[The Spatiotemporal Expression Patterns of Mechanical-Stress Related Regulatory Proteins in Mouse Molar Development].

OBJECTIVE: In order to better understand the role of mechanical stress in early tooth development, we examined the spatiotemporal expression patterns of mechanical-stress related regulatory protein (actin filament, or F-actin), non-muscle myosin ⅡB (NMⅡB) and vinculin at different stages of tooth development in mice. METHODS: Mouse first mandible molars were used as the research model. Immunofluorescence staining was performed to detect the expression patterns of F-actin, NMⅡB and Vinculin, the key molecules constituting the chemical mechanical system, at bud, cap, early bell and late bell stages of tooth. RESULTS: F-actin, NMⅡB and vinculin were all expressed in the tooth epithelium in an extensive or a limited way at different stages of tooth development, while F-actin was also expressed steadily in the mesenchymal cells. The quantitative analysis of fluorescence intensity showed that F-actin and NMⅡB exhibited significantly increase in the early stage of tooth development, but then dropped to their basal levels at the end of the late bell stage and the early bell stage respectively, with the differences of expression changes between successive developmental stages showing statistically significance ( P<0.05). Vinculin expression, however, remained at a relatively constant level except for the late bell stage when vinculin expression was slightly elevated compared to that of the early bell stage ( P<0.05). CONCLUSIONS: The findings suggest that mechanical stress is involved in early tooth development. F-actin may have an important role in dispersing and transmitting mechanical stress while NMⅡB may participate in tooth epithelial invagination and cusps formation. The findings also suggest that vinculin can respond to the mechanical stimuli and its interaction with cell adhesion molecules may play a role in tooth development. The mechanism of how actomyosin and cell adhesion interact with each other in regulating tooth development still needs further investigation.

The question about the numerical value and quantitative data transfer of implant prosthodontics-orom experience guidance to digital guidance.

The correct implant site design and placement are the basic clinical techniques that must be known for implant restoration. For a long time, most implants have been placed by free hands, and the choice of site is mostly dependent on the accumulation of long-term experience of the surgeon. The selection of implant site guided by this experience analogy logic is often based on the surgeon's level of experience,which often makes it very easy to produce complications related to the implant restoration of the incorrect site. In contrast, a clinical program using digital guidance and real-time measurable verification has emerged based on the restoration-oriented implantation concept, which marks the formation of an accurate, measurable and verifiable whole-process digital implant prototype. Furthermore, from the perspective of surveying, the numerical requirements that digital implant restoration relies on are actually incomplete to the four elements of measurement, which leading to the doubts about its authenticity. This article will question the numbers in implant restoration, and conduct a preliminary demonstration, and propose a new reliable actual measurement and verification method of the correct location and the numerical requirements of the restoration space and a new clinical program that relies on numbers from the perspective of the evolution of digital restoration, guided implantology and actual measurement technology. And this article further discusses the current mainstream implant restoration technology based on experience analogy which cannot effectively support the whole process of digital implant restoration and provides a new logical cognitive basis for the final realization of the entire process of digital implant restoration.

Questions about the numerical value and quantitative data transfer of tooth preparation-from experience guidance to digital guidance.

Tooth preparation is a common operation in dental clinical practice. This procedure is irreversible and invasive from the point of view of tooth preservation. Conditions of the abutment tooth, treatment methods, and restoration materials for target restoration affect tooth preparation. To achieve the goals of tooth tissue preservation, dental pulp protection, and periodontal health, dentistry professionals agreed on the importance of minimizing the amount of tooth reduction. The foundations for realizing this consensus are as follows. First, the available restoration materials with improved comprehensive performance need less target restoration space. Next, teeth can be prepared under a digital guide, and the real-time measurement of restoration space can be verified due to the invention of digital technologies for the analysis of the quantity and shape of the prepared tooth and tooth measurement. Moreover, guiding methods for preparation have been developed from freehand operation under the naked eye based on accumulated personal experience to digital-guidance jointing microscope. These innovations indicate the creation of a prototype of guided prosthodontics that is precise and applies real-time measurement throughout the process of tooth preparation. From the perspective of the evolution of digital, guided, and micro prosthodontics, this article raised seven questions about the numerical value and quantitative data transfer of tooth preparation and evaluated the authenticity of existing numerical requirements from the perspective of the four elements of measurement. Identifying unified measuring methods and developing measuring tools with a precision of hundred or ten microns will be the key to solving the problem about the authenticity of numerical measurement. Furthermore, this paper summarizes the methods of how to control tooth reduction and explains in depth why the currently dominant tooth preparation technology, which is based on empiricism, cannot effectively achieve the goals in digital prosthodontics. Therefore, we strongly call for rebuilding the digital foundation of prosthodontic treatment immediately.

