Neil Waddell

A comparison of fit of CNC-milled titanium and zirconia frameworks to implants.

BACKGROUND Computer numeric controlled (CNC) milling was proven to be predictable method to fabricate accurately fitting implant titanium frameworks. However, no data are available regarding the fit of CNC-milled implant zirconia frameworks. PURPOSE To compare the precision of fit of implant frameworks milled from titanium and zirconia and relate it to peri-implant strain development after framework fixation. MATERIALS AND METHODS A partially edentulous epoxy resin models received two Branemark implants in the areas of the lower left second premolar and second molar. From this model, 10 identical frameworks were fabricated by mean of CNC milling. Half of them were made from titanium and the other half from zirconia. Strain gauges were mounted close to the implants to qualitatively and quantitatively assess strain development as a result of framework fitting. In addition, the fit of the framework implant interface was measured using an optical microscope, when only one screw was tightened (passive fit) and when all screws were tightened (vertical fit). The data was statistically analyzed using the Mann-Whitney test. RESULTS All frameworks produced measurable amounts of peri-implant strain. The zirconia frameworks produced significantly less strain than titanium. Combining the qualitative and quantitative information indicates that the implants were under vertical displacement rather than horizontal. The vertical fit was similar for zirconia (3.7 µm) and titanium (3.6 µm) frameworks; however, the zirconia frameworks exhibited a significantly finer passive fit (5.5 µm) than titanium frameworks (13.6 µm). CONCLUSIONS CNC milling produced zirconia and titanium frameworks with high accuracy. The difference between the two materials in terms of fit is expected to be of minimal clinical significance. The strain developed around the implants was more related to the framework fit rather than framework material.

A novel in vitro approach to assess the fit of implant frameworks

OBJECTIVE To introduce a new strain gauge approach to assess the fit of fixed implant frameworks. MATERIALS AND METHODS A partially edentulous epoxy resin mandible model received two Straumann implants in the area of the lower left second premolar and second molar. The model was used to fabricate four zirconia and four identical cobalt-chromium alloy frameworks using a laboratory computer-aided design/computer-aided manufacturing (CAD/CAM) system. A total of four linear strain gauges were then bonded around each implant on the peri-implant structure (mesial, distal, buccal, and lingual). The experimental part was composed of two phases: qualitative and quantitative. For the qualitative assessment, the model was verified by recording the response of each strain gauge while applying a near-constant force of known directions on each implant. For the quantitative phase, the frameworks were attached on the implants and the screws were torqued to 15 N cm. RESULTS In the qualitative phase, the strain gauge response to every force direction was recorded. After attaching the frameworks, all frameworks produced measurable strains, but with different strain patterns. Upon correlating the two phases, the zirconia frameworks were found to be slightly smaller than the inter-implant distance, whereas the cobalt-chromium alloy frameworks tended to be slightly larger than the inter-implant distance. CONCLUSIONS The proposed technique is not only valid for detecting implant framework misfit but also for determining the form of inaccuracies. Model verification is an essential informative step to aid the interpretation of the pattern of framework distortion.

Experimental simulation of non-ballistic wounding by sharp and blunt punches

Despite a long history of gross and microscopic descriptions of blunt and sharp force injury to the dermal tissues, few have addressed the mechanisms underlying such trauma. The need to develop an understanding of how non-ballistic injury occurs calls for an ability to biomechanically model the process. We recently introduced a basic skin and subcutaneous model, which we used to investigate wounding from a spherical object. Here we employ the same model to examine wounding caused by a sharp wedge shaped object and a blunt rectangular object. Macroscopic examination and SEM views of the surface and cross sections of blunt and sharp force tears show that while in the former there is a clean cut through the skin into the underlying sponge, in the latter there is a tissue plug confined to the skin that is smaller than the impacting rectangle. Fracture initiation in the subdermal tissue occurs at the angles of the impacting object. In sharp force trauma, there is localized breaching of the skin layer coupled with the wedging action of the impacting object. Because the subdermal tissue, in this case the underlying hydrated foam, is attached to the base of the skin, it will contribute to further tearing of the foam beneath the line of contact.

