Effect of Different Bar Designs on Axial and Nonaxial Retention Forces of Implant-Retained Maxillary Overdentures: An In Vitro Study

PURPOSE

This in vitro study aimed to evaluate and compare the effect of different bar designs on the retention forces of implant-retained maxillary overdentures.

MATERIALS AND METHODS

A maxillary edentulous acrylic resin model without alveolar undercut was fabricated. Four implant analogs were placed in the canine and second premolar regions. Overdentures were made and attached to the analogs with Dolder bar, Hader bar, and milled bar attachments. A universal testing machine was used to measure axial (resistance to vertical displacement) and nonaxial (resistance to anterior, posterior, and lateral displacement) retention forces (in Newtons). Measurements were made at the start of the experiment (initial retention) and after 540 cycles of denture insertion and removal to simulate 6 months of clinical function (final retention).

RESULTS

Hader bar had the highest retention after insertions and removals, and Dolder bar had the lowest retention. Vertical displacement showed the highest retention for Dolder and milled bars, and posterior displacement showed the highest retention for Hader bar. Lateral displacement recorded the lowest retention for all bar designs. No significant difference in axial retention loss was observed between different bar designs. Dolder bar showed the highest nonaxial retention loss, and milled bar showed the lowest retention loss.

CONCLUSION

Hader bar is recommended to retain maxillary implant overdentures, as it was associated with higher axial and nonaxial retention compared with Dolder and milled bars after 6 months of simulated denture wear.

[A PhD completed. Maxillary overdentures: with a bar attachment system or locators?]

An overdenture on implants is the treatment of choice for patients with complaints about their conventional complete dentures. While a lot is known regarding the performance of implant-supported mandibular overdentures, much less is known regarding the performance of implant-retained maxillary overdentures. In this doctoral dissertation, various aspects of overdentures on 4 dental implants in the maxilla are discussed. From a systematic review of the literature, it appeared that an overdenture (maxillary or mandibular) on implants improved chewing efficiency, increased maximum bite force and increased patient satisfaction. Implants placed with a maximum dehiscence of two thirds of the buccal implant surface also appeared to function well after 5 years. An overdenture with a bar attachment system was associated with less marginal bone loss, a better subjective chewing efficiency and greater patient satisfaction than an overdenture retained by locators. The differences were, however, small and from a cost-effectiveness point of view, the use of overdentures retained by locators would not be a bad choice.

Splinted and unsplinted overdenture attachment systems: A systematic review and meta-analysis

Splinted and unsplinted overdenture attachment systems have unique advantages and disadvantages. The aim of the present systematic review was to determine the influence of splinted and unsplinted overdenture attachment systems on the marginal bone loss, prosthetic complications and implant survival rate. PubMed/MEDLINE, Scopus and Cochrane databases were searched for articles published up to October 2017, using the following search terms: "overdenture AND attachment OR overdenture AND bar OR overdenture splinted." The PICO question "Do splinted overdenture attachment systems promote better clinical results in comparison to unsplinted systems?" was evaluated. Eligible studies included randomized controlled clinical trials, prospective studies with at least 10 participants and a minimum follow-up of 6 months, and studies published in English that compared splinted and unsplinted attachment systems within the same study. The 95% confidence interval (CI) was considered for all outcomes analysed. After completion of the different steps in the article selection process, nine articles were included in the qualitative and quantitative analyses. A total of 984 implants were placed in 380 patients (mean age: 62.8 years). The meta-analysis demonstrated no statistically significant differences between splinted and unsplinted attachment systems with regard to marginal bone loss (P = .39; MD: -0.11; 95% CI: -0.37 to 0.14), complications (P = .31; RR: 1.26; CI: 0.80-1.99) and implant survival rate (P = .14; RR: 0.37% CI: 0.10-1.36). In addition, splinted and unsplinted overdenture attachment systems achieved similar results with regard to marginal bone loss, prosthetic complications and implant survival rate.

Bar versus ball attachments for implant-supported overdentures in complete edentulism: A systematic review

BACKGROUND

Implant-supported overdenture is one of the most predictable treatment options used in complete edentulism. However, differences have been reported between bar and ball attachments used to retain overdentures in terms of patient satisfaction and prosthesis retention.

PURPOSE

The purpose of this study is to compare the effectiveness of bar and ball attachments for conventionally loaded implant-supported overdentures in completely edentulous patients to improve patient satisfaction and prosthesis retention.

MATERIALS AND METHODS

We conducted the review according to the Cochrane methods and following MECIR standards. We searched Cochrane Oral Health Group Trial register, Cochrane Central Register of Controlled Trials, MEDLINE, and the WHO ICTRP (March 31, 2017). Two review authors assessed trials for inclusion and risk of bias, extracted data, and checked for accuracy. We have expressed results as risk ratio or mean differences, together with their 95% confidence intervals.

RESULTS

We included 10 trials (465 participants). After 5 y, one trial reported higher patient satisfaction when bar attachment was used (MD 1.30, 95% CI 0.20-2.40), and reported no difference between both systems in prosthesis retention (MD -0.90, 95% CI -1.90 to 0.10). Two trials reported no implant failures after 1 and 5 y in both attachments. Downgrading of evidence was based on the unclear risk of bias of included studies and the wide CI crossing the line of no effect.

CONCLUSIONS

There is insufficient evidence to support bar or ball attachment to be used with implant-supported overdentures in completely edentulous patients to improve patient satisfaction and prosthesis retention (PROSPERO 2014:CRD42014014594).

Load Transfer Characteristics of Three-Implant-Retained Overdentures with Different Interimplant Distances

PURPOSE

Implant-retained overdentures are the first choice of rehabilitation for edentulous mandibles. Bone morphology and anatomical landmarks may be influenced by the location and angulation of implants and distances between the implants. The purpose of this study was to investigate stress distribution characteristics and to compare stress levels of three different attachment designs of three-implant-retained mandibular overdentures with three different interimplant distances.

MATERIALS AND METHODS

Three photoelastic mandibular models with three implants were fabricated using an edentulous mandible cast with moderate residual ridge resorption. The center implants were embedded parallel to the midline, and the distal implants were aligned at a 20-degree angulation corresponding to the center implants. Distances between the center and distal implants were set at 11, 18, and 25 mm at the photoelastic models. Bar, bar-ball, and Locator attachment-retained overdentures were prepared for the models. Vertical loads were applied to the overdentures, and stress levels and distribution were evaluated by a circular polariscope.

RESULTS

The greatest observed stress level was moderate for the tested overdenture designs. The Locator attachment system showed the lowest stress level for the 11-mm and 25-mm photoelastic models. The bar attachment design transmitted less stress compared with the other tested designs for the 18-mm photoelastic model.

CONCLUSION

Stresses were observed on the loaded side of the photoelastic models. The lowest stress was found with the Locator and bar attachments for the 11-mm photoelastic model, which transmitted little or no discernible stress around the implants.

An Eight-year Follow-up to a Randomized Clinical Trial of Aftercare and Cost-analysis with Three Types of Mandibular Implant-retained Overdentures

Mandibular implant overdentures increase satisfaction and the quality of life of edentulous individuals. Long-term aftercare and costs may depend on the type of overdentures. One hundred and ten individuals received one of 3 types of implant-retained overdentures, randomly assigned, and were evaluated with respect to aftercare and costs. The follow-up time was 8 years, with only seven drop-outs. No significant differences (Kruskal-Wallis test) were observed for direct costs of aftercare (p = 0.94). The initial costs constituted 75% of the total costs and were significantly higher in the group with a bar on 4 implants, compared with the group with a bar on 2 implants and the group with ball attachments on 2 implants (p = 0.018). The last group needed a significantly higher number of prosthodontist-patient aftercare contacts, mostly for re-adjustment of the retentive system. It can be concluded that an overdenture with a bar on 2 implants might be the most efficient in the long term.

In Vitro Cyclic Dislodging Test on Retentive Force of Two Types of Female Parts of SFI-Bar

PURPOSE

This study aimed to compare the difference in mechanical behavior between two types of female-part clips of the Stress-Free Implant Bar (SFI-Bar) system during simulation of insertion-removal cycles.

MATERIALS AND METHODS

A total of 10 samples simulating SFI-Bar-attachment-retained implant overdentures were fabricated and randomly divided into two groups (n = 5). One group used E-clips (Elitor alloy) as the female part of the SFI-Bar, and the other used T-clips (all titanium grade IV with red nylon inserts). A total of 14,000 insertion-removal cycles were carried out on each sample. Retentive forces from each cycle were recorded for analysis.

RESULTS

Significant differences were found between the two groups (P < .05).

CONCLUSION

The retentive force of E-clips increased as the number of dislodging cycles increased, suggesting that some adjustment may be needed to lower this part's retentive force. T-clips with changeable nylon inserts were deformed after about 4,200 insertion-removal cycles, which interfered with insertion. This indicated that T-clips may need replacement after 2 to 3 years of clinical use.

Changes in Bone Levels Around Mini-Implants in Edentulous Arches

PURPOSE

To evaluate changes in marginal bone levels around maxillary and mandibular mini-implants stabilizing complete dentures and to explore possible risk factors associated with bone loss.

MATERIALS AND METHODS

All eligible patients from nine private dental practices were invited to participate. Panoramic radiographs were obtained postoperatively and at the follow-up examination. The changes in bone level were estimated with linear mixed models that included the factors sex, age, jaw, region (anterior versus posterior), smoking habits, and loading concept.

RESULTS

Of the 180 invited patients, 133 participated in the follow-up (response rate: 73.9%). Of 336 mini-implants in 54 maxillas and 402 mini-implants in 95 mandibles, 15 maxillary implants and 11 mandibular implants were lost after insertion, and 4 mandibular implants fractured. Radiographic evaluations in 11 participants were not possible. The mean marginal bone loss at the remaining 634 mini-implants in 122 patients was 0.8 mm in the maxilla and 0.5 mm in the mandible over a mean observation time of 2.2 ± 1.0 years. This difference in univariate estimation lost significance after adjusting for the other variables. Implants in former smokers showed more bone loss than implants in participants who had never smoked. Implants that were loaded 3 to 4 months after placement (delayed loading) showed more marginal bone loss than immediately loaded implants. No statistically significant differences were found between men and women, different age groups, or anterior and posterior implants.

CONCLUSION

Mean marginal bone loss around mini-implants used to stabilize complete dentures was insignificantly higher in the maxilla than in the mandible after a mean observation period of 2.3 years. These values are comparable with marginal bone loss around standard-diameter implants. A previous smoking habit and delayed loading after implant placement with a low insertion torque were shown to be possible risk factors for bone loss.

A Sequential Approach to Implant-Supported Overdentures

Fabrication of implant-supported maxillary or mandibular overdentures can seem to be difficult procedures. Many things could go wrong and/or unnoticed until the fabrication has been completed. Implants must be correctly surgically placed in viable bone at the proper angulation and spacing within an arch. The type of attachment must be considered and future treatment of the appliance should be simple and efficient. The appliance must function not only initially but also for many years to come. The author has found the use of the GPS attachment to be an ideal tool to achieve the goals of retention and stability. Careful planning is the most important part of this process, and understanding the benefits and risks of creating overdentures should be well understood by the dentists. By sequentially planning and treating these types of cases, the patient is able to function reasonably during the stages of implant healing. The final prosthesis is created and remaining teeth that held the transitional appliance in place are remove on the day of final seating. This is an excellent simplified retentive system option for those patients who are anxious about losing their teeth, even those teeth that are diseased and ugly.