[Interarch distance is a target restorative space value: clinical decisionmaking of implant restoration guided by measured value].

When design an implant restoration for edentulous patients, many doctors ignore the sufficiency of the interarch distance (vertical distance) or horizontal distance of the patient to accommodate the superstructure and restoration before designing the implant plan. However, the connotation of measuring the interarch distance or horizontal distance has not been clarified in clinical practice. It is often based on visual estimation after operation, and the decision-making path of implant restoration is inverted, resulting in many mistakes regarding the restoration after implantation. The main reason is the lack of standardized paths and practical methods to use before surgery. This article recommended initially establishing a maxillo-mandibular relationship based on natural teeth, old dentures, or new ones and then using the height and horizontal distance or angle of the target restorative space, which was easier to grasp as the measured index. The minimum vertical distance (including the height of the gingival surface and the bone surface) and the horizontal distance (or the angle from the bone or gingival surface to the proposed occlusal plane) should be measured before operation. A decision tree of edentulous jaw restoration guided by the values of the repair space was established based on the measured values. This article clarified the measuring points and planes and thus provided a quantitative relationship basis for the design of implant restoration.

Immediate precision of the digital osteotomy template in the digital stackable template: a clinical study.

OBJECTIVES: This study aimed to evaluate the immediate accuracy of the digital osteotomy template in the digital stackable template. METHODS: From November 2018 to January 2020, 4 patients with dentition loss were selected from the Prosthodontics Department, West China Stomatological Hospital. All patients met the conditions for immediate planting and immediate restoration. Owing to the lack of vertical target-restoration space, the implantation plan included intraoperative osteotomy. According to the preoperative cone beam CT (CBCT) data, combined with aesthetic digital smile design (DSD) analysis, virtual wax design, and so on, the ideal bone plane design was performed. According to the virtual osteotomy plane, the virtual implantation plan was designed, and then the digital stackable template assuming osteotomy template, implantation guide, and temporary restoration were made and 3D printed. Osteotomy was performed under the guidance of digital osteotomy template during the operation. The preoperative CBCT and postoperative CBCT of all patients overlapped, the deviation between the actual osteotomy and the ideal osteotomy was calculated, and the angle deviation between the postoperative bone plane and the ideal bone plane was measured. RESULTS: The ave-rage volume deviation between the postoperative design and the ideal one was 492.94 mm³, accounting for 21.21% of the preset osteotomy volume. The average deviation between the postoperative osteotomy and the ideal osteotomy in four patients was 0.024 8 mm. The average angle between the postoperative bone plane and the ideal bone plane was 6.03°. CONCLUSIONS: The displacement deviation of virtual osteotomy design and the actual osteotomy one under the guidance of digital osteotomy template in the digital stackable template are highly consistent with the original design. Thus, this clinical technique is worth popularizing, accurate, and quantifiable.

An investigation of the microstructure and mechanical properties of dental zirconia manufactured by digital light processing 3D printing.

OBJECTIVES: This study was performed to investigate the microstructure and mechanical properties of dental zirconia manufactured by digital light processing (DLP) 3D printing and the clinical application prospects of this material. METHODS: The experiment (DLP) group was zirconia manufactured by DLP 3D printing, and the control (MILL) group was milled zirconia. The density, grain size, and phase composition were measured to study the microstructure. Flexural strength was measured by using three-point bending tests, while Vickers hardness was determined through a Vickers hardness tester. Fracture toughness was tested using the single-edge V-notched beam method. RESULTS: Zirconia density of the DLP group was (6.019 8±0.021 3) g·cm-3, and the average grain size was (0.603 0±0.032 6) µm, but without statistical difference with the corresponding values of the MILL group (P>0.05). Tetragonal phase was found in the X-ray diffraction patterns of the DLP and MILL groups. The flexural strength of the DLP group was (1 012.7±125.5) MPa, and Vickers hardness was (1 238.5±10.8) HV1, which was slightly lower than that of the MILL group (P<0.05). The fracture toughness of the DLP group was (7.22±0.81) MPa·m1/2, which was not statistically different from that of the MILL group (P>0.05). CONCLUSIONS: Zirconia manufactured by DLP 3D printing had microstructure and mechanical properties similar to those of the milled zirconia. Only the flexural strength and the Vickers hardness of the experimental zirconia were slightly lower than those of the milled zirconia. Therefore, DLP-manufactured zirconia has a promising future for clinical use.

A study of labial groove-textures of upper central incisors by Shadow Moiré technology.

