Biomedical subjects

Ailbhe McDonald

Publications and source records attributed to Ailbhe McDonald.

6 recordsLinked to original sources

PubMed2006

The biaxial flexural strength and fatigue property of Lava Y-TZP dental ceramic.

OBJECTIVES: The development of yttrium oxide partially stabilized zirconia (Y-TZP) has allowed the use of ceramic in load-bearing sites. The aim of this study was to evaluate and compare the biaxial flexural strength, hardness and fatigue life of colored and uncolored zirconia in the LAVAtrade mark system. MATERIALS AND METHODS: Eight groups (n=30) of standardized disc specimens (15mmx1.3mm) were used to examine the biaxial flexural strength (ISO 6872 standard) using a Dartec HC10 Fatigue Tester (Zwick Ltd., UK) and Vickers hardness was also measured. The uncolored, FS4, FS7 groups were also submitted to dynamic fatigue testing to produce stress-number curves. The strength reliability was analyzed using Weibull distribution. RESULTS: All groups had a mean biaxial flexural strength, hardness and Weibull modulus (m) of approximately 1100MPa, 1300HV and 9.8-12.9, respectively. One-way analysis of variance (ANOVA) showed no significant difference in biaxial flexural strength among the eight groups (p>0.05). Two-way ANOVA showed no significant differences in hardness values among groups except FS1 and FS5 which had significantly higher hardness values than FS4 and FS7 (p<0.001) and FS5 also had a higher hardness value than FS3 (p<0.05). Additionally, uncolored, FS4 and FS7 survived at 5x10(5) cycles at a stress level in the range of 60-65% of the mean biaxial flexural strength. CONCLUSION: There was no difference in flexural strength of uncolored and colored Y-TZP ceramic. The fatigue limit of uncolored, FS4 and FS7 zirconia may be defined as lying between 60 and 65% of the stress to failure.

Analysis of Variance↗

PubMed2003

A pilot study comparing the effectiveness of conventional training and virtual reality simulation in the skills acquisition of junior dental students.

The use of virtual reality (VR) in the training of operative dentistry is a recent innovation and little research has been published on its efficacy compared to conventional training methods. To evaluate possible benefits, junior undergraduate dental students were randomly assigned to one of three groups: group 1 as taught by conventional means only; group 2 as trained by conventional means combined with VR repetition and reinforcement (with access to a human instructor for operative advice); and group 3 as trained by conventional means combined with VR repetition and reinforcement, but without instructor evaluation/advice, which was only supplied via the VR-associated software. At the end of the research period, all groups executed two class 1 preparations that were evaluated blindly by 'expert' trainers, under traditional criteria (outline, retention, smoothness, depth, wall angulation and cavity margin index). Analyses of resulting scores indicated a lack of significant differences between the three groups except for scores for the category of 'outline form', for group 2, which produced significantly lower (i.e. better) scores than the conventionally trained group. A statistical comparison between scores from two 'expert' examiners indicated lack of agreement, despite identical written and visual criteria being used for evaluation by both. Both examiners, however, generally showed similar trends in evaluation. An anonymous questionnaire suggested that students recognized the benefits of VR training (e.g. ready access to assessment, error identification and how they can be corrected), but the majority felt that it would not replace conventional training methods (95%), although participants recognized the potential for development of VR systems in dentistry. The most common reasons cited for the preference of conventional training were excessive critical feedback (55%), lack of personal contact (50%) and technical hardware difficulties (20%) associated with VR-based training.

Competency-Based Education↗

PubMed2003

A study comparing the effectiveness of conventional training and virtual reality simulation in the skills acquisition of junior dental students.

The use of virtual reality (VR) in the training of operative dentistry is a recent innovation and little research has been published on its efficacy compared to conventional training methods. Two groups of dental students, with no experience in operative dentistry, were trained solely by either VR or conventional training in the preparation of conventional class 1 cavities. The subjects all used the same operative armamentarium and phantom heads, and were allocated the same duration of practice periods. At the completion of these training periods, both groups produced two class 1 cavities on the lower left first molar, which were subsequently coded and blindly scored for the traditional assessment criteria of outline form, retention form, smoothness, cavity depth and cavity margin angulation. An ordinal score of 0-3 or 0-4 was assigned for each assessment criterion: the higher the score, the worse the evaluation. After initial independent scoring, the two examiners discussed any notable differences until an agreed score was reached. Once the codes were broken, non-parametric analyses were performed on the data. Wilcoxon Tests for the semiquantitative scores indicated significant differences between the VR and conventional training groups for outline form, depth and smoothness but not for retention or cavity margin angulation at P < 0.05 level, with the VR group receiving the higher, i.e. worse, scores. Cavity margin angulation approached significance with a P-value of 0.0536. The results indicated that VR-based skills acquisition is unsuitable for use as the sole method of feedback and evaluation for novice students.

