In Vitro Analysis of the Removability of Fractured Prosthetic Screws within Endosseous Implants Using Conventional and Mechanical Techniques.

STATEMENT OF PROBLEM: The extraction of fractured abutment screws can be a difficult challenge to overcome. PURPOSE: To compare the removal capacity, dental implant connection damage, and time required to remove the fractured abutment screws between three drilling techniques and a conventional method. MATERIALS AND METHODS: A total of 180 prefabricated screw-retained abutments were intentionally fractured in internal connection dental implants after being subjected to a cyclic load and a static compression load. Afterwards, three operators randomly removed the fractured abutment screws with the following drilling techniques and a conventional method: A: a conventional technique using an exploration probe and ultrasonic appliance (n = 45), Rhein83® (n = 45); B: Sanhigia® (n = 45); C: Phibo® (n = 45). Two-way ANOVA models were estimated to evaluate the mean time according to the method and operator used. RESULTS: The probability of removal of the screws with mobility was twelve times higher than that of the screws without mobility (OR = 12.4; p < 0.001). The success rate according to the operators did not show statistically significant differences (p = 0.371). The location of the fractured screw did not affect removal success (p = 0.530). The internal thread of the implant was affected after the removal process in 9.8% of the cases. The mean extraction time was 3.17 ± 2.52 min. The Rhein83® method showed a success rate of 84.4%, followed by the Phibo® and conventional methods (71.1%) and the Sanhigia® method (46.7%). CONCLUSIONS: The Rhein83® drilling technique increases the removal probability of fractured abutment screws. The initial mobility of the fragment is also a significant factor in the removal success.

Graphene-Doped Polymethyl Methacrylate (PMMA) as a New Restorative Material in Implant-Prosthetics: In Vitro Analysis of Resistance to Mechanical Fatigue.

BACKGROUND AND PURPOSE: Provisional prostheses in restorations over several implants with immediate loading in completely edentulous patients increase the risk of frequent structural fractures. An analysis was performed of the resistance to fracture of prosthetic structures with cantilevers using graphene-doped polymethyl methacrylate (PMMA) resins and CAD-CAM technology. METHODS: A master model was produced with four implants measuring 4 mm in diameter and spaced 3 mm apart, over which 44 specimens representing three-unit fixed partial prostheses with a cantilever measuring 11 mm were placed. These structures were cemented over titanium abutments using dual cure resin cement. Twenty-two of the 44 units were manufactured from machined PMMA discs, and 22 were manufactured from PMMA doped with graphene oxide nanoparticles (PMMA-G). All of the samples were tested in a chewing simulator with a load of 80 N until fracture or 240,000 load applications. RESULTS: The mean number of load applications required for temporary restoration until the fracture was 155,455 in the PMMA-G group versus 51,136 in the PMMA group. CONCLUSIONS: Resistance to fracture under cyclic loading was three times greater in the PMMA-G group than in the PMMA group.

Wear in Antagonist Teeth Produced by Monolithic Zirconia Crowns: A Systematic Review and Meta-Analysis.

BACKGROUND: The aim of this systematic review and meta-analysis was to determine the wear sustained in the natural antagonist tooth in cases of full-coverage fixed-base prosthetic restorations or monolithic zirconia tooth-supported crowns, as well as to determine the wear in the restoration itself, both in the short- and medium-term and considering the factors that may influence wear. MATERIAL AND METHODS: A systematic literature review and meta-analysis, based on Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) recommendations, of clinical studies that evaluated wear in antagonist teeth in relation to fixed-prosthesis monolithic zirconia crowns. A total of 5 databases were consulted in the literature search: Pubmed-Medline, Cochrane, Scopus, Embase and Web of Science (WOS). After eliminating duplicated articles and applying the inclusion criteria, eight articles were selected for the qualitative analysis and four for the quantitative analysis. RESULTS: Mean maximum wear of the antagonist tooth in relation to monolithic zirconia crowns of magnitude 95.45 µm (CI at 95% 79.57-111.33) was observed. By using a meta-regression model (R2 = 0.92) the significant effect of time in maximum wear rate (p < 0.001) was observed, estimated at 6.13 µm per month (CI at 95% 3.99-8.27). Furthermore, monolithic zirconia crowns are subject to a mean maximum wear of 58.47 µm (CI 95% 45.44-71.50). By using a meta-regression model (R2 = 0.53) the significant effect of time in the maximum wear value was observed (p = 0.053), estimated at 3.40 µm per month (CI al 95% -0.05-6.85). CONCLUSIONS: Monolithic zirconia crowns lead to a progressive maximum wear of the antagonist tooth over time which is greater than the maximum wear sustained in the crown itself. It is not possible to establish an objective and quantitative objection in relation to natural enamel wear or metal-ceramic crowns.

