Impact of CAD/CAM burs lifetime on surface properties of dental zirconia: Implications for biocompatibility of custom abutments.

OBJECTIVE: To evaluate the effect of the deterioration of computer aided design/computer aided manufacturing (CAD/CAM) burs during zirconia milling, on surface roughness, contact angle, and fibroblast viability. MATERIALS AND METHODS: Ceramic blocks were milled and 75 ceramic disks (8 × 1.5 mm) made and allocated into three groups (n = 25): G1-brand new 2L and 1L burs, G2-2L bur at the end of lifetime and brand new 1L bur and G3-both burs at the end of their lifetimes. Roughness (Ra, Rq, and Rz) was evaluated using a 3D optical profilometer, the contact angle by the sessile drop method and the cell viability of the mouse NIH/3T3 fibroblast, using the Alamar Blue assay at intervals of 24, 48, and 72 h (ISO 10993-5). Data were analyzed by one-way ANOVA and Kruskal-Wallis tests (p ≤ 0.05). RESULTS: Roughness increased as the burs deteriorated and G3 (0.27 ± 0.04) presented a higher value for Ra (p < 0.001). The highest contact angle was observed in G3 (86.2 ± 2.66) when compared with G1 (63.7 ± 12.49) and G2 (75.3 ± 6.36) (p < 0.001). Alamar Blue indicated an increase in cell proliferation, with no significant differences among the groups at 24 and 72 h (p > 0.05). CONCLUSIONS: The deterioration of the burs increased the surface roughness and decreased the wettability, but did not interfere in cell viability and proliferation. CLINICAL SIGNIFICANCE: The use of custom zirconia abutments represents an effective strategy for single crowns restorations. Our findings suggest that these abutments can be efficiently milled using CAD/CAM burs within their recommended lifetime.

Longevity of different abutments placed on narrow diameter implants: Assessment of structural damage and loosening.

OBJECTIVES: To evaluate structural damage and loosening of abutments placed on narrow diameter implants after cyclic fatigue. METHODS: Sixty Morse taper narrow diameter implants (Neodent, Brazil) received two types of abutments (1PA- one-piece abutment or 2PA- two-piece abutment), which were randomly divided into 3 fatigue experiments (n = 10). The implants were placed into a customized supporting holder and a software-assisted digital torque wrench secured the manufacturer recommended torque for each abutment. Cone beam computed tomography (CBCT) scans were acquired, before and after fatigue, and post-processed (software e-Vol DX) to assess damage and abutment displacement. The boundary fatigue method was adapted to use 2 × 106 cycles, 2 Hz of frequency and constant peak load of 80 N (first experiment) that varied according to the failure rate of previous specimens (second and third experiments). Failure was evaluated using CBCT scans and removal torque values. Data were used to estimate long-term torque degradation, probability of failure and Weibull modulus (software ALTA PRO9). RESULTS: All 2PA specimens became loosen independently of the applied fatigue load, and structural bending was observed in 14 abutments. Eight 1PA got loosen during the fatigue experiment. The Weibull analysis showed a lower modulus (m = 1.0; 0.7, 1.4) for 1PA than for 2PA (m = 2.6; 2, 3.4) resulting in longer predicted lifetimes and slower torque degradation for 1PA than for 2PA specimens. SIGNIFICANCE: 1PA showed greater long-term survival probability than 2PA. Predicting the lifetime and mechanical behavior of implant-abutment systems are useful information to clinicians during the decision-making process of oral rehabilitations.

Comparative Analysis of Internal Tapered Implant-Abutment Connections: Evaluating the Morse Effect.

