Russell A. Giordano

Mechanical properties of dense polylactic acid structures fabricated by three dimensional printing

Polylactic acid (PLA) is a bioresorbable polymer that is used in a number of clinical situations. Complex shapes of PLA are commonly machined for bone fixation and reconstruction. Solid free from fabrication methods, such as 3D printing, can produce complex-shaped articles directly from a CAD model. This study reports on the mechanical properties of 3D-printed PLLA parts. 3D printing is a solid free-form fabrication process which produces components by ink-jet printing a binder into sequential powder layers. Test bars were fabricated from low and high molecular weight PLA powders with chloroform used as a binder. The binder printed per unit line length of the powder was varied to analyze the effects of printing conditions on mechanical and physical properties of the PLA bars. Furthermore, cold isostatic pressing was performed after printing to improve the mechanical properties of the printed bars. The maximum measured tensile strength for the low molecular weight PLLA (53 000) is 17.40 +/- 0.71 MPa and for high molecular weight PLLA (312 000) is 15.94 +/- 1.50 MPa.

Solid free-form fabrication of drug delivery devices

Three-dimensional printing (3DP) is used to create resorbable devices with complex concentration profiles within the device. 3DP is an example of a solid free-form fabrication method where both the macro- and microstructure of the device can be controlled since objects are built by addition of very small amounts of matter. Application of this novel technology for fabrication of polymeric drug delivery systems is described in this article. The drug concentration profile is first specified in a computer model of the device which is then built using the 3DP process. Complex drug delivery regimes can be created in this way, such as the release of multiple drugs or multiphasic release of a single drug. This study demonstrates several simple examples of such devices and several construction methods that can be used to control the release of the drugs. Two dyes are used as model drugs in a matrix of biocompatible polymers. The dye release rate and release time are controlled by either specifying the position of the dye within the device or by controlling the local composition and microstructure with the 3DP process. The mechanism of resorption can also be controlled by manipulating the composition and microstructure of the device during construction. Polyethylene oxide and polycaprolactone were selected as matrix materials and methylene blue and alizarin yellow were used as drug models. Devices with erosion and diffusion controls are described in this report. Spectrophotometric analysis of dye release yielded reproducible results.

Flexural strength of an infused ceramic, glass ceramic, and feldspathic porcelain

In-Ceram material is a relatively new all-ceramic restorative material with improved properties that require research. The clinical selection of restorative materials is based on a number of parameters such as esthetics, fit, and strength. This study determined the flexural strength of In-Ceram system components and compared the core material with conventional feldspathic ceramics and with Dicor all-ceramic restorative material. Four-point flexural strength values of bend bars of each ceramic were 18.39 +/- 5.00 MPa for In-Ceram sintered alumina, 76.53 +/- 15.23 MPa for In-Ceram infusion glass, and 236.15 +/- 21.94 MPa for In-Ceram infused alumina core. Flexural strength of self-glazed feldspathic porcelain was 69.74 +/- 5.47 MPa, as-cast Dicor ceramic 71.48 +/- 7.17 MPa, and polished Dicor ceramic was 107.78 +/- 8.45 MPa.

The effect of hydrofluoric acid surface treatment and bond strength of a zirconia veneering ceramic

