Comparative evaluation of clinical success of Stainless Steel and Bioflx crowns in primary molar - A 12 month split mouth prospective randomized clinical trial.

PURPOSE: The purpose of this clinical trial was to assess and compare the clinical outcomes of Bioflx crowns (BFCs) with stainless steel crowns (SSCs) in primary molars (PMs). MATERIALS AND METHODS: This prospective split-mouth randomized controlled clinical trial was conducted between March 2022 and June 2023. Thirty-eight patients (17 females and 21 males) with a mean age of 5.21 years participated in this study. Each child (n = 38) received both SSC and BFC. Clinical and radiographic follow-up was performed at baseline, 3, 6, and 12 months using the modified United States Public Health System scoring criteria to evaluate various parameters. RESULTS: At the 3 and 6 months' follow-up, no significant difference was observed between the two groups. However, at 1-year follow-up, a statistically significant difference (P < 0.05) was evident in the frequency between the two groups for the criteria of crown retention after cementation and anatomic form of the crown, indicating a preference for SSC over prototype 1 BFC. CONCLUSION: The 12-month results indicate that BFC performed similarly to the established SSC for the restoration of PMs providing better esthetics.

Clinical application principles and new developments of zirconia crown.

Zirconia crown has been widely used in the field of prosthodontics. Traditional zirconia exhibits excellent mechanical properties but lacks translucency. The introduction of transparent zirconia significantly enhances its aesthetic performance. In clinical applications, factors affecting the aesthetic results of full zirconia crown should be comprehensively considered, and the most suitable restoration should be chosen. Additionally, clinicians need to design appropriate tooth preparation dimensions and methods based on an individual patient's actual situation. During the clinical bonding process of zirconia, proper surface treatment of the tooth and restoration is essential. The selection of suitable adhesives is crucial for achieving optimal bonding strength and aesthetics.

One case of complicated crown root fracture of upper anterior teeth managed by multidisciplinary joint approaches.

Complicated crown root fracture is a serious combined fracture of the enamel, dentin, and cementum in dental trauma. The treatment method is complicated. During the procedure, the condition of pulp, periodontal, and tooth body should be thoroughly evaluated, and a multidisciplinary approach combined with sequential treatment is recommended. This case reported the different treatment and repair processes of one case of two affected teeth after complicated crown root fracture of upper anterior teeth, including regrafting of broken crown after flap surgery at the first visit, direct resin repair to remove broken fragments, and pulp treatment and post-crown repair at the second visit. After 18 months of follow-up, the preservation treatment of the affected teeth with complicated crown root fracture was achieved. Therefore, fragment reattachment and post-crown restoration are feasible treatment options for children with complicated crown root fracture.

Trueness, physical properties, and surface characteristics of additive-manufactured zirconia crown.

OBJECTIVE: This study aimed to conduct a comparison of trueness and physical and surface properties among five distinct types of additive manufactured (AM) zirconia crowns and zirconia crowns produced using the subtractive manufacturing (SM). MATERIAL AND METHODS: Zirconia crowns were fabricated using five distinct techniques, each varying in the method of slurry transfer and photocuring source. Each experimental group utilized either one of the four digital light processing (DLP)-based techniques (DLP spreading, DLP spreading gradation, DLP vat and DLP circular spreading) or the stereolithography (SLA)-based technique (SLA spreading). The control (CON) group employed SM. To assess accuracy, trueness was measured between the scan and reference data. To analyze the physical properties, voids were examined using high-energy spiral micro-computed tomography scans, and the crystal structure analysis was performed using X-ray diffraction (XRD). Surface roughness was assessed through laser scanning microscopy. RESULTS: Differences in the trueness of internal surfaces of crowns were found among the groups (P < 0.05). Trueness varied across the measurement surfaces (occlusal, lateral, and marginal) in all the groups except for the DLP spreading gradation group (P < 0.05). Voids were observed in all AM groups. All groups showed similar XRD patterns. All AM groups showed significantly greater surface roughness compared to the CON group (P < 0.001). CONCLUSION: The AM zirconia crowns showed bubbles and a rougher surface compared to the SM crowns. All groups exhibited typical zirconia traits and trueness levels within clinically acceptable limits, suggesting that current zirconia AM techniques could be suitable for dental applications.

