Correlation among alveolar bone assessments provided by CBCT, micro-CT, and 14 T MRI.

OBJECTIVES: The aim of this study was to evaluate bone mineral adipose tissue (BMAT) volume in 21 alveolar bone specimens, as determined by 14 T MRI, and correlate them to the radiodensity values obtained pre-operatively of regions of interest (ROIs) by cone beam computed tomography (CBCT), and to the bone-volume-to-tissue-volume ratio values obtained by micro-CT, the gold-standard for morphometric data collection. METHODS: Partially edentulous patients were submitted to a CBCT scan, and the radiographic bone densities in each ROI were automatically calculated using coDiagnostiX software. Based on the CBCT surgical planning, a CAD/CAM stereolithographic surgical guide was fabricated to retrieve a bone biopsy from the same ROIs scanned preoperatively, and then to orientate the subsequent implant placement. The alveolar bone biopsies were then collected and scanned using the micro-CT and 14 T MRI techniques. Pearson's correlation test was performed to correlate the results obtained using the three different techniques. RESULTS: In the 21 eligible bone specimens (6 females, 15 males), age (mean age 52.9 years), micro-CT, and 14 T MRI variables were found to be normally distributed (p > 0.05). The strongest-and only statistically significant (p < 0.05)-correlation was found between micro-CT and 14 T MRI values (r = 0.943), and the weakest, between 14 T MRI and CBCT values (r = -0.068). CONCLUSIONS: The findings suggest that 14 T MRI can be used to evaluate BMAT as an indirect marker for bone volume, and that CBCT is not a reliable technique to provide accurate bone density values.

Correlation between magnetic resonance imaging and cone-beam computed tomography for maxillary sinus graft assessment.

PURPOSE: Little is known regarding the accuracy of clinical magnetic resonance imaging (MRI) protocols with acceptable scan times in sinus graft assessment. The aim of this study was to evaluate the correlations between MRI and cone-beam computed tomographic (CBCT) measurements of maxillary sinus grafts using 2 different clinical MRI imaging protocols. MATERIALS AND METHODS: A total of 15 patients who underwent unilateral sinus lift surgery with biphasic calcium phosphate were included in this study. CBCT, T1-weighted MRI, and T2-weighted MRI scans were taken 6 months after sinus lift surgery. Linear measurements of the maximum height and buccolingual width in coronal images, as well as the maximum anteroposterior depth in sagittal images, were performed by 2 trained observers using CBCT and MRI Digital Imaging and Communication in Medicine files. Microcomputed tomography (micro-CT) was also performed to confirm the presence of bone tissue in the grafted area. Correlations between MRI and CBCT measurements were assessed with the Pearson test. RESULTS: Significant correlations between CBCT and MRI were found for sinus graft height (T1-weighted, r=0.711 and P<0.05; T2-weighted, r=0.713 and P<0.05), buccolingual width (T1-weighted, r=0.892 and P<0.05; T2-weighted, r=0.956 and P<0.05), and anteroposterior depth (T1-weighted, r=0.731 and P<0.05; T2-weighted, r=0.873 and P<0.05). The presence of bone tissue in the grafted areas was confirmed via micro-CT. CONCLUSION: Both MRI pulse sequences tested can be used for sinus graft measurements, as strong correlations with CBCT were found. However, correlations between T2-weighted MRI and CBCT were slightly higher than those between T1-weighted MRI and CBCT.

Photoelastic analysis of the influence of residual ridge inclination in conjugated class I mandibular prostheses with different attachment systems.

OBJECTIVES: The aim of this study was to evaluate the stress distribution in mandibular free-end removable partial dentures (RPD) associated with FPD in the abutment teeth considering different inclinations of the residual ridge: (1) horizontal and (2) distal descending ridges and two designs of free-end RPD with different attachment systems were tested: (1) clasp and (2) system ERA. METHODS: Axial loads (100 N) were applied on the teeth of the RPD. The images were recorded and the stress distribution was evaluated through photoelastic fringes. RESULTS: In general, the distal descending ridge presented more photoelastic fringes in the region of the roots of the abutment teeth while the horizontal ridge exhibited higher compression in the base of the prosthesis. In the horizontal ridge, the denture with clasp presented more favourable stress distribution than the denture with the system ERA. In the distal descending ridge, the denture with the system ERA relieved the region of the abutment teeth and overloaded the residual ridge. CONCLUSION: The horizontal ridge presented more favourable performance; the dentures with clasp exhibited better performance for both ridges evaluated; the denture with the system ERA presented better results in the distal descending ridge.