The purpose of the present study was to evaluate the Morse effect of different internal tapered implant-abutment connections (ITCs) using a pullout test. Implants with different ITCs were selected: Short (Bicon, USA), G1; Novo Colosso (Medens, Brazil), G2; Epkut (SIN, Brazil), G3; Strong SW (SIN, Brazil), G4; Flash (Conexão, Brazil), G5 and Bone Level (Straumann, Switzerland), G6. The respective computer-aided design (CAD) files were loaded into the analysis software to measure each ITC's taper angle and implant-abutment contact area. Six implants from each group were embedded in acrylic resin blocks, and the respective universal abutments were fixed using a mallet (G1) or by applying 20 Ncm of torque (G2 to G6). After 10 minutes, each abutment's retention screw was removed, and the force necessary for abutment rupture was recorded using a universal testing machine at a crosshead speed of 0.5 mm/min. The groups were compared using a one-way analysis of variance and Tukey's test. Spearman's correlation was used to check the correlation of the taper angle and contacting area with the pullout strength. G1, a no-screw abutment with a 3° taper, and G2, a 10° tapered abutment tightened by 20 Ncm, presented the highest pullout strength (P < .05). The increased taper angle of G4, compared to G3, reduced the Morse effect despite their similar implant-abutment contacting areas (P < .05). The G5 and G6 abutments loosened after screw removal and did not exhibit pullout resistance. The closer the tapered angle (r = -.958) and the higher the implant-abutment contact area (r = .880), the higher the pullout strength (P < .001). Within the limits of this study, the Morse effect is different among tapered implant-abutment connections. The closer the tapered angle and the higher the interface area, the higher the Morse effect between the abutment and the implant.

Effect of laser-microtextured abutments on peri-implant outcomes: a systematic review and meta-analysis.

OBJECTIVES: To evaluate the potential of laser-microtextured abutments (LMAs) compared to machined abutments (MAs) in peri-implant clinical and radiographic outcomes. MATERIALS AND METHODS: Eligible studies consisted of randomized clinical trials (RCTs) retrieved from MEDLINE, Web of Science, Scopus, and Embase databases. The study adhered to the PRISMA statement, and the protocol was registered at the PROSPERO (registration number CRD42023443112). The risk of bias was evaluated according to version 2 of the Cochrane risk of bias tool (RoB 2). Meta-analyses were performed using random effect models. Afterward, the GRADE approach was used to determine the certainty of evidence. RESULTS: Four RCTs were included from a total of 2,876 studies. LMAs had lower peri-implant sulcus depth at 6-8 weeks (WMD: -0.69 mm; 95% CI: -0.97, -0.40; p = 0.15, I2 = 53%) and at one year (WMD: -0.75 mm; 95% CI: -1.41, -0.09; p = 0.09, I2 = 65%), but the certainty of evidence was low. In addition, the marginal bone loss favored the LMAs group (WMD: -0.29 mm; 95% CI: -0.36, -0.21; p = 0.69, I2 = 0%) with moderate evidence. There were fewer sites with bleeding on probing in the LMAs group (WMD: -1.10; 95% CI: -1.43, -0.77; p = 0.88, i2 = 0%). There was no statistical difference between groups for the modified gingival index and modified plaque index. Furthermore, all studies were classified as having some concerns risk of bias. CONCLUSIONS: There was low to moderate certainty evidence that LMAs can favor peri-implant clinical and radiographic parameters compared to MAs. CLINICAL RELEVANCE: Laser-microtextured abutments may benefit peri-implant clinical and radiographic outcomes.

Dental implant and abutment in PEEK: stress assessment in single crown retainers on anterior region.

OBJECTIVE: Stress distribution assessment by finite elements analysis in poly(etheretherketone) (PEEK) implant and abutment as retainers of single crowns in the anterior region. MATERIALS AND METHODS: Five 3D models were created, varying implant/abutment manufacturing materials: titanium (Ti), zirconia (Zr), pure PEEK (PEEKp), carbon fiber-reinforced PEEK (PEEKc), glass fiber-reinforced PEEK (PEEKg). A 50 N load was applied 30o off-axis at the incisal edge of the upper central incisor. The Von Mises stress (σvM) was evaluated on abutment, implant/screw, and minimum principal stress (σmin) and maximum shear stress (τmax) for cortical and cancellous bone. RESULTS: The abutment σvM lowest stress was observed in PEEKp group, being 70% lower than Ti and 74% than Zr. On the implant, PEEKp reduced 68% compared to Ti and a 71% to Zr. In the abutment screws, an increase of at least 33% was found in PEEKc compared to Ti, and of at least 81% to Zr. For cortical bone, the highest τmax values were in the PEEKp group, and a slight increase in stress was observed compared to all PEEK groups with Ti and Zr. For σmin, the highest stress was found in the PEEKc. Stress increased at least 7% in cancellous bone for all PEEK groups. CONCLUSION: Abutments and implants made by PEEKc concentrate less σvM stress, transmitting greater stress to the cortical and medullary bone. CLINICAL RELEVANCE: The best stress distribution in PEEKc components may contribute to decreased stress shielding; in vitro and in vivo research is recommended to investigate this.

