Influence of Implant-Abutment Contact Surfaces and Prosthetic Screw Tightening on the Stress Concentration, Fatigue Life and Microgap Formation: A Finite Element Analysis

Prati C., Tribst J.P., Dal Piva A.M., Borges A.L., Ventre M., Zamparini F., Ausiello P.

The aim of the present investigation was to calculate the stress distribution generated in the root dentine canal during mechanical rotation of five different NiTi endodontic instruments by means of a finite element analysis (FEA). Two conventional alloy NiTi instruments F360 25/04 and F6 Skytaper 25/06, in comparison to three heat treated alloys NiTI Hyflex CM 25/04, Protaper Next 25/06 and One Curve 25/06 were considered and analyzed. The instruments’ flexibility (reaction force) and geometrical features (cross section, conicity) were previously investigated. For each instrument, dentine root canals with two different elastic moduli(18 and 42 GPa) were simulated with defined apical ratios. Ten different CAD instrument models were created and their mechanical behaviors were analyzed by a 3D-FEA. Static structural analyses were performed with a non-failure condition, since a linear elastic behavior was assumed for all components. All the instruments generated a stress area concentration in correspondence to the root canal curvature at approx. 7 mm from the apex. The maximum values were found when instruments were analyzed in the highest elastic modulus dentine canal. Strain and von Mises stress patterns showed a higher concentration in the first part of curved radius of all the instruments. Conventional Ni-Ti endodontic instruments demonstrated higher stress magnitudes, regardless of the conicity of 4% and 6%, and they showed the highest von Mises stress values in sound, as well as in mineralized dentine canals. Heat-treated endodontic instruments with higher flexibility values showed a reduced stress concentration map. Hyflex CM 25/04 displayed the lowest von Mises stress values of, respectively, 35.73 and 44.30 GPa for sound and mineralized dentine. The mechanical behavior of all rotary endodontic instruments was influenced by the different elastic moduli and by the dentine canal rigidity.

Roccuzzo A., Stähli A., Monje A., Sculean A., Salvi G.

Dental implants may be considered a reliable routine procedure in clinical practice for the replacement of missing teeth. Results from long-term studies indicate that implant-supported dental prostheses constitute a predictable treatment method for the management of fully and partially edentulous patients. Implants and their restorations, however, are not free from biological complications. In fact, peri-implantitis, defined as progressive bone loss associated to clinical inflammation, is not a rare finding nowadays. This constitutes a concern for clinicians and patients given the negative impact on the quality of life and the sequelae originated by peri-implantitis lesions. The purpose of this narrative review is to report on the prevalence of peri-implantitis and to overview the indications, contraindications, complexity, predictability and effectiveness of the different surgical therapeutic modalities to manage this disorder.

Ausiello P., Dal Piva A.M., Borges A.L., Lanzotti A., Zamparini F., Epifania E., Mendes Tribst J.P.

The aim of the present study was to investigate the effect of shrinking and no shrinking dental filling materials combination in posterior restorations under the combined effects of polymerization shrinkage and occlusal load by means of 3D Finite Elements Analysis. Six computer-generated and restored class I or class II cavities models of a lower molar were designed in the CAD software and evaluated according to the cavity and restorative procedure. Different shrinking and no shrinking adhesive materials combination with diverse Young’s modulus were considered. A food bolus was modeled on the occlusal surface replicating the chewing load using static linear analyses Polymerization shrinkage was simulated for the shrinking different restorative materials. The maximum principal stress was selected as analysis criteria. All models exhibited higher stresses along the dentine restoration interfaces with different magnitude and a similar stress trend along enamel restoration interface. Stress values up to 22 MPa and 19 MPa were recorded in the enamel and restoration, respectively. The use of elastic not shrinking material layer in combination with bulk fill composite reduced the stress magnitude in dentine and enamel to replace dental tissues. Class I and class II posterior cavities adhesively restored with shrinking filling material’s combination showed the most unfavorable stress concentrations and the multilayer technique is a promising restorative alternative in posterior adhesive restorations when deep dentin and enamel volumes are missing.

Lee H., Jo M., Noh G.

