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Introduction: Despite the enhancing effects of hyaluronidase (HYAL) over duration of anesthesia, this enzyme could cause adverse effects when injected concomitantly with local anesthetics in dental blocks.Objective: This study aimed to assess the tissue alterations caused by a local anesthetic protocol consisting of a late HYAL injection and confirm its functional effectiveness.Materials and Methods: The protocol efficacy was proved by evaluating sensory and motor functions in rats. The sciatic nerve was blocked with 2% lidocaine (LID) with epinephrine (n = 25). Thirty minutes later, 75 TRU/ml HYAL was injected into the same site (experimental group, LID/HYAL). One week later, this protocol was repeated in the contralateral hindlimb, injecting only HYAL's vehicle (control group, LID/vehicle [LID/V]). To observe the integrity of the local tissues, histological specimens were obtained 1, 24, 48, and 72 h after treatment with LID/HYAL or LID/V (n = 16 each) and stained with hematoxylin/eosin and picrosirius red.Results: Local inflammation was similar in both groups. The integrity of the nerve fibers was preserved, in spite of some inflammation-associated injuries in the surrounding tissues. The reversible tissue disorganization caused by HYAL, probably facilitated the diffusion of the residual anesthetic to the nerve, resulting in a prolonged anesthetic effect (P < 0.05).Conclusions: No irreversible morphological alterations are caused by the administration of HYAL prior the end of the LID-induced block. Moreover, this protocol prolongs LID's anesthetic effect. [ABSTRACT FROM AUTHOR]

Introduction: Despite the enhancing effects of hyaluronidase (HYAL) over duration of anesthesia, this enzyme could cause adverse effects when injected concomitantly with local anesthetics in dental blocks., Objective: This study aimed to assess the tissue alterations caused by a local anesthetic protocol consisting of a late HYAL injection and confirm its functional effectiveness., Materials and Methods: The protocol efficacy was proved by evaluating sensory and motor functions in rats. The sciatic nerve was blocked with 2% lidocaine (LID) with epinephrine (n = 25). Thirty minutes later, 75 TRU/ml HYAL was injected into the same site (experimental group, LID/HYAL). One week later, this protocol was repeated in the contralateral hindlimb, injecting only HYAL's vehicle (control group, LID/vehicle [LID/V]). To observe the integrity of the local tissues, histological specimens were obtained 1, 24, 48, and 72 h after treatment with LID/HYAL or LID/V (n = 16 each) and stained with hematoxylin/eosin and picrosirius red., Results: Local inflammation was similar in both groups. The integrity of the nerve fibers was preserved, in spite of some inflammation-associated injuries in the surrounding tissues. The reversible tissue disorganization caused by HYAL, probably facilitated the diffusion of the residual anesthetic to the nerve, resulting in a prolonged anesthetic effect (P < 0.05)., Conclusions: No irreversible morphological alterations are caused by the administration of HYAL prior the end of the LID-induced block. Moreover, this protocol prolongs LID's anesthetic effect., Competing Interests: None