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Kopfzeile Seite 90: ORIGINAL WORK

Textrahmen:

S. Ries, J. Wolz1. D. Leising, E.-J. Richter1

BEGO-Semados single-tooth implants: a prospective, randomised study to investigate the influence of various parameters on the peri-implant bone level

Linke Spalte:

The preservation of peri-implant bone is the most important criterion for durable and successful osseointegration of dental implants. The aim of the study was to document the influence which various parameters have on the peri-implant bone level. Besides the question of whether or not the level of the junction between rough and machined implant surfaces is an influencing factor, the study also investigated the extent to which the ratio of implant length to extraosseous restoration length and also the number of implants (single or multiple) influence the peri-implant bone level.

Out of 100 implants placed, one was lost during the early healing phase; the remaining implants were monitored over a period of up to 36 months. In this study, neither the junction level between rough and machined surfaces nor the ratio of implant length to extraosseous restoration length had an influence on the peri-implant bone level. In cases where two or more adjacent implants were placed, a tendency for increased peri-implant bone resorption was observed, compared to those implants which were used to replace only a single-tooth.

Keywords: peri-implant bone resorption, implant surface, single-tooth implant, extraosseous restoration length, tooth-by-tooth replacement.

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Rechte Spalte: Introduction

Apart from successful osseointegration, preservation of the peri-implant tissue at the implant site is regarded as the most important criterion for the long-term success of dental implants. As a rule, the loss of marginal alveolar bone in the case of two-stage implants is highest within the first year after insertion of the abutment, and is stated as 1.2 mm to 1.6 mm on average [1, 7, 9, 18, 27]. Thereafter, the rate of resorption decreases to between 0.1 mm and 0.2 mm per year [22, 30], which is accepted as physiological. Various causes of the initial bone loss are discussed: besides deperiostation of the bone, surgical trauma to the tissue at the implant site and possible compression of the peri-implant bone when the implant is inserted [2, 16], implant-specific influences such as the macrostructure of the implant neck [19, 27], the thread configuration in the area of the implant shoulder [24] and the microstructure in the neck region [24, 13, 14] are considered as additional causes. Furthermore, histological studies and removal tests have clearly demonstrated that the configuration of the implant surface has a direct influence on the degree of implant-bone contact [8, 10, 12]: rough surfaces produce a significantly higher rate of bone apposition than smooth surfaces.

This positive effect of the rough surface structure can, however, turn into a negative effect if the bone resorption processes in the implant neck region cause the rough part of the implant to be exposed in the oral cavity. Seite 2

Kopfzeilen Seiten 91 –96:

S. Ries et al. / BEGO-Semados single-tooth implants

Abbildung:

Figure 1 Control implant (left) and test implant (right) differ only in their neck configuration: the surface of the first two cervical threads of the test implant was "as machined".

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Tabelllen:

Table 1 Number and distribution of implants Serienimplantate = Adjacent multiple implants Einzelzahnimplantate = Single-tooth implants

Gesamt = Total

Unterkiefer = Mandible

Oberkiefer = Maxilla

Table 2 Number of adjacent multiple implants per patient Anzahl Implantate/Patient = Number of implants per patient Unterkiefer = Mandible

Oberkiefer = Maxilla

Table 3 Time under risk

Serienimplantate = Adjacent multiple implants Einzelzahnimplantate = Single-tooth implants

Jahre = Years

Unterkiefer = Mandible

Oberkiefer = Maxilla

Linke Spalte:

If the oral microflora colonise the rough surface, this may lead to peri-implant inflammation of the soft tissue, which in turn may produce bone resorption. On the other hand, a so-called hybrid surface – with a smooth, machined section in the implant neck region and a rough surface in the middle and apical section of the implant – would enable both of the positive aspects of the respective

surface configurations to be combined, namely the high rate of bone apposition on the rough implant body and the relatively good plaque resistance in the "machined" transmucosal section. However, it is still unclear what influence a smooth surface in the crestal implant section has on peri-implant bone

resorption.

The objective of this study was to clarify the extent to which the type of surface morphology in the implant neck region ("as-machined" versus etched)

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demonstrate how the "crown-root ratio" (or more precisely, the ratio of extraosseous restoration length to intraosseous implant length) and the

absence of splinting of suprastructures in the case of adjacent multiple implants in the anterior region influence the marginal bone level.

