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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 ARTIFICIAL POSTERIOR TEETH WITH 0-DEGREE OF CUSPAL ANGULATIONS IN REMOVABLE PROSTHESIS - LITERATURE REVIEW
Mariana Dimova-Gabrovskal, Desislava Dimitrova2 lMedical University - Sofia, 2Dental Clinic "Edinstvo" - Sofia, Bulgaria
Abstract: The planning of removable denture is a highly responsible step that requires particular attention in terms of proper redistribution of the pressure, preserving the underlying tissues, providing chewing efficiency and satisfying the aesthetic needs of the patient. A key factor for success in these cases is the appropriate choice of occlusal forms of artificial teeth. The aim of this review is to identify possible applications and limitations on the use of posterior teeth with cuspal angulation of 0 degrees, in removable prosthesis. Material of this review is the data from 29 literary sources, selected from total number of 235 scientific papers by keywords, from August to October 2017. Results: In patients with cross bite, II and III class malocclusions, bruxism, etc., application of the non-anatomical teeth provide freedom of the movements, reduction of harmful horizontal forces, reduction of the compression on the underlying tissues and easy articulation. The disadvantages are related to food tearing problems and a possibility of disturbance in articulation of some sounds.
Conclusion: knowing the different occlusal forms and applying them according to anatomical and physiological requirements would help to improve the quality of the removable dentures and moreover increasing the degree of patient's satisfaction. Keywords: 0-degrees teeth, removable prosthesis
Introduction
Partial and complete dentures provide the opportunity to restore chewing function and improve the quality of life of patients. However, there are a number of studies showing resorption of alveolar bone in patients, who are wearing dentures. The reason for this is often complex - number of missing teeth, length of period without prosthesis, initial volume and height of the bone, etc. As a major factor for the resorption the pressure of the dentures is indicated (Tallgren, 2003). Often it passes the required threshold, which in turn leads to a disturbance of blood circulation and, consequently, a change in bone metabolic processes. Matsuo et al. (Matsuo, 1996) find that a pressure of 27 to 68 g/sm2 stimulates fibroblasts, which in turn initiates the alveolar bone remodeling. Other authors (Berg, 1967) found that the pressure transmitted to underlying tissues
should not exceed 1.3 kPa. All these give reason to emphasize the striving to preserve the condition of the oral structures and to reduce the provided stress.
Restoring chewing function through removable dentures requires a complex approach and attention in each of the manufacturing stages. This implies an in-depth analysis of the condition of the underlying tissues, assessment of the type of the bite, the general health of the patient, knowing the history of previous treatments, the economic status and motivation of the patient, as well as aesthetic considerations (Xie, 2015). Of particular importance are the knowledge and the potential of the dentist about the application of the laws of physics and biomechanics in the restoration of normal physiological functions. The purpose of their practical application is to provide balance between the functional-mechanical effects and the biological reactivity of the tissues, increase the chewing efficiency and maximum stability of the prosthetic structures (Bural, 2016) Making total or partial dentures is a complex process, which requires particular attention at every single stage. A key factor for the successful treatment in such cases is the choice of appropriate artificial teeth for each patient. Usually for the dental practitioners this is an automatic procedure, and often its importance is neglected. Nowadays, there is a tremendous variety of artificial teeth -different colors, shapes, length, width, cuspal angulation of the posterior teeth. The choice of suitable artificial teeth should be fully consistent with the properties of dental materials and, in particular, with the anatomical and physiological requirements of a patient (Vasantha Kumar, 2011).
Knowing the possibilities of using artificial posterior teeth with different cuspal angulation would be of particular advantage in the planning and making partial and complete dentures. Properly selected teeth are a prerequisite for proper pressure redistribution, saving the underlying tissues and fully satisfying the patient's needs.
Purpose
The aim of the present literature review is to present and analyze the current science data on the use of artificial posterior teeth with 0-degree cuspal angulation in a removable prosthesis.
