Morse taper performance: A finite element analysis study.

OBJECTIVES: To evaluate and compare the magnitude and distribution of stresses generated on implants, abutments and first molar metal-ceramic crowns using finite element analysis. METHODS: Preliminary three-dimensional models were created using the computer-aided design software SolidWorks. Stress and strain values were observed for two distinct virtual models: model 1 - Morse taper and solid abutment; model 2 - Morse taper and abutment with screw. A load (250 N) was applied to a single point of the occlusal surface at 15° to the implant long axis. Von Mises stresses were recorded for both groups at four main points: 1) abutment-retaining screws; 2) abutment neck; 3) cervical bone area; 4) implant neck. RESULTS AND CONCLUSION: Model 1 showed a higher stress value (1477.5 MPa) at the abutment-retaining screw area than the stresses found in model 2 (1091.1 MPa for the same area). The cervical bone strain values did not exceed 105 µm for either model.

Impact of Intentional Overload on Joint Stability of Internal Implant-Abutment Connection System with Different Diameter.

PURPOSE: To evaluate the axial displacement of the implant-abutment assembly of different implant diameter after static and cyclic loading of overload condition. MATERIALS AND METHODS: An internal conical connection system with three diameters (Ø 4.0, 4.5, and 5.0) applying identical abutment dimension and the same abutment screw was evaluated. Axial displacement of abutment and reverse torque loss of abutment screw were evaluated under static and cyclic loading conditions. Static loading test groups were subjected to vertical static loading of 250, 400, 500, 600, 700, and 800 N consecutively. Cyclic loading test groups were subjected to 500 N cyclic loading to evaluate the effect of excessive masticatory loading. After abutment screw tightening for 30 Ncm, axial displacement was measured upon 1, 3, 10, and 1,000,000 cyclic loadings of 500 N. Repeated-measure ANOVA and 2-way ANOVA were used for statistical analysis (α = 0.05). RESULTS: The increasing magnitude of vertical load and thinner wall thickness of implant increased axial displacement of abutment and reverse torque loss of abutment screw (p < 0.05). Implants in the Ø 5.0 diameter group demonstrated significantly low axial displacement, and reverse torque loss after static loading than Ø 4.0 and Ø 4.5 diameter groups (p < 0.05). In the cyclic loading test, all diameter groups of implant showed significant axial displacement after 1 cycle of loading of 500 N (p < 0.05). There was no significant axial displacement after 3, 10, or 1,000,000 cycles of loading (p = 0.603). CONCLUSIONS: Implants with Ø 5.0 diameter demonstrated significantly low axial displacement and reverse torque loss after the cyclic and static loading of overload condition.

Abutment screw loosening in angulation-correcting implants: An in vitro study.

STATEMENT OF PROBLEM: Techniques that allow angulation correction for screw-retained implant-supported restorations are now available. However, whether angulation correction built into the head of the implant affects abutment screw loosening is unclear. PURPOSE: The purpose of this in vitro study was to assess abutment screw loosening in angulation-correcting implants and straight implants subjected to simulated nonaxial occlusal loading. MATERIAL AND METHODS: Seven external connection 12-degree angulation-correcting implants and 7 straight implants were embedded in an acrylic resin housing, and titanium abutments were secured with titanium screws tightened to 32 Ncm. Each specimen was secured in a tooth wear machine and subjected to 1 000 000 cycles of 50-N nonaxial load to simulate 1 year of clinical service. The mean abutment screw removal torque values were calculated, and the association between number of cycles and the abutment screw removal torque was analyzed using a linear mixed-effects model and statistical software (α=.05) RESULTS: The mean abutment screw torque loss was 59.8% for the angulation-correcting implant group and 68.7% for the straight implant group. A statistically significantly greater mean abutment screw removal torque was recorded in the angulation-correcting implant group compared with the straight implant group after 1 000 000 cycles (P=.019). CONCLUSIONS: A significant loss of abutment screw torque was found in both implant groups with increased cycles of occlusal loading. The angulation-correcting implants resisted screw loosening significantly more than the straight implants because of the reduced angle of abutment screw loading.

