The International Journal of Oral & Maxillofacial Implants, 03/2021

Purpose: Bone density and implant primary stability parameters have been introduced that are based on calculating (1) the average of the instantaneous torque needed to keep the rotation speed of a bone density probe constant while it descends into bone or (2) the integral of the instantaneous torque-depth curve at implant insertion (I), a quantity that is equal to the insertion energy multiplied by a constant. This study aimed to determine how these two quantities are affected by the presence and thickness of a cortical bone layer. Materials and methods: An instantaneous torque-measuring micromotor was used to measure the density of six double-layer polyurethane foam blocks mimicking different cortical/cancellous bone combinations. Twenty measurements per block were collected, averaged, and compared. The insertion torque and the integral (I) of the instantaneous torque-depth curve at implant insertion were recorded when 20 3.75 × 12-mm cylindrical implants were inserted in each of nine blocks, including three single-layer blocks simulating the absence of a cortical layer, under three final cortical (countersink) preparations: 4.0, 3.7, and 3.5 mm. The relationship between the insertion torque, the integral of the instantaneous torque-depth curve at implant insertion (I), cortical thickness, and the final diameter preparation were investigated with regression and best-fit slope analyses. Results: Bone density measurements showed that the average of the instantaneous torque at probing allowed differentiation of five of six different bone classes (hard-hard, hard-normal, hard-soft, normal-normal, normal-soft, soft-soft); the post hoc analysis of variance (ANOVA) comparisons were all statistically significant except for the hard-soft-normal-soft pair. The insertion torque and the integral (I) of the instantaneous torque-depth curve at implant insertion increased proportionally with cortical bone thickness (Pearson's r > 0.96 in all cases). Conclusion: When the final preparation varied from 3.7 mm to 3.5 mm, the insertion torque-thickness plot slope did not change significantly, while that of the instantaneous torquedepth curve integral (I)-thickness plot did change, suggesting that the torque-depth curve at implant insertion integral (I) may detect the increase in implant stability consequent to slight anatomical changes or changes in the site preparation protocol better than the insertion torque when measuring the cortical bone layer stress while undergoing insertion. These findings concerning bone density and primary stability should be investigated further using different experimental settings. If confirmed, they might generate improvements in the predictability of implant and prosthetic rehabilitation outcomes. Keywords: bone density, cortical thickness, insertion torque, primary stability, torque-depth curve integral

Purpose: To undertake a systematic literature review of magnetic resonance imaging (MRI) employed in the three phases of implant-based oral rehabilitation: planning, execution, and follow-up. Materials and methods: MEDLINE (PubMed) and EMBASE bibliographic databases were searched up to January 2020 for studies assessing the use of MRI alone or in connection with CT and/or CBCT in the planning, execution, or follow-up of dental implant placement and/or bone grafting procedures in the maxilla or the mandible. Included studies were also assessed according to the diagnostic imaging efficacy scale presented by Fryback and Thornbury (F&T). Results: The search strategy yielded 10 studies, which were included in the systematic review. Six studies focused on the implant planning phase, one on the immediate follow-up phase, and three on both planning and follow-up. No studies acquired signal from the bone. There was no consensus on the gold standard, MRI sequence, or field strength (T). One study reached F&T level 1, eight reached level 2, and one reached level 3. Conclusion: The possible transition from radiography to ionizing-radiation-free imaging through MRI is still a novelty in dentistry and has yet to establish itself as a viable imaging modality suitable for replacing CT and CBCT. More studies are needed on the accuracy of the diverse MRI possibilities when applied for implant planning, execution, and follow-up before this diagnostic method can be considered as a reality for the clinician. Keywords: bone, dental implants, magnetic resonance, systematic review

Purpose: To investigate the effect of implant angulation, non-free-end partial edentulism, and number of scan bodies on the accuracy of digital impressions of multiple implants in partially edentulous arches. Materials and methods: Four reference models of partially edentulous mandibles with implants (RM1, RM2, RM3, and RM4) representing different intraoral situations were each scanned 10 times by an intraoral scanner. Reference scans were obtained by a laboratory scanner. Test scans were compared with reference scans to obtain the distance deviations (Δd) and angular deviations (Δθ) between scan bodies for trueness assessment. Differences among the repeated test scans of each model were measured and recorded as Δdp and Δθp for precision assessment. The Student t test (α = .05) was used to compare Δd, Δθ, Δdp, and Δθp of different reference models, including RM2 vs RM1 (effect of non-free-end partial edentulism), RM3 vs RM1 (effect of implant angulation), and RM4 vs RM1 (effect of number of scan bodies). Results: The implant with 17-degree angulation in RM3 showed significantly lower Δd, Δθ, and Δθp compared with the parallel implant in RM1 (Δd: P = .0382, Δθ: P = .0267, Δθp: P = .0417). The RM2 of non-free-end partial edentulism had lower distance and angular deviations than RM1, but without a significant difference. The number of scan bodies had no significant effect on the Δd, Δθ, Δdp, and Δθp of RM4 and RM1. Conclusion: Angulated implants showed better accuracy of digital impressions in partially edentulous arches compared with parallel implants. Non-free-end partial edentulism was attributed to improved accuracy, while the number of scan bodies showed no effect. Keywords: accuracy, dental implants, digital impression, edentulous, intraoral scan

Purpose: Microcomputed tomography (micro-CT) is a relatively new modality to investigate mechanical deformations. The purpose of this study was to assess the microgap at the implant-sleeve connection of a new two-piece dental implant with a replaceable sleeve. Materials and methods: Implants were assembled with 25-degree angulated abutments. Micro-CT was used to assess implant-sleeve connection gaps under the following mechanical conditions: (1) unloading; (2) compressive 10,000 cyclic loading with 400 N; (3) static compressive load of 200 N or 400 N for 24 hours. Results: The mean gap in the unloaded sample was 2.9 ± 0.9 μm. The mean gap difference after cyclic compressive load was 0.3 ± 0.15 μm, demonstrating a negligible effect for the cyclic loading. Under static compressive load, there was no increase in microgap size at 200 N. At 400 N, a significant (P < .05) increase was noted. While the mean values increased by 1.9 μm, the most pronounced significant increase in mean microgap was noted in the direction of force application (5.1 ± 2.14 μm), while a significant decrease in mean microgap (1.2 ± 1.47 μm) was noted on the opposite side. Conclusion: The mechanical behavior of the implant-sleeve connection under static and dynamic loads was found to be within the previously reported range of implant dentistry. Keywords: cyclic loading, dental implant, micro-CT, microgap, static loading

Purpose: To evaluate the insertion torque at the equicrestal and subcrestal positions of three implant designs in synthetic polyurethane blocks simulating different bone conditions. Materials and methods: Overall, 72 implants with three different designs (two conical and one cylindrical) were inserted at equicrestal and subcrestal positions (-2 mm) into polyurethane blocks simulating the anterior (0.32 g/cm³) and posterior (0.48 g/cm³) regions of the maxilla. The final insertion torque of all implants was measured using a digital torque meter, and the results were evaluated and statistically analyzed. Results: For all implant systems, insertion torque decreased significantly when placed at the subcrestal position (P < .05), except for cylindrical implants placed in the bone blocks with high cancellous density. The implants with higher body conicity and square threads had higher insertion torque values than the cylindrical and conical implants with a lower body conical angle and trapezoidal threads. The implants inserted into higher-density blocks showed greater stability. Conclusion: The different implant systems lost insertion torque in a nonuniform manner at the subcrestal position and varied according to bone density. Implant design significantly influenced the initial stability at the equicrestal and subcrestal positions, especially in lower-density bone. Keywords: bone density, dental implants, implant design, implant stability

Purpose: The aim of this study was to compare the bone collection capacity of bur drill systems used in implant surgery with different diameters, lengths, and drilling speeds. Materials and methods: This study was performed on bovine ribs. Two bur drill systems were studied: Implantium (Dentium) and Straumann (Institut Straumann). The groups were divided into subgroups according to the bur diameter. As a result, there were four Implantium subgroups (3.3, 3.8, 4.3, and 4.8 mm) and three Straumann subgroups (3.3, 4.1, and 4.8 mm). In addition, for each bur diameter, the bone collection capacities of the drill systems were evaluated at three different drilling speeds (150, 250, and 400 rpm) and two bur lengths (10 and 12 mm). The diameter, length, and speed changes were performed, and the results were compared between the two drill systems. Results: The mean bone weight collected by using the Straumann burs was higher than that of the Implantium burs at each drilling speed and bur length. Using the Straumann system, the different drilling speeds/lengths of the burs had no impact on the bone collection capacity, irrespective of the bur diameter (P > .05). However, the drilling speeds/lengths of the Implantium system resulted in a statistically significant difference in the same diameters (P < .05). Conclusion: Both bur systems were suitable for autogenous graft collection for bone grafting in implant surgery, but the Straumann burs were more successful than the Implantium burs. Keywords: autograft, bone collection, implant surgery

