-K • s • g l Report

An in vitro study of needle force penetration comparinga standard linear insertion to the new bidirectionalrotation insertion techniqueMark N, Hochman, DDSVMark J. Friedman,

Objective: The purpose ol this Study was to determine the eftect ol a bidirectional rotation insertiontechnique on the force neoessary to puncture and advance a needie through a tissuelike substance.Method and materials: Two in vitro penetration test models were constructed using different tissuelikesubstances of different densities. Each tissuelike substance was tested wifh 30-gauge, 27-gauge, and25-gauge needles ot two brands commonly used in dentistry. The needles were placed to a standardizeddepth of 0,5 inch (1,27 cm) at a standardized rate of insertion. A customized dental surveyor allowedcontrolled torces to be applied, A linear insertion technique and a newly described bidirectional rotationinsertion technique were tested. The force ot puncture and penetration drag was recorded wifh anelectronic digital scale, A total of 400 needle insertions were performed. Results; A multivariafe analysisof technique, material, needle gauge, and needle brand revealed fhe data to be sfafistioally significant,demonstrating no overlap. The post-hoc analysis of between-subject effects found that the needle insertiontechnique accounted for fhe most poweriul eftect in reducing lorce penetration. The bidirectional insertiontechnique had fhe greafest influence on reducing the force penetration irrespective of material, needlegauge, or needle brand tested in this study. Conclusion: The bidirectional rotation insertion techniquerequired two to three times less force than did a standard linear insertion fechnique, A continuous rotafionin a single direction would be expected to produce similar results. Needle gauge and needle design have asmaller effect on reducing force penetration than did fhe technique used during insertion. The in vitromodel used in this study represents a reliable dynamic festing system that can be used for fufure evalua-tion of needles. (Quintessence int 2001:32:789-796)

Key words: computer-controlled drug delivery, deflection, force penetrafion, insertion technique, local

anesthesia, needle

CLINICAL RELEVANCE: The bi-directional rotationinsertion produced greater efficiency during needlepenetrations. The reduction in torce needed to penetratefissues may lead to a more comfortable injectionexperience for patients.

The notion tbat a hollow-core needle could be usedto inject a local anesthefic solufion into the hody

was unknown until the late 1800s, When an Americansurgeon, Dr William Halstead,' demonstrated that aninterstitial injection of aqueous cocaine resulted in an

'Associate Clinical Prolessor, Department of Orthodontics and Departmenfof Implant Dentistry, New York Uniuersity, College oí Dentistry, New York,New York; Clinical Consulfant, Milesfone Scientific, Livingsfon, N w Jersey,

^Clinical Professor ot Restorafive Denfisfry, University of Southern Cali-

fornia, School of Dentistry, Los Angeles, California,

Reprlnf requests; Dr Mark N, Hochman, 26 Meadow Woods Road, Lake

Success, New York 11020. E-mail: PerioOrtho® AOL,COM

effective inferior aiveoiar nerve block, he ushered in anew era of local pain management for botb dentistryand medicine. Since tbat time, numerous improve-ments in the safety and efficacy of local anesthesiahave evolved. The majority of these advances havebeen related to the pharmacologj' and formulafion ofanesthefic agents, making local pain control safer andmore effective,̂ -̂ In contrast, improvements to thedrug-delivery device (ie, hypodermic syringe) havebeen few. The introduetion of the manual aspirafingsyringe used in dentistry today has actually made theinstrument less ergonomie for the operator to use thanthe nonaspirating version* (Figs la to lc).

Much advancement has been made in needledesign over tbe past century. The development of adisposable needle has had a major impact on allsyringe injecfions because it ensured sterility as well asconsistent sbarpness, Furtber advancements in metal-lurgy, surface treatments, and manufacturing tech-niques bave resulted in modern needles of unparal-leled sharpness,^ Presumably, a sharper needle

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Fig l a Palm-lhumb grasp with wrist inacute flexion, hyperextension ot thumb,and hand strain, resulting in unfavoratiieergonomics The undesirable hand positionis required wiien using a oonventionai aspi-rating syringe.

