3D-Image analysis of the impact of toothpaste abrasivity on the progression of simulated non-carious cervical lesions

Abstract

Objectives

To investigate the effect of toothpaste abrasive level on the progression of non-carious cervical lesions (NCCLs) using 3D-image subtraction.

Methods

Upper first premolars were allocated into seven groups (n = 16) of toothpaste/abrasive slurries: A-Zeodent113/5%, B-Zeodent124/10%, C-Zeodent103/15%, D-Sensodyne Pronamel, E-Crest Cavity-Protection, F-Crest Pro-Health-Whitening, and G-Deionized water (DIW). Teeth were mounted on acrylic blocks, and their root surfaces covered with acrylic resin, except for 2-mm near the cemento-enamel junction that was exposed to toothbrushing. Specimens were brushed with the slurries for 5000-, 15,000-, 35,000- and 65,000-strokes. Impressions were taken at baseline and after each brushing time, and then scanned by a 3D optical profilometer. Dentine volume loss was calculated by image subtraction software and subjected to mixed-model ANOVA and multiple comparison tests (α = 0.05).

Results

No significant differences among slurries were observed at 5000 and 15,000. At 35,000, F showed higher loss than all other groups except C, which did not differ from the others. At 65,000, F (4.19 ± 3.29 mm 3 ) showed the highest loss, followed by C (2.33 ± 1.47 mm 3 ), which differed from all the other groups except B (1.85 ± 0.91 mm 3 ). Groups B, A (1.35 ± 0.65 mm 3 ), D (1.17 ± 0.48 mm 3 ), E (1.40 ± 0.68 mm 3 ) and G (1.12 ± 0.73 mm 3 ) did not differ from each other. Groups F and C showed significant increase of volume loss starting at 35,000, while B, A, D and E only at 65,000; no increase loss was observed for G.

Conclusions

3D-image subtraction was able to quantify and differentiate tooth loss, but only at advanced stages. The progression of NCCLs was more evident and faster for highly abrasive slurries.

Clinical significance

Upon root dentin exposure, brushing with lower abrasive dentifrices is advisable to reduce the risk for NCCLs development.

Introduction

Non-carious cervical lesions (NCCLs) have long been described as highly prevalent [ ] but their etiological and physiopathological mechanisms remain unclear [ ]. In advanced stages, they result in functional and aesthetic problems, dentine hypersensitivity and often require extensive restorative work. Therefore, the management of NCCLs should focus on the early identification of these lesions and adoption of preventive measures.

NCCLs initiate and progress due to the interplay of different wear processes [ ], including abrasion (abrasive wear), erosion (corrosive wear) and abfraction (fatigue wear), which may act independently or in association. Abrasion results from either the contact of the tooth with harder asperities or the entrainment of harder particulates on its surface; while erosion develops by the contact of dental surfaces with non-bacterial acids and/or chelating agents [ ]. The existence of abfraction remains controversial and systematic reviews cannot confirm or reject an association between occlusal stress and NCCLs [ ].

Toothbrushing abrasion is probably the most relevant abrasive wear mechanisms affecting the cervical area, with a clearly established relationship [ ]. However, it has become more relevant recently due to the increasing tooth retention rates [ ], growing emphasis on oral hygiene procedures including toothbrushing for oral diseases prevention, and widespread availability of abrasive whitening toothpastes. Laboratory simulations have reported that toothbrushing can induce wedge-shaped NCCLs independently of other factors [ ]. Relevant aspects of toothbrushing include: toothpaste (abrasivity, composition), filament stiffness (soft, medium, firm), and behavioral aspects (brushing movement, force, frequency, duration) [ ]. A meta-analysis showed the association between NCCLs and frequency, method of toothbrushing and toothbrush stiffness [ ].

Although more abrasive toothpastes can hasten dental abrasion [ ], especially of exposed cervical dentine, no studies have yet clearly determined their impact on the initiation and progression of NCCLs over time. Clinical trials, while ideal, suffer from the lack of control of many variables to isolate abrasivity and brushing time effects. In addition, the majority of trials rely on subjective qualitative methods for the evaluation of NCCL progression. In this respect, the quantitative analysis of tridimensional images acquired by non-contact profilometry from NCCLs seems to be a promising evaluation method, in both the laboratory and clinical setting.

The aims of this in vitro study were to investigate the suitability of a subtraction analysis of profilometric 3D-images to measure the progression of NCCLs; and to use this method to investigate the influence of toothpaste abrasivity on the progression of NCCLs. The null hypotheses tested in this paper were: (1) the use of 3D-subtraction analysis could not detect and monitor the progression of simulated NCCLs over time; (2) the abrasive level of toothpastes did not affect the initiation and progression of NCCLs.

