Heat generation during removal of an abutment screw fragment from dental implants.

STATEMENT OF PROBLEM: Little information is available on the effect of drilling speed on surrounding bone during the removal of an abutment screw fragment. PURPOSE: The purpose of this in vitro study was to compare, in vitro, the peak temperature increase during the removal of fractured abutment screws from implants placed in a porcine mandible, using drilling speeds of 600 or 2000 rpm. MATERIAL AND METHODS: Twenty 4.3×13-mm dental implants were placed in 10 dissected porcine mandibles: 2 implants per mandible, 1 on each side. Localized defects were created in 20 surface-treated abutment screws, which were then tightened into each implant until a reproducible fracture occurred in each screw. The fractured screws were removed with a handpiece removal kit and irrigated with room-temperature water at either 600 or 2000 rpm. The temperature rise at the implant surface was measured at 3 levels with 3 type-K thermocouples. Repeated measure ANOVA was performed with the Tukey-Kramer post hoc test for mean pair-wise comparisons (α=.05 for all tests). RESULTS: Mean peak temperatures were significantly higher at 2000 rpm than at 600 rpm in the mid-body (P<.001) and crestal (P=.003) regions but not in the apical (P=.225) implant locations. No significant differences in mean peak temperatures were found among the 3 locations using 600 rpm (P=.179). In the 2000-rpm group, mean peak temperature in the mid-body area was consistently higher than that in the apical (P<.001) area, and more instances of temperature rise above 56°C and 60°C were observed. In 1 implant from this group, the estimated peak temperature exceeded the bone damage threshold value (50°C for 30 seconds). CONCLUSIONS: A drilling speed of 2000 rpm during the removal of abutment screw fragments caused overheating of the outer surface of the implant which may damage the surrounding bone; a speed of 600 rpm appears to be safe.

Changes in pediatric tracheostomy tubes exposed to home dishwashing.

OBJECTIVE: Determine the effects of household dishwashing on Tracheostomy Tube safety. INTRODUCTION: Tracheostomy tubes accumulate biofilms, which may limit their lifespan. Frequent cleaning of the tubes is a method for biofilm prevention. Cleaning practices vary widely. Some families prefer dishwashing of tubes, but its effects are currently unknown. We hypothesize that dishwashing has no significant effect on the physical properties of tracheostomy tubes and can be recommended as a safe way to clean tracheostomy tubes. METHODS: Twenty 4.0 Shiley™ pediatric tracheostomy tubes were randomly assigned into dishwashed (DW) and non-dishwashed (NDW) groups, 10/group. DW tubes were subjected to 12 wash cycles. Each tube's hardness along with the surface spectra were analyzed to assess for chemical composition changes. Three cannula samples from each group were also randomly assessed with scanning-electron microscopy and scored by blinded examiners to assess for changes in surface heterogeneity. RESULTS: Hardness testing revealed a statistically significant difference (p = 0.0009) between the NDW and the DW group indicating increased fragility in the dishwashed tubes. Spectral analysis revealed loss of plasticizers, indicating decreased flexibility. Blinded electron microscopy scoring revealed increased surface heterogeneity in the DW group (p = 0.00007). CONCLUSION: A significant decrease in tube hardness and increased surface heterogeneity were found with dishwashing. The spectral analysis demonstrated increasing fragility. We believe these effects could potentially lead to decreased mechanical safety. With increased surface heterogeneity there is a greater potential for biofilm formation. At this time, dishwashing cannot be recommended as a tracheostomy tube cleaning method.

Mechanical Modeling of the Human Cricoid Cartilage Using Computer-Aided Design: Applications in Airway Balloon Dilation Research.

