No abstract

The Bolton's analysis and Pont's analysis are very useful calculations for orthodontic diagnosis. In Nepal, there is no study about Bolton's and Pont's analysis. So here we examined 100 Nepalese subjects all subjects were with molar and canine class I relationship. We have measured the model to establish a normative standard of Bolton's OR and AR for Nepalese population and to find the reliability of Pont's index for Nepalese, and to comparing them between Caucasian and Chinese. The normative value on OR of Nepalese was found to be 91.22% with a standard deviation of 1.99 and AR was 78.04% with standard deviation of 2.72. The normative standard of OR for Nepalese is similar to that obtained by Bolton for Caucasian and that of Chinese, but the normative standard of AR obtained for Nepalese is significantly different than that obtained by Bolton for Caucasian and also that of Chinese. The correlation coefficient between the measured arch width values and the corresponding calculated values according to Pont's indexes were low in all cases with r values ranging from 0.07 to 0.29. Pont's Index is not reliable for predetermination of ideal arch width values for Nepalese.

A number of authors have listed the following qualities as ideal for maxillofacial material: (1) original physical and mechanical properties comparable to the human tissue that they are replacing, (2) the ability to sustain these properties during service, (3) compatibility with human tissues and the adhesives used to adhere the prostheses to tissue, and (4) the quality of being easy to process and an insensitivity to processing variables. Clinical experience has indicated that there is frequent and for the replacement of maxillofacial appliances because of rapid discoloration in the service environment and/or degradation of the physical and dynamic properties of the base elastomer. Color stability in the service environment may be the most important factor in patient acceptance of the prosthesis. The results of this study suggested that aging rather than exposure to sunlight results in most of the color changes observed in the HTV and RTV base polymers studied.

Although there is a significant clinical interest in suitable polymer-based soft liners, none have proven fully satisfactory in actual use. As a result there has been continued interest in the development of new materials. One major weakness in the development of improved materials has been the lack of clear understanding of structure/property relationships. This paper deals with the determination of visco-elastic properties such as E'(Storage modulus) and tan ;5 (damping factor) of four commercial materials. They represent the broad range of chemical types available for denture base soft liners. A DMA study of four materials: (1) Molloplast B (silicone); (2) Nevus (phosphazine); (3) Kurepeet (fluropolymer); and (4) Super Soft (acrylic) was made using a Perkin-Elmer DMA-7. Samples were made following the manufacturers' instructions, in the form of sheets 1.5 mm thick and 15.0 mm square. The samples were tested compressively using a 3 mm flat tip probe cycled at a frequency of 1 Hz. Wet and dry specimens were evaluated for E' and tan 8 over a 5-95 °C temperature range. Water sorption was determined gravimetrically at 37 °C. Changes in E' between the wet and dry conditions for Molloplast (B), Kurepeet and SuperSoft were insignificant. A significant increase in tan 8 for wet Nevus was observed, suggesting that the material is capable of dissipating more energy. The 'wet' modulus (E') is about 42% lower than the "'dry" modulus (E'). This difference may be attributed to the very high water sorption (34%) of Nevus. i.e. the significant decrease in E' indicates plasticization due to sorbed water. Changes in visco-elastic properties seem to occur for materials which take up large amounts of water at 37°C. DMA is found to be a useful supplement for the evaluation of soft lining materials in conjunction with the standard mechanical test methods.

The physical and mechanical properties of a series of commercial denture soft lining materials have been investigated. The materials were selected to provide a representative sample of the materials widely used for this application. A total of seven products were evaluated including established and widely used acrylic and silicone materials as well as newer polyphosphazine and fluoroelastomer materials. The objective of the study was to determine minimally acceptable and desirable levels for each property which could be used as criteria or standards for the selection of proposed new materials. The results identified several areas requiring attention and future work. In particular, the importance of using fully-water-equilibrated specimens was emphasized for acrylic polymers where large property changes occurred between wet and dry conditions, and in the case of the polyphosphazine materials where the long time required for full equilibration may lead to underestimates of the changes involved. Based upon the properties as measured, recommendations for appropriate standard level for each property are offered.