The Influence of Thickness on the Mechanical Behaviors of 3D Printing Resins for Orthodontic Retainers.

This study aimed to evaluate the mechanical behaviors of thermoformed and 3D-printed retainers with different thicknesses. Thermoformed retainers (Duran) and 3D-printed retainers (Dental LT Clear V2 and NextDent Ortho Flex) were fabricated at thicknesses of 0.5, 0.75, and 1 mm. Five samples of each material were subjected to compression, tensile, and flexural testing with the universal testing machine (Instron Ltd., Buckinghamshire, England). The results revealed that the mechanical behaviors were significantly influenced by thickness in each type of material. The increased thickness tended to increase strength and modulus in all three tests. However, Dental LT Clear V2 and Duran showed that flexural strength and modulus were inversely related to thickness. The compressive test revealed significantly greater compressive resistance in 3D-printed groups, except for the NextDent Ortho Flex at 0.5 mm. The tensile test showed that Dental LT Clear V2 at all thicknesses demonstrated significantly higher tensile strength and modulus, while NextDent Ortho Flex was significantly lowest at any thickness in tensile and flexural properties. In conclusion, the thickness significantly influenced the mechanical behaviors of the 3D-printed retainers. The 0.75 mm thickness of Dental LT Clear V2 could be considered as an alternative to fabricated retainers due to its similar mechanical properties compared with the thermoformed material.

Game-based learning in orthodontic education: a systematic review.

OBJECTIVE: To evaluate educational impact of game-based learning (GBL) in orthodontic education. METHODS: A systematic search was undertaken across four databases (Scopus, PubMed, ProQuest Dissertations & Theses Global, and Google Scholar) to identify relevant articles published from January 2000 to December 2023. Additionally, the reference lists of identified literature were examined to further search for relevant literature. The last search was performed on 28 January 2024. RESULTS: Following the article selection process, seven articles were included in this systematic review, comprising four randomized control trials and three questionnaire surveys. Six articles were assessed to have a moderate risk of biases, whereas one research exhibited a low risk of bias. GBL interventions assessed in five articles were designed in digital format, while one study implemented evaluated traditional learning, and another employed a card game format. Two RCTs indicated a greater effectiveness of GBL in enhancing learner performance compared to traditional learning methods, while one article found no significant difference. Across all articles, positive perceptions of GBL were consistently highlighted at both undergraduate and postgraduate levels. CONCLUSION: This systematic review supports the potential of GBL in orthodontic education. The implementation of GBL is recommended to integrate entertaining and educational elements, fostering learner performance within engaging learning environments. However, it is imperative to acknowledge that the overall quality of evidence is limited, primarily due to the moderate risk of biases identified in six of the included articles. Consequently, further high-quality experimental studies are required to validate the effectiveness of GBL in orthodontic education.

The accuracy of virtual setup in simulating treatment outcomes in orthodontic practice: a systematic review.

OBJECTIVES: To evaluate the accuracy of virtual orthodontic setup in simulating treatment outcomes and to determine whether virtual setup should be used in orthodontic practice and education. MATERIALS AND METHODS: A systematic search was performed in five electronic databases: PubMed, Scopus, Embase, ProQuest Dissertations & Theses Global, and Google Scholar from January 2000 to November 2022 to identify all potentially relevant evidence. The reference lists of identified articles were also screened for relevant literature. The last search was conducted on 30 November 2022. RESULTS: This systematic review included twenty-one articles, where all of them were assessed as moderate risk of bias. The extracted data were categorized into three groups, which were: (1) Virtual setup and manual setup; (2) Virtual setup and actual outcomes in clear aligner treatment; (3) Virtual setup and actual outcomes in fixed appliance treatment. There appeared to be statistically significant differences between virtual setups and actual treatment outcomes, however the discrepancies were clinically acceptable. CONCLUSION: This systematic review supports the use of orthodontic virtual setups, and therefore they should be implemented in orthodontic practice and education with clinically acceptable accuracy. However, high-quality research should be required to confirm the accuracy of virtual setups in simulating treatment outcomes.

