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Objective:To investigate the application of digital scanning combined with reverse engineering technology in the teaching of full crown preparation.Methods:A total of 30 undergraduate students in the fifth grade of stomatology were selected from Shantou University Medical College and were divided into experimental group and control group using a random number table. Two resin teeth were distributed to each student and were placed on dental head simulators to perform full crown preparation. The students in the control group received teaching with analogies of experience, and those in the experimental group received teaching with digital scanning, i.e., full crown preparation for the second time after digital scanning for the first time of full crown preparation. The score was determined based on China Stomatological Association Standards: Guideline for the tooth preparation of dental ceramic crowns (T/CHSA 008—2023), with a total score of 100 points. SAS9.4 software was used for the two-independent-samples t test and the paired t-test, and the Kendall W concordance coefficient was used to investigate the consistency of evaluators. Results:There were significant changes after teaching in the preparation scores of the right maxillary central incisor (76.27 pre-demonstration vs. 84.70 post-demonstration, P<0.001) and the right maxillary first molar (72.10 pre-demonstration vs. 82.37 post-demonstration, P<0.001). Compared with the control group, the experimental group had a significant increase in the mean preparation score of the right maxillary first molar (14.00 vs. 6.53, t=2.64, P=0.014). In the experimental group, there were significant increases in the preparation scores of the right maxillary first molar for the occlusal surface (15.40 pre-demonstration vs. 19.33 post-demonstration, P<0.001), the buccolingual surface (18.13 pre-demonstration vs. 20.87 post-demonstration, P=0.016), and the proximal surface (12.40 pre-demonstration vs. 14.07 post-demonstration, P=0.004), as well as significant increases in the scores of the convergence angles of the buccolingual surface (2.80 pre-demonstration vs. 4.07 post-demonstration, P=0.004) and the proximal surface (3.47 pre-demonstration vs. 4.47 post-demonstration, P=0.008). Conclusions:Application of digital teaching for difficult crown preparation of posterior teeth can effectively improve the quality of crown preparation among students, standardize the teaching process of crown preparation, and increase the precision of crown preparation, thereby laying a foundation for promoting uniformity in talent cultivation for dental prosthodontics.
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OBJECTIVE@#This study evaluates the effects of different endodontic access methods and full-ceramic crown on the stress distribution in the maxillary central incisor by using three-dimensional finite element analysis.@*METHODS@#Computed tomography scans of the maxillary central incisor were used to construct a three-dimensional finite element model of the maxillary central incisor. According to the different methods of endodontic and the prosthetic treatments, four models were established, namely, group A (traditional access cavity preparation with resin filling), group B (traditional access cavity preparation restored full-ceramic crown), group C (minimally invasive endodontics with resin filling) and group D (minimally invasive endodontics restored full-ceramic crown). A static force of 100 N and a direction of 45° was applied to the long axis of the tooth at the junction of the incisal section one-third and middle section one-third. The maximum principal stress, the von Mises stress and the modified von Mises stress of the tooth tissue were analyzed using the finite-element analysis software.@*RESULTS@#1) Stress peaks: the stress peaks of the maximum principal stress, the von Mises stress and the modified von Mises in group A were the largest, except that the stress peak of von Mises stress in group D was slightly lower than that in group C. The stress peaks of the maximum principal stress and the modified von Mises in group C were the lowest. The stress peaks of the maximum principal stress and the modi-fied von Mises stress in group D were lower than those in groups A and B. 2) Stress distribution: compared with group A, the stress distribution of cervical dentin and the area of stress concentration in group C was lower and smaller. In the root dentin, the stress distribution in group C was more uniform than that in group A, and the stress was dispersed to several areas of the root apex. After crown restoration, no significant difference was observed in stress distribution between groups B and D in the root region. The stress distribution state of group B was not significantly different from that of group A. No significant difference was observed in the stress distribution state between groups D and C.@*CONCLUSIONS@#1) From the perspective of biomechanics, the minimally invasive access was adopted for the maxillary central incisor. 2) Full crown restoration is recommended after traditional access cavity preparation. No obvious advantage is observed in stress analysis for minimally invasive endodontics-restored full-ceramic crown.
