The influence of functional forces on the biomechanics of implant-supported prostheses--a review

Objectives: To evaluate published evidence related to the influence of functional forces on the biomechanics of implant-supported prostheses.

Data and sources. The literature was searched for original research articles relating control of loads on dental implants, effects of early and late occlusal loads, the influence of bone quality, prosthesis type, prosthesis material, number of supporting implants, and engineering techniques employed for evaluating mechanical and biomechanical behavior of implants using MEDLINE^® and manual tracing of references cited in key papers otherwise not elicited.

Study selection. Current literature on implant biomechanics as main focus and pertinent to key aspects of the review.

Conclusions. The outcome of implant treatment is often maximized when implants are placed in dense bone, number of supporting implants are increased, implant placement configuration reduces the effects of bending moments, and when a fixed prosthesis is delivered to the patient.     

Comparison of post-gel shrinkage strains in light-polymerized composite resins

STATEMENT OF PROBLEM: Polymerization shrinkage is associated with light-polymerized and polyacid-modified composites. PURPOSE: This in vitro study compared the polymerization shrinkage of a light-polymerized hybrid composite, a posterior composite, and a polyacid-modified composite. MATERIAL AND METHODS: Five disk-shaped specimens (1 cm in diameter and 2 mm in thickness) were prepared in a mold from each of the following test materials: a light-polymerized hybrid composite (3M Valux Plus), a posterior composite (Filtek P60), and a polyacid-modified composite (Dyract AP). The hybrid composite served as the control material. A linear strain gauge was placed at the center of each specimen. After the specimens were light-polymerized for 60 seconds under 400-mW/cm(2) light intensity, microstrains were recorded with the strain indicator continuously every 4 seconds for 120 seconds. The data were evaluated with 1-way analysis of variance (P<.05) followed by a post hoc least significant difference test. RESULTS: During the first 20 seconds of light polymerization, all materials exhibited tensile strains between 6 and 55 mu epsilon that quickly converted into compressive strains and continued rising after the light source was removed. The strains for all materials increased at a declining rate until they reached a constant level between 148 and 180 seconds. The polymerization shrinkage recorded for Filtek P60 was the lowest (-190.56 mu epsilon), followed by 3M Valux Plus (-303.94 mu epsilon) and Dyract AP (-345.64 mu epsilon) (P<.05). The dimensional change between Filtek P60 and Dyract AP and between Filtek P60 and 3M Valux Plus was significant (P=.001). However, the difference between Dyract AP and 3M Valux Plus specimens was not significant (P=.208). CONCLUSION: Within the limitations of this study, the light-polymerized posterior composite tested demonstrated less polymerization shrinkage than the polyacid-modified and hybrid composites tested. Polymerization shrinkage velocity significantly affected the magnitude of strains.     

Shear bond strengths of three different resin luting cements to bovine teeth

This study evaluated the shear bond strengths of dentin/porcelain and enamel/ porcelain specimens bonded with three different dual-cure cements. The specimens were prepared using the heat-pressed ceramic technique. Three different dual-cure cements were used to bond samples to previously prepared bovine enamel and dentin surfaces. The specimens were thermocycled and tested in shear until failure. The shearbond data was subjected to one-way ANOVA, followed by Duncan's multiple range test at a significance level of p < 0.05. The shear bond strengths of Variolink II were significantly higher than those of Rely-X ARC and Panavia F for enamel and dentin (p < 0.05). Bond strenghts in enamel were higher than those of dentin in all materials (p < 0.05).     

Antibacterial activity of two adhesive systems using various microbiological methods

