Retention force measurement of telescopic crowns

This study deals with the determination of the retentive force between primary and secondary telescopic crowns under clinical conditions. Forty-three combined fixed–removable prostheses with a total of 140 double crowns were used for retention force measurement of the telescopic crowns prior to cementation. The crowns had a preparation of 1–2°. A specifically designed measuring device was used. The retentive forces were measured with and without lubrication by a saliva substitute. The measured values were analyzed according to the type of tooth (incisors, canines, premolars, and molars). Additionally, a comparison between lubricated and unlubricated telescopic crowns was done. As maximum retention force value 29.98 N was recorded with a telescopic crown on a molar, while the minimum of 0.08 N was found with a specimen on a canine. The median value of retention force of all telescopic crowns reached 1.93 N with an interquartile distance of 4.35 N. No statistically significant difference between lubricated and unlubricated specimens was found. The results indicate that retention force values of telescopic crowns, measured in clinical practice, are often much lower than those cited in the literature. The measurements also show a wide range. Whether this proves to be a problem for the patient’s quality of life or not can however only be established by a comparison of the presented results with a follow-up study involving measurement of intraoral retention and determination by e.g. oral health impact profile.     

All-ceramic primary telescopic crowns with Cerec inLab

On the one hand, all-ceramic primary telescopic dentures serve to satisfy the growing esthetic needs of older patients, and on the other hand guarantee good adhesive stability. With the aid of the Cerec inLab system, primary telescopic crowns made of Vita In-Ceram infiltration ceramic can be designed and milled after previous conventional determination of the over all insertion direction. The raw crowns gained in this way then require only minor improvement. The secondary parts are produced with the aid of electroforming. These are adhesively bonded to the tertiary structure. The special feature of adhesive bonding of the primary telescopic crowns requires uncompromisingly good cooperation between dentist and laboratory.     

套简冠固位力不同调节方式的体外比较

目的:应用裂隙冠技术与常规技术制作的套筒冠进行体外模拟实验,探讨并完善非贵金属套筒冠固位力的调节方式.方法:制作标准金属试件27个,随机分为3组,常规钴铬合金组、钴铬合金裂隙冠组和金钯合金组,每组9个,循环摘戴后测其固位力值.采用SPSS12.0软件包对数据进行单因素方差分析.结果:金钯合金组与钴铬合金裂隙冠组比常规钴铬合金组固位力大,差异有显著性(P＜0.05);钴铬合金裂隙冠组的最大固位力大于金钯合金组,差异有显著性(P＜0.05);金钯合金组和钴铬合金裂隙冠组比较,循环次数为800次时,差异无显著性(P＞0.05);其他循环次数,差异均有统计学意义(P＜0.05).结论:裂隙冠技术使套简冠固位力下降的效果与贵金属相近,提示钴铬合金裂隙冠可以弥补非贵金属在固位上的不足.     

Performance of PEEK based telescopic crowns,a comparative study

ObjectiveTelescopic crowns are suitable components of partial dentures to efficiently anchor dental supra-structures to teeth or dental implants and achieve high chewing performance and wear comfort.Usually alloy- or metal-based structures are used for the primary and the secondary crowns. The advantage is the possibility to produce precise structures with a high perfection and sufficient friction force, but the disadvantage is the corrosion instability. The recent introduction of zirconia ceramics has enabled the fabrication of ceramic primary crowns, thus reducing corrodibility.The novel application of the high-performance polymer polyetheretherketone (PEEK) as another metal-free alternative material offers a new perspective for such applications.Therefore, the aim of this work was to assess the performance of telescopic crowns of PEEK by comparing telescopic crowns based on the combination of PEEK (prim. crown) + PEEK (sec. crown) with the pairings ZrO₂ (prim. crown) + PEEK (sec. crown) and CoCr-alloy (prim. crown) + PEEK (sec. crown).MethodsAll specimens were CAD/CAM planned and manufactured based on a model of a tooth 26. One master dental technician performed the post-treatment. For each group of material pairing, n = 9 telescopic crown pairs were manufactured and tested. Herein not only the maximum retention force was measured but also the retention force vs. pull-off distance were analyzed. As there is no commonly accepted test protocol available, the influence of various pull off speeds were tested as well. All measurements were first made with three blocks of three crowns (3C), subsequently with three blocks of two crowns (2C) and finally with nine single crowns (1C). The long-term behavior was estimated by performing 10.000 cycles, which is related to a life-time of more than 10 years.ResultsThe maximum retention force in case of PEEK + PEEK was higher in comparison to the other tested material pairings. In the range between 1 and 10 mm/ min pull off speed there was no significant influence by the pull off speed. More influence on the friction force would be expected by changes of the number of the crowns acting simultaneously. The friction force was decreasing with decreasing number of crowns but not linearly in any tested case. The long-term test has shown that the friction force remained constant.SignificanceThe performance of PEEK + PEEK telescopes is comparable with the usually applied material pairings. Over long time no loss in retention force could be observed. The retention force - distance progression in the PEEK + PEEK pairing offers more security against a possible loss of retention during repair or relining. For further tests of the performance of telescopic crowns or to estimate of friction force limits, a setup with at least two, but preferably three, crowns tested in parallel is suggested.     