Morse taper performance: A finite element analysis study

OBJECTIVES: To evaluate and compare the magnitude and distribution of stresses generated on implants, abutments and first molar metal-ceramic crowns using finite element analysis. METHODS: Preliminary three-dimensional models were created using the computer-aided design software SolidWorks. Stress and strain values were observed for two distinct virtual models: model 1 - Morse taper and solid abutment; model 2 - Morse taper and abutment with screw. A load (250 N) was applied to a single point of the occlusal surface at 15° to the implant long axis. Von Mises stresses were recorded for both groups at four main points: 1) abutment-retaining screws; 2) abutment neck; 3) cervical bone area; 4) implant neck. RESULTS AND CONCLUSION: Model 1 showed a higher stress value (1477.5 MPa) at the abutment-retaining screw area than the stresses found in model 2 (1091.1 MPa for the same area). The cervical bone strain values did not exceed 105 µm for either model.

Polyetheretherketone Overlay Prosthesis over High Noble Ball Attachments to Overcome Base Metal Sensitivity: A Clinical Report.

A modified polyetheretherketone (PEEK) framework material in combination with heat-polymerized denture base acrylic resin was used for the fabrication of an overlay prosthesis for a patient sensitive to base metals. High noble metal was used for the fabrication of the post/coping/ball attachment assemblies to promote retention and stability. These protruding attachments into the acrylic resin could result in stress concentration; therefore, a framework is often used to strengthen the prosthesis. PEEK frameworks could be a treatment alternative to high noble or Ti frameworks since they combine good mechanical properties with biocompatibility, reduced cost, and common laboratory procedures.

Retentive Properties of O-Ring and Locator Attachments for Implant-Retained Maxillary Overdentures: An In Vitro Study.

PURPOSE: To evaluate and compare retentive properties of O-ring and Locator attachments for implant-retained maxillary overdentures. MATERIALS AND METHODS: Four implant analogs were inserted in canine and second premolar areas of an acrylic edentulous maxillary model. A metal-reinforced experimental acrylic overdenture was constructed and connected to the analogs using either O-ring (group I) or Locator (group II) attachments. Locators were divided into 3 subgroups according the degree of retention of the patrix nylon insert: Locator extra-light retention (group IIa), Locator light retention (group IIb), and Locator medium retention (group IIc). Vertical and oblique (lateral, anterior, and posterior) dislodging forces were measured at the beginning of the study (initial retention) and after 540 cycles of denture insertion and removal (final retention). RESULTS: For vertical, lateral, and anterior dislodging, group IIc recorded the highest initial and final retention, and group I recorded the lowest retention. For posterior dislodging, group I recorded the highest retention, and group IIa recorded the lowest retention. For group II, vertical dislodging recorded the highest initial and final retention, and lateral dislodging recorded the lowest retention. For group I, posterior dislodging recorded the highest initial and final retention, and lateral dislodging recorded the lowest retention. For all dislodging forces (except posterior dislodging), the highest retention loss was recorded in group I, and the lowest retention loss was recorded in group IIa. CONCLUSION: Locator medium attachment was associated with favorable retention during axial (vertical) and nonaxial (anterior and lateral) dislodging compared to other types of Locator inserts and O-ring attachments after a simulated 6-month period of overdenture use.

Hollow Abutment Screw Design for Easy Retrieval in Case of Screw Fracture in Dental Implant System.

