Biomechanical behavior of endocrown restorations with different cavity design and CAD-CAM materials under a static and vertical load: A finite element analysis.

STATEMENT OF PROBLEM: The influence of different restorative materials, the divergence angle, and the preparation design of the pulp chamber floor in endocrowns on stress distribution is unclear. PURPOSE: The purpose of this finite element analysis study was to evaluate the stress distribution and maximum von Mises stress values in endocrown restorations and remaining teeth. MATERIAL AND METHODS: An endodontically treated first mandibular molar was prepared with 2-mm occlusal reduction, a butt-joint margin, and a mesial box with a 4-mm buccolingual extension to receive an endocrown restoration. The model was then scanned, and the exported standard tessellation language file was designed according to the anatomic references by using a computer-aided design software program. The reference model was duplicated, and 27 variations were formed: restorations made of IPS e.max, Vitablocs MarkII, and Vita Enamic, as well as different divergence angles of 6, 12, and 16 degrees prepared with 3 variations of pulp chamber floor designs, keeping the natural form, adding a 1-mm glass ionomer pulp chamber base, and adding a 2-mm extension into the distal canal. Stress distribution under axial loading and maximum von Mises stress values were analyzed and calculated by using the Ansys software program. RESULTS: The endocrown restoration presented the lowest von Mises stress values when a 6-degree divergence angle was used with Vitablocs MarkII. However, in other layers such as enamel, resin cement, and pulpal floor, the lowest von Mises stress values were observed in IPS e.max restorative material when the divergence angle was increased to 16 degrees. No difference was found in the stress distribution pattern and maximum von Mises stress values in the alveolar bone or periodontal ligament. CONCLUSIONS: Endocrowns fabricated with lithium disilicate ceramics without intraradicular extension exhibited lower stresses on tooth structure. An increase in the divergence angle improved the stress distribution on tooth structure; however, sound dental tissue should not be removed to achieve better stress distribution.

Evaluation of the effect of milling mode and margin definition on adaptation of chairside digitally designed and fabricated ceramic veneers.

AIM: The present study aimed to evaluate the effect of the milling mode and margin defining method on the marginal and internal adaptation of digitally designed and fabricated ceramic veneers. MATERIALS AND METHODS: Forty extracted central incisors were prepared for ceramic veneers. The veneers were categorized into four groups (n = 10) based on the milling mode (fine or extra-fine) and design (automatic or manual defining of cervical and incisal margins). The veneers were cemented to the teeth using resin cement and then polished. After cementation, the teeth were embedded in clear polyester resin, then cut into three sections. Absolute marginal gap at the cervical margins (AMGC), marginal gap at the incisal (MGI) and cervical (MGC) margins, and internal gap (IG) at the axial wall were evaluated using a scanning electron microscope. Two-way analysis of variance (ANOVA) and t tests were used (α = 0.05) for the statistical analysis. RESULTS: The margin defining method affected the adaptation of the internal and incisal margin; the automatic (software) margin defining method resulted in a smaller MGI (P = 0.038) and IG (P = 0.009) than the manual defining method. CONCLUSION: The type of milling mode did not affect the marginal gap. The margin defining method affected the marginal gap at the incisal margin and the internal gaps. (Int J Comput Dent 2022;25(3):277-285; doi: 10.3290/j.ijcd.b2588153).

Marginal and internal adaptation of single crowns and fixed dental prostheses by using digital and conventional workflows: A systematic review and meta-analysis.

