Mechanical and chemical characterization of contemporary occlusal splint materials fabricated with different methods: a systematic review.

OBJECTIVE: To systematically review studies on various occlusal splint materials and describe their mechanical and chemical properties. METHODS: MEDLINE (PubMed), Scopus, and Web of Science searches were conducted for in vitro studies focusing on occlusal splint materials. Two reviewers performed an assessment of the identified studies and data abstraction independently, and this was complimented by an additional hand search. The articles were limited to those in the English language that were published between January 1st, 2012, and December 1st, 2022. RESULTS: The initial search yielded 405 search results of which 274 were selected for full-text review following abstract evaluation. 250 articles that did not meet the inclusion criteria were excluded, and the remaining 25 articles (with 1 article identified from the reference lists of included articles) providing mechanical and chemical values were used in this review. Poly methyl methacrylate (PMMA) -based occlusal splint materials showed the highest values in terms of hardness, wear resistance, flexural strength, flexural modulus, e-modulus, and fracture toughness. The material group with the highest water sorption and water solubility was 3D printed (PR) splint materials. In addition, the lowest degree of double bond conversion was also observed in this group of materials. CONCLUSIONS: The outcome of this review suggests that mechanically and chemically acceptable properties can be attained with PMMA-based occlusal splint materials using both conventional and digital production methods. PR splint materials should not be considered as the primary choice for long-term treatments due to their low mechanical and chemical properties. CLINICAL RELEVANCE: This review provides clinical recommendations for selecting the appropriate material and fabrication method for occlusal splints while taking the patients' needs and the materials´ mechanical and chemical properties into account.

In vitro biocompatibility testing of 3D printing and conventional resins for occlusal devices.

OBJECTIVE: To assess and compare the in vitro biocompatibility of new resins (Keysplint Soft (Keystone Industries), NextDent Ortho Rigid (3D System), and Freeprint Splint (Detax)) and traditional resins (Orthocryl (Dentaurum)) used for dental splints. METHODS: Standardized discs (n = 40) and 1:1, 1:2, and 1:4 extracts of the tested materials were prepared. Human gingival fibroblasts (hGFs) were isolated from gingival tissues. Different biological tests were carried out, including MTT assays to assess cell metabolic activity, cell migration assays, cell cytoskeleton staining, cell apoptosis, generation of intracellular reactive oxygen species (ROS), and scanning electron microscopy (SEM). Statistical analyses were performed using one-way ANOVA and Tukey's post hoc test (p<0.05). RESULTS: MTT experiments showed that Freeprint Splint significantly reduces the hGF metabolic activity (***p<0.001), whereas SEM analysis showed almost no cells adhered on its surface. Cell migration was significantly lower after exposure to undiluted extracts of Freeprint Splint at 48 and 72 h (***p<0.001). Cell cytoskeleton staining assays showed fewer attached cells in 1:1 and 1:2 dilutions of Freeprint Splint. Annexin-V and 7-AAD staining assays showed that only cells exposed to Keysplint Soft extracts displayed similar cell viability to the control group. Finally, ROS levels detected in undiluted extracts of all resins were significantly enhanced compared to the control group (***p<0.001). CONCLUSIONS: The 3D-printed resins and the conventional dental resin showed a similar biocompatibility, except for Freeprint Splint, which was the most cytotoxic on hGFs. CLINICAL SIGNIFICANCE: 3D printing has been on the rise in recent years and its use in daily clinical practice is expanding over time. Two of the three 3D-printed resins tested in this study performed as well in the cytotoxicity tests as the conventional one, supporting their use, but caution and further testing are required.

Wear Behavior of Occlusal Splint Materials Manufactured By Various Methods: A Systematic Review.

