Comparative study of axial displacement in digital and conventional implant prosthetic components.

Axial displacement of prosthetic components is a major concern in implant dentistry, particularly during screw tightening. However, implant manufacturers provide different recommended torques for tightening implant prosthetic components, which can lead to errors in prosthesis fit before and after impression making. Implant-abutment connection angle or abutment geometries can affect axial displacement. This study aimed to compare the axial displacement between conventional and digital components based on the tightening torque and differences in the implant-abutment connection angles and geometries. The results showed that scan bodies with different implant-abutment connection geometries exhibited smaller axial displacement with increasing tightening torque than other prosthetic components. Except for the scan bodies, there was no difference in the axial displacement of prosthetic components when tightened with the same torque. However, regardless of the use of digital or conventional method of impression making, the axial displacement between the impression making component and the abutment when tightened to the recommended torques were significantly different. In addition, axial displacement was affected by the internal connection angle. The results of this study indicate that the tightening torque and geometry of prosthetic components should be considered to prevent possible misfits which can occur before and after impression making.

In vitro comparison of guide planes for removable partial dentures prepared with CAD-CAM-assisted templates, guiding rod templates, and freehand.

OBJECTIVES: This study aimed to evaluate the accuracy of computer-aided design and computer-aided manufacturing (CAD-CAM)-assisted templates (CCAT), guiding rod templates (GRT), and freehand (FH) preparation of guide planes. METHODS: Forty-five identical maxillary resin casts were divided into three groups, in which the guide planes of the two abutment teeth were prepared using a CCAT (n=15), GRT (n=15), and FH (n=15). The CCAT and GRT were digitally designed on a digital cast of virtually prepared guide planes and fabricated using three-dimensional printing (3DP) technology. To assess the 3D trueness, the prepared guide planes were digitally scanned and compared to the virtually designed guide planes. The angle deviation was measured to assess the trueness of the direction of the guide plane preparation. Shapiro-Wilk and Levene's tests were used to check the normality and equivalence of the variance of the data. The data were compared by using the Kruskal‒Wallis H test (α=0.05). RESULTS: The CCAT group exhibited significantly better 3D trueness (78.5±19.8 µm) than the GRT group (211.3±42.4 µm, p<0.05) and the FH group (198.9±44.3 µm, p<0.05). Additionally, the CCAT group (1.31±0.50°) showed significantly smaller direction trueness compared to the GRT (4.65±0.72°, p<0.05) and FH (5.64±0.70°, p<0.05) groups. CONCLUSIONS: The novel CAD-CAM-assisted template significantly improved the quality of the guide planes compared with the GRT and FH procedures. This enhancement suggests that removable partial dentures can be predictably inserted immediately after guide plane preparation. CLINICAL SIGNIFICANCE: CAD-CAM-assisted templates improve the quality of guide plane preparation.

Comparison of misfit and roughness of CAD-CAM ZrO, selective laser sintered CoCr and preformed Ti implant abutment crowns.

BACKGROUND: Marginal misfit and surface roughness of customized implant abutments is critical for restorative success. However, little is known about the comparison of misfit and surface roughness of CAD-CAM Zirconium oxide (ZrO), selective laser melting (SLM) Cobalt Chrome (CoCr) and preformed abutments. The aim of the study is to investigate the relation of misfit and micro-roughness of selective laser melting (SLM), preformed and CAD-CAM implant abutments. METHODS: Thirty internal connection, endosseous dental implants (Ø 4.0 mm x 10 mm, Dentium) were mounted in Polymethyl methacrylate vertically. Ten preformed Titanium alloy (Ti) abutments with 1 mm soft tissue height and Ø 4.5 mm were included as controls. Ten each of Y-TZP and SLM-CoCr, abutment/crowns were fabricated using CAD-CAM milling (CAD-CAM-ZrO) and SLM techniques. Surface micro-roughness (Ra) of the fabricated implant abutment/crown was evaluated with a 3D optical non-contact microscope. All implant restorations were torqued to implants (30 Ncm) using a Tohnichi BTGE digital torque gauge and were analyzed with Bruker micro-CT (Skyscan 1173) to detect micro-gaps at pre-selected points at implant abutment interface. The Ra and misfit data were compared using ANOVA, Tukey-Kramer, Kruskal-Wallis test and Pearson correlation (p < 0.05). RESULTS: Mean Ra among SLM CoCr abutments [0.88 (0.09) µm] were lower than CAD-CAM-ZrO and higher than preformed Ti abutments. Horizontal misfit among SLM-CoCr [45.43 (9.41) µm] and preformed Ti [36.87 (13.23) µm] abutments was not statistically different (p > 0.05). Misfit was significantly higher in Y-TZP samples compared to SLM-CoCr (p = 0.031) and preformed Ti abutments (p = 0.01). Preformed Ti abutments showed significantly lower misfit compared to SLM-CoCr abutments (p = 0.01). A positive linear correlation was observed between the surface roughness (Ra) and vertical misfit (r = 0.61, p < 0.05). CONCLUSION: SLM CoCr abutments showed rough surface compared to preformed Ti abutments, while horizontal misfit was comparable among SLM-CoCr and preformed abutments. Misfit was significantly greater in Y-TZP abutments, compared to SLM and preformed abutments. SLM abutment fabrication technique needs further improvement to provide better fit and surface topography.

