			Home About us Contact

Tooth Contact (tooth + contact)

Distribution by Scientific Domains

Polymers and Materials Science	9%

Selected Abstracts

Calculation of sliding power loss in spur gear contacts

LUBRICATION SCIENCE, Issue 1 2002
Arto Lehtovaara
Abstract An engineering-level calculation model for sliding power loss in spur gear contacts is presented. Teeth contact through the line of action is modelled as a constantly changing roller contact whose radius, speed, and load can be calculated from the gear geometry under the given operating conditions. The gear mesh cycle is approximated by a large number of elastohydrodynamic contacts. A constant film thickness and a Hertzian pressure distribution are assumed in each contact. The model includes non-Newtonian lubricant behaviour together with temperature and mixed lubrication effects in contact. The numerical solver is reasonably fast in evaluating effectively the sliding power loss dependence on the essential gear and lubricant parameters. The features and behaviour trends of the calculated sliding power losses have a close similarity with published results obtained from measurements and experiment-based power loss models with mineral oil. The limiting shear stress of the lubricant is observed to have an essential role in the power loss behaviour especially at high loads. [source]

Relationship between tooth contacts in the retruded contact position and mandibular positioning during retrusion

JOURNAL OF ORAL REHABILITATION, Issue 11 2006
S. YAMASHITA
summary, We conducted a series of studies with the purpose to investigate the locations of tooth contacts in the retruded contact position (RCP) and to discuss their significance in the stomatognathic system. In the present study, the relationship between the locations of RCP contacts and mandibular positioning during retrusion was examined. Thirty dentists and clinical residents were selected as subjects. One specialist in prosthetic dentistry examined each subject for the location of the RCP contacts. The mandibular positioning during retrusion was measured using a mandibular movement analysis system with six degrees of freedom. Originally programmed software was developed. Five reference points were selected: the central lower incisor (point I), the first molars on both sides (points RM and LM) and the condyles on both sides (points RC and LC). Tooth contact was observed most frequently at the second molar, followed by the first premolar. Points I, RM and LM all moved in an inferior-posterior direction, whereas points RC and LC moved in various directions ranging from superior-posterior to inferior-posterior. When the subjects were divided into two groups according to the most anterior tooth of occlusion in the RCP, the condylar positioning tended to be more superior in the group with molar contact than that with premolar contact. These results suggest that the locations of RCP contacts could be an important factor in jaw guidance during retrusion. [source]

Neuromuscular function in healthy occlusion

JOURNAL OF ORAL REHABILITATION, Issue 9 2010
S. E. FORRESTER
Summary, This study aimed to measure neuromuscular function for the masticatory muscles under a range of occlusal conditions in healthy, dentate adults. Forty-one subjects conducted maximum voluntary clenches under nine different occlusal loading conditions encompassing bilateral posterior teeth contacts with the mandible in different positions, anterior teeth contacts and unilateral posterior teeth contacts. Surface electromyography was recorded bilaterally from the anterior temporalis, superficial masseter, sternocleidomastoid, anterior digastric and trapezius muscles. Clench condition had a significant effect on muscle function (P = 0·0000) with the maximum function obtained for occlusions with bilateral posterior contacts and the mandible in a stable centric position. The remaining contact points and moving the mandible to a protruded position, whilst keeping posterior contacts, resulted in significantly lower muscle activities. Clench condition also had a significant effect on the per cent overlap, anterior,posterior and torque coefficients (P = 0·0000,0·0024), which describe the degree of symmetry in these muscle activities. Bilateral posterior contact conditions had significantly greater symmetry in muscle activities than anterior contact conditions. Activity in the sternocleidomastoid, anterior digastric and trapezius was consistently low for all clench conditions, i.e. <20% of the maximum voluntary contraction level. In conclusion, during maximum voluntary clenches in a healthy population, maximum masticatory muscle activity requires bilateral posterior contacts and the mandible to be in a stable centric position, whilst with anterior teeth contacts, both the muscle activity and the degree of symmetry in muscle activity are significantly reduced. [source]

Influence of different load models on gear crack path shapes and fatigue lives

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 5 2008
S. PODRUG
ABSTRACT A computational model for determination of the service life of gears with regard to bending fatigue at gear tooth root is presented. In conventional fatigue models of the gear tooth root, it is usual to approximate actual gear load with a pulsating force acting at the highest point of the single tooth contact. However, in actual gear operation, the magnitude as well as the position of the force changes as the gear rotates. A study to determine the effect of moving gear tooth load on the gear service life is performed. The fatigue process leading to tooth breakage is divided into crack-initiation and crack-propagation period. The critical plane damage model has been used to determine the number of stress cycles required for the fatigue crack initiation. The finite-element method and linear elastic fracture mechanics theories are then used for the further simulation of the fatigue crack growth. [source]

