Performance of crowns cemented on a fiber-reinforced composite framework 5-unit implant-supported prostheses: in silico and fatigue analyses

ObjectiveTo characterize the biomechanical performance of fiber-reinforced composite 5-unit implant-supported fixed dental prostheses (FDPs) receiving individually milled crowns by insilico and fatigue analyses.MethodsEighteen implant-supported five-unit fiber-reinforced composite frameworks with an individually prepared abutment design were fabricated, and ninety resin-matrix ceramic crowns were milled to fit each abutment. FDPs were subjected to step-stress accelerated-life testing with load delivered at the center of the pontic and at 2nd molar and 1st premolar until failure. The reliability of the prostheses combining all loaded data and of each loaded tooth was estimated for a mission of 50,000 cycles at 300, 600 and 900 N. Weibull parameters were calculated and plotted. Fractographic and finite element analysis were performed.ResultsFatigue analysis demonstrated high probability of survival at 300 N, with no significant differences when the set load was increased to 600 and 900 N. 1st and 2nd molar dataset showed high reliability at 300 N, which remained high for the higher load missions; whereas 1st premolar dataset showed a significant decrease when the reliability at 300 N was compared to higher load missions. The characteristic-strength of the combined dataset was 1252 N, with 1st molar dataset presenting higher values relative to 2nd molar and 1st premolar, both significantly different. Failure modes comprised chiefly cohesive fracture within the crown material originated from cracks at the occlusal area, matching the maximum principal strain location.SignificanceFive-unit implant-supported FDP with crowns individually cemented in a fiber-reinforced composite framework presented a high survival probability. Crown fracture comprised the main failure mode.     

Effect of axial loads on implant-supported partial fixed prostheses by strain gauge analysis

Objectives

The present study used strain gauge analysis to perform an in vitro evaluation of the effect of axial loading on 3 elements of implant-supported partial fixed prostheses, varying the type of prosthetic cylinder and the loading points.

Material and methods

Three internal hexagon implants were linearly embedded in a polyurethane block. Microunit abutments were connected to the implants applying a torque of 20 Ncm, and prefabricated Co-Cr cylinders and plastic prosthetic cylinders were screwed onto the abutments, which received standard patterns cast in Co-Cr alloy (n=5). Four strain gauges (SG) were bonded onto the surface of the block tangentially to the implants, SG 01 mesially to implant 1, SG 02 and SG 03 mesially and distally to implant 2, respectively, and SG 04 distally to implant 3. Each metallic structure was screwed onto the abutments with a 10 Ncm torque and an axial load of 30 kg was applied at five predetermined points (A, B, C, D, E). The data obtained from the strain gauge analyses were analyzed statistically by RM ANOVA and Tukey''s test, with a level of significance of p<0.05.

Results

There was a significant difference for the loading point (p=0.0001), with point B generating the smallest microdeformation (239.49 με) and point D the highest (442.77 με). No significant difference was found for the cylinder type (p=0.748).

Conclusions

It was concluded that the type of cylinder did not affect in the magnitude of microdeformation, but the axial loading location influenced this magnitude.     

Effect of veneering material on the deformation suffered by implant-supported fixed prosthesis framework

Knowing how stresses are dissipated on the fixed implant-supported complex allows adequate treatment planning and better choice of the materials used for prosthesis fabrication.

Objectives

The aim of this study was to evaluate the deformation suffered by cantilevered implant-supported fixed prostheses frameworks cast in silver-palladium alloy and coated with two occlusal veneering materials: acrylic resin or porcelain.

Material and Methods

Two strain gauges were bonded to the inferior surface of the silver-palladium framework and two other were bonded to the occlusal surface of the prosthesis framework covered with ceramic and acrylic resin on each of its two halves. The framework was fixed to a metallic master model and a 35.2 N compression force was applied to the cantilever at 10, 15 and 20 mm from the most distal implant. The measurements of deformation by compression and tension were obtained. The statistical 2-way ANOVA test was used for individual analysis of the experiment variables and the Tukey test was used for the interrelation between all the variables (material and distance of force application).

