Cephalometric evaluation of changes in vertical dimension and molar position in adult non-extraction treatment with clear aligners and traditional fixed appliances.

INTRODUCTION: Orthodontists have been using clear aligners to treat malocclusions, and one potential effect of treatment with orthodontic aligners is the intrusion and/or resists extrusion of the posterior teeth. This "bite-block effect" is primarily anecdotal due to the frequent occurrence of posterior open bites in patients after clear aligner therapy. OBJECTIVE: The purpose of this study was to compare changes promoted by clear aligners and traditional fixed appliances in cephalometric measurements of the vertical dimension and molar position in adult patients with Class I malocclusion treated with non-extraction. METHODS: Pre- and post-treatment lateral cephalometric radiographs of adult patients treated with either clear aligners (n=44) or traditional fixed appliances (n=22) were selected for retrospective analysis. Eight interval measurements and one nominal measurement were evaluated: anterior overbite (OB), mandibular plane angle related to cranial base (SN_MP) and related to Frankfort (FMA), lower molar height (L6H) and upper molar height (U6H), palatal plane to mandibular plane angle (PP_MP), lower facial height (LFH), total facial height (TFH), and posterior open bite (Posterior_OB). A single evaluator traced all cephalographs, and changes in select measures of the vertical dimension were compared within and between groups. RESULTS: OB decreased (1.15 mm) and L6H increased (0.63 mm) in the traditional fixed appliance group. Mandibular plane angles (related to cranial base and to Frankfort) increased (0.43° and 0.53°, respectively) in the clear aligner group, but just FMA showed significant difference between groups (difference of 0.53°). LFH and TFH increased (ranging from 0.52 mm to 0.80 mm) in both groups, with no differences between treatment modality. Presence of visible posterior open bite significantly increased over the course of treatment. OB, FMA and L6H exhibited an interaction between treatment stage (pre- and post-treatment) and modality (clear aligner therapy and traditional fixed appliances), but no interaction among these three variables was found. CONCLUSIONS: The evidence does not support the theory that clear aligner therapy produces better vertical dimension control than traditional fixed appliances. Traditional fixed appliance therapy slightly extruded the lower molar, and clear aligner therapy produced a slightly mandibular backward rotation.

Cephalometric evaluation of changes in vertical dimension and molar position in adult non-extraction treatment with clear aligners and traditional fixed appliances

ABSTRACT Introduction: Orthodontists have been using clear aligners to treat malocclusions, and one potential effect of treatment with orthodontic aligners is the intrusion and/or resists extrusion of the posterior teeth. This "bite-block effect" is primarily anecdotal due to the frequent occurrence of posterior open bites in patients after clear aligner therapy. Objective: The purpose of this study was to compare changes promoted by clear aligners and traditional fixed appliances in cephalometric measurements of the vertical dimension and molar position in adult patients with Class I malocclusion treated with non-extraction. Methods: Pre- and post-treatment lateral cephalometric radiographs of adult patients treated with either clear aligners (n=44) or traditional fixed appliances (n=22) were selected for retrospective analysis. Eight interval measurements and one nominal measurement were evaluated: anterior overbite (OB), mandibular plane angle related to cranial base (SN_MP) and related to Frankfort (FMA), lower molar height (L6H) and upper molar height (U6H), palatal plane to mandibular plane angle (PP_MP), lower facial height (LFH), total facial height (TFH), and posterior open bite (Posterior_OB). A single evaluator traced all cephalographs, and changes in select measures of the vertical dimension were compared within and between groups. Results: OB decreased (1.15 mm) and L6H increased (0.63 mm) in the traditional fixed appliance group. Mandibular plane angles (related to cranial base and to Frankfort) increased (0.43° and 0.53°, respectively) in the clear aligner group, but just FMA showed significant difference between groups (difference of 0.53°). LFH and TFH increased (ranging from 0.52 mm to 0.80 mm) in both groups, with no differences between treatment modality. Presence of visible posterior open bite significantly increased over the course of treatment. OB, FMA and L6H exhibited an interaction between treatment stage (pre- and post-treatment) and modality (clear aligner therapy and traditional fixed appliances), but no interaction among these three variables was found. Conclusions: The evidence does not support the theory that clear aligner therapy produces better vertical dimension control than traditional fixed appliances. Traditional fixed appliance therapy slightly extruded the lower molar, and clear aligner therapy produced a slightly mandibular backward rotation.

