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Научни трудове на Съюза на учените в България-Пловдив. Серия Г. Медицина, фармация и дентална медицина т. XXII. ISSN 1311-9427 (Print), ISSN 2534-9392 (On-line). 2017. Scientific works of the Union of Scientists in Bulgaria-Plovdiv, series G. Medicine, Pharmacy and Dental medicine, Vol.XXII. ISSN 13119427 (Print), ISSN 2534-9392 (On-line). 2018.
APPLICATION OF 20-DEGREES TEETH IN REMOVABLE PROSTHEEICS - LITERATURE REVIEW Mariana Dimova-Gabrovskal, Desislava Dimitrova2 lMedical University - Sofia, 2Dental Clinic "Edinstvo" - Sofia, Bulgaria
Abstract: There are different teeth according to their occlusal forms. Their effectiveness varies depending on a number of factors such as alveolar bone atrophy, jaw ratio, underlying tissues, patient adaptability, etc. This implies knowing the details of their possible application in order to achieve better removable dentures. The purpose of this review is to present and analyze the literature data on the use of semi-anatomic 20-degree teeth in removable prosthetics. Material of the review is the list of 38 scientific papers discovered after an electronic keyword search. The results indicate the possibility of application of the 20-degree teeth most commonly to total dentures and patients with semi-resorbed alveolar crests. The advantages of their application are: relatively high chewing efficiency, protection of the underlying tissues due to soft transmission of forces, easy achievement of balanced occlusion, stability, easy adaptability, patient comfort and good aesthetic appearance. As pointed out disadvantages are the minimal horizontal forces, which are result of the presence of shallow tubercles. In conclusion, the use of a specific occlusal tooth form, specifically chosen according to anatomical and physiological requirements, can greatly improve the quality of the removable prosthetics and hence the quality of life of the patients. Keywords: removable prosthetics, 20-degrees teeth
Introduction
Partial or total edentoulism can lead to chronic inability of the patients to perform particularly important actions such as nutrition, speech and communication. The loss of teeth significantly affects aesthetics and appearance. All this leads to changes not only in the health but also in the disturbance of the emotional and social condition of the patients (Xie, 2015). Despite of the big progress of preventive dental medicine and the many efforts to protect and save patients' teeth, there is a tendency of increasing the need of prosthetic treatment in a large group of proportion of the developing countries (Felton, 2009). This is due to the aging population and the growing demographic crisis. According to the World Health Organization, the prevalence of patients suffering from a complete lack of teeth at age 65 in England are 46% (Peterson, 2005). In support of this, Axell's research (Axell, 1979) found that 30.3% of the 20,000 citizens surveyed in Sweden suffered from teeth loss. Lang (Lang, 1994) also determines that the population of Canada aged over 65 is having a high need for prosthesis.
Studies (Bilhan, 2012) (Grant, 1994) show that removable dentures are commonly used and they are cost-effective and easy way to restore partial or total edentulous patients. They provide the possibility of restoring normal speech and chewing function, and thus the normal lifestyle of the patients. Despite the tremendous development in prosthetic methods and used materials, conventional removable dentures are considered to be an appropriate solution for poor condition of the oral tissues and in financial impossibility.
Due to different circumstances, complications often arise in separate stages of the planning and design of total and partial dentures. In their study, Wagner and Kern (Wagner, 2000) indicated that
only 36.6% of removable prosthesis was successful and 23.8% are partially successful. Part of the reasons indicated for failure are an incorrectly defined central relationship, inaccuracies in vertical ratios, inappropriate choice of artificial teeth and their arrangement. Baran et al. (Baran, 2007) also indicate that between 20% and 30% of patients are not satisfied with their total and / or partial dentures. All this suggest focusing dental practitioners' attention on an in-depth analysis of both biological and mechanical factors in removable prosthesis.
