Pain and prevention in extraction of the mandibular third molar / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To study the post-operative pain-re1ated factors in lower third molar extraction, and to find an effective prevention program.</p><p><b>METHODS</b>The first phase of the study was a clinical follow-up of 450 cases of lower third molar extraction. Factors associated with post-operative pain were analyzed, and difficulty assessment protocol of the tooth extinction was build. On this hasis, a pain-prevention clinical plan was constitute, and implemented in the second phase of 450 cases (selectively systemic or local medication). Treatment effects were observed.</p><p><b>RESULTS</b>There were no significant differences between the two phase groups oh the distribution of ages, sex, difficulty of tooth extraction, operation time, and other related factors, means that they were statistically comparable. Tooth extraction difficulty and operation time were most important predictive factors for post-operative pain. Local infective factors (including caries) and women's menstrual cycle also account for late stage pain. Through targeted pre-operative medication or post-operative alveolar socket treatment, pain was significantly reduced or prevented.</p><p><b>CONCLUSION</b>Reasonable peri-operative drug control basing on the difficulty assessment can provide a comprehensive and individualized control of pain after tooth extraction. Also, excessive or inappropriate using of drugs is largely avoided.</p>

Diameter and length double objectives robust analysis of cylinder dental implant / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To determine the jaw bone stress variation affected by cylinder implant diameter and length simultaneously in Ansys DesignXplorer module.</p><p><b>METHODS</b>Finite element model of segment mandible with a cylinder implant was created. The range of the implant diameter (D) and length (L) were set from 2.5 mm to 5.0 mm and from 6.0 mm to 16.0 mm respectively. The maximum Von Mises stresses in jaw bone and sensitivity to D and L were evaluated.</p><p><b>RESULTS</b>Under axial (buccolingual) load, when one variable equaled to median, the amplification of maximum Von Mises stresses in cortical bone and cancellous bone were 44.66% (71.32%) and 51.45% (58.50%) respectively with the D increasing. The amplification of maximum Von Mises stresses in cortical bone and cancellous bone were 45.97% (21.66%) and 52.15% (37.75%) respectively with the L increasing. When D exceeded 3.7 mm and L exceeded 10.0 mm, the response curve curvatures of maximum Von Mises stresses to L and D in jaw bone ranged from -1 to 0. And the variation of the maximum Von Mises stresses in jaw bone was more sensitive to D than to L.</p><p><b>CONCLUSION</b>Stresses in jaw bone under buccolingual and axial load are apt to be affected by implant diameter and length respectively. And to a cylinder implant, the diameter exceeds 3.7 mm and length exceeds 10.0 mm are optimal selections. Diameter should pay more attention to than to length for cylinder implant. Expanding the width of the jaw bone is more important than expanding the height of the jaw bone in clinical experience.</p>

Optimized thread pitch design and stress analysis of the cylinder screwed dental implant / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To determine the optimal thread pitch for an experimental cylinder implant in Ansys Work-bench Design Xplorer environment.</p><p><b>METHODS</b>Finite element models of segment jaw bone with a V-shaped thread implant were created. The thread pitch (P) was set from 0.5 mm to 1.6 mm. The maximum Equivalent stresses (EQV stresses) in jaw bone and in implant were evaluated.</p><p><b>RESULTS</b>Under axial load, the amplification of maximum EQV stresses in cortical bone, cancellous bone and implant were 7.1%, 123.4% and 28.7% respectively. Under bucco-lingual load, the amplification of maximum EQV stresses in cortical bone, cancellous bone and implant were 2.8%, 28.8% and 14.9% respectively. When P exceeded 0.8 mm, the response curve curvature of maximum EQV stresses in jaw bone and in implant to P was ranged from -1 to 1.</p><p><b>CONCLUSION</b>Stresses in cancellous bone are more sensitive to thread pitch than in cortical bone. Stresses in jaw bone under axial load are easier affected by thread pitch than under bucco-lingual load. Thread pitch plays a greater role in protecting dental implant under axial load than under bucco-lingual load. Thread pitch exceed 0.8 mm should be the optimal design in a cylinder implant, but oversized pitch should be avoided too.</p>

Design and application of internal devices for automatic elasticity distraction osteogenesis / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To improve the design of the devices used for autoatic elasticity distraction osteogenesis, and to preliminarily testify their feasibility for clinical application.</p><p><b>METHODS</b>The internal automatic distraction devices were constructed by three parts, including sinusoid shape memory alloy distractor, reconstructive plate and mini-plate. The animal model of trifocal bone transport reconstruction of canine mandibular mentis was duplicated, in which a 6 cm mandibular mentis segment was removed and the transport disc was created by osteotomy in both ends of the mandibular defect. The plates were used for internal fixation and shape reconstruction of the mandible. They also served as transport distraction guidance for the elasticity distractor.</p><p><b>RESULTS</b>The new devices could complete bone transport as expected. Regenerated bone segments were formed in two months and both sides of the mandibular body were lengthened. Because of the narrow angle and obstruction from the thick soft tissues in the mentis area, the ultimate symphysis mentalis was not reconstructed.</p><p><b>CONCLUSION</b>The design of the internal elasticity distraction devices showed potential feasibility for clinical practice. But further studies are still needed for better control of the strength and balance of distraction forces.</p>