Anisotropic elasticity of cortical and cancellous bone in the posterior mandible increases peri-implant stress and strain under oblique loading

The aim of this study was to compare implant-bone interface stresses and peri-implant principal strains in anisotropic versus isotropic three-dimensional finite element models of an osseointegrated implant in the posterior mandible. We obtained anisotropic (transversely isotropic) elastic constants for mandibular bone and derived equivalent isotropic constants by averaging over all possible spatial orientations. A finite element model was constructed using ten-node tetrahedral p-elements, providing curved edges where necessary and increasing the accuracy of the results in regions of high stress gradients. Perfect bonding was assumed at the implant-bone interface. An oblique load was applied at the coronal aspect of the crown with 100 N vertical and 20 N bucco-to-lingual components. Implant-bone interface stresses exceeded reported bond strengths and principal strains reached yield strain levels in the cortical crest. Anisotropy increased what were already high levels of stress and strain in the isotropic case by 20 to 30% in the cortical crest. In cancellous bone, anisotropy increased what were relatively low levels of interface stress in the isotropic case by three- to four-fold to exceed bond strength levels. Anisotropy has subtle, yet significant effects on interface stresses and peri-implant strains and careful consideration should be given to its use in finite element studies of dental implants.     

Use of buccal fat pad to repair post-extraction peri-implant bone defects in the posterior maxilla. A preliminary prospective study

Background

Extensive literature exists about the use of the BFP in the treatment of oral defects but, to our knowledge, no article refers to the use of the BFP as a substitute of the membrane barriers for treatment of peri-implant bone defects. The aim was to evaluate the use of the buccal fat pad as a coating material for bone grafting in the peri-implant bone defect regeneration of immediate implants placed in the posterior maxilla.

Material and Methods

A preliminary prospective study of patients involving immediate implants in which the buccal fat pad was used as a coating material to peri-implant bone defects was carried out. The outcome measures assessed were: postoperative pain and swelling, complications related to buccal fat pad surgery, implant survival and success rates and peri-implant marginal bone loss at 12 months of prosthetic loading.

Results

Twenty-seven patients (17 women and 10 men) with a mean age of 55.3 ± 8.9 years, and a total of 43 implants were included. Two-thirds of the patients reported either no pain or only mild intensity pain and moderate inflammation, two days after surgery. Post-operative period was well tolerated by the patients and no serious complications occurred. None wound dehiscence occurred. Implant survival and success rates were 97.6% and the average marginal bone loss 1 year after loading was 0.58 ± 0.27 mm.

Conclusions

Within the limits of this preliminary study, the use of the buccal fat pad as a coating material for bone grafting in peri-implant bone defects placed in the upper posterior maxilla was a well-tolerated technique by patients; high implant success rate was achieved with a minimal peri-implant marginal bone loss at 12 months of prosthetic loading. Key words:Buccal fat pad, immediate implant, peri-implant bone defect.     

种植体-基台连接形式对种植体周围骨组织应力分布的影响

目的分析种植体-基台连接形式对种植体周围骨组织应力分布的影响，从生物力学角度探讨平台转换连接形式防止或减少种植体周围骨吸收的可能机制。方法利用COSMOSM2．85软件包建立种植体支持的下颌第一磨牙三维有限元模型，种植体-基台的连接形式分别采用平齐对接（模型A）和平台转换（模型B）。采用垂直和斜向两种形式加载，载荷均为200N，比较两种模型种植体周围骨组织的应力分布情况以及种植体-骨界面颊舌侧相同位置的von Mises应力大小。结果不同加载条件下两种模型种植体周围骨组织应力集中在种植体颈部颊舌侧骨皮质内，斜向加载时最大von Mises应力值高于垂直加载时。模型A和模型B骨组织内最大von Mises应力值在垂直加载时，分别为11．61MPa和7．15MPa，斜向加载时分别为22．07MPa和11．87MPa。距离种植体-基台连接处越远，von Mises应力值越小，骨皮质到骨松质交界处的应力变化最明显。与模型A相比，模型B种植体-骨界面相同节点的最大von Mises应力值较小。结论与平齐对接形式相比，平台转换设计可改善种植体周围骨组织的应力分布，降低种植体颈部骨组织所受的应力。     