Results

The results showed that both variables had influence on the studied factors (deformation by compression and tension).

Conclusion

The ceramic coating provided greater rigidity to the assembly and therefore less distortion compared with the uncoated framework and with the resin-coated framework. The cantilever arm length also influenced the prosthesis rigidity, causing higher deformation the farther the load was applied from the last implant.     

Three-dimensional finite element analysis of buccally cantilevered implant-supported prostheses in a severely resorbed mandible

PURPOSEThe aim of the study was to compare the lingualized implant placement creating a buccal cantilever with prosthetic-driven implant placement exhibiting excessive crown-to-implant ratio.MATERIALS AND METHODSBased on patient''s CT scan data, two finite element models were created. Both models were composed of the severely resorbed posterior mandible with first premolar and second molar and missing second premolar and first molar, a two-unit prosthesis supported by two implants. The differences were in implants position and crown-to-implant ratio; lingualized implants creating lingually overcontoured prosthesis (Model CP2) and prosthetic-driven implants creatingan excessive crown-to-implant ratio (Model PD2). A screw preload of 466.4 N and a buccal occlusal load of 262 N were applied. The contacts between the implant components were set to a frictional contact with a friction coefficient of 0.3. The maximum von Mises stress and strain and maximum equivalent plastic strain were analyzed and compared, as well as volumes of the materials under specified stress and strain ranges.RESULTSThe results revealed that the highest maximum von Mises stress in each model was 1091 MPa for CP2 and 1085 MPa for PD2. In the cortical bone, CP2 showed a lower peak stress and a similar peak strain. Besides, volume calculation confirmed that CP2 presented lower volumes undergoing stress and strain. The stresses in implant components were slightly lower in value in PD2. However, CP2 exhibited a noticeably higher plastic strain.CONCLUSIONProsthetic-driven implant placement might biomechanically be more advantageous than bone quantity-based implant placement that creates a buccal cantilever.     

Stress analysis of a fixed implant-supported denture by the finite element method (FEM) when varying the number of teeth used as abutments

Objectives

In some clinical situations, dentists come across partially edentulous patients, and it might be necessary to connect teeth to implants. The aim of this study was to evaluate a metal-ceramic fixed tooth/implant-supported denture with a straight segment, located in the posterior region of the maxilla, when varying the number of teeth used as abutments.

Materials and Methods

A three-element fixed denture composed of one tooth and one implant (Model 1), and a four-element fixed denture composed of two teeth and one implant (Model 2) were modeled. A 100 N load was applied, distributed uniformly on the entire set, simulating functional mastication, for further analysis of the SEQV (Von Mises) principal stresses, which were compared with the flow limit of the materials.

Results

In a quantitative analysis, it may be observed that in the denture with one tooth, the maximum SEQV stress was 47.84 MPa, whereas for the denture with two teeth the maximum SEQV stress was 35.82 MPa, both located in the region between the pontic and the tooth.

Conclusion

Lower stresses were observed in the denture with an additional tooth. Based on the flow limit of the materials, porcelain showed values below the limit of functional mastication.     

Clinical outcome of removable prostheses supported by mini dental implants. A systematic review

Introduction: For many years, edentulous patients have had no other option than conventional dentures to reestablish their oral function. To avoid the need for bone graft surgery, some professionals have suggested the use of mini dental implants (MDIs) to support prostheses. The MDIs are narrow implants, ranging approximately from 1.8 to 2.9?mm in diameter. Recently, the promising results of mini implants regarding osseointegration and patient satisfaction have led clinicians to accept them as a definitive treatment option. Objective: Therefore, the proposition of this systematic review was to assess information on the outcomes of MDIs supporting removable prostheses. Methods:The PubMed and Cochrane databases were searched for articles published before September 2017, which yielded a total of 774 studies for analysis. After exclusion and inclusion criteria, 22 prospective studies were included in this systematic review. Results: Most mini implants were placed in a flapless single-stage surgery and loaded immediately. Most studies reported failures in the first year and prosthetic complications. The mean survival rate of the selected studies was 95.6%, and mean follow-up was 22.8 months. Conclusion: The MDI-supported removable prostheses successfully improved patients’ chewing and speaking ability, quality of life, and satisfaction, suggesting that MDIs are a viable and safe option to support removable prostheses in the mandibular arch.     

