In Vitro Analysis of the Removability of Fractured Prosthetic Screws within Endosseous Implants Using Conventional and Mechanical Techniques.

STATEMENT OF PROBLEM: The extraction of fractured abutment screws can be a difficult challenge to overcome. PURPOSE: To compare the removal capacity, dental implant connection damage, and time required to remove the fractured abutment screws between three drilling techniques and a conventional method. MATERIALS AND METHODS: A total of 180 prefabricated screw-retained abutments were intentionally fractured in internal connection dental implants after being subjected to a cyclic load and a static compression load. Afterwards, three operators randomly removed the fractured abutment screws with the following drilling techniques and a conventional method: A: a conventional technique using an exploration probe and ultrasonic appliance (n = 45), Rhein83® (n = 45); B: Sanhigia® (n = 45); C: Phibo® (n = 45). Two-way ANOVA models were estimated to evaluate the mean time according to the method and operator used. RESULTS: The probability of removal of the screws with mobility was twelve times higher than that of the screws without mobility (OR = 12.4; p < 0.001). The success rate according to the operators did not show statistically significant differences (p = 0.371). The location of the fractured screw did not affect removal success (p = 0.530). The internal thread of the implant was affected after the removal process in 9.8% of the cases. The mean extraction time was 3.17 ± 2.52 min. The Rhein83® method showed a success rate of 84.4%, followed by the Phibo® and conventional methods (71.1%) and the Sanhigia® method (46.7%). CONCLUSIONS: The Rhein83® drilling technique increases the removal probability of fractured abutment screws. The initial mobility of the fragment is also a significant factor in the removal success.

Marginal Bone Loss Compared in Internal and External Implant Connections: Retrospective Clinical Study at 6-Years Follow-Up.

The aim of this study was to assess and compare the marginal bone loss between two different categories of implants (Winsix, Biosafin, Ancona, Italy) having the same diameter and belonging to the Torque Type® (TT®) line, in the internal hexagon version (TTi, Group A) and in the external hexagon configuration (TTx, Group B). Patients with one or more straight implants (insertion parallel to the occlusal plane) in the molar and premolar regions in association with tooth extraction at least 4 months prior to implant insertion, who have a fixture diameter of 3.8 mm, who followed up for at least 6 years, and whose radiographic records were available were enrolled in this study. Depending on implant connections (externally or internally), the sample was divided into groups A and B. For externally connected implants (66), the marginal resorption was 1.1 ± 0.17 mm. The subgroup of single and bridge implants showed no statistically significant differences with a marginal bone resorption of 1.07 ± 0.15 mm and 1.1 ± 0.17 mm, respectively. Internally connected implants (69) showed an overall marginal resorption of 0.91 ± 0.17 mm, while the subgroup of single and bridge implants showed resorption of 0.90 ± 0.19 mm and 0.90 ± 0.17 mm, respectively, with no statistically significant differences. According to the obtained results, internally connected implants showed less marginal bone resorption than externally connected implants.

Relevant Aspects of the Dental Implant Design on the Insertion Torque, Resonance Frequency Analysis (RFA) and Micromobility: An In Vitro Study.

The major problems for the osseointegration of dental implants are the loosening of the screw that fixes the dental implant to the abutment and the micromovements that are generated when mechanical loads are applied. In this work, torque differences in the tightening and loosening of the connection screws after 1 cycle, 10 cycles and 1000 cycles for 4 dental implants with 2 external and 2 internal connections were analyzed. The loosening of 240 implants (60 for each system) was determined using high-precision torsimeters and an electromechanical testing machine. A total of 60 dental implants for each of the 4 systems were inserted into fresh bovine bone to determine the micromovements. The implant stability values (ISQ) were determined by RFA. The mechanical loads were performed at 30° from 20 N to 200 N. By means of the Q-star technique, the micromovements were determined. It was observed that, for a few cycles, the loosening of the screw did not exceed a loss of tightening of 10% for both connections. However, for 1000 cycles, the loss for the external connection was around 20% and for the internal connection it was 13%. The micromovements showed a lineal increase with the applied load for the implant systems studied. An external connection presented greater micromotions for each level of applied load and lower ISQ values than internal ones. An excellent lineal correlation between the ISQ and micromobility was observed. These results may be very useful for clinicians in the selection of the type of dental implant, depending on the masticatory load of the patient as well as the consequences of the insertion torque of the dental implant and its revisions.