Influence of forces on peri-implant bone

Abstract: Occlusal forces affect an oral implant and the surrounding bone. According to bone physiology theories, bones carrying mechanical loads adapt their strength to the load applied on it by bone modeling/remodeling. This also applies to bone surrounding an oral implant. The response to an increased mechanical stress below a certain threshold will be a strengthening of the bone by increasing the bone density or apposition of bone. On the other hand, fatigue micro-damage resulting in bone resorption may be the result of mechanical stress beyond this threshold. In the present paper literature dealing with the relationship between forces on oral implants and the surrounding bone is reviewed. Randomized controlled as well as prospective cohorts studies were not found. Although the results are conflicting, animal experimental studies have shown that occlusal load might result in marginal bone loss around oral implants or complete loss of osseointegration. In clinical studies an association between the loading conditions and marginal bone loss around oral implants or complete loss of osseointegration has been stated, but a causative relationship has not been shown.     

下颌后牙区不同时机游离龈移植的效果对比

目的对不同时机的游离龈移植术（FGG）增加下颌后牙区种植体周颊侧角化龈的临床效果进行评价。 方法选择2018年10月至2020年10月就诊于东莞健力口腔医院修复种植科下颌后牙区单牙缺失角化牙龈不足的患者（宽度为2 ~ 4 mm）共40例,将纳入的40例患者进行编号,以随机数字表法抽取20例为实验组,其余20例为对照组。实验组种植Ⅰ期手术时放置愈合基台同期行FGG。对照组种植Ⅰ期手术潜入式愈合,3个月Ⅱ期手术时放置愈合基台同期行FGG。术后观察移植物的存活情况,测量术前牙槽嵴顶剩余角化龈宽度,测量颊侧FGG后即刻、移植术后2个月、戴牙后即刻和戴牙后6个月的颊侧角化龈宽度,使用SPSS 20.0软件对移植物存活率、颊侧不同时间点角化龈宽度等进行统计分析,采用配对t检验进行比较,以P<0.05认为差异有统计学意义。 结果两组手术均获得成功,伤口正常愈合,组织瓣均存活。术前实验组和对照组牙槽嵴顶余留角化龈宽度分别为（2.9 ± 0.3）和（3.0 ± 0.3）mm,差异无统计学意义。实验组和对照组术后即刻种植体颊侧龈缘中点角化龈宽度分别为（4.9 ± 0.5）和（4.9 ± 0.5）mm,差异无统计学意义（t = 0.2,P = 0.8）。实验组和对照组术后2个月颊侧龈缘中点角化龈宽度分别为（4.2 ± 0.4）和（4.5 ± 0.4）mm,差异有统计学意义（t = -2.9,P<0.05）。实验组和对照组戴牙当天种植体颊侧龈缘中点角化龈宽度为（3.2± 0.4）和（3.7± 0.5）mm,差异有统计学意义（t = -2.6,P<0.05）。实验组和对照组戴牙后6个月种植体颊侧龈缘中点角化龈宽度为（3.1 ± 0.4）和（3.5 ± 0.3）mm,差异有统计学意义（t = -3.7,P<0.05）。 结论当下颌后牙区剩余角化龈为2 ~ 4 mm时,FGG在种植Ⅰ期手术同期及Ⅱ期手术同期均能获得较好的增加角化龈的效果。相比于种植Ⅰ期手术同期进行FGG,Ⅱ期手术同期FGG能获得更好的颊侧角化龈的宽度,但会增加手术次数。     

Correlation between clinical parameters characterising peri-implant and periodontal health: A practice-based research in Spain in a series of patients with implants installed 4-5 years ago