A feasible in vitro method to evaluate bacterial infiltration in three implant-abutment connection systems / Método in vitro factible para evaluar la infiltración bacteriana en tres sistemas de conexión implante-pilar

Introduction: Microorganism infiltration through the im-plant-abutment interface causes oral health problems such as periimplantitis, leading to implant loss. Materials and Methods: A feasible new method to quantify the Streptococcus mutans (S. mutans) infiltration through the implant-abutment interface gap is introduced in the present work. Internal hexagon (IH; n = 10), external hexagon (EH; n = 10), Morse taper (MT; n = 10), and a control for each group (n = 1) were tested. Bacteria suspension was prepared at 1.5x108 CFU/mL (CFU: colony forming units), and the implants were individually submerged up to the connection level, allowing the bacteria to contact it. The abutment was removed, and bacteria count was performed. Results: The implant sets were tested under normal bacterial growth and early and late biofilm growth conditions. Colony-forming units per mL were obtained, and the results were compared among groups. Differences in bacterial count between the MT and EH (p<0.001) and the MT and IH (p<0.001) groups were significantly higher in the MT-type implant. There was a significant increment of bacterial infiltration in the MTs submitted to late biofilm growth conditions. EH and IH connections are more effective in preventing bacterial infiltration independent of the growth condition. Conclusions: The proposed methodology is feasible to evaluate the infiltration of microorganisms through the implant-abutment interface.

Introducción: La infiltración de microorganismos a través de la interfaz implante-pilar provoca problemas de salud bucal como la periimplantitis, que conduce a la pérdida del implante. Materiales y Métodos: En el presente trabajo se presenta un nuevo método factible para cuantificar la infiltración de Streptococcus mutans (S. mutans) a través de la brecha de la interfaz implante-pilar. Se probaron el hexágono interno (IH; n = 10), el hexágono externo (EH; n = 10), el cono Morse (MT; n = 10) y un control para cada grupo (n = 1). Se preparó una suspensión de bacterias a 1,5x108 UFC/mL y los implantes se sumergieron individualmente hasta el nivel de conexión, permitiendo que las bacterias entraran en contacto con él. Resultados: Se retiró el pilar y se realizó recuento de bacterias. Los conjuntos de implantes se probaron en condiciones de crecimiento bacteriano normal y de crecimiento temprano y tardío de biopelículas. Se obtuvieron unidades formadoras de colonias por ml y los resultados se compararon entre grupos. Las diferencias en el recuento bacteriano entre los grupos MT y EH (p<0,001) y MT e IH (p<0,001) fueron significativamente mayores en el implante tipo MT. Hubo un incremento significativo de la infiltración bacteriana en los MT sometidos a condiciones tardías de crecimiento de biopelículas. Las conexiones EH e IH son más efectivas para prevenir la infiltración bacteriana independientemente de las condiciones de crecimiento. Conclusión: La metodología propuesta es factible para evaluar la infiltración de microorganismos a través de la interfaz implante-pilar.

Evaluation of Vertical Misfit and Torque Loss of Different Abutments for Tri-Channel Type Internal Connection Dental Implants After Mechanical Cycling.

The aim of this study was to evaluate the mechanical behavior of UCLA and Mini-conical abutments for implants with Tri-channel connections regarding torque loss and vertical misfit. Twenty 3-element metal-ceramic fixed partial dentures (FPD) supported by 2 implants were manufactured and divided into 2 groups (n = 10): UCLA (group 1) and Mini-conical Abutments (group 2). The evaluation of torque loss was carried out before and after mechanical cycling, while the vertical fit was evaluated throughout the different stages of manufacturing the prostheses, as well pre- and postcycling (300,000 cycles, 30 N). Statistical analyses of torque loss and vertical misfit were performed using the linear mixed effects model. Both groups showed torque loss after mechanical cycling (P < .05); however, there was no significant percentage differences between them (P = .795). Before cycling, the groups showed a significant difference in terms of vertical misfit values (P < .05); however, this difference was no long observed after cycling (P = .894). Both groups showed torque loss after the cycling test, with no significant difference (P > .05). There was no significant difference in vertical misfit after mechanical cycling; however, in group 1 (UCLA) there was accommodation of the implant-UCLA abutment interface, while group 2 (Mini-conical abutment) did not show changes in the interface with the implant after the test. Both groups behaved similarly regarding the torque loss of the prosthesis retention screws pre- and postmechanical cycling, with greater loss after the test.