The effect of tooth clenching on the sensory and pain perception in the oro-facial region of symptom-free men and women

JOURNAL OF ORAL REHABILITATION, Issue 7 2009
I. OKAYASU
Summary, The aim of this study was (i) to examine the effect of light tooth contact as in diurnal tooth clenching on the tactile detection threshold (TDT), the filament-prick pain detection threshold (FPT) and the pressure pain threshold (PPT) in the oro-facial region and (ii) to examine the possible gender difference in this effect on the tactile and pain perception. Twenty healthy volunteers participated. The TDT and the FPT were measured by means of Semmes-Weinstein monofilaments, on the cheek skin (CS) overlying the masseter muscles (MM) and on the skin overlying the palm side of the thenar skin (TS). The PPT was measured at the central part of the MM using a pressure algometer. Each parameter was measured before and after keeping light tooth contact for 5 min (session 1) and after keeping the jaw relaxed for 5 min (session 2) as a control. Although there were no significant session effects on any of the parameters, there were significant effects of experimental condition on the TDT in both men and women (P < 0·001). Men had a significant higher FPT of the left CS (P < 0·05) and TS (P < 0·01) and a significant higher PPT of the MM than women (P < 0·001). These results illustrate that sensitivity to pain (FPT, PPT) was higher in women than in men. Although there were no significant gender differences in habituation of sensory perception, the increase of TDT after clenching/no clenching was larger in women, which warrants further study. [source]

An investigation of overeruption of posterior teeth with partial occlusal contact

JOURNAL OF ORAL REHABILITATION, Issue 4 2007
H. L. CRADDOCK
Summary, The need and demand for replacement of missing posterior teeth may increase as the UK population is predicted to be at least partially dentate for life. Replacement with either fixed or removable prostheses may be indicated, and the tooth positional changes of adjacent or opposing teeth may require consideration. The objectives of this study are to: (1) Investigate the extent of overeruption associated with partially opposed posterior teeth; (2) Determine if overeruption is associated with tipping of the partially opposed tooth and examine the extent of tip. Ninety-one patients with either partially or completely unopposed posterior teeth were included in the study. For each group the extent of overeruption of the tooth was measured. Differences in the extent of overeruption and tipping were analysed. Correlations between the presence of partial tooth contact and the extent of overeruption and degree of tipping of the unopposed tooth were analysed. There was no significant difference in the extent of overeruption between the unopposed and partially opposed groups. The partially opposed teeth displayed a greater degree of tipping than the unopposed group. There was no significant correlation between the extent of overeruption and the degree of tipping, nor between the extent of overeruption and the presence of partial tooth contact. There was, a significant correlation between the degree of tooth tip and the presence of partial tooth contact. (1) Partial tooth contact does not appear to prevent or reduce overeruption; (2) Partially opposed teeth show an increased degree of tip relative to teeth with complete lack of occlusal contact. The findings suggest that partial tooth contact should not be relied on clinically to maintain vertical tooth position. [source]

Reduction in parafunctional activity: a potential mechanism for the effectiveness of splint therapy

JOURNAL OF ORAL REHABILITATION, Issue 2 2007
A. G. GLAROS
summary, Interocclusal splints may be an effective modality in the management of temporomandibular disorders (TMD), but there is little evidence regarding the mechanism by which splints work. This study tested the hypothesis that pain reduction produced by splints is associated with reduction in parafunctional activity. In a two-group, single-blinded randomized clinical trial, patients diagnosed with myofascial pain received full coverage hard maxillary stabilization splints. Patients were instructed to maintain or avoid contact with the splint for the 6 weeks of active treatment. Patients who decreased the intensity of tooth contact were expected to show the greatest alleviation of pain, and those who maintained or increased contact were expected to report lesser reductions in pain. Experience-sampling methodology was used to collect data on pain and parafunctional behaviours at pre-treatment and during the final week of treatment. Patients were reminded approximately every 2 h by pagers to maintain/avoid contact with the splint. The amount of change in intensity of tooth contact accounted for a significant proportion of the variance in pain change scores. Patients who reduced tooth contact intensity the most reported greater relief from pain. Splints may produce therapeutic effects by reducing parafunctional activities associated with TMD pain. [source]

