Probabilistic analysis of peri-implant strain predictions as influenced by uncertainties in bone properties and occlusal forces

OBJECTIVES: The purpose of this study was to examine the influence of variability in bone properties and loading on peri-implant crestal and cancellous bone strains using a probabilistic approach, in combination with finite element (FE) analysis. MATERIAL AND METHODS: Oblique occlusal loading was applied to a single endosseous implant embedded in a two-dimensional (2-D) FE model of a premolar section of a mandible. Perfect bonding was assumed at all interfaces. Five independent parameters (cortical bone thickness (T), cortical (ECORT) and cancellous (ECANC) bone Young's moduli, and vertical (FVERT) and horizontal (FHOR) occlusal forces) were assigned statistical distributions based on data in the literature. Two cancellous bone distribution models were examined, one with a lower mean and range (LM) and the second with a higher mean and range (HM) of cancellous bone Young's modulus values. Sets of randomly chosen values for the five parameters were selected from the distributions and FE analyses were performed for all randomly selected sets. RESULTS: In the LM model, 50% of the cases experienced hyper-physiologic peri-implant crestal strains in the region of commonly reported saucerization, compared with about 25% of the cases in the HM model. Relative probabilistic sensitivities (%) of bone strains to the independent input parameters (T, ECORT, ECANC, FVERT and FHOR) were as follows: 29, 11, 30, 13, and 17 for the LM model, and 17, 11, 35, 21, and 15 for the HM model, respectively. CONCLUSION: Probabilistic analyses of FE models suggest that up to twice as many cases in the LM distribution may be at risk of saucerization as compared with the HM distribution model. Although based on hypothetical distribution values and the limitations inherent to a 2-D analysis, this probabilistic study demonstrated that FE models are very sensitive to the often arbitrarily assigned values for cancellous bone Young's modulus, and also to values used for cortical bone thickness, when the cancellous bone modulus is low.     

Development of a treatment outcome standard as a result of a clinical audit of the outcome of fixed appliance therapy undertaken by hospital-based consultant orthodontists in the UK

Bristol's much-publicised cardiac surgery problems and subsequent enquiry(1) have drawn attention to the need for audit of treatment outcomes throughout all hospital specialties. Patient anxiety, government policy and the desire of the professions to re-establish public confidence, have further encouraged changes to the system. For medical and dental specialties, such challenges have already been taken up by the Royal Colleges with the establishment of clinical effectiveness committees. Hospitals have modified their procedures and, for consultants, yearly appraisal is already a reality. The Orthodontic Clinical Effectiveness Working Party of the Royal College of Surgeons of England (now the Clinical Effectiveness Committee of the British Orthodontic Society) set up this audit to measure the outcome of fixed appliance treatment and to establish a benchmark for the standard of treatment to be expected from a consultant orthodontist. This paper describes how the audit was carried out, presents the findings and goes on to discuss some of the wider issues involved in audit, clinical governance and appraisal. The Consultant Orthodontists Group of the British Orthodontic Society funded this audit and the results and data set of dental casts remain their property.     

Susceptibility of a polycaprolactone-based root canal filling material to degradation. I. Alkaline hydrolysis

Polycaprolactone, a thermoplastic aliphatic polyester, is reportedly susceptible to both alkaline and enzymatic hydrolyzes. This screening study examined the susceptibility of Resilon, a polycaprolactone-based root filling composite, to alkaline hydrolysis. There were 15-mm diameter disks of Resilon and Obtura gutta-percha prepared by compressive molding and immersed in 20% sodium ethoxide for 20 or 60 min. Control disks were immersed in ethanol for 60 min. These disks were examined using field-emission scanning electron microscopy and energy dispersive X-ray analysis. For Resilon, the surface resinous component was hydrolyzed after 20 min of sodium ethoxide immersion, exposing the spherulitic polymer structure and subsurface glass and bismuth oxychloride fillers. More severe erosion occurred after 60 min of sodium ethoxide treatment. Gutta-percha was unaffected after immersion in sodium ethoxide. As Resilon is susceptible to alkaline hydrolysis, it is possible that enzymatic hydrolysis may occur. Biodegradation of Resilon by bacterial/salivary enzymes and endodontically relevant bacteria warrants further investigation.     

Dentoalveolar relations in children born with a unilateral cleft lip and palate (UCLP) in Western Australia.

OBJECTIVE: Our objective was to evaluate complete unilateral cleft lip and palate repair outcome in the Cleft Unit in Perth, Western Australia, by assessment of dentoalveolar relationships. DESIGN: This is a retrospective study. SETTING: Our subjects were individuals under the care of the cleft team in Perth, Western Australia. PARTICIPANTS: All patients with unilateral cleft lip and palate and available 6-year casts who had been born since January 1, 1985, were identified from the cleft unit's database. The nature of the cleft was verified by examination of birth study models and photographs. A total of 54 such patients were identified. MAIN OUTCOME MEASURES: Main outcome measures were identified through dental arch relationship grading of study models using the 5 Year Old Study Model Index. RESULTS: Interexaminer and intraexaminer agreement kappa statistics revealed good to very good agreement using this index. The results indicate that the surgical outcome was graded as excellent, good, or fair for 77% of patients and poor or very poor for 23% of patients. CONCLUSIONS: The results of the Western Australia study compare favorably to the overall U.K. outcome (the Clinical Standards Advisory Group study) but unfavorably to the results of some European centers, such as Oslo.     

