Influence of build direction, post-polymerization time, and aging on the fracture resistance and marginal and internal discrepancies of three-dimensional printed provisional crowns.

To evaluate the effect of build direction, post-polymerization time, and aging on the fracture resistance, failure mode, margin quality and Marginal (MD) and Internal Discrepancies (ID), and degree of conversion of tridimensional (3D) printed provisional crowns using the liquid crystal display technique (LCD). A left mandibular first molar was prepared and scanned. After, a full crown was designed (ExoCad) and exported to the LCD-printer software. One hundred and eighty crowns were printed at two build directions (30°, 90°) and post-polymerized for different periods (15, 30, 45 min). Half of the samples were aged (ST) in distilled water (37 °C/90 days). The marginal quality of the crowns was evaluated by the Schriwer method under a stereomicroscope (40x). The replica technique was used to measure the MD and ID and measured under a stereomicroscope (10x), through 20 reference points defined in 5 regions: Occlusal (O), Cusp (CP), Axial (AX), Chamfer (CH), and Finish Line (F). After, the crowns were cemented onto the respective dies using temporary cement and submitted to compression test (ISO150, 1 mm/min, 100 kgf).The failure mode was classified by Burke's fracture mode. The degree of conversion was evaluated through Fourier Transform Infrared Spectroscopy. The data (µm) of MD and ID and fracture resistance (N) were subjected to ANOVA (3 factors) and Tukey's test (5%); Weibull analysis was also performed for fracture resistance data (N). For MD, ID and fracture resistance ANOVA revealed that all factors (P < .001) were significant. For aged groups, the crowns printed at 30° showed lower MD (Tukey). The O_90_30 min (172.13A µm) and O_90_15 min (170.20A µm) groups showed the highest ID values. Higher resistance values were observed for the 30_45 min (844.30A N), 30_30 min (835.35A N), and 90_30 min (820.62A N) groups (Tukey). In the margin analysis, 98.6% of the crowns printed at 30° showed smooth margins without defects. The most prevalent fracture mode (41.7%) was Burke type 5. The degree of conversion (DC) increased with increasing post-polymerization time and aging. Printing provisional crowns at 30° provided lower crown MD and ID, as well as higher fracture resistance. A post-polymerization time of 30 min resulted in higher crown fracture resistance, while aging reduced the resistance of the crowns.

Fracture resistance, marginal and internal adaptation of innovative 3D-printed graded structure crown using a 3D jet printing technology.

PURPOSE: This in vitro study aimed to create a graded structured dental crown using 3D printing technology and investigate the fracture resistance and the adaptation of this new design. MATERIALS AND METHODS: A dental crown with a uniform thickness of 1.5 mm was designed, and the exported stereolithography file (STL) was used to manufacture 30 crowns in three groups (n = 10), solid (SC), bilayer (BL), and multilayer (ML) crowns using  3D jet printing technology. Marginal and internal gaps were measured using the silicone replica technique. Crowns were then luted to a resin die using a temporary luting agent and the fracture resistance was measured using a universal testing machine. One-way ANOVA and Tukey post hoc tests were used to compare the fracture resistance and the adaptation of crowns at a significance level of 0.05. RESULTS: Mean marginal and internal gap of the ML group were 80 and 82 mm, respectively; which were significantly (p < 0.05) smaller than BL (203 and 183 mm) and SC (318 and 221 mm) groups. The SC group showed the highest mean load at fracture (2330 N) which was significantly (p < 0.05) higher than the BL (1716 N) and ML (1516 N) groups. CONCLUSION: 3D jet printing technology provides an opportunity to manufacture crowns in a graded structure with various mechanical properties. This study provided an example of graded structured crowns and presented their fracture resistance. SC group had the highest fracture resistance; however, ML had the best marginal and internal adaptation.

Fracture Resistance of Zirconia Surveyed Crowns With Digitally Designed and Hand-Modified Occlusal Rest Seats.

