Abstract Objectives The aim of this study was to correlate the rate and magnitude of dentinal fluid flow (DFF) with cuspal displacement in response to resin composite restorative procedures. Methods ...Ten extracted human maxillary premolar teeth with an extensive MOD cavity preparation were connected to an automated fluid flow measurement apparatus (Flodec), and a direct current differencial transformer (DCDT) was attached to each cusp. The rate, magnitude and direction of DFF and cuspal displacement were recorded simultaneously in response to each stage of resin composite restorative procedures. Results Cuspal displacement and DFF in outward and inward directions accompanied each stage of the procedures. Drying produced rapid cuspal contraction. Bonding caused slight cuspal expansion, whereas light curing of resin induced gradual but extensive cuspal contraction, which persisted following light curing. During baseline outward DFF was low and increased slightly during etching. In contrast, substantial outward DFF occurred during drying. Light curing of the bonding agent and the resin composite produced inward DFF. Following light curing, an outward DFF began and continued for atleast 15 min. Significance The large, rapid fluid movement and cuspal displacement during restoration, and the prolonged outward fluid flow post-curing have implications for post-operative sensitivity. While mechanical stresses within dentin associated with cuspal displacement appear capable of inducing DFF, the net fluid movement is the result of complex interactions either directly or indirectly of several stimuli (thermal, evaporation, osmotic, and possibly mechanical).
Statement of problem Little information comparing the fracture resistance of internal connection titanium and zirconia abutments exists to validate their use intraorally. Purpose The purpose of this ...study was to determine the fracture resistance of internal connection titanium and zirconia abutments by simulating cyclic masticatory loads in vitro. Material and methods Twenty-two specimens simulating implant-supported anterior single crowns were randomly divided into 2 equal test groups: Group T with titanium abutments and Group Z with zirconia abutments. Abutments were attached to dental implants mounted in acrylic resin, and computer-aided design/computer-aided manufacturing (CAD/CAM) crowns were fabricated. Masticatory function was simulated by using cyclic loading in a stepped fatigue loading protocol until failure. Failed specimens were then analyzed by using scanning electron microscopy (SEM) and fractographic analysis. The load (N) and the number of cycles at which fracture occurred were collected and statistically analyzed by using a 2-sample t test (α=.05). Results The titanium abutment group fractured at a mean (SD) load of 270 (56.7) N and a mean (SD) number of 81 935 (27 929) cycles. The zirconia abutment group fractured at a mean (SD) load of 140 (24.6) N and a mean (SD) number of 26 296 (9200) cycles. The differences between the groups were statistically significant for mean load and number of cycles ( P <.001). For the titanium abutment specimens, multiple modes of failure occurred. The mode of failure of the zirconia abutments was fracture at the apical portion of the abutment without damage or plastic deformation of the abutment screw or implant. Conclusions Within the limitations of this in vitro study, 1-piece zirconia abutments exhibited a significantly lower fracture resistance than titanium abutments. The mode of failure is specific to the abutment material and design, with the zirconia abutment fracturing before the retentive abutment screw.
To compare the mean shear bond strength (SBS) and failure mode of a resin-modified glass-ionomer luting cement (RM-GIC) to five different metals using unsupported and supported cement specimens with ...different placement of the shear load.
A RM-GIC was bonded to five metals using "unsupported" and "supported" techniques at a SBS-specimen diameter of 2.36 mm. The bond was stressed to failure using shear knife and wire loop debonding protocols. For the shear knife method, the distance of the shear force from the interface was 0 mm or 0.3 mm. Failure analysis was assessed by stereomicroscope and SEM.
Two-way ANOVA and post-hoc Tukey's test revealed a significant difference between the unsupported and supported mean SBS. The SBS of supported specimens, where the shear force was applied to the mold that enclosed the specimens, were in most cases statistically significantly higher (p < 0.05) than specimens that were not supported. The mean bond strengths of RM-GIC ranged from 4.5 ± 2.3 MPa to 27.4 ± 3.7 MPa. Analysis of the failure mode showed significant differences (p < 0.001) for the test methods except for adhesion to gold-based metal. The adhesive failure mode was between 91% and 97% for supported specimens and between 47% and 63% for unsupported specimens.
