Effects of prosthesis design and impression techniques on human cortical bone strain around oral implants under load.

PURPOSE: The purpose of this study was to evaluate the effects of two different prosthetic designs (screw-retained versus cement-retained) and two impression techniques (open versus closed tray) on bone-level strains around implants. MATERIALS AND METHODS: Two Ø 4.1 mm x 10 mm Straumann implants were placed in the bilateral fibulas of six fresh cadavers; bone segments were removed en bloc. Twelve implant-level and six abutment-level (18 total) working casts were made to fabricate fixed partial dentures, resulting in three test groups: Group 1: closed-tray technique/implant-level model/screw-retained prostheses; Group 2: closed-tray technique/abutment-level model/cement-retained prostheses; Group 3: open-tray technique/implant-level model/screw-retained prostheses. Linear strain-gauges were bonded to the cortical bone between implants and the lateral wall of the fibula in close proximity to the implant necks in each bone fragment. Strain-gauge signals were digitized by a data acquisition system and corresponding software at a sample rate of 10 KHz, simultaneously monitored from the computer during application of an external static load of 150 N on the middle of the pontic, using a loading frame. RESULTS: The approximal and lateral strains were extremely similar in both prosthetic groups (p>0.05). Within-group comparisons for the indirect impression technique showed that approximal and lateral strains in screw- and cement-retained prostheses were similar (p>0.05). Neither the prostheses design nor the impression technique had any discernable effect on bone-level strain. CONCLUSION: Strains on the cortical bone around two implant supported, 3-unit screw- or cement-retained fixed prostheses, fabricated either by direct or indirect impression techniques on Straumann dental implants, are similar under a 150 N static load.

Dynamic fatigue resistance of implant-abutment junction in an internally notched morse-taper oral implant: influence of abutment design.

PURPOSE: To compare dynamic fatigue resistance of one- and two-piece abutments connected to internally notched morse-taper oral implants. MATERIAL AND METHODS: Sixteen synOcta ITI implants were tightened into two metal models. SynOcta abutments for cement-retained restorations and solid abutments were divided into two equal groups and were torque-tightened into the implants. Each implant received a cement-retained crown. Cyclic dynamic axial and lateral peak loads of 75+/-5 N were applied on the implants for a duty of 500,000 cycles at 0.5 Hz, and at an angle of 20 degrees. Prior to the experiments and at each 100,000 cycles of loading, periotest values (PTVs) were measured. Removal torque values (RTVs) of the abutments were also measured with a custom-made torque device at the termination of the experiment. RESULTS: All abutments and implants were clinically immobile and without any signs of mechanical failure. The final PTVs for both abutments were similar and the difference between groups was insignificant (P>0.05). The RTVs of solid abutments were significantly higher than synOcta abutments (P<0.05). CONCLUSION: Predictable long-term clinical results can be achieved with solid abutments and synOcta abutments for cement-retained restorations. Solid abutments possess higher removal torque resistance than synOcta abutments when connected to synOcta ITI implants.

Force transmission of one- and two-piece morse-taper oral implants: a nonlinear finite element analysis.

PURPOSE: To compare force transmission behaviors of one-piece (1-P) and two-piece (2-P) morse-taper oral implants. MATERIAL AND METHODS: A three-dimensional finite element model of a morse-taper oral implant and a solid abutment was constructed separately. The implant-abutment complex was embedded in a phi 1.5 cm x 1.5 cm acrylic resin cylinder. Vertical and oblique forces of 50 N and 100 N were applied on the abutment and solved by two different analyses. First, contact analysis was performed in the implant-abutment complex to evaluate a 2-P implant. Then, the components were bonded with a separation force of 10(20) N to analyze a 1-P implant. RESULTS: Von Mises stresses in the implant, principal stresses, and displacements in the resin were the same for both designs under vertical loading. Under oblique loading, principal stresses and displacement values in the resin were the same, but the magnitudes of Von Mises stresses were higher in the 2-P implant. The principal stress distributions around both implants in the acrylic bone were similar under both loading conditions. CONCLUSION: 2-P implants experience higher mechanical stress under oblique loading. Nevertheless, the 1-P- or 2-P morse-taper nature of an implant is not a decisive factor for the magnitude and distribution of stresses, and displacements in supporting tissues.

