The influence of medial implant location in three-unit posterior cantilever fixed partial dentures on stress distribution in surrounding mandibular bone

This study examined the influence of medial implant location in three-unit posterior cantilever fixed partial dentures (FPDs) on stress distribution in mandibular bone surrounding two implants. A three-dimensional finite element model that included three-unit FPD and two cylindrical-type implants (4 mm in diameter and 10 mm in length) osseointegrated in the posterior mandible, was digitized. Five different models were created according to the medial implant location between the missing second premolar and the first molar location. The distal implant was fixed at the missing second molar location. Oblique bite force of 100 N at 30 degrees buccal to the vertical direction was directed on each of three artificial teeth, respectively and simultaneously, while the lower surface of the mandible was fixed. The maximum equivalent stress in the cortical and the trabecular bone generally increased as the medial implant shifted to a distal position. Under the simultaneous bite force, relatively low maximum stresses within the cortical bone: between 55 MPa and 57 MPa, were shown in the models with the medial implant placed within the range of one implant diameter from the most medial position, while higher maximum stresses: between 64 MPa and 73 MPa, were demonstrated with more distally placed medial implants. The results suggest that reasonably low mechanical stress in the surrounding bone may be assured when the medial implant is placed in the range between the missing second premolar position and one implant diameter distal from that location.     

植入部位对种植固定桥受力影响的三维有限元分析

目的:采用三维有限元方法比较种植体不同植入部位对下颌后牙四单位种植固定桥应力分布的影响.方法:建立4种不同植入部位四单位种植同定桥的有限元模型,分别为456X、45X7、4X67、X567,采用分散垂直、分散斜向、集中垂直、集中斜向4种加载方式,利用ABAQUS有限元分析软件,分析各种载荷下的应力分布情况.结果:分散载荷下,不管是垂直向还是斜向,4种植入方案的最大Von Mises应力均位于种植体颈部-皮质骨界面处;斜向载荷的Von Mises应力在皮质骨和种植体上明显增高,为垂直向的2.9～5.6倍.集中载荷下,4种植入方案的最大VonMises应力都位于邻近桥体的种植体颈部皮质骨处.远中悬臂设计应力集中最为明显.结论:四单位种植固定桥应避免远中悬臂456X设计方案,在本实验所假设的条件下,45X7植入方案力学分布更为均匀.     

动态载荷下种植体位置和直径对悬臂梁种植固定义齿应力影响的三维有限元研究

目的 应用三维有限元法分析动态加载下种植体植入位置和直径对悬臂梁种植固定义齿应力的影响。方法 建立左下颌第二前磨牙、第一磨牙、第二磨牙缺失种植固定义齿的三维有限元模型,远中种植体的位置和直径保持不变;近中种植体依次向远中移动形成中轴与第一前磨牙远中面距离D分别为5.5、8.0、10.5、13.0 mm的悬臂梁种植固定义齿,分别采用4.1和4.8 mm两种直径的种植体;以250 N 牙合力模拟咀嚼周期0.875 s的动态载荷加载于颊尖和舌尖上,应用有限元分析软件MSC.Marc和Partran分析种植体-骨组织界面的Von Mises应力情况。结果 随着近中种植体逐渐向远中移动,近远中种植体Von Mises应力均有不同程度增高,近中种植体中轴与第一前磨牙远中面距离D≤8.0 mm范围内种植体最大Von Mises应力增幅缓和,D>8.0 mm时应力急剧加大;近中种植体直径增大,则近远中种植体的应力减小;各加载阶段最大Von Mises应力均处于近远中种植体颈部与皮质骨交界处;斜向加载种植体应力显著大于垂直加载。结论 种植体植入位置是影响悬臂梁种植固定义齿应力的重要因素,悬臂梁长度不超过前磨牙宽度时行种植固定义齿设计是可行的,直径的选择要考虑骨量和悬臂梁长度双重因素。     

Comparisons of tactile thresholds between implant-supported fixed partial dentures and removable partial dentures.