Background and Objective Understanding fatigue failure and microgap formation in dental implants, abutments, and screws under various clinical circumstances is clinically meaningful. In this study, these aspects were evaluated based on implant diameter, connection type, and bone density. Methods Twelve three-dimensional finite element models were constructed by combining two bone densities (low and high), two connection types (bone and tissue levels), and three implant diameters (3.5, 4.0, and 4.5 mm). Each model was composed of cortical and cancellous bone tissues, the nerve canal, and the implant complex. After the screw was preloaded, vertical (100 N) and oblique (200 N) loadings were applied. The relative displacements at the interfaces between implant, abutment, and screw were analyzed. The fatigue lives of the titanium alloy (Ti–6Al–4V) components were calculated through repetitive mastication simulations. Mann–Whitney U and Kruskal–Wallis one-way tests were performed on the 50 highest displacement values of each model. Results At the implant/abutment interface, large microgaps were observed under oblique loading in the buccal direction. At the abutment/screw interface, microgap formation increased along the implant diameter under vertical loading but decreased under oblique loading (p Conclusions Tissue-level implants possess biomechanical advantages compared to bone-level ones. Two-piece implants with diameters below 3.5 mm should be avoided in the posterior mandibular area.

Vinhas A.S., Aroso C., Salazar F., López-Jarana P., Ríos-Santos J.V., Herrero-Climent M.

Introduction: Different implant–abutment connections have been developed to reduce mechanical and biological failure. The most frequent complications are loss of preload, screw loosening, abutment or implant fracture, deformations at the different interfaces, and bacterial microleakage. Aim: To review the evidence indicating whether the implant–abutment connection type is significant regarding the following issues: (1) maintenance of the preload in static and dynamic in vitro studies; (2) assessment of possible deformations at the implant–abutment interfaces, after repeated application of the tightening torque; (3) evaluation of the sealing capability of different implant connections against microleakage. Materials and Methods: In June 2020, an electronic literature search was performed in Medline, EBSCO host, and PubMed databases. The search was focused on the ability of different implant connections to maintain preload, resist deformation after tightening and retightening, and prevent microleakage. The related titles and abstracts available in English were screened, and the articles that fulfilled the inclusion criteria were selected for full-text reading. Results: The literature search conducted for this review initially resulted in 68 articles, among which 19 articles and 1 systematic review fulfilled the criteria for inclusion. The studies were divided according to the three proposed objectives, with some studies falling into more than one category (maintenance of preload, surface abutment–implant deformation, and resistance to microleakage). Conclusions: Conical abutment appears to result in fewer mechanical complications, such as screw loosening or fractures, and higher torque preservation. After SEM evaluation, damage was observed in the threads of the abutment screws, before and after loading in internal and external connections. Internal hexagon implants and predominantly internal conical (Morse taper) implants showed less microleakage in dynamic loading conditions. We suggest further studies to guarantee excellence in methodological quality.

García-González M., Blasón-González S., García-García I., Lamela-Rey M.J., Fernández-Canteli A., Álvarez-Arenal Á.

Mechanical complications in implant-supported fixed dental prostheses are often related to implant and prosthetic design. Although the current ISO 14801 provides a framework for the evaluation of dental implant mechanical reliability, strict adherence to it may be difficult to achieve due to the large number of test specimens which it requires as well as the fact that it does not offer any probabilistic reference for determining the endurance limit. In order to address these issues, a new software program called ProFatigue is presented as a potentially powerful tool to optimize fatigue testing of implant-supported prostheses. The present work provides a brief description of some concepts such as load, fatigue and stress-number of cycles to failure curves (S-N curves), before subsequently describing the current regulatory situation. After analyzing the two most recent versions of the ISO recommendation (from 2008 and 2016), some limitations inherent to the experimental methods which they propose are highlighted. Finally, the main advantages and instructions for the correct implementation of the ProFatigue free software are given. This software will contribute to improving the performance of fatigue testing in a more accurate and optimized way, helping researchers to gain a better understanding of the behavior of dental implants in this type of mechanical test.

Kim J., Noh G., Hong S., Lee H.

Torres-Alemany A., Fernández-Estevan L., Agustín-Panadero R., Montiel-Company J.M., Labaig-Rueda C., Mañes-Ferrer J.F.