OBJECTIVES: Balloon dilation is generally considered first-line treatment for airway stenosis. Some dilation systems utilize a compliant balloon that can conform around rigid structures. Others use a noncompliant balloon that does not conform, allowing for dilation of more rigid stenoses. We hypothesized that subglottic dilation with a noncompliant balloon increases the likelihood of fracture of the cricoid when compared to a compliant balloon. METHODS: Three fresh human cricoid cartilages were placed in a universal testing system to determine the expansile force necessary for cricoid fracture. Using these data, a 3D printer was used to construct a synthetic cricoid model possessing near identical physical characteristics to the human cricoid. Simulated dilation was then performed on the model using a compliant and a noncompliant balloon. RESULTS: Human cricoid fracture occurred at 97.25 N (SD = 8.34), and the synthetic cricoid model fractured at 100.10 N (SD = 7.32). Both balloons fractured the model in every replicate experiment. Mean balloon internal pressure at fracture was 7.67 ATM (SD = 1.21) for the compliant balloon and 11.34 ATM (SD = 1.29) for the noncompliant balloon. CONCLUSIONS: These data show that fracture of the cricoid is a valid concern in balloon dilation procedures where the balloon spans the subglottis. Furthermore, the hypothesis was rejected in that the compliant balloon system was at least as likely to fracture the cricoid model as the noncompliant.

Biomechanical changes from long-term freezer storage and cellular reduction of tracheal scaffoldings.

OBJECTIVES/HYPOTHESIS: To determine structural biomechanical changes in tracheal scaffolds resulting from cellular reduction and storage at -80(o) C. STUDY DESIGN: Laboratory-based study. METHODS: Forty-four rabbit tracheal segments were separated into four treatment groups: untreated (group A, control), cellular-reduced (group B), storage at -80(o) C followed by cellular reduction (group C), and cellular-reduced followed by storage at -80(o) C (group D). Tracheal segments were subjected to uniaxial tension (n = 21) or compression (n = 23) using a universal testing machine to determine sutured tensile yield load and radial compressive strengths at 50% lumen occlusion. Mean differences among groups for tension and compression were compared by analysis of variance with post-hoc Tukey-Kramer test. RESULTS: The untreated trachea (group A) demonstrated mean yield strength of 5.93 (± 1.65) N and compressive strength of 2.10 (± 0.51) N. Following treatment/storage, the tensile yield strength was not impaired (group B = 6.79 [± 1.58] N, C = 6.21 [± 1.40] N, D = 6.26 [± 1.18]; P > 0.10 each). Following cellular reduction, there was a significant reduction in compressive strength (group B = 0.44 N [± 0.13], P < 0.0001), but no further reduction due to storage (group C = 0.39 N [± 0.10]; P = 0.97 compared to group B). CONCLUSION: The data suggest cellular reduction leads to loss of compressive strength. Freezing at -80°C (either before, or subsequent to cellular reduction) may be a viable storage method for tracheal grafts.

Accuracy and precision of as-received implant torque wrenches.

STATEMENT OF PROBLEM: Previous implant torque evaluation did not determine if the target value fell within a confidence interval for the population mean of the test groups, disallowing determination of whether a specific type of wrench met a standardized goal value. PURPOSE: The purpose of this study was to measure both the accuracy and precision of 2 different configurations (spring style and peak break) of as-received implant torque wrenches and compare the measured values to manufacturer-stated values. MATERIAL AND METHODS: Ten wrenches from 4 manufacturers, representing a variety of torque-limiting mechanisms and specificity of use (with either a specific brand or universally with any brand of implant product). Drivers were placed into the wrench, and tightening torque was applied to reach predetermined values using a NIST-calibrated digital torque wrench. Five replications of measurement were made for each wrench and averaged to provide a single value from that instrument. The target torque value for each wrench brand was compared to the 95% confidence interval for the true population mean of measured values to see if it fell within the measured range. RESULTS: Only 1 wrench brand (Nobel Biocare) demonstrated the target torque value falling within the 95% confidence interval for the true population mean. For others, the targeted torque value fell above the 95% confidence interval (Straumann and Imtec) or below (Salvin Torq). CONCLUSIONS: Neither type of torque-limiting mechanism nor designation of a wrench to be used as a dedicated brand-only product or to be used as a universal product on many brands affected the ability of a wrench to deliver torque values where the true population mean included the target torque level.