Fig l b Peniike grasp oiiginaliy taught inthe eariy 1900s before dentai syringes weredesigned with an aspirating ring. The neu-trai hand position minimized tendon flexionand muscie strain. The peniike graspoffered optimai ergonomics for proper handposition

Fig 1c Peniike grasp used with a com-puter-controlled local anesthetic deliverysystem designed with a lightweight, dis-posable, peniike handpiece.

Fig 2 Differences observed during use of linear insertion andbidirectional rotation insertion techniques. Linear insertion of a 30-gauge needle demonstrates defiection aiong the intended path.Bidirectional rotation insertion of the same needie shows littie if anybending of the needie during penetration of a tissuelike medium.

penetrates body tissues more easily, thus resulting inless discomfort for the patient.'̂ -"

Specific characteristics of the hollow-core need!ehave received close attention in the dental literatureover the past 3 decades. Needle defiection, aspirationefficiency, and the patient's perception of pain of vary-ing needle gauges are all elements that have beeninvestigated.'-" One parameter that has received far

less attention is the penetration force required topuncture and advance a needle through oral tissues. Itseems axiomatic that the finer a needle gauge, the lessdiscomfort it will elicit. Surprisingly, some of the paststudies conducted have concluded that the neediegauges used for dentistry do not have a direct correla-tion with subjective pain response of the test sub-jects.'̂ -̂ ^ However, these studies selected injection sitesin areas of loose connective tissue instead of areas ofdense connective tissue, such as the palate, which aretypically more painful to penetrate.'^'' One frequentlycited dental study did not even utilize an injection sitewithin the oral cavity; instead the injections wereadministered in the antecubital fossa.'" Because thesesubjective pain perception studies were designed withdifferent methodologies, correlation of the results fromdifferent investigations is difficult.

A novel approach to needle insertion has beenintroduced by Hochman and Friedman'^ to overcomethe undesirable effects of needle deflection. The useof a new anti deflection insertion method works suc-cessfully, irrespective of the needle gauge or the beveldesign selected. Instead of a static needle insertion,the rotational needle insertion technique'^ requiresthe operator to rotate the needle during insertion.This technique recommends a 180-degree rotation ofthe needle around the long axis, in a back-and-forthmotion; the procedure has been named the bidirec-tional rotation insertion technique. It has beendemonstrated that this clinical technique will effec-tively defeat the vector forces responsihle for needledefiection, thereby resulting in a straighter path ofneedle movement'^ (Fig 2). The authors hypothesizedthat the straighter needle path created by rotationwill result in a reduction of force required duringpenetration.

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The primary objective of this study was to deter-mine the effect a rotational insertion techniquewould have on the force necessary to puncture andadvance a needle through a tissuelike substance. Asecondary objective was to determine if needle gaugeand bevel design would bave an effect on force pene-tration. A third objective was to determine whetheran in vitro mode! might serve as a dynamic testingmethod for quantitative evaluation of the force pene-tration of any needle type, design, and manufacturingcharacteristic.

METHOD AND MATERIALS

Aldous^ devised an in vitro study to investigate needledeflection. It consisted of a dental surveyor (Ney)modified to create consistent needle penetrations intovarious tissuelike substances. Needle deflection wasrecorded on radiographie film and measured. Hoch-man and Friedman'^ reported the results of a study onneedle deflection using an analogous apparatus. Thecurrent investigation utilized a similarly modified sur-veyor device, previously described.'^ To measure theforce of puncture and penetration drag, an electronicdigital scale (Omaha) was positioned on the surveyorstage (Pig 3), A tissuelike substance was placed overthe center of the scale platform so that the test needlewould penetrate the substance at a 90-degree angle.Data were obtained by visual digital readout and byautomated recording tbrougb an RS-232 sériai portconnected to a laptop computer (IBM Thinkpad365XD), The maximum force readings were recordedfor each needle insertion test.

