Bioassay of an experimental liner for composite resin restorations

J. Perry McGinnis,

Jr., D.D.S.,*

Oral Roberts University, College of Dental Medicine, Charleston,

and John H. Hembree,

of Dentistry, S.C.

Tulsa,

Okla.,

T

he biologic responses of normal tissues to a newly developed dental material (to be called the experimental material) were evaluated by application of (1) acute system toxicity value, (2) mucous membrane response, and (3) pulp irritation determination.’

METHODS AND RESULTS Acute system toxicity Ten albino rats, each weighing approximately 275 gm, were used as test animals. The reacted experimental materialt was pulverized, suspended in water, and administered by a stomach tube to each animal. A dosage level of 1 gm/kg body weight was used. The animals were observed daily over a period of 2 weeks for the appearance of toxic effects. Results. Two of the ten animals died within the first 24 hours. One animal died on the ninth day, while seven surviving animals were found to be free of toxic manifestations at the termination of the 2-week observation period. Mucous

membrane

idtation

Eleven adult golden hamsters were used as test animals. The experimental material was mixed according to the manufacturers’ directions, molded into spheres approximately 5 mm in diameter, and allowed to react. Polyvinyl chloride was used as a positive control, while gutta-percha served as a negative control. One cheek pouch of each animal was everted and the specimen placed in the terminal portion of the pouch. Tissue was drawn forward to enclose the specimen, and it was secured in place with

silk

sutures

in

such

a

way

as

to

hold

the

*Professor and Director of Oral Pathology, Department of Oral Medicine. **Professor and Chairman, Department of Operative Dentistry. tThe Lorvic Corp., St. Louis, MO.

0022-3913/79/090295

+ 04500.40/O

0 1979 Tbe C. V. Mosby

Co.

and

Jr., D.D.S.** Medical

University

of South

Carolina,

College

substance tightly against the mucous membrane surface. A control specimen of similar size was secured in the opposite pouch. Six animals received positive controls, and five received negative controls. At the end of the P-week observation period the animals were killed by decapitation. Each pouch was surgically removed and fixed in 10% buffered formalin. Standard paraffin-embedded sections were cut at 6 pm and stained with hematoxylin and eosin. Results. Histologically there was no evidence of inflammation or granulation tissue within the cheek pouch following contact with the experimental material. This result compared favorabiy with the lack of irritation noted in the negative control specimen. Pulp irritation

determination

Evaluation of the pulpal response to the experimental material was made on 96 teeth of 12 adult dogs. Class V cavities were prepared on the facial surfaces at high speed with No. 35 carbide burs and an adequate water spray coolant. An attempr was made to prepare uniform cavities with as nearly equal widths and depths as possible. In each animal, cavities in a maxillary canine and fourth premolar, as well as a mandibular canine and fourth premolar, were lined with the experimental material and restored with a composite resin. * A maxillary canine and fourth premolar were lined ,with calcium hydroxide? and restored with composite resin; the remaining mandibular canine and fourth premolar were restored with composite resin alone. Therefore, 48 teeth restored with the experimental material and 48 controls were available for study. Three dogs were “Portrait, The Lorvic Corp., St. Louis, MO. PMPC, Kerr Mfg. Co., Romulus, Mich.

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Table I. Remaining &day

Postoperative period 2 Days (6D-9)X 2 Day5 (6D-10) 2 Days (6D-18) 8 Days (6D-11) 8 Days (6D-19) 8 Days (6D-22)

dentin

in floor

of cavity preparation

and reparative

dentin

thickness

(z-day

AND

HEMBREE

and

periods)

Right maxillary canine (Exper)

Left maxillary canine (MPC)

Left mandibular canine (Comp)

Right mandibular canine (Exper)

Right maxillary premolar (Exper)

Left maxillary premolar (MPC)

Left mandibular premolar (Comp)

Right mandibular premolar (Exper)

0.35

0.35

0.65

0.15

0.85

0.12

Exposure

0.25

0.35

0.20

0.43

0.65

0.35

0.42

0.95

0.75

0.40

0.25

0.45

0.35

0.40

0.25

0.45

0.45

0.53

0.50

0.80

0.80

0.75

1.03

0.27

0.35

0.65

0.23

0.30

0.65

0.45 0.05t 0.20

0.50

0.18

0.30

0.85

0.35 0.05t 0.43 0.07t 0.55

0.40

0.65

I!?.+, Experimental material. MPC, Calcium hydroxide. Camp, Composite. Note: Remaining dentin values reflect measurement in millimeters at deepest *Values in parentheses indicate least and greatest thickness of dentin +Reparative dentin thickness. ‘&Specimen No.

