Evaluating Streptococcus mutans Colonization on 3D-Printed, Milled, and Conventional Acrylic Resin Materials: An In Vitro Study.

Purpose: To compare surface roughness and bacterial colonization of Streptococcus mutans to 3D printed (3DP), milled (M), and conventional (CV) acrylic resin. Methods: Thirty-six discs (n equals 12 per group) were fabricated from 3DP, M, and CV materials. One surface of sample was polished (Po); the opposite surface was left unpolished (UPo). Surface roughness (µm) was assessed using a contact profilometer. The specimens were placed in S. mutans suspension and incubated at 37 degrees Celsius overnight. The attached colonies were separated using a sonicator, and the resulting solution was diluted to 10-3 to assess colony-forming units per milliliter (CFU/ml) after 48 hours. The colonies were categorized into a quantitative S. mutans (QS) index. Data were analyzed using one-way ANOVA, chi-squares, and multivariate analysis of variance analysis with the least significant difference (LSD) post-hoc test (P<0.05). Results: Roughness average (Ra) values of CV were higher than 3DP and M for UPo surfaces (P<0.001; 3DP=0.10; M=0.13; CV=0.26 µm, respectively). For Po and UPo surfaces, the CV harbored more S. mutans colonies than M and 3DP (P<0.001; 3DP=5.2x10 6 ; M=4.7x10 6 ; CV=1.49x10 7 CFU/ml, respectively). M group had the lowest range of QS scores, while CV had the highest range (P<0.001). Conclusions: Digitally manufactured material provides smoother surfaces than the conventional group, resulting in fewer Streptococcus mutans colonies. However, all the material groups must still be adequately polished to prevent the colonization of S. mutans, regardless of the manufacturing methods, as higher S. mutans counts were observed with an increase in surface roughness values.

Evaluating the effects of splinting implant scan bodies intraorally on the trueness of complete arch digital scans: A clinical study.

STATEMENT OF PROBLEM: A predictable protocol for accurately scanning implants in a complete edentulous arch has not been established. PURPOSE: The purpose of this clinical study was to investigate the effect of splinting implant scan bodies intraorally on the accuracy and scan time for digital scans of edentulous arches. MATERIAL AND METHODS: This single center, nonrandomized, clinical trial included a total of 19 arches. Definitive casts with scan bodies were fabricated and scanned with a laboratory scanner as the reference (control) scan. Each participant received 2 intraoral scans, the first with unsplinted scan bodies and the second with resin-splinted scan bodies. The scan time was also recorded for each scan. To compare the accuracy of the scans, the standard tessellation language (STL) files of the 2 scans were superimposed on the control scan, and positional and angular deviations were analyzed by using a 3-dimensional (3D) metrology software program. The Mann-Whitney U test was used to compare the distance and angular deviations between the splinted group and the unsplinted group with the control. The ANOVA test was conducted to examine the effect of the scan technique on trueness (distance deviation and angular deviation) and scan time (α=.05 for all tests). RESULTS: Statistically significant differences were found in the overall 3D positional and angular deviations of the unsplinted and splinted digital scans when compared with the reference scans (P<.05). No statistically significant differences in overall 3-dimensional positional deviations (P=.644) and angular deviations (P=.665) were found between the splinted and unsplinted experimental groups. A faster scan time was found with the splinted group in the maxillary arch. CONCLUSIONS: Conventional complete arch implant impressions were more accurate than digital complete arch implant scans. Splinting implant scan bodies did not significantly affect the trueness of complete arch digital scans, but splinting appeared to reduce the scan time. However, fabricating the splint was not considered in the time measurement.

Wear Resistance Comparison of Prefabricated Primary Crowns Using a Novel 3D Computed Tomography Method.

PURPOSE: The purpose of this study was to compare the wear resistance of stainless steel crowns, (SSCs), zirconia crowns (ZRCs), and nanohybrid crowns (NHCs) using a 3D tomography method. METHODS: Prefabricated SSCs, ZRCs, and NHCs (n equals 80) were worn for 400,000 cycles, equivalent to three years of simulated clinical wear, at 50 N and 1.2 Hz using the Leinfelder-Suzuki wear tester. Wear volume, maximum wear depth, and wear surface area were computed using a 3D superimposition method and 2D imaging software. Data were statistically analyzed using one-way analysis of variance with the least significant difference post hoc test (P<0.05). RESULTS: After a wear simulation of three years, NHCs had a 45 percent failure rate; NHCs also had the greatest wear volume loss (0.71 mm³), maximum wear depth (0.22 mm), and wear surface area (4.45 mm²). SSCs (0.23 mm³ , 0.12 mm, 2.63 mm²) and ZRCs (0.03 mm³ , 0.08 mm, 0.20 mm ²) had less wear volume, area, and depth (P<0.001). ZRCs were the most abrasive to their antagonists (P<0.001). The NHC (against SSC wearing group) had the greatest total wear facet surface area (4.43 mm²). CONCLUSIONS: Stainless steel crowns and zirconia crowns were the most wear-resistant materials. Based on these laboratory findings, in the primary dentition, nanohybrid crowns are not recommended as long-term restorations beyond 12 months (P=0.001).

