Biomechanical Analysis of Different Framework Design, Framework Material and Bone Density in the Edentulous Mandible With Fixed Implant-Supported Prostheses: A Three-Dimensional Finite Element Study.

PURPOSE: The objective of this finite element study was to investigate the effect of different framework designs, framework materials, and bone densities on the stress distribution of fixed implant-supported prostheses for edentulous mandibles. MATERIALS AND METHODS: Under the condition of 2-mm cortical bone, 16 models were created in the edentulous mandible to simulate different framework designs (1-piece or 3-piece frameworks) with different framework material (pure titanium, zirconia, polyetheretherketone, or carbon fiber-reinforced polyetheretherketone) in-high or low-density trabecular bone. Then, vertical loading and oblique loading at 75° were applied to the anterior and posterior regions. The stress distribution and stress concentration region of implant and peri-implant bone with different combinations were compared by finite element analysis. RESULTS: The use of the 1-piece zirconia framework in high-density trabecular bone improved stress distribution on implants and peri-implant bone. The region of stress concentration is located in the buccal cervix of the distal implants and the distobuccal portion of the cortical bone in all models. To improve the stress distribution on fixed implant-supported dentures for edentulous mandibles, the 1-piece framework and zirconia represent the better combination. CONCLUSION: Under the condition of 2-mm cortical bone thickness, the full-arch zirconia framework had minimum von Mises stress on implants and peri-implant bone in all models, and high trabecular bone density greatly decreased the stress on cortical bone.

Biomechanical analysis of inclined and cantilever design with different implant framework materials in mandibular complete-arch implant restorations.

STATEMENT OF PROBLEM: Inclined distal implants with posterior framework cantilevers are an alternative to straight implants for the treatment of edentulous jaws, avoiding grafting procedures and utilizing pre-existing bone. However, little is known about the implant, framework, and peri-implant bone stresses exerted by this design. PURPOSE: The purpose of this finite element analysis study was to assess the biomechanical properties of the inclined versus straight design, with different implant framework material to generate implant-supported complete-arch fixed mandibular prostheses. MATERIAL AND METHODS: A finite element model of the edentulous mandible was generated by using 4 implants in 2 distinct configurations: the inclined design and the straight design. Different framework materials were tested: pure titanium, cobalt-chromium alloy, type IV gold alloy, zirconia, polyetheretherketone (PEEK), and carbon fiber-reinforced polyetheretherketone (CFR-PEEK). A 300-N load at a 75-degree angle was applied to the occlusal plane from the lingual side of the buccal cusps of the 2 premolars and the first molar teeth. Subsequently, stresses on the implant, surrounding bone, and framework were measured and analyzed quantitatively and qualitatively. RESULTS: In terms of implant configurations, the inclined design demonstrated less stress on the posterior cortical bone, implants, and framework than the straight design. Comparing the framework materials, zirconia and metal exhibited reduced cortical bone and implants stresses but elevated framework stress when compared with the polymeric frameworks. CONCLUSIONS: From a biomechanical viewpoint, in edentulous patients with excessive posterior alveolar bone resorption, the inclined design exhibited more favorable stress distribution around the posterior implants than the straight design. In implant-supported complete-arch fixed mandibular prostheses, zirconia and metal, particularly cobalt-chromium alloy, distributed the stresses more effectively to the implants and supporting bone than polymeric materials.

Evaluation of 1-Piece Versus 3-Piece Framework Designs for the Edentulous Mandible with Fixed Implant-Supported Prostheses: A Clinical, Occlusal and Biomechanical Study.

PURPOSE: This study aims to evaluate the clinical, occlusal and biomechanical performance of 1-piece and 3-piece designs for implant-supported fixed dentures in the edentulous mandible. MATERIALS AND METHODS: A total of 65 patients with edentulous mandibles who underwent fixed implant-supported restorations were recruited and subsequently assigned to 1 of 2 groups based on the framework design (1-piece or 3-piece). The participants underwent clinical and occlusal examination using a periodontal probe, T-Scan III system, and electromyography 12 months after prosthesis delivery. Two mandibular finite element models were created to evaluate stress values and their distribution during function. RESULTS: Ninety-five point four percent (n = 62) of participants in the follow-up period underwent clinical and occlusal examination after prosthesis delivery. Clinical examination revealed a trend towards increased inflammation around the implants in the 1-piece prostheses. Occlusal parameters indicated that the 1-piece design was superior for the masticatory system than the 3-piece design. Biomechanical analysis revealed the highest stress values in the posterior region of the 3-piece design. CONCLUSIONS: On the basis of ease of ensuring oral hygiene, when compared to the 3-piece design, the 1-piece framework design might be the superior therapy for restoring an edentulous mandible, based on occlusal and biomechanical outcomes.

[Gnathology in implant-supported fixed restoration in edentulous mandible].

