PERRY v. NOLL

Filing 4

ENTRY Dismissing Complaint and Directing Further Proceedings - The request to proceed in forma pauperis [dkt. 2 ] is granted. Mr. Noll's complaint must be dismissed for the reason set forth above. Nothing in this action prevents Mr. Noll fro m filing a malpractice action in state court. Mr. Noll shall have through February 23, 2017, in which to show cause why Judgment consistent with this Entry should not issue. (See Entry.) Copy to Plaintiff via U.S. Mail. Signed by Judge Tanya Walton Pratt on 1/24/2017. (Attachments: # 1 Article)(JLS)

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Occurrence of paresthesia after
dental local anesthetic administration
in the United States
Gabriella A. Garisto, DDS; Andrew S. Gaffen, DDS; Herenia P. Lawrence, DDS, MSc, PhD;
Howard C. Tenenbaum, DDS, PhD; Daniel A. Haas, DDS, PhD

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Background. Several studies have suggested
that the likelihood of paresthesia may depend on
the local anesthetic used. The purpose of this study
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A UING EDU 1
was to determine if the type of local anesthetic
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ICLE
administered had any effect on reports of paresthesia in
dentistry in the United States.
Methods. The authors obtained reports of paresthesia involving dental
local anesthetics during the period from November 1997 through August
2008 from the U.S. Food and Drug Administration Adverse Event
Reporting System. They used χ2 analysis to compare expected frequencies, on the basis of U.S. local anesthetic sales data, with observed reports
of oral paresthesia.
Results. During the study period, 248 cases of paresthesia occurring
after dental procedures were reported. Most cases (94.5 percent) involved
mandibular nerve block. The lingual nerve was affected in 89.0 percent of
cases. Reports involving 4 percent prilocaine and 4 percent articaine were
7.3 and 3.6 times, respectively, greater than expected (χ2, P < .0001) on
the basis of local anesthetic use by U.S. dentists.
Conclusions. These data suggest that paresthesia occurs more commonly after use of 4 percent local anesthetic formulations. These findings
are consistent with those reported in a number of studies from other
countries.
Clinical Implications. Until further research indicates otherwise,
dentists should consider these results when assessing the risks and benefits of using 4 percent local anesthetics for mandibular block anesthesia.
Key Words. Paresthesia; local anesthetics; prilocaine; articaine; inferior alveolar nerve block; mandibular nerve block.
JADA 2010;141(7):836-844.
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ABSTRACT

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lthough local anesthetics are safe, effective
and essential drugs for
dentistry, their use may
involve complications.
One such potential outcome is paresthesia, which refers to a neuropathy
that manifests as persistent anesthesia or an altered sensation
ranging from complete numbness to
burning, tingling or continual pain.1-3
Most oral paresthesias are caused
by direct trauma associated with a
surgical procedure, such as a dental
extraction or orthognathic surgery.
However, studies have shown that
paresthesia also can occur after
nonsurgical dentistry.4-9 The exact
cause of this is not known, but it
may be one or a combination of several factors: traumatic injury to the
nerve via direct contact with the
needle, hemorrhage into the nerve
sheath, hydrostatic pressure from
the injection or potential neurotoxicity from the local anesthetic itself.2
The hypothesis that local anesthetics may be neurotoxic is controversial.10,11 An initial report with
results suggesting this possibility
was a retrospective examination of
nonsurgical paresthesia in Ontario,

Dr. Garisto is a master’s/specialty student in graduate dental anaesthesia, Faculty of Dentistry, University of Toronto.
Dr. Gaffen is a master’s/specialty student in graduate endodontics, Faculty of Dentistry, University of Toronto.
Dr. Lawrence is an associate professor, Discipline of Dental Public Health, Faculty of Dentistry, University of Toronto.
Dr. Tenenbaum is a professor, Discipline of Periodontology, Faculty of Dentistry, University of Toronto.
Dr. Haas is the Chapman Chair, an associate dean, a professor and the head, Discipline of Dental Anaesthesia, Faculty of Dentistry, University of Toronto,
124 Edward St., Toronto, Ontario M5G 1G6, Canada, e-mail “[e-mail]”. Address reprint requests to Dr. Haas.

