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Biomedical subjects

M R Norton

Publications and source records attributed to M R Norton.

At least 19 recordsLinked to original sources
PubMed2005

Seasonal patterns of growth, dehydrins and water-soluble carbohydrates in genotypes of Dactylis glomerata varying in summer dormancy.

BACKGROUND AND AIMS: Summer dormancy in perennial grasses has been studied inadequately, despite its potential to enhance plant survival and persistence in Mediterranean areas. The aim of the present work was to characterize summer dormancy and dehydration tolerance in two cultivars of Dactylis glomerata (dormant 'Kasbah', non-dormant 'Oasis') and their hybrid using physiological indicators associated with these traits. METHODS: Dehydration tolerance was assessed in a glasshouse experiment, while seasonal metabolic changes which produce putative protectants for drought, such as carbohydrates and dehydrins that might be associated with summer dormancy, were analysed in the field. KEY RESULTS: The genotypes differed in their ability to survive increasing soil water deficit: lethal soil water potential (Psi(s)) was -3.4 MPa for 'Kasbah' (although non-dormant), -1.3 MPa for 'Oasis', and -1.6 MPa for their hybrid. In contrast, lethal water content of apices was similar for all genotypes (approx. 0.45 g H(2)O g d. wt(-1)), and hence the greater survival of 'Kasbah' can be ascribed to better drought avoidance rather than dehydration tolerance. In autumn-sown plants, 'Kasbah' had greatest dormancy, the hybrid was intermediate and 'Oasis' had none. The more dormant the genotype, the lower the metabolic activity during summer, and the earlier the activity declined in spring. Decreased monosaccharide content was an early indicator of dormancy induction. Accumulation of dehydrins did not correlate with stress tolerance, but dehydrin content was a function of the water status of the tissues, irrespective of the soil moisture. A protein of approx. 55 kDa occurred in leaf bases of the most dormant cultivar even in winter. CONCLUSIONS: Drought avoidance and summer dormancy are correlated but can be independently expressed. These traits are heritable, allowing selection in breeding programmes.

Australia↗
PubMed2002

Catastrophic failure of the Elite Plus total hip replacement, with a Hylamer acetabulum and Zirconia ceramic femoral head.

We report catastrophic early failure of a cemented total hip replacement comprising a modular femoral component with a Zirconia ceramic head and an acetabular component of cross-linked ultra-high molecular-weight polyethylene (Hylamer). Between 1995 and 1999 we implanted 29 hips in 26 patients with a mean age of 49.2 years. Survivorship analysis in this group revealed a failure rate of 67.6% at five years. All hips which failed did so because of aseptic loosening with progressive osteolysis or radiolucencies. We therefore recommend early and regular review of all patients with this combination of implants and early revision surgery in order to avoid massive bone loss.

Adult↗
PubMed2002

The Johnson-Elloy (Accord) total knee replacement. Poor results at 8 to 12 years.

We have found poor mid-term results in a multisurgeon series of 94 Johnson-Elloy (Accord) total knee replacements. A total of 27 knees (29%) has required revision, in 26 for aseptic loosening. Only 18 (19%) remain in situ, and these give poor function, are painful and most show radiological evidence of early failure. At 12 to 13 years the survival rate is 43% (confidence interval 29 to 57) with failure requiring revision as the endpoint. Proximal migration of the femoral component is associated with considerable loss of bone stock. We believe that all patients who have this implant should be recalled for regular review in order to anticipate this problem.

Arthroplasty, Replacement, Knee↗
PubMed2001

Bone classification: an objective scale of bone density using the computerized tomography scan.

Dental implants are subject to masticatory loads of varying magnitude. Implant performance is closely related to load transmission at the bone-to-implant interface where bone quality will be highly variable. The type and architecture of bone is known to influence its load bearing capacity and it has been demonstrated that poorer quality bone is associated with higher failure rates. To date, bone classifications have only provided rough subjective methods for pre-operative assessment, which can prove unreliable. The results of an extensive analysis of computerized tomography scans using Simplant software (Columbia Scientific Inc., Columbia, MD, USA) demonstrate that an objective scale of bone density based on the Houndsfield scale, can be established and that there is a strong correlation between bone density value and subjective quality score (P = 0.002) as well as between the bone density score and the region of the mouth (P < 0.001).

