| Abstract|| |
Composite resin is presently used primarily as a direct esthetic restorative material. The esthetics of these tooth-coloured restorations is heavily dependent on surface finish Polishing of composite resin can produce potentially injurious temperature rise within the pulp chamber.
This study was conducted to compare and evaluate the pulp chamber temperature rise associated with the polishing of light cured composite veneer restorations using 2 different polishing systems (Astropol, Shofu- Snap kit).
40 extracted maxillary central incisors were used in this study. They were randomly divided into 4 groups-Groups 1, II (Dry Continuous, Intermittent respectively) and Groups III, IV (Wet, Continuous, Intermittent respectively).
Groups I, II were polished with the Shofu System and Groups Ill, IV were polished using Astropo System. The temperature rise was recorded within each group and the remaining dentin thickness (RDT) was measured after sectioning of the teeth.
The results indicated:
- There were significant differences in the temperature rise between the dry and the wet systems.
- The correlation of the temperature rise and the remaining dentin thickness was significant for the dry, intermittent group and was dependent on application time of the disks.
- Remaining dentin thickness is an important factor in regulating the magnitude of temperature rise during polishing of restorations.
|How to cite this article:|
Singh A, Kavitha S, Narayanan L L. A Comparative evaluation of pulp chamber temperature rise associated with polishing of light cured composite restorations using 2 different polishing systems. J Conserv Dent 2006;9:21-31
|How to cite this URL:|
Singh A, Kavitha S, Narayanan L L. A Comparative evaluation of pulp chamber temperature rise associated with polishing of light cured composite restorations using 2 different polishing systems. J Conserv Dent [serial online] 2006 [cited 2021 May 7];9:21-31. Available from: https://www.jcd.org.in/text.asp?2006/9/1/21/41305
| Introduction|| |
Composite resin is presently used primarily as a direct esthetic restorative material. The esthetics of these tooth-coloured restorations is heavily dependent on surface finish  .
Finishing refers to the gross contouring or reducing of the restoration to obtain the desired anatomy. Polishing refers to the reduction of the roughness and scratches created by the finishing instrument. Residual surface roughness of restorations encourages plaque accumulation, which may result in gingival inflammation, superficial staining and secondary caries  . The finished surface apart from esthetics also affects the longevity of the restoration as well as its biocompatibility with the oral tissues ,
The surface of resin composites can be finished and polished using a variety of instruments such as burs, discs, pastes  . Abrasive disks are used for gross reduction, contouring, finishing and polishing. Most types of disks are coated with aluminium oxide abrasive with moisture - resistant backings / paper backings.
The finishing and polishing involves contouring the restoration with 12 - flute carbide / 30-100 micron diamond burs or coarse abrasive disks, followed by fine and extra fine diamond burs, white stones, disks and finally polish with extra fine abrasive coated disks / rubber coated disks, cups or points. Some systems also employ an aluminium oxide / diamond extra fine paste for polishing. Some operators prefer to work without coolant in an intermittent/ continuous manner due to the difficulties in controlling water cooling when flexible disks are used  . It is possible that the temperature reached in this manner could be detrimental to the pulp  . Little research has been conducted to determine whether these working methods result in detrimental changes in the pulp. For many years the possibly damaging effects of temperature increses on the pulp tissue during restorative treatment procedures like polishing has been a matter of concern to dentistry. According to Zach & Cohen  , a temperature increase of 5.6° C causes irreversible damage to healthy pulps. In addition, irritated pulps can be damaged by even lower increases in temperatures.
Polishing of composite resin can produce potentially injurious temperature rise within the pulp chamber. Studies done evaluating temperature rise in the pulp chamber during high-speed tooth prepartion with diamond burs have shown upto 4°C temperature rise in 30 seconds 14.
The aim of this study was to establish the pulp chamber temperature rise produced during polishing of cured composite resin using a dry and a wet polishing system and the effect of time and polishing technique on the temperature rise
| Materials and Methods|| |
1. Preparation of Samples
40 human extracted intact similar sized maxillary central incisors with single, straight canals were selected for the study. The teeth were stored in 10% formalin until use. The teeth were also cleaned ultrasonically before starting the procedure.
