Correlation between maximum bite force and craniofacial morphology of young adults in Indonesia

Dental age estimation using the Kvaal method-an evaluation of length and width ratios: a systematic review

This study aimed to systematically review the correlational accuracy between width ratios and length ratios based on the Kvaal methodology with chronological age. This systematic review followed Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA). The search strategy included ProQuest, PubMed, Science Direct, and Taylor and Francis and Willey online without time or language restriction using Kvaal method of age estimation as key words for the search up to December 2021. A team of two researchers independently selected the studies and extracted the data. The Covidence platform was used to systematically organize all titles. The full texts of eligible studies were analyzed. Risk of bias (RoB) was assessed using a modified (to the specific characteristics of this systematic review) checklist based on Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement checklist for observational studies. A total of 658 articles were initially reviewed, but 22 were selected for inclusion. The risk of bias was estimated to be unclear to low overall. Among the length ratios, ratio R showed a strong association with chronological age, followed by ratio P. For the width ratios, ratio B demonstrated a close association with chronological age, followed by ratio C. The results suggest that width ratios correlate better with chronological age than length ratios. This systematic review suggests the width ratios are more strongly associated with chronological age than the length ratios. Using a width ratio could serve as a convenient and rapid way to estimate dental age. Our results apply equally to all types of ethnic groups.

Is the distribution of cortical bone in the mandibular corpus and symphysis linked to loading environment in modern humans? A systematic review

OBJECTIVE

The human mandible is a unique bone with specific external and internal morphological characteristics, influenced by a complex and challenging loading environment. Mandibular cortical thickness distribution in cross-sections is reported to be related to facial divergence patterns, cultural and dietary habits and more generally, specific loading environment. This review hypothesises that a process of environmental mechanical sensitivity is involved in the distribution of cortical bone in the mandibular corpus and symphysis in modern humans, and that loading regimes can influence this distribution pattern. Based on a review of the recent literature, this study aims to answer the following question: "Is the distribution of cortical bone in the mandibular corpus and symphysis linked to the loading environment in modern humans?"

DESIGN

A systematic review was undertaken using the PubMed/Medline, Scopus and Cochrane Library databases for publications from 1984 to 2022 investigating the relationship between cortical bone distribution in the mandibular corpus and the loading environment. A subgroup meta-analysis was performed to determine the overall effect of facial divergence on cortical thickness.

RESULTS

From a total of 2791 studies, 20 fulfilled the inclusion criteria. The meta-analyses were performed in eight studies using a randomised model, finding a significant overall effect of facial divergence on cortical thickness in posterior areas of the mandible (p < 0.01).

CONCLUSIONS

Within the limitations of this review, specific loading regimes and their consequent variables (diet, culture, facial divergence) were linked to cortical thickness distribution. Sex was found to be unrelated to cortical thickness pattern.

Association between gonial angle on orthopantomogram and reline frequency in removable partial denture wearers

PURPOSE

Removable dentures are a reasonable option for prosthetic treatment. However, continuous residual ridge resorption and reline procedures are inevitable owing to the strong pressure exerted on the mucosa or inappropriate pressure distribution. This study aimed to elucidate the association between the gonial angle on orthopantomogram (GAO) with occlusal force and reline frequency in removable partial denture wearers.

METHODS

Participants were patients who had previously received removable partial denture treatment for a free-end defect. Age, sex, number of remaining teeth, remaining opposing teeth, and occlusal support were investigated. GAO was measured using panoramic radiographs. The mean relining interval was calculated as the mean number of days between denture insertion and the first relining or subsequent relining. The association between the mean relining interval and each factor was investigated.

RESULTS

Sixty-five subjects (33 females) were analyzed. The median value of the mean relining interval was 533.3 days, and the median GAO was 123º. There was a significant positive correlation between the mean relining interval and GAO (rs = 0.335). The number of remaining opposing teeth and occlusal support exhibited weak negative correlations with mean relining interval (rs = -0.187 and -0.214, respectively). Multivariate analysis using a generalized linear model showed that GAO was a significant explanatory variable for the m ean relining interval.

CONCLUSIONS

Within the limitations of this study, GAO was found GAO was found to contribute to the increased frequency of relining due to ridge resorption in patients with a small GAO.