Photoelastic analysis of biomechanical behavior of single and multiple fixed partial prostheses with different prosthetic connections.

The aim of this study was to evaluate the stress distribution on external hexagon, internal hexagon, and Morse taper implant in single and 3-unit implant-supported fixed partial prostheses (FPPs) using photoelasticity. Six models were fabricated with the photoelastic resin PL-2: 3 models for the 3-unit implant-supported FPP with implants of 4.0 × 10.0 mm in the region of the second premolar and molar including 1 model for each type of implant connection, and 3 models for the single prosthesis for each implant type. The prostheses fabrication was standardized. A circular polariscope was used, and axial and oblique (45 degrees) loads of 100 N were applied in a universal testing machine. The results were photographed and analyzed qualitatively. The internal hexagon implant exhibited better stress distribution and lower intensity of fringes followed by the external hexagon and Morse taper implants for the models with the 3-unit prostheses. For the single implants, the Morse taper implant presented better stress distribution, followed by the internal and external hexagon implants. The oblique loading increased the number of photoelastic fringes in all models. It was concluded that the internal hexagon implant exhibited better biomechanical behavior for the 3-unit implant-supported FPP, whereas the Morse taper implant was more favorable for the single implant-supported prosthesis. The oblique loading increased the stress in all models.

Photoelastic analysis of cemented or screwed implant-supported prostheses with different prosthetic connections.

The aim of this study was to evaluate the stress distribution of different retention systems (screwed or cemented) associated with different prosthetic connections (external hexagon, internal hexagon, and Morse taper) in 3-unit implant-supported fixed partial dentures through photoelasticity. Six models were fabricated with photoelastic resin PL-2, and each model contained two implants of 4.0 × 10.0 mm. The models presented different retention systems (screwed and cemented) and different connections (external hexagon, internal hexagon, and Morse taper). The prostheses were standardized and fabricated in Ni-Cr alloy. A circular polariscope was used and axial and oblique (45°) loads of 100 N were applied in a universal testing machine. The results were photographed and analyzed qualitatively with a graphic software (Adobe Photoshop). The screwed retention system exhibited higher number of fringes for both axial and oblique loadings. The internal hexagon implant presented better and lower stress distribution for both cemented and screwed prostheses. The oblique loading increased the number of fringes in all models tested. The cemented retention system presented better stress distribution. The internal hexagon implant was more favorable according to the biomechanical standpoint. The oblique load increased stress in all systems and connections tested.

Photoelastic stress analysis in screwed and cemented implant-supported dentures with external hexagon implants.

The aim of this study was to assess the stress distribution of the retention systems (screwed and cemented) for implant-supported fixed partial dentures by means of photoelastic method. Two models were made of photoelastic resin PL-2 with 2 implants (phi = 4.00 x 10 mm) located in the second premolar and molar region in each photoelastic model, varying the retention system (screwed and cemented). The implant-supported fixed partial dentures were standardized and made of Ni-Cr alloy. Axial and oblique (45 degrees) forces of 100 N were applied on the occlusal surface by means of a Universal Testing Machine (EMIC-DL 3000; São José dos Pinhais, Paraná, Brazil). The results were observed and photographed in the field of a circular polariscope and qualitatively analyzed with the aid of computer software (Adobe Photoshop, San Jose, CA). The screw retention system presented the highest number of fringes when the loads were applied on the premolar, pontic, and molar and showed this behavior in all load applications, under axial and oblique loads. It was concluded that there was a better stress distribution and lower magnitude of stress on the cemented implant-supported dentures, under axial and oblique loads. Oblique load caused an increase in stress concentrations in all the models.

Influence of ridge type on mandibular distal extension removable partial denture.

