Occlusal Loading Research Articles

Screw preload loss under occlusal load as a predictor of loosening risk in varying dental implant designs

PurposeScrew loosening is a critical aspect of an implant design, as it can lead to implant failure. This study proposes a methodology and qualitatively assesses the potential of screw loosening risk for various types of screw heads and implant fixture-abutment connections. It is assumed that the risk of screw loosening is related to the drop in loosening moment under occlusal loads. The methodology and an assumption is verified by confronting the results with laboratory tests. MethodsNumerical simulations supplemented with semi-empirical equations were employed to estimate a loosening moment change under occlusal loads. The loosening risk was estimated by comparing the value before and after application of a compressive occlusal load of 150N. The procedure was carried out for 289 implant designs with smooth transition between flat to tapered shape of a screw head and an fixture-abutment connection. All analyses were conducted using Abaqus software. Pearson and Spearman correlation coefficients for normalised change in a screw loosening moment drop has been computed for numerical and laboratory tests. ResultsThe statistical analysis (Pearson, ρ = 0.8, Spearman, rs = 0.85) indicates very high correlation and confirms that the general tendencies observed in laboratory tests are reflected in the proposed procedure. The procedure was used for various geometries and the following results are presented: a screw loosening drop, implant stiffness and a tightening moment. The loosening moment drop achieves the extreme values of 6% and 24%. The biggest drop is an effect of a conical implant-abutment connection and a flat screw head while the lowest was recorded for a flat implant-abutment interface regardless of a screw head type. A low drop is also observed for a strongly conical screw head. ConclusionsThe proposed methodology exhibited very good correlation when confronted with laboratory tests, supporting a screw preload reduction under occlusal load as a key factor in screw loosening. Analysis across a wide spectrum of implant designs revealed geometry significantly impacts loosening potential under occlusal loads. Two key features were identified as favourable - an abutment-fixture butt joint and a tapered screw. The results also enable prediction of qualitative geometry effects on loosening risk.

Minimum detectable change in occlusal load – normative data for healthy and head and neck cancer populations

Traditionally, pain has been a signal to de-intensify jaw exercises for trismus to prevent tissue damage. It is unknown whether patients who have undergone surgery or radiotherapy for head and neck cancer have sufficient sensation to detect changes in occlusal load. This study sought to compare the minimum detectable occlusal load in a cohort of patients with head and neck cancer (HNC) and compare this with healthy controls. Twenty patients who were treated for HNC and 20 healthy controls were recruited from a single institution. A purpose-built pressure transducer was used to measure the minimum detectable force (measured in Newtons) applied to the jaw and the interincisal distance. Analysis was conducted using a mixed effects linear regression. The mean minimum detectable occlusal load in patients with HNC was 18.7N compared to 4.5N in healthy controls (mean difference 14.3N, 95% CI 12.2N to 16.4N, p < 0.001). Adjusted IID predicted force (0.15N per-mm IID, 95% CI 0.09 to 0.2, p < 0.001) with a weak interaction between treatment with radiotherapy and IID in HNC patients (p = 0.85). Patients who have been treated for HNC are less sensitive to changes in force applied to the jaw. This is concerning given that most jaw stretching devices use an unregulated and unknown amount of force to achieve greater mouth opening.

Fracture strength of endocrown maxillary restorations using different preparation designs and materials

PurposeThis study investigated the impact of preparation design and material types on fracture strength in maxillary premolars endocrowns after thermodynamic aging. Materials and methodsEighty two-rooted maxillary premolar crowns underwent endodontic treatment (N = 80, n = 10). The teeth were categorized into ten groups (4-mm deep with no intracanal extension lithium disilicate glass ceramic & multilayer zirconia endocrowns (LE0 & ZE0); 4-mm deep with 4-mm intracanal extension in one canal (LE1 & ZE1); 4-mm deep with 2-mm intracanal extensions in both canals (LE2 & ZE2); flat overlays with no endocore (LO & ZO); glass fiber reinforced post & core and crown (LC & ZC)). After cementation, all specimens were subjected to 1500 thermocycles and 1,200,000 chewing cycles with an axial occlusal load of 49 N. A static loading test was performed at a non-axial 45° loading using a universal testing machine and failure modes (Type I: restoration debonding; Type II: restoration fracture; Type III: restoration/tooth complex fracture above bone level; Type IV: restoration/tooth complex fracture below bone level) were evaluated using a stereoscope. Data were ananalzed using 2-way ANOVA and Tukey's tests (alpha = 0.05). ResultsThe endocrowns manufactured from multilayered zirconia and pressed lithium disilicate glass ceramic exhibited a fracture load ranging between 1334 ± 332 N and 756 ± 150 N, with ZC presenting the highest and LE2 the lowest values. The differences were not statistically significant (p > 0.05). ConclusionAll endocrowns tested in this study performed similar considering the different designs and materials tested. The distribution of fracture modes did not differ significantly depending on the design of the restoration and the type of material used.