Prosthetic Complications and Maintenance Requirements in Locator-attached Implant-Supported Overdentures: A Retrospective Study

Retrospective data of 32 patients supplied with implant-supported and Locator-attached overdentures were screened for prosthetic complications and maintenance requirements, which were recorded and statistically analyzed. Mean observation time was 4.78 ± 1.72) years. Loss of retention was the most frequently observed event (n = 22). Damage and exchange of the insert holders (n = 4) and loosening of locator attachments (n = 2) and fracture of the insert holder (n = 2) were uncommon events; no loss of locator attachments was observed. Loss of retention in Locator-attached overdentures is frequent; correlating patient-specific parameters with prosthetic complications is necessary to define recommendations for the use of Locator attachments.

Cast Titanium for Obturator Framework Construction in Maxillofacial Prosthodontics

A 37 year old male presented with the complaint of a loose and bulky acrylic obturator prosthesis. He had previously tried to using a different acrylic obturator prostheses as well as both cobalt chromium and titanium framework obturators. The most successful previous prosthesis was a titanium based obturator which had performed well prior to a fractured clasp. Accordingly, following an exploration of the available surgical and prosthodontic treatment options, a further tooth borne partial maxillary obturator was provided successfully. The case highlights the relative merits and limitations of the use of cast titanium as a denture base material in partial denture and obturator construction.

Load Transfer Characteristics of Various Designs of Three-Implant-Retained Mandibular Overdentures

PURPOSE

Many different attachment systems (eg, bars, studs, magnets, telescopic copings) have been used to retain overdentures. The current study aimed to investigate the load transfer characteristics and to compare the stress levels of four attachment designs for mandibular overdentures retained by one central implant and two inclined distal implants.

MATERIALS AND METHODS

Photoelastic mandibular models fabricated with three screw-type implants (Tapered Screw-Vent, 3.75 × 13 mm) were placed in the parasymphyseal area. The center implant was vertically oriented to the midline, and the other implants were embedded in the canine areas with a 20-degree angulation relative to the center implant. Four overdentures with different attachment designs (bar, bar/ball, bar/distally placed Rk-1s, and Locators) were studied in the context of this model. Vertical loads (100 N) were applied to the central fossa of the right first molar area of each overdenture. Stress levels that developed in the denture-bearing areas and around the implants were observed photoelastically and evaluated visually.

RESULTS

The studied attachment designs showed low and moderate stress levels. The greatest stress was found with the bar/ball design, while the lowest stress levels were observed with the Locator attachment design.

CONCLUSION

Stresses were concentrated on the loaded side for each design. All tested designs experienced moderate stress around the posterior edentulous area. None of the designs experienced more than moderate stress. The lowest stress was noted with the Locator attachments, which transmitted little discernible stress around the implants.

Influence of Diamondlike Carbon Coating of Screws on Axial Tightening Force and Stress Distribution on Overdenture Bar Frameworks with Different Fit Levels and Materials

PURPOSE

The aim of this study was to evaluate the axial tightening force applied by conventional and diamondlike carbon (DLC)-coated screws and to verify, through three-dimensional finite element analysis (FEA), the stress distribution caused by different framework materials and prosthetic screws in overdenture frameworks with different misfit levels.

MATERIALS AND METHODS

The axial tightening force applied by the screw was evaluated by means of a titanium matrix connected to a load cell. Conventional titanium or DLC-coated screws were tightened with a digital torque wrench, and the load values were recorded. The values were applied in an FEA to a bar-clip attachment system connected to two 4.0 × 11-mm external-hexagon titanium implants placed in an anterior edentulous arch. DLC-coated and conventional screws were modeled with their respective axial forces obtained on the experimental evaluation for three bar framework materials (titanium, nickel-chromium, and cobalt-chromium) and three levels of misfit (100, 150, and 200 μm). Von Mises stresses for prosthetic components and maximum principal stress and microstrains (maximum principal strains) for bone tissue were measured.

RESULTS

The mean force applied by the conventional screw was 25.55 N (± 1.78); the prosthetic screw coated with a DLC layer applied a mean force of 31.44 N (± 2.11), a statistically significant difference. In the FEA, the DLC screw led to higher stresses on the framework; however, the prosthetic screw suffered lower stress. No influence of screw type was seen in the bone tissue.

CONCLUSION

Titanium frameworks reduced the stress transmitted to the bone tissue and the bar framework but had no influence on the screws. Higher misfit values resulted in an increased stress/strain in bone tissue and bar framework, which was not the case for retention screws.

In vitro comparison of the retentive properties of ball and locator attachments for implant overdentures

PURPOSE

To compare the retentive properties of ball and locator attachments during 5,000 insertion-separation cycles, corresponding to approximately 4.5 years of clinical use.

MATERIALS AND METHODS

Four dental implants (diameter, 3.8 mm; length, 12 mm) were inserted into the prepared beds of two polyethylene blocks. Twenty acrylic prosthetic components were fabricated and connected to the ball and locator abutments. Tensile force was applied to the prosthetic components until the attachments were separated from the abutments. All samples were subjected to 5,000 insertion-separation cycles. Retention forces were measured after 10, 100, 200, 300, 400, 500, 1,000, 1,500, 2,000, 3,000, 4,000, and 5,000 insertion-separation cycles. Additionally, the wear of the attachments was measured using scanning electron microscopy. Data were analyzed to determine statistical equivalence among the two different attachments using the Student t test procedure and the Mann-Whitney U test procedure (α = .05).

RESULTS

Ball attachments showed significant retention loss after 100, 200, 400, 500, 1,500, and 4,000 cycles, and the locator attachments showed significant retention loss after 100, 200, 300, 500, and 3,000 cycles as compared with the previous cycle (P < .05). Retention loss after 5,000 cycles was detected significantly more often for ball attachments than for locator attachments (P = .049). No significant difference was detected between the retention losses of the two attachment systems during the other cycles as compared with the initial retention values (P > .05). No significant difference was detected between the wear on the two attachment systems after 5,000 cycles (P > .05).

