Root damage induced by intraosseous anesthesia–An in vitro investigation

Objectives: The principle of the intraosseous anesthesia (IOA) relies on the perforation of the cortical plate of the bone for direct application of the local anesthetic solution into the underlying cancellous structures. During this procedure, IOA needles might accidentally come in contact with the tooth roots. The aim of the current in vitro study was to examine the consequences of this ‘worst case scenario’ comparing five commercially available IOA systems. Material and Methods: Extracted human roots were randomly perforated using five different IOA systems with a drilling time ≤5s. To simulate normal in vivo conditions, the roots were kept humid during the drilling procedure. Data was statistically evaluated using F-test (SPSS16, SPSS Inc., Chicago, USA) and the significance level was set at p≤0.05. Results: All examined systems resulted in root perforation. Drill fractures occurred in either none 0% (Quicksleeper®, Anesto®, Intraflow®, Stabident®) or 100% (X-Tip®) of the applications. Excessive heat generation, as evident by combustion odor as well as metal and tooth discoloration, appeared in 30% (Quicksleeper®), 40% (Anesto®), 60% (Intraflow®), 90% (Stabident®) and 100% (X-Tip®) of all perforations. Conclusion: Within the limits of in-vitro studies, the results show a potential for irreversible root damage that might be inflicted by an improper use of IOA systems. Key words:Intraosseous anesthesia, complication, root damage.


Introduction
The �rinci�le o� the intraosseous anesthesia (IO�) relies on the idea o� �er�orating the cortical �late o� the bone to a��l� the local anesthetic solution directl� into the underl�ing cancellous substance (1). �lthough the technique was initiall� described almost a centur� ago (2). �mong the �ro�osed ad�antages o� IO� are its reliable profound anesthetic effect and the lack of any annoying numbness of the cheek and lip tissues (1). Current knowledge on the potential risks of any inferior alveolar nerve block makes it necessary to carefully analyze its risk-benefit ratio and to offer effective alter-nati�es to the �atients (3). �mong �ossible com�lications of the block anesthesia, including an occasional intra�ascular a��lication or an accidental direct ner�ous damage, an insufficient anesthetic effect was measured in 40-100% of all applications (4,5). The intraliga- (4,5). The intraliga-5). The intraliga-mentar� anesthesia� which is recommended as an ideal alternative (6), leads to an anesthetic success in only 53 -83% o� the cases (7)� might result in iatrogenic �ain and tissue damage and induces bacteremia in almost 100% o� the a��lications (8). IO� �resents a more reliable alternati�e� although being less popular (9). Literature marks the anesthetic success of IOA to be from 45-100% (10-1�). It can achieve an an- (10)(11)(12). It can achie�e an an-12). It can achie�e an anesthetic effect ranging even from 75-100% (4,11), when em�lo�ed as an adjunct to classical techniques. The current clinical indication o� IO� lies es�eciall� in se�erel� �ain�ul conditions� as in cases o� irre�ersible �ul�itis (13�14). Ne�ertheless� due to its limited anesthetic duration this method remains onl� restrictedl� suitable �or broader surgical interventions (15). Most o� the currentl� a�ailable commercial s�stems �or IO� can be well integrated into e�er�da� �ractice (16). Possible side e��ects such as a tem�orar� increase in �ulse rate (4�17) are o�ten mentioned in contrast to the rarel� re�orted root damage� drill �ractures� �osto�era-ti�e �ain or dela�ed wound healing (18)� which re�resent more serious com�lications (6). Howe�er� there exist no s�stematic in�estigations on the side e��ects o� IO� u� to now. �ccording to the manu�acturer's instructions� drilling is required to de�lo� the anesthetic solution be-tween the teeth roots. � �ossible accidental root damaging e��ect during IO� a��lication can there�ore not be excluded. Additionally, it is difficult to distinguish between IO� �er�orations o� either bone or root substance b� tactile means. In light of this background, the aim of the current in �itro stud� was to examine and com�are the �ossible root damaging effects of five different IOA systems.
-Procedure Ten �reshl� extracted human teeth (2 cus�ids� 2 bicuspids and 6 molars) were immersed for 15 minutes in a 3% NaOCl solution. Following 72 hours o� storage in 0.9% NaCl solution, the teeth were kept humid by embedding them in a silicone model with a built-in water reser�oir (Flexitime ® � hea��� Heraeus� Hanau� Ger-man�) ex�osing onl� one third o� their �acial sur�aces inciso-a�icall�. The hand �ieces o� the IO� s�stems under investigation were fixed in a 90° angle to the intended line o� �er�oration� using a s�eciall� designed and constructed jig (Fig. 1). The five different IOA systems were tested in random order on each root sur�ace. A total of fifty reproducible drillings (five on each root) were �er�ormed on the ten roots. The wet dental hard substances were �er�orated without the a��lication o� an� additional external coolant to simulate the intraosseous situation.

