Can Masticatory Electromyography be Normalised to Submaximal Bite Force?

The combination of bite force and jaw muscle electromyography (EMG) provides an insight into the performance of the stomatognathic system, especially in relation to dynamic movement tasks. Literature has extensively investigated possible methods for normalising EMG data encapsulating many different approaches. However, bite force literature trends towards normalising EMG to a maximal voluntary contraction (MVC), which could be difficult for ageing populations or those with poor dental health or limiting conditions such as temporomandibular disorder. The objectives of this study were to (i) determine whether jaw-closing muscle activity is linearly correlated with incremental submaximal and maximal bite force levels and (ii) assess whether normalising maximal and submaximal muscle activity to that produced when performing a low submaximal bite force (20 N) improves repeatability of EMG values. Thirty healthy adults (15 men, 15 women; mean age 21 ± 1·2 years) had bite force measurements obtained using a custom-made button strain gauge load cell. Masseter and anterior temporalis muscle activities were collected bilaterally using surface EMG sensors whilst participants performed maximal biting and three levels of submaximal biting. Furthermore, a small group (n = 4 females) were retested for reliability purposes. Coefficients of variation and intra-class correlation coefficients showed markedly improved reliability when EMG data were normalised compared to non-normalised. This study shows that jaw muscle EMG may be successfully normalised to a very low bite force. This may open possibilities for comparisons between at-risk sample groups that may otherwise find it difficult to produce maximal bite force values

Fluid Mechanics in Dentinal Microtubules Provides Mechanistic Insights into the Difference between Hot and Cold Dental Pain

Dental thermal pain is a significant health problem in daily life and dentistry. There is a long-standing question regarding the phenomenon that cold stimulation evokes sharper and more shooting pain sensations than hot stimulation. This phenomenon, however, outlives the well-known hydrodynamic theory used to explain dental thermal pain mechanism. Here, we present a mathematical model based on the hypothesis that hot or cold stimulation-induced different directions of dentinal fluid flow and the corresponding odontoblast movements in dentinal microtubules contribute to different dental pain responses. We coupled a computational fluid dynamics model, describing the fluid mechanics in dentinal microtubules, with a modified Hodgkin-Huxley model, describing the discharge behavior of intradental neuron. The simulated results agreed well with existing experimental measurements. We thence demonstrated theoretically that intradental mechano-sensitive nociceptors are not “equally sensitive” to inward (into the pulp) and outward (away from the pulp) fluid flows, providing mechanistic insights into the difference between hot and cold dental pain. The model developed here could enable better diagnosis in endodontics which requires an understanding of pulpal histology, neurology and physiology, as well as their dynamic response to the thermal stimulation used in dental practices

Fracture Resistance of Yttria-Stabilized Zirconia Dental Implant Abutments

Purpose: An in vitro study was performed to assess the effect of different degrees of clinical reduction of zirconia abutments on the failure load of clinical assemblies. Materials and Methods: Zirconia abutments (Y-TZP Ceramic Abutment, Astra Tech) were prepared with 0, 0.5, or 1 mm of external axial reduction starting 1 mm above the height-of-contour. Abutments (n = 10) were attached to implant analogs (25 Ncm torque) embedded in a stainless steel cylinder using Field's metal. Fracture loads (N) were determined when assemblies were loaded at 60° off-axis until failure (Instron, CHS = 0.1 mm/min). Groups were statistically compared using ANOVA ( p 0.05) among different abutment groups with a mean fracture load of 429 N (±140) for the control group, 576 N (±120) for 0.5-mm margins, and 547 (±139) for 1.0-mm margins. All fractures occurred at the interface where the abutment was connected to the analog. Conclusion: In this in vitro study of simulated ultimate assembly strength, the preparation of zirconia abutments did not significantly impair the fracture resistance of simulated implant assemblies. All implant abutments fractured at rates higher than the maximum incisal forces (90–370 N) estimated to occur in the anterior region of the mouth.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74231/1/j.1532-849X.2008.00378.x.pd