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

The purposes of this study were to investigate the satisfaction of use of removable denture elated to general, functional and esthetic factors among dental patients in national sorokdo hospital, and to establish the structure relationships of dental treatment satisfaction. Two hundred fifty hansen`s patients who consented with this survey were selected and examined their oral status. Satisfaction degree was estimated by means of self-developed questionarires, filled out by face-to-face interview. Collected data were analyzed by t-tast The obtained results were as follow : 1. The satisfaction degree of four subscales was highest in esthetic actor (3.17+/-0.36), denture retention factor(3.10+/-0.60), general treatment satisfaction factor(2.94+/-0.56), and masticatory function factor (2.90+/-0.68) in descending order. It was appeared that patients was generally satisfied with all four factor. 2. On the comparison between proportion of denture satisfaction and satisfactio 02n of subscales, as the satisfaction of general treatment, masticatory function and denture retention were increased, the proportion of denture satisfaction of esthetic function and proportion of denture satisfaction. 3. The masticatiory function factor, denture retention factor and genernal satisfaction of treatment factor were directly affected on the denture satisfaction, but esthetic factor was affected indirectly on the denture satisfaction as a result of path analysis
Dental Prosthesis* ; Denture Retention ; Dentures ; Humans

PURPOSE: The purpose of this study was to evaluate the influence of tightening technique and the screw coating on the loosening torque of screws used for Universal Abutment fixation after cyclic loading. MATERIALS AND METHODS: Forty implants (Titamax Ti Cortical, HE, Neodent) (n=10) were submerged in acrylic resin and four tightening techniques for Universal Abutment fixation were evaluated: A - torque with 32 Ncm (control); B - torque with 32 Ncm holding the torque meter for 20 seconds; C - torque with 32 Ncm and retorque after 10 minutes; D - torque (32 Ncm) holding the torque meter for 20 seconds and retorque after 10 minutes as initially. Samples were divided into subgroups according to the screw used: conventional titanium screw or diamond like carbon-coated (DLC) screw. Metallic crowns were fabricated for each abutment. Samples were submitted to cyclic loading at 106 cycles and 130 N of force. Data were analyzed by two-way ANOVA and Tukey's test (5%). RESULTS: The tightening technique did not show significant influence on the loosening torque of screws (P=.509). Conventional titanium screws showed significant higher loosening torque values than DLC (P=.000). CONCLUSION: The use of conventional titanium screw is more important than the tightening techniques employed in this study to provide long-term stability to Universal Abutment screws.
Crowns ; Dental Implants, Single-Tooth ; Dental Prosthesis Retention ; Dental Prosthesis, Implant-Supported ; Diamond ; Prosthesis Failure ; Titanium ; Torque*

OBJECTIVETo evaluate the effect of different auxiliary resistance forms on the resistance and marginal fitness of complete crowns for short molar preparations.

METHODSA total of 70 Nissin resin teeth were prepared with 20° total occlusal convergence, 2.5 mm of occlusocervical height, and a shallow finish line on a milling machine. The milled preparations were then randomly assigned to 7 groups of 10. The first group was used as the control group. A total of 30 dies were modified by preparing interproximal grooves with angles of 0°, 6°, and 20° centered on the mesial and distal surfaces of the dies. The rest of the teeth were prepared with occlusal holes in the center of the occlusal surface milled with the same burs to form 0°, 6°, and 20° holes. Cobalt-chromium copings were fabricated for all specimens. The marginal gap of specific points on the axial surface was measured before and after cementation. The resistance of each specimen was evaluated by applying an external force at an angle of 45° to the long axis of the die by using a universal testing machine in a lingual to buccal direction. The maximum force applied before crown dislodgement was measured. Data were analyzed using the SAS 9.2 software.

RESULTSThe results showed that the 0° groove, 0° hole, and 6° hole were effective in improving the resistance of the complete crowns (P<0.05). The 0° groove, 6° groove, 0° hole, 6° hole, and 20° hole had significant difference with the control group in terms of marginal discrepancies (P<0.05).