This study compared the tactile sensitivity of splinted abutment and denture teeth of 16 fixed partial dentures (FPD) supported by blade implants and 16 removable partial dentures (RPD) in patients with Kennedy Class I and Class II edentulous conditions. No significant differences were noted between the tactile thresholds of the natural abutment teeth and artificial teeth in the FPD and RPD groups. The splinted abutment teeth required 45.4 g, or 5.4 to 5.8 times higher occlusal loads than did those needed for the comparable nonsplinted teeth, to detect the stimulus. A further increase of 54% in thresholds with the FPD and over 100% with the placement of the RPD indicated the superiority of the RPD in terms of load distribution as a result of the cross-arch splinting and mucosal support. Moderate positive correlations (r = 0.37 to 0.46; P < .05) between tactile thresholds and masticatory performance were found, signifying that reduced tactile perception was not responsible for the incomplete restoration of the masticatory function with RPDs or FPDs but might be contributing to increased masticatory performance within both treatment groups.     

Fracture resistance of different zirconium dioxide three-unit all-ceramic fixed partial dentures

OBJECTIVE: This study evaluated the fracture resistance of different zirconia three-unit posterior all-ceramic fixed partial dentures before and after fatigue loading. MATERIAL AND METHODS: Forty-eight zirconia three-unit posterior all-ceramic fixed partial dentures were fabricated using different manufacturing systems and conventionally cemented on human teeth. The restorations were divided according to the system used for manufacturing the frameworks into 3 groups of 16 specimens each (DCS, Procera and Vita CerecInlab). Half of each group was artificially aged through dynamic loading and thermal cycling, whereas the other half was left with no artificial aging. Afterwards, all specimens were tested for fracture resistance using compressive load on the occlusal surface. Non-parametric ANOVA using the Kruskal-Wallis and Wilcoxon rank tests was performed to test for differences in fracture resistance values with a global significance level of 0.05. RESULTS: All artificially aged specimens survived with no failures. The median fracture resistance values (before; after artificial aging) were: DCS (1683 N; 1618 N), Procera (1522 N; 1256 N), and Vita CerecInlab (1702 N; 1556 N). No significant differences were found for comparisons between different groups before artificial aging. Artificial aging did not significantly influence the fracture resistance of different groups. After artificial aging, group Procera showed significantly lower fracture resistance than the Vita CerecInlab (p=0.015) and DCS (p=0.038) groups. CONCLUSIONS: All tested restorations have the potential to withstand occlusal forces applied in the posterior region and can therefore represent interesting alternatives for replacing porcelain-fused-to-metal restorations. Further assessment is needed before recommending such restorations in daily practice.     

Cement fixation and screw retention: parameters of passive fit. An in vitro study of three-unit implant-supported fixed partial dentures

It is generally assumed that passively fitting superstructures are a prerequisite for long-lasting implant success. In the study presented, the strain development of three-unit implant fixed partial dentures (FPDs) was evaluated at the bone surrounding the implant and on the superstructure using a strain gauge technique. Six groups of three-unit FPDs representing the commonly used techniques of bridge fabrication were investigated with 10 samples each, in order to quantify the influence of impression technique, mode of fabrication and retention mechanism on superstructure fit. Two ITI implants (Straumann, Waldenburg, Switzerland) were anchored in a measurement model according to a real-life patient situation and strain gauges were fixed mesially and distally adjacent to the implants and on the bridge pontics. The developing strains were recorded during cement setting and screw fixation. For statistical analysis, multivariate two sample tests were performed setting the level of significance at P=0.1. None of the investigated bridges revealed a truly passive fit without strains occurring. About 50% of the measured strains were found to be due to impression taking and model fabrication, whereas the remaining 50% were related to laboratory inaccuracies. The two impression techniques used did not reveal any significant differences in terms of precision. Both modes of fixation--i.e. cement and screw retention--provoked equally high stress levels. In the fabrication of screw-retained FPDs, similar results were obtained from the use of burn-out plastic copings and the technique of casting wax moulds to premachined components. Bonding bridge frames onto gold cylinders directly on the implants significantly reduces strain development.     

Effect of cantilever length and framework alloy on the stress distribution of mandibular-cantilevered implant-supported prostheses

Objectives: The purpose of this in vitro study was to analyze the stress distribution on components of a mandibular-cantilevered implant-supported prosthesis with frameworks cast in cobalt–chromium (Co–Cr) or palladium–silver (Pd–Ag) alloys, according to the cantilever length.
Material and methods: Frameworks were fabricated on (Co–Cr) and (Pd–Ag) alloys and screwed into standard abutments positioned on a master-cast containing five implant replicas. Two linear strain gauges were fixed on the mesial and distal aspects of each abutment to capture deformation. A vertical static load of 100 N was applied to the cantilever arm at the distances of 10, 15, and 20 mm from the center of the distal abutment and the absolute values of specific deformation were recorded.
Results: Different patterns of abutment deformation were observed according to the framework alloy. The Co–Cr alloy framework resulted in higher levels of abutment deformation than the silver–palladium alloy framework. Abutment deformation was higher with longer cantilever extensions.
Conclusion: Physical properties of the alloys used for framework interfere with abutment deformations patterns. Excessively long cantilever extensions must be avoided.     

