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This current study investigated which angle of canine inclination (angle between canine tooth axis (CA-line) and the line between the lateral canthus and the ipsilateral labial angle (EM-line)) is perceived to be most attractive in a smile. The second objective was to determine whether laymen and dental experts share the same opinion. A Q-sort assessment was performed with 48 posed smile photographs to obtain two models of neutral facial attractiveness. Two sets of images (1 male model set, 1 female model set), each containing seven images with incrementally altered canine and posterior teeth inclinations, were generated. The images were ranked for attractiveness by three groups (61 laymen, 59 orthodontists, 60 dentists). The images with 0° inclination, that is CA-line (maxillary canine axis) parallel to EM-line (the line formed by the lateral canthus and the ipsilateral corner of the mouth) (male model set: 54·4%; female model set: 38·9%), or -5° (inward) inclination (male model set: 20%; female model set: 29·4%) were perceived to be most attractive within each set. Images showing inward canine inclinations were regarded to be more attractive than those with outward inclinations. Dental experts and laymen were in accordance with the aesthetics. Smiles were perceived to be most attractive when the upper canine tooth axis was parallel to the EM-line. In reconstructive or orthodontic therapy, it is thus important to incline canines more inwardly than outwardly., (© 2014 John Wiley & Sons Ltd.)

Biomechanical features of occlusal contacts are important in understanding the role of the occlusion contributing to masticatory function. Cusp-fossa contact is the typical pattern of occlusion between upper and lower teeth. This includes static relations, such as that during clenching, and dynamic relations when mandibular teeth contact in function along the maxillary occlusal pathways, as during mastication. During clenching in the maximum intercuspal position (ICP), cuspal inclines may take the role of distributing the occlusal forces in multi-directions thus preventing excessive point pressures on the individual tooth involved. During chewing movement on the functional side, the mandible moves slightly from buccal through the maximum ICP to the contralateral side. The part of the chewing cycle where occlusal contacts occur and the pathways taken by the mandible with teeth in occlusal contacts are determined by the morphology of the teeth. The degree of contact is associated with the activity of the jaw muscles. To obtain repeatable static and dynamic occlusal contact information provided by the morphology of the teeth, maximum voluntary clenching and chewing movements with maximum range are needed. In conclusion, in addition to the standard occlusal concepts of centric relation/centric occlusion and group function/cuspid protection relation, biomechanics in static and dynamic cusp-fossa relationships should be included to develop an understanding of occlusal harmony which includes no interfering or deflective contacts in functional occlusal contact., (© 2012 Blackwell Publishing Ltd.)

Aim: To investigate the effect of orthodontic tooth movement involving the six maxillary anterior teeth on the pulp response to both thermal and electric stimuli during active orthodontic treatment and retention., Methodology: Forty-seven subjects who required fixed orthodontic appliances were used as a study group with 23 non-orthodontic subjects recruited as a control group. Cold and electrical stimuli were applied to the maxillary incisors and canines immediately before and after the placement of fixed appliances and at regular intervals for both groups during active treatment and 12 months into retention. The numbers of negative responses for each tooth at each time interval were recorded for both groups. The data were collected and tabulated, and chi-square tests were used to determine significant difference between the numbers of negative responses for the two types of tests used on the same tooth and between different teeth. The mean values of the electric pulp testing (EPT) thresholds were also obtained and used to assist in analysing the results., Results: In the control group, all teeth tested positively to the EPT and thermal pulp tests at all time intervals. In the orthodontic group, two teeth failed to respond to EPT and only one tooth to thermal testing at baseline (Time 0). After that, the number of negative responses to both tests increased gradually at each time interval reaching a peak after 2 months of active treatment (Time 3) and then declined gradually towards the end of observation period (Time 14). At baseline, response thresholds to electric testing were typically higher for orthodontic subjects, particularly for the maxillary lateral incisor tooth. For the control group, the response threshold over the study period was relatively constant. For the orthodontic group, application of force immediately increased the response threshold to EPT (Time 1), which peaked after 2 months (Time 3) and then gradually reduced. At the end of the active treatment, response thresholds remained elevated, but they returned to pre-treatment values towards the end of the retention phase., Conclusion: Dental practitioners should interpret responses to electrical pulp testing cautiously in orthodontic patients; thermal testing may be more reliable., (© 2011 International Endodontic Journal.)

