Application of biomimetic restoration in oral-maxillofacial hard tissue repair / 华西口腔医学杂志

Oral-maxillofacial hard tissue is the support of maxillofacial structure and appearance, and lays the foundation for functions of oral and maxillofacial system. Once the defect occurs, it will not only affect the physiological functions such as chewing and pronunciation, but also have a significant impact on the psychological and social life of patients. However, the self-repairing capability of the oral-maxillofacial hard tissue is pretty limited, in which case, substitute materials are required for tissue repair. A huge gap exists between the physical, chemical, structural characteristics of conventional substitute materials and those of human hard tissues, resulting in poor repair effect. Based on this, scholars simulated the process of biomineralization in the development of hard tissues, to improve the structure and function of materials through biomimetic mineralization technology and enhance the repair performance of materials. The current understanding of biomineralization theory and the construction of biomimetic repair technology is still in the stage of rapid development. In recent years, a mass of innovative studies are keeping emerging. In this review, the representative advances in the repair of oral-maxillofacial hard tissues of the past five years are reviewed.

Advancing antimicrobial strategies for managing oral biofilm infections / 国际口腔科学杂志·英文版

Effective control of oral biofilm infectious diseases represents a major global challenge. Microorganisms in biofilms exhibit increased drug tolerance compared with planktonic cells. The present review covers innovative antimicrobial strategies for controlling oral biofilm-related infections published predominantly over the past 5 years. Antimicrobial dental materials based on antimicrobial agent release, contact-killing and multi-functional strategies have been designed and synthesized for the prevention of initial bacterial attachment and subsequent biofilm formation on the tooth and material surface. Among the therapeutic approaches for managing biofilms in clinical practice, antimicrobial photodynamic therapy has emerged as an alternative to antimicrobial regimes and mechanical removal of biofilms, and cold atmospheric plasma shows significant advantages over conventional antimicrobial approaches. Nevertheless, more preclinical studies and appropriately designed and well-structured multi-center clinical trials are critically needed to obtain reliable comparative data. The acquired information will be helpful in identifying the most effective antibacterial solutions and the most optimal circumstances to utilize these strategies.

Anti-proteolytic capacity and bonding durability of proanthocyanidin-biomodified demineralized dentin matrix / 国际口腔科学杂志·英文版

Our previous studies showed that biomodification of demineralized dentin collagen with proanthocyanidin (PA) for a clinically practical duration improves the mechanical properties of the dentin matrix and the immediate resin-dentin bond strength. The present study sought to evaluate the ability of PA biomodification to reduce collagenase-induced biodegradation of demineralized dentin matrix and dentin/adhesive interfaces in a clinically relevant manner. The effects of collagenolytic and gelatinolytic activity on PA-biomodified demineralized dentin matrix were analysed by hydroxyproline assay and gelatin zymography. Then, resin-/dentin-bonded specimens were prepared and challenged with bacterial collagenases. Dentin treated with 2% chlorhexidine and untreated dentin were used as a positive and negative control, respectively. Collagen biodegradation, the microtensile bond strengths of bonded specimens and the micromorphologies of the fractured interfaces were assessed. The results revealed that both collagenolytic and gelatinolytic activity on demineralized dentin were notably inhibited in the PA-biomodified groups, irrespective of PA concentration and biomodification duration. When challenged with exogenous collagenases, PA-biomodified bonded specimens exhibited significantly less biodegradation and maintained higher bond strengths than the untreated control. These results suggest that PA biomodification was effective at inhibiting proteolytic activity on demineralized dentin matrix and at stabilizing the adhesive/dentin interface against enzymatic degradation, is a new concept that has the potential to improve bonding durability.