Structural and torque changes in implant components of different diameters subjected to mechanical fatigue.

OBJECTIVES: To evaluate torque maintenance and structural damage in implant components of different diameters subjected to a fatigue challenge. METHODS: Thirty 10-mm-long, morse taper connection, titanium dental implants and their corresponding one-piece abutments were divided into three groups (n = 10) according to implant diameter: 4.3 mm (I4.3), 3.5 mm (I3.5), and 2.9 mm (I2.9). The implants were placed into a load-bearing fixture simulating bone tissue (modified G10), and the abutments were screwed into the implants to a final torque of 20 Ncm for the I4.3 and I3.5 and 15 Ncm for I2.9. The torque was secured by a digital torque meter. Cone-beam computed tomography (CBCT) scans were acquired and post-processed (e-Vol DX software) for all implant/abutment sets before and after subjecting them to fatigue in 37 °C distilled water (2 million cycles, constant load and frequency). The removal torque was measured using the same digital torque meter to calculate the difference in torque before and after fatigue. RESULTS: I2.9 showed substantial structural deformation compared with the other implant diameters (I3.5 and I4.3). However, the experimental groups did not show statistical differences for abutment loosening. SIGNIFICANCE: Implants smaller than 3.5 mm in diameter have a higher probability of structural deformation than standard-diameter implants. The association between tomographic scans and e-Vol DX software showed satisfactory consistency with the direct assessment using the digital torque meter, offering an additional tool to evaluate implant component loosening and structural deformations.

Precision of polyether ether ketone (PEEK) or cobalt-chrome implant bar fit to implants after mechanical cycling.

Based on its mechanical properties, PEEK (polyether-ether-ketone) might be useful in restorative procedures. In oral rehabilitation, its viability has been studied mainly for prostheses and dental implants. AIM: The aim of this study was to evaluate the fit accuracy of dental implant bars made of either PEEK or cobalt-chrome submitted to cycling mechanics. MATERIALS AND METHOD: This was an experimental in vitro study, where units were treated with two implants and mini-abutments, joined by cobalt-chrome or polyether-ether-ketone PEEK bars. A total 20 bars were prepared (n=10 per group) and subjected to mechanical cycling tests (1 million cycles on the distal cantilever of the bar in the vertical direction, 120N and sinusoidal loading, at a frequency of 2Hz). The fit at the abutment/implant interface was measured before and after cycling, and the counter-torque of the vertical screw of the mini abutments was measured after cycling, using a digital torquemeter. Data were analyzed by three-way ANOVA and Tukey's test at 5% significance level. RESULTS: No statistically significant interaction was found among the three factors considered (bar material, implant positioning and mechanical cycling) (p = 0.592). No significant difference was identified in the interaction between bar material and implant positioning (p = 0.321), or between implant positioning and mechanical cycling (p = 0.503). The association between bar material and mechanical cycling was statistically significant (p = 0.007), with the cobalt-chrome bar resulting in greater misfit with mechanical cycling. There was no difference in counter-torque values between groups. CONCLUSIONS: The PEEK bar provided better fit of the mini abutments to the implants, even after mechanical cycling. The counter-torque of the screws was similar in all scenarios considered.

O PEEK (Poli-éter-éter-cetona) é um material considerado para uso em procedimentos restauradores devido às suas propriedades mecânicas. Na reabilitação oral, sua viabilidade tem sido estudada principalmente para uso em próteses e implantes dentários. Objetivos: O objetivo deste estudo foi avaliar a precisão da adaptação de duas barras diferentes do tipo protocolo confeccionadas em PEEK ou Cobalto-Cromo, após serem submetidas à mecânica ciclística. Materiais e Método: As unidades experimentais foram constituídas por barras confeccionadas em Poli-ether-ether-Ketone (PEEK) e em Cobalto-Cromo (Co-Cr). Trata-se de um estudo experimental, in vitro, onde verificou-se unidades constituídas por dois implantes e mini pilares unidos com barras de Cobalto-Cromo ou PEEK. Foram confeccionados um total de 20 barras (n=10 em cada grupo) e as barras foram submetidas a ensaios de ciclagem mecânica (1 milhão de ciclos no cantilever distal da barra no sentido vertical, 120N e carregamento senoidal, a uma frequência de 2Hz). Antes e após a ciclagem realizou-se a mensuração da desadaptação na interface pilar/implante e após a ciclagem foi medido o contra-torque do parafuso vertical dos mini-pilares através de torquímetro digital TQ 8800 (LT Lutron, Taiwan). Os dados foram submetidos a ANOVA a três critérios e teste de Tukey ao nível de significância a 5%. Resultados: Constatou-se que não houve interação estatisticamente significativa entre os três fatores estudados, ou seja, entre o material da barra, o posicionamento do implante e a ciclagem mecânica (p = 0,592). Também não se identificou diferença estatística significativa da interação entre o material da barra e o posicionamento do implante (p = 0,321), nem entre o posicionamento do implante e a ciclagem mecânica (p = 0,503). Já a associação entre o material da barra e a ciclagem mecânica foi estatisticamente significativa (p = 0,007), onde a barra de Cobalto-Cromo resultou em maior desadaptação com a ciclagem mecânica. Não houve diferença nos valores dos contra-torques entre os grupos. Conclusões: Conclui-se que a barra de protocolo fabricada em PEEK proporcionou melhor adaptação dos mini pilares aos implantes mesmo após a ciclagem mecânica. Por fim, o contra-torque dos parafusos foi semelhante em todos os cenários avaliados.