Fracture Load of CAD/CAM Fabricated Cantilever Implant-Supported Zirconia Framework: An In Vitro Study

The fracture resistance of computer-aided designing and computer-aided manufacturing CAD/CAM fabricated implant-supported cantilever zirconia frameworks (ISCZFs) is affected by the size/dimension and the micro cracks produced from diamond burs during the milling process. The present in vitro study investigated the fracture load for different cross-sectional dimensions of connector sites of implant-supported cantilever zirconia frameworks (ISCZFs) with different cantilever lengths (load point). A total of 48 ISCZFs (Cercon, Degudent; Dentsply, Deutschland, Germany) were fabricated by CAD/CAM and divided into four groups based on cantilever length and reinforcement of distal-abutment: Group A: 9 mm cantilever; Group B: 9 mm cantilever with reinforced distal-abutment; Group C: 12 mm cantilever; Group D: 12 mm cantilever with reinforced distal-abutment (n = 12). The ISCZFs were loaded using a universal testing machine for recording the fracture load. Descriptive statistics, ANOVA, and Tukey's test were used for the statistical analysis (p < 0.05). Significant variations were found between the fracture loads of the four ISCZFs (p = 0.000); Group-C and B were found with the weakest and the strongest distal cantilever frameworks with fracture load of 670.39 ± 130.96 N and 1137.86 ± 127.85 N, respectively. The mean difference of the fracture load between groups A (810.49 + 137.579 N) and B (1137.86 ± 127.85 N) and between C (670.39 ± 130.96 N) and D (914.58 + 149.635 N) was statistically significant (p = 0.000). Significant variations in the fracture load between the ISCZFs with different cantilever lengths and thicknesses of the distal abutments were found. Increasing the thickness of the distal abutment only by 0.5 mm reinforces the distal abutments by significantly increasing the fracture load of the ISCZFs. Therefore, an increase in the thickness of the distal abutments is recommended in patients seeking implant-supported distal cantilever fixed prostheses.

Relationships between skeletal morphology and patterns of bilateral agenesis of third molars in Japanese orthodontic patients

The aim of this study was to reveal the correlations between bilateral agenesis of third molars (M3s) and skeletal morphology in Japanese male and female orthodontic patients. Sixty patients (30 males, 30 females), with bilateral agenesis of maxillary M3s and without agenesis of mandibular M3s (group U), and 60 patients (30 males, 30 females), with bilateral agenesis of mandibular M3s and without agenesis of maxillary M3s (group L), were selected as agenesis groups. Additionally, 60 patients (30 males, 30 females) with all four M3s were selected as the control group (group C). Patients in these three groups had no agenesis of teeth other than M3s. Lateral cephalograms of each patient were used to evaluate skeletal morphology of the maxilla and mandible. Two-way analysis of variance was used for statistical comparisons. Groups U and L had significantly smaller maxillary length and area than group C. Group U exhibited a significantly smaller lower facial height than group C. Males showed significantly larger maxillary length; total mandibular and mandibular body length; mandibular ramus height; SNB angle; maxillary area; and mandibular symphysis, corpus and ramus areas than females. Females had significantly larger lower facial height, gonial angle and ANB angle than males. Smaller maxillary length and area and lower facial height should be considered in planning orthodontic treatment for patients with bilateral agenesis of maxillary and mandibular M3s.

Fracture loads of screw-retained implant-supported zirconia prostheses after thermal and mechanical stress

PURPOSE

The objective of the present study was to evaluate fracture loads of screw-retained implant-supported zirconia prostheses after artificial aging.

METHODS

Four types of screw-retained implant-supported prostheses were fabricated (n=11 each); porcelain-veneered zirconia prosthesis (PVZ), indirect composite-veneered zirconia prosthesis (IVZ), porcelain-fused-to-metal prosthesis (PFM), and monolithic zirconia prosthesis (ML). The specimens were subjected to 10,000 thermocycles and cyclic loading for 1.2 million cycles. Fracture loads were measured, and the data were analyzed with the Kruskal-Wallis and Steel-Dwass tests (α=0.05).

RESULTS

All specimens survived the artificial aging procedures. The fracture loads for the PVZ (1.52kN), IVZ (1.62kN), and PFM groups (1.53kN) did not significantly differ; however, the fracture load for the ML group (6.61kN) was significantly higher than those for the other groups. The fracture load for the IVZ group was comparable to those for the PVZ and PFM groups.

CONCLUSIONS

The monolithic zirconia prostheses exhibited significantly higher fracture loads than the bilayered prostheses. All the investigated types of screw-retained implant-supported zirconia prostheses appear sufficient to resist posterior masticatory forces during long-term clinical use.

Relationships of maxillofacial morphology and malocclusion with handgrip strength in adult women

OBJECTIVES

Maxillofacial morphology and malocclusion are related to maximum occlusal force (MOF). Although it has been reported that MOF was related to handgrip strength (HS), the relationships between maxillofacial morphology/malocclusion and HS remain unclear. This study aimed to examine the relationships between maxillofacial morphology, malocclusion and HS.

