Lakshmi Ajithan S¹, Pradeep Dathan², Ambadi Jayakumar¹, Chandrathara T K³, Shahin Ismail⁴, Dhanya P Nampoothiri⁴ and K Chandrasekharan Nair⁵*

¹P.G. Student, Department of Prosthodontics, Sri Sankara Dental College, Akathumuri, Varkala, Kerala State, India
²Professor and Head of the Department, Department of Prosthodontics, Sri Sankara Dental College, Akathumuri, Varkala, Kerala State, India
³Reader, Department of Prosthodontics, Sri Sankara Dental College, Akathumuri, Varkala, Kerala State, India
⁴Senior Lecturer, Department of Prosthodontics, Sri Sankara Dental College, Akathumuri, Varkala, Kerala State, India
⁵Professor Emeritus, Department of Prosthodontics, Sri Sankara Dental College, Akathumuri, Varkala, Kerala State, India

*Corresponding Author: K Chandrasekharan Nair, Professor Emeritus, Department of Prosthodontics, Sri Sankara Dental College, Akathumuri, Varkala, Kerala State, India.

Received: March 18, 2021; Published: April 16, 2021

Abstract

  Denture polishing is an inevitable process in the fabrication of dentures. Dentures in the unpolished state can result in plaque accumulation which may lead to various problems ranging from staining to patient discomfort. Often it is not practiced with due diligence, in spite of recognizing the importance of the process. The main reason can be the laborious nature of the techniques employed for denture polishing. In this context this article provides an overview about the importance of polishing a denture and how it can be carried out systematically.

Keywords: Polishing; Trial Dentures; Tungsten Carbide Burs; Rag Wheel; Dental Lathe; Wool Buff

Introduction

  Acrylic resin dentures in an unpolished state, very easily harbor denture plaque, which results in colonization of microorganisms (Figure 1 and 2). Eventually these microorganisms can cause denture stomatitis. Along with this, food debris can also get accumulated, challenging the hygienic standards of the denture. Heavy deposits and stains provide an awful sight both to the denture and to the patient. This condition further deteriorates with an offensive halitosis. All of these can be avoided by providing a highly polished surface to the denture.

Figure 1: Unpolished denture.

Figure 2: Mandibular denture with deposits.
(Source: https://www.researchgate.net/figure/Heavy-encrustation-of-calculus-and-plaque-arrowed-on-maxillary-a-and-mandibular_fig1_256291459.)

  Polishing is the process of making the denture surface smooth and glossy without causing major changes to the contour (Figure 3). Roughness of 0.2 μm is considered the threshold value for polish [1-4]. If the roughness is above this, the denture surface can attract plaque and microorganisms. Dentures supplied by the laboratories are usually well polished by the technicians. However, frequent post insertion adjustments are necessitated in clinical practice which may leave a rough surface. It is the dentist’s responsibility to leave a polished surface on dentures and other acrylic appliances.

Figure 3: Polished complete dentures.
(Source: https://www.balmoraldental.com.au/dentures.)

  In partially edentulous situations, denture plaque can cause dental and root caries and may initiate periodontal disease. Denture plaque has the common presence of yeasts belonging to the genus Candida; but various other pathogens have been observed to grow in denture plaque. Pathogenicity of denture plaque is not exclusively due to Candida species. An increased adhesion of Candida albicans and Streptococcus oralis to rough acrylic resin surfaces has been observed by many authors (cite authors).

  Polishing of a denture begins with the polishing of trial dentures (Figure 4). A properly polished trial denture (Figure 5 and 5a) will provide a reasonable polish to the final prosthesis, which could be further enhanced (with?). The mechanical polishing system of acrylic denture starts with trimming excess material using tungsten carbide trimmers. This is followed by finishing with 150, 180 and 220 sandpaper to obtain a flat regular surface. Subsequently, waterproof sandpaper with grits 400, 600, and 1200 is used with limited flood (flow?) of water until a uniform surface is obtained. Later polishing is done with a combination of pumice and water on a cotton cloth wheel [5]. The finest marks left with sand papers are eliminated by this (by what?) and a shiny surface is observed. The appliance is then cleaned and dried to eliminate the presence of pumice. The final polishing of the appliance is done with a woollen wheel with or without polishing liquids. At the end, a soap wash is indicated to remove all the polishing materials from the acrylic surface.

Figure 4: Unpolished trial denture. (Source: https://www.jcdr.net/article_fulltext.asp?issn=0973709x&year=2017&month=April&volume=11&issue=4&page=ZC61&id=9683.)

Figure 5: Polished maxillary trial denture. (Source: https://www. slideshare.net/shammasm/11complete-denture -waxup-and-flasking-procedure.)

