ABSTRACT
Objective·To compare the stress distribution at abutments, edentulous ridge, and peri-implant tissue under the vertical load between the RPI-type removable partial denture supported by implants with different diameter and the conventional RPI-type removable partial denture using a three-dimensional photoelastic method. Methods·The mandibular Kennedy I type denture defect models were fabricated according to the standard mandibular model. Four Straumann system soft tissue level implants with different diameters (two 4.1 mm implants and two 3.3 mm implants) were implanted into the bilateral first molar areas. Planting nails and epoxy resin teeth were inversely put into the mandibular silicone rubber molds to fabricate the epoxy resin photoelastic models and the regular neck (RN) healing abutments were screwed into the implants. A simulated alveolar mucosa with thickness of 2mm and a conventional RPI-type removable partial denture were placed on the epoxy resin models with or without implants. Then a force of 1 kg was vertically applied by a bite force loading device which fixed the model and denture in the centric occlusion. After the stress was frozen, model slices at different areas were cut and the stress fringes were observed. The stress was calculated according to the fringe value of per unit thickness. Results·For the conventional RPI-type removable partial denture, the maximum stress of distal abutment was mainly concentrated on the apical regions and the maximum stress of edentulous ridge was concentrated on the first molar area, particular on the lingual side of alveolar bone. For the implant-supported RPI-type removable partial denture, the maximum stress of distal abutment was lower than that of the conventional RPI-type removable partial denture, and the maximum stress of edentulous ridge (without the implants) was similar to that of abutment and supporting tissues and was lower than that of the conventional RPI-type removable partial denture. The stress around the implant was the largest and the peri-apical stress of implant was greater than the neck stress of implant. Meanwhile, the maximum stress around the implant was increased with the decrease of implant diameter. Conclusion·Compared to the conventional RPI-type removable partial denture, removable partial dentures supported by implants are more stable with a more balanced stress distribution in supporting tissues, thus benefit the health of abutments and supporting tissues.
ABSTRACT
Objective To collect the information about types and clinically-used materials for the dentures, and evaluate the current conditions and characteristics of prosthodontic treatment in Shanghai. Methods Three municipal public hospitals and two private commercial dental labs in Shanghai were served as sample units. The application information on fixed partial dentures, removable partial dentures and complete dentures from January 2005 to December 2007 was collected. The number of dentures in each sample unit, the total proportion of each type of dentures, and the proportion of each type of dentures in public hospitals or private labs were retrospectively analysed. Results From 2005 to 2007, the number of dentures increased by approximately 20% annually. The number of dentures made in private labs increased by 43.58% in 2005 to 2006 and 23.23% in 2006 to 2007.As to the types of dentures, fixed partial dentures constituted the largest proportion (74.49%-76.19% for public hospitals and more than 80% for private labs), while complete dentures accounted for the smallest proportion (5.07% to6.24% for public hospitals and 1.02% to 1.38% for private labs) . Conclusion With an ever-growing awareness of oral health, prosthodontics has been developing rapidly in Shanghai. The rapid increase trend of private dental clinics is noticeable. Fixed partial dentures constitute the largest proportion, while the proportion of complete denture gradually decreases year by year.
ABSTRACT
<p><b>OBJECTIVE</b>The aim of this article was to discover the corrosion resistance of magnetic attachments, which were encapsulated in stainless steel, when pH value of artificial saliva was lower than normal.</p><p><b>METHODS</b>Three kinds of magnetic retainers were exposed for 6 months to artificial saliva with pH ranging from 5.6 to 7.0, thermostated at 36.5 degrees C. This study included electrochemical test as polarization curves, chemical test as immersion test and SEM to analyze the corrosion behavior of the materials.</p><p><b>RESULTS</b>Fe3+ ions in stainless steel released more than ten times in an environment pH 5.6 than pH 7.0. The higher concentration of H+, the more elemental release. That pH value of artificial saliva reduced may affect the corrosion speed. The magnetic retainers were not resistant to acidic environments during exposure.</p><p><b>CONCLUSION</b>Transient exposure of stainless steel to an acidic oral environment can increase elemental release significantly. So acid resistance of magnetic retainers was relatively weak, and it would affect the life span of magnets.</p>