PURPOSE: To systematically review studies on various materials and methods used for wear testing of occlusal devices and their antagonists in vitro and in vivo. METHODS: An electronic search in OVID, Web of Science, PubMed and Scopus was conducted using the following terms (MeSH words) with any synonyms and closed terms: "Splint*" OR "occlusal splint*" OR "night guard" OR "occlusal device" OR "occlusal devices" OR "deprogrammer" OR "bite splint" OR "bite plane" OR "orthotic appliance*" OR "orthotic devices" AND "wear" OR "two-body wear" OR "three-body wear" OR "tooth wear" OR "wear measurement*" OR "wear behaviour" OR "wear behavior" OR "abrasion" AND "Polymethyl Methacrylate" OR "PMMA" OR "acrylic resin*" OR "dental material*" OR "dental enamel" OR "CAD" OR "CAM" OR "PEEK" OR "material* testing". Database search was limited to English-language publications and published between 2001 and 1st of September 2021. A further hand search was done to ensure all materials were captured. RESULTS: After the removal of duplicates, 115 studies were identified, and 11 were chosen for review. Studies showed that the lowest volumetric loss was observed in PEEK occlusal device materials, whereas heat-cure, CAD-milled, and 3D printed occlusal device materials had no significant difference in wear. Vacuum-formed materials showed the highest wear among all groups. Testing parameters were found to be inconsistent across all studies. CONCLUSION: There is a need for standardization of in vitro and in vivo wear measurement and testing protocols as this study revealed a wide variety of testing protocols which potentially could influence the outcome. Polishing procedures are required for the material. Limited studies are available on 3D printed occlusal device materials and would therefore require further investigation, especially on printing build angles and settings. Further clinical studies would be advantageous to provide guidance on the selection of the best occlusal device material that would last the longest without remake.

Polymers for conventional, subtractive, and additive manufacturing of occlusal devices differ in hardness and flexural properties but not in wear resistance.

OBJECTIVES: To investigate the wear resistance of polymers for injection molding, subtractive and additive manufacturing of occlusal devices in comparison with enamel antagonist wear and material properties (i.e., hardness, flexural strength, and flexural modulus). METHODS: Injection molding was compared with milling and the additive technologies stereolithography, low force stereolithography, and digital light processing. For each material, eight specimens were produced for wear measurements. Extracted human premolars served as indenters. All samples were subjected to two series of a 2-body wear test consisting of 200,000 circular loading cycles with an applied load of 1) 20 N and 2) 50 N in a thermocycling environment (5/55 °C, 30 s, 3860 cycles, H2O). Wear resistance was characterized by means of maximum depth and volume of the resulting traces. In addition, enamel wear of the indenters and Vickers hardness, flexural strength, and flexural modulus of the polymers were determined. Wear was statistically analyzed with linear general models for repeated measures and material properties with one-way ANOVA with post-hoc Tukey-HSD tests. RESULTS: Wear of the antagonists was not influenced by the material (P ≥ 0.343). Likewise, no differences in wear resistance were found between materials after cyclic loading with 20 N or 50 N (P ≥ 0.074). Material properties investigated revealed decreased values for the resins for the additive manufacturing with the exception of flexural strength of one material. SIGNIFICANCE: Within the limitations of this in-vitro study, arylates for conventional, subtractive, and additive manufacturing of occlusal devices differ in material properties but not in wear resistance and antagonist wear.

Accuracy and its impact on fit of injection molded, milled and additively manufactured occlusal splints.

Occlusal devices to reduce symptoms of bruxism and temperomandibular disorders can nowadays be manufactured in a digital workflow but studies comparing the accuracy of those occlusal devices are still limited. Therefore, the aim of this investigation was to investigate the accuracy of injection molding compared with four computer-aided design (CAD) and computer-aided manufacturing (CAM) techniques for the manufacturing of occlusal devices. In addition, the number of contact points and retention were evaluated to assess clinical relevance. A conventional workflow consisting of alginate impression, wax-up, and injection molding (IM) and digital workflows including intraoral scanning, digital design, and subtractive manufacturing (SM) or additive manufacturing by using stereolithography (SLA), digital light processing (DLP), and material jetting (Polyjet) were investigated. Sixteen splints were fabricated with each method. The intaglio surfaces of the splints were laser scanned and superimposed with the reference data sets to analyze the surface deviations. In addition, the number of contact points after repositioning the splints on the reference model was evaluated with occlusal foil. Finally, the retention was measured in a tensile test. One-way ANOVA with post hoc Tukey tests were used for statistical analyses (α = .05). IM and SM splints demonstrated the highest manufacturing accuracy without significant differences to each other (P > .985). Additive manufactured splints revealed greater deviations with equal results for SLA and Polyjet (P > .949) and significantly higher deviations for DLP compared to all other groups (P < .002). Comparable retention force was measured for IM, SM, and SLA (P > .923), whereas Polyjet splints showed the greatest variability. IM and SM splints presented the most contact points (P = .505). Additive manufactured splints demonstrated fewer contacts without significant difference to each other (P > .116). It can be concluded, that there is no difference in manufacturing accuracy, retention, and number of contacts between IM and SM splints. AM splints demonstrated higher, however, clinically acceptable deviations.

