Influence of thickness and restorative system on the mechanical behavior of CAD/CAM minimally invasive occlusal veneers - in vitro study.

AIM: The aim of this study was to evaluate the physical-mechanical behavior of the occlusal veneers when subjected to thermomechanical cycling. MATERIALS AND METHODS: Sixty specimens were divided into 04 groups (n=15 per group), according with the different restorative materials and thicknesses: material - lithium dissilicate LD (IPS e.max CAD, Ivoclar Vivadent) and nano- ceramic-resins NCR (ESPE Lava Ultimate, 3M); thickness - 0.6 and 1.2mm. The occlusal veneers were bonded over human flattened fresh extracted molars with dual-polymerizing luting agent (Variolink N, Ivoclar Vivadent and RelyX Ultimate 3M) using the respective adhesive system following the selective-etch technique (self-etch in dentin and total etch in enamel). The resin cement was light cured for 40 seconds each face, using a LED light cure equipment (BlueStar II, Microdont, 1100 mW/cm2). The response variables consisted of veneer survival rates (crack formation, catastrophic cracks and debonding) when subjected to thermal cycling from 5° to 55° C and simultaneous mechanical cycling performed at load intensities of 100, 200, 300, 400 and 450N for 20,000 cycles each. RESULT: Data were submitted to the Kruskall Wallis test and Pairwise Comparison, adopting a significance level of 5%. NCRs presented a lower incidence of failures (p<0.05) when compared to LD. According to thickness factor, 1.2mm thick occlusal veneers withstand higher cycling loads. CONCLUSION: NCR occlusal veneers with 1.2mm thickness presented superior physical-mechanical behavior than lithium disilicate and 0.6mm restorations.

Comparative physical and mechanical properties of a 3D printed temporary crown and bridge restorative material.

Background: The objective was to compare physic-mechanical properties of different materials used for temporary restorations. Material and Methods: Protemp 4/bisacrylic resin, Jet/acrylic resin, and Nexdent C&B/3D-printed resin samples (10mm diameter x 2mm thickness) were analyzed for surface roughness and color stability tests (baseline, after 5 thousand brushing cycles; and after artificial aging in water at 60oC for 24 hours) and Knoop microhardness. All data were checked for normality using Shapiro-Wilk test. Surface roughness and color stability were analyzed using two-way repeated measurements ANOVA, microhardness data was subjected to one-way ANOVA. All tests were followed by Tukey test and were performed with α=0.05. Results: For roughness, material (p=.002), time points (p=.002) and interaction between both (p<.001) were significant. All groups presented similar roughness for measurements of baseline and after brushing. After artificial aging, 3D printed resin showed decreased roughness when compared with other resins, and with its baseline reading. Acrylic resin showed an increase in surface roughness (when compared with measurement after brushing cycles). Considering color stability, only the material (p=.039) and the time (p<0.001) were significant. All groups showed similar color variation before and after artificial aging. There was an increase in color alteration after artificial aging for all groups. Considering microhardness test (p<.001), the 3D printed resin showed the highest values and acrylic resin the lowest. Bysacylic resin was similar to both 3D printed and acrylic resins. Conclusions: The tested 3D printed resins present similar or better properties than other tested temporary materials while being integrated with the digital workflow. Key words:Disinfection methods, hydroxyl radical, environment, surfaces, dentistry.

CODA standard 2-24 h-"replacement of teeth" dilemma: Unintended consequences and proposed solutions.

BACKGROUND: The Commission on Dental Accreditation (CODA) was established in 1975 with the goal of serving the public and the dental profession by developing and implementing standards that guide and maintain the quality of dental educational programs. These standards are defined broadly around competencies reflective of an evidence-based definition of general dentistry and that should be met by the new graduates to function as an entry level provider. Consequently, CODA "expects each school to develop specific competency definitions and assessment methods in the context of the broad scope of general dental practice". CODA Standard 2-24 h was implemented a decade ago to address concerns that dental schools are not sufficiently proactive in incorporating implant-related curricula and clinical competencies. When the standard was implemented, most patients already preferred dental implants over FPDs. This market trend, together with the prescriptive format of the standard, had the unintended consequence of creating pressure on programs that struggled to find enough patients who will chose FPDs as a treatment option. DISCUSSION: As a short term solution, we suggest a tooth replacement competency construct that has the potential to alleviate this burden. This solution incorporates principles of ethical decision making, patient-centered care, and evidence-based dentistry, without compromising educational aspects and competency development. For the longer term, we suggested to revise and rephrase the standard so that it will be clinically-centered rather than focused on technical tools that may evolve, change, or disappear as a result of technological progress and other market trends. This, in turn, will be conducive to fulfill the intent of Standard 2-24 to allow the schools to identify "competencies that will be included in the curriculum based on the school's goals, resources, accepted general practitioner responsibilities and other influencing factors."

