Prosthetic Screw Research Articles

Influence of Implant Inclination and Prosthetic Abutment Type on the Biomechanics of Implant-Supported Fixed Partial Dentures.

Obtaining parallelism during implant placement is often difficult, leading to inclination of implants. The present study evaluated the stress distribution in 3-unit fixed partial dentures supported by 2 implants with different inclinations and prosthetic abutments. Universal castable long abutments (UCLAs) or tapered abutments were used considering 17° of implant angulation in different directions (mesial, distal, buccal, or lingual). To do so, 3-dimensional finite element models were built and exported to specific analysis software. Forces were applied to the functional cusps. Data were obtained with regard to the maximum principal and von Mises stresses (in MPa). No relevant differences were observed in the stress values in the cortical and cancellous bone nor in the prosthesis with UCLA or tapered abutments. However, a relevant stress reduction in the prosthetic screws of the tilted implant was observed when using UCLA abutments. According to the obtained results, it is possible to suggest that both UCLA or tapered abutments can be used for 3-unit fixed partial dentures when 1 of the implants is tilted. UCLA abutment might lead to less biomechanical problems related to screw loosening or fracture.

Biomechanical behavior of an implant system of carbon fiber-reinforced polyether ether ketone (PEEK) bars with different designs: finite elements analysis

We used finite elements analysis to assess the biomechanical behavior of lower protocol bars made of Polyether Ether Ketone (PEEK) reinforced by carbon fiber, with different designs on All-on-four® system, subjected to physiological occlusal loads. The models were built to have an I-shaped or an inverse T-shaped section. We also assessed the stress distribution on the peri implant bone, implants, prosthetic intermediates, prosthetic intermediate screws, and prosthetic screws. In the simulations, strength peaks were similar for both inverse T and I shaped models; however, the I-shaped bars showed larger resistance in comparison with the inverse T shape. Since it is a new material in dentistry, further research is necessary for a better assessment of PEEK's mechanical and clinical performance.

Treatment of Resorbed Mandibles with Titanium Plate and Immediate Implant-Supported Prosthesis - Case Series.

Severely resorbed mandibles with only cortical bone remaining can fracture during or after implant placement. This case series presents a technique to reduce the risk or the consequences of mandibular fracture. Seven patients with only cortical mandibular bone remaining were treated with the fixation of a titanium plate in the frontal surface previously to implant placement, during the same surgical procedure. Immediate complete-arch implant supported prosthesis were installed. Patient's systemic and local conditions that could influence implant survival were registered previously to surgery and during the follow up period. Biological and biomechanical complications were recorded. The condition of peri-implant tissues was evaluated. The follow-ups ranged from 12 to 84 months. Twenty-nine implants were placed and no implant failure or other biological complication was observed. The peri-implant tissue evaluation demonstrated most implants was surrounded by keratinized tissue (89.5%). No marginal recession (implant platform cervical to gingival margin) was observed. Probing depth was normal, ranging from 0 to 3 mm. Low scores of plaque index or bleeding on probing were recorded. Biomechanical complications evolved loosening of 4 prosthetic screws and 1 fractured. The use of a titanium plate for the fixation of severely resorbed mandibles with only cortical bone remaining was a safe treatment procedure, avoiding biological and major biomechanical complications in the treatment with immediate complete-arch implant-supported prosthesis.

Incidence of abutment screw failure of single or splinted implant prostheses: A review and update on current clinical status.