Alveolar Process↗
PubMed2001

Biologic and mechanical stability of single-tooth implants: 4- to 7-year follow-up.

BACKGROUND: Single-tooth implants have been reported to achieve a high level of surgical and prosthetic success. However, close inspection of the literature reveals a paucity of data on the follow-up of single-tooth implants in function for 5 years or more. Since unsplinted implants may be considered to be subject to greater functional stresses, there is a need to report on the long-term biologic and mechanical integrity of such implant-supported restorations. PURPOSE: To report on the long-term follow-up of single-tooth implants, restored and in function for 4 to 7 years. MATERIALS AND METHODS: Twenty-seven Astra Tech single-tooth implants were subject to a clinical audit to evaluate implant and prosthetic success as well as response of both hard and soft tissues over a 1- to 4-year follow-up. This current report presents data on the biologic and mechanical integrity of 23 of these single-tooth implants, which have been in function for up to 7 years (mean, 63 mo). Data are provided with respect to implant survival, maintenance of marginal bone levels, soft-tissue health, and the recording of any adverse events, including prosthetic complications. RESULTS: Only 14 implants in 13 patients were available for review, with no failures for this group of implants. One patient from the original group, who was lost to follow-up, was known to have suffered an implant failure. Furthermore, in accordance with established criteria, the remaining 13 implants that are not included in this report must at this time also be considered as potential failures. As such, the best-case scenario would be a 95.6% success rate for the 23 implants included in this review and the worst-case scenario would be a 60.8% success rate. Mean marginal bone loss measured 0.49 mm mesially and 0.76 mm distally, with a frequency of bone loss of 50%. Soft tissues were clinically healthy. There were few adverse events, with only one case of abutment screw loosening, detected at the 6-year review. In addition, crown decementation was recorded three times in two patients. CONCLUSIONS: It can be concluded that the Astra Tech single-tooth implant can achieve long-term biologic and mechanical stability when used to restore single missing teeth, over the long-term.

Adult↗
PubMed2001

Single-tooth implant-supported restorations. Planning for an aesthetic and functional solution.

The single-tooth implant has found widespread support within the field of implant dentistry, with numerous studies reporting high success rates that surpass those recorded for splinted implant bridgework. Improvements in implant design, range of prosthetic components and restorative materials have made it possible to achieve optimal functional and cosmetic results. Coupled with an appropriate approach to treatment planning and patient assessment, use of the single-tooth implant may be considered a highly predictable treatment solution.

Ceramics↗
PubMed2000

In vitro evaluation of the strength of the conical implant-to-abutment joint in two commercially available implant systems.

STATEMENT OF PROBLEM: The cone-screw abutment has been shown to diminish micromovement, reducing the burden of component loosening and fracture. However, it is unclear whether the conical taper and joint design influence strength of the interface, with respect to unfavorable bending moments. PURPOSE: This comparative study evaluated the resistance to bending for the ITI Straumann and Astra Tech ST implant systems using an 8- and 11-degree internal cone, respectively. MATERIAL AND METHODS: Assembled units from each system were mounted in a 3-point bending apparatus. High load tests were performed, 4 mm from the joint, and bending moments necessary to induce first point of plastic deformation and ultimate failure were measured. All units were inspected to determine the critical zone of failure. RESULTS: Bending moments necessary to induce first point of plastic deformation were considered well above that expected in clinical function for both systems. However, the critical zones of failure differed in that the solid Astra abutment deformed before the cone joint with its 11-degree taper and smooth transition into the neck of the screw, preventing screw fracture. By contrast, all ITI screws fractured at the head of the screw where it met the base of the 8-degree cone. It is unclear which aspects of the joint design were responsible for the difference observed in mode of failure or if it was a direct result of the experimental design. CONCLUSION: For clinically relevant levels of bending moment, no problems were anticipated with respect to component failure for either system.