Complete-arch accuracy of seven intraoral scanners measured by the virtual-fit method.

OBJECTIVES: This study compared the accuracy of seven intraoral scanners (IOS) by the virtual-fit method. METHODS: Four maxillary arches with tooth abutments were scanned with an industrial reference scanner (n=1) and by Aoralscan3, EmeraldS, Helios600, Lumina, Mediti700, Primescan, and Trios5 IOSs (each n=12). Two complete-arch fixed frameworks were designed on each IOS scan with a 70 µm (group 70) and a 90 µm internal cement space (group 70+20, additional 20 µm at the margin). The virtual-fit method was comprised of superimposing the framework designs onto the reference scan using a non-penetrating algorithm simulating the clinical try-in. Internal and marginal gaps were measured. Precision was estimated by the mean absolute errors (MAE). RESULTS: In group 70, Mediti700 (43 µm), Primescan (42 µm), and EmeraldS were in the best homogenous subset for the marginal gap, followed by the Lumina (67 µm), Aoralscan3 (70 µm), and Trios5 (70 µm), whereas Helios600 (118 µm) was in the third subset. Based on the MAE at the margin, Mediti700, Trios5, and EmeraldS were in the first-best homogenous subset, followed by Primescan. Lumina and Helios600 were in the third subset, and Aoralscan3 was in the fourth subset. In group 70+20, the marginal gap was significantly decreased for Lumina and Aoralscan3, whereas MAE significantly decreased for EmeraldS and Aoralscan3. The rank of IOSs was similar for the internal gap. CONCLUSION: EmeraldS, Mediti700, Primescan, and Trios5 meet the marginal and internal fit criteria for fixed tooth-borne complete arch restorations. Increasing the cement space during design could enhance restoration fit. CLINICAL SIGNIFICANCE: The virtual-fit alignment method can effectively evaluate the accuracy of different intraoral scanners, offering valuable clinical guidance for distinguishing among them. Recent software and hardware versions of long-standing IOS manufacturers are suitable for fabricating complete arch restoration.

Perfect digital impression of natural abutment teeth without using retraction cords.

Digital technologies are gradually gaining ground in dentistry. In particular, taking impressions with intraoral scanners is becoming routine; however, even this must often be preceded by the use of retraction cords. This article presents an innovative technique to record digital impressions of natural tooth abutments using interim restorations relined with impression material instead of retraction cords. In the laboratory, using computer-aided design, the technician can segment the internal surface of the interim restoration and use it to replace the abutment of the intraoral scan, thus obtaining an accurate coping that yields more detailed information about the supragingival and intrasulcular surface of the preparation.

Clinical outcomes of single implant supported crowns utilising the titanium base abutment: A 7.5-year prospective cohort study.