Inhibitory effect of a novel crosslinking quaternary ammonium methacrylates on matrix metalloproteinases / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the anti-matrix metalloproteinase (MMP) activity of a novel crosslinking quaternary ammonium methacrylates, 2-methacryloxylethyl dodecylmethyl ammonium bromide (MAE-DB).</p><p><b>METHODS</b>The effects of MAE-DB at different concentrations (1%, 3%, 5%, 7%) on soluble matrix metalloproteinase-8 (MMP-8) were investigated using fluorescent assay kit. Readings were taken every 20 min for 3 h. The 1, 10-phenanthroline provided by the assay kit served as control group. Demineralized dentin beams were randomly divided into three groups (n = 50) and immersed in different solutions: artificial saliva, MAE-DB incorporated artificial saliva and chlorhexidine incorporated artificial saliva. After temperature cycling, the changes of ultimate tensile strength were measured to determine the effect of MAE-DB on the activity of matrix-bound endogenous matrix metalloproteinases. The morphology of dentin collagen fibrils in the three groups was observed via transmission electron microscopy (TEM).</p><p><b>RESULTS</b>MAE-DB could effectively inhibit the activity of soluble MMP-8. The inhibition percentage of 3% MAE-DB was 99.53% after 1 h, and it was significantly higher than that of 1, 10-phenanthroline (95.71%, P < 0.05). After temperature cycling, the ultimate tensile strengths of MAE-DB groups were significantly higher than those of the artificial saliva groups and the chlorhexidine groups (P < 0.05). TEM micrographs of MAE-DB group revealed that the microstructure of the collagen fibrillar was intact, while the fibrillar in the artificial saliva group was disrupted, indicating a protective function of MAE-DB on dentin collagen.</p><p><b>CONCLUSIONS</b>MAE-DB can inhibit the activity of MMP and protect dentin collagen from enzyme degradation.</p>

Effect of quaternary ammonium methacrylates incorporation into a dental adhesive on the resistance of enzymatic degradation of resin-dentine interfaces / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the effect of quaternary ammonium methacrylates incorporation into a dental adhesive on the resistance of enzymatic degradation of resin-dentine interfaces.</p><p><b>METHODS</b>Thirty caries-free extracted human third molars were randomly divided into three groups (n = 10): 2-methacryloxylethyl dodecylmethyl ammonium bromide (MAE-DB) incorporated adhesive served as the experimental group, pre-treatment with chlorhexidine (CHX) served as a positive control, Adper(TM) Single Bond 2 served as a negative control. The resin-dentin interfaces were prepared using total etch bond system. After storage in distilled water at 37 °C for 24 h, the bonded teeth were vertically sectioned into beams. Beams were respectively immersed in artificial saliva containing 2 g/L MMP-8 at 37 °C for 0 h, 24 h and 120 h (n = 30). Micro-tensile bond strength, failure modes and nanoleakage were examined.</p><p><b>RESULTS</b>There were no significantly differences of micro-tensile bond strength between groups before hydrolysis (P > 0.05). After the enzymatic hydrolysis of 24 h and 120 h, the micro-tensile bond strength of MAE-DB groups [(31.13 ± 8.77) MPa, (24.14 ± 6.64) MPa] were significantly higher than that of the negative control groups [(25.63 ± 6.90) MPa, (15.22 ± 6.57) MPa] (P < 0.05). Most of the failures were found in the base part of the hybrid layer in the negative control group, while failures occurred through the top of the hybrid layer in CHX and MAE-DB groups after the enzymatic hydrolysis.Specimens from each immediate group showed minor silver deposits in hybrid layer. After beams being enzymatic hydrolyzed for 120 h, it was shown that the silver nitrate uptake in the negative control group were significantly different from those in the CHX and MAE-DB groups (P < 0.05).</p><p><b>CONCLUSIONS</b>Dental adhesive incorporation of MAE-DB could improve the anti-degrade ability of resin-dentin interfaces.</p>

