A Quantitative Study of Cementum Removal With Hand Curettes Nancy B. Coldiron, * Raymond A. Yukna,f Jim Weir, * and Richard F. Caudilfi An in vitro study was conducted to quantitatively measure the depth of root surface removal using curettes of standardized sharpness and with definite stroke number. Extracted periodontally healthy teeth from patients 10 to 15, 16 to 25, and 26 to 40 years old had periodontal ligament remnants removed with dry gauze before being secured in a vertical position during root planing. The force applied to the root surface was measured with a tension load cell. The "bright line" test was used to assess curette sharpness. After histologie processing, the thickness of cementum adjacent to the root defect, the cementum (if any) in the root defect, total amount of cementum removed, and depth of root defect were measured by a microscopic ocular grid. Teeth from each age range were evenly distributed into 6 groups of 10 teeth each. In the majority of teeth from the 20 stroke group through the 70 stroke group, complete cementum removal was observed at the site of planing. However, in some sections from each group, fragments of cementum remained on the root surface. A positive relationship (r/s 1) was found between the number of strokes and the force applied to the root surface and the mean depth of defect (P < 0.05). However, an inverse relationship existed between mean force per stroke and mean defect depth (r/s .99) such that as mean force per stroke increased, the mean defect depth decreased. As the root surface became smoother with an increasing number of strokes, the forces increased and were more consistent. This study showed that for "healthy" root surfaces, total cementum removal was generally achieved with a mini=



of 20 strokes at the

same exact



the root

surface; however, cementai

fragments remained in various sections even in the 70 stroke group. This finding emphasizes the inconsistency of present mechanical therapy and points to the significance of chemical treatment or detoxification in achieving a predictable healing response. The results also suggest that effective root planing in a quadrant would take at least 90

minutes. / Periodontol 1990;61:293-299.

Key Words: Curettage; tooth root;


Root planing for the removal of plaque, calculus, and involved cementum is generally accepted as a necessary and beneficial procedure in periodontal therapy.1"3 Three electron microscopic studies have revealed a hypermineralized surface zone extending 40 to 100 µ deep in exposed cementum4"6 but one has not.7 Changes in the organic matrix, namely a loss of collagen crossbanding near the cementum surface, has been noted in transmission electron microscopic studies.8 Both light microscopic and transmission electron microscopic studies have revealed the pres*Private practice, Beaufort, SC; previously, Postgraduate Periodontics Student, Louisiana State University School of Dentistry. fPrivate practice, Denver CO; previously, professor and coordinator Postgraduate Periodontics, Louisiana State University, School of Dentistry.


of Oral

Dentistry. 'Department

of Periodontics.


Louisiana State


School of

of "granules" in exposed root surfaces.9'10 Increasing evidence suggests these granules may be bacteria.11-13 Studies have shown that cementum exposed to a periodontal pocket is cytotoxic to epithelium14 and fibroblasts15'16 when placed in tissue culture. Endotoxins have been extracted from diseased root surfaces and may be responsible for this cytotoxicity. However, root planing of the exposed cementum allows the fibroblasts to adhere to both "diseased" and "non-diseased" areas of the root.15-17 A new connective tissue attachment appears to be dependent on complete removal of the contaminated root surface via root planing. Also, results demonstrating new attachment after root surface demineralization with citric acid suggest the importance of complete removal Of the hypermineralized zone on the root surface.18 21 The depth of root surface removal necessary to reach a "healthy" region of the root is unknown. Several studies enee



Table 1. Distribution of Tooth

Type Molars

Bicuspids Cuspids

Incisors Totals


J Periodontol May 1990






6 21 10 9 46

10 26 6 4

16 47 16 13 92

have determined the amount of tooth structure removed

using power-driven scaling instruments,22"31 air-powder abrasives,32 and conventional periodontal hand instru-

ments.22·2426·29·30·33"37 The loss of tooth substance follow-

ing root planing has been evaluated by measuring the size of the instrument marks,22-23-27 by calculating the weight of the removed tooth substance,25-26 and by inspecting the treated surfaces by üght.24,30,31,34-37 or scanning electron28-31 microscopy. Complete or almost complete cementum removal2'28-30-32-35"38 and mean depths of root substance removed of 12 µ to 75 µ 22·32·34 have been reported using conventional periodontal curettes. All of these studies, as well as those evaluating mechanical devices, fail to standardize the number of strokes, the time of application, the pressures used, and/or the sharpness of the instruments. Therefore, an in vitro study was designed to measure the depth of root surface removal using a single type of periodontal hand curette with standardized pressure, sharpness, and stroke number.