SETTING AND SAMPLE POPULATION

Eighty-five women with malocclusion, aged 18-40 years, were selected.

MATERIALS AND METHODS

Lateral cephalometric radiographs (SNA, SNB, ANB, mandibular plane-FH, and gonial angles, overjet and overbite), the Peer Assessment Rating (PAR) index and HS were measured. Subjects were classified by the Japanese normal mean value of cephalometric analysis or the reference value which was defined by degree of malocclusion in each PAR index measurement item (small/low: value < mean/reference value, large/high: value ≧ mean/reference value). Measurements were then compared between groups.

RESULTS

HS of the large-gonial angle group was lower than that of the small-gonial angle group. In the small-overbite group or high-transverse (PAR index score showing crossbite/scissor bite in the canine and molars) group, HS in the large-gonial angle group was significantly lower than that in the small-gonial angle group.

CONCLUSIONS

Our results suggest that gonial angle is the largest factor affecting HS. HS may be especially low in those subjects with a large gonial angle and a small overbite or a crossbite/scissor bite in the molar section.

Relationships between craniofacial morphology and masticatory muscle activity during isometric contraction at different interocclusal distances

OBJECTIVE

The aim was to investigate relationships amongst interocclusal distances, masticatory muscle electromyographic (EMG) activity during isometric contraction of masticatory muscles, and craniofacial morphology.

DESIGN

Twenty-eight women and 12 men (25.3 ± 3.8 years old) participated. After measuring maximal voluntary occlusal bite force (MVOBF) between the right-first premolars, the participants were asked to bite at submaximal levels of 0 (= holding the bite force transducer), 15, 22.5, and 30% MVOBF with the use of visual feedback. The thickness of a bite force transducer was set at 10, 12, 13, 14, 16, 17, 18, 19, 20, 22, and 24 mm (= interocclusal distance: IOD). Nine soft tissue craniofacial factors were assessed through digital photograph: face height, middle face height, lower face height, face width, inter-pupil distance and mandibular plane angle, lower face height / face height ratio, inter-pupil distance / facial width ratio and face width / face height ratio.

RESULTS

In the masseter muscle, EMG activity decreased with increased IODs. The participants with higher mandibular plane angle had more negative slope coefficients of IOD-EMG graphs at 0% MVOBF especially in male temporalis and female masseter and temporalis muscles, suggesting that a greater mandibular plane angle is associated with lower EMG activity at longer IOD.

CONCLUSIONS

Overall the findings support the notion that craniofacial morphology is associated with differences in neuromuscular activity of the masticatory muscles, and suggest that the neuromuscular effects of oral appliances may be dependent on patients' craniofacial morphology and the thickness of the device. (247/250 words).

Effects of gum chewing exercise on maximum bite force according to facial morphology

Development of the masticatory system is influenced by functional needs. Furthermore, masticatory exercise can improve masticatory function. The aim of this study was to evaluate the potential effect of the gum chewing exercise on the maximum bite force (MBF) in adult subjects with different facial morphologies. MBF was measured by a portable occlusal force gauge and lateral cephalogram was used for evaluation of craniofacial morphology in 19 individuals (7 males and 12 females) with a mean age of 25.4 years (SD ± 4.3). The volunteers underwent gum chewing exercise for 5 min twice a day for 4 weeks. MBF was measured before (T1) and after the 4‐week exercise (T2). The facial morphology of the subjects was classified into the brachy (n = 7), mesio (n = 7), and dolicho (n = 5) facial types. In all three groups, exercise was associated with a significant increase in MBF, though the percent increase was highest in the dolicho facial type. We conclude that gum chewing exercise can improve masticatory performance, especially in individuals with dolicho facial morphology.

Differences in bite force between dolichofacial and brachyfacial individuals: Side of mastication, gender, weight and height

PURPOSE

Due to the bite force importance in functionality of the masticatory system, this study aimed to characterize it in dolichofacial and brachyfacial individuals.

METHODS

A sample comprised by 190 patients was divided into two groups: 90 severe dolichofacial, and 100 severe brachyfacial individuals classified according to the VERT index and the face height ratio (Jarabak quotient). Bite force was measured by using an adjusted digital dynamometer and proper methodology.

RESULTS

The sample met the parametric assumptions and presented statistical significance when right and left sides of dolichofacial and brachyfacial individuals were compared. However, within the same group, no differences between the left and right sides were found. Generally, bite force was higher for male, left masticator, age between 41-50 years, weighing over 100kg and between 1.81 and 1.90m tall.