Short implants are an increasingly common alternative to other surgical techniques in areas where bone availability is reduced. Despite the advantages they offer, a variety of biological repercussions have been described in the literature that can even lead to the loss of these. The aim of this systematic review and meta-analysis was to analyze the impact of the use of short implants on their survival and on peri-implant bone loss, evaluating the influence that length, diameter, and crown-to-implant ratio (C/I) have on these parameters. This systematic review was based on guidelines proposed by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). An electronic search was conducted using terms related to the use of short implants in partially or totally edentulous patients. A total of five databases were consulted in the literature search: PubMed, Embase, Cochrane, Scopus, and Web of Science. After eliminating the duplicate articles and assessing which ones met the inclusion criteria, 15 articles were included for the qualitative analysis and 14 for the quantitative study. Through meta-analysis, the percentage of implant loss and peri-implant bone loss was estimated. Relating these parameters to length, diameter, and C/I ratio, no significant differences have been found for implant loss (values of p = 0.06, 0.10, and 0.9, respectively for length, diameter, and C/I ratio), nor for peri-implant bone loss (values of p = 0.71, 0.72, and 0.36, respectively for length, diameter, and C/I ratio). In conclusion, the use of short implants does not seem to have a significant influence on marginal bone loss or the survival rate of implants.

Tribst J.P., Dal Piva A.M., Lo Giudice R., Borges A.L., Bottino M.A., Epifania E., Ausiello P.

The current study aimed to evaluate the mechanical behavior of two different maxillary prosthetic rehabilitations according to the framework design using the Finite Element Analysis. An implant-supported full-arch fixed dental prosthesis was developed using a modeling software. Two conditions were modeled: a conventional casted framework and an experimental prosthesis with customized milled framework. The geometries of bone, prostheses, implants and abutments were modeled. The mechanical properties and friction coefficient for each isotropic and homogeneous material were simulated. A load of 100 N load was applied on the external surface of the prosthesis at 30° and the results were analyzed in terms of von Mises stress, microstrains and displacements. In the experimental design, a decrease of prosthesis displacement, bone strain and stresses in the metallic structures was observed, except for the abutment screw that showed a stress increase of 19.01%. The conventional design exhibited the highest stress values located on the prosthesis framework (29.65 MPa) between the anterior implants, in comparison with the experimental design (13.27 MPa in the same region). An alternative design of a stronger framework with lower stress concentration was reported. The current study represents an important step in the design and analysis of implant-supported full-arch fixed dental prosthesis with limited occlusal vertical dimension.

Armentia M., Abasolo M., Coria I., Albizuri J.

Fatigue is the most common mechanical failure type in dental implants. ISO 14801 standardizes fatigue testing of dental implants, providing the load-life curve which is most useful for comparing the fatigue behavior of different dental implant designs. Based on it, many works were published in the dental implant literature, comparing different materials, component geometries, connection types, surface treatments, etc. These works are useful for clinicians in order to identify the best options available in the market. The present work is intended not for clinicians but for dental implant manufacturers, developing a design tool that combines Finite Element Analysis, fatigue formulation and ISO 14801 experimental tests. For that purpose, 46 experimental tests were performed on BTI INTERNA® IIPSCA4513 implants joined with INPPTU44 abutments by means of INTTUH prosthetic screws under three different tightening torque magnitudes. Then, the load case was reproduced in a FE model from where the nominal stress state in the fatigue critical section was worked out. Finally, Walker criterion was used to represent accurately the effects of mean stress and predict fatigue life of the studied dental implant assembly, which can be extended to most of the products of BTI manufacturer. By means of this tool, dental implant manufacturers will be able to identify the critical design and assembly parameters in terms of fatigue behavior, evaluate their influence in preliminary design stages and consequently design dental implants with significantly better fatigue response which in turn will reduce future clinical incidences.

Tribst J.P., Dal Piva A.M., Borges A.L., Anami L.C., Kleverlaan C.J., Bottino M.A.

Different techniques are available to manufacture polymer-infiltrated ceramic restorations cemented on a chairside titanium base. To compare the influence of these techniques in the mechanical response, 75 implant-supported crowns were divided in three groups: CME (crown cemented on a mesostructure), a two-piece prosthetic solution consisting of a crown and hybrid abutment; MC (monolithic crown), a one-piece prosthetic solution consisting of a crown; and MP (monolithic crown with perforation), a one-piece prosthetic solution consisting of a crown with a screw access hole. All specimens were stepwise fatigued (50 N in each 20,000 cycles until 1200 N and 350,000 cycles). The failed crowns were inspected under scanning electron microscopy. The finite element method was applied to analyze mechanical behavior under 300 N axial load. Log-Rank (p = 0.17) and Wilcoxon (p = 0.11) tests revealed similar survival probability at 300 and 900 N. Higher stress concentration was observed in the crowns’ emergence profiles. The MP and CME techniques showed similar survival and can be applied to manufacture an implant-supported crown. In all groups, the stress concentration associated with fractographic analysis suggests that the region of the emergence profile should always be evaluated due to the high prevalence of failures in this area.

