Prospective Study on PDL Anesthesia as an Aide to Decrease Palatal Infiltration Pain

Abstract

Objective:

The purpose of this prospective randomized study was to assess using a periodontal ligament (PDL) injection as an aide to decrease palatal infiltration pain.

Methods:

A total of 133 subjects randomly received a PDL injection and alternative palatal infiltration or a mock PDL injection and conventional palatal infiltration at 2 separate appointments. PDL injection was given in the mid-palatal sulcus of the maxillary first molar. Mock PDL injection consisted of only needle insertion. All subjects then received a palatal infiltration administered into the blanched gingival tissue 3 mm (alternative palatal infiltration) or 7 mm (conventional palatal infiltration) from the gingival collar. Subjects recorded needle insertion and solution deposition pain using a Heft-Parker visual analog scale (VAS).

Results:

The combined PDL injection and alternative palatal infiltration had significantly decreased mean VAS ratings for needle insertion and solution deposition pain (P < .0001). Incidence of moderate/severe pain for needle insertion and solution deposition was reduced from 65% to 1% and from 65% to 2%, respectively.

Conclusion:

Providing PDL anesthesia into the mid-palatal sulcus of the maxillary first molar and then administering an alternative palatal infiltration into the blanched collar around the PDL molar site led to significant reductions in needle insertion and solution deposition pain compared with a mock PDL and conventional palatal infiltration.

Palatal injections can be painful,^1,2 primarily due to the palatal tissues being relatively noncompliant and tightly bound to the periosteum.³ Local anesthetic injections create increased pressure and displacement of the palatal tissue relative to loosely bound submucosal tissue leading to more pain.³ Previous studies have attempted to reduce palatal infiltration pain by topical/pressure anesthesia,^4–9 slow computer-controlled delivery,^1,2 and cold application.^9–12 Although topical/pressure anesthesia may reduce needle insertion pain, moderate discomfort during solution deposition may occur 32% to 38% of the time.¹ For palatal infiltration, solution deposition pain would be little affected by topical anesthetics or other surface methods involving application of pressure or cold. Moderate/severe pain may be experienced 42% to 68% of the time during the palatal deposition of anesthetic solution.^1,2

Periodontal ligament (PDL) injections have been extensively studied for pulpal anesthesia as either a primary or supplemental technique. However, there are no objective studies on the effectiveness of PDL injections for palatal anesthesia. Although the PDL injection has been described anecdotally in a case report as a technique for palatal anesthesia,¹³ there was no objective information included on the anesthetic effectiveness or duration.

PDL injection may reduce palatal infiltration pain by delivering enough local anesthetic to anesthetize the gingival collar of a tooth. Subsequent injection into that blanched anesthetized tissue during palatal infiltration may decrease solution deposition pain. The purpose of this study was to evaluate use of the PDL injection as an aide to decrease palatal infiltration pain. We compared the pain of a PDL injection and alternative palatal infiltration (PDL-aPI) to a mock PDL injection and conventional palatal infiltration (mPDL-cPI). The anatomic distribution of palatal anesthesia between the 2 approaches was also evaluated.

MATERIALS AND METHODS

This prospective randomized study was approved by The Ohio State University Human Subjects Review Committee and included 133 asymptomatic adult subjects who were all in good health as determined by a health history and oral questioning. Inclusion criteria included adults aged 18 to 65 years in good health (American Society of Anesthesiologists physical status class I or II) with healthy periodontium of the first molar as determined by periodontal probing at the mesiopalatal, mid-palatal, and distopalatal sites. All subjects included in the study had normal pocket depths. Exclusion criteria consisted of allergy to local anesthetics or epinephrine, history of significant medical problem (American Society of Anesthesiologists class ≥ III), recent central nervous system depressant use (eg, alcohol, analgesics, or sedatives), current pregnancy or lactation, and inability to give informed consent. Written informed consent, Health Insurance Portability and Accountability Act authorization, and medical history were obtained from each subject. Subjects rated their level of anxiety using Corah's Dental Anxiety Scale¹⁴ prior to starting the study.