The presence of non-working occlusal contacts is often considered harmful for the temporomandibular joint. Thus, the purpose of this study was to investigate the effect of non-working occlusal contacts on the condylar position during submaximal and maximal clenching. The study comprised 22 healthy subjects having a canine-guided occlusion. None of them had a third molar and none of them had a missing tooth or showed tooth mobility. All subjects clenched on (i) the canine, (ii) the canine while a stiff bite registration material was positioned between the second premolar and the first molar on the non-working side. The clenching level was controlled by surface electromyography of the masseter muscle. During clenching, the vertical and horizontal condylar position was predicted using six degrees of freedom ultrasonic motion analyser. Clenching on the canine caused a cranial movement of the non-working side condyle. This movement was reduced by 0.6-0.9 mm when the subjects clenched while the artificial non-working side contacts were in place. These results indicate that the contacts on the non-working side may be able to prevent upward joint movement.

Aim: To evaluate ex vivo whether a simulated pulpal microcirculation inside a pulp chamber influenced intrapulpal temperature rise following application of heat on tooth surfaces., Methodology: An ex vivo model that allowed the circulation of 37 degrees C warm water inside the pulp chamber of an extracted human tooth was designed. The experimental model resembled pulpal microcirculation. After application of specific thermal stimuli for 30 s to the external surface of 15 maxillary central incisors, lateral incisors and canines, temperature changes were measured in the pulp chamber. The Greenhouse-Geisser and Bonferroni tests were used for analysis of the data. The level of significance was set at 0.05., Results: Significant differences were found in all three groups of teeth between temperature measurements with or without intrapulpal water flow. Additionally, temperature changes resulting from the application of different stimuli to the group of lateral incisors were significantly greater compared with the other groups of teeth (P < 0.05)., Conclusions: The importance of the cooling effect of simulated pulp microcirculation in the thermal behaviour of the dentine was established. Thickness of tooth tissue influenced significantly pulp temperature rise ex vivo.

The present study aimed to examine the effect of custom tray designs on the displacement of mobile tooth and local impression pressures during the impression procedure, using partially edentulous simulation models with six anterior teeth containing a mobile tooth prepared in previous studies. The custom trays were designed by altering the thickness of the respective spaces on the labial and lingual sides of the remaining tooth arch. In previous studies, the mobile tooth was displaced in the labial direction and local impression pressures of the mobile tooth were greater against the lingual side than the labial side for all custom tray designs. Furthermore, the custom trays perforated with holes on the lingual side were effective to reduce mobile tooth displacement, labial and lingual impression pressures against the mobile tooth, and the differences between them. Therefore, the present study was performed focusing on the labial and lingual thickness of spaces in custom tray designs. It was found that mobile tooth displacement, labial and lingual impression pressures against the mobile teeth and their differences were less in trays with spaces>3.0 mm thick on both the labial and lingual sides, but markedly greater in trays with a 1.5 mm-thick space on the labial side. These results indicate that the thickness of spaces on the labial side in the tray should not be reduced to prevent mobile tooth displacement.

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.

Aim: The aims of this study were to define the average time of eruption of permanent teeth, the range of variation of the eruption time of each tooth, and their sequence of eruption amongst boys and girls in Tehran, Iran., Methods: The population under study comprised 3744 pupils and students in the 4-15-year-old age group (1786 girls and 1958 boys) who were randomly selected from schools and training centres in the 20 districts covered by the General Department of Education and Training in Tehran. The research was carried out on a cross-sectional basis. The average age at eruption of permanent teeth, excluding third molars, was given as the mean (+/- SD) and median in months for each gender. A table of percentiles of the eruption time was also determined., Results: The results show that, with the exception of the maxillary second premolars, the average age at eruption of permanent teeth in girls is less than in boys. The results also show that mandibular teeth have an earlier eruption time than maxillary teeth in both boys and girls. By the age of 96 months, 97% of the girls had all their first permanent molars. In boys, the corresponding age was 99 months. Amongst girls, maxillary canines erupt earlier than maxillary second premolars., Conclusion: On average, girls have their permanent teeth erupt earlier than boys. The sequence of eruption differs between girls and boys for maxillary canines and maxillary second premolars.