Three different needle gauges, 30-gauge, 27-gauge,and 25-gauge dental needles, were selected for evalua-tion. Two different needle manufacturers were selected{Becton Dickinson and Sherwood Davis).

To simulate different resistances to needle penetra-tion, two tissuelike substances were selected. Anunripened, unpeeled banana and an uncooked hotdogserved as tbe tissuelike substances in tbis study. Thebanana was selected because it provided a denseouter surface and uniform inner density. The hotdogserved as the second medium, representing a lessdense tissuelike substance. Both tissuelike substanceswere refrigerated at 50" F prior to use. All bananastested came from a single buncb. Testing was per-formed within a 24-hour period. Although it isunknown how the density of these tissuelike sub-stances directly compares to those of intraorai tissues,incorporating a wide range of substances does pro-vide meaningful information about the net effect ofvaried material density (ie, tissue density} on needleforce penetration.

Fig 3 Modified dental surveyor allowingcontrolied bidirectional rotation and iinearinsertion techniques to be performed. Theelectronic digitai scale is positioned on asur̂ ieyor stage, recording force penetrationmeasurements when the tissuelike mediumis penetrated

Two insertion techniques were tested: the standardlinear insertion technique and the bidirectional rota-tion insertion technique. The bidirectional rotationinsertion is a movement tbat is analogous to endodon-tic file instrumentation or acupuncture needle inser-tion.^"'^' Tbe rotational movement is continuouslymaintained during the process of needle advancement.

A total of 20 test groups were performed. Eachgroup consisted of testing a given needle size andbrand in the selected tissuelike substance with eitherthe linear or the bidirectional rotation insertion tech-nique. Each insertion was performed with a new nee-dle randomly selected from a standard box of 100 nee-dles. All needles were obtained from one local dentaldistributor. After use, the needles were discarded in anappropriate sharps container (Becton Dickinson).

Each needle was inserted into the tissuelike sub-stance to a standardized depth of 0.5 inch (1.27 cm).The total time of insertion was 12 seconds, therebystandardizing the rate of insertion for the specifieddistance. A stopwatch was employed to measure theelapsed time to the nearest second.

Each of the 20 tests consisted of 20 needle insertions.Two hundred needle insertions were performed witheach technique. Two hundred needle insertions wereperformed on each material. Three types of needleswere used in the study. The 30-gauge needle wasinserted 80 times with each technique. The 27-gaugeneedle was inserted 80 times using each technique andthe 25-gauge needle was inserted 40 times using eachtechnique. The Sherwood Davis 25-gauge needle wastested on both tissuelike substances; the BectonDickinson 25-gauge needle was unavailable at the timeof testing. An overall total of 400 needle insertions wereperformed.

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TABLE 1 Multivariate analysis of variance

Source

Corrected modelInterceptTechniqueMaterialBrandGaugeTechnique x materiaiTechnique x brandMaterial x brandTechnique x material x brandTechnique x gaugeMateriai x gaugeTechnique x material x gaugeBrand x gaugeTechnique x brand x gaugeMaterial x brand x gaugeTechnique x material

X brand x gaugeErrorTotaiCorrected total

Type ill sumat squares

19828.68851253.75214665.764

1124,980110.450

1692.1819.686

16,200352.800

8.450791.115173,381100,96548,05028,80031,25016.200

794,75073179.00020623,438

Of

191111211112221111

380400399

Statistical analysis demonstraled thai tlie type ot insertion tetant variable when technique, m ale rial, brand, and gauanalysis. The data are statistically significant.