Adolfi D., Tribst J., Borges A., Bottino M.

Lauritano D., Moreo G., Lucchese A., Viganoni C., Limongelli L., Carinci F.

Introduction: Osseointegration are often suffering from oral conditions, especially, the micro gap at the implant–abutment connection represents a site for bacterial plaque aggregation, leading to increased inflammatory cells and causing peri-implantitis. Aim: The aim of this narrative review was to describe the different kinds of implant–abutment connections and their ability to reduce bacterial leakage and thus prevent peri-implantitis. Materials and methods: The following databases were consulted: Pubmed, Scopus, Cochrane Library, and Research gate and a total of 528 articles were found. After reading the abstract and titles, 473 items were excluded. The remaining articles (n = 55) were assessed for full-text eligibility. Thirty-three studies were included in the review. Results and Conclusions: We selected 22 clinical trials and 11 reviews, examining a total sample of 2110 implants. From the review, it was clear that there exists a relationship between the implant–abutment interface and bacterial leakage. All the connections presented an amount of micro-gap and bacterial micro-leakage, though conical and mixed connection systems seemed to behave better. Moreover, both connections seemed to have a better load distribution and the mixed system also had anti-rotational properties which are very useful during the positioning of the prosthesis.

Kim K., Lim Y.

The aim of this study was to examine the settling of abutments into implants and the removal torque value under static loading. Five different implant-abutment connections were selected (Ext: external butt joint + two-piece abutment; Int-H2: internal hexagon + two-piece abutment; Int-H1: internal hexagon + one-piece abutment; Int-O2: internal octagon + two-piece abutment; Int-O1: internal octagon + one-piece abutment). Ten implant-abutment assemblies were loaded vertically downward with a 700 N load cell at a displacement rate of 1 mm/min in a universal testing machine. The settling of the abutment was obtained from the change in the total length of the entire implant-abutment unit before and after loading using an electronic digital micrometer. The post-loading removal torque value was compared to the initial torque value with a digital torque gauge. The settling values and removal torque values after 700 N static loading were in the following order, respectively: Ext < Int-H1, Int-H2 < Int-O2 < Int-O1 and Int-O2 < Int-H2 < Ext < Int-H1, Int-O1 (α = 0.05). After 700 N vertical static loading, the removal torque values were statistically different from the initial values, and the post-loading values increased in the Int-O1 group and Int-H1 group (α = 0.05) and decreased in the Ext group, Int-H2 group, and Int-O2 group (α = 0.05). On the basis of the results of this study, it should be taken into consideration that a loss of the preload due to the settling effect can lead to screw loosening during a clinical procedure in the molar region where masticatory force is relatively greater.

Fernández-Asián, Martínez-González, Torres-Lagares, Serrera-Figallo, Gutiérrez-Pérez

(1) Background: In today's dentistry, implantology has become a therapeutic resource of choice in certain clinical situations. The design of implants has evolved in several aspects since their inception. Dental implants were initially designed with an external hex connection, although due to force transmission and security in the adjustment of the prosthesis, later implants featured an internal hex connection. This study aims to analyse the mechanical properties of two types of implants (an internal connection and an external connection) from the same manufacturer and their different prosthetic components (union screw between implant and prosthetic abutment, and the abutment itself) when subjected to different types of load. (2) Materials and methods: Intraosseous dental implants of similar shape, design and size, although different in type of connection (external vs. internal), were studied. The specifications of the UNI EN ISO 14801 test standard were used, with all determinations being carried out three times. Finally, the dimensional characterisation of the samples analysed after the dynamic load study was carried out, and the values of both study groups were compared by means of the non-parametric Mann–Whitney U test to find statistically significant differences (p < 0.05). (3) Results: For the static characterisation test, we found between 610.9 N and 986.1 N for the external connection and between 1263.6 N and 1324 N for the internal connection (p = 0.011). All of the dynamic load tests were positive and there was no failure in any of the components studied. (4) Conclusions: After the analysis of the samples studied in vitro, satisfactory results were obtained, demonstrating that both connections can support considerable mechanical loads according to international standards (UNI EN ISO 14801).

