Optical Identification of Inaccuracies Caused by Improper Handling on Type IV Gypsum Casts

Type IV gypsum (stone gypsum) is an essential material in prosthetic treatment. Improper handling can change hardness, expansion and compressive strength and it is the most common reason for inaccurate casts. In that case even the most perfect impressions will result in inadequate prosthetic treatment. Using optical instruments-digital camera (2.5 million pixels) and digital microscope we attempted to identify the visual appearance of inadequate casts and relate them to specific causes. All casts were poured in highly controlled conditions and only one factor, whose influence we tried to determine, was changed during the procedure. Most common mistakes are: outdated gypsum, incorrect powder to water ratio, mixing without a vacuummixer, pourring without a vibrator and etching by alginate acid. All the mistakes were visualised, easily recognized and categorized by using digital optical equipment

Electromyographic Evaluation of the Influence of Denture Adhesive on Retention and Stability of Complete Dentures

Improving retention and stability of complete dentures is of considerable interest in prosthetic dentistry. Approaches to this problem over the years have included overdentures, implants and denture adhesives. Although denture adhesives are widely used, there are few quantitative data on the effects of an adhesive on denture retention and stability during normal functional activities. The purpose of this investigation was to study the influence of denture adhesive on the surface EMG activity of the masticatory muscles in a sample of complete denture wearers. In this study 6 denture wearers were investigated. Surface EMG recordings were obtained from left and right anterior temporal and masseter muscle and from the sub-mandibular group in the region of the anterior belly of the digastric muscle on the left and right side. Data were recorded during standardized jaw positions that included clenching in the position of maximal intercuspation of teeth (at 100%, 50% and 25% of the maximum activity), lateral eccentric positions, maximal lateral eccentric positions, protrusion, maximal protrusion and wide opening. The results demonstrated higher digastric muscle activity in protrusion with the teeth at an edge-toedge position after the use of adhesive (p0.05). This investigation demonstrated that patients were able to produce greater levels of muscle activity in protrusive and laterotrusive positions with the use of adhesive

Prosthetic Dentistry on the Internet

Since the late sixties when the ARPANET- first computer network was developed, Internet has had a great impact on the way of thinking, buying, teaching, learning and everyday life, including dentistry. The beginning of internet in science and research, has proved to be irreplaceable way of communication between researchers all over the word. Currently (April 2002) one of the most popular search engines on the net (Google) indexed about 2 billion web pages, 35 million of non HTML documents and 700 million Usenet messages, which makes the Internet the greatest information service ever. The purpose of this study was to investigate which part of the web space is taken by prosthetic dentistry and the importance which it gains on the Internet. The method used was standard Internet search engine keyword queries preformed using six web search engines: Google, Lycos, Infoseek, AltaVista, Northern Light, HotBotand Excite. Research results suggest that there is currently (May 2002) about 30 thousand pages (0.0015% of searched web space) which contain terms: prosthetic dentistry or prosthodontics and about one thousand web pictures connected to these terms. Content analysis suggests that quality and real informative value of the majority of those pages is low. To conclude-informative space on the Internet concerning prosthetic dentistry is still in development and the need for confirmation and authorized information is obvious

Measurement of Factors Influencing Mandibular Function in Dental Students in Croatia

The aim of this study was to measure main variables influencing mandibular function-movements of mandible during chewing, speech and breathing. Measurements taken were: vertical and horizontal overlap of central incisives, side shift from centric relation (CR) to maximal intercuspation (MI) measured in the sagittal and frontal plain, maximal mouth opening, maximal mouth opening using force, maximal dextrotrusion and sinistrotrusion. Method used included the same number of subjects and examiners. This was achieved by educating final year dental students before the measurement took place. They were both examiners and subjects for each other. Comparison of this method to single examiner and multiple experienced examiner methods revealed no statistically different results. Measurements were divided by gender, dental status, and the number of signs and symptoms related to temporomandibular dysfunctions (TMD) that were then statistically analyzed. There were no significant differences between the results of this study and findings in current literature

The EMG Activity of Masticatory Muscles During Different Chewing Tasks

Mastication is a highly coordinated neuromuscular function that involves fast effective movements of the jaw and continuous modulation of muscle force. To understand the relationship between muscles during mastication it is necessary to know the position and direction of movement of the mandible. MATERIAL AND METHODS: Twenty-four young healthy adults, age ranged 17 to 27, participated in this study. They were chosen among dental students of School of Dental Medicine University in Zagreb and had to be free of sign and symptoms of TMD. Surface EMG recordings were obtained from left and right anterior temporal muscle, left and right masseter muscle and from left and right digastric muscle on the 8 channel PC based EMGA-1, apparatus for simultaneous recording of myoelectrical activity (6 differential EMG channels, input impedance 100 MW, CMRR> 95 dB at 50 Hz, bandwidth 2 Hz-1 kHz, programmable input sensitivity from 100mVpp to 20 mVpp, an 8 bit resolution A/D conversion, 2 kHz sampling rate) - occlusal sound (2 audio channels), specially designed and developed for the purpose of kinesyological examinations of stomatognathic system’s function. The disc electrodes (Ag/AgCl, diameter 10 mm) were placed 2 cm apart in the main direction of the muscle fibres. RESULTS: 1. Main effect of factor "functional movement" was significant at p<0.01, and values were the highest for gum chewing, and the lowest for empty chewing except fordigastric muscle which had lowest values at continuous isometric contraction. 2. Main effect of factor “muscles” was significant at p<0.01 for all muscles involved, values were similar for the same muscles on left and right side. 3. Main effect of factor “time” was statistically significant p<0.05 for all cases showing decreasing trends except in last minute during functional movements. 4. Interactions between factors “functional movement” and “time” were present at significance p<0.01