Osseointegrated implants have been widely used for decades with high survival and success rates. However, mechanical complications continue to be reported in the literature, and their clinical management can be often very challenging for the clinician while there is no consensus on the ideal management. The aim of this manuscript was to review the risk factors of abutment screw complications, to identify the most recent incidence of screw failure in the clinical setting and report on the methodology used and the outcome of intervention. Clinical studies and reports were reviewed that reported on abutment screw looseness and/or fracture. A search of the electronic database PUBMED was conducted in November 2018, including manuscripts published in English from 2004 to 2018. Study selection: animal studies, narrative reviews, expert opinions and communications/letters were excluded. Further exclusion criteria included reports on occlusal prosthetic screws and fracture of abutments, and reports that did not provide adequate data. A total of 12 manuscripts were finally included that reported on single implant crowns or 2-unit implant fixed dental prosthesis. To conclude, the most current abutment screw loosening incidence ranges between 7% and 11%, while the abutment screw fracture incidence was found to be 0.6%. The majority reported on fracture of the screw body. Screw loosening or fracture was often located at the first molar restored area, while the maxillary central incisor area was also reported as an area that presented screw fracture. No single abutment screw failure management can be identified as the ideal treatment approach.

Retrospective clinical evaluation of implant-supported single crowns: Mean follow-up of 15years.

To retrospectively assess the clinical outcomes of implant-supported single crowns and the supporting implants. This retrospective study included all patients treated with implant-supported single crowns at one specialist clinic. Implant and prosthesis failure, and mechanical/technical complications (ceramic fracture/chipping; crown loss of retention/mobility; crown failure/fracture; loosening/loss/fracture of prosthetic screw; and implant failure/fracture) were the outcomes analyzed. Any condition/situation that led to the removal/replacement of crowns was considered prosthesis failure. A total of 438 patients with 567 crowns were included. Mean±SD follow-up of 183.4±69.3months. A total of 37 implants (6.5%) and 54 crowns (9.5%) failed. If only technical problems were considered, the crown failure rate decreased to 4.1% (23/567). Most common reasons for crown failure: esthetic issue (n=12), crown constantly mobile (n=9), change to another type of prosthesis together with other implants (n=8), crown fracture (n=7), and crown in infraposition in comparison with adjacent teeth (n=7). The odds of crown failure were shown to be statistically significantly higher for the following factors: younger patients, maxillary crowns, and screw-retained crowns. Loose prosthetic screw was much more prevalent in screw-retained than in cemented crowns. Ceramic fracture/chipping was more prevalent in screw-retained crowns, maxillae, females. Crown fracture was more prevalent in ceramic crowns, screw-retained crowns, maxillae, posterior region, females. However, these differences were statistically significant only for crown fractures in females. The odds of crown failure were significant for some factors, but one must keep in mind that non-technical complications are as common as technical ones as reasons for the replacement of implant-supported single crowns.

Does the transversal screw design increase the risk of mechanical complications in dental implants? A finite elements analysis.

The transversal screw was introduced in order to overcome some disadvantages of the transocclusal screw. However, its mechanical risk has not been studied sufficiently. The main purpose of this research was to assess and compare stress distribution in the screws and abutment of a single-crown implant with transversal and transocclusal screw models. Two 3D models were assembled to analyse a single-implant-supported prosthesis with transversal and transocclusal screws embedded in the jawbone. The crown was subjected to a static load of value 300N with different levels of inclination. The transversal screw model, with an axial load of 15°, was the one with lowest stress values in all its components. However, the stress was greater with more inclined loads when compared with the transocclusal model. The prosthetic transversal screw showed much less stress than the rest of the components for any load inclination. The transversal screw design is the option with the lowest risk of mechanical complications, both in the prosthetic screw and in the abutment screw, when applying forces of lower inclination. The more oblique forces favoured a better biomechanical environment in the abutment and its screw in the transocclusal screw model.

Dimensional precision of implant-supported frameworks fabricated by 3D printing

Statement of problemSelective laser melting (SLM) is a promising additive technology for clinical practice, but data on dimensional precision assessed by marginal fit combined with stress and strain investigations of implant-supported fixed partial dentures (FPDs) are lacking. PurposeThe purpose of this in vitro study was to verify whether the SLM additive manufacturing technology provides better dimensional precision for 3-unit FPD frameworks than subtractive manufacturing with soft metal block (SMB) milling and the standard casting technique. Material and methodsThirty 3-unit implant-supported FPDs with Co-Cr frameworks were made by the casting, SMB milling, and SLM methods (n=10). The marginal fit between the framework and the implant abutment was evaluated with photoelastic (PH) and strain gauge (SG) models. Stress and strain in the implant-supported system were measured by quantitative PH and SG analyses after prosthetic screw tightening. Data were subjected to the Kruskal-Wallis test, Mann-Whitney U test, and Spearman correlation test (α=.05). ResultsThe framework manufacturing method affected the marginal fit (P<.001), stress, and strain values (P<.05). The SLM group showed the best mean ±standard deviation marginal fit (μm) (PH model: 8.4 ±3.2; SG model: 6.9 ±2.1) in comparison with SMB milling (PH model: 42.3 ±15.7; SG model: 41.3 ±15.3) and casting (PH model: 43.5 ±27.8; SG model: 41.3 ±24.6) (P<.05). SLM showed lower mean ±standard deviation stress and strain values (60.3 ±11.6 MPa; 91.4 ±11.1 μstrain) than casting (225.5 ±142.8 MPa; 226.95 ±55.4 μstrain) and SMB milling (218.6 ±101.7 MPa; 289.7 ±89.3 μstrain) (P<.05). A positive correlation was observed between fit and stress or strain for all groups (P<.05). ConclusionsThree-unit FPD frameworks made using the SLM technology showed better dimensional precision than those obtained with the casting or SMB milling methods.

Evaluation of the accuracy and stress distribution of 3-unit implant supported prostheses obtained by different manufacturing methods

The purpose of this in vitro study was to measure the vertical, positive-horizontal, and negative-horizontal misfit (VM, PHM, and NHM, respectively) of the zirconia three-element prosthetic framework, fabricated using different methods, and compare them with conventional fabrication methods (lost-wax casting). Furthermore, this study aimed to evaluate the influence of the misfit values on the biomechanical behavior of the 3-unit fixed prosthetic frameworks using three-dimensional finite element analysis (3D-FEA). Forty frameworks (n = 10) were fabricated as follow: G1, Cerec Bluecam; G2, iTero; G3, 3Series; and G4, conventional method. The samples were randomized to measure marginal misfit using a high-precision three-dimensional (3D)-optical microscope. The results were submitted to analysis of variance (ANOVA), with the significance level set at 5%. The mean VM values of each group were used in creating the models by 3D-FEA with the misfit found in optical microscopy. The programs used were the InVesalius, Rhinoceros, SolidWorks, FEMAP and NEiNastran. The von Mises map was plotted for each model. The G4 showed the lowest mean VM value (16.73 μm), followed by G3 (20.71 μm), G2 (21.01 μm), and G1 (41.77 μm) (p < 0.001). G2 was more accurate than G1 (p < 0.05) and similar to G3 (p = 0.319). For PHM, G4 was the most accurate and did not present overextended values. With regard to NHM, the computer-aided design and computer-aided manufacturing (CAD-CAM) systems were more accurate (−61.91 μm) than G4 (−95.36 μm) (p = 0.014). In biomechanical analysis, stress concentration caused by oblique loading is greater than caused by axial loading. In axial loading, G4 was the most favorable while G1 was the least favorable, biomechanically, in oblique loading, similar stress patterns were observed in all the models. The prosthetic screw was the most overloaded structure, but the material did not influence the stress distribution. The misfit prostheses showed a greater degree of stress than the controls (without misfit). The manufacturing method influenced the marginal misfit of the frameworks, with the conventional method being the most accurate and the Cerec Bluecam System (closed system) the least accurate. Biomechanically, fitting prostheses were more favorable than misfit prostheses.

Stress distribution of complete-arch implant-supported prostheses reinforced with silica-nylon mesh.