Analysis of Predisposing Factors for Rapid Dental Calculus Formation.

BACKGROUND: Calculus accumulation varies widely between individuals. Dental calculus has been associated with the principal periodontal diseases. The aim of this study was to analyze individual characteristics, and salivary and microbiological parameters among patients considered to be rapid calculus formers and patients who form calculus slowly. METHODS: Individual characteristics were recorded in a sample of 74 patients (age, sex, smoking, periodontal diagnosis, and dental crowding), as well as salivary parameters (unstimulated saliva flow, pH, and biochemical analysis of saliva) and microbiological parameters (by means of semi-quantitative polymerase chain reaction (PCR) analysis). RESULTS: A statistically significant association (p = 0.002) was found between the rate of calculus formation and the diagnosis of periodontal disease. A greater presence of dental crowding was observed among the group of rapid calculus formers. Urea and phosphorus levels were higher among rapid calculus formers. Regarding microbiological parameters, differences were found in Streptococcus mutans, this being higher in the group of slow formers. CONCLUSIONS: Rapid calculus formation appears to be linked to patients diagnosed with more severe periodontal diseases. Rapid calculus-forming patients present more dental crowding and a lower proportion of S. mutans.

Maxillary Implant-Supported Overdentures: Mechanical Behavior Comparing Individual Axial and Bar Retention Systems. A Cohort Study of Edentulous Patients.

Background and objectives: To compare the medium- to long-term mechanical behavior of overdentures with two different retention systems: overdentures with Locator® axial retention, and vertical insertion overdentures with bar retention, used to rehabilitate edentulous maxillar. Material and Methods: This prospective study assessed patients presenting complete maxillary edentulism, rehabilitated by means of implant-supported overdentures (n = 20), 10 with Locator® axial retention (ODA group) and 10 with overdentures on bars (ODB group). Patients also completed a questionnaire to determine their satisfaction with treatment. Results: The mean follow-up time in both groups was 11.4 years, with follow-up times in both groups ranging from 5 to 14 years. The ODA group suffered mechanical complications such as retention loss, need for nylon retention insert changes, resin fracture, and need for relining. In the ODB group, prosthetic dental wear, screw loosening, and complete prosthetic failure were more common. A total of 19 implants failed (23.8%); of these, 11 were in the ODA group (failure rate = 27.5%) and eight in the ODB group (failure rate = 20%). The patient satisfaction questionnaire obtained a mean score of 7.9 out of 10 in the ODA group, and 9.75 in the ODB group. Conclusions: in rehabilitations of edentulous maxillar by means of implant-supported overdentures, both the systems assessed were shown to be effective in the medium to long term. Patients expressed a high level of satisfaction with the treatments received.

Periodontal Behavior Around Teeth Prepared with Finishing Line for Restoration with Fixed Prostheses. A Systematic Review and Meta-Analysis.