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Crowns , Dental Stress Analysis , Dentin , Finite Element Analysis , Incisor , Post and Core Technique , Stress, Mechanical , Tooth CrownABSTRACT
Objective To evaluate the clinical effects of anterior teeth repair of three different restorations made of Co-Cr alloy,Ag-Pd alloy and all-ceramic crowns.Methods 90 cases who needed the both maxillary and mandibular anterior teeth restarations were selected and treated respectively with Co-Cr alloy porcelain fused to metal crowns (PFM)(60 teeth),Ag-Pd alloy PFM (46 teeth)and IPS e.max Press Porcelain full crown (38 teeth).Gingival index was observed before restoration and in 6 and 12 months after restoration.Meanwhile,clinical indicators of two restorations were evaluated as cervical margin's coloration,margin fitness degree,color of restorations,fracture of restorations and contour of restorations,etc.Results The healthy condition of gingiva in groups of Ag-Pd alloy PFM and IPS e.max Press Porcelain full crown were superior to the group of Co-Cr alloy PFM (P＜0.05).There was no cervical margin's coloration in groug of all-ceramic PFM.The color and contour of this group was superior to the group of Co-Cr alloy PFM (P ＜0.05).The significant difference between group of Co Cr alloy and group of Ag-Pd alloy was cervical margin's coloration and marginal density of the restoration (P＜0.05).Conclusions The clinical effects of both groups of Ag-Pd alloy PFM and IPS e.max Press Porcelain full crown is superior to the group of Co-Cr alloy PFM.The IPS e.max Press Porcelain full crown group works best.
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<p><b>OBJECTIVE</b>The objective of this paper is to analyze the stress distribution in the deep wedge-shaped defective mandibular first premolars restored with different methods.</p><p><b>METHODS</b>Three-dimensional finite element models of mandibular first premolar with deep wedge-shaped defect were created. The model, which was untreated after root canal treatment, served as the control group. Then, according to different treatment designs, four experimental groups were established as follows: resin filling (A), post restoration after resin filling (B), crown restoration after resin filling (C), and post and crown restoration after resin filling (D). Four different post materials were then chosen for establishing the subgroup models: fiber post (B1, D1), AuPd post (B2, D2), pure Ti post (B3, D3), and CoCr post (B4, D4). A force of 100 N was applied at a 30° angle on the buccal-inclined surface near the top of the buccal cusp. The maximum principal stress and Von Mises stress were investigated using finite element analysis software.</p><p><b>RESULTS</b>1) For the control group, the maximum principal stress and Von Mises stress of the residual dentine were the same as those of the tip of the defect. 2) Compared with the control group, the maximum principal stress and Von Mises stress of groups A, B, C, and D decreased greatly (P<0.05). The maximum principal stress and Von Mises stress of groups C and D with crowns were similar. The maximum principal stress and Von Mises stress of the post-dentine surface of groups B and D with fiber post were less than those in the cast metal post models (P<0.05). 3) The displacement of the buccal cusp of group A was similar to that of the control group (P>0.05) and larger than those in groups B, C, and D (P<0.05).</p><p><b>CONCLUSIONS</b>It is necessary for deep wedge-shaped defective teeth to be treated with full crowns, but a post is not necessary. If a post is used, fiber post with elastic modulus closer to the dentine is more suitable than metal post. .</p>
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Humans , Bicuspid , Crowns , Dentin , Finite Element Analysis , Post and Core Technique , Root Canal Therapy , Tooth CrownABSTRACT
Objective To explore the effect of preservation of inclined fractured permanent molars by transverse fixation with screw post,and provide a practical method for reserving the inclined fractured permanent molars.Methods Clinical data of 50 patients with inclined fractured permanent molars by transverse fixation with screw post in the Department of Stomatology of Tianjin First Central Hospital between January 2010 to December 2011 were reviewed retrospectively.After fixing the crown with steel-wire binding and root canal treatment,the molars were drilled a hole buccolingually and placed screw post.The flowable light-curing composite resin was used to seal the crack and bond screw post to prevent the relative movement.All treated molars were restored with full crown.All patients were followed up for 10-60 months.The therapeutic effects were observed.Results After 5 year-follow-up,41 cases were cured completely,6 cases were cured clinically,and 3 cases failed treatment.Conclusion The transverse fixation with screw post and bonding technique can preserve the inclined fractured molars to gain chewing function and avoid or reduce the extraction of affected teeth,which provides a better restoration effect.
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Objective This paper will study the effect of the replantation and full crown prosthesis in the treatment of refractory molar periapical disease as well as their related factors .Methods The retrospective analysis will be used in this paper.There were 98 patients who were diagnosed as refractory molar periapical disease in our dental clinic from 2012 to 2015.These 98 cases are divided into two groups:the study group and the control group .This paper will make a comparison of the study group which represents the replantation and full crown prosthesis in the treatment and the control group which re -presents endodontic therapy .Results Through the comparison , the average effective rate of the study group is 93.9%while the control group 65.3%.There is a significant difference between two groups (P<0.01) and the rate of the study group is higher than that of the control group .Conclusion Through the analysis , this paper finds that the joint optimization of replan-tation and full crown prosthesis can provide an unconventional approach to treat refractory periapical of teeth and effectively preserve the tooth .