In vitro vertical misfit evaluation of cast frameworks for cement-retained implant-supported partial prostheses

Objectives

To evaluate the influence of the alloy type and the associated investing and casting techniques, on the marginal adaptation of bridge structures luted onto prefabricated implant abutments.

Methods

Thirty frameworks for three-unit posterior-lower bridges were waxed and cast (10 of cobalt–chromium, 10 of titanium and 10 of palladium–gold). Each structure was cemented onto two prefabricated implant abutments with a special clamp designed to maintain constant seating pressure. The vertical discrepancy around the abutments’ margins was assessed by scanning electron microscopy (SEM). One-way ANOVA for independent samples and Scheffe’s test were applied to analyze the effect of the alloy type and its recommended investing and casting system on vertical misfit. Student’s t-test for independent samples was used to compare misfit values concerning the abutment design (premolar and molar). The significance level was set at α = 0.05.

Results

Cobalt–chromium samples recorded the greatest vertical discrepancies, revealing significant differences with respect to both titanium and palladium–gold structures (p < 0.0001). Vertical gaps of the palladium–gold and the titanium casts were not significantly different (p = 0.292). Neither statistically significant differences were found between the anterior and posterior abutments’ vertical misfit independently from the alloy type and nor within each group of alloys tested (p > 0.05).

Conclusions

The vertical fit of the frameworks cast for implant-cemented bridges was influenced by the alloy type and the investing and casting methods. The marginal discrepancy of the three tested alloys could be considered clinically acceptable. A polished technique in the management of titanium could optimize the accuracy of this cast frameworks.     

The influence of functional forces on the biomechanics of implant-supported prostheses--a review

Objectives: To evaluate published evidence related to the influence of functional forces on the biomechanics of implant-supported prostheses.

Data and sources. The literature was searched for original research articles relating control of loads on dental implants, effects of early and late occlusal loads, the influence of bone quality, prosthesis type, prosthesis material, number of supporting implants, and engineering techniques employed for evaluating mechanical and biomechanical behavior of implants using MEDLINE^® and manual tracing of references cited in key papers otherwise not elicited.

Study selection. Current literature on implant biomechanics as main focus and pertinent to key aspects of the review.

Conclusions. The outcome of implant treatment is often maximized when implants are placed in dense bone, number of supporting implants are increased, implant placement configuration reduces the effects of bending moments, and when a fixed prosthesis is delivered to the patient.     

Fracture loads of screw-retained implant-supported zirconia prostheses after thermal and mechanical stress

PurposeThe objective of the present study was to evaluate fracture loads of screw-retained implant-supported zirconia prostheses after artificial aging.MethodsFour types of screw-retained implant-supported prostheses were fabricated (n = 11 each); porcelain-veneered zirconia prosthesis (PVZ), indirect composite-veneered zirconia prosthesis (IVZ), porcelain-fused-to-metal prosthesis (PFM), and monolithic zirconia prosthesis (ML). The specimens were subjected to 10,000 thermocycles and cyclic loading for 1.2 million cycles. Fracture loads were measured, and the data were analyzed with the Kruskal–Wallis and Steel–Dwass tests (α = 0.05).ResultsAll specimens survived the artificial aging procedures. The fracture loads for the PVZ (1.52 kN), IVZ (1.62 kN), and PFM groups (1.53 kN) did not significantly differ; however, the fracture load for the ML group (6.61 kN) was significantly higher than those for the other groups. The fracture load for the IVZ group was comparable to those for the PVZ and PFM groups.ConclusionsThe monolithic zirconia prostheses exhibited significantly higher fracture loads than the bilayered prostheses. All the investigated types of screw-retained implant-supported zirconia prostheses appear sufficient to resist posterior masticatory forces during long-term clinical use.     