BACKGROUND: The objective of this systematic review and meta-analysis was to analyze the periodontal behavior around teeth prepared with horizontal finishing crowns supporting fixed metal-ceramic and zirconia full coverage crowns and fixed partial dentures (FDPs). MATERIALS AND METHODS: An electronic search was conducted to locate relevant clinical trials in four databases: PubMed, Embase, Cochrane, and Scopus. A manual search was made in the reference sections of the articles identified for any additional articles. No restrictions were applied regarding year of publication or language. The following variables were considered in quantitative and qualitative analysis: probing pocket depth (PPD); probing attachment level (PAL); plaque control record (PCR); bleeding on probing (BOP); and gingival margin migration. RESULTS: Twenty articles were selected for qualitative synthesis, and of these, nine underwent meta-analysis. Higher PCR was found in control teeth, while BOP, PPD, and PAL were higher around teeth prepared with horizontal finishing lines supporting complete coverage crowns/FDPs Gingival migration results were the clearest manifestation of compromised periodontal health around teeth prepared with horizontal finishing lines. CONCLUSIONS: Meta-analysis revealed that teeth prepared with horizontal finishing lines supporting crowns and FDPs present more periodontal disorders than untreated control teeth.

In vitro retention capacity of two overdenture attachment systems: Locator® and Equator®.

BACKGROUND: It is necessary to know the in vitro behavior of different attachment systems to be used clinically. The evolution of retention capacity over 10 years (14,600 insertion/de-insertion cycles) was determined in vitro, evaluating two overdenture attachment systems (Locator® and OT Equator®). MATERIAL AND METHODS: The study used an implant replica compatible with the abutments of both systems. 10 Locator® and 10 OT Equator® attachments were screwed to the abutments. Nylon inserts were attached and tested, subjecting them to 14,600 insertion and de-insertion cycles (representing 10 years functional life) in axial direction. The universal test machine crosshead speed was 50 mm/min with a de-insertion range of 2 mm. RESULTS: The initial retention of Locator® was 17.02 N and of Equator® 16.36 N. After 14,600 cycles, Locator® suffered a mean loss of retention of 50.89%, while Equator® lost 69.28%. Both systems showed retention increases up to the first 1,000 cycles, which decreased thereafter up to 14.600 cycles. Statistically significant differences between the systems were found after 7,500 cycles. CONCLUSIONS: Both systems presented acceptable retention capacities after 14,600 cycles. Significant differences in retention force between the systems evolved after 7,500 cycles (5 years in vitro use). These results should be treated with caution and should be verified clinically. Key words:Denture, mandibular prosthesis implantation, attachment, dental implant-abutment connection, denture retention.

Interventions to Maintain Locator-Retained Mandibular Overdentures on Both External Hex and Internal Connection Implants: A Retrospective Study.

PURPOSE: To quantify the rate of maintenance interventions of mandibular prostheses: complete dentures and overdentures retained by two implants, with either internal hex or external hex connections. MATERIALS AND METHODS: This study analyzed patients with edentulous mandibles treated with distinct treatment protocols: a control group received complete dentures; a second group received Locator-retained overdentures supported by two external hex connection implants; and a third group received overdentures supported by internal hex connection implants. All of the maintenance interventions associated with the prosthetic treatment after delivery were recorded (starting from 2000 until the final assessment in 2012). Moreover, patient satisfaction was assessed using a 0 to 10 visual analog scale. RESULTS: The final sample was composed of 136 patients: 56 in the control group, 31 in the hex implant overdenture group, and 49 in the internal connection overdenture group followed over a period of 60 months (ranging from 3 to 144 months). Prosthetic adjustment was the most frequent intervention carried out, particularly within the control group (a mean rate of 1.1 ± 1.9 times/subject/year) in comparison with the internal connection (0.6 ± 0.8 times/subject/year) and hex implant overdenture groups (0.3 ± 0.2 times/subject/year). Relining was also frequently required, occurring on average every 4 years in the control group and every 7 years in the overdenture groups. Abutment loosening was more frequent in the hex implant overdenture group than in the internal connection overdenture group (8/31 versus 8/49), as well as abutment wear (5/31 versus 5/49). Gingival inflammation was significantly more common in the hex implant overdenture group (19/31 patients), as compared with the controls (16/56 subjects), and satisfaction was higher in patients in the two overdenture groups (mean Oral Satisfaction Scale [OSS] score of 8.1 ± 1.9 for external and 8.4 ± 1.6 for internal connections) than in the control group (5.3 ± 3.3). CONCLUSION: Locator-retained overdentures needed less than half the number of maintenance interventions when compared with the control group, and maintenance was required every 2 to 4 years.

