Longitudinal Observation of Micromotion upon Loading of Implant-Abutment Connection.

While technological advances have made implants a good treatment option with a good long-term prognosis, peri-implantitis, which results in alveolar bone resorption around implants, has been observed in some cases. Micromotion at the implant abutment connection can cause peri-implantitis. However, the temporal progression of micromotion upon loading remains unclear. Therefore, we aimed to longitudinally measure micromotion upon loading application on an implant. Implants with Morse-tapered connections were prepared. Custom titanium abutments were fabricated and tightened onto implant bodies at 35 N. A 100 N vertical load was applied for 200,000 cycles. Micromotion was measured when the load was applied, as was the total implant length and removal torque before and after loading. The micromotion was measured from the position data of the jig of the testing machine during loading. The average removal torque was 30.67 N after 10 min of tightening and 27.95 N after loading, indicating a decrease due to loading. The implant length reduced by 3.6 µm under the load. The average micromotion was 0.018 mm at 2 cycles, 0.016 mm at 100,000 cycles, and 0.0157 mm at 200,000 cycles, indicating implant length reduction under the load but not reaching 0. The micromotion between the implant and abutment under a cyclic load decreased over time but did not completely cease. These results highlight the relationship between micromotion and loading, underscoring the importance of careful monitoring and management to mitigate potential complications, such as peri-implantitis, and ensure optimal performance and durability of the implant.

A Study of the Associated Risk Factors for Early Failure and the Effect of Photofunctionalisation in Full-Arch Immediate Loading Treatment Based on the All-on-Four Concept.

Early implant failure occurring within 1 year after implantation has been attributed to various factors. Particularly, early failure can lead to challenges in maintaining a full-arch prosthetic device, necessitating prompt intervention, including reoperation. This study aimed to retrospectively examine implant- and patient-related factors and the effects of photofunctionalisation associated with early failure in patients who underwent treatment using the all-on-four concept in both the maxilla and mandible. We conducted this retrospective study comprising 561 patients with 2364 implants who underwent implant-supported immediate loading with fixed full-arch rehabilitation using the all-on-four concept. We aimed to assess the survival rate within 1 year after implantation and determine the risk factors influencing early failure. The 1-year survival rates after implantation were 97.1% (patient level) and 98.9% (implant level) for the maxilla and 98.5% (patient level) and 99.6% (implant level) for the mandible. There was a significant difference in the implant-level survival rates between the maxilla and mandible, with a lower rate in the maxilla (p = 0.043). The risk factors associated with early implant failure according to the all-on-four concept included the maxilla (implant level) and smoking (patient level). We could not find a significant effect of photofunctionalisation on early failure (p = 0.25) following this treatment protocol.

Risk Factors for Early Implant Failure and Selection of Bone Grafting Materials for Various Bone Augmentation Procedures: A Narrative Review.

Implant therapy is now an established treatment with high long-term success and survival rates. However, early implant failure, which occurs within one year of superstructure placement, occurs at a higher rate than late failure, which is represented by peri-implantitis caused by bacterial infection. Furthermore, various risk factors for early failure have been reported, including patient-related factors, such as systemic diseases, smoking, and bone quality and quantity, as well as surgery-related factors, such as surgeons' skill, osteogenesis technique, and selection of graft material, and implant-related factors, such as initial implant fixation and implant length diameter. Due to the wide variety of relevant factors reported, it is difficult to identify the cause of the problem. The purpose of this review is to discuss the risk factors associated with various types of bone augmentation which have a close causal relationship with early implant failure, and to determine the optimal bone grafting material for bone augmentation procedures to avoid early implant failure.

Bacterial Flora in Screw-Fixed Superstructures with Different Sealing Materials: A Comparative Clinical Trial.

A screw-fixed superstructure is predominantly selected for implant prostheses because of the concern regarding developing peri-implantitis, although its infection route remains unclear. Focusing on microleakage from access holes, the present study clinically investigated the bacterial flora in access holes with different sealing materials. We examined 38 sites in 19 patients with two adjacent screw-fixed superstructures. Composite resin was used in the control group, and zinc-containing glass ionomer cement was used in the test group. Bacteria were collected from the access holes 28 days after superstructure placement and were subjected to DNA hybridization analysis. The same patient comparisons of the bacterial counts showed a significant decrease in 14 bacterial species for the red, yellow, and purple complexes in the test group (p < 0.05). In addition, the same patient comparisons of the bacterial ratios showed a significant decrease in six bacterial species for the orange, green, yellow, and purple complexes in the test group (p < 0.05). Furthermore, the same patient comparisons of the implant positivity rates showed a significant decrease in the six bacterial species for the orange, yellow, and purple complexes in the test group. The results of this study indicate that zinc-containing glass ionomer cement is effective as a sealing material for access holes.