STATEMENT OF PROBLEM: Digital and conventional options for definitive impressions and for the fabrication of fixed dental prostheses (FDPs) have been compared in previous studies. However, a comprehensive review with concluding data that determined which method provided the minimal internal and marginal adaptation is lacking. PURPOSE: The purpose of this systematic review and meta-analysis of in vivo and in vitro studies was to compare the marginal and internal adaptation of complete-coverage single-unit crowns and multiunit FDPs resulting from digital and conventional impression and fabrication methods. MATERIAL AND METHODS: The review protocol was registered in International Prospective Register of Systematic Reviews (PROSPERO) and followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. PubMed, Cochrane Trials, Scopus, and Open Grey databases were used to identify relevant articles. Based on fixed prostheses impression and fabrication methods, groups from each study were categorized into 4 groups: conventional impression and fabrication (CC), conventional impression and digital fabrication (CD), digital scanning and conventional fabrication (DC), and digital scanning and fabrication (DD). The risk of bias was assessed by using the Cochrane Collaboration tool for clinical trials and the modified Methodological Index for Non-Randomized Studies (MINORS) for in vitro studies. Heterogeneity was evaluated among studies, and meta-analysis was performed with random-effect models (α=.05). Subgroup analysis was conducted when possible. RESULTS: Eight clinical trials and 21 in vitro studies were eligible for analysis. There was no significant difference between the CD and DD clinical groups for marginal adaptation (P=.149); However, the DD group had significantly less internal discrepancy than the CD group (P=.009). The in vitro studies found no significant difference in marginal adaptation among the CC-CD, CC-DC, and CC-DD pairs (P=.437, P=.387, P=.587), but in the comparison CD versus DD group, a significantly better marginal adaptation was observed for the DD group (P=.001). All the compared in vitro groups were similar in terms of internal adaptation. CONCLUSIONS: Impression and fabrication techniques may affect the accuracy of fit of complete-coverage fixed restorations. A completely digital workflow yielded restorations with comparable or better marginal adaptation than the other methods.

A clinical comparison of digital and conventional impression techniques regarding finish line locations and impression time.

OBJECTIVE: This study compared digital and conventional impression techniques regarding impression time, frequency of adjustments, and adaptation of cobalt-chromium (Co-Cr) copings with supragingival and subgingival finish lines. MATERIALS AND METHODS: Thirty premolars prepared for single-unit metal-ceramic restorations with supragingival and subgingival finish lines (n = 15). Conventional impression and digital scan of prepared teeth were made. Using computer aided design/computer aided manufacturing (CAD/CAM) system the copings were produced by a milling machine from Co-Cr blocks and internal and marginal discrepancies were measured using silicone replica technique. Data were analyzed using repeated measures ANOVA and Mann-Whitney test (alpha = .05). RESULTS: The impression technique had a significant effect on the magnitude of gap (P < .001). The internal and marginal gaps in the digital technique (49.43 µ and 60.07 µ, respectively) were significantly lower than the values in the conventional method (91.88 µ and 96.96 µ, respectively-P < .001). Finish line positions had no significant effect on the fit and marginal gap of copings (P = .54 and .243, respectively). The mean impression time (19':27″ in conventional technique and 10':31″ in digital technique) was significantly shorter (P < .001) and the mean frequency of adjustments (2.2 times for conventional and 1.3 times for digital technique) was significantly lower in the digital technique (P < .001). The gingival biotype (thick or thin) had no significant effect on marginal and internal fit (P = .052 and .319, respectively). CONCLUSION: The digital technique was superior in terms of fit, impression time, and frequency of adjustments. Finish line positions had no significant effect on the fit of copings. CLINICAL SIGNIFICANCE: Using intraoral scanner promotes the fits of restorations in supragingival and subgingival finish lines.

Effect of Serrating Abutment-Implant Mating Surface on Torque Stability of Implant-Abutment Connection, Before and After Cyclic Loading.

