Fabrication trueness and internal fit of different lithium disilicate ceramics according to post-milling firing and material type.

OBJECTIVES: To evaluate whether post-milling firing and material type affect the fabrication trueness and internal fit of lithium disilicate crowns. METHODS: A prefabricated cobalt chromium abutment was digitized to design a mandibular right first molar crown. This design file was used to fabricate crowns from different lithium disilicate ceramics (nano-lithium disilicate (AM), fully crystallized lithium disilicate (IN), advanced lithium disilicate (TS), and lithium disilicate (EX)) (n = 10). Crowns, the abutment, and the crowns when seated on the abutment were digitized by using an intraoral scanner. Fabrication trueness was assessed by using the root mean square method, while the internal fit was evaluated according to the triple scan method. These processes were repeated after the post-milling firing of AM, TS, and EX. Paired samples t-tests were used to analyze the effect of post-milling firing within AM, TS, and EX, while all materials were compared with 1-way analysis of variance and Tukey HSD tests (α = 0.05). RESULTS: Post-milling firing reduced the surface deviations and internal gap of AM and EX (P ≤ 0.014). AM mostly had higher deviations and internal gaps than other materials (P ≤ 0.030). CONCLUSIONS: Post-milling firing increased the trueness and internal fit of tested nano-lithium disilicate and lithium disilicate ceramics. Nano-lithium disilicate mostly had lower trueness and higher internal gap; however, the maximum meaningful differences among tested materials were small. Therefore, the adjustment duration and clinical fit of tested crowns may be similar. CLINICAL SIGNIFICANCE: Tested lithium disilicate ceramics may be suitable alternatives to one another in terms of fabrication trueness and internal fit, considering the small differences in measured deviations and internal gaps.

Retention and fatigue performance of modified polyetheretherketone clasps for removable prosthesis.

PURPOSE: Polyetheretherketone (PEEK) is considered as an alternative to metal material for removable partial denture (RPD). However, the retentive force is not strong as a metal RPD. This study investigated the retention and fatigue performance of PEEK clasps with different proportions of clasp arm engaging the undercut to verify a new strategy to improve their clinical performance. METHODS: Three groups (n = 10/group) of PEEK clasps with their terminal 1/3, 2/3 and the whole of retentive arms engaging the undercut were fabricated along with a group (n = 10) of conventional cobalt-chrome (CoCr) clasps as control group. Retentive forces were measured by universal testing machine initially and at an interval of 1500 cycles for a total of 15,000 fatigue cycles. The fatigue cycles were conducted by repeated insertion and removal of the clasp using fatigue testing machine. Each clasp was scanned by Trios3 scanner before and after fatigue test to obtain digital models. The deformation of the clasp was evaluated by root mean square (RMS) through aligning the two models in Geomagic wrap (2021). Scanning electron microscopy (SEM) and finite element analysis were carried out to observe the abrasion and the von Mises stress of the clasp arm. Kruskal-Wallis H test was used to compare the retentive forces and the RMSs of the studied groups followed by Bonferroni multiple comparisons. RESULTS: The whole of PEEK clasp arm engaging the undercut provided higher mean retentive forces (7.99 ± 2.02 N) than other PEEK clasp groups (P < 0.001) and was closer to CoCr clasps (11.88 ± 2.05 N). The RMSs of PEEK clasps were lower than CoCr clasps (P < 0.05) while the differences among PEEK clasps were of no statistical significance (P > 0.05). SEM showed that evidences of surface abrasion were observed on the section that engaged the undercut for all groups of clasps. The stress concentration mainly occurred on the initial part of the retentive arm. The maximum von Mises stress of each group was below the compressive strength of PEEK. CONCLUSIONS: Proportions of PEEK clasp arm engaging the undercut positively influenced the retentive force and the fatigue resistance of PEEK clasps was superior than CoCr clasps. It is a feasible method to improve the retention of PEEK clasps by increasing the proportion of clasp arm engaging the undercut. Clinical trials are needed to further verify this innovation.

Does the choice of the measuring technique affect the comparison of fit between zirconia and cobalt-chromium prostheses?