Before the experiment, each subject was assigned by coinflip two 6-digit numbers from a random number table (www.random.org) signifying either the PDL-aPI or the mPDL-cPI. Subjects randomly received either the PDL-aPI or the mPDL-cPI as determined using the 6-digit random numbers at 1 of 2 appointments spaced at least 2 weeks apart. Subjects received the opposite treatment at the second appointment. Side randomization (right/left) was determined by random group assignment in sets of 25. All injections were administered by the first author (BC).

Prior to each appointment, the volume of 2% lidocaine with 1:100,000 epinephrine (LE) was premeasured by the investigator (BC) to provide 0.4 mL of LE for the PDL injection and 0.9 mL of LE for the palatal infiltrations. A black singular line was drawn around the cartridge for each anesthetic volume, indicating the amount to be deposited for each injection. Cartridges were preloaded into a standard dental syringe prior to subject arrival and covered with a paper napkin for subject blinding.

Subjects rated the pain of each phase (needle insertion and solution deposition/mock deposition) using a 170-mm Heft-Parker visual analog scale (VAS) after each individual injection (ie, PDL, aPI, mPDL, and cPI).¹⁵ The VAS was divided into 4 categories (no, mild, moderate, and severe pain), some of which included additional descriptors (Figure 1). Subjects received instructions on using the VAS forms prior to the injections.

Figure 1. .

The Heft Parker VAS. The numbers at the top of the scale were omitted on the patients' VAS. VAS indicates visual analog scale.

PDL + Alternative Palatal Infiltration

PDL injection with 0.4 mL of LE was administered using a standard dental syringe and a 27-gauge ultra-short needle with the subject supine. The needle was firmly placed in the mid-palatal gingival sulcus of the maxillary first molar (needle insertion phase) with the bevel facing the palate, and anesthetic was deposited slowly over 30 seconds under backpressure (solution deposition phase; Figure 2).

Figure 2. .

PDL injection. Placement of the 27-gauge ultra-short needle in the gingival sulcus and initial blanching of the gingival collar at the start of the PDL injection. PDL indicates periodontal ligament.

If solution was visualized escaping from the gingival sulcus, the needle was immediately rotated clockwise with firm apical pressure, and the steps outlined above resumed. A saliva ejector was placed distal to the needle while injecting to capture any escaping solution to ensure subject blinding.

One minute following the PDL injection, palatal infiltration with 0.9 mL LE was performed using a standard dental syringe with a 27-gauge 1-inch needle. Palatal infiltration was performed over 60 seconds in the blanched alveolar mucosa ∼3 mm superior to the gingival collar of the maxillary first molar's palatal root.

Mock PDL + Conventional Palatal Infiltration

To blind the experiment, a mock PDL injection was used. The subject was placed in the supine position, and using the same protocol discussed above, needle insertion was performed but no anesthetic was delivered. The portion of the needle normally penetrating into the anesthetic cartridge was bent to prevent any solution from being expressed. The needle was held in place for 30 seconds with firm apical pressure to mimic the PDL injection time and feel. A saliva ejector was placed just distal to the mock PDL injection site for subject blinding.

One minute after the mock PDL injection, conventional palatal infiltration with 0.9 mL of LE was performed using a standard dental syringe with a 27-gauge 1-inch needle. The conventional palatal infiltration was performed over 60 seconds in the nonblanched alveolar mucosa ∼7 mm superior to the gingival collar of the maxillary first molar's palatal root.

Extent of Palatal Anesthesia

For both injection sequences, the area of palatal anesthesia was evaluated using a dental explorer after completing the VAS ratings. Anatomic mapping was performed at 1, 5, 10, 15, 20, 25, and 30 minutes. The explorer was gently placed on the palatal mucosa starting at the needle insertion site and moved anteriorly until the subject reported pain. This distance was measured and recorded. This was repeated posteriorly, medially, and laterally.