Can postpolymerization for 3D-printed interim restorations be improved?

STATEMENT OF PROBLEM: Postpolymerization methods influence the properties of 3-dimensionally (3D) printed materials. Nevertheless, it is a time-consuming step that could lead dentists to avoid the chairside use of 3D printing. Information assessing the impact of different postpolymerization workflows on flexural strength and color stability is sparse. PURPOSE: The purpose of this in vitro study was to analyze the impact of different postpolymerization methods on the flexural strength and color stability of 3D-printed resins used for interim restorations. MATERIAL AND METHODS: Three resin materials: CT (Cosmos Temp; Yller Biomaterials), DT (Denture Teeth; Formlabs), and CB (C&B MFH; NextDent) were submitted to 4 methods of postpolymerization: a Form Cure polymerization chamber (FC) (Form Cure; Formlabs), a broadband LED device (Valo Grand; Ultradent Products, Inc) operating at 1000 mW/cm2 for 2 different polymerization times (40 seconds/V40 or 120 seconds/V120), and a custom-made polymerization chamber with a 24 W UV LED Strip (CC). The specimens were assessed for flexural strength using an universal testing machine immediately after polymerization or after 10 000 thermal cycles, and the color stability was evaluated using a spectrophotometer at baseline, after 7 days in dark, dry storage at 37 °C and after 24 hours of artificial aging in water at 60 °C. The data were evaluated using 3-way ANOVA (flexural strength) and 3-way repeated measurements ANOVA (color stability), followed by the Tukey HSD test (α=.05). RESULTS: Flexural strength showed significant differences for resin, postpolymerization method, time, and for the interaction between all effects. CT showed the highest overall flexural strength, while DT showed the lowest. In general, V120 produced specimens with higher flexural strength. Thermocycling did not reduce flexural strength except for CB polymerized with FC and V120, and DT polymerized with V40. For color stability, significant differences were found for resin, postpolymerized method, time, and for the interaction between all effects. The highest ΔE values were observed for DT polymerized using V40 after artificial aging. The lowest values were observed for the same resin but polymerized using V120 after 7 days in dark, dry storage at 37 °C. CONCLUSIONS: Postpolymerization with the broadband LED device for 120 seconds can produce specimens with higher flexural strength values and higher color stability when compared with the other postpolymerization workflows tested in this study.

The relationship between periodontal and kidney disease: a critical review.

Periodontal disease has been associated with various systemic diseases including kidney disease. However, a causal relationship is yet to be established. One possible association is that periodontitis may cause an increased inflammatory response in kidney disease patients which in turn destroys endothelial vasculature. This may contribute to development of risk factors of kidney disease such as diabetic neuropathy and cardiovascular events leading the progression and mortality in kidney disease patients. The role of periodontal inflammation driving kidney disease is still under investigation. This review article highlights the role of periodontal inflammation in the development and progression of kidney disease. It is crucial that dental practitioners and nephrologists understand the association between periodontal and kidney disease. Early periodontal screening and educating patients about the importance of good oral hygiene may play an important role in prevention of progression of kidney disease.

3D printed implant surgical guides with internally routed irrigation for temperature reduction during osteotomy preparation: A pilot study.

