Self-drilling and self-tapping screws: an ultrastructural study

Immediate and late inflammatory and bone healing response post implantation of self-tapping and self-drilling osteosynthesis screws

The aim of this study was to comparatively analyse osseointegration after the implantation of self-tapping screws (STS) and self-drilling screws (SDS). Thus, 24 four-month-old male Wistar rats, received SDS and STS screws in their left and right tibias, respectively. Sample collection was performed immediately at 0 hours (0h), two, seven, and 21 days after implantation (2d, 7d, 21d). Samples from immediately and 21 days after were analysed by micro computed tomography (MicroCT). All time points were evaluated by histology (Haematoxylin and Eoisin and Goldner's Trichrome) and immunohistochemistry for tartrate-acid resistant phosphatase positive (TRAP+) osteoclasts. MicroCT images revealed an intimate contact between bone and each type of screw at 0h. However, SDS group presented decreased bone volume (BV, mm3) at 21 days in comparison with STS. Both SDS and STS post implantation presented areas of suitable new bone formation surrounding screw threads from seven days, and inflammation decreased from two to 21 days. Also, TRAP+ osteoclasts were mainly identified at seven days in both STS and SDS groups, particularly surrounding areas of pressure, with significant differences between groups. In conclusion, differences in shape and insertion technique for SDS and STS screws did not affect immediate and late inflammatory and bone healing response post implantation in this animal model. Both osteosynthesis screws allowed satisfactory post-surgical outcomes.

Comparative Evaluation of Drill-Free and Self-Tapping Titanium Miniscrews for Semi-Rigid Internal Fixation in Maxillofacial Trauma

Introduction

Conventional semi-rigid fixation systems in maxillofacial trauma use self-tapping titanium miniscrews (STS) that require preliminary drilling of a pilot hole. Although drill-free miniscrews (DFS) accompany these systems, they have not dominated practice despite their allure of improved screw-bone contact and holding power. The COVID-19 pandemic has brought these DFS to light as they avoid aerosol production. The present study has compared DFS to STS in patients being treated with miniplate fixation for maxillofacial trauma to understand their feasibility for maxillofacial fracture fixation.

Methodology

This prospective case–control study sampled 16 patients each with zygomaticomaxillary buttress fracture and parasymphysis fracture of the mandible and grouped alternating patients as case (DFS) and control (STS). Intraoperatively duration of fixation, incidence of screw failures and fragment stability; postoperatively occlusion, neurosensory deficits, teeth vitality and infection and removal rates were evaluated at postoperative week 1, 3, 6, 12 and 24 using Cramer's V test. A P value < 0.05 was considered significant.

Results

In the 32 patients evaluated, DFS reduced internal fixation time at zygomaticomaxillary buttress (P = 0.001) but not at parasymphysis (P = 0.206). No significant difference in screw failures or fragment stability was observed. Stable occlusion was maintained in all groups with vital teeth and intact neurosensory function, but the summative incidence of infection was significant at week 24 when STS was used at parasymphysis (P = 0.019).

Discussion

While DFS may facilitate ease of insertion with a single instrument pick-and-screw-in approach, avoiding thermal osteonecrosis and aerosol production, they fail to confer any other clinical advantage.

Effects of seawater immersion on open traumatic brain injury in rabbit model

We emulated instances of open traumatic brain injuries (TBI) in a maritime disaster. New Zealand rabbit animal models were used to evaluate the pathophysiological changes in open TBI with and without the influence of artificial seawater. New Zealand rabbits were randomly divided into 3 groups. Control group consisted of only normal animals. Animals in TBI and TBI + Seawater groups underwent craniotomy with dura mater incised and brain tissue exposed to free-fall impact. Afterward, only TBI + Seawater group received on-site artificial seawater infusion. Brain water content (BWC) and permeability of blood-brain barrier (BBB) were assessed. Reactive oxygen species levels were measured. Western blotting and immunofluorescence were employed to detect: apoptosis-related factors Caspase-3, Bax and Bcl-2; angiogenesis-related factors CD31 and CD34; astrogliosis-related factor glial fibrillary acidic protein (GFAP); potential neuron injury indicator neuron-specific enolase (NSE). Hematoxylin & eosin, Masson-trichrome and Nissl stainings were performed for pathological observations. Comparing to Control group, TBI group manifested abnormal neuronal morphology; increased BWC; compromised BBB integrity; increased ROS, Bax, CD31, CD34, Caspase-3 and GFAP expressions; decreased Bcl-2 and NSE expression. Seawater immersion caused all changes, except BWC, to become more significant. Seawater immersion worsens the damage inflicted to brain tissue by open TBI. It aggravates hypoxia in brain tissue, upregulates ROS expression, increases neuron sensitivity to apoptosis-inducing factors, and promotes angiogenesis as well as astrogliosis.