Technology-enhanced simulation-based learning in orthodontic education: A scoping review.

INTRODUCTION: Technology-enhanced simulations seem to be effective in dentistry, as they can support dental students to improve competencies in simulated environments. However, implementation of this technology in orthodontic education has not been reviewed. OBJECTIVE: This scoping review aimed to comprehensively summarize the use of technology-enhanced simulations in orthodontic practice. METHODS: A systematic search was conducted to identify literature on technology-enhanced simulation-based learning in orthodontic education published from 2000 to 2021. The search was conducted up to September 2021 to identify articles from Scopus, Embase, PubMed, ProQuest Dissertations & Theses Global, Google Scholar and the reference lists of identified articles. RESULTS: The search identified 177 articles. Following the inclusion and exclusion criteria, 16 articles of 14 digital simulators were included in this review. The findings demonstrated an increasing use of technology-enhanced simulations in orthodontic education. They were designed in several formats, including three-dimensional virtual format, augmented reality, virtual reality, automaton, haptic, and scenario-based simulations. These simulations were implemented in varied areas of orthodontics including diagnosis and treatment planning, bracket positioning, orthodontic procedures, facial landmark, removable appliance and cephalometric tracing. Most included articles demonstrated the development process without outcome evaluation. Six studies provided outcome evaluations at reaction or learning levels. None of them provide the evaluation at behaviour and results levels. CONCLUSION: Insufficient evidence has been generated to demonstrate the effectiveness of technology-enhanced simulations in orthodontic education. However, high-fidelity computer-based simulations together with robust design research should be required to confirm educational impact in orthodontic education.

Significance of Non-Statistically Significant Results in the Prediction of Oral Health-Related Quality of Life in Orthodontic Patients: A Survey Using Two Linking Questionnaires.

Patients with a fixed orthodontic appliance may have difficulties in maintaining good oral health-related quality of life (OHRQoL), and evaluating self-perceived OHRQoL in orthodontic patients could be challenging for their orthodontists. Therefore, this research was conducted to investigate whether orthodontic postgraduates would accurately evaluate the OHRQoL of their patients. Two self-administered questionnaires were designed for patients to rate their OHRQoL and for their orthodontic postgraduates to evaluate them on OHRQoL. All pairs of patients and their orthodontic postgraduates were requested to independently complete the questionnaires. Pearson's correlation and multiple linear regression were performed to determine the relationships of the variables and to identify significant predictors on OHRQoL, respectively. There were 132 pairs of orthodontic patients and their residents who completed the questionnaires. There were no significant correlations between OHRQoL perceived by patients and evaluated by their orthodontic postgraduates in all aspects of treatment needs and dietary difficulties (p > 0.05). In addition, the regression model demonstrated no significant predictors for the self-perceived treatment needs and dietary difficulties of orthodontic patients. There seemed to be challenges for orthodontic postgraduates to evaluate their patients' oral health-related quality of life. Therefore, the OHRQoL measures should be increasingly implemented in orthodontic education and practice in order to enhance the concept of patient-centered care.

Technology-enhanced simulation-based learning in orthodontic education: A scoping review