Marginal Bone Loss in Internal Conical Connection Implants Placed at the Crestal and Subcrestal Levels before Prosthetic Loading: A Randomized Clinical Study.

The vertical position concerning the bone in which the implants are placed has been related as one of the factors causing marginal bone loss. The objective of this study was to evaluate the bone loss that occurs before prosthetic loading around tapered internal connection (CIC) implants placed at the crestal (C) and subcrestal (S) levels. METHOD: A randomized clinical trial (RCT) was carried out, with a sample size of 62 implants placed in 27 patients who underwent radiological controls on the day of placement, at one month, and at 4 months, and stability was measured by resonance frequency analysis (RFA) on three occasions. RESULTS: Bone loss in implants C and S from the time of placement (T0) and the month after (T1) was not significant (p = 0.54) (C = 0.19 mm and S = 0.15 mm). The difference between one month (T1) and four months (T2) (C = 0.17 mm and S = 0.22 mm) was not significant either (p = 0.26). The difference between the day of placement (T0) and the third and last measurement (T2) was almost null (p = 0.94) (C = 0.35 mm and S = 0.36). The overall success rate of the implants was 97.8%. The stability of the implants measured with RFA went from 70.60 (T0) to 73.16 (T1) and 74.52 (T2). CONCLUSIONS: No significant differences were found in the bone loss for implants placed at the C and S levels. The millimeters of bone loss detected in both vertical positions did not have a significant impact on the stability of the implants.

Comparative study of bacterial microfiltration in the implant-abutment interface, with straight and conical internal connections, in vitro.

OBJECTIVE: to determine the presence of marginal bacterial microfiltration in the IAI in different implant/abutment systems, in vitro. MATERIAL AND METHODS: Fifty-six implants from seven different brand names, 4 with cone and 3 with straight connections were used, implant and abutment were connected using the Ncm tightening as indicated by each of the manufacturers and then were sealed. The samples were subjected occlusal load and thermal cycling, a first sample of each group was observed by micro CT and in a second sample (both samples randomly selected) length of connection was measured, while the rest of the samples were mounted on devices according to the bacterial microfiltration model with Porphyromonas gingivalis. RESULTS: Two of the conical connection system groups did not present bacterial microfiltration, one of the three straight connection groups only microfiltered in one sample, while the other two conical as well as the two straight connection samples showed different and important levels of bacterial microfiltration, all groups presented a direct relationship between the implant-abutment adjustment determined by micro-CT and bacterial microfiltration levels, not related to the connection length. CONCLUSION: Only two conical connection systems presented no bacterial microfiltration.

La eficacia clínica a largo plazo de los implantes con conexión interna y superficie arenada y grabada / Long-term clinical efficacy of implants with internal connection and sandblasted-acid-etched surface