Purpose: To compare the amount of bone expansion, bone density change, and implant primary stability with an osseodensification technique to a conventional drilling protocol. Materials and methods: Twenty-four bovine rib segments (20 × 25 × 4 mm) with a 1-mm outer layer of cortical bone were randomly divided into two groups: an osseodensification group and a conventional drilling group. Each bone sample received one 4.1 × 10-mm implant. The density of the peri-implant bone before and after osteotomy was measured. After implant placement, primary stability was assessed. A laser surface scanner was used before and after implant placement to compare the dimension of crestal bone width and volumetric expansion. Histomorphometric analysis was performed to compare the bone-to-implant contact percentage (BIC%) of the two groups. Results: The peripheral and apical bone mineral density around the implants was significantly increased, and a statistically significantly higher peripheral BIC% was found in the osseodensification group. A significant increase in volume and bone width after implant placement was found in both groups. However, there were no significant differences in volume and bone width change at all three locations and in implant stability between the osseodensification and conventional drilling protocols. Conclusion: Within the limitations of this study, the osseodensification protocol increased the bone mineral density and primary bone-to-implant contact. Also, this study suggests that implant placement by osseodensification or conventional drilling can increase ridge dimensions in narrow alveolar ridges. Keywords: bone mineral density, bone-to-implant contact, histomorphometric, osseodensification, ridge expansion

Purpose: To evaluate the factors that could influence the fracture resistance of implant-supported posterior monolithic zirconia crowns. Materials and methods: Sixty zirconia molar crowns with three different occlusal thicknesses of 0.5, 1.0, and 1.5 mm (20 samples per group) were prepared for implant abutments using a CAD/CAM system. In each group, 10 crowns were luted on the abutment with resin cement (Panavia F), and the other 10 crowns were luted with resin-modified glass-ionomer cement (Ketac Cem Plus). Dynamic loading (1.2 × 10⁶ cycles; 70 N) and thermal cycling were applied to the samples using a chewing simulator before evaluating their fracture resistance with a universal testing machine and examining their fracture type using a stereomicroscope. One-way analysis of variance (ANOVA), the Duncan test, and two-way ANOVA were used for data evaluation (α = .05). Results: The occlusal thickness (P < .001) and cement type (P < .01) affected the fracture load of the monolithic zirconia crowns. The highest fracture resistance was found in 1.5-mm-thick crowns luted with resin cement (4,212 ± 501 N), and the lowest fracture resistance was found in 0.5-mm and 1-mmthick crowns luted with resin-modified glass-ionomer cement (1,198 ± 116 N and 1,197 ± 66 N). A significant difference was not found in the mean maximum fracture load between the 1.5-mm-thick crowns cemented with resin cement and glass-ionomer resin cement. Conclusion: Both the occlusal thickness and cement type remarkably affected the fracture resistance of the crowns, but occlusal thickness was more significant. Implant-supported posterior zirconia crowns can withstand physiologic occlusal forces even with a thickness as low as 0.5 mm. Resin luting cement is recommended for implant-supported posterior zirconia crowns with reduced occlusal thickness. Keywords: CAD/CAM, cement, fracture resistance, implant-supported crown, monolithic zirconia crown, occlusal thickness

Purpose: To evaluate the abutment removal torque and the morphologic aspects of wear in frictional Morse taper connections after axial loading with or without biofilm immersion. Materials and methods: Thirty sets of Morse taper implants and prosthetic abutments were divided into six groups based on the number of mechanical loading cycles and immersion in biofilm derived from human saliva: without load, without biofilm; without load, with biofilm; 100,000 cycles of load, without biofilm; 100,000 cycles of load, with biofilm; 500,000 cycles of load, without biofilm; and 500,000 cycles of load, with biofilm. Mechanical loading was applied at a force of 80 ± 15 N with a frequency of 2 Hz for 100,000 or 500,000 cycles. After removal torque evaluation, the internal surface of the implants was evaluated by scanning electron microscopy and optical profilometer. The results were statistically analyzed at a significance level of P = .05. Results: Overall, the removal torque increased for samples submitted to loading (100,000 cycles of load, without biofilm = 83.8 ± 15.8 Ncm; 100,000 cycles of load, with biofilm = 160.6 ± 16.2 Ncm; 500,000 cycles of load, without biofilm = 147.0 ± 29.3 Ncm; 500,000 cycles of load, with biofilm = 154.5 ± 14.0 Ncm) compared to samples without loading (without load, without biofilm = 23.0 ± 9.4 Ncm; without load, with biofilm = 27.2 ± 7.5 Ncm). The removal torque was not different between groups that received the same number of loading cycles and varied on biofilm exposure (P > .05). However, samples immersed in biofilm showed higher values of removal torque. Surface analysis revealed that the damage on the internal surface of implants was lower in samples not submitted to cyclic mechanical loading (P < .05) independently of immersion in biofilm medium. Conclusion: Cyclic mechanical load on the frictional implant-abutment connection of Morse taper implants increased the removal torque of abutments. The findings of this research suggest that the presence of biofilm can potentially increase the removal torque in frictional Morse taper connections, although more studies are recommended to support this affirmation. Oral biofilm did not interfere with the presence of wear areas along the internal surface of Morse taper implants but increased the roughness values. Keywords: biofilm, dental implants, frictional implants, implant-abutment connection, removal torque, wear