Digitally designed occlusion of an implant-supported crown considering physiological tooth displacement under occlusal loading

Physiological natural tooth displacement under occlusal loading can influence intraoral occlusal contacts. However, gypsum casts and digital scans cannot simulate the physiological tooth displacement under occlusal loading. The occlusal design of the implant-supported crowns has been based mainly on the experience of dental laboratory technicians, lacking accuracy and individualization. Therefore, a digital technique that considers physiological tooth displacement is presented to design the occlusion of implant-supported single crowns.

Photoelastic Stress in Mandibular Overdenture Retained by Two Implants

Objectives: The aim of this study was to verify the effect of occlusal and axial single loads in the photoelastic stress in overdenture retained by two implants placed in the anterior region of the mandible. Materials and Methods: Occlusal load (10, 20, and 30 kgf) was exerted by the conventional maxillary complete denture in occlusion with the overdenture adapted in the mandibular photoelastic model. Axial single load was also exerted on the first left or right molar of the overdenture. Qualitative analysis was made in polariscope images and quantitative analysis by the FRINGES program. Results: Qualitative analysis: The occlusal load showed similar stress in the region between the two implants. Axial single load induced in the first molars promoted stress in the implant apexes, and between the implant and mandible posterior region for the three loads. Quantitative analysis for occlusal load: 10 kgf (T = 265.03; N = 0.57); 20 kgf (T = 989.81; N = 2.11); 30 kgf (T = 1055.40; N = 2.26). Axial single load in the left molar: 10 kgf (T = 267.38; N = 0.57); 20 kgf (T = 270.07; N = 0.58) and 30 kgf (T = 281.84; N = 0.60). Axial single load in the right molar: 10 kgf (T = 952.14; N = 2.03); 20 kgf (T = 1038.58; N = 2.22); and 30 kgf (T = 926.92; N = 1.98). Conclusions: Different photoelastic stress levels occurred in the overdenture retained by two implants when submitted to occlusal or axial single load in the first left or right molar. Clinical Relevance: Artificial teeth intercuspation in the overdenture supported by two implants must have the same importance given to the vertical relationship to relieve the chewing effort.

Stress-strain and fatigue life numerical evaluation of two different dental implants considering isotropic and anisotropic human jaw.

Dental prostheses are currently a valid solution for replacing potential missing tooth or edentulism clinical condition. Nevertheless, the oral cavity is a dynamic and complex system: occlusal loads, external agents, or other unpleasant events can impact on implants functionality and stability causing a future revision surgery. One of the failure origins is certainly the dynamic loading originated from daily oral activities like eating, chewing, and so on. The aim of this paper was to evaluate, by a numerical analysis based on Finite Elements Method (FEM), and to discuss in a comparative way, firstly, the stress-strain of two different adopted dental implants and, subsequently, their fatigue life according to common standard of calculations. For this investigation, the jawbone was modeled accounting for either isotropic or anisotropic behavior. It was composed of cortical and cancellous regions, considering it completely osseointegrated with the implants. The impact of implants' fixture design, loading conditions, and their effect on the mandible bone was finally investigated, on the basis of the achieved numerical results. Lastly, the life cycle of the investigated implants was estimated according to the well-established theories of Goodman, Soderberg, and Gerber by exploiting the outcomes obtained by the numerical simulations, providing interesting conclusions useful in the dental practice.

