Current situation and problems of the clinical application of completely digital workflow in fixed prosthodontics / 中华口腔医学杂志

Compared with traditional prosthodontic methods, digital prosthodontic technology greatly simplifies the treatment process of patients and improves the accuracy of prosthesis. The fully digital workflow is becoming an important direction of the development of fixed prosthodontics. It can not only effectively improve the efficiency, accuracy and predictability of prosthodontics, but also help the cooperation between multiple disciplines to ensure the systematic treatment. This article systematically discusses the concept process, key technology, material progress and application of completely digital prosthodontic process, as well as the remaining problems, in order to provide reference for its clinical application.

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.

The masseter inhibitory reflex and the recovery of the reflex after magnetic stimulation in normal subjects / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To analyze the masseter inhibitory reflex (MIR) and the recovery cycle of the MIR reflex after magnetic stimulation in normal subjects.</p><p><b>METHODS</b>In 30 healthy subjects we studied the MIR evoked by single magnetic stimulation in the mental territory. Masseter electromyographic activity, latency and duration of the early silent periods (SP1) and late silent periods (SP2), and SP2 amplitude percent were recorded. Paired stimuli technique was used, conditioning and test stimuli were delivered at different interstimulus intervals (ISI), ie.100, 200, 300, 400, 500, and 600 ms, then the recovery cycle of the MIR was analyzed.</p><p><b>RESULTS</b>Latency of SP1 was 12.1 (11.1, 14.4) ms, and duration of the SP1 was (17.3 ± 2.9) ms. Latency of SP2 was (47.7 ± 6.0) ms, and duration of the SP2 was (39.7 ± 13.3) ms. SP2 amplitude percent was 100.0%. With the paired stimuli technique, SP1 of the inhibitory reflex evoked by the test stimuli was found to be stable at every ISIs, but SP2 of the inhibitory reflex evoked by the test stimuli, instead, varied according to different ISI. With the short ISI, the area of SP2 evoked by the test stimuli was reduced, and with the increase of the ISI, the recovery degree of the area of SP2 evoked by the test stimuli was ascending, at 100 ms the SP2 amplitude percent was 17.1%, at 400 ms it was 93.4%, and it was close to 100% at 600 ms.</p><p><b>CONCLUSIONS</b>The study indicates that the use of the MIR elicited by the single and paired magnetic stimulation may be useful to examine or quantify some craniofacial diseases.</p>

The influence of thickness ratios on the fatigue behaviors of two kinds of dental ceramic / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the intensity changes of different thickness ratios of Empress II glass ceramic and GI- II glass-infiltrated alumina ceramic before and after Hertzian contact cyclic fatigue.</p><p><b>METHODS</b>Disk-shaped specimens of different thickness ratios of Empress II glass ceramic and GI-II glass-infiltrated alumina ceramic were respectively fabricated. Hertzian contact technique was imposed on the specimens. Critical loads of the specimens before and after 10(5) cycles loading were recorded.</p><p><b>RESULTS</b>The average values of critical loads of all specimens reduced significantly after cycles loading (P < 0.05), and critical loads declined with diminishing thickness of the core ceramic. The critical load of GI-II glass-infiltrated alumina ceramic was significantly higher than Empress II glass ceramic before and after cycle loading(P < 0.05).</p><p><b>CONCLUSION</b>Cycle loading can reduce the strengths of the two kinds of dental ceramic, and the latter is better than the former in the resistance to fracture and cyclic fatigue. Critical loads of the two kinds of dental ceramic are mainly influenced by the core ceramic's strength and thickness.</p>

Research of morphology for the toothmark in pocket limb / 华西口腔医学杂志

<p><b>OBJECTIVE</b>The purpose of this study was to observe the morphological changes of toothmarks in pocket limbs and to explore the durative development of bitemarks.</p><p><b>METHODS</b>Firstly a toothmark model was established by using a universal testing machine and a self-made incisor nod which was pressed particularly on pocket limbs. The changes of toothmarks were observed on alive and dead animals with time elapsing. The scopes of bruise and inden were analyzed by soft on digital photos. The depth data of inden were collected by three dimensional laser measurement.</p><p><b>RESULTS</b>The changes in the alive group were faster than that in dead group. There was no obvious fadeaway of bruise during 24 h. The scopes of inden were decreased remarkably in 1 h, while the decrease slowed down in the following hours.</p><p><b>CONCLUSION</b>The changes of indent are fast in pocket limb. It implies that bitemark evidence should be collected as fast as possible in cases.</p>

Compared study of cyclic fatigue behaviors in two kinds of dental ceramic layers structures / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To compare the difference in strength degradation and morphology damage of two dental ceramic materials after Hertzian contact cyclic fatigue.</p><p><b>METHODS</b>Hertzian contact technique was used to investigate the response of Empress II glass ceramic and GI- II glass-infiltrated alumina ceramic to cyclic fatigue. Critical loads of specimens after different fatigue cycles were recorded.</p><p><b>RESULTS</b>For Empress II glass ceramic, critical load had significantly difference between specimens after 10(5) cycles loading. No significant difference of critical load was found in GI- II glass-infiltrated alumina ceramic after cycles loading.</p><p><b>CONCLUSION</b>GI- II glass-infiltrated alumina ceramic has better capability in resistance to cyclic loading. It may attribute to microstructure of material. Empress II glass ceramic shows a brittle damage model.</p>

Cyclic fatigue of Vita mark II machinable ceramics under Hertzian's contact / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the cyclic fatigue modes of Vita mark II machinable ceramics under Hertzian's contact.</p><p><b>METHODS</b>Hertzian's contact technique (WC spheres r = 3.18 mm) was used to investigate the cyclic fatigue of Vita mark II machinable ceramic. All specimens were fatigued by cyclic loading in moist environment, furthermore, surviving strength was examined by three point test and morphology damage observation.</p><p><b>RESULTS</b>In homogeneous Vita mark II machinable ceramics, two fatigue damage modes existed after cyclic loading with spheres under moist environment, including conventional tensile-driven cone cracking (brittle mode) and shear-driven microdamage accumulation (quasi-plastic mode). The latter generated radial cracks and deeply penetrating secondary cone crack. Initial strength degradation were caused by the cone cracks, subsequent and much more deleterious loss was caused by radial cracks.</p><p><b>CONCLUSION</b>Cyclic fatigue modes of Vita mark II machinable ceramics includes brittle and quasi-plastic mode.</p>

A comparative study on cyclic and static fatigue of dental ceramic by means of Hertzian's contact / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To compare the difference in strength degradation and morphology damage of brittle dental ceramic after static load and cyclic fatigue.</p><p><b>METHODS</b>Hertzian's contact technique with a tungsten carbide sphere was used to investigate the response of feldspathic dental porcelain to static load and cyclic fatigue. All specimens were subjected to static or cyclic loading in moist environment. Furthermore the surviving strength of specimens was examined by the three-point test and the morphology damage was observed. Statistical analyses were performed with ANOVA and a P-value less than 0.05 was considered to be significant.</p><p><b>RESULTS</b>Outer cone crack and associated strength degradation simultaneously occurred both after the first cyclic loading and static loading. Up to 1,000 cycles, the specimens showed inner cone cracks and strength degradation was aggravated. No significant difference in the strength degradation among all static loading specimens and no inner cone cracks occurred in static loading specimens.</p><p><b>CONCLUSIONS</b>Both static and cyclic fatigue influence dental ceramic strength, but cyclic fatigue is more deleterious.</p>