Background In light of the trend of using zirconia crowns, clinicians will likely face abutment included in removable partial dentures (RPD) designs with existing zirconia. However, the decision to replace the existing crown with a surveyed crown or modify the existing crown to accept the RPD is unclear. To the best of our knowledge, there is a lack of literature on the effect of preparing a rest seat on the existing monolithic zirconia crown in the patient's mouth on the fracture resistance of the crown. Therefore, in this study, we aimed to evaluate the fracture resistance of computer-aided design/computer-aided manufacturing (CAD/CAM) zirconia surveyed crowns with digitally designed rest seats and hand-modified rest seats. Methods Thirty CAD/CAM zirconia surveyed crowns were digitally designed and fabricated and divided into groups (n=10 per group) as follows: Group 1 comprised surveyed crowns with no occlusal rest seat; Group 2 comprised surveyed crowns with a digitally designed mesial rest seat; and Group 3 comprised surveyed crowns with a hand-modified mesial rest seat. Then, with all the crowns cemented to metal dies, the specimens were subjected to a fracture resistance test using a universal testing machine (Model 8501 Instron, Norwood, MA, USA). Results Surveyed crowns without any rest seat and those with digitally created and hand-modified rest seats displayed different fracture resistances: crowns with no rest seat offered the highest fracture resistance (5831 ± 895.15 N), followed by those with a digitally designed and milled rest seat (5280 ± 1673.33 N). Crowns with a hand-modified rest seat provided the lowest fracture resistance (4976 ± 322.5 N). Based on our results, surveyed crowns without a rest seat displayed higher fracture resistance than those with a rest seat. Conclusion The fracture resistance of crowns with a digitally designed and milled rest seat was statistically similar to that of control crowns with no rest seat, whereas hand-modified rest seats significantly reduced the fracture resistance of surveyed zirconia crowns.

Comparison of five different obturation approaches for resistance against fracture in root canal treated teeth.

Endodontist should know about the fracture resistance of endodontic treated teeth in different obturation techniques to make a proper choice for obturation of mechano-chemically prepared root canals. Therefore, it is of interest to compare the fracture resistance of endodontically obturated teeth in five different obturation techniques namely single cone obturation (SCO), cold lateral compaction (CLC), cold free flow condensation, warm vertical compaction, injection molded thermo-plasticized technique. Among experimental categories, maximum fracture resistance was observed in cold free flow condensation technique while minimum fracture resistance was observed in injection molded thermo-plasticized technique. Cold free flow condensation technique using Gutta Flow2 has the potential to be used as obturation technique with minimum fracture resistance. Conventional techniques like CLC and SOC also offered good fracture resistance.

Comparison of fracture strength in implant supported zirconia-titanium base abutments.

The fracture strength of implant supported zirconia-titanium base (Zi-Ti) base restorations with and without modification of submucosal cervical contour is of interest to dentists. 80 zirconia specimens were adjusted onto the Ti-base. One category consisted of specimens that underwent modification. Other category consisted of abutments without modification. There was polishing and recon touring at the interface of Zi-Ti base in cervical regions. Using the universal testing apparatus fracture resistance was assessed for every sample in every category in Newtons (N). The fracture strength of abutments with modification ranged between 4465.79 - 6523.50 N with mean value of 5604.24 ± 497.62 N. On the other hand, values of fracture strength varied between 5511.42 - 7064.33 N. in abutments without modification with mean fracture strength values of 6265.95 ± 331.61. It was observed that the fracture strength was lesser in abutments that underwent modification.

Enhancing intermediate temperature fracture resistance of stone matrix asphalt with untreated recycled concrete aggregate-Experimental dataset.

