In Vitro Evaluation of Remineralization Potential of Five Toothpastes on Soft Drink-Eroded Human Enamel and Dentine.

OBJECTIVE: The purpose of this in vitro study was to evaluate the potential remineralization of enamel and dentine erosion lesions after the application of five different toothpastes. METHODOLOGY: A total of 104 enamel and dentine samples were prepared from maxillary third molars. Each group was divided according to the toothpaste application mode (topical = 56; brushing = 48) and the toothpaste used seven topical groups and six brushing groups (n = 8). The groups included negative control (NC), positive control (PC), Sensodyne Pronamel (SP), Regenerate (R), Regenerate with boosting serum (R+), Colgate Duraphat 5000 (CD), and tooth mousse (TM). RESULTS: The statistical analysis showed significant surface microhardness (SMH) change. All enamel groups showed a significant decrease in SMH compared to NC for both application modes. However, no significance was recorded between test groups. Similar results were observed between dentine groups and their relevant controls for both application modes, except brushed R and R+ groups, which were insignificant to their NC. For topical groups, TM showed a significant increase in SMH. While R and R+ showed lower loss than SP and CD. CONCLUSIONS: All tested agents offered a degree of remineralization in both enamel and dentine with no significant difference between agents in enamel groups while R, R+, and TM offered better results in dentine groups. CLINICAL SIGNIFICANCE:  For dentine groups, similar findings were observed with superior tooth surface protection with the application of TM over other agents. Tooth surface remineralization was achieved when agents were either applied topically or brushed over the surface.

Prevalence of antibiotic resistance genes in the oral cavity and mobile genetic elements that disseminate antimicrobial resistance: A systematic review.

The objective of this review was to assess the prevalence of antibiotic resistance genes in the oral cavity and identify mobile genetic elements (MGEs) important in disseminating them. Additionally, to assess if age, geographic location, oral site, bacterial strains and oral disease influence the prevalence of these genes. Three electronic databases (Medline, Embase and the Cochrane Library) were used to search the literature. Journals and the grey literature were also hand searched. English language studies from January 2000 to November 2020 were selected. Primary screening was performed on the titles and abstracts of 1509 articles generated. One hundred and forty-seven full texts were obtained to conduct the second screening with strict inclusion and exclusion criteria. Forty-four final articles agreed with the inclusion criteria. Half of the studies were classed as low quality. tet(M) was the most prevalent gene overall and the conjugative transposon Tn916 the most common MGE associated with antibiotic resistance genes in the oral cavity. In babies delivered vaginally, tet(M) was more prevalent, whilst tet(Q) was more prevalent in those delivered by C-section. Generally, countries with higher consumption of antibiotics had higher numbers of antibiotic resistance genes. Agricultural as well as medical use of antibiotics in a country should always be considered. Between healthy, periodontitis and peri-implantitis subjects, there was no difference in the prevalence of tet(M); however, erm(B), tet(M) and tet(O) were higher in carious active children than the non-carious group. Subjects with poor oral hygiene have more pathogenic bacteria that carry resistance genes compared to those with good oral hygiene. Enterococcus faecalis isolates demonstrated significant tetracycline resistance (tet(M) up to 60% prevalence in samples) and erythromycin resistance (erm(B) up to 61.9% prevalence in samples), periodontal pathogens showed significant beta-lactam resistance with blaZ and cfxA present in up to 90%-97% of samples and the normal oral flora had a high level of erythromycin resistance with mef(A/E) present in 65% of Streptococcus salivarius isolates. The most common resistance gene was tet(M) in root canals, cfxA in subgingival plaque, erm(B) in supragingival plaque and tet(W) in 100% of whole saliva samples. The review highlights that although many studies in this area have been performed, 50% were classed as low quality. We advise the following recommendations to allow firm conclusions to be drawn from future work: the use of large sample sizes, investigate a broad range of antibiotic resistance genes, improved methodologies and reporting to improve the quality of genetic testing in microbiology and randomisation of subject selection.

Compromised dental cells viability following teeth-whitening exposure.