Postoperative Probing Depths

Subjects were scheduled for a follow-up evaluation 1 month after the second visit to evaluate soft tissue healing using gingival probing. Sulcus probing depths at the mesiopalatal, mid-palatal, and distopalatal aspects of the first molar were measured and recorded.

Statistical and Power Analyses

Differences in VAS pain ratings for the PDL, mock PDL, and palatal infiltrations were analyzed using repeated measure analyses of variance and paired t tests to account for the individual differences. R Project (R version 4.0.3) was used for the statistical analysis. With a nondirectional alpha risk of .05 and assuming a standard deviation of 27 mm and a correlation of 0.4, a sample size of 133 subjects provided a power of .95 to demonstrate a difference of ± 10 mm on the VAS using a retrospective power analysis.

RESULTS

A total of 133 subjects participated in this study, producing 266 sets of injections. Of the subjects, 67 were males and 66 were females, ranging in age from 19 to 43 years with an average age of 25 years. The average Corah Dental Anxiety score was 5, which corresponded to low dental anxiety.¹⁴

PDL Mean Pain Scores

The mean VAS pain ratings for needle insertion and solution deposition for the PDL (38 mm and 30 mm) and mock PDL injections (41 mm and 38 mm) were not significantly different (P > .05; Table 1). The mean VAS pain scores for the PDL and mock PDL corresponded to the “mild pain” category. Most subjects reported “mild pain” for needle insertion and solution deposition with either the PDL or mock PDL (80% and 78% vs 75% and 71%, respectively).

Table 1. .

Needle Insertion and Solution Deposition VAS Pain Ratings for PDL and Mock PDL Techniques*

	None	Mild	Moderate	Severe	Mean ± SD (mm)	P value†
Needle insertion						.34
PDL	3% (4/133)	80% (107/133)	16% (21/133)	1% (1/133)	38 ± 26
Mock PDL	4% (5/133)	75% (100/133)	21% (28/133)	0% (0/133)	41 ± 25
Solution deposition						.08
PDL	11% (15/133)	78% (103/133)	11% (15/133)	0% (0/133)	30 ± 25
Mock PDL	11% (15/133)	71% (94/133)	17% (23/133)	1% (1/133)	38 ± 27

^*VAS indicates visual analog scale; PDL, periodontal ligament.

^†Comparing differences in means between the 2 anesthetic techniques for needle insertion or solution deposition.

Palatal Infiltration Mean Pain Scores

Mean VAS pain ratings for needle insertion and solution deposition for the conventional palatal infiltration (71 mm and 76 mm) and the alternative palatal infiltration (6 mm and 8 mm) were significantly different (P < .0001; Table 2). The mean VAS scores corresponded with “mild pain” for the alternative palatal infiltration and “moderate pain” for the conventional palatal infiltration.

Table 2. .

Needle Insertion and Solution Deposition VAS Pain Ratings for Palatal Injections Using the PDL + Alternative Palatal and Mock PDL + Conventional Palatal Techniques*

	None	Mild	Moderate	Severe	Mean ± SD (mm)	P value†
Needle insertion						<.0001
PDL + alternative PI	61% (81/133)	38% (51/133)	0% (0/133)	1% (1/133)	6 ± 14
Mock PDL + conventional PI	3% (4/133)	32% (42/133)	59% (79/133)	6% (8/133)	71 ± 32
Solution deposition						<.0001
PDL + alternative PI	44% (59/133)	54% (71/133)	2% (3/133)	0% (0/133)	8 ± 15
Mock PDL + conventional PI	1% (1/133)	35% (46/133)	49% (65/133)	16% (21/133)	76 ± 35

^*VAS indicates visual analog scale; PDL, periodontal ligament; PI, palatal injection.

^†Comparing differences in means between the 2 anesthetic techniques for needle insertion or solution deposition.

Subjects reported significantly lower pain for palatal needle insertion and solution deposition with the PDL-aPI technique. For palatal needle insertion, 99% of subjects reported “none/mild pain” with the PDL-aPI versus 35% of subjects with the mPDL-cPI. For palatal solution deposition, 98% of subjects reported “none/mild pain” with the PDL-aPI versus 36% of subjects with the mPDL-cPI (Table 2). The VAS categorical pain ratings for needle insertion and solution deposition are illustrated in Figure 3.