The potential effect of proanthocyanidins on the stability of resin-dentin bonds against thermal cycling / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the potential effect of proanthocyanidins (PA), a natural cross-linker, on the stability of resin-dentin bonds against thermal cycling.</p><p><b>METHODS</b>Ten percent, 15% PA-based preconditioners, and 5% glutaraldehyde were prepared for the transient pretreatment of demineralized dentin before bonding. Specimens without pretreatment were used as negative controls (n = 4 teeth for each group). Microtensile bond strength, failure mode, micromorphologies of resin-dentin interface and the collagen degradation of bonded specimens after thermal cycling were evaluated.</p><p><b>RESULTS</b>After thermal cycling, the microtensile bond strength values of resin-dentin bond in groups pretreated with 15% PA for 120 s and 60 s [(23.09 ± 3.19) and (21.88 ± 3.49) MPa] were significantly higher than that in control group [(15.47 ± 3.78) MPa] (P < 0.05). Mixed fractures were the most prevalent failure mode. Specimens with pretreatment presented compact hybrid layer, while some narrow gaps were found in hybrid layer of non-treated specimens. Collagen biodegradation rates in groups with pretreatment were significantly lower than that in control group (P < 0.05). Among them, specimens pretreated by 15% PA preconditioner for 120 s exhibited the lowest biodegradation rates [(0.316 ± 0.019) mg/g].</p><p><b>CONCLUSIONS</b>The application of natural cross-linker PA on demineralized dentin reduced the bond degradation against aging by thermal cycling, and can be helpful to create more durable bonds to dentin.</p>

The cytotoxicity of methacryloxylethyl cetyl ammonium chloride, a cationic antibacterial monomer, is related to oxidative stress and the intrinsic mitochondrial apoptotic pathway

Antibacterial monomers incorporated in dentin bonding systems may have toxic effects on the pulp. Thus, the cytotoxicity of antibacterial monomers and its underlying mechanisms must be elucidated to improve the safety of antibacterial monomer application. The influence of an antibacterial monomer, methacryloxylethyl cetyl ammonium chloride (DMAE-CB), on the vitality of L929 mouse fibroblasts was tested using MTT assay. Cell cycle progression was studied using flow cytometry. Production of intracellular reactive oxygen species (ROS) after DMAE-CB treatment was measured using 2,7-dichlorodihydrofluorescein diacetate staining and flow cytometry analysis. Loss of mitochondrial membrane potential, disturbance of Bcl-2 and Bax expression, as well as release of cytochrome C were also measured using flow cytometry analysis or Western blot to explore the possible involvement of the mitochondrial-related apoptotic pathway. DMAE-CB elicited cell death in a dose-dependent manner and more than 50 percent of cells were killed after treatment with 30 µM of the monomer. Both necrosis and apoptosis were observed. DMAE-CB also induced G1- and G2-phase arrest. Increased levels of intracellular ROS were observed after 1 h and this overproduction was further enhanced by 6-h treatment with the monomer. DMAE-CB may cause apoptosis by disturbing the expression of Bcl-2 and Bax, reducing the mitochondrial potential and inducing release of cytochrome C. Taken together, these findings suggest that the toxicity of the antibacterial monomer DMAE-CB is associated with ROS production, mitochondrial dysfunction, cell cycle disturbance, and cell apoptosis/necrosis.

A study on the bonding properties of four resin cements / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the dentin and enamel bonding strength and resin-dentin interfaces of four resin cements.</p><p><b>METHODS</b>Twenty-four sound freshly extracted molars were sectioned with low-speed saw under running water. Two mesial-distal enamel disc and two buccal-lingual dentin discs were sectioned from each molar. Four resin cements (A group: Panavia(TM) F; B group: RelyX(TM) ARC; C group: RelyX(TM) Unicem; D group: Clearfil(TM) SA Cement) were applied to the surface of these enamel and dentin discs according to manufacturers' guidance. The bonded specimen were prepared for shear bond strength test and sectioned occluso-gingivally into two slabs for scanning electron microscopy (SEM) observation.</p><p><b>RESULTS</b>The bonding strength between resin and enamel in B group [(29.38 ± 6.28) MPa] was higher than that in D group [(27.25 ± 7.03) MPa], and both of them were significantly higher than those in A [(22.92 ± 7.13) MPa] and C group [(10.92 ± 3.41) MPa] (P < 0.05). The highest dentin bonding strength was shown in B group [(27.28 ± 6.79) MPa], followed by A [(14.23 ± 6.39) MPa], D [(10.09 ± 3.26) MPa] and C group [(6.43 ± 1.60) MPa, P < 0.05].</p><p><b>CONCLUSIONS</b>The four resin cements have different enamel or dentin bonding properties.</p>