killed by drug overdose at the end of Z-day and B-day periods and two each at 24-day, go-day, and 173-day intervals. Each treated tooth was removed by surgical sectioning with an autopsy saw. The roots were partially excised during the removal process to enhance fixation of the pulp. Coagulated debris was removed from the root canal openings prior to immersion in the fixative. Following surgical removal, an additional opening’ into the coronal pulp chamber of each premolar was made with a round bur to further enhance fixation of the pulp. This opening was made at a site distant to the test cavity. The tissues were processed for histologic examination. Sections were cut at 6 pm and stained with hematoxin and eosin. Two-day results. Inflammatory cells were evident in two of five specimens restored with the composite resin alone. One tooth restored with composite resin was not included because of a mechanical exposure. There was one focus of mild inflammation in one specimen lined with the experimental material, while a second exhibited a few widely scattered inflammatory cells. Congestion and hemmorrhage were consistent findings in all sections and ranged from mild to severe. However, there was no significant difference

Average

thickness

Exper

0.53 (0.35-0.75) (0.3zJ.45) 0.53 (0.35-0.8) 0.28 (0.2-0.43) 0.64 (0.5-0.85)

0.66 o.ost

of remaining

dentin*

MPC

Comp

0.24 (0.12-0.35) 0.31 (0.2-0.42) ,0.25 (0.25) 0.63 (0.5-0.75) 0.33 (0.3-0.35) 0.29 (0.18-0.4)

0.65 (0.65) 0.69 (0.43-0.95) 0.45 (0.45) 0.92 (0.8-1.03) 0.65 (0.65) 0.46 (0.3-0.65)

level of preparation.

in the intensity of this response in the experimental and control teeth. Odontoblastic displacement was not a common finding but was more apparent in the composite resin-restored teeth, with three of five showing this change. Two of six teeth containing MPC and four of 12 teeth with the experimental material exhibited this feature. Eight-day results. Inflammation at the eighth postoperative day was evident in those pulps of three of six teeth restored only with composite resin. The intensity of the response ranged from a scattering of inflammatory cells in one tooth to a mild to moderate infiltration in the remaining two. A few round cells were found in one specimen containing experimental material and in one MPC-treated tooth. Hemorrhage remained a relatively consistent finding and ranged from scattered red cells to focal accumulation of moderate to severe involvement. Hemorrhagic foci were present in nine of the 12 teeth containing the experimental material, in four of the six teeth containing MPC, and three of the six composite resin specimens. Odontoblastic disarrangement remained as a finding in two of the teeth containing only composite resin, but neither this change nor displacement was apparent in the other sections. Reparative dentin

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BIOASSAY

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Table II. Remaining dentin reparative dentin thickness?

Postoperative Period

Right maxillary canine (Ever)

Left maxillary canine (MT)

in floor of cavity (Z&day, go-day,

Left mandibular canine (Comp)

Right mandibular canine (Exper)

preparation, and 173-day

Right maxillary premolar (Exper)

24 Days (6D-48)s

0.26 O.lO*

0.49 0.09*

0.31 0.07*

0.475 0.085*

0.22 0.09t

24 Days (6D-55)

0.15

0.135 0.065*

0.43 0.03* 0.535 0.075*

0.19 0.06*

90 Days (6D-5)

90 Days (6D-25)

0.06* 0.19

0.375

0.11t 0.10 0.191

0.075t 0.40

0.10*

173 Days (6D-8)

0.245

0.375

0.125t

0.1251

173 Days (6D-13)

0.42 0.301‘

0.42 0.20t

0.15

0.09t Sections lost 0.22 0.28?

0.385

0.35 0. lot 0.435

0.125t 0.35

0.055t 0.40

0.20t Sections lost

0.16t

0.29 0.20t

0.26

*Regular dentin; not morphologically consistent with $Morphologically consistent with reparative dentin. $Least and greatest dentin thickness in parentheses. fiSpecimen No. .Wr: Measurements in millimeters.

Left maxillary premolar (MPC) 0.235 0.035t 0.255

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DENTISTRY

Right mandibular premolar (Exper)

0.36 o.os*

Exposure

test period,*

Average

thickness

and

of remaining

dentinx

MPC

ComP

0.32 (0.22-0.475)

0.36 (0.49-0.235)

0.34 (0.31-0.36)

0.195

Ex~41.

