OBJECTIVETo show the trend of the retention change during the circulation of the clasp dislodging and inserting, and to discuss the proper depth of the undercut for a specific clasp. It is also a basic study for the best designing of RPD.

METHODSThe Chatillon force measuring instrument was used to record the variation of the retention of Co-Cr alloy casting Akers clasp when they were dislodging from undercuts of different depths (0.25 mm, 0.50 mm, 0.75 mm) on bicuspid and molar.

RESULTSThe data was analysed of Correlation and Regression by SPSS 10.0 statistic software. The variations of the retention in the circulation are obvious from the different teeth and different undercut depths. It shows an attenuation trend in circulation (P < 0.01). After 400 times dislodging, in bicuspid group, the retention of the clasp used in 0.50 mm undercut became less than the one used in 0.25 mm undercut. While the retention of the clasp used in 0.75 mm decreases most obviously, it values 0.7670 kg. In molar group, the attenuations of the retention at different depths of undercut are similar, the retentions of the clasp still rank as, from great to less, 0.75 mm, 0.50 mm and 0.25 mm, in the depth of undercut.

CONCLUSIONthe proper depth of the undercut for bicuspid is 0.25 mm, and 0.50 mm for molar.

Dental Clasps ; Dental Prosthesis Retention ; Humans

OBJECTIVETo study the retentive force and deformation of acetal resin clasp.

METHODS40 premolars and 40 molars were cast respectively. Undercut of 0.25 mm or 0.50 mm depth were measured for each with undercut gage. According to the type of abutment and the depth of undercut, the specimens were divided into 4 groups: Premolars with 0.25 mm undercut, premolars with 0.50 mm undercut, molars with 0.25 mm undercut and molars with 0.50 mm undercut, 20 specimens each group. 10 three-arm clasps with resin and Co-Cr alloy were fabricated in each group, respectively. The clasps were set into the corresponding abutments and soaked in distilled water. The retentive force of the clasps when 0, 720, 1440, 2160, 2880, 3600, 4320 consecutive times of setting in and removing out from the abutments were measured. The distance between the tips of retentive arm and resistant arm after 0 and 4320 cycles were recorded.

RESULTS1) The mean retentive force of resin clasps (1.69 N) was significantly lower than that of Co-Cr clasps (5.87 N) (P<0.01). With the same factors, the retentive force of resin clasps were significantly less than that of Co-Cr clasps (P<0.01). The retentive force of molar clasps were significantly lower than that of premolar models (P<0.01). The retentive force of 0.25 mm undercut clasps were significantly lower than that of 0.50 mm undercut clasps (P<0.01). With increasing time of the cycles, the retentive force of Co-Cr clasps significantly reduced (P<0.01), but the retentive force of resin clasps didn't change significantly (P>0.05). 2) After 4320 times, the distance between the tips of retentive arm and resistant arm of Co-Cr clasps increased significantly (P<0.05), but the distance between the tips of resin clasps didn't change significantly (P>0.05).

CONCLUSIONThe retentive force and deformation of the resin clasp are significantly lower than those of Co-Cr clasp.

Bicuspid ; Chromium Alloys ; Dental Clasps ; Denture Retention ; Humans ; In Vitro Techniques

OBJECTIVETo investigate the change of retentive forces of cast cobalt-chromium (Co-Cr) alloy clasp in cyclic fatigue test.

METHODSSamples of three types of cast Co-Cr alloy (Group A: Hardalloy; B: Regalloy™; C: Vera PDN™) clasps were fabricated and placed at undercut depths of 0.25 mm, 0.50 mm. The clasps were drawn from the model molar cyclicly to simulate 5 years of clinical use in an universal testing machine. Retentive force were record at 21 different time point for each clasp during the whole fatigue testing process. Data were subjected to ANOVA, Chi-square test and linear regression analysis.

RESULTSAll clasps showed decreasing retention during the cyclic fatigue test. Clasps engaged in 0.50 mm undercut depth exhibited greater initial retentive force [Group A: (8.714 +/- 1.104) N, B: (9.072 +/- 0.653) N, C: (9.588 +/- 1.980) N] as well as greater loss of retention [Group A: (4.408 +/- 0.662) N, B: (3.484 +/- 0.494) N, C: (3.290 +/- 1.484) N] at the end of the test than clasps engaged in 0.25 mm undercut did [initial forces were (7.940 +/- 0.357), (7.834 +/- 1.308) and (8.156 +/- 1.067) N for Group A, B, C, respectively; loss of retention were (2.444 +/- 0.736) N, (2.954 +/- 1.048) N and (1.832 +/- 1.180) N for group A, B, C, respectively]. Negative correlation was found between the clasp retention and the logarithm of cycling times.

CONCLUSIONSCo-Cr alloy cast clasp could provide adequate retentive force for 5 years of clinical use.

