Scanning electron microscope study of scalers

Evaluation of three different manual techniques of sharpening curettes through a scanning electron microscope: a randomized controlled experimental study

OBJECTIVE

The purpose of this study was to compare the effectiveness of three different techniques for manually sharpening of periodontal curettes (PCs) by examining the blades with the aid of scanning electron microscope (SEM).

METHODS

Three groups were considered based on three sharpening methods used: group A (moving a PC over a stationary stone); group B (moving a stone over a stationary PC) and group C (moving a PC over a stone fixed, placed on a 'sharpening horse'). After the sharpening, the blades were examined using SEM. The SEM images were assessed independently by five different independent observers. An evaluation board was used to assign a value to each image. A preliminary pilot study was conducted to establish the number of samples. Pearson's correlation test was used to assess the correlations between measurements. anova test with Bonferroni's post hoc test was used to compare the three groups.

RESULTS

Sixty PCs (20 PCs per group) were used in this study. Statistically significant differences emerged between the three groups (P-value = 0.001). Bonferroni's test showed that the difference between groups A and B was not statistically significant (P-value = 0.80), while it was significant for the comparisons between groups A and C (P-value = 0.005) and between groups B and C (P-value = 0.001).

CONCLUSIONS

The sharpening technique used in group C, which involved the use of the sharpening horse, proved the most effective.

Scanning electron microscope evaluation of two methods of resharpening periodontal curets: a comparative study

BACKGROUND

Effective root planing demands sharp cutting edges on dental curets. However, after several strokes, they become dull and must be resharpened frequently. The purpose of this study was to evaluate by scanning electron microscopy (SEM) the quality of the cutting edge of periodontal curets resharpened by 2 different methods.

METHODS

Forty new detachable Gracey curets were used in this study. After similar blunting, all instruments were resharpened either with 10 strokes using an Arkansas fine-grit sharpening stone (AR), or with 7 strokes using a high-grit and -density aluminum oxide stone (CH). The cutting edges of each instrument were examined using SEM at 1 mm and 2 mm from the tip before and after the resharpening procedure. Bevel measurement and the amount of functional and non-functional wire edges (WE) on the cutting edge were evaluated. Data were statistically analyzed using analysis of variance (ANOVA) with repeated measures, 2-way ANOVA, and Fisher's exact test.

RESULTS

After blunting and resharpening, differences in bevel between groups were statistically non-significant. Generally, after resharpening, there were significantly more functional and non-functional WE in the AR group than in the CH group. There were significantly more instruments with a complete absence of WE in the CH group.

CONCLUSIONS

The CH stone resulted in a smoother and better cutting edge than the AR stone. The procedure was easy to perform and required fewer strokes of the curet on the stone.

Clinical response to experimental forces and non-surgical therapy of teeth with various alveolar bone loss

Firm lateral force is necessary for the thorough removal of calculus during scaling and root planning (SRP) with hand instruments. However, this firm lateral force should be applied to root surfaces without considering the tooth's loss of supporting tissues. The purpose of the present study was two-fold: firstly, to evaluate the initial pain response of periodontally diseased non-molar teeth with two different levels of alveolar bone loss (ABL) to experimental lateral and vertical pull forces; and secondly, to examine the clinical response of these teeth to non-surgical therapy. Twenty patients with chronic periodontitis were specifically selected in two groups according to the level of ABL at non-molar teeth. Group I consisted of 10 patients who have 141 non-molar teeth with a radiographic evidence of 40-65% ABL. Group II consisted of 10 patients who have 132 non-molar teeth with a radiographic evidence of > or =70% ABL. All patients were systemically healthy, free of pain, and reported no current medication usage. Starting from 0 and gradually increasing an experimental lateral force with digital force gauge, and also an experimental vertical pull force with mechanical force gauge were applied to each tooth and measured. As a result of a single experimental force applied to each non-molar tooth, the initial pain response emerged in the patients was determined by means of electronic bell system used by patients themselves. Each patient was treated with SRP using specific hand instruments under local anesthesia. Plaque index (PI), gingival index (GI), probing depth (PD), clinical attachment level (CAL) and periotest values (PV scores) were compared in both groups at initial and at month 3. A mean experimental lateral force of 24.6 N and a mean experimental vertical pull force of 48.3 N caused initial pain response in group I. Initial pain response occurred with a mean experimental lateral force of 5.3 N and a mean experimental vertical pull force of 19.4 N in group II. Only group I showed statistically significant decrease in PI, GI, PD and a significant attachment gain at month 3 (P < 0.05). There was a decrease of 6 PV in group I at month 3 (P < 0.05), whereas an increase of 4 PV was observed in group II (P > 0.05). This study showed that lateral and vertical forces required for effective SRP do not cause any problem in the group with 40-65% ABL. However, they may cause trauma in the group with approximately 70% ABL. Thus, the results suggest that the degree of healing would be different in the group with > or =70% ABL and in the group with 40-65% ABL.