Introducción: La implantología oral representa una opción importante en el tratamiento de los pacientes con pèrdida dental total y parcial. El estudio a largo plazo muestra la evaluación de los pacientes tratados mediante carga precoz de implantes con conexión interna y superficie arenada y grabada. Mètodos: 40 pacientes con pèrdidas dentales fueron tratados con implantes Frontier GMI ® con conexión interna y superficie arenada y grabada. Los implantes fueron cargados tras un periodo de tiempo de 6 semanas en la mandíbula y 8 semanas en el maxilar superior. Los hallazgos clínicos (implantológicos y prostodóncicos) se han seguido durante al menos 6 años. Resultados: 103 implantes fueron insertados en ambos maxilares, 46 implantes (44,7%) en el maxilar superior y 57 implantes (55,3%) en la mandíbula, para su rehabilitación prostodóncica. 37 implantes (35,9%) fueron insertados en el sector anterior y 66 implantes (64,1%) en el sector posterior. 70 implantes (68%) de forma sumergida (2 cirugías) y 33 implantes (32%) de forma no sumergida (una cirugía). Despuès de un seguimiento clínico de 92,2 meses, los resultados indican una supervivencia de los implantes del 96,2%; ya que se perdieron 4 implantes. La pèrdida ósea marginal fuè de 0,99 ± 0,84 mm. Las restauraciones prostodóncicas incluyeron 31 coronas unitarias, 15 puentes fijos, 5 sobredentaduras con bolas, 2 rehabilitaciones totales fijas y una rehabilitación completa híbrida. Las complicaciones tardías fueron 11 implantes (10,7%) con periimplantitis y 6 prótesis (11,1%) con complicaciones protèsicas. Conclusiones: Los hallazgos clínicos del estudio indican que el tratamiento con carga precoz mediante prótesis de los implantes con conexión interna y superficie arenada y grabada, representa una terapèutica odontológica con èxito. (AU)

Introduction: Implant dentistry constitute an important option in the prosthodontic treatment of patients with partial and total tooth loss. This long-term study reports the evaluation of patients treated by early loading of implants with internal connection and sandblasted-acidetched surface. Methods: 40 patients with tooth loss were treated with Frontier GMI ® sandblasted and acid-etched surface implants. Implants were loaded after a healing free-loading period of 6 weeks (mandible) and 8 weeks (maxilla). Clinical findings (implants and prosthodontics) were followed during at least 6 years. Results: 103 implants were inserted (46 maxillary (44.7%), and 57 mandibular (55.3%)) for prosthodontic rehabilitation. 37 implants (35.9%) were inserted in anterior sites and 66 implant (64.1%) in posterior sites. Seventy implants (68%) were placed submerged (two stages) while that 33 implants (32%) were placed nonsubmerged (one stage). After at a mean follow-up of 92.2 months, clinical results indicate a survival rate of implants of 96.2%. Four implants were lost during the treatment. Mean marginal bone loss were 0.99 ± 0.84 mm. Prosthodontic restorations included 31 single crowns, 15 fixed bridges, 5 overdentures, 2 fixed totally rehabilitation and an hybrid full rehabilitation. Delayed complications include 11 implants (10.7%) with peri-implantitis and 6 prostheses (11.1%) with technical complications. Conclusions: Clinical results of this study indicate that prosthodontic rehabilitation by early loading of internal connection and sandblasted and etched- implants can be a successful dental treatment. (AU)

Influence of Implant Connection, Abutment Design and Screw Insertion Torque on Implant-Abutment Misfit.

BACKGROUND: An accurate fit at the implant-abutment interface is an important factor to avoid biological and mechanical complications. The aim of this study was to evaluate the marginal misfit at the implant-abutment interface on external and Morse taper connection, with straight and angulated abutments under different insertion torque loads. MATERIALS AND METHODS: A total of 120 implants were used, 60 with external connection (EC) and 60 with Morse taper connection (IC). Straight (SA) (n = 60) and angulated abutments (AA) (n = 60) were randomly screwed to each connection at different torque levels (n = 10 each): 10, 20 and 30 Ncm. All specimens were subjected to thermal and cyclic loading and the misfit was measured by scanning electron microscopy. Data were analyzed with one-way ANOVA, t-test and Kruskal-Wallis test. RESULTS: Significant differences (p < 0.001) were found between connections and abutments regardless of the torque applied. Morse taper connections with straight and angulated abutments showed the lowest misfit values (0.6 µm). Misfit values decreased as torque increased. CONCLUSIONS: The misfit was affected by the type of connection. The type of abutment did not influence the fit in the Morse taper connection. The higher the tightening torque applied the increase in the fit of the implant-abutment interface.