Patient-centered and clinical outcomes of mandibular overdentures retained with the locator system: A prospective observational study.

STATEMENT OF PROBLEM: Whether clinical or demographic variables affect the perception of treatment in terms of quality of life and satisfaction is unknown. PURPOSE: The purpose of this prospective study was to make an evidence-based assessment of the treatment outcomes (patient- and clinically based) of locator-retained mandibular overdentures. MATERIAL AND METHODS: This prospective observational study assessed patients with edentulism who had worn mandibular overdentures supported by 2 implants and retained by the locator system for at least 1 year of functional life (N=80). Medical histories were reviewed, and patients underwent oral examinations. Prosthetic clinical outcomes and patient well-being were registered using the Oral Health Impact Profile 20 (OHIP-20) and Oral Satisfaction Scale (OSS). RESULTS: Patient well-being scored an overall OHIP-20 score of 19.0 ±14.0 of 80 (the higher the score, the greater the impact and the worse the oral health-related quality of life); overall oral satisfaction was 8.3 ±1.7 of 10. Women suffered greater social impact (0.8 ±1.0) and disability (0.4 ±0.8) than men (0.4 ±0.7 versus 0.2 ±0.4, respectively). Impact on well-being was inversely proportional to both patient age and the age of the prosthesis (r=-0.25; P<.01). Implants had been placed on average 73.6 ±39.2 months previously, showing a survival rate of 82.5%. Most of the overdentures had been functioning for over 60 months. Relining (46.3%), readjustments (82.5%), and changes of nylon retention (1.5 ±1.8 per patient over 60 months of use) devices negatively influenced well-being. CONCLUSIONS: Mandibular overdentures produced good results with regard to quality of life and oral satisfaction, but attention should be paid to factors affecting clinical outcomes and patient well-being.

Effect of retention design of artificial teeth and implant-supported titanium CAD-CAM structures on fracture resistance.

BACKGROUND: For implant-supported hybrid prostheses, high mastication forces and reduced acrylic resin thickness over a metal substructure often cause failures arising from tooth or resin fractures. To assay fracture resistance of artificial teeth and resin in implant-supported hybrid prostheses in relation to the titanium structure and retention design supporting teeth. MATERIAL AND METHODS: 40 specimens bearing incisors were divided into four groups according to the titanium structure supporting the teeth and the type of load force applied: Group I (Control; n=10): Application of static loading to ten incisors set over a metal structure with internal retention. Group II (Control; n=10): Application of static loading to ten incisors set over a metal structure with external retention. The remaining study specimens (n=20) were subjected to 120,000 masticatory and thermal cycles in a chewing simulator. Afterwards, static loading was applied until the point of fracture using an Instron machine. Group III (Study; n=10): Application of dynamic and static loading to ten incisors set over a metal structure with internal retention. Group IV (Study; n=10): Application of dynamic and static loading to ten incisors set over a metal structure with external retention. Data obtained for the four groups was analyzed and compared, determining the type of fracture (cohesive or adhesive) using a reflected light microscope. RESULTS: Statistical analysis confirmed that there were significant differences in fracture resistance between the four groups. External retention was found to have more fracture resistance than the internal retention. CONCLUSIONS: Hybrid prostheses with titanium substructures and external retention obtained significantly better results than samples with internal retention. KEY WORDS: Chewing simulator, thermocycler, fatigue, implant-supported hybrid prosthesis, acrylic teeth, fracture, metal structure design.

Oral health-related quality of life of implant-supported overdentures versus conventional complete prostheses: Retrospective study of a cohort of edentulous patients.