Marginal fit of 3-unit implant-supported fixed partial dentures: Influence of pattern fabrication method and repeated porcelain firings.

BACKGROUND: Marginal fit significantly impacts the long-term success of dental restorations. Different pattern fabrication methods, including hand-waxing, milling, or 3D printing, may affect restorations accuracy. The effect of porcelain firing cycles on the marginal fit of metal-ceramic restorations remains controversial, with conflicting findings across studies. PURPOSE: The aim was to evaluate the potential effects of multiple porcelain firings (3, 5, 7 cycles) as well as pattern fabrication method (conventional hand-waxing, milling, and 3D printing) on the marginal adaptation of 3-unit implant-supported metal-ceramic fixed partial dentures. It was hypothesized that neither the wax pattern fabrication method nor repeated ceramic firings would significantly affect the marginal adaptation of metal-ceramic crowns. METHODS: In this in-vitro study, 30 Cobalt-Chromium alloy frameworks were fabricated based on pattern made through three techniques: conventional hand-waxing, CAD-CAM milling, and CAD-CAM 3D printing (n = 10 per group). Sixteen locations were marked on each abutment to measure the vertical marginal gap at four stages: before porcelain veneering and after 3, 5, and 7 firing cycles. The vertical marginal gap was measured using direct microscopic technique at ×80 magnification. Mean vertical marginal gap values were calculated and two-way ANOVA and Tukey's post hoc tests were used for inter-group comparisons (α = 0.05). RESULTS: The 3D printing group showed significantly lower (P<0.001) mean vertical marginal gaps (60-76 µm) compared to the milling (77-115 µm) and conventional hand-waxing (102-110 µm) groups. The milling group exhibited a significant vertical gap increase after 3 firing cycles (P<0.001); while the conventional (P = 0.429) and 3D printing groups (P = 0.501) showed no significant changes after 7 firing cycles. Notably, the vertical marginal gap in all groups remained below the clinically acceptable threshold of 120 µm. CONCLUSION: CAD-CAM 3D printing provided superior marginal fit compared to CAD-CAM milling and conventional hand-wax pattern fabrication methods. The impact of porcelain firing on the mean marginal gap was significant only in the milling group. All three fabrication techniques yielded clinically acceptable vertical marginal adaptation after repeated firings. Additive manufacturing holds promise to produce precise implant-supported prostheses.

[Evaluation of the effect of MTF-S on the removal of impacted mandibular wisdom teeth with complete or partial crown impaction].

PURPOSE: To evaluation the effect of modified triangular flap-secondary healing (MTF-S) on the treatment of mandibular impacted wisdom teeth with full or partial bone impaction. METHODS: A total of 207 patients with mandibular impacted wisdom teeth were selected in Shaoxing Stomatological Hospital from June 2022 to June 2023. Among them, 86 patients had completely impacted wisdom teeth (group A), and 121 patients had partially impacted wisdom teeth (group B). All patients had bilateral impacted wisdom teeth. One of the wisdom teeth was removed first and was sutured with triangular flap-primary healing (TF-P). The other wisdom tooth was removed two weeks later and was sutured with MTF-S. Patients in groups A and B were divided into two subgroups based on suture methods, with TF-P used for group A1 and B1, and MTF-S used for groups A2 and B2. Perioperative indicators, including surgical time, root loss rate, and completeness of extraction sockets were recorded; Postoperative complications of four groups, including pain, swelling, and limited mouth opening were compared. SPSS 22.0 software package was used for statistical analysis. RESULTS: The surgical time of group A1, A2, B1 and B2 was (17.69±3.28), (18.22±3.06), (12.37±3.72) and (12.64±4.13) minutes, respectively. The surgical time of group A1 and A2 was significantly longer than that of group B1 and B2 (P＜0.05). Seven days after surgery, the VAS scores of group A1, A2, B1 and B2 were (1.17±0.34), (0.93±0.29), (0.48±0.15) and (0.76±0.21), respectively. The VAS scores of group B1 and B2 were lower than those of group A1 and A2, and group A2 was lower than group A1 and B2 was higher than group B1 group(P＜0.05). On the 1st day, 3rd day, and 7th day after surgery, the swelling degree in group A1 was greater than that in group B1, and the swelling degree in group B1 was greater than that in group A2 and B2(P＜0.05); while the limitation of mouth opening mouth in group A2 and B2 was lower than that in group A1 and B1, and the limitation of opening mouth in group B2 was lower than that in group A2(P＜0.05). CONCLUSIONS: Compared with partially impacted wisdom teeth, the extraction of completely impacted wisdom teeth has a longer surgical time. For completely impacted wisdom teeth, MTF-S is beneficial for reducing postoperative pain, swelling and mouth opening limitations. For partially impacted wisdom teeth, MTF-S is beneficial for reducing postoperative swelling and mouth opening limitations, but the effect is not significant in reducing patient pain.