This study aimed to assess the viability of dental cells following time-dependent carbamide peroxide teeth-whitening treatments using an in-vitro dentin perfusion assay model. 30 teeth were exposed to 5% or 16% CP gel (4 h daily) for 2-weeks. The enamel organic content was measured with thermogravimetry. The time-dependent viability of human dental pulp stem cells (HDPSCs) and gingival fibroblast cells (HGFCs) following either indirect exposure to 3 commercially available concentrations of CP gel using an in-vitro dentin perfusion assay or direct exposure to 5% H2O2 were investigated by evaluating change in cell morphology and by hemocytometry. The 5% and 16% CP produced a significantly lower (p < 0.001) enamel protein content (by weight) when compared to the control. The organic content in enamel varied accordingly to the CP treatment: for the 16% and 5% CP treatment groups, a variation of 4.0% and 5.4%, respectively, was observed with no significant difference. The cell viability of HDPSCs decreased exponentially over time for all groups. Within the limitation of this in-vitro study, we conclude that even low concentrations of H2O2 and CP result in a deleterious change in enamel protein content and compromise the viability of HGFCs and HDPSCs. These effects should be observed in-vivo.

Quality of life and other psychological factors in patients with tooth wear.

Aim To investigate the relationship between generic and condition-specific (CS) quality of life, general psychological wellbeing and personality in patients with tooth wear.Materials and methods Ethical approval was granted (REC:10/H0709/21). Patients aged 18-70 years with tooth wear completed the Oral Impact on Daily Performance (OIDP) quality of life questionnaire, the NEO-FFI Personality questionnaire and the General Health Questionnaire-12 (GHQ). Tooth wear was measured with the Basic Erosive Wear Examination (BEWE).Results In total, 102 subjects were recruited. Increased BEWE scores were correlated with older age and worse generic and CS-related quality of life. Increased neuroticism was correlated with increased: generic and CS OIDP scores; generic and CS eating scores; CS smiling scores; and CS carrying out major work scores. Increased GHQ scores were positively correlated with increased: generic and CS OIDP scores; generic and CS eating scores; CS speaking scores; generic and CS cleaning scores; generic relaxing scores; generic and CS smiling scores; and generic emotional state scores (p <0.05). Multivariable linear regression analyses showed that increased neuroticism and decreased GHQ both had an independent effect on generic and CS OIDP scores when adjusted for tooth wear severity (p <0.05).Conclusion Quality of life perception is complex and was not only affected by worsening levels of tooth wear.

Digital Image Correlation and Strain Gauges to Map and Compare Strain in Teeth with Different Quantity and Quality of Remaining Tooth Structure.

PURPOSE: To evaluate strain in teeth with differing quality and quantity of tooth surface loss by utilizing surface displacement field measured using digital image correlation (DIC) and strain gauges (SG). MATERIALS AND METHODS: A total of 80 mesio-occlusodistal preparations were carried out in human maxillary premolars. Ten sound premolars served as a control group, and treated samples were divided into two groups of 40 each according to the composition of the prepared walls (composed of either enamel and dentin [E + De] or dentin only [De]). Each group was then divided into four subgroups of 10 each according to the selected cusp height-to-width ratio (A = 2:1 mm; B = 3:1 mm; C = 3:1.5 mm; D = 4.5:1.5 mm). The samples were uni-axially loaded to 130 N, and strain was recorded using DIC and SG. RESULTS: With SG testing, control samples recorded the lowest strain values and were significantly different from all test groups. However, DIC failed to detect strain in control samples, as it was too low. With DIC, group D showed the lowest strain readings among all the dimension groups and was significantly different from groups A and B, but the composition of the remaining tooth structure did not show any significant effects. With SG testing, remaining wall dimension and composition both had significant effects: Group A scored the highest strain at all compositions, and E + De had better resistance to load stresses than De only. CONCLUSION: For both testing methodologies, height (≥ 3 mm) and width (1 to 1.5 mm) of the remaining tooth structure had an effect on strain. Tooth compositions of E + De resisted strain better than De counterparts at all dimensions.

The Effect of Different Water Temperatures on Retention Loss and Material Degradation of Locator Attachments.

PURPOSE: To examine the changes in Locator attachments after exposure to different water temperatures and cyclic loading. MATERIALS AND METHODS: Four groups of pink Locator attachments (3.0 lb. light retention replacement patrix attachments; 10 per group) were soaked for the equivalent of 5 years of use in distilled water at the following temperatures: 20°C, 37°C, 60°C. One group was kept dry to test the effect of water. A universal testing machine was used to measure the retention force of each treated attachment during 5500 insertion and removal cycles, simulating approximately 5 years of use. The results were compared using Kruskal-Wallis one-way ANOVA by ranks. Surface changes of tested attachments were examined using scanning electron microscopy (SEM). RESULTS: The exposure to 60°C water significantly increased the percentage of retention loss in Locator attachments (p < 0.05) compared to the 20°C water group and significantly reduced the final retention force compared to the other groups (p < 0.05). SEM examinations revealed severe cracking and material degradation in Locator attachments after exposure to 60°C water and cyclic loading, which were not evident in other groups. Cracking was observed after exposure to 60˚C water before cyclic loading. CONCLUSIONS: Exposure to 60°C water, potentially similar to denture cleansing procedures, could cause cracking in Locator attachments. Cracking is associated with hydrolytic degradation of nylon at 60°C. The change in structure could result in a significant loss of retention.