Purpose: To review the evidence from the clinical outcomes of immediately loaded implants with fixed prostheses in edentulous maxillae. Materials and methods: An electronic search was performed in PubMed/MEDLINE, Embase, and Cochrane to identify studies investigating the outcome of implants subjected to immediate loading with fixed dental prostheses in edentulous maxillae. Only clinical studies with more than 10 patients and a mean follow-up time of more than 12 months were included. Meta-analysis was utilized to compare the clinical outcomes between immediately loaded implants and conventionally loaded implants. For immediately loaded implants, a cumulative implant survival rate (ISR) was weighted by the duration of follow-up and number of implants. The weighted marginal bone loss (MBL) was also assessed. Results: A total of 33 studies (16 retrospective studies and 17 prospective studies) were included, which involved 2,635 patients and 12,480 implants. Meta-analysis did not reveal a significant difference of ISR or MBL between the two loading groups. For immediately loaded implants, the weighted cumulative ISR was 95.53% (median: 97.50%) with a mean follow-up of 46.07 months (SD: 30.92). Fourteen studies reported on the MBL of implants, and the mean MBL was 1.19 mm (SD: 0.88) with a mean period of 57.70 months (SD: 32.56). The results should be interpreted with caution due to the lack of randomized controlled trials (RCTs) and the heterogeneity of the data. Conclusion: Despite the lack of RCTs, immediate implant loading with a fixed prosthesis in the edentulous maxilla seems to be a reliable treatment alternative with a high ISR, when appropriate inclusion/exclusion criteria are followed. Keywords: dental implants, edentulous maxilla, full-arch prosthesis, immediate loading

Purpose: To assess the effects of grade IV titanium ultrasonic tip instrumentation on different grade IV titanium implant surfaces and compare the decontamination of different implant surfaces using chlorhexidine, blue laser, or ozone. Materials and methods: Profilometry and energy-dispersive x-ray spectroscopy (EDS) analyses were performed on smooth, laser-micropatterned, and sandblasted grade IV titanium sample disks before (t₀) and after (t₁) ultrasonic instrumentation with an ultrasonic grade IV titanium tip. Samples were also incubated with a Streptococcus sanguinis culture. Each surface type was then treated with chlorhexidine, blue laser, or ozone (three test groups + control group). Scanning electron microscopy (SEM) images were taken after bacterial growth and after decontamination. Results: After ultrasonic instrumentation, surface roughness (R_a) decreased on sandblasted and micropatterned surfaces, whereas it remained substantially unvaried on the smooth surface. SEM images revealed that the laser-micropatterned structure remained substantially unvaried after instrumentation. EDS revealed a minimal quantity of carbon and iron, found in the laser-treated and sandblasted group at t0. A minimal quantity of aluminum and oxygen was found on the sandblasted surface at t₀ and t₁. Ozone therapy achieved the highest decontaminating effect, regardless of implant surface topography. Conclusion: Among the alternative therapies to ultrasonic instrumentation with titanium tips, ozone appears to be effective regardless of the type of implant surface; it can be used for the decontamination treatment of implants without altering the surface structure. Keywords: chlorhexidine, implants, laser, ozone, titanium, ultrasonic

