Marginal and internal fit of CAD-CAM composite resin and ceramic crowns before and after internal adjustment.

STATEMENT OF PROBLEM: With the development of computer-aided design and computer-aided manufacturing (CAD-CAM) technology, dentists may determine internal spacing by using the CAD-CAM software program and make internal adjustments during the clinical evaluation appointment. How these factors affect marginal adaptation is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the marginal and internal adaptation of CAD-CAM ceramic and composite resin crowns with different internal spacings before and after internal adjustment by using microcomputed tomography. MATERIAL AND METHODS: Eight third molars were prepared for a complete crown, and 32 crowns were milled at chairside from composite resin and ceramic materials with different internal spacing (30 µm and 80 µm). After an initial microcomputed tomography scan, the same crowns were adjusted and scanned again. Axial space, occlusal space (OS), marginal discrepancy, and absolute marginal discrepancy were evaluated in both analyses. The need for internal adjustment was determined by an experienced clinician by using a silicone film. The number of internal adjustments was also recorded. The data were analyzed by using a 3-way ANOVA (material, internal spacing, and internal adjustment) and the Bonferroni correction (α=.05). RESULTS: For axial space, only the material factor was significantly different (P<.001), with the ceramic having the lowest value. For OS, both internal spacing and adjustments presented a statistical difference among groups with the lowest OS values obtained for 80-µm spacing after adjustment. For marginal discrepancy and absolute marginal discrepancy, the adjustment factor also had a significant effect, and the adjustment resulted in smaller measures for both variables. The 30-µm spacing required more adjustments than the 80-µm spacing (P<.05). CONCLUSIONS: Both the internal adaptation and marginal adaptation were influenced by the internal adjustment, resulting in improved values for both. Although no differences were observed between the 30-µm and 80-µm spacings after internal adjustment for marginal adaptation, the 30-µm spacing required twice as many adjustments, resulting in longer clinical sessions.

Evaluation of a two-step pouring technique for implant-supported prostheses impression.

The aim of this study was to evaluate the efficacy of a pouring technique for implant-supported prostheses impressions. A metallic matrix (control group) with two implants positioned at 90 and 65 degrees was fabricated. The matrix was submitted to the direct transfer impression technique. In group CP (conventional pouring - n = 10), casts were obtained by the conventional pouring technique. In group EP (experimental pouring - n = 10), the analogs were embraced with latex tubes before the first pouring and then submitted to a second pouring. Vertical misfit and implants/analogs inclinations were evaluated. Data were analyzed by analysis of variance and Tukey's test (p < .05). Results demonstrated significant difference (p < .05) between control and experimental groups for misfit measurement in perpendicular implant/analog and between control group and group EP in leaning implant/analog. Considering inclination, there were significant differences (p < .05) between control and experimental groups for leaning analogs. Independently of the pouring technique, perpendicular implants produced more accurate casts.

Evaluation of a two-step pouring technique for implant-supported prostheses impression

The aim of this study was to evaluate the efficacy of a pouring technique for implant-supported prostheses impressions. A metallic matrix (control group) with two implants positioned at 90 and 65 degrees was fabricated. The matrix was submitted to the direct transfer impression technique. In group CP (conventional pouring - n=10), casts were obtained by the conventional pouring technique. In group EP (experimental pouring - n=10), the analogs were embraced with latex tubes before the first pouring and then submitted to a second pouring. Vertical misfit and implants/analogs inclinations were evaluated. Data were analyzed by analysis of variance and Tukey's test (p<.05). Results demonstrated significant difference (p<.05) between control and experimental groups for misfit measurement in perpendicular implant/analog and between control group and group EP in leaning implant/analog. Considering inclination, there were significant differences (p<.05) between control and experimental groups for leaning analogs. Independently of the pouring technique, perpendicular implants produced more accurate casts.

O objetivo do estudo foi avaliar a eficacia de uma tecnica de vazamento para moldagens de proteses sobre implante. Uma matriz metalica (grupo controle) contendo dois implantes posicionados a 90° e 65° de inclinacao foi confeccionada. A matriz foi submetida a tecnica de moldagem de transferencia direta. No grupo CP (vazamento convencional - n=10), os modelos foram obtidos atraves da tecnica de vazamento convencional. No grupo EP (vazamento experimental - n=10), os analogos dos implantes foram revestidos por tubos de latex anteriormente ao primeiro vazamento e, entao, submetidos a um segundo vazamento. A desadaptacao vertical e a inclinacao dos implantes/analogos foram avaliadas. Os dados foram submetidos a Analise de Variancia e teste de Tukey (p<.05). Os resultados demonstraram diferenca significante (p<.05) entre os grupos controle e experimentais para a mensuracao da desadaptacao no implante/analogo perpendicular e entre os grupos controle e EP em relacao ao implante/analogo inclinado. Considerando a inclinacao, houve diferencas (p<.05) entre os grupos controle e experimentais em relacao a implante /analogos inclinados. Independentemente da tecnica de vazamento, implantes perpendiculares geraram modelos mais precisos.