Barry K. Norling

Development of an antimicrobial resin—A pilot study

OBJECTIVES To demonstrate that silver nanoparticles (AgNPs) could be synthesized in situ in acrylic dental resins. METHODS Light-cure (LC; bisphenol A glycidyl methacrylate, tetraethyleneglycol dimethacrylate, bisphenol A ethoxylate dimethacrylate blend) and chemical-cure systems (CC; orthodontic denture resin) were used to synthesize AgNPs using different concentrations of Ag benzoate (AgBz). RESULTS Rockwell hardness for LC resins showed that resins could be cured with up to 0.15% AgBz, while the hardness of CC resins were unaffected in the concentrations tested. UV-Vis spectroscopy and transmission electron microscopy confirmed the presence of AgNPs in both LC and CC resins. Generally, CC resins had better distribution of and much smaller AgNPs as compared to LC resins overall. In some samples, especially in LC resins, nanoclusters were visible. An in vitro release study over four-weeks showed that CC resins released the most Ag(+) ions, with release detected in all samples. However, LC resins only released Ag(+) ions when AgBz concentration was greater than 0.1% (w/w). AgNP-loaded CC resins made with 0.2 and 0.5% (w/w) AgBz were tested for antibacterial activity in vitro against Streptococcus mutans, and results showed 52.4% and a 97.5% bacterial inhibition, respectively. Further work is now warranted to test mechanical properties and to optimize the initiator system to produce commercially useful dental and medical resins. SIGNIFICANCE Success in this work could lead to a series of antimicrobial medical and dental biomaterials that can prevent secondary caries and infection of implants.

Lifelong food restriction prevents senile osteopenia and hyperparathyroidism in F344 rats

Studies were carried out on male F344 rats to examine the influence of aging and life-prolonging food restriction on bone and circulating parathyroid hormone levels. In ad libitum fed animals, the weight, density and calcium content of the femur increased with age and achieved their peak levels by 12 months of age. These levels remained stable until about 24 months and by 27 months of age the ad libitum fed animals had lost appreciable amounts of bone. The maturation of the femurs of the animals maintained on 60% of the ad libitum food intake was delayed and their bones were lighter, less dense and contained less calcium than bones from ad libitum fed rats of corresponding ages. But at 6, 12 and 24 months of age, the femur strength to body weight ratios were very highly significantly greater (P less than 0.0001) for the restricted animals compared to the ad libitum fed controls. Circulating immunoreactive parathyroid hormone increased progressively with aging in the animals fed ad libitum and the animals that experienced bone loss at advanced age also had the highest level of the hormone. In contrast, in the food restricted animals aging was not associated with a marked increase in serum parathyroid hormone or with senile bone loss. The data are discussed in relation to the mechanism of the observed changes.

Thickness, strength, and plastic deformation of occlusal registration strips

T he selection of an appropriate occlusal registration strip enables the dentist to work with precision and provides valuable information on occlusion. There are significant differences in the thickness, strength, and plastic deformation of the various articulating papers and occlusal registration strips. The patient’s perception of occlusal thickness ranges from 12.5 to 100 prn.“‘j The thickness of an occlusal registration strip should be below the patient’s perception. The purpose of this study was to determine the thickness, strength, and plastic deformation of selected occlusal registration strips and to list those registration strips that meet desirable standards.

Evaluation of the bonding of three porcelain repair systems.

1. Fractured porcelain bars repaired with Fusion/Concise displayed significantly greater repair strength (p less than .05) than bars repaired with Den-Mat and Cervident. 2. Comparing mean strengths of all samples before and after repair with Fusion/Concise indicated that only 18% of the original strength was regained following repair. 3. The low repair strengths of the tested materials indicate that their use is a temporary clinical procedure.

The effect of nonionic surfactants on bubble entrapment in elastomeric impression materials

The incorporation of certain nonionic surfactants into silicone and polysulfide elastomers increases their wettability by gypsum products and consequently results in less bubble entrapment in poured casts. The choice of the most effective surfactant is critical and differs not only between types of elastomer, but also between brands of a single type. The beneficial effect of the optimal surfactant is not reduced by rinsing the impression prior to pouring. While the working time of silicone is increased by surfactant additions, that of polysulfide is essentially unaffected, as are the dimensional accuracies and permanent deformations of both materials.

Effect of Varying Fixture Width on Stress and Strain Distribution Associated with an Implant Stack System

&NA; The purpose of this investigation was to evaluate the dissipation of a force applied to an assembled stack of implant components. The stack consisted of a 10‐mm threaded implant, a screw‐retained abutment and a screw‐retained gold crown. The dissipation of force was analyzed in relation to varying the implant diameter with and without a concomitant change in abutment diameter. Two experimental groups were evaluated. The first group consisted of 25 titanium screw‐form implants (Implant Innovations, Inc.). These implants measured 10 mm in length and 3.25 mm, 3.75 mm, 4.0 mm, 5.0 mm, and 6.0 mm in diameter. The second group included 15 titanium screw‐form implants (Nobel Biocare, Inc.) measuring 10 mm in length and 3.75 mm, 4.0 mm, and 5.0 mm in diameter. All implants were embedded in standardized photoelastic resin blocks. Points of interest were marked on each block using standardized templates to ensure consistency. Implants were restored using system‐specific conical abutments and standardized single‐unit restorations. A strain gauge was affixed to each abut ment, and an eccentric load of 176 N was applied to the restoration. Periimplant stresses were measured using photoelastic analysis. Abutment strain was determined using an electronic strain indicator. Data were collated and compared using ANOVA and the Duncan multiple range statistical tests. When stress was analyzed at points on the resin‐implant interface or a fixed distance from the interface, stress tended to decrease from the 5‐mm‐wide implant to the 6‐mm‐wide implant. Stress in relation to the 3.25‐mm, 3.75‐mm, and 4.0‐mm implant was not as well defined, indicating the possibility that some deformation of implants was occurring. Increased abutment width resulted in decreased abutment strain. Therefore, using a wider abutment may be helpful in preventing preload reduction in clinical applications. This may reduce the incidence of loosening and fracture of abutment and restoration screws. (Implant Dent 2000;9: 310‐320)