The assessment of bite forces on healthy single tooth appears essential for a correct quantification of the actual impact of single implant oral rehabilitations. In the present study, a new single tooth strain-gauge bite transducer was used in 52 healthy young adults (36 men, 16 women) with a complete permanent dentition. The influences of tooth position along the dental arch, of side, and of sex, on maximum bite force were assessed by an ANOVA. No significant left-right differences were found. On average, in both sexes the lowest bite force was recorded on the incisors (40-48% of maximum single tooth bite force), the largest force was recorded on the first molar. Bite forces were larger in men than in women (P < 0.002), and increased monotonically along the arch until the first or second permanent molar (P < 0.0001). The present data can be used as reference values for the comparison of dental forces in patients.

Lower rigidly connected long span bridges supported by natural abutments or implants sometimes become loose, come off, or fracture after a period of usage. Many reasons have been discussed for these failures. However, few researchers have shown the influence of mandibular elastic deformation on the abutments, although this influence is likely to produce a distortion force between the abutment and prosthesis. Therefore, this study measured the elastic deformation of the human mandibular arch during clenching on pivots by using charge-coupled device (CCD) cameras and an image analysing system. When the subjects clenched on the canines (unilaterally or bilaterally) or bilateral second molars, no mandibular deformation was found; whereas when the subjects clenched on the unilateral second molars, the mandibular arch on the non-pivot side moved upward and inward and the straight line distances between the right and left measurement points decreased by 0.2 mm. The magnitude of deformation is smaller than the depressible limit of periodontal membrane. This suggests that the influence of mandibular deformation on the connected prosthesis is negligible in the case of the natural root supported long span bridge but should probably be considered in the case of the implant supported bridge.

Objectives: The need for an adequate quantity of saliva to maintain oral health has been widely reported. It is not only the quantity that is important, but also how the saliva is distributed once it enters the mouth. Several studies have looked at how saliva is distributed around adult mouths. The aim of this experiment was to describe the distribution of stimulated saliva around the mouth in children., Sample and Methods: In order to demonstrate the distribution of saliva around the mouth under stimulated conditions, 25 child subjects were asked to chew a piece of chewing gum containing 1.5 mg erythrosin for 3 min on one side of the mouth. The distribution of dye in the mouth was recorded on standardized charts., Results: In all cases, dye was present ipsilateral to the chewing side. In 13 cases (52%) the dye did not cross the midline and of the remaining 12 children the dye only reached the contralateral canines in four of them (16%)., Conclusions: Evidence is presented which suggests that during unilateral chewing in children, saliva is not well distributed around the mouth and has a tendency to stay on the side of the mouth from where it was secreted (P < 0.01).

The purpose of this study was to investigate the association of temporomandibular joint (TMJ) clicking with the types of canine guidance, the tracing patterns of mandibular laterotrusion and, especially, with the movements of the working side condyle. In a young subject group, the movements of left and right mandibular laterotrusion were measured at the incisal and the lateral pole point of the working side condyle. All samples were divided into one of two groups according to the mesial (M) or distal (D) canine guidance. They were also divided into protrusive laterotrusion (PL) or retrusive laterotrusion (RL) groups according to the tracing patterns. The incidence of clicking was 23.8% in all 84 TMJs. There was no significant difference between the M and the D groups. However, clicking occurrence was significantly higher in the RL than in the PL group (P<0.05). The condyles in clicking joints moved more posterior in ipsilateral laterotrusion than the condyles in non-clicking joints. The condyles in RL also moved more posterior than those in PL. It is suggested that the posterior movement of the working side condyle in RL has a strong relationship with the internal derangement of the TMJ. However, it is not related to the type of canine guidance.

The effect of different types of canine guidance on the patterns of laterotrusive tracing at the incisal point and the relationship between the laterotrusive inclinations and the working side condylar movements were investigated in 42 young subjects. The subjects were divided into M and D groups according to their mesial and distal canine guidance, and were also divided into protrusive laterotrusion (PL) and retrusive laterotrusion (RL) groups according to their laterotrusive tracing patterns. No differences of laterotrusive inclinations and working side condylar movements were found between the M and D groups. The laterotrusive tracing pattern had no corresponding association with the type of canine guidance. In relation to the movements of the working side condyles, significant differences were found between the PL and RL groups. The condyles moved laterally and posteriorly in the RL group, but moved lateral and inferior in the PL one. The distance of condylar movement in the X direction was correlated with the horizontal and sagittal inclinations of laterotrusion. The results indicate that the movements of the working side condyle were affected functionally by the laterotrusion, but not by either the mesial or the distal type of canine guidance.