Objectives: To explore periimplant health (and relation with periodontal status) 4-5 years after implant insertion. Study Design: A practice-based dental research network multicentre study was performed in 11 Spanish centres. The first patient/month with implant insertion in 2004 was considered. Per patient four teeth (one per quadrant) showing the highest bone loss in the 2004 panoramic X-ray were selected for periodontal status assessment. Bone losses in implants were calculated as the differences between 2004 and 2009 bone levels in radiographs. Results: A total of 117 patients were included. Of the 408 teeth considered, 73 (17.9%) were lost in 2009 (losing risk: >50% for bone losses ≥7mm). A total of 295 implants were reviewed. Eight of 117 (6.8%) patients had lost implants (13 of 295 implants installed; 4.4%). Implant loss rate (quadrant status) was 1.4% (edentulous), 3.6% (preserved teeth), and 11.1% (lost teeth) (p=0.037). The percentage of implant loss significantly (p<0.001) increased when the medial/distal bone loss was ≥3 mm. The highest (p≤0.001) pocket depths were found in teeth with ≥5mm and implants with ≥3mm bone losses, with similar mean values (≥4mm), associated with higher rates of plaque index and bleeding by probing. Conclusions: The significant bi-directional relation between plaque and bone loss, and between each of these two parameters/signs and pocket depths or bleeding (both in teeth and implants, and between them) together with the higher percentage of implants lost when the bone loss of the associated teeth was ≥3 mm suggest that the patient’s periodontal status is a critical issue in predicting implant health/lesion. Key words:Implants, periimplantitis, periodontitis, oral health, practice-based research     

Idiopathic bone cavity on the posterior buccal surface of the mandible.

A cavity on the posterior buccal surface of four dry mandibles (n = 8282) is reported. The shape, size, unilaterality, and sex distribution of this phenomenon are similar to anterior and posterior idiopathic bone cavities (i.e., defects) on the lingual cortex. Posterior buccal mandibular defects differ from posterior lingual cavities in their unilateral occurrence and age distribution. The differential diagnosis for posterior buccal mandibular defects includes an anatomic variant, an aneurysmal erosion, erosion by a lymphoid nodule, and a neural neoplasm.     

右下颌骨后部静止性骨腔并发翼下颌韧带乳头状瘤1例

自1942年Stafne首次报告34例静止性骨腔后,国外已有几十篇报道,但国内近20年只有6篇文章,仅11例报道[1-3].静止性骨腔是在下颌骨体内偶见唾液腺的一种特殊解剖结构,通常穿过舌侧密质骨,以蒂与正常下颌下腺或舌下腺相连,故又称为Stafne骨腔[4].因其病因未明,文献中对其命名尚未统一,种类繁多[5].St...     

Teaching the placement of posterior resin-based composite restorations in Spanish dental schools

Objectives: In an area of esthetic dentistry such as posterior composites, in which new materials and techniques are being devolved continuously, it is important to confirm that dental students have a clear understanding of the basic principles of clinical application of this knowledge. Considering that the preparation of dental graduates in Spain may be of interest to competent dental authorities and employers with whom they can work worldwide, this study investigated the teaching of posterior composite restorations in Spanish dental schools. Study design: In late 2009⁄ early 2010, a questionnaire seeking information on the teaching of posterior composites was emailed to the professor responsible for teaching operative dentistry in each of the fifteen dental schools having complete undergraduate dental degree programs in Spain. Results: The response rate was 100%. Most investigated topics did not show noteworthy differences depending on whether the schools were public or private. Variations were found among Spanish dental schools in both the amount and content of the teaching programs concerning posterior composite restorations. Differences were recorded in the teaching of cavity design, contraindications to composite placement, indications for liners and bases, matrix and wedging techniques, composite and bonding systems, light curing and finishing procedures for composite restorations. More consistency was observed in teaching methods of moisture-control, indirect composites and amalgam bonding. Conclusions: As recommended in previously surveyed countries, efforts must be made to promote harmonization of dental curricula to make it easier for graduates to work elsewhere, and to ensure they meet the needs of their patients on entering independent practice. Key words:Aesthetic dentistry, composite restoration, dental education, teaching program, undergraduate dental student.     