Currently, there is a variety of artificial teeth, whose occlusal shapes have different degrees of the slope of the tubercles. The correct choice depends on number of factors such as the physiological condition of the underlying tissues, alveolar bone atrophy, bite type, general condition of the patient, the presence of parafunctions, occlusal forms used in previous prosthesis, and many others (Yoshida, 1988). This implies a broad analysis of the anatomical, physiological and physical requirements of the patient. Knowing the possibilities and limitations of various forms of artificial teeth is of particular importance for the planning of removable dentures. The application of different degrees teeth, pursuant to the patient's individual needs, would lead to a significant increase in the chewing efficiency, stability and comfort. A major advantage of dentures with nonstandard occlusal forms is that proper redistribution of chewing pressure and reduction of harmful forces is provided, which in turn leads to inhibition of atrophic processes occurring in alveolar bone (Hadjieva, 2005)(Slavicek, 1983).
Aim
The purpose of this review is to present and analyze current literature data on the possibilities and limitations of application of the teeth with cuspal angulation of 20-degrees in removable prosthetics.
Materials and methods
An electronic search was conducted in the following databases: Google, PubMed, Lilac (September 2017 to October 2017) by keywords in Bulgarian: „изкуственизъби", „наклоннатуберкули", „20-градусов наклон", "целипротези", „частичнипротези" and their equivalents in English, German, Russian and French: artificial teeth", „cuspal angulations", "200 posteriors", "partialdentures", "totaldentures", „Prothesenzahne", „Hockerneigung", „20-GradNeigung", „Vollprothesen", „Teilprothesen", „протезныезубы",„наклонбушрков", „20-градусный наклон", „полныепротезы", „частичныепротезы", „inclination des cuspides 0 degrees", "Prothesespartiellesamovibles", "Prothesestotales". 127 literary sources have been found, excluding those whose titles are not related to the topic of the review, final selection is consisted by 38 scientific papers. The data are analyzed, summarized and presented in the main part of this review.
Results and discussion
The semi-anatomical or 20-degrees teeth have shallow tubercles slopes that provide the minimum hindrances. They are most often shown for prosthetics with total dentures and in cases of semi-resorbed ridge. They are usually placed in a bilaterally balanced occlusion or lingual occlusion (Moses, 1954). Due to the small tubercle angles, the lateral compressive forces are reduced and the chewing efficiency is significantly increased compared to the non-anatomical 0-degree teeth. 20-degrees teeth are designed to work in sync with the mandibular movements, and their shape provides higher stability and denture holding. Self-cleaning fissures prevent plaque build-up, which is also one of the factors for easy patient adaptation (Woelfel, 1962). According to Kayano (Kayano et al., 1962) 20-degrees teeth combine elements of anatomical and non-anatomical teeth. The presence of reduced tubercles provides less traumatisation of the underlying tissues, while at the same time due to the minimal inclination of the opposing teeth, an increase in the stability of the denture during chewing is provided, which is of particular importance for the patient's sense of safety and comfort. Although they transmit minimal lateral pressure, the semi-anatomical teeth provide a harmonious function, and their appearance closely resembles natural teeth. Shallow tubers allow food to be ruptured while at the same time they provide acceptable freedom of
movement for the lower jaw. According to Trapozzano and Lazzari (Trapozzano, Lazzari, 1952), 20-degrees teeth are significantly more effective in chewing function, compared to non-anatomical tooth shapes, as confirmed by the Thompson study (Thompson, 1937). The author follows the changes in the chewing efficiency before and after the period of adaptation to the removable prosthetics. The initial chewing efficiency in patients with 20-degrees teeth is 57%, and after the adaptation, the chewing efficiency is decreased to 53%. According to the author, this is due to the abrasion of the small cutting tops of the manufactured teeth. For 0-degree teeth, no difference is recorded before and after the adaptation period, but the initial chewing efficiency was lower than that established for the 20-degrees teeth.