Effects of Apical Barriers and Root Filling Materials on Stress Distribution in Immature Teeth: Finite Element Analysis Study.

PURPOSE: A finite element analysis (FEA) study was performed to determine whether the material of apical barrier used for root apexification and/or the use of canal reinforcement affect the stress distribution in an endodontically treated immature permanent tooth in order to infer in which clinical scenarios a fracture is more likely to occur based on the ultimate tensile strength threshold of dentin. METHODS AND MATERIALS: An extracted human immature mandibular premolar was selected as the reference model and scanned by micro-computed tomography (micro-CT). The digital model was segmented and converted to STL (Standard Tessellation Language) using Simpleware Scan-IP and exported in IGES (Initial Graphics Exchange Specification) to Ansys 19. Six experimental models were designed with different combinations of composite, mineral trioxide aggregate (MTA), and Biodentine (BIO). Using FEA, a static 300 N load at a 135 angle with respect to the axis of the tooth was applied to each model and von Mises stress values (MPa) were measured at the sagittal, apical 8-mm, 5-mm, 2-mm, and 1-mm levels. RESULTS: In all regions examined, the control (NT model) had lower stress in the root compared WITH experimental models. At the mid-root level, models with composite, MTA, and BIO reinforcement exhibited lower stresses in the root dentin than those with pulp or gutta-percha. BIO models had equal or greater average von Mises stress values than those of MTA models in all regions. Both, MTA and BIO, caused increases in stress of surrounding root dentin, with BIO causing a greater increase than MTA. CONCLUSIONS: Stress distribution in immature permanent teeth treated by apexification is affected by the types of materials used. Root dentin's stress was lower when the mid-root canal was reinforced by composite, MTA, or BIO, which provided similar stress reduction to the root dentin. MTA is a more favorable apical barrier material from a mechanical standpoint because it induces less stress on apical root dentin than BIO.

Evaluation of microbial air quality and aerosol distribution in a large dental clinic.

PURPOSE: To evaluate the microbial air quality during dental clinical procedures in a large clinical setting with increasing patient capacity. METHODS: This was a single-center, observational study design evaluating the microbial air quality and aerosol distribution during normal clinical sessions at 5% (sessions 1 and 2) and at > 50% (session 3) treatment capacity of dental aerosol generating procedures. Sessions 1 and 2 were evaluated on the same day with a 30-minute fallow time between the sessions. Session 3 was evaluated on a separate day. For each session, passive air-sampling technique was performed for three collection periods: baseline, treatment, and post-treatment. Blood agar plates were collected and incubated at 37°C for 48 hours. Colonies were counted using an automatic colony counter. Mean colony forming units (CFU) per plate were converted to CFU/m²/h. RESULTS: Kruskal Wallis test was performed to compare the mean CFU/m²/h between the clinic sessions. Statistically significant differences were observed between sessions 1 and 2 (P< 0.05), but not between sessions 2 and 3 (P> 0.05). Combining all clinical sessions, the mean CFU/m²/h were 977 (baseline), 873 (treatment), and 1,631 (post-treatment) for the collection periods. A decrease-to-increase CFU/m²/h trend was observed from baseline to treatment, and from treatment to post-treatment that was observed for all clinic sessions and was irrespective to treatment capacity. Higher amounts of CFU/m²/h were found near the air exhaust outlets for all three clinic sessions. Microbial aerosol distribution is most likely due to the positions and power levels of the air inlets and outlets, and to a lesser extent with patient treatment capacity. CLINICAL SIGNIFICANCE: Dental clinics should be designed and optimized to minimize the risk of airborne transmissions. The results of this study emphasize the need to evaluate dental clinic ventilation systems.

Biomechanical Role of Trabecular Microstructure on Peri-implant Strain Based on Micro-CT Finite Element Modeling of Aging Mice.