Clinical evaluation of resorbable polylactic acid (PLA) intracanal posts for primary incisor restoration. Randomized controlled clinical trial.

This randomized, controlled clinical trial compares the clinical performance of glass-fibre and resorbable polylactic acid (PLA) intracanal posts used to restore carious primary incisors in young patients. The study sample includes 180 primary upper central incisors of 90 children aged 3 to 4 years. All patients were randomly divided into two equal groups of 45 children who received PLA and glass-fibre (GFP) intracanal posts. The clinical assessment of incisor restorations was carried out immediately upon completion and at months 3, 6 and 12 according to the following criteria: anatomical form, marginal adaptation, surface roughness, marginal pigmentation, colour match, secondary caries and contact point. The Gingival Index (GI), the Bleeding Index (Cowell modification; mBI), and bite force (BF) were measured. At the 3-month follow-up, the occlusal BF of patients who received PLA posts was higher than the baseline; the GI and mBI scores were lower, by contrast (p < 0.05). This tendency was even more pronounced 6 and 12 months after the restoration. The incidence of side effects or symptoms (apical inflammation, cervical fracture, loosening of the crown) after the PLA posts was significantly lower than after the GFP (p < 0.05). No statistically significant differences were present between the two groups with respect to colour matching, anatomical form, marginal adaptation, marginal pigmentation, surface roughness, occlusal contact and secondary caries. Based on the results, applying PLA intracanal posts and cyanoacrylate to residual anterior crowns in young children can improve their gingival health, reduce side effects, and increase the likelihood of successful restoration.

Dentinogenesis imperfecta: case report with nanoceramic resin crowns restorative treatment.

Children with dentinogenesis imperfecta require restorative or prosthodontic treatment to minimize the aesthetic and functional impact of the condition. This clinical case report describes the oral rehabilitation procedure in a 12-year-old patient with dentinogenesis imperfecta type II using nanoceramic resin crowns fabricated with Computer-Aided Design/Computer-Aided Manufacturing (CAD/CAM) technology and the patient's progression over eight years. This minimal intervention approach enabled functional and aesthetic reestablishment along with tooth wear prevention. The result simplified an extensive prosthetic procedure and facilitated an affordable rehabilitation for the young patient while providing excellent long-term outcomes.

Comparative analysis of stress distribution in residual roots with different canal morphologies: evaluating CAD/CAM glass fiber and other post-core materials.