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Canada, from 1973 through 1993.4 Investigators
in that study found an overall incidence of paresthesia to be 1:785,000, with the two drugs most
often implicated being 4 percent prilocaine and
4 percent articaine. The number of annual cases
of paresthesia increased beginning in 1985,
shortly after the introduction of articaine into the
Canadian market. Results from that study also
showed that the lingual nerve was affected in
64 percent of all reported cases. Results from a
follow-up study in which researchers investigated
reports from 1994 through 1998 found, once
again, that paresthesia most often was associated
with 4 percent prilocaine and 4 percent articaine
and that the lingual nerve was involved in 70 percent of the cases.5 More recently, an analogous
study of nonsurgical paresthesia in Ontario
during the period from 1999 through 2008 yielded
similar results; as before, 4 percent prilocaine and
4 percent articaine were associated more frequently with neuropathy than were any of the
other local anesthetics available in dental cartridges.12 Also as before, the lingual nerve was
affected most frequently, being involved 79.1 percent of the time. Thus, all three studies from
Ontario had consistent findings.
The results of a study conducted in northern
California before the release of articaine in the
United States showed that 4 percent prilocaine
was reported more often than other local anesthetics with respect to permanent paresthesia
after local anesthetic administration.6 Results of
another study conducted in northern California
showed that there were more reports of 4 percent
prilocaine’s being associated with paresthesia,
and reports of 4 percent articaine’s association
and 2 percent lidocaine’s association were proportional to and lower than, respectively, those predicted on the basis of their estimated use.13
In Denmark, investigators found that 88 percent of reports of nerve injuries involved articaine.8 Results of another study conducted in
Denmark showed an increase in cases of paresthesia after the market introduction of 4 percent
articaine and that the lingual nerve was affected
in 78 percent of cases.9
To summarize, reported studies of paresthesia
have been conducted in Ontario, Canada; Denmark; and northern California. Yet, no comparable
assessment has been done in the United States as
a whole. Therefore, our purpose in this study was
to determine if the type of local anesthetic administered had any effect on reports of paresthesia in

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dentistry in this country. We accomplished this by
retrospectively analyzing cases of nonsurgical
paresthesia associated with dental local anesthetics that were voluntarily reported to the U.S.
Food and Drug Administration (FDA) from
November 1997 through August 2008.
METHODS

We obtained ethics approval for this study from
the University of Toronto Health Sciences
Research Ethics Board. We obtained voluntarily
submitted adverse event reports involving the
dental local anesthetics currently available in the
United States—namely, articaine, bupivacaine,
lidocaine, mepivacaine and prilocaine—from the
FDA’s Adverse Event Reporting System (AERS).
The AERS is a computerized information database designed to support the FDA’s postmarketing safety surveillance program for all
approved drug and therapeutic biological products. The FDA began entering adverse event
reports into the AERS on Nov. 1, 1997. The
system relies on voluntary reports submitted by
health care professionals, consumers or others
who become aware of a possible drug-related
adverse event. This information is available to
the public at large through the Freedom of Information Act.14
We examined all reports during this period
that denoted a neuropathy, including paresthesia,
hyperesthesia, hypoesthesia, dysesthesia, dysgeusia, ageusia and a burning sensation. Inclusion criteria were all of the following three items:
an oral paresthesia; a dental procedure; a case in
the United States. Exclusion criteria included any
one of the following: a surgical procedure such as
extraction, implant placement or periodontal
surgery, because such procedures can cause
paresthesia; use of an intraosseous device, which
can traumatize the nerve directly; a local anesthetic such as etidocaine that is no longer available in dental cartridges in the United States; or
a case report obtained only from the scientific literature. We extracted the following case parameters and subjected them to descriptive statistical
analysis by using software (SPSS, version 17,
SPSS, Chicago): the local anesthetic’s generic
name; the year in which the adverse event
occurred; the age and sex of the patient; the route

