Shear bond strength between Ni-Cr alloy bonded to a ceramic substrate.

INTRODUCTION: The aim of this study was to evaluate the shear bond strength between a Ni-Cr alloy and a ceramic system submitted or not to thermocycling. MATERIALS AND METHODS: Forty-eight cylinder blocks of Ni-Cr with 3.0 mm diameter by 4.0 mm hight and 48 disc-shaped specimens (7.0 mm in diameter by 2.0 mm thick) composed of ceramic were prepared. The Ni-Cr cylinder blocks were randomised in two groups of 24 specimens each. One group was submitted to air-particle abrasion (sandblasting) with 50 µm Al(2)O(3) (0.4-0.7 MPa) during 20 s, and the other group was submitted to mechanical retentions with carbide burrs. Each group was subdivided into other two groups (n = 12), submitted or not to thermocycling (500 cycles, 5-55°C). The cylinder blocks were bonded to the disc-shaped ceramic specimens under 10 N of load. The shear bond strengths (MPa) were measured using a universal testing machine at a cross head speed of 0.5 mm/min and 200 kgf of load. The data were submitted to statistical analysis (anova and Tukey's test). RESULTS: The air-particle abrasion group exhibited significantly higher shear bond strength when compared to drilled group (p < 0.05). CONCLUSIONS: Thermocycling decreased significantly the bond strengths for all groups tested.

Comparative study of intermaxillary relationships of manual and swallowing methods.

This study compared the mandibular displacement from three methods of centric relation record using an anterior jig associated with (A) chin point guidance, (B) swallowing (control group) and (C) bimanual manipulation. Ten patients aged 25-39 years were selected if they met the following inclusion criteria: complete dentition (up to the second molars), Angle class I and absence of signs and symptoms of temporomandibular disorders and diagnostic casts showing stability in the maximum intercuspation (MI) position. Impressions of maxillary and mandibular arches were made with an irreversible hydrocolloid impression material. Master casts of each patient were obtained, mounted on a microscope table in MI as a reference position and 5 records of each method were made per patient. The mandibular casts were then repositioned with records interposed and new measurements were obtained. The difference between the two readings allowed measuring the displacement of the mandible in the anteroposterior and lateral axes. Data were analyzed statistically by ANOVA and Tukey's test at 5% significance level. There was no statistically significant differences (p>0.05) among the three methods for measuring lateral displacement (A=0.38 +/- 0.26, B=0.32 +/- 0.25 and C=0.32 +/- 0.23). For the anteroposterior displacement (A=2.76 +/- 1.43, B=2.46 +/- 1.48 and C=2.97 +/- 1.51), the swallowing method (B) differed significantly from the others (p<0.05), but no significant difference (p>0.05) was found between chin point guidance (A) and bimanual manipulation (C). In conclusion, the swallowing method produced smaller mandibular posterior displacement than the other methods.

Comparative study of intermaxillary relationships of manual and swallowing methods

This study compared the mandibular displacement from three methods of centric relation record using an anterior jig associated with (A) chin point guidance, (B) swallowing (control group) and (C) bimanual manipulation. Ten patients aged 25-39 years were selected if they met the following inclusion criteria: complete dentition (up to the second molars), Angle class I and absence of signs and symptoms of temporomandibular disorders and diagnostic casts showing stability in the maximum intercuspation (MI) position. Impressions of maxillary and mandibular arches were made with an irreversible hydrocolloid impression material. Master casts of each patient were obtained, mounted on a microscope table in MI as a reference position and 5 records of each method were made per patient. The mandibular casts were then repositioned with records interposed and new measurements were obtained. The difference between the two readings allowed measuring the displacement of the mandible in the anteroposterior and lateral axes. Data were analyzed statistically by ANOVA and Tukey's test at 5 percent significance level. There was no statistically significant differences (p>0.05) among the three methods for measuring lateral displacement (A=0.38 ± 0.26, B=0.32 ± 0.25 and C=0.32 ± 0.23). For the anteroposterior displacement (A=2.76 ± 1.43, B=2.46 ± 1.48 and C=2.97 ± 1.51), the swallowing method (B) differed significantly from the others (p<0.05), but no significant difference (p>0.05) was found between chin point guidance (A) and bimanual manipulation (C). In conclusion, the swallowing method produced smaller mandibular posterior displacement than the other methods.

Este estudo comparou o deslocamento mandibular a partir de 3 métodos de registro da relação cêntrica usando um jig anterior associado com: (A) guia da ponta do mento; (B) deglutição grupo controle (C) manipulação bimanual. As moldagens dos arcos maxilares e mandibulares foram feitas com hidrocolóide irreversível. Os modelos de estudo de cada paciente foram obtidos e montados em máxima intercuspidação como uma posição de referência no microscópio. Foram obtidos 5 registros de cada método em 10 pacientes. Os modelos mandibulares foram reposicionados com os registros interpostos e novas medidas foram obtidas. A diferença entre as duas leituras permitiu a medida do deslocamento mandibular nos eixos ântero-posterior e laterais. ANOVA não demonstrou diferença estatisticamente significativa entre os 3 métodos em relação ao registro do deslocamento lateral (A = 0,38 ± 0,26, B = 0,32 ± 0,25 e C = 0,32 ± 0,23). Quanto ao deslocamento anteroposterior, ANOVA e o teste de Tukey (a=0,05) indicaram diferença estatisticamente significante entre os três métodos (A=2,76 ± 1,43, B=2,46 ± 1,48 e C=2,97 ± 1,51). Não houve diferença estatisticamente significante entre A e C. A deglutição propiciou menor deslocamento mandibular posterior que os outros métodos.