Effects of acid etching time on the degradation of type I collagen in dentin / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the effects of acid etching time on the degradation of type Icollagen in dentin.</p><p><b>METHODS</b>Dentin was conditioned with 37% phosphoric acid for 10, 15, 30 and 60 s. There was no treatment for the control group. Quantity of collagen degradation in each group was determined by enzyme linked immunosorbent assay. Observations were carried out by means of a field emission in-lens scanning electron microscope (FEISEM).</p><p><b>RESULTS</b>Samples conditioned with 37% phosphoric acid for 60 s showed the most degradation of collagen, which was 4.86 (1.55) mg/g, followed by 30 s group and 15 s group, which were 2.76 (0.87) mg/g and 1.93 (0.88) mg/g, respectively. Group of 10 s was 0.95 (0.38) mg/g. The control group showed the least degradation of 0.06 (0.03) mg/g. Significant differences in collagen degradation were found among groups (P < 0.005). Smear layer were removed well but tubular orifices and collagen fibrils were covered by particles after dentin being etched with 37% phosphoric acid for 10 s, while open and clear tubular orifices were observed for 15 s group. Smoother surfaces of exposed collagen fibrils and fewer globular particles were found in 30 s group than in 15 s group. In the 60 s group, the number of major fibrils decreased while minor branching fibrils increased, which indicate that the intratubular structure collapsed and fibrils fractured.</p><p><b>CONCLUSIONS</b>Dentin conditioned with 37% phosphoric acid for 15 s can result in mineral dissolution without collagen structure damage. However, longer applications of 37% phosphoric acid within 60 s may increase collagen degradation.</p>

Effects of tetrapod-like zinc oxide whiskers incorporation on antibacterial activity of composite resin / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate effects of incorporating tetrapod-like zinc oxide whisker (T-ZnOw) antibacterial agent on the antibacterial activity of composite resin, compared with that of the silver-based inorganic antibacterial agent.</p><p><b>METHODS</b>The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of the two different antibacterial agents against Streptococcus mutans were investigated using the broth dilution test. Then the antibacterial activities of the self-cured composite resin specimens with different incorporating concentrations of the two antibacterial agents were evaluated using direct contact test. And the antibacterial activities of the resin specimens were examined again after 3 months of accelerating aging.</p><p><b>RESULTS</b>The MIC (MBC) of the T-ZnOw antibacterial agent and silver-based inorganic antibacterial agent were 0.15625 (0.3125) g/L and 0.15625 (0.15625) g/L. When the concentrations of T-ZnOw added to composite resin were 3%, 5%, and 10% (w/w), the antibacterial ratios of the resin specimens were (84.85+/-5.16)%, (94.22+/-3.73)%, and (99.43+/-0.48)% respectively. When the concentrations of the silver-based antibacterial agent added to composite resin were 1%, 3%, and 5%, the antibacterial ratios were (71.01+/-7.67)%, (90.76+/-5.91)%, and (97.19+/-4.10)% respectively. The antibacterial ratios of the resin specimens containing 5% of both antibacterial agents were (89.89+/-5.55)% and (78.79+/-7.81)% respectively after 3 months of accelerating aging.</p><p><b>CONCLUSIONS</b>Incorporation of the T-ZnOw antibacterial agent in composite resin can improve the antibacterial performance of the resin, and the resin exhibits better antibacterial performance than that incorporating silver-based inorganic antibacterial agent after 3 months of aging.</p>

