Minimal invasive microscopic tooth preparation based on endodontic, periodontal and functional health / 华西口腔医学杂志

Tooth preparation is the primary and core operation technique for dental esthetic restoration treatment, due to its effect of providing restoration space, bonding interfaces and marginal lines for dental rehabilitation after tooth tissue reduction. The concept of microscopic minimal invasive dentistry put forward the issue of conducting high-quality tooth preparation, conserve tooth-structure, protect vital pulp and periodontal tissue simultaneously. This study reviewed the concepts, physiology background, design and minimal invasive microscopic tooth preparation, and in the meantime, individualized strategies and the two core elements of tooth preparation (quantity and shape) are listed.

All-ceramic premolar guiding plate retains resin-bonded fixed partial dentures / 华西口腔医学杂志

OBJECTIVE@#This study aims to investigate the fracture resistance and short-term restorative effects of resin-bonded fixed partial dentures (RBFPDs) made from heat-pressed lithium-disilicate-based glass-ceramic (IPS e.max press) and zirconia ceramic (WIELAND) and retained by all-ceramic guiding plates when used to restore missing mandibular second premolars.@*METHODS@#A total of 64 human mandibular first premolars and first molars were prepared as abutments, then were randomly divided into 4 groups (n=8): E0, heat-pressed ceramic RBFPDs, no cyclic loading; E1, heat-pressed ceramic RBFPDs exposed to 300 000 cycles of dynamic loading; W0, zirconia ceramic RBFPDs, no cyclic loading; and W1, zirconia ceramic RBFPDs exposed to 300 000 cycles of dynamic loading. Fracture strength was tested in a universal testing machine.@*RESULTS@#The medians of fracture strength were 1 242.85 N±260.11 N (E0), 1 650.85 N±206.77 N (W0), 1 062.60 N±179.98 N (E1), and 1 167.61 N±265.50 N (W1). Statistical analysis showed that all the groups exhibited significantly higher fracture strength compared with the maximum bite force in the premolar region (360 N; P0.05). Significant statistical differences were found between the zirconia ceramic groups (W0 and W1, P0.05) after dynamic loading.@*CONCLUSIONS@#The RBFPDs retained by all-ceramic guiding plates exhibited promising fracture properties and optimal short-term restorative effects when used to restore missing mandibular second premolars.

Changes of bone mineral density and biomechanical properties of the femur after ipsilateral tibia fracture and fixation in rats / 医用生物力学

Objective To investigate the changes of bone mineral density (BMD) and biomechanical properties of the femur after ipsilateral tibia fracture in rats, and its relationship with the tibia fracture union. Methods Forty 3-month-old female SD rats were divided into 2 groups randomly and evenly: the surgery group and the control group. The surgery group received middle shaft fracture and fixation surgery on the right tibia. BMD of the right femur was measured both before the surgery and at 2nd, 4th, 6th, 8th, 10th, 12th week after the surgery, respectively. Ten rats in the surgery group and ten rats in the control group were executed at 6th and 12th week after the surgery, respectively, to test the biomechanical properties of their right tibia and femur. Results The radiological union rate and mechanical union rate of the tibia were 50% and 70%, respectively, at 6th week after the surgery, and those at 12th week after the surgery were both 100%. At 2nd, 4th, 6th, 8th week after the surgery, BMD of the right femur in the surgery group was significantly lower than that in the control group (P<0.05). Compared with the control group, there was no statistical difference in BMD of the right femur at 10th, 12th week after the surgery. Biomechanical properties of the right tibia and femur at 6th week after the surgery showed obviously worse than those at 12th week after the surgery (P<0.05). Analysis showed that the fracture union was highly related with mechanical properties of the tibia (P<0.01), which was also highly related with BMD and mechanical properties of the femur (P<0.001). Conclusions In the early stage of tibia fracture, disuse osteoporosis might occur due to the decrease of BMD and worse mechanical properties in the ipsilateral femur, but as the tibia fracture united, BMD and biomechanical properties of the femur became normal again.