Silorane- and high filled-based"low-shrinkage" resin composites: shrinkage, flexural strength and modulus

This study compared the volumetric shrinkage (VS), flexural strength (FS) and flexural modulus (FM) properties of the low-shrinkage resin composite Aelite LS (Bisco) to those of Filtek LS (3M ESPE) and two regular dimethacrylate-based resin composites, the microfilled Heliomolar (Ivoclar Vivadent) and the microhybrid Aelite Universal (Bisco). The composites (n = 5) were placed on the Teflon pedestal of a video-imaging device, and VS was recorded every minute for 5 min after 40 s of light exposure. For the FS and FM tests, resin discs (0.6 mm in thickness and 6.0 mm in diameter) were obtained (n = 12) and submitted to a piston-ring biaxial test in a universal testing machine. VS, FS, and FM data were submitted to two-way repeated measures and one-way ANOVA, respectively, followed by Tukey's post-hoc test (a = 5%). Filtek LS showed lower VS than did Aelite LS, which in turn showed lower shrinkage than did the other composites. Aelite Universal and Filtek LS exhibited higher FS than did Heliomolar and Aelite LS, both of which exhibited the highest FM. No significant difference in FM was noted between Filtek LS and Aelite Universal, while Heliomolar exhibited the lowest values. Aelite LS was not as effective as Filtek LS regarding shrinkage, although both low-shrinkage composites showed lower VS than did the other composites. Only Filtek LS exhibited FS and FM comparable to those of the regular microhybrid dimethacrylate-based resin composite.

Silorane- and high filled-based "low-shrinkage" resin composites: shrinkage, flexural strength and modulus.

This study compared the volumetric shrinkage (VS), flexural strength (FS) and flexural modulus (FM) properties of the low-shrinkage resin composite Aelite LS (Bisco) to those of Filtek LS (3M ESPE) and two regular dimethacrylate-based resin composites, the microfilled Heliomolar (Ivoclar Vivadent) and the microhybrid Aelite Universal (Bisco). The composites (n = 5) were placed on the Teflon pedestal of a video-imaging device, and VS was recorded every minute for 5 min after 40 s of light exposure. For the FS and FM tests, resin discs (0.6 mm in thickness and 6.0 mm in diameter) were obtained (n = 12) and submitted to a piston-ring biaxial test in a universal testing machine. VS, FS, and FM data were submitted to two-way repeated measures and one-way ANOVA, respectively, followed by Tukey's post-hoc test (a = 5%). Filtek LS showed lower VS than did Aelite LS, which in turn showed lower shrinkage than did the other composites. Aelite Universal and Filtek LS exhibited higher FS than did Heliomolar and Aelite LS, both of which exhibited the highest FM. No significant difference in FM was noted between Filtek LS and Aelite Universal, while Heliomolar exhibited the lowest values. Aelite LS was not as effective as Filtek LS regarding shrinkage, although both low-shrinkage composites showed lower VS than did the other composites. Only Filtek LS exhibited FS and FM comparable to those of the regular microhybrid dimethacrylate-based resin composite.

Influence of filler addition, storage medium and evaluation time on biaxial flexure strength and modulus of adhesive systems.

OBJECTIVE: This study evaluated the effects of filler addition, storage medium and time on biaxial flexural strength and flexural modulus of six adhesive systems. MATERIALS AND METHODS: The adhesives were either unfilled resins: Single Bond, Prime&Bond 2.1 and One-Step; or filled resins: Single Bond Plus, Prime&Bond NT and One-Step Plus. Resin discs of each product (0.5 mm thick × 6.0 mm diameter) were prepared using silicon molds (n = 10). The discs were stored dry, in water, mineral oil or ethanol for 1 week or 3 months before biaxial flexural testing. Data were statistically analyzed by 3-way ANOVA and Tukey's post-hoc test (α = 0.05). The specimens were tested in a universal testing machine at 1.27 mm/min until failure occurred. RESULTS: In general, the storage in ethanol led to significantly lower flexural strength and flexural modulus values than the other storage conditions for all adhesives in both storage periods. Filler addition increased flexural strength and flexural modulus for Prime&Bond NT, when it was stored dry or in water for 1 week. For Single Bond Plus, the filler addition resulted in higher flexural modulus, when it was stored for 1 week in oil and in ethanol. No significant differences in flexural modulus were observed between One-Step and One-Step Plus in any storage medium. CONCLUSIONS: Results suggested that filler addition does not necessarily have to increase the flexural strength and flexural modulus. Ethanol and oil storages tended to yield opposite effects.

