Influence of heat stress to matrix  on bone formation.
OBJECTIVE
It is important to know the etiology of implant failure. It has been reported that heat stress during drilling was one of the causes for failure and the threshold was 47 degrees C. However, clinically, we encounter cases in which overheating does not seem to affect osseointegration eventually. The purpose of this study was to assess histologically the spatio-temporal effect of heat stress on bone formation after overheating the bone matrix.


METHODS
Rat calvarial bone was heated to 37 degrees C, 43 degrees C, 45 degrees C and 48 degrees C for 15 min by a temperature stimulator. Paraffin sections were prepared 1, 3 and 5 weeks after heating and investigated histologically under light microscopy. Hematoxylin and eosin staining, alkaline phosphatase (ALP), osteopontin (OPN), heat shock protein 27 (Hsp27) and heat shock protein 70 (Hsp70) immunohistochemistry and tartrate-resistant acid phosphatase (TRAP) enzyme histochemistry were carried out. The area of dead osteocytes was calculated and statistically analyzed. Apoptotic osteocytes were detected by the terminal deoxynucleotidyltransferase-mediated dUTP nick end-labeling (TUNEL) method.


RESULTS
Along with the temperature increase, the area of dead osteocytes increased and regeneration of the periosteal membrane was delayed. Hsps- and TUNEL-positive cells were only seen in the 48 degrees C group. Spatio-temporal changes of TRAP- and ALP-positive cell numbers were observed, while OPN expression was mostly absent. Even after 48 degrees C stimulation, bone formation on the calvarial surface was observed after 5 weeks.


CONCLUSIONS
Although there was a temperature-dependent delay in bone formation after heat stress, the 48 degrees C heat stress did not obstruct bone formation eventually. This delay was probably caused by slow periosteal membrane regeneration.
Yoshida
Keiko
K
Oral Implant Clinic, Niigata University Medical and Dental Hospital, Niigata, Japan.
Uoshima
Katsumi
K
Oda
Kimimitsu
K
Maeda
Takeyasu
T
D000135:Acid Phosphatase / Q000378:metabolism; D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism; D006358:Hot Temperature; D007124:Immunoenzyme Techniques; D020287:In Situ Nick-End Labeling; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D010011:Osteocytes / Q000378:metabolism*; D010012:Osteogenesis / Q000502:physiology*; D053495:Osteopontin / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012886:Skull / Q000601:surgery*; D013194:Staining and Labeling; D000071681:Tartrate-Resistant Acid Phosphatase
D015415:Biomarkers; D006360:Heat-Shock Proteins; D007527:Isoenzymes; D053495:Osteopontin; D000469:Alkaline Phosphatase; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase