Fumio Takeshige

Comparison of polymerization contraction stresses between self- and light-curing composites

OBJECTIVES The objective of this study was to examine the distributions and the magnitudes of the internal stresses in self- and a light-curing composite restorations resulting from polymerization shrinkage. METHODS Butt-joint box-shaped cavities (5.0 x 2.0 mm2, 2.0 mm in depth) prepared in composite molds were filled with either a self- or light-curing transparent resin composite. The restorations were cross-sectioned perpendicular to the longitudinal axes of the cavities and observed using polarizing microscopes. The principal stresses in the restorations, normal and shear stresses at the cavity wall were evaluated by photoelastic analysis. RESULTS The distributions of the principal stresses and the stresses generated at the cavity wall in both the self- and the light-curing composite restorations were similar. The maximum stress generated at the cavity wall in the light-curing composite restorations was twice as large as that seen in the self-curing restorations. CONCLUSIONS The results of this study indicated that the difference in the magnitude of the internal stresses between self- and light-curing composites was not related to the distribution of the stresses. The velocity of polymerization appeared to be the most important factor contributing to the magnitude of the internal stresses generated in the composite restorations in this study.

Prognosis of Intentional Replantation of Vertically Fractured Roots Reconstructed with Dentin-Bonded Resin

There is no particular treatment established to preserve vertically fractured teeth. We evaluated the long-term prognosis of the intentional replantation of 26 vertically fractured roots after reconstruction with 4-META/MMA-TBB dentin-bonded resin. Replanted teeth were evaluated according to clinical criteria and radiographic examinations for periods ranging from 4 to 76 months. Eighteen cases were functional and retained, with six fully successful; the others needed further observation. Eight cases failed to respond to treatment because of refracture, recurrence of gingival inflammation, or both. Longevity was calculated as 88.5% at 12 months after replantation, 69.2% at 36 months, and 59.3% at 60 months. All failures occurred in premolar and molar teeth. Longitudinal fractures extending more than 2/3 from the cervical portion toward the apex showed significantly shorter longevity compared with fractures within the 2/3 area (log-rank test, p = 0.02). Intentional replantation of vertically fractured roots reconstructed with dentin-bonded resin may be considered for incisors as an alternative to extraction, although the long-term success is not optimal.

Short-term evaluation of intentional replantation of vertically fractured roots reconstructed with dentin-bonded resin.

The purpose of this study was to evaluate intentional replantation of vertically fractured roots reconstructed with dentin-bonded resin. Twenty vertically fractured teeth were extracted intentionally and reconstructed with 4-META/MMA-TBB dentin-bonded resin. After reconstruction, the teeth were replanted into the original sockets. The replanted teeth were evaluated by clinical criteria and radiographic examination. The observation periods ranged between 4 and 45 months. Longevity was calculated by the Kaplan-Meier method, and factors that had significant influence on the longevity were analyzed with the Log rank test at a 95% level of confidence. From this short-term observation, 14 of 20 cases were functioned in the oral environment. Of these 14 cases, 6 could be considered truly successful and 8 cases needed further observation. The other six cases were total failures and were extracted. The longevity was calculated as 83.3% at 12 months and 36.3% at 24 months. Teeth with thin roots or with longitudinal fractures extending over 2/3 of the root from the cervical portion toward the apex showed significantly lower longevity. It was concluded that this method had the potential to preserve vertically fractured teeth.

Relationship between the color of carious dentin with varying lesion activity, and bacterial detection.