Antibacterial effects of a dental adhesive incorporating a quaternary ammonium monomer against Streptococcus mutans / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To incorporate an antibacterial monomer, methacryloxylethyl cetyl dimethyl ammonium chloride(DMAE-CB), into a dental adhesive, and to evaluate the antibacterial activity against Streptococcus mutans (Sm) of this DMAE-CB-incorporated adhesive after being cured.</p><p><b>METHODS</b>DMAE-CB was incorporated into a dimethacrylates-based dental adhesive as experimental group. The adhesive without DMAE-CB served as a negative control. Thirty-nine specimens were fabricated for each group. The effects of the cured adhesives on the growth and adherence of Sm were evaluated with growth inhibition assay and spectrophotometry respectively. The influence of aging treatment and saliva treatment on the antibacterial efficiency of the modified adhesive was evaluated. Moreover, the bacterial growth of Sm in the eluents of two different adhesives was examined.</p><p><b>RESULTS</b>Compared with negative control, the cured DMAE-CB-incorporated dental adhesive exhibited inhibitory effect on the growth and adherence of Sm. The inhibition rate was 99% and the absorbance value was (0.332 +/- 0.063) for experimental group, significantly lower than that of negative control (0.434 +/- 0.093, P = 0.021). Moreover, after aging treatment the DMAE-CB-incorporated adhesive could still inhibit the growth and adherence of Sm; the inhibition rate was 99%, and the absorbance value of experimental group was (0.372 +/- 0.062), significantly lower than that of negative control (0.455 +/- 0.066, P = 0.022). After saliva treatment the DMAE-CB-incorporated adhesive could still inhibit the growth and adherence of Sm; the inhibition rate was 90%, and the absorbance value of experimental group was (0.299 +/- 0.061), significantly lower than that of negative control (0.370 +/- 0.068, P = 0.045). However, the eluent of DMAE-CB-incorporated adhesive didn't show inhibitory effect on the growth of Sm when compared with negative control, and the antibacterial effect and the doubling time of experimental group [(130.5 +/- 8.4) min] had no statistical difference than negative control [(126.4 +/- 7.0) min, P = 0.298].</p><p><b>CONCLUSIONS</b>The incorporation of DMAE-CB can render the dental adhesive with antibacterial activity after polymerization via influencing the growth and adherence of Sm.</p>

An experimental study on the adaptation of three kinds of porcelain fused-to-metal restorations / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To compare the adaptation of porcelain fused-to-metal (PFM) restorations made from Ni-Cr alloy, precious alloy and galvanized forming copings after cementation and to provide a theory guidance for their application.</p><p><b>METHODS</b>Three kinds of crowns (Ni-Cr alloy, precious alloy and galvanized forming) were manufactured and cleaned by ultrasonic vibrate with alcoholic solution for 5 minutes, and cemented on their dies as their order. All the crowns were cemented by polycarboxylate zinc-cement and maintained 10 minutes. After coated in the center of methyl acrylic resins, all the samples were cut vertically along buccolingual direction. The cement thickness of PFM was measured by scanning electron microscope and the data were analyzed by multivariate ANOVA.</p><p><b>RESULTS</b>No significant difference was found between the cement thickness of precious alloy crown and galvanized forming crown (P>0.05), while both of these two kinds of crown had significant differences in cement thickness with Ni-Cr crown (P<0.05).</p><p><b>CONCLUSION</b>The adaptation of precious alloy crown and galvanized forming crown are superior to Ni-Cr crown.</p>

Effects of three different zinc oxide incorporation on the antibacterial activity against Streptococcus mutans of composite resin / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the effects of incorporating three different zinc oxide (ZnO) on the antibacterial activity of composite resin.</p><p><b>METHODS</b>The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of nano-ZnO, tetrapod-like zinc oxide whiskers (T-ZnOw), micro-ZnO against Streptococcus mutans were examined by the broth dilution test. Then the three different ZnO were added to the powder of one kind of bicomponent self-cured composite resin at 5% respectively, and the antibacterial activities of the resin specimens were evaluated using the membrane covering method before and after 3-month accelerating aging.</p><p><b>RESULTS</b>The MIC values of the three different ZnO against Streptococcus mutans were 78.13, 312.50 and 1 250.00 microg/mL respectively and the MBC values were 156.25, 625.00, 1,250.00 microg/mL respectively. The antibacterial ratios of the resin specimens incorporating with 5% of the three different ZnO were (93.58+/-5.95)%, (89.42+/-4.11)% and (78.97+/-3.90)% respectively, while after 3-month accelerating aging those were (89.01+/-7.91)%, (84.63+/-4.72)% and (72.27+/-3.89)%.</p><p><b>CONCLUSION</b>The three different ZnO could improve the antibacterial activity of the composite resin. The nano-ZnO exhibit the strongest antibacterial activity, while the micro-ZnO weakest. The T-ZnOw presents comparatively strong antibacterial activity although with smaller specific surface area.</p>