BACKGROUND: The selection of post-core material holds significant importance in endodontically treated teeth, influencing stress distribution in the dental structure after restoration. The use of computer-aided design/computer-aided manufacturing (CAD/CAM) glass fiber post-core possesses a better adaptation for different root canal morphologies, but whether this results in a more favorable stress distribution has not been clearly established. MATERIALS AND METHODS: This study employed finite element analysis to establish three models of post-core crown restoration with normal, oversized, and dumbbell-shaped root canals. The three models were restored using three different materials: CAD/CAM glass fiber post-core (CGF), prefabricated glass fiber post and resin core (PGF), and cobalt-chromium integrated metal post-core (Co-Cr), followed by zirconia crown restoration. A static load was applied and the maximum equivalent von Mises stress, maximum principal stress, stress distribution plots, and the peak of maximum displacement were calculated for dentin, post-core, crown, and the cement acting as the interface between the post-core and the dentin. RESULTS: In dentin of three different root canal morphology, it was observed that PGF exhibited the lowest von Mises stresses, while Co-Cr exhibited the highest ones under a static load. CGF showed similar stress distribution to that of Co-Cr, but the stresses were more homogeneous and concentrated apically. In oversized and dumbbell-shaped root canal remnants, the equivalent von Mises stress in the cement layer using CGF was significantly lower than that of PGF. CONCLUSIONS: In oversized root canals and dumbbell-shaped root canals, CGF has shown good performance for restoration of endodontically treated teeth. CLINICAL RELEVANCE: This study provides a theoretical basis for clinicians to select post-core materials for residual roots with different root canal morphologies and should help to reduce the occurrence of complications such as root fracture and post-core debonding.

Impact of Auxiliary Features on Retention of Short Dental Crowns: An In-Vitro Analysis of Box and Groove Preparations.

BACKGROUND Several auxiliary features have been proposed to achieve sustainable retention for short-prepared dental crowns; however, achieving retention is challenging. This study aimed to assess the impact of increased total occlusal convergence and auxiliary preparation factors like box and groove on the retention form of short tooth preparations. MATERIAL AND METHODS Eighty resin machine-milled dies with a height of 3 mm and a deep chamfer margin of 1 mm were prepared to mimic the short-prepared molar. Initially, 2 teeth were prepared following the guidelines, and the total occlusal convergence was kept at 10° and 20°, respectively. Auxiliary features such as the proximal box and buccal groove were prepared on separate 20° dies. Eighty dies were prepared with 10 samples each for 10°, 20°, 20° with proximal box and 20° with buccal groove for zirconia (n=40) and metal crowns (n=40). Cementation was done with glass ionomer luting cement, and a pull-off test was conducted. Data were analyzed using one-way analysis of variance and post hoc fisher least significant difference test (P<0.05). RESULTS The highest mean was observed in the proximal box group with the metal crown (14.59), and the lowest in the group with 20° zirconia crowns (9.12). Within groups, the highest retentive values were found for the 20° taper with proximal box preparation; the lowest was for the 20° taper group. CONCLUSIONS Within the study limitations, it could be concluded that incorporating a proximal box or buccal groove in short tooth preparations with an increased total occlusal convergence improved retentive values.

Trueness of Crown Preparation Dies in Dental Models: An In Vitro Assessment of Digital and Analog Workflows.

PURPOSE: To assess crown die trueness using additive manufacturing (AM) based on intraoral scanning (IOS) data and compare it with stone models. MATERIALS AND METHODS: Crown dies with four finish line types- equigingival shoulder (SAE), subgingival shoulder (SAS), equigingival chamfer (CAE), and subgingival chamfer (CAS)-were incorporated into a reference model and scanned with a coordinate measurement machine (CMM; n = 1 scan). Trios4 (3Shape) scans generated a second reference dataset (IOS; n = 10 scans). Using scans, crown dies were produced with two different 3D printers (MAX UV385 [Asiga] and NextDent 5100 [3DSystems]; n = 10 per system). Stone dies were created from conventional impressions (n = 10). Specimens were digitized with a laboratory scanner (E4, 3Shape). Trueness was evaluated with Geomagic Control X (3DSystems). Data analysis was done using Shapiro-Wilk, Levene, ANOVA, and t tests (α < .05). RESULTS: All crown dies fell within the clinically acceptable trueness range (150 µm). IOS exhibited significantly lower (P < .05; Δ ≤ 21.7 µm) or similar trueness compared to stone models. Asiga dies demonstrated similar and NextDent significantly lower marginal trueness than IOS (P < .05; Δ ≤ 57.3 µm). Most AM margin areas had significantly lower trueness than stone (P < .001; Δ ≤ 57.2 µm). Asiga outperformed NextDent (P < .001). Shoulder trueness surpassed chamfer in optical scans (P = .01). Finish line design and gingiva location did not have a significant impact on AM and stone models (P > .05). CONCLUSIONS: Combining IOS and AM achieves clinically acceptable crown die trueness for single molar teeth. The choice of AM device is critical, with Asiga outperforming NextDent. Finish-line design has an impact on optical scans. Finish-line design and marginal gingiva location have little effect on AM trueness.

