Jennifer Neo

The use of ultrasonic endodontic instrumentation in the re-treatment of a paste-filled endodontic tooth

A technique using ultrasonic endodontic instruments in re-treating hard-paste--filled root canals is presented. The technique is time-consuming but may eliminate the necessity for a surgical approach in the re-treatment of paste-filled teeth.

Riboflavin as a dentin crosslinking agent: Ultraviolet A versus blue light

OBJECTIVES To investigate the effect of photo-activation of riboflavin either by ultraviolet (UVA) or visible blue light (BL) on the biodegradation resistance, strength of demineralized dentin matrix, bond strength to dentin and resin/dentin interface morphology. METHODS Dentin beams were demineralized, treated with 0.1% or 1% riboflavin solution for 5min and photo-activated with UVA or BL for 20s. The ultimate tensile strength (UTS) and hydroxyproline (HYP) release were assessed after 24h collagenase challenge. For micro-tensile bond strength (μTBS) testing and resin/dentin interface morphology investigation, dentin was acid-etched, crosslinked with riboflavin and bonded with an etch-and-rinse adhesive system. Riboflavin was photo-activated separately with UVA or BL followed by photo-polymerization of the bonding resin with BL (two-step) or both riboflavin photo-activation and bonding resin photo-polymerization were done in one-step using BL. RESULTS Significant improvement in the UTS and biodegradation resistance against collagenase challenge was found when riboflavin was photo-activated either with UVA or BL. However, UVA showed more significant improvement compared to BL. After 4months of water-storage, both UV and BL two-step photo-activation methods significantly preserved higher values of the μTBS compared to the non-crosslinked control group, where UVA showed significantly higher μTBS than BL. SIGNIFICANCE Although UVA most effectively activated riboflavin, visible blue light showed to be a promising substitute for UVA as it is clinically more applicable and acceptable, and still managed to increase the biodegradation resistance, enhance the mechanical properties of dentin collagen and improve and maintain the bond strength and interface integrity after short-term water storage.

Characterization of Riboflavin-modified Dentin Collagen Matrix

Crosslinking is considered a possible approach to increasing the mechanical and structural stability and biodegradation resistance of the dentin collagen matrix. The aim of this study was to investigate the mechanical and chemical variations and collagen degradation resistance associated with crosslinking of the dentin collagen matrix with UVA-activated riboflavin. Dentin collagen matrix specimens were treated with 0.1 and 1% riboflavin for 2 min and photo-activated with 7 mW/cm2 UVA (368 nm) for 2 min. The structural change of the dentin collagen network with collagenase exposure was investigated by AFM and SEM at different time-points. The variations in surface/bulk mechanical properties and biodegradation resistance were characterized by nano-indentation, conventional mechanical testing, and hydroxyproline liberation at different time-points. Chemical changes associated with riboflavin/collagen-matrix interaction were analyzed by micro-Raman spectroscopy. UVA-activated riboflavin increased the mechanical properties, mechanical stability, and biodegradation resistance of the dentin collagen matrix. Higher collagen-network structural resistance against collagenolytic challenges was found with crosslinking. micro-Raman spectroscopy showed a strong dependency, in both intensity and wave-number, of certain Raman bands (1242-1667 cm-1) with crosslinking indicating the collagen/riboflavin interactions. UVA-activated riboflavin (1%) more efficiently crosslinked the dentin collagen matrix within a relatively clinically acceptable time-frame compared with 0.1% riboflavin.

The effect of dentin bonding agents on the microleakage of porcelain veneers

OBJECTIVES This in vitro study was conducted to investigate the effect of dentin bonding agents on the microleakage of porcelain veneers cemented on dentin margins. METHODS Forty human premolars were prepared on both the buccal and palatal surfaces. Each half was randomly assigned to eight groups. The veneer preparation of one group was cut entirely within enamel, to serve as controls. The remaining groups had cervical margins extending 1 mm beyond the cemento-enamel junction. Six dentin bonding agents were tested. The specimens were subjected to thermocycling and evaluated for marginal leakage using a silver nitrate stain technique. After sectioning, the extent of microleakage was measured at four interfaces: (1) incisal porcelain-composite; (2) incisal tooth-composite; (3) cervical porcelain-composite; and (4) cervical tooth-composite. RESULTS Statistical analysis showed that the cervical tooth-composite interface had a significantly higher leakage value (p < 0.05) than the other three interfaces when the cervical margins were in dentin. SIGNIFICANCE The dentin bonding agents tested did not significantly reduce the marginal leakage of the porcelain veneers cemented on dentin margins.