Kydd (Kydd, 1960) also conducted a study of the chewing function while using different forms of occlusal teeth in removable dentures, as well as the degree of deformation of the prosthetic base in these cases. He uses 0-, 20-, 33-degrees teeth and finds that 33- and 20-degrees teeth cause a higher compression-based deformation based on the prosthesis, compared to zero-degrees. Regarding to the chewing function, the presence of the tubercular inclination does not significantly increase the chewing efficiency. Evidence for this is the lack of a statistically significant difference in the mechanical efficiency of the 30-, 20- and 0-degree teeth found by Nasr et al. (Nasr, 1967) in testing with a specially design for the purpose apparatus. Contrary to this research, is the study by Bellini et al. (Bellini, 2009), which found that patient satisfaction and subjective assessment of chewing efficiency was significantly higher in patients using semi-anatomical teeth, compared to those using dentures with anatomical or non-anatomical teeth. Heydecke et al. (Heydecke, 2007) also investigates the changes in the chewing efficiency of different in hardness foods in patients prosthetically treated with different occlusal forms. They find that the presence of even shallow tubercular slopes significantly increases the possibility of fragmentation more solid food. Data obtained from the study by Farias-Neto et al. (Farias-Neto, 2013) show that patients find removable dentures with anatomical and semi-anatomical teeth significantly more effective in terms of chewing efficiency, aesthetic appearance, stability and retention. In a comparative assessment (Matsuda, 2015) of dentures made by using a BioFunctional Prosthetic System and conventional removable dentures made with 20-degree teeth, patients indicate as that equally satisfactory in terms of function, aesthetics, retention, and comfort. This proves that simplified and time-saving methods for making removable structures can successfully restore chewing function and speech and to respond to the patient requirements (Cunha, 2013).
An object of interest is the Frechette study (Frechette, 1955), which aim is to establish the distribution of the chewing pressure on the underlying tissues, using total dentures with different occlusal tooth shapes. For the purpose - 3 pairs of dentures - with 0-, 20- and 30-degrees teeth were prepared for each patient. Tests for the distribution of the chewing forces are made with the help of an electronic system whose sensors are placed on the plate in the area of the crest of the alveolar ridge, in place of the first molar and respectively one sensor - buccal and palatal (or lingual). The total number of sensors for one jaw is 6 in number, and for both 12. Tests are made during chewing carrots, peanuts and roast beef. The results for the 20-degree teeth show the highest pressure compared to the 0- and 30-degree teeth in the sensor area on the alveolar ridge on the one side and the other two side sensors located in the other half. The mean arithmetic provided pressure in the side sensors with 20-degrees teeth is the least, compared to that of the other occlusal form teeth. In addition, the author also takes into account the degree of chewing efficiency with different occlusal tooth forms, as well as the degree of patient satisfaction. 75.61% of chewing efficiency is found for the 20-degree teeth, and patients find them satisfactory in every aspect and as a preferable in comparison with the other tested teeth.
Arksornnukit (Arksornnukit, 2011) examines the transmission and distribution of pressure in removable prosthesis with different occlusal form teeth made of acrylic and porcelain. For this purpose, they use special pressure-sensing plates and an electronic system that measures the average pressure value and the maximum pressure value. 0-, 20-, 33-, 35-degree teeth used. The result shows that 20-degree acrylic teeth show no significant difference in both values compared to 33-degree plastic teeth. However, a significantly smaller pressure transmission zone was observed
at the 20-degree compared to 33-degree, that is why the authors accept semi-anatomical teeth as preferable to the 33-degree ones. The study concludes that smaller angulation is a prerequisite for smaller areas of pressure transfer to underlying tissues. In the investigation of the 20-degrees porcelain teeth, significantly lower average values of the transmitted pressure are established compared with the 35-degrees, but the results are not statistically significant. According to the authors, in the cases of prosthesis with ceramic teeth, it is recommended using of 0-degree and 20-degrees occlusal shapes, due to better results than the 35-degrees ones. This statement is also supported by Chowdhary (Chowdhary et al., 2008), according to him - flat occlusal surface or shallow tuberous slopes are preferred because they carry less force and pressure to underlying tissues. In addition, according to Boucher (Boucher, 1975), the use of 20-degree teeth gives opportunity for more balanced occlusion compared to 0-degree teeth.