The effect of high fiber fraction on some mechanical properties of unidirectional glass fiber-reinforced composite

Objectives

This study was designed to evaluate the effect of an increase of fiber-density on some mechanical properties of higher volume fiber-reinforced composite (FRC).

Methods

Five groups of FRC with increased fiber-density were fabricated and two additional groups were prepared by adding silanated barium-silicate glass fillers (0.7 μm) to the FRC. The unidirectional E-glass fiber rovings were impregnated with light-polymerizable bisGMA-TEGDMA (50-50%) resin. The fibers were pulled through a cylindrical mold with an opening diameter of 4.2 mm, light cured for 40 s and post-cured at elevated temperature. The cylindrical specimens (n = 12) were conditioned at room temperature for 2 days before testing with the three-point bending test (Lloyd Instruments Ltd.) adapted to ISO 10477. Fiber-density was analyzed by combustion and gravimetric analyzes.

Results

ANOVA analysis revealed that by increasing the vol.% fraction of E-glass fibers from 51.7% to 61.7% there was a change of 27% (p < 0.05) in the modulus of elasticity, 34% (p < 0.05) in the toughness, and 15% (p < 0.05) in the load bearing capacity, while there was only 8% (p < 0.05) increase in the flexural strength although it was statistically insignificant. The addition of particulate fillers did not improve the mechanical properties.

Significance

This study showed that the properties of FRC could be improved by increasing fibervolume fraction. Modulus of elasticity, toughness, and load bearing capacity seem to follow the law of ratio of quantity of fibers and volume of the polymer matrix more precisely than flexural strength when high fiber-density is used.     

Adhesive bonding of resin composite to various titanium surfaces using different metal conditioners and a surface modification system

Objective

This study evaluated the effect of three metal conditioners on the shear bond strength (SBS) of a prosthetic composite material to cpTi grade I having three surface treatments.

Material and Methods

One hundred sixty eight rivet-shaped specimens (8.0x2.0 mm) were cast and subjected to polishing (P) or sandblasting with either 50 mm (50SB) or 250 mm (250SB) Al₂O₃. The metal conditioners Metal Photo Primer (MPP), Cesead II Opaque Primer (OP), Targis Link (TL), and one surface modification system Siloc (S), were applied to the specimen surfaces, which were covered with four 1-mm thick layers of resin composite. The resin layers were exposed to curing light for 90 s separately. Seven specimens from each experimental group were stored in water at 37ºC for 24 h while the other 7 specimens were subjected to 5,000 thermal cycles consisting of water baths at 4ºC and 60ºC (n=7). All specimens were subjected to SBS test (0.5 mm/min) until failure occurred, and further 28 specimens were analyzed using scanning electron microscope (SEM) and X-ray energy-dispersive spectroscopy (EDS). Data were analyzed by 3-way ANOVA followed by post-hoc Tukey''s test (α=0.05).

Results

On 50SB surfaces, OP groups showed higher SBS means than MPP (P<0.05), while no significant difference was found among OP, S, and TL groups. On 250SB surfaces, OP and TL groups exhibited higher SBS than MPP and S (P<0.05). No significant difference in SBS was found between OP and TL groups nor between MPP and S groups. The use of conditioners on 250SB surfaces resulted in higher SBS means than the use of the same products on 50SB surfaces (P<0.05).

Conclusion

Sandblasting associated with the use of metal conditioners improves SBS of resin composites to cpTi.     

Prosthetic misfit of implant-supported prosthesis obtained by an alternative section method

PURPOSE

Adequate passive-fitting of one-piece cast 3-element implant-supported frameworks is hard to achieve. This short communication aims to present an alternative method for section of one-piece cast frameworks and for casting implant-supported frameworks.

MATERIALS AND METHODS

Three-unit implant-supported nickel-chromium (Ni-Cr) frameworks were tested for vertical misfit (n = 6). The frameworks were cast as one-piece (Group A) and later transversally sectioned through a diagonal axis (Group B) and compared to frameworks that were cast diagonally separated (Group C). All separated frameworks were laser welded. Only one side of the frameworks was screwed.