In each sample tooth, the apical 1/3rd of the root was sectioned and removed using diamond disk with water spray. Any pulp tissue was removed using a barbed broach through the retro section.
Canal and pulp chamber content was cleaned with 2.5% Sodium Hypochlorite from a 30-giuage needle for thorough canal debridement. The prepared specimens were then stored in distilled water until use.
2. Canal Preparation and Mounting
The specimen teeth canals were enlarged from the apex towards the pulp chamber using K files upto No.80. The canals were thoroughly cleaned with saline.
The prepared teeth were embedded in round die-stone blocks (measuring 1 x 1x2 cms) for stabilization during veneer preparation and thermocouple wire placement.
40 specimen were randomly divided into 40 groups each containing 10 specimen. The specimen were numbered I, II, III, IV and specimen numbers 1 to 10. (E.g.IV6)
3. Preparation of Veneers
Veneer prepartion was done in all 40 specimens. Depth orientation grooves were made upto 1.0mm using a 3-ring veneer preparation bur and high-speed handpiece (NSK). The preparation was outlined using Shofu preparation kit. The outline was window preparation involving the incisal edge and extending proximally without involving approximate contact areas. The preparation was finished with finishing burs (Shofu) to produce a smooth preparation and definite margins.
In order to minimize experimental variables in veneer preparation, a single operator using a standardised technique performed all the preparations.
4. Restorations of Veneers :
All prepared teeth were restored with an anterior light cured composite resin Charisma (Heraeus Kulzer, No CE 10044).
Acid etching was done for 15 seconds using 35% Phosphoric acid gel (Gluma Etch Gel No. 216082, 206083) followed by rinsing for 15 seonds. The teeth were blot dried and application of 2 coats of Bonding Agent (Gluma Comfort Bond, No.26150) was done.
The specimen were then light cured with a Quartz Halogen light-curing unit (Astralis LC unit) for 20 seconds. Each specimen was restored with Charisma composite material utilizing 2-3 increments of composite materials and light cured for 20 seconds.
5. Measurement of temperature rise with polishing
The restored specimens were visually examined for any surface discrepancies like voids, and gross over or under contouring. Any discrepancies were rectified before the process of finishing and polishing. All specimens were finished with composite finishing burs (Mani - Yellow, Red).
Type K-Chromel-alumel thermocouples were used to measure the temperature rise. The thermocouples were used to measure the temperature rise. The thermocouple wires were bare 0.005" wires insulated to the full length except the tip, which acts as a sensor for measuring temperature.
Thermocouple wire was secured using cyanoacrylate ester and their position was verified radiographically.
A multipoint digital temperature (Thermotronic Instruments, Chennai) indicator, calibrated to record temperatures in the range of 0-60° C accurately was used to measure the temperature changes.
Each group was used to measure the temperature changes. Each group specimens were polished upto a total cumulative period of 2 minutes (120 seconds) to approximate and simulate clinical situations.
The procedure of polishing in each group was as follows;
Group I : Dry Continuous Polishing
Shofu Discs (Box AE 063) - Fine (Green coloured) and Superfine (Red coloured) were used to polish the specimens in dry continuous manner with a slow - speed contra-angled hand piece (NSK) operating at 10,000 rpm. The fine disc (Green) was used continuously for 60 seconds, followed by the ultra fine disc for 60 seconds. The disks were used in a roll on motion on various parts of the restored surface. The disks were not centered over a single area for more than 10 seconds.
The temparature rise was including the exact periods of rise in temperature (latent period). The polishing was carried out in all areas of the restoration.
Group II : Dry, Intermittent Polishing
Each specimen in this group was finished with the Shofu disks (Fine and Superfine) used intermittently for 15 seconds, followed by a gap 10 seconds between each polishing cycle. The disks were used in a planar motion across the restoration and were not centered on the area for more than 10 seconds. Any debris on the surface was removed with a blast of air spray between the polishing cycles. The fine disc (Green) was used intermittently for 60 seconds (4 cycles of 15 seconds), followed by the ultra fine disc for 60 seconds (4 cycles of 15 seconds).
