**8. References**

340 Biomaterials – Physics and Chemistry

Collagen fiber orientation (CFO) has been measured by circularly polarized light microscopes as one parameter to represent the collagen network and to predict post-yield energy of bone tissue.84 Hence, the post-yield behavior revealed by ERT rats' bone tissue could partially stem from a highly organized collagen fiber network. Though the information regarding collagen orientation in the present study is not available in our previous rodent studies,55,77 it has been reported that dogs after one-year of intensive endurance running (40km/day) revealed a higher organization of collagen fibers in bone tissues.87 Such highly organized collagen fibers seemed to be able to compensate for the 10% BMD decrease in running dogs. Thus, a highly organized CFO would be expected in rodent studies. As mentioned above, rats subjected to short-term freefall landing exercise (5 days, 10 or 30 times per day) from a height of 40cm also showed enhanced post-yield energy of ulnae.79 In that study, authors tried to measure the CFO of cross-sectional ulnae. Unfortunately, no difference in CFO between exercise and control groups was found. One major reason for this lack of significant results could be species difference. That is, CFO analysis might not be sensitive enough to detect biomaterial differences in rodents. To date, CFO-related analysis in bone tissue specimens have all been obtained from big mammals,88, 89 which have more mature Haversian's systems and visible osteons. However, in smaller mammals (e.g. young adult rodents), it is not possible to find Haversian's systems or complete osteon.90, 91 Per our observation, the organization of collagen fiber tends to be relatively irregular in rats and, thus, CFO analysis might not be sensitive enough to predict post-yield material properties. On the other hand, cross-links within collagen networks might be another contributor to changes in tissue post-yield behaviors.92 In an exercise-related study, Kohn and colleagues verified that cortical toughness enhanced by a 21-day ERT could be correlated with the

In addition to individually measure CFO or cross-links, the biomaterial properties (e.g. tissue strength or tissue post-yield behaviors) might benefit from better integration between collagen and its crosslinks. Related measurement methods are awaited and are worthy of

Finally, microdamage is another factor influencing tissue's post-yield behavior. Accumulation of microdamages (or microcracks) would lead to a fragile bone with lower capability in post-yield energy dissipation.84, 94 However, such accumulated microdamages seemed to be more related to aging. Also, as in CFO-related studies, microdamage studies have been more frequently done in big mammals. Whether microdamage measurement can

Endurance running is a popular aerobic activity and typical training type. However, related human studies reveal no significant benefits to bone health based on densitometric measurement of bone mineral. On the other hand, animal studies apparently indicate that ERT enhances biomaterial of bone tissue in a size-independent way. The effects of endurance running on the organic bone matrix or other parameters, as well as their

This study was supported by a grant from the National Science Council: NSC 99-2410-H-006

relationship to mechanical properties of bone tissues, are worthy of further study.


be performed on exercise-related rodent study needs further verification.

overall maturity of collagen cross-links.93

further study.

**6. Summary** 

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**17** 

*Korea* 

**Effect of the Er, Cr: YSGG Laser Parameters on Shear Bond Strength and Microstructure** 

Eun Mi Rhim1, Sungyoon Huh2, Duck Su Kim3, Sun-Young Kim4,

*3Kyung Hee University, Dental Hospital, Dept. of Conservative Dentistry, Seoul* 

*6Kyung Hee University, Dental Hospital at Gandong, Dept. of Periodontology,* 

*7Kyung Hee University Dental Hospital at Gandong, Dept. of Conservative Dentistry* 

The developments of laser technology have enabled their use in multiple dental procedures, such as soft tissue operations, composite restorations, tooth bleaching, root canal irrigation, caries removal and tooth preparations with minimal pain and discomfort (Turkmen et al., 2010) Recently, the Er,Cr:YSGG laser was recommended for minimally invasive purposes due to its precise ablation of the enamel and dentin without side-effects to the pulp and surrounding tissues. It has a 2780-nm wavelength and absorbed strongly by both water and hydroxyapatite. The sudden evaporation of bound water causes micro-explosions that blast

Previous studies reported that irregularities and the crater-shaped appearance of ablated dentin was comparable to the dentine surface after acid etching, which might promote micromechanical interlocking between dental restorative materials and the tooth surface (Visuri et al., 1996; Armengol et al., 1999; Martínez-Insua et al., 2000; Carrieri et al., 2007; Gurgan et al., 2008). Despite its efficiency, reports on the bond strengths of composite resin to a tooth substrate prepared by a laser are often confusing and contradictory. Some studies reported higher bond strengths to laser-prepared dentin than to acid-etched dentin (Visuri et al., 1996; Carrieri et al., 2007). Others have reported significantly lower bond strengths on laser preparation (Armengol et al., 1999; Martínez-Insua da Silva Dominguez et al. 2000; Gurgan Kiremitci et al. 2008) and others have reported no significant differences (Abdalla &

Generally there are three adhesive systems. The first uses 30–40% phosphoric acid to remove the smear layer (etch-and-rinse (ER) technique). This bonding mechanism to dentin

**1. Introduction** 

Davidson, 1998).

away tiny particles of the tooth (Obeidi et al., 2010).

Su-Jin Ahn5, Kyung Lhi Kang6 and Sang Hyuk Park4,7

*4Kyung Hee University, Dept. of Conservative Dentistry, Seoul,* 

*1The Catholic University of Korea, St. Paul's Hospital,* 

*5Kyung Hee University, Dental Hospital at Gandong,* 

*2Shingu University, Dept. of Dental Hygiene, Seongnam,* 

**on Human Dentin Surface** 

*Dept. of Conservative Dentistry, Seoul,* 

 *Dept. of Biomaterials & Prosthodontics,* 

mechanical strength in loss of mineral density after one-year running training? Journal of Bone and Mineral Research 1999;14:321-9.