Reproducibility of lateral excursive tooth contact in a semi-adjustable articulator depending on the type of lateral guidance

JOURNAL OF ORAL REHABILITATION, Issue 3 2005
A. J. CARO
summary, The purposes of this study were (i) to compare the reproducibility of lateral tooth contacts of casts mounted in a semi-adjustable articulator when condylar guidance was set by different methods and (ii) to assess the margin of error of the variations of condylar guidance without changing lateral tooth contacts, depending on the type of lateral guidance. In subjects with different types of lateral guidance, intraoral lateral tooth contacts identified with occlusal registration strips were compared with those identified by use of a semi-adjustable articulator, setting the condylar guidance in four different ways: using protrusive wax wafers, by axiography and by adding and subtracting 5° from the value of condylar guidance obtained by protrusive wax wafers. Tolerance to variations of condylar guidance without changing lateral tooth contacts was determined by increasing and decreasing the value of condylar guidance until lateral tooth contacts changed. Different ways of setting condylar guidance on a semi-adjustable articulator give rise to different values of condylar guidance in the same subject. The occlusal repercussions of these variations of condylar guidance values depend on the type of lateral guidance. Canine protection had the greatest tolerance to variations in the setting of condylar guidance without changing lateral occlusal contacts. [source]

Investigation of the factors related to the formation of the buccal mucosa ridging

JOURNAL OF ORAL REHABILITATION, Issue 6 2003
I. Takagi
summary, The aim of this study was to clarify the factors related to the formation of the buccal mucosa ridging, which has been mentioned to be a clinical sign of clenching. Twenty-one individuals were investigated and divided into three groups: (i) those without buccal mucosa ridging, (ii) the buccal mucosa ridging located in all the posterior teeth region, and (iii) the buccal mucosa ridging corresponding only to the molar teeth region. A pressure sensor was used and placed at two points: first upper premolar and second upper molar. The recording tasks were: (i) silent reading at rest, (ii) light voluntary clenching, (iii) maximum voluntary clenching, (iv) holding the cheeks tightly against the teeth while light voluntary clenching, (v) holding the cheeks tightly against the teeth without tooth contact, (vi) pulling angle of mouth laterally while light voluntary clenching, (vii) pulling angle of mouth laterally without tooth contact and (viii) swallowing. No significant differences were found between groups in all the recording tasks except for the swallowing, at which significant difference (P < 0·05) was found between the groups of individuals having buccal mucosa ridging and without it. Based on these results it became clear that the buccal mucosa pressure exerted on the buccal aspect of teeth during swallowing plays an important role in the formation of buccal mucosa ridging. [source]

Effects of interocclusal appliances on EMG activity during parafunctional tooth contact

JOURNAL OF ORAL REHABILITATION, Issue 6 2003
A. L. Roark
summary, To test the hypothesis that a flat plane interocclusal appliance affects the electromyographic (EMG) activity of the temporalis and masseter muscles in pain-free individuals, maxillary splints were fabricated for 20 individuals who reported no history, signs or symptoms of myofascial pain or arthralgia as determined by two trained, independent examiners. Subjects were instructed to establish light tooth contact, maximum clenching, and moderate clenching with/without the splint in place (as determined by random assignment) while EMG data from the left and right temporalis and masseter muscles were recorded. A 5-min biofeedback training session to relax the masticatory muscles was followed by a repetition of the tooth contact/clenching tasks with/without the splint in place. With the splint in place, the activity of the temporalis muscles decreased for all tasks, significantly for the left and right temporalis under maximal clenching and for the right temporalis under moderate clenching. In contrast, the activity of the masseter muscles increased under light and moderate clenching (significantly for the left masseter under moderate clenching) and decreased slightly under maximal clenching. The effectiveness of interocclusal appliances may be due to mechanisms other than redistribution of adverse loading. [source]