PURPOSE: To evaluate the influence of age and trabecular microstructure on peri-implant strain in aging and young mice models under compressive load. MATERIALS AND METHODS: Eighteen 4-week-old female C57BL/6 mice (n = 6) were subjected to a 1.2% calcium content diet (young normal calcium group), and 7-month-old mice (n = 12) were randomly subjected to 0.01% and 1.2% calcium content diets (aging low and normal calcium groups, respectively) for 3 weeks. Histomorphometric and microcomputed tomography (micro-CT) analyses were used to investigate local alveolar bone microstructure. One maxilla segment from each group was reconstructed using micro-CT images to highlight the trabecular microstructure. A finite element analysis based on a computational model of the maxilla segment was performed to investigate peri-implant strain. Implants with three different diameters (0.3, 0.4, and 0.5 mm) were analyzed in these models. RESULTS: The aging low calcium group showed worse cancellous microstructure in hematoxylin and eosin (HE) staining, significantly increased osteoclast numbers (P < .05), and reduced bone volume fraction and trabecular thickness compared with the aging normal calcium group (P < .05). However, the young normal calcium group presented no difference in trabecular microstructure and osteoclast numbers compared with the aging normal calcium group. The aging low calcium group demonstrated increased strain intensity compared with the aging normal calcium group, whereas the young normal calcium and aging normal calcium groups showed comparable strain magnitude. The strain intensity of peri-implant bone increased with worse cancellous microstructure. When the diameter increased from 0.3 mm to 0.4 mm, the percentages of pathologic overload decreased regardless of bone microstructure. CONCLUSION: Deteriorated bone microstructure induced by a low calcium diet determined higher strain intensity, whereas, whenever age had no significant effect on trabecular microstructure, consequently, there was no substantial influence on strain. An increase of implant diameters can improve the strain distribution. Clinical decision-making should take into consideration the patient-specific and site-specific trabecular microstructure in preoperative assessment.

Enhancement of peripheral seal of medical face masks using a 3-dimensional-printed custom frame.

BACKGROUND: During the COVID-19 pandemic, American Society for Testing and Materials level 3 and level 2 medical face masks (MFMs) have been used for most health care workers and even for the first responders owing to a shortage of N95 respirators. However, the MFMs lack effective peripheral seal, leading to concerns about their adequacy to block aerosol exposure for proper protection. The purpose of this study was to evaluate the peripheral seal of level 3 and level 2 MFMs with a 3-dimensional (3D-) printed custom frame. METHODS: Level 3 and level 2 MFMs were tested on 10 participants with and without a 3D-printed custom frame; the efficiency of mask peripheral seal was determined by means of quantitative fit testing using a PortaCount Fit Tester based on ambient aerosol condensation nuclei counter protocol. RESULTS: The 3D-printed custom frame significantly improved the peripheral seal of both level 3 and level 2 MFMs compared with the masks alone (P < .001). In addition, both level 3 and level 2 MFMs with the 3D-printed custom frame met the quantitative fit testing standard specified for N95 respirators. PRACTICAL IMPLICATIONS: The 3D-printed custom frame over level 3 and level 2 MFMs can offer enhanced peripheral reduction of aerosols when using collapsible masks. With the shortage of N95 respirators, using the 3D-printed custom frame over a level 3 or level 2 MFM is considered a practical alternative to dental professionals.

A clinical investigation of dental evacuation systems in reducing aerosols.

BACKGROUND: The route of transmission of severe acute respiratory syndrome coronavirus 2 has challenged dentistry to improve the safety for patients and the dental team during various treatment procedures. The purpose of this study was to evaluate and compare the effectiveness of dental evacuation systems in reducing aerosols during oral prophylactic procedures in a large clinical setting. METHODS: This was a single-center, controlled clinical trial using a split-mouth design. A total of 93 student participants were recruited according to the inclusion and exclusion criteria. Aerosol samples were collected on blood agar plates that were placed around the clinic at 4 treatment periods: baseline, high-volume evacuation (HVE), combination (HVE and intraoral suction device), and posttreatment. Student operators were randomized to perform oral prophylaxis using ultrasonic scalers on 1 side of the mouth, using only HVE suction for the HVE treatment period and then with the addition of an intraoral suction device for the combination treatment period. Agar plates were collected after each period and incubated at 37 °C for 48 hours. Colony-forming unit (CFU) counts were determined using an automatic colony counter. RESULTS: The use of a combination of devices resulted in significant reductions in CFUs compared with the use of the intraoral suction device alone (P < .001). The highest amounts of CFUs were found in the operating zone and on patients during both HVE and combination treatment periods. CONCLUSIONS: Within limitations of this study, the authors found significant reductions in the amount of microbial aerosols when both HVE and an intraoral suction device were used. PRACTICAL IMPLICATIONS: The combination of HVE and intraoral suction devices significantly decreases microbial aerosols during oral prophylaxis procedures.