The effect of filler addition on biaxial flexure strength and modulus of commercial dentin bonding systems.

OBJECTIVE: To evaluate the effects of filler addition on the biaxial flexural strength and modulus of two commercial adhesive systems. METHOD AND MATERIALS: The systems were either unfilled (Adper Single Bond [3M ESPE] and Prime and Bond 2.1 [Dentsply]) or filled (Adper Single Bond Plus [3M ESPE] and Prime and Bond NT [Dentsply]). Resin disks of each product (0.6 mm thick and 6.2 mm in diameter) were prepared in Teflon molds (n = 11 each group; 44 in total). The adhesive solutions were light activated with a halogen light-curing unit. The disks were stored dry in the dark 24 hours before biaxial flexural testing in a universal testing machine until fracture (1.27 mm/minute; model 5844, Instron). Data were statistically analyzed by one-way ANOVA and Tukey post hoc test at a preset alpha of 0.05. RESULTS: Flexural strength values (MPa) (SD) were Single Bond 62 (16); Single Bond Plus 46 (15); Prime and Bond 59 (13); and Prime and Bond NT 85 (16). The flexural moduli (MPa) (SD) were Single Bond 1,026 (241); Single Bond Plus 1,180 (188); Prime and Bond 744 (146); and Prime and Bond NT 1,539 (267). Based on the results, Prime and Bond NT (filled) exhibited higher flexural strength and modulus than Prime and Bond (unfilled), while no significant difference in both parameters was noted between Single Bond and Single Bond Plus. CONCLUSION: Filler addition to bonding agents can increase the flexural strength and modulus; however, results are product dependent.

Polymeric-calcium phosphate cement composites-material properties: in vitro and in vivo investigations.

New polymeric calcium phosphate cement composites (CPCs) were developed. Cement powder consisting of 60 wt% tetracalcium phosphate, 30 wt% dicalcium phosphate dihydrate, and 10 wt% tricalcium phosphate was combined with either 35% w/w poly methyl vinyl ether maleic acid or polyacrylic acid to obtain CPC-1 and CPC-2. The setting time and compressive and diametral tensile strength of the CPCs were evaluated and compared with that of a commercial hydroxyapatite cement. In vitro cytotoxicity and in vivo biocompatibility of the two CPCs and hydroxyapatite cement were assessed. The setting time of the cements was 5-15 min. CPC-1 and CPC-2 showed significantly higher compressive and diametral strength values compared to hydroxyapatite cement. CPC-1 and CPC-2 were equivalent to Teflon controls after 1 week. CPC-1, CPC-2, and hydroxyapatite cement elicited a moderate to intense inflammatory reaction at 7 days which decreased over time. CPC-1 and CPC-2 show promise for orthopedic applications.

Effect of vital tooth bleaching on solubility and roughness of dental cements.

