Finite element stress analysis of the effect of short implant usage in place of cantilever extensions in mandibular posterior edentulism.

Although the destructive effect of cantilevered implant supported fixed partial prosthesis is well known, in some cases usage of cantilever extension seems to be inevitable for many clinicians. The purpose of this study was to evaluate the effect of additional placement of a shorter implant in place of a cantilever extension on stress distribution compared with cantilevered fixed prosthesis in mandibular posterior edentulism. A mandibular Kennedy II finite element model was constructed. Six different implant supported fixed partial prosthesis were designed according to two main configurations; anterior and posterior cantilever extensions compared with the placement of additional shorter implant configurations. An oblique occlusal load of 400 N was applied. Tensile and compressive stress values in the cortical bone surrounding the cervical regions of implants and Von Misses stress values in the implants were evaluated. Significant lower stress values were recorded at the shorter implant placement configurations compared with the cantilevered prosthesis. Posterior cantilever extension performed higher stress values than the anterior counterpart. In clinical applications where cantilevered fixed partial prosthesis seems to be inevitable because of anatomical restrictions and/or complications such as loss of implant, an additional placement of a shorter implant should be considered.

The influence of the location of load transfer on strains around implants supporting four unit cement-retained fixed prostheses: in vitro evaluation of axial versus off-set loading.

Prudent control of the biomechanical load on dental implants is imperative to achieve long-term clinical success. The design of the final prosthesis and location of force transmission have a definitive influence on the quantification of induced strains and load partitioning among implants. While axial loading of implants generate an even distribution of stresses in the bone around implants, off-set loading, which is particularly observed in screw retained prosthesis increases the stresses at the bone-implant interface. This study evaluated the cervical strains on dental implants supporting four unit cement retained fixed prostheses under 50 N static axial and off-set loading conditions. As the type of strains are also dependent on the point of load transfer, design of the prosthesis and implant positioning, the study comprised the evaluation of induced strains through a simulation of five cement retained prosthetic options. The results revealed that off-set loading increases the magnitude of strains. However, it was not significant for all configurations (P < 0.05). This finding emphasizes the accompanying effect of implant location, angulation and macrogeometry of the prosthesis and, that the biomechanical evaluation of affecting factors is a multifaceted phenomenon.

Finite element stress analysis of the influence of staggered versus straight placement of dental implants.

Bending moments resulting from non-axial overloading of dental implants may cause stress concentrations exceeding the physiologic supporting capacity of cortical bone, leading to various kinds of failures. The aim of this study was to evaluate the effect of staggered (offset, tripodization) implant placement configuration and placement of wider-diameter implants in a straight-line configuration in mandibular posterior edentulism. A mandibular Kennedy Class II partially edentulous finite element model was constructed. Seven different partial fixed prostheses supported by 3 implants were designed according to 2 main configurations: straight-line or staggered implant placement. In 5 of the designs, implants with various diameters and length were placed along a straight line. In the other 2 models, offset placement of the middle implant buccally and lingually was simulated. A 400 N static load was applied perpendicular to the buccal inclination of the buccal cusps on each unit. Tensile and compressive stress values on cortical bone in the cervical region of the implants were evaluated. Lower stress values were recorded for the configuration with wider implants placed in a straight line. Other configurations, including staggered implant placement, produced similar stress values. Despite the offset implant placement, the stresses were not decreased; however, straight placement of wider implants may decrease bending moments.

Evaluation of the effect of the residual bone angulation on implant-supported fixed prostheses in mandibular posterior edentulism. Part I: Spiral computed tomography study.

Dental implants are usually angulated buccolingually because of the anatomy of the residual bone in mandibular posterior edentulous cases. Although angulated dental implants compromise the construction of implant-supported prostheses, the effect of buccolingual angulation of the residual bone has not been clearly stated. This study is performed to determine the biomechanical effect of buccolingual angulation. The goal was to reveal the actual buccolingual angulation values of the residual bone in which implants were to be placed. Thirty mandibular Kennedy I and II cases comprised of forty edentulous posterior regions with missing second premolars and first, second, and third molars were included. Buccolingual angulation values along the 28 mm of residual bone were measured on 1-mm spacing cross-sectional images of spiral computed tomography. Paired sample t test was used for the statistical analysis. The minimum angulation values at the second premolar, first molar, and second molar region were 0 degrees, 3 degrees, and 9 degrees, respectively. The average angulation values were 4 degrees, 10 degrees, and 15 degrees, respectively, and the maximum angulation values were 11 degrees, 18 degrees, and 22 degrees, respectively. The ability to measure the buccolingual angulation of mandibular posterior residual bone before dental implantation may help the clinician at the implant treatment-planning phase.

