Nobuhiro Yoda

Development of in vivo measuring system of the pressure distribution under the denture base of removable partial denture

PURPOSE To develop a system to measure the pressure distribution under the base of a removable partial denture (RPD) and to apply it in vivo. METHODS A tactile sensor sheet with 100 sensing points and a measuring system (I-SCAN, Nitta, Osaka, Japan) were used. The sensor was calibrated before being applied in vivo. A subject with a mandibular RPD (Kennedy class II, division 1) participated in this study, and the RPD was duplicated as the experimental denture. The basal surface at distal extension was accommodated to the sensor in a manner similar to direct relining. Measurements were performed with three patterns of occlusal rest design (mesial and distal rests, mesial rest only, and without a rest) during maximal voluntary clenching (MVC) and gum chewing. RESULTS The calibration measurements showed that the output value from each sensing point and total output of sensing points were positively correlated with the applied load. The pressures recorded in vivo varied depending on the locations of sensing points on the basal surface of the denture. During MVC the pressure distribution changed with the clenching level, and the highest pressure was registered near the residual ridge crest. The pressure distribution also changed according to the number of occlusal rests. The load center shifted about 2mm during MVC and about 4mm during gum chewing. CONCLUSION The measuring system developed here enabled us to measure the pressure distribution under the denture base of RPD. The pressure distribution varied along with the design of the occlusal rest.

Biological-data-based finite-element stress analysis of mandibular bone with implant-supported overdenture

BACKGROUND This study aimed to evaluate the stress distribution in a mandibular bone with an implant-supported overdenture by a biological-data-based finite element analysis (FEA) utilizing personal CT images and in vivo loading data, and to evaluate the influence of the number and alignment of implants and bone conditions on the stress in peri-implant bone. METHODS FEA models of a mandible were constructed for two types of overdentures: 4 implants supported overdenture (4-OD) and 2 implants supported overdenture (2-OD). The geometry of these models was constructed from CT images of a subject, who wore an implant-supported overdenture. The magnitude and direction of the loads on the implants for two types of overdentures during the maximal voluntary clenching were measured with 3D force transducers. FEA using these loads was carried out to observe stress distributions in peri-implant bone. RESULTS Higher stress was observed in cortical bone around the implant neck. Stress in peri-implant bone for 4-OD was reduced in comparison with those for the 2-OD. For the 4-OD, notwithstanding such reduction of the stress, the stress concentrated at the cortical bone around the implant aligned with large deviation from load direction. CONCLUSIONS In this study, biological data from a certain subject was successfully duplicated to the FEA models. The results demonstrate the mechanical prominence of using more implants. Even in 4 implants model, high stress was found around an implant with a large inclination and with thin cortical bone. This suffices to demonstrate the capability and usefulness of the biological-data-based FEA.

Stress distribution in the peri-implant bone with splinted and non-splinted implants by in vivo loading data-based finite element analysis.

The aim of this study was to evaluate stress distribution in peri-implant bone and to investigate the influence of splinting implants by finite element analysis (FEA) with in vivo loading data. The magnitude and direction of the force exerted on implants during maximal voluntary clenching of a subject were recorded with 3-D piezoelectric force transducers. FEA using in vivo loading data was conducted on splinted and non-splinted models with two implants. Overall, the splinted model reduced stress in peri-implant bone in comparison with the non-splinted model.

In vivo load measurement for evaluating the splinting effects of implant-supported superstructures: a pilot study.

The purpose of this in vivo study was to evaluate the biomechanical effects of splinting of implant-supported superstructures using piezoelectric transducers to measure the three-dimensional forces exerted on implants supporting fixed superstructures. Measuring devices were set into the implant fixtures at the mandibular right second premolar and first molar. During clenching, force magnitudes were allocated more evenly to the two implants if they were splinted compared with the unsplinted control implants. However, this equalization of load distribution was not apparent during wax biting. Splinting of implant-supported fixed superstructures affects the force exerted on implants, especially during clenching.

Role of implant configurations supporting three‐unit fixed partial denture on mandibular bone response: biological‐data‐based finite element study

Implant-supported fixed partial denture with cantilever extension can transfer the excessive load to the bone around implants and stress/strain concentration potentially leading to bone resorption. This study investigated the effects of implant configurations supporting three-unit fixed partial denture (FPD) on the stress and strain distribution in the peri-implant bone by combining clinically measured time-dependent loading data and finite element (FE) analysis. A 3-dimensional mandibular model was constructed based on computed tomography (CT) images. Four different configurations of implants supporting 3-unit FPDs, namely three implant-supported FPD, conventional three-unit bridge FPD, distal cantilever FPD and mesial cantilever FPD, were modelled. The FPDs were virtually inserted to the molar area in the mandibular FE models. The FPDs were loaded according to time-dependent in vivo-measured 3-dimensional loading data during chewing. The von Mises stress (VMS) and equivalent strain (EQS) in peri-implant bone regions were evaluated as mechanical stimuli. During the chewing cycles, the regions near implant necks and bottom apexes experienced high VMS and EQS than the middle regions in all implant-supported FPD configurations. Higher VMS and EQS values were also observed at the implant neck region adjacent to the cantilever extension in the cantilevered configurations. The patient-specific dynamic loading data and CT-based reconstruction of full 3D mandibular allowed us to model the biomechanical responses more realistically. The results provided data for clinical assessment of implant configuration to improve longevity and reliability of the implant-supported FPD restoration.