Bone level change at implant-supported fixed partial dentures with and without cantilever extension after 5 years in function

OBJECTIVE: The aim of this study was to retrospectively analyze whether the inclusion of cantilever extensions increased the amount of marginal bone loss at free-standing, implant-supported, fixed partial dentures (FPDs) over a 5-year period of functional loading. MATERIAL AND METHODS: The patient material comprised 45 periodontally treated, partially dentate patients with a total of 50 free-standing FPDs supported by implants of the Astra Tech System. Following FPD placement (baseline) the patients were enrolled in an individually designed supportive care program. A set of criteria was collected at baseline to characterize the FPDs. The primary outcome variable was change in peri-implant bone level from the time of FPD placement to the 5-year follow-up examination. The comparison between FPDs with and without cantilevers was performed at three levels: FPD level, implant level, and surface level. Bivariate analysis was performed by the use of the Mann-Whitney U-test and stepwise regression analysis was utilized to evaluate the potential influence of confounding factors on the change in peri-implant bone level. RESULTS: The overall mean marginal bone loss for the implant-supported FPDs after 5 years in function was 0.4 mm (SD, 0.76). The bone level change at FPDs placed in the maxilla was significantly greater than that for FPDs in the mandible (0.6 versus 0.2 mm; p<0.05). No statistically significant differences were found with regard to peri-implant bone level change over the 5 years between FPDs with and without cantilevers at any of the levels of comparisons. The multivariate analysis revealed that the variables jaw of treatment and smoking had a significant influence on peri-implant bone level change on the FPD level, but not on the implant or surface levels. The model explained only 10% of the observed variance in the bone level change. CONCLUSION: The study failed to demonstrate that the presence of cantilever extensions in an FPD had an effect on peri-implant bone loss.     

Distribution of occlusal forces along unilateral posterior two-unit cantilever segments in cross-arch fixed partial dentures

Axially directed occlusal forces over unilateral posterior two-unit cantilever segments of cross-arch fixed partial dentures were measured during natural functioning by using built-in transducers, one in each cantilever unit. The mean local maximal occluding and maximal chewing forces were significantly larger over the first (124 N and 64 N) than over the second (21 N and 29 N) cantilever unit. The average intraindividual ratio between the forces over the first and second cantilever unit amounted to 12:1 for maximal occlusion and 3:1 for maximal chewing. Despite the smaller mean total maximal chewing (92 N) than mean total maximal occluding cantilever force (145 N), the resulting axially directed mean bending moments in the joint between the distal abutment crown and the cantilever segment did not differ significantly. This is explained by the larger mean maximal chewing (29 N) than mean maximal occluding (21 N) force over the second cantilever unit. This demonstrated that not only the magnitude of occluding and chewing forces over cantilever segments but also their distribution along the cantilevers is of importance for the magnitude of functional stress created in cantilever fixed prosthesis.     

Marginal adaptation of three-unit fixed partial dentures constructed from pressed ceramic systems

PURPOSE: This study compares the marginal accuracy of posterior metal ceramic (MC), all-ceramic IPS Empress 2 and experimental pressed ceramic (EPC-VP 1989/4) three-unit fixed partial dentures (FPD), before and after luting and after thermo-mechanical fatigue in a dual-axis chewing simulator. MATERIALS AND METHODS: Caries-free human teeth (n=160) were used as abutments for the fabrication of eighty posterior three-unit FPD, divided into two test-groups, IPS Empress 2 and EPC, of 32 samples each and one control group of 16 samples metal ceramic FPD. All FPD were cemented with Variolink II dual-curing resin cement. Half of the samples in each group were exposed to a dual-axis chewing simulator. RESULTS: The geometric mean marginal gap values (microm, before cementation, after cementation and after thermo-mechanical fatigue) amounted to 53, 63 and 62 for the ceramic metal FPD, 57, 71 and 68 for the Empress 2 FPD and 55, 67 and 68 for the EPC FPD. In all groups a statistically significant increase in marginal gap width was observed after cementation. The effect of functional loading in the chewing simulator on marginal gap was not significant. Marginal gap was lowest in the control group but differences with all-ceramic materials were small in all evaluation stages. CONCLUSION: Within the limits of this investigation, it can be concluded that marginal gap values of these all-ceramic materials and conventional MC techniques are on a similar level. In particular, almost all marginal gap values observed in this study were within the limits of clinical acceptance.     