OBJECTIVE: To assess radiographic, clinical and patient-reported outcomes of single zirconia implant-supported crowns on titanium base abutments (TBA) over a 7.5-year period. METHODS: Twenty-four patients received bone-level titanium implants and screw-retained zirconia implant crowns utilising TBA. Marginal bone level (MBL), clinical parameters (probing depth-PD, bleeding on probing-BoP, plaque control record-PCR), technical complications (USPHS criteria) and patient satisfaction were assessed at crown delivery (baseline), 1 year (FU-1) and at 7.5 years (FU-7.5) of follow-up. RESULTS: Eighteen patients were available for re-examination at 7.5 years. The mean MBL at FU-7.5 (0.35 ± 0.20mm) did not significantly change compared to baseline (0.54 ± 0.39, p=.352) and to FU-1 (0.54 ± 0.45mm, p=0.524). From baseline to 7.5 years, the mean PD increased significantly, from 3.0 ± 0.6mm to 3.7 ± 0.8mm (p=0.005). However, BoP and PCR did not significantly change; (BOP: from 27.1 ± 20.7% to 25.0 ± 20.0%, p=0.498; PCR: from 11.1 ± 21.2% to 25.0 ± 25.1%, p=0.100). Nine patients presented with more than one bleeding site. This denoted a peri-implant mucositis prevalence of 50%, whilst none of the implants presented peri-implantitis. One incidence of minor and major ceramic chipping were reported on 2 out of the 18 crowns, resulting in a prosthetic survival rate of 94.4%. Seventeen patients were highly satisfied with their result. CONCLUSION: Single implant-supported zirconia crowns on TBA displayed: (i) minor number of technical complications, (ii) high prosthetic survival rate, (iii) stable marginal bone level and (iv) high patient satisfaction at 7.5 years. CLINICAL IMPLICATIONS: Titanium base abutments despite their high use in clinical practice, lacked medium- and long-term studies. The presented findings highlight their clinical performance at 7.5 years as they display satisfying radiographic, clinical and patient-related outcomes. TBA appear to be a suitable abutment choice for medium-term implant-supported restorations.

Roughness affects the response of human fibroblasts and macrophages to sandblasted abutments.

BACKGROUND: A strong seal of soft-tissue around dental implants is essential to block pathogens from entering the peri-implant interface and prevent infections. Therefore, the integration of soft-tissue poses a challenge in implant-prosthetic procedures, prompting a focus on the interface between peri-implant soft-tissues and the transmucosal component. The aim of this study was to analyse the effects of sandblasted roughness levels on in vitro soft-tissue healing around dental implant abutments. In parallel, proteomic techniques were applied to study the interaction of these surfaces with human serum proteins to evaluate their potential to promote soft-tissue regeneration. RESULTS: Grade-5 machined titanium discs (MC) underwent sandblasting with alumina particles of two sizes (4 and 8 µm), resulting in two different surface types: MC04 and MC08. Surface morphology and roughness were characterised employing scanning electron microscopy and optical profilometry. Cell adhesion and collagen synthesis, as well as immune responses, were assessed using human gingival fibroblasts (hGF) and macrophages (THP-1), respectively. The profiles of protein adsorption to the surfaces were characterised using proteomics; samples were incubated with human serum, and the adsorbed proteins analysed employing nLC-MS/MS. hGFs exposed to MC04 showed decreased cell area compared to MC, while no differences were found for MC08. hGF collagen synthesis increased after 7 days for MC08. THP-1 macrophages cultured on MC04 and MC08 showed a reduced TNF-α and increased IL-4 secretion. Thus, the sandblasted topography led a reduction in the immune/inflammatory response. One hundred seventy-six distinct proteins adsorbed on the surfaces were identified. Differentially adsorbed proteins were associated with immune response, blood coagulation, angiogenesis, fibrinolysis and tissue regeneration. CONCLUSIONS: Increased roughness through MC08 treatment resulted in increased collagen synthesis in hGF and resulted in a reduction in the surface immune response in human macrophages. These results correlate with the changes in protein adsorption on the surfaces observed through proteomics.

Effect of Implant-Abutment Connection and Abutment Angulations on Peri-implant Stress Levels: A Finite Element Analysis Study.