Clinical longevity of removable partial dentures retained by telescopic crowns: outcome of the double crown with clearance fit

PURPOSE: It was the aim of this study to investigate the long-term success of a telescopic crown system that can be used for both rigid and resilient support and to evaluate by means of a literature review whether the use of resilient support may be advantageous compared to other double crown systems when the restoration is placed on only a few remaining teeth. MATERIALS AND METHODS: Patient records were used to evaluate 125 dentures (with 460 abutment teeth) based on the Marburg double crown system. The loss of abutment teeth, endodontic treatment, and fracture of the metallic framework were investigated with regard to the different types of denture support. RESULTS: The probability that a patient would have kept all abutment teeth was 84% after 5 years and 66% after 10 years. No significant differences were found for the two groups "resilient support" (< or = three abutment teeth) and "rigid support" (> or = four abutment teeth). For abutment teeth with a double crown with clearance fit, the risk of loss was 4% after 5 years and 15% after 10 years for rigid support, and 10% and 24%, respectively, for resilient support. The risk of endodontic treatment was 7% after 5 years and 9% after 10 years for rigid support, and 3% and 7%, respectively, for resilient support. None of the denture frameworks showed a fracture during the observation period. CONCLUSION: Removable partial dentures retained by double crowns with clearance fit and constructed without major or minor connectors provide good clinical longevity. The survival rates of abutment teeth were comparable to those reported in the literature for other double crown systems. There was no significant increase of the risk of abutment loss when the restoration was placed on three or fewer remaining teeth and the concept of resilient support was applied.     

Maxillary removable prostheses retained by telescopic crowns on two implants or two canines

Precision telescopic attachments allow for rigid connection between removable prostheses and abutments. However, it is still unknown whether implants can bear similar long-term loading forces as teeth when telescopic crowns are used as retention devices. It was the aim of this prospective clinical study to observe maxillary removable partial dentures that were retained by telescopic crowns on two endosseous implants in the canine regions. In a control group, identical dentures were fabricated that were retained by telescopic crowns on the maxillary canines. The implant group consisted of 14 patients, and the control group included 8 patients. Mean observation time of the prostheses was 25.6 months. Radiographic bone levels and periodontal parameters did not reveal specific differences between the two groups. However, five implants failed, and there were no failures in the control group. Survival rates were 48.9% for the implant group and 100% for the control group, with a significant difference between the two groups. Within the limits of this study, it is concluded that the telescopic connection might be too rigid (thus delivering overloading) for two single implants in the canine region of the maxilla supporting a removable denture.     

Frictional telescopic crowns in severely reduced dentitions: a 5-year clinical outcome study

Clinical outcomes for frictional telescopic crowns supporting removable prostheses in patients with severely reduced dentitions with one to three remaining teeth per arch have been inadequately documented. Seventy-four patients with severely reduced dentitions received 82 telescopic removable partial dentures that were supported by 173 frictional telescopic crowns. The recorded individual telescopic abutment survival rate over a 60-month period was 80.6%. This observation was significantly influenced by sex and tooth vitality and mobility (Kaplan-Meier). The risk of loss of telescopic crowns was significantly influenced by sex, arch, vitality, and abutment tooth distribution (Cox regression). Telescopic removable partial dentures were proven to be a favorable treatment concept for severely reduced dentitions in the selected group of patients.     

Clinical evaluation of castable apatite ceramic crowns.

Thirty-three castable apatite ceramic crowns were constructed for 26 patients. The crowns were clinically evaluated for anatomic form, marginal adaptation, cavosurface marginal discoloration, surface roughness, and color match for a period of 2 years at regular intervals. Results showed that all restoration had satisfactory anatomic form; all but one exhibited good marginal adaptation. Slight abrasion was noticed at the functioning cusps and all but three of the restorations demonstrated excellent color matching.     