Magnetic attachment for complete overdenture: A case report

Background: Overdenture is a partial or complete denture that has support from natural tooth roots that have been treated with endodontic treatment. Retain the remaining teeth prevent resorption of alveolar ridge. An overdenture with a magnetic attachment can be used to increase the retention of the denture. The magnets transfer the occlusal load to the bone through the periodontal ligament of retained roots that are attached with remaining root structure Objectives: This case report is aimed to report the step-by-step treatment of complete denture mandibula and complete overdenture maxilla with magnetic attachment retained design Case Report: A 62-year-old female visited the Prosthodontic Clinic of Dentistry Faculty, Airlangga University with a chief complaint of difficulty in eating. Clinical examination shown partial edentulous in the mandibula. The remaining teeth were 18, 14, 23, 25 and 43. Case management: After thorough observation from the clinical presentation and radiographic, magnetic attachment was planned on 14 in order to retain the remaining tooth and improving retention and stabilization of the maxillary denture. Conclusion: Magnetic maxilla overdenture is able to provide support, stability and retention.

An Ex-Vivo Model for Investigating Bacterial Extrusion from Infected Root Canals during Masticatory Function

IntroductionThe extrusion of bacteria from infected root canals may lead to increase in symptoms, expansion of periapical lesions, and contribution to systemic diseases. The aim of this study is to investigate a potential proof-of-concept model to study the extent to which bacteria can escape from infected root canals under dynamic loading (simulated chewing). MethodsThe study was completed in 2 experiments performed at 2 institutions. Biofilms of Streptococcus intermedius in the first experiment and S. intermedius and Actinomyces naeslundii were allowed to grow in root canals of single-rooted extracted teeth for 3 weeks. The roots of the teeth were suspended in a small chamber containing dental transport medium and were mounted on a lower sample holder of a chewing simulator. In the experimental group, simulated chewing cycles equivalent to 1 year of function were conducted, and then bacterial migration was quantified and compared with stationary teeth. ResultsAll experimental samples of the loading group revealed bacterial penetration in both experiments. Several of the unloaded samples revealed no bacterial penetration. In the first experiment, a significantly higher number of bacteria were able to escape into the periapex of the loaded group compared with the unloaded group (P = .017). In the second experiment, there was no significant difference between the 2 bacterial species used in the amount of extruded bacteria; however, there was a highly significant effect for occlusal loading (P = .0001). ConclusionsThe potential for occlusal forces to enhance bacterial extrusion from infected root canals should be further explored.

Effects on different full-coverage designs and materials of crack propagation in first mandibular molar: an extended finite element method study.

Objectives: This study aims to investigate the biomechanical properties of fracture resistance in cracked teeth using five different full-coverage restorations made of three different materials. Materials and Methods: A 3D model of a mandibular first molar was created to design five different full-coverage repair models: crown, crown with composite resin filling inside, occlusal veneer, occlusal veneer with composite resin filling inside and onlay. These repair models were fabricated using three different materials, namely, zirconia, lithium disilicate (LDS), and a hybrid polymer-infiltrated ceramic network material (PIC). In total, 15 repair models were tested using the extended finite element method (XFEM), with an occlusal load of 5000N applied slowly to the occlusal surface of the restoration. The analysis of stress distribution in the restoration and dentin crack line was conducted to measure and record the crack initial load on the restoration and dentin. Results: The results showed that restorations on the occlusal surface significantly improved crack resistance, with zirconia exhibiting superior fracture resistance among the materials tested. Restorations of crown with composite resin filling inside demonstrated the highest resistance to fracture, while occlusal veneers showed the lowest. MPS concentration was observed at the interface between the restoration and dentin and at the root bifurcation, with the highest values at the top of crack development. Dentin covered by oxidized restorations had the highest displacement, while PIC restorations exhibited the lowest. Pulp analysis revealed selective MPS concentration and strain patterns in models with zirconia restorations and onlay, with pronounced pulp displacement in zirconia restorations and onlay. Enamel analysis indicated larger MPS values and displacements in zirconia restoration models and onlay, with higher strain in onlay. Restoration played a crucial role in protecting the tooth, with crack propagation initial loads in dentin surpassing restorations in experimental groups. Conclusion: This study confirms that full-coverage restorations significantly increased the fracture resistance of cracked teeth, with zirconia restorations significantly protecting the underlying cracked tooth. Elimination of fracture lines in the restoration design can improve fracture resistance in cracked teeth. The findings have implications for dental prosthetic design and clinical practice.