eare

Meansquare

1043.61551253,75214665.764

1124,980110,450846,091

9,68616,200

352,8008,450

393,55786,69150,48248,050

31,25016,200

2.091

h nique (bi direction a

F

498 99224506,355

7012.256537,895

52,810404,548

4,6317,746

168.6874,040

189,13141,45024,13722,97513,77014,9427.746

P

< .001< ,001<.OO1<,001<.OO1<.OO1<,05< ,01< ,001< ,05< ,001<,001<,001<,001< 001< ,001> .01

rotation insertion) is the mostcompared. Force is kept as the dependent variabie

•>

961

985

949

586

122

680012020307011499179113057035,038,020

mpor-inthe

RESULTS

This study consisted of an experiment comparing nee-dle force penetration of two neetlle insertion tech-niques into two different injection mediums usingthree different needle gauges of two brands of needlescommonly used in dentistry. Statistical data analysiswas performed with a multivariate analysis of variancewith a 2x2x3x2 design. The following variables wereanalyzed: technique, material, needle gauge, and nee-dle brand. Data were found to be statistically signifi-cant, demonstrating no overlap {Table 1), The post-hoc analysis of between-subject effects found that theneedle insertion technique accounted for the mostpowerful effect in reducing force penetration. Thebidirectional insertion technique had the greatestinfluence on redtjcing the force penetration, irrespec-tive of material, needle gauge, or needle brand testedin this study.

Finer-gauge needles were found to require lessforce during insertion and penetration with both tech-niques. Comparison of the two brands of needles usedfor this study revealed that one brand (Becton

Dickinson} demonstrated a modest reduction in theforce needed for needle insertion. The total meanforce required for a 30-gauge, 27-gauge, and 25-gaugeneedle was 9,0 g, 12,0 g, and 15,3 g, respectively. Insharp contrast, when the linear bidirectional rotationinsertion techniques were compared, the meanamount of total force required was 17,5 g and 5.5 g,respectively. The linear insertion technique consis-tently required two to three times the force necessaryto penetrate a given material using the same needlegauge {Table 2),

DISCUSSION

A review of the dental literature pertaining to needleforce penetration characteristics was conducted. Thisresearch included a variety of different study models,Hamburg'^ was one of the early investigators to reporton needle penetration and its relationship to patients'subjective pain response. Three different needlegauges were compared (18-gauge, 21-gauge, and 25-gauge) during venipuncture in the antecubital fossa of

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TABLE 2 Estimated marginal means

Variable

TechniqueLinear insertionRotational insertion

MaterialHotdogBanana

BrandBecton DickinsonSheni/ocd Davis

Needle30-Gauge27-Gauge25-Gauge

SE = Slardard error.

Mean

17.4655.460

9,63013,295

9,90612,500

8,98713.00015.338

SE

0.1020.102

0,1020,102

0.1140.093

0,1140.1t40,t62

95% Confidence interval

t-ower bound

17,2645,259

9,42913.094

9.68112.316

8.76311.77515,020

Upper bound

17.6665,661

9,83113,496

10.13112.684

9.21212,22515,655

the atrm. A total of 400 patients participated in thestudy, which concluded that the initial needle penetra-tion in the skin is responsible for eliciting pain.Hamhurg'* also reported that patients are unable toaccurately distinguish between needle gauges rangingfrom 18-gauge to 25-gauge needles,

Lehtincn and Oksala^ conducted an intraora! studyon needle penetration. The study tested six differentneedle types by penetrating the buccal alveolarmucosa approximating the apices of the left and rightlateral incisors. They stated that the needle pointdesign had the greatest effect on tissue penetrationand its association with patients' pain perception,Lehtinen« conducted another intraorai study compar-ing the force required to penetrate the buccal mucosawith both 27-gauge and 30-gauge needles in 50patients. His findings detnonstrated that 27-gauge nee-dles required twice as much force as 30-gaiige needlesfor the same petietration. He stated that the differencein subjective pain perception elicited by the two nee-dle gauges was statistically significant. He recom-mended the use of a finer-gauge needle whenever pos-sible to minimize the pain of an injection.

