Faculty Bibliography

AIM: There is little information considering the framework association between cast clasps and attachments. The aim of this study was to evaluate the retention strength of frameworks match circumferential clasps and extra resilient attachment cast in three different alloys (cobalt-chromium, nickel-chromium titanium and commercially pure titanium), using two undercut (0.25 and 0.75 mm) and considering different period of time (0, 1/2, 1, 2, 3, 4 and 5 years). METHODS: Using two metallic matrices, representing a partially edentulous mandibular right hemiarch with the first molar crown, canine root and without premolars, 60 frameworks were fabricated. Three groups (n = 20) of each metal were cast and each group was divided into two subgroups (n = 10), corresponding the molar undercut of 0.25 mm and 0.75 mm. The nylon male was positioned at the matrix and attached to the acrylic resin of the prosthetic base. The samples were subjected to an insertion and removal test under artificial saliva environment. RESULTS: The data were analyzed and compared with ANOVAs and Tukey's test at 95% of probability. The groups cast in cobaltchromium and nickel-chromium-titanium had the highest mean retention strength (5.58 N and 6.36 N respectively) without significant difference between them, but statistically different from the group cast in commercially pure titanium, which had the lowest mean retention strength in all the periods (3.46 N). The association frameworks using nickel-chromium- titanium and cobalt-chromium could be used with 0.25 mm and 0.75 mm of undercut, but the titanium samples seems to decrease the retention strength, mainly in the 0.75 mm undercut. The circumferential clasps cast in commercially pure titanium used in 0.75 mm undercuts have a potential risk of fractures, especially after the 2nd year of use. CONCLUSION: This in vitro study showed that the framework association between cast clasp and an extra resilient attachment are suitable to the three metals evaluated, but strongly suggest extra care with commercially pure titanium in undercut of 0.75 mm. CLINICAL SIGNIFICANCE: Frameworks fabricated in Cp Ti tend to decrease in retentive strength over time and have a potential risk of fracture in less than 0.75 mm of undercut.

BACKGROUND: Chemical modification of implant surface is typically associated with surface topographic alterations that may affect early osseointegration. This study investigates the effects of controlled surface alterations in early osseointegration in an animal model. METHODS: Five implant surfaces were evaluated: 1) alumina-blasting, 2) biologic blasting, 3) plasma, 4) microblasted resorbable blasting media (microblasted RBM), and 5) alumina-blasting/acid-etched (AB/AE). Surface topography was characterized by scanning electron microscopy and optical interferometry, and chemical assessment by x-ray photoelectron spectroscopy. The implants were placed in the radius of six dogs, remaining 2 and 4 weeks in vivo. After euthanization, specimens were torqued-to-interface failure and non-decalcified-processed for histomorphologic bone-implant contact, and bone area fraction-occupied evaluation. Statistical evaluation was performed by one-way analysis of variance (P <0.05) and post hoc testing by the Tukey test. RESULTS: The alumina-blasting surface presented the highest average surface roughness and mean root square of the surface values, the biologic blasting the lowest, and AB/AE an intermediate value. The remaining surfaces presented intermediate values between the biologic blasting and AB/AE. The x-ray photoelectron spectroscopy spectra revealed calcium and phosphorus for the biologic blasting and microblasted RBM surfaces, and the highest oxygen levels for the plasma, microblasted RBM, and AB/AE surfaces. Significantly higher torque was observed at 2 weeks for the microblasted RBM surface (P <0.04), but no differences existed between surfaces at 4 weeks (P >0.74). No significant differences in bone-implant contact and bone area fraction-occupied values were observed at 2 and 4 weeks. CONCLUSION: The five surfaces were osteoconductive and resulted in high degrees of osseointegration and biomechanical fixation.

OBJECTIVES: Etching resorbable blasting media (RM) processed implants is a common engineering procedure, but the interplay between the resulting physicochemical properties and its effects on early bone healing have not been thoroughly addressed. METHODS: Screw-root form implant surfaces were treated with 1 of 3 methods: grit (alumina) blasted/acid etching, RM, and RM + acid etching (RMAA). Surface topography (n = 3 each) was characterized by scanning electron microscopy and atomic force microscopy and chemical characterization by x-ray photoelectron spectroscopy analysis. The implants were placed at the distal femur of 16 rabbits, where 3 implants, 1 from each surface, were placed bilaterally remaining 4 and 8 weeks in vivo. After euthanization, one half of the specimens were torqued to interface failure at a rate of approximately 0.196 radians/min and the other half were nondecalcified processed for histomorphology and bone-to-implant contact evaluation. RESULTS: Physicochemical characterization showed that the grit (alumina) blasted/acid-etched surface was rougher than RM and RMAA. Higher levels of calcium and phosphorous were observed for the RM surface compared with the RMAA surface. No significant differences were observed in torque and bone-to-implant contact between surfaces at 4 or 8 weeks. Histomorphologic evaluation showed woven bone formation around all surfaces at 4 weeks, and its initial replacement by lamellar bone at 8 weeks. CONCLUSIONS: Despite differences in texture/chemistry, all implant surfaces were biocompatible and osseoconductive, and led to comparable in vivo bone fixation and measurable histomorphometric parameters.