Figure 3. .

Pain ratings by VAS category. The first 4 columns represent needle insertion and solution deposition for the PDL and mock PDL injections. The last 4 columns represent needle insertion and solution deposition for the PDL-aPI injections and the mPDL-cPI injections. VAS indicates visual analog scale; PDL, periodontal ligament; PDL-aPI, PDL injection and alternative palatal infiltration; mPDL-cPI, mock PDL injection and conventional palatal infiltration.

Extent of Palatal Anesthesia

The extent of palatal anesthesia 1 minute after PDL-aPI (14 mm anteriorly, 14 mm posteriorly, 10 mm medially, and 3 mm laterally) was smaller than after mPDL-cPI (18 mm anteriorly, 17 mm posteriorly, 12 mm medially, and 7 mm laterally; Figure 4). At 5 minutes, the measured area of anesthesia had increased with both the PDL-aPI (17 mm anteriorly, 17 mm posteriorly, 12 mm medially, and 3 mm laterally) and the mPDL-cPI (21 mm anteriorly, 19 mm posteriorly, 13 mm medially, and 7 mm laterally). Values remained consistent with similar readings for 30 minutes, although the extent of palatal anesthesia remained larger with the mPDL-cPI technique.

Figure 4. .

Models of the Extent of Palatal Anesthesia. The top image is the PDL-aPI technique, and the bottom image is the mPDL-cPI technique. The small “dot” on each image is the location of the approximate palatal injection site. The mPDL-cPI technique produced a larger area of soft tissue anesthesia. PDL-aPI indicates PDL injection and alternative palatal infiltration; mPDL-cPI, mock PDL injection and conventional palatal infiltration.

Postoperative Probing Depths

Sulcus probing depths at the mesiopalatal, mid-palatal, and distopalatal aspects of the subjects' first molar were all within normal limits at the 1-month evaluation.

DISCUSSION

Mean pain values for needle insertion and solution deposition during the PDL and mock PDL were not significantly different between the 2 groups and were generally rated as “mild.” Although statistically insignificant, the mock PDL reported higher pain scores compared with the PDL for solution deposition despite no anesthetic being administered (Table 1). The primary explanation is that during the PDL, initial pain is experienced as the solution is deposited but wanes quickly as the anesthetic begins to take effect. During the mock PDL, apical pressure was applied throughout the procedure mimicking the apical pressure needed for solution deposition with the PDL technique, but there was no anesthetic effect. Therefore, more pain was experienced with the mock PDL due to the lack of administered local anesthetic, although the difference was insignificant.

Previous studies on pain with PDL injections found needle insertion was more painful (32% incidence of moderate pain) than solution deposition (14% incidence of moderate pain).^16–19 Although the pain ratings in the current study were lower than previous reports of PDL needle insertion and solution deposition, our findings were consistent with the existing literature on needle insertion being more painful than solution deposition. Although the previous studies also used LE for PDL injections in posterior teeth, they notedly all used a mesial interproximal injection site rather than a mid-palatal site. In this study, the incidence of moderate pain was 11% to 16% (Table 1), which was lower than the reported pain from a mesial site PDL injection.^16–19

Mean pain values during palatal needle insertion and solution deposition were significantly lower in the PDL-aPI group. Compared with the mPDL-cPI, the PDL-aPI decreased the combined incidence of moderate to severe pain for needle insertion by 64% and solution deposition by 62% (Table 2; Figure 3). This demonstrated that when anesthesia was first deposited via PDL injection, it resulted in a less painful way to give a palatal injection.

Previous studies have attempted to reduce the pain associated with a palatal infiltration by applying topical anesthesia, pressure, or cold.^1,2,4–9 Bhalla et al⁶ found topical anesthetic somewhat reduced the pain of needle insertion for palatal infiltration but did not provide clinical pain relief for solution deposition. Malamed⁷ describes an atraumatic palatal infiltration protocol that includes using pressure anesthesia with a cotton tip applicator at the injection site before and during the injection. However, Malamed⁷ provides no objective pain ratings for this technique.