PURPOSE: To compare the antibacterial activities of two dentin bonding systems (DBS), Clearfil Protect Bond and Xeno III, by agar well, paper and dentin disks, and a cavity tooth model. MATERIALS AND METHODS: For the well technique, the test materials were filled in the agar wells inoculated with Streptococcus mutans (ATCC 25175). The paper disks were embedded in adhesives and placed on the seeded agar plates for the second technique. The adhesives were applied on the dentin disks and placed in holes in the plates for the third technique. After 48 h, the zones of inhibition were measured. In the cavity tooth model test, 3 cavities were prepared in the flat occlusal dentin of extracted human molars. The teeth were left in S. mutans for 72 h to allow bacterial invasion. The DBS were applied in the same manner as in clinical application on each of the two infected cavities and the third was left unapplied for control. The teeth were kept in saline for 72 h. Standard amounts of dentin chips were obtained from the cavity walls and the number of bacteria recovered was counted. RESULTS: The results were analyzed by factorial ANOVA and Dunnett C test. Clearfil Protect Bond primer exhibited the greatest inhibition zones followed by Consepsis and unpolymerized Xeno III in all the techniques tested (p < or = 0.05). Clearfil Protect Bond resulted in significantly less bacterial recovery than Xeno III by the tooth cavity method (p < or = 0.05). CONCLUSION: Clearfil Protect Bond was found to be the most antibacterial material with all the techniques used. Furthermore, Clearfil Protect Bond was able to inactivate the bacteria in the cavity more effectively than Xeno III.     

The Abbé island flap for the reconstruction of severe secondary cleft lip deformities

Primary repair of the cleft lip is often associated with secondary deformities, which require revision and secondary reconstruction. Patients with one or all of the following, a tight lip restricting use of orthodontic appliances, absence of a Cupid's bow, or absence of vermilion tubercle, were treated with the Abbé island flap. A triangular muco-musculo-cutaneous island flap was designed in the central segment of the lower lip. A full-thickness incision of skin, muscle, and mucosa was made in the midline of the upper lip, dividing the lip into two segments, and the island Abbé flap was inserted. One week after surgery, the pedicle of the island flap was divided and the inset of the flap completed. Sixty patients with severe secondary cleft lip deformities (36 males and 24 females) were treated. Good aesthetic and functional results were achieved during 1 to 17 years of follow-up. Insertion of the Abbé flap resulted in release of the tight upper lip and a new, inconspicuous scar. Use of orthodontic appliances was facilitated, and tightness of the tissue, which restricted the expansion of the alveolar process, was eliminated. Adequate tissue was transferred to the upper lip, which improved the bulk of the lip and vermilion tubercle. The retrusion of the midface and the projection of the upper lip were also improved, and the upper and lower lips became better balanced. Donor site morbidities were insignificant. Use of the Abbé flap in selected patients resulted in successful reconstruction of secondary cleft lip deformities.     

Bactericidal effect of Er,Cr:YSGG laser on Streptococcus mutans

The aim of this study was to compare the antibacterial activities of Er,Cr:YSGG laser with two different power outputs against a chlorhexidine gluconate-based cavity disinfectant. A cavity tooth model test was used to determine the antibacterial activity. Four cylindrical cavities were prepared on the dentin surface of 10 bovine incisors and left in contact with Streptococcus mutans for 72 hours to allow bacterial invasion. Following which, Er,Cr:YSGG laser with 0.75 W and 1 W power outputs and a chlorhexidine gluconate-based cavity disinfectant were applied separately on one of the three infected cavities, whereas the fourth was left untreated for control. Standardized amounts of dentin chips were obtained from the cavity walls, and the number of bacteria recovered was counted. Statistical analysis was carried out using one-way ANOVA and Dunnett's C test (p=0.05). No significant differences were observed among the data obtained from the chlorhexidine gluconate-based cavity disinfectant and the two Er,Cr:YSGG laser groups (p>0.05). However, when compared to the control group, both Er,Cr:YSGG laser groups and the chlorhexidine gluconate-based cavity disinfectant resulted in significantly less bacterial recovery (p<0.05). In conclusion, the antibacterial activity on S. mutans demonstrated by Er,Cr:YSGG laser with both energy outputs was similar to that of the tested chlorhexidine gluconate-based cavity disinfectant.     

Comparison of autogenous mucosal grafts and collagen-based, solvent-preserved allografts for vestibuloplasty.

This study was designed to determine whether solvent-preserved dura mater and fascia lata grafts would be as effective as palatal mucosal grafts for vestibuloplasty. All graft systems succeeded in covering the alveolar ridge with firmly attached tissue, which is needed to ensure prosthetic stability. There was no remarkable reduction in area until the stents were removed. However, after 6 months of vestibuloplasty, there was a significant reduction in gained vestibular area in the fascia lata group, whereas no significant difference between dura mater and palatal grafts was observed. These findings suggest that dura mater could serve as a biologic oral dressing for mucosal defects as effectively as palatal grafts in vestibuloplasty.     