Materials and methods
An electronic search was conducted in the following databases: PubMed, Google (August 2017 to October 2017) by keywords: „изкуственизъби", „наклоннатуберкули", „0-градусов наклон", "целипротези", „частичнипротези" and the corresponding terms in English, German, Russian and French: artificial teeth", „cuspal angulations", "0°posteriors", "partial dentures", "total dentures", „Prothesenzähne", „Höckerneigung", „0-GradNeigung", „Vollprothesen", „Teilprothesen", „протезныезубы"„,наклонбугорков", „0-градусный наклон", „полныепротезы", „частичныепротезы", „inclination des cuspides 0 degrees", "Prothesespartiellesamovibles", "Prothesestotales". 235 literary sources have been found; those whose are not related to the subject of this review are excluded, which resulted in a final selection of 29 scientific papers. The data are analyzed, summarized and presented in the main part of this review.
Results and discussion
The artificial posterior teeth with cuspal angulation of the 0 degrees are considered as non-anatomic, which provide complete freedom in the lateral movements of the lower jaw. They are suitable for preparation of total prostheses where the 0-degrees teeth are preferred. The wider vestibular-lingual surface contributes to the function and significantly reduces the period of adaptation, and their appearance resembles worn natural teeth. Such teeth can be arranged in a bilaterally balanced occlusion with an individual compensation curve or in a flat linear occlusion (Jani, 1974). According to some authors (Honorato Villa et al., 1962) they can be aligned with their lingual surfaces in a straight line, which in turn provides a level of buccal contour for good aesthetic appearance and function. According to Davies et al. (Davies, 2001) the ideal occlusion of the prosthesis is that which limits the inclination of the structure itself and ensures minimal distortion of the peripheral sealing. For the construction of total prostheses, the underlying tissues and the chewing pattern are of particular importance. The author recommends the use of 0-degree teeth in patients who perform mainly vertical chewing movements in which only static occlusion
needs to be balanced, without need for balanced dynamic articulation. Such teeth are suitable for patients with flat alveolar ridges or where over-implant dentures are occluding with conventional dentures.
Pozzi (Pozzi, 2015) defines the non-anatomical teeth as appropriate in cases of cross bite and advanced atrophy of the alveolar bone, where stability is reduced. In cases where cross alignment is required, the use of 0-degrees teeth eliminates the use of lower teeth in the upper jaw. Due to the absence of a tubercular ratio, the position of the upper and lower distal teeth can be changed to a condition where there is alignment between the upper and lower alveolar ridges, which greatly relieves provided stress on the underlying tissues. According to the same authors, such teeth should be arranged without overlap in the frontal zone.
Jones P. (Jones, 1972) points out the benefits of using 0-degrees posterior teeth. According to him, they are more adaptable to unusual jaws relations such as Class II and Class III malocclusions, as well as a cross bite. They give the patient a sense of freedom, as they do not interfere with lateral and protrusive sliding movements. Of particular importance is their ability to eliminate horizontal forces considered to be more damaging than vertical ones. It is assumed that such teeth occlude in more than one position, and then the consideration of whether the central relation is a point or a region is dropped. The use of non-anatomical teeth allows using of a simplified and time-saving technique and in the same time offering good comfort and efficiency over a long period of time.
Kydd (Kydd, 1960) investigates the chewing efficiency and the degree of deformation of the base of the prosthesis in various forms of posterior teeth - with cuspal angulation of 0-degrees, 20-degrees and 33-degrees. He found that the 20 and 33-degree teeth caused a more extensive compressive deformation of the bases of the dentures compared to the 0-degree teeth. Concerning chewing efficiency, the data did not show a statistically significant difference in the values of the different types of teeth. It is believed that the most suitable choice of tooth shape is those that neutralize or minimize the horizontal and lateral forces that are the main cause of progressive atrophy of the alveolar bone. Through a special test-machine, Nasr et al. (Nasr, 1967) examined the mechanical effectiveness of the various teeth with different occlusal shapes and the results showed a lack of statistically significant differences between the individual groups.
