In vitro investigation of mechanical properties of latest-generation CAD-CAM Composites - Dr. Yousef KAREVAN, 2025

                                                 

This thesis conducted different in vitro investigations aimed at addressing two critical issues in Computer‐Aided Design/Computer‐Aided Manufacturing (CAD-CAM) materials for dental prostheses: fractures and debonding from titanium implant abutment (Ti-base). Specifically, the work focused on evaluating the mechanical performance of latest generation CAD-CAM composites compared to established lithium-based glass-ceramic material. Fatigue behavior was analyzed to provide a clinically relevant insight. Interfacial fracture toughness approach was used to examine debonding issue, comparing different CAD-CAM ceramic and composite materials.

Additionally, as flexural strength is the most common approach for analyzing the properties of dental materials, this work also conducted a series of analyses to determine the optimal statistical analysis of the flexural strength data, and to provide deep insight into related interblock and intrablock inhomogeneity.

Despite latest generation dispersed-filler CAD-CAM composites having shorter lifetimes than lthium-based glass-ceramic, they show similar resistance to fatigue degradation. Time-dependent factors seem to significantly influence composites fatigue at lower stress levels. Thus, extended fatigue testing in water, despite being time-consuming and costly, is essential for understanding material behavior under clinical conditions.

Moreover, this thesis reveals that the CAD-CAM composites differ from each other; their microstructure and chemical composition substantially affecting their mechanical properties and the interface with Ti-base. Particularly, novel microstructures, such as polymer-infiltrated ceramic networks (PICN), exhibited a superior interface with Ti-base than dispersed filler composites.

Minimally invasive treatment strategies with Polymer Infiltrated-Ceramic-Network (PICN) materials - Dr Julie OUDKERK, 2024

                                                   

Tooth wear (TW) is a multifactorial issue, making the understanding of its risk factors essential for effective management. Despite its importance, a comprehensive review to guide clinical decisions is lacking. Bruxism and TW may be linked to various chronic diseases, but current data are limited, highlighting the need for further research. Diagnosis and prevention of TW are crucial, but selecting appropriate restorative treatments is equally important. Currently, there is no consensus on the optimal technique or material for restoring severely worn dentition, particularly due to the lack of long-term studies. The One-Step No-Prep technique is a non-invasive restorative approach for generalized TW, using Polymer-Infiltrated Ceramic Network (PICN or hybrid ceramic, Vita Enamic) CAD-CAM restorations. Introduced in 2018, the technique has shown successful preliminary results, but its long-term effectiveness needs to be validated. PICN materials seem well-suited for this technique, but their clinical performance, especially long-term, is not well-studied, particularly regarding wear resistance—an important factor for bruxism patients.

The primary aim of this thesis was to contribute to the assessment of the One-Step No-Prep technique. Additionally, this study sought to advance TW diagnosis and to investigate the intraoral wear of PICN materials. The first work package (WP) introduced the ToWeR checklist, a tool to enhance the understanding of TW risk factors in clinical practice. The second WP explored the association between bruxism, TW, and MSDs, emphasizing a holistic approach. The third part of this work presents a critical review of the evolution of indirect composites to better understand their properties and the contributions of new materials to improved treatment strategies. Subsequent WPs focused on evaluating the One-Step No-Prep technique in a prospective clinical context.

The fourth WP investigated PICN restorations’ clinical performance and their impact on patients' oral health-related quality of life over two-year in seven patients. The fifth WP evaluated the intraoral wear of PICN CAD-CAM composite restorations over five years using ex vivo 3D profilometry analyses. The sixth WP reported up to nine years of follow-up in 24 patients, assessing restoration thickness's influence on fracture rates. PICN was confirmed as well-suited to the One-Step No-Prep protocol due to its thin milling capability, adaptability during in-mouth adjustments, and ease of repair, especially in bruxers. The material's polymer component aids in occlusal stress absorption. At nine years, the survival rate was 98.4%, with a success rate of 79.7%, rising to 86.7% when excluding minor chipping. The thesis demonstrated that maintaining a restoration thickness of 0.56 mm could reduce minor chipping. After five years, PICN restorations exhibited wear values slightly lower than natural enamel, without significant abrasive effects, maintaining occlusal stability. The esthetic properties of PICN, particularly with Vita Enamic multiColor blocks, were rated as excellent or good over time, outperforming direct composites in resistance to staining and discoloration. The One-Step No-Prep protocol was shown to combine the benefits of direct techniques—minimally invasive, easy repair—with those of indirect techniques, such as access to superior materials and efficient restoration anatomy creation. This work highlights the successful long-term outcomes of the One-Step No-Prep technique and exhibits the clinical performance 

