The surface characterization of ultrafine grained titanium after roughness treatment of different types / 实用口腔医学杂志

Objective:To investigate the surface characterization,cell adhension and proliferation of ultrafine grained titanium (UFG Ti) after different sand blasting and acid-etching(SLA).Methods:The billets of UFG Ti and commercially pure titanium Ti(CP Ti) were incised into cylindrical specimens with 7 mm in diameter and 2 mm in height.The specimens were sand blasted at the air pressure of 0.2,0.4,0.6 and 0.8 MPa respectively(n =10) and then acid-etched.The surface morphology,roughness and surface wettability of the specimens were examined.Rat embryo osteoblasts MC3T3-E1 were cultured on the speciments for 1 d,3 d and 5 d respectively,the cell morphology and cell density were observed.Results:The different hierarchical porous topographies were formed on the surface of UFG and CP Ti after modified by SLA.The sizes of blasted holes on the surface and the surface roughness of both materials increased with the increase of blast pressure,but the values of UFG Ti were lower than those of CP Ti correspondingly(P ＜ 0.05).The surface wettability of them was also changed with the blast pressure,but the values of UFG Ti was significantly smaller than those of CP Ti(P ＜ 0.05).When the blast pressure was 0.6 Mpa,the UFG Ti exhibited excellent wettability,the cell density was the highest,the morphology of MC3T3-E1 cells on UFG Ti was superior to that on CP Ti.Conclusion:UFG Ti exhibits proper surface morphology,roughness and excellent wettability,which is more appropriate for adhension and proliferation of MC3T3-E1 cells after modification by SLA at blast pressure of 0.6 Mpa.

Effect of bite force on the periodontal tissue remodeling of molar with different levels of periodontal attachment ment / 华西口腔医学杂志

<p><b>OBJECTIVE</b>The theory of strain energy density (SED) was combined with finite element analysis to investigate alveolar bone remodeling of the mandibular first molar with different levels of periodontal attachment under mastication loading.</p><p><b>METHODS</b>Three-dimensional finite element models of the mandibular first molar with different levels of periodontal attachment were established. Based on SED theory, the user material subroutine (UMAT) (used by ABAQUS software) was developed by ourselves to simulate the remodeling process of mandibular bone. The stress distributions and bone density changes were analyzed under different mastication loading. The influence of loading magnitude on alveolar bone remodeling with different levels of periodontal attachment was investigated.</p><p><b>RESULTS</b>The results showed that the neck of buccal, lingual regions and root apex area experienced a higher stress. The stress and the density of alveolar bone increased gradually with the enhancing of the bite force at the beginning. Then the density would appear declining when the bite force exceeded the extreme load. The extreme load reduced from 420 N to 240 N with the periodontal attachment falling from normal to 1/2 of root length also. And the remodeling rate of the bone was faster as the loading increasing.</p><p><b>CONCLUSION</b>The capability of the periodontal tissue for supporting the teeth will drop gradually as the periodontal attachment level dropping. And the decline of bone density also appeared in earlier time. The change of density is associated with mastication loading during the bone remodelling. And reducing the occlusal force properly to the molar with different attachment level is benefit for clinical treatment and prognosis of periodontal disease.</p>

Analysis of residual stress between core and veneer ceramics by finite element method / 实用口腔医学杂志

Objective:To study the residual stress distribution through the thickness of bilayered dental ceramic subjected to thermal stress, in order to improve the restoration. Methods: The finite element model of bilayered dental ceramic was set up based on International Organization for Standardization(ISO) 96936:1999. The residual stresses were calculated in viscoelastic and elastic phases during cooling of dental ceramic to analyze the residual stress distribution. Results: The deformation of core was greater than the veneer ceramics during the cooling period of dental ceramic. The residual stress increased with the decreasing of the temperature approaching the interface of core and veneer ceramics. But it decreased with the increasing of the thickness of veneer ceramics.Conclusion: Thermal compatibility of core and veneer ceramics is very important to the residual stress distribution in the bilayered dental ceramic, which may benefit to All-ceramic restorations. The viscoelastic behavior of ceramic should be taken into account in the thermal compatibility.

The application of infinite element method to endodontic endosseous implant stress analysis / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To study the precise stress distribution of the apical foramen area of endodontic endosseous implant, in order to improve the prosthetics of endodontic endosseous implant.</p><p><b>METHODS</b>After analysis of the two-dimensional endodontic endosseous implants model with finite element method, left and right areas beside the apical foramen were selected as infinite domains to calculate. D-N interactive method was used to connect the finite and infinite domains.</p><p><b>RESULTS</b>Under 45 degrees axial right oblique loading, the stress concentration occurred in both infinite domains of the apical foramen. The infinite domain nearing the load side was tension stress concentration, but the other side was compressive stress concentration. Two stress concentration points were just at the central points, which were intersections between implant and dentin. The stress reduced in all directions from these two stress concentration points, but in the ligament, the result was contrary.</p><p><b>CONCLUSIONS</b>The change of the tooth rotational center is helpful to the tooth stability and carrying capacity after restoration. In the implant area, the diameter of implant at the apical foramen of root shall not be reduced to protect root in clinical work. It is very important to preserve the tissue of periodontal ligament for endodontic endosseous implants.</p>

The establishment of a two-dimensional infinite element analysis model for endodontic endosseous implants / 实用口腔医学杂志

砄bjective: To establish two dimensional infinite model for endodontic endosseous implants in order to set up infinite element method and study the stress distribution of the apical foramen area of endodontic endosseous implant. Methods: Based on the analysis of two dimensional endodontic endosseous implants model with finite element method, left and right areas beside the apical foramen were selected as infinite domains including implant dentin and ligament sections. D N interactive method was used to connect the finite and infinite domains. Results: After ten times interaction between finite and infinite domains with D N interactive method, the outcome approached to a stable numerical value close to the displacement of both domains. Conclusion: The infinite model of two dimensional endodontic endosseous implants established by D N interactive method is efficient and accurate.

The study of stress to endodontic endosseous implants with infinite element method / 实用口腔医学杂志

Objective: To study the precise stress distribution in the apical foramen area of endodontic endosseous implant. Methods:After analysis of the two-dimensional endodontic endosseous implants model with finite element method, left and right areas beside the apical foramen were selected as infinite domains for calculation. Results:Under 45? axial right oblique loading, the stress concentration occurred in both infinite domains of the apical foramen. The tension stress concentrated in the infinite domain near the load side,but the other side was compress concentrated. Two stress concentration points were just at the central points, which were intersections between implant and dentin. In the implant and dentin section, the stress reduced in all directions from two stress concentration points, but in the ligament section, the result was contrary. Conclusion:It is helpful to keep the root stable when the fulcrum of the root changed to lower part after restoration. In the implant area,the diameter of implant at the apical foramen of root shouldn't be reduced for the protection of root in clinical work;It is very important to preserve the tissue of periodental ligament for endodontic endosseous implants.