Clinical evaluation of all-ceramic crowns

STATEMENT OF PROBLEM: There are few in vivo studies on the clinical performance of all-ceramic crowns. PURPOSE: The aim of this study was to evaluate the clinical performance of IPS Empress crowns. MATERIAL AND METHODS: Thirty-seven all-ceramic IPS Empress crowns were placed in 20 patients. Twenty crowns were luted with Variolink II low-viscosity resin cement in combination with Syntac Classic dentin adhesive; the remaining 17 were luted with Variolink II in combination with Syntac Single Component. All procedural steps were performed by the same prosthodontist. Using the California Dental Association's (CDA) quality evaluation system, 2 calibrated evaluators examined the crowns for margin integrity, anatomic form, surface, and color for a period of 12 to 41 months, with a mean of 24.56 months after insertion. Kaplan-Meier statistical analysis was used to calculate the survival rate of the crowns. Values obtained for plaque and gingival conditions were compared to control teeth with use of the Wilcoxon signed ranks test (P<.05). RESULTS: Based on the CDA criteria, 94.6% of the crowns were rated satisfactory. Fracture was registered in only 1 crown. One endodontically treated tooth failed due to the dislodgement of the prefabricated dowel. No significant difference was observed in the gingival health status of crowns that had margins placed above or at the level of the gingival margin. However, in crowns that had subgingival margin finish lines, the percentage of bleeding on probing was significantly higher than that of the contralateral control teeth. CONCLUSION: In this in vivo study, IPS Empress crowns luted with both dentin bonding agents functioned satisfactorily with a relatively low fracture rate over a mean evaluation period of 24.56 months.     

球帽式与套筒冠式下颌种植覆盖义齿的三维有限元分析

目的:应用三维有限元分析,比较球帽式和套筒冠式附着体对下颌种植覆盖义齿的应力分布的影响。方法:本实验应用三维有限元法分析,模拟下颌覆盖义齿在正中咬合状态下的受力情形。结果:两种模型中,骨组织界面应力主要都集中在种植体颈部周围的皮质骨中。球帽式附着体模型中牙槽嵴表面上的最大压应力峰值为-1.601Mpa,而套筒冠式附着体模型的压应力峰值为-0.296Mpa。套筒冠式附着体模型的中央种植体、侧方种植体上的应力峰值均小于球帽式附着体的种植体。结论:套筒冠式覆盖义齿较球帽式可降低种植体及剩余牙槽骨表面的应力,更有助于保存牙槽骨组织和种植体。     

Clinical application of all-ceramic fixed partial dentures and crowns.

The esthetic demands of patients have increased considerably during recent years. Due to this increasing interest in esthetics, as well as concerns about toxic and allergic reactions, the use of all-ceramic restorations has increased. One of the systems introduced for all-ceramic restorations is the IPS Empress system. This article examines one all-ceramic restoration system, IPS Empress, and presents patient cases in which all-ceramic crowns and fixed partial dentures have been utilized.     

CAD/CAM氧化锆全瓷冠修复临床疗效评价

目的：探讨CAD／CAM氧化锆全瓷冠的修复效果。方法：选择82例（192颗患牙）,分别在CAD／CAM氧化锆全瓷冠粘接后1、3、6、12个月进行随访观察。采用美国公共健康协会的修订标准对修复体的临床效果进行评价。结果：观察期间失访4例,随访78例共181件修复体,结果显示CAD／CAM全瓷冠颜色达到好以上91．2％,CAD／CAM氧化锆全瓷冠的崩瓷率2．76％,与修复体部位有明显相关性（P〈0．01）,在粘接12个月后有1个修复体的边缘密合度欠佳,所有复诊患者在12个月的临床观察中均未见边缘着色,继发龋和基牙松动。结论：氧化锆全瓷修复体具有良好的稳定性和生物相容性,近期临床效果满意。     

氮化钛涂层对循环摘戴后套筒冠固位力的影响

目的:研究氮化钛涂层对循环摘戴后圆锥型套筒冠固位力的影响.方法:使用精密数控车床制作标准金属内、外冠试件14 对,随机分成2 组(实验组和对照组),每组7 对,在实验组套筒冠内冠表面和外冠内面沉积2 μm氮化钛(TiN),未镀TiN组为对照组,测定2 组套筒冠经循环摘戴后固位力值.采用SPSS 13.0软件包对实验数据进行成组t检验统计分析.结果:镀TiN组套筒冠初始固位力较未镀膜组小, 2 组固位力随循环次数的增加而降低,未镀膜组固位力下降速度较镀膜组更为显著.镀TiN组套筒冠在循环3 000 次后固位力开始下降,3 000 次前和7 000 次后固位力下降平缓.结论:圆锥型套筒冠内、外冠沉积氮化钛涂层可以降低套筒冠固位力衰减速度,能够保持持久的固位力.