Fuller et a l ' ' compared three different needlegauges {25-gauge, 27-gauge, and 30-gauge) in a totalof six patients. Their study examined needle penetra-tion in the mucQsal tissues of the retromolar fossa.Penetration of the tissue was limited to a depth of 2 to3 mm, A rapid in-and-out puncture technique that

took approximately 1 second to complete wasemployed. Fuller and coworkers" concluded thatthere is no significant difference in the perception ofpain elicited by the different needle gauges tested intheir study.

Brownbill and coworkers'' compared a 30-gaugeneedle to a 25-gauge needle in a subjective painresponse study during the administration of an inferioralveolar nerve block injection. A total of 138 injec-tions were performed on children with a mean age of10 years. The results from this study demonstratedthat a 30-gauge needle tended to receive a slightlylower pain score than the 27-gauge needle. However,the differences were small and not statistically signifi-cant. The investigators concluded that no clinical dif-ference in perceived pain could be demonstratedbetween the two needle gauges.

Needle penetration has been identified as an impor-tant aspect of the injection process,^ '̂" It affects bothphysical and psychological aspects of the injectionexperience for the patient,^* The limited ntimber ofcontrolled studies make it difficult for clinicians toarrive at a meaningful conclusion. This lack of consen-sus is further complicated by the inconsistencies foundbetween what is reported in the literature and what isutilized in daily clinical practice,' Needle manufactur-ers (Becton Dickinson} report that finer-gauge needlesare more popular, based on the higher sales figures ofthese needles; this conflicts with the dental literature,

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Fig 4 (left) Vector force system applied to the beveled end of a needie. (right) Vector anaiysisiiiusfrating the path taken during needle insertion wifh the linear ana :he bidirectionai rotafioninsertion techniques.

which would seem to suggest that the finer-needlegauge would not represent a benefit in needle perfor-manee or patient comfort,

Tbe limited data previously avaiiabie on force pen-etration do not support the existenee of perceptibledifferences among different needle types and the forcerequired to puncture and traverse tissue,'^•'^•'"However, these data have been primarily generatedfrom investigations on unattaebed mucosa. In theclinical setfing, many dental injections are adminis-tered not in loose connecfive fissue, but rather in highdensity tissues such as the palate, attached gingiva,periodontal ligament, and muscle. Furthermore, noconsistent tesfing methodology for force penetrationhas been established.

Topical anesthetic has been employed by manyclinicians to reduce the pain associated with needlepenetration. Studies have demonstrated varied posi-tive results, depending on the amount of time and thetype of oral tissues to which these medicaments areapplied,"-2' Topical anesthetic can pass throughmucous membranes but bas limited effectiveness indiffusing through orthokeratinized epithelium suchas that found on the palate and attached gingiva,'^Therefore, the pharmacoiogic benefit of its use mayvary from injeetion site to injection site, dependingon locafion. Topical anesthefics have heen shown toreduce the percepfion of pain, providing a psycholog-ical henefit, but are not noted to reduce the force

required for puncture or penetration," Force pene-trafion is a direct function of the technique used, theneedle design, and the type of tissue encountered.The current study was an initial attempt to design astandardized in vitro model to test needle force pene-trafion. An in vitro model bas limitations in clinicalinterpretation. However, it is important that a stan-dardized and reproducible testing analog model bedeveloped as a responsible prerequisite to testing onanimal subjects. The data that can be collected withsucb a model can serve as a starting point for furtherinvestigafions.

Clinical use of a hollow-core dental needle in localanesthesia administration requires that it first pene-trate the outer surface of an epithelium and then tra-verse connective tissue. Basic knowledge of oralanatomy teaches that the oral cavity comprises of avariety of tissue types with a speetrum of densities.Certain oral tissues, espeeially tissues tbat are com-posed of densely packed connective tissue, covered byorthokeratinized epithelium, present a greater chal-lenge to penetrate than the unattached mucosa of thebuccal vestihule. An understanding of the factors thatplay a role in diminishing the force required to pene-trate a substance may produce a more comfortableexperience for the pafient. In addition, a decrease inthe force required to penetrate and traverse tissues hasthe potential to limit fissue damage and undesirahlepostoperative sequelae.