AIMS: The objectives of the study were to compare the adaptation of presintered zirconia and cobalt- chromium prostheses using microcomputed tomography (µCT), scanning electron microscopy (SEM), and stereomicroscope (SM). MATERIALS AND METHODS: Twenty-four fixed dental prostheses (FDPs) were fabricated on metal abutments, duplicated from maxillary first premolar and first molar prepared on a typodont model. Teeth were reduced to obtain chamfer of 1.2 mm and reduction occlusaly of 2 mm occlusal. Scanning of the abutments was done with random assignment to two groups receiving the FDPs made from soft-milled Co-Cr (n = 12) and zirconia (n = 12). Marginal and internal gaps were assessed using three evaluation techniques (X-ray microcomputer tomography, SEM, and stereomicroscopy). STATISTICAL ANALYSIS USED: Comparison of the results was made using Levene and analysis of variance tests (α =0.05). RESULTS: Irrespective of the material tested, statistical differences were found between the measuring techniques (P = 0.001 overall); the obtained mean gaps were for CT scan (92.60 ± 13.31), for SEM (101.92 ± 23.03), and for SM (113.44 ± 14.68): the multiple comparisons between techniques found a significant difference between CT and SM (P < 0.001), and SEM and SM (P = 0.025). When materials were compared within each measuring technique, Co-Cr showed lower values compared to zirconia in SEM (P < 0.001) and Stereo (P = 0.049); similar results were found in CT. CONCLUSIONS: Results values differed with the chosen measuring technique. Co-Cr prostheses had a better fit than zirconia prostheses in SEM and Stereo. µCT showed comparable results to SEM, smaller than SM results.

The Effect of Different Ageing Protocols on the Shear Bond Strength of the Ceromer Indirect Composite on Two Different Substructure Materials.

BACKROUND: The evolution of restorative materials in prosthodontics has led to the emergence of indirect composite resins, including ceromers, as alternatives to traditional metal-ceramic restorations. However, research gaps exist regarding the impact of ageing protocols on the bond strength of ceromer composites to different metal substructures, necessitating further investigation in this area. AIM: This study aimed to determine the effect of five different ageing protocols on the shear bond strength (SBS) of ceromer indirect composites on two different substructures. METHODS: In this in vitro study, 120 metallic discs (10 × 2 mm) were cast from cobalt-chromium (Co-Cr) alloy (n = 60) and spark erosion treated from grade V titanium (n = 60). Each sample was sandblasted. The M.L. primer (Shofu, Germany) and layers of opaque were applied to the surface following the manufacturer's instructions. A special jig (6 × 2 mm) was placed on each disc. The ceromer was condensed in it and light-cured separately for 90 s. Following polishing, specimens were separated into five ageing groups: distilled water (as a control), thermal cycling, tea, coffee, and gastric acid immersion. All samples were placed in 37°C incubation for 28 days for distilled water, coffee, and tea, and 7 days for gastric acid immersion and thermal cycling for 5000 cycles (5-55°C). A universal test machine was used to measure the SBS. The samples were evaluated for failure modes using stereomicroscopy. Data were analyzed using one-way analysis of variance (ANOVA) (P < 0.05). RESULTS: According to one-way ANOVA, the mean SBS (MPa) between the two groups was compared in each ageing protocol, and there were no significant differences between the Co-Cr-C and Ti-C groups (P > 0.05). The most frequent mode of failure in all groups was mixed. CONCLUSIONS: Applying the ageing protocols, the type of substructure material had no significant effect on the SBS of the ceromer indirect composite except for tea immersion.

Customizable Nichrome Wire Heaters for Molecular Diagnostic Applications.

Accurate sample heating is vital for nucleic acid extraction and amplification, requiring a sophisticated thermal cycling process in nucleic acid detection. Traditional molecular detection systems with heating capability are bulky, expensive, and primarily designed for lab settings. Consequently, their use is limited where lab systems are unavailable. This study introduces a technique for performing the heating process required in molecular diagnostics applicable for point-of-care testing (POCT), by presenting a method for crafting customized heaters using freely patterned nichrome (NiCr) wire. This technique, fabricating heaters by arranging protrusions on a carbon black-polydimethylsiloxane (PDMS) cast and patterning NiCr wire, utilizes cost-effective materials and is not constrained by shape, thereby enabling customized fabrication in both two-dimensional (2D) and three-dimensional (3D). To illustrate its versatility and practicality, a 2D heater with three temperature zones was developed for a portable device capable of automatic thermocycling for polymerase chain reaction (PCR) to detect Escherichia coli (E. coli) O157:H7 pathogen DNA. Furthermore, the detection of the same pathogen was demonstrated using a customized 3D heater surrounding a microtube for loop-mediated isothermal amplification (LAMP). Successful DNA amplification using the proposed heater suggests that the heating technique introduced in this study can be effectively applied to POCT.

Does the Build Orientation Parameter Affect the Fit of Fixed Partial Dentures Fabricated by Additive Manufacturing?