ABSTRACT Introduction: Technology-enhanced simulations seem to be effective in dentistry, as they can support dental students to improve competencies in simulated environments. However, implementation of this technology in orthodontic education has not been reviewed. Objective: This scoping review aimed to comprehensively summarize the use of technology-enhanced simulations in orthodontic practice. Methods: A systematic search was conducted to identify literature on technology-enhanced simulation-based learning in orthodontic education published from 2000 to 2021. The search was conducted up to September 2021 to identify articles from Scopus, Embase, PubMed, ProQuest Dissertations & Theses Global, Google Scholar and the reference lists of identified articles. Results: The search identified 177 articles. Following the inclusion and exclusion criteria, 16 articles of 14 digital simulators were included in this review. The findings demonstrated an increasing use of technology-enhanced simulations in orthodontic education. They were designed in several formats, including three-dimensional virtual format, augmented reality, virtual reality, automaton, haptic, and scenario-based simulations. These simulations were implemented in varied areas of orthodontics including diagnosis and treatment planning, bracket positioning, orthodontic procedures, facial landmark, removable appliance and cephalometric tracing. Most included articles demonstrated the development process without outcome evaluation. Six studies provided outcome evaluations at reaction or learning levels. None of them provide the evaluation at behaviour and results levels. Conclusion: Insufficient evidence has been generated to demonstrate the effectiveness of technology-enhanced simulations in orthodontic education. However, high-fidelity computer-based simulations together with robust design research should be required to confirm educational impact in orthodontic education.

RESUMO Introdução: Simulações aprimoradas por tecnologia parecem ser eficazes em Odontologia, pois podem ajudar os estudantes a melhorar suas competências em ambientes simulados. No entanto, a implementação dessa tecnologia na educação ortodôntica ainda não foi revisada. Objetivo: A presente revisão de escopo teve como objetivo resumir, de forma abrangente, o uso de simulações aprimoradas por tecnologia na prática ortodôntica. Métodos: Uma busca sistemática foi realizada para identificar publicações de 2000 a 2021 sobre aprendizado na educação ortodôntica baseado em simulação aprimorada por tecnologia. A busca foi realizada até setembro de 2021 para identificar artigos na Scopus, Embase, PubMed, ProQuest Dissertations & Theses Global, Google Scholar e nas listas de referências dos artigos identificados. Resultados: A busca identificou 177 artigos. Foram incluídos nessa revisão 16 artigos, com 14 simulações digitais, que atenderam aos critérios de inclusão e exclusão. Os resultados demonstraram um uso crescente de simulações aprimoradas por tecnologia na educação ortodôntica. Elas foram projetadas em vários formatos, incluindo formato tridimensional virtual, realidade aumentada, realidade virtual, autômato, háptico e simulações baseadas em cenários. Essas simulações foram implementadas em diversas áreas da Ortodontia, incluindo diagnóstico e planejamento de tratamento, posicionamento de braquetes, procedimentos ortodônticos, identificação de pontos de referência faciais, aparelhos removíveis e traçados cefalométricos. A maioria dos artigos incluídos demonstrou o processo de desenvolvimento, sem avaliar os resultados. Seis estudos forneceram avaliações de resultados em níveis de reação ou aprendizado. Nenhum deles forneceu a avaliação em níveis de comportamento e resultados. Conclusão: Não foram geradas evidências suficientes para demonstrar a eficácia das simulações aprimoradas por tecnologia na educação ortodôntica. No entanto, simulações de alta fidelidade baseadas em computador, juntamente com pesquisas robustas de design, são necessárias para confirmar o impacto educacional na área ortodôntica.

A Novel Alveolar Distractor Incorporating Nickel-Titanium Alloy Springs: A Preliminary In Vitro Study.

A new design of an alveolar distractor using nickel−titanium (NiTi) open-coil springs was developed and investigated to produce distraction forces against the tensile forces of porcine attached gingiva to simulate human gingiva. We subjected 15 mm long NiTi open-coil springs (Highland and ORMCO) with three levels of forces (light, medium and heavy) to mechanical testing in a 37 ± 1 °C water bath. Ten strips of porcine mandibular attached gingiva were subjected to tensile tests to determine the resistance force. The forces from the springs were compared with the tensile forces from the porcine attached gingiva. Data between groups were analyzed with independent-samples T-tests (p-value < 0.05). The tensile strength and the Young modulus were greater in buccal compared to lingual porcine attached gingiva. Compared to other spring dimensions and companies, forces generated from 0.014 × 0.036″ ORMCO springs were the highest and could overcome the tensile resistance from porcine attached gingiva over the longest distraction range of 1.6 mm. This preliminary in vitro study introduced a new design of an alveolar distractor incorporated with NiTi open-coil springs that could generate light and continuous forces to overcome the resistance from porcine attached gingiva.