This data article presents details on the assessment of fracture parameters of laboratory asphalt mixtures produced using both natural and recycled concrete aggregates. The gap-graded stone matrix asphalt (SMA) is created by incorporating Trinidad Lake Asphalt (TLA) binder with carefully calibrated mixtures of recycled concrete aggregates (0 %, 10 %, 35 %, and 50 %) and natural aggregates (limestone and dust filler). The dataset variables were chosen based on the specifications of the single-edge notched beam (SENB) and semi-circular bending (SCB) tests, which are currently used for quality control and assurance (QC & QA) assessment of asphalt concrete mixtures. The data parameters provided include air void content, voids in mineral aggregates, voids filled with asphalt, density, Marshall Stability, Flow, test temperature, peak loads, RCA content, and notch depths. The fracture resistance of the mixes was studied by analysing the fracture energy, tensile strength, and fracture toughness for the collected dataset. The data shows that incorporating up to 10 % of RCA into SMA mixes, similar fracture properties can be achieved compared to traditional SMA mixtures. This presents a sustainable and environmentally advantageous option, however, it is important to exercise caution as the RCA content increases.

Effect of calcium hydroxide as an intracanal medication on dentine fracture resistance: A systematic review and network meta-analysis.

INTRODUCTION: Bacterial infections necessitate effective root canal disinfection during endodontic therapy. Calcium hydroxide (CH), a widely used intracanal medication, shows conflicting effects on dentine fracture resistance in different studies. This study aimed to perform a comprehensive systematic review and network meta-analysis to evaluate the effects of CH on the fracture resistance of dentine in human teeth across different periods. METHODS: PubMed, EMBASE, MEDLINE (EBSCO), Cochrane Library, Scopus, Google Scholar, and ProQuest databases were exhaustively searched to identify studies published until February 29, 2024, with no language restrictions. Laboratory studies that investigated dentine fracture resistance in human permanent teeth following intracanal CH exposure were included. The risk of bias was evaluated using modified criteria derived from previous studies. Network meta-analysis was performed using the frequentist method. Prespecified subgroup analyses focused on simulating immature teeth. RESULTS: The search yielded 2,265 studies from all databases, and 27 met the inclusion criteria, involving 3,879 teeth or roots. The overall results from network meta-analysis indicated that CH affected the fracture resistance of human dentine. Subgroup analysis revealed that the duration influencing fracture resistance was ≥4 weeks for mature teeth, but no specific time limitation for immature teeth. The overall quality of the evidence showed a moderate to high risk of bias. CONCLUSIONS: Short-term use of CH does not compromise human root dentine strength, supporting its routine application in clinical practice. CH remains a viable treatment strategy for over 4 weeks medication needs but requires carefully considering the associated risks and benefits emphasizing on preservation and disease resolution.

Optimizing Root Canal Therapy: An In Vitro Comparative Study of Innovative File Systems on Mandibular Premolar Fracture Resistance.

INTRODUCTION AND AIM:  Root canal therapy is a vital procedure for saving teeth by removing infection and cleaning the complex root canal system. However, a delicate balance exists between thorough cleaning and preserving tooth strength. The study aims to evaluate the instrumentation effect of three innovative file systems, XP-endo® shaper, Reciproc®, and Self-adjusting file (SAF) on fracture resistance of mandibular premolars. MATERIALS AND METHODS: Thirty single-rooted mandibular premolars were collected; a standard access cavity was prepared and the working length was established 1 mm short of the apex. The teeth were randomly divided into three groups(n=10). In Group 1, the shaping of the specimens was achieved using XP-endo® shaper; in Group 2, it was instrumented using Reciproc® file; and in Group 3, it was instrumented using SAF. All samples were decoronated and the roots were mounted vertically in acrylic resin and subjected to fracture resistance under a universal testing machine. RESULTS: Intergroup analysis was done by one-way ANOVA followed by Bonferroni post hoc test, which did not report a statistically significant difference (p>0.05). CONCLUSION: All three tested file systems were similar in fracture resistance. XP-endo® shaper exhibited better fracture resistance on root canal instrumentation when compared to Reciproc® and SAF although they are not statistically significant.

Effect of Pulp Chamber Access, Instrumentation, Obturation, and Restoration on the Fracture Resistance of Endodontically Treated Canine Teeth in Dogs.

