Contemporary Clinical Dentistry

ORIGINAL ARTICLE
Year
: 2016  |  Volume : 7  |  Issue : 1  |  Page : 36--40

Effect of palatal form on movement of teeth during processing of complete denture prosthesis: An in-vitro study


Sumanth Babu1, Shaurya Manjunath2, Mayuri Vajawat3,  
1 Department of Substitutive Dental Sciences, College of Dentistry, University of Dammam, Dammam 31441, Kingdom of Saudi Arabia
2 Vikram Perfect Multispecialty Center, Mysore, Karnataka, India
3 Department of Periodontology and Implantology, Jodhpur Dental College General Hospital, Jodhpur, Rajasthan, India

Correspondence Address:
Sumanth Babu
Department of Substitutive Dental Sciences, College of Dentistry, University of Dammam, P.O. Box 1982, Dammam 31441
Kingdom of Saudi Arabia

Abstract

Aim: The aim of this in-vitro study was to assess the influence of shallow and deep palatal forms on the movement of teeth during the processing of complete denture prosthesis. Materials and Methods: Maxillary casts with shallow and deep palatal forms were selected and duplicated to make 10 casts of each palatal form. Base plates were constructed and teeth were arranged in their anatomic positions. Metal pins with true apex were placed on the central groove of the right and left first molars and one on the incisive papilla area as a reference point. Casts were scanned using i-CAT Vision Q 1.9 (i-CAT cone beam 3D dental imaging system by Imaging Sciences International, PA, USA), which has 360° rotational tomography. The distances between the apices of metallic pin inserts on the teeth and fitted point of reference were recorded in buccopalatal axes at waxed up stage, after deflasking, and after finishing and polishing. Results: Results showed a statistically significant movement of teeth in shallow and deep palatal forms during all stages of complete denture processing. In shallow palatal form dentures, there was a significant tooth movement in palatal direction between Stages 1 and 2 (P ≤ 0.05) and buccal movement between Stages 2 and 3. In deep palatal form dentures, teeth showed a statistically significant (P ≤ 0.05) movement in buccal direction during all stages of denture processing. Conclusion: Teeth showed significant movement during processing of acrylic resin dentures. Overall, the movement of teeth in shallow palatal form dentures was in palatal direction, whereas in deep palatal form dentures, the movement of teeth was in buccal direction.



How to cite this article:
Babu S, Manjunath S, Vajawat M. Effect of palatal form on movement of teeth during processing of complete denture prosthesis: An in-vitro study.Contemp Clin Dent 2016;7:36-40


How to cite this URL:
Babu S, Manjunath S, Vajawat M. Effect of palatal form on movement of teeth during processing of complete denture prosthesis: An in-vitro study. Contemp Clin Dent [serial online] 2016 [cited 2020 Sep 23 ];7:36-40
Available from: http://www.contempclindent.org/text.asp?2016/7/1/36/177101


Full Text



 Introduction



Functional occlusion in complete denture prosthesis is one of the basic objectives in prosthodontic therapy. Knowledge of jaw movements, occlusal anatomy, appreciation of accurate procedures, and choice of sensitive instruments, which precisely simulate functional jaw movements are desirable to meet this objective.[1] Much meticulous consideration should be given to these clinical procedures and instrumentation. Any occlusal discrepancies that result during complete denture processing will have detrimental effect on complete denture prosthesis occlusion.[1],[2]

Occlusal discrepancies during the processing of waxed up dentures have been well recognized. The skill and meticulousness of the operator in executing the laboratory procedures is important for successful reproduction of the waxed up denture to its completed form.[3] Movement of teeth during processing results in increased vertical dimension which, in turn, produce the first sign of discomfort and strain to the patient.[1],[2],[3]

The movement of teeth during processing of complete denture disturbs the harmonious occlusal scheme achieved at the try in stage.[1],[2],[3],[4] There are many factors that influence the dimensional changes and tooth movements that occur during the processing of complete dentures. These movements can be in any direction and can occur due to different investing procedures, thickness of the denture base, careless packing of acrylic resins and improper closure of the two flask halves, and dimensional changes of acrylic resin denture base during the curing procedure.[5],[6],[7],[8],[9],[10]

Hegde and Patil [11] observed that dimensional changes were maximum in deep or V-shaped palatal vault dentures. The dimensional changes that occur at the posterior palatal region of maxillary dentures indicate that the different palatal forms may influence the tooth movement during processing of complete denture prosthesis.