In vitro evaluation of the antibiofilm properties of chlorhexidine and delmopinol on dental implant surfaces.

Biofilm development on the internal surfaces of dental implants and dental implant components may be associated with peri-implant hard and soft tissue abnormalities. Currently, no protocols have been established for effective disinfection of removable implant components. The purpose of this study was to evaluate the antibiofilm properties of commonly used dental antimicrobial agents (chlorhexidine and delmopinol) on multispecies biofilms. Biofilms of 48 h and 168 h maturity were exposed to 0.2% chlorhexidine, 2% chlorhexidine and a product containing 0.2% delmopinol for 5, 10 and 20 min. 2% chlorhexidine was the most effective agent, achieving a total viable biofilm reduction ranging from 96.2% to >99.99% depending on the time of exposure and the stage of biofilm development.

A new three-component formulation for the efficient whitening of teeth (Carbamide Plus).

OBJECTIVES: This study aimed to develop and characterise a new three-component dental whitening formulation which is as effective as the currently used carbamide peroxide but at significantly lower hydrogen peroxide concentrations. MATERIALS AND METHODS: The new formulation (Carbamide Plus) was prepared containing hydrogen peroxide, urea, and sodium tripolyphosphate and compared directly with carbamide peroxide (containing just hydrogen peroxide and urea). To evaluate the clinical effectiveness of 5% Carbamide Plus, a randomised double-blind placebo-controlled clinical trial was conducted comparing the tooth colour of 33 patients using L*a*b* scores at baseline and after a 2-week whitening treatment. The behaviour of the three components in solution was determined by (1)H and (31)P NMR spectroscopy and pH dilution experiments. RESULTS: This clinical trial revealed that 5% whitening gels containing Carbamide Plus were as effective as those containing 10% carbamide peroxide. (1)H and (31)P NMR spectroscopy revealed strong intermolecular interactions between hydrogen peroxide and both urea and sodium tripolyphosphate (STPP) with little apparent interaction between urea and STPP. CONCLUSIONS: In this manuscript, we postulate that this increased whitening efficiency is due to a marked increase in local pH upon dilution which destabilises the hydrogen peroxide and expedites the whitening process. We postulate Carbamide Plus to be a three-component adduct with two molecules of carbamide peroxide binding to a central STPP unit with no direct interaction between STPP and urea. There were no statistically significant differences between Carbamide Plus and 10% carbamide peroxide in tooth-whitening achieved at 2 weeks. These results were recorded following 2 weeks of 2-h daily wear of at-home trays. CLINICAL RELEVANCE: Carbamide Plus offers the potential of using significantly lower levels of hydrogen peroxide concentration to achieve similar dental whitening effects.

The influence of interimplant divergence on the retention characteristics of locator attachments, a laboratory study.

PURPOSE: The aim of the study was to assess the influence of interimplant divergence on retention of two Locator attachments before and after in vitro simulation of 3 to 5 years of use. MATERIALS AND METHODS: A hydraulic universal testing machine was used to measure the retention of two blue Locator attachments during 5500 seating and unseating cycles. Ten pairs of Locators were tested with interimplant divergences of 0°, 10°, and 20°. Scanning electron microscopy (SEM) was used to examine surface changes of the components. The results were tested with ANOVA and Bonferroni post hoc correction when normally distributed. Results that were not normally distributed were tested with Kruskal-Wallis one-way ANOVA by ranks. RESULTS: At the start of the experiment the 10° group showed significantly more retention than the 0° group, but no significant difference was found between the 0° and 20° groups or the 10° and 20° groups. After 5500 cycles, there was no significant difference in retention between any of the groups. The SEM images showed an approximately equal amount of wear in the nylon patrix inserts from all the groups. CONCLUSIONS: The retention of Locator pairs was not impaired by interimplant divergence of up to 20°. Retention after 5500 removal cycles was less than the initial retention in all groups. The nylon Locator patrices showed wear defects of similar location, type, and magnitude in the SEM images, regardless of interimplant angulation.