The prosthetic component of dental implant is attached on the abutment which is connected to the fixture with an abutment screw. The abutment screw fracture is not frequent; however, the retrieval of the fractured screw is not easy, and it poses complications. A retrieval kit was developed which utilizes screw removal drills to make a hole on the fractured screw that provides an engaging drill to unscrew it. To minimize this process, the abutment screw is modified with a prefabricated access hole for easy retrieval. This study aimed to introduce this modified design of the abutment screw, the concept of easy retrieval, and to compare the mechanical strengths of the conventional and hollow abutment screws by finite element analysis (FEA) and mechanical test. In the FEA results, both types of abutment screws showed similar stress distribution in the single artificial tooth system. A maximum load difference of about 2% occurred in the vertical load by a mechanical test. This study showed that the hollow abutment screw may be an alternative to the conventional abutment screws because this is designed for easy retrieval and that both abutment screws showed no significant difference in the mechanical tests and in the FEA.

Impression technique for a complete-arch prosthesis with multiple implants using additive manufacturing technologies.

This article describes an impression technique for a complete-arch prosthesis supported by multiple implants where additive manufacturing technologies were used to fabricate a splinting framework and a custom tray. The technique presented uses a shim method to control the homogenous splinting acrylic resin and impression material during the procedure, thereby reducing laboratory and chairside time and the number of impression copings and laboratory analogs needed.

Micromovement Evaluation of Original and Compatible Abutments at the Implant-abutment Interface.

INTRODUCTION: Use of compatible abutments may increase micromovements between the abutments, and the inner part of the implant may increase the stress on marginal bone level. Also micromovement will change the volume of the inner space of the implant-abutment complex. The resulting pumping effect can transport even initially immobile microorganisms from the exterior to the interior and vice versa. OBJECTIVES: The purpose of the study was to evaluate the mechanical comportment of OsseoSpeed™ Tx implants connected with original and compatible abutments in vitro under simulated clinical loading conditions. MATERIALS AND METHODS: A total of 15 OsseoSpeed™ TX implants (4 × 11 mm) were used and divided into three groups (n = 5). Three types of abutments were used in the study; group I: Five original Ti Design™ abutments, group II: Five Natea™ abutments, and group III: Implanet™ abutments. Abutments used in groups II and III were all compatible with Astra Tech Implant System™. Implants were embedded into resin. Simulating the human masticatory cycle, the axial force vector was increased up to a defined maximum (25, 50, 75, 100, 125, 150, 175, and 200 N) and inclined 30° to the implant axis. A radiograph amplifier was used to convert the X-ray projection into a picture. The visual evaluation of the frames and the provided X-ray videos were evaluated for an existing microgap in width and length between the implant and the abutment. RESULTS: An initial width gap was observed in groups II and III in four of the five samples with an average of 6.5 and 5 µm respectively. When the axial forces reach 75 N, only groups II and III demonstrated a gap width of 5.2 ± 3.63 and 4.8 ± 3.03 µm, and a gap length of 5.2 ± 3.63 and 94 ± 125.3 µm respectively. At 200 N, group I showed a gap width of 8.4 ± 1.67 µm and a gap length of 187.6 ± 43.6 µm, while groups II and III showed a gap width of 12.4 ± 3.29 and 22.8 ± 5.76 µm, and a gap length of 387.2 ± 84.36 and 641.2 ± 122.6 µm respectively. CONCLUSION: Within the limitations of this study and under the parameters used and from the resulting data collected, we can presume that the use of compatible components leads to significant micromovement when compared with the use of original ones. CLINICAL SIGNIFICANCE: The use of compatible prosthetic components with original implants showed significant micromovements when compared with the use of abutment and implant from the same manufacturer. Clinically, the micromovements when associated with leakage leads to bone loss around the neck of the implant and later to peri-implantitis.

Effect of Double Screw on Abutment Screw Loosening in Single-Implant Prostheses.