PURPOSE: This in vitro study evaluated the adaptation of cobalt-chromium (Co-Cr) fixed dental prostheses (FDPs) fabricated by selective laser melting (SLM) with different build angles. MATERIALS AND METHODS: Maxillary right first premolars and first molars from a typodont were prepared with 1-mm chamfer, 2-mm occlusal reduction, and total taper of 8 degrees to receive three-unit FDPs. After framework design, data were sent to a laser machine, and 30 specimens were fabricated from Co-Cr metal powder by SLM. Specimens were assigned to three groups (n = 10 per group) with different build angles of 0 (A0), 30 (A30), and 45 (A45) degrees. Marginal and internal fit were evaluated. Results were compared among build orientation groups and abutments. Data were analyzed using the Levene test, t test, and analysis of variance (α = .05). RESULTS: A statistical difference was found between different angle groups (P = .015). At the abutment level, a significant difference was found in the gap values between build orientation groups for the molars (P = .048). Group A0 reported the smallest mean discrepancy values, and group A45 the highest. Statistical differences were found between group A45 and groups A0 (P < .001) and A30 (P < .024). CONCLUSIONS: The fit of printed metal FDPs was affected by the build orientation but remained clinically acceptable.

The impact of femoral head size on the wear evolution at contacting surfaces of total hip prostheses: A finite element analysis.

Total Hip Arthroplasty has been a revolutionary technique in restoring mobility to patients with damaged hip joints. The introduction of modular components of the hip prosthesis allowed for bespoke solutions based on the requirements of the patient. The femoral stem is designed with a conical trunnion to allow for assembly of different femoral head sizes based on surgical requirements. The femoral head diameters for a metal-on-polyethylene hip prosthesis have typically ranged between 22 mm and 36 mm and are typically manufactured using Cobalt-Chromium alloy. A smaller femoral head diameter is associated with lower wear of the polyethylene, however, there is a higher risk of dislocation. In this study, a finite element model of a standard commercial hip arthroplasty prosthesis was modelled with femoral head diameters ranging from 22 mm to 36 mm to investigate the wear evolution and material loss at both contacting surfaces (acetabular cup and femoral stem trunnion). The finite element model, coupled with a validated in-house wear algorithm modelled a human walking for 10 million steps. The results have shown that as the femoral head size increased, the amount of wear on all contacting surfaces increased. As the femoral head diameter increased from 22 mm to 36 mm, the highly cross-linked polyethylene (XLPE) volumetric wear increased by 61% from 98.6 mm3 to 159.5 mm3 while the femoral head taper surface volumetric wear increased by 21% from 4.18 mm3 to 4.95 mm3. This study has provided an insight into the amount of increased wear as the femoral head size increased which can highlight the life span of these prostheses in the human body.

Analysis of subgingival microbiota and IL-1ß, TNF-α and CX3CL1 levels in gingival crevicular fluid of fixed dental prostheses.

Prosthetic biomaterials can affect the composition of the subgingival microbiota and consequently the production of proinflammatory cytokines, causing damage to the periodontium. A total of 40 patients were divided into two groups: 20 with monolithic zirconia (MZ) prostheses and 20 with porcelain fused to metal (PFM) with nickel-chromium (Ni-Cr) alloy prostheses. Subgingival plaque and gingival crevicular fluid samples were taken. The Checkerboard technique for DNA-DNA hybridization and the enzyme-linked immunosorbent assay technique were performed. Teeth with MZ presented a lower percentage of bleeding on probing and tooth mobility compared to teeth with PFM with Ni-Cr alloy. Prosthodontic teeth harbored higher total levels of the 18 bacterial species than non-prosthodontic teeth. There was a higher prevalence of S. gordonii and V. parvula species in PFM with Ni-Cr alloy compared to MZ. There was an increase in IL-1ß, TNF-α and CX3CL1 levels in PFM with Ni-Cr alloy compared to MZ. MZ is a candidate biomaterial with fewer negative effects on the periodontium, allowing for longer prostheses longevity in the mouth.

Long-term polyethylene wear rates and clinical outcomes of oxidized zirconium femoral heads on highly cross-linked polyethylene in total hip arthroplasty.