Effect of cavity design on tooth surface strain.

STATEMENT OF PROBLEM: The loss of tooth structure can increase cuspal flexure, thereby reducing the fracture resistance of the tooth, or open the tooth-restoration interface, leading to microleakage. PURPOSE: The purpose of this study was to evaluate tooth strain in teeth with different cavity preparations after loading and unloading. MATERIAL AND METHODS: Ten intact human maxillary premolars were selected and embedded in epoxy resin molds. Constantan strain gauges were used and tested as an intact tooth (group I), occlusal cavity (group O), mesio-occlusal cavity (group MO), and finally mesio-occluso-distal cavity (group MOD). All teeth were subjected to gradual nondestructive occlusal loading and unloading (50 N, 70 N, 90 N, 110 N, 130 N, 50 N, 0 N) in a servohydraulic testing machine. All data were analyzed statistically by performing a repeated measures ANOVA with load and cavity as factors to compare the relevant mean strains, and a Bonferroni post hoc test was performed for multiple comparisons (α=.05). RESULTS: The repeated measures ANOVA did not provide any evidence of an interaction between load and cavity but indicated a significant difference in the mean strains both between the loads (P<.001) and between the cavity groups (P<.001). CONCLUSIONS: MOD cavities presented statistically significantly higher values of strain than MO, O, or intact teeth, and a significant increase in the values of mean strain for all cavities was observed, even with intact teeth, when nondestructive occlusal loading was increased.

Susceptibility of MRSA biofilms to denture-cleansing agents.

Methicillin-resistant Staphylococcus aureus (MRSA) is an important nosocomial pathogen, which is responsible for considerable morbidity and mortality in the United Kingdom. The major reservoir of this organism is thought to be the anterior nares, but there is increasing evidence that this pathogen is present in the oral cavity, particularly in denture wearers. The purpose of this study was to determine whether MRSA, grown as biofilms on denture acrylic resin, could be eradicated using commercially available agents. EMRSA-15 or EMRSA-16 was grown in a model system on the surface of denture acrylic resin for 4, 24 or 120 h before the samples were exposed to a range of disinfectants for time intervals of 1, 5 and 10 min. All of the agents reduced the number of cultivable MRSA bacteria present on the acrylic resin surface at 4 h, with 2% sodium hypochlorite (NaOCl) eliminating MRSA below the level of detection after an exposure of 1 min. However, the established MRSA biofilms (24 and 120 h) were more resistant to killing by the agents, although 2% NaOCl was still able to eradicate all ages of MRSA biofilms within 1 min of exposure.

Flexural strength, fatigue life, and stress-induced phase transformation study of Y-TZP dental ceramic.

OBJECTIVES: Yttria partially-stabilized zirconia polycrystalline (Y-TZP) has been the subject of extensive research because of its high strength and toughness. The aim of this study was to evaluate the biaxial flexural strength, fatigue life, and to investigate in more detail on single cycle specimens, the pressure-induced phase transformation of a Y-TZP dental ceramic using Raman microspectroscopy. MATERIALS AND METHODS: Thirty standardized discs (15 x 1.2 mm(2)) were used to examine the biaxial flexural strength (ISO 6872 standard) using a Dartec HC10 Servohydraulic testing machine (Zwick Ltd., UK). The specimens were also submitted to Vickers hardness (on polished and as-received surfaces within the same specimen) and dynamic fatigue test. The initial bulk phases were examined via X-ray diffraction and the local phase transformations that occurred in the zirconia induced by the various Vickers indentation loads (20-50 kg) were examined via Raman microspectroscopy on single cycle specimens. The fracture surface after biaxial flexural testing was also examined via Raman spectroscopy. RESULTS: The Cercon specimens tested had flexural strength and Weibull modulus (m) of approximately 823.3 (+/-114.7) MPa and 8.3, respectively. As-received surfaces (1378.7 +/- 51.8 Hv) had slightly higher hardness value compared with polished surfaces (1354.33 +/- 50.9 Hv); however, two-way analysis of variance showed no significant difference in hardness values between polished and as-received surfaces (P > 0.05). Additionally, the specimens survived to 5 x 10(5) cycles when using a load of 70% of the mean biaxial flexural strength or lower. Raman microspectroscopy showed transformation of tetragonal to cubic and monoclinic phases within the indentation area. The fraction of monoclinic phase showed only limited variation with load or distance from the center to indentation edge. The level of cubic phase, however, was greatest at the indentation center. Transformation to cubic phase was observed on the lower surfaces (tension side) of fractured specimens. It was also observed near the specimen center exposed upon fracture. In the latter region an increase in monoclinic phase was additionally observed. Further work will be carried out using Raman microspectroscopy to assess the effect of fatigue on phase transformations. CONCLUSION: The zirconia based ceramic has mechanical properties that may allow it to withstand the loading found in posterior areas. Transformation toughening was found when high loads impacted on the surface of zirconia. However it should be born in mind that this work was not carried out on veneered specimens, which exhibit different failure modes.