Influence of surface penetration on measured fluid force on a hand model

The purpose of this study was to quantify the effect of wave drag due to surface penetration on drag and lift forces (C(d) and C(l)) acting on a hand model. The values of C(d) and C(l) had been acquired to gain the hydrodynamic characteristics of the swimmers hand and predict force on the swimmers hand. These values have also been used to benchmark computational fluid dynamics analysis. Because the previous studies used a hand/forearm model which penetrated the waters surface, the values of C(d) and C(l) include the effect of the surface wave on the model. Wave formation causes pressure differences between the frontal and rear sides of a surface-penetrating model as a result of depressions and elevations in the waters surface. This may be considered as wave drag due to surface penetration. Fluid forces due to wave drag on the forearm should not be included in the measured C(d) and C(l) of a swimmers hand that does not sweep near the waters surface. Two hand/forearm models are compared, one with the hand rigidly connected to the forearm. The other model was constructed to isolate the fluid forces acting on the hand from the influence of wave drag on the forearm. The measurements showed that the effect of wave drag on the hand model caused large increases in the values of C(d), up to 46-98% with lesser increases in C(l) of 2-12% depending on the hand orientation. The present study provides an improved method to determine the values of C(d) and C(l) that eliminates the effect of wave drag on a hand/forearm model by isolating the measurement of fluid forces on the forearm of the hand/forearm model in order to separately acquire the forces on the hand.

Gunshot residue preservation in seawater

Little is known about the persistence of gunshot residue (GSR) in soft tissue and bones during decomposition in marine environments. For a better understanding, qualitative and quantitative data were obtained on GSR retention on soft tissue and bony gunshot wounds (GSWs). A quantity of 36 fleshed and 36 defleshed bovine ribs were shot at contact range with 0.22 calibre hollow point ammunition using a Stirling 0.22 calibre long rifle. Bone specimens in triplicate were placed in three environments: submerged, intertidal and in supralittoral zone. Sets of triplicates were recovered on day 3, 10, 24 and 38, and analysed with scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDX), and inductive coupled plasma mass spectrometry (ICP-MS). The SEM-EDX recorded GSR-indicative particles surrounding the bullet entrance on all bone types (fleshed and defleshed) in all environments throughout the study. GSR-unique particles were only detected on the supralittoral bones. The ICP-MS analysis showed faster GSR loss on submerged than intertidal and supralittoral defleshed specimens. Fleshed specimens showed a faster GSR loss on intertidal than submerged and supralittoral specimens. In conclusion, the GSR disappeared faster from submerged and intertidal than non-submerged specimens. The difference of detection of GSR between analysed specimens (defleshed versus fleshed) disappeared upon defleshing. This study highlights the potential of finding evidence of GSR in a submerged body and the potential of microscopic and analytical methods for examining suspected GSW in highly decomposed bodies in marine habitats.

The deer femur – A morphological and biomechanical animal model of the human femur

BACKGROUND The need for continued refinement of animal models in orthopaedic studies persists despite decades of research. OBJECTIVE This study investigates the merits of deer bone in comparison to the more commonly used pig and sheep bone as an animal model for the human femur. METHOD A morphological and biomechanical comparison of deer, pig and sheep rear femurs to those of the human femur is presented. Morphological parameters measured include bone length, cortical and medullary diaphyseal diameters, cortical thickness, cortical cross-sectional area and bone density along the diaphysis. Biomechanical tests included whole-bone four-point flexure tests to determine the bending stiffness (N/mm), Youngs modulus of bending (GPa), and ultimate strength in bending (MPa). In addition torsional stiffness (Nm/degree) as well as mid-diaphyseal cortical compressive elastic modulus (GPa) and strength (MPa) is investigated. RESULTS On average, deer bone was found to be the least dissimilar from human femur. However, no single bone type consistently resembled the human femur. CONCLUSION Deer femora should be considered a suitable animal model for the human femur.