Aims: Oxidized zirconium (OxZi) and highly cross-linked polyethylene (HXLPE) were developed to minimize wear and risk of osteolysis in total hip arthroplasty (THA). However, retrieval studies have shown that scratched femoral heads may lead to runaway wear, and few reports of long-term results have been published. The purpose of this investigation is to report minimum ten-year wear rates and clinical outcomes of THA with OxZi femoral heads on HXLPE, and to compare them with a retrospective control group of cobalt chrome (CoCr) or ceramic heads on HXLPE. Methods: From 2003 to 2006, 108 THAs were performed on 96 patients using an OxZi head with a HXLPE liner with minimum ten-year follow-up. Harris Hip Scores (HHS) were collected preoperatively and at the most recent follow-up (mean 13.3 years). Linear and volumetric liner wear was measured on radiographs of 85 hips with a minimum ten-year follow-up (mean 14.5 years). This was compared to a retrospective control group of 45 THAs using ceramic or CoCr heads from October 1999 to February 2005, with a minimum of ten years' follow-up. Results: Average HHS improved from 50.8 to 91.9 and 51.0 to 89.8 in the OxZi group and control group, respectively (p = 0.644), with no osteolysis in either group. Linear and volumetric wear rates in the OxZi group averaged 0.03 mm/year and 3.46 mm3/year, respectively. There was no statistically significant difference in HHS scores, nor in linear or volumetric wear rate between the groups, and no revision for any indication. Conclusion: The radiological and clinical outcomes, and survivorship of THA with OxZi femoral heads and HXLPE liners, were excellent, and comparable to CoCr or ceramic heads at minimum ten-year follow-up. Wear rates are below what would be expected for development of osteolysis. OxZi-HXLPE is a durable bearing couple with excellent long-term outcomes.

Efficient removal and transformation of Cr(VI) from alkaline wastewater to form a ferrochromium spinel multiphase via a modified ferrite process.

Chromium-containing wastewater causes serious environmental pollution due to the harmfulness of Cr(VI). The ferrite process is typically used to treat chromium-containing wastewater and recycle the valuable chromium metal. However, the current ferrite process is unable to fully transform Cr(VI) into chromium ferrite under mild reaction conditions. This paper proposes a novel ferrite process to treat chromium-containing wastewater and recover valuable chromium metal. The process combines FeSO4 reduction and hydrothermal treatment to remove Cr(VI) and form chromium ferrite composites. The Cr(VI) concentration in the wastewater was reduced from 1040 mg L-1 to 0.035 mg L-1, and the Cr(VI) leaching toxicity of the precipitate was 0.21 mg L-1 under optimal hydrothermal conditions. The precipitate consisted of micron-sized ferrochromium spinel multiphase with polyhedral structure. The mechanism of Cr(VI) removal involved three steps: 1) partial oxidation of FeSO4 to Fe(III) hydroxide and oxy-hydroxide; 2) reduction of Cr(VI) by FeSO4 to Cr(III) and Fe(III) precipitates; 3) transformation and growth of the precipitates into chromium ferrite composites. This process meets the release standards of industrial wastewater and hazardous waste and can improve the efficiency of the ferrite process for toxic heavy metal removal.

[Mitigating metal artifacts from cobalt-chromium alloy crowns in cone-beam CT images through deep learning techniques].

Objective: To develop and evaluate metal artifact removal systems (MARS) based on deep learning to assess their effectiveness in removing artifacts caused by different thicknesses of metals in cone-beam CT (CBCT) images. Methods: A full-mouth standard model (60 mm×75 mm×110 mm) was three-dimensional (3D) printed using photosensitive resin. The model included a removable and replaceable target tooth position where cobalt-chromium alloy crowns with varying thicknesses were inserted to generate matched CBCT images. The artifacts resulting from cobalt-chromium alloys with different thicknesses were evaluated using the structural similarity index measure (SSIM) and peak signal-to-noise ratio (PSNR). CNN-MARS and U-net-MARS were developed using a convolutional neural network and U-net architecture, respectively. The effectiveness of both MARSs were assessed through visualization and by measuring SSIM and PSNR values. The SSIM and PSNR values were statistically analyzed using one-way analysis of variance (α=0.05). Results: Significant differences were observed in the range of artifacts produced by different thicknesses of cobalt-chromium alloys (all P<0.05), with 1 mm resulting in the least artifacts. The SSIM values for specimens with thicknesses of 1.0, 1.5, and 2.0 mm were 0.916±0.019, 0.873±0.010, and 0.833±0.010, respectively (F=447.89, P<0.001). The corresponding PSNR values were 20.834±1.176, 17.002±0.427, and 14.673±0.429, respectively (F=796.51, P<0.001). After applying CNN-MARS and U-net-MARS to artifact removal, the SSIM and PSNR values significantly increased for images with the same thickness of metal (both P<0.05). When using the CNN-MARS for artifact removal, the SSIM values for 1.0, 1.5 and 2.0 mm were 0.938±0.023, 0.930±0.029, and 0.928±0.020 (F=2.22, P=0.112), while the PSNR values were 30.938±1.495, 30.578±2.154 and 30.553±2.355 (F=0.54, P=0.585). When using the U-net-MARS for artifact removal, the SSIM values for 1.0, 1.5 and 2.0 mm were 0.930±0.024, 0.932±0.017 and 0.930±0.012 (F=0.24, P=0.788), and the PSNR values were 30.291±0.934, 30.351±1.002 and 30.271±1.143 (F=0.07, P=0.929). No significant differences were found in SSIM and PSNR values after artifact removal using CNN-MARS and U-net-MARS for different thicknesses of cobalt-chromium alloys (all P>0.05). Visualization demonstrated a high degree of similarity between the images before and after artifact removal using both MARS. However, CNN-MARS displayed clearer metal edges and preserved more tissue details when compared with U-net-MARS. Conclusions: Both the CNN-MARS and U-net-MARS models developed in this study effectively remove the metal artifacts and enhance the image quality. CNN-MARS exhibited an advantage in restoring tissue structure information around the artifacts compared to U-net-MARS.