Purpose: The purpose of this study was to evaluate in vitro the accuracy of different splinting techniques using transfers combined with different tray types. Materials and methods: The research group fabricated a maxillary master cast with four implants and a passive metallic bar on this master cast. For the impression techniques, 48 casts were used with six different impression techniques: (1) metal tray with resin splinted transfers, (2) metal tray with metal and resin splinted transfers, (3) plastic tray with resin splinted transfers, (4) plastic tray with metal and resin splinted transfers, (5) multifunctional guide with resin splinted transfers, and (6) multifunctional guide with metal and resin splinted transfers (n = 8) using polyvinyl siloxane impression material. This study used a passive metallic bar to measure the malalignment between the framework and the analogs (A, B, C, and D) in 2D and 3D. The master and experimental casts were scanned with a contact scanner to compare the accuracy in 3D impression techniques. Discrepancies between the analogs were measured in three x-, y-, and z-axes. Results: There was no statistically significant difference (P > .05) between the groups in vertical malalignments (2D). In the 3D evaluation, for the z-axis and combination of xz-axis, plastic tray with metal, and resin splinted transfers (z = 487 μm; xz = 888 μm), there was a statistically significant difference compared with the multifunctional guide and resin splinted transfers (z = 772 μm; xz = 1,380 μm). When analyzing by analog, in C, the multifunctional guide with metal and resin splinted transfers (302 μm) presented a statistically significant difference compared with the multifunctional guide and resin splinted transfers (492 μm). Conclusion: The evaluation methods for the accuracy impression technique presented different results between them. There was no difference in vertical malalignments (2D), but in 3D, the bonding with metal and acrylic resin presented better results than the bond with only acrylic resin when using the plastic tray and multifunctional guide, respectively, in the z-axis and the combination between the xz-axes. The bonding technique of the transfers with metal and acrylic resin presents better results in the 3D analysis for the multifunctional guide impressions. Keywords: dental implant, dental materials, dental prosthesis

Purpose: The purpose of this study was to survey practicing clinicians and determine if differences existed concerning their use of torque-limiting devices (TLDs) and screw-tightening protocols, comparing this with existing universal industry standards. Materials and methods: A nine-question survey was administered with 428 dentists providing data for three specific areas: (1) demographic information-TLD ownership, device age, frequency of use, and observations of screw loosening; (2) recognition information-calibration, reading measurements of the TLD, and the meaning of preload; (3) usage information-screw-tightening protocols and effect of speed during actioning of the TLD. Data collection was compared with industry standards for use of hand torque tools including ISO-6789 1,2:2017 and related texts pertaining to screw fastener protocols. Results: The beam-type TLD was the most popular; however, 33% surveyed used it incorrectly. Most TLDs being used were older than 1 year, with only 6% calibrated. Forty-eight percent observed screw loosening less than once per year, while 44% reported three or more occurrences per year. A similar number used the TLD for implant placement and abutment screw tightening. Screw-tightening protocols varied. Preload was not understood by the majority of those surveyed. Conclusion: Dentistry does not appear to adhere to the protocols and standards recommended by other industries that also rely on screw-fastening mechanisms and TLDs. Further education and training appears to be warranted in this area of implant dentistry to reduce the risks of screw-associated complications. Keywords: abutment screw loosening, calibration, implant screws, preload, screw-tightening, torque-limiting device

Purpose: The aim of this study was to investigate if repeated use of pilot and depth drills for implant site preparation in combination with resterilization leads to any significant changes in cutting edges or in preparation times. Materials and methods: With drills of different lengths and widths (pilot, parallel, and tapered), osteotomies were performed under constant conditions in pig jaws. After each osteotomy, the drills were processed and sterilized. The required time for finishing the osteotomy was noted and analyzed. At the end of each osteotomy cycle, consisting of 10 osteotomies and 10 sterilizations, the cutting edge wear of the drill was analyzed using scanning electron microscopy. Unused but sterilized drills served as a control group. Results: There was no statistically significant difference in the evaluated wear between pilot drills and depth drills as well as between the test and the control group. After 60 osteotomies, implant drills showed considerable signs of wear at the major cutting edge (P > .05). Osteotomy led to a significant increase in the drilling time. While pilot drills showed an increase of drilling time of the factor 33.3, and the tapered drills of the factor 5.37, the parallel drills remained constant in their performance. Conclusion: Within the limitations of this study, it can be concluded that the process of sterilization as well as the number of performed osteotomies play a major role in the wear of the cutting edge and the performance of implant drills. Keywords: microsurface, oral and maxillofacial, surface

Purpose: This study aimed to report a practicable and noninvasive two-stage technique for sinus elevation and delayed implant insertion in the augmented site with residual bone height down to 3 mm or even lower. Materials and methods: The surgical technique employed a two-stage process for rehabilitation of posterior maxillary single-tooth edentulous areas, involving, in the first step, transcrestal maxillary sinus floor augmentation with a collagen sponge to fill the intrabony cavity resulting from the detachment of the sinus membrane; the second step consisted of another indirect sinus floor elevation using magnetoelectric surgery with immediate implant placement and no grafting material. Changes in bone height were evaluated by a comparison of the computed tomography scans acquired before treatment and after surgery (at 3 months and 5 years of the survey). Statistically significant differences between the times and the tooth sites were evaluated by nonparametric statistics (matched and independent), with P < .01. Results: Forty patients were retrospectively selected. The preoperative height of the available alveolar bone was 2.9 ± 0.6 mm. A significant increase in bone height (P < .01) was found for both the first and the second surgery (3.1 ± 0.6 mm and 4.4 ± 0.6 mm, respectively). The overall bone height was measured at 3 years after the first surgery (10.3 ± 0.6 mm). Measurements of the bone height ranked for tooth positions showed no significant difference between premolars and molars. None of the selected patients registered an implant failure. Conclusion: Two-stage osteotome-mediated sinus elevation appeared to be a predictable technique that enabled practitioners to increase the bone height and to obtain successful outcomes even if the amount of bone was approximately 3 mm in height. Keywords: CBCT, dental implant, osteotome sinus elevation, single crown, two-step technique