An investigation of new metal framework design for metal ceramic restorations

STATEMENT OF PROBLEM Metal ceramic restorations have been implicated in the discoloration of associated gingival tissues. Attempts to remedy this by altering the design of the metal frameworks for such restorations may lead to unacceptable decreases in fracture resistance. PURPOSE This study evaluated a new metal framework design for metal-ceramic restorations. MATERIAL AND METHODS Twenty artificial crowns were fabricated with various degrees of facial metal reduction; 0, 1, 2, and 3 mm. The study was conducted in two parts. The first part evaluated changes in light transmission into adjacent root tissue. A light box was fabricated so sample crowns could be illuminated on a mounted natural tooth. The root of the tooth remained outside the light box, and the light transmitted through the crowns into root tissue was measured with a light meter. The second part of the study evaluated changes in fracture strength. The sample crowns were subjected to a vertical load until fracture with use of an Instron machine at a crosshead speed of 1 mm per minute. The load at fracture was recorded. RESULTS Results indicated a statistically significant increase in light transmission with 1 mm framework reduction or greater, and fracture strengths did not decrease with up to 1 mm of framework reduction. A 1 mm facial axial reduction of the metal framework may be indicated for anterior metal-ceramic restorations.

Quantification of leucite concentration using X-ray diffraction

OBJECTIVES This study sought to evaluate the efficacy of using an X-ray diffractometer for the determination of leucite in Finesse, Ceramco II, and IPS Empress porcelains. METHODS An internal standard, copper, was used. Two quantification methods are presented: (1) the generation of a calibration curve using peak height ratios; and (2) the generation of a calibration curve using peak area ratio. RESULTS The leucite concentration obtained from the peak height versus concentration calibration curve was observed to be statistically different from leucite concentration obtained from the peak area versus concentration calibration curve. Other information obtained from X-ray powder diffraction include the lattice parameters and volume of the unit leucite cell. SIGNIFICANCE The leucite contained in the dental porcelains (Finesse, Ceramco II, and Empress) has expanded a-lattice spacings and contracted c-lattice spacings relative to standard leucite. These changes in the lattice parameters resulted in a net expansion of the leucite cell volume.

The Effect of Surface Treatment of the Interfacial Surface on Fatigue-Related Microtensile Bond Strength of Milled Zirconia to Veneering Porcelain

PURPOSE The success of zirconia-reinforced all-ceramic crowns depends on the formation of a stable bond between the zirconia core and the veneering porcelain. The purpose of this study was to test the effects of liner application and airborne particle abrasion of a postsintered Y-TZP core on the bond strength between the zirconia core and veneering porcelain with or without cyclic loading. MATERIALS AND METHODS Kavo Everest® Y-TZP blank disks were sintered and divided into three treatment groups: airborne particle abrasion, IPS e.max® Ceram Zirliner application, or no surface treatment. The disks were then veneered with IPS e.max® ZirPress veneering porcelain. Half the veneered disks from each group were cyclically loaded. This created six experimental groups: three surface treatment groups cyclically loaded and three not loaded. The disks were then sectioned into microbars for microtensile bond strength (MTBS) testing (40 specimens per group). Specimens were luted to a fixture mount and loaded to failure using a universal testing machine (MTS Insight). The maximum force was measured and bond strength computed. Data were analyzed with a two-way ANOVA and Tukeys HSD test (α= 0.05). RESULTS Airborne particle abrasion significantly decreased MTBS values (p= 0.043), and ZirLiner application did not have a significant effect on MTBS values compared to control. Cyclic loading did not have a significant effect on MTBS values. The predominant failure mode in all groups was mixed. CONCLUSIONS Airborne particle abrasion of the interfacial surface of the Everest® Y-TZP core significantly decreased the MTBS to ZirPress veneering porcelain when compared to no interfacial surface treatment. Application of ZirLiner to the interfacial surface of the Everest® Y-TZP core did not significantly increase or decrease the MTBS to ZirPress veneering porcelain, compared to the other surface treatments. Cyclic loading did not affect bond strengths in any of the groups, regardless of surface treatment. Neither cyclic loading nor surface treatment affected the failure mode of the specimens.

Fracture strength of molars containing three surface amalgam restorations

L onservative amalgam preparations have been recommended over the past 25 years.‘-” In general, the more recent textbooks on operative dentistry have also stated that dental tissue should be conserved whenever possible.‘-’ Two studies have determined the axial load required to fracture teeth with varying widths of occlusal preparation.” * Mandibular molars with Class I preparations one-third greater than the intercuspal width were found to be significantly stronger than those with small restorations or no restoration at all.* Previous fracture studies dealt only with the effect of varying the widths of the occlusal preparation in molar teeth and the mesiocclusodistal preparation in premolar teeth.‘, p This article reports the effect of three surface amalgam restorations on the fracture strength of human mandibular molars.