This study evaluated the effect of adding serration to the abutment-implant connection on torque maintenance before and after loading. Two implant systems with the same dimensions and connection design (internal 8° Morse taper octagon) were selected: one with nonserrated abutments (Simple line II) and the other one with serrated abutments (F & B). The removal torque value (RTV) was measured in 2 groups for each system: one group with one-piece abutments and the other group with 2-piece abutments, before and after cyclic loading (n = 10 in each group). The initial RTV of the abutment screw was measured with a digital torque meter. Each abutment received a cement-retained metal crown with 30° occlusal surface. Cyclic axial peak load of 75 ± 5 N was applied to the implants for 500 000 cycles at 1 Hz. The post-load RTV was then measured. Two-way and repeated-measures analysis of variance (ANOVA), and independent t test were applied to assess the effects of cyclic loading, connection design, abutment type, and their interaction on the percentage of torque loss (α = .05). Two-way ANOVA showed that serration of mating surfaces had a significant effect on torque maintenance before (P < .001) and after (P = .004) cyclic loading. Repeated-measures ANOVA also showed that loading had a significant effect on the torque loss percentage (P < .01). Comparison of the groups with t test showed that the torque loss of the serrated groups was lower than that of non- serrated groups. Despite the limitations of this study, the stability of the implant-abutment connection in the serrated design was higher than that of non-serrated group.

Effect of 5 Popular Disinfection Methods on Microflora of Laboratory: Customized Implant Abutments.

PURPOSE: To compare the efficacy of 5 different decontamination methods of titanium abutments and to assess their possible effects on surface roughness of titanium. MATERIALS AND METHODS: Micrococcus luteus, Acinetobacter baumannii, Enterococcus faecalis, and Candida albicans were cocultured to form a multispecies biofilm on 18 titanium discs. In another group, Bacillus subtilis, a spore-forming species, was cultivated on another set of 18 titanium discs. Each group was further divided into 5 test groups: high-pressure steam cleaning (4 Mpa, 5 seconds), NaOCl (1% active chlorine, 5 minutes), H2O2 (3%, 5 minutes), GaAlAs laser (810 nm, CW, 1 W, 400-µm fiber, 1-mm distance, 1 minute), Er:YAG laser (2940 nm, pulse mode, 100 mJ, 10 Hz, 230-µm noncontact handpiece, 4-mm distance, 50/50% air/water, 1 minute), and a control group of no treatment. After each decontamination procedure, the remaining microbial load was reported as colony-forming unit/disc. To evaluate the effect of each treatment on titanium discs, surface roughness parameters including Sa, Sq, Ssk, Sku, Sal, and Sdr were measured at 6 points of each disc using an atomic force microscope. RESULTS: Complete disinfection was achieved using high-pressure steam, NaOCl, H2O2, and Er:YAG laser. GaAlAs laser was able to reduce microbial count over 90%. Sa and Sq parameters were only increased significantly in diluted NaOCl group in comparison with control group, whereas Sdr was increased significantly in both absolute and diluted NaOCl groups. CONCLUSION: All the methods could decontaminate machined titanium surfaces, although complete microbial elimination was not achieved by diode laser. None of the treatments altered surface roughness significantly, except for sodium hypochlorite (NaOCl).

The effect of conventional, half-digital, and full-digital fabrication techniques on the retention and apical gap of post and core restorations.

STATEMENT OF PROBLEM: Conventional cast metal posts and cores are fabricated using direct and indirect techniques, both of which need impression materials and considerable laboratory work. Digital techniques have the capacity to substitute for conventional methods in fabricating the posts and cores. However, the accuracy of restorations resulting from a digital workflow is unknown. PURPOSE: The purpose of this in vitro study was to compare the retention of posts and cores fabricated using full-digital, half-digital, and conventional techniques and to define the accuracy of each technique in terms of the apical gap. METHOD AND MATERIALS: Thirty newly extracted mandibular first and second premolar teeth were selected for this in vitro study. Impressions were made using direct acrylic resin patterns (conventional), indirect silicone impressions of the intracanal which scanned with a 3Shape laboratory scanner (half digital), and intracanal scan posts captured with an intraoral 3Shape scanner (full digital). Casting and milling were conducted for the conventional impression and digital scans. The obtained posts were cemented using zinc phosphate cement. A universal pullout test was used to measure retention at a crosshead speed of 0.5 mm/min. The apical gap of each post in the canals was defined with parallel digital radiography. The data were analyzed using the Kruskal-Wallis test (α=.05) and Mann-Whitney test at the adjusted α=.016. RESULTS: Significant differences were found among the conventional, full-digital, and half-digital techniques in terms of the apical gap (0.11, 0.29, and 0.66 mm; P<.001) and retention (171.6 ±1.9, 107.1 ±5.6 and 91.8 ±6.6 N; P<.001). The correlation between gap and retention in conventional (P=.43), full-digital (P=.09), and half-digital techniques (P=.06) was not statistically significantly different. CONCLUSIONS: The conventional technique was more accurate and resulted in higher retention than both the full- and half-digital techniques. However, the retention and gap of all the posts fell within clinical guidelines.