BACKGROUND: This work aims to confirm if implant-supported overdentures are a good treatment option for edentulous patients and offer an improvement in quality of life compared with traditional complete prostheses (dentures). MATERIAL AND METHODS: This retrospective clinical descriptive study included three evaluation groups: validation group (n=57); control group of patients with complete removeable prostheses (n=56); study group of patients with implant-supported overdentures retained with the Locator® system (n=80). The study also validated the Oral Health Impact Profile-20 questionnaire. Individual protocols were created that included socio-demographic data, the Oral Health Impact Profile-20 (OHIP-20) questionnaire and Oral Satisfaction Scale (OSS). Descriptive and bivariate statistical analysis was carried out applying χ², Pearson, Kruskal-Wallis, and Student t tests, transferring data into SPSS-Windows® software from a Microsoft® Excel spreadsheet. RESULTS: The OHIP-20 proved to be a valid instrument and provided reliable assessment of health-related quality of life among both the Spanish general population and edentulous patients. The control and study groups proved comparable, showing socio-demographic homogeneity. For patients with overdentures retained by means of the Locator® system, these restorations had significantly lower impact on quality of life (19 vs 33), both generally and for each individual questionnaire item, and much higher satisfaction with the state of their oral cavities (8.3 vs 5.3) than patients wearing dentures; both sets of data showed a direct linear relationship, so that as the level of impact on quality of life increased, perceived oral satisfaction worsened. CONCLUSIONS: Patients rehabilitated with implant supported overdentures retained by the Locator® system, presented significantly lower levels of impact on their quality of life and significantly higher oral satisfaction than patients with conventional complete prostheses.

Accuracy combining different brands of implants and abutments

Objective: To evaluate the vertical misfit between different brands of dental implants and prosthetic abutments, with or without mechanical torque, and to study their possible combination. Study design: Five different brands of implant were used in the study: Biofit (Castemaggiore, Italy), Bioner S.A.(Barcelona, Spain), 3i Biomet (Palm Beach, U.S.A.), BTI (Alava, Spain) and Nobel Biocare (Göteborg, Sweden), with standard 4.1 mm heads and external hexagons, and their respective machined prosthetic abutments. The implant-toabutmentfit/misfit was evaluated at four points (vestibular, lingual/palatine, mesial and distal) between implants and abutments of the same brand and different brands, with or without mechanical torque, using SEM micrographs at5000X. Image analysis was performed using NIS-Elements software (Nikon Instruments Europe B.V.).Results: Before applying torque, vertical misfit (microgaps) of the different combinations tested varied between1.6 and 5.4 microns and after applying torque, between 0.9 and 5.9 microns, an overall average of 3.46±2.96microns. For manual assembly without the use of mechanical torque, the best results were obtained with the combination of the 3i implant and the BTI abutment. The Nobel implant and Nobel abutment, 3i-3i and BTI-BTI and the combination of 3i implant with BTI or Nobel abutment provided the best vertical fit when mechanical torque was applied. Conclusions: The vertical fits obtained were within the limits considered clinically acceptable. The application of mechanical torque improved outcomes. There is compatibility between implants and abutments of different brand and so their combination is a clinical possibility (AU)

Accuracy combining different brands of implants and abutments.