Influence of luting agent on the microleakage of all-ceramic crowns

PURPOSE: In this in-vitro study, microleakage of all-ceramic crowns was evaluated at enamel and dentin margins. MATERIALS AND METHODS: Forty maxillary central incisors were randomly divided into 4 groups (n = 10). While buccal and palatal margins were placed on enamel, mesial and distal margins were placed below the cementoenamel junction. In groups 1 to 3, IPS Empress 2 crowns were luted with Variolink 2/Syntac Classic (group 1), Bifix DC/Solobond Plus (group 2) and Calibra/Prime & Bond NT combinations (group 3), respectively. In the control group (group 4), porcelain-fused-to-metal crowns were luted with a zinc-phosphate cement. All specimens were subjected to 5000 thermocycles (at 5 degrees C to 55 degrees C; 30-s dwell time). After immersion in India ink for 48 h at 37 degrees C, the specimens were sectioned both buccolingually and mesiodistally. Each section was evaluated for microleakage under a stereomicroscope at 24X magnification. RESULTS: According to the Krukal-Wallis test, in all groups, there were significant differences in microleakage at the enamel margins (p = 0.001). Nevertheless, the margins finished in dentin showed no significant differences (p = 0.163). According to the Mann-Whitney U-test, statistically significant differences were observed in microleakage between groups 1 and 3 (p = 0.049), groups 1 and 4 (p = 0.001), groups 2 and 4 (p = 0.002), and between groups 3 and 4 (p = 0.045) at the enamel margin. In group 1, significantly greater microleakage was observed at the dentin margin compared to the enamel margin (p = 0.007). CONCLUSION: The adhesive luting technique demonstrated an excellent ability to minimize microleakage of all-ceramic crowns at the enamel margins. Water-based dentin bonding systems showed less microleakage than the water-free acetone-based dentin bonding system at the enamel margin.     

The anti-MMP activity of benzalkonium chloride

Objective

This study evaluated the ability of benzalkonium chloride (BAC) to bind to dentine and to inhibit soluble recombinant MMPs and bound dentine matrix metalloproteinases (MMPs).

Methods

Dentine powder was prepared from extracted human molars. Half was left mineralized; the other half was completely demineralized. The binding of BAC to dentine powder was followed by measuring changes in the supernatant concentration using UV spectrometry. The inhibitory effects of BAC on rhMMP-2, -8 and -9 were followed using a commercially available in vitro proteolytic assay. Matrix-bound endogenous MMP-activity was evaluated in completely demineralized beams. Each beam was either dipped into BAC and then dropped into 1 mL of a complete medium (CM) or they were placed in 1 mL of CM containing BAC for 30 days. After 30 days, changes in the dry mass of the beams or in the hydroxyproline (HYP) content of hydrolysates of the media were quantitated as indirect measures of matrix collagen hydrolysis by MMPs.

Results

Demineralized dentine powder took up 10-times more BAC than did mineralized powder. Water rinsing removed about 50% of the bound BAC, whilst rinsing with 0.5 M NaCl removed more than 90% of the bound BAC. BAC concentrations 0.5 wt% produced 100% inhibition of soluble recombinant MMP-2, -8 or -9, and inhibited matrix-bound MMPs between 55 and 66% when measured as mass loss or 76-81% when measured as solubilization of collagen peptide fragments.

Conclusions

BAC is effective at inhibiting both soluble recombinant MMPs and matrix-bound dentine MMPs in the absence of resins.     

Recurrence of left atrial myxoma mimicking a mitral annuloplasty ring thrombosis

Cardiac myxomas (CM) is by far the most common type of primary cardiac neoplasm that commonly arise within the left atria and is composed of primitive connective tissue cells and stroma. Despite the benign nature, the CMs are often surgically removed because they can lead to severe complications. Large, thin, and hypermobile forms are unusual. The frequency of recurrence is about 22% for complex forms and 12% for other familial forms and 1% to 3% for sporadic myxomas, which seldom recur after surgery. Although transesophageal echocardiography shows usually accurate imaging capabilities to detect the myxoma, further imaging methods including computed tomography, cardiovascular magnetic resonance imaging, and ¹⁸F-fluorodeoxyglucose positron-emission tomography/computed tomography may be useful to diagnosis for it. Surgery is the mainstay of treatment