Buccal Fat Pad-Derived Stem Cells in Three-Dimensional Rehabilitation of Large Alveolar Defects: A Report of Two Cases.

This case report seeks to describe efficient clinical application of adipose-derived stem cells (AdSCs) originated from buccal fat pad (BFP) in combination with conventional guided bone regeneration as protected healing space for reconstruction of large alveolar defects after extraction of multiple impacted teeth. The first case was a 19-year-old woman with several impacted teeth in the maxillary and mandibular regions, which could not be forced to erupt and were recommended for surgical extraction by the orthodontist. After this procedure, a large bone defect was created, and this space was filled by AdSC loaded natural bovine bone mineral (NBBM), which was protected with lateral ramus cortical plates, microscrews, and collagen membrane. After 6 months of post-guided bone regeneration, the patient received 6 and 7 implant placements, respectively, in the maxilla and mandible. At 10 months postoperatively, radiographic evaluation revealed thorough survival of implants. The second case was a 22-year-old man with the same complaint and large bony defects created after his teeth were extracted. After 6 months of post-guided bone regeneration, he received 4 dental implants in his maxilla and 7 implants in the mandible. At 48 months postoperatively, radiographs showed complete survival of implants. This approach represented a considerable amount of 3-dimensional bone formation in both cases, which enabled us to use dental implant therapy for rehabilitation of the whole dentition. The application of AdSCs isolated from BFP in combination with NBBM can be considered an efficient treatment for bone regeneration in large alveolar bone defects.

Detection of Residual Excess Zinc Oxide-Based Cement With Laser Fluorescence (DIAGNOdent): In Vitro Evaluation.

Because of its importance in the development of peri-implant mucositis and peri-implantitis, detection of residual excess cement (REC) is often the focus of studies addressing cement-retained implant-supported restorations. The purpose of this study was to evaluate the sensitivity and specificity of laser fluorescence (DIAGNOdent) for detecting residual excess zinc oxidebased cement around dental implants. In this in vitro study, 15 tissue-level implants were embedded in acrylic resin. To simulate gingiva around the implants, the transgingival part of each implant was covered with a gingival mask silicon material. Cement (Tempobond; 1 × 1 × 1 mm) was applied to 30 areas, 4 mm below the gingival-mimicking line using a custom-made template. A DIAGNOdent laser device was used by 2 independent examiners to evaluate the presence or absence of cement in a selected area. The examiners were allowed to probe the gingival sulcus (2-mm depth) 2 times with a 5-minute interval between tests. The residual cement was recognized by gently walking the device tip around the implant. A detection score less than 16 indicated an absence of cement, and scores of 16 or greater indicated the presence of excess luting agent in the implant sulcus. The sensitivity and specificity of DIAGNOdent to detect REC in the sulcus were 100% and 96.67%, respectively. Based on our findings, we propose that DIAGNOdent could be used to detect REC in the sulcus of cement-retained implant supported restorations.

Effect of Implant Connection Type and Depth on the Seating Accuracy of Hand-Tightened Abutments.