0.455 0.075*

0.085 0.065*

0.194 (0.085-0.35)

(0.135-0.255)

0.438 (0.43-0.445)

0.35 0.1ot

0.45 0.2ot

0.425 0.075t

0.359 (0.19-0.435)

0.363 (0.35-0.375)

0.493 (0.45-0.535)

0.495 0.075t

0.22

0.268 (0.1-0.4)

0.4

0.06$

0.323 (0.15-0.495)

0.52 0.06* 0.99

0.60 0. lot

0.305 (0.07-0.6)

0.645 0.175t

0.404 (0.26-0.645)

.07

,325

.18t

.075*

Exposure

0.181

formation was evident in four of the 12 teeth treated with the experimental material but was not a feature of either the MPC or composite resin-restored teeth. Data found in Table I provide information concerning the depths of the preparations and quantity of reparative dentin formation for the 2- and 8-day specimens. Twenty-four-day results. Inflammatory cells were found in the pulps of two of the four teeth restored with composite resin alone. In one the inflammation was of mild to moderate intensity, while in the other specimen a diffuse scattering of cells was found. One tooth containing experimental material was not included because of pulp exposure. Significant congestion and hemorrhage were no longer apparent in any of the treated specimens at this postoperative interval. Occasional congested capillaries and a few widely scattered congested odontoblastic capillaries were found in the pulps of four of eight teeth treated with the experimental material and in two of four teeth restored only with composite resin. This change was not observed in the MPC-containing teeth. Neither inflammation nor hemorrhage was apparent; evidence of odontoblastic disarrangement remained in one of the composite resin-restored teeth and in one containing the experimental material.

Left mandibular premolar (Comp)

during

0.065*

Exposure

reparative

dentin formed periods)

0.10*

(0.4) 0.35 (0.325-0.375) 0.42 (0.42)

0.52 (0.52) 0.605 (0.28-0.99)

dentin.

Table III. Average thickness of dentin produced subsequent to cavity preparation and insertion of restorative materials

Test period 24 Days 90 Days 173 Days

Experimental material

Calcium hydroxide NW

Composite

resin

80 (3.33)

63 (2.63)

56 (2.33)

122 (1.36) 181 (1.05)

92 (1.02) 133 (0.77)

110 (1.22) 146 (0.84)

Note: Average values expressed in microns. Value in parentheses average daily production of dentin for period indicated.

is

Reparative dentin was present in varying thicknesses in 13 of 15 specimens but was not found in one MPC tooth and one composite resin-restored tooth. Data concerning reparative dentin formation and depths of cavity preparations may be found in Table II. One tooth possessing MPC was not included because of pulp exposure.

One hundred and seventy-three-day results. One of the composite resin-restored teeth and one possessing experimental material were lost in processing. One MPC-treated tooth was not included due to pulp exposure. The pulpal responses of inflammation, congestion, hemorrhage, and odontoblastic disarrangement or displacement were

297

MCGINNIS

absent. Reparative dentin was found in each of the teeth containing the experimental material, in two of three restored with MPC, and in one of the three composite resin-restored teeth. Reparative dentin data and cavity preparation depths are given in Table II.

CONCLUSIONS Acute system toxicity. Fewer than 50% of the animals died during the test period following the administration of the experimental material. The material complied with the requirements of the acute systemic toxicity test. Mucous membrane irritation. The histologic features present in the tissues of the hamster cheek pouch following the exposure to the experimental material for 2 weeks were similar to those present in the gutta-percha control specimens. These results comply with the requirements as specified in the mucous membrane irritation test. Pulp irritation determination. Evidence of inflammation was found in only three of 46 available teeth possessing the experimental material and in one of 22 specimens treated with MPC. However, at least two composite resin-restored teeth in each of the three earlier test periods exhibited inflammation. The test material did not evoke a significant pulpal response. The initial pulpal response to the

AND

HEMBREE

experimental material was no more severe than rhe pulpal response to $IPC. The experimental material evoked less intense odontoblastic changes than the composite resin. As information in Table III would indicate, the stimulation of dentin formation subsequent to the insertion of the experimental material was greater than for either the MPC or composite resin. This formative process appeared to be most active during the earlier posttreatment periods but showed a marked decrease in production by the end of 90 days. This suggested that the initial reactions caused by the operative procedure and placement of the experimental material were well controlled by the pulp, and a subsequent return toward normal was apparent. It is proposed, therefore, that the experimental material does comply with the requirements as outlined in the pulp irritation test.

REFERENCE 1.

Council on Dental Materials and Devices: Materials and Devices, ed 8. Chicago, Dental Association, pp 200-209.

Guide 1976,

to Dental American

Reprint rqucsts CC DR. JOHN H. HEMBREE, JR. UNIVERSITY OF TENNESSEE COLLEGE OF DENTISTRY MEMPHIS, TENN. 38163

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