Merits of soft nitriding scalers

BACKGROUND

It has been demonstrated that nitriding modifies the physical characteristics of metals. The purpose of this study was to evaluate the changes induced by 3 levels of inexpensive soft nitriding treatments on commercial sickle scalers.

METHODS

Taglite scalers (NT) were soft nitrided for 30 (SN30), 60 (SN60), or 90 (SN90) minutes. The cumulated scaled material was weighed every 10 strokes x 10 and thereafter every 1,000 to 8,000 strokes by an automatic scaling apparatus against epoxy resin. Weight differences were used to indicate abrasion resistance; the relative efficiency (RE) was calculated as the ratio of scaled amount at a given number of strokes (SN/NT). The hardness and the tensile strengths were determined for each soft nitriding treatment level. The nitrided layer thickness of representative SN scalers was observed by electron probe x-ray microanalysis.

RESULTS

The SN60 was not significantly different from SN30 or SN90, but the SN90 was more efficient than SN30 for the first 100 strokes (P<0.01). The RE of all SN scalers was significantly greater (2.3 to 2.7 times) than the NT scalers from the beginning of the study and throughout all time periods (SN90 > SN60 > SN30); it increased further during the first 100 strokes (9.7 to 15.5 times), indicating the NT scalers wore out faster than SN scalers. The untreated scalers' performance decreased to 10% of baseline after 100 strokes; but even after 1,000 strokes, the SN60 and SN90 performed better than new untreated scalers. Thereafter, all scalers' performance, including SN scalers, decreased. While the NT blades ceased to cut measurable amounts after 7,000 to 8,000 strokes, all SN scalers continued to cut. Although SN90 scalers had the thickest soft layer and were the hardest (P<0.01), the SN60 had the highest tensile strength (P <0.01), suggesting that it might be the safest in practice.

CONCLUSIONS

Sixty minutes of soft nitriding treatment of commercially available taglite scalers seem to be the optimal treatment duration to increase their durability, on the order of 100 to 1,000 times, without jeopardizing safety for clinical use.

Engineering specifics of the periodontal curet's cutting edge

Much has been reported on the qualitative, and to some degree, the quantitative effects of wear and sharpening of the periodontal curet's cutting edge. Presented here is an engineering model of the periodontal curet's cutting edge during wear and sharpening, and an estimated life of a typical periodontal curet. Although not confirmed by scientific experiments, this engineering model provides a framework for further scientific analysis. It also gives a clinical appreciation for the longevity of such periodontal instruments.

Periodontal files--a comparative study

Periodontal files are used by many dentists for instrumentation of root surfaces as a part of periodontal treatment. The purposes of this study were: 1) to examine, evaluate, and compare several periodontal files in 3 different conditions: new, used, and used/sharpened and 2) to evaluate the efficacy of 5 sharpening devices. The main characteristics observed included: the number, shape, and interval of blades; the active, rake, and lip angles; changes induced by wear; the influence of sharpening; and the type of metal surfaces comprising the blades. There was a wide range of active angles on each individual file, from a high of 75 degrees to a low of 51 degrees. The range of active angles for all blades on all new files was even greater, from a high of 87 degrees to a low of 30 degrees. Wear, observed on some but not all blades, was not extensive and appeared either as abrasion or, occasionally, as fracture of the blade edge. Sharpness scores (5 = sharpest and 1 = dullest) for new file blades were also extremely variable and spanned the full range of values, with a majority of blades scoring 3.5 and below. Attempts to sharpen files with several devices produced inconsistent results. All 5 sharpening devices had significant shortcomings. It was concluded that the extreme ranges both in active angles and in sharpness scores probably have a significant influence on effectiveness of root instrumentation.