The temperature rise was noted including the exact periods of rise in temperature (latent period). The polishing was carried out in all areas of the restoration. The disks were used in a roll on motion on various parts of the restored surface. The disks were not centered over a single area for more than 10 seconds.
Group III : Wet, Continuous Polishing
This group was polished using the Astropol system. Astropol system rubber impregnated polishing cups - Polishing (Green) and High gloss polishing (Pink) were used in a continuous manner for 60 seconds each.
A copious water spray was used during the polishing cycle using a slow-speed handpiece (NSK) operating at 10,000 rpm.
The rubber cups were used in a roll on motion on various parts of the restored surface. The cups were not centered over a single area for more than 10 seconds. The temperature rise was noted including the exact periods of rise or fall in temperature. The polishing was carried out in all areas of the restoration.
Group IV : Wet, Intermittent Polishing
This group was polished using the Astropol system. Astropol system rubber impregnated polishing cups - Polishing (Green) and gloss polishing (Pink) were used in an intermittent manner for a total of 120 seconds. Each specimen in this group was polished with the Astropol system rubber impregnated polishing cups - Polishing (Green) and High gloss polishing (Pink) used intermittently for 15 seconds, followed by a gap of seconds between each polishing cycle A copious water spray was used during the polishing cycle using a slow-speed handpiece (NSK) operating at 10,000 rpm.
The rubber cups used in a roll on motion on various parts of the restored surface. The cups were not centered over a single area for more than 10 seconds. The temperature rise was noted including the exact periods of rise or fall in temperature. The polishing was carried out in all areas of the restoration.
6. Sectioning of specimens and Measurement of the Remaining Dentin Thickness
All samples were sectioned carefully in the sagittal plane using a mounted carborundum disk. The Remaining Dentin Thickness (RDT) was measured using a depth guage (Medesy) which was graduated to a minimum of 0.1 mm.
The RDT was measured at three location and the least measurement was recorded as the RDT value for each specimen. The corresponding composite thickness was also recorded (mm) and the mean composite thickness calculated and recorded (mm).
7. Statistical Analysis
The mean and standard deviation were estimated from the sample for each study Group. Mean values were compared by Student's paired t-test / One way ANOVA appropriately. Multiple range tests by Tukey-HSD procedure was employed to identify the significant group. If P-value in One-way ANOVA was significant.
Pearson's correlating analysis was done to assess the linear relationship between diferences in temperature rise and the remaining denting thickness (RDT) in various study groups.
| Results|| |
The values obtained during this study were tabulated and graphically represented [Table 1],[Table 2],[Table 3],[Table 4]. The mean and standard deviations were estimated from the sample for each study group. Mean values were compared by Student's paired t-test / One way ANOVA appropriately.
Multiple range tests by Tukey-HSD Procedure was employed to identify the significant group, if P-value in One-way ANOVA was significant.
The results indicated that the test of significance at 5% for temperature rise was significant for Group I versus Group III, IV and Group II versus Group III, IV (P<0.000 1).
Pearson's correlating analysis was done to assess the linear relationship between differences in temperature rise and the remaining dentin thickness (RDT) in various study groups.
In the present study, P<0.05 was considered as the level of significance. Pearson's correlation analysis of temperature rise with remaining dentin thickness (RDT) indicated significance in Group II (P value 0.01).
| Discussion|| |
A finished and polished restoration is a prosthesis or direct restoration whose outer surface has been progressively refined to a desired state of surface finish . Proper finishing and polishing of dental restoratives are critical clinical procedures that enhance aesthetics and longevity of restorations.
Finishing refers to the gross contouring or reducing of the restoration to obtain the desired anatomy. Polishing refers to the reduction of scratches created by the finishing instrument. Finished and polished restorations provide three benefits of dental care: oral health, function and aesthetics  . A well-contoured and polished restoration promotes oral health by resisting the accumulation of food debris and pathogenic bacteria through a reduction in total surface area and reduced roughness of restoration surface. Dental plaque is usually readily removed from composite restorations where the surface are accessible to the patient for cleansing, but subgingival interproximal areas may remain bacteria laden after completion of routine oral home care  . Nevertheless, a highly polished composite restoration is necessary to help promote a plaque free environment, as surface roughness seems to affect the initial adhesion of bacterial cells.