Veterinary studies documenting the effect of endodontic treatment on tooth fracture resistance are scarce. The objective of this ex vivo study was to evaluate the effects of mesial access preparation and restoration, as well as pulp chamber access, instrumentation, obturation, and restoration, on the fracture resistance and characteristics of canine teeth in dogs. Sixty-five dog canine teeth were divided into 4 groups: 1. Standard endodontic treatment through a mesial access only; 2. Treatment as per group 1, adding an incisal access, instrumentation and obturation of the pulp chamber, and restoration of the access; 3. Treatment as per group 2, without pulp chamber obturation or restoration of the incisal access; and 4. Untreated teeth. The fracture resistance and characteristics of each group were documented using axial compression testing, angled 45° disto-occlusal to the long axis of the crown. The maximum force prior to fracture in groups 1, 3, and 4 were not statistically different, demonstrating that restored mesial and incisal accesses with pulp chamber instrumentation did not statistically affect fracture resistance. However, obturated and restored group 2 teeth demonstrated decreased fracture resistance compared to all other groups (P < .001). Additionally, 26.7% of group 1 teeth sustained complicated crown fractures, while 100% of group 2 teeth fractured within the obturation or restorative materials, preventing pulp exposure in these cases. Although the cause and clinical importance of decreased tooth fracture resistance following pulp chamber obturation and restoration remains unknown, it may provide protective value for maintaining a coronal seal in the event of tooth fracture.

Impact of Pericervical Dentin on Fracture Resistance of Endodontically Treated Posterior Permanent Teeth: A Systematic Review and Meta-analysis.

OBJECTIVE: The main aim of this present systematic review is to evaluate if the preservation of pericervical dentin (PCD) increases the fracture resistance of endodontically treated permanent posterior teeth. MATERIALS AND METHODS: Two independent reviewers conducted a comprehensive review of all published studies from 2007 (1/1/2007) to 2023 (31/5/23) since the concept of PCD first appeared in the literature in 2007. Searches were conducted in multiple electronic database engines: PubMed, Scopus, EBSCO (Dentistry and oral health sciences), Web of Sciences (WOS), Cochrane, Google Scholar and Open Grey, Ovid and Shodhganga, in addition to cross-references and hand search. Articles were chosen according to a certain inclusion and exclusion criteria, which, in brief, are laboratory-based studies published in English that assess the impact of PCD on fracture resistance of endodontically treated permanent posterior teeth. Using domains, such as sample size, sample dimensions, and control group as quality assessment criteria, evaluated the selected articles and classified them according to their risk of bias into low, moderate, and high. A meta-analysis was conducted using random effects modeling at a significance level of p < 0.05. RESULTS: A total of studies 6,043 were retrieved from 10 different electronic search databases and hand searches, but only 12 laboratory-based studies were selected after removing duplicates and applying the eligibility criteria. Of the included 12 studies, nine studies showed low risk of bias and three studies showed moderate risk of bias. Two studies showed related data for meta-analysis, the difference observed between the two studies is statistically non-significant. CONCLUSION: Based on the results of the study, there is evidence to support that PCD preservation offers fracture resistance to the endodontically treated posterior teeth. CLINICAL SIGNIFICANCE: The practice of conservative cavity preparation and avoiding the usage of instruments with high taper increases the fracture resistance of the tooth by retaining the PCD. How to cite this article: Haridoss S, Rajendran M, Swaminathan K, et al. Impact of Pericervical Dentin on Fracture Resistance of Endodontically Treated Posterior Permanent Teeth: A Systematic Review and Meta-analysis. J Contemp Dent Pract 2024;25(4):372-385.

Effect of Fiber-Reinforced Composite Placement Site on Fracture Resistance of Premolar Teeth: An in vitro Study.