A Frachette study (Frachette, 1955) aims to identify the distribution of chewing forces in the prosthesis of patients with total dentures but with a different slope of the tubercles of the teeth. Three pairs of prostheses were made for each patient - with non-anatomic (0-degrees), semi-anatomic (20-degrees) and anatomical (30-degrees) teeth. The distribution of forces is reported with the help of an electronic system during chewing carrots, peanuts and roast beef. At 0-degrees teeth, the highest pressure of each tooth is seen on the one side of the alveolar ridge and lowest pressure on the other side, while the 30-degrees teeth show the smallest compression at both sides of the alveolar bone. Regarding to the efficiency of the chewing function, the following values are established: 30-degrees teeth - 81.40%, 20-degrees teeth - 75.61% and 0-degrees teeth - 74.66%. Within the same study, the degree of satisfaction of patients with dentures with different occlusal shape of the used teeth was also taken into account. They point out that the anatomical teeth are great for breaking the food but significantly limit the free sliding movements, the semi-anatomical - as satisfactory in every aspect, as far as non-anatomical are initially assumed skeptically as teeth crushing the food, in the subsequent they are considered as very satisfactory, despite the inability to tear the food. Berg (Berg,1988) also investigates the degree of satisfaction of patients with total dentures made with 0-degree and 30-degree teeth. Participants express their opinion during the insertion of the prosthesis after one and two years after insertion. The results did not show a statistically significant difference in patient satisfaction in the two groups.
Arksornnukit (Arksornnukit et al., 2011) also investigates the distribution of pressure in prosthesis with different material and occlusal shape artificial teeth. 0-degree teeth show significantly lower mean and maximum compression values compared to 33- and 35-degree teeth, regardless of the material they are made of. This allows the authors to determine non-anatomical teeth as suitable for patients with advanced atrophy of the alveolar bone as they provide lower
pressure on underlying tissues. Mankani et al. (Mankani, 2013) also gives an assessment of the provided stress on the underlying tissues under dentures with different teeth. With help of specially designed software and 3D scanner, virtual models of alveolar bone and oral mucosa are created by scanning dentures from patients. Specific areas for reading the values were selected, and the study was performed with a vertical static load of 100N. The results showed the highest values of provided stress on the underlying tissues in 33-degrees teeth and the lowest in 0-degrees teeth.
The study of Sharry et al. (Sharry, 1960) is also of interest, the aim of which is to determine the effect of occlusal forms on bone defect in prosthetics with whole dentures. With the help of a specially-made test-platform, 18 edentulous skulls with applied total prostheses with anatomic and non-anatomical teeth were tested successively. To imitate the muscle pull in the lateral and protrusive movements of the lower jaw, 6 kg of weights are additionally attached. The results show that under identical load, greater bone deformation is detected under the anatomical forms, and that the deformation is not limited to the area of the alveolar bone supporting the prosthesis, but spreads to more distant areas including, for example, the nasal bones, the medial wall of the orbit and processus zygomaticus.
According to Thompson (Thompson, 1937), non-anatomical teeth are widely used in making of whole dentures because they are less likely to cause discomfort to the patient during chewing function. As an advantage for the dentists, he points out the relatively easier and quicker articulation of the dentures. Poor lateral compression, with the use of 0-degree teeth, is again confirmed, suggesting that the contours and height of the alveolar bone will be maintained for a long period of time.
