Effect of filament types and loops number on the force degradation of elastomeric chains used for orthodontic treatment: an in-vitro study

BACKGROUND

In orthodontic treatment, closing spaces, specifically the extraction and scattered spaces of the anterior teeth, requires some auxiliary bias, such as an elastomeric chain. Many factors affect the mechanical properties of elastic chains. In this study, we investigated the relationship of the filament type, the number of loops, and the force degradation of elastomeric chains under thermal cycling conditions.

METHODS

The orthogonal design included three filament types (i.e., close, medium, and long). Four, five, and six loops of each elastomeric chain were stretched to have an initial force of 250 g in an artificial saliva environment at 37 °C and thermocycling between 5 and 55 °C three times a day. The remaining force of the elastomeric chains was recorded at different time points (4 h, 24 h, 7 days, 14 days, 21 days, and 28 days), and the percentage of the remaining force was calculated.

RESULTS

The force decreased significantly in the initial 4 h and degraded mostly within the first 24 h. In addition, the percentage of force degradation increased slightly between 1 and 28 days.

CONCLUSIONS

Under the same initial force, the longer the connecting body is, the fewer the number of loops and the greater the force degradation of the elastomeric chain are.

Tensile and shear bond strengths of a stainless steel used in orthodontic brackets bonded to bovine enamel using two types of resin cement

The purpose of this study was to examine the relationship between the bond strength of stainless steel with two types of resin cements (MMA- and composite-based) on bovine enamel depending on the directionality of the applied force. The specimens were either placed in water or subjected to thermal cycles (TC), and the shear or tensile bond strengths (SBS or TBS) were determined. The SBS showed significantly greater than the TBS for both types of cement, and the SBS and TBS for composite-based cement had larger than MMA-based one. No significant difference in SBS was observed in the cements even after being subjected to TC. Cohesive failures of the cement and bovine enamel in the composite-based group, while adhesive failures were observed in MMA-based one. Consequently, the direction of the force at both cements affected the retention of stainless steel, and MMA-based cement was preferred when prioritizing less enamel damages.

Impact of temperature changes to the adhesion strength of molar tubes: an in vitro study

Background

The main purpose of this was to determine study adhesion strength of molar tubes bonding with a composite adhesive after exposure to a sudden change in temperature (thermal cycles).

Methods

The study sample consisted of 40 recently extracted human first permanent molars, which were randomly divided into two groups of 20: group 1 was the experimental group (affected by thermal cycles), and group 2 was the control group. Molar tubes were bonded with a light-cure tube adhesive. The experimental group teeth were dipped 2,000 times in saline at 5 °C and at 55 °C. The control group were immersed in 37 °C saline. Molar tubes for both groups were removed with an adapted Mecmesim Multitesters 2.5—I, and the data were recorded with EMPEROR software. ANOVA was used to calculate and compare the results.

Results

In the experimental group of the teeth, the maximum force was obtained at 94.2 N and the lowest force was 19.69 N. In the control group of the teeth, the maximum force was obtained at 159.1 N and the lowest force was 28.1 N. In the experimental group, the mean debonding force (59.12 N) was statically significantly smaller than in the control group (79.88 N), p = 0.0345. The forces in the control group were by 1.35 times greater than those in the experimental group.

Conclusions

The forces of the adhesion of molar tubes to the tooth surface were reduced after exposure to a sudden change in temperature (thermal cycles). The results were significantly different between the experimental group and the control group.

Handling properties and surface characteristics of universal resin composites

OBJECTIVE

This study investigated the handling and surface characteristics of universal resin composites and determined the interrelations among the composites' handling, mechanical, and physical properties.

METHODS

Five recently introduced universal resin composites were tested. Twelve specimens per material were used to measure the stiffness and stickiness (handling properties) of the resin composite pastes. Additionally, surface properties (Knoop hardness number [KHN], surface roughness [Sa], surface gloss [SG], water contact angle [CA], and surface free energy [SFE]) of cured resin composites were determined in 12 specimens per material immediately after preparation (baseline) and after subjection to thermal cycles (TCs).

RESULTS

Handling and surface properties of the resin composites were material dependent. All the resin composites showed significantly lower KHN in the post-TC subgroups than that in the baseline subgroups. However, the influence of TC on the other surface properties was dependent on the material used. Some resin composites did not indicate any significant differences in Sa, SG, or CA between the baseline and post-TC groups.

SIGNIFICANCE

Although the resin composites in the baseline groups presented with different handling and surface properties, the surface properties of most of the composites were significantly affected by TC. Extremely strong positive or negative correlations were observed between stiffness and stickiness, KHN and Sa, KHN and SG, Sa and SG, and CA and SFE. Most correlations between the handling and surface properties were weak. Therefore, the selection of resin composites in clinical situations should be based on comprehensive consideration of their properties.

Evaluation of the repair capacities and color stabilities of a resin nanoceramic and hybrid CAD/CAM blocks

PURPOSE

This study evaluated the color stabilities of two computer-aided design and computer-aided manufacturing (CAD/CAM) blocks and a nanofill composite resin and the microtensile bond strength (µTBS) between the materials.

MATERIALS AND METHODS

Twelve specimens of 4 mm height were prepared for both Lava Ultimate (L) and Vita Enamic (E) CAD/CAM blocks. Half of the specimens were thermocycled (10,000 cycle, 5° to 55℃) for each material. Both thermocycled and non-thermocycled specimens were surface treated with one of the three different methods (Er,Cr:YSGG laser, bur, or control). For each surface treatment group, one of the thermocycled and one of non-thermocycled specimens were restored using silane (Ceramic Primer II), universal adhesive (Single Bond Universal), and nanofill composite resin of 4-mm height (Filtek Ultimate). The other specimens were restored with the same procedure without using silane. For each group, 1 × 1 × 8 mm bar specimens were prepared using a microcutting device. Bar specimens were thermocycled (10,000 cycle, 5° to 55℃) and microtensile tests were performed. Staining of the materials in coffee solution was also compared using a spectrophotometer. Data were analyzed using one-way ANOVA, t-test and post-hoc Scheffe tests.

RESULTS

µTBS were found similar between the thermocycled and non-thermocycled groups (P>.05). The highest µTBS (20.818 MPa) was found in the non-thermocycled, bur-ground, silane-applied E group. Silane increased µTBS at some E groups (P<.05). Composite resin specimens showed more staining than CAD/CAM blocks (P<.05).

CONCLUSION

CAD/CAM blocks can be repaired with composite resins after proper surface treatments. Using silane is recommended in repair process. Color differences may be shown between CAD/CAM blocks and the nanofill composite after a certain time period.

The Microstructure and Pitting Resistance of 2002 Lean Duplex Stainless Steel after the Simulated Welding Thermal Cycle Process

In this paper, thermal cycles with different heat inputs and cooling rates were investigated for a novel lean duplex stainless steel 2002 using a welding simulation. The microstructure and pitting resistance of the simulated heat-affected zones were studied. With the increasing heat input, the amount and size of the austenite phase both increased, along with a transformation from rods to dendritic structures. The critical pitting temperature (CPT) and the pitting potential (E_pit) both increased first and then declined as the heat input increased, indicating a strong dependence of pitting resistance on the heat input. For the different cooling rates, the amount of ferrite increased as the cooling rate increased from 0.25 °C/s to 20 °C/s. The CPT and E_pit both increased with the increasing cooling rates, indicating an improved pitting resistance. The pits initiated preferentially at the boundaries of ferrite and austenite due to the precipitation of M₂₃C₆ in the specimens with different cooling rates.