Therefore, the purpose of this study was to assess the effect of shallow and deep palatal forms on tooth movement in buccopalatal axis during the processing of complete denture prosthesis using stone core investing procedure.

 Materials and Methods



Two maxillary casts with shallow and deep palatal form (total 4 casts) were selected according to the palatal form index by Abuzar et al. in 1995.[2] Labial and buccal undercuts were blocked and casts were duplicated using reversible hydrocolloid (WiroGel M by BEGO, USA) to produce 10 casts for each palatal forms (total 40 casts). A 1.5 mm thick thermoplastic sheet (Erkopress by ERKODENT Erich Kopp GmbH, Germany) was vacuum pressed on the cast and processed to form heat cure acrylic resin denture bases of uniform thickness for all the samples. Prefabricated Hard Pink S-U-Wax bite rims (Schuler Dental, Germany) were used to maintain an equal amount of wax added for all samples. Anterior and posterior teeth were arranged in their respective anatomic positions (Ivoclar Vivadent Inc., Schaan, Liechtenstein). Two metal pins with true apex were placed in the central grooves of the right and left first molars, and one pin was placed in the incisive papilla area for reference.

Immediately before processing, waxed-up dentures (Stage 1, trial denture) with cast were transferred onto a rectangular block for recording tooth position. Dentures were scanned using i-CAT Vision Q 1.9 (i-CAT cone beam 3D dental imaging system by Imaging Sciences International, PA, USA) with 360° rotational tomography, image matrix size of 536 × 536 at 120 KV and 5 ma with Voxel dimensions capable of 0.003 mm. Distance between the apices of metallic pin inserts on the teeth and the reference pin was recorded in buccopalatal axes using axial view of the scan [Figure 1].{Figure 1}

Scanning of samples and distance measurements were standardized and performed similarly for all samples during all stages of denture processing. The trial dentures of all the samples were acrylized using stone core investing method, trial packing, and standard curing cycle (curing started at room temperature and gradually increased to 74°C for 90 min and then at 100°C for 30 min). After deflasking (Stage 2) and after finishing and polishing (Stage 3), each denture was scanned to measure the position of teeth using ICAT Vision Q 1.9, as mentioned earlier.

 Results



[Table 1] and [Table 2] show a statistical comparison in tooth movement between the right and left molars in all three stages of processing of dentures in shallow and deep palatal form.{Table 1}{Table 2}

Considering buccopalatal axis, the Wilcoxon signed-rank sum test showed a significant tooth movement in shallow and deep palatal form dentures during all three stages of processing (P ≤ 0.05). The direction and the amount of tooth movement during all stages of processing are shown in [Figure 2], [Figure 3], [Figure 4].{Figure 2}{Figure 3}{Figure 4}

Movement of teeth between Stages 1 and 2

In shallow palatal form dentures, movement of teeth was in palatal direction (positive values) and in deep palatal form dentures, movement of teeth was in buccal direction (positive values).

Movement of teeth between Stages 2 and 3

Irrespective of palatal form, the movement of teeth was in buccal direction (positive values).

Movement of teeth between Stages 1 and 3

Overall, the movement of teeth in shallow palatal form dentures was in palatal direction (positive values). Whereas in deep palatal form dentures, the movement of teeth was in buccal direction (positive values).