Chromium Alloys ; chemistry ; Dental Alloys ; chemistry ; Dental Casting Technique ; Dental Clasps ; Dental Stress Analysis ; Denture Retention

Not only can esthetic clasps removable partial dentures reserve some advantages that removable partial denture itself has such as non-preparation or less preparation and cheap price, but also can bring metal-free smile to the patients, which is an new effective and affordable treatment option for partial edentulism. This article introduced the basic concepts, principle, various types of estheticdesign and related clinical application.
Dental Clasps ; Denture Design ; Denture Retention ; Denture, Partial, Removable ; Esthetics ; Esthetics, Dental ; Humans

OBJECTIVETo analyze the stress distribution on cast retentive clasp arms in dislodging denture, and to discuss the deepest undercuts of the second mandibular premolar (abutment) for cobalt-chromium alloy cast clasps with different widths.

METHODSThree-dimensional finite element models of the abutment with different depths of undercuts and retentive arms with different widths were set up. Dynamic displacement load (3 mm/s) was exerted on the middle of the retentive arms to analyze the stress in retentive arms while they were being removed from the abutment.

RESULTSThe peak stress in retentive arms was positively correlated to the undercuts displaced by clasp tips, and those were not obviously related to the undercuts displaced by the middle of retentive arms. When width/thickness of retentive arms was 3, the increase of peak stress of retentive arms with similar locations of clasp tips was significantly related to the increase of the arm width. The deepest undercuts of the second mandibular premolar for cobalt-chromium alloy cast retentive arms with different widths of 1.8 mm, 1.6 mm, and 1.4 mm were 0.25 mm, 0.30 mm, and 0.35 mm respectively.

CONCLUSIONSWhen width/thickness of the retentive clasp arm is fixed, the wider the arm is, the smaller depth it should be placed on the undercut of abutment. Retentive clasp arms with different widths should be placed on different depths of undercuts in order to prevent their permanent deformation.

Chromium Alloys ; Dental Casting Technique ; Dental Clasps ; Dental Prosthesis Design ; Dental Stress Analysis ; Denture Retention ; Finite Element Analysis ; Humans

OBJECTIVE: To compare the retentions of different designs of cobalt-chromium (Co-Cr), pure titanium (CP Ti), and titanium alloy (Ti-6Al-4V) removable partial denture (RPD) circumferential clasps manufactured by selective laser melting (SLM) and to analyze the stress distribution of these clasps during the removal from abutment teeth. METHODS: Clasps with clasp arm size A (1.9 mm width/1.1 mm thickness at the body and 0.8-taper) or B (1.2 times A) and 0.25 mm or 0.50 mm undercut engagement were modeled on a prepared first premolar die, named as designs A1, A2, A3, and A4, respectively. The density and elastic modulus of SLM-built Co-Cr, CP Ti, and Ti-6Al-4V were measured and given to different groups of clasps. The density, elastic modulus, and Poisson ' s ratio of enamel were given to the die. The control group was the cast Co-Cr clasp with design A1, to which the density and elastic modulus of cast Co-Cr alloy were given. The Poisson's ratio of all metals was 0.33. The initial 5 N dislodging force was applied, and the maximum displacement of the clasp along the insertion path was computed. The load was reapplied with an increment of 5 N than in the last simulation until the clasp was completely dislodged. The retentive force range of different groups of clasps was obtained. The retentive forces of the SLM-built Co-Cr, CP Ti, and Ti-6Al-4V clasps with equivalent computed retentive force range to the control group were validated through the insertion/removal experiment. The von Mises stress distributions of these three groups of SLM-built clasps under 15 N loads were analyzed. RESULTS: SLM-built Co-Cr, CP Ti, and Ti-6Al-4V clasps with designs B1 or B2, and Co-Cr clasps with design A2 had higher retentive forces than those of the control group. SLM-built CP Ti and Ti-6Al-4V clasps with design A1 had lower retentive forces than those of the control group. SLM-built Co-Cr clasp with design A1 and SLM-built CP Ti and Ti-6Al-4V clasps with design A2 had equivalent retentive forces to those of the control group. The insertion/removal experiment showed that the measured retentive forces of these three groups of SLM-built clasps were (21.57±5.41) N, (19.75±4.47) N, and (19.32±2.04) N, respectively. No statistically significant measured retentive force difference was found among these three groups of SLM-built clasps (P>0.05). The maximum von Mises stress of these three groups of SLM-built clasps exceeded their responding yield strength except for the Ti-6Al-4V one. CONCLUSION SLM-built Co-Cr circumferential clasps had higher retention than CP Ti and Ti-6Al-4V ones with the same clasp arm size and undercut engagement. The retention of SLM-built circumferential clasps could be adjusted by changing the undercut engagement and clasp arm size. If SLM-built circumferential clasps are used in clinical practice, the Ti-6Al-4V clasp with clasp arm size A and 0.50 mm undercut engagement is recommended considering the long-term use of RPD in the patient's mouth.
Chromium Alloys ; Dental Clasps ; Denture Retention ; Denture, Partial, Removable ; Finite Element Analysis ; Humans ; Lasers ; Titanium

OBJECTIVETo study the influence of three kinds of retainers on the abutment movement of removable partial dentures (RPDs) for restoring the dentition with unilateral distal-extended tooth missing.