The labial groove-textures of upper central incisors were defined and explored to imitate the elaborate groove-textures for aesthetic restorations. In the current study, 158 upper central incisors were selected from 79 volunteers aged from 19 to 24 and recruited from Sichuan University in Chengdu of China. The length, width, depth, combination and distribution of the horizontal and vertical grooves on the labial surface were investigated by an optical measurement method, based on the Shadow Moiré technology and Temporal Fourier analysis. Vertical grooves were confirmed to be present in 94% of the samples and horizontal grooves in 77%. Perfect symmetry was shown in the vertical grooves of the same tooth, as well as in the homonymous teeth. The majority of horizontal grooves were distributed in the proximity of the cervical fourth and the middle of the crown. Based on the combination and distribution of the grooves, eight basic labial groove-texture types of maxillary central incisors were classified. The subtle morphological characters of natural teeth could be recorded by the new method, and it could also provide the minute groove-texture for dentists and technicians to achieve an aesthetic appearance for a restoration.

[Clinical pathway and preparation method of high-precision tooth shoulder platform].

A clear shoulder platform that can be easily identified by doctors and technicians or machines (mouth scan and warehouse scan) is important to obtaining a good long-term and stable fixed prosthesis treatment effect. At present, the pre-paration of the shoulder platform is usually based on free hands, and the practical operation is mainly guided by experience. Moreover, no comprehensive and objective preoperative design, intraoperative verification, and final test are available. Thus, the accuracy of shoulder platform preparation needs to be improved. In this study, the clinical pathway of "three determination, three selection, and three steps" with high accuracy of preparation and the precise shoulder preparation method of "bur-tip guidance" are proposed in detail.

[Digital workflow of orthodontic and prosthetic treatment for subgingival residual root preservation guided by target restoration space].

The use of orthodontic traction to preserve healthy subgingival residual root is a classical method combining the treatment of restoration and orthodontics. Based on the target restoration space (TRS), by establishing a TRS digital model, the final traction position of the subgingival residual root can be preset. After evaluating the key parameters such as crown-to-root ratio and minimum crown height, clinicians can estimate the treatment time and exclude cases with bad preset position. The time of traction treatment can be effectively reduced, and the efficiency and efficacy of the entire treatment can also be improved.

[A technique to design the framework of removable partial denture by multi-stage expert system].

This study aims to apply a new expert system to design removable partial denture (RPD) framework. The RPD design is completed in three steps, namely, "selecting missing teeth", "selecting abutment condition", and "selecting personalized clasp". The system can help auxiliary dentists develop personalized treatment plans to reduce their clinical workload. It can also generate a dental preparation guideline for clinical preparation, which can prevent tooth preparation mistakes. By generating the standard electronic drawings of the framework design, the system can reduce the inconvenience caused by manual drawing, thereby facilitating dentist-technician communication and reducing the rate of remade.

[Precise implant insertion technology for measuring dental implant placement].

Identifying the ideal implantation site is important for the long-term stability and effectiveness of follow-up restorations. Implant surgical guide and navigation are used to determine the implantation site in clinic and improve the precision of implantation. However, due to difficulties in digital methods, such as multiple procedures, high cost, and actual accuracy of more than 1 mm, many physicians still prefer to operate with free hand. In preoperative, intraoperative, and postoperative procedures, time-saving and practical methods for implant site evaluation are lacking. In many cases, oral physicians found that the position deviates only by cone beam CT, which was costly to modify the position. In this article, we presented a precise implantation insertion technology that is guided by a measurable technique throughout the implantation application for all implant systems. This method was guided by a dynamic control measuring ruler, which functions together with the measuring and intraoperative locating rulers. The 3D space of the operative area was measured by a measuring ruler prior to operation, and the implant plan and quantitative guidance design were conducted according to the measured and cone beam CT data. The whole implantation process was guided by the dynamic control measuring ruler, and measuring verification results were also considered. This method can realize the quantification of the entire preoperative space analysis, intraoperative precise implantation guidance, and postoperative site measurement and evaluation. This practical technique also helps to adjust the position, improve the implantation accuracy and is suitable in generalizing dental implantation.

[Precise tooth preparation technique guided by 3D printing guide plate with quantitative hole].

The minimum amount of tooth preparation that can be fully controlled is crucial in achieving long-term, stable, and effective aesthetic restoration, which is also a major difficulty in aesthetic restoration. The tooth preparation can be imple-mented efficiently and accurately through digital technology based on the fixed-deep hole guiding technology. Prior the actual tooth preparation, the technology first designs the virtual contour, layering, and virtual occlusion of the prosthesis on the computer. Then, virtual tooth preparation is carried out by cutting back according to the virtual prosthesis. Next, the virtual drilling operation plan is designed according to the shape of the virtual tooth preparation and the contour of the abutment tooth. Finally, the tooth preparation guide plate is designed and printed in 3D. It realizes the whole process of quantitative and precise guidance of dental preparation, visualizes the restoration space, reduces the clinical operation time, and guarantees the quality of dental preparation. It also promotes the improvement of the teaching quality of digital practical exercises.

[Criteria for success in dental implants].