PURPOSE: Improper seating of abutment on the implant is a common problem. This study investigated the effect of the type of implant/abutment interface on the complete seating of the abutments on the head of implants placed at different gingival depths. MATERIALS AND METHODS: Three implant systems with three different connections including straight external hexagon, butt-joint internal tri-lobed, and conical internal hexagon were used. Two gingival thicknesses (2 and 7 mm) were created using pink baseplate wax around the straight abutments seated on the implants. After placing the implants in acrylic blocks, the wax was replaced with the gingival mask material to simulate the gingival drape around the implant heads. Afterwards, 15 prosthodontists were asked to hand-tighten the straight abutments in the corresponding implant bodies relying only on their tactile sense. At the final stage, the gingival mask was removed, and the seating quality of the abutments on implant bodies was assessed visually. The effect of implant connection and depth on abutment seating accuracy was analyzed using Kruskal-Wallis and multiple-comparison tests. RESULTS: No significant difference was found regarding the effect of either depth or connection design on the accuracy of the abutment seating (p > 0.05); however, pairwise comparison of the combined effect of the depth and connection design was significant (p = 0.009). Accuracy of abutment seating on the Nobel Active implants at both 2 and 7 mm depths were significantly better than Replace system with 7 mm depth (p = 0.027). The same results were obtained in comparison between Nobel Active system at both 2 and 7 mm depths with Branemark system with 7 mm depth (p = 0.006). CONCLUSION: An increase in implant placement depth meant a decrease in accuracy of the abutment seating. The internal conical connection design showed the best result in abutment positioning in deep implants as compared with external and internal butt-joint connection designs.

A Clinical Comparative Study of 3-Dimensional Accuracy between Digital and Conventional Implant Impression Techniques.

PURPOSE: To evaluate the accuracy of a digital implant impression technique using a TRIOS 3Shape intraoral scanner (IOS) compared to conventional implant impression techniques (pick-up and transfer) in clinical situations. MATERIALS AND METHODS: Thirty-six patients who had two implants (Implantium, internal connection) ranging in diameter between 3.8 and 4.8 mm in posterior regions participated in this study after signing a consent form. Thirty-six reference models (RM) were fabricated by attaching two impression copings intraorally, splinted with autopolymerizing acrylic resin, verified by sectioning through the middle of the index, and rejoined again with freshly mixed autopolymerizing acrylic resin pattern (Pattern Resin) with the brush bead method. After that, the splinted assemblies were attached to implant analogs (DANSE) and impressed with type III dental stone (Gypsum Microstone) in standard plastic die lock trays. Thirty-six working casts were fabricated for each conventional impression technique (i.e., pick-up and transfer). Thirty-six digital impressions were made with a TRIOS 3Shape IOS. Eight of the digitally scanned files were damaged; 28 digital scan files were retrieved to STL format. A coordinate-measuring machine (CMM) was used to record linear displacement measurements (x, y, and z-coordinates), interimplant distances, and angular displacements for the RMs and conventionally fabricated working casts. CATIA 3D evaluation software was used to assess the digital STL files for the same variables as the CMM measurements. CMM measurements made on the RMs and conventionally fabricated working casts were compared with 3D software measurements made on the digitally scanned files. Data were statistically analyzed using the generalized estimating equation (GEE) with an exchangeable correlation matrix and linear method, followed by the Bonferroni method for pairwise comparisons (α = 0.05). RESULTS: The results showed significant differences between the pick-up and digital groups in all of the measured variables (p < 0.001). Concerning the transfer and digital groups, the results were statistically significant in angular displacement (p < 0.001), distance measurements (p = 0.01), and linear displacement (p = 0.03); however, between the pick-up and transfer groups, there was no statistical significance in all of the measured variables (interimplant distance deviation, linear displacement, and angular displacement deviations). CONCLUSIONS: According to the results of this study, the digital implant impression technique had the least accuracy. Based on the study outcomes, distance and angulation errors associated with the intraoral digital implant impressions were too large to fabricate well-fitting restorations for partially edentulous patients. The pick-up implant impression technique was the most accurate, and the transfer technique revealed comparable accuracy to it.