Comparative analysis of the retention force and deformation of PEEK and PEKK removable partial denture clasps with different thicknesses and undercut depths.

STATEMENT OF PROBLEM: The retentive force and deformation of milled polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) removable partial denture (RPD) frameworks are not well understood. PURPOSE: The purpose of this in vitro study was to assess the retentive force and deformation of PEEK and PEKK Akers clasps with different designs and undercut depths. MATERIAL AND METHODS: A master model containing the first and second molar abutments was used to design Akers clasps of different cross-sectional dimensions, undercut depths (0.5 and 0.75 mm), and materials. The components of the removable partial denture framework also included an occlusal rest and were manufactured using a milling machine (n=5). The fatigue resistance of the Akers clasps was measured before and after deformation regarding the retentive forces. RESULTS: The PEEK2-U50 clasp had the largest retentive force with no significant difference among all groups before and after the insertion and removal cycle. In addition, the increased cross-sectional dimensions of the design resulted in significant differences in retentive forces between the PEEK1 and PEEK2 groups and between the PEEK and PEKK materials. CONCLUSIONS: Increasing the clasp's cross-sectional dimensions significantly impacted retentive forces, especially between different PEEK groups and between PEEK and PEKK materials.

Role of femoral head material on readmission and mortality rates following elective primary total hip arthroplasty in Medicare patients.

INTRODUCTION: The role of different femoral head materials for total hip arthroplasty (THA) has been widely studied in the context of wear properties and corrosion. Cobalt chrome (CoCr) femoral heads are commonly used as a standard of comparison to other materials such as ceramic and oxidized zirconium (OxZi). This study aims to evaluate the impact of femoral head material on clinical outcomes in elective primary THA patients. METHODS: Retrospective analysis of THA patients within the Medicare claims database between October 2017 and September 2020 using diagnosis-related group codes was conducted. Information collected included sex, age, Charlson Comorbidity Index, and femoral head type. Patients with CoCr femoral heads were compared against patients with either OxZi or ceramic femoral heads using 1:1 propensity score matching. Z-testing and Chi-square analysis were used to determine between-group significance. RESULTS: In total, 112,960 elective THA patients were included, with 56,480 in OxZi or ceramic and 56,480 in CoCr. Readmission rates were lower in patients that received OxZi or ceramic femoral heads at 30-day (p < 0.0001), 60-day (p < 0.0001), and 90-day postoperatively (p < 0.0001) compared to CoCr. Mortality rates were also lower in patients that received OxZi or ceramic femoral heads at 30-day (p = 0.004), 60-day (p = 0.018), and 90-day postoperatively (p = 0.009) compared to CoCr. CONCLUSION: CoCr femoral heads had higher rates of readmissions and mortality compared to OxZi or ceramic. Further analysis of bearing surface combinations and sub-group analyses to determine significance between-group differences is needed. LEVEL III EVIDENCE: Retrospective analysis.

Wear at the implant-framework interface between titanium implant platform and the additively manufactured titanium and cobalt-chromium frameworks.