STATEMENT OF PROBLEM Clinicians are frequently faced with a challenge in selecting materials for adjacent restorations, particularly when one tooth requires a zirconia-based restoration and the next requires a veneer. While it may be desirable to use the same veneering ceramic on adjacent teeth, little information is available about the use of veneering ceramics over a zirconia-based material. PURPOSE The purpose of this study was threefold: (1) to study the influence of hydrofluoric acid-etched treatment on the surface topography of the zirconia veneering ceramic, (2) to test the bond strength of zirconia veneering ceramic to enamel, and (3) to evaluate the flexural strength and the elemental composition of ceramic veneers. MATERIAL AND METHODS Three zirconia veneering ceramics (Cerabien CZR (CZ), Lava Ceram (L), and Zirox (Z)) and 4 conventional veneering ceramics (Creation (C), IPS d.Sign (D), Noritake EX-3 (E), and Reflex (R)) were evaluated. Twenty ceramic bars of each material were fabricated and surface treated with hydrofluoric acid according to the manufacturers recommendations. Ten specimens from each group of materials were examined with a profilometer, and a sample of this group was selected for quantitative evaluation using a scanning electron microscope (SEM). Another 10 acid-etched specimens from each group of materials were treated with silane prior to cementing with resin cement (Variolink II) on enamel surfaces. These luted specimens were loaded to failure in a universal testing machine in the shear mode with a crosshead speed of 0.05 mm/min. The data were analyzed with a 1-way ANOVA, followed by Tukeys HSD test (alpha=.05). An additional 10 ceramic bars from each material group were fabricated to evaluate flexural strength and elemental composition. The flexural strength (MPa) of each specimen was determined by using a 4-point-1/4-point flexure test. A Weibull statistic tested the reliability of the strength data; pairwise differences among the 7 groups were evaluated at confidence intervals of 95%. The chemical composition of each bar was determined by energy dispersive spectroscopy (EDS). RESULTS There was a significant difference in the surface roughness in all testing groups. Conventional veneering ceramics (groups C and R) had a mean surface roughness higher than the groups of zirconia veneering ceramics (P<.001). Group D showed no difference in surface roughness compared with the groups of zirconia veneering ceramics. The SEM micrographs revealed differences in the acid-etched surfaces of ceramics. Zirconia veneering ceramics were smooth, with some groove formations, while conventional veneering ceramics had an amorphous, spongy-like structure with numerous microporosites. The mean bond strength (SD) of zirconia veneering ceramics to enamel revealed a significant difference. Group R (25.16 (3.40) MPa) followed by group C (22.51 (2.82) MPa) had significantly higher mean bond strength than the groups of zirconia veneering ceramics (P<.001, P=.009 respectively). Groups D (16.54 (2.73) MPa) and E (17.92 (3.39) MPa) showed no differences. Only group L (9.45 (1.62) MPa) exhibited significantly lower mean bond strength when compared with conventional veneering ceramics (P<.001). For flexural strength, only 1 group, group CZ, had a significantly lower flexural strength than all other groups (P<.001). CONCLUSIONS Effective ceramic interface management, such as acid etching and enamel bonding, is essential for successful ceramic laminate veneer restorations. Not all zirconia veneering ceramics display the same quality of surface roughness after hydrofluoric acid etching and the same bond strength to enamel when used as laminate veneer materials.

Flexural strength of feldspathic porcelain treated with ion exchange, overglaze, and polishing

Feldspathic porcelains, which are used in the construction of porcelain-fused-to-metal (PFM) restorations, have an inherent weakness because of their brittle nature and processing flaws. A relatively new product, the Tuf-Coat ion exchange system, claims to substantially strengthen feldspathic porcelains. This study compared the strengthening effect of the Tuf-Coat system with that of surface treatments such as overglazing, polishing, and finishing. Bend bars of Vita VMK 68 porcelain were made and randomly assigned to eight different surface treatment groups to examine these effects. The flexural strengths revealed that although Tuf-Coat treatment strengthened the porcelain, it was not significantly different from overglazing, and the strengthening effect was lost if the porcelain was subsequently self-glazed or finished.