MATERIALS AND METHODS The experimental material consisted of 92 extracted teeth composed of impacted third molars, bicuspids removed for orthodontic reasons, and periodontally healthy teeth removed for prosthodontic reasons (Table 1). All teeth were free of visible calculus and had no known previous periodontal therapy. After extraction the teeth were stored in deionized water and collected in jars labelled for the following ages: 10 to 15 years, 16 to 25 years, and 26 to 40 years. The teeth were then scrubbed with dry gauze and rinsed with deionized water to remove soft debris. The crowns of the teeth were grooved with an inverted cone bur in a high-speed handpiece and positioned with periphery wax in 5 ml plastic vials. The vials were then filled with clear casting acrylic until the entire crown was embedded. The embedding medium was allowed to air dry for 24 hours, at which time the vials were inverted for re-hydration of the roots in deionized water for 3 days. A pilot study was conducted using 32 teeth to determine the minimum number of strokes necessary to create a measurable surface defect and the maximum number of strokes until sharpening of the curette was necessary. Roots were planed at the same exact location on the buccal and distal surfaces, avoiding the mesial root surface because of its more extreme concavities. All instrumentation was per-

formed by one operator using 20 new #11/12 Gracey curettes11 held in the recommended relation to the root surface.33 The "bright-line" test under a binocular magnifier of 8 diopters was used to insure sharpness of the cutting edge. A dull edge reflects light according to the amount of deformation present. As the edge is restored, a more regular "line angle" develops that reflects progressively less light; thus when minimum light is reflected, no further sharpening is necessary.39 Sharpening was performed with fine grit TriAngleU sharpening stones, used as directed by the manufacturer. Using a modified pen grasp and a vertical pull stroke, the straightest root surface was root planed from the CEJ to near the apex of the root. Force or pressure on the tooth was measured with a tension load cell which linearly changes resistance as the loads change. The signal from the cell was fed into a Strain Gauge Conditioner and Amplification System# which accurately detected these resistance changes and transduced these changes into voltages. These voltages were amplified by the conditioner and were fed into a Gould Strip Recorder.* From the deflection of the pen, the force was computed as shown below.40

1 volt 59 nn lbs 2.2046 lbs/Kg




10 lbs volts



(C mm)










Grams of force

The results of the pilot study revealed that with 25 strokes of the curette and a mean force of 680 grams, a measureable surface defect was created. Also, the curettes had to be sharpened every 10 strokes to maintain a standardized

sharpness. The remaining 60 teeth were then

divided into 6 groups of 10 teeth each. The three different age groups of teeth were distributed evenly within each of the six experimental groups based on the number of strokes used. Following instrumentation, the crowns of the teeth were transected at the CEJ with a water-cooled tapered fissure bur in a high-speed handpiece. The roots were then decalcified in 10% formic acid/10% sodium formate for 7 to 10 days, washed in running water for 16 hours, and immersed in 70% ethanol for 3 days. The roots were horizontally sectioned at the cervical, middle, and apical thirds with a #15 scalpel blade. One millimeter block sections were started 1 mm from the CEJ with approximately 2 mm between the remaining sections. The root slices were then processed for paraffin embedding and semi-serial cross sections, 6 µ thick, were cut and stained with H&E. The surface defects were measured by a light microscopic ocular grid at 100 x magnification. Measurement of the deepest portion of the

JHu-Friedy Mfg. Co., Chicago, IL. "Spyderco, Inc., Golden, CO. "Vishay Intertechnology, Inc., Raleigh, *Gould,


Cleveland, OH.