A scanning electron microscope study comparing the effectiveness of different types of sharpening stones and curets

The effects of various types of sharpening stones on standard carbon steel Gracey type curets, and the influence of the sharpened curets on periodontally involved root surfaces, during in vitro scaling and root planing, was evaluated by means of scanning electron microscopy (SEM). Six different sharpening stones of varying texture, two of aluminum oxide, two India, and two Arkansas stones were assigned to sharpen six groups of 10 curets each. The curets were first examined under SEM and photographed and all exhibited edge irregularities. They were then sharpened with the different stones and again examined and photographed using SEM. The sharpness of each instrument was graded, related to the type of stone used, and the data compared statistically. A positive correlation was found between the texture of stone used and the surface sharpness it produced on the cutting edge of the instrument. The curets were then used to root plane the root surfaces on periodontally involved, extracted teeth. Replicas of the root surfaces were examined with SEM before and after removal of the smear layer with 10% EDTA. The planed and cleaned root surfaces revealed the effects of the sharpened instruments, with the relative surface roughness of the instrument being imparted to the tooth surface. The curets sharpened with finger grit stones produced smoother surfaces than those sharpened with the rough or coarse grit stone. It may be concluded that the sharpness of curets is related to the type of sharpening stone used and in turn to the smoothness of the planned root.

A newly-developed electrodeposited diamond scaler with high abrasive resistance

A diamond scaler on which blade diamond particles were coated by electrodeposition was developed to improve the abrasive resistance of scaler blades. The electrodeposited coating was tested with diamond particles of four different sizes, designated D-4000 with 2 to 4 microns diameter of the particles; D-800 with 12 to 25 microns; D-600 with 20 to 30 microns; and D-400 with 30 to 40 microns. The abrasive resistance of the scalers was examined quantitatively using a recently-developed automatic scaling apparatus that simulated the scaling process of hand instrumentation, as well as SEM observation of the blades. A series of abrasion tests suggested that all the diamond scalers except D-4000 showed better abrasive resistance than the control (D-0), and that D-600 showed the highest abrasive resistance and cutting quality. The SEM observation also suggested that D-600 and D-400 might have higher abrasive resistance. Furthermore, the profilometric evaluation of the surface roughness of the scaled natural dentin after hand instrumentation indicated that the average surface roughness increased in the order of D-4000, D-800, D-600, and D-400, although no marked differences were observed among D-4000, D-800, D-600 and D-0, but not D-400. These results suggested that the electrodeposited diamond scaler with 20 to 30 microns diamond particles (D-600) might have marked abrasive resistance as well as cutting quality without remarkable damage to the tooth surface after conventional scaling procedure.

Quantitative evaluation of the cutting quality and abrasive resistance of scalers

An automatic scaling apparatus that simulated the scaling process of hand instrumentation was developed to quantitatively analyze the cutting quality and abrasive resistance of scalers. We first tested 4 synthetic resins as the abraded material. Of the 4 synthetic resins tested, polycarbonate resin proved most similar to dentin. The effects of lateral scaling forces (700, 500, and 300 dyne) and scaler angles (70 degrees to 95 degrees) on the cutting quality and abrasive resistance of scalers were evaluated quantitatively by the amount of the abraded material worn away in 1,000 strokes. Comparison of the 3 scaling forces showed a greater amount of abrasion at higher force than that at lower force. This suggests that the decrease in the amount due to abrasion could be compensated by increasing the lateral scaling force. Regarding the scaler angle, results indicated that the amount of material removed increased with an increase of the scaler angle up to 70 degrees, but then rapidly decreased at an angle of 90 degrees or more. The most effective scaling angle was 87 degrees, and this was not affected by scaling force. These results suggest that a greater amount of removal could be obtained at a scaling angle of 87 degrees and a scaling force of 700 dyne. The present findings suggested the automatic scaling apparatus could be a useful tool for quantitatively evaluating the cutting quality and abrasive resistance of scalers.