Influence of occlusal loading on peri-implant clinical parameters. A pilot study

Objectives: To investigate the relation between occlusal loading and peri-implant clinical parameters (probing depth, bleeding on probing, gingival retraction, width of keratinized mucosa, and crevicular fluid volume) in patients with implant-supported complete fixed prostheses in both arches. Material and Methods: This clinical study took place at the University of Valencia (Spain) dental clinic. It included patients attending the clinic for regular check-ups during at least 12 months after rehabilitation of both arches with implant-supported complete fixed ceramo-metallic prostheses. One study implant and one control implant were established for each patient using the T-Scan®III computerized system (Tesco, South Boston, USA). The maxillary implant closest to the point of maximum occlusal loading was taken as the study implant and the farthest (with least loading) as the control. Occlusal forces were registered with the T-Scan® III and then occlusal adjustment was performed to distribute occlusal forces correctly. Peri-implant clinical parameters were analyzed in both implants before and two and twelve months after occlusal adjustment. Results: Before occlusal adjustment, study group implants presented a higher mean volume of crevicular fluid (51.3±7.4 UP) than the control group (25.8±5.5 UP), with statistically significant difference. Two months after occlusal adjustment, there were no significant differences between groups (24.6±3.8 UP and 26±4.5 UP respectively) (p=0.977). After twelve months, no significant differences were found between groups (24.4±11.1 UP and 22.5±8.9 UP respectively) (p=0.323). For the other clinical parameters, no significant differences were identified between study and control implants at any of the study times (p>0.05). Conclusions: Study group implants receiving higher occlusal loading presented significantly higher volumes of crevicular fluid than control implants. Crevicular fluid volumes were similar in both groups two and twelve months after occlusal adjustment. Key words:Occlusal loading, crevicular fluid, peri-implant clinical parameters, T-Scan®.     

Influence of controlled immediate loading and implant design on peri-implant bone formation

AIM: Tissue formation at the implant interface is known to be sensitive to mechanical stimuli. The aim of the study was to compare the bone formation around immediately loaded versus unloaded implants in two different implant macro-designs. MATERIAL AND METHODS: A repeated sampling bone chamber with a central implant was installed in the tibia of 10 rabbits. Highly controlled loading experiments were designed for a cylindrical (CL) and screw-shaped (SL) implant, while the unloaded screw-shaped (SU) implant served as a control. An F-statistic model with alpha=5% determined statistical significance. RESULTS: A significantly higher bone area fraction was observed for SL compared with SU (p<0.0001). The mineralized bone fraction was the highest for SL and significantly different from SU (p<0.0001). The chance that osteoid- and bone-to-implant contact occurred was the highest for SL and significantly different from SU (p<0.0001), but not from CL. When bone-to-implant contact was observed, a loading (SL versus SU: p=0.0049) as well as an implant geometry effect (SL versus CL: p=0.01) was found, in favour of the SL condition. CONCLUSIONS: Well-controlled immediate implant loading accelerates tissue mineralization at the interface. Adequate bone stimulation via mechanical coupling may account for the larger bone response around the screw-type implant compared with the cylindrical implant.     

Multivariate analysis of the influence of peri-implant clinical parameters and local factors on radiographic bone loss in the posterior maxilla: a retrospective study on 277 dental implants

Clinical Oral Investigations - The aim of the present study was to investigate whether peri-implant clinical parameters (modified plaque index (mPI), bleeding and/or suppuration on probing (B/SOP))...     