ABBREVIATION KEY. AERS: Adverse Event Reporting System. FDA: Food and Drug Administration.
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reported to the
FDA’s AERS for the
five local anesthetics
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of interest. The FDA
provides line listings
25
that summarize the
information about
Articaine
20
individual adverse
Bupivacaine
Lidocaine
events. Actual hardMepivacaine
Prilocaine
15
copy reports conMultiple
taining further
10
details can be
obtained on request.
5
Our review of each
of these listings pro0
vided information
1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
that warranted
YEAR
requesting 533
Figure 1. Reported number of cases of nonsurgical paresthesia, according to year and local anesthetic drug.
detailed reports.
Further analysis of
of drug administration; dental arch; side; specific
these 533 reports revealed that 248 of them satisanatomic structures affected (to allow us to deterfied our inclusion and exclusion criteria. In addimine which branch of the trigeminal nerve was
tion to these 248, there were 19 cases involving
involved); injection-associated events, such as
dental care in which surgery was specified, one of
pain, electric shock or positive aspiration of blood;
which involved the use of multiple agents. In 89
any additional symptoms; the dental procedure
of the 248 cases, nonsurgical dentistry was speciinvolved; multiple drugs injected; vasoconstrictor
fied. For the 159 of the 248 cases for which no
use; and resolution of the adverse event.
procedure was listed, we assumed that they
We obtained data regarding the sales of dental
involved nonsurgical dentistry. Single agents
local anesthetic cartridges in the United States,
were used in 226 of the 248 cases, and 22 involved
yearly from 1997 through 2008, from a research
the use of multiple drugs, all of which included
company (Strategic Data Marketing, Rochelle
either prilocaine or articaine. In reports involving
Park, N.J., unpublished data, 2009).
only one drug, a total of 116 (51.3 percent) cases
We used statistical analysis to test the null
involved 4 percent articaine, 97 (42.9 percent)
hypothesis that each local anesthetic had no
involved 4 percent prilocaine, 11 (4.9 percent)
effect on the frequency of reporting of cases of
involved 2 percent lidocaine, one (0.4 percent)
dental paresthesia. We used the χ2 test to cominvolved 0.5 percent bupivacaine and one
pare the expected frequencies of oral paresthesia,
(0.4 percent) involved 3 percent mepivacaine. We
on the basis of sales data, with observed reports
excluded one case in which an intraosseous injecof such paresthesia made to the AERS. When the
tion (Stabident, Fairfax Dental, Miami) was used,
expected frequency in any one group was less
as it may directly traumatize the nerve.
than five, we considered χ2 to be less reliable, so
Figure 1 shows the observed cases of pareswe used the exact binomial probability distributhesia per local anesthetic drug according to year.
tion instead to compare outcomes. All statistical
Data for 1997 represent only two months because
tests were two-tailed and interpreted at the 5 perthe AERS began in November of that year, and
cent level. If inspection of these data revealed
data for 2008 involve only eight months because
that reporting frequencies were higher than
we requested adverse event reports up to and
expected for any one drug, we then analyzed the
including August 2008. Articaine was introduced
data further with that drug excluded.
into the U.S. market in May 2000. Therefore, as
expected, no cases were reported for this drug
RESULTS
before this time. As shown in Figure 1, the
During the period from November 1997 through
majority of adverse events reported before the
August 2008, 11,003 adverse events were
year 2000 involved prilocaine. After 2000, the
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NUMBER OF CASES

