A 3D finite element analysis of stress distribution on different thicknesses of mineral trioxide aggregate applied on various sizes of pulp perforation.

OBJECTIVES: The aim of this study was to evaluate the stress distribution on different thicknesses of mineral trioxide aggregate (MTA) placed on various widths of pulp perforations during the condensation of the composite resin material. MATERIALS AND METHODS: The mandibular molar tooth was modeled by COSMOSWorks program (SolidWorks, Waltham, MA). Three finite elemental analysis models representing 3 different dimensions of pulp perforations, 1, 2, and 3 mm in diameter, were created. The perforation area was assumed as filled with MTA with different thicknesses, 1, 2, and 3 mm for each pulp perforation width, creating a total of 9 different models. Then, a composite resin material was layered on MTA for each model. A 66.7 N load was applied and an engineering simulation program (ANSYS, Canonsburg, US) was used for the analysis. Results were presented considering von Mises stress criteria. RESULTS: As MTA thickness increased, the stress values recorded within the area between pulp and MTA decreased. Strain was decreased when the thickness of MTA increased. CONCLUSIONS: Stresses at MTA-pulp interface and strain on MTA decreased with the increase in MTA thickness. CLINICAL RELEVANCE: In clinical practice, when MTA is required for pulp capping, using a thick layer of the material seems to be a better option in order to reduce the stress under forces of hand condensation of overlying restorative materials.

Natural bites, food consistency and feeding behaviour in man.

Complete feeding sequences (bite to terminal swallow) were recorded in 11 individuals (Class I occlusions) feeding on apple, banana and biscuit (hard cookie) to establish whether jaw movements characteristic of the stage I transport, chewing, stage II transport and swallowing processes found in non-human mammals could be identified in man. All participants took large natural bites (known weight) of each food, but seven were supplied standard 6-g pieces of apple. Jaw movements (three axes) were recorded using a locally calibrated Sirognathograph. Discrete stage I transport movements (bite moved from incisors to postcanines), were found in most records, but least frequently for banana. The number of chewing cycles before the first in-sequence swallow increased in the order: banana, ( = ) apple without peel, apple with peel, biscuit. Chewing cycles showed subtle changes in gape profile but significant variation in mediolateral movement cycle to cycle. Morphologically distinct stage II transport cycles could not be identified. Swallows occurred intermittently during chewing (79% of all sequences, n = 146) with cycle durations in excess of 1 s in contrast to the range for chewing (0.6-0.7 s). Almost all sequences ended with a period, clearance, of highly irregular jaw movements often including swallows. Clearance has not been described in other mammals. Food consistency affected feeding behaviour. The "chew/swallow' ratio (total number of chews/total number of swallows) increased with food hardness. The number of chewing cycles before the first in-sequence swallow also increased. Food type significantly affected sequence duration. The duration of clearance was also affected by bite weight and food hardness. It is concluded that initial food consistency determines the number of chewing cycles before the first swallow and overall sequence duration. The change in the pattern of jaw movement in both the vertical and mediolateral directions cycle to cycle suggests continuous sensory modulation of the motor output to the mandibular musculature.

Recording mandibular movement: technical and clinical limitations of the Sirognathograph.

It is essential to know the limitations of any equipment used for research or clinical purposes. Clinical electronic equipment is commonly sold for "black box" use without specification of artifacts. This study tested the technical and clinical limitations of the Sirognathograph, which is a device used for recording mandibular movement. From a technical point of view, the Sirognathograph's slow sampling speed and sample artifacts have been shown to be the system's main limitations; however, it was possible to eliminate sampling artifacts by using a customized pulse generator and software for controlled data acquisition. Clinically, the Sirognathograph appears to have some inherent limitations in its accuracy. The effect of cranial movements during mastication can cause a baseline drift with consequent errors in the recording of mandibular position. This problem was controlled in this study by using a headband to stabilize the cranial movements during mastication. Also, the spatial relationships between the aerial and both the cranial base and the magnet were found to be critical for repeatability of the recordings.

The efficacy of two prototype chewing gums for the removal of extrinsic tooth stain.