Results
-�rilling time and de�th The drilling time �or all s�stems ranged between 4.0s and 5.0s with a mean of 4.5±0.3s (Table �). Drilling with the SD, QS and XS system for a specific time resulted in indentations without com�lete root �enetration. I� and �� caused com�lete root �er�oration in 70% (I�) and 80% (��) o� all a��lications res�ecti�el�. Notabl�� the ti� o� the X� s�stem ad�anced into the root substance until its guiding slee�e touched the tooth sur�ace� �re-�enting the ti� �rom �urther ad�ancement. -�e�ormation and �racture For the I� and the �� s�stems� loss o� bur material was noted in all a��lications. On the other hand� drilling with ��� I� and X� s�stems resulted in drill �ractures (Table 2). The a�erage �ressure �or the �er�oration �rocess ranged between 7.3±3.4N (QS) and 17.1±7.5N (XS). A significantly higher incidence of drill breakages (100%) was noted �or the X� s�stem. A significantly lower torque of the advancing needle was �urther noted �or the Q� s�stem� lowering its root damaging indentation �otential ( Table 2). The torque �alues �or the �� and X� s�stem were not measurable (Table 2) as the combustion signs (metal tem�ering color) on the ti�s o� both s�stems made an angle determination� e�en under magnification, impossible (Fig. �).  1. Teeth embedded in a silicone model with a built-in water reservoir. IOA system hand-piece fixed at a 90° angle to the intended line o� �er�oration� using the s�eciall� designed s�lint with a �ressure-calibrated su��ort �late.

e133
-Heat induced changes Heat generation� as e�ident b� combustion odor as well as metal and tooth discoloration� was noted in 30-100% o� all a��lications ( Table 2). For the �� and Q� s�stems significantly less signs of heat generation were noted (30% and 40% res�ecti�el�).

Discussion
The initial ste� o� an� IO� technique is the �er�oration o� the cortical �late o� the bone em�lo�ing thin drills (�ull metal drill max. Ø 0.36 mm or drilling s�ringes max. Ø 0.55 mm). Considering the pressure and speed applied, this would allow cortical bone �er�oration without the need �or an additional coolant (1�19)� while inducing no thermal tissue damage (16�20). There�ore� no coolant was incor�orated in our ex�erimental design a�art �rom the water reservoir, which kept the roots humid. In systems em�lo�ing rotating s�ringes� as the ��� I� and Q� s�s-tems� the su��lied s�ringe additionall� �unctioned as a drill� whereas in the �� and the X� s�stem an access hole had to be made with a s�ecial drill �rior to the s�ringe insertion into the �re-drilled hole. In the current stud�� �� and I� s�stems demonstrated a high cutting efficiency. However, although an associated syringe deformation was noted, the incidence of breakage in these s�stems remained �er� low (10% o� all a��lications)� indicating a high structural stabilit� and strength o� the used s�ringes in these two s�stems. � common �o�ular a��roach to �re�ent instrument �ractures is to control s�eed� rotation torque and drilling time b� com-�uter. This was ado�ted b� the Q� s�stem. This com�uter controlled s�stem allowed e�en lower s�ringe diameters (Ø 0.04 mm) to be sa�el� em�lo�ed without a �otential risk of syringe breakage or root perforation as was evident in the QS system showing 0% breakage. Such an event of accidental syringe breakages would harbor great risks as the broken needle would be technically hard to retrieve, especially if such breakages occurred at or below the le�el o� the cortical �late� and could require an extensi�e surgical �rocedure to gain access to it. Com�ared to s�stems em�lo�ing a rotar� s�ringe (��� I�� Q�)� the use o� �ull metal drilling s�stems (��� X�) significantly increased the risk for thermal damage as was demonstrated b� the o�erheating signs. In all s�stems under in�estigation� thermall� damaged sites showed t��ical signs o� excessi�e heating as e�ident b� combustion odor� metal as well as tooth discoloration (21). This short but massi�e rise in tem�erature o� solid states (50-�50°C) could possibly lead to pulpal (��) and �eriodontal tissue damages (23� 24) in �i�o. In our in �itro stud�� the wet hard tooth tissue model (tooth were imbedded in silicon with a reser�oir o� water) was designed to simulate the root's thermal conduction in �i�o (�4). All five tested IOA systems operated according to the manu�acturer's instructions without external coolant usage. Pre�ious in �itro in�estigations showed intraosseous tem�erature changes below the tissue damaging threshold �or IO� s�stems (�5,26). The higher tem�erature rise during an accidental intra dental �er-�oration� as noted in the current stud�� re�resents an increased risk for thermal tissue damage. The potential thermal damages �or the �ul� or the �eriodontium might be similar to those induced b� �ower dri�en scaling or laser system root surface applications with insufficient cooling (27). �n external root resor�tion (28) or e�en osteonecrosis with an accom�an�ing bone sequestration might result as a consequence o� such an excessi�e o�er-heating e��ect (18). � �ossible accidental root contact should there�ore be absolutel� a�oided� es�eciall� as an earlier in �itro �ilot stud� using an anatomic human model showed no tactile di��erence between bone or root �er�oration �or IO� s�stems. �mong the �ro�osed �re�enti�e strategies are care�ul clinical examinations to determine an� bulges o� the cortical �late indicati�e o� underl�ing roots and �reo�erati�e x-ra�s to determine the location o� the roots accuratel�. In this context the �rime im�ortance o� profound anatomical knowledge as well as the dentist's clinical ex�erience ha�e to be underlined. Ultimatel�� in the e�ent o� an accidental root sur�ace contact� all IO� s�stems in�estigated in this stud� might induce an irre�ersible tooth damaging e��ect. Irre�ersible dental injuries can only be avoided with sufficient care and ex�erience o� the clinician and a good understanding of the potential risks and restrictions for this anesthetic method.