RESULTS

The results on the tightened side were significantly lower in Group C (6.43 ± 3.24 µm) when compared to Groups A (16.50 ± 7.55 µm) and B (16.27 ± 1.71 µm) (P<.05). On the opposite side, the diagonal section of the one-piece castings for laser welding showed significant improvement in the levels of misfit of the frameworks (Group A, 58.66±14.30 µm; Group B, 39.48±12.03 µm; Group C, 23.13±8.24 µm) (P<.05).

CONCLUSION

Casting diagonally sectioned frameworks lowers the misfit levels. Lower misfit levels for the frameworks can be achieved by diagonally sectioning one-piece frameworks.     

Importance of a distal proximal contact on load transfer by implant-supported single adjacent crowns in posterior region of the mandible: a photoelastic study

Objective

This study aimed to evaluate the importance of a distal proximal contact on the load transfer to the posterior region of the mandible by non-splinted adjacent implant-supported crowns using photoelastic stress analysis.

Material and Methods

A rectangular model (68x30x15 mm) was made of polymethylmethacrylate resin to simulate half of the mandibular arch. One model was completed with resin replicas representing the first premolar and second molar and with two 3.75 mm dia.x11 mm internal hexagon threaded implants replacing the second premolar and first molar. The other model was manufactured in the same way but without the second molar. Both models were duplicated using photoelastic resin. The roots of the teeth replicas were covered with a layer of polyether impression material to simulate the periodontal ligament. Two different vertical loads were applied to the crowns as follows: 1 - single static point load alternately applied to the crowns replacing the second premolar and first molar (50 N); 2 - simultaneous static point loads applied to both of the crowns replacing the second premolar and first molar (100 N). The resulting isochromatic fringe pattern in the photoelastic model was monitored and photographed.

Results

All loading conditions studied showed that the presence of the second molar has changed the load transmission and the pattern of stresses.

Conclusion

Results showed that the presence of a second molar proximal contact can help minimize the stresses around the implants.     

Evaluation of the marginal precision of one-piece complete arch titanium frameworks fabricated using five different methods for implant-supported restorations

Objective: The aim of the present work was to compare the marginal precision of titanium frameworks for a complete arch‐fixed prosthesis fabricated using five different methods. Methods: A prospective study was designed. Fifteen titanium frameworks for totally edentulous upper or lower jaws, each supported by five to nine implants, were assigned to five study groups, so as to have three frameworks in each group for each technique: (1) lost wax technique frameworks, (2) cast titanium sovrastructures laser welded to prefabricated titanium copings, (3) Procera ^® Implant Bridge, (4) Cresco Ti System^? and (5) CAM StructSURE^® Precision Milled Bar. The microgap between the framework and the shoulders of implant analogues was measured on the master cast with a stereomicroscope at a magnification of 100 × at four different locations, yielding a total of 364 data points on 91 implants. Data were analyzed using an ANOVA and a Tukey post hoc test (P=<0.05). Results: The mean values for the microgap were 78 μm (SD±48) for lost wax technique frameworks, 33 μm (SD±19) for cast titanium sovrastructures laser welded to titanium copyings, 21 μm (SD±10) for the Procera ^® implant bridge, 18 μm (SD±8) for the Cresco Ti System^? and 27 μm (SD±15) for the CAM StructSURE^®. The differences among the mean values were statistically significant (P<0.01 or P<0.05). The comparisons among groups 3, 4, and 5 and between groups 2 and 5 were not significant (P>0.05). Conclusion: The computer‐aided procedures analyzed in the present study were able to produce a precision‐fitting framework, with no significant differences among them and, at the same time, showed a greater precision compared with the traditional casting methods or with the use of prefabricated titanium copings. However, it should be noted that, even if group 2 frameworks were not as accurate as groups 3 and 4, cast titanium sovrastructures laser welded to prefabricated titanium copings showed significantly better marginal precision than the frameworks produced with the lost wax technique.     