OBJECTIVE: The purpose of this study was to test a novel through-the-guide means of irrigation in an in-vitro bovine bone model and to explore the method clinical applicability. MATERIALS AND METHODS: Surgical guides were designed to fit over five fresh bovine samples. Control osteotomy sites were compared to experimental sites irrigated through a 3D printed surgical guide with customized channels that direct the coolant toward the interface of the alveolar crest and drill. Temperature was measured during surgery with thermocouples located at 3 and 6 mm from the crestal height of the bone, and with an infrared thermal camera taking direct temperature readings from a window cut into axial wall at 9 mm from the crestal height of the ridge. RESULTS: Incorporation of routed irrigation significantly decreased heat generation, keeping temperature consistently below 47°C. A clinical case illustrates the method applicability using standard implant planning software, 3D printing technology, and regular implant armamentarium. CONCLUSIONS: The in-vitro analysis shows that this method mitigates temperature increase caused by static surgical guide irrigation blockade at the osteotomy site. This technique can be incorporated in the surgical guide design using commercially available software and 3D printing technology and has immediate applications in practice. CLINICAL SIGNIFICANCE: The in-vitro analysis shows that this method can significantly mitigate the temperature increase caused by static surgical guide irrigation blockade at the osteotomy site. This technique also has the advantage that it can be incorporated in the digital surgical guide design using commercially available software and 3D printing technology. The method has immediate applications in practice, and especially in the treatment of edentulism in esthetic zone where use of guided surgery for implant placement is crucial in obtaining consistent results.

Evaluation of the accuracy of multiple digital impression systems on a fully edentulous maxilla.

OBJECTIVE: This study aimed to compare the accuracy performance of five different intraoral scanning systems for a full-arch scan on an edentulous cadaver maxilla. METHOD AND MATERIALS: Five digital intraoral impression systems were used to scan a fully edentulous cadaver maxilla. A master scan obtained with an ATOS Capsule industrial grade scanner provided the point of comparison. Experimental scans were compared to the master scan using a metrology software that allows images to be overlayed on one another and deviations interpreted. Once aligned, three comparisons were made between the experimental scans and the reference: the entire maxilla, the ridge area only, and the palate area only. RESULTS: Trueness deviations between the experimental scans and the master digital model were up to 0.1 mm in the 75th percentile. For the whole maxilla, only the Medit scanner had statistically significantly inferior trueness compared to other scanners. When only the palate was considered, Medit was significantly different from Element (P = .0025) and Trios 4 (P = .0040), with no differences found between other scanners. For the ridge region the results replicate the trend observed for the whole maxilla. In regard to precision, differences were found only in the whole maxilla and the ridge area. In both areas, only Medit's precision was significantly different compared to other scanners, with the exception of Element. However, Element performance was similar to all other scanners. CONCLUSION: Most intraoral scanners exhibited similar performance. Although several statistically significant differences were identified, the clinical impact of these variances is probably not meaningful. (Quintessence Int 2021;52:488-495; doi: 10.3290/j.qi.b1244373).

The effect of software updates on the trueness and precision of intraoral scanners.

OBJECTIVES: The goal of the study was to determine the effects of software updates on the trueness and precision of digital impressions obtained with a variety of intraoral scanner (IOS) systems. METHOD AND MATERIALS: Seven IOS systems were investigated. Each system was tested using two versions of software, with the second version being the latest at the time of conducting the study. Scans were performed on a custom mandibular typodont model with natural teeth that were either unrestored or restored with amalgam, composite, lithium disilicate, zirconia, and gold. Eight scans were obtained for each software version on any of the tested IOS systems. Experimental IOS scans were compared against an industry-standard master scan of the typodont obtained with an ATOS Capsule scanner proven to have a trueness of 3 µm and a precision of 2 µm. Isolation of each substrate material on the digital experimental and master scans was achieved using the Geomagic metrology software for subsequent analysis of the substrate influence on accuracy. A generalized linear mixed model was used to determine the influence of the software version on the trueness and precision of the impression scan. RESULTS: For some IOS systems, scans made with older software versions differ in accuracy compared with those obtained with the most recent software versions. Trueness was improved for most scanners following the software update, although the Element2 IOS performance deteriorated. Software updates had lesser effects on precision and showed variable trends among different systems. Software updates also influence different substrate materials scans' accuracy, although the results show variability among IOS systems. When comparisons were done among IOS systems updated with the latest software version, best performers for complete arch trueness were the Emerald S, Trios 3, and Primescan systems. CONCLUSION: Software updates have a statistically significant effect on the trueness and precision of different IOS systems. These updates can have both positive and negative effects on scan accuracy, although it appears that these variations are within the clinical acceptability levels.

Aerosol and spatter mitigation in dentistry: Analysis of the effectiveness of 13 setups.

