Effect of material composition and thickness of orthodontic aligners on the transmission and distribution of forces: an in vitro study.

OBJECTIVES: To investigate the effects of material type and thickness on force generation and distribution by aligners. MATERIALS AND METHODS: Sixty aligners were divided into six groups (n = 10): one group with a thickness of 0.89 mm using Zendura Viva (Multi-layer), four groups with a thickness of 0.75 mm using Zendura FLX (Multi-layer), CA Pro (Multi-layer), Zendura (Single-layer), and Duran (Single-layer) sheets, and one group with a thickness of 0.50 mm using Duran sheets. Force measurements were conducted using Fuji® pressure-sensitive films. RESULTS: The lowest force values, both active and passive, were recorded for the multi-layered sheets: CA Pro (83.1 N, 50.5 N), Zendura FLX (88.9 N, 60.7 N), and Zendura Viva (92.5 N, 68.5 N). Conversely, the highest values were recorded for the single-layered sheets: Duran (131.9 N, 71.8 N) and Zendura (149.7 N, 89.8 N). The highest force was recorded at the middle third of the aligner, followed by the incisal third, and then the cervical third. The net force between the incisal and cervical thirds (FI-FC) showed insignificant difference across different materials. However, when comparing the incisal and middle thirds, the net force (FI-FM) was higher with single-layered materials. Both overall force and net force (FI-FM) were significantly higher with 0.75 mm compared to those with a thickness of 0.50 mm. CONCLUSIONS: Multi-layered aligner materials exert lower forces compared to their single-layered counterparts. Additionally, increased thickness in aligners results in enhanced retention and greater force generation. For effective bodily tooth movement, thicker and single-layered rigid materials are preferred. CLINICAL RELEVANCE: This research provides valuable insights into the biomechanics of orthodontic aligners, which could have significant clinical implications for orthodontists. Orthodontists might use this information to more effectively tailor aligner treatments, considering the specific tooth movement required for each individual patient. In light of these findings, an exchangeable protocol for aligner treatment is suggested, which however needs to be proven clinically. This protocol proposes alternating between multi-layered and single-layered materials within the same treatment phase. This strategy is suggested to optimize treatment outcomes, particularly when planning for a bodily tooth movement.

The Performance Characterization and Optimization of Fiber-Optic Acoustic Pressure Sensors Based on the MOEMS Sensitized Structure.

In order to investigate the factors affecting the acoustic performance of the extrinsic Fabry-Perot interferometer (EFPI) fiber-optic acoustic pressure sensor and to effectively improve its detection capability, this paper enhances the sensor's detection sensitivity by adding more sensitized rings to its acoustic pressure-sensitive film. Furthermore, a novel real-time coupled acoustic test method is proposed to simultaneously monitor the changes in the spectral and acoustic metrics of the sensor to characterize its overall performance. Finally, an EFPI-type fiber-optic acoustic pressure sensor was developed based on the Micro-Optical Electro-Mechanical System (MOEMS). The acoustic tests indicate that the optimized fiber-optic acoustic pressure sensor has a sensitivity as high as 2253.2 mV/Pa, and the acoustic overload point (AOP) and signal-to-noise ratios (SNRs) can reach 108.85 dB SPL and 79.22 dB, respectively. These results show that the sensor produced through performance characterization experiments and subsequent optimization has a very high acoustic performance index, which provides a scientific theoretical basis for improving the overall performance of the sensor and will have broad application prospects in the field of acoustic detection.

Relationship between two pressure-sensitive films for testing reduced occlusal force in diagnostic criteria for oral hypofunction.

OBJECTIVE: To measure the occlusal force in the same group of patients with the Dental Prescale 50H type R and the Dental Prescale II, examine the association between them, and determine the reference value for Dental Prescale II that corresponds to the 50H type R 200 N reference value used to make a diagnosis of oral hypofunction. BACKGROUND: Reduced occlusal force, a measure of frailty in older persons, was previously determined with Prescale 50H type R pressure-sensitive film, but it has been replaced by the Prescale II. MATERIALS AND METHODS: The study participants were 441 men and women aged ≥ 65 (mean, 71.8 ± 5.3) years. The occlusal force was measured with the two different types of pressure-sensitive film, and their association was examined. Receiver operating characteristic curves for the Prescale II measured values were created with the 200 N reference value used for the 50H type R film as the cut-off value. RESULTS: The analysis set included 391 participants for whom measurements were obtained using both the 50H type R and the Prescale II. Linear regression analysis produced regression equations, and a ROC curve analysis provided reference values of 500 N for the Prescale II (without pressure filter) and 350 N for the Prescale II (with pressure filter). CONCLUSION: In occlusal force tests for making a diagnosis of oral hypofunction, reference values for the Prescale II (without pressure filter) and for the Prescale II (with pressure filter) were determined. The findings suggested that the Prescale II can be used as a diagnostic examination for oral hypofunction.

The correlation between two occlusal analyzers for the measurement of bite force.