INTRODUCTION: Placement of an implant in the maxillary anterior region is challenging due to the angulation of bone in this area. Angled abutments may be used to achieve proper restorative contours. The present study was undertaken to examine and compare the stress levels of implants in the maxillary anterior region having different types of internal connections and different abutment angulations. MATERIAL AND METHODS: Implants with three types of abutment connections, internal conical, Morse taper, and internal hex, were modeled using SolidWorks software. Three abutment angulations of 0, 15, and 30 degrees were used for each type of implant. A 100 N axial load was applied to the implants, and the stresses on the implant, abutment, and bone were analyzed by finite element analysis. RESULTS: Among the straight abutments, the most stress was in model 3A (62.60 MPa). The stress value among angled abutments was highest with 30-degree angled abutments. The value was highest in model 3C (94.83 MPa). Internal hex connection showed the highest stress levels in all degrees of angulation of the abutment, and Morse taper connection showed the least amount of stress in all three abutment angles. The most stress concentration was seen in the cortical bone on the buccal surface in the implant-abutment junction. CONCLUSION: The Morse taper design of implant exhibited the least-highest stress levels on the alveolar bone. The stress levels increased with the increasing angulation of the implant or implant-abutment connection.

[Short-term follow up of treatment effect using one-time one-abutment placement in implant restoration in 35 patients with single posterior teeth loss].

PURPOSE: To evaluate the effet of one-time one-abutment placement on peri-implant tissues. METHODS: Thirty-five patients with single posterior loss were collected, who received definitive abutment at the moment of implant placement. One day and after 1 year of implant loading, radiographic assessment of marginal bone level changes and clinical status of peri-implant soft tissues were conducted. Plaque index, pocket depth as well as sulcus bleeding index were assessed. RESULTS: During 1 year follow-up period after loading, no implant failure was observed. The mean marginal bone loss of implants were (0.225±0.113) mm mesially and (0.439±0.123) mm distally. Standard periodontal probes were used to measure plaque index, probing depth, and gingival crevicular bleeding index immediately after repair and 1 year later. CONCLUSIONS: In the posterior region, one-time one-abutment placement may better protect peri-implant tissues as an ideal treatment protocol.

Simulating the Entire Clinical Process for an Implant-Supported Fixed Prosthesis: In Vitro Study on the Vertical Implications of Implant-Abutment Connections and Rotational Freedom.

OBJECTIVES: The aim of this in vitro study was to investigate whether and to what extent different scenarios of rotational freedom in different IAC designs affect the vertical dimension of a three-part fixed partial denture (FPD). At the same time, the experimental setup should simulate all clinical and laboratory steps of the implementation of such an FPD as accurately as possible. MATERIAL AND METHODS: Twenty identical pairs of jaw models were fabricated from aluminum, each lower-jaw model holding two implants with conical or flat IACs. Three impressions of each model were taken to fabricate stone casts and three-unit FPDs. Three assembly scenarios were compared for the vertical position stability they offered for these FPDs, differing by how the sequential implant components (impression posts > laboratory analogs > abutments 1 > abutments 2) were aligned with the positional index of the IAC. In this way, a total of 60 stone casts and FPDs were fabricated and statistically analyzed for changes in vertical dimension (p < 0.05). RESULTS: Regardless of whether a conical/flat IAC was used (p > 0.05), significantly greater mean changes in vertical dimension were consistently (all comparisons p < 0.0001) found in a "worst-case scenario" of component alignment alternating between the left- and right-limit stop of the positional index (0.286/0.350 mm) than in a "random scenario" of 10 dentists and 10 technicians with varying levels of experience freely selecting the alignment (0.003/0.014 mm) or in a "best-case scenario" of all components being aligned with the right-limit stop (-0.019/0.005 mm). CONCLUSIONS: The likelihood of integrating a superstructure correctly in terms of vertical dimension appears to vary considerably more with assembly strategies than with IAC designs. Specifically, our findings warrant a recommendation that all implant components should be aligned with the right-limit stop of the positioning index.

Effect of two esthetic digitally produced materials used in fabrication of extracoronal attachments on the stresses Induced in removable partial dentures.