CONCLUSIONS

Based on the results of this cross-sectional study, it was possible to conclude that the bite force in severe brachyfacial individuals was significantly higher than in severe dolichofacial individuals, being influenced by gender, weight and height.

Maximum Bite Force of Edentulous Patients before and after Dental Implant Rehabilitation: Long-Term Follow-Up and Facial Type Influence

PURPOSE

(1) To evaluate patients' long-term maximum bite force (MBF) after rehabilitation with mandibular implant-supported prosthesis, (2) to assess the influence of facial pattern in MBF, and (3) to evaluate the relation between the dominant chewing side and MBF.

MATERIALS AND METHODS

Twenty-nine patients were selected. Pre- (T0) and immediate post-rehabilitation (T1) data of MBF were collected. In a follow-up visit 3 to 5 years after rehabilitation (T2), 24 patients participated. The patients were asked about dominant chewing side, and facial pattern was obtained by the initial lateral radiographs.

RESULTS

There was statistically significant increase in MBF in T1 - T0 = 5.4 ± 4.3 kgf, T2 - T1 = 5.5 ± 6.0 kgf. There was no statistically significant difference in MBF considering facial type, brachyfacial (T0 = 4.4, T1 = 10.7, T2 = 17.6 kgf), mesofacial (T0 = 4.1, T1 = 9.7, T2 = 16.5 kgf), and dolichofacial (T0 = 3.4, T1 = 7.9, T2 = 12.6 kgf).

CONCLUSIONS

There was no statistically significant relation between MBF and the dominant chewing side. It can be concluded that mandibular rehabilitation with dental implants improves MBF independent of the facial pattern and dominant chewing side.

Mandibular morphology in two archaeological human skeletal samples from northwest Europe with different masticatory regimes

Mandibular morphology, assessed osteometrically, is studied in two historic human skeletal series (N = 64 individuals) from northwest Europe, one from Zwolle, the Netherlands (19th century CE), the other from Wharram Percy, England (10th-19th century). Both groups show greater dental wear than modern Western populations, but the rate of wear is greater at Wharram Percy than at Zwolle, suggesting a more vigorous masticatory regime. The aim is to evaluate any differences in mandibular morphology between the two groups that might relate to the inferred difference in biomechanical loading upon the chewing apparatus consequent upon the different physical properties of the diets consumed. Results indicate that the mandibles from Zwolle are generally smaller than those from Wharram Percy, especially in the gonial and ramus region and in the height of the post-canine corpus. These differences are consistent with those predicted on biomechanical grounds. That clear differences were observed in two samples whose masticatory regimes were distinct but not very different is an indication of the sensitivity of mandibular morphology to biomechanical input, and supports its value for investigating differences in physical properties of diets in palaeopopulations.

Maximum bite force following unilateral fixed prosthetic treatment: a within-subject comparison to the dentate side

OBJECTIVES

We evaluated the maximum occlusal bite force (MBF) among individuals with fixed partial dentures compared to the opposite dentate side and determined the relationship between MBF and gender, age, and body mass index (BMI).

SUBJECTS AND METHODS

A total of 85 subjects (43 males and 42 females, age range 28-66 years) with fixed partial dentures on one side and dentate on the other side participated in the study. The MBF was measured at the first molar area on both sides using a digital hydraulic bite force gauge. The highest MBF value was recorded from three measurements of bite force at each side (with 45-second intervals between measurements).

RESULTS

The mean MBF was 596.2 ± 76.3 N at the dentate side and 580.9 ± 74.3 N at the fixed partial denture side. The difference was statistically significant (p < 0.05). The MBF values were greater in males as well as in taller and heavier participants. Nevertheless, the BMI had no relationship with MBF values (p >0.05).

CONCLUSIONS

Within the same subjects, the measured MBF values at the dentate side were higher than those at the fixed partial denture side. Females, lighter, and shorter participants had lower MBF values. Meanwhile, the BMI had no significant relationship to MBF values.

Evaluation of masseter muscle morphology in different types of malocclusions using cone beam computed tomography

OBJECTIVES

To evaluate the length and orientation of masseter in different types of malocclusions using Cone Beam Computed Tomography (CBCT).