The Effects of Temperature and Time of Heat Treatment on Thermo-Mechanical Properties of Custom-Made NiTi Orthodontic Closed Coil Springs.

Nickel-Titanium (NiTi) springs have been increasingly used in orthodontics; however, no optimum condition of heat treatment has been reported. Therefore, this research was conducted to determine the optimum heat-treatment temperature and duration for the fabrication of NiTi-closed coil springs by investigating their effects on thermo-mechanical properties. As-drawn straight NiTi wires of 0.2 mm diameter were used to fabricate closed coil springs of 0.9 mm lumen diameter. The springs were heat-treated at three different temperatures (400, 450, and 500 °C) with three different durations (20, 40, and 60 min). Electron Probe Micro-Analysis (EPMA) and Differential Scanning Calorimetry (DSC) were used to investigate element composition and thermo-mechanical properties, respectively. Custom-made NiTi closed coil springs composed of 49.41%-Ti and 50.57%-Ni by atomic weight, where their DSC curves of 500 °C presented the obvious endothermic and exothermic peaks, and the austenite finish temperature (Af) were approximately 25 °C. With increasing temperature, deactivation curves presented decreased plateau slopes generating higher superelastic ratios (SE ratios). At 500 °C, closed coil springs showed superelastic tendency with lower stress hysteresis. The thermo-mechanical properties were significantly influenced by heat-treatment temperature rather than duration. The optimum parameter appeared to be 500 °C for 40 min to produce appropriate force delivery levels, relatively low plateau slope, and lower hysteresis for orthodontic use.

The Implementation of PROMs/PREMs in the Assessment of Orthodontic Treatment Outcomes: A Questionnaire Survey.

Objectives: The aim of this study was to explore the impact of self-perceived treatment outcomes and experiences on psychological aspects, reflecting the importance of patient-reported outcome measures (PROMs) and patient-reported experience measures (PREMs) in orthodontic practice. Materials and Methods: A questionnaire was constructed using the PROMs/PREMs concepts. It contained five parts: "Demographic data", "Self-perceived esthetics", "Self-perceived functional concern", "Satisfaction of treatment procedures", and "Psychological aspect". The questionnaire was piloted in five experts and 50 orthodontic patients to ensure its quality, using content validity, test-retest reliability, and Cronbach's alpha. The validated version was provided to patients who had a complete fixed appliance orthodontic treatment. These data were analyzed using descriptive statistics, Mann-Whitney U test, and Spearman correlation. In addition, a multiple linear regression was used to analyze whether there were any influential factors on a psychological aspect. Statistical significance was taken at P < 0.05. Results: A total of 271 respondents completed the questionnaire. They tended to have positive perceptions toward the outcomes of orthodontic treatment. There was a significant difference in self-perceived esthetics between the male and female groups. Self-perceived esthetic and functional concerns as well as satisfaction of treatment procedures were found to have significant correlations with the psychological aspect. Sex and self-perceived esthetics were also found to be significant predictors of the psychological aspect. Conclusion: PROMs/PREMs should be considered as an important tool to assess treatment outcomes in orthodontic practice. There appeared to be significant impact of self-perceived esthetics on psychological aspects. Consequently, PROMs and PREMs should be introduced in orthodontic postgraduate programs to enhance the concept of patient-centered care in orthodontic practice.

Self-perceived Needs for Orthodontic Retreatment among Dental Students: A Qualitative Study.