Effect of attachment type on load distribution to implant abutments and the residual ridge in mandibular implant-supported overdentures

This study aimed to investigate the effect of attachment type on the load transmitted to implants and the residual ridge in a mandibular two-implant-supported overdenture in a model study. Ball attachments, locator attachments, and round-bar attachments were selected and examined. Static and dynamic vertical loads of 100 N were applied in the right first molar region. The load on the implants was measured by piezoelectric three-dimensional force transducers, and the load on the residual ridge beneath the denture base was measured using a tactile sheet sensor. The load on the implants with ball attachments was significantly higher than that with the other two attachments. The load on the residual ridge with round-bar attachments was significantly higher than that with the other two attachments. Our findings indicate that the three-dimensional load on implants and the residual ridge beneath the denture base is significantly associated with the type of attachment used in implant-supported overdentures.

An in vivo study on load distribution in different implant configurations for supporting fixed partial dentures

PURPOSE The aims of this study were to develop a device for in vivo measurement of three-dimensional (3D) loads on implants and to investigate the effects of implant configuration on the load distribution under a three-unit fixed partial denture (FPD). MATERIALS AND METHODS A 67-year-old female patient with three implants (in the mandibular left second premolar, first molar, and second molar regions) was recruited. Four implant configurations for a three-unit FPD depending on the number and position of the implants were considered in this study. They included a three-implant prosthesis and three types of two-implant prosthesis: a central pontic, posterior cantilever, and anterior cantilever, with the same superstructure (splinted three crowns) for the same occlusal contact. Customized abutments and 3D piezoelectric force transducers were fixed to the implants of the four configurations with the superstructure. The loads on the implants were recorded during maximum voluntary clenching (MVC-test) and when chewing a piece of chewing gum (GUMtest). RESULTS The occlusal forces on the dental arch during MVC-test with the four implant configurations did not exhibit significant differences. In the three-implant prosthesis, there were no significant differences in the mean maximum resultant load on each implant in both tests. In the central pontic, the load on the second premolar was significantly greater than that on the second molar in the MVC-test but there were no significant differences in the GUM-test. High loads were detected on the first molar in both the posterior cantilever and anterior cantilever. The highest load was detected on the first molar in the posterior cantilever during the GUMtest. CONCLUSION The in vivo 3D load-measuring device using the piezoelectric force transducers enabled the measurement of the functional load on implants supporting a FPD. The results suggested, within the limitations of this study, that a three-implant prosthesis and central pontic provide biomechanically beneficial designs compared with the posterior cantilever and anterior cantilever in terms of the equal distribution of loads on supporting implants.

Bone morphological effects on post-implantation remodeling of maxillary anterior buccal bone: A clinical and biomechanical study.

PURPOSE This study combines clinical investigation with finite element (FE) analysis to explore the effects of buccal bone thickness (BBT) on the morphological changes of buccal bone induced by the loaded implant. METHODS One specific patient who had undergone an implant treatment in the anterior maxilla and experienced the buccal bone resorption on the implant was studied. Morphological changes of the bone were measured through a series of cone-beam computed tomography (CT) scans. A three-dimensional heterogeneous nonlinear FE model was constructed based on the CT images of this patient, and the in-vivo BBT changes are correlated to the FE in-silico mechanobiological stimuli; namely, von Mises equivalent stress, equivalent strain, and strain energy density. The anterior incisory bone region of this model was then varied systematically to simulate five different BBTs (0.5, 1.0, 1.5, 2.0, and 2.5mm), and the optimal BBT was inversely determined to minimize the risk of resorption. RESULTS Significant changes in BBTs were observed clinically after 6 month loading on the implant. The pattern of bone resorption fell into a strong correlation with the distribution of mechanobiological stimuli onsite. The initial BBT appeared to play a critical role in distributing mechanobiological stimuli, thereby determining subsequent variation in BBT. A minimum initial thickness of 1.5mm might be suggested to reduce bone resorption. CONCLUSIONS This study revealed that the initial BBT can significantly affect mechanobiological responses, which consequentially determines the bone remodeling process. A sufficient initial BBT is considered essential to assure a long-term stability of implant treatment.

Simulation of multi-stage nonlinear bone remodeling induced by fixed partial dentures of different configurations: a comparative clinical and numerical study

This paper aimed to develop a clinically validated bone remodeling algorithm by integrating bone’s dynamic properties in a multi-stage fashion based on a four-year clinical follow-up of implant treatment. The configurational effects of fixed partial dentures (FPDs) were explored using a multi-stage remodeling rule. Three-dimensional real-time occlusal loads during maximum voluntary clenching were measured with a piezoelectric force transducer and were incorporated into a computerized tomography-based finite element mandibular model. Virtual X-ray images were generated based on simulation and statistically correlated with clinical data using linear regressions. The strain energy density-driven remodeling parameters were regulated over the time frame considered. A linear single-stage bone remodeling algorithm, with a single set of constant remodeling parameters, was found to poorly fit with clinical data through linear regression (low