Clinical behavior and intraoral low-temperature degradation of zirconia dental protheses - Dr. Vinciane KOENIG, 2021  

Thèse Koenig

The use of zirconia in the field of dental prostheses has grown significantly since its introduction in the 2000s, following the advent of computer-aided design and manufacturing technologies. First-generation zirconia-based restorations (ZBR) are bilayered structures composed of a framework and a glassceramic veneer, which imparts an essential esthetic appearance. However, the first clinical reports regarding veneered ZBR indicated a high rate of short-term failures due to cohesive fractures (chipping) of the veneering ceramic. To address this, a retrospective study on veneered ZBR was conducted to investigate the influence of clinical parameters, such as patientrelated risk factors, on chipping failures. Zirconia is now used to fabricate monolithic dental prostheses without the veneering ceramic layer and the only presence of a thin cosmetic glaze. These prostheses were notably developed to remedy chipping and, thus, obtain prostheses with an increased durability. Therefore, zirconia materials exhibiting greater translucency have been developed for monolithic restorations However, second generation zirconia materials are prone to show greater metastable behavior, which could promote low-temperature degradation (LTD). The main objective of this study was to evaluate the intraoral LTD of zirconia monolithic restorations and the influence of occlusal stresses and glaze protection on this process. Secondary objectives included the investigation of the general clinical behavior and material wear of the restorations. This work introduces an original protocol, including ex vivo analyses, to evaluate the LTD process of monolithic zirconia prostheses in the oral environment and to study their general clinical behavior, primarily in terms of material wear. LTD was shown to develop in 3 mol% yttria-doped tetragonal zirconia polycrystal monolithic restorations six months after intraoral placement and then progresses over time. After two years, the tetragonalmonoclinic transformation became non-uniform, with the presence of localized clusters of transformed grains. In axial areas, the grain aspect was typical of the classical nucleation-growth process reported for LTD. However, in occlusal areas, tribological stress generated surface crushing and grain pull-out from the clusters, causing an underestimation of the aging degree when the evaluation was limited to monoclinic phase quantification. Glazing cannot be considered a protection against LTD because it is worn away in occlusal areas after one year. Two years after their implantation, the Kaplan-Meier survival rate of restorations was 93.3% (100% for fixed partial dentures) and the success rate was 81.8%. It was found that eighty percent of major failures occurred in patients exhibiting clinical signs of bruxism. Complications such as root fracture, periodontal disease or composite chipping were also observed in antagonistic teeth. Wear in zirconia was observed to be less than 15 µm. The success rate of single-unit restorations was not as high as expected, the weak link being the prosthesis support or the antagonist tooth. One hypothesis is that zirconia’s stiffness and lack of ability to deform do not promote occlusal stress accommodation, which can be critical in patients affected by bruxism. Furthermore, several unexpected clinical failures were observed, including chipping and major fracture of the material, which may have been induced through LTD. If LTD occurs through the same mechanisms in dental prostheses as in orthopedic prostheses, its clinical impact remains unknown and needs to be evaluated through a thorough analysis of fractured prostheses in the framework of long-term studies.