METHODS

Samples of 180 patients seeking orthodontic treatment at the University of Nevada, Las Vegas School of Dentistry, were included in the study. Pre-treatment multi-slice CBCT scans of these patients were divided into three anteroposterior groups: Class I subjects with ANB angle 0° to 5°; Class II subjects with ANB angle >5°; and Class III subjects with ANB angle <0°. CBCT scans were also divided into three vertical groups: normodivergent subjects with mandibular plane angle 22° to 30°; hyperdivergent subjects with mandibular plane angle >30°, hypodivergent subjects with mandibular plane angle <22°. The masseter was identified and landmarks were placed on the anterior border, at the origin and insertion of the muscle in 3-D mode of the Dolphin Imaging 10.5 Premium software. The Frankfort Horizontal Plane was used as a reference plane and an angular measurement was obtained by intersection of a line produced by the masseter landmarks to calculate the orientation of the muscles. The length of the masseter was measured and data were analyzed using ANOVA and matched pairs test.

RESULTS

ANOVA found significant differences in muscle length among the three vertical groups for both the left and right muscles. Paired t test showed significantly shorter muscle length for the hypodivergent group (43.3 ± 4.0 mm) compared to the normodivergent group (45.6 ± 4.5 mm, P < 0.05) and shorter muscle length for the hyperdivergent group (42.3 ± 4.7 mm) compared to the hypodivergent group, P < 0.05. No significant differences were found in muscle length among the three anteroposterior groups. However, significant differences in muscle orientation angle were found among the three anteroposterior groups (P < 0.05). Class II subjects were found to have the most acute orientation angle (67.2 ± 6.6°) and Class III had the most obtuse orientation angle (81.6 ± 6.8°).

CONCLUSIONS

These results suggest that certain types of malocclusion may have different masseter lengths and orientations and these differences may have implications for the mechanical advantage in bite force. For example, Class III individuals may have greater bite force than Class II individuals because the muscle fibers are oriented more along the arch of closure.

Loss of molar occlusion and mandibular morphology in adults in an ancient human population consuming a coarse diet

The purpose of the study is to investigate the link between number of molar teeth retained in occlusion and mandibular morphology in adults in an ancient, high dental wear human population. The study material comprises skeletons from Mediaeval Wharram Percy, England (N = 50 female, 69 male adults). It was hypothesized that adults retaining fewer occluding molars would show reduction in mandibular dimensions, particularly in the ascending ramus and gonial regions where the main muscles of mastication have their insertions. Molar occlusal status is assessed using the concept of functional units. Mandibular morphology is assessed using a suite of ten linear measurements plus the mandibular angle. Results show no evidence for any association between number of molars retained in occlusion and mandibular angle. There was an association between mandibular size and number of molars retained in occlusion, with smaller mandibular dimensions in those retaining fewer occluding molars. Some measurements were affected more than others so that there was also some shape alteration. Alteration of mandibular dimensions was more clearly demonstrable in females than in males. Only in females could significant reduction in the ascending ramus and gonial regions be demonstrated. Reasons for the apparent difference in response to loss of molar occlusion between male and female mandibles are unclear, but sex differences in bony metabolism mediated by hormonal factors may be implicated. Results suggest that care should be exercised when including mandibles from individuals showing loss of molar occlusion in morphological studies.

Association of gonial angle with morphology and bone mineral content of the body of the adult human mandible with complete permanent dentition

We investigated the differences between 2 gonial angle (GA) size groups with respect to the morphometry and quantitative bone mineral content (QBMC) of mandibles with all teeth erupted and normal occlusion. We used 19 dried mandibles that were obtained from an Indian population and stored in our department. These mandibles were at Hellman's developmental dental stage VA and were divided into low gonial angle (LGA) (GA ≤ 120°; 8 specimens; 16 sides) and high gonial angle (HGA) (GA ≥ 125°; 11 specimens; 22 sides) groups. After lateral radiography of the mandibles using a titanium step wedge, linear measurements and the QBMC were determined, on hard copies and digital images, respectively. The age and sex of the cadavers to which the specimens belonged were unknown. The mandibular cortical width (MCW) and the antegonial notch depth of the LGA group were significantly larger than those of the HGA group. No significant difference was found in the distribution of the 3 categories of mandibular cortical index (MCI) or in cortical and trabecular bone mineral contents (CBMC and TBMC). The GA size was negatively and moderately associated with the MCW and the mandibular cortical width on the point AG (MCWAG), but was not significantly associated with either variable for CBMC and TBMC. These results suggested that the GA size of these stage-VA mandibles influenced changes in the width of inferior cortex and morphology of antegonial notch. The GA size did not influence QBMC under the mental foramen of the mandible and had negative associations with the MCW and MCWAG.

Effects of masticatory muscle training on maximum bite force and muscular endurance

OBJECTIVE

This study evaluates the effects of chewing training on strength and endurance of the masticatory muscles.