AIMS: The aims of this research were to explore perceptions of Mahidol dental students toward orthodontic retreatment and to examine whether there were any influential factors in a dental school toward their decision to receive the retreatment. MATERIALS AND METHODS: Mahidol dental undergraduates who were requesting orthodontic retreatment were recruited into this research. A semi-structure interview with a topic guide was conducted to collect in-depth information. All responses were recorded using a digital voice recorder and transcribed using a verbatim transcription technique. The data were then analyzed using a framework analysis. RESULTS: The common reasons for requesting orthodontic retreatment among dental students were self-perceived esthetic and functional concerns. Knowledge and experiences of dental students could raise awareness of dental problems, so they were likely to detect even a small defect of their teeth. The students also worried if their dental problems were presented to patients or other dental students. In addition, although they were requesting for orthodontic retreatment, they felt quite worried with the complications they had learned from the dental program. The students also reported that these concerns could affect their psychological well-being. CONCLUSION: Dental knowledge and experiences as well as surrounding people such as their peers and patients in a dental school seemed to have impact on awareness of dental problems and a decision to receive orthodontic retreatment.

The effect of LED photobiomodulation on the proliferation and osteoblastic differentiation of periodontal ligament stem cells: in vitro.

BACKGROUND: The aim of this study was to investigate the influence of three different light-emitting diode (LED) wavelengths on the proliferation and osteoblastic differentiation of periodontal ligament stem cells (PDLSCs) in vitro. METHODS: PDLSCs seeded on 96- and 24-well plates, for proliferation and osteoblastic differentiation, respectively, were irradiated daily by LED light with peak emission wavelengths of 630, 680, and 830 nm at constant energy densities of 3.5 J/cm2. Cultures were grown for 8 days for the proliferation assay, 10 days for the alkaline phosphatase (ALP) assay, and 28 days for Alizarin red staining. Mitochondrial activity, ALP enzyme level, and the ability to form calcium phosphate deposits were measured and compared across cultures. RESULTS: Results obtained from statistical analysis of the experimental data indicated that the rate of proliferation (P < 0.05) in 830-nm irradiated cultures were significantly higher than the control samples at day 6 and 8; whereas, for the 630- and 680-nm groups, test results showed lower proliferation rates at day 8. For osteoblastic differentiation, significantly greater mineralization than the control samples was detected in the red-light groups (630 and 680 nm) during the late differentiation period (P < 0.001), which was supported by a higher ALP activity of the 630- and 680-nm groups in the early stage (P < 0.01). CONCLUSION: The results of this study demonstrate that the PDLSCs responded differently to specific LED wavelengths. For enhancing cellular proliferation, 830-nm LED irradiation was more effective. On the other hand, the wavelengths of 630 and 680 nm were better for stimulating osteoblastic differentiation.

Comparison of friction forces between stainless orthodontic steel brackets and TiNi wires in wet and dry conditions.

In sliding mechanics, frictional force is an important counter-balancing element to orthodontic tooth movement, which must be controlled in order to allow application of light continuous forces. The purpose of this study was to compare the frictional forces between a stainless steel bracket and five different wire alloys under dry and wet (artificial saliva) conditions. TiNi, TiNiCu, TiNiCo, commercial wires A and commercial wires B with equal dimensions of 0.016×0.022'' were tested in this experiment. The stainless steel bracket was chosen with a slot dimension of 0.022''. Micro-hardness of the wires was measured by the Vickers micro-hardness test. Surface topography of wires was measured by an optical microscope and quantified using surface roughness testing. Static and kinetic friction forces were measured using a custom-designed apparatus, with a 3-mm stretch of wire alloy at a crosshead speed of 1mm/min. The static and dynamic frictions in the wet condition tended to decrease more slowly than those in the dry condition. Therefore, the friction of TiNiCu and commercial wires B would increase. Moreover, these results were associated with scarred surfaces, i.e. the increase in friction would result in a larger bracket microfracture. From the results, it is seen that copper addition resulted in an increase in friction under both wet and dry conditions. However, the friction in the wet condition was less than that in dry condition due to the lubricating effect of artificial saliva.

