What is the optimal number of implants for removable reconstructions? A systematic review on implant-supported overdentures

The aim of this systematic review was to assess the optimal number of implants for removable reconstructions.

Comparative study of four retentive anchor systems for implant supported overdentures--retention force changes

OBJECTIVES: Wear of attachments leads to a loss of retention and potentially reduces the function of complete dentures. This study evaluated the retention force changes of different prefabricated attachment systems for implant-supported overdentures to estimate the wear constancy and applicability in clinical practice. METHODS: Four prefabricated attachment systems were tested [Group SG: retentive ball attachment (Straumann, Switzerland) with gold matrix, Group ST: retentive ball attachment (Straumann, Switzerland) with titanium spring matrix, Group IB: UNOR i-Ball with Ecco matrix (UNOR, Switzerland) and Group IMZ: IMZ-TwinPlus ball attachment with gold matrix (DENTSPLY Friadent, Germany)]. Ten samples of each system were subjected to 10,000 insertion-separation cycles. RESULTS: Results showed that all types of attachments showed wear, which led to a loss of retention force after an initial increase at the beginning of the wear simulation. Attachments with a plastic retention insert or gold matrices underwent the smallest changes in retention force. The titanium spring system showed the largest changes in retention force and a greater variation between the different cycles and specimen. This behaviour is probably caused by a large fitting tolerance of the titanium spring. CONCLUSIONS: Attachment systems which possess a male and female component of different material composition are preferable. They show smaller changes in the retention force. For retention force increase and wear compensation, an attachment system should be adjustable.

Patient-reported outcomes of maxillary implant-supported overdentures compared with conventional dentures

OBJECTIVE The aim of the present prospective clinical study was to compare patient-reported outcomes for maxillary conventional dentures and maxillary implant-supported dentures. MATERIAL AND METHODS Twenty-one patients (6 women and 15 men) being edentulous in the maxilla and encountering problems with their existing dentures were included. Twelve patients (4 women and 8 men) received a new set of conventional dentures, due to insufficient dentures. In nine patients (2 women and 7 men), the existing dentures were adjusted by means of relining or rebasing. All patients received implant-supported dentures on two retentive anchors. In total, 42 implants were inserted in the anterior maxilla. The participants rated their satisfaction on their existing conventional dentures, 2 months after insertion of new conventional dentures and 2 months after insertion of implant-supported dentures. Thereby, patients responded to questionnaires capturing the oral health impact profile (OHIP) using visual analog scales. Seven domains (functional limitation, physical pain, psychological discomfort, physical, psychological and social disability and handicap) were assessed. Higher scores implied poorer patient satisfaction. In addition, the questionnaire involved the evaluation of cleaning ability, general satisfaction, speech, comfort, esthetics, stability, and chewing ability. Higher scores implied higher patient satisfaction. RESULTS Patient satisfaction significantly increased for implant-supported dentures compared with old dentures in all seven OHIP subgroups, as well as for cleaning ability, general satisfaction, ability to speak, comfort, esthetics, and stability (P < 0.05). The comparison of new conventional dentures and implant-supported dentures revealed a statistically significantly increased satisfaction for functional limitation (difference of 33.2 mm), psychological discomfort (difference of 36.7 mm), physical disability (difference of 36.3 mm), and social disability (difference of 23.5 mm), (P < 0.05). Additionally, general satisfaction, chewing ability, speech, and stability significantly improved in implant-supported dentures (P < 0.05). CONCLUSIONS Within the limits of this study, maxillary dentures retained by two implants provided some significant short-term improvements over conventional dentures in oral- and health-related quality of life.