METHODSThe combined clasp, the extension clasp and the telescopic crown were designed to retain RPDs. When food chip was masticated between dentitions, the displacement of abutments was measured by a high-sensitive-laser-transferring-detector, and then the data was statistically analyzed.

RESULTSAll of abutments showed the inclination, torsion and vertical translocation. Of them, abutments with telescopic crowns had the lowest horizontal torsion (P < 0.01) and the highest vertical translocation (P < 0.01).

CONCLUSIONSCompared with the combined clasp and the extension clasp, the telescopic crowns enable abutments to bear the load more axial and the stress to be distributed more even, so the design of the telescopic crown may be considered more favourable for the health of abutments.

Crowns ; Dental Abutments ; Dental Clasps ; Dental Stress Analysis ; methods ; Denture Retention ; instrumentation ; methods ; Denture, Partial, Removable ; Humans ; Tooth Movement Techniques

OBJECTIVETo investigate the elastic limit and relevant enclasp force of the non-precious metal casting clasp.

METHODSCasting clasp samples of five cobalt-chromium alloys and one 18 - 8 nickel-chromium alloy were made from prefabricated clasp wax by invesing, casting, sandblasting, and ultrasonic cleaning. The process of casting clasp samples deflected by loading and returned by unloading was tested and electric signals were collected by an omnipotent material machine. The analog electric signal was converted to digital signal by an analog to digital converter and stored in a computer. The elastic limit and the relevant enclasp force were analyzed using a relative software.

RESULTSThe elastic limit and the relevant enclasp force of the casting clasp made from the 18 - 8 nickel-chromium alloy were smallest and those of the clasps made from the cobalt-chromium alloys in various brands were different. The range of the elastic limit of the cobalt-chromium alloy casting clasp with the length of 5.0 mm in undercut was 0.28 mm-0.33 mm and the relevant enclasp force was 14.42 g-19.28 g.

CONCLUSIONSIn clinic, we should select the suitable undercut deepness wherein the cobalt-chromium alloy casting clasps, according to different brands of the casting alloy, undercut length, undercut slope, and the clasp thickness.

Chromium Alloys ; Cobalt ; Dental Alloys ; Dental Clasps ; Dental Stress Analysis ; Denture, Partial, Removable ; Elasticity ; Humans ; Nickel ; chemistry ; Stress, Mechanical

OBJECTIVEThe objective of this study was to investigate the tarnish induced by Streptococcus sobrinus serotype g on Co-Cr, Ni-Cr and casting titanium alloys.

METHODSCo-Cr, Ni-Co and casting titanium alloys were respectively machined into a size of 10 mm x 10 mm x 1 mm in tablets, and totally 90 specimens with 30 of each were prepared for the test. The 30 specimens of each alloy were randomly and equally divided into three subgroups, including the blank control group, the media control group and the inoculated media group. Under the aerobic condition, the surfaces of the sucrose agar media were inoculated with Streptococcus sobrinus serotype g. The labeled sterile specimens were placed on the surface of the media for 10 weeks. The specimens were changed to a new sucrose media with bacteria each week. The specimens were removed after 10 weeks of incubation, immersed in 0.05% glutaraldehyde solution to eliminate AaY4, rinsed with distilled water. After 2 weeks, the specimens were removed and observed visually or examined by MINOLTA CR-100 color apparatus.

RESULTSCompared with the blank control, the control media without bacteria did not influence the alloy specimens (P > 0.05). Streptococcus sobrinus serotype g caused tarnish on specimens. There was significant difference between the control media group and the blank control group with inoculated media group on all the specimens (P < 0.05).

CONCLUSIONStreptococcus sobrinus serotype g affects the color of Co-Cr, Ni-Cr and casting titanium alloys, but the color does not change from yellow-green range to red-yellow range.

Chromium Alloys ; chemistry ; Cobalt ; chemistry ; Color ; Dental Alloys ; chemistry ; Dental Casting Technique ; Dental Clasps ; Dental Stress Analysis ; Denture Design ; Denture Retention ; instrumentation ; Denture, Partial, Removable ; Materials Testing ; Nickel ; chemistry ; Streptococcus sobrinus ; classification ; physiology ; Surface Properties ; Tensile Strength ; Titanium ; chemistry