Materials and methods

Experimental design

The experiment followed a factorial 7 × 4 design with two factors: 1. slurries, at 7 levels, prepared from either abrasives: higher (Zeodent 103/15%), medium (Zeodent 124/10%) and lower (Zeodent 113/5%) or marketed toothpastes: lower (Sensodyne Pronamel), medium (Crest Cavity Protection) and higher (Crest Pro-Health-Whitening) abrasive ( Table 1 ); deionized water (DIW) was used as negative control; 2. Brushing time, at 4 levels: 5000, 15,000, 35,000 and 65,000 strokes. The main response variable was dentine volume loss, in mm 3 . Secondary outcomes were lesion shape classification (%) and lesion angle (degrees).

Table 1
Abrasive and toothpaste slurries composition and abrasivity a .
Abrasive/Toothpaste Abrasive load (%) Amount (g) 0.5% CMC (g) DI-water (g) RDA (SE) a Manufacturer
A. Zeodent 113 (low) 5 3 57 69.2 (2.6) Huber Engineered Materials, Havre de Grace, MD, USA
B. Zeodent 124 (mid) 10 6 54 146.9 (3.5) Huber Engineered Materials, Havre de Grace, MD, USA
C. Zeodent 103 (high) 15 9 51 208.0 (9.4) Huber Engineered Materials, Havre de Grace, MD, USA
D. Sensodyne Pronamel (low) 25 40 30.1 (1.1) GlaxoSmithKline Consumer Healthcare, Brentford, UK
E. Crest Cavity Protection (mid) 25 40 98.6 (2.9) Procter & Gamble Co., Cincinnati, OH, USA
F. Crest Pro-Health Whitening (high) 25 40 220.0 (6.8) Procter & Gamble Co., Cincinnati, OH, USA
G. Deionized water (control) 60

a Radioactive Dentin Abrasivity mean (standard-error) using ISO 11609 methodology.

Specimen preparation

A total of 112 out of 200 upper 1st premolars were selected with no restorations, stains or any type of enamel and root defects. The use of human teeth was reviewed and approved by the local Institutional Review Board under the number # NS0911-07. Teeth were cleaned with a periodontal scaler and allocated into seven groups each with 16 teeth of similar anatomy and dimensions (mesio-distal 9 ± 0.5 mm and bucco-lingual 11 ± 0.5 mm) at the cemento-enamel junction (CEJ). Teeth were mounted on acrylic blocks in which each block carried two teeth, resulting in a total of eight pairs for each group. Pairing was done in order to better simulate the horizontal toothbrushing technique with concentration of filament stress in the cervical area. Root portions were covered by a light-polymerizing acrylic resin sheet (Triad, VLC material, Dentsply Int., York, PA, USA), with the exception of the root surface area 2-mm near the CEJ ( Fig. 1 ). After contouring and exposing the root surface area with the aid of a scalpel, the specimen set was light-cured for 5 min.

Fig. 1
Mounted teeth on acrylic block with their root portions covered with acrylic resin, except for 2-mm near the cemento-enamel junction.

Reference areas apical and occlusal to the brushing surfaces were determined and protected from the brushing abrasion by fabrication of a protective bleaching tray. Briefly, 1-mm thick plastic tray sheets were molded against each pair of teeth using a bleaching tray vacuum machine (ECONO-VAC, Buffalo Dental Mfg Co, Syosset, NY, USA). After that, a window was cut in the plastic tray material in the area of the CEJ and 2 mm of the root surface above it, leaving the reference areas protected by the plastic tray. Reference areas were used to aid in the positioning of the images for the 3D image subtraction analysis.

Impression

Impressions of the specimens were taken at baseline and after each brushing period (5000, 15,000, 35,000, 65,000 strokes), with the aid of a petri dish. The eight specimen pairs for each group were mounted on the dish and the impression material (Hydrophilic Vinyl Polysiloxan, Examix NDS Injection Type; GC America, Alsip, IL, USA) loaded on the lid and positioned against the specimens. This guided method allowed the impressions to be taken at similar angles and directions, facilitating the alignment of scans for the subtraction analysis.

Toothbrushing

The specimens were positioned in a V-8 toothbrushing machine, with their long-axis perpendicular to the long-axis of the toothbrushes (Oral B-40, Procter and Gamble, Cincinnati, OH, USA). A brushing load of 200 g was used during the experiment. Slurries were prepared using the different abrasives or toothpastes ( Table 1 ). A volume of 60 ml was used for each specimen block. The reference areas were protected using plastic trays and specimens brushed for 5000, 15,000, 35,000, and 65,000 double strokes. After finishing each brushing period, the specimens were thoroughly rinsed in deionized water and impressions were taken as described above.