BackgroundThis study evaluated the presence of a silica-nylon mesh and two cantilever lengths on the biomechanical behavior of complete-arch implant-supported prostheses.Material and MethodsTwenty-four (24) complete mandibular arch implant-supported prostheses were divided into 4 groups according to the presence of reinforcing mesh (with or without) and the cantilever length (molar – 15 mm or premolar – 5 mm). The specimens were submitted to strain gauge analysis (30-kgf, 10 s) at different points (molar and premolar). Three-dimensional models were created based on the in vitro specimens, and the results in the bone (microstrain), prostheses (tensile stress), implants and prosthetic screws (von-Mises stress) were evaluated using the finite element method (FEM). All materials were considered homogeneous, isotropic and linear. Strain gauge data were submitted to 3-way analysis of variance and the Tukey test (α=.05). FEM results were qualitatively analyzed using colorimetric graphs.ResultsThe microstrain magnitude for the prostheses with reinforcement was 519.91±359 and 583.33±661 without reinforcement (p=.001). The microstrain values for loading on the molar was 867.49±784 and on the premolar was 235.75±145. FEM corroborated with the in vitro findings for the bone behavior. The load application in the premolar showed reduced stress concentration, and a significant difference was observed between the presence or absence of the reinforcement for the prostheses.ConclusionsSilica-nylon mesh reduced the peri-implant microstrain and the prosthesis stress regardless of the cantilever extension. For temporary complete-arch implant-supported prostheses, the limitation of the cantilever to the premolar region improves the biomechanical response during load application. Key words:Finite element analysis, biomechanical response, dental implants, prosthetic dentistry.

Mechanical Behavior of Different Micro Conical Abutments in Fixed Prosthesis.

To evaluate the biomechanical behavior between two different micro conical abutments: two-piece and one-piece abutments. Four groups were divided according to the prosthetic connection (internal or external hexagon) and abutment type. The vertical misfit between the abutment and implant was evaluated under stereomicroscope. Next, the implants were divided into pairs and embedded in polyurethane to receive two-element prostheses. The initial removal torque was measured for abutments and for prosthesis fixation. The samples were mechanically cycled (200 N, 2 Hz, 2 × 106 cycles) before measuring the torque loss in the same regions. For stress verification, a finite element analysis was used. For vertical misfit, one-piece (4.70 ± 0.26 μm) < two-piece (16.8 ± 0.32 μm). For preload in abutment screw, two-piece = one-piece. For prosthetic screw, a higher percentage of preload was found for two-piece, but no statistical difference was observed after fatigue cycling between the groups. For stress analysis, no difference (10%) was observed for abutments, retention screw, or for the bone. The one-piece abutment maintained even amounts of preload after cyclic loading and presented less vertical misfit in comparison with the two-piece abutment for both implant connections. The use of one-piece abutments did not increase the stress and strain concentration, suggesting acceptable biomechanical behavior.

Evaluation of three cements in the ability to fill the interior of the dental implant using computerized microtomography

Background The microgap that exists in the interface of the components of 2 or 3 part implants has been the object of studies on their capacity of biological seal (bacterial, fungus…) and micronutrients in the saliva. In vivo studies have shown that the internally of 2 or 3-piece implant and prosthetic components are heavily contaminated with pathogenic bacteria from Peri-implant disease. This heavy contamination affects the external hexagon, Inner Hexagonal and Cone Morse prosthetic platforms. The limitation of prosthetic platforms, external hexagon internal hexagonal and cone morse in converting the mechanical seal into effective biological seal in vivo is a reality. Aim/Hypothesis We propose the investigation of 3 zinc oxide based cements with and without antimicrobial incorporation in the filling of the internal spaces of the implant Abutment. Material and Methods Ten implants (Conexão, Brazil) were used, prosthetic components suggested by the company. Of the implants used 5 were External Hexagon and 5 Morse Cone. All implants had the prosthetic screws tightened with a torque of 32 Ncm. Each screw abutment was initially tightened to 20 Ncm with a digital torque gauge to stabilize the abutment to the implant. The second torque, 32 Ncm, was applied 15 minutes after the initial torque. Subsequently, they were submitted to Micro-CT, being divided into 3 groups- Sealer Implant® Zinc Oxide (Group A) Sealer Implant® própolis Zinc Oxide and Propolis (B) Sealer Implant® Clorex Zinc Oxide and Chlorhexidine (C). All micro-CT scans were acquired on a Triumph multi-modality system (Gamma Medica, Northridge, CA) using the following sampling parameters- tube voltage 80 kVp, tube current 250 A, detector pixel size 50 m, focal spot size 50 m and a field-of-view of 59 or 93 mm. The spatial resolution was 39 and 28 m, and the radiation dose was 8.3 and 19.7 cGy for field-of-view of 93 and 59 mm, respectively. Results The results showed that in all analyzed parts without use of fillers both in the implants 2 or 3 pieces wide spaces inside the implant and abutments. Using the Image software, the internal spaces were quantified. In the Grupo Hexagono Externo it had an average value of 22% of internal space, in Cone Morse 2 pieces 18% and 3 pieces 18%. There was no statistically significant difference between the groups investigated in relation to the empty internal volume. In relation to filling capacity, the cements of Group A, B and C had similar results (P > 0.01). Conclusions and Clinical Implications This study on the filling capacity of the analyzed cements did not find a statistically significant difference between the analyzed groups. the mean filling level was 98% of the internal spaces, which demonstrates efficacy of the analyzed cements being an alternative of material in order to prevent the formation of microbioma and ecosystem within the implants.