The purpose of this study was to evaluate the relationship between the clenching level and the intercuspal contact area in different regions of the dental arch. Twenty-five healthy subjects with natural normal dentitions and good occlusal support performed clenching tasks in the intercuspal position at four different levels (10, 30, 70 and 100% levels of maximum voluntary contraction) through EMG visual feedback from bilateral masseter and anterior temporal muscles. Simultaneously, the occlusal contacts were recorded with a silicone occlusal contact checking material (Black Silicone, GC Dental Industrial Corp., Tokyo, Japan). The occlusal records were analysed by an image analyser. Every area of the thickness less than 50 microm was determined to be an occlusal contact area. The occlusal contact areas on the anterior teeth (incisors and canines), the premolars (first and second premolars) and the molars (first and second molars) were calculated separately. The posterior occlusal contact area increased with an increase in the clenching levels but that of the anterior did not. The results of this study indicate that the increase in clenching forces affects the anterior and posterior occlusal contact areas differently.

This study aimed to assess mandibular mobility and the prevalence of functional occlusal contacts in subjects treated to a Class 1 incisor relationship by fixed orthodontic appliance therapy. Two hundred and thirty subjects participated (mean age=18 years) of whom 42 underwent orthognathic surgery. All subjects were in retention with a mean time of 7 months between debond and examination. Maximal mandibular opening, lateral and protrusive excursions were all significantly reduced in the surgical cases compared to the non-surgical group. Centric and eccentric non-ideal occlusal contacts were not different between surgical and non-surgical groups. Non-working side contacts occurred in 30% of subjects, posterior contacts on protrusion in 20% and RCP-ICP prematurities in 18% of subjects. Non-working side contacts were significantly more frequent in post-graduate cases compared to staff cases (P<0.05). An overbite less than the mean of 2.4 mm resulted in a reduced likelihood of canine guidance on the working side (P<0.001) and an increased frequency of non-working side contacts and posterior contacts on protrusion (P<0.001).

The purpose of this study was to explore the occlusal force distribution on the dental arch in the intercuspal position and to evaluate the relationship between the clenching strength and the occlusal force distribution. These variables were recorded using the Dental Prescale System in 16 healthy young adults. The number of tooth contacts, occlusal force and occlusal contact area increased linearly as clenching strength increased. The distribution of the occlusal force was greatest at the molar region followed by the premolar and anterior teeth region. The proportion of occlusal force (occlusal force at each region/total occlusal force) on molar regions increased as clenching strength increased. On the contrary, the proportion of occlusal force on the premolar and anterior teeth regions decreased as clenching strength increased. These findings suggest that control of occlusal force is important in diagnosis of the nature of occlusal contacts.

The relationship between anterior guidance and the mesiodistal inclination of the lower incisors relative to the existence of temporomandibular joint (TMJ) noise was investigated. One hundred and thirty-four individuals, 21 to 40 years of age (mean age 23.8; 104 men and 30 women), were examined. A highly significant correlation was observed between the mean lower-incisor inclination and the difference in steepness between the right and left anterior guidances in the subject group showing TMJ noise (P<0.001), whereas no significant correlation was observed in the group without TMJ noise.

The lack of easily measurable, objective physiological activity parameters of the masseter and temporalis muscle during jaw movements in humans has led to the consideration to revise data of surface electromyographies (EMGs) by applying a computerized quantification method. The aim of this follow-up analysis was to get quantitative data out of EMG-records of an earlier study. These records were obtained with two different splints, splint 1 providing an anterior front-canine guidance and splint 2 providing bilateral balanced occlusion. Utilizing a computer aided integration method led to numeric results which statistically proves the prediction of the previous investigation. Applying the integration method, the EMG raw signal was transformed into area-values which enabled a statistical work up of the data. Wilcoxon test statistics shows a significant (P<0.05) lower muscle activity in patients wearing dentures providing anterior front-canine guidance compared to those with balanced occlusion. It is concluded that the neuromuscular activity of the elevator muscles is highly reproducible and that the neuromuscular function is similar in edentulous subjects to that found in people with natural teeth. Furthermore, the study statistically proves earlier visual data that all those subjects, whose muscle activities were observed with anterior guidance (splint 1) compared to bilateral balanced occlusion (splint 2) showed significantly lower values with regard to subjects wearing splint 2.