Within the limits of this study, supported specimens exhibited higher mean SBS than unsupported specimens. The method of debonding had a significant effect on the mean SBS for RM-GIC bonded to metal. Mold-supported specimens had a higher incidence of adhesive failure than unsupported cement specimens.
Biomechanics of medial hamstring lengthening Dagge, Benjamin; Firth, Gregory B.; Palamara, Joseph E. A. ...
ANZ journal of surgery,
05/2012, Volume:
82, Issue:
5
Journal Article
Peer reviewed
Background: Medial hamstring lengthening is frequently used to correct contractures in neuromuscular conditions such as cerebral palsy. Surgical techniques vary considerably and little is known ...about the lengthening characteristics of muscle‐tendon‐units after surgical intervention.
Methods: A randomized trial was performed on paired cadaver medial hamstring muscle‐tendon‐units comparing ‘High’ (proximal) versus ‘Low’ (distal) lengthening procedures. The paired muscle‐tendon‐units were subjected to tensile testing utilizing an Instron® (Instron Corporation, Canton, MA, USA) machine under controlled conditions. Prior to tensile testing, the paired semitendinosus and paired gracilis received either high or low intramuscular tenotomy. Load (N) versus displacement (mm) was recorded continuously for each test. The difference in lengthening and load at failure for intact and surgical simulation muscle‐tendon‐units was recorded and compared with paired t‐tests.
Results: Both low and high lengthenings increased the amount of lengthening achieved compared with intact controls and the lengthening was achieved at lower applied load. Low intramuscular tenotomy of the semitendinosus resulted in a 30% greater lengthening when compared with high intramuscular tenotomy. For the gracilis muscle, the low intramuscular tenotomy achieved 39% greater lengthening than the high intramuscular tenotomy and these differences were significant.
Conclusion: Biomechanical testing of formalin‐preserved human cadaveric medial hamstring muscle‐tendon‐units confirms that it is possible to achieve lengthening in continuity following an intramuscular tenotomy or fascial striping procedure. The site of the surgical procedure (high versus low) results in a different effect on the lengthening characteristics, dictated by the anatomy of the particular muscle‐tendon‐unit.
The purpose of this study was to compare fluid flow rates across dentin surfaces treated with four conditioners. The effect of conditioning on the micro‐shear bond strengths of glass ionomer cement ...(Fuji IX GP) and resin‐based adhesives (Single Bond 2 or Clearfil SE Bond) were also investigated. Under a simulated pressure of 1.3 kPa, two dentin conditioners, phosphoric acid, and a self‐etching primer were applied to the dentin surfaces. Dentinal fluid flows at baseline and after conditioning were recorded for 15 min each. The conditioned surfaces were examined using a scanning electron microscope. The micro‐shear bond strengths of the glass ionomer cement and of the resin‐based adhesives bonded to conditioned dentin surfaces were evaluated while simulated intrapulpal pressure was maintained at 0 or 1.3 kPa. Only the dentin surface etched with phosphoric acid showed a significant increase in permeability. Micro‐shear bond strengths of Fuji IX GP were not affected by conditioning the dentin surfaces or by bonding at different intrapulpal pressures (0 or 1.3 kPa). The effects on bond strengths of resin‐based adhesives depended on the system used. The simulated positive intrapulpal pressure during bonding significantly affected the adherence of Single Bond 2, whereas Clearfil SE Bond was unaffected.
The purpose of the study was to determine whether rotary nickel-titanium (NiTi) canal preparation strengthens roots, and whether the fracture pattern can be predicted by finite element analysis (FEA) ...models. From a fracture mechanics viewpoint, structural defects, cracks or canal irregularities are likely to play a major role in fracture susceptibility of the roots, because stresses can be exponentially amplified at these sites. By incorporating defects into a smooth round canal using rotary NiTi, theoretically the roots could be strengthened. 25 teeth were prepared using hand files and another 25 using rotary NiTi. After obturation, all teeth were subject to loading until fracture; load and patterns were recorded. Four FEA models were created from fractured roots. No significant difference of fracture load between the two techniques was found. Mesio-distal fracture occurred more often in the rotary NiTi group. Stress patterns in three of the four FEA models correlated well with the observed fracture patterns.