Background: This study aimed to investigate the fracture behavior of upper premolars with deep MOD cavities that were restored with Ribbond resin-reinforced fibers (FRCs) placed in different orientations. Methods: A total of 54 extracted maxillary premolars were randomly divided into nine groups. The experimental groups underwent MOD cavity preparation with or without root canal treatment, followed by FRCs placed in the pulpal floor, proximal walls, or both. Fracture resistance was tested using an Instron Machine. The samples were visually inspected to analyze the fracture mode. Results: The highest fracture resistance was observed in intact teeth (1299.98 ± 284.66 MPa). Placing Ribbond fibers in the pulpal floor (1155.86 ± 244.21 MPa) or the proximal walls (1077.56 ± 260.60 MPa) significantly improved fracture resistance (p= <0.05), compared to cavities restored with only resin composite (804.58 ± 93.34 MPa). However, placing Ribbond fibers in both the pulpal and proximal walls did not enhance fracture resistance. In the MOD-RCT groups, fracture resistance was improved only when Ribbond fibers were placed in the pulpal floor and the proximal walls. Fracture mode analysis revealed a combined fracture in most of the groups. Conclusion: This study concluded that using FRCs significantly improved the fracture resistance of MOD cavities in premolars and revealed that the placement site could be a determinant factor.

This study investigated the fracture behavior of upper premolars with deep MOD cavities restored with Ribbond resin-reinforced fibers (FRCs) placed in different orientations.Placing Ribbond fibers in the pulpal floor or the proximal walls significantly improved the fracture resistance of premolars with deep MOD cavities.In the MOD-RCT groups, fracture resistance was improved only when Ribbond fibers were placed in the pulpal floor and the proximal walls.Fracture mode analysis revealed a combined fracture in most of the groups. This study concluded that using FRCs significantly improved the fracture resistance of MOD cavities in premolars and revealed that the placement site could be a determinant factor.

Exploring access cavity through non-carious cervical lesions: Impacts on instrumentation, obturation, and fracture resistance in mandibular incisors.

AIM: To compare the effects of Cervical Access Cavity (CervAC) and Traditional Access Cavity (TradAC) on root canal preparation, root canal filling, and fracture resistance in mandibular incisors. METHODOLOGY: Twenty recently extracted and intact mandibular incisors were initially scanned using a micro-CT device. The specimens were anatomically matched to create two groups (n = 10). A wedge-shaped non-carious cervical lesion (NCCL) was created on the buccal aspect of all teeth using a double-faced segmented diamond disc. In group 1, a TradAC was prepared, whilst in group 2, access was created through the simulated NCCL using a round diamond bur 1012. After root canal preparation with Rotate instruments sizes 15/0.04, 20/0.04, and 25/0.04, the teeth were scanned again and evaluated for root canal volume and surface area, static voxels, volume of removed dental tissue, and dentine thickness. After that, the root canals were filled using the single-cone technique, teeth were restored with composite resin, and subsequently rescanned to calculate the volume of filling materials and voids. Then, the restored teeth were subjected to fracture resistance tests using a universal testing machine. Statistical comparisons between groups were performed with the Mann-Whitney test or the Student's t-test, with a statistical significance level of 5%. RESULTS: Statistical comparisons indicated no significant differences between groups in terms of root canal volume, surface area, static voxels, removed root dentine, root canal filling volume, percentage of voids, or fracture resistance load (p > .05). Conversely, teeth prepared with TradAC showed a significantly higher percentage of dental tissue removed from the crown (p = .001) and a greater volume of filling material remnants in the pulp chamber (p < .001) compared to the CervAC group. A significantly lower percentage reduction in dentine thickness was observed only on the mesial aspect of root at Level 1 in TradAC group (p = .008). CONCLUSIONS: CervAC can be considered a viable alternative approach in the presence of NCCL in mandibular incisors.

Effect of placement strategies and connector designs in CAD/CAM technology on fracture resistance of multilayered monolithic zirconia fixed dental prostheses: An in vitro study.

This study evaluated fracture resistance of monolithic fixed dental prostheses (FDPs) fabricated using different placement strategies of various connector designs in multilayered zirconia disc. Monolithic FDPs were placed in translucent and dentin layers of multilayered zirconia disc and fabricated with V-shaped and U-shaped connector designs gained by sharp and blunt millings. The FDPs were cemented on abutment models made of polymer material, underwent thermal cycles, and loaded to fracture using the universal testing machine. Fracture loads and modes were analyzed using two-way ANOVA, Tukey's post hoc test, and Fisher exact test (p≤0.05). The chosen placement strategy and connector designs gained by different milling procedures in computer-aided design/computer-aided manufacturing technology affect fracture resistance of monolithic FDPs made of multilayered zirconia materials. Placing the connector in translucent layer rather than dentin layer of multilayered zirconia disc and using sharp milling significantly reduces fracture resistance of monolithic multilayered zirconia FDPs.