Influence of inorganic antibacterial agents on the systemic toxicity and cytotoxicity of a self-etching primer / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the influence of incorporating inorganic antibacterial agents on the systemic toxicity and cytotoxicity of an experimental self-etching primer (ESP).</p><p><b>METHODS</b>Six kinds of inorganic agents were incorporated respectively into the primer. Systemic toxicity in vivo tests in rats and direct contact in vitro cytotoxicity tests with NIH fibrohiasts were conducted.</p><p><b>RESULTS</b>Systemic toxicity tests revealed neither toxic manifestations nor significant differences in body weight gain hetween control and other groups. There were no significant differences between experimental groups and empty control on cell vitality and cell proliferation rates. Toxicity was only observed in areas heneath the specimens and/or in the direct vicinity of the specimen edge. There was no influence on the cell density over the limit of specimens.</p><p><b>CONCLUSION</b>The incorporation of tested inorganic antibacterial agents with a proper concentration had no significant influence on the systemic toxicity and cytotoxicity of the tested self-etching primer.</p>

Preparation and antibacterial activity of quaternary ammonium salt monomers / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To prepare three quaternary ammonium salt (QAS) monomers, and to compare their antibacterial activities against four oral bacterial strains.</p><p><b>METHODS</b>Three antibacterial monomers [methacryloxyethyl benzyl dimethyl ammonium chloride (DMAE-BC), methacryloxyethyl m-chloro benzyl dimethyl ammonium chloride (DMAE-m-CBC), methacryloxyethyl cetyl dimethyl ammonium chloride (DMAE-CB)] were synthesized according to the general structure of target monomers. Their antibacterial effects were investigated using the broth dilution test on Gram-positive and Gram-negative bacterial strains (Streptococcus mutans, Streptococcus sanguis, Porphyromonas gingivalis, Prevotella melaninogenica ).</p><p><b>RESULTS</b>Three different monomers were successfully obtained. All the tested bacterial strains were susceptible to the three monomers, among which DMAE-CB exhibited the lowest minimal inhibitory concentrations (MIC) ranging from 1.2 to 4.8 mg/L.</p><p><b>CONCLUSIONS</b>All these three QAS monomers have different antibacterial activities against four oral bacteria strains. The data indicate that DMAE-CB may be a candidate antibacterial agent for oral infectious diseases.</p>

Preliminary report on measurement of human periodontal biologic width / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To observe and measure the biologic width in Chinese people.</p><p><b>METHODS</b>Jaws of three male Han Chinese cadavers were collected. All specimens were taken as autopsy as block sections. A total of 174 mesiodistal and buccolingual sections in 6 microm thickness were cut and stained with hematoxylin and eosin. The biologic width was measured under microscope with a micrometer at the middle of the mesial, distal, buccal, and lingual sides. Differences in biologic width were compared among 4 measurement sites, as well as among anterior tooth, premolar, and molar groups.</p><p><b>RESULTS</b>The mean of biologic width of measured teeth was 2.17 mm, with the average width of junctional epithelium being 1.07 mm and the average width of connective tissue being 1.10 mm. No statistic difference was found among 4 measured sites. The biologic width of premolars (2.23 mm) and molars (2.25 mm) was larger than that of anterior teeth (2.07 mm).</p><p><b>CONCLUSIONS</b>The average biologic width of three Chinese people is 2.17 mm. The biologic width of posterior teeth is larger than that of anterior teeth.</p>