Periodontitis and systemic conditions : a contribution - Dr. Leila SALHI, 2020

1Thèse Salhi

This thesis investigated the relationship between periodontitis and systemic conditions as in a metaphorical approach of the relation between the “microcosm (periodontitis) and the macrocosm (systemic conditions)”, as well as their inverse relationship. Expressed more extensively, on the one hand, the influence of periodontitis (the bacterial” microcosm”) on a systemic condition (AAA, “a macro-disease”), and inversely, the influence of a systemic condition (smoking, “microcosm”) on periodontitis (“macro-disease”).
The investigation of these relationships is founded on several research questions. 
The first research question (RQ 1) focused on the influence of periodontitis on the progression of abdominal aortic aneurysm. In order to answer the RQ 1 a systematic review entitled “Can periodontitis influence the progression of abdominal aortic aneurysm? 1 was carried out and the results indicated an emphasis of the role of periodontal pathogens in the initiation and the progression of AAA. More precisely, in the included preclinical studies, the animals infected by Porphyromonas gingivalis (Pg) presented a significant destruction of the elastic fibers of the abdominal aorta as well as a significant proteolytic activity inside both the aortic wall and the the intraluminal thrombus (ILT). Among the results of the included clinical studies, the AAA diameters and the ILT were significantly correlated also to the presence of Pg antibodies in the plasma and inside the AAA wall. As a result, periodontitis infection seems to be associated with AAA progression. 
Moreover, in both the preclinical and clinical studies, DNA of periodontal pathogens was found inside AAA samples. This fact demonstrates that bacteria can invade blood circulation and reach AAA wall or thrombus where, as a result, increased inflammatory / immune response and proteolytic activity may occur. However, only one clinical study supported that AAA was significantly correlated with Pg antibodies both in plasma and in aortic wall. Therefore, the findings of this systematic review highlighted that periodontitis infection seems to participate in the physiopathology of AAA.
The second research question (RQ 2) explored the correlations between the clinical severity of periodontitis (RQ 2a), microbiological (RQ 2b) and immunological (RQ 2c) profiles with the stability and the severity of AAA .To answer to these research questions, a cross sectional clinical study entitled (“Further evidence on the relationship between abdominal aortic aneurysm and periodontitis: a cross-sectional study2) was performed. In 61 AAA patients, the periodontal clinical parameters, the microbiological profiles as well as the blood biomarkers characteristics were correlated with AAA features.
In the RQ 2a, we observed that periodontitis was highly prevalent in both stable and unstable AAA patients while severe periodontitis with a rapid rate of progression (stage IV and grade C) tended to be more frequent in the unstable AAA patient group. Periodontal parameters were comparable but the proportion of patients with high PIRI scores, reflecting the periodontal risk of infectiousness, was higher in those with unstable AAA (51.6% vs. 23.3%). Additionally, the pocket depth (PD) and the proportion of PD >6mm were positively correlated with AAA size and thrombus volume. 
The RQ 2b, focusing on periodontal microbiology profile of AAA patients, revealed that Pg was observed in all oral samples (saliva, supragingival and subgingival plaque) and Pg concentration was correlated with the diameters and the volumes of AAA. Moreover, Tf was also related to AAA diameters and volumes but only in saliva.
In the RQ 2c, aiming to characterise the perio-specific immunological profiles of AAA patients, emphasized that anti- Pg and anti-Aa antibodies were present in all blood samples, but no associations were found between periodontitis and AAA diameters and volumes. Moreover, the CRP was significantly correlated with the AAA instability.
The potential associations between microbiology and immunology profiles (RQ 2b and 2c) were also explored and the saliva and sub-gingival plaque Pg concentration were significantly associated with higher LPS blood levels.
The third research question (RQ 3) explored the influence of the Fagerström test for nicotine dependence (FTND), as an indicator of smoking status, on the severity of periodontitis. To answer the RQ 3 an observational cross-sectional study entitled “Fagerström test for nicotine dependence as an indicator for tobacco-related studies in periodontology”, was performed. To investigate, the role of smoking as a systemic condition on periodontitis, the periodontal clinical features were measured in 34 patients and correlated with 2 indicators of smoking status: (i) nicotine dependence (FTND) and (ii) number of consumed cigarettes (NCC). The study suggested the interest of the use of nicotine dependence as a complementary indicator to NCC in order to assess the smoking status in periodontal trials or even in routine clinical periodontal practice. Indeed, when compared to NCC, FTND appears to be more
correlated to severe periodontal features and yielded an improved discrimination between stage III and stage IV of periodontitis.
The fourth research question (RQ 4) investigated the influence of smoking on the outcomes of periodontal non-surgical treatment (PNST) (oral hygiene instructions and debridement) and on patient related outcome measures (PROMs). To investigate the RQ 4, a prospective controlled clinical study entitled “Respective effects of oral hygiene instructions and
periodontal non-surgical treatment (debridement) on clinical parameters and patient-reported outcome measures with respect to smoking” 4, was conducted on seventy-five patients distributed in three groups (non-smokers, former smokers and smokers). Although the smoker patients of the present study presented more severe periodontitis than non-smokers, in general, the periodontal non-surgical treatment presented better outcomes in the non-smoker and former smoker groups. In addition, in smoker patients, only the debridement improved periodontal parameters (PG, BOP, PISA) while in non-smokers (or former smokers) a significant improvement of these features was already observed after the OHI. Finally, as the former smokers displayed similar outcomes than the non-smokers, smoking cessation should be encouraged while providing a periodontal initial therapy.
In conclusion, the research of this thesis and the reflexions that result from it show how much periodontitis is not a singular disease... developing in a specific point of the human body, the mouth. 
Indeed, this singularity (periodontitis) is at the centre of interactions (systemic conditions) with living beings (general health). By an allegorical allusion to the singularity of space (microcosme) generating the big bang and our universe (macrocosm), periodontitis maintains, through systemic conditions, invisible but perceptible relationships with living beings and their general health. 
Ultimately, the whole of this thesis is made up of a set of chapters linked to each other, whose meaning is revealed thanks to their entwinement, like a constellation made up of the singular stars that compose it ... However, in the same way that new stars are discovered, more studies will be needed to improve our knowledge of the relationship between periodontitis and systemic conditions. 
Future contributions could be those proposed through my perspectives for further research.