Tribst J.P., Özkara N., Blom E.J., Kleverlaan C.J., Ausiello P., Bruhnke M., Feilzer A.J., Dal Piva A.M.

Aims: This in silico study aimed to investigate the effect of implant–abutment contact surfaces on the stress generation of Morse taper implants under oblique loading. Materials and methods: Three-dimensional finite element models of Bone-Level and Tissue-Level implants were simulated with Standard and Partial contacts between the abutment and implant. The dimensional parameters followed the ISO 14801 guidelines, and an oblique load of 300 N was applied to the implants. The von Mises stress was acquired. Results: The Tissue-Level design showed a significant difference in the stress level when the connection with the implant, abutment, and screw was Partial. For the implant fixture, abutment, and screw, the Tissue-Level design showed 13% more stress in the implant, abutment, and screw when the connection was Partial. The Bone-Level design did not affect the connection and showed an overall 42% lower stress than the Tissue-Level design for the implant fixture. However, in the screw, there was a difference between the Bone-Level implants with a Standard and Partial connection. In contrast, for the Tissue-Level implant, this difference was less evident with higher stress peaks in the entire set. Conclusion: To achieve optimal outcomes, it is highly recommended to use original abutments, as they provide a more precise fit. The stress peaks were notably lower in Bone-Level implants compared to Tissue-Level implants. Furthermore, an implant–abutment connection with more contacting areas significantly reduced stress concentration, especially in Tissue-Level implant designs. By choosing well-fitting abutments, one can ensure more stable and durable implant performance with less stress.

Abdullah N.A., Mohd Sani M.S., Ghazali M.F., Mutra R.R.

Joining for sheet metal is a widely used process in product manufacturing in diverse industries such as automotive, aerospace, electronics, constructions and others. Finite element has become a vital tool when it comes to simulating the structural integrity and performance of many types of joining that are being used such as mechanical fastener, welding, adhesives and many more. This review paper provides a comprehensive overview of finite element modelling techniques applied to sheet metal joining based on existing studies from other researchers. The paper discusses the methods, advantages and limitations for each modelling approaches and highlights their key applications. This paper also discusses the role of finite element analysis when studying the performance of these models for joints. This will enable researchers to predict failure behaviours and enhance design efficiency. The strengths and limitations of various modelling approaches such as simplified and detailed methods and identified key areas for future research and development were also examined. By summarising the current knowledge and methodologies, this paper aims to contribute to the advancement of joint modelling techniques, which can lead to more accurate and reliable modelling method for joining in sheet metal.

Naguib G.H., Abougazia A.O., Al-Turki L.E., Mously H.A., Hashem A.B., Mira A.I., Qutub O.A., Binmahfooz A.M., Almabadi A.A., Hamed M.T.

This study investigates the impact of tightening torque (preload) and the friction coefficient on stress generation and fatigue resistance of a Ti-6Al-4V abutment screw with an internal hexagonal connection under dynamic multi-axial masticatory loads in high-cycle fatigue (HCF) conditions. A three-dimensional model of the implant–abutment assembly was simulated using ANSYS Workbench 16.2 computer aided engineering software with chewing forces ranging from 300 N to 1000 N, evaluated over 1.35 × 107 cycles, simulating 15 years of service. Results indicate that the healthy range of normal to maximal mastication forces (300–550 N) preserved the screw’s structural integrity, while higher loads (≥800 N) exceeded the Ti-6Al-4V alloy’s yield strength, indicating a risk of plastic deformation under extreme conditions. Stress peaked near the end of the occluding phase (206.5 ms), marking a critical temporal point for fatigue accumulation. Optimizing the friction coefficient (0.5 µ) and preload management improved stress distribution, minimized fatigue damage, and ensured joint stability. Masticatory forces up to 550 N were well within the abutment screw’s capacity to sustain extended service life and maintain its elastic behavior.

Soleimani M., Żmudzki J., Pakieła W., Jaśkowska A., Krasny K.

Re-tightening the loosened dental implant abutment screw is an accepted procedure, however the evidence that such screw will hold sufficiently is weak. The purpose of this study was material analysis of lost dental implant abutment screws made of the TiAlV alloy from various manufacturers, which became lost due to unscrewing or damaged when checking if unscrewed; undamaged screws could be safely re-tightened. Among 13 failed screws retrieved from 10 cases, 10 screws were removed due to untightening and 3 were broken but without mechanical damage at the threads. Advanced corrosion was found on nine screws after 2 years of working time on all surfaces, also not mechanically loaded. Sediments observed especially in the thread area did not affect the corrosion process because of no pit densification around sediments. Pitting corrosion visible in all long-used screws raises the question of whether the screws should be replaced after a certain period during service, even if they are well-tightened. This requires further research on the influence of the degree of corrosion on the loss of the load-bearing ability of the screw.

Muhsin S.A., Mohammed E.K., Bander K.

This virtual study was designed to evaluate the stress-deformation of a metal fixed partial dentures (FPDs) pontic under different loads using two different connectors. The STL file was generated for a RPD of two implant-supported restorations. The Co-Cr metal substructure was designed with two types of connector design. The pontic is connected to implant-supported crowns with square and round shape connectors. This study was designed for a cementless-retained implant-supported FPD. Finite element modeling (FEM) is used to assess the stress and deformation of the pontic within a metal substructure as the FEM might provide virtual values that could have laboratory and clinical relevance. The Co-Cr alloy mechanical properties like the Poisson ratio and modulus of elasticity were based on the parameters of the three-dimensional structure additive method. Nonparametric analyses (Mann-Whitney <i>U</i> test) was used. The use of square or round connectors often resulted in non-significant changes in stress, and deformation under either three or each loaded point on the occlusal surface of a pontic (<i>P</i> &#62; 0.05). However, the deformation revealed distinct variations between loads of the three points compared to each loaded point (<i>P</i> &le; 0.05). According to this study data, the pontic occlusal surface appears to be the same in stress and deformation under different loads depending on whether square or round connectors are used. While at the same connector designs, the pontic occlusal surface deformed significantly at three loaded points than it did at each point.

Walton T.R.

Purpose: The objective of the study was to qualitatively assess the micro-gap dimensions, connecting fitting surface profile, and bacterial leakage of cast high-gold-alloy UCLA abutments, with or without electrodeposited gold coatings attached to external hexagon implants. Materials and methods: Sixteen plastic UCLAs (PUCLAs) were cast with a high-gold-content alloy. Eight were electrolytically gold plated. Five machined cast-to-UCLA (GUCLA) control abutments were cast with the same alloy. All abutments were attached to external hexagon implants, giving 21 implant-abutment combinations (IACs). External perimeter micro-gaps measured with SEM under shadow eliminating silhouette illumination and 2000× magnification were averaged over three regions. The IACs were examined for E. coli leakage following an initial sterility test. Disassembled combinations were examined with SEM, and surface profiles were qualitatively assessed. Results: External micro-gap measurements did not reflect the variable connecting surface profiles, but average values < 5.0 μm were observed for all IACs measured under the shadow eliminating silhouette illumination for both cast and pre-machined external hexagon abutments with and without Au plating. E. coli transfer was observed in 3 of 5 PUCLA-plated and 2 of 5 PUCLA-non-plated IACs. No transfer occurred in the 3 GUCLA-non-plated or 2 GUCLA-plated control IACs. Abutment connecting surfaces, both Au-plated and not Au-plated, showed plastic deformation (smearing) in variable mosaic patterns across the micro-gap. Conclusions: Micro-gap dimensions < 5μm were obtained with both the high noble metal cast and pre-machined control external hexagon abutments with and without Au electrodeposited on the abutment connecting surface. Regions of intimate contact due to plastic deformation (smearing) of these surfaces were observed. A continuous smeared region around the circumference of the surfaces can provide an effective barrier to the egress of E. coli bacteria from the internal regions of the implant under static loading. The sample size was insufficient to determine if the gold coating resulted in a superior bacterial barrier.

Hedeșiu M., Pavel D.G., Almășan O., Pavel S.G., Hedeșiu H., Rafiroiu D.