Materials and method

At the Department of Prosthodontics of Dental School of the Bavarian Julius Maximilians University in Würzburg, 59 patients aged between 18 and 69, 33 of whom were women, were selected as test subjects for the study. A total of 100 implants were placed in the conventional way.

Rechte Spalte:

50 of these implants were standard Bego-Semados implants with the normal microroughness in the implant neck region (control implants), while the other 50 were test implants with a machined surface in the region of the implant shoulder as far as the third thread (Fig. 1). The only difference between the test implants and control implants was the neck configuration.

The choice of implant type was random. Implants with lengths of 11.5, 13 and 15 mm and diameters of 3.75, 4.5 and 5.5 mm were available. Healing took place submerged. The healing period was six months in the maxilla and three months in the mandible. The implants were fixated in local bone – augmentation in the implant neck region simultaneously with implantation was not permitted. Intraoperatively, the initial spatial relationship of the implant shoulder to the bone was measured and documented. 58 of the 100 implants were placed as adjacent multiple implants (Tables 1 and 2), i.e. two or more implants in

neighbouring positions. The superstructure was fabricated in the form of screw-retained or cement-screw-retained single crowns (porcelain fused to metal crowns). In the case of adjacent multiple implants, the neighbouring crowns were not splinted to each other (Figs. 2 to 10). For "purely" single-tooth implants, no distinction was made between terminal and intermediate implants. The constructions were observed and documented over a period of up to three years following prosthetic treatment (Table 3).

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Following attachment of the superstructure, standardised long-cone X-rays were taken using the right-angle technique and with the aid of bite guards customised for each individual patient. Further X-ray check-ups were performed at intervals of 6, 12, 24 and 36 months after the crowns had been fitted.

However, not all the patients came regularly to all follow-up evaluations. Seite 3

Linke Spalte: Abbildungen:

Figure 2 Implant-retained single crowns in the region right upper 2nd premolar, right upper 1st and 2nd molars – lateral view

Figure 3 Unsplinted single crowns on implants in the region right upper 2nd premolar, right upper 1st and 2nd molars – occlusal view

Computer-assisted evaluation of the X-rays was carried out using the Digora for Windows 2.0 Rev 2 (Orion Corporation Soredex) program. The reader did not know which implants had been inserted as test specimens and which ones as controls. Furthermore, it was not possible to distinguish between the study implants and the control implants on the basis of the radiographic

documentation. The reference points used for calculating the rate of bone resorption were the implant shoulder and the point of the first implant-bone contact; the intraoperatively determined initial relationship between the implant shoulder and the marginal bone was taken into account when calculating the bone level.

Rechte Spalte Abbildungen:

Figure 4 Situation after right upper sinus augmentation and implantation 4/2002

Figure 5 Implants in the region right upper 2nd premolar, right upper 1st and 2nd molar are provided with unsplinted single crowns (X-ray from 11/2002)

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Figure 6 Condition of the restorations 9/2004

The distances were measured mesially and distally in each case, taking the length of the implant as a reference. On the basis of the mesial and distal measurements, mean values were calculated for the respective measuring times. For statistical evaluation of bone resorption in the case of adjacent multiple implants, only one of these implants per patient was evaluated so as to eliminate the risk of intra-individual influences. Exclusion of the non-evaluated adjacent multiple implants of each patient was randomised.

The Kolmogorov-Smirnov test did not produce a normal distribution, so the data was statistically evaluated via two independent samples by means of the Mann-Whitney-U test, using the SPSS 11.5 for Windows program. The level of

significance was set at p ≤ 0.05. Box plots were prepared for the purpose of descriptive statistics.

Seite 4 Linke Spalte: Abbildungen:

Figure 7 Implant-retained single crowns in the region left lower 1st and 2nd premolars and left lower 1st and 2nd molars – occlusal view

Figure 8 Unsplinted single crown restorations – lateral view

Results

With the exception of one out of the group of test implants, which had to be removed during the healing phase due to a postoperative infection, all the implants healed without any complications. There were no further implant losses within the observation period. In the Kaplan-Meier survival analysis, this gave a median survival probability of 98.2% in the test group and 100% in the control group over an observation period of up to three years. The survival rate of the implants following prosthetic treatment was 100% in both groups. Over

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the entire observation period, no prosthetic complications in the form of loosening of the abutment screw or decementation of the porcelain fused to metal single crowns were observed.