OBJECTIVE: This study aims to investigate the occlusal and myoelectric characteristics of implant-supported fixed denture in the mandibular region and provide reference for the design of fixed restoration. METHODS: Sixty edentulous patients with implant-supported fixed denture were selected and divided into three groups: group A, 20 cases with implant-supported fixed restoration in the maxillary region; group B, 20 cases with natural dentition, and group C, 20 cases with removable partial denture. The T-scan 8.0 digital occlusion analysis system was used to evaluate the occlusal characteristics of patients in the three groups at intercuspal, protrusion, and left and right lateral positions. Electromyography was used to analyze the myoelectric amplitude and bilateral asymmetry index of the anterior temporalis and masseter of the three groups in different states such as resting and clenching. The relationship between occlusion and myoelectricity was also investigated. RESULTS: In the occlusion analysis by T-scan, the occlusion time, the balance of left and right bite force, the left and right asymmetry of the occlusion center, the trajectory of central occlusion force, and the disclusion time were higher in group C than in groups A and B (P<0.05). No significant differences were observed in the anterior and posterior asymmetry of the occlusion center and percentage of bite force at anterior region among the three groups. In the analysis of myoelectricity, the myoelectric amplitude at resting state and the asymmetry index of masticatory muscles in group C were higher than those in groups A and B (P<0.05). The myoelectric amplitude during clenching in groups A and B groups was higher than that in group C (P<0.05). CONCLUSIONS: In implant-supported fixed restoration at edentulous mandibular, when maxillary includes the removable partial denture, degree of occlusal instability and left and right asymmetry of occlusion center are greater than those with the natural dentition and implant-supported fixed denture at maxillary. The myoelectricity is closely related to occlusion. The removable partial denture can increase the myoelectric activity and reduce the potential of the masticatory muscle. The asymmetry of bilateral myoelectricity is related to the occlusion imbalance.

[Occlusal analysis of implant-supported fixed denture in edentulous patients].

OBJECTIVE: This study aims to evaluate the occlusal characteristics of full edentulous patients with implant-supported prostheses and to provide a reference with the occlusal situation for clinicians. METHODS: A Teetester occlusal analysis system was used with 30 full edentulous patients of implant-supported fixed denture (test group) in comparison with 30 natural dentition (control group). The percentage of occlusal force distribution were measured, as well as the occlusal time at the intercuspal, protrusion, and left and right lateral positions. RESULTS: Compared with control group, the occlusion time, maximum occlusal force in intercuspal of test group significantly reduced (P<0.05); while control group was obviously superior to test group in the left and right bit force degree. Disclusion time in protrusion, occlusion times in lateral positions of test group also significantly reduced (P<0.05). There were no significant differences in average occlusion force, percentage of total force in anterior teeth, and lateral occlusion between test group and control group. CONCLUSIONS: The maximum occlusal force in intercuspal of full edentulous patients with implant-supported prostheses reduce. The occlusal force in protrusive occlusion is concentrated in the front teeth, and the group function occlusion is the main lateral occlusal pattern.

[Short-term evaluation of clinical effect of bone ring grafting and immediate insertion].

OBJECTIVE: To observe the short-term clinical effectiveness of bone ring graft technique and to summarize the key points of related surgical operation to provide comprehensive clinical guidelines. METHODS: Fifteen patients with severe alveolar bone absorption were selected to receive bone ring grafting and immediate dental implant. Final fixed prostheses were cemented five months after initial implantation. Cone beam CT scans were conducted on all subjects before the procedure, as well as four months post-operation to evaluate alveolar bone height and level of bone height and absorption around the implants. Four to six months after prosthesis installation, each implant's Jemt classification, gingiva attachment, and probing depth (PD) were analyzed. The difference of PD between implants and adjacent teeth, as well as the difference of the bone absorption between labial and lingual sides, was compared. The survival rate of the bone ring and the retention rate of implants were calculated. Complications and patient satisfaction were also investigated. RESULTS: Bone graft survival rate was 94.4% and dental implantation retention rate was 100% four months post-operation. Average bone level increase was (6.06 +/- 1.06) mm, average bone absorption was (1.33 +/- 0.84) mm, and average bone thickness at the neck of the dental implant body was (6.94 +/- 0.73) mm. Approximately 4 to 6 months after crown restoration, average bone level increase was (5.62 +/- 1.03) mm, average bone absorption was (1.51 +/- 1.02) mm, and average bone thickness at the neck of the dental implant body was (6.77 +/- 0.72) mm. The PD around the implant body and the adjacent teeth was statistically insignificant. No major post-operative complication was observed, restorations were successful, and patient satisfaction level was high. CONCLUSION: Bone ring graft technique and immediate dental implantation are relatively simple to perform, and these techniques facilitate reduction in required treatment time. Short-term effect is reliable and satisfactory, whereas long-term outcomes require further follow up and study.

Preparation and properties of plasma electrolytic oxidation coating on sandblasted pure titanium by a combination treatment.

Plasma electrolytic oxidation (PEO) is one of the most applicable methods to produce bioceramic coating on a dental implant and sandblasting is a primary technique to modify metal surface properties. This study aims to deposit bioceramic Ca- and P-containing coatings on sandblasted commercially pure titanium by PEO technique to improve its bioactive performance. The time-dependent modified surfaces are characterized in terms of their microstructure, phase, chemical composition, mechanical properties and bioactivities. The results show that the combination-treated coating exhibits better properties than the PEO-treated one, especially in bioactivities, as evidenced by the HA formation after immersion in simulated body fluid (SBF) for 5 days and the cell viability after seeding for 1 or 3 days. The enhancement of the modified surface is attributed to a combination of the mechanical sandblasting and the microplasma oxidation.