AIM: To compare the potential efficacy of two prototype chewing gums in extrinsic stain removal on natural teeth. SETTING: Dental school clinics. DESIGN: Double-blind, two groups, parallel design. PARTICIPANTS: 76 adult volunteers (32m, 44f, mean age: 20.6 years old). METHODS: Oral hard and soft tissue health was examined. The subjects were randomly assigned to use either Product A (without active ingredients) or Product B (with active ingredients). Each subject was asked to brush their teeth for one minute twice daily (mornings and nights) and chew the gums supplied for 15 min (2 dragees each time), three times daily, once after each meal (breakfast, lunch and dinner) for the entire four-week duration. Dental stain assessment was made on the 12 incisors using the Lobene Stain Index (LSI). RESULTS: The overall difference between the stain scores after 4-weeks' use of the chewing gums was statistically significant (p<0.01) for both test Product A (10.84) and Product B (7.77) with regard to the mean baseline stain scores (21.57). This difference represented a 48% reduction in stain scores for those subjects using Product A, while the reduction was 64% for the subjects using Product B. CONCLUSIONS: The results of this in vivo study suggest that chewing gums with and without active ingredients have potential effect on stain removal after regular use for one month.

Dental caries prevalence, tooth brushing and periodontal status in 150 young people in Istanbul: a pilot study.

OBJECTIVE: To evaluate periodontal conditions, prevalence and determination of dental caries and oral health behaviours in a group of young people in Istanbul. DESIGN: Subjects were orally examined and questioned. SETTING: A high school in Istanbul. SUBJECTS: One hundred of fifty students. RESULTS: This study showed that 28 per cent of teenagers had adequate oral hygiene. These findings suggest that 72 per cent of the subjects needed oral hygiene education and required restorative dental care. CONCLUSIONS: The present study showed that dental treatment need is very high in the sample group. Strong co-operation should be set up between families, schools, communities, regulators and legislators in order to develop and implement comprehensive oral health promotion programmes.

Shear bond strength of luting agents to fixed prosthodontic restorative core materials.

BACKGROUND: Bonding properties of luting cements are important for retention of restorative core materials. The aim of this study was to compare the bonding performance of a resin-modified glass ionomer cement and a self-adhesive resin cement to various fixed prosthodontic core materials. METHODS: Cylindrical specimens with a thickness of 2 mm and a diameter of 5 mm were fabricated from Au-Pd-Ag, Co-Cr, Ni-Cr-Mo, Ni-Cr-Fe alloys, titanium, zirconia and Empress II (n = 20). Each group was divided into two subgroups to be luted with two different luting agents. Composite resin blocks were cemented onto specimens with RelyXUnicem and FujiCem. A shear bond strength machine with 50 kg load cell and 0.50 mm/min crosshead speed was used. Kruskal Wallis test, Dunn's Multiple Range test and Mann-Whitney-U test were used for statistical analysis. The results were evaluated in a confidence interval of p < 0.05. RESULTS: The highest bond strength was obtained between Ni-Cr-Fe-RelyXUnicem (8.22 +/- 2.15 MPa) and the lowest was between Empress II-FujiCem (1.48 +/- 0.9 MPa). In FujiCem groups, Co-Cr and Ni-Cr-Fe showed significantly higher bond strength than Au-Pd-Ag and Empress II. In RelyX Unicem groups, Ni-Cr-Fe showed higher bond strength than Empress II. CONCLUSIONS: The types of luting agents and restorative core materials may have a significant influence on bond strength.

In vivo and in vitro study of fungal presence and growth on three tissue conditioning materials on implant supported complete denture wearers.

In this study three type of tissue conditioning materials were used in vitro and in vivo to investigate the presence and growth of Candida albicans, considered to be the pathogenic member of the genus. In vitro test results of different tissue conditioners showed that they have a tendency to have an inhibiting effect on C. albicans at the third day of incubation. For the in vivo tests tissue conditioners were placed in existing maxillary prosthesis of 21 patients who had been treated with endosseous dental implants (seven in each group). The results showed that yeast forms were observed after 3 days in two patients' dentures which were relined with Fitt. Yeasts forms were also seen in three patients' dentures after 6 days, two of them relined with Fixo-gel and the other one relined with Visco-gel. The hyphal form of Candida was seen in four patients' dentures, relined with Fitt, and also in three patients' dentures, relined with Fixo-gel and Visco-gel.