Two-year follow-up of a patient with oligodontia treated with implant- and tooth-supported fixed partial dentures: a case report.

Dental implants have become an accepted treatment modality for aging patients with either completely or partially edentulous arches. However, growing patients with congenitally missing primary and/or permanent teeth often need dental implant treatment, even before puberty, for optimum functional and/or psychosocial development. From a developmental perspective, dental implants cannot accompany the physiologic differentiation of the alveolar bone because of the difference in anchorage between an osseointegrated dental implant and a tooth in bone. Nevertheless, reports in the literature suggest that dental implants can be used successfully in partially and completely edentulous arches affected by congenital disorders such as ectodermal dysplasia. In this case report, a multidisciplinary team approach, which included an orthodontist, an oral surgeon, and prosthodontists, in the treatment of a patient with oligodontia is discussed. The orthodontic and prosthodontic treatment sequence, growth analysis from age 14 to 18 years, and successful therapy of an implant associated with late failure is presented.

Evaluation of the mechanical characteristics of the implant-abutment complex of a reduced-diameter morse-taper implant. A nonlinear finite element stress analysis.

The purpose of this study was to evaluate the mechanical characteristics of the implant-abutment connection of a reduced-diameter ITI dental implant. A finite element model of a slashed circle 3.3 mm x 10 mm ITI solid-screw implant and a 6 degrees solid abutment 4 mm in height was constructed, and the implant-abutment complex was embedded vertically in the center of a slashed circle 1.5 cm x 1.5 cm acrylic cylinder. Static vertical and oblique loads of 300 N were applied in separate load cases. The contact area was defined between the implant-abutment connection and nonlinear finite element stress analysis was performed. The magnitude and distribution of Von Mises stresses and displacement characteristics were evaluated. In vertical loading, Von Mises stresses concentrated around the implant-abutment connection at the stem of the screw and around the implant collar. Oblique loading resulted in a 2-fold increase in stresses at the implant collar, which was close to the yield strength of titanium. Displacement values under both loading conditions were negligible. We conclude that, in a reduced-diameter ITI dental implant, vertical and oblique loads are resisted mainly by the implant-abutment joint at the screw level and by the implant collar. The neck of this implant is a potential zone for fracture when subjected to high bending forces. The reduced-diameter ITI dental implant might benefit from reinforcement of this region.

Facemask therapy with rigid anchorage in a patient with maxillary hypoplasia and severe oligodontia.

In this report, we describe the treatment of a 10-year-old girl with a Class III skeletal relationship with maxillary hypoplasia and severe oligodontia. The maxillary arch was in a complete crossbite relationship with the mandibular arch. The treatment plan called for displacing the maxillary complex anteriorly with a facemask. Because of the lack of available teeth, a rigid anchorage implant was used in combination with the remaining teeth to provide anchorage. A titanium lag screw was placed in the maxillary alveolus. Three weeks later, 800 g of orthodontic force was applied. A significant anterior displacement of the nasomaxillary complex was achieved with the facemask. At the end of treatment, a temporary removable partial denture was placed.

Comparison of non-linear finite element stress analysis with in vitro strain gauge measurements on a Morse taper implant.