MATERIALS AND METHODS

Of the 49 healthy young adults included in the study, nine served as controls for a baseline measurement of bite force. The 40 participants who actively trained their masticatory muscles were randomly divided into a 'continuous training group' (CTG) and an 'intermittent training group' (ITG). The participants performed oral motor training by clenching silicon tubes (Chewy Tubes(™)) according to a designed protocol. The muscular strength was studied in terms of maximum bite force. Muscular endurance was evaluated by measuring the duration for which the participants held 50% of their maximum bite force value.

RESULTS

Both the maximum bite force and the muscular endurance capacity increased after intensive training for both groups. After 2 months, the ITG stopped training for 1 month. At this point, a significant difference was identified both in the mean bite force values and the mean muscular endurance duration: the ITG exhibited lower values. For both groups, the highest values were attained after 3 months of training. The maximum bite force values and the muscular endurance duration were observed to follow similar patterns. The effects attained decreased rapidly in both groups when the training stopped.

CONCLUSIONS

For both the continuous and intermittent training groups, 4 months of chewing exercises strengthened masticatory muscles, but such effects diminished gradually for both groups when the exercises stopped.

Differences in 5 anatomic parameters of mandibular body morphology by gonial angle size in dentulous Japanese subjects

This study aimed to determine the differences in 5 anatomical parameters of the mandibular body on dental panoramic radiographs (DPRs) of 234 dentulous Japanese subjects (21-78years; mean, 25.76; median, 27 teeth) according to gender and gonial angle (GA) size, and to analyse the correlations between GA size and each variable by gender. The subjects were divided into low (LGA≤120°) and high gonial angle (HGA≥125°) groups. Linear, angular, and morphological measurements were obtained using the DPRs. Statically significant differences were determined using the Mann-Whitney U and χ(2) tests and simple regression analysis. Mandibular cortical width - MCW, antegonial notch depth - AD and angle - AA, and panoramic mandibular index - PMI in the LGA group were significantly larger than those of the HGA group. In men, a significant difference was observed in the distribution of the 3 mandibular cortical index categories between both GAs. Sexual dimorphism for MCW and AD was significantly greater in men than in women. There were significantly negative low correlations between the GA and variables of the MCW, AD, and PMI. These results suggest that the MCW and AD can show significantly different morphology according to gender and GA size.

Occlusal force, electromyographic activity of masticatory muscles and mandibular flexure of subjects with different facial types

Objective

The aim of this study was to evaluate whether vertical facial patterns influence maximal occlusal force (MOF), masticatory muscle electromyographic (EMG) activity, and medial mandibular flexure (MMF).

Material and Methods

Seventy-eight dentate subjects were divided into 3 groups by Ricketts's analysis: brachyfacial, mesofacial and dolychofacial. Maximum occlusal force in the molar region was bilaterally measured with a force transducer. The electromyographic activities of the masseter and anterior temporal muscles were recorded during maximal voluntary clenching. Medial mandibular flexure was calculated by subtracting the intermolar distance of maximum opening or protrusion from the distance in the rest position. The data were analyzed using ANOVA followed by Tukey's HSD test. The significance level was set at 5%.

Results

Data on maximum occlusal force showed that shorter faces had higher occlusal forces (P<0.0001). Brachyfacial subjects presented higher levels of masseter electromyographic activity and medial mandibular flexure, followed by the mesofacial and dolychofacial groups. Additionally, dolychofacial subjects showed significantly lower electromyographic temporalis activities (P<0.05).

Conclusion

Within the limitations of the study, it may be concluded that maximum occlusal force, masticatory muscle activity and medial mandibular flexure were influenced by the vertical facial pattern.

Relationship between masseter muscle size and maxillary morphology

The aim of this study was to investigate the relationship between masseter muscle size and craniofacial morphology, focusing on the maxilla. Twenty-four patients (11 males and 13 females; mean age 27.6 ± 5.6 years) underwent cephalometric analyses. Ultrasonography was used to measure the cross-sectional area (CSA) of the masseter muscle and bite force was measured using pressure sensitive film. The results showed that CSA-relaxed was positively correlated with upper anterior face height (UAFH)/total anterior face height (TAFH) and negatively with lower anterior face height (LAFH)/TAFH and LAFH (P < 0.05). CSA-clenched was correlated positively with SN-palatal, FH-palatal, UAFH/TAFH, and lower posterior face height (LPFH)/total posterior face height (TPFH) and negatively with LAFH/TAFH, LAFH, upper posterior face height (UPFH)/TPFH, and UPFH (P < 0.05). Bite force was positively correlated with LPFH/TPFH and negatively with UPFH/TPFH (P < 0.05). As the masseter became larger, the anterior maxillary region tended to shift downwards relative to the cranial base, whereas the posterior region tended to shift upwards. The decrease in LAFH/TAFH and increase in LPFH/TPFH as the size of the masseter muscle increases may be influenced not only by the inclination of the mandibular plane but also by the clockwise rotation of the maxilla.