Purpose: To evaluate the clinical outcomes of unsplinted implant-supported single crowns placed in adolescents, ages 10 to 19 years, and followed up from 5 to 15 years. Materials and methods: This retrospective case series evaluated the outcomes of implant-supported single crowns placed in adolescents between June 2002 and January 2015. The patients were treated with locking-taper connection implants under a two-stage rehabilitation technique. The variables assessed included patient identification, age and reason for implant placement, implant dimensions, follow-up time, status at follow-up, and event description. To analyze peri-implant changes, bone crest level relative to the adjacent tooth was measured from periapical radiographs taken after implantation and the latest follow-up. A paired t test was performed to determine initial and follow-up differences, and data are shown as mean and 95% confidence interval. Cumulative Kaplan-Meier survival rates for implants and prostheses were calculated. Results: Twenty-one adolescent patients with ages ranging from 14 to 19 years, mainly 16 to 18 years, received a total of 37 implant-supported single crowns more frequently placed in the anterior maxilla as a result of congenital aplasia and trauma. Mean changes in bone crests were 1.99 (± 0.4) mm at the day of crown insertion and 2.23 (± 0.4) mm at the latest follow-up (average: 10 years; P = .08). No implant was lost during the follow-up period, leading to 100% implant survival. A total of 34 surviving crowns and 3 crown failures at the time of the latest follow-up led to a cumulative survival rate of 70%. The most commonly observed event was loss of proximal contacts and infraocclusion, which were handled chairside by adding resin composite. Conclusion: Unsplinted implant-supported single crowns placed in adolescents showed high implant and prosthesis survival rates, with a mean bone crest level increase of approximately 0.23 mm relative Keywords: adolescents, dental implants, survival rates

Purpose: The aim of this preclinical study was to evaluate whether implant flossing could leave floss residues in three different implant-prosthetic conditions. Materials and methods: Using an anatomical model, three different conditions were studied: correct connection between the implant and abutment and complete insertion of the implant threads into the plaster (control group); misfit of approximately 220 to 230 μm between the implant platform and abutment in the absence of any thread exposure (misfit group); partial exposure of implant threads but absence of misfit (thread group). Twenty-one microstructured tapered threaded implants were divided among the three groups. Each sample was subjected to a flossing procedure using spongy floss, standardized in terms of movement, frequency, time, and pressure. Subsequently, a stereomicroscope examination with a standardized magnification of 10× was performed in order to highlight the possible presence of floss residues on the implant surface. Results: No floss residue was ever detected for the control group. Both misfit and thread groups showed floss residues that were discernible in two different types: microfilaments and amorphous particles. Statistical analysis showed a significant difference for the presence of floss remnants between the control group and the other two experimental groups (P = .005). No difference was observed between the misfit and thread groups. Conclusion: This study shows that exposed threads and misfit can induce the release of floss residues during maintenance procedures. Keywords: dental implants, implant flossing, implant maintenance, oral hygiene, spongy floss

Purpose: To evaluate marginal bone level changes over 3 years around platform-shifting implants with internal conical connections, and to identify the factors relating to bone level changes. Materials and methods: Systemically healthy patients who lost one tooth or two consecutive teeth were enrolled in the study. The subjects received one or two implants with platform-shifting and internal conical connections in healed bone in a submerged manner. Digital standardized periapical radiographs were obtained at the time of implant placement, at prosthesis delivery, at 1 year, and at 3 years after the definitive restorations. Marginal bone level changes were measured at the mesial and distal aspects of each implant. Spearman correlation coefficients were calculated to examine the correlation between marginal bone level changes and clinical factors (age, vertical mucosal thickness, implant length and diameter, insertion torque value, and vertical implant position). Results: Twenty-five patients with 30 implants (8 men and 17 women, mean age: 61.24 ± 13.18 years) were followed up to 3 years after the definitive restorations. The implant survival rate was 100%, and no remarkable complications were found. Mean peri-implant marginal bone level changes were -0.41 ± 0.61 mm (from placement to prosthesis delivery: C1); -0.08 ± 0.54 mm (from prosthesis delivery to 1 year: C2); -0.04 ± 0.95 mm (from prosthesis delivery to 3 years: C3); and 0.04 ± 0.60 mm (from 1 year to 3 years: C4), respectively. Statistically significant differences in bone level changes were observed between C1 and C3, and C1 and C4. Significant correlations of marginal bone level changes with implant diameter in C1 and with vertical implant position in C2 and C3 were observed. Conclusion: Within the limitations of this study, platform-shifting implants with internal conical connections appeared to prevent marginal bone resorption, especially after delivery of definitive prostheses, although marginal bone resorption attributed to the reestablishment of biologic width following subcrestal placement might be unavoidable. Keywords: internal conical connection, marginal bone level, platform-shifting, radiographic evaluation