The Effect of Milling Metal Versus Milling Wax on Implant Framework Retention and Adaptation.

PURPOSE: The metal framework of implant-supported restorations can be made using different methods. For a successful outcome, the acceptability of each method depends on the retention and fit of the restoration. The aim of this study was to evaluate and compare the retention and adaptation of copings fabricated using two methods: casting wax patterns made by computer-aided design/computer-aided manufacturing (CAD/CAM) technology, and milling sintered chromium-cobalt (Cr-Co) blocks. MATERIALS AND METHODS: Twenty-four abutment analogs (height, 5.5 mm) were divided into two groups according to the framework fabrication method. In one group, wax patterns were prepared using a CAM milling machine, and they were cast with a Ni-Cr-Ti metal alloy. In the second group, the copings were milled from Cr-Co blocks using a CAD/CAM milling machine. All copings were equal in contour, thickness, and internal relief and were seated on the abutment analogs after the necessary adjustments. The vertical marginal discrepancy was investigated using a silicone replica method and stereomicroscope with 75× magnification. After copings were cemented onto the abutment analogs using zinc phosphate, a tensile resistance test was performed using a universal testing machine. Mann-Whitney U and Student's t-test were used for statistical analyses at a significance level of 0.05. RESULTS: An independent sample t-test revealed a significant difference between the two groups for retention (p = 0.010), and the milled wax group showed higher tensile resistance compared with the milled metal group. There was also a significant difference between the two groups in marginal discrepancy (p < 0.001), with a larger marginal gap in the milled metal group compared with the milled wax group. The milled metal copings required more adjustments to fit on the abutment analogs compared with the wax milled copings (p < 0.001). CONCLUSIONS: The CAD/CAM technique for wax milling resulted in more retentive copings with better marginal and internal adaptations compared with milling the metal blocks.

In Vivo and In Vitro Comparison of Internal and Marginal Fit of Digital and Conventional Impressions for Full-Coverage Fixed Restorations: A Systematic Review and Meta-analysis.

PURPOSE: This study aims to evaluate digital and conventional impressions for full-coverage restorations in terms of marginal and internal discrepancies. STUDY SELECTION: The analysis included in vivo and in vitro studies reporting the marginal or internal gap of full-coverage restorations that provide both the conventional and digital impression. The PubMed, Cochrane Trials, and Scopus databases were searched. The quality of clinical trials was rated using Cochrane Collaboration's tool, and the quality of the evidence was evaluated using the Grading of Recommendations, Assessment, Development, and Evaluation tool. Heterogeneity among the studies was evaluated, and a meta-analysis with subgroup analysis was conducted whenever it was possible. RESULTS: Thirty-three articles (8 prospective clinical trials and 26 in vitro studies) were selected to extract data after applying the predefined selection criteria. The standard mean difference (SMD) of the meta-analysis for marginal adaptation was -0.76 (95% confidence interval: -1.23 to -0.29) and -0.59 (95% confidence interval: -0.93 to -0.24) for in vitro and in vivo studies, respectively, indicating digital impressions provided significantly less marginal gap than conventional impressions in in vitro studies (P = .002). The impression technique did not significantly influence the internal adaptation. CONCLUSIONS: Differences in marginal adaptation between the digital and conventional groups are not significant for in vivo studies, but for in vitro studies, the digital impression resulted in better marginal adaptation. Based on the Grading of Recommendations, Assessment, Development, and Evaluation approach for marginal adaptation, clinical studies were classified as high confidence and in vitro studies were graded moderate because of the inconsistency. Furthermore, high-quality studies are needed to confirm our results (the International Prospective Register of Systematic Reviews; CRD42017077925).

Prevention of coronal discoloration induced by regenerative endodontic treatment in an ex vivo model.