Evaluation of Stress Distribution on Implant-Retained Auricular Prostheses: The Finite Element Method.

PURPOSE: The purpose of this study was to evaluate stress distribution around two craniofacial implants in an auricular prosthesis according to the removal forces. Three attachment combinations were used to evaluate the stress distribution under removal forces of 45 and 90 degrees. MATERIALS AND METHODS: Three attachment designs were examined: (1) a Hader bar with three clips; (2) a Hader bar with one clip and two extracoronal resilient attachments (ERAs); and (3) a Hader bar with one clip and two Locators. The removal force was determined by means of an Instron universal testing machine with a crosshead speed of 10 mm/minute. All three designs were created in three dimensions using SolidWorks. The applied removal force and the models were then introduced to finite element software to analyze the stress distribution. RESULTS: The angle of removal force greatly affected the magnitude and direction of stress distribution on the implants. The magnitude of stress under the 45-degree removal force was higher than the stress at 90 degrees. The combination of the 1,000-g retention clip and 2,268-g retention Locator exhibited the highest stress on the implant flange when the removal force was applied at 45 degrees. CONCLUSION: The removal angle greatly influences the amount of force and stress on the implants. Prosthodontists are encouraged to inform patients to remove the prosthesis at 90 degrees and, if possible, use a low-retentive attachment to reduce stress.

The effect of light-emitting diode irradiation at different wavelengths on calcification of osteoblast-like cells in 3D culture.

This study aimed to investigate the effect of four different light-emitting diode (LED) wavelengths on calcification and proliferation of osteoblast-like cells in vitro. MC3T3-E1 cells were seeded within three-dimensional collagen scaffolds and irradiated daily by LED light with peak emission wavelengths of 630-, 680-, 760- and 830-nm at constant fluency of 3.1 J/cm(2) (irradiance intensity 2 mW/cm(2)). Cultures were measured for calcium content at day 0, 7, 14, 21, 28, 35 and 42. The significant enhancement in calcium content was observed at the early stage of culture (days 7 and 14) (p<;0.05). After that, the calcium content of irradiated groups was similar to that of the controls group. This suggests the transient effect of light irradiation on osteoblastic cell calcification. Only 680-nm irradiated samples revealed a significant enhancement of calcium content until the late stages of culture (from days 21 to 42) (p<;0.001). The cyclin D mRNA expression that was investigated 3 hours after stimulation at day3 also show that the 680-nm LED irradiation can enhance cyclin D expression more than others. For enhancing bone mineralization, LED irradiation at the 680-nm is more effective than those at 630-, 760- and 830-nm. Further studies should be investigated in order to obtain the most effective parameters of LLLI on bone regeneration in clinical setting.

Photobiomodulation accelerates orthodontic alignment in the early phase of treatment.

BACKGROUND: Numerous strategies have been proposed to decrease the treatment time a patient requires in orthodontic treatment. Recently, a number of device-accelerated therapies have emerged in orthodontics. Photobiomodulation is an emerging area of science that has clinical applications in a number of human biological processes. The aim of this study was to determine if photobiomodulation reduces the treatment time in the alignment phase of orthodontic treatment. METHODS: This multicenter clinical trial was performed on 90 subjects (73 test subjects and 17 controls), and Little's Index of Irregularity (LII) was used as a measure of the rate of change of tooth movement. Subjects requiring orthodontic treatment were recruited into the study, and the LII was measured at regular time intervals. Test subjects used a device which produced near-infrared light with a continuous 850-nm wavelength. The surface of the cheek was irradiated with a power density of 60 mW/cm2 for 20 or 30 min/day or 60 min/week to achieve total energy densities of 72, 108, or 216 J/cm2, respectively. All subjects were fitted with traditional orthodontic brackets and wires. The wire sequences for each site were standardized to an initial round alignment wire (014 NiTi or 016 NiTi) and then advanced through a progression of stiffer arch wires unit alignment occurred (LII<1 mm). RESULTS: The mean LII scores at the start of the clinical trial for the test and control groups were 6.35 and 5.04 mm, respectively. Multi-level mixed effect regression analysis was performed on the data, and the mean rate of change in LII was 0.49 and 1.12 mm/week for the control and test groups, respectively. CONCLUSIONS: Photobiomodulation produced clinically significant changes in the rates of tooth movement as compared to the control group during the alignment phase of orthodontic treatment.

