Sung Kyo Kim

Critical Review on Methacrylate Resin–based Root Canal Sealers

INTRODUCTION Four generations of methacrylate resin-based sealers have been available commercially. Three of these were introduced during the last 5 years when the concept of simultaneous bonding of root canal sealers to root filling materials and dentin was popularized. METHODS This article presents an overview of methacrylate resin-based sealers, with the objectives of clarifying the behavior of these materials and delineating their limitations in clinical application. RESULTS The first generation sealer was introduced in the mid-1970s. The initial enthusiasm associated with its use eventually diminished as a result of its suboptimal physical, biologic, and clinical properties. With advances in self-etching adhesive technology acquired from adhesive dentistry, methacrylate resin-based sealers were reintroduced in the beginning of the 21st century to support the introduction of bondable root canal filling materials. Three different generations of these sealers have since been available commercially. Although some in vitro studies on the sealing ability, self-etching potential, biocompatibility, and removability of the sealers showed better potential over conventional nonbonding sealers, accomplishing the ideal goal of a monoblock in the root canal space with these materials is still regarded as a major challenge. CONCLUSIONS On the basis of the in vitro and in vivo data available to date, there appears to be no clear benefit with the use of methacrylate resin-based sealers in conjunction with adhesive root filling materials at this point in their development.

Failure of a Glass Ionomer to Remineralize Apatite-depleted Dentin

Remineralization of demineralized dentin lesions adjacent to glass-ionomer cements (GICs) has been reported in the literature. This study tested the hypothesis that a strontium-based GIC can remineralize completely demineralized dentin by nucleation of new apatite crystallites within an apatite-free dentin matrix. Human dentin specimens were acid-etched, bonded with Fuji IXGP, and immersed in a calcium-and-phosphate-containing 1.5X simulated body fluid (SBF) for 1–4 months. Polyacrylic acid and polyvinylphosphonic acid biomimetic analogs were added to the SBFs to create 2 additional remineralization media. Specimens were processed by transmission electron microscopy (TEM). No apatite deposition could be identified in the completely demineralized dentin in any of the specimens immersed in the 3 remineralization media, despite TEM/EDX evidence of diffusion of ions specific to the strontium-based GIC into the demineralized dentin. The hypothesis was rejected; mineral concentration alone is not a sufficient endpoint for assessing the success of contemporary remineralization strategies.

Expression of Metabotropic Glutamate Receptor mGluR5 in Human Dental Pulp

Accumulating evidence indicates that the metabotropic glutamate receptor mGluR5 is involved in the peripheral mechanisms of inflammatory nociception. To investigate whether mGluR5 may mediate the inflammatory pain and thermal hyperalgesia in the dental pulp, we examined the expression of mGluR5 and transient receptor potential vanilloid 1 (TRPV1) in human dental pulp by immunohistochemistry and electron microscopy; mGluR5-immunopositive (+) axons were observed in nerve bundles and branched extensively within the peripheral coronal pulp. Most of the mGluR5+ axons were unmyelinated. A large fraction of these axons (36.5%) were immunostained for TRPV1. Immunoreactivity for mGluR5 and TRPV1 was also observed in odontoblasts. These results support the possibility that the nerve fibers in the dental pulp mediate inflammatory pain and thermal hyperalgesia through coactivation of mGluR5 and TRPV1 and also suggest a possible role for odontoblasts in the transduction of nociceptive signals via mGluR5-mediated mechanism.

