OBJECTIVE: To analyze the cement flow in the abutment margin-crown platform switching structure by using the three-dimensional finite element analysis, in order to prove that whether the abutment margin-crown platform switching structure can reduce the inflow depth of cement in the implantation adhesive retention. METHODS: By using ANSYS 19.0 software, two models were created, including the one with regular margin and crown (Model one, the traditional group), and the other one with abutment margin-crown platform switching structure (Model two, the platform switching group). Both abutments of the two models were wrapped by gingiva, and the depth of the abutment margins was 1.5 mm submucosal. Two-way fluid structure coupling calculations were produced in two models by using ANSYS 19.0 software. In the two models, the same amount of cement were put between the inner side of the crowns and the abutments. The process of cementing the crown to the abutment was simulated when the crown was 0.6 mm above the abutment. The crown was falling at a constant speed in the whole process spending 0.1 s. Then we observed the cement flow outside the crowns at the time of 0.025 s, 0.05 s, 0.075 s, 0.1 s, and measured the depth of cement over the margins at the time of 0.1 s. RESULTS: At the time of 0 s, 0.025 s, 0.05 s, the cements in the two models were all above the abutment margins. At the time of 0.075 s, in Model one, the gingiva was squeezed by the cement and became deformed, and then a gap was formed between the gingiva and the abutment into which the cement started to flow. In Model two, because of the narrow neck of the crown, the cement flowed out from the gingival as it was pressed by the upward counterforce from the gingival and the abutment margin. At the time of 0.1 s, in Model one, the cement continued to flow deep inside with the gravity force and pressure, and the depth of the cement over the margin was 1 mm. In Model two, the cement continued to flow out from the gingival at the time of 0.075 s, and the depth of the cement over the margin was 0 mm. CONCLUSION When the abutment was wrapped by the gingiva, the inflow depth of cement in the implantation adhesive retention can be reduced in the abutment margin-crown platform switching structure.
Finite Element Analysis ; Cementation/methods* ; Gingiva ; Crowns ; Dental Abutments ; Dental Cements ; Dental Stress Analysis

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.
Dental Abutments ; Denture Design ; Denture, Partial, Removable ; Expert Systems ; Tooth

OBJECTIVE: To compare the residual cement between computer aided design/computer aided manufacturing customized abutments (CCA) and stock abutments (SA), and to evaluate the feasibility of digital measurement for residual cement volume by three-dimensional scanning. METHODS: Twenty master models needed in this study were all taken from one 47-year-old patient with arrested periodontitis, who had already had an implant placed at his right upper central incisor site in the Department of Periodonto-logy, Peking University School and Hospital of Stomatology. After 4 weeks of soft tissue conditioning by means of customized healing abutment, the height of peri-implant soft tissue was measured, from the implant platform to mucosal margin, as 5 mm. Using customized impression coping, the impression was taken and twenty models were fabricated and allocated to 4 groups according to the type of abutments: CCA1 (5 mm transmucosal height CCA, with margin at tissue level), CCA2 (4 mm transmucosal height CCA, with 1 mm submucosal margin), SA1 (3 mm transmucosal height SA, with 2 mm submucosal margin) and SA2 (1 mm transmucosal height SA, with 4 mm submucosal margin). Crowns were cemented to the abutments, which were seated on the working models. Excess cement was removed by a prosthodontic specialist. Thereafter, the volume of residual cement was evaluated by using three-dimensional scanning technique. The area proportion of residual cement was calculated on photographs taken by a single lens reflex camera. The weight of residual cement was weighed by an analytical balance. And the correlation of residual cement volume data with residual cement area proportion or weight of residual cement acquired by traditional methods was analyzed. RESULTS: Residual cement was observed on all the experiment samples. The residual cement volume of CCA was significantly less than that of SA [(0.635 3±0.535 4) mm³ vs. (2.293 8±0.943 8) mm³, P < 0.001]. Consistently, CCA had less residual cement area proportion and weight than those of SA [area proportion: 7.57%±2.99% vs. 22.68%±10.06%, P < 0.001; weight: (0.001 5±0.001 0) g vs. (0.003 7±0.001 4) g, P < 0.001]. The residual cement volume was strongly correlated with the residual cement area proportion and residual cement weight (r>0.75, P < 0.001). CONCLUSION These in vitro results suggest that CCA minimized the residual cement more effectively than SA. The method to digitally evaluate the residual cement volume is feasible, but its validity and reliability need to be further studied.
Aged, 80 and over ; Bone Cements ; Computer-Aided Design ; Crowns ; Dental Abutments ; Dental Prosthesis, Implant-Supported ; Glass Ionomer Cements ; Humans ; Reproducibility of Results