Impact of implant overloading on the peri-implant bone in inflamed and non-inflamed peri-implant mucosa

OBJECTIVE: To assess the impact of overloading on peri-implant bone level and the bone-to-implant contact (BIC) in the presence of healthy or inflamed peri-implant tissues. MATERIALS AND METHODS: Four screw-shaped machined implants were placed bilaterally in the mandible of four beagle dogs and left submerged for 3 months. Prosthetic abutments were connected either in supra-occlusal contact with the opposite teeth (overloaded) or in infra-occlusal position (unloaded). In each dog, cotton floss ligatures were placed unilaterally around abutments to promote plaque accumulation; the contralateral side was brushed three times a week. There were four experimental sites, two implants in each: loaded uninflamed (LU), loaded inflamed (LI), unloaded uninflamed (UU), and unloaded inflamed (UI). Clinical and radiographic parameters were recorded at baseline and every 3 months throughout the observation period. At 12 months, the dogs were sacrificed and histomorphometric analysis was performed. RESULTS: Implants with ligature-induced peri-implantitis presented high inflammatory indices throughout the observation period. Clinical parameters did not change from baseline for both LU and UU. Loading significantly increased the percentage of BIC (BIC%) (P<0.05) and slightly increased crestal bone resorption, but not apical to the implant neck. Both LI and UI groups showed significant peri-implant bone loss (P<0.01), mostly horizontal on the buccal aspect and angular on the lingual aspect, which exposed implant threads. Loading significantly (P<0.05) increased implant thread exposure due to buccal and lingual vertical bone resorption. CONCLUSIONS: In the presence of uninflamed peri-implant mucosa, overloading of implants in the dog model increased BIC% and slightly reduced marginal bone level. However, resorption did not progress beyond the implant neck. Overloading aggravated the plaque-induced bone resorption when peri-implant inflammation was present.     

牙种植体表面多孔层厚度对骨界面应力分布的影响

目的 研究牙种植体表面多孔层厚度对周围骨应力分布的影响.方法 通过采集健康成年男性的下颌骨CT三维数据进行三维重建,建立Ⅲ类下颌骨三维模型,运用UG NX8.0软件绘制实心的和4种不同表面多孔层厚度(0.5mm,1.0mm,1.5mm,全多孔)的种植体模型.将5种种植体模型依次与下颌骨模型进行配准、网格划分和赋予材料学参数,在种植体基台表面施加118.2N的15°斜向力,用ABAQUS有限元分析软件处理运算骨界面的应力.结果 皮质骨和种植体颈部松质骨的应力峰值均随种植体表面多孔层厚度增加而增大(P＜0.05),全多孔组最大(分别为58.3MPa和11.28MPa),实心组最小(分别为50.2MPa和9.68MPa).种植体根端松质骨的应力峰值无显著差异(P＞0.05).结论 在种植体表面引入多孔结构以及增加多孔层厚度,能增大种植体周围骨应力,缓解应力遮蔽效应.     

下颌后牙区软组织水平种植体边缘骨吸收相关因素的临床研究

目的研究下颌后牙软组织水平种植体边缘骨吸收的影响因素,为减少种植体边缘骨吸收量,提高种植体存留率提供理论依据。方法 选择76例患者行下颌后牙区软组织水平种植,共植入种植体116枚。记录患者的一般情况、种植体特征、种植体植入部位特征及修复体特征,在术后即刻、种植后3个月、修复后3个月、修复后12个月行锥形束CT检查,利用One Vlume Viewer软件测量并计算边缘骨吸收量,采用SPSS 20.0软件进行统计学分析。结果 吸烟、骨密质厚度、种植体长轴与牙冠长轴夹角、种植体局部卫生情况在各组间的差异有统计学意义（P<0.05）,患者性别、年龄、种植体长度、种植体直径、种植体系统、种植体边缘骨高度和修复体类型在各组间的差异无统计学意义（P>0.05）。结论 吸烟、骨密质较厚、种植体长轴与牙冠长轴夹角较大、种植体局部卫生差是引起种植体边缘骨吸收的危险因素,其中,局部卫生差与种植体边缘骨吸收的相关性较强。