RESUMO Introdução: Ortodontistas têm usado os alinhadores transparentes para tratar más oclusões, e um potencial efeito desse tratamento é a intrusão e/ou resistência à extrusão dos dentes posteriores. Esse efeito de "bloco de mordida" é principalmente empírico, devido à ocorrência frequente de mordidas abertas posteriores em pacientes após a terapia com alinhadores transparentes. Objetivo: O objetivo do presente estudo foi comparar as mudanças promovidas pelos alinhadores transparentes e aparelho fixo convencional nas medidas cefalométricas de dimensão vertical e posição do molar em pacientes adultos com má oclusão de Classe I tratados sem exodontias. Métodos: Radiografias cefalométricas laterais pré- e pós-tratamento de pacientes adultos tratados com alinhadores transparentes (n=44) ou com aparelho fixo tradicional (n=22) foram selecionadas para uma análise retrospectiva. Oito medidas de intervalo e uma medida nominal foram avaliadas: trespasse vertical anterior (OB), ângulo do plano mandibular em relação à base do crânio (SN_MP) e em relação ao Plano de Frankfurt (FMA), altura do molar inferior (L6H) e altura do molar superior (U6H), ângulo do plano palatal ao plano mandibular (PP_MP), altura facial inferior (LFH), altura facial total (TFH) e mordida aberta posterior (Posterior_OB). Um único avaliador fez todos os traçados cefalométricos, e as mudanças nas medidas da dimensão vertical foram comparadas intra e intergrupos. Resultados: OB reduziu (1,15 mm) e L6H aumentou (0,63 mm) no grupo de aparelho fixo tradicional. Os ângulos do plano mandibular (em relação à base do crânio e ao plano de Frankfurt) aumentaram (0,43° e 0,53°, respectivamente). No grupo dos alinhadores invisíveis, apenas o FMA apresentou diferença significativa entre os grupos (diferença de 0,53º). LFH e TFH aumentaram (variando de 0,52 mm a 0,80 mm) em ambos os grupos, sem diferenças entre as modalidades de tratamento. A presença de uma mordida aberta posterior visível aumentou significativamente durante o curso do tratamento. OB, FMA e L6H exibiram interação entre o estágio do tratamento (pré- e pós-tratamento) e a modalidade (terapia com alinhadores invisíveis ou aparelho fixo tradicional), porém não foi encontrada interação entre essas três variáveis. Conclusões: A evidência não suporta a teoria de que a terapia com alinhadores invisíveis produz melhor controle da dimensão vertical do que o aparelho fixo. O tratamento com aparelhagem fixa extruiu ligeiramente o molar inferior, e o tratamento com alinhadores invisíveis produziu uma ligeira rotação posterior da mandíbula.

Mechanical properties of resin-ceramic CAD-CAM materials after accelerated aging.

STATEMENT OF PROBLEM: The development of polymer-based computer-aided design and computer-aided manufacturing (CAD-CAM) milling bocks and the limited availability of independent studies on these materials make it pertinent to evaluate changes in their mechanical properties after simulated aging to identify strengths and limitations. PURPOSE: The purpose of this in vitro study was to measure the effect of thermocycling on the flexural properties of ceramic, resin, and resin-ceramic CAD-CAM materials. MATERIAL AND METHODS: Studied materials included Lava Ultimate Restorative (LVU; 3M ESPE), Enamic (ENA; VITA Zahnfabrik), Vitablocs Mark II (VM2; VITA Zahnfabrik), and Paradigm MZ100 (MZ1; 3M ESPE). Polished 4×1.2×14 mm bars (n=45 per material) were prepared from standard-size milling blocks. The 2 distilled water baths of the thermocycling apparatus were set to 5°C and 55°C, with a specimen immersion time of 15 seconds and transfer time of 4 seconds. Fifteen specimens from each material group were subjected to a 3-point flexural test at 3 different thermocycling intervals: 0 (control), 5000, and 10 000 cycles. The flexural test was performed over a 12-mm span with a crosshead speed of 0.5 mm/min. Data were subjected to multiple analyses of variance and the Tukey HSD post hoc tests (α=.05). RESULTS: Mean flexural strength values for 0, 5000, and 10 000 cycles were 133, 130, and 128 MPa for VM2; 175, 139, and 134 MPa for LVU; 154, 144, and 138 MPa for MZ1; and 149, 136, and 132 MPa for ENA. Mean flexural modulus values were 51, 52, and 54 GPa for VM2; 14, 13, and 13 GPa for LVU; 16, 15, and 15 GPa for MZ1; and 31, 30, and 31 GPa for ENA. Mean modulus of resilience values were 0.17, 0.16, and 0.15 MPa for VM2; 10.1, 0.76, and 0.72 MPa for LVU; 0.77, 0.69, and 0.62 MPa for MZ1; and 0.42, 0.31, and 0.28 MPa for ENA. A significant difference was found among the materials in the mean change of flexural strength (P<.001) and modulus of resilience (P<.05) after thermocycling. No significant difference was found among the materials in the mean change of flexural modulus after thermocycling (P=.113). CONCLUSIONS: The mean flexural strength of resin-ceramics is significantly different from that of the feldspathic ceramic control at 0 and 5000 cycles, but not at 10 000 cycles. The mean modulus of resilience of resin-ceramics varies significantly after thermocycling, unlike the feldspathic ceramic control. Conversely, the mean flexural modulus of tested materials did not vary significantly after thermocycling.