A four year retrospective study of 1,062 patients presenting with maxillofacial emergencies at a specialist paediatric hospital

AIMS: To examine the nature of maxillofacial injuries that presented to the Birmingham Children's Hospital according to aetiology, incidence and characteristics of patients. METHODS: The maxillofacial unit at Diana Princess of Wales Birmingham Children's Hospital serves a catchment area of 5.2 million. We examined all children who presented with maxillofacial trauma from 2002 to 2006. Details including characteristics of patients and aetiology and nature of injury, were entered prospectively into a database. RESULTS: The total number of patients who presented was 1062. The ratio of boys to girls was 2:1. The main reason for attendance was a fall (70%). 149 (17%) patients presented after interpersonal violence. Soft tissue injuries accounted for 70% of injuries and 14% presented with a maxillofacial fracture. CONCLUSIONS: Our data indicate that the range and mechanism of presenting injuries have not changed within the time frame. Despite public perception of increasing interpersonal violence, this was not reflected in our series of patients.     

Which patients are most at risk of methicillin resistant Staphylococcus aureus: a review of admissions to a regional maxillofacial ward between 2001 and 2005

This study aimed to identify all Staphylococcus aureus (MRSA) cases on a Regional Maxillofacial ward, to estimate incidence and to ascertain who were most at risk. The study also explored clinical and demographic factors associated with MRSA in a subset of consecutive patients managed by primary surgery for previously untreated oral and oropharyngeal squamous cell carcinoma (OOSCC) over the same time period. Patients admitted from 1st April 2001 to 31st March 2006 to the Regional Maxillofacial Unit ward, Liverpool were identified by a retrospective review of the hospital MRSA database and there were 10109 patient admissions. MRSA (1.1%) occurred in 115 patient episodes involving 97 patients. There were 84 patients having a single episode and 13 more than one. There were no cases of mortality due to MRSA. Of the MFU patients 73 were oncology and 7 trauma. In the oncology group the commonest primary sites were wound (41) and sputum (11). Of new patients admitted for definitive treatment for OOSCC, 14% had MRSA and the two main risk factors were stage of cancer (P<0.001) and free flap (P<0.001). The risk of MRSA infection on our maxillofacial ward is low though MRSA infection is more prevalent among oncology patients particularly those requiring free tissue transfer. Careful adherence to infection prevention and control precautions is essential and practical methods to reduce MRSA need further evaluation.     

A Survey of U.S. Prosthodontists and Dental Schools on the Current Materials and Methods for Final Impressions for Complete Denture Prosthodontics

PURPOSE: The purpose of this study was to survey members of The American College of Prosthodontists (ACP) to evaluate current materials and methods for final impressions for complete denture prosthodontics in the United States. In addition, those methods were compared with methods and materials taught in U.S. dental schools via a second survey sent to the chairpersons of prosthodontic/restorative departments. MATERIALS AND METHODS: An anonymous questionnaire was mailed to all 1762 active ACP members in the United States in 2003. A slightly modified questionnaire was also distributed to chairpersons of prosthodontic/restorative departments in the 54 U.S. dental schools. Data analysis was performed via frequency distribution and chi-square statistics. RESULTS: Nine hundred and forty-five questionnaires were returned by members of the ACP (54% return rate) and 42 questionnaires were returned by the U.S. dental schools (78% return rate). The majority of the reporting prosthodontists (88%) and dental schools (98%) use a border-molded custom tray for final impressions for complete denture prosthodontics. The most popular material for border molding was plastic modeling compound (67% of reporting ACP members, and 95% of the responding dental schools). Variability of the materials used for final impressions was observed, with the most popular materials being polyvinylsiloxane for the ACP members (36%) and polysulfide for the dental schools (64%). Statistically significant differences were found in the materials used for border molding by prosthodontists based on the time elapsed since completion of prosthodontic training. No differences were found in the materials used for impression of edentulous arches based on years of experience. Geographic location did not influence the materials and methods used by prosthodontists for complete denture final impressions. CONCLUSIONS: There was variability of the materials and techniques used for final impressions by ACP members and dental schools; however, overall there was an agreement on the materials and techniques used by prosthodontists and dental schools. Distinct trends for increasing use of polyvinylsiloxane and polyether for border molding procedures and impressions of edentulous arches were observed both in members of the ACP and in the U.S. dental schools.     

Anisotropic elastic properties of cancellous bone from a human edentulous mandible

The elastic moduli have not been reported for cancellous bone from the edentulous mandible. Accurate values are needed for finite element modeling of the mandible. The aim of this study was to determine elastic modulus values in three orthogonal directions for cancellous bone taken from an edentulous jaw and to relate these values to apparent density and volume fraction. Seven samples were obtained from the edentulous mandible of a 74-year-old female. Young's modulus was determined by compression testing of cubes cut with the faces aligned with the anatomic axes. Bone volume fraction averaged 0.33 (SD 0.14) and apparent density averaged 0.55 g/cc (SD 0.29). Young's modulus was greatest in the mesio-distal direction (mean 907 MPa, SD 849 MPa), followed by the bucco-lingual (mean 511 MPa, SD 565 MPa) and infero-superior direction (mean 114 MPa, SD 78 MPa). The infero-superior direction was less than the bucco-lingual (P = 0.03) and mesio-distal (P = 0.002). The mesio-distal and bucco-lingual directions could not be shown to be different (P = 0.32). This suggests a model of transverse isotropy for cancellous bone in the jaw, where the symmetry axis is along the infero-superior (weakest) direction.     

Arterial embolisation of a facial haemangioma.

Non-invasive investigations in the diagnosis of highly vascular lesions are without doubt a sound principle. A case is presented however, in which the clinical diagnosis of a haemangioma was confirmed by ultrasound and magnetic resonance imaging (MRI) but required further investigation by angiography to facilitate treatment. Embolisation is a well established technique available in most large radiology departments, but may not be well known by general dental practitioners.