Systematic review fracture resistance of endodontically treated posterior teeth restored with fiber reinforced composites- a systematic review

BackgroundLarge cavity designs and access cavities impair endodontically treated tooth fracture resistance. As the tooth’s strength is known to reduce significantly after the root canal treatment, occlusal loading as a result of functions such as chewing, biting and certain parafunctional tendencies makes the endodontically treated tooth vulnerable to fracture. Hence, after endodontic treatment, it is vital to give adequate and appropriate restorative material to avoid tooth fractures. Accordingly, the choice of such restorative material should be dictated by the property of fracture resistance.ObjectiveThe goal of this study was to conduct a systematic review and critical analysis of available data from in vitro studies examining the fracture resistance of endodontically treated posterior teeth restored with fiber-reinforced composites.MethodologyThe Preferred Reporting Items for Systematic Review and Meta-Analysis (PRIS-MA) Statement was used to guide the reporting of this systematic review A comprehensive literature search was performed using MEDLINE (via PubMed), Scopus, ScienceDirect, Google Scholar, and LILACS. A manual search of the reference lists of the articles was also performed. The databases provided a total of 796 studies from the electronic systematic search. The databases provided a total of 796 studies from the electronic systematic search. Two reviewers scrutinized the papers for eligibility based on inclusion/exclusion criteria and extracted data. The studies were assessed for their potential risk of bias. Based on modified JBI & CRIS (checklist for reporting in vitro studies) guidelines, along with the methodology and treatment objective, we have formulated 13 parameters specifically to assess the risk of bias. A total of 18 studies met the inclusion criteria and were included for qualitative analysis. Considering the high heterogeneity of the studies included, a meta-analysis could not be performed.ResultsThe majority of the included studies had a moderate or high risk of bias. When compared to traditional hybrid composites, fiber-reinforced composites showed increased fracture resistance of endodontically treated teeth in the majority of investigations. On the other hand, limited evidence was found for the bulk fill composites. Moreover, moderate evidence was found for the fracture resistance of inlays and fiber posts with fiber-reinforced composites for core build-up in endodontically treated teeth. No evidence could be found comparing the fracture resistance of endo crowns and fiber-reinforced composites in endodontically treated teeth.ConclusionAccording to the research, using fiber-reinforced composites instead of conventional hybrid composites improves the fracture resistance of endodontically treated teeth. However, there was a high risk of bias in the research considered. No judgments could be reached about the superiority of one material over another based-on comparisons between other core restorations.

Analysis of implant-supported cantilever fixed partial denture: An in vitro comparative study on vertical misfit, stress distribution, and cantilever fracture strength.

To evaluate the vertical misfit, stress distribution around dental implants, and cantilever fracture strength of 3-unit implant-supported cantilever fixed partial dentures (FPDs) using frameworks made from different materials and manufacturing techniques. Forty FPDs were fabricated and divided into 5 groups (n = 8) based on the framework material used: LAS Co-Cr (Conventional casting-laser welding); TIG Co-Cr (Conventional casting -TIG welding); OP Co-Cr (Conventional casting-one-piece); CAD Co-Cr (CAD-CAM); and CAD Zr (CAD-CAM ZrO2). The vertical misfit was evaluated before porcelain application (T1) and before (T2), and after thermomechanical cycling (T3) by stereomicroscopy. Cantilever fracture strength was tested with a 50 kN (5000 kgf) load cell at a crosshead speed of 0.5mm/min. Qualitative and quantitative photoelastic analysis was performed to evaluate stress distribution at seven specific points in five FPDs (n = 1/group) subjected to occlusal loading. Only the molar showed interaction among the three factors (G × S × T; F(20.932) = 1.630; p = 0.044). Thermomechanical cycling (T2 vs. T3) had a significant effect on intra-group vertical misfit in molar, especially in LAS Co-Cr (Δ = 5.87; p = 0.018) and OP Co-Cr (Δ = 5.39; p = 0.007), with no significant effect in premolar (p > 0.05). Ceramic application combined with thermomechanical cycling (T1 vs. T3) caused a significant intra-group increase in vertical misfit in all groups, both in the molar and premolar (p < 0.05). OP Co-Cr was associated with greater vertical misfit and stress concentration. Frameworks manufactured by the CAD-CAM system exhibited lower vertical misfit and better stress distribution. FPDs with metal frameworks (>410.83 ± 72.26 N) showed significantly higher fracture strength (p < 0.05) than zirconia (277.47 ± 39.10 N), and the first signs of ceramic veneering fracture were observed around 900 N. FPDs with frameworks manufactured using a CAD-CAM system appear to be associated with lower vertical misfit and better stress distribution, although the section of the frameworks followed by welding may be a viable alternative. In addition, metal frameworks exhibit high fracture strength.