OBJECTIVES: The aim of this study was to assess the effect of sealing the pulp chamber walls with a dentin-bonding agent (DBA) on prevention of discoloration induced by regenerative endodontic procedures (REPs) in an ex vivo model. MATERIALS AND METHODS: Ninety-six bovine incisors were prepared and randomly divided into two groups. In one group, the pulp chamber walls were sealed with DBA before placement of triple antibiotic paste (TAP) containing minocycline inside the root canals, but in the other group, DBA was not applied. After 4 weeks, the root canals were filled with human blood and each group was then randomly divided into four subgroups (n = 12) according to the endodontic cements placed over the blood clot (ProRoot MTA, OrthoMTA, RetroMTA, or Biodentine). The color changes (∆E) were measured at different steps. The data were analyzed using t test and two-way ANOVA. RESULTS: The specimens in which dentinal walls of pulp chamber were sealed with DBA showed significantly less coronal discoloration at each step of regenerative treatment (p < 0.001). However, application of DBA did not completely prevent the clinically perceptible coronal color change. Sealing the blood clot with different endodontic cements did not result in significant difference in coronal discoloration (p > 0.05). CONCLUSIONS: Sealing the pulp chamber walls before insertion of TAP decreased coronal discoloration following REP using different endodontic cements but did not prevent it. CLINICAL RELEVANCE: Discoloration of teeth undergoing REPs is an unfavorable outcome. Considering the significant contribution of TAP containing minocycline to the coronal tooth discoloration even after sealing the pulp chamber walls, the revision of current guidelines in relation to the use of TAP with minocycline might need to be revised.

Digital Implant Impression Technique Accuracy: A Systematic Review.

PURPOSE: The objective was to provide a comprehensive systematic review about the accuracy of digital implant impression in comparison with the conventional implant impression approach. MATERIALS AND METHODS: PubMed, Google Scholar and Cochrane databases were used to classify the related articles with no year limitation in 3 stages by 2 reviewers. Finally, 10 articles were included based on inclusion and exclusion criteria. RESULTS: Five articles supported the use of intraoral scanners in implant dentistry. The two in vivo pilot studies showed that digital scanning is not reliable and could not be used in clinical routine. CONCLUSION: Because each study included in this review has its unique methodology and design, it is therefore early to conclude whether to use digital scanners for clinical practice or not. More well-conducted in vitro and clinical trials studies are recommended to investigate the accuracy of intraoral scanners.

Clinician-generated torque on abutment screws using different hand screwdrivers.

STATEMENT OF PROBLEM: Many clinicians use hand screwdrivers to tighten prosthetic and abutment screws. The impact of the screwdriver type, the location of the implant, and the sex of the practitioner on the generated torque is not well understood. PURPOSE: The purpose of this in vitro study was to compare the torque generated by different hand screwdrivers when used in the anterior and posterior regions and to evaluate the correlation between the applied torque and the sex and body mass index (BMI) of the practitioner. MATERIAL AND METHODS: A mandibular typodont with anterior and posterior implants was mounted in a mannequin head. Fifty clinicians (6 prosthodontists, 8 graduate prosthodontic students, and 36 dental students) used their maximum force to tighten the abutment screws in the anterior and posterior regions, using 3 different hand screwdrivers, with handles of different shapes and sizes (small, medium, and large). The torque values generated were measured using torque meters connected to the implants. The generated torque, sex, age, height, and weight were also recorded for each clinician. A generalized linear model was used to find correlations between the different factors and the generated torque (α=.05). RESULTS: Significant differences were observed among the applied torque values when different screwdrivers were used (P<.001). Higher torque values were generated in the anterior region than in the posterior region (P<.001). The interaction of the sex and BMI of the participants significantly affected the generated torque values (P=.044). CONCLUSIONS: The type of screwdriver and location of the implant affected the generated torque. Torque values generated by the large screwdriver were higher than those of small and medium screwdrivers. Higher torque was applied in the anterior region.

Interim Prosthesis Options for Dental Implants.