Comparison of different designs of implant-retained overdentures and fixed full-arch implant-supported prosthesis on stress distribution in edentulous mandible - A computed tomography-based three-dimensional finite element analysis

A finite element analysis was used to compare the effect of different designs of implant-retained overdentures and fixed full-arch implant-supported prosthesis on stress distribution in edentulous mandible. Four models of an human mandible were constructed. In the OR (O'ring) group, the mandible was restored with an overdenture retained by four unsplinted implants with O'ring attachment; in the BC (bar-clip) -C and BC groups, the mandibles were restored with overdentures retained by four splinted implants with bar-clip anchor associated or not with two distally placed cantilevers, respectively; in the FD (fixed denture) group, the mandible was restored with a fixed full-arch four-implant-supported prosthesis. Models were supported by the masticatory muscles and temporomandibular joints. A 100-N oblique load was applied on the left first molar. Von Mises (σvM), maximum (σmax) and minimum (σmin) principal stresses (in MPa) analyses were obtained. BC-C group exhibited the highest stress values (σvM=398.8, σmax=580.5 and σmin=-455.2) while FD group showed the lowest one (σvM=128.9, σmax=185.9 and σmin=-172.1). Within overdenture groups, the use of unsplinted implants reduced the stress level in the implant/prosthetic components (59.4% for σvM, 66.2% for σmax and 57.7% for σmin versus BC-C group) and supporting tissues (maximum stress reduction of 72% and 79.5% for σmax, and 15.7% and 85.7% for σmin on the cortical and trabecular bones, respectively). Cortical bone exhibited greater stress concentration than the trabecular bone for all groups. The use of fixed implant dentures and removable dentures retained by unsplinted implants to rehabilitate edentulous mandible reduced the stresses in the periimplant bone tissue, mucosa and implant/prosthetic components. © 2013 Elsevier Ltd.

Implant-supported mandibular overdentures and cortical bone formation: clinical and radiographic results

PURPOSE: The aim of this study was to evaluate the hard and soft tissue parameters around implants supporting overdentures and the possible influence of increased periimplant bone density (IPBD) on implant success. MATERIALS AND METHODS: A total of 44 dental implants placed in the mandible of 12 patients were included in the study. Implants were divided in 2 groups in relation to the optically detected IPBD. Periimplant clinical and radiographic variables were collected over the period of 5 years. RESULTS: Periimplant clinical and radiographic parameters for all implants did not change significantly throughout the observation period (P > 0.05). Significant differences were observed between implants with and without IPBD for periimplant soft tissue parameters and Periotest values (P < 0.05). Implants with and without IPBD at 5-year control showed mean bone loss of 0.04 ± 0.48 mm and 0.55 ± 0.96 mm, respectively (P = 0.026). All density values decreased throughout the observation period, except maximal values for implants with IPBD that overcome the initial values at the 5-year control. CONCLUSIONS: Implants supporting overdentures were clinically successful over the period of follow-up. IPBD may be related to the maintenance of the periimplant bone level.

Evaluation of Stress Patterns Produced by Implant-Retained Overdentures and Implant-Retained Fixed Partial Denture

The purposes of this study were to photoelastically measure the biomechanical behavior of 4 implants retaining different cantilevered bar mandibular overdenture designs and to compare a fixed partial denture (FPD). A photoelastic model of a human edentulous mandible was fabricated, which contained 4 screw-type implants (3.75 x 10 mm) embedded in the parasymphyseal area. An FPD and 3 overdenture designs with the following attachments were evaluated: 3 plastic Hader clips, 1 Hader clip with 2 posterior resilient cap attachments, and 3 ball/O-ring attachments. Vertical occlusal forces of 100 N were applied between the central incisor and unilaterally to the right and left second premolars and second molars. Stresses that developed in the supporting structure were monitored photoelastically and recorded photographically. The results showed that the anterior loading, the overdenture with 3 plastic Hader clips, displayed the largest stress concentration at the medium implant. With premolar loading, the FPD and overdenture with 3 plastic Hader clips displayed the highest stresses to the ipsilateral terminal implant. With molar loading, the overdenture with 3 ball/O-ring attachments displayed the most uniform stress distribution in the posterior edentulous ridge, with less overloading in the terminal implant. It was concluded that vertical forces applied to the bar-clip overdenture and FPD created immediate stress patterns of greater magnitude and concentration on the ipsilateral implants, whereas the ball/O-ring attachments transferred minimal stress to the implants. The increased cantilever in the FPD caused the highest stresses to the terminal implant.