STATEMENT OF PROBLEM: Vital tooth bleaching may affect properties of dental cements used for fixed prostheses. PURPOSE: The purpose of this study was to examine the effect of a combined in-office and at-home bleaching regimen on changes in surface roughness and depth loss of a variety of commercially available dental cements. MATERIAL AND METHODS: Five cement classifications were tested: glass ionomer, resin-modified glass ionomer, resin,self-adhesive resin cement, and zinc phosphate. Cements were placed in multiple wells in plastic blocks. After setting,the surface profile of each block was determined, and average roughness and vertical height of cement surface from the specimen holder were recorded. Blocks were water stored (control) or subjected to in-office and at-home bleaching(n=12). Surfaces were rescanned and pre- and posttest parameter changes were calculated. Statistical analysis consisted of Mann-Whitney-Wilcoxon Rank Sum and Student t tests applied to control and bleaching parameterc hanges within the same cements. A family-wise alpha of .05 was maintained by using a Bonferroni-adjusted level of significance preset to .01 per test. RESULTS: Zinc phosphate showed the only significant depth increase (P=.004) from bleaching: 0.9 +/- 0.7 microm deeper than the water-control group. Only resin-modified glass ionomer showed a significant (P=.004) increase in roughness from bleaching; values increased by 0.05 +/- 0.03 microm over the water-control group. CONCLUSIONS: In-office and at-home bleaching significantly increased depth loss of zinc phosphate and increased resinmodified glass ionomer roughness. However, the absolute values of differences observed, as compared to the wateronly control, were considered to be clinically insignificant. (J Prosthet Dent 2009;102:148-154)

Evaluation of biaxial flexural strength and modulus of filled and unfilled adhesive systems / Avaliação da resistência flexural biaxial e módulo de flexão de sistemas adesivos

Purpose: The purpose of this study was to evaluate the flexural strength and modulus of two adhesive systems using biaxial flexural strength test. Methods: The bonding agents (Pentron Clinical Technologies) tested were: Bond 1 (B1) and NanoBond (NB). Thirteen disks (6.1 mm diameter and 0.6 mm thick) were prepared with adhesive solutions of each bonding agents using Teflon molds. The adhesive solutions within the molds were light-activated with XL 3000 curing unit (3M ESPE) for 10 s on both sides. The disks were stored for 10 days and were tested in a universal testing machine (1.27 mm/min - Instron 5844). Data were statistically analyzed by one-way ANOVA (á=0.05). Results: The mean values of fracture strength (±SD) for adhesive systems were (in MPa):B1- 89.7±7.6 e NB- 131.1±9.5. Modulus means (±SD) were (in MPa): B1- 1999.9±258.4 e NB- 2314.5±271.0. Conclusion: The filled adhesive system (NB) exhibited higher strength and flexural modulus means than the unfilled adhesive B1.

Objetivo: O objetivo deste estudo foi avaliar a resistência flexural e o módulo de flexão de dois sistemas adesivos, através de ensaio de resistência flexural biaxial. Metodologia: Os adesivos (Pentron Clinical Technologies) estudados foram: Bond 1 (B1) e NanoBond (NB). Treze discos de cada adesivo foram preparados com dimensões aproximadas de 6,1 mm de diâmetro e 0,6 mm de espessura. Os discos de adesivos foram confeccionados utilizando-se moldes de teflon e fotopolimerizados com aparelho XL 3000 (3M ESPE). Após armazenamento por 10 dias, os discos foram testados em máquina universal de ensaio (Instron 5844), com velocidade de 1,27 mm/min. Os dados foram submetidos à análise de variância (1 fator) ao nível de significância de 0,05. Resultados: Os valores médios (±DP) de resistência flexural para os adesivos foram (em MPa): B1- 89,7±7,6 e NB- 131,1±9,5. Os valores médios de módulo flexural (±DP) foram (em MPa): B1- 1999,9±258,4 e NB- 2314,5±271,0.Conclusão: O adesivo contendo partículas de carga (NB) mostrou maiores valores de resistência flexural e módulo de flexão que o adesivo B1.

Brushing-induced surface roughness of nickel-, palladium-, and gold-based dental casting alloys.