CONCLUSION

Both attachment systems showed decreased retentive forces after 5,000 insertion-separation cycles. However, after 5,000 insertion-separation cycles, locator attachments showed better retentive properties than ball attachments.

Overdenture retaining bar stress distribution: a finite-element analysis

OBJECTIVE

Evaluate the stress distribution on the peri-implant bone tissue and prosthetic components of bar-clip retaining systems for overdentures presenting different implant inclinations, vertical misfit and framework material.

MATERIALS AND METHODS

Three-dimensional models of a jaw and an overdenture retained by two implants and a bar-clip attachment were modeled using specific software (SolidWorks 2010). The studied variables were: latero-lateral inclination of one implant (-10°, -5°, 0°, +5°, +10°); vertical misfit on the other implant (50, 100, 200 µm); and framework material (Au type IV, Ag-Pd, Ti cp, Co-Cr). Solid models were imported into mechanical simulation software (ANSYS Workbench 11). All nodes on the bone's external surface were constrained and a displacement was applied to simulate the settling of the framework on the ill-fitted component. Von Mises stress for the prosthetic components and maximum principal stress to the bone tissue were evaluated.

RESULTS

The +10° inclination presented the worst biomechanical behavior, promoting the highest stress values on the bar framework and peri-implant bone tissue. The -5° group presented the lowest stress values on the prosthetic components and the lowest stress value on peri-implant bone tissue was observed in -10°. Increased vertical misfit caused an increase on the stress values in all evaluated structures. Stiffer framework materials caused a considerable stress increase in the framework itself, prosthetic screw of the fitted component and peri-implant bone tissue.

CONCLUSIONS

Inclination of one implant associated with vertical misfit caused a relevant effect on the stress distribution in bar-clip retained overdentures. Different framework materials promoted increased levels of stress in all the evaluated structures.

Mandibular implant-supported overdentures: attachment systems, and number and locations of implants--Part I

The use of dental implants in replacing missing teeth is an integral part of restorative dental treatment. Use of conventional complete dentures is associated with several problems such as lack of denture stability, support and retention. However, when mandibular complete dentures were used with two or more implants, an improvement in the patients' psychological and social well-being could be seen. There is general consensus that removable implant-supported overdentures (RISOs) with two implants should be considered as the first-choice standard of care for an edentulous mandible. This treatment option necessitates the use of attachment systems that connect the complete denture to the implant. Nevertheless, each attachment system has its inherent advantages and disadvantages, which should be considered when choosing a system. The first part of this article provides an overview on options available to restore the mandibular edentulous arch with dental implants. Different types of attachment systems, their features and drawbacks are also reviewed.

Contemporary "All-on-4" concept

Restoration of the atrophic edentulous maxilla and mandible with implant retained prostheses has involved the use of axially placed implants in regions of the maxilla and mandible based on the adequate availability of bone, often using a staged surgical approaches. Anatomic limitations including pneumatized maxillary sinus, proximity of the inferior alveolar nerve and lack of available native bone have many clinicians performing traditional grafting procedure prior to implant placement. Utilization of the "All-on-4" concept has overcome these anatomic restrictions by allowing placement of 2 vertical and 2 angled implants in the premaxilla and anterior mandible. This technique has enabled immediate placement of full arch fixed restoration at the time of implant surgery if sufficient torque is achieved. It has biomechanical advantages including increasing in A-P spread, enhancing load distribution with cross arch stabilization, shorten cantilever, longer implants to be placed by titling them posteriorly, and maintenance of marginal bone height. High implant survival rates of in the maxilla (92.5-100%), in the mandible (93-100%) and restoration (99.2-100%) prove that the "All-on-4" concept is a viable treatment option for edentulous patients with atrophic alveolar ridges circumventing these traditional grafting procedures.

Adhesive strength of the luting technique for passively fitting screw-retained implant-supported prostheses: an in vitro evaluation

PURPOSE

This in vitro study evaluated the adhesive strength of a technique to lute implant cylinders to metal frameworks in implant-supported prostheses and ensure a good passive fit.

MATERIALS AND METHODS

Different height samples were tested: In group 1, implant cylinders were 5 mm long; in group 2, they were 10 mm long. A universal testing machine (Instron) was used to perform pullout tests.

RESULTS

The luting technique provided enough adhesive strength for clinical use with greater adhesive strength in group 2 (mean pull-out strength: 2.85 kN in group 1 versus 3.79 kN in group 2).

CONCLUSIONS

The luting technique provides enough adhesive strength for clinical use. Moreover, specimens with a larger surface for adhesion demonstrated higher adhesive strength compared with shorter specimens.

Maxillary implant-retained partial overdenture with Dolder bar attachment: a clinical report

This article describes a technique for maintaining a maxillary Kennedy III partial removable dental prosthesis design in a patient who had non-restorable failing abutments by replacing the abutments with dental implants. Two implants were placed immediately after extraction of the abutment teeth in the anterior maxilla. After the implants were fully integrated, a Dolder bar attachment was fitted onto the implants. A new maxillary partial removable dental prosthesis was fabricated using the implants and the remaining natural teeth as abutments to restore function and esthetics. With the aid of dental implants, this Kennedy III maxillary removable dental prosthesis design could provide additional retention and support by promoting cross-arch stability and tissue, implant and tooth support. The patient's satisfaction was significantly increased.

The Bond Strength of Resin Bonded Bridge Retainers to Abutments of Differing Proportions of Enamel and Composite

Four groups of specimens were constructed using bovine enamel and composite resin. After a period of ageing, the specimens were roughened and acid etched before they were cemented to air abraded base metal alloy beams with a universal resin cement. After further ageing, tensile peel testing was carried out using a Universal Testing Machine. The force required to produce failure increased as the amount of composite resin on the bonding surface of the abutment increased. This difference reached statistical significance (p < 0.5) when the abutments contained > 50% composite. The mode of failure was mixed on the majority of retainers. Within the limitations of the study, findings suggest that RBB retainers can be cemented to abutments restored with composite resin without a reduction in bond strength.