Figure 5a: Polished mandibular trial denture.

  Micromotor is a slow/medium/high speed rotary instrument used in dentistry. Slow and medium speed micromotor runs at 35000 rpm. High speed micromotors can run at 60000 rpm. Micromotors are brushless with high torque of 9.2N.cm. It can be attached to the dental chair or can be used without dental chair with the help of a control box. The power requirement is 220 - 240V (50 - 60Hz).

Figure 6: Lab micromotor.

  For shaping, removing and smoothening of hard substances carbide cutters are generally used. Cutters are available in different ranges like extra fine, fine, medium, coarse and super coarse. By the design of blade configuration, they can be identified as plane, cross cut or spiral cutters. The main shapes of dental rotary instruments are cylinder, cone, ball and bud. ISO classification has assigned colour and number code for each type of cutter.

Figure 7: Fine plain cut. (Source: https://kmizmarket.com/catalog/carbide-cutters/.)

Figure 8: Fine cross cut. (Source: https://kmizmarket.com/catalog/carbide-cutters/.)

Figure 9: Medium cross cut. (Source: https://kmizmarket.com/catalog/carbide-cutters/.)

Figure 10: Coarse cross cut. (https://kmizmarket.com/cata-log/carbide-cutters/)

• White: Super fine.
• Yellow: Extra fine.
• Red: Fine.
• Blue: Standard.
• Green: Coarse.
• Black: Super coarse.

Figure 11: Colour coding of tungsten carbide cutters. (Source: https://www.dfs-diamon.de/en/dental-lab/carbideburs.)

  For finishing restorations, dental lathe occupies an important place in the lab. Because of the powerful motors, trimming and polishing of restorations become simple and efficient. Dental lathes are usually mounted to the bench for stability. Lathes have either one or two spindles for the attachments. The motor turns a bur or wheel and allows easy access to the restorations for grinding and polishing. Most of the dental lathes have 1/3 HP power and run at 3000 rpm.

Figure 12: Dental lathe. (Source: https://www.dentalplanet.com/shop/product/pr75-ray-foster-pr-75-polishing-lathe.)

  Dental rag wheels are used for buffing acrylic restorations such as denture bases. These soft wheels are often fabricated from muslin or other rag-type fabric and they are gentle on the material being polished. Designed for extra oral use, these wheels can be used more than once.

Figure 13: Cloth wheel

Wool polishing buff is used to remove swirl marks and surface defects to obtain a fine polished finish.

Figure 14: Wool buff.

Available in different shades like pink, white and green.

Figure 15: Stone burs. (Source: https://kyk.com.ph/products/10pcs-set-mounted-stone/.)

  Sand paper is made by binding fine particles of natural and synthetic origin and not exactly sand. The particles known as grains or grits are sorted by size by passing through different screens and then bonded with adhesive to the paper. On the sandpaper, numbers can be seen such as 80-grit, 100-grit, or 200-grit. The grit of sandpaper printed on it indicates the size of the abrasive particle bonded to it. Higher number indicates the smaller size of grains and the fineness of the sand paper. And conversely, lower numbers indicate larger grains and overall coarser sandpaper. Sandpaper grit is measured in microns. A piece of 100-grit sandpaper grains measure approximately 100 to140 microns in size.

Figure 16: Sandpaper. (Source: https://ask.solutions/different-sandpaper-grits/.)

  Pumice is a siliceous material with light gray colour. This is a product of volcanic activity. Pumice in its finely ground form is used to polish tooth enamel as well as restorative materials like gold, silver amalgam and acrylic resin. Pumice is a friable abrasive. Powder or slurry form of pumice can be contaminated with microorganisms of oral and non-oral origin. Therefore, the chances of cross contamination exist and measures should be taken to prevent infections to dentists, technicians and patients. One can sterilize or disinfect all attachments, such as stones, rag wheels, and bands, between uses or throw them away. The lathe unit must be disinfected twice a day.

  Immediately after deflasking, the gross trimming is done using tungsten carbide burs attached to a straight hand piece of a lab micromotor to eliminate acrylic flash. TC burs are available in different colour codes like black (super coarse), green (coarse), red (fine), blue (standard), yellow (extra fine) and head shapes like round, cone, cylinder, and bullet.

  The palatal finish line and posterior palatal seal areas are apparently visible on the processed denture so the flash in this area is first removed and the finish line is trimmed. Care to be taken not to trim or remove any bulk of denture border or periphery as it will affect the seal and thereby the retention of the denture. Further trimming is carried out with stone burs.

  Using suitable fine grade sandpaper, the lightly trimmed surface of the exposed periphery and reduced post dam areas can be refined [6]. Following the refinement using sandpapers, the polishing begins with the use of a polishing lathe.