PURPOSE: To measure the wear at the implant interface between the Grade 4 titanium (Ti) of the implant and frameworks fabricated using two additively manufactured alloys (Ti alloy and cobalt-chromium [Co-Cr]) pre- and post-artificial aging. MATERIAL AND METHODS: Three-unit frameworks supported by two implants were additively manufactured (Atlantis; Dentsply Sirona) using Ti and Co-Cr dental alloys. Two implants (OsseoSpeed EV, Astra Tech; Dentsply Sirona) were torqued on each non-engaging framework. The assembled implant-frameworks were secured into polyurethane foam blocks. Groups were created based on the material and surface assessed: framework (Ti-framework and Co-Cr-framework groups) and implant (Ti-implant group). Two subgroups were created depending on the location: premolar (PM) and molar (M). Computed tomography images were obtained pre- (as manufactured) and post-simulated mastication procedures. The pre- and post-simulated mastication files of each specimen were aligned using the best-fit algorithm using a metrology program. Wear was measured by calculating the volumetric discrepancies at the implant interface on 64 measurement points per area analyzed. Three-way ANOVA and Tukey tests were used to analyze the data (α = 0.05). RESULTS: The mean volumetric discrepancy values ranged from 0.8 to 3.1 µm among all the subgroups tested. The group (framework vs. implant) (p < 0.001) and tooth location (p < 0.001) were significant factors of the mean volumetric discrepancy values obtained. The framework group presented with significantly lower volumetric discrepancy mean values (1 µm) compared with the implant group (3 µm), whereas the premolar area obtained significantly lower mean volumetric discrepancy values (1.9 µm) compared with the molar location (2.3 µm). CONCLUSIONS: Volumetric discrepancies were found at the implant-framework interface tested between the pre- and post-artificial aging measurements ranging from 1 to 3 µm after 1,200,000 cyclic loading that simulated approximately 12 months of function.

Biomechanical Analysis of 2 Versus 4 Rods Across the Cervicothoracic Junction in a Human Cadaveric Model.

BACKGROUND AND OBJECTIVES: Posterior reconstruction of the cervicothoracic junction poses significant biomechanical challenges secondary to transition from the mobile cervical to rigid thoracic spines and change in alignment from lordosis to kyphosis. After destabilization, the objectives of the current investigation were to compare the rod strain and multidirectional flexibility properties of the cervicothoracic junction using a 4-rod vs traditional 2-rod reconstructions. METHODS: Ten human cadaveric cervicothoracic specimens underwent multidirectional flexibility testing including flexion-extension, lateral bending, and axial rotation. After intact analysis, specimens were destabilized from C4 to T3 and instrumented from C3 to T4. The following reconstructions were tested: (1) 3.5-mm titanium (Ti) 2-rod, (2) 3.5-mm Ti 4-rod, (3) 4.0-mm cobalt chrome (CoCr) 2-rod, (4) 4.0-mm CoCr 4-rod, and (5) Ti 3.5- to 5.5-mm tapered rod reconstructions. The operative level range of motion and rod strain of the primary and accessory rods were quantified. RESULTS: The addition of accessory rods to a traditional 2-rod construct improved the biomechanical stability of the reconstructions in all three loading modalities for Ti ( P < .05). The accessory CoCr rods improved stability in flexion-extension and axial rotation ( P < .05). The addition of accessory rods in Ti or CoCr reconstructions did not significantly reduce rod strain ( P < .05). CoCr 2 and 4 rods exhibited less strain than both Ti 2 and 4 rods. CONCLUSION: Supplemental accessory rods affixed to traditional 2-rod constructs significantly improved stability of Ti alloys and CoCr alloy materials. The 4.0-mm CoCr rods provided greater stability than 3.5-mm Ti rods in flexion-extension, lateral bending, and axial rotation. While rod strain was not significantly reduced by the addition of accessory rods, it was reduced in CoCr rod treatment groups compared with the Ti rods.

Outcomes of resin-bonded attachments for removable dental prostheses.

PURPOSE: This clinical study aimed to evaluate the outcomes of resin-bonded attachments (RBAs) for precision-retained removable dental prostheses (RDPs) after at least two years of clinical maintenance. METHODS: Since December 1998, 205 RBAs (44 bonded to posterior teeth, 161 to anterior teeth) have been inserted in 123 patients (62 females and 61 males; mean age, 63.6 ± 9.6 years) who were recalled annually. The abutment teeth underwent a minimally invasive preparation limited to the enamel. RBAs were cast in a cobalt-chromium alloy with a minimum thickness of 0.5 mm and adhesively luted with a luting composite resin (Panavia 21 Ex or Panavia V5, Kuraray, Japan). We evaluated caries activity, plaque index, periodontal condition, and tooth vitality. The Kaplan-Meier survival curves were used to account for the reasons for failure. RESULTS: The mean observation time of RBAs until the last recall visit was 84.5 ± 51.3 months (range, 3.6-270.6). During the observation period, 33 RBAs debonded in 27 patients (16.1%). The 10-year success rate according to the Kaplan-Meier analysis was 58.4%, which dropped to 46.2% after 15 years of observation if debonding was considered a failure. If rebonded RBAs were regarded as surviving, the 10- and 15-year survival rates would be 68.3% and 61%, respectively. CONCLUSIONS: The use of RBAs for precision-retained RDPs appears to be a promising alternative to conventionally retained RDPs. As reported in the literature, the survival rate and frequency of complications were comparable with those of conventional crown-retained attachments for RDPs.