Purpose: The aim of this study was to evaluate the clinical use of a high-performance polymer, polyether ether ketone (PEEK), as a material for use in provisional fixed dental prostheses (FDPs) that can be retained by reciprocated guide surfaces of hexagonal-shaped healing abutments during dental implant treatment. Materials and methods: Patients requiring teeth replacement with dental implants for partially and fully edentulous cases in the maxilla and mandible were included. The provisional FDP was fabricated with hex castable copings and PEEK granules using the lost wax technique. The common path of insertion was established by reducing the coping that is in obstruction to the healing abutment. Retention was provided by the reciprocated guide surfaces of multiple hexagonal-shaped healing abutments. Results: Twenty-three custom provisional PEEK FDPs supported by 166 implants in 20 partially and fully edentulous patients were provided during the treatment period. The mean functional periods of the provisional PEEK FDPs for maxillary and mandibular cases were 6.95 ± 0.84 months and 1.90 ± 0.62 months, respectively. All provisional PEEK FDPs functioned as intended for the entire treatment period. There were a total of 10 complications: 4 cases had resin and denture veneers debond from the PEEK framework; 3 partially edentulous cases required supplementary screw retention; and 3 implants in separate cases did not osseointegrate, requiring extended use of the provisional prosthesis. Two provisional mandibular PEEK FDPs with prolonged usage (over 2 years) were excluded from calculations. No fracture of the PEEK framework was observed. Conclusion: The results from this study suggest that PEEK can be a suitable material for use in provisional FDPs during dental implant treatment. Prosthetic complications were frequent but were resolved intraorally. The reciprocated guide surfaces of multiple hexagonal-shaped healing abutments can provide adequate retention and resistance for edentulous cases during the implant treatment period. However, in partially edentulous cases, a prosthesis without cross-arch stabilization supplementary screw retention was required. Keywords: biomaterials, dental implant treatment, healing abutment, provisional fixed/removable prosthesis, polyether ether ketone (PEEK), reciprocated guide surfaces

Purpose: The objectives of this retrospective study were to describe a transcrestal sinus floor elevation technique combining the use of a hydraulic device and a nanohydroxylapatite paste and to report on 4-year clinical and radiographic outcomes. Materials and methods: The sinus floor elevation procedure used a specially designed drill (SinusJet) to start sinus membrane unsticking and a nanohydroxylapatite paste (Ostim) for further sinus membrane elevation and bone augmentation. It was performed as a one-step procedure with immediate implant placement or a two-step procedure with delayed implant placement 9 months later. Implant survival rate, sinus membrane perforation, postoperative complications, and the level of intraoperative and postoperative patient comfort using a visual analog scale were analyzed retrospectively. A nonparametric Wilcoxon matched-pairs test and parametric paired t test were used to identify significant differences. Results: One hundred thirty-six sinus floor elevations were performed in 110 patients at two dental clinics in Belgium with a mean follow-up period of 48 months. In the one-step procedure, the mean 6-month elevation was 8.5 ± 2.7 mm; 194 implants were placed. In the two-step procedure, the mean 9-month elevation was 9.5 ± 2.4 mm; 8 implants were placed. The osteotomy, sinus membrane elevation, and bone grafting typically took less than 3 minutes. Sinus membrane perforation was observed in 2.9% (n = 4/136). The 4-year implant survival rate was 97% (n = 196/202), with six early implant losses. 96.4% of patients reported either no or minimal discomfort. Conclusion: This minimally invasive transcrestal sinus floor elevation procedure that combines a hydraulic device and nanohydroxylapatite paste appears to be safe and predictable. However, further randomized controlled studies are needed to validate the results of this retrospective observational study. Keywords: atrophic posterior maxilla, bone augmentation, dental implant, hydraulic device, nanocrystalline hydroxyapatite, sinus floor elevation, transcrestal procedure