A Finite Element Analysis to Compare Stress Distribution on Extra-Short Implants with Two Different Internal Connections.

BACKGROUND: The goal of this study was to analyze the stress distribution on two types of extra-short dental implants with 5 mm of length: An internal hexagon (IH) and morse taper connection (MT). METHODS: The three-dimensional model was composed of trabecular and cortical bone, a crown, an extra-short dental implant and their components. An axial load of 150 N was applied and another inclined 30° with the same magnitude. RESULTS: Stress concentrations on the IH implant are observed in the region of the first threads for the screw. However, in the MT implant the highest stress occurs at the edges of the upper implant platform. CONCLUSIONS: In view of the results obtained in this study the two types of prosthetic fittings present a good stress distribution. The Morse taper connections presented better behavior than the internal in both loading configurations.

Deformation of the Internal Connection of Narrow Implants after Insertion in Dense Bone: An in Vitro Study.

Implant connections must resist surgical and prosthetic procedures without deformation. This study evaluated the deformation of different internal connections (IC) of narrow dental implants (NDI) after their insertion in artificial dense bone. Thirty NDI, with different IC geometries, Group A (internal hexagon), Group B (tri-channeled), and Group C (four-channeled), with the same length and similar narrow diameters, were inserted in type II density bone blocks. Drilling protocols for dense bone from each implant manufacturer were followed. The Insertion torque (IT), connection length, vertex angles, and wall deformations were analyzed before and after the insertion of the implants. ANOVA (Analysis of Variance) and Tukey post-test were used for statistical comparisons. IT values were higher for Group A, surface damage, and titanium particles were observed in the IC in all the groups. Angle deformations between 5 and 70 degrees were present in all the groups, and the walls of Group B connection were the most affected by deformations (p < 0.05). Within the limitations of this experiment, it can be concluded that narrow diameter implants will suffer deformation of the implant connection and will also experience surface damage and titanium particle release when inserted in type II bone density.

Measurement of Fracture Strength of Zirconia Dental Implant Abutments with Internal and External Connections Using Acoustic Emission.

A single paragraph of about 200 words maximum. For research articles, abstracts should give a pertinent overview of the work. We strongly encourage authors to use the following style of structured abstracts, but without headings: (1) Background: Place the question addressed in a broad context and highlight the purpose of the study; (2) Methods: Describe briefly the main methods or treatments applied; (3) Results: Summarize the article's main findings; and (4) Conclusions: Indicate the main conclusions or interpretations. The abstract should be an objective representation of the article, it must not contain results which are not presented and substantiated in the main text and should not exaggerate the main conclusions. Please add in this section. The aim of the study was to investigate the fracture behaviour of four different groups of zirconia abutments with internal and external connections: (A) Astra Tech ZirDesign™ abutment on Astra Tech Implants, (B) Procera® Esthetic abutment on Nobel Biocare MK III Groovy Implants, (C) IPS e.max® on Straumann Implants, and (D) ZiReal® Posts on Biomet 3I implants. The load was applied on the assemblies using a Zwick universal testing machine: the initial and final failure loads and amplitude were recorded using acoustic emission technique. Mean initial and final failure force was found to be significantly different in each group (P < 0.001). IPS e.max® Straumann abutments exhibited the highest resistance to final fracture force compared to other abutment types. Acoustic emission can be used as one of the methods to detect fracture behaviour of implant abutments. There were no significant differences in fracture loads between the internal and externally connected zirconia abutments studied. However, externally connected abutments demonstrated screw loosening and some deformations.

In vitro assessment of connection strength and stability of internal implant-abutment connections.

BACKGROUND: Various connections have been machined to improve the fit between the dental abutment and implant. In vivo, the instability created by imprecisely fitting components can cause soft tissue irritation and bacterial colonization of the implant system. The aim of this study was to quantify abutment stability under in vitro force applications. METHODS: Abutment stability and fit were quantitatively measured after application of rotational, vertical, and horizontal forces. FINDINGS: The abutment connection held by friction (Friction-Fit) was the only group to have 0° angular rotation. A significantly greater vertical force was required to pull the abutment from the implant for the Friction-Fit connection as compared to all other experimental groups. The abutment connection held by a mechanically locking friction-fit with four grooves (CrossFit) and Friction-Fit demonstrated significantly lower lateral movement as compared to all other connections. The remaining connections evaluated included two hexagon connections that rely on screw placement for abutment fit (Conical + Hex #1 and Conical + Hex #2), one connection with protruding slots to align with recessed channels inside the implant (Conical + 6 Indexing Slots), and an internal connection that allows for abutment indexing every 120° (Internal Tri-Channel). INTERPRETATION: Internal connection geometry influenced the degree of abutment movement. Friction-Fit and CrossFit connections exhibited the lowest rotational and horizontal motions. Significant differences were found between Friction-Fit and CrossFit following the application of a vertical force, with the Friction-Fit requiring a significantly greater pull force to separate the abutment from the implant.

Cast accuracy obtained from different impression techniques at different implant angulations (in vitro study).

BACKGROUND: Angulated implants may result in inaccurate impressions, and the impression technique may affect the accuracy of the definitive cast. This study was designed to compare the dimensional accuracy of casts obtained from three impression techniques for three definitive lower casts with implants at different angulations. METHODS: Three Osseolink implants were placed in three reference models with different angles (parallel, 15° and 30°). Impressions of each model were made with three techniques (n = 10 per group): indirect, unsplinted direct, and acrylic resin-splinted direct technique. Impressions were poured with type IV dental stone. Inter-implant distances were measured for casts using a coordinate measuring machine, and the deviations from the reference models (Δr) were calculated. Data were analyzed using one-way ANOVA followed by post hoc tests to detect significance between groups (α = 0.05). RESULTS: This study showed that the deviations in micrometers from the reference model were the least for acrylic resin-splinted direct technique (Δr1 = 49.96, Δr2 = 50.36) versus indirect (Δr1 = 93.8, Δr2 = 90.9) and unsplinted direct techniques ((Δr1 = 67.07, Δr2 = 68.66) in 30° angulated implant situation (p value < 0.0001* for both Δr1 and Δr2). In 15° angulated implants, both the acrylic resin-splinted direct (Δr1 = 44.64, Δr2 = 45.58) and unsplinted direct techniques (Δr1 = 47.39, Δr2 = 55.28) were more accurate than indirect technique (Δr1 = 64.8, Δr2 = 68.3) (p value < 0.0001* for both Δr1 and Δr2). While in parallel condition, no difference was found between all three techniques (p value = 0.085, 0.056 for Δr1 and Δr2, respectively). CONCLUSIONS: The impression technique affected the accuracy of definitive casts. The acrylic resin splinted direct technique produced the most accurate casts, followed by direct unsplinted and indirect techniques. Furthermore, implant angulation affected the impression accuracy. When implant angulation increased from parallel implants to 30°, the forces of deformation increased, which resulted in increased distortion.

Bacterial microleakage at the abutment-implant interface, in vitro study.

INTRODUCTION: In implant rehabilitation, a microspace is created at the abutment-implant interface (AII). Previous research has shown that oral microbiome can proliferate in this microspace and affect periimplant tissues, causing inflammation in peri-implant tissues. Preventing microbial leakages through the AII is therefore an important goal in implantology. OBJECTIVE: To determine the presence of marginal bacterial microleakage at the AII according to the torque applied to the prosthetic implant in vitro. MATERIAL AND METHODS: Twenty-five Ticare Inhex internal conical implants (MG Mozo-Grau, Valladolid, España) were connected to a prosthetic abutment using torques of <10, 10, 20, 30, and 30 N and then sealed. The samples were submitted to cycles of occlusal loads and thermocycling, then one sample of each group was observed by micro TC, while the rest were mounted on devices according to the bacterial leakage model with Porphyromonas gingivalis. RESULTS: Bacterial leakage was observed only in the <10 and 10 N torque samples, and the same groups presented poor abutment/implant adjustment as determined by micro-CT. CONCLUSION: The different torques applied to the abutment-implant system condition the bacterial leakage at the implant interface. No microleakage was observed at 20 and 30 N.