Chitosan/Riboflavin-modified demineralized dentin as a potential substrate for bonding.

Previous studies have suggested different approaches to modify dentin collagen for potential improvement in bonding to dentin. Here, we are proposing a new approach to reinforce dentin collagen fibrils network by chitosan as a reinforcement phase and UVA-activated riboflavin as crosslinking agent within clinically acceptable time-frame as potential substrate for bonding. The effect of modifying demineralized dentin substrates with chitosan/riboflavin, with a gradual increase in chitosan content, was investigated by SEM, nano-indentation, conventional-mechanical testing and hydroxyproline (HYP) release at collagenolytic and/or hydrolytic challenges. The resin/dentin interface morphology, immediate bond strength and short-term bond durability were also investigated using etch-and-rinse dentin adhesive. Modification with chitosan/riboflavin increased the mechanical properties, enhanced the mechanical stability of demineralized dentin substrates against hydrolytic and/or collagenolytic degradation challenges and decreased HYP release with collagenase exposure. When chitosan was added to riboflavin at 20%v/v ratio, significant improvement in bond strength at 24 h and 6 months in distilled water was found indicating the positive dual effect on bonding to dentin. With the gradual increase in chitosan content, obliteration of interfibrillar-spaces that might adversely affect bonding to dentin was found. Although it has a synergetic effect, chitosan content is crucial for any subsequent application in adhesive dentistry.

The Effect of Preparation Height and Luting Agent on the Resistance form of Cemented Cast Crowns Under Load Fatigue

STATEMENT OF PROBLEM The minimum amount of resistance form required for the success of a clinical crown is unknown.There is little information on the fatigue performance of complete coverage restorations on natural tooth preparations cemented with different luting cements. PURPOSE The purpose of this study was to evaluate the effect of tooth preparation height and luting agent on resistance form using unidirectional load fatigue testing. For a given tooth preparation with a clinically relevant total occlusal convergence (TOC), the adequacy of resistance form was investigated. MATERIAL AND METHODS Sixty-four human maxillary premolars were prepared with occlusal-cervical dimensions of 2, 3,4, or 5 mm and a TOC of 20 degrees. Complete metal crowns were cemented using either zinc phosphate cement (HY Bond;ZP groups) or resin cement (Panavia F; PF groups). Cyclic load fatigue testing was done with an applied load of 6.0 kg at 2.6 Hz. Load cycles to preliminary failure were detected with a strain gauge at the palatal crown-tooth interface. Results were subjected to the Kruskal-Wallis test and the Wilcoxon post-hoc rank sum test (alpha=.05). RESULTS Groups ZP4, ZP5, PF2, PF3, PF4, and PF5 had the highest mean number of cycles to preliminary failure,while group ZP2 had the lowest mean number of cycles to failure. Group ZP2 was significantly different (P<.001) from all other test groups for the number of cycles to failure. CONCLUSIONS For the 2- and 3-mm preparation height groups, zinc phosphate cement exhibited a poorer fatigue performance compared to Panavia F. There was no significant difference in the number of cycles to failure for groups ZP4,ZP5, PF2, PF3, PF4, and PF5. For both cements, the number of cycles to failure increased with increasing resistance length. (J Prosthet Dent 2009;102:155-164)