Influence of remaining coronal tooth morphology with resin abutment and fiber post on static and dynamic fracture resistances.

This study aimed to clarify the fracture resistance of resin abutments built on endodontically treated roots with the remaining coronal teeth via static and cyclic loading tests. Endodontically treated bovine roots, which had a remaining coronal tooth covered with an occupied area for a quarter and half of the circumference at the tensile side or covered the circumference at both the tensile and compressive sides, were fabricated to build up to the resin abutment. Fracture resistance was evaluated via static and cyclic loading tests by applying a load of 30° to the tooth axis. Half of the circumference of the remaining coronal tooth showed a significantly higher static fracture load and survival rate. The remaining coronal tooth on the compressive side improved the dynamic fracture resistance associated with severe fractures. The occupied area and location of the remaining coronal tooth affected the static and dynamic fracture resistances.

Evaluation of fracture resistance and marginal fit of implant-supported interim crowns fabricated by conventional, additive and subtractive methods.

BACKGROUND: Interim crowns are utilized for restoring implants during and after the process of osseointegration. However, studies on adaptation and fracture strength of implant-supported interim crowns are rare. AIM OF THE STUDY: The aim of this in vitro study is evaluating marginal fit and fracture resistance of conventional, subtractive, and additive methods of fabricating implant-supported interim crowns. MATERIALS AND METHODS: An implant was placed in an epoxy resin model with a missing first molar. A scan body was attached, and scanned with an intraoral scanner (IOS), the STL file was used to fabricate eighteen master models with standardized implant digital analogue spaces. The digital analogues and their corresponding abutments were attached to the master models and scanned with the IOS, the STL files were used to fabricate eighteen crowns using three different techniques (n = 6): conventional (CR); from Autopolymerizing composite resin, subtractive (SM); milled from PMMA resin blanks, and additive (AM); from 3D printed resin material. The crowns were fitted and cemented on their corresponding abutments and subjected to cyclic loading and thermocycling. The marginal fit was evaluated using a stereomicroscope. The crowns were then loaded until fractured in a universal testing machine. The Shapiro-Wilk and the Kolmogorov-Smirnov tests revealed that data of Marginal gap was non-parametric. Kruskal-Wallis test followed by the Dunn test was used (α = 0.05). While data of Fracture resistance test was parametric. ANOVA (F-test) was used followed by the Tukey test (α = 0.05). RESULTS: For marginal gap, a significant difference was shown between the study groups (P = .001) according to Kruskal-Wallis test. Groups SM and AM had significantly lower marginal gap values compared to group CR (P = .003). No significant difference was found between groups SM and AM (P = .994). For fracture resistance, One-way ANOVA revealed a significant difference in fracture resistance between study groups (P < .001). Group SM had significantly higher fracture strength followed by group AM and group CR (P = .001). CONCLUSIONS: Group SM and AM showed better marginal adaptation than group CR. Group SM showed superior fracture resistance compared to other groups. All study groups showed acceptable marginal gap and fracture resistance.

Comparative Evaluation of Fracture Resistance of Composite Core Buildup Materials: An In Vitro Study.