Detection of misfits at the abutment-prosthesis interface in the esthetic zone: Implications of the radiographic technique and the magnitude of the misfit.

STATEMENT OF PROBLEM: Misfits in the abutment-prosthesis interface represent a setback for implant-supported prostheses. Periapical radiographs have been used as an auxiliary method in the evaluation of prosthesis fit to the abutments; however, the evidence supporting the use of this method is still restricted to studies of low to moderate quality. Furthermore, studies on the diagnostic accuracy of different periapical techniques used to detect misfits in the abutment-prosthesis interface, especially in the esthetic zone, are lacking. PURPOSE: The purpose of this in vitro study was to assess the discrimination power of 3 periapical radiographic techniques in detecting misfits at the abutment-prosthesis interface in the esthetic zone and evaluate whether the magnitude of the misfit influenced the diagnosis. MATERIAL AND METHODS: A total of 15 implants with an internal conical connection were installed in the central incisor region in polyamide jaws. Custom ceramic copings for cemented crowns were made by using a computer-aided design and computer-aided manufacturing (CAD-CAM) system. Misfits of 50, 100, and 150 µm were simulated by interposing 1, 2, or 3 50-µm-thick polyester strips at the abutment-prosthesis interface; the absence of the strip represented the control group. Digital radiographs were obtained by using film holders for the following periapical techniques: bisecting angle (PBA), standard paralleling (PSP), and modified paralleling (PMP). Two radiologists and 1 prosthodontist evaluated a total of 180 radiographs. The values of the area under the receiver operating characteristic curve (Az) were regarded as a measure of diagnostic accuracy and subjected to the Friedman test with post hoc Durbin-Conover (α=.05). RESULTS: The PSP (Az=0.873) had higher Az values than the PBA (Az=0.753) for the 50-µm misfits (P<.05). Larger misfits resulted in greater accuracy than smaller misfits (P<.05). Interactions between the factors radiographic technique and misfit magnitude resulted in statistically significant differences for all comparisons (P<.05), except between the PSP for the 100-µm misfits (Az=0.976) and the PMP for the 150-µm misfits (Az=0.998). CONCLUSIONS: The PSP was more accurate than the PBA in detecting the 50-µm misfits at the abutment-prosthesis interface; larger misfits resulted in more accurate diagnoses, regardless of the technique used.

Fatigue life estimation of dental implants using a combination of the finite element method and traditional fatigue criteria.

Failure by fatigue can be sudden and catastrophic. Therefore, ensuring that dental implants, which are under constant cyclic loading, do not fail to fatigue is imperative. The majority of the studies about the topic only performed in vitro tests, which are expensive and time-consuming. The Finite Element (FE) method is less costly and it allows the simulation of several different loading scenarios. Nonetheless, there are only a few studies analysing fatigue in dental prostheses using FE models, and the few available did not include all the relevant parameters, such as geometry effect, surface finishing, etc. Therefore, this study aimed to analyse the fatigue behaviour of a single-unit dental implant with two screws using a combination of the numerical results and the traditional fatigue criteria - a combination that was not yet fully and correctly explored. A finite element model comprising a single implant, one abutment, one abutment screw, one fixation screw and one prosthetic crown was developed. Material properties were assigned based on literature data. A 100 N load was applied to mimic the mastication forces and fatigue analysis was conducted using the Gerber, Goodman and Soderberg fatigue criteria. The fatigue analysis demonstrated that the abutment screw could fail in less than 1 year, depending on the criteria, while the fixation screw exhibits an infinite life. The results illustrated the importance of analysing the fatigue behaviour of dental implants and highlighted the potential of finite element models to simulate the biomechanical behaviour of dental implants.

