Evidence-based dentistry (EBD) is an approach to oral healthcare that integrates the best available scientific evidence with clinical expertise and patients’ needs to make decisions about patient care. By applying the principles of EBD, dental professionals can provide patients with the most effective and appropriate care based on the best available evidence. However, scientific evidence is extremely limited in the dental field, and clinicians are often forced to rely solely on their initial training. The project here presented is placed in this context and aims to make a step towards filling the evidence gap in dental restorations-related surgical techniques, thus potentially improving the outcomes of dental treatments. During this work, a series of experiments was conducted to explore biomechanical aspects of split crest (i.e., a bone augmentation surgical technique) and cemented prosthetic retrievability (i.e., the possibility to perform a conservative disassembly of the prosthesis). The tests were performed in vitro, using specially designed test benches to simulate the conditions encountered in clinical practice. Throughout these tests, design of experiments (DoE) guidelines were followed to ensure the validity and reliability of the applied methods. The variables with an expected strong influence on the phenomena under study were determined from the experience of clinicians and adopted as study factors, and the levels were decided according to prior knowledge. The bias due to other variables which could have affected the results was limited through the principles of blocking and randomization. A full factorial design was adopted: tests were performed for all possible combinations of the factors. The biomechanics of the split crest technique was investigated as described in Chapter 2. The split crest is an established surgical technique for horizontal bone augmentation that allows placing implants of adequate diameter in sites where the bone would be too thin for implantation. In this study, dental implants (diameter 4.3 mm) were inserted ex vivo into bovine ribs (average thickness 3.51 mm). Three different implant site preparation techniques were performed employing two instruments. The sites were prepared with zero, one, or two relief cuts (i.e., additional osteotomies performed in clinical practice to maximize the bone augmentation), and the cortices were separated using threaded bone expenders or a piezoelectric tool. Digital image correlation was used to measure the bone external surface displacement throughout the surgical procedures. The bones with zero relief osteotomies underwent a significantly lower external displacement compared to the bones with one or two, while no statistical differences were found between the instruments. Nonetheless, all procedures provided an adequate volume for implant insertion, and bone accidental fracture only occurred during split crest with threaded bone expanders, when two relief osteotomies were performed. For these reasons, the split crest performed with piezoelectric devices and no relief cuts was considered safer than the other techniques and equally efficient. Once the dental implant is inserted in the jawbone, a prosthesis must be anchored to it, and it can be either screw- or cement-retained. In recent years, cement-retained prosthetics have gained popularity compared to the alternative screw-retained type, and this rise served to highlight the importance of retrievability. Therefore, the study reported in Chapter 3 aimed to determine the influence of the luting agent, abutment height, and taper angle on the retrievability of abutment–coping cementations. Abutments with 9 different combinations of height and taper angle were screwed onto titanium dental implants and their noble metal alloy copings were cemented using three different luting agents. The removals were performed employing Coronaflex – an automated compressed air-driven tool – and the number of impulses and the forces were recorded and analyzed with Kruskal-Wallis tests. Copings cemented with Harvard Cement needed the highest number of impulses for retrieval, followed by Telio CS Link and Temp Bond NE. However, the luting agent had no significant influence on the number of impulses needed for the retrieval or the load transmitted to the implant. Abutment height and taper showed a greater effect on the copingsretrievability, significatively influencing both variables (p < 0.05). Long and tapered abutments provided the best compromise between retrievability and retention in terms of impulses needed for complete disassembly. The influence of the luting agent and the abutment geometry on the copings retrieval performed by Coronaflex reflects data from literature about the influence of the same factors on the maximum force reached during uniaxial tensile tests. However, the impulsive force was not highlighted as a strong descriptor of the prostheses retrievability compared to the number of impulses, as it was influenced by the dependent variable with less steadiness. In Chapter 4 a similar procedure was conducted on cemented fixed partial dentures (FPDs, i.e., three-unit dental bridges). Fourteen copings from the previous study were selected and used to create 7 different dental bridges, each composed of two copings and a noble metal bar. The bridges were cemented with the previously mentioned luting agents