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Objective:To observe the clinical effect of endodontic therapy and full crown restoration in the treatment of cracked teeth. Methods:The trace and depth of 50 cracked teeth were carefully examined under root canal microscope.According to the depth and scope of the cracks,the cracked teeth were classficated into the degree of Ⅰ,Ⅱ and Ⅲ,treated endodontically and restored with full crown.Results:During 1 year follow-up,34 cases showed successful effect,5 progressive,1 1 failure.The general effectiveness rate was 78.0%.The effectiveness rate of group Ⅰ,Ⅱ and Ⅲ was 93.3%,82.1 % and 28.6% respectively.Group Ⅰand Ⅱ vs Ⅲ,P 0.05.Conclusion:The treatment effect of cracked teeth is closely related to the depth and scope of cracks.
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Objective:To explore the effects of different full-crown materials on the periodontal tissues.Methods:120 defected teeth were restored by full-crown with Ni-Cr alloy,Co-Cr alloy and all ceramic respectively(n =40).Periodontal clinical examination (include SGI,PLI,PD)and PCR detection of Porphyromonas gingivalis(Pg),Actinobacillus actinomycetemcomitans(Aa),Prevotella intermedia(Pi)and Fusobacterium nucleatum(Fn)in subgingival plaque of the abutment teeth were performed before and after restora-tion.Results:6 -24 months after restoration SGI,PLI and PD of Ni-Cr and Co-Cr groups were increased(P 0.05).12 months after restoration the detection rate of periodontal pathogens of Ni-Cr and CO-Cr groups was higher than that of all ceramic group(P <0.05).Conclusion:All ceramic is superior to Co-Cr and Ni-Cr in crown resto-ration for periodental tissue.
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Objective:To investigate the the retention force changes of 2 kinds of T bar clasps on Cr-Co crowns and the surface ab-rasion of the crowns.Methods:Standard Cr-Co crowns were made,and standard T bar clasps were made of Cr-Co alloy and Vitalli-um2000 with 0.25 mm and 0.5 mm undercut depth respectively.1 800 times repeated placement and removal(fatigue test)were car-ried out on instron testing machine in or without saliva soak condition.The attenuation curves of the maximum retention force was an-alysed.The surface abrasion of the crowns was observed before and after the fatigue test by SEM.Results:The retention force attenu-ation of the clasps in every group was accord with the logarithm attenuation law.SEMexamination showed that in the same condition, there was less surface abrasion in Vitallium2000 group than that in Cr-Co group.Vitallium2000 clasp was superior to Cr-Co clasp in maintaining the retention force.Conclusion:Vitallium2000 T bar clasp may provide better retention force with less furface abrasion on Cr-Co crown than Cr-Co clasp.
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Objective To explore the clinical effect of agar alginate combined impression preparation of a fLxed partial denture impressions.Methods 88 cases of patients with fixed partial dentures were divided into experimental group(group A) and control group(group B).Group A of 45 patients with 93 abutments,the legal system to take an impression of agar and alginate combined impression; group B of 43 patients with 80 base,the use of alginate impression preparation of an impression.Were observed with a magnifying glass impression of the type and number of records the number of abutments,impression defects.Results 63(67.8％) of group A were ideal,30(32.2％) had defects,33(41.2％) of group B were ideal,47(58.8％) had defects,there were significant differences(x2 =19.36,19.28,all P ＜ 0.05).At the cervical margin of bubbles,the gingival sulcus and shoulder were not clear,there was significant difference(x2 =10.46,11.25,all P ＜ 0.05).There were no significant difference in tear or defect of the neck at the edge of the two impression.Conclusion Agar and alginate impression of the legal systemcan take an impression of reduced defects,which is worthy of clinical application
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Objective: To study the effect of the sharp marginal ridge of the abutment on the casting of the fit metal full crown in dental preparation.Methods: We established the models of the designed crown-based-teeth(American Dental Association style,No2 trail) with a sharp or smooth marginal ridge,and cast a metal crown for each model.We injected silicone into the crown and immediately fixed it onto each model.Then we took out the solidified silicone and measured its thickness between the crown and the occlusal face of each model.The thinner the thickness,the better the fitness.Results: The average silicone thickness was 250 ?m in the smooth marginal ridge group and 1 660 ?m in the sharp marginal ridge group,with significant difference in between(P