Mastication, EMG activity and occlusal contact area in subjects with different facial types

Dentofacial morphology may affect orofacial functions, therefore the aim of the current study was to evaluate the influence of craniofacial morphology on masticatory function, occlusal contact area (OCA), and masticatory muscles activity. Seventy-eight (78) subjects were divided into three groups according to vertical facial pattern: 1. mesofacial; 2. brachyfacial; and 3. dolichofacial. Artificial material and the sieving method were used to access masticatory efficiency (ME). OCA was determined by registration of posterior teeth. Electromyographic (EMG) activity of the masseter and anterior temporal (AT) muscles was accessed bilaterally at rest and at maximal vertical clenching (MVC). ME (%) was significantly higher in brachyfacial and lower in dolichofacial subjects. Brachyfacials presented the highest OCA (mm2) followed by meso and dolichofacial subjects. The EMG of the masseter and AT at rest and at MVC showed that dolichofacial subjects presented the lowest activity values, while brachyfacial subjects presented significantly higher measurements. Craniofacial morphology affected masticatory function, OCA, and EMG activity of the masticatory muscles.

Masticatory features, EMG activity and muscle effort of subjects with different facial patterns

It has been suggested that craniofacial morphology plays an important role in masticatory function, however, there are controversies and unsolved questions that still require elucidation. The aims of this study were to evaluate masticatory performance, mandibular movement, electromyographic (EMG) activity and muscle effort of masseter and anterior temporal muscles during mastication. Seventy-eight dentate subjects were selected and divided into three groups according to vertical facial pattern: brachyfacial, mesofacial and dolichofacial. Silicon-based material was used for chewing tests. Masticatory performance was determined by a 10-sieve method, and masticatory movements during mastication were assessed using a 3D mandibular tracking device. Electromyographic activities of masseter and anterior temporal muscles were evaluated during mastication, and muscle effort was calculated by the percentage of activity required for mastication based on maximum muscle effort. Data were analysed using anova and anova on-ranks tests. Dolichofacial subjects presented significantly poorer masticatory performance (6·64±2·04; 4·33±0·70 and 3·67±0·63), slower rate of chewing (1·34±0·27, 1·18±0·22 and 1·21±0·20 cycles per second) and larger posterior displacement during mastication (6·22±2·18; 5·18±1·87 and 5·13±1·89) than meso- and brachyfacial individuals, respectively. No statistical difference was detected among groups for the other masticatory movement parameters. There was no difference in absolute EMG amplitudes of masseter and anterior temporal muscles during mastication among groups, but the relative effort of both muscles was higher in dolichofacial, followed by meso- and brachyfacial subjects (masseter: 39·34± 2·25; 36·87±4·05 and 33·33±4·15; anterior temporal: 38·12±1·61; 38·20±8·01 and 35·75±2·48). It was concluded that the vertical facial pattern influences masticatory performance, mandibular movement during mastication and the effort masticatory muscles required for chewing.

Relationships between the gonial angle and mandibular ramus morphology in dentate subjects: a panoramic radiophotometric study

Analysis of dental panoramic radiographs (DPRs) is an indispensable diagnostic tool for dental implants both pre and post operation. Many studies on linear and angular morphometry of the mandibular body have been conducted, but those on the mandibular ramus have not yet been reported. The purpose of this study was to investigate the differences in the morphometric parameters of the mandibular ramus between high and low gonial angles (GAs) on DPRs as well as between genders, and to determine the relationships between GA and variables of the mandibular ramus morphometry. The DPRs of 156 dentate subjects (78 for each gender) with more than 15 teeth present, a mean age of 49.54 years, and a mean number of teeth of 26.20 were examined. The films were divided into the following 2 groups of GA: less than 120° (low gonial angle, LGA) and more than 125° (high gonial angle, HGA) in both the right and left sides. The parameters for Ar'-Go, MaF-Go, RW, and RD in the LGA group were significantly larger than those in the HGA group in both men and women, but that for the ramus angle (RA) was significantly smaller in the LGA group than in the HGA group. Significant gender differences in the 2 GA groups were recognized with respect to the Ar'-Go, MaF-Go, RW, and RD parameters. Significant negative low and moderate correlations were found between GA and the Ar'-Go, MaF-Go, RW, and RD variables, whereas significant positive low correlation was found between GA and the RA variable. Within the limits of this study, the analysis of the mandibular ramus morphometry on DPRs in terms of GA size and gender was found to be useful for devising a highly predictive and strategic plan for implant-supported oral rehabilitation.