The All-on-four concept for fixed full-arch rehabilitation of the edentulous maxilla and mandible: a longitudinal study in Japanese patients with 3-17-year follow-up and analysis of risk factors for survival rate.

PURPOSE: Implant-supported immediately loaded fixed full-arch rehabilitation via All-on-four treatment yields good long-term results for both the maxilla and the mandible. However, the risk factors affecting long-term implant survival are unknown, and the long-term prognosis of All-on-four concept procedures in Japanese individuals has not been elucidated. We aimed to determine the cumulative implant survival rate after 3-17-year follow-up and identify the associated risk factors. METHODS: We analysed 561 cases (307 maxillae, 254 mandibles) with 2364 implants (1324 maxillae, 1040 mandibles) that received All-on-four treatment. We investigated the cumulative implant- and patient-level survival rates and various risk factors for implant failure. Statistical analysis was performed using the log-rank test for differences in Kaplan-Meier curves, univariate analysis using the Chi-square test, and multivariate analysis for risk factors affecting the survival rate. RESULTS: The cumulative survival rate was 94.4% by patient level and 97.4% by implant level for the maxilla, and 96.7% by patient level and 98.9% by implant for the mandible, with up to 17 years of follow-up. The maxillary survival rate at the implant level was significantly lower (p < 0.05). Furthermore, the maxillary survival rate within 24 months was significantly lower at the implant level (p < 0.01). Multivariate analysis revealed that the maxilla was the most significant risk factor (p < 0.01). CONCLUSIONS: All-on-four treatment yielded high long-term survival rates in Japanese patients. However, the maxilla showed a significantly lower cumulative survival rate than the mandible, while early failure was significantly higher. Furthermore, the maxilla was a significant risk factor influencing the survival rate.

The Effectiveness and Practicality of a Novel Barrier Membrane for the Open Window in Maxillary Sinus Augmentation with a Lateral Approach, with Risk Indicators for Bone Graft Displacement and Bone Height Decrease: A Prospective Study in Humans.

Maxillary sinus augmentation with a lateral approach (MSA) is a well-established treatment. In this prospective study, we evaluated risk factors for postoperative bone graft displacement and reported the clinical application of long-term resorbable L-lactic acid/-caprolactone (PLA/PCL) as a barrier membrane to cover the open window in the lateral wall in MSA. Twenty-four patients underwent MSA according to the relevant criteria; CT data obtained before and 1 week (1 w) and 5-6 months (5 m) post-MSA, bone height changes, bone height reduction rates at 1 w and 5 m post-MSA, bone graft displacement measurements, and risk factors were examined. All patients showed bone height increments (p < 0.005). However, no difference was observed between 1 w and 5 m post-MSA. Bone graft displacement was observed in eight patients; the reduction rate from 1 w to 5 m post-MSA was 8.38% ± 4.88%. Sex, septa, maxillary sinus floor-palatal bone distance, and maxillary sinus floor-maxillary ostium distance were associated with bone graft displacement (p < 0.05). The height from the maxillary sinus floor to the palatal bone and the sinus angle influenced the augmentation degree (p < 0.05). The PLA/PCL membrane is compared favorably with other membranes and may be useful as a barrier membrane for the MSA open window.

Effects of implant surface mechanical instrumentation methods on peri-implantitis: An in vitro study using a circumferential bone defect model.

Background/purpose: Although several mechanical and chemical debridement techniques have been reported for the management of peri-implantitis, there is no consensus on the most effective method at present. This in vitro study aimed to examine the effects of different mechanical instrumentation techniques on the debridement of hard calcified materials, which are present on the implant surface, as well as the effect of the defect morphology. Materials and methods: From a total of 15 implants, five each were assigned to one of three decontamination groups (Rotary titanium brush [Ti], tricalcium phosphate air powder abrasive treatment [Air], and titanium ultrasonic scaler [US] groups); the exposed hydroxyapatite (HA)-coated portion was divided into three 1-mm sections (coronal, middle, and apical). The residual-HA of each portion was measured using a digital microscope. Results: The overall percentage of residual HA coating was significantly lower in the US group than in the Ti or Air groups (p < 0.01). The percentage of residual HA in the coronal portion was significantly lower in the Ti and US groups than in the Air group (p < 0.05 and p < 0.01, respectively). The percentage of residual HA in the middle portion was significantly lower in the US group than in the Air group (p < 0.01). The percentage of residual HA in the apical portion was significantly lower in the Ti group than in the Air or US groups (p < 0.01). Conclusion: Ti and US were more effective for shallow defects, whereas US was more effective for deeper defects.