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FREQUENCY OF PARESTHESIA

number of reported cases involving articaine
increased markedly, and articaine became the
Prilocaine
6 Percent
local anesthetic most reported to be associated
Articaine
with paresthesia across the entire study period.
Mepivacaine
14 Percent
18 Percent
We obtained the yearly U.S. sales of local anesthetics from 1997 through 2008; Figure 2 shows
Bupivacaine
the relative percentage of each anesthetic’s
4 Percent
market share during this period. These sales data
provided a basis for determining an expected distribution of paresthesia reports if the null hypothesis was correct and the type of local anesthetic
Lidocaine
administered had no effect on the development of
58 Percent
this condition.
Figure 3 shows the observed cases of paresthesia compared with the expected frequencies
per drug. χ2 analysis showed that articaine and
Figure 2. U.S. local anesthetic sales percentages from November
prilocaine were the only two drugs associated
1997 through 2008. Source: Strategic Data Marketing, unpublished
with a higher-than-expected frequency of paresdata, 2009.
thesia (P < .0001 for each) on the basis
of market share (Table 1). Cases
involving prilocaine were 7.3 times
140
more numerous than expected and
120
those involving articaine 3.6 times
more numerous than expected. Given
100
these findings, and in an attempt to
more accurately identify whether each
80
of these two drugs had individual significance, we then analyzed data for
60
both articaine and prilocaine with the
other drug excluded from calculations
40
to determine if significance remained.
Table 2 shows the results of this further
20
analysis: the χ2 values for prilocaine
0
and for articaine increased, demonArticaine
Bupivacaine
Lidocaine
Mepivacaine
Prilocaine
strating a highly significant difference
DRUG
when we compared the observed reports
Expected Frequency
Observed Frequency
of paresthesia with the expected
reports. Because articaine was introFigure 3. Expected versus observed frequency distribution per local anesthetic
duced into the U.S. market in 2000, we
drug from November 1997 through August 2008.
repeated the analysis from that year
on, as Table 3 (page 841) shows. Once again, χ2
the overall analysis from 1997 through 2008,
analysis showed that each of these two drugs was
shown in Tables 1 and 2, as we know that they
reported to have caused neuropathy significantly
occured within this study period, but we omitted
more frequently than expected (P < .0001).
them in the subanalysis from 2000 through 2008,
Given this finding, as before, we analyzed
shown in Tables 3 and 4, because of the uncerthese two drugs separately to test for any statistitainty of the year. Among cases reported from 1997
cally significant associations. This analysis
through 2008, no year of occurrence was specified
revealed that paresthesias associated with artifor four cases involving articaine, four cases
caine and prilocaine were significantly greater
involving lidocaine and 16 cases involving prilothan expected (P < .00000001) on the basis of
caine. Although the cases involving articaine
market share (Table 4, page 841). A number of
almost certainly occurred from 2000 onward, we
reports did not specify the year of the adverse
used n = 112 instead of n = 116 in the subanalyses
event occurrence. These cases were included in
shown in Tables 3 and 4 to be consistent with the
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to the AERS and the total number of
cartridges sold in the United States
Observed and expected* frequencies of
during this 12-year period. The reported
paresthesia as reported to the Adverse Event
incidences were as follows: prilocaine,
Reporting System involving dental local
1:2,070,678; articaine, 1:4,159,848; bupivacaine, 1:124,286,050; lidocaine,
anesthetics from 1997 through 2008 in the
1:181,076,673; and mepivacaine,
†
United States.
1:623,112,900. The overall reported inciLOCAL ANESTHETIC
OBSERVED
EXPECTED
dence was 1:13,800,970.
FREQUENCY
FREQUENCY
Patients’ age and sex. The mean
Articaine Comparison ‡
age of affected patients was 41.9 years,
Articaine
116
31.86
and the age range was 15 to 78 years.
Most of the cases reported involved
Other anesthetics
110
194.14
patients in their third, fourth or fifth
TOTAL
226
226
decades of life. In all, in cases in which
§
Prilocaine Comparison
the sex of the patient was reported, 130
Prilocaine
97
13.26
involved female patients (61.0 percent),
Other anesthetics
129
212.74
which was significantly greater than
TOTAL
226
226
the 83 cases involving male patients
* Observed frequency: Number of cases. Expected frequency: Total number of cases × frac(39.0 percent) (P < .01).
tional use of specific drug.
† Does not include cases involving the use of more than one agent (n = 22).
Injection technique, arch and
‡ The difference was statistically significant (χ = 258.7, P < .0001).
side. The particular injection technique
§ The difference was statistically significant (χ = 561.8, P < .0001).
used was reported in 219 of the 248
TABLE 2
cases. Of these, 207 (94.5 percent)
involved a mandibular nerve block, two
Observed and expected* frequencies of
(0.9 percent) involved a mental nerve
paresthesia as reported to the Adverse Event
block and 10 (4.6 percent) involved
Reporting System involving articaine and
infiltration. In 213 cases, the mandibular arch was affected (95.1 percent), in
prilocaine from 1997 through 2008 in the
10 cases the maxillary arch was affected
United States, analyzed with the other
(4.5 percent) and in one case both arches
significant drug excluded from the
were affected (0.4 percent). Leaving out
calculations.†
the one case in which both arches were
affected, significantly more cases
LOCAL ANESTHETIC
OBSERVED
EXPECTED
FREQUENCY
FREQUENCY
involved the mandibular arch than the
‡
maxillary arch (P < .0001). There was no
Articaine Comparison
predilection in terms of affected side
Articaine
116
19.32
(when it was reported), with 46 cases
Other anesthetics minus prilocaine
13
109.68
(52.3 percent) involving the right side
TOTAL
129
129
and 42 cases (47.7 percent) involving
Prilocaine Comparison §
the left side (P = .67).
Prilocaine
97
7.51
Affected area. Figure 4 (page 842)
Other anesthetics minus articaine
13
102.49
shows the affected sites. Of 191 reports
TOTAL
110
110
in which an affected anatomical struc* Observed frequency: Number of cases. Expected frequency: Total number of cases × fracture was identified, 170 cases involved
tional use of specific drug.
the tongue, which is innervated by the
† Does not include cases involving the use of more than one agent (n = 22).
‡ The difference was statistically significant (χ = 569.0, P < .0001).
lingual nerve. In 14 cases, the lower lip,
§ The difference was statistically significant (χ = 1,144.5, P < .0001).
innervated by a branch of the inferior
alveolar nerve, was affected. In seven
analyses of the other drugs from 2000 onward. The
cases, both were affected.
result remains statistically significant either way.
Injection events and other symptoms. PosiWe calculated the overall reported incidence of
tive aspiration of blood or the feeling of electric
paresthesia on the basis of the number of reports
shock, which may indicate direct contact of the
TABLE 1