Chlorhexidine Nanocapsule Drug Delivery Approach to the Resin-Dentin Interface

In this study, we are introducing a new drug-delivery approach to demineralized dentin substrates through microsized dentinal tubules in the form of drug-loaded nanocapsules. Chlorhexidine (CHX) is widely used in adhesive dentistry due to its nonspecific matrix metalloproteinase inhibitory effect and antibacterial activities. Poly(ε-caprolactone) nanocapsules (nano-PCL) loaded with CHX were fabricated by interfacial polymer deposition at PCL/CHX ratios of 125:10, 125:25, and 125:50. Unloaded nanocapsules (blank) were fabricated as control. The fabricated nanocapsules were characterized in vitro in terms of particle size, surface charges, particle recovery, encapsulation efficiency, and drug loading. Nanocapsule morphology, drug inclusion, structural properties, and crystallinity were investigated by scanning and transmission electron microscopes (SEM/TEM), energy-dispersive x-ray analysis, Fourier transform infrared spectroscopy, and x-ray diffraction. Initial screening of the antibacterial activities and the cytotoxicity of the nanocapsules were also conducted. Nanocapsules, as carried on ethanol/water solution, were delivered to demineralized dentin specimens connected to an ex vivo model setup simulating the pulpal pressure to study their infiltration, penetration depth, and retention inside the dentinal tubules by SEM/TEM. Nanocapsules were Ag labeled and delivered to demineralized dentin, followed by the application of a 2-step etch-and-rinse dentin adhesive. CHX-release profiles were characterized in vitro and ex vivo up to 25 d. Spherical nanocapsules were fabricated with a CHX core coated with a thin PCL shell. The blank nanocapsules exhibited the largest z-average diameter with negatively charged ζ-potential. With CHX incorporation, the nanocapsule size was decreased with a positive shift in ζ-potential. Nano-PCL/CHX at 125:50 showed the highest drug loading, antibacterial effect, and CHX release both in vitro and ex vivo. SEM and TEM revealed the deep penetration and retention of the CHX-loaded nanocapsules inside dentinal tubules and their ability to be gradually degraded to release CHX in vitro and ex vivo. Ag-labeled nanocapsules revealed the close association and even distribution of nanocapsules throughout the resin tag structure. This study demonstrated the potential of introducing this novel drug-delivery approach to demineralized dentin substrates and the resin-dentin interface with nanosized CHX-loaded nanocapsules through the microsized dentinal tubules.

A retrospective clinical study of endodontically treated mandibular incisors in a selected Chinese population

Clinical studies of incidences of the number of canals in human teeth should correlate with the percentages obtained in laboratory samples. In this study the incidence of two canals in the mandibular incisors was compared with figures obtained from in vitro extracted teeth, as well as from one clinical study. A very low percentage was obtained from the examination of clinical records, and this could be due to racial differences in the samples examined.

The effect of tooth and foundation restoration heights on the load fatigue performance of cast crowns.

STATEMENT OF PROBLEM In badly damaged teeth and teeth with short clinical crown heights, the placement of foundation restorations has been advocated to permit the development of retention and resistance form. However, there is little information on the effect of these foundation restorations on the clinical performance of the definitive restoration. PURPOSE The purpose of this study was to evaluate the load fatigue performance of teeth restored with posts and cores, with varying tooth heights, and to compare them with similar groups having no posts and cores. A secondary purpose was to determine whether a critical tooth height existed at which the placement of a foundation restoration resulted in no significant difference in the load fatigue performance. MATERIAL AND METHODS Three test groups (n=10) with prepared tooth heights of 2, 3, and 4 mm were tested. These were compared with another 3 groups with similar tooth heights that were restored with prefabricated titanium posts and core heights of 4, 3, and 2 mm, respectively. Cast complete crowns were then fabricated and cemented with zinc phosphate cement. A fatigue load of 58.8 N was applied at an angle of 135 degrees to the long axis of each crown-tooth specimen. The number of cycles to preliminary failure was determined. Significant differences in cycles to preliminary failure were assessed with 1-way ANOVA, followed by Tukey HSD tests (α=.05). RESULTS The group with the greatest preparation height (4 mm) and a 2-mm post-retained foundation had the highest number of cycles to preliminary failure (437,701), while the group with the shortest preparation height and no foundation had the lowest number of cycles (53,806). The Tukey HSD multiple comparison tests showed that for all 3 tooth heights, groups with foundation restorations had a significantly higher number of cycles to preliminary failure than those without foundation restorations. CONCLUSIONS For a given tooth height, teeth restored with foundation restorations had a significantly better load fatigue performance than those with no foundation restoration.

Shear bond strength of orthodontic brackets using Panavia: An in-vitro study

In this study, Panavia (a phosphonated Bis-GMA resin which is known to develop very high bond strengths with resin-bonded bridges) is compared to a conventional no-mix orthodontic Bis-GMA bracket adhesive. Results showed that there was no statistically significant difference in the shear bond strengths between the two resins when used as adhesives for bonding orthodontic brackets. Coupled with the fact that Panavia requires an anaerobic environment for complete polymerization, its routine use as a bracket adhesive in direct bonding of orthodontic brackets is not indicated.