Oral function is enhanced with a well-polished restoration as food glides more freely over occlusal and embrasure surfaces during mastication  . Rough material surfaces also lead to the development of high contact stresses that can cause the loss of functional and stabilizing contacts between teeth. Finishing and polishing these surfaces can improve the strength of the restoration especially in areas that are under tension. The goals of finishing and polishing procedures are to obtain the desired anatomy, proper occlusion and the reduction of roughness, gouges and scratches that were produced by the contouring and finishing instruments.
Resin based composites contain a relatively soft resin matrix with hard filler particles in its structure. This results in selective grinding associated with the soft material and the harder particles (especially apparent with hybrid composites). The final finish of a composite restoration depends on the fillers and matrix, the preparation design, curing effectiveness and the post curing time required for the material to achieve its final properties 
The curing of composites against a Mylar polyester strip produces the smoothest surface, which minimizes porosities and the oxygen - inhibition layer, a fact that encourages most in-vitro studies to use these surface as comparative controls. However, it is often difficult to achieve proper contour and marginal adaptation without some amount of finishing because the plastic Mylar strip is often difficult to adapt to the different convex and concave surfaces of the tooth. Therefore, in the clinical environment most restorations need to be finished and polished.
A variety of instruments are commonly used for finishing and polishing tooth coloured restorations including carbide burs (8-,12-, 16-, and 30-fluted), 2550 micron diamonds abrasive disks, strips and polishing pastes, and soft and hard polymeric cups, points, wheels impregnated with specific types and sizes of abrasive particles  .
During finishing, particles of a substrate material are removed by the action of a harder material that comes into functional contact with the substrate. This generates sufficient tensile and shear stresses to break atomic bonds and release a particle from the substrate  . The blades of a carbide bur or the tips of abrasives transfer this force to the substrate (composite surface). The advantage of using burs is that the effectiveness of the water - cooling system is not affected during finishing and polishing.
Coated abrasive disks and strips are fabricated by securing abrasive particles to a flexible backing material (heavyweight paper, metal or Mylar) with a suitable adhesive material. Disks and strips are further classified as moisture resistant and non-resistant  . It is advantageous to use abrasive disks or strips with moisture-resistant backing, as their effectiveness is not reduced by water degradation. Due to the difficulties in controlling water cooling when flexible abrasive disks are used. Some manufacturers recommend working without coolant in an intermittent or continous manner  . It is possible that temperature elevation reached during polishing could be detrimental to the pulp.
According to Zach and Cohen  , a temperature increase of 5.6"C causes irreversible damage to healthy pulps. In addition, irritated pulps can be damaged by even lower increases in temperature Sato  and Schuchard  reported that excessive heat adduction can result in structural changes of the hard dental tissues and damage the dental pulp. The duration of the thermal stimulus and the peak temperatures generated determine whether and to what extent heat related trauma occurs. Thermal changes during cutting with a bur cause thermal changes in the dental pulp which are influenced by the size and shape of the bur, speed of the bur, amount and direction of pressure, the amount of moisture in the field, length of time of contact, type of tooth structure being cut (enamel, dentin)  .
Cohen and Zach  recorded in animal studies 15% of dental pulps became necrotic with a 5.6-degree temperature elevation and 60% with an 11.1° C temperature elevation. Raab and Muller  reported temperature higher than 43° C produce an increase in pulpal blood flow and that temperature greater than 49° C causes irreversible damage to the micro circulation of the pulp.
Pohto and Scheinin  documented an increased capillary permeability as the first sign of heat related pulp damage when the temperature increased between 5-6° C. A temperature of 41.5°C must be seen as the critical limit for pulpal fibroblasts  .
Standardised veneer prepartions (depth 1.0mm) were done with a high-speed handpiece (using a 3-ring depth cut bur and finished with diamond burs.)
Briseno and Ems  studied the rise in pulp temperature when finishing and polishing composite resins using different working speeds, use of coolants and varying pressure and concluded that flexible discs used withcoolant continuously at a speed of 10,000 rpm with continuous pressure were safe ,
The selection of materials and methods used in this study was based on the results obtained from the pre-trial. The pre-trial showed no difference in temperature rise with and without use of a bonding agent. However, to simulate clinical conditions and co-relate the remaining dentin thickness (RDT) with temperature rise, the specimens were restored with the use of a bonding agent.