Comparison of external and internal implant-abutment connections for implant supported prostheses. A systematic review and meta-analysis.

OBJECTIVE: The systematic review and meta-analysis aimed to answer the PICO question: "Do patients that received external connection implants show similar marginal bone loss, implant survival and complication rates as internal connection implants?". DATA: Meta-analyses of marginal bone loss, survival rates of implants and complications rates were performed for the included studies. Study eligibility criteria included (1) randomized controlled trials (RCTs) and/or prospective, (2) studies with at least 10 patients, (3) direct comparison between connection types and (4) publications in English language. The Cochrane risk of bias tool was used to assess the quality and risk of bias in RCTs, while Newcastle-Ottawa scale was used for non-RCTs. SOURCE: A comprehensive search strategy was designed to identify published studies on PubMed/MEDLINE, Scopus, and The Cochrane Library databases up to October 2017. STUDY SELECTION: The search identified 661 references. Eleven studies (seven RCTs and four prospective studies) were included, with a total of 530 patients (mean age, 53.93 years), who had received a total of 1089 implants (461 external-connection and 628 internal-connection implants). The internal-connection implants exhibited lower marginal bone loss than external-connection implants (P<0.00001; Mean Difference (MD): 0.44mm; 95% Confidence interval (CI): 0.26-0.63mm). No significant difference was observed in implant survival (P=0.65; Risk Ratio (RR): 0.83; 95% CI: 0.38-1.84), and complication rates (P=0.43; RR: 1.15; 95% CI: 0.81-1.65). CONCLUSION: Internal connections had lower marginal bone loss when compared to external connections. However, the implant-abutment connection had no influence on the implant's survival and complication rates. Based on the GRADE approach the evidence was classified as very low to moderate due to the study design, inconsistency, and publication bias. Thus, future research is highly encouraged. CLINICAL SIGNIFICANCE: Internal connection implants should be preferred over external connection implants, especially when different risk factors that may contribute to increased marginal bone loss are present.

Influence of internal connection length on screw loosening in internal connection implants / 대한치과보철학회지

PURPOSE: The purpose of this study was to evaluate whether the internal abutment length affected screw stability in an internal connection implant. MATERIALS AND METHODS: Twenty long internal connection implants (Replus system, 4.7 × 11.5 mm) were selected for this investigation. Abutments were assigned to four groups depending on the length of the internal connection (abutments with internal lengths of 1, 2, 3, and 4 mm, respectively). Each implant fixture specimen was embedded in resin medium and connected to an abutment with an abutment screw. A load of 100 N, applied at an angle of 30° to the long axis of the implant, was repeated for 1.0 × 10⁶ cycles. Reverse torque values (RTV) were recorded before and after loading, and the change in RTV was calculated. Data were analyzed with the Kruskal-Wallis test. RESULTS: The change in RTV was not significantly different among the groups (P>.05). Screw loosening and fractures were not observed in any groups, and joint stability was maintained. CONCLUSION: The internal length of the abutment may not significantly affect the degree of screw loosening.