Object of interest is also the study of Mankani (Mankani, 2013), which aim is to determine the extent and route of transmission of the chewing pressure, stress concentration zones, and deformation of the underlying structures using 0-, 20- and 33-degree teeth. The study is conducted in vitro with the help of specially developed software. 3D patterns of underlying tissues and structures were created by scanning total dentures from patients. The occlusal aspect is modeled so as to create prototypes of conventional dentures with teeth different in their angulation of tubercular slopes. The tests are performed with a vertical static load of 100 N, which corresponds approximately to this reported in the occlusal molar zone in patients with removable dentures. The results show significantly higher values of load on underlying tissues and more areas with concentrated stress in the anatomical and semi-anatomical teeth. These data are also confirmed by other studies (Lopuck, 1978) (Sherry, 1959), according to which using of the 0-degree teeth, the forces that effect on the alveolar bone were significantly less than these with the 20- and 30-degrees. The occlusal form of artificial teeth used for removable prosthesis also affects the activity of masticatory muscles during chewing. The use of teeth with tubercular slopes requires less effort on the part of the closing muscles for all tested foods compared to non-anatomical teeth (Hichkey, 1963).
According to the Sutton's study (Sutton, 2007) semi-anatomical teeth are more aesthetically pleasing, compared to non-anatomical teeth and are more compatible with the surrounding oral environment.
Levin (Levin, 1972) points out one more advantage of the teeth with cuspal angulation of 20-degrees- they are modified to be adaptive to the condylar and incisal guidance and they are not a prerequisite for correct articulation of the sounds since they do not require 0 degrees of incisal guidance, unlike the teeth with cuspal angulation of 0-degrees. There is another proof (Sutton, 2007) of satisfactory results from the application of semi-anatomical teeth. Considerable improvement in chewing function and respectively lower relative proportion of areas with hyperemia and inflammation in the oral cavity with the use of non-and semi-anatomical teeth for removable prosthesis are reported.
According to the literature (Marchini, 2014), there is no objective evidence of full acceptance of anatomical, semi-anatomical or non-anatomical teeth as the most suitable for removable prosthesis. In order to achieve an optimal result in the rehabilitation of partially or completely edentulous patients, an individual approach to each case is needed. The choice of the occlusal shape of the teeth should be made after careful analysis of joint and inter-jaw ratios, alveolar bone atrophy, surrounding tissue condition and chewing pattern (Sutton, 2005). According to Davies (Davies, 2001) the dentists should evaluate which occlusal form is appropriate for the patient. People which have alveolar ridges with medium or minimal atrophy, where it is necessary and possible to achieve a balanced dynamic occlusion, some suitable occlusal shape artificial teeth are 20- or 30-degree. In patients with advanced atrophy of alveolar ridges, removable dentures with semi-anatomical teeth or anatomical teeth would result in the occurrence of harmful horizontal forces due to the incision of the teeth. This would undoubtedly lead to the acceleration of atrophic processes and in inability to achieve good retention and stability.
Conclusion
In conclusion of the literature review it can be summarized the indications of using artificial 20-degrees posterior in removable prosthesis and related benefits. Semi-anatomic teeth are most often shown for total and partial dentures and for patients with semi-resorbed alveolar ridge bone. Their usage allows to achieve balanced occlusion which is in harmony with the mandibular movements. They can provide high chewing efficiency, stability and comfort by patients and are rated as easily adaptive, because of the shallow tubercular slopes. An important advantage of the conventional dentures with 20-degrees teeth is the possibility of significantly relieving the underlying tissues from occlusal overloads, which increases the prophylactic value of prosthetic treatment and has relevance to good long-term prognosis. Last but not least, there is the aesthetic look of the semi-anatomical teeth, which resembles that of natural with functional abrasion. As the only limitations that can be mentioned are the occurrence of minimal horizontal forces during function and the difficult use of semi-anatomical teeth in patients with severe malocclusions.
Knowing the different occlusal forms of the artificial posterior teeth and their application greatly enhances the ability to plan and carry out high quality treatment with removable prosthesis.
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