PURPOSE: This study was conducted to assess the effect of using a double screw on the prevention of abutment screw loosening. MATERIALS AND METHODS: Internal connected abutment with a single screw (IS), internal connected abutment with a double screw (ID), external connected abutment with a single screw (ES), and external connected abutment with a double screw (ED) groups were prepared (n = 10 in each group). After 50,000 loading cycles, postload removal torque loss (RTL) percentage was measured. RESULTS: Postload RTL of ID and ED were smaller than those of IS and ES (P = .000 and P = .039, respectively). CONCLUSION: This study showed that a double screw was more effective in prevention of screw loosening.

Evaluation of resistance against bacterial microleakage of a new conical implant-abutment connection versus conventional connections: an in vitro study.

The aim of the present in vitro study was to evaluate bacterial microleakage from inside to outside the implant-abutment assembly in a new design of internal conical connection compared to eight different internal connections. The design of this connection should prevent or limit microbiologic leakage into the surrounding implant tissue, that could contribute to infections without bone loss (mucositis) or with bone loss (peri-implantits). In order to investigate bacterial microleakage, the inner part of each system was inoculated with an Escherichia coli suspension. Eight different groups were considered; each group was composed of 10 dental implants, for a total of 80 implants. Groups 1-7 were considered controls, while group 8 was the test connection (an internal connection characterized by a double taper principle). Results showed that in control implants (Group 1 to 7), little microleakage was observed after the first 6 hours (500 CFU/ µl) and, after 24 hours of incubation, they showed a significant bacterial contamination in all samples (>100.000 CFU/ µl). In group 8 (test connection) no contamination was found in the first 6 hours, with 7 out of 10 implants showing no contamination even after 96 hours. Statistically significant differences were found between Group 8 and the other groups (p<0.05), whereas no significant differences were found among implants of the control groups (from group 1 to 7). Within the limits of the present study, the new connection studied presented significantly less microleakage at 96 h in comparison with the other control internal connections.

Comparative Microstrain Study of Internal Hexagon and Plateau Design of Short Implants Under Vertical Loading.

PURPOSE: To quantify microstrain development during axial loading using strain gauge analysis for short implants, varying the type of fixture-abutment joint and thread design. MATERIALS AND METHODS: An internal hexagon implant (4 × 8 mm) and a plateau design implant (4 × 8 mm) were embedded on the center of 10 polyurethane blocks with dimensions of 190 × 30 × 12 mm. The respective abutments were screwed onto the implants. Four strain gauges (SGs) were bonded onto the surface of each block, and 4 vertical SGs were bonded onto the side of each block. Axial load of 30 kgf was applied for 10 seconds in the center of each implant. RESULTS: The data were analyzed statistically by analysis of variance for repeated measures and Tukey test (P < 0.05). The interaction between implant and region factors have been statistically significant (P = 0.0259). Tukey test revealed a difference on plateau's horizontal region. The cervical region presented higher microstrain values, when compared with the medium and apical regions of the implants. CONCLUSION: Within the purpose of the study, the type of fixture-abutment joint is a relevant factor to affect the amount of stress/strain in bone simulation. The microstrain development was concentrated on the cervical region of the implant.

Case for implant platform unswitching.

Platform switching was introduced to reduce marginal bone loss and therefore maintain the gingival architecture, leading to a more favorable esthetic result. In the patient presented, recession had resulted in the exposure of the implant neck and threads; this was managed with a custom-made additional prosthetic component. The result, although not ideal esthetically, provided an implant abutment interface that was easier for the patient to clean.

Mechanical resistance of screwless morse taper and screw-retained implant-abutment connections.