OBJECTIVES To investigate the relationship between the color of carious dentin with varying lesion activity, and bacterial detection in the lesions. METHODS In 26 extracted human molars with coronal dentin caries and four extracted sound human molars, dentin was removed by a round bur every 150 microm from the dentin surface, in the direction of the pulp chamber. Before and after removal, images of nine-color samples and the dentin surface stained with a caries detector dye (1% acid red in propylene glycol) were taken simultaneously by a charge-coupled device (CCD), and dentinal tissue samples were taken with a new round bur. From the images, corrected L*, a* and b* values (CIE 1976 L*a*b* color system) of the dentin surfaces were calculated from the color changes of the nine-color samples. Bacterial DNA in the dentinal tissues was detected by polymerase chain reaction. RESULTS Before removal of dentin, the L* of sound molars (L*>50) was significantly larger than that of carious molars (L*<50) (ANOVA, Scheffes F-test, P<0.05). In addition, the carious molars were divided into type I (a*>20, characteristics of active caries) and type II (a*<20, characteristics of arrested caries), and there was a significant difference in the a* value (P<0.05). For both carious types, the area under the receiver operating characteristic curve of L* was significantly larger than that of a* or b* (univariate Z score test, P<0.05), and the rate of bacterial detection decreased as the L* of dentinal tissue increased, and bacterial DNA was not detected when L* was >60. CONCLUSIONS Sound and types I and II carious dentin were discriminated by the combination of L* and a* values of dentinal tissue stained with the caries detector dye before removal of dentin. In carious lesions, the a* values of carious dentin stained with the dye were related to the carious lesion activity before removal of carious tissue, and the L* values were related to the degree of caries progression.

Accumulation of advanced glycation end-products in human dentine.

Cross-linking of collagen by Advanced Glycation End-products (AGEs) occurs by non-enzymatic glycation (Maillard reaction). The purpose of this study was to examine whether AGEs are formed in human dentinal collagen, and to consider any possible influence of AGEs on dentinal physiology. Mechanical characteristics, fluorescence spectra and immunohistochemical analyses of demineralized dentine sections from young subjects were compared with those of aged ones. The same investigations were performed with young dentine artificially glycated by incubation in 0.1M ribose solution. Indentation measurement indicated that the sections from aged dentine were mechanically harder than those from young dentine. The hardness of young dentine increased after incubation in ribose solution. Fluorescence peak wavelength of the young dentine was shorter than that of the aged one, but shifted towards the peak wavelength of the aged one after incubation in ribose solution. These changes were considered to be due to accumulation of AGEs. Existence of AGEs in dentinal collagen was confirmed by immunohistochemical analysis. The obtained results suggest that AGEs accumulation occurs in dentinal collagen and is affected by both human age and physiological conditions such as glucose level in blood because dentinal collagen receives nourishment via dental pulp and tubules.

Detection of Dentinal Microcracks Using Infrared Thermography

INTRODUCTION It is difficult to make a definite diagnosis of a cracked tooth solely based on an inspection within the root canal, especially in case of microcracks. At present, there seems to be no established method to detect dentinal microcracks in roots; therefore, the current detection techniques need to be improved. Vibrothermography (VibroIR) helps to detect microcracks by the friction heat generated from ultrasonic vibration. The purpose of this study was to establish a novel method using VibroIR to detect dentinal microcracks. METHODS The root canals of 20 roots with cracks and control roots were prepared after removing the tooth crowns. A tapered indenter was inserted into the root canal and pressed until a microcrack was created under an optical microscope. Using VibroIR, the detection trials for dentinal microcracks were performed with an ultrasonic vibration power ranging from 0.43 to 1.48 W at an angle of 0°, 30°, 45°, 60°, and 90° between the ultrasonic vibration point and the microcrack line. After the detection test, the microcrack width was measured with an optical microscope. RESULTS Frictional heat was detected in the microcracks with thermography at 0.89 to 1.48 W and at an ultrasonic vibration point angle less than 60° from the crack line for 10 seconds. Microcracks with a width of 4 to 35.5 μm were detected with this method. CONCLUSIONS VibroIR may be an effective method for the diagnosis of root dentinal microcracks.