Effects of acid hydrolysis and mechanical polishing on surface residual stresses of low-fusing dental ceramics

STATEMENT OF PROBLEM Cracks may arise in a ceramic restorative material over time, resulting in sudden fractures at stresses well below the yield stress. PURPOSE This study evaluated by means of indentation technique the effects of acid hydrolysis and mechanical polishing on the surface residual stresses of low-fusing ceramic materials. MATERIAL AND METHODS A total of 64 ceramic bars were formed to produce 4 groups of 16 bars each for 4 ceramic materials (Duceram-LFC Dentin, Duceram-LFC Enamel, Finesse Dentin, and Finesse Enamel). Four surface-treatment groups (n=4) were then formed for each of the 4 materials. The 4 surface treatments were control (autoglaze), hydrolysis, glaze/polish, and polish/glaze. A Vickers indenter contacted the Duceram-LFC specimens with a 5-N load and the Finesse specimens with a 3-N load for 10 seconds. Scanning electron microscope (SEM) was used to study surface texture before and after hydrolysis and polishing. Differences in mean crack lengths were analyzed with 1-way analysis of variance and least significant difference test (alpha=.05.) RESULTS SEM showed obvious surface flaws as a result of hydrolysis on Duceram-LFC Enamel and Dentin specimens. However, statistical analysis of the resulting crack lengths revealed no significant differences between values for the control groups (58.16 +/- 3.88) (53.53 +/- 2.67) and hydrolysis groups (57.11 +/- 4.09) (54.54 +/- 3.15) for Enamel (P=.081) and Dentin (P=.093) respectively. When comparing polished groups and nonpolished groups, the mean crack lengths were significantly shorter for polished specimens of Duceram-LFC Enamel (53.76 +/- 3.17), Finesse Enamel (40.56 +/- 3.31), and Finesse Dentin (39.76 +/- 3.81) porcelains compared with their control groups (58.16 +/- 3.88) (43.54 +/- 4.12) (41.19 +/- 3.47), respectively (P<.0001). The mean crack lengths were significantly longer for polished specimens of Duceram-LFC Dentin (59.16 +/- 3.52) porcelain compared with the control group (53.53 +/- 2.67) (P<.0001). CONCLUSION Within the limitations of this study, hydrolysis did not improve surface residual stresses of Duceram-LFC and Finesse ceramic materials. Mechanical polishing improved surface residual stresses of all materials tested, except Duceram-LFC Dentin porcelain.

Dimensional and formation analysis of a restorative ceramic and how it works

In-Ceram ceramic appears to use conventional powder/liquid processing techniques to form the coping substructure; however, the process results in a near net-shape restoration with minimal sintering shrinkage. Scanning electron microscopy, Brunauer-Emmett-Teller analysis, particle size classification, and linear dimensional changes during sintering were used to analyze In-Ceram ceramic. In-Ceram ceramic had a minimal linear shrinkage of 0.21% after the sintering of the alumina powder. This shrinkage can be readily compensated for by the expansion of conventional gypsum products and should result in acceptable clinical fits for In-Ceram ceramic restorations. Theories and explanations were described to account for the near net-shape and high strength of In-Ceram. Continuous interpenetrating phase composite technologies were used to create a substantial increase in strength. Future applications of this technology are encouraging.

The effect of different powder particle size on mechanical properties of sintered alumina, resin‐ and glass‐infused alumina

In this study, the compaction and sintering behavior of fine alumina powders of different particle sizes and the effect of matrix particle size on biaxial strength and fracture toughness of infused matrices were investigated. Three different alumina powders, In-Ceram alumina, A16SG, and RC172 were selected, representing a range of particle size and shape. RC172 and A16SG were dry-pressed. In-Ceram alumina was slip-cast following manufacturers recommendations. Dry-pressed ceramic blocks were sectioned into disks with a thickness of 1.5-mm. Uninfused disks were sintered at four temperatures between 1250 degrees C and 1400 degrees C. For glass or resin infused specimens, alumina disks were sintered at 1250 degrees C for 2 h and separated into two groups for glass infusion and resin (UDMA/TEGDMA) infusion. Disks were tested for biaxial flexural strength with a universal testing machine (Instron) at 0.5-mm/min crosshead speeds. One-way ANOVA and Duncans multiple range tests revealed that alumina disks with different smaller particle sizes have significantly higher biaxial strength (p < 0.05). The strength of the alumina matrix was greatly increased by glass and resin infusion. The biaxial strength of resin-infused alumina increased as particle size decreased, whereas strength of glass-infused alumina was constant.