Microbiological analysis of bacterial sealing of internal conical implants with different taper angles.

The present study evaluated the effect of the taper angle of different internal conical connection implants and cyclic loading on the implant-abutment bacterial seal. A total of 96 implant-abutment sets were divided into eight groups. Four groups of different taper degrees with cyclic mechanical loading of 500,000 cycles per sample, with a 120-N load at 2 Hz before analysis [16DC (16-degree, cycled), 11.5DC (11.5-degree, cycled), 3DC (3- degree, cycled) and 4DC (4- degree, cycled)] were compared to four control groups without cyclic loading [16D (16-degree), 11.5D (11.5-degree), 3D (3-degree), and 4D (4-degree)]. Microbiological analysis was performed by immersing all samples in a suspension containing Escherichia coli and incubating them at 37°C. After 14 days, the presence of bacterial seals was evaluated. Fisher-Freeman-Halton exact tests and binomial tests were performed (5% significance level). The groups showed significant differences in bacterial seal, and mechanical load cycling improved the bacterial seal in the 3DC group. In all other groups, no significant differences in bacterial seal were found between cycled and uncycled samples. To conclude, the internal conical connection with a 3-degree taper angle showed better results than the other connection with different angles when subjected to load cycling. However, none of the angles tested were fully effective in sealing the implant-abutment interface.

Anaerobic adhesives effect on counter-torque of abutment screws on implants with external hexagon and conical connections: An in vitro study.

BACKGROUND: Abutment screw loosening is a common complication of implant supported prostheses, especially for single crowns. In engineering, anaerobic adhesives (AA) are used to provide chemical locking between screw surfaces, but their application in implantology remains unclear. PURPOSE: The purpose of this article is to evaluate, in vitro, the effect of AA on counter-torque of abutment screws for cemented prosthesis on dental implants with external hexagon connection (EHC) and conical connection (CC). MATERIALS AND METHODS: Sample was composed by 60 specimens, 30 dental implants with EHC and 30 with CC. Abutments (transmucosal 3 mm straight universal abutment) were installed without AA (control group) or with application of AA with two different adhesive strength: medium strength (LOCTITE® 242) and high strength (LOCTITE® 277). The specimens were subjected to mechanical cycling at 37°C, with a load setting of 133 N, a 1.3 Hz frequency, and 1 200 000 cycles. The abutments were removed, and the counter-torque values were registered. Screws and implants were inspected using a stereomicroscope to verify the presence of residual adhesive and damage the internal structures. The data were analyzed using descriptive statistics and comparison tests (p < 0.05). RESULTS: Comparing to the torque of installation, the medium strength AA kept the counter-torque values for CC implants and the high strength AA kept the counter-torque for EHC implants and increased for CC implants. In the intergroup comparisons, control group presented significantly lower counter-torque values than other groups, both for EHC and CC implants. High strength AA presented similar results to medium strength AA in the EHC implants, but in the CC implants presented higher counter-torque values. Damage in threads was more frequent in the groups that received high strength AA. CONCLUSION: The use of AA increased the counter-torque of abutment screws, both in implants with EHC and CC.

Short implants: Influence of different diameters, torques, and transmucosal heights of straight prosthetic abutments on screw preload loss after cycling.

This study evaluated the influence of different implant diameters, insertion torques, and transmucosal heights on the loosening of abutments installed on short implants, after mechanical cycling. The Morse taper connection implants (n = 96) tested were 5 mm high, divided according to the platform diameter: 4 or 6 mm. A universal abutment was coupled to each implant (with different transmucosal heights: 1 or 5 mm). The sets were subdivided into 20- and 32-Ncm torque. After the cycle fatigue test, the detorque values were measured with a digital torque indicator. After mechanical cycling, the mean detorque values obtained for the abutment with 20-Ncm insertion torque were lower than for implants with 32-Ncm insertion torque, regardless of the platform diameter or transmucosal height. In the 20-Ncm torque group, there was no statistically significant difference in the detorque values between platform diameters or transmucosal heights. Otherwise, for 32-Ncm sets, a smaller platform diameter (4 mm), and a longer transmucosal height (5 mm) showed the lowest detorque values. In conclusion, implants placed with 32-Ncm insertion torque and abutments with 1 mm transmucosal height and a 6 mm implant diameter demonstrated the highest detorque values.