BACKGROUND: Preservation of the remaining structures while maintaining an esthetic appearance is a major objective in removable partial prosthodontics. So, the aim of the current study was to compare the stresses induced on the supporting structures by two digitally produced esthetic core materials; Zirconia and Polyetheretherketone when used as an extracoronal attachment in distal extension removable partial dentures using strain gauge analysis. METHODS: A mandibular Kennedy class II stone cast with the necessary abutments' preparations was scanned. The mandibular left canine and first premolar teeth were virtually removed. An acrylic mandibular left canine and first premolar teeth were prepared with heavy chamfer finish line and scanned. Virtual superimposition of the acrylic teeth in their corresponding positions was done. Two strain gauge slots were designed: distal to the terminal abutment and in the residual ridge. Two models and two sets of scanned teeth were digitally printed. The printed teeth were then placed in their corresponding sockets in each model and scanned. The attachment design was selected from the software library and milled out of Zirconia in the model ZR and Polyetheretherketone in the model PE. Five removable partial dentures were constructed for each model. The strain gauges were installed in their grooves. A Universal testing machine was used for unilateral load application of 100 N (N). For each removable partial denture, five measurements were made. The data followed normal distribution and were statistically analyzed by using unpaired t test. P value < 0.05 was considered to be statistically significant. RESULTS: During unilateral loading unpaired t test showed statistically significant difference (p = 0.0001) in the microstrain values recorded distal to the abutment between the models ZR (-1001.6 µÎµ ± 24.56) and PE (-682.6 µÎµ ± 22.18). However, non statistically significant difference (p = 0.3122) was observed in the residual ridge between them; ZR (16.2 µÎµ ± 4.53) and PE (15 µÎµ ± 3.74). CONCLUSIONS: In removable partial dentures, Polyetheretherketone extracoronal attachment induces less stress on the supporting abutments compared to the zirconia one with no difference in the stresses induced by them on the residual ridge.

Multi-objective optimization of custom implant abutment design for enhanced bone remodeling in single-crown implants using 3D finite element analysis.

The optimal configuration of a customized implant abutment is crucial for bone remodeling and is influenced by various design parameters. This study introduces an optimization process for designing two-piece zirconia dental implant abutments. The aim is to enhance bone remodeling, increase bone density in the peri-implant region, and reduce the risk of late implant failure. A 12-month bone remodeling algorithm subroutine in finite element analysis to optimize three parameters: implant placement depth, abutment taper degree, and gingival height of the titanium base abutment. The response surface analysis shows that implant placement depth and gingival height significantly impact bone density and uniformity. The taper degree has a smaller effect on bone remodeling. The optimization identified optimal values of 1.5 mm for depth, 35° for taper, and 0.5 mm for gingival height. The optimum model significantly increased cortical bone density from 1.2 to 1.937 g/cm3 in 2 months, while the original model reached 1.91 g/cm3 in 11 months. The standard deviation of density showed more uniform bone apposition, with the optimum model showing values 2 to 6 times lower than the original over 12 months. The cancellous bone showed a similar trend. In conclusion, the depth and taper have a significant effect on bone remodeling. This optimized model significantly improves bone density uniformity.

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

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

Experimental study on implant-abutment locking force and abutment subsidence in a pure Morse taper connection implant system.