Maintenance of implant-supported maxillary prostheses: a 2-year controlled clinical trial

To analyze maintenance service of fixed maxillary prostheses and overdentures based on conventional gold bars or titanium bars and frameworks fabricated with computer-aided design/computer-assisted manufacture (CAD/CAM) technology.

[Implant-supported bridges in the edentulous jaw. Clinical aspects of a simple treatment concept]

Clinical aspects of a simple treatment concept with fixed prostheses in the edentulous jaw are described. Fixed implant-supported reconstructions in the edentulous jaw require multiple implants, are technically complex, aesthetically demanding and metal-ceramic solutions are expensive. Specific surgical techniques to enhance the hard and soft tissue conditions become often necessary. Thus the bar-supported overdenture may be preferred, because problems with aesthetics and alveolar ridge deficiencies can be solved more easily and the number of implants is reduced. Both, the "All-on-Four" technique and the "Procera implant bridge" are simple type of fixed prostheses, comparable to overdentures or complete dentures with regard to design and technology. They present a cost-effective alternative, with predictable aesthetics and optimum passive fit.

Implant-retained overdentures did not have a significant improvement in dietary intake

DESIGN: Randomised controlled trial.

INTERVENTION: Patients aged 65 or above edentate for a minimum of five years, with sufficient bone for two implants in the anterior mandible, were recruited. Those with systemic disease that contraindicated implants or had a low mini-mental state evaluation score were excluded. Patients in both groups had a standard maxillary complete denture fabricated. Patients randomised to the treatment group received a two-implant mandibular overdenture while those in the control group received a standard mandibular complete denture. Three 24-hour dietary recalls were collected by telephone interviews at baseline and at 12 months.

RESULTS: 255 patients were randomised: 128 received a standard complete denture (CD) and 127 a two-implant mandibular overdenture (IOD). 127 patients were available at 12-month follow up, 114 in the CD group and 103 in the IOD group. No significant between-group differences were found.

CONCLUSIONS: Although there is much evidence supporting the adoption of two-implant mandibular overdenture (IOD) treatment as the standard of care for edentate patients, this evidence does not include an improvement in dietary intake at one year for medically healthy independent edentate elders when given no specific dietary counselling.

An Alternative Section Method for Casting and Posterior Laser Welding of Metallic Frameworks for an Implant-Supported Prosthesis

Purpose: The aim of this study was to compare the accuracy of fit of three types of implant-supported frameworks cast in Ni-Cr alloy: specifically, a framework cast as one piece compared to frameworks cast separately in sections to the transverse or the diagonal axis, and later laser welded. Materials and Methods: Three sets of similar implant-supported frameworks were constructed. The first group of six 3-unit implant-supported frameworks were cast as one piece, the second group of six were sectioned in the transverse axis of the pontic region prior to casting, and the last group of six were sectioned in the diagonal axis of the pontic region prior to casting. The sectioned frameworks were positioned in the matrix (10 N(.)cm torque) and laser welded. To evaluate passive fit, readings were made with an optical microscope with both screws tightened and with only one-screw tightened. Data were submitted to ANOVA and Tukey-Kramer`s test (p < 0.05). Results: When both screws were tightened, no differences were found between the three groups (p > 0.05). In the single-screw-tightened test, with readings made opposite to the tightened side, the group cast as one piece (57.02 +/- 33.48 mu m) was significantly different (p < 0.05) from the group sectioned diagonally (18.92 +/- 4.75 mu m) but no different (p > 0.05) from the group transversally sectioned (31.42 +/- 20.68 mu m). On the tightened side, no significant differences were found between the groups (p > 0.05). Conclusions: Results of this study showed that casting diagonally sectioned frameworks lowers misfit levels of prosthetic implant-supported frameworks and also improves the levels of passivity to the same frameworks when compared to structures cast as one piece.