and removed employing Coronaflex, considering the number of impulses needed for complete disassembly and the force transmitted to the implant as retrievability indexes. Similarly to the results obtained on single-implant prostheses, the abutment geometry had a stronger influence on the bridge retrievability compared to the luting agent. Although the abutment geometry and the luting agent type are the major factors that influence retrievability, several tools can be used to retrieve a cemented crown, and the selection might be a crucial aspect influencing the patients’ and clinicians’ experience. Clinical studies show weak or no correlation between the number of impulses needed for a prosthesis disassembly and the patients’ discomfort, while the retentive force of the cement significantly affects their perceptions. Therefore, Chapter 5 focuses on the comparison between three different tools in terms of removal efficiency and potential discomfort caused during the procedure. Seven dental bridges were cemented with Temp Bond NE and Harvard Cement, and removed with a sliding hammer, a Coronaflex, and a Magnetic Mallet. The three tools were compared in terms of percentage of successful retrievals and force transmitted to the implant; Kruskal-Wallis analyses and Tuckey-Kramer pairwise comparisons were performed to investigate the tools influence on the force. The sliding hammer resulted the most efficient tool in terms of removal percentage, being able to retrieve most bridges in all tests performed with the temporary cement, the ones with the most retentive geometries being the only exceptions. However, Magnetic Mallet had a similar efficiency in this regard, while also achieving a significantly lower force than the other tools (p < 0.05). According to the results obtained in this work, the Magnetic Mallet can be considered a more suitable tool to retrieve temporarily cemented dental prostheses compared to Coronaflex, andnalso preferable compared to a sliding hammer for most situations, in particular when only conical abutments are involved. Regarding the permanent cement, it resulted not suitable for retrievable prostheses, as some disassembly attempts resulted in damaging the implant-abutment retention screw. Overall, the project presented in this dissertation contributes to evidence-based dentistry by providing insights into split crest biomechanics and prosthetic retrievability, which can inform clinical decision-making and improve patient care. The study also highlights the importance of scientific evidence and the need for further research to advance oral healthcare practices.
Novel experimental methods for the investigation of dental surgery biomechanics
lugas
2023-01-01
Abstract
Evidence-based dentistry (EBD) is an approach to oral healthcare that integrates the best available scientific evidence with clinical expertise and patients’ needs to make decisions about patient care. By applying the principles of EBD, dental professionals can provide patients with the most effective and appropriate care based on the best available evidence. However, scientific evidence is extremely limited in the dental field, and clinicians are often forced to rely solely on their initial training. The project here presented is placed in this context and aims to make a step towards filling the evidence gap in dental restorations-related surgical techniques, thus potentially improving the outcomes of dental treatments. During this work, a series of experiments was conducted to explore biomechanical aspects of split crest (i.e., a bone augmentation surgical technique) and cemented prosthetic retrievability (i.e., the possibility to perform a conservative disassembly of the prosthesis). The tests were performed in vitro, using specially designed test benches to simulate the conditions encountered in clinical practice. Throughout these tests, design of experiments (DoE) guidelines were followed to ensure the validity and reliability of the applied methods. The variables with an expected strong influence on the phenomena under study were determined from the experience of clinicians and adopted as study factors, and the levels were decided according to prior knowledge. The bias due to other variables which could have affected the results was limited through the principles of blocking and randomization. A full factorial design was adopted: tests were performed for all possible combinations of the factors. The biomechanics of the split crest technique was investigated as described in Chapter 2. The split crest is an established surgical technique for horizontal bone augmentation that allows placing implants of adequate diameter in sites where the bone would be too thin for implantation. In this study, dental implants (diameter 4.3 mm) were inserted ex vivo into bovine ribs (average thickness 3.51 mm). Three different implant site preparation techniques were performed employing two instruments. The sites were prepared with zero, one, or two relief cuts (i.e., additional osteotomies performed in clinical practice to maximize the bone augmentation), and the cortices were separated using threaded bone expenders or a piezoelectric tool. Digital image correlation was used to measure the bone external surface displacement throughout the surgical procedures. The bones with zero relief osteotomies underwent a significantly lower external displacement