In vitro mechanical testing of glass fiber-reinforced composite used as dental implants

AIM: The aim of this study was to evaluate the design of fiber-reinforced composite (FRC) on some mechanical properties of a dental implant. METHODS AND MATERIALS: FRC implants were fabricated using different polymerization conditions and designs of the glass-fiber structure. Specimens were tested with a cantilever bending test and a torsional test. The degree of monomer conversion (DC%) was measured using a Fourier transform infrared spectroscopy (FTIR). RESULTS: Statistical analysis showed significant differences between groups revealing mean fracture load values from 437 N to 1461 N. The mean torsional force in fracture varied from 0.01 to 1.66 Nm. The DC% varied from 50% to 90%. CONCLUSION: This study suggests by modifying the polymerization conditions and fiber orientation of FRC implants, the biomechanical properties of an FRC can be tailored to the needs of dental implants.     

Electromyographic evaluation of implant-supported prostheses in hemimandibulectomy-reconstructed patients

OBJECTIVES: To assess the clinical conditions, patient's satisfaction and functional outcomes in oral neoplasia patients with hemimandibulectomy, bone reconstruction and implant-supported prosthesis. MATERIAL AND METHODS: Twelve patients after mandibular resection (with and without condyle), reconstruction and successful fixed implant-supported prosthesis rehabilitation were examined. Patients underwent clinical evaluation and filled in a questionnaire about their satisfaction toward oral functions. Surface electromyography (EMG) of the masticatory muscles was performed during a 15-s unilateral gum chewing test. EMG potentials were standardized as percentage of a maximum clench on cotton rolls and compared with reference data obtained from 20 healthy subjects. RESULTS: Excellent clinical and radiological parameters were found. Patients stated a decreased post-rehabilitation satisfaction toward mastication and phonetics, but an increased attention to oral care. Only patients with condylar resection reported augmented esthetic scores. In both the resected and the remaining sides, chewing frequency was higher in the patients than in the reference group (Wilcoxon's rank-sum test, P<0.001). Pooled muscle activities (sum of the integrated areas of the EMG potentials over time) were larger in patients than in control subjects, particularly in the non-operated side (P=0.001). The percentage contribution of working-side muscular activity in the operated side was similar to reference values, but significantly inferior in the opposite side (P<0.001). The patterns of muscle contraction during unilateral chewing were more variable in the reconstructed patients than in control subjects; the difference was significant only in the non-operated side (P<0.01). CONCLUSION: Post-rehabilitation median scores of the questionnaire indicated a positive judgment of the treatment. EMG analysis showed that functional recovery in hemimandibulectomy patients was satisfactory, although some alterations were observed in the non-operated side of mastication.     

下颌无牙颌种植固定修复早期负载的临床观察

目的:评价下颌无牙颌种植固定修复早期负载的可行性和临床疗效。方法:14例下颌无牙颌病例共植入94颗ITISLA种植体,种植体植入后第6周完成固定修复。于植入当天、第4周、修复后1年行影像学检查,观察种植部位牙槽骨吸收情况。在植入即刻及第4周行共振频率分析。结果:种植体1年成功率为100%,修复体的1年成功率为100%。影像学检查示种植体周无低密度影;种植部位牙槽骨水平未见明显吸收,均位于种植体第一螺纹的冠方,从全景片测量得1年牙槽骨水平吸收为(0.3±0.94)mm。共振频率分析显示,植入即刻与第4周分别为69.54±4.29和63.14±5.57。结论:ITI SLA种植体固定修复下颌无牙颌早期负载是可行的。     

A Prosthetic Alternative for Severely Angled Implants Beneath a Maxillary Overdenture: A Clinical Report

Implant‐retained overdentures have been shown to be a predictable, accepted option and represent a viable and cost‐effective treatment; however, patients with severe lack of bone volume and anatomical limitations are often a contraindication to the placement of osseointegrated implants without prior surgical procedures. In these situations, the placement of angled implants may offer a simple solution. This clinical report describes a case of dental rehabilitation using angled implants for a patient with a severely resorbed edentulous maxilla. The inclination has been solved by making a bar on the right side and individual pillars on the left side so as to obtain a functional and esthetic prosthetic result.