Evaluation of the Mechanical Properties of 3D-Printed Post and Core Systems.

PURPOSE: To evaluate and compare the fracture resistance and elastic modulus of 3D-printed post and core systems and fiber posts and composite cores. MATERIALS AND METHODS: Endodontic treatment was performed on 30 mandibular premolars, and post space preparation was performed. The teeth were then randomly divided into two groups (n = 15 per group): the 3D-printed (3DP) group and the fiber post and composite core (FPC) group. In the FPC group, fiber posts (Cytec Blanco 43.604, Hahnenkratt) were bonded with resin cement (RelyX U200, 3M), and the composite core dimension was standardized with a silicone index. In the 3DP group, the impression of the post space for each specimen was taken with pattern resin (Pattern Resin, GC America), and the coronal core was produced with the same silicone index. The impressions of the posts and cores were scanned, and then the custom post and core structures were fabricated from permanent crown resin material (Permanent Crown Resin, Formlabs) with a 3D printer (Form3B, Formlabs). Specimens were subjected to load tests with a universal testing machine (M500-25AT, Testometric). After fracture occurred, the fracture force and elastic modulus were calculated. The data were analyzed by independent sample t test (α = .05) Results: There was no statistically significant difference between the two groups in terms of peak fracture force (P = .626) and elastic modulus (P = .125), and no catastrophic root fractures were observed in either group. CONCLUSIONS: The fracture resistance of endodontically treated teeth was not significantly influenced by the post material. 3D-printed, custom-made resin posts were as effective as fiber glass posts with regard to fracture resistance.

Accuracy of Dental Restorations Fabricated Using Milling vs 3D-Printed Molds: A Pilot Study.

PURPOSE: To compare the accuracy of 12 different dental restorations fabricated with milling or 3D-printed molds and robotically controlled casting. MATERIALS AND METHODS: Twelve dental restorations (11 inlays and onlays and 1 crown) were made per restoration type, one per each of the 12 different teeth models (total of 24 restorations). On each tooth preparation, two restorations were manufactured using different CAD/ CAM techniques: (1) milling and (2) robotically controlled casting and 3D-printed molds. In addition, twolayer restorations were manufactured with 3D-printed molds. The marginal and internal gaps were evaluated at 120 points per restoration based on micro-CT 3D imaging. Internal gaps were evaluated using a replica technique with silicone. RESULTS: Median values (interquartile ranges) for marginal gaps, middle internal gaps, and central internal gaps were significantly lower for 3D-printed mold restorations (44.3 [65.4] µm, 95.4 [96.2] µm, and 104.6 [78.1] µm) compared to milled restorations (58.4 [93] µm, 145.9 [85.8] µm, and 138.6 [65.7] µm). Internal gaps in the 3D-printed mold group were 6% to 51% smaller than in the milled group. CONCLUSIONS: The accuracy of restorations fabricated with 3D-printed molds may be preferable compared to milled restorations, except in the case of crown restoration. However, additional studies with a larger number of samples and different types of restorations are needed to confirm the results.

Comparison of 3D-Printed Single Crown Outcomes Among Different Computer-Aided Design Software Programs.