2
1
2
1

2
1
2
1

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TABLE 3
needle with the nerve during injection,
was reported in 18 cases (7.3 percent).
Observed and expected* frequencies of
Although all cases involved paresthesia,
paresthesia as reported to the Adverse Event
some of the reports indicated further
Reporting System involving dental local
symptoms—specifically, taste disturbance in 44 cases (17.7 percent) and
anesthetics from 2000 through 2008 in the
dysesthesia in 54 cases (21.8 percent).
United States.†
Type of dental procedure. We
LOCAL ANESTHETIC
OBSERVED
EXPECTED
assumed that if the treatment was not
FREQUENCY
FREQUENCY
listed, surgery was not performed.
Articaine Comparison ‡
Therefore, we performed the primary
Articaine
112
25.01
analysis described above on the 226
single-drug cases to which this assump- Other anesthetics
22
108.99
tion applied. Of the 89 instances in
TOTAL
134
134
which nonsurgical dental treatment
Prilocaine Comparison §
was identified, restorative dentistry
Prilocaine
19
7.87
was most common, being performed in
Other anesthetics
115
126.13
66 cases (74.2 percent). Scaling was
TOTAL
134
134
reported in 10 cases (11.2 percent) and
* Observed frequency: Number of cases. Expected frequency: Total number of cases × fracendodontic treatment was reported in
tional use of specific drug.
† Does not include cases involving the use of more than one agent (n = 10).
13 cases (14.6 percent). To control for
‡ The difference was statistically significant (χ = 372.0, P < .0001).
the possibility that there were unidenti§ The difference was statistically significant (χ = 16.7, P < .0001).
fied surgical cases within the unknown
TABLE 4
procedures, we repeated analysis
among the five drugs after eliminating
Observed and expected* frequencies of
all cases with unknown procedures in
paresthesia as reported to the Adverse Event
addition to the known surgical cases.
Reporting System involving articaine and
When we analyzed the data for the 89
known procedure cases only, we found
prilocaine from 2000 through 2008 in the
that both prilocaine and articaine still
United States, analyzed with the other
produced a greater-than-expected
significant drug excluded from the
reported incidence of neuropathy on the
†
basis of market share than did the other calculations.
anesthetics (P < .0001), which was the
LOCAL ANESTHETIC
OBSERVED
EXPECTED
FREQUENCY
FREQUENCY
same finding as that in the primary
Articaine Comparison ‡
analysis (n = 226). Finally, we performed an analysis including the 18
Articaine
112
22.81
surgical cases in which only one agent
Other anesthetics minus prilocaine
3
92.19
was used (n = 244), with the results
TOTAL
115
115
once again showing the same statistiPrilocaine Comparison §
cally significant difference for prilocaine
Prilocaine
19
1.59
and articaine (P < .0001).
Other anesthetics minus articaine
3
20.41
Multiple drug injections. There
TOTAL
22
22
were 22 cases of multiple drug injec* Observed frequency: Number of cases. Expected frequency: Total number of cases × fractions. The ordering of administration
tional use of specific drug.
was listed in only eight of these. In one
† Does not include cases involving the use of more than one agent (n = 10).
‡ The difference was statistically significant (χ = 435.0, P < .0001).
case, the clinician had used the lower§ The difference was statistically significant (χ = 205.5, P < .0001), but there was an
concentration drug first, then the 4 perexpected value of less than 5. The difference was statistically significant (P < .00000001
according to exact binomial testing that was two-sided and used the method of small
cent solution. In the other seven cases,
P values).
the clinician had used the 4 percent
concentration first.
contain a vasoconstrictor. Where this distinction
Vasoconstrictor. Prilocaine and mepivacaine
was reported, prilocaine plain constituted 28 of
are marketed in formulations that are plain or
the single-drug cases, and prilocaine with
2
1
2
1