Influence of protrusive tooth contact on tapping point distribution

JOURNAL OF ORAL REHABILITATION, Issue 11 2000
T. Ueno
This study investigated the influence of protrusive tooth contacts (tooth contacts during mandibular protrusion) on the tapping point distribution. Nine healthy subjects volunteered for this study and the protrusive tooth contact pattern, as well as the retrusive tooth contact pattern, was altered on four maxillary occlusal splints. The first splint was adjusted to make the sagittal incisal path of protrusion and retrusion equivalent to that of the natural dentition. The second and third splints had partial and complete elimination of the protrusive tooth contact, respectively. The fourth splint had complete elimination of both protrusive and retrusive tooth contacts. The subjects were asked to use each splint continuously for 1 week. The tapping point distribution was measured on the 7th day after insertion of each splint. The four experimental occlusal conditions were found to have a significant effect on the tapping point distribution. The complete elimination of the protrusive tooth contact caused an anterior tapping point location and an increase in the tapping point area. The former tendency was found to be independent of the presence of the retrusive tooth contact. In conclusion, it was suggested that the protrusive tooth contact plays a significant role in maintaining the consistency and stability of the tapping point. [source]

Effects of load and indicator type upon occlusal contact markings

JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2008
Muhammad N. Saad
Abstract Statement of Problem: Clinicians use occlusal indicators to identify tooth contacts. However, the reliability of these indicators has been questioned. At times occlusal contacts are not identified or false positive occlusal contacts are observed. Purpose of Study: This study was designed to compare the number and size of occlusal indicator marks from both thick and thin occlusal indicator materials with different loads. Materials and Methods: Ivorine casts were articulated and mounted on an Hana Mate nonadjustable articulator. Loads of 100N, 150N, and 200N were applied with Accufim (25 ,m thick, Parkell, Farmingdale, NY) and Articulating Paper (60 ,m thick, G.E. Rudischauer Dental Articulating Paper, Brooklyn, NY) as the occlusal indicators. A fresh piece of indicator was used for each trial. Comparisons were made of the number and size of the contacts for both the thick and thin occlusal indicators at the different loads. Results: Observation of the marks recorded with the thicker occlusal indicator demonstrated both a greater number marks and a larger size to the marks when compared to the thinner Accufilm, p , 0.02,0.0001. However, there was no significant increase in the number or size of the marks with an increased load for either material. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008 [source]

Small unilateral jaw gap variations: equilibrium changes, co-contractions and joint forces

JOURNAL OF ORAL REHABILITATION, Issue 10 2009
H. J. SCHINDLER
Summary, After complex prosthetic reconstructions, small differences in vertical distances between the left and right side of the jaw may occur during jaw closing, nevertheless providing bilateral tooth contacts in intercuspation by small deformations of the mandible. Their effects on the co-contraction of the masticatory muscles, the temporomandibular joint reaction forces, and the point of application of the resultant bite force vector in the maxillary occlusion plane , the so-called reduction point , have not been investigated, thus far simultaneously in one sample. The main goal of this study was to investigate variations of these measures in an experimental intercuspation simulated by one anterior and two posterior force transmission points. [source]

Relationship between tooth contacts in the retruded contact position and mandibular positioning during retrusion

The influence of altered occlusal guidance on condylar displacement during submaximal clenching

JOURNAL OF ORAL REHABILITATION, Issue 10 2005
N. OKANO
summary As cited in literatures, canine protected occlusion has a potential to reduce clenching induced temporomandibular joint loadings. However, these previous studies did not perform a control of the clenching level which differed with the depending occlusal conditions. This result may be due largely to an associated reduced jaw closing muscle activity. The present study has investigated clenching induced condylar displacements with controlled clenching level. Twenty healthy human subjects (15 males and five females with an average age of 26·5 years) volunteered to participate in this study. Metallic occlusal overlays were fabricated for the lower working side canine and overlaid to the second molar and the non-working side second molar in order to simulate a canine protected occlusion, group function occlusion and bilateral balanced occlusion. Electromyographic (EMG) activity from the bilateral masseter, anterior temporalis, and posterior temporalis was recorded. These signals were rectified, summarized, and presented to each subject using an oscilloscope screen. Using this visual feedback, subjects were asked to perform clenching tasks at a 50% level of maximal voluntary contraction exerted with simulated group function occlusion and three-dimensional condylar displacements were recorded. An experimental occlusal pattern that shows statistically significant affects on condylar displacements (anova: P < 0·001) was found. When compared with the simulated canine protected occlusion, the simulated group function occlusion caused smaller working side condylar displacement and the simulated bilateral balanced occlusion caused significantly smaller non-working side and working side condylar displacements. These results suggest that the increased working side tooth contacts have a potential to reduce working side joint loadings, and a balancing side contact has a potential to reduce non-working side joint loadings, under the laboratory condition where the clenching level is controlled. [source]