Management of bridge with non-rigid connectors in cases with pier abutments

The type of denture bridge with pier abutments where there are stand-alone abutment teeth between the abutment terminals, requires the dentist to pay special attention. One crown is attached to a natural tooth, and the other crown is attached to a dental implant or other type of abutment, known as the pier abutment that can become a class I fulcrum if restored using a 5-unit bridge with rigid connectors, which can cause excessive force to be received by the retainer at the abutment terminal, leading to debonding of the retainer or even damage to the periodontal tissues of the abutment teeth. In addition to these problems, long-span bridges have a poor prognosis due to the mobility difference between the anterior and posterior teeth, which may cause excessive stress on the connector. The use of a non-rigid connector can overcome this problem, as it can be a stress breaker by allowing micro-movements in the connector. The design of semi-rigid bridge with pier abutments must consider factors such as span length, anticipated occlusal load, and mastication factor. Proper consideration of these factors ensures the safety and longevity of the bridge.

Indications, design considerations, and clinical outcomes of implant-supported fixed prostheses

Implant-supported fixed prostheses are a highly successful treatment option for replacing missing teeth, offering improved esthetics, function, and patient satisfaction. Design considerations play a crucial role in achieving optimal outcomes. Implant distribution and angulation should be carefully planned to ensure balanced load distribution and biomechanical stability. Occlusal considerations are vital to minimize mechanical complications and implant overloading, with proper adjustments and occlusal schemes implemented. The emergence profile should replicate natural tooth contours for esthetic integration and ease of oral hygiene maintenance. Material selection is essential, considering factors such as occlusal loading, esthetic requirements, and patient-specific considerations. Biomechanical analysis helps identify stress distribution patterns and optimize prosthesis design for long-term success. Patient satisfaction is high, with improved chewing ability, speech, and overall quality of life reported. Long-term success rates exceed 90%, influenced by implant survival, peri-implant health, maintenance of prosthesis integrity, and patient satisfaction. Thorough patient assessment, treatment planning, precise surgical and prosthetic execution, and comprehensive follow-up care are crucial for favorable outcomes. Implant-supported fixed prostheses provide functional and esthetic restorations, enhancing oral health and overall well-being.

Effect of Proximal Caries-driven Access on the Biomechanical Behavior of Endodontically Treated Maxillary Premolars

IntroductionThis study investigated the effects from the carious cavity and access from it on the fracture resistance of endodontically treated maxillary premolars using finite element analysis (FEA). MethodsA maxillary premolar was used to compare 3 types of access cavity related to having a proximal carious defect: caries-driven access (CDA), conservative access that has a mesial component (MCA), as well as traditional access with the same mesial component (MTA). Cyclic loading was simulated on the occlusal surface, and number of cycles until failure (NCF) was compared with the intact tooth model (IT). Mathematical analysis was done to evaluate the stress distribution patterns and calculated maximum von Mises (vM) and maximum principal stresses (MPS), with emphasis on pericervical region as a specific area of interest. ResultsMaximum vM registered on the IT was 6.14 MPa. CDA provided the highest NCF with 92.28% of the IT, followed by MCA (84.90%) and MTA (83.79%). The vM and MPS analysis showed that the stress values and patterns are affected more by the proximity of the occlusal load to the tooth/restoration interface. Concerning the pericervical region, maximum vM was registered for IT (4.11 MPa), followed by CDA (4.85 MPa) and then MCA (8.13 MPa) and MTA (8.61 MPa), whereas the MPS analysis revealed that CDA showed the highest magnitude of tensile stresses. ConclusionsA proximal CDA benefits the mechanical properties of maxillary premolars; however, its impact on the biological aspect should be assessed to provide a ruling for/against it.