BACKGROUND: Occlusal force represents masticatory function. Using quantifiable occlusal indicators provides a more objective occlusal force evaluation. In the recent dental practice, digital methods such as the Dental Prescale II (DP2, GC Corp., Tokyo, Japan) and T-scan (T-Scan III v8; Tekscan Inc.) are commonly used in clinics to evaluate treatment outcomes. The T-scan provides the relative bite force (%) compared to the maximal bite force on individual teeth or the unilateral arch. The DP2 can quantify occlusal force, measured in newtons (N), on the half arch or the overall bite, but it is difficult to identify the bite force on an individual tooth. It is difficult to select a device that fulfils all the requirements to record occlusal force. This study aimed to investigate the association between the bite measured by the DPS2 and T-scan to determine whether the measured bite force is comparable through calculation. METHODS: A total of 80 healthy adults, including 41 women and 39 men with a mean age of 38.2, were requested to bite pressure sensitive film sheets ten minutes apart. Linear regression analysis was used to estimate the measured bite force by the DP2 and T-scan. RESULTS: There was a significant positive correlation between the occlusal force measured by the DP2 and T-scan (P < 0.01) when intercept was equal to zero as confounders were adjused. These results provided the comparability of the measured occlusal forces determined by the DP2 and T-scan. CONCLUSION: The estimated bite force determined by DP2 and T-Scan is convertible using the linear equation from this study to increase the value for clinical applications. The estimated bite force from the two quantifiable occlusal indicators are comparable. The two commercially available quantifiable occlusal indicators can be fully adapted to all clinical requirements according to this result.

Investigating the Deterioration of Pavement Skid Resistance Using an Accelerated Pavement Test.

Stone matrix asphalt (SMA) mixture has been widely used in pavement engineering for its preferable in-service performance. However, deterioration of SMA pavement in skid resistance is apparent under traffic loading. There remains lacking attention on skid resistance attenuation of SMA pavement, which in turn is important for skid durability design in practice. Hence, this study aims to perform a thorough investigation to reveal the skid resistance attenuation law of SMA pavement. Multiple types of SMA-13 mixtures prepared by different material designs were selected to conduct a kneading test that simulates real surface states of in-service SMA pavement. Pressure-sensitive film and a 3D laser scanner were utilized for evaluating anti-skid performance and skid durability. The finite element (FE) method is introduced to simulate vehicle braking distance for skid-resistance evaluation. The results show that skid resistance attenuation of SMA pavement consists of two stages: In the first stage, the skid resistance of SMA pavement experiences a short enhancement, followed by a long-term weakening stage. Abundant surface texture of SMA helps to mitigate the impact of traffic load on skid resistance. The FE analysis and pressure-sensitive film results demonstrate the potential of skid durability design of SMA pavement based on the skid resistance attenuation law.

A Study on the Contact Characteristics of Tires-Roads Based on Pressure-Sensitive Film Technology.

Tire-road characteristics are a critical focus of research in the automotive and transportation industries. On the one hand, the research can help optimize tires' structural design; on the other hand, it can analyze the mechanical response of the pavement structure under the vehicle load. In addition, the non-uniformity distribution of the tire ground stress will also have a direct impact on the skid resistance, which determines the driving safety. Due to the limitation of testing technology, the measurement of tire ground pressure was mainly carried out on a flat test platform, ignoring the roughness of the actual pavement surface texture. The tire-road contact characteristics research on the macro-texture and micro-texture of asphalt pavement needs to be broken through. A high-precision pressure-sensitive film measurement system is utilized to examine the actual contact characteristics between two types of automobile tires and three types of asphalt pavement in this paper. The influence law of pavement texture and patterned tires on the contact area and stress was explored, and the concentration effect of tire-road contact stress was evaluated. The results indicate that the contact area of grounding tires exhibits a nearly linear relationship with tire inflation pressure and load. Notably, the change in load has a more significant influence on the contact area than tire inflation pressure. On asphalt pavement, the contact reduction rate decreases by approximately 5-10% for block pattern tires and 10-15% for longitudinal pattern tires. Furthermore, as the texture depth of the pavement increases, the contact area between tires and the pavement texture decreases. The actual tire-road interface experiences significant stress concentration due to the embedding and meshing effects between the tire and road surface. Even on a flat steel surface, the peak stress at the edge of the tread block exceeds the 0.7 MPa design load, which is about 2.5-3 times higher than the design uniform load. The peak stress between the tire and asphalt pavement reaches 4-10 times the design uniform load, with a rising trend as the pavement texture depth increases. This study can provide relevant experimental technical support for tire design and functional design of asphalt pavement.

Effect of trimming line design and edge extension of orthodontic aligners on force transmission: An in vitro study.