Development and terminal differentiation of pulp and periodontal nerve elements in subcutaneous transplants of molar tooth germs and incisors of the rat.

Ectopic tooth transplants are known to receive rich innervation of local neurons, but the precise location and structural features of neurites in the pulp and periodontal ligament (PDL) of such transplants are unclear. In this experiment, the molar tooth germs of rat embryos and incisors of young rats were subcutaneously transplanted into the dorsal regions of rats and processed, at various time intervals, for immunohistochemical demonstration of neural elements. Teeth with periodontal tissue elements developed in most of the molar transplants in 6 or 8 wk and received rich innervation, including some autonomic fibres, in the pulp. Nerve elements were also confirmed to be present in the PDL of these transplants, including specialized nerve ending-like structures reminiscent of the periodontal Ruffini endings. Mechanoreceptor-like structures were also induced in the regenerated PDL of similarly transplanted incisors, although the success rate was low. We conclude that rich and highly ordered innervation of the pulp, and occasional development of mechanoreceptors in the regenerated PDL of ectopic dental transplants, imply a high probability of successful induction of teeth with both nociceptive and mechanical sensations in the ectopic tooth and/or tooth germ transplant systems, although differentiation of mechanoreceptor-like nerve endings occurred in only a few rare cases.

Growth-associated protein-43 immunohistochemical and ultrastructural changes in jaw muscle spindles of the rat following loss of occlusion.

The effects of complete loss of occlusion on the structural and functional status of these muscle spindles were investigated by immunohistochemistry either for protein gene product 9.5 (PGP 9.5) or growth-associated protein-43 (GAP-43) by light and electron microscopy. All the upper molars of 4-week-old Wistar rats were extracted and the erupted portions of the upper and lower incisors of the same animals were cut-off at the level of the interdental papilla every other day. In a control group, immunoreactivity for GAP-43 was positive in the developing annulospiral endings of 2-week-old rats, but was not detected in any of the muscle spindles after 3 weeks of age. At 4 weeks of age, the PGP 9.5 immunostained spindles had well-differentiated annulospiral endings. Ultrastructurally, these afferent endings showed lenticular or circular profiles in cross-sections, and were differentially indented into the intrafusal-fibres. The inner surfaces of the terminals formed rather smooth myoneural junctions, while the outer surfaces were covered only by basal lamina continuous with that of the underlying intrafusal muscle fibres. After the experimental elimination of occlusal contact, GAP-43 immunoreactivity reappeared in some nerve endings of muscle spindles by 3 days, and persisted for at least 28 days. During this period, the afferent-terminals exhibited various fine structural abnormalities such as irregular outlines and invaginated neuromuscular interfaces. Some sensory-terminal (ST) profiles were completely engulfed by intrafusal-fibres. However, GAP-43 expression and ultrastructural alterations became undetectable within a week of the end of incisal cutting and the recovery of incisal-contact. These data indicate that remodelling of nerve terminals in muscle spindles, as assessed by GAP-43 expression and ultrastructural changes, occurs soon after a loss of occlusion, and ceases if incisal-contact is restored. It is concluded that possible changes in jaw muscle function, as well as a sudden loss of proprioceptive sensory input from the periodontal mechanoreceptors of molars and incisors, induce the structural reorganisation of nerve terminations in jaw muscle spindles that is associated with the appearance and disappearance of GAP-43 immunoreactivity.