An assessment of masticatory efficiency and occlusal load distribution in adolescent patients undergoing orthodontic treatment with functional jaw orthopedics: A prospective cohort study

IntroductionFunctional jaw orthopaedics, produces a radical change in the occlusal scheme and the masticatory apparatus, particularly in patients with Class II malocclusion. It remains to be seen how the changes brought about by a functional appliance alter the masticatory ability of a growing child, who needs the necessary nutrition to properly grow the craniofacial region. Materials and methodsPretreatment and Post-treatment values of masticatory efficiency and the distribution of the occlusal load at centric occlusion were evaluated and compared for 20 patients with Class II division 1 malocclusion undergoing functional jaw orthopaedics. ResultsSignificant increase in the masticatory efficiency was seen during and after treatment (p < 0.5) There was an increase in the anterior distribution of occlusal load associated with a concomitant decrease in the posterior region at centric occlusion. ConclusionImprovement in the masticatory efficiency was observed after treatment of a retrognathic mandible with functional jaw orthopaedics in the adolescent participants with Class II malocclusion. This highlights the importance of treatment with functional jaw orthopaedics, which apart from providing esthetic and functional improvement also improves the ability of a growing child to extract proper nutrition from his/her diet.

The effect of different abutment and restorative crown materials on stress distribution in single-unit implant-supported restorations: A 3D finite element stress analysis.

To evaluate the effect of restorative materials with or without resin content, modeled on zirconia and titanium abutment materials, on the stress distribution on the alveolar bone, implant, and prosthetic crowns with a 3D finite element stress analysis. Titanium and zirconia abutments were combined with three implant-supported crown materials (polymer infiltrated hybrid ceramic (PICN), lithium disilicate (LD), and zirconia-reinforced lithium silicate (ZLS)) to create six experimental groups. The 40×30×20mm alveolar bone, 3.75× 10mm implant, esthetic abutment, and maxillary first premolar crown bonded over the abutment were the components of the finite element models. On the lingual cusp of the crown, the 150 N occlusal loading was applied in the buccolingual direction at a 30° angle. Equivalent von Mises stress and maximum and minimum principal stresses were used for both the qualitative and quantitative evaluation of the stress distribution of the created models. The von Mises stress in implant and abutment did not differ according to the crown materials. The use of a zirconia abutment resulted in higher von Mises stress values in the abutment but lower stress values in the implant. The highest stress values were obtained in ZLS (196.65MPa) and LD (194.05MPa) crowns. The use of titanium abutments, regardless of crown materials, resulted in higher von Mises stress values in restorative crowns than in zirconia abutments. The principal stress values in alveolar bone showed similar distribution and concentration in all models. Changes in crown material did not affect stress distribution in the implant and peripheral bone. However, the zirconia esthetic abutment resulted in a lower stress concentration on the implant.

Investigating the etiology of non-carious cervical lesions: Novel µCT analysis

ObjectivesThe etiology of non-carious cervical lesions (NCCLs) is not fully understood, limiting treatment and prevention. Our aim was to evaluate the effect of mechanical loading and acid exposure on the cervical tooth region using a random spectrum loading model that simulates the nature of oral mastication. MethodsThirty extracted human premolars were divided into three experimental groups: 1) unloaded teeth immersed in acid (erosion group: Er), 2) loaded teeth immersed in acid (erosion with spectrum loading group: Er-SL), and 3) loaded teeth immersed in distilled water (spectrum loading group: SL). Random spectrum loading with loads ranging from 100 to 500 N was performed. All teeth were scanned using micro-CT. A novel 3D analysis was developed to evaluate the circumferential cervical tissue loss and regions under tension and compression. For parametric and non-parametric comparisons, one-way ANOVA with Tukey post-hoc tests and Kruskal-Wallis with Bonferroni post-hoc tests were used. ResultsA significant difference was observed in the circumferential volumetric loss, with the Er-SL exhibiting the greatest volume loss (p < 0.001). Moreover, in the loaded groups (Er-SL and SL), regions subjected to tension showed significantly greater loss (p < 0.001, p = 0.007) compared with regions subjected to compression. ConclusionsThe novel high-resolution micro-CT analysis provided new insights into the etiology of NCCLs. The results suggested that the cumulative effect of mechanical loading and acid exposure may play a major role in NCCL formation. Clinical significanceThis study investigates the etiology of NCCLs by examining the combined effects of occlusal loads and acid exposure on cervical tissue loss. Understanding the pathogenesis of NCCLs paves the way for the development of improved preventative measures and treatment strategies to prevent tooth structure degradation.