Prosthetic rehabilitation of an edentulous patient with an oronasal fistula

The presence of an oronasal fistula presents a challenge to maxillary complete denture fabrication because leakage of air from the nasal cavity through the fistula prevents the formation of an adequate border seal. Although surgical repair or dental implants are possible solutions, these options are invasive and sometimes not feasible. This clinical report illustrates an alternative prosthetic solution by integrating a small retentive component into a maxillary complete denture.

Short implants versus bone augmentation for placing longer implants in atrophic maxillae: One-year post-loading results of a pilot randomised controlled trial

PURPOSE

To evaluate whether short (5.0 to 8.5 mm) dental implants could be a suitable alternative to longer (at least 11.5 mm-long) implants placed in atrophic maxillae augmented with autogenous bone for supporting dental prostheses.

MATERIALS AND METHODS

Twenty-eight patients with fully edentulous atrophic maxillae, whom had 5 to 9 mm of residual crestal bone height which was at least 5 mm thick, measured using computerised tomography (CT) scans, were randomised into two groups either to receive 4 to 8 short (5.0 to 8.5 mm) implants (15 patients) or autogenous bone from the iliac crest to allow the placement of at least 11.5 mm-long implants (13 patients). Bone blocks and the windows at the maxillary sinuses were covered with rigid resorbable barriers. Grafts were left to heal for 4 months before placing implants which were submerged. After 4 months, provisional reinforced acrylic prostheses or bar retained overdentures were delivered. Provisional prostheses were replaced, after 4 months, by definitive screw-retained metal-resin cross-arch restorations. Outcome measures were prosthesis and implant failures, any complications, peri-implant marginal bone level changes and patient satisfaction. Patients were followed up to 1 year after loading.

RESULTS

All patients were rehabilitated with implant-supported prostheses but two patients dropped out from the augmented group. One bilateral sinus lift procedure failed for infection, although short implants could be placed. One implant failed in the augmented group versus two short implants in two patients (Fishers exact test P = 1.00; difference in proportions = 0.06; 95% CI -0.28 to 0.17). All failures occurred before loading. Significantly more complications occurred in augmented patients: eight complications occurred in 5 augmented patients (all of them complained of pain 1 month after bone harvesting from the iliac crest) versus no complications in the short implant (Fisher's exact test P = 0.013; difference in proportions = 0.38; 95% CI 0.11 to 0.65). Both groups presented a significant peri-implant marginal bone loss at 1 year after loading (P < 0.0001); -1.05 (0.20) mm for short implants and -1.01 (0.16) mm for the augmented group, respectively, with no statistically significant differences between the two groups (mean difference -0.04 mm; 95% CI -0.22 to 0.14; P = 0.59). All patients were fully satisfied with the treatment and would have it again.

CONCLUSIONS

This pilot study suggests that short implants may be a suitable, cheaper and faster alternative to longer implants placed in bone augmented with autogenous bone for rehabilitating edentulous atrophic maxillae, however, these preliminary results need to be confirmed by larger trials with follow-ups of at least 5 years.

Torque loss under mechanical cycling of long-span zirconia and titanium-cemented and screw-retained implant-supported CAD/CAM frameworks

OBJECTIVES

This study evaluated the screw joint stability after cyclic loading of implant-supported titanium and zirconia CAD/CAM frameworks for fixed dental prostheses (FDPs) with different retention methods.

MATERIAL AND METHODS

Twenty four one-piece frameworks supported by six threaded implants placed in the maxilla were fabricated using a CAD/CAM technique (NeoShape). Dry-pressed porcelain crowns were luted to the frameworks to standardize the specimens. The specimens were then divided into four groups (n = 6) according to framework material (titanium or zirconia) and retention method for the prosthesis (cement- or screw-retained): G1, Ti-cemented; G2, Ti-screw-retained; G3, Zr-cemented; and G4, Zr-screw-retained. A digital torque ratchet was used to assess the initial preload removal torque. Torque was then reapplied and the specimens were submitted to a 200 N cyclic load, at a frequency of 2 Hz, underwater in controlled temperature of 37°, and for 1 × 106 cycles. An opposing lower dental arch was fabricated using bis-acrylic resin to simulate occlusal contacts in centric. After cyclic loading, postload removal torque was measured. Preload and postload torque loss was expressed as a percentage of the initial load. Data were submitted to a linear mixed-effects model for statistical significance (α = 0.05) to evaluate the effect of cyclic loading in the screw torque loss used with frameworks of different materials and retention methods.

RESULTS

Significant screw torque loss (%) was found for the tested groups (before/after cyclic loading, respectively): G1 (39.77/61.83), G2 (37.57/50.96), G3 (34.87/54.10), and G4 (47.56/73.50) (P < 0.05).

CONCLUSIONS

The screw removal torque was significantly reduced for all groups in this study after cyclic loading the specimens. Screw-retained zirconia specimens presented the highest torque loss before and after the cyclic loadings compared with the other specimens that were tested.

Technical complications and failures of zirconia-based prostheses supported by implants followed up to 7 years: a case series

PURPOSE

To evaluate technical complications and failures of zirconia-based fixed prostheses supported by implants.

MATERIALS AND METHODS

Consecutive patients received zirconia-based single crowns (SCs) and fixed dental prostheses (FDPs) on implants in a private clinical setting between 2005 and 2010. One dentist performed all surgical and prosthetic procedures, and one master technician performed and coordinated all laboratory procedures. One-piece computer-aided design/ computer-assisted manufacture technology was used to fabricate abutments and frameworks, which were directly connected at the implant level, where possible. All patients were involved in a recall maintenance program and were finally reviewed in 2012. Data on framework fractures, chipping of veneering ceramics, and other technical complications were recorded. The primary endpoint was failure of the prostheses, ie, the need for a complete remake. A life table analysis was calculated.