STATEMENT OF PROBLEM: Alloys with high nickel content have been increasingly used for dental prostheses. These alloys have excellent hardness, elastic modulus, and strength, yet have high corrosion rates when exposed to chemical or physical forces that are common intraorally. PURPOSE: The purpose of the current study was to measure the susceptibility of several types of nickel-based alloys to brushing abrasion relative to gold- and palladium-based alloys. MATERIAL AND METHODS: Au-Pt, Au-Pd, Pd-Ag, Ni-Cr, and Ni-Cr-Be dental alloys were brushed with a toothbrush (Oral-B Soft) and toothpaste (Ultrabrite) in a linear brushing machine, then the surface roughness was measured by profilometry (R(a), R(v), R(p)). Specimens (n=4) were brushed for 48 hours in a saline solution (pH 7). The effect of brushing was determined using 2-sided t tests (alpha=.05), and roughness among alloys postbrushing was compared using 1-way ANOVA with Tukey post hoc analyses (alpha=.05). RESULTS: All polished alloy surfaces (before brushing) had roughnesses of 1 microm (R(a)). Ni-Cr alloys without Be had a postbrushing surface roughness of 0.25 microm (R(a)). Postbrushing roughness of all other alloys ranged from 0.1-0.25 microm (R(a)). R(v) and R(p) values behaved similarly to R(a) values for all alloys. CONCLUSIONS: Although they have many excellent mechanical properties, Ni-Cr-Be alloys may be prone to degradation from brushing.

Toothbrushing causes elemental release from dental casting alloys over extended intervals.

The release of elements from dental alloys has been linked to alloy biocompatibility. Much of the research measuring elemental release has been done in vitro under passive conditions. The current study supplements a previous report that measured elemental release from dental alloys during and after the equivalent of 1 week of toothbrushing. In the current study, toothbrushing times were extended to the equivalent of 2 years, and elemental release was measured during and after brushing, with and without toothpaste. The results showed that for the major classes of dental alloys, brushing alone caused no significant elemental release during the brushing, and only minor increases after brushing. Brushing with toothpaste caused significant increases in elemental release for all elements of all alloys, but the largest increases were for the two nickel-based alloys. Nickel released during brushing with toothpaste reached 600-800 microg/cm(2) of alloy surface. Both beryllium-containing and non-beryllium-containing nickel-based alloys behaved similarly, refuting claims that non-beryllium alloys are superior in this regard. Thus, brushing with toothpaste under these extended in vitro conditions appears to increase the biological liabilities from elemental release for all alloys, but primarily for nickel-based alloys.

Effect of toothbrushing on the toxicity of casting alloys.

STATEMENT OF PROBLEM: The biological properties of casting alloys have been assessed largely under passive conditions. The effect of common intraoral stresses such as brushing, toothpastes, and low pH on alloy toxicity are not known. PURPOSE: This study assessed the toxicity of 5 types of casting alloys commonly used in prosthodontics after toothbrushing, brushing in an acidic environment, or brushing with toothpaste. These toxicities were compared with those observed without any brushing. MATERIAL AND METHODS: Au-Pt, Au-Pd, Pd-Cu-Ga, Ni-Cr-Be, and Ni-Cr (no Be) alloys were brushed for 48 hours in a toothbrushing machine at 90 strokes/minute and 200g force. Alloys were brushed with either saline at pH 7, saline at pH 4 (acidified with sodium lactate), or saline with 1:7 (wt/wt) toothpaste. After the brushing regimen, the cytotoxicity of the alloys was assessed in a standard in vitro test. Cytotoxicities of the alloys after different brushing treatments were compared with unbrushed (control) specimens. Analysis of variance (ANOVA) and Tukey multiple comparison intervals (alpha=.05) were used to identify significant differences among brushing conditions. RESULTS: Brushing at pH 7 significantly increased the toxicity of the Pd-Cu-Ga alloy (15% to 20% over unbrushed specimens). Brushing at pH 4 increased the toxicity of the Au-Pt and Au-Pd alloys by 30% and the Pd-Cu-Ga alloy by >40%. The Ni-based alloys were not affected by acid. After being brushed with toothpaste, both Ni-based alloys were significantly more toxic, but Ni-Cr-Be was the worst, increasing more than 60% in toxicity over the controls. The toxicity of the Au-Pd alloy also increased significantly (15%). CONCLUSION: Brushing dental casting alloys may increase their cytotoxicity in vitro, but the increase depends heavily on the alloy type and brushing condition.