The aim of this study was to use photoelastic models to analyze the distribution of stress caused by the incidence of loads on a mandibular distal extension removable partial denture, both on the abutment teeth and on differently shaped residual ridges: distal ascending, descending-ascending, horizontal and distal descending. The best type of retainer and location of the rest on the last abutment tooth were determined for the different types of ridge. Four models were made from photoelastic resin (PL-1 for the teeth and PL-2 for the alveolar ridge), one for each kind of ridge. For each model, 4 removable partial dentures (RPD) were made (16 RPD altogether): T-bar retainer and distal rest, T-bar retainer and mesial rest, circumferential retainer and distal rest, and circumferential retainer and mesial rest. The models were placed on a circular polariscope and a 100 N axial load (point load) was applied to premolars and molars of the RPD. The formation of photoelastic bands was photographed for qualitative analysis. Results showed that the horizontal ridge had better distribution of stress, while the distal descending ridge had greater concentration of stress. The circumferential retainer had greater areas of stress for all types of ridges except the horizontal ridge, where there was no influence related to retainer type. The distribution of stress was similar among the different types of ridges when the rest was mesial or distal to the last abutment tooth, except for the distal descending ridge, where there was greater concentration of stress when the rest was located distally to the last abutment tooth. Thus, it may be concluded that (1) the situation was least favorable for the distal descending ridge and most favorable for the horizontal ridge, (2) the T-bar retainer had more favorable stress distribution, except when the ridge was horizontal, in which case there was no influence in relation to the type of retainer, (3) the location of the rest showed similar behavior in all except the distal descending ridge.

Influence of ridge type on mandibular distal extension removable partial denture

The aim of this study was to use photoelastic models to analyze the distribution of stress caused by the incidence of loads on a mandibular distal extension removable partial denture, both on the abutment teeth and on differently shaped residual ridges: distal ascending, descending-ascending, horizontal and distal descending. The best type of retainer and location of the rest on the last abutment tooth were determined for the different types of ridge. Four models were made from photoelastic resin (PL-1 for the teeth and PL-2 for the alveolar ridge), one for each kind of ridge. For each model, 4 removable partial dentures (RPD) were made (16 RPD altogether): T-bar retainer and distal rest, T-bar retainer and mesial rest, circumferential retainer and distal rest, and circumferential retainer and mesial rest. The models were placed on a circular polariscope and a 100 N axial load (point load) was applied to premolars and molars of the RPD. The formation of photoelastic bands was photographed for qualitative analysis. Results showed that the horizontal ridge had better distribution of stress, while the distal descending ridge had greater concentration of stress. The circumferential retainer had greater areas of stress for all types of ridges except the horizontal ridge, where there was no influence related to retainer type. The distribution of stress was similar among the different types of ridges when the rest was mesial or distal to the last abutment tooth, except for the distal descending ridge, where there was greater concentration of stress when the rest was located distally to the last abutment tooth. Thus, it may be concluded that (1) the situation was least favorable for the distal descending ridge and most favorable for the horizontal ridge, (2) the T-bar retainer had more favorable stress distribution, except when the ridge was horizontal, in which case there was no influence in relation to the type of retainer, (3) the location of the rest showed similar behavior in all except the distal descending ridge.

O objetivo da pesquisa foi analisar, atraves de modelos fotoelasticos, a distribuicao das tensoes formadas pela incidencia de cargas sobre a protese parcial removivel de extremidade livre mandibular, nos dentes suporte e no rebordo residual nas formas: ascendente distal, descendente-ascendente, horizontal e descendente distal. Nos diferentes tipos de rebordo foi verificado o melhor tipo de grampo e a localizacao do apoio no ultimo dente suporte da extremidade livre. Foram construidos 4 modelos de resina fotoelastica (PL-1 para os dentes e PL-2 para o rebordo alveolar), um modelo para cada tipo de rebordo. Para cada modelo foram confeccionados 4 proteses parciais removiveis (PPR)(total de 16 PPR): com grampo em barra T e apoio na face distal, com grampo em barra T e conector na mesial, grampo circunferencial e apoio na face distal e grampo circunferencial e apoyo na face mesial. Os modelos foram posicionados em um polariscopio circular e aplicado carga pontuais e axiais de 100 N nos pre-molares e molares das proteses. As franjas formadas foram fotografadas para analise. Os resultados foram analisados de uma forma qualitativa e podemos observar que o rebordo horizontal apresentou uma melhor distribuicao das tensoes, enquanto o rebordo descendente distal apresentou as maiores concentracoes de tensoes. O grampo circunferencial apresentou as maiores formacoes de tensoes em todos os tipos de rebordo, exceto no rebordo horizontal, onde nao houve influencia quanto ao tipo de grampo. Nao houve diferenca significante entre os tipos de rebordo ao posicionar o apoio na mesial ou distal do ultimo dente suporte, com excecao feita ao rebordo descendente distal, onde se acentuou a concentracao de tensoes ao posicionar o apoio na distal do ultimo dente. Desse modo, podemos concluir que (1) o rebordo mais desfavoravel foi o descendente distal e o mais favoravel o horizontal, (2) o grampo em barra T apresentou distribuicao de tensoes mais favoraveis, com excecao do rebordo horizontal, onde nao houve influencia quanto ao tipo de grampo, (3) e que a localizacao do apoio apresentou comportamentos semelhantes, a nao ser no rebordo descendente distal.