Fit analysis of CAD-CAM custom abutment using micro-CT / 대한치과보철학회지

PURPOSE: The purpose of this study was to investigate screw joint stability and sagittal fit between internal connection implant fixtures of two different manufacturers and customized abutments. MATERIALS AND METHODS: Internal connection implant systems from two different manufacturers (Biomet 3i system, Astra Tech system) were selected for this study (n=24 for each implant system, total n=48). For 3i implant system, half of the implants were connected with Ti ready-made abutments and the other half implants were connected with Ti CAD-CAM custom ones of domestic-make (Myplant, Raphabio Co., Seoul, Korea) and were classified into Group 1 and Group 2 respectively. Astra implants were divided into Group 3 and Group 4 in the same way. Micro-CT sagittal imaging was performed for fit analysis of interfaces and preloading reverse torque values (RTV) were measured. RESULTS: In the contact length of fixture-abutment interface, there were no significant differences not only between Group 1 and Group 2 but also between Group 3 and Group 4 (Mann-Whitney test, P>.05). However, Group 2 and Group 4 showed higher contact length significantly than Group 1 and Group 3 in abutmentscrew interface as well as fixture-screw one (Mann-Whitney test, P<.05). In addition, RTV was lower in CAD-CAM custom abutments compared to ready-made ones (Student t-test, P<.05). CONCLUSION: It is considered that domestically manufactured CAD-CAM custom abutments have similar fit at the fixture abutment interface and it could be used clinically. However, RTV of CAD-CAM custom abutments should be improved for the increase of clinical application.

Comparison of marginal and internal fit of zirconia abutments with titanium abutments in internal hexagonal implants / 대한치과보철학회지

PURPOSE: The aim of this study was to evaluate the fit accuracy of two zirconia and titanium abutments in internal hexagonal implants. MATERIALS AND METHODS: One titanium abutment and two zirconia abutments were tested in internal hexagonal implants (TSV, Zimmer). Prefabricated zirconia abutments (ZirAce, Acucera) and customized zirconia abutments milled by the Zirkonzahn system (Zirkonzahn Max, Zirkonzahn) were selected and prefabricated titanium abutments (Hex-Lock, Zimmer) were used as a control. Eight abutments per group were connected to implants with 30 Ncm torque. The marginal gaps at abutment-implant interface, the internal gaps at internal hex, vertical and horizontal gaps between screws and screw seats in abutments were measured after sectioning the embedded specimens using a scanning electron microscope. Data analysis included one-way analysis of variance and the Scheffe test (n=16, α=0.05). RESULTS: The mean marginal gap of customized zirconia abutment was higher than those of two prefabricated zirconia and titanium abutments. The internal gaps at internal hex showed no significant differences between customized and prefabricated abutments and were higher than those of prefabricated titanium abutments. The mean vertical and horizontal gaps at screw in prefabricated zirconia abutment were higher than those of prefabricated titanium abutment. In the case of customized zirconia abutment, the mean horizontal gap at screw was higher than those of both the prefabricated zirconia and the titanium abutment but the mean vertical gap was not even measureable. The screw seats were clearly formed but did not match with abutment screws in prefabricated zirconia abutments. They were not, however, precisely formed in the case of customized zirconia abutments. CONCLUSION: Within the limitations of this study, the prefabricated titanium abutments showed better fit than the zirconia abutments, regardless of customized or prefabricated. Also, the customized zirconia abutments showed significantly higher marginal gaps and the fit was less accurate between screws and screw seats than the prefabricated abutments, titanium and zirconia.

Influence of implant angulation on the fracture resistance of zirconia abutments.