Fatigue and fracture properties of yttria partially stabilized zirconia crown systems.

OBJECTIVES: The purpose of this study was to test in vitro the fatigue and fracture properties of the Zirconia Everest core material after being veneered with a sintered or a heat-pressed veneer material. METHODS: Fifty zirconium copings were made using Kavo Everest ZS-blanks and the CAD/CAM technology. These were divided equally into two groups. Group one was veneered by a heat-pressed material (IPS e.max ZirPress) and group two was veneered by a sintered material (IPS e.max Ceram). All the crown shapes were subjected to 50,000 cycles of cyclic loading in water between 20 and 200 N, at a rate of 1 Hz and then loaded dynamically at a crosshead speed of 1 mm/min, until failure. Specimens of the core and the veneering materials were characterized using X-ray diffraction (XRD) and secondary electron imaging (SEI). RESULTS: There was no statistically significant difference in the mean failure load (N+/-S.D.) between group 1: 2135.6+/-330.1 and group 2: 2189.9.1+/-317.6 (p>0.05). No difference was found in the Weibull modulus and characteristic failure load values between the two groups (p>0.05). The specimens displayed mainly cohesive failure within the veneering material. XRD of the zirconium powder before sintering revealed tetragonal and monoclinic phases while after sintering only tetragonal zirconia could be identified. SIGNIFICANCE: There was no difference in the fatigue properties of the Zirconia Everest core material following sintering or heat pressing of the veneering material (p>0.05).

In vitro study investigating the mass of tooth structure removed following endodontic and restorative procedures.

STATEMENT OF PROBLEM: There is limited scientific evidence which quantifies the amount of tissue removed during endodontic and restorative procedures. PURPOSE: The purpose of this study was to measure and compare the mass of tissue structure removed from incisor and canine teeth following successive preparations. MATERIAL AND METHODS: Twenty-two intact, disease- and restoration-free teeth (n=11/group) were collected from consenting patients undergoing dental extractions at Eastman Dental Hospital. The teeth were stored in 4% formaldehyde saline and successively prepared for an access opening (AC), endodontic instrumentation (EI), porcelain laminate veneer (PC), metal-ceramic (MC) crown, and post-and-core (PC) preparations. The baseline mass for each tooth was measured and recorded, in grams, at baseline and after each preparation, on a digital analytical balance. A standard protocol was applied to ensure accurate mass measurements. Repeated measures analysis of variance (ANOVA) was used to make comparisons between the incisor and canine groups (alpha =.05) for actual mass of tooth in milligrams, percentage of tooth mass remaining compared to baseline, and percentage decrease in mass compared to the preceding procedure. RESULTS: The estimated marginal percentage mass lost was significantly greater (P<.001) in the incisor group compared to the canine group, as an overall trend, with the incisors losing proportionally more mass for each procedure (P<.001). CONCLUSIONS: Mean percentage of removed tooth tissue increased successively from EI, AC, PC, and PV preparation, with greatest change from the previous procedure occurring for MC crown preparation.

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.

Interface dimensions of CEREC-3 MOD onlays.

Evaluation was undertaken of the interface dimensions of MOD ceramic onlays fabricated using the Cerec 3 system. A master die was prepared on a maxillary second premolar Ivorine tooth from which 20 Cerec 3 onlays and 20 feldspathic onlays were made. A total of 80 cement analogues were produced using elastomeric impression material and sectioned orthogonally. Interface dimension was measured using Image Analysis Software. The ceramic onlays constructed using Cerec 3 demonstrated significantly larger cement lute space compared with laboratory produced feldspathic porcelain onlays with mean thickness of 201.3 +/- 78.0 microm and 139.7 +/- 49.7 microm respectively (P < 0.001). Large interface dimensions were particularly noted in the proximal boxes. The multiple variables involved in the construction of the Cerec onlays as well as the complexity of the onlay design may be contributing factors to the large cement space.

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.

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.

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.

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.