RESULTS

A total of 289 implants supported 193 zirconia-based prostheses (120 SCs and 73 FDPs) in 127 patients (51 men, 76 women; average age: 62.5 ± 13.4 years) who were reviewed in 2012. Twenty-five (13%) prostheses were cemented on 44 zirconia abutments and 168 (87%) prostheses were screw-retained directly at the implant level. Fracture of 3 frameworks (1 SC, 2 FDPs) was recorded, and significant chipping resulted in the remake of 3 prostheses (1 SC, 2 FDPs). The 7-year cumulative survival rate was 96.4% ± 1.99%. Minor complications comprised 5 loose screws (these were retightened), small chips associated with 3 prostheses (these were polished), and dislodgement of 3 prostheses (these were recemented). Overall, 176 prostheses remained free of technical problems.

CONCLUSIONS

Zirconia-based prostheses screwed directly to implants are clinically successful in the short and medium term.

Immediate versus early loading of mini-implants supporting mandibular overdentures: a preliminary 3-year clinical outcome report

PURPOSE

The aim of this preliminary clinical report was to evaluate and compare the clinical outcomes of immediate and early loaded mini-implants (MIs) supporting mandibular overdentures.

MATERIALS AND METHODS

Thirty-six completely edentulous patients (20 men and 16 women) complaining of insufficient retention of their mandibular dentures were randomly assigned to two groups. Each patient received four MIs in the interforaminal area of the mandible using the nonsubmerged flapless surgical approach. In group 1 (G1), MIs were loaded with mandibular overdentures using the immediate loading protocol, while in group 2 (G2), MIs were loaded with overdentures using the early loading protocol. The cumulative survival rate was calculated using Kaplan-Meier analysis. Peri-implant health indices (Plaque Index/Bleeding Index), probing depths, and marginal bone levels were recorded for both groups after MI insertions and 6, 12, 24, and 36 months thereafter.

RESULTS

The cumulative implant survival rates were 91.7% and 96.7% for G1 and G2, respectively. G1 recorded significantly higher Plaque Index, Bleeding Index, and probing depths than G2 after 12 months, while other observation times demonstrated no significant difference between groups. Most of the recorded marginal bone loss occurred in the first year, and no significant bone loss was noted in subsequent years. After 6 months, marginal bone loss was significantly higher in G1 compared to G2, but no significant differences between groups were noted thereafter.

CONCLUSIONS

Within the limitations of this study's research design and duration of follow-up outcome analyses, immediate and early loading protocols showed good clinical results with favorable peri-implant tissue response 3 years after implant insertion. Early loading of MIs supporting a mandibular overdenture appears to be preferable to immediate loading.

A technique for relining bar-retained overdentures

This article describes a technique for relining a mandibular bar-retained overdenture that allows recording the soft tissue beneath the bar and makes it possible to replace or modify the retentive bar attachment simultaneously with the reline procedure.

Intraoral-extraoral combination prosthesis: improving retention using interconnecting magnets

Osseointegrated implants have been well documented for retaining an obturator prosthesis as well as a facial prosthesis. However, when the defect extends to both the facial area and the maxilla, it is difficult to rehabilitate those defects to the satisfaction of the patient, especially in cases where implants cannot be placed on both sites. This case report describes the use of magnets to connect two prostheses, thereby increasing retention and patient comfort.

Immediate versus delayed loading of dental implants in edentulous patients' maxillae: a 6-year prospective study

PURPOSE

This study compared the surgical protocol efficacy of immediate and delayed implant loading in edentulous maxillae opposed by natural or restored mandibular dentitions over an observational period of 6 years or longer. The selected outcome determinants included individual implant survival data, progressive measurements of peri-implant bone resorption, prosthodontic survival and success data, and report of complications.

MATERIALS AND METHODS

A convenience sample of 49 patients requiring fixed implant-supported maxillary prostheses was split into two groups. The test group (34 patients) was treated according to the Columbus Bridge Protocol, which prescribes the insertion of four to six implants, including distally tilted implants, and load within 24 hours. The control group (15 patients) was treated via a two-stage surgical protocol of 6 to 9 straight implants that were loaded a mean 8.75 months after stage-one implant surgery. Two hundred sixty implants (test: n = 163, control: n = 97) were placed, and all subjects were ultimately treated with screw-retained full-arch prostheses.

RESULTS

Two patients dropped out (one in the test group and one in the control group) by the time of the scheduled sixth annual visit. The other patients were followed up for 75.2 months (range: 72 to 90 months). At the 6-year follow-up, no differences in implant cumulative survival rates were found between groups. Significantly less bone loss was found in the test group (mean: 1.62 mm) compared with the control group (mean: 2.44 mm). All of the original prostheses were maintained throughout the study's observation period and were functioning satisfactorily at each patient's last recall appointment.

CONCLUSION

Patients who received immediate and delayed implant loading in their edentulous maxillae demonstrated similar survival outcomes. However, less marginal bone loss was recorded around the immediately loaded implants over the study's 6-year follow-up period.

A hinged two-part partial denture used in conjunction with severely tilted teeth: a case report

A two-part sectional denture can be a useful treatment option when the presence of severe hard tissue undercuts compromises the provision of a satisfactory conventional prosthesis. This article presents a case report illustrating the effective use of a hinged two-part denture in restoring a mandibular Kennedy Class IV edentulous area. A sectional denture approach was selected because of severe proximal and lingual undercuts.

A 3-year prospective clinical study of telescopic crown, bar, and locator attachments for removable four implant-supported maxillary overdentures

PURPOSE

To evaluate telescopic crown (TC), bar, and locator attachments used in removable four implant-supported overdentures for patients with edentulous maxillae.