2
1
2
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available for entering adverse event
reports on Nov. 1, 1997. It replaced an
89.0
earlier system, the Spontaneous
90
Reporting System, that held reports
80
from 1968 through October 1998.
70
Because reports to AERS are voluntary,
there is the likelihood of underre60
porting, and the true incidence most
50
likely is higher than that found in this
40
study. This phenomenon already has
30
been noted in the literature, with
results from one meta-analysis showing
20
a median underreporting rate of 94 per7.3
10
3.7
cent, meaning that only 6 percent of
0
adverse events were reported.15 FurTongue
Lower Lip
Tongue and Lower Lip
thermore, many dentists may not know
AFFECTED STRUCTURES
that the AERS exists and that they can
report paresthesia to this national dataFigure 4. Distribution of structures affected by paresthesia.
base. These factors likely could explain
the large difference in incidence
1:200,000 epinephrine constituted 61 cases. Our
reported by others.4-9 As a result, readers should
database for sales of prilocaine did not distinconsider the paresthesia rates calculated here only
guish between these two formulations, so we
as an absolute minimum estimate of incidence.
could not determine significance from these data.
Nevertheless, the AERS is the only U.S. national
There was only one single-drug report for mepivadatabase for this information, and its usefulness
caine, which was the 3 percent plain solution.
in corroborating the results of other studies has
This low number does not allow significance to be
been stated.16
determined.
A potential concern is the possibility that
Resolution. The duration of oral paresthesia
reported rates of paresthesia may differ among
was reported in 108 of the 248 cases. This period
drugs because of a recognition bias, a reporting
ranged from as little as one day to as many as 736
bias or both. This bias occurs when practitioners
days. Confirmed resolution of paresthesia was
preferentially report adverse reactions associated
reported in only 34 of the 108 cases. Of the cases
with certain drugs owing to recent attention in the
of paresthesia that did resolve, 25 did so in less
media or scientific literature.17,18 However, this
than two months, with the remaining nine
bias would not explain the high rates of reporting
resolving within 240 days.
for prilocaine in the late 1990s. This bias cannot
be ruled out entirely for the reports involving artiDISCUSSION
caine, but the magnitude of the increase, as shown
Our results are consistent with those of reports
in Figure 1, would tend to reduce the likelihood of
from Canada and Denmark.4,5,8,9 Furthermore,
this being the sole cause of the marked increase.
they corroborate earlier findings that suggested
Furthermore, we repeated the data analysis for all
that the use of either prilocaine alone,6,13 articaine
dental procedures conducted with and without
alone8,9 or both drugs4,5,12 may be associated with
surgery, as well as for all years and then for 2000
an increased risk of developing paresthesia. We
onward only, and the results showed that both
believe it is important to note that articaine and
prilocaine and articaine were reported as being
prilocaine are the only dental local anesthetics
involved significantly more often than any other
formulated as 4 percent solutions in the United
local anesthetic for all of these analyses. Thus, no
States, with all others being of lower concentramatter how we analyzed the data, the same assotion (bupivacaine is 0.5 percent, lidocaine is 2 perciation between prilocaine or articaine administracent and mepivacaine is either 2 or 3 percent).
tion and increased risk of experiencing paresDatabases used. We used two databases for
thesia remained.
this study. The source for the reports of paresThe second database was the information
thesia was the FDA’s AERS. This system became
obtained by a marketing company, Strategic Data