With the comprehensive application and development of implant dentistry in recent years, multi-institutional data have supported a large number of clinical research findings. A consensus was gradually reached on the evaluation of the state and effect of implants and types of indicators that were selected after restoration. This study aims to examine the frequently used criteria to define treatment success in implant dentistry.

[Advances in titanium dental implant surface modification].

Titanium dental implants have wide clinical application due to their many advantages, including comfort, aesthetics, lack of damage to adjacent teeth, and significant clinical effects. However, the failure of osseointegration, bone resorption, and peri-implantitis limits their application. Physical-chemical and bioactive coatings on the surface of titanium implants could improve the successful rate of dental implants and meet the clinical application requirements. This paper reviews the characteristics of surface modification of titanium implants from the aspects of physics, chemistry, and biology. Results provide information for research and clinical application of dental implant materials.

[A review of peri-implant microbiology].

Dental implants represent the majority of treatment strategies used to replace missing teeth. However, peri-implant diseases caused by disturbance in peri-implant microbiological balance are among the reasons for implant failure. Since the 1980s, peri-implant microorganisms have been a hot research topic in dental microbiology. The bacterial ecology between the disease and health largely differs, which directly or indirectly increases the risk of peri-implant diseases. Accordingly, the determination of the 'core microbiome' of peri-implantitis and peri-implant mucositis is a key point of recent research.

[Expert consensus on biomechanical research of dental implant].

Current biomechanical research of dental implants focuses on the mechanical damage and enhancement mechanism of the implant-abutment interface as well as how to obtain better mechanical strength and longer fatigue life of dental implants. The mechanical properties of implants can be comprehensively evaluated by strain gauge analysis, photo elastic stress analysis, digital image correlation, finite element analysis, implant bone bonding strength test, and measurement of mechanical properties. Finite element analysis is the most common method for evaluating stress distribution in dental implants, and static pressure and fatigue tests are commonly used in mechanical strength test. This article reviews biomechanical research methods and evaluation indices of dental implants. Results provide methodology guidelines in the field of biomechanics by introducing principles, ranges of application, advantages, and limitations, thereby benefitting researchers in selecting suitable methods. The influencing factors of the experimental results are presented and discussed to provide implant design ideas for researchers.

[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.

[Application of 3D printing in aesthetic oral rehabilitation].

3D printing technology can be used in prosthodontics to obtain detailed structures. The technique offers a possible supersession for the most conventional restorations technologies. Contemporary aesthetic restorations encounter difficulties in the consistency between the analysis and design stages and the clinical implementation stage. 3D printing transfers aesthetic designs to customize the finial restoration fabrication, which could be an appropriate optimization to the aformentioned problem. Meanwhile, 3D printing technology can be employed to manufacture target restoration space guide (TRS guide), which is a blueprint for the aesthetic ceramic restorations and presents a general functional and aesthetic situation of patients. The guidance provided by TRS guide ensures precision and minimal invasive operation in aesthetic restorations. These new digital technologies have revolutionized aesthetic rehabilitation. This paper introduces the application of 3D printing in aesthetic oral rehabilitation.

Platelet-rich plasma for regeneration of neural feedback pathways around dental implants: a concise review and outlook on future possibilities.

Along with the development of new materials, advanced medical imaging and surgical techniques, osseointegrated dental implants are considered a successful and constantly evolving treatment modality for the replacement of missing teeth in patients with complete or partial edentulism. The importance of restoring the peripheral neural feedback pathway and thus repairing the lack of periodontal mechanoreceptors after tooth extraction has been highlighted in the literature. Nevertheless, regenerating the nerve fibers and reconstructing the neural feedback pathways around osseointegrated implants remain a challenge. Recent studies have provided evidence that platelet-rich plasma (PRP) therapy is a promising treatment for musculoskeletal injuries. Because of its high biological safety, convenience and usability, PRP therapy has gradually gained popularity in the clinical field. Although much remains to be learned, the growth factors from PRP might play key roles in peripheral nerve repair mechanisms. This review presents known growth factors contributing to the biological efficacy of PRP and illustrates basic and (pre-)clinical evidence regarding the use of PRP and its relevant products in peripheral nerve regeneration. In addition, the potential of local application of PRP for structural and functional recovery of injured peripheral nerves around dental implants is discussed.

Review of research on the mechanical properties of the human tooth.

'Bronze teeth' reflect the mechanical properties of natural teeth to a certain extent. Their mechanical properties resemble those of a tough metal, and the gradient of these properties lies in the direction from outside to inside. These attributes confer human teeth with effective mastication ability. Understanding the various mechanical properties of human teeth and dental materials is the basis for the development of restorative materials. In this study, the elastic properties, dynamic mechanical properties (visco-elasticity) and fracture mechanical properties of enamel and dentin were reviewed to provide a more thorough understanding of the mechanical properties of human teeth.