OBJECTIVE: To evaluate the vertical misfit between different brands of dental implants and prosthetic abutments, with or without mechanical torque, and to study their possible combination. STUDY DESIGN: Five different brands of implant were used in the study: Biofit (Castemaggiore, Italy), Bioner S.A. (Barcelona, Spain), 3i Biomet (Palm Beach, U.S.A.), BTI (Alava, Spain) and Nobel Biocare (Göteborg, Sweden), with standard 4.1 mm heads and external hexagons, and their respective machined prosthetic abutments. The implant-to-abutment fit/misfit was evaluated at four points (vestibular, lingual/palatine, mesial and distal) between implants and abutments of the same brand and different brands, with or without mechanical torque, using SEM micrographs at 5000X. Image analysis was performed using NIS-Elements software (Nikon Instruments Europe B.V.). RESULTS: Before applying torque, vertical misfit (microgaps) of the different combinations tested varied between 1.6 and 5.4 microns and after applying torque, between 0.9 and 5.9 microns, an overall average of 3.46 ± 2.96 microns. For manual assembly without the use of mechanical torque, the best results were obtained with the combination of the 3i implant and the BTI abutment. The Nobel implant and Nobel abutment, 3i-3i and BTI-BTI and the combination of 3i implant with BTI or Nobel abutment provided the best vertical fit when mechanical torque was applied. CONCLUSIONS: The vertical fits obtained were within the limits considered clinically acceptable. The application of mechanical torque improved outcomes. There is compatibility between implants and abutments of different brand and so their combination is a clinical possibility.

Study of the interocclusal distortion in impressions taken with different typesof closed-mouth trays and two types of impression materials

The aim of this study was to compare different types of impression trays for the closed-mouth impression technique,using two different types of impression material. For this study, five different types of impression trayswere used with two different types of impression materials, one of addition silicone and the other of polyether. Wedesigned a model used for taking the impressions and for measuring interocclusal distortion. The results obtainedshow that the impression trays COE (GC (R) GC America INC. Alsip) and Premier (Premier (R), Premier DentalProducts Co. Canada) show a lesser degree of interocclusal distortion when taking closed-mouth impressions. Interms of impression materials, the polyether was the one that produced the best results. From a clinical point ofview, our study shows that the use of these types of trays is absolutely recommendable when used according tothe clinical indications for which they have been designed; that said, we must not fail to consider that selecting theproper type of tray is also important (AU)

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Study of the interocclusal distortion in impressions taken with different types of closed-mouth trays and two types of impression materials.

The aim of this study was to compare different types of impression trays for the closed-mouth impression technique, using two different types of impression material. For this study, five different types of impression trays were used with two different types of impression materials, one of addition silicone and the other of polyether. We designed a model used for taking the impressions and for measuring interocclusal distortion. The results obtained show that the impression trays COE (GC (R) GC America INC. Alsip) and Premier (Premier (R), Premier Dental Products Co. Canada) show a lesser degree of interocclusal distortion when taking closed-mouth impressions. In terms of impression materials, the polyether was the one that produced the best results. From a clinical point of view, our study shows that the use of these types of trays is absolutely recommendable when used according to the clinical indications for which they have been designed; that said, we must not fail to consider that selecting the proper type of tray is also important.

Bone resorption processes in patients wearing overdentures. A 6-years retrospective study

Objectives: 1. – To measure the alveolar resorption processes that occur in patients wearing mandibular overdentures on 2 implants and fully-removable maxillary dentures, and to evaluate the same process on patients wearing fully- removable dentures on both arches. 2.- To verify whether Kelly’s Combination Syndrome occurs in the group of patients wearing overdentures. Method and Material: Forty patients were evaluated, of which a “cases” group was formed by 25 patients wearing mandibular overdentures on 2 lower jaw implants and fully-removable dentures on the opposite arch. The other 15 patients formed a control group that wore fully-removable dentures on both arches. Each one of the patients underwent orthopantograms from the moment the dentures were inserted until an average of 6 years later, which were assessed based on the Xie et al. method to estimate vertical bone loss. Once the data was collected, it was subjected to statistical analysis. Results: In terms of the maxillary midline, we observed a greater loss in patients wearing overdentures, which was statistically significant, as it registered 0.32 mm/year. Mandibular bone loss was 2.5 times less in patients in the cases group. The rest of the clinical criteria for Kelly’s Combination Syndrome were not observed.
Conclusions: Kelly’s Combination Syndrome did not occur in the patients in the cases group. In spite of the greater bone loss on a premaxillary level in this group, the placing of the overdenture on the implants significantly reduced mandibular bone resorption (AU)