种植支持无牙颌固定修复体材料对种植体及其修复体存留率的影响：系统性回顾及Meta分析

目的: 评估无牙颌种植固定修复体的材料对其种植体及其修复体临床存留率的影响。文献检索： 根据PRISMA声明（系统性回顾及Meta分析优先报告的条目）,用电子数据库手动检索相关文献。检索范围为种植支持无牙颌固定修复体的临床研究,且研究的样本量不少于10人。本研究主要目的是评估不同修复体材料对种植体支持无牙颌固定修复种植体存留率及修复体存留率的影响。结果: 共检索到文献2254篇,其中41篇文献入选。统计结果显示不同常用修复材料的无牙颌种植修复种植体存留率为：金属烤瓷修复体：97%（95%CI [0.96;0.98]）, 全瓷修复体：99%（95%CI [0.98;1.00]）,金属烤塑修复体：97%（95%CI [0.96;0.98]）,三组有显著性差异（P=0.0337）。而修复体存留率为：金属烤瓷修复体：95%（95%CI [0.89;0.97]）,全瓷修复体：97%（95%CI [0.92;0.99]）,金属烤塑修复体：97%（95%CI [0.95;0.98])）,三者无显著性差异（P=0.3796）。三种修复体的饰面崩瓷率从低到高依次为：金属烤瓷修复体：8%（95%CI[0.03;0.20]）,全瓷修复体：15%（95%CI [0.06;0.32]）,金属烤塑修复体：22%（95%CI [0.13;0.33]）。进一步将修复体材料细分为5个亚组（非贵金属烤瓷,氧化锆烤瓷,贵金属烤塑,非贵金属烤塑,PMMA）进行种植体及修复体存留率的统计。与上述结果类似,不同常用修复材料的种植体存留率有显著性差异 （P=0.0126）,而修复体存留率无显著性差异。结论: 修复体材料的选择似乎对种植支持无牙颌固定修复的种植体及修复体存留率在临床上无明显影响。种植体支持的无牙颌修复体有较高的崩瓷率,仅修复体的存留率这一个参数难以描述该种修复材料实际的临床效果,参考价值有限。本研究纳入文献数量有限,在选择氧化锆烤瓷或金属烤塑作为种植无牙颌修复体时,建议临床医师要慎重。     

The influence of prosthetic material on implant and prosthetic survival of implant-supported fixed complete dentures: a systematic review and meta-analysis

PurposeEvaluating the impact of the prosthetic material on implant- and prosthetic survival of implant-supported fixed complete dentures.Study selectionElectronic and hand searches were conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) to identify clinical studies including at least 10 patients restored with implant-supported dentures. The primary outcome was to evaluate the implant survival rate according to the applied restorative materials. The prosthetic survival rate was evaluated as secondary outcomes.ResultsForty-one of 2254 studies were ?nally selected. A statistically significant difference (p = 0.0337) was found between implant survival rates in the main restorative groups (metal-ceramic:97%(95%CI [0.96;0.98]), all-ceramic:99%(95%CI [0.98;1.00]), metal-resin:97%(95%CI [0.96;0.98])). Prosthetic survival rates were: (metal-ceramic:95%(95%CI [0.89;0.97]), all-ceramic:97%(95%CI [0.92;0.99]), metal-resin:97%(95%CI [0.95;0.98]), with no statistically significant difference (p = 0.3796) between the groups. Chipping incidence rates were as follows: metal-ceramic:8%(95%CI[0.03;0.20]), all-ceramic:15%(95%CI [0.06;0.32]), and metal-resin:22%(95%CI [0.13;0.33]).Five types of exact restorative materials were identified (porcelain-fused-to-non-precious alloy, porcelain-fused-to-zirconia, precious-metal-acrylic-resin, non-precious-metal-acrylic resin, and PMMA). Again, implant survival rates were statistically significantly influenced by the applied restorative materials (p = 0.0126), whereas, no significant differences were reported regarding prosthetic survival rate.ConclusionsProsthetic material selection seems to have no clinically relevant influence on implant- and prosthetic survival rate in implant-supported fixed complete dentures. Due to the high chipping rate, quantifying prosthetic survival alone does not seem to be a reliable tool for evaluating the outcome of the restorations and providing recommendations. These results, along with the obvious lack of evidence, suggest that clinicians must exercise caution whenever porcelain-fused-to-zirconia or metal-resin restorations are considered.     

