锥度固位结合数字化技术在后牙连续多牙种植即刻修复中的应用

目的:评价口内扫描技术、计算机辅助设计/加工(computer-assisted design/computer-assisted manufacturing, CAD/CAM)技术结合锥度固位方式在种植即刻修复连续多牙缺失中的应用。方法: 选取2017年3月至2018年2月于北京大学口腔医院种植科就诊的连续多个后牙缺失的患者,在种植体植入即刻安放预成锥度固位帽,通过口内扫描制取数字化印模,以CAD/CAM技术制作聚甲基丙烯酸甲酯 (polymethyl methacrylate, PMMA) 临时联冠,临时联冠戴入后即刻负重;6个月后更换为CAD/CAM技术制作的氧化锆永久联冠,临时冠及永久冠戴入时分别拍摄平行投照牙片。通过种植体和修复体存留率、种植体颈部边缘骨水平变化、种植体和修复体并发症等指标评价临床效果,永久修复前用视觉模拟评分 (visual analogue score, VAS) 量表评价患者对即刻修复的满意度。结果:共计10例患者(男4例,女6例,平均55.5岁)纳入本研究,共植入34枚种植体,分别制作14件即刻PMMA修复体和14件永久氧化锆修复体,观察时间4~14个月;种植体及修复体存留率100%,种植体颈部骨水平在种植即刻为(1.06±0.97) mm,即刻修复后6个月时为(0.96±0.82) mm,两者差异无统计学意义(P>0.05);观察期内所有种植体和修复体均未发生并发症;患者满意度VAS评分87.2。结论:对于连续多牙缺失,在种植即刻以数字化流程制作,并结合锥度固位方式的联冠修复体,具有良好的临床效果和患者满意度。     

前牙区即刻种植短期临床研究

目的探讨前牙区即刻种植临床疗效。方法对28例因外伤、牙周病、龋病、乳牙滞留等原因拔除前牙的患者,即刻植入32颗Ankylos种植体,种植体与拔牙窝缺隙大于2 mm时,在间隙内填塞人工骨粉或于种植位点附近获取少量骨屑与人工骨粉拌合填塞缺隙,唇侧骨板有缺损或明显裂纹者应用骨引导再生技术。6个月后行烤瓷冠修复。随访3～12个月。结果随访期间32颗种植体均无松动,X线片观察种植体颈部边缘骨吸收均小于0.2 mm。结论严格掌握适应证,保证种植体良好的初期稳定性,前牙区行即刻种植能够获得良好的临床效果。     

Regular and platform switching: bone stress analysis varying implant type

Purpose: This study aimed to evaluate stress distribution on peri‐implant bone simulating the influence of platform switching in external and internal hexagon implants using three‐dimensional finite element analysis. Materials and Methods: Four mathematical models of a central incisor supported by an implant were created: External Regular model (ER) with 5.0 mm × 11.5 mm external hexagon implant and 5.0 mm abutment (0% abutment shifting), Internal Regular model (IR) with 4.5 mm × 11.5 mm internal hexagon implant and 4.5 mm abutment (0% abutment shifting), External Switching model (ES) with 5.0 mm × 11.5 mm external hexagon implant and 4.1 mm abutment (18% abutment shifting), and Internal Switching model (IS) with 4.5 mm × 11.5 mm internal hexagon implant and 3.8 mm abutment (15% abutment shifting). The models were created by SolidWorks software. The numerical analysis was performed using ANSYS Workbench. Oblique forces (100 N) were applied to the palatal surface of the central incisor. The maximum (σ_max) and minimum (σ_min) principal stress, equivalent von Mises stress (σ_vM), and maximum principal elastic strain (ε_max) values were evaluated for the cortical and trabecular bone. Results: For cortical bone, the highest stress values (σ_max and σ_vm) (MPa) were observed in IR (87.4 and 82.3), followed by IS (83.3 and 72.4), ER (82 and 65.1), and ES (56.7 and 51.6). For ε_max, IR showed the highest stress (5.46e‐003), followed by IS (5.23e‐003), ER (5.22e‐003), and ES (3.67e‐003). For the trabecular bone, the highest stress values (σ_max) (MPa) were observed in ER (12.5), followed by IS (12), ES (11.9), and IR (4.95). For σ_vM, the highest stress values (MPa) were observed in IS (9.65), followed by ER (9.3), ES (8.61), and IR (5.62). For ε_max, ER showed the highest stress (5.5e‐003), followed by ES (5.43e‐003), IS (3.75e‐003), and IR (3.15e‐003). Conclusion: The influence of platform switching was more evident for cortical bone than for trabecular bone, mainly for the external hexagon implants. In addition, the external hexagon implants showed less stress concentration in the regular and switching platforms in comparison to the internal hexagon implants.     

The role of single immediate loading implant in long class IV Kennedy mandibular partial denture

Background: The treatment of long‐span Kennedy class IV considers a prosthodontic challenge. This study evaluated the integrity of principle abutments in long Kennedy class IV clinically and radiographically, when rehabilitated with conventional metallic partial denture as a control group and mandibular partial overdentures supported with single immediately loaded implant in symphyseal as a study group. Material and Methods: Twelve male patients were divided randomly allotted into two equal groups. First group patients received removable metallic partial denture, whereas in the second group, patients received partial overdentures supported with single immediately loaded implant in symphyseal region. The partial dentures design in both groups was the same. Long‐cone paralleling technique and transmission densitometer were used at the time of denture insertion, 3, 6, and 12 months. Gingival index, bone loss, and optical density were measured for principle abutments during the follow‐up. Results: A significant reduction in bone loss and density were detected in group II comparing with group I. Gingival index had no significant change (p‐value < 0.05). Conclusion: A single symphyseal implant in long span class IV Kennedy can play a pivotal role to improve the integrity of the principle abutments and alveolar bone support.     