Influence of Mechanical Cycling on Torque Values of Tapped-In and Screw-In Implant-Supported Crowns.

This study investigated the influence of mechanical cycling on screwed-in and tappedin implants restored with screw-retained metallic crowns. Three implant-abutmentcrown systems were evaluated: T1 (multi abutment) and T2 (standard abutment) received tapped-in abutments and S received a screwed-in abutment. The specimens were subjected to two million cycles of 0-150 N load, at 2 Hz, 30° inclination in a dry medium, and torque evaluation. Survival and removal torque were analyzed using chisquare, ANOVA, followed by Tukey's test. Differences between installation and removal torque were determined using a T-test for dependent samples. Analyses were performed in SPSS, considering α = 0.05. All specimens survived mechanical cycling in S, 40% in T1, 80% in T2 (p=0.008). Failures occurred due to loosening of the crown screw. A significant decrease in torque (p=0.000) was found. Group T1 had the lowest removal torque (1.6 ± 0.84 N.Cm²), followed by T2 (3 ± 1.49 N.Cm²) and S (6.3 ± 1.16 N. Cm²), and a statistical difference was found between Groups T1 and S. Both types of implantabutment connections were stable and can be considered for rehabilitative treatment, but failure and removal torque were influenced by the design of prosthetic abutment. Crowns were more susceptible to becoming loose in tapped-in systems.

Comparative analysis of the mechanical limits of resistance in implant/abutment set of a new implant design: An in vitro study.

OBJECTIVE: The aim of the present in vitro study was to evaluate the resistance on quasi-static forces and in the fatigue mechanical cycling of a new implant design compared to two other conventional implant designs. MATERIALS AND METHODS: Eighty-eight implants with their respective abutments were tested and distributed into four groups (n = 22 per group): Morse taper connection implant (MT group), conventional external hexagon implant (EH con group), new Collo implant of external hexagon with the smooth portion out of the bone insertion (EH out group), and new Collo implant of external hexagon with the implant platform inserted to the bone level (EH bl group). All the sets were subjected to quasi-static loading in a universal testing machine, and we measured the maximum resistance force supported by each sample. Another 12 samples from each group were submitted to the cyclic fatigue test at 4 intensities of forces (n = 3 per force): 80%, 60%, 40%, and 20%. The number of cycles supported by each sample at each force intensity was evaluated. RESULTS: The three groups of implants with external hexagon connection had similar maximum strength values of the sets (p > 0.05). Meanwhile, samples from the MT group showed the highest resistance values in comparison to the other three groups (p < 0.05). In the fatigue test, the Collo out group supported a smaller number of cycles that led to the fracture than the other 3 groups proposed at loads of 80%, 60%, and 40%, and only at the load value of 20% all groups had the same performance. CONCLUSIONS: Within the limitations of the present in vitro study, the results showed that the new Collo implant performs better when installed at bone level.

The assessment of periimplant soft tissue condition with morse taper abutment connection: a rapid review

Aim: This study aims to evaluate the clinical assessment results of periimplant soft tissue with morse taper (internal abutment connection). Methods: The study was conducted using a rapid review by searching the articles from PubMed NCBI and Cochrane by using keywords. All articles were selected by the year, duplication, title, abstract, full-text, and finally, all selected articles were processed for final review. Following clinical parameters were included; Periimplant Probing Pocket Depth (PPD), Plaque Score (PS), modified Plaque Index (mPI), Mucosal Thickness (MTh), Gingival Height (GH), periimplant mucosal zenith, Pink Esthetic Score (PES), Bleeding On Probing (BOP), Sulcus Bleeding Index (SBI), and modified Gingival Index (mGI). Results: 9 selected articles were obtained from the initial literature searching count of 70 articles. The overall samples included 326 morse taper implants. Based on the evaluation, 3 out of 4 articles reported pocket depth < 4 mm, no bleeding was reported in 2 out of 4 articles. 4 out of 4 articles reported low plaque accumulation, low soft tissue recession was reported in 3 out of 3 articles, and 4 out of 4 articles reported acceptable PES values. Conclusion: The evaluations indicate that the morse taper (internal abutment connection) has favorable assessment results based on various clinical parameters

Evaluation of Removal Force in Prosthetic Components of Morse Taper Dental Implants.