The main objective was to examine the biomechanical behavior of the mandible under standardized trauma and to develop models of biomechanical responses when the mandible is subjected to various simulated impacts. A homogenous model based on the bone’s average mechanical properties was used. To simulate external loads on the mandible, forces on the chin, forces in an anteroposterior direction, and forces from the basilar edge were applied. To simulate mandibular biomechanics, we employed a model created in the ANSYS v19.0 software. The skull with the temporomandibular joint (TMJ) from the Grabcad website was used as the geometric mandibular model. We attempted to simulate the stresses developed in the mandible by impact forces. The amount of force (F) corresponded to the fall of a five-kilogram body (the head), from a height of two meters (F = 6666.7 N). The impact force was applied perpendicular to an arbitrary surface of an area of 10−3 m2. Impact on the chin region and lateral impact on the mandible, from the basilar edge to the gonion were examined. The investigated clinical situations were mandibular complete dentition; jaw with missing mandibular molars; missing third molar and first and second premolars; missing canine, third molar, first and second premolars, and complete edentation. In a normal bite, the highest stress was on the TMJ area. In case of impact on the chin, in complete edentation, a mandibular fracture occurred; in case of impact on the gonion, all stress values exceed the limit value above which the mandible in the condyle area may fracture.

Fathi A., Rismanchian M., Dezaki S.N.

Abstract Objective Opening of a healing abutment in two-stage implant systems is usually followed by a bad smell. Previous studies have found that presence of bacteria in microleakages of the implant-abutment interface results in further malodor. However, studies focusing on preventive treatments for this issue are scarce. Therefore, the aim of this study is to evaluate the effectiveness of two antimicrobial agents on prevention of malodor followed by opening the healing abutments. Materials and Methods Current double-blinded randomized clinical trial was performed on 51 eligible patients who were referred for their exposure surgery. They were divided equally into three parallel groups. In two groups, either chlorhexidine or tetracycline was added to the internal surface of the fixtures before screwing the healing abutments. One group did not receive any intervention. Three to 4 weeks later malodor was scored by sniffing the healing abutments immediately after uncovering them (odorless = 0/odor = 1). The three groups were then compared regarding malodor scores. Results Our findings showed that malodor was more frequent in the control group (58.82%) in comparison with groups of intervention (17.65 and 23.53%). There was a statistically significant difference between malodor in patients in whom antimicrobial agents (chlorhexidine and tetracycline) were used in their implants and the control group (p-value = 0.023). However, malodor in the chlorhexidine group and tetracycline group did not show any significant difference (p-value = 1). Conclusion Based upon the data from this study, it appears that local antimicrobial agents including chlorhexidine and tetracycline result in less malodor production within the implant-abutment interface. Clinical Significance A specific type of malodor is commonly seen after opening the healing abutment of a two-stage dental implant. Not only this issue is noticed by the dentist, but also annoyed the patient. Using local antimicrobial agents in the fixtures is likely to be a simple, easily applicable solution that satisfies both patients and dentists, and eliminates the possibility of further inflammation.

Omaish H.H., Abdelhamid A.M., Neena A.F.

The strain developed around implants with angled abutments should be considered when selecting a superstructure material. Studies that evaluated the strain developed around implants with angled abutments when using fiber-reinforced polymer as the implant superstructure material are lacking.The purpose of this in vitro study was to assess the strain developed around implants with angled abutments (15 and 25 degrees) of biocompatible high-performance polymer (BioHPP) and reinforced nanohybrid polymer with a multilayered glass fiber (TRINIA) superstructure under axial and oblique loading. The strain developed around implants was evaluated by using strain gauges.Thirty-two polyurethane test blocks were divided into 2 main groups (n=16) according to the degrees of buccal tilting of the implant platform (15 and 25 degrees). Each group was divided into 2 subgroups (n=8), and each subgroup received different superstructure materials (BioHPP or TRINIA). Two buccal and palatal strain gauges were installed on their corresponding prepared sites to measure the microstrains in the medium surrounding the implant. A universal testing machine was used to apply the static load from 0 to 100 N in the axial and 45-degree oblique direction, with the loading tip of the device on the loading point at the central fossa of the crown. For each tested implant, loads were applied, microstrains were recorded with the strain gauges, and the strain developed around the implant was statistically evaluated with 1-way ANOVA, followed by multiple pairwise comparisons by using the Bonferroni adjusted significance level (α=.05).For superstructure materials, the microstrain values recorded around implants restored with TRINIA were significantly lower than those restored with BioHPP in all groups (P

Todescan F.F., Hayashi M.M., Giugni L.R., Bottino M.A., Tribst J.P.

