The accuracy and efficacy of disinfection by spray atomization on elastomeric impressions

Five disinfectants applied by spray atomization were examined for possible dimensional distortion of elastomeric impression materials, polyether, polysulfide, and addition silicone, and the associated improved, type IV gypsum casts. The disinfectants did not affect, in a clinically significant manner, the three dimensions measured with an instrument accurate to 1 micron on improved gypsum casts that reproduced a stainless steel standard. The master cast represented two teeth of a fixed partial denture prepared for complete veneer retainers. The use of control casts from elastomeric impressions that were not treated with the disinfectants further supported previous investigations reporting the accuracy of dental casts as the function of the impression material. The use of a spray disinfectant will not appreciably alter the dimensional accuracy of improved stone casts made within elastomeric impressions. The most accurate stone cast system was produced by addition silicone impressions disinfected by a surface spray. It was also shown that four of the disinfectants applied by spray atomization were effective in disinfecting the surface of an elastomeric impression material contaminated with selected test organisms.     

Fracture strength of ceramic bracket tie wings subjected to tension

One of the most common areas of ceramic bracket fracture is within the tie-wing complex. When an archwire is ligated into position, tensile forces are placed under the tie wing. However, no study, to date, has focused specifically on the fracture resistance of the tie-wing complex. The aim of this study is to compare the tensile fracture strength of seven currently available ceramic brackets (Inspire, Fascination, Mystique, InVu, Clarity, Virage, and Luxi) as a function of bracket brand and bracket configuration, semitwin vs true-twin. Based on a power analysis of pilot data, 10 maxillary central incisor brackets per group were tested to failure with a tensile load placed directly under the distoincisal tie wing. The results ranged from a maximum mean fracture strength of 147.71 (5.87) MPa with Fascination brackets to a minimum mean fracture strength of 84.28 (7.01) MPa with Luxi brackets. The statistical analysis indicated a significant effect on fracture strength as a function of bracket brand (P < .05) and that semitwin brackets, Fascination, Mystique, and Virage, had significantly higher fracture strength than true-twin brackets, Clarity, lnVu, and Luxi (P < .05). Interestingly, the only monocrystalline bracket in the study, Inspire, could not be fractured using the investigation protocol. In fact, the steel ligature fixture wire would break before tie-wing fracture at a mean fixture failure of 198.65 MPa.     

The effect of casting conditions on the biaxial flexural strength of glass–ceramic materials

OBJECTIVE: To assess the effect of mould and glass casting temperatures on the biaxial flexural strength (BFS) of two different types of castable glass-ceramic, using existing laboratory equipment and techniques. METHODS: Two castable glass-ceramic materials were evaluated. One glass (LG3) is based on SiO2-Al2O3-P2O5-CaO-CaF2, and is similar in composition to glasses used in the manufacture of glass-ionomer cements. The other glass (SG3) is based on SiO2-K2O-Na2O-CaO-CaF2, and is a canasite-based material. Both materials were used to produce discs of 12 mm diameter and 2 mm thickness using the same lost-wax casting process as used for metal castings. Mould temperatures of between 500 degrees C and 1000 degrees C and glass casting temperatures of between 1100 degrees C and 1450 degrees C were evaluated. The cast discs were cerammed and the biaxial flexural strength determined with a Lloyd 2000 R tester. RESULTS: A significant difference was found for the BFS in the range of mould temperatures evaluated, with the optimum investment mould temperature being 590 degrees C for LG3 and 610 degrees C for SG3 (p = 0.0002 and p = 0.019, respectively). No significant differences were seen between any of the glass casting temperatures evaluated. SIGNIFICANCE: The mould temperature for castable glass-ceramic materials produced using the lost-wax casting process can have a significant effect on BFS. The optimum mould temperature may differ slightly depending on the type of material being used. The glass casting temperature of these materials does not appear to have a significant effect on BFS.     

Comparison of elemental concentrations in the acinar cells of the human labial salivary gland.

Two types of acinar cells were observed in human labial glands by conventional and analytical electron microscopic and light microscopic techniques. The predominant type contained large and prominent secretory granules that were strongly mucicarmine and PAS (with and without diastase) positive. The second type contained small, lacy, secretory granules, and these cells were faintly positive with these stains. The elemental contents of the two types of granules were measured by analytical electron microscopy using digital mapping and spot analysis applied to freeze-dried cryosections prepared from gland slices incubated in vitro under non-stimulated conditions. The large secretory granules had significantly higher Ca, S and Mg concentrations and significantly lower Cl and K concentrations than the small granules. The difference in elemental contents probably reflects differences in the content of secretory macromolecules. Specifically, the S content is thought to reflect the anionic properties of the secretory macromolecules, while the levels of divalent cations are thought to be determined by electroneutrality requirements for macromolecular folding and storage. No differences were found in nuclear or cytoplasmic elemental concentrations between the two cell types.     