Clinical Competence↗

PubMed2003

An in vitro study of the compressive load at fracture of Procera AllCeram crowns with varying thickness of veneer porcelain.

STATEMENT OF PROBLEM: When designing and cutting a crown preparation, a balance must be achieved between the amount of tooth structure conserved and the space created for the restoration. All-ceramic crowns, which contain a core, are usually veneered with porcelain to produce the desired aesthetics and contour. The effect of veneer porcelain on the strength of the restoration has been a cause of debate. PURPOSE: The purpose of this study was to investigate the effect of different thickness of veneer porcelain on the compressive load at fracture of Procera AllCeram crowns. MATERIAL AND METHODS: Sixty brass dies were fabricated with a crown-like preparation and a chamfer margin. Sixty crowns were fabricated with a 0.6-mm-thick core: Procera crowns with either a 0.4-mm- or 0.9-mm-thick veneer of AllCeram (Groups 1 and 2 respectively) and In-Ceram crowns with a 0.9-mm-thick veneer of Vitadur Alpha porcelain (Group 3). Each group consisted of 20 crowns. In-Ceram crowns were used as the control group. All crowns were measured at 4 axial and 1 occlusal random locations before autoglazing. They were air abraded and adhesively bonded onto the appropriate brass die using Clearfil Newbond Bonding Agent, Clearfil Porcelain Bond Activator, and Panavia 21 TC Dental Adhesive as the luting agent. After storage in distilled water at 37 degrees C for 24 hours, the specimens were placed in a compressive test rig within an Instron universal testing machine and loaded in the center of the occlusal surface with a 4-mm diameter stainless steel ball. An axial preload of 20 N was applied before compressive testing at a crosshead speed of 0.1 mm/minute until fracture occurred. An analysis of variance revealed no significant difference in the load at fracture between the 3 groups (P=.3). Using a Bonferroni correction, independent t tests revealed no significant difference in load at fracture for any of the pair-wise comparisons between the 3 test groups (P < .05). RESULTS: The mean load at fracture for Group 1 was 2197.6 N (SD = 776.4); Group 2, 2401.4 N (SD = 699.1); and Group 3, 2581.0 N (SD = 715.6). CONCLUSION: Within the parameters of this study, the axial thickness of veneer porcelain did not have a significant effect on the compressive load at fracture of Procera AllCeram crowns.

Aluminum Oxide↗

PubMedDate not supplied

Developing a tooth restorability index.

UNLABELLED: It is generally agreed that the inherent strength of a tooth is dependent on the remaining dentine. It therefore seems logical that preservation of coronal dentine is important to the survival of intra- and extra-coronal restorations. The clinical assessment of the amount of dentine needed for functional requirements and the strategic value of remaining tooth structure is currently based on clinical opinion. This paper discusses what recommendations have been published and proposes an index that may be useful in assessing the restorability of a tooth. CLINICAL RELEVANCE: An index used to assess the amount and contribution of remaining coronal dentine to resistance and retention form could be of value in treatment planning.

Dental Prosthesis Retention↗

PubMedDate not supplied

An in vitro study to investigate the load at fracture of Procera AllCeram crowns with various thickness of occlusal veneer porcelain.

PURPOSE: The aim of this study was to investigate the effect of occlusal veneer porcelain thickness on the load at fracture of Procera AllCeram crowns. MATERIALS AND METHODS: Fifty resin dies were manufactured to incorporate the features of an all-ceramic crown preparation on a premolar tooth. Fifty corresponding crowns were constructed and divided into five groups. Groups 1, 2, 3, and 4 were crowns with 0.6-mm-thick Procera cores and 0.4-mm-thick axial veneer porcelain and occlusal veneer porcelain thicknesses of 0.0 mm, 0.4 mm, 0.9 mm, and 1.4 mm, respectively. Group 5 specimens consisted of 0.6-mm-thick In-Ceram cores with 0.4 mm of axial porcelain and 0.4 mm of occlusal porcelain. The crowns were cemented onto their respective dies with a resin luting agent. Specimens were stored in distilled water at 37 degrees C for 24 hours prior to placing them in a universal testing machine and applying a controlled compressive load at a cross-head speed of 0.1 mm/min until fracture occurred. RESULTS: The mean loads at fracture were 419 N (group 1), 702 N (group 2), 1,142 N (group 3), 1,297 N (group 4), and 732 N (group 5). Statistical analysis revealed significant differences (P < .05) in the load at fracture between the groups, except for between groups 2 and 5. CONCLUSION: Increasing the thickness of the occlusal veneer porcelain increased the load at fracture for Procera AllCeram crowns. There was no significant difference in load at fracture between the Procera and In-Ceram crowns.

Aluminum Oxide↗