Comparison of Shear Bond Strength, Fatigue Limit and Fatigue Life in resin-bonded metal to enamel bonds

OBJECTIVE

To compare the Shear Bond Strength (SBS) of resin-bonded metal/enamel bonds with the Fatigue Limit and Fatigue Life of identical joints.

METHODS

285 discs of Ni/Cr-alloy (dia 5 mmx4 mm) were cast and treated by either (1) Sandblasting with aluminium oxide or (2) Sandblast+15 min electrolyticetch in HCl. The discs were bonded to etched enamel (37% HPO4/30 s) using 3 bonding systems. Ten discs of each group were subjected to a shear bond test (SBT) in a Universal Testing Machine5 (CHS=50 mm/min). Seventeen discs of each group were used to determine the Fatigue Limit using the Staircase method (5000 cycles, 4 kg increment). Further batches of 10 discs were subjected to cyclic loads of either 5, 10, or 20 kg to determine the number of cycles at failure (Fatigue Life). The SBS and Fatigue Limit results were compared by correlation analysis. The Fatigue-Life cycles were compared by Weibull analysis to determine the beta (reliability) and alpha (number of cycles) coefficients for the 3 loads.

RESULTS

For all materials and treatments, the Fatigue-Limit results were much lower than the SBS and there was no correlation between the values (r=0.49, p=0.18). The Fatigue Limit for the samples using 5000 cycles ranged from 10.7 to 16.1 MPa. In the Fatigue-Life study, the stress at which the samples were reliably able to withstand more than 1 million cycles (beta>5) was 2.5 MPa.

CONCLUSION

The Fatigue Limit of the bonds was much lower than the SBS and there was no correlation between the two values. In this study the Fatigue Limit was not a good predictor of the long term Fatigue-Life failure of the specimens.

Influence of different adhesive resin cements on the fracture strength of aluminum oxide ceramic posterior crowns

STATEMENT OF PROBLEM

The influence of different types of adhesive resin cements on the long-term prognosis of aluminum oxide ceramic posterior crowns is unclear.

PURPOSE

The purpose of this study was to evaluate the fracture resistance of aluminum oxide ceramic on maxillary posterior crowns cemented with different resin luting agents before and after cyclic thermomechanical loading. Material and methods Forty-eight maxillary first molars were prepared and restored with standardized aluminum oxide ceramic (In-Ceram Alumina) crowns. The test specimens were randomly divided into 3 groups (n=16). The crowns were luted with an acrylic resin cement (Super-Bond C&B, control, Group SB) and 2 composite luting agents (Panavia F, Group PV; and Rely X Unicem, Group RX). Half of the specimens were exposed to thermomechanical fatigue in a masticatory simulator. All specimens were tested for fracture strength (N) using quasistatic loading. The Wilcoxon rank sum test was used to compare the fracture strength (alpha=.05).

RESULTS

All specimens survived the exposure to the simulator. The following median fracture strength values were obtained without/with thermomechanical fatigue loading: Group SB, 2726 N/2673 N; Group PV, 2520 N/2083 N; and Group RX, 2036 N/2369 N. The fracture strength in Group PV after thermomechanical fatigue loading was significantly lower compared to the fracture strength in Group PV without artificial aging (P =.016), as well as significantly lower compared to Group SB with artificial aging (P =.003).

CONCLUSION

Within the limitations of this study, all tested cements are capable of successfully luting aluminum oxide ceramic crowns. The fracture strength of Group PV after artificial aging was comparatively low.

APPLICATION OF "PRESCALE" AS AN AID TO CLINICAL DIAGNOSIS IN ORTHODONTICS

We examined the feasibility of applying the Dental Prescale Occluzer System to the evaluation of occlusion in orthodontic patients. The patients were classified according to the type of malocclusion or facial pattern. The values of occlusal contact area and occlusal force obtained from these individuals differed depending on the type of occlusion or facial pattern. These values were higher in individuals with normal occlusion than in patients with malocclusion and higher in patients with the Brachyo facial pattern than in those with the Dolico facial pattern. Because this system can very easily analyze the occlusal contact area, the mean pressure on each occlusal contact point, and the occlusal force during the process of orthodontic treatments, it can be useful as an aid for the initial diagnosis of occlusal problems, the observation of the changes in occlusion during treatment, and the establishment of the final goal of orthodontic treatments.