Optical profilometry

An area 20-mm long (X) × 25-mm wide (Y) of each impression was scanned with an optical profilometer (Proscan 2000, Scantron, Taunton, UK). The sensor used was the 10-mm S65/10a (04.41.1665–10 mm), at 300 Hz and with 100 repetitions in X axis direction and 125 repetitions in Y axis direction. The step size was set at 0.2 mm for both X and Y directions. Each scan had the reference points automatically identified in the highest location of the protected areas (one in each of the two paired crowns and one in the acrylic area). Using a dedicated software (Proform, Scantron, Taunton, UK), the reference points guided the superimposition of the scans (each brushing period vs. baseline), allowing the natural curvature of the specimen to be considered in the evaluation. For the subtraction analysis, an area of 3 × 6 mm was selected in each tooth, covering the exposed dentine area (lesion) as well as the adjacent references (occlusal and apical). Dentine volume loss after each brushing time was calculated by a trained examiner (AS), previously checked for intra and inter-examiner agreement.

For agreement, three trained examiners (AS, AH and AK) evaluated the dentine loss of six specimens (2 per group) from 3 different groups (C, F, and G) over different brushing strokes (5000; 15,000; 35,000 and 65,000 strokes). Each examiner performed this evaluation three independent times, in random sequence and blind conditions to calculate the intra- and inter-examiner agreement. In addition, the within- and between examiner absolute errors were also determined.

Determination of lesion shape

After each brushing cycle, each specimen was photographed using Nikon SMZ 1500 (Nikon, Tokyo, Japan) and its associated software. Visual assessment of the lesion shape was done after the last brushing cycle by a single, blinded examiner, who classified the lesions into flat, cupped and wedged shape. The frequencies of each shape were then recorded for the different abrasive/toothpastes groups.

Determination of lesion angle

The internal angle between the occlusal and apical walls of the NCCLs was calculated using the two-dimensional function of dedicated software (Proscan, Scantron, Taunton, UK). After determining the deepest part of the lesion on the tooth long-axis direction, the two inclines were drawn (following the lesion walls) at a distance of approximately 1.5 mm from the identified deepest point. The angle between the inclines was measured by the software.

Statistical analysis

Intra-examiner and inter-examiner agreement were assessed using intraclass correlation coefficients. The within- and between examiner absolute errors were calculated based on the average lesion size that was 0.94 mm 3 .

Volume loss and lesion angle data were examined for normality using Shapiro-Wilk tests. Volume loss was summarized (mean and standard deviation) for each level of group (A, B, C, D, E, F, and G) and brushing stroke (5000, 15,000, 35,000 and 65,000) and mixed-model ANOVA was used to evaluate the effects of group, brushing stroke, and their interaction. Angle calculations were summarized (mean and standard deviation) for each level of group (A, B, C, D, E, F, and G) and mixed-model ANOVA was used to evaluate the effects of group. The absolute and relative frequencies of lesion shape were summarized. Pearson correlations were used to investigate associations between slurry abrasivity level, dentine volume loss and lesion angle. Statistical significance was set at 5%. All statistical analyses were performed using SAS version 9.4 (SAS Institute Inc., Cary, NC, USA).

Materials and methods

Experimental design

The experiment followed a factorial 7 × 4 design with two factors: 1. slurries, at 7 levels, prepared from either abrasives: higher (Zeodent 103/15%), medium (Zeodent 124/10%) and lower (Zeodent 113/5%) or marketed toothpastes: lower (Sensodyne Pronamel), medium (Crest Cavity Protection) and higher (Crest Pro-Health-Whitening) abrasive ( Table 1 ); deionized water (DIW) was used as negative control; 2. Brushing time, at 4 levels: 5000, 15,000, 35,000 and 65,000 strokes. The main response variable was dentine volume loss, in mm 3 . Secondary outcomes were lesion shape classification (%) and lesion angle (degrees).

Table 1
Abrasive and toothpaste slurries composition and abrasivity a .
Abrasive/Toothpaste Abrasive load (%) Amount (g) 0.5% CMC (g) DI-water (g) RDA (SE) a Manufacturer
A. Zeodent 113 (low) 5 3 57 69.2 (2.6) Huber Engineered Materials, Havre de Grace, MD, USA
B. Zeodent 124 (mid) 10 6 54 146.9 (3.5) Huber Engineered Materials, Havre de Grace, MD, USA
C. Zeodent 103 (high) 15 9 51 208.0 (9.4) Huber Engineered Materials, Havre de Grace, MD, USA
D. Sensodyne Pronamel (low) 25 40 30.1 (1.1) GlaxoSmithKline Consumer Healthcare, Brentford, UK
E. Crest Cavity Protection (mid) 25 40 98.6 (2.9) Procter & Gamble Co., Cincinnati, OH, USA
F. Crest Pro-Health Whitening (high) 25 40 220.0 (6.8) Procter & Gamble Co., Cincinnati, OH, USA
G. Deionized water (control) 60
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Jun 17, 2018 | Posted by in General Dentistry | Comments Off on 3D-Image analysis of the impact of toothpaste abrasivity on the progression of simulated non-carious cervical lesions
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