Nusstein et al¹ used a prepuncture technique with the Wand (a computer-controlled delivery device) or a conventional syringe for needle insertion during palatal infiltration. Following application of topical anesthetic, the technique involved placing the needle bevel against the palatal tissue without puncturing the tissue and slowly depositing anesthetic while a plain cotton tip applicator was firmly placed on the needle tip—supposedly forcing the anesthetic solution into the tissue. The needle was then repositioned, advancing 2 mm to 4 mm into the palatal tissue, and anesthetic solution (1.32 mL) was deposited. No significant differences were found in needle insertion ratings between the Wand and conventional syringes. Overall, moderate pain ranged from 32% to 38% even though topical anesthesia was used. Therefore, the prepuncture technique did not result in a painless needle insertion. Pain during anesthetic deposition was significantly less with the Wand (25% moderate pain) when compared with the conventional syringe (40% moderate pain).

Romero-Galvez et al² also found a controlled flow anesthetic technique with a Calaject (another computer-controlled delivery device) reduced moderate/severe pain to 28% for palatal infiltrations compared with 68% with a traditional syringe. However, both palatal infiltration techniques have a potential for moderate pain. Using 4 techniques for palatal infiltrations, Sattayut⁸ found there was no significant difference among low intensity laser, topical benzocaine (20%), pressure anesthesia, and light touch (control) for reducing overall palatal injection pain. Wiswall et al⁹ evaluated 3 palatal infiltration techniques compared with a control (no stimulation). They found needle insertion was less painful than anesthetic solution deposition. However, pressure, pressure with topical anesthetic, and pressure with cold (Endo Ice) showed no significant reduction in pain when compared with the control. Of note, the authors found the Endo Ice application injured the tissue.

By adding a PDL injection prior to palatal infiltration, it is important to ensure 1 painful injection is not traded for another. To be effective in providing less painful local anesthesia, there must be an obvious benefit and justification for delivering the PDL injection first. Mean VAS ratings for PDL injection equated to mild pain for needle insertion and solution deposition compared with moderate pain for palatal infiltration after mock PDL. Furthermore, considerably more subjects reported moderate/severe pain (65%) for palatal infiltration after a mock PDL, whereas only 1% to 2% of patients had moderate/severe pain after the PDL injection. Nusstein et al¹ studied palatal infiltration pain and demonstrated moderate pain of 32% to 38% with needle insertion (using topical anesthetic and a prepuncture technique) and 40% moderate pain with solution deposition using a conventional syringe. The incidence of moderate pain associated with the PDL injection in this study (11–16%) was much less than the moderate palatal infiltration pain (32–40%) found by Nusstein et al¹ and the moderate/severe pain (68%) found by Romero-Galvez et al.² The data from this study demonstrate the benefits of performing PDL injections prior to palatal infiltration and supports that a PDL injection is less painful than palatal infiltration. We feel patients would accept the level of pain associated with PDL injections in order to decrease the incidence of moderate/severe palatal infiltration pain.

The injection site for the alternative palatal infiltration was 3 mm from the gingival collar, whereas the conventional palatal infiltration was 7 mm from the gingival collar. We previously performed a repeated measures study of 60 separate subjects using a PDL-palatal infiltration and a mock PDL-conventional palatal infiltration, none of which were included in the current study. In the earlier study, both palatal injections were given 7 mm from the gingival collar (the recommended range of 5–10 mm was standardized to 7 mm)⁷ while applying pressure and causing tissue blanching with a mouth mirror handle throughout the injection. After breaking the random number codes and reviewing the data, we found only a slight reduction in moderate pain with needle insertion when using the mirror handle for pressure anesthesia. There was no difference in anesthetic solution deposition pain between the 2 techniques (moderate pain was very similar to the results of the current study). Therefore, the actual PDL injection did not provide soft tissue anesthesia (blanching) at the 7-mm site—even though 0.4 mL of LE was administered. The palatal infiltration was moved to 3 mm from the gingival collar for this study because tissue blanching was consistently noted to that depth following the PDL injection.