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.
Biomechanical Phenomena ; Computer Simulation ; Consensus ; Dental Abutments ; Dental Implant-Abutment Design ; Dental Implants ; Dental Prosthesis Design ; Dental Stress Analysis ; Finite Element Analysis ; Stress, Mechanical

OBJECTIVE: To analyze the risk factors of early dental implant failure,treatment and prognosis. METHODS: Cases of dental implants in the first clinical division from January 2000 to December 2016 were selected according to inclusion criteria. The differences of gender,age,smoking,location of implants, healing abutments and bone graft were compared between early failed implants and success implants. The general conditions of early failure patients, the early failure occurrence time, treatment and prognosis were recorded. Statistical methods were χ² test and descriptive analysis, P<0.05 had statistical significance. Statistical analysis software was IBM SPSS Statistics 19.0. RESULTS: There were 36 patients with 36 early failed implants and 4 381 patients with 6 564 success implants. The rate of early dental implant failure was 0.8% at individual level and 0.5% at implant level. There was no significant difference in gender between the failed implants and success implants (P=0.692). The failure rate of the patients ≥40 years old (1.0%) was higher significantly than that of the patients <40 years old(0.4%, P=0.033). The failure rate of smokers (1.3%) was higher significantly than that of non-smokers(0.3%,P<0.01). There was no significant difference of early failure among four implant locations, which were anterior maxilla, posterior maxilla, anterior mandibular and posterior mandibula (P=0.709). The early failure of implants with bone graft and healing abutments at the same time (1.1%) was significantly higher than that of the implants with bone and healing abutments separately (0.5%, P=0.039). Ten patents with early failed implants had general diseases, including 5 patients with diabetes, 3 with hypertension and 2 with coronary heart disease. All the patients with general diseases were controlled well. The median of early failure occurrence time was 30.5 after implant operations. 83.3% early failure implants was found by dentists at re-examinations. All of the early failure implants were removed when they were found failed. Twenty-six early failure implant sites were inserted with implants again, of which 23 implants were successful. CONCLUSION The early dental implant failure was possible to occur in one month after implants inserting. The possible risk factors were age≥40 years old, smoking and using bone graft and healing abutments at the same time. Most early dental implant failure was found by dentists at re-examinations. The implants should be removed when the early dental implant failure was found, which didn't influence the later implantation.
Adult ; Dental Abutments ; Dental Implantation, Endosseous ; Dental Implants ; Dental Prosthesis Design ; Dental Prosthesis, Implant-Supported ; Dental Restoration Failure ; Follow-Up Studies ; Humans ; Maxilla ; Retrospective Studies

OBJECTIVE: To observe the effects of a modified semi-fixed bridge to restore a missing posterior tooth for three years. METHODS: In the study, 38 cases with a posterior tooth missed were chosen as experiment group. The inclusion criteria for these cases required that one abutment tooth be defected, and another abutment intact. The missed posterior tooth was restored with a modified semi-fixed bridge in which a metal wing retainer was applied to the intact abutment tooth and a full crown retainer was applied to the defected abutment tooth, and the non-rigid connector linked to the metal wing retainer and the pontic, while the rigid connector linked to the full crown retainer and the pontic. And 42 cases with same abutment conditions were chosen as control group. These control patients were treated with classical rigidly-fixed partial dentures. The clinical effects regarding the bridge survival, abutment conditions, and etc. were observed by examination. RESULTS: The average observation time for experiment group was 40.3 months (from 9 to 60 months). One case failed with loose crown retainer after 7 months' usage. Another failed case was the same performance after 20 months' wearing. The restorations were rebounded after the inner face of crowns was treated, and they were used normally. No loose abutment and retainer, no decayed abutment teeth were found, and the marginal adaptations between retainers and abutment teeth were good. The average observation time of control group was 44.7 months(from 22 to 50 months). No secondary decays and loose abutment teeth were detected and the marginal adaptation of the retainers was good. CONCLUSION This modified semi-fixed bridge has similar survival rate and clinical effects to restore a missing posterior tooth when compared with the traditional rigidly-fixed partial dentures. But the long-term observation is required.
Crowns ; Dental Abutments ; Denture, Partial, Fixed ; Humans ; Tooth Loss