Early endosseous integration enhanced by dual acid etching of titanium: a torque removal study in the rabbit

Textured implant surfaces are thought to enhance endosseous integration. Torque removal forces have been used as a biomechanical measure of anchorage, or endosseous integration, in which the greater forces required to remove implants may be interpreted as an increase in the strength of bony integration. The purpose of this study was to compare the torque resistance to removal of screw-shaped titanium implants having a dual acid-etched surface (Osseotite) with implants having either a machined surface, or a titanium plasma spray surface that exhibited a significantly more complex surface topography. Three custom screw-shaped implant types - machined, dual acid-etched (DAE), and titanium plasma sprayed (TPS) - were used in this study. Each implant surface was characterized by scanning electron microscopy and optical profilometry. One DAE implant was placed into each distal femur of eighteen adult New Zealand White rabbits along with one of the other implant types. Thus, each rabbit received two DAE implants and one each of the machined, or TPS, implants. All implants measured 3.25 mm in diameter x 4.00 mm in length without holes, grooves or slots to resist rotation. Eighteen rabbits were used for reverse torque measurements. Groups of six rabbits were sacrificed following one, two and three month healing periods. Implants were removed by reverse torque rotation with a digital torque-measuring device. Three implants with the machined surface preparation failed to achieve endosseous integration. All other implants were anchored by bone. Mean torque values for machined, DAE and TPS implants at one, two and three months were 6.00+/-0.64 N-cm, 9.07+/-0.67 N-cm and 6.73+/-0.95 N-cm; 21.86+/-1.37 N-cm, 27.63+/-3.41 N-cm and 27.40+/-3.89 N-cm; and 27.48+/-1.61 N-cm, 44.28+/-4.53 N-cm and 59.23+/-3.88 N-cm, respectively. Clearly, at the earliest time point the stability of DAE implants was comparable to that of TPS implants, while that of the machined implants was an order of magnitude lower. The TPS implants increased resistance to reverse torque removal over the three-month period. The results of this study confirm our previous results that demonstrated enhanced bony anchorage to dual acid-etched implants as compared to machined implants. Furthermore, the present results indicate that dual acid etching of titanium enhances early endosseous integration to a level which is comparable to that achieved by the topographically more complex TPS surfaces.     

Teaching alternatives to the standard inferior alveolar nerve block in dental education: outcomes in clinical practice

Surveys were sent to Harvard School of Dental Medicine students and graduates from the classes of 2000 through 2006 to determine their current primary means of achieving mandibular anesthesia. Orthodontists and orthodontic residents were excluded. All subjects received clinical training in the conventional inferior alveolar nerve block and two alternative techniques (the Akinosi mandibular block and the Gow-Gates mandibular block) during their predoctoral dental education. This study tests the hypothesis that students and graduates who received training in the conventional inferior alveolar nerve block, the Akinosi mandibular block, and the Gow-Gates mandibular block will report more frequent current utilization of alternatives to the conventional inferior alveolar nerve block than clinicians trained in the conventional technique only. At the 95 percent confidence level, we estimated that between 3.7 percent and 16.1 percent (mean=8.5 percent) of clinicians trained in using the Gow-Gates technique use this injection technique primarily, and between 35.4 percent and 56.3 percent (mean=47.5 percent) of those trained in the Gow-Gates method never use this technique. At the same confidence level, between 0.0 percent and 3.8 percent (mean=0.0 percent) of clinicians trained in using the Akinosi technique use this injection clinical technique primarily, and between 62.2 percent and 81.1 percent (mean=72.3 percent) of those trained in the Akinosi method never use this technique. No control group that was completely untrained in the Gow-Gates or Akinosi techniques was available for comparison. However, we presume that zero percent of clinicians who have not been trained in a given technique will use the technique in clinical practice. The confidence interval for the Gow-Gates method excludes this value, while the confidence interval for the Akinosi technique includes zero percent. We conclude that, in the study population, formal clinical training in the Gow-Gates and Akinosi injection techniques lead to a small but significant increase in current primary utilization of the Gow-Gates technique. No significant increase in current primary utilization of the Akinosi technique was found.     