Previous studies have indicated that the PDL injection can cause postoperative soreness and sensitivity to chewing at the injection site.^16–19 Two studies^17,20 reported postoperative periodontal breakdown interproximally with subsequent deep pocketing. In the current study, periodontal evaluation at 1-month showed no periodontal pocketing or tissue complications. In general, periodontal pocketing associated with the PDL injection should be a rare occurrence.^{16–18,20–26} In the current study, the PDL injection was given over the palatal root rather than the more common mesial and distal interproximal sites, minimizing the number of injections and providing better visualization during the injection. Additionally, to be cautious, if any patient were to develop a periodontal defect from the PDL injection, a reparative periodontal procedure would likely be easier to perform in the area of the broad palatal root as opposed to a deep interproximal pocket.

Although the main purpose of this study was to evaluate a potential method for decreasing palatal injection pain, the extent of soft tissue anesthesia was also evaluated. Both techniques resulted in palatal anesthesia (Figure 4). A larger area of soft tissue anesthesia was present with the conventional palatal infiltration likely because the injection site was 7 mm from the gingival collar. This area is supposedly a transition from tightly bound tissue to looser, more flexible tissue.⁷ As a result, anesthetic solution could have spread more easily, thus allowing for a greater extent of soft tissue numbness.

To our knowledge, only 1 study has determined if there was a difference in palatal soft tissue anesthesia between a palatal infiltration of the second premolar and a greater palatine nerve block, both using 0.2 mL of anesthetic solution.²⁷ Based on the response to sharp probing and pressure-pain thresholds of the palatal gingiva, both sites provided similar soft tissue anesthesia. Furthermore, the mean duration of palatal anesthesia was 55 minutes with no statistical difference between the 2 techniques.²⁷ Therefore, objective evidence suggests no difference between a palatal infiltration and greater palatine nerve block for soft tissue anesthesia using equivalent doses. In the current study, a greater palatine nerve block was not performed because the location of our injection was at the first molar site.

In order to demonstrate a less painful palatal infiltration, it was important that the aPI approximate the location of the PDL injection. Generally, a third of the subjects had at least 3 mm of blanched mucosa after the PDL, whereas two-thirds had more than 3 mm. In an initial study of 10 injections, we found the palatal PDL injections of 0.2 mL resulted in very limited blanching of the palatal tissue. Subsequently, the volume was increased to 0.4 mL. None of these 10 subjects were included in the results of the current study. Because the PDL injection requires strong backpressure,^16–19 injecting a total amount of 0.4 mL of anesthetic solution slowly over 30 seconds was fairly easy.

No objective study has used a volume of 0.9 mL of anesthetic solution to anesthetize the palatal tissue. The half cartridge volume was arbitrarily chosen as a starting point for palatal infiltration anesthesia. We slowly administered the palatal infiltration of 0.9 mL solution over 60 seconds to try and minimize the amount of pain using a slow anesthetic solution deposition. We wanted to evaluate this volume and record the extent of soft tissue anesthesia. Further studies could assess the impact of different local anesthetic volumes.

Limitations

We strongly feel that operator bias played a very small role in this study. The data likely represent a function of the operator injecting into anesthetized versus nonanesthetized tissue rather than operator bias. Using a computer-controlled anesthetic device may reduce injection pain because of the slow controlled rate of solution deposition. Using less anesthetic volume for the palatal infiltration may also reduce pain and should be studied. Using a greater palatine injection with a smaller volume of anesthetic solution than used in the current study may also reduce pain and should be studied.

CONCLUSION

Providing PDL anesthesia into the mid-palatal sulcus of the maxillary first molar and then administering an alternative palatal infiltration into the blanched collar around the PDL molar site led to significant reductions in needle insertion and solution deposition pain compared with a mock PDL and conventional palatal infiltration.