 Discussion



The dimensional change that occurs during the denture processing is a critical factor in the retention and stability of the complete denture.[6],[12],[13] Understanding the phenomenon of tooth movement during denture processing helps one to construct functional complete dentures that require less occlusal adjustment in the articulator and patient's mouth.[2],[6],[14] The harmonious occlusal scheme developed at the final try in stage may be disturbed by the movement of teeth during the processing of complete denture.[1],[2] Technical or clinical judgment errors made by the dentist; technical errors made in the dental laboratory; and deficiencies of the techniques and materials used in the construction of the denture may result in inaccuracies in the occlusal harmony of completed prostheses. All the errors and inaccuracies should be corrected before the patient is permitted to wear the prostheses.[7],[15] Such corrections include time-consuming occlusal adjustment sequence that often results in the disfigurement of the anatomy of the artificial teeth.[7],[16]

Various palatal forms such as shallow, medium, and deep also influence the tooth movement to a great extent.[11] Dimensional changes that occur at the posterior peripheral region of the maxillary denture indicate that the height of the palate or the palatal form has an influence on the amount of palatal base distortion and the amount of tooth movement has taken place.[17],[18],[19]

Internal stresses developed within the acrylic resin dentures during polymerization are released during cooling and cause dimensional changes after deflasking and decasting and during finishing. The techniques used in finishing and polishing produce heat that may cause distortion of the denture base.[3],[20],[21]

Significant positive correlation was found between palatal forms and tooth movement measured before processing and after deflasking of the dentures (Stage 1–2). In the present study, it was found that in dentures constructed on casts with shallow palatal form, right and left molars' distance across each other decreased after deflasking whereas the distance increased in the case of deep palatal form dentures.

Phillips [3] demonstrated that teeth had tendency to move toward each other because of thermal shrinkage and release of stress during cooling. This is in agreement with the findings of the present study for dentures with shallow palatal form. It may also be explained that in casts with shallow palatal forms, the acrylic resin shrinkage occurred almost parallel to the flat palate and after cooling and deflasking, the release of stress pulled the opposing teeth together.

In dentures with deep palatal form, the thermal shrinkage occurred at an angle along the palatal slopes. After deflasking, the release of stress caused the denture to be pulled away from the cast. Glazier and Hegde and Patil [11],[18] reported that there will be greater palatal base distortion with an increase in palatal height. The palatal base distortion caused by the denture as it was pulled away from the palatal base of the cast has caused the teeth to move outward or buccally.[18],[19]

The positive or outward or buccal movement of teeth observed for both palatal forms after finishing and polishing (between Stages 2 and 3) might be due to heat-related warpage that occurred during denture trimming and/or due to water absorption and expansion of the denture.[20]

The overall movement of teeth during processing procedures from Stage 1 to 3 in dentures with shallow palatal form indicated that the teeth moved toward each other or palatally, whereas those with deep palatal forms, teeth moved outward or buccally.

As suggested by Lorton and Phillips,[3] the dimensional changes that occur in acrylic resin dentures during processing are complex. The results of this study showed that different palatal forms had a significant influence on the movement of teeth. Therefore, irrespective of the techniques and materials used, there will be movement of teeth during the processing of complete denture prosthesis and various factors influence this movement including the palatal form. The amount of tooth movement could be reduced during the processing of complete dentures by proper handling of wax, powder/liquid ratio for investing, technique of deflasking, and using manufacturers recommended curing cycles. The movements that took place during processing should be corrected by selective grinding. There was a tooth movement in shallow and deep palatal form dentures during all three stages of processing; hence, in patients with shallow and deep palatal when compared to those with medium palatal forms, the clinician should be alert of the possibility of the requirement of more occlusal adjustment during the insertion procedures.

 Conclusion



From the study, following conclusions could be drawn:

Processing of acrylic resin dentures resulted in tooth movements that were significantly influenced by the palatal form of dentures After deflasking (between Stages 1 and 2), in shallow palatal form dentures, teeth moved palatally or toward each other across the arch, whereas in dentures with deep palatal form, teeth showed a buccal or outward movement After finishing and polishing (between Stages 2 and 3), compared with the deflasking stage, teeth had a tendency to move buccally regardless of the palatal form The overall movement of teeth during the processing of dentures was in palatal direction with shallow palatal form and in buccal direction with deep palatal form.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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