The subject of interest is the Yoshida's study (Yoshida et al., 1988), which aims to establish criteria for selection of artificial posterior teeth. They point out that patients with weak neuromuscular control adapt difficult to dentures with anatomical teeth. The 0-degree teeth are again indicated as suitable for class II and class III malocclusions and cross bites. The authors also state that non-anatomical teeth are suitable for immediate dentures, unless there is a natural denture. The indicated advantages of using these teeth are: the reduction of harmful horizontal forces, the central relationship can be defined as an area rather than a point, freedom of movements, easy adaptation by the patient and easy positioning and articulation by the clinician. A study by other authors (Sutton et al., 2005) also indicates 0-degrees teeth as the most appropriate choice in cases of patients with irregular chewing muscular movements such as bruxism, because they have less resistance and hence less damage to underlying tissues. Singh et al. (Singh, 2012) recommends the use of conventional dentures with non-anatomical teeth in patients suffering from osteoradionecrosis. The aim of their application to reduce the risk of alveolar bone trauma, given the chances of disease-related changes.As a summary of the literary data so far, is the Spiva's statement (Spiva, 2010), which is based on over 40 years of experience in dental practice, namely that the removable dentures with 0-degree teeth and linear occlusion are more stable, balanced and create less chewing difficulties.
In the published literature (Hardy, 1951) (Slavicek, 1983), a number of 0-degree teeth disadvantages have also been reported. Often, patients may experience difficulty in breaking food due to flat teeth surfaces, reduced chewing efficiency compared to anatomical forms and aesthetics restrictions (often not like natural teeth). Thompson (Thompson, 1937) also reports reduced chewing efficiency of non-anatomical teeth compared to anatomical porcelain teeth. Sutton (Sutton, 2007) found that patients whose dentures had anatomic or semi-anatomical tooth forms suffered significantly less problems with chewing function and fewer reported red or inflamed areas in the cavity, compared to those which have dentures with 0-degrees teeth. In this direction, a subject of interes is the Levin's study (Levin, 1972), which finds out that 0-degree teeth require 0-degree incisal guidance, which in turn can lead to speech disorder and mis-pronunciation of individual sounds.
Howard Payne (Howard Payne, 1951) conducts a study about the degree of patient satisfaction during chewing function with dentures made with anatomical and non-anatomical
teeth. It is used various foods such as bread, celery, hard biscuit, steak and sandwich. The information obtained from this study shows that patients feel far more comfortable about the chewing function with teeth with anatomical shapes. Hickey et al. (Hickey, 1963) finds out that higher activity of the closing muscle during chewing of all tested foods is registered with dentures with non-anatomic teeth. In long term period, according to the authors, the prognosis of the prosthetics is connected with the discomfort and tension in masticatory muscles.
Conclusion:
From the data received so far, follows the conclusion, that indications for application artificial posterior teeth with cuspal angulation of 0-degrees are treatments with total dentures, in cases of cross bites, II and III maloocclusions, advanced atrophy of the alveolar ridges, bruxism, cases of weak neuromuscular control. Advantages of their usage is that they provide complete freedom of lateral and protrusive movements of the lower jaw, reduce harmful horizontal forces, comparatively low values of compression of underlying tissues, rapid adaptation, relatively easy procedure for determination central relation of the jaws and easy dental articulation. They also provide possibility of achieving bilaterally balanced occlusion or flat linear occlusion and have an acceptable appearance resembling worn natural teeth.
Limitations of artificial posterior teeth with cuspal angulation of 0-degrees - require arrangement without vertical overlap in the frontal zone and 0 degrees incisal guidance, which may lead to speech disorders, mainly in pronunciation of the dental-labial and labial-dental sounds; problems with breakage of food and reduced chewing efficiency compared to other occlusal forms, because of the missing tubercular inclination as a disruptive factor; tense during chewing, result of the increased muscle activity.
Knowing all these parameters regarding the application of various occlusal forms artificial posterior teeth favors the clinical practice of the dentist in the stages of planning the prosthetic constructions. Thus an objective prerequisites are created for recovering of the bio-mechanical balance of the chewing system, for improving the functional medical-biological indicator and for optimizing the quality of life of the patients.
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