The longevity of prosthetic rehabilitation is determined by the stability of the implant and abutment interfaces. True morse taper connections on dental restorations have been effective, however activation force still empirical. This work compared the activation strength and internal contact of Morse taper system according to the removal force. Eighty sets, composed of implants and prosthetic abutments, were evaluated with different internal contact areas; 15.12mm2 (G3.3) and 21.25mm2 (G4.3). The specimens were activated at 0° and 30°, with loads of 10, 20, 40 and 60N. The specimens were submitted to tensile test and the data to ANOVA and Tukey's tests (α=0.05). Representative specimens were examined under SEM. Removal force of G3.3 (2.15±1.33MPa) did not differed to G4.3 (1.99±1.03MPa). The activation at 0º (2.95±0.98MPa) statistically differed to 30º (1.19±0.54MPa). The 60N load was statistically superior for G3.3 and there was no statistical difference between 20N to 60N in G4.3. The values of 10N at 30o and 20N at the long axis of the morse taper implant, independent of the frictional contact area showed the best settlement.

Effects of tightening torque on screw stress and formation of implant-abutment microgaps: A finite element analysis.

STATEMENT OF PROBLEM: The mechanical behavior of the conical connection implant with different torque levels requires evaluation. PURPOSE: The purpose of this finite element analysis study was to investigate the impact of abutment screw torque on the formation of microgaps at the implant-to-abutment interface of a conical connection under oblique loading. This is important because it is thought that bacteria can invade the internal implant space through the abutment-implant microgaps, causing peri-implantitis. MATERIAL AND METHODS: Three-dimensional finite element analyses of the conical implant-abutment connection were performed by using screw torques of 20 Ncm and 30 Ncm. Oblique loads from 10 N to 280 N were applied to the prosthesis placed on the implant. The maximum von Mises stress in the abutment screw, the microgap formation process, and the critical load for bridging the internal implant space were evaluated. RESULTS: The stresses in the abutment screw under oblique loading had limited sensitivity to the screw torque. However, the residual stress in the screw with a 30-Ncm torque was 35% higher than that with a 20-Ncm torque in the absence of an external load. The area in contact at the implant-to-abutment interface decreased with increasing load for both torque values. The critical load for bridging the internal implant space was 160 N for a screw torque of 20 Ncm and 220 N for a screw torque of 30 Ncm. The maximum gap size was approximately 470 µm with all the loads. CONCLUSIONS: Increasing the screw torque can reduce the formation of microgaps at the implant-to-abutment interface. However, this will result in higher mean stress in the abutment screw, which may reduce its fatigue life and consequently that of the prosthesis. Further research is needed to evaluate the relationship between the abutment screw torque and microleakage in implant-supported restorations.

A New Proposal for Calibrated Gauges for Removable Partial Dentures: A Finite Element Analysis.

AIM: The aim of this study was to evaluate the stress distribution of a planned removable partial denture (RPD) using new proposals for calibrated gauges of 0.3 mm and 0.35 mm undercuts through the three-dimensional (3D) finite element methodology, and compare them with 0.25 mm and 0.5 mm gauges that are already existing in clinical practice. MATERIALS AND METHODS: Kennedy class-I edentulous 3D models and their respective RPDs (InVesalius software; Rhinoceros and SolidWorks CAD) were created and exported to the finite element program HyperMesh 2019 for mesh configuration. In the following steps, axial loading (0º) of 40 N per point was performed, with 3 points on the molars and 2 points on the premolars, totaling 280 N unilaterally. The model was processed by the OptiStruct 2019 software and imported into the HyperView 2019 software to obtain the stress maps (MPa). RESULTS: The use of 0.30 and 0.35 mm calibrated gauges presented tensions similar to those with the 0.25 mm gauge (gold standard) and caused no significant damage to biological structures. The use of a 0.5 mm undercut caused greater traction force in the periodontal ligament of the abutments. CONCLUSIONS: The 0.35 mm undercut seems promising as it presented more favorable results in this simulation, on the other hand, a 0.5 mm undercut is greater than that necessary for retainers made of CoCr. CLINICAL SIGNIFICANCE: This study aims to measure a new undercut gauge (0.35 mm) to increase the retention area in abutment teeth of removable partial dentures.