Methods used for assessing stresses in buccomaxillary prostheses: photoelasticity, finite element technique, and extensometry.

The authors describe a literature revision on assessing stresses in buccomaxillary prostheses photoelasticity, finite element technique, and extensometry. They describe the techniques and the importance for use of each method in buccomaxillary prostheses with implants and the need of accomplishing more studies in this scarce literary area.

Influência dos sistemas de retenção e da inclinação do rebordo residual em casos de próteses conjugadas Classe I mandibular: análise da distribuição das tensões pelo método da fotoelasticidade / Influence of retention systems and the inclination of the residual ridge in cases of conjugated Class I mandibular prosthesis: analysis of the distribution of tensions by the method of photoelasticity

A reabilitação de pacientes classe I de Kennedy mandibular através de Prótese Parcial Removível é de difícil resolução devido a diferença de resiliência existente entre o ligamento periodontal dos dentes suportes e a mucosa do rebordo residual. A inclinação do rebordo residual no sentido sagital pode influenciar na distribuição das tensões transmitidas pela incidência de cargas em próteses parciais removíveis de extremidade livre associadas a próteses parciais fixas. Na associação da prótese parcial removível com próteses parciais fixas, o profissional tem como alternativa aos grampos tradicionais, o uso de encaixes extra-coronários que podem melhorar a estética e o funcionamento biomecânico do conjunto. Desse modo, o objetivo desse estudo foi avaliar a característica da distribuição de tensões em próteses parciais removíveis mandibulares de extremidade livre associadas a próteses parciais fixas nos dentes suporte com diferentes sistemas de retenção: (1) grampo por ação de pontas; (2) sistema ASC-52; (3) sistema ERA; e (4) encaixe de semi-precisão Score-PD, pela metodologia da fotoelasticidade. E, analisar a distribuição de tensões em próteses parciais removíveis mandibulares de extremidade livre associadas a próteses parciais fixas nos dentes suporte com diferentes sistemas de retenção: (1) grampo por ação de pontas e (2) sistema ERA, variando duas inclinações de rebordo residual: (1) horizontal e (2) descendente distal. Cargas axiais de 100N foram aplicadas sobre os dentes das próteses parciais removíveis. As imagens das aplicações foram capturadas e a distribuição das tensões foi avaliada, pela formação das franjas fotoelásticas. No primeiro estudo, a prótese com encaixes de semi-precisão produziu os maiores níveis de tensão na região de ápice, entre as raízes dos últimos dentes suporte e na porção mais distal do rebordo residual. As próteses com encaixes resilientes apresentaram as maiores formações de franjas na região cervical distal do último dente...

The rehabilitation of patients mandibular class I of Kennedy through Removable Partial Denture is difficult to solve because the difference in strength between the periodontal ligament of the abutment teeth and the residual ridge mucosa. The inclination of the residual ridge towards sagital may influence the distribution of stresses transmitted by the incidence of loads in distal extension removable partial dentures associated with fixed partial dentures. In association removable partial denture – fixed partial dentures, the professional has as alternative to the traditional clasps, the use of extra-coronary attachments that can improve the aesthetics and the biomechanics. Therefore, the objective of this study was to evaluate the characteristic distribution of tensions in mandibular distal extension removable partial dentures (1) “I” bar clasps, (2) ASC-52system, (3) ERA system, and (4) semi-precision Score-PD system, by the methodology of photoelasticity. And, analyze the distribution of tensions in mandibular distal extension removable partial dentures associated to the fixed partial dentures in the abutment teeth with different retention systems: (1) “I” bar clasps and (2) ERA system, ranging from two inclinations residual ridge: (1) horizontal and (2) distal descending. Axial loads of 100N were applied on the teeth of removable partial dentures. The images of the applications were captured and distribution of stress was assessed by the formation of the photoelastic fringes. In the first study, the prosthesis with semi-precision attachment produced the highest levels of tension in the region of apex, between the roots of the abutment teeth and in the more distal portion of the residual ridge. The prostheses with resilient attachments showed the largest fringes formations in the cervical-distal of the last abutment tooth. In the second study, horizontal ridge presented a better distribution of tensions with the clasps design when compared to the ERA design...