PURPOSE: To investigate the effects of abutment design to correct for implant angulation and aging on the fracture resistance of zirconia abutments. Greater understanding of the fracture strength of the zirconia abutments under various clinical conditions may lead to improvement of clinical protocols and possibly limit potential failures of implant prosthetics. MATERIALS AND METHODS: Test specimens consisted of an implant-zirconia abutment-zirconia crown assembly with implant apex positioned at 0°, 20° to the facial (20F), and 20° to the lingual (20L) with respect to a constant crown contour. To keep the abutment design as the only variable, CAD/CAM technology was used to generate monolithic zirconia crowns identical both in external and internal dimensions and marginal contours to precisely fit all the abutments in an identical fashion. The monolithic zirconia abutments were designed to fit the constant crown contours and the internal connection of the implant at the three angulations. The customized abutments for the three implant angulations varied in emergence profile, screw hole location, and material thickness around the screw hole. Half the specimens from each group were subjected to steam autoclaving and thermocycling to simulate aging of the restorations in vivo. To mimic the off-axis loading of the central incisor, the specimens were loaded at the recommended cephalometric interincisal relationship of 135° between the long axis of the crown supported by the implant and the Instron force applicator simulating the mandibular incisor. The force applicator was positioned 2 mm from the incisal edge and loaded at a 1 mm/min crosshead speed. Data were evaluated by 2-way ANOVA (α = 0.05) and Tukey's HSD. RESULTS: The 20F group had the highest fracture values followed by the 0° group, and the 20L group had the lowest fracture values. Aging did not yield any significant difference in fracture force magnitudes. CONCLUSION: Within the limitations of this study, tilting the implant apex to the lingual significantly reduced the fracture strength of angle-corrected zirconia abutments. Accordingly, while the angle between the occlusal force application and the long axis of the implant decreases, the resistance (force) to fracture decreases.

Influence of the implant-abutment connection design and diameter on the screw joint stability.

PURPOSE: This study was conducted to evaluate the influence of the implant-abutment connection design and diameter on the screw joint stability. MATERIALS AND METHODS: Regular and wide-diameter implant systems with three different joint connection designs: an external butt joint, a one-stage internal cone, and a two-stage internal cone were divided into seven groups (n=5, in each group). The initial removal torque values of the abutment screw were measured with a digital torque gauge. The postload removal torque values were measured after 100,000 cycles of a 150 N and a 10 Hz cyclic load had been applied. Subsequently, the rates of the initial and postload removal torque losses were calculated to evaluate the effect of the joint connection design and diameter on the screw joint stability. Each group was compared using Kruskal-Wallis test and Mann-Whitney U test as post-hoc test (α=0.05). RESULTS: THE POSTLOAD REMOVAL TORQUE VALUE WAS HIGH IN THE FOLLOWING ORDER WITH REGARD TO MAGNITUDE: two-stage internal cone, one-stage internal cone, and external butt joint systems. In the regular-diameter group, the external butt joint and one-stage internal cone systems showed lower postload removal torque loss rates than the two-stage internal cone system. In the wide-diameter group, the external butt joint system showed a lower loss rate than the one-stage internal cone and two-stage internal cone systems. In the two-stage internal cone system, the wide-diameter group showed a significantly lower loss rate than the regular-diameter group (P<.05). CONCLUSION: The results of this study showed that the external butt joint was more advantageous than the internal cone in terms of the postload removal torque loss. For the difference in the implant diameter, a wide diameter was more advantageous in terms of the torque loss rate.

Microleakage of the prosthetic abutment/implant interface with internal and external connection: in vitro study.

OBJECTIVE: This study determined the degree of marginal microleakage of the abutment-implant interface on platforms with Morse taper connection and external connection. MATERIALS AND METHODS: For this in vitro study, 42 implants, 21 with external connection and 21 with Morse taper connection, were used, immersed in acrylic resin cylinders. Each implant was joined by a prosthetic abutment screw tightened at different degrees, forming the six study groups: (1) External connection, manual tightening (2) External connection, 20 Newton (N) tightening (3) External connection, 30 N tightening (4) Morse taper connection, manual tightening (5) Morse taper connection, 20 N tightening (6) orse taper connection, 30 N tightening. All samples were subjected to load cycling and thermocycling. Then, they were submerged in a solution of 0.2% methylene blue for 24 h. Finally, the microleakage was measured via 20× optical microscopy in each study group, average was obtained, and Mann-Whitney test was applied. RESULTS: Statistically significant differences (P < 0.001) were found between the levels of microleakage presented in the Morse taper connection implants (1.48) and external connection implants (2.8) in all three types of tightening. Microleakage levels decreases when increasing torque is applied to the screws. CONCLUSION: Morse taper connection implants showed lower levels of microleakage than external connection implants; also, it was observed that microleakage decreases in the way torque increases.