Influence of cantilever position and implant connection in a zirconia custom implant-supported fixed partial prosthesis: in silico analysis

Abstract Introduction A better tension distribution on implants and abutments in implant-supported fixed partial prosthesis is essential in the rehabilitation of posterior mandible area. Objective: To evaluate the influence of cantilever position and implant connection in a zircônia custom implant-supported fixed partial prosthesis using the 3-D finite element method. Material and method: Four models were made based on tomographic slices of the posterior mandible with a zirconia custom three-fixed screw-retained partial prosthesis. The investigated factors of the in silico study were: cantilever position (mesial or distal) and implant connection (external hexagon or morse taper). 100 N vertical load to premolar and 300 N to molar were used to simulate the occlusal force in each model to evaluate the distribution of stresses in implants, abutments, screws and cortical and cancellous bone. Result: The external hexagon (EH) connection showed higher cortical compression stress when compared to the morse taper (MT). For both connections, the molar cantilever position had the highest cortical compression. The maximum stress peak concentration was located at the cervical bone in contact with the threads of the first implant. The prosthetic and abutment screws associated with the molar cantilevers showed the highest stress concentration, especially with the EH connection. Conclusion: Morse taper implant connetions associated with a mesial cantilever showed a more favorable treatment option for posterior mandible rehabilitation.

Short-term report of an ongoing prospective cohort study evaluating the outcome of full-arch implant-supported fixed hybrid polyetheretherketone-acrylic resin prostheses and the All-on-Four concept.

More research is needed on the study of new materials for fixed prosthetic implant-supported rehabilitations. The purpose of this study was to report the short-term outcome of full-arch implant-supported fixed hybrid polyetheretherketone (PEEK)-acrylic resin prostheses and the all-on-four concept. This prospective cohort clinical study included 37 patients (29 women, eight men) with an average age of 60 years (range: 38-78 years) with 49 full-arch hybrid PEEK-acrylic resin prosthesis supported by implants through the all-on-four concept. Primary outcome measures were prosthetic survival. Two patients with two maxillary prostheses were lost to follow-up. One patient with a double full-arch rehabilitation fractured the mandibular PEEK framework, rendering a 98% prosthetic survival rate. No implants were lost. The average (SD) marginal bone remodeling after 1 year of follow-up was 0.37 mm (0.58 mm). Technical complications concerning the veneer adhesion occurred in six patients and were resolved in all patients (with exception of the patient with prosthetic failure) through the creation of mechanical retentions and changing the bonding primer. Mechanical complications occurred in three patients and five prostheses consisting in prosthetic screw loosening (n = 2 patients) and fracture of the acrylic resin teeth (the patient with a prosthetic failure). Within the limitations of this study, the results suggest that hybrid polymer (PEEK)-acrylic resin prostheses supported by implants for full-arch rehabilitation may represent a valid treatment option, still requiring longer-term validation.

