3D-printed custom trays with a Gothic arch for centric relation recording and definitive impression making for complete dentures: A dental technique.

An appliance was designed and fabricated by using computer-aided design and computer-aided manufacturing (CAD-CAM) and 3-dimensional (3D) printing to combine a custom tray with an intraoral Gothic arch. This helped simplify centric relation recording and combined definitive impression making and centric relation recording into a single step.

Trueness of One Stationary and Two Mobile Systems for Three-Dimensional Facial Scanning.

PURPOSE: To evaluate the trueness of one stationary and two mobile systems for 3D facial scanning. MATERIALS AND METHODS: Twenty participants were included in this study. After marking facial soft tissue landmarks, their faces were scanned using three facial scanning systems: the Bellus3D Dental Pro app on an iPad Pro 2020 (Apple; IP); the ARC-7 Face Scanning System (Bellus3D; BA); and the EinScan Pro 2X Plus (Shining 3D Tech; EP) following the manufacturers' operating instructions. Three-dimensional images were reconstructed with corresponding software and saved in object (OBJ) file format. The interlandmark distances were measured and compared to direct caliper measurements, and absolute error (AE) was chosen as the measurement to determine the trueness of the three scanners. The normal distribution and variance of homogeneity were measured, and then the data were analyzed using one-way ANOVA or Kruskal-Wallis H test. The significance level was set at P = .05. RESULTS: For the measurement of interlandmark distances, no significant differences were found among the four measuring techniques, and the mean AEs of the IP, BA, and EP systems were 1.17 ± 0.80 mm, 0.76 ± 0.61 mm, and 0.69 ± 0.65 mm. CONCLUSION: The three facial scanning systems tested provided a reliable 3D facial reconstruction. The portable IP system could meet the clinical requirements for facial scanning, but it is suggested to select the EP and BA systems when a higher trueness is required.

[Influence of canine vertical position on smile esthetic perceptions by using 3D digital facial reconstruction].

PURPOSE: To verify the impact of alterations in the vertical position of maxillary canine on smile esthetic perceptions, in order to find an optimal canine position. METHODS: A volunteer's dentition and facial images were scanned by intra-oral scanning and three-dimensional facial scanning, which were then calibrated. In virtue of dental computer-aided design software, the canine vertical positions were symmetrically modified in a variable of 0.5 mm, creating 4 new 3D virtual digital smile faces varying from 1.0 mm of intrusion to 1.0 mm of extrusion. A total of 5 3D virtual digital smile faces were evaluated from the front and 45°to the right sides by 60 dentists and 60 laypersons on a visual analog scale. The data were input into SPSS 20.0 software package, ANOVA of repeated measurement was used to compare the differences in the assessment scores between two groups and rank sum test was used to analyze the differences from different evaluation angles. RESULTS: Alterations in the vertical position of maxillary canine had significant influence on the esthetic evaluation of the smile(P<0.05); there was significant difference between the dentists' and laypersons' esthetic evaluations after the canine vertical position being modified(P<0.05), there was no significant difference on the evaluations of smile esthetics from different evaluation perspectives(P>0.05). CONCLUSIONS: The most attractive smile was the one with canine cusp 0.5 mm vertically higher than the incisal edge of the lateral incisor. The smile is not attractive when the cusp of canine is vertically lower than the incisal edge of lateral incisor. These results can be used as references in the esthetic treatment planning for anterior maxillary teeth.

[Minimal invasive microscopic tooth preparation based on endodontic, periodontal and functional health].

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.

BM-MSCs and Bio-Oss complexes enhanced new bone formation during maxillary sinus floor augmentation by promoting differentiation of BM-MSCs.

Bone marrow-derived mesenchymal stem cells (BM-MSCs) have been recognized as a new strategy for maxillary sinus floor elevation. However, little is known concerning the effect of the biomechanical pressure (i.e., sinus pressure, masticatory pressure, and respiration) on the differentiation of BM-MSCs and the formation of new bone during maxillary sinus floor elevation. The differentiation of BM-MSCs into osteoblasts was examined in vitro under cyclic compressive pressure using the Flexcell® pressure system, and by immunohistochemical analysis, qRT-PCR, and Western blot. Micro-CT was used to detect bone formation and allow image reconstruction of the entire maxillary sinus floor elevation area. Differentiation of BM-MSCs into osteoblasts was significantly increased under cyclic compressive pressure. The formation of new bone was enhanced after implantation of the pressured complex of BM-MSCs and Bio-Oss during maxillary sinus floor elevation. The pressured complex of BM-MSCs and Bio-Oss promoted new bone formation and maturation in the rabbit maxillary sinus. Stem cell therapy combined with this tissue engineering technique could be effectively used in maxillary sinus elevation and bone regeneration.

Excitability of the central masticatory pathways in patients with sleep bruxism.