CONCLUSIONAuxiliary resistance forms with less degree indicate greater resistance force but worse marginal fitness. In clinical practice, if the resistance of a preparation is enough, the auxiliary resistance forms should be avoided from being used.

Cementation ; Crowns ; Dental Prosthesis Design ; Dental Prosthesis Retention ; Humans ; Molar ; Tooth Crown

OBJECTIVETo determine ITI implants stability in different bone types using RFA and to provide evidence for feasibility of early loading.

METHODSA total of 104 ITI sand-blasted large-grit acid-etched (SLA) implants in 50 patients were classified into 3 groups according to bone type. Resonance frequency analysis was conducted at 0, 1, 4, 6, 8 and 12 weeks after installation.

RESULTSThe survival rate was 100%. Primary stability was affected by bone type (P < 0.001). The implant stability quotient (ISQ) was significantly higher in type I bone than in type IV bone. At 12 weeks, there was no significant difference among the 3 groups. Comparison of ISQ was made between 6 th week and 12 th week for all bone types, there was no significant difference for type I and III (P > 0.05) while there was for type IV (P < 0.001).

CONCLUSIONSEarly loading with ITI SLA implants placed in type I, III bone were highly predictable.

Bone Density ; Dental Implantation, Endosseous ; Dental Implants ; Dental Prosthesis Retention ; Humans

OBJECTIVEThe shear fracture strengths of carbon fiber post, IPS-Empress 2 all-ceramic post (without ZrO2 post), cast Ni-Cr alloy post, prefabricated zirconia ceramic post, human dentin and the shear bonding strengths of the first three kinds of post bonded in the human root canals were measured and compared, which are as the reference for dental clinic.

METHODSStandard cylindrical samples were made respectively in each group of carbon fiber post, IPS-Empress 2 all-ceramic post, cast Ni-Cr alloy post, prefabricated zirconia ceramic post, human dentin, three for each group. The shear fracture strengths of these samples were measured by universal testing machine (AUTOGRAPH DCS5000). Standard cylindrical samples were made respectively in each group of carbon fiber post, IPS-Empress 2 all-ceramic post (without ZrO2 post), cast Ni-Cr alloy post, five for each group. They were bonded in extracted human root canals that had been prepared to 3.0 mm length and 2.0 mm diameter with Glass ionomer cement (Japan Shofu). The shear bond strengths were measured by the same universal testing machine.

RESULTSThe shear fracture strengths of the carbon fiber post (199MPa), cast Ni-Cr alloy post (210MPa, shear bend strength) and prefabricated zirconia ceramic post (193MPa) were statistically higher than those of IPS-Empress 2 all-ceramic post (109MPa) and human dentin (100MPa). The shear fracture strength of the carbon fiber post was statistically similar to that of cast Ni-Cr alloy post and prefabricated zirconia ceramic post. There were no statistical differences between the shear bond strengths of carbon fiber post (2.4MPa) and cast Ni-Cr alloy post (3.8MPa). IPS-Empress 2 all-ceramic post broke before debonding (2.7, break value).

CONCLUSIONSCarbon fiber post, as well as cast Ni-Cr alloy post and prefabricated zirconia ceramic post, has a comparatively high shear fracture strength. The shear bond strengths of carbon fiber post is similar to cast Ni-Cr alloy post.

Carbon ; Chromium Alloys ; Dental Bonding ; Dental Prosthesis Retention ; Dental Stress Analysis ; Humans ; Tensile Strength

OBJECTIVETo analyze effects of different thread helix angles and densities on the primary stability of immediately loaded implants using the three-dimensional finite element model analysis.

METHODSFive models of three-dimensional finite element (0.8 mm, 1.6 mm, 2.4 mm, double-threaded, and triple-threaded) were created using the commercial codes of Pro/E software, Hypermesh software, and ABAQUS software. In conditions of horizontal and vertical loading, the micro-motion of the finite element models with different thread helix angles and densities were computed with ABAQUS software.