Innovatie Orthodontic Treatment Using Piezosurgery - Dr. Carole CHARAVET, 2020

COUVERTURE

An increasing number of adult patients are seeking orthodontic treatment for functional or aesthetic reasons, but treatment time is often a limitation. Several surgical techniques such as corticotomies have been developed to accelerate orthodontic treatment; however, these procedures are rather invasive. Recently, some authors have proposed minimally invasive techniques such as piezocision, possibly combined with tissue augmentation. Piezocision is a localized alveolar decortication approach that combines buccal micro-incisions and minimally invasive corticotomies (3mm in depth – 5 mm in length) performed with a piezotome. However, the level of clinical evidence backing this approach is scarce, and the underlying biological response regarding piezocision surgery is not fully understood. The aim of this PhD project was to investigate and understand the effects of piezocision on orthodontic treatment based on several clinical trials and multi-level biological analyses in a preclinical setting.

Based on two randomized controlled trials, the present work demonstrates the first clinical evidence of tooth movement facilitation with piezocision. A reduction in treatment time of respectively 40% and 36% was observed in cases of minor to moderate overcrowding. Moreover, patient-reported outcome measures (PROMs) regarding the piezocision procedure were investigated and revealed limited pain scores as well as high levels of acceptance and patient satisfaction. Furthermore, the potential benefit of combining piezocision with alveolar bone augmentation in the anterior mandibular region using biomaterial was explored in a prospective study. Most of the cases demonstrated a significant increase of the alveolar bone envelope and therefore expand the orthodontic scope in cases presenting bone deficiencies or thin buccal bone plate prior to orthodontic treatment.

Beyond the clinical validation, this PhD thesis was also dedicated to understanding the biological phenomenoma associated with the piezocison concept. Within the limit of a preclinical study, the efficacy of piezocision in accelerating orthodontic tooth movement was demonstrated, and the underlying biological responses at the tissue, cellular and molecular levels were highlighted. Increased three-dimensional bone demineralization and osteoclast recruitment were observed in the piezocision group compared to a conventional orthodontic approach. Moreover, an increase in bone remodeling, highlighted at the molecular level by the coupled RANKL-OPG expression, was demonstrated for the first time using piezocision-assisted alveolar decortication. These biological phenomena were shown to be transient and completely reversible.

The clinical and preclinical data collected in this thesis contributed to the validation of piezocision-assisted orthodontic treatment. According to the present results, this treatment approach can be considered to be a new therapeutic tool in adult orthodontics.

Properties and applications of polymer - infiltrated ceramic network materials - Dr. Maher ELDAFRAWY, 2019

mceclip0 - 2021-09-23 15h43m20s

Computer-aided design and manufacturing (CAD-CAM) materials are gaining popularity in the field of restorative dentistry. Among recently developed materials are polymer-infiltrated ceramic network (PICN) materials, a sub-class of CAD-CAM composites, comprised of 75 vol% sintered glass-ceramic network that is secondarily infiltrated with monomers and polymerized under high-temperature and pressure; whereas the other sub-class of CAD-CAM composites, dispersed fillers (DF), consist of inorganic fillers classically incorporated by mixing in an organic matrix that is secondarily polymerized under high-temperature. The first objective of this work was to use fracture mechanics, particularly the notchless triangular prism (NTP) specimen fracture toughness test to :

1) evaluate the interfacial fracture toughness (IFT) of a resin composite luting agent (RCLA) with PICNs, represented by an experimental and a commercial PICN (Vita Enamic), versus DF materials. Lithium disilicate glass-ceramic (IPS e.max CAD, EMX) was also tested as a gold standard for comparison. Samples were pretreated with hydrofluoric acid (HF) or gritblasting (GR), and the results were correlated with the developed interfacial area ratio (Sdr) of representative samples subjected to the same pretreatment procedures.