Dental implants have become a popular treatment modality for replacing missing teeth. In this regard, the importance of restoring patients with function during the implant healing period has grown in recent decades. Esthetic concerns, especially in the anterior region of the maxilla, should also be considered until the definitive restoration is delivered. Another indication for such restorations is maintenance of the space required for esthetic and functional definitive restorations in cases where the implant site is surrounded by natural teeth. Numerous articles have described different types of interim prostheses and their fabrication techniques. This article aims to briefly discuss all types of implant-related interim prostheses by different classification including provisional timing (before implant placement, after implant placement in unloading and loading periods), materials, and techniques used for making the restorations, the type of interim prosthesis retention, and definitive restoration. Furthermore, the abutment torque for such restorations and methods for transferring the soft tissue from interim to definitive prostheses are addressed.

Effect of Splinting on Dimensional Accuracy of Impressions Made of Implants with Different Subgingival Alignments.

PURPOSE: Placement of implants at deeper levels of gingiva is sometimes inevitable because of issues like esthetics or bone availability. The accuracy of impressions may be affected in these situations. The aim of this in vitro study was to evaluate the effects of splinting and length of impression copings on the accuracy of impressions made of deeply placed implants. MATERIALS AND METHODS: A metal model with two parallel implants (Implantium; Dentium) was fabricated. One hundred and twenty impressions were made using the direct impression technique with and without splinting the impression copings (using short and long impression copings). Impressions were made of implants at three subgingival levels (1, 3, and 6 mm) using regular viscosity poly(vinyl siloxane). The impressions were poured with type IV dental stone. Displacements in the x, y, and z axes, as well as rotational discrepancies and interimplant distances were measured with a coordinate measuring machine. Data were analyzed with Kruskal-Wallis, Mann-Whitney, and nonparametric adjusted rank transform tests. RESULTS: There was less rotational displacement using longer impression copings at different subgingival positions of the implants, either with splinted or nonsplinted direct technique (p < 0.05). Also, the nonsplinted technique produced more accurate impressions at different apico-coronal levels of implants than the splinted technique using short impression copings (p < 0.05). CONCLUSIONS: According to the findings of this study, longer impression copings yielded better results than shorter ones in both splinted and nonsplinted techniques. Also, nonsplinted short impression copings produced more accurate impressions than splinted short impression copings.

Cement Selection for Cement-Retained Implant-Supported Prostheses: A Literature Review.

Cement-retained implant-supported prostheses are widely used for restoring missing teeth; however, they show some complications in comparison to screw-retained restorations, such as difficulty in retrieving the restoration and biocompatibility of cement. Therefore, the practitioner should consider several important aspects when using this type of restoration. In this regard, one major concern is appropriate cement selection, with considerations including cement biologic compatibility, methods for limiting the excess cement, ease of removing the excess cement, radiographic view of the cement, and also the possibility of future retrieval of the prosthesis. The aim of this review article was to address most aspects related to this type of prosthesis in terms of cementation.

Does Ferrule Effect Affect Implant-Abutment Stability?

PURPOSE: This study investigated the influence of placing implant-supported crowns on the torque loss of the abutment screw before and after loading. MATERIAL AND METHODS: Twenty implant-abutment assemblies were randomly assigned to two groups. The first group was consisted of abutments with abutment-level finishing line (abutment-level), and in the second group the crown margin was placed on the implant shoulder (implant-level). Initial torque loss was recorded for all specimens. After 500000 cyclic load of 75 N and frequency of 2 Hz, post loading torque loss was recorded. Finite element model of each group was also modeled and screw energy, and stress were analyzed and compared between two groups. RESULTS: ANOVA for repeated measurements showed that the torque loss did not change significantly after cyclic loading (P=0.73). Crown margin also had no significant effect on the torque loss (P=0.56). However, the energy and stress of screw in abutment-level model (4.49 mJ and 22.74 MPa) was higher than implant-level model (3.52 mJ and 20.81 MPa). CONCLUSIONS: Although embracing the implant with crown produced less stress and energy in the abutment-implant screw, it did not have any significant influence on the torque loss of the screw.