The study aimed to determine fracture loads in tooth roots after canal preparation using different techniques. Mesiobuccal roots of 39 extracted mandibular molars were used. Three groups each of 13 ...roots were prepared by stainless steel hand files (K-files), and two rotary nickel-titanium techniques (Lightspeed and Greater Taper files). After obturation, a vertical load was applied by means of a spreader inserted into the canal until fracture occurred. The mean fracture load was 10.2 ± 4.4 kg for K-files, 15.7 ± 9.1 kg for Lightspeed and 13.2 ± 6.1 kg for Greater Taper files, but differences were not statistically significant (p > 0.05). Most fracture lines were incomplete fractures on the buccal surface, followed by proximal and compound fractures. Greater apical enlargement (Lightspeed) or increased canal taper (Greater Taper files) did not increase fracture susceptibility of tooth roots.
Vertical root fracture seems to result from stresses generated within the root canal and typically occurs in a buccolingual direction through the thickest part of dentin. Because stresses in the ...canal wall are difficult to measure experimentally, we have attempted to correlate stress patterns derived from finite element models of maxillary and mandibular incisors with strain measurements on the root surfaces of extracted teeth. Finite element analysis indicated that circumferential tensile stresses were concentrated on the buccal and lingual surfaces of the canal wall, corresponding to areas of greatest canal wall curvature. Surface stresses were much lower and were consistently tensile on the proximal root surfaces but variable on the buccal and lingual surfaces. The measurement of root surface stresses does not provide a reliable picture of internal stresses in the root. Canal wall curvature is a major factor in stress concentration and hence in the pattern of fracture.
The aim of this study was to investigate fluid flow in dentin after restoration of carious teeth with resin composite bonded with a total‐etching adhesive, with or without glass‐ionomer cement ...lining. The roots of extracted third molars were removed and the crowns were connected to a fluid flow‐measuring device. Each carious lesion was stained with caries detector dye and caries was removed using slow‐speed burs and spoon excavators. Caries‐excavated teeth were divided into two groups for restoration with resin composite bonded with a total‐etch adhesive: (i) without lining; and (ii) lined with glass‐ionomer cement before bonding. In non‐carious teeth, cavities of similar dimensions were prepared, divided into two groups, and restored in the same manner. Fluid flow was recorded, after restoration, for up to 1 month. Caries‐affected dentin was examined by scanning electron microscopy (SEM), and the bonded interfaces were observed using a confocal laser scanning microscope. No significant difference in fluid flow was observed between the two restorative procedures or between the carious and non‐carious groups. The SEM images showed that the dentinal tubules of acid‐etched, caries‐affected dentin were usually still occluded, while some were patent. Limited penetration of fluorescent dye into dentin and into the bonded interfaces of restored carious teeth was observed.
This study compared the ultimate tensile strength, micropunch shear strength, and microhardness of bleached and unbleached human dentin. Forty-four intact premolars were root canal treated and ...randomly divided into four groups. Bleaching agents were sealed in pulp chambers, as in clinical use. Group 1 (control) was treated with water, group 2 with 30% hydrogen peroxide, group 3 with sodium perborate mixed with water, and group 4 with sodium perborate mixed with 30% hydrogen peroxide. The teeth were stored in saline at 37°C for 7 days. The teeth were then sectioned and biomechanical tests were carried out on dentin specimens that were obtained from all teeth. Intracoronal bleaching with 30% hydrogen peroxide and sodium perborate used either alone or in combination weakened dentin. Hydrogen peroxide alone tended to be more damaging than sodium perborate used alone or sodium perborate mixed with hydrogen peroxide.
