METHODS: 75 human mandibular molars were randomly divided into five equal groups. Teeth were standardized, endodontically-treated and restored according the assigned group as follows: amalgam core only, prefabricated titanium post in the distal canal and amalgam core, composite core only; fiber post in the distal canal and composite core. One group of untreated sound teeth was used as a control. Non-precious metal crowns were fabricated and cemented on the prepared specimens with Rely X U200 resin cement. All specimens were subjected to a compressive load at crosshead speed 0.5 mm/minute, 25° to the long axis of the tooth. Failure loads and modes were recorded.
RESULTS: Mean failure loads among the groups were significantly different (P= 0.035). Post-hoc multiple pair-wise comparisons revealed the amalgam core and composite core groups produced significantly lower fracture resistance than the control group (P= 0.041 and P= 0.025, respectively) and no significant differences among the different intra-radicular techniques (P> 0.05). The composite core with fiber post and amalgam core with titanium posts showed the highest percentage of favorable failures (67%) and non-favorable failures (87%) respectively.
CLINICAL SIGNIFICANCE: The composite core with fiber post is the most appropriate intraradicular restoration in cases of severely compromised molars.
PURPOSE: The purpose of this in vitro study was to evaluate the significance of geometric heterogeneity on complete arch implant scanning by using a novel auxiliary geometric device. Three different clinical simulations were tested to assess its significance. The study also assessed whether scans produced using the auxiliary device would meet a clinically acceptable threshold.
MATERIAL AND METHODS: A total of 60 scans (n=20) were performed using an intraoral scanner in 3 different clinical simulations: 2 parallel implants, 4 parallel implants, and 4 implants with a 30-degree posterior angulation of the distal implants. Scanning alternated between using the auxiliary geometric scanning device (test groups; 4IP+, 4IA+, 2IP+) and not using the device (control groups; 4IP-, 4IA-, 2IP-). A reference scan for each model was prepared from a high precision laboratory scanner. The scans were analyzed for accuracy in 3-dimensional deviation, interimplant distance deviation, and angular deviation by using an inspection software program. The effect of the auxiliary device was statistically analyzed by comparing scans of the same group using the paired t test for normally distributed data and the Wilcoxon Signed Rank test when data were not normally distributed (α=.05).
RESULTS: Significant effects of the auxiliary geometric device were found in 3-dimensional, distance and angular deviations (P
PURPOSE: The purpose of this systematic review was to gather, compare, and appraise studies that attempted to determine the biological and mechanical tolerance of misfits.
MATERIAL AND METHODS: The review protocol was published in the Prospective Register for Systematic Reviews (PROSPERO; registration no. CRD42021268399) and follows the Preferred Reporting for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. An electronic search was conducted through PubMed, Ebscohost, and Web of Science followed by a manual search up to December 2021.
RESULTS: A total of 413 manuscripts were identified by electronic and manual search. After removing duplicates, nonrelevant titles, and abstract screening, 62 manuscripts were eligible for full-text assessment. Finally, a total of 13 articles (1 cross-sectional study, 1 retrospective and prospective, 7 in vitro studies, and 4 animal studies) met the eligibility criteria and were included in this review. A wide range of tolerable misfits were reported. Vertical misfit up to 1 mm and horizontal misfit up to 345 μm were associated with no adverse outcomes.
CONCLUSIONS: The current literature provides inadequate data to determine a clinical threshold of an acceptable misfit. However, this review demonstrated that the mechanical response to misfit is more critical than the biological response.
PURPOSE: The purpose of this in vitro study was to test a newly designed scan-aid apparatus for evaluating the effect of geometric heterogeneity and additional reference points on the time efficiency and scanning precision of complete arch implant scanning.
MATERIAL AND METHODS: A total of 60 scans (20 per group) were performed using an intraoral scanner in 3 different clinical simulations: 2 parallel implants, 4 parallel implants, and 4 implants; 2 anterior implants in parallel axial orientation; and 2 distal implants with a 30-degree posterior inclination. The scanning procedure was alternated between scanning with the scan-aid apparatus (test groups; 4IP+, 4IA+, 2IP+) and without (control groups; 4IP-, 4IA-, 2IP-). A 3-dimensional (3D) inspection software program was used to assess scan precision. Test group scans were compared with a reference scan for repeatability, with and without the scan-aid apparatus. One scan per group was the reference; the others were superimposed by using a best-fit algorithm. The 3D standard deviations were recorded for repeatability analysis. To assess time efficiency, the total scanning time, actual scanning time, and time lost were measured. A paired t test was used to compare means between the groups (α=.05).
RESULTS: Precision was significantly higher in the test groups using the scan-aid apparatus than in the control groups (P
OBJECTIVES: The aim of the study was to evaluate the effect of fiber post location on fracture resistance and failure mode of endodontically treated premolars with 2 roots.
MATERIAL AND METHODS: Fifty extracted maxillary first premolars with 2 roots were divided randomly into 5 groups. Group 1 was comprised of sound teeth, which received only metal crowns (control). Teeth from groups 2, 3, 4, and 5 were decoronated 2 mm above the cementoenamel junction (CEJ) and were endodontically treated. No post was placed in group 2 teeth. Teeth from groups 3, 4 and 5 were given a fiber post placed in the buccal canal, palatal canal, and both buccal and palatal canals, respectively. All teeth in groups 2, 3, 4, and 5 were built up with composite and full coverage metal crowns. A compressive static load was applied at an angle of 25° to the crowns with a crosshead speed of 0.5 mm/min, until fracture.
RESULTS: One-way analysis of variance (ANOVA) showed significant differences among the groups (p = 0.002). A post hoc test showed significantly lower fracture resistance of group 4 compared to group 5 (p = 0.011). Furthermore, group 2 had significantly less fracture resistance compared to group 1 (p = 0.021) and group 5 (p = 0.002). According to Fisher's exact test, different post locations are non-significantly associated with fracture mode (p = 0.256).
CONCLUSIONS: Fiber post location has a significant effect on fracture resistance of severely damaged, endodontically treated maxillary premolars with 2 roots. However, post placement in the palatal root is preferred, as it maintains the restorability of the tooth.
METHODS: Subjects with a history of periodontitis (test) and periodontally healthy subjects (control) received one of two types of dental implants with different surface characteristics: sandblasted acid-etched (SLA) or precision dimension laser-treated (PDL). Periodontal clinical measurements were collected at baseline (V1), 3 months after implant placement (V4), at zirconia crown placement (V6) and 3 months after zirconia crown placement (V8). Supragingival bacterial microbiota was studied using Illumina MiSeq sequencing.
RESULTS: Supragingival microbial community on SLA implants in test group significantly differed to control group at V8 (p 0.05). Co-occurrence network in test group of SLA implants and the adjacent tooth at V8 showed increased disease-associated bacteria and reduced health-associated bacteria. Health-associated bacteria were dominant in control group of SLA implants at V8.
CONCLUSION: The surface characteristics and prosthetic components of dental implants may be important risk factors in patients with a history of periodontitis.
CLINICAL RELEVANCE: Dysbiosis of supragingival microbiome may predispose dental implants to peri-implant diseases. Thus, a strict supportive periodontal care plan is imperative to prevent early onset of biological complications.
METHODS: Sixty-four extracted mandibular molars were root-treated and lined with flowable composite (1.5 mm thickness) before being embedded in epoxy resin blocks. The samples were divided into four groups (n = 16): three endocrown groups with different preparation designs (butt-joint, 0.8 mm chamfer, and 1.0 mm shoulder) and one group with conventional crowns. Crown preparations were performed with a high-speed handpiece mounted on a modified milling device, targeting a 2.0 mm anatomical occlusal reduction for conventional crowns and a 4.0 mm central chamber depth with a 2.0 mm axial wall height (ferrule) for endocrowns (except the butt-joint design, which had no ferrule preparation). Restorations were fabricated using the Chairside Economical Restoration of Esthetic Ceramics (CEREC) Computer-Aided Design and Computer-Aided Manufacturing (CAD/CAM) system with lithium disilicate (IPS e.max CAD; minimum occlusal thickness: 1.5 mm) as the restorative material and cemented with the RelyX Ultimate dual-cure resin adhesive. After 1,500 thermocycling cycles, the samples were divided into two subgroups (n = 8) for axial and oblique loading tests. The fracture resistance was tested using a universal testing machine at a crosshead speed of 0.5 mm/min, applying a load of up to 5,000 N until fracture. Failure modes were examined using a stereomicroscope at 5x magnification and categorized as catastrophic or non-catastrophic. The mean fracture resistance was compared using one-way Analysis of Variance (ANOVA) with Bonferroni post-hoc tests, and Fisher's exact test was used to assess the association between preparation designs and failure modes (p < 0.05).
RESULTS: Endocrowns with shoulder margins showed significantly higher fracture resistance (3,042.83 ± 850.76 N) than conventional crowns (1,908.28 ± 635.82 N) under axial loading (p = 0.02). No significant differences were found under oblique loading between the preparation designs. The preparation design significantly influenced the failure mode under axial loading (p = 0.049). Endocrowns exhibited a higher rate of catastrophic fractures than conventional crowns, regardless of loading direction.
CONCLUSIONS: Endocrowns provide a conservative alternative to conventional crowns, offering a higher fracture resistance under axial loading. Further research is needed to evaluate the endocrown performance under oblique loading.