OBJECTIVES: The current study aims to investigate the aerosol and spatter mitigation quality of 13 dry-field isolation methods in a simulated setup that replicates real-life work scenarios encountered in dental practices. METHODS: A crown preparation on a manikin was performed on tooth number 30 and repeated five times for each setup to simulate a patient under care. Aerosol, environmental, and operator face shield spatter, and sound intensity was measured. Generalized linear mixed models were used, and posthoc pairwise comparisons were performed to compare least-squares means when appropriate using a Tukey adjustment. RESULTS: All tested setups showed some environmental spatter formation; however, these were able to control most (and in some cases all) spatter on the operator face shield. All methods resulted in excellent aerosol mitigation when a second line of high-volume evacuation (HVE) was added to the device setup. However, in most setups, total sound levels exceeded 85 dB, posing a concern for prolonged noise exposure. CONCLUSIONS: The Prototype device and four other tested setups with secondary HVE addition completely eliminated aerosol creation as tested. Spatter of the Face Shield was best eliminated using the Prototype device. CLINICAL SIGNIFICANCE: Within the limitations of this study, it can be concluded that the dental community has at its disposal equipment that can effectively mitigate aerosol and spatter.

The digital denture replication method (DRM): a simplified method to fabricate a complete removable prosthesis.

The proposed denture replication method shows a predictable workflow for fabricating complete dentures for patients with existing dentures. The replication technique is a method of fabricating new removable complete dentures utilizing the existing prosthesis as the foundation for a new denture. The technique has some advantages such as allowing the clinician to copy the tooth shape and contours of the existing prosthesis while modifying borders and intaglio surfaces. The denture replication method links proven methods of obtaining functional impressions using soft reline materials to a straightforward digital process. Utilizing the new "copy-denture" feature in the 3Shape software, it is possible to significantly reduce the number of appointments and laboratory labor involved in denture fabrication. The denture replication method protocol is increasing efficiency by reducing the amount of clinical procedures and visits, resulting in decreased treatment time and costs while providing a satisfactory clinical solution.

Evaluation of the spatter-reduction effectiveness and aerosol containment of eight dry-field isolation techniques.

OBJECTIVE: The novel coronavirus that was first identified in Wuhan, China, in December 2019, created a pandemic that has the potential to change the paradigm of health care delivery. Of interest to the dental community is the presence of SARS-CoV-2 in the saliva of the affected patients that can potentially cause transmission of COVID-19 via droplets. The highly infectious nature of the pathogen has created a sense of urgency and a need for extra caution to prevent the spread of the disease and the potential infection of patients and the entire dental team. Spatter consists of droplets up to 50 µm in size that are effectively stopped by barriers such as gloves, masks, and gowns. Aerosols are defined as droplet particles smaller than 5 µm that can remain airborne for extended periods and that have been reported to be significant in viral respiratory infections. In this study, aerosol represented by particulate matter with a size of 2.5 µm (PM2.5) was measured. METHOD AND MATERIALS: Eight dry-field isolation methods were tested in a setup that included a realistic dental manikin and a high-speed handpiece that generated air-water spray. Environmental noise generated by the suction devices, suction flow rate of each setup, and the amount of environmental spatter and aerosols, were measured. RESULTS: The experimental setups showed significant variability in the suction flow rate, but this was not correlated to the level of sound generated. Some experimental setups caused a short-term level of noise that exceeded the NIOSH (National Institute for Occupational Safety and Health) guidelines and were close to the OSHA (Occupational Safety and Health Administration) recommended thresholds. It is also worth noting that the variability in the flow rate is not reflected in the efficacy of the experimental setups to mitigate spatter. All experimental setups, except the IsoVac system, provided statistically significantly better spatter mitigation compared to the control. All experimental setups also were efficient in mitigating aerosols compared with the positive control (P < .0001) and most systems yielded results similar to the negative control ambient PM (P > .05). CONCLUSION: Results indicate that spatter reduction was significantly better amongst the setups in which an additional high-volume evacuator (HVE) line was used. All setups were efficient at mitigating PM2.5 aerosols in comparison to the control. The conclusions of this study should be interpreted with caution, and additional mitigation techniques consistent with the Centers for Disease Control and Prevention recommendations must be implemented in dental practices.

Validation of a method of quantifying 3D leakage in dental restorations.