Impact of different CAD/CAM materials on internal and marginal adaptations and fracture resistance of endocrown restorations with: 3D finite element analysis

PurposeTo assess and compare the impact of various computers aided design/manufacturing (CAD/CAM) materials on internal and marginal discrepancies, fracture resistance and failure probability of Endocrown restorations with 3D Finite Element analysis.Material and methodsForty devitalized human maxillary first molars were collected. After endodontic treatment, they classified into 4 groups (n = 10) based on the materials used for endocrown fabrication. Group V (Vita-Enamic), Group N (Nacera Hybrid), Group T (Translucent Prettau Zirconia) and Group P (Pekkton ivory). All samples were exposed to artificial aging method simulating one year of clinical service. Silicone replica technique and stereomicroscope (25X) utilized to evaluate the marginal and internal gaps of endocrowns at different areas. Fracture resistance test used for cemented specimens followed by qualitative investigation utilizing Stereomicroscopy. Four models representing four endocrown systems used for restoration of severely-damaged endodontically treated upper first molar were generated for finite element analysis (FEA). Axially and centrally static occlusal compressive load was applied. Modified Von Mises and maximum principal stress values on the remaining tooth structure, cement lines and restorative materials were assessed independently. Resulted data were statistically analyzed at P-value ≤ 0.05.ResultsIn the current study, the highest mean values of internal and marginal discrepancies (μm) among studied groups were reported for Zirconia group (100.300 and 102.650) respectively, while the lowest mean value of internal discrepancy (μm) was observed for Nacera group (69.275) and the lowest mean value of marginal discrepancy (μm) was observed for PEKK group (78.4750). Regarding internal discrepancy, Vita-Enamic and PEKK groups did not exhibit any statistically significant differences (P = 0.293), however zirconia and the other tested groups exhibited statistically significant differences in the mean values of the marginal gap region (p 0.05).On the other hand, PEKK group showed the highest mean value of fracture resistance (1845.20 N) and the lowest value was observed for Vita-Enamic group (946.50 N). Regarding to stress distributions through 3D FEA, and according to modified von Mises (mvM) analysis, the greatest possible stress values were noticed in PEKK model in relation to tooth structure, cement line, and flowable composite as the following: (93.1, 64.5, 58.4 MPa) respectively, while Zirconia revealed lower maximum stress values (11.4, 13.6, 11.6 MPa) respectively.ConclusionsStatistically excellent marginal and internal fit was observed for PEKK in relation to other used endocrown materials. Also, PEKK material explained fracture resistance comparable to zirconia value while the lowest value was detected for Vita Enamic material.

In silico fatigue performance of molars restored with full crowns under alternating cyclic loadings

ObjectiveIn this study, a preclinical approach was used to analyze and directly compare the fatigue performance (fatigue life and damage percentage) and maximum principal stresses (Max. Ps) of prepared models treated with different materials and geometric parameters. MethodsFour groups of preparative parameters (crown width, crown length, degree of polymerization and material) were selected, each with five variables. An alternating cyclic occlusal load with an amplitude of 300 N was applied to the ball part along the longitudinal axis. The fatigue properties of the preparations and Max.Ps were analyzed. ResultsA shoulder width of 0.8 mm, a shoulder height offset of 0.2 mm, a degree of polymerization of 5°, and a crown material of ZC resulted in the smallest percentage of damage. In contrast, the effect of different modulus of elasticity (MOE) on Max.Ps was not significant (p = 0.609). ConclusionThe results suggest that the selection of larger modulus of elasticity MOE and larger Poisson's ratio material's, preparation of larger shoulder widths within safety, reasonable increase in crown length, and selection of larger degree of polymerization are favorable methods to protect the preparation.

Biomechanical Investigation of Patient-Specific Porous Dental Implants: A Finite Element Study

The design of the implant and osseointegration play an important role in the long-term stability of implants. This study aims to investigate the impact of porous implants on full and partial osseointegration in varying bone qualities. Finite element models of porous implants were modeled and assembled with normal and weak bones considering full and partial osseointegration. These assemblies were simulated under an occlusal load of 200 N when the outer surfaces of bones were fixed in all directions. The results showed that in the case of full osseointegration, the stresses in surrounding bones were increased with decreasing implant stiffness, while decreased in partial osseointegration. Moreover, the maximum octahedral shear strain in the weak bone exceeded 3000 µε in all the cases but decreased (from 7256 to 3632 µε) with decreasing implant stiffness. According to the mechanostat hypothesis, using porous implants in normal bone may enhance bone density in full osseointegration, while susceptivity of bone damage may reduce in weak bones using porous implants. Thus, careful selection of implant material and design based on the patient’s specific bone quality is crucial for successful outcomes.