Purpose: The aim of this in vitro study was to evaluate the temperature development of a novel, electropolished drill design during conventional and guided implant osteotomy in comparison to conventional drills under standardized conditions. Materials and methods: Single and sequential 12-mm-deep drilling protocols (guided and unguided) with a conventional (control groups) and novel drill (test groups) were performed in artificial bone blocks under external irrigation. Each drilling protocol was repeated 30 times with drill diameters of 2.2, 2.8, 3.5, and 4.2 mm. Temperature changes were recorded by an infrared camera, and the accumulated thermal energy was calculated. For group comparison, a one-way analysis of variance (ANOVA) and Tukey post hoc test were used with a level of significance set to = .05. Results: The highest temperatures were measured up to 77.9°C for small-diameter drills in the control and test groups. The 3.5-mm and 4.2-mm novel drills showed significantly lower heat generation during guided and unguided osteotomy preparation for single and sequential drilling. The accumulated thermal energy during guided osteotomy preparation was significantly lower with the electropolished drills. Conclusion: The drill design has an important impact on heat development during osteotomy, which was most pronounced for guided osteotomy with conventional drills and for small-diameter osteotomies. Keywords: drill design, electrochemical polishing, guided surgery, heat generation, infrared camera, sequential drilling, single drilling, temperature measurement, twist drills

Purpose: To evaluate the formation of reactive oxygen species in human leukocytes promoted by bone substitutes that are different in origin and morphology used for jawbone tissue regeneration. Materials and methods: This preclinical prospective randomized crossover study involved 10 subjects, from whom venous blood samples were taken. Leukocytes were separated and standardized. Sixty experimental samples consisted of leukocytes incubated with allogeneic, xenogeneic, or alloplastic bone substitutes at different bone weights (12.5 and 25 mg). The control samples consisted only of incubated leukocytes. Reactive oxygen species were quantitatively determined with the fluorimetric method. Statistical analysis was carried out using SPSS 23 software. Results: The highest average reactive oxygen species values were obtained in the allogeneic bone substitute group (P < .05), while the xenogeneic bone substitute group and control group presented equal reactive oxygen species formation rates (P > .05). A proportional difference (P < .05) of reactive oxygen species emission was obtained between different masses of bone substitute in the samples. Conclusion: Allogeneic and alloplastic bone substitutes affect leukocytes and promote reactive oxygen species emission. Xenogeneic bone substitute presents no leukocyte stimulation and maintains anti-inflammatory conditions. Larger bone substitute mass provokes greater oxidative stress. Keywords: bone augmentation, bone substitutes, foreign body reaction, leukocytes, oxidative stress, reactive oxygen species

Purpose: Clinical cases have shown that pterygoid implants are a successful alternative solution for the rehabilitation of atrophic posterior maxillae; however, little research on the biomechanical behavior has been produced. This study created 3D models of pterygoid implant-supported prostheses and compared the stress and strain distributions in the pterygoid implants and surrounding bone using finite element analysis. Materials and methods: Three-dimensional models of a standardized human skull, pterygoid implants, and conventional dental implants were created using Simpleware, based on microcomputed tomography (micro-CT) and CBCT images. Six constructs with varying implant positions and numbers were designed to simulate various clinical scenarios for patients with complete maxillary edentulism. Finite element volume meshes were created and exported to ABAQUS, where the modulus of elasticity and Poisson ratio were assigned for each respective structure. Two load scenarios were simulated with conditions as follows: (1) 150-N axial loading; and (2) 150-N axial loading with simultaneous 50-N lateral loading. Then, the Von Mises stress and maximum principle strain distributions for all models were collected, analyzed, and compared. Results: The maximum stress and strain in the pterygoid implants and surrounding bone under both loading scenarios were found in model 4, which had two pterygoid implants and two anterior implants, at the implant-abutment connection and crestal bone of the premolar region, respectively. The stress and strain in the pterygoid implants for all constructs analyzed were at values within the limit of material strength. Additionally, the stress and strain in the surrounding bone for all constructs analyzed were at values within the bone resorption threshold. The maximum stress in the surrounding bone for all models with pterygoid implants was lower than the stress in the control model, which contained no pterygoid implants. Conclusion: Pterygoid implants decreased the stress and strain level in the surrounding bone for all cases studied. Additional concern should be placed on the crestal bone of the premolar region and the implant-abutment connections of the pterygoid implants, since these locations had the highest recorded values. Keywords: 3D, FEA, finite element analysis, oral and maxillofacial, prostheses, pterygoid