Since sleep bruxism (SB) is defined as a stereotyped movement and mainly associated with rhythmic masticatory muscle activity, the aim of this study was to get a better understanding on the subcortical and cortical networks related to the excitability of the central masticatory pathways in SB patients. Of 26 SB patients (12 females and 14 males; mean age: 24.9±4.0 years) and 30 normal subjects (18 females and 12 males; mean age: 24.1±3.1 years) selected, the motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) in masseter muscles, and the masseter inhibitory reflex (MIR) elicited by magnetic stimulation with single and double-shock techniques were studied. The MEPs elicited by TMS were similar in both SB patients and normal subjects. As for the MIR elicited by single magnetic stimulation, the latency and duration of the early silent periods (SP1) between the two groups were similar; but in 5 patients the late silent periods (SP2) was absent, and this difference in the frequency of absence of the SP2 between SB patients and normal subjects was significant; with double-shock technique, the recovery of SP2 was significantly lower in SB patients compared to normal subjects. These results suggested an abnormal excitability of the central masticatory in SB patients; and it is also indicated that SB may be mainly under the influence of brainstem networks rather than that of cortical networks.

[Effect of self-made colloid paste on gingival retraction in dogs].

PURPOSE: To evaluate the efficiency of self-made paste on gingival retraction in dogs as well as its potential clinical application. METHODS: Forty teeth from two mature dogs were prepared with 0.5 mm wide shoulder in the lip and buccal sides of the teeth, and then divided into four groups randomly. The gingival grooves of the four groups were filled with self-made colloid paste, Expasyl gingival retraction paste, gingival retraction cord, and medicated (15.5% Fe2SO4 solution) gingival retraction cord, respectively. The gingival grooves models before and after gingival retraction were analyzed using the image precise mapper instrument; the gingival width and height of the gingival groove were compared using SAS6.12 software package. RESULTS: The changes of gingival width of the gingival groove before and after gingival retraction were not significant between the four groups. However, the gingival height of the gingival groove in the medicated gingival retraction cord group increased significantly [(0.423 + or - 0.348) mm before gingival retraction and (0.623 + or - 0.278) mm after gingival retraction] compared with the other three groups. CONCLUSIONS: The self-made colloid paste for gingival retraction is efficient like Expasyl gingival retraction paste and gingival retraction cord with potential clinical application, while the medicated gingival retraction cord can induce gingival shrinkage. Supported by Research Fund of Science and Technology Bureau of Huangpu District,Shanghai.

[The influence of thickness ratios on the fatigue behaviors of two kinds of dental ceramic].

OBJECTIVE: 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. METHODS: 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. RESULTS: 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). CONCLUSION: 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.

[Research of morphology for the toothmark in pocket limb].

OBJECTIVE: The purpose of this study was to observe the morphological changes of toothmarks in pocket limbs and to explore the durative development of bitemarks. METHODS: 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. RESULTS: 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. CONCLUSION: The changes of indent are fast in pocket limb. It implies that bitemark evidence should be collected as fast as possible in cases.

[Compared study of cyclic fatigue behaviors in two kinds of dental ceramic layers structures].

OBJECTIVE: To compare the difference in strength degradation and morphology damage of two dental ceramic materials after Hertzian contact cyclic fatigue. METHODS: 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. RESULTS: 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. CONCLUSION: 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.

[Cyclic fatigue of Vita mark II machinable ceramics under Hertzian's contact].

OBJECTIVE: To investigate the cyclic fatigue modes of Vita mark II machinable ceramics under Hertzian's contact. METHODS: 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. RESULTS: 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. CONCLUSION: Cyclic fatigue modes of Vita mark II machinable ceramics includes brittle and quasi-plastic mode.

[A comparative study on cyclic and static fatigue of dental ceramic by means of Hertzian's contact].

OBJECTIVE: To compare the difference in strength degradation and morphology damage of brittle dental ceramic after static load and cyclic fatigue. METHODS: 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. RESULTS: 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. CONCLUSIONS: Both static and cyclic fatigue influence dental ceramic strength, but cyclic fatigue is more deleterious.

[Cyclic fatigue of GI-II glass infiltrated ceramic in Hertzian's contact].

PURPOSE: To investigate the cyclic fatigue damage modes of GI-II glass infiltrated ceramic in Hertzian's contact. METHODS: All ceramic specimens were loaded by a r=3.18 mm WC ball to investigate their cyclic fatigue behavior in Hertzian's contact. Furthermore, the surviving stress was examined by three-point-flexure-test and morphological damages were observed. All statistical analysis were performed with one-way ANOVA. For all tests, a P-value less than 0.05 was considered to be significant. RESULTS: The strength of the specimens decreased from 395.7+/-46.5MPa to 318.6+/-40.3MPa after the 1st cycle when the load was 900N, 203.6+/-18.7MPa after 10(5) cycles, and 170+/-33.9MPa after 2 x 10(5) cycles. There was significant difference from that of the cycles (P<0.05). According to the loading cycles, the fatigue damage represented bend in loading area, worm-eaten abrasion or exfoliation around loading area and sequent massive exfoliation. But there was not significant different between the 1st cycle and the 105 cycles when the load was 500N. CONCLUSION: In Hertzian's contact,the fatigue damage mode is characterized by a quasi-plastic mode caused by crack tip shield and crystal bridging decline which are driven by shear and tensile stress.