Influence of Cross-Section Design and Vertical Misfit on Stress Distribution in Overdenture Retaining System: 3-Dimensional Finite Element Analysis.

To evaluate by 3-dimensional (3-D) finite element analysis the stress generated on overdenture-retaining bar system with different cross sections (round, ovoid, or Hader) and misfit levels (50, 100, and 200 μm) manufactured with different metallic alloys (Au type IV, Ag-Pd, Ti cp, and Co-Cr). Three-dimensional finite element models were modeled using specific 3-D software (SolidWorks) and imported into mechanical simulation software (ANSYS). A displacement simulating the settlement of the screw was performed until the infrastructure was settled properly on the prosthetic platform. Higher misfit levels caused higher stress on the overdenture-retaining bar system components, where (1) Hader bar presented the highest values (bar = 730.71; screw = 59.66, and periimplant bone tissue = 42.96, in megapascal) and (2) round bars made with type IV Au alloy presented lower stress values on the bar framework (193.99 MPa) and screw (10.27 MPa). Higher vertical misfit increased the stress values on the overdenture-retaining bar system; complex cross-sectional designs increased stress values on the bar framework, prosthetic screw, and periimplant bone tissue; stiffer alloys caused higher stress values on all the studied conditions.

An unconventional approach for retrieval of fractured prosthetic screw: A case report

Background Implant-supported restorations can fail biologically or mechanically. Mechanical failures include crown fracture, framework fracture, screw loosening, and screw fracture. Fracture of the implant abutment screw can be a serious problem leading to implant failure. Unavailability of universal standard screw retrieval kit in market makes it difficult to retrieve the fractured screw of various implant systems.Conclusion This clinical report describes the management of an implant prosthetic screw fracture using an unconventional technique and simple armamentarium available in regular clinic setup.

Comparative In Vitro Study of Implant-Supported Restorations: Implant-Abutment Complex With and Without Prosthetic Finishing Line

The aim of this study was to evaluate the mechanical behavior of implant-supported cemented restorations placed on two types of abutment design, with and without a prosthetic finish line, evaluating fracture resistance and the type of fracture produced in the abutment-crown complex. Eighty zirconia restorations supported by tapered implants were divided into two groups: group I, with 40 zirconia crowns cemented onto individualized zirconia abutments with a chamfered finish line (1 mm deep); and group II, with 40 zirconia crowns cemented onto individualized zirconia abutments without a finish line. All specimens underwent thermocycling and dynamic loading before static load testing to evaluate their fracture resistance. Fracture resistance values (N) and the type of fracture were analyzed. The mean fracture resistance was 462.1 ± 66.3 N in group I and 343 ± 40 N in group II. In group I, fractures were produced in the prosthetic fixation screw; in group II, all mechanical failures were produced in the transepithelial abutment's cervical area. Group I specimens showed greater fracture resistance than group II. The fracture type in group I occurred in the prosthetic screw. Group II fractures occurred in the zirconium oxide abutment.

Mechanical Complications Related to the Retention Screws of Prefabricated Metal Abutments With Different Angulations: A Retrospective Study With 916 Implants.

The present retrospective study assessed the clinical performance of abutment screws from prefabricated metal abutments and compared technical complication rates between straight and angled abutments. Dental charts were selected for patients with dental implant rehabilitations delivered between 1998 and 2012. Abutment angulation, prosthetic screw type, and presence of complications that occurred during the selected time period were collected. Technical complications registered included abutment screw loosening and/or fractures detected during clinical and radiographic examinations. The chi-square test was used for statistical analysis. Abutment angulations were divided into 2 groups: G1) prefabricated straight abutments and G2) prefabricated angled conical mini UCLA-type abutments. A total of 916 implants (799 straight and 117 angled conical mini UCLA-type abutments) were evaluated. G1 showed 91.1% had absence of failures, which were clinically defined as any screw loosening or fracture; and 8.9% reported some type of technical complication. G2 showed 92.3% and 7.7%, with and without technical complications, respectively. No significant differences were observed between abutment angulation and technical complications.