The acceleration of titanium implant osseointegration by low intensity pulsed ultrasound: an experimental study in rats / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To establish an animal model of titanium implant and to investigate the effects of low intensity pulsed ultrasound (LIPUS) on the implant osseointegration.</p><p><b>METHODS</b>Twenty-four female Sprague Dawley (SD) rats were used. Titanium implants were inserted into tibia metaphysis bilaterally in each SD rat. Since the second day following implant surgery, LIPUS stimulation were carried out around the implant on the right side for 20 minutes per day, and implants on the left side remain untouched as self-control. Eight rats were sacrificed and tibiae specimens were harvested on the end of the 4th, 8th, and 12th week respectively. X-ray picture, micro-CT analysis and histological sections were performed to evaluate the effects of LIPUS on the implant osseointegration.</p><p><b>RESULTS</b>Osseointegration at the interface between the implant and bone tissue was observed bilaterally. In the micro-CT histomorphometry analysis, the percentage of osseointegration (%OI) of experiment side were (45.708 ± 3.316)%, (46.231 ± 1.954)%, and (46.807 ± 1.451)% on the end of the 4th, 8th, and 12th week. Meanwhile, the %OI of control side were (43.021 ± 3.558)%, (44.272 ± 3.023)%, and (44.894 ± 4.215)% respectively. The %OI on the 4th weekend, bone volume ratio (BV/TV) on the 4th and 8th weekend, trabecular thickness (Tb. Th) and degree of anisotropy (DA) on the 8th and 12th weekend of the experiment side tibia were significantly greater than those on the control side (P < 0.05). The histological examination showed that the thickness of new bone around the implant and the bone-implant contact area was obviously greater in the LIPUS treated side compared to the control side.</p><p><b>CONCLUSIONS</b>The LIPUS therapy may accelerate the bone healing and osseointegration at the interface between titanium implant and bone, and promote remodeling of bone trabecula on the early stage.</p>

Study and preparation of a novel apatite-wollastonite bioactive glass-ceramic-calcium sulphate hemihydrate composite / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To prepare a novel apatite-wollastonite bioactive glass-ceramic-calcium sulphate hemihydrate(AW-BGC-CSH) composite, to study its biocompatibility, and to provide experimental support for its further clinical application.</p><p><b>METHODS</b>Samples of AW-BGC-CSH composite were prepared with different AW-BGC granules-CSH ratios (50%, 40%, 30%, 20%). Surface morphology, microstructure and mechanical features of the composite were measured. Osteoblasts were cultivated in vitro on the composite. Cell morphology, proliferation, and the alkaline phosphatase (ALP) activity of osteoblasts were examined to determine the biocompatibility of the composite.</p><p><b>RESULTS</b>The composite showed a three-dimensional pored structure with communicated micropores under scanning electron microscopy (SEM). The plasticity of the composite could be maintained within 3 - 5 min. Its top solidification temperature was 36.4°C and the maximum compressive strength was 9.3 MPa. The osteoblasts adhered to the composite and grew well. At 1, 3, 5, 7 d after cultivated, the microprotein contents of the composite were (251 ± 12), (296 ± 31), (580 ± 13) and (571 ± 15) mg/L, and the ALP activity of the composite were (4.50 ± 0.68), (6.90 ± 0.27), (12.05 ± 0.28) and (11.86 ± 0.63) U/mg. The results of the ALP activity and microprotein contents in the experiment group were significantly higher than those in the control group (P < 0.05).</p><p><b>CONCLUSIONS</b>The prepared AW-BGC-CSH composite has a three-dimensional pored structure, favourable plasticity, mechanical property and good biocompatibility.</p>

Effects of Sol-Gel coating on the corrosion resistance of nickel-chronium alloys / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the effects of Sol-Gel coating on the corrosion resistance of nickel-chronium alloys in vitro.</p><p><b>METHODS</b>The bond strength of coating-substrate interface sintered at different temperatures (300, 400, 500, 600 degrees C) was tested by scratching method. The Sol-Gel coating was analyzed by scanning electron microscope (SEM), and its corrosion resistance was assessed by a static immersion method.</p><p><b>RESULTS</b>The bond strength of coating-substrate interface reaches the peak at 400 degrees C. The Sol -Gel coating can apparently inhibit the release of metal ions and improve the corrosion resistance of nickel-chromium alloy.</p><p><b>CONCLUSION</b>Sol-Gel coating can evidently improve corrosion resistance of the nickel-chromium alloy, which has great potential in prospective clinical practice.</p>