Fusion machine learning model predicts CAD-CAM ceramic colors and the corresponding minimal thicknesses over various clinical backgrounds.

OBJECTIVES: This study has developed and optimized a machine learning model to accurately predict the final colors of CAD-CAM ceramics and determine their required minimum thicknesses to cover different clinical backgrounds. METHODS: A total of 120 ceramic specimens (2 mm, 1 mm and 0.5 mm thickness; n = 10) of four CAD-CAM ceramics - IPS e.max, IPS ZirCAD, Upcera Li CAD and Upcera TT CAD - were studied. The CIELab coordinates (L*, a* and b*) of each specimen were obtained over seven different clinical backgrounds (A1, A2, A3.5, ND2, ND7, cobalt-chromium alloy (CC) and medium precious alloy (MPA)) using a digital spectrophotometer. The color difference (ΔE) and lightness difference (ΔL) results were submitted to 39 different models. The prediction results from the top-performing models were used to develop a fusion model via the Stacking integrated learning method for best-fitting prediction. The SHapley Additive exPlanation (SHAP) was performed to interpret the feature importance. RESULTS: The fusion model, which combined the ExtraTreesRegressor (ET) and XGBRegressor (XGB) models, demonstrated minimal prediction errors (R2 = 0.9) in the external testing sets. Among the investigated variables, thickness and background colors (CC and MPA) majorly influenced the final color of restoration. To achieve perfect aesthetic restoration (ΔE<2.6), at least 1.9 mm IPS ZirCAD or 1.6 mm Upcera TT CAD were required to cover the CC background, while two tested glass-ceramics did not meet the requirements even with thicknesses over 2 mm. SIGNIFICANCE: The fusion model provided a promising tool for automate decision-making in material selection with minimal thickness over various clinical background.

Estudo in vitro de microdeformações ósseas comparando infraestruturas para próteses do tipo protocolo: impacto dos materiais cobalto-cromo e fibra de vidro reforçada com compósito / In vitro study of bone microdeformations comparing infrastructures for protocol-type prostheses: impact of cobalt-chrome materials and fiberglass reinforced with composite

Este estudo investigou a eficácia biomecânica de infraestruturas de próteses feitas de cobalto-cromo (CoCr) e compósito de fibra de vidro (FVRC), implantadas em mandíbulas edêntulas. A distribuição de densidade foi investigada utilizando um modelo ósseo sintético, equipado com extensômetros, para simular condições anatômicas e biomecânicas humanas. Os implantes de conexão interna cone morse fabricados pela Conexão Sistemas de Próteses, Arujá, São Paulo, Brasil, têm diâmetro e comprimento de 4.0mm e 13mm, respectivamente, e os intermediários protéticos selecionados foram Micro Unit Sólidos da mesma marca para plataforma cone morse, com altura de transmucoso 2,5 mm, foram utilizados para suportar as infraestruturas de próteses híbridas. Por meio de extensometria, mediu-se a deformação óssea sob carga ao redor dos quatro implantes, comparando as performances das infraestruturas CoCr e FVRC. Os resultados revelaram informações importantes sobre a seleção de materiais para infraestruturas de próteses, com foco específico nas barras de FVRC e CoCr. Os testes "in vitro" e análises estatísticas destacaram que as barras de FVRC produziram menores microdeformações em comparação com as de CoCr sob carga. Essa diferença foi estatisticamente significativa, indicando que a FVRC possui uma capacidade superior de absorver e distribuir carga de maneira mais eficiente. No entanto, ressalta-se a necessidade de estudos futuros, incluindo pesquisas clínicas, para explorar totalmente as implicações desses achados e aprimorar ainda mais as práticas de reabilitação oral com implantes (AU)

This study investigated the biomechanical effectiveness of prosthetic infrastructures made of cobalt-chromium (CoCr) and fiberglass composite (FGC), implanted in edentulous jaws. The density distribution was investigated using a synthetic bone model, equipped with strain gauges, to simulate human anatomical and biomechanical conditions. The morse cone internal connection implants manufactured by Conexão Sistemas de Próteses, Arujá, São Paulo, Brazil, have a length of 4.0mm and 13mm, respectively, and the prosthetic intermediates selected were Micro Unit Solids of the same brand for a morse cone platform, with a transmucosal height of 2.5 mm, were used to support hybrid prosthetic infrastructures. Using extensometry, bone deformation under load around the four implants was measured, comparing with the performance of the CoCr and FGC infrastructures. The results revealed important information about the selection of materials for prosthetic infrastructures, with a specific focus on FGC and CoCr bars. "In vitro" tests and statistical analyzes highlighted that FGC bars produced smaller microdeformations compared to CoCr bars under load. This difference was statistically significant, demonstrating that FGC has a superior capacity to absorb and distribute load more efficiently. However, the need for future studies, including clinical research, is highlighted to fully explore the implications of these findings and further improve oral rehabilitation practices with implants. (AU)

[Effect of 4 kinds of prosthodontic materials on masticatory and gingival function].