BACKGROUND: The authors analyzed the in vitro and in vivo performance of lithium disilicate glass-ceramic (LDGC) restorations and yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) (that is, zirconium oxide) restorations with regard to reliability, clinical performance and abrasion resistance. METHODS: In the in vitro study, four authors subjected samples of LDGC, Y-TZP and metal-ceramic crowns to step-stress fatigue testing. Four investigators assessed the in vivo clinical performance of LDGC and zirconium oxide-based restorations at four and seven years, respectively. In addition, one author conducted a randomized, controlled clinical trial to analyze the volumetric loss of enamel and ceramic antagonist surfaces. RESULTS: The LDGC crowns exhibited the highest fatigue load-to-failure values in the in vitro analysis. The results of the in vivo assessment showed that the clinical performance of the LDGC restorations at four years was comparable to that of the zirconium oxide-based crowns at seven years. The results of the in vivo, randomized, controlled clinical trial showed that LDGC crowns were not only resistant to wear, but also were wear friendly to enamel antagonist surfaces. CONCLUSIONS: The LDGC crowns in the in vitro and in vivo studies exhibited high durability, and they were wear friendly to opposing natural dentition. CLINICAL IMPLICATIONS: LDGC and zirconium oxide-based crowns are a clinically acceptable means of treating teeth that require full-coverage restorations. In addition, LDGC materials exhibit excellent clinical performance, as well as demonstrate acceptable abrasion compatibility with the opposing natural dentition

Several all-ceramic systems have been developed in dentistry to meet the increased expectations of patients and dentists for highly aesthetic, biocompatible, and long-lasting restorations. However, early bulk fractures or chippings have led the research community to investigate the mechanical performance of the all-ceramic systems. This overview explores the current knowledge of monolithic and bilayer dental all-ceramic systems, addressing composition and processing mechanisms, laboratory and clinical performance, and possible future trends for all-ceramic materials

The objective of the present study was to assess the influence of various clinically relevant scenarios on the strain distribution in the biomechanical surrounding of five different dental implant macrogeometries. The biomechanical environment surrounding an implant, i.e., the cortical and trabecular bone, was modeled along with the implant. These models included two different values of the study parameters including loading conditions, trabecular bone elastic modulus, cortical/trabecular bone thickness ratio, and bone loss for five implant designs. Finite element analysis was conducted on the models and strain in the bones surrounding the implant was calculated. Bone volumes having strains in four different windows of 0-200 muepsilon, 200-1000 muepsilon, 1000-3000 muepsilon, and > 3000 muepsilon were measured and the effect of each biomechanical variable and their two-way interactions were statistically analyzed using the analysis of variance method. This study showed that all the parameters included in this study had an effect on the volume of bones in all strain windows, except the implant design, which affected only the 0-200 muepsilon and >3000 muepsilon windows. The two-way interaction results showed that interactions existed between implant design and bone loss, and loading condition, bone loss in the 200-1000 muepsilon window, and between implant design and loading condition in the 0-200 muepsilon window. Within the limitations of the present methodology, it can be concluded that although some unfavorable clinical scenarios demonstrated a higher volume of bone in deleterious strain levels, a tendency toward the biomechanical equilibrium was evidenced regardless of the implant design.