The effect of disinfectant agents in eliminating the contamination of dental unit water.

High concentrations of water-borne organisms cause multiple public health problems. Contamination of water exiting the dental unit water lines could be inhibited with the use of some disinfectants. The purpose of this investigation was to establish the effect of two disinfectants and to test their capacity to eliminate colony forming units (CFU) per mL. Vacuum lines of four chairs were treated for a total of 2 weeks. Two disinfectants (Bio 2000 and Alpron) were used as per manufacturer's instructions. Water samples for hetereothrophic counts from each unit's air/water syringe line were collected before treating the first patient of the day. Baseline, daily, first and second week samples of 10 mL were plated on blood agar plates and eosin ethylene blue agar. For meosifilic bacterial counts, Mueller Hinton agar plates with 1 mL direct and 1/10 were used in sterile serum and CFU were counted. The suspected colonies were further evaluated using API 20E and API 20NE. No Gram(-) opportunistic pathogens were found during the entire observation. Baseline contamination level (>102 CFU mL-1) without use of disinfectants was significantly higher (P < 0.0001) than at both first and second weeks when disinfectants were used. No colony was formed when Bio 2000 was used after both first and second weeks, whereas small number of CFU mL-1 was found at the end of the first week when Alpron (<10) was used. In conclusion, when used daily, both disinfectants prevent the development of bacterial contamination after first and second weeks with no significant differences (P=0.35).

Existence of Candida albicans and microorganisms in denture stomatitis patients.

The aetiology of denture stomatitis is not clear from the literature. Some studies show its aetiology as Candida albicans, while other reports point out the significance of microorganisms. In this study the existence of C. albicans and microorganisms was investigated in subjects with and without denture stomatitis. The results showed that a combination of C. albicans and microorganisms is more likely to be responsible for denture stomatitis.

Oral hygiene habits, denture cleanliness, presence of yeasts and stomatitis in elderly people.

The purpose of this study was to determine oral hygiene habits, denture cleanliness, presence of yeasts and denture stomatitis in elderly people. Seventy complete denture wearers were investigated clinically and mycologically. Subjects were evaluated according to, presence of denture stomatitis, presence of yeasts, denture cleanliness, frequency of denture brushing and denture cleaning methods. Swabs were taken from the palate investigated mycologically in order to identify the yeast colonies. No statistical relationship was found between denture stomatitis and frequency of denture brushing and denture cleaning methods. However, there was a statistically significant relationship between denture stomatitis, yeasts' presence and denture cleanliness.

Scanning electron microscopic examination of different cleaners: surface contaminant removal from dentures.

Dentures were examined by scanning electron microscopy to evaluate removal of surface contaminants. Five complete dentures were obtained during patient appointments. The palatal surface of each denture was divided into eight pieces (1 cm2) then each sample cleaned with Corega, Dentipur, Fittydent, sodium hypochloride, Savlon, Ipanol, brushing methods and one sample was also kept as a control. They were prepared for SEM examination and photographed at x500. One photograph of each sample was evaluated in random order by three judges for a total of 120 observations. Photographs were compared with one of a clean denture sample. Statistical analysis of the results showed that soaking dentures in sodium hypochloride and Savlon removed significantly more contaminants than any of the other methods used in this study.

Contribution of periodontal receptors and food qualities to masseter muscle inhibition in man.

Previous studies of human muscle inhibition during chewing have shown that many factors contribute to the incidence and intensity of this reflex but few studies have been in a physiological context. During the first crushing cycle of brittle foods ipsilateral masseter muscle EMG, mandibular movement and vibration were recorded simultaneously in four healthy dentate subjects. Experiments were repeated before and during anaesthesia of the cheek teeth on the chewing side. The results suggest that vibration seems to be the most important factor in muscle inhibition during food crushing; conversely periodontal sensation, mandibular closing movement and the preload by the muscle at the onset of food fracture play a minor role.