Figure 11 and Table 4 show the bone resorption within the two different groups from the time of attaching the superstructure through to 36 months later. Rechte Spalte:

Abbildungen:

Figure 9 Situation after implantation in the region left lower 1st and 2nd premolars and 1st and 2nd molars in the X-ray (5/2003)

Figure 10 The X-ray from 7/2004 shows no progressive bone resorption despite disadvantageous loading direction

At the time when the crown was fitted, average bone resorption was 1.75 mm in the study group and approx. 1.60 mm in the control group. After twelve months, the average figures were 1.60 mm in the study group and 1.42 mm in the control group. At the end of the observation period, average bone resorption amounted to 1.49 mm in the study group and 1.15 mm in the control group. Thus, bone resorption decreased in both groups over the course of the observation period; this is particularly noticeable in the control implant group, but is not statistically significant.

The influence which the crown-implant length ratio has on marginal bone resorption is shown in Table 5 and Figure 12. No statistically significant influence of this parameter was observed in this study population.

Throughout the observation period, bone resorption tended to be higher for the adjacent multiple implants than for the "purely" single-tooth implants, which were inserted to replace just one lost tooth.

Seite 5 Tabelle:

Table 4 Distance of the marginal bone level from the implant shoulder at different points in time, as a function of implant type

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Zeitpunkt = Point in time

Implantattyp = Implant type

Mittelwert [mm] = Average

p-Wert = p value

Eingliederung Suprakonstruktion = Attachment of superstructure

Nach 6 Monaten = After 6 months

Nach 12 Monaten = After 12 months Nach 24 Monaten = After 24 months Nach 36 Monaten = After 36 months

Test = Test

Kontrolle = Control

(Im Englischen wird das Dezimalkomma durch einen Punkt ersetzt, z.B. 1,73 = 1.73)

Linke Spalte: Abbildung:

Figure 11 Box plot diagram of peri-implant bone resorption as a function of the surface roughness at the implant neck and time under risk

Eingliederung Suprakonstruktion = Attachment of superstructure

Month 6 = Month 6

Month 12 = Month 12

Month 24 = Month 24

Month 36 = Month 36

Knochenabbau in mm = Bone resorption in mm

Testimplantat = Test implant

Kontrollimplantat = Control implant

Implantattyp = Implant type

This was statistically significant both at the time of "Attachment of the superstructure" and "After 24 months", as can be seen in Table 4 and Figure 13.

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Discussion

The survival rate of the Semados implants over an observation period of three years was 98.2% for the test version and 100% for the control implants.

Rechte Spalte:

These figures are of the same order as those stated for other modern implants, namely 95.5% to 99.1% over a comparable period [5, 15, 17, 21, 29, 31].

An average crestal bone resorption rate of approx. 1.7 mm at the time when the superstructure was attached means that the peri-implant bone resorption was at the upper limit, but still within the standard range of resorption levels stated in the literature as being usual within the first year after prosthetic treatment [1, 7, 9, 18, 27]. However, subsequent continuous resorption of 0.1 mm to 0.2 mm per year, which is stated in the literature as being "physiological" for most systems [22, 30], was not observed in the population examined in this study. On the contrary, instead of further bone resorption, the tendency was rather for bone apposition, although the implants with a machined surface in the neck region up to the third thread generally displayed a slightly higher degree of bone resorption. Nevertheless, the average bone resorption in this group after three years was also slightly below the resorption level immediately after attachment of the superstructure.

According to previous studies, the ratio of superstructure length to implant length has an influence on marginal bone loss [6]. It was not possible to evaluate this in the present study, however. No change in the marginal bone level was observed either in the "purely" single-tooth implants or in the adjacent multiple implants in connection with the ratio of (extraosseous) crown length to (intraosseous) implant length.

In the case of treatment with adjacent multiple implants, priority has been given, for a long time, to splinted superstructures, because it was believed that splinting had a positive effect on both the implant survival rate and on complication-free functioning of the superstructure. This was postulated for the posterior teeth in particular [28]. In the meantime, however, more recent publications give reason to believe that unsplinted single crowns on posterior

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adjacent multiple implants – essentially corresponding to the natural state – have an equally positive effect on implant survival probability [11, 20, 23, 26]. Seite 6

Tabelle:

Table 5 Average peri-implant bone resorption as a function of the implant-crown length ratio

(Wie Tabelle 4 bis auf Spalte 2):

Implantat-Kronen-Längenverhältnis = Implant-crown length ratio Implantat > Krone Implant > crown

Implantat < Krone Implant < crown Linke Spalte:

Abbildung:

Figure 12 Box plot diagram of peri-implant bone resorption as a function of the implant-crown length ratio (more precisely: the ratio of intraosseous implant length to extraosseous restoration length)

Eingliederung Suprakonstruktion = Attachment of superstructure

Month 6 = Month 6

Month 12 = Month 12

Month 24 = Month 24

Month 36 = Month 36

Implantat-Kronen-Längenverhältnis = Implant-crown length ratio Implantat > Krone Implant > crown

Implantat < Krone Implant < crown

Overall the clinical use of unsplinted adjacent multiple implants can be regarded as advantageous for many reasons. Interdental and inter-implant hygiene is still possible, as is the accustomed use of dental floss. Furthermore, individual crowns can be fabricated more easily and more precisely, and the accuracy of fit is often better than with larger prosthetic constructions. Apart from imitating

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natural situations (single implants replace the missing teeth), unsplinted single-tooth implants ensure that the natural flexibility of the mandible is preserved. Rechte Spalte:

The most frequent complications with implant-retained single-tooth crowns stated in the literature are loosening of the abutment screw, veneer fractures, decementation of the restorations, and even fractures of the implants [3, 11, 25]. Screws working loose are the most common complication, occurring in up to 38% of cases in some study populations [4, 5, 17]. In comparison with this, the absence of any prosthetic complications whatsoever in the patient population described above is impressive! The stability of the screw connection is attributable firstly to the pretensioning of the screws, which is achieved with a torque of 30 Ncm, and secondly the conical support of the prosthetic post in the interior of the implant appears to be very effective in preventing any "micro-deformation", without a so-called "deep internal connection" being necessary. Only in some cases did this study show a significant difference in the peri-implant bone level between single-tooth peri-implants and adjacent multiple implants: the bone level was always significantly higher with the single-tooth implants than with the adjacent multiple implants. However, the average bone resorption with adjacent multiple implants was 1.7 mm after 36 months, which means that there was no deterioration from the initial figure (2.12 mm) in this group either. Nevertheless, it cannot be assumed that the absence of splinting of the superstructures had an influence on this parameter. At the point in time when the crowns were placed, a significant difference between the two groups in terms of the bone level was already identifiable (see Table 6): any influence by the superstructure can therefore be excluded. Thereafter, no negative influence due to the absence of splinting, e.g. in the form of increasing bone resorption, was detected.

Conclusions

The survival probability of BEGO-Semados implants for replacing (several) single teeth was very high (100% with standard implants) in the observation

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period of three years to date. The degree of initial bone resorption in the neck region of the implants was comparable to other implant systems.

Seite 7

Table 6 Peri-implant bone resorption as a function of the parameter "single-tooth implant" or "adjacent multiple implants"

(wie Tabelle 4 bis auf Spalte 2):

Einzelzahnimplantat = Single-tooth implant Serienimplantat = Adjacent multiple implants Linke Spalte:

Figure 13 Box plot diagram of peri-implant bone resorption as a function of the parameter "single-tooth implant" or "adjacent multiple implants".

Eingliederung Suprakonstruktion = Attachment of superstructure

Month 6 = Month 6

Month 12 = Month 12

Month 24 = Month 24

Month 36 = Month 36

Knochenabbau in mm = Bone resorption in mm Einzelzahnimplantat = Single-tooth implant Serienimplantat = Adjacent multiple implants Implantatanordnung = Implant arrangement

During function, however, bone apposition began to take place in this zone as time progressed! A machined surface extending over three threads in the implant neck region did tend to have an unfavourable effect on the bone level. Over the observation period of up to three years, no progression in bone resorption was observed in either the test implants or the control implants. Bone resorption was higher when two or more missing posterior teeth were replaced with single-tooth implants. The crown-implant length ratio was not found to have any influence on bone resorption in the implant neck region.

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Rechte Spalte: Literature

(Literaturverzeichnis wurde nicht übersetzt) Kasten unten:

Korrespondenzadresse = Correspondence addresses Prof. Dr. E.-Jürgen Richter

Poliklinik für Zahnärztliche Prothetik Pleicherwall 2 97070 Würzburg Tel.: 0049 - 931 – 20173010 Fax.: 0049 – 931 – 20173000 E-Mail: Richter_E@klinik.uni-wuerzburg.de Dr. Stefan Ries

Zahnarztpraxis am spitzen Turm Gerbergasse 10

97877 Wertheim

Tel.: 0049 – 9342 – 7054 Fax.: 0049 – 9342 – 859695

References

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