OBJECTIVE: The screwless morse taper (SMT) implant-abutment connection is an alternative to conventional external or internal screw-retained (ISR) connections. The aim of this in vitro study was to evaluate mechanical resistance of the SMT connection and to compare it with three different ISR connections. MATERIALS AND METHODS: Four implant systems were tested in this study: SMT system; Tasarimmed Octo (Istanbul, Turkey), ISR systems; Straumann Bone Level (Basel, Switzerland), Biohorizons Internal (Birmingham, AL, USA), and Dentsply Friadent Xive (Mannheim, Germany). Overall, 64 specimens with stylized single crowns were prepared: 32 for dynamic loading (DL) and 32 for static loading (SL). DL was carried out using a chewing simulator with 120 N at 1.75 Hz for 1.2 × 10(6) cycles, and SL was performed with a universal testing machine at a crosshead speed of 2 mm/min with an angulation of 30°. Cycles until failure from DL and fracture/bending loads at SL were recorded. Statistical analyses were made with Dunn's multiple comparison. RESULTS: Median cycles until failure in DL were as follows: Octo 86,354 (24,810-153,875), Straumann 1,200,000 (1,156,618-1,200,000), Biohorizons 539,719 (437,224-858,732), Xive 139,411 (139,411-139,411). Median fracture/bending loads in Newton at SL were as follows: Octo 429.6 (404.5-482.7), Straumann 574.6 (544.6-629.9), Biohorizons 548.7 (532.9-567.3), Xive 431.5 (412.5-520.5). There were significant differences between the implant systems under both loading conditions (P ≤ 0.05) revealing that the Octo implant system's SMT connection showed significantly lower cycles to failures and lower fracture/bending loads compared with the ISR connections of the Straumann and Biohorizons implant systems. However, there was no significant difference compared with the Xive implant system. CONCLUSION: The mechanical resistance of the screwless morse taper implant system is lower than that of the ISR implant systems that might result in more frequent clinical complications.

Platform switching and abutment emergence profile modification on peri-implant soft tissue.

Although the peri-implant hard tissue advantages of platform switching abutments have been well documented by many authors, the peri-implant soft tissue advantages of platform switching abutments has had limited mention. This article illustrates how the amount of peri-implant soft tissue volume is influenced by the dimensional extent of platform switching and the degree that an abutment's sulcular emergence profile has been modified. This article also introduces the term "abutment sulcular emergence profile enhancement" (ASEPE) to describe the combined effect of platform switching and abutment emergence profile modification. Three unrecognized clinical advantages of ASEPE are described by different clinical cases. First, elimination of excessive abutment impingement on gingival tissue adjacent to implants is achieved. Second, allowance for sufficient interproximal space between implant and adjacent tooth/implant for the entry of interproximal toothbrush is made possible. Third, excessive soft tissue blanching during abutment seating at prosthesis delivery is eliminated. Together, the combined application of platform switching and abutment emergence profile modification represents the opening of a new realm for managing soft tissue around implants to resolve dimensional problems.

Dynamic fatigue performance of implant-abutment assemblies with different tightening torque values.

Implant-abutment assemblies are usually subject to long-term cyclic loading. To evaluate the dynamic fatigue performance of implant-abutment assemblies with different tightening torque values, thirty implant-abutment assemblies (Zimmer Dental, Carlsbad, CA, USA) were randomly assigned to three tightening groups (24 Ncm; 30 Ncm; 36 Ncm), each consisted of 10 implants. Five specimens from each group were unscrewed, and their reverse torque values recorded. The remaining specimens were subjected to a load between 30 N~300 N at a loading frequency of 15 Hz for 5 × 10(6) cycles. After fatigue tests, residual reverse torque values were recorded if available. In the 24 Ncm tightening group, all the implants fractured at the first outer thread of the implant after fatigue loading, with fatigue crack propagation at the fractured surface showed by SEM observation. For the 30 Ncm and 36 Ncm tightening groups, a statistical significant difference (p<0.05) between the unloaded and loaded groups was revealed. Compared with the unloaded specimens, the specimens went through fatigue loading had decreased reverse torque values. It was demonstrated that insufficient torque will lead to poor fatigue performance of dental implant-abutment assemblies and abutment screws should be tightened to the torque recommended by the manufacturer. It was also concluded that fatigue loading would lead to preload loss.

A method for fabrication of implant-supported fixed partial dentures.