 2) Evaluate the influence of silane on the IFT of RCLA with PICN and DF after HF and GR, and correlate the results with the Sdr and surface wettability of representative samples. The results showed that the IFT of PICNs was significantly superior to DF, and IFT of etched experimental PICN was significantly higher than EMX. In addition, there was a strong correlation between the IFT and the Sdr of the representative samples, PICNs demonstrating significantly higher surface roughness than DF when pretreated. These results highlighted the importance of material microstructure and then class (DF vs PICN) on the bonding interface performance. Etching of PICN led to the selective dissolution of the glass-ceramic at the surface, creating an original polymer-based honeycomb structure that promoted the micromechanical retention of RCLA. This micromechanical retention is enhanced by the application of silane, which allows RCLA penetration in surface roughness. On the other hand, IFT of DF was not influenced by silane, regardless of the surface pretreatment, which was less effective

in creating surface roughness. The second objective was to introduce of a functionally-graded (FG) PICN block as a biomimetic material for CAD-CAM prostheses. FG-PICN is characterized by a gradient of mechanical and optical properties, in which the surface properties resemble the hardness and modulus of enamel, while the deeper layers resemble those of dentin. The flexural strength values at the dentin-like layer was similar to glass-ceramic EMX and flexural load energy was significantly higher than EMX and monolithic zirconia. These properties could promote occlusal stress absorbance in treatment of patients with bruxism, such as worn dentition cases, and on implant restorations. Finally, the third objective was to participate in two clinical studies performed following new treatment protocols developed with commercial PICN; a minimally invasive approach of worn dentition treatment with Vita Enamic bonded restorations; the “One-step No-prep” protocol and a novel approach for restoring a missing posterior tooth with immediate loading of an implant and a final crown made of PICN in a single visit; the “One-tooth One-time, 1T1T” protocol. The restorations success

rate after 2 years was high (93.75% for the former and 90% for the latter), highlighting some edge chipping in the first study, and debonding from the ti-base in the second. In conclusion, PICNs show a promising potential to be used in a variety of restorative applications, especially in minimally invasive dentistry, such as demonstrated in novel clinical applications of Vita Enamic. Indeed, in vitro studies highlighted the superiority of PICN, particularly the new PICN generation, to DF and lithium disilicate glass-ceramic in terms of IFT with RCLA. In addition, the original gradient of mechanical properties of the FG-PICN, opens the door for restorations with an improved bio-mechanical behavior compared to other CAD-CAM materials available on the market. Future perspectives include fatigue tests and clinical studies with experimental PICN materials.

The influence of biomaterials and the role of oxidative stress in bone regeneration under diabetic conditions - Dr. Mijlana BACEVIC, 2019

                                                             

 

Biocompatibility of polymer infiltrated cermic network materials - Dr. Charlotte GRENADE, 2017

 

1Thèse Charlotte

The development of computer-aided design and manufacturing (CAD-CAM) processes generated the recent emergence of innovative prosthetic materials, especially for the manufacture of transgingival implant components. In particular, Polymer Infiltrated Ceramic Network (PICN) materials look as a promising alternative to ceramics especially because of their good bio-mechanical properties, which are the consequence of their specific microstructure and innovative polymerization mode. However, the biological properties of these new materials, which are crucial in implant prosthetics, have been little studied. Therefore, the main objective of this work was to evaluate, in vitro, the biocompatibility of PICNs in comparison with current metallic and ceramic materials used for implant prostheses: titanium, zirconia and lithium disilicate glass-ceramic. The attachment, proliferation and spreading of human gingival fibroblasts (HGFs) and keratinocytes (HGKs) were evaluated. Titanium and zirconia showed the best results and can be considered as the gold standard of materials in terms of HGF and HGK behavior. On the other hand, PICNs presented intermediate and comparable or slightly better results than lithium disilicate glass- ceramics. The favorable behavior of PICNs, which are composite materials, compared to glass-ceramics was notably explained by the hypothesis of the influence of their high temperature and high pressure (HT-HP) innovative polymerization mode. Indeed, the polymerization mode and the degree of monomer conversion were previously reported to affect toxicity and cellular response. Therefore, the secondary objective of this study was to measure the indirect cytotoxicity of PICNs and the free monomer release from the tested samples. The results were found to be negative, reinforcing the idea that HT-HP polymerization mode could promote the biocompatibility of PICNs. On the other hand, many surface properties being reputed to influence cell adhesion and proliferation, the sample surface was characterized in terms of roughness, contact angle, surface morphology and chemistry. A correlation between cellular behavior and contact angle was established but none could be observed with surface roughness. Glass-ceramics were found to be much too hydrophilic while PICNs were slightly too hydrophobic compared to titanium and zirconia. These results highlight the complexity of the influence of material properties on cell behavior. The impact of PICN encouraging in vitro results with HGFs and HGKs now needs to be clinically investigated in regards to gingival tissues and implant health before recommending their routine use as transgingival prosthesis components, particularly for bone-level implants.

updated on 5/8/26

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