Mechanical and morphological evaluation of the bond-dentin interface in direct resin core build-up method

OBJECTIVES The purpose of this study was to evaluate the interfacial adhesion between resin and root canal dentin in the direct resin core build-up method in terms of microtensile bond strength (μTBS) and dentin micro morphology. METHODS Single-rooted human teeth were decoronated at the cementoenamel junction and endodontically treated. Post spaces were prepared in the roots to a depth of 10mm. The spaces were then treated with a dual-cure bonding system, and filled with dual-cure resin composite. After 24-h storage in water at 37 °C, they were trimmed into approximately 1.0-mm(2) beams for μTBS. Bond strength was analyzed with one-way ANOVA and Tukeys test. The fractured surfaces were examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDX). Sectioned specimens were observed by ultra-high-voltage transmission electron microscopy. RESULTS The bond strength of root dentin decreased gradually from the coronal to apical side, and the bond strength of the coronal section was significantly higher than that of the radicular section. Moreover, the failure modes in the coronal and apical sides of the specimens differed. The apical specimens fractured within the core material, while the coronal specimens fractured at the bonding layer. SEM and EDX analyses revealed that the core material penetrated into dentinal tubules in the apical region. SIGNIFICANCE In the direct resin core build-up method, the interfacial adhesion of resin to root canal dentin may be insufficient in the apical region of the root canal due to poor polymerization.

Immunohistochemical analysis of dentin matrix protein 1 (Dmp1) phosphorylation by Fam20C in bone: implications for the induction of biomineralization

Dmp1 is an acidic phosphoprotein that is specifically expressed in osteocytes. During the secretory process, the full-length, precursor Dmp1 is cleaved into N- and C-terminal fragments. C-terminal Dmp1 is phosphorylated, becoming a highly negatively charged domain that may assist in bone mineralization by recruiting calcium ions and influencing subsequent mineral deposition. It has been recently reported that the Golgi-localized protein kinase Fam20C phosphorylates Dmp1 in vitro. To investigate this phosphorylation in situ, we determined the locations of phosphorylated Dmp1 and Fam20C in rat bones using immunohistochemistry. During osteocytogenesis, osteoblastic, osteoid, and young osteocytes (but not old osteocytes) express Dmp1 mRNA and contain Dmp1 protein in the Golgi apparatus. These Dmp1-producing cells were distributed across the surface layer of cortical bone. Using immunofluorescence, we found that N- and C-terminal Dmp1 fragments were predominantly distributed along the lacunar walls and canaliculi of mineralized bone, respectively, but were not present in the osteoid matrix. We also found that Fam20C and its substrate, C-terminal Dmp1, colocalized in the Golgi of osteoblastic, osteoid, and young osteocytes. Furthermore, phosphorylated C-terminal Dmp1 was present in the Golgi of young osteocytes. Double-labeling immunoelectron microscopy revealed that phosphorylated C-terminal Dmp1 localized to the canalicular wall in mineralized bone. These findings suggest that C-terminal Dmp1 is phosphorylated within osteocytes and then secreted into the pericanalicular matrix of mineralized bone. Phosphorylated, negatively charged C-terminal Dmp1 in the pericanalicular matrix may play an important role in bone mineralization by recruiting calcium ions.

Decrease in fluorescence lifetime by glycation of collagen and its application in determining advanced glycation end-products in human dentin

Advanced Glycation End-products (AGEs) are produced by the Maillard reaction, which causes cross-linking of collagen and results in changes in the mechanical properties of collagen tissues. Several types of AGE fluoresce, and measurement of this fluorescence is effective for determining the presence of AGEs. Because fluorescence intensity by steady-state fluorometry is affected by sample surface condition and light source, we focused on fluorescence lifetime measurement (FLM). We found that fluorescence lifetime of collagen gel decreased with glycation progress. In vivo application of FLM for determination of AGEs was confirmed in human dentin.

Optimal Positioning for a Dental Operating Microscope During Nonsurgical Endodontics

The most comfortable positioning for a dental operating microscope (DOM) during nonsurgical endodontics for operators was investigated. Operators were categorized into 3 groups according to height. We recorded the time taken to obtain magnified images, and the angles of binoculars, microscope body, and the mirror to floor surfaces. For the group of shorter operators, observations were also made with an angled optics or a short objective lens (200 mm). It took longer to observe the mandibular molars than maxillary in every group. Although the differences in angles among each group were not remarkable for maxillary observation, we confirmed significant differences for the mandibular. Shorter operators had to adopt a strained position for mandibular observation in a standard setup but were more comfortable using angled optics or a short objective lens. By understanding the proper position, operators could learn to perform microendodontics more efficiently.