Efecto comparativo de la Actividad Física Aeróbica y los Dispositivos ortopédicos estabilizadores en el dolor orofacial de origen musculoesqueletal en individuos con Trastornos temporomandibulares / Efeito comparativo da atividade física aeróbica e dispositivos ortopédicos estabilizadores na dor orofacial de origem musculoesquelética em indivíduos com disfunção temporomandibular / Comparative effect of aerobic physical activity and occlusal stabilization appliances on musculoskeletal orofacial pain in individuals with temporomandibular disorders

Resumen: El presente estudio evaluó la eficacia comparativa entre la actividad física aeróbica (AFA) y los dispositivos ortopédicos estabilizadores(DOE) en el manejo del dolor orofacial de origen músculo esqueletal en individuos con trastornos temporomandibulares (TTM). Participaron voluntarios dentados bimaxilar con dolor de origen músculo esqueletal con edades comprendidas entre 18 y 40 años. Para la evaluación de la variable dolor el instrumento de medición fue la escala verbal análoga. Cada uno de los grupos de tratamientos estuvo compuesto por siete individuos, los cuales fueron evaluados durante ocho (AFA) y seis (DOE) semanas respectivamente. La AFA se caracterizó por un descenso semanal significativo de 0.155 puntos en la medición del dolor. En tanto con DOE la tendencia fue aún más pronunciada que en el tratamiento con AFA, siendo esta diferencia significativa. El presente estudio demostró que, tanto la intervención con DOE como con AFA contribuyeron a la disminución del dolor orofacial de origen músculo esqueletal en voluntarios con TTM.

Resumo: O presente estudo avaliou a eficácia da atividade física aeróbica (AFA) no tratamento da dor orofacial de origem muscular esquelética em indivíduos com disfunção temporomandibular em comparação ao tratamento com dispositivo ortopédico estabilizador (DOE). Participaram voluntários com dor muscular esquelética com idade entre 18 e 40 anos e dentes bimaxilares. Para a avaliação da variável dor, o instrumento de medida foi a escala verbal analógica. Cada um dos grupos de tratamento foi composto por sete indivíduos, avaliados por oito (AFA) e seis (DOE) semanas, respectivamente. AFA foi caracterizada por uma diminuição semanal significativa de 0,155 pontos na medição da dor. Quanto ao DOE, a tendência foi ainda mais acentuada do que no tratamento com AFA, sendo essa diferença significativa. O presente estudo demonstrou que a intervenção do DOE e do AFA contribuiu para a redução da dor musculoesquelética orofacial em voluntários com TTM.

Abstract This study evaluated the efficacy of aerobic physical activity (APA) in managing musculoskeletal orofacial pain in individuals with temporomandibular disorders (TMD) compared to treatment with an occlusal stabilization appliance (OSA). Volunteers with musculoskeletal pain aged between 18 and 40 and with bimaxillary teeth involved. The analog verbal scale was used to evaluate the pain variable. Each treatment group included seven individuals evaluated for eight (APA) and six (OSA) weeks, respectively. APA showed a significant weekly decrease of 0.155 points in pain measurement. As for the OSA, the trend was even stronger than in the APA treatment-the difference was substantial. This study demonstrated that both the OSA and APA contributed to reducing musculoskeletal orofacial pain in volunteers suffering from TMD.

A progressive approach for the use of occlusal devices in the management of temporomandibular disorders.

Temporomandibular disorders (TMDs) represent a broad spectrum of conditions associated with the temporomandibular joints and the neuromuscular system. Evidence-based diagnostic criteria for various TMDs are emerging, while corresponding treatment procedures remain less clear. As a result, the clinician may be uncertain how to best care for TMD patients. The objectives of this evidence-based review were to outline the various types of occlusal devices, assess the efficacy of occlusal splints in treating TMD patients, and create a treatment rubric based on diagnostic criteria and condition severity. A select literature review as to the effectiveness and efficacy of occlusal device TMD therapy revealed that stabilization splint intervention and control treatments had a positive effect in reducing TMD-related symptoms; minimal statistically significant differences were noted between intervention and control treatments. Stabilization splints are effective as a reversible treatment for patients with TMD. Other therapies and occlusal devices may be beneficial when used for a specific TMD diagnostic protocol. A treatment rubric based on diagnostic criteria and condition severity may assist the clinician.