Feasibility of permanent maxillary tooth removal using articaine anesthesia without palatal injection / 华西口腔医学杂志

<p><b>OBJECTIVE</b>This study was to test the feasibility of permanent maxillary tooth removal using articaine without a second palatal injection.</p><p><b>METHODS</b>Of 104 patients, 38 patients had bilateral extraction and 66 patients had unilateral extraction of maxillary tooth. In the test group, 1.7 mL articaine with 1:100000 epinephrine was injected into the buccal vestibule of the tooth and the tooth were extracted after 5 minutes. In the control group, the patients were subjected to both palatal injection with 2% lidocaine hydrochloride and buccal injection with articaine. All patients completed visual analog scales (VAS) after extraction.</p><p><b>RESULTS</b>The achievement ratio of permanent maxillary tooth anesthesia of test group was 96.2%. The achievement ratio of permanent maxillary tooth anesthesia of control group was 97.1%. There was no statistical significance between achievement ratio of test group and control group(P > 0.05).</p><p><b>CONCLUSION</b>Permanent maxillary tooth removal without palatal injection is possible by articaine injection to the buccal vestibule of the tooth.</p>

Influence of manufacture technique on translucency and color of dental porcelain / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To study the influence of manufacture technique on the translucency and color of dental porcelain.</p><p><b>METHODS</b>Specimens were made of VITA VMK 95 dentin porcelain and enamel porcelain and divided into 3 groups: Sintering times group (1, 2, 4, 6, 8 and 10 times), sintering temperature group (910, 920, 930, 940 and 950 degrees C), sintering vacuum group (95, 65, 35 and 0 kPa). Transmittance, Y, dominant wavelength and saturation were measured by PR-650 spectra scan spectrocolorimeter.</p><p><b>RESULTS</b>Transmittance of dentin porcelain increased after 6 times repeated sintering. Transmittance of enamel porcelain increased first after the second sintering, and then became decreasing when sintering more than 2 times. Transmittance of enamel porcelain deceased when sintering temperature was lower than standard. Decrease of sintering vacuum caused the transmittance of dentin and enamel porcelain decreased. The changing of value was coordinated with transmittance. Dominant wavelength and saturation had negative correlation with sintering times and temperature, and positive correlation with vacuum.</p><p><b>CONCLUSION</b>Sintering times, temperature and vacuum all had prominent effects on the translucency and color of dental porcelain. Comparing with dentin porcelain, enamel porcelain was more sensitive with the modification of manufacture technique.</p>

The effect of cryotreat on tensile properties of medium melting-point and high melting-point castable alloy / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To introduce cryotreat technique into prosthetic dentistry by testing the tensile properties of CW-H Co-Cr-Mo cast alloy before and after cryotreat and to observe the image changes by SEM to study the mechanism that changes the tensile properties of the alloy.</p><p><b>METHODS</b>15 CW-H cast alloy were divided into 3 groups, i.e. control group (G1), cryotreated group (G2) and cryotreated plus post-cryogenic treated group (G3). The gauge test technique was employed to test the modulus of elasticity. Then the strength and percentage elongation (PE) were tested. SEM images were used to analyze the mechanism that improved the tension properties of the alloy.</p><p><b>RESULTS</b>For CW-H alloy the strength and the modulus of elasticity of both G2 and G3 were effectively increased but PE effectively decreased than G1. There was no effectively difference between G2 and G3, but G3 was larger than G2. SEM images of G2 and G3 showed that secondary-carbonide separated out all over the alloy.</p><p><b>CONCLUSION</b>The results obtained above suggest that cryotreat is an effective method in enhancing tensile properties of CW-H Co-Cr-Mo cast alloy.</p>