Scanning electron microscope evaluation of wear of stainless steel and high carbon steel curettes

Root planing depends on quality instrument cutting edges. The sharpness and wear of stainless steel (SS) and high carbon steel (HCS) dental curettes were compared before and after standardized root planing procedures. Forty working edges of dental curettes, 20 of each alloy, were examined by scanning electron microscope (SEM) prior to any root planing (control), after 15 strokes, and after 45 strokes. Root planing was carried out on freshly extracted, single-rooted teeth, mounted in natural positions in mannikin jaws. Working areas measuring 3 x 5 mm were marked on root surfaces previously exposed by periodontitis. Each working edge was examined at points 1 mm and 2 mm from the tip under the same magnification (x 240). Microscopic observations showed that edge deformation increased from the control (factory sharpened) group, to the "15 stroke" group, and from the "15" to the "45 stroke" group, in both SS and HCS curettes. SS curettes, however, demonstrated significantly more wear than HCS curettes. After 45 strokes, only 5% of the SS curettes were sharp, compared to 20% of the HCS curettes. While 65% of the SS curettes showed severe edge deformation by the end of the study, only 20% of the HCS curettes were severely deformed (P less than 0.01). The results indicate that HCS curettes are more resistant to wear than SS curettes. Further study is indicated to evaluate the relationship between actual bevel dimensions and root planing effectiveness.

Scanning electron microscope evaluation of wear of dental curettes during standardized root planing

Root planing relies upon the quality of instrument cutting edges. This study evaluated the sharpness and wear of some dental curettes available in the market following standardized root planing procedures. Nine working edges of nine Gracey No. 1/2 DE curettes, three each from three different manufacturers, were used as controls. These unused factory-sharpened edges were examined by scanning electron microscope (SEM). Eighteen edges of nine curettes of the same brands were likewise examined after root planing procedures. Root planing was carried out on extracted one-rooted teeth mounted in natural positions in manikin jaws. Working areas measuring 3 X 5 mm were marked on root surfaces previously exposed by periodontitis. Root planing procedures included 15 vertical strokes done by either Side 1 or Side 2 of each instrument in relation to a single working area of a tooth, and the same procedure repeated 3 times using the opposite side of the curette. All working edges were examined at points 1 and 2 mm from the tip under 500 times magnification. Edge deformation increased significantly from the control group to the "15-stroke" group and from the "15-stroke" group to the "45-stroke" group. Factory-sharpened curettes (control) were sharp, with functional wire edges present on 55% of the specimens. After 15 strokes, nonfunctional wire edges and narrow edge deformations with bevels measuring less than 15 mu were present. After 45 strokes eight cutting edges (88.9%) showed bevels wider than 15 mu. The difference between the three brands was not significant in any group (i.e., controls, 15 strokes, 45 strokes). Further study is indicated to evaluate the relationships between bevel dimensions and root planing effectiveness.

Scanning electron microscopic evaluation of several resharpening techniques

The scanning electron microscope (SEM) was used to evaluate the cutting edges of curettes as they came from the manufacturer, after they had been made dull and after they were resharpened by several standard resharpening techniques and one experimental technique. Micrographs were taken of the cutting edges with the SEM at a standard magnification. The quality of the cutting edges was blindly evaluated by five independent examiners who unanimously agreed that the experimental resharpening technique produced the highest quality edge. The experimental resharpening technique used a Whittler Instrument Sharpener on the face of the blade followed by a rotating, abrasive impregnated, felt wheel on the lateral surface of the blade.

Effects of sterilization on periodontal instruments

The sharpness of surgical instruments is of particular importance to the periodontist. In order to study the effects of sterilization on the cutting edges of periodontal curets and scalers, new sharpened instruments were sterilized 10 cycles with saturated steam, formalin-alcohol vapor or dry heat. The instruments were evaluated before and after sterilization with a scanning electron microscope. No visual damage to the cutting edges of stainless steel instruments was evident after sterilization by saturated steam at 250 degrees F, formalin-alcohol vapor at 270 degrees F or dry heat up to 340 degrees F. Carbon steel instruments were not damaged by formalin-alcohol vapor at 270 degrees F or dry heat up to 340 degrees F. Saturated steam caused oxidation and dulling of carbon steel instruments.