compared to the bones with one or two, while no statistical differences were found between the instruments. Nonetheless, all procedures provided an adequate volume for implant insertion, and bone accidental fracture only occurred during split crest with threaded bone expanders, when two relief osteotomies were performed. For these reasons, the split crest performed with piezoelectric devices and no relief cuts was considered safer than the other techniques and equally efficient. Once the dental implant is inserted in the jawbone, a prosthesis must be anchored to it, and it can be either screw- or cement-retained. In recent years, cement-retained prosthetics have gained popularity compared to the alternative screw-retained type, and this rise served to highlight the importance of retrievability. Therefore, the study reported in Chapter 3 aimed to determine the influence of the luting agent, abutment height, and taper angle on the retrievability of abutment–coping cementations. Abutments with 9 different combinations of height and taper angle were screwed onto titanium dental implants and their noble metal alloy copings were cemented using three different luting agents. The removals were performed employing Coronaflex – an automated compressed air-driven tool – and the number of impulses and the forces were recorded and analyzed with Kruskal-Wallis tests. Copings cemented with Harvard Cement needed the highest number of impulses for retrieval, followed by Telio CS Link and Temp Bond NE. However, the luting agent had no significant influence on the number of impulses needed for the retrieval or the load transmitted to the implant. Abutment height and taper showed a greater effect on the copingsretrievability, significatively influencing both variables (p < 0.05). Long and tapered abutments provided the best compromise between retrievability and retention in terms of impulses needed for complete disassembly. The influence of the luting agent and the abutment geometry on the copings retrieval performed by Coronaflex reflects data from literature about the influence of the same factors on the maximum force reached during uniaxial tensile tests. However, the impulsive force was not highlighted as a strong descriptor of the prostheses retrievability compared to the number of impulses, as it was influenced by the dependent variable with less steadiness. In Chapter 4 a similar procedure was conducted on cemented fixed partial dentures (FPDs, i.e., three-unit dental bridges). Fourteen copings from the previous study were selected and used to create 7 different dental bridges, each composed of two copings and a noble metal bar. The bridges were cemented with the previously mentioned luting agents and removed employing Coronaflex, considering the number of impulses needed for complete disassembly and the force transmitted to the implant as retrievability indexes. Similarly to the results obtained on single-implant prostheses, the abutment geometry had a stronger influence on the bridge retrievability compared to the luting agent. Although the abutment geometry and the luting agent type are the major factors that influence retrievability, several tools can be used to retrieve a cemented crown, and the selection might be a crucial aspect influencing the patients’ and clinicians’ experience. Clinical studies show weak or no correlation between the number of impulses needed for a prosthesis disassembly and the patients’ discomfort, while the retentive force of the cement significantly affects their perceptions. Therefore, Chapter 5 focuses on the comparison between three different tools in terms of removal efficiency and potential discomfort caused during the procedure. Seven dental bridges were cemented with Temp Bond NE and Harvard Cement, and removed with a sliding hammer, a Coronaflex, and a Magnetic Mallet. The three tools were compared in terms of percentage of successful retrievals and force transmitted to the implant; Kruskal-Wallis analyses and Tuckey-Kramer pairwise comparisons were performed to investigate the tools influence on the force. The sliding hammer resulted the most efficient tool in terms of removal percentage, being able to retrieve most bridges in all tests performed with the temporary cement, the ones with the most retentive geometries being the only exceptions. However, Magnetic Mallet had a similar efficiency in this regard, while also achieving a significantly lower force than the other tools (p < 0.05). According to the results obtained in this work, the Magnetic Mallet can be considered a more suitable tool to retrieve temporarily cemented dental prostheses compared to Coronaflex, andnalso preferable compared to a sliding hammer for most situations, in particular when only conical abutments are involved. Regarding the permanent cement, it resulted not suitable for retrievable prostheses, as some disassembly attempts resulted in damaging the implant-abutment retention screw. Overall, the project presented in this dissertation contributes to evidence-based dentistry by providing insights into split crest biomechanics and prosthetic retrievability, which can inform clinical decision-making and improve patient care. The study also highlights the importance of scientific evidence and the need for further research to advance oral healthcare practices.
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