Dental Abutments↗
PubMed2000

An in vitro evaluation of the strength of a 1-piece and 2-piece conical abutment joint in implant design.

The performance and maintenance of implant-supported prostheses are primarily dependent upon load transmission both at the bone-to-implant interface and within the implant-abutment-prosthesis complex. The design of the interface between components has been shown to have a profound influence on the stability of screw joints. In this in vitro evaluation, implants utilizing an internal conical joint have demonstrated a parity in resistance to bending moments at the fixture-abutment interface, when comparing a 1-piece abutment to a 2-piece abutment, which is tightened via a separate abutment screw, with mean plastic bending moments of 4176 N mm and 4049 N mm respectively. The very small values for coefficient of variance measured in both systems would confirm that whilst the size of data is small it is nonetheless a reliable indication of the relative strength of these conical joint designs.

Dental Abutments↗
PubMed2000

Irrigation and suction technique to ensure reliable cement penetration for total knee arthroplasty.

We describe a new technique to enhance the preparation of the cancellous bone surfaces in total knee arthroplasty using bone suction and pressure lavage irrigation. This technique provides dry bone surfaces on which to cement (which is particularly valuable if a tourniquet is not used) and improves significantly the penetration of cement into the tibial plateau as assessed on plain postoperative radiographs. We review the results of this new technique by analyzing depths of cement penetration on postoperative radiographs to assess whether this technique offers improvements in cement penetration and bone surface preparation. This technique offers a simple, quick, and reliable method of ensuring reliable cement penetration into the bony trabeculae during cemented total knee arthroplasty.

Aged↗
PubMed1999

Assessment of cold welding properties of the internal conical interface of two commercially available implant systems.

STATEMENT OF PROBLEM: The cone-screw abutment has been shown to diminish micromovement by reducing the burden of component loosening and fracture. However, anecdotal concern for cold welding of cone-screw joints in implant design has been identified as a potential source for lack of retrievability. PURPOSE: This comparative study evaluated the loosening torque, as a percentage of tightening torque, for the ITI Straumann and Astra Tech (3.5 and 4.0 mm diameters) implant systems, which use an 8-degree and 11-degree internal cone, respectively. MATERIAL AND METHODS: Implants and abutments from each system were mounted in a torque device, and a range of tightening torques was applied. Loosening torques were then measured, and the influence of conus angle, interfacial surface area, saliva contamination, and time delay to loosening were all assessed. RESULTS: The loosening torque only exceeded tightening torque at the highest levels, just before component failure, when plastic deformation was expected. For all clinically relevant levels of torque, both in a dry environment and with components bathed in artificial saliva at 37 degrees C, loosening torque was always seen to be 80% to 90% of tightening torque, demonstrating that cold welding does not occur. There was a high correlation between loosening and tightening torque for all systems tested, but no statistical difference when comparing wet versus dry or comparing individual data for each system. CONCLUSIONS: It can be concluded that for clinically relevant levels of tightening torque, no problems are anticipated with respect to retrievability.

Cold Temperature↗
PubMed1999

The nonresilient hybrid removable prosthesis: treatment of choice for the atrophic maxilla.

This article presents the ments of the nonresilient hybrid removable prosthesis, which is the treatment of choice for the atrophic maxilla. The technique described may be adapted to yield a predictable outcome that provides functional and biomechanical stability that are superior to a resilient over-denture, along with a cosmetic and phonetic result that often proves superior to that of the fixed prosthesis.

Alveolar Bone Loss↗
PubMed1998

Marginal bone levels at single tooth implants with a conical fixture design. The influence of surface macro- and microstructure.