  Polishing lathe machine helps us with two kinds of polishing namely wet and dry polishing (Figure 17). Wet polishing is done using wet pumice on rag wheel. Polish labial, buccal, lingual and palatal external surfaces of the denture with wet pumice on a rag wheel attached to dental lathe running at slow speed. Care should be taken to keep plenty of pumice on the denture and move the denture at all times during polishing. Also make sure to press the denture lightly against the rotating wheel. Rinse the denture with water to remove the pumice, thoroughly dry, and inspect for remaining imperfections. If imperfections are not removed completely, repeat the use of rag wheel and pumice [7].

Figure 17: Dental lathe with dust collector and protector shield.

  Dry polishing is done with the help of felt cones or wool buff. Polish the borders and surfaces of denture using a dry felt cone and wool buff wheel attached to the spindle of the lathe. After the denture is completely polished, it is scrubbed thoroughly. Polished dentures are stored in water until they are delivered to the patient.

  Waxing, finishing and polishing of trial denture bases and prosthesis greatly influence the final surface finish of the prosthesis. Speed of lathe and the pressure to be applied while polishing are standardized but it cannot be expected in the labs always. Condition of the dental lathe and the manual dexterity of the operator can influence the polishing efficiency.

  Chairside denture prep and polishing kit is an all-inclusive bur kit that helps to eliminate many challenges clinicians face while processing overdentures. The Kit equips dentists, with the essential instruments that are needed to accurately and efficiently pick-up denture attachment housings either chairside or in the laboratory. Chair side polishing kit includes a set of instruments using which the process of picking up of denture attachment housings becomes easy. This fully autoclavable kit consists of six HP dental burs, including recess, undercut, vent, trim, and grind burs, as well as a polisher. Manufactured from high-quality materials, the instruments will help clinicians and dental laboratory technicians address the most frequent overdenture preparation requirements in an easier and faster fashion. Different commercially available kits are Zest chairside polishing kit, NTI chairside polishing kit, DMI chairside polishing kit (Figure 18) [8].

Figure 18: Chairside polishing kit. (Source: https://www.zestdent.com/chairside-denture-prep-polish-kit.)

  Chemical polishing is done by immersing the finished prosthesis into a heated methyl-methacrylate monomer bath kept at 75°C for 10s. This is useful to polish highly irregular surfaces of prosthesis which are encountered commonly in obturators [9,10].

Conclusion

  Polished acrylic resin surface, no doubt indicates the technical excellence of the technician but it stands testimony to the biologically acceptable tissue-prosthesis interface too. High rate of polishing can avoid depositions on the surface of prosthesis, thereby preventing the chances of infections especially in compromised health conditions.

References

1. Bollen CM., et al. “Comparison of surface roughness of oral hard materials to the threshold surface roughness for bacterial plaque retention: A review of the literature”. Dent Mater 13 (1997): 258-269.
2. Quirynen M and Bollen CM. “The influence of surface roughness and surface-free energy on supra- and subgingival plaque formation in man. A review of the literature”. Journal of Clinical Periodontology 22 (1995): 1-14.
3. O’Donnell EF., et al. “Chairside polishing of heat-cured acrylic resin: An SEM and EDA study”. The International Journal of Prosthodontics 16 (2003): 233-238.
4. Kuhar M and Funduk N. “Effects of polishing techniques on the surface roughness of acrylic denture base resins”. The Journal of Prosthetic Dentistry 1 (2005).
5. Serra Glaucio., et al. “Surface morphology changes of acrylic resins during finishing and polishing phases”. Dental Press Journal of Orthodontics 18 (2013): 26-30.
6. A Guide to Complete Denture Prosthetics, Urban Christen.
7. Welker WA., et al. “A technique for finishing and polishing denture bases”. The Journal of Prosthetic Dentistry2 (1978): 240-241.
8. Chatzivasileiou K., et al. “Polishing of Denture Base Acrylic Resin with Chairside Polishing Kits: An SEM and Surface Roughness Study”. The International Journal of Prosthodontics1 (2013).
9. Quirynen M and Bollen CM. “The influence of surface roughness and surface-free”.
10. Mohammed QA. “The effect of mechanical and chemical polishing techniques on the surface roughness of denture base acrylic resins”. The Saudi Dental Journal 22 (2010): 13-17.

Citation

Citation: K Chandrasekharan Nair., et al. “The Relevance of Polishing Acrylic Dentures - An Overview”. Acta Scientific Dental Sciences 5.6 (2021): 63-70.

Copyright

Copyright: © 2021 K Chandrasekharan Nair., et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.