STATEMENT OF PROBLEM: A reliable and validated protocol for nondestructive analysis of the entire restorative interface that could be applicable in studies assessing the adaptation of direct and indirect restorations is lacking. PURPOSE: The purpose of this in vitro study was to validate a 3D protocol for microleakage assessment in class II mesio-occluso-distal (MOD) cavities restored with composite resin. MATERIAL AND METHODS: Sixteen human third molars received standardized class II MOD preparations with cervical margins located 1 mm apical to the cemento-enamel junction. The specimens were restored with Filtek Bulk Fill Posterior (FBP) or Filtek Bulk Fill Flowable (FBF) and submitted to 10 000 thermocycles (5 °C and 55 °C with a 30-second dwell time at each temperature and 5-second transfer time). The specimens were scanned with microcomputed tomography (µCT) before and after immersion in 50% ammoniacal silver nitrate solution for 12 hours. Scanned data were processed, and the 3D amount of infiltrated silver nitrate was analyzed through the entire adhesive interface. In addition, the linear distance of silver nitrate infiltration was assessed using 3 axial images obtained from each specimen proximal box (2D analysis). Data were tested for homogeneity by using the Shapiro-Wilk test and evaluated by using 1-way ANOVA, followed by the post hoc Tukey HSD test (α=.05). RESULTS: FBP showed significantly lower leakage than FBF for both 2D and 3D analyses. A low correlation was observed between the assessment methods. CONCLUSIONS: Three-dimensional analysis of microleakage using µCT is a predictable and more reliable method for nondestructive and comprehensive analysis of the entire specimen.

Influence of resin-coating agents on the roughness and color of composite resins.

STATEMENT OF PROBLEM: Resin-coating agents can be used to fill microstructural defects within composite resin restorations, which might result in a smoother surface. Nevertheless, data about the color stability and surface roughness of coated restorations are lacking. PURPOSE: The purpose of this in vitro study was to compare the surface roughness and color stability of restorations before and after application of different resin-coating agents. MATERIAL AND METHODS: Forty specimens of composite resin (Filtek Z250) (diameter×height, 6×2 mm) were divided into 5 groups according to the surface treatments (n=8 per group): control (CTR), Fortify (FT), Lasting touch (LT), BisCover (BIS), and Fill Glaze (FG). The specimens were evaluated for surface roughness by using a profilometer with 3 readings for each specimen (separated by 300 µm) before immersion in a staining solution (coffee) and after 5 days immersed in coffee and for color stability (▵E) by using a spectrophotometer before being immersed in coffee (initial reading) and after 6 hours, 12 hours, 1, 2, 3, 4, and 5 days. RESULTS: Two-way ANOVA with repeated measures and the Tukey test showed that the CTR group showed the highest roughness values, similar to those of the FT and LT groups. The BIS and FG groups showed lower roughness than the other groups but similar results when compared with each other. All groups, except LT, showed increased roughness values after immersion in coffee solution, and the BIS group showed the lowest variation over time. Color alterations were found for all groups, with the CTR group showing the lowest ▵E values when compared with the other groups except for the BIS group. No correlation was found between surface roughness and degree of color change (P=.401). CONCLUSIONS: The BisCover surface sealant showed the lowest surface roughness and the best color stability. Surface sealants can be used to fill microcracks and microgaps but should not be used as a substitute for polishing.

Hyaluronic acid as adjunctive to non-surgical and surgical periodontal therapy: a systematic review and meta-analysis.