Effects of missing teeth and nasal septal deviation on maxillary sinus volume: a pilot study.

PURPOSE: Tooth extraction and the projection of the tooth roots into the maxillary sinus are reported to greatly reduce the bone height from the alveolar ridge to the maxillary sinus floor, while missing teeth are reported to lead to the expansion of the maxillary sinus, all of which are important considerations during dental implant treatment for the maxillary molar region. Therefore, assessing the anatomical characteristics of the maxillary sinus acting as complicating factors is crucial before sinus augmentation. We conducted a three-dimensional examination of the effects of missing teeth and nasal septal deviation (NSD) on maxillary sinus volume (MSV). METHODS: We selected participants with two or more missing teeth from patients who underwent maxillary sinus augmentation for a unilateral free-end saddle between April 2019 and December 2020. We calculated the MSV and NSD using cone-beam computed tomography (CBCT). We compared the relationships of the presence/absence of teeth and NSD with MSV bilaterally in each patient using the Wilcoxon t-test. p-values < 0.05 denoted statistical significance. RESULTS: This study included 30 patients (30 sinuses; 12 men, 18 women). The average patient age was 58.2 ± 10.2 years (men, 60.4 ± 3.7 years; women, 59.2 ± 4.5 years; range, 40-77 years). The mean number of missing teeth was 2.98 ± 1.01: 13 patients had two missing teeth and 17 had three or more missing teeth. Nine patients (30%) had NSD. The mean MSV on the ipsilateral and contralateral sides of the NSD was 21.50 ± 3.84 cm3 and 22.10 ± 3.56 cm3, respectively; thus, NSD did not affect MSV (p = 0.150). The mean MSV on the edentulous and non-edentulous sides was 21.58 ± 3.89 cm3 and 21.77 ± 4.30 cm3, respectively; thus, the MSV was significantly smaller on the edentulous side (p = 0.00036). CONCLUSION: Although this study was a limited preoperative study, three-dimensional measurement of the maxillary sinus with CBCT in partially edentulous patients revealed that missing teeth lead to substantial reductions in MSV, while NSD was not associated with MSV.

Variations in vertical mucosal thickness at edentulous ridge according to site and gender measured by cone-beam computed tomography.

BACKGROUND: The vertical thickness of the peri-implant mucosa is associated with the amount of post treatment marginal bone loss. However, the variations in mucosal thickness at the different edentulous sites have been sparsely documented. The purpose of the study was to conduct a survey of the frequency distribution of variations in mucosal thickness at the different sites of the edentulous alveolar ridge and to compare them according to gender. Our study included 125 partially edentulous patients having a total of 296 implant sites. Cone-beam computed tomography (CBCT) scans were obtained by placing a diagnostic template with a radiopaque crown indicator on the ridge to determine the mucosal thickness at the crest of the alveolar ridge. RESULTS: The mucosal thickness was 3.0±1.3 mm in the maxilla, which was significantly greater than the mucosal thickness of 2.0±1.0 mm in the mandible (p<0.001). In both the maxilla and the mandible, the mucosa was the thickest in the anterior region, followed by the premolar and molar regions. Sites were further classified into two groups based on whether the mucosal thickness was greater than 2 mm. In the mandible, more than half of the sites showed a mucosal thickness of 2 mm or less. CONCLUSIONS: Although this study was a limited preoperative study, the vertical mucosal thickness at the edentulous ridge differed between the maxillary and mandibular regions. The majority of sites in the mandibular molar region had a mucosal thickness of less than 2 mm. Practitioners might be able to develop an optimal dental implant treatment plan for long-term biologic and esthetic stability by considering these factors.

Factors influencing the sinus membrane thickness in edentulous regions: a cone-beam computed tomography study.