PERCENTAGE AFFECTED BY PARESTHESIA

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Marketing. The market share information provided by this company closely matches that
already reported in the literature. Investigators in
one study reported that the 2005 market shares
were 47 percent for lidocaine, 26 percent for articaine, 15 percent for mepivacaine and 6 percent
for prilocaine, with the reference cited as
Septodont (Lancaster, Pa.), October 2006.10 In
another study, the market shares cited for 2006
were 54 percent for lidocaine, 25 percent for articaine, 15 percent for mepivacaine and 6 percent
for prilocaine, with the reference quoted as a September 2006 personal communication from
Septodont.13 The data we obtained from Strategic
Data Marketing listed the 2005 market shares as
53.2 percent for lidocaine, 23.4 percent for articaine, 13.5 percent for mepivacaine and 6 percent
for prilocaine. For 2006, the shares the company
listed were 55.4 percent for lidocaine, 25 percent
for articaine, 12.9 percent for mepivacaine and
6 percent for prilocaine. Thus, our data were close
to the estimates provided independently by investigators in two other studies,10,13 and therefore we
can assume that these numbers are valid.
Nerve involvement in paresthesia. Our
results showed that the lingual nerve was
involved in 89.0 percent of the reports, consistent
with findings of previous studies.4,5,9,12 To determine why the lingual nerve is most commonly
affected, investigators in a study published in 2003
examined the histologic characteristics of lingual
nerves at the level of the lingula in 12 cadavers.19
That study’s results showed a range in the number
of fascicles present, and the authors speculated
that a unifascicular nerve may be injured more
easily than one with multiple fascicles. Four of the
12 lingual nerves had one fascicle, whereas the
inferior alveolar nerve was always multifascicular.
To date, this appears to be the most plausible
explanation for the finding of the predilection of
the lingual nerve to develop paresthesia.
The mechanism underlying nonsurgical paresthesia is not known. In a 2000 study, five patients
with permanent paresthesia secondary to injection with local anesthetic underwent surgical
exploration of their injuries; in all cases, there
was no evidence of damage to the nerve caused by
the anesthetic needle.6 Thus, mechanical trauma
alone appears to be an unlikely cause. Could
nerve damage be caused by neurotoxicity of the
local anesthetic in combination with a minor
trauma created by the needle? This is unknown,
although results from previous studies suggest it

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may be the cause.4,9 Supporting this theory is the
finding that there is a great deal of in vitro and
in vivo experimental evidence of a dose-dependent
neurotoxicity associated with local anesthetics.20-29
To date, results from randomized controlled
clinical trials generally have not shown that
either 4 percent prilocaine or 4 percent articaine
is superior to 2 percent lidocaine in achieving
mandibular nerve block.30 Practitioners should
take this equivalent benefit into account when
comparing the relative risks of these drugs.
CONCLUSION

The findings of our study confirm that paresthesia arising from a local anesthetic injection
alone is a rare event. Nevertheless, the findings
we report herein support those published previously4-9 and show that the 4 percent anesthetic
solutions used in dentistry, namely prilocaine and
articaine, are more highly associated with the
development of paresthesia than are those of
lower concentration. Therefore, dentists should
consider these results when assessing the risks
and benefits of using 4 percent local anesthetics
for mandibular block anesthesia. ■
Disclosure. None of the authors reported any disclosures.
An abstract of this study is scheduled to be presented at the International Association for Dental Research General Session in Barcelona,
Spain, in July 2010. These results constitute part of a thesis submitted
by Dr. Garisto in conformity with the requirements for the degree of
Master of Science in Dental Anesthesia at the University of Toronto.
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Copyright © 2010 American Dental Association. All rights reserved. Reprinted by permission.