Aim This study aimed to compare the fracture resistance of different materials used in composite core buildups, including conventional filler composite, nanofiller composite, and short fiber-reinforced composite (SFRC). Methods This in vitro study was conducted on 30 freshly extracted premolars. The teeth were treated using a uniform endodontic procedure, and Fiber Posts (REFORPOST, Angelus) were placed. The teeth were then divided into three groups and restored using different materials. Group 1 was restored using SFRC (everX Posterior, GC, Europe), Group 2 using microfiller composite (Te-Econom Flow, Ivoclar Vivadent), and Group 3 using nanofiller composite (Tetric N-Flow, Ivoclar Vivadent). The restoration materials were then light-cured for 40 seconds. The teeth were placed in a Universal Testing Machine (Instron) and a load was applied with a stainless-steel ball (4 mm diameter) until the tooth fractured. The fracture load for each tooth was recorded, and after the mechanical test, the experimental groups were examined for failure modes. Statistical analysis was performed using SPSS version 21.0 software. A one-way ANOVA test was conducted to compare more than two groups, followed by Tukey's test for post hoc pairwise comparison. Results The mean fracture resistance of the microfiller composite (346.94±44.63) was the lowest among the three groups. When analyzed using Tukey's test at p<0.05, fracture resistance was significantly higher in the SFRC, followed by nanofillers and microfiller composites. Conclusion Due to the increasing demand for aesthetic restorations in recent years, composites have become important in modern restorative dentistry. The development and implementation of composite dental restorative materials rely on a comprehensive understanding of each composite component and consideration of methods for modifying each component. As a result, the findings of this study will be beneficial in determining which material to use based on specific cases.

Reinforcement of Teeth Having Reenacted Perforating Internal Resorption Cavities After Repair Using Different Calcium Silicate-based Cements and Backfilling Materials: An In vitro Study.

To evaluate the fracture resistance (FR) of the teeth having reenacted perforating internal resorption cavities repaired by distinctive calcium silicate-based cements (CSCs) specifically: Endocem MTA, Biodentine, NeoMTA Plus, and backfilling materials. Ninety-six freshly extracted human mandibular premolar teeth were selected. Twelve roots were used as the negative control group. Rotary files were used to complete the final irrigation and root canal preparation on the remaining teeth. Following that, burs were used to make standardized internal resorption chambers in the middle part of the roots. Twelve of these samples were used as positive control samples. The remaining 72 root canals were obturated in the apical 4 mm using a single-cone approach, and they were separated into 6 groups based on the CSCs used to fill voids and the materials used as backfilling. Group 1: Endocem MTA (resorption) + Endocem MTA (coronal), Group 2: Endocem MTA (resorption) + Gutta-percha/sealer (coronal), Group 3: Biodentine (resorption) + Biodentine (coronal), Group 4: Biodentine (resorption) + Gutta-percha/sealer (coronal), Group 5: NeoMTA Plus (resorption) + NeoMTA Plus (coronal), and Group 6: NeoMTA Plus (resorption) + Gutta-percha/sealer (coronal). Specimens were inserted in acrylic resin and then subjected to fracture testing. Fracture strength tests were performed using a Universal Testing Machine. The force was employed vertically with a consistent speed of 1 mm/minute. The results were analyzed with Variance and Bonferrini tests at P < 0.005. The mean force of fracture values were 447.00, 201.25, 318.75, 187.50, 596.58, 258.75, 347.50, and 298.75 N for Group 1, 2, 3, 4, 5, 6, 7, and 8, respectively. "There was a significant difference (P < 0.001) between the experimental groups and the control group". Group 5 showed the highest FR as compared to other groups. Backfilling with CSCs appears to be a better material than a gutta-percha/sealer combination. Neo MTA plus furthermore appeared the highest fracture-resistant material, while Biodentine + Gutta percha/sealer showed the least FR.

Fracture resistance of CAD/CAM milled versus direct hand-made interim laminate veneers.