Computational Biomechanical Analysis of Engaging and Nonengaging Abutments for Implant Screw-Retained Fixed Dental Prostheses.

PURPOSE: To evaluate the stress distribution, using 3-dimensional finite element analysis (FEA), on different implant components of a mandibular screw-retained fixed dental prosthesis (FDP) situation when using different combinations of engaging and nonengaging abutments. MATERIAL AND METHODS: A model of artificial bone was digitally designed. Dental implants were positioned in the lower right posterior area of teeth #'s 28 (premolar - pm) and 30 (molar - m). Restorative implant components were digitally designed and placed into the implant model. Four different implant abutment situations were simulated through FEA: (1) Both engaging abutments (mE-pmE), (2) both nonengaging (mNE-pmNE), (3) molar nonengaging and premolar engaging (mNE-pmE), and (4) molar engaging and premolar nonengaging (mE-pmNE). Thirty-five (35) Ncm preload to the abutment screws and 160 N static load at 45° angle to the occlusal plane were applied in each group. RESULTS: The equivalent Von Mises stress was measured on each component. Stress distribution changed among the different configurations and ranged from 516.0 to 1304.6 MPa in the implants, and from 554.6 to 994.5 MPa with the abutments. Higher stress was found for the mNE-pmNE designs (1078.6-1106.9 MPa). Engaging and nonengaging abutments had different stress distributions on the screw (698.8-902.5 MPa). Peak stress areas were located on the upper part of the screws for the nonengaging configuration, and on the lower areas for the engaging abutments. The sum of the stress on both implants decreased in the following order: mNE-pmNE > mE-pmNE > mNE-pmE > mE-pmE. CONCLUSION: Under conditions of this study, abutment design produced different stress patterns to the implant components. The lowest and most balanced stress distribution was found for the mE-pmE configuration followed by the mNE-pmE configuration.

Three-dimensional nonlinear prediction of tooth movement from the force system and root morphology.

OBJECTIVES: To determine the different impact of moment-to-force ratio (M:F) variation for each tooth and spatial plane and to develop a mathematical model to predict the orthodontic movement for every tooth. MATERIALS AND METHODS: Two full sets of teeth were obtained combining cone-beam computed tomography (CBCT) and optical scans for two patients. Subsequently, a finite element analysis was performed for 510 different force systems for each tooth to evaluate the centers of rotation. RESULTS: The center of CROT locations were analyzed, showing that the M:F effect was related to the spatial plane on which the moment was applied, to the force direction, and to the tooth morphology. The tooth dimensions on each plane were mathematically used to derive their influence on the tooth movement. CONCLUSION: This study established the basis for an orthodontist to determine how the teeth move and their axes of resistance, depending on their morphology alone. The movement is controlled by a parameter (k), which depends on tooth dimensions and force system features. The k for a tooth can be calculated using a CBCT and a specific set of covariates.

Nonlinear dependency of tooth movement on force system directions.

INTRODUCTION: Moment-to-force ratios (M:F) define the type of tooth movement. Typically, the relationship between M:F and tooth movement has been analyzed in a single plane. Here, to improve the 3-dimensional tooth movement theory, we tested the hypothesis that the mathematical relationships between M:F and tooth movement are distinct, depending on force system directions. METHODS: A finite element model of a maxillary first premolar, scaled to average tooth dimensions, was constructed based on a cone-beam computed tomography scan. We conducted finite element analyses of the M:F and tooth movement relationships, represented by the projected axis of rotation in each plane, for 510 different loads. RESULTS: We confirmed that a hyperbolic equation relates the distance and M:F; however, the constant of proportionality ("k") varied nonlinearly with the force direction. With a force applied parallel to the tooth's long axis, "k" was 12 times higher than with a force parallel to the mesiodistal direction and 7 times higher than with a force parallel to the buccolingual direction. CONCLUSIONS: The M:F influence on tooth movement depends on load directions. It is an incomplete parameter to describe the quality of an orthodontic load system if it is not associated with force and moment directions.