This study investigates the definite influence of the working-side canine and balancing-side condylar guidances on mandibular lateral movement. Lateral movements were measured on 40 young adults (22 males and 18 females), using the three-dimensional mandibular movement analysing system. The inclinations of the paths were calculated on the working-side canine, incisor, balancing-side first and second molars and balancing-side condylar points in the frontal plane. Multiple regression analysis enabled quantitative evaluation of the influence of the canine path and condylar path on the path of each tooth. The canine path showed greater influence than the condylar path even on the balancing-side second molar path. There was no difference between male and female subjects in the influential ratio of the canine guidance to the condylar guidance on any tooth path. It was concluded that the influence of the anterior and posterior guidance on the lateral movement varied according to the type of tooth, but not to the gender of the subject. This functional characteristic was confirmed by the morphological finding that the relative location of the molars in relation to canine and condyle does not differ between the sexes. The difference in the guiding system between the protrusive and lateral movement is also described in this paper.

In 46 non-patients and 46 patients, the authors examined the presence (+) and absence (-) of canine tooth guidance (CG), i.e. dynamic dental articulation events in contrast to static dental occlusion events. During a right and a left laterotrusion of the mandible, the number of simple, mutually exclusive and exhaustive tooth guidance events (possibilities) was four. In addition, the authors examined the associations between temporomandibular joint (TMJ) sounds and canine guidance events. In non-patients, CG+ was relatively infrequent (30%), and CG- was relatively frequent (70%). In patients, CG+ was relatively infrequent (22%), and CG- was relatively frequent (78%). In both non-patients and patients, bilateral CG+ was rather infrequent (15%). In both non-patients and patients with the presence of TMJ sounds, CG+ was relatively infrequent (38%) while CG- was relatively frequent (61%). In non-patients as well as patients, no evidence was found that distal CG+ (putative lateral retrusive guidance) was associated with ipsilateral TMJ sounds (relative risk = 0%), nor that the association between mesial CG+ (putative lateral protrusive guidance) and ipsilateral TMJ sounds was beyond that of mere chance (relative risk = 50%).

The purpose of this study was to investigate occlusal schemes (canine guidance and group function) in relation to masticatory muscle activity. It was performed on 30 subjects, 15 with canine guidance and 15 with group function. Bilateral electromyographic recordings of masseter and anterior temporal muscles were obtained by surface electrodes during gum chewing and sliding laterally from centric relation while the teeth were in contact. The obtained data for both groups were compared statistically. Electromyograms were also evaluated visually. There was no significant difference in results between the occlusal schemes. However, canine guidance showed a narrower chewing model than group function and reduced anterior temporal muscle activity during sliding. This suggests that in the presence of healthy and good supportive canine teeth, canine guidance occlusion will be preferable.

Through electrognathography and surface electromyography of the right and left masseter muscle (MM), this methodologic study examined the excentric (lengthening) and concentric (shortening) contractions of brief (2000 ms) voluntary teeth grinding performed through canine as well as group function of the opposing teeth. We inferred that the most anterior and superior portions of the right and left MM were lengthened and shortened by at least 4.23 mm (right MM) and 4.82 mm (left MM). For the negative work efforts (excentric contractions) of canine function, the tensions of the ipsilateral MM ranged from 10 to 20% MVC and those of the contralateral MM from 4 to 14% MVC. For the positive work efforts (concentric contractions) of canine function, the tensions of the ipsilateral MM ranged from 11 to 44% MVC and those of the contralateral MM from 20 to 41% MVC. A comparison between canine and group function showed that the negative as well as positive work efforts of group function exceeded those of canine function.

The maximum bite force was recorded in five experimental volunteers with advanced tooth wear and five control volunteers who showed no abnormal wear. All subjects were then asked to maintain a force of 50% of the maximum for as long as possible while surface electromyograms from the masseter and temporalis muscles were recorded. The bite force and endurance time were found to be slightly increased in the experimental group, but no conclusions could be drawn regarding the state of fatigue. Two significant problems with regard to fatigue studies of the jaw-closing muscles emerged from the study, namely the use of the canine position for recording of the force, and the thickness of the force meter.

Physiological tooth movements during mandibular excursions with and without occlusion have been considered. Using electronic and pantographic techniques, anterior guidance and tooth movements during simulated mastication (without a bolus) were investigated. Investigations in the absence of occlusion showed that elastic deformation of the mandible gave rise to tooth movements. During occlusion three-dimensional tooth movements of up to 60 micro m in each direction occurred. Pantographic measurements of anterior guidance showed that each type of occlusion (balanced occlusion, group function and canine protected occlusion) has its own characteristic. Only canine protected occlusion gave values which corresponded to physiological data.