牙周炎患者种植体即刻负载的研究进展

即刻负载由于可以为患者提供即刻的功能和美观而成为近年来的研究热点。牙周炎患者作为一个广泛的特殊患者群体,长期以来学者在其种植修复方面持保守态度。然而近年来,随着种植技术的发展以及种植材料的进步,越来越多的学者对牙周炎患者采用即刻负载并获得了成功。有学者进一步指出:将即刻种植与即刻负载联合应用,可以在最短的治疗时间内获得最佳的疗效。本文就国内外学者对牙周炎患者即刻负载的研究进展作一综述。     

Comparison of immediate complete denture, tooth and implant-supported overdenture on vertical dimension and muscle activity

PURPOSE

To compare the changes in the occlusal vertical dimension, activity of masseter muscles and biting force after insertion of immediate denture constructed with conventional, tooth-supported and Implant-supported immediate mandibular complete denture.

MATERIALS AND METHODS

Patients were selected and treatment was carried out with all the three different concepts i.e, immediate denture constructed with conventional (Group A), tooth-supported (Group B) and Implant-supported (Group C) immediate mandibular complete dentures. Parameters of evaluation and comparison were occlusal vertical dimension measured by radiograph (at three different time intervals), Masseter muscle electromyographic (EMG) measurement by EMG analysis (at three different positions of jaws) and bite force measured by force transducer (at two different time intervals). The obtained data were statistically analyzed by using ANOVA-F test at 5% level of significance. If the F test was significant, Least Significant Difference test was performed to test further significant differences between variables.

RESULTS

Comparison between mean differences in occlusal vertical dimension for tested groups showed that it was only statistically significant at 1 year after immediate dentures insertion. Comparison between mean differences in wavelet packet coefficients of the electromyographic signals of masseter muscles for tested groups was not significant at rest position, but significant at initial contact position and maximum voluntary clench position. Comparison between mean differences in maximum biting force for tested groups was not statistically significant at 5% level of significance.

CONCLUSION

Immediate complete overdentures whether tooth or implant supported prosthesis is recommended than totally mucosal supported prosthesis.     

IPS-Empress II inlay-retained fixed partial denture reinforced with zirconia bar: Three-dimensional finite element and in-vitro studies

Abstract

Objective. This study evaluated von Mises stress distribution, flexural strength and interface micrographs of IPS-Empress II (IPS) inlay-retained fixed partial dentures (IRFPD) reinforced with Zirconia bars (Zb). Materials and methods: In the Finite element analysis, six three-dimensional models of IRFPD were designed using Solid Works 2006. Five models were reinforced with different Zb and a model without Zb was considered as a control. The bridges were loaded by 200 and 500 N forces at the middle of the pontic on the occlusal surface. Subsequently, von Mises stress and displacement of the models were evaluated along a defined path. In the experimental part, 21 bar shape specimens were fabricated from lithium disilicate and zirconia ceramic in three different designs. The zirconia-IPS interfaces and the fractured surfaces of flexural test were observed using SEM. Results. In the connector area, von Mises stress and displacement of the models with Zb under a load of 500 N were decreased compared to the model without the Zb; however, this difference was not considerable at a load of 200 N. In the mesial connector, Von Mises stress and displacement was decreased from 12.5 Mpa for the control model tested at 500 N to 7.0 Mpa for the model with Zb and from 0.0050–0.0041 mm, respectively. SEM analyses showed that, before fracture, interfacial gaps were not observed along the interfaces, but initiated cracks propagated along the interfaces after flexural loading. Conclusion: IPS IRFPD reinforced by Zb can tolerate higher stresses while still functioning effectively and the interfaces may have desirable adaption.     

Bone‐to‐Implant Contact Around Immediately Loaded Direct Laser Metal‐Forming Transitional Implants in Human Posterior Maxilla

Objective: Direct laser metal forming (DLMF) is a procedure in which a high‐power laser beam is directed onto a metal powder bed and programmed to fuse particles according to a computer‐aided design file, generating a thin metal layer. This histologic study evaluated the bone‐to‐implant contact (BIC%) around immediately loaded DLMF transitional implants retrieved after 2 months from posterior human maxillae. Methods: Twelve totally edentulous individuals (mean age, 66.14 ± 2.11 years) received DLMF transitional implants divided in twelve immediately loaded (IL) and twelve unloaded (UI) implants. These transitional implants were placed between conventional implants to support the interim complete maxillary denture during the healing period. After 8 weeks, the transitional implants and the surrounding tissue were removed and prepared for histomorphometric analysis. Results: Mature woven preexisting bone lined by newly formed bone in early stages of maturation were found around all retrieved implants. Histometric evaluation indicated that the mean BIC% was 45.20 ± 7.68% and 34.10 ± 7.85% for IL and UI, respectively (P <0.05). Conclusion: The present data obtained in humans showed that, although both IL and UI presented good BIC%, IL DLMF implants had a higher BIC% in the posterior maxilla.