The Use of Light/Chemically Hardened Polymethylmethacrylate, Polyhydroxyethylmethacrylate, and Calcium Hydroxide Graft Material in Combination With Polyanhydride Around Implants in Minipigs: Part I: Immediate Stability and Function

BACKGROUND The present study is designed as a proof-of-concept study to evaluate light/chemical hardening technology and a newly formulated polymethylmethacrylate, polyhydroxyethylmethacrylate, and calcium hydroxide (PPCH) plus polyanhydride (PA) (PPCH-PA) composite graft material as a bone substitute compared to positive and negative controls in a minipig model. METHODS PPCH-PA (composite graft); PPCH alone (positive control), PA alone (positive control), and no graft (negative control) were compared. Four mandibular premolar teeth per quadrant were extracted; a total of 48 implants were placed into sockets in three minipigs. Abutments were placed protruding into the oral cavity 4 mm in height for immediate loading. Crestal areas and intrabony spaces were filled with PPCH-PA, PPCH, or PA using a three-phase delivery system in which all graft materials were hardened by a light cure. In the negative control group, implant sites were left untreated. At 12 weeks, block sections containing implants were obtained. Evaluations included periodontal probing, pullout-force load, and stability measurements to determine implant stability, radiographs to examine bone levels, and scanning electron microscopy (SEM)-energy-dispersed spectroscopy to determine bone-to-implant contact. RESULTS Probing measurements did not reveal any pathologic pocket formation or bone loss. Radiographs revealed that immediate implant placement and loading resulted in bone at or slightly apical to the first thread of the implant in all groups at 12 weeks. Stability test values showed a relative clinical stability for all implants (range: -7 to +1); however, implants augmented with PPCH-PA exhibited a statistically significantly greater stability compared to all other groups (P <0.05). The newly formed bone in PPCH-PA-treated sites was well organized with less marrow spaces and well-distributed osteocytes. SEM revealed a tighter implant-socket interface in the PPCH-PA group compared to other groups with reduced microfissures and implant-bone interface fractures during pullout testing, whereas implants treated with PA or no graft showed ≈ 10-μm microfissures between the implant and bone with fractures of the intrathread bone. CONCLUSIONS The newly formulated chemically hardened graft material PPCH-PA was useful in immediate implant placement after tooth extraction and resulted in greater stability and a well-organized implant-bone interface with immediate loading, especially in those areas where cancellous bone was present. The results of this proof-of-concept study warranted further research investigating different healing times and longer durations.

Torsional strength of computer-aided design/computer-aided manufacturing–fabricated esthetic orthodontic brackets

OBJECTIVE To fabricate orthodontic brackets from esthetic materials and determine their fracture resistance during archwire torsion. MATERIALS AND METHODS Computer-aided design/computer-aided manufacturing technology (Cerec inLab, Sirona) was used to mill brackets with a 0.018 × 0.025-inch slot. Materials used were Paradigm MZ100 and Lava Ultimate resin composite (3M ESPE), Mark II feldspathic porcelain (Vita Zahnfabrik), and In-Ceram YZ zirconia (Vita Zahnfabrik). Ten brackets of each material were subjected to torque by a 0.018 × 0.025-inch stainless steel archwire (G&H) using a specially designed apparatus. The average moments and degrees of torsion necessary to fracture the brackets were determined and compared with those of commercially available alumina brackets, Mystique MB (Dentsply GAC). RESULTS The YZ brackets were statistically significantly stronger than any other tested material in their resistance to torsion (P < .05). The mean torques at failure ranged from 3467 g.mm for Mark II to 11,902 g.mm for YZ. The mean torsion angles at failure ranged from 15.3° to 40.9°. CONCLUSION Zirconia had the highest torsional strength among the tested esthetic brackets. Resistance of MZ100 and Lava Ultimate composite resin brackets to archwire torsion was comparable to commercially available alumina ceramic brackets.