MATERIALS AND METHODS

A total of 30 maxillary edentulous patients were enrolled in a 3-year prospective study. Ten patients (group A) were treated with overdentures supported by TCs, 10 patients (group B) with overdentures supported by bar attachments, and 10 patients (group C) with overdentures supported by locator attachments. A total of 120 implants were used to restore oral function. During the 3-year follow-up period, implant survival and success rates, biologic and mechanical complications, prosthodontic maintenance efforts, and patient satisfaction were evaluated.

RESULTS

All 30 patients were available for the 3-year follow-up and exhibited 100% implant survival and success rates. Peri-implant marginal bone resorption was not statistically significant for the three groups. There were lower plaque, bleeding, gingiva, and calculus indices in group C compared with groups A and B. The number of prosthodontic maintenance visits revealed eight complications in the TC group, seven complications in the bar group, and four complications in the locator group. However, there were no differences in the clinical effects of the overdentures in the three groups.

CONCLUSION

Within the limits of this prospective study, it was concluded that the locator system produced superior clinical results compared with the TC and bar attachments in terms of peri-implant hygiene parameters, the frequency of prosthodontic maintenance measures, cost, and ease of denture preparation. However, longer-term prospective studies are required to confirm these results.

A preliminary three-dimensional finite element analysis of mandibular implant overdentures

A treatment protocol that may lead to reduced mandibular posterior residual ridge resorption in patients with overdentures retained and supported by two interforaminal implants was investigated. The treatment included the addition of short implants in the posterior edentulous mandible for the presumed purpose of favorable provision of mechanical load stimulus to alveolar bone. Three-dimensional finite element analysis was used to model cited effective strains that may stimulate bone remodeling in two selected models. Based on this laboratory study, the addition of posterior short implants has a favorable effect in maintaining bone mass under implant retained overdentures.

A systematic review of implant-supported overdentures in the edentulous maxilla, compared to the mandible: how many implants?

BACKGROUND AND AIM

There is now overwhelming evidence from systematic reviews that a two implant overdenture is the first choice of treatment for the edentulous mandible. Conversely, consensus is lacking for implant-supported maxillary overdentures. Therefore, we systematically reviewed the treatment outcome of concepts used for implant-supported maxillary overdentures, focusing on the survival of implants, survival of maxillary overdentures and condition of the implant surrounding hard and soft tissues after a mean observation period of at least 1 year.

MATERIAL AND METHODS

MEDLINE (1950 to December 2013), EMBASE (1966 to December 2013) and CENTRAL (1800 to December 2013) were searched to identify eligible studies. Two reviewers independently assessed the articles using specific study design-related quality assessment forms.

RESULTS

Out of 195 primarily selected articles, 24 studies fulfilled the inclusion criteria. A metaanalysis showed an implant survival rate of 98.1% and overdenture survival of 99.5% per year in the case of ≥ 6 implants and a splinted (bar) anchorage. In the case of ≤ 4 implants and a splinted (bar) anchorage, implant survival rate and overdenture survival were 97.0% and 96.9% per year, respectively. In the case of ≤ 4 implants and a non-splinted anchorage (ball, locator, telescopic crown), implant survival rate and overdenture survival were 88.9% and 98.8% per year, respectively. The condition of the peri-implant tissues was not reported in most studies.

CONCLUSIONS

An implant-supported maxillary overdenture (all studies ≥ 4 implants) provided with a splinted anchorage is accompanied with a high implant and overdenture survival rate (both >95% per year), while there is an increased risk of implant loss when ≤ 4 implants with a non-splinted anchorage are used.

Use of implant-supported prostheses in edentulous mandibles among prosthodontists in Sweden

The aim of this study was to investigate the production of mandibular implant-supported fixed and removable prostheses among prosthodontic specialists in Sweden and to compare the results with findings in a similar study made in 2001 (17). Questionnaires regarding treatment with mandibular implant prostheses during 20011 were mailed to all specialists in prosthodontics in Sweden (n = 156, according to available data). Of the 156 questionnaires, 129 (83%) were returned and of those 114 were completed. The reported number of treatments with mandibular implant-supported prostheses varied much among the specialists. Fixed implant prostheses were more common than overdentures (means 11 and 3, median values 8 and 2, respectively). However, the range was large for both alternatives. Ten (9%) of the specialists reported no treatment with fixed implant prostheses while 29 (25%) had not made any implant overdenture during 2011. The most common anchorage system for overdentures in 2011 (as well as in 2001) was two un-splinted implants with ball attachments or Locator abutments. The most common reasons for choosing overdenture treatment instead of a fixed implant prosthesis in 2011 were the reduced cost and the patient's main wish to improve denture retention. A majority of the prosthodontists (58%) reported that patients with implant overdentures were as satisfied as those with fixed implant-supported prostheses, whereas 40% claimed they were less satisfied. Two respondents (2%) considered that overdenture patients were more satisfied than those with a fixed prosthesis. It can be concluded that the general attitude among Swedish prosthodontists towards implant overdentures has not changed much during the 10-year period between the present and the previous investigation.An overdenture is still a seldom-used option in implant treatment of patients with edentulous mandibles in Sweden. Instead, a fixed implant-supported prosthesis continues to be the preferred option,

Immediate loading of two flapless placed mandibular implants supporting cross-arch fixed prostheses: a 3-year follow-up prospective single cohort study

PURPOSE

To evaluate the clinical outcome of two implants placed flapless in fully edentulous mandibles and immediately restored with a metal-resin screw-retained cross-arch prostheses 3 years after loading.

MATERIALS AND METHODS

Eighty consecutively patients were recruited. Implants for immediate loading had to be inserted with a minimum torque of 80 Ncm. Outcome measures, evaluated by two independent assessors, were: prosthesis and implant failures, complications, marginal bone level changes, implant stability quotient (ISQ) values and patient satisfaction.