PURPOSE: Low-cost resin 3D printers have been used to produce affordable interim single crowns in public and private dental practices. The purpose of this study was to assess the impact of different computer-aided design (CAD) software programs on 3D trueness, microscopic marginal and internal gaps, time to design, and interproximal contacts of low-cost 3D-printed single crowns. MATERIALS AND METHODS: This in vitro study was performed on a total of 90 standardized resin-prepared teeth adapted to a dental manikin. For comparison among CAD software programs, 45 tooth preparations received 3D-printed crowns designed with one of three CAD software programs by an experienced technician and identified as groups TRIOS (n = 15), EXOCAD (n = 15), and ZZ (Zirkonzahn; n = 15). To assess interoperator reproducibility, 15 additional crowns were designed by a dental clinician (group ZZ-DENT) and 15 by a dental prosthetic technician (group ZZ-PROS), both with basic 1-week CAD/CAM training. Finally, as a control group, 15 crowns were milled using a high-end five-axis milling device (group ZZ-CONTROL). Statistically significant differences for 3D trueness, microscopic gaps, time to design, and interproximal contacts among groups were assessed with the Kruskal-Wallis test. RESULTS: No statistically significant differences in 3D trueness or marginal or internal gaps were found, either among different software programs or CAD operators (P > .05). However, Group TRIOS took significantly longer to design than EXOCAD and ZZ groups (P = .001). Less-experienced operators were significantly outperformed in time and interproximal contacts (P = .001) by the CAD technician using the same software program. Finally, control milled crowns (ZZ-CONTROL) significantly outperformed the respective 3D-printed copies (ZZ) in all assessed variables (P < .001). CONCLUSIONS: Different CAD software programs may affect the time required to design, but they do not significantly affect clinical outcomes of low-cost 3D-printed resin crowns if designed by an experienced CAD technician.

Effect of Thermo-mechanical Cycling on Fracture Resistance of Different CAD/CAM Crowns: An In Vitro Study.

AIM: To evaluate the effect of thermo-mechanical cycling (TMC) on fracture resistance of different computer-aided design/computer-aided manufacture (CAD/CAM) crowns. MATERIALS AND METHODS: A total of 42 CAD/CAM crowns were fabricated on epoxy resin maxillary first premolar teeth and divided into three groups (n = 14) according to the material used: IPS e.max CAD (Ivoclar Vivadent) lithium disilicate (LD), Vita ENAMIC (VE) (VITA Zahnfabrik), Tetric CAD (Ivoclar Vivadent). Also, each group was subdivided into two equal subgroups according to TMC (n = 7). Subgroups (O) without TMC and subgroup (W) with TMC (5-55°C, 30 second, 75,000 cycles). All samples in each group were cemented with a universal bond (Tetric N bond universal) and adhesive resin cement (Variolink Esthetic DC) (Ivoclar Vivadent). Subsequently, the samples were loaded to failure in a universal testing machine at a crosshead speed of 1 mm/min, and the fracture pattern and the fracture resistance in each group were recorded. RESULTS: Fracture resistance was analyzed by one-way analysis of variance (ANOVA) test, followed by Tukey's post hoc test for pairwise comparison. Fracture resistance showed a significant difference between the tested groups before and after TMC; IPS e.max CAD has the highest value (1233.35 ± 97.72, 1165.73 ± 199.54 N) followed by Tetric CAD (927.62 ± 42.5, 992.04 ± 53.46 N) and Vita ENAMIC has lowest value (506.49 ± 74.24, 354.69 ± 90.36 N). CONCLUSION: Thermo-mechanical cycling affected the fracture resistance of both polymer-based CAD/CAM crowns. CLINICAL SIGNIFICANCE: For dental practitioners, both IPS e.max CAD and Tetric CAD can be used clinically for posterior teeth, providing satisfactory results and resistance to fracture. How to cite this article: Elmokadem MI, Haggag KM, Mohamed HR. Effect of Thermo-mechanical Cycling on Fracture Resistance of Different CAD/CAM Crowns: An In Vitro Study. J Contemp Dent Pract 2024;25(1):29-34.

The Effect of Modified Framework Design on the Fracture Resistance of IPS e.max Press Crown after Thermocycling and Cyclic Loading.