The Self-etching Potential of RealSeal Versus RealSeal SE

INTRODUCTION This study evaluated the true self-etching potential of RealSeal and RealSeal SE to ensure that they are aggressive enough to etch through endodontic smear layers and demineralize the intact radicular dentin without adjunctive use of ethylenediaminetetraacetic acid (EDTA). METHODS Mixed RealSeal and RealSeal SE were applied to (1) instrumented canal wall dentin that was irrigated with water as the final rinse to preserve smear layers, (2) fractured radicular dentin that was devoid of smear layers, and (3) instrumented canal wall dentin that was irrigated with EDTA as the final rinse to remove smear layers. Sealer-bonded specimens were processed for transmission electron microscopy. RESULTS Unlike RealSeal, RealSeal SE could hardly demineralize the fractured dentin and was unable to etch beyond smear layers into the underlying intact dentin. EDTA dissolved smear layers completely and partially demineralized the intact dentin.. CONCLUSIONS RealSeal SE might not be aggressive enough to achieve optimal dentin bonding to root canal walls in locations that are not reachable by calcium chelating irrigants. Conversely, RealSeal possesses mild etching ability on the fractured and smear layer-covered radicular dentin.

Effect of Torsional Loading of Nickel-Titanium Instruments on Cyclic Fatigue Resistance

INTRODUCTION The aim of this study was to evaluate the effect of torsional preload on the cyclic fatigue life of nickel-titanium rotary instruments. METHODS ProFile (#25/0.06) (Dentsply Maillefer, Ballaigues, Switzerland) and ProTaper (F1; Dentsply Maillefer) were used. Each file was preloaded at 4 conditions (ie, no preloading and 25%, 50%, and 75% of mean ultimate torsional strength) of torsional prestress before the fatigue test. The torsional preloads were applied by securing 5 mm of the file tip while keeping the file straight, rotating it clockwise until the preset torque, and then returning to the original position. This motion was repeated until a preset number (10, 30, or 50) of repetitions were reached (n = 12). After torsional preloading, the number of cycles to failure was evaluated in a simulated canal. Data were analyzed using 2-way analysis of variance and the Duncan post hoc comparison. The fractured fragment surfaces were examined under a scanning electron microscope for the topographic features of fractured instruments. RESULTS For both instruments, there was a significant effect because of the extent of torsional preloads. The 50% and 75% torsionally preloaded ProFile and all ProTaper preloading groups had a higher number of cycles to failure than the other group(s). There was little difference in the lateral view appearance between new and torsionally preloaded files. After cyclic fatigue testing, all preloaded instruments showed numerous microcracks adjacent to the fracture site on lateral view examination. The microcracks did not seem to follow the machining grooves on the instrument surface but rather ran irregularly. CONCLUSIONS The torsional preloads within the superelastic limit of the material may improve the cyclic fatigue resistance of nickel-titanium rotary instruments.

Quantitative analysis of tooth pulp afferent terminals in the rat brain stem.

This study analyzed quantitatively the ultrastructural features of tooth pulp afferent terminals and their presynaptic axonal endings (p-endings) in the trigeminal principal (Vp), dorsomedial oral (Vdm), and caudal nuclei (Vc). Mitochondrial volume, active zone area, apposed surface area, and vesicle number were highly correlated with afferent bouton volume. The afferent bouton volume varied widely in Vp, compared to that in Vdm and Vc. The values of all parameters of p-endings were within a narrow range, and were smaller than those of afferent boutons. The afferent bouton volume correlated with the number of postsynaptic dendrites and p-endings. These results suggest that pulpal afferent information is regulated in a unique manner in the each trigeminal sensory nucleus.

Effect of alloy type on the life-time of torsion-preloaded nickel-titanium endodontic instruments

This study was aimed to evaluate the effect of torsional preloads on the cyclic fatigue life of nickel-titanium (NiTi) instruments with different history of heat treatments by manufacturers. WaveOne (Primary) made of M-wire, K3XF (#30/0.06) of R-phase, and ProTaper (F2) of conventional NiTi alloy was used. Each file was preloaded at four conditions (nil, 25, 50, and 75% of their mean ultimate torsional strength) before fatigue testing. The torsional preloads 10-, 30-, or 50-times were applied by securing 5 mm of the file tip, rotating it until the preset torque was attained before returning to the origin. Then, the number of cycles to failure (NCF) was evaluated by rotational bending in a simulated canal. Data were analyzed using multiple linear regression analysis and two-way ANOVA. Fractured instruments were examined under scanning electron microscope (SEM). SEM showed that most WaveOne after 75% preloading, regardless of repetitions, showed some longitudinal cracks parallel to the long axis of the file, which were rare for K3XF. Regression analysis revealed that the brand of instrument was the most critical factor. At up to 75% preloading, ProTaper and K3XF did not show any significant decline in NCF. For 30-repetition groups of WaveOne, the 50 and 25% torsion preloaded groups showed a significantly higher NCF than the 0 and 75% groups. Within the limitations of this study, the alloy type of NiTi instrument have a significant effect on the phenomenon that a certain amount of torsional preload may improve the cyclic fatigue resistance of NiTi rotary instruments.