RESULTS

Three years after loading, all prostheses were in function although one patient did not come back for the 1- and 3-year follow-ups. Two implants failed early in two patients, but were successfully replaced and their prostheses remade. Twelve complications occurred in 10 patients but were all successfully treated. After 3 years, mean marginal bone loss was 0.43 mm, mean ISQ values decreased from 75.4 to 75.3, and all but four patients were fully satisfied with the therapy. Four patients were partially satisfied because, lacking molars, they could not chew as they wished.

CONCLUSION

Immediately loaded mandibular cross-arch partial dentures can be supported by only two dental implants up to 3 years. Longer follow-ups (around 10 years) are needed to know the prognosis of this treatment modality.

A novel approach to implant screw-retained restorations: adhesive combination between zirconia frameworks and monolithic lithium disilicate

The use of zirconia is an esthetic alternative to metal for implant-supported frameworks, and it has increased primarily for its high biocompatibility, low bacterial surface adhesion, high flexural strength and high mechanical features. The zirconia frameworks in fixed prosthetic restorations that are supported by implants is commonly covered with hand-layered overlay porcelain. This technical procedure is highly esthetic but it can cause some complications, such as porcelain fractures. The purpose of this article is to introduce an innovative approach to create an esthetic fixed ceramic implant restoration to minimize and facilitate the repair of the mechanical complications, by combining the adhesive-cementation of lithium disilicate full coverage restorations on implant screw-retained zirconia frameworks.

Occlusion of artificial teeth in partial dentures in the "chewing center"--first exploratory population-based evaluations

Occlusal performance is a substantial determinant of the quality of dental prosthetic restorations. In the follow-up (SHIP 1) to the Study of Health in Pomerania (SHIP), a representative population of 3300 subjects was studied in the first exploratory evaluation of the occlusion of artificial teeth in the chewing center (first molar region) of partial dentures. A digital analysis of interocclusal records of habitual intercuspation position (ICP) was performed using the Greifswald Digital Analyzing System (GEDAS), a software package that identifies contact points as transparent areas. 562 subjects (280 men aged 61.7 ± 11.9 years and 282 women aged 60.7 ± 10.7 years) had maxillary removable partial dentures (RPDs), and 619 (271 men aged 65.0 ± 11.5 years and 348 women aged 62.4 ± 10.6 years) had mandibular RPDs. Most RPDs were retained with either attachment retainers (11.7% maxilla, 11.7% mandible), cast clasps (38.4% maxilla, 40.7% mandible), telescopes with double crowns (15.7% maxilla, 19.1% mandible), or wrought wire clasps (16.4% maxilla, 8.2% mandible). Some had a combination of different retention elements. The mean number of artificial teeth was 7.8 ± 2.9 in the maxilla and 7.5 ± 3.0 in the mandible. Only the artificial teeth (first molars) in mandibular partial dentures showed differences in the frequency of occlusal contacts between groups (chi-square test). Of these, telescopic crown-retained RPDs had the highest frequency of occlusal contacts (74.4% at tooth 36 and 77.1% at tooth 46), and wrought wire-retained RPDs had the lowest (48.4% at tooth 36 and 45.2% at tooth 46). The results for RPDs with a free-end saddle were comparable and analogous; contact frequencies for those with an interdental saddle did not differ significantly. Notably, the overall frequency of occlusal contacts was greater for tooth 46 (62.9%) than for tooth 36. In conclusion, when replacing teeth in the chewing center, particularly in the mandible, telescopic crown-retained RPDs offer a distinct advantage in terms of occlusal contacts and thus provide better occlusal stability.

Long and short term management of implant-supported mandibular overdentures

Common problems with the long term clinical use of implant-supported mandibular overdentures (ISMDs) include fractures of dentures, bars and clips, and reactivation of clips. Many general dental practitioners (GDPs) are reticent to be involved in the maintenance of ISMDs, especially if they have not had any further training or are unfamiliar with implant components and systems. This article highlights the need for the training of GDPs in maintenance and management of ISMDs as an increasing number of edentulous patients are being provided with ISMDs, resulting in an increasing need for the maintenance of the prosthesis in the primary care setting at a possible cost to the patient.

CLINICAL RELEVANCE

Implant-supported overdentures are becoming a common treatment option for edentulous patients, however, they are not without their clinical challenges, many of which can be easily rectified in a primary care environment, such as general practice.

Magnetic attachment for implant overdentures: influence of contact relationship with the denture base on stability and bending strain

This study evaluated how the contact height between the magnetic attachment and denture base influences stability and bending strain. An implant modified with strain gauges and a magnetic attachment mounted in an acrylic resin block were used to characterize systems with varying degrees or heights of contact with the abutment. Bending strain under lateral loading increased significantly as the contact height decreased. In the no contact and resilient contact groups, magnetic assemblies separated at reduced bending strain in all loading conditions. The contact height of the magnetic attachment influenced the stability and the amount of bending strain on the implant.

In vitro retention loss of attachment-retained removable partial denture

AIM

To investigate the importance of attachment types on the retention loss of extracoronal attachment-retained removable partial dentures depending on the usage period.

MATERIALS AND METHODS

In order to observe the retention loss of 5 different attachments (OT Strategy, OT Strategy-metal protected, Vario-stud-snap and Vario-soft 3 and ERA-RV) over time, attachment-retained partial dentures representing Kennedy II mod. I case were placed in a custom-made, retention test machine. For each minute, eight separating and joining movements were performed and retention values (Newton) of the attachments were recorded by computer. The retention tests implemented in 540,1080 and 2160 cycles. The data were evaluated statistically according to the two-way ANOVA and Tukey parametrical tests.

RESULTS

The slide type attachment providing the best retention force was observed to be the most worn out by this process (p < 0.01) while the ball type attachments, which typically have the lesser retention force, showed less retention loss (p < 0.01).

CONCLUSION

It can be concluded that the retention attributes of the attachment-retained dentures were affected by the specific type of precision attachment as well as the usage period.

CLINICAL SIGNIFICANCE

Precision attachments with ball-type plastic matrices may be recommended for the clinical use due to their retention stability over time.