OBJECTIVES: To evaluate the potential added benefit of the topical application of hyaluronic acid (HA) on the clinical outcomes following non-surgical or surgical periodontal therapy. MATERIALS AND METHODS: A systematic search was performed in Medline, Embase, Cochrane, Web of Science, Scopus and Grey literature databases. The literature search was preformed according to PRISMA guidelines. The Cochrane risk of bias tool was used in order to assess the methodology of the included trials. Weighted mean differences (WMDs) and 95% confidence intervals (CIs) between the treatment and controls were estimated using the random-effect model for amount of bleeding on probing (BOP), probing depth (PD) reduction and clinical attachment level (CAL) gain. In order to minimize the bias and to perform meta-analysis, only randomized clinical studies (RCTs) were selected. RESULTS: Thirteen RCTs were included: 11 on non-surgical periodontal treatment and two on surgical periodontal treatment. Overall analysis of PD reduction, CAL gain and BOP reduction in non-surgical therapy with adjunctive HA presented WMD of - 0.36 mm (95% CI - 0.54 to - 0.19 mm; p < 0.0001), 0.73 mm (95% CI 0.28 to 1.17 mm; p < 0.0001) and - 15% (95% CI - 22 to - 8%; p < 0.001) respectively, favouring the application of HA. The overall analysis on PD and CAL gain in surgical therapy with adjunctive HA presented WMD of - 0.89 mm (95% CI - 1.42 to - 0.36 mm; p < 0.0001) for PD reduction and 0.85 mm (95% CI 0.08 to 1.62 mm; p < 0.0001) for CAL gain after 6-24 months favouring the treatment with HA. However, comparison presented considerable heterogeneity between the non-surgical studies and a high risk of bias in general. CONCLUSIONS: Within their limits, the present data indicate that the topical application of HA may lead to additional clinical benefits when used as an adjunctive to non-surgical and surgical periodontal therapy. However, due to the high risk of bias and heterogeneity, there is a need for further well-designed RCTs to evaluate this material in various clinical scenarios. CLINICAL RELEVANCE: The adjunctive use of HA may improve the clinical outcomes when used in conjunction with non-surgical and surgical periodontal therapy.

Brittleness index and its relationship with materials mechanical properties: Influence on the machinability of CAD/CAM materials.

The aim of this study is to evaluate the machinability of four CAD/CAM materials (n = 13) assessed by brittleness index, Vickers hardness, and fracture toughness and interaction among such mechanical properties. The materials selected in this in vitro study are Feldspathic ceramic [FC], Lithium-disilicate glass ceramic [LD], leucite-reinforced glass ceramic [LR], and nanofilled resin material [RN]. Slices were made from the blocks following original dimensions 14 × 12 × 3 mm (L × W × H), using a precision slow-speed saw device and then surfaces were regularized through a polishing device. Brittleness index and fracture toughness were calculated by the use of specific equations for each one of the properties. The Vickers hardness was calculated automated software in the microhardness device. One-way Anova and Pearson's correlation were applied to data evaluation. LD obtained the highest values for brittleness index and was not significantly different from FC. LR presented statistically significant difference compared with RN, which had the lowest mean. Vickers hardness showed LD with the highest average, and no statistical difference was found between FC and LR. RN presented the lowest average. Fracture toughness showed FC and LR not statistically different from each other, likewise LD and RN. The brittleness index, considered also as the machinability of a material, showed within this study as positively dependent on Vickers hardness, which leads to conclusion that hardness of ceramics is related to its milling capacity. In addition, fracture toughness of pre-sintered ceramics is compared to polymer-based materials.

Biomechanical behavior of maxillary premolars with conservative and traditional endodontic cavities.

OBJECTIVE: The objective was to evaluate the effects of the configuration of endodontic cavities with parallel or divergent walls, versus traditional endodontic cavities, on stress distribution, fracture resistance, and fracture mode of maxillary premolars by using both fracture-strength and finite element tests. METHOD AND MATERIALS: Thirty-two maxillary first premolars were divided into four groups (n = 8), according to the type of endodontic cavities: without endodontic cavities (control); conservative; conservative with diverging walls; and traditional. After performing root canal treatment and restoration, fracture resistance was evaluated by oblique compressive load. The stress distribution was evaluated by nonlinear finite element analysis by means of micro-computed tomography, operated at 50 kV and 800 mA. The fracture resistance data were analyzed by statistical software. RESULTS: Higher stress concentration was observed on the coronal portion of the palatal cusp and the palatal root dentin. Stress concentration on the palatal root dentin was similar for all groups. The stress level on the palatal cusp and at the proximal crests was slightly increased in the traditional endodontic cavities group compared with conservative endodontic cavities. Stress distribution in restored teeth was similar to that of intact teeth. No significant differences were observed in the fracture resistance among different endodontic cavities' design (P = .32). All groups had values similar to those of the control group (P > .05). CONCLUSIONS: Regardless of the cavity design, conservative endodontic cavities that preserve marginal ridge integrity did not affect the resistance to fracture, failure mode, or stress distribution in maxillary premolars restored with composite resin. Endodontically treated teeth displayed biomechanical behavior similar to sound teeth.