Change in crown inclination accompanying initial tooth alignment with round archwires

ABSTRACT Objective: To evaluate, in-vitro, the change in crown inclination that occurs during orthodontic leveling and alignment using different archwire-bracket-ligation combinations. Materials and Methods: Four archwire types were tested: (1) 0.012-in stainless steel and (2) 0.0155-in stainless steel multi-stranded, (3) 0.012-in nitinol Orthonol® and (4) 0.012-in nitinol Thermalloy®. Combinations with five types of 0.022-in slot orthodontic brackets were tested: SmartClipTM and Time3® self-ligating brackets, Mini-Taurus® and Victory SeriesTM conventional brackets, and Synergy® conventional-low friction bracket. Conventional brackets were ligated with both stainless steel and elastomeric ligatures. The simulated malocclusion comprised 2.0mm gingival and 2.0mm labial displacements of a maxillary right central incisor. Rotation around the Y-axis (representing labio-palatal inclination) was measured for the different archwire-bracket-ligation combinations. Results: The largest rotation was measured whith Orthonol® and Thermalloy® wires when combined with SmartClipTM brackets (8.07±0.24º and 8.06±0.26º, respectively) and with Synergy® brackets ligated with stainless steel ligatures (8.03±0.49º and 8.0±0.37º, respectively). The lower rotation was recorded when Thermalloy®, multi-stranded, and Orthonol® wires were ligated with elastomeric rings to Mini-Taurus® brackets (1.53±0.18º, 1.65± 0.23º and 1.70±0.28º, respectively) and to Victory SeriesTM brackets (1.68± 0.78º, 2.92± 1.40º and 1.74±0.46º, respectively). Conclusions: All archwire-bracket-ligation combinations produced lingual crown inclination; however, lower changes were observed when the conventional brackets were ligated with elastomeric rings. The multi-stranded archwire produced less rotation with nearly every bracket-ligation combination, compared to the other archwires. The effect of the archwire-bracket-ligation combination on tooth inclination during leveling and alignment should be considered during planning treatment mechanics.

RESUMO Objetivo: Avaliar, in vitro, as mudanças na inclinação das coroas dentárias que acontecem durante o alinhamento e nivelamento usando diferentes combinações de arcos/braquetes/ligaduras. Material e Métodos: Foram usados quatro tipos de arcos ortodônticos: (1) 0,012" de aço inoxidável, (2) 0,0155" de aço multifilamentado, (3) Orthonol® 0,012" de nitinol e (4) Thermalloy® 0,012" de nitinol. Esses arcos foram combinados com cinco tipos de braquetes ortodônticos com slot 0,022": braquetes autoligáveis SmartClipTM e Time3®, braquetes convencionais Mini-Taurus® e Victory SeriesTM, e braquetes convencionais de baixo atrito Synergy®. Os braquetes convencionais receberam ligaduras de aço ou elastoméricas. A má oclusão simulada foi composta por um deslocamento do incisivo central superior direito em 2 mm para a cervical e 2 mm para a vestibular. A rotação ao redor do eixo Y (representando a inclinação vestibulolingual) foi medida para as diferentes combinações de arco/braquete/ligadura. Resultados: A maior rotação foi medida quando os arcos Orthonol® e Thermalloy® foram usados com os braquetes SmartClipTM (8,07±0,24º e 8,06±0,26º, respectivamente) e com os braquetes Synergy® com ligaduras metálicas (8,03±0,49º e 8,0±0,37º, respectivamente). A menor rotação foi vista quando os arcos Thermalloy®, multifilamentado e Orthonol® foram presos por ligaduras elastoméricas aos braquetes Mini-Taurus® (1,53±0,18º, 1,65±0,23º e 1,70±0,28º, respectivamente) e aos braquetes Victory SeriesTM (1,68±0,78º, 2,92±1,40º e 1,74±0,46º, respectivamente). Conclusões: todas as combinações arco-braquete-ligadura produziram inclinação palatina da coroa. Entretanto, as menores mudanças foram observadas quando os braquetes convencionais receberam ligaduras elastoméricas. O arco multifilamentado produziu menor rotação com quase todas as combinações braquete-ligadura, em comparação aos outros arcos. O efeito da combinação arco-braquete-ligadura na inclinação dentária durante o alinhamento e nivelamento deve ser considerado durante o planejamento da mecânica dos tratamentos.

Wear of double crown systems: electroplated vs. casted female part

OBJECTIVES: The wear of telescopic crowns is a common problem often reducing the patient's satisfaction with the denture and resulting in a renewal of the denture. The study aims to compare the wear behavior of conical crowns using electroplated copings (group E ) with standard telescopic crowns with cast female parts (group C). MATERIAL AND METHODS: 10 conical crowns were milled for each group of a cast gold alloy. The specimen of group E had a conicity of 2º. The cast secondary crowns of group C had a 0º design. The electroplated coping was established by direct electroforming. An apparatus accomplishing 10,000 wear cycles performed the wear test. The retentive forces and the correlating distance during insertion and separation were measured. The wear test was separated in a start phase, an initial wear phase and the long term wear period. The retention force value and the force-distance integral of the first 0.33 mm of each cycle were calculated. RESULTS: The retentive forces were significantly higher for group E and the integrals were significantly lower for this group except the integral at cycle 10,000. The changes of retention force and integral did not differ significantly between both groups in all phases. The change of the integrals as well as the integral at the particular cycles showed higher interquartile distances for group C. CONCLUSIONS: Within the limitations of this study the tested conical crowns showed clinically acceptable retentive properties. The values reached a range comparable to retentive elements tested in recent literature. The values of group C showed higher ranges. The force measured for group E was significantly higher than for group C but the integrals showed an opposite tendency. The results indicate that an exclusive analysis of the force is not sufficient as the integral is not equivalent to the force although it describes the retentive property of the system in a better way than the force over a distance is described. Both systems seem to be suitable for clinical practice.