OBJECTIVES: This study evaluated the influence of oestrogen deficiency and its therapies on bone tissue around osseointegrated implants. METHODS: Implants were placed in 66 female rats tibiae. The animals were assigned into five groups: control (CTL), sham, ovariectomy (OVX), oestrogen (EST), and alendronate (ALE). While CTL was sacrificed 60 days after implant placement, other groups were subjected to ovariectomy or sham surgery according to group and euthanized after 90 days. Blood and urine samples were collected at sacrifice day for osteocalcin (OCN) and deoxypyridinoline (DPD) quantification. Densitometry of femur and lumbar vertebrae was performed in order to evaluate rats' skeletal impairment. Non-decalcified sections were referred to fluorescent and light microscopy for analyses of mineral apposition rate (MAR), eroded and osteoclastic surfaces, bone-to-implant contact (BIC), and bone area fraction occupancy (BAFO). RESULTS: Results from the OVX group showed significantly lower bone mineral density (BMD), BIC, BAFO, and MAR, while OCN, deoxipiridinoline, eroded surface and ostecoclastic surface were increased compared with the other groups of the study. ALE reduced OCN and DPD concentrations, MAR, osteoclastic and eroded surfaces, and no difference was in BIC and BAFO relative to SHAM. EST and CTL showed similar results to SHAM for measurements. CONCLUSIONS: Oestrogen deficiency exerted a negative influence on bone tissue around implants, while oestrogen replacement therapy and alendronate were effective against its effects. Although alendronate therapy maintained the quantity of bone around implants, studies evaluating bone turnover kinetics are warranted.

OBJECTIVE: This study tested the hypothesis that bond strength of total- and self-etching adhesive systems to dentine is not affected by the presence of remnants from either eugenol-containing (EC) or eugenol-free (EF) temporary cements after standardized cleaning procedures. METHODS: Thirty non-carious human third molars were polished flat to expose dentine surfaces. Provisional acrylic plates were fabricated and cemented either with EC, EF or no temporary cements. All specimens were incubated for 7 days in water at 37 degrees C. The restorations were then taken out and the remnants of temporary cements were mechanically removed with a dental instrument. The dentine surfaces were cleaned with pumice and treated with either total-etching (TE) or self-etching (SE) dental adhesive systems. Atomic force microscopy was used to examine the presence of remnants of temporary cements before and after dentine cleaning procedures. Composite resin build-ups were fabricated and cemented to the bonded dentine surfaces with a resin luting cement. The specimens were then sectioned to obtain 0.9mm(2) beams for microtensile bond strength testing. Fractographic analysis was performed by optical and scanning electron microscopy. RESULTS: ANOVA showed lower mean microtensile bond strength in groups of specimens treated with EC temporary cement than in groups treated with either no cement or an EF cement (p<0.05). Mean microtensile bond strength was lower in groups employing the SE rather than the TE adhesive system (p<0.001). SE samples were also more likely to fail during initial processing of the samples. There was no evidence of interaction between cement and adhesive system effects on tensile strength. Fractographic analysis indicated different primary failure modes for SE and TE bonding systems, at the dentine-adhesive interface and at the resin cement-resin composite interface, respectively. CONCLUSION: The use of eugenol-containing temporary cements prior to indirect bonding restorations reduce, to a statistically similar extent, the bond strength of both total- and self-etching adhesive systems to dentine

This study investigated the effect of laser treatment on the fatigue resistance of a 3.5-mm diameter implant with an internal trilobe connection. Twenty two implants were embedded into acrylic resin blocks. Half the specimens were used as control group, and the other half were laser treated circumferentially around the 1.5-mm polished collar with argon shielding. Implants were fatigue tested using a step-stress accelerated lifetime test in a servo-hydraulic test machine. Despite the trend pointing towards higher fatigue resistance of laser treated specimens versus controls, step-stress analysis did not determine significant differences in the fatigue lifetimes.

Abstract This article describes the evolution of a computer-aided design/computer-aided manufacturing (CAD/CAM) process where ceramic paste is deposited in a layer-by-layer sequence using a computer numerical control machine to build up core and fixed partial denture (FPD) structures (robocasting). Al(2)O(3) (alumina) or ZrO(2) (Y-TZP) are blended into a 0.8% aqueous solution of ammonium polyacrylate in a ratio of approximately 1:1 solid:liquid. A viscosifying agent, hydroxypropyl methylcellulose, is added to a concentration of 1% in the liquid phase, and then a counter polyelectrolyte is added to gel the slurry. There are two methods for robocasting crown structures (cores or FPD framework). One is for the core to be printed using zirconia ink without support materials, in which the stereolithography (STL) file is inverted (occlusal surface resting on a flat substrate) and built. The second method uses a fugitive material composed of carbon black codeposited with the ceramic material. During the sintering process, the carbon black is removed. There are two key challenges to successful printing of ceramic crowns by the robocasting technique. First is the development of suitable materials for printing, and second is the design of printing patterns for assembly of the complex geometry required for a dental restoration. Robocasting has room for improvement. Current development involves enhancing the automation of nozzle alignment for accurate support material deposition and better fidelity of the occlusal surface. An accompanying effort involves calculation of optimal support structures to yield the best geometric results and minimal material usage