When restoring a partially edentulous arch with an implant-supported fixed partial denture, the optimal fit and function of the final restoration depend on the fabrication of an accurate impression and the registration of the interocclusal relationship. The present case report presents a method for the fabrication of impressions and the registration of the interocclusal relationship for implant-supported partial dentures. The described method allows the accurate transfer of the implant position and the registration of the interocclusal relationship using transfer key and electroformed gold copings. The key and copings were used to transfer the intraoral implant position to the cast, to position the abutments intraorally, and to facilitate the fabrication of the final partial denture.

Screw joint stability after the application of retorque in implant-supported dentures under simulated masticatory conditions.

STATEMENT OF PROBLEM: Screws can loosen through mechanisms that have not been clearly established. PURPOSE: The purpose of this study was to evaluate the influence of the tightening technique (the application of torque and retorque on the joint stability of titanium and gold prosthetic screws) in implant-supported dentures under different fit levels after 1 year of simulated masticatory function by means of mechanical cycling. MATERIAL AND METHODS: Ten mandibular implant-supported dentures were fabricated, and 20 cast models were prepared by using the dentures to create 2 fit levels: passive fit and created misfit. The tightening protocol was evaluated according to 4 distinct profiles: without retorque plus titanium screws, without retorque plus gold screws, retorque plus titanium screws, and retorque plus gold screws. In the retorque application, the screws were tightened to 10 Ncm and retightened to 10 Ncm after 10 minutes. The screw joint stability after 1 year of simulated clinical function was measured with a digital torque meter. Data were analyzed statistically by 2-way ANOVA and Tukey honestly significant difference (HSD) post hoc tests (α=.05). RESULTS: The factors of fit level and tightening technique as well as the interaction between the factors, were statistically significant. The misfit decreases the loosening torque. The retorque application increased joint stability independent of fit level or screw material, which suggests that this procedure should be performed routinely during the tightening of these devices. CONCLUSION: All tightening techniques revealed reduced loosening torque values that were significantly lower in misfit dentures than in passive fit dentures. However, the retorque application significantly increased the loosening torque when titanium and gold screws were used. Therefore, this procedure should be performed routinely during screw tightening.

[Comparison of leakage at the implant to abutment connection in several implants types using a gas flow method]. / Fuites de la connexion implantaire : comparaison de plusieurs types d'implants par la méthode de diffusion gazeuse.

INTRODUCTION: The aim of this study was to compare the leakage at the implant to abutment connection in several implants, using a new gas diffusion method. MATERIAL AND METHODS: Sixty-eight implants of 13 different types were used. Nitrogen leaking was measured after screwing the connections to the torque levels recommended by the manufacturers. RESULTS: A significant tightness difference was observed between the different implant types. This difference cannot be explained by the various connection designs (flat, conical) or by the various torques recommended by the manufacturers. CONCLUSION: The authors suggest that the tightness difference between the various implant systems could be mainly associated with quality and precision of machining.

Evaluation of radiographic technique using a new customized film holder for dental implant assessment.

PURPOSE: The aim was to evaluate the reproducibility of a radiographic technique using a new customized film holder in the follow-up of screwed single-tooth implants. MATERIALS AND METHODS: Ten implants placed in the mandible (n = 6) and maxilla (n = 4) of 8 patients were submitted to radiographic assessments. Radiographs were taken using a customized film holder adapted to implant abutment after 4 (T0) and 8 (T1) months of implant placement. Quantitative evaluations were performed through horizontal and vertical measurements to analyze radiographic standardization. RESULTS: No differences were detected after comparison of implant and abutment diameter measurements between radiographs after 4 and 8 months. No significant variations were detected in vertical measurements (implant and abutment length) between radiographs obtained in T0 and T1. CONCLUSIONS: The use of customized film holder adapted to the implant abutment seems to contribute to the standardization of radiographs at different times of screwed single-tooth implants.