Marginal fit of Zirconia posterior fixed partial dentures

The aim of this study was to investigate the marginal fit of posterior fixed partial dentures (FPDs) made with 2 computer-aided design/computer-assisted manufacture systems--Procera Bridge Zirconia (Nobel Biocare) and Lava AllCeramic System (3M ESPE)--and to analyze the differences between abutments and between buccal and lingual surfaces. Twenty standardized specimens were prepared to receive posterior 3-unit FPDs. FPDs were fabricated according to the manufacturer's instructions. A scanning microscope (JSM-6400, JEOL) with a magnification of 1,000x was used for measurements. Three-way analysis of variance showed significant differences (P < .001) in marginal adaptation between the ceramic groups. Procera Bridge Zirconia showed the lowest discrepancies (26 +/- 19 microm). No significant differences were observed between abutments and surfaces, and no significant interaction was observed among the ceramic system, abutments, and surfaces. The accuracy of fit achieved by both zirconia systems was within the range of clinical acceptability, with Procera Bridge Zirconia showing the best marginal fit.     

Avoiding osseous grafting in the atrophic posterior mandible for implant-supported fixed partial dentures: a report of 2 cases

Bone atrophy occurs after tooth extraction in the posterior mandible, placing the mandibular canal and its neural, arterial, and venous contents closer to the osseous facial aspect and the coronal crest. This proximity places the structure in danger of damage when dental implants are surgically placed to support fixed or removable prostheses. Several options are available to treat these areas for implant-supported fixed and removable complete or partial dentures. Osseous grafting and ridge expansion are surgical options that enable acceptance of standard sized dental implants but have serious morbidities. Additionally, vertical osseous augmentation is not predictable at this time. Narrow diameter dental implants can be placed to avoid the mandibular canal, but some bone volume situations preclude this. Very wide and very short (6.5 × 5 mm) dental implants may be placed at an angle in atrophic sites to successfully support fixed partial dentures. An anterior guidance occlusal scheme may be used in maxillary dentate patients or group function in maxillary complete denture patients. A 100 micron occlusal relief in fixed partial dentures in dentate patients may be required to account for natural tooth intrusion and to prevent occlusal overload of the implant-supported partial denture.     

Oral health-related quality of life in patients treated by implant-supported fixed dentures and removable partial dentures

Objectives: This study investigated the association between denture status [implant‐supported fixed dentures (IDs) and removable partial dentures (RPDs)] and oral health‐related quality of life (OHRQoL). Materials and methods: Consecutive patients with IDs and RPDs were recruited from the Prosthodontics Departments at Showa University and Tokyo Medical and Dental University. The Japanese version of the Oral Health Impact Profile (OHIP‐J‐49) was administered to each subject. For each OHIP‐J‐49 question, the subjects were asked to indicate the frequency with which they had experienced a dental problem during the last month. Responses were recorded on a 5 point Likert rating scale, with 0 being never and 4, very often. Summary scores were calculated and regression analyses conducted to investigate the association between denture status and OHIP‐J‐49 summary score. Results: In total 79 ID subjects (mean age±SD of 51.7±12.4 years, 44.3% men) and 109 RPD subjects (mean age of 66.5±8.6 years, 30% men) participated after giving informed consent. The regression analysis between the type of treatment and the OHIP‐J‐49 summary score revealed a significant association with a coefficient of 17.0 (Confidence interval, CI: 10.9–23.1). When age and duration of denture usage, which had significant associations with OHIP‐J‐49, were included in this model, the regression coefficient remained virtually unchanged at 17.4 (CI: 9.75–25.0), thus indicating little potential confounding by them. Conclusions: OHRQoL in patients with implant‐supported fixed dentures is generally less impaired than it is in those patients with RPDs. To cite this article :
Furuyama C, Takaba M, Inukai M, Mulligan R, Igarashi Y, Baba K. Oral health‐related quality of life in patients treated by implant‐supported fixed dentures and removable partial dentures.
Clin. Oral Impl. Res. 23 , 2012; 958–962
doi: 10.1111/j.1600‐0501.2011.02247.x