OBJECTIVES: This test aimed to investigate the factors affecting the locking force between the implant and abutment and the amount of abutment subsidence in pure Morse taper connection implant systems. METHODS: With reference to the Bicon implant abutment connection design, different types of implant specimens and their corresponding types of abutments were fabricated. The implant-abutment locking taper was uniformly 1.5°. The locking depths were 1.0, 2.0, and 3.0 mm. The diameters of the locking column were 2.5, 3.0, and 3.5 mm. The thicknesses of the outer wall of the implant were 0.15 and 0.30 mm. The loading forces of the testing machine were 200, 300, and 400 N. At least 10 specimens of each group of implant-abutment were used. All specimens were loaded in the same manner using a universal testing machine (finger pressure + specified loading force, five times). The total height of the implant-abutment was measured before finger pressure, after finger pressure, and after the testing machine was loaded for five times to calculate the amount of sinking of the abutment. Finally, the implant and abutment were pulled apart using the universal testing machine, and the subluxation force was observed and recorded. RESULTS: The test loading force, locking depth, and locking post diameter had an effect on the implant-abutment locking force and abutment subsidence. The implant-abutment locking force increased with the increase in the test loading force, locking depth, and locking post diameter (R=0.963, 0.607, and 0.372, respectively), with the test loading force having the most significant effect. Abutment subsidence increased with the increase in test loading force (R=0.645) and decreased with the increase in locking depth and locking post diameter (R=-0.807 and -0.280, respectively), with locking depth having the most significant effect on abutment subsidence. No significant correlation was found between the thickness of the outer wall of the implant and the change in the magnitude of the implant-abutment locking force. However, an increase in the thickness of the outer wall of the implant decreased the amount of abutment subsidence, which was inversely correlated. CONCLUSIONS: The locking force of the implant-abutment can be increased by adjusting the design of the pure Morse taper connection implant⁃abutment connection, increasing the locking depth and locking post diameter, and increasing the amount and number of times the abutment is loaded during seating. Problems, such as loosening or detachment of the abutment, can be reduced. The recommended abutment to be loaded should be no less than five times during seating to prevent the abutment from sinking and causing changes in the occlusal relationship in the later stages. Preliminary occlusal adjustments should only be conducted in the early stages of the use of temporary restorations, and final restorations and occlusal adjustments are recommended to be performed after using the abutment for a period of time.

Mechanical strength of stock and custom abutments as original and aftermarket components after thermomechanical aging.

OBJECTIVES: The study aimed to assess the impact on the mechanical strength and failure patterns of implant-abutment complexes of choosing different abutment types, designs and manufacturers, aiding in selecting the optimal restorative solution. Stock and custom abutments from original and aftermarket suppliers were subjected to thermomechanical aging. MATERIAL AND METHODS: Stock and custom abutments from the implant manufacturer (original) and a aftermarket supplier (nonoriginal) were connected to identical implants with internal connection. Custom abutments were designed in a typical molar and premolar design, manufactured using the workflow from the respective suppliers. A total of 90 implants (4 mm diameter, 3.4 mm platform, 13 mm length) equally divided across 6 groups (three designs, two manufacturers) underwent thermo-mechanical aging according to three different regimes, simulating five (n = 30) or 10 years (n = 30) of clinical function, or unaged control (n = 30). Subsequently, all samples were tested to failure. RESULTS: During aging, no failures occurred. The mean strength at failure was 1009N ± 171, showing significant differences between original and nonoriginal abutments overall (-230N ± 27.1, p < .001), and within each abutment type (p = .000), favoring original abutments. Aging did not significantly affect the failure load, while the type of abutment and manufacturer did, favoring original and custom-designed abutments. The most common failure was implant bending or deformation, significantly differing between original and nonoriginal abutments and screws. All failure tests resulted in clinically unsalvageable implants and abutments. CONCLUSIONS: Within the limitations of this study, original abutments exhibited a higher mechanical strength compared to the nonoriginal alternative, regardless of the amount of simulated clinical use. Similarly, custom abutments showed higher mechanical strength compared to stock abutments. However, mechanical strength in all abutments tested was higher than average chewing forces reported in literature, thus components tested in this study can be expected to perform equally well in clinical situations without excessive force.

The influence of implant depth, abutment height and mucosal phenotype on peri­implant bone levels: A 2-year clinical trial.