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It has been shown in the present study that the fac-tor that has the largest effect in reducing the forcerequired for penetration is the technique selected forinsertion. Among the factors tested in this study, thebidirectional rotation insertion technique was shownto have the greatest effect in reducing required force.

Reduction in force penetration is achieved bychanging the resultant force that act on the hevel ofthe needle during penetration. An eccentric pointedbeveled needle is manufactured with angled planes onwhich forces act during a nonrotating hnear insertion.Forward movement of the needle causes reactiveforces to bend the needle shaft as it is advanced. If theneedle shaft is bent or deflected as it simultaneouslymoves forward, greater force must be used.

With the use of a rotational insertion, all forces aredirected along the path of insertion, eliminating thoseforces that produce deflection (Fig 4). This allovre theforward movement to occur more efficiently. In addi-tion, rotation of a needle allows the cutting edge of thebevel to come into contact with the full circumferenceof a contacted surface. This is analogous to the "coringaction" used to remove an apple core with a culinarycoring instrument. It is hypothesized that reducedforce penetration may account for a reduction of painperceived by the patient during needle penetration incertain tissues of the oral cavity. This statementrequires further clinical testing to determine its validity.

The traditional dental syringe was designed for usewith a palm-thumb grasp; however, if it is held with apeniike grasp, a rotational technique could beemployed, resulting in the benefits described above. Analternative that can he considered is a new local dentalanesthetic delivery system (The Wand, MilestoneScientific). This system requires the use of a disposable,lightweight handpiece that requires the operator to usea peniike grasp. This option requires the purchase ofadditional equipment and supplies and should be eval-uated on an appropriate cost-benefit ratio.

A final option is the use of a centric pointed localanesthetic dental needle {Tru-ject, Cannuiae). This nee-dle, studied hy ]eske and Boshart,̂ ^ demonstrated aneffective nondeflecting characteristic of a bi-beveledneedle with a centric point. Although this needle hasnot been tested to determine if it benefits force penetra-tion, it stands to reason that less force may he requiredthan is needed with the traditional eccentric pointedneedle, hascd on its physical design. A comparison ofthe force penetration of a hi-heveled needle, the stan-dard dental needle, and the technique of bidirectionalrotation is an interesting area for future research.

The use of a peniike grip has also been shown toprovide improved operator ergonomics during clinicaluse.25'3« The use of a peniike grasp has the beneficialeffect of reducing repetitive hand strain, known to be

a negative occupational hazard of dentistry" (See Figsla to lc). Further investigations are suggested todetermine the clinical benefits that the operator mayencounter from the use of this alternative instrumentgrip.

CONCLUSION

The current experiment evaluated force penetration inthree different needle gauges, two different brands,and two different densities of material in a standardlinear insertion technique:

1. The factor that most greatly affected the forcerequired for a beveled needle to penetrate and tra-verse a tissuelike medium was the insertion tech-nique.

2. The insertion technique that demonstrated thegreatest reduction in force penetration was thebidirectional rotation insertion technique. A con-tinuous rotation in a single direction would beexpected to produce simiiar resuits. The bidirec-tional rotation insertion technique required two tothree times less force than did a standard linearinsertion technique.

3. Needie gauge and needle design have a smallereffect on reducing force penetration than did thetechnique used during insertion.

4. The in vitro model used in this study represents areliable dynamic testing system that can be used forfuture evaluation of needles.

Further investigations are necessary to determinewhether the results obtained in this in vitro study willcorrelate with a reduction in patients' subjective per-ception of pain during the clinical use of a bidirec-tional rotation insertion technique.

ACKNOWLEDGMENTS

The authors would like 10 ttiank Dr Eugene Hittleman, AssociateProtessor and Director of Behavior Science Programs. New YorkUniversity, College of Dentistry, for his generous effort in providingthe data analysis and interpretation of the statistical findings.

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