Ultrasonic-assisted drilling of cortical and cancellous bone in a comparative point of view.

Background: During bone drilling, a common procedure in clinical surgeries, excessive heat generation and drilling force can cause damage to bone tissue, potentially leading to failure of implants and fixation screws or delayed healing. With this in mind, the aim of this study was to evaluate the efficiency of ultrasonic-assisted drilling compared to conventional drilling as a potential method for bone drilling. Methods: This study examined optimal drilling parameters based on previous findings and investigated both cortical and cancellous bone. In addition to evaluating drilling force and temperature elevation, the effects of these factors on osteonecrosis and micro-crack formation were explored in ultrasonic-assisted and conventional drilling through histopathological assessment and microscopic imaging. To this end, three drilling speeds and two drilling feed-rates were considered as variables in the in vitro experiments. Furthermore, numerical modeling provided insight into temperature distribution during the drilling process in both methods and compared three different vibration amplitudes. Results: Although temperature elevations were lower in the conventional drilling, ultrasonic-assisted drilling produced less drilling force. Additionally, the latter method resulted in smaller osteonecrosis regions and did not produce micro-cracks in cortical bone or structural damage in cancellous bone. Conclusions: Ultrasonic-assisted drilling, which caused less damage to bone tissue in both cortical and cancellous bone, was comparatively more advantageous. Notably, this study demonstrated that to determine the superiority of one method over the other, we cannot rely solely on temperature variation results. Instead, we must consider the cumulative effect of both temperature elevation and drilling force.

A new look toward crown-to-implant ratio.

PURPOSE: To clarify how crown-to-implant ratio (C-I ratio) influences the bone biomechanically with its two components: crown height and implant length. METHODS: This three-dimensional finite element study was performed in two phases. The first phase aimed to show the influence of the C-I ratio on the stresses in the peri-implant bone and the second phase to reveal the impact of each of the two components of the C-I ratio: crown height and implant length. During analyses, all models were subject to three different loading conditions - axial, buccolingual, and oblique. RESULTS: The crown-to-implant ratio was significantly influential on stress distribution in the peri-implant bone. However, the crown's height was significantly more prominent than the length of the implant. The most substantial amount of stress was seen when long crowns were combined with off-axial loads. Being mostly dominated by the height of the crown and far less by the implant's length, the C-I ratio is not balanced and seems not to be a predictive parameter in implant dentistry. CLINICAL SIGNIFICANCE: Crown-to-implant ratio is recommended to be assessed by its two components: crown height and implant length because the former impacts stresses significantly more than the latter.

Appraising efficiency of OpSite as coolant in drilling of bone.

BACKGROUND: During drilling of bone, which is common in clinical surgeries, heat generation increases local temperature in the drilling site. Transmission of excessive heat to the surrounding bone tissue can cause thermal osteonecrosis. Consequently, it may lead to failure of implants and fixation screws or delay in healing process. Using cooling is a method for limiting temperature elevation. MATERIALS AND METHODS: In this study, through comparing three conditions of drilling without cooling, external cooling with normal saline, and external cooling with OpSite spray, the efficiency of OpSite as coolant is studied. In this regard, 2 drill bit diameters, 3 drilling speeds, and 3 drilling feed-rates are considered as drilling variables in the experiments. RESULTS: For the whole experiments, while cooling with normal saline resulted in lower maximum temperatures than without cooling condition, OpSite had even better results and limited the temperature elevation during drilling of bone efficiently. CONCLUSION: OpSite spray, which has lower infection risks than normal saline on one hand and lower maximum temperature rise with all combinations of drilling parameters on the other hand, can be considered in clinical surgeries for cooling applications.

A Comparative Analysis on Two Types of Oral Implants, Bone-Level and Tissue-Level, with Different Cantilever Lengths of Fixed Prosthesis.

PURPOSE: Depending on esthetic, anatomical, and functional aspects, in implant-prosthetic restoration of a completely edentulous jaw, the selection of implant type is highly important; however, bone- and tissue-level implants and their stress distribution in bone have not yet been comparatively investigated. Hence, finite element analysis was used to study the influence of cantilever length in a fixed prosthesis on stress distribution in peri-implant bone around these two types of oral implants. MATERIALS AND METHODS: A 3D edentulous mandible was modeled. In simulations, a framework with four posterior cantilever lengths and two types of implants, bone-level and tissue-level, was considered. A compressive load was applied to the distal regions of the cantilevers, and the von-Mises stress of peri-implant bone was investigated. The independent t-test and the Pearson correlation coefficient analyzed the results (α = 0.05). RESULTS: Stresses in the cortical bone around the bone-level implants were greater than those in the tissue-level implants with the same cantilever length. In addition, by extending the cantilever length, the stress values in peri-implant bone increased. Therefore, when the cantilever was at its maximum length, the maximum stress was in cortical bone and around the bone-level distal implants. CONCLUSION: The results of the present study indicate that treatment with tissue-level implants is potentially more advantageous than with bone-level implants for implant-supported fixed prostheses.

The effect of implant thread design on stress distribution in anisotropic bone with different osseointegration conditions: a finite element analysis.

PURPOSE: Whereas bone is anisotropic, nearly all previous mechanical analyses of implants assumed bone as an isotropic material. Another means to simplify a simulation of the biomechanics of the implant-bone interface is the assumption of complete or no osseointegration; in clinical reality, an implant never achieves 100% contact with the surrounding bone. This study evaluated different thread profiles while not taking into account these two common simplifications. This study sought to (1) investigate the effects of various implant thread designs on stress distribution in the peri-implant bone, (2) appraise previous efforts in this area, and (3) find an optimum basic thread-form design. MATERIALS AND METHODS: Through finite element analysis, four different basic commercial thread-form configurations for a solid screw-type implant were modeled: buttress, reverse buttress, V, and square. Bone was assumed to be transversely isotropic, and various degrees of osseointegration were simulated. RESULTS: Simulations showed that von Mises stresses were more distributed in the mesiodistal direction. Additionally, maximum stresses were concentrated at the cervical cortical bone region and the first thread. Moreover, in most of the models, von Mises stresses gradually increased in the supporting structure when the degree of osseointegration increased. CONCLUSION: The use of different thread designs and various osseointegration conditions did not affect the stress distribution patterns in the supporting bone. In this study, square threads showed the most favorable results according to the predicted values of von Mises equivalent stress, pressure, different shear stresses, and micromotion.