PURPOSE: To understand the mechanical and biomechanical behavior of dental Implants, validation of stress and strain measurements is required. The objective of this study was to compare a non-linear finite element stress analysis with in vitro strain gauge measurements on strains in an implant-abutment complex. MATERIALS AND METHODS: Strain gauges were bonded to an Implant-abutment complex and embedded in polymethylmethacrylate resin. A force of 75 N was applied vertically and laterally in separate load cases, and strains were recorded with a strain indicator. Then, a finite element model of the strain gauge model was constructed. Contact analysis with normal contact detection and separation behavior was performed between the Implant and the abutment. The same loading protocol was followed, and strains were recorded at regions where gauges were bonded. RESULTS: Under vertical loading, the qualification and quantification of strains were similar in both methods. Under lateral loading, the measurement of strains on the abutment and in the resin were similar in both methods. However, strains on the implant collar as measured by non-linear finite element analysis were higher. DISCUSSION AND CONCLUSION: There is a compatibility between non-linear finite element stress analysis and in vitro strain gauge analysis on the measurement of strains under vertical loading. However, there are differences between the methods in the quantification of strains on the collar of Implants under lateral loading.

The use of computerized tomography for diagnosis and treatment planning in implant dentistry.

Preoperative radiographic imaging of recipient sites for implant placement is imperative to obtain a functional and aesthetic implant-supported prosthesis. Although conventional radiographic techniques have inherent problems that restrict accurate imaging, the main drawback of panoramic and periapical radiography is the two-dimensional image. Computerized tomography provides cross-sectional radiographic images that facilitate proper assessment of potential recipient sites for implant placement. This paper reviews the role of computerized tomography in implant dentistry.

In vitro strain gauge analysis of axial and off-axial loading on implant supported fixed partial dentures.

The purpose of this study was to compare the in vitro strains on dental implants supporting cement-retained fixed partial dentures under axial and off-axial loading conditions. Ten implants incorporating strain gauges were placed in a certain configuration to simulate different clinical situations and were embedded in an experimental model. Two implant supported three-unit fixed partial dentures were fabricated on four groups of implants, and each group consisted of seven restorations. The prostheses were cemented with a temporary cement. Fifty N vertical load was applied on predetermined axial and off-axial loading locations on the prostheses. Strain indicator readings were recorded at a standardized time following each loading sequence. The point of load transfer affected strains on implants. For all prosthetic designs, off-axial loading generated more strain than axial loading on implants (P < 0.05). In comparison with axial loading, off-axial loading causes bending of the implants that may affect bone loss around the implant collar. Axial loading of implants should be provided by using wide diameter implants, narrow occlusal tables, and proper occlusal contacts on implant restorations.

Comparison of uniaxial resistance forces of cements used with implant-supported crowns.

PURPOSE: Provisional cements are commonly used to facilitate retrievability of cement-retained fixed implant restorations. While the functional life spans of these cements are unpredictable, the relative retentiveness of various permanent and provisional cements between dental alloys and titanium abutments is not well documented. The aim of this study was to compare the uniaxial resistance forces of permanent and provisional luting cements used for implant-supported crowns. MATERIALS AND METHODS: Seven samples on 4 different abutments (a total of 28 crowns) were cast using a gold-platinum-palladium alloy. The crowns were cemented with 3 different provisional, polycarboxylate, and glass-ionomer cements and 1 zinc phosphate cement. After storage of samples in artificial saliva for 24 hours, tensile tests were performed. RESULTS: While the highest uniaxial resistance forces were recorded for polycarboxylate cements, provisional cements exhibited significantly lower failure strengths (P < .05). The uniaxial resistance force of cements on different abutments exhibited notably different trends; however, more force was required to remove crowns cemented to long abutments (P < .05). DISCUSSION: Glass-ionomer and zinc phosphate cements may be used to increase the maintenance of implant-supported crowns. Temporary cementation of such restorations may necessitate frequent recementation, particularly for restorations on short abutments. CONCLUSIONS: Temporary cementation may be more suitable for restorations supported by multiple implants.

One-year follow-up of an implant with early radiographic signs of loss of osseointegration: case report.

