Straight wire appliance versus full edgewise
A scientific essay in Medical Sciences
DOCTORAL THESIS defended in public on 4th of September 1997
The general introduction in chapter 1 presents a short historical overview of orthodontic fixed appliance treatment and a description of the different edgewise appliances. A review of the literature on the Straight Wire Appliance is given. The main objectives of the study are presented as seven hypotheses that are to be tested.
Chapter 2 gives information about the design of the prospective randomized clinical trial. Patient selection, the participating orthodontists, treatment protocols and the data collection are discussed. A group of 149 Angle Class 11 patients were selected for this study. The experimental variable 'type of fixed appliance" was assigned by balanced allocation. The group of patients is described using the 10 balancing criteria for treatment allocation. Furthermore, some cephalometric characteristics of the sample are described.
Chapter 3 describes the results of a pilot study. It was studied whether it is possible to assess reliably crowding or spacing for an orthodontic diagnosis by eye instead of by measuring. It shows that assessment by eye and measurement results are wen comparable and reproducible. Assessment by eye has the practical advantage that it takes considerable less time.
The duration of treatment and the chairtime of both the orthodontist and his/her auxiliaries are described and analyzed in chapter 4. The treatment duration is, as assessed for the entire sample, not significantly different for both types of appliance. This goes for both extraction and non-extraction therapy. Within the single practices there are significant differences but these can not be explained by the type of appliance. The chairtimes for the orthodontists are comparable for both treatment types, but the auxiliaries spend more time on FPA treatment. Furthermore, the total chairtime for FPA treatment is significantly longer than for PPA treatment.
Chapter 5 consists of two parts. In the first part the results are described of a pilot study. In vitro and in vivo, the reliability is assessed of a new digital technique that is able to correct the solo radiographs from the begin and the end of treatment for different projections and orthodontic movement. It is concluded that this method is reliable to assess the prevalence and degree of apical root resorption on non standardized solo radiographs. In the second part of this chapter this technique is used to assess the prevalence and degree of apical root resorption on the central upper incisors of the patients in the sample of this study. The occurrence and the extent of apical root resorption are independent of the type of fixed appliance that is used.
Chapter 6 deals with discomfort as experienced by patients that are treated with fixed appliances. Two types of discomfort were deduced from the questionnaires that were filled in by the patients: psychological and physical. For both the degree was not dependent of the type of fixed appliance or the practice in which the treatment was conducted. The same goes for the satisfaction with the treatment result.
In chapter 7 the influence of fixed appliance treatment an periodontal parameters is described. Gingivitis is a commonly observed phenomenon that frequently occurs after placement of fixed appliances. The FPA design is considered to have a less unfavorable influence on the gingiva. The amount of dental plaque, the tendency for bleeding of the gingiva after probing and the pocketdepths were assessed at different points in time. Evaluation of the different assessments shows that the variable "type of fixed appliance" does not have an influence on any one of them.
In chapter 8 the treatment results as assessed with the PAR index are described. Both the reduction in PAR score and the post-treatment PAR score show no significant differences for both treatment options. There are, however, significant differences within the different practices. No interaction could be assessed between the type of fixed appliance and the orthodontist with respect to the reduction in PAR score or the post-treatment PAR score. Movement of teeth after extraction may cause undesired rotations.
In chapter 9 it is tested whether an FPA treatment can prevent these rotations better than a PPA treatment. This is assessed by using (a part of) the ITRI (= Ideal Tooth Relationship Index). It shows that no confirmation can be given that an FPA treatment can prevent these rotations in a better way than a PPA treatment.
In chapter 10 the treatment results are described using the Six Keys Analysis. Also, a limited number of cephalometric values are assessed. First, a description of the Six Keys Analysis is given. Evaluation shows that FPA treatment results in a significantly better angulation of the upper front ("artistic positioning") than PPA treatment. There are no further significant differences between both treatment options. Comparison between the non-extraction and the extraction therapy group shows that the non-extraction group scores better on the inclination of the lower front, rotations and AP molar relationship but worse on inclination of the lower (pre-)molars. No interaction between type of fixed appliance and (non-) extraction therapy could be assessed. Evaluation of the cephalometric values only shows a significant difference between the non-extraction and the extraction therapy group: the angle between the upper incisor and the occlusal plane is larger in the extraction group.
Finally, in chapter 11 a general discussion is given. The results of the different hypotheses are discussed and suggestions for further study are given. The most important conclusion of this study is that a good or a bad treatment result is not primarily set by the appliance that is used but by the person that handles the appliance.