Machinable property of a novel dental mica glass-ceramic / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the machinability of a novel dental mica glass-ceramic and analyze the effect of heat-treatment on its ductile machinable behavior.</p><p><b>METHODS</b>The drilling and turning experiment were used to measure the machinabilities of the control group (feldspar ceramic: Vita Mark II) and 7 experiment groups treated with different crystallization techniques. The microstructures were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD).</p><p><b>RESULTS</b>The average drilling depths in 30 s of the experimental groups ranged from (0.5 +/- 0.1) mm to (7.1 +/- 0.8) mm. There were significant differences between the control [(0.8 +/- 0.1) mm] and the experimental groups (P < 0.05) except the group crystallized at 740 degrees C for 60 min. When crystallized at 650 degrees C (60 min), continuous band chips could formed in machining at a high velocity and cut depth. The crystal portion of this group is only about 40%.</p><p><b>CONCLUSIONS</b>This material has a satisfactory machinability. The mechanism could be attributed to a combination of the interlocked structure of mica crystals and the low viscosity of glassy phase.</p>

Study on relationship between bent angles of dental fiber reinforced composites posts and their flexural properties / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To develop a new type of fiber reinforced composites (FRC) posts with optimal bent angles.</p><p><b>METHODS</b>Three kinds of experimental bent posts were made with bent angle of 5 degrees, 10 degrees, and 15 degrees respectively. The flexural strength of all FRC posts was tested with a 3-point bending test.</p><p><b>RESULTS</b>The flexural strength of the posts with 15 degrees was significantly lower than that of 5 degrees and 10 degrees post groups and prefabricated straight group (P < 0.05). There was no significant difference in flexural strength within other groups (P > 0.05).</p><p><b>CONCLUSIONS</b>The experimental FRC posts with bent angles of 0 degrees, 5 degrees, 10 degrees can be accepted clinically.</p>

Measurement and comparison of the spectral transmittance of cerinate porcelain and human enamel / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To measure the spectral transmittance of Cerinate porcelain veneer and enamel in different color and different thickness.</p><p><b>METHODS</b>Samples of Cerinate porcelain veneers were prepared in different thickness (0.50 mm, 0.75 mm, 1.00 mm) and different Vita shade (A1, A2, A3). Enamel samples in shade A2 were made with three thickness (0.50 mm, 0.75 mm, 1.00 mm). A spectrophotometer with spectra range (380-800 nm) was employed to measure the spectral transmittance.</p><p><b>RESULTS</b>Spectral transmittance decreased with the increasing in the thickness of specimens and decreasing in the color darkness. The transmittance of Cerinate porcelain veneer material and enamel in the same color and same thickness hadn't significant difference.</p><p><b>CONCLUSION</b>The key factor to spectral transmittance of porcelain veneer materials is veneer's thickness, and the color of the materials has also some influence on it. Cerinate porcelain veneers can properly recover the transparency of teeth.</p>

Comparison of dentin nanoleakage among six adhesives / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the nanoleakage appearance in 6 dentin adhesives.</p><p><b>METHODS</b>Superficial occlusal dentin of 12 human molars without caries extracted freshly was exposed with 600-grit SiC papers under running water. Six adhesives were applied to dentin surfaces according to the manufacturers' instructions. The bonded teeth were sectioned occluso-gingivally into 0.9-mm-thick serial slabs that were stored in ammoniacal silver nitrate solution in the dark for 24 h and prepared for transmission electron microscope. The extent of nanoleakage among 6 dentin adhesives was measured and compared using one-way ANOVA.</p><p><b>RESULTS</b>The nanoleakage was observed obviously at the dentin-resin interfaces of all 6 adhesives. The average dentin nanoleakage values of Group A [BangDuo, (16.09 +/- 2.08)%], Group B [Single Bond, (13.39 +/- 1.81)%], and Group C [Prime&Bond NT, (11.27 +/- 1.94)%] were all significantly different (P < 0.05). There was no significant difference in the dentin nanoleakage between Group D [B(1), (12.13 +/- 2.11)%] and Group E [Clearfil SE Bond, (12.35 +/- 2.60)%], but both of them were lower than Group F [Adper Prompt, (14.93 +/- 2.67)%].</p><p><b>CONCLUSIONS</b>The nanoleakage phenomena at the dentin-resin interface were all observed diversely in the contemporary dental adhesives.</p>