Marginal discrepancy of CAD-CAM complete-arch fixed implant-supported frameworks

Statement of problemComputer-aided design and computer-aided manufacturing (CAD-CAM) high-density polymers (HDPs) have recently been marketed for the fabrication of long-term interim implant-supported fixed prostheses. However, information regarding the precision of fit of CAD-CAM HDP implant-supported complete-arch screw-retained prostheses is scarce. PurposeThe purpose of this in vitro study was to evaluate the marginal discrepancy of CAD-CAM HDP complete-arch implant-supported screw-retained fixed prosthesis frameworks and compare them with conventional titanium (Ti) and zirconia (Zir) frameworks. Material and methodsA screw-retained complete-arch acrylic resin prototype with multiunit abutments was fabricated on a typodont model with 2 straight implants in the anterior region and 2 implants with a 30-degree distal tilt in the posterior region. A 3-dimensional (3D) laboratory laser scanner was used to digitize the typodont model with scan bodies and the resin prototype to generate a virtual 3D CAD framework. A CAM milling unit was used to fabricate 5 frameworks from HDP, Ti, and Zir blocks. The 1-screw test was performed by tightening the prosthetic screw in the maxillary left first molar abutment (terminal location) when the frameworks were on the typodont model, and the marginal discrepancy of frameworks was evaluated using an industrial computed tomographic scanner and a 3D volumetric software. The 3D marginal discrepancy at the abutment-framework interface of the maxillary left canine (L1), right canine (L2), and right first molar (L3) sites was measured. The mean values for 3D marginal discrepancy were calculated for each location in a group with 95% confidence limits. The results were analyzed by repeated-measures 2-way ANOVA using the restricted maximum likelihood estimation and the Satterthwaite degrees of freedom methods, which do not require normality and homoscedasticity in the data. The between-subjects factor was material, the within-subjects factor was location, and the interaction was included in the model. Tukey tests were applied to resolve any statistically significant source of variation (overall α=.05). ResultsThe 3D marginal discrepancy measurement was possible only for L2 and L3 because the L1 values were too small to detect. The mean discrepancy values at L2 were 60 μm for HDP, 74 μm for Ti, and 84 μm for Zir. At the L3 location, the mean discrepancy values were 55 μm for HDP, 102 μm for Ti, and 94 μm for Zir. The ANOVA did not find a statistically significant overall effect for implant location (P=.072) or a statistically significant interaction of location and material (P=.078), but it did find a statistically significant overall effect of material (P=.019). Statistical differences were found overall between HDP and the other 2 materials (P≤.037). ConclusionsWhen the tested materials were used with the CAD-CAM system, the 3D marginal discrepancy of CAD-CAM HDP frameworks was smaller than that of titanium or zirconia frameworks.

Effect of feldspathic porcelain layering on the marginal fit of zirconia and titanium complete-arch fixed implant-supported frameworks