AIM: This study aimed to investigate the effect of modified framework (MF) design on the fracture resistance of IPS e.max Press anterior single crown after thermocycling and cyclic loading. MATERIALS AND METHODS: Two types of IPS e.max Press frameworks were designed (n = 10); standard framework (SF) with a 0.5 mm uniform thickness and MF with a lingual margin of 1 mm in thickness and 2 mm in height connected to a proximal strut of 4 mm height and a 0.3 mm wide facial collar. The crowns were cemented to resin dies, subjected to 5,000 cycles of thermocycling, and loaded 10,000 cycles at 100 N. A universal testing machine was used to load specimens to fracture, and the modes of failure were determined. RESULTS: The mean and standard deviation (SD) of fracture resistance were 219.24 ± 110.00 N and 216.54 ±120.02 N in the SF and MF groups. Thus, there was no significant difference (p = 0.96). Mixed fracture was the most common failure mode in both groups. We found no statistically significant difference between the groups (p = 0.58). CONCLUSION: The MF design did not increase the fracture resistance of IPS e.max Press crown. CLINICAL SIGNIFICANCE: Framework design is an essential factor for the success of all-ceramic restorations and its modification might be regarded as an approach to increase fracture resistance. Furthermore, the modified design was evaluated in metal-ceramic or zirconia crowns while less attention was paid to the IPS e.max Press crowns. How to cite this article: Golrezaei M, Mahgoli HA, Yaghoobi N, et al. The Effect of Modified Framework Design on the Fracture Resistance of IPS e.max Press Crown after Thermocycling and Cyclic Loading. J Contemp Dent Pract 2024;25(1):79-84.

Effect of thermocycling on the mechanical properties of permanent composite-based CAD-CAM restorative materials produced by additive and subtractive manufacturing techniques.

BACKGROUND: The aim of the study was to determine and compare the biaxial flexural strength (BFS) and Vickers hardness (VHN) of additive and subtractive manufactured permanent composite-based restorative materials, before and after thermal aging. METHODS: A total of 200 specimens were prepared; 100 disc-shaped specimens (diameter 13 × 1.2 mm) for the BFS test and 100 square specimens (14 × 14 × 2 mm) for the VHN test. The specimens were made from various materials: two subtractive composite-based blocks (Cerasmart 270 [CS], Vita Enamic [VE]), two additive composite-based resins used for two different vat polymerization methods (digital light processing [DLP]; Saremco Print Crowntec [SC] and stereolithography [SLA]; Formlabs Permanent Crown Resin [FP]), and one feldspathic glass-matrix ceramic block (Vita Mark II [VM]) as the control group. Specimens of each material were divided into two subgroups: thermal cycled or non-thermal cycled (n = 10). BFS and VHN tests were performed on all groups. Data were analyzed with two-way ANOVA and post hoc Tukey test (α = 0.05). RESULTS: The type of restorative material used for the specimen had a statistically significant influence on both BFS and VHN values. However, thermal cycling did not affect the BFS and VHN values. After thermal cycling, the results of the BFS test were ranked from best to worst as follows: CS, FP, SC, VE, then VM. For the VHN values, the order from best to worst was as follows: VM, VE, CS, FP, then SC. CONCLUSIONS: 3D printed and milled composite groups showed higher BFS than feldspathic ceramics. When the VHN results were examined, it was seen that the 3D resin groups had the lowest VHN values. Furthermore, it was observed that the thermal cycle had no effect on BFS or VHN.

Influence of screw channel angulation on reverse torque value and fracture resistance in monolithic zirconia restorations after thermomechanical cycling: an in-vitro study.

