Long-Term Bonding Efficacy of CAD/CAM Hybrid Restorative Materials and Universal Adhesives

OBJECTIVES

In-office and lab milled prostheses are the staple for indirect restorations. It is therefore critical to determine their long-term bonding durability.

METHODS

CAD/ CAM blocks of two classes of restorative materials: 1) a nano-ceramic reinforced polymer matrix (NCPM) and, 2) a polymer-infiltrated ceramic network (PICN) were bonded using four different universal adhesives (UA) and silane systems. A lithium disilicate glassceramic (LDS) was used as a reference. The blocks were bisected and bonded with different UA/resin-cement pairs. Bonded blocks were then cut into 1.0x1.0x12.0 mm bar specimens for microtensile bond testing. Half the bars were subjected to bond strength testing immediately and the other half after aging by 50,000 thermal cycles between 5°C and 55°C. ANOVA and post-hoc tests were used to compare mean bond strength among groups.

RESULTS

NCPM presented consistently high bond strength regardless of bonding techniques, while the bond strength of PICN and LDS were lower when bonded with UA relative to traditional silanes. The more hydrophilic UA produced higher bond strengths.

DISCUSSION

Glass-ceramics exhibited lower bond strength with UA than the conventional etch-rinse-silane techniques. However, UAs preserved bonding interface in the long-term.

SIGNIFICANCE

NCPM displayed superior bond strength relative to PICN and LDS regardless of the type of adhesives and bonding techniques.

Endodontic Access Effect on Full Contour Zirconia and Lithium Disilicate Failure Resistance

Objectives:

To evaluate the effect of endodontic access on the failure load resistance of both adhesively and conventionally luted, full-contour monolithic yttria-stabilized zirconium dioxide (Y-TZP) and adhesively luted lithium disilicate (LD) crowns cemented on prepared teeth.

Methods and Materials:

Seventy-two human maxillary molars were prepared per respective guidelines for all-ceramic crowns with one group (n=24) restored with LD and the other (n=48) receiving Y-TZP crowns. Preparations were scanned using computer-aided design/computer-aided milling (CAD/CAM) technology, and milled crowns were sintered following manufacturer recommendations. All LD crowns and half (n=24) of the Y-TZP crowns were adhesively cemented, while the remaining Y-TZP specimens were luted using a conventional glass ionomer cement (GIC). One LD group, one Y-TZP adhesive group, and one GIC-luted group (all n=12) then received endodontic access preparations by a board-certified endodontist: the pulp chambers were restored with a dual-cure, two-step, self-etch adhesive and a dual-cure resin composite core material. The access preparations were restored using a nano-hybrid resin composite after appropriate ceramic margin surface preparation. After 24 hours, all specimens were loaded axially until failure; mean failure loads were analyzed using Mann-Whitney U test (α=0.05)

Results:

Endodontic access did not significantly reduce the failure load of adhesively luted LD or Y-TZP crowns, but Y-TZP crowns with GIC cementation demonstrated significantly less failure load.

Conclusions:

These initial findings suggest that endodontic access preparation may not significantly affect failure load resistance of adhesively luted Y-TZP and LD crowns. Definitive recommendations cannot be proposed until fatigue testing and coronal seal evaluations have been accomplished.

Linear Coefficient of Thermal Expansion Evaluation of Glass Ionomer and Resin-Modified Glass Ionomer Restorative Materials

OBJECTIVE

The purpose of this evaluation was to evaluate the linear coefficient of thermal expansion (LCTE) of 12 conventional glass ionomer (GIC) and four resin-modified glass ionomer (RMGI) restorative materials.

METHODS

GIC and RMGI specimens (2 mm × 5 mm × 5 mm) were fabricated (n=12) following manufacturer instructions and were placed in 0.2M phosphate-buffered saline and stored at 37°C and 98% humidity for one week. Specimens had LCTE determined with a thermomechanical analysis (TMA) unit using a 15°C-50°C heating cycle as well as a 50°C-15°C cooling cycle at a 5°C/min rate, using a 3-mm ball-point probe under 0.02 N probe pressure with all specimens kept saturated with PBS using a specially designed quartz container. Each specimen was tested three times, with the mean representing the specimen LCTE. Mean results between specimen heating and cooling were compared with paired Wilcoxon sign rank test, while results between materials were compared with Kruskal-Wallis/Dunn's ( α=0.05).

RESULTS

GIC LCTE ranged from approximately 5°C to 20°C ppm °K^-1, while the RMGI LCTE ranged from approximately 25°C to 47°C ppm °K^-1. With some exception, the LCTE during cooling displayed a greater trend.

SIGNIFICANCE

Under moisture conditions similar to the oral cavity, GIC materials overall had LCTE values closer to that reported for tooth structure. RMGI materials displayed higher values, which was thought to be related to the amount of resin in the matrix. A generally greater LCTE trend with cooling for all materials was noted, but the small magnitude of the difference is presently thought to be of minor clinical significance.