Volume 61 Number 5



in defect

C. Total cementum removal



D. Cementai thickness cent to cefect

of defect

Table 2. Mean Cementum Thickness and Mean Root Defect of Middle Histológica] Section in Area of Root Planing

Strokes Used

Cementum Thickness

20 30 40 50 60 70

29 61 75 65 57 88 =

Mean µ


± ± ±

± ±




Root Defect

25* 50 46 57 49 66

60 65 89 112 174


Depth 34 41 45

78 102


Frequency of the Presence of Residual Cementum Fragments Left in Root Defects Following in vitro Root Planing Table 3.

1. Schematic drawing of method of measurement of cementum thickness and root defect depth. A cementum depth of defect; remaining in defect; C area of total defect removal; D cementum thickness adjacent to defect. Dotted line exemplifies extrapolation of original root shape as measurement reference base.






determined by direct microscopic evaluation or by extrapolation from the adjacent cementum thickness of each horizontal section. The thickness of cementum adjacent to the defect, the cementum (if any) in the defect, and the total amount of the cementum removed was also measured (Fig. 1). The mean depth of defect was determined from measurement of the middle sections of the root surface in each group. Depth of defect on the root surface was correlated with the force applied and stroke number using Spearman's Rank Correlation. defect


RESULTS Clinical Observations The initial appearance of a reflected white line from the curette blade occurred after 12 strokes on the root surface. However, the curette sounded sharp and was cutting smoothly (fingernail test) at 35 strokes. The curettes were sharpened after every 10 strokes to maintain a standardized optimum


To determine the range of forces applied to a root surface during clinical root planing, nine faculty members of the Louisiana State University School of Dentistry Periodontics Department simulated root planing on a tooth attached to a gram scale. The range of force was from 700 to 1200 grams (mean 982 grams). The experimental mean force applied in this study ranged from 687 grams for the 20 stroke group, to 1032 grams for the 70 stroke group. Therefore, the experimental forces were clinically comparable to forces used by experienced practitioners during the root planing


Histologie Observations

Eight teeth and 10 sections of additional teeth were lost during histologie preparation. The 558 sections of the remaining 52 teeth were studied.

Strokes Used 20 30 40

50 60 70 *


Mid-Root Number


3/9* 2/10 3/8 1/10 1/8 0/10 Instances of cementum

Section %

Overall Number

33 20 38 10

20 30

5/25 9/30 8/23 3/28 4/21 1/22

13 0

being present/number of sections

35 11 19

5 studied.

Overall mean values for cementum thickness and root defect depth demonstrated that cementum was totally removed over the entire length of the instrumented root surface with a mininum of 20 strokes (Table 2). However, even within the 20 stroke group certain sections of individual teeth demonstrated complete removal of cementum, while other sections of the same tooth revealed varying amounts of residual cementum. Residual cementum fragments were present in some sections in each of the six groups (Table 3). Four different types of root defects were identified as a result of the root planing process: 1) curette-shaped, 2) sliced, 3) fragmented (cementum remaining in the defect), and 4) different cementai thickness on either side of the defect (Fig. 2A-2D). These variations were due to deflection of the curette during root planing secondary to root anatomy and density, and inconsistent level of sectioning through defects. In those teeth with different cementum thickness on either side of the defect, the thickest area of cementum was used in measuring the deepest portion of the defect. Another variable in measuring defects was the location of the cemento-dentinal junction in hypercementosed teeth. Statistical Analysis There was a positive relationship (r/s 1) using Spearman's Rank Correlation between the number of strokes applied to the root surface and the mean depth of root defect, such that as the number of strokes increased, the depth of root defect increased. The rank correlation differed significantly from zero (P < 0.05) (Fig. 3). There was a positive relationship (r/s 1) between the force applied and the mean depth of defect, such that with =


J Periodontol








-I-,-,-,-,-,-,-,-1 10









Number of Strokes

Number of curette strokes vs. root surface defect depth. Spearman's Rank Correlation Coefficient (r/s) 1, significant from zero fP

A quantitative study of cementum removal with hand curettes.

An in vitro study was conducted to quantitatively measure the depth of root surface removal using curettes of standardized sharpness and with definite...
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