OBJECTIVES: To investigate how the stress distribution and forces transmitted from orthodontic aligners to the tooth surface are affected by the geometry and extension of the trimming line. MATERIALS AND METHODS: Thirty-six aligners were thermoformed from Zendura FLX sheets (0.75 mm thick) and divided into four groups based on the design of the trimming line: Scalloped, Scalloped extended, Straight and Straight extended. Fuji pressure-sensitive films were used for pressure measurement. The pressurized films were scanned and evaluated. Pressures and forces were measured over the entire facial surface of an upper right central incisor (Tooth 11) and at 7 different locations [cervical, middle, incisal, mesio-incisal, mesio-cervical, disto-incisal, and disto-cervical]. In addition, the thickness of the aligners at these 7 sites was measured with a digital caliper. RESULTS: The active force ranged from (2.2 to 6.9) N, and the average pressure was (1.6-2.7) MPa. The highest values were recorded for the (straight extended) design, while the lowest values were recorded for the scalloped design. The forces and stresses were not uniformly distributed over the surface. When the values in each area were compared separately, significant differences were found between the different designs in the cervical area, with the scalloped design transmitting the lowest cervical forces. Aligner thickness was drastically reduced (60-75% thinning) over the entire tooth surface after thermoforming. CONCLUSIONS: The straight extended design of aligner's trimming line exhibited more uniform force transfer and stress distribution across the surface than the other designs. CLINICAL RELEVANCE: The trimming line design could have a significant impact on the clinical outcome of orthodontic aligner treatment.

Double-row repair of rotator cuff tears: Comparing tendon contact area between techniques.

BACKGROUND: In rotator cuff repair surgery, the double-row technique is widely performed. Studies have shown that with increased contact area and pressure between tendon and bone interface, better healing is promoted. AIM: To assess the different suture configurations with the double-row technique and how this influences the contact area of the rotator cuff tendon to bone. METHODS: This was a controlled laboratory study where identical tears were created in 24 fresh porcine shoulders over a 1.5 cm × 2.5 cm infraspinatus insertion footprint. Double-row repair techniques, with 3 to 4-suture anchors in different configurations (2 medial, 2 lateral vs 2 medial, 1 lateral vs 1 medial, 2 lateral), were employed for three control groups. Each group consisted of eight shoulders with identical repair configurations. Footprint contact areas of the repaired tendon against the tuberosity were determined using pressure sensitive Fujifilm placed between the tendon and tuberosity. RESULTS: The mean contact area between tendon and insertion footprint from the imprinted Fujifilm was obtained using computer software. The contact area measured from a standard 4-suture anchor double row repair was 75.1 ± 9.3 mm2, whereas areas obtained for the 2 lateral - 1 medial and 2 medial - 1 lateral anchor configurations were 72.9 ± 5.2 mm2 and 75.0 ± 4.9 mm2 respectively. No statistical significance was noted between the three groups. CONCLUSION: In the technique of double-row repair, using a 3-suture anchor configuration may offer a non-inferior alternative to the standard 4-anchor construct in terms of efficacy. This may also result in overall cost reduction and shorter surgical time.

Assessment of the impact of temporomandibular disorders on maximum bite force.

AIM: Temporomandibular disorders (TMD) refer to functional disorders of the masticatory system, temporomandibular joint (TMJ) and masticatory muscles. The main objective of this study was to determine whether and to what extent temporomandibular disorders (TMD) affect the maximum bite force (MBF). METHODS: The present study included subjects with and without temporomandibular disorder. The presence of TMD was assessed by means of the Helkimo clinical dysfunction index analysis. We measured the maximum bite pressure (MBP) and occlusal contact area (OCA) by means of a Fuji Prescale Pressure measurement film. Based on the MBP and OCA values obtained, MBF values were determined. RESULTS: The MBF values were significantly lower in patients with TMD compared to subjects without TMD (P Conclusion: TMDs have a significant impact on MBF and masticatory muscle action potential. More research is needed to determine the impact of reduced maximum bite force on the functional efficiency of the masticatory system.

Analysis of the disc pressure of the upper thoracic spine using pressure-sensitive film: an experimental study in porcine model-implications for scoliosis progression.

There has been few studies focusing on the disc pressure of the upper thoracic spine and it still lacks the quantitative pressure measurement of each spinal disc segment. The aim of this study was to study the pressure changes of intervertebral disc in porcine upper thoracic spine using pressure-sensitive film. Twelve porcine thoracic motion segments were harvested and successively loaded with vertical loads of 100 N, 150 N, and 200 N during 5° of anterior flexion, 5° of posterior extension and 5° of lateral bending. The resulting pressure values were measured. During anterior flexion, the anterior annulus of all segments at all loads showed higher mean pressure values than those during vertical compression, whereas the posterior annulus did not show higher mean values. During posterior extension, the anterior annulus of all segments showed lower mean pressure values than those during vertical compression, whereas the posterior annulus did not show lower mean pressure values. During lateral bending, the annulus of all segments showed higher mean pressure values than those during vertical compression. The posterior thoracic vertebra plays an important role in the motion of the upper thoracic vertebral segment and pressure distribution. During lateral bending, the concave side pressure of the annulus increases obviously, suggesting that asymmetrical force is a contributory factor for scoliosis progression.