Production of class A biosolids with anoxic low dose alkaline treatment and odor management

The feasibility of full-scale anoxic disinfection of dewatered and digested sludge from Winnipeg, Manitoba with low lime doses and lagoon fly ash was investigated to determine if a class A product could be produced. Lime doses of 50 g, 100 g, and 200 g per kg of biosolids (dry) were used along with fly ash doses of 500 g, 1,000 g, and 1,500 g per kg of biosolids (dry). The mixed product was buried in eight-10 cubic metre trenches at the West End Water Pollution Control Center in Winnipeg. The trenches were backfilled with dirt and trapped to simulate anoxic conditions. Sampling cages were packed with the mixed product and pathogens non-indigenous to Winnipeg's biosolids. The cages were buried amongst the mixed biosolids in the trench. The non-indigenous pathogens spiked in the laboratory were the helminth Ascaris suum and the enteric virus reovirus. Samples were removed at days 12, 40, 69, 291, and 356 and were tested for the presence of fecal Coliform, Clostridium perfringens spores, Ascaris suum eggs, and reovirus. The pH, total solids, and free ammonia content of the mixed product were also determined for each sample. Odor was quantified for samples at both 291 and 356 days. Fecal Coliform bacteria and reovirus were completely inactivated for doses as low as 100 g lime per kg biosolids (dry) and 50 g lime + 500 g fly ash per kg biosolids (dry). Spores of the bacteria C. perfringens experienced a 4-log reduction when treated with 100 g lime per kg biosolids and a 5-log reduction when treated with doses as low as 50 g lime + 500 g fly ash per kg biosolids (dry) after 69 days. Ascaris eggs were completely inactivated in 5 gram packets for all treatments involving 100 g lime per kg biosolids (dry) after 69 days. Class A pathogen requirements were met for all treatments involving a lime dose of at least 100 g per kg biosolids. The odor potential from the produced biosolids is also assessed.

Minimum detectable level of Salmonellae using a binomial-based bacterial ice nucleation detection assay (BIND)

A modified bacterial ice nucleation detection (BIND) assay was used for rapid and sensitive detection of several Salmonella species. For the BIND assay, Salmonella cells are infected with bacteriophage genetically modified to contain DNA encoding an ice nucleation protein (INP). After infection, de novo protein synthesis occurs and INPs are incorporated into the outer membrane of the organism. After supercooling (-9.3 degrees C), only buffer solutions containing transfected salmonellae freeze, causing a phase-sensitive dye to change color. This technique, and a probability-based protocol modification, provided quantitative detection with a minimum detectable level (MDL) of 2.0 +/- 0.3 S. enteritidis cells/mL in buffer (about 3 h). The MDLs for S. typhimurium DT104 and S. abaetetuba were 4.2 +/- 0.2 and 11.1 +/- 0.4 cells/mL, respectively. Using salmonellae-specific immunomagnetic bead separation technology in conjunction with the modified BIND protocol, we achieved an MDL of about 4.5 S. enteritidis cells/mL with an apparent capture efficiency of 56%.

Pre-implantation endometrial leukocytes in women with recurrent miscarriage

Immunohistochemistry was used to investigate the leukocyte populations in the endometrium of women suffering recurrent miscarriage. Mid-luteal phase endometrial biopsies were taken from 22 patients with idiopathic recurrent miscarriage and from nine women with normal obstetric histories. The samples were dated histologically and stained with a panel of monoclonal antibodies to identify leukocytes. The outcome of any pregnancy in subsequent cycles following the biopsy was determined. Similar numbers of cluster designation (CD)3(+) and CD8(+) cells were seen in both groups. However, CD4(+), CD14(+), CD16(+), CD56(+) and MHC class II(+) cells were significantly higher in the recurrent miscarriage group than in the controls. Two patients had B cells (CD22(+)) in their endometrium. No CD57(+) cells were seen in the controls; however, eight of the patients had a few CD57(+) cells present. Only two patients, both from the recurrent miscarriage group, had CD69(+) leukocytes in their endometrium. Patients who had miscarriages following endometrial biopsy had significantly more CD4(+), CD8(+), CD14(+), CD16(+), and CD56(+) leukocytes in their endometrium than either those who had live births or women with proven fertility. A different population of leukocytes was found in the pre-implantation endometrium from recurrent miscarriage patients as compared to those from fertile controls. These differences were accentuated in women who had a miscarriage subsequent to the biopsy compared with those who subsequently had a live birth.

Pediatric patients, DRG hospital payment, and comorbidities

To determine whether the diagnosis related group (DRG) hospital payment system is causing financial pressure on pediatric hospitals similar to that shown in our previous work in other settings, we analyzed resource consumption for pediatric patients in any of the 251 DRGs not stratified by comorbidities. The new DRG prospective "all payor system" is in effect at our hospital. Analysis of 12,771 pediatric patients by payer (Medicaid and commercial insurance such as Blue Cross) in these DRGs for a 3-year period demonstrated that, as a group, pediatric patients with more comorbidities generated higher total hospital costs, a longer hospital length of stay, a greater percentage of procedures per patient, financial risk under DRG payment, more outliers (expensive patients), and a higher mortality rate than pediatric patients in the same DRGs with fewer comorbidities. This study confirms major inequities in DRG prospective hospital payment for many pediatric patients.

Expression in Escherichia coli of a fusion protein product containing a region of the adenovirus DNA polymerase

The bulk of an open reading frame extending from map coordinates 23.3 to 14.2 in region E2b of the adenoviral genome has been cloned and expressed from a chimeric plasmid in Escherichia coli. The cloning strategy used created a fusion protein of 124,000 daltons, which contained greater than 98% adenovirus-encoded sequences. Antiserum raised against this protein reacted with the authentic 140,000-dalton adenovirus DNA polymerase. Another serum raised against a synthetic hexapeptide whose sequence corresponded to the predicted carboxyl terminus of adenovirus-encoded DNA polymerase also reacted with the fusion protein and authentic adenovirus DNA polymerase. These results demonstrate that the cloned region of DNA encodes the adenovirus DNA polymerase.