Statement of problemVeneering with porcelain may adversely affect the marginal fit of long-span computer-aided design and computer-aided manufacturing (CAD-CAM) implant-supported fixed prostheses. Moreover, data regarding the precision of fit of CAD-CAM–fabricated implant-supported complete zirconia fixed dental prostheses (FDPs) before and after porcelain layering are limited. PurposeThe purpose of this in vitro study was to evaluate the effect of porcelain layering on the marginal fit of CAD-CAM–fabricated complete-arch implant-supported, screw-retained FDPs with presintered zirconia frameworks compared with titanium. Material and methodsAn autopolymerizing acrylic resin–fixed complete denture framework prototype was fabricated on an edentulous typodont master model (all-on-4 concept; Nobel Biocare) with 2 straight in the anterior and 2 distally tilted internal-hexagon dental implants in the posterior with multiunit abutments bilaterally in canine and first molar locations. A 3-dimensional (3D) laser scanner (S600 ARTI; Zirkonzahn) was used to digitize the prototype and the master model by using scan bodies to generate a virtual 3D CAD framework. Five presintered zirconia (ICE Zirkon Translucent - 95H16; Zirkonzahn) and 5 titanium (Titan 5 - 95H14; Zirkonzahn) frameworks were fabricated using the CAM milling unit (M1 Wet Heavy Metal Milling Unit; Zirkonzahn).The 1-screw test was applied by fixing the frameworks at the location of the maxillary left first molar abutment, and an industrial computed tomography (CT) scanner (XT H 225 - Basic Configuration; Nikon) was used to scan the framework-model complex to evaluate the passive fit of the frameworks on the master model. The scanned data were transported in standard tessellation language (STL) from Volume Graphics analysis software to PolyWorks analysis software by using the maximum-fit algorithm to fit scanned planes in order to mimic the mating surfaces in the best way. 3D virtual assessment of the marginal fit was performed at the abutment-framework interface at the maxillary right canine (gap 3) and right first molar (gap 4) abutments without prosthetic screws. The facial or buccal aspects of the teeth on frameworks were layered with corresponding porcelain (Initial Dental Ceramic System; GC) and CT-scanned again using the same protocol. Marginal fit measurements were made for 4 groups: titanium (Ti) (control), porcelain-layered titanium (Ti-P) (control), zirconia (Zir), and porcelain-layered zirconia (Zir-P). 3D discrepancy mean values were computed and calculated, and the results were analyzed with a repeated measures 3-way ANOVA using the maximum likelihood estimation method and Bonferroni adjustments for selected pairwise comparison t-tests (α=.05). ResultsThe 3D fit was measured at gap 3 and gap 4. Statistically significant differences in mean 3D discrepancies were observed between Zir-P (175 μm) and Zir (89 μm) and between Zir-P and Ti-P (71 μm) (P<.001). ConclusionsPorcelain layering had a significant effect on the marginal fit of CAD-CAM–fabricated complete-arch implant-supported, screw-retained FDPs with partially sintered zirconia frameworks. 3D marginal discrepancy mean values for all groups were within clinically acceptable limits (<120 μm), except for the layered zirconia framework.

Peri-implant conditions and marginal bone loss around cemented and screw-retained single implant crowns in posterior regions: A retrospective cohort study with up to 4 years follow-up.

The aim of the present study was to identify the peri-implant conditions (bleeding on probing (BOP), pocket probing depth (PPD), modified plaque index (mPI)) and marginal bone loss (MBL, marginal bone level change between follow-up and occlusal loading) around cemented and screw-retained posterior single crowns on tissue-level implants. The study was a retrospective cohort study with up to 4 years (mean 2.5 years) follow-up. Patients with either cemented or screw-retained crowns in posterior regions were included. Implant survival, technical complications, BOP, PPD, mPI, MBL, biologic complications (peri-implant mocositis and peri-implantitis) were evaluated. Mann-Whitney U test was used to test the difference between the screw-retained group (SG) and cemented group (CG). 176 patients (SG: 94, CG: 82) were included. The implant survival rates were 100% in SG and 98.8% in CG. Prosthetic screw loosening was found in 8 restorations (8.7%) at follow-up visit. Peri-implant mucositis rate was significantly higher in the SG group (42.1%) than that in the CG group (32.2%) (P = 0.04). Six patients (6.38%) in the screw-retained group and 5 patients (6.10%) in the cemented group were diagnosed with peri-implantitis, the difference did not reach statistical significance (P>0.05). No significant difference of PPD, mPI and MBL were found between two groups (P = 0.11, 0.13 and 0.08, respectively). High implant survival rates were achieved in both groups. Cemented single crowns on tissue-level implants showed comparable peri-implant conditions in comparison with two-piece screw-retained crowns. Well-designed prospective cohort or randomized controlled clinical trials with longer follow-up are needed to confirm the result.