MPa) was significantly greater (p < 0.001) than Vita Omega 900 11.51 +/- 2.35 MPa) and Empress II (11.12 +/- 1.78 MPa). There were no significant differences among the ARI scores. The mode of failure was a mixture of adhesive and cohesive failure. CONCLUSION: The results indicate that the bond strengths of stainless steel orthodontic brackets bonded to Finesse and Empress II porcelains are clinically acceptable.

Interface of unloaded titanium implants in the iliac crest, fibula, and scapula: a histomorphometric and biomechanical study in the pig.

PURPOSE: Prefabrication of free vascularized fibular flaps is a 2-stage procedure for the reconstruction of maxillary and mandibular defects. The delay between prefabrication and flap transfer is 6 weeks and depends on biomechanical stability and osseointegration of the implants. The purpose of this animal study was to evaluate implant stability by measuring the removal torque values (RTVs) at 3, 6, and 12 weeks and to compare the results with interface strength of the bone-implant surface in the fibula, the scapula, and the iliac crest under unloaded conditions. MATERIALS AND METHODS: ITI implants (n = 108) with a sandblasted and acid-etched surface were placed in the fibula, the scapula, and the iliac crest of 6 Yorkshire pigs. Biomechanical, histologic, and histomorphometric results were collected at 3, 6, and 12 weeks, respectively. RESULTS: Bicortical anchored 8-mm implants in the fibula (63.7 to 101.8 Ncm) showed RTVs similar to those of monocortical anchored 12-mm implants in the scapula (62.3 to 99.7 Ncm). The RTVs of monocortical anchored 8-mm and 10-mm implants in the iliac crest (19.1 to 44.3 Ncm) and the scapula (27.2 to 55.3 Ncm) were significantly lower. The bone-to-implant contact in the fibula at 3, 6, and 12 weeks (35.2%, 44.4%, and 46.8%, respectively) was similar to that in the iliac crest (24.2%, 44.2%, and 52.5%, respectively), but significantly lower than in the scapula (63.7%, 73.8%, and 74.2%, respectively). DISCUSSION AND CONCLUSION: Bicortical anchorage determined implant stability in the fibula, whereas interfacial strength seemed to define stability in the scapula. The quality and type of bone determined the bone's response in terms of biomechanical press fit or biologic interface strength.

Measurement of Poisson's ratio of dental composite restorative materials.

The aim of this study was to determine the Poisson ratio of resin-based dental composites using a static tensile test method. Materials used in this investigation were from the same manufacturer (3M ESPE) and included microfill (A110), minifill (Z100 and Filtek Z250), polyacid-modified (F2000), and flowable (Filtek Flowable [FF]) composites. The Poisson ratio of the materials were determined after 1 week conditioning in water at 37 degrees C. The tensile test was performed with using a uniaxial testing system at crosshead speed of 0.5 mm/min. Data was analysed using one-way ANOVA/post-hoc Scheffe's test and Pearson's correlation test at significance level of 0.05. Mean Poisson's ratio (n=8) ranged from 0.302 to 0.393. The Poisson ratio of FF was significantly higher than all other composites evaluated, and the Poisson ratio of A110 was higher than Z100, Z250 and F2000. The Poisson ratio is higher for materials with lower filler volume fraction.

Comparative hardness and modulus of tooth-colored restoratives: a depth-sensing microindentation study.

The objective of this study was to compare the hardness and modulus of the continuum of direct tooth-colored restorative materials using a depth-sensing microindentation approach. The effects of thermal fatigue on mechanical properties were also evaluated. Six restorative materials representing the continuum were selected. They included an ormocer (Admira [AM], Voco), a giomer (Beautifil [BF], Shofu), a compomer (Dyract Extra [DE], Dentsply), a minifill composite (Esthet-X [EX], Dentsply), resin-modified (Fuji II LC [FL], GC) and highly viscous (Fuji IX [FN], GC) glass ionomer cements (GICs). Fourteen specimens (3 mm wide x 3 mm long x 2 mm deep) were made for each material. The specimens were randomly divided into two groups and treated as follows: Group A--stored in distilled water at 37 degrees C for 30 days; Group B--thermal cycled for 5000 cycles (35 degrees C [28s], 15 degrees C [2s], 35 degrees C [28s], 45 degrees C [2s]) and stored for 26.5 days. Hardness and modulus of the materials were determined using depth-sensing microindentation testing with the Instron MicroTester. Hardness was computed by dividing the peak load over the maximum projected contact area while modulus was calculated by analysis of the loading/unloading load-displacement (P-h) curves and the analytical model according to Oliver and Pharr (J. Mater. Res. 7 (1992) 1564). Results were analyzed using ANOVA/Scheffe's post hoc test and independent samples T-test (p<0.05). Hardness ranged 46.44-72.65 and 49.11-78.97 HV, while modulus ranged 7.86-12.78 and 8.12-13.13 GPa for Groups A and B, respectively. Although the ranking of mechanical properties were generally similar for both groups, disparities in statistical differences between materials were observed between Groups A and B for both hardness and modulus. For both groups, BF was significantly harder than DE, AM, FL and EX was significantly harder than FL. The modulus of FN was significantly greater than EX, DE, AM and FL was significantly stiffer than AM. With the exception of BF, no significant change in hardness and modulus was observed for all materials with thermocycling. The hardness and modulus of some glass ionomer-based/containing materials may be comparable or even superior to minifill and ormocer composites. Thermal fatigue should be considered when comparing mechanical properties between materials.