The surface micromorphology of resin based composites after finishing and polishing depends on characteristics of the filler particles (sizes, hardness and amount of fillers). Factors related to the abrasive systems include flexibility of the backing material in which the abrasive is embedded; hardness of the abrasive, the geometry of instruments and how the instruments are used also contribute to the surface roughness of composites as well as the temperature rise  . The polishing systems used in this study were the Shofu Super-Snap kit (Shofu Dental) and the Astropol polishing system (Ivoclar Vivadent). The former consists of abrasive disks for finishing (black, purple) and polishing (green, pink) which are recommended to be used in a dry field. The Astropol system consists of abrasive (aluminium oxide, silicon carbide) impregnated rubber cups and disks for finishing (Grey) and polishing (Green, Pink). The recommended speed is 7,500 - 10,000 rpm with use of water spray. [Figure 5]
Two minutes was chosen as an appropriate approximate time period to complete polishing in a clinical set up  . The tooth pulp detects and responds to dentin injury resulting from caries, trauma, restorative dental procedures, attrition, and abrasion by the deposition of a tertiary dentin matrix (reparative and
reactionary dentin) ,, . In general, reactionary dentin is secreted by pre-existing odontoblasts and newly differentiated odontoblastlike cells secrete reparative dentin , . The difficulty with measuring pulpal responses to a preparation / restoration cut into dentin is that the pulpal reaction are the end result of all the preparation and restoration events .[Figure 1],[Figure 2],[Figure 3],[Figure 4]
The cutting of tooth dentin has been shown to be a powerful stimulus for the initiation and progression of a reactionary dentinogenesis response. For every 1mm decrease in remaining dentin thickness (RDT) between the floor of a cavity and the odontoblastic surface, the mean area of reactionary dentin matrix increased by 1.187 square millimeters. The buffering effect of the remaining dentin thickness (RDT) to provide pulp protection can be expected to vary not only with dentinal tubule distance from the prepared cavity floor to pulp tissue, but also with dentinal tubule permeability. Tubule permeability is an important factor in allowing the progression of caries, bacterial leakage and chemical irritants towards pulp tissue. Consequently, the width of affected tubules and the peritubular secretion of dentin in reduction their width to help mediate pulp protection are important. Therefore, the RDT may be similar between patients but dentin permeability and pulp reaction quite different. The successful outcome of restorative treatment depends on understanding and making decisions that are congruent with the natural repair responses of the tooth  .
In this study, remaining dentin thickness (RDT) was measured as the shortest distance from the veneer floor to pulp tissue, primarily because of eace of measurement and avoidance of measuring complications ,between different samples. The composite veneer thickness was also calculated at the region of least remaining dentin thickness (RDT).
The results indicated the correlation of the temperature rise and the RDT to be significant during polishing in a dry field, intermittently.
Clinical extrapolation of the results of this study is difficult. The methodology employed does not allow elucidation of the cause of the rise in temperature. Different in-vivo variables such as individual pulpal blood circulation, thickness of dentin, number and diameter of dentinal tubules are difficult to standardize in in-vitro studeies and, therefore were not taken into consideration.
In this study, working in an intermittent I continuous manner with water - cooling resulted in clinically acceptable maximal temperature rises. These results are in agreement with those reported by Zach and Cohen  . The presence of water coolant resulted in dissipation of the frictional heat produced during polishing and caused minimal increases in temperatures. Dry, continuous polishing resulted in temperatures higher than 40° C (41° C temperature was recorded in 2 specimens). Thus irreversible pulpal damage under these conaitions is likely  .
In conclusion, wet polishing procedures produced a minimal temperature rise, which may be due to the dissipation of the frictional heat produced during polishing by the water coolant, and therefore is safely recommendable.
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Dept. of Conservative Dentistry & Endodontics Saveetha Dental College & Hospitals, No. 162, Poonamallee High Road, Chennai - 600 077
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2]