The concept of a conical implant design to accommodate single tooth replacement, has previously been shown to result in excessive bone loss, around the machined titanium conical collar, usually down to the 1st thread. This unusually aggressive loss of bone was shown to occur within a short period of time, post loading, with greater than 3 mm of bone loss occurring within the 1st 6 months to 1 year. The influence of implant design, surface texture and microleakage have all been highlighted as a potential cause. A modification of the surface structure, both at the macroscopic and microscopic level, as well as an altered fixture-abutment interface design has resulted in the maintenance of marginal bone around a single tooth titanium implant with a similar conical design. The radiographic follow-up of 33 implants loaded for up to 4 years, has revealed, by comparison, a most favourable maintenance of marginal bone around the conical collar, with a mean marginal bone loss of 0.32 mm mesially and 0.34 mm distally for the whole group. The cumulative mean marginal bone loss mesially and distally is 0.42 mm and 0.40 mm from 1 to 2 years, 0.54 mm and 0.43 mm from 2 to 3 years, 0.51 mm and 0.24 mm from 3 to 4 years, and 0.62 mm and 0.60 mm for implants past their 4 year recall.

Adolescent↗
PubMed1997

An in vitro evaluation of the strength of an internal conical interface compared to a butt joint interface in implant design.

Dental implants are subject to large and highly complex loads of varying magnitude, duration and vector. Bridge performance is closely related to load transmission both at the bone to implant interface and between components within the implant-abutment-bridge cylinder complex. The design of the interface between components within this complex may have a profound influence on the long term function of the implant supported prosthesis. An in vitro evaluation of implants 3.5 mm in diameter, utilizing an internal conical interface has demonstrated increased resistance to bending moments at the fixture-abutment interface (P = 0.00010) and at the abutment-bridge cylinder interface (P < 0.01), when compared to a standard 3.75 mm implant with a hex mediated, butt joint interface. The relatively small values for coefficient of variance measured in both systems would confirm that whilst the size of data is small, it is nonetheless a reliable indication of the relative strength of these implant designs.

Alveolar Process↗
PubMed1997

The Astra Tech Single-Tooth Implant System: a report on 27 consecutively placed and restored implants.

This article presents the components and treatment protocol for the Astra Tech Single-Tooth Implant System, whose concept and design has been tailored to the specific needs of single-tooth replacement. Since July 1991 the author has consecutively placed 39 single-tooth implants, of which 27 are restored and in function. To date there have been no recorded fixture failures, and the bone loss seen around fixtures in the first and subsequent years is insignificant. Two crowns have had to be replaced, and three were recemented over the follow-up period. All patients have expressed considerable satisfaction with their restorations from an esthetic perspective, and the system has been shown to avoid undesirable complications when employed in patients with normal masticatory function.

Adolescent↗
PubMed1994

A histomorphometric evaluation of bone-to-implant contact on machine-prepared and roughened titanium dental implants. A pilot study in the dog.

This investigation was performed to assess the bone-to-implant surface contact at fixtures of titanium that either had a standard machine prepared or a TiO2-blasted surface. Five beagle dogs were used in the experiment. Extractions of the premolars were performed in the maxilla. After 4 months of healing, 5 standard machine-prepared fixtures and 5 prepared according to the TioBlast technique were inserted. Two months later another 5 "standard" and 5 TioBlast-prepared implants were inserted. Four months after the first fixture installation, the animals were killed and ground sections prepared from each implant site. Of the 20 implants installed, 19 were successfully incorporated. The mean bone-to-implant surface for "standard" fixtures was about 40% both at the 2 and 4 months observation interval. The corresponding figures for the TioBlast-prepared fixtures were similar during the first 2 months of observation, while subsequently the TioBlast-prepared fixture surface seemed to stimulate to a more close bone-to-implant contact (65%) than the "standard" one.

Analysis of Variance↗
PubMed1991

Bilateral accessory digastric muscles.

Anomalies of the anterior bellies of the digastric muscles are uncommon. The description of such anomalies do exist in the literature dating from the 19th Century, but recently radiologists have drawn attention to their existence to avoid confusion with abnormal lesions when scanning the floor of the mouth and the submental space. Bilateral accessory muscles crossing the midline are described.

Adult↗