Background: Comparative studies of interim veneer restorations crafted using subtractive computer-aided manufacturing (s-CAM) milling technology and traditional direct hand-made approaches are needed. Purpose: This comparative in vitro study evaluated the fracture resistance of two types of provisional veneer restorations for maxillary central incisors: milled (s-CAM) and traditional direct hand-made bis-acryl veneers. Materials and methods: Fifty maxillary right central incisor veneers (25 specimens per group) were fabricated and divided according to the fabrication method: (1) s-CAM milled (Structure CAD, VOCO Dental); and (2) hand-made (Protemp Plus, 3M). The restorations were cemented onto 3D-printed resin dies using temporary cement and subjected to 1000 cycles of thermal cycling between 5° and 55 °C. These restorations subsequently were subjected to compressive loading until fracture occurred. Images of the fractured samples were captured using a scanning electron microscope (SEM). Statistical analysis was performed using the one-way ANOVA test and the Mann-Whitney U test. Results: Significant differences (p < 0.001) in the fracture resistance were observed between the two groups. s-CAM milled interim veneers displayed higher fracture resistance values (439.60 ± 26 N) compared to the traditional method (149.15 ± 10 N). Conclusion: The manufacturing method significantly influences the fracture resistance of interim veneer restorations. s-CAM interim laminate veneer restorations for maxillary central incisors exhibit a fracture resistance superior to that of the traditional method using bis-acryl.Clinical relevanceClinicians should consider CAD/CAM milled veneers for scenarios demanding long-term interim restoration and the withstanding of high occlusal forces.

The influence of hygroscopic expansion of resin supporting dies on the fracture resistance of ceramic restorations during thermal cycling.

OBJECTIVES: To evaluate the hygroscopic expansion characterization of resin composite dies during thermal cycling, and their influence on the fracture resistance of dental ceramic materials as well as the effect of pre-immersion on these measurements. METHODS: Disc-shaped specimens (φ = 15.0 mm, h = 1.2 mm) and anatomical crown dies of four resin composites (epoxy, Z350, P60, G10) were fabricated. Disc-shaped samples were continuously soaked in distilled water and the volume expansion was measured at different time point by Archimedes method. Disc-shaped samples were pre-immersed for 0, 7, or 30 days, elastic modulus and hardness were measured using Nanoindentation test; thermal cycling (TC) test was performed (5 °C-55 °C, 104 cycles), and volume expansion during TC was measured. Four kinds of resin die with pre-immersion for 0, 7, or 30 days were cemented to 5Y-Z crown, or epoxy dies without pre-immersion were cemented to 5Y-Z, 3Y-Z and lithium disilicate glass (LDG) crowns, and load-to-failure testing was performed before and after TC. Finite element analysis (FEA) and fractography analysis were also conducted. RESULTS: The hygroscopic expansion was in the order: epoxy > Z350 > P60 > G10. Except for G10, the other three resin composites exhibited different degrees of hygroscopic expansion during TC. Only the elastic modulus and hardness of epoxy decreased after water storage. However, only the fracture loads of 5Y-Z and LDG crowns supported by epoxy dies were significantly decreased after TC. FEA showed a stress concentration at the cervical region of the crown after volume expansion of the die, leading to the increase of the peak stress at the crown during loading. SIGNIFICANCE: Only the hygroscopic expansion of epoxy dies caused by TC led to the decrease in the fracture resistance of the 5Y-Z and LDG crown, which may be related to the decrease in the elastic modulus of the epoxy die and the tensile stress caused by it.

Fracture Resistance of Direct versus Indirect Restorations on Posterior Teeth: A Systematic Review and Meta-Analysis.

The aim of this systematic review and meta-analysis was to compare static compression forces between direct composite resin restorations and indirect restorations for posterior teeth. All studies comparing mechanical properties of direct versus indirect restorations of posterior teeth were included from 2007 up to February 2024. A meta-analysis was conducted for static compression fracture resistance. Medline, Central, and Embase databases were screened. Twenty-four articles were included in the qualitative synthesis, and sixteen studies were finally included in the quantitative synthesis. There was no difference in terms of fracture resistance between direct and indirect restorations for posterior teeth (p = 0.16 for direct and indirect composite resin restorations and p = 0.87 for direct composite resin restorations and indirect ceramic restorations). Also, sub-group analysis with or without cusp coverage in each group revealed no discernable difference. Based on this study, it can be concluded that the choice between direct and indirect restoration approaches may not significantly impact fracture resistance outcomes. There was no statically significant difference between direct and indirect restorations for posterior teeth in all cases of restorations with or without cusp coverage and no matter the used materials. However, to better evaluate these materials, further studies are warranted.