The regeneration of oral maxillofacial hard tissues is currently one of the issues of most concern in public health. This complex process involves a variety of cell types residing in a specialized microenvironment known as the adult stem cell niche in living organisms. Within this niche, adult stem cells are considered to play a central role in the regeneration of hard tissues, which undergo rapid proliferation and differentiation into progenitor cells to replace lost tissue, throughout postnatal life. Their fate is tightly regulated by the niche factors secreted by the nonstem niche cells present within the same microenvironment. Over the past decades, the advent of lineage tracing techniques has revolutionised the in vivo study of cell dynamics. Through tissue- and temporally-specific labelling of Cre-expressing cells, this method enables researchers to depict the defined cell fates and differentiation trajectories. The present review summarises the progress made in lineage tracing studies of hard tissue formation cell populations residing in the oral and maxillofacial regions, with a focus on stem cells, progenitor cells and niche cells. The aim is to provide new clues for future research endeavours.
 
Keywords: adult stem cell niche, hard tissue formation, lineage tracing, niche cell, oral maxillofacial region, progenitor cell, stem cell

Objective: To assess the impact of incorporating various weight fractions of nanometre-sized particulate fillers on specific properties of microfilled composite resin.
Methods: Microfilled composite resin was prepared by mixing 29 wt.% of resin matrix (Bis- GMA/TEGDMA) with the 71 wt.% of silane treated particulate fillers (Ø 0.4 μm). Then, various fractions of nanometre-sized (180 nm) fillers (0, 5, 10, 15, 20, 25, 30 and 35 wt.%) were added gradually using a high-speed mixing machine. For each composite resin, flexural properties (n = 8) were evaluated using a three-point bending test on a universal testing machine (ISO standard 4049). Fourier transform infrared (FTIR)-spectrometry was used to calculate the degree of monomer conversion (DC%). Surface microhardess (Vickers) was also determined. Surface gloss was measured before and after polishing (4,000-grit paper). A two-body wear test was performed in a ball-on-flat configuration using a chewing simulator with 15,000 cycles. A non-contact 3D optical profilometer was utilised to measure wear depth. An analysis of variance (ANOVA) was applied to interpret the results statistically, then a post hoc Tukey analysis was performed.
Results: ANOVA revealed that the fraction of nanofillers had a significant effect (P < 0.05) on flexural modulus, DC%, microhardness, gloss and wear depth. The group without nanofillers showed the highest DC% (56.6%), gloss after polishing (76.2 GU) and wear resistance (24.2 μm) values, whereas the group with 35 wt.% of nanofillers had the highest flexural modulus (9 GPa) and microhardness (70 VH).
Conclusion: It is beneficial to add nanofillers to microfilled composite resin; however, it is essential to assess the proportion ratio carefully. Optimising all the properties of composite resin at once with just one formulation is challenging.
 
Keywords: microfilled composite resin, nanofiller fractions, properties

Osteonecrosis involving the permanent tooth germ in primary dentition is a rare condition that can affect dental and maxillofacial development without correct intervention. This case report presents the successful recovery from drug-induced mandibular osteonecrosis involving the permanent tooth germ in a child. A healthy 4-year-old Chinese girl visited the clinic with an unhealed gingival wound and alveolar bone exposure of the missing primary molar area after 1-day arsenic trioxide sealing during pulp therapy. Radiographic examinations indicated inflammation and sequestrum formation in the jaw. The diagnosis was mandibular osteonecrosis. The treatment plans involved sequestrectomy without extended curettage and removal of the affected permanent tooth germ with systemic antibiotic therapy. A 6-year follow-up revealed no recurrence of the lesion or complications, a gradual increase in bone density of the osteonecrosis area and the development of adjacent permanent tooth germs. A conservative treatment regimen without extended curettage may be an option for young patients with jaw osteonecrosis.
 
Keywords: arsenic trioxide, deciduous teeth, osteonecrosis, sequestrectomy, tooth germ

Objective: To compare the sequential healing of maxillary sinuses grafted with two different xenogeneic bone substitutes processed at either a low (300°C) or high (1200ºC) temperature.
Methods: A sinus augmentation procedure was performed bilaterally in 20 rabbits and two different xenogeneic bone grafts were randomly used to fill the elevated spaces. Healing was studied after 2 and 10 weeks, in 10 rabbits during each period.
Results: After 2 weeks of healing, very small amounts of new bone were observed in both groups, and were mainly confined to close to the sinus bone walls and osteotomy edges. After 10 weeks of healing, new bone was found in all regions, with higher percentages in those close to the bone walls and to the osteotomy. In this period of healing, the proportion of new bone in the 300°C group was 20.0% ± 4.3%, and in the 1200ºC group it was 17.2% ± 4.3% (P = 0.162). In the 1200ºC group, translucent, dark fog-like shadows in regions of the grafts were hiding portions of new bone (interpenetrating bone network).
Conclusion: Both biomaterials provided conditions that allowed bone growth within the elevated space, confirming that both biomaterials are suitable to be used as a graft for sinus floor augmentation.
 
Key words: animal study, bone healing, histology, sinus floor augmentation, sinus membrane
 

Objective: To investigate the differences between temporomandibular articular fossa bone surface and the envelope surface of the mandibular condyle movement.
Methods: Thirty-four healthy adults underwent skull base and mandible scans using CBCT and performed mandibular border movement using the mandibular movement recording system. Landmarks of the fossa and tubercle were indicated and distance and angle parameters were measured on the 3D models reconstructed from the CBCT. The condyle movement envelope surfaces were formed according to models reconstructed from CBCT and the mandibular movement trajectory using computer simulation. The highest and lowest points of the envelope surface were indicated to create parameters. The data were analysed using a paired t test in SPSS (version 24.0, IBM, Armonk, NY, USA).
Results: The mandibular fossa bone surface was statistically different to the envelope surface for the height of the first peak of the envelope surface (3.280 ± 1.319 mm) and depth of the mandibular fossa (6.338 ± 2.389 mm) (the ratio was 51.75%), the height of the second peak of the envelope surface (1.463 ± 0.745 mm) and the height of the tubercle (2.000 ± 0.968 mm) (the ratio was 73.15%), and the downwards angle of the envelope surface (25.933 ± 7.539 degrees) and the posterior slope angle of the articular tubercle (35.059 ± 5.224 degrees) (the ratio was 73.97%).
Conclusion: The downwards angle of the envelope surface was statistically significantly smaller than the posterior slope angle of the articular tubercle, suggesting that the condyle movement is flatter than the mandibular fossa bone surface.
 
Key words: artificial fossa component, condyle movement, envelope surface, mandibular fossa bone surface, temporomandibular joint