[Application of attached gingiva reconstruction in implant-supported dental prosthesis].

PURPOSE: To explore a method of attached gingiva reconstruction around dental implants and to evaluate its clinical outcomes and technical characters. METHODS: From January 2011 to August 2011, a total of 10 implants were included in this study from 8 patients who had inadequate attached gingiva and needed to undergo secondary operation. A modified apically positioned flap technique was applied to reconstruct attached gingiva at the time of secondary operation. Crown restoration was finished 4 weeks after the operation and the patients were recalled 6 months after restoration. Effective keratinized mucosal width was recorded separately before the operation, 4 weeks after the operation and 6 months after restoration. Clinical examination was conducted 6 months after restoration including modified plaque index(mPI), probing depth(PD), bleeding index(BI) and percentage of bleeding on probing. Statistical analysis was performed using Wilcoxon signed rank test with SPSS18.0 software package. RESULTS: Four weeks after the operation, there was an average increase of 2.41 mm in effective keratinized mucosal width compared with the preoperative value (P<0.05). After 6 months of function, the newly formed keratinized mucosa remained stable and attached to the crown tightly without obvious inflammation. The mean width was (2.64±0.53) mm. Clinical examinations showed a mean mPI of 0.70±0.82, a mean PD of (1.80±0.36) mm, and a mean BI of 0.73±0.64. In terms of bleeding on probing, 23.3% of sites showed positive outcome. CONCLUSIONS: By using the modified apically positioned flap technique at the time of secondary operation, the attached gingiva around implants can be effectively reconstructed. The short-term effects are satisfactory.

Poly(ethylene glycol)-block-cationic polylactide nanocomplexes of differing charge density for gene delivery.

Representing a new type of biodegradable cationic block copolymer, well-defined poly(ethylene glycol)-block-cationic polylactides (PEG-b-CPLAs) with tertiary amine-based cationic groups were synthesized by thiol-ene functionalization of an allyl-functionalized diblock precursor. Subsequently the application of PEG-b-CPLAs as biodegradable vectors for the delivery of plasmid DNAs (pDNAs) was investigated. Via the formation of PEG-b-CPLA:pDNA nanocomplexes by spontaneous electrostatic interaction, pDNAs encoding luciferase or enhanced green fluorescent protein were successfully delivered to four physiologically distinct cell lines (including macrophage, fibroblast, epithelial, and stem cell). Formulated nanocomplexes demonstrated high levels of transfection with low levels of cytotoxicity and hemolysis when compared to a positive control. Biophysical characterization of charge densities of nanocomplexes at various polymer:pDNA weight ratios revealed a positive correlation between surface charge and gene delivery. Nanocomplexes with high surface charge densities were utilized in an in vitro serum gene delivery inhibition assay, and effective gene delivery was observed despite high levels of serum. Overall, these results help to elucidate the influence of charge, size, and PEGylation of nanocomplexes upon the delivery of nucleic acids in physiologically relevant conditions.

[Three-dimension finite element analyses of interior stress of two kinds of Replace implant].

OBJECTIVE: To establish three-dimension finite element model of mandible with two kinds of Replace implant, and to study stress of implant and abutment. METHODS: The data of components of the dental implant was measured, cross section of the mandible was scanned by spiral CT and image reconstruction technique was conducted. Three-dimension finite element analysis software UG and MSC. Marc/Mentat were used to built the conjunction model and bone model of two implant systems. Axial loading (200N) and 30 degrees oblique loading (100N) were applied on the models respectively, the stress distribution patterns of the implant and abutment of two implant systems were analyzed. RESULTS: The peak stress district was concentrated on the structure of the implant cervix, which was more obviously displayed on the Replace Select implant. The peak stress of oblique loading was higher than that of axial loading. The peak stress on the implant cervix of Replace Select implant was higher than that of Replace External Hex implant in all loadings. CONCLUSION: To Replace Select especially, oblique force should be avoided on clinical practice in case of the implant fracture.

[Clinical analysis on causes of dental implant failure: report of 32 cases].

OBJECTIVE: To analyze the causes associated with the failure of dental implant restoration. METHODS: The patients who received dental implant restoration from January 2001 to December 2008 in Center of Dental Implant, School of Stomatology, Shandong University were reviewed and analyzed. The cases with implant loosening, broken or removed were considered failure. RESULTS: There were a total of 38 failure implants in 32 patients found in this group of patients. Of those, 33 implants loosened (17 cases before restoration and 16 cases after restoration), two were broken, two retention screws broken and one implant perforated on buccal side. The causes of failure included doctor-related factors in 19 cases, patient-related factors in 9 cases, implant-related factors in two cases and two uncertainties. CONCLUSIONS: Doctor-related factor is the main cause of dental implant failure, followed by patient-related factor and implant-related factor.