An increasing number of implant restoration abutment types are produced with the rapid development of dental implantology. Although various abutments can meet different clinical demands, the selection of the appropriate abutment is both difficult and confusing. This article aims to help clinicians select the appropriate abutment by describing abutment design, types, and selection criteria.
Dental Abutments ; Dental Implant-Abutment Design ; Dental Implants ; Humans ; Tooth

PURPOSE: The aim of this in vitro study is to investigate load bearing capacity of esthetic abutments according to the type of material and wall thickness. MATERIALS AND METHODS: 70 specimens equally divided into seven groups according to their abutment wall thicknesses. The abutments prepared with titanium 0.5 mm wall thickness were used as a control group (Ti-0.5), whereas zirconia abutments and resin nano ceramic abutments with wall thickness 0.5 mm, 0.8 mm and 1.0 mm were prepared as test groups (Zir-0.5, Zir-0.8, Zir-1.0 and RNC-0.5, RNC-0.8, RNC-1.0). All specimens were tested in a universal testing machine to evaluate their resistance to fracture and all of them underwent thermo-cycling before loading test. Mean fracture values of the groups were measured and statistical analyses were made using two-way ANOVA. RESULTS: Zir-1.0 showed the highest mean strength (2,476.3 ± 342.0 N) and Zir-0.8 (1,518 ± 347.9 N), Ti-0.5 (1,041.8 ± 237.2 N), Zir-0.5 (631.4 ± 149.0 N) were followed. The strengths of RNC groups were significantly lower compared to other two materials (RNC-1.0 427.5 ± 72.1, RNC-0.8 297.9 ± 41.2) and the strengths of all the test groups decreased as the thickness decreases (P < .01). RNC-0.5 (127.4 ± 35.3 N) abutments were weaker than all other groups (P < .05). CONCLUSION: All tested zirconia abutments have the potential to withstand the physiologic occlusal forces in anterior and posterior regions. In resin nano ceramic abutments, wall thickness more than 0.8 mm showed the possibility of withstanding the occlusal forces in anterior region.
Bite Force ; Ceramics* ; Dental Abutments ; In Vitro Techniques ; Titanium ; Weight-Bearing

Dentists often place post and core buildups on endodontically treated abutments for crown and bridge restorations. This article analyzes the bio-mechanical purposes, advantages and disadvantages of placing a core or a post and core in an endodontically treated tooth and reviews literature on post and core biomechanics. The author assesses the scientific rationale of the claim that the main purpose of a post is to retain a core, or the claim that posts weaken teeth. More likely, the main function of a post is to help prevent the abutment, on which a crown is cemented, from fracturing such that the abutment separates from the tooth root, at a fracture plane that is located approximately and theoretically at the level of the crown (or ferrule) margin. A post essentially improves the ferrule effect that is provided by the partial fixed denture prosthesis. This paper also explores the difference between bio-mechanical failures of crowns caused by lack of retention or excess taper, versus failures due to a sub-optimal ferrule effect in crown and bridge prostheses.
Crowns* ; Dental Abutments ; Dentists ; Dentures ; Finite Element Analysis ; Humans ; Post and Core Technique ; Prostheses and Implants ; Tooth ; Tooth Crown ; Tooth Root

Dentists often place post and core buildups on endodontically treated abutments for crown and bridge restorations. This article analyzes the bio-mechanical purposes, advantages and disadvantages of placing a core or a post and core in an endodontically treated tooth and reviews literature on post and core biomechanics. The author assesses the scientific rationale of the claim that the main purpose of a post is to retain a core, or the claim that posts weaken teeth. More likely, the main function of a post is to help prevent the abutment, on which a crown is cemented, from fracturing such that the abutment separates from the tooth root, at a fracture plane that is located approximately and theoretically at the level of the crown (or ferrule) margin. A post essentially improves the ferrule effect that is provided by the partial fixed denture prosthesis. This paper also explores the difference between bio-mechanical failures of crowns caused by lack of retention or excess taper, versus failures due to a sub-optimal ferrule effect in crown and bridge prostheses.
Crowns* ; Dental Abutments ; Dentists ; Dentures ; Finite Element Analysis ; Humans ; Post and Core Technique ; Prostheses and Implants ; Tooth ; Tooth Crown ; Tooth Root