title: [Study of accuracy of one-piece casted and laser welded bridges].
abstract: OBJECTIVE
  To assess whether laser welded bridge be fit for the clinical usage, this study compares the accuracy of laser welded multi-unit bridges with one-piece casted bridges.
  
  
  METHODS
  A precise stainless mold which was 20 mm length composed of two abutments (one premolar and one molar) and one pontic (two missed teeth) was made. 5 wax patterns of four-unit FPD frame-works in one-piece casting based on the mold were made. After that, they were invested with inner (Bellavest) and outer investment (phosphate and gypsum). Then they were casted with CW-PA (Ni-Cr-Nb) alloys. The other 5 wax patterns of four-unit FPD frameworks were invested and casted in two halves. Each couple of frameworks were ultra-sonic washed in distilled water and inserted to the standard metal FPD mold accurately. Laser welding machine (DL-2002) was used to weld each couple of frameworks at 305V, 20 ms. Both groups of specimens were tested on their mesiodistal span dimensions and the diameters of alloy crowns. Then they were inserted to their original stainless mold, where the marginal fitness was examined.
  
  
  RESULTS
  1. The one-piece casted fixed multi-unit bridge couldn't be inserted to abutments completely because of distortion, while the laser welded bridge could be inserted to abutments completely. The average marginal opening of laser welded bridges was about 74 microns and conformed to clinical standard of fitness. 2. Mesiodistal dimensions of one-piece casted bridges at the inner, bottom and top margins were 19.5600 +/- 0.3877 mm, 41.2206 +/- 0.4140 mm, 41.0598 +/- 0.3379 mm respectively; while those of laser welded bridges were 20.2950 +/- 0.1191 mm, 41.9625 +/- 0.0788 mm, 42.0584 +/- 0.1089 mm, which were obviously close to metal abutments (P < 0.05). 3. The alloy crowns' diameters of one-piece casted bridges were examined as following, the premolar: phi IJ = 9.8386 +/- 0.0567 mm, phi LK = 9.9596 +/- 0.0548 mm, the molar: phi EF = 11.7948 +/- 0.0252 mm, phi HG = 11.9412 +/- 0.0763 mm; The alloy crowns' diameters of laser bridges were as following, the premolar: phi IJ = 9.7927 +/- 0.0636 mm, phi LK = 9.9438 +/- 0.0726 mm, the molar: phi EF = 11.8287 +/- 0.0863 mm, phi HG = 11.8893 +/- 0.1049 mm. There was no significant difference between the two groups (P < 0.05).
  
  
  CONCLUSIONS
  Laser welding greatly improve the fitness of multi-unit fixed bridges.
authors.affiliation: College of Stomatology, West China University of Medical Sciences.
authors.forename: H
authors.initials: H
authors.lastname: Li
authors.forename: M
authors.initials: M
authors.lastname: Li
authors.forename: Y
authors.initials: Y
authors.lastname: Zhao
authors.forename: X
authors.initials: X
authors.lastname: Meng
mesh_terms: D000044:Dental Abutments; D003735:Dental Casting Technique / Q000295:instrumentation; D012994:Dental Soldering / Q000379:methods; D003779:Denture Design; D003830:Denture, Partial, Fixed; D006801:Humans; D007834:Lasers; D016876:Metal Ceramic Alloys; D013314:Stress, Mechanical; D014896:Welding / Q000379:methods
chemical_list: D016876:Metal Ceramic Alloys