OBJECTIVES: To evaluate the bone changes around equicrestal and subcrestal implants, analyzing the effect of abutment height [short abutments (SA < 2 mm) and long abutments (LA > 2 mm)] and the three components of the peri­implant soft-tissue phenotype. METHODS: Twenty-six patients received 71 implants that were placed according to supracrestal tissue height (STH) in an equicrestal (n = 17), shallow subcrestal ≈1 mm (n = 33), or deep subcrestal ≈2 mm (n = 21) position. After 3 months of healing, rehabilitation was completed using metal-ceramic crowns on multi-unit abutments of 1.5 mm, 2.5 mm, or 3.5 mm in height, depending on the prosthetic space and STH. Longitudinal clinical parameters (STH, mucosal thickness, and keratinized mucosa width) and radiographic data [bone remodelling and marginal bone loss (MBL)] were collected at 3, 6, 12, and 24 months postsurgery. RESULTS: The gain in STH was significantly greater around the implants placed in a subcrestal ≈2 mm position. After 2 years, the mean change in bone remodelling in the SA group was significantly greater than in the LA group. According to the multiple linear regression, bone remodelling depends primarily on abutment height (ß = -0.43), followed by crestal position (ß = 0.34), and keratinized mucosa width (ß = -0.22), while MBL depends on abutment height (ß = -0.37), and the patient's age (ß = -0.36). CONCLUSIONS: Implants placed in an equicrestal or subcrestal ≈1 mm position with LA undergo less bone remodelling, while the lowest level of MBL occurs in subcrestal ≈2 mm implants with LA. Differing soft-tissue thicknesses combined with the use of either SA or LA produced significant intergroup differences in bone remodelling and MBL. CLINICAL SIGNIFICANCE: Abutment height is the most powerful predictor variable affecting bone remodelling and MBL. Depending on the dimensions of the peri­implant soft-tissue phenotype, placing the implants subcrestally may also be a viable option to decrease bone remodelling and, consequently, reduce MBL. CLINICAL TRIAL REGISTRATION: identification number: NCT05670340.

The effect of thermomechanical aging on the fracture resistance of additively and subtractively manufactured polyetheretherketone abutments.

OBJECTIVES: To evaluate the fracture resistance (FR) of polyetheretherketone (PEEK) abutments produced by additive and subtractive methods compared to milled zirconia abutments. METHODS: Custom abutments were designed on Ti-base abutments and produced from three different materials, namely additively manufactured PEEK (PEEK-AM), subtractively manufactured PEEK (PEEK-SM), and zirconia (N = 60). PEEK-AM abutments were printed using PEEK filaments (VESTAKEEP®i4 3DF-T, Evonik Industries AG) on a M150 Medical 3D Printer (ORION AM) by fused filament fabrication (FFF). All surface treatments were carried out according to the manufacturer's instructions. All abutments were cemented on Ti-bases with hybrid abutment cement and then restored with milled zirconia crowns. Each subgroup was divided into non-aged and aged subgroups (n = 10). The aged groups were subjected to thermomechanical aging (49 N, 5-55 °C, 1.2 million cycles). FR tests were performed by using an universal testing machine. Data were statistically analyzed with one-way and two-way ANOVA and t-test. RESULTS: The survival rate of the specimens after aging was determined as 100%. It was found that both the material and aging had a significant effect on the FR (p<.001). There was a statistical difference among the fracture values of the groups (p<.001). In both the aged and non-aged groups, PEEK-AM showed the statistically lowest FR, while the highest FR was seen in the zirconia group, which was significantly higher than the PEEK-SM (p<.001). CONCLUSION: Hybrid abutments were successfully manufactured, and extrusion-based processed PEEK seems to be a good alternative to subtractive processed PEEK. However, since subtractive manufacturing still appears to be superior, further developments in additive manufacturing are needed to further improve the quality of 3D-printed PEEK parts, especially in terms of accuracy and bonding between adjacent layers. CLINICAL SIGNIFICANCE: Additively manufactured PEEK abutments have the potential to be an alternative for implant-supported restorations in the posterior region.

The effect of different implant-abutment types and heights on screw loosening in cases with increased crown height space.

OBJECTIVES: The stability of the abutment screw is pivotal for successful implant-supported restorations, yet screw loosening remains a common complication, leading to compromised function and potential implant failure. This study aims to evaluate the effect of different implant-abutment types and heights on screw loosening in cases with increased crown height space (CHS). MATERIALS AND METHODS: In this in vitro study, a total of 64 abutments in eight distinct groups based on their type and height were evaluated. These groups included stock, cast, and milled abutments with heights of 4 mm (groups S4, C4, and M4), 7 mm (groups S7, C7, and M7), and 10 mm (groups C10 and M10). Removal torque loss (RTL) was assessed both before and after subjecting the abutments to dynamic cyclic loading. Additionally, the differences between initial RTL and RTL following cyclic loading were analyzed for each group (p < .05). RESULTS: The C10 group demonstrated the highest RTL, whereas the S4 group exhibited the lowest initial RTL percentage (p < .05). Furthermore, the study established significant variations in RTL percentages and the discrepancies between initial and postcyclic loading RTL across different abutment groups (p < .05). Additionally, both abutment types and heights were found to significantly influence the RTL percentage (p < .05). CONCLUSION: The type and height of the implant abutment affected screw loosening, and in an increased CHS of 12 mm, using a stock abutment with a postheight of 4 mm can be effective in minimizing screw loosening.