Self-Drilling Versus Self-Tapping Screws: A 3D Finite Element Analysis

Study Design

Self-tapping and self-drilling screws are two modalities available for plate fixation. When compared to self-drilling, self-tapping screws have a few drawbacks like screw loosening, thermal osteolysis, equipment dependent, and time-consuming.

Aim

The aim of this study was to compare the efficacy of self-tapping and self-drilling screws with relation to plate retention and stability in internal fixation of mandibular fractures using 3D finite element analysis (FEA).

Objectives

The objective of this study was to determine the influence of screw placement technique on stress concentration and deformation occurring at the screw-bone interface in self-drilling and self-tapping screws.

Materials and Methods

A 3D computer-aided design modeling system was used to build a trilaminate mandibular bone, self-tapping screw and self-drilling screw, and a 2-holed miniplate with gap that were converted into finite element models using Hypermesh 13.0 software. Material properties and boundary conditions were assigned to these models. Pullout, torque, and torsional forces were applied to evaluate the stress concentration and deformation at the screw-bone interface.

Results

The comparison of stress concentration and deformation values between the two types of screws was interpreted using ANSYS software version 14.5. Results of torque test, pullout test, and torsional test showed maximum Von Mises stress, and deformation around the screw-bone interface was higher in self-tapping screw than in self-drilling screw.

Conclusion

Within the limitations of the 3D FEA, the findings provided significant evidence to suggest that self-tapping screws have a greater incidence of fatigue when compared to self-drilling screws as there was more stress distribution and deformation at their screw-bone interface.

Development of a quantitative preclinical screening model for implant osseointegration in rat tail vertebra

Objectives

Functional tooth replacement and bone regeneration are parts of the daily practice in modern dentistry, but well-reproducible and relatively inexpensive experimental models are still missing. We aimed to develop a new small animal model to monitor osseointegration utilizing the combination of multiple evaluation protocols.

Material and methods

After cutting the tail between the C4 and C5 vertebrae in Wistar rats, costume made, parallel walled, non-threaded implants were placed into the center of the tail parallel with its longitudinal axis using a surgical guide. Osseointegration of the titanium implants was followed between 4 and 16 weeks after surgery applying axial extraction force, and resonance frequency analysis as functional tests, and histomorphometry and micro-CT as structural evaluations.

Results

In functional tests, we observed that both methods are suitable for the detection of the time-dependent increase in osseointegration, but the sensitivity of the pull-out technique (an approximately five times increase with rather low standard error) was much higher than that of the resonance frequency analysis. In structural evaluations, changes in the detected bone implant contact values measured by histomorphometry (yielding 1.5 times increase, with low variations of data) were more reliable than micro-CT based evaluations to screen the developments of contact between bone and implant.

Conclusion

Our results provide evidence that the caudal vertebrae osseointegration model is useful for the preclinical evaluation of implant integration into the bone.

Clinical relevance

The combination of the biomechanical and structural tests offers a well-reproducible small animal system that can be suitable for studying the integration of various implant materials and surface treatments.

Heat generated during seating of dental implant fixtures

Frictional heat can be generated during seating of dental implants into a drill-prepared osteotomy. This in vitro study tested the heat generated by implant seating in dense bovine mandible ramus. A thermocouple was placed approximately 0.5 mm from the rim of the osteotomy during seating of each dental implant. Four diameters of implants were tested. The average temperature increases were 0.075°C for the 5.7-mm-diameter implant, 0.97°C for the 4.7-mm-diameter implant, 1.4°C for the 3.7-mm-diameter implant, and 8.6°C for the 2.5-mm-diameter implant. The results showed that heat was indeed generated and a small temperature rise occurred, apparently by the friction of the implant surface against the fresh-cut bone surface. Bone is a poor thermal conductor. The titanium of the implant and the steel of the handpiece are much better heat conductors. Titanium may be 70 times more heat conductive than bone. The larger diameter and displacement implant may act as a heat sink to draw away any heat produced from the friction of seating the implant at the bone-implant interface. The peak temperature duration was momentary, and not measured, but this was approximately less than 1 second. Except for the 2.5-mm-diameter implants, the temperature rises and durations were found to be below those previously deemed to be detrimental, so no clinically significant osseous damage would be expected during dental implant fixture seating of standard and large-diameter-sized implants. A 2.5-mm implant may generate detrimental heat during seating in nonvital bone, but this may be clinically insignificant in vital bone. The surface area and thermal conductivity are important factors in removing generated heat transfer at the bone-implant interface. The F value as determined by analysis of variance was 69.22, and the P value was less than .0001, demonstrating significant differences between the groups considered as a whole.