PURPOSE: To investigate the effect of 4 kinds of prosthodontic materials on masticatory and gingival function. METHODS: A total of 167 patients with dental defects who underwent prosthodontic treatment from October 2019 to January 2022 were collected. They were randomly divided into 4 groups with 41 cases in the pure titanium group, 40 cases in the cobalt-chromium alloy group, 43 cases in the nickel-chromium alloy group and 43 cases in the zirconium dioxide group. The curative effect and satisfaction degree after 6 months of treatment in 4 groups were recorded and compared. The masticatory function (chewing efficiency, bite force), gingival function[plaque index(PLI), gingival index(GI) and sulcus bleeding index(SBI)], gingival crevicular fluid inflammation-related indicators[tumor necrosis factor alpha(TNF-α), interleukin-6(IL-6), aspartate aminotransferase(AST) and alkaline phosphatase (alkaline phosphatase, ALP)] before and after treatment were measured and compared in 4 groups. Statistical analysis was performed with SPSS 20.0 software package. RESULTS: There was no significant difference in curative effect in 4 groups(P＞0.05). Before and after treatment, there was no significant difference in mastication efficiency and bite force in 4 groups(P＞0.05). Before treatment, there was no significant difference in PLI, GI, SBI, gingival crevicular fluid weight, TNF-α, IL-6, AST and ALP in gingival crevicular fluid in 4 groups(P＞0.05). Compared with before treatment, PLI, GI and SBI in 4 groups were decreased after treatment (P＜0.05), and the decrease was in the order of cobalt-chromium alloy group≈nickel-chromium alloy group＜pure titanium group＜zirconia dioxide group. Before treatment, there was no significant difference in the weight of gingival crevicular fluid, TNF-α, IL-6, AST and ALP in gingival crevicular fluid in 4 groups(P＞0.05). The crevicular fluid weight, TNF-α, IL-6, AST and ALP in gingival crevicular fluid were significantly increased(P＜0.05), and the increase was in the order of zirconia group＜pure titanium group＜cobalt-chromium alloy group≈nickel-chromium alloy group. There was no significant difference in restoration integrity and color satisfaction in 4 groups(P＞0.05), but there was significant difference in marginal fitness and sensitivity satisfaction in 4 groups(P＜0.05). CONCLUSIONS: Pure titanium, cobalt-chromium alloy, nickel-chromium alloy and zirconium dioxide can be used for the treatment of dentition defects, and they all can obtain satisfactory chewing function. In addition, zirconium dioxide restoration has the effect of improving gingival function and inflammation-related indicators of gingival crevicular fluid with a broader application prospect.

Accuracy of fit for cobaltchromium bar over two implants fabricated with different manufacturing techniques: an in-vitro study.

OBJECTIVE: The purpose of the invitro research was to compare the fit of Cobalt Chromium customized bar fabricated with different manufacturing processes cast metal bar, milled bar and 3D printed bar using scanning electron microscope. MATERIALS AND METHODS: Clear epoxy resin molds were prepared. In each mold two parallel implants with a 14 mm distance from each other were embedded. Thirty Co-Cr custom bars were constructed and were divided equally into three groups: Group (I) (Co-Cr conv), group (II) milled bar (Co-Cr milled), and group (III) printed bar (Co-Cr print). The marginal fit at implant-abutment interface was scanned using scanning electron microscope (SEM). RESULTS: There was a significant difference between the three studied groups regarding marginal misfit the between implant and fabricated bars with p-value < 0.001. The highest value of micro-gap distance was found in Co-Cr conventional group (7.95 ± 2.21 µm) followed by Co-Cr 3D printed group (4.98 ± 1.73) and the lower value were found in Co-Cr milled (3.22 ± 0.75). CONCLUSION: The marginal fit of milled, 3D printed and conventional cast for Co-Cr alloy were within the clinically acceptable range of misfit. CAD/CAM milled Co-Cr bar revealed a superior internal fit at the implant-abutment interface. This was followed by selective laser melting (SLM) 3D printed bar and the least fit was shown for customized bar with the conventional lost wax technique.