Comparative analysis of the fit of 3-unit implant-supported frameworks cast in nickel-chromium and cobalt-chromium alloys and commercially pure titanium after casting, laser welding, and simulated porcelain firings

This study compared the vertical misfit of 3-unit implant-supported nickel-chromium (Ni-Cr) and cobalt-chromium (Co-Cr) alloy and commercially pure titanium (cpTi) frameworks after casting as 1 piece, after sectioning and laser welding, and after simulated porcelain firings. The results on the tightened side showed no statistically significant differences. On the opposite side, statistically significant differences were found for Co-Cr alloy (118.64 mu m [SD: 91.48] to 39.90 mu m [SD: 27.13]) and cpTi (118.56 mu m [51.35] to 27.87 mu m [12.71]) when comparing 1-piece to laser-welded frameworks. With both sides tightened, only Co-Cr alloy showed statistically significant differences after laser welding. Ni-Cr alloy showed the lowest misfit values, though the differences were not statistically significantly different. Simulated porcelain firings revealed no significant differences.

Digital image correlation analysis of the load transfer by implant-supported restorations

This study compared splinted and non-splinted implant-supported prosthesis with and without a distal proximal contact using a digital image correlation method. An epoxy resin model was made with acrylic resin replicas of a mandibular first premolar and second molar and with threaded implants replacing the second premolar and first molar. Splinted and non-splinted metal-ceramic screw-retained crowns were fabricated and loaded with and without the presence of the second molar. A single-camera measuring system was used to record the in-plane deformation on the model surface at a frequency of 1.0 Hz under a load from 0 to 250 N. The images were then analyzed with specialist software to determine the direct (horizontal) and shear strains along the model. Not splinting the crowns resulted in higher stress transfer to the supporting implants when the second molar replica was absent. The presence of a second molar and an effective interproximal contact contributed to lower stress transfer to the supporting structures even for non-splinted restorations. Shear strains were higher in the region between the molars when the second molar was absent, regardless of splinting. The opposite was found for the region between the implants, which had higher shear strain values when the second molar was present. When an effective distal contact is absent, non-splinted implant-supported restorations introduce higher direct strains to the supporting structures under loading. Shear strains appear to be dependent also on the region within the model, with different regions showing different trends in strain changes in the absence of an effective distal contact. (C) 2011 Elsevier Ltd. All rights reserved.

Modified section method for laser-welding of ill-fitting cp Ti and Ni-Cr alloy one-piece cast implant-supported frameworks

P>This study aimed to verify the effect of modified section method and laser-welding on the accuracy of fit of ill-fitting commercially pure titanium (cp Ti) and Ni-Cr alloy one-piece cast frameworks. Two sets of similar implant-supported frameworks were constructed. Both groups of six 3-unit implant-supported fixed partial dentures were cast as one-piece [I: Ni-Cr (control) and II: cp Ti] and evaluated for passive fitting in an optical microscope with both screws tightened and with only one screw tightened. All frameworks were then sectioned in the diagonal axis at the pontic region (III: Ni-Cr and IV: cp Ti). Sectioned frameworks were positioned in the matrix (10-Ncm torque) and laser-welded. Passive fitting was evaluated for the second time. Data were submitted to anova and Tukey-Kramer honestly significant difference tests (P < 0 center dot 05). With both screws tightened, one-piece cp Ti group II showed significantly higher misfit values (27 center dot 57 +/- 5 center dot 06 mu m) than other groups (I: 11 center dot 19 +/- 2 center dot 54 mu m, III: 12 center dot 88 +/- 2 center dot 93 mu m, IV: 13 center dot 77 +/- 1 center dot 51 mu m) (P < 0 center dot 05). In the single-screw-tightened test, with readings on the opposite side to the tightened side, Ni-Cr cast as one-piece (I: 58 center dot 66 +/- 14 center dot 30 mu m) was significantly different from cp Ti group after diagonal section (IV: 27 center dot 51 +/- 8 center dot 28 mu m) (P < 0 center dot 05). On the tightened side, no significant differences were found between groups (P > 0 center dot 05). Results showed that diagonally sectioning ill-fitting cp Ti frameworks lowers misfit levels of prosthetic implant-supported frameworks and also improves passivity levels of the same frameworks when compared to one-piece cast structures.

Effect of abutment's height and framework alloy on the load distribution of mandibular cantilevered implant-supported prosthesis

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