An In Vitro Evaluation of Periotest Implant Stability Measurements Taken on Implant Retained Crowns and Healing Abutments.

OBJECTIVE: To assess the reliability of implant stability measurements recorded with the Periotest device and to investigate the differences in values when these measurements were taken on implant retained crowns and healing abutments. MATERIALS AND METHODS: Fifty-six implants in eight synthetic bone blocks were used to carry out implant stability measurements using the Periotest device by two different operators. Each block constituted an example of bone of density D1, D2, D3, or D4, and two blocks of each density were used. The healing abutments placed were of a height to allow approximately 6 mm of the implant-abutment complex to be supracrestal and temporary crowns were made to match the dimensions of an average central incisor. Descriptive statistics were used to describe the perio test values (PTVs) at each of the different heights on the implant abutments and implant crowns. Means for each site were calculated and distribution of data assessed using the Kruskal Wallis test. The interclass correlation coefficient (ICC) was used to determine the relationship between the PTVs recorded on the implant abutments and implant crowns. RESULTS: The mean PTV (±standard devidation) recorded across all sites was 5.57 ± 11.643 on the implant abutments, and 12.27 ± 11.735 on the temporary crowns. Excellent/good inter-operator ICCs were recorded for the mid-abutment site in all bone blocks D1-D4 (ICC = 0.814, p < 0.001, ICC = 0.922, p < 0.001, ICC = 0.938, p < 0.001, ICC = 776, p < 0.001). For mid crown sites, ICC between operators was excellent/good only for recordings in D2 bone (ICC = 0.897, p < 0.001). CONCLUSIONS: Periotest device seems to be able to reliably measure implant stability across all types of bones when the implant stability is assessed at approximately 3 mm coronal to the implant platform for abutments and 4.5 mm for implant supported single crowns.

Ceramic conversion treated titanium implant abutments with gold for enhanced antimicrobial activity.

INTRODUCTION: Peri-implantitis is an inflammatory process around dental implants that is characterised by bone loss that may jeopardize the long-term survival of osseo integrated dental implants. The aim of this study was to create a surface coating on titanium abutments that possesses cellular adhesion and anti-microbial properties as a post-implant placement strategy for patients at risk of peri-implantitis. MATERIALS AND METHODSMETHODS: Titanium alloy Grade V stubs were coated with gold particles and then subjected to ceramic conversion treatment (CCT) at 620 °C for 3, 8 and 80 h. The surface characteristics and chemistry were assessed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) analysis. The leaching profile was investigated by inductively coupled plasma mass spectroscopy (ICP-MS) for all groups after 7, 14 and 28 days in contact with distilled water. A scratch test was conducted to assess the adhesion of the gold coating to the underlying titanium discs. Two bacterial species (Staphylococcus aureus (SA) & Fusobacterium nucleatum (FN)) were used to assess the antibacterial behaviour of the coated discs using a direct attachment assay test. The potential changes in surface chemistry by the bacterial species were investigated by grazing angle XRD. RESULTS: The gold pre-coated titanium discs exhibited good stability of the coating especially after immersion in distilled water and after bacterial colonisation as evident by XRD analysis. Good surface adhesion of the coating was demonstrated for gold treated discs after scratch test analysis, especially titanium, following a 3-hour (3 H) ceramic conversion treatment. All coated discs exhibited significantly improved antimicrobial properties against both tested bacterial species compared to untreated titanium discs. CONCLUSIONS: Ceramic conversion treated titanium with a pre-deposited gold layer showed improved antimicrobial properties against both SA and FN species than untreated Ti-C discs. Scratch test analysis showed good adherence properties of the coated discs the oxide layer formed is firmly adherent to the underlying titanium substrate, suggesting that this approach may have clinical efficacy for coating implant abutments.