Effect of casting technique on surface roughness and consequent mass loss after polishing of NiCr and CoCr base metal alloys: a comparative study with titanium.

STATEMENT OF PROBLEM: Surface roughness of cast metal frameworks may lead to difficulties in finishing or polishing procedures and weaken the framework. PURPOSE: The aim of this study was to assess the surface roughness of 2 base metal alloys, submitted to different casting techniques, to determine the influence of surface roughness on loss of mass after polishing compared to commercially pure titanium castings. MATERIAL AND METHODS: Forty disk-shaped wax patterns (8 x 2 mm) were randomly assigned to 5 groups (n=8): (1) CoCr alloy (Wironit), acetylene-oxygen flame casting (WFC), (2) NiCr alloy (Verabond II), acetylene-oxygen flame casting (VFC), (3) CoCr alloy, vacuum casting (WVC), (4) NiCr alloy, vacuum casting (VVC), and (5) commercially pure Ti alloy (Ti) melted by electric arc in argon gas atmosphere. WFC and VFC served as controls. Both NiCr and CoCr alloys were invested in phosphate-bonded investment (Termocast). Ti was invested in ammonium dihydrogen phosphate (Rematitam Plus). The wax patterns and casting techniques were standardized. All specimens were cleaned with airborne-particle abrasion (aluminum oxide). Surface roughness (Ra) was assessed using a surface-test analyzer at 3 different sites. To evaluate the loss of mass, the specimens were weighed on a precision balance, then polished with 150-600 grain sandpaper until clinically acceptable (minimum roughness of 0.09 microm). The specimens were then reweighed. A 1-way analysis of variance (ANOVA) and Tukey HSD test (alpha=.05) were performed. RESULTS: Statistical analysis showed that VVC and WVC had significantly (P=.0050; P=.0057) smoother surfaces (2.43 +/- 0.53 and 2.23 +/- 0.49, respectively) than VFC and WFC (2.99 +/- 0.44 and 2.83 +/- 0.61, respectively), but were not significantly different from Ti (2.49 +/- 0.62). The loss of mass (in %) was not significantly different for any group (3.18 +/- 0.72, 3.14 +/- 0.93, 3.36 +/- 1.05%, and 4.14 +/- 1.28% for VVC, WVC, VFC, and WFC, respectively). The mass loss of Ti was 4.32 +/- 1.16. CONCLUSION: Within the limitations of this study, the base metal alloys submitted to vacuum casting showed decreased surface roughness, similar to that of titanium, compared to base metal alloys submitted to acetylene-oxygen flame casting. There were no significant differences in loss of mass after polishing for all tested specimens.

Combination therapies in the treatment of temporomandibular disorders: a clinical report.

Numerous implant systems exist that have the versatility to create a custom implant abutment with an anatomic shape. This clinical report describes the use of a digital scanner with CAD/CAM technology to create (copy mill) an anatomically shaped abutment.

Comparative study of circumferential clasp retention force for titanium and cobalt-chromium removable partial dentures.

STATEMENT OF PROBLEM: The interest in using titanium to fabricate removable partial denture (RPD) frameworks has increased, but there are few studies to support its use. PURPOSE: The objective of this study was to compare circumferential RPD clasps made of commercially pure titanium and identical clasps made of 2 different cobalt (Co)-chromium (Cr) alloys by testing insertion/removal and radiographically inspecting the casts for defects. MATERIAL AND METHODS: On refractory casts that represent a partially edentulous mandibular right hemi-arch segment, 36 frameworks were cast from commercially pure titanium (n = 12) and 2 Co-Cr alloys (n = 12 each) with identical prefabricated patterns and the manufacturer-designated investment and casting technique. Each group was divided into 2 subgroups, corresponding to .25-mm and .50-mm undercuts, respectively. No polishing procedures were performed to ensure uniformity. Only nodules and burs were carefully removed with tungsten burs under magnification when necessary. The specimens were radiographed and subjected to an insertion/removal test simulating 5 years of framework use. The data were subjected to analysis of variance and the Tukey complementary test (P<.01) to compare the retentive forces of RPDs made with the different materials. The Student t test (P<.01) was used to compare the retentive forces of RPDs fabricated with the same alloy with different undercuts. RESULTS: A total of 20% of the titanium specimens demonstrated porosity, showing casting difficulties, and any defect detected on the clasps determined the sample replacement. For Co-Cr alloys, casting difficulties were not found. The data were subjected to analysis of variance and the Tukey complementary test to compare materials for the same undercut. For the .25-mm undercut, no significant difference was found between Magnum and Rematitan alloys; they were both different from the Remanium alloy (P<.01). For the.50-mm undercut, no significant difference was found between Co-Cr alloys; they were both different from Rematitan alloy (P<.01). The Student t test used to compare the same alloys with different undercuts showed no significant difference between Remanium with .25-mm and .50-mm undercuts. For Magnum and Rematitan alloys, there was a significant difference between different undercuts (P=.01). CONCLUSION: Within the limitations of this simulation study, the results suggest that commercially pure titanium clasps maintained retention over a simulated 5-year period, with lower retention force than identical Co-Cr clasps.