BACKGROUND: While the concept of angled screw channels has gained popularity, there remains a scarcity of research concerning the torque loss and fracture strength of monolithic zirconia restorations with various screw channel angulations when exposed to thermomechanical cycling. This in-vitro study aimed to evaluate the reverse torque value and fracture resistance of one-piece screw-retained hybrid monolithic zirconia restorations with angulated screw channels after thermomechanical cycling. METHODS: One-piece monolithic zirconia restorations, with angulated screw channels set at 0°, 15°, and 25° (n = 6 per angulation) were fabricated and bonded to titanium inserts using a dual-cure adhesive resin cement. These assemblies were then screwed to implant fixtures embedded in acrylic resin using an omnigrip screwdriver, and reverse torque values were recorded before and after thermomechanical cycles. Additionally, fracture modes were assessed subsequent to the application of compressive load. One-way ANOVA and Bonferroni post hoc test were used to compare the groups (α = 0.05). RESULTS: The study groups were significantly different regarding the fracture resistance (P = 0.0015), but only insignificantly different in the mean percentage torque loss (P = 0.4400). Specifically, the fracture resistance of the 15° group was insignificantly higher compared to the 0° group (P = 0.9037), but significantly higher compared to the 25° group (P = 0.0051). Furthermore, the fracture resistance of the 0° group was significantly higher than that of the 25° group (P = 0.0114). CONCLUSIONS: One-piece hybrid monolithic zirconia restorations with angulated screw channels can be considered an acceptable choice for angulated implants in esthetic areas, providing satisfactory fracture strength and torque loss.

Opinions of UK General Dental Practitioners on the Restoration of Posterior Root Filled Teeth: a Vignette Survey.

OBJECTIVE: To investigate factors which influence UK general dental practitioners (GDPs) when restoring posterior root filled teeth. METHOD: An electronic survey was designed to explore current strategies of treatment of posterior root filled teeth by UK-based GDPs working in primary care. Three vignette cases included in the questionnaire explored a variety of tooth, patient, and financial factors. The survey was distributed by email and social media platforms between December 2018 and February 2019. RESULTS: A total of 528 valid responses were collected. The majority of participants (84.1%) regularly restored posterior root filled teeth with an indirect restoration. Presence of persistent symptoms post root canal treatment (RCT) completion would impact the management of 85% of the surveyed respondents. Referral to a specialist, deferral of provision of the definitive restoration, and fear of litigation were reported by the GDPs as influencing factors. CONCLUSION: This survey highlights that decision making regarding restoration of root filled teeth is a multifactorial process. Tooth, patient, and financial factors were all shown to influence the restorative management of the posterior root filled teeth.

Auxiliary occlusal devices for IO scanning in a complete digital workflow of implant-supported crowns: a randomized controlled trial.

OBJECTIVES: To compare the crown accuracy and time efficiency of a complete digital workflow, utilizing an auxiliary occlusal device and IO scanning, with a conventional workflow, for multiple implant-supported single crowns. MATERIALS AND METHODS: 24 patients with two adjacent posterior implants were included. 12 patients were randomly assigned to digital workflow group, involving intra-oral scanning with an auxiliary occlusal device and manufacture of customized abutments and zirconia single crowns (test group). The other 12 were assigned to the conventional workflow (control group), involving conventional impression and CAD-CAM crowns based on stone casts. Crown scanning was done before and after clinical adjustment using an intraoral scanner. Two 3D digital models were overlapped to assess dimension changes. Chair-side and laboratory times for the entire workflow were recorded and a linear mixed model and Independent-sample t tests were used for the statistical analysis. RESULTS: The maximum occlusal deviation was 279.67 ± 112.17 µm and 479.59 ± 203.63 µm in the test and control group, respectively (p < 0.001). The sizes of the occlusion adjustment areas were 12.12 ± 10.51 mm2 and 25.12 ± 14.14 mm2 in the test and control groups, respectively (p = 0.013). The mean laboratory time was 46.08 ± 5.45 and 105.92 ± 6.10 min in the test and control groups, respectively (p < 0.001).The proximal contact adjustment and mean chair-side time showed no statistically significant difference between two groups. CONCLUSIONS: A digital workflow for two implants-supported single crowns using an auxiliary device required fewer occlusal crown adjustments, and less laboratory time compared to conventional workflow. CLINICAL RELEVANCE: The use of auxiliary occlusal devices in IOS enhances the accuracy of virtual maxillomandibular relationship in extended edentulous spans. Consequently, employing a digital workflow for multiple implants-supported crowns using IO scanning and an auxiliary occlusal device proves to be a feasible, accurate and efficient approach.