Xu Hockin H K, Weir Michael D, Sun Limin
Department of Endodontics, Prosthodontics and Operative Dentistry, University of Maryland Dental School, 650 West Baltimore Street, Baltimore, MD 21201, USA.
Dent Mater. 2009 Apr;25(4):535-42. doi: 10.1016/j.dental.2008.10.009. Epub 2008 Dec 20.
Secondary caries and restoration fracture are the two main challenges facing tooth cavity restorations. The objective of this study was to develop a composite using tetracalcium phosphate (TTCP) fillers and whiskers to be stress-bearing, and to be "smart" to increase the calcium (Ca) and phosphate (PO(4)) ion release at cariogenic pH.
TTCP was ball-milled to obtain four different particle sizes: 16.2, 2.4, 1.3, and 0.97 microm. Whiskers fused with nano-sized silica were combined with TTCP as fillers in a resin. Filler level mass fractions varied from 0 to 75%. Ca and PO(4) ion releases were measured vs. time at pH of 7.4, 6, and 4. Composite mechanical properties were measured via three-point flexure before and after immersion in solutions at the three pH.
TTCP composite without whiskers had flexural strength similar to a resin-modified glass ionomer (Vitremer) and previous Ca-PO(4) composites. With whiskers, the TTCP composite had a flexural strength (mean+/-S.D.; n=5) of (116+/-9)MPa, similar to (112+/-14)MPa of a stress-bearing, non-releasing hybrid composite (TPH) (p>0.1). The Ca release was (1.22+/-0.16)mmol/L at pH of 4, higher than (0.54+/-0.09) at pH of 6, and (0.22+/-0.06) at pH of 7.4 (p<0.05). PO(4) release was also dramatically increased at acidic pH. After immersion, the TTCP-whisker composite matched the strength of TPH at all three pH (p>0.1); both TTCP-whisker composite and TPH had strengths about threefold that of a releasing control.
The new TTCP-whisker composite was "smart" and increased the Ca and PO(4) release dramatically when the pH was reduced from neutral to a cariogenic pH of 4, when these ions are most needed to inhibit caries. Its strength was two- to threefold higher than previously known Ca-PO(4) composites and resin-modified glass ionomer. This composite may have the potential to provide the necessary combination of load-bearing and caries-inhibiting capabilities.
继发龋和修复体折断是牙体窝洞修复面临的两大主要挑战。本研究的目的是开发一种使用磷酸四钙（TTCP）填料和晶须的复合材料，使其能够承受应力，并具有“智能性”，即在致龋性pH值下增加钙（Ca）和磷酸根（PO₄）离子的释放。
对TTCP进行球磨以获得四种不同的粒径：16.2、2.4、1.3和0.97微米。将与纳米二氧化硅融合的晶须与TTCP作为填料加入树脂中。填料水平质量分数从0%到75%不等。在pH值为7.4、6和4的条件下，测量Ca和PO₄离子随时间的释放量。通过三点弯曲试验测量复合材料在三种pH值的溶液中浸泡前后的力学性能。
不含晶须的TTCP复合材料的弯曲强度与树脂改性玻璃离子水门汀（Vitremer）和先前的Ca-PO₄复合材料相似。添加晶须后，TTCP复合材料的弯曲强度（平均值±标准差；n = 5）为（116±9）MPa，与一种能承受应力且不释放离子的混合复合材料（TPH）的（112±14）MPa相似（p>0.1）。在pH值为4时，Ca释放量为（1.22±0.16）mmol/L，高于pH值为6时的（0.54±0.09）mmol/L和pH值为7.4时的（0.22±0.06）mmol/L（p<0.05）。在酸性pH值下，PO₄释放量也显著增加。浸泡后，TTCP-晶须复合材料在所有三种pH值下的强度均与TPH匹配（p>0.1）；TTCP-晶须复合材料和TPH的强度均约为可释放对照材料的三倍。
新型TTCP-晶须复合材料具有“智能性”，当pH值从中性降低到致龋性pH值4时，Ca和PO₄的释放量显著增加，而在这个pH值下最需要这些离子来抑制龋齿。其强度比先前已知的Ca-PO₄复合材料和树脂改性玻璃离子水门汀高出两到三倍。这种复合材料可能有潜力提供承重和抑制龋齿能力的必要组合。