Proper maxillomandibular relationship registration can be clinically challenging during a digital workflow in full-arch rehabilitations. This dental technique requires the manufacturing and use of a hybrid surgical guide custom scanning device, indicated to be used during implant placement surgery, in addition to being used to simultaneously register the maxillomandibular relationship and transfer the implants’ 3D positioning, ensuring a fully digital workflow in full-arch implant-supported prosthesis rehabilitation. The sequence of steps presented here will allow dentists and dental technicians to conduct rehabilitations from denture to the final implant-supported prosthesis using a full-digital protocol, using a minimal quantity of intraoral devices and digital tools.

Nakano L.J., Gomes L.C., de Queiroz T.S., Paes-Junior T.J.

The aim of this study was to compare the screw removal torque of mini-conical prosthetic components and straight trunnion of indexed morse taper implants after mechanical cycling. The sample consisted of 40 implants and 20 mini-conical prosthetic components (MC group) and 20 straight trunnion components (ST group). Each group consisted of 10 specimens, with 2 implants in each, and cobalt–chromium metallic crowns were screwed into each sample. The components of the MC group received a torque of 20 N-cm with a digital torque wrench, and after 10 min were retightened with the same value as the initial torque. The components of the ST group received a torque of 30 N-cm, with a digital torque wrench, and after 10 min, they were retightened with the same value. The screws of the respective crowns of the two groups received a torque of 10 N-cm and after 10 min were retightened with the same value. Each group was subjected to the fatigue test in a mechanical cycler at 2,000,000 cycles, with a load of 250 N and frequency of 4 Hz. At the end of the fatigue test, the loosening torque of each screw of the specimens was measured through a digital torque wrench. The data were analyzed by two-way ANOVA and a Tukey test. In both groups, there were loss of torque. The results showed no statistic difference between MC and ST groups (p > 0.05).

Bottino M.A., de Oliveira F.R., Sabino C.F., Dinato J.C., Silva-Concílio L.R., Tribst J.P.

This study aimed to evaluate the survival rates of several external hexagon implants directly connected to zirconia crowns after thermomechanical fatigue. The deformation of the hexagons and the integrity of zirconia crowns were also evaluated. A monolithic zirconia crown (Y-TZP) and four different external hexagon dental implants (n = 10, N = 40) were mounted together and embedded in polyurethane. The specimens were subjected to thermomechanical cycling for 2.5 × 106 cycles, at 3.0 Hz frequency, at 200 N loading. The interface of the implant/zirconia crown system, zirconia crowns integrity before and after cycling, and the implant hexagon surface were evaluated under stereomicroscopy and SEM. A nanohardness analysis was performed to verify the hardness of zirconia and implants. Statistical analysis was performed using the Kaplan-Meier test, Multi-Sample Survival Tests, Logrank Test, (p = 0.05). The data did not show significant differences in the survival rates of different implant groups. However, some crowns presented fractures (16.67%) and the external hexagon region of the implants presented plastic deformations (100%). During chewing simulation, the interface between titanium implant and zirconia abutment can promote plastic deformation in the metal and surface defects in the ceramic. In addition, the types of interface defects can be affected by the external hexagon design.

Campaner L.M., Alves Pinto A.B., Demachkia A.M., Paes-Junior T.J., Pagani C., Borges A.L.

The objective of this study was to analyze the effect of cement thickness on the strain and stresses resulting from the polymerization of resin cement using photoelasticity and Finite Element Analysis (FEA). For this study, twenty upper first premolars with inlay cavity preparation were constructed from photoelastic resin and restored with composite resin inlay. The samples were divided into two groups (n = 10) according to the film thickness of resin cement material. For Group 1, the film thickness was 100 μm; for Group 2, the film thickness was 400 μm. After polymerization of the cement, photoelastic analysis and finite element analysis (FEA) were performed. In the photoelastic analysis, Group 2 showed higher strain with the presence of second-order fringe even after 24 h. In Group 1, the formation of first order fringes was not observed, even after 24 h. In the FEA analysis, the greatest cusp deflection and tensile stress occurred in Group 2 (0.00026 mm and 0.305 MPa, respectively) due to the polymerization shrinkage in the lingual cusp compared to Group 1 (0.000107 mm and 0.210 MPa, respectively). It can be concluded that the thickness of the resin cement influences the cusp deflection, with the greater thickness of the cement layer, the greater stresses and deformations in the tooth structure occur.