Evaluation of the effect of the residual bone angulation on implant-supported fixed prosthesis in mandibular posterior edentulism. Part II: 3-D finite element stress analysis.

Buccolingual angulation of the mandibular posterior edentulous region may affect the prosthetic load conditions, so as to cause high stress concentrated areas that may easily lead to failure. The aim of this study was to evaluate the effect of various predetermined buccolingual angulation values on stress distribution in the mandibular posterior edentulous region restored with implant-supported fixed partial dentures, using three-dimensional finite element analysis. Stress analyses were performed applying 400N oblique force to implant-supported fixed prosthesis. Stress analyses indicated tensile stress values on the buccal surface and compressive stress values on the lingual surface of cortical bone were increased as the angulation of the edentulous bone increased (especially corresponding to the cervical region of the implants). Compressive stress values, observed where two implants were placed at the second premolar and second molar regions (5-7 design) and first and second molar regions (6-7 design), respectively, were very close to or even exceeded the ultimate compressive strength of bone. It is concluded that when a definite buccolingual angulation is added to other existing risk factors such as bruxism, placing an implant for every missing tooth might reduce the high stress concentration areas.

A multidisciplinary approach to single-tooth, implant-supported prostheses: a report of three cases.

Dental implants and their successful long-term results have begun a new era in dentistry. In recent years, the increasing trend of using dental implants at single-tooth edentulous cases has been taken into consideration. Although treatment goals and objectives are similar for both prosthodontists and orthodontists, they rarely cooperate. Usually prosthodontists are in need of preprosthodontic orthodontic preparations for younger patients. In this paper, different preprosthodontic orthodontic procedures that may be required before the placement of implants at single-tooth edentulous cases are presented. In the first and second cases, decreased mesio-distal space was regained by different orthodontic treatment methods, whereas the occlusal relationship was corrected for better function in the third case.

An experimental analysis of the stresses on the implant in an implant-tooth-supported prosthesis: a technical note.

When a natural tooth connected to an implant abutment by a framework is displaced within physiologic limits under functional loads, the superstructure acts as a cantilever moment arm and the implant is loaded additionally during that moment effect. The effects of a deflecting support connected to an IMZ implant, with either the IMC resilient or the titanium rigid element, were evaluated through an experimental model. The strain values measured when the moment arm was not allowed to deflect were only 30% lower than the strains measured when it was deflected within the limits of physiologic tooth mobility. The IMC was effective and achieved a reduction in the cervical strains up to 60% when compared with the rigid connector.

Efficacy of the intramobile connector in implant tooth-supported fixed prostheses: an experimental stress analysis.

An experimental model was designed to evaluate the effects of the intramobile connector in reducing stress concentration in an IMZ implant in fixed connection with a natural tooth abutment. The study analyzed the stresses produced at the cervical level of the implant when the superstructure arm was deflected within the limits of physiologic mobility under static axial loads. The designed experimental model was sensitive to changes in strain data with the applied loads and different internal elements. The intramobile connector resilient component reduced strain up to 60% compared to the rigid internal element.

An analysis of edentulous maxillary arch width and palatal height.

This study involving 500 edentulous patients (250 males, 250 females) was undertaken to introduce a dimensionless factor termed the "palatal height ratio," defined as the ratio of the width of the edentulous maxillary arch to the height of the palate. The authors categorized the height, width, and anteroposterior dimensions of the edentulous maxillae. Measurements were made on diagnostic casts at five defined points. The difference between males and females was statistically analyzed and the variables were categorized. The results of this study may be helpful for a better standardization of the same variables in future studies.