Diurnal variation of intraoral pH and temperature

Objective/Aims:The aim of this study was to measure continuously the intraoral pH and temperature of healthy individuals to investigate their diurnal variations.Materials and Methods:Seventeen participants (mean age, 31±9 years) wore a custom-made intraoral appliance fitted with a pH probe and thermocouple for two sets of 24 h, while carrying out normal daily activities including sleep. The continuous changes in intraoral pH and temperature were captured using a sensor placed on the palatal aspect of the upper central incisors. The collected data were categorised into different status (awake and sleep) and periods (morning, afternoon, evening and night). Both quantitative and qualitative analyses were conducted.Results:The intraoral pH change was found to show a distinctive daily rhythm, showing a 12-h interval between maximum (7.73) and minimum (6.6) pH values. The maximum and minimum values were found to repeat after 24 h. The mean pH over 48 h (two sets of 24 h) was found to be 7.27 (±0.74). There was significant difference found in pH when subjects were awake and asleep and different periods during the day (P<0.001). The mean intraoral temperature was 33.99 °C (±4.9), with less distinctive daily rhythm compared with pH. There was a significant difference found in temperature depending on the time of the day, except between morning and afternoon (P=0.78).Conclusion:Our results showed that there is a distinctive daily, circadian-like pattern in intraoral pH variation over a 24-h period, which has been considered as one of the risk factors in sleep-related dental diseases.

Interarch comparison of intraoral pH and temperature: a pilot study

Purpose of study:The severity of tooth wear is known to have an association with intraoral pH and temperature depending on the site.Objective:To compare the intraoral pH and temperature between the maxillary and mandibular arch.Methods:Fourteen participants (mean age=25.8 years) wore a custom-made intraoral appliance fitted with a pH probe and thermocouple for 24 h while carrying out normal activities including sleep. All participants wore a maxillary appliance; four participants repeated the process and wore the mandibular appliance. Measurements were taken from the palatal aspect of the upper central incisors and lingual aspect of the lower canines. Both qualitative and quantitative statistical analyses were conducted.Results:The mean intraoral pH from the maxilla was 7.32 (±0.52) and 7.07 (±0.26) for the mandible. During daytime, there was no statistical significance difference between the two arches (P=0.12). During sleep, there was a significant difference (P<0.001) between the mean pH of the maxilla, 7.0 (±0.46), and mandible, 6.46 (±0.31). The fluctuation patterns of pH and temperature from both arches were similar, but the maxilla showed more variations. The mean temperature from the mandible was slightly higher (36.18 °C (±0.96)) than the maxilla, 33.12 °C (±5.51) during daytime; however, there was no statistically significance difference in temperature between the arches during daytime (awake) or sleep (P=0.27).Conclusion:The results showed that there is significant difference in mean intraoral pH between the maxilla and the mandible during sleep, but not during the day and this difference may be associated variations in tooth wear between the arches.

BIOMECHANICS OF RIB FRACTURE: PERIMORTEM AND POSTMORTEM TRAUMA PATTERNS IN A PIG MODEL

The morphology of a rib fracture is often used by forensic investigators to determine whether trauma was sustained perior post-mortem, yet the distinction between such fractures is still not fully resolved [Pechnikova et al., 2011]. Love et al. [2004] comprehensively outlined the difficulties involved in relating rib fractures to the mechanical circumstances that cause them and presented a classificatory system for characterizing fracture patterns. However, they noted that simple consideration of bone’s material behaviour was insufficient for understanding the range of fracture patterns seen in blunt force trauma victims. The aim of this study was to address these concerns by investigating the material properties and fracture behaviour of ribs using a pig model.