Effect of repetitive pecking at working length for glide path preparation using G-file

Objectives Glide path preparation is recommended to reduce torsional failure of nickel-titanium (NiTi) rotary instruments and to prevent root canal transportation. This study evaluated whether the repetitive insertions of G-files to the working length maintain the apical size as well as provide sufficient lumen as a glide path for subsequent instrumentation. Materials and Methods The G-file system (Micro-Mega) composed of G1 and G2 files for glide path preparation was used with the J-shaped, simulated resin canals. After inserting a G1 file twice, a G2 file was inserted to the working length 1, 4, 7, or 10 times for four each experimental group, respectively (n = 10). Then the canals were cleaned by copious irrigation, and lubricated with a separating gel medium. Canal replicas were made using silicone impression material, and the diameter of the replicas was measured at working length (D0) and 1 mm level (D1) under a scanning electron microscope. Data was analysed by one-way ANOVA and post-hoc tests (p = 0.05). Results The diameter at D0 level did not show any significant difference between the 1, 2, 4, and 10 times of repetitive pecking insertions of G2 files at working length. However, 10 times of pecking motion with G2 file resulted in significantly larger canal diameter at D1 (p < 0.05). Conclusions Under the limitations of this study, the repetitive insertion of a G2 file up to 10 times at working length created an adequate lumen for subsequent apical shaping with other rotary files bigger than International Organization for Standardization (ISO) size 20, without apical transportation at D0 level.

Endodontic treatment of maxillary lateral incisors with anatomical variations

Maxillary lateral incisors usually exhibit a single root with a single canal. However, maxillary lateral incisor teeth with unusual morphology of root canal system are frequently reported. These cases of variable root canal anatomy can be treated well by nonsurgical endodontic methods. A detailed description of root canal morphology is fundamental for successful endodontic treatment. Treatment using an operating microscope, radiographs from different angles, and cone-beam computerized tomography (CBCT) can produce more predictable endodontic outcomes.

Effect of local anesthesia on pulpal blood flow in mechanically stimulated teeth

The aims of the study were to evaluate the effect of epinephrine-containing local anesthetics on pulpal blood flow (PBF) and to investigate its effect on cavity preparation-induced PBF change. PBF was recorded using a laser Doppler flowmeter (Perimed Co., Sweden) from canines of nine cats under general anesthesia before and after injection of local anesthetics and after cavity preparation. 2% lidocaine hydrochloride with 1 : 100,000 epinephrine was administered by local infiltration given apical to the mandibular canine at the vestibular area and the same volume of isotonic saline was injected on the contralateral tooth as a control. A round carbide bur was operated at slow speed with isotonic saline flushing to grind spherical cavities with increasing depth through the enamel and into the dentin on both teeth. The obtained data was analyzed with paired t-test. Cavity preparation caused significant increase of PBF (n = 9, p < 0.05). Local infiltration of lidocaine with epinephrine resulted in decreases of PBF (n = 9, p < 0.05), whereas there was no significant change of PBF with the physiologic saline as a control. Cavity preparation on tooth anesthetized with lidocaine with epinephrine caused significantly less increase of PBF than in control tooth ( p < 0.05). Therefore, the result of the present study demonstrates that local infiltration of 2% lidocaine with 1 : 100,000 epinephrine effectively reduces PBF increase caused by cavity preparation. (J Kor Acad