RESULTSConcerning different thread helix angles, the micro-motion of single-threaded implant was the minimum and that of the triple-threaded was the maximum with vertical and horizontal loading. The micro-motion of doubled-threaded implant was the minimum compared with thread pitch 1.6 mm and the micro-motion of triple-threaded implant was the minimum compared with thread pitch 2.4 mm with vertical and horizontal loading.

CONCLUSIONSThe thread helix angle and density of implants can greatly affect the vertical interfacial micro-motion. With increasing thread pitchs, the resistance of implant to vertical load is weakened; with increasing thread helix angle, the resistance of implant to vertical load is weakened; with increasing thread density, the resistance of implant to the vertical load is weakened.

Dental Implants ; Dental Prosthesis Design ; Dental Stress Analysis ; Denture Retention ; Finite Element Analysis

OBJECTIVETo investigate the manufacture method and the effects of Cosmopost ceramic posts, to summarize the indications of Cosmopost ceramic post in clinic.

METHODS228 pieces Cosmopost ceramic posts and cores were made for 96 patients. 2l7 pieces full ceramic crowns and 8 pieces full ceramic bridgs for Cosmopost ceramic posts and cores were made. The fitness of Cosmopost ceramic post were checked, and the color of all full ceramic crowns and full ceramic bridgs were checked in clinic. The amount of loosening and broken in all restorations were checked every year in clinic. follow up 2 - 3 years.

RESULTS1 Cosmopost ceramic post was fracture about 1.5 mm before the full ceramic crown was worn. 227 pieces Cosmopost ceramic posts were perfect. All of the full ceramic crowns and bridgs for full ceramic posts were excellent in color. No loosening and broken cases were checked in 0.5 - 3 years. But the indications of Cosmopost ceramic posts were strict in clinic.

CONCLUSIONCosmopost ceramic post has natural aesthetic effect and good strength. it can be used in clinic.

Adolescent ; Adult ; Color ; Dental Porcelain ; Dental Prosthesis Design ; Dental Prosthesis Retention ; Female ; Humans ; Male ; Middle Aged ; Post and Core Technique

This study was aimed to assess the effects of remain of residual tooth on the retention of postpost-core was made,casted and cemented. The post-core was tested at the speed of 10 mm/min on the Instron4302, and the retention force was recorded. Other samples were made and subjected to the test for cohesion of polymethylmethacrylate and metal. The result showed that retention significantly increased with the adding of the residual tooth. When the length of post was longer than 8 mm and 1 mm was added to tooth remain, the difference in retention between the two groups was statistically significant. It was noted that there existed relationships of retention to length of post and tooth remain, of cohesion to length of post and tooth remain, and of frictiion resistence to length of post and tooth remain; moreover, the relevant linear regression equations were obtained. So during the tooth preparation of post-core system, the tooth tissue should be reserved as much as possible.
Crowns ; Dental Prosthesis Retention ; Dental Stress Analysis ; Humans ; Post and Core Technique ; Tooth Root

Fifty-four simulated tooth roots made of polymethacrylate (PMMA) were divided into six groups according to the root canal convergence angles of 0 degrees, 3.93 degrees, 5.71 degrees, 7.48 degrees, 11.31 degrees, 14.71 degrees. Cast post and cores were manufactured and cemented with Zinc phosphate cement (ZP). The retention capacities of the posts were tested. The bonding strength of ZP at different convergence angles were tested with some casted wafers, and linear regression was made. So the effect of interlocking and the proportion could be calculated. With these results, we made some curvilinear regressions. The results showed that the retention of cast post declined and the bonding strength of ZP fell with the increase of convergence angles. There were significant differences in the bonding strength and retention among groups, P<0.05. The experiment indicates that the dentists should reduce the convergence angles of posts as much as possible to obtain greater retention.
Cementation ; Crowns ; Dental Prosthesis Retention ; Dental Stress Analysis ; Post and Core Technique ; Tensile Strength