BACKGROUND: During implant treatment in the maxillary molar area, maxillary sinus floor augmentation is often performed to ameliorate the reduced alveolar bone height attributable to bone remodeling and pneumatization-induced expansion of the maxillary sinus. However, this augmentation may cause complications such as misplaced implants, artery damage, and maxillary sinus mucosal perforation; infections like maxillary sinusitis; and postsurgical complications such as bone graft leakage and postoperative nasal hemorrhaging. To reduce the complications during maxillary sinus floor augmentation and postoperative infections, we performed retrospective investigations of various systemic and local factors that influence pre-operative sinus mucosal thickness (SMT) by using cone-beam computed tomography (CBCT). Subjects included patients who underwent maxillary sinus floor augmentation in an edentulous maxillary molar area with a lateral approach. Pre-operative SMT, existing bone mass, and nasal septum deviation were measured using CBCT images. Relationships between SMT and the following influencing factors were investigated: (1) age, (2) sex, (3) systemic disease, (4) smoking, (5) period after tooth extraction, (6) reason for tooth extraction, (7) residual alveolar bone height (RBH), (8) sinus septa, and (9) nasal septum deviation. Correlations were also investigated for age and RBH (p < 0.05). RESULTS: We assessed 35 patients (40 sinuses; 11 male, 24 female). The average patient age was 58.90 ± 9.0 years (males, 57.9 ± 7.7 years; females, 59.9 ± 9.4 years; age range, 41-79 years). The average SMT was 1.09 ± 1.30 mm, incidence of SMT > 2 mm was 25.0%, incidence of SMT < 0.8 mm was 50.0%, and the average RBH was 2.14 ± 1.02 mm. The factors that influenced SMT included sex (p = 0.0078), period after tooth extraction (p = 0.0075), reason for tooth extraction (p = 0.020), sinus septa (p = 0.0076), and nasal septum deviation (p = 0.038). CONCLUSIONS: Factors associated with higher SMT included male sex, interval following tooth extraction < 6 months, periapical lesions, sinus septa, and nasal septum deviation. Factors associated with SMT > 2 mm were sex and reason for tooth extraction, while factors associated with SMT < 0.8 mm were time following tooth extraction and nasal septum deviation. Despite the limitations of this study, these preoperative evaluations may be of utmost importance for safely conducting maxillary sinus floor augmentation.

Influence of the Conditioning Method for Pre-Sintered Zirconia on the Shear Bond Strength of Bilayered Porcelain/Zirconia.

This study evaluated the bond strength of veneering porcelain with an experimental conditioner-coated zirconia. Pre-sintered Y-TZP specimens (n = 44) were divided in two groups based on conditioning type. After sintering, all sample surfaces were sandblasted and layered with veneering porcelain. Additionally, half of the specimens in each group underwent thermal cycling (10,000 cycles, 5-55 °C), and all shear bond strengths were measured. After testing, the failure mode of each fractured specimen was determined. Differences were tested by parametric and Fisher's exact tests (α = 0.05). The differences in bond strength were not statistically significant. Adhesive fractures were dominantly observed for the non-thermal cycled specimens. After thermal cycling, the conditioner-coated group showed cohesive and mixed fractures (p = 0.0021), whereas the uncoated group showed more adhesive fractures (p = 0.0021). Conditioning of the pre-sintered Y-TZP did not change the shear bond strength of the veneering porcelain, but did improve the failure mode after thermal cycling.

Influence of the rigidity of a provisional restoration supported on four immediately loaded implants in the edentulous maxilla on biomechanical bone-implant interactions under simulated bruxism conditions: a three-dimensional finite element analysis.

PURPOSE: The aims of this study were to (1) establish a biomechanical model that simulates the full-arch restoration supported by immediately loaded implants, which is customized for individual patients, and (2) clarify the effect of the implant placement and rigidity of a provisional restoration on the biomechanical response at the bone-implant interface. MATERIALS AND METHODS: Three-dimensional finite element analysis models of a maxillary full-arch prosthesis supported by four immediately loaded implants were created from computed tomography data of maxillary edentulous patients. Displacements of the implants and equivalent stress on the bone around the implants under the loading conditions that simulated sleep bruxism were then calculated for these models. The effects of the implant placement angle (vertical or inclined), the reinforcement of the provisional restoration (with or without reinforcement), and the implant length on the maximum displacements of each implant were investigated, in addition to the average equivalent stress of the bone around the implant. RESULTS: A longer implant and rigid restoration with reinforcement have the potential to reduce implant displacements and associated bone stress; however, the rigidity of the restoration had a much more significant effect on these parameters. CONCLUSIONS: The rigidity of full-arch provisional restorations supported by four immediately loaded implants should be improved by reinforcements, which could ensure the successful achievement of osseointegration by reducing load-induced micromovements of the implants.