BACKGROUND: Failures in dental implant treatment are classified as early and late and depend on certain complications. Proposed preventions and treatment modalities for late complications have been comprehensively reviewed in the literature. Since early implant failures are characterized by lack of osseointegration, generally, removal of the implant is suggested to prevent extensive bone loss that would further complicate implant placements in future. PURPOSE: This case report presents the controversy between clinical findings and radiographic examinations in evaluating the nature of contact between an implant surface and the bone during the healing period. MATERIALS AND METHODS: In one patient scheduled for implant treatment in both jaws, four maxillary and two mandibular implants showed excellent healing, whereas one mandibular implant showed an extensive radiolucent area indicating early failure after 6 weeks of healing. The latter implant was clinically stable and was not removed. RESULTS: Radiographic evaluation 1 year later showed no sign of peri-implant radiolucency of the mandibular implant as seen after primary healing. CONCLUSION: When the bone-implant interface appears to be compromised radiographically but not clinically, such implants may have a favorable prognosis through a currently unknown biologic host response.

A comparison of three-dimensional finite element stress analysis with in vitro strain gauge measurements on dental implants.

PURPOSE: The purpose of this study was to evaluate the compatibility of three-dimensional finite element stress analysis and in vitro strain gauge analysis in the measurement of strains on a dental implant. MATERIALS AND METHODS: Two vertically placed implants embedded in a poly(methyl methacrylate) model were used. Strain gauges were bonded to the cervical parts of the implants, and seven cement-retained fixed partial dentures were fabricated. A three-dimensional model of the strain gauge analysis model was constructed, and an additional model in which human bone simulation was provided was also constructed. A static vertical load of 50 N was applied at certain locations to simulate centrally positioned axial and laterally positioned axial loading for strain gauge analysis and three-dimensional finite element stress analysis. RESULTS: Statistically significant increases in strain levels were recorded between loading types in the strain gauge analysis (P < .05). Strains obtained from strain gauge analysis were higher than for three-dimensional finite element stress analysis. There was a remarkable difference between the two finite element models under the conditions of laterally positioned axial loading. CONCLUSION: There are differences regarding the quantification of strains between strain gauge analysis and three-dimensional finite element stress analysis. However, there is a mutual agreement and compatibility between three-dimensional finite element stress analysis and in vitro strain gauge analysis on the determination of the quality of induced strains under applied load.

A surgical guide for accurate mesiodistal paralleling of implants in the posterior edentulous mandible.

Malaligned implants often complicate the clinical and laboratory procedures employed for the fabrication of superstructures. Due to improper load distribution, an overall increase in stress concentrations on supporting implants may occur; in the long run, this may compromise the maintenance of the bone-implant interface. The utilization of surgical stents is imperative for optimum implant installation. This article describes a modified surgical stent that serves as a guide to proper mesiodistal paralleling of dental implants.

Comparative evaluation of the effect of diameter, length and number of implants supporting three-unit fixed partial prostheses on stress distribution in the bone.

OBJECTIVES: The purpose of this study was to compare the effects of the diameter, the length and the number of implants on stress distribution in the bone around the implants supporting three-unit fixed partial prostheses in the mandibular posterior edentulism. MATERIALS AND METHOD: A mandibular Kennedy II three-dimensional finite element model was constructed. Four fixed partial prostheses with two terminal implant supports of various lengths and diameters, and two fixed partial prostheses with three implant supports of various lengths were designed. In separate load cases, 400 N oblique, 200 N vertical, and 57 N horizontal forces were simulated. The tensile and the compressive stress values in the cortical bone around the collar of the implants and Von Mises stresses in the implants were evaluated. RESULTS: Although the change in the length of implants did not decrease the stress levels, lower tensile and compressive stress values were observed in the bone for wider implant placement configurations. Similar stress distributions and close stress levels were observed for two wider implant supports in comparison with the three-implant-supported fixed partial prostheses. CONCLUSION: With the use of two implants of 4.1-mm diameter and 10-mm length as terminal supports for three-unit fixed prostheses, the magnitude and the distribution of stresses in the cortical bone around the implant collar is within the normal physiological limits.