Role of african-american fathers in child-rearing and oral health practices in an inner city environment--a brief communication

OBJECTIVE: This study assesses parenting behaviors, health behaviors and attitudes in a sample of disadvantaged African-American fathers and evaluates the potential of fathers as recipients of oral health promotion interventions. METHODS: Participants were 60 African-American fathers whose children were enrolled in a childhood caries prevention study at Women and Infant Child Program (WIC) (n=25) or who were members of a Young Fathers' Program (n=35) at an urban health center. Demographic factors, oral health knowledge, dental self-efficacy, parenting behaviors, readiness to change, and health promotion behaviors were assessed. RESULTS: Participants averaged 30.8 years of age (sd=8.6); children averaged 2.1 years (sd=0. 9). Half of the fathers always have lived with their own children and 92% had regular physical contact with their children. Almost half of the sample reported 'fair/poor' oral health status, while less than 25% reported 'fair/poor' general health. Fathers had high oral health knowledge scores (x=7.7 correct of 9 items), and high readiness for change scores at the action stage (X=12.2 of 15; sd=1.9). dental self-efficacy scores were moderate (X=15.7 of 24; sd=5.5). Half of the fathers shared or had sole responsibility for brushing their children's teeth; 90% report children's teeth were brushed daily. CONCLUSIONS: African- American fathers participated in childrearing and oral health promotion behaviors.     

A comparison of student performance in a simulation clinic and a traditional laboratory environment: three-year results

With simulation clinics, dental schools have improved their preclinical laboratories to provide a more realistic clinical teaching environment. However, there is very little data to support the assumption that these facilities actually improve student performance of technical skills. This study compared the scores of two fixed preparations for full cast crowns by third-year dental students. One of the preparations was made in the simulation clinic manikin, and the other was prepared on the bench top. Three prosthodontic faculty members scored the preparations in the areas of occlusal reduction, axial reduction, resistance and retention, and margination. The study also compared the performance of three classes of dental students: one class with no experience in the simulation clinic, one with one year of experience, and one with two years of experience. The amount of time since completing the fixed prosthodontics course among the students was also evaluated. This was done because the third-year students at the University of Iowa rotate through a series often-week clerkships rather than a comprehensive care model. (Therefore, not all students start clinical prosthodontics at the same time.) In addition, all student participants completed a questionnaire that addressed their perception of their clinical readiness prior to treating their first fixed prosthodontic patient. When we compared the classes of years 1, 2, and 3 by average preparation score, we found a significant difference among the scores for teeth prepared on the bench top (p = 0.0001) but not for the teeth prepared in the mannequin (p = 0.1176). For Year 1 (no simulation clinic experience), the amount of elapsed time following completion of the fixed prosthodontic course was not significant for the tooth prepared on the bench top or in the manikin (p = 0.57113 and 0.0661). For Year 2 (one year of simulation clinic experience), the elapsed time following completion of the fixed prosthodontic course was significant for the tooth prepared on the bench top (p = 0.0482), but it was not significant for the tooth prepared in the manikin (p = 0.2968). For Year 3 (two years of simulation clinic experience), the amount of elapsed time following completion of the fixed prosthodontic course was not significant for the tooth prepared on the bench top or in the manikin (p = 0.7275 and 0.6007). The questionnaire revealed that, in general, the majority of the students perceived their clinical readiness as more than adequate. These results are mixed in that students with more bench top experience scored better on the bench top, and students with more manikin experience scored equally in both environments.     

Evaluation of Stresses and Forces in Selected I-Bars Using the Finite Element Method

Purpose Three-dimensional models of half-round, tapered and full-round, untapered I-bar clasps of varying configurations and material properties were constructed. The purpose of this study was to examine the stresses and reaction forces produced within each model upon deflection to 0.01 in (0.254 mm), 0.02 in (0.508 mm), and 0.03 in (0.762 mm) at 1 mm from the tip using the finite element method. Materials and Methods Three-dimensional computer models of half-round and full-round clasps were constructed using solid eight-node brick elements. The half-round, tapered I-bar clasp model was 2.4 and 1.4 mm in diameter at the base and tip, respectively. The full-round, tapered I-bar clasp model was 1 mm in diameter. Three design groups were created for each clasp form. Group A had 25% of the total length in the straight anchor end of the I-bar clasp, B had 35%, and C had 50%. All models were 31 mm in length and had a radius of curvature of 5 mm. Different material properties were incorporated into the models. Each model was deflected at a point 1 mm from the tip to 0.01 in (0.254 mm), 0.02 in (0.508 mm), and 0.03 in (0.762 mm). Results The stresses and forces produced as a result of the deflection applied to each clasp were viewed and displayed graphically. The maximum von Mises stresses in megapascals and the reaction force in newtons (N) were recorded. Stresses varied in each clasp in the range of 0 to 154.3 MPa for the half-round, tapered I-bar clasp models, and 0 to 100.9 MPa for the full-round I-bar clasp models at 0.01-in deflection. Reaction force measured near the tip of the clasp models was between 1.60 N and 6.31 N for the half-round, and between 0.22 N to 2.13 N for the full-round I-bar clasp models. For all clasps studied, as the deflection increased, the location of stress within each group remained the same regardless of the material properties; however, the stress and force values increased linearly. Conclusions The location of maximum stress varied with the length of the anchor portion of the clasps studied. Maximum stresses were located on the flat side of the half-round, tapered I-bar clasp model.